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6 Dechlorination and Degradation of PCBs in Contaminated Sediments and Soils

6 Dechlorination and Degradation of PCBs in Contaminated Sediments and Soils

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24 “Dehalobium chlorocoercia” DF-1—from Discovery to Application



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have a limited capacity to attack highly chlorinated congeners often found in the

environment (Abraham et al. 2002). In contrast, microbial reductive dechlorination attacks more extensively chlorinated PCB congeners with flanked chlorines

ultimately complementing the aerobic process by removing 2,3 and 3,4 substitutions. Prior to identification and isolation of PCB respiring bacteria, attempts to

treat PCB contaminated sediments by bioaugmentation with PCB-enriched sediment yielded mixed results. Wu and Wiegel (1997) observed no significant stimulation and Bedard et al. (1997) observed only slight stimulation of weathered

Aroclor 1260 dechlorination in Housatonic River sediment bioaugmented with

PCB-enriched sediment slurries, although this activity could be increased by addition of 2,3,4,5,6-pentachlorobiphenyl as a biostimulant. Natarajan et al. (1997)

reported dechlorination of weathered Aroclor 1242 and 1248 in Raisin River sediment microcosms inoculated with microbial granules from an upflow anaerobic

sludge blanket digestor. However, the granules were not grown or maintained

with PCBs or other organochlorides. The study did not rule out the possibility that

the observed activity resulted from hydrogen generated from fermentative bacteria in the granules, which would stimulate indigenous PCB dechlorinating bacteria, rather than bioaugmentation with organohalide respiring bacteria. At the time

these reports were published PCB respiring bacteria had not yet been identified as

Dehalococcoides and related bacteria within the Chloroflexi. More recently, the

commercial PCB mixture Aroclor 1260 was reported to be significantly dechlorinated by a consortium consisting of one or more phylotypes within the Chloroflexi

enriched from sediment microcosms (Fagervold et al. 2007), sediment-free microcosms (Bedard et al. 2007) and by an individual strains of D. mccartyi (Fennell

et al. 2004; LaRoe et al. 2014; Adrian et al. 2009; Wang et al. 2014). The different dechlorination patterns observed in the environment have been attributed to the

diversity of indigenous PCB dechlorinators that attack different chlorine substituted positions within a congener. This conclusion is further supported in a report

by Fagervold et al. demonstrating that the overall pathway for dechlorination of

spiked Aroclor 1260 could be altered by adding different combinations of PCB

respiring bacteria to sediment microcosms (Fagervold et al. 2011). Since PCBs

generally accumulate in soils and sediments the challenges for their remediation

differ from those developed for volatile halogenated contaminants such as chlorinated ethenes in groundwater. Efforts to enhance the dechlorination of PCBs in

contaminated sediments with strain DF-1 and other organohalide respiring bacteria

are discussed below.



24.6.1 Biostimulation

There have been efforts to identify factors affecting dechlorination and degradation activities in laboratory microcosms (Abramowicz et al. 1993; Tiedje et al.

1993; Berkaw et al. 1996; Wu et al. 1996; Cho et al. 2004) with the goal of accelerating the natural processes in the environment. Although PCB respiring bacteria



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can be enriched in laboratory microcosms, they require PCBs at concentrations

ranging from 10 to 100 mg mL−1 to observe growth and activity, which is significantly greater than concentrations often detected in most contaminated sites.

As the addition of high concentrations of PCBs as a biostimulant to a contaminated site is not a practical solution for treating PCB contamination, investigators have attempted to enhance dechlorination of PCB contaminated sediments

by addition of an alternative halogenated electron acceptor, often referred to as a

haloprimer, to stimulate the activity of indigenous organohalide respiring bacteria. The first in situ stimulation of PCB dechlorination was reported over 20 years

ago (Bedard et al. 1995). In that study, the application of a high concentration

of 2,6-dibromobiphenyl (109 mg kg−1) as a haloprimer successfully stimulated

a 74 % decrease in hexa- to octachlorobiphenyls in 1 year. Other strategies have

been effective for halopriming PCB contaminated sediments in laboratory microcosms including the addition of 2,3,4,5,6-pentachlorobiphenyl (Van Dort et al.

