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Polyfluoroalkyl chemicals in house dust
ARTICLE IN PRESS Environmental Research 109 (2009) 518–523
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Environmental Research journal homepage: www.elsevier.com/locate/envres
Polyfluoroalkyl chemicals in house dust$ Kayoko Kato, Antonia M. Calafat , Larry L. Needham Division of Laboratory Sciences, National Center for Environmental Health, Centers for Disease Control and Prevention, 4770 Buford Hwy., Mailstop F53, Atlanta, GA 30341, USA
a r t i c l e in f o
a b s t r a c t
Article history: Received 12 September 2008 Received in revised form 5 January 2009 Accepted 15 January 2009 Available online 3 March 2009
We developed a high throughput analytical method using on-line solid phase extraction coupled with isotope dilution high-performance liquid chromatography–tandem mass spectrometry (on-line SPE–HPLC–MS/MS) to simultaneously determine the concentrations of 17 polyfluoroalkyl chemicals (PFCs) in house dust. The sample preparation includes dispersion of the dust samples in 0.1 M formic acid:MeOH (1:1), followed by agitation and filtration, addition of the isotope-labeled internal standard solution to the filtrate, and analysis by on-line SPE–HPLC–MS/MS. The limits of quantitation were o4.0 ng/g. The method accuracies ranged between 73.2% and 100.2% for the different analytes at two spike levels. We confirmed the validity of the method by analyzing 39 household dust samples collected in 2004. Of the 17 PFCs measured, 6 of them—perfluorobutane sulfonate (PFBuS), N-ethylperfluorooctane sulfonamide, 2-(N-ethyl-perfluorooctane sulfonamido) acetic acid (Et-PFOSA-AcOH), 2-(N-methyl-perfluorooctane sulfonamido) ethanol (Me-PFOSA-EtOH), perfluorohexane sulfonate (PFHxS), and perfluorooctane sulfonate (PFOS)—had detection frequencies 470%. We detected PFOS, PFBuS, and PFHxS at the highest median concentration, followed by Et-PFOSA-AcOH and Me-PFOSA-EtOH. Published by Elsevier Inc.
Keywords: Dust Polyfluoroalkyl chemicals Exposure PFCs
1. Introduction Polyfluoroalkyl chemicals (PFCs) owe many of their unique properties to the remarkable strength of the carbon–fluorine bond. PFCs have been used in a variety of commercial applications such as water, oil, soil and grease repellents for fabric, leather, rugs, carpets, stone, and tile; fire-fighting foams; alkaline cleaners; floor polish; sizing agents (to resist the spreading and penetration of liquids) for packaging and paper products; and leveling agents for coatings (Lau et al., 2007). PFCs are found around the world at concentrations in the low parts-per-billion in wildlife, humans, water, air, and soil (Giesy and Kannan, 2001, 2002; Kannan et al., 2004a, 2004b, 2002a, 2002b, 2005; Karrman et al., 2006; Lau et al., 2007; Martin et al., 2003a, 2003b, 2004; Olsen et al., 2003a, 2004a, 2004b; Prevedouros et al., 2006; Tittlemier et al., 2007). Because of their stable structure, some PFCs resist hydrolysis, photolysis, and biodegradation in the environment, and are of considerable concern as persistent organic pollutants. The toxicity of PFCs has been indicated in animal studies (Kennedy et al., 2004; Lau et al., 2004, 2007), although at serum concentrations that are orders of magnitude higher than those observed in the general population. The main source(s) and pathway(s) of exposure to PFCs in humans are yet to be clearly defined (EFSA, 2008). Drinking water can be an important exposure source (Emmett et al., 2006; Holzer
et al., 2008) as well as diet (Ericson et al., 2008; Fromme et al., 2007; Tittlemier et al., 2007). Additionally, dust, which has been used as indicator of indoor exposure to pesticides, could be a potential source of exposure to PFCs (Katsumata et al., 2006; Kubwabo et al., 2005; Martin et al., 2002; Moriwaki et al., 2003; Shoeib et al., 2004, 2005; Strynar and Lindstrom, 2008). Data on the concentrations of PFCs in children are limited and available only for the United States (Calafat et al., 2007a, 2007b; Olsen et al., 2004a) and the Faroe Islands (Weihe et al., 2008). The fact that concentrations of some PFCs in children appear to be higher than in adults suggested that there might be different sources and routes of exposure to PFCs for children and adults (Calafat et al. 2007a, 2007b; Olsen et al., 2004a). In particular, young children may be more exposed to dust than adults (US EPA, 2006) because children are in close contact with floors and dusty surfaces, and tend to put their hands in their mouth. In this study, we developed a rapid, accurate method for measuring PFCs in dust using a simple sample preparation and on-line solid-phase extraction (SPE) coupled with high-performance liquid chromatography (HPLC)–tandem mass spectrometry (MS/MS). As part of the validation of the method, we determined the concentrations of selected PFCs in household dust samples.
