Staff

Ralf Kägi

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Dr. Ralf Kägi

Department Process Engineering

About Me

Research Interests

  • Detection and fate of particulate contaminants (engineered, incidental and natural, micro- and nanoplastic particles) in natural environments and engineered systems
  • Fluxes and impacts (nano)particulate of contaminants (engineered, incidental and natural  (nano)particles, microplastics)  through and on urban (waste)water systems
  • Development and validation of new analytical approaches for (nano)particle detection and structural characterization

Research statement

Particulate contaminants (including engineered, incidental and natural nanoparticles (NP), colloids, micro- and nanoplastics) reach aqueous environments (both engineered and natural) through many different pathways. Whereas some of these contaminants are of less of concern due to their limited impact on ecosystems (e.g. clay minerals), others may have long-term and negative impacts on environmental health and are thus of increasing concern (e.g., toxic metals sorbed to iron colloids, carbon nanotubes, microplastics). The (unintended) release and the fate of these particulate contaminants into the aquatic environment are only poorly understood mainly due to the he lack of adequate analytical techniques to detect and characterize such materials in the environment. My research therefore, aims at combining well established standard characterization methods from colloidal sciences, with novel methods from materials science and with own developments to detect, quantify and understand the impacts of the particulate contaminants in the aquatic environment. The following research areas are of particular interest:

Fate of particulate contaminants in the natural environment and engineered systems.
Although a large variety of analytical methods exist to characterize nano scale materials (and especially nanoparticles), these methods were mainly developed for materials science applications. Therefore, these methods were optimized for detecting pure substances in high concentrations (such as Ag-NP in concentrated stock solutions). Transferring the methods to investigate (nano)particulate contaminants, present at trace concentrations and in complex matrices (e.g., soil, slugde) is very challenging. We therefore try to separate aquatic colloids, including engineered NP, microplastics or rate earth element-colloids from their surrounding matrices using different approaches such as density separation, field flow fractionation, magnetic seeded filtration, oxidative and enzymatic digestions. Isolated particles are the characterized and quantified using for example light scattering (DLS, SLS), mass and vibration spectroscopic (ICP-MS,µ-FT-IR) or (electron) microscopic (SEM, TEM) techniques.

To study the fate of (nano)contaminants in (waste)water systems, our state of the art analytical facilities are complemented by a series of experimental facilities ranging from lab to pilot scale. This allows us to mimick real world conditions and address open questions at the most suitable (experimental) scale.   

Development and validation of new approaches to quantify particulate (nano)contaminants
Electron microscopy represents an alternative and powerful approach to i) characterize individual (nano) particles down to the single digit nm range and ii) to extend the automated measurements of microplastic down to 1µm. In concert with other, bulk  analytical methods, including inductively coupled plasma spectroscopy and synchrotron x-ray absorption spectroscopy, we  use (automated) electron microscopy techniques (including own developments) to decipher the fate of (nano)particulate pollutant in managed waste facilities.

Currently, the lack of validated methods is one of the biggest challenge in microplastics research and hampers the comparison of results obtained from different studies. On the one hand address this issue by developing our own quality assurance and quality control measures, and on the other we are establishing uncertainty budgets for the whole analytical chain tailed for microplastics analysis.   


Experimental facilities

  • Wastewater

        Conventional activated sludge system (nitrification, denitrification, secondary clarification)

        Anaerobic digestion ('Apollo')

  • Surface water

        Custom made drum sieve designed for collection of particulate matter (e.g., microplastics) (planning         phase)

  • Weathering

        UV-exposure (SunTESTER, CPS+) -> Photooxidation

        Mechanical abrasion (Roller Mill, RM1) -> simulation of beach environments

        Temperature fluctuations (computer controlled temperature baths) -> simulating freeze - thaw cycles         (collaboration with Prof. Stephan Gruber, Carlton UNiversity, Ottawa, Canada) 


Analytical facilities

  • Particle size analysis

       Dynamic Light Scattering (DLS) Analyzer (Zetasizer, NanoZS, Malvern)

       Laser Diffraction Particle Size Analyzer (LS 13 320, Beckman Coulter)

        asymmetric flow field flow fractionation system (Eclipse, Wyatt) in-line coupled to UV-DAD detector.         DLS - detector, static light scattering (SLS) detector (Helios, Waytt) and a fraction collector.

  • visible light microscope (VHX-7000, Keyence)
  • Fourier Transform Infrared (FT-IR) Spectroscopy

        Focal plain array (FPA)-µ-FT-IR microscope (Cary 670-IR, FTIR, Cary 610 IR Mikroskop)

  • Electron microscopes

        Scanning electron microscope (Gemini 460, equipped with 2 EDX detectors (Extreme and Ultrmate,         Oxford) Zeiss). Shared with and operated by Empa

        Transmission electron microscope (Talos, FEI and HD2700Cs, Hitachi). Both instruments are         operated by ScopeM (access via user training).

        

Particle Laboratory

Apart from my own research outlined above I also run the particle laboratory at Eawag. The particle laboratory is a contact-point for all sorts of particle-related questions, especially concerning microscopic work. My engagement in different projects covers all ranges from simple advice over a few measurements for a feasibility study up to solid collaborations. Thanks to very good contacts to the electron microscopy centers at ETHZ and Empa, experts on any kind of materials can be consulted if necessary.


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Publications

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Galgani, F., Lusher, A. L., Strand, J., Haarr, M. L., Vinci, M., Molina Jack, E., … van Bavel, B. (2024). Revisiting the strategy for marine litter monitoring within the european marine strategy framework directive (MSFD). Ocean and Coastal Management, 255, 107254 (11 pp.). doi:10.1016/j.ocecoaman.2024.107254, Institutional Repository

Marine litter and non-degradable plastic pollution is of global concern. Regular monitoring programs are being established to assess and understand the scale of this pollution. In Europe, the goal of the European Marine Strategy Framework Directive (MSFD) is to assess trends in Good Environmental Status and support large-scale actions at the regional level. Marine litter monitoring requires tailored sampling strategies, protocols and indicators, that align with specific objectives and are tailored for local or regional needs. In addition, the uneven spatial and temporal distributions of marine litter present a challenge when designing a statistically powerful monitoring program. In this paper, we critically review the existing marine litter monitoring programs in Europe. We discuss the main constraints, including environmental, logistical, scientific, and ethical factors. Additionally, we outline the critical gaps and shortcomings in monitoring MSFD beaches/shorelines, floating litter, seafloor litter, microplastics, and harm. Several priorities must be established to shape the future of monitoring within the MSFD. Recent developments in analytical approaches, including optimizing protocols and sampling strategies, gaining a better understanding of the spatiotemporal heterogeneity of litter and its implications for survey design and replication, and the inclusion of newly validated methodologies that have achieved sufficient technical readiness, must be considered. Although there are well-established methods for assessing beaches, floating and seafloor litter, it will be necessary to implement monitoring schemes for microplastics in sediments and invertebrates as robust analytical methods become available for targeting smaller particle size classes. Furthermore, the inclusion of indicators for entanglement and injury to marine organisms will have to be considered in the near future. Moreover, the following actions will enhance the effectiveness of monitoring efforts: (1) creating an inventory of accumulation areas and sources of specific types of litter (e.g., fishing gear), (2) monitoring riverine inputs of litter, (3) monitoring atmospheric inputs including microplastics, (4) accidental inputs during extreme weather events, and (5) studying how species at risk may be transported by litter. We provide recommendations to support long-term, effective, and well-coordinated marine litter monitoring within the MSFD to achieve a comprehensive and accurate understanding of marine litter in EU waters. This will allow the development of measures to mitigate the impacts of marine pollution and eventually to evaluate the success of the respective measures.
Grigg, A. R. C., Notini, L., Kaegi, R., ThomasArrigo, L. K., & Kretzschmar, R. (2024). Aluminium substitution affects jarosite transformation to iron oxyhydroxides in the presence of aqueous Fe(II). Geochimica et Cosmochimica Acta, 374, 72-84. doi:10.1016/j.gca.2024.04.008, Institutional Repository

Jarosite is an abundant mineral in acidic environments, often found in acid sulfate soil (ASS) and acid-mine drainage (AMD). As a store of Fe, K, S and acidity, and a scavenger for major and trace elements, jarosite plays an important role in the biogeochemistry of acid sulfate environments. When ASS and AMD become anoxic, reducing conditions can set in, producing conditions that are outside the thermodynamic stability field of jarosite. In this study, we investigated the transformation of synthetic and natural jarosite with various degrees of Al-for-Fe substitution under circumneutral anoxic conditions in the presence of Fe(II), to understand the rates and pathways of jarosite and Al-jarosite transformation, the role of competing transformation pathways, the fate of Al during transformation and the different reactivity of natural and synthetic Al-jarosite. Synthetic jarosite (containing 0 %–7 % Al-for-Fe substitution) and a natural Al-substituted jarosite sample from an ASS in Thailand were suspended in solutions of 57Fe(II) at pH 7 for 24 h under anoxic conditions. The chosen experimental conditions mimic the Fe(II) concentrations and pH found in flooded ASS under reducing conditions. Changes in mineral composition of the suspensions were determined by Rietveld analysis of X-ray diffraction patterns at six time points. The fate of Al was determined by XRD, Raman spectroscopy and energy dispersive X-ray spectroscopy analysis of the jarosite and product minerals. Different transformation pathways that occurred simultaneously were traced by using 57Fe Mössbauer spectroscopy and aqueous Fe isotope composition. The analysis showed that 7 % Al-for-Fe substitution in jarosite more than halved the mineral transformation rate compared to unsubstituted jarosite, regardless of the Fe(II) concentrations. Indeed, 7 % Al-for-Fe substitution had a greater effect on the transformation rate than an order-of-magnitude decrease in the Fe(II) concentrations in all Al-for-Fe substitution treatments. The transformation products in all samples were goethite, lepidocrocite and ferrihydrite, with minor amounts of magnetite forming from jarosite with no or low Al-for-Fe substitution reacted with high Fe(II) concentrations. Lepidocrocite was the dominant product in reactors without aluminium, but lepidocrocite was not strongly enriched in 57Fe, suggesting that it may not have formed exclusively from Fe in solution during the Fe(II)-catalysed transformation of other minerals. In high-Al systems, lepidocrocite appeared to be a sink for Al, although its formation in Al-rich samples was suppressed. Natural jarosite reacted more than an order of magnitude more slowly than the synthetic jarosite and Al-jarosite, indicating that the properties of the synthetic jarosite do not completely account for the stability of natural jarosite under anoxic circumneutral conditions. The results provide an important baseline for understanding the drivers of jarosite transformation or stability in ASS and AMD.
Grigg, A. R. C., Notini, L., Kaegi, R., ThomasArrigo, L. K., & Kretzschmar, R. (2024). Structural effects of aluminum and iron occupancy in minerals of the jarosite-alunite solid solution. ACS Earth and Space Chemistry, 8(2), 194-206. doi:10.1021/acsearthspacechem.3c00174, Institutional Repository

The alunite supergroup of minerals contains several hydroxysulfate mineral phases that commonly occur in acidic natural and engineered environments. The main division of the mineral supergroup defines two minerals, jarosite and alunite, based on the relative structural occupancy by Al or Fe, respectively. However, intermediate members of the jarosite-alunite solid solution have not been extensively characterized, especially in the environment. Here, we link the mineral unit cell sizes measured by X-ray diffraction, peak shifts in Raman spectra, fitting parameters in Mössbauer spectroscopy, and elemental quantification by EDX spectroscopy to known amounts of Al substitution in two synthetic series of Al-substituted jarosite (up to Al-for-Fe substitution of 9.5%) and unknown Al substitution in a natural jarosite isolated from an acid sulfate soil. Strong correlations were observed between the Al substitution of the jarosite samples and unit cell size, position of several vibrational peaks in Raman spectroscopy, and the temperature of magnetic ordering. In addition, elemental mapping provided a robust way to characterize the Al content of jarosite. As the techniques were effective in quantifying the Al or Fe content of jarosite-alunite supergroup mineral samples, without the need for sample dissolution, the findings support the application of these spectroscopy techniques to characterize natural jarosite-alunite samples. Using these techniques, we demonstrate at least 5% Al-for-Fe substitution in a jarosite sample from an acid sulfate soil. Application to environmental samples is especially useful in cases where it is otherwise difficult to directly measure the Al content of a mineral sample or when Al-for-Fe substitution influences the spectral responses to substitution at other sites in the crystal structure.
Kuehr, S., Kaegi, R., Raths, J., Sinnet, B., Kipf, M., Rehkämper, M., … Georgantzopoulou, A. (2024). Reduced bioavailability of Au and isotopically enriched 109Ag nanoparticles transformed through a pilot wastewater treatment plant in Hyalella azteca under environmentally relevant exposure scenarios. Science of the Total Environment, 949, 174768 (13 pp.). doi:10.1016/j.scitotenv.2024.174768, Institutional Repository

Wastewater Treatment Plants (WWTP) are a major repository and entrance path of nanoparticles (NP) in the environment and hence play a major role in the final NP fate and toxicity. Studies on silver nanoparticles (AgNP) transport via the WWTP system and uptake by aquatic organisms have so far been carried out using unrealistically high AgNP concentrations, unlikely to be encountered in the aquatic environment. The use of high AgNP concentrations is necessitated by both the low sensitivity of the detection methods used and the need to distinguish background Ag from spiked AgNP.
In this study, isotopically enriched 109AgNP were synthesized to overcome these shortcomings and characterized by a broad range of methods including transmission electron microscopy, dynamic and electrophoretic light scattering. 109AgNP and gold NP (AuNP) were spiked to a pilot wastewater treatment plant fed with municipal wastewater for up to 21 days. AuNP were used as chemically less reactive tracer. The uptake of the pristine and transformed NP present in the effluent was assessed using the benthic amphipod Hyalella azteca in fresh- and brackish water exposures at environmentally relevant concentrations of 30 to 500 ng Au/L and 39 to 260 ng Ag/L. The unique isotopic signature of the 109AgNP allowed to detect the material at environmentally relevant concentrations in the presence of a much higher natural Ag background. The results show that the transformations reduce the NP uptake at environmentally relevant exposure concentrations. For 109Ag, lower accumulation factors (AF) were obtained after exposure to transformed NP (250–350) compared to the AF values obtained for pristine 109AgNP (750–840). The reduced AF values observed for H. azteca exposed to effluent from the AuNP-spiked WWTP indicate that biological transformation processes (e.g. eco-corona formation) seem to be involved in addition to chemical transformation.
Nopp-Mayr, U., Layendecker, S., Sittenthaler, M., Philipp, M., Kägi, R., & Weinberger, I. (2024). Microplastic loads in Eurasian otter (Lutra lutra) feces - targeting a standardized protocol and first results from an alpine stream, the River Inn. Environmental Monitoring and Assessment, 196(8), 707 (14 pp.). doi:10.1007/s10661-024-12791-z, Institutional Repository

Microplastics (MP) are omnipresent in a wide range of environments, constituting a potential threat for aquatic and terrestrial wildlife. Effects in consumers range from physical injuries to pathological reactions. Due to potential bioaccumulation of MP, predators are of particular concern for MP induced health effects. The Eurasian otter is an apex predator in (semi-)aquatic habitats feeding primarily on fish. Furthermore, the species is classified as “near threatened” on the IUCN Red List. Thus, the Eurasian otter is of conservation concern and may serve as a bioindicator for MP pollution. Feces can be used to detect pollutants, including MP. Initial studies confirmed the presence of MP in otter feces (= spraints). However, as specific, validated protocols targeting at an efficient and standardized extraction of MP from otter spraints are missing, experimental results reported from different groups are challenging to compare. Therefore, we (i) present steps towards a standardized protocol for the extraction of MP from otter feces, (ii) give recommendations for field sample collection of otter spraints, and (iii) provide a user-friendly step-by-step workflow for MP extraction and analysis. Applying this framework to field samples from five study sites along the River Inn (n = 50), we detected MP of different sizes and shapes (ranging from microfibers to road abrasion and tire wear) in all otter spraint samples.
Schwarzfischer, M., Ruoss, T. S., Niechcial, A., Lee, S. S., Wawrzyniak, M., Laimbacher, A., … Spalinger, M. R. (2024). Impact of nanoplastic particles on macrophage inflammation and intestinal health in a mouse model of inflammatory bowel disease. Nanomaterials, 14(16), 1350 (15 pp.). doi:10.3390/nano14161350, Institutional Repository

Background: The increasing presence of plastics in the human diet is raising public concern about the potential risks posed by nanoplastic (NP) particles, which can emerge from the degradation of plastic debris. NP ingestion poses particular risks to individuals with inflammatory bowel disease (IBD), as compromised epithelial barriers may facilitate NP translocation. Methods: In vitro, bone-marrow-derived macrophages (BMDMs) were exposed to 25 nm polymethacrylate (PMMA) or 50 nm polystyrene (PS) particles to assess morphological changes and alterations in pro- and anti-inflammatory gene expression. In vivo, mice received PMMA NP particles for 6 months before acute dextran sodium sulfate (DSS) colitis was induced to investigate NP impacts on intestinal health and inflammation. Results: PMMA and PS NP exposure in BMDMs induced morphological changes indicative of a proinflammatory phenotype characterized by enlarged amoeboid cell shapes. It also triggered an inflammatory response, indicated by increased expression of proinflammatory cytokines such as Tnfa and Il6. Unexpectedly, long-term PMMA NP administration did not affect the intestinal epithelial barrier or exacerbate acute DSS-induced colitis in mice. Colonoscopy and histological analysis revealed no NP-related changes, suggesting adverse effects on intestinal health or inflammation. Conclusion: Our findings from animal models offer some reassurance to IBD patients regarding the effects of NP ingestion. However, variations in lifestyle and dietary habits may lead to significantly higher plastic intake in certain individuals, raising concerns about potential long-term gastrointestinal effects of lifelong plastic consumption.
Stetten, L., Kaegi, R., Hofmann, T., & von der Kammer, F. (2024). Depth-dependent transformation of ZnO and Ag nanoparticles in sulfate-reducing sediments tracked using scanning transmission electron microscopy. Environmental Science: Nano, 11(1), 136-148. doi:10.1039/d3en00550j, Institutional Repository

Studies on the transformation of engineered nanomaterials (ENMs) based on relevant environmental exposure scenarios are scarce. In this context, we investigated the use of Transmission Electron Microscopy (TEM) grids to expose minute amounts of ZnO and Ag nanoparticles (NPs) to artificial and natural aqueous media and follow their transformation using scanning transmission electron microscopy coupled with energy dispersive X-ray spectroscopy. Short-term experiments conducted with inorganic sulfides confirmed the potential of using TEM grids to monitor the transformation of ENMs at the single particle level. After 30 min, Ag NPs transformed into Ag-sulfides, with Ag : S ratios ≈ 2 : 1, while ZnO NPs showed little evidence of Zn-sulfides precipitation after 6 hours. Ag NPs and ZnO NPs were also exposed to depth-dependent pore water concentration gradients in freshwater sediment columns. After three days and four weeks, all the Ag NPs observed were transformed into Ag-sulfides with various morphologies and Ag : S ratios (1 ≤ Ag/S ≤ 2), depending on the depth and duration of the exposure. Furthermore, a depth-dependent transformation was observed for ZnO NPs. At low sulfide concentration, in the first millimeters below the water-sediment interface, ZnO NPs were completely transformed into ZnS harboring empty shell structures, together with smaller particles in their vicinity. By contrast, ZnO cores persisted in the deeper layers, indicating that ZnO NPs dissolution was inhibited at high sulfide concentrations. Our results demonstrate the advantage of experimental and analytical strategies adapted to study the transformation of ENMs under environmentally relevant conditions, to unravel transformation rates and products not yet considered in risk assessment studies.
la Cecilia, D., Philipp, M., Kaegi, R., Schirmer, M., & Moeck, C. (2024). Microplastics attenuation from surface water to drinking water: impact of treatment and managed aquifer recharge – and identification uncertainties. Science of the Total Environment, 908, 168378 (12 pp.). doi:10.1016/j.scitotenv.2023.168378, Institutional Repository

River water can be used to recharge aquifers exploited for drinking water production. Several recent studies reported microplastics (MPs) in river water, and therefore, the potential contamination of groundwater by MPs is a growing concern among stakeholders and citizens. In this research, we investigate the fate of MPs (> 20 μm) along six different stages of a major Managed Aquifer Recharge (MAR)-water supply system in Switzerland. About 20 l of water were filtered using steel meshes at each location in triplicates. In the laboratory, MPs deposited on the anodisc filters were identified using Focal Plane Array (FPA) micro-Fourier-Transform-InfraRed (μFTIR) spectroscopy. The obtained hyperspectral data were processed using the imaging software Microplastics Finder for MPs identification and classification. Our results revealed a 20-fold decrease in MPs concentration from the Rhine River bed water (112 ± 27.4 MPs/l) to after the coagulation, flocculation and sedimentation (5.5 ± 2.2 MPs/l), a further 3-fold decrease to after the sand-filtration system (1.8 ± 0.9 MPs/l), corresponding to an overall removal efficiency of 98.4 %. The MPs concentrations remained low following MAR (2.7 ± 0.7 MPs/l) through a Quaternary gravel aquifer. Activated carbon filters did not substantially further reduce MPs concentrations. The percentage of fragments (≈95 %) prevailed over fibers (≈5 %) at all locations, with fibers being longer and more abundant in the river water. Overall, this study demonstrates the effectiveness of the treatment systems to remove MPs larger than 20 μm. Finally, we calculated an uncertainty in MPs concentrations of one order of magnitude depending on the user-defined parameters inside the MPs identification and classification model. The Quality Assurance/Quality Control approach followed during laboratory analysis highlighted an accumulation of surrogate particles at the edges of the disc, which would have an impact for MPs number upscaling.
Ballikaya, P., Brunner, I., Cocozza, C., Grolimund, D., Kaegi, R., Murazzi, M. E., … Cherubini, P. (2023). First evidence of nanoparticle uptake through leaves and roots in beech (Fagus sylvatica L.) and pine (Pinus sylvestris L.). Tree Physiology, 43(2), 262-276. doi:10.1093/treephys/tpac117, Institutional Repository

Trees have been used for phytoremediation and as biomonitors of air pollution. However, the mechanisms by which trees mitigate nanoparticle pollution in the environment are still unclear. We investigated whether two important tree species, European beech (Fagus sylvatica L.) and Scots pine (Pinus sylvestris L.), are able to take up and transport differently charged gold nanoparticles (Au-NPs) into their stem by comparing leaf-to-root and root-to-leaf pathways. Au-NPs were taken up by roots and leaves, and a small fraction was transported to the stem in both species. Au-NPs were transported from leaves to roots but not vice versa. Leaf Au uptake was higher in beech than in pine, probably because of the higher stomatal density and wood characteristics of beech. Confocal (3D) analysis confirmed the presence of Au-NPs in trichomes and leaf blade, about 20–30 μm below the leaf surface in beech. Most Au-NPs likely penetrated into the stomatal openings through diffusion of Au-NPs as suggested by the 3D XRF scanning analysis. However, trichomes were probably involved in the uptake and internal immobilization of NPs, besides their ability to retain them on the leaf surface. The surface charge of Au-NPs may have played a role in their adhesion and uptake, but not in their transport to different tree compartments. Stomatal conductance did not influence the uptake of Au-NPs. This is the first study that shows nanoparticle uptake and transport in beech and pine, contributing to a better understanding of the interactions of NPs with different tree species.
Ballikaya, P., Brunner, I., Cocozza, C., Grolimund, D., Kaegi, R., Murazzi, M. E., … Cherubini, P. (2023). Nanoparticles are everywhere, even inside trees. Chimia, 77(4), 256. doi:10.2533/chimia.2023.256, Institutional Repository
Gottschalk, F., Debray, B., Klaessig, F., Park, B., Lacome, J. M., Vignes, A., … Kaegi, R. (2023). Predicting accidental release of engineered nanomaterials to the environment. Nature Nanotechnology, 18, 412-418. doi:10.1038/s41565-022-01290-2, Institutional Repository

Challenges in distinguishing between natural and engineered nanomaterials (ENMs) and the lack of historical records on ENM accidents have hampered attempts to estimate the accidental release and associated environmental impacts of ENMs. Building on knowledge from the nuclear power industry, we provide an assessment of the likelihood of accidental release rates of ENMs within the next 10 and 30 years. We evaluate risk predictive methodology and compare the results with empirical evidence, which enables us to propose modelling approaches to estimate accidental release risk probabilities. Results from two independent modelling approaches based on either assigning 0.5% of reported accidents to ENM-releasing accidents (M1) or based on an evaluation of expert opinions (M2) correlate well and predict severe accidental release of 7% (M1) in the next 10 years and of 10% and 20% for M2 and M1, respectively, in the next 30 years. We discuss the relevance of these results in a regulatory context.
Joëlle Kubeneck, L., ThomasArrigo, L. K., Rothwell, K. A., Kaegi, R., & Kretzschmar, R. (2023). Competitive incorporation of Mn and Mg in vivianite at varying salinity and effects on crystal structure and morphology. Geochimica et Cosmochimica Acta, 346, 231-244. doi:10.1016/j.gca.2023.01.029, Institutional Repository

Vivianite, a ferrous phosphate mineral, can be an important phosphorus (P) sink in non-sulfidic, reducing coastal sediments. The Fe in the crystal structure of vivianite can be substituted by other divalent metal cations such as Mn2+ or Mg2+. Since Mg is much more abundant in coastal porewaters than Mn, the more frequent reports of Mn substitution in vivianites of coastal sediments has been suggested to indicate a preferential incorporation of Mn over Mg into the crystal structure of vivianite. However, although both Mn and Mg substitution in vivianite are environmentally relevant, it is yet unknown whether Mn or Mg is preferentially incorporated and how these isomorphic substitutions alter the crystal structure and morphology of vivianite, parameters which may influence vivianite reactivity. Here, we studied the incorporation of Mn and/or Mg in vivianites formed by co-precipitation at pH 7 in the presence of varying dissolved Mn and/or Mg concentrations and solution salinities resembling an estuarine gradient from 0 to 9 psu. In total, 19 different vivianites were synthesized, with up to 50% of Fe substituted by Mn and Mg. Thermodynamic equilibrium calculations showed that aqueous Mg speciation was altered with increasing salinity, while Mn speciation was less affected, likely explaining the preferential incorporation of Mn in the vivianite structure at higher salinities. 57Fe-Mössbauer spectroscopy revealed that both Mn and Mg were preferentially incorporated in the double-octahedral Fe position, at which intervalence charge transfer is possible during the oxidation of vivianite. In contrast to Mg, which is redox inactive, incorporated Mn can participate in heteronuclear intervalence charge transfer with Fe. Thus, incorporation of either cation may impact the reactivity of vivianite under oxidizing conditions in element specific ways. Results of complementary analyses including X-ray diffraction, electron microscopy and Fe K-edge X-ray absorption spectroscopy further showed that incorporation of Mn and/or Mg led to smaller particle size, increased crystal roughness and thinner crystals, as well as systematic changes in unit cell parameters. These observed changes in crystal morphology might impact the reactivity of vivianite in natural environments and thus the effect of cation incorporation in vivianite should be considered when studying Fe and P cycling in coastal sediments.
Nenonen, V. V., Kaegi, R., Hug, S. J., Göttlicher, J., Mangold, S., Winkel, L. H. E., & Voegelin, A. (2023). Formation and transformation of Fe(III)- and Ca-precipitates in aqueous solutions and effects on phosphate retention over time. Geochimica et Cosmochimica Acta, 360, 207-230. doi:10.1016/j.gca.2023.09.004, Institutional Repository

Exfiltration of anoxic phosphate-rich groundwater into surface water leads to the oxidation of dissolved Fe(II) and the formation of Fe(III)-precipitates that can retain phosphate (PO4) and thereby attenuate eutrophication. Fresh Fe(III)-precipitates transform into more stable phases over time, and retained PO4 may be released again. In parallel, CO2 outgassing can promote the formation of Ca-phosphates or -carbonates that also sequester PO4. In laboratory experiments, we studied the effects of Mg, Ca, silicate (SiO4) and PO4 on these processes. Fresh Fe(III)-precipitates were formed in bicarbonate-buffered aqueous solutions at pH ∼ 7.0 via the oxidation of 0.5 mM Fe(II) in the presence of 0.15 or 0.025 mM PO4, at Mg or Ca concentrations of 0, 0.4, 1.2 or 4 mM and in the absence or presence of 0.5 mM SiO4. After CO2 outgassing, the suspensions were allowed to age for 100 d at pH ∼ 8. Changes in the composition and structure of Fe(III)- and Ca-precipitates over time were probed with spectroscopic and microscopic techniques and were linked to variations in the retention of PO4. The oxidation of Fe(II) led to effective PO4 removal via the formation of Fe(III)-precipitates that consisted of amorphous (Ca-)Fe(III)-phosphate ((Ca)FeP), ferrihydrite (Fh) and, in SiO4-free treatments, lepidocrocite (Lp). During aging, FeP and Fh that had formed in the absence of Mg, Ca and SiO4 rapidly and nearly completely transformed into Lp. Via effects on molecular- and nanoscale precipitate structure, Mg slowed down FeP transformation into Fh, stabilized Fh, and decreased the crystallinity of Lp (in SiO4-free suspensions), Ca stabilized CaFeP against transformation into Fh, and SiO4 stabilized Fh and (Ca)FeP. Core/shell CaFeP/Fh particles formed in electrolytes that contained Ca and SiO4 hardly transformed within 100 d. Calcite only formed at low dissolved PO4 concentrations and, by incorporation of PO4, contributed to PO4 retention. Higher levels of dissolved PO4 inhibited calcite formation but could induce Ca-phosphate precipitation. Differences in precipitate formation and transformation pathways and kinetics were reflected in the extents of PO4 release over the 100-d aging period, ranging from rapid release of 77% of the total PO4 in the treatment without Mg, Ca and SiO4 at 0.15 mM total PO4 to slow release of only 0.1% of the total PO4 at initial concentrations of 4 mM Ca, 0.5 mM SiO4, and 0.025 mM PO4. In summary, this study reveals the conditions and the extents and timescales over which Fe(III)- and Ca-precipitates form and transform and how these processes affect PO4 immobilization in near-neutral natural waters. The detailed new insights into the coupling between Fe(III)- and Ca-precipitate formation and into the interdependent effects of Mg, Ca, SiO4 and PO4 are not only relevant with respect to PO4 but also with respect to the cycling of trace elements in natural and engineered systems.
Pulido-Reyes, G., Bianco, C., Magherini, L., Sethi, R., von Gunten, U., Kaegi, R., & Mitrano, D. M. (2023). Rückhalt von Nanoplastik-Partikeln bei der Wasseraufbereitung. Aqua & Gas, 103(7-8), 30-35. , Institutional Repository

Nanoplastik-Partikel (NP) werden bei einer klassischen Wasseraufbereitung bestehend aus Schnell- und Langsamsandfiltration sowie Aktivkohlefiltration gut aus Seewasser entfernt. Eine simulation einer Wasseraufbereitungsanlage ergab ein Eliminationseffizient von > 99,9%. Der Biofilm des Langsamsandfilters ist dabei das wichtigste Element. Die Ozonbehandlung verändert die NP kaum und hat somit keinen Einfluss auf den Rückhalt der NP bei der nachgeschalteten Sandund Aktivkohlefiltration.
Sodnikar, K., Kaegi, R., Christl, I., Schroth, M. H., & Sander, M. (2023). Transport of double-stranded ribonucleic acids (dsRNA) and deoxyribonucleic acids (DNA) in sand and iron oxide-coated sand columns under varying solution chemistries. Environmental Science: Processes and Impacts, 25(12), 2067-2080. doi:10.1039/d3em00294b, Institutional Repository

Assessing ecological risks associated with the use of genetically modified RNA interference crops demands an understanding of the fate of crop-released insecticidal double-stranded RNA (dsRNA) molecules in soils. We studied the adsorption of one dsRNA and two double-stranded DNA as model nucleic acids (NAs) during transport through sand- and iron oxide-coated sand (IOCS)-filled columns over a range of solution pH and ionic compositions. Consistent with NA-sand electrostatic repulsion, we observed only slight retention of NAs in sand columns. Conversely, pronounced NA retention in IOCS columns is consistent with strong and irreversible NA adsorption involving electrostatic attraction to and inner-sphere complex formation of NAs with iron oxide coatings. Adsorption of NAs to iron oxides revealed a fast and a slow kinetic adsorption regime, possibly caused by the excluded-area effect. Adsorption of NAs to sand and IOCS increased in the presence of dissolved Mg2+ and with increasing ionic strength, reflecting cation-bridging and screening of repulsive electrostatics, respectively. The co-solute phosphate and a pre-adsorbed dissolved organic matter isolate competitively suppressed dsRNA adsorption to IOCS. Similar adsorption characteristics of dsRNA and similarly sized DNA suggest that existing information on DNA adsorption to soil particles helps in predicting adsorption and fate of dsRNA molecules in soils.
Xu, J., Chen, C., Hu, X., Chen, D., Bland, G., Wielinski, J., … Lowry, G. V. (2023). Particle-scale understanding of arsenic interactions with sulfidized nanoscale zerovalent iron and their impacts on dehalogenation reactivity. Environmental Science and Technology, 57(51), 21917-21926. doi:10.1021/acs.est.3c08635, Institutional Repository

Co-occurrence of organic contaminants and arsenic oxoanions occurs often at polluted groundwater sites, but the effect of arsenite on the reactivity of sulfidized nanoscale zerovalent iron (SNZVI) used to remediate groundwater has not been evaluated. Here, we study the interaction of arsenite [As(III)] with SNZVI at the individual-particle scale to better understand the impacts on the SNZVI properties and reactivity. Surface and intraparticle accumulation of As was observed on hydrophilic FeS-Fe0 and hydrophobic FeS2-Fe0 particles, respectively. X-ray absorption spectroscopy indicated the presence of realgar-like As-S and elemental As0 species at low and high As/Fe concentration ratios, respectively. Single-particle inductively coupled plasma time-of-flight mass spectrometry analysis identified As-containing particles both with and without Fe. The probability of finding As-containing particles without Fe increased with the S-induced hydrophobicity of SNZVI. The interactions of SNZVI materials with coexisting arsenite inhibited their reactivity with water (∼5.8-230.7-fold), trichloroethylene (∼3.6-67.5-fold), and florfenicol (∼1.1-5.9-fold). However, the overall selectivity toward trichloroethylene and florfenicol relative to water was improved (up to 9.0-fold) because the surface-associated As increased the SNZVI hydrophobicity. These results indicate that reactions of SNZVI with arsenite can remove As from groundwater and improve the properties of SNZVI for dehalogenation selectivity.
Grigg, A. R. C., ThomasArrigo, L. K., Schulz, K., Rothwell, K. A., Kaegi, R., & Kretzschmar, R. (2022). Ferrihydrite transformations in flooded paddy soils: rates, pathways, and product spatial distributions. Environmental Science: Processes and Impacts, 24(10), 1867-1882. doi:10.1039/d2em00290f, Institutional Repository

