Modes of occurrence and bioavailability of Cd in soils of the urban-rural integration area

Abstract：Characteristics of chemical forms of Cd in soils of the Urban-Rural-Integration-Area (URIA) in Chongqing were studied by using the sequential extraction method. Relations between the forms of Cd and the extent of metal accumulation in the asparagus lettuce were analyzed. The results show that the soils and the asparagus lettuce in the study area have been heavily polluted, and that different forms of Cd in soils are distributed in order of RES > ORG > EXC > CAB > OXI> WS, with the active exchange state Cd accounting for a relatively large proportion. The major factors affecting the chemical forms of Cd in soils are physical clay and powder content. Regression analysis shows that Cd in the EXC form has relatively high bioavailability. The Cd pollution in soils and vegetables has become rather serious in the study area，and thus this paper suggests the strengthening of the environmental management in the URIA.