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.

This project on cyanopeptides “from source to tap” was carried out in collaboration with the water works Zürich (Wasserversorgung Zürich, WVZ). Here we asked 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
  • Ozone: Determining second-order rate constants for the reaction of a wide range of cyanopeptides with ozone
  • Deliniating transformation products and pathways

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. We were able to fill this knowledge gap for the reactivity of a large variety of cyanopeptides and transformation product formation during ozonation and biotransformation in the treatment plant. A better understanding of these three aspects will advance our ability to predict their fate during water treatment and to assess potential risks.

Publications

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      originalId => protected36410 (integer)
      authors => protected'Rougé, V.; Dax, A.; Köster, O.; von Gunten, U.; Jansse
         n, E. M. -L.' (103 chars)
      title => protected'Degradation of toxins and metabolites of cyanobacteria and micropollutants d
         uring biological sand filtration' (108 chars)
      journal => protected'Environmental Science and Technology' (36 chars)
      year => protected2026 (integer)
      volume => protected60 (integer)
      issue => protected'12' (2 chars)
      startpage => protected'9647' (4 chars)
      otherpage => protected'9659' (4 chars)
      categories => protected'cyanotoxin; drinking water treatment; enzymes; kinetic; biodegradation; biot
         ransformation products' (98 chars)
      description => protected'Cyanobacteria produce complex mixtures of secondary metabolites (cyano-metab
         olites), some of which are toxic and pose a growing concern for water utilit
         ies. While physical treatments such as filtration can efficiently remove cel
         ls, their lysis can release dissolved cyano-metabolites. This study investig
         ated the efficiency of laboratory-scale sand filtration to abate 19 cyano-me
         tabolites representing various structural classes. Furthermore, abatement of
          cyano-metabolites in a full-scale sand filtration is presented. Most cyano-
         metabolites showed abatement similar to or higher than the biodegradable ben
         chmark micropollutants atenolol, paracetamol, and valsartan. Among cyano-met
         abolites, anabaenopeptins and cyanopeptolins had the highest abatement, whil
         e cyclamides and microcystin-LR had the lowest abatement. Abiotic controls a
         nd formation trends of 10 identified biotransformation products demonstrated
          that biodegradation played a major role in their removal. Laboratory-scale 
         sand filters showed a sharp increase in biodegradation efficiency within day
         s due to their adaptation to cyano-metabolites. Increasing the contact time 
         and temperature both enhanced the abatement of most compounds, which could b
         e kinetically modeled. High cyano-metabolite concentrations suppressed their
          own relative abatement, possibly due to metabolic enzyme inhibition or satu
         ration. These findings suggest that sand filtration can serve as a dual-barr
         ier against cyano-metabolites, including particle removal and biodegradation
         . However, biodegradation will be affected by the temperature and cyano-meta
         bolite intake dynamics.' (1619 chars)
      serialnumber => protected'0013-936X' (9 chars)
      doi => protected'10.1021/acs.est.5c16532' (23 chars)
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      authors => protected'Rougé, V.; von Gunten, U.; Janssen, E. M. L.' (70 chars)
      title => protected'Reactivity of cyanobacteria metabolites with ozone: multicompound competitio
         n kinetics' (86 chars)
      journal => protected'Environmental Science and Technology' (36 chars)
      year => protected2024 (integer)
      volume => protected58 (integer)
      issue => protected'26' (2 chars)
      startpage => protected'11802' (5 chars)
      otherpage => protected'11811' (5 chars)
      categories => protected'cyanopeptides; planktothrix; microcystis; micropollutant; ozonation; toxins;
          microcystin' (88 chars)
      description => protected'Cyanobacterial blooms occur at increasing frequency and intensity, notably i
         n freshwater. This leads to the introduction of complex mixtures of their pr
         oducts, i.e., cyano-metabolites, to drinking water treatment plants. To asse
         ss the fate of cyano-metabolite mixtures during ozonation, a novel multicomp
         ound ozone (O<sub>3</sub>) competition kinetics method was developed. Sixtee
         n competitors with known second-order rate constants for their reaction with
         
         
         . The apparent second-order rate constants (<em>k</em><sub>app,O3</sub>) at 
         pH 7 were simultaneously determined for 31 cyano-metabolites. <em>k</em><sub
         >app,O3</sub> for olefin- and phenol-containing cyano-metabolites were consi
         stent with their expected reactivity (0.4–1.7 × 10<sup>6</sup> M<sup>–1
         </sup> s<sup>–1</sup>) while <em>k</em><sub>app,O3</sub> for tryptophan- a
         nd thioether-containing cyano-metabolites were significantly higher than exp
         ected (3.4–7.3 × 10<sup>7</sup> M<sup>–1</sup> s<sup>–1</sup>). Cyano
         -metabolites containing these moieties are predicted to be well abated durin
         g ozonation. For cyano-metabolites containing heterocycles, <em>k</em><sub>a
         
         
         tivity of this class of compounds. Due to lower O<sub>3</sub> reactivities, 
         heterocycle- and aliphatic amine-containing cyano-metabolites may be only pa
         rtially degraded by a direct O<sub>3</sub> reaction near circumneutral pH. H
         ydroxyl radicals, which are formed during ozonation, may be more important f
         or their abatement. This novel multicompound kinetic method allows a high-th
         roughput screening of ozonation kinetics.' (1865 chars)
      serialnumber => protected'0013-936X' (9 chars)
      doi => protected'10.1021/acs.est.4c02242' (23 chars)
      uid => protected33024 (integer)
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Degradation of toxins and metabolites of cyanobacteria and micropollutants during biological sand filtration

Cyanobacteria produce complex mixtures of secondary metabolites (cyano-metabolites), some of which are toxic and pose a growing concern for water utilities. While physical treatments such as filtration can efficiently remove cells, their lysis can release dissolved cyano-metabolites. This study investigated the efficiency of laboratory-scale sand filtration to abate 19 cyano-metabolites representing various structural classes. Furthermore, abatement of cyano-metabolites in a full-scale sand filtration is presented. Most cyano-metabolites showed abatement similar to or higher than the biodegradable benchmark micropollutants atenolol, paracetamol, and valsartan. Among cyano-metabolites, anabaenopeptins and cyanopeptolins had the highest abatement, while cyclamides and microcystin-LR had the lowest abatement. Abiotic controls and formation trends of 10 identified biotransformation products demonstrated that biodegradation played a major role in their removal. Laboratory-scale sand filters showed a sharp increase in biodegradation efficiency within days due to their adaptation to cyano-metabolites. Increasing the contact time and temperature both enhanced the abatement of most compounds, which could be kinetically modeled. High cyano-metabolite concentrations suppressed their own relative abatement, possibly due to metabolic enzyme inhibition or saturation. These findings suggest that sand filtration can serve as a dual-barrier against cyano-metabolites, including particle removal and biodegradation. However, biodegradation will be affected by the temperature and cyano-metabolite intake dynamics.
Rougé, V.; Dax, A.; Köster, O.; von Gunten, U.; Janssen, E. M. -L. (2026) Degradation of toxins and metabolites of cyanobacteria and micropollutants during biological sand filtration, Environmental Science and Technology, 60(12), 9647-9659, doi:10.1021/acs.est.5c16532, Institutional Repository

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