[Federal Register Volume 76, Number 29 (Friday, February 11, 2011)]
[Proposed Rules]
[Pages 7762-7767]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: 2011-2603]
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ENVIRONMENTAL PROTECTION AGENCY
40 CFR Part 141
[EPA-HQ-OW-2008-0692, EPA-HQ-OW-2009-0297; FRL-9262-8]
RIN 2040-AF08
Drinking Water: Regulatory Determination on Perchlorate
AGENCY: Environmental Protection Agency (EPA).
ACTION: Regulatory determination.
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SUMMARY: This action presents EPA's (or the Agency's) regulatory
determination for perchlorate in accordance with the Safe Drinking
Water Act (SDWA). Specifically, EPA has determined that perchlorate
meets SDWA's criteria for regulating a contaminant--that is,
perchlorate may have an adverse effect on the health of persons;
perchlorate is known to occur or there is a substantial likelihood that
perchlorate will occur in public water systems with a frequency and at
levels of public health concern; and in the sole judgment of the
Administrator, regulation of perchlorate in drinking water systems
presents a meaningful opportunity for health risk reduction for persons
served by public water systems. Therefore, EPA will initiate the
process of proposing a national primary drinking water regulation
(NPDWR) for perchlorate.
DATES: For purposes of judicial review, the regulatory determination is
issued as of February 11, 2011, as provided in 40 CFR 23.7.
ADDRESSES: EPA has established dockets for this action under Docket ID
numbers EPA-HQ-OW-2008-0692 and EPA-HQ-OW-2009-0297. All documents in
these dockets are listed on the http://www.regulations.gov Web site.
Although listed in the index, some information is not publicly
available, e.g., Confidential Business Information or other information
whose disclosure is restricted by statute. Certain other material, such
as copyrighted material, is not placed on the Internet, but will be
publicly available in hard copy form. Publicly available docket
materials are available either electronically through http://www.regulations.gov or in hard copy at the Water Docket, EPA/DC, EPA
West, Room 3334, 1301 Constitution Ave., NW., Washington, DC. The
Public Reading Room is open from 8:30 a.m. to 4:30 p.m., Monday through
Friday, excluding legal holidays. The telephone number for the Public
Reading Room is (202) 566-1744, and the telephone number for the EPA
Docket Center is (202) 566-2426.
FOR FURTHER INFORMATION CONTACT: Eric Burneson, Office of Ground Water
and Drinking Water, Standards and Risk Management Division, at (202)
564-5250 or e-mail burneson.eric@epa.gov. For general information
contact the EPA Safe Drinking Water Hotline at (800) 426-4791 or e-
mail: hotline-sdwa@epa.gov.
SUPPLEMENTARY INFORMATION:
Table of Contents
I. General Information
Does this action impose any requirements on my public water
system?
II. Background
A. What is the purpose of this action?
B. Background on Perchlorate Regulatory Determinations
C. What is EPA's final regulatory determination on perchlorate
and what happens next?
III. Final Regulatory Determination for Perchlorate
A. May perchlorate have an adverse effect on the health of
persons?
B. Is perchlorate known to occur or is there a substantial
likelihood that perchlorate will occur in public water systems with
a frequency and at levels of public health concern?
C. Is there a meaningful opportunity for the reduction of health
risks from perchlorate for persons served by public water systems?
D. Regulatory Determination
E. Key Commenter Issues
1. Health Implications of Perchlorate Exposure above the RfD
2. Other Thyroid Inhibiting Chemicals
3. Perchlorate in Food
4. Iodide Nutritional Status
5. Physiologically-Based Pharmacokinetic (PBPK) Modeling
F. Next Steps
IV. References
Abbreviations and Acronyms
CBI--confidential business information
CCL--Contaminant Candidate List
EPA--U.S. Environmental Protection Agency
FR--Federal Register
HRL--health reference level
kg--kilogram
L--liter
MCL--maximum contaminant level
MRL--Minimum Reporting Limit
NOEL--no observed effect level
NPDWR--National Primary Drinking Water Regulation
NRC--National Research Council
PBPK--Physiologically-Based Pharmacokinetic
PWS--public water system
RfD--reference dose
SDWA--Safe Drinking Water Act
UCMR--Unregulated Contaminant Monitoring Rule
[mu]g--microgram (one-millionth of a gram)
U.S.--United States
I. General Information
Does this action impose any requirements on my public water system?
