Département Chimie de l’environnement

Orbitrap mass spectrometry with electrospray ionization (ESI-Orbitrap MS) enables¹⁸O/¹⁶O ratio measurements in phosphate and organophosphorus compounds, which offers promising avenues for the study of metabolic, biogeochemical, and environmental processes. While the instrumental feasibility of such¹⁸O/¹⁶O ratio measurements has been shown, the applicability of such analyses in aqueous matrices on multipurpose mass spectrometers remains unaddressed. Here, we (i) evaluated the interplay between instrument parameters and the long-term accuracy and precision of ESI-Orbitrap MS for the determination of δ¹⁸O(PO₄) from H₂PO₄^–vs PO₃^–fragments of phosphate, (ii) identified properties of methanolic sample solutions that are critical for accurate and precise measurements, and (iii) propose a sample purification procedure for the elimination of matrix-based interferences. In 10 measurement campaigns over two years, we observed a long-term reproducibility of δ¹⁸O(PO₄) within ±2.8‰. Results of in-source fragmentation experiments of H₂PO₄^–to PO₃^–show excellent agreement of δ¹⁸O and offer promising opportunities to probe for¹⁸O/¹⁶O ratios in organophosphorus compounds. By investigating the effect of the aqueous matrix and interfering anions on¹⁸O/¹⁶O ratio measurements, we found that a water content exceeding 50 vol % and the presence of oxyanions such as nitrate and sulfate limit measurement accuracy due to interferences of matrix constituents in the ESI source. To overcome these challenges, we evaluated selective phosphate extraction with a zirconium-based metal–organic framework (MOF) as sorbent. The resulting purification procedure allowed for successful extraction and recovery of phosphate from nitrate- and sulfate-containing aqueous solutions, resulting in methanolic phosphate samples that enabled accurate analyses of δ¹⁸O(PO₄) by ESI-Orbitrap MS.

The comprehensive evaluation of pollutant abatement during chemical oxidation processes and the identification of potentially hazardous transformation products are fundamental challenges in water and wastewater treatment. Here, we demonstrate how high-throughput computational chemistry enables the elucidation of reaction pathways via automated, quantum-chemistry-based chemical reaction network (CRN) explorations. We evaluated the predictive capabilities of this computational approach using the Software for Chemical Interaction Networks (SCINE) for studying the reactions of ozone with two olefins, ethene and tetramethylethene, in aqueous solution. Following a benchmarking of the quantum chemical methodology for structure optimization and energy calculations, we generated CRNs containing hundreds of compounds and thousands of reactions, identified reaction mechanisms, and evaluated product formation kinetics through microkinetic modeling. These CRN explorations led to the correct reproduction of experimental evidence for mechanisms and products of olefin ozonolysis for reactions of ozone and ethene solely on the basis of defining the reactants and their initial concentrations. The study of reactions of ozone and tetramethylethene also matched experimental data for the main products but revealed consequences of the limited exploration depth and shortcomings of the implicit solvation model. We envision that CRN explorations not only offer novel means for predicting pollutant transformation pathways but also will support chemical analysis and the assessment of effects on human and environmental health.

