Quantifying the movement of microplastics in soil in response to overland flow and splash erosion

Microplastics are ubiquitous in the environment. While it is well documented that microplastics can be harmful to aquatic and terrestrial life, little is understood about how microplastics affect soil environments. Understanding the processes enhancing or constraining microplastic transport through the environment, including within soils, is essential in order to minimize the negative impacts of microplastic pollution. Soil erosion is thought to be a primary process responsible for translocating microplastics from soils to aquatic environments. This study aims to investigate the processes controlling microplastic movement in response to rainfall and overland flow in laboratory rainfall simulations. Using fluorescent photography, we compared the real- time movement of a natural soil particle, sand, with two types of microplastics of differing densities (linear low-density polyethylene and acrylic) in two size fractions (250-355 μm and 500-600 μm). We quantified the rate and number of microplastic particles transported by overland flow and splash erosion, along with the depth to which the particles migrate into the soil profile. The results from this study represent some of the first empirical data that seek to quantify microplastic surface transport processes. Ultimately, additional research in this area will be required to more accurately estimate the extent to which microplastics are exported from soils and the factors that control this export.