Laboratory Studies on the Fate of Perfluoroalkyl Carboxylates and

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Laboratory Studies on the Fate of Perfluoroalkyl Carboxylates and Sulfonates during Snowmelt Merle M. Plassmann,*,†,§ Torsten Meyer,‡ Ying Duan Lei,‡ Frank Wania,‡ Michael S. McLachlan,† and Urs Berger† † ‡

Department of Applied Environmental Science (ITM), Stockholm University, 10691 Stockholm, Sweden Department of Physical and Environmental Sciences, University of Toronto Scarborough, 1265 Military Trail, Toronto, Ontario, M1C1A4 Canada

bS Supporting Information ABSTRACT: Perfluoroalkyl acids (PFAAs) are anthropogenic chemicals that occur in snow from both remote and source regions. Experiments were conducted to determine how PFAAs are released from a melting snowpack. Different PFAAs eluted from the snowpack at different times, those with short chains eluting early, those with long chains eluting late. The concentrations in the meltwater of PFAAs with medium chain lengths of 6 to 9 perfluorinated carbon atoms first increased and then decreased during the melt period. Such a peak elution had not been previously observed for any other chemicals. The specific snow surface area (SSA) influenced this elution type, with peak concentrations occurring earlier in a snowpack with lower SSA. Model simulations suggested that the snow surface decrease during the melt alone was insufficient to explain the observations. It was ruled out that the calcium concentration affected PFAA sorption to the snow surface in a similar way as sorption to sediments. Adsorption coefficients of PFAAs to the snow surface were estimated by fitting the measured and modeled elution profiles.

’ INTRODUCTION Perfluoroalkyl carboxylates and sulfonates (PFCAs and PFSAs), together referred to as perfluoroalkyl acids (PFAAs), are anthropogenic compounds, which are persistent, bioaccumulative, and ubiquitously found in the environment.1 Some of them are toxic.2 PFAAs can originate either from direct sources, for instance from releases during production or due to their use in consumer products, or from indirect sources like the atmospheric oxidation of volatile precursors.3 Fluorotelomer alcohols and perfluoroalkane sulfonamides have been shown to degrade to PFAAs.4,5 Occurrence of these volatile precursor groups in the atmosphere is widespread.6,7 PFAAs formed in the atmosphere can be deposited onto the ground via wet or dry deposition including snow. Concentrations of PFAAs in rain and snow are mostly in the low ng L 1 range8 10 but can be in the pg L 1 range in remote places like the Arctic ice caps.11 During the winter season snow collects chemicals12 and can act as a storage reservoir.13 During melt, the timing of a chemical’s release from the snowpack depends on its water solubility and its sorption to the surface of snow crystals or particles present in the bulk snow.14 High concentrations may arise at certain times during the melt period, causing a risk for sensitive organisms developing in early spring. Laboratory studies have so far simulated the snowpack release of ions15 and neutral organic chemicals, such as pesticides,16 polycyclic aromatic hydrocarbons,14,15 and semifluorinated n-alkanes.17 Two types of releases were observed. Highly water-soluble r 2011 American Chemical Society

chemicals (including ions) were released early during a melt period, while hydrophobic chemicals that preferentially sorb to particles were released with the particles at the end of the snowmelt. The purpose of this study was to determine the release behavior of PFAAs from a snowpack in an experimental snowmelt chamber. A mechanistic understanding of this behavior is required to predict whether snowmelt processes can result in unacceptably high contaminant loads in receiving waters. In addition, a previously developed snowmelt model18 was tested for its ability to qualitatively reproduce the experimental results.

