The Transport of Microplastics from Soil in Response to Surface Runoff and Splash Erosion

Erosion is hypothesized to be a significant process transporting microplastics (MPs) from soils to aquatic environments, however, the factors controlling this process are poorly understood. Using a novel combination of high-frequency photography and fluorescent particles, we compared the transport of three MPs to that of a sand particle during rainfall simulations: linear low-density polyethylene (LLDPE), polystyrene (PS), and poly(methyl methacrylate) (PMMA). We measured the "real time" movement of particles on the soil surface alongside the number of particles transported through splash erosion and surface runoff. Our results show that MPs of all polymer types demonstrated more rapid transport from the soil surface compared to sand particles throughout the rainfall simulations. Prior to surface runoff, ∼65-75% of MPs and sand particles were removed from the soil surface through raindrop-driven incorporation into the soil matrix. Surface runoff and splash erosion accounted for the transport of approximately 47% of PMMA and 57% of PS, while only 30% of sand particles were mobilized by these processes. This research establishes a benchmark for evaluating MP mobility to current knowledge of soil particle movement, which is critical for estimating the redistribution of MPs within soils and their ultimate flux to aquatic ecosystems.