Distribution of Microplastics in Freshwater Mussels across a Watershed

Microplastic research is an emerging field of study, and we do not yet fully understand the scope or effects of microplastic pollution. Microplastics are ubiquitous in the environment, but the field suffers from a lack of unified, accessible protocols and an ecosystems approach to evaluating microplastic contamination. During autumn 2020, we collected water, mussel, and sediment samples from five sites along the Yadkin–Pee Dee River Basin, North Carolina. These samples were digested, filtered, and analyzed for microplastic particles. We found significant differences in microplastic particles in water, mussel tissue, and sediment samples among sites. Low microplastic concentrations at the upstream site and high concentrations at the downstream site contributed to these differences. Water sample microplastic concentrations were positively correlated with drainage area, and sediment concentrations were negatively correlated with elevation. Mussel microplastic concentrations were negatively correlated with weight but were positively correlated with drainage area. These results reveal that microplastics do not always move readily between water, biota, and sediment. Our study highlights the need for a standardized and accessible protocol that can be used to process and analyze samples of water, sediment, and biota. The protocol we developed was effective and relatively low-cost; it may facilitate microplastic research in understudied regions and provide results that are more readily comparable across studies.