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Fate of New Persistent Organic Chemical 3,6-Dichlorocarbazole in Chlorinated Drinking Water

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journal contribution
posted on 22.07.2021, 08:13 by Guowei Wang, Kefu Ye, Shixiang Gao, Huijie Hou, Bingchuan Liu, Keke Xiao, Jingping Hu, Sha Liang, Jiakuan Yang
Polyhalogenated carbazoles (PHCZs) make up a group of persistent, bioaccumulative, and toxic contaminants and are newly identified as chlorinated disinfection byproducts. However, the fates of these compounds in prolonged chlorination are largely unknown, leading to a great threat to the safety of drinking water. This study investigated the transformation of PHCZs during prolonged chlorination by using 3,6-dichlorocarbazole (36-CCZ) as a model congener, providing important information about the fates of PHCZs in drinking water. The degradation kinetics of 36-CCZ showed a strong pH dependency with apparent second-order rate constants of 1.52–5.17 M–1 s–1 at pH 6–10. The degradation rates are comparable to that of pyrene in chlorination. Seven new chlorine-containing products P1–P7 were detected. Transformation pathways, involving electrophilic chlorination, nucleophilic water addition, aromatic ring opening, and HCl elimination, were proposed, and the reaction mechanism was explored. The product evolution versus time showed the first generation of the highly halogenated carbazoles of 1,3,6-trichlorocarbazole (P1) and 1,3,6,8-tetrachlorocarbazole (P2), followed by the generation of hydroxylated products P3–P7. The persistence of the seven products in chlorinated water over 24 h indicated that human exposure to PHCZs and/or their transformation products was highly possible. This study provides novel insights into the behaviors of PHCZs in drinking water.

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