ARTICLE pubs.acs.org/est
Detection of a Cyclic Perfluorinated Acid, Perfluoroethylcyclohexane Sulfonate, in the Great Lakes of North America Amila O. De Silva,* Christine Spencer, Brian F. Scott, Sean Backus, and Derek C. G. Muir Water Science and Technology Directorate, Environment Canada, 867 Lakeshore Road, Burlington, ON Canada L7R 4A6
bS Supporting Information ABSTRACT: Perfluoroethylcyclohexanesulfonate (PFECHS) is a cyclic perfluorinated acid (PFA) mainly used as an erosion inhibitor in aircraft hydraulic fluids. It is expected to be as recalcitrant to environmental degradation as aliphatic PFAs including perfluorooctanoate (PFOA) and perfluorooctane sulfonate (PFOS). For the first time, PFECHS is reported in top predator fish (10 t/y) chemical. In a government document from the United Kingdom, worldwide usage of PFECHS was estimated to be 2.2 t per year, one-third of which was assumed to be in the European Union.9 According to the Material Safety Data Sheet by 3M, the composition of FC-98 consisted of 6670% PFECHS, 1822% perfluoro-4-methylcyclohexane sulfonate (PFMeCHS, CAS 6815607-0), 913% dimethylperfluorocyclohexane sulfonate, and 1 3% perfluorocyclohexane sulfonate. The patent literature describes the use of PFECHS as an erosion inhibitor when dissolved in aircraft hydraulic fluids thereby improving conductivity, solubility, and surface activity.10 3M ceased production of PFECHS by 2002 along with other perfluorooctyl-based compounds. In 2002 Boeing Co. wrote to the USEPA to request that FC-98 be excluded from restrictions based on its use as an antierosion additive in fire resistant phosphate ester hydraulic fluids.1113 In Canada and the U.S., usage of this chemical is permitted based on the lack of alternatives, its critical role in the safe performance of aircraft, and anticipated minimal environmental release.14 Special Issue: Perfluoroalkyl Acid Received: January 12, 2011 Accepted: April 25, 2011 Revised: April 20, 2011 Published: April 29, 2011 8060
dx.doi.org/10.1021/es200135c | Environ. Sci. Technol. 2011, 45, 8060–8066
Environmental Science & Technology
8061
a
2.18 ( 0.21 1.03 ( 0.13 1.83 ( 0.26 0.94 ( 0.19 4.31 ( 0.36
All analytes were quantified using the linear isomer standards purchased from Wellington Laboratories (Guelph, ON, Canada). In surface water samples, PFOA, PFHxS, and PFOS were observed as a mixture of isomers. As such, data are presented for these analytes as solely the linear isomer as well as the total isomer concentration. For PFOS and PFHxS, quantification was based on the 499f80 m/z and 399f80 m/z transitions, respectively with the 99 m/z product for confirmation. Total isomer concentration was estimated by assuming equivalent detector response to each isomer for a particular analyte and quantifying using the summed peak area and linear isomer calibration curve. b Method detection limit (MDL) based on method blank analysis corresponds to 0.0010 ng/L (C5), 0.0054 ng/L (C6), 0.007 ng/L (C7), 0.0121 ng/L (C8), 0.0018 ng/L (C9), no C10 observed in blanks, 0.0011 ng/L (C11), no PFBS or PFHxS, PFECHS, or PFMeCHS in blanks, 0.0023 ng/L PFOS. For all other analytes, MDL corresponds to lowest calibration standard 0.003 ng/L (0.003 ng/mL in 0.5 mL).
