Transformation of microplastics during UV-LED based water disinfection: Mechanistic insights and environmental implications

Microplastic (MP) pollution poses an urgent environmental challenge. UV-based disinfection processes generate oxidative radicals (e.g., hydroxyl (HO^•) and chloride radicals (Cl^•, Cl₂^•¯)), which may alter MPs' polymer structures during water treatment. However, their impacts on MPs' characteristics and environmental behaviors remain insufficiently understood. This study evaluated UV/H₂O₂, UV/chlorine, and UV/peracetic acid treatments on polystyrene, polyethylene, and polyvinyl chloride MPs. Spectroscopic and microscopic analysis revealed significant morphological changes, including surface cracks and pits. Chemically, oxygen-containing functional groups (e.g., carboxyl, hydroxyl) formed, while water contact angle tests showed decreased hydrophobicity. LC-MS identified various low- and high-molecular-weight degradation products. Acute toxicity assessments (using ECOSAR software) indicated that small-molecule products from polystyrene and polyvinyl chloride MPs showed high toxicity, while medium-molecule products from polyethylene MPs also exhibited notable toxicity. These findings highlight the formation of potentially hazardous byproducts during UV-based disinfection. We further assessed the natural decomposition of aged MPs across different water matrices and their sorption behavior toward hydrophobic and hydrophilic micropollutants in mixed wastewater. This research aims to provide critical insights into MPs' transformations during UV-based treatments, informing strategies for mitigating MP pollution while minimizing associated environmental risks.