Kinetics and degradation mechanism of Benzophenone-3 in chlorination and UV/chlorination reactions

Benzophenone-3 (BP3) is a potential phenolic endocrine disrupter that is widely used as a sunscreen and ultraviolet (UV) stabilizer. The degradation of BP3 in water during chlorination and UV/chlorination reactions was investigated. The degradation of BP3 by both reactions followed pseudo-first-order kinetics. The pH profile of the observed pseudo-first-order rate constants (k(obs)) were bell shapes that depended on pH, and the highest k(obs) values were obtained at pH 8 for both reactions. The contribution of OH radicals (center dot OH) on BP3 degradation under UV/chlorination conditions increased at acidic pH values, and the contribution of reactive chlorine species (RCS) such as center dot Cl increased at neutral and basic pH values. The BP3 degradation rate was enhanced by the presence of HCO3- ions, but was inhibited by humic acid. A total of seven transformation products (TPs) of BP3 were identified during chlorination (TP-262, TP-296, TP-192, TP-226, and TP-118) and UV/chlorination (TP-244, TP-262, TP-278, and TP-296) reactions. Among the TPs, chloroform (TP-118) was only found in the chlorination reaction. The BP3 degradation pathways during both reactions were proposed based on these TPs. Degradation of BP3 was mainly associated with electrophilic aromatic halogenation in both reactions. Finally, the bioluminescence inhibition of Vibrio fischeri by the TPs produced from the BP3 during the UV/chlorination reaction was lower than that of the TPs obtained during chlorination, implying that the additional oxidation of BP3 occurs by the reactive radicals produced during the UV/chlorination reaction.