Quantification and identification of microplastics in James River and York River, two tributaries of Chesapeake Bay

Microplastics are an emerging contaminant with potential negative effects on public and environmental health. Detection and quantification of microplastics are the first steps to evaluate the environmental risk of microplastics in an aquatic ecosystem. However, many major aquatic ecosystems, such as Chesapeake Bay, have few reports of microplastic concentrations. In addition, wastewater treatment plants’ (WWTPs) contribution to microplastic loading has not been examined in the Chesapeake Bay. This study aimed to quantify microplastics, identify common polymer types, and evaluate the impact of WWTPs as a point source of microplastics in the James River and the York River, two tributaries of the Chesapeake Bay. These rivers were chosen because land cover surrounding the James River is much more urban and industrial than that of the York River. We conducted surface water sampling at multiple locations along a salinity gradient in both rivers. In addition, the effluent of one WWTP in the York River and three WWTPs in the James River were sampled to estimate microplastic discharge. Particles from water samples were concentrated on filters and density separation was performed as needed. Organic matter was then removed from the concentrated samples through hydrogen peroxide digestion. A Nile Red staining method was used to detect and quantify microplastics (10µm-300µm), while Raman microspectroscopy was used to identify polymer types on a subset of samples. The York River had a range of 1,400 to 15,000 microplastic particles per liter (MP/L), significantly higher than the James River (700-9,000 MP/L). These concentrations are higher than previously reported, although there are few studies examining our size range. Primary polymer type in both rivers was polyethylene as expected due to its low density and prevalence in surface water. WWTP effluent contained a range of 1,200-5,500 MP/L. We identified WWTPs as significant point sources of microplastics to both rivers.