INVESTIGATION OF POLLUTION LEVELS OF SOILS WITHIN PETROLEUM DEPOTS IN NIGERIA

Abstract

The petroleum depots are housing facilities for the erected petroleum storage tanks, which serve the purpose of keeping petroleum products. The threats posed by the storage tanks on the environment cannot be overlooked. Levels of chemical components of soil around the storage tanks of Nigerian National Petroleum Corporation (NNPC) depots in Kwara and Oyo States were assessed using exposure limits, health standards as well as pollution indices. Parameters such as pH, Electrical Conductivities (EC) and heavy metals (Fe, Cd, Pb, Cr, Cu, Zn, Mn, Co and Ni) were determined in the soil around the storage tanks of the depots using standard methods. Average levels of heavy metals in soil followed the decreasing order Fe > Zn > Mn > Pb > Ni > Cr > Cu > Co > Cd for Kwara Petroleum depot and Fe > Zn > Mn > Pb > Ni > Cr > Co > Cu > Cd for Oyo Petroleum depot. Zn (1.77 mg/g) and Mn (1.13 mg/g) were respectively above the regulatory limit of FEPA (0.75 mg/g and 0.48 mg/g), permissible limits of WHO (0.3 mg/g and 0.05 mg/g) and maximum permissible limits of USEPA (0.2 mg/g and 0.08 mg/g) for Kwara Petroleum depot. Fe was above the regulatory limit of FEPA (5.0 mg/g) for both depots. Oyo Petroleum depot had considerable degree of contamination (17.444) of heavy metals while Kwara Petroleum depot had a very high degree of contamination (42.325) of heavy metals. Metal Pollution Index values (1.351 and 1.632) for Oyo Petroleum depot and Kwara Petroleum respectively indicated pollution in both depots. The Pearson Correlation (at 0.05 significant level) showed significant correlation between most heavy metals which signified that they were likely from the same source. Installation of primary treatment plant or proper maintenance measures are recommended to be put in place.