Revised Document Based on Interagency Working Comments on Draft Language 

under EO 12866 Review. January 28, 2011

Page 1 of 35

ENVIRONMENTAL PROTECTION AGENCY

[EPA-HQ-OW-2008-0692, EPA-HQ-OW-2009-0297; FRL-_______-_______]

RIN 2040-AF08

Drinking Water: Final Regulatory Determination on Perchlorate

AGENCY: Environmental Protection Agency (EPA).

ACTION: Notice.

SUMMARY: This action presents EPA‘s (or the Agency‘s) final 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. 
Revised Document Based on Interagency Working Comments on Draft Language 

under EO 12866 Review. January 28, 2011

Page 2 of 35

DATES: For purposes of judicial review, the regulatory determination in this notice is issued as 

of [INSERT DATE OF PUBLICATION IN THE FEDERAL REGISTER], 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.govhotline-sdwa@epa.gov.

Formatted: Default Paragraph Font, Font:

Arial, 10 pt

Field Code Changed
Revised Document Based on Interagency Working Comments on Draft Language 

under EO 12866 Review. January 28, 2011

Page 3 of 35

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 

Occurs with a Frequency and at Levels of Public Health Concern in Public Water Systems?

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

Formatted: Default Paragraph Font, Font:

Times New Roman, 12 pt, Bold, Do not check

spelling or grammar

Field Code Changed

Formatted: Default Paragraph Font, Font:

Times New Roman, 12 pt, Italic, Do not check

spelling or grammar

Field Code Changed

Formatted: Default Paragraph Font, Font:

Times New Roman, 12 pt, Bold, Do not check

spelling or grammar

Field Code Changed

Formatted: Default Paragraph Font, Font:

Times New Roman, 12 pt, Italic, Do not check

spelling or grammar

Field Code Changed

Formatted: Default Paragraph Font, Font:

Times New Roman, 12 pt, Italic, Do not check

spelling or grammar

Field Code Changed

Formatted: Default Paragraph Font, Font:

Times New Roman, 12 pt, Italic, Do not check

spelling or grammar

Field Code Changed

Formatted: Default Paragraph Font, Font:

Times New Roman, 12 pt, Bold, Do not check

spelling or grammar

Field Code Changed

Formatted ...

Field Code Changed

Formatted ...

Field Code Changed

Formatted ...

Field Code Changed

Formatted ...

Field Code Changed

Formatted ...

Field Code Changed

Formatted ...

Field Code Changed

Formatted ...

Field Code Changed
Revised Document Based on Interagency Working Comments on Draft Language 

under EO 12866 Review. January 28, 2011

Page 4 of 35

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

Formatted: Default Paragraph Font, Font:

Times New Roman, 12 pt

Field Code Changed

Formatted: Default Paragraph Font, Font:

Times New Roman, 12 pt, Italic, Do not check

spelling or grammar

Field Code Changed

Formatted: Font: Times New Roman, 12 pt,

Italic, No underline, Font color: Auto, Do not

check spelling or grammar
Revised Document Based on Interagency Working Comments on Draft Language 

under EO 12866 Review. January 28, 2011

Page 5 of 35

RfD—reference dose 

SDWA—Safe Drinking Water Act 

UCMR—Unregulated Contaminant Monitoring Rule

μg—microgram (one-millionth of a gram) 

U.S.—United States

SUPPLEMENTARY INFORMATION

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. 

Formatted: apple-style-span, Font color: Auto
Revised Document Based on Interagency Working Comments on Draft Language 

under EO 12866 Review. January 28, 2011

Page 6 of 35

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. EPAHQ-OW-2009-0297 for this notice.)

