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Appl Environ Microbiol, March 1998, p. 1052-1058, Vol. 64, No. 3
0099-2240/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Microbial Reductive Dechlorination of Aroclor 1260 in Anaerobic Slurries of Estuarine Sediments
Qingzhong
Wu,1
Kevin R.
Sowers,2 and
Harold D.
May1,*
Department of Microbiology and Immunology,
Medical University of South Carolina, Charleston, South
Carolina,1 and
Center of Marine
Biotechnology, University of Maryland Biotechnology Institute,
Baltimore, Maryland2
Received 6 August 1997/Accepted 16 December 1997
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ABSTRACT |
Reductive dechlorination of Aroclor 1260 was investigated in
anaerobic slurries of estuarine sediments from Baltimore Harbor (Baltimore, Md.). The sediment slurries were amended with 800 ppm
Aroclor 1260 with and without the addition of 350 µM
2,3,4,5-tetrachlorobiphenyl (2,3,4,5-CB) or 2,3,5,6-tetrachlorobiphenyl
(2,3,5,6-CB) and incubated in triplicate at 30°C under methanogenic
conditions in an artificial estuarine medium. After 6 months, extensive
meta dechlorination and moderate ortho
dechlorination of Aroclor 1260 occurred in all incubated cultures
except for sterilized controls. Overall, total chlorines per biphenyl
decreased by up to 34%. meta chlorines per biphenyl
decreased by 65, 55, and 45% and ortho chlorines declined
by 18, 12, and 9%, respectively, when 2,3,4,5-CB, 2,3,5,6-CB, or no
additional congener was supplied. This is the first confirmed report of
microbial ortho dechlorination of a commercial
polychlorinated biphenyl mixture. In addition, compared with incubated
cultures supplied with Aroclor 1260 alone, the dechlorination of
Aroclor 1260 plus 2,3,4,5-CB or 2,3,5,6-CB occurred with shorter lag
times (31 to 60 days versus 90 days) and was more extensive, indicating that the addition of a single congener stimulated the dechlorination of
Aroclor 1260.
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INTRODUCTION |
Polychlorinated biphenyls (PCBs) and
other anthropogenic pollutants adsorb to sediments due to the
hydrophobic nature of the compounds. As sediments settle, adsorbed PCBs
accumulate in the lower anoxic layers of the sediment column, where
reductive dechlorination of PCBs by anaerobic microorganisms has been
demonstrated to occur in the laboratory and in situ (1, 2, 4, 5,
10, 12, 22). The turnover of naturally formed halogenated
organics in marine coastal regions suggests that these environments
have a significant potential for dechlorination (14, 18).
However, few studies have focused on the dechlorination of PCBs in
marine and estuarine sediments (2, 11, 20).
Anaerobic PCB dechlorination has the potential to reduce the toxicity
of the PCBs (5, 11, 23) and convert highly persistent congeners, frequently the more extensively chlorinated congeners, into
forms that are more amenable to aerobic degradation (6, 8, 13, 15,
26). However, only the loss of meta and/or para chlorines has been demonstrated when preexisting or
freshly added commercial PCB mixtures (e.g., Aroclors 1242, 1254, and 1260, etc.) have been microbially dechlorinated in sediments from the
Hudson River (N.Y.), Silver Lake (Pittsfield, Mass.), Woods Pond
(Lenox, Mass.), and Puget Sound (2, 3, 7, 20, 21).
ortho dechlorination of an Aroclor has not been
demonstrated, and microbial dechlorination of Aroclor 1260, preexisting
or freshly added to sediments, has not been very extensive. The
addition of single PCB congeners, in a process called priming,
stimulated the dechlorination of Aroclor 1260 residue in Woods Pond
sediments, but priming did not promote ortho dechlorination
of the residual Aroclor 1260 (3, 5, 7, 31).
Baltimore Harbor (BH; Baltimore, Md.) has been heavily impacted by
industrial activity over the last 150 years, and PCBs have accumulated
in sediments throughout the harbor (27). We recently reported that the single congeners 2,3,5,6-chlorobiphenyl (2,3,5,6-CB), 2,3,5-CB, and 2,3,6-CB were ortho dechlorinated by
enrichment cultures that contained sediments collected from the
northwest branch of the harbor (9). Here we describe the
anaerobic dechlorination of Aroclor 1260 by enrichment cultures
prepared with these sediments. The data demonstrate extensive
meta dechlorination and moderate ortho
dechlorination. Furthermore, we show that the meta and
ortho dechlorinations are stimulated by the addition of
single PCB congeners.
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MATERIALS AND METHODS |
Sediment collection and storage.
