evidence for dechlorination of polychlorinated biphenyls and polychlorinated dibenzo- p -dioxins and...

Evidence for Dechlorination of Polychlorinated Biphenyls andPolychlorinated Dibenzo-p-Dioxins and -Furans in WastewaterCollection Systems in the New York Metropolitan AreaLisa A. Rodenburg,*,† Songyan Du,† Hui Lui,†,‡ Jia Guo,† Nicole Oseagulu,† and Donna E. Fennell†

†Department of Environmental Sciences, Rutgers University, 14 College Farm Road, New Brunswick, New Jersey 08901, UnitedStates‡Department of Biochemistry and Microbiology, Rutgers University, 76 Lipman Drive, New Brunswick, New Jersey 08901, UnitedStates

*S Supporting Information

ABSTRACT: Polychlorinated biphenyls (PCBs) and polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) are persistent organic pollutants targeted bythe Stockholm Convention. Both contain aromatic chlorines and are subject tomicrobial dechlorination. Dechlorination of PCBs in sewers in the Delaware Riverbasin was recently reported. In this work, two data sets on concentrations of PCBs andPCBs+PCDD/Fs in wastewater treatment plant influents and effluents were analyzedto look for evidence that these compounds undergo dechlorination in the sewers ofthe New York/New Jersey Harbor area. The two data sets come from theContamination Assessment and Reduction Project (CARP) and were analyzed viaPositive Matrix Factorization (PMF). Analysis of the data set containing only PCBconcentrations suggests that PCBs are dechlorinated in the sewers of the NY/NJHarbor via the same pathways observed in the sewers of the Delaware River basin andthat advanced dechlorination of PCB mixtures is more likely to occur in combinedsewers vs separate sanitary sewers. When the combined data set of PCBs+PCDD/Fs was analyzed, the factor containing PCBdechlorination products also contained high proportions of 1,2,3,4,6,7,8-heptachlorodibenzo-p-dioxin (HpCDD), a knownproduct of the dechlorination of octachlorodibenzo-p-dioxin (OCDD), and other known dechlorination products of PCDD/Fs.Despite being the most abundant PCDD/F congener in all of the samples in the database, OCDD was a minor component in thedechlorination factor. This provides the first evidence that PCDD/Fs may be dechlorinated in sewers.

■ INTRODUCTIONPolychlorinated biphenyls (PCBs) are toxic, persistent organicpollutants that have been targeted for elimination under theStockholm Convention.1 Although PCB use and manufacturehave been banned in most countries, PCBs are still present atunacceptably high levels in many aquatic systems because theywere produced in such large quantities and are extremelypersistent. One of the few pathways for their transformation inthe environment is dechlorination by anaerobic bacteria, whichremoves chlorines but does not destroy the PCB backbone.2

This process is usually desirable because it decreases PCB mass,and because it produces lightly chlorinated congeners thattypically have lower toxicity and are more amenable to aerobicdegradation and volatilization.2 Anaerobic dechlorination ofPCBs has been studied extensively in the sediments of lakes,river, and harbors, but in these environments dechlorination isoften too slow to significantly impact ambient concentrations ofPCBs in the water column.Recently, we published evidence that PCBs are dechlorinated

in a variety of environments other than aquatic sediments.3 Ouranalysis of data on PCB concentrations in effluents fromdischargers on the Delaware River indicated that PCBs are

extensively dechlorinated in landfills and sewers as well as ingroundwater at contaminated sites. Dechlorination in sewers isparticularly fortuitous because of the large flows of wastewaterand the large masses of PCBs that enter the sewer. Sewers actas collectors and aggregators of a wide variety of pollutants inurban areas.It has long been known that wastewater treatment plants

(WWTPs) remove hydrophobic organic pollutants fromwastewater by sequestering them in the sludge. Often 90% ormore of the PCBs in the waste stream are removed in thisfashion.4−6 Sediment material in sewers also sequestershydrophobic organic pollutants such as PCBs. For example,Rocher et al.7 calculated that the gross bed solids in sewerscontained 98% of the total inventory of polycyclic aromatichydrocarbons. Sediments are expensive to remove from sewersand therefore are usually removed only when necessary. As aresult, sediment can have a very long residence time in the

