Order Code RS21961
Updated June 15, 2005
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 main ingredient of solid rocket fuel and has been used mainly by
the Department of Defense (DOD), the National Aeronautics and Space Administration
(NASA), and related industries. This highly soluble and persistent compound has been
disposed of on the ground for decades, and now has been detected in sources of drinking
water for more than 11 million people. It also has been found in milk and vegetables.
Thus, concern has grown regarding the potential health risks of exposure to perchlorate.
The Environmental Protection Agency’s (EPA’s) efforts to make a determination
whether to regulate perchlorate in drinking water have been slowed by uncertainties
regarding the health effects of exposure at low levels, and because of the need for more
research on water treatment technologies. Related issues involve environmental cleanup
and water treatment costs, which will depend on the level at which a standard is set.
Because of scientific uncertainties and interagency disagreement over the risks of
perchlorate, several federal agencies asked the National Research Council (NRC) of the
National Academy of Sciences to assess perchlorate’s health effects and EPA’s draft risk
assessment. The NRC issued its report in January 2005, and on February 18, EPA
adopted the NRC’s recommended safe level, or reference dose, for perchlorate exposure.
This report reviews perchlorate issues and will be updated to reflect developments.
Background
Ammonium perchlorate is widely used in solid propellant for rockets and missiles,
and other perchlorate salts are used to manufacture various products including fireworks,
air bags, and road flares. Uncertainty over perchlorate’s health effects has slowed federal
and state efforts to establish drinking water standards and environmental cleanup
standards for this compound. However, given perchlorate’s persistence in water, concern
has escalated with its detection in the groundwater or surface water in 33 states. No
federal or state drinking water standard has been established for perchlorate, but efforts
are underway, and several states have issued public health goals or advisory levels.
Congressional Research Service ˜ The Library of Congress
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Occurrence. Perchlorate has been used heavily by DOD and its contractors, and
perchlorate contamination of ground and surface water has been found most often near
weapons and rocket fuel manufacturing facilities and disposal sites, research facilities,
and military bases.1 Fireworks and other manufacturing facilities and construction sites
also have been sources of contamination. Regulators were aware of contamination in
California and Nevada in the 1980s; however, before 1997, perchlorate could not be
detected at concentrations below 400 parts per billion (ppb). In 1997, the California
Department of Health Services developed a new analytical method for monitoring
perchlorate that lowered the detection limit to 4 ppb. This development prompted several
states to test for perchlorate. Within two years, perchlorate had been detected in drinking
water sources for more than 11 million people in the Southwest and in surface or ground
water in scattered locations across the United States.2 The contamination has most often
been found in wells; however, perchlorate has been detected at low levels in the Colorado
River, which is a major source of drinking water and irrigation water in California,
Nevada, and Arizona.3 Perchlorate also has been detected in dairy milk in several states,
especially California and Texas, and one source of this perchlorate is thought to have been
the water used to irrigate the alfalfa crops that were consumed by dairy cows. Perchlorate
also occurs naturally, as it does in West Texas, and it is present in organic fertilizer from
Chile, which has been used on organic crops.
In 1999, EPA required drinking water monitoring for perchlorate under the
Unregulated Contaminant Monitoring Rule (UCMR) to determine the frequency and
levels at which perchlorate is present in public water supplies nationwide. The regulation
required monitoring by all water systems serving more than 10,000 persons and by a
representative sample of smaller systems. In 2004, EPA reported that perchlorate had been
detected in public water systems in 24 states and Puerto Rico.4 The agency also reported
perchlorate contamination at 65 DOD facilities, 7 other federal facilities, and 37 private
sites. In sampling done by California water systems, perchlorate has been detected in 379
sources of drinking water that supply 96 public water systems.5 A recent American Water
Works Association perchlorate study found the compound in 26 states and Puerto Rico.
1 U.S. Army Center for Health Promotion and Preventive Medicine, Directorate of Environmental
Health Engineering, Perchlorate in Drinking Water, Aberdeen Proving Ground, MD. This
document notes that perchlorate has a short shelf life as an effective propellant and must be
replaced periodically within the DOD’s missile and rocket inventory. Also, the detonation of
rockets, missiles, and fireworks leaves residual perchlorate in the affected areas.
2 U.S. Environmental Protection Agency, Region 9 Perchlorate Update, June 1999, p. 1.
3 A key source of perchlorate in the Colorado River has been the Kerr McGee Chemical Plant in
Nevada, where perchlorate production began in 1951. Since 1997, the state of Nevada and the
U.S. EPA have worked with Kerr McGee to control the source of perchlorate releases. Since
2002, perchlorate has been below 6 ppb. In 2004, 9 of 12 monthly samples had non-detectable
(i.e., less than 4 ppb) levels of perchlorate. U.S. Environmental Protection Agency, Region 9,
Perchlorate Monitoring Results: Henderson, Nevada to the Lower Colorado River, Dec. 2004.
