Levels of Toxic Metals in Soil from Irrigated Farmland in Kaduna Metropolis, Nigeria

Levels of Cd, Co, Cr and Pb in (mg/kg) were determined in topsoil from an irrigated farmland using Atomic Absorption Spectrophotometer (AAS). The soil physico-chemical parameters, pH and percentage organic matter (%OM) content were also determined. Levels of Cd, Co, Cr and Pb in the soils were 0.17-0.50, 1.50-7.00, 1.00-6.00 and 7.00-69.00 mg/kg dry weight, respectively. The soil pH showed slightly acidic to neutral which ranged from 4.27-7.63 and the mean pH was 6.05�0.84 while the soil percentage organic matter ranged from 0.17-2.52% and the mean percentage organic matter content was 1.19�0.74. The mean concentrations of soil samples studied were found to follow the decreasing orders; Pb greater than Co greater than Cr greater than Cd respectively. There is correlation between soil physico-chemical parameters and metals such as Co, Cr and Pb in soil samples. The toxic elements were examined for dependency upon some soil factors through the use of correlation analysis, pH and organic matter. pH correlated positively with Pb indicating that this factor largely controls the concentration of these element in the soil. The study has found out that the use of river water from these sites for irrigation has increased the contamination of Pb in the soils which can lead to plant uptake causing potential health risk in the long term from this practice.