Complex interactions between redox-driven element cycles in soils influence iron mineral transformation processes. The rates and pathways of iron mineral transformation processes have been studied intensely in model systems such as mixed suspensions, but transformation in complex heterogeneous porous media is not well understood. Here, mesh bags containing 0.5 g of ferrihydrite were incubated in five water-saturated paddy soils with contrasting microbial iron-reduction potential for up to twelve weeks. Using X-ray diffraction analysis, we show near-complete transformation of the ferrihydrite to lepidocrocite and goethite within six weeks in the soil with the highest iron(II) release, and slower transformation with higher ratios of goethite to lepidocrocite in soils with lower iron(II) release. In the least reduced soil, no mineral transformations were observed. In soils where ferrihydrite transformation occurred, the transformation rate was one to three orders of magnitude slower than transformation in comparable mixed-suspension studies. To interpret the spatial distribution of ferrihydrite and its transformation products, we developed a novel application of confocal micro-Raman spectroscopy in which we identified and mapped minerals on selected cross sections of mesh bag contents. After two weeks of flooded incubation, ferrihydrite was still abundant in the core of some mesh bags, and as a rim at the mineral–soil interface. The reacted outer core contained unevenly mixed ferrihydrite, goethite and lepidocrocite on the micrometre scale. The slower rate of transformation and uneven distribution of product minerals highlight the influence of biogeochemically complex matrices and diffusion processes on the transformation of minerals, and the importance of studying iron mineral transformation in environmental media.
Kocic, J., Dirin, D. N., Kägi, R., Kovalenko, M. V., Günther, D., & Hattendorf, B. (2022). Direct analysis of nanoparticles in organic solvents by ICPMS with microdroplet injection. Journal of Analytical Atomic Spectrometry, 37(8), 1738-1750. doi:10.1039/d1ja00358e, Institutional Repository

In recent years, the capabilities for characterizing inorganic nanoparticles (NPs) in aqueous solvents with respect to their elemental composition, mass and particle number concentration have been expanded using single particle inductively coupled plasma mass spectrometry (sp-ICPMS). However, NPs with high monodispersity, size, shape and surface chemistry control are frequently synthesized using hot-injection methods, utilizing hydrophobic organic ligands which are only soluble in non-polar organic solvents. Due to several instrumental limitations, suspensions in organic solvents are not commonly analysed by sp-ICPMS. In this study, we investigated the direct introduction of toluene and mesitylene into an ICPMS using a microdroplet generator. With this configuration the solvent load in the ICP is substantially reduced and soot formation, causing instrumental drift, was minimized while maintaining a transport efficiency (TE) of 100%. Furthermore, the effect of different vacuum interface configurations and the addition of oxygen or nitrogen on the detection efficiency (DE) and instrumental background signals was investigated for Al, Si, Ti, Fe Cu, Ag, Cd, and Pb. The highest DE was obtained for a “Jet” interface with the addition of nitrogen at a flow rate of 10 mL min−1, resulting in an increase by a factor of 2-8 depending on the element. The lowest detectable mass, based on counting statistics, was 1.4 ag for Pb, which corresponds to a diameter of 6.1 nm of a spherical, metallic NP. The approach can not only be used for NP characterization, but also holds promise for the sensitive determination of trace elements in organic solvents.
Murazzi, M. E., Cherubini, P., Brunner, I., Kägi, R., Saurer, M., Ballikaya, P., … Gessler, A. (2022). Can forest trees take up and transport nanoplastics?. iForest, 15(2), 128-132. doi:10.3832/ifor4021-015, Institutional Repository

Plastic contamination of ecosystems has increased dramatically over the last decades, raising concerns about the negative impacts of plastic particles on aquatic and terrestrial systems. In recent years, the focus of most research has shifted from large fragments (macroplastic) to micro- (<5 mm) and more recently to nano-plastic (<1000 nm) particles as more evidence has come to light about their ubiquity in water, soils, and living systems, and their effects on ecosystem and human health. In this study, we investigate nanoplastic uptake in the roots of seedlings (1-2 years old) of three different tree species and assess their transport to different tissues. Parts of the main roots of silver birch (Betula pendula Roth), sessile oak (Quercus petraea Matt. [Liebl.]), and Norway spruce (Picea abies [L.] Karst.) were immersed for one or four days in a suspension containing 13C-labelled nano-sized polystyrene particles (13C-nPS; 99% 13C, d = 28 ± 8 (1 σ) nm). Carbon stable isotope analysis showed significant 13C enrichment (P < 0.05) in the immersed part of the root after one day of treatment in all three species, and after four days in Q. petraea alone. Signals of significant 13C enrichment were also found in the aboveground tissues of the trees. The stem of B. pendula in particular showed a significant 13C enrichment after one day of treatment (P < 0.01). This indicates that nanoplastic particles can be taken up through tree roots into the tree’s central cylinder, where they are subsequently conveyed through the tree by acropetal transport via the xylem.
Notini, L., ThomasArrigo, L. K., Kaegi, R., & Kretzschmar, R. (2022). Coexisting goethite promotes Fe(II)-catalyzed transformation of ferrihydrite to goethite. Environmental Science and Technology, 56(17), 12723-12733. doi:10.1021/acs.est.2c03925, Institutional Repository

In redox-affected soil environments, electron transfer between aqueous Fe(II) and solid-phase Fe(III) catalyzes mineral transformation and recrystallization processes. While these processes have been studied extensively as independent systems, the coexistence of iron minerals is common in nature. Yet it remains unclear how coexisting goethite influences ferrihydrite transformation. Here, we reacted ferrihydrite and goethite mixtures with Fe(II) for 24 h. Our results demonstrate that with more goethite initially present in the mixture more ferrihydrite turned into goethite. We further used stable Fe isotopes to label different Fe pools and probed ferrihydrite transformation in the presence of goethite using 57Fe Mössbauer spectroscopy and changes in the isotopic composition of solid and aqueous phases. When ferrihydrite alone underwent Fe(II)-catalyzed transformation, Fe atoms initially in the aqueous phase mostly formed lepidocrocite, while those from ferrihydrite mostly formed goethite. When goethite was initially present, more goethite was formed from atoms initially in the aqueous phase, and nanogoethite formed from atoms initially in ferrihydrite. Our results suggest that coexisting goethite promotes formation of more goethite via Fe(II)-goethite electron transfer and template-directed nucleation and growth. We further hypothesize that electron transfer onto goethite followed by electron hopping onto ferrihydrite is another possible pathway to goethite formation. Our findings demonstrate that mineral transformation is strongly influenced by the composition of soil solid phases.
Philipp, M., Bucheli, T. D., & Kaegi, R. (2022). The use of surrogate standards as a QA/QC tool for routine analysis of microplastics in sewage sludge. Science of the Total Environment, 835, 155485 (9 pp.). doi:10.1016/j.scitotenv.2022.155485, Institutional Repository

The efficient retention of microplastic particles (MP) during wastewater treatment results in their accumulation in the sewage sludge. Thus, sewage sludge represents a key matrix for understanding MP flows between engineered and natural systems. Building on previous reports, we present a sample preparation protocol optimized for digested sewage sludge. The key steps include acid digestion supported by Fenton reagents, enzymatic digestion, and density separation using sodium polytungstate (density of 1.9 gcm−3). We use colored polyethylene (PE) spheres as surrogate standards to assess sample specific recoveries in terms of number and size, based on visible light (vis) microscopy and focal plane array - micro-Fourier transform - infrared (FPA-μ-FT-IR) imaging. The FT-IR spectra of common MP were identical before and after the digestion procedures and morphological changes were observed for polylactide fibers only. Average recovery rates for PE spheres, polypropylene fibers and polyethylene terephthalate fragments extracted from spiked digested sewage sludge and determined using (automated) vis microscopy ranged from 80% to 100%. Similar recovery rates of around 80% were also obtained for PE spheres based on FPA-μ-FT-IR measurements. The median diameters of red and blue PE spheres in dry state and recovered from spiked deionized water and from extracts of spiked digested sewage sludge determined using vis microscopy ranged between 46 μm and 67 μm. These diameters were similar to 54 μm and 61 μm obtained from the FPA-μ-FT-IR measurements of the corresponding deionized water samples and digested sludge extracts and in line with data from the producer (53 μm–63 μm). Using our digestion protocol in combination with surrogate standards, we measured MP number concentrations of around 10,000 #/g in dried, digested sewage sludge, in agreement with recent results from other studies.
Pulido-Reyes, G., Magherini, L., Bianco, C., Sethi, R., von Gunten, U., Kaegi, R., & Mitrano, D. M. (2022). Nanoplastics removal during drinking water treatment: laboratory- and pilot-scale experiments and modeling. Journal of Hazardous Materials, 436, 129011 (13 pp.). doi:10.1016/j.jhazmat.2022.129011, Institutional Repository

Microplastics detected in potable water sources and tap water have led to concerns about the efficacy of current drinking water treatment processes to remove these contaminants. It is hypothesized that drinking water resources contain nanoplastics (NPs), but the detection of NPs is challenging. We, therefore, used palladium (Pd)-labeled NPs to investigate the behavior and removal of NPs during conventional drinking water treatment processes including ozonation, sand and activated carbon filtration. Ozone doses typically applied in drinking water treatment plants (DWTPs) hardly affect the NPs transport in the subsequent filtration systems. Amongst the different filtration media, NPs particles were most efficiently retained when aged (i.e. biofilm coated) sand was used with good agreements between laboratory and pilot scale systems. The removal of NPs through multiple filtration steps in a municipal full-scale DWTP was simulated using the MNMs software code. Removal efficiencies exceeding 3-log units were modeled for a combination of three consecutive filtration steps (rapid sand filtration, activated carbon filtration and slow sand filtration with 0.4-, 0.2- and 3.0-log-removal, respectively). According to the results from the model, the removal of NPs during slow sand filtration dominated the overall NPs removal which is also supported by the laboratory-scale and pilot-scale data. The results from this study can be used to estimate the NPs removal efficiency of typical DWTPs with similar water treatment chains.
Rhein, F., Nirschl, H., & Kaegi, R. (2022). Separation of microplastic particles from sewage sludge extracts using magnetic seeded filtration. Water Research X, 17, 100155 (11 pp.). doi:10.1016/j.wroa.2022.100155, Institutional Repository

Microplastic particles (MP) are efficiently retained in wastewater treatment plants and enriched in sewage sludge. For monitoring MP contents in wastewater systems, sewage sludge is thus well suited, but also requires an isolation of MP from the sludge matrix, as other sewage sludge components may interfere with the MP identification and quantification. Although organic matter in sludge samples can be removed through acid and enzymatic digestion procedures, cellulose - mainly from toilet paper - remains in the digests, due to its high chemical resistivity and similar density to MP. We apply the separation concept of magnetic seeded filtration to isolate MP through selective hetero-agglomeration with magnetic seed particles. MP and cellulose differ in their hydrophobic properties and we investigate to what extent these differences can be exploited to selectively form MP-magnetite hetero-agglomerates in the presence of cellulose. These hetero-agglomerates are subsequently separated using a magnet. Five MP types (Polyethylene terephthalate (PET), polypropylene (PP), low density polyethylene (LDPE), polyvinyl chloride (PVC) and polystyrene (PS)) and cellulose particles were mixed in different combinations with both hydrophilic and hydrophobic (silanized) magnetite particles. PET, PP, LDPE and PS only poorly agglomerated with pristine (hydrophilic) magnetite, but efficiently formed hetero-agglomerates with hydrophobic magnetite and were successfully removed from suspensions (80 - 100 %). PVC agglomerated more efficiently with pristine than with hydrophobic magnetite and cellulose only agglomerated to a limited extent with either hydrophilic or hydrophobic magnetite, resulting in a high process selectivity. Results from experiments conducted at different ionic strengths and with hydrophilic and hydrophobic magnetite suggests that the agglomeration process was dominated by hydrophobic interactions. Enzymatic and oxidative treatment of the MP only marginally affected the separation efficiencies and (treated) MP spiked to sewage sludge extracts were successfully recovered using magnetic seeded filtration.
Schwarzfischer, M., Niechcial, A., Lee, S. S., Sinnet, B., Wawrzyniak, M., Laimbacher, A., … Spalinger, M. R. (2022). Ingested nano- and microsized polystyrene particles surpass the intestinal barrier and accumulate in the body. NanoImpact, 25, 100374 (9 pp.). doi:10.1016/j.impact.2021.100374, Institutional Repository

Plastic pollution is a major global challenge of our times, baring a potential threat for the environment and the human health. The increasing abundance of nanoplastic (NP) and microplastic (MP) particles in the human diet might negatively affect human health since they - particularly in patients suffering from inflammatory bowel disease (IBD) – might surpass the intestinal barrier. To investigate whether ingested plastic particles cross the intestinal epithelium and promote bowel inflammation, mice were supplemented with NP or MP polystyrene (PS) particles for 24 or 12 weeks before inducing acute or chronic dextran sodium sulfate (DSS) colitis with continuous plastic administration. Although ingested PS particles accumulated in the small intestine and organs distant from the gastrointestinal tract, PS ingestion did not affect intestinal health nor did it promote colitis severity. Although the lack of colitis-promoting effects of small PS particles might be a relief for IBD patients, potential accumulative effects of ingested plastic particles on the gastrointestinal health cannot be excluded.
Stetten, L., Hofmann, T., Proux, O., Landrot, G., Kaegi, R., & von der Kammer, F. (2022). Transformation of zinc oxide nanoparticles in freshwater sediments under oxic and anoxic conditions. Environmental Science: Nano, 9(11), 4255-4267. doi:10.1039/d2en00709f, Institutional Repository

The transformation of zinc oxide nanoparticles (ZnO NPs) has been largely investigated in wastewater treatment plants, recognized as important intermediates before the discharge of NPs into the environment. However, considering direct releases of the pristine ZnO NP forms, additional studies on ZnO NP fate in different environmental compartments are encouraged. In this work, we investigated ZnO NP transformation in lacustrine sediments under defined redox conditions. Using X-ray absorption spectroscopy and wet chemical analyses, we followed ZnO NP and Zn2+ fate over a three-month period in sediments incubated under oxic or anoxic sulfide-rich conditions. Under oxic conditions, ZnO NPs were dissolved within a few hours. By contrast, ZnO NP dissolution under anoxic conditions was much slower, with ∼19% of ZnO NPs remaining at the end of the incubation, together with ∼41% of ZnS, ∼15% of Zn adsorbed onto phyllosilicates and ∼27% of Zn-phyllosilicate-like species. The transient formation of Zn–organic complexes under oxic conditions supports that ZnO NP dissolution is driven by organic compounds, followed by Zn adsorption onto phyllosilicates and the subsequent formation of Zn-layered minerals. Under anoxic conditions, ZnO NP dissolution is inhibited by the precipitation of amorphous ZnS and controlled by the progressive growth of ZnS NPs. These results improve the understanding of ZnO NP transformation in slightly alkaline freshwater sediments and highlight the need to assess NP fate under environmentally relevant conditions.
Szakas, S. E., Lancaster, R., Kaegi, R., & Gundlach-Graham, A. (2022). Quantification and classification of engineered, incidental, and natural cerium-containing particles by spICP-TOFMS. Environmental Science: Nano, 9, 1627-1638. doi:10.1039/d1en01039e, Institutional Repository

Cerium containing nanoparticles (Ce-NPs) from geogenic and anthropogenic sources are frequently found in the environment, and the ability to determine the origins of Ce-NPs relies on the presence of other rare earth elements (REEs), such as La. In this study, we develop a scheme to classify individual natural, incidental, and engineered Ce-containing particles using spICP-TOFMS. Well-characterized CeO2 engineered particles (Ce-ENPs), incidental particles (Ce-INPs) from ferrocerium mischmetal, and natural particles (Ce-NNPs) from ground minerals (bastnaesite and parisite) are used as a model particle system. Based on mixtures of these three Ce-NP types, we demonstrate that the measured signals of Ce, La, and Nd in Ce-NNPs follow Poisson statistics and have conserved element ratios. The Ce-INPs we measure have similar Ce : La mass ratios to those of the Ce-NNPs, and Ce : Nd mass ratios can be used to distinguish these two Ce-NP types. Based on this, we develop particle-type-specific detection limits (LD,sp) for the measurement of La and Nd in Ce-NNPs. Our approach establishes LD,sp values with defined confidence intervals to control false-positive particle-type assignments, and allows us to accurately classify engineered, incidental, and natural Ce-NPs down to effective spherical diameters of 32, 35, and 45 nm, respectively. In pure Ce-NNP suspensions, this approach accurately classifies 68% of all detected Ce-NPs with <4% false assignments. For ternary mixtures of Ce-ENPs, INPs, and NNPs, we classify 56% to 76% of all detected Ce-NPs. We demonstrate a linear response with increasing concentrations of Ce-INPs and Ce-ENPs across approximately three orders of magnitude and can classify particles down to ratios of ∼1:50 for anthropogenic : natural Ce-NPs.
Berg, M., Suess, E., Cayo, L., Bouchet, S., Hug, S. J., Kaegi, R., … Buser, A. M. (2021). Quecksilber im Schweizer Abwasser. Konzentrationen, Massenflüsse, Speziierung und Rückhalt. Aqua & Gas, 101(1), 14-20. , Institutional Repository

In einer landesweiten Studie wurde Quecksilber in Abwässern und Klärschlämmen analysiert, jährliche Gesamtmengen des abwasserbürtigen Quecksilbers ermittelt und die Einhaltung der gesetzlichen Vorgaben überprüft. Ebenso wurde die durchschnittliche Fracht pro Einwohner und der Beitrag der Abwasserreinigungsanlagen zur Quecksilberbelastung der Oberflächengewässer ermittelt. Auf nationaler Ebene waren diese Kennzahlen bisher nicht bekannt.
Etique, M., Bouchet, S., Byrne, J. M., Thomasarrigo, L. K., Kaegi, R., & Kretzschmar, R. (2021). Mercury reduction by nanoparticulate vivianite. Environmental Science and Technology, 55(5), 3399-3407. doi:10.1021/acs.est.0c05203, Institutional Repository

Mercury (Hg) is a toxic trace element of global environmental concern which has been increasingly dispersed into the environment since the industrial revolution. In aquatic and terrestrial systems, Hg can be reduced to elemental Hg (Hg0) and escape to the atmosphere or converted to methylmercury (MeHg), a potent neurotoxin that accumulates in food webs. FeII-bearing minerals such as magnetite, green rusts, siderite, and mackinawite are recognized HgII reducers. Another potentially Hg-reducing mineral, which commonly occurs in Fe- and organic/P-rich sediments and soils, is the ferrous iron phosphate mineral vivianite (FeII3(PO4)2·8H2O), but its reaction with HgII has not been studied to date. Here, nanoparticulate vivianite (particle size ∼ 50 nm; FeII content > 98%) was chemically synthesized and characterized by a combination of chemical, spectroscopic, and microscopic analyses. Its ability to reduce HgII was investigated at circumneutral pH under anoxic conditions over a range of FeII/HgII ratios (0.1–1000). For FeII/HgII ratios ≥1, which are representative of natural environments, HgII was very quickly and efficiently reduced to Hg0. The ability of vivianite to reduce HgII was found to be similar to those of carbonate green rust and siderite, two of the most effective Hg-reducing minerals. Our results suggest that vivianite may be involved in abiotic HgII reduction in Fe and organic/P-rich soils and sediments, potentially contributing to Hg evasion while also limiting MeHg formation in these ecosystems.
Kaegi, R., Gogos, A., Voegelin, A., Hug, S. J., Winkel, L. H. E., Buser, A. M., & Berg, M. (2021). Quantification of individual Rare Earth Elements from industrial sources in sewage sludge. Water Research X, 11, 100092 (11 pp.). doi:10.1016/j.wroa.2021.100092, Institutional Repository

Rare Earth Elements (REEs) are used in increasing amounts in technical applications and consumer products. However, to date, the contribution of industrial sources to the loads of individual REEs in wastewater streams have not been quantified. Here, we determine the REE contents in sludge collected from 63 wastewater treatment plants (WWTPs) across Switzerland. To quantify the industrial fraction of individual REEs in the sewage sludge, we develop two complementary approaches, based on REE ratios and REE pattern fitting. Unspecific (background) inputs, with REE patterns similar to the averaged REE pattern of soils collected across Switzerland, dominate the REE budget of most WWTPs. A few WWTPs receive significant REE inputs from specific industrial sources. Based on population equivalents of Switzerland, we estimate a total annual load of 4200 kg Cerium (Ce, 0.5 g Ce year-1 capita-1), with an industrial contribution of 2000 kg year-1. The latter agrees with estimates of probabilistic mass flow models for engineered nanoscale CeO2 particles discharged to the sewer network. About 7 kg year-1 of Samarium (Sm,total for Switzerland: 184 kg year-1 or 0.02 g Sm year-1 capita-1) and 3 kg year-1 of Europium (Eu,total for Switzerland: 44 kg year-1 or 0.005 g Eu year-1 capita-1) are assigned to industrial inputs from single WWTPs. Gadolinium (Gd) is used in the form of a stable complex as contrast agent in magnetic resonance imaging. Assuming 10% removal of Gd during wastewater treatment, we calculate an annual discharge of 90 kg of Gd from one individual WWTP to surface waters. WWTPs with exceptionally high industrial inputs of specific REEs warrant detailed investigations to identify the respective sources and to assess whether REE concentrations in effluents are elevated to the same degree.
Kaegi, R., Fierz, M., & Hattendorf, B. (2021). Quantification of nanoparticles in dispersions using transmission electron microscopy. Microscopy and Microanalysis, 27(3), 557-565. doi:10.1017/S1431927621000398, Institutional Repository

The quantification of the particle size and the number concentration (PNC) of nanoparticles (NPs) is key for the characterization of nanomaterials. Transmission electron microscopy (TEM) is often considered as the gold standard for assessing the size of NPs; however, the TEM sample preparation suitable for estimating the PNC based on deposited NPs is challenging. Here, we use an ultrasonic nebulizer (USN) to transfer NPs from aqueous suspensions into dried aerosols which are deposited on TEM grids in an electrostatic precipitator of an aerosol monitor. The deposition efficiency of the electrostatic precipitator was ≈2%, and the transport efficiency of the USN was ≈7%. Experiments using SiO2NPs (50-200 nm) confirmed an even deposition of the nebulized particles in the center of the TEM grids. PNCs of the SiO2NPs derived from TEM images underestimated the expected PNCs of the suspensions by a factor of up to three, most likely resulting from droplet coagulation and NP aggregation in the USN. Nevertheless, single particles still dominated the PNC. Our approach results in reproducible and even deposition of particles on TEM grids suitable for morphological analysis and allows an estimation of the PNC in the suspensions based on the number of particles detected by TEM.
Kuehr, S., Diehle, N., Kaegi, R., & Schlechtriem, C. (2021). Ingestion of bivalve droppings by benthic invertebrates may lead to the transfer of nanomaterials in the aquatic food chain. Environmental Sciences Europe, 33(1), 35 (16 pp.). doi:10.1186/s12302-021-00473-3, Institutional Repository

Background: Manufactured nanomaterials (MNMs) are released into the environment in increasing quantities. Consequently, MNMs also reach the aquatic environment, where they can interact with different organisms. Previous studies have already shown that filter-feeding bivalves can ingest nanomaterials from the surrounding water leading to higher concentration of the material. Furthermore, they have been shown to be vectors for environmental chemicals and pathogens to other organisms, as their feces/pseudofeces (F/pF) play a crucial role as a food source for other species. We exposed bivalves (Corbicula sp.) to MNMs and performed experiments to investigate the possible transport of MNMs by their feces to the benthic amphipod Hyalella azteca. Silver (Ag) and gold (Au) nanoparticles (NPs) as well as fluorescent polystyrene nanoparticles were used in this study. They allowed the investigation of the metal content of the bivalves’ feces and the amphipods feeding on it, as well as the localization of the fluorescent particles in the body of the animals.
Results: Examination of the feces by fluorescence microscope and determination of the total metal content by inductively coupled plasma mass spectrometry (ICP-MS) showed a high accumulation of the exposed MNMs in the F/pF. The examination of fecal matter, using transmission electron microscopy confirmed the nanoparticulate character of the metals in the examined fecal matter. After exposure of amphipods to the MNMs containing fecal matter, the fluorescent MNMs were localized in the animals gut. The chronic exposure of juvenile amphipods over 21 days to feces enriched with Au MNMs caused significant effects on the growth of the amphipods. The transfer of both metals (Ag and Au) from the fecal matter to the amphipods was confirmed after total metal measurements.
Conclusion: Probably, for the first time, it has been shown that when exposed to MNMs bivalves can transfer these particles to other benthic species. Transfer is via released F/pF upon which the benthic species feed and thus could ingest the particles. The high concentrations of MNMs in the fecal matter raises concerns about the potential accumulation and transfer of the materials and associated ecotoxicological effects in invertebrates such as benthic amphipods.
Kuehr, S., Kaegi, R., Maletzki, D., & Schlechtriem, C. (2021). Testing the bioaccumulation potential of manufactured nanomaterials in the freshwater amphipod Hyalella azteca. Chemosphere, 263, 127961 (15 pp.). doi:10.1016/j.chemosphere.2020.127961, Institutional Repository

Standardized experimental approaches for the quantification of the bioaccumulation potential of nanomaterials in general and in (benthic) invertebrates in particular are currently lacking. We examined the suitability of the benthic freshwater amphipod Hyalella azteca for the examination of the bioaccumulation potential of nanomaterials. A flow-through test system that allows the generation of bioconcentration and biomagnification factors was applied. The feasibility of the system was confirmed in a 2-lab comparison study. By carrying out bioconcentration and biomagnification studies with gold, titanium dioxide and silver nanoparticles as well as dissolved silver (AgNO3) we were able to assess the bioaccumulation potential of different types of nanomaterials and their exposure pathways. For this, the animals were examined for their total metal body burden using inductively coupled mass spectroscopy (ICP-MS) and for the presence of nanoparticulate burdens using single-particle ICP-MS. The role of released ions was highlighted as being very important for the bioavailability and bioaccumulation of metals from nanoparticles for both examined uptake paths examined (bioconcentration and biomagnification). In 2018 a tiered testing strategy for engineered nanomaterials was proposed by Handy et al. that may allow a waiver of bioaccumulation fish studies using inter alia invertebrates. Data gained in studies carried out with invertebrates like the developed Hyalella azteca test may be included in this proposed tiered testing strategy.
Mehrabi, K., Kaegi, R., Günther, D., & Gundlach-Graham, A. (2021). Emerging investigator series: automated single-nanoparticle quantification and classification: a holistic study of particles into and out of wastewater treatment plants in Switzerland. Environmental Science: Nano, 8(5), 1211-1225. doi:10.1039/d0en01066a, Institutional Repository

Single particle inductively coupled plasma time-of-flight mass spectrometry (sp-ICP-TOFMS), in combination with online microdroplet calibration, allows for the determination of particle number concentrations (PNCs) and the amount (i.e. mass) of ICP-MS-accessible elements in individual particles. Because sp-ICP-TOFMS analyses of environmental samples produce rich datasets composed of both single-metal nanoparticles (smNPs) and many types of multi-metal NPs (mmNPs), interpretation of these data is well suited to automated analysis schemes. Here, we present a new data analysis approach that includes: 1. automatic particle detection and elemental mass determinations based on online microdroplet calibration, 2. correction of false (randomly occurring) multi-metal associations caused by measurement of coincident but distinct NPs, and 3. unsupervised clustering analysis of mmNPs to identify unique classes of NPs based on their element compositions. To demonstrate the potential of our approach, we analyzed water samples collected from the influent and effluent of five wastewater treatment plants (WWTPs) across Switzerland. We determined elemental masses in individual NPs, as well as PNCs, to estimate the NP removal efficiencies of the individual WWTPs. From WWTP samples collected at two points in time, we found an average of 90% and 94% removal efficiencies of single-metal and multi-metal NPs, respectively. Between 5% to 27% of detected NPs were multi-metal; the most abundant particle types were those rich in Ce-La, Fe-Al, Ti-Zr, and Zn-Cu. Through hierarchical clustering, we identified NP classes conserved across all WWTPs, as well as particle types that are unique to one or a few WWTPs. These uniquely occurring particle types may represent point sources of anthropogenic NPs. We describe the utility of clustering analysis of mmNPs for identifying natural, geogenic NPs, and also for the discovery of new, potentially anthropogenic, NP targets.
Mehrabi, K., Kaegi, R., Günther, D., & Gundlach-Graham, A. (2021). Quantification and clustering of inorganic nanoparticles in wastewater treatment plants across Switzerland. Chimia, 75(7-8), 642-646. doi:10.2533/chimia.2021.642, Institutional Repository

Single particle Inductively Coupled Plasma Time-of-Flight Mass Spectrometry (sp-ICP-TOFMS), in combination with online microdroplet calibration, allows the determination of particle number concentrations (PNCs) and the masses of elements in individual particles. Because sp-ICP-TOFMS analyses of environmental samples produce rich datasets composed of both single-metal nanoparticles (smNPs) and many types of multi-metal NPs (mmNPs), interpretation of these data is well suited to automated analysis schemes. Here, we present a data analysis approach that includes automatic particle detection and elemental mass determinations based on online microdroplet calibration, and unsupervised clustering analysis of mmNPs to identify unique classes of NPs based on their element compositions. To demonstrate the potential of our approach, we analyzed wastewater samples collected from the influent and effluent of five wastewater treatment plants (WWTPs) across Switzerland. We determined elemental masses in individual NPs, as well as PNCs, to estimate the NP removal efficiencies of the individual WWTPs. Through hierarchical clustering, we identified NP classes conserved across all WWTPs; the most abundant particle types were those rich in Ce-La, Fe-Al, Ti-Zr, and Zn-Cu. In addition, we found particle types that are unique to one or a few WWTPs, which could indicate point sources of anthropogenic NPs.
Schulz, K., ThomasArrigo, L. K., Kaegi, R., & Kretzschmar, R. (2021). Stabilization of ferrihydrite and lepidocrocite by silicate during Fe(II)-catalyzed mineral transformation: impact on particle morphology and silicate distribution. Environmental Science and Technology, 56(9), 5929-5938. doi:10.1021/acs.est.1c08789, Institutional Repository

Interactions between aqueous ferrous iron (Fe(II)) and secondary Fe oxyhydroxides catalyze mineral recrystallization and/or transformation processes in anoxic soils and sediments, where oxyanions, such as silicate, are abundant. However, the effect and the fate of silicate during Fe mineral recrystallization and transformation are not entirely understood and especially remain unclear for lepidocrocite. In this study, we reacted (Si-)ferrihydrite (Si/Fe = 0, 0.05, and 0.18) and (Si-)lepidocrocite (Si/Fe = 0 and 0.08) with isotopically labeled 57Fe(II) (Fe(II)/Fe(III) = 0.02 and 0.2) at pH 7 for up to 4 weeks. We followed Fe mineral transformations with X-ray diffraction and tracked Fe atom exchange by measuring aqueous and solid phase Fe isotope fractions. Our results show that the extent of ferrihydrite transformation in the presence of Fe(II) was strongly influenced by the solid phase Si/Fe ratio, while increasing the Fe(II)/Fe(III) ratio (from 0.02 to 0.2) had only a minor effect. The presence of silicate increased the thickness of newly formed lepidocrocite crystallites, and elemental distribution maps of Fe(II)-reacted Si-ferrihydrites revealed that much more Si was associated with the remaining ferrihydrite than with the newly formed lepidocrocite. Pure lepidocrocite underwent recrystallization in the low Fe(II) treatment and transformed to magnetite at the high Fe(II)/Fe(III) ratio. Adsorbed silicate inactivated the lepidocrocite surfaces, which strongly reduced Fe atom exchange and inhibited mineral transformation. Collectively, the results of this study demonstrate that Fe(II)-catalyzed Si-ferrihydrite transformation leads to the redistribution of silicate in the solid phase and the formation of thicker lepidocrocite platelets, while lepidocrocite transformation can be completely inhibited by adsorbed silicate. Therefore, silicate is an important factor to include when considering Fe mineral dynamics in soils under reducing conditions.
Wielinski, J., Gogos, A., Voegelin, A., Müller, C. R., Morgenroth, E., & Kaegi, R. (2021). Release of gold (Au), silver (Ag) and cerium dioxide (CeO2) nanoparticles from sewage sludge incineration ash. Environmental Science: Nano, 8(11), 3220-3232. doi:10.1039/D1EN00497B, Institutional Repository

Engineered nanoparticles (NPs) that are released into wastewater are retained by wastewater treatment plants (WWTPs) and accumulate in sewage sludge. Increasing shares of sludge are incinerated and landfilled, especially in industrialized countries. It is debated whether certain types of NPs can outlive the incineration process and subsequently be released from sewage sludge ash (SSA) landfills. To investigate the release of different types of NPs from SSA, we spiked gold (Au), silver (Ag) and cerium dioxide (CeO2) NPs to a pilot WWTP increasing the Au, Ag and Ce concentrations to 30, 43 and 389 mg kg-1 (dry matter basis) in the digested sludge. The spiked sludge was incinerated in a pilot fluidized bed reactor resulting in SSA with Au, Ag and Ce concentrations of 61, 103 and 854 mg kg-1. In addition, two sludge samples from a full-scale WWTP with Au concentrations of 5 and 16 mg kg-1 were incinerated, resulting in SSA with 9 mg kg-1 and 30 mg kg-1 Au. The spiked Au-NPs remain largely unaltered during the wastewater treatment and incineration process, whereas Ag-NPs and CeO2-NPs undergo transformation. During simulated landfill leaching in columns flushed with 400 to 500 pore volumes of artificial rainwater, Ag and Ce were retained in the ash, whereas about 17% of the spiked Au was released, mainly in particulate form. Lower fractions of mostly particulate Au were released from the ashes (3 and 9%) of unspiked SSA. In conclusion, unaltered Au-NPs significantly leach from landfilled SSA, whereas the incorporation of Ag-NPs and CeO2-NPs as transformed species into the SSA matrix limits the leaching of (nano)particulate and dissolved Ag and Ce compounds.
Wielinski, J., Voegelin, A., Grobéty, B., Müller, C. R., Morgenroth, E., & Kaegi, R. (2021). Transformation of TiO2 (nano)particles during sewage sludge incineration. Journal of Hazardous Materials, 411, 124932 (14 pp.). doi:10.1016/j.jhazmat.2020.124932, Institutional Repository

Titanium dioxide (TiO2) (nano)particles are produced in large quantities and their potential impacts on ecosystems warrants investigations into their fate after disposal. TiO2 particles released into wastewater are retained by wastewater treatment plants and accumulate in digested sludge, which is increasingly incinerated in industrialized countries. Therefore, we investigated the changes of the Ti-speciation during incineration of as-received sludge and of sludge spiked with anatase (d=20–50 nm) or rutile (d=200–400 nm) using X-ray absorption spectroscopy (XAS) and transmission electron microscopy (TEM). In the as-received sludge, rutile and anatase were the dominant Ti bearing minerals and both remained unaffected by the anaerobic treatment. During incineration, Ti reacts with hematite to members of the hematite-ilmenite solid solution series (Hem-Ilm). Up to 80% of the Ti spiked as anatase transformed into Hem-Ilm, a distorted 6-fold coordinated Ti (Ti(IV)sulfate) and rutile during incineration. Up to 30% and 60% of rutile transformed into Hem-Ilm and Ti(IV)sulfate represented phases in fly and bottom ash, respectively. Fe and Ti were spatially correlated in ash derived from as-received and anatase spiked sludge, whereas only a thin layer of the spiked rutile reacted with Fe, in line with XAS data. This study highlights the transient nature of nano-Ti species during sewage sludge incineration.
Al-Sid-Cheikh, M., Rowland, S. J., Kaegi, R., Henry, T. B., Cormier, M. A., & Thompson, R. C. (2020). Synthesis of 14C-labelled polystyrene nanoplastics for environmental studies. Communications Materials, 1(1), 97 (8 pp.). doi:10.1038/s43246-020-00097-9, Institutional Repository