4 U.S. Environmental Protection Agency, Federal Facilities Restoration and Reuse: Known
Perchlorate Releases in the U.S. -Sept. 23, 2004, available at [http://www.epa.gov/fedfac/
documents/perchlorate_links.htm#occurrences], visited June 14, 2005.
5 California Department of Health Services, Perchlorate in California Drinking Water:
Monitoring Update, December 7, 2004. For detailed monitoring results, see [http://dhs.ca.gov/ps/
ddwem/chemicals/perchl/monitoringupdate.htm], visited June 14, 2005.
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Health Effects. Perchlorate is known to disrupt the uptake of iodine in the thyroid,
and health effects associated with perchlorate exposure are expected to be similar to those
caused by iodine deficiency.6 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. Various human studies
indicate that thyroid changes occur in humans at significantly higher concentrations of
perchlorate than the amounts typically observed in water supplies.7 Studies have not
directly measured the impact of perchlorate on human metabolism and growth. (Health
effects studies are discussed further in section below on EPA regulation of perchlorate.)
Federal Responses to Perchlorate Contamination
Various federal, state, tribal, and local government agencies have been examining
issues related to perchlorate contamination for nearly a decade. A federal interagency
perchlorate working group was convened in 2002, to discuss perchlorate risk assessment,
research, and regulatory issues. Members of this group include DOD; NASA; EPA; the
Department of Energy; and, within the Executive Office of the President, the Office of
Science and Technology Policy, the Council on Environmental Quality, and the Office of
Management and Budget. DOD, EPA, and the Food and Drug Administration are among
the federal agencies that have been assessing perchlorate contamination and occurrence.
Department of Defense. The DOD, which has the greatest number of identified
sites with perchlorate contamination, has spent $26 million on developing and testing
perchlorate treatment technologies and is funding several more demonstration projects
during FY2005. Perchlorate cleanup is proceeding at several sites; however, DOD’s
general policy is to remediate sites to meet drinking water standards. In the absence of
a perchlorate standard, this approach has been problematic for communities that are
experiencing perchlorate contamination of their water supplies.
In September 2003, the DOD adopted a perchlorate sampling policy that includes
sampling on Base Realignment and Closure (BRAC) properties. However, DOD was
criticized by Members of Congress, communities, and states for not evaluating other DOD
sites. In October 2004, DOD and the California EPA adopted a procedure for prioritizing
perchlorate sampling efforts at DOD facilities in California. The procedure document is
intended to provide guidance on the steps that the state and DOD will take to identify and
prioritize the investigation of areas on military sites where perchlorate has likely been
6 California Environmental Protection Agency, Office of Environmental Health Hazard
Assessment, Public Health Goal for Perchlorate, March 2004, pp. 1-2. In March 2004,
California published a final public health goal (PHG) of 6 ppb for perchlorate. A PHG is set at
a level determined to pose no significant risk to individuals, including sensitive groups (i.e.,
infants, pregnant women, and individuals with iodine deficiency). California officials will use
the public health goal to establish an enforceable drinking water standard, which must be set as
close to the goal as is economically and technologically feasible.
7 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.
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released near drinking water sources. DOD has stated that it will characterize and respond
to identified problems under its existing environmental response programs.
A key issue for DOD concerns the potential perchlorate cleanup cost, which will
depend largely on any standards set by EPA and/or a state. This is because federal and
state drinking water standards are used as cleanup standards, specifically at Superfund
sites, but in other cases as well. Similarly, public water suppliers that will have to treat
their water to meet federal and state drinking water standards are interested in seeing that
a standard is set at a level that assures public health protection, but is not so strict that
added costs would be incurred without providing any further public health benefits.
EPA Regulation of Perchlorate. EPA has taken steps toward establishing a
drinking water standard for perchlorate, but has not yet made a determination to regulate
perchlorate. In 1997, when a better detection method became available for perchlorate
and water monitoring increased, scientific information for perchlorate was extremely
limited. In 1998, EPA placed perchlorate on the list of contaminants that are candidates
for regulation, but concluded that information was insufficient at that time to make a
determination as to whether perchlorate should be regulated under the Safe Drinking
Water Act (SDWA). The agency 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 that would be expected to protect against
any health threats. An RfD is an estimate (with uncertainty spanning perhaps an order of
magnitude) of a daily oral exposure that is likely to be without appreciable risk of adverse
non-cancer 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 resulting draft RfD range of 0.0001 to 0.0005 milligrams per kilogram
(mg/kg) body weight per day would be equivalent to a drinking water level of 4 ppb-18
ppb. EPA takes the RfD into consideration when setting a drinking water standard. The
agency also must consider cost, 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 would convert 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 assessors and risk managers use the standing reference
dose range of 4-18 ppb for perchlorate-related assessment activities.
