Soil Gas Oxygen Tension and Pentachlorophenol Biodegradation

Laboratory tests were conducted to determine the effect of soil gas oxygen concentration on the degradation and mineralization of spiked 14C-pentachlorophenol and nonlabeled pentachlorophenol (PCP) present in soil taken from a prepared-bed land treatment unit at the Champion International Superfund Site in Libby, Mont. This soil was contaminated with wood preserving wastes including creosote and PCP. Degradation rates of 14C-PCP and nonlabeled PCP were found to be enhanced under soil gas oxygen concentrations between 2 and 21% in the contaminated soil. Between 48 and 64% of 14C-PCP spiked onto the soil was mineralized after 70 days at soil gas oxygen levels between 2 and 21%. No statistically significant mineralization of PCP was found to occur at 0% oxygen concentrations. Mineralization of 14C-PCP in contaminated soil poisoned with mercuric chloride was determined to be less than 0.2%. Degradation of indigenous nonradiolabeled PCP in the nonpoisoned soil was statistically significantly greater than in poisoned soil. These results indicated that degradation of PCP was biological and would occur under low oxygen concentrations. Soil gas oxygen concentrations necessary for PCP biodegradation (2–5%) 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