Bioremediation of soils and sediments contaminated by polychlorinated biphenyls

This review discusses the prospects of using the potential of microorganisms for bioremediation of PCB-contaminated natural environments (soil, sediments, and sewage 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-contaminated matrices strongly depends on the character and degree of contamination. In the case of aerobic bioremediation, the best results were obtained with moderately contaminated soils and sediments (20 to 700 PCB/kg), in which the level of contamination decreased by 40–75%. These results could be achieved by repeated inoculation of a consortium of specific microorganisms (isolated or engineered) with concurrent addition of biphenyl as an inducer and of biosurfactants; their effect increased in a slurry bioreactor. PCB concentration decreased mainly due to the degradation of congeners with one to three chlorine atoms. The content of higher-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 freshly spiked 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.