Adsorption profiles and potential risks of PAHs and PCBs on microplastics in stormwater runoff: Influence of underlying surfaces and polymer materials

Microplastics in stormwater can adsorb polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs), may pose risks to rainwater harvesting and environmental sustainability. However, characteristics and toxicities of PAHs and PCBs on microplastics in different stormwater runoffs remain poorly understood. Therefore, this study investigated the effect of underlying surface types and polymer materials on PAHs and PCBs adsorption by microplastics in runoff. The results showed that the total concentrations of PAHs and PCBs adsorbed on microplastics in the runoff ranged from 0.727 to 9.416 ​mg/kg and 0.011–0.086 ​mg/kg, respectively. The highest PAHs adsorption was found on microplastics in rooftop runoff, and the highest PCBs adsorption was found in road runoff, while PAHs types in campus runoff were more diverse. In terms of materials, polyethylene (PE) and polypropylene (PP) had higher adsorption capacities for PAHs than other tested polymers, whereas PP and polystyrene (PS) had higher adsorption of PCBs. Characterizing surfaces and functional groups of the microplastics showed that the differences in PAHs and PCBs adsorption can be related to their molecular structures and aging behaviors. As for toxicities, microplastics in the campus runoff and the green space runoff exhibited the highest toxicities of PAHs and PCBs, respectively, indicating that the toxicity is more associated with the types of pollutants adsorbed. This study suggested that PAHs and PCBs adsorbed by microplastics in stormwater runoff are higher than those in freshwater, so they could serve as critical vectors for transporting PAHs and PCBs into aquatic environments. But the adsorption capacity of natural cellulose for PAHs and PCBs is higher than microplastics, and the related risks cannot be ignored, especially considering its prevalence. Underlying surfaces and materials affect both adsorption capacities and toxicities of PAHs and PCBs, which should be considered in stormwater harvesting, in terms of water source selection, treatment process design, and construction material selection. • Underlying surfaces affects PAHs and PCBs on microplastics with rooftops shows highest PAH. • PP and PE exhibit strong adsorption and cellulose adsorbed more than microplastics. • Campus-runoff microplastics carry high-toxicity PAHs, may related to diverse activities. • The study informs risk control and sustainable stormwater reuse strategies.