Distribution characteristics and mechanism of microplastics mediated by soil physicochemical properties

Interaction between microplastics and soil is essential for the environmental fate of plastic particles. In this study, polystyrene microplastic particles (PSMPs) with a size of 0.047 μm were selected as the representative of microplastics. Five soil samples from different provinces in China were selected (named Harbin S1, Huainan S2, Jiangxi S3, Shaanxi S4 and Hainan S5, respectively) and their interaction characteristics and mechanism with PSMPs were investigated, which provided new insights into the environmental behavior of microplastics. The experimental data showed that the pseudo-first-order model well fit for the sorption kinetics data, and the microplastic sorption ability of the soil accorded with the following sequence: S3 > S2 > S1 > S4 > S5. The sorption isotherm data of PSMPs on soils fit a linear model well (R² = 0.998). The sorption of MPs on soils was affected by pH, and the sorption ability weakened as the pH increased. Soil physicochemical properties play important roles in sorption of PSMPs, especially the content of soil organic carbon. The sorption capacity was positively correlated with soil organic carbon (R² = 0.999) and Fe₂O₃ content (R² = 0.967), while the sorption of clay showed opposite trend (R² = 0.952). The sorption mechanisms of PSMPs on soils included surface sorption, electrostatic and hydrophobic interactions. Results of this study could be useful to better study the role of soil in the fate and transportation of plastic particles.