Received: February 10, 2012Revised: May 1, 2012Accepted: May 8, 2012Published: May 8, 2012

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© 2012 American Chemical Society 6612 dx.doi.org/10.1021/es300560q | Environ. Sci. Technol. 2012, 46, 6612−6620

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sewer.8 Our research indicates that dechlorination of PCBs inthe sewer, which probably occurs in the sewer sediment, servesas an additional process by which loads of PCBs to ambientwaters are reduced. The sewer serves as an anaerobic bioreactorthat pretreats the sewage, converting high molecular weight(MW) PCB congeners to lighter, less toxic congeners that maybe degraded aerobically or volatilize in the WWTP. A betterunderstanding of the factors that favor dechlorination in sewerswould allow utilities to alter the design or management of

sewers to enhance this process, thereby reducing their loads ofPCBs to receiving waters.Like PCBs, polychlorinated dibenzo-p-dioxins and dibenzo-

furans (PCDD/Fs) are persistent organic pollutants targeted bythe Stockholm Convention.1 PCBs and PCDD/Fs arestructurally similar in that they both contain aromatic chlorines.Several studies indicate that bacterial strains that are capable ofdechlorinating PCBs can also dechlorinate PCDD/Fs.9−11 Oneof the goals of this study was to look for evidence of PCDD/Fdechlorination in sewers by analyzing a data set in which both

Figure 1. Resolved factors from the PCB-only data set (data set 1).

Environmental Science & Technology Article

dx.doi.org/10.1021/es300560q | Environ. Sci. Technol. 2012, 46, 6612−66206613

PCBs and PCDD/Fs were measured in the same sewageeffluent samples collected as part of the ContaminationAssessment and Reduction Project (CARP).12 The CARPwas initiated in the late 1990s to measure contaminants insuspected sources such as wastewater effluents and stormwateroutfalls, as well as in the ambient water column and thesediments of the New York/New Jersey Harbor.12,13 Microbialdechlorination of PCDD/Fs can follow either the peri-dechlorination pathway, which removes chlorines at the 1, 4,6, and 9 positions, producing 2,3,7,8-substituted products, orthe peri-lateral pathway that removes chlorines at the 2, 3, 7,and 8 positions, resulting in the production of congeners thatare not 2,3,7,8-substituted.11,14−16 For this reason, PCDD/Fdechlorination is easier to detect when all of the 210 PCDD/Fcongeners are measured. Unfortunately, CARP, like many othermonitoring programs, measured only the 17 2,3,7,8-substitutedPCDD/F congeners, so that only the products of the peri-dechlorination pathway were measured. However, previouswork by Barabas et al.17 has demonstrated that such data setscan reveal evidence of dechlorination. Thus, the CARPdatabase provides a unique opportunity to look for evidenceof dechlorination of PCDD/Fs in sewers. In this work, datafrom the CARP on PCB and PCDD/F concentrations in theeffluents (and some influents) of WWTPs in the New YorkCity metropolitan area were examined to look for evidence ofPCB and PCDD/F dechlorination in sewers.

■ METHODSThe CARP program was designed to identify the sources of avariety of pollutants to the sediments of the New York/NewJersey Harbor. The watershed of the harbor is home to about20 million people and contains New York City, the largest cityin the United States. The CARP involved sampling of air, water,sediment, and biota in the Harbor region from 1999 to 2004,including effluents and some influents to WWTPs thatdischarge into the harbor. 12 The harbor receives more than2000 million gallons of treated effluent each day from morethan 30 WWTPs.18 All of these WWTPs serve sewer systemsthat contain at least some combined sewers.The CARP data are publicly available by request to the

