Chemical partitioning of Cu, Pb and Zn in the soil profile of a semi arid dry woodland

Abstract

The chemical partitioning of Cu, Pb and Zn was examined in the soil profile of the woodland system in Keoladeo National Park, India using a five-step sequential extraction procedure (SEP). Metal partitioning was assessed in the soil up to a depth of 100cm with 25-cm intervals. The amount of metals obtained from the SEP exceeded pseudototal metal levels obtained from aqua regia digestion. The SEP results showed high preferential attachment of metals with Fe22Mn hydroxides. All the three metals showed least preferences to the exchangeable pool. The attachment of metals to the OM-S phase was also less, may be because of the low organic matter in the soil. In the case of Cu, the order of the fractions in terms of metal concentrations was Fe-Mn>OM-S>CA>EXC and in the case of Pb the order was Fe-Mn>OM-S>RES>CA>EXC. Zn was different from Cu and Pb in showing higher affinity towards RES phase and the order of its concentration was RES>Fe-Mn>OM-S>EXC>CA. This suggests hydrous oxides of Fe-Mn as an important binding site for Cu and Pb, whereas silicate mineral matrix (RES phase) for Zn.