Environ. Sci. Technol. 2007, 41, 3455-3461
Perfluorinated Acids in Arctic Snow: New Evidence for Atmospheric Formation CORA J. YOUNG,† VASILE I. FURDUI,† JAMES FRANKLIN,‡ ROY M. KOERNER,§ DEREK C. G. MUIR,| AND SCOTT A. M A B U R Y * ,† Department of Chemistry, University of Toronto, 80 St. George Street, Toronto, Ontario, Canada M5S 3H6, CLF-Chem Consulting, 28 Rue Edouard Olivier, Brussels, Belgium BE-1170, Geological Survey of Canada, 601 Booth Street, Ottawa, Ontario, Canada K1A 0E8, and Water Science and Technology Directorate, Environment Canada, 867 Lakeshore Drive, Burlington, Ontario, Canada L7R 4A6
Perfluorinated acids (PFAs) are ubiquitously found in water and biota, including remote regions such as the High Arctic. Under environmental conditions, PFAs exist mainly as anions and are not expected to be subject to longrange atmospheric transport in the gas phase. Fluorinated telomer alcohols (FTOHs) are volatile and can be atmospherically oxidized to form perfluorocarboxylic acids. Analogously, fluorosulfamido alcohols can be oxidized to form perfluorooctane sulfonate (PFOS). High Arctic ice caps experience contamination solely from atmospheric sources. By examining concentrations of PFAs in ice cap samples, it is possible to determine atmospheric fluxes to the Arctic. Ice samples were collected from high Arctic ice caps in the spring of 2005 and 2006. Samples were concentrated using solid-phase extraction and analyzed by LC-MS-MS. PFAs were observed in all samples, dating from 1996 to 2005. Concentrations were in the lowmid pg L-1 range and exhibited seasonality, with maximum concentrations in the spring-summer. The presence of perfluorodecanoic acid (PFDA) and perfluoroundecanoic acid (PFUnA) on the ice cap was indicative of atmospheric oxidation as a source. Ratios of PFAs to sodium concentrations were highly variable, signifying PFA concentrations on the ice cap were unrelated to marine chemistry. Fluxes of the PFAs were estimated to the area north of 65°N for the 2005 season, which ranged from 114 to 587 kg year-1 for perfluorooctanoic acid (PFOA), 73 to 860 kg year-1 for perfluorononanoic acid (PFNA), 16 to 84 kg year-1 for PFDA, 26 to 62 kg year-1 for PFUnA, and 18 to 48 kg year-1 for PFOS. The PFOA and PFNA fluxes agreed with FTOH modeling estimations. A decrease in PFOS concentrations through time was observed, suggesting a fast response to changes in production. These data suggest that atmospheric oxidation of volatile precursors is a primary source of PFAs to the Arctic.
* Corresponding author phone: 416-978-1780; fax: 416-978-3596; e-mail:
[email protected]. † University of Toronto. ‡ CLF-Chem Consulting. § Geological Survey of Canada. | Environment Canada. 10.1021/es0626234 CCC: $37.00 Published on Web 03/28/2007
2007 American Chemical Society
Introduction Widespread contamination of waters and biota with perfluorinated acids (PFAs) has been observed in remote regions, including the High Arctic (1-3). In these areas where local usage would not be expected to contribute significantly to contamination, questions are raised regarding the source of these pollutants. The low volatility and high water solubility of PFAs in their anionic form implies that they are not susceptible to long-range atmospheric transport. Thus, another transport mechanism must be at work. It has been postulated that these compounds could be transported via ocean currents and that with concentrations measured in open ocean water, it is possible to calculate a yearly flux of between 2 and 12 t of perfluorooctanoic acid (PFOA) to the Arctic (4). However, this flux may not contribute significantly to the observed biota contamination, as evidence suggests that transport from the Atlantic into the Arctic Ocean will be at a depth greater than 200 m, while atmospherically deposited PFAs may have a greater influence on the biologically productive near-surface waters (5). In addition, transport to the Arctic via the ocean is estimated to take on the order of decades (6), leading to a lag between production and observed changes. The atmospheric oxidation of volatile precursors is another potential source of PFAs to the Arctic. Fluorotelomer alcohols (FTOHs) are volatile and have sufficient persistence in the atmosphere to reach the Arctic (7). They have been observed to undergo atmospheric oxidation to form perfluorocarboxylic acids (PFCAs) under low NOx conditions, such as those found in remote Arctic regions (8, 9). Analogously, the source of perfluorooctane sulfonate (PFOS) to the Arctic could be atmospheric oxidation of volatile perfluorooctane sulfamido alcohols (10, 11). FTOHs and perfluorooctane sulfamido alcohols are present as residuals in some fluoropolymer products, and these residuals can be released into air (12). Both FTOHs and perfluorooctane sulfamido alcohols have been shown to be present ubiquitously in the atmosphere (13-15), including in the Arctic (3, 16). Their presence has also been demonstrated in indoor air, which may be a source to the atmosphere (15). Industry has responded to the presence of perfluorinated compounds in the environment. In 2001-2002, PFOS and related chemistries, including perfluorosulfamido alcohols containing eight carbons, were voluntarily removed from the market (17). As such, emissions of these potential precursors should be significantly decreased, although not yet zero, due to continued use of products. Additionally, some producers of FTOH-containing polymer products have announced their intention to decrease the residuals present in their products (18). Temporal analyses of PFAs in ringed