Environ. Sci. Technol. 2006, 40, 1862-1868
Atmospheric Chemistry of N-methyl Perfluorobutane Sulfonamidoethanol, C4F9SO2N(CH3)CH2CH2OH: Kinetics and Mechanism of Reaction with OH JESSICA C. D’EON,† MICHAEL D. HURLEY,‡ TIMOTHY J. WALLINGTON,‡ AND S C O T T A . M A B U R Y * ,† Department of Chemistry, University of Toronto, 80 St. George Street, Toronto, Ontario, Canada M5S 3H6, Ford Motor Company, SRL 3083, P.O. Box 2053, Dearborn, Michigan, 48121-2053
Relative rate methods were used to measure the gasphase reaction of N-methyl perfluorobutane sulfonamidoethanol (NMeFBSE) with OH radicals, giving k(OH + NMeFBSE) ) (5.8 ( 0.8) × 10-12 cm3 molecule-1 s-1 in 750 Torr of air diluent at 296 K. The atmospheric lifetime of NMeFBSE is determined by reaction with OH radicals and is approximately 2 days. Degradation products were identified by in situ FTIR spectroscopy and offline GC-MS and LC-MS/MS analysis. The primary carbonyl product C4F9SO2N(CH3)CH2CHO, N-methyl perfluorobutane sulfonamide (C4F9SO2NH(CH3)), perfluorobutanoic acid (C3F7C(O)OH), perfluoropropanoic acid (C2F5C(O)OH), trifluoroacetic acid (CF3C(O)OH), carbonyl fluoride (COF2), and perfluorobutane sulfonic acid (C4F9SO3H) were identified as products. A mechanism involving the addition of OH to the sulfone double bond was proposed to explain the production of perfluorobutane sulfonic acid and perfluorinated carboxylic acids in yields of 1 and 10%, respectively. The gas-phase N-dealkylation product, N-methyl perfluorobutane sulfonamide (NMeFBSA), has an atmospheric lifetime (>20 days) which is much longer than that of the parent compound, NMeFBSE. Accordingly, the production of NMeFBSA exposes a mechanism by which NMeFBSE may contribute to the burden of perfluorinated contamination in remote locations despite its relatively short atmospheric lifetime. Using the atmospheric fate of NMeFBSE as a guide, it appears that anthropogenic production of N-methyl perfluorooctane sulfonamidoethanol (NMeFOSE) contributes to the ubiquity of perfluoroalkyl sulfonate and carboxylate compounds in the environment.
Introduction Perfluoroalkylsufonamido compounds are used as stain protectants for carpets, fabrics, and paper products (1). In 2000, 3M, the major manufacturer of these compounds, announced the discontinuation of its perfluorooctane-based * Corresponding author phone: (416) 978-1780; fax: (416) 9783596; e-mail:
[email protected]. † University of Toronto. ‡ Ford Motor Company. 1862
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compounds due to concerns regarding persistence, worldwide dissemination, toxicity, and bioaccumulation (2-4). Recently, 3M returned to the market with a product containing only four perfluorinated carbons, N-methyl perfluorobutane sulfonamidoethanol (NMeFBSE). The atmospheric fate of this new industrial compound is of interest for two reasons. First, to predict future environmental consequences of the release of NMeFBSE. Second, as a model for the environmental distribution of its perfluorooctane predecessors the N-methyl and N-ethyl FOSE alcohols. Previous atmospheric studies, involving both fluorotelomer alcohols (F(CF2CF2)xCH2CH2OH) (5-7) and perfluorinated sulfonamides (FCnF2nSO2NH(-CH2CH3 or -CH3)) (8), have purported to explain the distribution of perfluorocarboxylic acids (PFCA) to remote regions. PFCAs are prevalent environmental contaminants both in remote and urban settings, they are extremely persistent, and those with more than seven perfluorinated carbons have been shown to bioaccumulate (3, 9-12). Fluorotelomer alcohols (FTOHs) have tropospheric lifetimes which are long enough to account for their wide distribution in the North American atmosphere (5). FTOHs are susceptible to tropospheric oxidation, producing small amounts (5-10%) of PFCAs (6, 7). The PFCAs produced are presumably scavenged by wet and dry deposition, ultimately resulting in the deposition of these relatively nonvolatile persistent organic pollutants to remote locations (6). This established atmospheric transport theory was identified as relevant for the gas-phase oxidation of N-ethyl perfluorobutane