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Occurrence and characteristics of microplastics in urban rainwater runoff and in oysters from the Mississippi Gulf Coast
Proceedings of the 2023 Mississippi Water Resources Conference

Year: 2023 Authors: Cizdziel J., Wontor K.

Awareness of microplastics (MPs) as a global pollutant continues to grow among scientists, politicians, and the public. MPs are a diverse suite of contaminants that range in size from 1 μm to 5 mm and that occur in a variety of shapes. The Mississippi River acts as a conduit continually transporting plastic litter in runoff to the Gulf Coast where MPs accumulate and can affect susceptible organisms. Filter-feeding species, like oysters, are particularly vulnerable. The proportion of MPs in aquatic ecosystems stemming from urban runoff has grown with urbanization. Here we report our findings on MP pollution in runoff from parking lots and roads in Oxford, MS as well as in oysters (Crassostrea virginica) from the Mississippi Gulf Coast. We used a YSI ProSampler to collect rainwater runoff at set intervals during storm events, conducted a density separation to isolate MPs, and used stereomicroscopy and FTIR micro-spectroscopy to characterize the particles. We observed >150 MPs/L at the start of the rain event, with concentrations declining with time. Most MPs were fragments (~80%), followed by fibers (~18), and most (~80%) were <200 μm in size. MPs were mainly composed of polyethylene, polyester, polypropylene, polyvinyl chloride, and polystyrene. For oysters, locations inside bays near population centers had higher average concentrations. Oysters seem to accumulate more MPs on their external tissues than in their digestive system. MP concentrations in oysters was not correlated with oyster condition index. Further characterizing the types of MPs present in oysters may provide insight into likely sources of contamination at different sites. Overall, this work provides much-needed empirical data on the abundances and sizes of MPs in both urban runoff and in oysters from the Mississippi Sound, and suggests that lawmakers need to consider federal legislation to address MP pollution in river systems at a national level.

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