In 2002, EPA completed a draft risk assessment for perchlorate that concluded that
the potential human health risks of perchlorate exposures include effects on the
developing nervous systems 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 draft document has been controversial, both for its implications for cleanup costs and
for science policy reasons. For example, comments from some expert peer reviewers and
stakeholders expressed concern about EPA’s use of a new risk assessment approach, and
the selection of certain rat studies as the basis for conducting the risk assessment.
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In 2003, EPA affirmed the 1999 Interim Guidance that recommended continuing the
use of the 1992 and 1995 draft reference doses for perchlorate assessment activities.
Based on this RfD range (0.0001 to 0.0005 mg/kg per day), clean-up levels range from
4 ppb to 18 ppb. The 1999 guidance remains the applicable guidance, until replaced by
new guidance that will be based on the finalized risk assessment and new RfD.
NRC Perchlorate Study. In an effort to resolve some of the uncertainty and
debate over perchlorate’s health effects and EPA’s 2002 assessment, the interagency
perchlorate working group asked the National Research Council (NRC) to review the
science for perchlorate and EPA’s draft risk 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. Based on its scientific findings,
this independent expert committee suggested several changes to EPA’s draft risk
assessment. The committee determined that, because of major 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, and that hypothyroidism occurs only if daily iodide
intake is less than about 10%-20% of average U.S. intake. 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 thought that EPA’s
model for perchlorate toxicity represented the possible early sequence of events after
exposure, but did not think that the model provided an accurate representation of possible
outcomes after changes in thyroid hormone production. Also, 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 conservative point of departure, the reliance on human studies, and the use of
an uncertainty factor of 10 (for intraspecies differences), the NRC’s recommendations
lead 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 is supported by clinical
8 National Research Council, Health Implications of Perchlorate Ingestion, Committee to Assess
the Health Implications of Perchlorate Ingestion, National Academy of Sciences, Jan. 2005, p.9.
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studies, occupational and environmental epidemiologic studies, and studies of long-term
perchlorate administration to patients with hyperthyroidism.9
In February, EPA adopted the NRC recommended reference dose, and the agency’s
Superfund office is revising its cleanup guidance to reflect this RfD. The RfD translates
to a drinking water equivalent level (DWEL) of 24.5 ppb. The DWEL is the concentration
of a contaminant in water that is expected to have no adverse effect; it includes a margin
of safety to protect the fetuses of pregnant women who might have a pre-existing thyroid
condition or insufficient iodide intake. It is based on the assumption that all exposure
would come from drinking water. Thus, if EPA were to develop a drinking water standard
for perchlorate, it would adjust the DWEL to account for other sources of exposure.
Food and Drug Administration. In 2004, FDA collected 500 samples of foods,
including various vegetables, milk, and bottled water, to determine the presence and
levels of perchlorate in food. Samples were taken in areas where water sources were
believed to be contaminated with perchlorate. The FDA found perchlorate in roughly
90% of lettuce samples (average levels ranged from 11.9 ppb to 7.7 ppb for different
lettuce types in 4 states), and in 101 of 104 milk samples collected at retail locations (with
an average level of 5.7 ppb across 14 states).10 Perchlorate was detected in two bottled
water samples at roughly 0.5 ppb. The FDA plans to analyze 750 samples this year.
FDA’s research is relevant to EPA’s standard-setting efforts, because EPA would take
into account exposures to perchlorate from food and other sources when establishing a
drinking water standard. Specifically, if other exposure sources are significant, EPA
would set a stricter standard to account for those exposures.
Congressional Actions
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; H.R. 18 would
authorize such grants for local water authorities within the Santa Anna River watershed.
H.R. 213 would require EPA to issue a perchlorate drinking water standard by July 2007.
The 108th Congress enacted several perchlorate-related provisions. The National
Defense Authorization Act for FY2004 (P.L. 108-136) required DOD to provide for a
health study on exposure to perchlorate in drinking water. The conference report for the
Military Construction Appropriations Act for FY2004 (P.L. 108-132) directed DOD to
submit a report identifying sources of perchlorate on BRAC properties and plans to
remediate these sites. (DOD submitted its report in July 2004.) The conference report
for the DOD FY2004 appropriations (P.L. 108-87) directed DOD to study perchlorate
contamination of groundwater in the Southwest. The National Defense Authorization Act
for FY2005 (P.L. 108-375) included a “Sense of Congress” that DOD should develop a
plan to remediate contamination, continue remediating sites that pose a serious health
threat, and evaluate sites in the absence of a drinking water standard. Congress also
funded perchlorate cleanup activities in several communities in appropriations acts.
9 Ibid. p. 10.
10 U.S. Food and Drug Administration, Exploratory Data on Perchlorate in Food, Nov. 2004.