Microplastics in Lake Washington and the Surrounding Watershed

Large plastic debris in marine environments has received considerable attention from scientists, policy makers and the media. Only recently, however, has much consideration been given to the unique problems presented by microplastics (5.0mm - 0.33mm) in aquatic habitats. The small size of these plastic particulates makes them difficult to study, and potentially more hazardous to marine and freshwater environments. Initial efforts to quantify microplastics have concentrated in marine environments; however, this study investigates microplastics load in freshwater bodies by sampling Lake Washington and the surrounding watershed. Water samples were obtained with flow meter-equipped plankton nets modified for accurate surface collection, and then processed using an oxidation reaction and visual inspection method developed by UW Tacoma. Concentrations in Lake Washington varied from 0.85 mg/m³ to 0.034 mg/m³ across three sampling sites spanning the length of the lake. Results suggest significant freshwater origins for microplastics found in the Puget Sound Basin (based on lake drainage into the Sound), underscoring the contribution of nonpoint sources to marine microplastic pollution.