Microplastics distribution, ecological risk and outflows of rivers in the Bohai Rim region of China - A flux model considering small and medium-sized rivers

Microplastics (MPs) pollution and its ecological risks have attracted increasing global attention. The Bohai Rim region (BRR), as the economic and population center of the entire northern China, still lacks a precise assessment of MPs pollution. Although current attention on MPs pollution mainly focuses on large rivers, small and medium-sized rivers are more numerous and more closely connected to human activities. In this study, measurement data of MPs from 11 estuaries in the BRR was collected to understand MPs distribution and ecological risk. The results indicate that the overall MPs pollution in these estuaries is still at a low level, with an average abundance of 1254.3 particles m. While the pollution load index (1.85) is relatively low, the potential ecological risk of PVC in some area (S8, E = 1433.78, III) warrants further attention. Then we integrated data from 22 relevant rivers (covering all size rivers) in this region from the literature to fit a MPs flux model and assessed the MPs outflow from the four provinces and cities in the region. A strong correlation is achieved between modeled estimates and field measurements (r = 0.74), which can well estimate the river MPs outflows in northern China such as the Nanfei River. The MPs outflow from the four provinces (cities) is calculated to be 123.235 (range 44.415-242.314) T year, of which Shandong accounted for >80 % (104.066 T year). The small and medium-sized rivers accounted for 47 % (58.08 T year), whose contribution to MPs outflows should not be underestimated. This study can help us to accurately assess MPs pollution in different coastal areas in northern China, benefiting the formulation of precise control measures and policies for marine MPs pollution.