Distribution in the environment of degradative capacities for gasoline attenuation

A methodology allowing the detailed assessment of the capacities of microflorae to degrade gasoline in aerobic conditions has been developed. It consisted in the determination of the degradation of a gasoline model mixture in liquid cultures in optimal conditions. The gasoline model mixture contained 23 representative hydrocarbons of gasoline (GM23). The kinetics and extent of biodegradation were evaluated by continuous overall monitoring of CO2 production and final chromatographic analysis (usually after about 30 days) of the consumption of each hydrocarbon. The methodology was used with soil and water samples from polluted and non polluted sites. The experimentation aimed at assessing the distribution of the degradative capacities in the environment and the prospects for natural attenuation of gasoline. Nine microflorae were tested. The intrinsic biodegradability (existence of mechanisms of biodegradation) appeared total for GM23 as shown by the results obtained with several microflorae. The degradative capacities of microflorae from non polluted samples were high (total degradation rates at least 85%). Incomplete degradation was observed essentially for trimethylalkanes (2,2,4-trimethylpentane and 2,3,4-trimethylpentane) and for cyclohexane. In several cases, samples from polluted sites exhibited more extensive degradative capacities, with total degradation of all hydrocarbons being observed for three out of the six samples.