MICROBIOLOGICAL, POLYCYCLIC AROMATIC HYDROCARBON AND HEAVY METAL CONTENT OF SOIL AND WATER SOURCES IN COMMUNITY AROUND PETROLEUM PRODUCTSDEPOT SULEJA, NIGERIA

Abstract

Contamination by petroleum products is a common occurrence in various petroleum depots in Nigeria. This study was aimed at assessing the microbiological, polycyclic aromatic hydrocarbons (PAHs) and heavy metal quality of soil and water sources in communities around Petroleum Products Marketing Company (PPMC), Suleja, Nigeria. Soil and water samples were collected from the petroleum depot (Plot 3) and the five communities designated as plots (TungaShanu - Plot 1, Dikko - Plot 2, Dagweru - Plot 4, Tunga Koro -Plot 5 and Maje - Plot 6) around the petroleum products depot and a control site. Microorganisms in the soil and water samples were enumerated by spread inoculation on general purpose media and selective media, characterized and identified using biochemical and molecular techniques. Bacterial and fungal isolates were tested for their potential to utilize petroleum products in a Bushnell Haas Broth containing 0.05 mL of petroleum products (diesel, kerosene, engine oil, crude oil) as sole source of carbon and energy. The utilization rate was determined by spectrophotometry and viable cell counts. The capacities of selected bacterial and fungal isolates to mineralize crude oil and PAHs were further tested in minimal salt medium. The soil and water samples were also analyzed for PAHs and heavy metals; Lead (Pb), Cadmium (Cd), Arsenic (As) Copper (Cu), Chromium (Cr), Manganese (Mn) to evaluate the potential contaminant contribution attributed to PPMC activities. The bacteria isolated were species of Staphylococcus, Streptococcus, Proteus, Pseudomonas, Bacillus and Escherichia; while the fungal isolates were Penicillium, Aspergillus, Mucor, and Rhizopus. Total coliform bacteria and hydrocarbon utilizing bacteria were also among the isolates identified. Soil samples had higher aerobic heterotrophic bacterial counts than the water samples (11.0 x 106 cfu/g – 62.0 x106cfu/g and 3.2 x104cfu/mL – 9.8 x104cfu/mL) respectively. Crude oil was most utilized by the microbial isolates than other petroleum products. Pseudomonas and Bacillus among bacteria had the highest capacity in utilizing the petroleum products while Aspergillus and Penicillium exhibited greater capacity among fungi. The total PAHs ranged from 4.00 - 428.00 mg/kg, 4.11 - 584.03mg/kg, 8.00 - 324.00mg/kg, 4.00 - 452.00mg/kg, 4.00 - 376.00mg/kg, and 8.05 - 388.00mg/kg for Plots 1,2,3,4,5 and 6 respectively in soil samples. Total PAHs concentration in water samples ranged from undetectable level to 0.3372 μg/mL in all the Plots. The mean concentration of the heavy metals in the soil for the various plots ranged from Cr 0.25-1.21 mg/kg, Cd 1.69-3.15 mg/kg, Pb 4.11-8.27 mg/kg, As 1.42-2.50 mg/kg, Mn 2.15-4.75, and Cu 1.10- 3.32 mg/kg. Mean concentration of the heavy metals in water samples for the various plots ranged from Cr 0.05-1.24 mL/L, Cd 0.01-1.95 mL/L, Pb 0.01-3.72 mL/L, As 0.00-2.24 mL/L, Mn 1.14-3.75 mL/L, and Cu 0.00-1.26 mL/L. Geo-accumulation indices showed heavy metals in the decreasing order; As(2.99) > Cr (1.07) > Cd (0.88) > Pb (0.63) > Cu( 0.29) > Mn (0.14). The contamination factor (CF) and pollution load indices (PLI) were in the order: Pb > Cd > Cr > As > Cu > Mn. Present study revealed microbial isolates capable of utilizing the various petroleum products and PAHs and therefore can be useful in oil spill bioremediation in the tropical environment. The results also revealed that the concentration of some PAHs particularly Phenanthrene, Naphthalene and Benzo (b)fluoranthene and most of the heavy metals were higher than the permissible limits set by the World Health Organization and may constitute health challenges and ecological risks in the study areas.