Heavy Metal Distribution and Pollution Evaluation in Soils of Dagbala-Atte District, Southwestern Nigeria

Abstract

Agricultural soils of Dagbala-Atte District in Igarra area of southwestern Nigeria were investigated for the distribution pattern and possible pollution of the following ten heavy metals: Ag, As, Cd, Co, Cr, Cu, Hg, Ni, Pb and Zn. The investigation was propelled by the fact that soil pollution by heavy metals has serious health implication on animals and human beings via the food chain involving the consumption of crops/vegetables grown on such soils. Forty nine (49) soil samples were collected from 2x3 uniform grids in the district. The aforementioned ten heavy metals were partially extracted from the soils using modified aqua regia digestion method and analyzed by ICP-MS. The analytical results were used to produce geochemical distribution maps for the elements and were also subjected to univariate statistical analysis to determine the mean concentration of the heavy metals in the district. The degree of pollution of these soils by these heavy metals was evaluated by calculating enrichment factors (EF), pollution load index (PLI) and geo-accumulation index (Igeo). The study revealed that Co, Cr, Cu, Ni, Pb and Zn are widely distributed in the soils of the district while Ag, As and Hg are fairly widely distributed and Cd has restricted distribution. As, Cr, Cu and Hg have their highest concentrations in the northern part, Co and Ni in the southwestern part, Pb in the eastern part and Zn in the southern part of the district. The computation of the EF, PLI and Igeo for the ten heavy metals yielded results that indicate that all the 49 soils sites are practically unpolluted in the district. Therefore the range of concentration values for the different heavy metals in the study area can serve as baseline environmental data against which the degree of pollution of these heavy metals can be evaluated in future.