Railroad Ties
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Chlorinated Phenols

Pentachlorophenol (PCP) was one of the most widely used biocides in the U.S., and despite residential use restrictions, is still used industrially as a wood preservative. In addition to PCP, tetrachlorophenol and trichlorophenol isomers were also used as fungicides in wood preserving formulations. 2,4-Dichlorophenol and 2,4,5-trichlorophenol were used as chemical intermediates in herbicide production, and chlorophenols are known byproducts of chlorine bleaching in the pulp and paper industry.

Pentachlorophenol

Degradation Pathways

Under anaerobic conditions, chlorinated phenols can serve as an electron acceptor for some Desulfitobacterium and Dehalococcoides species. In each case, however, complete reductive dechlorination of PCP to phenol was not observed. Under aerobic conditions, PCP can be utilized as a sole source of carbon and energy by some bacteria.  qPCR assays targeting PCP monooxygenases that initiate aerobic PCP biodegradation have been developed.

Analysis Packages

For more information on the molecular biological tools that can be used to assess the biodegradation of chlorinated phenols, click the section of interest in the dropdown menu below. For guidance tailored to your current needs, contact our project success team at 865-573-8188 or [email protected].

Anaerobic Biodegradation

Under anaerobic conditions, pentachlorophenol (PCP) can serve as an electron acceptor for some Desulfitobacterium and Dehalococcoides species. In each case however, complete reductive dechlorination of PCP to phenol was not observed. Instead, PCP dechlorination by Dehalococcoides resulted in the production of a mixture of dichloro- and monochlorophenols. Likewise, Desulfitobacterium strain PCP-1 dechlorinates PCP to 3-chlorophenol but other Desulfitobacterium species are only capable of ortho-dechlorination. Thus the net production of lesser chlorinated phenol must be considered when evaluating reductive dechlorination as a mechanism for PCP biodegradation.

QuantArray®-Chlor includes quantification of all Targets listed in the table below. Alternatively, CENSUS® qPCR can be performed to quantify a select subset such as Dehalococcoides and Desulfitobacterium.

TARGETCODERELEVANCE / DATA INTERPRETATION
DehalococcoidesDHCWhile the range of compounds utilized varies by strain, some Dehalococcoides isolates are capable of reductive dechlorination of PCP and other chlorinated phenolic compounds. Dehalococcoidesstrain CBDB1 is capable of utilizing PCP and all three tetrachlorophenol (TeCP) congeners, all six trichlorophenol (TCP) congeners, and 2,3-dichlorophenol (2,3-DCP). PCP dechlorination by strain CBDB1 produces a mixture of 3,5-DCP, 3,4-DCP, 2,4-DCP, 3-CP and 4-CP. In the same study however, Dehalococcoides mccartyi strain 195 dechlorinated a more narrow spectrum of chlorophenols which included 2,3-DCP, 2,3,4-TCP and 2,3,6-TCP but no other TCPs or PCP.
DesulfitobacteriumDSBSimilar to Dehalococcoides, some species and strains of Desulfitobacterium are capable of utilizing PCP and other chlorinated phenols. Desulfitobacterium hafniense PCP-1 is capable of reductive dechlorination of PCP to 3-CP. However, the ability to biodegrade PCP is not universal among Desulfitobacterium isolates. Desulfitobacterium sp. Strain PCE1 and D. chlororespirans strain Co23 for example can utilize TCP and DCP isomers but not PCP for growth.
Total BacteriaEBACIndex of total bacterial biomass.
MethanogensMGNMethanogens utilize hydrogen and can compete with halorespiring bacteria for available electron donor.
Sulfate Reducing BacteriaAPSSulfate reducing bacteria can compete with halorespiring bacteria for available hydrogen.

Aerobic Biodegradation

Under aerobic conditions, PCP can be utilized as a sole source of carbon and energy by some bacteria.  PCP biodegradation is initiated by PCP 4-monooxygenase (PcpB) followed by two successive dehalogenation reactions (PcpC). The intermediate produced is then cleaved by a dioxygenase (PcpA) and further metabolized.