Today's action notifies interested parties of EPA's determination
to regulate perchlorate, but imposes no requirements on public water
systems (PWSs). However, this action also initiates the process to
develop a national primary drinking water regulation (NPDWR) for
perchlorate. At such time as the Agency establishes an NPDWR, certain
PWSs will be required to take action to comply with the regulation in
accordance with the schedule specified in the regulation.
II. Background
A. What is the purpose of this action?
The purpose of today's action is to present EPA's final
determination to regulate perchlorate in drinking water, the rationale
EPA used to make this regulatory determination, and EPA's response to
certain key issues raised by commenters on previous Federal Register
(FR) notices on the drinking water regulatory determination for
perchlorate. (All comments are addressed in a Response to Comments
document that is available in EPA's docket ID No. EPA-HQ-OW-2009-0297
for this regulatory determination.)
B. Background on Perchlorate Regulatory Determinations
The statutory and regulatory background for this action is
described in detail in the October 10, 2008, FR notice discussing EPA's
preliminary regulatory determination for perchlorate (73 FR 60262;
USEPA 2008a). Briefly, SDWA section 1412(b)(1)(A), as amended in 1996,
requires EPA to make a determination whether to regulate at least five
contaminants from its Contaminant Candidate List (CCL) every five
years. To regulate a contaminant in drinking water, EPA must determine
that it meets three criteria: (1) The contaminant may have an adverse
effect on the health of persons; (2) the contaminant is known to occur
or there is a substantial likelihood that the
[[Page 7763]]
contaminant will occur in public water systems with a frequency and at
levels of public health concern; and (3) in the sole judgment of the
Administrator, regulation of such contaminant presents a meaningful
opportunity for health risk reduction for persons served by public
water systems. Once EPA makes a determination to regulate a contaminant
in drinking water, SDWA requires that EPA issue a proposed NPDWR within
24 months and a final NPDWR within 18 months of proposal.
EPA included perchlorate on the first, second, and third CCLs that
were published in the Federal Register on March 2, 1998 (63 FR 10273;
USEPA 1998), February 24, 2005 (70 FR 9071; USEPA 2005a), and October
8, 2009 (74 FR 51850; USEPA 2009a), respectively. On May 1, 2007, EPA
published an update on the Agency's evaluation of perchlorate as part
of the preliminary regulatory determination for 11 other CCL 2
contaminants (72 FR 24016; USEPA 2007). The Agency did not make a
preliminary determination for perchlorate as part of this regulatory
determination, but requested public comment on the options that the
Agency was evaluating for perchlorate and requested information that
could assist the Agency in its regulatory determination. EPA received
eight comment letters in response to the May 2007 document (72 FR
24016; USEPA 2007) that addressed perchlorate. Public comments on the
May 2007 document can be found online at http://www.regulations.gov
(Docket ID No. EPA-HQ-OW-2007-0068).
On October 10, 2008, EPA published a preliminary regulatory
determination for perchlorate (73 FR 60262; USEPA 2008a), requesting
public comment on its determination that perchlorate did not occur with
a frequency and at levels of public health concern and regulation of
perchlorate did not present a meaningful opportunity for health risk
reduction for persons served by public water systems (the second and
third criteria for regulating a contaminant under SDWA). The October
2008 notice describes in detail EPA's basis for its preliminary
determination not to develop an NPDWR for perchlorate (73 FR 60262;
USEPA 2008a). The Agency received nearly 33,000 comment letters on the
October 2008 notice. Public comments on the October 2008 notice and
supporting materials are available electronically at http://www.regulations.gov (Docket ID No. EPA-HQ-OW-2008-0692).
On August 19, 2009, EPA published the Perchlorate Supplemental
Request for Comments (74 FR 41883; USEPA 2009b) requesting comment on
additional approaches to analyzing data related to EPA's perchlorate
regulatory determination. These additional comments were sought in an
effort to ensure consideration of all potential options for evaluating
whether there is a meaningful opportunity for human health risk
reduction of perchlorate through a NPDWR. EPA stated that the
alternative analyses presented in this notice could lead the Agency to
make a determination to regulate perchlorate. EPA received over 6,000
comments on the August 2009 notice.
EPA has evaluated the approximately 39,000 public comments received
on the May 2007 document, the October 2008 notice, and August 2009
notice. EPA has prepared a response to comment document that addresses
the comments related to the perchlorate regulatory determination
(USEPA, 2010a). This response to public comment document, the public
comments on the August 2009 notice, and supporting materials are
available electronically at http://www.regulations.gov (Docket ID No.
EPA-HQ-OW-2009-0297).
C. What is EPA's final regulatory determination on perchlorate and what
happens next?
