Emerging investigator series: release and phototransformation of benzophenone additives from polystyrene plastics exposed to sunlight

Abstract

There are increasing concerns about the human and environmental health impacts of plastic exposure, which include the risks associated with plastic additives. However, despite their presence in most plastic products, the factors governing the release and transformation of chemical additives in the aquatic environment are poorly understood. In this study, we examined the simultaneous release and transformation behavior of four benzophenone-type chemical additives from polystyrene (PS) under natural and accelerated photochemical weathering conditions. Liquid chromatography coupled with high resolution-mass spectrometry (LC-HRMS) quantitatively determined additive concentrations in plastic leachates and identified the formation of phototransformation products. Although the passive release of benzophenones from PS followed a time^0.5 dependence, the presence of sunlight (active release) altered the concentration of leached benzophenones in solution depending on the relative photostability of the compounds. In accelerated lab-based studies using >300 nm irradiation, a second stage of increased additive release was observed for prolonged irradiation times, an effect ascribed to distinct stages of PS photodegradation. LC-HRMS analysis identified various photodegradation products, including carboxylic acids and hydroxylated species. Quencher experiments indicated that these transformation products were produced by the formation of excited triplet states and hydroxyl radicals generated by benzophenone photoexcitation. Hydroxyl radicals are also likely responsible for the complete mineralization of irradiated benzophenones as evidenced by total organic carbon analysis. This work identifies the impact of photolysis on both additive release and transformation of benzophenones.