Biodegradation of Kuwait crude oil in the presence and absence of the dispersant Corexit 9527

Abstract

Kuwait crude oil was subjected to a time series, laboratory simulation of biodegradation by incubation in nutrient enhanced seawater with a mixed culture of oil degrading microorganisms isolated from the Gulf of Mexico. The effect of a non-toxic, biodegradable dispersant on these processes was evaluated. More than 40% of the initial mass of the oil was lost after 92 days, of which 25% was attributed to biodegradation. The saturate fraction lost 50% of its initial weight, with 35% being due to biodegradation. The aromatic fraction had a 30% loss of its initial mass, but the extent of loss by biodegradation alone could not be calculated. There was an increase in the mass of the resin fraction, and small and non-significant decrease in the asphaltenes' mass. Biodegradation of n-alkanes was rapid, with most of the loss of individual compounds occurring in the first 30 days of incubation. There was a preference for n-alkanes with chain lengths less than C₂₄. Longer chain n-alkanes were degraded concurrently with simple aromatics (C₀ and C₁ naphthalene). The isoprenoids were less preferred than the n-alkanes, and pristane was preferred over phytane. The steranes and hopanes were not significantly biodegraded. However, the monoaromatic steranes showed significant amounts of biodegradation. There was preferential degradation of the individual aromatic compounds dependent on the degree of alkylation. The order of preference was approximately: naphthalene and C₁ naphthalene > C₂ naphthalene > phenanthrene and dibenzothiophene > C₁ phenanthrene and C₁ dibenzothiophene. The other aromatic homologs analyzed (C₃ naphthalene, and C₂ and C₃ phenanthrene and dibenzothiophene) were not affected within 92 days, but showed some loss in long-term (>1 year) incubations. This was interpreted as a continuation of the trends established after 92 days incubation. Isomeric specificity was demonstrated for dimethylnaphthalenes, and for methylphenanthrenes and dibenzothiophenes. The use of the dispersant Corexit 9527 temporarily retarded the degradation of hydrocarbons. It has been shown to be biodegradable, and the timing of its disappearance concurs with the timing of the retardation of hydrocarbon biodegradation.