Distribution and Inventories of Polychlorinated Biphenyls in the Polar

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Distribution and Inventories of Polychlorinated Biphenyls in the Polar Mixed Layer of Seven Pan-Arctic Shelf Seas and the Interior Basins € Daniel Carrizo and Orjan Gustafsson* Department of Applied Environmental Science (ITM), Stockholm University, 106 91 Stockholm, Sweden

bS Supporting Information ABSTRACT: Assessment of the Arctic as a global repository of polychlorinated biphenyls (PCBs) and of uptake processes in the base of its marine food chain hinges on reliable information of PCB distribution in surface seawater, yet there is a scarcity of qualityassured PCB measurements in this key compartment. Here, surface seawater PCB concentrations and congener fingerprints are evaluated for all seven pan-Arctic shelf seas and for the interior basins. Particulate and dissolved PCBs were collected via trace-clean protocols onPthree basin-wide expeditions (AO-01, Beringia-2005, and ISSS-08). Concentrations of the sum of 13 abundant congeners ( 13PCB) were 0.13-21 pg/L, with higher concentrations in the shelf seas and lower concentrations in the Central Arctic Basin. Trichlorinated PCBs constituted about half of the total loadings in the Eastern Arctic (Beaufort, Chukchi, East Siberian, and Laptev Seas) and in the Central Basin, indicating an atmospheric source. In contrast, hexachlorinated PCBs were more abundant than tri-PCBs in the western sector, suggesting a roleP also for waterborne transport from regions of heavy PCB consumption in North America and Europe. Finally, the inventory of 13PCB in the polar mixed layer of the entire Arctic Ocean was 0.39 ton, which implies that only 0.0008% of historical PCB emissions are now residing in Arctic surface waters.

’ INTRODUCTION Polychlorinated biphenyls (PCBs) are persistent, bioaccumulating, and toxic (i.e., PBT) high-volume chemicals that, despite their production being banned decades ago, are still being mobilized and spreading throughout the global environment. Approximately 97% of PCB usage was in the northern hemisphere, largely between 30° and 60° N.1 International assessments suggest that PCBs continue to be one of the compound classes of highest ecotoxicological concern for the Arctic ecosystem and its top consumers, including humans (e.g., refs 2 and 3). While it is broadly recognized that the uptake and levels of PCBs in the base of the Arctic Ocean food web are governed by dissolved PCB exposure in seawater (e.g., refs 3-8), there are few observations of quality-assured PCB concentrations in Arctic surface seawater 7-11 and sea ice.12 This largely reflects the substantial analytical challenge posed by their trace levels and risk for contamination during the sampling and handling steps. Furthermore, model-based investigations of the regional-global cycling of PCBs have emphasized the potential importance of the Arctic as a repository after long-range transport (e.g., refs 13 and 14). Physicochemical properties of PCBs and their resulting partitioning under environmental conditions between, for example, air, ocean, and land surfaces has been inferred to make these chemicals prone to long-range transport to the Arctic Ocean through both atmospheric circulation, ocean currents, and runoff by the large Arctic rivers, with yet unconstrained relative magnitudes. Model predictions would be well complemented by observations of the actual abundance and distribution patterns of PCBs in the Arctic. Taken together, improved assessment of both food web uptake and the proposed importance of the Arctic in global PCB cycling would benefit from constraining the PCB r 2011 American Chemical Society

distribution in surface seawater on the basin scale of the Arctic Ocean. Hence, the objectives of the current study were to (a) provide quality-assured data of PCB concentration (dissolved þ particulate) in the polar mixed layer (PML) during the vegetative season for all seven shelf seas and the Canadian and Eurasian interior basins of the Arctic Ocean, (b) explore PCB congener profiles and spatial distributions toward attributions of sources and transport modes, and (c) constrain the overall inventories of PCBs in the PML of the entire Arctic Ocean to deduce to what extent this compartment may enter into the global accounting of PCBs.

’ MATERIALS AND METHODS Sampling and Handling Strategy. Quantification of tracelevel hydrophobic pollutants such as PCBs in remote seawater samples constitutes a substantial analytical challenge due to a combination of the low ambient levels (frequently high attomolar-femtomolar concentrations of individual congeners) and the risk for contamination of sample and handling systems by these semivolatile function chemicals ubiquitously employed in installations on ships and elsewhere. It has been demonstrated that substantial precautions and specialized sampling approaches are necessary to obtain uncompromised measures of PCB concentration in remote seawater, including all-stainless-steel systems, specialized in situ pumps, and working in controlled prefiltered Received: October 21, 2010 Accepted: December 22, 2010 Revised: December 14, 2010 Published: January 11, 2011 1420

