Chemical Partitioning of Cadmium, Copper, Nickel and Zinc in Soils and Sediments Containing High Levels of Heavy Metals

Abstract

Three soils and a sediment which had undergone prior massive additions of heavy metals were sequentially extracted so that Cd, Cu, Ni, and Zn could be partitioned into five operationally defined geochemical fractions: exchangeable, bound to carbonates, bound to Fe‐Mn oxides, bound to organic matter, and residual. Metal recoveries were within ± 10% of the independently measured total Cd, Cu, Ni, and Zn concentrations. The highest amount of Cd (ca. 37%) was foand in the exchangeable fraction, and Cu was the only metal significantly associated with the organic fraction. The Fe‐Mn oxide fraction contained 23, 24, 26, and 39%, and the residual fractions 15, 34, 55, and 14% of the Cd, Cu, Ni, and Zn, respectively. The amount of Cd in the residual fraction was 50 times higher than typical for unpolluted soils. Assuming that mobility and biological availability are related to the solubility of the geochemical form of the metals and decreases in the order of extraction, the apparent mobility and potential metal bioavailability for these highly contaminated soils and sediment is: Cd > Zn > Cu ≅ Ni.