ARTICLE pubs.acs.org/est
Investigation on Per- and Polyfluorinated Compounds in Paired Samples of House Dust and Indoor Air from Norwegian Homes Line S. Haug,*,† Sandra Huber,‡ Martin Schlabach,§ Georg Becher,†,^ and Cathrine Thomsen† †
Norwegian Institute of Public Health, P.O. Box 4404 Nydalen, NO-0403 Oslo, Norway Norwegian Institute for Air Research (NILU), FRAM Centre, Hjalmar Johansens gate 14, NO-9296 Tromsø, Norway § Norwegian Institute for Air Research (NILU), Instituttveien 18, NO-2007 Kjeller, Norway ^ Department of Chemistry, University of Oslo, P.O. Box 1033 Blindern, NO-0315 Oslo, Norway ‡
bS Supporting Information ABSTRACT: Per- and polyfluorinated compounds (PFCs) have been found to be ubiquitously distributed in human populations, however the sources of human exposure are not fully characterized. A wide range of PFCs were determined in paired samples of indoor air and dust from 41 Norwegian households. Up to 18 ionic and 9 neutral PFCs were detected. The concentrations found are comparable to or lower than what has previously been reported in North America, Europe, and Asia. The highest median concentrations in dust were observed for perfluorohexanoic acid (28 ng/g), perfluorononanoic acid (23 ng/g), perfluorododecanoic acid (19 ng/g), and perfluorooctanoic acid (18 ng/g). However, perfluoroalkyl sulfonic acids (PFSAs) were also frequently detected. Fluortelomer alcohols were the most prominent compounds found in indoor air, with median concentrations for 8:2 fluortelomer alcohol, 10:2 fluortelomer alcohol, and 6:2 fluortelomer alcohol of 5173, 2822, and 933 pg/m3 air, respectively. All perfluoroalkyl sulfonamides and sulfonamidoethanols (FOSA/FOSEs) were detected in more than 40% of the air samples. For the first time, significant positive correlations (p < 0.05) between PFSAs in house dust and FOSA/FOSEs in the indoor air have been shown, supporting the hypothesis that FOSA/FOSEs may be transformed to PFSAs. Further, we found the age of the residence to be a predictor of PFC concentrations in both indoor air and house dust. These results are important for estimating the exposure to PFCs from the indoor environment and for characterization of exposure pathways.
’ INTRODUCTION In everyday life, we regularly come in contact with a wide variety of consumer products containing numerous chemicals. One large group of widely used chemicals is the per- and polyfluorinated compounds (PFCs), which have been used during the last 50 years in many commercial applications including surfactants, lubricants, paints, polishes, paper and textile coatings, food packaging, and fire-fighting foams.1 PFCs comprise a diverse class of chemicals consisting of an alkyl chain which is partly (poly) or fully (per) fluorinated and have different functional groups attached. Among the PFCs are perfluoroalkyl carboxylic acids (PFCAs), perfluoroalkyl sulfonic acids (PFSAs), fluorotelomer alcohols (FTOHs), perfluoroalkyl sulfonamides (FOSAs), and perfluoroalkyl sulfonamidoethanols (FOSEs). The physical and chemical properties, such as persistence and volatility, vary depending on the functional groups. Concerns about the persistence and bioaccumulative properties of PFCs were raised when the widely used surfactant perfluorooctane sulfonic acid (PFOS) was found to be ubiquitously distributed in wildlife and in humans.2,3 Further, several PFCAs r 2011 American Chemical Society
