Environ. Sci. Technol. 1997, 31, 3300-3307
Priming Microbial meta-Dechlorination of Polychlorinated Biphenyls That Have Persisted in Housatonic River Sediments for Decades HEIDI M. VAN DORT,† LYNN A. SMULLEN,‡ RALPH J. MAY, AND DONNA L. BEDARD* Characterization and Environmental Technology Laboratory, GE Corporate Research and Development, Schenectady, New York 12301
We recently demonstrated a strategy for stimulating or “priming” the indigenous microorganisms to dechlorinate weathered PCBs in sediments, but the dechlorination exhibited a very narrow para-dechlorination specificity. We tested the priming activity of various PCB congeners to discover those that would prime broader and more extensive PCB dechlorination activity. 2,3,4,5,6-Pentachlorobiphenyl (23456-CB), 2346-CB, and 236-CB primed extensive and sustained meta-dechlorination (Process N) of the Aroclor 1260 residue in Housatonic River sediment. The dechlorination targeted most of the hexa-, hepta-, and octachlorobiphenyls and converted them to tetra- and pentachlorobiphenyls containing mostly ortho- and para-chlorines. Both 234-CB and 2345-CB also primed Process N dechlorination, but the dechlorination ceased at 7 weeks and was much less extensive. 245-CB primed a narrow specificity paradechlorination (Process P). 2356-CB, 235-CB, and 23-CB did not prime PCB dechlorination. The results indicate that the 236-substitution pattern is important for maximal priming of dechlorination Process N. A chlorine at position 5 suppressed the priming activity, but the suppression was overcome by a chlorine at position 4. The discovery of non-PCB primers that are both effective and environmentally acceptable could lead to the development of practical methods for in situ PCB bioremediation.
Introduction The persistence of polychlorinated biphenyls (PCBs) in river and harbor sediments worldwide has become a focus for environmental regulation because PCBs accumulate in biota and are potentially toxic to wildlife and humans. The discovery that microbial PCB dechlorination was occurring in situ in freshwater and estuarine sediments (1-3) raised hopes for natural restoration because dechlorination is expected to detoxify the PCBs and at the same time make them more degradable and less persistent (4, 5). Microbial dechlorination of PCBs has had a major impact at some locations such as the Hudson River (1, 2, 6), but it has had a much smaller impact at other locations such as the * Corresponding author e-mail:
[email protected]. † Present address: Department of Chemistry, Purdue University, West Lafayette, IN. ‡ Present address: Chemical Process Technology Laboratory, GE Corporate Research and Development, Schenectady, NY 12301.
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Housatonic River (7). An effective method for stimulating or “priming” the activity of indigenous PCB-dechlorinating microbes would have great potential for accelerating natural restoration at the latter sites. The upper Housatonic River and Woods Pond, an impoundment on the river, are contaminated with PCBs used in the production of PCB transformers in Pittsfield, MA, from 1934 to 1978. The sediments in Woods Pond are contaminated with weathered hydrocarbon oil and with the residue of a partially dechlorinated mixture of Aroclors 1260 and 1254 (95:5) (7). These Aroclors contain, respectively, an average of six and five chlorines per biphenyl. We recently demonstrated that 2,5,3′,4′-tetrachlorobiphenyl (25-34-CB) and 24-34-CB primed the indigenous microorganisms to dechlorinate the decades-old PCBs in Housatonic River sediments (8). The dechlorination primed by these congeners exhibited a very narrow para-dechlorination specificity (8). However, our analyses of the in situ microbial dechlorination that has occurred in these sediments suggested that they also harbor a microbial population with a broad meta-dechlorination specificity that would potentially effect more extensive PCB dechlorination (7, 8). Our objective was to find a way to prime the metadechlorination activity because it attacks nearly all Aroclor congeners with six or more chlorines. We initially tested the priming activity of five PCB congeners in parallel incubations. The congeners selected were 23456-CB, 2345-CB, 2356-CB, 234-CB, and 245-CB. We chose these particular congeners for several reasons: (a) We chose congeners containing phenyl rings substituted with three to five chlorines, at least two of which were adjacent, because it is known that such congeners are the most susceptible to dechlorination (4, 9). (b) We hoped to learn more about how small changes in the number and position of chlorines in a series of related chlorophenyl substitution patterns affect dechlorination. (c) 234-, 245-, and 2345-CB are among the most common chlorophenyl substitution patterns in Aroclors 1254 and 1260 (10) and hence seemed good candidates to prime dechlorination of these Aroclors. (d) We chose congeners substituted on only a single ring to eliminate potential steric effects of bulky substitutions on the opposite ring and to facilitate product identification. This also had the effect of minimizing coelution of the dechlorination products of the primer with congeners in the Aroclor residue. One of the congeners tested, 23456-CB, primed extensive and sustained meta-dechlorination of the Aroclor 1260 residue that has persisted in the Housatonic River sediment for decades. Hence, it is clear that the indigenous microorganisms can be primed to effectively access and dechlorinate the PCBs despite high concentrations of oil. We subsequently determined that 236-CB and 2346-CB primed the same strong dechlorination activity. Comparison of the activity of various other congeners permitted us to determine how the chlorine substitution pattern affects priming activity.