1.13 ( 0.15 2.84 ( 0.29 2.63 ( 0.17 0.23 ( 0.02
3.00 ( 0.50 5.51 ( 0.89 4.35 ( 0.65 0.30 ( 0.05 0.94 ( 0.09 0.80 ( 0.07 0.76 ( 0.07 0.12 ( 0.02
0.56 ( 0.12 2.00 ( 0.15 5.65 ( 0.31 0.42 ( 0.02
Ontario, n = 9
0.49 ( 0.02
0.81 ( 0.13
0.53 ( 0.03 0.46 ( 0.03
0.72 ( 0.11 0.84 ( 0.29
0.043 ( 0.019 0.49 ( 0.05
0.11 ( 0.03 0.29 ( 0.08 1.86 ( 0.16 1.63 ( 0.13 2.22 ( 0.18 0.75 ( 0.11 5.46 ( 1.11
0.16 ( 0.02 2.22 ( 0.18 Michigan, n = 4 1.29 ( 0.60 2.99 ( 0.86 0.77 ( 0.24 4.10 ( 0.39
Erie, n = 3
Superior, n = 8 Huron, n = 8
totala lineara
PFOS PFHxS
totala lineara
PFHxS
PFBS PFDA
C10 C9
PFNA PFOA
C8 lineara
PFOA
C8 totala C7
PFHpA PFHxA
C6 C5
Standards and Reagents. Perfluorohexanoate (PFHxA), perfluoroheptanoate (PFHpA), PFOA, perfluorononanoate (PFNA), perfluorodecanoate (PFDA), perfluoroundecanoate (PFUnA), perfluorododecanoate (PFDoA), perfluorotridecanoate (PFTrA), perfluorotetradecanoate (PFTeA), perfluorobutane sulfonate (PFBS), perfluorohexane sulfonate (PFHxS), PFOS and perfluorodecanesulfonate (PFDS) were quantified using a full suite of native and isotopically labeled standards available from Wellington Laboratories (Guelph, ON). A neat standard of the potassium salt of PFECHS (94%) was obtained from Wako Chemicals (Richmond, VA, USA). HPLC grade water, Omnisolv methanol (99.9%), and Suprapur ammonia (25%) were from EMD Chemicals, Gibbstown, NJ, USA. The HPLC grade water used for mobile phase and extraction was pretreated by passing through a conditioned Oasis WAX solid phase extraction (SPE) cartridge (6 cm3, 150 mg, 30 μm) from Waters (Milford, MA, USA) to reduce any background PFA contamination. Fish. Lake trout were collected in Lake Superior, Lake Huron, Lake Erie (eastern basin), and Lake Ontario between 2006 and 2008 (Table 1) using gill nets. Walleye (Sander vitreus), a top predator in the western basin of Lake Erie, were also caught to assess spatial differences since these fish are representative of the top trophic level in the relatively shallow (mean depth 7 m) and physically distinct western basin of Lake Erie. Fish were transported frozen for sizing, sex determination, and aging using otoliths. Whole fish samples were homogenized using a commercial meat grinder and stored at 25 °C before analysis.22 The method reported by Powley et al. was used to extract PFAs from 0.20.3 g of homogenate.23 After adding 40 μL of recovery standard consisting of isotopically labeled surrogate PFAs (Table S-4, Supporting Information), the sample was shaken with 5 mL of methanol. After centrifuging and removing the solvent extract, an additional 5 mL aliquot of methanol was added and the procedure was repeated. The combined methanolic extract was taken to dryness using a nitrogen evaporator.
PFPeA
’ MATERIALS AND METHODS
Lake
Table 1. Mean ( Standard Error Concentration of PFAs (ng/L) in Surface Water (1 to 10 m Depth) in the Laurentian Great Lakes
PFOS
PFECHS
PFMeCHS
PFECHS and related sulfonyl fluorides were included in the USEPA’s significant new use rule on PFSAs14 which requires notification prior to any manufacturing or import, implying a high level of concern about the health and environmental effects of the chemical. However, to date, there are no environmental measurements available for PFECHS. Unlike most persistent organic pollutants, PFAs do not partition extensively into lipid and, instead, are associated with proteineous tissues such as blood and liver.15 In lake trout (Salvelinus namaycush), which are a top predator in the Great Lakes, perfluorooctane sulfonate (PFOS) levels were 5121 ng/g wet weight (whole body homogenate) collected in 2001.16,17 A homologous series of PFCAs consisting of C8C15 chain lengths was also observed. PFAs in water from the Great Lakes and tributaries indicate a dominance of PFOS and perfluorooctanoate (PFOA) but unlike biota, PFAs with >9 carbon atoms are generally not observed in water samples.1820 These data suggest a propensity for bioaccumulation of longer chain aliphatic PFAs, which was supported by lab-based dietary and water-borne exposure of PFAs to rainbow trout.15,21 In the current research, we explore the propensity for bioaccumulation of PFMeCHS and PFECHS relative to C4C10 PFSAs and C5C12 PFCAs using lake trout in the binational Great Lakes as a model organism.