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Environmental Science & Technology atmosphere both in ship laboratory and in shore-based analytical laboratory (e.g., refs 9,12, and 15-18). In addition to exhaustive field blank assessments, it is frequently informative to assess the integrity of obtained results by considering whether obtained PCB patterns are compatible with known biogeospheric system functioning; this is sometimes referred to as geochemical consistency testing. Below, we first briefly describe the three extensive ship-based expeditions in the high Arctic and then outline the employed sampling and handling protocols. Cruise Tracks of Three Arctic Ocean Expeditions. AO-01 2001. Surface seawater samples were collected for PCBs onboard I/B Oden during the 65-day Swedish Arctic Ocean 2001 (AO-01; officially SWEDARCTIC 2001) expedition from June to August 2001. The sampling stations roughly follow a latitudinal northward transect across the Norwegian Sea through Barents Sea and cover both the Nansen and Amundsen Basins of the Eurasian High Arctic, including the North Pole and extending into the Makarov Basin in the Canada Basin (62-89° N) (Figure S1 in Supporting Information). Station descriptions and total-phase (i.e., particulate þ dissolved) PCB concentration in surface seawater samples of AO-01 have been described in our earlier report 9 and are included here for completeness and comprehensive interpretation together with the two expeditions not previously reported. Beringia-2005. Samples were collected onboard I/B Oden during the 60-day Swedish Arctic Ocean expedition (SWEDARCTIC 2005) from July to August 2005 that had a focus on the Beringia region and eastern Arctic Ocean. The samples were taken along a transect from the North Sea across the northern North Atlantic Ocean, rounding south of Greenland and extending through Baffin Bay, the Canadian Arctic Archipelago, and Beaufort Sea and passing out and then back in through the Bering Strait, followed by a northward track through the American sector of the Chukchi Sea and into the Beaufort Gyre of the deep Canada Basin (Figure S1 and Table S2 in Supporting Information). ISSS-08 Expedition. Samples were collected onboard the H/V Yacob Smirnitskyi (Archangelsk) during the 45-day International Siberian Shelf Study 2008 (ISSS-08) expedition from August to September 2008 as part of the International Polar Year (IPY) activities (Figure S1 and Table S3 in Supporting Information). After a transect through the Barents Sea, samples were taken in the Kara Sea, Laptev Sea, East Siberian Sea, and Russian sector of the Chukchi Sea. Oceanographic Setting. The Beaufort Gyre and the Transpolar Drift are two main features that characterize the surface water and sea-ice circulation in the Arctic Ocean. The Beaufort Gyre is a large clockwise gyre over the Canadian Basin (Figure S1 in Supporting Information). Some water is exported from Beaufort Sea through the Canadian Archipelago to Baffin Bay, with another component entering the Transpolar Drift and instead exiting the central Arctic Basin through the Fram Strait. The Transpolar Drift runs from the East Siberian Shelves with a northward departure centered approximately on the Laptev Sea, across the interior Basin via the North Pole area, and exits the Arctic Ocean through the western Fram Strait (Figure S1 in Supporting Information). Surface waters in the Eurasian Basin tend to move from east to west, passing the North Pole area, following the Transpolar Drift. North Atlantic waters enter the Arctic Ocean through eastern Fram Strait (NW Spitsbergen current) and Barents Sea (St. Anna Trough). Pacific Ocean waters enter the Bering Strait and then flow into the Arctic

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interior via either the Chukchi Canyon or the Herald Canyon or pass into the East Siberian Sea through the Long Strait south of Wrangel Island. An extensive ice area covers the Arctic Ocean (Figure S1 in Supporting Information) due to average cold water/air temperatures during most of the year. The area covered by sea ice in the Arctic varies seasonally, and this variation has direct implications for water circulation and contaminant dynamics (e.g., air-water exchange). The Arctic Ocean is on a volume basis the ocean with the highest input of freshwater and organic matter, with about 10% of the global river discharge entering the Arctic Ocean that holds only 1% of the global ocean volume. The extensive watersheds of the pan-Arctic rivers makes fluvial discharge a potentially important supply route of persistent organic pollutants to the pelagic ecosystems of the Arctic Ocean. This high river/freshwater input also has implications for Arctic Ocean circulation (e.g., stratification and vertical mixture) and thus in the delivery of contaminants to other water masses. The freshwater lense from rivers and the seasonal ice melt causes formation of a strongly stratified surface ocean mixed layer that in the Arctic is termed the polar mixed layer (PML). Inspection of a large number of salinity-temperature-depth (CTD) profiles from the three expeditions suggest that the PML extends to about 30 m in the deep interior basins and to about 15 m on the pan-Arctic shelves. Shipboard Sampling Protocol. The overarching strategy to overcome contamination artifacts was to employ trace-clean sampling and handling methodology and to collect large seawater samples. For both I/B ODEN and H/V Yacob Smirnitskyi, stainless steel seawater intake (SWI) systems were constructed with intakes placed under the prow of the ship, which was 8 m for I/B Oden and 4 m for H/V Yacob Smirnitskyi, both well within the PML. With both systems, seawater from the PML was delivered by a stainless steel rotary vein pump at about 50 L/min through a closed seawater distribution system to shipboard laboratories, for example, for online filtration and adsorbent extraction of particulate and dissolved PCBs. Approximately 2 L/min of the total SWI flow, recorded by a digital online flowmeter, was diverted through the all-stainless-steel ultraclean PCB sampling system. The pressure over the filter was constantly monitored with a pressure indicator and never allowed to exceed 1 bar to minimize cell lysing. For the AO-01 and Beringia-2005 cruises onboard the I/B Oden, the PCB sampling system was located in a permanent shipboard clean laboratory, located inside the main laboratory complex. The atmosphere in Oden’s clean room is overpressurized and the air is filtered through double activated carbon and high-efficiency particulate air (HEPA) filters. Only specifically trained research personnel accessed this restricted area through an intermediate air lock, where the researcher changed into clean-room clothing, shoes, and caps of low-lint nylon and plastics. For the ISSS-08 cruise, the same PCB sampling setup was placed in a renovated laboratory container dedicated for high-volume seawater filtration. This container was placed on the ship foredeck. Filters and polyurethane foam adsorbents (PUFs) were changed in a HEPA-filtered laminar flow bench. To meet limits of quantification, seawater volumes on the order of 1000 L were sampled on all three expeditions (e.g., Tables S1 and S2 in Supporting Information and ref 9). The column capacity of the PUF configuration in the employed PCB sampling setup and employed flow rates has been demonstrated to yield full recoveries across the congener spectrum up to at least 1400 L.19 Specifically, particle-associated PCBs were collected on precombusted borosilicate filters (GFF 293 mm, nominal pore size 1421

