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.
