Synergistic interplay of weathered microplastics: Coupling sorption-leaching behavior and environmental risk implications

Weathered microplastics (MPs) are a growing environmental concern due to their altered physicochemical properties affecting pollutant interactions. While previous studies examined isolated aspects of weathered MPs, this study provides an integrated investigation of photo-weathering effects on MPs’ properties and associated human health risks. Polystyrene (PS) and polyvinyl chloride (PVC) MPs were exposed to UVC and Xenon light to simulate photo-weathering. Surface analyses revealed that UVC irradiation caused more distinct changes in surface oxidation and hydrophilicity compared to Xenon exposure, with carbonyl index (CI) increasing at rates of 0.002/h and 0.001/h for PS and PVC, respectively, with UVC irradiation. The O/C ratio reached 0.0978 for PS and plateaued at higher values for PVC under UVC exposure, while contact angles decreased for both MPs. Weathering did not impact heavy metal (As, Cu, Pb, Zn) adsorption onto MPs; instead, adsorption capacity varied primarily based on metal species and MP type. Photo-weathering severely accelerated the leaching of di(2-ethylhexyl) phthalate (DEHP) from PVC, with the leaching rate constant being approximately 5 times faster for weathered MPs exposed for 600 h compared to virgin. Probabilistic human health risk assessment using Monte Carlo simulation showed while both hazard quotient (HQ) and excess cancer risk (ECR) remained below regulatory thresholds, weathered MPs exhibited twice the risk values compared to virgin MPs. Thus, the role of weathered MPs as carriers of heavy metals and increased risks due to leaching of hazardous materials highlights the need for more in-depth and systematic investigation of various weathered MPs.