Metal partitioning in soil profiles in the vicinity of an industrial complex, New South Wales, Australia

The industrial complex of Port Kembla, NSW, Australia comprises a copper smelter, steelworks and associated industries. As part of an investigation into the regional extent of a suite of metals in soils, sequential extraction was undertaken in selected soil profiles. A single aqua regia extraction and a six-step sequential extraction procedure were applied to soil samples at six different horizons to a depth of 50 cm from: (i) a contaminated, disturbed site located about 70 m from a major point source (C1); (ii) a contaminated undisturbed area situated 1 km from the contamination source (C2); and (iii) an uncontaminated, undisturbed area located 22 km from the complex (C3). Cadmium, Cr, Cu, Ph and Zn were determined by inductively coupled plasma mass spectrometry (ICP-MS) and ICP atomic emission spectrometry (ICP-AES). In the uncontaminated soil profile, metals were preferentially bound to the less mobile fractions (crystalline Fe oxides, sulfides and organic matter) except for Pb, which was preferentially bound to hydrous Fe-Mn oxides. Metal partitioning was relatively constant with depth, except for Zn. In the contaminated undisturbed soil profile (C2), the proportion of mobile metals decreased with depth. Metal partitioning at the lower levels was similar to that of core C3. At the surface, Cr was found in the sulfides and organic matter fractions, and Cu was preferentially bound to hydrous Fe-Mn oxides, crystalline Fe oxides, and sulfides and organic matter. Lead was preferentially bound to carbonates, and Zn was fairly evenly distributed among the different fractions. In the contaminated disturbed soil profile, a large proportion of metals were found in the labile forms to a depth of 40-50 cm. Based on the assumption that the mobility of metals decreases in the order of the extraction sequence, the difference in mobility amongst metals in the three soil cores measured in this study were in the order: (Cd) > Zn ≈ Cu > Pb > Cr. The two contaminated sites may represent potential health and environmental hazards because of their high soluble metal content and hence a site-specific investigation is required.