Collection of estuarine
sediments from BH was described previously (9), and the
sediment samples were stored anaerobically at room temperature for 14 months in the dark before use in these experiments. No background PCBs
were detected in these sediments based on methods described below
(detection limit, ~0.01 µg/g of PCB standard used).
Preparation of slurries and incubation.
Estuarine medium
without sulfate (E-Cl) was prepared as described by Berkaw et al.
(9). In an anaerobic chamber (Coy Laboratory Products, Ann
Arbor, Mich.) containing 95% nitrogen-5% hydrogen, sediment slurries
were prepared by mixing 1 volume of wet BH sediment with 4 volumes of
E-Cl medium (equivalent to 0.06 g [dry weight] of sediment per
ml). Aliquots of the slurries (30 ml) were dispensed into 50-ml serum
bottles and allowed to stand for 5 days in the anaerobic chamber.
To prepare sterile controls, slurries were autoclaved twice for 1 h at 121°C on 2 consecutive days. Live cultures and sterile controls
prepared in triplicate were amended with 800 ppm Aroclor 1260 (800 µg
per g [dry weight] of sediment or 133 µmol per liter of slurry) and
either 350 µM (µmol per liter of slurry) 2,3,4,5-CB, 350 µM
2,3,5,6-CB, or no additional congener. All enrichment cultures were
incubated at 30°C in the dark. Each month, all enrichments were
supplemented with a fatty acid mixture (2.5 mM each acetate, propionate, and butyrate).
Sample preparation, extraction, and analysis.
The
dechlorination of 2,3,4,5-CB, 2,3,5,6-CB, and Aroclor 1260 in each
culture was analyzed at various time points throughout a 6-month
period. Samples were drawn and extracted in ethyl acetate (high-performance liquid chromatography grade; Fisher Scientific, Pittsburgh, Pa.), and the organic fraction was passed over a
Florisil-copper column as described previously (9). PCBs
were analyzed with a Hewlett-Packard 5890 series II gas chromatograph
(GC) equipped with an RTX-1 capillary column (30 m by 0.25 mm [inside
diameter] by 0.25 µm; Restek Corp., Bellefonte, Pa.) and a
Ni63 electron capture detector as described previously
(9).
Congeners 2,3,4,5-CB and 2,3,5,6-CB and their dechlorination products
were identified by matching their retention times with
those of
authentic standards (>90% purity; AccuStandard, New Haven,
Conn.) and
were quantified by use of a piecewise-fit calibration
curve generated
from these standards at 9 to 16 calibration levels
(
9). PCB
congeners in Aroclor 1260 and their dechlorination
products were
identified by matching their GC retention times
with a customized PCB
standard prepared by supplementing Aroclor
1260 with the dechlorination
products observed in Woods Pond (
24)
or a standard mixture
composed of 3-3-CB, 3-4-CB, 3,5-3-CB, 3,5-4-CB,
2,4-3,5-CB, and
2,5-3,5-CB. Congener assignments were made in
accordance with those
reported by Frame et al. (
16). Each congener
in the Aroclor
mixture was quantified by use of a piecewise-fit
calibration curve
generated from standards at 4- to 8-point calibration
levels. Congener
and homolog distributions for each sample were
calculated and reported
in units of moles percent. Congener distributions
for each enrichment
culture with Aroclor and 2,3,4,5-CB (or 2,3,5,6-CB)
were calculated
after subtracting the peaks corresponding to 2,3,4,5-CB
(or 2,3,5,6-CB)
and their potential dechlorination products. Therefore,
values for
dechlorination of Aroclor 1260 in those incubations
are conservative.
Mass selective analysis was performed with a Hewlett-Packard 6890 series GC equipped with an HP-5MS capillary column (30 m
by 0.25 mm
[inside diameter] by 0.25 µm; Hewlett-Packard, Atlanta,
Ga.) and a
Hewlett-Packard 6890 series mass selective detector
(MS).
Chromatographic conditions were identical to those described
previously
for the GC-electron capture detector (
9). Our analysis
found
that 2,4-3,5-CB was not resolved with 2,3,6-2,6-CB on a
DB-1 column.
Thus, we used GC-MS to identify 2,4-3,5-CB (
m/z 292)
and
2,3,6-2,6-CB (
m/z 326) due to different molecular formulas
between these two congeners. In addition, analysis of our PCB
standard
mixtures on an HP-5MS capillary column resulted in the
resolution of
2,4-3,5-CB from 2,3,6-2,6-CB. We also found that
2,5-3,5-CB was not
resolved from 2,3,4-2-CB, 2,3,6-4-CB, and 2,6-3,4-CB
on a DB-1 column
as reported previously (
16). However, 2,5-3,5-CB
was
resolved from these congeners by using an HP-5MS column with
GC-MS.
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RESULTS |
Dechlorination of Aroclor 1260 in BH enrichment cultures was
detected within 4 months (Fig. 1).
