Exploration of Microplastics in the Lower Puyallup River Watershed

Microplastics are polymers < 5mm, varying in shape, color, chemical composition, and density. Manufactured plastics are primary microplastics which include pellets, fibers, and microbeads. Secondary microplastics are plastics fragmented through photodegradation and/or mechanical weathering. Research has documented microplastics in high densities (e.g., 100,000 items per m3) in marine environments, but little work has been conducted in riverine environments. Our study is focusing on the Puyallup River Watershed, located in Washington State, and its role in microplastic transport. The Puyallup River and its two principal tributaries, the White River and the Carbon River, drain a watershed of approximately 1,040 square miles and stream from several glaciers located on Mount Rainier, including the Puyallup Glacier. During our preliminary research, samples were collected monthly, both upstream and downstream of municipal wastewater treatment plants, from five cities in the lower reaches of the Puyallup River Watershed. Fibers, fragments, and foams were identified, characterized and quantified. Only 1-foam and 5-fragments were found, with the majority being fibers. The concentration of fibers, ranged from 0 to 204 fibers/L, with an average of 22-fibers/L in each sample collected. Results were statistically inconclusive to determine if wastewater treatment plants were a point source of plastic pollution to the Puyallup River Watershed, although more fiber numbers were located upstream than downstream at most sites.