The contamination of agricultural soils with heavy metals is of concern because if soil is contaminated, the metals can be transferred to food crops. The availability of these metals to food crops depends on the forms in which they are present in the soils. In this study sequential extraction technique was applied to assess the exchangeable, carbonate- bound, Fe-Mn oxide bound, organic bound and residual fractions in topsoil of farmlands in Kogi State, North Central Nigeria. Proportions in non-residual soil phases were 82.6 % Cd, 48.6 % Co, 72.5 % Cu, 73.2 % Ni, 41.9 % Pb, and 84.3 % Zn. Lead (Pb) and cobalt (Co) showed the highest phase of 58.1% and 51.4 % respectively in the residual phase. The low concentration of lead in the non-residual fraction (41.9 %) and the highly mobile exchangeable phase and pH sensitive carbonate phase is an indication that there is no increase in anthropogenic input of Pb into the environment. Cadmium, zinc and nickel are mostly abundant in exchangeable fraction and this can be of concern especially cadmium.
Key words: Heavy metals, metal speciation, farmlands, food crops, metal uptake
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