Environ. Sci. Technol. 1998, 32, 3496-3501
Remediation at a Marine Superfund Site: Surficial Sediment PCB Congener Concentration, Composition, and Redistribution B A R B A R A J . B E R G E N , * ,† KENNETH A. RAHN,‡ AND WILLIAM G. NELSON† U.S. Environmental Protection Agency, Atlantic Ecology Division, 27 Tarzwell Drive, Narragansett, Rhode Island 02882, and Graduate School of Oceanography, University of Rhode Island, Narragansett, Rhode Island 02882
New Bedford Harbor (NBH) is an estuary severely contaminated with polychlorinated biphenyls (PCBs) and is undergoing a multistage Superfund remediation. A longterm monitoring program was developed to assess the effectiveness of this remediation. Seventy-two stations were monitored in the harbor and in adjacent Buzzards Bay. Sediments were collected at each station before and after the initial remedial phase (the “hot spot” removal), and the concentrations of 18 PCB congeners were quantified. A qualitative graphical technique was combined with exploratory statistical techniques to examine the spatial and temporal variability in concentrations of PCBs and proportions of the congeners. The combination of the two techniques with PCB congener ratios revealed subtle changes after remediation that were not evident by a more traditional statistical analysis of total PCB concentrations. Although major redistributions of contaminated sediments were confined to the immediate vicinity of remedial activities, there is evidence that low molecular weight PCBs were transported farther.
Introduction The accumulation of anthropogenic contaminants has produced numerous contaminated terrestrial and aquatic areas throughout the United States. Sites that pose the greatest risk to human health and the environment are considered hazardous waste sites and are listed on the Environmental Protection Agency’s (EPA) National Priorities List (NPL) for cleanup under CERCLA and SARA (Superfund) legislation. One marine Superfund site undergoing remediation currently is New Bedford Harbor (NBH), an estuary located in southeastern Massachusetts (Figure 1a). NBH’s primary contaminant is polychlorinated biphenyls (PCBs) (1). For over 40 years, these organic compounds were used in transformers and other applications by New Bedford electronic industries. PCBs released by these industries have accumulated in the food chain and forced approximately 70 km2 of NBH and adjacent Buzzards Bay to be closed to commercial and recreational fishing. Also, it has been demonstrated that PCBs can cause adverse human health * To whom all correspondence should be addressed. voice: (401)782-3059;fax: (401)782-3030;e-mail:
[email protected]. ‡ University of Rhode Island. † U.S. Environmental Protection Agency. 3496
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TABLE 1. Name, Substitution Pattern, and Log Kow of the Congeners Quantified in This Study namea
substitution pattern
log Kowb
CB008 CB018 CB028 CB052 CB044 CB066 CB101 CB118 CB153 CB105 CB138 CB187 CB128 CB180 CB170 CB195 CB206 CB209
2,4′2,2′,52,4,4′2,2′,5,5′2,2′,3,3′2,3′,4,4′2,2′,4,5,5′2,3′,4,4′,52,2′,4,4′,5,5′2,3,3′,4,4′2,2′,3,4,4′,5′2,2′,3,4′,5,5′,62,2′,3,3′,4,4′2,2′,3,4,4′,5,5′2,2′,3,3′,4,4′,52,2′,3,3′,4,4′,5,62,2′,3,3′,4,4′,5,5′,6decachlorobiphenyl
5.07 5.24 5.67 5.84 5.75 6.20 6.38 6.74 6.92 6.65 6.83 7.17 6.74 7.36 7.27 7.56 8.09 8.11
a Coelutions: CB028 with CB031, CB066 with CB095, and CB105 with CB132. b Values are from Hawker and Connell (8) and are derived from surface area estimates.