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P Figure 1. Total concentration of 13PCBs in the Arctic polar mixed layer of the three expeditions. Congener-specific concentrations for each of the dissolved and particulate phases are available in tables in the Supporting Information).

0.7 μm; Whatman International Ltd., Maidstone, England), which were followed by polyurethane foam adsorbents (PUF; diameter 37 mm, length 160 mm; Sunde S€om & Skumplast AS, Norway, punched out by Special-Plast AB, Vallentuna, Sweden) to collect the dissolved PCBs. The PUFs were extensively cleaned prior to expeditions to minimize the blank. The cleaning procedure included 90 °C washing with detergent (1 h), drying at 50 °C (24 h), Soxhlet extraction in toluene (24 h) and in acetone (24 h), and finally drying under vacuum in a desiccator with a PUF scrubber at the gas inlet. The prepared PUF adsorbents were placed in double layers of precombusted Al foil envelopes in turn placed in double plastic bags and stored in a freezer (-18 °C) until sampling. Collected samples were placed in the same precombusted Al envelopes and stored in double-sealed plastic bags in a freezer (-18 °C) until analysis. Laboratory Extraction and Analyses. Concentrations of 13 PCB congeners were determined in filters and adsorbents (PCB IUPAC numbers 18, 28, 52, 70, 101, 110, 118, 105, 149, 153, 138, 180, and 194) following previously described methods (ref 9 and references therein). Briefly, internal standards in the form of seven 13C-labeled PCB congeners were added to each sample prior to 24-h Soxhlet extraction with toluene (glass-distilled quality; Burdick & Jackson, Fluka Chemie AG, Buchs, Switzerland), with a Dean-Stark trap for collection of water. All extracts were eluted on an open silica column, containing three layers of modified silica (SiO2/H2SO4 10 mm, SiO2/KOH 10 mm, and SiO2/H2O 10 mm). Finally, samples were quantified

on a HP6890 (Hewlett-Packard, Avondale, PA) gas chromatograph (GC) equipped with a PTE-5 capillary column (30 m  0.25 mm i.d., 0.25 μm film thickness; Supelco Inc., Bellefonte, PA) with a high-resolution mass spectrometer (HRMS) (Autospec Ultima; Micromass, Altrincham, U.K.) operated in the electron-impact mode. A 13C-labeled standard (PCB 153) was added to all samples before injection on the GC-HRMS in order to check the sensitivity of the instrument during the sample injections. Quality Assurance. The integrity of the obtained results was assessed in several ways. The surface seawater intake system was blank-tested both prior to and during the AO-01 expedition by simultaneous sampling with stainless steel tubes and in situ KISP pumps deployed to the same 8 m depth as the seawater intake line. Identical results were obtained.9,12 A series of field blanks and laboratory blanks were analyzed for each expedition to control any contamination from the described sampling and analytical steps. Extraction and cleanup methods and laboratory blanks were monitored before and during the sampling handling, by spiking cleaned GFFs, PUFs, and solvent with validation standards for the PCBs (seven 13C-PCBs), extracted and analyzed in the same way as samples. Mean laboratory blanks for the not previously reported Beringia-2005 and ISSS-08 campaigns were 2.25 pg (n = 6) for PCB 52, 0.900 pg (n = 6) for PCB 110, and 1.72 pg (n = 6) for PCB 138. The amount of PCB 52 in field blanks varied between 5 and 25 pg, and PCB 138 varied between 2 and 10 pg. Average recoveries for the seven 13C-labeled PCBs 1422