However, the lag time decreased to 31 days in sediment slurries
additionally supplied with 2,3,4,5-CB. Congener 2,3,5,6-CB also
stimulated the onset of Aroclor dechlorination but not as quickly as
2,3,4,5-CB. In addition, the overall dechlorination of Aroclor 1260 was
enhanced more by the presence of 2,3,4,5-CB than by 2,3,5,6-CB (Table
1 and Fig. 1). After 6 months, only a
small level of meta dechlorination continued in the
congener-supplemented cultures and all ortho dechlorination
had ceased. No biphenyl was detected (by GC-MS) in any of the
enrichment cultures, and no PCB dechlorination was observed in
sterilized slurries (the total chlorine per biphenyl ± standard
deviation of triplicate controls was 6.32 ± 0.01).
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FIG. 1.
Chlorine distribution of Aroclor 1260 over the
incubation time. Averaged data of triplicate samples are presented.
Errors bars indicate standard deviations of triplicate samples; if no
error bar is evident, the standard deviation is less than 0.09 and is
masked by the symbols.
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Dechlorination of added congeners 2,3,4,5-CB and 2,3,5,6-CB was
detected after 20 and 27 days, respectively, and preceded the
dechlorination of Aroclor 1260. After 181 days, 67 mol% of 2,3,4,5-CB
and 99 mol% of 2,3,5,6-CB were transformed to the same products
reported by Berkaw et al. (9). Monochlorobiphenyls were
produced, including 26 and 12 mol% of 3-CB and 4-CB, respectively, in
cultures incubated with 2,3,4,5-CB and Aroclor 1260 and 1 and 32 mol%
of 2-CB and 3-CB, respectively, in enrichment cultures supplied with
Aroclor 1260 plus 2,3,5,6-CB. Previous (9) and subsequent
studies of BH sediments incubated with 2,3,5,6-CB alone have not
resulted in the production of 2-CB. We cannot exclude the possibility
that 2-CB, or any other monochlorobiphenyl produced, came from the
transformation of Aroclor 1260. However, since we cannot unequivocally
determine the source of these monochlorobiphenyls, they are discounted
in our overall assessment of Aroclor dechlorination when the
supplemental congeners are added. No monochlorobiphenyls were detected
in samples from slurry enrichments supplied with Aroclor 1260 alone.
The homolog distribution data for Aroclor 1260 before and after
incubation can be found in Table 1. Overall, hexa- to
nonachlorobiphenyls decreased by 65, 75, and 88% in incubated cultures
supplied with Aroclor 1260 alone, Aroclor 1260 plus 2,3,5,6-CB, and
Aroclor 1260 plus 2,3,4,5-CB, respectively, indicating more extensive dechlorination of Aroclor 1260 in enrichment cultures supplied with
2,3,4,5-CB. Significant decreases were seen in all of the major hexa-
and heptachlorobiphenyls, e.g., 2,3,6-2,4,5-CB, 2,4,5-2,4,5-CB, 2,3,4-2,4,5-CB, 2,3,5,6-2,4,5-CB, 2,3,4,5-2,3,6-CB,
2,3,4,5-2,4,5-CB, and 2,3,4,5-2,3,4-CB. Large increases
occurred in tri- and tetrachlorobiphenyls such as 2,4-3-CB, 2,4-3,5-CB,
2,4-2,4-CB, 2,4-2,5-CB, and 2,4-2,6-CB. Small changes in the
concentration of pentachlorobiphenyls may indicate an intermediary role
for these homologs.
Chlorine distribution of Aroclor 1260 over time indicated that
meta dechlorination was predominant but was accompanied by a
significant, yet more moderate, level of ortho
dechlorination (Fig. 1 and Table 1). After 181 days, 45 to 65% of the
meta chlorines and 9 to 18% of the ortho
chlorines had been removed depending upon congener supplementation.
Only a slight decrease of para chlorines was observed,
although significant para dechlorination of 2,3,4,5-CB
resulted in cultures supplied with Aroclor 1260 and 2,3,4,5-CB.
Comparisons of the congener distributions (± standard deviations) for
incubations with Aroclor 1260 alone, Aroclor 1260 plus 2,3,4,5-CB, and
Aroclor 1260 plus 2,3,5,6-CB are given in Table
2. Figure
2 presents the data for the
2,3,4,5-CB-supplemented cultures in graphical form, including a
difference plot. The data demonstrate that meta
dechlorination led to substantial increases in 2,4-2,4-CB, 2,4-2,5-CB,
and 2,4-2,6-CB and decreases in 2,4,5-2,5-CB, 2,3,6-2,4,5-CB,
2,4,5-2,4,5-CB, 2,3,4-2,4,5-CB, 2,3,4,5-2,3,4-CB, and 2,3,4,5-2,4,5-CB
under all conditions. These changes were similar to results reported
previously (5, 21). However, 2,3,5,6-2,4-CB, which increased
during meta dechlorination of Aroclor 1260 residue in Woods
Pond sediment (5), was not detected after 6 months of
incubation.
