HxCDF and 1,2,3,6,7,8-HxCDF by a pe

HxCDF and 1,2,3,6,7,8-HxCDF by a peri chlorine removal in
aquifer microcosms. This resulted in increased toxicity
because the produced HxCDFs both have TEFs of 0.1, 10-fold higher than that of the parent compound.Dehalococcoidessp. strain CBDB1 dechlorinated 1,2,3,7,8-pentachlorodibenzo-p-dioxin (1,2,3,7,8-PeCDD) with a TEF of 1, slowly
(2.8 mol % within 104 days), to mainly 2,3,7,8-TeCDD, also
with a TEF of 1, and small amounts of 1,3,7,8-TeCDD (22).
Strain CBDB1 further detoxified the 2,3,7,8-TeCDD intermediate, forming 2,3,7-TrCDD, 2,7-DCDD, and/or 2,8-DCDD
(22). This pattern of dechlorination was similar to what had
been demonstrated by strain CBDB1 with 1,2,3,4-TeCDD. A
pure culture ofD. ethenogenesstrain 195 did not dechlorinate
2,3,7,8-TeCDD after 249 days (23).
Considering the generally slow rates of dechlorination of
PCDD/Fs by dechlorinating bacteria (16–20, 22, 23), and this
study), transient intermediates might exist in the environment
for years and have great environmental impact. The formation
of equally or more toxic intermediates will not reduce the
threat to the environment and biota. The TEF values of the
17 2,3,7,8-substituted PCDD/Fs normally increase with a
decreasing number of chlorines on the carbon backbone.
Dechlorination from a peri position mostly increases the