Article pubs.acs.org/est
Identification of Novel Fluorinated Surfactants in Aqueous Film Forming Foams and Commercial Surfactant Concentrates Lisa A. D’Agostino and Scott A. Mabury* Department of Chemistry, University of Toronto, 80 St George Street, Toronto, M5S 3H6 Ontario, Canada S Supporting Information *
ABSTRACT: Recent studies comparing the results of total organofluorine-combustion ion chromatography (TOF-CIC) to targeted analysis of perfluoroalkyl and polyfluoroalkyl substances (PFASs) by liquid chromatography tandem mass spectrometry (LC-MS/MS) have shown that a significant yet variable portion of the total organofluorine in environmental and biological samples is in the form of unknown PFASs. A portion of this unknown organofluorine likely originates in proprietary fluorinated surfactants not included in LC-MS/MS analyses and not fully characterized by the environmental science community, which may enter the environment through use in aqueous film forming foams (AFFFs) for firefighting. Contamination of water, biota, and soils with various PFASs due to AFFF deployment has been documented. Ten fluorinated AFFF concentrates, 9 of which were obtained from fire sites in Ontario, Canada, and two commercial fluorinated surfactant concentrates were characterized in order to identify novel fluorinated surfactants. Mixed-mode ion exchange solid phase extraction (SPE) fractionated fluorinated surfactants based on ionic character. High resolution mass spectrometry assigned molecular formulas to fluorinated surfactant ions, while collision induced dissociation (CID) spectra assisted structural elucidation. LC-MS/MS detected isomers and low abundance fluorinated chain lengths. In total, 12 novel and 10 infrequently reported PFAS classes were identified in fluorinated chain lengths from C3 to C15 for a total of 103 compounds. Further research should examine the environmental fate and toxicology of these PFASs, especially their potential as perfluoroalkyl acid (PFAA) precursors.
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seawater from Japan,7 and 2 to 44% of the anionic fraction of EOF in Lake Ontario surface sediments.8 AFFF, which is used in extinguishing hydrocarbon fuelled fires, is a potential source of incompletely characterized PFASs to the environment as it contains proprietary fluorinated surfactants,9 which are typically not clearly listed on the Material Safety Data Sheet (MSDS) for an AFFF. Two fluorinated surfactants in AFFF that were characterized recently are the 6:2 fluorotelomermercaptoalkylamido sulfonate (FTSAS; Figure 1I, n = 6)10,11 and the 6:2 fluorotelomer sulfonamide alkylbetaine (FTAB) marketed as Forafac 1157 (Figure 1L, n = 6).12,13 PFASs in AFFFs from United States military bases have been characterized using accurate masses from liquid chromatography-time-of-flight mass spectrometry (LC-TOF-MS) to assign molecular formulas and solely patent searching to assign structures.14 Subsequently, groundwater from military bases decommissioned at least six years and AFFF samples were analyzed by LC-MS/MS for eight novel PFAS
INTRODUCTION
Since the worldwide dissemination of perfluorooctane sulfonate (PFOS) was detected in human blood and in wildlife around the world in 2001, research into perfluoroalkyl and polyfluoroalkyl substances (PFASs) in the environment has been extensive.1−3 Nevertheless, there remains a great deal unknown about the identity of the specific PFASs present in environmental samples based on studies comparing general techniques for organofluorine analysis with targeted quantitation by liquid chromatography-tandem mass spectrometry (LCMS/MS). Following an accidental AFFF release in Ontario, Canada, in 2000, quantitative 19F-NMR results showed approximately 5-fold higher concentrations of materials giving signals similar to PFOS and perfluorooctanoate (PFOA) than did LC-MS/MS analysis of selected perfluoroalkyl carboxylates (PFCAs) and perfluoroalkane sulfonates (PFSAs) in surface water.4 More recent studies also suffer from incomplete coverage of PFASs based on comparisons of TOF-CIC results with LC-MS/MS. Known PFASs accounted for approximately 11% of extractable organic fluorine (EOF) in shrimp in Hong Kong,5 approximately 30−85% of EOF in human blood samples from around China,6 10 to 30% of organofluorine in © 2013 American Chemical Society
Received: Revised: Accepted: Published: 121
August 21, 2013 October 28, 2013 November 20, 2013 November 20, 2013 dx.doi.org/10.1021/es403729e | Environ. Sci. Technol. 2014, 48, 121−129
Environmental Science & Technology
Article
Figure 1. Structures and chain lengths observed for novel and infrequently reported PFASs in AFFF and commercial fluorinated surfactants.
