Aerobic and Anaerobic Biodegradation of PCBs: A Review

This review summarizes recent research results on the biodegradation of polychlorinated biphenyls (PCBs). These compounds, commonly believed to be indestructible, have repeatedly been shown to biodegrade under a variety of conditions. Two distinct classes of bacteria have now been identified that biodegrade PCBs by different mechanisms. The focus of this manuscript is current research involving the aerobic biodegradation of PCBs (natural strains, recombinant organisms, and soil applications) and the dramatic new results demonstrating microbial reductive dechlorination of even highly chlorinated PCBs under anaerobic conditions.These two PCB-degradative systems include aerobic bacteria which live in oxygenated environments and anaerobic bacteria which live in oxygen free environments such as aquatic sediments. The aerobes attack PCBs oxidatively, breaking open the carbon ring and destroying the compounds. Anaerobes, on the other hand, leave the biphenyl rings intact while removing the chlorines. This anaerobic dechlorination degrades highly chlorinated compounds into less chlorinated derivatives. These two naturally occurring processes are complementary, and a two step treatment may permit the biological destruction of nearly all of the PCB mixtures commonly used.