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 
Revised Document Based on Interagency Working Comments on Draft Language 

under EO 12866 Review. January 28, 2011

Page 7 of 35

substantial likelihood that the 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 

notice, 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 notice (72 FR 

24016; USEPA 2007) that addressed perchlorate. Public comments on the May 2007 notice 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 

Formatted: No underline, Font color: Auto

Formatted: Font color: Auto

Formatted: No underline, Font color: Auto
Revised Document Based on Interagency Working Comments on Draft Language 

under EO 12866 Review. January 28, 2011

Page 8 of 35

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 

notice, 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 

Formatted: No underline
Revised Document Based on Interagency Working Comments on Draft Language 

under EO 12866 Review. January 28, 2011

Page 9 of 35

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 based on our August 2009 evaluation of infants and developing children and now 

concludes, based on the analysis presented in this notice, 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 notice. EPA will consider the public comments and expects 

to promulgate a final regulation within 18 months of the proposal.
Revised Document Based on Interagency Working Comments on Draft Language 

under EO 12866 Review. January 28, 2011

Page 10 of 35

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 
Revised Document Based on Interagency Working Comments on Draft Language 

under EO 12866 Review. January 28, 2011

Page 11 of 35

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 hasmay have an adverse effect on the health of persons. 

B. Is Perchlorate Known to Occur or is There a Substantial Likelihood that Perchlorate 

Occurswill Occur in Public Water Systems with a Frequency and at Levels of Public Health 

Concern in Public Water Systems?

Yes. EPA has determined that perchlorate occurs or there is a substantial likelihood that 

perchlorate will occur with a frequency and at 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 health reference levels (HRLs) based on the reference dose (RfD) for 

perchlorate.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 
Revised Document Based on Interagency Working Comments on Draft Language 

under EO 12866 Review. January 28, 2011

Page 12 of 35

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). . 

 

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.
Revised Document Based on Interagency Working Comments on Draft Language 

under EO 12866 Review. January 28, 2011

Page 13 of 35

.‖ EPA‘s Integrated Risk Information System (IRIS) adopted the NRC‘s recommendations 

resulting in an RfD of 0.7 μg/kg/day (USEPA, 2005b).

In the October 2008 preliminary regulatory determination, EPA had derived a single 

HRL of 15 μg/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) (identified in Table 1)

using the RfD and life stage-specific exposure information in the August 9, 2009, notice (74 FR 

41883; USEPA 2009b). These HRLslevels range from 1 μg/L to 47 μg/L and are the 

concentrationconcentrations of perchlorate in drinking water that may result in total perchlorate 

exposures (from food and water) greater than the RfD for individuals at thiseach 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 has determined that the HRLs in Table 1 are more appropriate as the levels of public 

health concern for purposes of this regulatory determination because the NRC identified infants 

and developing children as additional sensitive life stages, and the HRL values in Table 1
Revised Document Based on Interagency Working Comments on Draft Language 

under EO 12866 Review. January 28, 2011

Page 14 of 35

account for the greater drinking water consumption on a per body weight basis for infants and 

developing children. When EPA proposes the NPDWR for perchlorate, the Agency will also 

propose a Maximum Contaminant Level Goal (MCLG) for perchlorate. The MCLG is the 

―maximum level of a contaminant in drinking water at which no known or anticipated adverse 

effect on the health of persons would occur, and which allows an adequate margin of safety.‖ 

Maximum contaminant level goals are ―non-enforceable health goals‖ (CFR 141.2). EPA 

expects to select an MCLG from among the HRL values for infants, children, and pregnant 

women in Table 1.

Table 1–Life Stage-Specific HRLs.

