Microplastics in Sediment Samples of Nash Run, Urban Tributary to the Anacostia River

Microplastics (small plastic particles <5mm) are an emerging pollutant of concern, especially in freshwater environments where they are relatively understudied in comparison to marine environments. Microplastics are ubiquitous in the environment and found in the water and sediments of aquatic habitats due to human disposal of plastics and inadequate waste management. Plastic contains complex mixtures of additives, monomers, and oligomers. These additives are weakly bound to the core polymer of the plastic and will leach from the plastic over time in the environment. Therefore, sediment composition, geochemistry, water quality, and fauna may be affected by microplastics as the sediments serve as a sink for more dense plastic particles. Identifying microplastic sources, fates, and interactions with the environment is imperative in understanding the consequences and management of microplastic pollution. Nash Run, a small tributary in a high-density urban neighborhood in Washington, D.C., is the subject of monitoring and restoration. This waterway acts as a model to show how land based-pollution enters the Anacostia River, and subsequently the Chesapeake Bay. Our study aims to determine the concentrations and distributions of microplastics in Nash Run sediment samples across eight transects over three seasons. Microplastics are identified and counted using dry sieving and microscopy and then classified according to the NOAA Marine Debris methods. Then, microplastic particles are extracted from the sediment samples for additive and polymer analysis using Thermal Desorption and Pyrolysis GC/MS. Preliminary results show significant differences in microplastic concentrations between transects and no significant changes in concentrations over the three seasons. Microplastic concentrations range from 0 to 148 MPP/g sediment with higher concentrations in sediment samples collected from transects closer to urban activity. The quantification of microplastics and possibly the identification of their sources in Nash Run will provide useful information for future research in the Anacostia Watershed and add to the existing data of microplastics in the Chesapeake Bay.