Distribution Patterns Of Heavy Metals In Surface Sediments Of The Bohai Sea And The Yellow Sea And Ecological Risk Assessment

In order to assess the heavy metal pollution in surface sediments, the distribution of seven heavy metal elements were determined in sediments at 135 sampling stations in the Bohai Sea and the Yellow Sea. Grain size of surface sediments of the study area was determined and the characteristics of the surface sediments were analyzed. The contents of TOC of surface sediments of the study area were also determined. In order to research the impact and control factors for the distribution of heavy metal elements, correlations analysis of heavy metal elements, the correlation of contents of heavy metal elements with grain size, contents of TOC and terrigenous inputs were discussed. The level of pollution and ecological risk attributed to heavy metals was evaluated using single factor method, geoaccumulation indexes method and potential ecological risk index method.The surface sediments of the Bohai Sea were mainly consisted of clayey silt, sandy silt, silty clay and silty sand; the surface sediments of the middle and north areas of the Yellow Sea were consisted of clayey silt, silt and sandy silk.The average contents (mg/kg) of heavy metal elements in surface sediments of the Bohai Sea followed the order:Zn (54.47)> Cr (34.87)> Pb (20.78)> Cu (18.75)> As (5.59)> Cd (0.27)> Hg (0.07). The contents of heavy metal elements were relatively higher in the Bohai Bay and the Liaodong Bay, while relatively lower in the middle area of the Bohai Sea. The average contents (mg/kg) of heavy metal elements in surface sediments of the middle and north areas of the Yellow Sea followed the order:Zn (44.16)> Cr (37.85)> Pb (18.37)> Cu (17.69)> As (5.52)> Cd (0.17)> Hg (0.04). The contents of heavy metal elements were relatively higher in the Shandong Peninsula inshore area and lower in the offshore area.Correlation analysis results showed that heavy metal elements, except for Hg, had positive correlation with TOC contents, indicated that TOC was a control factor for the distribution of heavy metal elements.The results of single factor method showed that the mean single factor value of heavy metal elements of the surface sediments was less than 1, heavy metal elements of Hg, Cu, Pb, Cd, Cr, Zn in several sampling stations were in medium pollution level, the 38 sampling station in the Jinzhou Bay was in high pollution level. Results showed that the studying area was not contaminated or slightly contaminated by heavy metals.The results of geoaccumulation indexes method showed that Cu, Cd, Cr, Zn, As were in pollution-free level, Pb was in mild pollution level, Hg was in medium pollution level of surface sediments of the Bohai Sea; Hg, Pd, Cr, Zn, As were in pollution-free level, Cu and Cd were in mild pollution level of surface sediments of the middle and north areas of the Yellow Sea.The results of potential ecological risk index method showed that the pollution degree of the heavy metals in the surface sediments of the Bohai Sea followed the order:Cd (16.12)> Hg (10.7)> Pb (4.16)> As (3.73)> Cu (3.12)> Cr (1.16)> Zn (0.68). The 38 sampling station in the Jinzhou Bay was in strong ecological risk level while other areas were in mild ecological risk level. The pollution degree of the heavy metals in the surface sediments of the middle and north areas of the Yellow Sea followed the order:Cd (10.16)> Hg (6.53)> As (3.68)> Pb (3.67)> Cu (2.95)> Cr (1.26)> Zn (0.55). The ecological risk level in the middle and north areas of the Yellow Sea was mild.