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FIG. 2.
Congener distribution of Aroclor 1260 at time zero
(T0) and after 181 days (T181) of incubation in
incubated cultures supplied with Aroclor 1260 and 2,3,4,5-CB. Averaged
data of triplicate samples are presented.
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ortho dechlorination was evident in all enrichment cultures
by the appearance of dechlorination products 2,4-3,5-CB, 2,5-3,5-CB, 2,4-3-CB, and 2,5-3-CB, which are not in Aroclor 1260 (16,
17). Both 2,4-3,5-CB and 2,5-3,5-CB were identified by GC-MS
analysis (see Materials and Methods). Although 2,4-3,5-CB and
2,5-3,5-CB could be products of meta or para
dechlorination rather than ortho dechlorination, the
quantity of substrate congener for such reactions is far less than the
amounts of 2,4-3,5-CB and 2,5-3,5-CB observed. As reported by Frame et
al. (16), congeners in Aroclor 1260 which were transformed
to 2,4-3,5-CB or 2,5-3,5-CB exclusively by meta and
para dechlorination are 2,3,4-3,4,5-CB (0.02 mol%), 2,4,5-3,4,5-CB (0.21 mol%), and 2,3,4,5-3,4,5-CB (0.08 mol%). Far
greater than 1.0 mol% each of 2,4-3,5-CB and 2,5-3,5-CB remained in
all of our enrichment cultures after 6 months (Fig. 2). However, even
higher levels (3.52 to 8.37 mol% of 2,4-3,5-CB and 1.86 to 4.12 mol%
of 2,5-3,5-CB) were present in the slurries at earlier times in the
experiment. These levels exceed the combined totals of the substrate
congeners by more than an order of magnitude. Therefore, the majority
of the observed 2,4-3,5-CB and 2,5-3,5-CB in our enrichment cultures is
due to ortho dechlorination of Aroclor 1260. As the levels
of 2,4-3,5-CB and 2,5-3,5-CB declined, corresponding increases in
2,4-3-CB and 2,5-3-CB, which are not present in Aroclor 1260, were
observed. The presence of both 2,4-3-CB and 2,5-3-CB was further
supported by GC-MS analysis showing the presence of a molecular ion of
m/z 258 for both of these products. The existence of these
trichlorobiphenyls confirms the ortho dechlorination that
produced 2,4-3,5-CB and 2,5-3,5-CB.
The formation of the non-ortho-chlorinated biphenyls 3-3-CB,
3-4-CB, and 3,5-3-CB (Table 2 and Fig. 2) was observed in sediment slurries incubated with Aroclor 1260 plus 2,3,4,5-CB or 2,3,5,6-CB. In
addition, 3,5-4-CB was produced in cultures incubated with only Aroclor
1260 and was further dechlorinated in the other cultures. Since none of
these congeners are present in Aroclor 1260 (16, 17), they
must be products of ortho dechlorination because all congeners in virgin Aroclor 1260 contain at least one ortho
chlorine. 3-4-CB coelutes with 3,4-CB, which is a potential
dechlorination product of 2,3,4,5-CB, but we have not observed the
formation of 3,4-CB in incubations with only 2,3,4,5-CB. Therefore,
3-4-CB is most likely the result of Aroclor dechlorination. Due to our discount of monochlorobiphenyl production, we do not know whether the
non-ortho congeners were further dechlorinated to
monochlorobiphenyls. Conversely, we observed
ortho-only-chlorinated congener 2,6-2,6-CB at a low mole
percent but no 2,6-2-CB or 2,6-CB/2-2-CB was detected, indicating
that dechlorination of 2,6-2,6-CB did not occur in our enrichment
cultures.
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DISCUSSION |
meta dechlorination of Aroclor 1260.