’ METHODS Snow Chamber Experiments. The experimental setup for snow production, aging, and melting is described in detail elsewhere.14 Briefly, artificial snow was produced in a cold room at temperatures below 20 °C using a snow gun. The snow was collected in a rectangular steel vessel (0.24 m3, height 40 50 cm, length 100 cm, width 55 cm). Tap water used for snow production was spiked with the target analytes resulting in concentrations in the produced snow of approximately 30 ng L 1 snow-water Received: April 13, 2011 Accepted: July 8, 2011 Revised: July 1, 2011 Published: July 08, 2011 6872

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Environmental Science & Technology

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Table 1. Mass Balance in % of Target Compounds from Three Snowmelt Experiments and Partition Coefficients for PFAAs Used in the Model exp 2 total (thereof in the exp 3 total (thereof in abbreviation

a

full name

exp 1 total

particle fraction)

the particle fraction)

log KOCa,b log KAWc,d log (KIA/m) log (KIW/m)

PFBS PFHxS

perfluorobutane sulfonate perfluorohexane sulfonate

42 45

71 67

76 75

1.2b 1.9b

3.7d 3.1d

1.9 1.2

5.7 4.3

PFOS

perfluorooctane sulfonate

71

73 (2)

78 (0.4)

2.6a

2.4c

b

0.9

3.3

PFHxA

perfluorohexanoate

85

67

83 (2)

1.4

3.0c

2.3

5.3

PFHpA

perfluoroheptanoate

79

63

75 (2)

1.7b

2.7c

2.1

4.8

PFOA

perfluorooctanoate

66

68

75 (0.2)

2.1a

2.4c

1.8

4.2

PFNA

perfluorononanoate

61

72

75 (0.2)

2.4a

2.0c

1.7

3.7

PFDA

perfluorodecanoate

63

80 (0.1)

71 (1)

2.8a

1.8c

1.6

3.3

PFDoDA PFTeDA

perfluorododecanoate perfluorotetradecanoate

32 5

73 (22) 58 (36)

58 (41) 84 (83)

3.5b 4.2b

1.2d 0.6d

0.8 0.4

2.0 0.9

FOSA

perfluorooctane sulfonamide

83

53 (2)

63 (4)

Values determined by Higgins and Luthy.22

b

Values extrapolated from these. c Values taken from Arp et al.23 d Values extrapolated from these.

equivalent for each analyte. The target analytes were PFCAs with chain lengths of 6 to 10, 12, and 14 carbons, PFSAs with perfluoroalkyl chains with 4, 6, and 8 carbons, and perfluorooctane sulfonamide (FOSA) (Table 1, information about supplier and purity can be found in Table S1 in the Supporting Information SI). Samples were taken from the freshly produced snow to determine the exact concentrations, which varied for the different analytes due to adsorption to the tubing during snowmaking. Three experiments were conducted. During the first experiment, the snow was melted the day after it had been made. This snow exhibited a relatively large initial specific snow surface area (SSA). The snow was melted from above with infrared light (Figure S1 in the SI). A cooling liquid flowing through the double sided bottom of the vessel prevented bottom melt. The meltwater was collected continuously from a hole in the bottom of the vessel. When 2 L had accumulated, the conductivity was measured, and a 120 mL aliquot was filled into a polypropylene-bottle for analysis. After approximately eight hours when all snow had melted, the vessel was rinsed with 120 mL of deionized water to collect the remaining particles. During the second and third experiment, snow was aged by applying six melt-freeze cycles over six days by increasing and decreasing the temperature of the cold room. This procedure caused the snow grains to grow substantially, leading to a relatively small SSA. No meltwater left the vessel during this procedure. Subsequently, the snow was melted as described above, but this time 1.7 L meltwater samples were taken to increase the sample frequency. The pH of the meltwater fractions was also recorded, and the aqueous particle rinse was followed by an additional solvent rinse of the vessel walls with 120 mL of methanol. During experiment 3, calcium chloride was spiked into the tap water to achieve a four to five times higher calcium concentration compared to experiment 2. The pressure of the deionized water supply in our laboratory is too low for use in the snow gun, which prevented us from making snow with a very low ion concentration. Extraction of Samples. Meltwater Samples. The extraction procedure is described in detail elsewhere.19 Briefly, formic acid and ammonium acetate were added to the samples. Subsequently, the samples were spiked with 50 μL of internal standard solution (MPFAC-MXA, Wellington, Guelph, Canada, containing 50 pg μL 1 each of 13C and 18O mass-labeled PFAAs in methanol, see Table S1 in the SI for a detailed list). Oasis HLB Plus solid phase

