The effect of urban point source contamination on microplastic levels in water and organisms in a cold-water stream

We examined the influence of point and nonpoint source contamination on microplastic (MP) levels in water, macroinvertebrates, and trout in a small, cold-water stream in western Wisconsin, U.S.A. We collected samples along an urbanization gradient centered around a 6-mile corridor that receives numerous MP inputs from stormwater outfalls and a wastewater plant. We digested samples using a wet peroxide oxidation method. Particles filtered from digestates were stained with Nile Red dye, then viewed using fluorescence microscopy. We quantified fluorescing MPs using ImageJ software. MP concentrations in water increased significantly from upstream to downstream reaches and appeared to influence organism MP levels. Macroinvertebrates and trout collected upstream of the city had significantly lower MP levels than macroinvertebrates and trout collected within the city, and for trout, downstream of the city. MP particle lengths were significantly longer in macroinvertebrates compared to water and trout, perhaps indicating preferential accumulation of longer particles from the water column.