Micro and Nanoplastic Aggregation and Deposition in Subsurface Environments

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The widespread production, use, and disposal of plastic products has led to the release of plastic wastes into the environment. Plastics are "aged" by weathering processes and break down to smaller pieces including microplastics (MPs) (100 nm-5 mm) and nanoplastics (NPs) (<100 nm). MPs/NPs are harmful to aquatic organisms, human health, and ecosystems due to their physical hazards and chemical toxicity. To evaluate the environmental impacts of MPs/NPs, understanding the fate and transport of these emerging contaminants is essential. Aggregation (particles attach to each other to form large aggregate) and deposition (particles attach to transport media) are among the most important processes influencing the fate and transport of MPs/NPs in subsurface environments. The properties of MPs/NPs, water chemistry, and mineral and organic composition of transport media are expected to significantly influence MPs/NPs aggregation and deposition. Yet, most studies have examined only pristine polystyrene MPs/NPs but not the polyethylene or polypropylene MPs/NPs that are more abundant in the environment. "Aging" alters MPs/NPs (e.g., shape and size) and how this may influence their environmental behaviour is largely unknown. Moreover, most investigations use artificial electrolyte solutions with simple composition as background solution, and clean quartz sand columns as transport media to study MPs/NPs aggregation and deposition. MPs/NPs behaviour in these model solutions may not fully represent that in natural water that contains multiple interacting components. Also quartz sand is not a good proxy for the complex composition of natural soils. The short-term objective of my research program is to fill these knowledge gaps by carrying out experiments to investigate MPs/NPs aggregation and deposition under environmentally relevant conditions. A variety of polyethylene, polypropylene, and polystyrene MPs/NPs with distinct properties will be prepared, "aged", and characterized. The aggregation of the MPs/NPs in artificial electrolyte solutions, and in soil solutions with complex compositions will be systematically investigated. MPs/NPs deposition will be examined using columns packed with natural soils or mineral mixtures to determine the effect of individual and multiple natural components. Regression methods, theoretical calculation, and mathematical modeling will be used to analyze the experimental results. The knowledge gained on MPs/NPs aggregation and deposition under environmentally relevant geochemical conditions will enable more accurate prediction of the environmental behaviour of MPs/NPs, which helps industries and governments establish proper practices and guidelines for tackling the negative environmental impacts of plastic wastes. Furthermore, the proposed research will provide well-rounded and high-quality training, which will contribute to the creation of a top-notch Canadian scientific workforce.