Occurrence, characteristics, and multiple ecological risks of microplastics in surface water-sediment system of the Yangtze River basin, China

Microplastics (MPs) pollution poses a significant threat to large river basins, yet a systematic assessment within the water-sediment system of the Yangtze River Basin (YRB) has been lacking. This work systematically analyzed and assessed the occurrence, distribution, and risks of MPs across four media within the YRB based on synthesized published data, employing both deterministic index and uncertainty probability methods: river water (RSW), lake/reservoir water (LRSW), and their corresponding sediments (RS and LRS). The average abundance was 2203.17 items/m 3 in surface water and 437.04 items/kg in sediments, showing correlated yet spatially heterogeneous patterns, with the Chengdu section of the Minjiang River and lakes in the middle and lower reaches of the YRB identified as significant pollution zones. Dominant MPs were small-sized (75.56%), transparent (39.75%), fibrous (57.75%) particles composed mainly of PP (37.25%) and PE (23.75%). Correlation analyses between influencing factors and MPs characteristics revealed that human activities distinctly affected MPs characteristics in each medium. Deterministic ecological risk assessment (DERA) indicated low pollution load and potential risk, but high polymer hazards. In contrast, the probabilistic ecological risk assessment (PERA) indicated that the overall probability of ecological risk in the YRB is relatively low, with high-hazard polymers contributing significantly to MPs risks, while also reducing the uncertainty associated with the DERA. This study systematically and scientifically revealed the ecological risk status of MPs in the YRB, providing the scientific basis for targeted management measures.