Available analytical methods cannot detect nanoplastics at environmentally realistic concentrations in complex matrices such as biological tissues. Here, we describe a one-step polymerization method, allowing direct radiolabeling of a sulfonate end-capped nano-sized polystyrene (nPS; proposed as a model nanoplastic particle representing negatively charged nanoplastics). The method, which produces nanoplastics trackable in simulated environmental settings which have already been used to investigate the behavior of a nanoplastic in vivo in a bivalve mollusc, was developed, optimized and successfully applied to synthesis of 14C-labeled nPS of different sizes. In addition to a description of the method of synthesis, we describe the details for quantification, mass balance and recovery of the labelled particles from complex matrices offered by the radiolabelling approach. The radiolabeling approach described here, coupled to use of a highly sensitive autoradiographic method for monitoring nanoplastic body burden and distributions, may provide a valuable procedure for investigating the environmental pathways followed by negatively charged nanoplastics at low predicted environmental concentrations. Whether the behaviour of the synthetic nPS manufactured here, synthesised using a very common inititator, represents that of manufactured nPS found in the environment, remains to be seen.
Dörner, L., Schmutz, P., Kägi, R., Kovalenko, M. V., & Jeurgens, L. P. H. (2020). Electrophoretic deposition of nanoporous oxide coatings from concentrated CuO nanoparticle dispersions. Langmuir, 36(28), 8075-8085. doi:10.1021/acs.langmuir.0c00720, Institutional Repository

Electrophoretic deposition (EPD) of nanoporous oxide coatings is an interesting research avenue owing to the experimental simplicity and broad scope of applications and materials. In this study, the properties of concentrated (up to 5000 mg/L), nonaqueous CuO nanoparticle (NP) dispersions were tailored to produce micrometer-thick, nanoporous CuO films by EPD. In particular, we performed a systematic investigation of the electrophoretic mobilities and size distributions of dispersed CuO aggregates and developing agglomerates in different organic solvents for concentrations ranging from 50 to 5000 mg/L with and without surfactant addition. Time-resolved dynamic light scattering analyses showed that aggregate mobilities and agglomeration rates decrease with increasing hydrocarbon chain length of the organic solvent (from ethanol to hexanol) and thus with increasing viscosity. The highest electrophoretic mobility was obtained for CuO NP aggregates and agglomerates dispersed in ethanol as a solvent. However, the addition of ≥0.5 wt % acetylacetone as a surfactant is required to stabilize these dispersions for subsequent EPD and at the same time introduce a net attractive (electrostatic) interaction between neighboring agglomerates on the substrate to promote layer formation during the EPD step. The produced micrometer-thick nanoporous CuO coatings can serve as high surface area nanostructured materials or nanoporous scaffolds in catalysis, combustion, propellants, and nanojoining.
Frehland, S., Kaegi, R., Hufenus, R., & Mitrano, D. M. (2020). Long-term assessment of nanoplastic particle and microplastic fiber flux through a pilot wastewater treatment plant using metal-doped plastics. Water Research, 182, 115860 (9 pp.). doi:10.1016/j.watres.2020.115860, Institutional Repository

In recent years, several studies have investigated the flux of particulate plastic through municipal waste water treatment plants (WWTP). Challenges related to time consuming analytical methods have limited the number of sampling points and detection limits have hampered quantification of nanoplastic and microplastic fiber fluxes through WWTPs. By synthesizing nanoplastic particles and microplastic fibers labeled with a rare metal (Pd and In, respectively) which can be measured as a proxy for the plastic itself, we have circumvented major analytical pitfalls associated with (micro)plastic measurements. In this study, we spiked the labeled materials to a pilot WWTP mimicking the activated sludge process (nitrification, de-nitrification and secondary clarification). Using a mass flow model for WWTP sludge, we assessed the behavior of particulate plastic in relation to the removal of organic matter. Triplicate samples were collected from the mixed liquor and from the effluent at least twice weekly over the entire experimental run time of 40 d. Our findings show that in discrete grab samples during steady state conditions, at least 98% of particulate plastics were associated with the biosolids. A positive correlation between total suspended solids (TSS) and plastic concentrations was observed in the sludge as well as in the effluent. Because of the strong association between particulate plastic and TSS, TSS removal is likely a good indicator of plastic removal in a full scale WWTP. Therefore, additional process steps in a full-scale WWTP which further reduce the TSS load will likely retain nanoplastic particles and microplastic fibers effectively and consequently increase the removal rates.
Geitner, N. K., Ogilvie Hendren, C., Cornelis, G., Kaegi, R., Lead, J. R., Lowry, G. V., … Wiesner, M. R. (2020). Harmonizing across environmental nanomaterial testing media for increased comparability of nanomaterial datasets. Environmental Science: Nano, 7(1), 13-36. doi:10.1039/c9en00448c, Institutional Repository

The chemical composition and properties of environmental media determine nanomaterial (NM) transport, fate, biouptake, and organism response. To compare and interpret experimental data, it is essential that sufficient context be provided for describing the physical and chemical characteristics of the setting in which a nanomaterial may be present. While the nanomaterial environmental, health and safety (NanoEHS) field has begun harmonization to allow data comparison and re-use (e.g. using standardized materials, defining a minimum set of required material characterizations), there is limited guidance for standardizing test media. Since most of the NM properties driving environmental behaviour and toxicity are medium-dependent, harmonization of media is critical. A workshop in March 2016 at Duke University identified five categories of test media: aquatic testing media, soil and sediment testing media, biological testing media, engineered systems testing media and product matrix testing media. For each category of test media, a minimum set of medium characteristics to report in all NM tests is recommended. Definitions and detail level of the recommendations for specific standardized media vary across these media categories. This reflects the variation in the maturity of their use as a test medium and associated measurement techniques, variation in utility and relevance of standardizing medium properties, ability to simplify standardizing reporting requirements, and in the availability of established standard reference media. Adoption of these media harmonization recommendations will facilitate the generation of integrated comparable datasets on NM fate and effects. This will in turn allow testing of the predictive utility of functional assay measurements on NMs in relevant media, support investigation of first principles approaches to understand behavioral mechanisms, and support categorization strategies to guide research, commercial development, and policy.
Gogos, A., Wielinski, J., Voegelin, A., von der Kammer, F., & Kaegi, R. (2020). Quantification of anthropogenic and geogenic Ce in sewage sludge based on Ce oxidation state and rare earth element patterns. Water Research X, 9, 100059 (8 pp.). doi:10.1016/j.wroa.2020.100059, Institutional Repository

Emissions of Ce from anthropogenic activities (anthropogenic Ce) into urban wastewater systems and the environment result from its widespread industrial use (abrasives, catalysts, nanotechnology). Because Ce in sewage sludge can also be of geogenic origin, the quantification of anthropogenic Ce in sewage sludge remains elusive. In this study, we evaluated the suitability of Ce oxidation state and rare earth element (REE) patterns for the quantification of anthropogenic Ce fractions in sewage sludge. A diverse set of soil samples served to gain baseline information on geogenic Ce. Geogenic Ce in the soils was characterized by high Ce(III) fractions (≥70%) and their REE patterns were comparable to the REE patterns of the upper continental crust. The sewage sludges contained on average ∼80% Ce(IV) (range 18–108%), pointing to the importance of anthropogenic inputs of Ce(IV). The quantification of the anthropogenic Ce fraction based on Ce oxidation state, however, was associated with considerable uncertainty because geogenic and anthropogenic Ce cannot exclusively be assigned to Ce(III) and Ce(IV), respectively. The REE patterns of most sewage sludges indicated a clear enrichment of Ce compared to heavier REE. Based on the assumption that the industrially used Ce is free of (most) other REE, we estimated the fraction of anthropogenic Ce in the sludges based on individual Ce/REE ratios. For the individual sludges the anthropogenic contributions were very variable (10–100%) but consistent fractions were obtained for individual sludges when calculated based on Ce/Dy (dysprosium), Ce/Er (erbium) and Ce/Eu (europium) ratios. Electron microscopy analysis of sludges dominated by anthropogenic Ce revealed that the Ce was mostly contained in nanoscale particles devoid of elements characteristic of Ce-bearing minerals. Thus, anthropogenic Ce contents derived from REE patterns may be used to validate current mass flow models for engineered CeO2 nanoparticles.
Hagemann, N., Schmidt, H. P., Kägi, R., Böhler, M., Sigmund, G., Maccagnan, A., … Bucheli, T. D. (2020). Wood-based activated biochar to eliminate organic micropollutants from biologically treated wastewater. Science of the Total Environment, 730, 138417 (11 pp.). doi:10.1016/j.scitotenv.2020.138417, Institutional Repository

Implementing advanced wastewater treatment (WWT) to eliminate organic micropollutants (OMPs) is a necessary step to protect vulnerable freshwater ecosystems and water resources. To this end, sorption of OMP by activated carbon (AC) is one viable technology among others. However, conventional AC production based on fossil precursor materials causes environmental pollution, including considerable emissions of greenhouse gases. In this study, we produced activated biochar (AB) from wood and woody residues by physical activation and evaluated their capability to eliminate OMPs in treated wastewater. Activated biochar produced under optimized conditions sorbed 15 model OMPs, of which most were dissociated at circumneutral pH, to the same or higher extent than commercial AC used as a reference. While wood quality played a minor role, the dosage of the activation agent was the main parameter controlling the capacity of ABs to eliminate OMP. Our results highlight the possibility for local production of AB from local wood or woody residues as a strategy to improve WWT avoiding negative side effects of conventional AC production.
Hoffmann, K., Bouchet, S., Christl, I., Kaegi, R., & Kretzschmar, R. (2020). Effect of NOM on copper sulfide nanoparticle growth, stability, and oxidative dissolution. Environmental Science: Nano, 7(4), 1163-1178. doi:10.1039/c9en01448a, Institutional Repository

Metal sulfide nanoparticles have recently been discovered in natural environments subject to fluctuating redox conditions such as wetlands and river floodplains, which are often very rich in natural organic matter (NOM). Strong binding of chalcophile metals like copper by NOM is expected to interfere with sulfide precipitation and is likely to affect the growth of these nanoparticles. We therefore conducted experiments on the formation of copper sulfide nanoparticles (CuxS NPs) in anoxic solutions with varying Cu (50, 500 μmol L-1) and sulfide (100, 1000 μmol L-1) concentrations in the absence and presence of Suwannee River fulvic acid (SRFA, 0, 5, 50 mg C L-1). The size development of the CuxS nanoparticles and their stability were tracked over 4 weeks using transmission electron microscopy (TEM) and size-exclusion chromatography coupled to ICP-MS (SEC-ICP-MS). Additional dissolution experiments were performed in closed containers in the absence and presence of O2 and fulvic acid over several months providing insights into the oxidative dissolution behavior of CuxS. Our results highlight the high colloidal stability of CuxS nanoparticles in anoxic environments irrespective of the NOM concentration. Median particle diameters ranged between a few and a few tens of nanometers with larger particles forming in more concentrated suspensions. At low Cu and S concentrations, fulvic acid restricted particle growth by up to 25% compared to SRFA-free suspensions and metal sulfide clusters even smaller than 1 nm were detected. The CuxS nanoparticles exhibited a remarkable chemical stability against oxidative dissolution and were only dissolved when both fulvic acid and O2 were present.
Hoffmann, K., Christl, I., Kaegi, R., & Kretzschmar, R. (2020). Effects of natural organic matter (NOM), metal-to-sulfide ratio and Mn2+ on cadmium sulfide nanoparticle growth and colloidal stability. Environmental Science: Nano, 7(11), 3385-3404. doi:10.1039/d0en00764a, Institutional Repository

Redox-dynamic environments such as river floodplains and wetlands have been identified as sources of natural metal sulfide nanoparticles (MS NPs). However, little information is available on how their growth and colloidal stability are affected by the concentrations of metals and sulfide in solution, the presence of natural organic matter (NOM), and the possible incorporation of other metal cations such as Fe2+ or Mn2+. Here, we performed experiments on the formation of CdS nanoparticles (CdS NPs) in anoxic solutions with varying Cd (50, 100, 500 μmol L-1) and sulfide (50, 100, 1000 μmol L-1) concentrations in the absence and presence of Suwannee River fulvic acid (SRFA, 0, 5, 50 mg C per L). Additionally, we studied the influence of different metal-to-sulfide ratios and varying Mn2+ (0, 0.1, 0.5, 1 mmol L−1) concentrations on CdS aggregation using dynamic light scattering (DLS), transmission electron microscopy (TEM), and electrophoretic mobility measurements. The incorporation of Mn into the crystal lattice of CdS over 8 weeks was investigated with X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS). Our results show that after 24 hours, small CdS primary particles with median diameters of a few nanometers (d~TEM = 2-14 nm) formed large aggregates (d~TEM = 167 nm) and that increasing SRFA concentrations progressively constrained the size of these aggregates (down to 19 nm) irrespective of the initial reactant stoichiometry. When NOM was absent or at low concentration, higher metal-to-sulfide ratios (≥1) and Mn2+ concentrations (≥0.5 mmol L-1) led to reduced colloidal stability of the suspensions. We found that in suspensions containing Mn2+, 10-30% of the Cd atoms in the crystal lattice were substituted by Mn during the formation of CdS, which was prevented by NOM.
Mast, J., Verleysen, E., Hodoroaba, V. D., & Kaegi, R. (2020). Characterization of nanomaterials by transmission electron microscopy: measurement procedures. In V. D. Hodoroaba, W. E. S. Unger, & A. G. Shard (Eds.), Micro and nano technologies. Characterization of nanoparticles. Measurement processes for nanoparticles (pp. 29-48). doi:10.1016/B978-0-12-814182-3.00004-3, Institutional Repository
Pulido-Reyes, G., Mitrano, D. M., Kägi, R., & von Gunten, U. (2020). The effect of drinking water ozonation on different types of submicron plastic particles. In M. Cocca, E. Di Pace, M. E. Errico, G. Gentile, A. Montarsolo, R. Mossotti, & M. Avella (Eds.), Springer Water. Proceedings of the 2nd international conference on microplastic pollution in the Mediterranean Sea (pp. 152-157). doi:10.1007/978-3-030-45909-3_24, Institutional Repository

Plastic pollution has increased in line with the increased plastic production over the last 60 years, having reached all environments globally and potentially affecting drinking water supplies [1, 2, 3]. For example, microplastics have recently been detected in both potable water sources and bottled water for consumption [4], leading researchers to question the efficacy of current water treatment practices. [...]
Suess, E., Berg, M., Bouchet, S., Cayo, L., Hug, S. J., Kaegi, R., … Buser, A. M. (2020). Mercury loads and fluxes from wastewater: a nationwide survey in Switzerland. Water Research, 175, 115708 (10 pp.). doi:10.1016/j.watres.2020.115708, Institutional Repository

Mercury (Hg) pollution threatens ecosystems and human health. Wastewater treatment plants (WWTPs) play a key role in limiting Hg discharges from wastewaters to rivers and lakes, but large-scale studies to estimate Hg loads and discharge at national levels are scarce. We assessed the concentration, flux, speciation, and removal of Hg in municipal wastewater throughout Switzerland by investigating 64 WWTPs in a pre-study and a subset of 28 WWTPs in the main study. We also studied the behavior and pathways of Hg along the various treatment steps in a state-of-the-art WWTP. The resulting dataset, representative of industrialized countries, provides an overview of (i) current Hg concentration ranges, (ii) average per capita loads, and (iii) wastewater Hg inputs into surface waters. The results allowed estimation of a total Hg (THg) load in Swiss wastewater of 130 ± 30 kg THg/year (15.7 mg/capita/y), of which 96 ± 4% is retained in sewage sludge. About 4.7 ± 0.5 kg THg/year (0.57 mg/capita/y) is discharged with the treated wastewater into surface waters. This corresponds to only 1.5-3% of the THg load carried by the major Swiss rivers, indicating that >95% of riverine Hg originates from other sources. Extrapolation to the population of Europe would yield a total amount of 11,700 kg THg/year in raw wastewater, with some 480 kg THg/year discharged to surface waters. Monomethyl mercury on average accounted for 0.23% of THg, and its fraction remained constant along the different treatment steps.
Svendsen, C., Walker, L. A., Matzke, M., Lahive, E., Harrison, S., Crossley, A., … Spurgeon, D. J. (2020). Key principles and operational practices for improved nanotechnology environmental exposure assessment. Nature Nanotechnology, 15, 731-742. doi:10.1038/s41565-020-0742-1, Institutional Repository

Nanotechnology is identified as a key enabling technology due to its potential to contribute to economic growth and societal well-being across industrial sectors. Sustainable nanotechnology requires a scientifically based and proportionate risk governance structure to support innovation, including a robust framework for environmental risk assessment (ERA) that ideally builds on methods established for conventional chemicals to ensure alignment and avoid duplication. Exposure assessment developed as a tiered approach is equally beneficial to nano-specific ERA as for other classes of chemicals. Here we present the developing knowledge, practical considerations and key principles need to support exposure assessment for engineered nanomaterials for regulatory and research applications.
ThomasArrigo, L. K., Bouchet, S., Kaegi, R., & Kretzschmar, R. (2020). Organic matter influences transformation products of ferrihydrite exposed to sulfide. Environmental Science: Nano, 7(11), 3405-3418. doi:10.1039/d0en00398k, Institutional Repository

In redox-dynamic environments, sorption to poorly-crystalline, nanometer-sized Fe(III)-(oxyhydr)oxides like ferrihydrite influences the biogeochemical cycling of nutrients and trace elements. Under sulfate-reducing conditions, the reductive dissolution of ferrihydrite leads to the release of associated constituents, which may be re-immobilized via sorption to secondary Fe minerals. To date, studies following the kinetics and transformation pathways of Fe(III)-(oxyhydr)oxides upon exposure to dissolved sulfide (S(-II)) have largely focused on pure Fe minerals. However, in nature, Fe(III)-(oxyhydr)oxides are often found in association with organic matter (OM). Because ferrihydrite-OM associations exhibit characteristics and biogeochemical reactivity differing from those of pure ferrihydrite, in this study, we compared sulfidization kinetics and transformation pathways of a pure ferrihydrite to those of ferrihydrite coprecipitated with contrasting organic ligands; polygalacturonic acid, galacturonic acid, and citric acid (C/Fe molar ratio ~0.55). Incorporating aqueous- and solid-phase S and Fe speciation analyses (via wet chemistry techniques and S and Fe X-ray absorption spectroscopy) in addition to X-ray diffraction and electron microscopy, we studied both rapid (<7 days) and long-term (12 months) mineral transformations as well as the impact of varying S(-II)/Fe molar ratios at neutral pH. Our results showed that at low S(-II)/Fe molar ratios (=0.1), poorly-crystalline Fe sulfide minerals (e.g. mackinawite) did not form in any (co)precipitate. In contrast, at higher S(-II)/Fe molar ratios (=0.5), mackinawite rapidly precipitated, with higher contributions detected in the coprecipitates than in the pure ferrihydrite. Aging of the samples led to further mineral transformations, including divergent pyrite and greigite precipitation, and an overall increase in the crystallinity of secondary mineral phases. Still, the fraction of residual ferrihydrite at 12 months was higher in the OM-containing coprecipitates, with the most ferrihydrite preservation observed in coprecipitates comprising carboxyl-poor ligands (galacturonic acid and citric acid). This suggests that the presence of OM inhibited S(-II)-induced ferrihydrite mineral transformations and that the composition of the associated OM influenced mineral transformation pathways. Collectively, these results suggest that further studies regarding sulfidization pathways should include OM in order to better represent environmental conditions.
Urstoeger, A., Wimmer, A., Kaegi, R., Reiter, S., & Schuster, M. (2020). Looking at silver-based nanoparticles in environmental water samples: repetitive cloud point extraction bridges gaps in electron microscopy for naturally occurring nanoparticles. Environmental Science and Technology, 54(19), 12063-12071. doi:10.1021/acs.est.0c02878, Institutional Repository

The growing use of silver-based nanoparticles (Ag-b-NPs) in everyday products goes hand in hand with their release into the environment, resulting in ng L–1 traces in natural water bodies. In order to assess their fate, possible transformations and ecotoxicology—essential information to proper risk assessment—particle size, shape, and chemical composition have to be determined. Transmission electron microscopy coupled with energy dispersive X-ray spectroscopy (TEM-EDX) is a powerful tool for determining these particle characteristics, but it requires high particle concentrations in order to produce statistically reliable results. In this study, we will present the extraction of Ag-b-NPs at environmentally relevant concentrations down to 5 ng L–1 from artificial as well as environmental water samples via cloud point extraction on a repetitive basis. The combination with an on-grid centrifugation technique ensures an efficient concentration and deposition of the extracted particles onto the TEM grid for subsequent TEM-EDX measurements. Furthermore, electron microscopy investigations were supplemented by single particle inductively coupled plasma mass spectrometry (sp-ICP-MS) measurements. Ag-b-NPs were successfully visualized and characterized at environmentally relevant concentrations of 5 ng L–1 with TEM-EDX and sp-ICP-MS measurements. Their size, shape, and chemical composition were not affected by the sample preparation.
Velimirovic, M., Wagner, S., Monikh, F. A., Uusimäki, T., Kaegi, R., Hofmann, T., & von der Kammer, F. (2020). Accurate quantification of TiO2 nanoparticles in commercial sunscreens using standard materials and orthogonal particle sizing methods for verification. Talanta, 215, 120921 (10 pp.). doi:10.1016/j.talanta.2020.120921, Institutional Repository

The implementation and enforcement of product labeling obligation as required, for example, by the cosmetic product regulation, needs simple and precise validated analytical methods. This also applies to the analysis of nanoparticles in products such as cosmetics. However, the provision of such methods is often hampered by inaccurate sizing due to unwanted nanoparticle changes, interference of matrix components with sizing and interactions between nanoparticles and analytical instrumentation. It is, therefore, necessary to develop appropriate sample preparation methods that preserve NP properties and reduce or remove matrix compounds that interfere with sizing. Further, accurate particle size analysis of samples containing unknown and possibly multiple nanoparticulate constituents is needed. In this study, we evaluated three sample preparation methods to identify and quantify TiO2 nanoparticles in sunscreens. Specifically, we used a combination of ultracentrifugation and hexane washing, thermal destruction of the matrix, and surfactant assisted particle extraction. The method accuracy was assessed by two internal reference samples: pristine TiO2 nanoparticles (NM104) and similar TiO2 nanoparticles dispersed in a sunscreen matrix. The PSDs were determined using an asymmetrical flow field-flow fractionation hyphenated with multi-angle light scattering and inductively coupled plasma-mass spectroscopy. Particle sizing was based on size calibration of the particle retention time in the AF4. Computation of radius of gyration from MALS data was used as an orthogonal particle sizing approach to verify ideal elution and particle size data from the AF4 calibration. Among the three tested sample preparation methods surfactant assisted particle extraction revealed TiO2 nanoparticle recoveries of above 90% and no increase in particle size due to sample preparation was observed. Finally, the sample preparation methods were applied to two commercial sunscreen samples revealing the existence of TiO2-NP < 100 nm. Conclusively, the surfactant assisted particle extraction method can provide valid data for TiO2-NPs in sunscreen and possibly for cosmetic samples of similar matrix.
Wielinski, J. J. (2020). Investigations into the fate of engineered transition metal nano particles during sewage sludge incineration (Doctoral dissertation). doi:10.3929/ethz-b-000473625, Institutional Repository

Engineered nanoparticles (ENP) are applied in consumer products and industrial processes to increase profitability and sustainability through reduced resource consumption, e.g., TiO2-NP in sun screens, ZnO-NP in cosmetics and paints or Ag-NP and CuO-NP as anti-microbial agents. However, critical discussions about unintended, adverse effects of ENP on humans, soil- and aquatic organisms have always accompanied their usage. Therefore, investigations into the fate of ENP after their use phase are necessary to enable a reliable assessment of the risks associated with the use of such novel materials. Previous research efforts showed that after usage, large shares of ENP applied in consumer products are discharged to wastewater and transported to wastewater treatment plants (WWTPs). WWTPs retain > 95% of ENP leading to their accumulation in sewage sludge. In Switzerland, sewage sludge is incinerated preferably in mono-combustion fluidized bed reactors (FBRs) and the resulting ashes are landfilled for resource recovery in the future. To contribute to a better understanding of the fate and behavior of ENP in the urban environment, the following research questions were addressed: (i) how can the kinetics of sewage sludge devolatilization be quantified, (ii) what chemical and physical transformations of ENP occur during the sewage sludge combustion, (iii) what are the possibilities of synchrotron hard X-ray chemical imaging to study transformation products of ENP, and lastly (iv) to what extent are ENP released from sewage sludge ash landfill sites? [...]

Künstlich produzierte Nanopartikel (NP) werden in Konsumgütern und industriellen Prozessen zur Steigerung von Effizienz und Nachhaltigkeit durch reduzierten Ressourceneinsatz verwendet, z.B. TiO2-NP in Sonnencreme, ZnO-NP in Kosmetika und Farbe oder Ag-NP und CuO-NP zu antimikrobiellen Zwecken. Allerdings ist stets vor ungewollten, nachteiligen Effekten solcher NP gegenüber Menschen, sowie Boden- und Wasserorganismen gewarnt worden. Daher sind Studien über die Transformation und den Verbleib von NP nach ihrer Nutzungsphase notwendig um die oben genannten Risiken der Nutzung solcher neuartigen Materialen zuverlässig abschätzen zu können. Vorangegangene Studien haben gezeigt, dass ein grosser Teil der NP in Konsumgütern in Abwasserkanäle entlassen wird und in Abwasserreinigungsanlangen (ARAs) gelangt. ARAs halten über 95% der einkommenden NP zurück, welche folglich im Faulschlamm aufkonzentriert werden. In der Schweiz wird Faulschlamm vorzugsweise in speziell dafür errichteten Wirbelbettreaktoren verbrannt und die anfallende Asche wird von Asche aus anderen Brennstoffen getrennt deponiert um daraus in der Zukunft Ressourcen rückzugewinnen.
Um ein besseres Verständnis des Verhaltens von NP in städtischen Abwassersystemen und insbesondere während der Klärschlammverbrennung zu gewinnen, wurden die folgenden Forschungsfragen adressiert: (i)Wie lässt sich die Verbrennungskinetik von Klärschlamm quantifizieren, (ii) welche physikalischen und chemischen Transformationsprozesse unterlaufen NP während der Klärschlammverbrennung, (iii) wie können Transformationsprodukte von NP mithilfe synchrotronbasierter, chemische Bildgebung identifiziert werden und (iv) wie gross ist das Freisetzungspotential von NP aus Klärschlammaschedeponien? [...]
Wielinski, J., Marafatto, F. F., Gogos, A., Scheidegger, A., Voegelin, A., Müller, C. R., … Kaegi, R. (2020). Synchrotron hard X-ray chemical imaging of trace element speciation in heterogeneous samples: development of criteria for uncertainty analysis. Journal of Analytical Atomic Spectrometry, 35, 567-579. doi:10.1039/C9JA00394K, Institutional Repository

Synchrotron hard X-ray spectroscopy with focussing optics allows recording X-ray fluorescence (XRF) maps at energies around element specific X-ray absorption edges. Stacking multiple XRF maps along the energy axis yields chemical images that contain spatially resolved information on the speciation of the absorber in the sample matrix at the micrometre scale. Short dwell times needed to keep measurement time and radiation-induced sample changes within acceptable limits result in spectral noise that affects the uncertainty in data analysis. In this study, we develop a model to quantify the uncertainty associated with the processing of XRF image stacks using Bayesian inference. To demonstrate the potential of our approach, the model is applied to stacks of XRF maps collected around the copper (Cu) K-edge (pixel size: 3 × 3 μm2, map sizes: 500 × 500 μm2). The investigated samples include digested sewage sludge spiked with either CuO nanoparticles (NP) or dissolved CuSO4 and their corresponding ashes obtained through incineration. The chemical imaging data reveal differences in species distribution between sludge spiked with CuO NP or dissolved Cu. These differences disappear during the incineration process and the resulting ashes exhibit almost identical Cu species distribution. The uncertainty analysis approach developed in this study can be used for data interpretation, but can also be used for the planning of chemical imaging experiments at synchrotron beamlines.
Wigger, H., Kägi, R., Wiesner, M., & Nowack, B. (2020). Exposure and possible risks of engineered nanomaterials in the environment - current knowledge and directions for the future. Reviews of Geophysics, 58(4), e2020RG000710 (25 pp.). doi:10.1029/2020RG000710, Institutional Repository

The consequences that engineered nanomaterials (ENMs) may cause in the environment have been under investigation for more than 15 years. Hundreds of millions of euros/dollars have been invested into safety issues of ENMs, and much progress has been made in the understanding of their fate and effects in the environment. After an initial phase of "observing the effects," research has shifted toward elucidating the mechanisms of fate and ecotoxicological effects. This also included a stronger focus on exposure issues and the development of analytical methods and computational models to predict exposure. First environmental risk assessments for ENM were performed, and much progress has been achieved on the way to nanospecific and material‐specific assessments. The release of ENM from products and their transformation in technical and natural compartments profoundly affect the form in which the ENMs are present in the environment. A crucial aspect in all areas is if there are truly nanospecific issues of the novel‐added functionalities of ENM that are different from dissolved metals, larger particles, or natural particles. This review outlines progress in understanding the environmental dimensions of ENMs and areas that merit further investigation: To what extent are ENMs different from their natural counterparts and how "long" do we need to track them in natural and technical systems? A major challenge will be in developing methods for studying particle‐mediated processes and their effects on ecosystems and organisms in a more general sense, going beyond just ENM, for example, to natural nanoparticles, microplastics, and extracellular vesicles.
Xu, J., Avellan, A., Li, H., Clark, E. A., Henkelman, G., Kaegi, R., & Lowry, G. V. (2020). Iron and sulfur precursors affect crystalline structure, speciation, and reactivity of sulfidized nanoscale zerovalent iron. Environmental Science and Technology, 54(20), 13294-13303. doi:10.1021/acs.est.0c03879, Institutional Repository

The reactivity of sulfidized nanoscale zerovalent iron (SNZVI) is affected by the amount and species of sulfur in the materials. Here, we assess the impact of the Fe (Fe2+ and Fe3+) and S (S2O42-, S2-, and S62-) precursors used to synthesize both NZVI and SNZVI on the resulting physicochemical properties and reactivity and selectivity with water and trichloroethene (TCE). X-ray diffraction indicated that the Fe precursors altered the crystalline structure of both NZVI and SNZVI. The materials made from the Fe3+ precursor had an expanded lattice in the Fe0 body-centered-cubic (BCC) structure and lower electron-transfer resistance, providing higher reactivity with water (∼2-3 fold) and TCE (∼5-13 fold) than those made from an Fe2+ precursor. The choice of the S precursor controlled the S speciation in the SNZVI particles, as indicated by X-ray absorption spectroscopy. Iron disulfide (FeS2) was the main S species of SNZVI made from S2O42-, whereas iron sulfide (FeS) was the main S species of SNZVI made from S2-/S62-. The former SNZVI was more hydrophobic, reactive with, and selective for TCE compared to the latter SNZVI. These results suggest that the Fe and S precursors can be used to select the conditions of the synthesis process and provide selected physicochemical properties (e.g., S speciation, hydrophobicity, and crystalline structure), reactivity, and selectivity of the SNZVI materials.
Xu, J., Avellan, A., Li, H., Liu, X., Noël, V., Lou, Z., … Lowry, G. V. (2020). Sulfur loading and speciation control the hydrophobicity, electron transfer, reactivity, and selectivity of sulfidized nanoscale zerovalent iron. Advanced Materials, 32(17), 1906010 (10 pp.). doi:10.1002/adma.201906910, Institutional Repository

Sulfidized nanoscale zerovalent iron (SNZVI) is a promising material for groundwater remediation. However, the relationships between sulfur content and speciation and the properties of SNZVI materials are unknown, preventing rational design. Here, the effects of sulfur on the crystalline structure, hydrophobicity, sulfur speciation, corrosion potential, and electron transfer resistance are determined. Sulfur incorporation extended the nano-Fe0 BCC lattice parameter, reduced the Fe local vacancies, and lowered the resistance to electron transfer. Impacts of the main sulfur species (FeS and FeS2) on hydrophobicity (water contact angles) are consistent with density functional theory calculations for these FeSx phases. These properties well explain the reactivity and selectivity of SNZVI during the reductive dechlorination of trichloroethylene (TCE), a hydrophobic groundwater contaminant. Controlling the amount and speciation of sulfur in the SNZVI made it highly reactive (up to 0.41 L m-2 d-1) and selective for TCE degradation over water (up to 240 moles TCE per mole H2O), with an electron efficiency of up to 70%, and these values are 54-fold, 98-fold, and 160-fold higher than for NZVI, respectively. These findings can guide the rational design of robust SNZVI with properties tailored for specific application scenarios.
Zeumer, R., Hermsen, L., Kaegi, R., Kühr, S., Knopf, B., & Schlechtriem, C. (2020). Bioavailability of silver from wastewater and planktonic food borne silver nanoparticles in the rainbow trout Oncorhynchus mykiss. Science of the Total Environment, 706, 135695 (12 pp.). doi:10.1016/j.scitotenv.2019.135695, Institutional Repository

Silver nanoparticles (AgNPs) are present in a wide field of applications and consumer products and are likely to be released into the environment, mainly via urban and industrial sewage due to their extensive use. Even though AgNPs are mostly retained within the sludge of wastewater treatment plants (WWTPs), a small amount of mainly sulfidized particles still enters the aquatic environment, where they can be taken up by various aquatic organisms and transferred along the food chain. In this study, uptake and bioavailability of Ag from AgNPs following aqueous and dietary exposure were investigated in the rainbow trout Oncorhynchus mykiss. AgNPs in the effluent of model WWTPs and in tap water were used to perform aqueous exposure studies. No significant Ag uptake into the gills and carcass of the analyzed fish could be found for wastewater-borne AgNPs. However, when added to tap water at a concentration of 12.4 μg L-1, a maximum total Ag tissue concentrations of around 100 μg kg-1 and 50 μg kg-1 in gills and carcass were measured, respectively. For the dietary exposure studies, freshwater zooplankton was exposed to AgNPs, and used for the preparation of food pellets with a total Ag concentration of 121.5 μg kg-1. During the feeding study with rainbow trout significant total Ag concentrations up to 34.3 μg kg-1 could be found in the digestive tract. However, only a limited transfer of Ag through the intestinal walls into the carcass could be detected. AgNPs in plankton and WWTP effluent were characterized by transmission electron microscopy (TEM) in combination with energy dispersive X-ray spectroscopy (EDX) and found to be sulfidized. This transformation most presumably has led to their limited bioavailability for fish. The results emphasize the importance of realistic test conditions for the risk assessment of AgNPs by the use of environmental matrices.
Aeppli, M., Vranic, S., Kaegi, R., Kretzschmar, R., Brown, A. R., Voegelin, A., … Sander, M. (2019). Decreases in iron oxide reducibility during microbial reductive dissolution and transformation of ferrihydrite. Environmental Science and Technology, 53(15), 8736-8746. doi:10.1021/acs.est.9b01299, Institutional Repository

Ferrous iron formed during microbial ferric iron reduction induces phase transformations of poorly crystalline into more crystalline and thermodynamically more stable iron (oxyhydr)oxides. Yet, characterizing the resulting decreases in the reactivity of the remaining oxide ferric iron toward reduction (i.e., its reducibility) has been challenging. Here, we used the reduction of six-line ferrihydrite by Shewanella oneidensis MR-1 as a model system to demonstrate that mediated electrochemical reduction (MER) allows directly following decreases in oxide ferric iron reducibility during the transformation of ferrihydrite into goethite and magnetite which we characterized by X-ray diffraction analysis and transmission electron microscopy imaging. Ferrihydrite was fully reducible in MER at both pHMER of 5.0 and 7.5. Decreases in iron oxide reducibility associated with ferrihydrite transformation into magnetite were accessible at both pHMER because the formed magnetite was not reducible under either of these conditions. Conversely, decreases in iron oxide reducibility associated with goethite formation were apparent only at the highest tested pHMER of 7.5 and thus the thermodynamically least favorable conditions for iron oxide reductive dissolution. The unique capability to adjust the thermodynamic boundary conditions in MER to the specific reducibilities of individual iron (oxyhydr)oxides makes this electrochemical approach broadly applicable for studying changes in iron oxide reducibility in heterogeneous environmental samples such as soils and sediments.
Aeppli, M., Kaegi, R., Kretzschmar, R., Voegelin, A., Hofstetter, T. B., & Sander, M. (2019). Electrochemical analysis of changes in iron oxide reducibility during abiotic ferrihydrite transformation into goethite and magnetite. Environmental Science and Technology, 53(7), 3568-3578. doi:10.1021/acs.est.8b07190, Institutional Repository

