Perchlorate Contamination of Drinking Water:
Regulatory Issues and Legislative Actions
Mary Tiemann
Specialist in Environmental Policy
August 6, 2009
Congressional Research Service
7-5700
www.crs.gov
RS21961
CRS Report for Congress
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repared for Members and Committees of Congress
Perchlorate Contamination of Drinking Water: Regulatory Issues and Legislative Actions
Summary
Perchlorate is the explosive component of solid rocket fuel, fireworks, road flares, and other
products. Used heavily by the Department of Defense (DOD) and related industries, perchlorate
also occurs naturally and is present in some organic fertilizer. This soluble, persistent compound
has been detected in drinking water supplies, especially in California. It also has been found in
milk and many foods. Because of this widespread occurrence, concern over the potential health
risks of perchlorate exposure has increased, and some states, water utilities, and Members of
Congress have urged the Environmental Protection Agency (EPA) to set a federal drinking water
standard for this chemical. Regulatory issues have involved the health risk reduction benefits and
the costs of federal regulation, including environmental cleanup and water treatment costs, both
of which are driven by federal and state standards.
EPA has spent years assessing perchlorate’s health effects and occurrence to determine whether a
national standard is warranted. The Food and Drug Administration (FDA) has supported this
effort by testing produce and other foods for the presence of perchlorate. Interagency
disagreements over the risks of perchlorate exposure led several federal agencies to ask the
National Research Council (NRC) to evaluate perchlorate’s health effects and EPA’s risk
analyses. In 2005, the NRC issued its report, and EPA adopted the NRC’s recommended reference
dose (i.e., the expected safe dose) for perchlorate exposure. Subsequent studies raised more
concerns about the potential effects of low-level exposures, particularly for infants in certain
cases.
In October 2008, EPA made a preliminary determination not to regulate perchlorate in drinking
water. Then, in early January 2009, the agency announced that it again would seek advice from
the NRC before making a final determination. EPA also announced that it was replacing the
preliminary remediation goal for perchlorate of 24.5 parts per billion (ppb) with an interim health
advisory, which contains a value of 15 ppb.
In August 2009, the EPA Administrator announced that the agency would reevaluate the science
regarding perchlorate’s potential health effects, with particular emphasis on evaluating the effects
of perchlorate exposure on infants and young children. The agency determined not to ask the
NRC to conduct further review of issues related to perchlorate, having concluded that additional
NRC review would unnecessarily delay the regulatory decision-making process. EPA intends to
consider public comments before making a final regulatory determination. Legislation (H.R.
3206) has been introduced to require EPA to promulgate a drinking water standard for
perchlorate. This report reviews perchlorate contamination issues and related developments.
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Perchlorate Contamination of Drinking Water: Regulatory Issues and Legislative Actions
Contents
Background ................................................................................................................................ 1
Occurrence............................................................................................................................ 1
Health Concerns.................................................................................................................... 2
EPA Assessment of Perchlorate for Regulation ............................................................................ 2
Perchlorate Risk Assessment ................................................................................................. 3
NRC Perchlorate Study ......................................................................................................... 4
EPA’s Response and Subsequent Actions ............................................................................... 4
DOD Perchlorate Actions ............................................................................................................ 6
Legislative Actions...................................................................................................................... 6
Contacts
Author Contact Information ........................................................................................................ 7
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Perchlorate Contamination of Drinking Water: Regulatory Issues and Legislative Actions
Background
Ammonium perchlorate is the key ingredient in solid fuel for rockets and missiles; other
perchlorate salts are used to manufacture products such as fireworks, air bags, and road flares.
Uncertainty about the health effects of perchlorate exposure has slowed efforts to establish
drinking water and environmental cleanup standards. However, because of perchlorate’s
persistence in water and ability to affect thyroid function, concern has escalated with the detection
of perchlorate in water in at least 33 states. In the absence of a federal standard, states have begun
to adopt their own measures. Massachusetts set a drinking water standard of 2 parts per billion
(ppb, or micrograms per liter [μg/L]) in 2006, and California adopted a 6 ppb standard in 2007.