2. Materials and methods 2.1. Reagents
$
Disclaimer: The findings and conclusions in this paper are those of the authors and do not necessarily represent the views of the CDC. Corresponding author. Fax: +1770 488 4371. E-mail address: [email protected] (A.M. Calafat). 0013-9351/$ - see front matter Published by Elsevier Inc. doi:10.1016/j.envres.2009.01.005
Methanol and acetonitrile were purchased from Caledon (Georgetown, Ont., Canada) and were HPLC grade. Formic acid (99%) and acetic acid (glacial) were purchased from Sigma–Aldrich (St. Louis, MO). Ammonium hydroxide (30%) was
ARTICLE IN PRESS K. Kato et al. / Environmental Research 109 (2009) 518–523 purchased from J.T. Baker (Phillipsburg, NJ). Perfluorooctane sulfonamide (PFOSA, 98.9%), N-methyl-perfluorooctane sulfonamide (Me-PFOSA, 93.3%), N-ethylperfluorooctane sulfonamide (Et-PFOSA, 99.3%), 2-(N-methyl-perfluorooctane sulfonamido) ethanol (Me-PFOSA-EtOH, unknown purity), 2-(N-ethyl-perfluorooctane sulfonamido) ethanol (Et-PFOSA-EtOH, 97.7%), 2-(N-methyl-perfluorooctane sulfonamido) acetic acid (Me-PFOSA-AcOH, unknown purity), 2-(N-ethyl-perfluorooctane sulfonamido) acetic acid (Et-PFOSA-AcOH, 98.6%), perfluorobutane sulfonate potassium salt (PFBuS, 97.9%), perfluorohexane sulfonate potassium salt (PFHxS, 98.6%), perfluorooctane sulfonate potassium salt (PFOS, 86.9%), and perfluorooctanoic acid ammonium salt (PFOA, 95.2%) were provided by 3 M Company (Saint Paul, MN). Perfluorohexanoic acid (PFHxA, 97%), perfluoroheptanoic acid (PFHpA, 98%), perfluorononanoic acid (PFNA, unknown purity), perfluorodecanoic acid (PFDeA, unknown purity), perfluoroundecanoic acid (PFUA, 96%), and perfluorododecanoic acid (PFDoA, 96%) were purchased from Oakwood Products (West Columbia, SC). 1,2-13C-perfluorooctanoic acid (13C2-PFOA) was provided by Dupont Company (Wilmington, DE). 18O2-perfluorooctane sulfonate ammonium salt (18O2-PFOS) and 18O2-perfluorooctane sulfonamide (18O2-PFOSA) were purchased from RTI Laboratories (RTP, NC). Perfluoro-n-[1,2,3,4,5-13C5] nonanoic acid (13C5-PFNA), 2-perfluorooctyl [1,2-13C12]-ethanoic acid (13C2-PFDeA), N-methyld3-perfluoro-1-octanesulfonamide (D3-Me-PFOSA-AcOH), and N-ethyl-d5-perfluoro1-octanesulfonamide (D5-Et-PFOSA-AcOH) were purchased form Wellington Laboratories (Guelph, ON, Canada). We used Ottawa sand standard 20–30 mesh (Fisher Scientific) as a blank dust matrix. All chemicals and solvents were used without further purification. 2.2. Sample collection Household dust samples used for method validation had been collected in 2004 for an evaluation of the concentrations of polybrominated diphenyl ethers (Sjodin et al., 2008) from the United Kingdom (N ¼ 9), Australia (N ¼ 10), Germany (N ¼ 10), and Atlanta, GA, United States (N ¼ 10). Additional details about the origin of the dust samples and sampling procedures are detailed elsewhere (Sjodin et al., 2008). The particulate fraction (o2 mm) of these dust samples had been stored at the Centers for Disease Control and Prevention (CDC) (Atlanta, GA) in Ziplocs bags at room temperature until analysis.
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the isotope-labeled internal standards and 300 mL of 0.1 M formic acid. The contents of the autosampler vial were mixed well by use of a vortex mixer and analyzed by using on-line SPE–HPLC–MS/MS. 2.4. On-line SPE–HPLC–MS/MS The on-line SPE–HPLC–MS/MS system was built using a ThermoFinnigan Surveyor liquid chromatograph (ThermoFinnigan, San Jose, CA, USA) coupled with a ThermoFinnigan TSQ Quantum Ultra triple–quadrupole mass spectrometer equipped with a heated electrospray ionization interface (HESI), a ThermoFinnigan Surveyor LC pump, a ThermoFinnigan Surveyor sample pump, and a 6-port switching valve (Rheodyne MX7960, Rohnert Park, CA, USA). The ThermoFinnigan Xcalibur software controlled the operation of the pumps, switching valve, and mass spectrometer. After injection of the entire sample (425 mL), the PFCs in the dust extract were loaded on a Betasil C8 guard column (3.0 mm 10 mm, 5 mm, Thermo Electron Corporation, Bellefonte, PA) by the sample pump using 0.1% formic acid at 1000 mL/min for 1.5 min. Then the column was washed with 15% MeOH/85% 0.1% formic acid at 500 mL/min for 1.5 min, followed by 0.3% NH4OH in H2O at 500 mL/min for 1 min. After 4 min, the switching valve changed position, and the analytes were eluted from the column by the HPLC pump. The HPLC pump operated at a 300 mL/min flow rate with 20 mM ammonium acetate (pH 4) in water as mobile phase A and acetonitrile as mobile phase B. We used a Betasil C8 HPLC analytical column (2.1 mm 50 mm, 3 mm) for the chromatographic separation of the analytes. The HPLC gradient program (17 min) was as follows: started at 15% B (4 min), B content changed to 20% and increased to 90% (4–16 min), and then B content decreased to 15% (16–17 min). We used HESI in the negative ion mode under the following fixed instrument settings: spray ion voltage, 3000 V; HESI vaporizer temperature, 200 1C; sheath gas (N2) pressure, 50 arbitrary units; auxiliary gas (N2) pressure, 4 arbitrary units; ion sweep gas (N2), 26 arbitrary units; capillary temperature, 285 1C; collision gas (Ar) pressure, 1.5 mTorr. Ionization parameters and collision cell parameters were optimized for each analyte. Unit resolution was used for both Q1 and Q3 quadrupoles. The mass spectrometer was operated in selective reaction monitoring mode (Table 1). We monitored one precursor/product ion transition for each analyte and its isotope-labeled internal standard.
2.3. Extraction procedure and sample preparation 2.5. Data analysis We transferred approximately 300 mg dust to a 15 mL polypropylene tube and added 2000 mL of 0.1 M formic acid and 2000 mL of MeOH. We mixed the dust suspension by use of a vortex mixer for 10 s and in an ultrasonic bath for 10 min. Then the samples were left to pass by gravity through an empty (i.e., without sorbent) SPE cartridge (3 mL, Varian) fitted with two consecutive frits (20 mm polyethylene), and the filtrate was collected in a polypropylene tube. We then transferred 100 mL of the filtered methanol solution to a polypropylene autosampler vial, to which we also added 25 mL of methanol solution containing