Extensive
meta dechlorination of Aroclor 1260 in BH sediment resulted
in significant decreases of PCBs with 2,3,4-, 2,4,5-, 2,3,4,5-, and
2,3,4,6-chlorophenyl groups and corresponding increases in 2,4- and
2,4,6-chlorophenyl groups. These products are the same as those found
in Aroclor 1260-contaminated freshwater sediments that have been
exposed to dechlorination Process N (2, 7, 21, 31). Process
N is characterized by an almost exclusive loss of flanked
meta chlorines (5, 21). No unflanked
meta dechlorination of Aroclor 1260 has been reported. In
addition to Process N, we observed unflanked meta
dechlorination of PCBs (e.g., 2,4-3,5-CB
2,4-3-CB and
2,5-3,5-CB2,5-3-CB) with our enrichment cultures. We suspect that
this is primarily due to the ortho dechlorination preceding
the unflanked meta dechlorination in our enrichments. Quensen et al. (21) reported a 19% decrease in the
meta and para chlorines of freshly added Aroclor
1260 with anaerobic microorganisms eluted from Silver Lake after a
19-week incubation. Alder et al. (2) demonstrated a 30%
removal of meta and para chlorines from freshly
added Aroclor 1260 with PCB-contaminated sediment from Silver Lake
after an 11-month incubation. In comparison to the aforementioned
investigations, our results exhibited more extensive meta
dechlorination (up to 65 mol%) in a relatively shorter period of time.
This further demonstrates the potential for reductive dechlorination of
haloaromatic compounds in estuarine sediments.
ortho dechlorination of Aroclor 1260.
At least six
distinct microbial dechlorination processes can be recognized as
occurring in various contaminated sediments on the basis of congener
selectivity and the products observed in situ and in laboratory studies
(5, 10, 12). In all previous reports, PCBs are dechlorinated
only by loss of meta and/or para chlorines. Here
we have demonstrated the occurrence of ortho dechlorination of Aroclor 1260 added to BH sediment. The results suggest that such
activity could play a role in the bioremediation of Aroclors in marine
and estuarine sediments. This is the first confirmed report of
ortho dechlorination of PCB mixtures, although
ortho dechlorination of single congeners has also been
reported (9, 19, 28-30). Maximal chlorine removal appears
to require the complementary action of two or more dechlorination
processes (5, 21). For example, in Process N (flanked
meta dechlorination of Aroclor 1260), elevated amounts
of 2,3,5,6-2,4-CB are produced by meta dechlorination of
2,3,5,6-2,4,5-CB and 2,3,5,6-2,3,4-CB, and 2,3,5,6-chlorophenyl substituents are recalcitrant in Aroclor 1260 (5). However, no 2,3,5,6-2,4-CB was observed in our slurry enrichments because the
2,3,5,6-2,4,5-CB and 2,3,5,6-2,3,4-CB were ortho and
meta dechlorinated to 2,4-3,5-CB and 2,4-3-CB. Thus, the
combination of ortho dechlorination plus flanked and
unflanked meta dechlorination resulted in more
dechlorination than that produced by the flanked meta
dechlorination of Process N.
Specificity of ortho dechlorinating
activity.
A modest amount of ortho dechlorination
was observed in comparison to the amounts of meta
dechlorination in all of our enrichment cultures. We hypothesize that
the moderate ortho dechlorination of the Aroclor in our
enrichments is dependent on the specificity of ortho
dechlorinating microorganisms in BH sediment. Previously, we reported on the ortho dechlorination of a few
single PCB congeners (9). Among those congeners, ~99 mol%
of 2,3,5-CB, ~20 mol% of 2,3,6-CB, and ~92 mol% of 2,3,5,6-CB
were ortho dechlorinated. In that report, no
ortho dechlorination was observed in BH sediment incubations
supplied with 2-CB, 2,3-CB, 2,4-CB, 2,5-CB, 2,6-CB, 2,4,6-CB,
2,6-2,6-CB, or 2,3,4,5-CB over a 6-month period. However, after
incubating the cultures for more than a year, we have now observed the
ortho dechlorination of 2,4-CB and 2,4,6-CB to 4-CB and a
small amount of 2,6-2,6-CB to 2,6-2-CB in enrichment cultures supplied
with these single congeners (data not shown). Others have also reported
on the ortho dechlorination of unflanked
ortho chlorines after extended incubation (29,
30). These results indicate that although some
unflanked ortho dechlorination will occur after extended
incubation, the ortho dechlorinators in BH sediment favor
removal of flanked ortho chlorines, with the exception of
2,3-CB and 2,3,4,5-CB. In Aroclor 1260 (16), only 12 mol% of the congeners bear 2,3,5- and 2,3,5,6-chlorophenyl groups. Congeners
carrying 2,3,6-chlorophenyl groups (14 mol%) and 2,3,4-, 2,4,5-, and 2,3,4,5-chlorophenyl groups (55 mol%) are far more prevalent.
Therefore, relatively smaller amounts of PCBs with 2,3,5- and
2,3,5,6-substitutions in Aroclor 1260 may explain why only moderate
levels of ortho dechlorination of Aroclor 1260 were observed
in our BH sediment enrichment cultures. Based on the results presented
here and previously with single congeners (9), we propose
pathways for the dechlorination of Aroclor 1260 to the major
ortho dechlorination products observed in these experiments (Fig. 3).
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FIG. 3.