Hudson River Foundation. The data were provided in severalMicrosoft Access databases, with the New York and New Jerseydata in separate databases. The main challenge associated withanalyzing the CARP data is the high degree of heterogeneity inthe data set. CARP samples were collected by severalorganizations, including the New Jersey Department ofEnvironmental Protection and the New York State Departmentof Environmental Conservation, using a variety of differentsampling methods. PCDD/Fs and PCBs were not alwaysmeasured in the same samples. For PCB analysis, some sampleswere analyzed as whole water samples, so that the reported datarepresented the dissolved plus particle phases. In other cases,the sampling protocol attempted to separate the dissolved andparticulate fractions by pumping water through one (or two)filters and then through one (or two) columns containingXAD-2 resin. For PCDD/F analysis, typically only the filtersamples (particle phase) were analyzed. Furthermore, sampleswere sent to at least four different contract laboratories foranalysis via EPA method 161319 for the 17 2,3,7,8-subsitutedPCDD/F congeners and method 1668A20 or equivalent forPCBs. Method 1668A allows two possible gas chromatographycolumns, and both columns were used by the various contractlaboratories, which led to different congener coelution patterns.

Because of this, the PCB data set was more heterogeneous thanthe PCDD/F data set.For PMF analysis, two data sets were constructed. These are

described in more detail in Supporting Information. The firstdata set contained PCB measurements in treated effluents andsome influents from both the NY and NJ databases. The finalPCB data set submitted for PMF analysis contained 64congeners (or coeluting congener groups) in 149 samples. Thesecond data set contained both PCB and PCDD/F measure-ments from the New York database only. New Jersey data werenot included in this data set because 13 of the 17 PCDD/Fcongeners were below detection limit in virtually all of the NJsamples. Even in the NY data set, two of the 17 PCDD/Fcongeners had to be discarded because they were belowdetection limit in a majority of the samples: 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and 1,2,3,7,8,9-hexa-chlorodibenzofuran (HxCDF). The second data set thereforecontained 15 PCDD/F congeners plus 50 PCB congeners in 65samples. These data sets were examined via PMF 2.0software.21

Loads of PCBs and PCDD/Fs to the New York/New JerseyHarbor from the WWTPs were calculated by multiplying thegeometric mean concentration of each factor by the flow rate ofeach plant. Flow rates were obtained from the 2007 InterstateEnvironmental Commission Annual Report.18

■ RESULTSPCB Data Set. For the PCB data set, the correct number of

factors was determined to be seven (Figure 1). This conclusionwas based on three lines of evidence. First, the 7-factor modelyielded a stable model solution with an RSD of 1% for 9 PMFruns with seed values from 1 to 9. (Requesting more factorsresulted in RSD values greater than 10%). Second, the sevenfactors were interpretable. Third, the 7-factor model adequatelydescribed the data set. The R2 value for the measured vsmodeled concentrations was >0.83 for all congeners and was0.99987 for ΣPCBs.

Aroclor Factors. Based on the congener profiles of theAroclors from Rushneck et al.,22 factors 2, 4, 5, and 7 stronglyresembled Aroclors 1242, 1248, 1254, and 1260, respectively,with R2 values >0.9. These factors represented 7%, 11%, 11%,and 53% of the mass in the data set, respectively. Their relativeimportance is very different when examined on the basis ofloads to the harbor: these four factors represent 22%, 13%,37%, and 9% of the total load, respectively. The differencebetween the load and the mass in the data set arises from theimportance of heavier Aroclors in the influent and CSOsamples, which is related to the fact that the heavier Aroclorsare more effectively removed by the WWTPs (see below).Factor 6 somewhat resembled a 70/30 mixture of Aroclors

1254 and 1260 (R2 = 0.77). It represented 12% of the mass inthe data set, but only 7% of the load of PCB to the Harbor fromthese WWTPs.

