Environ. Sci. Technol. 2009, 43, 6507–6514
Polyfluorinated Compounds in the Atmosphere of the Atlantic and Southern Oceans: Evidence for a Global Distribution A N N E K A T R I N D R E Y E R , * ,† I N G O W E I N B E R G , †,‡ C H R I S T I A N T E M M E , †,# A N D RALF EBINGHAUS† Institute for Coastal Research, GKSS Research Centre, Max Planck Strasse 1, 21502 Geesthacht, Germany, and Institute for Ecology and Environmental Chemistry, Leuphana University Lu ¨ neburg, Scharnhorststrasse 1, 21335 Lu ¨ neburg, Germany
Received March 30, 2009. Revised manuscript received June 19, 2009. Accepted July 21, 2009.
High volume air samples taken onboard several research vessels in the Atlantic Ocean, the Southern Ocean, and the Baltic Sea as well as at one land-based site close to Hamburg, Germany, in 2007 and 2008 were analyzed for per- and polyfluorinated organic compounds (PFCs). A set of neutral, volatile PFCs such as fluorotelomer alcohols (FTOH) or perfluoroalkyl sulfonamides and ionic nonvolatile PFCs like perfluorinated carboxylates (PFCA) and sulfonates (PFSA) were collected on PUF/XAD-2/PUF cartridges and glass fiber filters and determined using GC-MS and HPLC-MS/MS. PFCs were detected in all air samples, even in Antarctic regions, and occurred predominantly in the gas phase. Total gas-phase concentrations of ship-based samples ranged from 4.5 pg m-3 in the Southern Ocean to 335 pg m-3 in European source regions. Concentrations of 8:2 FTOH, the analyte that was usually observed in highest concentrations, were between 1.8 and 130 pg m-3. PFC concentrations decreased from continental regions toward marine regions and from Central Europe toward the Arctic and Antarctica. Southern hemispheric concentrations of individual PFCs were significantly lower than those of the northern hemisphere. On the basis of this data set, marine background PFC concentrations and atmospheric residence times were calculated. This study gives further evidence that volatile PFCs undergo atmospheric long-range transport to remote regions and may contribute to their contamination with persistent PFCA and PFSA.
Introduction Since persistent, bioaccumulative, and toxic polyfluorinated compounds (PFCs) such as perfluorooctane sulfonate (PFOS) and perfluorooctanoate (PFOA) (1, 2) have been detected in humans (3) as well as in polar fauna (4, 5), there is an ongoing interest concerning their environmental fate and transport. * Corresponding author e-mail:
[email protected]; phone: +49-4152-872352; fax: +49-4152-872332. † GKSS Research Centre. ‡ Leuphana University Lu ¨ neburg. # Current address: Eurofins GfA GmbH, Geierstrasse 1, D-22305 Hamburg, Germany. 10.1021/es9010465 CCC: $40.75
Published on Web 08/03/2009
2009 American Chemical Society
A couple of key questions to resolve are how and to what extent these perfluorinated carboxylates (PFCA) and sulfonates (PFSA), starting from their point of emission, reach remote locations where they are being accumulated. PFCA and PFSA, especially those of chain lengths less than ten carbon atoms, have been detected globally in rivers and oceans and are considered to be transported significantly via that pathway (6-8). It is estimated that the majority of these compounds is emitted directly to the water phase during manufacturing and use (9, 10). The amount of PFOA that reaches the Arctic via oceanic transport is calculated to be between 2 and 23 t a-1 (annum) (9, 11, 12). Being dissolved in the water phase or enriched at the water surface, these ionic PFC may also be transported into the air as marine aerosols (9). However, atmospheric removal by wet and dry deposition is expected to occur in the order of a few days (13). Atmospheric transport and degradation of PFCA and PFSA precursors is considered as other main transport mechanism. Basically, PFCA and PFSA precursors like fluorotelomer alcohols (FTOH) and acrylates (FTA) or perfluoroalkyl sulfonamids (FASA) and sulfonamido ethanols (FASE) are thought to be emitted to the atmosphere during their manufacturing or the production of fluoropolymers (9, 10) and more importantly by diffuse sources during use and disposal (10, 14-16). Precursors are more volatile than PFCA and PFSA and, therefore, are more likely to undergo atmospheric long-range transport. Being in the atmosphere, these volatile compounds are degraded to