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Environmental Science & Technology ranges from 83% to 110% for both GFF filters and PUF adsorbents at all stations. The recovery for the more volatile internal standard (13C-PCB 28) was 62% ( 17%. The previously reported AO-01 campaign 9 reported an average recovery for the seven 13C-PCBs of 71% ( 19%, with laboratory and field blanks for PCB 52 ranging from 3 to 11 pg (n = 15), which thus is in the same range as values found in this new work. Reported concentrations are corrected for individual recoveries. Detection limits were calculated as the mean blank concentrations plus 3 standards deviations in the Beringia-2005 and ISSS-08 expeditions. The impression that the obtained seawater PCB concentrations are robust is also provided by (i) geochemical/system consistency in spatial distribution of concentrations and congener distributions and (ii) similarity in concentrations from the same region sampled several years apart on different expeditions. For instance, the PCB seawater concentrations in the combined data set are found to be lower in the interior high-Arctic basins than in the fringe seas, closer to source areas (Figure 1), and the latitudinal trend from the North Sea to the North Pole in changing congener fingerprint, by this employed analytical 9 approach, follows P the vapor pressure of the assessed congeners. Finally, the 13PCB concentration at the interior basin station OC-05-21 of the Beringia-2005 cruise was 0.91 pg/L, which compares well with 0.75 ( 0.36 pg/L values of the three AO-01 stations similarly placed in or near the Canadian Basin, albeit at even higher P latitudes. Similarly, the Beringia-2005 cruise recorded a 13PCB concentration of 1.3 pg/L in the Eurasian side of the Chukchi Sea that compares well with 1.6 pg/L from a nearby location surveyed during ISSS-08 (all data in Table S4 in Supporting Information). Taken together, there are multiple indications that the current data set of PCB seawater concentrations in the Arctic is reliable.

’ RESULTS AND DISCUSSION Geochemical Description of Surface Water Regimes of the Pan-Arctic Shelf Seas and Interior Basins. All samples were

obtained within the well-defined surface water compartment of the Arctic Ocean termed the polar mixed layer (PML). The temperature in the PML is kept close to the freezing point when under ice cover, whereas the salinity exhibits seasonal/geographical fluctuations caused by freezing and melting of sea ice and input of freshwater from the river runoff. Information about the exact sampling locations, sample volumes, salinity, temperature, and bulk organic matter characteristics are given in Tables S1 (AO-01 2001 expedition), S2 (Beringia-2005 expedition), and S3 (ISSS-08 expedition) in the Supporting Information. During the AO-01 expedition, the temperature varied between 1.7 and 10.8 °C and salinity varied from 31.01 to 34.89. During the North American 2005 expedition, seawater temperature varied from -1.4 to 11.1 °C, salinity varied between 17.38 and 35.18. In the Eurasian 2008 expedition, the seawater temperature varied from 0.2 to 12.1 °C and the salinity varied between 2.07 and 30.23. Particulate organic carbon (POC) concentrations varied between stations, with the highest value of 6550 μg/L at station ISSS-08-7 collected under the influence of the Indigirka River mouth in the western East Siberian Sea. Another high POC value (5070 μg/L) was found at station OC-05-18 corresponding to the Bering Strait Area, which was strongly influenced by Pacific Ocean waters with likely high primary productivity (δ13C of -22.6% and salinity of 32.82). Much lower POC levels (factor of 20) were generally found in the regions covered by the AO-01

