Mechanism, kinetics and toxicity assessment of OH-initiated transformation of triclosan in aquatic environments

The mechanisms and kinetics of OH-initiated transformation of triclosan (TCS) in aquatic environments were modeled using high-accuracy molecular orbital theory. TCS can be initially attacked by center dot OH in two ways, OH-addition and H-abstraction. Twelve OH-addition routes were reported, and the C atom adjacent to the ether bond in the benzene ring (RaddB1) was found as the most easily attacked position by center dot OH, producing center dot TCS OHai. Seven H-abstraction routes were reported, and the center dot OH exclusively abstracted the phenolic hydroxyl (RabsOH) H atom, to form TCS( H). The kinetics results showed that the RaddBi and RabsOH routes would occur preferentially in aquatic environments, and the half-life depended on the center dot OH concentration ([center dot OH]). At low [center dot OH], the main intermediates, center dot TCS OHBi and TCS(-H), can be converted into 2,4-dichlorophenol and polychlorinated dibenzo-p-dioxins, respectively. However, when enough center dot OH is present, such as in advanced oxidation process (AOP) systems, they would be fully decomposed. The acute and chronic toxicities of TCS and its products were assessed at three trophic levels using the ecological structure activity relationships program. The toxicity of the products decreased through the RaddBi route, while the toxicity of the products first increased and then decreased through the other degradation routes. These results should help reveal the mechanism of TCS transformation as well as risk assessment in aquatic environments, and will help design further experimental studies and industrial application of AOPs. (C) 2013 Elsevier Ltd. All rights reserved.