Use of halogenated benzoates and other halogenated aromatic compounds to stimulate the microbial dechlorination of PCBs

We recently reported that certain polychlorinated biphenyl (PCB) congeners and bromobiphenyl congeners activate or "prime" dechlorination of the Arocl or 1260 in Housatonic River sediments. In this study, we tested the ability of halogenated benzoates and other halogenated aromatic compounds to prime PCB dechlorination in the same sediments. We found that none of the fluori nated or chlorinated benzoates primed PCB dechlorination, but several bromi nated and iodinated benzoates initiated this activity. Of the halogenated b enzoates tested, 4-bromobenzoate, 4-iodohenzoate, and 2,5-dibromobenzoate p rimed the most extensive PCB dechlorination, decreasing the hexa-through no nachlorobiphenyl fraction of Aroclor 1260 by 40- 70%, 10-50%, and 10-50%, r espectively. None of the halogenated benzoates were as effective at priming PCB dechlorination as 2,6-dibromobiphenyl, which primed a 60- 80% decrease of the hexa- through nonachlorobiphenyl fraction of Aroclor 1260. Several other brominated aromatic compounds were also tested for their ability to p rime PCB dechlorination. Monobrominated isomers of acetophenone, phenol, or toluene did not prime PCB dechlorination, but all monobrominated isomers o f benzonitrile, 2-bromo-, 4-bromo-, and 2,5-dibromonitrobenzene, 4-bromoben zamide, 4-bromobenzophenon 4-bromobenzoic hydrazide, 4-bromobenzoic methyl ester, and 2,5-dibromobenzene sulfonate primed PCB dechlorination in Housat onic River sediments. All of the compounds primed PCB Dechlorination Proces s N (primarily flanked meta dechlorination) except 4-bromonitrobenzene, whi ch primed Dechlorination Process P (flanked para dechlorination). These res ults indicate that halogenated aromatic compounds that are not structural a nalogues to PCBs can prime PCB dechlorination.