Insight into the generation of toxic products during chloramination of carbamazepine: Kinetics, transformation pathway and toxicity.

As a widely used antiepileptic drug, carbamazepine (CBZ) has been frequently detected in aquatic environments, even in drinking water. Chloramine is a widely used alternative disinfectant due to its low-level formation of regulated disinfection byproducts (DBPs). However, there is previous evidence linking product mixtures of chloraminated CBZ to stronger DNA damage effects than those caused by CBZ itself. The present study further investigated the reaction rate, transformation mechanism and multi-endpoint toxicity of transformation products (TPs) of CBZ treated with NH ₂ Cl under different pH conditions. The results showed that the reaction between CBZ and NH ₂ Cl at pH 8.5, where NH ₂ Cl is stable, is a second-order reaction with a rate of 4.2 M ^-1  h ^-1 . Compared to both alkaline and acidic conditions, CBZ was quickly degraded at pH 7. This indicated that HOCl produced from NH ₂ Cl hydrolysis is more effective in degrading CBZ than NH ₂ Cl and NHCl ₂ . Furthermore, the concentration variation of four TPs formed during the chloramination of CBZ under different pH conditions was investigate by quantitative analysis, and the transformation pathway from CBZ to 9(10H)-acridone was confirmed. Three of the detected TPs showed cytotoxicity, DNA damage effects or chromosome damage effects. Acridine and 9(10H)-acridone, which accumulated with increasing time, showed higher cytotoxic or genotoxic effects than CBZ itself. In addition, a similar transformation mechanism was observed in real ambient water during simulated chloramination with a low level of CBZ. These results suggested that despite the chloramination of CBZ being slower than chlorination, TPs with higher cytotoxicity or genotoxicity may lead to greater toxic risks.
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