United States Office of Water
oEFft Environmental Protection OST
Agency EPA
PUBLICATION #
EPA/822/R-22/004
INTERIM
Drinking Water Health Advisory:
Perfluorooctane Sulfonic Acid (PFOS)
CASRN 1763-23-1
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INTERIM
Drinking Water Health Advisory:
Perfluorooctane Sulfonic Acid (PFOS)
CASRN 1763-23-1
Prepared by:
U.S. Environmental Protection Agency
Office of Water (4304T)
Office of Science and Technology
Health and Ecological Criteria Division
Washington, DC 20460
EPA Document Number: EPA/822/R-22/004
June 2022
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Acknowledgments
This document was prepared by the Health and Ecological Criteria Division (HECD), Office of
Science and Technology (OST), Office of Water (OW) of the U.S. Environmental Protection
Agency (EPA).
The OW scientists and managers who provided valuable contributions and direction in the
development of this health assessment are, from OST: Carlye Austin, PhD (lead); Czarina
Cooper, MPH; Susan Euling, PhD; Colleen Flaherty, MS; Brittany Jacobs, PhD; Casey
Lindberg, PhD; and from the Office of Ground Water and Drinking Water (OGWDW): Ryan
Albert, PhD; Stanley Gorzelnik, PE; Ashley Greene, MS; and Daniel P. Hautman.
The document underwent a technical edit by the contractor Tetra Tech (contract number
68HERC20D0016).
This Health Advisory document was provided for review by staff in the following EPA program
Offices and Regions:
• Office of Water
• Office of Chemical Safety and Pollution Prevention, Office of Pollution Prevention and
Toxics
• Office of Land and Emergency Management
• Office of Policy
• Office of Children's Health Protection
• Office of Research and Development
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Contents
Abbreviations and Acronyms iii
1.0 Introduction: Background and Scope of Interim Health Advisory 1
1.1 PFOS General Information and Uses 2
1.2 Occurrence in Water and Exposure to Humans 3
1.2.1 Occurrence in Water 3
1.2.2 Exposure in Humans 4
1.3 Source of Toxicity Information for Interim Health Advisory Development 4
1.4 Exposure Factor Information 5
1.5 Approach for Lifetime HA Calculation 6
2.0 Interim Health Advisory Derivation: PFOS 6
2.1 Toxicity 7
2.2 Exposure Factors 8
2.3 Relative Source Contribution 9
2.4 Derivation of Health Advisory Value: Interim Lifetime Noncancer HA 10
3.0 Analytical Methods 11
4.0 Treatment Technologies 11
4.1 Sorption Technologies 12
4.1.1 Activated C arb on 13
4.1.2 Ion Exchange 14
4.2 High-Pressure Membranes 15
4.3 Point-of-Use Devices for Individual Household PFOS Removal 16
4.4 Treatment Technologies Summary 16
5.0 Consideration of Noncancer Health Risks from PFAS Mixtures 16
6.0 Interim Health Advisory Characterization 18
7.0 References 19
Tables
Table 1. Draft Chronic RfD, Critical Effect, and Critical Study Used to Develop the
Lifetime iHA for PFOS 7
Table 2. EPA Exposure Factors for Drinking Water Intake for Candidate Sensitive
Populations Based on the Critical Effect and Study 9
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Abbreviations and Acronyms
AIX
anion exchange
GAC
granular activated
ANSI
American National
carbon
Standards Institute
HA
Health Advisory
AWWA
American Water
HECD
Health and Ecological
Works Association
Criteria Division
BMD
benchmark dose
HESD
Health Effects
BMDL
benchmark dose
Support Document
lower confidence
HI
hazard index
limit
HQ
hazard quotient
Br-DBP
brominated
iHA
interim Health
disinfection by-
Advisory
product
i
mixture component
bw or BW
body weight
chemical
CCL
Contaminant
IRIS
Integrated Risk
Candidate List
Information System
CDC
Centers for Disease
L/(m2hr)
liter per square meter
Control and
per hour
Prevention
lbs
pounds
CDR
Chemical Data
LC/MS/MS
liquid
Reporting
chromatography/tande
CI
confidence interval
m mass spectrometry
CSF
cancer slope factor
LOAEL
lowest-observed-
DBP
disinfection by-
adverse-effect level
product
MCL
Maximum
DOM
dissolved organic
Contaminant Level
matter
MCLG
Maximum
DQO
data quality objectives
Contaminant Level
DWI
drinking water intake
Goal
DWI-BW
body weight-adjusted
mg/kg-day
milligram per
drinking water intake
kilogram per day
E
human exposure
mg/L
milligram per liter
EBCT
empty bed contact
m/hr
meter per hour
time
MPa
megapascal
EF
exposure factor
MRL
minimum reporting
EFH
Exposure Factors
level
Handbook
NF
nanofiltration
EPA
U.S. Environmental
ng/L
nanogram per liter
Protection Agency
NHANES
National Health and
FCID
Food Commodity
Nutrition
Intake Database
Examination Survey
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NOAEL
no-ob served-adverse-
effect level
SAB
NOM
natural organic matter
SAB PFAS Panel
NPDWR
National Primary
Drinking Water
Regulation
OGWDW
Office of Ground
Water and Drinking
SDWA
Water
ORD
Office of Research
and Development
SNUR
OST
Office of Science and
Technology
TSCA
OW
Office of Water
UCMR
PAC
powdered activated
carbon
PBPK
physiologically-based
pharmacokinetic
UCMR3
PFAS
per- and
polyfluoroalkyl
UCMR 5
substances
PFBS
perfluorobutane
UF
sulfonic acid
PFOA
perfluorooctanoic
acid
UFa
PFOS
perfluorooctane
sulfonic acid
UFc
pKa
acid dissociation
constant
UFd
POD
point of departure
UFh
PODhed
point of departure
UFl
human equivalent
dose
ppq
parts per quadrillion
ppt
parts per trillion
PWS
public water system
QC
quality control
UFs
RfD
reference dose
RfV
reference value
RO
reverse osmosis
RPF
relative potency factor
Hg/L
RSC
relative source
contribution
Science Advisory
Board
Science Advisory
Board Per- and
Polyfluoroalkyl
Substances Review
Panel
Safe Drinking Water
Act
Significant New Use
Rule
Toxic Substances
Control Act
Unregulated
Contaminant
Monitoring Rule
third Unregulated
Contaminant
Monitoring Rule
fifth Unregulated
Contaminant
Monitoring Rule
uncertainty factor
interspecies
uncertainty factor
composite uncertainty
factor
database uncertainty
factor
intraspecies
uncertainty factor
lowest observed
adverse effect level-
to-no observed
adverse effect level
extrapolation
uncertainty factor
sub chroni c-to-chroni c
exposure duration
extrapolation
uncertainty factor
microgram per liter
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1.0 Introduction: Background and Scope of Interim Health
Advisory
The Safe Drinking Water Act (SDWA) (42 U.S.C. § § 300f - 300j-27) authorizes the U.S.
Environmental Protection Agency (EPA) to develop drinking water Health Advisories (HAs).1
HAs are national non-enforceable, non-regulatory drinking water concentration levels of a
specific contaminant at or below which exposure for a specific duration is not anticipated to lead
to adverse human health effects.2 HAs are intended to provide information that tribal, state, and
local government officials and managers of public water systems (PWSs) can use to determine
whether actions are needed to address the presence of a contaminant in drinking water. HA
documents reflect the best available science and include HA values as well as information on
health effects, analytical methodologies for measuring contaminant levels, and treatment
technologies for removing contaminants from drinking water. EPA's lifetime HAs identify levels
to protect all Americans, including sensitive populations and life stages, from adverse health
effects resulting from exposure throughout their lives to contaminants in drinking water.
