Field-Scale Reduction of PCB Bioavailability with Activated Carbon

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Field-Scale Reduction of PCB Bioavailability with Activated Carbon Amendment to River Sediments Barbara Beckingham and Upal Ghosh* Department of Chemical, Biochemical, and Environmental Engineering, University of Maryland Baltimore County, 1000 Hilltop Circle, Baltimore, Maryland 21250, United States

bS Supporting Information ABSTRACT: Remediation of contaminated sediments remains a technological challenge because traditional approaches do not always achieve risk reduction goals for human health and ecosystem protection and can even be destructive for natural resources. Recent work has shown that uptake of persistent organic pollutants such as polychlorinated biphenyls (PCBs) in the food web is strongly influenced by the nature of contaminant binding, especially to black carbon surfaces in sediments. We demonstrate for the first time in a contaminated river that application of activated carbon to sediments in the field reduces biouptake of PCBs in benthic organisms. After treatment with activated carbon applied at a dose similar to the native organic carbon of sediment, bioaccumulation in freshwater oligochaete worms was reduced compared to preamendment conditions by 69 to 99%, and concentrations of PCBs in water at equilibrium with the sediment were reduced by greater than 93% at all treatment sites for up to three years of monitoring. By comparing measured reductions in bioaccumulation of tetra- and penta-chlorinated PCB congeners resulting from field application of activated carbon to a laboratory study where PCBs were preloaded onto activated carbon, it is evident that equilibrium sorption had not been achieved in the field. Although other remedies may be appropriate for some highly contaminated sites, we show through this pilot study that PCB exposure from moderately contaminated river sediments may be managed effectively through activated carbon amendment in sediments.

’ INTRODUCTION Fish consumption is known to have several health benefits for humans, but accumulation of legacy toxic chemicals, such as polychlorinated biphenyls (PCBs), in both farmed and wild caught fish can pose a hazard.1,2 It has been estimated that fish consumption advisories now cover 43% of the area of lakes and 39% of all river miles in the United States.3 In many of these deteriorated inland and estuarine water bodies some remedial action will be needed to address contaminated sediments, which often serve as the long-term source of legacy contaminants to the aquatic food web. A recent study by the National Research Council found that of the 26 sediment megasites (remediation expense > $50M) that have undergone dredging operations, about half did not achieve the contaminant cleanup levels in sediment immediately following remediation and very few sites documented long-term success .4 Sediment risk assessments are often based on bulk total concentrations and the presumption that all of the chemicals in sediments are available for exposure, which can overestimate risk and lead to bias against any remedy other than sediment removal by dredging or isolation by capping.5
7 Biological availability of hydrophobic contaminants in sediments, such as PCBs and polycyclic aromatic hydrocarbons, is affected by the nature of binding to native sediment organic matter types, especially to strongly sorbing black carbons, such as soot, coke, and charcoal.8,9 The two key pathways of exposure to fish as illustrated in Figure S1 r 2011 American Chemical Society

are (1) dietary uptake following accumulation in benthic invertebrates (related to contaminant bioavailability in sediments) and (2) flux of contaminants to the water column and uptake in the pelagic food web (related to diffusive and resuspension driven flux into the water column, impacted by partitioning and hydrodynamics). Exposure through both of these pathways can be reduced by altering sediment geochemistry through amendment of stable sorbents such as activated carbon. Activated carbon has a long history of use in air and water cleanup applications such as in gas masks, water treatment systems, and mercury capture in coal-fired power plants. Activated carbon can be produced from coal or from renewable biomass sources such as coconut shells and other agricultural residue, has a very high specific surface area for sorption (∼1000 m2/g), and is the best low-cost adsorbent for a wide range of toxic compounds including PCBs, dioxins/ furans, polyaromatic hydrocarbons, and chlorinated pesticides. When made from a biomass source and ultimately buried in sediments, activated carbon also has the potential for carbon storage.10,11 Several laboratory studies have demonstrated that amendment of activated carbon (AC) to sediments can suppress biouptake in Received: June 28, 2011 Accepted: November 10, 2011 Revised: November 6, 2011 Published: November 10, 2011 10567

