DISTRIBUTION PATTERN OF HEAVY METALS IN SURFACE SEDIMENTS OF THE YANGTZE ESTUARY AND ADJACENT AREAS AND ITS ECOLOGICAL RISK

The concentration and distribution pattern of heavy metals of Cu,Mn,Pb,Zn,Cr,Fe,Hg,Cd in the surface sediments of the Yangtze estuary and its adjacent areas were studied.Hakanson index method was used to evaluate the pollution level of the heavy metals of Cu,Pb,Zn,Cr,Hg,Cd and their ecological vulnerability.It is found that the elements of Cu、Mn、Pb、Zn、Cr、Fe are distributed in a declined pattern from the coast to the offshore within the estuary and its adjacent areas.The contents of these heavy metals are,in general,higher in the Xiangshan County and Zhoushan Islands rather than in the northern part.Hg is higher in the southern estuary and declines from the west to the east,while Cd is high in the south but lower in the middle estuary.Ecological assessment proves that the major part of the surface sediment in the Yangtze estuary and its adjacent areas is slightly vulnerable except some sites which are in the rank of moderate ecological risk.The risk index of these heavy metals are in an order of CdHgCuPbCrZn.The heavy metals which might bring ecological danger to the environment within the estuary and its adjacent areas are firstly Cd and then Hg.According to the results of cluster analysis,we conclude that Xiangshan County and the offshore area out of the Yangtze Estuary up to the southwest of the Cheju Island are more vulnerable,and,therefore,more attention is required.