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Legacy and Emerging Perfluoroalkyl Substances Are Important
Drinking Water Contaminants in the Cape Fear River Watershed of
North Carolina
Mei Sun,*'�'*@ Elisa Arevalo,* Mark Strynar,� Andrew Lindstrom,§ Michael Richardson,ll Ben Kearns,"
Adam Pickett, I Chris Smith, and Detlef K U. Knappet
tDepartment of Civil and Environmental Engineering, University of North Carolina at Charlotte, Charlotte, North Carolina 28223,
United States
*Department of Civil, Construction, and Environmental Engineering, North Carolina State University, Raleigh, North Carolina
27695, United States
National Exposure Research Laboratory, U.S. Environmental Protection Agency Research, Triangle Park, North Carolina 27711,
United States
"Cape Fear Public Utility Authority, Wilmington, North Carolina 28403, United States
-'Town of Pittsboro, Pittsboro, North Carolina 27312, United States
#Fayetteville Public Works Commission, Fayetteville, North Carolina 28301, United States
© Supporting Information
ABSTRACT: Long -chain per- and polyfluoroalkyl substances Point & A Legacy PFAS�
(PFASs) are being replaced by short -chain PFASs and non -point A
fluorinated alternatives. For ten legacy PFASs and seven sources 01 B PFPrOPrA ("GenX")
recently discovered perfluoroalkyl ether carboxylic acids c
,R
(PFECAs), we report (1) their occurrence in the Cape Fear ?!s , 0 200 aoo 600 800
River (CFR) watershed, (2) their fate in water treatment F.; PFAS Concentration (ng/L)
processes, and (3) their adsorbability on powdered activated F F GB
F FI FI
PFECAs were not detected in raw water of a drinking water F I 1 I OH Fluorochemical
treatment plant (DWTP) but concentrations of legacy PFASs F F F Manufacturer
were h' n . The U.S. Environmental Protection Agency's PFPrOPrA "GenX' C
lifetime health advisory level (70 ng/L) for perfluorooctane-
sulfonic acid and perfluorooctanoic acid (PFOA) was exceeded on 57 of 127 sampling days. In raw water of a DWTP
downstream of a PFAS manufacturer, the mean concentration of perfluoro-2-propoxypropanoic acid (PFPrOPrA), a replacement
for PFOA, was 631 ng/L (n = 37). Six other PFECAs were detected; with three exhibiting chromatographic peak areas up to 15
times that of PFPrOPrA. At this DWTP, PFECA removal by coagulation, ozonation, biofiltration, and disinfection was negligible.
The adsorbability of PFASs on PAC increased with increasing chain length Replacing one CFZ group with an ether oxygen
decreased the affinity of PFASs for PAC, while replacing additional CFZ groups did not lead to further affinity changes.
0 INTRODUCTION
Per- and polyfluoroalkyl substances (PFASs) are extensively
used in the production of plastics, water/stain repellents,
firefighting foams, and food -contact paper coatings. The
widespread occurrence of PFASs in drinking water sources is
closely related to the presence of sources such as industrial
sites, military fire training areas, civilian airports, and waste-
water treatment plants.' Until 2000, long -chain perfluoroallcyl
sulfonic acids 1C.F111S03H; n > 6 (PFSAs)] and perfluoro-
alkyl carboxylic acids [CnFzn+'COON; n > 7 (PFCAs)] were
predominantly used? Accumulating evidence about the
ecological persistence and human health effects associated
with exposure to long -chain PFASs3'4 has led to an increased
level of regulatory attention. Recently, the U.S. Environmental
Protection Agency (USEPA) established a lifetime health
A,CS Publications O XXXX American Chemical Society
advisory level (HAL) of 70 ng/L for the sum of
perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic
acid (PFOS) concentrations in drinking water.5'6 Over the past
decade, production of long -chain PFASs has declined in Europe
and North America, and manufacturers are moving toward
short -chain PFASs and fluorinated alternatives?—" Some
fluorinated alternatives were recently identified,8,'1 but others
remain unknown'2—" because they are either proprietary or
manufacturing byproducts.