Interim or provisional HA values can be developed to provide information in response to an
urgent or rapidly developing situation. EPA has developed an interim noncancer lifetime HA
(iHA) for perfluorooctane sulfonic acid (PFOS) to replace the 2016 lifetime HA of 0.07
micrograms per liter (|ig/L) (70 parts per trillion [ppt]) because analyses of more recent health
effects studies show that PFOS can impact human health at exposure levels much lower than
reflected by the 2016 PFOS lifetime HA. EPA has developed an interim rather than a final HA
for PFOS because the input values used to derive the iHA are currently draft values and EPA has
identified a pressing need to provide information to public health officials prior to their
finalization.
In 2009, EPA developed a provisional HA for PFOS (U.S. EPA, 2009a) based on the best
information available at that time. Also, PFOS was included on the third and fourth drinking
water Contaminant Candidate Lists (CCLs)3 (U.S. EPA, 2009b, 2016a). After PFOS was listed
on the third CCL in 2009, EPA initiated development of a Health Effects Support Document
(HESD) for PFOS to assist officials and PWS managers in protecting public health when PFOS
is present in drinking water. The HESD was published in 2016 after peer review (U.S. EPA,
2016b). EPA developed a final HA for PFOS (U.S. EPA, 2016c) based on data and analyses in
the 2016 HESD and agency guidance on exposure and risk assessment.
In March 2021, EPA published a final determination to regulate PFOS with a National Primary
Drinking Water Regulation (NPDWR) under SDWA (U.S. EPA, 2021a). NPDWRs include
legally-enforceable Maximum Contaminant Levels (MCLs) and/or treatment technique
requirements that apply to PWSs. To support the development of the NPDWR, EPA developed
1 SDWA §1412(b)(1)(F) authorizes EPA to "publish health advisories (which are not regulations) or take other appropriate
actions for contaminants not subject to any national primary drinking water regulation." www.epa.gov/sites/default/files/2020-
05/documents/safe_drinkiiig_water_act-title_xiv of public _health_service_act.pdf
2 This document is not a regulation and does not impose legally binding requirements on EPA, states, tribes, or the regulated
community. This document is not enforceable against any person and does not have the force and effect of law. No part of this
document, nor the document as a whole, constitutes final agency action that affects the rights and obligations of any person. EPA
may change any aspects of this document in the future.
3 The CCL is a list (published every five years) of contaminants that are not currently subject to any National Primary Drinking
Water Regulation (NPDWR) but are known or anticipated to occur in PWSs and may require future regulation under SDWA.
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the Proposed Approaches to the Derivation of a Draft Maximum Contaminant Level Goal for
Perfluorooctane Sulfonic Acid (PFOS) (CASRN1763-23-1) in Drinking Water (U.S. EPA,
2021b) (hereafter referred to as "draft PFOS document") which includes an updated health
effects assessment of the peer-reviewed literature, draft chronic reference dose (RfD), and draft
relative source contribution (RSC) value. The development of the draft noncancer chronic RfD
for PFOS was performed by a cross-agency per- and polyfluoroalkyl substances (PFAS) Science
Working Group to support the PFAS NPDWR. In November 2021, EPA announced the Science
Advisory Board (SAB) PFAS Review Panel's (SAB PFAS Panel's) review (U.S. EPA, 2021c) of
the draft PFOS document along with three other draft documents supporting the NPDWR (U.S.
EPA, 2022a).
The 2021 data and analyses described in the draft PFOS document indicate that PFOS exposure
levels at which adverse health effects have been observed are much lower than previously
understood when EPA issued an HA for PFOS in 2016. As a result, EPA announced in 20214
that it would move quickly to update the 2016 HA for PFOS to reflect the latest, best available
science as well as input from the SAB PFAS Panel. An updated PFOS HA is consistent with
EPA's commitments for action on PFAS described in EPA's PFAS Strategic Roadmap (U.S.
EPA, 202Id).
In April 2022, the SAB PFAS Panel made public a draft report of its review of the draft PFOS
document (U.S. EPA, 2022a), which indicated general support for the draft conclusions but
recommended additional analyses be performed prior to finalizing the RfD and RSC. Because
the RfD in the draft PFOS document is much lower than the RfD used to derive the 2016 HA,
there is a pressing need to provide updated information on the current best available science to
public health officials prior to finalization of the health effects assessment. Therefore, EPA has
decided to issue an iHA using the draft chronic RfD and RSC values. An updated 10"6 cancer risk
concentration was not derived in this iHA document because the draft PFOS document
concluded that, based on EPA guidelines (U.S. EPA, 2005a), the available human and animal
studies provide suggestive evidence of carcinogenic potential (U.S. EPA, 2021b). Given the
identified uncertainties in the available evidence (see Section 2.0 for further information), the
draft PFOS document concluded that these data did not support a quantitative characterization of
cancer risk associated with PFOS exposure.
After receiving SAB's final report, EPA will fully address SAB feedback and recommendations,
which could lead EPA to draw different conclusions than are reflected in the draft PFOS
document and this iHA document. EPA anticipates proposing a NPDWR in fall 2022 and
finalizing the NPDWR in fall 2023. EPA may update or remove the iHA for PFOS upon
finalization of the NPDWR.
1.1 PFOS General Information and Uses
PFOS is a synthetic fluorinated organic chemical that has been manufactured and used in a variety
of industries since the 1940s (U.S. EPA, 2018). It repels water and oil, is chemically and thermally
stable, and exhibits surfactant properties. Based on these properties, it has been used in the
manufacture of many materials, including cosmetics, paints, polishes, and nonstick coatings on
fabrics, paper, and cookware. It is very persistent in the human body and the environment (Calafat
4 EPA Advances Science to Protect the Public from PFOA and PFOS in Drinking Water [Press release], Nov 16, 2021:
https://www.epa.gov/newsreleases/epa-advances-science-protect-public-pfoa-and-pfos-drinkiiig-water
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et al., 2007, 2019). More information about PFOS's uses and properties can be found in the 2016
HA document for PFOS (U.S. EPA, 2016c) and the draft PFOS document (U.S. EPA, 2021b).
In 2000, the principal manufacturer of PFOS agreed to a voluntary phase-out of PFOS
production and use. This phase-out was completed in 2002 (U.S. EPA, 2007). PFOS is included
in EPA's Toxic Substances Control Act (TSCA) Significant New Use Rule (SNUR) issued in
December 2002, which ensures that EPA will have an opportunity to review any efforts to
reintroduce PFOS into the marketplace and take action, as necessary, to address potential
concerns (U.S. EPA, 2002a). Limited existing uses of PFOS-related chemicals, including as an
anti-erosion additive in fire-resistant aviation hydraulic fluids and as a component of anti-
reflective coating in the production of semiconductors, were excluded from the regulation (U.S.
EPA, 2013). PFOS was not reported as manufactured (or imported) in the United States as part
of the 2006, 2012, or 2016 TSCA Chemical Data Reporting (CDR) effort, which requires
reporting if a certain production volume threshold is met at any single site (the threshold for
PFOS was 25,000 pounds [lbs] in 2006 and 2012, and 2,500 lbs in 2016).5 PFOS manufacture or
importation has not been reported to EPA as part of this collection effort since 2002.
1.2 Occurrence in Water and Exposure to Humans
1.2.1 Occurrence in Water
EPA requires sampling at drinking water systems under the Unregulated Contaminant
Monitoring Rule (UCMR) to collect data for contaminants that are known or suspected to be
found in drinking water and do not have health-based standards under SDWA. A new UCMR is
issued every five years. The first four UCMRs required monitoring of all large public drinking
water systems (> 10,000 people) and a subset of smaller systems serving < 10,000 people. The
third UCMR (UCMR 3), conducted from 2013-2015, is currently the best available source of
national occurrence data for PFOS in drinking water (U.S. EPA, 2017a, 2021a,b,e). A total of
292 samples from 95 PWSs (out of 36,972 total samples from 4,920 PWSs) had detections of
PFOS (i.e., greater than or equal to the minimum reporting level [MRL]6 of 0.04 |ig/L). PFOS
concentrations for these detections ranged from 0.04 |ig/L (the MRL) to 7 |ig/L (median
concentration of 0.06 |ig/L; 90th percentile concentration of 0.25 |ig/L).
