Neglected Microplastics and Their Risks in Rivers Throughout the Three Gorges Reservoir Area

Microplastics have become a global environmental issue, and this challenge has also emerged in river environments. In this study, the Three Gorges Reservoir (TGR) was selected as the research area, and microplastics in water and sediments were chosen as the objects. The occurrence characteristics of microplastics were presented in rivers of the TGR through the methods of field sample collection and laboratory testing, and the risks of microplastics were evaluated using the pollution risk index (PRI) and potential ecological risk index. The results showed that the average abundances of microplastics in water and sediments of the rivers from the TGR were 15,464 particles/m³ and 1838 particles/kg, respectively. Furthermore, the main colors of microplastics in water and sediments of the TGR were black and blue, and the particle sizes were concentrated in the range of 200 to 500 μm. Polypropylene and polyethylene were the major polymers of microplastics in the water of the TGR, while the polypropylene-polyethylene copolymer was dominant in sediments. The PRIs in the water of the Yangtze River and its tributary from the TGR area were 2.45 and 1.72, respectively, and their PRIs were 2.43 and 2.01 in sediments, respectively, showing a low risk of pollution (level I). The average comprehensive potential ecological risk indices (RIs) for the Yangtze River and its tributaries were 27.28 and 18.82 in the water of the TGR, respectively, indicating low and moderate risk grades. However, there was a significantly high risk in sediment, and the average RI was 130.57 for the Yangtze River and 70.05 for the tributaries. Importantly, the neglected risks of microplastics in the river environment of the TGR area have been revealed, which provides a critical basis for the prevention and control of microplastic pollution here.