and ecological effects (2). On the basis of these continuing risks to ecology and human health, it was determined that the PCB-contaminated sediments and co-located heavy metals should be dredged from the harbor. A 1987 pilot study examined options for dredging and disposal of contaminated sediment. Dredging was found to be feasible both from an engineering perspective (sediments could be removed with minimal resuspension) and an environmental perspective (remediation did not cause unacceptable ecological damage) (3). In 1990, a Record of Decision (ROD) was signed to remove approximately 7600 m3 of the most highly contaminated sediment from the upper harbor (PCB concentrations >4000 ppm), in an area designated as the “hot spot” (Figure 1b). Dredging of the hot spot was completed in the fall of 1995. Other contaminated sediments from the upper, lower, and outer harbor areas will be removed in the future. The EPA’s Atlantic Ecology Division (AED; Narragansett, RI) developed a long-term monitoring program to assess the effectiveness of the remediation (4). A systematic, probabilistic sampling design was used to select approximately 80 monitoring stations in NBH and Buzzards Bay. Sediments were collected at each station before and after the remediation (October 1993 and October 1995, respectively). In addition to other biological and chemical variables, the 18 PCB congeners utilized by the National Oceanic and Atmospheric Administration’s (NOAA) Status and Trends Program (NS&T) were quantified. This paper will describe the spatial and temporal variability in concentrations and patterns of PCB congeners before and after the remediation. Because the sampling design was statistically rigorous (4), quantitative statements could be made about the spatial and temporal changes observed in total PCB concentration and patterns of congeners. For this purpose, several exploratory statistical techniques such as cluster analysis and linear discriminatory analysis were used (5). The data also were examined using graphical analyses because plots are often easier to interpret than statistics. Graphical analysis also can reveal smaller patterns in data and help to determine the appropriate statistics to use (e.g., whether the data are distributed log-normally). 10.1021/es980413o CCC: $15.00
1998 American Chemical Society Published on Web 10/02/1998
FIGURE 1. (a) Overview map of New Bedford Harbor, (b) upper NBH with station numbers and hot spot dredging area highlighted, (c) lower NBH with station numbers, and (d) outer NBH with station numbers.
Methods Sampling stations are shown in Figure 1 b-d. Sediment was collected at each station with a grab sampler. The top 2 cm of several grabs were composited for later chemical analyses and kept frozen until that time. For a detailed discussion of the analytical methods and the extensive quality assurance project plan (QAPP) employed in the New Bedford Harbor Long-Term Monitoring Program (NBHLTM), please see Nelson et al. (6). Briefly, the analysis consisted of adding an internal standard (CB198) to approximately 1 g of wet sediment and then extracting it with acetone and methylene chloride. After the extracts were treated with sulfuric acid to remove lipids and with activated copper to remove sulfur, they were solvent-exchanged to hexane and reduced in volume. PCB congeners were then quantified on a HewlettPackard7 5890 Series II gas chromatograph equipped with
a splitless injection port, a 30-m fused silica capillary column (0.25 mm inner diameter, 0.25 µm DB-5 film, J&W Scientific), and an electron capture detector. Eighteen congeners (Table 1) were quantified against the CB198 internal standard, and the results reported as nanograms per gram dry weight. With each batch of samples, laboratory blank analyses were conducted. Results for blanks showed either no or trace levels of PCB congeners. Triplicate analyses indicated that the relative standard deviations were less than 12% for the 18 congeners measured. Spike and recovery experiments and method detection limits were within quality assurance guidelines established in the QAPP. To avoid biasing the graphical and statistical analyses, only those congeners detected at every station (i.e., with concentrations above the sample detection limits) were used. The software used for all of the statistical analysis was VOL. 32, NO. 22, 1998 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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FIGURE 3. Some of the stations in the lower and outer harbor exhibiting upper harbor PCB patterns (202, 230, 304, 310 preremediation). The congener pattern of upper harbor station 111 is shown for comparison.
FIGURE 2. Pre-remedial (1993) ratios of PCB congeners relative to CB138 at all stations: (a) upper NBH, (b) lower NBH, and (c) outer NBH. Ratios in Aroclor 1242 are shown for comparison. STATISTICA for Windows, version 4.5. Data plotting was accomplished with Cricket Graph 1.31 for Macintosh.