Several states have issued health goals or advisory levels ranging from 1 ppb in Maryland
(advisory level) and New Mexico (drinking water screening level) to 17 ppb in Texas (residential
protective cleanup level) and, also in Texas, 51 ppb (industrial cleanup level).
Occurrence
Perchlorate has been used heavily by the DOD and its contractors, and perchlorate contamination
has been found near weapons and rocket fuel manufacturing facilities and disposal sites, research
facilities, and military bases. Fireworks, road flares, construction sites, and other manufacturing
activities and facilities also have been sources of contamination. Moreover, perchlorate occurs
naturally (in West Texas, for example), is present in organic fertilizer imported from Chile, and
can occur as a breakdown product of other products. It has been detected in drinking water
sources, primarily in the Southwest and in scattered locations across the country. Contamination
has been found most often in ground water, including some large aquifers in California.
In 1999, EPA required public water systems to monitor for perchlorate under the Unregulated
Contaminant Monitoring Rule (UCMR) to determine the frequency and levels at which it is
present in public water supplies nationwide. The UCMR required monitoring by all systems
serving more than 10,000 persons and by a sample of smaller systems. Of 3,865 public water
systems tested, perchlorate was detected at levels greater than or equal to 4 µg/L (the minimum
detection level of the test) in 160 (4.1%) systems in 26 states and two commonwealths, including
58 systems in California. In 14 systems, perchlorate levels exceeded EPA’s preliminary
remediation goal of 24.5 ppb. Approximately 1.9% (637) of a total of 34,331 samples collected
by the systems had detections of perchlorate at levels of 4 µg/L or greater. The average
concentration of perchlorate for the samples with positive detections was 9.85 µg/L. California
has required more comprehensive monitoring, and perchlorate has been detected at least twice in
241 active or standby sources of drinking water in that state since 2002.
In 2005, EPA reported perchlorate contamination had been found at 65 DOD facilities, 7 other
federal facilities, and 37 private sites.1 All sampling results combined (i.e., soil, public and private
drinking water wells, groundwater monitoring wells, and surface water), the Government
Accountability Office reported that perchlorate had been detected at 395 sites.2
1 EPA, Federal Facilities Restoration and Reuse, Known Perchlorate Releases in the U.S., March 25, 2005, at
http://www.epa.gov/fedfac/documents/perchlorate_links.htm#occurrences.
2 U.S. Government Accountability Office, Perchlorate: A System to Track Sampling and Cleanup Results is Needed,
GAO-05-462, May 2005, pp. 29-44.
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Monitoring also has been conducted to assess the presence of perchlorate in foods. In 2004, the
Food and Drug Administration (FDA) tested 500 samples of foods, including vegetables, milk,
and bottled water for perchlorate. Samples were taken in areas where water was thought to be
contaminated. The FDA found perchlorate in roughly 90% of lettuce samples (average levels
ranged from 11.9 ppb to 7.7 ppb for lettuces), and in 101 of 104 bottled milk samples (with an
average level of 5.7 ppb). To assess the presence of perchlorate in a wider range of foods, the
FDA began testing all samples in its Total Diet Study in 2005.3 Perchlorate was detected in 625 of
1065 (50%) of samples, and in 211 of the 285 (74%) foods tested.4 In most cases, perchlorate
levels were in the low single digits; however, levels were higher in some foods (e.g., shrimp,
tomatoes, spinach, and bacon). The study found that 2-year-olds have the highest total perchlorate
intake per kilogram body weight per day, followed by infants (6 to 12 months of age) and
children 6 to 10 years of age. The widespread detection of perchlorate in food is relevant to EPA’s
standard-setting efforts, because EPA considers non-water exposures when determining whether
to establish a standard for a contaminant, and at what level to set a standard.