Received: October 13, 2016
Revised: November 8, 2016
Accepted: November 10, 2016
Published: November 10, 2016
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One group of fluorinated alternatives, perfluoroalkyl ether
carboxylic acids (PFECAs), was recently discovered in the Cape
Fear River (CFR) downstream of a PEAS manufacturing
facility 11 Identified PFECAs included perfluom-2-methoxy>
acetic acid (PFMOAA), perfluoro-3-methoxypropanoic acid
(PFMOPrA), perfluoro-4-methoxybutanoic acid (PFMOBA),
perfluoro-2-propoxypropanoic acid (PFPrOPrA), perfluoro-
(3,5-dioxahexanoic) acid (PFO2HxA), perfluoro(3,5,7-trioxa-
octanoic) acid (PF030A), and perfluoro(3,5,7,9-tetraoxadeca-
noic) acid (PF04DA) (Table S1 and Figure S1). The
ammonium salt of PFPrOPrA is a known PFOA alternative's
that has been produced since 2010 with the trade name
"GenX". To the best of our knowledge, the only other
published PFECA occurrence data are for PFPrOPrA in Europe
and China,ls and no published data about the fate of PFECAs
during water treatment are available. Except for a few studies
(most by the manufacturer),'6-20 little is known about the
toxicity, pharmacokinetic behavior, or environmental fate and
transport of PFECAs.
The strong C—F bond makes PFASs refractory to abiotic and
biotic degradation,Z1 and most water treatment processes are
ineffective for legacy PFAS removaL22-27 Processes capable of
removing PFCAs and PFSAs include nanofiltration,,s reverse
osmosis,Zs ion exchange,28'29 and activated carbon adsorp-
tlon,28,29 with activated carbon adsorption being the most
widely employed treatment option.
The objectives of this research were (1) to identify and
quantify the presence of legacy PFASs and emerging PFECAs
in drinking water sources, (2) to assess PFAS removal by
conventional and advanced processes in a full-scale drinking
water treatment plant (DWTP), and (3) to evaluate the
adsorbability of PFASs on powdered activated carbon (PAC).
■ MATERIALS AND METHODS
Water Samples. Source water of three DWTPs treating
surface water in the CFR watershed was sampled between June
14 and December 2, 2013 (Figure S2). Samples were collected
from the raw water tap at each DWTP daily as either 8 h
composites (DWTP A, 127 samples) or 24 h composites
(DWTP B, 73 samples; DWTP C, 34 samples). Samples were
collected in 250 mL HDPE bottles and picked up (DWTPs A
and B) or shipped overnight (DWTP C) on a weekly basis. All
samples were stored at room temperature until they were
analyzed (within 1 week of receipt). PFAS losses during storage
were negligible on the basis of results of a 70 day holding study
at room temperature. On August 18, 2014, grab samples were
collected at DWTP C after each unit process in the treatment
train [raw water ozonation, coagulation/flocculation/sedimen-
tation, settled water ozonation, biological activated carbon
(BAC) filtration, and disinfection by medium -pressure UV
lamps and free chlorine]. Operational conditions of DWTP C
on the sampling day are listed in Table S2. Samples were
collected in 1 L HDPE bottles and stored at room temperature
until they were analyzed. On the same day, grab samples of
CPR water were collected in six 20 L HDPE carboys at William
0. Huske Lock and Dam downstream of a PFAS manufacturing
site and stored at 4 'C until use in PAC adsorption experiments
(background water matrix characteristics listed in Table S3).
Adsorption Experiments. Adsorption of PFASs by PAC
was studied in batch reactors (amber glass bottles, 0.45 L of
CPR water). PFECA adsorption was studied at ambient
concentrations (-1000 ng/L PFPrOPrA, chromatographic
peak areas of other PFECAs being approximately 10-800%
of the PFPrOPrA area). Legacy PFASs were present at low
concentrations (<40 ng/L) and spiked into CPR water at
—1000 ng/L each. Data from spiked and nonspiked experi-
ments showed that the added legacy PFASs and methanol (1
ppmo) from the primary stock solution did not affect native
PFECA removal. A thermally activated, wood based PAC
(PicaHydro MP23, PICA USA, Columbus, OH; mean diameter
of 12 pra, BET surface area of 1460 m2/ )30 proven to be
effective for PFAS removal in a prior study, was used at doses
of 30, 60, and 100 mg/L. These doses represent the upper
feasible end for drinking water treatment. Samples were taken
prior to and periodically after PAC addition for PFAS analysis.