Life Stage

RfD

(μg/kgday) RSCa

90th Percentile Ingestion 

Rateb

(mL/kg-day)c

Life stage-specific HRLd

(μg/L)

Birth to < 1 month 0.7 59% 235e2

1 to < 3 months 0.7 59% 228e2

3 to < 6 months 0.7 59% 148 3

 Birth to < 6 months 0.7 59% 184 2

6 to < 12 months 0.7 59% 112 4

1 to < 2 years 0.7 44% 56 6

2 to < 3 years 0.7 44% 52 6

3 to < 6 years 0.7 60% 49 9

6 to < 11 years 0.7 71% 35 14

11 to < 16 years 0.7 84% 26 23

16 to < 18 years 0.7 80% 24 23

18 to < 21 years 0.7 80% 29 19

Pregnant Womenf0.7 62%e33e13

Women 15 to 44 years 0.7 80% 32 18

aRelative Source Contribution (RSC) calculated for nearest age range based on the mean dietary intake from FDA‘s 

Total Diet Study (see Table 5 at 73 FR 60275; USEPA 2008a). RSC for pregnant women and women ages 15-44 

based on the 90th percentile dietary intake from the National Health and Nutrition Examination Survey-UCMR 

analysis (see Table 6 at 73 FR 60276; USEPA 2008a).

b

Ingestion rate is adjusted for the self-reported body weights from the CFSII. 
Revised Document Based on Interagency Working Comments on Draft Language 

under EO 12866 Review. January 28, 2011

Page 15 of 35

c

Drinking Water Ingestion Rates for consumers only in Community Water Systems taken from EPA‘s  ̳ ̳ChildSpecific Exposure Factors Handbook‘‘ (USEPA, 2008b). Except for values for infants from birth to 6 months, 

which are taken from Tables 5.2.A2 of EPA‘s ―Estimated Per Capita Water Ingestion and Body Weight in the 

United States—An Update‖ (USEPA, 2004), and for Pregnant Women and Women Ages 15–44 which are taken 

from Table 6.2.A2 of EPA‘s ―Estimated Per Capita Water Ingestion and Body Weight in the United States—An 

Update‖ (USEPA, 2004). 

d Health reference levels (HRLs) are calculated by the following equation: HRL = RfD x Drinking Water Ingestion 

Rate x RSC.

e

The sample sizes for the estimates of ingestion rates for these life stages do not meet the minimum data 

requirements as described in the ―Third Report on Nutrition Monitoring in the United States‖ (LSRO, 1995). 

f

The most sensitive population identified by the NRC are the fetuses of pregnant women who might have 

hypothyroidism or iodide deficiency.

EPA has compared these HRLEPA 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 μg/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 μg/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 μg/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 
Revised Document Based on Interagency Working Comments on Draft Language 

under EO 12866 Review. January 28, 2011

Page 16 of 35

samples with positive detections for perchlorate was 9.85 μg/L and the median concentration was 

6.40 μg/L. 

Table 21 presents the number and percentage of PWSs that reported perchlorate at levels 

exceeding the various life stage-specific HRLs listed in Table 1.threshold concentrations. Note 

that the MRL for perchlorate under the UCMR 1 was 4 μg/L. Table 2 indicates that the number 

and percentage of PWSs that reported perchlorate at levels exceeding the HRL of 2 μg/L are at 

least equal to the number and percentage of systems that reported perchlorate concentrations at 

levels equal to or greater than the MRL. Therefore, these values would likely be greater if the 

UCMR 1 MRL had been lower than 4 μg/L. EPA plans to develop a Bayesian analysis of the 

perchlorate occurrence to estimate the additional number of PWSs and entry points where 

perchlorate is likely to occur at levels between 2 and 4 μg/L. EPA intends to present this 

analysis as part of the proposed NPDWR. 

Table 21–Percent Public Water System Estimates for Perchlorate above Life Stage HRLs at 90th

Percentile Drinking Water Ingestion Rates.Thresholds of Interest 

Life Stage-Specific

HRL Threshold 

Concentrationa

PWSs with at Least 1 Detection 

> Threshold of Interest

PWS Entry or Sample Points with at Least 

1 Detection > Threshold of Interestb

2 μg/L a At least 4.1%

(160 of 3,865)

At least 2.6 % 

(387 of 14,987) 

4 μg/L

4.0% 

(155 of 3,865)

2.5%

(371 of 14,987)

