Research | Children’s Health
Isomer Profiles of Perfluorochemicals in Matched Maternal, Cord, and
House Dust Samples: Manufacturing Sources and Transplacental Transfer
Sanjay Beesoon,1 Glenys M. Webster,2 Mahiba Shoeib,3 Tom Harner,3 Jonathan P. Benskin,1
and Jonathan W. Martin1
1Division of Analytical and Environmental Toxicology, Department of Laboratory Medicine and Pathology, University of Alberta,
Edmonton, Alberta, Canada; 2Centre for Health and Environment Research, School of Environmental Health, University of British
Columbia, Vancouver, Canada; 3Science and Technology Branch, Environment Canada, Toronto, Ontario, Canada
BACKGROUND: Perfluorochemicals (PFCs) are detectable in the general population and in the
human environment, including house dust. Sources are not well characterized, but isomer patterns
should enable diferentiation of historical and contemporary manufacturing sources. Isomer-speciic
maternal–fetal transfer of PFCs has not been examined despite known developmental toxicity of
perluorooctane sulfonate (PFOS) and perluorooctanoate (PFOA) in rodents.
OBJECTIVES: We elucidated relative contributions of electrochemical (phased out in 2001) and
telomer (contemporary) PFCs in dust and measured how transplacental transfer eiciency (TTE;
based on a comparison of maternal and cord sera concentrations) is afected by perluorinated chain
length and isomer branching pattern.
METHODS: We analyzed matching samples of house dust (n = 18), maternal sera (n = 20), and
umbilical cord sera (n = 20) by isomer-speciic high-performance liquid chromatography tandem
mass spectrometry.
RESULTS: PFOA isomer signatures revealed that telomer sources accounted for 0–95% of total
PFOA in house dust (median, 31%). his may partly explain why serum PFOA concentrations are
not declining in some countries despite the phase-out of electrochemical PFOA. TTE data indicate
that total branched isomers crossed the placenta more eiciently than did linear isomers for both
PFOS (p < 0.01) and PFOA (p = 0.02) and that placental transfer of branched isomers of PFOS
increased as the branching point moved closer to the sulfonate (SO3–) end of the molecule.
CONCLUSIONS: Results suggest that humans are exposed to telomer PFOA, but larger studies that
also account for dietary sources should be conducted. he exposure proile of PFOS and PFOA isomers can difer between the mother and fetus—an important consideration for perinatal epidemiology studies of PFCs.
KEY WORDS: isomers, perluorochemicals, PFOA, PFOS, transplacental transfer. Environ Health
Perspect 119:1659–1664 (2011). http://dx.doi.org/10.1289/ehp.1003265 [Online 14 July 2011]
The most prominent perfluorochemicals
(PFCs) in human samples are perluorooctane
sulfonate (PFOS), perluorooctanoate (PFOA),
and perluorohexane sulfonate (PFHxS), yet
the sources and pathways of human expo
sure to these, and other PFCs are not well
characterized. Perluorinated acids are ubiqui
tous in the global environment, owing to their
long history of manufacture and resistance
to biological and environmental degradation
pathways. Speciically for PFOA, the manu
facturing sources responsible for its presence
in various environments are not well under
stood, and future human exposure is there
fore diicult to predict. here are two main
manufacturing methods leading to PFOS and
PFOA: electrochemical fluorination (ECF)
and telomerization. he 3M Company man
ufactured the bulk of PFOS (and higher
molecularweight precursor materials), PFHxS,
and PFOA by ECF until 2001, at which time
they voluntarily phased out these chemistries.
Nonetheless, PFOS and its precursors con
tinue to be manufactured by other companies
in Asia (Martin et al. 2010). Telomerization
continues to be used to manufacture PFOA.
ECF and telomerized PFOA can be readily
distinguished analytically because ECF PFOA
Environmental Health Perspectives •
VOLUME
consists of a mix of linear and branched iso
mers (Loveless et al. 2006; Reagen WKL,
Jacoby CB, Purcell RG, Kestner TA, Payfer
RM, et al., unpublished data), whereas
telomerized PFOA is almost exclusively the
linear isomer (Kissa 1994).
If humans are exposed predominantly
to ECF sources of PFOS and PFOA, serum
concentrations should be decreasing because
of their phaseout. In fact, when the 3M
Company stopped manufacturing PFOS
and PFOA by its ECF technique, blood lev
els of PFOS declined steadily in Americans.
However, for PFOA the initial rate of decline
was much less than anticipated (Olsen et al.