extraction (SPE) cartridges from Waters (Milford, MA) were conditioned with 20 mL of methanol and 1 mL of water. The samples were loaded, and the cartridges were washed with 2 mL of methanol/water (40/60) solution and dried by sucking laboratory air through them. Analytes were eluted with 8 mL of methanol, and the extracts were concentrated to 150 μL. A procedural blank extract was produced without using water by spiking the internal standards into the wash solution during SPE cleanup, followed by the procedure described above. Particle Samples and Methanol Rinse. The particle sample from experiment 1 was treated exactly as the water samples. As this did not result in satisfactory extraction recoveries for long chain compounds (0-45%) and ionization enhancement effects (recoveries >150%) for short chain compounds were observed, the particle sample and methanol rinse from experiments 2 and 3 were filtered over a glass fiber filter. The aqueous phase of the particle sample was then treated as the meltwater samples. The methanol rinse was evaporated to 150 μL and analyzed without further treatment. The filters (together with a blank filter) were extracted by sonication in 10 mL of methanol for 30 min. After centrifugation for 10 min at 3000 rpm the supernatant was transferred to a new vial. The extraction was repeated once, and the combined extracts were concentrated to 0.5 mL, cleaned-up by adding 25 mg of graphitized carbon and 50 μL of glacial acetic acid, vortexed, and centrifuged. The supernatant was removed and further concentrated to 150 μL. Quantified PFAA concentrations from the particle sample and methanol rinse, including the particles on the filters, were summed and are further referred to as the particle fraction. Instrumental Analysis. Prior to instrumental analysis 50 μL of a perfluoro-3,7-dimethyl branched decanoic acid (bPFDA) solution (20 pg μL 1 in methanol) was added to all extracts as a volumetric standard as well as 200 μL of 4 mM aqueous ammonium acetate. The instrumental analysis is described in detail elsewhere.20 Samples from experiments 1 and 2 were analyzed using a high performance liquid chromatograph Alliance 2695 (Waters) coupled to a Quattro II triple quadrupole mass spectrometer (Micromass, Altrincham, UK). An aliquot of 25 μL was injected onto an Ace C18 column (150 2.1 mm, 3 μm particles, Advanced Chromatography Technologies, Aberdeen, Scotland). For samples from experiment 3 an Acquity ultra performance liquid chromatograph 6873

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Figure 1. Change in conductivity and pH of the meltwater measured during all experiments and during experiments 2 and 3, respectively.

(Waters) coupled to a Xevo TQ-S triple quadrupole mass spectrometer (Waters) was used. An aliquot of 5 μL was injected onto an Acquity UPLC BEH C18 column (50 2.1 mm, 1.7 μm particles, Waters). On both instruments a binary gradient with 190 μL min 1 was run with buffered methanol and HPLC water (2 mM ammonium acetate). Ionization was achieved using negative electrospray ionization (ESI-). Mass-to-charge ratios of precursor and product ions, collision energies, and cone voltages for all analytes as well as other instrument specific parameters can be found in Table S1 in the SI. A one point calibration and a solvent blank were injected every 5 to 7 samples. The recoveries of the internal standards can be found in Table S2 in the SI. The quantified absolute PFAA concentrations are incidental, because they depend on the amount of analytes spiked into the water for snow making. The results are therefore presented as relative concentrations. Snow Melt Model. The model predicting mechanistically the elution of organic substances from a melting snowpack is described in detail elsewhere.18 In the model, equilibrium partitioning calculations within different layers of a multilayer snowpack iterate with calculations of downward analyte transport along with the percolating meltwater. Partitioning between the four phases aqueous meltwater, snow surface, air pore space, and particles is a function of chemical properties and snowpack characteristics. Model Input Parameters for Snow. The physical properties of the snowpack are described by the parameters snow density, SSA, liquid water content, particle content, permeability of the snowpack to particles, and snow depth.18 In the model the SSA was assumed to decrease linearly from 7500 to 2880 m2 m 3 during experiment 1 and from 2000 to 845 m2 m 3 during experiments 2 and 3. These values were estimated from snow macrophotographs taken during earlier studies,14 the derived effective snow grain diameter deff, and the formula SSA = 6/(deff 0.92) from Jacobi et al.21 In reality SSA may have decreased nonlinearly; however, the model output was hardly influenced by the assumed shape of the declining SSA trends. Model Input Parameters for Chemicals. Input values for the partition coefficients required by the model are given in Table 1. Those between organic matter and water (KOC) were taken from Higgins and Luthy;22 those for the partition coefficient between air and water (KAW) were the COSMOtherm predicted values from Arp et al.23 This software was found to perform best for fluorinated compounds, and the value for PFOA fits reasonably well with the only experimentally determined log KAW value of 2.99.24 Missing values of KOC and KAW for long chain PFCAs and some PFSAs were obtained by extrapolation (see Table S3 in the SI for details). These extrapolated KOC and KAW values are