6 μg/L 2.5%

(97 of 3,865)

1.5%

(219 of 14,987)

9 μg/L

1.5%

(56 of 3,865)

0.77%

(115 of 14,987)

13 μg/L

0.93%

(36 of 3,865)

0.37%

(56 of 14,987)

14 μg/L 0.85% 0.32%
Revised Document Based on Interagency Working Comments on Draft Language 

under EO 12866 Review. January 28, 2011

Page 17 of 35

Life Stage-Specific

HRL Threshold 

Concentrationa

PWSs with at Least 1 Detection 

> Threshold of Interest

PWS Entry or Sample Points with at Least 

1 Detection > Threshold of Interestb

(33 of 3,865) (48 of 14,987)

19 μg/L

0.62%

(24 of 3,865)

0.20%

(30 of 14,987)

23 μg/L

0.39%

(15 of 3,865)

0.13%

(19 of 14,987)

a Values for 2 μg/LaAll occurrence measures in this table were approximated using PWSs with 

detectionsconducted on a basis reflecting values greater than or equal to 4 μg/L. Values would likely be greater 

if the UCMR 1 minimum reporting limit had been lower than 4 μg/L.

EPA has determined that the listed thresholds. Five systems detected perchlorate 

concentrations which are greater than the HRLs in Table 1 are the levels of public health concern. 

EPA has reversed its October 2008 preliminary determination that perchlorate occurs 

infrequently at levels of health concern in public water systems. In the October 2008 preliminary 

regulatory determination, EPA had derived a single HRL of 15 μg/L to reflect exposure to a 

pregnant woman and her fetus. EPA stated in the October 2008 notice that there are a small 

percentage of public water systems (0.8 percent) where drinking water above the HRL of 15 

μg/L, in combination with perchlorate from food, may result in exposures to pregnant women at 

levels that exceed the EPA reference dose for perchlorate. However, based on EPA‘s selection

of the life stage-specific HRLs in Table 1 (many of which are lower than 15 μg/L) as the more 

appropriate levels of public health concern, EPA now concludes that perchlorate occurs in PWSs 

with a frequency and at levels of health concern. EPA estimates that at least 4.1 percent of 

PWSs have perchlorate exceeding one or more of the HRLs in Table 1 and that some of the 

consumers of these PWSs may be exposed to perchlorate (from their food and water combined) 

at levels that may cause them to exceed the RfD. These systems are located in 26 States and 2 

territories. Therefore, EPA has determined that perchlorate occurs with a frequency and at levels 

of public health concernequal to 4 μg/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. 

Formatted: Font: 11 pt, No underline

Formatted: Font: 11 pt, No underline

Formatted: Font: 11 pt, No underline

Formatted: Line spacing: single

Formatted: Font: 11 pt, No underline, Font

color: Black

Formatted: Font: 11 pt, No underline, Font

color: Black

Formatted: Font: 11 pt, No underline, Font

color: Black

Formatted: Font: 11 pt
Revised Document Based on Interagency Working Comments on Draft Language 

under EO 12866 Review. January 28, 2011

Page 18 of 35

C. Is There a Meaningful Opportunity for the Reduction of Health Risks from Perchlorate for 

Persons Served by Public Water Systems? 

Yes. EPA estimates that at least 5.2 to 16.8 million people are served by PWSs, for 

which we have data, that have detected perchlorate and at least 350,000 to 1.1 million infants and 

children may be exposed to perchlorate in drinking water at levels that in combination with the 

perchlorate in their food results in exposures that exceed the RfD for perchlorate. (Note that the 

MRL for perchlorate under the UCMR 1 was 4 μg/L, which is greater than the lowest life stagespecific HRL of 2 μg/L in Table 1. Therefore, EPA approximated the population who are served 

water that has perchlorate concentrations above 2 μg/L using the population served by PWSs 

with perchlorate detections greater than or equal to 4 μg/L.) These population estimates would 

likely be greater if the UCMR 1 MRL had been lower than 4 μg/L. EPA also estimated that 

about 20,000 to 30,000 pregnant women would be exposed to perchlorate in drinking water 

above their life stage-specific HRL of 13 μg/L. EPA has determined that a NPDWR for 

perchlorate could reduce perchlorate exposures for these infants, children, and pregnant women 

to levels below the RfD, and therefore believes that this perchlorate exposure reduction presents 

a meaningful opportunity for the reduction of health risks for persons served by PWSs. 