Dechlorination Factors. The remaining two factors appearto be dechlorination signals. Factor 1 is dominated by PCBs 4(2-2; 46% of ΣPCBs) and 19 (26-2; 9%). (In this notation,numbers before the dash refer to the chlorine positions on ring1, and the numbers after the dash refer to the chlorine positionson ring 2). Factor 3 is dominated by PCBs 43 + 52 + 73 (235-2, 25-25, and 26-35 respectively), 44 + 47 + 65 (23-25, 24-24,2356, respectively), and 45 + 51 (236-2, 24-26, respectively).These three coeluting congener groups constitute 9%, 13%, and8% of the ΣPCBs, respectively. These results are very similar to



those obtained in our analysis of the PCB congener patterns ineffluents of dischargers on the Delaware River,3 where twodechlorination signals were obtained (Figure 2). The first wasdominated by PCBs 4 and 19 and was assumed to represent anadvanced stage of dechlorination. The second was dominatedby PCBs 44 + 47 + 65 and 45 + 51, and was interpreted as asign of partial dechlorination. In the factors resolved from theCARP data set, PCB 4 dominates the advanced dechlorinationsignal even more than it did in the Delaware River BasinCommission (DRBC) advanced dechlorination factor. Incontrast, PCBs 44 + 47 + 65 and 45 + 51 were less dominantin the CARP partial dechlorination factor than in the DRBCpartial dechlorination factor (Figure 2). The relative weaknessof the partial dechlorination factor in the CARP data set may berelated to the fact that all of the WWTPs in the CARP areaserve combined sewers. In our previous work,3 the partialdechlorination signal was most prevalent in effluents fromWWTPs that serve separate sewer systems. We speculate thatthis is because separate sewer systems are less likely toexperience methanogenic conditions, since they develop deepbeds of cohesive sediment. In contrast, sulfidogenic conditionsare more likely to prevail in separate sewers, which generallybuild up less sediment.23

These two dechlorination signals are present in all of the 32WWTPs sampled (Figure 3), suggesting that the dechlorinationoccurred in the sewers and not in the anaerobic digestersemployed at about half of these plants. Factors 1 and 3averaged more than 5% of the sum of PCBs in a majority of theWWTPs sampled. Factor 1 comprised more than 10% of theΣPCBs in eight of the WWTPs (Bowery Bay, Coney Island,Hunts Point, North River, Poughkeepsie, Rensselaer, andRockland County municipal WWTPs, and the Fresh KillsLandfill Leachate Treatment Plant). In contrast, only five plantshad more than 10% of factor 3, the partial dechlorination factor,in their effluents: Bowery Bay, Edgewater, Fresh Kills,Newtown Creek, and Red Hook.Figure 3 demonstrates that the CARP New York plants,

which serve combined sewers, emit a larger fraction ofadvanced dechlorination products than most of the plants

serving separate sanitary sewers, such as most of the DRBCplants. This supports the conclusion in our previous work3 thatadvanced dechlorination is more prevalent in combined sewers.However, the fact that the CARP NJ plants (which also servecombined sewers) emit fewer dechlorination products thanmost of the other plants indicates that there are other, as yetunidentified, factors that influence the extent of dechlorination.These factors could include the age of the sewer system; theslope of the sewer, which governs the rate of flow of the sewageand therefore the rate of accumulation of sewer sediment; andthe quality of the sewage itself (amount of carbon and othernutrients).In the CARP data set, the advanced dechlorination factor

comprises 6.0% of the loads of PCBs to the harbor from theseWWTPs, and the partial dechlorination factor comprises 6.4%of the loads. Our previous study found that 19% of the loads ofPCBs to the Delaware River consisted of dechlorinated PCBs.3

Thus dechlorination is less important overall in the CARP dataset. This arises partly because some of the plants with thelargest flows have relatively low amounts of dechlorinationproducts in their effluents. The three plants with the largestflow in the CARP data set (Passaic Valley SewerageCommission, Ward’s Island, and Newtown Creek) compriseabout 35% of the total flow, but less than 13% of the PCBs intheir effluents consist of dechlorination products. Again, thissuggests that there are other, as yet unidentified, factors thatinfluence the extent of dechlorination. It is well documentedthat dechlorination of PCBs occurs in the sediments of theUpper Hudson River, and this dechlorination signal can beobserved in the water column of the lower Hudson River/CARP study area.24 However, this cannot account for thedechlorination observed in the treated effluents. This issue isdiscussed in more detail in the Supporting Information.