In 2016, EPA recommended that when PFOS and perfluorooctanoic acid (PFOA) co-occur at the
same time and location in drinking water sources, a conservative and health-protective approach
is to consider the sum of the concentrations. An analysis of the UCMR 3 data showed that 506
samples from 162 PWSs (out of 36,971 samples from 4,920 PWSs) had detections of PFOA
and/or PFOS (i.e., at or above the MRL of 0.02 |ig/L for PFOA or 0.04 |ig/L for PFOS). The
sum of reported PFOA and/or PFOS concentrations ranged from 0.02 to 7.22 |ig/L. Although it
is not possible to determine the full extent of PFOS and/or PFOA occurrence based on UCMR 3
detections, sites where elevated levels of PFOS and/or PFOA were detected during UCMR 3
monitoring may have taken steps to mitigate exposure including installing treatment systems
5 The TSCA CDR requires manufacturers (including importers) to provide EPA with information on the production and use of
chemicals if they meet certain production volume thresholds. For more information, see www.epa.gov/clieniical-data-reportiiig
6 The MRL refers to the quantitation level selected by EPA to ensure reliable and consistent results. It is the minimum
quantitation level that can be achieved with 95 percent confidence by capable analysts at 75 percent or more of the laboratories
using a specified analytical method (U.S. EPA, 202If).
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and/or blending water from multiple sources, or remediating known sources of contamination
(U.S. EPA, 2021a).
The fifth UCMR (UCMR 5) will require monitoring for 29 PFAS using EPA methods 533 (U.S.
EPA, 2019a) and 537.1 (U.S. EPA, 2020). UCMR 5 monitoring will take place from 2023-2025
and will include all large public drinking water systems serving > 10,000 people, all systems
serving 3,300-10,000 people (subject to the availability of appropriations), and a subset of
smaller systems serving < 3,300 people (U.S. EPA, 2021f). EPA established an MRL for PFOS
of 0.004 |ig/L under UCMR5, which is 10-fold lower than the MRL used in UCMR 3.
Some states have conducted monitoring for PFOS in drinking water (by selecting sampling
locations randomly, and/or sampling from targeted locations). PFOS has been detected in the
finished drinking water for at least 19 states (ADEM, 2021; AZDEQ, 2021; CADDW, 2021;
CDPHE, 2020; GAEPD, 2021; ILEPA, 2021; KYDEP, 2019; MAEEA, 2021; MDE, 2021;
MEDEP, 2020; MIEGLE, 2021; NCDEQ, 2021; NHDES, 2021; NJDEP, 2021; OHDOH, 2020;
PADEP, 2021; RIDOH, 2020; SCDHEC, 2020; VTDEC, 2021).
1.2.2 Exposure in Humans
As noted in the draft PFOS document (U.S. EPA, 2021b), the Centers for Disease Control and
Prevention (CDC) National Health and Nutrition Examination Survey (NHANES) has measured
blood serum concentrations of several PFAS in the general U.S. population since 1999. PFOS
has been detected in up to 98% of serum samples collected in biomonitoring studies that are
representative of the U.S. general population; however, blood levels of PFOS declined by more
than 80% between 1999 and 2014, presumably due to restrictions on PFOS commercial usage in
the United States (CDC, 2017). NHANES biomonitoring data from 1999-2000 reveal a mean
serum PFOS concentration of 30.4 |ig/L (95% confidence interval [CI] of 27.1-33.9 |ig/L) and a
90th percentile serum PFOS concentration of 57 |ig/L (95% CI 50.2-71.7 |ig/L) across 1,562
samples representative of the U.S. population. For 2013-2014, mean and 90th percentile serum
PFOS concentrations were 4.99 |ig/L (95% CI 4.5-5.52 |ig/L) and 13.9 |ig/L (95% CI 11.9-15.5
Hg/L), respectively (2,165 samples) (CDC, 2021). In 2017-2018, the mean serum PFOS
concentration was 4.25 |ig/L (95% CI 3.90-4.62 |ig/L) and the 90th percentile serum PFOS
concentration was 11.5 |ig/L (95% CI 10.0-13.1 |ig/L) across 1,929 samples (CDC, 2021). For
additional information about PFOS exposure in humans, see sections 3.3 and 5.0 of U.S. EPA
(2021b).
1.3 Source of Toxicity Information for Interim Health Advisory Development
The lifetime noncancer iHA for PFOS is derived from draft values (i.e., chronic RfD based on
updated toxicity information and RSC) and relies on the best available science as derived in the
draft PFOS document (U.S. EPA, 2021b), which is currently undergoing peer review by the SAB
PFAS Panel. To develop the updated toxicity information in the draft PFOS document, a
systematic review and evidence-mapping approach was utilized to identify, screen, and evaluate
health effects data for PFOS. A literature search was performed to identify studies on the health
effects of PFOS exposure in animals and humans published since the 2016 HESD and HA for
PFOS. The search results were screened for relevancy, and literature identified as relevant
underwent study quality evaluation and data extraction (please see U.S. EPA [2021b] for more
details). Evidence for each health outcome was analyzed and synthesized, and overall judgments
about the strength of the evidence were developed. The best available health effects information
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identified and analyzed using systematic review was then used in the derivation of the chronic
RfD. This systematic review process has been peer reviewed and is used by EPA's Office of
Research and Development (ORD) Integrated Risk Information System (IRIS) program, as
summarized in the draft PFOS document (U.S. EPA, 2021b). Similarly, a systematic review
approach was used to identify, screen, and evaluate exposure information to develop the RSC
based on the best available science.
1.4 Expo sure F actor Information
An exposure factor (EF), such as body weight-adjusted drinking water intake (DWI-BW), is one
of the input values for deriving a drinking water HA. EFs are factors related to human activity
patterns, behavior, and characteristics that help determine an individual's exposure to a
contaminant. EPA's Exposure Factors Handbook (EFH)7 is a resource for conducting exposure
assessments and provides EFs based on information from publicly available, peer-reviewed
studies. Chapter 3 of the EFH presents EFs in the form of drinking water intake values (DWIs)
and DWI-BWs for various populations or life stages within the general population (U.S. EPA,
2019b). The use of EFs in HA calculations is intended to protect sensitive populations within the
general population from adverse effects resulting from exposure to a contaminant.
When developing HAs, the goal is to protect all ages of the general population including
potentially sensitive populations such as children. The approach to select the EF for drinking
water HA derivation includes a step to identify potentially sensitive population(s) or life stage(s)
(i.e., populations or life stages that may be more susceptible or sensitive to a chemical exposure)
by considering the available data for the contaminant. Although data gaps can prevent
identification of the most sensitive population (e.g., not all windows of exposure or health
outcomes have been assessed for PFOS), the critical effect and point-of-departure (e.g., human
equivalent benchmark dose [BMD]) that form the basis for the RfD can provide some
information about potentially sensitive populations because the critical effect is typically
observed at the lowest tested dose among the available data. Evaluation of the critical study,
including the exposure interval, may identify a particularly sensitive population or life stage
(e.g., pregnant women, formula-fed infants, lactating women). In such cases, EPA can select the
corresponding EFs for that sensitive population or life stage from the EFH (U.S. EPA, 2019b) for
use in HA derivation. When multiple potentially sensitive populations or life stages are identified
based on the critical effect or other health effects data (from animal or human studies), EPA
selects the population or life stage with the greatest DWI-BW because it is the most health
protective. For deriving lifetime HA values, the RSC corresponding to the selected sensitive life
stage is also determined when data are available (see Section 2.2). In the absence of information
indicating a potentially sensitive population or life stage, the EF corresponding to all ages of the
general population may be selected.
