Comparison of the distribution and degradation of plastic debris along shorelines of the Great Lakes, North America

The distribution patterns, compositions and textures of plastic debris along the Lake Erie and St. Clair shorelines were studied in order to determine the roles of potential source locations, surface currents, and shoreline types in the accumulation of plastic litter. The results were compared with those previously determined from Lake Huron, where abundant plastic pellets characterize the southeastern shoreline. Lake Erie and St. Clair shorelines contained some pellets, but were mainly characterized by plastic fragments and intact products, respectively. The potential sources for the pellets include spillage within factories or during transport and off-loading; whereas intact products were derived from urban waste. Once entering the lake environment, low density floating polymers such as polyethylene and polypropylene were degraded by UVB radiation at either the water surface or once deposited on shorelines. Mechanical degradation by wave action and/or sand abrasion fragmented intact products into cm-size particles. Certain textures identified on the surfaces of plastic particles could be related to the nature of the depositional environment. Plastics sampled from infrequently visited muddy, organic-rich shorelines were characterized by more adhering particles and less mechanical pits than those from sandy shorelines. In terms of relative distribution, the Lake St. Clair shoreline contained the least amount of plastic debris of the three lakes. This is a function of the breakwaters and retaining walls built along Lake St. Clair, which replace natural sandy or muddy sinks for floating polymers. This study represents the first detailed record of plastics distribution along multiple, but related fresh water shorelines.