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Environmental Science & Technology a variety of invertebrate species (Table S1). For example, PCB bioaccumulation in oligochaetes decreased by 70
90%, depending on mixing time and particle size, after the addition of 2.6% activated carbon to freshwater sediments, a dose which amounted to half the sediment native organic carbon.12 Although recent laboratory studies have demonstrated contaminant bioavailability reductions in sediment and a small field study was conducted in a marine mudflat, 13,14 more experience is needed to better understand the feasibility of field-scale application of activated carbon in river sediments and effectiveness in PCB bioavailability reduction in the field. We report here on a unique study conducted in a PCB-impacted river to evaluate the novel approach of sediment remediation using sorbent amendments. The objectives of the research were to demonstrate that activated carbon application to contaminated river sediments is feasible using large-scale equipment, the applied carbon is stable in the flowing river environment, and is effective in reducing contaminant release into water and uptake at the base of the food chain. Also, we compare bioavailability reductions with field amendment to the levels that may be achieved under optimal conditions, such as when most PCBs are associated with the activated carbon in sediment.

’ MATERIALS AND METHODS Field Location and Pilot Study Design. The field site for this study was the lower Grasse River, a tributary to the St. Lawrence River which has been impacted by historic releases of PCBs from an industrial facility and is currently under a fish-consumption advisory. The river is relatively slow-flowing and approximately 4.6 m deep. A full description of the pilot study location is given by Beckingham and Ghosh.15 The lower Grasse River, near Massena, NY, USA is currently undergoing deliberation of remedial alternatives to address legacy sediment contamination by PCBs. The pilot study site is located approximately 5.6 km downstream from a former industrial source of PCBs to the river. Sediments in the study area are composed primarily of sand and silt and in 2006 measured in the range of 2.0
3.9 μg/g dry wt. for total PCB concentration and averaged 5.8 ( 0.7% by dry wt. (N = 13) for total organic carbon content. In 2006, granular activated carbon (particle size: 75
300 μm) was added to sediments at a target dose of 3.75% by dry weight to the top ∼15 cm of surficial sediment as a slurry by three modes of amendment: (1) mixed (using an enclosed tilling device), (2) layered (without mixing), and (3) injected (injection into surficial sediments using two rows of hollow tines) (Figure 1A and B). Bituminous coal-based AC (Carbsorb, Calgon Carbon Corp.) was amended in the mixed and injected applications, and a coconut shell-based AC (055C-CNS-V000, Calgon Carbon Corp.) was used in the layered application. Monitoring sites were established within each of three treatment areas: six in the mixed treatment area (M1
M6), three in the injected treatment area (UTA 3, 5, 9), and three in the layered treatment area (UTA 14, 15, 17) (Figure 1C). An upstream background site was established approximately 150 m upstream of the treatment areas for monitoring changes naturally occurring in the river. Two additional background sites, located 15 m up- and downstream of the original background site, were also monitored in 2008 and 2009. Monitoring conducted in 4 years (before amendment and up to 3 years postapplication) at several sites within the upstream background and treatment areas included distribution of activated carbon in bulk sediments and single-point or 5-point composite cores, bioaccumulation from

