Article pubs.acs.org/est
Phosphorus-Containing Fluorinated Organics: Polyfluoroalkyl Phosphoric Acid Diesters (diPAPs), Perfluorophosphonates (PFPAs), and Perfluorophosphinates (PFPIAs) in Residential Indoor Dust Amila O. De Silva,*,† Cody N. Allard,† Christine Spencer,† Glenys M. Webster,‡ and Mahiba Shoeib§ †
Water Science Technology Directorate, Environment Canada, Burlington, Ontario, Canada, L7R 4A6 Faculty of Health Sciences, Simon Fraser University, Burnaby, British Columbia, Canada, V5A 1S6 § Air Quality Processes Research Section, Environment Canada, Toronto, Ontario, Canada, M3H 5T4 ‡
S Supporting Information *
ABSTRACT: Indoor dust is thought to be a source of human exposure to perfluorocarboxylates (PFCAs) and perfluorosulfonates (PFSAs), but exposures to emerging organofluorine compounds, including precursors to PFCAs and PFSAs via indoor dust, remain unknown. We report an analytical method for measuring several groups of emerging phosphorus-containing fluorinated compounds, including polyfluoroalkyl phosphoric acid diesters (diPAP), perfluorophosphonates (PFPA), and perfluorophosphinates (PFPIA), as well as perfluoroethylcyclohexane sulfonate (PFECHS) in indoor dust. This method was used to analyze diPAP, PFPA, and PFPIA levels in 102 residential dust samples collected in 2007−2008 from Vancouver, Canada. The results indicated a predominant and ubiquitous presence of diPAPs (frequency of detection 100%, mean and median ΣdiPAPs 7637 and 2215 ng/g). Previously measured median concentrations of perfluorooctane sulfonate (PFOS), perfluorooctanoate (PFOA), and fluorotelomer alcohols (FTOHs) in the same samples were 14−74 times lower than ΣdiPAP levels, i.e. 71 ng/g PFOS, 30 ng/g PFOA, and 152 ng/g ΣFTOHs. PFPAs and PFPIAs were detected in 62% and 85% of samples, respectively, at concentrations nearly 3 orders of magnitude lower than diPAPs (median 2.3 ng/g ΣPFPAs and 2.3 ng/g ΣPFPIAs). PFECHS was detected in only 8% of dust samples. To the best of our knowledge, this is the first report of these compounds in indoor dust. In this study, diPAP concentrations represented 98% ± 7% of the total measured analytes in the dust samples. Detection of diPAPs at such high concentrations in indoor dust may represent an important and as-yet unrecognized indirect source of PFCA exposure in humans, given the identified biotransformation pathways. Identifying the sources of diPAPs to the indoor environment is a priority for future research to improve air quality in households.
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INTRODUCTION Perfluorocarboxylates (PFCAs) and perfluorosulfonates (PFSAs), particularly perfluorooctanoate (PFOA) and perfluorooctanesulfonate (PFOS), have been the subject of intense scientific and regulatory scrutiny1 due to their persistence and global occurrence2 and their consistent detection in the blood of humans at ng/mL levels.3 In addition, their biomagnification potential in foodwebs,4−6 toxicity in animal studies,7 and association with health effects in humans continue to be studied. Federal environmental departments in the US and Canada have restricted the use of PFCAs and some PFCA precursors.8,9 However, many other fluorinated compounds including newly identified precursors to PFCAs - remain in widespread use. Comparison of known PFCAs and PFSAs to total organic fluorine analysis in human blood has suggested a large fraction, as high as 75%, of the organofluorine content in humans has not been well characterized.10 This highlights the need to identify and characterize unknown fluorochemicals and to evaluate their environmental presence, particularly in samples relevant to human exposure, such as indoor dust. © 2012 American Chemical Society
Polyfluoroalkyl phosphates (PAPs) have recently been identified as potential precursors to PFCAs, including PFOA.11 PAPs are phosphoric acid esters which possess at least one polyfluoroalkyl group, F(CF2)xCH2CH2, where x is typically an even number. The disubstituted polyfluoroalkyl phosphates (diPAPs) have two polyfluoroalkyl groups that can have the same or different number of perfluorocarbons (Figure 1). Nomenclature for diPAPs is based on the number of carbons in the perfluoroalkyl moiety versus the hydrocarbon linkage. For example, 4:2 diPAP corresponds to the disubstituted phosphoric acid containing two F(CF2)4CH2CH2 groups. For diPAPS with two different perfluorocarbon chain lengths x and y, the nomenclature follows x:2/y:2 diPAP. For example, polyfluoroalkyl groups in 6:2/8:2 diPAP are F(CF2)6CH2CH2 and F(CF2)8CH2CH2 substitutions . Received: Revised: Accepted: Published: 12575
August 4, 2012 October 5, 2012 October 26, 2012 October 26, 2012 dx.doi.org/10.1021/es303172p | Environ. Sci. Technol. 2012, 46, 12575−12582
Environmental Science & Technology
Article
