COVARIANCE OF PARTICLE SIZE AND SHAPE OF MICROPLASTIC POLLUTANTS TRANSPORTED TO TERRESTRIAL DUNES FROM THE SHORES OF LAKE ERIE AND LAKE ONTARIO, NY AND PA

Geologic study of microplastic pollutants is in its infancy. Microplastics are plastic particles that are <5 mm in size and occur in three main forms: spheres/disks, fragments, and fibers. Previous studies have focused on terrestrially produced microplastics in aquatic systems, whereas landward transport of microplastics to terrestrial dunes on the Great Lakes has been documented only recently (Costello and Ebert 2016).

Sediment samples were collected and analyzed from terrestrial dunes along the shores of two Great Lakes, Erie and Ontario, in New York and Pennsylvania. Two samples were collected from each location: surface samples and shallow sub-surface samples (1 m²). Sixteen samples from five locations were collected along Lake Erie: Sunset Bay, Dunkirk Harbor, Point Gratiot, Presque Isle State Park (PA) Beach #11, and a dune located near the mouth of Canadaway Creek, Dunkirk, NY. At Sandy Island Beach State Park on Lake Ontario, 6 samples were taken, along three points in the dunes. Standard textural analyses were performed on each sample. Microplastics >1mm were picked by hand. Microplastics <1mm were separated by density with a dilute lithium metatungstate solution. Organic matter in the <1.5 g/mL fraction was digested in a solution of Fe (II) and Hydrogen Peroxide (H₂O₂) to ease observation of microplastics.

Onshore winds entrain microplastics from beaches and deliver a wide range of particle sizes and all known microplastic shapes to terrestrial dunes. Samples from Sandy Island Beach and Presque Isle State Park Beach #11 (PA) had the most abundant microplastics with 3-4 spheres and disks per m² (sizes >1mm). These spheres and disks are, on average, 1.5 to 2.0 phi coarser than their corresponding siliciclastic modes. Most microplastics <1mm are fragments and fibers. Thus, particle shape and grain size of microplastics correlate. The origin and detailed textural attributes of these fragments and fibers await further study.

Although the ecological ramifications of microplastics in lacustrine and marine ecosystems have been investigated, the impact of these pollutants in terrestrial ecosystems is completely unstudied. The widespread presence of microplastics in terrestrial and aquatic environments suggests that these pollutants may become significant stratigraphic markers in the future rock record.