GEOGENIC AND ANTHROPOGENIC EVALUATION OF HEAVY METALS IN SOILS NEAR GRANITE QUARRIES

ABSTRACT

The research was carried out to determine the chemical composition of soils, the concentration of heavy metals and to determine the pollution index of heavy metals present in the soil at the research location Ikpeshi, Edo State. The result of the chemical composition of soil from ten (10) sampled sites in Ikpeshi showed the average pH value ranged from 6.01 – 7.22 at the topsoil(0- 15cm) with a mean of 6.69 and ranged from 4.47 – 7.86 at the subsurface (15-30cm) with a mean of 6.64. This suggests that the soil is slightly acidic in the study area.High soil pH according to (Mandal et al, 2022; Rengel 2015) limits metal mobility. The mean concentration of heavy metals analyzed in topsoil and subsurface soil of the study area showed that Heavy metals ( in order of decreasing magnitude), was Fe>Zn>Cu>Ni>Cr>Mn>Co>Pb>Cd for topsoil and Fe>Zn>Cu>Ni>Cr>Mn> Co >Pb >Cd for subsurface soil. In this study, majority of the metal content increase with depth (15-30cm) with the exception of Mn, Cd, and Ni. The high amount of available metals in the subsurface soil could be attributed to leaching of contaminants as a result of effluents discharge during mining operations and due to high sorption capacity of the soil. Assessment of mean data of heavy metal concentration indicated that all metals were within the DPR and WHO permissible limits apart from Cd. The pollution index of heavy metals in the study area was determined using multivariate statistical analyses such as correlation,principal component analysis was developed. Total heavy metals concentration is a consistent indicator of environmental contamination; however heavy metals analyzed in this work were below the DPR 2002 permissible standard. The result of this study also showed that the pH has a negative correlation with Mn in topsoil and subsurface soil, suggestive of the acidic nature of the soil. It has been stated by (Somnath et al., 2022) that in alkaline soils, pH always have positive relationship with Mn. It can be concluded that the accumulation and deposition of heavy metals in soils at Ikpeshi, Edo state area are influenced by other anthropogenic sources (traffic situations, vehicular emissions, destruction of mechanical parts of vehicles) and geogenic sources including weathering and crustal erosion.