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sediments in a freshwater oligochaete worm, Lumbriculus variegatus, and measures of aqueous equilibrium, a surrogate for direct pore water measurements. For mixed treatment area and background sites, bioaccumulation tests were performed both in the field and in the laboratory. Also, at sampling locations approximately 150 m down-river the potential redistribution of AC to the sediment bed downstream was monitored. Sediment Collection. Bulk sediments for use in bioaccumulation tests, PCB analysis, and aqueous equilibrium measurements were collected using a petit Ponar dredge. Several dredges were combined to obtain enough sediment for all tests. Although effort was made to minimize sediment mixing during collection, some mixing occurred during allocation of sediment between in situ exposure chambers and glass jars which were shipped for laboratory tests. Sediment cores were collected to analyze the depth distribution of activated carbon application within each treatment area (Figure 1C) using manual push cores with Lexan tubing such that the top 30.5 cm of sediment was obtained. Cores were either analyzed separately as single points, or as a composite of 5 cores collected within a ∼1 m2 area to estimate an areaaverage activated carbon dose which is less impacted by smallscale variability. Single-point cores were sectioned into 6 increments (0
3.8, 3.8
7.6, 7.6
11.4, 11.4
15.2, 15.2
22.9, and 22.9
30.5 cm) and 5-point composite cores were sectioned into 3 increments (0
7.6, 7.6
15.2, and 15.2
30.5 cm) below the sediment
water interface. Laboratory and Field Bioaccumulation Tests. Detailed methods for conducting bioaccumulation tests in the laboratory and in the field are described in Beckingham and Ghosh.15 Bioaccumulation tests were performed with L. variegatus, a freshwater oligochaete worm, by standard exposure tests conducted in the laboratory for 14 days with bulk sediments collected from each background and treatment area monitoring site in beakers with daily water renewal.16 There were 5 replicate exposure beakers for each site each containing ∼0.5 g wet wt. of organisms, ∼150 mL of sediment, and ∼100 mL of Grasse River water. A 16:8 light/dark photoperiod was provided. Water quality parameters were monitored in pooled replicates on a daily (temperature, dissolved oxygen) and weekly (conductivity, alkalinity, ammonia-nitrogen) basis, and met criteria established in the guidelines with the exception of a few minor deviations from the temperature criteria. Organisms were exposed in the field according to a method adapted from Burton et al.17 and described in detail elsewhere.15 Site sediments and L. variegatus were introduced to small plastic cylindrical enclosures with end-caps and fine polypropylene mesh screens on opposite sides to allow water flow-through. Chambers were attached in replicates of 6 to a wire basket and anchored to the sediment bottom at 6 mixed treatment sites and 1
3 upstream background sites. Following the 14-d exposures to sediments in the laboratory or the field, worms were collected and cleaned of debris with gentle streams of water, allowed to depurate gut contents for 6 h, and then tissues were weighed and frozen until analysis. Bioaccumulation Tests with Spiked PCBs. An additional laboratory bioaccumulation study exposed L. variegates, according to the same guidelines noted above,16 to either clean sediment spiked with PCBs or activated carbon (coal-based, 75
300 μm) spiked with PCBs and then added to clean sediment. The purpose of this experiment was to test the maximum achievable bioavailability alteration of PCBs with activated carbon amendment in a scenario where most of the PCBs are on the AC and 10568

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Figure 1. (A) Pilot-scale application of activated carbon was carried out in a PCB-impacted river within a 2000 m2 area. The site was enclosed with a silt curtain and application was performed in 2006 using a barge-mounted crane. (B) Placement of the AC was achieved using two custom-made devices: (1) a 2.5 m  4 m rototiller-type enclosed mixing unit with slurry injectors (left) that was used to place and mix activated carbon into surficial sediment or used to apply carbon as a layer on sediment without the mixing action; and (2) a 2 m  3 m tine sled device (right) with nozzles that injected a slurry of activated carbon into surficial sediments (< 10 cm). (C) Diagram of the treatment area locations with respect to one another and the sampling sites. Bulk sediment sampling sites (0) coincided with deployment of field bioaccumulation chambers. Sediment cores were collected as single cores (Δ) and as 5-point composite cores (b). The arrow points in the direction of river flow. The colored boxes delineate the target area for activated carbon application: 23  46 m for mixed and 15  30 m for each of the injected and layered treatment areas. (Photo in A courtesy of R.G. Luthy, Stanford University).

fouling is minimal. The clean sediment used in this experiment was obtained from the Rhode River in MD, USA. Total organic carbon content was measured as 3% by dry wt. and PCB concentrations were determined to be below the level of detection (0.01 mg/kg dry wt.). The two treatments were prepared in replicates of four in 500-mL glass wide-mouth jars, by spiking either a slurry of activated carbon (∼2 g) or sediments (∼210 g wet wt.) in 200 mL of filtered streamwater with PCB Aroclor 1260, a commercial mixture of PCB congeners in methanol, then placing the jars on a roller for a 10-d contact period. Following the 10-d contact, the same mass of sediments as in the sediment-only treatment was added to the activated carbon replicates, and both treatments were allowed to settle for 48 h. In this spiking study, the total concentration of PCBs in both treatment groups was 2 μg/g dry wt., and the dose of activated carbon in sediment was 5% by dry weight.

