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World-wide indoor exposure to polyfluoroalkyl phosphate esters (PAPs) and other PFASs in household dust Ulrika Eriksson , and Anna Kärrman Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.5b00679 • Publication Date (Web): 22 May 2015 Downloaded from http://pubs.acs.org on May 25, 2015
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Environmental Science & Technology
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World-wide indoor exposure to polyfluoroalkyl
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phosphate esters (PAPs) and other PFASs in
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household dust
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Ulrika Eriksson*, Anna Kärrman
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Man-Technology-Environment (MTM) Research Centre, School of Science and Technology,
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Örebro University, SE-701 82 Örebro, Sweden
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KEYWORDS: monoPAPs, diPAPs, triPAPs, indoor exposure, globally distribution
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ABSTRACT. Human exposure to perfluorooctanoic acid (PFOA) and other per- and
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polyfluoroalkyl substances (PFASs) is ongoing and in some cases increasing, despite efforts
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made to reduce emissions. The role of precursor compounds such as polyfluorinated phosphate
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esters (PAPs) has received increasing attention, but there are knowledge gaps regarding their
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occurrence and impact on human exposure. In this study, mono-, di- and triPAPs, perfluorinated
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alkyl acids (PFAAs), saturated and unsaturated fluorotelomer carboxylic acids (FTCA/FTUCAs),
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perfluoroalkane sulfonamides and sulfonamidethanols (FOSA/FOSEs), and one fluorotelomer
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sulfonic acid (FTSA)) were compared in household dust samples from Canada, the Faroe Islands,
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Sweden, Greece, Spain, Nepal, Japan and Australia. Mono-, di-, and triPAPs, including several
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diPAP homologues, were frequently detected in dust from all countries, revealing an ubiquitous
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spread in private households from diverse geographic areas, with significant differences between
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countries. The median levels of monoPAPs and diPAPs ranged from 3.7 ng/g to 1 023 ng/g and
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3.6 ng/g to 692 ng/g, respectively, with the lowest levels found in Nepal and the highest in Japan.
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The levels of PAPs exceeded those of the other PFAS classes. These findings reveal the
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importance of PAPs as a source of PFAS exposure world-wide.
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Introduction
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Per- and polyfluorinated substances (PFASs) have been produced and used in a wide range of
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applications for more than 60 years.1 The global spread of PFASs in humans and the
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environment, together with their bioaccumulation potential, persistence and toxicity, has led to
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increased scientific attention and enhanced awareness amongst policymakers. Perfluorooctane
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sulfonic acid (PFOS) and related substances, produced by electrochemical fluorination (ECF),
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were voluntarily phased out by 3M in 2001 and later restricted in accordance with the Stockholm
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Convention on Persistent Organic Pollutants (POPs).2 As a result, PFOS and PFOS-like
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compounds were replaced by shorter-chained PFASs (C 1.3, kurtosis > 3.8).
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Skewness was also confirmed by visual observation of data histograms. The homogeneity of
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variance for PFAS concentrations in dust from different countries were tested for with Levene’s
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test. All PFAS concentrations had unequal variance (p < 0.05). Therefore, non-parametric
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methods were chosen for statistical analysis. Spearman rank order correlations (rho) with
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Bonferroni adjusted significance level were used for analysis of correlations. Wilcoxon rank-sum
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test was performed to compare PFAS concentrations in different countries. Correlations were
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considered significant if p < 0.05.
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Exposure assessment
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The following formula was used for exposure assessment:
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Edust = (Cdust x Qdust x Fuptake x Fbiotransform) / mbw
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where Cdust is the PFAS concentration in the dust (ng/g), Qdust is dust intake (mg/day), Fuptake is
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the uptake fraction, mbw is body weight (kg), and Fbiotransform is the biotransformation factor.
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Factors for dust ingestion were obtained from EPA’s Exposure Factors Handbook.28 For the
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biotransformation factor, a value of 100% was used in high exposure scenario, and in the low
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exposure scenario 10% was used for diPAP homologue moieties ≥ C8, and 1% for diPAP
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homologue moieties ≤ C6. These biotransformation factors have been estimated in a rat study
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where animals were dosed with monoPAPs and diPAPs.29 Since no biotransformation factor was
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estimated for the monoPAPs in the previous study, a factor of 100% was used in this study for
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exposure assessment of monoPAPs. There are large uncertainties regarding biotransformation
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factors for FOSA/FOSE,30 therefore a value of 100% was used. For the uptake fraction, a value of
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66% estimated from animal studies was used for PFCAs and PFSAs in low exposure scenario.31
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A value of 100% was used in high exposure scenario. Since large variation in uptake fractions for
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PAPs has been reported,29 and lack of information for FOSA/FOSE, same uptake fractions as for
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PFCAs were used for those classes.
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Results and discussion
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PFAS concentrations
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PAPs were predominating in the PFAS profile. PFCAs, PFSAs, monoPAPs, diPAPs, triPAPs,
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FTUCA/FTCA, and FOSA/FOSE were found in dust samples from all countries. Concentrations
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are summarized in table 1.
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PAPs. The monoPAPs and the diPAPs accounted for a vast majority of the analyzed PFASs. In
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comparison to the total PFAS concentrations, including semi-quantified PAPs homologues,
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monoPAPs accounted for 8-47 weight% and diPAPs accounted for 21-47 weight% (fig. S8).
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Levels of monoPAPs were similar to levels of diPAPs. Total amounts of PAPs classes should be
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considered conservative, since many of the homologues are semi-quantified. However, excluding
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them could lead to severe underestimation. The semi-quantified monoPAPs and diPAPs
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homologues accounted for about half of the total PAPs amount (fig. S6, S7).
