Heavy Metals Contamination and their Potential Toxicity in Petroleum Sludge Impacted Soils from Itsekiri Communities, Delta State, Nigeria

Abstract

The concentrations of some heavy metals (Chromium, Cadmium, Lead, Nickel, Copper, Cobalt, Manganese, Iron and Zinc) in petroleum sludge impacted soils were determined to evaluate their contamination levels using atomic absorption spectrophotometer.  The petroleum sludge samples were collected from the discharge pit of Warri Refinery and Petrochemical Company (WRPC)  while the  soil samples were collected from five selected oil-impacted communities (Ubeji – 500 m, Ekpan – 1.5 km, Aja-Etan – 2.5 km,  Ifie-Kporo – 3.0 km, Ijala-Ikenren – 3.8 km from Warri refinery and were coded A, B, C, D and E respectively). A control sample was also collected 8.5 km away from the refinery. The results obtained revealed that with the exception of Fe, the sludge samples contained the highest concentrations (in mg/kg dry weight) of Chromium (2462.6±0.5), Lead (406.7±0.2), Copper (201.3±0.0), Manganese (8335.1±0.9) and Zinc (1009.2±0.3) while Iron was highest (10313.5±2.3) in site A. All the metals were higher in the studied sites than the control sites and a stepwise decrease in metal contents were observed from A to E. Some geochemical assessment techniques, including enrichment factor (EF) and geoaccumulation index (Igeo), were used to determine the levels of metal toxicity in the sediments. Computed enrichment factors showed that the soil samples have suffered significant systematic heavy metals enrichment following proximity to the refinery. Values of geoaccumulation index (Igeo) indicated different contamination and toxicity levels of Chromium, Cadmium, Lead, Copper, Manganese, and Zinc while Nickel was not detected.