Health Concerns
Perchlorate is not known to cause cancer. It is known to disrupt the uptake of iodine in the
thyroid, and health effects associated with perchlorate exposure are expected to parallel those
caused by iodine deficiency. Iodine deficiency decreases the production of thyroid hormones,
which help regulate the body’s metabolism and growth. A key concern is that impairment of
thyroid function in pregnant women can affect fetuses and nursing infants and can result in
delayed development and decreased learning capacity. Several human studies have indicated that
thyroid changes occur in humans at significantly higher levels of perchlorate than the amounts
typically observed in water supplies.5 However, a 2006 study by the Centers for Disease Control
and Prevention (CDC) of a representative sample of the U.S. population found that environmental
exposures to perchlorate have an effect on thyroid hormone levels in women with iodine
deficiency. (No effect was found in men.) Fully 36% of the 1,111 women in this study were found
to be iodine deficient, and the median level of urinary perchlorate measured in the women was
2.9 ppb.6
EPA Assessment of Perchlorate for Regulation
Over the past decade, EPA has evaluated perchlorate to determine whether a federal drinking
water standard is needed. Under the Safe Drinking Water Act (SDWA, §1412(b)(1)), EPA must
regulate a contaminant if the Administrator determines that the contaminant (1) may have an
adverse health effect, (2) occurs in public water systems at a frequency and level of public health
concern, and (3), in the sole judgment of the Administrator, regulation of the contaminant
3 The FDA test results are available online at http://www.cfsan.fda.gov/~dms/clo4dat2.html.
4 Clarence W. Murray et al., “U.S. Food and Drug Administration’s Total Diet Study: Dietary Intake of Perchlorate and
Iodine,” Journal of Exposure Science and Environmental Epidemiology (2008), 1-10.
5 Michael A. Kelsh et al., “Primary Congenital Hypothyroidism, Newborn Thyroid Function, and Environmental
Perchlorate Exposure Among Residents of a Southern California Community,” Journal of Occupational Environmental
Medicine, 2003, p. 1117.
6 Benjamin C. Blount, James L. Pirkle, et al., “Urinary Perchlorate and Thyroid Hormone Levels in Adolescent and
Adult Men and Women Living in the United States,” Centers for Disease Control and Prevention, in Environmental
Health Perspectives, December 2006, p. 1865.
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Perchlorate Contamination of Drinking Water: Regulatory Issues and Legislative Actions
presents a meaningful opportunity for reducing health risks. In 1997, when a sensitive detection
method became available for perchlorate and detections increased, scientific information was
limited. In 1998, EPA placed perchlorate on the list of contaminants that were candidates for
regulation, but concluded that information was insufficient to determine whether perchlorate
should be regulated under the SDWA. EPA listed perchlorate as a priority for further research on
health effects and treatment technologies and for collecting occurrence data. In 1999, EPA
required water systems to monitor for perchlorate under the Unregulated Contaminant Monitoring
Rule to determine the frequency and levels at which it is present in public water supplies
nationwide. In January 2007, EPA reported that it had collected sufficient occurrence data, and
that further monitoring was not needed for the agency to make a regulatory determination (72
Fed. Reg. 367, January 4, 2007).
Perchlorate Risk Assessment
In 1992, and again in 1995, EPA issued draft reference doses (RfDs) for perchlorate exposure. An
RfD is an estimate (with uncertainty spanning perhaps an order of magnitude) of a daily oral
exposure that is not expected to cause any adverse, non-cancer health effects during a lifetime. In
developing an RfD, EPA incorporates factors to account for sensitive subpopulations, study
duration, inter- and intraspecies variability, and data gaps. The draft RfDs range of 0.0001 to
0.0005 milligrams per kilogram (mg/kg) body weight per day translated to a drinking water
equivalent level of 4 ppb-18 ppb. EPA takes the RfD into account when setting a drinking water
standard; it also considers costs, the capabilities of monitoring and treatment technologies, and
other sources of perchlorate exposure, such as food.
EPA’s 1999 draft risk characterization resulted in a human risk benchmark of 0.0009 mg/kg per
day (with a 100-fold uncertainty factor), which converted to a drinking water equivalent level of
32 ppb. However, EPA determined that the available health effects and toxicity database was
inadequate for risk assessment. In 1999, EPA issued an Interim Assessment Guidance for
Perchlorate, which recommended that EPA risk managers use the earlier reference dose range and
drinking water equivalent level (DWEL) of 4-18 ppb for perchlorate-related assessment activities
at hazardous waste sites.