Experimental Section Sediment Collection and Storage. Sediment was collected near the western shore of Woods Pond (7) in Lenox, MA, by repeated coring using a Lexan tube (2 in. diameter) and was transferred to glass jars, topped with site water, and stored at 4 °C until use. The sediment used in these experiments contained approximately 50 µg/g PCBs and 5 mg/g oil on a dry weight basis. Preparation of Slurries. Slurry preparation and sampling were carried out in an anaerobic chamber in an atmosphere of nitrogen and 3-5% hydrogen. Methanogenic slurries were prepared by mixing two volumes of wet sediment with three
S0013-936X(97)00347-7 CCC: $14.00
1997 American Chemical Society
volumes of revised anaerobic mineral medium (RAMM) (11) reduced with L-cysteine hydrochloride (0.1%). The slurries (30 mL each) were dispensed into serum bottles and 23456-CB or another PCB congener (99% purity, AccuStandard, New Haven, CT) was added from a concentrated stock solution (70 mM in acetone) to give a final concentration of 350 µmol/L of slurry (or 87-111 µg/mL depending on the molecular weight of the congener). This corresponds to about 610-775 µg/g on a dry sediment basis. Most incubations were set up in duplicate. The bottles were crimp-sealed with Teflon-lined butyl rubber septa (Wheaton). Controls were pasteurized at 75 °C for 20 min to kill vegetative cells and activate spores, then incubated at 23-25 °C for 24 h to allow spores to germinate, and finally autoclaved at 121 °C for 3 h to kill vegetative spores. Samples and controls were incubated in the dark at 23-25 °C without shaking. Sample Extraction and Analysis. Samples of the slurries were taken for analysis frequently, especially for the first 10 weeks. After vigorous vortexing, aliquots (1 mL) of the slurries were sampled with a 1-mL micropipettor (Gilson Pipetman) in an anaerobic chamber. The first 2-4 mm were cut off the pipet tips to facilitate sampling. PCBs were extracted with anhydrous diethyl ether (5 vol) by vigorous agitation for 24 h on a horizontal platform shaker. Elemental mercury (1/4 vol) was added to remove sulfur. Sample extracts were analyzed by gas chromatography (GC) using a HewlettPackard 5880 GC fitted with a Ni63 electron capture detector (ECD) and a DB-1 poly(dimethylsiloxane) capillary column (J&W Scientific, 30 m × 0.25 mm i.d. × 0.25 µm) as previously described (12). Analysis of PCB Primers and Their Products. The concentration of PCB congeners used as primers was approximately 16-fold higher than the concentration of the Aroclor residue in the sediment. This permitted quantification of these congeners and their products without interference from the PCB congeners that contaminate the sediment. Dechlorination products of the PCB primers were initially identified by comparing their elution positions with tables giving elution positions for all potential dechlorination products on the same GC system (13). We subsequently used a Hewlett-Packard 5890/5971A GC/mass spectrometer (GC/ MS) operated in the selected ion mode (SIM) to obtain quantitative data for the time course of dechlorination of each primer. We used a SPB-fused silica (poly-n-octyl,methyl siloxane) capillary column (30 m × 0.25 mm i.d. × 0.25 µm film thickness, Supelco, Inc., Bellefonte, PA), which resolved all of the dechlorination products of each congener. Reference standards (99% purity, AccuStandard Inc.) for each congener and its daughter products were used to confirm the identity of each product and to prepare calibration mixtures. Extracts of the samples that had undergone the most extensive dechlorination were scanned for biphenyl and monochlorobiphenyls (mono-CBs). Since none were detected by GC/ MS, they were not included in the calibration standards. We constructed a seven-point calibration curve for each congener and its observed dechlorination products. The calibration curves spanned the concentration range of 0.5-150 µM. The total concentration of each congener and its daughter products in our GC samples was approximately 70-100 µM. For each PCB congener, we monitored the ratio of the areas of the two most abundant ions of the molecular cluster over elution windows chosen to include all possible congeners in that homolog class. The masses monitored were as follows: mono-CB (m/z 188 and 190), di-CB (m/z 222 and 224), tri-CB (m/z 256 and 258), tetra-CB (m/z 290 and 292), and penta-CB (m/z 324 and 326). For biphenyl, we monitored the ratio of the two largest ions of the molecular cluster (m/z 154 and 152) and the characteristic ion formed by the loss of a phenyl group (m/z 76). Congener-Specific Analysis of Aroclor Residue in the Sediment. Changes in the PCB congener distribution profile of
