Photochemical transformation of microplastics-derived dissolved organic matter altered the photoaging of microplastics

Microplastics-derived dissolved organic matter (MPs-DOM), as a novel and non-negligible of DOM, significantly influences the photoaging of coexisting microplastics (MPs), but their interactions remain underexplored. In this study, we investigated the effects of different MPs-DOM (aromatic polystyrene DOM (PS-DOM), aliphatic polyethylene DOM (PE-DOM), and biodegradable poly(butylene adipate-co-terephthalate) DOM (PBAT-DOM)) on the aging behavior of PS-MPs and their transformations characteristics within 96 d of UVA irradiation. Result demonstrated that MPs-DOM notably accelerated the PS-MP aging (especially PBAT-DOM), and the aging rate was closely correlated with MP-DOM evolution. Notably, PS-MP exhibited significant and rapid increase in aging within the first 6 h, which was attributed to the presence of highly unsaturated and phenolic compounds in MPs-DOM that promote the generation of reactive oxygen species (ROS). Throughout this process, these compounds were transformed into the saturated and low-aromatic compounds via the carboxylic acid and dealkylation reactions. As the reaction proceeded, PS-DOM released from PS-MP gradually became the dominant component in MP-DOM. The highly unsaturated components of PS-DOM have higher ability to produce ROS, thereby further accelerating PS-MPs aging. These findings provide valuable insights into the interactions between MPs and MPs-DOM and contribute to a better understanding of their environmental implications and risks.