Electron transfer to ferric iron in (oxyhydr-)oxides (hereafter iron oxides) is a critical step in many processes that are central to the biogeochemical cycling of elements and to pollutant dynamics. Understanding these processes requires analytical approaches that allow for characterizing the reactivity of iron oxides toward reduction under controlled thermodynamic boundary conditions. Here, we used mediated electrochemical reduction (MER) to follow changes in iron oxide reduction extents and rates during abiotic ferrous iron-induced transformation of six-line ferrihydrite. Transformation experiments (10 mM ferrihydrite-FeIII) were conducted over a range of solution conditions (pHtrans = 6.50 to 7.50 at 5 mM Fe2+ and for pHtrans = 7.00 also at 1 mM Fe2+) that resulted in the transformation of ferrihydrite into thermodynamically more stable goethite or magnetite. The changes in iron oxide mineralogy during the transformations were quantified using X-ray diffraction analysis. MER measurements on iron oxide suspension aliquots collected during the transformations were performed over a range of pHMER at constant applied reduction potential. The extents and rates of iron oxide reduction in MER decreased with decreasing reaction driving force resulting from both increasing pHMER and increasing transformation of ferrihydrite into thermodynamically more stable iron oxides. We show that the decreases in iron oxide reduction extents and rates during ferrihydrite transformations can be linked to the concurrent changes in iron oxide mineralogy.
Bakshi, M., Liné, C., Bedolla, D. E., Stein, R. J., Kaegi, R., Sarret, G., … Larue, C. (2019). Assessing the impacts of sewage sludge amendment containing nano-TiO2 on tomato plants: a life cycle study. Journal of Hazardous Materials, 369, 191-198. doi:10.1016/j.jhazmat.2019.02.036, Institutional Repository

Increasing evidence indicates the presence of engineered nanoparticles (ENPs) in sewage sludge derived from wastewater treatment. Land application of sewage sludge is, therefore, considered as an important pathway for ENP transfer to the environment. The aim of this work was to understand the effects of sewage sludge containing nano-TiO2 on plants (tomato) when used as an amendment in agricultural soil. We assessed developmental parameters for the entire plant life cycle along with metabolic and bio-macromolecule changes and titanium accumulation in plants. The results suggest that the sewage sludge amendment containing nano-TiO2 increased plant growth (142% leaf biomass, 102% fruit yield), without causing changes in biochemical responses, except for a 43% decrease in leaf tannin concentration. Changes in elemental concentrations (mainly Fe, B, P, Na, and Mn) of plant stem, leaves and, to a lesser extent fruits were observed. Fourier-transformed infrared analysis showed maximum changes in plant leaves (decrease in tannins and lignins and increase in carbohydrates) but no change in fruits. No significant Ti enrichment was detected in tomato fruits. In conclusion, we evidenced no acute toxicity to plants and no major implication for food safety after one plant life cycle exposure.
Dörner, L., Cancellieri, C., Rheingans, B., Walter, M., Kägi, R., Schmutz, P., … Jeurgens, L. P. H. (2019). Cost-effective sol-gel synthesis of porous CuO nanoparticle aggregates with tunable specific surface area. Scientific Reports, 9, 11758 (15 pp.). doi:10.1038/s41598-019-48020-8, Institutional Repository

CuO nanoparticles (NPs) are applied in various key technologies, such as catalysis, energy conversion, printable electronics and nanojoining. In this study, an economic, green and easy-scalable sol-gel synthesis method was adopted to produce submicron-sized nanoporous CuO NP aggregates with a specific surface area > 18 m²/g. To this end, a copper-carbonate containing precursor was precipitated from a mixed solution of copper acetate and ammonia carbonate and subsequently calcinated at T ≥ 250 °C. The thus obtained CuO nanopowder is composed of weakly-bounded agglomerates, which are constituted of aggregated CuO NPs with a tunable size in the range of 100–140 nm. The CuO aggregates, in turn, are composed of equi-axed primary crystallites with a tunable crystallite size in the range of 20–40 nm. The size and shape of the primary CuO crystallites, as well as the nanoporosity of their fused CuO aggregates, can be tuned by controlled variation of the degree of supersaturation of the solution via the pH and the carbonate concentration. The synthesized submicron-sized CuO aggregates can be more easily and safely processed in the form of a solution, dispersion or paste than individual NPs, while still offering the same enhanced reactivity due to their nanoporous architecture.
Gogos, A., Wielinski, J., Voegelin, A., Emerich, H., & Kaegi, R. (2019). Transformation of cerium dioxide nanoparticles during sewage sludge incineration. Environmental Science: Nano, 6, 1765-1776. doi:10.1039/C9EN00281B, Institutional Repository

Production volumes of cerium dioxide nanoparticles (CeO2 NP) are predicted to increase in the near future, which will result in increasing amounts of CeO2 NP discharged into wastewater systems and their accumulation in the sewage sludge. At the same time, thermal treatments of sewage sludge, especially incineration, are gaining in importance. Therefore, knowledge on the physical–chemical transformations of CeO2 NP during wastewater treatment and sludge incineration is critical for assessing possible (eco-) toxicological effects related to the increased use of CeO2 NP. We, thus, incinerated unspiked municipal sewage sludge as well as sludge spiked with CeO2 of different particle sizes (4 nm (CeO2-s1), 26 nm (CeO2-s2) and >16 μm (CeO2-s3)) in a pilot fluidized bed reactor to investigate the (size dependent) transformation of CeO2 under conditions mimicking full-scale incineration facilities. We used Ce K- and LIII-edge X-ray absorption spectroscopy (XAS) complemented by analytical electron microscopy to assess the changes in Ce speciation and to characterize the morphology of the pristine and the transformed Ce-(nano)particles. After one week of incubation in digested sludge under anaerobic conditions, CeO2-s1 already showed partial reduction (≈40%) to a Ce(III)-phase. Cerium dioxide of larger particle size (CeO2-s2 and -s3) was less reactive and did not show any detectable reduction within the same reaction time. Incineration of the sludge in general led to a further reduction of Ce, irrespective of whether the Ce was spiked (CeO2-s1, CeO2-s2, CeO2-s3) or already present in the sludge. Reduction during incineration was nearly complete for CeO2-s1 but much less pronounced for CeO2-s2 and -s3. Ce(IV) in larger (primary-) particle sizes thus was more resistant to reduction during anaerobic digestion and incineration. In addition, elemental distribution maps of the CeO2-s1 fly ash revealed elevated Ce signal intensities evenly distributed over areas of several 100 nm. The complementary results obtained from spectroscopic and microscopic analyses indicate that incineration led to the reductive decomposition of the initial CeO2-s1 NP and the sequestration of Ce(III) into a mineralogical phase with probably allanite-like local Ce(III) coordination. Our results, thus, highlight the importance of particle size and the surrounding matrix both affecting the transformation of CeO2 during sewage sludge incineration.
Hagemann, N., Bucheli, T. D., Schmidt, H. P., Kägi, R., Böhler, M., & McArdell, C. S. (2019). Aktivkohle - Made in Switzerland!. Aqua & Gas, 99(1), 32-38. , Institutional Repository

Die Elimination von Mikroverunreinigungen in der Abwasserreinigung mit Aktivkohle oder Ozon ist eine wichtige Massnahme zum vorbeugenden Schutz der Gewässer und der Trinkwasserressourcen der Schweiz. Während der Einsatz von Ozon mit einem hohen Energieverbrauch einhergeht, führt der Einsatz von Aktivkohle andernorts zu negativen Umweltauswirkungen, da die Aktivkohle zum Teil aus fossilen Ausgangsstoffen wie Stein- oder Braunkohle hergestellt und zudem über weite Strecken transportiert wird. Aktivkohlen mit sehr guten Eliminationsleistungen könnten aber auch in der Schweiz aus einheimischen erneuerbaren Roh- und Reststoffen hergestellt werden.
Hoppe, M., Schlich, K., Wielinski, J., Köser, J., Rückamp, D., Kaegi, R., & Hund-Rinke, K. (2019). Long-term outdoor lysimeter study with cerium dioxide nanomaterial. NanoImpact, 14, 100170 (9 pp.). doi:10.1016/j.impact.2019.100170, Institutional Repository

Fate and impact of cerium dioxide nanomaterials (CeO2 NM) in soil remains uncertain. Most of the recent environmental studies used high doses of CeO2 NM in short-term laboratory experiments and stated soil as large sink for NM. Recent studies covering the life cycle of plants found evidence for particle uptake in crop plants, and triggered concern about NM entering the food chain. Here, we present a 25 months outdoor lysimeter study that investigates the translocation, biological impact, and transformation of CeO2 NM in soils cultivated with different crops (wheat (Triticum aestivum L.), canola (Brassica napus L.), and barley (Hordeum vulgare L.)). Low doses of CeO2 NM (NM-212, 10 and 50 mg CeO2 NM kg−1 soil) were applied to a Cambisol by sewage sludge or artificial rainwater. To simulate ploughing, the CeO2 NM was mixed into the first 20 cm of the lysimeter soil. Three weeks after the NM application by sewage sludge and five days after the latest NM application by artificial rainwater wheat seeds were sown.
We found no vertical Ce translocation to deeper soil layers as well as negligible release of Ce into percolating water, confirming that soil is a sink for CeO2 NM. Furthermore, no inhibition of the NM sensitive ammonium oxidizing bacteria (AOB) was observed which implies a low bioavailability of CeO2 NM in soil. The detected Ce root uptake for canola (Ce < 35.7 mg kg−1) and barley (Ce < 61.8 mg kg−1) indicates that physico-chemical conditions in the rhizosphere or the aging of the NM in soil can remobilize the applied CeO2 NM to some extent. One can speculate that the obtained reduction of Ce4+ to Ce3+ (≈ 50% after 25 months) was coupled to different conditions (ionic strength, pH, water content, soil organic matter content) in the rhizosphere and necessary for the root accumulation of Ce.
Due to negligible mobility in the soil-water interface, as well as non-toxicity to AOB, the environmental risk of the tested CeO2 NM appears to be low, compared to other highly mobile emergent pollutants. Nonetheless, further long-term investigations need to focus on the speciation and localization of NM in plants to clarify uptake and impact of NM to crops.
Salas, P., Odzak, N., Echegoyen, Y., Kägi, R., Sancho, M. C., & Navarro, E. (2019). The role of size and protein shells in the toxicity to algal photosynthesis induced by ionic silver delivered from silver nanoparticles. Science of the Total Environment, 692, 233-239. doi:10.1016/j.scitotenv.2019.07.237, Institutional Repository

Because of their biocide properties, silver nanoparticles (AgNPs) are present in numerous consumer products. The biocidal properties of AgNPs are due to both the interactions between AgNP and cell membranes and the release of dissolved silver (Ag+). Recent studies emphasized the role of different nanoparticle coatings in complexing and storing Ag+. In this study, the availability of dissolved silver in the presence of algae was assessed for three AgNPs with different silver contents (59%, 34% and 7% of total Ag), silver core sizes and casein shell thicknesses. The impact of ionic silver on the photosynthetic yield of Chlamydomonas reinhardtii was used as a proxy to estimate the amount of ionic silver toxically active during in vivo assays. The results showed that cysteine, a strong silver ligand, mitigated the toxicity of AgNPs in all cases, demonstrating the key role of Ag+ in this toxicity. The results showed that the AgNPs presenting an intermediate level of silver (34%) were 10 times more effective in terms of total mass (EC50 ten times smaller) than those presenting more (59%) or less (7%) silver. The higher toxicity was due to the higher release of Ag+ under biotic conditions due to the high surface/mass ratio of the nanoparticle silver core. Protein shells played a minor role in altering the availability of Ag+, probably acting as intermediate reservoirs. This study highlighted the utility of a very sensitive biological endpoint (i.e., algal photosynthesis) for the optimization of ionic silver delivery by nanomaterials.
Surette, M. C., Nason, J. A., & Kaegi, R. (2019). The influence of surface coating functionality on the aging of nanoparticles in wastewater. Environmental Science: Nano, 6(8), 2470-2483. doi:10.1039/C9EN00376B, Institutional Repository

Efforts to predict the environmental fate of engineered nanomaterials (ENMs) are frequently based on the physiochemical properties and behavior of the ENMs in their pristine, “as-produced” state. However, it is well-established that ENMs can be physically, biologically, and chemically transformed, resulting in altered physiochemical properties and behavior. Wastewater treatment plants (WWTPs) represent an important stage in an ENM's life-cycle where they can be transformed. To better understand the properties of ENMs discharged from WWTPs into surface waters, we investigated how the transformation processes of aggregation and corona formation are influenced by the surface coating applied to ENMs during their manufacture. Using 40 nm gold nanoparticles coated with polyethylene glycol, lipoic acid, or branched polyethylenimine as model ENMs, batch experiments were performed to investigate aggregation and corona formation during the primary clarification and activated sludge treatment stages. A tangential flow filtration system was used to evaluate if the initial transformations were altered as the aquatic chemistry of the background matrix was changed, mimicking the varying conditions ENMs would experience during transport through a WWTP. Using a combination of corroborative techniques including dynamic light scattering, phase analysis light scattering, ultraviolet-visible light spectroscopy, and transmission electron microscopy, we find that the model ENMs aggregated in each wastewater matrix, regardless of the initial surface coating. Differences in the UV-vis spectra indicate that the nature of the corona acquired by the ENMs differed as a function of the surface coating of the pristine ENMs. In addition, initial ENM transformations during exposure to the influent wastewater persisted even as the background matrix changed. These results support the finding that ENMs discharged from WWTPs will not resemble their pristine analogs. Furthermore, the corona acquired by ENMs in WWTPs may vary in relation to their pristine properties and be dictated by conditions during early stage exposures.
ThomasArrigo, L. K., Kaegi, R., & Kretzschmar, R. (2019). Ferrihydrite growth and transformation in the presence of ferrous iron and model organic ligands. Environmental Science and Technology, 53(23), 13636-13647. doi:10.1021/acs.est.9b03952, Institutional Repository

Ferrihydrite (Fh) is a poorly crystalline Fe(III)-oxyhydroxide found in abundance in soils and sediments. With a high specific surface area and sorption capacity at circumneutral pH, ferrihydrite is an important player in the biogeochemical cycling of nutrients and trace elements in redox-dynamic environments. Under reducing conditions, exposure to Fe(II) induces mineral transformations in ferrihydrite; the extent and trajectory of which may be greatly influenced by organic matter (OM). However, natural OM is heterogeneous and comprises a range of molecular weights (MWs) and varied functional group compositions. To date, the impact that the chemical composition of the associated OM has on Fe(II)-catalyzed mineral transformations is not clear. To address this knowledge gap, we coprecipitated ferrihydrite with model organic ligands selected to cover a range of MWs (25 000–50 000 vs <200 Da) as well as carboxyl content (polygalacturonic acid (PGA) > citric acid (CA) > galacturonic acid (GA)). Coprecipitates (C:Fe ≈ 0.6) were reacted with 1 mM 57Fe(II) for 1 week at pH 7, with time-resolved solid-phase analysis (via X-ray diffraction, X-ray absorption spectroscopy, and electron microscopy) revealing that all ligands inhibited Fe(II)-catalyzed ferrihydrite mineral transformations and the formation of crystalline secondary mineral phases compared to a pure ferrihydrite. For carboxyl-rich coprecipitates (Fh-PGA and Fh-CA), mineral transformations were less inhibited than in the carboxyl poor Fh-GA, and a crystalline lepidocrocite "shell" was formed surrounding the residual ferrihydrite core. However, Fe isotope analysis revealed that all coprecipitates underwent near complete atom exchange. Collectively, our results highlight that ferrihydrite is indeed an active mineral phase in redox-dynamic environments, but that its stability under reducing conditions, and thus capacity for nutrient and trace element retention, depends on the chemical characteristic of the associated OM, specifically OM-induced changes in the particle surface charge and the distribution of organic functional groups.
Uusimaeki, T., Wagner, T., Lipinski, H. G., & Kaegi, R. (2019). AutoEM: a software for automated acquisition and analysis of nanoparticles. Journal of Nanoparticle Research, 21(6), 122 (11 pp.). doi:10.1007/s11051-019-4555-9, Institutional Repository

The era of research on (engineered) nanomaterials (NM) has been thriving for more than a decade and has delivered many beneficial applications, but also raised concerns about potential negative impacts on human health and ecosystems. The precautionary principle, hence, calls for a regulation of certain types of NM, which in consequence requires their unambiguous identification. Most of the currently available definitions of NM rely on an evaluation of the size of the constituent particles and therefore methods have to be developed to measure this parameter. Transmission electron microscopy (TEM) is one of the most promising techniques, as its resolving power well covers the nanosize range. However, limited automation of TEM analyses and possible user bias are major drawbacks of the technique and currently put severe constraints on its broader applications in nanometrology.
Therefore, the goal of this study was to develop a software code, referred to as AutoEM, to automatically acquire TEM images, measure particle sizes and extract the respective particle size distributions (PSD) of (nano)-materials. The AutoEM software also incorporates methods for elemental analyses of individual particles using electron energy loss and energy dispersive X-ray spectroscopy (EELS/EDX) allowing the extraction of element-specific PSDs. Additionally automated acquisition of energy-filtered images (EFTEM) is implemented in the AutoEM software, which can be used, e.g., to derive thickness maps and, thus, to evaluate the thickness of individual (plate-like) particles.
Verleysen, E., Wagner, T., Lipinski, H. G., Kägi, R., Koeber, R., Boix-Sanfeliu, A., … Mast, J. (2019). Evaluation of a TEM based approach for size measurement of particulate (nano)materials. Materials, 12(14), 2274 (20 pp.). doi:10.3390/ma12142274, Institutional Repository

An approach for the size measurement of particulate (nano)materials by transmission electron microscopy was evaluated. The approach combines standard operating procedures for specimen preparation, imaging, and image analysis, and it was evaluated on a series of certified reference materials and representative test materials with varying physical properties, including particle size, shape, and agglomeration state. The measurement of the median value of the minimal external particle diameter distribution was intra-laboratory validated. The validation study included an assessment of the limit of detection, working range, selectivity, precision, trueness, robustness, and ruggedness. An uncertainty that was associated to intermediate precision in the range of 1–7% and an expanded measurement uncertainty in the range of 7–20% were obtained, depending on the material and image analysis mode. No bias was observed when assessing the trueness of the approach on the certified reference materials ERM-FD100 and ERM-FD304. The image analysis method was validated in an inter-laboratory study by 19 laboratories, which resulted in a within-laboratory precision in the range of 2–8% and a between-laboratory precision of between 2% and 14%. The automation and standardization of the proposed approach significantly improves labour and cost efficiency for the accurate and precise size measurement of the particulate materials. The approach is shown to be implementable in many other electron microscopy laboratories.
Voegelin, A., Senn, A. C., Kaegi, R., & Hug, S. J. (2019). Reductive dissolution of As(V)-bearing Fe(III)-precipitates formed by Fe(II) oxidation in aqueous solutions. Geochemical Transactions, 20(2) (13 pp.). doi:10.1186/s12932-019-0062-2, Institutional Repository

Iron(III)-precipitates formed by the oxidation of dissolved Fe(II) are important sorbents for major and trace elements in aquatic and terrestrial systems. Their reductive dissolution in turn may result in the release of associated elements. We examined the reductive dissolution kinetics of an environmentally relevant set of Fe(II)-derived arsenate-containing Fe(III)-precipitates whose structure as function of phosphate (P) and silicate (Si) content varied between poorly-crystalline lepidocrocite, amorphous Fe(III)-phosphate, and Si-containing ferrihydrite. The experiments were performed with 0.2–0.5 mM precipitate-Fe(III) using 10 mM Na-ascorbate as reductant, 5 mM bipyridine as Fe(II)-complexing ligand, and 10 mM MOPS/5 mM NaOH as pH 7.0 buffer. Times required for the dissolution of half of the precipitate (t50%) ranged from 1.5 to 39 h; spanning a factor 25 range. At loadings up to ~ 0.2 P/Fe (molar ratio), phosphate decreased the t50% of Si-free precipitates, probably by reducing the crystallinity of lepidocrocite. The reductive dissolution of Fe(III)-phosphates formed at higher P/Fe ratios was again slower, possibly due to P-inhibited ascorbate binding to precipitate-Fe(III). The slowest reductive dissolution was observed for P-free Si-ferrihydrite with ~ 0.1 Si/Fe, suggesting that silicate binding and polymerization may reduce surface accessibility. The inhibiting effect of Si was reduced by phosphate. Dried-resuspended precipitates dissolved 1.0 to 1.8-times more slowly than precipitates that were kept wet after synthesis, most probably because drying enhanced nanoparticle aggregation. Variations in the reductive dissolution kinetics of Fe(II) oxidation products as reported from this study should be taken into account when addressing the impact of such precipitates on the environmental cycling of co-transformed nutrients and contaminants.
Wielinski, J., Gogos, A., Voegelin, A., Müller, C., Morgenroth, E., & Kaegi, R. (2019). Transformation of nanoscale and ionic Cu and Zn during the incineration of digested sewage sludge (biosolids). Environmental Science and Technology, 53(20), 11704-11713. doi:10.1021/acs.est.9b01983, Institutional Repository

Engineered nanoparticles (NP) discharged to sewers are efficiently retained by wastewater treatment plants and accumulate in the sewage sludge, which is commonly digested. The resulting biosolids are either used as fertilizer or incinerated. In this study, we address the transformation of Cu and Zn during sewage sludge incineration and evaluate whether the form of Cu or Zn (nanoparticulate versus dissolved) added to the digested sewage sludge affects the fate of the metals during incineration. We spiked CuO-NP, dissolved CuSO4, ZnO-NP, or dissolved ZnSO4 into anaerobically digested sewage sludge to reach Cu and Zn concentrations of ≈2500 and ≈3700 mg/kg and maintained the sludge under mesophilic, anaerobic conditions for 24 h. Subsequently, the sludge was incinerated in a pilot fluidized bed reactor. The speciation of Cu and Zn in the sludge, derived from X-ray absorption spectroscopy measurements, was dominated by sulfidic species, with >90% of Cu and >60% of Zn coordinated to reduced sulfur groups. In the ash, both Cu (>60%) and Zn (≈100%) were coordinated to oxygen. The chemical speciation of Cu and Zn in the ashes was independent of whether they were spiked in the dissolved or nanoparticulate form and closely matched the speciation of Cu and Zn observed in ashes from full-scale incinerators.
Xu, J., Wang, Y., Weng, C., Bai, W., Jiao, Y., Kaegi, R., & Lowry, G. V. (2019). Reactivity, selectivity, and long-term performance of sulfidized nanoscale zerovalent iron with different properties. Environmental Science and Technology, 53(10), 5936-5945. doi:10.1021/acs.est.9b00511, Institutional Repository

Sulfidized nanoscale zerovalent iron (SNZVI) has desirable properties for in situ groundwater remediation. However, there is limited understanding of how the sulfidation type and particle properties affect the reactivity and selectivity of SNZVI toward groundwater contaminants, or how reactivity changes as the particles age. Here, SNZVI synthesized by either a one-step (SNZVI-1) or two-step (SNZVI-2) process were characterized, and the reactivity of both fresh and aged (1d to 60 d) nanoparticles was assessed. The measured S/Fe ratio was 5.4 ± 0.5 mol % for SNZVI-1 and 0.8 ± 0.1 mol % for SNZVI-2. XPS analysis indicates S2-, S22-, and Sn2- species on the surface of both SNZVI-1 and SNZVI-2, while S22- is the dominant species inside of the SNZVI nanoparticles. SNZVI-1 particles were hydrophobic (contact angle = 103 ± 3°), while the other materials were hydrophilic (contact angles were 18 ± 2° and 36 ± 3° for NZVI and SNZVI-2, respectively). SNZVI-1, with greater S content and hydrophobicity, was less reactive with water than either NZVI or SNZVI-2 over a 60 d period, resulting in less H2 evolution. It also had the highest reactivity with TCE and the lowest reactivity with nitrate, consistent with its higher hydrophobicity. In contrast, both NZVI and SNZVI-2 were reactive with both TCE and nitrate. Both types of SNZVI remained more reactive after aging in water over 60 d than NZVI. These data suggest that the properties of the SNZVI made from a one-step synthesis procedure may provide better reactivity, selectivity, and longevity than that made from a two-step process.
Zheng, Y., Mutzner, L., Ort, C., Kaegi, R., & Gottschalk, F. (2019). Modelling engineered nanomaterials in wet-weather discharges. NanoImpact, 16, 100188 (8 pp.). doi:10.1016/j.impact.2019.100188, Institutional Repository

The impacts of the unintended release of engineered nanomaterials (ENMs) and the resulting exposure to the ecosystems are still poorly understood and intensively debated. In current mass flow models, a global transfer coefficient is used to account for ENMs discharged from sewer systems to surface waters during rain events.
However, different types of sewer systems and specific ENM applications likely require a more elaborate approach to quantify ENM loads entering surface waters during rain events. Therefore, we evaluated the impact of distinguishing between different application areas of ENMs (indoor/outdoor) and different types of sewer systems (combined/separate) on the loads of selected ENMs passing through wastewater systems and reaching the surface water. We applied a dynamic mass flow analysis to eight substances (TiO2, ZnO, Ag, SiO2, FeOx, CuO, CeO2 and carbon black) for six different sewer system configurations. To estimate the runoff from streets and facades, we used a hydrological model developed for dissolved substances. For areas with separate sewer systems only and ENMs predominantly used in and released from outdoor applications (e.g. CuO, carbon black), up to ~80% of the annual loads entering the sewer systems never reach a sewage treatment plant. Those ENMs are directly discharged to surface waters via stormwater outlets. For combined sewer systems and ENMs mainly applied indoors (e.g. Ag, ZnO), the percentage of ENM bypassing sewage treatment plants remains below 2%. Although the model is setup for Switzerland and other geographical areas will show for example different rain characteristics, the relative importance of the different release pathways will broadly remain the same and the results should, therefore, be transferrable to other countries.
Giese, B., Klaessig, F., Park, B., Kaegi, R., Steinfeldt, M., Wigger, H., … Gottschalk, F. (2018). Risks, release and concentrations of engineered nanomaterial in the environment. Scientific Reports, 8(1), 1565 (8 pp.). doi:10.1038/s41598-018-19275-4, Institutional Repository

For frequently used engineered nanomaterials (ENMs) CeO2-, SiO2-, and Ag, past, current, and future use and environmental release are investigated. Considering an extended period (1950 to 2050), we assess ENMs released through commercial activity as well as found in natural and technical settings. Temporal dynamics, including shifts in release due to ENM product application, stock (delayed use), and subsequent end-of-life product treatment were taken into account. We distinguish predicted concentrations originating in ENM use phase and those originating from end-of-life release. Furthermore, we compare Ag- and CeO2-ENM predictions with existing measurements. The correlations and limitations of the model, and the analytic validity of our approach are discussed in the context of massive use of assumptive model data and high uncertainty on the colloidal material captured by the measurements. Predictions for freshwater CeO2-ENMs range from 1 pg/l (2017) to a few hundred ng/l (2050). Relative to CeO2, the SiO2-ENMs estimates are approximately 1,000 times higher, and those for Ag-ENMs 10 times lower. For most environmental compartments, ENM pose relatively low risk; however, organisms residing near ENM 'point sources' (e.g., production plant outfalls and waste treatment plants), which are not considered in the present work, may be at increased risk.
Gogos, A., Voegelin, A., & Kaegi, R. (2018). Influence of organic compounds on the sulfidation of copper oxide nanoparticles. Environmental Science: Nano, 5(11), 2560-2569. doi:10.1039/C8EN00523K, Institutional Repository

Dissolved organic matter (DOM) influences the colloidal properties of engineered nanomaterials (ENMs) and impacts their transport and transformation in the environment. Sulfidation affects the fate and the ecological effects of released chalcophile ENMs. For copper oxide nanoparticles (CuO-NPs), the sulfidation and its kinetics have been described. However, the influence of DOM on this reaction has not been investigated yet. In wastewater systems, having high bisulfide contents, the DOM mainly consists of proteins, polysaccharides and humic substances. We therefore investigated the influence of the organic compounds bovine serum albumin (BSA, model protein), alginate (ALG, model polysaccharide), and polyacrylic acid (PAA, natural organic matter analogue) as well as that of natural humic acid (HA) and filtered wastewater (FW) on the sulfidation of CuO-NPs. Experiments were conducted in solutions buffered to pH 8.0 at concentrations of 1.3 mM CuO and ∼3.2 mM HS−. Increasing amounts of organic compounds were added to reach concentrations of 10–1000 mg L−1. Reacted CuO-NPs were collected at selected time points and characterized using Cu K-edge X-ray absorption spectroscopy and analytical electron microscopy. The sulfidation of the CuO-NPs was complete after 3 h in all experiments, except in the presence of 1000 mg L−1 BSA where ∼30% of CuO remained untransformed. Complete sulfidation of the CuO-NPs as observed in experiments conducted in FW suggests quantitative sulfidation of CuO-NPs in real wastewater. Without organic compounds, initially formed amorphous CuxS transformed into covellite over time. The presence of BSA, HA, ALG, and FW (but not PAA) hampered this transformation resulting in higher fractions of CuxS after sulfidation. Different amounts of CuxS with sizes of 10 kDa up to 10 nm formed during sulfidation depending on the type of organic compound. The properties of the CuxS-NPs formed by CuO-NP sulfidation must be considered when assessing their environmental impact.
Gondikas, A., Von Der Kammer, F., Kaegi, R., Borovinskaya, O., Neubauer, E., Navratilova, J., … Hofmann, T. (2018). Where is the nano? Analytical approaches for the detection and quantification of TiO2 engineered nanoparticles in surface waters. Environmental Science: Nano, 5(2), 313-326. doi:10.1039/c7en00952f, Institutional Repository

Detecting and quantifying engineered nanoparticles (ENPs) in complex environmental matrices requires the distinction between natural nanoparticles (NNPs) and ENPs. The distinction of NNPs and ENPs for regulatory purposes calls for cost-efficient methods, but is hampered by similarities in intrinsic properties, such as particle composition, size, density, surface chemistry, etc. Titanium dioxide (TiO2) ENPs, for instance, are produced in very large quantities but Ti also commonly occurs naturally in nano-scale minerals. In this work, we focus on utilizing particle size and composition to identify ENPs in a system with a significant background concentration of the target metal. We have followed independent approaches involving both conventional and state-of-the-art analytical techniques to detect and quantify TiO2 ENPs released into surface waters from sunscreen products and to distinguish them from Ti-bearing NNPs. To achieve this, we applied single particle inductively coupled plasma mass spectrometry with single-element (spICPMS) and multi-element detection (time-of-flight) spICP-TOFMS, together with transmission electron microscopy (TEM), automated scanning electron microscopy (autoSEM), and bulk elemental analyses. A background concentration of Ti-bearing NPs (approximately 5 × 103 particles per ml), possibly of natural origin, was consistently observed outside the bathing season. This concentration increased by up to 40% during the bathing season. Multi-element analysis of individual particles using spICP-TOFMS revealed that Al, Fe, Mn, and Pb are often present in natural Ti-bearing NPs, but no specific multi-element signatures were detected for ENPs. Our data suggests that TiO2 ENPs enter the lake water during bathing activities, eventually agglomerating and sedimenting. We found adhesion of the TiO2 ENPs to the air-water interface for short time periods, depending on wind conditions. This study demonstrates that the use of spICP-TOFMS and spICPMS in combination with other conventional analytical techniques offers significant advantages for discriminating between NNPs and ENPs. The quantitative data produced in this work can be used as input for modeling studies or as a benchmark for analysis protocols and model validations.
Hagemann, N., Spokas, K., Schmidt, H. P., Kägi, R., Böhler, M. A., & Bucheli, T. D. (2018). Activated carbon, biochar and charcoal: linkages and synergies across pyrogenic carbon's ABCs. Water, 10(2), 182 (19 pp.). doi:10.3390/w10020182, Institutional Repository

Biochar and activated carbon, both carbonaceous pyrogenic materials, are important products for environmental technology and intensively studied for a multitude of purposes. A strict distinction between these materials is not always possible, and also a generally accepted terminology is lacking. However, research on both materials is increasingly overlapping: sorption and remediation are the domain of activated carbon, which nowadays is also addressed by studies on biochar. Thus, awareness of both fields of research and knowledge about the distinction of biochar and activated carbon is necessary for designing novel research on pyrogenic carbonaceous materials. Here, we describe the dividing ranges and common grounds of biochar, activated carbon and other pyrogenic carbonaceous materials such as charcoal based on their history, definition and production technologies. This review also summarizes thermochemical conversions and non-thermal pre- and post-treatments that are used to produce biochar and activated carbon. Our overview shows that biochar research should take advantage of the numerous techniques of activation and modification to tailor biochars for their intended applications.
Kampe, S., Kaegi, R., Schlich, K., Wasmuth, C., Hollert, H., & Schlechtriem, C. (2018). Silver nanoparticles in sewage sludge: bioavailability of sulfidized silver to the terrestrial isopod Porcellio scaber. Environmental Toxicology and Chemistry, 37(6), 1606-1613. doi:10.1002/etc.4102, Institutional Repository

Silver nanoparticles (AgNPs) are efficiently converted during the wastewater‐treatment process into sparingly soluble Ag sulfides (Ag2S). In several countries, sewage sludge is used as a fertilizer in agriculture. The bioavailability of sulfidized Ag to the terrestrial isopod Porcellio scaber was investigated. Sewage sludge containing transformed AgNPs was obtained from a laboratory‐scale sewage‐treatment plant operated according to Organisation for Economic Co‐operation and Development (OECD) guideline 303a. The results of transmission electron microscopy with energy dispersive X‐ray of sludge samples suggest that AgNPs were completely transformed to Ag2S. Adult isopods were exposed to OECD 207 soil substrate amended with the AgNP spiked sludge for 14 d (uptake phase) followed by an elimination phase in unspiked soil of equal duration. Most of the Ag measured in P. scaber at the end of the uptake phase was found in the hindgut (71%), indicating that only a minor part of the estimated Ag content was actually assimilated by the isopods with 16.3 and 12.7% found in the carcass and hepatopancreas, respectively. As a result of this, the Ag content of the animals dropped following transition to unspiked sludge within 2 d to one‐third of the previously measured Ag concentration and remained stable at this level until the end of the elimination period. The present study shows that Ag2S in sewage sludge is bioavailable to the terrestrial isopod P. scaber.
Neidhardt, H., Winkel, L. H. E., Kaegi, R., Stengel, C., Trang, P. T. K., Lan, V. M., … Berg, M. (2018). Insights into arsenic retention dynamics of Pleistocene aquifer sediments by in situ sorption experiments. Water Research, 129, 123-132. doi:10.1016/j.watres.2017.11.018, Institutional Repository

