Bioremediation of a Crude Oil-Polluted Soil: Biodegradation,Leaching and Toxicity Assessments

The combined fate and effects of hydrocarbons (HC) on a soilecosystem affected by bioremediation were studied during 480days in a field experiment. The HC removal rates, the HC andmetabolites mobility and the potential toxicity were assessed.A clayey soil polluted by 18 000 mg HC kg^-1 dry soil, wastreated with either static-ventilated biopile or series of fivewindrows periodically tilled in order to determine the relativeinfluence of nutrients, bulking agents, aeration and soiltemperature. HC concentrations were determined by infraredspectrometry, gravimetry, gas chromatography andthermodesorption. Between 70 to 81% of the initial HC wereremoved through biological processes in fertilized soils,whereas natural attenuation without added nutrients was 56%.When adding fertilizers, residual HC were cyclic compoundspoorly biodegraded and strongly trapped on the organo-mineralmatter. Leaching of HC and water-soluble metabolites wasdemonstrated during the first stages of biodegradation. Lowlevels of the HC were detected in the leachates at day 480.Maximal toxicity was highest immediately after the introductionof oil then decreased as biodegradation proceeded. No toxiceffect was recorded on worms survival and on seeds germinationat day 480. However growth of plants was reduced in treatedsoils and a potential residual toxicity was observed on thebasis of photosynthesis inhibition and bacterial bioluminescence (Microtox) tests.