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expedition. This is related to the lack of extensive freshwater input to the Barents Sea and lower primary productivity in the ice-covered high-Arctic basins during time of sampling.20 The generally high POC values on the Eurasian shelves likely reflect the influence of extensive river runoff and coastal erosion processes in this system (e.g., refs 21 and 22). The δ13C signature of the POC varied from -21.1% to -29.8%. This range of values span from a pure oceanic biological production material (e.g., phytoplankton at ∼ -21%) to an overwhelmingly terrestrial/freshwater input (∼ -29% from the Eurasian Arctic rivers). The humic substances (HS) were inversely correlated with salinity, with higher values correlated with freshwater input through river discharge. For instance, station OC-05-15 (3.27 μg of Quinine Sulfate Equivalents (QSE) 3 L-1) was under the Mackenzie River discharge influence and ISSS-08-3 (26.41 μg of QSE 3 L-1) was under the influence of the Lena River. Taken together, the different oceanic regimes assessed for their PCB signals during the Beringia-2005 and ISSS-08 expeditions can be described with respect to both water mass and bulk geochemical characteristics. A similar description already exists for the AO-01 samples.9,12 Following the cruise track of the Beringia-2005 expedition, the initial stations sampled for PCBs (OC-05-3 and OC-05-8) are influenced by sub-Arctic northern North Atlantic water with an autotrophic regime (δ13C of -21.1% and -23.1%, respectively). Sample OC-05-10 is located in the Baffin Bay, which had waters originated in the Beaufort Gyre and the Transpolar Drift. The Beaufort Sea stations OC-05-14 and OC-05-15 are located under the freshwater influence of the Mackenzie River and may also have some influence from the Alaskan Coastal Current. Stations OC-05-17 and OC-05-18 are located in the Bering Strait and reflects waters from the Pacific Ocean (salinities of 32.79 and 32.82, respectively, and water temperatures of 2.5 and 2.1 °C, respectively). Stations OC-05-19, OC-05-20, and OC-05-21 were taken along a northbound transect stretching over the Chukchi Shelf Sea to the deep Arctic interior of the Canada Basin (reflected by the low temperatureof -1.4 °C and salinity of 27.29). For the ISSS-08 expedition, samples ISSS-08-1 to ISSS-08-3 were taken in the Laptev Sea; particularly station ISSS-08-3 in the Bhuor-Kaya Bay has a large freshwater influence of the Lena River with a salinity of only 2.07, warm river water temperature of 12.0 °C, a highly depleted (terrestrial) δ13C of -29.8%, and a high POC concentration of 2862 μg/L. Stations ISSS-08-4, ISSS08-6, and ISSS-08-7 were sampled in the East Siberian Sea waters; station ISSS-08-7 has a direct influence of the freshwater from the Indigirka River and/or possibly from coastal erosion along Oyagosski Yar (δ13C of -28%, 6550 μg/L POC, and salinity of 18.84). Station ISSS-08-5 corresponds to the Chukchi Sea waters; this station has a strong oceanic influence (probably of Pacific waters), as can be seen by the high salinity value (30.23) and the -22% for δ13C, which reflects oceanic primary production (i.e., phytoplankton). Station ISSS-08-8 corresponds to the Kara Sea waters (salinity of 27.75) and is influenced by the Yenisey/Ob freshwater discharge (δ13C -27.5%). Spatial Pattern of PCB Concentrations in Surface Seawater of the Arctic Ocean. Total-phase (i.e., dissolved þ particulate) P seawater concentrations of the analyzed PCB congeners ( 13PCB) varied between the different Arctic rim shelf seas and the interior Arctic Ocean basin of the AO-01, Beringia2005, and ISSS-08 expeditions (Figure 1; Table S4 in Supporting Information). Evaluation of the solid-water distribution is beyond the scope of the present study that instead seeks to 1423

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P Figure 2. 13PCBs inventories (kilograms) and relative congener distribution based on the degree of chlorination for each of the seven Arctic shelf seas and for the Central Interior Basin.

provide an Arctic-scale elucidation of PCB spatial distribution and inventory. Nevertheless, dissolved and particulate concentrations for each of the analyzed PCB congeners are available for the three expeditions in the Supporting Information: Beringia2005 (Table S5), ISSS-08 (Table S6), and AO-01 expeditions (Table S7). P Higher 13PCB concentrations were generally found on the pan-Arctic shelf seas, of the European, Asian, and American sectors alike, compared to the concentrations in the interior Central Arctic P of both the Eurasian and Canadian Basins (Figure 1). The 13PCB concentrations of the pan-Arctic shelf seas had a mean of 3.4 pg/L, median of 2.4 pg/L, and range of 0.3-21.1 P pg/L (Figure 1; Table S4 in Supporting Information). Lower 13PCB concentrations were found in the Central Arctic Basin, with a mean of 0.5 pg/L, median of 0.5 pg/L, and range of 0.1-1.1 pg/L. P By far the highest concentrations of 13PCB were found at station ISSS-08-7 in the East Siberian Sea (21.1 pg/L). This station was strongly influenced by the Indigirka River, as illustrated by carrying also the highest POC concentration (6550 μg/L). The salinity (18.84), temperature (3.4 °C), and δ13C-POC (-28.0%) strongly suggest an overwhelmingly terrestrial origin of the particulate organic matter. It is unlikely that the high PCB concentration reflects a strong source in the drainage basin. First, the congener fingerprint is quite similar to

nearby Chukchi and Laptev Seas (Figure 2) and instead is suggestive of long-range atmospheric transport P (see section below). It is more likely that the elevated 13PCB in this location off the Indigirka River results from the particularly high POC concentration, which was >5 times higher than at other stations, as hydrophobic organic compounds are known to partition into organic matter (i.e., the chemical activity is notP higher in this sample) (e.g., ref 5). Approximately 93% of the 13PCB was found in the particulate fraction in this sample. The lowest P 13PCB concentration of the not-before-reported Beringia2005 and ISSS-08 expeditions was found at station OC-05-21 of Beringia-2005, which was taken in the Central Arctic Ocean P waters ( 13PCB of 0.9 pg/L). This station had a large influence of northern North Pacific waters (e.g., δ13C of -23.8%). This water has probably recirculated for a long time in the Beaufort Gyre (≈7 years), which could have had a cleaning effect on PCBs through particle scavenging and settling to deeper waters.18,23 The high-latitude location is also likely to contribute to the minute levels due to wet and dry deposition during the longrange atmospheric transport (e.g., refs 9 and 24). From an analytical-quality point of view, it is encouraging that samples taken in similar regimes but on different expeditions (albeit with common trace-clean methodology) yielded quite similar concentrations (Figure 1). For instance, the 0.9 pg/L value at OC05-21 compares well with the three North Pole/Canadian Basin 1424

