Reductive dechlorination: Difference between revisions
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Biological reductive dechlorination is often catalyzed by certain species of [[bacteria]]. Sometimes the bacterial species are highly specialized for organochlorine respiration and even a particular electron donor, as in the case of ''[[Dehalococcoides]]'' and ''[[Dehalobacter]]''. In other examples, such as ''[[Anaeromyxobacter]]'', bacteria have been isolated that are capable of using a variety of electron donors and acceptors, with a subset of possible electron acceptors being organochlorines.<ref>Smidt and de Vos. Anaerobic microbial dehalogenation. Annu Rev Microbiol (2004) vol. 58 pp. 43-73 {{PMID|15487929}}</ref> These reactions depend on a molecule which tends to be [https://www.sciencedaily.com/releases/2017/01/170131080152.htm very aggressively sought after] by some microbes, [[vitamin B12]].<ref>https://motherboard.vice.com/en_us/article/with-help-from-bacteria-biochemists-learn-how-to-break-up-environmental-toxins</ref> |
Biological reductive dechlorination is often catalyzed by certain species of [[bacteria]]. Sometimes the bacterial species are highly specialized for organochlorine respiration and even a particular electron donor, as in the case of ''[[Dehalococcoides]]'' and ''[[Dehalobacter]]''. In other examples, such as ''[[Anaeromyxobacter]]'', bacteria have been isolated that are capable of using a variety of electron donors and acceptors, with a subset of possible electron acceptors being organochlorines.<ref>Smidt and de Vos. Anaerobic microbial dehalogenation. Annu Rev Microbiol (2004) vol. 58 pp. 43-73 {{PMID|15487929}}</ref> These reactions depend on a molecule which tends to be [https://www.sciencedaily.com/releases/2017/01/170131080152.htm very aggressively sought after] by some microbes, [[vitamin B12]].<ref>https://motherboard.vice.com/en_us/article/with-help-from-bacteria-biochemists-learn-how-to-break-up-environmental-toxins</ref> |
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'''Bioremediation using reductive dechlorination''' |
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In many instances, microbiological reductive dechlorination of chlorinated organic molecules is important for [[bioremediation]] of polluted groundwater. One particularly important example for public health<ref>Kielhorn et al. Vinyl chloride: still a cause for concern. Environ Health Perspect (2000) vol. 108 (7) pp. 579-88 {{PMID|10905993}}</ref> is the organochloride respiration of the dry-cleaning solvent, [[tetrachloroethylene]] (PCE), and the engine degreasing solvent [[trichloroethylene]] (TCE) by naturally occurring [[anaerobic bacteria]], often members of the candidate genera ''Dehalococcoides''. Bioremediation of these [[chloroethene]]s can occur when other microorganisms at the contaminated site provide H<sub>2</sub> as a natural byproduct of various [[Fermentation (biochemistry)|fermentation]] reactions. The dechlorinating bacteria use this H<sub>2</sub> as their electron donor, ultimately replacing [[chlorine]] atoms in the chloroethenes with hydrogen atoms via hydrogenolytic reductive dechlorination. If the soil and groundwater contain enough organic electron donor and the appropriate strains of ''Dehalococcoides'', 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 [[ethene]], a harmless end-product.<ref>McCarty. Breathing with chlorinated solvents. Science (1997) vol. 276 (5318) pp. 1521-2 {{PMID|9190688}}</ref> |
In many instances, microbiological reductive dechlorination of chlorinated organic molecules is important for [[bioremediation]] of polluted groundwater. One particularly important example for public health<ref>Kielhorn et al. Vinyl chloride: still a cause for concern. Environ Health Perspect (2000) vol. 108 (7) pp. 579-88 {{PMID|10905993}}</ref> is the organochloride respiration of the dry-cleaning solvent, [[tetrachloroethylene]] (PCE), and the engine degreasing solvent [[trichloroethylene]] (TCE) by naturally occurring [[anaerobic bacteria]], often members of the candidate genera ''Dehalococcoides''. Bioremediation of these [[chloroethene]]s can occur when other microorganisms at the contaminated site provide H<sub>2</sub> as a natural byproduct of various [[Fermentation (biochemistry)|fermentation]] reactions. The dechlorinating bacteria use this H<sub>2</sub> as their electron donor, ultimately replacing [[chlorine]] atoms in the chloroethenes with hydrogen atoms via hydrogenolytic reductive dechlorination. If the soil and groundwater contain enough organic electron donor and the appropriate strains of ''Dehalococcoides'', 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 [[ethene]], a harmless end-product.<ref>McCarty. Breathing with chlorinated solvents. Science (1997) vol. 276 (5318) pp. 1521-2 {{PMID|9190688}}</ref> |