For data acquisition and analysis, we used a program created with the Xcalibur software on a PC-based data system. The data analysis program automatically selected and integrated the signals for each transition of interest in the chromatogram. We manually corrected the peak integrations, if necessary. We used a response factor (RF), calculated as the peak area of each analyte ion divided by the peak area of its internal standard, for quantification. We used 18O2PFOSA internal standard for PFOSA, Me-PFOSA, Et-PFOSA, Me-PFOSA-EtOH,
Table 1 Mass spectrometric parameters for the analysis of household dust for polyfluoroalkyl chemicals. Abbreviation
Analyte
(M–H)precursor ion/product ion (m/z)
Collision energy (V)
T lens
PFBuS PFHxS PFOS 18 O2-PFOS PFHxA PFHpA PFOA 13 C2-PFOA PFNA 13 C5-PFNA PFDeA 13 C2-PFDeA PFUA PFDoA PFOSA 18 O2-PFOSA Me-PFOSA Et-PFOSA Me-PFOSA-AcOH D3-Me-PFOSA-AcOH Et-PFOSA-AcOH D5-Et-PFOSA-AcOH Me-PFOSA-EtOH Et-PFOSA-EtOH
Perfluorobutane sulfonate Perfluorohexane sulfonate Perfluorooctane sulfonate
299/99 399/99 499/99 503/103 313/269 363/319 413/369 415/370 463/419 468/423 513/469 515/470 563/519 613/569 498/78 502/82 512/169 526/169 570/512 573/515 584/526 589/531 616/59 630/59
33 36 27 27 13 13 14 14 13 13 15 15 17 18 27 27 33 23 19 19 21 21 16 19
93 103 104 104 70 70 74 74 97 97 109 109 120 114 100 100 109 109 132 132 122 122 116 109
Perfluorohexanoic acid Perfluoroheptanoic acid Perfluorooctanoic acid Perfluorononanoic acid Perfluorodecanoic acid Perfluoroundecanoic acid Perfluorododecanoic acid Perfluorooctane sulfonamide N-methyl-perfluorooctane sulfonamide N-ethyl-perfluorooctane sulfonamide 2-(N-methyl-perfluorooctane sulfonamido) acetic acid 2-(N-ethyl-perfluorooctane sulfonamido) acetic acid 2-(N-methyl-perfluorooctane sulfonamido) ethanol 2-(N-ethyl-perfluorooctane sulfonamido) ethanol
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Table 2 Method performance parametersa. Analyte
PFBuS PFHxS PFOS PFHxA PFHpA PFOA PFNA PFDeA PFUA PFDoA PFOSA Me-PFOSA Et-PFOSA Me-PFOSA-AcOH Et-PFOSA-AcOH Me-PFOSA-EtOH Et-PFOSA-EtOH
Accuracy (RSD, %)b
Extraction recovery (%) Low concentration
High concentration
Low concentration
High concentration
84.3 88.2 100.2 85.3 95.8 92.8 83.8 89.4 79.5 75.3 79.5 79.9 79.8 78.3 89.3 81.5 73.2
82.5 85.0 92.0 82.8 97.2 98.6 87.4 91.3 81.4 79.7 78.3 76.7 82.4 81.8 76.7 78.7 84.7
95.2 93.5 98.5 96.4 103.5 97.5 94.8 100.2 94.7 102.5 93.5 98.6 94.8 97.5 96.8 94.6 91.8
93.5 92.9 96.7 93.3 105.2 101.5 93.7 97.7 92.4 104.8 95.8 91.2 92.7 98.7 103.8 95.7 93.5
(7.8) (4.4) (4.6) (5.8) (6.3) (3.5) (2.9) (5.1) (7.4) (6.5) (2.8) (6.2) (7.2) (4.8) (3.2) (8.4) (6.8)
(6.4) (5.2) (5.2) (5.1) (4.9) (2.8) (3.3) (3.8) (8.5) (5.3) (2.6) (3.9) (9.7) (5.4) (3.4) (9.9) (7.2)
a The limits of quantitation are 2.6 ng/g, except for PFHpA, Me-PFOSA-EtOH, and Et-PFOSA-EtOH (4.0 ng/g). The extraction recovery and accuracy (i.e., spiked recovery) were estimated at low (30 ng/g, except for PFOS [300 ng/g]) and high (400 ng/g, except for PFOS [800 ng/g]) concentrations. b The precision of five replicate measurements (% RSD) is given in parentheses.
Et-PFOSA-EtOH; 18O2-PFOS for the three sulfonates; 13C2-PFOA for PFOA, PFHpA, PFHxA; and 13C2-PFDeA for PFDeA, PFUA, and PFDoA. We used 9 standard analyte concentrations, spiked into 0.1 M formic acid, encompassing the entire linear range of the method (0.1–500 ng/mL for PFOS and 0.1–100 ng/mL for other analytes) to construct daily calibration curves, weighted by the reciprocal of the standard amount (1/x), of RF versus the standard amount. The calibration curves were linear over three orders of magnitude and had correlation coefficients exceeding 0.99. Calibration curves were obtained from the standards spiked in 0.1 M formic acid and in Ottawa sand. Because slopes of the calibration curves from both matrices were similar (data not shown), only the calibration curve obtained from formic acid was used for quantification. Reagent blanks were analyzed along with the dust samples to control for any potential contamination during the analytical procedure.
2.6. Method recovery calculation Blank dust samples (i.e., Ottawa sand) were spiked with A) standard and isotope-labeled internal standard solution or B) standard only, and then analyzed following the method described above. We expressed the method recovery as follows: 100[analyte concentration from B]/[analyte concentration from A] (Table 2).
3. Results Spiked blank dust (i.e., Ottawa sand) samples were analyzed repeatedly to determine the limits of quantitation (LOQs) for each analyte, precision and the accuracy of the method. The LOQs were determined as 10S0, where S0 is the standard deviation as the concentration approaches zero (Taylor, 1987). S0, determined from 3 repeated measurements of the four lowest-concentration standards, was the y-intercept of the best-fit line of a plot of the standard deviation of these measurements versus the standard concentration. LOQs were 4.0 ng/g for PFHpA, Me-PFOSA-EtOH, Et-PFOSA-EtOH, and 2.6 ng/g for other PFCs. The method accuracy and precision were assessed through 5 replicate analyses of blank dust spiked at two different concentrations (30 and 400 ng/g; 300 and 800 ng/g for PFOS) and expressed as a percentage of the expected value. The method accuracy ranged between 91.8% and 105.2% for all analytes (Table 2). The method precision, expressed as the relative standard deviation was below 10% for all analytes (Table 2).
Table 3 Frequency of detection, selected percentiles concentrations, and maximum concentrations (ng/g) of polyfluoroalkyl chemicals in a group of 39 household dust samples. Analyte
PFBuS PFHxS PFOS PFHxA PFHpA PFOA PFNA PFDeA PFUA PFDoA PFOSA Me-PFOSA Et-PFOSA Me-PFOSA-AcOH Et-PFOSA-AcOH Me-PFOSA-EtOH Et-PFOSA-EtOH
Selected percentilesa 25th
50th
75th
86.3 47.7 31.7 oLOQ 33.9 oLOQ oLOQ oLOQ oLOQ oLOQ oLOQ oLOQ 86.2 oLOQ 92.4 64.8 oLOQ
359.0 185.5 479.6 oLOQ 97.3 96.5 oLOQ oLOQ oLOQ oLOQ oLOQ oLOQ 200.7 oLOQ 243.5 218.6 176.8
782.1 632.2 1456.6 409.4 532.5 667.7 26.2 61.0 oLOQ 37.6 16.1 oLOQ 424.6 110.3 417.9 416.7 462.2
Maximumb
Frequency of detection (%)
7718 43765 18071 3671 5195 9818 832 1965 732 1048 184 216 3974 4520 3795 3200 11507
92.3 79.5 74.4 46.2 61.2 64.1 25.6 38.5 20.5 43.6 23.1 10.3 87.8 33.3 87.2 79.6 38.5
a Limits of quantitation (LOQs) are 2.6 ng/g, except for PFHpA, Me-PFOSAEtOH, and Et-PFOSA-EtOH (4.0 ng/g). b All minimum values were oLOQ.
