Effect of PVC microplastics on pesticide sorption behavior in soil: Key roles of particle size and aging

Microplastics (MPs) have emerged as one of critical factors influencing the environmental fate of pesticides in the soil. This study examined the sorption of the one type of pesticide, named spirotetramat (SP), onto agricultural soil with pristine and aged PVC MPs at varying concentrations (1 % and 3 % w/w) and particle sizes (1 and 150 μm). Characterization indicated aging significantly enhanced surface area, roughness, porosity, and oxygen groups, especially in smaller PVC MPs (1 μm), resulting in faster sorption equilibrium (≤ 4 h) and higher adsorption capacity for SP (4.88 mg·g^-1), driven by charge-assisted hydrogen bonding (CAHB). The smaller-sized and aged MPs also exhibited greater adsorption capacities and affinities. Desorption hysteresis was minimal in pristine MPs (Hysteresis Index: HI ≤ 0.13) but significant in aged MPs (HI ≥ 1.05) due to CAHB and halogen bonding (XB). Increased pH notably enhanced SP adsorption through strengthened CAHB interactions, whereas ionic strength had negligible effects, validating CAHB as the primary sorption mechanism. In soil systems, adding PVC MPs (1 % and 3 % (w/w)) significantly enhanced SP adsorption capacity in soil, particularly for aged and smaller ones. These results emphasized the importance of incorporating MPs into environmental risk assessments of pesticides in soil.