Theoretical and Experimental Simulation of the Fate of

Aug 12, 2010 - Department of Applied Environmental Science (ITM),. Stockholm ... with different chain lengths and degrees of fluorination using the. S...
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Environ. Sci. Technol. 2010, 44, 6692–6697

Theoretical and Experimental Simulation of the Fate of Semifluorinated n-Alkanes during Snowmelt M E R L E M . P L A S S M A N N , * ,† TORSTEN MEYER,‡ YING DUAN LEI,‡ FRANK WANIA,‡ MICHAEL S. MCLACHLAN,† AND URS BERGER† Department of Applied Environmental Science (ITM), Stockholm University, 10691 Stockholm, Sweden and Department of Physical and Environmental Sciences, University of Toronto Scarborough, 1265 Military Trail, Toronto, Ontario, M1C1A4 Canada

Received May 8, 2010. Revised manuscript received July 15, 2010. Accepted July 20, 2010.

Semifluorinated n-alkanes (SFAs) are highly fluorinated anthropogenic chemicals that are released into the environment through their use in ski waxes. Nothing is known about their environmentalpartitioningingeneralandtheirfateduringsnowmelt in particular. Properties were estimated for a range of SFAs with different chain lengths and degrees of fluorination using the SPARC calculator and poly parameter linear free energy relationships (ppLFERs). The calculations resulted in very low water solubility and vapor pressures and, consequently, high log KOW and log KOA values. Artificially produced snow in a cold room was spiked with a range of SFAs and subsequently melted with infrared lamps. Melt water, particles, and air samples taken during melting were analyzed. Both calculations and experiments showed that SFAs used in ski waxes will bind to particles or snow grain surfaces during snowmelt and thus are predicted to end up on the soil surface in skiing areas.

Introduction The combination of hydrophobic and lipophobic properties makes highly fluorinated organic chemicals suitable for application in many consumer products including coatings, repellents, and additives in fire-fighting foams (1, 2). Most of these chemicals are either very persistent or are degraded to persistent perfluorinated chemicals and are widespread in the environment, even in remote regions (3). Semifluorinated n-alkanes (SFAs) with the general formula F(CF2)n(CH2)mH (or, briefly FnHm) constitute a group of highly fluorinated chemicals whose environmental behavior is so far unknown. They are used in ski waxes to reduce friction and repel dirt, which enhances the glide. Mostly applied in cross-country skiing, fluorinated waxes can contain up to 15% SFAs with chain lengths of n ) 6-16 and m ) 14, 16, and 18 (4) (further referred to as long-chain SFAs). In addition to long-chain SFAs, the corresponding semifluorinated n-alkenes (SFAenes) with the general formula F(CF2)nCHd * Corresponding author phone: +46 8674 7188; e-mail: [email protected]. † Stockholm University. ‡ University of Toronto Scarborough. 6692

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CH(CH2)m-2H (or, briefly FnHmene) have been detected in fluorinated ski waxes (4). Perfluorinated alkanes are also used in ski waxes, and several other fluorinated chemicals such as triblock SFAs (5) and tetrakis(perfluoroalkyl)alkane (6) are under discussion for addition to ski waxes. The current worldwide production of fluorinated ski waxes has been roughly estimated to be several tons per year (personal communication with the ski wax manufacturer Rex, Finland). Short-chain SFAs with chain lengths of up to 14 carbon atoms have been tested for medical applications such as oxygen carriers (7) and tamponades in ophthalmology (8). However, to the best of our knowledge, SFAs are primarily released to the environment through skiing activities. Recently developed analytical methods revealed concentrations of various SFAs between 1 and 1260 ng L-1 in snow samples (analyzed as meltwater) from a small skiing area in Sweden (4). The purpose of this study was to predict and understand the environmental distribution and fate of SFAs after abrasion from the ski base onto snow. This was done by a combination of model calculations and snowmelt experiments. Physicochemical properties of SFAs were estimated and used to predict their distribution in a snowpack. Snow melt experiments were conducted to understand the distribution of SFAs during and after snowmelt and the results were compared with the predicted distribution.