After careful review and consideration of public comments on the
May 2007, October 2008, and August 2009 notices, the Agency has made a
determination to regulate perchlorate in drinking water. EPA has found
that perchlorate may have an adverse effect on human health. EPA has
reversed its October 2008 preliminary determination not to develop an
NPDWR for perchlorate and now concludes, based on the analysis
presented in this regulatory determination, that there is a substantial
likelihood that perchlorate will occur in public water systems with a
frequency and at levels of public health concern. Finally, EPA has
determined that regulation of perchlorate presents a meaningful
opportunity to reduce health risk for persons served by public water
systems.
EPA is initiating the development of a proposed NPDWR for
perchlorate. EPA intends to publish a proposed regulation and analyses
required by SDWA for public review and comment within 24 months of this
regulatory determination. EPA will consider the public comments and
expects to promulgate a final regulation within 18 months of the
proposal.
III. Final Regulatory Determination for Perchlorate
In making final regulatory determinations, EPA uses the criteria
mandated by the 1996 SDWA Amendments. Specifically, EPA has found that
perchlorate may have an adverse effect on the health of persons, that
perchlorate occurs or there is a substantial likelihood that
perchlorate will occur in public water systems with a frequency and at
levels of public health concern, and that regulation of perchlorate in
drinking water systems presents a meaningful opportunity for health
risk reduction for persons served by public water systems.
A. May perchlorate have an adverse effect on the health of persons?
Yes. The perchlorate anion is biologically significant specifically
with respect to the functioning of the thyroid gland. Perchlorate can
interfere with the normal functioning of the thyroid gland by
inhibiting the transport of iodide into the thyroid, resulting in a
deficiency of iodide in the thyroid. Perchlorate inhibits (or blocks)
iodide transport into the thyroid by chemically competing with iodide,
which has a similar shape and electric charge. The transfer of iodide
from the blood into the thyroid is an essential step in the synthesis
of thyroid hormones. The thyroid hormones play an important role in the
regulation of metabolic processes throughout the body and are also
critical to developing fetuses and infants, especially with respect to
brain development. Because the developing fetus depends on an adequate
supply of maternal thyroid hormone for its central nervous system
development during the first and second trimester of pregnancy, iodide
uptake inhibition from low-level perchlorate exposure has been
identified as a concern in connection with increasing risk of
neurodevelopmental impairment in fetuses of hypothyroid mothers. Poor
iodide uptake and subsequent impairment of the thyroid function in
pregnant and lactating women have been linked to delayed development
and decreased learning capability in their infants and children (NRC,
2005). Additionally, deficiency during childhood reduces child growth
and cognitive motor function (Zimmerman, 2009). Therefore, EPA finds
that perchlorate may have an adverse effect on the health of persons.
B. Is perchlorate known to occur or is there a substantial likelihood
that perchlorate will occur in public water systems with a frequency
and at levels of public health concern?
Yes. EPA has determined that perchlorate occurs or there is a
substantial likelihood that perchlorate will occur with a frequency and
at
[[Page 7764]]
levels of health concern in public water systems. EPA has made this
determination by comparing the best available data on the occurrence of
perchlorate in PWSs to potential health reference levels (HRLs) for
perchlorate. HRLs are not final determinations about the level of a
contaminant in drinking water that is necessary to protect any
particular population. Rather they are benchmarks against which EPA
compares the concentration of a contaminant found in public water
systems to determine if it is at levels of public health concern.
In January 2005, the National Research Council (NRC) published
``Health Implications of Perchlorate Ingestion,'' a review of the state
of the science regarding potential adverse health effects of
perchlorate exposure and mode of action for perchlorate toxicity (NRC,
2005). The NRC recommended that EPA use data from the Greer et al.
(2002) human clinical study as the basis for deriving a reference dose
for perchlorate (NRC, 2005). Although the NRC committee concluded that
hypothyroidism is the first adverse effect in the continuum of effects
of perchlorate exposure, NRC recommended that ``the most health-
protective and scientifically valid approach'' was to base the
perchlorate RfD on the inhibition of iodide uptake by the thyroid,
which the NRC considered a non-adverse effect (NRC, 2005). The NRC
recommended that EPA apply an intraspecies uncertainty factor of 10 to
the no observed effect level (NOEL),\1\ to account for differences in
sensitivity between the healthy adults in the Greer et al., (2002)
study and the most sensitive population, fetuses of pregnant women who
might have hypothyroidism or iodide deficiency. They viewed this as
conservative and protective of health given that the NOEL is based on a
non-adverse effect (iodide uptake inhibition), which precedes the
adverse effect in a continuum of possible effects of perchlorate
exposure. The NRC also noted that ``any decrease (in thyroid hormone)
is potentially more likely to have adverse effects in sensitive
populations (people with thyroid disorders, pregnant women, fetuses,
and infants). EPA's Integrated Risk Information System (IRIS) adopted
the NRC's recommendations resulting in an RfD of 0.7 [mu]g/kg/day
(USEPA, 2005b).
