Enhanced phototransformation of atorvastatin by polystyrene microplastics: Critical role of aging

Reactive oxygen species (ROS) generated from light irradiation of microplastics (MPs) can potentially affect the environmental fate of organic contaminants when they coexist in the same environment. This study investigated the effect of polystyrene (PS) MPs with different aging degrees on the phototransformation of atorvastatin (ATV) under simulated sunlight. Results showed that the presence of PS MPs facilitated the phototransformation of ATV, and the degradation rate was linearly correlated with the aging degree (i.e., carbonyl index) of MPs. The enhanced effects mainly depended on the contents of oxygen-containing functional groups of PS MPs, which increased the absorption of light energy and the generation of ROS (e.g., singlet oxygen (¹O₂) and triplet-excited state PS (³PS*)). Quenching experiments indicated that ¹O₂ generated from photosensitization of PS was the major contributor to the increased phototransformation of ATV. Additionally, the role of ³PS* became more important in the photodegradation mediated by higher degree aged MPs because much more ¹O₂ was generated from the ³PS* . PS MPs also increased the types and yields of degradation products, especially for higher degree aged MPs, despite the low effect on leachate toxicity. The findings provide a novel insight into the critical role of MPs in the fate of organic contaminants in aquatic environments.