Toxic Equivalency Quotients. PCBs are reasonablyanticipated to be carcinogens and also display a range ofnoncancer health effects.25 The reduction in toxicity due tothese many types of health effects is difficult to estimate.However, PCBs also display dioxin-like toxicity which can bequantified. The PCB data set contained five of the dioxin-like

Figure 2. Comparison of the advanced and partial dechlorination factors isolated from the Delaware River Basin Commission (DRBC) andContamination Assessment and Reduction Project (CARP) databases.



PCB congeners (PCBs 105, 118, 156 + 157, and 167). Basedon the toxic equivalency factors (TEFs) recently adopted bythe U.S. EPA,26 Factor 3 (the partial dechlorination signal) hasthe lowest toxic equivalency quotient (TEQ) of the sevenfactors. Dechlorination to factor 3 decreases the TEQ for theAroclor factors by 13−92%. Dechlorination to factor 1represents a 17−82% reduction in TEQ for most factors(although it actually represents an increase in TEQ for factor 7,the Aroclor 1260 factor). In contrast, the reduction in massupon dechlorination is just 9−30% for the advanceddechlorination signal. Thus the reduction in TEQ is greaterthan the reduction in mass. In comparison, the reduction inTEQ for the factors isolated from the DRBC data set3 is evenmore dramatic. In that data set, which included six dioxin-like

congeners (PCBs 77, 105, 118, 156 + 157, and 167),dechlorination to the advanced dechlorination signal repre-sented a reduction in TEQ of more than 98% for all of theAroclor factors, and reduction to the partial dechlorinationsignal resulted in reduction in TEQ of between 32% and 86%depending on the starting Aroclor. These calculations highlightthe important impact of dechlorination in reducing not justmass but dioxin-like toxicity of PCB mixtures.

Influent Samples. One sample of influent was collected ateach of ten of the New York WWTPs. These samples werelabeled as “CSO” samples in the database, since all of the NewYork WWTPs have combined sewer systems. As with theDelaware River data set, the CARP data reveal that thedechlorination signal is present in higher concentrations in theinfluent than in the effluent at all ten plants, suggesting themost or all of the dechlorination occurred in the collectionsystem, i.e., the sewers. For each of these ten plants, theremoval (R) of PCBs from the wastewater stream wascalculated as

= − ·⎛⎝⎜

⎞⎠⎟R

CC

1 100%eff

in (1)

where Ceff is the average concentration of the factor in theeffluent, and Cin is the concentration of the factor in theinfluent sample. For the sum of PCBs, the average (±standarddeviation) removal was 95 ± 4%. The average (±standarddeviation) removal for factors 1 through 7 was 63 ± 26%, 89 ±7%, 89 ± 6%, 95 ± 4%, 89 ± 8%, 98 ± 2%, and 97 ± 4%. Theremoval of factor 1 was thus more variable that the removal ofthe other factors, and application of the F-test demonstratesthat the % removal of factor 1 is significantly (p < 0.05) lessthan the removal of the other factors. It is possible that somedechlorination of PCBs occurred in the anaerobic sludgedigesters employed at all 10 of these plants, which wouldincrease the dechlorination products in the effluent and lead tolower calculated removal. However, if the lower removal ofdechlorination products is instead due to the reducedhydrophobicity of the products, this has implications for theremoval of PCB toxicity by the wastewater collection andtreatment system. Even though dechlorination results in asignificant decrease in TEQ, this may be partially offset by thegreater mass of dechlorination products released to receivingwaters due to the WWTP’s lesser ability to remove thesedechlorinated congeners from the waste stream.

