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UBC Theses and Dissertations

Urban discharge and fate of microplastics : characterizing the role of combined sewer overflows and microplastics in the Fraser River in British Columbia Parizi, Amir Hossein


Over the past few years, microplastics (MPs) have emerged as contaminants of global environmental concern, but important questions remain regarding their source, transport and fate. Because of their complexity, quantification and identification of MPs remain a major analytical challenge. The goals of this study were to examine the importance of Combined Sewer Overflows (CSOs) as one of the pathways for MPs to urban watersheds, and the fate of urban MPs in the receiving waters. In addition, a new statistical protocol to guide efficient and accurate analysis of MPs was also developed. Focusing on the Vancouver metropolitan area, this study provides novel data on MPs in CSOs in Canada and in the Fraser River, BC – a major river in western North America. MPs were detected in all CSOs and the Fraser River samples, ranging in concentration from 1,833─13,673 MPs/m³ and 4─30 MPs/m³, respectively. A preliminary assessment of the annual emission rates of MPs by the two CSOs under study was carried out, with values ranging from 0.82 to 14.6 × 10⁹ MPs/year. This implies that CSO emissions of MPs require further research and should not be overlooked in management strategies. The much lower concentrations of MPs in the receiving waters of CSOs and significantly shorter fibers suggest a complex fate, which may involve mixing with other sources, sinking and/or rapid dilution upon entry to the environment. This research also suggests that the Fraser River is an important conduit for MPs to the Strait of Georgia, given the estimates of 0.67─3.35 trillion annual microparticles flux derived in this study. While the dimensions, polymer types, and shapes of MPs varied in space and time, synthetic fibers were most common (58─78% in CSO samples and 76─86% in river samples) and were dominated by polyester. Fibers emitted with CSOs had a median width of 24 µm, which is consistent with the average width of textile fibers. Fragments were also present and comprised mostly of polyethylene in both CSOs and river samples (0─70%). This study helps better understand the sources and transfer of MPs in urbanized watersheds, with management strategies and other solutions are also discussed.

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