Chlorine/UV Process for Decomposition and Detoxification of Microcystin-LR

• Published in: Environmental science & technology Vol. 50; no. 14; pp. 7671 - 7678
• Main Authors: Zhang, Xinran, Li, Jing, Yang, Jer-Yen, Wood, Karl V, Rothwell, Arlene P, Li, Weiguang, Blatchley III, Ernest R
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 19.07.2016
• Subjects: absorption; arginine; Bacteria; byproducts; chemical degradation; chlorination; Chlorine; Cyanobacteria; Cyanobacteria - chemistry; cytotoxicity; Decomposition; detoxification (processing); Drinking water; hepatocytes; hepatotoxicity; hepatotoxins; humans; irradiation; Mass Spectrometry; microcystin-LR; Molecules; oxidation; Oxidation-Reduction; Toxicity; Ultraviolet radiation; Water Supply
• ISSN: 0013-936X; 1520-5851; 1520-5851
• DOI: 10.1021/acs.est.6b02009

Microcystin-LR (MC-LR) is a potent hepatotoxin that is often associated with blooms of cyanobacteria. Experiments were conducted to evaluate the efficiency of the chlorine/UV process for MC-LR decomposition and detoxification. Chlorinated MC-LR was observed to be more photoactive than MC-LR. LC/MS analyses confirmed that the arginine moiety represented an important reaction site within the MC-LR molecule for conditions of chlorination below the chlorine demand of the molecule. Prechlorination activated MC-LR toward UV254 exposure by increasing the product of the molar absorption coefficient and the quantum yield of chloro-MC-LR, relative to the unchlorinated molecule. This mechanism of decay is fundamentally different than the conventional view of chlorine/UV as an advanced oxidation process. A toxicity assay based on human liver cells indicated MC-LR degradation byproducts in the chlorine/UV process possessed less cytotoxicity than those that resulted from chlorination or UV254 irradiation applied separately. MC-LR decomposition and detoxification in this combined process were more effective at pH 8.5 than at pH 7.5 or 6.5. These results suggest that the chlorine/UV process could represent an effective strategy for control of microcystins and their associated toxicity in drinking water supplies.