2008), and the most recent data from the
National Center of Health Statistics of
the U.S. Centers for Disease Control and
Prevention (Kato et al. 2011) indicate that
serum PFOA did not decline between April
2003 and August 2007 and may be increasing
[see Supplemental Material, Figure 1 (http://
dx.doi.org/10.1289/ehp.1003265)]. This
suggests that exposure to recently produced
telomer sources of PFOA might be impor
tant, but the relative importance of ECF
and telomerderived PFC exposures through
different exposure pathways (e.g., diet,
119 | NUMBER 11 | November 2011
dust, water, air) is unknown. Nonetheless,
the potential for telomer PFOA exposure is
recognized, and in 2006 a global stewardship
program was implemented to reduce emis
sions of this chemical [U.S. Environmental
Protection Agency (EPA) 2006].
For many environmental chemicals, house
dust can be a major source of exposure (Butte
and Heinzow 2002), particularly for children
(U.S. EPA 2008). For PFOS and PFOA, food
is a major source of exposure, but house dust
can also be important under scenarios of high
dust ingestion (Bjorklund et al. 2009; Goosey
and Harrad 2011; Haug et al. 2011; Shoeib
et al. 2011; Tittlemier et al. 2007). hus, it is
important from a risk mitigation perspective
to understand whether PFCs in house dust
are from current or historical manufacturing
sources. PFOS and PFOA have been meas
ured in dust previously (Kato et al. 2009;
Kubwabo et al. 2005), but isomerspecific
PFC analytical methods (Benskin et al. 2007;
Langlois and Oehme 2006) have not been
used to determine the manufacturing origins
of PFOA and other PFCs in house dust.
Loveless et al. (2006) demonstrated that
linear ammonium PFOA was generally more
toxic than branched PFOA, but the isomer
speciic toxicity of PFCs has not been exam
ined because of the lack of available standards.
Studies in rats and zebraish show that PFOA
and PFOS are developmental toxicants (Lau
et al. 2004), and many human epidemiology
studies are now emerging on the potential
perinatal efects of PFCs. For example, some
Address correspondence to J.W. Martin, 10102
Clinical Sciences Building, Division of Analytical
and Environmental Toxicology, Department of
Laboratory Medicine and Pathology, Faculty of
Medicine and Dentistry, University of Alberta,
Edmonton, Alberta, Canada T6G 2G3. Telephone:
(780) 4921190. Fax: (780) 4927800. Email: jon.
martin@ualberta.ca
Supplemental Material is available online (http://
dx.doi.org/10.1289/ehp.1003265).
We thank M. Hill (Health Canada, Ottawa) for
project coordination. We thank Alberta Health and
Wellness for support of daily laboratory operations.
We acknowledge Health Canada for funding. S.B.
and J.P.B. acknowledge support from the Alberta
Heritage Foundation for Medical Research and
Alberta Ingenuity, respectively.
he authors declare they have no actual or poten
tial competing inancial interests.
Received 29 November 2010; accepted 14 July
2011.
1659
Beesoon et al.
epidemiology studies have shown inverse
associations between PFOA exposure and
birth weight (Apelberg et al. 2007; Fei et al.
2008), whereas others did not ind an associa
tion (Monroy et al. 2008; Nolan et al. 2009).
Furthermore, other adverse human health
efects associated with PFCs are being detected
in both background (Nelson et al. 2010) and
highly exposed populations (Steenland et al.
2010). From a public health perspective, and
recognizing that many PFCs occur as multiple
isomers of unknown relative toxicity, it may
be important to characterize the exact nature
of PFC exposure to humans, including for the
mother and the fetus.
Understanding the maternal–fetal trans
mission of PFCs is necessary to clearly under
stand the risks and mechanisms of human
developmental toxicity. Of studies that have
reported the maternal–fetal transfer of PFCs,
Hanssen et al. (2010) produced the only study
to examine branched isomers separately from
linear isomers. However, individual branched
isomers were not examined separately (i.e.,
total branched PFOS was compared with lin
ear PFOS). Although we are beginning to
understand the pharmacokinetic properties
of speciic branched PFCs in animal models
(De Silva et al. 2009), no study has yet inves
tigated isomerspeciic PFC pharmacokinetics
in humans. In an attempt to understand the
transplacental transfer of PFCs (mainly PFOS
and PFOA), multiple studies have tested
maternal and umbilical cord blood samples
from diferent populations (Fei et al. 2007;
Fromme et al. 2010; Hanssen et al. 2010;
Inoue et al. 2004; Kim et al. 2011; Midasch
et al. 2007; Monroy et al. 2008; Needham
et al. 2011). One consistent finding in all
these studies is that cord serum has lower
total PFOA and lower total PFOS than does
maternal serum; however the isomerspeciic
transplacental transfer of the various branched
isomers has not been examined despite evi
dence that the placental transfer is greater for
total branched PFOS isomers than for linear
PFOS (Hanssen et al. 2010).
In the present study we collected dust from
the homes of 20 pregnant women who also
donated a blood sample at 15 weeks of gestation
and a cord blood sample at delivery. We meas
ured PFC concentrations and isomer proiles
in all samples in an efort to identify sources of
PFCs in house dust and to examine the isomer
speciic transfer of PFCs across the placenta.