The migration of arsenic (As) enriched groundwater into Pleistocene aquifers as a consequence of extensive groundwater abstraction represents an increasing threat to the precious water resources in Asian delta regions. Pleistocene aquifer sediments are typically rich in FeIII-(hydr)oxides and are capable to adsorb high amounts of As. This results in a pronounced accumulation of As in Pleistocene aquifers, where high As groundwater infiltrates from adjacent Holocene aquifers. However, As retention by Pleistocene aquifers over long-term time scales remains largely unknown. We studied As sorption in situ by placing natural Pleistocene sediments and pure mineral phases directly inside groundwater monitoring wells at a study site near Hanoi (Vietnam). This in situ exposure allows for constant flushing of the samples with unaltered groundwater and the establishment of undisturbed sorption equilibria similar to those in local aquifer sediments, which is not readily attainable in traditional laboratory sorption experiments. The groundwaters in our experimental wells were characterized by different As concentrations (0.01–6.63 μmol/L) and redox states, reaching from suboxic to anoxic conditions (Eh of +159 to −4 mV). Results show that adsorption is the dominant As retention mechanism, independent from the respective groundwater chemistry (i.e. concentrations of dissolved P, HCO3− and Si). Whilst most of the As sorbed within the first week, sorption further increased slowly but consistently by 6–189%, respectively, within six months. Hence, the As sorption behavior of Pleistocene aquifer sediments should be determined over longer periods to avoid an underestimation of the As sorption capacity. Accompanying desorption experiments revealed that about 51% of the sorbed As was remobilized within six months when exposed to low As groundwater. We therefore conclude that a considerable proportion of the As accumulated in the aquifer sediments is prone to remobilization once the As concentrations in migrating groundwater decline. Remobilization of As should be considered in local water management plans to avoid contamination of precious groundwater resources with this As legacy.
Pradas del Real, A. E., Castillo-Michel, H., Kaegi, R., Larue, C., de Nolf, W., Reyes-Herrera, J., … Sarret, G. (2018). Searching for relevant criteria to distinguish natural vs. anthropogenic TiO2 nanoparticles in soils. Environmental Science: Nano, 5(12), 2853-2863. doi:10.1039/c8en00386f, Institutional Repository

Nanosized TiO2 is one of the most produced nanomaterials. Agricultural soils are a major compartment of accumulation of TiO2-NPs after release from consumer products into the sewer system, due to the use of sewage sludge as a soil amendment. TiO2 is naturally present in soils, and distinguishing between anthropogenic and natural TiO2 in soils is thus important to assess the risks associated with the increased use of nano-TiO2. Methods to distinguish these materials in complex matrices such as soils are currently lacking. The purpose of this study was, therefore, to search for characteristic physical and chemical properties of natural and engineered nano-TiO2, based on a combination of bulk, micro and nanofocused X-ray fluorescence and X-ray absorption spectroscopy, transmission electron microscopy, X-ray diffraction and chemical analyses. Digested sewage sludge, agricultural soil and sludge-amended soil were studied by these techniques. The particle size distribution was not a relevant criterion since the sludge and the sludge-amended soil contained a variety of nanometer- and micrometer sized Ti-containing particles. Both the sludge and the soil contained a mixture of rutile and anatase, with a minor proportion of amorphous TiO2. In the sludge, there was no trend relating particle size and Ti mineralogy. The morphology of the TiO2 particles proved to be different in the two matrices, with smooth faceted particles in the sludge and rough irregular ones in the soil. In addition, natural TiO2 particles were included in micro and macroaggregates of the soil and formed intricate assemblages with minerals and organic compounds. In the sludge, TiO2 formed homo and heteroaggregates of simpler structure, richer in organic matter. Thus, the study of the morphology of TiO2 particles and their status in unperturbed mineral-organic assemblages may provide some insights into their origin. The observed differences may attenuate over time, due to the incorporation of the sludge material within the soil structure.
Senn, A. C., Hug, S. J., Kaegi, R., Hering, J. G., & Voegelin, A. (2018). Arsenate co-precipitation with Fe(II) oxidation products and retention or release during precipitate aging. Water Research, 131, 334-345. doi:10.1016/j.watres.2017.12.038, Institutional Repository

The co-precipitation of arsenate (As(V)) with Fe(III)-precipitates is of great importance in water treatment and critically affects the fate of As in environmental systems. We studied the effects of dissolved phosphate (P; 0-1 mM), silicate (Si; 0 or 0.5 mM) and Ca (0, 0.5 and 4 mM) on the sequestration of 7 μM As(V) by Fe(III)-precipitates formed by the oxidation of 0.5 mM Fe(II) in aerated bicarbonate-buffered solutions with an initial pH of 7.0 as well as the retention or release of As(V) after precipitate aging for 30 d at 40 °C. Dissolved As(V) concentrations in fresh precipitate suspensions greatly varied as a function of the initial dissolved P/Fe ratio ((P/Fe)init) and the concentrations of Ca and Si. Limited As(V) removal was observed at (P/Fe)init that exceeded the critical ratio (P/Fe)crit above which exclusively (Ca-)Fe(III)-phosphate forms. Effective As(V) removal was observed at (P/Fe)init < (P/Fe)crit, where initial formation of (Ca-)Fe(III)-phosphate is followed by the formation of Si-ferrihydrite in Si-containing electrolytes and of poorly-crystalline lepidocrocite and hydrous ferric oxide in the Si-free electrolytes. The retention of As(V) and P by fresh Fe(III)-precipitates was most effective in systems containing both Ca and Si. In the Si- and Ca-free electrolytes at (P/Fe)init of ~0.2–0.6, the rapid onset of precipitate aging with conversion of Fe(III)-phosphate to ferrihydrite resulted in a substantial remobilization of As(V) (up to 55% of initially precipitated As(V)). Ca reduced As remobilization during aging by stabilizing Ca-Fe(III)-phosphate and promoting Ca-phosphate formation, and Si by stabilizing Si-ferrihydrite against transformation. Consequently, also after aging, the lowest dissolved As(V) and P fractions were observed in precipitate suspensions containing both Ca and Si.
Thalmann, B., Kägi, R., & von Gunten, U. (2018). Metalle in der Ozonung. Verhalten von ausgewählten Metallen: Oxidation von Metallsulfiden und Metallkomplexen. Aqua & Gas, 98(4), 68-77. , Institutional Repository

Metallsulfide (CuS, ZnS, CdS) werden während der Ozonbehandlung von geklärtem Abwasser nahezu vollständig in Metallionen und Sulfat umgewandelt. Auch organische Komplexbildner, wie EDTA oder NTA, werden durch die Ozonung teilweise zerstört. Dies führt zu einer Freisetzung der entsprechenden Metallionen. Toxische Effekte, hervorgerufen durch erhöhte Konzentrationen von Metallionen, wurden jedoch nur für sehr hohe Kupferkonzentrationen, die dem Abwasser als Kupfersulfide zugegeben worden waren, beobachtet und sind deshalb im «normalen» Abwasser nicht zu erwarten.
Thalmann, B., von Gunten, U., & Kaegi, R. (2018). Ozonation of municipal wastewater effluent containing metal sulfides and metal complexes: kinetics and mechanisms. Water Research, 134, 170-180. doi:10.1016/j.watres.2018.01.042, Institutional Repository

Ozonation can be applied to mitigate the discharge of organic micropollutants from municipal wastewater treatment plants (WWTPs) to the aquatic environment. The toxicity of metals also present in WWTP effluents strongly depends on their speciation. Therefore, knowledge on the change of the metal speciation during ozonation of a WWTP effluent is essential to assess possible negative impacts. The kinetics and the stoichiometries of the reactions of ozone with three metal sulfides (ZnS, CuS and CdS) and metal-ethylenediaminetetraacetate (EDTA)/nitriloriacetic acid (NTA) complexes of Cu(II), Cd(II), Ni(II), Zn(II), Mg(II) and Pb(II) were investigated. With a stoichiometric factor of 2.6–3.9 moles of ozone per mole of sulfide and apparent second-order rate constants at pH 8 > 104 M−1 s−1, a complete oxidation of the sulfides and a concomitant release of the respective metals is expected during ozonation of a WWTP effluent for enhanced micropollutant abatement. The apparent second-order rate constants at pH 8 for the reactions of metal-EDTA complexes with ozone ranged from 42 M−1s−1 to 2.0 × 104 M−1s−1 and increased in the order Cd(II) < Cu(II) < Mg(II) < Ni(II) < Zn(II). Approximately 40% of Cd(II)-EDTA spiked to a WWTP effluent was oxidized at typical specific ozone doses of 0.5–0.7 gO3/gDOC. For the other metal-EDTA complexes a significantly higher fraction was oxidized. The bioavailable fraction determined by the diffusive-gradient thin films (DGT) method in the WWTP effluent increased during ozonation, due to the oxidative release of the metal ions. Algal toxicity (chlamynomodas reinhardtii) tests with CuS/CdS spiked WWTP effluent revealed a high tolerance toward Cu and Cd in the respective media. A toxic response was only observed at Cu concentrations above 10 μM, which is above typical WWTP effluent concentrations. Biological post-treatment after ozonation generally reduced the bioavailability of the metals, which resulted in a lower toxicity. Therefore, the biological post-treatment serves as an additional barrier to protect the downstream ecology of receiving waters.
Ulmer, P., Kaegi, R., & Müntener, O. (2018). Experimentally derived intermediate to silica-rich arc magmas by fractional and equilibrium crystallization at 1·0 GPa: an evaluation of phase relationships, compositions, liquid lines of descent and oxygen fugacity. Journal of Petrology, 59(1), 11-58. doi:10.1093/petrology/egy017, Institutional Repository

Differentiation of hydrous primary, mantle-derived magmas is a fundamental process to generate evolved intermediate to SiO2-rich compositions forming the bulk of the continental and island arc crust. This study focuses on the results of equilibrium and fractional crystallization experiments at 1·0 GPa using two different primary magmas representing deep (90 km) and shallow (35 km) mantle extraction depths. Experiments on a hydrous high-Mg basalt were conducted at graphite-saturated and more oxidized conditions (NNO to NNO + 2, where NNO is nickel–nickel oxide buffer) to exploit the influence of fO2 on phase assemblages and the evolution of derivative liquids. The liquid line of descent (LLD) was simulated from liquidus to near-solidus conditions ranging from 1330°C to 720°C. H2O contents varied from about 2·0 to more than 10 wt %. The LLD covers the entire compositional range from high-Mg basalt to high-silica rhyolite and evolves from metaluminous to peraluminous compositions at 56–60 wt % SiO2 under oxidizing conditions. The observed crystallization sequences and the LLD reveal contrasting behavior depending on oxidation state, H2O content and equilibrium versus fractional crystallization. Equilibrium crystallization of high-Mg basalt under reducing conditions is initially dominated by olivine fractionation followed by Cr-rich spinel, clinopyroxene (cpx), and orthopyroxene (opx). Finally, between 1060 and 1000°C, amphibole formed by a peritectic reaction consuming cpx + olivine and forming amphibole + opx, resulting in 16% silica-undersaturated trachy-basaltic liquid. Equilibrium crystallization of the same composition under oxidizing conditions is characterized by strongly enhanced olivine and cpx fractionation and suppression of opx only occurring as a result of the peritectic amphibole-forming reaction at and below 1040°C. The liquid at 980°C is a peraluminous, alkali-poor, high-Al andesite representing ∼15% residual liquid. Fractional crystallization of the high-Mg basalt under oxidizing conditions evolves through fractionation of early olivine joined by cpx at 1200°C, followed by opx and hercynitic spinel (1140–1080°C) and amphibole at 1050°C coexisting with cpx (and spinel) to 980°C. At 950°C both garnet and plagioclase (plag) join amphibole as liquidus phases. This paragenesis (plus ilmenite and apatite) persists to 750°C with 16% residual liquid relative to the initial basaltic composition. Liquids evolve continuously from basalt to rhyolite, crossing the metaluminous–peraluminous boundary at about 60 wt % SiO2. Fractional crystallization of the basaltic andesite starting material differs at high temperature, where opx and cpx are the liquidus phases (1200–1080°C), followed by amphibole at the expense of opx. Below 950°C the phase assemblage is identical except at the lowest temperature (720°C), where quartz saturates in a high-silica rhyolitic liquid representing 20% of the initial basaltic andesite. Liquid compositions of the two starting compositions converge below 950°C, with the exception of K2O, which behaves incompatibly along the liquid line of descent. The H2O-undersaturated fractional crystallization experiments on the high-Mg basaltic composition under relatively reducing conditions evolve towards tholeiitic or alkalic compositions owing to early plagioclase (at 1140°C) and abundant opx (at 1110°C) crystallization followed by garnet–cpx–plag–ilmenite at 1080°C. Closed-system equilibrium crystallization under relatively oxidized conditions is characterized by significant expansion of the olivine stability field (>250°C, 1280–1000°C) relative to more reducing conditions, causing depletion of the liquid in ferrous iron and increase of ferric iron. The resulting fO2 of the coexisting basaltic liquids increases by more than 3 log units from about NNO + 2 to NNO + 5·5 over the temperature range >1200–1040°C, potentially offering an explanation for the more oxidized character of hydrous arc magmas as opposed to low-H2O tholeiitic magmas.
Vriens, B., Voegelin, A., Hug, S., Kaegi, R., Berg, M., & Winkel, L. (2018). Spurenelemente in Schweizer Abwasser. Aktuelle Konzentrationen und Frachten. Aqua & Gas, 98(1), 40-46. , Institutional Repository

In einem landesweiten Screening wurden in 64 Schweizer Kläranlagen die aktuellen Konzentrationsbereiche und Frachten von Spurenelementen erfasst. Anhand dieser Werte wurde die Einhaltung der gesetzlichen Vorgaben überprüft sowie die gegenwärtigen durchschnittlichen Pro-Kopf-Elementfrachten und der ökonomische Wert der Elementfrachten berechnet. Bisher waren für viele Spurenelemente diese Kennzahlen nicht bekannt.
Wielinski, J., Müller, C., Voegelin, A., Morgenroth, E., & Kaegi, R. (2018). Combustion of sewage sludge: kinetics and speciation of the combustible. Energy and Fuels, 32(10), 10656-10667. doi:10.1021/acs.energyfuels.8b02106, Institutional Repository

Combustion of sewage sludge has become a viable route for sewage sludge management especially as the agricultural use of sewage sludge has become increasingly difficult due to more stringent requirements regarding the quality of sewage sludge. Combustion of digested sewage sludge in dedicated monocombustion facilities is advantageous, as it substantially reduces the volume of the sludge and still allows for a recovery of phosphorus from the sewage sludge ash at a later stage. Despite increasing amounts of sewage sludge being combusted, knowledge on the respective combustion kinetics is still fragmentary. The goal of this study was, therefore, to identify the major combustion reactions of sewage sludge, assess their Arrhenius parameters (activation energy and pre-exponential factor), and assign suitable reference compounds to the individual reactions. For that purpose, experiments were conducted using a thermogravimetric analyzer (TGA). With matrix inversion, we identified 10 individual reactions. Despite the apparent kinetic compensation most likely caused by insufficient precision of the TGA temperature setting, we were able to relate the major reactions of sewage sludge combustion to the combustion of individual reference compounds. In addition to cellulose and lignin, which dominated the weight loss with 35% and 20%, respectively, hemicellulose, xylan, alginate, and calcite were identified. The dominant fraction of cellulose is consistent with recent studies identifying cellulose mainly originating from toilet paper as a major organic constituent in wastewater. As the identified model compounds explain more than 80% of the total weight loss observed, our approach allows a rough speciation of the combustibles of sewage sludge based on TGA experiments.
Auvinen, H., Kaegi, R., Rousseau, D. P. L., & Du Laing, G. (2017). Fate of Silver Nanoparticles in Constructed Wetlands - a Microcosm Study. Water, Air, and Soil Pollution, 228(3) (11 pp.). doi:10.1007/s11270-017-3285-9, Institutional Repository

Nano-enabled materials are produced at growing volumes which increases the likelihood of nanoparticles being released into the environment. Constructed wetlands (CWs) are likely to receive wastewater containing nanoparticles leaching from products during usage. Therefore, we investigate the retention of silver nanoparticles (Ag-NPs) in microcosms simulating CWs treating domestic wastewater. The effects of aeration and organic matter content on the Ag-NP removal efficiencies are studied in particular. CWs remove most of the Ag (80-90%) and the largest fraction of Ag is found in/on the biofilm. Detailed electron microscopy analyses suggest that Ag-NPs are transformed into Ag2S in all microcosm experiments. The good correlation between total suspended solids (TSS) and the Ag concentration measured in the effluent indicates that Ag-NPs are bound to the solids in the effluent. Aeration of the microcosms does not affect the release of Ag-NPs from the systems but increasing organic matter leads to increased amounts of Ag passing the CWs, correlating with the increased release of TSS from the CWs. These results suggest that Ag-NPs are retained with the (suspended) solids in CWs and that the removal efficiency of TSS is an important factor determining the discharge of Ag-NPs from CWs.
Gogos, A., Thalmann, B., Voegelin, A., & Kaegi, R. (2017). Sulfidation kinetics of copper oxide nanoparticles. Environmental Science: Nano, 4(8), 1733-1741. doi:10.1039/C7EN00309A, Institutional Repository

Sulfidation of copper oxide nanoparticles (CuO NPs) in urban wastewater systems is expected to influence their impact on the environment. However, the kinetics of this reaction has not been studied to date and the reaction mechanism remains largely unexplored. We therefore investigated the sulfidation kinetics of CuO NPs reacted with bisulfide (HS−) at concentrations relevant to wastewater systems. Pristine CuO NPs (50 nm, 7.7 μM) were reacted with HS− (26.4–105.6 μM) in oxic solutions buffered to pH 8.0. The reaction progress was monitored using silver nitrate to quench the reaction and selectively dissolve the copper sulfides (Cux) and zincon to spectrophotometrically quantify the released Cu2+. In addition, the reaction products were characterized at selected time points using analytical electron microscopy and X-ray absorption spectroscopy (XAS). The sulfidation rate of the CuO NPs was best described by a pseudo first order rate law and the corresponding half-life times ranged between 1 and 6 minutes. XAS results showed that crystalline CuO NPs rapidly transformed into amorphous CuxS and gradually into crystalline CuS (covellite). The comparable size of pristine and transformed primary particles, the similar morphology of their aggregates, and the initial formation of CuO–CuxS core–shell structures revealed by analytical electron microscopy suggest that the initial sulfidation occurred via a direct conversion reaction mechanism. Our findings suggest that CuO NPs released from various sources into wastewater will rapidly transform into amorphous CuxS and eventually recrystallize into covellite.
Kaegi, R., Englert, A., Gondikas, A., Sinnet, B., von der Kammer, F., & Burkhardt, M. (2017). Release of TiO2 – (nano) particles from construction and demolition landfills. NanoImpact, 8, 73-79. doi:10.1016/j.impact.2017.07.004, Institutional Repository

A large fraction of engineered nanomaterials (ENM) will be deposited in landfills and it is assumed that ENM are securely locked in landfill sites and cannot leach into the environment (e.g. surface waters). However, experimental evidence supporting this assumption is lacking, as current production volumes of ENM are still too small and/or analytical techniques not sensitive enough to allow for the detection and quantification of ENM in landfill leachates. TiO2 particles are currently used in large quantities, for example in construction materials such as paints and renders as white pigments and their sizes extend into the nano-size range. We, therefore, selected TiO2 particles as a surrogate to assess the potential release of ENM from construction and demolition (C & D) landfill sites. We collected leachate samples from a landfill over one year and used complementary analytical techniques, including inductively coupled plasma (ICP) – optical emission spectroscopy (OES), automated scanning electron microscopy (auto SEM), transmission electron microscopy (TEM) and single particle ICP - mass spectrometry (spICPMS) to quantify TiO2 particles in landfill leachates. Total elemental Ti contents were mostly around a few tens of μg L− 1 and were strongly correlated with total suspended solids. Based on the volumetric discharge of the landfill leachate water from the landfill, we estimate a total amount of ~ 0.5 kg of TiO2 particles that are released annually from the landfill. Ti concentrations derived from ICP-OES measurements were in good agreement with quantifications based on TiO2 particles detected by auto SEM analyses. spICPMS measurements indicated a number concentration of Ti-containing particles in the order of 105 mL− 1 and TEM analyses dominantly revealed nanoscale TiO2 particles with a spherical shape typically observed for TiO2 particles used as white pigments. In addition, angular TiO2 particles with a well-defined crystal habitus were detected, suggesting that also natural TiO2 particles of comparable sizes are present in the landfill leachates. The results from this study indicate that (nanoscale) TiO2 particles are released from C & D landfill sites (~ 5 g/year). Although the amount of TiO2 particles released from C & D landfill sites may still be rather low, these particles may serve as proxy for assessing the future release of ENM from C & D landfill sites, which may become relevant as an increasing use of ENM is predicted for construction materials in general.
Kraas, M., Schlich, K., Knopf, B., Wege, F., Kägi, R., Terytze, K., & Hund-Rinke, K. (2017). Long-term effects of sulfidized silver nanoparticles in sewage sludge on soil microflora. Environmental Toxicology and Chemistry, 36(12), 3305-3313. doi:10.1002/etc.3904, Institutional Repository

The use of silver nanoparticles (AgNPs) in consumer products such as textiles leads to their discharge into wastewater and consequently to a transfer of the AgNPs to soil ecosystems via biosolids used as fertilizer. In urban wastewater systems (e.g., sewer,wastewater treatment plant [WWTP], anaerobic digesters) AgNPs are efficiently converted into sparingly soluble silver sulfides (Ag2S), mitigating the toxicity of the AgNPs. However, long-termstudies on the bioavailability and effects of sulfidized AgNPs on soilmicroorganisms are lacking. Thus we investigated the bioavailability and long-term effects of AgNPs (spiked in a laboratory WWTP) on soil microorganisms. Before mixing the biosolids into soil, the sludges were either anaerobically digested or directly dewatered. The effects on the ammonium oxidation process were investigated over 140 d. Transmission electron microscopy (TEM) suggested an almost complete sulfidation of the AgNPs analyzed in all biosolid samples and in soil, with Ag2S predominantly detected in long-term incubation experiments. However, despite the sulfidation of the AgNPs, soil ammonium oxidation was significantly inhibited, and the degree of inhibition was independent of the sludge treatment. The results revealed that AgNPs sulfidized under environmentally relevant conditions were still bioavailable to soil microorganisms. Consequently, Ag2S may exhibit toxic effects over the long term rather than the short term.
Praetorius, A., Gundlach-Graham, A., Goldberg, E., Fabienke, W., Navratilova, J., Gondikas, A., … von der Kammer, F. (2017). Single-particle multi-element fingerprinting (spMEF) using inductively-coupled plasma time-of-flight mass spectrometry (ICP-TOFMS) to identify engineered nanoparticles against the elevated natural background in soils. Environmental Science: Nano, 4(2), 307-314. doi:10.1039/c6en00455e, Institutional Repository

The discrimination of engineered nanoparticles (ENPs) from the natural geogenic background is one of the preeminent challenges for assessing their potential implications. At low ENP concentrations, most conventional analytical techniques are not able to take advantage of inherent differences (e.g. in terms of composition, isotopic signatures, element ratios, structure, shape or surface characteristics) between ENPs and naturally occurring nanoscale particles (NNPs) of similar composition. Here, we present a groundbreaking approach to overcome these limitations and enable the discrimination of man-made ENPs from NNPs through simultaneous detection of multiple elements on an individual particle level. This new analytical approach is accessible by an inductively-coupled plasma time-of-flight mass spectrometer (ICP-TOFMS) operated in single-particle mode. Machine learning is employed to classify ENPs and NNPs based on their unique elemental fingerprints and quantify their concentrations. We demonstrate the applicability of this single-particle multi-element fingerprinting (spMEF) method by distinguishing engineered cerium oxide nanoparticles (CeO2 ENPs) from natural Ce-containing nanoparticles (Ce-NNPs) in soils at environmentally relevant ENP concentrations, orders of magnitude below the natural background.
Senn, A. C., Kaegi, R., Hug, S. J., Hering, J. G., Mangold, S., & Voegelin, A. (2017). Effect of aging on the structure and phosphate retention of Fe(III)-precipitates formed by Fe(II) oxidation in water. Geochimica et Cosmochimica Acta, 202, 341-360. doi:10.1016/j.gca.2016.12.033, Institutional Repository

Iron(III)-precipitates formed by Fe(II) oxidation in aqueous solutions affect the cycling and impact of Fe and other co-precipitated elements in environmental systems. Fresh Fe(III)-precipitates are metastable and their transformation into more stable phases during aging may result in the release of initially co-precipitated ions. Phosphate, silicate, Mg and Ca play key roles in determining the structure and composition of fresh Fe(III)-precipitates. Here we examine how these ions affect the structure and phosphate retention of Fe(III)-precipitates formed by oxidation of 0.5 mM dissolved Fe(II) at pH 7.0 after aging for 30 days at 40 °C.
Iron K-edge X-ray absorption spectroscopy (XAS) shows that aged precipitates consist of the same structural units as fresh precipitates: Amorphous Fe(III)- or Ca-Fe(III)-phosphate, ferrihydrite, and poorly crystalline lepidocrocite. Mg, Ca, and dissolved phosphate stabilize (Ca-)Fe(III)-phosphate against transformation into ferrihydrite. Silicate further attenuates (Ca-)Fe(III)-phosphate transformation. The crystallinity of lepidocrocite formed in phosphate- and silicate-free solutions slightly increases during aging. The transformation of Fe(III)- and Ca-Fe(III)-phosphate into ferrihydrite and ongoing ferrihydrite crystallization during aging result in the release of co-precipitated phosphate. Dissolved Ca on the other hand limits phosphate concentrations to values consistent with solubility control by octacalciumphosphate. Owing to the combined effects of Ca and silicate, phosphate is most effectively retained by Fe(III)-precipitates formed and aged in Ca- and silicate-containing solutions. The results from this study contribute to an improved understanding of the formation and transformation of Fe(III)-precipitates and emphasize that the complexity of Fe(III)-precipitate dynamics in the presence of multiple interfering solutes must be considered when addressing their impact on major and trace elements in environmental systems.
Vriens, B., Voegelin, A., Hug, S. J., Kaegi, R., Winkel, L. H. E., Buser, A. M., & Berg, M. (2017). Quantification of element fluxes in wastewaters: a nationwide survey in Switzerland. Environmental Science and Technology, 51(19), 10943-10953. doi:10.1021/acs.est.7b01731, Institutional Repository

The number and quantities of trace elements used in industry, (high-tech) consumer products, and medicine are rapidly increasing, but the resulting emissions and waste streams are largely unknown. We assessed the concentrations of 69 elements in digested sewage sludge and effluent samples from 64 municipal wastewater treatment plants as well as in major rivers in Switzerland. This data set, representative of an entire industrialized country, presents a reference point for current element concentrations, average per-capita fluxes, loads discharged to surface waters, and economic waste-stream values. The spatial distribution of many individual elements could be attributed either to predominant geogenic or to anthropogenic inputs. Per-capita element fluxes ranged from <10 μg day−1 (e.g., Au, In, and Lu) to >1 mg day−1 (e.g., Zn, Sc, Y, Nb, and Gd) and >1 g day−1 (e.g., for P, Fe, and S). Effluent loads of some elements contributed significantly to riverine budgets (e.g., 24% for Zn, 50% for P, and 83% for Gd), indicating large anthropogenic inputs via the wastewater stream. At various locations, precious metal concentrations in sludge were similar to those in profitable mining ores, with total flux values of up to 6.8 USD per capita per year or 15 USD per metric ton of dry sludge.
Kaegi, R. (2016). Separation and analysis of nanoparticles (NP) in aqueous environmental samples. In B. Xing, C. D. Vecitis, & N. Senesi (Eds.), Wiley-IUPAC series in biophysico-chemical processes in environmental systems. Engineered nanoparticles and the environment. Biophysicochemical processes and toxicity (pp. 53-74). doi:10.1002/9781119275855.ch4, Institutional Repository

Engineered nanoparticles (NP) are defined as intentionally manufactured particles with at least one dimension between 1 and 100 nm. Colloids are roughly defined as particles with a diameter between 1 nm and 1 μm (Buffle and Leeuwen, 1992). Engineered NP, thus, represent a small subgroup of colloids. It has been suggested to distinguish between natural NP, incidental NP, and engineered NP (Christian et al. 2008; Farre et al. 2009; Hassellöv and Kaegi 2009). Several trace metals of geogenic origin are bound to colloids, such as clay minerals, or even form eigencolloids (e.g., metal hydroxides and metal sulfides). As these colloids often occur in the nanoscale range (Lead and Wilkinson 2006), they are classified as natural NP. In addition to being in the nanoscale range (1-100 nm), incidental NP are the by-products of human activities. For example, they are emitted from internal combustion engines (e.g., diesel soot) or coal-fired power plants (e.g., fly ash). Engineered NP, such as carbon nanotubes (CNT) or titanium dioxide (TiO2)-NP, can have the same elemental composition as natural or incidental NP, but they are synthesized on purpose with additional functionalities. To assess the effects of human activities on the environment, incidental and engineered NP have to be separated from natural NP and, even more specifically, to assess the impact of engineered NP on the environment, particles of this specific subgroup have to be distinguished from the other two NP types at each stage of their life cycle (Wiesner et al. 2009). Therefore, it is necessary to develop methods that allow a quantitative detection of engineered NP in complex matrices of different environmental compartments. [...]
Meier, C., Voegelin, A., Pradas Del Real, A., Sarret, G., Mueller, C. R., & Kaegi, R. (2016). Transformation of silver nanoparticles in sewage sludge during incineration. Environmental Science and Technology, 50(7), 3503-3510. doi:10.1021/acs.est.5b04804, Institutional Repository

Silver nanoparticles (Ag-NP) discharged into the municipal sewer system largely accumulate in the sewage sludge. Incineration and agricultural use are currently the most important strategies for sewage sludge management. Thus, the behavior of Ag-NP during sewage sludge incineration is essential for a comprehensive life cycle analysis and a more complete understanding of the fate of Ag-NP in the (urban) environment. To address the transformation of Ag-NP during sewage sludge incineration, we spiked metallic Ag0-NP to a pilot wastewater treatment plant and digested the sludge anaerobically. The sludge was then incinerated on a bench-scale fluidized bed reactor in a series of experiments under variable conditions. Complementary results from X-ray absorption spectroscopy (XAS) and electron microscopy–energy dispersive X-ray (EM–EDX) analysis revealed that Ag0-NP transformed into Ag2S-NP during the wastewater treatment, in agreement with previous studies. On the basis of a principal component analysis and subsequent target testing of the XAS spectra, Ag0 was identified as a major Ag component in the ashes, and Ag2S was clearly absent. The reformation of Ag0-NP was confirmed by EM–EDX. The fraction of Ag0 of the total Ag in the ashes was quantified by linear combination fitting (LCF) of XAS spectra, and values as high as 0.8 were found for sewage sludge incinerated at 800 °C in a synthetic flue gas atmosphere. Low LCF totals (72% to 94%) indicated that at least one relevant reference spectrum was missing in the LCF analysis. The presence of spherical Ag-NP with a diameter of <50 nm extending into the sub-nm range was revealed by electron microscopy analyses. The rapid formation of Ag0-NP from Ag2S during sewage sludge incineration, as demonstrated in this study, needs to be considered in the life cycle assessment of engineered Ag-NP.
Petersen, E. J., Flores-Cervantes, D. X., Bucheli, T. D., Elliott, L. C. C., Fagan, J. A., Gogos, A., … Winchester, M. R. (2016). Quantification of carbon nanotubes in environmental matrices: current capabilities, case studies, and future prospects. Environmental Science and Technology, 50(9), 4587-4605. doi:10.1021/acs.est.5b05647, Institutional Repository

Carbon nanotubes (CNTs) have numerous exciting potential applications and some that have reached commercialization. As such, quantitative measurements of CNTs in key environmental matrices (water, soil, sediment, and biological tissues) are needed to address concerns about their potential environmental and human health risks and to inform application development. However, standard methods for CNT quantification are not yet available. We systematically and critically review each component of the current methods for CNT quantification including CNT extraction approaches, potential biases, limits of detection, and potential for standardization. This review reveals that many of the techniques with the lowest detection limits require uncommon equipment or expertise, and thus, they are not frequently accessible. Additionally, changes to the CNTs (e.g., agglomeration) after environmental release and matrix effects can cause biases for many of the techniques, and biasing factors vary among the techniques. Five case studies are provided to illustrate how to use this information to inform responses to real-world scenarios such as monitoring potential CNT discharge into a river or ecotoxicity testing by a testing laboratory. Overall, substantial progress has been made in improving CNT quantification during the past ten years, but additional work is needed for standardization, development of extraction techniques from complex matrices, and multimethod comparisons of standard samples to reveal the comparability of techniques.
Pradas del Real, A. E., Castillo-Michel, H., Kaegi, R., Sinnet, B., Magnin, V., Findling, N., … Sarret, G. (2016). Fate of Ag-NPs in sewage sludge after application on agricultural soils. Environmental Science and Technology, 50(4), 1759-1768. doi:10.1021/acs.est.5b04550, Institutional Repository

The objective of this work was to investigate the fate of silver nanoparticles (Ag-NPs) in a sludge-amended soil cultivated with monocot (Wheat) and dicot (Rape) crop species. A pot experiment was performed with sludges produced in a pilot wastewater treatment plant containing realistic Ag concentrations (18 and 400 mg kg–1, 14 mg kg–1 for the control). Investigations focused on the highest dose treatment. X-ray absorption spectroscopy (XAS) showed that Ag2S was the main species in the sludge and amended soil before and after plant culture. The second most abundant species was an organic and/or amorphous Ag—S phase whose proportion slightly varied (from 24% to 36%) depending on the conditions. Micro and nano X-ray fluorescence (XRF) showed that Ag was preferentially associated with S-rich particles, including organic fragments, of the sludge and amended soils. Ag was distributed as heteroaggregates with soil components (size ranging from ≤0.5 to 1–3 μm) and as diffused zones likely corresponding to sorbed/complexed Ag species. Nano-XRF evidenced the presence of mixed metallic sulfides. Ag was weakly exchangeable and labile. However, micronutrient mobilization by plant roots and organic matter turnover may induce Ag species interconversion eventually leading to Ag release on longer time scales. Together, these data provide valuable information for risk assessment of sewage sludge application on agricultural soils.
Thalmann, B., Voegelin, A., Morgenroth, E., & Kaegi, R. (2016). Effect of humic acid on the kinetics of silver nanoparticle sulfidation. Environmental Science: Nano, 3(1), 203-212. doi:10.1039/c5en00209e, Institutional Repository

The sulfidation of metallic silver nanoparticles (AgNP) observed in urban wastewater systems and in natural waters reduces their toxicity by several orders of magnitude. However, the reaction rate of this transformation is only poorly understood and the influence of humic acid (HA) on AgNP sulfidation has not been studied to date. We therefore investigate the sulfidation kinetics of AgNP reacted with bisulfide (HS−) in the absence and presence of HA and evaluate different kinetic models to describe the observed reaction kinetics. Citrate-stabilized AgNP of different sizes (20–200 nm) were reacted with an excess of HS− in the absence of HA as well as at HA concentrations ranging from 50 to 1000 mg L−1. The extent of AgNP sulfidation after the selected reaction times was determined by X-ray absorption spectroscopy (XAS). The overall sulfidation rate increased with decreasing AgNP size and increasing HA concentration. The sulfidation rate of the AgNP was best described by a diffusion-limited solid state reaction model (parabolic rate law). The corresponding half-lives of the AgNP ranged from minutes to hours. The increase of the sulfidation rate with increasing HA concentration may be explained by the adsorption of HA onto the AgNP surface facilitating the access of HS− to the particle surface. The results from analytical transmission electron microscopy suggest that the AgNP were sulfidized asymmetrically in the absence of HA. In the presence of HA, the initially formed concentric core–shell Ag0–Ag2S structures developed into hollow Ag2S nanoparticles with increasing reaction time, possibly via the Kirkendall effect.
Vriens, B., Berg, M., Hug, S., Kägi, R., Voegelin, A., & Winkel, L. (2016). Ermittlung der Konzentrationsbereiche von Spurenelementen in Abwasserreinigungsanlagen. Zusammenfassender Schlussbericht. Dübendorf: Eawag. , Institutional Repository
Burkhardt, M., Dietschweiler, C., Schmidt, S., Englert, A., Hemmann, J., Sinnet, B., & Kägi, R. (2015). Titandioxid. Leitsubstanz für Nanopartikel im Deponiesickerwasser. Aqua & Gas, 95(12), 40-47. , Institutional Repository

