Pollution Status of Heavy Metals in Spent Oil-Contaminated Soil in Gwagwalada

The pollution status of some selected heavy metals namely: Pb, Fe, Zn, Cu, Cr, Ni and Cd, in spent oil-contaminated soil were investigated. The soil samples were obtained from different spots of the automobile mechanic workshop, wet digested and the concentrations of the heavy metals in the soil digest determined using Atomic Absorption Spectrophotometer (AAS). The concentration of Pb was significantly higher (p<0.05) than the concentrations of each of the other six heavy metals while cadmium had the least concentration. In most of the sampling spots analyzed, the concentrations Cd were below the detection limit of the instrument used. The order of the concentrations of the heavy metals were Pb> Fe> Zn> Cu> Cr> Ni> Cd and Fe > Cr > Zn> Pb> Cu> Ni> Cd for the spent oil-contaminated and control soils respectively. The concentration of iron, cadmium, copper, nickel and zinc in the control soil were significantly lower (p<0.05) than the concentration of iron, zinc and lead in the oil-contaminated soil. The concentration of Pb exceeded the limits of both the background and intervention lead value set by DPR (Department of Petroleum Resources) of Nigeria. The contamination and potential ecological factors of Zn, Cu, Fe, Cr and Cd were categorized low except Pb which was categorized as having very high contamination factor and moderate potential ecological risk factor. The entire studied spots showed moderate degree of contamination. The potential risk index of the heavy metals ranged from 44.23 to 51.91, which had a low grade category; implying that the heavy metals have caused low harm to the soil of the workshop. This paper gives information on the present status of heavy metals in the soil and the need for continuous monitoring so as to avert further contamination of this workshop.