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.