Free radical-enhanced formation of toxic byproduct benzoyl benzoquinone during the combined UV-chlorine treatment on BP-1

2,4-Dihydroxybenzophenone (BP-1), an important benzophenone-type (BPs) UV filter, is widely used in personal care products and other industrial products, it has been frequently detected in environmental media and even in organism samples. The transformation behaviors of BPs during environmental processes and their potential risk should be concerned. In this study, the variation of acute toxicity and transformation characteristics of BP-1 during the combined UV-chlorine disinfection process were explored. The acute toxicity of reaction mixtures was significantly higher than that of BP-1, a key toxic product (2-chloro-3-hydroxyl-6-benzoyl benzoquinone) was successfully identified, whose toxicity was about 40 times higher than BP-1. It was firstly found that ¹O₂ played crucial role in the toxic products formation during UV alone and combined UV-chlorine systems. Besides, Cl₂⁻• and HO• had great impact on the transformation of both BP-1 and toxic products. Overall, this work comprehensively revealed the formation mechanisms of toxic benzoyl benzoquinone from benzophenone-type UV filter during combined UV-chlorine process, it is expected that these results can provide scientific evidence for optimizing water disinfection process and evaluating potential risk of benzophenone-type UV filter.