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\1\ No observed effect level (NOEL)--an exposure level at which
there are no statistically or biologically significant increases in
the frequency or severity of any effect between the exposed
population and its appropriate control.
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In the October 2008 preliminary regulatory determination, EPA had
derived a single HRL of 15 [mu]g/L based upon the RfD, an estimate of
perchlorate exposure from food for pregnant women, and traditional
adult body weight (70 kg) and drinking water consumption (2 L/day)
values. This single HRL was derived to reflect exposure to a pregnant
woman and her fetus, which the NRC identified as ``the most sensitive
population.''
Since the NRC also identified infants and developing children as
additional life stages, EPA derived potential alternative HRLs for 14
life stages (age groups) using the RfD and life stage-specific exposure
information in the August 9, 2009, notice (74 FR 41883; USEPA 2009b).
These levels range from 1 [mu]g/L to 47 [mu]g/L and are the
concentrations of perchlorate in drinking water that may result in
total perchlorate exposures (from food and water) greater than the RfD
for individuals at each life stage. These HRLs are calculated based on
individuals who consume an average amount of perchlorate from food
(except for pregnant women where EPA used a 90th percentile dietary
intake estimate), but who consume equal or more water on a per body
weight basis than 90 percent of their cohorts. EPA is evaluating these
potential alternative HRLs and considers them to be levels of public
health concern for purposes of this determination. EPA has compared
these values to the data provided by PWSs subject to the first
Unregulated Contaminant Monitoring Rule (UCMR 1). EPA collected and
analyzed drinking water occurrence data for perchlorate from 3,865 PWSs
between 2001 and 2005 under the UCMR 1. The minimum reporting level
(MRL) for perchlorate under the UCMR 1 was 4 [mu]g/L.
EPA found that 160 (approximately 4.1 percent) of the 3,865 PWSs
that sampled and reported had at least 1 analytical detection of
perchlorate (in at least 1 sampling point) at levels greater than or
equal to the MRL of 4 [mu]g/L. These 160 PWSs are located in 26 States
and 2 territories. Of these 160 PWSs, 8 are systems serving 10,000 or
fewer people and 152 are systems serving more than 10,000 people. These
160 systems reported 637 detections of perchlorate at levels greater
than or equal to 4 [mu]g/L, which is approximately 11.3 percent of the
5,629 samples collected by these 160 PWSs and approximately 1.9 percent
of the 34,331 samples collected by all 3,865 PWSs. The average
concentration of perchlorate for those samples with positive detections
for perchlorate was 9.85 [mu]g/L and the median concentration was 6.40
[mu]g/L.
Table 1 presents the number and percentage of PWSs that reported
perchlorate at levels exceeding various threshold concentrations. Note
that the MRL for perchlorate under the UCMR 1 was 4 [micro]g/L.
Table 1--Percent Public Water System Estimates for Perchlorate Above Thresholds of Interest
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PWSs with at least 1 PWS entry or sample points
Threshold concentration \a\ detection > threshold of with at least 1 detection >
interest threshold of interest \b\
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4 [micro]g/L...................................... 4.0% 2.5%
(155 of 3,865) (371 of 14,987)
6 [micro]g/L...................................... 2.5% 1.5%
(97 of 3,865) (219 of 14,987)
9 [micro]g/L...................................... 1.5% 0.77%
(56 of 3,865) (115 of 14,987)
13 [micro]g/L..................................... 0.93% 0.37%
(36 of 3,865) (56 of 14,987)
14 [micro]g/L..................................... 0.85% 0.32%
(33 of 3,865) (48 of 14,987)
19 [micro]g/L..................................... 0.62% 0.20%
(24 of 3,865) (30 of 14,987)
[[Page 7765]]
23 [micro]g/L..................................... 0.39% 0.13%
(15 of 3,865) (19 of 14,987)
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\a\ All occurrence measures in this table were conducted on a basis reflecting values greater than the listed
thresholds. Five systems detected perchlorate levels equal to 4 [micro]g/L and are therefore not presented in
this table.
