DISTRIBUTION OF HEAVYMETALS IN THE SOIL OF AUTO-MECHANIC WORKSHOPS IN AKURE, ONDO STATE,NIGERIA

Abstract

Total metal concentrations and five-stage sequential extraction schemes were employed to investigate the potential environmental risk of seven important metals in the soil of selected auto-mechanic workshops in Akure metropolis, Ondo State, Nigeria. Soil’s physicochemical parameters were also determined with the following results. pH ranged from 5.50-6.32 (acidic soil), total organic carbon from 0.96-1.56%. Particle size showed soil to be mainly sandy, Cation Exchange Capacity ranged from 7.00-9.00 Cmol/Kg. The concentrations of trace metals in each fraction were determined using AAS BUCK SCIENTIFIC 210VGP. The concentrations (mg/kg) for the seven metals in Ilesha-Garage soil samples were 4.25±1.06 (Cd), 17.00±0.00 (Cr), 20.75±0.35 (Cu), 4750.00±0.00 (Fe), 4.00±0.70 (Ni), 40.50±0.70 (Pb), 40.75±0.35 (Zn) while the mean metal concentrations (mg/kg) in Oyemekun soil samples were 7.50±0.00 (Cd), 22.00±0.70 (Cr), 33.25±0.35 (Cu), 6475.00±0.35 (Fe), 5.00±0.01 (Ni), 60.00±0.00 (Pb) and 48.50±0.70 (Zn) respectively. Cd content in the soil samples exceeded the target values of the Department for Petroleum Resources (DPR) regulatory Standards for soil. The percentage of the studied heavy metals in the various fractions are in the following order; Cd: Residual >Fe-MnO> Organic> Carbonate >Exchangeable. Cr: Residual > Fe-MnO > Exchangeable> Organic > Carbonate. Cu: Fe-MnO> Residual > Carbonate > Organic > Exchangeable. Fe: Residual > Fe-MnO > Carbonate > Organic > Exchangeable. Ni: Residual > Fe-MnO > Carbonate > Organic > Exchangeable. Pb: Residual > Fe-MnO > Organic > Carbonate > Exchangeable. Zn: Fe-MnO > Residual > Carbonate > Organic > Exchangeable. Chemical speciation study applying the five-stage sequential extraction schemes revealed that the average percentage concentration of Cd, Cr, Ni, Pb and Fe were more prevalent in residual fractions, while Zn and Cu were found more in Iron-Manganese Oxides,carbonate and residual fractions.