PCB+PCDD/F Data Set. The correct number of factorsderived from the combined data set containing 65 PCB andPCDD/F congeners in 65 samples was determined to be five(here designated factors A through E to avoid confusion withthe PCB-only model). The five-factor model was chosenbecause it resulted in a reasonably low RSD of the G matrix of8.7%, it produced meaningful and interpretable factors, and itsatisfactorily described the data matrix. The R2 value for themeasured versus modeled concentrations of the sum of all 65analytes was 0.998, and was >0.8 for 62 of the 65 analytes. TheR2 values for the three remaining analytes (PCB 4, PCBs 61 +70 + 74 + 76, and PCB 194) increased to >0.8 when one or twooutliers were excluded. The R2 value for OCDD was 0.88 andwas better than 0.92 for the rest of the PCDD/Fs.

Identification of Factors. Four of the five factors generatedwere dominated by PCBs, which comprised more than 99% ofthe mass in those factors (Figure 4). Only factor E wasdominated by PCDD/Fs, which comprised 54% of its mass. As

Figure 3. Comparison of the percent of the ΣPCBs in the effluent thatconsisted of the advanced (white) and partial (black) dechlorinationfactors in each WWTP from the CARP and DRBC databases, sortedby state. Among the DRBC plants, only six serve combined sewersystems: the three plants of the Philadelphia Water Department(PWD), DELCORA, Wilmington, and Camden County MunicipalUtilities Authority (CCMUA). All of the CARP plants serve combinedsewers.



in most environmental samples, octachlorodibenzo-p-dioxin(OCDD) was the most abundant PCDD/F congener in all ofthe samples, comprising 56−88% of the sum of the 15 PCDD/F congeners in the data set (Σ15PCDD/Fs). Because of itsabundance, factor analysis studies of PCDD/Fs frequentlyobserve that OCDD dominates in all of the resolvedfactors.27,28 Its presence is therefore not useful in identifyingthe factor, and for this reason, OCDD is sometimes excludedfrom the data set.17,27

OCDD does dominate the PCDD/F congener pattern offour of the five PCB+PCDD/F factors, but it is unusually scarcein factor A, where it comprises just 3% of Σ15PCDD/Fs. FactorA is dominated by PCB 4 (23% of the total PCB+PCDD/Fmass), indicating that it represents advanced dechlorination.Figure 4 demonstrates that the PCDD/F signal of factor A isdominated by 1,2,3,4,6,7,8-heptachlorodibenzo-p-dioxin(HpCDD), which comprises 79% of Σ15PCDD/Fs in thisfactor. The ratio of 1,2,3,4,6,7,8-HpCDD to OCDD in factors Bthrough E is less than 0.2, but is 23 in factor A, thedechlorination factor. Barkovskii and Adriaens14 observed1,2,3,4,6,7,8- HpCDD as a product of the peri-dechlorinationof OCDD in microcosms constructed using sediment from the

Passaic River, which is within the New Jersey portion of theCARP study area. Because OCDD is the most abundantPCDD/F congener in the sewers, it is a likely substrate fordechlorination. The presence of a documented dechlorinationproduct of OCDD, and the relative absence of thedechlorination substrate, OCDD, in the same factor thatcontains dechlorinated PCBs is a strong indication thatdechlorination of OCDD occurs in sewers.Similarly, highly chlorinated PCDF congeners such as

octachlorodibenzo-p-furan (OCDF) and the HpCDFs areunusually scarce in factor A. They comprise about 0.5% ofΣ15PCDD/Fs in factor A, compared to >1.3% for the other fourfactors. Dechlorination of weathered OCDF with 1,2,3,4,7,8,9-HpCDF postulated as the product has been observed inKymijoki sediment both in situ in Finland as well as inmicrocosms developed from this sediment and spiked withOCDF.29 Lower chlorinated congeners including 1,2,3,6,7,8-HxCDF and 1,2,3,6,7,8-HxCDD are more abundant in factor A.Barabas et al.17 likewise noted these two congeners as productsof in situ dechlorination of PCDD/Fs in the Passaic River. Ourresults raise the possibility that the dechlorination observed byBarabas et al.17 in the Passaic River sediment occurred not in

Figure 4. Resolved factors for the data set containing both PCB and PCDD/F congeners. PCBs are plotted as fraction of Σ50PCBs, and PCDD/Fsare plotted as fraction of Σ15PCDD/Fs. The percent of the total mass of each factor that consists of PCDD/F congeners is shown in the upper rightof each panel.