sulfonamide (NEtFBSA) (8). Along with primary carbonyl products resulting from oxidation of the N-ethyl chain, the entire suite of PFCAs were identified. After a loss of the sulfonamide moiety, the mechanism of PFCA formation was speculated to follow the same path as outlined for the gas-phase oxidation of the FTOHs. Despite the termination of large-scale industrial production, perfluorooctane sulfonamido compounds remain ubiquitous contaminants (10, 11, 13). The environmental legacy left by these compounds includes the presence of N-ethyl perfluorooctane sulfonamide (NEtFOSA) and both the Nmethyl and N-ethyl versions of perfluorooctane sulfonamidoethanol (NMeFOSE, NEtFOSE) in the North American troposphere (14-16). Perfluorooctane sulfonate (PFOS) has been detected in Canadian rainwater (17). PFOS and perfluorooctane sulfonamide (PFOSA) are ubiquitous contaminants in Arctic biota, with PFOS being the most prevalent single contaminant found in polar bear livers (11, 13). Perfluorinated compounds are produced by two distinct methods: electrochemical fluorination (ECF), traditionally used in the production of perfluoroalkyl sulfonamido chemistries, and telomerization, used in the production of fluorotelomer-based compounds. The two processes are distinguishable by their characteristic isomer profiles, with telomerization producing only straight-chain molecules and ECF generating a distinct array of structural isomers. Some input from perfluoroalkyl sulfonamido compounds to the load of PFCAs in the Arctic is suggested by the isomer pattern observed for perfluorooctanoic acid (PFOA) in polar bear livers by DeSilva et al. (18). Although anthropogenic perfluorinated sulfonates are the sole source of these compounds to the environment, the mechanism by which they are transported to remote regions is not yet fully developed. While ocean currents may play some role, atmospheric circulation is established as a significant mode of transport for other organic pollutants, such as polychlorinated biphenyls (PCB) (19). Smithwick et al. (13) compared the concentration of PFOS in polar bear liver samples from several 10.1021/es0520767 CCC: $33.50
2006 American Chemical Society Published on Web 02/09/2006
locations to the concentrations of select PCBs in adipose tissue from the corresponding populations (20). Significant correlations were found between the concentration of PFOS and PCB 180, with modest correlations to PCBs 153, 138, and 99. This relationship suggests a similar transport phenomenon and, as a result, suggests PFOS may be of atmospheric origin in remote locations. With a pKa estimated to be around -3 (21), PFOS essentially exists entirely in the anionic form under environmental conditions. As a charged species, PFOS does not have an appreciable vapor pressure, making direct atmospheric transport unlikely. Therefore, an atmospheric source would presumably involve neutral precursors akin to those implicated in the production of PFCAs. Degradation to the perfluoroalkyl sulfonates found in environmental samples may involve direct production in the gas-phase or transformation, either abiotically or biologically, after deposition. Xu et al. (22) found perfluorooctane sulfonamidoethanol (PFOSE), PFOSA, and PFOS to be metabolic transformation products of NEtFOSE upon exposure to rat liver microsomes, demonstrating that these observed pollutants may be formed in vivo after exposure to precursor contaminants. Here we present an investigation of the tropospheric kinetics and oxidation products of N-methyl perfluorobutane sulfonamidoethanol (NMeFBSE), relevant both as a currentuse industrial compound and to model the mechanism of perfluoroalkyl distribution to remote locations. While its perfluorooctane equivalent, NMeFOSE, is no longer in production, it was used extensively as a carpet and fabric stain protectant (1), and as such remains a relevant pollutant. Using the atmospheric fate of NMeFBSE as a guide, it appears that anthropogenic production of NMeFOSE contributes to the ubiquity of perfluoroalkyl sulfonate and carboxylate compounds in the environment.