highly uncertain. However, all compounds with extrapolated values (except PFHxS) are either very water-soluble or very hydrophobic, and the model results were relatively insensitive to the actual numerical values of log KAW and log KOC. A sensitivity analysis revealed that, aside from PFHxS, only PFDoDA and PFBS experienced slight changes in elution behavior due to variations of the extrapolated log KAW value by 1 order of magnitude. Further, the partition coefficients between snow grain surface and air (KIA) and snow grain surface and water (KIW) were required to run the model. However, sorption coefficients of PFAAs to the snow surface from either air or water have not been reported, and they could not be estimated using the available polyparameter linear free energy relationships, as these are not suitable for ionic substances.25 Therefore, KIW values were estimated using a model fitting procedure (see next section). KIA values could finally be calculated using the thermodynamic triangle log (KIW/m) = log KAW + log (KIA/m) (for a discussion of the applicability of this thermodynamic triangle see the SI in Meyer et al.18). Model Fitting Procedure. KIW values were selected for the various PFAAs that yielded a good agreement between measured and calculated elution profiles. This was done in steps: We first sought to obtain a good match between the measured and calculated elution profiles of one compound, PFNA. It became apparent that no good agreement could be obtained using a constant value of KIW for PFNA. We therefore also fitted the rate of change in KIW during the melt period to obtain a good fit. An initial log (KIW/m) of 3.7 that dropped logarithmically by 0.71 log units during the period of melting gave the best fit for the observed elution profile of PFNA during experiments 1 and 2, while it dropped by 0.35 log units from an initial value of 3.9 during experiment 3. In the next step, we fitted the KIW used for each PFAA. The KIW values obtained by this procedure are included in Table 1. Here, we assumed that the drop in the KIW during the snowmelt period should be the same for all PFAAs. The KIW and KIA values derived here should only be considered order of magnitude estimates. The uncertainties for their calculation lie especially in the uncertainties of the KAW values, the assumed decrease in KIW during melting, and the application of the thermodynamic triangle.

’ RESULTS AND DISCUSSION Meltwater Characteristics. Conductivity and pH changes during snowmelt are shown in Figure 1. The conductivity during all three experiments decreased exponentially, consistent with 6874



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Figure 2. Measured and simulated elution pattern (in %, y-axis) of PFCAs from a melting snowpack during experiments 1, 2, and 3. The x-axis shows the sample number, the last sample representing the particle bound fraction.

early eluting ions. Similar conductivity curves have been observed previously during similar snowmelt studies.15,26 Calcium and chloride ion concentrations during experiment 3 were initially four to five times higher than during the other experiments; therefore, the conductivity was very high in the first meltwater fractions. However, after the first 5 fractions the curves of all experiments resembled each other. The pH decreased from 9 to 8 during experiment 2. This was due to the tap water used for snow production, which contained high concentrations of hydroxide ions. As these ions were washed out at the beginning, the pH decreased. During experiment 3 the pH increased slightly from 7.5 to 7.8. The differences were due to differences in the tap water used. Natural snow is often acidic, containing hydronium ions, which, when washed out, results in an increase in pH during melting.15 Even though the pKa values for PFAAs are somewhat uncertain,27 one can assume that the PFAAs were completely dissociated within the pH ranges of the experiments. However, while the change in pH during melting should not have had any influence on the dissociation of PFAAs, it could still have influenced the surface properties of organic matter and snow.