Given the range of potential alternative HRLs, EPA has reversed its
October 2008 preliminary determination not to regulate perchlorate in
drinking water. Based on the data in Table 1 and the range of potential
alternative HRLs, EPA has determined that perchlorate is known to occur
or there is a substantial likelihood that it will occur with a
frequency and at levels of public health concern.
C. Is there a meaningful opportunity for the reduction of health risks
from perchlorate for persons served by public water systems?
Yes. EPA has made this determination based on a consideration of
the best available peer reviewed science and data collected in
accordance with accepted methods related to perchlorate occurrence in
drinking water, the presence of perchlorate in foods, and the potential
health effects of exposure to perchlorate.
Table 2 presents EPA's estimates of the population served by PWSs
that were monitored under UCMR 1 for which the highest reported
perchlorate concentration was greater than the thresholds identified in
Table 1. EPA has determined that a NPDWR for perchlorate could reduce
perchlorate exposures for these populations to levels below the
potential alternative HRLs that EPA has identified as levels of public
health concerns for purposes of this determination, and that such
exposure reductions present a meaningful opportunity for the reduction
of health risks for persons served by PWSs.
Specifically, Table 2 presents EPA's estimates of the population
served by PWSs that were monitored under UCMR 1 for which the highest
reported perchlorate concentration was greater than the thresholds
identified in Table 1. The second column of Table 2 presents a range of
estimates of the population served by PWSs that had at least one sample
with perchlorate concentrations greater than the threshold. The
population range represents both a high end estimate, as well as a
central value estimate. These population estimates were derived using
the UCMR 1 monitoring data. The high end estimate of the population
served drinking water above a threshold is derived by adding the entire
system population of all PWSs in which at least one sample was found to
contain perchlorate above the threshold. EPA considers this a high end
estimate because it is based on the assumption that the entire system
population is served water from the entry point that had the highest
reported perchlorate concentration. In fact, many PWSs have multiple
entry points into which treated water is pumped for distribution to
their consumers. For the PWSs with multiple entry points, it is
unlikely that the entire service population receives water from the one
entry point with the highest single concentration. Therefore, EPA also
provides a central value estimate of the population served water with
perchlorate above a threshold in the second column in Table 2. EPA
developed this central value estimate by assuming the population was
equally distributed among all entry points and added only the
proportion of the total population served by those entry points in a
PWS that had at least one sample with perchlorate concentrations
greater than the threshold. For example, if a PWS with 10 entry points
serving 200,000 people had a sample from a single entry point with a
concentration at or above a given threshold, EPA assumed that the entry
point served one-tenth of the PWS population, and added 20,000 people
to the total when deriving the central value population estimate. In
contrast, for the high end estimate using the example above, EPA added
the entire PWS population of 200,000 to the total population. The
latter is likely an overestimate. The UCMR 1 population estimates in
Table 2 are for people at all life stages.
Table 2--Population Estimates for PWSs That Detected Perchlorate Above
Various Thresholds
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Range of population
served by PWSs with at
Threshold \a\ least 1 detection >
threshold \b\ (million)
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4 [micro]g/L................................... 5.1-16.6
6 [micro]g/L................................... 3.0-11.8
9 [micro]g/L................................... 1.6-5.2
14 [micro]g/L.................................. 0.9-2.1
19 [micro]g/L.................................. 0.7-1.6
23 [micro]g/L.................................. 0.4-1.0
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\a\ All occurrence measures in this table were conducted on a basis
reflecting values greater than the listed thresholds. All population
estimates in this table are rounded.
\b\ Population estimates are derived from UCMR 1 data.
D. Regulatory Determination
EPA has determined that perchlorate meets the criteria for
regulating a contaminant in Section 1412(b)(1)(A) of SDWA. As
previously discussed in this regulatory determination, perchlorate may
have an adverse effect on the health of persons and perchlorate is
known to occur or there is a substantial likelihood that perchlorate
will occur in public water systems with a frequency and at levels of
public health concern. Moreover, in light of the discussion in this
regulatory determination and the information available at this time,
the Administrator finds that regulation of perchlorate in drinking
water systems presents a meaningful opportunity for health risk
reduction for persons served by public water systems. Therefore, EPA
will initiate the process of proposing a NPDWR for perchlorate.
E. Key Commenter Issues
EPA received a total of approximately 39,000 comments from
individuals or organizations on the May 2007 document, and the October
2008, and August 2009 Federal Register notices regarding the
perchlorate regulatory determination. This section briefly discusses a
number of the key issues raised by commenters and EPA's response to
these concerns. Responses
[[Page 7766]]
to all of the comments received are available in the ``Comment Response
Document for the Final Regulatory Determination on Perchlorate''
(USEPA, 2010a) available at http://www.regulations.gov (Docket ID No.
