Occurrence characteristics and ecological risk assessment of microplastics in Urban river in cold regions during ice-covered periods

Abstract

Abstract The ice-covered periods is a natural phenomenon where ice forms on the water surface of rivers in areas with high latitude and cold climate. Ice blocks the diffusion of pollutants, thus causing changes in water quality characteristics. 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 ice and water of urban inland rivers and estuaries during the ice-covered periods. The results identified the discharge of domestic sewage as the main source of MPs in urban inland rivers. The abundance of MPs in MaJiaGou average of 324.36 ± 261.45 item/L, the abundance of MPs in SongHua ice raverage of 65.02 ± 68.15 item/L, while in the water with different depths of SongHua, the MPs it ranged from 1.03 ± 0.66 item/L to 12.86 ± 9.35 item/L,average is 5.59 ± 7.57 item/L.The amount of MPs in ice is about 11 times that in water.Ice formation caused a decline in MPs prevalence within the aquatic environment primarily due to the inclusion of a relatively large proportion of MPs within the ice mass during freezing. Additionally, it restricted atmospheric MPs from entering the river waters, contributing to the decrease.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 fibrous and white in shape and color, respectively, with a particle size < 0.5 mm. The fragmentation of micro plastics in ice is greater than that in water. Polyethylene, polypropylene, and polyacrylonitrile,etc were the main types of polymers. The results of ecological risk assessment showed that the MPs 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. The research results have important reference significance for providing basic information for river pollution control and ecological protection in cold regions, providing a new direction for future research. In the future, more attention should be directed to the transfer and toxic effects of environmental MPs.