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Additionally, reductive dechlorination can be further used in bioremediation of other [[Toxin|toxins]] such as [[PCB]]s and [[CFC]]s. The reductive dechlorination of PCBs is performed by anaerobic microorganisms that utilize the PCB as an electron sink. The result of this is the reduction of the "meta" site, followed by the "para" site, and finally the "ortho" site, leading to a dechlorinated product.<ref name=":7">{{Cite journal|last=Payne|first=Rayford B.|last2=May|first2=Harold D.|last3=Sowers|first3=Kevin R.|date=2011-10-15|title=Enhanced Reductive Dechlorination of Polychlorinated Biphenyl Impacted Sediment by Bioaugmentation with a Dehalorespiring Bacterium|url=http://dx.doi.org/10.1021/es201553c|journal=Environmental Science & Technology|volume=45|issue=20|pages=8772–8779|doi=10.1021/es201553c|issn=0013-936X}}</ref><ref name=":6">{{cite journal|last1=Tiedje|first1=James M.|last2=Quensen|first2=John F.|last3=Chee-Sanford|first3=Joann|last4=Schimel|first4=Joshua P.|last5=Boyd|first5=Stephen A.|title=Microbial reductive dechlorination of PCBs|journal=Biodegradation|date=1994|volume=4|issue=4|pages=231–240|doi=10.1007/BF00695971}}</ref><ref name=":5">{{cite journal|last1=QUENSEN|first1=J. F.|last2=TIEDJE|first2=J. M.|last3=BOYD|first3=S. A.|title=Reductive Dechlorination of Polychlorinated Biphenyls by Anaerobic Microorganisms from Sediments|journal=Science|date=4 November 1988|volume=242|issue=4879|pages=752–754|doi=10.1126/science.242.4879.752}}</ref> Under experimental conditions, microorganisms undergoing reductive dechlorination in the Hudson River have shown to remove 53% of the total chlorine levels following 16 weeks. This is accompanied by a 9 fold increase in the proportion of monochlorobiphenyls and dichlorobiphenyls which are less toxic and more easily degradable by [[Aerobic organism|aerobic organisms]] compared to their [[chlorinated]] counterparts.<ref name=":5" /> The prominent drawback that has prevented the widespread use of reductive dechlorination for PCB detoxification and has decreased its feasibility is the issue of the slower than desired dechlorination rates.<ref name=":6" /> However, recently, it has been suggested that [[bioaugmentation]] with DF-1 can lead to enhanced reductive dechlorination rates of PCBs through stimulation of dechlorination. Additionally, high inorganic carbon levels do not affect dechlorination rates in low PCB concentration environments.<ref name=":7" /> |
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Another potent toxin that can possibly be bioremediated using reductive dechlorination is CFCs.<ref>{{Cite journal|last=Lovley|first=Derek R.|last2=Woodward|first2=Joan C.|date=1992-05-01|title=Consumption of Freons CFC-11 and CFC-12 by anaerobic sediments and soils|url=http://dx.doi.org/10.1021/es00029a009|journal=Environmental Science & Technology|volume=26|issue=5|pages=925–929|doi=10.1021/es00029a009|issn=0013-936X}}</ref> Reductive dechlorination of CFCs including CFC-11, CFC-113, chlorotrifluoroethene, CFC-12, HCFC-141b, and tetrachloroethene occur through [[hydrogenolysis]]. Reduction rates of CFC mirror theoretical rates calculated based on the [[Marcus theory]] of electron transfer rate.<ref>{{Cite journal|last=Balsiger|first=Christian|last2=Holliger|first2=Christof|last3=Höhener|first3=Patrick|title=Reductive dechlorination of chlorofluorocarbons and hydrochlorofluorocarbons in sewage sludge and aquifer sediment microcosms|url=http://linkinghub.elsevier.com/retrieve/pii/S0045653505003802|journal=Chemosphere|volume=61|issue=3|pages=361–373|doi=10.1016/j.chemosphere.2005.02.087}}</ref> |
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==Electrochemical== |
==Electrochemical== |
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Revision as of 04:51, 20 November 2017
Reductive dechlorination is degradation of chlorinated organic compounds by chemical reduction with release of inorganic chloride ions.