To validate the method, we analyzed 39 dust samples collected in 2004 from Germany, United Kingdom, Australia, and United States (Sjodin et al., 2008). Of the 17 analytes measured, six were detected (PFBuS, Et-PFOSA, Et-PFOSA-AcOH, Me-PFOSA-EtOH, PFHxS, and PFOS) in 470% of the samples; frequencies of detection of PFOA and PFHpA were 460% (Table 3). PFOS, PFBuS, and PFHxS were detected at the highest median concentration, followed by Et-PFOSA-AcOH and Me-PFOSA-EtOH. Except for the sulfonamido ethanol derivatives, the ethyl sulfonamides were detected more frequently and at higher median concentrations than the corresponding methyl sulfonamides. Statistically significant correlations were found between the concentrations of PFOS and PFOA (Spearman’s rank correlation
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Table 4 Spearman’s rank correlation coefficients for selected polyfluoralkyl chemicalsa.
PFBuS PFHxS PFOS PFHpA PFOA Et-PFOSA Et-PFOSA-AcOH a
PFHxS
PFOS
PFHpA
PFOA
Et-PFOSA
Et-PFOSA-AcOH
Me-PFOSA-EtOH
0.355
0.473 0.827
0.256 0.656 0.725
0.288 0.685 0.821 0.925
0.236 0.581 0.570 0.290 0.428
0.276 0.570 0.565 0.276 0.397 0.999
0.500 0.526 0.503 0.255 0.319 0.503 0.503
The correlation coefficients were computed only for the polyfluoroalkyl chemicals that had been detected in at least 50% of the dust samples analyzed for this study.
coefficient r ¼ 0.821) and PFHxS (r ¼ 0.827), between PFOA and PFHpA (r ¼ 0.925), and between Et-PFOSA-AcOH and Et-PFOSA (r ¼ 0.999) (Table 4).
In the typical chromatogram of the Ottawa sand (blank matrix) spiked with analytical standards of the PFCs of interest, several PFCs displayed a characteristic pattern (i.e., more than one unresolved signal or a shoulder adjacent to a major signal) (data not shown). To calculate the concentration of these analytes, we combined the area counts from the unresolved chromatographic peaks. Because the dust samples analyzed displayed a chromatographic pattern for these PFCs similar to that of the spiked standards, we assumed that the standard mixture was representative of the mixture identified in the samples. Although the formation of the product ion from a precursor ion may be different for the linear and branched PFC isomers, for the purposes of quantitation, we assumed equivalent responses for the different PFC isomers and calculated the concentrations on the basis of a single precursor/product ion transition (Table 1). The LOQs and accuracy of the method are comparable to those reported before (Kubwabo et al., 2005; Moriwaki et al., 2003; Strynar and Lindstrom, 2008) and are therefore adequate to evaluate the concentrations of PFCs in dust. In agreement with previous studies (Kubwabo et al., 2005; Moriwaki et al., 2003; Strynar and Lindstrom, 2008), PFOS was detected at the highest median concentrations followed by PFBuS and PFHxS. PFBuS is a final degradation product of perfluorobutanesulfonyl fluoride and related materials that are being introduced as replacements for the C-6 and C-8 surfactants analogs (Ehresman et al., 2007) which are no longer produced in the United States. PFHxS was used as a building block for compounds incorporated in fire-fighting foams and specific postmarket carpet treatment applications (Olsen et al., 2003b). One potential explanation for our findings is that carpeted floors trap dust, which may contain PFCs, such as PFHxS and PFBuS. A previous report showed that the mean concentrations of PFHxS in archived house dust samples collected in 2000–2001 in the United States were higher than for other PFCs (Strynar and Lindstrom, 2008); indoor dust concentration data on PFBuS, except for those reported here, are not available. The correlations between the concentrations of several PFCs (Table 4; e.g., PFOA and PFOS; PFOS and PFHxS) suggest that these PFCs may share similar sources or routes of exposure. More importantly, the frequency of detection of PFOS, PFOA, and PFHxS were comparable to the values reported before for samples collected from homes in the United States, Japan, and Canada (Kubwabo et al., 2005; Moriwaki et al., 2003; Strynar and Lindstrom, 2008) (Fig. 1). These data suggest that similar trends
Frequency of detection (%)
4. Discussion
100
PFHxS PFOS PFOA
80 60 40 20 0
Fig. 1. Comparison among studies of the frequency of detection of selected polyfluoroalkyl chemicals in household dust. The Canadian samples were collected in 2002–2003 (Kubwabo et al., 2005), the US samples were collected in 2000–2001 (Strynar and Lindstrom, 2008), and the samples used for this study were collected in 2004. The date of collection for the Japanese samples is unknown (Moriwaki et al., 2003). N represents the number of samples.
in the presence of these PFCs in household dust might exist regardless of geographical location. The median and maximum concentrations of PFHxS, PFOS, and PFOA by country in the present study were comparable to each other and also comparable to concentrations reported before for other localities in various countries (Fig. 2). Furthermore, median concentrations of other PFCs (e.g., PFHpA: 97.3 ng/g; PFNA, PFDeA, PFUA, and PFDoA:o2.6 ng/g), were similar to the median concentrations reported before from household dust collected in Ohio and North Carolina in the United States (Strynar and Lindstrom, 2008). These results suggest that although PFCs dust concentrations may vary according to the indoor environment, the concentrations from the current study are in the general range found in house dust from previous studies (Kubwabo et al., 2005; Moriwaki et al., 2003; Strynar and Lindstrom, 2008).
5. Conclusions We developed a simple, sensitive, accurate automated on-line SPE–HPLC–MS/MS method for the simultaneous measurement of 17 PFCs in dust. The method required minimum sample pretreatment and is labor and cost effective. Our results suggest that it is analytically possible to measure several of these PFCs in house-
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PFHxS PFOS PFOA 100000
Concentration (ng/g)
10000
1000
100
10
1 Canada Kubwado et al.
Japan USA Germany Moriwaki Strynar et al. et al.
UK
Australia
USA
Present study
Fig. 2. Comparison among studies of median (top of bar) and maximum (whisker) concentrations of selected polyfluoroalkyl chemicals in household dust samples (Kubwabo et al., 2005; Moriwaki et al., 2003; Strynar and Lindstrom, 2008). Only the maximum values are displayed for the German samples since the median concentrations were below the limit of quantitation (2.6 ng/g).
hold dust samples collected from various countries. However, comparing PFCs dust concentrations among different countries/ studies must be conducted with caution since important considerations, such as year of sample collection, collection protocols, and handling and storage of the samples may differ. Nevertheless, taken together, these data suggest that house dust could be an exposure source of PFCs in humans, although further research is needed to elucidate the exact exposure mechanism.
