Evaluation of Polycyclic Aromatic Hydrocarbons, Total Petroleum Hydrocarbons and Some Heavy Metals in Soils of Nnpc Oil Depot Aba Metropolis, Abia State, Nigeria

Abstract

Heavy metals concentrations 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 PAHs (total) concentration were performed with the aid of Chromatography mass spectrometer. Pollution indices such as contamination factor (CF) and geoaccumulation 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– 10cm, 10 – 20 cm and 20 – 30 cm. The concentrations of Zn, Cu, As, Pb, Cd and Hg ranged between 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 157.00, 3.84, 1.40, 22.30, 7.02 and 0.89 mg/kg respectively in soils of NNPC depot. 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 (toxic metals). 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 Aba by Hg, Pb, Cd, PAHs and TPH compounds. The decreasing order of heavy metals concentration in the study site is presented as follows: Zn>Pb>Cd>Cu>As>Hg.