ASSESSMENT OF HEAVY METAL POLLUTION OF THE SURFACIAL SEDIMENT IN NORTHWESTERN BOHAI SEA

189 surfacial samples collected from the offshore area of north-eastern Bohai sea are analyzed for heavy metal elements, grain size and organic carbon (TOC) in this paper. The distribution pattern of the heavy metals and potential pollution levels are studied. Results show that the spatial distribution of As, Cr, Pb, Zn is more or less balanced, whereas the Cd, Cu, Hg are rather high. Low values of the spatial variation coefficients appear in the coastal waters of Changli, and high values occur in the coastal estuaries. In general, the coefficient decreases from northwest to southeast.Cu, Cr, Pb and Hg show a strong correlation with clay and TOC content of the sediment. Pearson correlation analysis suggests that clay is the main carrier of heavy metal elements, and the TOC is the second factor which plays significant roles in heavy metal pollution. Geological accumulation index (Igeo) evaluation shows that the nearshore areas of northwest Bohai sea are not polluted by heavy metals except a few places where slight pollution may occur. The heavy metal enrichment factor (EF), however, tells us another picture that the pollution of sediments in the study area is on a moderate level, significantly higher than that Igeo says, probably owing to the higher regional background used for calculation of the EF values.All the two methods used for evaluation of heavy metal element pollution confirm that Hg element pollution does exist in the coast estuaries to certain extent, and it is directly related to human activities. The pollutants are discharged into the rivers by human being, and then carried by rivers to the sea.