FIGURE 1. Time course for the dechlorination of 23456-CB showing all observed products: (9) 23456-CB, (2) 2356-CB, (b) 246-CB, (O) 2346-CB, (4) 236-CB, (0) 26-CB. The data shown are for one of duplicate incubations. The data for both incubations were nearly identical except for a differences of a day or two in the time frame. the Aroclor residue in the sediment were monitored frequently by visual inspection of the chromatograms. Selected samples were sent to Northeast Analytical, Schenectady, NY, for quantitative analysis. These samples were Soxhlet extracted and analyzed on a DB-1 column as described (7, 13). Congener and homolog distributions for each sample were calculated and reported in units of mole percent after subtracting the peaks corresponding to the PCB primer and its dechlorination products. Congener assignments for Aroclor peaks that are composed of coeluting congeners include only those congeners determined to be significant peak components in Aroclors 1260 or 1254 (13) and dechlorination products verified by qualitative GC/MS as initially described by Bedard and May (7). This was necessary because the congener distributions produced by dechlorination differ from those in Aroclors (7). Statistics. The data for duplicate samples were analyzed by a two-sample, one-tailed, t-test with unequal variance (14) to test whether the increases and decreases observed in the mole percent contributions of the various congeners and homologs were significant.
Results Dechlorination of 23456-CB. Dechlorination of 23456-CB was first detected at 20 days in duplicate incubations. Approximately 98% of the 23456-CB was converted to products over the next 9 weeks. Figure 1 shows the time course for one of the incubations. Approximately 81% of the 23456-CB was converted to 246-CB via loss of both meta-chlorines. Only very low concentrations of 2346-CB were observed, but accumulation of 246-CB began at 28 days; hence, the data indicate that most of the 2346-CB was dechlorinated to 246-CB almost as soon as it was formed (Figure 1). No dechlorination of 246-CB was observed. Approximately 17% of the 23456-CB was para-dechlorinated to 2356-CB, which accumulated and was not further dechlorinated. Very small amounts of 236-CB and 26-CB were observed (Figure 1). These products were most likely formed from 2346-CB by the
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FIGURE 2. Dechlorination pathway of 23456-CB and final distribution of products (mol %). Black arrows indicate the major pathway of dechlorination. pathway 2346-CB f 236-CB f 26-CB. No ortho-dechlorination was observed, and no biphenyl or other PCB products were detected. Figure 2 shows the complete dechlorination pathway and the final product distribution. Dechlorination of the Aroclor 1260 Residue in the Sediment Primed by 23456-CB. Beginning at 6 weeks, when approximately 50-60 mol % of the 23456-CB had been dechlorinated, changes in the congener distribution profile of the Aroclor residue in the sediment provided evidence of new dechlorination. Figure 3 compares the PCB congener distributions at the beginning of incubation and after 20 weeks