EPA-HQ-OW-2009-0297).
1. Health Implications of Perchlorate Exposure Above the RfD
EPA received comments indicating that the levels of perchlorate in
drinking water that result in exposures greater than the RfD are not
levels of public health concern because the RfD is based on a precursor
to an adverse effect. EPA believes the NRC appropriately based the RfD
on iodide uptake inhibition to the thyroid, for the reasons discussed
in its report. EPA also received a substantial number of comments
supporting the Agency's current view. EPA notes that the data
underlying the definition of iodide uptake inhibition as a precursor
effect and the relationship of iodide uptake inhibition to the
continuum of adverse outcomes reflects an understanding of effects in
adults; it may not reflect the relationship of the precursor event to
adverse outcomes in neonates and infants, who may not have iodide
stores sufficient to offset the effects of reduced iodide uptake. The
less resilient neonatal and infant system makes the exposure gap
between a precursor event (iodide uptake inhibition due to perchlorate)
and reduced T3/T4 levels likely to be narrower than for adults, and in
fact, the distinction between the two may be blurred for the very young
(Greer et al., 2002; Savin et al., 2003; van den Hove et al., 1999).
The NRC noted that, ``[T]he minimal prolonged decrease in thyroid
hormone production that would be associated with adverse health effects
is not known; any decrease is potentially more likely to have adverse
effects in sensitive populations (people with thyroid disorders,
pregnant women, fetuses, and infants) but data are not available to
determine the magnitude of the decrease needed to cause adverse effects
in those populations.''
2. Other Thyroid Inhibiting Chemicals
EPA received a number of comments that the Agency should consider
the comparative effect on iodine uptake of perchlorate exposure in
drinking water to nitrate and thiocyanate exposure in drinking water in
determining whether there is a meaningful opportunity for risk
reduction. Other commenters, including EPA's Office of Inspector
General (USEPA, 2008c), believe that a NPDWR for a group of chemicals
may be appropriate based on a yet-to-be-conducted cumulative risk
assessment that assesses and characterizes the combined human health
risk from perchlorate, nitrate, and thiocyanate.
While EPA acknowledges that nitrate and thiocyanate have the same
mode of action as perchlorate, and that the effects of combined
exposure to perchlorate, nitrate, and thiocyanate are additive, EPA
does not believe there are sufficient scientific data currently
available to assess and characterize the combined risk of these
contaminants. EPA has committed to a drinking water strategy that
outlines four principles to expand public health protection for
drinking water (USEPA, 2010b). One of these principles is to address
contaminants as groups. However, EPA does not believe that regulatory
action to address perchlorate should be further delayed. Therefore, EPA
intends to develop a proposed rule for perchlorate. At such time as a
NPDWR is promulgated, EPA is required to review and revise, as
appropriate, its drinking water standards at least every six years. Any
revision must at least maintain or improve public health protection.
When there are sufficient scientific data to assess the cumulative
risks of perchlorate and other contaminants, EPA will review this
information to evaluate whether any revisions of NPDWRs are
appropriate.
3. Perchlorate in Food
A commenter wrote that a drinking water regulation for perchlorate
does not present a meaningful opportunity for health risk reduction
because perchlorate contamination in food is widespread. Other
commenters indicated that EPA should regulate perchlorate in drinking
water to reduce the public's overall exposure to perchlorate. EPA
agrees that perchlorate contamination is more widespread in foods than
in PWSs; however, EPA does not believe that the widespread presence of
perchlorate in food overrides the need for public health risk reduction
for persons served by PWSs with perchlorate contamination. The Agency
presented an extensive evaluation of dietary exposure to perchlorate in
the October 2008 and August 2009 notices (73 FR 60262; USEPA 2008a and
74 FR 41883; USEPA 2009b). EPA has used this dietary exposure data to
account for the relative source contribution (RSC) of perchlorate from
food to estimate the range of levels of public health concern. EPA
recognizes that a drinking water regulation would not eliminate total
perchlorate exposure, but believes that the reduction in perchlorate
exposure in drinking water presents a meaningful opportunity for health
risk reduction for persons served by PWSs contaminated by perchlorate.
