How the Yangtze River transports microplastic to the east China sea

Land transportation in the Yangtze River basin is an important source of microplastics in the East China Sea, so it is significant to clarify the source, fate and river-sea transition of microplastics. Taking the Yangtze River as the study area, the interpolation method was used to analyze the monthly changes of the microplastic load in the estuary, the input-output model was used to estimate the flux of microplastics into the sea, and the inflow process of microplastics was studied through correlation analysis. The results showed that: (1) The load of microplastics in the Yangtze River estuary varied with season, reaching the maximum in October, with a monthly load of 3.91 Gg; (2) The total amount of microplastics entering the sea in the Yangtze River basin was higher than the medium level, which was 7.02 Gg. Among them, tributary input was the most important source, accounting for 62.9%. Non-point and point sources were further subdivided into 11 categories, with the largest proportion of microplastics generated during vehicle trip. Spatially speaking, the microplastics transported in the midstream accounted for the largest proportion, accounting for 55.56%; (3) microplastics had a strong correlation with COD and TP, indicating that the inflow process of microplastics was similar to that of traditional pollutants, which were river retention, wastewater treatment plant removal, water consumption removal and inflow to the East China Sea. Although the proportion of the last one was only 8.05%, the ecological risk was still not negligible due to the huge amount.