Pharmaceuticals and their human metabolites are significant sources of micropollutants in the aquatic environments due to incomplete removal during wastewater treatment. While parent compounds have been widely studied, the fate of their metabolites across treatment stages remains poorly understood, despite the fact that most pharmaceuticals are excreted in metabolized forms. Using a combination of full-scale wastewater treatment plant (WWTP) observations, laboratory experiments, and modeling, this study aimed to assess and compare the removal of 290 parent pharmaceuticals and 154 human metabolites across biological and advanced wastewater treatment stages, to evaluate the influence of human metabolic modifications on removal rates. The findings from the field data confirmed that phase II metabolites are often efficiently degraded during biological treatment, and cleaved into corresponding parent compounds or phase I metabolites, with median removals of 84% to 97% in the three WWTPs. In contrast, phase I metabolites show a similar behavior to their parent compounds and are often not more efficiently abated, with median removals ranging between 38% to 53% for parents and phase I metabolites. Advanced treatments, including ozonation with and without granular activated carbon filtration, showed significant median reductions of 79% to 92% for parent pharmaceuticals and 54% to 82% for metabolites, with removal efficiencies correlating with ozone doses. Laboratory biotransformation experiments identified reaction-specific pseudo-first-order rate constants, with carboxylic acids showing increased persistence, potentially as a result of their high oxidation state, which limits further degradation under aerobic conditions. Moreover, the laboratory experiments confirmed that acetylated and glucuronidated phase II metabolites are more efficiently abated during biological treatment, while sulfates are more stable compared to their parent compounds. A mechanistic model using the experimentally determined biotransformation rate constants was established, showing strong agreement with measured data for compounds with high or low biotransformation rates. Predictions for partially degraded compounds showed higher uncertainty, reflecting the complex interactions between biotransformation, sorption and operational parameters. This work provides a detailed assessment of the behavior and fate of pharmaceuticals and especially their metabolites during wastewater treatment, emphasizes the importance of understanding transformation pathways, and offers valuable insights for optimizing removal strategies and minimizing environmental impacts.

Tintenstrich communities are specialized lithic biofilms dominated by free-living cyanobacteria, also occurring in lichen associations, forming a unique ecological interface between rock environments and aquatic habitats in mountainous areas. To better understand their composition and genetic and metabolic potential, we analyzed 207 samples from the Swiss Alps and Jura Mountains. We determined how key environmental factors shaped cyanobacterial abundance, assessed whether these communities harbor genes for toxin biosynthesis, characterized their taxonomic composition at the family and genus level, and evaluated the actual occurrence of cyanotoxins and other bioactive metabolites. Cyanobacterial abundance proved to be influenced by factors such as elevation, exposure, and their interaction with siliceous rock substrata. Targeted PCR and Sanger sequencing revealed the presence of toxin-encoding genes, particularly for ndaF/mcyE fragments, which may encode microcystin and/or nodularin biosynthesis, while specific genes for microcystins, anatoxins, and cylindrospermopsins were rather rare. Metabarcoding analysis identified 11 cyanobacterial families, with Chroococcaceae, Nostocaceae, and Leptolyngbyaceae being the most abundant. Complementary high-resolution mass spectrometry confirmed the occasional presence of nodularins and microcystins, alongside more frequent detection of other bioactive peptides such as anabaenopeptins and cyanopeptolins. Overall, these findings provide the most comprehensive insight to date into Tintenstrich-associated cyanobacteria, underscoring their environmental significance given their genetic and metabolic potential.

Cyanobacteria produce toxic and bioactive secondary metabolites, posing risks to ecosystems and human health, yet their transformation pathways in surface waters remain unclear. We assessed biotransformation for 40 cyanopeptides including microcystins, anabaenopeptins and cyanopeptolins in surface waters and in situ enriched biofilm suspensions. In surface waters, most cyanopeptides did not degrade significantly over the course of 7 days. A wide range of biodegradability across cyanopeptides was apparent in biofilm suspensions from three rivers. Increasing the biofilm density shortened the lag time and increased initial removal of cyanopeptides. Increasing the initial cyanopeptide concentration lengthened the lag time and decreased their initial removal, supporting inhibitory effects of cyanopeptides toward enzymes involved in their own transformation. Transformation kinetics and product analysis demonstrated a structure–reactivity relationship across and within cyanopeptide classes. Anabaenopeptins were hydrolyzed at the C-terminus when arginine, tyrosine and (iso)leucine were present, but not when phenylalanine or tryptophan was present. Microcystins showed tetrapeptide formation when adda linked to arginine but not when it linked to alanine, leucine, or tyrosine. Oxidation of tyrosine and deamination of arginine residues showed an interdependence across cyanopeptide classes. These novel insights into biotransformation products and pathways of a wide range of cyanopeptides facilitate assessment of exposure scenarios in surface waters and inform about kinetics and product formation in biological water treatment.