Acknowledgments We thank Dr. Andreas Sjodin (CDC) for providing the dust samples.
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Polyfluoroalkyl chemicals in house dust$ Kayoko Kato, Antonia M. Calafat , Larry L. Needham Division of Laboratory Sciences, National Center for Environmental Health, Centers for Disease Control and Prevention, 4770 Buford Hwy., Mailstop F53, Atlanta, GA 30341, USA
a r t i c l e in f o
a b s t r a c t
Article history: Received 12 September 2008 Received in revised form 5 January 2009 Accepted 15 January 2009 Available online 3 March 2009
We developed a high throughput analytical method using on-line solid phase extraction coupled with isotope dilution high-performance liquid chromatography–tandem mass spectrometry (on-line SPE–HPLC–MS/MS) to simultaneously determine the concentrations of 17 polyfluoroalkyl chemicals (PFCs) in house dust. The sample preparation includes dispersion of the dust samples in 0.1 M formic acid:MeOH (1:1), followed by agitation and filtration, addition of the isotope-labeled internal standard solution to the filtrate, and analysis by on-line SPE–HPLC–MS/MS. The limits of quantitation were o4.0 ng/g. The method accuracies ranged between 73.2% and 100.2% for the different analytes at two spike levels. We confirmed the validity of the method by analyzing 39 household dust samples collected in 2004. Of the 17 PFCs measured, 6 of them—perfluorobutane sulfonate (PFBuS), N-ethylperfluorooctane sulfonamide, 2-(N-ethyl-perfluorooctane sulfonamido) acetic acid (Et-PFOSA-AcOH), 2-(N-methyl-perfluorooctane sulfonamido) ethanol (Me-PFOSA-EtOH), perfluorohexane sulfonate (PFHxS), and perfluorooctane sulfonate (PFOS)—had detection frequencies 470%. We detected PFOS, PFBuS, and PFHxS at the highest median concentration, followed by Et-PFOSA-AcOH and Me-PFOSA-EtOH. Published by Elsevier Inc.
Keywords: Dust Polyfluoroalkyl chemicals Exposure PFCs
1. Introduction Polyfluoroalkyl chemicals (PFCs) owe many of their unique properties to the remarkable strength of the carbon–fluorine bond. PFCs have been used in a variety of commercial applications such as water, oil, soil and grease repellents for fabric, leather, rugs, carpets, stone, and tile; fire-fighting foams; alkaline cleaners; floor polish; sizing agents (to resist the spreading and penetration of liquids) for packaging and paper products; and leveling agents for coatings (Lau et al., 2007). PFCs are found around the world at concentrations in the low parts-per-billion in wildlife, humans, water, air, and soil (Giesy and Kannan, 2001, 2002; Kannan et al., 2004a, 2004b, 2002a, 2002b, 2005; Karrman et al., 2006; Lau et al., 2007; Martin et al., 2003a, 2003b, 2004; Olsen et al., 2003a, 2004a, 2004b; Prevedouros et al., 2006; Tittlemier et al., 2007). Because of their stable structure, some PFCs resist hydrolysis, photolysis, and biodegradation in the environment, and are of considerable concern as persistent organic pollutants. The toxicity of PFCs has been indicated in animal studies (Kennedy et al., 2004; Lau et al., 2004, 2007), although at serum concentrations that are orders of magnitude higher than those observed in the general population. The main source(s) and pathway(s) of exposure to PFCs in humans are yet to be clearly defined (EFSA, 2008). Drinking water can be an important exposure source (Emmett et al., 2006; Holzer
et al., 2008) as well as diet (Ericson et al., 2008; Fromme et al., 2007; Tittlemier et al., 2007). Additionally, dust, which has been used as indicator of indoor exposure to pesticides, could be a potential source of exposure to PFCs (Katsumata et al., 2006; Kubwabo et al., 2005; Martin et al., 2002; Moriwaki et al., 2003; Shoeib et al., 2004, 2005; Strynar and Lindstrom, 2008). Data on the concentrations of PFCs in children are limited and available only for the United States (Calafat et al., 2007a, 2007b; Olsen et al., 2004a) and the Faroe Islands (Weihe et al., 2008). The fact that concentrations of some PFCs in children appear to be higher than in adults suggested that there might be different sources and routes of exposure to PFCs for children and adults (Calafat et al. 2007a, 2007b; Olsen et al., 2004a). In particular, young children may be more exposed to dust than adults (US EPA, 2006) because children are in close contact with floors and dusty surfaces, and tend to put their hands in their mouth. In this study, we developed a rapid, accurate method for measuring PFCs in dust using a simple sample preparation and on-line solid-phase extraction (SPE) coupled with high-performance liquid chromatography (HPLC)–tandem mass spectrometry (MS/MS). As part of the validation of the method, we determined the concentrations of selected PFCs in household dust samples.
2. Materials and methods 2.1. Reagents
$
Disclaimer: The findings and conclusions in this paper are those of the authors and do not necessarily represent the views of the CDC. Corresponding author. Fax: +1770 488 4371. E-mail address: [email protected] (A.M. Calafat). 0013-9351/$ - see front matter Published by Elsevier Inc. doi:10.1016/j.envres.2009.01.005
Methanol and acetonitrile were purchased from Caledon (Georgetown, Ont., Canada) and were HPLC grade. Formic acid (99%) and acetic acid (glacial) were purchased from Sigma–Aldrich (St. Louis, MO). Ammonium hydroxide (30%) was
ARTICLE IN PRESS K. Kato et al. / Environmental Research 109 (2009) 518–523 purchased from J.T. Baker (Phillipsburg, NJ). Perfluorooctane sulfonamide (PFOSA, 98.9%), N-methyl-perfluorooctane sulfonamide (Me-PFOSA, 93.3%), N-ethylperfluorooctane sulfonamide (Et-PFOSA, 99.3%), 2-(N-methyl-perfluorooctane sulfonamido) ethanol (Me-PFOSA-EtOH, unknown purity), 2-(N-ethyl-perfluorooctane sulfonamido) ethanol (Et-PFOSA-EtOH, 97.7%), 2-(N-methyl-perfluorooctane sulfonamido) acetic acid (Me-PFOSA-AcOH, unknown purity), 2-(N-ethyl-perfluorooctane sulfonamido) acetic acid (Et-PFOSA-AcOH, 98.6%), perfluorobutane sulfonate potassium salt (PFBuS, 97.9%), perfluorohexane sulfonate potassium salt (PFHxS, 98.6%), perfluorooctane sulfonate potassium salt (PFOS, 86.9%), and perfluorooctanoic acid ammonium salt (PFOA, 95.2%) were provided by 3 M Company (Saint Paul, MN). Perfluorohexanoic acid (PFHxA, 97%), perfluoroheptanoic acid (PFHpA, 98%), perfluorononanoic acid (PFNA, unknown purity), perfluorodecanoic acid (PFDeA, unknown purity), perfluoroundecanoic acid (PFUA, 96%), and perfluorododecanoic acid (PFDoA, 96%) were purchased from Oakwood Products (West Columbia, SC). 1,2-13C-perfluorooctanoic acid (13C2-PFOA) was provided by Dupont Company (Wilmington, DE). 18O2-perfluorooctane sulfonate ammonium salt (18O2-PFOS) and 18O2-perfluorooctane sulfonamide (18O2-PFOSA) were purchased from RTI Laboratories (RTP, NC). Perfluoro-n-[1,2,3,4,5-13C5] nonanoic acid (13C5-PFNA), 2-perfluorooctyl [1,2-13C12]-ethanoic acid (13C2-PFDeA), N-methyld3-perfluoro-1-octanesulfonamide (D3-Me-PFOSA-AcOH), and N-ethyl-d5-perfluoro1-octanesulfonamide (D5-Et-PFOSA-AcOH) were purchased form Wellington Laboratories (Guelph, ON, Canada). We used Ottawa sand standard 20–30 mesh (Fisher Scientific) as a blank dust matrix. All chemicals and solvents were used without further purification. 2.2. Sample collection Household dust samples used for method validation had been collected in 2004 for an evaluation of the concentrations of polybrominated diphenyl ethers (Sjodin et al., 2008) from the United Kingdom (N ¼ 9), Australia (N ¼ 10), Germany (N ¼ 10), and Atlanta, GA, United States (N ¼ 10). Additional details about the origin of the dust samples and sampling procedures are detailed elsewhere (Sjodin et al., 2008). The particulate fraction (o2 mm) of these dust samples had been stored at the Centers for Disease Control and Prevention (CDC) (Atlanta, GA) in Ziplocs bags at room temperature until analysis.
