keywords: Geo-accumulation index, total petroleum hydrocarbon, soil contamination, heavy metal
The study attempt to evaluate the presence of some heavy metals and Total petroleum Hydrocarbons in NNPC Aba soils. Heavy metals concentrations in soil samples were determined using Atomic Absorption Spectrophotometer (UNICAM SOLAR 32). Gas chromatography-flame ionization detector instrument was used in the detection and evaluation of levels of TPH while measurements of total PAHs concentration were performed with the aid of gas chromatography coupled to mass spectrometry (GC-MS). Pollution indices such as contamination factor (CF) and geo- accumulation index (Igeo) as well as established guidelines of some selected countries and organizations on site contamination were used to compare results. Soil samples were obtained in triplicates and in soil depths of 0–10 cm, 10–20 cm and 20–30 cm. The concentrations of Zn, Cu, As, Pb, Cd and Hg in soils of NNPC depot ranged from 112.30 to 202.10 mg/kg, 0.90 to 5.80 mg/kg, 0.08 to 2.50 mg/kg, 16.10 to 32.3 mg/kg, 1.90 to 11.78 mg/kg and 0.30 to 1.66 mg/kg with mean concentrations of 157.0, 3.84, 1.40, 22.30, 7.02 and 0.89 mg/kg respectively. Results of analysis of PAHs and TPH ranged from 6.30 to 7.40 mg/kg and 5120.50 to 24902.23 mg/kg, respectively. Values of geo-accumulation index revealed that the study site was contaminated with Pb, Hg and Cd. Established guidelines on assessment of site contamination soils from several countries used to compare this result demonstrated high levels of contamination of soils from NNPC depot by Hg, Pb, Cd, PAHs and TPH compounds. Heavy metals in the study site are presented in increasing order of concentration as follows: Hg ˂ As ˂ Cu ˂ Cd ˂ Pb ˂ Zn.
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