1997), halobenzoates (Deweerd and Bedard 1999) and pentachloronitrobenzene (Park et al. 2011). Chlorobenzenes and chlorophenols stimulated reductive

dechlorination in sediments spiked with a high concentration of Aroclor 1248

(ca. 100 mg kg−1), but were not tested with sediments contaminated with low

levels of PCBs (Cho et al. 2002). Wu et al. (1999) used a most probable number

method to show that halopriming with 2,6-dibromobiphenyl increased the number of PCB- and 2,6-dibromobiphenyl dehalogenators, suggesting that increased

dechlorination rates observed resulted from increasing the population size of the

indigenous organohalide respiring population. Although biostimulation shows

potential for treating PCB-impacted sediments, all of the effective electron acceptors known at this time are halogenated aromatic compounds and their release into

the environment is subject to regulatory restrictions. Polybrominated biphenyls,

often used in flame retardants, are restricted under the Restriction of Hazardous

Substances Directive in the EU and in several other countries (http://eur-lex.

europa.eu). Although dibromobiphenyls are not found in commercial polybrominated biphenyl mixtures they could be subject to the same regulatory restrictions.

Chlorobenzenes, chlorophenols and halogenated benzoates, used in a wide range

of industrial applications are a large group of potentially toxic environmental pollutants (Bhatt et al. 2007). Pentachloronitrobenzene, which is widely used as a

fungicide in several countries, is perhaps the most tractable option for biostimulation. However, application of pentachloronitrobenzene as a fungicide has been

subject to periodic restrictions by the U.S. Environmental Protection Agency.

Several non-organohalide biostimulants such as lactate and iron have a stimulatory effect on the anaerobic reductive dechlorination of organohalides (Bruce

and Henry 2010). However, the addition of sodium lactate and zerovalent iron

as potential electron donors did not have a significant effect on dechlorination of

PCB-impacted sediment mesocosms bioaugmented with “D. chlorocoercia” strain

DF-1 (Payne et al. 2013) or a highly enriched organohalide respiring consortium

from the Raisin River (Winchell and Novak 2008). FeSO4, was reported to stimulate PCB dechlorination in sediment microcosms spiked with a high concentration

of Aroclor 1242 (Zwiernik et al. 1998). The authors suggested that the stimulation



24 “Dehalobium chlorocoercia” DF-1—from Discovery to Application



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resulted from PCB dechlorinating sulfate reducing bacteria (SRB), however, they

did not rule out the possibility that stimulation of SRB indirectly increased the

size of the organohalide respiring population by increasing hydrogen production

by fermentation and interspecies hydrogen exchange. Since organohalide respiring

bacteria have a lower Ks for hydrogen uptake, an increased hydrogen pool would

be available to them without competition with SRB (Fennell and Gossett 1998).

That study was conducted with highly enriched cultures spiked with Aroclor 1242

and the effectiveness of FeSO4 as a biostimulant for PCB dechlorination in situ

with low PCB concentrations remains untested. At this time, a non-organohalide

biostimulant for use in situ that specifically targets “D. chlorocoercia” strain DF-1

or other PCB respiring bacteria has not been identified.



24.6.2 Electrostimulation

An intriguing approach to bioremediation is the electrostimulation of biodegradative and dechlorinating microorganisms (Jin and Fallgren 2014; Lu et al. 2014).

The application of electrochemistry to the reductive dechlorination of organohalides is reviewed by Aulenta elsewhere in this book. By applying electrodes to contaminated groundwater, sediment, or soil, one may supply electron donor and/or

acceptor possibly through direct interactions with the electrodes or by the generation of other chemical reductants or oxidants. In addition, oxygen and hydrogen

may be supplied to the degradative/dechlorinating microorganisms through water

electrolysis. In the case of PCBs, both reductive and oxidative processes may be

required for full and effective biodegradation. A two-electrode application, perhaps with alternating polarity, has the potential to stimulate microbial degradation

of PCBs in contaminated sediment.