Experimental Section Relative Rate Kinetics. Experiments were performed in a 140-liter borosilicate glass reactor interfaced to a Mattson Sirus 100 fourier transform infrared (FTIR) spectrometer (23). The reactor was surrounded by 22 fluorescent blacklamps (GE F15T8-BL) that were used to photochemically initiate the production of OH radicals in air. Relative rate techniques
CH3ONO + hv f CH3O + NO
(1)
CH3O + O2 f HO2 + HCHO
(2)
HO2 + NO f OH + NO2
(3)
were used to measure the rate constant of interest relative to a reference reaction whose rate constant has been established previously. OH kinetics were studied by irradiating CH3ONO/NO/reactant/reference mixtures in air using UV fluorescent blacklamps. The relevant reactions in the system were reactions 1-5. In these experiments, the loss of
OH + reactant f products
(4)
OH + reference f products
(5)
reactant and reference are given by
-d[reactant] ) k4[OH][reactant] dt
(1)
-d[reference] ) k5[OH][reference] dt
(2)
Integration gives
( (
ln
ln
) )
[reactant]to [reactant]t
[reference]to [reference]t
) k4[OH]t
(3)
) k5[OH]t
(4)
where [reactant]to, [reactant]t, [reference]to, and [reference]t are the concentrations of reactant and reference at times t0 and t; k4 and k5 are the rate constants for reactions 4 and 5; and [OH] is the OH radical concentration. The reactant and reference have equal exposure to OH radicals, hence
(
ln
)
[reactant]to [reactant]t
)
(
)
[reference]to k4 ln k5 [reference]t
(5)
Plots of ln([reactant]to/[reactant]t) versus ln([reference]to/ [reference]t) should be linear, pass through the origin, and have a slope of k4/k5. The loss of NMeFBSE and the reference compounds were monitored in situ by FTIR spectroscopy using an infrared path length of 27 m and a resolution of 0.25 cm-1. Infrared spectra were derived from 32 co-added interferograms. In situ concentrations were determined by monitoring the following IR spectral features: 1407 cm-1 for NMeFBSE, 726 cm-1 for C2H2, and 950 cm-1 for C2H4. The reactant and reference compounds were subject to a repeat freeze/pump/thaw procedure before use. Neat NMeFBSE is a solid at room temperature. Introduction into the chamber was accomplished by passing a slow stream of purified air over the solid sample of NMeFBSE and into the smog chamber. A typical experiment involved introducing NMeFBSE as described above while the chamber was filling with ultrahigh purity air from 40 to 650 Torr total pressure. The remaining chamber constituents were added by filling calibrated volumes and subsequently flushing them into the chamber with either purified air or N2. For OH experiments the final pressures within the chamber were 3 and 1 mTorr for C2H4 and C2H2 respectively, 98 mTorr for CH3ONO, and 10 mTorr for NO. For the Cl experiment the final pressure of Cl2 within the chamber was 98 mTorr. For the OH- and Cl-initiated reactions, total irradiation times varied from 4 to 7 min and 0.5-2 min, respectively. Chemicals. N-methyl perfluorobutane sulfonamidoethanol (NMeFBSE, 99.55%) and perfluorobutane sulfonate (PFBS, 97%) were donated by 3M. Before introduction into the smog chamber NMeFBSE was further purified by repeated sublimation. Perfluorobutanoic acid (PFBA, 97%), perfluoropropanoic acid (PFPA, 97%), and trifluoroacetic acid (TFA, >98%) were purchased from Sigma-Aldrich Inc. (Oakville, ON). Perfluoropentanoic acid (PFPeA, 97%) was purchased from Oakwood products Inc. (West Columbia, SC). Modified M+4 perfluorooctane sulfonate (MPFOS, >99%) was obtained from Wellington Laboratories Inc. (Guelph, ON). Unless otherwise indicated, all chemicals were used without further purification. Offline Sample Collection. Offline analysis was performed by sampling 5 L of air from the chamber onto XAD resin cartridges (Amberlite XAD-2, 400/200 mg), DNPH imbedded cartridges (LpDNPH H10), and bubbling through pH 11 aqueous Na2CO3 solution. All sampling material was purchased from Sigma-Aldrich Inc. (Oakville, ON) and used without further purification. Offline Product Analysis. XAD resin samples were extracted with two 5 mL aliquots of ethyl acetate. The combined extracts were concentrated under a slow stream of N2 to 1 mL, 100 µL of which was taken for analysis by GC-MS. Each remaining extract was blown to dryness under N2, and reconstituted in 100 µL of methanol with 5 ppb of both PFPeA and MPFOS as internal standards for LC-MS/ VOL. 40, NO. 6, 2006 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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FIGURE 1. Loss of NMeFBSE versus C2H2 (squares) and C2H4 (circles) in the presence of OH radicals in 750 Torr of air at 296 K. All rate constants are shown in units of cm3 molecule-1 s-1. MS analysis. DNPH imbedded cartridges were eluted with 2 mL of methanol. Aqueous Na2CO3 solutions were analyzed directly by LC-MS/MS. To 200 µL of Na2CO3 solution, 20 µL of 0.5 M tetrabutylammonium sulfate (TBAS) was added as an ion-pairing agent to improve chromatography, 10 µL of 500 ppb MPFOS and 1 µL of 2 ppm PFPeA were added as internal standards. NMeFBSE, NMeFBSA, and perfluorobutane sulfonamidoethanol (PFBSE) were monitored by GC-MS using the following mass fragments in positive chemical ionization mode: NMeFBSE 358 (M + 1) and 340 (M - 18) m/z, NMeFBSA 314 (M + 1) m/z, PFBSE 344 (M + 1), and 326 (M - 18) m/z, and were separated on a 30 m DB-35 column using the following oven program: T0 at 45 °C, hold 2 min, ramp at 50 °C/min to 150 °C, ramp at 10 °C/min to 180 °C, ramp at 50 °C/min to 240 °C, hold 1 min. The PFCAs, PFBS, and MPFOS were monitored both in the analysis of the Na2CO3 solutions and of the reconstituted XAD samples. PFCAs were analyzed using a cone voltage of 24 V and a collision energy of 9 eV, while monitoring for the following transitions: PFPeA 263 > 219, PFBA 213 > 169, PFPA 163 > 119, TFA 113 > 69 m/z. PFBS was observed using the transition 299 > 80 m/z with a cone voltage of 42 V and a collision energy of 31 eV. MPFOS was monitored using the transition 503 > 99 m/z with a cone voltage of 55 V, and a collision energy of 45 eV. All compounds were analyzed using a capillary voltage of 3.0 kV, and separated using a C18 reverse phase column with initial conditions of 20:80 methanol:water holding 2 min, followed by an 8 min linear ramp to 5% water holding for 2 min. The carbonyl product, C4F9SO2N(CH3)CH2CHO, was observed by LC-MS/MS of the eluted DNPH cartridges, looking at 535 m/z using a cone voltage of 25 V. NMeFBSE and NMeFBSA were monitored by LC-MS/MS of the reconstituted XAD samples monitoring 375 > 59 for the acetate adduct of NMeFBSE with a cone voltage of 20 V and a collision energy of 10 eV, and 312 > 219 for NMeFBSA with a cone voltage of 45 V and a collision energy of 17 eV. All the products mentioned above were observed with a capillary voltage of 3.0 kV and were isolated chromatographically using a C18 reverse phase column with a gradient starting at 40:60 methanol:water with an immediate linear ramp over 7 min to 5% water holding for 5 min.
Results and Discussion Relative Rate Study of the Gas-Phase OH-Initiated Oxidation of N-Methyl Perfluorobutane Sulfonamidoethanol (NMeFBSE). After introduction into the chamber a 14-18% loss of NMeFBSE was observed during the first 10 min when 1864
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the reaction mixture was left to stand in the dark. In the next 30 min there was no further loss ( [PFPA]. The 1866
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concentration of both PFBA and PFPA increased as the reaction proceeded. TFA was observed in the samples above the level of the blank but below the limit of quantification. As shown in Figure 2, the mechanism producing these PFCAs is expected to be identical to that first proposed for the oxidation of the FTOHs. Upon production of a perfluorinated carbon-centered radical, reaction with molecular oxygen yields a peroxy radical. This peroxy radical can react with another peroxy radical forming a perfluorinated alcohol that can proceed to lose HF, generating a perfluorinated acid fluoride, which, upon contact with water, will give the corresponding carboxylic acid. The entire suite of shorter chain acids can be formed from a single perfluorinated chain length because the peroxy radical mentioned above may lose COF2, regenerating the perfluorinated carbon-centered radical. In this manner the perfluorinated chain is “unzipped” (6). This oxidation mechanism was also used to explain the production of PFCAs in the Cl-initiated oxidation of NEtFBSA (reaction 10) (8). Whereas in the previous study involving the Cl radical, we proposed the disintegration of the sulfonamide moiety to produce the perfluorocarbon-centered radical (8), as shown in Figure 2; we postulate that the OH radical can add to the sulfone double bond producing a sulfonyl radical. To reform a closed-shell system this radical can cleave either the S-C or the S-N bond. Cleavage of the S-C bond results in the formation of both a sulfonamido compound and a perfluorocarbon-centered radical that proceeds to form the PFCAs as described above. Cleavage of the S-N bond results in both a nitrogen-centered radical and perfluorobutane sulfonate (PFBS). As a test of this mechanism the offline samples were analyzed for PFBS. While PFBS was below the limit of detection by direct analysis of the Na2CO3 solutions, it was present above the level of the blank after 27% consumption of NMeFBSE in the reconstituted XAD samples. The detection of PFBS supports the proposed mechanism. To quantify the difference in production between PFCAs and PFBS, a mass balance was carried out for the two degradation products. After 50% consumption
of NMeFBSE, the cumulative concentration of PFCAs and PFBS accounted for approximately 10 and 1%, respectively, of the loss of NMeFBSE. In the mechanism proposed in Figure 2, the production of PFCAs and PFBS is connected by a shared initial step. The measured concentrations of PFCAs were consistently greater than that of PFBS, implying that cleavage of the S-C bond is favored over that of the S-N bond. Carboncentered radicals are more stable than the corresponding nitrogen-centered radicals (35), and so the observation that PFCAs are formed in a yield which is approximately 10 times that of PFBS appears consistent with the mechanism in Figure 2. To provide further insight into NMeFBSE oxidation, Clinitiated product experiments were conducted (reaction 12).
