Microplastic Hotspots in the Snake and Lower Columbia Rivers: AJourney from the Greater Yellowstone Ecosystem to the PacificOcean

摘要

It is widely understood that microplastics (MPs) are ubiquitous in the marine environment yet less is known about MP abundance in freshwater rivers, particularly those of the western United States. This study documents MP pollution along the Snake River (~1735 km) and from its confluence with the Columbia River to the Pacific Ocean. Grab and plankton net samples (mesh size 100 μm) were collected from the top 25 cm of surface water every 80.5 river km. MPs were identified if they met visual criteria and were verified with the hot needle test. A small representative subset of MPs from the net samples (16.7%) were selected based on appearance for micro-Raman spectroscopy in effort to provide examples of polymer types found in this study. Seventy-five percent of grab samples and 92.8% of net samples contained MPs, with concentrations ranging from 0 to 5.405 MPs L⁻¹ and 0 to 0.014 MP L⁻¹ (0 to 13.7 MP m⁻³), respectively. The majority of fragments, films and beads were between 100 μm-333 μm. This study identifies potential hotspots of MP pollution along the Snake and Lower Columbia rivers and prioritizes areas where more intensive sampling is needed. Sites with low flow or those further down river had higher numbers andthe top two hotspots were located in areas with low population density but highagricultural use. Monitoring MP abundance in freshwater systems is important forestablishing baseline levels of MP pollution and can direct laboratorytoxicology studies in using more environmentally relevant concentrations for abetter indication of how MP pollution affects ecosystems.