“D. chlorocoercia” strain DF-1 grown in a defined minimum medium provides

the opportunity to examine the donation of electrons for PCB reductive dechlorination with a cathode to an organohalide respiring microbe under controlled conditions. However, a successful experiment as such has not been reported. Incubating

strain DF-1 at a graphite cathode of a 3-electrode bioelectrochemical cell that was

poised at −600 mV versus the standard hydrogen potential did not result in detectable dechlorination of 2,3,4,5-tetrachlorobiphenyl (unpublished data, C. Chun,

K. Sowers, H. May). At this potential a graphite cathode will produce H2, but the

amount is not appreciable unless the system is sealed and the H2 is allowed to

accumulate. These tests were conducted with N2: CO2 (4:1) sparged through the

cell. Therefore, these results indicate that PCB dechlorination by “D. chlorocoercia” strain DF-1 is not likely to be facilitated through direct electron transfer of

electrons from an electrode. However, one may expect that PCB dechlorination by

the microbe would occur if H2 were allowed to accumulate in the electrochemical

cell or at depth in sediment. Furthermore, the addition of a soluble electron mediator or sediment, which may supply a mediator, could potentially support PCB

dechlorination by “D. chlorocoercia” strain DF-1 or a consortium containing such

organohalide respiring microorganisms.



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H.D. May and K.R. Sowers



Fig. 24.5  Schematic

representation of a

bioelectrochemical reactor for

testing the effect of current

on PCB transformation

in sediment microcosms.

Reprinted with permission

from (Chun et al. 2013).

Copyright 2013 Elsevier



Chun et al. (2013) examined the application of voltage to live sediment with

weathered PCBs (Aroclor 1242 in sediment from Fox River, Neenah, WI) with

and without the addition of 2-monochlorobiphenyl and 2,3,4,5-tetrachlorobiphenyl. The sediment was maintained in sediment bioelectrochemical reactors (SBRs)

that were maintained open to the atmosphere in order to mimic field conditions

(Fig. 24.5). Two graphite electrodes were applied vertically into the sediment and

voltage was applied at 1.5, 2.2, and 3.0 V. After 88 days the entire contents of the

SBR were analyzed for PCBs and compared with sediment in control reactors that

were identically prepared but did not receive power (Fig. 24.6). Even with only

1.5 V applied to the system, which was below the voltage required to electrolytically generate O2 at the cathode, greater than ~50–60 % of the total PCBs were

eliminated. Small amounts of chlorobenzoates, products of PCB oxidation and

most likely transient, were detected with (2-, 2,6-, and 2,3,5-chlorobenzoate) and

without (2-, 2,3-, and 3,4-chlorobenzoate) the addition of 2-monochlorobiphenyl and 2,3,4,5-tetrachlorobiphenyl. Aerobic PCB degrading microbes and PCB

dechlorinators were enriched from the sediments in experiments independent of

the electrochemical experiments within this study.

Reductive dechlorination of PCBs may have been supported by H2 that would

be formed with this amount of voltage, but the reduction in total PCBs was so

extensive that PCB dechlorination was not discernible. Since no PCBs were lost

from the controls, it was concluded that oxidative PCB biodegradation must have

occurred due to either the introduction of oxygen, perhaps by benthic worms

whose mobility was observed to be increased when voltage was applied, or to

the anaerobic oxidation of the PCBs coupled to electrode reduction. The oxidation of aromatic compounds coupled to electrode reduction by microbes has

been reported (Bond et al. 2002; Zhang et al. 2010). In addition, the cycling of



24 “Dehalobium chlorocoercia” DF-1—from Discovery to Application



577



Fig. 24.6  Total concentration of weathered Aroclors in sterilized and live Sediment Bioelectrochemical Reactors (SBR) with (a) and without (b) the addition of 2-monochlorobiphenyl and

2,3,4,5-tetrachlorobiphenyl. The sample size of T = 0 and 0 V at 88 days is 18 (triplicate samples

from 6 reactors) and 5 (triplicate samples from one reactor and one sample from two reactors),

respectively. For SBRs with the applied voltage at 88 days, triplicate samples were analyzed

from the homogenized contents of each. Each datum point represents the mean and standard

deviation of three replicates samples



inorganic and organic molecules in the SBRs due to abiotic and biotic reactions

driven by the application of the voltage may support the observed elimination of

the PCBs. These results are promising but a better understanding of the mechanism at work will require further research, particularly to know if and how microbial dechlorination may participate under the conditions tested. Finally, it remains

to be seen if electrostimulation may further stimulate the treatment of weathered

PCBs following bioaugmentation.



