Oxidation of diclofenac by aqueous chlorine dioxide: Identification of major disinfection byproducts and toxicity evaluation

• Published in: The Science of the total environment 2014-03, Vol.473-474, p.437-445
• Main Authors: Wang, Yingling, Liu, Haijin, Liu, Guoguang, Xie, Youhai
• Format: Article
• Language: English
• Subjects: Anti-Inflammatory Agents, Non-Steroidal - chemistry; Byproducts; Chlorine Compounds - chemistry; Chlorine dioxide; Cleavage; Decarboxylation; Degradation; Diclofenac; Diclofenac - chemistry; Disinfectants - chemistry; Hydroxylation; Mechanism; Models, Chemical; Oxidation; Oxidation-Reduction; Oxides - chemistry; Toxicity; Water Purification - methods; Water treatment
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2013.12.056

Diclofenac (DCF), a synthetic non-steroidal anti-inflammatory drug, is one of the most frequently detected pharmaceuticals in the aquatic environment. In this work, the mechanism and toxicity of DCF degradation by ClO2 under simulated water disinfection conditions were investigated. Experimental results indicate that rapid and significant oxidation of DCF occurred within the first few minutes; however, its mineralization process was longer than its degradation process. UPLC–MS and 1H NMR spectroscopy were performed to identify major disinfection byproducts that were generated in three tentative degradation routes. The two main routes were based on initial decarboxylation of DCF on the aliphatic chain and hydroxylation of the phenylacetic acid moiety at the C-4 position. Subsequently, the formed aldehyde intermediates were the starting point for further multistep degradation involving decarboxylation, hydroxylation, and oxidation reactions of CN bond cleavage. The third route was based on transient preservation of chlorinated derivatives resulting from electrophilic attack by chlorine on the aromatic ring, which similarly underwent CN bond cleavage. Microtox bioassay was employed to evaluate the cytotoxicity of solutions treated by ClO2. The formation of more toxic mid-byproducts during the ClO2 disinfection process poses a potential risk to consumers. [Display omitted] •Diclofenac oxidation by ClO2 was investigated under simulated water treatment.•UPLC–MS and 1H NMR were performed to identify major disinfection byproducts.•Microtox bioassay was employed to evaluate acute toxicity of reaction solutions.•The intermediates were more toxic than parent compound.