Experimental Section Estimation of Physicochemical Properties. To estimate the partitioning properties and phase distribution of SFAs, software packages and poly parameter linear free energy relationships (ppLFERs) were used. Melting point temperatures of SFAs with various chain lengths were predicted using the quantitative structure-activity relationship (QSAR) MPBPWIN v 1.42 within EpiWin (9). These melting points, together with SMILES strings, were entered into the SPARC calculator v 4.2 (released August 2007) to estimate boiling point, vapor pressure, water solubility, Henry’s law constant (H: in water, Hhexadecane: in hexadecane, both in Pa m3 mol-1) and the unitless partition coefficient between octanol and water (KOW). SPARC (10) determines physical properties by using molecular descriptors defined by the molecular structure of a compound (11, 12). Subsequently the unitless partition coefficient between air and water (KAW) was calculated using: KAW ) H/RT with R being the ideal gas constant (8.314 Pa m3 K-1 mol-1), and T being the absolute temperature in K. The unitless partition coefficient between octanol and air (KOA) could then be derived using: log KOA ) log KOW - log KAW When predicting the fate of a chemical in a snowpack, the distribution between the snow grain surface, organic matter (represented by humic acid content), air, and meltwater is decisive. Therefore, besides KAW, estimates of the partition coefficients between the snow grain surface and air (KIA) and between humic acid and air (KHA/A) were needed. They were obtained using ppLFERs by Roth et al. (13, 14) and Niederer et al. (15), respectively. These ppLFERs required the input of various solute descriptors, namely A and B (hydrogen bond acidity and basicity, respectively), V (McGowan volume), and S (polarizability). These were estimated by Absolv in ADME suite (version 3.5, ACD/Laboratories, 10.1021/es101562w

 2010 American Chemical Society

Published on Web 08/12/2010

Toronto, Canada). As Α and Β were estimated to be 0 for SFAs due to the absence of functional groups in the molecules, the equations by Roth et al. (13, 14) are simplified to single parameter LFERs: log (KIA /m)(-6.8 °C) ) 0.639 log L16 - 6.85 or log (KIA /m)(15 °C) ) 0.635 log L16 - 8.47 with L16 being the partition coefficient between hexadecane and air (calculated by L16 ) RT/Hhexadecane). The log KIA value was temperature corrected to 0 °C using: log(KIA/m)(T) ) log(KIA/m)(Tref) + ∆HIA / (2.303R)(1/T - 1/Tref) where ∆HIA is the enthalpy of sorption, estimated using a single parameter LFER by Roth et al. (13): ∆HIA ) -5.52 · ln(KIA /m)(15 °C) - 107 Finally, the unitless partition coefficient between humic acid and air (KHA/A) was calculated using a ppLFER developed by Niederer et al. (15): log KHA/A(0 °C) ) 0.85 log L16 + 0.13V + 1.34S - 0.82 Chemicals. The SFAs F6H8, F6H14, F8H10, and F8H16 of unspecified purity were obtained from ABCR (Karlsruhe, Germany). F10H2 (97% purity) was obtained from Apollo Scientific (Stockport, England). F6H16, F10H16, F12H14, and F12H16ene (all of purity >95%) were custom synthesized by Synthon-Lab Ltd. (St. Petersburg, Russia). Cyclohexane (AnalaR NORMAPUR) was obtained from VWR BDH Prolabo (West Chester, PA). Snow Chamber Experiments. The method for producing snow is given in detail elsewhere (16, 17). Minor modifications to this method were made in the present study and are described here. Artificial snow was produced with a snow gun in a cold room at temperatures below -20 °C. This resulted in pellet-shaped snow grains with a diameter of approximately 100 µm, a density of 0.16 ( 0.01 g cm-3, and a specific surface area (SSA) of 580 ( 50 cm2 g-1 (16). The snow was collected in a rectangular steel vessel (0.24 m3, height 40-50 cm, length 100 cm, width 55 cm) with a conical shaped bottom leading to a meltwater outflow. A solution containing the above-listed SFAs in 10 mL of cyclohexane (at amounts ranging from 2 to 200 µg total for the different SFAs, depending on their instrumental response) was applied as evenly as possible to the top of the snow surface using a glass pipet. The amount of spiked SFAs was chosen to ensure detection of 1% or less in single samples with the applied methods (see below). Immediately after spiking a lid was placed on the vessel and sealed using silicone. Air sampling was started at once by drawing 2 mL min-1 through an Isolute ENV+ solid phase extraction (SPE) cartridge connected to a hole in the lid using a personal sampling pump 400S from BGI (Waltham, MA). Air inflow was presumably provided through the meltwater outlet in the bottom of the vessel. The vessel was left overnight in the cold room, which was allowed to warm up, but did not exceed -5 °C. This caused the snow to age slightly, resulting in a somewhat lower SSA (18). The next day melting was induced by infrared lamps directed to the side walls of the vessel, heating them up and thus slowly causing the snow to melt (see Figure S1 in the Supporting Information (SI)). This procedure might differ slightly from natural conditions, as it also caused some of the snow at the bottom of the vessel to melt early in the process, which might have led to different partitioning of SFAs between particles and the vessel walls. Melt water samples of 500 mL each