fluorinated surfactants to be PFAA precursors motivates identification of specific PFASs in AFFFs and commercial fluorinated surfactants to facilitate evaluation of this potential. Weiner et al. recently examined AFFF samples from fire sites in Ontario, Canada, and a commercial AFFF from 3M using 19 F-NMR, TOF-CIC, and LC-MS/MS analysis of known PFASs (i.e.: PFSAs; PFCAs; 6:2 and 8:2 FTSAs; and 4:2, 6:2, and 8:2 FTSASs)11 and this study extends the characterization of many of the same samples by identifying unknown PFASs. Two mixed-mode ion exchange solid phase extraction (SPE) methods were developed to fractionate PFASs according to their ionic nature, simplifying samples for subsequent analysis and assisting in assigning ionic/ionizable functionalities. These methods were used along with TOF-CIC, quadrupole-time-of-
classes. Only FTSASs and structures shown in Figure 1R and T could be detected in groundwater.15 Prior to the electrochemical fluorination (ECF) PFOS phase out in 2002, AFFF was often formulated using ECF sulfonamide-based surfactants,14,16 which may be precursors to PFSAs since N-ethyl perfluorooctanesulfonamidoethanol (EtFOSE) biotransforms to PFOS in rats,17 wastewater treatment plant (WWTP) sludge,18 and marine sediments.19 A number of fluorotelomer compounds, such as polyfluoroalkyl phosphate esters (PAPs),20,21 8:2 fluorotelomer acrylate,22 6:2 FTSA,23 and the AFFF component 6:2 FTSAS11 have been demonstrated to biotransform to PFCAs in WWTP sludge,11,20,23 rats,21 and rainbow trout.22 This suggests fluorotelomer-based surfactants, dominant in AFFF produced after 2002,16 may be PFCA precursors. The potential for 122
dx.doi.org/10.1021/es403729e | Environ. Sci. Technol. 2014, 48, 121−129
Environmental Science & Technology
Article
flight mass spectrometry (QTOF-MS), Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS), and LCMS/MS to identify 22 classes of novel or infrequently reported fluorinated surfactant in various fluorinated chain-lengths for a total of 103 compounds that may be released through use of AFFF or other applications. Structural assignments are supported by QTOF-MS CID spectra, which is a first for 18 of the PFASs.
electrospray ionization (ESI) in full scan and product ion scan modes (resolution ∼ 8000). Detection of PFASs in SPE fractions was based on discrepancy with the theoretical mass to charge (m/z) less than 5 ppm. Method details are in the SI. FTICR-MS. Internally calibrated FTICR-MS spectra (resolution ∼ 120 000) were generated for AFFFs and commercial surfactants diluted between 1000 and 100 000 times with methanol or 1:1 methanol/water in positive ion mode ESI (ESI +) and negative ion mode ESI (ESI−). Method details are provided in the SI. LC-MS/MS. Several LC-MS/MS methods using both ESI+ and ESI− were developed in order to separate the SPE model compounds and the PFASs identified in AFFF and commercial surfactants, as described in the SI. MS/MS transitions for model compounds and PFASs were developed through infusion of model compound solutions or SPE fractions for abundant chain length congeners and minor congeners were predicted from these results (SI Tables S4 and S5). Duplicate LC-MS/ MS chromatograms of diluted AFFF and fluorinated surfactant samples were obtained and used qualitatively to assess the presence of PFASs and isomers. S yn t h e s i s o f N- ( 3 - ( d im e t h y l a m i n o ) p r o p y l ) perfluorononanamide (DMAPFNAE). DMAPNFAE (Figure 1A, n = 8) was synthesized by amidation of perfluorononanoyl chloride with 3-(dimethylamino)-1-propylamine as described in the SI.