In 2002, EPA prepared a draft risk assessment that concluded that the potential human health risks
of perchlorate exposures include effects on the developing nervous system and thyroid tumors,
based on rat studies that observed benign tumors and adverse effects in fetal brain development.
The document included a draft RfD of 0.00003 mg/kg per day, which translated to a drinking
water equivalent level of 1 ppb. This document was controversial, both for its implications for
cleanup costs and for science policy reasons. (For example, some peer reviewers expressed
concern over EPA’s risk assessment methodology and reliance on rat studies.) DOD, water
suppliers, and other commentors expressed concern that the draft RfD could lead to unnecessarily
stringent and costly cleanups of perchlorate releases at federal facilities and in water supplies. In
2002, a federal interagency perchlorate working group convened to discuss perchlorate risk
assessment, research and regulatory issues, and related agency concerns. Working group members
included DOD, EPA, the Department of Energy, the National Aeronautics and Space
Administration, the Office of Science and Technology Policy, the Council on Environmental
Quality, and the Office of Management and Budget.
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NRC Perchlorate Study
To resolve some of the uncertainty and debate over perchlorate’s health effects and the 2002 draft
risk assessment, the interagency working group asked the National Research Council (NRC) to
review the available science for perchlorate and EPA’s draft assessment. The NRC was asked to
comment and make recommendations. The NRC Committee to Assess the Health Implications of
Perchlorate Ingestion issued its review in January 2005 and suggested several changes to EPA’s
draft risk assessment. The committee concluded that because of key differences between rats and
humans, studies in rats were of limited use for quantitatively assessing human health risk
associated with perchlorate exposure. Although the committee agreed that thyroid tumors found
in a few rats were likely perchlorate treatment-related, it concluded that perchlorate exposure is
unlikely to lead to thyroid tumors in humans. The committee noted that, unlike rats, humans have
multiple mechanisms to compensate for iodide deficiency and thyroid disorders. Also, the NRC
found flaws in the design and methods used in the rat studies. The committee concluded that the
animal data selected by EPA should not be used as the basis of the risk assessment.
The committee also reviewed EPA’s risk assessment model. It agreed that EPA’s model for
perchlorate toxicity represented a possible early sequence of events after exposure, but it did not
think that the model accurately represented possible outcomes after changes in thyroid hormone
production. Further, the committee disagreed with EPA’s definition of a change in thyroid
hormone level as an adverse effect. Rather, the NRC defined transient changes in serum thyroid
hormone as biochemical events that might precede adverse effects, and identified hypothyroidism
as the first adverse effect.
Because of research gaps regarding perchlorate’s potential effects following changes in thyroid
hormone production, the committee made the recommendation that EPA use a nonadverse effect
(i.e., the inhibition of iodide uptake by the thyroid in humans) rather than an adverse effect as the
basis for the risk assessment. The committee explained that “[i]nhibition of iodide uptake is a
more reliable and valid measure, it has been unequivocally demonstrated in humans exposed to
perchlorate, and it is the key event that precedes all thyroid-mediated effects of perchlorate
exposure.”7 Based on the use of this point of departure, the reliance on human studies, and the use
of an uncertainty factor of 10 (for intraspecies differences), the NRC’s recommendations led to an
RfD of 0.0007 mg/kg per day. The committee concluded that this RfD should protect the most
sensitive population (i.e., the fetuses of pregnant women who might have hypothyroidism or
iodide deficiency) and noted that the RfD was supported by clinical studies, occupational and
environmental epidemiologic studies, and studies of long-term perchlorate administration to
patients with hyperthyroidism. In addition, the NRC identified data gaps and research needs. The
committee has received some criticism for the extent to which it relied on a small, short-term
human study, and debate over perchlorate’s health risks has continued.