were collected through the outlet at the bottom of the vessel. Air sampling cartridges were exchanged regularly, resulting in a total of 6 samples (C1: 0-4.6 h, C2: 4.6-20.6 h C3: 20.6 (start of snowmelt) - 22.1 h, C4: 22.1-23.6 h, C5: 23.6-25.1 h, and C6: 25.1-28.5 h (end of melting)). The particles remaining in the vessel after all snow had melted were rinsed out using 500 mL of deionized water. The particles originated from the water used for snow production and from the air in the cold room. Afterward the vessel walls were rinsed with 200 mL of cyclohexane to extract adsorbed SFAs and to rinse out residual particles. This sample is hereafter referred to as solvent rinse. The whole experiment was performed twice. After the second experiment some paper towels soaked in cyclohexane were additionally used to clean the vessel walls and subsequently analyzed to determine if adsorbed SFAs had been collected quantitatively in the solvent rinse. Extraction of Samples. Meltwater, Particles, and Solvent Rinse. The extraction methods are described in detail elsewhere (4). Briefly, water samples and the particles collected in deionized water were extracted twice by liquid-liquid extraction (LLE) using 30 mL of cyclohexane. The paper towels used in the second experiment were extracted twice with cyclohexane by sonication for 10 min. The combined extracts as well as the solvent rinse were concentrated to 0.5 mL using nitrogen and purified using a silica SPE cartridge (1 g, 6 mL, Agilent Technologies, Santa Clara, CA). The cartridges were conditioned with 3 mL of cyclohexane, then the sample extracts were applied and SFAs were eluted using 5 mL of cyclohexane. The extracts were concentrated to 0.5 mL, and 5 µL of F8H10 solution (500 µg mL-1 in cyclohexane) was added as volumetric standard, prior to analysis by GC-ECD (see below). Air. Before sampling, the Isolute ENV+ cartridges were conditioned with 3 mL of cyclohexane and dried by drawing air through them for 2 min using a vacuum manifold. After sampling, the SFAs were eluted from the cartridges using 10 mL of cyclohexane, which was concentrated to 0.5 mL and spiked with 5 µL of F8H10 solution (see above) prior to analysis by GC-ECD. Instrumental Analysis and Quantification. A gas chromatograph (Agilent 6890N) equipped with an electron capture detector (GC-ECD) was employed for analysis. Samples (1 µL) were injected at an inlet temperature of 250 °C in splitless mode. Analytes were separated on a HP-5 GC column (60 m length, 0.25 mm i.d., 0.25 µm film thickness, Agilent) using helium as the mobile phase (column head pressure 22 psi). Chromatographic separation was achieved with a temperature program starting at 60 °C followed by a ramp of 5 °C min-1 to 300 °C, which was held for 5 min. The detector temperature was 320 °C and nitrogen was used as make up gas at a pressure of 60 psi. An external eight-point calibration curve was analyzed with every sample batch. To ensure the quality of the extraction methods, recoveries were tested during each snow experiment. Standard mixtures containing all SFAs in cyclohexane at three different concentration levels (spanning 2 orders of magnitude) were spiked into 500 mL of tap water or on Isolute ENV+ cartridges (with subsequent pumping of 0.24 m3 air) and extracted as described above. Extraction blanks were conducted by extracting 500 mL of tap water and air sampling cartridges (after pumping 0.24 m3 laboratory air). Quantification was done externally using the eight-point calibration curve after area normalization by the areas of the volumetric standard F8H10. No correction for recoveries was made.