Results and Discussion Baseline Conditions: October 1993. From the upper harbor hot spot to Buzzards Bay, total PCB congeners concentrations in the surface sediments decrease by over 4 orders of magnitude. Such large differences in total concentration can mask small-scale differences in proportions of congeners, particularly when statistical techniques are used. Therefore, various methods of normalizing these data were examined. Normalizing to congener CB138, a hexachlorobiphenyl, was found to be the most appropriate. CB138 has a relatively high molecular weight, does not volatilize extensively, is present in most of the primary Aroclor mixtures (1242, 1254, 1260) utilized in the harbor, and was detected in all samples. Graphical analysis showed that both the raw data and the ratios to CB138 were distributed log-normally. Extensive graphical examination of the ratios to CB138 revealed several patterns among the congeners (Figure 2). This figure shows overall patterns within each segment of the harbor and is 3498
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FIGURE 4. Representative dendogram created from Ward’s method, city-block (Manhattan) distances cluster analysis. (a) Pre-remedial (1993) data. (b) Post-remedial (1995) data. The largest clusters are identified, and stations are listed on the x-axis group outside their area of origin. not intended to differentiate between specific stations. Also plotted on each graph are the ratios to CB138 in Aroclor 1242, one of the lower molecular weight (LMW) Aroclor PCB mixtures known to have been used by New Bedford industries. The patterns observed in the surficial sediments closely match Aroclor 1242, except for the LMW congeners (those eluting before CB118), which are less abundant. The most likely explanation for this divergence is that these lighter, more-soluble congeners were preferentially lost to the air and water before being incorporated into the sediment. In all three segments of the harbor, stations are distinguished from each other by the patterns of the LMW congeners (Figure 2). Toward the upper harbor, the LMW congeners show increased ratios to CB138. Furthermore, within the upper harbor segment, the magnitude of this increase was greatest closest to the hot spot. The congeners that increase the most
TABLE 2. K-Means Cluster Analysis Results for the 1993 and 1995 Sediment PCB Data: All Stations cluster no.
1993 stations contained in cluster
1995 stations contained in cluster
1
109, 111, 117, 123, 202, 306, 311, 339
105, 108, 109, 111, 114, 117, 121, 123, 126
2
105, 108, 114, 115, 120, 121, 125, 126, 128, 130, 131, 134, 135, 139, 140, 147, 150, 152, 155, 204, 207, 230
115, 120, 125, 128, 130, 131, 134, 135, 138, 139, 140, 147, 150, 151, 154, 155, 202
3
rest of the stations: n ) 44
rest of stations: n ) 49
FIGURE 5. (a) Pre-remedial (1993) linear discriminatory analysis. (b) Post-remedial (1995) linear discriminatory analysis. In each case, incorrectly grouped stations are identified. relative to CB138 are CB028 and CB052. A consistent but less prominent increase is also evident with CB118 and CB153. Congeners CB028 and CB052 are less enriched in sediments of the lower and outer harbors. However, some of these stations (202, 207, 226, 227, 230, 304, 310, and 339) did exhibit upper harbor signatures (Figure 3). Note that stations in the upper harbor are labeled 1xx, those in the lower harbor are labeled 2xx, and those in the outer harbor are labeled 3xx. Stations 202 and 207 are located near the Coggeshall Street and Rte 195 bridges, and stations 226, 227, and 230 are located near the Rte 6 bridge. Because some of these stations are located near combined sewer overflows (CSO), it is possible also that contaminated sediment from the CSO preferentially lost LMW congeners to the harbor. Stations 304 and 310 in the outer harbor are near another manufacturing plant, Cornell-Dublier, that used PCBs. Station 339 (not shown) is downstream from the outfall for the Clarks Point sewage treatment plant. CSO effluent coming into the plant may be responsible for the upper harbor signature at this station. The results of this graphical analysis were supported by the exploratory statistical techniques. Seven different methods of cluster analysis were used to explore the data, and each showed the same overall patterns. Outer harbor stations 306 and 339 always clustered with the most contaminated stations of the upper harbor, independent of cluster analysis
