Pelagic plastic pollution within the surface waters of Lake Michigan, USA

During the summer of 2013, a total of 59 surface water samples were collected across Lake Michigan making it the best surveyed for pelagic plastics of all the Laurentian Great Lakes. Consistent with other studies within the Great Lakes, Mantra-trawl samples were dominated by particles less than 1 mm in size. Enumeration of collected plastics under a microscope found fragments to be the most common anthropogenic particle type, followed by fibers, with more minor contributions from pellets, films and foams. The majority of these pelagic plastic particles were found to be polyethylene, with polypropylene being the second most common polymeric type, which is consistent with manufacturing trends and beach survey results. The pelagic plastic was found to be fairly evenly distributed across the entire Lake Michigan surface, despite the formation of a seasonal gyre at the southern end of the lake. We found that an average plastic abundance of ~ 17,000 particles/km2, which when multiplied by the total surface area, gives on the order of 1 billion plastic particles floating on the surface of Lake Michigan. As the majority of these particles are extremely small, less than 1 mm in size, which allows for easy ingestion, these results highlight the need for additional studies with regard to the possible impacts upon aquatic organisms.