MICROPLASTICS IN GROUNDWATER AND THE ROLE OF SOIL THICKNESS IN MITIGATING SEPTIC EFFLUENT AS A SOURCE

The occurrence of microplastics in surface water is well-documented but the sources, abundance, and transport of microplastics through groundwater is poorly understood. Where microplastics have been found in karst aquifers, septic effluent was identified as a likely source. The fraction of microplastics in septic effluent that reach the aquifer will be governed by their size, shape, and interactions between the solid and liquid phase of the soil system. Transport of plastic microspheres found in cosmetics and other household products behave as colloids, but the transport of synthetic microfibers shed from fabrics is complicated by their size and tendency to become entrained by soil aggregates. The purpose of this study was to investigate the role of soil thickness in determining the type and abundance of microplastics in septic effluent that are most likely to be observed karst or hard rock aquifers. Transport of 1-10 µm polyethylene microspheres and polyester microfibers were determined using sand columns and modeled using Hydrus-1D. The results indicate that colloidal microplastics are more effectively transmitted through porous media than fibers and that the transport behavior of fibers is more strongly affected by soil thickness.