4. Iodide Nutritional Status
Some commenters stated that public health concerns over iodide
uptake inhibition could be addressed more efficiently through promotion
of iodide nutrition than through regulation of perchlorate. EPA agrees
that promoting iodide nutrition is good public health policy and may
have a positive influence in reducing the iodide uptake inhibition
effects associated with exposure to perchlorate. However, the Agency
does not think it is appropriate to rely on the promotion of iodide
nutrition in this case, especially since these activities are outside
of EPA's SDWA authority. As a result, while the health concerns
associated with perchlorate may be addressed through other means, it is
the Administrator's judgment that a standard limiting perchlorate in
drinking water can reduce health risk, particularly to fetuses, infants
and children.
5. Physiologically-Based Pharmacokinetic (PBPK) Modeling
EPA reviewed, modified, and applied the perchlorate PBPK models,
which were originally developed by Merrill et al. (2005) for adults and
Clewell et al. (2007) for other life stages, to estimate the iodide
uptake inhibition in the thyroid for each life-stage (73 FR 60262;
USEPA 2008a). Estimated ingestion rates were then used to estimate the
internal dose and resulting iodide uptake inhibition for several life
stages, including susceptible populations (e.g., pregnant women and
their fetuses, as well as breast-fed and bottle-fed infants).
In the August 2009 notice, EPA stated that it was re-evaluating how
best to incorporate the PBPK modeling analysis into its evaluation of
perchlorate--if at all. The Agency sought comments on ways to use the
PBPK modeling analysis to inform the regulatory determination.
Several commenters supported the use of the PBPK model to inform
the regulatory determination only if the significant limitations of the
current model are addressed. For example, the inability of the model to
reflect iodide nutritional status was cited by commenters and three of
four peer reviewers as an important limitation (USEPA, 2008d). Also,
several commenters stated that the risks to breast-fed infants and
young children are not adequately addressed by the model. They
challenged that the modeling analysis is based on average weight
infants and healthy adults, while the sensitive life stages for
perchlorate
[[Page 7767]]
include premature infants and hypothyroid women.
After further consideration of the peer review and public comments,
EPA concludes that the PBPK modeling analysis, in the context of the
perchlorate regulatory determination, is useful in examining which life
stages are most susceptible to the effects of perchlorate. For example,
the model indicates that a fetus may be seven times more sensitive to
the effects of perchlorate than a pregnant woman. The model also allows
for the estimation of the concentration of perchlorate in breast milk
(thus breast-fed infant exposure) at various maternal perchlorate
exposure levels. However, because of the stated limitations, EPA has
decided the model does not directly bear on the current decision
regarding the need for a NPDWR for perchlorate. EPA is continuing to
evaluate whether the model could be used in setting a NPDWR for
perchlorate.
F. Next Steps
EPA is initiating the development of a proposed NPDWR for
perchlorate. However, this is not the end of a decision process but a
middle step in a process that leads to a final drinking water standard.
Based on this decision, EPA intends to publish a proposed NPDWR for
public review and comment within 24 months of this regulatory
determination.\2\ EPA will continue to evaluate the science as we
develop the proposed NPDWR. EPA will, as part of the proposed NPDWR,
present a health risk reduction and cost analyses, an analysis of
feasible treatment methods, and an analysis of small system compliance
technologies. EPA will also consult with the National Drinking Water
Advisory Council, the Science Advisory Board, and the Secretary of
Health and Human Services, as required under SDWA.
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\2\ On January 8, 2009, EPA issued an interim health advisory to
provide guidance to State and local officials in their efforts to
address perchlorate contamination. The interim health advisory
(USEPA, 2008e) can be found at: http://www.epa.gov/safewater/contaminants/unregulated/pdfs/healthadvisory_perchlorate_interim.pdf and in EPA's docket ID No. EPA-HQ-OW-2009-0297 for this
notice. EPA expects to make a final decision on the interim health
advisory at such time as a definitive decision has been made with
respect to the promulgation of a final perchlorate regulation.
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IV. References
Clewell, R.A., E.A. Merrill, J.M. Gearhart, P.J. Robinson, T.R.
Sterner, D.R. Mattie, and H.J. Clewell, III. 2007. Perchlorate and
radioiodide kinetics across life stages in the human: Using PBPK
models to predict dosimetry and thyroid inhibition and sensitive
subpopulations based on developmental stage. Journal of Toxicology
and Environmental Health. Part A. Vol. 70. Issue 5. p. 408-428.
Greer, M.A., G. Goodman, R.C. Pleuss, and S.E. Greer. 2002. Health
effect assessment for environmental perchlorate contamination: The
dose response for inhibition of thyroidal radioiodide uptake in
humans. Environ Health Perspect Vol. 110. p. 927-937.