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 

Formatted: Font: 12 pt, No underline, Font

color: Auto

Formatted: Normal
Revised Document Based on Interagency Working Comments on Draft Language 

under EO 12866 Review. January 28, 2011

Page 19 of 35

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 32 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 HRLsthresholds identified in Table 1. HRLs presented in the table are derived 

using the 90th percentile drinking water ingestion rates for the various life stages shown in Table 

1. 

 The second column of Table 32 presents a range of estimates of the population served 

by PWSs that had at least one sample with perchlorate concentrations greater than the 

HRLthreshold. 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 an HRLa threshold is 

derived by adding the entire system population of all PWSs in which at least one sample was 

Formatted: Font: 12 pt, No underline, Font

color: Auto
Revised Document Based on Interagency Working Comments on Draft Language 

under EO 12866 Review. January 28, 2011

Page 20 of 35

found to contain perchlorate above the HRLthreshold. 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 an HRLa 

threshold in the second column in Table 32. 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 HRLthreshold. 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 32 are for people at all life stages. 

Table 32–Population Estimates for PWSs that detected Perchlorate above HRLsVarious 

Thresholds.

Life Stage-Specific 

HRLaThresholda

Range of Population Served by PWSs with 

at Least 1 Detection > HRLbthresholdb
Revised Document Based on Interagency Working Comments on Draft Language 

under EO 12866 Review. January 28, 2011

Page 21 of 35

(Million)

2 μg/Lc At least

5.2 - 16.8

4 μg/L 5.1 - 16.6

6 μg/L 3.0 - 11.8

9 μg/L 1.6 - 5.2

14 μg/L 0.9 - 2.1

19 μg/L 0.7 - 1.6

23 μg/L 0.4 - 1.0

a HRLs presented in the table are derived using the 90th percentile drinking water ingestion rates for the various life 

stages shown in Table 1. AllaAll occurrence measures in this table were conducted on a basis reflecting values 

greater than the listed HRLsthresholds. All population estimates in this table are rounded. 

b

Population estimates are derived from UCMR 1 data. 

c Values for 2 μg/L were approximated using population served by PWSs with perchlorate detections greater than or 

equal to 4 μg/L. Values are approximated and would likely be greater if the UCMR 1 minimum reporting limit had 

been lower than 4 μg/L.

Table 4 presents EPA‘s estimates of the portion of the population (from Table 3) that is in 

one of the life stages identified in Table 1 at any given time and is served by PWSs with 

perchlorate concentrations above the corresponding life stage-specific HRL. The life stages (age

range) corresponding to each HRL are presented in the first column of Table 4. The second 

column of Table 4 shows the range of population estimates for the portion of the population 

(from column 2 in Table 3) that is in an individual life stage at any given time and is potentially 

served perchlorate above their life stage-specific HRL. This range of population estimates is 

derived using U.S. Census data (U.S. Census Bureau, 2008, using population estimates for July 

1, 2005) to estimate the percentage of the total U.S. population in each individual life stage at 

any given time. The estimated percentages of the total U.S. population for each individual life 

stage were then multiplied by the estimates of the population served by PWSs (from column 2 of 