Aqueous Equilibrium Tests. Aqueous equilibrium concentrations were measured at yearly monitoring events according to previously established methods.15,18 In brief, bulk sediments collected from each site and Grasse River water with sodium azide as biocide were gently placed as distinct phases in glass jars and contacted on a very slow orbital shaker for 30 d. The gentle mixing allowed the overlying water column to be mixed without resuspending sediments. At the end of the contact period, the water phase was flocculated with alum to remove colloids, and transferred to a separatory funnel for liquid
liquid extraction with hexane to transfer PCBs to the solvent phase for congener-level PCB analysis. Analytical Methods. Tissue and sediment samples were extracted by ultrasonication in hexane/acetone mixture (1:1 by volume) and samples were processed by standard U.S. EPA 10569

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Environmental Science & Technology guidelines (SW846 methods 3550B, 3660B, 3665A, and 3630C). Prior to extraction, surrogate recovery standards (PCB BZ#14 and 65) were added to assess processing efficiency. Percent surrogate recovery in all analyzed worm, bulk sediment, and aqueous equilibrium samples was within the criteria of 100 ( 30% with only few exceptions for worm samples in 2006 and 2007 where recovery was 100 ( 40%. Congener-level quantification of polychlorinated biphenyls in tissue, sediment, and aqueous equilibrium extracts was performed by gas chromatography with electron capture detection using PCB BZ#30 and 204 as internal standards. A quality control plan was implemented to ensure that the chemical analyses performed were accurate. Matrix blank and matrix spike samples analyzed for cultured L. variegatus found PCB concentrations in organisms to be below the limit of quantification and indicated no matrix effects (percent recovery of matrix spike was 100 ( 30% at spike levels of 610 μg and 183 μg total PCBs). Sediment matrix spike recoveries were within 100 ( 30% for background unamended sediments. However, a matrix effect was observed for activated carbon treated sediments. PCBs were found to be not as extractable from AC-treated sediments and therefore, data from the background sites only are used to assess trends in surficial sediment PCB concentration over time (see Figure S2 for details). Activated carbon content of sediments was measured by wet chemical oxidation.19 This method entails oxidation of natural organic matter with sulfuric acid and potassium dichromate, followed by thermal oxidation of the black carbon remaining in the sample by a Shimadzu TOC analyzer. The value of black carbon content measured by the instrument is corrected for carbon content of the AC to determine AC dose in the sediment sample.

’ RESULTS AND DISCUSSION Distribution of AC in Sediments. Measurements of activated carbon content in bulk sediment and sediment cores demonstrated that the amendment was largely applied in surficial sediments (0
15 cm depth), was present at or above the target dose at most sites in each year, and showed significant small-scale variability (Figures 2 and S3). Activated carbon was not lost from the application area after 3 years of field exposure and could not be detected in sediments downstream of the treatment area. For instance, the average black carbon content of bulk surficial sediments in the study area before activated carbon amendment was 0.20 ( 0.03% (N = 13), which compares well to the downstream measurements in sediment cores in Figure 3D. Also, the average recovery of AC from the top 15 cm of sediment based on composite core analysis (Figure 3A
C) ranged 97
156% for the mixed sites, 121
192% for the layered sites, and 133
189% for the injected sites over the 3 years of monitoring after AC application. The generally higher than expected recovery is partly influenced by the high spatial variability of the AC and dry bulk density of the sediment. Over time, the AC content of treated sediments in the composite core sections closest to the sediment
water interface (0
8 cm depth) changed little, while the content of the deeper section (8
15 cm depth) increased. Single-point cores show similar results but the topmost (0
4 cm) section decreases in AC content over time and deeper cores indicate an increase in AC content. For example, in the mixed treatment area, the highest level of AC in 2007 was found in the 0
4 cm depth, and in 2009 was found in the 8
11 cm depth. However, single cores are also impacted by small-scale hetereogeneity of activated

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Figure 2. Average activated carbon (or black carbon for downstream site) content in sectioned composite-cores taken in 2007 (stripe), 2008 (white), and 2009 (gray) in the (A) mixed (N = 10), (B) layered (N = 8), and (C) injected (N = 8) treatment areas, and (D) downstream (N = 2) of treatment areas. Error bars show (1 standard deviation among core sections.

