Occurrence and characteristics of microplastics across the watershed of the world's third-largest river.

While rivers as primary conduits for land-based plastic particles transferring to their "ultimate" destination, the ocean, have garnered increasing attention, research on microplastic pollution at the scale of whole large river basins remains limited. Here we conducted a large-scale investigation of microplastic contamination in water and sediment of the world's third-largest river, the Yangtze River. We found concentrations of microplastics in water and sediment to be 5.13 items/L and 113.9 items/kg (dry weight), respectively. Moreover, microplastic pollution levels exhibited a clear decreasing trend from upstream to downstream. The detected microplastics were predominantly transparent in color, with fibrous shapes predominating, sizes mainly concentrated below 1 mm and composed primarily of PP and PE polymers. Our analysis results indicated that compared to geographical and water quality parameters, anthropogenic factors primarily determined the spatial distribution pattern of microplastics. Moreover, the microplastic abundance in sediment upstream of the dam was significantly higher than that in the downstream sediment, while the trend of microplastic concentrations in water was opposite. Therefore, more effort is needed to monitor microplastic contamination and their ecological environmental effects of sediment before dams in future research.