The fate of microplastic pollution in the Changjiang River estuary: A review

Plastic pollution is currently one of the environmental pollution issues of global concern, and microplastics (plastics with a size <= 5 mm) have also attracted much attention due to their large specific area, higher pollutant adsorption capacity, and higher migration performance. As the population increases and more chemical products are manufactured, the level of microplastic pollution continues to increase. Microplastics discharged from sewage treatment systems will enter the ocean and rivers, so estuary ecosystems are vital to controlling marine microplastics. As the estuary of China's most significant river entering the East China Sea, the Changjiang River Estuary has become one of the typical areas for microplastic research in estuaries. This paper systematically reviews the sources, hazards, and impacts of microplastics in the Changjiang Estuary. Firstly, the research on microplastics in the Changjiang Estuary was analyzed, and we found that the bioaccumulation, removal, and interaction with microorganisms of microplastics have become a new research hotspot. At the same time, the current abundance of microplastics in the surface water of the Changjiang River Estuary is 1.71 +/- 3.12 MP/L, which is lower than that of the Changjiang River area and the river farmland in Shanghai, but still higher than the 0.22 +/- 0.27 MP/L in the area adjacent to the East China Sea. Microplastics smaller than 1000 mu m accounted for 68% of the total, while transparent, white, blue, and black were the primary colors of microplastics in the Changjiang Estuary. In addition, polyethylene and polypropylene are the primary materials of microplastics in the central Changjiang River Estuary and related water bodies, and fibers are the main shape of microplastics. Industry, agriculture, domestic sewage, and air deposition may be the primary sources of microplastics in the Changjiang Estuary. The numerous lakes and water conservancy facilities in the Changjiang River Basin can reduce the number of microplastics reaching the Changjiang Estuary to a certain extent. At the same time, seasonal rainfall and ocean currents will affect the abundance of microplastics in the surface waters of the Changjiang River Estuary. Finally, this paper puts forward relevant suggestions based on the actual situation of the Changjiang River Estuary and the developed microplastic treatment technologies. This article will provide a structured reference for future research on microplastics in the Changjiang Estuary and assist in assessing microplastics' impact on the ecological environment.