and PFSAs are suggested to have long elimination half-lives in humans46 and animal studies have shown hepatotoxicity, developmental toxicity, and immunotoxicity, as well as effects on thyroid hormones.2 PFOS has recently been included as a persistent organic pollutant (POP) in Annex B of the Stockholm Convention.7 For traditional POPs, such as dioxins and polychlorinated biphenyls, the major exposure route for general populations is through the diet.8 Dietary exposure has also been suggested to be the main exposure route for the PFCs,9,10 but in a recent study from the United States, the contribution from dust ingestion for two-year-old children was estimated to be nearly as great as the exposure from food.11 In a current review by Harrard et al.12 the importance of evaluating exposure from ingestion of house dust and Special Issue: Perfluoroalkyl Acid Received: October 13, 2010 Accepted: March 8, 2011 Revised: February 17, 2011 Published: March 18, 2011 7991
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Table 1. List of Analytes, Abbreviations, and Group Abbreviations compound
abbreviation
group abbreviation
determined in
ionic PFCs 6:2 fluorotelomer unsaturated carboxylic acid 8:2 fluorotelomer unsaturated carboxylic acid 10:2 fluorotelomer unsaturated carboxylic acid
6:2 FTUCA 8:2 FTUCA 10:2 FTUCA
FTUCAs
dust
6:2 fluorotelomer sulfonate 8:2 fluorotelomer sulfonate
6:2 FTS 8:2 FTS
FTSs
dust
perfluorobutane sulfonic acid perfluoropentane sulfonic acid perfluorohexane sulfonic acid perfluoroheptane sulfonic acid perfluorooctane sulfonic acid perfluorononane sulfonic acid perfluorodecane sulfonic acid
PFBS PFPeS PFHxS PFHpS PFOS PFNS PFDS
PFSAs
dust
perfluorobutanoic acid perfluoropentanoic acid perfluorohexanoic acid perfluoroheptanoic acid perfluorooctanoic acid perfluorononanoic acid perfluorodecanoic acid perfluoroundecanoic acid perfluorododecanoic acid perfluorotridecanoic acid perfluorotetradecanoic acid perfluoropentadecanoic acid
PFBA PFPeA PFHxA PFHpA PFOA PFNA PFDA PFUnDA PFDoDA PFTrDA PFTeDA PFPeDA
PFCAs
dust
neutral PFCs 4:2 fluortelomer alcohol 6:2 fluortelomer alcohol 8:2 fluortelomer alcohol 10:2 fluortelomer alcohol
4:2 FTOH 6:2 FTOH 8:2 FTOH 10:2 FTOH
FTOHs
air
perfluorooctane sulfonamide N-methylperfluorooctane sulfonamide N-ethylperfluorooctane sulfonamide 2-(N-methylperfluoro-1-octanesulfonamido)- ethanol 2-(N-ethylperfluoro-1-octanesulfonamido)-ethanol
PFOSA MeFOSA EtFOSA MeFOSE EtFOSE
FOSA/FOSEs
dust and air
inhalation of indoor air was underlined. At present, the understanding of relationships between use of PFC-containing consumer products and indoor contamination and exposures is limited. There are some data available for concentrations of PFCs in house dust,1321 while the data on concentrations of PFCs in indoor air are limited to three Canadian studies.14,22,23 In addition, concentrations of PFCs have been determined in samples of indoor air and house dust from Norwegian homes in two small studies, each comprising less than ten samples.24,25 The study by Huber et al.25 was a pilot study for the present study in order to test and demonstrate the applicability of the sampling methods. It has been demonstrated that FTOHs and FOSAs can be transformed in the atmosphere to PFCAs26,27 and that FOSA/ FOSEs can biodegrade to PFSAs.28 Thus, additional exposure to PFCAs and PFSAs may occur through degradation of “precursors” such as FTOHs and FOSA/FOSEs. No studies have so far explored associations between volatile PFCs in indoor air (FOSA/FOSEs and FTOHs) and ionic PFCs (PFCAs and PFSAs) in house dust from the same households. A positive association between these compounds would indicate that FOSA/FOSEs and FTOHs in indoor air contributes considerably to the concentrations of PFCAs and PFSAs in house dust.
The aims of this study were to determine concentrations of PFCs in paired samples of dust and air from 41 Norwegian households, explore correlations among the determined compounds and possible associations to different factors likely to influence the indoor atmosphere (e.g., presence of certain products, characteristics of the room and building).
