Catalytic wet peroxide oxidation (CWPO) of widespread cyanotoxins: Degradation pathways and toxicity assessment

The widespread occurrence of cyanotoxins in water bodies presents a significant health risk due to their high toxicity and persistence in the environment. Exposure to these toxins can lead to severe health issues, from gastrointestinal distress to organ failure, underscoring the urgent need for advanced water treatment methods. Catalytic Wet Peroxide Oxidation (CWPO) has proven effective for cyanotoxin removal; however, the specific degradation pathways during CWPO remain unclear. This study elucidates the possible degradation pathways of some of the most globally prevalent cyanotoxins, including microcystin-LR (MC-LR) and cylindrospermopsin (CYN), through CWPO using magnetite as a catalyst. These pathways involve hydroxylation, dehydrogenation, decarboxylation, functional group substitution, and ring opening, identifying new degradation by-products. The evolution of ecotoxicity during CWPO was also examined, revealing an initial increase in effluent toxicity under sub-stoichiometric H₂O₂ conditions, but eventually declines below the toxicity of the original cyanotoxins. Raising the oxidant concentration to stoichiometric levels efficiently eliminates cyanotoxins, yielding primarily short-chain organic acids in a completely non-toxic effluent. These findings are critical for optimizing CWPO as a safe, efficient, and sustainable approach for treating cyanotoxins in water, marking important progress towards cost-effective and environmentally friendly water treatment solutions.