Chlorinated Hydrocarbon Metabolism


The widespread global distribution of chlorinated hydrocarbons, their high lipophilicity and their recalcitrance have contributed to their importance as environmental toxicants. Their metabolism under oxic and anoxic conditions mediated by prokaryotic and eukaryotic cells is discussed. Various aerobic bacteria are able to use chlorinated hydrocarbons as the sole source of carbon and energy and some anaerobic bacteria can use some of these as an artificial electron acceptor in reductive dechlorination. Liver enzymes are responsible for the formation of hydrophilic metabolites ready for excretion which often lead to highly reactive and potentially toxic intermediates. In contrast, fungi, especially ligninolytic ones, usually only exhibit ‘side activities’ for the transformation of chlorinated hydrocarbons. The capabilities of bacteria had led to the development of various bioremediation processes. Both, successes and failures within these processes are known. Therefore, current research aims at a better understanding of global community interactions.

Key Concepts

  • Chlorinated hydrocarbons have been produced by the chemical industry since decades in large amounts, but they can also be observed as natural compounds, sometimes exceeding the industrially produced amounts.
  • Even though toxicological properties have pushed the chlorochemistry into the focus of considerable debate and governmental regulatory action, chlorinated hydrocarbons remain essential for certain applications.
  • The aerobic metabolism of chlorinated hydrocarbons by bacteria has been studied in detail and an immense amount of information is available on pathways, enzymes and genes involved in the mineralisation of chloroaromatics.
  • The anaerobic degradation of chlorinated hydrocarbons is due to the capability of anaerobic bacteria to use them in anaerobic respiration, which results in dechlorination.
  • Dehalococcoides organisms are the most versatile reductive dehalogenators as being capable to dehalogenate chlorinated dioxins, biphenyls, benzenes and vinyl chloride, among others.
  • Microbial activities have been widespread used for bioremediation purposes through natural attenuation, biostimulation and bioaugmentation.
  • The poor understanding of the functioning of the complex microbial activities in situ made bioremediation efforts quite unreliable.
  • The rapid development of molecular techniques in recent years allows immense insights into the processes in situ, but also on the overall physiology of biocatalysts.

Keywords: biodegradation; bioremediation; chlorochemistry; dechlorination; toxicology

Figure 1. Representative examples of chlorinated and nonchlorinated hydrocarbons known as environmental pollutants.
Figure 10. Simplified presentation of the dehalorespiration process, that is, use of chloroaliphatic or chloroaromatic compounds as the terminal electron acceptors leading to the elimination of the chlorine substituent (R = alkyl or arene).
Figure 2. Organohalogen compounds produced in natural systems (a) complex compounds carrying chloro‐, bromo‐, iodo‐ or fluorosubstituents, (b) compounds with antibiotic behaviour, (c) compounds with high potential of environmental risk: chloro‐ and bromodibenzo‐p‐dioxin or furan.
Figure 3. Schematic presentation and comparison of logarithmic octanol–water partition coefficients log Kow, water solubilities Swater (mol m−3), vapour pressures p (Pa) and dimensionless Henry's law constants H (mol Lair−1/mol Lwater−1) for some selected chlorinated aliphatic and aromatic hydrocarbons. Grey scales indicate areas of similar partition behaviour between environmental compartments (see text).
Figure 4. Degradation pathways for chlorinated aromatic compounds used by aerobic bacteria: peripheral, funnelling pathways and chlorocatechol‐degradative modified ortho‐ and meta‐pathway. Subscript numbers depict the amount of chlorine atoms present in the molecule. Only 3‐chlorocatechol is channelled into the meta‐pathway (right column).
Figure 5. Degradation pathways for chlorinated aromatic compounds used by aerobic bacteria: Hydroquinone pathway determined for 2,4,5‐trichloro‐ and pentachlorophenol.
Figure 6. Metabolic transformations of chloroaromatic compounds by ligninolytic fungi: Proposed pathway for 2,4‐dichlorophenol by peroxidases and whole cells of Phanerochaete chrysosporium.
Figure 7. Metabolic transformations of chloroaromatic compounds by liver: Initial reaction steps and intermediates during chlorobenzene metabolism.
Figure 8. Degradation of chlorinated aliphatic compounds by aerobic bacteria: Dechlorination mechanisms used during growth with chloroaliphatic compounds.
Figure 9. Degradation of chlorinated aliphatic compounds by liver: Toxicologically critical reaction types responsible for the formation of highly reactive metabolites during chloroaliphatic metabolism.


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Reineke, Walter, Mandt, Christian, Kaschabek, Stefan R, and Pieper, Dietmar H(Jul 2020) Chlorinated Hydrocarbon Metabolism. In: eLS. John Wiley & Sons Ltd, Chichester. [doi: 10.1002/9780470015902.a0000472.pub4]