Reductive dechlorination

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Reductive dechlorination is a biological process that is used to describe certain types of biodegradation of chlorinated solvents in groundwater.

[edit] Biological

Tetrachloroethylene (PCE) and trichloroethylene (TCE) and other chlorinated aliphatic hydrocarbons as well as aromatic hydrocarbons in groundwater can be biodegraded by naturally occurring anaerobic bacteria, most commonly of the genera dehalococcoides. This occurs when other anaerobic bacteria present in the contaminated site take electrons from organic compounds (the "electron donors") and produce H₂. The dechlorinating bacteria use the electrons in the H₂ to replace a chlorine atom in TCE/PCE.

If the site soil and groundwater contain organic electron donors, this process can proceed until all of the chlorine atoms are removed, and TCE is dechlorinated completely via dichloroethene (DCE) and vinyl chloride (VC) to ethylene gas, a harmless end-product. Other solvents, such as 1,1,1-TCA and carbon tetrachloride, can also be degraded by reductive dechlorination.

[edit] Radiation

It is known that by gamma irradiation of PCBs that they can be converted into biphenyl and inorganic chloride, this is formally a reduction of the organic compound as hydrogen is added. See the Polychlorinated biphenyl page for more details of this destruction method. This reductive destruction method works for many organochlorine compounds, for instance carbon tetrachloride when irradiated tends to form chloroform and chloride anions.