the river but in the combined sewers that frequently overflowinto the tidal Passaic. These combined sewers flow to thePassaic Valley Sewerage Commission (denoted as “PVSC” inFigure 3). 1,2,3,4,7,8- and 1,2,3,6,7,8-HxCDFs are alsoabundant in factor A; Adriaens and Grbic-Galic30 observedthese congeners as products of the dechlorination of1,2,3,4,6,7,8-HpCDF in microcosms using sediment from theHudson River. Also, Liu and Fennell observed thatDehalococcoides ethenogenes strain 195 can dechlorinate1,2,3,4,7,8-HxCDF via a peri-lateral pathway to produce non-2,3,7,8-substituted congeners.11 Thus it is possible that1,2,3,4,6,7,8-HpCDF is a dechlorination intermediate in thesewer system. In general, factor A contains a wider variety oflower molecular weight PCDD/F congeners than any of theother factors, suggesting that sequential dechlorination stepsmay produce a wide variety of PCDD/F congeners, and thatOCDD is not the only substrate for dechlorination in thesewers.As noted above, only the peri-dechlorination products were

measured in the CARP database. Evidence that dechlorinationoccurs by this pathway in sewers suggests that the peri-lateraldechlorination pathway may also occur in sewers. Also,dechlorination products with fewer than four chlorines mayalso be present, but were not measured in these samples.The PCB portions of the combined PCB+PCDD/F factors

were compared with the Aroclors. Only factor D clearlyresembled a single Aroclor (Aroclor 1260, R2 = 0.96). As aresult, factor D also resembled factor 7 of the PCB-only model(R2 = 0.97). The other four factors did not resemble a singleAroclor or even a linear combination of Aroclors. Factor Aresembled factor 1 of the PCB-only model (R2 = 0.78), sinceboth were dominated by PCB 4 and represent advanceddechlorination. The other three PCB+PCDD/F factors did notstrongly resemble any of the PCB-only factors. We speculatethat this change in the composition of the factors suggests thatwhen more than one class of contaminant is investigated, thePMF model is more likely to identify secondary sources, i.e.,processes that transport the contaminants from their locationsof release to the receptor point, rather than primary sourcessuch as Aroclors.TEQs. For factors A, B, and C, the total TEQ was dominated

by TEQ associated with the PCDD/Fs, even though theyconstituted less than 0.5% of the mass in those factors. ThePCB associated TEQ in factors A, B, and C represented just2.0%, 2.9%, and 6.3% of the overall TEQ respectively. TheTEQ of factor D, which represents Aroclor 1260, was splitequally between the PCB-associated TEQ and PCDD/F-associated TEQ even though PCDD/Fs make up just 0.015%of the mass in this factor. Not surprisingly, the TEQ of FactorE, which consists of 54% PCDD/Fs by mass, is dominated bythe PCDD/F-associated TEQ. The PCB-associated TEQ ofthis factor was just 0.02% of the total.Factor D, the Aroclor 1260 factor, had the lowest overall

TEQ. Factor A, the advanced dechlorination factor, had thenext lowest TEQ which was nine times higher than the factor DTEQ. The factor B TEQ was 32 times higher than factor D, thefactor C TEQ was 44 times higher, and the TEQ of factor E,the mass of which is dominated by PCDD/Fs, was about 2600times higher than the TEQ of factor D. 2,3,7,8-TCDD has thehighest TEF among the PCDD/Fs, but since it was notincluded in this data set, the major source of TEQ among thePCDD/Fs was 1,2,3,7,8-PeCDD, usually followed by1,2,3,4,6,7,8- HpCDD, and then by 1,2,3,6,7,8-HxCDD.