Results and Discussion Estimation of Physicochemical Properties. All properties were calculated for SFAs with a wide range of chain lengths (as displayed in the chemical space plots below). However, VOL. 44, NO. 17, 2010 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

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TABLE 1. Physicochemical Properties (at 25 °C if Not Otherwise Stated) of SFAs Derived from SPARC and ppLFERs (The Calculated Values Are Rough Estimations Which Could Deviate by up to 3 Orders of Magnitude from the Real Values) F10H2 melting point (°C)a vapor pressure (Pa)b,f boiling point (°C)b water solubility (mg L-1)b,f henry Constant (Pa m3 mol-1)b L16 b Sc Vc log KOWb log KOA log KAW log (KIA/m) (0 °C)d log KHA/A (0 °C)e

F6H14

F6H16

F8H16

F10H16

F12H14

F12H16

F12H16ene

-9.45 696 56

4.96 5.8 340

F6H8

67.3 5.4 × 10-4 481

86.2 1.9 × 10-5 329

108 2.6 × 10-6 569

130 4.6 × 10-7 608

134 3.8 × 10-6 587

144 1.3 × 10-7 637

140 8.7 × 10-7 656

2 × 10-4

1.6 × 10-3

9.6 × 10-8

2.2 × 10-9

7.6 × 10-12

1.2 × 10-14

6 × 10-16

1.1 × 10-17

5.3 × 10-14

1.9 × 109

1.6 × 106

4.2 × 106

5.5 × 106

2.6 × 108

3.3 × 1010

6.9 × 1012

1.1 × 1013

1.4 × 1010

2.8 -1.14 2.17 9.2 3.4 5.9 -5.1 0.3

5.7 -0.62 2.31 8.4 5.6 2.8 -3.2 3.5

8.9 -0.6 3.16 11.5 8.3 3.2 -1.1 6.3

10.0 -0.59 3.44 12.6 9.2 3.3 -0.5 7.3

10.3 -0.83 3.79 14.6 9.6 5.0 -0.2 7.3

10.5 -1.08 4.14 17.0 9.8 7.1 -0.1 7.2

9.5 -1.34 4.21 18.5 9.0 9.4 -0.8 6.0

10.6 -1.33 4.49 19.6 9.9 9.7 -0.1 7.0

9.4 -1.23 4.45 16.4 9.6 6.7 -0.8 6.1

a Values calculated by EpiWin. b Values calculated by SPARC. c Values calculated by ADME. d Roth et al. (13, 14). Niederer et al. (15). f Nonsubcooled properties were calculated, as SFAs present in ski waxes are abraded onto the snow in their solid or crystalline form. e

values are reported here only for the SFAs that were also included in the experimental part of the study (Table 1); values for other chain lengths can be found in Table S1 in the SI. According to the calculations SFAs exhibit low vapor pressures (except for short-chain SFAs not used in ski waxes), extremely low water solubilities, and high Henry’s law constants. SFAs very much favor octanol over water, which is expressed in high log KOW values of 8.4 and more (Table 1). Relatively low log KOA and log KHA/A values were estimated for short-chain SFAs (due to higher vapor pressure), but very high log KOA and log KHA/A values were estimated for longchain SFAs used in ski waxes (above 9.0 and 6.0, respectively). The log KHA/A values decrease with increasing fluorinated chain length of FnHm for any given m (see Table 1 for e.g., m ) 16). This result is counterintuitive. It is caused by the calculated S values, which are negative and decrease with increasing fluorinated chain length. This is an artifact of the way the Absolv program calculates these values (19). The S values given in Tables 1 and S1 might thus not well reflect the real values. However, the differences between the estimated log KHA/A values of long-chain SFAs are small. Additionally, the predicted distribution of SFAs in snow and after snowmelt (see below) is not sensitive to changes in log KHA/A values. Therefore the values were used as calculated. The log KAW values span over a wide range of 2.2 to 8.3, increasing with the length of the fluorinated chain. However, the partitioning between air and water might be irrelevant for long-chain SFAs, as they will adsorb to particles present in both the air and water compartment. Even in the absence of particles, SFAs might stick to any surface present, including the air-water interface itself, or they might form micelles (20). Short-chain SFAs showed a low partitioning to the snow grain surface from air with a log (KIA/m) as low as -5.1, while values for long-chain SFAs are close to 0. Previous studies mentioned that the use of L16 in ppLFERs underestimates the adsorption to snow or water surfaces and that the use of molar refractivity would be preferable for highly fluorinated chemicals (21, 22). This implies that the real KIA values of SFAs might be even higher than the estimated values given in Tables 1 and S1. However, this does not change the overall trends based on chain length. To put these values into relation with other organic chemicals, SFAs were added to a chemical space plot from Brown and Wania (23) including 1460 organic chemicals (Figure 1). Figure 1 shows that the short-chain SFAs exhibit log KOA and log KAW values similar to other chemicals (F6H8 lies close to fluorotelomer alcohols (FTOHs) and decamethylcyclopentasiloxane (D5) in the plot), while the long6694