Proposed pathway of meta and ortho
dechlorination of PCB congeners in Aroclor 1260 to produce 2,4-3,5-CB,
2,5-3,5-CB, 2,4-3-CB, 2,5-3-CB, and 2-3-CB. Superscript a
designates a decreased congener after incubation; superscript
b designates a congener appearing after incubation;
superscript c designates a proposed intermediate, which
could not be identified due to its coelution with 2,4,5-2,4-CB.
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Although we did not perform controlled experiments, we have observed in
general that PCB dechlorination is more stable, i.e.,
more extensive
and with shorter lag times, when sediments are
stored anaerobically at
room temperature (20 to 22°C) than at
4°C. K. R. Sowers
has also observed this with the storage of sediments
from several sites
used for methanogenic enrichments. Room temperature
storage is a
possible explanation for why
ortho dechlorination
could be
activated even after the sediment had been stored for
14 months. Other
laboratory studies have revealed that a prolonged
storage time of
sediment at 4 to 7°C increased the incubation
time required to
transform 50% of the substrate tested for chlorophenol
dechlorination
(
32) and changed the PCB dechlorination primed
by
4-bromobenzoate (
25). However, it is also important to note
that room temperature storage of an estuarine or marine sediment
does
not ensure the development of
ortho dechlorination. Using
identical storage and enrichment conditions, we have not been
able to
enrich for
ortho dechlorination with three of five
Charleston
Harbor (Charleston, S.C.) sediments and one sediment from
the
middle of the Chesapeake Bay near the mouth of the Potomac River.
meta or
para dechlorination developed with each
of these sediments
(data not shown). Therefore, something specific
to the site, perhaps
the microbial population, is more critical for the
development
of
ortho dechlorination than storage
temperature.
Effect of added 2,3,4,5-CB and 2,3,5,6-CB on dechlorination of
Aroclor 1260.
Microbial PCB dechlorination of Aroclor 1260 residue
can be primed by the addition of elevated concentrations (200 to 500 µM) of certain PCB congeners (3, 5, 7, 31). Bedard and
colleagues (3, 7) found that they could stimulate Process N
and Process P (flanked para dechlorination) of Aroclor 1260 residue in Woods Pond sediment by the addition of 2,3,4,5,6-CB and
2,5-3,4-CB, respectively. The addition of 2,3,4,6-CB also stimulated
Process N, Process P, and Process LP (unflanked para dechlorination) of Aroclor 1260 residue in Woods Pond sediment and led
to a 34% decrease in meta and para chlorines
after 12 months of incubation at 25°C (31). Our results
indicate that the addition of single PCB congeners (2,3,4,5-CB and
2,3,5,6-CB) stimulates meta and ortho
dechlorination of Aroclor 1260 in these sediments (shorter lag time and
more extensive dechlorination), further supporting the hypothesis that
anaerobic bacteria derive energy by donating electrons to halogenated
biphenyls (10, 12, 22).
In summary, anaerobic microorganisms in BH estuarine sediments
reductively dechlorinate Aroclor 1260. The dechlorination of
Aroclor
1260 is extensive and results in removal of
meta and
ortho chlorines. The addition of single PCB congeners
stimulates the
meta and
ortho dechlorination of
Aroclor 1260. Reviewed together,
these results demonstrate that the
biocatalytic capability of
anaerobic microorganisms to reductively
dechlorinate PCBs is broader
than previously realized. Such activity
could prove useful in
the bioremediation of PCBs and awaits testing
with PCB-contaminated
(aged) sediments.
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ACKNOWLEDGMENTS |
We thank Donna L. Bedard and Lynn A. Smullen from General
Electric Co. for supplying a customized PCB standard.
The work was supported by the Office of Naval Research, U.S. Department
of Defense (grant N00014-96-1-0116 to H.D.M. and grant N00014-96-1-0115
to K.R.S.).
| |
FOOTNOTES |
*
Corresponding author. Mailing address: Medical
University of South Carolina, Department of Microbiology & Immunology,
171 Ashley Ave., Charleston, SC 29425-2230. Phone: (803) 792-7140. Fax:
(803) 792-2464. E-mail: MAYH{at}MUSC.EDU.
| |
REFERENCES |
| 1.
|
Abramowicz, D. A.
1994.
Aerobic PCB degradation and anaerobic PCB dechlorination in the environment.
Res. Microbiol.
145:42-46[Medline].
|
| 2.
|
Alder, A. C.,
M. M. Häggblom,
S. Oppenheimer, and L. Y. Young.
1993.
Reductive dechlorination of polychlorinated biphenyls in anaerobic sediments.
Environ. Sci. Technol.
27:530-538.
|
| 3.
|
Bedard, D. L.,
S. C. Bunnell, and L. A. Smullen.
1996.
