Impact of Ultraviolet Aging Under Different Environmental Factors on the Leaching Behavior of Phthalate Esters (DnBP and DEHP) from Polyvinyl Chloride Microplastic

As microplastics act as ubiquitous carriers for endocrine-disrupting additives in aquatic environments, understanding their leaching dynamics is of critical concern. This study systematically investigated the effects of ultraviolet (UV) aging on the release behavior of phthalates (di-n-butyl phthalate [DnBP] and di(2-ethylhexyl) phthalate [DEHP]) from polyvinyl chloride (PVC) microplastics across diverse environmental conditions, along with the underlying mechanisms. Kinetic analyses and experimental results indicated that the release of plasticizers under UV irradiation was driven by a dynamic competition between the photochemical stability of the plasticizers and the aging of the microplastics: the apparent cumulative amount of photolabile DnBP decreased as irradiation time increased. In contrast, the release of photoresistant DEHP significantly exceeded that under dark conditions in the later stages of aging. Furthermore, highly variable environmental factors exhibited significant selectivity in regulating the release: high ionic strength inhibited plasticizer release through salting-out and cationic bridging effects, with divalent ions (Mg2+) in particular suppressing DEHP release by up to 96%; conversely, dissolved humic acid caused a 13-fold surge in DEHP release via robust hydrophobic solubilization. Comprehensive multitechnique characterizations (including SEM, FTIR, XRD, and XPS) confirmed that UV-induced aging—encompassing intense dehydrochlorination reactions, a marked increase in polar oxygen-containing functional groups and the amorphization of crystalline regions—fundamentally dismantled the internal mass transfer resistance, thereby creating physical pathways for the outward migration of internal plasticizers. Ultimately, this study emphasizes that the synergistic interactions between material aging and complex hydrochemical conditions must be fully integrated into assessments of long-term ecological risks and predictions of the real-world environmental fate of microplastic-associated contaminants.