EPA’s Response and Subsequent Actions
In 2005, EPA adopted the NRC recommended reference dose of 0.0007 mg/kg per day, which
translates to a drinking water equivalent level of 24.5 ppb. The DWEL is the concentration of a
contaminant in water that is expected to have no adverse effects; it is intended to include a margin
7 National Research Council, Health Implications of Perchlorate Ingestion, Committee to Assess the Health
Implications of Perchlorate Ingestion, National Academy of Sciences, 2005, p. 9.
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Perchlorate Contamination of Drinking Water: Regulatory Issues and Legislative Actions
of safety to protect the fetuses of pregnant women who might have a preexisting thyroid
condition or insufficient iodide intake. Notably, EPA based the DWEL on the assumption that all
exposure would come from drinking water. If EPA were to develop a drinking water standard for
perchlorate, it would lower the DWEL to account for other sources of exposure, particularly food.
In January 2006, EPA’s Superfund office issued guidance adopting the NRC reference dose and
the DWEL of 24.5 ppb as the recommended value to be considered as the preliminary
remediation goal (PRG) to guide perchlorate assessment and cleanup at Superfund sites. In
March, EPA’s Children’s Health Protection Advisory Committee (CHPAC) wrote to the EPA
Administrator that the PRG did not protect infants, who are highly susceptible to
neurodevelopmental toxicity and may be more exposed than fetuses to perchlorate. The CHPAC
noted that perchlorate is concentrated in breast milk and that nursing infants could receive daily
doses greater than the RfD if the mother is exposed to 24.5 ppb perchlorate in tap water. The
committee recommended that the Superfund office lower the PRG and that the Office of Water
develop a standard for perchlorate and, in the interim, issue a drinking water health advisory that
takes into account early life exposures.
In October 2008, EPA announced a preliminary determination not to regulate perchlorate, noting
that less than 1% of water systems have perchlorate levels above the health reference level. EPA
concluded that perchlorate failed to meet two of SDWA’s regulatory criteria (i.e., that a
contaminant occur frequently at levels of health concern, and that establishing a national drinking
water standard would provide a “meaningful opportunity for health risk reduction”). In response,
EPA’s Science Advisory Board’s (SAB’s) Drinking Water Committee argued that, given
perchlorate’s occurrence and well-documented toxicity, EPA must have a compelling basis to
support a determination not to regulate. The SAB requested more time to review the new model
EPA relied on, and to comment on the preliminary determination.
On January 8, 2009, EPA announced that it would seek further advice from the NRC before
making a final determination on whether or not to set a drinking water standard for perchlorate.
EPA also announced that it was replacing the perchlorate preliminary remediation goal of 24.5
ppb with an interim health advisory, which contains a value of 15 ppb.8 Health advisories are
nonregulatory, but can be useful to state and local officials in addressing drinking water
contamination and making cleanup decisions for Superfund sites. EPA based the 15 ppb level on
the reference dose recommended by the NRC. The agency explained that it calculated the
advisory level to protect the most sensitive population that was identified by the NRC perchlorate
committee (the fetuses of pregnant women), and took into account exposures from food as well as
water. This approach does not appear to address a key concern of EPA’s Children’s Health
Protection Advisory Committee which identified nursing infants as potentially more exposed than
fetuses. The evaluation of impacts to infants and young children is one of the scientific issues that
EPA wanted the NRC to evaluate. EPA also was considering asking the NRC to evaluate recent
studies, EPA’s use of models, and its derivation of the 15 ppb health reference level.
In August 2009, the EPA Administrator announced that the agency would reevaluate the science
regarding perchlorate’s potential health effects, with particular emphasis on evaluating the effects
of perchlorate exposure on infants and young children. The agency determined not to ask the
8 Health advisories establish nonenforceable concentrations of contaminants in drinking water at which no adverse
health effects are expected to occur over specific timeframes. Advisories include information on health effects,
occurrence, exposure, monitoring methods, and treatment technologies. EPA’s Interim Drinking Water Health
Advisory for Perchlorate is available at, http://www.epa.gov/safewater/contaminants/unregulated/perchlorate.html.
