Effects of Petroleum Oil Pollution on the Microbiological Populations of the Desert Soil of Kuwait PDF

Keywords

petroleum, pollution, desert, Kuwait

Abstract

During the invasion of Kuwait, Iraqi invaders destroyed oil wells. As a result 60-80 million barrels of crude oil contaminated about 49 km^2 in the desert of Kuwait. The residual oil in a polluted areas in the desert of Kuwait was measured during the years 1992, 1993 and 1994. Results of the analysis of residual oil show that the saturates fraction decreased from 23.4% in the first year to 11.9% in the second year, and nearly disappeared in the third year. The aromatic and the resin fractions decreased then increased again, while the asphaltene fractions increased and accumulated during the last two years. The residual n-alkanes and iso-alkanes of the saturates fraction were followed by gas chromatography. During the first year less quantities were removed during the second year. On the other hand most of the n-alkanes (except traces of some components) were removed during the last year. It was observed that high molecular weight n-alkane (C31) was accumulated in the soil samples collected during this year. Oil-degrading bacteria showed positive response to the exposure to oil pollutants, their ratios of the counts of the polluted samples (SP) to that of control samples (SC) ranged from 3.7-50. In contrast the SP/SC ratios of the total bacteria, actinomycetes, cellulose decomposers and thermophiles were in the range of 0.03-4.2. Fungi were of positive response to oil pollutants than bacteria, their SP/SC ratios ranged from 4.7-11.1. The microbial mixture activity of each soil samples to biodegrade petroleum oil and its fractions was studied. It was found that biodegradation activity of the microbial population of the polluted soil samples decreased with decreasing the residual oil pollutants. In soil samples of 3.9% residual oil, 37.5% crude oil, 51.2% of the saturates and 17.4% of the aromatics were biodegraded. When the residual oil was 0.1% in the last year, 17.0% of the added crude oil and 20.3% of its saturates fraction were biodegraded, while none of its aromatic fraction was biodegraded. As a comparison, microbial population of the control soil samples showed less biodegradation activity. The utilization of n-alkanes of the saturates fraction was followed by gas chromatography. Kuwait crude oil (KOC Blend) contains n-alkanes C12- C34 as well as a number of iso-alkanes. Weathering was found to remove C12- C13, most of C14 and slight reduction in the other components. The pattern of n-alkanes utilization varied according to the structure of the microbial community and the amount of residual oil present in each soil sample. Microbial population present in polluted soil samples collected during 1992 and 1993 resulted in the removal of all n-alkanes except traces of some components. Microbial populations of the soil samples collected during the last year, removed large quantities of such components. On the other hand microbial communities found in the control soil samples also succeeded in removing large quantities of n-alkanes, but slightness than those of the polluted soil samples. A total of 92 fungal isolates (62 from the polluted samples and 30 from the control samples) were identified. Aspergillus spp and Stemphylium spp were sensitive to oil pollution. Aspergillus spp, the dominant fungus in the polluted samples was identified as Aspergillus terreus, it was selected and studied for its biodegradation activities. The results show that this fungal species was able to utilize in 21 day 30% of the crude oil, 31.8% of the saturates fraction and 13.8% of the aromatic fraction. It succeeded to utilize most of the components of the n-alkanes. A total of 90 bacterial isolates were isolated from colonies appeared on oil- silica gel plates. All strains from soil samples collected during 1994 and of control soil samples were Arthrobacter spp. Pseudomonas was more frequent (80%) in soil samples of 3.7% pollutants. Six isolates, two Pseudomonas spp and four Arthrobacter spp representing cultures showing very good growth on media containing petroleum as the only carbon source, were selected and studied for their abilities to degrade crude petroleum and its fractions. Pseudomonas spp showed biodegradation activity more than the Arthrobacter spp. They degraded 11.2- 16.8% of the crude oil, 26% of the saturates and 5.6 -6.8% of the aromatics. On the other hand Arthrobacter spp isolated from the polluted soil samples showed more activities than Arthrobacter spp of the control soil samples. Three strains of Arthrobacter were able to degrade 1.3- 4.6% of the resin fraction. Results of the utilization of n-alkanes by the above bacterial strains show that biodegradation accomplished by Pseudomonas spp resulted in the removal of most of the n-alkanes. On the other hand Arthrobacter spp showed less activities than the Pseudomonas. Arthrobacter spp (1 & 2) isolated from the polluted soil samples were found to removemore n-alkanes than those isolated from the control soil samples. The appearance of an increase of n-alkanes C30 was noted during the growth of Pseudomonas spp and Arthrobacter spp.