Drinking Water: Regulatory Determination on Perchlorate, 7762-7767 [2011-2603]

Agencies

• ENVIRONMENTAL PROTECTION AGENCY

[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 https://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 https://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 https://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 https://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 https://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
------------------------------------------------------------------------
\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 https://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.
---------------------------------------------------------------------------

    \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: https://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.
---------------------------------------------------------------------------

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: 
https://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: https://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: https://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: https://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