Assessment of heavy metals in a soil contaminated by oil spill: a case study in Nigeria

Surface and subsurface soil samples contaminated with crude oils were collected from an impacted site at Bodo City in the Niger Delta, Nigeria, after a field reconnaissance survey. An uncontaminated soil sample collected 100 m from the impacted site, but within the same geographical area, was used as a control. Trace elements such as, As, Cu, Cr, Cd, Fe, Pb, Ba, Ni, V, Hg and cation-exchange capacity constituents of the contaminated and uncontaminated soils were determined by atomic absorption spectroscopy. Trace element concentrations were: Cu, 0.5–13.4 mg kg− 1; Cr, 0.2–0.8 mg kg− 1; Fe, 6.2–8.7 mg kg− 1; Ba 80.0–108.0 mg kg− 1; Ni, 0.6–4.8 mg kg− 1; and V, 4.0–9.4 mg kg− 1; cation-exchange capacity ranged from 43.6 to 57.2 mg kg− 1 in surface and subsurface soils. Results showed that eigenvalues for the two first principal components represent up to 49% of the total variance. A positive correlation of the first principal component with Cu, Cr and cation-exchange capacity shows pollution from oil spillage, while a positive correlation of the second principal component with Cr, Fe, V, and dissolved oxygen (DO) shows both oil pollution and allochthonous inputs.