To derive a chronic HA, EPA typically uses a DWI normalized to body weight (i.e., DWI-BW in
L of water consumed/kg bw-day) for all ages of the general population or for a sensitive life
stage, when identified. The Joint Institute for Food Safety and Applied Nutrition's Food
Commodity Intake Database (FCID) Consumption Calculator Tool8 includes the EPA EFs and
7 Available at https://www.epa.gov/expobox/about-exposure-factors-handbook. The latest edition of the EFH was released in
2011, but since October 2017, EPA has begun to release chapter updates individually.
8 Joint Institute for Food Safety and Applied Nutrition's Food Commodity Intake Database, Commodity Consumption Calculator
is available at https://fcid.foodrisk.org/percentiles
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can also be used to estimate DWIs and DWI-BWs for specific populations, life stages, or age
ranges. EPA uses the 90th percentile DWI-BW to ensure that the HA is protective of the general
population as well as sensitive populations or life stages (U.S. EPA, 2000a, 2016c). In 2019,
EPA updated its EFs for DWI and DWI-BW based on newly available science (U.S. EPA,
2019b).
1.5 Approach for Lifetime HA Calculation
The following equation is used to derive an interim or final lifetime noncancer HA. A lifetime
noncancer HA is designed to be protective of noncancer effects over a lifetime of exposure and is
typically based on a chronic in vivo experimental animal toxicity study and/or human
epidemiological data.
DWI-BW = the 90th percentile DWI for the selected population, adjusted for body weight, in
units of L/kg bw-day. The DWI-BW considers both direct and indirect consumption of tap water
(indirect water consumption encompasses water added in the preparation of foods or beverages,
such as tea or coffee).
RfD = chronic Reference Dose—an estimate (with uncertainty spanning perhaps an order of
magnitude) of a daily oral exposure of the human population to a substance that is likely to be
without an appreciable risk of deleterious effects during a lifetime.
RSC = Relative Source Contribution—the percentage of the total oral exposure attributed to
drinking water sources where the remainder of the exposure is allocated to all other routes or
sources (U.S. EPA, 2000a).
2 J Interim Health Advisory Derivation: PFOS
A lifetime noncancer iHA was derived for PFOS. The DWI-BW selected to derive the iHA is for
0- to < 5-year-old children because PFOS exposure was measured in 5-year-old children in the
critical study, and it is reasonable to expect that PFOS exposure levels were similar from birth
through age 5 (see Section 2.2). Since a DWI-BW for 0- to < 5-year-old children was used, the
iHA for PFOS is expected to be protective of children and adults of all ages in the general
population; however, available data on the most sensitive population or life stage are limited.
Short-term iHAs (e.g., one- or ten-day iHAs) were not derived for PFOS because the draft PFOS
document did not derive an RfD for short-term exposure. Additionally, EPA considers the
lifetime iHA for PFOS to be applicable to short-term as well as lifetime risk assessment
scenarios because the critical health effect on which the draft chronic RfD used to calculate the
HA is based (i.e., deficient antibody response to diphtheria vaccine in children) resulted from
PFOS exposure during a developmental life stage. EPA's risk assessment guidelines indicate that
adverse effects can result from even brief exposure during a critical period of development (U.S.
(Eq. 1)
Where:
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EPA, 1991). Therefore, the lifetime iHA for PFOS (calculated in Section 2.4) and the draft
chronic RfD from which it is derived (see Table 1) are considered applicable to short-term PFOS
exposures via drinking water.
As noted in the draft PFOS document (U.S. EPA, 2021b), there is suggestive evidence of
carcinogenic potential of PFOS based on EPA's Guidelines for Carcinogen Risk Assessment
(U.S. EPA, 2005a). Epidemiological study results suggest a potential association between PFOS
exposure and bladder or prostate cancers as discussed in the 2016 HESD for PFOS (U.S. EPA,
2016b). More recent epidemiological studies examining the association between PFOS and
breast cancer show mixed results, and study characteristics (e.g., small sample sizes, narrow
exposure levels) limit the ability to draw stronger conclusions about PFOS and breast cancer.
The single available chronic duration cancer bioassay in animals reported increased incidences of
liver, thyroid, and mammary gland tumors in rats, but a dose-response pattern was not observed.
As noted in the draft PFOS document (U.S. EPA, 2021b), a draft cancer slope factor (CSF) was
not derived for PFOS. This is consistent with EPA's Guidelines for Carcinogen Risk Assessment
(U.S. EPA, 2005a) which state that when the available evidence is suggestive for
carcinogenicity, a quantitative risk estimate is generally not derived unless there exists a well-
conducted study that could facilitate an understanding of the magnitude and uncertainty of
potential risks, ranking potential hazards, or setting research priorities. In the draft PFOS
document, EPA concluded that the available human and animal studies for PFOS are not
sufficient to establish a reasonable understanding of the magnitude and uncertainty of potential
risks for PFOS exposure and tumor incidence, and therefore do not justify a quantitative cancer
assessment (U.S. EPA, 2021b). Since a draft CSF was not developed for PFOS, an interim 10"6
cancer risk concentration was not derived.
2.1 Toxicity
Table 1 reports the draft chronic RfD derived in the draft PFOS document (U.S. EPA, 2021b)
that was used to develop the lifetime iHA for PFOS.
Table 1. Draft Chronic RfD, Critical Effect, and Critical Study Used to Develop the
Lifetime iHA for PFOS.
Source
For the Lifetime iHA for PFOS
RfD
(mg/kg-
day)
PFOS Exposure
in Critical Study
Critical Effect
Principal and
Associated Studies
(Study Type)
Proposed Approaches to
the Derivation of a Draft
Maximum Contaminant
Level Goal for
Perfluorooctane Sulfonic
Acid (PFOS) (CASRN
1763-23-1) in Drinking
Water [Draft] (U.S. EPA,
2021b)
7.9 x 10"9
PFOS measured in
serum of 5-year-
old children
Developmental
immune health
outcome
(suppression of
diphtheria vaccine
response in 7-year-
old children)
Grandjean et al.,
2012; Budtz-
Jorgensen and
Grandjean, 2018
(epidemiological
study)
Note: mg/kg-day = milligram per kilogram per day.
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Decreased serum anti-diphtheria antibody concentration in children, which was associated with
increased serum PFOS concentrations (Budtz-Jorgensen and Grandjean, 2018; Grandjean et al.,
2012), was selected as the critical effect for draft chronic RfD derivation. As noted in the draft
PFOS document (U.S. EPA, 2021b), selection of this draft critical effect is expected to be
protective of all other adverse health effects in humans because this adverse effect of decreased
immune response to vaccination was observed after exposure during a sensitive developmental
life stage, and it yields the lowest point of departure (POD) human equivalent dose (PODhed)
among the candidate PODshed. Other candidate RfDs were derived based on other health effects
(e.g., development/growth) observed in epidemiology studies; all of the candidate RfDs are
associated with low daily oral exposure doses, ranging from ~10"7 to 10"9 milligrams per
kilogram per day (mg/kg-day) (U.S. EPA, 2021b; Table 23).
