Soil microplastics as carriers of organic pollutants: Sorption mechanisms and environmental behavior

Soil is a major aggregate of microplastics and organic pollutants (antibiotics, pesticides). The long-term coexistence of microplastics and these organic pollutants in soil leads to inevitable interactions, which in turn affect their environmental behaviors. Based on recent research findings on microplastics in agricultural and urban soils, it is found that agricultural soils receive a large amount of microplastic inputs mainly through plastic mulching films, sewage sludge, compost, and atmospheric deposition, while microplastics in urban soils mainly originate from traffic, landfills, and industrial activities. Besides, the inherent characteristics of microplastics (polymer type, particle size, crystallinity, surface chemical properties), the chemical characteristics of antibiotics and pesticides (ionization, hydrophobicity, functional groups), and key environmental parameters (pH, ionic strength, soil depth, mineral composition, and dissolved organic matter) all affect the adsorption behavior and mechanism of microplastics on organic pollutants. Aging, dissolved organic matter, clay minerals, and biofilms can significantly alter the surface of microplastics, transforming the adsorption mechanism from simple hydrophobic partitioning to a complex interplay involving hydrogen bonds, electrostatic attraction, and π-π interactions. These processes can change the mobility, bioavailability, and persistence of the combined pollutants, thereby having a continuous negative impact on soil organisms, terrestrial food webs, and potential groundwater pollution. Therefore, it is imperative to reduce emissions at the source and develop soil risk management strategies as soon as possible to mitigate the long-term threats these emerging compound pollutants pose to soil ecological functions and human health.