Materials and Methods
Nomenclature and acronyms. For structural
isomers, we use the nomenclature defined
by Benskin et al. (2007). Using PFOS as
an example, the following annotations are
used to represent the structure of each isomer
based on relative position of perluoromethyl
substitution: linear perluorooctane sulfonate
1660
(nPFOS), perfluoroisopropyl (isoPFOS),
5perluoromethyl (5mPFOS), 4perluoro
methyl (4mPFOS), 3perfluoromethyl
(3mPFOS), 1perluoromethyl (1mPFOS),
tertperfluorobutyl (tbPFOS), and sum of
all dimethyl isomers (Σm2PFOS). Except
for nPFOS, all of the abovementioned iso
mers are branched isomers [for structures,
see Supplemental Material, Figure 2 (http://
dx.doi.org/10.1289/ehp.1003265)].
PFC chemical standards. The 3M
Company donated ECF PFOS [30%
branched and 70% linear, by 19F nuclear
magnetic resonance (NMR)] and PFOA
(22% branched and 78% linear, by 19 F
NMR) standards (Reagen WKL, Jacoby CB,
Purcell RG, Kestner TA, Payfer RM, et al.,
unpublished data). All other PFC standards,
including PFOS and PFOA isomer standards
and linear mass labeled internal standards
for perfluorobutanoate, perfluorohexanoate
(PFHxA), PFHxS, PFOA, perluorononano
ate (PFNA), PFOS, perfluoro decanoate
(PFDA), perfluoroundecanoate (PFUnA),
and perfluorododecanoate (PFDoA), were
obtained from Wellington Laboratories
(Guelph, ON, Canada).
Blood collection. Samples (n = 20) analyzed
in this study are a subset of the Chemicals,
Health and Pregnancy (CHirP) cohort
recruited in 2007–2008 in Vancouver (BC,
Canada) (Webster et al. 2011). All participants
provided informed consent. Laboratory per
sonnel collected blood samples from pregnant
volunteers in Vancouver at 15 weeks of gesta
tion, and samples of cord blood (n = 20) were
collected at delivery. After serum separation,
all samples were stored at –80°C. Ethical clear
ance was obtained from the research ethics
boards of the University of British Columbia,
the University of Alberta, Health Canada, and
the three participating hospitals.
Serum preparation. The method of
Kuklenyik et al. (2004) was adapted for
the extraction of PFCs from serum using a
Rapid Trace system (Caliper Life Sciences,
Hopkinton, MA, USA). The solidphase
extraction cartridge (OasisHLB, Waters,
Milford, MA, USA; 60 mg/3 mL) was condi
tioned with 2 mL methanol followed by 2 mL
of 0.1 M formic acid. Serum was prepared for
extraction by mixing 3 mL of 0.1 M formic
acid with 1.0 mL serum. After the addition of
masslabeled internal standards (10 ng each),
the mixture was vortexed and sonicated for
20 min. Prepared serum was added to the col
umn and washed successively with 3 mL of
0.1 M formic acid, 6 mL of 50% 0.1 M formic
acid/50% methanol, and 1 mL of 1% ammo
nium hydroxide. he cartridge was drained by
vacuum, and PFCs were eluted with 1.0 mL of
1% ammonium hydroxide in acetonitrile. he
eluate was concentrated to 100 μL followed by
the addition of 200 μL of 90% 20 mM acetic
VOLUME
acid in 10% methanol. Method blanks con
taining calf serum, a calf serum sample spiked
at 0.5 ng/mL of each PFC, and a human serum
sample spiked at 10 ng/mL were analyzed with
the study samples.
Dust collection and extraction. Dust sam
ples were also a subset of those collected for
the larger CHirP study (Shoeib et al. 2011).
At 20–24 weeks of gestation, participants
donated a used vacuum cleaner bag from their
vacuum cleaner, or we took grab samples
from the participants’ bagless vacuum cleaners
(n = 18). Samples were stored at –20°C, and
before analysis a portion of each dust sample
was sieved using a stainlesssteel sieve (mesh
size, 150 μm; VWR International, Montreal,
QC, Canada). Sieved dust (0.1 g) was spiked
with 3.3 ng masslabeled internal standards;
4 mL methanol was added, and the sample
was vortexed for 5 min, sonicated for 1 hr,
and centrifuged at 3,400 rpm for 10 min. A
2mL aliquot was reduced by evaporation to
100 μL, and 200 μL of 20 mM acetic acid
with 10% methanol was added before high
performance liquid chromatography tandem
mass spectrometry (HPLCMS/MS).
Total PFC analysis. For total PFC con
centrations, separation was by HPLC on a
150mm Synergi HydroRP C18 col
umn (Phenomenex, Torrance, CA, USA).