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Environmental Science & Technology stations sampled during the AO-01 expedition that report P 13PCB of 0.75 ( 0.36 pg/L (ref 9, Figure 1, and Table S4A in Supporting P Information). Similarly, the Beringia-2005 cruise recorded a 13PCB concentration of 1.3 pg/L in the Eurasian side of the Chukchi Sea that compares well with 1.6 pg/L from a nearby location surveyed during ISSS-08 (Figure 1). The same spatial trend is evident in the individual congener concentrations. For instance, the volatile tetra-CB 52 was found at higher concentration in the pan-Arctic shelf seas with a mean of 0.44 pg/L, a median of 0.31 pg/L, and a range between 0.09 and 2.54 pg/L. In contrast, in the Central Arctic Basins the same congener has a mean of just 0.08 pg/L, a median of 0.08 pg/L, and a range of 0.06-0.26 pg/L. The hexa-CB 138 shows a similar trend but lower values in both areas, with mean concentrations in the pan-Arctic shelf seas of 0.19 pg/L and lower in the Central Arctic Ocean of 0.02 pg/L (Table S4A in Supporting Information). Comparison with other Arctic seawater studies is detailed below, but we will first assess any spatial differences in congener/chlorination fingerprint. Spatial Pattern of PCB Fingerprint in Surface Seawater of the Arctic Ocean. A picture emerges of spatial differences in congener distribution from assessing the information of all three basin-wide expeditions collectively. The congener distribution is skewed toward higher contribution of lighter PCBs (e.g., PCB 18 and PCB 28) at stations located in the Interior Arctic Ocean and in the eastern Arctic shelf seas of the Beaufort, Chukchi, East Siberian, and Laptev Seas (Figure 2). Trichlorinated congeners make up half or more of the total PCB in this eastern basin of the Arctic Ocean. This feature of low-chlorinated biphenyls (e.g., triCBs) making up a dominant fraction of total PCB over extensive Arctic scales suggests an atmospheric delivery mode, yet particlemediated scavenging, favoring surface-ocean export of the highchlorinated congeners to deeper water column strata, cannot be excluded (e.g., refs 15,17, and 18). Nevertheless, this congener profile is overall in accordance with the composition commonly found in air and marine samples from unpolluted land-based Arctic sites.25-27 An increase in concentrations of more volatile PCB congeners (e.g., tri-CB 18/28 and tetra-CB 52) have been shown to be associated with long-range transport back-trajectories from western Europe and central Russia, while lowest concentrations were associated with air passing over the Arctic Ocean (e.g., refs 2 and 25). In contrast, a distinctly different congener pattern, skewed toward heavier congeners, is apparent in the western regimes. For instance, at Beringia-2005 stations OC-05-3 and OC-05-8 (Figure S1 in Supporting Information), located in the IcelandGreenland overflow region, the hexachlorinated congeners (PCB 153 and PCB 138) were the most abundant. Similarly, for the Barents Sea stations, also in the Atlantic sector, both penta- and hexachlorinated congeners were each more abundant than trichlorinated congeners (Figure 2). This congeneric fingerprint in the west may reflect the influence from highly industrialized areas in nearby northeast North America and northern Europe, the key consumption areas for PCBs, 1 with a possible role for ocean currents (e.g., Gulf Stream and Norwegian coastal current) as northbound conveyors in addition to atmospheric long-range transport, often associated with a lighter PCB fingerprint. In sum, different congener fingerprints may signal different delivery modes, with the western Arctic Ocean (largest contribution of trichlorinated CBs) putatively impacted predominantly by atmospheric long-range delivery and the eastern regimes (hexachlorinated CBs more abundant than trichlorinated CBs) presumably