’ EXPERIMENTAL SECTION Data Collection. The work presented in this paper is part of a larger study aiming at characterizing different human exposure pathways for PFCs by comparing estimates of exposure from food, indoor air, and house dust with biomarkers of exposure. We also wanted to assess infants’ exposure through breast milk, and therefore aimed at recruiting breast-feeding mothers for the study. A study group of 41 female volunteers from the area of Oslo, Norway, was established. Informed consent was obtained from all the participants and the project was approved by the Regional Committee for Medical Research Ethics and the Data Inspectorate. Samples of house dust as well as indoor air from the participants’ residences were collected between February and May 2008 according to procedures described by Huber et al.25 The samples of air and dust were 7992
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Table 2. Concentrations of PFCs in Dust and Air from Norwegian Households LOQ mean
6:2 FTUCA 8:2 FTUCA 6:2 FTS 8:2 FTS PFOSA MeFOSA EtFOSA MeFOSE PFBS PFHxS PFHpS PFOS PFDS PFPeA PFHxA PFHpA PFOA PFNA PFDA PFDoDA PFTrDA PFTeDA 4:2 FTOH 6:2 FTOH 8:2 FTOH 10:2 FTOH MeFOSA EtFOSA MeFOSE EtFOSE a
35 11 9.0 15 1.8 0.56 2.3 13 1.3 8.4 0.29 11 3.5 3.9 33 10 20 29 4.1 22 8.8 5.3 4.8 1492 6438 4088 14 9.6 346 97
min
25th pa
50th pa
75th pa
4.3 1.0 2.2 2.2 0.22 0.27 0.26 3.5 0.17 0.21 0.10 1.2 0.15 1.5 4.3 4.5 6.2 3.9 1.1 1.4 1.1 1.1
6.6 2.8 3.5 3.6 0.36 0.43 0.51 6.3 0.29 0.40 0.16 2.4 0.61 2.3 11 6.7 11 10 2.7 9.2 3.7 2.2
dust, ng/g 10 3.6 4.8 5.3 0.45 0.51 0.61 9.0 0.40 0.60 0.19 3.1 1.1 3.0 28 9.4 18 23 4.1 19 6.8 3.3
0.70 63 921 377 0.40 0.30 63 3.7
1.7 477 3771 1850 0.73 0.40 125 38
air, pg/m3 2.4 933 5173 2822 8.3 0.50 265 78
19 6.4 8.8 9.5 0.66 0.66 0.88 14 0.74 1.3 0.24 8.1 3.4 3.9 54 12 25 43 4.8 34 12 5.3 3.9 2166 7758 4868 20 14 392 137
max
301 78 53 99 41 1.1 33 90 9.8 142 2.1 94 42 29 96 28 56 92 12 78 46 35 38 9414 25323 28898 70 95 1433 338
ndetb
min
max
3 8 4 6 10 1 6 4 9 22 4 41 41 1 30 5 35 25 10 40 39 3
6.1 1.5 1.2 3.1 3.1 0.34 0.46 0.49 5.0 0.23 0.30 0.15 0.09 0.06 2.1 5.2 6.3 4.9 5.5 2.6 1.2 1.4
426 15 11 75 75 1.2 1.5 1.8 30 1.1 1.1 0.88 0.61 0.28 13 30 40 31 43 17 7.9 8.8
7 40 40 40 27 16 40 40
0.94 0.79 0.32 0.76 0.35 0.36 0.90 0.70
10 26 7.9 25 3.4 2.7 3.1 2.4
Percentiles. b ndet: number of samples in which the PFC concentrations were > LOQ (total n = 41 (dust) and 40 (air)).