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the isotope-labeled internal standards and 300 mL of 0.1 M formic acid. The contents of the autosampler vial were mixed well by use of a vortex mixer and analyzed by using on-line SPE–HPLC–MS/MS. 2.4. On-line SPE–HPLC–MS/MS The on-line SPE–HPLC–MS/MS system was built using a ThermoFinnigan Surveyor liquid chromatograph (ThermoFinnigan, San Jose, CA, USA) coupled with a ThermoFinnigan TSQ Quantum Ultra triple–quadrupole mass spectrometer equipped with a heated electrospray ionization interface (HESI), a ThermoFinnigan Surveyor LC pump, a ThermoFinnigan Surveyor sample pump, and a 6-port switching valve (Rheodyne MX7960, Rohnert Park, CA, USA). The ThermoFinnigan Xcalibur software controlled the operation of the pumps, switching valve, and mass spectrometer. After injection of the entire sample (425 mL), the PFCs in the dust extract were loaded on a Betasil C8 guard column (3.0 mm 10 mm, 5 mm, Thermo Electron Corporation, Bellefonte, PA) by the sample pump using 0.1% formic acid at 1000 mL/min for 1.5 min. Then the column was washed with 15% MeOH/85% 0.1% formic acid at 500 mL/min for 1.5 min, followed by 0.3% NH4OH in H2O at 500 mL/min for 1 min. After 4 min, the switching valve changed position, and the analytes were eluted from the column by the HPLC pump. The HPLC pump operated at a 300 mL/min flow rate with 20 mM ammonium acetate (pH 4) in water as mobile phase A and acetonitrile as mobile phase B. We used a Betasil C8 HPLC analytical column (2.1 mm 50 mm, 3 mm) for the chromatographic separation of the analytes. The HPLC gradient program (17 min) was as follows: started at 15% B (4 min), B content changed to 20% and increased to 90% (4–16 min), and then B content decreased to 15% (16–17 min). We used HESI in the negative ion mode under the following fixed instrument settings: spray ion voltage, 3000 V; HESI vaporizer temperature, 200 1C; sheath gas (N2) pressure, 50 arbitrary units; auxiliary gas (N2) pressure, 4 arbitrary units; ion sweep gas (N2), 26 arbitrary units; capillary temperature, 285 1C; collision gas (Ar) pressure, 1.5 mTorr. Ionization parameters and collision cell parameters were optimized for each analyte. Unit resolution was used for both Q1 and Q3 quadrupoles. The mass spectrometer was operated in selective reaction monitoring mode (Table 1). We monitored one precursor/product ion transition for each analyte and its isotope-labeled internal standard.
2.3. Extraction procedure and sample preparation 2.5. Data analysis We transferred approximately 300 mg dust to a 15 mL polypropylene tube and added 2000 mL of 0.1 M formic acid and 2000 mL of MeOH. We mixed the dust suspension by use of a vortex mixer for 10 s and in an ultrasonic bath for 10 min. Then the samples were left to pass by gravity through an empty (i.e., without sorbent) SPE cartridge (3 mL, Varian) fitted with two consecutive frits (20 mm polyethylene), and the filtrate was collected in a polypropylene tube. We then transferred 100 mL of the filtered methanol solution to a polypropylene autosampler vial, to which we also added 25 mL of methanol solution containing
For data acquisition and analysis, we used a program created with the Xcalibur software on a PC-based data system. The data analysis program automatically selected and integrated the signals for each transition of interest in the chromatogram. We manually corrected the peak integrations, if necessary. We used a response factor (RF), calculated as the peak area of each analyte ion divided by the peak area of its internal standard, for quantification. We used 18O2PFOSA internal standard for PFOSA, Me-PFOSA, Et-PFOSA, Me-PFOSA-EtOH,
Table 1 Mass spectrometric parameters for the analysis of household dust for polyfluoroalkyl chemicals. Abbreviation
Analyte
(M–H)precursor ion/product ion (m/z)
Collision energy (V)
T lens
PFBuS PFHxS PFOS 18 O2-PFOS PFHxA PFHpA PFOA 13 C2-PFOA PFNA 13 C5-PFNA PFDeA 13 C2-PFDeA PFUA PFDoA PFOSA 18 O2-PFOSA Me-PFOSA Et-PFOSA Me-PFOSA-AcOH D3-Me-PFOSA-AcOH Et-PFOSA-AcOH D5-Et-PFOSA-AcOH Me-PFOSA-EtOH Et-PFOSA-EtOH
Perfluorobutane sulfonate Perfluorohexane sulfonate Perfluorooctane sulfonate
299/99 399/99 499/99 503/103 313/269 363/319 413/369 415/370 463/419 468/423 513/469 515/470 563/519 613/569 498/78 502/82 512/169 526/169 570/512 573/515 584/526 589/531 616/59 630/59
33 36 27 27 13 13 14 14 13 13 15 15 17 18 27 27 33 23 19 19 21 21 16 19
93 103 104 104 70 70 74 74 97 97 109 109 120 114 100 100 109 109 132 132 122 122 116 109
Perfluorohexanoic acid Perfluoroheptanoic acid Perfluorooctanoic acid Perfluorononanoic acid Perfluorodecanoic acid Perfluoroundecanoic acid Perfluorododecanoic acid Perfluorooctane sulfonamide N-methyl-perfluorooctane sulfonamide N-ethyl-perfluorooctane sulfonamide 2-(N-methyl-perfluorooctane sulfonamido) acetic acid 2-(N-ethyl-perfluorooctane sulfonamido) acetic acid 2-(N-methyl-perfluorooctane sulfonamido) ethanol 2-(N-ethyl-perfluorooctane sulfonamido) ethanol
