Crude Oil Biodegradation in Shatt Al-Arab River, Iraq

Oil degrading bacteria in Shatt Al-Arab River were widely distributed to constitute a big percentage of heterotrophic bacteria. Their numbers and biodegradation potential were higher during summer and in sediment than during winter and in water. They belonged to the genera Micrococcus, Vibrio, Flavobacterium, Corynebactrium, Pseudomonas, Arthrobacter, Bacillus, Staphylococcus, Nocardia, Aeromonas, and Acintobacter. The most active degraders degraded the crude oil by more than 50 % over a 21 days period. The UV mutated degrader (P. putida) and Arthrobacter sp. mixed culture degraded the crude oil by 92 % over the same period. The rates of biodegradation in open water were limited by temperature and available nutrients. The adding of nutrients and oil degraders cultures to crude oil contaminated site was enhanced biodegradation. All components of crude oil were biodegraded at different rates. The biodegradation of aromatic hydrocarbons were much lower than n– and branched alkanes. INTRODUCTION The production, transportation and distribution of petroleum during the past century resulted in hydrocarbons contamination becoming a major environmental problem. Petroleum has contaminated waters, soils, threatening human heath and damaging the environment (NRC, 2003). However, most of the environmental inputs of petroleum are accommodated largely due to capacities of microorganisms to biodegrade hydrocarbons (Atlas, 1981; Harayama et al., 2004). Such hydrocarbons degrading microorganisms are ubiquitously distributed in the environment, and that the rates of hydrocarbon biodegradation are limited by abiotic environmental factors (Van Hamme et al., 2003). The persistence of petroleum pollutants depend on the quantity and quality of the hydrocarbon mixture and on the properties of the affected ecosystem. In one environment, petroleum hydrocarbons can persist almost indefinitely, whereas under another set of conditions, the same hydrocarbons can be completely biodegraded within a few hours or days (Atlas, 1995). This paper will report the potential of Shatt Al-Arab River ecosystem for petroleum biodegradation. Shatt Al-Arab River is the most important river and the only source of freshwater in the arid surroundings of southern Iraq. It is the prime freshwater source and pours about 5x109 m3 nutrient rich water into the Arabian Gulf each year (Al-Saad, 1995). Its water is liable to contain petroleum contaminants because of numerous operations. Farid et al. (2008) reported that the oil refinery effluents and losses during loading operations have been identified as the major sources of oil contamination in the water of Shatt Al-Arab River which empties into the North West Arabian Gulf. Little is known about hydrocarbons biodegradation process in Shatt Al-Arab River environment. The most previous studies in the river focused on the isolation and distribution of hydrocarbons utilizing microorganisms (Shamshoom et al, 1990). There is a need to understand the fate and behavior of hydrocarbon contaminants in this ecological system. Therefore, the present study was achieved. The results obtained in this study can service as a baseline for future biodegradation studies in the region. The objective of present work was to 1determine the density of oil degrading bacteria in the water and sediment samples of Shatt Al-Arab River. 2isolate the indigenous oil degrading bacteria from the river area. 3determine in vitro the hydrocarbons biodegradation potential of a variety of samples and isolates. 4know the seasonal variations exist in the petroleum biodegradation potential. 5mutate the indigenous oil degrading bacteria to obtain on bacterial inoculum with higher ability to degrade crude oil hydrocarbons. And finally, 6evaluate in situ the effects of adding mixed cultures of exogenous oil degrading bacteria and nutrients on the bioremediation of crude oil. MATERIALS AND METHODS Description of study area and sampling The Shatt Al-Arab River originates from the confluence of the two major rivers of Iraq (Tigris and Euphrates) at Qurna. Karun River, the only tributary of the Shatt Al-Arab River, joins its eastern bank south of Basrah City (Figure 1). The length of the Shatt Al-Arab River from Qurna i.e. its place of origin, to its mouth in Arabian Gulf, extends about 175 km. Its with varies at different points, ranging from 0.4 km at Basrah City to 1.5 km at its mouth. The water depth increases in general towards the Gulf with a maximum of 12.2 m. The water level is, however, affected by the high and low tides of the Arabian Gulf where the average tidal range is about 1.7 m. Shatt Al-Arab water characterized as being well mixed with limited vertical stratification of temperature and chlorinities. The water of Shatt Al-Arab mouth may be traced as far as 5 km into the Arabian Gulf. The discharge of this river reaches the waters of Kuwait Bay during the flood season.