Increased mobility, toxicity, and bioaccessibility of arsenate adsorbed onto UV-aged polyvinyl chloride microplastics

Microplastics (MPs) can act as vectors for toxic pollutants; however, most previous studies have examined the effects of environmental aging on contaminant adsorption or toxicity separately, while the integrated effects on bioaccessibility and risk remain poorly understood. This study evaluated aging-driven changes in surface characteristics of polyvinyl chloride (PVC) MPs following UVC aging and their effects on arsenate (As(V)) adsorption, ecotoxicity, bioaccessibility, and human health risk. After 600 h of UV aging, carbonyl index variation, increased O/C ratio (0.1412-0.2213), and decreased contact angle (72.41°-34.14°) collectively suggested surface oxidation of PVC MPs. The maximum adsorption capacity of As(V), estimated using the Langmuir isotherm model after a 48 h equilibrium adsorption experiment, decreased approximately 16-fold following aging (from 0.0636 to 0.0039 mg/g). In contrast, oral bioaccessibility under simulated gastric conditions, evaluated using the solubility bioaccessibility research consortium (SBRC) method, increased approximately 16-fold after aging (from 3.9% to 63.7%). Results of the 24 h acute toxicity test using Daphnia magna showed higher immobilization in aged MP treatments (100%) than in virgin MPs (50 ± 14%). Human health risk assessment based on dietary exposure scenarios showed that the hazard quotient and excess cancer risk increased approximately 2.6-fold after aging. These results show that UV aging can reduce adsorption capacity yet increase bioaccessibility and potential ecological and human health risk. This study provides integrated quantitative evidence that aging-induced surface transformation can increase the ecological and human health relevance of MP-associated metal/metalloid contaminants and should be explicitly considered in MPs risk assessment frameworks.