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FIGURE 1. Organic contaminants plotted in a log KOA vs log KAW chemical space from Brown and Wania 2009 (23). Values were added for SFAs, fluorotelomer alcohols (FTOHs) (24, 25), and decamethylcyclopentasiloxane (D5) (26). chain SFAs lie outside the range of all other chemicals. This is predominantly due to extraordinarily high log KAW values of SFAs. Addition of two carbon atoms to the fluorinated part of SFAs increases both the log KAW and log KOW values by about two units, while the addition of two hydrogenated carbon atoms has a comparatively minor influence on log KAW and log KOW. On the other hand, adding two hydrogenated carbon atoms increases log KOA by about one unit, while the addition of fluorinated carbon atoms has little influence. The uncertainty in the calculated properties is unknown. The accuracy is possibly low due to the fact that SPARC has not been calibrated for SFAs and different versions of the software have been shown to calculate varying values (21). However, SPARC has at the same time been shown to give reasonable estimates of the properties of various other fluorinated compounds (21). Estimation of Phase Distribution of SFAs in Snow. Chemicals can be present in different compartments of the bulk snow, i.e., sorbed to the snow grain surface or organic matter, dissolved in meltwater, or as vapors in the pore space. The relative affinity of chemicals for the different compartments is expressed by partition coefficients, and the dominant phase in which a chemical partitions can be displayed in chemical space plots using these partition coefficients as

FIGURE 2. Plots of the chemical space defined by the partition coefficients between humic acid and the gas phase log KHA/A and between the snow grain surface and the gas phase log (KIA/m). The estimated equilibrium phase distribution of SFAs with different chain lengths and different degrees of fluorination is shown. A snowpack with characteristics comparable to those in the snow used in the experiments is shown at an early (a) and late (b) stage of snowmelt (for details see text). coordinates (17, 27). Figure 2 shows the chemical space plot for a snowpack with properties comparable to that used in the experimental part of the study, using log (KIA/m) and log KHA/A as the coordinates and assuming a fixed log KAW value of 1.7 (the smallest estimated value for all plotted SFAs, see Table S1 in the SI). The use of KHA/A to describe partitioning to particles in snow implies the assumption that the sorption capacity of the particles is entirely due to the organic matter in those particles. If atmospheric aerosols are the major source of particles in natural snow, then there are other partition coefficients that may be more appropriate (28, 29). Figure 2 only shows regions of predominant partitioning to the snow grain surface, air pore space, and organic matter, but not to meltwater. However, for chemicals with log KAW values as high as for the SFAs (see Table 1), partitioning to the meltwater is estimated to be negligible (less than 0.15%), which makes the use of log KAW as a third dimension in the chemical space redundant (17, 27). The location of the lines separating the regions of dominant phase partitioning in Figure 2 depends on the composition of the snow (density and porosity, SSA, concentration of organic matter) (17). The snow properties used in the construction of Figure 2 were estimated based on measurements of artificial snow produced similarly to the snow in the experimental part of this study (16, 17). For the slightly aged and melting snowpack depicted in Figure 2a, a snow density of 0.2 g cm-3 with a SSA of 400 cm2 g-1, an organic matter concentration of 5 mg L-1, and a water content of 6% was applied. At a late stage of melting, when only 5% of the original amount of snow was left (Figure 2b), the snowpack was assumed to have a snow density of 0.25 g cm-3 with a SSA of 100 cm2 g-1, an organic matter concentration of 100 mg L-1, and a water content of 6%. The SFAs are predicted to be present in different compartments depending on their chain length (Figure 2a). Short-chain SFAs are predominantly present in the snow pore space, while long-chain SFAs used in ski waxes have a preference for the snow grain surface, but may also be found sorbed to the organic matter in snow. The addition of two fluorinated carbon atoms slightly increases the preference for the snow grain surface (shift to the upper left), which is mostly due to a decrease in log KHA/A values and thus might not be entirely correct (see explanation above). The addition of two hydrogenated carbon atoms does not result in a notable change in the phase distribution between snow grain surface and organic matter, despite causing a larger change in the partitioning properties (shift to the upper right). The distribution of SFAs in snow can be compared with FTOHs

