Biodegradation of polychlorinated biphenyls and volatile chlorinated hydrocarbons in contaminated soils and ground water in field condition

Three sites with a long history of contamination with polychlorinated biphenyls (PCBs) or chlorinated ethenes (CIUs) were investigated to evaluate the natural attenuation process. Data showed that both the rates and mechanisms of biodegradation differed and that the occurrence of aerobic and anaerobic microorganisms differed qualitatively and quantitatively. Criteria for feasibility of spontaneous degradation of CIUs and PCBs in ground water and soil are formulated. (a) Congener analysis was applied to evaluate the long-term exposure of individual congeners of PCBs in the environment. In the course of approximately 20 years the small changes in congener composition could be probably due to slow biodegradation of light congeners in the relatively good oxygenated superficial layers of soil. (b) Enhanced reductive dehalogenation of PCBs was accomplished by the solid-state fermentation in reactors of 15 cubic metres of volume. Efficiency of biodegradation of individual congeners was evaluated and limits of the method were determined. (c) Different reaction rates of CIU degradation in ground water have been ascribed to the presence and/or activity of anaerobic bacteria in field conditions.