Surfactant influence on PAH biodegradation in a creosote-contaminated soil

This study consisted of assessing the biodegradation of 13 of the 16 US Environmental Protection Agency priority polycyclic aromatic hydrocarbons (PAHs) in a creosote-contaminated soil, using both biological and chemical surfactants. The assumption was that surfactants may enhance the mobilization of the hydrophobic PAHs, and possibly their biodegradation. The rhamnolipid biosurfactants were produced by Pseudomonas aeruginosa UG2. The chemical surfactant was sodium dodecyl sulfate. Over a period of 45 weeks, PAHs were periodically extracted from soil and quantified by gas chromatography/mass spectrometry. Results showed that, at three studied concentrations, surfactant addition did not enhance PAH biodegradation in the creosote-contaminated soil. Furthermore, for the four-ring PAHs, surfactant presence seemed harmful to the biodegradation process, the residual concentrations of each studied PAH decreasing more slowly than those found in the untreated soil. Moreover, this effect increased as a function of surfactant concentration. The negative effect was less evident with biosurfactants than for the chemical surfactant. The high-molecular-weight PAHs were not degraded by the indigenous microorganisms. For the PAHs in general, the higher the molecular weight, the more recalcitrant was the contaminant. It is suggested that the surfactants were used as a preferential substrate by the indigenous microflora, which may have interfered withmore » the biodegradation of the PAHs.« less