Microplastics and Polycyclic Aromatic Hydrocarbons: Abundance, Distribution, and Chemical Analyses in the Nash Run, an Urban Tributary to the Anacostia River (Washington, DC, USA)

Microplastics (small plastic particles < 5 mm, MPs) are an emerging pollutant of concern as they are found in the water and sediment of aquatic habitats. Polycyclic aromatic hydrocarbons (PAHs) are persistent organic pollutants which tend to accumulate in aquatic sediments and may be associated with MP degradation. Urban streams have a large impact on these pollutant budgets of large rivers and marine areas. Up to today, there are just a few studies performed on MPs and PAHs together in river systems. MPs and PAHs were investigated to study their abundance and spatial distribution in the Nash Run, a tributary of the Anacostia River in Washington, DC, USA. A chemical characterization of the MPs in the sediment samples was also performed. The total MP concentration ranged from 24 to 127 MP particles/L in water samples. In the sediments, the MP concentrations varied from 0.35 to 4.1 MP particles/g showing a correlation to distance from roadways. Chemical MP analysis revealed that high-density polyethylene (HDPE) was the main chemical MP composition and chemical additives were also identified. Three PAHs, phenanthrene, fluoranthene, and pyrene, were observed in the sediment samples. These PAHs (commonly associated with microplastics) showed a higher concentration than those often occurring in sediments of similar freshwater environments. This is the first study that shows the presence of MPs in both water and sediment and the presence of specific PAHs in sediment at the same sites in a Washington, DC freshwater system.