Distribution and enrichment of arsenic, cadmium, mercury, and nutrient elements in surface sediment of Shenzhen Bay

The characteristics of content, spatial distribution, enrichment, source, and ecological risk for arsenic (As), cadmium (Cd), mercury (Hg), nitrogen (N), phosphorus P), and organic carbon (OC) in surface sediment of Shenzhen Bay (Shenzhen, Guangdong, South China) were studied based on sediment samples obtained in 2020. The contents of As, Cd, Hg, TN (total N), TP (total P), and TOC (total OC) in the surface sediment of Shenzhen Bay were 16.46±3.78 μg/g, 0.26±0.10 μg/g, 0.110±0.044 μg/g, 947±281 μg/g, 631±214 μg/g, and 1.41%±0.41%, respectively. The contents of three heavy metals are relatively high outside the Shenzhen River estuary and along the coast of the Shekou Port. The contents of TN, TP, and TOC are relatively high in the inner bay. The inputs of human activities such as pollution discharges lead to the enrichments of TN, TP, As, and Cd in surface sediment. TN was enriched significantly throughout the entire bay, while other three elements were mainly enriched in the Shenzhen River estuary, the northern coast of inner bay and port area in the bay mouth. As and Cd might come from mainly vessel discharge, while TN and TP derived probably from coastal domestic sewage. The contents of As, Cd, Hg, and TOC in surface sediment were lower than China’s national Class 1 benchmark thresholds for sediment within most of the Shenzhen Bay, which means they could meet the current environment functional requirements for general industrial water use and coastal scenic tourism. However, As, TN, TOC and TP shall be paid with continuous attention as they may pose negative impacts on some sensitive benthos.