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Table 2 Method performance parametersa. Analyte
PFBuS PFHxS PFOS PFHxA PFHpA PFOA PFNA PFDeA PFUA PFDoA PFOSA Me-PFOSA Et-PFOSA Me-PFOSA-AcOH Et-PFOSA-AcOH Me-PFOSA-EtOH Et-PFOSA-EtOH
Accuracy (RSD, %)b
Extraction recovery (%) Low concentration
High concentration
Low concentration
High concentration
84.3 88.2 100.2 85.3 95.8 92.8 83.8 89.4 79.5 75.3 79.5 79.9 79.8 78.3 89.3 81.5 73.2
82.5 85.0 92.0 82.8 97.2 98.6 87.4 91.3 81.4 79.7 78.3 76.7 82.4 81.8 76.7 78.7 84.7
95.2 93.5 98.5 96.4 103.5 97.5 94.8 100.2 94.7 102.5 93.5 98.6 94.8 97.5 96.8 94.6 91.8
93.5 92.9 96.7 93.3 105.2 101.5 93.7 97.7 92.4 104.8 95.8 91.2 92.7 98.7 103.8 95.7 93.5
(7.8) (4.4) (4.6) (5.8) (6.3) (3.5) (2.9) (5.1) (7.4) (6.5) (2.8) (6.2) (7.2) (4.8) (3.2) (8.4) (6.8)
(6.4) (5.2) (5.2) (5.1) (4.9) (2.8) (3.3) (3.8) (8.5) (5.3) (2.6) (3.9) (9.7) (5.4) (3.4) (9.9) (7.2)
a The limits of quantitation are 2.6 ng/g, except for PFHpA, Me-PFOSA-EtOH, and Et-PFOSA-EtOH (4.0 ng/g). The extraction recovery and accuracy (i.e., spiked recovery) were estimated at low (30 ng/g, except for PFOS [300 ng/g]) and high (400 ng/g, except for PFOS [800 ng/g]) concentrations. b The precision of five replicate measurements (% RSD) is given in parentheses.
Et-PFOSA-EtOH; 18O2-PFOS for the three sulfonates; 13C2-PFOA for PFOA, PFHpA, PFHxA; and 13C2-PFDeA for PFDeA, PFUA, and PFDoA. We used 9 standard analyte concentrations, spiked into 0.1 M formic acid, encompassing the entire linear range of the method (0.1–500 ng/mL for PFOS and 0.1–100 ng/mL for other analytes) to construct daily calibration curves, weighted by the reciprocal of the standard amount (1/x), of RF versus the standard amount. The calibration curves were linear over three orders of magnitude and had correlation coefficients exceeding 0.99. Calibration curves were obtained from the standards spiked in 0.1 M formic acid and in Ottawa sand. Because slopes of the calibration curves from both matrices were similar (data not shown), only the calibration curve obtained from formic acid was used for quantification. Reagent blanks were analyzed along with the dust samples to control for any potential contamination during the analytical procedure.
2.6. Method recovery calculation Blank dust samples (i.e., Ottawa sand) were spiked with A) standard and isotope-labeled internal standard solution or B) standard only, and then analyzed following the method described above. We expressed the method recovery as follows: 100[analyte concentration from B]/[analyte concentration from A] (Table 2).
3. Results Spiked blank dust (i.e., Ottawa sand) samples were analyzed repeatedly to determine the limits of quantitation (LOQs) for each analyte, precision and the accuracy of the method. The LOQs were determined as 10S0, where S0 is the standard deviation as the concentration approaches zero (Taylor, 1987). S0, determined from 3 repeated measurements of the four lowest-concentration standards, was the y-intercept of the best-fit line of a plot of the standard deviation of these measurements versus the standard concentration. LOQs were 4.0 ng/g for PFHpA, Me-PFOSA-EtOH, Et-PFOSA-EtOH, and 2.6 ng/g for other PFCs. The method accuracy and precision were assessed through 5 replicate analyses of blank dust spiked at two different concentrations (30 and 400 ng/g; 300 and 800 ng/g for PFOS) and expressed as a percentage of the expected value. The method accuracy ranged between 91.8% and 105.2% for all analytes (Table 2). The method precision, expressed as the relative standard deviation was below 10% for all analytes (Table 2).
Table 3 Frequency of detection, selected percentiles concentrations, and maximum concentrations (ng/g) of polyfluoroalkyl chemicals in a group of 39 household dust samples. Analyte
PFBuS PFHxS PFOS PFHxA PFHpA PFOA PFNA PFDeA PFUA PFDoA PFOSA Me-PFOSA Et-PFOSA Me-PFOSA-AcOH Et-PFOSA-AcOH Me-PFOSA-EtOH Et-PFOSA-EtOH
Selected percentilesa 25th
50th
75th
86.3 47.7 31.7 oLOQ 33.9 oLOQ oLOQ oLOQ oLOQ oLOQ oLOQ oLOQ 86.2 oLOQ 92.4 64.8 oLOQ
359.0 185.5 479.6 oLOQ 97.3 96.5 oLOQ oLOQ oLOQ oLOQ oLOQ oLOQ 200.7 oLOQ 243.5 218.6 176.8
782.1 632.2 1456.6 409.4 532.5 667.7 26.2 61.0 oLOQ 37.6 16.1 oLOQ 424.6 110.3 417.9 416.7 462.2
Maximumb
Frequency of detection (%)
7718 43765 18071 3671 5195 9818 832 1965 732 1048 184 216 3974 4520 3795 3200 11507
92.3 79.5 74.4 46.2 61.2 64.1 25.6 38.5 20.5 43.6 23.1 10.3 87.8 33.3 87.2 79.6 38.5
a Limits of quantitation (LOQs) are 2.6 ng/g, except for PFHpA, Me-PFOSAEtOH, and Et-PFOSA-EtOH (4.0 ng/g). b All minimum values were oLOQ.
