Loss of toxicity of microcystins in UV/H2O2 and UV/Cl2 treatment

Abstract

Advanced oxidation processes are one of the best treatments for algal toxins in drinking water, but because it involves chemical transformation of microcystins, there is a concern that the products may retain toxicity. An established advanced oxidation process (UV/H2O2) was compared with an emerging one (UV/Cl2) in terms of effectiveness for detoxifying the two most common variants of algal hepatotoxin microcystin (LR and YR). LC-MS/MS analysis of the products indicated that the ADDA group of the molecule responsible for their toxicity is susceptible to damage in the UV/H2O2 and UV/Cl2 process, suggesting that the transformation products lose their toxicity. This was confirmed by ADDA-specific ELISA analysis of treated samples of the LR variant. ELISA-measured concentrations of microcystins in the treated samples matched the LC-MS/MS-measured concentrations of the parent molecule remaining after treatment, which confirmed that the ADDA group is damaged during the UV/H2O2 and UV/Cl2 treatment. Microcystin-LR was also highly susceptible to a reaction with chlorine (>99 % decrease at 60 min·mg/L) and direct UV photolysis, with quantum yield of photolysis of 0.032 ± 0.007 for 254 nm UV wavelength, and 0.11 ± 0.00 for the 200–300 nm spectrum.