Microplastics Distribution, Ecological Risk and Outflows of Rivers in the Bohai Rim Region of China - a Flux Model Considering Small and Medium-Sized Rivers

Abstract

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 33 estuaries in the BRR was collected and analyzed to understand MPs distribution and ecological risk. The HDI-based MPs flux model was re-calibrated and its parameters were optimized to predict the MPs outflow in BRR. Our 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-3. While the pollution load index (0.42) is relatively low, the potential ecological risk of PVC in some areas warrants further attention. A strong correlation is achieved between modeled estimates and field measurements, with a regression coefficient of r2 = 0.74. The MPs outflow from the four provinces to the Bohai Sea is calculated to be 123.235 (range 44.415-242.314) T year-1. The Yellow River contributes more than half of it (65.16 T year-1), which is comparable to that of the Pearl River Delta (66 T year-1). 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.

Keywords: microplastics, Bohai Sea, Outflow, Ecological risk, Modeling