Overview of microplastic content in Lake Superior’s surface water, fish stomachs, and beach sand

Session: Poster Session

Roselynd Lin, Large Lakes Observatory, UMD, [email protected]
Kathryn Schreiner, Large Lakes Observatory and Dept of Chemistry & Biochemistry, UMD, [email protected]
Thomas Hrabik, University of Minnesota-Duluth, [email protected]
Brenda Lafrancois, National Park Service, [email protected]
Elizabeth Minor, University of Minnesota-Duluth, Large Lakes Observatory, [email protected]

Abstract

The abundance of microplastics are a growing problem for the environment, even in relatively pristine waters such as those of Lake Superior. In this study, microplastics found in surface water, fish stomachs, and beach sand samples were analyzed. Water samples collected during the spring and summer by Manta net were sieved, oxidized, density extracted, and counted by microscopy using a hot needle test, yielding a range of 22,000-70,000 plastic particles/km². Six Cisco stomachs were processed using oxidation and microscopy. Five stomachs contained microplastics (range: 2-18 microplastics; note: matching method blanks contained 1-7 microplastics). Samples of sand (481.3 cm², 1.4 cm depth) were taken from beaches in the Apostle Islands National Lakeshore. They were dried, sieved, and processed using density fractionation, filtration and microscopy. The most abundant plastic morphologies across all sample types were fibers and fragments. A subset of microplastic particles identified by melt testing was evaluated with attenuated total reflectance-Fourier-transform infrared spectroscopy and Pyrolysis Gas Chromatography Mass Spectrometry; these were mostly polyethylene and polypropylene. Each beach sand aliquot (200 grams) contained hundreds of fibers that did not melt during microscopic examination. The composition and source of these fibers remains unknown.