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INVESTIGATION OF THE BEST APPROACH FOR ASSESSING HUMAN EXPOSURE TO POLY- AND PERFLUOROALKYL SUBSTANCES THROUGH INDOOR AIR Juan A. Padilla-Sánchez, Eleni Papadopoulou, Somrutai Poothong, and Line S. Haug Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.7b03516 • Publication Date (Web): 10 Oct 2017 Downloaded from http://pubs.acs.org on October 11, 2017
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INVESTIGATION OF THE BEST APPROACH FOR ASSESSING HUMAN EXPOSURE TO POLY- AND PERFLUOROALKYL SUBSTANCES THROUGH INDOOR AIR Juan A. Padilla-Sánchez*, Eleni Papadopoulou, Somrutai Poothong, Line S. Haug Department of Environmental Exposure and Epidemiology, Domain of Infection Control and Environmental Health, Norwegian Institute of Public Health, P.O. Box 4404 Nydalen, NO0403 Oslo, Norway.
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Abstract
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Per- and polyfluoroalkyl substances (PFASs), including fluorotelomer alcohols (FTOHs),
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perfluoroalkyl sulfonamidoethanols (FOSEs) and perfluoroalkyl sulfonamides (FOSAs) were
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assessed in 61 residential indoor air and 15 personal air samples collected in Oslo area,
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Norway.
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FTOHs were detected in all samples, and the median concentrations in residential indoor air
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were 2970, 10400 and 3120 pg m-3 for 6:2, 8:2 and 10:2 FTOH, respectively. This is similar
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to or higher than previously reported in studies from the same geographical area and
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worldwide. FOSEs and FOSAs were detected in 49–70% and 7–13% of the residential indoor
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air samples, respectively.
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The median FTOH concentrations observed in personal air were 1970, 7170, and 1590 pg m-3
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for 6:2, 8:2 and 10:2 FTOH, respectively, which is 30 to 50% lower than the median
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concentrations in residential indoor air. No FOSEs or FOSAs were detected above the method
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detection limit (MDL) in the personal air samples.
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Intakes of perfluorohexanoate (PFHxA), perfluoroheptanoate (PFHpA), perfluorooctanoate
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(PFOA), perfluorononanoate (PFNA), perfluorodecanoate (PFDA), perfluoroundecanoate
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(PFUnDA) and perfluorooctyl sulfonate (PFOS) through inhalation and biotransformation of
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PFAS precursors in air were estimated. Median intakes of 1.7, 0.17, 5.7, 0.57, 1.8, 0.18 and
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2.3 pg kg bw-1 day-1, were obtained in residential indoor air, while 1.0, 0.10, 3.3, 0.33, 0.88
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and 0.09 pg kg bw-1 day-1 were found in personal air for PFHxA, PFHpA, PFOA, PFNA,
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PFDA, PFUnDA and PFOS, respectively. The median PFOA intakes from residential indoor
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air (5.7 pg kg bw-1 day-1) and personal air (3.3 pg kg bw-1 day-1) were both around five orders
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of magnitude lower than the tolerable daily intake (TDI) reported by the European Food
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Safety Authority (EFSA).
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Keywords:
PFOS,
PFOA,
intakes,
biotransformation,
personal
air.
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INTRODUCTION
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Per- and polyfluoroalkyl substances (PFASs) are highly versatile substances and are frequently
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used in consumer products such as in water and oil proofing agents, in inks, varnishes, waxes,
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lubricants, leather, paper, textiles, and fluoropolymers, due to their unique physicochemical
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properties (1,2). The release of PFASs from consumer products to the indoor environment can
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represent an important human exposure source (1). Perfluorooctanoate (PFOA) and
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perfluorooctane sulfonate (PFOS) are the most frequently studied PFASs and their occurrence in
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wildlife and humans has been thoroughly described. For both PFOA and PFOS toxic effects have
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been observed in several types of animals (2-4). Further, many epidemiological studies have been
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reporting associations between exposure to these compounds and health effects (5,6).
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Increasing concern about PFASs have led to several measures taken by public bodies and
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industry. PFOS and its salts were included in the list of Persistent Organic Pollutants (POPs)
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under Stockholm Convention in 2009 (7). In 2006, the U.S. Environmental Protection Agency
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(U.S. EPA) together with eight fluoropolymer and fluorotelomer manufacturers, launched a
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PFOA stewardship program with the aim to eliminate emissions of perfluoroalkyl carboxylic
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acids (PFCAs), their precursors and products by 2015 (8). In addition, PFOA has been included
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in the Candidate List of Substances of Very High Concern for Authorization in the European
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Union (EU) under the REACH regulation (9). These measures were thought to lead to a
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substantial decrease in the human body burdens of PFOA and PFOS. However, previous studies
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have found that the decline in PFOA concentrations in human blood was not according to its
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observed half-life, thus indicating additional indirect sources of human exposure to PFASs (10).