FIGURE 6. Post-remedial (1995) ratios of PCB congeners relative to CB138 at all stations: (a) upper NBH, (b) lower NBH, and (c) outer NBH. Ratios in Aroclor 1242 are shown for comparison. procedure. A representative dendogram (Ward’s method, city-block (Manhattan) distances) is shown in Figure 4. Stations 202, 204, 207, 211, 230, 306, and 339 clustered with the least-contaminated upper harbor stations. Therefore, the patterns of congener distributions at these lower and outer harbor stations had more in common with the upper harbor stations than with nearby stations. When cluster analysis was applied to the variables, the LMW congeners CB028 and CB052 always clustered together, which supports the graphical analysis. VOL. 32, NO. 22, 1998 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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FIGURE 7. Difference between the 1995 and 1993 data sets at several stations. Because the sediments were collected from three distinct areas of NBH, another type of clustering (K-means) was used to ascertain whether these areas could be differentiated statistically. The data were sorted into three clusters (Table 2). Cluster 1 had the highest ratios of congeners CB008, CB018, CB028, CB044, CB052, CB066, and CB101 as well as the most contaminated upper harbor stations and stations 202, 306, 311, and 339. Cluster 2 had median ratios of the same congeners and contained 22 members, all of the remaining upper stations plus 204, 207, and 230. Cluster 3 contained the remaining 44 stations. Again, stations 202, 204, 207, 230, 306, and 339 had more in common with the upper harbor than with other stations of their respective segments. Discriminant analysis was used to examine which variables best distinguished the groups of stations. Each station was labeled as to its harbor location (upper, lower, outer). A forward stepwise discrimination was performed; and two discriminant functions were calculated. Figure 5a shows root 1 plotted against root 2 for the 1993 data set. The standardized coefficients for the canonical variables indicated that the first function used congeners CB008, CB018, and CB028 to separate the upper from the outer segments. Identifying these three LMW congeners as the discriminating variables supported the graphical interpretation (Figure 2) that the congener distributions in the three harbor segments were separated by their LMW congeners. The second function used changes in congener CB153 to separate the lower harbor stations from the two other segments (Figure 5a). When these functions were used to reclassify the samples, upper harbor stations 146 and 150 were classified into the lower harbor; outer harbor station 311 was classified into the upper harbor; and stations 304, 317, 324, and 331 were classified into the lower harbor. Overall, 90% of the stations were classified into their actual segments. Post Hot Spot Remediation: October 1995. Because the entire upper harbor will eventually be remediated, minor, localized increases in sediment PCB concentrations above the Coggeshall Street Bridge were considered acceptable. The criterion was that redistribution of contaminated sediments during the hot spot remediation should not require 3500
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additional remediation to the lower and outer harbors. In the outer harbor, PCB distributions and concentrations remained virtually unchanged. In the lower harbor, some concentrations of total PCB in surficial sediment did change: 27% of the values increased by >10%, while 61% decreased. The increases were not enough to require any additional remediation; therefore, one of the main criteria for successful completion of the hot spot remediation was satisfied. Figure 6 shows the post-remedial congener patterns. While the ratios of the higher molecular weight (HMW) congeners remain unchanged, the amount of CB052 relative to CB138 increased in the upper and lower harbors. At several stations, this increase is greater than the amount that could be accounted for by Aroclor 1242 or the 1993 sediments. Congener CB028 also increased at several stations in the lower harbor. Although total concentrations of PCB at the majority of stations either remained constant (within the analytical variability) or decreased, it does appear that some LMW congeners were transported as far as the Hurricane Barrier. One interesting post-remediation observation is that the stations in the lower and outer harbor that exhibited upper harbor signatures in 1993 could no longer be identified by the statistical techniques utilized on the 1995 data set. Evidently, the localized increases in LMW congeners at these stations had been masked by a widespread increase in LMW congeners in 1995. Figure 7 shows the difference between the 1993 and 1995 data sets for several stations (i.e., the overlay of Figures 6 and 2). This depicts graphically the changes that occurred post-remediation in congener distributions. Some stations in the upper harbor had large increases in CB028 ratios and small but consistent increases in CB052. Farther down the harbor, an increase in a wider range of LMW congeners is evident. One possible explanation is that sediments dredged near the hot spot contained higher amounts of LMW congeners, and these were transported down the estuary. Increases in LMW congeners have been observed in deeper sediment cores from the upper harbor and may be byproducts of dechlorination pathways hypothesized to be operating in these areas (7). This may explain
