Coremediation of Petroleum Products by Fungi Isolated from Irvingia Gabonensis Seeds
A Thesis Submitted to the School of Postgraduate Studies, University of Lagos
The Petroleum Industry has a huge potential for the pollution of the environment at every stage of its operation, hence the need to constantly fashion out new strategies for maintaining the sanctity of our environment. Fungi associated with diseased Irvingia gabonensis (Baill) seeds found in the open markets were suspected to possess the ability to degrade the hydrocarbon substances contained in these seeds. These fungi were isolated bimonthly from the diseased seeds of I.gabonensis from four open markets in the Lagos metropolis over a two year period. Simultaneously, fungi were also isolated from the soil from five other places, namely two mechanic villages, one public dump site, and two agricultural sites. Three important concepts, namely, mycodeterioration, mycodegradation and mycoremediation were investigated with regards to the hydrocarbon utilizing potentials of these fungal isolates. A preliminary screening of these fungal isolates for their petroleum hydrocarbon utilizing abilities was carried out by culturing the fungal isolates under fume from crude oil. A total of twenty five fungal isolates from the genus Aspergillus were able to grow under the crude oil fume. These isolates were selected for their ability to biodegrade Crude oil (Co) and four other petroleum products namely Spent Engine oil (SEO), kerosene (kero), diesel and Fresh engine oil (FEO) as well as one vegetable hydrocarbon (oil extracted from I.gabonensis seed- I.O.) using spectrophotometric techniques. The results from this mycodegradation studies showed that the fungi had a significant (p≤0.05) effect on the optical densities of each of the six different hydrocarbon sources at the wavelengths of 530 and 620 nm. The results of the confirmatory studies for the mycodegradation of the different hydrocarbon sources by the fungal isolates conducted on the 40th day showed a Gas Chromatographic (GC) value that indicated a reduction in the Total Petroleum Hydrocarbon (TPH) value for each of the petroleum hydrocarbon compounds thus: Co from 9.84 x 105 to 7.85 x 105 mg/l, SEO from 9.56 x 105 to 8.5 x 105 mg/l, kero from 9.88 x 105 to 8.74 x 105 mg/l, diesel from 9.73 x 105 to 8.35 x 105 mg/l and FEO from 9.8 x 105 to 8.57 x 105 mg/l. There was also a change in the fatty acid methyl ester (FAME) level of the vegetable hydrocarbon compound at day forty when compared to what was available at day zero. This result therefore confirms the ability of these organisms to utilize (mycodegrade) petroleum and vegetable hydrocarbon compounds. The results of the field mycoremediation studies show that the Aspergillus oryzae deployed to remediate the SEO polluted field had by the 6th month after the SEO spillage achieved between 98.9 - 99.1% reduction in the level of the initial TPH present on the spillage site. In addition, this fungus was also able to effect a steady rise in the level of the total nitrogen (from 0.07 – 0.12%), available potassium (from 0.81 – 2.95 Meq/100g), phosphorus (from 1.23 – 11.94 mg/kg) and magnesium (from 0.55 – 1.03 Meq/100g) present in the SEO polluted soil to levels significantly (p≤0.05) higher than the control values by the 3rd and the 6th months after the SEO spillage. Also, the addition of A. oryzae as a mycoremediation agent on a SEO polluted field further caused a significant (p≤ 0.05) increase in the vegetation cover of the field to levels higher than the controls at the 2nd, 4th and 6th months after the SEO spillage. The results from the mycodeterioration studies show that the A. oryzae (isolated from the diseased seeds of I.gabonensis from Ajegunle market), caused some significant changes in the physico-chemical and the nutritional qualities of the oil and the flour respectively from I.gabonensis seed. A Gas Chromatographic confirmatory analysis of the oils from both the healthy and diseased seeds of I.gabonensis further confirmed some significant differences in the free fatty acid profiles of both oils. The results of the DNA studies showed a noticeable diversity in the genetic base of the fungal isolates. This phenomenon, coupled with the obvious variation in their utilization of the different nutrient sources (hydrocarbons) and some variation in their growth pattern in the plates may eventually lead to a renaming of some of the fungal isolates that were encountered in this research. This research has thus contributed to fulfilling the need for the much desired efficient and ecologically sound strategies for neutralizing in our environment the inadvertent or the deliberate spillage of hazardous pollutants such as petroleum and its refined products.