PFAS losses in PAC -free blanks were negligible.
PFAS Analysis. Information about analytical standards and
liquid chromatography —tandem mass spectrometry (LC —MS/
MS) methods for PFAS quantification is provided in the
Supporting Information.
■ RESULTS AND DISCUSSION
Occurrence of PFASs in Drinking Water Sources. Mean
PFAS concentrations in source water of three DWTPs treating
surface water from the CFR watershed are shown in Figure 1.
PFBA ■ PFPeA ■ PFRXA m PFHpA n PFOA a PMA
v PFDA ■ PM a PFRxS ■ PFOS ■ PFPrOPrA
Community A
n-127
CommunityB
n-73
community c
n-34
0 2DD 400 600 8W
Average concentration in drinking waterwurce (ng/L)
Figure 1. Occurrence of PFASs at drinking water intakes in the CPR
watershed. Concentrations represent averages of samples collected
between June and December 2013. Individual samples with
concentrations below the quantitation limits (QLs) were considered
as 0 when calculating averages, and average concentrations below the
QLs were not plotted.
In communities A and B, only legacy PFASs were detected
(mean ZPFAS of 355 ng/L in community A and 62 ng/L in
community B). Detailed concentration data are shown in Table
S6 and Figure S3. In community A, PFCAs with four to eight
total carbons, perfluorohexanesulfonic acid (PFHxS), and
PFOS were detected at mean concentrations above the
quantitation limits (QLs). During the 127 day sampling
campaign, the sum concentration of PFOA and PFOS exceeded
the USEPA HAL of 70 ng/L on 57 days. The mean sum
concentration of PFOA and PFOS over the entire study period
was 90 ng/L, with approximately equal contributions from
PFOS (44 ng/L) and PFOA (46 ng/L). Maximum PFOS and
PFOA concentrations were 346 and 137 ng/L, respectively.
Similar PFOS and PFOA concentrations were observed in the
same area in 2006,31 suggesting that PFAS source(s) upstream
of community A have continued negative impacts on drinking
water quality. Also, our data show that legacy PFASs remain as
surface water contaminants of concern even though their
production was recently phased out in the United States. It is
important to note, however, that among the PFCAs that were
measured in both 2006 and 2013 (PFHxA to PFDA), the
PFCA speciation shifted from long -chain (-80-85%
C„F2r,+1COOH; n = 7-9) in 2006 to short -chain (76%
C"F2n+1COOH; n = 5-6) in 2013. In contrast, the PFSA
speciation was dominated by PFOS in both 2006 and 2013.
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Relating total PFAS concentration to average daily streamflow
(Figure S4) illustrated a general trend of low PFAS
concentrations at high flow, and high concentrations at low
flow, consistent with the hypothesis of one or more upstream
point sources.
In community B, perfluorobutanoic acid (PFBA) and
perfluoropentanoic acid (PFPeA) were most frequently
detected with mean concentrations of 12 and 19 ng/L,
respectively. Mean PFOA and PFOS concentrations were
below the QLs, and the maximum sum concentration of PFOA
and PFOS was 59 ng/L. Lower PFAS concentrations in
community B relative to community A can be explained by the
absence of substantive PFAS sources between the two
communities, dilution by tributaries, and the buffering effect
of Jordan Lake, a large reservoir located between communities
A and B.
