Dechlorination and Detoxification of 1,2,3,4,7,8-hexachlorodibenzofuran by a Mixed Culture Containing Dehalococcoides Ethenogenes Strain 195

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 containing Dehalococcoides 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.