collected on two consecutive days while the residence was in regular use. In brief, airborne PFCs in gaseous and particulate phase were trapped on polyurethane foam PUF-XAD2-PUF tubes using lowvolume active air samplers (4 L/min per tube for 24 h). Two parallel tubes were connected to the pump to increase the amount of air sampled, giving a total volume of 11.52 m3 air sampled. House dust was sampled by the research team using a vacuum cleaner equipped with a special forensic nozzle with a one-way filter housing placed in front of the vacuum cleaner tube. The dust samples were collected from elevated surfaces such as bookshelves and window sills (deposited dust) and not from the floor, as dust collected from elevated surfaces may reflect the exposure of adults better. The air sampler tubes and the filter housing containing the house dust were wrapped in aluminum foil, and each sample set was packed in a polyethylene bag and stored at below 18 C until sample preparation. The women completed a detailed questionnaire covering different lifestyle and household factors (see Supporting Information). Chemicals and Analysis. An overview of the analytes, their abbreviations, and abbreviations for compound groups is given in Table 1. The samples of house dust and indoor air were extracted and analyzed according to methods described by Huber et al.25 and Berger et al.29 More information regarding the analyses can be found in the Supporting Information. The vapor pressures of PFCAs and PFSAs in their dissociated forms are expected to be very low,30 thus these PFCs are expected to be mainly bound to particles. Neutral PFCs have high vapor pressures and are found predominately in the gas phase.30
Therefore, only neutral PFCs were determined in the samples of indoor air, and the ionic PFCs were determined in the samples of house dust. The FOSA/FOSEs can also be determined along with the ionic PFCs using liquid chromatographymass spectrometry in samples of house dust, but were observed above the limit of quantification (LOQ) only in a few samples and in low concentrations, as expected. Statistics. SPSS version 17.0 (SPSS Inc. Chicago, IL, USA) was used for the statistical analyses. PFCs that were not detected or found in concentrations below the LOQs (see Supporting Information), were replaced by the LOQs divided by the square root of two.31 The concentrations of PFCs in dust and air were not normally distributed, hence Spearman rank correlation was used to investigate bivariate relationships and logarithmic transformation was applied prior to multiple linear regression analyses. A significance level of p = 0.05 was used. Bivariate correlations were explored for PFCs found in more than 40% of either the dust or air samples. A list of all the variables that were assessed is given in Supporting Information Table S1. Factors that were significantly correlated (p < 0.05) to one or more of the determined PFCs are presented in Table 2. All factors with p < 0.2 were evaluated in the multiple linear regression analyses.
’ RESULTS AND DISCUSSION Concentrations. Samples of house dust and indoor air were collected from 41 households in the Oslo area to investigate ranges of PFCs in the indoor environment in a variety of Norwegian homes, as 7993
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Figure 1. Clustered bar charts of concentrations of all detected PFCAs (A), PFSAs (B), FTS/FTUCA (C), and FOSA/FOSEs (D) in the individual samples of house dust and FTOHs (E) and FOSA/FOSEs (F) in indoor air.
part of a larger study on exposure pathways. In Table 2 descriptive statistics for the 27 PFCs detected in at least one sample are given. 10:2 FTUCA, PFPS, PFNS, PFBA, PFUnDA, PFPeDA, and EtFOSE were not detected in any of the house dust samples. Only PFOS and PFDS were detected in all samples of house dust, while more than 50% of the samples contained PFHxS, PFHxA, PFOA, PFNA, PFDoDA, and PFTrDA above the LOQs. The FTUCAs, FTSs, FOSA/FOSEs, and the remaining PFCAs and PFSAs were detected in less than 25% of the samples. The highest median concentration in the dust was observed for PFHxA (28 ng/g) followed by PFNA (23 ng/g), PFDoDA (19 ng/g), and PFOA (18 ng/g). Of the PFSAs the highest median concentrations were seen for PFOS (3.0 ng/g), PFDS (1.1 ng/g), and PFHxS (0.60 ng/g). In
Figure 1ad clustered bar charts of concentrations of all detected PFCAs (a), PFSAs (b), FTS/FTUCAs (c), and FOSA/FOSEs (d) in the individual dust samples are presented. A few samples had considerably higher concentrations of the PFSAs (Figure 1b) or the FOSA/FOSEs (Figure 1d) than the other samples, while the concentrations of sum PFCAs were more equally distributed (Figure 1 a). This may indicate that there are several sources of PFCAs in Norwegian homes while the sources of PFSAs and FOSA/ FOSEs are more distinct and thus present in only some of the homes. FTS/FTUCAs were observed in 18 of the 41 samples and no particular pattern was seen. The concentrations of PFCs in house dust found in the present study are comparable to what was reported in homes 7994
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Table 3. Spearman Rank Correlations between PFCs in Samples of Dust and Air from Norwegian Households (Significant Correlations Are Presented in Bold Text) air
dust
8:2 FTOH 10:2 FTOH MeFOSA MeFOSE
EtFOSE
PFHxA
0.072
- 0.362*
PFOA
PFNA
PFDoDA PFTrDA
PFHxS
PFOS
PFDS
0.012
air 6:2 FTOH 8:2 FTOH 10:2 FTOH MeFOSA
0.395*
0.327*
0.075
0.111
0.079
0.031
0.166
0.137
0.116
0.050
0.608**
0.101 0.008
0.169 0.277
0.227 0.324*
0.146 0.169
0.058 0.288
0.044 0.15
0.013 0.054
0.031 0.163
0.058 0.105
0.220 0.472**
0.184 0.334*
0.589**
0.473**
0.164
0.119
0.016
- 0.333*
0.042
0.160
0.364*
0.337*
0.226
0.202
0.185
0.08
0.307
0.200
0.228
0.234
0.236
0.071
0.394*
0.366*
**
MeFOSE
0.560
0.095
0.276 *
EtFOSE
0.391
0.169
0.147
**
0.336*
**
0.407
0.277
0.178
0.338*
0.419
dust PFHxA PFOA
0.147
0.28 0.047
PFNA PFDoDA
0.104 **
0.713 0.300
PFTrDA PFHxS
0.314*
0.162
0.363
0.143 0.055
0.126 0.057
0.135 0.189
0.107
0.100
0.139
0.674**
0.609** 0.708**
PFOS *
*
**
Correlation was significant at the 0.05 level (two tailed). Correlation was significant at the 0.01 level (two tailed).