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affected by shorter-range transport from emissions in highconsumption areas in northeastern North America and northern Europe, with a possible role also for an ocean transport vector. Next, we employ a cluster analysis technique to investigate relationships between ambient fingerprint and various technical PCB mixtures. Cluster Analysis of PCB Fingerprint in Arctic Seawater versus Technical Mixtures. All the samples were compared with technical PCB mixtures by cluster analysis (SPSS Inc., Chicago, IL) according to the relative P contribution P of the different degree of chlorination (e.g., % tri to % hepta). Data compositions of standard technical PCB mixtures were also included in the cluster analysis. They were Clophens (A30, A40, A50, and A60), Aroclors (1016, 1221, 1232, 1242, 1248, 1254, 1260, and 1262), Kanechlors (KC 300, 400, 500, 600, 1000, and KC-Mix), Sovol, and Trichloridiphenyl (TCD). In the cluster analysis all data were combined into six clusters (Figure S2 in Supporting Information). The first cluster combined PCB technical mixtures (e.g., Kanechlor, Clophen, Aroclor, and Sovol), mainly composed by penta- and hexa-CB congeners. The second cluster is formed by some samples from the AO-01 expedition and one Beringia-2005 station located near Iceland (OC-05-3). This cluster is composed of stations with high contributions from hexa- and penta-CB congeners. This cluster could reflect the influence from North Atlantic waters carrying heavier PCB congeners originating in the northeast North American coast. The following two clusters (3 and 4) are mainly composed by technical mixtures, with different degree of chlorination (e.g., Aroclor, Kanechlors, and Clophens). Cluster 5 combines stations from the Barents Sea, Canadian Archipelago, Baffin Bay, Bering Strait, East Siberian Sea, and Kara Sea with PCB composition found in these stations dominated by tri- and tetra-CB congeners. This cluster can be explained by input from atmospheric long-range transport of lighter-chlorinated PCBs to this region. The last clusters are composed of the majority of the East Siberian stations from the Beaufort and Chukchi Seas and the technical mixture TCD. Those stations are characterized by a high percentage of low chlorinated congeners (>40% trichlorinated PCBs) that could reflect the influence of high production/ consumption of the trichlorinated mixture (TCD) in the former Soviet Union. The TCD mixture has trichlorinated congeners as a major constituent (49%), along with tetrachlorinated (32%) and dichlorinated (14%).28 However, the consistently high proportion of lower chlorinated congeners found in the surface reservoir over extensive spatial scales could equally well indicate long-range transport of highly volatile PCB congeners. Comparison with Other Arctic Studies. There is a deficiency of quality-controlled PCB data for Arctic seawater to which these results may be compared. A key reason for this shortage is the challenge to collect enough material cleanly to overcome shipboard and analytical laboratory contamination.9,12,15,16,29 The Arctic Ocean surface seawater concentrations Pobserved from the three basin-wide expeditions, expressed as 13PCB(dissþpart), were either substantially lower or in a similar range to others reported. The pan-Arctic shelf and interior basin P stations, except the Indigirka mouth, exhibited a range of P13PCB(dissþpart) concentrations of 0.13-6.1 pg/L. Dissolved 13PCB concentrations found in this work (range 0.09-2.12 pg/L) are in reasonable agreement with those found in surface waters in northern North Atlantic and Arctic waters just north of Svalbard and between P Svalbard and Greenland reported by Gioia et al.11 for 12PCB (0.79-3.54 pg/L). 1425

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Environmental Science & Technology

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Table 1. Inventories of Major PCB Congenersa in the Polar Mixed Layer of Seven Shelf Seas and Interior Basin of the Arctic Ocean

Arctic Seas

areab

mean

(103km2)

depthb (m)

P

7

PCB 28

Chukchi Sea

620

80

East Siberian Sea

987

58

50.9

Laptev Sea

498

48

13.4

Kara Sea

926

131

6.72

Barents Sea

1512

200

Beaufort Sea

178

SNCAAc

146 4489

2748

Central Arctic Ocean Basin Total Arctic Ocean

P

PCB congener (kg)

7.81

PCB 52

PCB 118

PCB 153

PCB 138

PCB 180

PCBsa (kg)

13

PCBsa (kg)

2.04

0.784

0.974

1.39

0.327

16.6

9.92

1.46

3.41

4.57

0.674

86.4

4.52

3.07

0.895

1.53

2.28

0.501

26.2

3.36

3.87

0.959

1.86

2.83

0.489

20.1

35.0

4.49

5.72

5.31

3.06

4.69

2.87

1.59

27.7

46.0

124

1.45

1.18

0.53

0.236

0.379

0.568

0.129

4.47

338

3.18

2.15

0.94

0.465

0.865

0.905

0.113

8.62

18.8 107

3.26

PCB 101

15.4

17.8 53.4

8.30 33.9

3.79 11.7

4.58 18.3

3.69 19.1

1.81 5.64

58.8 249

24.5 129 36.7

6.99 10.8 104 394

a Sum of seven ICES congeners and of 13 most abundant PCB congeners; defined in Table S4B in Supporting Information. b Reference 21. c Shelf of Northern Canadian Arctic Archipelago.