Mass Balances of PFAAs during Snowmelt. The PFAA amounts found in all meltwater samples added up to between 32 and 85% of the amount in the freshly produced snow, except for PFTeDA with 5% during experiment 1 (Table 1). Losses might have been due to irreversible sorption to the vessel walls, sample bottles, or particles. Low mass balances for PFDoDA and PFTeDA during experiment 1 were most probably due to insufficient extraction of the particle sample using SPE cartridges or due to the fact that the vessel was not rinsed with methanol after snowmelt. The extraction of the particle fraction during experiments 2 and 3 was changed and resulted in more complete mass balances. An explanation for the relatively low mass balances for PFBS and PFHxS during the first experiment was not found. Measured Elution of PFAAs during Snowmelt. The measured elution profiles for different PFAAs from the melting snow are shown in Figures 2 and 3. PFAAs of different chain lengths behaved very differently during snowmelt and were effectively fractionated in the meltwater samples. Three types of elution were observed: a first flush elution, a peak elution in the middle of snowmelt, and a late elution. 6875



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Figure 3. Measured and simulated elution pattern (in %, y-axis) of PFSAs and FOSA from a melting snowpack during experiments 1, 2, and 3. The x-axis shows the sample number, the last sample representing the particle bound fraction.

The PFAAs with short perfluoroalkyl chains (PFHxA, PFHpA, and PFBS) were greatly enriched in the first meltwater fractions. This elution pattern, referred to as type 1 enrichment,28 is typical for relatively water-soluble chemicals such as atrazine,15,16 which are washed out of the snowpack by the first meltwater percolating downward through the snow. The PFAAs with long perfluoroalkyl chains (PFDoDA, PFTeDA) and the nonionic FOSA were enriched in the late meltwater and particle fractions. This behavior, termed enrichment type 2 or 3,28 depending on the extent of enrichment, is observed for substances that have a high affinity for snow grain surfaces and particles. Chemicals that are slightly less enriched (type 3) can become dissolved in the meltwater as the snow surface disappears toward the end of the snowmelt period. The elution pattern of PFAAs with an intermediate perfluoroalkyl chain length (PFOA, PFNA, PFDA, PFHxS, and PFOS) showed first increasing and then decreasing concentrations in meltwater, i.e. the chemicals were enriched in the middle of the melt period. With increasing chain length the peak in meltwater concentrations occurred later during the melt period PFDA and PFOS almost showed a type 3 elution. This type of elution has not been observed in melt experiments before for any other compound. The snowmelt model by Meyer and Wania has not predicted such behavior either.18 PFCAs showed the same elution pattern as PFSAs with one fluorinated carbon atom less, i.e. the elution profiles of PFOA and PFHxS and those of PFDA and PFOS matched each other (Figures 2 and 3). This suggests that the sulfonate group sorbs more strongly to the snow grain surface than the carboxylate group. Similar relative sorption behavior of PFCAs and PFSAs has been found by Higgins and Luthy for sediments.22 The results from experiments 1 and 2 demonstrate that the SSA had a major impact on the elution profile of the PFAAs. In general all compounds eluted earlier from the aged snow with the smaller SSA (experiment 2). This was especially apparent for the PFAAs with intermediate chain lengths, which showed enrichment in the middle of the melt period. For example, whereas the