Gradient elution at 600 μL/min used A
[20 mM ammonium acetate (pH 4) in water]
and B (methanol) mobile phases. Initial con
ditions were 60% A for 1 min, ramped to
20% A by 3 min, a 5min hold, an increase to
100% B by 8.5 min, and a hold until 14 min,
at which time initial conditions were rees
tablished. MS/MS data were collected on
an Applied Biosystems API 3000 mass spec
trometer (Applied Biosystems, Carlsbad, CA,
USA) using electrospray ionization in nega
tiveion mode [for mean recoveries of total
PFCs in serum and dust, see Supplemental
Material, Table 1 (http://dx.doi.org/10.1289/
ehp.1003265)].
Isomer-specific PFC analysis. he isomer
speciic HPLCMS/MS method was adapted
from Benskin et al. (2007). Briely, 3 μL of
the same extracts analyzed for total PFCs was
injected onto a FluoroSep RP Octyl column
(ES Industries, West Berlin, NJ, USA). Flow
rate was 200 μL/min, and starting conditions
were 60% A (water adjusted to pH 4.0 with
ammonium formate) and 40% B (methanol).
Initial conditions were held for 0.3 min, then
ramped to 64% B by 1.9 min; increased to
66% B by 5.9 min, 70% B by 7.9 min, 78%
B by 40 min, 88% B by 42 min and inally to
100% B by 45 min; and held until 60 min.
Mass spectral data were collected using a
5000Q mass spectrometer (MDS Sciex,
Concord, ON, Canada) equipped with an
electrospray interface operating in negative
ion mode. Chromatograms were recorded
119 | NUMBER 11 | November 2011 • Environmental Health Perspectives
PFC isomer profiles in blood and dust
Total PFC concentrations in house dust. All
total PFCs, except for perfluorodecane sul
fonate (PFDS), were lognormally distributed
[Shapiro–Wilk test; for distributions, see
Supplemental Material, Table 2 (http://dx.doi.
org/10.1289/ehp.1003265)]. he three major
PFCs in all dust samples (n = 18) were PFOA,
PFOS, and PFHxA, with similar median
values of 38, 37, and 35 ng/g, respectively.
However, PFHxS exceeded PFOS in four sam
ples. his pattern, whereby PFOA, PFOS, and
PFHxA were the dominant PFCs, is similar to
results from Strynar and Lindstrom (2008),
who monitored U.S. house dust collected in
2001/2002 and found median PFOA, PFOS,
and PFHxA concentrations of 142, 201, and
54.2 ng/g, respectively. he higher concentra
tions of PFOS and PFOA observed by Strynar
and Lindstrom (2008) are understandable
given that these dust samples were collected
years earlier than in the present study, around
the time of the phaseout of ECF C8 perluo
rocarbon chemistries, although sampling strat
egy and geography may also have contributed
to diferences.
PFC isomer profiles in house dust. For
PFOS, we detected six major branched iso
mers in dust: 1m, 3m, 4m, 5m, iso, and
Σm2PFOS. All the dust samples had PFOS
isomer proiles that were very similar to the
3M Company ECF standard of PFOS, with
a mean (± SD) branched isomer content
of 30 ± 2.7%, and relatively low variability
among individual branched isomers in various
samples [Supplemental Material, Figure 3A,
Table 3 (http://dx.doi.org/10.1289/
ehp.1003265)]. his was not surprising given
that the 3M Company produced the bulk of
PFOS (Paul et al. 2009) and that the historical
batchtobatch variation of branched isomer
Environmental Health Perspectives •
VOLUME
Isomerspeciic chromatograms of house
dust clearly indicate that other perfluoro
carboxylates (i.e., PFCs with –CO 2– as a
functional group) had only minor branched
isomer content (data not shown). Authentic
standards were not available for conirmation,
so we identified peaks as branched isomers
only when two characteristic MS/MS transi
tions responded at the same retention time.
Most perluorocarboxylates other than PFOA
appeared exclusively linear, but in a minority
of dust samples PFNA had up to four minor
branched isomers, whereas PFHxA, PFDA,
PFUnA, and PFDoA each had up to two
minor branched isomers. he manufacturing
sources of these particular branched perluoro
carboxylates cannot be conirmed because of
limited information on their manufacturing
sources and a lack of reference materials, but
they may be residuals from ECF manufactur
ing of PFOS and PFOA. Perluorosulfonates,
such as PFDS, perfluoroheptane sulfonate,
and PFHxS, are generally assumed to have
been produced exclusively by ECF, and these
all had major branched isomer content based
on peak areas (data not shown). However,
because reference materials were not available,
we could not examine how closely they resem
bled authentic ECF manufacturing sources.
Total PFCs in maternal and cord sera.
Concentrations of total PFOS (n = 20), PFOA
(n = 20), PFNA (n = 20), PFDA (n = 16), and
PFHxS (n = 8) in maternal serum were always
significantly higher (p < 0.01) than in cord
serum, consistent with previous maternal–fetal
transfer studies of PFOS and PFOA (Table 1).