and PCBs, which are discussed in Meyer and Wania 2008 (27). FTOHs show a distribution similar to that of mediumchain SFAs (FnH10 and FnH12) and will also be found partly adsorbed to particles and partly to the snow grain surface. PCBs, in contrast, are bound only to particles. However, all of these compounds (PCBs, FTOHs, and SFAs) would probably end up on the underlying compartment (in the environment usually soil) after snowmelt. At a late stage of the melting process, the SSA has decreased and the amount of particles has increased relative to the amount of snow left (Figure 2b). This results in a larger fraction of long-chain SFAs becoming bound to particles. The phase partitioning calculations thus suggest that as the snow grain surface gradually disappears during melting, long-chain SFAs will increasingly sorb to the organic particles present in the snow, whereas short-chain SFAs will volatilize from the snowpack. FnH2 and FnH4 will presumably already volatilize from the freshly produced snow, while FnH6 would likely partly volatilize later during the melting process and partly bind to the organic carbon. The uncertainties in the calculations make it difficult to predict at which chain length volatilization is not significant any more. However, even if the calculated values would deviate by up to 3 orders of magnitude from the real values, the long-chain SFAs would still be predicted to bind to particles or other surfaces during the snowmelt process. Experimental Snowmelt Study. Extraction and Instrumental Analysis. Analytical recoveries of all SFAs spiked into both water and air sampling cartridges were generally 62-105% for all three spike levels, except for F10H2 and F6H8, which showed low recoveries for extraction from water (0-9.4% and 0-44.7%, respectively). This might be due to their high vapor pressure causing evaporative losses during spiking and volume reduction. Low recoveries for these compounds were considered acceptable as the short-chain SFAs are not used in ski waxes and are therefore not of environmental concern, but had only been included in the study to evaluate the effect of differences in SFA chain lengths. Results for F10H16 are not presented, because interfering peaks and nonreproducible recoveries prevented reliable quantification. Except for F10H16, the quantification applying GCECD was accurate for the kind of samples analyzed in this study. Given the good recoveries, no blank problems and low limits of detection enabling quantification of 1% or less of the spiked amount of SFAs in single samples, the analytical methods were evaluated as suitable for the purpose of this study. VOL. 44, NO. 17, 2010 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

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FIGURE 3. Recoveries of SFAs in different compartments after snowmelt (average of two replicates). The meltwater represents only the last water sample with a high particle content.

FIGURE 4. Volatilization of short-chain SFAs over time for the six air samples C1 to C6 during the snowmelt experiments, illustrated in average percentage with error bars showing the individual values for the two experiments. The sum of all six samples was normalized to 100%. C1 and C2 are samples taken after snow production, C3 to C6 were sampled during the melting process; for a detailed sample description of C1 to C6 see experimental section. Distribution of SFAs. A mass balance analysis showed that in both experiments between 36 and 85% of the spiked amounts of SFAs were recovered in the analyzed samples (air, meltwater, particles, and solvent rinse), except for F10H2 with only 10% (Figure 3). Losses may have occurred due to volatilization prior to closing the vessel lid, during air sampling (for example as a result of cartridge breakthrough of F10H2), or during the analytical procedure (see above). No explanation could be found for the somewhat lower total recovery of F12H16 compared to the other long-chain SFAs (Figure 3). Overall recoveries for all SFAs were comparable between the first and second experiments, which led to the conclusion that the solvent rinse quantitatively extracted adsorbed SFAs from the vessel walls. The paper towel rinse (accounting for maximum 5% recovery) and solvent rinse were thus added in the second experiment. The two experiments gave in general very similar results, therefore, average results from both experiments are discussed hereafter. Figure 3 shows the distribution of SFAs between the different sample types during the experiment. The divergent behavior of short and long-chain SFAs is evident. F10H2 and F6H8 were detected solely in air samples, whereas none of the long-chain SFAs were detected in any of the air samples. The temporal trend of the volatilization of F10H2 and F6H8 during the experiments is displayed in Figure 4. F10H2 already evaporated to a large extent during the dry aging of the snow, while only a remnant of 5% was released during the melt. F6H8 also volatilized largely during aging (57%), but also 6696

