Substantial burial of terrestrial microplastics in the Three Gorges Reservoir, China

Small microplastics are preferentially retained in Three Gorges Reservoir sediments and the dam likely substantially reduces the microplastic flux in the Yangtze River, according to sedimentary analyses from the upper and lower reaches of the Three Gorges Dam, China between 2008 and 2020. Hydropower dams impact the transport of microplastics from rivers to the ocean. The Yangtze River is a large source of plastics to the ocean. Here, we report microplastic concentrations and compositions across a range of size fractions for sediment samples collected in the upper and lower reaches of the Three Gorges Dam in 2008, 2015, 2019 and 2020. We find a gradual increase in microplastic abundance over time, with preferential retention of small-sized (<300 mu m) microplastics in the dam reservoir sediments. Small microplastics accounted for between approximately 44 and 90% of identified microplastics, and 82% of all polyethylene particles, which were the dominant polymer type. Our estimate of the total plastic mass load in reservoir sediments suggests that the Three Gorges Dam retains as much as 8048 +/- 7494 tons yr(-1) microplastics in sediments, which is equivalent to 47 +/- 44% of the Yangtze River microplastic flux to the ocean.