[Bioremediation of soils and sediments polluted by polychlorinated biphenyls]

This review discusses the real prospects of using the potential of microorganisms for bioremediation of PCB-polluted natural environments (soil, sediments, and wastewater sludge) under anaerobic and aerobic conditions. A detailed analysis of the research conditions of original works has shown that the efficiency of bioremediation of PCB-polluted objects strongly depends on the character and degree of pollution. In the case of aerobic bioremediation, the best results were obtained with moderately polluted soils and sediments (20 to 700 PCB/kg), in which the level of pollution decreased by 40-75%. These results could be achieved only by repeated inoculation of a consortium of specific microorganisms (isolated or constructed) with concurrent addition of biphenyl as an inducer and of biosurfactants; their effect increased in a liquid phase bioreactor. PCB concentration decreased mainly due to the degradation of congeners with one to three chlorine atoms. The content of highly chlorinated PCB can be noticeably decreased only under sequential anaerobic-aerobic treatment; the best effect was achieved with anaerobic granules. However, only in individual cases, mainly in laboratory experiments with newly introduced PCB at moderate concentrations, was it possible to reduce their content to a level permissible for technogenic soils. The review begins with the description of the main metabolic pathways and patterns of biodegradation of these pollutants in natural and artificial environments.