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during the later stages of melting, when the snow grains disintegrate and the snow grain surface area decreases rapidly. F10H2 is clearly more volatile than F6H8, which is consistent with the estimated lower (KIA/m) values. This could be due to both a shorter carbon chain and a higher degree of fluorination. The finding that F6H8 volatilized almost quantitatively seems to be in disagreement with the calculations, which predicted approximately 10% of F6H8 to partition to air in both fresh and aged snow (see Figure 2). However, the calculations predicted the equilibrium phase distribution, whereas during the experiments the air from the pore space was constantly removed and thus F6H8 probably underwent successive desorption from the snow grain surface. Long-chain SFAs (F6H14 and longer) all showed a very similar phase distribution (Figure 3). A minor fraction (less than 6%) was found in the very last meltwater sample with a high particle content. Between 20 and 30% was associated with the particles that remained in the bottom of the vessel after melting, while the largest fraction was present in the solvent rinse, i.e., adsorbed to the vessel walls or to particles still present in the vessel after rinsing with deionized water. Not all SFAs might have come in contact with particles during melting and thus the vessel bottom was the surface they adsorbed to after having been released from the snow. The concentration of organic matter present in the snow has been estimated in earlier studies to be in the range of 1-10 mg L-1, which are concentrations resembling the ones in natural snow (30). The extraordinary low water solubility and low vapor pressure of long-chain SFAs prevented them from dissolving in the meltwater or evaporating from the snow surface. Fate of Long-Chain SFAs after Snowmelt. The results of the experiments showed that SFAs used in ski waxes will eventually be released to the underlying ground, either because they sorb to particles in the snow, or when the last snow grain surface disappears. The calculations showed that SFAs will be sorbed to the snow grain surface with a shift toward the particles (or other surfaces) at the end of the melting process. This would also explain the large fraction of SFAs found adsorbed to the vessel walls in the experiments. The results obtained for long-chain SFAs with both methods, theoretical calculations and snowmelt experiments, agreed well with each other, despite uncertainties in the calculations. Long-chain SFAs found in ski waxes would not be expected to volatilize notably even under natural conditions, where they may stay in the snow for many weeks before and during melting. No experiments have so far been performed on degradation of these compounds, which might be limited in snow, but could occur at higher ambient temperatures in soil after snowmelt. Comparing the snow chamber behavior of SFAs to other chemicals tested earlier with the same experimental setup, SFAs will exhibit a final fate similar to three PAHs (phenanthrene, pyrene, and benzo(ghi)perylene) (17). These also showed a peak release at the end of the melt, associated with particles and the solvent rinse. However, a small percentage of the PAHs was also found in earlier meltwater fractions (17), which was not the case for SFAs. Where SFAs sorbed to particles during snowmelt will finally accumulate depends on the fate of these particles. Particles were found to coagulate during melt-freeze cycles and tend to accumulate on top of the snow (31-34). Three factors determine where meltwater and particles end up, i.e., the nature of the terrain (flat or mountainous), the state of the soil during melting (frozen and thus impermeable for meltwater, or not), and the intensity of melting. In flat terrain the latter two factors are almost negligible. The snow will melt on the spot and thus SFAs will end up on the underlying soil surface, vegetation, or water (ski tracks on frozen lakes). However, in mountainous terrain the meltwater may flow to

rivers and streams carrying a high particle load, especially if the ground is frozen and the melting is intense. What is the fate of SFAs released from the snow? Degradation or summer time volatilization from soil or water surfaces might occur. However, it is also possible that SFAs (or their degradation products) accumulate over years in skiing areas. This might eventually lead to concentrations that trigger effects in vulnerable ecosystems.

Acknowledgments We thank Trevor Brown for supplying us with the data for Figure 1. This study was financed by the Swedish Research Council FORMAS (project 216-2006-550).

Supporting Information Available A table containing the calculated properties for all SFAs displayed in Figure 2 and pictures of the snowmelt vessel during the melting process. This information is available free of charge via the Internet at http://pubs.acs.org.

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