Transport behavior of microplastics in soil‒water environments and its dependence on soil components

Microplastic (MP) pollution has become a global concern, and the transport behavior of MPs in soil-water systems is vital in determining their distribution and potential risks to the subsurface environment. To reveal the role of various soil components on MP migration, the downward transport behavior of polystyrene (PS) MPs were explored in this study via column experiments with mono or multi-soil components as porous media. Compared with the selected soil mineral volcanic rock (VR) and fine river sand (RS), condensed soil organic matter (SOM) resulted in higher transport efficiencies for PS microparticles, with greater than 90% total mass recovery under the experimental conditions. The more surface charges of SOM than minerals contribute to the high migration efficiency of PS MPs, and electrostatic repulsion is assumed a significant driving mechanism in the migration of negatively charged PS particles in soils. The ionic strength of porewater influenced the PS migration behaviors by altering the electrostatic interactions between the MPs and soil grains. The uniform mixing of SOM with mineral grains significantly enhanced the transport efficiency of PS MPs in the columns. The results provide supports for the prediction and prevention of the risks of MPs to the subsurface environment.