Stimulation of microbial para-dechlorination of polychlorinated biphenyls that have persisted in Housatonic River sediment for decades.
Environ. Sci. Technol.
30:687-694.
|
| 4.
|
Bedard, D. L., and R. J. May.
1996.
Characterization of the polychlorinated biphenyls (PCBs) in the sediment of Woods Pond: evidence for microbial dechlorination of Aroclor 1260 in situ.
Environ. Sci. Technol.
30:237-245.
|
| 5.
|
Bedard, D. L., and J. F. Quensen, III.
1995.
Microbial reductive dechlorination of polychlorinated biphenyls, p. 127-216. In
L. Y. Young, and C. Cerniglia (ed.), Microbial transformation and degradation of toxic organic chemicals.
Wiley-Liss Division, John Wiley & Sons, Inc., New York, N.Y.
|
| 6.
|
Bedard, D. L.,
R. Unterman,
L. H. Bopp,
M. J. Brennan,
M. L. Haberl, and C. Johnson.
1986.
Rapid assay for screening and characterizing microorganisms for the ability to degrade polychlorinated biphenyls.
Appl. Environ. Microbiol.
51:761-768[Abstract/Free Full Text].
|
| 7.
|
Bedard, D. L.,
H. M. Van Dort,
S. C. Bunnell,
L. M. Principe,
K. A. DeWeerd,
R. J. May, and L. A. Smullen.
1993.
Stimulation of reductive dechlorination of Aroclor 1260 contaminant in anaerobic slurries of Woods Pond sediment, p. 19-21.
Anaerobic dehalogenation and its environmental implications, Abstracts of the 1992 American Society Microbiology Conference.
Office of Research and Development, U.S. Environmental Protection Agency, Washington, D.C.
|
| 8.
|
Bedard, D. L.,
R. E. Wagner,
M. J. Brennan,
M. L. Haberl, and J. F. Brown, Jr.
1987.
Extensive degradation of Aroclors and environmentally transformed polychlorinated biphenyls by Alcaligenes eutrophus H850.
Appl. Environ. Microbiol.
53:1094-1102[Abstract/Free Full Text].
|
| 9.
|
Berkaw, M.,
K. R. Sowers, and H. D. May.
1996.
Anaerobic ortho dechlorination of polychlorinated biphenyls by estuarine sediments from Baltimore Harbor.
Appl. Environ. Microbiol.
62:2534-2539[Abstract].
|
| 10.
|
Brown, J. F., Jr.,
D. L. Bedard,
M. J. Brennan,
J. C. Carnahan,
H. Feng, and R. E. Wagner.
1987.
Polychlorinated biphenyl dechlorination in aquatic sediments.
Science
236:709-712[Abstract/Free Full Text].
|
| 11.
|
Brown, J. F., Jr., and R. E. Wagner.
1990.
PCB movement, dechlorination, and detoxication in the Acushnet estuary.
Environ. Toxicol. Chem.
9:1215-1233.
|
| 12.
|
Brown, J. F., Jr.,
R. E. Wagner,
H. Feng,
D. L. Bedard,
M. J. Brennan,
J. C. Carnahan, and R. J. May.
1987.
Environmental dechlorination of PCBs.
Environ. Toxicol. Chem.
6:579-593.
|
| 13.
|
Commandeur, L. C. M.,
R. J. May,
H. Mokross,
D. L. Bedard,
W. Reineke,
H. A. J. Govers, and J. R. Parsons.
1996.
Aerobic degradation of polychlorinated biphenyls by Alcaligenes sp. JB1: metabolites and enzymes.
Biodegradation
7:435-443[Medline].
|
| 14.
|
Faulkner, D. J.
1995.
Marine natural products.
Nat. Prod. Rep.
12:223-269.
|
| 15.
|
Focht, D. D.
1993.
Microbial degradation of chlorinated biphenyls, p. 341-400. In
J. M. Bollag, and G. Stotzky (ed.), Soil biochemistry, vol. 8.
Marcel Dekker, Inc., New York, N.Y.
|
| 16.
|
Frame, G. M.,
J. W. Cochran, and S. S. Bøwadt.
1996.
Complete PCB congener distributions for 17 Aroclor mixtures determined by 3 HRGC systems optimized for comprehensive, quantitative, congener-specific analysis.
J. High Resolut. Chromatogr.
19:657-668.
|
| 17.
|
Frame, G. M.,
R. E. Wagner,
J. C. Carnahan,
J. F. Brown, Jr.,
R. J. May,
L. A. Smullen, and D. L. Bedard.
1996.
Comprehensive quantitative congener-specific analyses of eight Aroclors and complete PCB congener assignments on DB-1 capillary GC columns.
