toxicity in the system. On the cont

toxicity in the system. On the contrary, dechlorination from
a lateral position greatly reduces the toxicity of the 2,3,7,8-substituted congeners. The TEF of 1,2,3,4,7,8-HxCDF is 0.1,
while the TEFs of potential 2,3,7,8-substituted products
2,3,4,7,8-PeCDF, 1,2,3,7,8-PeCDF, and 2,3,7,8-TeCDF are 0.3,
0.03, and 0.1, respectively. Dechlorination of 1,2,3,4,7,8-HxCDF to 2,3,4,7,8-PeCDF would be a detrimental rather
than favorable process, and the system TEQ would increase.
If 1,2,3,7,8-PeCDF or 2,3,7,8-TeCDF was formed from dechlorination, the TEQ would decrease or remain the same. We
have demonstrated detoxification during the dechlorination
of an environmentally relevant 2,3,7,8-substituted PCDF
congener by a mixed culture containingD. ethenogenesstrain
195, and an additional halogenated substrate, 1,2,3,4-TeCB,
enhanced this process. Here, TEQ in 1,2,3,4,7,8-HxCDFspiked systems decreased from 187µg/L at time 0 to 108,
157, and 163µg/L in the treatments amended with 1,2,3,4-TeCB, PCE, and no additional halogenated substrate, respectively.Dehalococcoidesspp. and closely relatedChloroflexihave been implicated in PCDD/F dechlorination in
environmental samples (21, 41). Obtaining more information
about the bacteria and dehalogenases involved in PCDD/F
dechlorination could enable advances in using this process
for bioremediation