Photochemical transformation of decachlorobiphenyl (PCB-209) on the surface of microplastics in aqueous solution

Abstract

• Photochemical transformation of PCB-209 on PS microplastics in water was studied. • ROS attacked PCB-209 and PS to form chlorine-related radicals and polymer radicals. • Direct photolysis, photooxidation and radical reactions were main reactions. • Products from interactions of PS with PCB-209 were also detected. • DFT calculations were used to interpret reactions of PS with OH. The accumulation of persistent organic pollutants (POPs) and microplastics in the water environment has attracted widespread attention. Given the easy adsorption of PCB-209 by microplastics, this work aimed at examining the photochemical transformation behaviors of PCB-209 on the surface of polystyrene (PS) under simulated solar irradiation. The slowest degradation was observed at pH 7.0, with a rate constant of 0.0158(±0.0004) h −1 . The presence of NO 3 − , NH 4 + and high concentrations of humic acid would inhibit the removal of PCB-209, due to the decreased amount of available free radicals. The direct photolysis of PCB-209 resulted in the formation of lower chlorinated PCBs, while the irradiation of PS could produce reactive oxygen species (ROS) and various polymer radicals. Hydroxyl radicals, as the major ROS, would attack PCB-209 to form hydroxyl substitution products, with the release of chlorine and pentachlorobenzene radicals. Polymer radicals would undergo oxidation or scission to generate olefin type products and styrene/benzene-containing products, or react with chlorine/pentachlorobenzene radicals to form (poly)chlorinated PS products. Thus, the respective transformation products of PCB-209 and PS, as well as products resulting from the interactions of the polymer with the compound were detected. Toxicity predictions by ECOSAR revealed that some intermediate products are toxic to aquatic organisms. This study provides some new insights on the environmental fate of PCBs and the photochemical roles of microplastics in sunlit surface waters.