Microplastics in the black-odor rivers in Harbin city, China: Abundance, characteristics, and ecological risk assessment

Microplastics (MPs) pollution has been found in natural water environments, but there are no studies on the presence of MPs in black-odor rivers. In this paper, the microplastics were initially identified by chemical digestion and microscopic identification, and then the abundance, characteristics and polymer types of MPs in water and sediment samples were identified by laser infrared spectroscopy. Then, the correlation of MPs and various environmental factors were examined, and discussed the source analysis, environmental impact factors, and potential ecological risks of MPs. Results showed that the microplastic abundance of the black-odor rivers in Harbin city was at an upper middle level. PET, PP, PE, PU and ACR were the major polymers. Fiber, transparent, and 50–100 μm were dominant shape, color, and size of MPs, respectively. Major sources of MPs in Dongfeng River and Hejia River were domestic sewage, sewage treatment plant effluent, and agricultural source. Microplastics abundance in surface water of black-odor rivers was inversely related to dissolved oxygen (DO) and positively related to the concentration of total organic carbon (TOC), ammonia nitrogen (NH₄-N), and phosphates (H₃PO₄). Indices of pollution load (PLI_river) and the hazard index (PHI_river) yielded a Hazard Level I and III for MPs pollution in black-odor rivers, respectively. Potential ecological risk of the composite MPs polymer (ERI_river) is at a medium to considerable risk level. Our findings established the first set of baseline data on MPs pollution in black-odor rivers which would improve the understanding of MPs fate and ecological risk in polluted rivers.