Application of Sequential Extraction of BCR to Forms Distribution of Heavy Metals in Polluted Black Soil

State and mobility of Cadmium(Cd),Lead(Pb),Copper(Cu) and Zinc(Zn) pollution were investigated at different depths of polluted farmland black soil,and the application of the BCR sequential extraction was studied.The results showed that the mobility order of the heavy metals is CdCuPbZn.Cadmium occurred more abundantly in mobile fraction than did the other elements.The concentration of Pb in the acetic acid extractable fraction,as well as the concentration of hydroxide-bound fraction of Pb,Cu near the roadsides and Cd,Pb and Zn in the suburb all increased with the depth of profiles,indicated some downward movement of heavy metals.The concentrations of organically-bound fraction of the heavy metals in most of sampling area were all higher in the plow layer,which indicated the accumulation of heavy metals of this fraction in the surface layer.The results showed that application of sequential extraction of BCR was useful in assessing the pollution and movement of heavy metals in soil.