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Perchlorate is a naturally occurring and manmade chemical. Naturally
occurring perchlorate, for example, is found in arid states in
southwestern United States (U.S.), as well as in nitrate fertilizer
deposits in Chile and potash ore found in U.S. and Canada. Perchlorate
can also form naturally in the atmosphere, leading to trace levels of
perchlorate in precipitation. Perchlorate is also an industrial
chemical that is used as an oxidizing agent in rocket propellant, in
fireworks and flares, and for other purposes. It has been detected in a
variety of foods and in drinking water from some locations in the U.S.
In order to work toward development of an assessment of the
potential risk of perchlorate, the Food and Drug Administration (FDA)
started an initial exploratory survey in 2004 and expanded the
exploratory survey in 2005 to better understand the occurrence and
levels of perchlorate in a variety of foods from various locations. In
2005 and 2006, FDA conducted Total Diet Study (TDS) surveys to obtain
perchlorate levels in TDS foods that are more comprehensive and
nationally representative (see Question 6). The levels of perchlorate
found in the foods are analyzed to better understand perchlorate
exposure from food and to support action, if warranted, to protect the
Based on the perchlorate data obtained from the exploratory and TDS
surveys, the estimated average perchlorate intakes by the U.S.
population were below the perchlorate reference dose (RfD) of 0.7
micrograms per kilogram body weight per day (µg/kg bw/day) recommended
by the National Academy of Sciences and adopted by the U.S.
Environmental Protection Agency (see questions 2, 8, and 13).
What are the effects of perchlorate on the human body?
Human exposure to high dosages (e.g., pharmacological) of
perchlorate can interfere with iodide uptake into the thyroid gland,
disrupting the functions of the thyroid and potentially leading to a
reduction in the production of thyroid hormone. In fact, perchlorate
has been used as a drug to treat hyperthyroidism (excess thyroid
hormone production) and to diagnose disorders related to thyroid or
iodine metabolism. In adults, the thyroid plays an important role in
regulating metabolism. In fetuses and infants, thyroid hormones are
critical for normal growth and development of the central nervous
system. Therefore, pregnant women and their fetuses and newborns have
the greatest potential for risk of adverse health effects following
exposure to perchlorate.
Perchlorate-induced changes in thyroid function have not been
demonstrated in studies of human groups intentionally exposed to levels
of perchlorate below the therapeutic range, even at doses as high as
500 microgram per kilogram body weight per day (µg/kg bw/day). However,
in a recent study by Blount
et al. (Environmental Health
Perspective 114:1865, 2006), the authors reported a statistically
significant association between perchlorate exposure and changes in
thyroid hormone levels in women with sub-optimal urine iodine levels
(less than 100 microgram per liter (µg/L)) that may indicate iodine
deficiency. The study analyzed cross-sectional data from the 2001-2002
National Health and Nutrition Examination Survey (NHANES) dataset.
Thirty-six percent of the women tested had less than 100 µg/L iodine in
their urine. Blount
et al. used the 100 µg/L cut-off based on the World Health Organization (WHO) definition of sufficient iodine status.
et al. have stated that the study should be affirmed
with another large population-based study that includes hundreds of
women with low iodine levels as a vulnerable population group. The
study will include measurement of other analytes that can be indicators
of thyroid function, in addition to free T4 and thyroid stimulating
Has a safe level for perchlorate in water and food been established?
In 2003, the Environmental Protection Agency (EPA), the
Department of Defense (DOD), the Department of Energy (DOE), and the National
Aeronautics and Space Administration (NASA) asked the National Academy of
Sciences (NAS) to review EPA's draft health assessment for perchlorate. In January 2005, the NAS Committee to
Assess the Health Implications of Perchlorate Ingestion released its study
report (see "Health Implications of Perchlorate Ingestion"
that recommended a perchlorate reference dose
(RfD) of 0.7 microgram per kilogram body weight per day (µg/kg bw/d).
