Order Code RS21961
Updated January 10, 2007
Perchlorate Contamination of Drinking Water:
Regulatory Issues and Legislative Actions
Mary Tiemann
Specialist in Environmental Policy
Resources, Science, and Industry Division
Summary
Perchlorate is the explosive component of solid rocket fuel, fireworks, road flares,
and other products. Used mainly by the Department of Defense (DOD) and related
industries, perchlorate occurs naturally and is present in some organic fertilizer. This
soluble, persistent compound has been detected in sources of drinking water for more
than 11 million people. It also has been found in milk, fruits, and vegetables. Concern
over the potential health risks of perchlorate exposure has increased, and some states
and Members of Congress have urged the Environmental Protection Agency (EPA) to
set a drinking water standard for perchlorate. The EPA has not determined whether to
regulate perchlorate in drinking water and has cited the need for more research on health
effects, water treatment techniques, and occurrence. Related issues have involved
environmental cleanup and water treatment costs, which will be driven by federal and
state standards. 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 the EPA’s risk analyses. In 2005, the NRC issued its
report, and the EPA adopted the NRC’s recommended reference dose (i.e., the expected
safe dose) for perchlorate exposure. However, new studies raise more concerns about
potential health risks of low-level exposures, particularly for infants. Perchlorate
legislation in the 110th Congress includes S. 150, which requires EPA to set a standard.
This report reviews perchlorate contamination issues and related developments.
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 has slowed efforts to
establish drinking water and environmental cleanup standards for it. 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 [:g/L]) in
2006, and California has proposed a 6 ppb standard. Several states have issued health

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goals or advisory levels ranging from 1 ppb in Maryland (advisory level) and New
Mexico (drinking water screening level) to 51 ppb in Texas (industrial cleanup level).
Occurrence. Perchlorate has been used heavily by the Department of Defense
(DOD) and its contractors, and perchlorate contamination of water has been found most
often near weapons and rocket fuel manufacturing facilities and disposal sites, research
facilities, and military bases. Fireworks and other manufacturing facilities and
construction sites also have been sources of contamination. Perchlorate also occurs
naturally (in West Texas, for example) and is present in organic fertilizer imported from
Chile.1 In 1997, a new test method lowered the detection limit for perchlorate in drinking
water from 400 parts per billion to 4 ppb, prompting several states to begin testing.
Within two years, perchlorate was detected in drinking water sources for more than 11
million people in the Southwest and in surface and ground water in scattered locations
across the country. Contamination has been found most often in ground water; however,
it has been detected at low levels in the Colorado River, a major source of drinking water
and irrigation water for Arizona, California, and Nevada.2 Perchlorate also has been
detected in dairy milk in various states, especially California and Texas.
In 1999, the EPA required public 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. The rule required monitoring by all
water systems serving more than 10,000 persons and by a representative sample of smaller
systems. Of some 3,700 water systems tested, perchlorate was detected in 153 systems
in 26 states and 2 commonwealths.3 Of those 153 systems, 14 had perchlorate levels
above EPA’s reference dose of 24.5 ppb.4 The EPA also reported perchlorate
contamination at 65 DOD facilities, 7 other federal facilities, and 37 private sites. In
California, where most perchlorate releases have been identified, perchlorate has been
detected at least twice in 276 sources of drinking water that supply 77 water systems.
Monitoring also has been undertaken 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
1 Purnendu K. Dasgupta, et al., “Perchlorate in the United States: Analysis of Relative Source
Contributions to the Food Chain,” Environmental Science and Technology, v. 40, n. 21, Nov. 21,
2006, p. 6608-6614. This study suggests that although Chilean fertilizer is a much smaller source
of perchlorate than oxidizers, the fertilizer may have a proportionally greater impact as a source
of perchlorate in the food chain because it is applied directly to crop land. This article reports
that processing methods have reduced the perchlorate content of Chilean fertilizer in recent years.
2 A key source of perchlorate in the Colorado River has been a facility in Nevada, where
perchlorate production began in 1951. Since 1997, Nevada and the EPA have worked with Kerr
McGee to control the source of releases. From January 2004 through June 2005, only three of
the monthly samples had detectable levels of perchlorate. U.S. EPA, Region 9, Perchlorate
Monitoring Results: Henderson, Nevada to the Lower Colorado River, June 2005.
3 EPA, Federal Facilities Restoration and Reuse, Known Perchlorate Releases in the U.S., Mar.
25, 2005, at [http://www.epa.gov/fedfac/documents/perchlorate_links.htm#occurrences].
4 U.S. Government Accountability Office, Perchlorate: A System to Track Sampling and Cleanup
Results is Needed, GAO-05-462, May 2005, p. 3.

