CHEMICAL FRACTIONATION OF CADMIUM, COPPER, NICKEL, AND ZINC IN CONTAMINATED SOILS

Heavy metals are potentially toxic to human life and the environment. Metal toxicity depends on chemical associations in soils. For this rea son, determining the chemical form of a metal in soils is important to evaluate its mobility and bioavailability. Sequential extraction was used to fractionate four heavy metals (Cd, Cu, Ni, and Zn) from nine c ontaminated soils into six operationally defined groups: water soluble , exchangeable, carbonate, Fe-Mn oxide, organic, and residual. The res idual fraction was the most abundant pool for all four metals examined . A significant amount (2.4-44%) of Zn was present in the potentially available fraction: nonresidual fraction. A major portion (40-74%) of Cu was associated with the organic, Fe-Mn oxide, and carbonate fractio ns in most of the soils. Contamination of Cd and Ni in these soils was not as severe as Zn and Cu. Assuming that mobility and bioavailabilit y of these metals are related to their solubility and geochemical form s, and that they decrease in the order of extraction sequence, the app arent mobility and potential bioavailability for these four metals in the soils were: Zn > Cu > Cd > Ni. Metal distributions in different ch emical fractions in these soils depended on respective total metal con centrations, except for Zn.