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One possible indirect exposure pathway could be exposure to volatile PFAS precursors, such as
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fluorotelomer alcohols (FTOHs), perfluorooctane sulfonamides (FOSAs) and perfluorooctane
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sulfonamidoethanols (FOSEs) through indoor air, and subsequent biotransformation in the human
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body. Biotransformation of FTOHs to PFOA have been reported in rats (11) as well as in animal
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and human cells (12), while other studies have reported biotransformation of FOSAs and FOSEs
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to PFOS (13,14).
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Several studies have reported the occurrence of FTOHs, FOSAs and FOSEs in indoor air
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worldwide (15-21). In these studies, sample collection was performed in specific places, such as
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homes, offices, or shops, using active or passive stationary air samplers placed at the same point
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during the entire collection period, which might not be representative of all PFASs exposure 3 ACS Paragon Plus Environment
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through air. To our knowledge, no studies have evaluated how well these fixed point samplers
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represent the actual exposure, as we are usually spending our days in several different places, for
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instance at work, in public or private transport, sport centers, homes, etc. Type and number of
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consumer products might vary between these places and exposure could thus vary substantially
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(22,23). To gain knowledge on this, different sampling approaches should be compared in order
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to provide more reliable information about PFASs exposure through indoor air.
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The overall aim of this study was to determine and compare the concentrations of volatile PFASs
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in residential indoor air and personal air samples. To achieve this, sixty-one residential indoor air
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and fifteen personal air samples were collected by placing stationary air samplers in houses and
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attaching personal samplers to the participants, respectively, during 24h. Differences and
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correlations between sampling methods were evaluated, and based on the determined
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concentrations the human exposure to selected PFASs through indoor air was evaluated.
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MATERIAL AND METHODS
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Chemicals Volatile PFASs, 6:2 FTOH, 8:2 FTOH 10:2 FTOH, MeFOSA, EtFOSA, MeFOSE
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and EtFOSE were included in this study. Further information on these compounds is found in the
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supporting information (SI), in the “Chemicals and reagents” section.
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Study population. This study is part of a comprehensive sampling campaign that has been
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thoroughly described elsewhere (24). In brief, a study group of 61 adults, males and females,
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from Oslo, Norway was recruited and a wide variety of environmental and biological samples
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were collected from the participants and their houses. This included house dust and air samples,
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hand wipes, foods and drinks, blood, urine, saliva, nails, and hair. In addition, detailed
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information on dietary habits, the indoor domestic environment, and other lifestyle characteristics
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of the participant was collected through questionnaires. The sampling campaign was conducted
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from November 2013 to April 2014.
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Collection of air samples. Residential indoor air samples were collected by connecting four
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parallel ENV + cartridges (200 mg, 6 mL) to a SKC Leland Legacy low volume pump (SKC Inc.,
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Eight Four, PA, USA). The low volume pump was placed in participants' living rooms and
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programmed to collect air for 24 h. The flow rate was set at 5 L min−1, resulting in a total air
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volume of 7.2 m3. When the sampling equipment was installed (samplers were placed
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approximately 1.2 m above the floor), doors, windows, stoves and display screens surroundings 4 ACS Paragon Plus Environment
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were avoided. Sample collection was conducted during the winter period when the proportion of
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time spent indoors is at a maximum and ventilation is at its minimum.
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Personal air samples were collected using one ENV+ cartridge (1000 mg and 25 mL, Biotage,
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Uppsala, Sweden) connected to a low volume SKC pump 224-PCMTX4 (SKC Inc., Eight Four,
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PA, USA) at 1 L min−1 flow rate. A total air volume of 1.44 m3 was collected. The pump was
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placed in a backpack that accompanied the participants throughout the 24 h sampling period. The
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air sampler was attached to the participant's shoulder and participants were advised to keep the
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sampler close to their face during the entire 24 h sampling event, including sleeping hours. Due
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to sampling design limitations only 15 personal air samples, out of 61, were available for PFASs
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analysis. SPE cartridges used as samplers were stored in -20°C until analysis. Additional
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information on the sampling procedure can be found in Papadopoulou et al. 2016 (24).
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To get an indication of the exposure to volatile PFASs at workplace, triplicate air samples were
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collected in two offices in two consecutive days using the described method for residential indoor
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air collection.
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Analysis and quality assurance.
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The method used for sample preparation and analysis is thoroughly described in the SI.