In community C (downstream of a PFAS manufacturing
site), only mean concentrations of PFBA and PFPeA were
above the QLs. The relatively low concentrations of legacy
PFASs in the finished drinking water of community C are
consistent with results from the USEPA's third unregulated
contaminant monitoring rule for this DWTP 32 However, high
concentrations of PFPrOPrA were detected (up to —4500 ng/
L). The average PFPrOPrA concentration (631 ng/L) was
approximately 8 times the average summed PFCA and PFSA
concentrations (79 ng/L). Other PFECAs had not yet been
identified at the time of analysis. Similar to communities A and
B, the highest PFAS concentrations for community C were also
observed at low flow (Figure S4). Stream flow data were used
in conjunction with PFPrOPrA concentration data to
determine PFPrOPrA mass fluxes at the intake of DWTP C.
Daily PFPrOPrA mass fluxes ranged from 0.6 to 24 kg/day with
a mean of 5.9 kg/day.
Fate of PFASs in Conventional and Advanced Water
Treatment Processes. To investigate whether PFASs can be
removed from impacted source water, samples from DWTP C
were collected at the intake and after each treatment step.
Results in Figure 2 suggest conventional and advanced
treatment processes (coagulation/flocculation/sedimentation,
raw and settled water ozonation, BAC filtration, and
disinfection by medium -pressure UV lamps and free chlorine)
did not remove legacy PFASs, consistent with previous
studies.22-26 The data further illustrate that no measurable
PFECA removal occurred in this DWTP. Concentrations of
some PFCAs, PFSAs, PFMOPrA, PFPrOPrA, and PFMOAA
may have increased after ozonation, possibly because of the
oxidation of precursor compounds.15 Disinfection with
medium -pressure UV lamps and free chlorine (located between
the BAC effluent and the finished water) may have decreased
concentrations of PFMOAA, PFMOPrA, PFMOBA, and
PFPrOPrA, but only to a limited extent. Small concentration
changes between treatment processes may also be related to
temporal changes in source water PFAS concentrations that
occurred in the time frame corresponding to the hydraulic
residence time of the DWTP.
Results in Figure 2 further illustrate that the PFAS signature
of the August 2014 samples was similar to the mean PFAS
signature observed during the 2013 sampling campaigns shown
in Figure 1; i.e., PFPrOPrA concentrations (400-500 ng/L)
greatly exceeded legacy PFAS concentrations. Moreover, three
PFECAs (PFMOAA, PFO2HxA, and PF030A) exhibited peak
areas 2-113 times greater than that of PFPrOPrA (Figure 2b).
(a) Raw water
Pro -ozone effluent
Settled water
Settled -ozone effluent
BAC effluent
Finished water
0 M 200 300 400 500 tip = "
Concentration of traditional PFASs
at a WTP in Community C tnWU
■ PFPr0PrA PFBA a PFPeA ■ PFHxA B PFHPA n PFOA
* PFNA a PFDA ■ FFBS n PFHS ■ PFQS
rot Raw water
Pre -ozone effluent
Settled water
Settled -ozone effluent
BAC effluent
Finished water
M
0 50,000 100,010 150,0W 200,0W 250,OOD 300,000
Peak area counts of emerging PFASs
at a WTP in Community C
s PFPr0PrA ■ PFMOAA PFMOPrA a PFMOBA
PF02HxA m PF030A PF04DA
Figure 2. Fate of (a) legacy PFASs and PFPrOPrA and (b) PFECAs
through a full-scale water treatment plant. Because authentic standards
were not available for PFECAs other than PPPrOPrA, chromato-
graphic peak area counts are shown in panel b. PFPrOPrA data are
shown in both panels and highlighted with dashed ovals for reference.
Compounds with concentrations below the QIs were not plotted.
The existence of high levels of emerging PFASs suggests a need
for their incorporation into routine monitoring.