Biological
In a biological context chlorine behaves similarly to other atoms in the halogen chemical series, and thus reductive dechlorination can be considered to fall within a somewhat broader class of biological reactions known as reductive dehalogenation reactions, in which the removal of a halogen substituent from an organic molecule occurs with a simultaneous addition of electrons to the molecule. This can be further subdivided into two types of reaction processes, the first of which, hydrogenolysis, is the replacement of the halogen atom with a hydrogen atom. The second, vicinal reduction (sometimes called, dihaloelimination), involves the removal of two halogen atoms that are adjacent on the same alkane or alkene molecule, leading to the formation of an additional carbon-carbon bond.[1]
Biological reductive dechlorination is often catalyzed by certain species of bacteria. Sometimes the bacterial species are highly specialized for organochlorine respiration and even a particular electron donor, as in the case of Dehalococcoides and Dehalobacter. In other examples, such as Anaeromyxobacter, bacteria have been isolated that are capable of using a variety of electron donors and acceptors, with a subset of possible electron acceptors being organochlorines.[2] These reactions depend on a molecule which tends to be very aggressively sought after by some microbes, vitamin B12.[3]
Bioremediation using reductive dechlorination
In many instances, microbiological reductive dechlorination of chlorinated organic molecules is important for bioremediation of polluted groundwater. One particularly important example for public health[4] is the organochloride respiration of the dry-cleaning solvent, tetrachloroethylene (PCE), and the engine degreasing solvent trichloroethylene (TCE) by naturally occurring anaerobic bacteria, often members of the candidate genera Dehalococcoides. Bioremediation of these chloroethenes can occur when other microorganisms at the contaminated site provide H2 as a natural byproduct of various fermentation reactions. The dechlorinating bacteria use this H2 as their electron donor, ultimately replacing chlorine atoms in the chloroethenes with hydrogen atoms via hydrogenolytic reductive dechlorination. If the soil and groundwater contain enough organic electron donor and the appropriate strains of Dehalococcoides, 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 ethene, a harmless end-product.[5]
Additionally, reductive dechlorination can be further used in bioremediation of other toxins such as PCBs and CFCs. The reductive dechlorination of PCBs is performed by anaerobic microorganisms that utilize the PCB as an electron sink. The result of this is the reduction of the "meta" site, followed by the "para" site, and finally the "ortho" site, leading to a dechlorinated product.[6][7][8] Under experimental conditions, microorganisms undergoing reductive dechlorination in the Hudson River have shown to remove 53% of the total chlorine levels following 16 weeks. This is accompanied by a 9 fold increase in the proportion of monochlorobiphenyls and dichlorobiphenyls which are less toxic and more easily degradable by aerobic organisms compared to their chlorinated counterparts.[8] The prominent drawback that has prevented the widespread use of reductive dechlorination for PCB detoxification and has decreased its feasibility is the issue of the slower than desired dechlorination rates.[7] However, recently, it has been suggested that bioaugmentation with DF-1 can lead to enhanced reductive dechlorination rates of PCBs through stimulation of dechlorination. Additionally, high inorganic carbon levels do not affect dechlorination rates in low PCB concentration environments.[6]
Another potent toxin that can possibly be bioremediated using reductive dechlorination is CFCs.[9] Reductive dechlorination of CFCs including CFC-11, CFC-113, chlorotrifluoroethene, CFC-12, HCFC-141b, and tetrachloroethene occur through hydrogenolysis. Reduction rates of CFC mirror theoretical rates calculated based on the Marcus theory of electron transfer rate.[10]
Electrochemical
The electrochemical reduction of chlorinated chemicals such as chlorinated hydrocarbons and chlorofluorocarbons (CFCs) can be carried out by electrolysis in appropriate solvents, such as mixtures of water and alcohol. The cathode transfers electrons to the molecule, which decomposes to produce the corresponding hydrocarbon (hydrogen atoms substitute the original chlorine atoms) and free chloride ions. For instance, the reductive dechlorination of CFCs is complete and produces several HFCs plus chloride.[11]
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.
