Distribution of Cadmium, Zinc, Copper, and Lead in Soils of Industrial Northwestern Indiana

Abstract

Five undisturbed locations of sandy Oakville and Plainfield soils under oak forest in the heavily industrialized region of northwestern Indiana were sampled at four depths, to assess the nature and extent of Cd, Zn, Cu, and Pb contamination. The litter layer and top 2.5 cm of soil at a site within 5 km of the center of the industrial complex were highly contaminated with Cd, Zn, Cu, and Pb. Levels of Cd and Zn decreased rapidly with distance to the south and east, while Cu and Pb decreased more erratically, with all metals reaching nearly background levels at 18 km. Samples taken deeper in the profiles (30 to 36 cm) did not show elevated metal levels compared with a rural site 67 km to the south. Sequential extraction methods applied to the top 2.5‐cm soil samples showed large amounts of relatively labile metals associated with exchange sites (KNO₃‐extractable: 23, 10, 1, and 8% of total Cd, Zn, Cu, and Pb, respectively), bound by soil organic matter (Na₄P₂O₇‐extractable: 21, 33, 24, and 41% of the total Cd, Zn, Cu, and Pb), and associated with carbonates and/or noncrystalline Fe oxides (EDTA‐extractable: 12, 8, 26, and 28% of the total Cd, Zn, Cu, and Pb). Minimal amounts of the metals were within the small amount of crystalline Fe and Mn oxides present in these soils. Non‐extractable (residual) metals amounted to 26, 32, 23, and 4% of the total Cd, Zn, Cu, and Pb.