the anomalously high increases in some LMW congeners relative to both the 1993 surface sediments and Aroclor 1242. It is also possible that these deep sediments preserved other Aroclor formulations introduced into the harbor over time. Statistical analysis from 1995 produced different results from 1993. As shown by the graphical analysis, stations in the lower and outer harbor did not cluster with those from the upper harbor. Regardless of the procedure used, upper harbor stations plus 202 clustered together (Figure 4b). K-clustering the 1995 data showed that all of those stations except 202, which grouped with the upper harbor (i.e., 204, 207, 230, 306, and 339) in 1993, now grouped with the other stations in their respective segments (Table 2). If dredged material had been extensively transported to the lower harbor, the discriminant analysis should have classified more lower harbor stations as upper harbor in 1995 than in 1993. Conversely, only one station (202) was misclassified as originating in the upper harbor (96% were correctly classified). Plotting two discriminant functions (Figure 5b) showed that the upper harbor stations were separated from the outer harbor stations by congeners CB052 and CB044. In 1993, these areas were separated by the LMW congeners CB008, CB018, and CB028. This also indicates that, after remediation, fewer differences in the LMW congeners were observed between segments. As in 1993, the lower harbor stations were distinguished by CB153. During the remediation, a significant proportion of the total PCB mass was dredged and removed. Neither a graphical nor a statistical examination of the data showed extensive transport of PCBs due to this remedial activity either in total PCB concentration or PCB congener patterns. The only effect potentially attributable to dredging was the deposition of LMW PCBs as far south as the Hurricane Barrier. However, other factors such as meteorological events may be responsible for this observation. It should be noted that because NBH is a very shallow estuarine system, storms can dramatically redistribute sediments within the harbor. Over the 2 years between sampling periods, several intense storms have passed through this area and could have been responsible for redistributing PCBs in the harbor. Combined statistical and graphical examination of this data set has proven useful for identifying subtle differences in patterns of congeners. For example, the qualitative graphical analysis differentiated the three harbor segments by LMW congeners. More quantitative statistical analysis (linear discriminatory analysis) supported this observation.
In addition, the use of exploratory statistics such as cluster analysis and linear discriminatory analysis highlighted much of the structure in the data that was missed by more traditional statistical analyses. Overall, we conclude that the hot spot was removed with little effect on PCBs in surficial sediments, particularly in the areas of the lower harbor and Buzzards Bay that are not scheduled for remediation.
Acknowledgments The authors thank Dr. James Lake, Dr. James Latimer, and Dr. James Heltshe for their thoughtful technical reviews of the manuscript. Although the information in this document has been funded wholly by the U.S. Environmental Protection Agency (EPA), it does not necessarily reflect the view of the agency, and no official endorsement should be inferred. The use of trade names or commercial products does not constitute endorsement or recommendation by the EPA. This paper is AED Contribution No. 1953.
Literature Cited (1) Weaver, G. Environ. Sci. Technol. 1984, 18, 22A-27A. (2) Farrington, J. W.; Davis, A. C.; Brownawell, B. J.; Tripp, B.W.; Clifford, C. H.; Livramento, J. B. In Organic Marine Geochemistry; Sohn, M. L., Ed.; American Chemical Society: Washington, DC, 1986; Chapter 11. (3) Nelson, W. G.; Hansen, D. J. Environ. Manage. 1991, 15, 105112. (4) Nelson, W. G.; Bergen, B. J.; Benyi, S. J.; Morrison, G.; Voyer, R. A.; Strobel, C. J.; Rego, S.; Thursby, G.; Pesch, C. E. New Bedford Harbor Long-Term Monitoring Assessment Report: Baseline Sampling; U.S. Environmental Protection Agency, National Health and Environmental Effects Research Laboratory, Atlantic Ecology Division: Narragansett, RI, 1996; EPA-600-R-96-097. (5) Pielou, E. C. Mathematical Ecology; John Wiley & Sons: New York, 1977. (6) Nelson, W. G.; Strobel, C. S.; Bergen, B. J. New Bedford Harbor Long-Term Monitoring Program Quality Assurance Project Plan; U. S. Environmental Protection Agency, National Health and Environmental Effects Research Laboratory, Atlantic Ecology Division: Narragansett, RI, 1995; AED Contribution No. 2033. (7) Lake, J. L.; Pruell, R. J.; Osterman, F. A. In Organic Substances and Sediments in Water, Vol. 3; Baker, R. A., Ed.; Lewis Publishers: Chelsea, MI, 1991; Chapter 11. (8) Hawker, D. W.; Connell, D. W. Environ. Sci. Technol. 1988, 22, 382-387.
Received for review April 21, 1998. Revised manuscript received July 28, 1998. Accepted August 24, 1998. ES980413O
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