The status of the soil microbial flora and oil content of Imore, a coastal community in Lagos state, Nigeria after petroleum spill and fire outbreak

Petroleum spill on soil is perilous, however, natural occurring hydrocarbon degrading microorganisms have the capacity to utilize the hydrocarbon as source of carbon and energy, thereby, enhancing their transformation and mineralization. Therefore, to ascertain the extent of damage and natural restoration of an oil spill site, this study compared its microbial flora and hydrocarbon content with an adjacent unpolluted zone, after 40 weeks. The results revealed that the number of heterotrophic bacteria and hydrocarbon utilizers remained at least one order of magnitude higher in the polluted zones (2.5 x 107 to 3.2 x 104) than in the unpolluted zone (2.3 x 103 to 2.8 x 104) throughout the study period. Conversely, the fungi population, which was three orders of magnitude higher at 0 d, drastically decreased later (120 - 150 d) with all zones having approximately 1.3 x 104 cfug-1. At the end of the study, the extent of oil reduction was 1.6 % at the control zone while the polluted sites showed between 33 to 35%. The rate of hydrocarbon reduction was between 9.2 x10-5 to 9.9 x 10-5 mgd-1by 90 d, but declined to 3.3 x 10-5 to 4.1 x 10-5 mgd-1by 150 d. Consequently, though the soil microbial flora seems to have adapted to the excess oil, the extent and rate of oil removal is not satisfactory, hence, additional remediation treatment is required for complete restoration.