Insights into the Photoaging Behavior of Microplastics: Environmental Fate and Ecological Risk

The widespread occurrence and potential ecotoxicity of microplastics (MPs) have attracted global concern. In the natural environment, MPs undergo various weathering processes, with photoaging as the dominant mechanism. Strengthening the understanding of MP photoaging behavior is essential for elucidating their environmental fate and ecological risks. This work provides a comprehensive overview of ultraviolet (UV)-induced photoaging of MPs, progressing from general oxidative mechanisms to polymer-specific degradation and environmentally persistent free radical (EPFR)-mediated pathways. Mechanistic insights are translated into measurable indicators through the systematic evaluation of representative photoaging indices. Polymer properties and environmental conditions are examined to identify factors governing these transformations, integrating recent advances into an updated synthesis. The biotoxicity of photoaged MPs is critically assessed, with particular attention to the release of dissolved organic matter (DOM) as a previously underrecognized ecological stressor. Changes in surface properties significantly impact the adsorption of coexisting pollutants, the degradation of surrounding contaminants, and the transport dynamics of MPs across environmental compartments. This work offers a novel perspective by linking photoaging and plastisphere formation, with microbial colonization and surface aging jointly shaping the fate, mobility, and ecological interactions of MPs. This review advances the understanding of MP photoaging by bridging degradation mechanisms with ecological consequences.