The RfD is an estimate (with uncertainty spanning perhaps an order of
magnitude) of a daily oral exposure to the human population (including
sensitive subgroups) that is likely to be without an appreciable risk
of deleterious effects over a lifetime. The RfD for perchlorate
includes a 10-fold uncertainty factor. In addition, the NAS used a non
adverse end point, inhibition of iodine uptake, to derive the reference
dose. Inhibition of iodine uptake is a precursor that can lead to
hypothyroidism, the adverse effect considered by the NAS committee. As
a result, the reference dose was considered conservative and health
protective by the NAS committee. The NAS also considered pregnant women
and their fetuses to be the most sensitive populations to the health
effects of perchlorate and emphasized the importance of ensuring that
all pregnant women have adequate iodine intake.
February 2005, the Environmental Protection Agency (EPA) adopted the NAS
recommended RfD of 0.7 µg/kg bw/day for perchlorate (see "EPA Sets Reference Dose for Perchlorate"),which
focuses on protecting the most sensitive population, the fetuses of
pregnant women who might have hypothyroidism or iodine deficiency. If
all exposure is assumed to come from drinking water, the RfD translates
to a drinking water equivalent level (DWEL) of 24.5 parts per billion
(ppb) based on two (2) liters of drinking water consumption per day by
adults. However, because EPA's RfD is relevant to assessing total
intake, information on total exposure from both water and food is
needed to evaluate the impact of perchlorate on populations, including
The EPA's drinking water equivalent
level for perchlorate is 24.5 parts per billion (ppb). Is this the
standard for perchlorate in bottled water?
No. FDA has not established a standard (i.e., an allowable level)
for perchlorate in bottled water. In February 2005, EPA adopted the NAS
recommended RfD of 0.7 µg/kg bw/day for perchlorate (see "EPA Sets Reference Dose for Perchlorate"),
which focuses on protecting the most sensitive population, the fetuses
of pregnant women who might have hypothyroidism or iodine deficiency.
If all perchlorate exposure is assumed to come from drinking water, the
RfD translates to a drinking water equivalent level (DWEL) of 24.5 ppb
based on two (2) liters of drinking water consumption per day by
adults. EPA has not yet determined whether a drinking water standard
(i.e., a maximum contaminant level or MCL) is warranted for
EPA has been gathering and evaluating information on the perchlorate
health effects and occurrence in public water systems to determine
whether or not a drinking water standard presents a meaningful
opportunity to reduce risk for those persons served by public water
systems. Understanding overall exposure to perchlorate, including the
potential contribution from food, is important to making a decision
about regulating perchlorate in drinking water. EPA is working with
FDA, as well as other federal agencies and states to better understand
perchlorate exposure and the impact on EPA's policies.
Under the Federal Food, Drug, and Cosmetic Act, if EPA establishes
an MCL for perchlorate in public drinking water, FDA is required to
establish an allowable level for perchlorate under the quality standard
regulations for bottled water or make a finding that such a regulation
is not necessary to protect the public health because the contaminant
is found in water in public water systems but not in water used for
bottled drinking water.
In some areas of California, perchlorate has been found in tap water. Do bottled water manufacturers test for perchlorate?
FDA has not established a standard for perchlorate in bottled water,
and FDA's current bottled water regulations do not require bottled
water manufacturers to test for perchlorate. If EPA establishes a
standard for perchlorate in public drinking water, FDA will consider
establishing a quality standard for perchlorate in bottled water. If
FDA establishes such a standard, bottlers will be required to test for
The bottled water industry is aware of the potential for perchlorate
contamination in source waters for bottling and some bottlers may
voluntarily test for perchlorate. Consumers should contact bottled
water producers for more information.
Has FDA developed a method to detect perchlorate in foods?
Yes. FDA has developed a rapid, sensitive, and specific ion
chromatography-tandem mass spectrometry (IC-MS/MS) method for
determining perchlorate in selected foods. The smallest amount of
perchlorate that this method can detect, or the limit of detection
(LOD), is 0.30 ppb for fruits, fruit juices, and vegetables; 1.00 ppb
for milk, grain products, fish, and shrimp; and 0.20 ppb for bottled
water. An article, entitled "Rapid Determination of Perchlorate Anion in Foods by Ion Chromatography-Tandem Mass Spectrometry," describing FDA's method has been published in the September 15, 2004 issue of the scientific journal
Analytical Chemistry (Analytical Chemistry. 2004, 76, 5518-5522).