from Tromsø (Norway)25 and Belgium,21 and in general lower than observed in Sweden,15 USA,16,17,20 Japan,18 UK,16,20 Germany,16,20 Australia,16,20 Canada,13,20 France,20 Kazahkstan,20 and Thailand.20 However, even lower concentrations have been found in house dust from China.19 As pointed out by Harrard et al.,12 a variety of approaches to sampling indoor dust has been applied, complicating comparisons among studies. The only two studies that used comparable sampling methods as in the present study were the studies from Tromsø25 and Sweden.15 In addition to the many sampling approaches and extraction methods used, differences in concentrations among studies could also be due to geographic and temporal variations in use of PFC-containing products. In the study by Bj€orklund et al.,15 using a very similar sample preparation method, higher concentrations were reported. It is thus not likely that our sample preparation method is the reason for our generally low PFC levels. Five of eight PFCs determined in indoor air were observed above the LOQs in all samples (see Table 2). The median concentrations of the most prominent compounds, 8:2 FTOH, 10:2 FTOH ,and 6:2 FTOH, were 5173, 2822, and 933 pg/m3 air, respectively. The concentrations of FTOHs observed were similar to what has previously been found.22,24,25 MeFOSE and EtFOSE were the dominating FOSA/FOSEs with median values of 265 and 78 pg/m3. FOSA/FOSEs were observed in concentrations comparable to those found by Huber et al.,25 but lower than those reported elsewhere.14,23,24 FTOHs and FOSA/ FOSEs are often used as active compounds in surfactants for impregnation treatment of furniture and floors. In consumer products like waterproofing agents, papers, textiles, leather, and carpets which have been produced the last years, FTOHs are generally detected in higher concentrations than FOSA/FOSEs (Dorte Herzke, personal communication), which is in accordance with the relative distribution patterns observed in the present study.
Correlations. Associations between the PFCs frequently found in house dust and air were explored using Spearman Rank Correlations (see Table 3). Significant correlations (p < 0.05) were observed among the FTOHs and FOSA/FOSEs in indoor air. In addition, 10:2 FTOH was weakly but significantly correlated (p < 0.05) to EtFOSE. In house dust, significant associations (p < 0.05) were seen among all the PFSAs, while correlations within the PFCAs as well as between PFCAs and PFSAs were less frequent. It has been demonstrated that FTOHs are likely to degrade to PFCAs in the atmosphere,26 which should result in positive associations between FTOHs and PFCAs in air and dust. However, except for a negative association between 6:2 FTOH and PFHxA no such correlations were observed in this study. Biodegradation of EtFOSA to PFOS has been reported28 and it has been anticipated that FOSA/FOSEs may also be transformed to PFSAs in the atmosphere. In the present study significant correlations (p < 0.05) between PFOS and PFDS in house dust and most FOSA/FOSEs in the indoor air was observed supporting this hypothesis. Significant correlations (p < 0.05) were also seen between 10:2 FTOH in air and PFOS or PFDS in house dust. Determinants. Several factors are likely to influence the indoor atmosphere and the concentrations of PFCs found in indoor air and house dust. Identification of such factors will contribute to the knowledge on pathways for human exposure to PFCs. Based on information from the questionnaire, we explored the effect of room characteristics (e.g., volume, floor space, ventilation), building characteristics (e.g., age, apartment/house) and proximity to a high-traffic road, on concentrations of PFCs determined in indoor air and house dust. Further, the influence of housekeeping practice, consumer habits (buying new or used products), and presence of products potentially containing PFCs (e.g., rugs, kitchen utensils, clothes, shoes) were also assessed. In 7995
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ARTICLE * Correlation was significant at the 0.05 level (two tailed). ** Correlation was significant at the 0.01 level (two tailed). a Factors that were significantly correlated (p < 0.05) to one or more of the PFCs are presented. A list of all variables assessed is presented in Supporting Information Table S1.
