Degradation of climbazole by UV/chlorine process: Kinetics, transformation pathway and toxicity evaluation

Climbazole is an antifungal agent widely used in household personal care products, and it was found persistent in chlorination disinfection process. Here we investigated the kinetics and mechanism of climbazole degradation by UV/chlorine process. The results showed that the UV/chlorine process dramatically enhanced degradation of climbazole when compared to the UV photolysis and chlorination alone. The neutral condition (pH 7) produced the highest reaction rate for the climbazole by UV/chlorine among the various pH conditions. Dissolved organic matter and inorganic ions in natural water showed moderate inhibition effects on the degradation of climbazole in the UV/chlorine process. Hydroxyl radical (OH and chlorine radical (Cl) were found to be the main reactive species in the degradation of climbazole, with the second-order rate constant of 1.24 × 10¹⁰ M^-1 s^-1 and 6.3 × 10¹⁰ M^-1 s^-1, respectively. In addition, the OH and Cl in the UV/chlorine at 100 μM accounted for 82.2% and 7.7% contributions to the removal of climbazole, respectively. Eleven of main transformation products of climbazole were identified in the UV/chlorine process. These oxidation products did not cause extra toxicity than climbazole itself. The findings from this study show that the combination of chlorination with UV photolysis could provide an effective approach for removal of climbazole during conventional disinfection process.