title: Experimental and theoretical insights into photochemical transformation kinetics and mechanisms of aqueous propylparaben and risk assessment of its degradation products.
abstract: The kinetics and mechanisms of ultraviolet photochemical transformation of propylparaben (PPB) were studied. Specific kinetics scavenging experiments coupled with quantum yield determinations were used to distinguish the roles of various reactive species induced by self-sensitized and direct photolysis reactions, and the excited triplet state of PPB ((3) PPB*) was identified as the most important species to initiate the photochemical degradation of PPB in aquatic environments. The computational results of time-resolved absorption spectra proved that (3) PPB* is a highly reactive electron acceptor, and a head-to-tail hydrogen transfer mechanism probably occurs through electron coupled with proton transfer. Physical quenching by, or chemical reaction of (3) PPB* with, O2 was confirmed as a key step affecting the initial PPB transformation pathways and degradation mechanisms. The transformation products were identified and the toxicity evolutions of PPB solutions during photochemical degradation under aerobic and anaerobic conditions were compared. The results indicate that anaerobic conditions are more likely than aerobic conditions to lead to the elimination and detoxification of PPB but less likely to lead to PPB mineralization.
authors.affiliation: State Key Laboratory of Organic Geochemistry and Guangdong Key Laboratory of Environmental Resources Utilization and Protection, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou, People's Republic of China.
authors.forename: Taicheng
authors.initials: T
authors.lastname: An
authors.forename: Hansun
authors.initials: H
authors.lastname: Fang
authors.forename: Guiying
authors.initials: G
authors.lastname: Li
authors.forename: Shilong
authors.initials: S
authors.lastname: Wang
authors.forename: Side
authors.initials: S
authors.lastname: Yao
mesh_terms: D000042:Absorption; D054750:Ecotoxicology; D004583:Electrons; D007700:Kinetics; D008956:Models, Chemical; D010100:Oxygen / Q000737:chemistry; D010226:Parabens / Q000737:chemistry*; D010782:Photolysis; D018570:Risk Assessment; D012996:Solutions; D014466:Ultraviolet Rays; D014867:Water / Q000737:chemistry*; D014874:Water Pollutants, Chemical / Q000737:chemistry*
chemical_list: D010226:Parabens; D012996:Solutions; D014874:Water Pollutants, Chemical; D014867:Water; D010100:Oxygen; C006068:propylparaben
keywords: Ecotoxicology assessment; Endocrine disruptors; Environmental transformation; Parabens; Photoenhanced toxicity