Deciphering the\nNatural Attenuation of Cyanotoxins:\nDissipation, Transformation Pathways, and Genotoxicity

Microcystin-LR (MC-LR) and cylindrospermopsin (CYN) are\ntoxic cyanotoxins\nfrequently found in drinking water sources, posing significant health\nrisks. This study conducted a microcosm experiment using surface lake\nwater exposed to sunlight to investigate the natural attenuation processes\nof MC-LR and CYN. Results indicated that photodegradation plays a\ncrucial role in the natural attenuation of cyanotoxins. The half-lives\nof MC-LR and CYN were 1 and 7 days in summer under a combined effect\nof direct and indirect photodegradation, respectively. The effectiveness\nof these natural processes varied seasonally, with faster dissipation\nrates observed during summer. Bacterial degradation notably affected\nonly MC-LR in summer, with a negligible effect on CYN. The identified\ntransformation products showed that the conversion of MC-LR involved\noxidation, hydroxylation, and/or bond cleavage with Adda and Mdha\nmoieties, while it entails the oxidation of the tricyclic guanidine\nmoiety and opening of the uracil ring for CYN. The Ames assay confirmed\nthat these transformation products from the natural attenuation of\nMC-LR and CYN did not induce genotoxicity or mutagenicity. While these\nfindings enhance our understanding of natural attenuation mechanisms,\nthey also offer valuable insights that could guide artificial control\nstrategies or improve the efficiency of cyanotoxin management. However,\nnatural degradation processes alone, particularly in large water bodies,\nmay be insufficient to fully mitigate cyanotoxin risks, highlighting\nthe continued need for comprehensive management approaches.