The major total PFCs in maternal and cord
sera were PFOS, PFOA, PFHxS, and PFNA,
similar to previous indings (Inoue et al. 2004;
Midasch et al. 2007; Monroy et al. 2008). In
the present study, the mean concentrations of
PFOS, PFOA, PFHxS, PFNA, and PFDA in
maternal serum (cord serum) were 5.5 (1.8),
120
900
Percent telomer
PFOA (ng/g)
800
100
700
80
600
500
60
400
a
300
40
200
20
Total PFOA concentration (ng/g)
Results and Discussion
content was small: 30 ± 0.8% branched PFOS
in 18 lots over 20 years (Reagen WKL, Jacoby
CB, Purcell RG, Kestner TA, Payfer RM,
et al., unpublished data).
Unlike PFOS, PFOA isomer profiles in
dust were often substantially diferent from
the 3M ECF PFOA standard. Although the
relative profile among individual branched
PFOA isomers was consistent among dust
samples [Supplemental Material, Figure 3B,
Table 3 (http://dx.doi.org/10.1289/
ehp.1003265)], we observed an excess signal
of linear PFOA in many of the samples com
pared with the 3M Company ECF standard.
Like 3M Company PFOS, batches of 3M
Company PFOA also had a consistent isomer
composition: 22 ± 1.2% branched isomers in
18 lots over 20 years (Reagen WKL, Jacoby
CB, Purcell RG, Kestner TA, Payfer RM,
et al., unpublished data). Therefore, these
observations suggest that a signiicant propor
tion of PFOA in these house dust samples
came from a manufacturing source that used
telomerization instead of ECF. We calculated
the “percent telomer” PFOA in each dust
sample from the excess signal of linear isomer
in samples (m/z 413/369 transition) com
pared with 3M Company ECF PFOA. he
percent telomer ranged from 0 to 95%, with a
median of 31%, among all samples (Figure 1).
he presence of telomer PFOA in the human
household environment may partly explain
why total PFOA in serum has declined so
slowly after the phaseout of ECF perfluo
rooctyl chemistries by 3M Company in the
United States [see Supplemental Material,
Figure 1 (http://dx.doi.org/10.1289/
ehp.1003265)] (Olsen et al. 2008). However,
telomer PFOA also may be present in food,
and telomer PFOA precursors used in food
packaging may be absorbed and biotrans
formed to PFOA after ingestion (D’eon and
Mabury 2011).
Percent telomer PFOA
by multiple reaction monitoring with 3–13
transitions per analyte.
Quality control. Triplicate recovery exper
iments were performed at two concentrations
of native linear standards spiked to calf serum
or dust [see Supplemental Material, Table 1
(http://dx.doi.org/10.1289/ehp.1003265)].
here are no masslabeled internal standards
for branched PFOS or PFOA isomers, so a
standard addition experiment was done in
dust to rule out possible matrix effects on
the measured isomer profiles. Additionally,
a vacuuming experiment was done to check
whether offgassing during vacuuming may
bias the dust isomer profile. The results of
these two experiments clearly showed that
matrix efects and ofgassing during vacuum
ing were not a problem. he percent recov
ery during serum extraction was similar for
all PFOS and PFOA isomers, such that the
extraction step had no efect on the resulting
isomer proiles (Benskin et al. 2007).
100
0
0
21
29
24
36
18
14
20
47
30
11
6
22
8
26
23
32
12
13
Dust sample ID
Figure 1. Percent telomer PFOA and total PFOA concentration in house dust samples (left to right, lowest
to highest total PFOA concentration), by ID (identification number).
aSample
collected by mechanical sweeper instead of vacuum.
119 | NUMBER 11 | November 2011
1661
Beesoon et al.
1.8 (1.1), 1.7 (0.7), 0.9 (0.4), and 0.4 (0.1)
ng/mL, respectively. We detected PFUnA,
PFDoA, and perluorotetradecanoate (PFTA)
(detection limit, 0.1 ng/mL) in six, two, and
three maternal samples, respectively, but in no
cord samples.
We estimated transplacental transfer ei
ciencies (TTEs) by dividing the PFC concen
trations in cord serum at delivery by maternal
serum concentration at 15 weeks of gestation
for each mother–cord pair (Table 2). Mean
TTEs were always < 1.0, indicating lower con
centrations in cord serum than in maternal
serum (all p < 0.01). Overall, the PFOS and
PFOA TTEs were within the range reported
in the literature. However, it is likely that our
TTEs slightly underestimate actual TTE values
because they do not relect hematologic changes
that occur later in pregnancy, including expan
sion of total plasma volume (Whittaker et al.