Adsorption of PFASs by PAC. PAC can effectively remove
long -chain PFCAs and PFSAs, but its effectiveness decreases
with decreasing PFAS chain length.2425'19 It is unclear,
however, how the presence of ether group(s) in PFECAs
impacts adsorbability. After a contact time of 1 h, a PAC dose
of 100 mg/L achieved >80% removal of legacy PFCAs with
total carbon chain lengths of >7. At the same PAC dose,
removals were 95% for PF04DA and 54% for PF030A, but
<40% for other PFECAs. Detailed removal percentage data as a
function of PAC contact time are shown in Figure S5. There
was no meaningful removal of PFMOBA or PFMOPrA, and the
variability shown in Figure SS is most likely associated with
analytical variability. PFMOAA could not be quantified by the
analytical method used for these experiments; however, on the
basis of the observations that PFAS adsorption decreases with
decreasing carbon chain length and that PFECAs with one or
two more carbon atoms than PFMOAA (i.e., PFMOPrA and
PFMOBA) exhibited negligible removal (Figure 3), it is
expected that PFMOAA adsorption is also negligible under
the tested conditions.
To compare the affinity of different PFASs for PAC, PFAS
removal percentages were plotted as a function of PFAS chain
length [the sum of carbon (including branched), ether oxygen,
and sulfur atoms] (Figure 3b). The adsorbability of both legacy
and emerging PFASs increased with increasing chain length.
PFSAs were more readily removed than PFCAs of matching
chain length, a result that agrees with those of previous
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100a
9 20%
Po0 0%
y -20%
°
0`� 0 0 0
L 6�.
PFCAs Mono-etherPFECAs Multi-ethml`FECAs PFSAs
(b)
6
3 5 7 9 11
Chain length
—a—PFCAs —Mono ether PFECAs --a—Multi-ether PFECAs—d—PFSAs
Figure 3. PFAS adsorption on PAC (a) at carbon doses of 30, 60, and 100 mg/L and (b) as a function of PEAS chain length. The PAC contact time
in CPR water was 1 h. Legacy PFASs were spiked at —1000 ng/L, and the emerging PFASs were at ambient concentrations. Figures show average
PFAS removal percentages, and error bars show one standard deviation of replicate experiments.
studies 24,25'29 PFECAs exhibited adsorbabilities lower than
those of PFCAs of the same chain length (e.g., PFMOBA <
PFHxA), suggesting that the replacement of a CFZ group with
an ether oxygen atom decreases the aff ndty of PFASs for PAC.
However, the replacement of additional CF2 groups with ether
groups resulted in small or negligible affinity changes among
the studied PFECAs (e.g., PFMOBA — PFO2HxA, PFPrOPrA
— PF030A). Alternatively, if only the number of perfluorinated
carbons were considered as a basis of comparing adsorbability,
the interpretation would be different. In that case, with the
same number of perfiuorinated carbons, PFCAs have an affinity
for PAC higher than that of monoether PFECAs (e.g., PFPeA >
PFMOBA) but an affinity lower than that of multi -ether
PFECAs (e.g., PFPeA < PF030A).
To the best of our knowledge, this is the first paper reporting
the behavior of recently identified PFECAs in water treatment
processes. We show that PFECAs dominated the PFAS
signature in a drinking water source downstream of a
fluorochemical manufacturer and that PFECA removal by
many conventional and advanced treatment processes was
negligible. Our adsorption data further show that PFPrOPrA
('GenX") is less adsorbable than PFOA, which it is replacing.
Thus, PFPrOPrA presents a greater drinking water treatment
challenge than PFOA does. The detection of potentially high
levels of PFECAs, the continued presence of high levels of
legacy PFASs, and the difficulty of effectively removing legacy
PFASs and PFECAs with many water treatment processes
suggest the need for broader discharge control and contaminant
monitoring.
■ ASSOCIATED CONTENT
© Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.esdett.6b00398.
Six tables, five figures, information about PFASs,
analytical methods, and detailed results (PDF)
■ AUTHOR INFORMATION
Corresponding Author
*E-mail: msun8@a unccedu. Phone: [phone].
ORCID G
Mei Sun: 0000-0001-5854-9862
Notes
The views expressed in this article are those of the authors and
do not necessarily represent the views or policies of the
USEPA.
The authors declare no competing financial interest.
■ ACKNOWLEDGMENTS
This research was supported by the National Science
Foundation (Grant 1550222), the Water Research Foundation
(Project 4344), and the North Carolina Urban Water
Consortium.
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