Cl + C4F9SO2N(CH3)CH2CH2OH f products (12) The products of Cl-atom initiated oxidation of NMeFBSE were similar to those observed in the OH-radical initiated oxidation experiments. The N-dealkylation product was present and the full suite of PFCAs and PFBS detected, all with similar concentration profiles to that observed for the OH-initiated reaction. Implications for Atmospheric Chemistry. Perfluoroalkyl sulfonates are important industrial compounds and persistent environmental pollutants. Unfortunately, because of the difficulties with handling these relatively low-volatility compounds, their atmospheric chemistry is largely unknown and assessments of their environmental impact are highly uncertain. Building upon our previous studies of the atmospheric chemistry of FTOHs (5-7) and NEtFBSA (8), we present the first study of the atmospheric chemistry of NMeFBSE. The atmospheric lifetime of NMeFBSE and, by analogy, the prevalent atmospheric contaminant NMeFOSE, was determined to be approximately 2 days. The results from the present work suggest that despite its short atmospheric lifetime, NMeFOSE is capable of contributing to perfluorooctane sulfonate (PFOS) and PFCA deposition in remote locations via the intermediacy and further gas-phase degradation of its longer-lived N-dealkylation product, NMeFOSA. Atmospheric oxidation of NMeFBSE leads to the formation of PFBS and short chain PFCAs which are not bioaccumulative and are not expected to pose any significant environmental threat.
Acknowledgments We thank Bill Reagen and Dale Bacon (3M, St. Paul, MN) for the NMeFBSE standard material and helpful discussions. We thank Gilles Arsenault (Wellington laboratories Inc., Guelph, ON) for providing the M + 4 MPFOS standard. This research was funded, in part, by the Natural Sciences and Engineering Research Council of Canada (NSERC) through a strategic grant.
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Literature Cited (1) 3M. Fluorochemical Use, Distribution and Release Overview; U.S. Public Docket AR-226-0550; St. Paul, MN, 1999. (2) U.S. Environmental Protection Agency. Perfluoroalkyl sulfonates; significant new use rule. Fed. Regist. 67, 72854-72867. (3) Hansen, K. J.; Clemen, L. A.; Ellefson, M. E.; Johnson, H. O. Compound-specific, quantitative characterization of organic fluorochemicals in biological matrixes. Environ. Sci. Technol. 2001, 35, 766-770. (4) Giesy, J. P.; Kannan, K. Global distribution of perfluorooctane sulfonate in wildlife. Environ. Sci. Technol. 2001, 35, 13391342. (5) Ellis, D. A.; Martin, J. W.; Mabury, S. A.; Hurley, M. D.; Sulbaek Andersen, M. P.; Wallington, T. J. Atmospheric lifetime of fluorotelomer alcohols. Environ. Sci. Technol. 2003, 37, 38163820. (6) Ellis, D. A.; Martin, J. W.; De Silva, A. O.; Mabury, S. A.; Hurley, M. D.; Sulbaek Andersen, M. P.; Wallington, T. J. Degradation
(21) (22)
(23)
(24)
of fluorotelomer alcohols: a likely atmospheric source of perfluorinated carboxylic acids. Environ. Sci. Technol. 2004, 38, 3316-3321. Hurley, M. D.; Ball, J. C.; Wallington, T. J.; Sulbaek Andersen, M. P.; Ellis, D. A.; Martin, J. W.; Mabury, S. A. Atmospheric chemistry of 4:2 fluorotelomer alcohol (CF3(CF2)3CH2CH2OH): products and mechanism of Cl atom initiated oxidation. J. Phys. Chem. A 2004, 108, 5635-5642. Martin, J. W.; Ellis, D. A.; Hurley, M. D.; Wallington, T. J.; Mabury, S. A. Atmospheric chemistry of perfluoroalkylsulfonamides: kinetic and product studies of the OH radical and Cl atom initiated oxidation of N-ethyl perfluorobutylsulfonamide (C4F9SO2N(H)CH2CH3). Environ. Sci. Technol. 