Nanopartikel können auf Deponien und von dort mit dem Sickerwasser in Vorfluter gelangen. Als Leitsubstanz für Nanopartikel wurde das Weisspigment Titandioxid in Wasserproben der lnertstoffdeponien Bruni und Schwanental untersucht. Vorgestellt werden insbesondere die Herausforderungen an die analytischen Methoden zur Erfassung von Nanopartikeln in Wasserproben und die ermittelten Massenflüsse.
Fedotova, N., Kaegi, R., Koch, J., & Günther, D. (2015). Influence of dispersion agents on particle size and concentration determined by laser-induced breakdown detection. Spectrochimica Acta B: Atomic Spectroscopy, 103-104(1), 92-98. doi:10.1016/j.sab.2014.12.002, Institutional Repository

Laser-induced breakdown detection (LIBD) is a very promising analytical technique to determine the size and the concentration of nanoparticles (NPs) in aqueous suspensions. The measurement principle is based on the formation of individual plasma events selectively produced when a pulsed, focused laser beam hits a NP. The breakdown probability (BDP) is defined as the ratio of the number of plasma events detected to the total number of laser pulses applied. Energy curves are established by recording the BDP as a function of the laser energy which is increased in a stepwise manner. The size and the concentration of NPs in aqueous suspensions can be extracted from recorded energy curves. Although several studies have already documented the potential of the LIBD technique to detect NPs at trace concentrations in aqueous suspensions, the effect of dissolved matrix constituents (e.g. dispersion agents, which are frequently used to stabilize NPs in suspension) on the LIBD signal has not been addressed, yet.
We therefore recorded energy curves of ultrahigh purity (UHP) water and NP suspensions both spiked with different dispersion agents at different concentrations. An increasing shift of the energy curves towards lower energies was observed with increasing concentrations of dispersion agents. The LIBD-derived size of the NPs was less affected by the presence of dispersion agents than the LIBD-derived particle number concentrations, which deviated by up to 300% from the expected values. The effects on the calculated concentrations were most pronounced at low (2 · 107 particles mL− 1) NP concentrations and at higher NP concentrations (3 · 108 particles mL− 1), the effect of the dispersion agents on the energy curves became negligible. These results show that dissolved matrix constituents substantially affect LIBD measurements, especially at low NP concentrations.
Hofacker, A. F., Behrens, S., Voegelin, A., Kaegi, R., Lösekann-Behrens, T., Kappler, A., & Kretzschmar, R. (2015). Clostridium species as metallic copper-forming bacteria in soil under reducing conditions. Geomicrobiology Journal, 32(2), 130-139. doi:10.1080/01490451.2014.933287, Institutional Repository

Recent studies have reported the formation of Cu0 nanoparticles (CuNP) by suspended bacteria in pore water of periodically flooded soils, but the bacteria have not yet been identified. The aim of this study was to identify the CuNP-forming bacteria and to determine the location of CuNP formation relative to the bacterial cell surface. Electron microscopy revealed that the bacteria were rod-shaped spore formers and suggested that CuNP were formed in the periplasm. Combined results from denaturing gradient gel electrophoresis, 16S rRNA gene clone libraries, and classic microbiological cultivation techniques provided strong evidence for a Clostridium sp. strain as the CuNP-forming bacteria. Clostridia are well-adapted to frequent flooding and drying due to their ability to form spores and may play an important role in Cu cycling and metallic Cu formation in redox-dynamic environments.
Kaegi, R., Voegelin, A., Sinnet, B., Zuleeg, S., Siegrist, H., & Burkhardt, M. (2015). Transformation of AgCl nanoparticles in a sewer system - a field study. Science of the Total Environment, 535, 20-27. doi:10.1016/j.scitotenv.2014.12.075, Institutional Repository

Silver nanoparticles (Ag-NP) are increasingly used in consumer products and their release during the use phase may negatively affect aquatic ecosystems. Research efforts, so far, have mainly addressed the application and use of metallic Ag(0)-NP. However, as shown by recent studies on the release of Ag from textiles, other forms of Ag, especially silver chloride (AgCl), are released in much larger quantities than metallic Ag(0). In this field study, we report the release of AgCl-NP from a point source (industrial laundry that applied AgCl-NP during a piloting phase over a period of several months to protect textiles from bacterial regrowth) to the public sewer system and investigate the transformation of Ag during its transport in the sewer system and in the municipal wastewater treatment plant (WWTP). During the study period, the laundry discharged ~85 g of Ag per day, which dominated the Ag loads in the sewer system from the respective catchment (72–95%) and the Ag in the digested WWTP sludge (67%). Combined results from electron microscopy and X-ray absorption spectroscopy revealed that the Ag discharged from the laundry to the sewer consisted of about one third AgCl and two thirds Ag2S, both forms primarily occurring as nanoparticles with diameters < 100 nm. During the 800 m transport in the sewer channel to the nearby WWTP, corresponding to a travel time of ~30 min, the remaining AgCl was transformed into nanoparticulate Ag2S. Ag2S-NP also dominated the Ag speciation in the digested sludge. In line with results from earlier studies, the very low Ag concentrations measured in the effluent of the WWTP (< 0.5 μg L− 1) confirmed the very high removal efficiency of Ag from the wastewater stream (> 95%).
Müller, P., Mielke, J., Hodoroaba, V. D., Kägi, R., & Ryner, M. (2015). Assessment of different electron microscopy techniques for particle size quantification of potential nanomaterials. Microscopy and Microanalysis, 21(S3), 2403-2404. doi:10.1017/S1431927615012799, Institutional Repository
Senn, A. C., Kaegi, R., Hug, S. J., Hering, J. G., Mangold, S., & Voegelin, A. (2015). Composition and structure of Fe(III)-precipitates formed by Fe(II) oxidation in water at near-neutral pH: interdependent effects of phosphate, silicate and Ca. Geochimica et Cosmochimica Acta, 162, 220-246. doi:10.1016/j.gca.2015.04.032, Institutional Repository

We studied the interdependent effects of phosphate, silicate and Ca on the formation of Fe(III)-precipitates by oxidation of 0.5 mM Fe(II) in near-neutral bicarbonate-buffered aqueous solutions at concentrations relevant for natural water resources. Complementary results obtained by a suite of analytical techniques including X-ray absorption spectroscopy and transmission electron microscopy showed that the ratio of initially dissolved phosphate over Fe(II) ((P/Fe)init) had a major impact on precipitate formation. At (P/Fe)init above a critical ratio ((P/Fe)crit) of ∼0.5 in 8 mM NaHCO3 and ∼0.8 in 4 mM Ca(HCO3)2 electrolyte, Fe(II) oxidation led to exclusive formation of amorphous basic Fe(III)-phosphate or Ca–Fe(III)-phosphate ((Ca-)Fe(III)-phosphate) with maximum precipitate P/Fe ratios ((P/Fe)ppt) of ∼0.7 in Na and ∼1.1 in Ca electrolyte. Enhanced phosphate uptake in the presence of Ca was due to phosphate-Ca interactions coupled to Fe precipitation, mainly formation of mitridatite-like Ca–Fe(III)-phosphate polymers and Ca-phosphate polymers. At (P/Fe)init < (P/Fe)crit, in the absence of silicate, (Ca-)Fe(III)-phosphate precipitation was followed by the formation of poorly crystalline lepidocrocite and concomitant transformation of the (Ca-)Fe(III)-phosphate into a phosphate-rich ferrihydrite-type precipitate with a (P/Fe)ppt of ∼0.25. In the presence of 0.5 mM silicate, initially formed (Ca-)Fe(III)-phosphate nanoparticles became coated with silicate-rich ferrihydrite during continuing Fe(II) oxidation and only limited transformation of the (Ca-)Fe(III)-phosphate occurred. The results from this study indicate the complexity of Fe(III)-precipitate formation in the presence of interfering solutes and its consequences for precipitate structure and phosphate sequestration. The findings provide a solid basis for further studies of the reactivity of different Fe(III)-precipitate types and for the systematic assessment of their impact on Fe, phosphate and trace elements dynamics in natural and engineered systems.
Thalmann, B., Voegelin, A., von Gunten, U., Behra, R., Morgenroth, E., & Kaegi, R. (2015). Effect of ozone treatment on nano-sized silver sulfide in wastewater effluent. Environmental Science and Technology, 49(18), 10911-10919. doi:10.1021/acs.est.5b02194, Institutional Repository

Silver nanoparticles used in consumer products are likely to be released into municipal wastewater. Transformation reactions, most importantly sulfidation, lead to the formation of nanoscale silver sulfide (nano-Ag2S) particles. In wastewater treatment plants (WWTP), ozonation can enhance the effluent quality by eliminating organic micropollutants. The effect of ozonation on the fate of nano-Ag2S, however, is currently unknown. In this study, we investigate the interaction of ozone with nano-Ag2S and evaluate the effect of ozonation on the short-term toxicity of WWTP effluent spiked with nano-Ag2S. The oxidation of nano-Ag2S by ozone resulted in a stoichiometric factor (number of moles of ozone required to oxidize one mole of sulfide to sulfate) of 2.91, which is comparable to the results obtained for the reaction of bisulfide (HS–) with ozone. The second-order rate constant for the reaction of nano-Ag2S with ozone (k = 3.1 × 104 M–1 s–1) is comparable to the rate constant of fast-reacting micropollutants. Analysis of the ozonation products of nano-Ag2S by transmission electron microscopy (TEM) and X-ray absorption spectroscopy (XAS) revealed that ozonation dominantly led to the formation of silver chloride in WWTP effluent. After ozonation of the Ag2S-spiked effluent, the short-term toxicity for the green algae Chlamydomonas reinhardtii increased and reached EC50 values comparable to Ag+. This study thus reveals that ozone treatment of WWTP effluent results in the oxidation of Ag2S and, hence, an increase of the Ag toxicity in the effluent, which may become relevant at elevated Ag concentrations.
Thalmann, B. A. D. (2015). Transformations of silver nanoparticles in urban wastewater and water systems (Doctoral dissertation). doi:10.3929/ethz-a-010579189, Institutional Repository

Metallic silver nanoparticles (AgNP) are increasingly applied in consumer products from which they are probably released to the urban wastewater and water system. Due to the antimicrobial activity of AgNP, they are of high ecotoxicological concern and an engineered nanomaterial of priority for environmental risk assessment. Transformations of AgNP can have large efects on their toxicity toward aquatic organism. Most importantly, the sulidation of AgNP is known to reduce the toxicity of Ag by several orders of magnitude. Thus, a proper understanding of the sulidation of AgNP in the urban wastewater and water system is crucial for in-depth environmental risk assessments. Furthermore, the ozonation of the eluent of wastewater treatment plant (WWTP) to mitigate micropollutants is likely to further change the Ag speciation. he irst objective of this thesis was to understand the sulidation kinetics of AgNP with bisulide (HS-) and metal sulides. The second objective was to study the impact of ozone treatment on sulidized AgNP. [...]

Silber Nanopartikel (AgNP) werden vermehrt in Konsumgütern angewandt, von welchen die Partikel durch den Gebrauch in das urbane Abwasser und Wasser ausgewaschen werden können. Aufgrund ihrer antimikrobieller Wirkung stellen sie ein potentielles Risiko für die Umwelt dar, welches abgeschätzt werden sollte. Durch Umwandlung in der Umwelt ändert sich die Speziierung der AgNP was die Toxizität gegenüber aquatischen Organismen und Planzen beeinlusst. Die Reaktion von AgNP mit Suliden, genannt Sulidierung, zum Beispiel reduziert die Ag Toxizität um mehrere Grössenordnungen. Deshalb ist es für eine Risikoeinschätzung der AgNP in der Umwelt wichtig die Sulidierung im urbanen Abwasser und Wasser zu verstehen. Im Abwasser ist die dominante Sulid Quelle Bisulid (HS-), welches in erhöhten Konzentrationen zu inden ist. Für das Oberlächengewässer hingegen ist die Sulidierung mit Metallsuliden wahrscheinlicher, da sie persistenter gegen die Oxidation mit Sauerstof sind. Das erste Ziel dieser Dissertation war deshalb die Sulidierung von AgNP mit HS- und Metallsuliden zu verstehen. [...]
Duester, L., Burkhardt, M., Gutleb, A. C., Kaegi, R., Macken, A., Meermann, B., & von der Kammer, F. (2014). Toward a comprehensive and realistic risk evaluation of engineered nanomaterials in the urban water system. Frontiers in Chemistry, 2, 39 (6 pp.). doi:10.3389/fchem.2014.00039, Institutional Repository

The European COoperation in Science and Technology (COST) Action ES1205 on the transfer of Engineered Nano materials from wastewater Treatment and stormwatEr to Rivers (ENTER) aims to create and to maintain a trans European network among scientists. This perspective article delivers a brief overview on the status quo at the beginning of the project by addressing the following aspects on engineered nano materials (ENMs) in the urban systems: (1) ENMs that need to be considered on a European level; (2) uncertainties on production-volume estimations; (3) fate of selected ENMs during waste water transport and treatment; (4) analytical strategies for ENM analysis; (5) ecotoxicity of ENMs, and (6) future needs. These six step stones deliver the derivation of the position of the ES1205 network at the beginning of the projects runtime, by defining six fundamental aspects that should be considered in future discussions on risk evaluation of ENMs in urban water systems.
Gogos, A., Kaegi, R., Zenobi, R., & Bucheli, T. D. (2014). Capabilities of asymmetric flow field-flow fractionation coupled to multi-angle light scattering to detect carbon nanotubes in soot and soil. Environmental Science: Nano, 1(6), 584-594. doi:10.1039/c4en00070f, Institutional Repository

Analytical detection and quantification of multi-walled carbon nanotubes (MWCNTs) in complex matrices such as soils is very challenging. In an initial approach to this task, we identify MWCNTs by making use of their different (e.g., rod-like) shape compared to other (native) soil particles and in particular soot, which is ubiquitously present in soils. A shape factor ρ, determined using asymmetric flow field-flow fractionation coupled to multi-angle light scattering (aF4-MALS), was used to discriminate MWCNTs of different aspect ratios, as well as mixtures of soot and MWCNTs, in pure suspensions. MALS results were additionally confirmed using automated electron microscopy image analysis. We then analyzed different soil types which consistently showed ρ-values that differed from pure MWCNTs. To test the performance of the method for MWCNT detection in such complex matrices, we conducted standard additions of a MWCNT as well as soot to an agricultural soil. Extracts from these MWCNT-spiked soils showed increased ρ-values compared to soot-spiked or native soil. The method detection limit for the MWCNT was 1.6 to 4.0 mg g−1 soil and lies within the range of commonly used black carbon quantification methods, but is much higher than any currently predicted environmental concentration. Additionally, the method is currently limited by a relatively narrow dynamic range of ρ. Despite these limitations, our results suggest that aF4-MALS provides specific shape information that may be linked to an actual MWCNT presence in soils. Further method improvement potential is outlined along different steps of the workflow.
Grass, R. N., Schälchli, J., Paunescu, D., Soellner, J. O. B., Kaegi, R., & Stark, W. J. (2014). Tracking trace amounts of submicrometer silica particles in wastewaters and activated sludge using silica-encapsulated DNA barcodes. Environmental Science and Technology Letters, 1(12), 484-489. doi:10.1021/ez5003506, Institutional Repository

Although silica particles are among the widest utilized engineered nanoparticles, the measurement of silica particles at low exposure concentrations is impeded by the high background concentrations of silicates in the environment. To circumvent this analytical limitation, we describe a new method for tracing submicrometer silica particles in water by the usage of silica particles fully encapsulating unique DNA codes. Because DNA can be detected at extremely low concentrations by quantitative polymerase chain reaction (PCR), the encapsulation of DNA in silica allows an indirect measure of the concentration of silica particles down to the sub-parts per billion range (micrograms per liter). To provide insight into the capability of this novel technology, we utilized DNA-loaded submicrometer silica particles to follow the fate of silica particles in the analytically most demanding biological stages of wastewater treatment solutions (activated sludge). At various initial particle concentrations ranging from 10 ppb (10 µg/L) to 10 ppm (10 mg/L) and under both aerobic and anoxic conditions, we are able to show that >97% of the particles were removed from the wastewater by incorporation into sludge biomass.
Kroll, A., Behra, R., Kaegi, R., & Sigg, L. (2014). Extracellular polymeric substances (EPS) of freshwater biofilms stabilize and modify CeO2 and Ag nanoparticles. PLoS One, 9(10), e110709 (16 pp.). doi:10.1371/journal.pone.0110709, Institutional Repository

Streams are potential receiving compartments for engineered nanoparticles (NP). In streams, NP may remain dispersed or settle to the benthic compartment. Both dispersed and settling NP can accumulate in benthic biofilms called periphyton that are essential to stream ecosystems. Periphytic organisms excrete extracellular polymeric substances (EPS) that interact with any material reaching the biofilms. To understand the interaction of NP with periphyton it is therefore crucial to study the interaction of NP with EPS. We investigated the influence of EPS on the physicochemical properties of selected NP (CeO2, Ag) under controlled conditions at pH 6, 7.6, 8.6 and light or dark exposure. We extracted EPS from five different periphyton communities, characterized the extracts, and exposed CeO2 and carbonate-stabilized Ag NP (0.5 and 5 mg/L, both 25 nm primary particle size) and AgNO3 to EPS (10 mg/L) over two weeks. We measured NP size distribution, shape, primary particle size, surface plasmon resonance, and dissolution. All EPS extracts were composed of biopolymers, building blocks of humic substances, low molecular weight (Mr) acids, and small amphiphilic or neutral compounds in varying concentrations. CeO2 NP were stabilized by EPS independent of pH and light/dark while dissolution increased over time in the dark at pH 6. EPS induced a size increase in Ag NP in the light with decreasing pH and the formation of metallic Ag NP from AgNO3 at the same conditions via EPS-enhanced photoreduction. NP transformation and formation were slower in the extract with the lowest biopolymer and low Mr acid concentrations. Periphytic EPS in combination with naturally varying pH and light/dark conditions influence the properties of the Ag and CeO2 NP tested and thus the exposure conditions within biofilms. Our results indicate that periphytic organisms may be exposed to a constantly changing mixture of engineered and naturally formed Ag NP and Ag+.
Neidhardt, H., Berg, M., Stengel, C., Winkel, L. H. E., Kaegi, R., Trang, P. T. K., … Viet, P. H. (2014). Arsenic adsorption on iron mineral phases under reducing conditions: results from an in-situ field experiment. In M. I. Litter, H. B. Nicolli, M. Meichtry, N. Quici, J. Bundschuh, P. Bhattacharya, & R. Naidu (Eds.), One century of the discovery of Arsenicosis in Latin America (1914-2014) (pp. 83-84). London: CRC Press. , Institutional Repository

Intrusion of As-rich groundwater into previously As-free aquifers due to extensive groundwater extraction is an increasing cause of concern, especially in Southeast Asia. We studied in-situ As adsorption processes by exposing synthetic Fe-mineral coated sand, as well as original sediment material, to high As groundwater under reducing conditions. Samples were placed in three monitoring wells located in a well-investigated study area (Van Phuc, Vietnam). The amount of adsorbed As reflected an As adsorption potential in the following order: hematite sand > ferrihydrite sand > original Pleistocene sand > goethite sand, and increased proportionally to the concentration of dissolved As in the respective groundwater. Results further indicate transformation of the exposed Fe-minerals, which is presumably controlled by biogeochemical processes. This alteration is expected to cause pronounced changes in the As adsorption potential of the Fe-minerals over time, which is subject to ongoing research.
Thalmann, B., Voegelin, A., Sinnet, B., Morgenroth, E., & Kaegi, R. (2014). Sulfidation kinetics of silver nanoparticles reacted with metal sulfides. Environmental Science and Technology, 48(9), 4885-4892. doi:10.1021/es5003378, Institutional Repository

Recent studies have documented that the sulfidation of silver nanoparticles (Ag-NP), possibly released to the environment from consumer products, occurs in anoxic zones of urban wastewater systems and that sulfidized Ag-NP exhibit dramatically reduced toxic effects. However, whether Ag-NP sulfidation also occurs under oxic conditions in the absence of bisulfide has not been addressed, yet. In this study we, therefore, investigated whether metal sulfides that are more resistant toward oxidation than free sulfide, could enable the sulfidation of Ag-NP under oxic conditions.
We reacted citrate-stabilized Ag-NP of different sizes (10–100 nm) with freshly precipitated and crystalline CuS and ZnS in oxygenated aqueous suspensions at pH 7.5. The extent of Ag-NP sulfidation was derived from the increase in dissolved Cu2+ or Zn2+ over time and linked with results from X-ray absorption spectroscopy (XAS) analysis of selected samples. The sulfidation of Ag-NP followed pseudo first-order kinetics, with rate coefficients increasing with decreasing Ag-NP diameter and increasing metal sulfide concentration and depending on the type (CuS and ZnS) and crystallinity of the reacting metal sulfide. Results from analytical electron microscopy revealed the formation of complex sulfidation patterns that seemed to follow preexisting subgrain boundaries in the pristine Ag-NP. The kinetics of Ag-NP sulfidation observed in this study in combination with reported ZnS and CuS concentrations and predicted Ag-NP concentrations in wastewater and urban surface waters indicate that even under oxic conditions and in the absence of free sulfide, Ag-NP can be transformed into Ag2S within a few hours to days by reaction with metal sulfides.
Voegelin, A., Kaegi, R., Berg, M., Nitzsche, K. S., Kappler, A., Lan, V. M., … Steininger, R. (2014). Solid-phase characterisation of an effective household sand filter for As, Fe and Mn removal from groundwater in Vietnam. Environmental Chemistry, 11(5), 566-578. doi:10.1071/EN14011, Institutional Repository

Household sand filters are widely used in Vietnam to remove As, Fe and Mn from anoxic groundwater used as a drinking water resource. To expand the mechanistic knowledge of the filter functioning, we investigated the bulk and micrometre-scale distribution of Fe, As, P and Mn and the speciation of Fe, Mn and As in a sand filter after 8 years of operation using bulk and micro-focussed X-ray fluorescence spectrometry (XRF) and X-ray absorption spectroscopy (XAS) and scanning electron microscopy coupled with energy dispersive X-ray detection (SEM-EDX). Effective oxygenation of the anoxic groundwater enables the oxidative removal of Fe, As and Mn in the filter sand. Our results show that Fe is retained in the filter as a 2-line ferrihydrite-like FeIII-precipitate that coats sand grains, and that As accumulates dominantly as pentavalent arsenate. The very close spatial correlation of accumulated As and P with Fe throughout the filter sand and down to the micrometre-scale and the effective Fe, P and As retention at an estimated average water residence time of only 30 min suggest that their uptake is governed by a combination of fast sorption reactions, surface-catalysed FeII oxidation and mediated AsIII co-oxidation. In contrast, Mn is retained in separate MnIV/III-(oxyhydr)oxide coatings and concretions, probably as a result of coupled surface-catalysed and microbial MnII oxidation. Silicate sorbed to the ferrihydrite-like FeIII-coatings inhibits their crystallisation and associated remobilisation of P and As. The periodic drainage and aeration of the filter favours the oxidation of any residual FeII and AsIII and the formation of dense Fe precipitates and may thereby contribute to effective filter operation over several years.
Wenk, C. B., Kaegi, R., & Hug, S. J. (2014). Factors affecting arsenic and uranium removal with zero-valent iron: laboratory tests with Kanchan-type iron nail filter columns with different groundwaters. Environmental Chemistry, 11(5), 547-557. doi:10.1071/EN14020, Institutional Repository

Zero-valent iron (ZVI)-based filters are able to remove arsenic and other pollutants from drinking water, but their performance depends on the form of ZVI, filter design, water composition and operating conditions. Kanchan filters use an upper bucket with ZVI in the form of commercial iron nails, followed by a sand filter, to remove arsenic and pathogens. We evaluated factors that influence the removal of arsenic and uranium with laboratory columns containing iron nails with six different synthetic groundwaters with 500 μg L–1 AsIII, 50 μg L–1 U, 2 mg L–1 B, and with 0 and 2 mg L–1 P (added as o-phosphate), 0.25 and 2.5 mM Ca, 3.2 and 8.3 mM HCO3–, at pH 7.0 and 8.4 over 30 days. During the first 10 days, As removal was 65–95 % and strongly depended on the water composition. As removal at pH 7.0 was better than at pH 8.4 and high P combined with low Ca decreased As removal. From 10–30 days, As removal decreased to 45–60 % with all columns. Phosphate, in combination with low Ca concentrations lowered As removal, but had a slightly positive effect in combination with high Ca concentrations. U removal was only 10–70 %, but showed similar trends. The drop in performance over time can be explained by decreasing release of iron to solution due to formation of layers of FeIII phases and calcite covering the iron surface. Mobile corrosion products contained ferrihydrite, Si-containing hydrous ferric oxides, and amorphous Fe–Si–P phases. Comparisons with another type of ZVI filter (SONO-filter) were used to evaluate filter design parameters. Higher ZVI surface areas and longer contact times should lead to satisfactory As removal with Kanchan-type filters.
Yang, Y., Doudrick, K., Bi, X., Hristovski, K., Herckes, P., Westerhoff, P., & Kaegi, R. (2014). Characterization of food-grade titanium dioxide: the presence of nanosized particles. Environmental Science and Technology, 48(11), 6391-6400. doi:10.1021/es500436x, Institutional Repository

Titanium dioxide (TiO2) is widely used in food products, which will eventually enter wastewater treatment plants and terrestrial or aquatic environments, yet little is known about the fraction of this TiO2 that is nanoscale, or the physical and chemical properties of TiO2 that influence its human and environmental fate or toxicity. Instead of analyzing TiO2 properties in complex food or environmental samples, we procured samples of food-grade TiO2 obtained from global food suppliers and then, using spectroscopic and other analytical techniques, quantified several parameters (elemental composition, crystal structure, size, and surface composition) that are reported to influence environmental fate and toxicity. Another sample of nano-TiO2 that is generally sold for catalytic applications (P25) and widely used in toxicity studies, was analyzed for comparison. Food-grade and P25 TiO2 are engineered products, frequently synthesized from purified titanium precursors, and not milled from bulk scale minerals. Nanosized materials were present in all of the food-grade TiO2 samples, and transmission electron microscopy showed that samples 1–5 contained 35, 23, 21, 17, and 19% of nanosized primary particles (<100 nm in diameter) by number, respectively (all primary P25 particles were <100 nm in diameter). Both types of TiO2 aggregated in water with an average hydrodynamic diameter of >100 nm. Food-grade samples contained phosphorus (P), with concentrations ranging from 0.5 to 1.8 mg of P/g of TiO2. The phosphorus content of P25 was below inductively coupled plasma mass spectrometry detection limits. Presumably because of a P-based coating detected by X-ray photoelectron spectroscopy, the ζ potential of the food-grade TiO2 suspension in deionized water ranged from −10 to −45 mV around pH 7, and the iso-electric point for food-grade TiO2 (2 (Si content of 0.026–0.062% and Al content of 0.0006–0.810%) was also different from the case for P25 and would influence the environmental fate of TiO2. X-ray diffraction analysis confirmed the presence of anatase and/or rutile in the food-grade materials, and although the presence of amorphous TiO2 could not be ruled out, it is unlikely on the basis of Raman analysis. The food-grade TiO2 was solar photoactive. Cationic dyes adsorbed more readily to food-grade TiO2 than P25, indicating very different potentials for interaction with organics in the environment. This research shows that food-grade TiO2 contains engineered nanomaterials with properties quite different from those of P25, which has previously been used in many ecotoxicity studies, and because food-grade TiO2 is more likely than P25 to enter the environment (i.e., potentially higher exposure levels), there is a need to design environmental (and human) fate and toxicity studies comparing food-grade to catalytic TiO2.
Hofacker, A. F., Voegelin, A., Kaegi, R., & Kretzschmar, R. (2013). Mercury mobilization in a flooded soil by incorporation into metallic copper and metal sulfide nanoparticles. Environmental Science and Technology, 47(14), 7739-7746. doi:10.1021/es4010976, Institutional Repository

Mercury is a highly toxic priority pollutant that can be released from wetlands as a result of biogeochemical redox processes. To investigate the temperature-dependent release of colloidal and dissolved Hg induced by flooding of a contaminated riparian soil, we performed laboratory microcosm experiments at 5, 14, and 23 °C. Our results demonstrate substantial colloidal Hg mobilization concomitant with Cu prior to the main period of sulfate reduction. For Cu, we previously showed that this mobilization was due to biomineralization of metallic Cu nanoparticles associated with suspended bacteria. X-ray absorption spectroscopy at the Hg LIII-edge showed that colloidal Hg corresponded to Hg substituting for Cu in the metallic Cu nanoparticles. Over the course of microbial sulfate reduction, colloidal Hg concentrations decreased but continued to dominate total Hg in the pore water for up to 5 weeks of flooding at all temperatures. Transmission electron microscopy (TEM) suggested that Hg became associated with Cu-rich mixed metal sulfide nanoparticles. The formation of Hg-containing metallic Cu and metal sulfide nanoparticles in contaminated riparian soils may influence the availability of Hg for methylation or volatilization processes and has substantial potential to drive Hg release into adjacent water bodies.
Hofacker, A. F., Voegelin, A., Kaegi, R., Weber, F. A., & Kretzschmar, R. (2013). Temperature-dependent formation of metallic copper and metal sulfide nanoparticles during flooding of a contaminated soil. Geochimica et Cosmochimica Acta, 103, 316-332. doi:10.1016/j.gca.2012.10.053, Institutional Repository

Riparian floodplains in temperate regions are affected by pronounced seasonal variations in soil and water temperature. This affects the rates and interplay of microbial and abiotic geochemical processes that control the fate of metals in contaminated floodplain soils, including potential release into surface and groundwater during periodic flooding. Here, we investigated how temperature affects chalcophile trace metal contaminants (Cu, Cd, Pb) upon flooding of a riparian soil contaminated by past mining activities. In soil microcosms incubated at 23, 14, and 5 °C, the reductive dissolution of Mn(III,IV) and Fe(III) (oxyhydr)oxides and the release of dissolved Mn2+ and Fe2+ were significantly slower and less intense at the lower temperatures, which was reflected in a decrease of trace metal mobilization via the dissolution of metal oxide sorbents and cation competition for sorption sites. The onset of sulfate reduction was significantly delayed at lower temperatures and the apparent rate of sulfate reduction was decreased, especially at 5 °C. This resulted in elevated high dissolved Cu, Cd, and Pb concentrations over weeks of flooding at 5 °C, whereas colloidal metal sulfide formation dominated Cu, Cd, and Pb pore water dynamics at higher temperatures of 14 and 23 °C due to fast sulfate reduction. Cu K-edge X-ray absorption fine structure spectroscopy revealed metallic Cu(0) as the main colloidal Cu species prior to sulfate reduction at all three temperatures. Analytical electron microscopy showed that Cu(0) particles were associated with suspended bacteria, suggesting biomineralization of Cu(0). Upon onset of sulfate reduction, metallic Cu particles were transformed into CuxS with incorporation of smaller amounts of Cd and Pb. Concomitantly, freely dispersed mixed Cu–Cd–Pb sulfide nanoparticles precipitated in the pore water. Other metals with higher metal sulfide solubility products did not react with the limited amounts of biogenic sulfide. The median size of the mixed metal sulfide nanoparticles increased from 21 nm at 23 °C to 70 nm at 5 °C. During ∼30 days of soil flooding at 23 and 14 °C, Cu speciation in the soil matrix changed from Cu(II) bound to soil organic matter in the oxic soil to 66% CuxS, with intermittent formation of about 14% metallic Cu(0). In contrast, at 5 °C, sulfate reduction and formation of Cu(0) were strongly retarded. After ∼30 days of flooding at 23 and 14 °C, nearly all Cd and about 25% of total Pb in the soil, were precipitated in mixed metal sulfides. Our results demonstrate that temperature controls trace metal dynamics during soil flooding via its influence on microbial reduction of terminal electron acceptors. Even at low temperatures, soil flooding may trigger the release of chalcophile metals from contaminated floodplain soils by sorbent reduction, competitive sorption, and formation of nanoparticulate metal-bearing colloids.
Kaegi, R., Voegelin, A., Ort, C., Sinnet, B., Thalmann, B., Krismer, J., … Mueller, E. (2013). Fate and transformation of silver nanoparticles in urban wastewater systems. Water Research, 47(12), 3866-3877. doi:10.1016/j.watres.2012.11.060, Institutional Repository

Discharge of silver nanoparticles (Ag-NP) from textiles and cosmetics, todays major application areas for metallic Ag-NP, into wastewater is inevitable. Transformation and removal processes in sewers and wastewater treatment plants (WWTP) will determine the impact of Ag-NP on aquatic and terrestrial environments, via the effluents of the WWTP and via the use of digested sludge as fertilizer. We thus conducted experiments addressing the behavior of Ag-NP in sewers and in WWTP.
We spiked Ag-NP to a 5 km long main trunk sewer and collected 40 wastewater samples after 500 m, 2400 m and 5000 m each according to the expected travel times of the Ag-NP. Excellent mass closure of the Ag derived by multiplying the measured Ag concentrations times the volumetric flow rates indicate an efficient transport of the Ag-NP without substantial losses to the sewer biofilm. Ag-NP reacted with raw wastewater in batch experiments were sulfidized to roughly 15% after 5 h reaction time as revealed by X-ray absorption spectroscopy (XAS). However, acid volatile sulfide (AVS) concentrations were substantially higher in the sewer channel (100 μM) compared to the batch experiments (3 μM; still sufficient to sulfidize spiked 2 μM Ag) possibly resulting in a higher degree of sulfidation in the sewer channel. We further investigated the removal efficiency of 10 nm and 100 nm Ag- and gold (Au)-NP coated with citrate or polyvinylpyrrolidone in activated sludge batch experiments. We obtained very high removal efficiencies (∼99%) irrespective of size and coating for Ag- and Au-NP, the latter confirming that the particle type was of minor importance with respect to the degree of NP removal. We observed a strong size dependence of the sulfidation kinetics. We conclude that Ag-NP discharged to the wastewater stream will become sulfidized to various degrees in the sewer system and are efficiently transported to the WWTP. The sulfidation of the Ag-NP will continue in the WWTP, but primarily depending on the size the Ag-NP, may not be complete. Very high removal efficiencies in the WWTP will divert most of the Ag-NP mass flow to the digester and only a small fraction of the Ag will be released to surface waters.
Neumann, A., Kaegi, R., Voegelin, A., Hussam, A., Munir, A. K. M., & Hug, S. J. (2013). Arsenic removal with composite iron matrix filters in Bangladesh: a field and laboratory study. Environmental Science and Technology, 47(9), 4544-4554. doi:10.1021/es305176x, Institutional Repository

The main arsenic mitigation measures in Bangladesh, well-switching and deep tube wells, have reduced As exposure, but water treatment is important where As-free water is not available. Zero-valent iron (ZVI) based SONO household filters, developed in Bangladesh, remove As by corrosion of locally available inexpensive surplus iron and sand filtration in two buckets. We investigated As removal in SONO filters in the field and laboratory, covering a range of typical groundwater concentrations (in mg/L) of As (0.14–0.96), Fe (0–17), P (0–4.4), Ca (45–162), and Mn (0–2.8). Depending on influent Fe(II) concentrations, 20–80% As was removed in the top sand layer, but As removal to safe levels occurred in the ZVI-layer of the first bucket. Residual As, Fe, and Mn were removed after re-aeration in the sand of the second bucket. New and over 8-year-old filters removed As to <50 μg/L and mostly to <10 μg/L and Mn to <0.2 mg/L. Vertical concentration profiles revealed formation of Fe(II) by corrosion of Fe(0) with O2 and incorporation of As into forming amorphous Fe phases in the composite iron matrix (CIM) of newer filters and predominantly magnetite in older filters. As mass balances indicated that users filtered less than reported volumes of water, pointing to the need for more educational efforts. All tested SONO filters provided safe drinking water without replacement for up to over 8 years of use.
Schwyzer, I., Kaegi, R., Sigg, L., & Nowack, B. (2013). Colloidal stability of suspended and agglomerate structures of settled carbon nanotubes in different aqueous matrices. Water Research, 47(12), 3910-3920. doi:10.1016/j.watres.2013.01.057, Institutional Repository

Carbon nanotubes (CNTs) are often processed in suspended form and therefore a release of CNT-suspensions into the aquatic environment is plausible. In this study, the behaviour of two physico-chemically very different CNT types in the presence of varying, environmentally relevant calcium-containing media was investigated, including the long-term colloidal stability and the sedimentary structures of settled CNTs. Calcium induced CNT flocculation, however, the stability of the CNTs in the medium did not monotonously decrease with increasing calcium concentration. At intermediate calcium concentrations (0.5–1.5 mM Ca) pre-dispersed CNTs were stabilized in humic acid medium to similar, temporarily even to higher degree than in the absence of calcium. Between pH 5 and 8 only at the highest pH an influence on CNT stability was observed by either promoting flocculation or stabilisation depending on the CNT type. Humic acid stabilized CNTs much better than fulvic acid. Generally, the colloidal stability of the long, thick CNTs with higher surface oxygen content was less affected by the media composition.
An investigation of the settled CNT material using analytical electron microscopy revealed the presence of spheroidal, bundle-like and net like CNT-agglomerate structures. Calcium possibly acted as bridging agent linking CNTs in a network like manner, temporarily increasing the CNT concentrations stabilized in the supernatants due to the low density of these structures. With increasing settling time the CNTs formed a fluffy sediment layer at the bottom of the reaction vessels. Bundle-like CNT agglomerates were also observed within that layer of settled CNTs, possibly caused by calcium neutralizing the surface charges. Furthermore, the CNT suspensions contained spheroidal CNT agglomerates, most likely residues from the original dry powder that were not disaggregated. The analysis of settled CNT material is a novelty and illustrates CNT agglomerate structures possibly accumulating in the sediments of aquatic systems subsequent to CNT emissions.
Voegelin, A., Senn, A. C., Kaegi, R., Hug, S. J., & Mangold, S. (2013). Dynamic Fe-precipitate formation induced by Fe(II) oxidation in aerated phosphate-containing water. Geochimica et Cosmochimica Acta, 117, 216-231. doi:10.1016/j.gca.2013.04.022, Institutional Repository

We studied the effect of phosphate on the precipitation of Fe during the oxidation of 1 mM Fe(II) in aerated 8 mM NaHCO3–CO2 buffered aqueous solutions at near-neutral pH. The structure and morphology of the precipitates were analyzed by X-ray diffraction (XRD), extended X-ray absorption fine structure (EXAFS) spectroscopy at the Fe K-edge, and transmission electron microscopy (TEM). Up to an initial dissolved P/Fe ratio of ∼0.55, most phosphate was incorporated into the fresh Fe(III)-precipitates. At dissolved P/Fe ratios from 0.55 to 1.91, the precipitate P/Fe ratios only exhibited a minor increase from 0.56 to 0.72. XRD patterns and Fe EXAFS spectra indicated a shift in precipitate type from mostly poorly-crystalline lepidocrocite in the absence of phosphate to amorphous Fe(III)–phosphate (mostly monomeric and oligomeric Fe(III) coordinated with phosphate) at dissolved P/Fe ratios >0.55. A time-resolved oxidation experiment at an initial dissolved P/Fe ratio of 0.29 revealed that amorphous Fe(III)–phosphate formed during Fe(II) oxidation until phosphate was nearly depleted from solution. During continuing Fe(II) oxidation, about half of the newly formed Fe(III) contributed to the polymerization of Fe–phosphate into phosphate-rich hydrous ferric oxide with a maximum P/Fe ratio of 0.25 (HFO-P; edge-sharing linkage of Fe(III) octahedra) and about half precipitated as poorly-crystalline lepidocrocite in the phosphate-depleted solution. At initial P/Fe ratios <0.2, initially formed Fe(III)–phosphate was fully transformed into HFO-P during continuing Fe(II) oxidation. The dynamic interactions between phosphate and Fe described in this study impact the structure of fresh Fe(III)-precipitates at redox transitions in environmental and technical systems. The modulating effects of other dissolved species such as silicate and Ca on Fe precipitate formation and implications for co-transformed trace elements require further study.
Bonalumi, M. (2012). Effect of pumped-storage operations on temperature, turbidity and sedimentation in reservoirs and possible mitigation measures (Doctoral dissertation). doi:10.3929/ethz-a-007586451, Institutional Repository

Temperature, suspended-particle distribution and sedimentation were surveyed and modeled in two pumped-storage hydropower plants, both located in Switzerland.
One of them, the Grimselsee-Oberaarsee plant, consists of two reservoirs connected with a pumped-storage scheme since more than 30 years. Due to different glacier coverage of the catchment, the two reservoirs exhibit different particle concentration and sedimentation. Our investigation performed between 2007 and 2009 shows that the originally clearer reservoir (Oberaarsee) has become colder, more turbid and subject to higher sedimentation, while pumped-storage operations have decreased these parameters in the formerly more turbid reservoir (Grimselsee). However, pumped-storage operations show no direct effect on particles, as particlesize changes due to the turbulent shear stress occurring in the penstocks could not be determined. [...]