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incubation. The most visible changes were increases in specific tetra- and pentachlorobiphenyls. Gradually all of the major hexa- and heptachlorobiphenyl peaks decreased, and the peak containing 24-24-CB became the most prominent in the chromatogram. Although the dechlorination of 23456-CB was essentially complete by day 80, changes indicative of continuing dechlorination of the Aroclor residue were still evident between days 127 and 141. No dechlorination occurred in autoclaved controls, and subsequent experiments showed that no dechlorination occurred in comparable sediment slurries incubated without a PCB primer but with the amount of acetone normally used as a carrier for the PCB primer. Congener-Specific Quantification of PCB Dechlorination. The Aroclor residue in samples primed with 23456-CB was analyzed by comprehensive congener-specific quantitative analysis at the beginning of incubation and after 141 days incubation. Table 1 gives the congener assignments, the IUPAC number, and the mole percent distribution for all PCB peaks detected. Our analysis measures all PCB components and resolves them into 115 peaks (for a complete listing see refs 7 and 8), but we have presented data only for peaks that were actually detected in at least one sample. For peaks that contain two or more different homologs, we have reported the mole percent of PCBs assigned to each homolog class. Subtraction of the peaks corresponding to 23456-CB and its dechlorination products resulted in the loss of data for two components of the Aroclor residue: 234-24-CB and 236-236-CB which constitute, respectively, 0.4-0.5 and 0.81.2 mol % of the total PCBs in typical sediment samples from Woods Pond (7). These congeners were not resolved from the large peak containing 23456-CB. 2346-CB, 2356-CB, and 246-CB did not coelute with any other congeners, but subtraction of the peaks for 236-CB and 26-CB resulted in the loss of data for two potential dechlorination products with which they coelute, 26-3-CB and 2-2-CB, respectively. Of the 86 PCB peaks detected, 74 showed significant increases or decreases as determined by a t-test analysis (P e 0.05). Nearly all of the hexa- and heptachlorobiphenyls showed significant decreases. Overall, the hexa-, hepta, and octachlorobiphenyls decreased by 47%, 44%, and 21%, respectively (Table 2). Many pentachlorobiphenyls were decreased, but others were formed by dechlorination of the hexa-, hepta-, and octachlorobiphenyls. Most of the congeners that increased were tetrachlorobiphenyls, but a few tri- and hexachlorobiphenyls also increased (Table 1). Specificity of the Dechlorination. Evaluation of the chlorine distribution of the Aroclor residue in the sediment samples before and after dechlorination (Table 2) reveals that the dechlorination was almost exclusively meta-dechlorination. It has recently been shown that phenyl rings with chlorine substitution patterns of 2,4,5- (245-), 234-, and 2345constitute more than 55 mol % of the chlorophenyl rings in Aroclor 1260 (10). Complete meta-dechlorination of these chlorophenyl groups would produce abundant 24-chlorophenyl groups. Similarly, 24 mol % of the chorophenyl groups in Aroclor 1260 bear the substitution patterns 2356and 236- (10). Complete meta-dechlorination of these chlorophenyl rings would generate 26-chlorophenyl rings. About 10 mol % of the chlorophenyl groups in Aroclor 1260 are chlorinated at positions 235-, 25-, and 23-, 3.5 mol % at position 34-, and 5 mol % at positions 2346- and 23456- (10). Complete meta-dechlorination of the chlorophenyl rings in the latter three groups would generate 2-, 4-, and 246chlorophenyl rings, respectively. A comparison of this information with the chlorophenyl composition of the congeners produced by dechlorination permits us to determine which meta-chlorines were targeted by the dechlorination. Table 1 shows that the congeners showing the largest increases (ranging, respectively, from 11.37 to 0.94 mol %)
FIGURE 3. Change in PCB congener distribution in Woods Pond sediment after priming with 23456-CB. (A) Congener distribution before priming. (B) Congener distribution 141 days after priming. (C) Net change in PCB congener distribution as a result of priming. Data shown are the mean of duplicate samples.
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TABLE 1. Changes in Individual PCB Congeners after Priming with 23456-CB mol % of total PCBsc DB-1 peak no.
IUPAC No.
