Microplastic Occurrence Characteristics and Ecological Risk Assessment of Urban River in Cold Regions during Ice-Covered Periods

This paper focuses on the Harbin section of the Songhua River in the cold region of northern China. The occurrence characteristics and pollution level of microplastics (MPs) are explored in both the ice and water of urban inland rivers and estuaries during the ice-covered periods. The abundance of MPs in Majiagou ice averaged 324.4 ± 261.5 particles/L, and the abundance of MPs in Songhua ice averaged 65.0 ± 68.2 particles/L. In the water with different depths of Songhua, the MP abundance ranged from 1.0 ± 0.7 particles/L to 12.9 ± 9.4 particles/L, with an average of 5.6 ± 7.6 particles/L. The amount of MPs in ice is about 11 times that in water, where ice formation is mainly responsible for the decline in the MP abundance in aquatic environments. The abundance of MPs in urban inland rivers gradually increased from south to north, while that in the mainstream of the Songhua River showed an increasing trend from east to west. Detected MPs were mainly fiber and white in shape and color, respectively, with a particle size < 0.5 mm. The extent of microplastics in ice is greater than that in water, and melting in the following spring will exacerbate the environmental impact. The results identified the discharge of domestic sewage as the main source of MPs in urban inland rivers. Polyethylene, polypropylene, and polyacrylonitrile were the main types of polymers. The results of the ecological risk assessment showed that the MP pollution in the Harbin section of the Songhua River reached moderate and severe pollution levels during the ice-covered periods. Its potential risk should receive more attention, and control should be strengthened.