Evaluating non-point source microplastic pollution and its impact on biota in the Huron River

Contaminants of emerging concern (CECs), like microplastics and pharmaceuticals, are a growing threat to aquatic ecosystems across the globe. Microplastics can be transported into waterways through a myriad of sources, including point sources such as wastewater treatment plants (WWTPs) and nonpoint sources, such as runoff. Microplastics can act as vectors for other CECs, such as non-steroidal anti-inflammatory drugs (NSAIDs), into biota. The goal of this study was to evaluate 1) the importance of non-point sources of microplastic pollution to the Huron River, 2) if aquatic filter feeders ingest microplastics, and 3) how the interaction of microplastics and pharmaceuticals affect filter feeders. To address my first goal, I measured the microplastic load of the Huron River at Waterworks Park in Ypsilanti, MI, between September and November 2021 and May and August 2022 over a range of river discharge. There was a strong positive relationship between river discharge and microplastic load, suggesting that runoff is an important source of microplastic pollution to the river. To address my second and third goals, I conducted manipulative experiments exposing zebra mussels (Dreissena polymorpha) in microcosms to microplastics and pharmaceuticals in a factorial design. On average, mussels ingested 57.5 ± 35.2 MP/individual during the 24-day experiment. Results from this experiment indicate that exposure to microplastics, ibuprofen, and diclofenac for 24 days reduced mussel feeding rate in some treatments after 19-20 days but had no detectable effects on mussel growth and metabolism