Comparative Interaction of Pesticides with Microplastics and Soil Organic Matter: A Molecular Simulation Study

Microplastics (MPs), a type of emerging persistent pollutant, are attracting increasing attention from both scholars and governments. Agricultural soil is considered an important sink for MPs due to the use of plastic mulches and the application of sewage sludge to fields. Widely used pesticides often coexist with MPs in soils, potentially causing co-contamination that threatens the ecosystem. The interaction between pesticides and soil organic matter (SOM) influences the behavior and toxicity of pesticides in the soil environment, and MPs may participate in this interaction. Preliminary theoretical studies using a combination of molecular mechanics (MM), molecular dynamics (MD), and quantum mechanics (QM) simulations revealed that model MPs and fragments of humic substances (HS) exhibited different adsorption affinities for chlorpyrifos (CPF), a model organophosphorus pesticide, in both vacuum and water. Polypropylene (PP) MPs showed significantly higher adsorption capacity than HS in vacuum, while HS outperformed polyethylene (PE) MPs in water significantly. Furthermore, PP consistently exhibited a significantly higher adsorption capacity than PE regardless of the medium. The adsorption between HS and CPF, as well as between MPs and CPF, was attributed to physical interaction. Furthermore, van der Waals interactions contributed to the mechanism underlying the interactions of MPs/HS with CPF. These findings theoretically demonstrate that MPs can serve as important vectors for the migration of pesticides through the soil system. This work offers a new perspective on the role of MPs in the environmental behavior and toxic effects of pesticides under field-relevant conditions.