Polycyclic Aromatic Hydrocarbon Biodegradation as a Function of Oxygen Tension in Contaminated Soil

Laboratory tests were conducted to determine the effect of soil gas oxygen concentration on the degradation and mineralization of spiked C-pyrene and nonspiked 16 priority pollutant polycyclic aromatic hydrocarbons (PAHs) present in the soil. The soil used for the evaluation was taken from a prepared bed land treatment unit at the Champion International Superfund Site in Libby, Montana. This soil was contaminated with wood preserving wastes including creosote composed primarily of polycyclic aromatic hydrocarbons and pentachlorophenol. Degradation rates of C-pyrene and PAH compounds were found to be enhanced under soil gas oxygen concentrations between 2% and 21% in the contaminated soil. Between 45% and 55% of C-pyrene spiked onto the soil was mineralized after 70 days at soil gas oxygen levels between 2% and 21%. No statistically significant mineralization was found to occur at 0% oxygen concentrations. Mineralization of C-pyrene in contaminated soil poisoned with mercuric chloride was determined to be less than 0.5%. Degradation of indigenous nonradiolabeled PAHs in nonpoisoned soil was statistically significantly greater than in poisoned soil. These results indicated that degradation of C-pyrene and PAH compounds was biological and would occur under low oxygen concentrations that could be maintained, for example, using bioventing technology in order to achieve continued treatment of buried lifts of soil while new lifts are added, thus decreasing the total time for soil remediation of the prepared bed.