The selected draft PODhed for this critical effect was derived by performing BMD modeling (see
Appendix B.l of U.S. EPA, 2021b) on measured PFOS serum concentrations at age five reported
in the critical study, which yielded an internal serum concentration POD in milligrams per liter
(mg/L). This internal serum concentration POD was then converted to an external dose
(PODhed) in mg/kg-day using the updated physiologically-based pharmacokinetic (PBPK)
model developed by Verner et al. (described in section 4.1.3.2 of U.S. EPA, 2021b). Specifically,
the PODhed was calculated as the external dose {in utero through age five) that results in the
internal serum concentration measured at five years of age in the critical study. (Note that the
model predicted slightly different values for male and female children; the lower PODhed was
selected to be more health protective). An intraspecies uncertainty factor (UFh) of 10 was
applied to the selected draft PODhed to account for variability in the response within the human
population in accordance with methods described in EPA's A Review of the Reference Dose and
Reference Concentration Processes (U.S. EPA, 2002b). EPA applied a value of 1 for the
remaining four uncertainty factors (UFs): interspecies UF (UFa), because the critical effect was
observed in humans and there is no need to account for uncertainty associated with animal-to-
human extrapolation; lowest-observed-adverse-effect level (LOAEL)-to-no-observed-adverse-
effect level (NOAEL) extrapolation UF (UFl), because a benchmark lower dose confidence limit
(BMDL) instead of a LOAEL was used as the basis for PODhed derivation; sub chronic-to-
chronic exposure duration extrapolation UF (UFs), because the critical effect on the developing
immune system in children was observed after exposure during gestation and/or early childhood,
a sensitive period that can lead to severe effects without lifetime exposure; and a database UF
(UFd), because the database of animal and human studies on the effects of PFOS is
comprehensive (see the draft PFOS document [U.S. EPA, 2021b] for further details). Thus, the
total or composite UF (UFc) used to derive the PFOS RfD was 10.
2.2 Exposure Factors
To identify potentially sensitive populations, EPA considered the sensitive life stage of exposure
associated with the critical effect on which the draft chronic RfD was based. The critical study
that was selected for draft chronic RfD derivation (see Table 1) established an association in
children between PFOS serum concentration (measured at age five, after three of four diphtheria
vaccinations) and decreased anti-diphtheria antibody concentration (measured at age seven,
approximately two years after all four diphtheria vaccinations) (Budtz-Jorgensen and Grandjean,
2018). Based on limited available data to inform the critical PFOS exposure window for this
critical developmental immune effect, the serum PFOS concentrations measured in 5-year-old
children in this study are assumed to represent PFOS exposure from birth to the time of
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measurement. EPA acknowledges that the DWI-BW varies between ages 0 and 5 years (U.S.
EPA, 2019b); however, the available data do not permit a more precise identification of the most
sensitive or critical PFOS exposure window for the developmental immune outcome because
studies with different exposure intervals have not been performed.
EPA calculated and considered DWI-BWs for other potentially sensitive age ranges indicated by
the critical study data (e.g., 0 to < 7 years; 1 to < 5 years; 1 to < 7 years; Table 2). The DWI-BW
for children aged 0 to < 5 years was selected among the DWI-BWs (see Table 2) because it is the
greatest value and therefore the most health-protective. EPA also considered the use of a DWI-
BW for formula-fed infants (i.e., infants fed primarily or solely with water-reconstituted infant
formula) because their DWI-BW is higher (U.S. EPA, 2019b) and the infant life stage occurs
within the 0-to- < 5-year age range. However, a greater RSC would be used for formula-fed
infants than for 0-to- < 5-year-olds, which would result in a less health-protective iHA value (see
Section 2.3). Therefore, EPA selected the DWI-BW for 0-to- < 5-year-olds.
Table 2. EPA Exposure Factors for Drinking Water Intake for Candidate Sensitive
Populations Based on the Critical Effect and Study.
Population
DWI-BW
(L/kg bw-day)
Description of Exposure
Metric
Source
Children aged 0 to < 5 yrs
0.0701
90th percentile direct and
indirect consumption of
community water,
consumers-only population,
two-day average3
Exposure Factors
Handbook, Chapter 3
(U.S. EPA, 2019b),
NHANES 2005-2010b
Children aged 0 to < 7 yrs
0.0553
Children aged 1 to < 5 yrs
0.0447
Children aged 1 to < 7 yrs
0.0426
Notes', yrs = years; L/kg bw-day = liters of water consumed per kilogram bodyweight per day. The DWI-BW used to calculate
the iHA is in bold.
a Community water = water from PWSs; consumers only population = quantity of water consumed per person in a population
composed only of individuals who consumed water during a specified period.
b DWI-BWs are based onNHANES 2005-2010 data which is also reported in the EFH. DWI-BWs for the age ranges in this table
were calculated using the FCID Commodity Consumption Calculator (available at https://fcid.foodrisk.org/percentiles).
2.3 Relative Source Contribution
When calculating HA values, EPA applies an RSC which represents the proportion of an
individual's total exposure to a contaminant that is attributed to drinking water ingestion
(directly or indirectly in beverages like coffee or tea, as well as from transfer to dietary items
prepared with the local drinking water) relative to other exposure pathways. The remainder of
the exposure equal to the RfD is allocated to other potential exposure sources (U.S. EPA, 2000a);
for PFOS, other potential exposure sources include food and food contact materials, consumer
products (e.g., personal care products), ambient and indoor air, and indoor dust. The purpose of
the RSC is to ensure that the level of a contaminant (e.g., the HA value), when combined with
other identified sources of exposure common to the population of concern, will not result in
exposures that exceed the RfD (U.S. EPA, 2000a).
To determine the RSC, EPA follows the Exposure Decision Tree for Defining Proposed RfD (or
POD/UF) Apportionment in EPA's Methodology for Deriving Ambient Water Quality Criteria
for the Protection of Human Health (U.S. EPA, 2000a). EPA conducted a broad literature search
in 2019 to identify and evaluate information on sources of human PFAS (including PFOS)
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exposure to inform RSC determination, and subsequently updated the search through March
2021 (see U.S. EPA [2021b] for more details on the literature search methodologies and results
described in the draft PFOS document). This literature search focused on real-world occurrences
(measured concentrations) primarily in media commonly related to human exposure (outdoor
and indoor air, indoor dust, drinking water, food, food packaging, articles and products, and
soil). The initial search identified 3,622 peer-reviewed papers that matched search criteria (U.S.
EPA, 2021b). Despite the U.S. phase-out of production, EPA has found widespread PFOS
contamination in water, sediments, and soils. Exposure to PFOS can occur through food
(including fish and shellfish), water, house dust, and contact with consumer products. The search
did not identify adequate exposure information across potential exposure sources and specific to
children aged 0 to < 5 years that could be used to quantify exposure and inform RSC derivation.
The findings indicate that many other sources of PFOS exposure beyond drinking water
ingestion exist (e.g., food, indoor dust), but that data are insufficient to allow for quantitative
characterization of the different exposure sources. EPA's Exposure Decision Tree approach
states that when there is insufficient environmental and/or exposure data to permit quantitative
derivation of the RSC, the recommended RSC for the general population is 20%. This means that
20% of the exposure equal to the RfD is allocated to drinking water, and the remaining 80% is
attributed to all other potential exposure sources.
2.4 Derivation of Health Advisory Value: Interim Lifetime Noncancer HA
The lifetime iHA for PFOS is calculated as follows:
Based on EPA's Guidelines for Developmental Toxicity Risk Assessment, the lifetime iHA can be
applied to short-term scenarios because the critical effect identified for PFOS is a developmental
effect that can potentially result from short-term PFOS exposure during a critical period of
development (U.S. EPA, 1991). EPA concludes that the lifetime iHA of 0.02 nanograms per liter
(ng/L) (or 20 parts per quadrillion [ppq]) for PFOS can be applied to both short-term and chronic
risk assessment scenarios.
(Eq. 1)
Lifetime iHA = 0.00000002 ——
J_j
= 0.00002 -f
J_j
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3 J Analytical Methods
EPA developed the following liquid chromatography/tandem mass spectrometry (LC/MS/MS)
analytical methods to quantitatively monitor drinking water for targeted PFAS that include
PFOS: EPA Method 533 (U.S. EPA, 2019a) and EPA Method 537.1, Version 2.0 (U.S. EPA,
2020).