In contrast to the PCB mixtures, we cannot estimate thechange in TEQ upon dechlorination for the PCDD/Fs exceptto note that if dechlorination primarily converts OCDD (with aTEF of 0.0003) to 1,2,3,4,6,7,8- HpCDD (with a TEF of 0.01),then dechlorination increases the TEQ of the mixture.However, since dechlorination could produce non-2,3,7,8-substituted PCDD/Fs which theoretically have no “dioxin-like”toxicity, dechlorination may actually reduce the overall toxicityof the PCDD/F mixture.11

Influent samples. PCB+PCDD/F concentrations in influentsamples were available for four WWTPs: Coney Island,Newtown Creek, Owl’s Head, and Port Richmond. At thesefour plants, percent removal of the highest molecular weightfactors (B, C, D, and E) was always greater than 85%. Removalof factor A, the advanced dechlorination factor, was morevariable, ranging from 30% at Coney Island to 80% at PortRichmond. As noted above, the lesser removal of thedechlorination factor is probably related to the fact that itcontains lower MW congeners that are generally more soluble,although there could be some contribution from dechlorinationof PCBs and PCDD/Fs in the anaerobic digesters employed atall of these plants. As noted above, less efficient removal ofdechlorination products during wastewater treatment leavesgreater concentrations of these products in the effluents, whichcan counteract any reduction in toxicity achieved viadechlorination.

Implications. The high degree of heterogeneity in theCARP database of PCB measurements is regrettable and limitsthe utility of the CARP data. The use of multiple contractlaboratories is not the main driver of heterogeneity within theCARP PCB data. Our earlier analysis used data collected byfacilities that discharge to the Delaware River and reported tothe Delaware River Basin Commission (DRBC). The DRBCdata set was likewise generated from multiple contractlaboratories chosen by the dischargers. DRBC was able togenerate a more homogeneous data set by constructing athorough and thoughtful set of guidelines that each laboratoryfollowed. These guidelines stipulated the GC column to beused in the analysis as well as the maximum acceptabledetection limits, among other things. CARP suffered from alack of cooperation among multiple state and federal agencies.Despite these limitations, analysis of the CARP data provided

useful insights into the dechlorination of persistent organicpollutants in sewer systems. Taken together, analysis of thesetwo data sets via PMF suggests that dechlorination of PCBsoccurs in the sewers of the NY/NJ Harbor area via the samepathways observed in most of the sewer systems in theDelaware River basin. The results suggests that dechlorinationof PCBs has only a small effect on the mass load of PCBs, sincethe reduction in mass of the PCB congeners due todechlorination is small and partially offset by decreased removalefficiency during the waste treatment process. However, thereduction in TEQ for dioxin-like PCB congener is substantial,perhaps as large as 20% compared to similar emissions ofunweathered PCB formulations. The wastewater collectionsystems in the NY/NJ Harbor area contain primarily combinedsewers. Dechlorination of PCBs therefore appears to occur invirtually all combined sewer systems and most separate sewersystems. The analysis of the combined PCB+PCDD/F data setprovides tantalizing evidence that PCDD/Fs are dechlorinatedin sewers, and suggests that 1,2,3,4,6,7,8-HpCDD or the ratioof 1,2,3,4,6,7,8-HpCDD to OCDD may be used as a tracer ofthe dechlorination of PCDD/Fs. This observation is likely to be



particularly useful in data sets that measured only the 172,3,7,8-substituted PCDD/F congeners. This analysis bolstersthe general view that environmentally important microbialprocesses are occurring in sewers. Other anaerobic bacterialprocesses, such as additional reductive dehalogenation path-ways and mercury methylation,31 may also occur in sewers.

■ ASSOCIATED CONTENT*S Supporting InformationDetails on the construction of data sets and the possibleinfluence of dechlorination in the sediments of the UpperHudson River. This material is available free of charge via theInternet at http://pubs.acs.org.

■ AUTHOR INFORMATIONCorresponding Author*Phone: 732-932-9800 x 6218; fax: 732-932-8644; e-mail:[email protected] authors declare no competing financial interest.

■ ACKNOWLEDGMENTSWe thank Simon Litten for his help in understanding the CARPdata. Simon served as the mastermind of the NY CARP datacollection effort and recently retired from the NYSDEC. Wewish him a blissful retirement.

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mailto:[email protected]

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