24.6.3 Bioaugmentation

Bedard et al. (2007) observed that a critical mass of Dehalococcoides cells was

required before reductive dechlorination was detected in a sediment-free enrichment culture spiked with Aroclor 1260 and proposed that low indigenous numbers of organohalide respiring bacteria might explain why substantial attenuation

of PCBs is rarely observed in the environment. Growth of organohalide respiring

bacteria is linked to reductive dechlorination of PCBs in laboratory cultures containing high concentrations of PCBs (Fagervold et al. 2007; Adrian et al. 2009).

However, Lombard et al. (2014) calculated that the aqueous concentrations of

PCBs typically found in environmental samples is insufficient to support the critical mass of cells necessary to cause high rates of PCB dechlorination. An alternative strategy for stimulating in situ PCB dechlorination in sediment impacted with

low levels of PCBs is to bioaugment sediment with high numbers of organohalide

respiring microorganisms. Bedard (1997) demonstrated that bioaugmentation with



H.D. May and K.R. Sowers



578



sediment slurries enriched for PCB dechlorinating bacteria by sequential transfer

with 2,3,4,5,6-pentachlorobiphenyl as a haloprimer reduced hexa- through nonachlorobiphenyls of relatively high levels (50 ppm) of weathered Aroclor 1260 in

Housatonic River sediment by 19.7 % in 312 days. Krumins et al. (2009) found

that the addition of D. mccartyi strain 195 stimulated the dechlorination of PCBs

in sediment contaminated with a low concentration (2.1 ppm) of Aroclors 1248,

1254 and 1260 in laboratory microcosms, although pentachloronitrobenzene

was also added as a haloprimer. May et al. (2008a, b) demonstrated that bioaugmentation with a pure culture of “D. chlorocoercia” strain DF-1 stimulated the

reductive dechlorination of low concentrations of Aroclor 1260 (4.6 ppm) by

8.9 mol% in contaminated soil microcosms containing indigenous organohalide

respiring bacteria and in the absence of a haloprimer. Based on the latter results

(Payne et al. 2011) tested the efficacy of scaling up bioaugmentation with “D.

chlorocoercia” strain DF-1 in 2-L laboratory mesocosms containing sediment

contaminated with weathered Aroclor 1260 (1.3 ppm) and water from Baltimore

Harbor, MD (Fig. 24.7). In this study total penta- and higher chlorinated PCBs

decreased by approximately 56 % (by mass) in bioaugmented mesocosms after

120 days in contrast to un-amended controls that showed no measureable activity.

Bioaugmentation with “D. chlorocoercia” strain DF-1 enhanced the dechlorination of doubly flanked chlorines as expected, but also stimulated the dechlorination of singly flanked chlorines as a result of an apparent synergistic effect on the

indigenous population. Furthermore, although “D. chlorocoercia” strain DF-1” is

not indigenous to Baltimore Harbor, the inoculum was sustained throughout the

dechlorination process. This study affirmed the feasibility of using bioaugmentation with a PCB respiring microorganism to stimulate in situ reductive dechlorination of PCBs in contaminated sediments.



4.8



Cl per Biphenyl



4.6

4.4

4.2

4

3.8

0



30



60



90



120



Time (Day)



Fig. 24.7  Changes in the ratio of chlorines per biphenyl in mesocosms over time after treatment

with sterilized spent growth medium (open circle), sterilized spent growth medium and GAC

(open square), “D. chlorocoercia” inoculated into sediment (filled circle), and “D. chlorocoercia”

inoculated into sediment adsorbed onto GAC (filled square). Each datum point represents the

mean and standard deviation of three replicates samples. Reprinted with permission from (Payne

et al. 2011). Copyright 2011 American Chemical Society



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24.6.4 Coupling Reductive Dechlorination by

“D. chlorocoercia” Strain DF-1 with Aerobic

Degradation

Natural microbial attenuation of PCBs in the environment is presumed to occur

by the complementary processes of anaerobic dechlorination of more highly

chlorinated congeners and subsequent aerobic degradation of those dechlorination products (Abramowicz 1995), and this has been suggested to be a potential

treatment strategy for PCB-impacted sediment. Anaerobic incubation of PCBimpacted sediment in a microcosm with an Aroclor followed by transfer into

an aerobic culture containing Burkholderia xenovorans strain LB400 has been

reported to effectively degrade Aroclors by as much a 70 % (Evans et al. 1996;

