Effect of weathering on the release of secondary microplastic fragments and dissolved organics from microplastics

Environmental microplastics (MPs) release hazardous secondary MPs and total organic carbon (TOC) during aging processes. However, release mechanisms under varied aging conditions remain unclear. This study systematically investigated the effects of polymer types (polyvinyl chloride (PVC), polyethylene (PE), polybutylene adipate-co-terephthalate (PBAT)), physical form (sheet, powder), and aging methods-including ultraviolet (UV) irradiation, mechanical abrasion (MA), and their sequential combination - on the continuous release of secondary MPs and TOC. For UV aging, we further distinguished between the aging duration and the subsequent static leaching time; whereas MA and combined aging involved simultaneous abrasion and aqueous exposure. PBAT (powder), susceptible to hydrolysis, released the highest amounts of TOC and secondary MPs due to ester bonds cleavage. After 30 days of UV aging, secondary MPs release from PBAT (powder) increased from 10,618 to 13,600 particles per gram, while TOC release increased by 108 %. MPs in powder form consistently exhibited greater release than those in sheet form due to higher specific surface area. Combined aging resulted in the most significant degradation, enhancing secondary MPs release from PBAT by 72 % and 46 % compared to UV and MA alone, and increasing TOC release by factors of 1.29 and 2.21, respectively. These findings highlight the critical roles of polymer chemistry, physical form, and aging conditions in controlling MPs fragmentation and leaching, providing a mechanistic basis for environmental risk assessment and pollution management.