2005, 40, 864-872. Moody, C. A.; Martin, J. W.; Kwan, W. C.; Muir, D. C. G.; Mabury, S. A. Monitoring perfluorinated surfactants in biota and surface water samples following an accidental release of fire-fighting foam into Etobioke Creek. Environ. Sci. Technol. 2002, 36, 545551. Kannan, K.; Corsolini, S.; Falandysz, J.; Fillmann, G.; Kumar, K. S.; Loganathan, B. G.; Mohd, M. A.; Olivero, J.; Van Wouwe, N.; Yang, J. H.; Aldous, K. M. Perfluorooctanesulfonate and related fluorochemicals in human blood from several countries. Environ. Sci. Technol. 2004, 38, 4489-4495. Martin, J. W.; Smithwick, M. M.; Braune, B. M.; Hoekstra, P. F.; Muir, D. C. G.; Mabury, S. A. Identification of long-chain perfluorinated acids in biota from the Canadian Arctic. Environ. Sci. Technol. 2004, 38, 373-380. Martin, J. W.; Mabury, S. A.; Solomon, K. R.; Muir, D. C. G Bioconcentration and tissue distribution of perfluorinated acids in rainbow trout (Oncorhynchus mykiss). Environ. Toxicol. Chem. 2003, 22, 196-204. Smithwick, M.; Mabury, S. A.; Solomon, K. R.; Sonne, C.; Martin, J. W.; Born, E. W.; Dietz, R.; Derocher, A. E.; Letcher, R. J.; Evans, T. J.; Gabrielsen, G. W.; Nagy, J.; Stirling, I.; Taylor, M. K.; Muir, D. C. G. Circumpolar study of perfluoroalkyl contaminants in polar bears (Ursus maritimus). Environ. Sci. Technol. 2005, 39, 5517-5523. Martin, J. W.; Muir, D. C. G.; Moody, C. A.; Ellis, D. A.; Kwan, W. C.; Solomon, K. R.; Mabury, S. A. Collection of airborne fluorinated organics and analysis by gas chromatography/ chemicals ionization mass spectrometry. Anal. Chem. 2002, 74, 584-590. 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. Shoeib, M.; Harner, T.; Ikonomou, M.; Kannan, K. Indoor and outdoor air concentrations and phase partitioning of perfluoroalkyl sulfonamides and polybrominated diphenyl ethers. Environ. Sci. Technol. 2004, 38, 1313-1320. Loewen, M.; Halldorson, T.; Wang, F.; Tomy, G. Fluorotelomer carboxylic acids and PFOS in rainwater from an urban center in Canada Environ. Sci. Technol. 2005, 39, 2944-2951. DeSilva, A. O.; Mabury, S. A. Isolating isomers of perfluorocarboxylates in polar bear (Ursus maritimus) from two geographical locations. Environ. Sci. Technol. 2004, 38, 6538-6545. Norstrom, R. J.; Simon, M.; Muir, D. C. G.; Schweinsburg, R. E. Organochlorine contaminants in arctic marine food chains: identification, geographical distribution, and temporal trends in polar bears. Environ. Sci. Technol. 1988, 22, 1063-1071. Verreault, J.; Muir, D. C. G.; Norstrom, R. J.; Stirling, I.; Fisk, A. T.; Gabrielsen, G. W.; Derocher, A. E.; Evans, T. J.; Dietz, R.; Sonne, C.; Sandala, G. M.; Gebbink, W.; Riget, F. F.; Born, E. W.; Taylor, M. K.; Nagy, J.; Letcher, R. J. Chlorinated hydrocarbon contaminants and metabolites in polar bears (Ursus maritimus) from Alaska, Canada, East Greenland, and Svalbard: 19962002. Sci. Total Environ. 2005, 351, 352, 369-390. Environmental risk evaluation report: perfluorooctanesulphonate (PFOS); Environment Agency: Wallingford, UK, 2004. Xu, L.; Krenitsky, D. M.; Seacat, A. M.; Butenhoff, J. L.; Anders, M. W. Biotransformation of N-ethyl-N-(2-hydroxyethyl)perfluorooctanesulfonamide by rat liver microsomes, cytosol, and slices and by expressed rat and human cytochromes P450. Chem. Res. Toxicol. 2004, 17, 767-775. Wallington, T. J.; Japar, S. M. Fourier transform infrared kinetic studies of the reaction of HONO with HNO3, NO3 and N2O5 at 295 K. J. Atmos. Chem. 1989, 9, 399-409. Sorensen, M.; Kaiser, E. W.; Hurley, M. D.; Wallington, T. J.; Nielsen, O. J. Kinetics of the reaction of OH radicals with acetylene in 25-8000 Torr of air at 296 K. Int. J. Chem. Kinet. 2003, 35, 191-197.
