Distinct interferences of conventional and biodegradable microplastics on adsorption of pesticide mixture in agricultural soils

The presence of microplastics (MPs) strongly influences the environmental behaviour of pesticides, creating unignorable risks to soil and surrounding compartments. This study focused on the adsorption of a pesticide mixture (chlorpyrifos (CPF), pendimethalin (PDM), and pyraclostrobin (PCS)) in soils (sandy soil, loamy soil, and silty soil) with/without conventional MPs (low-density polyethylene (LDPE)) and biodegradable MPs (polybutylene adipate terephthalate (PBAT), and starch-based (starch)-MPs) to assess pesticide-MP interactions and their environmental implications. Results showed that the adsorption efficiency of pesticides on MPs reached 65-88%, and the distribution coefficients ( K d ) of pesticides on PBAT and starch-MPs is 3-8 times higher than on LDPE-MPs. In soil + MP matrices, the presence of LDPE-MPs inhibited pesticide adsorption, while PBAT and starch-MPs enhanced pesticide adsorption compared to soil matrices. Moreover, the inhibitory effects of LDPE-MPs were stronger in the loamy and silty soils (18%-29%) than in the sandy soil (14-17%), but the enhancing effects of PBAT and starch-MPs were strongest in the sandy soil (218-421%). The mantel test analysis suggested that the K d values of pesticides significantly correlated with soil properties and the pesticide octanol-water coefficients ( LogKow ) in soil and soil + LDPE-MP matrices but only correlated with LogKow in soil + PBAT-MP and soil + starch-MP matrices. The structural equation model indicates that the K d values of pesticides on MPs (path coefficient: 0.78) dominantly affected pesticide adsorption in MP-contaminated soils. Overall, our findings highlight the strong influence of MPs on pesticide adsorption capacity, implying large complexities and uncertainties in predicting pesticide fate and risk in soils, which are affected by ubiquitous MP contamination.