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NRC to conduct further review of issues related to perchlorate, having concluded that additional
NRC review would unnecessarily delay the regulatory decision-making process. Instead, EPA
published a Supplemental Request for Comments notice in the Federal Register, seeking public
comment on additional ways to analyze data related to the regulatory determination for
perchlorate. EPA noted its intent to consider a broader range of alternatives for interpreting the
available data on the level of health concern, the frequency of occurrence of perchlorate in
drinking water, and the opportunity for health risk reduction through a national drinking water
standard. EPA is reevaluating perchlorate exposure to sensitive life stages including infants and
developing children, expanding the previous emphasis on pregnant women and their developing
fetuses as the most sensitive subpopulations. EPA intends to take public comments into account
before making a final regulatory determination. The agency’s announcement noted that the final
decision may be a determination to regulate.9
DOD Perchlorate Actions
DOD is responsible for some large releases of perchlorate into the environment and has allotted
significant resources to address this problem. DOD has spent more than $114 million on research
activities regarding perchlorate treatment technologies, detection methods, toxicity studies, and
substitutes. Additional funds have been spent on cleanup.
Although remediation has proceeded at some sites, cleanups typically are driven by drinking
water standards or other established cleanup standards. With no federal standard, cleanup goals
and responsibilities have been ambiguous outside of California and Massachusetts where
standards have been set. In 2006, after EPA established a DWEL for perchlorate and issued
cleanup guidance based on the DWEL, DOD adopted a policy setting 24 ppb as the level of
concern to be used in managing perchlorate releases (unless a more stringent federal or state
standard exists. The policy applies broadly to DOD installations and former military lands, and
directs the services to test for perchlorate when it is reasonably expected that a release has
occurred. Under the policy, if perchlorate levels exceed 24 ppb, a site-specific risk assessment
must be conducted; if the assessment indicates that the perchlorate could result in adverse health
effects, then the site must be prioritized for risk management. DOD uses a relative risk site
evaluation framework to help prioritize environmental restoration work and to allocate resources
among sites.10 EPA has withdrawn the 2006 perchlorate remediation guidance and recommends
that its Regional offices now consider using the interim health advisory level of 15 ppb for
cleanup. The DOD may follow suit and adopt the new level for managing perchlorate releases.
Legislative Actions
Several perchlorate bills were considered, but none were enacted during the 110th Congress.
Responding to EPA’s 2007 decision not to require further monitoring for perchlorate as an
unregulated contaminant, S. 24 was introduced to require community water systems to test for
perchlorate and disclose its presence in annual consumer reports. S. 150 and H.R. 1747 would
9 For more information see EPA’s perchlorate website, http://www.epa.gov/safewater/contaminants/unregulated/
perchlorate.html.
10 Links to Department of Defense perchlorate information, policies, and other resources are available through
http://www.epa.gov/fedfac/documents/perchlorate_links.htm#state_adv.
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have required EPA to set a standard for perchlorate. The Senate Environment and Public Works
Committee reported S. 24 (S.Rept. 110-483) and S. 150 (S.Rept. 110-484). Additionally,
H.Con.Res. 347 expressed the sense of Congress that the CDC and FDA should take action to
educate the public on the importance of adequate iodine intake. (Iodine is protective against
perchlorate exposure.)
In the 111th Congress, legislation has been introduced concerning regulation of perchlorate under
the Safe Drinking Water Act and the cleanup of perchlorate contamination of ground water and
public drinking water supplies. H.R. 3206 would require EPA to propose a drinking water
regulation for perchlorate within 12 months of enactment of the legislation, and to promulgate a
final regulation no later than 18 months after publishing the proposed rule. The report
accompanying the House-passed Department of Defense Appropriations Act, 2010 (H.R. 3326,
H.Rept. 111-230), includes $2 million for the cleanup of perchlorate contaminated wells. H.R.
102 would authorize additional appropriations for the San Gabriel Basin Restoration Fund, and
would establish a 35% non-federal matching requirement for the recipient water districts after a
specified amount of federal funds had been appropriated.
Author Contact Information
Mary Tiemann
Specialist in Environmental Policy
mtiemann@crs.loc.gov, 7-5937
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