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MATERIALS AND METHODS Materials. The reagents, solvents and standards used are listed in the Supporting Information (SI). Samples. Foams 1 to 11 were an AFFF sample set collected by the Ontario Ministry of the Environment from sites where the AFFFs were used in firefighting in Ontario, Canada. Foams 6 and 9 were previously found to contain only residual organofluorine and were not examined further.11 A commercial AFFF sample was obtained from 3M (St. Paul, MN, U.S.A.) and is called Foam 12. Two commercial fluorinated surfactant concentrates, referred to by their trade names, FS-330 and FS1520, were from Mason Chemicals (Arlington Heights, IL, USA). Locations and dates of sample collection and relevant information from MSDSs are in SI Table S1, and sampling details are in the SI. Product literature for FS-330 and FS-1520 mention applications in alkaline cleaners, mining operations and photographic emulsions, coatings, and polishes.24,25 FS1520 is also marketed for use in hair conditioners, oil well stimulation fluids, and AFFFs.25 Ion Exchange SPE. Two SPE fractionation methods were developed with one utilizing Oasis weak anion exchange (WAX) SPE cartridges and the other utilizing Oasis weak cation exchange (WCX) SPE cartridges from Waters (Milford, MA) and are described in detail in the SI. Briefly, the sequence of elution solvents for WAX SPE was methanol to elute neutral, amphoteric, and cationic surfactants; 2% formic acid in methanol to elute weak acids (e.g., carboxylates); methanol; and 1% NH4OH in methanol to elute strong acids (e.g.: PFCAs, sulfonates). Excluding the second methanol rinse, these fractions are termed the neutral WAX, weak acid and strong acid fractions, respectively. WCX cartridges were eluted sequentially with methanol to elute neutral, amphoteric, and anionic surfactants; 2% NH4OH in methanol to elute bases (e.g., amines); methanol; and 2% formic acid in methanol to elute permanent cations (e.g., quaternary ammoniums). Excluding the second methanol rinse, these fractions are named the neutral WCX, base, and permanent cation fractions, respectively. These procedures were developed using model compounds including, PFOA (strong acid), 7:3 fluorotelomer carboxylic acid (weak acid), perfluorooctane sulfonamide (nonionic), N,N-dimethyldodecylamine (base), cetyltrimethylammonium chloride (CTMA, permanent cation), 3-(N,Ndimethyloctylammonio)propanesulfonate (amphoteric), and Empigen BB detergent (amphoteric) with recovery and distribution of these compounds determined by LC-MS/MS as described in the SI. AFFF and commercial surfactant samples were extracted in batches with a solvent blank. TOF-CIC. SPE fractions of AFFFs, commercial surfactants, and solvent blanks were analyzed by TOF-CIC, as described previously,11,26 to screen for PFAS-containing fractions requiring further investigation. Method details are in the SI. QTOF-MS. SPE fractions determined to contain organic fluorine using TOF-CIC were direct loop injected on an AB/ Sciex QStar XL (MDS Sciex, Concord, ON, Canada) using
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RESULTS AND DISCUSSION Analytical Strategies. Using both WAX and WCX SPE, average recoveries of all model compounds in corresponding fractions were acceptable and were 70 to 125% for all compounds except for CTMA, which had average recoveries of 135% (WCX) and 63% (WAX, SI Table S7). For AFFF and fluorinated surfactant samples, total fluorine content of the SPE fractions by TOF-CIC is shown in SI Figure S22. In mass spectra, PFASs differing in fluorinated chain length are separated by 50 Da (−CF2−) for ECF products or 100 Da (−CF2CF2−) for fluorotelomer products.14,27 PFASs can also be identified by their low mass defects (approximately −0.1 to 0.15 Da)14 caused by the negative mass defect of fluorine (−0.0016 Da) and their relatively high m/z, generally greater than 300. A mass defect is the difference between the accurate and whole number masses for an ion. Elemental formulas were generated based on accurate masses from FTICR-MS and QTOF-MS using Analyst 1.5.1 (MDS Sciex, Concord, ON, Canada) with even electron state, −0.5 to 10 double bond equivalents, a charge state of +1 or −1, 0−60 carbon, 5−40 fluorine, 0−100 hydrogen, 0−4 nitrogen, 0−26 oxygen, and the number of sulfur atoms suggested by isotope patterns. Likely formulas were selected based on a discrepancy from the theoretical m/z less than 1.5 mDa by FTICR-MS (preferably