elution profile of PFNA peaked after 2/3rd of the melt in experiment 1, the peak already occurred after 1/4th of the melt during experiment 2. The results from experiments 2 and 3 demonstrate that the increased ion concentration only had a minor impact on the elution profiles. The peaks in general eluted at the same time in both experiments. However, there were differences at the beginning of the elution with up to 2-fold increased elution of medium chain PFAAs in the first 1 2 fractions during experiment 3 compared to experiment 2. These were also the fractions where the difference in ion concentrations was largest. The ions, present at higher concentrations in experiment 3, may have competed with the PFAAs for sorption to the snow surface. Differences in the elution of long chain PFDoDA and PFTeDA at the end of snowmelt were most probably due to differences in particle content and composition. The particles originated from indoor air and thus may have been different in each experiment. Model-Simulated Elution of PFAAs during Snowmelt. The modeled elution patterns are included in Figures 2 and 3 for easy comparison with experimental results. The modified model was not only able to reproduce the previously observed enrichment of water-soluble and highly sorptive substances during the early and late phases of the melt period, it also succeeded in reproducing the enrichment of the PFAAs with intermediate chain lengths in the middle of the melt period. In particular, the good agreement between model and experiments for PFNA, which was due to the fitting of the log (KIW/m) and the rate of decrease of the log (KIW/m) of PFNA, showed that the assumption of a decreasing log (KIW/m) value during melting was sufficient to simulate concentrations in meltwater that increased and decreased as the melt progressed. The fitted increases in the sorption coefficients to the snow grain surface with increasing chain length were 0.4 0.65 log units per CF2 addition, while a change of the ionic moiety from carboxylate to sulfonate accounted for 0.4 0.5 log units. These changes in sorption to snow were similar to the changes in the sorption coefficients to sediments reported by Higgins and Luthy.22 6876


Environmental Science & Technology The good agreement between experimental and modeled elution lends support to the assumption that the rate of decrease in log (KIW/m) during melting was approximately the same for all PFAAs. Critical Parameters for the Elution of PFAAs during Snowmelt. Earlier studies had indicated that the elution of chemicals from a snowpack depends strongly on the snow-water partition coefficient (KIW),16 but no elution profile with a maximum in the middle of the snowmelt period had been observed previously. PFAAs are surface active chemicals, and thus a decline of the sorptive capacity of the snow surface during the melt may be more important for their elution behavior than for the neutral organic chemicals tested so far. The experiments revealed that the extent of PFAA retention in the snowpack decreased during melting. In particular, there appeared to be a threshold for the sorptive capacity of the snow grain surface below which a PFAA started to elute with the meltwater. Different PFAAs with different KIW reached that threshold at different times, leading to the observed fractionation of the PFAAs in the meltwater. The sorptive capacity of the snow grain surface for organic chemicals decreases during snowmelt partially due to the decrease in the SSA.14 However, the SSA decrease was not sufficient to reproduce the experimental elution profiles with the model. An additional decrease of the KIW values for PFAAs over the course of the melt period needed to be implemented to achieve agreement between experiment and simulation. A decrease in calcium ion concentrations was accompanied by a decrease in sorption of PFAAs from water to sediments.22 Also, decreasing pH has been shown to increase the sorption of PFAAs to sediments, due to changes in the charge of organic matter22 and mineral surfaces.29 If sorption to the snow surface would be similar to sorption to sediments, the increased ion concentration in experiment 3 should have led to an increase in sorption (increased KIW) and thus to a later elution. Our experiments, however, showed an opposite trend, with higher percentage elution (decreased KIW) for medium chain PFAAs (PFOA, PFNA, PFDA and PFHxS, PFOS) in the first fractions collected during experiment 3. The presence of calcium therefore affected the sorption of PFAAs to snow differently than the sorption to sediments. A decrease in pH on the other hand caused increased sorption to both snow surface and sediments. Experiment 3 showed slightly later elution of PFNA and PFDA compared to experiment 2, indicating increased sorption to snow at lower pH (0.5 log units lower pH during experiment 3 in the second half of the melt period, see Figure 1). For a detailed understanding of the mechanisms of sorption of PFAAs to the snow surface, further investigation is needed. Smaller scale experiments varying pH, ion concentrations, and particle content may be useful in this regard.