Pioneering work by Schulz-Bull et al.17 in deep water masses from the North Atlantic near Iceland found concentrations in a range between 0.01 and 1.05 pg/L for the dissolved and between 0.28 and 11.24 pg/L for the particulate phase for the sum of 23 PCB congeners. Lohmann et al.10 found total-phase concentrations of 0.42 pg/L for the seven ICES (International Council for the Exploration of the Seas; PCBs 28, 52, 101, 118, 138, 153, and 180) congeners of PCBs in surface water in the Norwegian Sea. Our studies using trace-clean sampling and handling protocols recovered 40 times lower dissolved concentrations for the Ob and Yenisei estuaries in the dissolved phase than those reported by Carroll et al. 30 (for the same 10 PCB congeners). Other reports of PCB seawater concentrations from Arctic marginal seas are similarly substantially higher than the findings of the present study. For instance, reports for the Chukchi and Bering Seas had 3 times higher concentrations 31 and waters off the industrial Kola Peninsula were 100 times higher 32 than our reported concentrations for Barents and Kara Sea. Clearly, trace-clean protocols are necessary and the data quality must be thoroughly interpreted with respect to realistic field blanks and geochemical consistency of obtained results. Inventory of PCBs in the Polar Mixed Layer of the Arctic Ocean. Using the surface water PCB concentrations obtained over extensive spatial scale of the two new expeditions combined with the same type of data from the AO-01 expedition,9 we estimated the inventories of PCBs in the stratified upper water column (i.e., PML: approximately 15 m for the Arctic Shelf Seas and 30 m in the Central Arctic Ocean) for each of the seven shelf seas and for the Interior Central Basin (Table 1, Figure 2). A previous study showed that the PCB concentration in Arctic Ocean sea ice is about the same as in the surrounding seawater;12 we thus assumed that the waterP concentrations are representative for the entire PML. The total 13PCB inventory for the whole Arctic Ocean was 394 kg (249 kg for the sum of the seven ICES PCB congeners) (Table 1). The overall most abundant congeners in Arctic surface waters are PCB 28 (107 kg) and PCB 52 (53 kg) with the sum of the hexachlorinated PCBs 153 and 138 at 37 kg (Table 1). The seven pan-Arctic shelf seas combine to a P 289 kg 13PCB stock for an area that is about equal to that of the combined Interior Basins, which holds 105 kg (note that PML is twice as deep in the interior). The PPML of the vast East Siberian Sea holds the largest individual 13PCB stock of all shelf seas P with 86 kg (Table 1). The 7-ICESPCB inventory of 249 kgP for this all-Arctic PML compartment can be compared with the 7ICESPCB inventory estimated based on a large database for the mixed surface sediment of the pan-Arctic shelves (the world’s

largest continental shelf system) of 139 tons,33 which thus is ∼500 times greater. The Arctic surface ocean inventory may also be compared with global emission estimates of Breivik et al.34 Those workers provided three different estimates, termed low, mid, and high, but reasoning in their work and in others (e.g., ref 33) implies that their high estimate should be regarded as the most realistic. The inventory in the Arctic Ocean polar mixed layer corresponds to a mere 0.0008% of these historical emission estimates.34 Hence, a very small percentage of the total emitted PCBs is actually found in the Arctic Ocean surface water ecosystem. This work provides the first comprehensive view of seawater PCB concentrations for the entire Arctic Ocean. A general predominance of low-chlorinated PCBs suggests an important role for atmospheric input. However, distinctly different congener distributions were found in the eastern Arctic ocean P (∼ half of 13PCB made up of trichlorinated congeners) versus in the Atlantic sector, where hexachlorinated congeners were more abundant than trichlorinated counterparts. Travel distances and travel modes (air vs ocean currents) with associated scavenging mechanisms should be investigated to elucidate the mechanisms behind this distinct spatial difference in PCB fingerprint. The documented seawater PCB concentrations provide the basis for estimating uptake in the base of the Arctic pelagic food web, yet the Arctic surface ocean holds a tiny portion (∼0.001%) of the PCBs that have been historically emitted to the environment.

’ ASSOCIATED CONTENT

bS

Supporting Information. Seven tables listing stations information, congener total concentrations, and particulate and dissolved congener concentrations and two figures showing station locations and general description of the Arctic Ocean and cluster analysis. This material is available free of charge via the Internet at http://pubs.acs.org.

’ AUTHOR INFORMATION Corresponding Author

*E-mail: [email protected]; tel: þ46-703247317.

’ ACKNOWLEDGMENT Anna Sobek is acknowledged for her efforts as part of the Swedish Arctic Ocean expedition 2001 (AO-01). Ralf Dahlkvist is acknowledged for his work on the Swedish Arctic Ocean 1426

dx.doi.org/10.1021/es103542f |Environ. Sci. Technol. 2011, 45, 1420–1427

Environmental Science & Technology expedition 2005 (Beringia-2005). Martin Krusa and Bart van Dongen are acknowledged for PCB sampling during the ISSS-08 expedition. We are also grateful to G€oran Bj€ ork for CTD data, Laura Sanchez-Garcia for ISSS-08 humic substance data, and Johan Gelting and Fredrik Nordblad for ISSS-08 hydrosonde data. The EU 7 FP project ArcRisk (Contract 1346810) funded € part of this work. O.G. also received support as an Academy Researcher from the Royal Swedish Academy of Sciences through a grant from the Knut and Alice Wallenberg Foundation (Grant 629-2002-2309). The Swedish Polar Research Secretariat provided efficient logistical support for all three expeditions. The Knut and Alice Wallenberg Foundation provided the major logistical and ship charter funding for the ISSS-08 expedition.

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