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The most frequent detected monoPAP homologue was 8:2 monoPAP, which was found in 76%
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of the samples, followed by 6:2 monoPAP (69%) and 10:2 monoPAP (57%). Median levels of
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quantified and semi-quantified monoPAPs ranged from 3.7 ng/g in Nepal to 1023 ng/g in Japan.
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Australia, Canada, the Faroe Islands and Japan had all significantly higher median monoPAPs
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levels (365 ng/g, 305 ng/g, 451 ng/g, 1023 ng/g, respectively) than Greece, Spain and Nepal (6.0
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ng/g, 14 ng/g, 3.7 n/g, respectively). Sweden had significantly lower monoPAPs levels (105 ng/g)
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than Canada and the Faroe Islands but higher than Greece and Nepal. To our knowledge, this is
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the first time monoPAPs have been detected in household dust.
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The median levels of quantified and semi-quantified diPAPs ranged between 3.6 ng/g in Nepal to
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692 ng/g in Japan. Similar to the monoPAPs, there were significantly higher levels in Australia,
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Canada, the Faroe Islands and Japan (343 ng/g, 352 ng/g, 450 ng/g, 692 ng/g, respectively) than
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in Greece, Spain and Nepal (25 ng/g, 14 ng/g, 3.6 ng/g). Sweden had significantly lower diPAPs
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median levels (62 ng/g) than Australia, Canada, and the Faroe Islands. Most frequently detected
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were 6:2 diPAP, 6:2/8:2 diPAP, 8:2 diPAP, and 6:2/10:2 diPAP which were found in 100% of
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the samples. Previously, 6:2, 6:2/8:2 and 8:2 diPAP in Canadian dust have been found at median
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levels of 460, 614 and 535 ng/g, respectively. 22 In this study, median levels of 6:2, 6:2/8:2, and
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8:2 diPAP in the Canadian dust were 164, 43, and 33 ng/g, and about one order of magnitude
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lower for 6:2 and 6:2/8:2 diPAP. It should be noted that the variation amongst the samples was
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large, and levels up to 1491, 819, and 641 ng/g were observed for 6:2, 6:2/8:2, and 8:2 diPAP,
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respectively. No significant difference for 6:2 diPAP was observed between this study and the
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Canadian study.
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Of the countries with proportionally higher PAP dust levels, only Canada and Japan are close to
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regions with fluorotelomer production.1 The fact that Australia and the Faroe Islands also have
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substantially higher levels indicates that occurrence of PAPs in household dust is more related to
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life-style in connection with the consumer products used in the home, other than closeness to
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regions with fluorotelomer production. Considering the fact that diPAPs are the major substance
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group in production,16 there is a remarkably high contribution from the monoPAPs to the total
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PFAS concentration. Proportions in production of sulfonamid-based polyfluorinated phosphate
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esters (SAmPAPs) have been reported to be 10%, 85% and 5% of mono-, di- and tri-SamPAPs.32
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The comparatively high levels of monoPAPs in dust is likely due to microbial degradation of
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diPAPs into monoPAPs.18 In the degradation pathway of diPAPs, microbial hydrolysis of the
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phosphate ester bond yields one FTOH and one monoPAPs, which in turn yields another FTOH.
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Further oxidation of FTOH yields the intermediates FTCA and FTUCA, and further formation of
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PFCA. FTUCAs were frequently detected in the dust samples (74%). FTCAs were less frequently
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detected (22%). These intermediates are not produced and are solely degradation products from
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fluorotelomers. Presence of FTCA/FTUCA in the dust in this study and others34 confirms
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degradation from precursor compounds.33 The proportionally higher levels of monoPAPs
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compared to diPAPs can be explained by different biodegradation rates. In microbial degradation
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experiments performed in waste water and sludge, 6:2 diPAP was shown to produce more FTOH
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than 6:2 monoPAP, hence more labile to microbial hydrolysis.18 The yield to FTOH in the study
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was 5% for 6:2 diPAP, compared to 1% for 6:2 monoPAP.
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It could be hypothesized that the lower charge density of the diPAPs in comparison to the
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monoPAPs, together with steric hindrance, decreases the sorption capacity of diPAPs towards
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particles in the dust and makes them more bioavailable than monoPAPs, leading to an
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accumulation of monoPAPs in the dust. Disparity in degradation rate between hydrocarbon
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phosphate monoesters and hydrocarbon phosphate diesters has been observed in soil and
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sediment, where accumulation of hydrocarbon phosphate monoesters in soils was attributed to
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sorption to soil mineral.34 Although it’s not entirely comparable to dust, diPAP proved to be more
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labile to microbial degradation than monoPAPs in experiments with simulated wastewater
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treatment plant sludge.18
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In addition to quantified and semi-quantified levels of monoPAP and diPAP, five homologues of
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triPAPs were detected in the samples, 6:2 triPAP, 6:2/6:2/8:2 triPAP, 6:2/8:2/8:2 triPAP,
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6:2/6:2/10:2 triPAP and 8:2 triPAP (Fig. S5). Due to lack of labeled standards and matrix effects,
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the levels could not be quantified, but were estimated to be in the low pg/g range using the
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response of the labeled diPAP standard. The most frequently detected was 6:2 triPAP, which was
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detected in a majority of the samples. These triPAPs homologues have previously been found in
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food packaging material.27 To our knowledge, this is the first time triPAPs have been detected in
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household dust.
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PFCA/PFSA. Median ∑PFCA levels ranged from 0.2 ng/g in Nepal to 230 ng/g in Japan (Table
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1, S7). The levels of PFCAs were at about the same level among most countries, except for
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Nepal, where the levels were significantly lower than all other countries (p
