Bioamendment of petroleum contaminated ultisol: effect on oil content, heavy metals and pH of tropical soil.

The effect of organic amendments on the oil content, heavy metals concentration and pH of petroleum contaminated sandy loam ultisol obtained from Rumuekpe oil field in Emohua Local Government Area of Rivers State, Nigeria was determined. Petroleum contaminated soils were treated with wood ash, compost and sawdust. The addition of organic amendments resulted in a significant (at 95% probability level) decrease in oil content by 92% for composting, 81% for soil treated with sawdust and 58% for soil with ash supplementation, over 6 months. The effect of treatments on the iron(Fe), copper(Cu) and lead(Pb) concentration was significant at P < 0.001. The remediation also affected the pH of soil. This initial pH of 5.6 was depressed by the application of compost and sawdust supplements respectively to a final pH of 5.2 and 5.3. On the other hand, amending the soil with wood ash raised the pH from 5.6 to 6.2. Increased acidity caused a decrease in the heavy metals concentration in the contaminated soil. Soil treatment with compost generally gave the best remediation results, followed by sawdust and then ash. Adjusting the pH of oil contaminated soil to high acidic levels may promote the availability and migration of heavy metals in remediated soils and not necessarily the rate of oil mineralization.