An Assessment of Heavy-Metal Accumulation in Soils in Selected Auto Mechanic Workshops Using Pollution Indices in Osun-State, Nigeria

The study investigated the accumulation of heavy metals (Zn, Fe, Mn, Cu, Cr, and Ni) in soils from auto-mechanic workshops in Ile Ife and Modakeke, South-west Nigeria. Soil samples exhibited significantly high levels of the investigated heavy metals compared to the control sample. In Modakeke, the distribution pattern was Fe > Zn > Mn > Cu > Ni > Cr, with concentrations of 1076.54, 1020.85, 92.31, 32.43, and 25.00 mg/kg, respectively. In Ile-Ife, the distribution was Mn > Fe > Zn > Cu > Ni > Cr, with concentrations of 1000.00, 748.85, 303.94, 59.35, 26.56, and 16.56 mg/kg, higher than the control soil sample.

Pollution indices indicated very high contamination factors (CF) above 6 in Ile-Ife, while Modakeke followed a similar pattern except for Cu with CF 5.71. The Quantification of Soil Contaminant (QOC) in Ile-Ife followed the pattern Zn > Mn > Ni > Cr > Cu, while in Modakeke, the pattern was Mn > Zn > Ni > Cr > Cu. Geo-accumulation index (I-geo) showed a strong pollution for Zn and Ni, indicating anthropogenic origin. Enrichment factor (EF) varied, with Zn showing moderate EF at both sites, Mn with moderate EF in Ile-Ife, and other heavy metals showing minimum EF.

Single Factor Pollution Index (SPI) in Modakeke indicated pollution indices for Zn, Cu, Mn, Ni, and Cr, while in Ile-Ife, Mn, Cu, Zn, Ni, and Cr exhibited pollution indices. The Potential Ecological Risk Index (PERI) highlighted very high ecological risk for Zn, considerable risk for Ni, and moderate risk for Mn and Cu in Ile-Ife, while Modakeke showed moderate risk for Ni and Zn, and low risk for Cu and Mn. The integrated ecological risk index indicated considerable risk for Ile-Ife and moderate risk for Modakeke.