Formatted Table
Revised Document Based on Interagency Working Comments on Draft Language 

under EO 12866 Review. January 28, 2011

Page 22 of 35

Table 3) for which the highest reported perchlorate concentration was greater than their

corresponding life stage-specific HRLs. For example, in Table 3, EPA estimated that 5.1 million 

to 16.6 million people would be served perchlorate by PWSs above the HRL of 4 μg/L. The life 

stage at the HRL of 4 μg/L is children from 6 months to less than 12 months of age. Using data 

from the U.S. Census Bureau (U.S. Census Bureau, 2008), EPA estimated the percentage of the 

total U.S. population from 6 months to less than 12 months of age at any given time, and then 

multiplied that percentage by the population of 5.1 million to 16.6 million people to estimate that 

about 40,000 to 120,000 children from 6 months to less than 12 months of age would be served 

perchlorate by PWSs with at least 1 detection above their corresponding life stage-specific HRL 

of 4 μg/L.

Column 3 of Table 4 presents estimates of the cumulative life stage population whose 

total perchlorate exposure may be reduced to below the RfD if perchlorate levels in their 

drinking water were reduced from the levels measured under the UCMR to the HRL indicated in 

Table 4. Note that at the lower HRLs there are more people whose exposure could be reduced 

below the RfD because generally, the HRLs for the younger life stages are lower than the HRLs 

for the older life stages. These cumulative estimates were derived by summing the individual 

life stage populations at any given time (from column 2 of Table 4) above each HRL. For 

example, at the HRL of 6 μg/L, EPA summed the individual life stage populations of all life 

stages with an HRL of 6 μg/L or greater, which included all life stages from 1 to 21 years of age. 
Revised Document Based on Interagency Working Comments on Draft Language 

under EO 12866 Review. January 28, 2011

Page 23 of 35

Table 4–Estimates of Population above Life Stage-Specific HRLs.

Life Stage-Specific

HRLa

Range of Population in Individual 

Life Stage Served by PWSs with 

at Least 1 Detection > HRLb

(Thousand)

Cumulative Life Stage 

Population Served by PWSs 

whose exposure may be reduced 

to levels below the RfD if 

perchlorate levels in drinking 

water are reduced to the HRL

(Thousand)c

Birth to < 6 mo.

2 μg/L

d

At least

40 – 120

At least

350 – 1,080

6 to < 12 mo.

4 μg/L

40 – 120 310 – 960

1 to < 3 yr.

6 μg/L

80 – 330 280 – 850

3 to < 6 yr.

9 μg/L

60 – 210 190 – 520

6 to < 11 yr.

14 μg/L

60 – 140 130 – 310

18 to < 21 yr.

19 μg/L

30 – 70 70 – 170

11 to < 18 yr.

23 μg/L

40 – 100 40 – 100

a HRLs presented in the table are derived using the 90th percentile drinking water ingestion rates for the various life 

stages shown in Table 1. All occurrence measures in this table were conducted on a basis reflecting values greater 

than the listed HRLs. All population estimates in this table are rounded. 

b Population estimates are derived using U.S. Census Bureau Annual Estimates of Resident Population by SingleYear of Age and Sex for the U.S. and States: April 2, 2000, to July 1, 2008, using population estimates for July 1, 

2005 (U.S. Census Bureau, 2008 available at: http://www.census.gov/popest/states/asrh/). 

c Cumulative life stage population estimates were derived by summing the individual life stage population estimates 

above each HRL (From column 2 of Table 4). Note that the population estimates in this column were rounded after 

summing the non-rounded values for the individual life stage population estimates.

d Values for 2 μg/L were approximated using population served by PWSs with perchlorate detections equal to 4 

μg/L or greater. Values are approximated and would likely be greater if the UCMR 1 minimum reporting limit had 

been lower than 4 μg/L.

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 notice, perchlorate may have 
Revised Document Based on Interagency Working Comments on Draft Language 

under EO 12866 Review. January 28, 2011

Page 24 of 35

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 notice and the 

information available at this time, the Administrator finds that regulation of perchlorate in 

drinking water systems at this time 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, 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 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).
Revised Document Based on Interagency Working Comments on Draft Language 

under EO 12866 Review. January 28, 2011

Page 25 of 35

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 disagrees, andbelieves 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. 