seals from the Canadian Arctic show recent trends that are in line with a fast response to changing production patterns of PFAs. PFOS concentrations were observed to increase steadily up until 1998 or 2000, after which concentrations began to decrease (19). Time to transport contaminants via the ocean is on the order of decades, while via the atmosphere it is days to weeks. Thus, a short response time points to an atmospheric source. Using estimated emissions of FTOHs based on air concentrations and a three-dimensional model, 0.4 t y-1 of perfluorooctanoic acid was calculated to be deposited at latitudes north of 65°N via atmospheric oxidation (20). Measuring past and present atmospheric fluxes of PFAs into the Arctic would shed light on whether atmospheric degradation of volatile precursors provides the primary source VOL. 41, NO. 10, 2007 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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of PFAs to the Arctic. Measured fluxes would also provide a test of the recent model results. Ice caps, with their high altitude, should receive contamination solely from the atmosphere. Layers of accumulated snow on ice caps are subject to little change and the temporal record can be reasonably well established (21). Few past studies have looked at persistent organic pollutants in ice caps. The limitations of traditional sampling technology have made it difficult to obtain large enough samples in which to detect the low levels of organic pollutants found in these remote regions (22). Ice caps have the potential to provide long-term temporal trends of atmospheric concentrations, which are important for assessing regulatory effectiveness. Utilizing large-volume snow samples and state-of-the-art analytical equipment, it is possible to take advantage of the information stored in ice caps. The objective of this study was to use High Arctic ice caps to determine seasonal cycles, temporal trends, and atmospheric fluxes in order to illuminate the source of selected PFAs to the Arctic.
Experimental Section Chemicals. See the Supporting Information (SI) for a full list of chemicals used. Deep ice core water for use as a blank was obtained from the Geological Survey of Canada (Ottawa, ON) from a core taken on Agassiz Ice Cap in 1977. The ice used was taken from 150 to 200 m depth and is greater than 2000 years old. Deep ice samples were wrapped in polyethylene and stored at the Geological Survey of Canada at -20 °C. The outside of the core was removed with stainless steel tools before melting. Sample Collection. Surface samples, representing the end of the melt season to the time of sampling in the following spring were collected in the spring of 2005 and 2006 from locations in the Canadian Arctic: Melville Ice Cap, Melville Island, Northwest Territories (75° 27N, 114° 59W); Agassiz Ice Cap, Ellesmere Island, Nunavut (80° 7N, 73° 1W); and Meighen Ice Cap, Meighen Island, Nunavut (79° 27N, 99° 08W, 2006 only). A map of sampling locations can be found in the SI. Depth samples were collected from the Devon Ice Cap, Devon Island, Nunavut (75° 20N, 82° 40W, 1797 m above sea level) in spring 2006 (a depth range-finding study was done in the spring of 2005). To avoid contamination, fluoropolymer products were strictly avoided at all sampling sites. For full sampling details, please see the SI. Sample Preparation and Analysis. Full method details can be found in the SI. Briefly, samples were concentrated 100× using solid-phase extraction and eluted with methanol. Samples were analyzed using liquid chromatography with tandem mass spectrometry detection, using an isocratic method (23). Quantification of analytes was done using labeled internal standards, which were available for PFOS, PFOA, perfluorononanoic acid (PFNA), perfluorodecanoic acid (PFDA) and perfluoroundecanoic acid (PFUnA). PFUnA quantification was done using labeled PFDA.
Results and Discussion QA/QC. For full details on all QA/QC, please see the SI. Instrumental contamination was not observed to be a problem. Variability was minimized with the use of labeled internal standards and triplicate injections. Extraction blanks and spike and recoveries were used to validate the extraction method. Recoveries were acceptable and ranged from 83 to 110%. A field blank test indicated that field sampling did not result in contamination of the samples. Dating Arctic Snow. Density, conductivity, and major ion measurements, along with visual inspection of ice layers, are all useful for the determination of age of Arctic snow (24). These properties are all expected to vary over the course of a year and allow seasonal and annual markers to be identified 3456
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along a profile. Observed concentrations of major ions, densities, and conductivities from the Devon Ice Cap are shown in the SI. Utilizing this information, along with visual inspection, it is possible to assign dates to the depth of the pit. A pit of depth 6.8 m appears to go back to the year 1996. Little snow is available from 2006, as the majority of snow in the Arctic falls in equal parts in the summer and fall. Thus, the last year for which a flux of PFAs can be determined is 2005. Concentrations of PFAs in Arctic Snow. PFAs were observed in all surface and depth samples at pg L-1 concentrations. Observed concentrations were corrected for density by multiplying concentrations measured in meltwater by the observed density of the snow. Concentrations were as follows: 2.6-86 pg L-1 for PFOS, 12-147 pg L-1 for PFOA; 5.0-246 pg L-1 for PFNA;