PFCA and PFSA by OH radical initiated oxidation (17-20). Precursors were determined in a number of field studies in North America, Europe, Asia, and the Atlantic Ocean (14, 21-25), and modeling results reveal the ubiquitous atmospheric distribution of FTOH and its degradation products (26). The actual extent to which the atmospheric transport and degradation of precursors contribute to the PFCA and PFSA contamination of remote regions is a controversial subject, although its importance is sustained by the fast response to changes in PFOS production observed in snow samples from the High Arctic (27). Some studies estimated that the atmospheric pathway is less important than oceanic transport, mainly due to the low PFCA and PFSA yields of the degradation reactions and too low historic precursor emissions (9, 11). Several recent studies estimated the Arctic deposition of perfluorooctanoate from FTOH oxidation to be between 50 and 500 kg a-1 (11, 26, 28, 29) whereas an earlier estimate by Ellis et al. (18) assumed an approximate flux of 0.1-10 t a-1 of PFCA to the Arctic. Nevertheless, the presence of PFCA and PFSA in glacial ice caps that received their contamination solely from the atmosphere (27), their existence in air and lake water of remote mountains (30), or the occurrence of precursor degradation intermediates in precipitation (31, 32), Arctic sediments, and air particles (33) reveal that the atmospheric transport and degradation is an important contamination mechanism in remote locations. The objective of this study was to determine concentrations of a variety of airborne PFC on a global scale with one method and short sampling intervals. Specifically, spatial gradients of PFC air concentrations will be evaluated. The PFC contamination of Arctic and for the first time of Antarctic air will be assessed and hemispheric (background) levels will be defined. Therefore, air samples with a 1-3 day resolution were taken onboard research vessels during several sampling campaigns in the Atlantic Ocean along north-south transects from the Arctic to the Antarctica and along east-west transects from North/South America to Europe/Africa as well as on a rather regional scale in the North and Baltic Sea. Data VOL. 43, NO. 17, 2009 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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obtained in this study are also valuable to validate and improve existing models since this data comprehensively covers regions that have not been investigated before.
Experimental Section Chemicals. All chemicals, standard compounds, and gases were of high quality and purity. Details on chemicals concerning their abbreviations, supplier, and purity can be found in the Supporting Information. Sampling. High volume air samples were taken on the observation deck of different research vessels (RV Polarstern, RV Maria S. Merian, RV L’Atalante, RV Atair) during several sampling campaigns along north-south and east-west transects of the Atlantic and Southern Oceans as wells as in coastal areas of the Baltic Sea (Atair 155, German Bight, North Sea, 09/2007; MSM05/1, Las Palmas, Spain to St. John’s, Canada, 04/2007; MSM05/6, Longyearbyen, Norway to Kiel, Germany, 08/2007; MSM08/3, Rostock, Germany to Tallinn, Estonia to Kiel, Germany, 06/2008; AntXXIV-1 and AntXXV1, Bremerhaven, Germany to Cape Town, South Africa, 11/ 2007, 11/2008; AntXXV-2, Cape Town, South Africa to Neumayer Station, Antarctica to Cape Town, South Africa, ¨ D, Recife, Brazil to Dakar, 12/2008; L’Atalante leg 2 MARSU Senegal, 01/2008; Figure S1 in the Supporting Information). Sampling height varied between 16 and 20 m. In dependence on the expected contamination degree, sampling duration varied between 1 and 3 days. To minimize ship-borne contamination, air samplers were controlled by a computer connected to the ship’s meteorological system assuring that the sampling was interrupted when relative winds were arriving from the rear of the ship. For the determination of continental PFC air concentrations, a permanent land-based sampling site was established at Barsbu ¨ ttel (BAR) in the vicinity of Hamburg (1 770 000 inhabitants) (25). In general, sampling durations varied from 3 to 4 days at that site. The average sampling rate for land- and ship-based samples was about 450 m3 d-1. Airborne PFCs were