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(25) Calvert, J. G.; Atkinson, R.; Kerr, J. A.; Madronich, S.; Moortgat, G. K.; Wallington, T. J.; Yarwood, G. The Mechanisms of Atmospheric Oxidation of the Alkenes; Oxford University Press: Oxford, 2000. (26) Prinn, R. G.; Huang, J.; Weiss, R. F.; Cunnold, D. M.; Fraser, P. J.; Simmonds, P. G.; McCulloch, A.; Harth, C.; Salameh, P.; O’Doherty, S.; Wang, R. H. J.; Porter, L.; Miller, B. R. Evidence for substantial variations of atmospheric hydroxyl radicals in the past two decades. Science 2001, 292, 1882-1887. (27) Lawrence, M. G.; Jo¨ckel, P.; von Kuhlmann R., What does the global mean OH concentration tell us?. Atmos. Chem Phys. 2001, 1, 37-49. (28) Sulbaek Andersen, M. P.; Nielsen, O. J.; Hurley, M. D.; Wallington, T. J.; DeMore, W. B. Atmospheric chemistry of CF3OCF2CF2H and CF3OC(CF3)2H: reaction with Cl atoms and OH radicals, degradation mechanism, global warming potentials, and empirical relationship between k(OH) and k(Cl) for organic compounds J. Phys. Chem. A 2005, 109, 3926-3934. (29) Stock, N. L.; Muir, D. C. G.; Mabury, S. A. Airborne polyfluorinated sulfonamides and telomer alcohols in Toronto: a long-term study. In Fluoros International Symposium on Fluorinated Alkyl Organics in the Environment, Toronto, ON, Canada, August 1820, 2005. (30) Kwok, E. S. C.; Atkinson, R. Estimation of hydroxyl radical reaction rate constants for gas-phase organic compounds using
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a structure-reactivity relationship: an update. Atmos. Environ. 1995, 29, 1685-1695. (31) Finlayson-Pitts, B. J.; Pitts, J. N. J. Chemistry of the Upper and Lower Atmosphere: Theory, Experiments, and Applications; Academic Press: San Diego, 1999. (32) Woodrow, J. E.; Crosby, D. G.; Mast, T.; Moilanen, K. W.; Seiber, J. N. Rates of transformation of trifluralin and parathion vapors in air. J. Agric. Food Chem. 1978, 26, 1312-1316. (33) Tauber, A.; von Sonntag, C. Products and kinetics of the OHradical-induced dealkylation of Atrazine. Acta hydrochim. hydrobiol. 2000, 28, 15-23. (34) Huang, J.; Mabury, S. A. A new method for measuring carbonate radical reactivity towards pesticides. Environ. Toxicol. Chem. 2000, 19, 1501-1507. (35) Bordwell, F. G.; Cheng, J.-P.; Harrelson, J. A. Homolytic bond dissociation energies in solution from equilibrium acidity and electrochemical data. J. Am. Chem. Soc. 1988, 110, 1229-1231.
Received for review October 19, 2005. Revised manuscript received January 6, 2006. Accepted January 9, 2006. ES0520767
