Spatial Distribution and Contamination Assessment of Surface Heavy Metals off the Western Guangdong Province and Northeastern Hainan Island

Surface sediments collected from the continental shelf off the western Guangdong Province and northeastern Hainan Island are analyzed for selected heavy metals contents including Cd, Cr, Cu, Pb, Zn, and As to determine spatial distribution, potential ecological risks, and sources. In addition, some of the controlling factors of heavy metals distribution are also discussed. The average heavy metals contents decrease in the order of Zn > Cr > Pb > Cu > As > Cd. The averaged pollution degree, as shown by the index of geo-accumulation (I_geo), decreases in the order of Zn > Cu > Pb > Cr > Cd > As. Due to the barrier of islands, the I_geo values of Zn, Pb, Cr, Cu, and Cd near the Hailing and Xiachuan Islands are larger than those in other areas. Meanwhile, the I_geo value of As near the coastal area off the estuary of Wanquan River is clearly larger than that in other areas. Based on the results of potential ecological risk index, Cd, Cu, and As should be paid more attention for the contamination risk in future. The results of Pearson correlation analysis and principal component analysis indicate that Zn, Cr, Pb, Cu, and Cd are mainly from the Pearl River and surrounding small rivers, whereas As originates from the Hainan Island. The grain size is one of the main controlling factors for heavy metals distribution, and the anthropogenic activity also plays an important role.