Heavy Metal Toxicity Levels and Ecological Risk Assessment of Petroleum-Based Pollutants in the Sediments of the Soku Oil and Gas Field of Southern, Nigeria

The Soku Gas Plant and associated oil facilities in South-south Nigeria has been a source of continuous discharge of oil spills and other industrial wastes to the ecosystems surrounding it. Standard methods were used to analyse the concentrations of heavy metals (Zn, Pb, Ni, Cr and Cd) and PAHs in the sediments. The result of this study revealed that the concentration of both PAHs and heavy metals were within the PEL and TEL guideline values. Five methods of pollution assessment of metals were conducted including the Geo-accumulation Index (I-geo), Contamination Factor (Cf), Pollution Load Index (PLI), Potential Ecological Risk Index (PERI) and Metal Toxicity. The result of CF, CD, and PLI In this study, Cd had the highest and Cr had the lowest CF average values among the five metals studied. The contamination factor in the study area showed higher levels for cadmium and lower levels for chromium in all stations while the calculated PERI for all the sample stations in the study area indicated low potential ecological risk. The potential ecological risk index (PERI) can be ranked in the following order: Station 3 (Pangapingi)> Station 4 (Soku Jetty) > Station 2(Gas plant) > Station 1(Elem Sangama). Spatial distribution of single risk indices (Eir) showed moderate to low risk. The I-geo classes for the study area varied across metals and sites ranging from uncontaminated to moderately contaminated. Clean-up of oil pollution and payment of compensation as required by law and convention was recommended.