Order Code RS21961
Updated November 29, 2006
CRS Report for Congress
Received through the CRS Web
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 also occurs naturally and is present in organic nitrate fertilizer
from Chile. This very soluble, persistent compound has been disposed of in the ground
for decades and has been detected in sources of drinking water for more than 11 million
people. It also has been found in milk, fruits, grains and vegetables. Thus, concern has
increased about the potential health risks from perchlorate exposure. The Environmental
Protection Agency’s (EPA’s) effort to make a determination whether to regulate
perchlorate in drinking water has been slowed by uncertainties regarding the health
effects of exposure at low levels and by the need for further research on occurrence and
treatment technologies. Related issues include environmental cleanup and water
treatment costs, which will be driven by federal and state standards. Because of
scientific uncertainties and interagency disagreement regarding the risks of perchlorate
exposure, several federal agencies asked the National Research Council (NRC) to assess
perchlorate’s health effects and the EPA’s draft risk assessment. The NRC issued its
report in January 2005, and the EPA has adopted the NRC’s recommended reference
dose (i.e., the expected safe dose) for perchlorate exposure. The reference dose provides
a basis for developing a standard; however, the EPA has not decided to regulate
perchlorate, and new studies raise more questions about what level of exposure might
be safe. This report reviews perchlorate water contamination issues and related 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 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
Congressional Research Service ˜ The Library of Congress

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2006, and California has proposed a 6 ppb standard. 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 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
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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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 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,
but 36% of the women in this large study were found to be iodine deficient.7 The median
level of urinary perchlorate measured in 1,111 women in the study was 2.9 ppb.
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 the contaminant 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 as a priority for collecting occurrence data.
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, 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
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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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 standing 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.
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

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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
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.
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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Department of Defense
Having the largest number of identified sites with perchlorate contamination, the
DoD has been under state and congressional pressure to address perchlorate releases.
Cleanup has proceeded at some sites; however, 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. (In Massachusetts, for example, the drinking water standard of 2
ppb would apply). The new policy applies broadly to DoD installations and former
military lands, and under it, the services are directed 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, and 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 accordingly.
The DoD has tested at least 800 sites at 101 facilities. 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.
Congressional Actions
The 109th Congress has 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 the National Institute for Environmental Health Sciences to support
studies on the long-term health effects of perchlorate. The conference report for the
FDA’s FY2006 funding act (P.L. 109-97) directs the FDA to continue conducting
perchlorate surveys of food and bottled water and to report back to Congress. An array of
bills focus on California, where most contamination has been found. The House has
passed two bills to address perchlorate contaminated groundwater in California: H.R. 186
would authorize the Secretary of the Interior to make grants to the Santa Clara Valley
Water District for groundwater remediation projects, and H.R. 18 would authorize such
grants for water authorities within the Santa Anna River watershed. H.R. 3053 also
would authorize funding for perchlorate remediation in Santa Clarita. H.R. 4798 and S.
2298 would authorize appropriations for a California Perchlorate Cleanup Fund to provide
grants for remediating perchlorate contaminated drinking water sources and supplies;
these bills also express the sense of Congress that the EPA should establish a drinking
water standard for perchlorate. H.R. 213 would require the EPA to issue a perchlorate
drinking water standard in 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].