Chemosphere
33:603-623.
|
| 18.
|
King, G. M.
1988.
Dehalogenation in marine sediments containing natural sources of halophenols.
Appl. Environ. Microbiol.
54:3079-3085[Abstract/Free Full Text].
|
| 19.
|
Montgomery, L., and T. M. Vogel.
1992.
Dechlorination of 2,3,5,6-tetrachlorobiphenyl by a phototrophic enrichment culture.
FEMS Microbiol. Lett.
94:247-250.
|
| 20.
|
Øfjord, G. D.,
J. A. Puhakka, and J. F. Ferguson.
1994.
Reductive dechlorination of Aroclor 1254 by marine sediment cultures.
Environ. Sci. Technol.
28:2286-2294.
|
| 21.
|
Quensen, J. F., III,
S. A. Boyd, and J. M. Tiedje.
1990.
Dechlorination of four commercial polychlorinated biphenyl mixtures (Aroclors) by anaerobic microorganisms from sediments.
Appl. Environ. Microbiol.
56:2360-2369[Abstract/Free Full Text].
|
| 22.
|
Quensen, J. F., III,
J. M. Tiedje, and S. A. Boyd.
1988.
Reductive dechlorination of polychlorinated biphenyls by anaerobic microorganisms from sediments.
Science
242:752-754[Abstract/Free Full Text].
|
| 23.
|
Quensen, J. F., III,
J. M. Tiedje,
S. A. Boyd,
C. Enke,
R. Lopshire,
J. Giesy,
M. Mora,
R. Crawford, and D. Tillitt.
1992.
Evaluation of the suitability of reductive dechlorination for the bioremediation of PCB-contaminated soils and sediments, p. 91-100.
International Symposium on Soil Decontamination using Biological Processes, Karlsruhe, Germany (December 1992).
Dechema, Frankfurt am Main, Germany.
|
| 24.
|
Smullen, L. A.,
K. A. DeWeerd,
D. L. Bedard,
W. A. Fessler,
J. C. Carnahan, and R. E. Wagner.
1993.
Development of a customized congener specific PCB standard for quantification of Woods Pond sediment PCBs, p. 45-66.
Twelfth Progress Report of Research and Development Program for the Destruction of PCBs.
General Electric Co. Corporate Research and Development, Schenectady, N.Y.
|
| 25.
|
Stokes, R. W.,
K. A. Deweerd, and D. L. Bedard.
1994.
Variables affecting the microbial dechlorination Aroclor 1260 in Woods Pond sediment slurries stimulated with 4-bromobenzoate, p. 27-41.
Thirteenth Progress Report of Research and Development Program for the Destruction of PCBs.
General Electric Co. Corporate Research and Development, Schenectady, N.Y.
|
| 26.
|
Sylvestre, M., and M. Sondossi.
1994.
Selection of enhanced polychlorinated biphenyl-degrading bacterial strains for bioremediation: consideration of branching pathways, p. 47-73. In
G. R. Chaudry (ed.), Biological degradation and bioremediation of toxic chemicals.
Discorides Press, Portland, Oreg.
|
| 27.
|
Technical and Regulatory Services Administration of the Maryland Department of the Environment.
1996.
.
Toxics Regional Action Plan for Baltimore Harbor.
Technical and Regulatory Services Administration of the Maryland Department of the Environment, Baltimore.
|
| 28.
|
Van Dort, H. M., and D. L. Bedard.
1991.
Reductive ortho and meta dechlorination of a polychlorinated biphenyl congener by anaerobic microorganisms.
Appl. Environ. Microbiol.
57:1576-1578[Abstract/Free Full Text].
|
| 29.
|
Williams, W. A.
1994.
Microbial reductive dechlorination of trichlorophenyls in anaerobic slurries.
Environ. Sci. Technol.
28:630-635.
|
| 30.
|
Wu, Q.,
D. L. Bedard, and J. Wiegel.
1997.
Effect of incubation temperature on the route of microbial reductive dechlorination of 2,3,4,6-tetrachlorobiphenyl in polychlorinated biphenyl (PCB)-contaminated and PCB-free freshwater sediments.
Appl. Environ. Microbiol.
63:2836-2843[Abstract].
|
| 31.
|
Wu, Q.,
D. L. Bedard, and J. Wiegel.
1997.
Temperature determines the pattern of anaerobic microbial dechlorination of Aroclor 1260 primed by 2,3,4,6-tetrachlorobiphenyl in Woods Pond sediments.
Appl. Environ. Microbiol.
63:4818-4825[Abstract].
|
| 32.
| Zhang, X., and J. Wiegel. Personal communication.
|
Appl Environ Microbiol, March 1998, p. 1052-1058, Vol. 64, No. 3
0099-2240/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
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Top
Abstract
Introduction
