Abstract:
Five heavy metals (Cd, Cr, Ni, Pb and Fe) were analyzed in the soil samples collected from the vicinity of five waste dumps located in Ajaokuta Steel Plant site, Ajaokuta L.G.A, Kogi State, Nigeria. The physicochemical properties of the soils such as pH, electrical conductivity, soil texture, organic matter content and soil exchangeable bases were evaluated using standard methods; five step sequential chemical extractions were carried out to determine the mobility and biological availability of these heavy metals to plants and in the environment. The results showed that high proportions of all the metals were associated with the residual fraction which implies that the metals are naturally present in the soil matrix. While lower proportions were detected in the non-residual fractions which are said to be biologically available to be mobilized in the environment. The average mobility of metals analyzed was in the increasing order: Fe <Ni <Cr <Pb<Cd. Total metal concentrations in the sample were within the set limits of the regulatory bodies. Ladder of the alluvial soil was appraised using pollution indices: Pollution Load Index and Index of geo-accumulation to establish the extent of heavy metal pollution of the studied area. PLI was less than one (PLI < 1), in all the sampling points of the Steel Plant Complex indicating no pollution of the soil of the industrial environment. Geo-accumulation Index revealed that most of the sampled sites were below the level of uncontaminated soil category. Igeo has negative value at most of the sampling stations meaning no pollution. However, it was in uncontaminated to slightly contaminated class by iron only at sampling stations 2, 3, 4 and 6 representing pump house No 3, Permanent Water Intake, Sinter Plant and the Control respectively. Concentration of each element analyzed not above stipulated limit, hence, may not be injurious. Therefore the alluvial soil of the studied industrial area could be said not to be under any serious threat of heavy metal contamination/pollution. Apart from Fe, the selected heavy metals are not of any pollution concern at the time of this present study. The result of this study will provide important baseline data in the assessment of distribution of these heavy metals in the vicinity of some waste dump soils of Ajaokuta Steel Complex. Further study may focus on the crops and plants grown in the studied area to assess the soil-plant transfer factor in the food chain of the area.
