Department Environmental Chemistry

CyanO3: cyano-metabolites from source to tap

Source: Valentin Rougé, Eawag
Occurence of cyanopeptide and their fate during drinking water treatment

Cyanobacterial bloom events are frequently observed in freshwater resources across the globe and produce known toxins. Microcystins, one class of cyanopeptides, have been studied intensively and the wealth of evidence regarding exposure concentrations and toxicity led to their inclusion in the World Health Organisation water quality guidelines. However, cyanobacteria produce a large diversity of cyanopeptides beyond this class of microcystins. The question arises, whether the other cyanopeptides are of human and ecological concern.

We are currently working on cyanopeptides “from source to tap” in collaboration with the water works Zürich (Wasserversorgung Zürich, WVZ). Here we ask the questions, whether these compounds reach the drinking water treatment plants and whether the latter are abated to prevent cyanopeptides form reaching the consumer's taps.

Focus of this project:

  • Investigating seasonal cyanopeptide profiles in Lake Zurich (the source water) and at the intake to the drinking water treatment plant
  • Assessing abatement of cyanopeptides during water treatment
  • Determining second-order rate constants for the reaction of cyanopeptides with ozone in novel multitarget method
  • Evaluating potential toxicity of transformation products

Ozonation is widely used in Switzerland as an efficient barrier against microorganisms, taste and odour compounds and micropollutants. Ozone can also degrade known cyanotoxins such as microcystins, and thus is a desired process in treatment plants affected by cyanobacterial blooms. However, little is known about the efficiency of ozone for other cyanopeptide classes. This project aims to fill the knowledge gap on the reactivity of a large variety of cyanopeptides, transformation product formation, and evolution of cyanopeptide-induced toxicity during ozonation. A better understanding of these three aspects will advance our ability to predict their fate during water treatment and to assess potential risks.

Publications

Reactivity of cyanobacteria metabolites with ozone: multicompound competition kinetics

Cyanobacterial blooms occur at increasing frequency and intensity, notably in freshwater. This leads to the introduction of complex mixtures of their products, i.e., cyano-metabolites, to drinking water treatment plants. To assess the fate of cyano-metabolite mixtures during ozonation, a novel multicompound ozone (O3) competition kinetics method was developed. Sixteen competitors with known second-order rate constants for their reaction with O3 ranging between 1 and 108 M–1 s–1 were applied to cover a wide range of the O3 reactivity. The apparent second-order rate constants (kapp,O3) at pH 7 were simultaneously determined for 31 cyano-metabolites. kapp,O3 for olefin- and phenol-containing cyano-metabolites were consistent with their expected reactivity (0.4–1.7 × 106 M–1 s–1) while kapp,O3 for tryptophan- and thioether-containing cyano-metabolites were significantly higher than expected (3.4–7.3 × 107 M–1 s–1). Cyano-metabolites containing these moieties are predicted to be well abated during ozonation. For cyano-metabolites containing heterocycles, kapp,O3 varied from <102 to 5.0 × 103 M–1 s–1, giving first insights into the O3 reactivity of this class of compounds. Due to lower O3 reactivities, heterocycle- and aliphatic amine-containing cyano-metabolites may be only partially degraded by a direct O3 reaction near circumneutral pH. Hydroxyl radicals, which are formed during ozonation, may be more important for their abatement. This novel multicompound kinetic method allows a high-throughput screening of ozonation kinetics.
Rougé, V.; von Gunten, U.; Janssen, E. M. L. (2024) Reactivity of cyanobacteria metabolites with ozone: multicompound competition kinetics, Environmental Science and Technology, 58(26), 11802-11811, doi:10.1021/acs.est.4c02242, Institutional Repository