’ ASSOCIATED CONTENT

bS

Supporting Information. Information on the chemicals used, analytical instrumental parameters, recoveries of internal standards, extrapolation of the partition coefficients, and pictures of the snow chamber. This material is available free of charge via the Internet at http://pubs.acs.org.

’ AUTHOR INFORMATION Corresponding Author

*Phone: +49 341 235 1083. E-mail: [email protected]. Present Addresses §

Department Effect-Directed Analysis, Helmholtz Centre for Environmental Research UFZ, Permoserstrasse 15, 04318 Leipzig.

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’ ACKNOWLEDGMENT This study was financed by the Swedish Research Council FORMAS (project 216-2006-550). The research on snow of the Canadian authors was supported by the Natural Sciences and Engineering Research Council. ’ REFERENCES (1) Giesy, J. P.; Kannan, K. Global distribution of perfluorooctane sulfonate in wildlife. Environ. Sci. Technol. 2001, 35, 1339–1342. (2) Lau, C.; Anitole, K.; Hodes, C.; Lai, D.; Pfahles-Hutchens, A.; Seed, J. Perfluoroalkyl acids: A review of monitoring and toxicological findings. Toxicol. Sci. 2007, 99, 366–394. (3) Prevedouros, K.; Cousins, I. T.; Buck, R. C.; Korzeniowski, S. H. Sources, fate and transport of perfluorocarboxylates. Environ. Sci. Technol. 2006, 40, 32–44. (4) Ellis, D. A.; Martin, J. W.; De Silva, A. O.; Mabury, S. A.; Hurley, M. D.; Andersen, M. P. S.; Wallington, T. J. Degradation of fluorotelomer alcohols: A likely atmospheric source of perfluorinated carboxylic acids. Environ. Sci. Technol. 2004, 38, 3316–3321. (5) D’eon, J. C.; Hurley, M. D.; Wallington, T. J.; Mabury, S. A. Atmospheric chemistry of N-methyl perfluorobutane sulfonamidoethanol, C4F9SO2N(CH3)CH2CH2OH: Kinetics and mechanism of reaction with OH. Environ. Sci. Technol. 2006, 40, 1862–1868. (6) Dreyer, A.; Weinberg, I.; Temme, C.; Ebinghaus, R. Polyfluorinated compounds in the atmosphere of the atlantic and southern oceans: Evidence for a global distribution. Environ. Sci. Technol. 2009, 43, 6507–6514. (7) Stock, N. L.; Lau, F. K.; Ellis, D. A.; Martin, J. W.; Muir, D. C. G.; Mabury, S. A. Polyfluorinated telomer alcohols and sulfonamides in the north American troposphere. Environ. Sci. Technol. 2004, 38, 991–996. (8) Scott, B. F.; Spencer, C.; Mabury, S. A.; Muir, D. C. G. Poly and perfluorinated carboxylates in North American precipitation. Environ. Sci. Technol. 2006, 40, 7167–7174. (9) Kim, S. K.; Kannan, K. Perfluorinated acids in air, rain, snow, surface runoff, and lakes: Relative importance of pathways to contamination of urban lakes. Environ. Sci. Technol. 2007, 41, 8328–8334. (10) Liu, W.; Jin, Y. H.; Quan, X.; Sasaki, K.; Saito, N.; Nakayama, S. F.; Sato, I.; Tsuda, S. Perfluorosulfonates and perfluorocarboxylates in snow and rain in Dalian, China. Environ. Int. 2009, 35, 737–742. (11) Young, C. J.; Furdui, V. I.; Franklin, J.; Koerner, R. M.; Muir, D. C. G.; Mabury, S. A. Perfluorinated acids in Arctic snow: New evidence for atmospheric formation. Environ. Sci. Technol. 2007, 41, 3455–3461. (12) Lei, Y. D.; Wania, F. Is rain or snow a more efficient scavenger of organic chemicals?. Atmos. Environ. 2004, 38, 3557–3571. (13) Halsall, C. J. Investigating the occurrence of persistent organic pollutants (POPs) in the Arctic: their atmospheric behaviour and interaction with the seasonal snow pack. Environ. Pollut. 2004, 128, 163–175. (14) Meyer, T.; Lei, Y. D.; Wania, F. Measuring the release of organic contaminants from melting snow under controlled conditions. Environ. Sci. Technol. 2006, 40, 3320–3326. (15) Sch€ondorf, T.; Herrmann, R. Transport and chemodynamics of organic micropollutants and ions during snowmelt. Nord. Hydrol. 1987, 18, 259–278. (16) Meyer, T.; Lei, Y. D.; Muradi, I.; Wania, F. Organic contaminant release from melting snow. 1. Influence of chemical partitioning. Environ. Sci. Technol. 2009, 43, 657–662. (17) Plassmann, M. M.; Meyer, T.; Lei, Y. D.; Wania, F.; McLachlan, M. S.; Berger, U. Theoretical and experimental simulation of the fate of semifluorinated n-alkanes during snowmelt. Environ. Sci. Technol. 2010, 44, 6692–6697. (18) Meyer, T.; Wania, F. Modeling the elution of organic chemicals from a melting homogeneous snow pack. Water Res. 2011, 45, 3627–3637. (19) McLachlan, M. S.; Holmstrom, K. E.; Reth, M.; Berger, U. Riverine discharge of perfluorinated carboxylates from the European continent. Environ. Sci. Technol. 2007, 41, 7260–7265. 6877



