A unique biodegradation pattern of the oil spilled during the 1991 Gulf War

A laboratory degradation study of the oil spilled during the 1991 Gulf War has shown a unique degradation pattern. Very fast degradation rates of several polynuclear aromatic hydrocarbons (PAH) and sulphur-containing PAH compounds were observed compared with the saturated n-alkane fraction of the oil. The degradation pattern and rate of biodegradation were found to be dependent on the oil concentration and on the presence of nutrients. Faster rates were observed at lower oil concentrations, while the addition of nutrients greatly slowed the degradation of PAHs and enhanced the degradation of the saturates. The study suggested the presence of naturally occurring micro-organisms in the oil/water system which are very effective in rapidly biodegrading several PAH compounds. However, it appears that the activity of these micro-organisms is greatly affected by nutrientsʹ addition. Minimal PAHs degradation was noticed during the experimentʹs time frame when nutrients were added to the system. The study has also shown that the use of C17/pristane and C18/phytane ratios may underestimate the magnitude of oil biodegradation in the presence of these micro-organisms. These results supported the need to monitor the changes in both saturates and aromatic hydrocarbons in order to assess the biodegradation of spilled oil. If changes in one fraction were monitored, prediction of the effect on the other fractions of the oil could not be made.