EPA Method 533 monitors for 25 select PFAS with published measurement accuracy and
precision data for PFOS in reagent water, finished ground water, and finished surface water. For
further details about the procedures for this analytical method, please see Method 533:
Determination of Per- and Polyfluoroalkyl Substances in Drinking Water by Isotope Dilution
Anion Exchange Solid Phase Extraction and Liquid Chromatography/Tandem Mass
Spectrometry (U.S. EPA, 2019a).
EPA Method 537.1 (an update to EPA Method 537 [U.S. EPA, 2009c]) monitors for 18 select
PFAS with published measurement accuracy and precision data for PFOS in reagent water,
finished ground water, and finished surface water For further details about the procedures for this
analytical method, please s ee Method 537.1, Version 2.0, Determination of Selected Per- and
Polyfluorinated Alkyl Substances in Drinking Water by Solid Phase Extraction and Liquid
Chromatography/Tandem Mass Spectrometry (LC/MS/MS) (U.S. EPA, 2020).
Drinking water analytical laboratories have different performance capabilities dependent upon
their instrumentation (manufacturer, age, usage, routine maintenance, operating configuration,
etc.) and analyst experience. Some laboratories will effectively generate accurate, precise,
quantifiable results at lower concentrations than others. Organizations leading efforts that include
the collection of data need to establish data quality objectives (DQOs) to meet the needs of their
program. These DQOs should consider establishing reasonable quantitation limits that
laboratories can routinely meet, without recurring quality control (QC) failures that will
necessitate repeating sample analyses, increase costs, and potentially reduce laboratory capacity.
Establishing a quantitation limit that is too high may result in important lower-concentration
results being overlooked.
EPA's approach to establishing DQOs within the UCMR program serves as an example. EPA
established MRLs for UCMR 5,9 and requires laboratories approved to analyze UCMR samples
to demonstrate that they can make quality measurements at or below the established MRLs. EPA
calculated the UCMR 5 MRLs using quantitation-limit data from multiple laboratories
participating in an MRL-setting study. The laboratories' quantitation limits represent their lowest
concentration for which future recovery is expected, with 99% confidence, to be between 50 and
150%.
The UCMR 5-derived and promulgated MRL for PFOS is 0.004 |ig/L (4 ng/L).
4 J Treatment Technologies
This section summarizes the available drinking water treatment technologies that have been
demonstrated to remove PFOS from drinking water, but it is not meant to provide specific
9 Information about UCMR 5 is available at https://www.epa.gov/dwcira/fiflh-unregulated-contamiiiant-monitoriiig-rule
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operational guidance or design criteria. In terms of treatment efficacy, PFOS generally shares
many characteristics with PFOA but in most circumstances will be removed more easily using
the same technologies (Sorengard et al., 2020). Sorption-based treatment processes such as
granular activated carbon (GAC), powdered activated carbon (PAC), and anion exchange (AIX),
as well as high-pressure membrane processes such as nanofiltration (NF) and reverse osmosis
(RO), have been shown to successfully remove PFOS from drinking water to below the 0.004
|ig/L MRL for UCMR 5 (Holzer et al., 2009). These treatment processes may have additional
benefits on finished water quality by removing other contaminants and disinfection by-product
(DBP) precursors. Care should be taken when introducing one of these processes into a well-
functioning treatment train, as there can be interactions with other treatment processes. Care
should also be taken for system operators unfamiliar with proper operation and potential hazards.
General information and published PFAS treatment data for these processes may be found in
EPA's Drinking Water Treatability Database (U.S. EPA, 2022b).
Non-treatment PFOS management practices such as changing source waters, source water
protection, or consolidation are also viable PFOS drinking water reduction options. One resource
for protecting source water from PFAS, including PFOS, is the PFAS - Source Water Protection
Guide and Toolkit (ASDWA, 2020), which shares effective strategies for addressing PFAS
contamination risk in source waters. Source water protection is particularly important since
PFOS can withstand biotic and abiotic degradation mechanisms except in unique situations that
cannot be controlled in situ or results in complete defluorination (Huang and Jaffe, 2019;
Rahman et al., 2014), indicating that PFOS is persistent and thus, natural attenuation is not a
valid PFOS management strategy.
4.1 Sorption Technologies
Sorption technologies remove substances present in liquids by accumulation onto a solid phase
(Crittenden et al., 2012). The two main sorption technologies that have been successfully used
for full-scale PFOS removal are activated carbon and AIX. Activated carbon has been
successfully applied in contactors as GAC or in powdered as well as slurry forms (PAC). Key
considerations in choosing sorption technologies include influent water quality and desired
effluent quality. Influent water quality can greatly impact the ability of sorption technologies to
treat drinking water. Desired water quality can drive both operational and capital expenditures.
When using a technology requiring a contactor, sizing the contactor is an important consideration
that should include a pilot study. Pilot scale testing is highly recommended to ensure the
treatment performance will be maximized for given source waters. EPA's ICR Manual for
Bench- and Pilot-Scale Treatment Studies (U.S. EPA, 1996) contains guidance on conducting
pilot studies for contactors which are used for GAC and AIX. Contactor efficacy can be
compromised by particulate, organic and inorganic constituents.
Both GAC and AIX can typically be regenerated when treatment performance reaches an
unacceptable level. The choice between regeneration and replacement is a key planning decision.
Regeneration can be on- or off-site. On-site regeneration typically requires a higher spatial
footprint and capital outlay. Given water quality and other considerations, regenerated media can
become totally exhausted or "poisoned" with other contaminants not removed during the
regeneration process and must be replaced. However, most AIX resins in current use for PFOS
technologies are single use resins and not designed to be regenerated.
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Two common interferences with sorption technologies relevant to PFAS are preloading (when a
non-targeted compound is removed ahead of the targeted contaminant and prevents the targeted
contaminant from accessing the sorption site) and competitive sorption (when one compound
inhibits the removal of another by direct competition). The interferences can result in slowed
sorption kinetics and reduced sorption capacities. It is also important to note that sorption
technologies are largely reversible. PFAS in general, and PFOS specifically, can detach from
sorbents and re-enter drinking water under certain conditions. In addition, direct competition
with stronger sorbing constituents can lead to effluent PFOS concentrations temporarily
exceeding influent concentration (known as chromatographic peaking). This has been
documented in full-scale treatment plants (Appleman et al., 2013; Eschauzier et al., 2012;
McCleaf et al., 2017; Takagi et al., 2011). Common PFOS competitors for binding sites on
sorptive media include natural or dissolved organic matter (NOM/DOM) which lowers treatment
efficacy (McNamara et al., 2018; Park et al., 2020; Pramanik et al., 2015; Yu et al., 2012).
Preloading may be controlled in the design phase through pretreatment processes. For more
information about managing preloading, see AWWA (2018a). Competitive sorption may be
controlled by changing or regeneration of the sorptive media at appropriate intervals.
4.1.1 Activated Carbon
Activated carbon is a highly porous media with high internal surface areas (U.S. EPA, 2017b).
Activated carbon can be made from a variety of materials. Designs that work with carbon made
from one source material activated in a specific way may not be optimized for other carbon
types. There is some indication that of the common trace capacity tests, higher methylene blue
numbers are most correlated with higher PFOS removal (Sorengard et al., 2020). Installing
activated carbon as a treatment method may also have ancillary benefits on finished water
quality, particularly regarding disinfectant byproduct control, other contaminants, and well as
taste-and-odor compounds.
Activated carbon tends to remove non-polar, larger compounds more easily from water than
smaller, more polar compounds. Adsorption of acids and bases on activated carbon is pH-
dependent. Adsorption of neutral forms, as opposed to anionic forms, is generally stronger, so
lowering the pH increases PFOS sorption. However, the calculated acid dissociation constant
(pKa) of PFOS is about 3 (Larsen and Giovalle, 2015) and lowering the pH may not be practical
operationally.
