Stable Cu and Zn isotope ratios as tracers of sources and transport of Cu and Zn in contaminated soil

Copper and Zn metals are produced in large quantities for different applications. During Cu production, large amounts of Cu and Zn can be released to the environment. Therefore, the surroundings of Cu smelters are frequently metal-polluted. We determined Cu and Zn concentrations and Cu and Zn stable isotope ratios (delta Cu-65, delta Zn-66) in three soils at distances of 1.1, 3.8,and 5.3 km from a Slovak Cu smelter and in smelter wastes (slag, sludge, ash) to trace sources and transport of Cu and Zn in soils. Stable isotope ratios were measured by multicollector inductively coupled plasma mass spectrometry (MC-ICP-MS) in total digests. Soils were heavily contaminated with concentrations up to 8087 mu g g(-1) Cu and 2084 mu g g(-1) in the organic horizons. The delta Cu-65 values varied little (-0.12 parts per thousand to 0.36 parts per thousand) in soils and most wastes and therefore no source identification was possible. In soils, Cu became isotopically lighter with increasing depth down to 0.4 m, likely because of equilibrium reactions between dissolved and adsorbed Cu species during transport of smelter-derived Cu through the soil. The delta Zn-66(IRMM) values were isotopically lighter in ash (-0.41 parts per thousand) and organic horizons (-0.85 parts per thousand to -0.47 parts per thousand) than in bedrock (-0.28 parts per thousand) and slag (0.18 parts per thousand) likely mainly because of kinetic fractionation during evaporation and thus allowed for separation of smelter-Zn from native Zn in soil. In particular in the organic horizons large variations in delta Zn-66 values occur, probably caused by biogeochemical fractionation in the soil plant system. In the mineral horizons, Zn isotopes showed only minor shifts to heavier delta Zn-66 values with depth mainly because of the mixing of smelter-derived Zn and native Zn in the soils. In contrast to Cu, Zn isotope fractionation between dissolved and adsorbed species was probably only a minor driver in producing the observed variations in delta Zn-66 values. Our results demonstrate that metal stable isotope ratios may serve as tracer of sources, vertical dislocation, and biogeochemical behavior in contaminated soil. (C) 2010 Elsevier Ltd. All rights reserved.