Sources and distribution of microplastics in the east China sea under a three-dimensional numerical modelling

Microplastics are new pollutants found in various environments; moreover, high concentrations of microplastics have been proved to harm aquatic organisms. To understand the high abundance of microplastics in the East China Sea (ECS), where the Zhoushan fishing ground is located, this study investigated the transportation and spatial distribution of microplastics from the Changjiang River Estuary (CE) to the ECS via three-dimensional numerical modelling. Utilising observations of microplastics at the surface of the ECS and backward particle tracking, three sources of microplastics were identified: the Changjiang River, Hangzhou Bay, and coastal area of Nantong city. Moreover, Southern Korea contributed to the microplastics in ECS. After microplastics are released from these sources, monsoons, currents, the Changjiang plume, and tides cause significant seasonal differences in the hot spots for microplastics in the ECS; moreover, the generation of ocean fronts may promote microplastic accumulation. In addition, the settling characteristics of microplastics were shown to influence their distributions; for example, large amounts of microplastics accumulated at the bottom of the riverbeds. This study enables a more complete assessment of microplastic transport from estuaries to the open sea and provides a spatial and temporal distribution of microplastics at the surface of the ECS.