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A test study of Oscillatoria bornettia for application in bioremediation of crude oil polluted terrestrial ecosystem.

Introduction

Crude oil, also called petroleum serves as the mainstay of petroleum exporting countries of the world (1). To Nigeria, the contributions of crude oil to her economy cannot be overemphasized. Crude oil was first discovered in Nigeria at Oloibiri, Bayelsa State (in the Niger Delta) in 1956 (2; 3). The discovery of the mineral marked the birth of Nigeria's oil and gas industry. Due to oil price explosion in the world oil market of the 70s, Nigeria intensified and expanded oil exploration in the onshore areas of the Delta and moved into the continental shelf of the Atlantic Ocean adjacent to Niger Delta of Nigeria. The result of the expanded exploration was increased oil production which stands today at 2.4 billion barrels per day.

Proceed from oil is the backbone of Nigeria's national income. According to Adedipe (4), crude oil revenue accounted for 47.5% of gross domestic product (GDP) and 72.9% visible trade of Nigeria in the year 2000. It is the foundation of Nigeria's economic growth and industrial development (5; 6).

However, increased crude oil exploitation in Niger Delta has led to increased and widespread pollution of soil, creeks, swamps and groundwater (7; 8; 9). This situation has become the hazard facing the environment of the area (1). Petroleum hydrocarbon pollution adversely affects the environment. It has been reported to increase soil bulk density, water porosity and reduced soil capillarity, aeration and water holding capacity (10), reduce biomass accumulation in Telfairia occidentalis,a major vegetable crop cultivated in Nigeria (11). It has also been reported to delay seed emergence, germination and reduce germination percentage of seeds (12). These effects are detrimental to survival of biota and by extension to man.

Bioremediation is becoming an increasingly an important remedial option for mitigation of environmental pollution problems. It has a great potential for destroying environmental pollutants (13) hence its various aspects are currently being studied and explored as solution source to pollution problems.

The thrust of this study was to evaluate the potential of Oscillatoria bornettia (a cyanobacterium) to degrade crude oil in a sandy-loam tropical soil. The result of the study may aid understand the feasibility of the test organism for application in bioremediation of crude oil spill, the menace of Niger Delta environment.

Materials and Methods

Sources of Materials

Petroleum hydrocarbon spill-free sandy-loam topsoil was collected within 1-10cm soil depth from 10m x 10m plot marked out in over 5-year old fallow land behind Department of Gas Engineering, University Park, University of Port Harcourt, Nigeria. Soil was homogenized by mixing thoroughly, air-dried and sieved through 2mm soil sieve to remove boulders and plant materials. Light crude oil was obtained from Shell Petroleum Development Company (SPDC), Nigeria and wild scum of Oscillatoria bornettia and water were collected from petroleum hydrocarbon impacted stagnant drainage adjacent to automobile maintenance workshop. The alga together with the water was brought in open 500ml transparent plastic vases to the research laboratory of Plant Science and Biotechnology Department, University of Port Harcourt.

Soil (350g) was placed in three 2.5 L capacity plastic trays. The soil in the trays was wetted by spraying 30ml of the water collected with the alga. One tray was treated with 5ml of the crude oil and the others were treated with 10ml and 15ml. The soil after treatment was allowed for 24-hr for the crude oil to percolate into it before being seeded with the scum of the alga. The control had same weight of soil but was not treated with crude oil (i.e. 0ml) and not seeded with the alga. The treatments and the control were each replicated five times. The set-ups were laid out in a screened house exposed to sunlight for the test organism providing optimum condition for the alga to survive and carry out metabolism. The treatments were regularly watered with the water.

Initial soil samples using composite sampling technique made of subsamples, thoroughly mixed together were collected from the replicates of treatments and control 24-hour after treatment and analysized on total petroleum hydrocarbon (TPH), pH, total organic carbon (TOC), nitrate content, phosphate content, soil conductivity and soil cation exchange capacity as assessment parameters. At the end of the experiment, final samples were also collected and analyzed on same parameters.

Total petroleum hydrocarbon (TPH) content was measured by gas chromatographic method through flame ionization detection (GC/FID) after extraction using dichloromethane as extraction solvent while pH and soil conductivity were measured by means of pH meter (Hannah 8314) and conductivity meter (HACH Ectestr microprocessor series) respectively using 50:50 (w/v) of soil to distilled water mixture and stirring vigorously. The mixture was allowed to stand for 30 minutes and reading displayed by meter recorded. Soil nitrate and phosphate were determined through spectrophotometric method, total organic carbon through the method of (14) while cation exchange capacity was determined using titration method. The results obtained were presented in composite vertical bar charts using Microsoft office excel 2003 package.