Before the addition of activated carbon to an existing treatment train, there are issues which
should be considered. For instance, activated carbon may change system pH or release leachable
metals (particularly arsenic and antimony) especially when new carbon media is first used
without acid washing. These effects are typically mitigated through an acid wash or forward
flushing. Activated carbon may also impact disinfection efficacy depending on process
placement and requires consideration to mitigate its effects; for more information, please see the
American Water Works Association (AWWA) GAC standard (American National Standards
Institute (ANSI)/AWWA B604-18; AWWA, 2018a) or the AWWA published standard for PAC
(ANSI/AWWAB600-16; AWWA, 2016). Activated carbon can also shift the bromide-to-total
organic carbon ratio and increase brominated (Br)-DBP concentrations (Krasner et al., 2016);
however, despite increased Br-DBP, studies have indicated a decreased overall DBP
concentration and risk (Wang et al., 2019). In conclusion, DBPs may be mitigated through NOM
(DBP precursor) removal; please see Zhang et al. (2015) for additional information.
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4. I. /. / Granular Activated Carbon
PFOS can be effectively removed from water by using GAC; contactors are normally placed as a
post-filter step. Key design criteria include empty bed contact time (EBCT), superficial velocity,
and carbon type. Typical EBCTs for PFOS removal are 10-20 minutes and superficial linear
velocities are normally 5-15 meters per hour (m/hr). Normal height-to-diameter ratios are around
1.5 to 2.0; lower ratios can cause problems with too-shallow beds and require more space, and
higher ratios can induce greater head drops. AWWA has published a GAC standard
(ANSI/AWWA B604-18; AWWA, 2018a) and a standard for GAC reactivation (ANSI/AWWA
B605-18; AWWA, 2018b).
4.1.1.2 Powdered A ctivated Carbon
PAC is the same material as GAC, but it has a smaller particle size and is applied differently.
PAC is typically dosed intermittently although it can be employed continuously if there are
spatial constraints restricting contactor use. PAC dosage and type, along with dosing location
contact time and water quality, often influence process cost as well as treatment efficiency
(Heidari et al., 2021). For more information on employing PAC, please see the Drinking Water
Treatability Database (U.S. EPA, 2022b).
While relatively unstudied in PFAS, increasing PAC dose with other contaminants increases
removal to a point, after which it starts to decrease. Jar testing is typically used to empirically
determine the optimal PAC dosage; doses between 45 and 100 mg/L are generally suitable for
PFOS (Dudley, 2012; Hopkins et al., 2018; Sun et al., 2016). Standardized jar testing procedures
have been published (ASTM International, 2019; AWWA, 2011). The AWWA published
standard for PAC is ANSI/AWWA B600-16 (AWWA, 2016).
PAC can pose additional safety considerations including depleting oxygen in confined or
partially enclosed areas, fire hazards including spontaneous combustion when stored with
hydrocarbons or oxidants, and inhalation hazards and must be managed accordingly. PAC is also
a good electrical conductor and can create dangerous conditions when it accumulates (AWWA,
2016). These dangers can be effectively mitigated through various occupational safety programs
such as confined space or fire safety programs. See AWWA (2016) for more information.
4.1.2 Ion Exchange
Ion exchange involves the exchange of an aqueous ion (e.g., contaminant) for an ion on an
exchange resin. Once the resin has exchanged all its ions for contaminants, it can either be
replaced (single-use) or regenerated (i.e., restoring its ions for further use).
Different resin types preferentially bind certain ions over others; therefore, resin selection is an
important consideration. As PFOS will predominantly exist in an anionic form in water and is a
strong acid (U.S. EPA, 2021g), strongly basic AIX resins will be the most relevant for PFOS.
Regenerating PFOS-saturated resins has been accomplished effectively with a brine of > 20%
sodium chloride and ammonium chloride. Sodium hydroxide may be added to added to the
sodium chloride solution to combat organic fouling; this is referred to as 'brine squeeze' and
helps in solubilizing NOM and unplugging pores (Dixit et al., 2021). Regenerated media can be
"poisoned," meaning that a non-target ion not removed by the in-place regeneration procedures
eventually crowds out available active sites. When this happens or if media is not regenerated, it
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must be disposed of appropriately. Once PFAS-contaminated spent brine is recovered, it must be
treated or disposed of. Resin regeneration may not be practical for water utilities from safety
and/or cost perspectives (Liu and Sun, 2021).
In some situations, AIX may outperform activated carbon for removing PFOS from drinking
water (Liu and Sun, 2021). Key design parameters for GAC also apply to AIX, and they can be
operated similarly. AIX typically uses 2-to-5-minute EBCTs, allowing for lower capital costs
and a smaller footprint; compared to GAC, smaller height-to-diameter ratios are typically used in
exchange columns. However, AIX resin is typically more costly compared to GAC which may
increase overall operational costs. Columns used in pilot studies are scaled directly to full-scale
if loading rates and EBCTs are kept constant (Crittenden et al., 2012).
Before the addition of AIX to an existing treatment train, there are effects which must be
considered. For instance, AIX can increase water corrosivity and/or release amines and will
increase concentrations of the counter-ion used (typically chloride). These effects may usually be
mitigated through prior planning which may include corrosion control adjustments; for more
information about corrosion control, see U.S. EPA (2016d). Additionally, PFOS-saturated resin
regeneration creates an additional PFOS waste stream which will require appropriate handling.
For more information about AIX, please see Crittenden et al. (2012), Dixit et al. (2021), Tanaka
(2015), Tarleton (2014), and the EPA Drinking Water Treatability Database (U.S. EPA, 2022b).
4.2 I _ 1-Pressu.re Membranes
NF and RO are high-pressure processes where water is forced across a membrane. The water that
transverses the membrane is known as permeate or produce, and has few solutes left in it; the
remaining water is known as concentrate, brine, retentate, or reject water and forms a waste
stream with concentrated solutes. NF has a less dense active layer than RO, which enables lower
operating pressures but also makes it less effective at removing contaminants. Higher operating
pressures and initial flux generally enhance removal. Temperature and pH are also significant
parameters affecting performance. In general, organic NF membranes have lower operating costs
and easier processing than inorganic membranes while maintaining appropriate robustness for
PFOS treatment (Jin et al., 2021). NF and RO tend to take up less space than sorptive separation
technologies; however, both NF and RO also tend to have higher operating expenses, use a
significant amount of energy, and generate concentrate waste streams which require disposal.
Generally, NF and RO require pre- and post-treatment processes. Higher expenses typically
associated with NF and RO are only rarely competitive from an economic perspective for
removing a specific contaminant; however, for waters requiring significant treatment and where
concentrate disposal options are reasonably available, NF and RO may be the best option.
PFOS removal fluxes are generally 20-80 liters per square meter per hour (L/[m2hr]) at 0.2-1.2
megapascal (MPa) operating pressure (Mastropietro et al., 2021) with removal from 90% to >
99% (Jin et al., 2021). Temperature can dramatically impact flux; it is common to normalize flux
to a specific reference temperature for operational purposes (U.S. EPA, 2005b). It is important to
note that water may traverse the membranes from outside-in or inside-out; different system
configurations operating at the same flux produce differing quantities of finished water. This
means that membrane systems with differing configurations cannot be directly compared based
on flux. Total flow per module and cost per module are more important decision support
indicators for capital planning. Unlike low-pressure membranes, NF and RO systems are not
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manufactured as proprietary equipment and membranes from one manufacturer are typically
interchangeable with those from others (U.S. EPA, 2005b).
High-pressure membranes may have effects when added onto a well-functioning treatment train.
For instance, high-pressure membranes may remove beneficial minerals and increase corrosivity.