Master et al. 2002). Although creating sequential anaerobic–aerobic conditions are

possible in closed laboratory microcosms, it is difficult to reproduce these conditions in situ. To address this problem Payne et al. (2013) tested the efficacy of

bioaugmentation with anaerobic PCB respiring “D. chlorocoercia” strain DF-1

and aerobic PCB degrading B. xenovorans strain LB400 added concurrently in

2 L laboratory mesocosms containing sediments historically contaminated with

Aroclor 1260, but also contaminated with relatively high concentrations of di-,

tri- and tetra-chlorobiphenyls. In contrast to prior studies that employed sequential anaerobic and aerobic treatments, Payne et al. (2013) employed static sediment

mesocosms open to the air to simultaneously create both aerobic and anaerobic

zones, employed only indigenous water rather than culture medium, and did not

employ aromatic biostimulants, such as biphenyl, brominated biphenyls, or chlorobenzoates. The premise of the study was that under in situ conditions anaerobic

and aerobic regions coexist throughout the sediments column as a result of microniches within particles and dynamic cycling of redox conditions by bioturbation.

Bioaugmentation with “D. chlorocoercia” and B. xenovorans together resulted in

an 80 % decrease by mass of PCBs, from 8 to less than 2 mg/kg after 120 days

(Fig. 24.8). The mesocosm inoculated with both the aerobe and anaerobe did not

show a significant increase in the extent of degradation compared with the aerobe alone. However, in the mesocosm bioaugmented with both microorganisms,

there was a 20 % greater decrease in mass of hexa- through nona-chlorobiphenyl

homologs and there was a shift in the overall congener pattern, compared with

bioaugmentation with the aerobe alone. This observation indicates that both anaerobic dechlorination of highly chlorinated congeners and aerobic degradation of

less chlorinated congeners occurred concurrently. In contrast, non-bioaugmented

controls containing filtered culture supernatant showed only a 25 % decrease in

total levels of PCBs after 365 days. Most aerobic degradation was detected in the

first 120 days and then continued to day 365 at a reduced rate. However, both the

PCB transforming anaerobe and aerobe were viable at the end of the study. This

result indicates that “D. chlorocoercia” and aerobic B. xenovorans could successfully compete with the indigenous populations and the long-term viability suggests that enhanced dechlorination has the potential to continue beyond 365 days.



H.D. May and K.R. Sowers



580



(a)



PCB (mg/kg dry wt)



(b)



4

3

2

1

0

1



2



3



4



5



6



7



8



9



10



Homolog



Fig. 24.8  Effect of bioaugmentation with “D. chlorocoercia” strain DF-1 with the aerobic PCB

degrader B. xenovorans strain LB400. Panel A shows total reduction in levels of PCBs in bioaugmented and non-bioaugmented Baltimore Harbor sediment mesocosms after 90 days. Panel B

PCB homolog distribution in Baltimore Harbor sediment mesocosms at day 0 (white bars, n = 9)

and day 365 in mesocosms augmented with filtered growth medium (slashed bars, n = 3), LB400

(gray bars, n = 3), and LB400 plus DF1 (black bars, n = 3). Each datum point represents the

mean and standard deviation of three replicates samples Reprinted with permission from (Payne

et al. 2013). Copyright 2013 American Chemical Society



Even at a reduced rate this enhanced dechlorination could result in long-term

dechlorination/degradation after the initial transformation of the most bioavailable

congeners. Overall, the results indicate that in situ treatment employing the simultaneous application of anaerobic and aerobic microorganisms could be an effective

and environmentally sustainable strategy to reduce PCB levels in contaminated

sediments.



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24.6.5 In Situ Bioremediation with “D. chlorocoercia”

Strain DF-1—Future Challenges

One current challenge with in situ bioremediation is that Aroclors contain varying percentages of ortho-substituted PCB congeners. Payne et al. (2011, 2013)

reported an accumulation of ortho-substituted tri- and tetra-chlorinated biphenyls

after bioaugmentation with “D. chlorocoercia” strain DF-1 and B. xenovorans

strain LB400. Reductive dechlorination PCB congeners in the ortho position has

been reported infrequently in the environment and tri- and tetra-ortho chlorinated

congeners are often recalcitrant to aerobic degradation (Bedard et al. 2003). One

potential approach for further reducing the residual concentrations of PCBs after

in situ treatment of a PCB-impacted site is by bioaugmentation with an orthodechlorinating organohalide respiring bacterium in order to prevent a buildup of

more recalcitrant ortho-PCBs. Fagervold et al. (2011) reported that a coculture of

“D. chlorocoercia” strain DF-1 and organohalide respiring strain o-17, which is

capable of reducing PCBs in ortho-substituted positions, significantly reduced the

accumulation of ortho-substituted PCBs in sediment microcosms. Although this

approach has the potential to lead to more complete degradation of Aroclors it has

not been tested with low concentrations of Aroclors either in sediment mesocosms

or in situ.