Results and Discussion

The results of the study were presented in the charts below. Initial TPH contents of were 407.14 ppm, 528.57ppm and 489.29ppm for 5ml, 10ml and 15ml pollution respectively (Fig. 1). These, reduced to 177.4ppm, 150.6ppm and 207.7ppm in the order of treatment concentration as above at the end of the study. The reductions in TPH contents correspond to 56.4%, 71.5% and 57.5%. However, there was no change in TPH content between initial and final results of the control. The observed reduction in TPH in treatment is in agreement with (15 ;16) which in a field study at Gulf of Suez coast oil spill, reported efficient degradation of crude oil in the presence of light by Oscillatoria bornettia. It explained that the degradation results from direct emulsification of the pollutant into smaller droplets by the extracellular polysaccharides of Oscillatoria bornettia cells as place of contact. It furthermore explained that indirect degradation of crude oil occurred through the activities of oil degrading bacteria immobilized in the extracellular polysaccharides of the alga using oxygen and nitrogen as mineral nutrients.

[FIGURE 1 OMITTED]

There was no significant difference in soil pH in the treatments between the initial and final results obtained. The pH values of treatments and control were within 5.77 6.08 (Fig. 2) which is in the weak acid pH range. The pH result is same as (17; 18; 19). The low pH was explained by (17; 20) to result from leaching of soil cations and nutrients down soil profile due to high precipitation characteristic of tropical environment. The leached soil cations were therefore replaced by hydrogen ions of the soil which is responsible for the general low soil acidity.

[FIGURE 2 OMITTED]

Soil phosphate content was observed to reduce significantly in the treatments while it remained constant (i.e. 17.9 ppm) in the control (Fig. 3). This is in accordance with (10; 21) and at variance with (19) who reported increase in phosphate content with increase in pollution percentage of crude oil. Similarly, soil nitrate content was observed to reduce in the treatments (Fig. 4) which disagrees with (22) who reported elevated nitrate content in refined oil contaminated soil of Isiukwuato, Abia State, Nigeria.

[FIGURE 3 OMITTED]

[FIGURE 4 OMITTED]

The result of soil total organic carbon (TOC) content is presented in Fig. 5. TOC remained constant throughout the study period in the control but was observed to increase in the treatments. The increase in soil organic carbon corroborates Jobson et al. (23; 24; 25) and is postulated to result due to addition of carbon from the pollutant.

[FIGURE 5 OMITTED]

Soil electrical conductivity was observed to be generally high in all the treatments: 200[micro]S/cm, 210[micro]S/cm and 180uS/cm for 5ml, 10ml and 15ml treatments respectively. Final conductivity value for 5ml pollution was reduced to 40.00[micro]S/cm while 10ml and 15ml pollutions were still high (Fig. 6). The high conductivity result is in order with Benka-Coker and Ekundayo (1995) and was attributed to presence of high concentrations of TPH content in 10ml and 15ml treatments.

[FIGURE 6 OMITTED]

Effective cation exchange capacity was significantly reduced in the treatments compared with the control. This was constant (i.e. 8.46 meq/kg) in the control (Fig. 7) and ranged between 2.04-2.08 meq/kg in the treatments. The result agrees with Abii and Nwosu (2009) which reported similar result in a study of crude oil spill at Eleme, Rivers State in Niger Delta.

[FIGURE 7 OMITTED]

Conclusion

The results of this short-term study revealed that Oscillatora bornettia degrades crude oil, a notorious environmental pollutant. This cyanobacterium is common in drainage systems especially petroleum hydrocarbon impacted ones that has the presence of water. Therefore, the application of the alga in field hydrocarbon pollution remediation need to be further investigated as it may provide a cheap option in petroleum hydrocarbon pollution clean-up. The results have also shown that crude oil pollution has no impact on pH of tropical soil of Niger Delta area as the presence of petroleum hydrocarbon in soil has been observed to lower effective soil cation exchange capacity. It is considered possible that soil electrical conductivity could improve with more time allowed as TPH content would also be further reduced.

References

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[22] Akubugwu, E. I., Ogbuji, G. C., Chinyere, G. C. and Ugbogu, E.A. (2009). Physicochemical properties and enzymes activity studies in a refined oil contaminated soil in Isiukwuato, Abia State, Nigeria. Biokemistri 21(2): 79-94.

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* Albert E. and Anyanwu D.I.

Department of Plant Science and Biotechnology, Faculty of Science, University of Port Harcourt, P.M.B. 5323 Port Harcourt, Nigeria

*Corresponding Author E-mail: ejikemealbert@yahoo.com
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Author:Albert, E.; Anyanwu, D.I.
Publication:International Journal of Applied Environmental Sciences
Geographic Code:6NIGR
Date:Jul 1, 2012
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