1996). Such an efect was shown by Monroy
et al. (2008), who reported lower serum PFOS
and PFOA levels in maternal serum samples
collected at delivery versus 24th through 28th
weeks of gestation, and by Fei et al. (2007),
who reported that cord:maternal ratios based
on maternal serum samples were higher when
collected during the second trimester than dur
ing the irst trimester (Table 1). We used the
data from Monroy et al. (2008) (see Table 1
notes) to estimate timeofdelivery maternal
serum concentrations, based on our 15week
data, but this had little efect on the resulting
TTEs, and both adjusted and unadjusted TTE
values were within the range of TTEs reported
previously (Table 1).
Table 1. Summary of existing studies on maternal–fetal transfer of total PFOA and total PFOS.
Study
Needham et al. 2011
Kim et al. 2011
Fromme et al. 2010
Hanssen et al. 2010
Monroy et al. 2008
Midasch et al. 2007
Fei et al. 2007
Sampling year
2000
2007
2007–2009
2005–2006
2004–2005
2003
1996–2002
Inoue et al. 2004
Present study
2003
2007
Location
Faroe Islands
Korea
Germany
South Africa
Canada
Germany
Denmark
Japan
Canada
Sample size
12
20
27
58
101
11
50c
50d
15
20d
20e
Mean cord:maternal
serum concentration
(correlation coefficient)
PFOA
PFOS
0.72 (0.91)a
0.34 (0.82)a
0.69 (0.88)a
0.36 (0.50)b
0.70 (0.94)b
0.30 (0.89)b
0.71 (0.67)b
0.45 (0.88)b
0.81 (0.88)a
0.45 (0.83)a
1.26 (0.72)b
0.60 (0.42)b
0.55
0.29
0.68 (0.84)a
0.34 (0.72)a
0.32 (0.88)a
0.61 (0.63)b
0.33 (0.81)b
0.71 (0.76)b
0.36 (0.81)b
aPearson
correlation. bSpearman rank correlation. cMaternal serum was sampled in the first trimester. dMaternal serum
was sampled in the second trimester. eTTE adjusted from 15 weeks to time of delivery (~ 40 weeks) using data from
Monroy et al. (2008), whereby PFOS declined 10% and PFOA declined 12% between the 24th to 28th week and delivery.
Table 2. TTE calculated from cord:maternal serum concentrations.
Compound
Total, linear, and branched PFOS
Total PFOS
n-PFOS
Iso- PFOS
5m-PFOS
5m-PFOS
4m-PFOS
3m-PFOS
1m-PFOS
Σm2-PFOS
Total, linear, and branched PFOA
Total PFOA
n-PFOA
Iso-PFOA
5m- PFOA
4m- PFOA
3m-PFOA
tb-PFOA
Other PFCs
Total PFNA
Total PFDA
Total PFHxS
Arithmetic
mean
Median
SD
Minimum
Maximum
na
0.33
0.33
0.36
0.53
0.53
0.55
0.67
0.87
0.84
0.31
0.30
0.34
0.52
0.52
0.52
0.68
0.88
0.78
0.09
0.12
0.14
0.18
0.18
0.19
0.23
0.23
0.37
0.20
0.10
0.09
0.25
0.25
0.20
0.21
0.36
0.22
0.53
0.58
0.60
0.93
0.93
0.85
1.12
1.24
1.72
20
20
20
20
20
20
20
20
20
0.61
0.62
0.84
0.86
0.64
0.76
0.25
0.63
0.61
0.67
0.54
0.68
0.68
0.25
0.17
0.20
0.58
0.99
0.34
0.59
0.32
0.32
0.26
0.16
0.09
0.09
0.07
0.02
0.96
1.00
2.56
2.26
1.29
2.74
0.48
20
20
20
4
19
18
2
0.41
0.34
0.41
0.38
0.23
0.38
0.17
0.25
0.12
0.13
0.00
0.29
0.78
1.10
0.56
20
16
8
Values < 1 indicate higher concentrations in maternal serum; > 1.0, higher concentrations in cord serum.
aNumber of maternal–cord pairs that were available for calculating TTE. When concentrations were nondetect in maternal or cord samples, that pair was excluded in the analysis. Mean TTEs were always < 1.0, indicating lower concentrations in the cord serum than maternal serum (all p < 0.01). Linear PFOS and PFOA are denoted as n-PFOS and n-PFOA
respectively.
1662
VOLUME
A comparison of TTEs among the three
major perfluoroalkyl carboxylates (PFOA,
PFNA, and PFDA) suggests that the
longerchain carboxylates were more eiciently
blocked by the placental barrier (Figure 2A),
consistent with the results of Kim et al.
(2011). he same trend was also evident for
the two major perfluorosulfonates (PFHxS
and PFOS; Figure 2B). Overall, shorterchain
PFCs crossed the placenta more efficiently
than did longerchain PFCs, consistent with
the indings of Needham et al. (2011).