carbon placement (Figure S4). This trend of increasing AC in deeper cores with time indicates that there was burial of the amendment by sediment deposition onto the treatment plots and some mixing of carbon into these deposited sediments, perhaps by bioturbation. Observation of burial of AC with time is consistent with previous reports of historical long-term average deposition rate of 2
3 cm/yr using 137Cs dating of sediment cores.20 Reduction in PCB Bioaccumulation. Compared to baseline bioaccumulation measurements at each site, total PCB concentrations in worm tissues from sediment exposures in 2009 were reduced by 85
97% (field exposures) and 89
98% (laboratory exposures) in sites where the AC was mixed with the sediment (Figure 3). Similar bioaccumulation reductions were observed at the layered application sites (92
96%) and injected application sites (90
95%). These reductions in bioaccumulation are in a range similar to or higher than those observed in laboratory studies with sediments from other sites (Table S1). The exceptional reductions reported here may be attributed to the relatively low intrinsic binding capacity of Grasse River sediments and dominance of lower chlorinated PCBs. For instance, the fraction of fast desorbing PCBs based on a Tenax desorption study was 66
83% for Grasse River sediment,12 compared to 25
35% for Hunters Point sediment.13 Total PCB concentrations in worms from each monitoring site are presented in Figure S5 to show variability among exposure replicates. A large reduction in PCB bioaccumulation occurred in the first year after amendment (69
95% at all sites above the target AC dose), and in the subsequent 2 years of monitoring this lowered bioaccumulation was either maintained or improved. The background untreated site also demonstrated reductions in PCB bioaccumulation over the monitoring period, 46% for field exposures and 81% for laboratory exposures. Part of this reduced bioaccumulation at the control sites can be explained by the overall reduction of 40% in 10570

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Figure 4. Average percent reduction in bioaccumulation of the 60 most abundant PCB congeners for field exposures at mixed treatment sites compared to (A) baseline and (B) background in each year show increased effectiveness over the monitoring period, especially in 2009 for the more chlorinated, hydrophobic PCBs with higher octanol
water partitioning coefficients (Log KOW).

Figure 3. Relationship between (A) laboratory bioaccumulation, (B) field bioaccumulation, and (C) laboratory aqueous equilibrium concentration and activated carbon dose at different treatment area sites in each year show increasing effectiveness with activated carbon dose.

sediment PCB concentration over time (Figure S6), mainly caused by deposition of fresh (cleaner) sediment in the study area. Therefore, ongoing natural recovery processes in the river, including deposition of cleaner sediment, biodegradation, and other losses of PCBs from sediment, influence interpretation of results from the pilot-study. Whereas deposition of less contaminated sediment can result in PCB concentration reductions in the control untreated area, the same process has a reverse effect in the treated areas by depositing untreated sediment on top of carbon-amended sediment. However, despite this reduction over time in background bioaccumulation, biouptake in L. variegatus from sites receiving the target AC dose was reduced by 62
93% in field tests and 63
99% in laboratory tests when compared to the background site in the same year as illustrated in

Figure 3. At mixed treatment sites, the reductions in the higher chlorinated PCBs for field bioaccumulation tests improved with time in comparison to baseline and background sediments, suggesting that longer contact time is needed for the slowly diffusing, more hydrophobic congeners to be sequestered into the AC. As shown in Figure 4, the percent reduction in bioaccumulation 1 year after AC amendment fell sharply with PCB congener hydrophobicity (log KOW). However, with time this trend was lost, and in 2009, 3 years after AC amendment, the percent reductions in bioaccumulation were mostly greater than 80%. This is consistent with descriptions of mass transfer modeling of PCBs in activated carbon-amended sediments which indicate that the higher chlorinated PCBs are more slow to transfer from sediment to AC.21 Reduction in PCB Aqueous Equilibrium. Aqueous equilibrium concentrations were reduced by 95% to greater than 99% compared to background sites (and >93% compared to baseline) for all treatment sites with AC at the target dose or higher in each year (Figure 3). These reductions were comparable to observations at Hunters Point, where mixed addition of 3.2% by dry wt. of coal-based activated carbon reduced aqueous equilibrium concentrations by more than 95% compared to untreated sediments up to 18 months postapplication.13 Aqueous concentration reductions were highest for the monochloro biphenyls 10571