-0.318* -0.435** -0.362* 0.199 0.288 0.360* 0.074 0.149 0.12 0.383* 0.3 0.339* 0.023 0.135 0.226 0.058 0.087 0.138 0.143 0.052 0.044 0.204 0.064 0.035 0.087 0.103 0.08 0.053 0.022 0.016 0.118 0.1 -0.318* 0.095 0.172 0.165 0.052 0.058 0.095 0.364* 0.151 0.185 0.062 0.139 0.244 0.368* 0.175 0.163 0.087 0.009 0.181 0.17 -0.521** 0.147 0.156 0.231 0.117 0.012 0.148 0.287 0.295 0.091 0.141 0.116 0.182 0.004 0.012 0.023 0.099 0.021 0.126 0.087 0.207 0.02 0.057 0.194 0.187 0.338* 0.037 0.103 0.139 0.139 0.25 0.096 0.146 0.124 0.152 0.191 0.011 0.26 0.148 0.186 0.135 0.094 0.292 0.017 0.255 0.085 -0.355* 0.111 0.149 0.457** 0.081 0.213 0.244 0.083 0.021 0.07 0.178 0.101 -0.372* 0.049 0.013 0.125 0.265 0.2 0.03 0.042 0.082 0.008 0.266 0.089 0.122 0.248 0.168 0.091 0.133 0.085 0.13 0.028 -0.392* -0.313* 0.048 0.152 0.384* 0.083 0.321* 0.085 0.069 0.006 age of the residence (years) number of years the residence has been occupied by the participant (years) presently residing in an apartment (as opposed to a house) (yes/no) volume of living room (m3) forced ventilation in the residence (yes/no) has a rug in the living room (yes/no) has a synthetic rug in the living room (yes/no) owns Gore-tex or similar clothing (yes/no) has kitchen utensils of nonstick material (yes/no) number of times the living room is vacuumed/washed per month
PFDS PFOS PFHxS dust
PFDoDA PFTrDA PFNA PFOA
air
6:2 FTOH 8:2 FTOH 10:2 FTOH MeFOSA MeFOSE EtFOSE PFHxA parametera
Table 4. Spearman Rank Correlations between PFCs in Samples of Dust and Air from Norwegian Households and Indoor Parameters (Significant Correlations are Presented in Bold Text)
Environmental Science & Technology
Table 4, different factors that were significantly correlated (p < 0.05) to one or more of the PFCs are presented. A list of all variables assessed is presented in Supporting Information, Table S1. As can be seen, 6:2 FTOH and 10:2 FTOH were significantly associated (p < 0.05) with the age of the residence, and 8:2 FTOH was borderline significant (p = 0.10). Further, the concentration of 6:2 FTOH was also influenced by how long the women had been living in the apartment, whether the apartment had forced ventilation, and whether or not a synthetic rug was present in the living room. A significant positive correlation (p < 0.05) between the concentration of MeFOSA and how long the women had been living in this apartment was observed, while lower levels of MeFOSE were found when using nonstick cookware. The amount of PFOA measured in house dust was not associated to any of the factors investigated, but the age of the residence was borderline significant. Having clothes with a Gore-tex membrane or similar was a predictor for PFHxA concentrations in house dust, while a rug in the living room was associated with an increase in the concentration of PFDoDA. A significant positive correlation (p < 0.05) between the amount of PFTrDA in the house dust and frequency of cleaning the floor in the living room was observed. Lower levels were found for PFTrDA and PFNA when living in an apartment as opposed to living in a house or semidetached house. The age of the residence was a significant predictor (p < 0.05) for all three PFSAs, with highest concentrations found in new buildings. The volume of the living room was also found to be important for the concentrations of PFHxS and PFDS, a borderline significance was observed for PFOS (p = 0.056). Furthermore, PFDS was significantly associated (p < 0.05) to how long the women had been living in the residence. As only 41 households were included in this study, these associations must be interpreted with care. For most of the studied factors significant relationships (p < 0.05) were observed for only one or two compounds. This can of course be due to different sources or specific physicalchemical properties for these compounds, but could also indicate that the relationships are accidental. However, the age of the residence seems to be a factor influencing air and dust concentrations of several PFCs thus making a causal relationship more likely. In