PFC isomer profiles in maternal and cord
sera. The percent branched content of total
PFOS was consistently and signiicantly higher
in cord serum than in corresponding maternal
serum and dust samples (Figure 3). Branched
PFOS isomers contributed 27–44% (median,
36%) of total PFOS in maternal serum and
36–54% (median, 46%) in cord serum. A
paired ttest indicated statistically greater pro
portions of branched PFOS in the cord serum
(p < 0.01). Overall, all branched PFOS iso
mers were transferred more eiciently (median
TTEs of the different branched isomers,
0.34–0.88) than was the linear isomer (median
TTE, 0.30) (Table 2). his is similar to results
of the Hanssen et al. (2010) study, which
found a statistically greater relative abundance
of linear PFOS in maternal serum than in cord
serum relative to total branched PFOS isomers
(p < 0.05 by Wilcoxon’s signed rank test).
Unlike Hanssen et al. (2010), who quanti
fied total branched PFOS isomers together,
we analyzed individual branched isomers, and
results suggest a structure–activity relationship
for TTE. Speciically, among the perluorom
ethyl PFOS branched isomers, TTE increased
as the branching point moved closer to the
sulfonate moiety: 1m > 3m > 4m ≈ 5m > iso
(Figure 2C). In fact, for 1m, 3m, and par
ticularly Σm2PFOS, the concentrations were
sometimes higher in cord serum than in cor
responding maternal serum (resulting in maxi
mum TTE values > 1.0), which was never the
case for total PFOS or linear PFOS (Table 2).
Branched PFOA isomers contributed
0.43–4.3% (mean, 1.9%) of total PFOA in
maternal serum and 0.71–5.7% (mean, 2.2%)
in cord serum. Such highly linear isomer pro
files of PFOA in human serum have previ
ously been reported (De Silva and Mabury
2006), yet it is important to note that these
cannot be used to quantitatively assess expo
sure sources (i.e., telomer vs. electrochemi
cal) because in animal models the branched
isomers of PFOA are accumulated to a lesser
extent than are linear PFOA (De Silva et al.
2009). No structure–activity relationship was
evident for PFOA isomers (Figure 2D), but
a paired ttest indicated significantly higher
total branched PFOA isomers in cord serum
than in maternal serum (p = 0.02). In some
cases, the concentrations of 5m, 4m, and
119 | NUMBER 11 | November 2011 • Environmental Health Perspectives
PFC isomer profiles in blood and dust
Environmental Health Perspectives •
VOLUME
are opposite that in rats (De Silva et al.
2009) or that some humans are exposed to
an unusually high branched PFOS source
in the diet, an alternative explanation is that
a significant proportion of the PFOS body
burden comes from metabolism of PFOS
precursors. Benskin et al. (2009) demon
strated that branched isomers of a PFOS
precursor could be biotransformed at greater
rates than the corresponding linear precur
sor, and Haug et al. (2011) found a signii
cant association between PFOS precursors in
air and increasing branched PFOS content
of serum. In the present samples, maternal
and cord serum PFOS concentrations were
higher (p < 0.01 for maternal serum, p = 0.01
for cord serum) when we detected Nmethyl
perluorooctanesulfonamidoacetate (a PFOS
precursor) in the same sample, but we found
no signiicant association between total dust
PFOS precursors and the branched PFOS
content of serum (p = 0.47).
Study limitations. One limitation of
this study is the relatively small sample size.
Larger studies are recommended to elucidate
the relative importance of ECF and telomer
derived sources of PFCs to humans in other
areas. The present study was not designed
to test whether PFC signatures in dust were
responsible for PFC signatures in maternal
or cord serum; rather, it was an exploratory
investigation of the variability of isomer
profiles in dust to elucidate manufacturing
sources, and of the variation of isomer proiles
0.7
7
1.0
0.6
0.8
0.5
TTE
TTE
1.2
0.6
0.4
0.4
0.3
0.2
0.2
9
0.1
0
PFOA (C-8)
PFNA (C-9)
PFDA (C-10)
PFHxS (C-6)
PFOS (C-8)
Chain lengths of perfluorosulfonates
2.0
2.0
1.5
1.5
TTE
TTE
Chain lengths of perfluorocarboxylates
1.0
10
1.0
0.5
0.5
0
0
n
iso
5m
4m
3m
Σm2
1m
n
PFOS: linear and branched isomers
4m
iso
3m
PFOA: linear and branched isomers
Figure 2. TTE distributions for different-chain-length perfluorocarboxylates (A) and perfluorosulfonates
(B) and for linear and branched PFOS (C) and PFOA (D) isomers. The upper and lower bounds of the
boxes indicate the 75th and 25th percentiles, respectively, and the horizontal lines within the boxes indicate median values. The upper and lower limits of the whiskers indicate minimum and maximum values,
respectively, and points above or below the whiskers indicate outlier values. In A, B, and D, the number
attached to each outlier is the number of a specific sample.
60
Percent branched PFOS isomers
3mPFOA were higher in the cord serum than
in corresponding maternal serum (resulting in
maximum TTE > 1.0), which was never the
case for total PFOA or linear PFOA (Table 2).