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Environmental Science & Technology approaching 100%, and decreased with increasing level of chlorination. While removal of DOC by adsorption to AC and resulting loss of DOC-associated PCBs could partly contribute to total aqueous PCB reduction, we would have seen a greater reduction of more chlorinated PCBs compared to the less chlorinated PCBs if this was a dominant mechanism. Reduction in equilibrium aqueous PCBs demonstrates the effectiveness of activated carbon amendment to reduce pore water concentrations, and subsequently the driving force for diffusive flux of PCBs from sediments to the water column. Based on the 3-year post-treatment monitoring data, we show that PCB bioaccumulation and aqueous concentration decreased with increasing dose of AC up to an AC dose close to the native organic carbon content of the sediment (Figure 3). Above an AC dose of 3
5%, reductions in total PCB aqueous equilibrium concentration approached 100%, but reduction in total PCB concentration in worm tissue in 2009 compared to background are less (72
99%) which may be due to the dominance of lower chlorinated congeners in the dissolved phase (80% mono and di) which tend to transfer more easily into AC, and additional route of worm exposure to sediment PCBs through sediment ingestion22 where the ingested sediments have not yet achieved equilibrium distribution of PCBs with AC and water. Comparison of Predicted and Observed Reductions in Bioaccumulation and Aqueous PCBs. To provide perspective on how the level of reductions achieved in the field related to the reductions that may be expected under optimum conditions, bioaccumulation measurements from field-amended sediments were compared to the exposures where AC was first preloaded with PCBs. As shown in Figure S7, when PCB Aroclor 1260 (more chlorinated than Grasse River sediment PCBs) is preloaded on AC and amended to clean sediment, the bioaccumulation is 93% less for total PCBs, with bioaccumulation of tetra and penta chlorobiphenyls less by 98 and 96%, respectively. Bioaccumulation in laboratory exposures with mixed treatment area sediments was plotted against activated carbon dose for PCB congeners that were at similar concentrations in the Grasse River field sediments and in the direct-AC spiked exposures (one coeluting pair of tetra-chlorinated PCBs BZ#66 + 95 and a pentachlorinated PCB BZ#101). As shown in Figure 5, bioaccumulation is greatly reduced with field-aged AC amendment, but not to the level achieved when the majority of PCBs have been transferred to the AC, as in the case of the spiked AC. The difference indicates that optimum equilibrium sorption has not been achieved in the field, likely as a result of the combination of relatively slow mass transfer kinetics and sorption attenuation of PCBs in the field by natural organic matter. To the same purpose, aqueous equilibrium measurements were compared to modeled pore water concentrations assuming equilibrium conditions with a range of activated carbon doses according to a two-carbon model: CS ¼ f OC K OC CPW þ f AC K AC ðCPW Þn where sediment concentration (CS; mg/kg dry wt.) and sediment organic carbon content (fOC) are known values measured for background untreated sediments in 2007 and 2006, KOC values are site-specific determined from batch equilibrium studies with background untreated and mixed treated sites (N = 7) in 2006, and Freundlich partitioning coefficients (KAC) and linearity parameters (n) were measured in isotherm tests for Carbsorb AC (see Table S2). The Freundlich parameter, n, was found to be

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Figure 5. Bioaccumulation measured in laboratory exposures with mixed treatment area sediments over time ()) for representative (A) tetra- and (B) penta-chlorinated PCB congeners compared to bioaccumulation under optimum conditions when the majority of PCBs are sorbed to AC.

close to 1 over a relatively narrow, low concentration range in the isotherm near the concentrations found in Grasse River water and therefore partitioning was modeled as linear. Werner et al.23 also recently supported the use of a linear partitioning model for black carbon at low, environmentally relevant concentrations (picogram to microgram per liter). The aqueous pore water concentrations of several dominant PCB congeners modeled at equilibrium are 1
2 orders of magnitude lower than the aqueous equilibrium batch test results for mixed treatment sites over the 3-year monitoring period (Figure 6). This implies that more time is needed to reach equilibrium status in the field, or that sorption capacity of the activated carbon for PCBs is attenuated in the field due to competition with other sorbates, such as natural organic matter. However, it is important to note that this large apparent difference is partly accentuated by the fact that several of the aqueous equilibrium concentrations (20 out of 54) for ACtreated sediments were not detected and these data points may actually lie closer to the predictions which are below detection limits. We demonstrate for the first time that primary exposure pathways to the aquatic food web can be restricted through pollutant binding in activated carbon amended into contaminated river sediments. Furthermore, AC was successfully applied using both the enclosed tiller (mixed and unmixed) and injection tine devices, and the amendment was stable over time. Although reductions in bioavailability measurements were similar among 10572