Figure 2 scatterplots between age of the residence and logarithmic concentrations of PFOA (a), PFOS (b), 6:2 FTOH (c), and MeFOSE (d) are depicted, illustrating decreasing concentrations with increasing age of the apartment for these compounds. To explore this further, multiple linear regressions were performed for the three FTOHs, the three PFSAs, and for PFOA, including all factors with p < 0.2 in the bivariate correlations. The age of the residence remained a significant factor (p < 0.05) for all compounds also in the multiple regression models (results not shown), confirming the findings in the bivariate analyses. An explanation for the lower levels observed in old houses compared to new ones (range 3128 years) might be differences in the construction of the buildings, the building materials, and the age of the building materials. Older houses were probably less tightly constructed, and had thus “higher natural ventilation rates”. It could also be that persons living in old residences own less PFC-containing consumer products, however this was not reflected in the information given in the questionnaire (see Supporting Information Table S1). Previously, a study from Canada showed that old houses had lower concentrations of PFHxS, PFOS, and PFOA in house dust compared to new ones.13 It turned out that the percentage of home carpeting was positively correlated to these compounds, and as old houses tended to have less carpeting this was 7996
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Figure 2. Scatterplot between “age of the residence” and logarithmic concentrations of PFOA (A) and PFOS (B) in house dust (ng/g) and 6:2 FTOH (C) and MeFOSE (D) in indoor air (ng/m3).
suggested to be the reason for the lower PFC levels found in the old houses. Carpets were also identified as possible sources of several PFCAs and PFSAs in a second study from Canada,32 while a third study showed contradicting results.14 None of the apartments in our study had wall to wall carpets. We therefore investigated having a rug in the living room in relation to the level of the PFCs in dust and air, but no associations were seen (with the exception of PFHxA, for which there was no association to the age of the residence). This study showed the presence of a wide range of PFCs in house dust and indoor air from Norwegian households, in concentrations comparable to or lower than what has previously been reported. For the first time, associations between volatile PFCs in indoor air and ionic PFCs in house dust from the same houses have been explored. Significant positive correlations (p < 0.05) between FOSA/FOSEs in air and PFSAs in dust have been shown, supporting the hypothesis that FOSA/FOSEs may degrade abiotically to PFSAs and thereby contribute to indoor pollution with PFSAs. This information is valuable for characterization of exposure pathways as well as for modeling purposes in general. Significantly (p < 0.05)
lower concentrations of several PFCs were observed in old houses compared to new ones, but the cause of this remains to be clarified.
’ ASSOCIATED CONTENT
bS
Supporting Information. Description of methods used for determinations and the variables that were assessed for bivariate correlations to concentrations of PFCs in indoor air and house dust. This information is available free of charge via the Internet at http://pubs.acs.org/.
’ AUTHOR INFORMATION Corresponding Author
*Tel: þ47 21076549; fax: þ47 21076686; e-mail: line.smastuen.
[email protected].
’ ACKNOWLEDGMENT We greatly acknowledge all the participants who allowed us to collect samples of house dust and indoor air in their homes and 7997
dx.doi.org/10.1021/es103456h |Environ. Sci. Technol. 2011, 45, 7991–7998
Environmental Science & Technology made an effort to fill in the extensive questionnaires, May Frøshaug and Ole Henning Jakobsen for help with the sample preparations, Christian Dye and Anders Røsrud Borgen for performing the LC-MS analysis, as well as the Research Council of Norway for financial support.
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