Distribution, Sources and Risk Assessment of Microplastics in Sediments of an Urban Water Supply Reservoir, China

In freshwater ecosystems, previous studies on microplastics have been mostly focused on natural rivers and lakes, with limited consideration of urban water source areas. Sediments, recording the steady process of microplastics accumulation during a long period of time, can act as an important sink for microplastics. In this study, we investigated the distribution, characteristics and ecological risks of microplastic contaminants in sediments of a water supply reservoir of Hefei City (the Dafangying Reservoir). Meanwhile, the differences of microplastic concentrations in sediments between the rural and urban areas were also compared. The average microplastics abundance of sediments in rural areas was 83.20 ± 32.99 n/100g dry weight (dw), and 182.67 ± 72.21 n/100g (dw) in urban areas. The total microplastic concentrations were significantly higher in sediments of urban sites than that in rural sites (p < 0.01), which can be ascribed to more complex and diverse microplastic sources triggered by intensive anthropogenic activity in cities. Specifically, we also demonstrated significantly higher microbead abundance (p < 0.01) in urban sites, which may result from the widespread use of microbead in personal care products. Our results detected five shapes (fibers, debris, films, foams and microbeads) and seven colors (white, black, transparency, red, blue, green and brown) of microplastics in sediments of the Dafangying Reservoir, with fibers and transparency accounting for the dominant shape and color, respectively. Given the complexity and diversity of microplastics in urban areas, we exhibited a relatively higher abundance of microplastics in the Dafangying Reservoir than that in other rural larger reservoirs. According to the index of geoaccumulation, the sedimentary microplastics were assessed as moderately polluted. Our study provides valuable references for microplastic contaminants in urban water supply reservoir, and highlights the importance of microplastics assessment in aquatic ecosystems.