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could be a way to reduce variability and incorporate AC into freshly depositing cleaner sediments more evenly both spatially and also within the surficial sediment depth. Amendment with AC will be most effective at sites that are depositional in nature, less prone to sediment erosion, where native bioavailability of contaminants is high, and ongoing contributions from upstream and terrestrial sources have been controlled. AC amendment provides several advantages over traditional remediation methods, including less disruption to benthic habitats in sensitive rivers and wetlands, amenability to shallow or constricted locations, and potential for lower cost. In situ amendments can also be used in combination with other remedies. This pilot study shows the promise of AC amendment as a new strategy to help address the widespread need to reduce contamination of the aquatic food web from exposure to sediment-bound legacy hydrophobic contaminants.

’ ASSOCIATED CONTENT

bS

Supporting Information. Additional figures and tables. This material is available free of charge via the Internet at http://pubs.acs.org.

’ AUTHOR INFORMATION Corresponding Author

*E-mail: [email protected]; phone: 410-455-8665.

Figure 6. Aqueous equilibrium concentrations measured in batch tests with mixed treatment area sediments over time ()) for representative (A) di-, (B) tri-, and (C) tetra-chlorinated PCB congeners compared to pore water concentrations modeled assuming equilibrium conditions. Measured values below detection limit have not been plotted in the figure.

application sites, it is difficult to use this result as a basis for supporting a general recommendation for a particular application mode. There may have been some impact of unmeasured natural mixing in the field, upon collection of sediment, or by bioturbation of worms within exposure chambers that masks the influence of application method on bioavailability reduction. Previous laboratory work12 also showed that application of AC without mixing is nearly as effective as application with initial brief mixing, especially when benthic organisms are present that induce mixing through bioturbation. Sediment core analysis showed that there was significant small-scale variability in AC dose achieved in sediments. Further improvements in engineering application are needed to reduce AC variability and to improve efficiency. For example, multiple applications in small doses over a few years

’ ACKNOWLEDGMENT We thank Alcoa, the U.S. Environmental Protection Agency, Anchor-QEA, and Arcadis-BBL for their support and inputs to the implementation of this project. L. McShea, B. Cook, R.G. Luthy, C. Patmont, P. LaRosa, H. Vanderwalker, D. Buys, and Y. Chang are thanked for initial discussions, planning, and field implementation for this study. We also thank R.G. Luthy for the picture in Figure 1A. Adam Grossman is thanked for sediment carbon measurements. The monitoring and laboratory component of this research was supported in part by an unrestricted research gift to UMBC from Alcoa. B.B. was also partly supported by the National Science Foundation Integrative Graduate Education and Research Traineeship “Water in the Urban Environment” program (Grant 0549469). U.G. is a coinventor of two patents related to the technology described in this paper for which he is entitled to receive royalties. One invention was issued to Stanford University (U.S. Patent 7,101,115 B2), and the other to the University of Maryland Baltimore County (UMBC) (U.S. Patent 7,824,129). In addition, U.G. is a partner in a startup company (Sediment Solutions) that has licensed the technology from Stanford and UMBC and is transitioning the technology in the field. ’ REFERENCES (1) Hites, R. A.; Foran, J. A.; Carpenter, D. O.; Hamilton, M. C.; Knuth, B. A.; Schwager, S. J. Global assessment of organic contaminants in farmed salmon. Science 2004, 303, 226–229. (2) Kelly, B. C.; Ikonomou, M. G.; Blair, J. D.; Morin, A. E.; Gobas, F. A. P. C. Food web
specific biomagnification of persistent organic pollutants. Science 2007, 317, 236–239. (3) U.S. Environmental Protection Agency. 2008 Biennial National Listing of Fish Advisories: Technical Fact Sheet; EPA-823-F-09-007; September 2009; www.epa.gov/fishadvisories. (accessed April 2011). 10573

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dx.doi.org/10.1021/es202218p |Environ. Sci. Technol. 2011, 45, 10567–10574