Temperatura, particelle in sospensione e sedimentazione sono state oggetto di studio in due diversi sistemi di pompaggio/turbinaggio, entrambi situati in Svizzera.
Il primo, Grimselsee-Oberaarsee, consiste in due laghi artificiali connessi ormai da più di 30 anni. A causa della presenza dei ghiacciai, che variano da un bacino imbrifero all’altro, la concentrazione di particelle e la sedimentazione risulta essere differente nei due laghi. Le nostre campagne di studio (periodo 2007-2009) mostrano infatti che, causa pompaggio/turbinaggio il lago inizialmente più limpido (Oberaarsee) si è intorbidito, raffreddato ed è aumentata la sedimentazione mentre che nel lago originariamente più torbido (Grimselsee) i parametri appena elencati sono diminuti. L’effetto delle pompe/turbine resta confinato ai due laghi artificiali, anche perché una analisi del diametro delle particelle prima e dopo il passaggio attraverso le macchine idrauliche (origine di sforzi turbulenti di taglio) non ha evidenziato variazioni. [...]
Hagendorfer, H., Kaegi, R., Parlinska, M., Sinnet, B., Ludwig, C., & Ulrich, A. (2012). Characterization of silver nanoparticle products using asymmetric flow field flow fractionation with a multidetector approach - a comparison to transmission electron microscopy and batch dynamic light scattering. Analytical Chemistry, 84(6), 2678-2685. doi:10.1021/ac202641d, Institutional Repository

Due to the already prevalent and increasing use of silver-nanoparticle (Ag-NP) products and the raised concerns in particular for the aquatic environment, analytical techniques for the characterization of such products are of need. However, because Ag-NP products are of different compositions and polydispersities, analysis especially of the size distribution is challenging. In this work, an asymmetric flow field flow fractionation (A4F) multidetector system (UV/vis, light scattering, inductively coupled plasma mass spectrometry - ICPMS), in combination with a method to distinguish and quantify the particle and dissolved Ag fractions (ICPMS after ultracentrifugation), for the characterization of Ag-NP products with different degrees of polydispersities is presented. For validation and to outline benefits and limitations, results obtained from batch dynamic light scattering (batch-DLS) and transmission electron microscopy (TEM) were compared. With the developed method a comprehensive understanding in terms of dissolved Ag and Ag-NP concentration as well as an element selective, mass- and number particle size distribution (PSD) was obtained. In relation to batch-DLS, the reliability of the data was improved significantly. In comparison to TEM, faster measurement times and the ability to determine the samples directly in dispersions are clearly advantageous. The proposed setup shows potential for a rapid- and reliable characterization method of virtually any polydisperse metallic NP dispersion, many of them available on the market already.
Mertens, J., Rose, J., Kägi, R., Chaurand, P., Plötze, M., Wehrli, B., & Furrer, G. (2012). Adsorption of arsenic on polyaluminum granulate. Environmental Science and Technology, 46(13), 7310-7317. doi:10.1021/es204508t, Institutional Repository

The kinetics and efficiencies of arsenite and arsenate removal from water were evaluated using polyaluminum granulates (PAG) with high content of aluminum nanoclusters. PAG was characterized to be meso- and macroporous, with a specific surface area of 35 ± 1 m2 g–1. Adsorption experiments were conducted at pH 7.5 in deionized water and synthetic water with composition of As-contaminated groundwater in the Pannonian Basin. As(III) and As(V) sorption was best described by the Freundlich and Langmuir isotherm, respectively, with a maximum As(V) uptake capacity of 200 μmol g–1 in synthetic water. While As(III) removal reached equilibrium within 40 h, As(V) was removed almost entirely within 20 h. Micro X-ray fluorescence and electron microscopy revealed that As(III) was distributed uniformly within the grain, whereas As(V) diffused up to 81 μm into PAG. The results imply that As(V) is adsorbed 3 times faster while being transported 105 times slower than As(III) in Al hydroxide materials.
Schwyzer, I., Kaegi, R., Sigg, L., Smajda, R., Magrez, A., & Nowack, B. (2012). Long-term colloidal stability of 10 carbon nanotube types in the absence/presence of humic acid and calcium. Environmental Pollution, 169(1), 64-73. doi:10.1016/j.envpol.2012.05.004, Institutional Repository

The colloidal stabilities of ten carbon nanotubes (CNTs) having varying physico-chemical properties were compared in long-term experiments. The presence of Suwannee River Humic Acid (SRHA) increased the fraction of CNTs in the supernatants (4–88% for the various CNT types) after addition in pre-dispersed form and 20 days of shaking and 5 days of settling. These suspensions were monomodal, containing individually suspended CNTs with highly negative surface charges. Calcium (2 mM) removed most of the CNT types from the supernatant, due to CNT-agglomerate formation initiated by reduction in surface charge. The amount of SRHA adsorbed to the different CNT types did not correlate (r2 < 0.1) with the percentage of CNTs remaining in suspension. Multiple linear regression analysis revealed that the oxygen content and the diameter of the CNTs significantly influenced the percentage of stabilized CNTs, resulting in an increased fraction of functionalized and large-diameter CNTs that remained in suspension.
Sternitzke, V., Kaegi, R., Audinot, J. N., Lewin, E., Hering, J. G., & Johnson, C. A. (2012). Uptake of fluoride from aqueous solution on nano-sized hydroxyapatite: examination of a fluoridated surface layer. Environmental Science and Technology, 46(2), 802-809. doi:10.1021/es202750t, Institutional Repository

Hydroxyapatite (Ca10(PO4)6(OH)2, HAP), both as a synthetic material and as a constituent of bone char, can serve as an effective and relatively inexpensive filter material for fluoride (F–) removal from drinking water in low-income countries. Fluoride uptake on HAP can occur through different mechanisms, which are, in principle, influenced by solution composition. Suspensions of HAP (2 g L–1) were equilibrated under controlled pH conditions (pH 6.5, 7.3, 9.5) at 25 °C for 28 d after the addition of different F– concentrations (0.5–7.0 mM). The reacted HAP solids were examined with Transmission Electron Microscopy (TEM), Fourier Transform Infrared Spectroscopy (FTIR), X-ray Photoelectron Spectroscopy (XPS), and Nano Secondary Ion Mass Spectroscopy (NanoSIMS). Fluoride uptake on HAP was dependent on pH, with the highest capacity at pH 6.5; the lowest uptake was found at pH 9.5. Under all experimental conditions, the thermodynamically stable mineral phase was fluorapatite, (Ca10(PO4)6F2, FAP). Fluoride uptake capacity was quantified on the basis of FTIR and XPS analysis, which was consistent with F– uptake from solution. The results of XPS and NanoSIMS analyses indicate that a fluoridated surface layer with a thickness of several nanometers is formed on nanosized HAP.
Bonalumi, M., Anselmetti, F. S., Kaegi, R., & Wüest, A. (2011). Particle dynamics in high-Alpine proglacial reservoirs modified by pumped-storage operation. Water Resources Research, 47(9), 1-15. doi:10.1029/2010WR010262, Institutional Repository

Temperature and suspended particle distribution were surveyed and modeled in two high-Alpine reservoirs in Switzerland, connected by pumped-storage operations for ∼30 years. Due to different glacier coverage of the catchments, the two reservoirs exhibit different particle concentrations and temperatures. After ice-breakup, the lower reservoir with a higher glacier cover in its catchment experiences a higher particle input becoming more turbid than the upper reservoir, which in contrast becomes warmer and thermally more stratified. The pumped-storage operations, which replace the basin volumes annually at least 6 (larger lower basin) to 10 (smaller upper basin) times, modify the physical characteristics of the two reservoirs. This is especially so in winter, when they are ice-covered, without riverine input and at low water level. Our reservoir investigations between 2007 and 2009 and the subsequent particle-balance model show that the upper and lower basins have become more and less turbid, respectively. Pumped-storage operations modify the stratification and particle distribution in both reservoirs and therefore alter the particle outflow and sedimentation. However, on the basis of particle concentrations and reservoir volumes, it is evident that the annually integrated particle release to downstream (∼40% of total) and to overall sedimentation (∼60%) have hardly changed. The budget model was useful in the prediction of particle distribution and sedimentation dynamics in the pumped-storage system. It implies that this approach can be useful for further employment during planning stages of power plants in order to modify and mitigate downstream particle loads in reservoir operations.
Bukowiecki, N., Zieger, P., Weingartner, E., Jurányi, Z., Gysel, M., Neininger, B., … Baltensperger, U. (2011). Ground-based and airborne in-situ measurements of the Eyjafjallajökull volcanic aerosol plume in Switzerland in spring 2010. Atmospheric Chemistry and Physics, 11(19), 10011-10030. doi:10.5194/acp-11-10011-2011, Institutional Repository

The volcanic aerosol plume resulting from the Eyjafjallajökull eruption in Iceland in April and May 2010 was detected in clear layers above Switzerland during two periods (17–19 April 2010 and 16–19 May 2010). In-situ measurements of the airborne volcanic plume were performed both within ground-based monitoring networks and with a research aircraft up to an altitude of 6000 m a.s.l. The wide range of aerosol and gas phase parameters studied at the high altitude research station Jungfraujoch (3580 m a.s.l.) allowed for an in-depth characterization of the detected volcanic aerosol. Both the data from the Jungfraujoch and the aircraft vertical profiles showed a consistent volcanic ash mode in the aerosol volume size distribution with a mean optical diameter around 3 ± 0.3 μm. These particles were found to have an average chemical composition very similar to the trachyandesite-like composition of rock samples collected near the volcano. Furthermore, chemical processing of volcanic sulfur dioxide into sulfate clearly contributed to the accumulation mode of the aerosol at the Jungfraujoch. The combination of these in-situ data and plume dispersion modeling results showed that a significant portion of the first volcanic aerosol plume reaching Switzerland on 17 April 2010 did not reach the Jungfraujoch directly, but was first dispersed and diluted in the planetary boundary layer. The maximum PM10 mass concentrations at the Jungfraujoch reached 30 μg m−3 and 70 μg m−3 (for 10-min mean values) during the April and May episode, respectively. Even low-altitude monitoring stations registered up to 45 μg m−3 of volcanic ash related PM10 (Basel, Northwestern Switzerland, 18/19 April 2010). The flights with the research aircraft on 17 April 2010 showed one order of magnitude higher number concentrations over the northern Swiss plateau compared to the Jungfraujoch, and a mass concentration of 320 (200–520) μg m−3 on 18 May 2010 over the northwestern Swiss plateau. The presented data significantly contributed to the time-critical assessment of the local ash layer properties during the initial eruption phase. Furthermore, dispersion models benefited from the detailed information on the volcanic aerosol size distribution and its chemical composition.
Hagendorfer, H., Kaegi, R., Traber, J., Mertens, S. F. L., Scherrers, R., Ludwig, C., & Ulrich, A. (2011). Application of an asymmetric flow field flow fractionation multi-detector approach for metallic engineered nanoparticle characterization - prospects and limitations demonstrated on Au nanoparticles. Analytica Chimica Acta, 706(2), 367-378. doi:10.1016/j.aca.2011.08.014, Institutional Repository

In this work we discuss about the method development, applicability and limitations of an asymmetric flow field flow fractionation (A4F) system in combination with a multi-detector setup consisting of UV/vis, light scattering, and inductively coupled plasma mass spectrometry (ICPMS). The overall aim was to obtain a size dependent-, element specific-, and quantitative method appropriate for the characterization of metallic engineered nanoparticle (ENP) dispersions. Thus, systematic investigations of crucial method parameters were performed by employing well characterized Au nanoparticles (Au-NPs) as a defined model system.
For good separation performance, the A4F flow-, membrane-, and carrier conditions were optimized. To obtain reliable size information, the use of laser light scattering based detectors was evaluated, where an online dynamic light scattering (DLS) detector showed good results for the investigated Au-NP up to a size of 80 nm in hydrodynamic diameter. To adapt large sensitivity differences of the various detectors, as well as to guarantee long term stability and minimum contamination of the mass spectrometer a split-flow concept for coupling ICPMS was evaluated. To test for reliable quantification, the ICPMS signal response of ionic Au standards was compared to that of Au-NP. Using proper stabilization with surfactants, no difference for concentrations of 1–50 μg Au L−1 in the size range from 5 to 80 nm for citrate stabilized dispersions was observed. However, studies using different A4F channel membranes showed unspecific particle–membrane interaction resulting in retention time shifts and unspecific loss of nanoparticles, depending on the Au-NP system as well as membrane batch and type. Thus, reliable quantification and discrimination of ionic and particular species was performed using ICPMS in combination with ultracentrifugation instead of direct quantification with the A4F multi-detector setup.
Figures of merit were obtained, by comparing the results from the multi detector approach outlined above, with results from batch-DLS and transmission electron microscopy (TEM). Furthermore, validation performed with certified NIST Au-NP showed excellent agreement. The developed methods show potential for characterization of other commonly used and important metallic engineered nanoparticles.
Kaegi, R., Voegelin, A., Sinnet, B., Zuleeg, S., Hagendorfer, H., Burkhardt, M., & Siegrist, H. (2011). Behavior of metallic silver nanoparticles in a pilot wastewater treatment plant. Environmental Science and Technology, 45(9), 3902-3908. doi:10.1021/es1041892, Institutional Repository

We investigated the behavior of metallic silver nanoparticles (Ag-NP) in a pilot wastewater treatment plant (WWTP) fed with municipal wastewater. The treatment plant consisted of a nonaerated and an aerated tank and a secondary clarifier. The average hydraulic retention time including the secondary clarifier was 1 day and the sludge age was 14 days. Ag-NP were spiked into the nonaerated tank and samples were collected from the aerated tank and from the effluent. Ag concentrations determined by inductively coupled plasma-mass spectrometry (ICP-MS) were in good agreement with predictions based on mass balance considerations. Transmission electron microscopy (TEM) analyses confirmed that nanoscale Ag particles were sorbed to wastewater biosolids, both in the sludge and in the effluent. Freely dispersed nanoscale Ag particles were only observed in the effluent during the initial pulse spike. X-ray absorption spectroscopy (XAS) measurements indicated that most Ag in the sludge and in the effluent was present as Ag2S. Results from batch experiments suggested that Ag-NP transformation to Ag2S occured in the nonaerated tank within less than 2 h. Physical and chemical transformations of Ag-NP in WWTPs control the fate, the transport and also the toxicity and the bioavailability of Ag-NP and therefore must be considered in future risk assessments.
Lorenz, C., Hagendorfer, H., von Goetz, N., Kaegi, R., Gehrig, R., Ulrich, A., … Hungerbühler, K. (2011). Nanosized aerosols from consumer sprays: experimental analysis and exposure modeling for four commercial products. Journal of Nanoparticle Research, 13, 3377-3391. doi:10.1007/s11051-011-0256-8, Institutional Repository

Consumer spray products are already on the market in the cosmetics and household sector, which suggest by their label that they contain engineered nanoparticles (ENP). Sprays are considered critical for human health, because the lungs represent a major route for the uptake of ENP into the human body. To contribute to the exposure assessment of ENP in consumer spray products, we analyzed ENP in four commercially available sprays: one antiperspirant, two shoe impregnation sprays, and one plant-strengthening agent. The spray dispersions were analyzed by inductively coupled plasma mass spectrometry (ICPMS) and (scanning-) transmission electron microscopy ((S)TEM). Aerosols were generated by using the original vessels, and analyzed by scanning mobility particle sizer (SMPS) and (S)TEM. On the basis of SMPS results, the nanosized aerosol depositing in the respiratory tract was modeled for female and male consumers. The derived exposure levels reflect a single spray application. We identified ENP in the dispersions of two products (shoe impregnation and plant spray). Nanosized aerosols were observed in three products that contained propellant gas. The aerosol number concentration increased linearly with the sprayed amount, with the highest concentration resulting from the antiperspirant. Modeled aerosol exposure levels were in the range of 1010 nanosized aerosol components per person and application event for the antiperspirant and the impregnation sprays, with the largest fraction of nanosized aerosol depositing in the alveolar region. Negligible exposure from the application of the plant spray (pump spray) was observed.
Schwyzer, I. I. (2011). Colloidal stability of carbon nanotubes in aqueous media of environmental relevance (Doctoral dissertation). doi:10.3929/ethz-a-007317859, Institutional Repository

Carbon nanotubes (CNTs) are engineered nanoparticles with unique physical and chemical properties making them promising for a broad range of industrial applications. Large scale synthesis and wide spread use of CNTs has increased the likelihood of the unintended release of CNTs into the environment. Environmental exposure of CNTs can occur during their whole life-cycle - production, use and disposal of CNTs, and CNTcontaining products. CNTs may reach the aquatic environment through waste water, runoff from contaminated areas, and aerosol-deposition. Knowledge about the partitioning of CNTs between the water column and the sediment is required to assess the potential impact of CNTs on the ecosystem. Depending on where (sediment or solution) and in which form (single CNTs or CNT agglomerates) CNTs are present in the aquatic environment, different organisms (benthic or pelagic) can be exposed and varying degrees of bioavailability would be expected, respectively. [...]

Kohlenstoffnanoröhrchen (CNTs) sind synthetisch hergestellte Nanopartikel mit einzigartigen physikalischen und chemischen Eigenschaften, was sie für vielfältigste Anwendungen attraktiv macht. CNT Synthese und Anwendung in grossem Stil birgt das Risiko, dass CNTs ungewollt in die Umwelt gelangen. Eine Freisetzung in die Umwelt ist dabei während des gesamten Lebenszyklus der CNTs möglich, d.h. während der Produktion, der Nutzung und der Entsorgung von CNTs und Produkten, die diese enthalten. Die aquatische Umwelt kann über Abwasser, über Abschwemmung von kontaminierten Stellen und über Aerosol-Deposition betroffen sein. Um potenzielle Risiken der CNTs auf das Ökosystem abschätzen zu können, ist es relevant zu wissen, ob der Verbleib der CNTs mehrheitlich im Sediment oder in der Wassersäule zu erwarten ist. Je nach dem wo (Sediment oder Wassersäule) und in welcher Form die CNTs (einzeln oder als Agglomerate) vorliegen, werden andere Organismen exponiert sein (benthische oder pelagische) und wird die Bioverfügbarkeit der Partikel variieren. [...]
Schwyzer, I., Kaegi, R., Sigg, L., Magrez, A., & Nowack, B. (2011). Influence of the initial state of carbon nanotubes on their colloidal stability under natural conditions. Environmental Pollution, 159(6), 1641-1648. doi:10.1016/j.envpol.2011.02.044, Institutional Repository

The colloidal stability of dry and suspended carbon nanotubes (CNTs) in the presence of amphiphilic compounds (i.e. natural organic matter or surfactants) at environmentally realistic concentrations was investigated over several days. The suspensions were analyzed for CNT concentration (UV–vis spectroscopy), particle size (nanoparticle tracking analysis), and CNT length and dispersion quality (TEM). When added in dry form, around 1% of the added CNTs remained suspended. Pre-dispersion in organic solvent or anionic detergent stabilized up to 65% of the added CNTs after 20 days of mild shaking and 5 days of settling. The initial state of the CNTs (dry vs. suspended) and the medium composition hence are critical determinants for the partitioning of CNTs between sediment and the water column. TEM analysis revealed that single suspended CNTs were present in all suspensions and that shaking and settling resulted in a fractionation of the CNTs with shorter CNTs remaining predominantly in suspension.
Burkhardt, M., Zuleeg, S., Kägi, R., Sinnet, B., Eugster, J., Boller, M., & Siegrist, H. (2010). Verhalten von Nanosilber in Kläranlagen und dessen Einfluss auf die Nitrifikationsleistung in Belebtschlamm. Fate of nanosilver in wastewater treatment plants and their impact on nitrification activity in sewage sludge. Umweltwissenschaften und Schadstoff-Forschung, 22(5), 529-540. doi:10.1007/s12302-010-0153-2, Institutional Repository

Background, aim and scope The application of nanosilver is increasing. Knowledge on the fate and behavior of nanosilver in wastewater and wastewater treatment plants is scarce. Studies under real world conditions are completely lacking. We studied (1) the impact of nanosilver on the nitrification of sewage sludge, (2) quantified the mass flow of nanosilver in a pilot-plant, and (3) verified the mass balance in a full-scale municipal wastewater treatment plant where nanosilver is introduced to the municipal plant by an indirect discharger.
Materials and Methods The addition of four different nanosilver additives on ammonia oxidation in activated sludge has been studied in batch-reactors at two concentrations (1, 100 mg/L Ag) with two exposure times (2 h, 6 days). The pilot-plant treating 70 population equivalents of domestic wastewater is operated with a 12 day sludge age. Nanosilver was applied to the activated sludge tank within two sludge ages. The silver concentrations were measured in sludge and effluent samples during dosing and the following two sludge ages. The adsorption and speciation of silver particles has been analyzed using scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDX). Influent, effluent and sludge were sampled on a full-scale plant (60 000 equivalent inhabitants) and analyzed for silver.
Results Silver nitrate, metallic nanosilver, nano-scaled silver chloride and microcomposite silver did not show any effect on ammonia oxidation after the addition of 1 mg/L Ag to the activated sludge (corresponding to 250 mg Ag per kg solids). In contrast, 100 mg/L Ag inhibited the nitrification process by 100 % after the addition of silver nitrate and 20–30 % after addition of colloidal polymer-coated nanosilver. A complete mass balance of the pilot-plant, a steady-state system with known fluxes, demonstrates significant enrichment of silver in the sewage sludge (96 %) after the addition of silver chloride to the plant and small losses of silver into the secondary effluent (4 %). The mass fluxes are similar to metallic colloidal nanosilver investigated under the same conditions. The mass balance has been consistently confirmed by the full-scale study in a municipal wastewater treatment plant. The silver fluxes correspond to the fluxes of the suspended solids in sludge and effluent. Overall, it is estimated that from public wastewater treatment plants about 4–40 mg/a Ag per inhabitant equivalent are discharged annually to the receiving water. The analysis by SEM-EDX demonstrates adsorption and incorporation of nanosilver on biological flocs. This method yields first insight into complex building and transformation of silver associated with sulfide after adding metallic nanosilver and silver chloride to wastewater.
Discussion Silver ions released from nanosilver react immediately with large amounts of chloride present in wastewater to form silver chloride. Silver ions may react with organic ligands or sulfide groups additionally. Consequently, even silver nitrate added with 1 mg/L Ag (250 mg Ag/kg TS) to activated sludge did not inhibit nitrification activity. Very high amounts of nanosilver, i. e. 100 mg/L Ag, overburdened the system and equilibrium condition between silver ion release and ligands was not reached. The mass balance reflects the excellent attachment of nanosilver to activated sludge and biological flocs. Therefore, the main elimination process of nanosilver is attachment to the activated sludge. The elimination of nanosilver is high compared to organic and inorganic micro pollutants omnipresent in wastewater. Any further reduction of suspended solids in the effluent water will reduce the silver load.
Conclusions Generally, in wastewater nanosilver occurs bonded to activated sludge flocs and therefore the elimination of nanosilver is efficient under operation conditions typical for wastewater treatment plants. The major fraction of nanosilver is removed from the system by the excess sludge withdrawal. Nonetheless, the efficiency may be further improved by a tertiary filtration step. All analyses of influent, effluent and sludge confirmed that silver exists as silver sulfide. Due to a negligible water solubility of this silver species, silver ions are not subsequently released.
Recommendations and perspectives Nanosilver research should be driven to the identification of transformation processes in real environmental matrices and the influence of coatings on the adsorption behavior. There is no need for action to take special measures for nanosilver removal in the area of municipal wastewater treatment plants compared to ubiquitous hazardous organic pollutants may present in wastewater. Nevertheless, source control measures following the precautionary principle should be performed.
Glaus, R., Kaegi, R., Krumeich, F., & Günther, D. (2010). Phenomenological studies on structure and elemental composition of nanosecond and femtosecond laser-generated aerosols with implications on laser ablation inductively coupled plasma mass spectrometry. Spectrochimica Acta B: Atomic Spectroscopy, 65(9–10), 812-822. doi:10.1016/j.sab.2010.07.005, Institutional Repository

In laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS), the properties of laser-generated aerosols, such as size and composition, are crucial for matrix-independent quantification. In this study, the aerosol particle morphology and elemental composition generated by two state-of-the-art laser systems (ArF excimer nanosecond-UV laser and Ti:sapphire femtosecond-IR laser) were investigated by electron microscopic techniques. Electrostatic sampling of the aerosols directly onto transmission electron microscopy (TEM) grids allowed us to study the morphology and elemental composition of the aerosols using TEM and TEM–EDX (energy dispersive X-ray spectroscopy) analyses, respectively. The results of the electron microscopic studies were finally compared to the LA-ICPMS signals of the main matrix components. The investigations were carried out for non-conducting materials (glass and zircon), metallic samples (steel and brass) and semiconductors (sulfides). The studies confirm that ns-LA-generated aerosols dominantly consist of nanoparticle agglomerates while conducting samples additionally contain larger spherical particles (diameter typically 50 to 500 nm). In contrast to ns-laser ablation, fs-LA-generated aerosols consist of a mixture of spherical particles and nanoparticle agglomerates for all investigated samples. Surprisingly, the differences in elemental composition between nanoparticle agglomerates and spherical particles produced with fs-LA were much more pronounced than in the case of ns-LA, especially for zircon (Si/Zr fractionation) and brass (Cu/Zn fractionation). These observations indicate different ablation and particle formation mechanisms for ns- and fs-LA. The particle growth mechanism for ns-LA is most likely a gas-to-particle conversion followed by agglomeration and additional hydrodynamic sputtering for conducting samples. On the other hand, phase explosion is assumed to be responsible for the mixture of large spherical particles and nanoparticle agglomerates as found for fs-LA-generated aerosols. Based on these mechanisms, the overall temporal elemental fractionation effects in ns-LA-ICPMS seem to occur mainly during the ablation. This effect was not observed for fs-LA-ICPMS despite the element separation into different particle fractions, which, on the other hand, could induce severe ICP-induced fractionation.
Hagendorfer, H., Lorenz, C., Kaegi, R., Sinnet, B., Gehrig, R., Goetz, N. V., … Ulrich, A. (2010). Size-fractionated characterization and quantification of nanoparticle release rates from a consumer spray product containing engineered nanoparticles. Journal of Nanoparticle Research, 12(7), 2481-2494. doi:10.1007/s11051-009-9816-6, Institutional Repository

This study describes methods developed for reliable quantification of size- and element-specific release of engineered nanoparticles (ENP) from consumer spray products. A modified glove box setup was designed to allow controlled spray experiments in a particle-minimized environment. Time dependence of the particle size distribution in a size range of 10–500 nm and ENP release rates were studied using a scanning mobility particle sizer (SMPS). In parallel, the aerosol was transferred to a size-calibrated electrostatic TEM sampler. The deposited particles were investigated using electron microscopy techniques in combination with image processing software. This approach enables the chemical and morphological characterization as well as quantification of released nanoparticles from a spray product. The differentiation of solid ENP from the released nano-sized droplets was achieved by applying a thermo-desorbing unit. After optimization, the setup was applied to investigate different spray situations using both pump and gas propellant spray dispensers for a commercially available water-based nano-silver spray. The pump spray situation showed no measurable nanoparticle release, whereas in the case of the gas spray, a significant release was observed. From the results it can be assumed that the homogeneously distributed ENP from the original dispersion grow in size and change morphology during and after the spray process but still exist as nanometer particles of size <100 nm. Furthermore, it seems that the release of ENP correlates with the generated aerosol droplet size distribution produced by the spray vessel type used. This is the first study presenting results concerning the release of ENP from spray products.
Kaegi, R., Voegelin, A., Folini, D., & Hug, S. (2010). Effect of phosphate, silicate, and Ca on the morphology, structure and elemental composition of Fe(III)-precipitates formed in aerated Fe(II) and As(III) containing water. Geochimica et Cosmochimica Acta, 74(20), 5798-5816. doi:10.1016/j.gca.2010.07.017, Institutional Repository

We investigated Fe(III)-precipitates formed from Fe(II) oxidation in water at pH 7 as a function of dissolved Fe(II), As(III), phosphate, and silicate in the absence and presence of Ca. We used transmission electron microscopy (TEM), including selected area electron diffraction (SAED) and energy dispersive X-ray spectroscopy (EDX) to characterize the morphology, structure and elemental composition of the precipitates. Results from our companion X-ray absorption spectroscopy (XAS) study suggested that the oxidation of Fe(II) leads to the sequential formation of distinct polymeric units in the following order: Fe(III)–phosphate oligomers in the presence of phosphate, silicate-rich hydrous ferric oxide (HFO-Si) at high Si/Fe (>0.5) or 2-line ferrihydrite (2L-Fh) at lower Si/Fe (0.1–0.5), and lepidocrocite (Lp) in the absence of phosphate at low Si/Fe (<0.1). Results from this study show that the size of the polymeric units increased along the same sequence and that the aggregation of these polymeric units resulted in spherical particles with characteristic surface textures changing from smooth to coarse. The diameter of the spherical particles increased from 15 to 380 nm as the molar ratio (P + Si + As)/Fe(II) in the starting solution decreased and larger spherical particles precipitated from Ca-containing than from Ca-free solutions. These trends suggested that the size of the spherical particles was controlled by the charge of the polymeric units. Spherical particles coagulated into flocs whose size was larger in the presence than in the absence of Ca. Further observations pointed to the importance of Fe(II) oxidation and polymerization versus polymer aggregation and floc formation kinetics in controlling the spatial arrangement of the different polymeric units within Fe(III)-precipitates. The resulting structural and compositional heterogeneity of short-range-ordered Fe(III)-precipitates likely affects their colloidal stability and their chemical reactivity and needs to be considered when addressing the fate of co-transformed trace elements such as arsenic.
Kaegi, R., Sinnet, B., Zuleeg, S., Hagendorfer, H., Mueller, E., Vonbank, R., … Burkhardt, M. (2010). Release of silver nanoparticles from outdoor facades. Environmental Pollution, 158(9), 2900-2905. doi:10.1016/j.envpol.2010.06.009, Institutional Repository

