Toxic polychlorinated dibenzo-p-dio

Toxic polychlorinated dibenzo-p-dioxins and dibenzofurans
(PCDD/Fs) with chlorines substituted at the lateral 2, 3, 7, and
8 positions are of great environmental concern. We investigated
the dechlorination of 1,2,3,4,7,8-hexachlorodibenzofuran (1,2,3,4,7,8-HxCDF) and 1,2,3,4,6,7,8,9-octachlorodibenzo-p-dioxin (OCDD)
by a mixed culture containingDehalococcoides ethenogenes
strain 195. The 1,2,3,4,7,8-HxCDF was dechlorinated to 1,3,4,7,8-pentachlorodibenzofuran and 1,2,4,7,8-pentachlorodibenzofuran
and further to two tetrachlorodibenzofuran congeners, which
were identified as 1,3,7,8-tetrachlorodibenzofuran and 1,2,4,8-tetrachlorodibenzofuran. Because no 2,3,7,8-substituted congeners
were formed as dechlorination products from 1,2,3,4,7,8-HxCDF, this dechlorination represents a detoxification reaction.
Tetrachloroethene (PCE) and 1,2,3,4-tetrachlorobenzene (1,2,3,4-TeCB) were added as additional halogenated substrates to
enhance the degree of 1,2,3,4,7,8-HxCDF dechlorination. The 1,2,3,4-TeCB enhanced the extent of dechlorination of 1,2,3,4,7,8-HxCDF approximately 3-fold compared to PCE or no additional
substrate amendment. No dechlorination products were
detected from OCDD. Bioremediation of PCDD/Fs by bacterial
reductive dechlorination should address the pathway of
dechlorination to ensure detoxification.