Kinetics and mechanism of 4-methylbenzylidene camphor degradation by UV-activated persulfate oxidation.

4-Methylbenzylidene camphor (4-MBC), a widely used ultraviolet (UV) filter detected in various aquatic environments, has been shown to evoke estrogenic activity. In this study, the use of UV light-activated persulfate for 4-MBC degradation is evaluated for the first time. Our results showed that the combination of UV and persulfate (UV/persulfate) can significantly remove 4-MBC, with a pseudo-first-order rate constant (kobs) of 0.1349 min−1 under the conditions of [4-MBC]0 = 0.4 μM, [persulfate]0 = 12.6 μM, and initial pH = 7. The kobs and persulfate dose exhibited a linear proportional relationship in the persulfate dose range of 4.2–42 μM. The kobs remained similar at pH 5 and pH 7 but significantly decreased at pH 9. A radical scavenging test indicated that SO4−• was the dominant species in 4-MBC degradation; the second-order rate constant of SO4−• with 4-MBC was calculated to be (2.82 ± 0.05) × 109 M−1 s−1. During the UV/persulfate reaction, 4-MBC was continuously degraded, while SO4−• was gradually converted to SO42−. 4-MBC degradation involved the hydroxylation and demethylation pathways, resulting in the generation of transformation byproducts P1 (m/z 271) and P2 (m/z 243), respectively. The Microtox® acute toxicity test (Vibrio fischeri) showed increasing toxicity during the UV/persulfate degradation of 4-MBC. The 4-MBC degradation rate was markedly lower in outdoor swimming pool water than in deionized water.