Occurrence of microplastics pollution in the Yangtze River: Distinct characteristics of spatial distribution and basin-wide ecological risk assessment

The widespread presence of microplastics (MPs) in the Yangtze River, the third longest river in the world, has drawn increasing attention. Although numerous studies have been conducted recently to investigate and analyze the MPs exposure to the surface water of the river, most merely focus on a certain part of the Yangtze River, and knowledge of MPs based on the basin-wide is still scattered. This article reveals the spatial distribution characteristics of MPs in the Yangtze River from the whole watershed scale. Among the five areas in the basin, the upstream and the midstream were demonstrated to contain more MPs (3598.6 particles/m and 3226.8 particles/m). The obtained results suggested the MP presented in the entire watersheds was uneven and the 'hotspots' occurred, where the MPs concentrations were relatively higher than the surrounding. The discharging of the wastewater treatment plants along the river, the locations of dams, and the stability and fragment of MPs, were demonstrated to be the important driving factors in the spatial distribution of MPs and leading to the appearance of the MP 'hotspots' in the Yangtze River, but were previously overlooked. It is the first study to evaluate the ecological risk of MPs exposure to the surface water of the Yangtze River with multiple assessment methods, taking not only abundance but also morphological characteristics, polymer composition and toxic effect into account. More importantly, based on the multiple individual MPs risk assessment methods, we developed the BetaMP method which achieves a comprehensive assessment of MP risk in basin-wide by taking multiple MP characteristics into account for the first time. This is conducive to better understanding the environmental impacts of MPs pollution in the different regions of the river.