Reductive Dechlorination of Chlorobenzenes

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Reductive Dechlorination of Chlorobenzenes

• Xuan Luo
• Department of MEE
• University of California, Santa Barbara

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Chorinated Benzene

• Widely used in industry as solvents, odorizers,
  insect repellents, fungicides and intermediates
  in the manufacturing of various chemicals
• Toxic, persistent, and bioaccumulative
• Hexachlorobenzene (HCB), pentachlorobenzene
  (QCB), 1,2,3,5-tetrachlorobenzene(TeCB), and
  1,3,5-trichlorobenzene (TCB), dichlorobenzene
  (DCB) and monochlorobenzene (CB)

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Chorinated Benzene(2)

• Under aerobic conditions, CB and DCB can be
  completely mineralized and they are used as
  carbon and energy sources.
• HCB, QCB, 1,2,3,5-TeCB and 1,3,5-TCB are
  resistant to aerobic transformation. They can
  only be transformed by reductive dechlorination
  in anaerobic condition

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Reductive Dechlorination

• An electron transfer reaction involves the
  release of the chlorine ion and its replacement
  by hydrogen.
• The reduction of chlorinated benzenes under
  anaerobic conditions leads to the formation of
  less chlorinated benzenes, and the release of
  chloride and protons into the medium.

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Reductive Dechlorination in Mixed Cultures
Source Enrichment and properties of a 1,2,4-
trichlorobenzene-dechlorinating methanogenic
microbial consortium
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Pathways of Dechlorination
Source Enrichment and properties of a 1,2,4-
trichlorobenzene-dechlorinating methanogenic
microbial consortium
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Source Enrichment and properties of an anaerobic
mixed culture reductively dechlorinating
1,2,3-trichlorobenzene to 1,3-dichlorobenzene
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Source Microbial transformation of chlorinated
benzenes under anaerobic conditions
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Reductive Dechlorination in A Pure Culture

• Dehalococcoides sp. Strain CBDB1 is the only
  known anaerobic bacterium
• Requires vitamin B12 and grows in a purely
  synthetic medium
• Carbon source acetate
• Electron donor hydrogen
• Electron acceptor chlorobenzenes

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Future Research

• In the lab
• whether other chlorobenzene dechlorinating
  reactions also catalyzed by Dehalococcoides-like
  bacteria or if other bacteria are responsible
• the kinetics, substrates specificities and
  genetic organization of dechlorinating enzymes
• In the field
• to what extent does chlorobenzene dechlorination
  occur in nature
• how can reductive dechlorination be initiated or
  accelerated at a contaminated site?

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Thank you!