Post Remediation Assessment of Residual Hydrocarbons in Contaminated Soil in Ogoni Using Gas Chromatographic Fingerprinting Technique and Phytotoxicity Bioassay

Abstract

Post-remediation assessment of residual total petroleum hydrocarbon (TPH) in an aged crude oil-contaminated soil (ACOCS) in Ogoni after seventy-day enhanced remediation by bio stimulation was investigated using gas chromatographic fingerprinting technique and phytotoxicity bioassay. Seven treatments were designed and composted water hyacinth (EC), Mexican sunflower (TD) and Bermuda grass (CD) was applied as bio stimulants. EC, TD and CD (2,500g each) were used to bio stimulate 4,000 g of ACOCS in situ in TPA (treatment plot A) through TPG. The treatments were monitored for a period of seventy days and the rate of crude oil biodegradation analyzed. Gas chromatographic fingerprints of crude oil in the soil showed the absence of n-C1 to n-C8 carbon length and could be attributed to weathering processes. Carbon lengths between n-C9 to n-C34 were significantly (ρ >0.05) attenuated in plots with 2 nutrients, thus indicating microbial utilization of crude. Crude oil attenuation as depicted by the trend in the disappearance of low-molecular-weight hydrocarbons could be due to their preferential utilization by microbes. TPG with all 3 supplements had TPH reduced significantly (ρ >0.05) from 93,867 ppm to 1,002 ppm, (99% loss), meeting the Department of Petroleum Resources intervention value of 5000 mg/kg. The decreasing peak counts show that the crude were from petrogenic source. The germination index of L. sativum ranged from 65 and 100% thus, could be considered non-phytotoxic and ecologically save.