Another issue is production of adequate biomass of PCB-dechlorinating bacteria for full-scale treatment of PCB-impacted sediment. Payne et al. (2011; Payne

et al.) showed that approximately 105 cells g−1 (wet wt) sediment was required

to effectively stimulate dechlorination of weathered Aroclor 1260. “D. chlorocoercia” strain DF-1 can thus far be grown to a maximum cell density of only 108

cells ml−1, therefore large-scale culturing in facilities with capacities of thousands

of liters would be required for full-scale treatment of PCB-impacted sites of an

acre or more (Sowers and May 2013). Postproduction removal of residual organohalides after cell production before use of the biomass in bioaugmentation must

also be addressed. The only electron acceptors known to support growth of PCB

dechlorinating bacteria are halogenated aliphatic or aromatic compounds that are

also considered to be environmental contaminants. Unless a nontoxic electron

acceptor is identified, methods need to be developed to readily remove halogenated compounds from the bioaugmentation inocula. Miller et al. (2005) reported

that “D. chlorocoercia” strain DF-1 pre-grown with tetrachloroethene showed no

significant lag in growth when transferred to 2,3,4,5-tetrachlorobiphenyl, which

suggests that residual volatile substrates such as chlorinated ethenes could be

removed from cultures by gas sparging before harvesting. Alternatively, substituting limited amounts of more readily biodegraded electron acceptors such as brominated biphenyls (discussed above) as a growth substrate and depleting most of

the brominated biphenyls during harvesting might be a viable approach for preparation of bioaugmentation inocula (Bedard et al. 1998).

Finally, a means of deploying bioamendments into PCB-impacted sediments is required for effective bioremediation. More soluble organohalides such



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as chlorinated ethenes, which are common contaminants of groundwater, have

been successfully bioaugmented by pumping microorganisms and nutrients into

groundwater plumes. In contrast, PCBs are hydrophobic and tend to become

immobilized by adsorption to sediment particles that settle in open water bodies such as lakes and oceans. Effective bioaugmentation of PCB-impacted sediments will require a method for inoculating sediment either by direct injection or

deployment on solid particles that will pass through a water column. Payne et al.

(2011, 2013) demonstrated that bioaugmentation with “D. chlorocoercia” strain

DF-1 adsorbed to granulated activated carbon was effective for reducing PCB concentrations in mesocosms containing sediments contaminated with Aroclor 1260.

Although organic particles such as clay or granulated activated carbon strongly

sorb PCBs in an aqueous environment, they also provide a substrate for biofilm

formation in close proximity to the hydrophobic PCBs. The ability to use a solid

substrate such as clay or GAC particles for inoculation of cells offers a possible

solution for dispersing cells into sediments.



24.7 Summary

“D. chlorocoercia” strain DF-1 grows by organohalide respiration of PCB congeners and chlorinated benzenes with doubly flanked chlorines, and both tetra- and

tri-chloroethene. This was the first organohalide respiring isolate demonstrated

to dechlorinate weathered commercial mixtures of PCBs as a bioamendment.

Although its range of dechlorination for an Aroclor is limited in comparison with

other organohalide respiring species, it is capable of facilitating extensive overall

degradation of weathered PCBs in sediments co-augmented with an aerobic PCB

degrader. Kinetic studies demonstrate that “D. chlorocoercia” strain DF-1 dechlorinates PCBs at subsaturating aqueous concentrations typically found in sediments

impacted with low levels of PCBs and it is osmotolerant enabling it to be active in

both freshwater and estuarine sediments. The fortuitous ability to apply this strict

anaerobe with an aerobe to treat PCBs comprehensively in weathered sediment is

now being tested in the field.



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6 Dechlorination and Degradation of PCBs in Contaminated Sediments and Soils

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