Chlorination of microcystin-LR in natural water: Kinetics, transformation products, and genotoxicity

• Published in: Journal of environmental management 2023-07, Vol.338, p.117774-117774, Article 117774
• Main Authors: Feng, Jinlu, Li, Xi, Manzi, Habasi Patrick, Kiki, Claude, Lin, Lifeng, Hong, Jiaxing, Zheng, Wenzhen, Zhang, Chuchu, Wang, Shengda, Zeng, Qiaoting, Sun, Qian
• Format: Article
• Language: English
• Subjects: Benzene; Chlorination; Chlorine; Drinking Water; Genotoxicity (mutagenicity); Halogenation; Humans; Kinetics; Microcystin-LR; Microcystins - chemistry; Microcystins - toxicity; Potential transformation pathways; Transformation products; Water Purification
• ISSN: 0301-4797; 1095-8630
• DOI: 10.1016/j.jenvman.2023.117774

Microcystin-LR (MC-LR), a type of cyanotoxin commonly found in natural water bodies (sources of drinking water), poses a threat to human health due to its high toxicity. It is essential to successfully remove this cyanotoxin from drinking water sources. In this study, chlorine was used to oxidize MC-LR in Milli-Q water (MQ) (control test) and natural water collected from Lake Longhu (LLW) as a drinking water source. The removal efficiency, proposed transformation pathways, and genotoxicity were investigated. In the chlorine dose range investigated (4.0 mg L−1 - 8.0 mg L−1), the apparent second-order rate constants for MC-LR chlorination varied from 21.3 M−1s−1 to 31.9 M−1s−1 in MQ, higher than that in LLW (9.06 M−1s−1 to 17.7 M−1s−1) due to a faster chlorine decay attributed to the water matrix (e.g., natural organic matter) of LLW. Eleven transformation products (TPs) of MC-LR were identified in the two waters. The conjugated diene moieties and benzene ring of Adda moiety (3-amino-9-methoxy-2,6,8-trimethyl-10-phenyldeca-4,6-dienoic acid), and the double bond of Mdha moiety (N-methyldehydroalanine) were the major susceptible reaction sites. Attacking unsaturated bonds by hydroxyl and chlorine radicals to generate monochloro-hydroxy-MC-LR was the primary initial transformation pathway, followed by nucleophilic substitution, dehydration, and cleavage in MC-LR. Chlorine substitution on the benzene ring was also observed. Based on the bacterial reverse-mutation assay (Ames assay), TPs in treated natural water did not induce genotoxicity/mutagenicity. These findings shed light on the role of chlorination in controlling the risk of cyanotoxins in drinking water treatment plants. [Display omitted] •Removal rate of MC-LR via chlorination in natural water, decreased due to water matrix.•Degradation products of MC-LR by chlorine were identified.•There was no genotoxicity for MC-LR degradation after chlorination based on Ames assay.