Increased water corrosivity may need to be addressed through corrosion control treatment
modifications and water may require remineralization. For more information, see AWWA (2007)
or U.S. EPA (2016d).
4.3 Point-of-Use Devices for Individual Housek "OS Removal
Although the focus of this treatment technologies section is the different available options for
removal of PFOS at drinking water treatment plants, centralized treatment technologies can also
often be used in a decentralized fashion as point-of-entry (where the distribution system meets a
service connection) or point-of-use (at a specific tap or application) treatment in cases where
centralized treatment is impractical or individual consumers wish to further reduce their
individual household risks. Many home drinking water treatment units are certified by
independent third-party accreditation organizations using ANSI standards to verify contaminant
removal claims. NSF International has developed protocols forNSF/ANSI Standards 53
(sorption) and 58 (RO) that establish minimum requirements for materials, design, and
construction, and performance of point-of-use systems. Previously, NSF P473 was designed to
certify PFOS reduction technologies below EPA's 2016 HA of 70 ppt for PFOS; in 2019, these
standards were retired and folded into NSF/ANSI 53 and 58. PFOS removal by faucet filters has
reportedly averaged 99%, whereas pitcher filters had an average of 71% removal, refrigerator
filters 6P/o, single-stage under-sink filters > 99%, two-stage filters 99%, and RO filters 100%.
Some filters can remove PFOS to below the 0.004 |ig/L UCMR 5 reporting limit (Herkert et al.,
2020). Boiling water is not an effective point-of-use PFOS treatment, as it will concentrate
PFOS.
4.4 Treatment Technologies Summary
Non-treatment PFOS management options, such as changing source waters, source water
protection, or consolidation are viable options for reducing PFOS concentrations in finished
drinking water. Should treatment be necessary, GAC, PAC, AIX, NF, and RO are the best means
for removing PFOS from drinking water and can be used in central treatment plants or in point-
of-use applications. These treatment processes are separation technologies and produce waste
streams with PFOS, and all processes may have unintended effects on the existing treatment
trains. Some treatment processes have been shown to increase PFOS concentrations, most likely
through precursor oxidation. PFOS treatment technologies often require pre- as well as post-
treatment and may help remove other unwanted contaminants and DBP precursors. Boiling water
will concentrate PFOS and should not be considered as an emergency action.
5 J Consideration of N oncancer Health Risks from PFAS Mixtures
EPA recently released a Draft Framework for Estimating Noncancer Health Risks Associated
with Mixtures of Per- and Polyfluoroalkyl Substances (PFAS) (U.S. EPA, 2021h) that is
currently undergoing SAB PFAS Panel review. That draft document describes a flexible, data-
driven framework that facilitates practical component-based mixtures evaluation of two or more
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PFAS based on current, available EPA chemical mixtures approaches and methods (U.S. EPA,
2000b). Examples are presented for three approaches—Hazard Index (HI), Relative Potency
Factor (RPF), and Mixture BMD—to demonstrate application to PFAS mixtures. To use these
approaches, specific input values and information for each PFAS are needed or can be
developed. These approaches may help to inform PFAS evaluation(s) by federal, state, and tribal
partners, as well as public health experts, drinking water utility personnel, and other stakeholders
interested in assessing the potential noncancer human health hazards and risks associated with
PFAS mixtures.
The HI approach, for example, could be used to assess the potential noncancer risk of a mixture
of four component PFAS for which HAs, either final or interim, are available from EPA (PFOA,
PFOS, GenX chemicals [hexafluoropropylene oxide dimer acid and its ammonium salt], and
perfluorobutane sulfonic acid [PFBS]). In the HI approach described in the draft framework
(U.S. EPA, 2021h), a hazard quotient (HQ) is calculated as the ratio of human exposure (E) to a
human health-based toxicity value (e.g., reference value [RfV]) for each mixture component
chemical (i) (U.S. EPA, 1986). The HI is dimensionless, so in the HI formula, E and the RfV
must be in the same units (Eq. 2). In the context of PFAS in drinking water, a mixture PFAS HI
can be calculated when health-based water concentrations (e.g., HAs, Maximum Contaminant
Level Goals [MCLGs]) for a set of PFAS are available or can be calculated. In this example,
HQs are calculated by dividing the measured component PFAS concentration in water (e.g.,
expressed as ng/L) by the relevant HA (e.g., expressed as ng/L) (Eqs. 3, 4). The component
chemical HQs are then summed across the PFAS mixture to yield the mixture PFAS His based
on interim and final HAs.
i=l i=l
(Eq. 2)
HI = HQpfqa + HQppos + HQGenX + HQPFBS
(Eq. 3)
:r]\
/[PFOAwater]\ /[PFOSwater]\ /[GenXwater]\ /[PFBSwater]
" V [PFOAiHA] J [ [PFOSiHA] J [ [GenXHA] J [ [PFBSHA]
Where:
HI = hazard index
n = the number of component (i) PFAS
HQ, = hazard quotient for component (i) PFAS
Ei = human exposure for component (i) PFAS
RfVi = human health-based toxicity value for component (i) PFAS
HQpfas= hazard quotient for a given PFAS
[PFASwater] = concentration for a given PFAS in water
[PFASha] = HA value, interim or final, for a given PFAS
(Eq. 4)
17
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In cases when the mixture PFAS HI is greater than 1, this indicates an exceedance of the health
protective level and indicates potential human health risk for noncancer effects from the PFAS
mixture in water. When component health-based water concentrations (in this case, HAs) are
below the analytical method detection limit, as is the case for PFOA and PFOS, such individual
component HQs exceed 1, meaning that any detectable level of those component PFAS will
result in an HI greater than 1 for the whole mixture. Further analysis could provide a refined
assessment of the potential for health effects associated with the individual PFAS and their
contributions to the potential joint toxicity associated with the mixture. For more details of the
approach and illustrative examples of the RPF approach and Mixture BMD approaches, please
see U.S. EPA (202lh).
6 J Interim Health Advisory Characterization
The purpose of developing the lifetime iHA for PFOS is to reflect the best available scientific
information which indicates that PFOS can lead to adverse noncancer health effects at exposure
levels that are much lower than previously understood (U.S. EPA, 2016c). The PFOS iHA of
0.02 ng/L is considered applicable to both short-term and chronic risk assessment scenarios
because the critical effect identified for PFOS can result from developmental exposure and leads
to long-term adverse health effects. Therefore, short-term PFOS exposure during a critical period
of development may lead to adverse health effects across life stages.
In 2019, EPA initiated an updated literature search and analysis of health effects information for
PFOS to better characterize the health hazards and risks of exposure using information published
since EPA developed the 2016 HA for PFOS (draft PFOS document; U.S. EPA, 2021b). The
draft PFOS document includes an updated draft chronic RfD and draft RSC. The draft PFOS
document is currently undergoing review by the SAB PFAS Panel as part of EPA's process for
developing a NPDWR for PFOS under SDWA. The draft report of the SAB PFAS Panel's
review (U.S. EPA, 2022a) is supportive of the draft conclusions; however, the SAB PFAS Panel
is recommending analyses that may impact the final RfD and RSC. Because the iHA is based on
draft values, it is subject to change.
EPA expects to propose an MCLG and NPDWR for PFOS in the fall of 2022 and to promulgate
a final MCLG and NPDWR by the fall of 2023 after considering public comment. EPA will
complete its revisions to address the final SAB report's comments in the proposed PFOS MCLG
and NPDWR. EPA may update or remove the iHA for PFOS at that time. Based, however, on
the updated systematic review of the best available science on PFOS exposure and health effects,
and taking into consideration the work EPA is doing now to address SAB comments, the health-
based drinking water values for PFOS (HA and MCLG) are anticipated to remain below the
current UCMR 5 analytical MRL (0.004 |ig/L or 4 ng/L).
18
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