Synergistic Transformation of Microplastics and Benzo(a)pyrene under Simulated Sunlight Irradiation: The Role of Chromophores and Reactive Oxygen Species

Polyaromatic hydrocarbons and microplastics are common atmospheric pollutants, but their interaction processes and influence on one another under sunlight irradiation are unknown. Herein, the synergistic transformation of polystyrene microplastics (PS-MP) adsorbed with benzo[a]pyrene (B[a]P) was studied upon exposure to simulated sunlight. During this process, B[a]P accelerated the photoaging process of PS-MP. UV-visible near-infrared diffuse reflectance spectrometer (UV-vis RDS) analysis of the PS-MP/B[a]P complex revealed that B[a]P and its photodegradation products containing chromophore groups, such as ethers, ketones, carboxylic compounds, and aromatic compounds, significantly expanded the wavelength range and enhanced the absorption intensity of sunlight by PS-MP. Moreover, the absorbed light energy was transferred to PS-MP in the form of energy or electrons, which expedited the bond breaking of PS-MP and generated additional binding sites for oxygen. Meanwhile, direct photolysis of B[a]P was initially impeded by PS-MP due to its shielding effects. Subsequently, reactive oxygen species (ROS) induced by persistent free radicals (PFRs) on the photoaged PS-MP promoted B[a]P degradation. The synergistic interaction between PS-MP and B[a]P enhanced PFRs and ROS generation, potentially elevating their environmental risk. This research offered novel perspectives on ecological behavior and the associated risks of MP with exogenous organic pollutants.