Microplastics reduce soil detachment capacity by modulating soil physical properties: experimental evidence from concentration gradients

Microplastics derived from plastic mulch significantly alter soil physical characteristics, including water permeability and pore structure. However, their effects on soil detachment capacity remain poorly understood. To address this issue, we tested the soil porosity, water-holding capacity, and saturated water conductivity of four types of polyethylene microplastic concentrations (0%, 0.5%, 1%, and 2%) in the soil. Additionally, we conducted scouring experiments under different hydraulic conditions. The results demonstrated that soil without microplastics exhibited the highest saturated hydraulic conductivity and saturated water capacity. In contrast, while the addition of microplastics significantly reduced both saturated hydraulic conductivity and capillary porosity. Increasing microplastic concentration led to a decrease in detachment capacity by 8.31%–14.51%. Mechanistically, Microplastics diminished soil detachment capacity by altering capillary porosity, which in turn influenced soil detachment behavior. These findings elucidate the interactions between microplastics and soil, providing a mechanistic basis for assessing the environmental risks associated with microplastic pollution.