7 8 14 15 17 19 20 21 22 24 25 26 29 31 32 33 37/4e 37/5e 38 39 41 42 43 44 45 46 47 48/4e 48/5e 49 50 51 53 54 55/5e 55/6e 56 57/5e 57/6e 58 61 62 64 65/5e 65/6e 67/5e 67/6e 69/5e 69/6e 71 72 73 74/5e 74/6e 75 77 78 79 80 81 82 83 84 85 87 88 89 90 91 92 93 94
6 8; 5 18 17 32; 16 54 29 26 25 28 53 51 46 52 49 47 44 104 42; 59 71; 64; 41 96 40 103 100 63 94 70 66 95; 102 91 56; 60 92; 84 90; 101 99 119 150 83; 112 97 152 87; 117; 115 110; 148 154 151 124 135 109 147 118 149 134; 114 131 146 105 132 153 141 179 137 130 176 138, 163, 164 158 129 178 175 187 128 183 167 185 174 177
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PCB congener
identificationa,b
2-3 2-4; 23 25-2 24-2 26-4; 23-2 26-26 245 25-3 24-3 24-4 25-26 24-26 23-26 25-25 24-25 24-24 23-25 246-26 23-24; 236-3 26-34; 236-4; 234-2 236-26 23-23 246-25 246-24 235-4 235-26 25-34 24-34 236-25; 245-26 236-24 23-34; 234-4 235-25; 236-23 235-24; 245-25 245-24 246-34 236-246 235-23; 2356-3 245-23 2356-26 234-25; 2356-4; 2346-4 236-34; 235-246 245-246 2356-25 345-25 235-236 235-34 2356-24 245-34 236-245 2356-23; 2345-4 2346-23 235-245 234-34 234-236 245-245 2345-25 2356-236 2345-24 234-235 2346-236 234-245; 2356-34; 236-34 2346-34 2345-23 2356-235 2346-235 2356-245 234-234 2346-245 245-345 23456-25 2345-236 2356-234
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T0
T141
0.09 ( 0.00 0.18 ( 0.02 0.53 ( 0.00 0.30 ( 0.00 0.41 ( 0.01 0.06 ( 0.00 0.04 ( 0.04 0.57 ( 0.01 0.80 ( 0.00 1.27 ( 0.01 0.97 ( 0.01 0.58 ( 0.00 0.32 ( 0.00 2.05 ( 0.01 2.85 ( 0.01 3.14 ( 0.03 0.58 ( 0.00 0.03 ( 0.00 0.67 ( 0.00 0.64 ( 0.00 0.60 ( 0.00 0.07 ( 0.00 0.66 ( 0.01 0.68 ( 0.01 0.12 ( 0.01 0.26 ( 0.00 0.60 ( 0.01 1.46 ( 0.02 0.87 ( 0.01 1.42 ( 0.02 0.15 ( 0.00 1.40 ( 0.01 3.02 ( 0.04 1.32 ( 0.02 0.52 ( 0.00 0.16 ( 0.00 0.22 ( 0.00 0.19 ( 0.00 0.07 ( 0.00 0.35 ( 0.00 1.59 ( 0.01 0.48 ( 0.01 2.67 ( 0.03 0.10 ( 0.00 0.84 ( 0.01 0.20 ( 0.00 0.72 ( 0.01 1.57 ( 0.00 4.76 ( 0.01 0.33 ( 0.00 0.34 ( 0.01 1.82 ( 0.02 0.25 ( 0.00 0.90 ( 0.00 8.57 ( 0.02 1.28 ( 0.01 1.75 ( 0.03 0.13 ( 0.00 0.46 ( 0.01 0.37 ( 0.01 6.91 ( 0.01 0.53 ( 0.00 0.13 ( 0.00 0.90 ( 0.01 0.37 ( 0.01 4.20 ( 0.01 0.37 ( 0.00 2.04 ( 0.01 0.41 ( 0.01 0.48 ( 0.00 3.14 ( 0.01 1.88 ( 0.00
