Electronic Thesis and Dissertation Repository

Thesis Format

Monograph

Degree

Master of Science

Program

Geology

Collaborative Specialization

Environment and Sustainability

Supervisor

Corcoran, Patricia L.

Abstract

Understanding plastic pollution in the Laurentian Great Lakes system requires investigation of all plastic debris sizes and categories. Visible polymeric debris (VPD) mainly characterize shorelines, and microplastics (MPs;mm) are found in benthic and beach sediment. Field sampling of VPD from all five Great Lakes, visual and chemical identification of VPD types, and implementation of a matrix scoring technique (MST) indicate that plastic industries, urban areas, and shoreline recreation are major sources of VPD. Sampling for MPs in the St. Clair system, followed by preliminary density separation, and microscopy, suggest that wastewater treatment plants are a major source. This work is the first freshwater study to use an MST and the largest published lacustrine VPD study. The results should encourage industry, policy makers, and the general public to work towards a circular economy.

Summary for Lay Audience

The Laurentian Great Lakes and their tributaries are major sinks for plastic debris. Visible polymeric debris (VPD) were sampled from 66 beaches across all five Great Lakes. All VPD were categorized, and multiple determinations and analyses were made based on the characterizations. In total, 21,595 VPD items were collected. Plastic pre-production pellets, attributed to the plastics industry, were characterized as a part of a separate, published study. These pellets were the most abundant VPD, accounting for 12,595 items or 58.3% of the total count.

Detailed, multi-step characterizations of all VPD items were performed by morphology (e.g. film, fragment, textile, pellet), colour, size fraction (micro: 1-5 mm; meso: 5-25 mm; and macro: >25 mm), and whether the item was intact. When appliable, VPD were described by item use (e.g. pen), polymer (e.g. polystyrene), and other materials present (e.g. aluminum). Polymers were identified through a variety of methods including physical identification and known usage in conjunction with a spectrometer. This study represents the first to use multiple identification methods supplemented with spectroscopy for polymer determination. Branded items were assigned to parent companies, and country of origin (US or Canada) was determined when possible, whereas multiple categorization schemes were applied based on item use. The top 50 ranked items, excluding pellets, were scored with a matrix scoring technique (MST) to determine the probable origin of VPD from three general sources – shoreline recreation, sewage related debris (urban sources), and agriculture. It was determined that VPD in the MST mostly originated from shoreline and urban sources, whereas pellets originated from the plastics industry. Additional evidence, including the presence of shotgun wads/gas seals and intact cigarette butts on beaches, points to a strong influence of local sources.

Additionally, microplastics were sampled from St. Clair system benthic sediment and beach sediment. Although this research is ongoing, potential microplastic concentrations from benthic sediment samples are within the range reported from other Great Lakes samples. The results from this study should encourage a move towards a more circular economy and provide a basis for future methodology for VPD characterization and sourcing.

Creative Commons License

Creative Commons Attribution 4.0 License
This work is licensed under a Creative Commons Attribution 4.0 License.

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