Solar photodegradation of the UV filter 4-methylbenzylidene camphor in the presence of free chlorine

UV filters are essential ingredients in sunscreens and many personal care products. The coexposure of UV filters to solar photolysis and free chlorine (solar/free chlorine) is inevitable in outdoor swimming pools and many other aquatic matrices, and this study aims to investigate the degradation mechanism of one specific UV filter, 4-methylbenzylidene camphor (4MBC), under solar/free chlorine system. Under solar irradiation alone, 4MBC only undergoes isomerization from (E)- to (Z)-4MBC; however, in the solar/free chlorine system, 4MBC was significantly degraded, with a pseudo-first-order rate constant of 0.0137 s(-1) (pH= 7). The effects of the initial free chlorine concentration, solution pH andwater matrix (presence of dissolved organicmatter, HCO3- and Cl-) were studied. The results revealed that reactive chlorine species (RCS) are the dominant species influencing 4MBC degradation via solar/free chlorine, while center dot OH and O-3 played minor roles. These specieswould likely reactwith the 4methylstyrene moiety of 4MBC and subsequently lead to 4MBC degradation through hydroxylation, chlorine substitution, oxidation and demethylation. Nevertheless, the dramatic increase in acute toxicity (Microtox (R)) during solar/free chlorine degradation of 4MBC highlights the need to further explore the transformation byproducts as well as their associated risks to humans and the environment. (C) 2018 Elsevier B.V. All rights reserved.