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(20) Holmstr€om, K. E.; Berger, U. Tissue Distribution of perfluorinated surfactants in Common Guillemot (Uria aalge) from the Baltic Sea. Environ. Sci. Technol. 2008, 42, 5879–5884. (21) Jacobi, H. W.; Domine, F.; Simpson, W. R.; Douglas, T. A.; Sturm, M. Simulation of the specific surface area of snow using a onedimensional physical snowpack model: implementation and evaluation for subarctic snow in Alaska. Cryosphere 2010, 4, 35–51. (22) Higgins, C. P.; Luthy, R. G. Sorption of perfluorinated surfactants on sediments. Environ. Sci. Technol. 2006, 40, 7251–7256. (23) Arp, H. P. H.; Niederer, C.; Goss, K. U. Predicting the partitioning behavior of various highly fluorinated compounds. Environ. Sci. Technol. 2006, 40, 7298–7304. (24) Li, H. X.; Ellis, D.; Mackay, D. Measurement of low air-water partition coefficients of organic acids by evaporation from a water surface. J. Chem. Eng. Data 2007, 52, 1580–1584. (25) Roth, C. M.; Goss, K. U.; Schwarzenbach, R. P. Sorption of diverse organic vapors to snow. Environ. Sci. Technol. 2004, 38, 4078–4084. (26) Meyer, T.; Lei, Y. D.; Muradi, I.; Wania, F. Organic contaminant release from melting snow. 2. Influence of snow pack and melt characteristics. Environ. Sci. Technol. 2009, 43, 663–668. (27) Burns, D. C.; Ellis, D. A.; Li, H.; Mcmurdo, C. J.; Webster, E. Experimental pKa determination for perfluorooctanoic acid (PFOA) and the potential impact of pKa concentration dependence on laboratory-measured partitioning phenomena and environmental modeling. Environ. Sci. Technol. 2008, 42, 9283–9288. (28) Meyer, T.; Wania, F. Organic contaminant amplification during snowmelt. Water Res. 2008, 42, 1847–1865. (29) Johnson, R. L.; Anschutz, A. J.; Smolen, J. M.; Simcik, M. F.; Penn, R. L. The adsorption of perfluorooctane sulfonate onto sand, clay, and iron oxide surfaces. J. Chem. Eng. Data 2007, 52, 1165–1170.

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