CENSUS® qPCR can be performed to quantify pentachlorophenol monooxygenases.

TARGETCODERELEVANCE / DATA INTERPRETATION
Pentachlorophenol MonooxygenasesPCPqPCR assay specifically targeting oxygenase genes encoding the enzymes responsible for initial oxidation of PCP and aromatic ring cleavage.

Complementary Tools

In Situ Microcosms (ISMs)

In Situ Microcosms (ISMs) are field deployed microcosm units containing passive samplers that provide the microbial, chemical, and geochemical data for simultaneous, cost-effective evaluation of multiple remediation options.

To evaluate aerobic bioremediation of pentachlorophenol, an ISM study typically includes:

    • An unamended MNA unit to evaluate monitored natural attenuation
    • A BioStim unit amended with an electron acceptor product (e.g. oxygen releasing material)

Site managers may also want to evaluate enhanced anaerobic bioremediation approaches especially at sites impacted by additional chlorinated hydrocarbons. To evaluate anaerobic bioremediation of chlorinated phenols, an ISM study typically includes:

    • An unamended MNA unit to evaluate monitored natural attenuation
    • A BioStim unit amended with an electron donor
    • A BioAug unit amended with a commercial bioaugmentation culture and an electron donor

Each ISM unit contains passive samplers – passive diffusion bags (PDBs) for VOCs analysis of contaminant concentrations, passive geochem samplers for dissolved gases (ethene, ethane, methane) and anions like sulfate, and Bio-Traps® for QuantArray®-Chlor or CENSUS® qPCR quantification of key contaminant degrading bacteria and functional genes.

By comparing contaminant concentrations, geochemical conditions, and concentrations of halorespiring bacteria between the MNA, BioStim, and BioAug units, site managers can evaluate each remediation option at a fraction of the cost of a lab bench treatability study or pilot scale study.

References

REFERENCE
Adrian L, Hansen SK, Fung JM, Görisch H, Zinder SH. Growth of Dehalococcoides strains with chlorophenols as electron acceptors. Environmental Science & Technology. 2007;41:2318–23. https://doi.org/10.1021/es062076m.
Bouchard B, Beaudet R, Villemur R, McSween G, Lepine F, Bisaillon J-G. Isolation and characterization of Desulfitobacterium frappieri sp. nov., an anaerobic bacterium which reductively dechlorinates pentachlorophenol to 3-chlorophenol. International Journal of Systematic and Evolutionary Microbiology. 1996;46:1010–5. https://doi.org/10.1099/00207713-46-4-1010.
Crawford RL, Jung CM, Strap JL. The recent evolution of pentachlorophenol (PCP)-4-monooxygenase (PcpB) and associated pathways for bacterial degradation of PCP. Biodegradation 2007;18;525–539. https://doi.org/10.1007/s10532-006-9090-6.
Gerritse J, Renard V, Gomes TP, Lawson PA, Collins MD, Gottschal JC. Desulfitobacterium sp. strain PCE1, an anaerobic bacterium that can grow by reductive dechlorination of tetrachloroethene or ortho-chlorinated phenols. Archives of Microbiology. 1996;165:132–40. https://doi.org/10.1007/s002030050308.
Sanford RA, Cole JR, Löffler F, Tiedje JM. Characterization of Desulfitobacterium chlororespirans sp. nov., which grows by coupling the oxidation of lactate to the reductive dechlorination of 3-chloro-4-hydroxybenzoate. Applied and Environmental Microbiology. 1996;62:3800–8. https://doi.org/10.1128/aem.62.10.3800-3808.1996.
Thakur IS, Verma P, Upadhayaya K. Molecular Cloning and Characterization of Pentachlorophenol-Degrading Monooxygenase Genes of Pseudomonas sp. from the Chemostat. Biochemical and Biophysical Research Communications. 2002;290:770-774. https://doi.org/10.1006/bbrc.2001.6239.