Bacteriological and heavy metal evaluation of abandoned crude oil–contaminated sites in Gio community, Ogoniland, Nigeria

The environmental pollution in the Niger Delta has been a course of concern. Microorganisms such as bacteria have proved to be of great benefit in the degradation of petroleum derived hydrocarbons. This study evaluated the bacteriological and heavy metal concentration of abandoned crude oil–contaminated sites in Gio community, Ogoniland, Nigeria. Soil, water, and sediment samples were collected from the sites. pH and selected heavy metals in the samples were monitored. Isolation and biochemical characterization were done to determine the heterotrophic and hydrocarbon utilizing bacteria present in the samples. Soil and sediment samples had pH values of 4.80±0.04 and 4.8±0.07 respectively while the surface and ground water samples had pH values of 6.40±0.216 and 6.50±0.01. Iron had the highest heavy metal concentration in all the samples, especially the sediment (1000.80±0.01 mg/kg) while copper and lead had the lowest concentration of < 0.001mg/kg in all the samples except sediment sample. The total petroleum hydrocarbon in the soil (9114.86±0.036 mg/kg), exceeded DPR intervention limit while sediment (1034.46±0.022 mg/kg), surface water (2.515±0.003 µg/L) and ground water sample (32.38±0.99 µg/L) were below DPR’s limit. The soil sample had the highest total culturable heterotrophic bacterial counts and total culturable hydrocarbon utilizing bacterial counts of 5.20 ± 0.21 X 10⁸ CFU/g and 4.00 ± 0.11 X 10⁷ CFU/g, respectively. The following heterotrophic bacteria were isolated and identified from the samples; Pseudomonas spp, Bacillus spp, Acidiphilium spp, Acidibrevibacterium spp and Leptospirillum spp. This study has shown the presence of indigenous resident bacteria which possess the ability to degrade hydrocarbons. These bacteria can be improved through bioaugmentation and bio stimulation for the bioremediation of these sites.