PFPAs and PFPIAs are fully perfluorinated and do not contain the hydrocarbon linkage typical of fluorotelomer chemicals including FTOHs and PAPs. Therefore, it has been hypothesized that PFPAs and PFPIAs are environmentally recalcitrant, akin to the PFCAs and PFSAs.21,22,25 However, metabolism of PFPIAs to PFPAs was observed in a dietary exposure study with rainbow trout.26 It is unknown whether C−P bond cleavage occurs analogously in mammals, with subsequent impact on PFPIA and PFPA bioaccumulation in humans. Other than the potential transformation of PFPIAs to PFPAs, there are no known precursors to these two groups of chemicals.16 PFPAs were not detected in a recent human serum study, but 6 PFPIA congeners, including C6/C6, C6/C8, C8/ C8, C6/C10, C8/C10, and C6/C12 PFPIAs, were above detection limits (LOD).16 The most prevalent congeners were C6/C6 PFPIA (mean 3.7 ± 1.3 pg/mL) and C6/C8 PFPIA (mean 7.7 ± 1.9 pg/mL).16 Guo et al. also detected 5.6 to 8.8 pg/g C6/C6 PFPIA and 8.7 to 12 pg/g C6/C8 PFPIA in fish fillet from Lake Ontario and Lake Erie, suggesting that fish consumption may be a source of human exposure to these compounds.27 Overall, these findings suggest that PFPIAs and possibly PFPAs may represent a proportion of the unknown extractable organofluorines found in human serum and, by extension, their exposure sources.10 To date, levels of PFPAs and PFPIAs have not been investigated in indoor dust samples. Cyclic PFSAs have emerged as environmental pollutants and chemicals of commerce.21,28 Among them, perfluoroethylcyclohexane sulfonate (PFECHS, Figure 1) was detected at ng/g levels in fish and ng/L in the water of the Great Lakes28 and was also observed downstream of an international airport in amphipods and turtles.29 The major reported use of PFECHS is as an erosion inhibitor in aircraft hydraulic fluid.28 To date, it has not been monitored in general human exposure sources such as food, drinking water, indoor air, indoor dust, household products, or in residential wastewater influent and human blood. Based on the limited reported uses for PFECHS, it is hypothesized that this chemical is not ubiquitous in the indoor environment. The indoor environment, including air and dust, is thought to be an important source of human exposure for many organofluorine compounds for several reasons. First, several studies have reported higher concentrations of PFCAs, PFSAs, FTOHs, and perfluorooctylsulfonamides (PFSAm) in indoor versus outdoor air.30,31 Shoeib et al. detected PFSAm, which are semivolatile neutral PFOS precursors, in indoor air that were 10−20× higher than in outdoor air.30 Similar indoor > outdoor air trends have also been observed for a larger suite of neutral volatile precursors as well as the ionic substances PFSAs and PFCAs.32 Second, elevated levels of fluorochemicals have been found in indoor dust.30,33,34 For example, the median ΣPFSAm in dust samples collected in 2002−2003 in 59 homes from Ottawa, ON was 2612 ng/g.30 In previous analyses of the same dust samples used in the current study, median concentrations were 47 ng/g ΣPFSAm (much lower than in the Ottawa study), 152 ng/g ΣFTOHs, 280 ng/g PFOS, 97 ng/g PFOA (n = 132, Vancouver, BC).32 Finally, several studies (including one using the same dust samples as used in the study) have reported associations between certain fluorinated chemicals in either indoor air35 or dust36,37 and levels in human serum. The goal of this study is to expand current knowledge about organofluorine chemicals in indoor dust to include emerging organofluorine phosphorus compounds such as diPAPS, PFPAs, and PFPIAs as well as the cyclic PFSA, PFECHS. In
Figure 1. Structures of emerging fluorinated chemicals analyzed in dust.
PAPs, including diPAPs, have been identified in food paper packaging12−14 and are used in many other surface treatment and protectant applications15 including personal care products such as cosmetics.16 Recent research confirms that humans are exposed to diPAPs. D’eon et al. measured diPAPs in 20 human sera samples from the U.S. in 2008 and noted that 6:2 diPAP was the most prevalent congener with a mean concentration of 0.63 ± 0.13 ng/mL.17 In a follow up study, Lee and Mabury (2011) reported mean 0.13 ± 0.04 ng/mL 6:2 diPAP (n = 10) in U.S. human serum sampled in 2009.16 A suite of diPAP congeners, including 6:2, 6:2/8:2, 8:2, 8:2/10:2, 10:2, and 10:2/12:2 diPAPs, were detected in the biosolids products of 6 wastewater treatment plants and comprised 50−200 ng/g ΣdiPAPs, comparable to PFOS levels and far exceeding levels of PFCAs.17 PAPs were also measured in drinking water from 3 cities in China ranging from 0.2 to 98 ng/L.18 When dosed with PAPs, biotransformation in rats and microbes yielded fluorotelomer alcohol (FTOH) intermediates and ultimately PFCAs.11,19 Given their levels in environmental samples, the presence in human blood and potential for metabolism to PFCAs, it is likely that diPAPs represent an indirect source of exposure to PFCAs in humans.20 To date, diPAP levels have not been investigated in indoor dust. Perfluoroalkyl-phosphonates and phosphinates (PFPAs and PFPIAs, respectively) have recently emerged as two other understudied groups of perfluorochemicals with wide commercial applications.21 The PFPAs (Cx PFPA, F(CF2)xP(O)O2−2) have a −2 charge on the hydrophilic headgroup and possess a single perfluoralkyl moiety where x is an even number (Figure 1). The PFPIAs (Cx/Cy PFPIA) have two perfluoroalkyl moieties where x and y are even numbers and a −1 charge on the hydrophilic headgroup, P(O)O− (Figure 1). PFPAs and PFPIAs are surfactants used as leveling and wetting agents in industrial and commercial applications including household surfactants.15,22 D’eon et al. detected C6, C8, and C10 PFPAs in freshwater creeks and rivers and also in wastewater treatment plant effluent, all in Canada.22 The C8 PFPA was the dominant PFPA, reaching 3.4 ng/L in a freshwater creek and 2.5 ng/L in wastewater effluent.22 The C8 PFPA was also detected at 1 ng/ L in surface water and