Life Sciences Research Office (LSRO), Federation of American Studies
for Experimental Biology Prepared for the Interagency Board for
Nutrition Monitoring and Related Research. 1995. Third Report on
Nutrition Monitoring in the United States: Volume 1. U.S. Government
Printing Office, Washington, DC.
Merrill, E.A., R.A. Clewell, P.J. Robinson, A.M. Jarabek, T.R.
Sterner, and J.W. Fisher. 2005. PBPK model for radioactive iodide
and perchlorate kinetics and perchlorate-induced inhibition of
iodide uptake in humans. Toxicological Sciences. Vol. 83. p. 25-43.
National Research Council (NRC). 2005. Health Implications of
Perchlorate Ingestion. National Academies Press, Board on
Environmental Studies and Toxicology. January 2005. p. 276.
Savin, S., D. Dvejic, O. Nedic, R. Radosavljevic. 2003. Thyroid
Hormone Synthesis and Storage in the Thyroid Gland of Human
Neonates. J. Pediatric Endocrinology & Metabolism. Vol. 16. p. 521-
528.
U.S. Census Bureau. 2008. U.S. Census Bureau Annual Estimates of
Resident Population by Single-Year of Age and Sex for the U.S. and
States: April 2, 2000 to July 1, 2008. Available on the Internet at:
http://www.census.gov/popest/states/asrh/.
USEPA. 1998. Announcement of the Drinking Water Contaminant
Candidate List; Notice. Federal Register. Vol. 63, No. 40. p. 10273,
March 2, 1998.
USEPA. 2004. Estimated Per Capita Water Ingestion and Body Weight in
the United States--An Update. Office of Science and Technology,
Washington, DC; EPA/822/R-00-001.
USEPA. 2005a. Drinking Water Contaminant Candidate List 2; Final
Notice. Federal Register. Vol. 70, No. 36. p. 9071, February 24,
2005.
USEPA. 2005b. ``Integrated Risk Information System (IRIS),
Perchlorate and Perchlorate Salts.'' February 2005. Available on the
Internet at: http://www.epa.gov/iris/subst/1007.htm. Accessed
February 2, 2005.
USEPA. 2007. Drinking Water: Regulatory Determinations Regarding
Contaminants on the Second Drinking Water Contaminant Candidate
List--Preliminary Determinations, Federal Register, Vol. 72, No. 83.
p. 24016, May 1, 2007.
USEPA. 2008a. Drinking Water: Preliminary Regulatory Determination
on Perchlorate, Federal Register, Vol. 73, No. 198. p. 60262,
October 10, 2008.
USEPA. 2008b. Child-Specific Exposure Factors Handbook. National
Center for Environmental Assessment, Washington, DC; EPA/600/R-06/
096F.
USEPA. 2008c. Scientific Analysis of Perchlorate (External Review
Draft). Office of Inspector General, Washington, DC; Assignment No.
2008-0010. Available on the Internet at: http://www.epa.gov/oig/reports/2010/20100419-10-P-0101.pdf.
USEPA. 2008d. Comment Response Summary Report, Peer Review of
Drinking Water Health Advisory for Perchlorate. Office of Science
and Technology, Washington, DC; December 2008.
USEPA. 2008e. Interim Drinking Water Health Advisory for
Perchlorate. Office of Science and Technology, Washington, DC; EPA
822-R-08-025.
USEPA. 2009a. Drinking Water Contaminant Candidate List 3--Final.
Federal Register. Vol. 74, No. 194. p. 51850, October 8, 2009.
USEPA. 2009b. Drinking Water: Perchlorate Supplemental Request for
Comments, Federal Register, Vol. 74, No. 159. p. 41883, August 19,
2009.
USEPA. 2010a. Comment Response Document for the Final Regulatory
Determination on Perchlorate (Categorized Public Comments). EPA XXX-
XXX. December, 2010.
USEPA. 2010b. A New Approach to Protecting Drinking Water and Public
Health. EPA 815-F-10-001. Available on the Internet at: http://water.epa.gov/lawsregs/rulesregs/sdwa/dwstrategy/index.cfm
van den Hove, M.F., C. Beckers, H. Devlieger, F. de Zegher, P. De
Nayer. 1999. Hormone synthesis and storage in the thyroid of human
preterm and term newborns: Effect of thyroxine treatment. Biochimie.
Vol. 81. p. 563-570.
Zimmerman, M. 2009. Iodide Deficiency. Endocrine Reviews. Vol. 30,
No. 4. p. 376-408.
Dated: February 2, 2011.
Lisa P. Jackson,
Administrator.
[FR Doc. 2011-2603 Filed 2-10-11; 8:45 am]
BILLING CODE 6560-50-P