Small microplastic particles dominate Yangtze River particulate pollution

Rivers serve as critical conduits for terrigenous plastics entering the sea. Although accurate estimation of plastic loading into the sea has been a global concern, the spatio-temporal variability of plastic particle flux is completely overlooked. Here we conducted annual field monitoring of plastic particle fluxes in the Yangtze River, accounting for both vertical and horizontal variations in plastic distribution within the estuary. We observed a ubiquitous presence but spatially and temporally heterogeneous distribution of microplastics at different sampling sites. Moreover, the abundance of microplastics gradually decreased with increasing water depth, and the central channel exhibited lower microplastic abundance compared to the left and right channels. Furthermore, consistent monthly trends in microplastic abundance were observed across different channels within the same water layer. Hydrological patterns were identified as the primary factors influencing the occurrence of MPs, with microplastic abundance decreasing as hydrological flow rates increased. In particular, the particle size and hydrological flow rate exhibited a positive correlation. Our calculations indicated an annual particle flux of 5.20×1015 microplastic particles. Notably, small microplastic particles constituted 74.6% of the total particle flux, posing a substantial threat to the marine ecosystem owing to their high toxicity and potential for ingestion.