0.90 ( 0.22 0.88 ( 0.16 0.19 ( 0.02 0.65 ( 0.12 0.485 ( 0.09 0.086 ( 0.013 0.067 ( 0.025 0.14 ( 0.05 0.033 ( 0.002 0.013 ( 0.007 0.16 ( 0.03 0.26 ( 0.04 0.16 ( 0.03 85% with the exception of PFTrA and PFTeA which had mean recoveries of 71 and 45%, respectively. Routine method blanks were assessed by extracting blanks using surrogate standards and all reagents to determine method detection limits (MDL). MDL was defined as the concentration yielding the mean response plus 3 times the standard deviation of the blank response. PFOA and PFNA were the only analytes detected in method blanks with corresponding method detection limits (MDLs) of 0.42 ng/g and 0.14 ng/g expressed on a per wet weight basis, respectively. For all other analytes, MDL was defined by instrument detection limits corresponding to 0.10 ng/g based on the lowest calibration standard yielding a response with 3 times the signal-to-noise. Based on good recoveries and low blanks, concentrations reported herein were not corrected for recoveries, blank signal, or matrix effects. Surface Water. Bulk unfiltered water samples were taken at locations throughout the Great Lakes (Table S1 Supporting Information) in 2005, 2006, 2007, and 2010. Samples were collected by Environment Canada personnel aboard the Canadian Coast Guard vessel Limnos using a polytetrafluoroethenefree Go-flo (General Oceanics Inc., Florida) sampler at depths of 1, 5, or 10 m. Samples were stored in methanol-rinsed 1-L polyethylene bottles. Samples were extracted in 500-mL aliquots using Oasis WAX solid phase extraction (SPE) cartridges per the method reported by Taniyasu et al. using a full suite of isotopically labeled PFA surrogates.24 Method blanks consisted of extracting SPE cartridges, spiked with isotopically labeled recovery standards in order to assess contamination arising from reagents and materials used postsample collection and to calculate MDL. MDL was defined as the concentration yielding the mean method blank response plus 3 times the standard deviation of the blank response. MDLs corresponded to 0.0010 ng/L for PFPeA, 0.0054 ng/L PFHxA, 0.0070 ng/L PFHpA, 0.0121 ng/L PFOA, 0.0018 ng/L PFNA, 0.0011 ng/L PFUnA, and 0.0023 ng/L PFOS. There were no peaks with S/N > 3 in method blanks for PFBS, PFHxS, PFECHS, PFMeCHS, and PFDA. For these analytes, the MDL was estimated to be the instrumental detection limit, 0.0010 ng/L corresponding to the lowest calibration standard yielding a response with signal-to-noise >3. Analysis of PFECHS and other PFAs by LC-MS/MS. Fish extracts were analyzed using LC-MS/MS comprised of an Agilent 1200 series liquid chromatograph coupled to a Sciex API 2000 triple quadrupole mass spectrometer (Applied Biosystems-MDS Sciex, Concord, ON, Canada) using conditions outlined by Houde et al.25 Separation was carried out using a pentafluorophenyl stationary phase (Hypersil Gold PFP 150 3 mm, 3 μm, Thermo Scientific). Surface water extracts were analyzed by LC-MS/MS using an Agilent 1100 LC coupled to a Sciex 4000 QTRAP mass spectrometer (Applied
ARTICLE
Biosystems-MDS Sciex) using instrument parameters specified by Scott et al.20 Infusion of 50 ng/mL PFECHS solution in methanol into the mass spectrometer indicated two major MRM transitions, 461f99 and 461f381 m/z corresponding to [M] f [FSO3] and [M] f [M SO3] (Figure S1, Supporting Information), consistent with mass spectral studies by Hunt et al.26 Perfluoromethylcyclohexanesulfonate (PFMeCHS) was a minor component of the standard with MRM transitions 411f99 and 411f330 m/z and was judged to be 6% by mass of the PFECHS standard, assuming equivalent MS response. Because isotopically labeled surrogates for perfluorocyclohexane sulfonates are not available, PFECHS and PFMeCHS were quantified in sample extracts by using calibration curves based on relative response of PFECHS to 18O1,2-PFHxS. Linearity for all calibration curves was suitable with r2 > 0.999. Data Analysis. Bioaccumulation factors (BAFs) were estimated by dividing the mean ng 3 kg1 wet weight PFA concentration in fish by the mean surface water ng 3 L1 PFA concentration. Mean concentrations were only calculated when concentrations for >50% of the sample set were greater than MDL for a particular analyte. For the purposes of calculating mean, nondetects (i.e.,