To validate the method, we analyzed 39 dust samples collected in 2004 from Germany, United Kingdom, Australia, and United States (Sjodin et al., 2008). Of the 17 analytes measured, six were detected (PFBuS, Et-PFOSA, Et-PFOSA-AcOH, Me-PFOSA-EtOH, PFHxS, and PFOS) in 470% of the samples; frequencies of detection of PFOA and PFHpA were 460% (Table 3). PFOS, PFBuS, and PFHxS were detected at the highest median concentration, followed by Et-PFOSA-AcOH and Me-PFOSA-EtOH. Except for the sulfonamido ethanol derivatives, the ethyl sulfonamides were detected more frequently and at higher median concentrations than the corresponding methyl sulfonamides. Statistically significant correlations were found between the concentrations of PFOS and PFOA (Spearman’s rank correlation
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Table 4 Spearman’s rank correlation coefficients for selected polyfluoralkyl chemicalsa.
PFBuS PFHxS PFOS PFHpA PFOA Et-PFOSA Et-PFOSA-AcOH a
PFHxS
PFOS
PFHpA
PFOA
Et-PFOSA
Et-PFOSA-AcOH
Me-PFOSA-EtOH
0.355
0.473 0.827
0.256 0.656 0.725
0.288 0.685 0.821 0.925
0.236 0.581 0.570 0.290 0.428
0.276 0.570 0.565 0.276 0.397 0.999
0.500 0.526 0.503 0.255 0.319 0.503 0.503
The correlation coefficients were computed only for the polyfluoroalkyl chemicals that had been detected in at least 50% of the dust samples analyzed for this study.
coefficient r ¼ 0.821) and PFHxS (r ¼ 0.827), between PFOA and PFHpA (r ¼ 0.925), and between Et-PFOSA-AcOH and Et-PFOSA (r ¼ 0.999) (Table 4).
In the typical chromatogram of the Ottawa sand (blank matrix) spiked with analytical standards of the PFCs of interest, several PFCs displayed a characteristic pattern (i.e., more than one unresolved signal or a shoulder adjacent to a major signal) (data not shown). To calculate the concentration of these analytes, we combined the area counts from the unresolved chromatographic peaks. Because the dust samples analyzed displayed a chromatographic pattern for these PFCs similar to that of the spiked standards, we assumed that the standard mixture was representative of the mixture identified in the samples. Although the formation of the product ion from a precursor ion may be different for the linear and branched PFC isomers, for the purposes of quantitation, we assumed equivalent responses for the different PFC isomers and calculated the concentrations on the basis of a single precursor/product ion transition (Table 1). The LOQs and accuracy of the method are comparable to those reported before (Kubwabo et al., 2005; Moriwaki et al., 2003; Strynar and Lindstrom, 2008) and are therefore adequate to evaluate the concentrations of PFCs in dust. In agreement with previous studies (Kubwabo et al., 2005; Moriwaki et al., 2003; Strynar and Lindstrom, 2008), PFOS was detected at the highest median concentrations followed by PFBuS and PFHxS. PFBuS is a final degradation product of perfluorobutanesulfonyl fluoride and related materials that are being introduced as replacements for the C-6 and C-8 surfactants analogs (Ehresman et al., 2007) which are no longer produced in the United States. PFHxS was used as a building block for compounds incorporated in fire-fighting foams and specific postmarket carpet treatment applications (Olsen et al., 2003b). One potential explanation for our findings is that carpeted floors trap dust, which may contain PFCs, such as PFHxS and PFBuS. A previous report showed that the mean concentrations of PFHxS in archived house dust samples collected in 2000–2001 in the United States were higher than for other PFCs (Strynar and Lindstrom, 2008); indoor dust concentration data on PFBuS, except for those reported here, are not available. The correlations between the concentrations of several PFCs (Table 4; e.g., PFOA and PFOS; PFOS and PFHxS) suggest that these PFCs may share similar sources or routes of exposure. More importantly, the frequency of detection of PFOS, PFOA, and PFHxS were comparable to the values reported before for samples collected from homes in the United States, Japan, and Canada (Kubwabo et al., 2005; Moriwaki et al., 2003; Strynar and Lindstrom, 2008) (Fig. 1). These data suggest that similar trends
Frequency of detection (%)
4. Discussion
100
PFHxS PFOS PFOA
80 60 40 20 0
Fig. 1. Comparison among studies of the frequency of detection of selected polyfluoroalkyl chemicals in household dust. The Canadian samples were collected in 2002–2003 (Kubwabo et al., 2005), the US samples were collected in 2000–2001 (Strynar and Lindstrom, 2008), and the samples used for this study were collected in 2004. The date of collection for the Japanese samples is unknown (Moriwaki et al., 2003). N represents the number of samples.
in the presence of these PFCs in household dust might exist regardless of geographical location. The median and maximum concentrations of PFHxS, PFOS, and PFOA by country in the present study were comparable to each other and also comparable to concentrations reported before for other localities in various countries (Fig. 2). Furthermore, median concentrations of other PFCs (e.g., PFHpA: 97.3 ng/g; PFNA, PFDeA, PFUA, and PFDoA:o2.6 ng/g), were similar to the median concentrations reported before from household dust collected in Ohio and North Carolina in the United States (Strynar and Lindstrom, 2008). These results suggest that although PFCs dust concentrations may vary according to the indoor environment, the concentrations from the current study are in the general range found in house dust from previous studies (Kubwabo et al., 2005; Moriwaki et al., 2003; Strynar and Lindstrom, 2008).
5. Conclusions We developed a simple, sensitive, accurate automated on-line SPE–HPLC–MS/MS method for the simultaneous measurement of 17 PFCs in dust. The method required minimum sample pretreatment and is labor and cost effective. Our results suggest that it is analytically possible to measure several of these PFCs in house-
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PFHxS PFOS PFOA 100000
Concentration (ng/g)
10000
1000
100
10
1 Canada Kubwado et al.
Japan USA Germany Moriwaki Strynar et al. et al.
UK
Australia
USA
Present study
Fig. 2. Comparison among studies of median (top of bar) and maximum (whisker) concentrations of selected polyfluoroalkyl chemicals in household dust samples (Kubwabo et al., 2005; Moriwaki et al., 2003; Strynar and Lindstrom, 2008). Only the maximum values are displayed for the German samples since the median concentrations were below the limit of quantitation (2.6 ng/g).
hold dust samples collected from various countries. However, comparing PFCs dust concentrations among different countries/ studies must be conducted with caution since important considerations, such as year of sample collection, collection protocols, and handling and storage of the samples may differ. Nevertheless, taken together, these data suggest that house dust could be an exposure source of PFCs in humans, although further research is needed to elucidate the exact exposure mechanism.
Acknowledgments We thank Dr. Andreas Sjodin (CDC) for providing the dust samples.
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