Occurrence and risk assessment of microplastics on the Shenzhen coast, South China

Microplastics (MPs) have attracted increasing attention worldwide owing to their widespread presence and potential risks to terrestrial and marine ecosystems. Estimating the pollution status and risk levels of MPs in coastal ecosystems is necessary; however, these are poorly understood in coastal megacities. Here, the abundance and characteristics of MPs in seawater, marine sediment, marine organisms, and beaches in the Shenzhen coastal ecosystems and land sources (river and sewage outfall) were simultaneously investigated, and the annual MPs load of rivers and MP-induced ecological risks were evaluated. The results showed that MPs pollution was prevalent in Shenzhen coastal ecosystems, with the average abundances of 2.40 ± 2.48 items/m³, 404.21 ± 431.48 items/kg, 1.66 ± 1.96 items/individual, and 1648.99 ± 1908.19 items/kg in seawater, marine sediment, marine organisms, and beach sands, respectively. The detected MPs were predominantly fibrous/granular, transparent/white, < 1 mm in size, and polyethylene terephthalate/polyethylene/polystyrene. The spatial distribution patterns of marine MPs are influenced mainly by anthropogenic activities and freshwater inflows (rivers and sewage outfalls). Pollution hotspots of MPs were identified in the Pearl River Estuary, which has a high population, gross domestic product, and river and wastewater discharge. Furthermore, the negative correlation between the abundance of MPs in seawater and salinity indicates that freshwater inflow carrying MPs to the sea is an important source of marine MPs pollution. It has been estimated that approximately 8320 billion MPs particles, weighing 274.55 tons, flow into the Shenzhen coast annually through river input. Based on the MPs polymer types and quantities, the ecological risk of MPs pollution in the Shenzhen coastal ecosystem is moderate and deserves further attention. These findings deepen the understanding of MPs pollution, sources, and ecological risks in the southern coastal region of China, and are helpful for employing effective management strategies to control marine MPs pollution.