Soil Contamination by Refined Crude Oil Using Lumbricus terrestris as Toxicity Indicator at a Petroleum Product Depot, Ibadan, Nigeria

Refined petroleum products may contain toxic compounds as additives causing environmental pollution, with adverse effects on living organisms. The study assessed the ecotoxicological effects and level of soil contamination of the tank farm area at a petroleum product depot in Ibadan, Nigeria.
Surface soils (0-15 cm) and earthworms (Lumbricus terrestris) were sampled at four different tank areas; petroleum motor spirit (PMS), regular motor spirit (RMS), automotive gas oil (AGO) and dual purpose kerosene (DPK) as well as control site without prior petrochemical activities. Concentrations of heavy metals and total petroleum hydrocarbons (TPHs) were determined using atomic absorption spectrophotometer (AAS) and gas chromatography mass spectrophotometer (GC-MS). Earthworm’s lysosomal membrane stability, a biomarker was also determined using the neutral red retention time (NRRT) assay.
The results showed that soil lead (Pb) and cadmium (Cd) concentrations significantly (P<.05) varied from 831.9 to 2055.8 mg/kg and 0.8 to 6.3 mg/kg respectively while Pb and Cd concentrations in earthworms varied from 101.3 to 328.8 mg/kg and 0.08 to 0.26 mg/kg respectively. The average NRRT observed at AGO, DPK and RMS tank farm areas were 28.3, 38.3 and 46.7 minutes respectively, implying a possible compromised state of the sampled earthworm’s lysosomal membrane. Soil-and earthworm-accumulated Pb significantly correlated with NRRT (r2=-0.65, P<.05; r2=-0.94, P<.01 respectively). A naphthalene compound (2.4%) was found in soil samples around the PMS tank area. Generally, soil Pb concentration of the study area exceeded the USEPA permissible concentration (400 mg/kg) and detected naphthalene indicated soil contamination with potential harm to humans and soil organisms. This also, suggests possible importation into Nigeria of petroleum products still containing Pb.