Intrinsic capacities of soil microflorae for gasoline degradation

A methodology to determine the intrinsic capacities of a microflora to degrade gasoline was developed, in particular for assessing the potential of autochtonous populations of polluted and non polluted soils for natural attenuation and engineered bioremediation. A model mixture (GM23) constituted of the 23 most representative hydrocarbons of a commercial gasoline was used. The capacities of the microflorae (kinetics and extent of biodegradation) were assessed by chromatographic analysis of hydrocarbon consumption and of CO2 production. The degradation of the components of GM23 was assayed in separate incubations of each component and in the complete mixture. For the microflora of an unpolluted spruce forest soil, all hydrocarbons of GM23 except cyclohexane, 2,2,4- and 2,3,4-trimethylpentane isomers were degraded to below detection limit in 28 days. This microflora was reinforced with two mixed microbial communities selected from gasoline-polluted sites and shown to degrade cyclohexane and 2,2,4-trimethylpentane. With the reinforced microflora, complete degradation of GM23 was observed. The degradation patterns of individual components of GM23 were similar when the compounds were present individually or in the GM23 mixture, as long as the concentrations of 2-ethyltoluene and trimethylbenzene isomers were kept sufficiently low (< or = 35 mg.l-1) to remain below their inhibitory level.