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lettuce samples (average levels ranged from 11.9 ppb to 7.7 ppb for lettuces in four
states), and in 101 of 104 bottled milk samples (with an average level of 5.7 ppb across
14 states). 5 This research is relevant to the EPA’s standard-setting efforts, as EPA would
take into account other exposures to perchlorate when setting a drinking water standard.
Health Effects. Perchlorate 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 infants and can
result in delayed development and decreased learning capability. Several human studies
have indicated that thyroid changes occur in humans at significantly higher concentrations
of perchlorate than the amounts typically observed in water supplies.6 However, a new
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.7
EPA Regulation of Perchlorate
The EPA has taken steps toward establishing a standard for perchlorate in drinking
water but has not made a determination to regulate it. Under the Safe Drinking Water Act
(SDWA, §1412(b)), the EPA must establish a standard for a contaminant if the
Administrator determines that it occurs at a frequency and level of public health concern
and that its regulation presents a meaningful opportunity for reducing health risks. In
1997, when a better detection method became available for perchlorate and detections
increased, scientific information was limited. In 1998, the 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.
The EPA listed perchlorate as a priority for further research on health effects and
treatment technologies and for collecting occurrence data. In 1999, the 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. The EPA recently determined that it had collected sufficient data and that
further monitoring was not needed (72 Federal Register 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
5 The FDA test results are available online at [http://www.cfsan.fda.gov/~dms/clo4data.html].
6 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.
7 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, October 2006.

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cause any adverse, non-cancer health effects during a lifetime. In developing an RfD, the
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. The 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.
The EPA continued to assess perchlorate risks, and its 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, the EPA determined that the available health effects and toxicity database was
inadequate for risk assessment. In 1999, the 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, the EPA completed 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 the EPA’s risk
assessment methodology and reliance on rat studies.) The 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 the DOD, the 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.
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 are 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 the
EPA should not be used as the basis of the risk assessment.

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The committee also reviewed the EPA’s risk assessment model. It agreed that the
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 the
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 unusual 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.”8 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.9 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 continues.
EPA’s Response. In 2005, the 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 of safety to protect the fetuses
of pregnant women who might have a preexisting thyroid condition or insufficient iodide
intake. The DWEL is based on the assumption that all exposure would come from
drinking water. If the EPA were to develop a drinking water standard for perchlorate, it
would adjust the DWEL to account for other sources of exposure, such as food.
In January 2006, the 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, the EPA’s Children’s Health Protection Advisory Committee
(CHPAC) wrote to the EPA Administrator that the PRG does not protect infants, who are
highly susceptible to neurodevelopmental toxicity and may be more exposed to
perchlorate than fetuses. 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 drinking water
8 National Research Council, Health Implications of Perchlorate Ingestion, Committee to Assess
the Health Implications of Perchlorate Ingestion, National Academy of Sciences, 2005, p. 9.
9 Ibid., p. 10.

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standard for perchlorate and, in the interim, issue a drinking water health advisory that
takes into account early life exposures. CHPAC’s assessment, combined with the new
CDC study and ongoing data gaps, could further complicate EPA regulatory efforts.
Department of Defense
The DOD has the largest number of identified sites with perchlorate contamination
and has allotted significant resources to address this problem. Through FY2006, the DOD
had spent roughly $88 million on perchlorate-related research activities, including $64
million on treatment technologies, $9.5 million on health and toxicity studies, and $11.6
million on pollution prevention. Additional funds have been spent on testing and 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
and just one promulgated state standard, cleanup goals and responsibilities have been
ambiguous. In January 2006, following EPA’s establishment of a reference dose and
DWEL for perchlorate, the DOD adopted a policy that establishes 24 ppb as the level of
concern to be used in managing perchlorate releases, unless a more stringent federal or
state standard has been promulgated. The policy applies broadly to DOD installations and
former military lands. The policy directs the services to test for perchlorate when it is
reasonably expected that a release has occurred. 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.10 The DOD uses a relative risk site evaluation framework across DOD to
evaluate the risks posed by one site relative to other sites. The DOD uses this framework
to help prioritize environmental restoration work and to allocate resources.
Congressional Actions
The 109th Congress targeted some funding for perchlorate cleanup in conference
reports for various appropriations acts, including DOD and EPA appropriations acts for
FY2006 (P.L. 109-148 and P.L. 109-54, respectively). In the conference report for the
Department of Health and Human Services FY2006 appropriations act (P.L. 109-149),
conferees encouraged support for studies on the long-term effects of perchlorate exposure.
The conference report for the FDA’s FY2006 funding act (P.L. 109-97) directed the FDA
to continue conducting surveys of perchlorate in food and to report to Congress. An array
of bills addressed cleanup of perchlorate-contaminated water in California. The House
passed two such bills, H.R. 186 and H.R. 18, but no action occurred in the Senate. Other
bills called for EPA to issue a standard for perchlorate in drinking water.
In the 110th Congress, perchlorate is back on the agenda. Responding to the EPA
decision to not require further monitoring for perchlorate as an unregulated contaminant,
S. 24 would require water systems to test for perchlorate and disclose its presence in
annual consumer confidence reports. S. 150 would direct the EPA to issue a perchlorate
health advisory within 90 days of enactment and to establish a drinking water standard by
December 31, 2007.
10 For more information, see the DOD perchlorate website regarding policy and guidance,
[http://www.denix.osd.mil/denix/Public/Library/MERIT/Perchlorate/efforts/policy/index.html].

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