Heavy metals in the surface sediments of the northern portion of the South China Sea shelf: distribution, contamination, and sources

The concentrations of seven heavy metals (Cr, Ni, Cu, Zn, As, Cd, and Pb) in the surface sediments of the northern portion of the South China Sea (SCS) shelf collected between 2012 and 2014 were measured to assess the potential contamination levels and determine the environmental risks that are associated with heavy metals in the area. The measured concentrations in the sediments were 12.4–72.5 mg kg−1 for Cr, 4.4–29.2 mg kg−1 for Ni, 7.1–38.1 mg kg−1 for Cu, 19.3–92.5 mg kg−1 for Zn, 1.3–12.1 mg kg−1 for As, 0.03–0.24 mg kg−1 for Cd, and 8.5–24.4 mg kg−1 for Pb. These results indicate that the heavy metal concentrations in the sediments generally meet the China Marine Sediment Quality criteria and suggest that the overall sediment quality of the northern portion of the SCS shelf has not been significantly impacted by heavy metal pollution. However, the enrichment factor (EF) and geoaccumulation index (Igeo) clearly show that elevated concentrations of Cd occur in the region. A Pearson’s correlation analysis was performed, and the results suggest that Cr, Ni, Cu, and Zn have a natural origin; Cd is primarily sourced from anthropogenic activities, with partial lithogenic components, and As and Pb may be affected by factors such as varying input sources or pathways (i.e., coal burning activities and aerosol precipitation). Heavy metal contamination mostly occurred to the east of Hainan Island, mainly because of the rapid economic and social developments in the Hainan Island. The results of this study will be useful for marine environment managers for the remediation of pollution sources.