Distribution of Different Forms of Lead, Zinc, Cadmium and Copper in a Contaminated Calcareous Soil

The aim of this study was to investigate the chemical forms of Pb, Zn, Cd, and Cu in two concentrations and three pH values in a calcareous soil. Metals as nitrate salts were added at two levels of 1.0 and 10 mmol kg-1 for Pb and Zn and at two levels of 0.1 and 1 mmol kg-1 for Cu and Cd all at three levels of pH (6, 7 and 8). The soil to solution ratio (w/v) was 1 to 20. The soils were incubated at 30±1°C for 30 days. Chemical forms of metals in the soils were determined by Tessier method. The results showed that the distribution of native forms of Pb and Zn was independent of pH. With increasing pH values from 6 to 8, the residual form of Cu decreased, whereas its organic form increased. Regarding the limit of quantitation (LOQ) for the atomic absorption instrument, the native cadmium was not measurable. The effect of pH on metal distribution between different forms varied with respect to metal nature and its concentration. The oxide and organic forms were dominant in low concentration of Pb and the oxide and carbonate forms were dominant in high concentration of this metal. Moreover, the added Zn and Cu were mainly dominated in oxide and organic forms, respectively. The added Cd was accumulated in organic form at low concentration and accumulated in exchangeable form at high concentration.