Migration of Nanoplastic in Soil: Effects of Polymer Properties and Rainfall Conditions

The pervasive presence of nanoplastics (NPs) in the soil environment has been widely documented. However, the mechanisms governing their transport through soil remain poorly understood. This study investigated the migration and vertical distribution of NPs under simulated rainfall, examining the effects of NP properties (concentration, polymer type, aging) and rainfall conditions (duration, pH). The results demonstrated that rainfall facilitated the entry and retention of NPs in soil, with long-term rainfall promoting gradual migration to deeper layers or groundwater. NP mobility was inversely related to their contamination levels. Lower concentrations enhanced downward transport, while higher concentrations led to preferential retention in the topsoil. Due to its hydrophilicity, polyamide (PA) exhibits greater mobility in soil than hydrophobic polystyrene (PS). Both UV aging and acidic rainfall conditions inhibited the migration of NPs, which increased their long-term retention in soil, thereby elevating ecological risk. These results highlight the need for increased attention to the risk of groundwater contamination posed by hydrophilic NPs following long-term rainfall, as well as the threat posed by hydrophobic NPs, particularly after aging and under acidic rainfall conditions, to soil organisms and food safety. Our findings provide critical insights for assessing NP risks in soil environments.