Physicochemical Profiles of Various Bioremediated Petroleum Contaminated Sites in Ogoniland, Nigeria

This study was carried out to evaluate the physicochemical statuses of bioremediated sites in Ogoniland (K-Dere, Bodo, and Biara), Rivers State, Nigeria after a certified bioremediation protocol. Three bioremediated soils of different fallow ages (6 months, 12 months, and 18 months after bioremediation-AB) and an uncontaminated soil (Bera) were collected and analyzed for various parameters- pH, electrical conductivity (EC), total organic matter (TOM), particle size distribution, cation exchange capacity (CEC), nitrogen and phosphorus, heavy metals (lead, cadmium, nickel and copper), total petroleum hydrocarbons (TPH), poly aromatic hydrocarbons (PAH), and intermediary metabolites. Results obtained indicate that the particle size distribution of the four soil samples were similar in terms of their content of sand, silt and clay. The pH of 12m-AB and 18m-AB bioremediated soil samples were 6.34 and 6.50 respectively and were slightly lower than pH of uncontaminated soil. The EC as well as the CEC of the bioremediated soil samples were considerably lower when compared to the uncontaminated soil sample. The range of values for TOM was between 0.095 – 1.232 % with 6m-AB soil having the least value; whereas 0m-AB and 12mAB had the highest value of 1.232 %. Sample 18m-AB had the highest concentration of nitrogen whereas, 12m-AB sample had the least concentration. The phosphorus content in each bioremediated soil was significantly lower than in uncontaminated soil. The residual TPH content of each bioremediated soil sample was above the recommended EGASPIN target TPH value of 50 mg/kg but below the intervention level of 5,000 mg/kg. The TPH contents in bioremediated soil samples were 161.25 mg/kg (6m-AB), 51.72 mg/kg (12m-AB) and 91.50 mg/kg (18m-AB). TPH was not detected in the uncontaminated soil sample. All four samples had no trace of PAH. Heavy metals were below detectable limits in all soil samples. Screening of the soil samples using gas chromatography-mass spectrometer revealed a number of metabolic intermediates in bioremediated soil samples when compared to the uncontaminated pristine soil (control). Some of the identified metabolites are known carcinogens and are deleterious to plant growth thus suggesting the unhealthy status of the bioremediated soils for agricultural productivity.