Influence of Varying Hydrocarbon and Heavy Metal Concentrations on the Microbial Density of Agricultural Soil Samples Polluted With Crude Oil

The research  study was aimed at investigating the influence of varying hydrocarbon and heavy metal concentrations on the microbial density of agricultural soil samples polluted with crude oil. Soil samples were randomly collected at depths of 0-15cm and 15-30cm from Botanical Garden  of  University of Calabar, Calabar . The study was completed within a duration of six months. Standard microbiological techniques were used to isolate, identify and characterize isolates from the collected soil samples. The result obtained from the study showed that the mean total heterotrophic bacterial and fungal counts were higher in the soil samples collected during the wet season compared to its counterpart collected during the dry season. The mean total heterotrophic bacterial and fungal counts were higher in the crude oil polluted soil sample compared to its un-polluted soil counterpart. The microbial density of the analyzed soil samples increased with a corresponding increase in crude oil exposure (0% - 10%) but decreased at 15% of crude oil exposure.  Also, the microbial density of the collected soil samples were observed to decrease with  increasing concentrations (0%, 5%, 10%, 15%) of lead, manganese, and zinc (mg/l). Microbial diversity in the polluted soil sample were identified as Bacillus, Escherichia coli, Pseudomonas, Klebsiella, Aeromonas, Serratia, Enterobacter, Corynebacterium, Yersinia, Shigella, Penicillium, Aspergillus and Candida. Comparison of the mean physicochemical parameters of the crude oil polluted and the un-polluted soil samples showed significantly (Pu003c 0.05) lower values of pH and available phosphorus in the polluted soil sample, whereas the organic carbon, and total nitrogen, exchangeable cat ion capacity, lead, manganese, and  zinc were significantly (Pu003c0.05)  higher in the polluted soil compared to that of the un-polluted soil sample. However, from this study, it is evident that the presence of crude oil in soil environment influences the microbial density, diversity and physicochemical characteristics of soil, and this in-turn could stimulate a wide variety of environmental issues, therefore these calls for environmental consciousness to be instilled into the public to avoid indiscriminate spillage or disposal of oil.