Susceptibility of the Algal Toxin Microcystin-LR to UV/Chlorine Process: Comparison with Chlorination

Microcystin-LR (MC-LR), an algal toxin (cyanotoxin) common in sources of drinking water, poses a major human health hazard due to its high toxicity. In this study, UV/chlorine was evaluated as a potentially practical and effective process for the degradation of MC-LR. Via mass spectrometry analysis, fewer chlorinated-MC-LR products were detected with UV/chlorine treatment than with chlorination, and a transformation pathway for MC-LR by UV/chlorine was proposed. Different degrees of rapid degradation of MC-LR were observed with varying pH (6–10.4), oxidant dosage (0.5–3 mg L–1), natural organic matter (0–7 mg L–1), and natural water sources. In contrast to the formation of primarily chloroform and dichloroacetic acid in deionized water where MC-LR serves as the only carbon source, additional chlorinated disinfection byproducts were produced when sand filtered natural water was used as a background matrix. The UV/chlorine treated samples also showed quantitatively less cytotoxicity in vitro in HepaRG human liver cell line tests than chlorination treated samples. Following 16 min (96 mJ cm–2) of UV irradiation combined with 1.5 mg L–1 chlorine treatment, the cell viability of the samples increased from 80% after exposure to 1 mg L–1 MC-LR to 90%, while chlorination treatment evidenced no reduction in cytotoxicity with the same reaction time.