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 14C-pyrene and nonspiked 16 priority pollutant polycyclic aromatic hydrocarbons (PAH) 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 14C-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 14C-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 14C-pyrene in contaminated soil poisoned with mercuric chloride was determined to be less than 0.5%. Degradation of indigenous nonradiolabeled PAH in non-poisoned soil was statistically significantly greater than in poisoned soil. These results indicated that the degradation of 14C-pyrene and PAH compounds was biological and would occur under low oxygen concentrations. For example, the use of soil aeration technology in order to achieve continued treatment for buried lifts of soil while new lifts are added will decrease the total time for soil remediation of the prepared-bed