collected on glass fiber filters and cartridges filled with a sandwich of polyurethane foam (PUF) and Amberlite XAD-2. Prior to the sampling, 50 µL of an internal standard solution containing mass-labeled PFCs were added to the cartridge to account for analytes losses in the gas phase during sampling and sample preparation. Samples were sealed airtight and stored at -20 °C until analysis in the laboratory. Sample Preparation and Instrumental Analysis. Detailed descriptions of sample preparations and instrumental analyses are given elsewhere (34, 35). Briefly, gas-phase samples were extracted three times using methyl-tert-butyl ether (MTBE)/acetone (1:1). Particle-phase samples were extracted with MTBE/acetone (1:1) or methanol to determine neutral volatile PFC or ionic PFC, respectively. Mass-labeled internal and injection standards were applied. Detection of MTBE/ acetone extracted PFC was performed by GC-MS using positive chemical ionization. Methanol-extracted PFC were determined by HPLC-MS/MS. Compounds were classified as not detected (nd) with signal-to-noise ratio (S/N) below 3 and not quantified (nq) with S/N below 10. Analyte concentrations were calculated with the internal standards method using a seven point calibration. Internal standards were used to correct for analytes losses. Average recovery rates of gas-phase analytes ranged from 21 ( 27% (13C 4:2 FTOH, n ) 127) to 68 ( 32% (MeFOSE D7, n ) 173) for shipbased samples and from 21 ( 13% (13C 4:2 FTOH, n ) 45) to 60 ( 27% (EtFOSE D9, n ) 118) for land-based samples. Average recovery rates for particle bound analytes were between 41 ( 15% (13C 4:2 FTOH, n ) 117) and 123 ( 76% (13C PFUnDA, n ) 43) for ship-based samples and between 24 ( 31% (13C 4:2 FTOH, n ) 47) and 106 ( 48% (13C PFDoDA, n ) 103) for BAR samples. Analytical performance of particle 6508
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extraction strongly depended on the particle load and kind of particles and was worst with a lot of pollen (land-based samples) or sea salt (ship-based samples) on the filters. See Supporting Information for further information on recoveries. Blanks. Solvent blanks (for gaseous samples) and filter blanks (for particle samples) were taken with each set of samples that was extracted. Most of the compounds were detected in solvent and filter blanks at very low concentrations (on average 0.2 pg m-3 and 0.7 pg m-3, respectively). Therefore, all concentrations reported were blank-corrected. Except for FTOH in the particle phase, field blanks were usually in the range of solvent and filter blanks, revealing that contamination was most likely not due to sampling or sample handling. Blank concentrations are reported in the Supporting Information. Trajectory Analysis. Seven day air mass backward trajectories were calculated with the model Hysplit 4.8 using NCEP’s Global Data Assimilation System (GDAS) data with 1° latitude/longitude resolution provided by NOAA-Air Resources Laboratory (36). Trajectories were calculated for intervals of 3 and 6 h with the sampling height as arrival height. Statistical Analysis. Because particle-phase concentrations were often close to the detection limit only gas-phase data were statistically evaluated. Concentrations of poly- and perfluorinated compounds were tested for normal distribution. The differences between hemispheric average concentrations were evaluated using the t test. Normal-distributed analyte concentrations in the gas phase were tested for correlation using Pearson Correlation. Atmospheric Residence Time. The atmospheric residence times (τ) of gas-phase PFC were calculated using the empirical relation τ × σ ) 0.14 years (σ: relative standard deviation of the mixing ratio) developed by Junge (37). We calculated the atmospheric residence time for ship-based samples (spatial approach) and land-based samples (temporal approach) separately. Alternatively, residence times of gases that partition to the particle phase were calculated by the method suggested by Manchester-Neesvig (38). Given a residence time of particles in the northern hemisphere of 6 days (38), the residence time of the gas would be 6/φ with φ being the fraction of the gas in a given volume that is associated with particles. Further aspects on the residence time calculations are given in the Supporting Information.
