PELLETS AND FRAGMENTS ARE MOST COMMON MICROPLASTICS ON THE LAKE MICHIGAN BEACHES OF INDIANA

The presence of microplastics in marine coastal environments has been a concern since the mid to late 1970s, however it was not until recent years that much thought had been given to microplastics within the Great Lakes environment. The objective of this study is to expand on our previous work determining the amount and types of microplastics found along Indiana beaches of Lake Michigan and how these quantities compare with microplastics from beaches of the other Great Lakes. We used four methods – 1) volume reduced, swash line (5 m²) collection, 2) bulk sampling of quadrats (625 cm²) perpendicular to shoreline, 3) by area using lines perpendicular to transect line parallel to shoreline, and 4) by area using 1 m² bins – to determine amount of microplastics on five Lake Michigan beaches (Dunbar, Porter, Portage Lakefront, Marquette, and Whihala). Collection of microplastics was done in all seasons, both during stable weather and following storms. Generally, westernmost beach, Whihala, contained largest amount of microplastics, and easternmost beach, Dunbar, contained the least amount of microplastics. Microplastic (< 5mm) was classified into five categories: film, foam, fragments, fiber (line) and pellets (beads). The most common type of microplastic found along the southern Lake Michigan shoreline was pellets (44%), followed by foam (42%), fragments (12%), film (0.66%) and line (0.44%). The beach with largest amount of microplastic was Whihala with an average of 46.96 particles per m². The beach with the least amount of microplastic was Porter with only 10.49 particles per m². The average amount of microplastic per m² along the five beaches is 25.12. This is five times higher than that found on Lake Huron shoreline (5.43); it is even higher when compared to beaches of Lakes Ontario, Erie, and St. Clair. It is important to point out that factors such as plastic density, proximity of major ports, as well as natural factors such as littoral drift direction and proximity of lake tributaries, may cause variations in quantities amongst the beaches. This study will contribute to the growing body of knowledge on microplastics presence within the Great Lakes, an important part of communicating the problem to the general public, as well as addressing it.