0.10 ( 0.01 0.24 ( 0.00 0.62 ( 0.02 0.46 ( 0.00 1.35 ( 0.01 0.45 ( 0.00 0.00 ( 0.00 0.57 ( 0.00 0.86 ( 0.01 2.38 ( 0.01 2.40 ( 0.02 3.09 ( 0.06 0.71 ( 0.01 2.08 ( 0.01 6.06 ( 0.01 14.51 ( 0.18 0.39 ( 0.00 0.02 ( 0.00 0.82 ( 0.02 1.23 ( 0.01 2.08 ( 0.01 0.02 ( 0.00 1.52 ( 0.01 3.37 ( 0.06 0.39 ( 0.01 0.72 ( 0.01 0.33 ( 0.01 1.02 ( 0.02 0.61 ( 0.01 3.35 ( 0.13 0.06 ( 0.00 1.55 ( 0.00 3.97 ( 0.02 1.10 ( 0.05 1.32 ( 0.00 0.40 ( 0.00 0.22 ( 0.00 0.18 ( 0.00 0.07 ( 0.00 0.41 ( 0.01 0.28 ( 0.02 1.09 ( 0.02 2.11 ( 0.01 0.05 ( 0.00 0.37 ( 0.00 0.79 ( 0.01 2.85 ( 0.02 0.50 ( 0.01 1.52 ( 0.04 0.24 ( 0.00 0.48 ( 0.00 1.15 ( 0.03 0.02 ( 0.00 0.07 ( 0.00 2.95 ( 0.08 0.14 ( 0.01 1.34 ( 0.01 0.18 ( 0.00 0.12 ( 0.00 0.13 ( 0.00 2.91 ( 0.02 0.11 ( 0.00 0.01 ( 0.01 0.79 ( 0.01 0.16 ( 0.00 2.90 ( 0.01 0.02 ( 0.00 1.05 ( 0.00 0.13 ( 0.00 0.18 ( 0.00 1.31 ( 0.01 0.86 ( 0.00
significant changesd incr
decr (%)
+ + + +
+ + + + + + + 33 + + + 65 + + + + 45 30 30 + 59 + + 16 + +
+ 82 + 21 56 56 + + 68 68 30 + 37 92 92 66 89 23 + 74 64 58 80 96 12 58 31 96 48 68 61 58 54
TABLE 1 (Continued) mol % of total PCBsc identificationa,b
DB-1 peak no.
IUPAC No.
PCB congener
95/6e
156 171 202 173 201 172 197 180 193 191 200 170 190 198 199 196; 203 189 195 208 207 194 205 206
2345-34 2346-234 2356-2356 23456-23 2346-2356 2345-235 2346-2346 2345-245 2356-345 2346-345 23456-236 2345-234 23456-34 23456-235 2345-2356 2345-2346; 23456-245 2345-345 23456-234 23456-2356 23456-2346 2345-2345 23456-345 23456-2345
95/7e 96 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117
T0
T141
0.36 ( 0.00 0.76 ( 0.00 0.21 ( 0.01 0.04 ( 0.00 0.27 ( 0.01 0.72 ( 0.01 0.05 ( 0.00 7.34 ( 0.05 0.31 ( 0.00 0.08 ( 0.00 0.24 ( 0.01 2.31 ( 0.01 0.58 ( 0.01 0.08 ( 0.00 1.47 ( 0.01 1.65 ( 0.01 0.07 ( 0.00 0.64 ( 0.01 0.04 ( 0.00 0.04 ( 0.00 1.28 ( 0.01 0.05 ( 0.00 0.71 ( 0.02
0.14 ( 0.00 0.29 ( 0.00 0.16 ( 0.00 0.01 ( 0.00 0.21 ( 0.00 0.41 ( 0.00 0.04 ( 0.00 4.05 ( 0.00 0.26 ( 0.00 0.04 ( 0.00 0.16 ( 0.00 1.21 ( 0.00 0.31 ( 0.00 0.06 ( 0.00 1.17 ( 0.00 1.32 ( 0.01 0.04 ( 0.00 0.49 ( 0.01 0.03 ( 0.00 0.03 ( 0.01 1.06 ( 0.02 0.04 ( 0.00 0.64 ( 0.02
significant changesd incr
decr (%) 62 62 24 69 23 43 19 45 18 44 32 48 48 21 20 39 23 17
a The order in which congeners are reported indicates the relative contributions we believe they make to the peak when the peak is highest. Only congeners believed to be present are listed. b The congener designations denote the positions of the chlorine atoms on each ring of biphenyl, and the hyphen represents separation of the rings. c Quantitation was done by GC/ECD using a DB-1 capillary column as described. Values are shown ( average deviation. d P e 0.05 by t-test analysis. e For peaks containing two different homologs, we have reported the mol % of PCBs assigned to each, e.g., 37/4 and 37/5 refer to the tetra- and pentachlorobiphenyls that coelute in peak 37.