References
- ^ Mohn and Tiedje. Microbial reductive dehalogenation. Microbiol Rev (1992) vol. 56 (3) pp. 482-507 PMID 1406492
- ^ Smidt and de Vos. Anaerobic microbial dehalogenation. Annu Rev Microbiol (2004) vol. 58 pp. 43-73 PMID 15487929
- ^ https://motherboard.vice.com/en_us/article/with-help-from-bacteria-biochemists-learn-how-to-break-up-environmental-toxins
- ^ Kielhorn et al. Vinyl chloride: still a cause for concern. Environ Health Perspect (2000) vol. 108 (7) pp. 579-88 PMID 10905993
- ^ McCarty. Breathing with chlorinated solvents. Science (1997) vol. 276 (5318) pp. 1521-2 PMID 9190688
- ^ a b Payne, Rayford B.; May, Harold D.; Sowers, Kevin R. (2011-10-15). "Enhanced Reductive Dechlorination of Polychlorinated Biphenyl Impacted Sediment by Bioaugmentation with a Dehalorespiring Bacterium". Environmental Science & Technology. 45 (20): 8772–8779. doi:10.1021/es201553c. ISSN 0013-936X.
- ^ a b Tiedje, James M.; Quensen, John F.; Chee-Sanford, Joann; Schimel, Joshua P.; Boyd, Stephen A. (1994). "Microbial reductive dechlorination of PCBs". Biodegradation. 4 (4): 231–240. doi:10.1007/BF00695971.
- ^ a b QUENSEN, J. F.; TIEDJE, J. M.; BOYD, S. A. (4 November 1988). "Reductive Dechlorination of Polychlorinated Biphenyls by Anaerobic Microorganisms from Sediments". Science. 242 (4879): 752–754. doi:10.1126/science.242.4879.752.
- ^ Lovley, Derek R.; Woodward, Joan C. (1992-05-01). "Consumption of Freons CFC-11 and CFC-12 by anaerobic sediments and soils". Environmental Science & Technology. 26 (5): 925–929. doi:10.1021/es00029a009. ISSN 0013-936X.
- ^ Balsiger, Christian; Holliger, Christof; Höhener, Patrick. "Reductive dechlorination of chlorofluorocarbons and hydrochlorofluorocarbons in sewage sludge and aquifer sediment microcosms". Chemosphere. 61 (3): 361–373. doi:10.1016/j.chemosphere.2005.02.087.
- ^ P. L Cabot, M. Centelles, and L. Segarra and Juan Casado Palladium-Assisted Electrodehalogenation of 1,1,2-Trichloro-1,2,2-trifluoroethane on Lead Cathodes Combined with Hydrogen Diffusion Anodes J. Electrochem. Soc., Volume 144, Issue 11, p. 3749 (1997)