Long-Lived Organic Radicals Drive the Photodegradation of Plastic Additives in Microplastic-Derived Dissolved Organic...

Microplastic-derived dissolved organic matter (MP-DOM) plays an important role in aquatic environments; however, its influence on the photodegradation of plastic additives remains unclear. In this study, bisphenol A (BPA) was selected as a representative plastic additive to investigate the effects of polystyrene-derived DOM (PS-DOM) on the photodegradation kinetics and mechanisms of BPA at different concentrations. PS-DOM significantly enhanced the photodegradation of BPA, with the promoting effect becoming more pronounced at lower BPA concentrations. Kinetic modeling revealed that as BPA levels decrease from high to low, the dominant contributor to BPA photodegradation shifts from the excited triplet state of PS-DOM (generated via photosensitization) to long-lived organic radicals (LLORs). This finding highlights the indispensable role of LLORs in the photodegradation of trace-level BPA (nM-μM) in surface waters. Probe experiments revealed that the one-electron reduction potentials of LLORs generated by various MP-DOM are around 1.50 V, indicating that LLORs have the potential to degrade plastic additives with oxidation potentials below this range. Furthermore, correlation analysis revealed that variations in unsaturated functional groups and electron-donating moieties (e.g., tannins and lignins) within MP-DOM were key factors controlling the quantum yield coefficients of LLORs across different MP-DOM types. This study provides novel insights into the photochemical reactivity of MP-DOM and its potential role in regulating the environmental transformation of plastic additives.