In this study we investigate the release of metallic silver nanoparticles (Ag-NP) from paints used for outdoor applications. A facade panel mounted on a model house was exposed to ambient weather conditions over a period of one year. The runoff volume of individual rain events was determined and the silver and titanium concentrations of 36 out of 65 runoff events were measured. Selected samples were prepared for electron microscopic analysis. A strong leaching of the Ag-NP was observed during the initial runoff events with a maximum concentration of 145 μ Ag/l. After a period of one year, more than 30% of the Ag-NP were released to the environment. Particles were mostly <15 nm and are released as composite colloids attached to the organic binders of the paint. Microscopic results indicate that the Ag-NP are likely transformed to considerably less toxic forms such as Ag2S.
Latkoczy, C., Kägi, R., Fierz, M., Ritzmann, M., Günther, D., & Boller, M. (2010). Development of a mobile fast-screening laser-induced breakdown detection (LIBD) system for field-based measurements of nanometre sized particles in aqueous solutions. Journal of Environmental Monitoring, 12(7), 1422-1429. doi:10.1039/c002020f, Institutional Repository

Laser-induced breakdown detection (LIBD) is a promising method to detect trace amounts of nanoparticles (NP, <100 nm) in aqueous suspensions. Based on available systems, we developed a mobile LIBD, designed for on-site and on-line measurements. We used the energy ratio of every laser pulse before and after passing the laser beam through the aqueous sample as a new method to detect laser-induced plasma events. The particle size and the particle number density are derived from recorded energy curves. Our LIBD is operated with a Nd:YAG laser at 100 Hz significantly reducing the measurement times compared to other LIBD systems operated at 20 Hz and increasing the capabilities for monitoring purposes. Long-term experiments on water samples revealed losses of NP up to 75% in 15 mL and 35% in 5 L sample containers after 3 months. The size of the particles remained constant (5 L) or slightly decreased (15 mL) indicating significant adsorption of NP to the walls of the sampling containers. Furthermore, we monitored the NP content of water after different purification steps at a drinking water plant (Maennedorf, Lake Zurich, Switzerland). Activated carbon filtration resulted in an increase of the particle size from ∼20 nm to ∼75 nm possibly caused by the release of organic fragments derived from the biology within the activated carbon tank. After the final ultrafiltration step the particle size was around 10 nm in agreement with the nominal cutoff of 100 kDa of the membrane. The results underline the strength of a fast-screening LIBD to detect relative changes in NP size and concentration.
Leisinger, S. M., Lothenbach, B., Saout, G. L., Kägi, R., Wehrli, B., & Johnson, C. A. (2010). Solid solutions between CrO4- and SO4-ettringite Ca6(Al(OH)6)2[(CrO4)x(SO4)1-x]3*26 H2O. Environmental Science and Technology, 44(23), 8983-8988. doi:10.1021/es100554v, Institutional Repository

Chromate is a toxic contaminant of potential concern, as it is quite soluble in the alkaline pH range and could be released to the environment. In cementitous systems, CrO42− is thought to be incorporated as a solid solution with SO42− in ettringite. The formation of a solid solution (SS) could lower the soluble CrO42− concentrations.
Ettringite containing SO42− or CrO42− and mixtures thereof have been synthesized. The resulting solids and their solubility after an equilibration time of 3 months have been characterized. For CrO4-ettringite at 25 °C, a solubility product log KS0 of −40.2 ± 0.4 was calculated: log KCrO4−ettringite = 6log{Ca2+} + 2log{Al(OH)4−} + 3log{CrO42−} + 4log{OH−} + 26log{H2O}. X-ray diffraction and the analysis of the solution indicated the formation of a regular solid solution between SO4- and CrO4-ettringite with a miscibility gap between 0.4 ≤ XCrO4 ≤ 0.6. The miscibility gap of the SO4- and CrO4-ettringite solid solution could be reproduced with a dimensionless Guggenheim fitting parameter (a0) of 2.03.
The presence of a solid solution between SO4- and CrO4-ettringite results in a stabilization of the solids compared to the pure ettringites and thus in an increased uptake of CrO42− in cementitious systems.
Leisinger, S., Lothenbach, B., Lesaout, G., Kägi, R., Wehrli, B., & Johnson, C. A. (2010). Sulphate and chromate-AFt solid solutions; characterization and thermodynamic modeling (p. (4 pp.). Presented at the International RILEM symposium on concrete modelling – CONMOD'10. Lausanne, Switzerland. , Institutional Repository

The aim of the research project is to determine the processes controlling the solubility of chromate in cementitious matrices in order to be able to predict porewater concentrations from solid-phase composition. In the absence of thermodynamic data concerning possible CrO4 limiting phases we are at present not in a position to predict solubility of CrO42- in cementitious systems. In a first step solid solutions of CrO4- and SO4-AFt have been prepared, characterized and thermodynamic stability ranges were determined. Solubility calculations of the solid solution series were carried out using the geochemical modelling code GEMS (Gibbs Energy Minimization Selektor). Solubility data are presented in a Lippmann diagram.
Mikutta, C., Frommer, J., Voegelin, A., Kaegi, R., & Kretzschmar, R. (2010). Effect of citrate on the local Fe coordination in ferrihydrite, arsenate binding, and ternary arsenate complex formation. Geochimica et Cosmochimica Acta, 74(19), 5574-5592. doi:10.1016/j.gca.2010.06.024, Institutional Repository

In oxic environments contaminated with arsenate (As(V)), small polyhydroxycarboxylates such as citrate may impact the structure of precipitating ferrihydrite (Fh) and thus the surface speciation of As(V). In this study, ‘2-line’ Fh was precipitated from ferric nitrate solutions that were neutralized to pH 6.5 in the presence of increasing citrate concentrations and in the absence or presence of As(V). The initial citrate/Fe and As/Fe ratios were 0–50 mol% and 5 mol%, respectively. The reaction products, enriched with up to 0.32 mol citrate per mole Fe, were characterized by X-ray diffraction, transmission electron microscopy, and Fe and As K-edge X-ray absorption spectroscopy. Citrate decreased the particle size of Fh by impairing the polymerization of Fe(O,OH)6 octahedra via edge and corner linkages. In the presence of citrate and As(V), coordination numbers of Fe decreased by up to 28% relative to pure Fh. Citrate significantly reduced the static disorder of Fe–O bonds, implying a decreased octahedral distortion in Fh. Mean bond distances in Fh were not affected by citrate and remained constant within error at 1.98 Å for Fe–O, 3.03 Å for Fe–Fe1, and 3.45 Å for Fe–Fe2. Likewise, citrate had no effect on the As–Fe (3.31 Å) bond distance in As(V) coprecipitated with Fh. The As K-edge EXAFS data comply with the formation of (i) only monodentate binuclear (2C) As(V) surface complexes and (ii) combinations of 2C, monodentate mononuclear (1V), and outersphere As(V) surface complexes. Our results suggest that increasing citrate concentrations led to a decreasing 1V/2C ratio and/or that citrate increasingly impaired the formation of outersphere As(V) complexes. Moreover, citrate stabilized colloidal suspensions of Fh (pH 4.3–6.6, I 0.45 M) and reduced Fh formation at the expense of soluble Fe(III)-citrate complexes. At initial citrate/Fe ratios 25 mol%, between 8% and 41% of total Fe was bound in Fe(III)-citrate complexes after Fh formation. Polynuclear Fe(III)-citrate species were found to bind As(V) via surface complexes indistinguishable by EXAFS from those of As(V) adsorbed to or coprecipitated with Fh. Our study implies that low molecular weight polyhydroxycarboxylates may enhance the mobility of As(V) in aqueous systems of high ionic strength (e.g., neutralizing acid mine drainage) by colloidal stabilization of suspended Fh particles and the formation of ternary As(V) complexes.
Voegelin, A., Kaegi, R., Frommer, J., Vantelon, D., & Hug, S. J. (2010). Effect of phosphate, silicate, and Ca on Fe(III)-precipitates formed in aerated Fe(II)- and As(III)-containing water studied by X-ray absorption spectroscopy. Geochimica et Cosmochimica Acta, 74(1), 164-186. doi:10.1016/j.gca.2009.09.020, Institutional Repository

We studied the local coordination and structure of Fe(III)-precipitates formed in aerated Fe(II)- and As(III)-containing water (buffered to pH 7 by 8 mM bicarbonate) using synchrotron-based X-ray absorption spectroscopy (XAS) at the K-edges of Fe, P, Ca, and As. Dissolved phosphate, silicate, and Ca at different ratios relative to each other and to Fe affect the forming Fe(III)-phases in a complex manner. The high affinity of phosphate for Fe(III) results in the predominant precipitation of Fe(III)-phosphate as long as dissolved phosphate is present, with Fe(III) polymerization limited to small oligomers. In Ca-containing solution, Ca uptake by Fe(III)–Ca-phosphate involves the linkage and coagulation of negatively charged Fe(III)-phosphate oligomers via Ca–O–P bonds. In the absence of phosphate, dissolved silicate at Si/Fe ratios above ~0.5 results in the formation of hydrous ferric oxide (HFO) with mainly edge-sharing Fe–Fe linkage. At lower Si/Fe ratios of ~0.5–0.1, mainly 2-line ferrihydrite (2L-Fh) with both edge- and corner-sharing Fe–Fe linkage forms. Only in the absence of phosphate at low Si/Fe ratio, lepidocrocite (Lp) forms. In solutions containing sufficient Fe(II), aeration results in the sequential precipitation of Fe(III)-(Ca-)phosphate, HFO or 2L-Fh (depending on solution Si/Fe), and finally Lp. The amount and oxidation state of As co-precipitated with Fe(III) are controlled by the co-oxidation of As(III) with Fe(II), which increases with initial Fe/As ratio, and the competitive uptake of phosphate, As(V) and less strongly sorbing silicate and As(III). This study demonstrates that the diversity and sequence of short-range-ordered Fe(III)-precipitates forming by Fe(II) oxidation in near-neutral natural waters depend on water chemistry. Because differences in the colloidal stability and biogeochemical reactivity of these phases will affect the fate of associated major and trace elements, the different Fe(III)-precipitates and their specific biogeochemical properties must be taken into account when addressing nutrient and contaminant dynamics at redox boundaries in natural and engineered systems.
Behra, R., Kägi, R., Navarro, E., Burkhardt, M., & Sigg, L. (2009). Effects of engineered nanoparticles. Eawag News [engl. ed.], 67, 22-24. , Institutional Repository

As nanoparticles are already widely used, it was only too likely that they would ultimately find their way into the environment. This has now been demonstrated for the first time by Eawag studies - which also show how engineered nanoparticles can exert toxic effects on aquatic organisms.
Behra, R., Kaegi, R., Navarro, E., Burkhardt, M., & Sigg, L. (2009). Les nanoparticules synthétiques et leurs effets. Eawag News [éd. fr.], 67, 22-24. , Institutional Repository

Les nanoparticules sont déjà employées dans un grand nombre de domaines. Il semble donc hautement probable qu’elles se retrouvent tôt ou tard dans l’environnement. Des études de l’Eawag ont démontré pour la première fois la réalité de ce phénomène et ­montrent d’autre part de quelle manière les nanoparticules synthétiques peuvent perturber les organismes aquatiques.
Behra, R., Kaegi, R., Navarro, E., Burkhardt, M., & Sigg, L. (2009). Synthetische Nanopartikel und ihre Wirkung. Eawag News [dtsch. Ausg.], 67, 22-24. , Institutional Repository

Nanopartikel werden heute bereits breit eingesetzt. Da ist es nur wahrscheinlich, dass sie früher oder später auch in der Umwelt landen. Studien der Eawag wiesen dies nun erstmals nach und zeigen darüber hinaus, auf welche Weise sich synthetische Nanopartikel negativ auf Gewässerorganismen auswirken können.
Burkhardt, M., Zuleeg, S., Etter, B., Marti, T., Landert, J., Eugster, J., … Vonmont, H. (2009). Nanosilber in Fassadenbeschichtungen. Auswaschung im Vergleich mit Titandioxid und organischen Bioziden. Dübendorf: Eawag; Empa. , Institutional Repository

Die Anwendung von Nanopartikeln, die antimikrobiell wirksam sind, unterliegt der Zulassung durch die Biozidprodukteverordnung. Dies gilt insbesondere für Nanosilber, da die freigesetzten Silberionen ökotoxisch hoch wirksam sind. Derzeit ist unklar, ob Nanopartikel in Fassaden dauerhaft eingebettet sind und welche Belastung sich mit einer möglichen Auswaschung verbindet.
Zur Klärung der Fragen wurde die Auswaschung von Nanosilber und Titandioxid aus Fassaden unter standardisierten Versuchsbedingungen sowie unter natürlichem Witterungseinfluss untersucht. Berücksichtigt wurde eine Aussenfarbe mit Nanosilber. Im Weisspigment Titandioxid mit einem mittleren Grösse von 200-400 nm liegen weniger als 0.1% der Masse in Nanogrösse (<100 nm) vor. Dieser geringe Massenanteil entspricht aber rund 10% der gesamten Partikelanzahl. Daher wurde auch Titandioxid untersucht und als Leitsubstanz für die Auswaschung von Nanopartikeln in Farben und Putzen herangezogen. [...]
Hassellöv, M., & Kaegi, R. (2009). Analysis and characterization of manufactured nanoparticles in aquatic environments. In J. R. Lead & E. Smith (Eds.), Environmental and human health impacts of nanotechnology (pp. 211-266). doi:10.1002/9781444307504.ch6, Institutional Repository

This chapter aims to discuss the minimum set of key properties that describe nanoparticles (NPs) in aquatic environments, and to review suitable analysis and characterization methods. Special focus is on characterization of manufactured NPs and associated nanoscale processes (Gilbert and Banfield, 2005). Manufactured NPs have recently raised concerns because of their potential effects on human health and the environment (Colvin, 2003; Donaldson et al., 2004; Handy et al., 2008; Nel et al., 2006; Oberdorster et al., 2005). Therefore, the analytical demands related to both exposure and effect assessment are discussed. Atmospheric NPs and airborne exposure are not covered in this chapter, but within Chapters 5 and 8, and also reviewed elsewhere (Burleson et al., 2004; Maynard, 2000); Powers et al., 2007). One aim has been to bring together concepts and knowledge from analytical chemistry, (e.g. quantitative determination of chemical composition in nanoparticle ensembles, such as size fractions or on a single NP), the mature field of particle size analysis (mainly developed for micron particles) (Barth and Flippen, 1995), environmental colloid science (Wilkinson and Lead, 2007) and the young field of nanometrology (Graham, 2007).
Kaegi, R., Wenk, C., & Hug, S. (2009). Elimination de l'arsenic par le fer colloïdal. Eawag News [éd. fr.], 66, 13-15. , Institutional Repository

Face à une contamination de l’eau potable par l’arsenic, la filtration est un bon moyen de lutte. Les systèmes employés sont basés sur la capacité des colloïdes de fer à piéger l’arsenic. Mais selon la composition chimique de l’eau, le fonctionnement des filtres est plus ou moins efficace. L’Eawag a recherché les causes potentielles de perturbation et étudié les possibilités d’optimisation technique des filtres.
Kaegi, R. (2009). Les nanoparticules dans l'eau potable. Eawag News [éd. fr.], 66, 7-9. , Institutional Repository

De plus en plus de produits du quotidien renferment des nanoparticules synthétiques. Nos connaissances sur leur émission et leur comportement dans l’environnement sont cependant encore très limitées. En outre, on ignore aussi très largement quelles sont les quantités de nanoparticules naturellement présentes, notamment dans l’eau potable. Nous avons tenté de dresser un état des lieux.
Kaegi, R., & Sinnet, B. (2009). Nanoparticles in drinking water. Eawag News [engl. ed.], 66, 7-9. , Institutional Repository

Synthetic nanoparticles are increasingly being used in everyday products, but little is known about environmental releases of these materials. Our knowledge of how many natural nanoparticles occur in drinking water is also inadequate. An initial assessment is presented here.
Kägi, R., Wenk, C., & Hug, S. (2009). Arsenentfernung mittels Eisenkolloiden. Eawag News [dtsch. Ausg.], 66, 13-15. , Institutional Repository

Ist Trinkwasser mit Arsen belastet, können Filtersysteme Abhilfe schaffen. Darin bindet das Arsen an Eisenkolloide. Doch je nach Wasserzusammensetzung funktionieren die Filter nicht optimal. Die Eawag erforschte nun, woran das liegt und wie zukünftige Filter konstruiert sein müssen.
Kägi, R., Wenk, C., & Hug, S. (2009). Arsenic removal using iron colloids. Eawag News [engl. ed.], 66, 13-15. , Institutional Repository

Drinking water contaminated with arsenic can be treated using filters in which arsenic is adsorbed onto iron colloids. However, the performance of these systems may not be optimal, depending on the composition of the water. Eawag has now investigated the processes involved - and how the design of future filters could be optimized.
Kägi, R., & Sinnet, B. (2009). Nanopartikel im Trinkwasser. Eawag News [dtsch. Ausg.], 66, 7-9. , Institutional Repository

Immer mehr Produkte in unserem Alltag enthalten synthetische Nanopartikel. Noch aber ist wenig über ihren Eintrag in die Umwelt bekannt. Genauso wenig weiss man, wie viele natürliche Nanopartikel überhaupt im Trinkwasser vorkommen. Eine erste Bestandsaufnahme.
Vernooij, M. G. C., Mohr, M., Tzvetkov, G., Zelenay, V., Huthwelker, T., Kaegi, R., … Grobéty, B. (2009). On source identification and alteration of single diesel and wood smoke soot particles in the atmosphere; an X-Ray microspectroscopy study. Environmental Science and Technology, 43(14), 5339-5344. doi:10.1021/es800773h, Institutional Repository

Diesel and wood combustion are major sources of carbonaceous particles in the atmosphere. It is very hard to distinguish between the two sources by looking at soot particle morphology, but clear differences in the chemical structure of single particles are revealed by C(1s) NEXAFS (near edge X-ray absorption fine structure) microspectroscopy. Soot from diesel combustion has a dominant spectral signature at ~285 eV from aromatic π-bonds, whereas soot from wood combustion has the strongest signature at ~287 eV from phenolic carbon bonds. To investigate if it is possible to use these signatures for source apportionment purposes, we collected atmospheric samples with either diesel or wood combustion as a dominant particle source. No spectra obtained from the atmospheric particles completely matched the emission spectra. Especially particles from the wood dominated location underwent large modifications; the phenolic spectral signature at ~287 eV is greatly suppressed and surpassed by the peak attributed to the aromatic carbon groups at ~285 eV. Comparison with spectra from diesel soot samples experimentally aged with ozone show that very fast modification of the carbon structure of soot particles occurs as soon as they enter the atmosphere. Source attribution of single soot particles with microspectroscopy is thus hardly possible, but NEXAFS remains a powerful tool to study aging effects.
Weber, F. A., Voegelin, A., Kaegi, R., & Kretzschmar, R. (2009). Contaminant mobilization by metallic copper and metal sulphide colloids in flooded soil. Nature Geoscience, 2, 267-271. doi:10.1038/NGEO476, Institutional Repository

Colloids, such as submicrometre mineral particles or bacterial cells, can act as carriers enhancing the mobility of poorly soluble contaminants in subsurface environments1,2. In sulphate-reducing soils and sediments, metal sulphide precipitation has been proposed3-6 to generate contaminant-bearing sulphide colloids, which could transport contaminants traditionally thought to be immobilized by metal sulphide formation7. However, direct evidence for such a process is lacking. Here, we report the composition and morphology of pore-water colloids formed in contaminated floodplain soil when flooded with synthetic river water over a four-week period. We show that, on flooding, bacteria dispersed in the pore water mobilize copper by inducing biomineralization of metallic copper(0). We suggest that copper(0) crystals form by disproportionation of copper(I), which is released by copper-stressed bacteria to maintain copper homeostasis8,9. Sulphate reduction, which started on the fourth day of flooding, resulted in the mobilization of cadmium and lead, which were partitioned to copper-rich sulphide colloids showing two types of morphology: bacterium-associated 50–150-nm-diameter hollow particles formed through copper(0) transformation, and dispersed <50 nm nanoparticles, probably formed through homogeneous precipitation. The slow deposition of both types of sulphide colloid ensured elevated contaminant concentrations in the pore water for weeks. Our findings imply that colloid formation can enhance contaminant release from periodically sulphate-reducing soils and sediments, potentially polluting surface- and groundwaters.
Zuleeg, S., Burkhardt, M., Boller, M., Kägi, R., Sinnet, B., Eugster, J., & Siegrist, H. (2009). Charakterisierung und Bilanzierung von Silber im Abwasser einer Wäscherei. Dübendorf: Eawag: Das Wasserforschungs-Institut des ETH-Bereichs. , Institutional Repository

Die Anwendung von Silber zur Textilveredelung wurde in einer industriellen Wäscherei bilanziert und der Eintrag in das Abwasser erfasst. Der Silbereinsatz erfolgt in Form von Silberchlorid. Quantifiziert wurden die Einsatzmenge, das Vorkommen über einzelne Schritte im Waschvorgang und die Abflusskonzentrationen. Dabei kamen chemische und mikroskopische Methoden zur Analyse des Silbers zum Einsatz.
Zunächst wurde eine Wasserbilanz über die einzelnen Prozessschritte der Wäscherei erarbeitet. Auf dieser Basis wurde die im Ablauf der Wäscherei zu erwartende Silbermenge abgeschätzt. Die Wäschereibilanz und der Eintrag in Richtung einer Abwasserreinigungsanlage (ARA) wurden mit gezielten Probenahmen und chemischer Analytik verifiziert. Die Konzentrationen von Silber im Abwasser der Wäscherei liegen im Bereich von 500-800 μg/L bei einem täglichen Abwasservolumen von ca. 150 m3 am Tag. Dies entspricht einer Tagesfracht von 75-120 g Silber, die regelmässig werktags der ARA zugeleitet werden. [...]
Zuleeg, S., Burkhardt, M., Boller, M., Kägi, R., Sinnet, B., Eugster, J., & Siegrist, H. (2009). Charakterisierung und Bilanzierung von Silberpartikeln in Abwasserreinigungsanlagen. Dübendorf: Eawag: Das Wasserforschungs-Institut des ETH-Bereichs. , Institutional Repository

In der vorliegenden Studie wurden der Verbleib und das Verhalten von Silberpartikeln in Belebtschlamm und in Abwasserreinigungsanlagen (ARA) untersucht. Das Projekt besteht aus drei Teilprojekten:
(1) Hemmung der Nitrifikation im Belebtschlamm durch verschiedene Silberformen
(2) Bilanzierung von Silber in einer Pilot-ARA
(3) Vorkommen von Silber in einer realen ARA.
In den Laborversuchen wurden marktübliche Silberadditive eingesetzt, die in der Industrie - vornehmlich im textilen Bereich - zur Anwendung kommen. [...]
von Gunten, U., Egli, T., Hammes, F., Helbing, J., Kaegi, R., & Pronk, W. (2009). Wave21. Drinking water for the 21st century. Final report. Schriftenreihe der Eawag: Vol. 20. Retrieved from http://www.lib4ri.ch/institutional-bibliography/eawag/schriftenreihe-der-eawag.html, Institutional Repository
Burkhardt, M., Kägi, R., Sinnet, B., Zuleeg, S., Simmler, H., Vonbank, R., … Boller, M. (2008). Biozide - Suche nach Alternativen. Nanopartikel in Fassadenbeschichtungen. Coviss, 4, 14-17. , Institutional Repository

Gegen Algen und Pilze auf Fassaden werden in der Regel Biozide eingesetzt. Ob Nanosilber und photoaktives Nanotitandioxid unproblematische Alternativen oder Ergänzungen zu Bioziden darstellen, ist unklar. Die Eawag und Empa, zwei Forschungsinstitute des ETH-Bereichs, untersuchen erstmals die Auswaschung aus Fassadenanstrichen im Labor und unter Feldbedingungen. Damit werden wesentliche Grundlagen zur Dauerhaftigkeit und Risikobewertung erarbeitet.
Jermann, D., Pronk, W., Kägi, R., Halbeisen, M., & Boller, M. (2008). Influence of interactions between NOM and particles on UF fouling mechanisms. Water Research, 42(14), 3870-3878. doi:10.1016/j.watres.2008.05.013, Institutional Repository

This study focused on the mechanistic effects of molecular interactions between inorganic particles (kaolinite) and the two main NOM fouling fractions of polysaccharides (alginate) and humics (humic acids) in ultrafiltration. Fouling effects were studied during the dead-end filtration of individual and mixed compounds as well as during the subsequent filtration of individual compounds. SEM analyses were performed to further study the fouling-layer structure. A significant synergistic effect was observed during combined particle–NOM fouling, which was considerably greater than the sum of particle and organic fouling alone. Synergistic fouling could be explained by NOM–particle interactions in the feed solution and during the fouling process. Kaolinite alone formed a fouling layer of particle aggregates, whereas humic acid adsorption onto kaolinite resulted in a fouling layer of stabilized colloids of humic acid and kaolinite. In the case of alginate, simultaneous pore-blocking and cake-layer formation of NOM and kaolinite dominated the fouling. In both cases, incorporation of the organics in the kaolinite fouling layer resulted in a fouling cake of significantly reduced porosity compared to individual particle filtration. Irreversible fouling by NOM could not be prevented by kaolinite. SEM images showed patches of the particle-fouling layer remaining on the membrane surface after backwashing, which can be linked to particle–membrane associations by NOM bridging.
Kaegi, R., Wagner, T., Hetzer, B., Sinnet, B., Tzvetkov, G., & Boller, M. (2008). Size, number and chemical composition of nanosized particles in drinking water determined by analytical microscopy and LIBD. Water Research, 42(10–11), 2778-2786. doi:10.1016/j.watres.2008.02.009, Institutional Repository

In this paper we comprehensively characterized particles in drinking water originating from a lake water source. We focused on particles smaller than a few hundred nm. Several analytical techniques were applied to obtain information on number concentration, size distribution, morphology and chemical composition of the particles. Morphological information was obtained by atomic force microscopy (AFM) analysis. Two types of particles, spherical aggregates up to a few tens of nm and elongated fibers were identified. Similar structures were also observed in transmission electron microscope (TEM) images. A size distribution of the particles was obtained by applying image analysis (IA) tools on the TEM images. IA results showed an exponential increase of the particle number concentration down to 40 nm, which is the lower detection limit of our setup. The total number of particles down to 10 nm and the average particle diameter were determined with the laser-induced breakdown detection (LIBD) method. The results were in good agreement with the TEM-IA data and showed a total number concentration of roughly 108 particles/mL in the purified water. The carbon of the particles was investigated with scanning transmission X-ray microscopy (STXM), which revealed that most particles were organic matter; the C-1s spectra were typical for dissolved organic matter.
The methods were applied to characterize the particles from two different drinking waters treated with different methods (conventional vs. ultrafiltration (cut-off 100 kDa)). The results showed that the particle number density following ultrafiltration was lower by a factor of 5–10, compared to conventional treatment. However, the average particle diameter in the finished water of both treatment trains was roughly the same.
Kaegi, R., Ulrich, A., Sinnet, B., Vonbank, R., Wichser, A., Zuleeg, S., … Boller, M. (2008). Synthetic TiO2 nanoparticle emission from exterior facades into the aquatic environment. Environmental Pollution, 156(2), 233-239. doi:10.1016/j.envpol.2008.08.004, Institutional Repository

We present direct evidence of the release of synthetic nanoparticles from urban applications into the aquatic environment. We investigated TiO2 particles as these particles are used in large quantities in exterior paints as whitening pigments and are to some extent also present in the nano-size range.
TiO2 particles were traced from exterior facade paints to the discharge into surface waters. We used a centrifugation based sample preparation which recovers TiO2 particles between roughly 20 and 300 nm. Analytical electron microscopy revealed that TiO2 particles are detached from new and aged facade paints by natural weather conditions and are then transported by facade runoff and are discharged into natural, receiving waters. Microscopic investigations are confirmed by bulk chemical analysis. By combining results from microscopic investigations with bulk chemical analysis we calculated the number densities of synthetic TiO2 particles in the runoff.
Navarro, E., Piccapietra, F., Wagner, B., Marconi, F., Kaegi, R., Odzak, N., … Behra, R. (2008). Toxicity of silver nanoparticles to Chlamydomonas reinhardtii. Environmental Science and Technology, 42(23), 8959-8964. doi:10.1021/es801785m, Institutional Repository

Silver nanoparticles (AgNP) are likely to enter the aquatic environment because of their multiple uses. We have examined the short-term toxicity of AgNP and ionic silver (Ag+) to photosynthesis in Chlamydomonas reinhardtii using fluorometry. AgNP ranged in size from 10 to 200 nm with most particles around 25 nm. As determined by DGT (diffusive gradients in thin films), by ion-selective electrode, and by centrifugal ultrafiltration, about 1% of the AgNP was present as Ag+ ions. Based on total Ag concentration, toxicity was 18 times higher for AgNO3 than for AgNP (in terms of EC50). However, when compared as a function of the Ag+ concentration, toxicity of AgNP appeared to be much higher than that of AgNO3. The ionic Ag+ measured in the AgNP suspensions could not fully explain the observed toxicity. Cysteine, a strong Ag+ ligand, abolished the inhibitory effects on photosynthesis of both AgNP and Ag+. Together, the results indicate that the interaction of these particles with algae influences the toxicity of AgNP, which is mediated by Ag+. Particles contributed to the toxicity as a source of Ag+ which is formed in presence of algae.
Burkhardt, M., Kägi, R., Simmler, H., Ulrich, A., & Boller, M. (2007). Nanopartikel auf Fassaden erforschen. Thema Umwelt, 2, 12-13. , Institutional Repository

Nanosilber und Nanotitandioxid haben das Potenzial, problematische Biozide zur Bekämpfung von Algen und Pilzen auf Fassaden zu ergänzen oder zu ersetzen. Allerdings ist bis heute völlig unklar, ob und in welchem Umfang diese Nanopartikel die Umwelt und die menschliche Gesundheit beeinträchtigen können. Um die Chancen und Risiken dieser Technologie abwägen und mit den heute üblichen Bioziden vergleichen zu können, haben Eawag und Empa, zwei Forschungsinstitute des ETH-Bereichs, ein Forschungsprojekt lanciert.
Fierz, M., Kaegi, R., & Burtscher, H. (2007). Theoretical and experimental evaluation of a portable electrostatic TEM sampler. Aerosol Science and Technology, 41(5), 520-528. doi:10.1080/02786820701253327, Institutional Repository

In this study, we present the design, calibration, and performance evaluation of a portable TEM sampler to collect ultrafine particles on TEM grids. The sampler is based on electrostatic deposition. We performed calibration experiments with monodisperse model particles of different size, morphology, and chemistry to evaluate the efficiency of the device. Additionally, we modeled the performance of the TEM sampler using finite element calculations to calculate the sampling efficiency as function of particle size. We find a good agreement between the model calculations and calibration experiments, but with a systematic deviation of about 30%. We present further experiments with polydisperse particles and derive particle size distributions and absolute number concentrations from TEM images. The shape of the size distribution is very similar to the corresponding SMPS measurements, while the total number concentration has a larger uncertainty. Thanks to the compact design of the sampler, it can be used to collect ultrafine particles even in remote or hostile environments, where no electric power is available.
Lorenzo, R., Kaegi, R., Gehrig, R., Scherrer, L., Grobéty, B., & Burtscher, H. (2007). A thermophoretic precipitator for the representative collection of atmospheric ultrafine particles for microscopic analysis. Aerosol Science and Technology, 41(10), 934-943. doi:10.1080/02786820701581834, Institutional Repository

In this article, the potential of a thermophoretic sampling device to derive quantitative particle size distributions and number concentrations of aerosols based on microscopic single particle analysis is explored. For that purpose a plate-to-plate thermophoretic precipitator to collect ultrafine atmospheric particles for TEM (transmission electron microscopy) analysis has been calibrated and characterized. The representativeness of the samples has been verified in a series of experiments. Results show that, for particles with diameters of 15 nm to 300 nm, the precipitator's collection efficiency is independent of size, shape, and composition of the particles. Hence, its samples accurately represent the original aerosol. A numerical model of thermophoretic deposition within the device has been developed and tailored to the specifications of the precipitator. The model has been used to derive the particle number density and size distribution of several calibration aerosols using the TEM analysis of the samples taken with the thermophoretic precipitator as input parameters. The results agree very well with the on-line measurements of the calibration aerosols. This work demonstrates that our thermophoretic sampling device can be used to derive quantitative particle size distributions and number concentrations of ultrafine particles based on microscopic single particle analysis.
Yang, T., Holzer, L., Kägi, R., Winnefeld, F., & Keller, B. (2007). In situ nanomanipulators as a tool to separate individual tobermorite crystals for AFM studies. Ultramicroscopy, 107(10–11), 1068-1077. doi:10.1016/j.ultramic.2007.02.042, Institutional Repository

Atomic force microscopy (AFM) studies of cementitious materials are limited, mainly due to the lack of appropriate sample preparation techniques. In porous autoclaved aerated concrete (AAC), calcium silicate hydrate (C–S–H) is produced in its crystalline form, tobermorite. The crystals are lath-like with a length of several micrometers. In this work, we demonstrate the application of nanomanipulators to separate an individual tobermorite crystal from the bulk AAC for subsequent AFM investigations. The nanomanipulators are operated directly in an environmental scanning electron microscope (ESEM). We studied the interaction between moisture and the tobermorite surface under controlled relative humidity (RH). The results of topography and adhesion force measurements with AFM suggest that the surface of tobermorite is hydrophobic, which contrasts the macroscopic material properties (e.g. moisture transport in capillary pores).
Kaegi, R., & Gasser, P. (2006). Application of the focused ion beam technique in aerosol science: detailed investigation of selected, airborne particles. Journal of Microscopy, 224(2), 140-145. doi:10.1111/j.1365-2818.2006.01669.x, Institutional Repository

The focused ion beam technique was used to fabricate transmission electron microscope lamellas of selected, micrometre-sized airborne particles. Particles were sampled from ambient air on Nuclepore polycarbonate filters and analysed with an environmental scanning electron microscope. A large number of particles between 0.6 and 10 μm in diameter (projected optical equivalent diameter) were detected and analysed using computer-controlled scanning electron microscopy. From the resulting dataset, where the chemistry, morphology and position of each individual particle are stored, two particles were selected for a more detailed investigation. For that purpose, the particle-loaded filter was transferred from the environmental scanning electron microscope to the focused ion beam, where lamellas of the selected particles were fabricated. The definition of a custom coordinate system enabled the relocation of the particles after the transfer. The lamellas were finally analysed with an analytical transmission electron microscope. Internal structure and elemental distribution maps of the interior of the particles provided additional information about the particles, which helped to assign the particles to their sources. The combination of computer-controlled scanning electron microscopy, focused ion beam and transmission electron microscopy offers new possibilities for characterizing airborne particles in great detail, eventually enabling a detailed source apportionment of specific particles. The particle of interest can be selected from a large dataset (e.g. based on chemistry and/or morphology) and then investigated in more detail in the transmission electron microscope.
Mavrocordatos, D., Kaegi, R., & Schmatloch, V. (2002). Fractal analysis of wood combustion aggregates by contact mode atomic force microscopy. Atmospheric Environment, 36(36-37), 5653-5660. doi:10.1016/S1352-2310(02)00702-1, Institutional Repository

Atomic force microscopy (AFM) is a powerful tool for the characterization of nanoparticles allowing to obtain fundamental parameters of morphology such as the size of individual particles, the number of particles per aggregate, the size distribution and finally the AFM allows one to determine the volume. All these parameters are accessible for the native aspect of the particles while AFM works under ambient temperature and pressure. We present here the analysis of wood combustion particles and their morphological parameters. Using our results for the 3D values, we were able to calculate the fractal dimension (Df) of the aggregates. As the Df is characteristic to the aggregation regime that particles undergo, we determined that wood particle aggregates follow a diffusion limited aggregation regime (Df=1.95). In parallel, in-situ analysis of the hydration effect has been studied in water at pH 7 and shows that the morphology is significantly influenced by the hydration. The composition observed by analytical electron microscopy (AEM) and atomic emission spectrometry (AES) enabled us to correlate the in-situ measurements by AFM with the hydration behavior of these particles and the fractal dimension.

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