Order Code RS21961
Updated November 9, 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 also occurs naturally and is present in some organic fertilizer.
This soluble, persistent compound has been detected in numerous drinking water
supplies, especially in California. 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. EPA has not determined whether
to regulate perchlorate and has cited the need for more research on health effects and
water treatment techniques. Related issues involve environmental cleanup and water
treatment costs, as both are driven by federal and state standards. (California and
Massachusetts have set 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 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. However, new studies raise more
concerns about potential health risks of low-level exposures, particularly for infants in
certain cases. H.R. 1747, which would direct EPA to set a standard within 30 months,
was forwarded to the full Committee on Energy and Commerce on November 8, 2007.
This report reviews perchlorate water contamination issues and recent 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 exposure 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
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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 October 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 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, road flares, 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 10
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,
for several years it was 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, 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 some 3,700 water systems tested, perchlorate was detected in 153 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. Most
perchlorate releases have been identified in California, and perchlorate has been detected
more than once in 241 active and standby sources of drinking water since November
2002. In 2005, EPA reported perchlorate contamination at 65 DOD facilities, seven other
federal facilities, and 37 private sites.3 All sampling results combined (public and private
drinking water wells, groundwater monitoring wells, surface water, and soil), the
Government Accountability Office reported that perchlorate has been found at 395 sites.4
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,
November 21, 2006, pp. 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.
2 A key, but diminished, source of perchlorate in the Colorado River has been a old perchlorate
production facility in Nevada. Since 1997, Nevada and EPA have worked with the facility 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., March
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, pp. 29-44.
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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
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 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 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.6 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.7
EPA Regulation of Perchlorate
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)(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) 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, 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. EPA recently determined that it
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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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
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 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, 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 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 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 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.
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
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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 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, 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 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, 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 does not protect infants, who are
highly susceptible to neurodevelopmental toxicity and may be more exposed to
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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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.
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, 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, 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. This framework is used to help
prioritize environmental restoration work and to allocate resources among sites.
Congressional Actions
The 109th Congress targeted some funding for perchlorate cleanup in California (see
conference reports for P.L. 109-148 and P.L. 109-54). 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.
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 community water systems to test for perchlorate and disclose its
presence in annual consumer reports. S. 150 and H.R. 1747 would require EPA to
establish a drinking water standard for perchlorate.
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].