Degradation of refinery products and oils from polluted sites by the autochthonous microorganisms of contaminated and pristine soils.

The degradation of five refinery products with different boiling ranges and four mineral oils extracted from long-term contaminated soils was monitored by measuring oxygen consumption and the concentration of the total hydrocarbons. Degradation was catalyzed by the isolated communities of the microorganisms from contaminated and pristine soils in an aqueous medium, and partly also directly in the soils. Degradation exceeding 95% was achieved for diesel fuel and spindle oil. The higher-boiling raffinates and the extracts of long-term contaminated soils were degraded by 40-60%. The extracted oils have higher boiling ranges and are therefore more difficult to degrade. Moreover, the progressive enrichment of persistent (including lower-boiling) hydrocarbons decreases the degree of degradation attainable of such aged oils. Whereas in the medium term the autochthonous microorganisms of the contaminated soils showed better degradation efficiency, in the long term the populations of the natural soils caught up with them. This may be due to a sociological adaptation process.