Characterization of Heavy Metal Fractions in Agrizcultural Soils Using Sequential Extraction Technique

The accumulation of copper in cocoa plantations due to the application of copper-based fungicides in the control of black pod disease is of environmental concern. It is well known that, heavy metals have affinity for different compartment in soil. The risk associated with the presence of metals in soil is their potential ecotoxicity and ability to enter the food chain. Total metal content of a soil is inadequate for predicting the toxicity of heavy metals in soil. Hence, sequential extraction was used to fractionate Cu, Pb, Zn and Cd in soils collected from selected cocoa plantations in Cross River State in order to determine the fraction of the total metal content that is bioavailable. Copper and Zn were mostly associated with the organic fraction, Pb was mostly associated with the exchangeable fraction while Cd was extractable fraction for Lead and residual for cadmium. The apparent mobility and bioavailability for these four metals in the studied soils were in the order: Pb>Zn>Cd>Cu. This implies that lead has the highest mobility in the studied soils.