Passive difusion is often the mechanism
by which chemicals cross the placental barrier
(Syme et al. 2004), so the TTE of hydrophilic
compounds is generally lower than for hydro
phobic compounds (Van der Aa et al. 1998).
Based on earlier elution in reversephase chro
matography, branched PFOS isomers are
anticipated to be more hydrophilic than lin
ear PFOS, and shortchain carboxylates (e.g.,
PFOA) should be more hydrophilic than
longerchain carboxylates (e.g., PFNA and
PFDA), so the present results are unexpected.
However, perluorinated acids are highly pro
tein bound in serum (Jones et al. 2003), and
the dynamics of protein binding are likely to
inluence TTE. For example, if the binding
affinity of linear PFOS to maternal serum
protein is higher than for branched PFOS iso
mers, a higher free fraction of branched PFOS
would be available to cross the placenta.
For the major PFCs in maternal serum,
we examined whether the branched isomer
content was correlated to the branched isomer
content in the corresponding house dust sam
ple. Although we did not observe a signiicant
correlation between serum and dust branched
isomer content for PFOS (Spearman correla
tion coeicient = –0.10, p = 0.35) or PFHxS
(Spearman correlation coeicient = –0.11, p =
0.33), we found a borderline signiicant cor
relation for PFOA (Spearman correlation coef
icient = 0.35, p = 0.08). However, we cannot
confirm that dust was a source of branched
PFOA isomers in these women, given the small
sample size (n = 20) and the potential contri
bution of other sources of exposure, including
diet, water, and air (Haug et al. 2011).
In contrast with expectations, we observed
a higher mean percentage of branched PFOS
isomers in maternal serum [36%; 95% coni
dence interval (CI): 33.6, 38.2%] than in his
toric 3M Company ECF PFOS (30%; 95%
CI: 29.3, 30.7%) (Reagen WKL, Jacoby CB,
Purcell RG, Kestner TA, Payfer RM, et al.,
unpublished data) or in house dust samples
(30%; 95% CI: 28.6, 31.3%). A paired ttest
showed signiicantly higher branched PFOS
content in maternal serum than in house dust
(6% higher; 95% CI: 3.1, 8.9%; p < 0.001).
Studies in rodents show that branched PFOS
isomers are no more bioaccumulative than
linear PFOS (De Silva et al. 2009), so it
would seem pharmacokinetically impossible
to accumulate > 30% branched PFOS iso
mers if the only source of exposure was ECF
PFOS. Nonetheless, Karrman et al. (2007)
and Hanssen et al. (2010) also reported high
proportions of branched PFOS isomers in
human serum. Although it is possible that
PFOS isomer pharmacokinetics in humans
Maternal serum
Cord serum
50
40
30
20
10
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
Mother–cord serum pair
Figure 3. Percent branched PFOS isomers [Σbranched/(Σbranched + linear)] in 20 matched samples of
maternal serum at 15 weeks of gestation and cord serum at delivery. Samples are arranged, from left to
right, by increasing branched PFOS isomer content of the maternal sample.
119 | NUMBER 11 | November 2011
1663
Beesoon et al.
between maternal and cord samples to exam
ine whether branched isomers crossed the pla
centa to diferent extents.
A second limitation was that the time of
sampling of pregnant women (15 weeks) was
relatively early in the pregnancy, and it is not
clear whether the isomer proile might have
been different at time of delivery. For two
women in our study we also analyzed 18week
serum samples, and total PFOS and individ
ual PFOS isomers were not substantially dif
ferent over these 3 weeks (data not shown).
Although this is a narrow window of time, it
is not an insigniicant period because hemato
logic indices change signiicantly beginning as
early as the 7th week of pregnancy, including
expansion of total blood plasma volume by
16% between 12 and 20 weeks (Whittaker
et al. 1996).
Conclusion
Both ECF and telomer manufacturing sources
contributed to household dust PFOA concen
trations in this exploratory study. Some homes
with the highest PFOA dust concentrations
had a near exclusive telomer PFOA signal, and
such results may help explain why PFOA con
tinues to be a major contaminant of human
serum despite the ECF PFOA phaseout.
Largerscale studies that examine manufactur
ing sources while simultaneously accounting
for dietary pathways would be beneicial. It is
recognized that such investigations are techni
cally challenging because isomer profiles in
biological samples (i.e., food) may bias source
apportionment due to diferential uptake of
the various isomers. The TTE of PFCs was
inversely related to chain length, and TTEs
suggest that most branched PFOA and PFOS
isomers crossed the placenta to a greater extent
than the corresponding linear isomer. In some
cases, minor PFOA and PFOS branched iso
mers were more concentrated in cord serum
than maternal serum, indicating that isomer
speciic analysis should be performed in future
studies of PFCs and birth outcomes.
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119 | NUMBER 11 | November 2011 • Environmental Health Perspectives