TABLE 2. Comparison of Dechlorination of Aroclor 1260a: 50 Years in Woods Pond Sediment vs 141 Days after Priming
PCB homologe di-CB tri-CB tetra-CB penta-CB hexa-CB hepta-CB octa-CB nona-CB hexa-nona-CB chlorine distribution ortho chlorines per biphenyl meta chlorines per biphenyl para chlorines per biphenyl
Aroclor 1260
Woods Pond T50yrsc
primed Woods Pond T141daysd
0.00 0.03 0.74 10.23 46.36 35.80 6.23 0.61 89.00
0.27 ( 0.01 3.92 ( 0.00 14.25 ( 0.04 15.24 ( 0.07 32.25 ( 0.02 27.36 ( 0.01 5.94 ( 0.06 0.78 ( 0.02 66.33 ( 0.12
0.34 ( 0.00 6.23 ( 0.01 33.56 ( 0.17 22.05 ( 0.10 17.04 ( 0.14 15.35 ( 0.02 4.71 ( 0.05 0.71 ( 0.02 37.81 ( 0.09
2.46 2.57 1.35
2.35 ( 0.00 2.21 ( 0.00 1.28 ( 0.00
2.39 ( 0.00 1.54 ( 0.00 1.24 ( 0.00
significant changesb incr decr (%)
+ + + + 47 44 21 43
30 3
a Quantitation of the PCBs in Woods Pond sediment was done by GC/ECD using a DB-1 capillary column as described. b P e 0.05 by t-test analysis. Result of dechlorination in situ over a period of about 50 years. d Result of further dechlorination primed by 23456-CB in 141 days. e Units are mol % ( average deviation. c
were 24-24-CB, 24-25-CB, 246-24-CB, 24-26-CB, 2356-24-CB, 236-24-CB, 236-26-CB, 25-26-CB, 24-4-CB, 235-24-CB, and 26-4-CB. Hence the congeners produced in the highest amounts by the dechlorination contained chlorophenyl groups with chlorine substitutions at positions 24-, 26-, and 246-. Small amounts of congeners with chlorophenyl groups substituted at positions 235-, 236-, 2356-, and 4- were also produced, but no congeners with 2-chlorophenyl groups were produced. The data indicate that the best substrates for dechlorination were chlorophenyl groups with substitution patterns 23456-, 2345-, 2346-, 234-, 245-, and 34-. Chlorophenyl groups with substitution patterns 2356- and 236- were also substrates for dechlorination as evidenced by the production of congeners with 26-chlorophenyl rings. However, some congeners
with 236- and 2356-chlorophenyl groups increased, indicating that these substrates were dechlorinated less efficiently. It appears that little or no dechlorination of 23-, 25-, or 235chlorophenyl rings occurred. Collectively, these data indicate that meta chlorines on chlorophenyl rings that had a-para chlorine were the best substrates and that unflanked metachlorines, e.g., the chlorine in position 5 on 25- and 235chlorophenyl rings, were not targets. This specificity matches that of dechlorination Process N (4), which was first reported in experiments using microorganisms from Silver Lake (Pittsfield, MA) (15). Dechlorination Primed by Other PCB Congeners. The four other congeners tested for priming ability in parallel incubations were each dechlorinated, but were less effective primers than 23456-CB. Most of the 2345-CB was dechlo-
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rinated to 235-CB (75-85% of the total) and the rest to 245-CB (Supporting Information Figure 1). Apparently the 245-CB was almost immediately dechlorinated to 24-CB and 25-CB. 235-CB persisted from day 20 to day 70 and then was dechlorinated to 25-CB. Like 23456-CB, 2345-CB primed Process N dechlorination of the Aroclor residue, and initially the dechlorination progressed like that primed by 23456-CB. However, the dechlorination ceased when 2345-CB was depleted at 50 days and did not resume when 235-CB was dechlorinated to 25-CB. Subsequent attempts to use 235-CB as a primer confirmed that it did not prime PCB dechlorination. The second congener, 234-CB, was rapidly dechlorinated to 24-CB (>99%) and 23-CB (99%), and only a small amount of 24-CB (