Results and Discussion PFC Concentrations. Neutral volatile and semivolatile PFCs were detected almost exclusively in the gas phase. Only MeFBSA, MeFOSA, EtFOSA, MeFBSE, MeFOSE, and EtFOSE were observed on particles. On average, the particle-phase contribution of these compounds did not exceed 20%. PFC gas-phase concentrations are presented in Table S21 in the Supporting Information. Although not always detected above the detection limit in each sample, PFCs were detected in all air samples, even in Antarctica, and in concentrations above laboratory and/or field blanks, suggesting the atmospheric long-range transport of these compounds as well as their global distribution. Total gas-phase concentrations of shipbased samples ranged from 4.5 pg m-3 in the Southern Ocean to 335 pg m-3 in source regions. Concentrations of 8:2 FTOH, the analyte that was usually observed in highest concentrations, were between 1.8 and 130 pg m-3. Overall, gas-phase PFC concentrations of this study are in the same range as in studies covering similar locations (14, 22, 23). Concentrations of individual particle-bound precursors were usually below 1 pg m-3. Maximum particle-phase concentrations were reached for MeFOSE in the port of Hamburg (9 pg m-3). MeFOSA and MeFOSE were the compounds that were most frequently observed. FASE was observed in higher concentrations than FASA.
TABLE 1. Average Gas- and Particle-Phase PFC Composition (%) of Ship-Based and Land-Based Air Samplesa gas-phase proportion (%)
particle-phase proportion (neutral and ionic analytes; %)
compound
ship average
BAR average
ship average
BAR average
compound
ship average
BAR average
4:2 FTOH 6:2 FTOH 8:2 FTOH 10:2 FTOH 12:2 FTOH Σ FTOH 6:2 FTA 8:2 FTA 10:2 FTA Σ FTA MeFBSA MeFOSA Me2FOSA EtFOSA PFOSA Σ FASA MeFBSE MeFOSE EtFOSE Σ FASE
0 13 41 14 7 75 3 2 1 6 3 4 0 3 1 11 2 5 1 8
0 17 49 14 6 86 1 2 1 4 2 2 0 1 0 5 2 2 1 5
0 0 0 0 0 0 0 0 0 0 0 22 0 13 0 35 7 30 28 65
0 0 0 0 0 0 0 0 0 0 0 1 0 1 6 7 4 58 30 93
PFBS PFHxS PFHpS PFOS PFDS Σ PFSA PFBA PFPA PFHxA PFHpA PFOA PFNA PFDA PFUnDA PFDoDA PFTriDA PFTeDA PFHxDA PFOcDA Σ PFCA
2 2 0 7 0 11 30 2 7 7 20 8 5 3 3 1 0 0 0 92
0 0 1 54 0 55 14 1 4 1 13 3 3 2 2 0 1 0 0 45
a Particle-phase neutral and ionic PFC were evaluated separately. BAR: land-based sampling station Barsbu¨ttel. Corresponding concentration averages are given in the Supporting Information.
Of ionic PFC, only PFBS, PFHxS, PFOS, PFBA, PFPA, PFHxA, PFOA, PFNA, PFDA, PFUnDA, PFDoDA, and PFTriDA were detected in the particle fraction (Table S22 in the Supporting Information). Most frequently, PFOS, PFBA, PFHxA, PFOA, PFNA, and PFDA were quantified. The average concentrations of individual PFSA (