The 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 children. We know that thyroid hormone status in neonates and 

infants is less resilient than in adults. That is, in general, neonates and infants, who may not have 

iodide stores sufficient to offset the effects of reduced iodide uptake. Half-lives for circulating 

hormones in neonates and infants are shorter than for adults, making neonates and infants less 

able to maintain stable hormone levels in the face of a chemical insult. 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 
Revised Document Based on Interagency Working Comments on Draft Language 

under EO 12866 Review. January 28, 2011

Page 26 of 35

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.‖ The additional sensitivity of these groups to perturbations in thyroid hormone 

levels, and the uncertainty about the point in the continuum of effects at which adverse effects

occur are important considerations in concluding that perchlorate exposures above the RfD are 

likely to have an adverse effect on the health of sensitive life stages. Therefore, we do not agree 

with those commenters who stated that levels of perchlorate in drinking water that result in 

exposures greater than the RfD are not levels of public health concern.

 

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-beconducted cumulative risk assessment that assesses and characterizes the combined human 

health risk from perchlorate, nitrate, and thiocyanate. 

Formatted: Font: Times New Roman, No

underline, Font color: Auto

Formatted: Font: Times New Roman
Revised Document Based on Interagency Working Comments on Draft Language 

under EO 12866 Review. January 28, 2011

Page 27 of 35

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 
Revised Document Based on Interagency Working Comments on Draft Language 

under EO 12866 Review. January 28, 2011

Page 28 of 35

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 HRLs in Table 1. EPA has further evaluated the populations exposed to perchlorate 

from both food and drinking water in Tables 3 and 4. In Table 3, EPA has estimated the 

population whose total perchlorate exposure may exceed the RfD (based on the population 

whose levels of perchlorate in drinking water under UCMR 1 exceed the HRLs). In Table 4, 

EPA has estimated the cumulative life stage population served by PWSs whose total perchlorate 

exposure may be reduced to levels below the RfD if those levels in drinking water were reduced

to the HRL.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
Revised Document Based on Interagency Working Comments on Draft Language 

under EO 12866 Review. January 28, 2011

Page 29 of 35

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). 
Revised Document Based on Interagency Working Comments on Draft Language 

under EO 12866 Review. January 28, 2011

Page 30 of 35

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). EPA agrees with the stated 

limitations of the model. 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 include premature infants and hypothyroid women. EPA agrees.

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.
Revised Document Based on Interagency Working Comments on Draft Language 

under EO 12866 Review. January 28, 2011

Page 31 of 35

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 notice.2EPA 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: 

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. 

Formatted: Line spacing: single, Adjust space

between Latin and Asian text, Adjust space

between Asian text and numbers

Formatted: Font: Times New Roman, 12 pt

Formatted: Font: Times New Roman, No

underline

Field Code Changed
Revised Document Based on Interagency Working Comments on Draft Language 

under EO 12866 Review. January 28, 2011

Page 32 of 35

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 radiodide 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 D.C.

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. 276 p.
Revised Document Based on Interagency Working Comments on Draft Language 

under EO 12866 Review. January 28, 2011

Page 33 of 35

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. 

Formatted: Font: Arial, 10 pt, No underline,

Font color: Auto

Field Code Changed
Revised Document Based on Interagency Working Comments on Draft Language 

under EO 12866 Review. January 28, 2011

Page 34 of 35

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-F10-001. Available on the Internet at:

http://water.epa.gov/lawsregs/rulesregs/sdwa/dwstrategy/index.cfm
Revised Document Based on Interagency Working Comments on Draft Language 

under EO 12866 Review. January 28, 2011

Page 35 of 35

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:

Lisa P. Jackson,

Administrator.

BILLING CODE 6560-50-P