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Internal standards (ISs) were added to the sample cartridges before analysis. 13C 6:2 FTOH, 13C
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8:2 FTOH,
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MeFOSA was used as IS for MeFOSA and EtFOSA while d-N-MeFOSE was used as IS for
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MeFOSE and EtFOSE.
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Breakthrough was tested before the sampling campaign started, by coupling two SPE cartridges
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in series and spiking the top cartridge with a high amount of internal standards. Subsequently, air
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was drawn through the cartridges for 24h at a flow of 5 L min-1. No major losses were observed
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for the analytes studied (see SI and Figure S1 of the SI).
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Flow rates for both personal and residential indoor air were measured both at the beginning and
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end of sampling and in each sampling site, in order to check that the flow was constant. In
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addition, since personal pumps required a manually battery change by researchers within the 24h
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sampling period, the flow rate was also measured before and after the battery change.
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Three field blanks, i.e. cartridges brought along with cartridges used for sample collection but not
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connected to the pump, were collected in order to assess possible contamination during transport
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to/from sampling sites. These field blanks and one procedural blank were analyzed with each
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C 10:2 FTOH were used as IS for 6:2, 8:2 and 10:2 FTOH, respectively. d-N-
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batch of samples. Low concentrations of 6:2 FTOH (in more than 50% of blanks) and 8:2 FTOH
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(in 100% of blanks) were observed, with procedural blanks showing higher concentrations than
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field blanks for 8:2 FTOH. As air samples and field blanks were collected with SPE cartridges
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from the same lot number, it was decided to discard the results for the procedural blanks taken
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from a different lot number. Concentrations measured in the samples were subtracted by the
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mean concentration of all analyzed field blanks.
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Intake estimations. An inhalation rate of 13.3 m3 day-1 was used, and the absorption of FTOHs
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and MeFOSE through lungs was assumed to be 100%, as was previously suggested for PFOA
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(2). Indirect exposure to PFCAs through biotransformation of FTOHs was estimated using the
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concentrations obtained for 6:2 FTOH, 8:2 FTOH and 10:2 FTOH in residential indoor air and
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personal air. Intakes of PFHxA and PFHpA were estimated from 6:2 FTOH, PFOA and PFNA
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from 8:2 FTOH, and PFDA and PFUnDA from 10:2 FTOH. There is indication that 8:2 FTOH
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may also be biodegraded to PFHxA, but the biotransformation factor is unknown and likely very
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low (25). Thus, this transformation of 8:2 FTOH to PFHxA and similarly 10:2 FTOH to PFOA
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has not been considered. Indirect exposure to PFOS was estimated using the results obtained for
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MeFOSE. A biotransformation rate of 8:2 FTOH to PFOA of 0.003 was used (26). Further, based
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on studies finding the biotransformation of 8:2 FTOH to PFNA being approximately one order of
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magnitude lower than 8:2 FTOH to PFOA (25), a biotransformation rate of 0.0003 was used for
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8:2 FTOH to PFNA. Biotransformation rates for 6:2 FTOH and 10:2 FTOH has not yet been
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reported. Thus, the same rates as for 8:2 FTOH were used, i.e. 6:2 FTOH to PFHxA and PFHpA
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was set to 0.003 and 0.0003, respectively, while 10:2 FTOH to PFDA and PFUnDA was set to
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0.003 and 0.0003, respectively. A biotransformation rate of MeFOSE to PFOS of 0.1 was used
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based on the assumption that the transformation rate of EtFOSE to PFOS is the same as for
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MeFOSE to PFOS(27).
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Statistical analysis. PFAS concentrations in residential indoor air and personal air samples were
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presented using descriptive statistics. Only compounds with detection frequency >50% (i.e.,
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FTOHs and MeFOSE in residential indoor air, and FTOHs in personal air) were included in
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further statistical analyses. All non-detects were replaced by half of the method detection limit
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(MDL) reported for this compound.
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Since all concentrations failed the Shapiro-Wilk test of normality, Spearman’s rank correlation
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was used to assess correlations and Wilcoxon signed rank test was used to test differences
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between residential indoor air and personal air concentrations. The significance level was set to
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p=0.05. Scatter plots were used to graphically present associations. SPSS v.22 (Chicago, IL,
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USA) was used for the statistical analyses.
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RESULTS AND DISCUSSION
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PFAS concentrations in residential indoor air. FTOHs were detected in all samples and the
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concentrations ranged from 604 pg m-3 (6:2 FTOH) to 446000 pg m-3 (8:2 FTOH) (Figure 1a and
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Table S2). Median concentrations for 6:2, 8:2 and 10:2-FTOHs were 2970, 10400, and 3120,
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respectively. MeFOSE was observed in 70% of the samples with concentrations ranging from
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