Dechlorination of polychlorinated biphenyls by an anaerobic mixed culture

The reductive dechlorination of polychlorinated biphenyls (PCBs) in enriched medium with an anaerobic chlorophenol (CP)-adapted consortium was investigated in order to define the conditions which control PCB dechlorination in naturally anaerobic environments. The fastest observed dechlorination rates of 2,3,4-CB or 2,3,4,5-CB (1 mg/L concentration) to the intermediate products dichlorobiphenyl or trichlorobiphenyl were 0.15 and 0.14 mg/L/day at 30 degrees C and pH7.0. For PCB congeners with higher chlorine content (2,2',4,4',6,6'-CB, 2,2`,3,4,4',5,5`-CB), the dechlorination rate dropped sharply to below 0.01 mg/L/day. The congeners 2,2',3,3',4,4'-CB and 2,2',3,3',4,4',5,5'-CB were not dechlorinated to lower chlorinated congeners even after a 100-day incubation period. The addition of electron donors did not enhance the dechlorination rates for 2,3,4-CB, 2,3,4,5-CB or 2,2',4,4',6,6'-CB, For these three congeners, dechlorination was enhanced under methanogenic conditions but inhibited under sulfate-reducing or denitrifying conditions.