FDA's 2005/2006 Total Diet Study Surveys
What is FDA's Total Diet Study?
FDA's Total Diet Study (TDS) is the Agency's ongoing market basket
survey in which 285 core foods (TDS foods) in the U.S. food supply are
collected and analyzed to determine levels of various contaminants and
nutrients in those foods. The foods collected in the TDS (referred to
as the TDS food list) represent the major components of the diet of the
U.S. population. The food list is based on results of national food
consumption surveys and is updated from time to time to reflect changes
in food consumption patterns.
Four market baskets are generally collected each year, one in each
of four geographic regions of the U.S. (i.e., West, North Central,
South, and Northeast). For each market basket, samples of each TDS food
are collected from grocery stores and fast food restaurants in three
cities within the region, prepared table-ready, and composited for
analysis. Therefore, each data point for a contaminant or a nutrient
represents the analytical result for a composite of three samples of
the TDS food. For more information on the TDS, see Total Diet Study.
Did FDA test TDS foods for perchlorate and iodine?
Yes. For perchlorate, 54 out of 57 TDS baby foods were analyzed in
four market baskets collected in FY05; the remaining three baby foods
were analyzed in three market baskets because they were not available
for analysis in the fourth market basket for FY05. The other 228 TDS
foods were collected and analyzed in FY06; of those, 128 were analyzed
for four market baskets and 100 were analyzed for two market baskets.
The complete set of perchlorate data obtained from FY05 and FY06 TDS
surveys is available on FDA's website. For iodine, 285 TDS foods from
five markets baskets collected in FY03 and FY04 were analyzed (iodine
results are available at Total Diet Study).
On January 2, 2008, FDA published a study entitled "U.S. Food and
Drug Administration's Total Diet Study: Dietary Intake of Perchlorate
and Iodine" in the Journal of Exposure Science and Environmental
Epidemiology. This study reports on the estimated average dietary
intakes of perchlorate and iodine based on analytical results for
perchlorate from FDA's TDS samples collected in FY 05/06 and for iodine
from TDS samples collected in FY03/04.
What were the estimates of the
dietary intake of perchlorate from the "U.S. Food and Drug
Administration's Total Diet Study: Dietary Intake of Perchlorate and
The estimated lower bound to upper bound average perchlorate intakes
by the 14 age-gender subgroups (see below) range from 0.08 to 0.39
µg/kg bw/day, all below the RfD of 0.7 µg/kg bw/day recommended by the
National Academy of Sciences and adopted by the U.S. Environmental
The 14 age-gender subgroups consist of infants (6-11 months),
children (2 years), children (6 years), children (10 years), teenage
girls (14-16 years), teenage boys (14-16 years), women (25-30 years),
men (25-30 years), women (40-45 years), men (40-45 years), women (60-65
years), men (60-65 years), women (70 + years), and men (70 + years).
Children 2 years of age, with estimated average intakes ranging from
0.35 to 0.39 µg/kg bw/day, have the highest total perchlorate intake
per kilogram body weight per day, but are below the RfD of 0.7 µg/kg
bw/day recommended by the National Academy of Sciences and adopted by
the U.S. Environmental Protection Agency. Total average intake ranges
for infants 6-11 months, children 6, and children 10 years of age are
estimated to be 0.26 to 0.29 µg/kg bw/day, 0.25 to 0.28 µg/kg bw/day,
and 0.17 to 0.20 µg/kg bw/day, respectively. The estimated total
average intakes by the other age-gender subgroups ranged from 0.08 to
0.14 µg/kg bw/day.
What were the estimates of the
dietary intake of iodine from the "U.S. Food and Drug Administration's
Total Diet Study: Dietary Intake of Perchlorate and Iodine" study?
Because human exposure to high dosages of perchlorate can interfere
with iodide uptake into the thyroid gland, it is important to consider
the levels of iodine in the body. The estimated average iodine intakes
by the 14 age-gender subgroups show a range from 138 to 353
µg/person/day. The estimated average iodine intakes for infants, 6-11
months exceeded their adequate intake (AI) of 135 µg/person/day. The
estimated average iodine intakes by all other 13 children and adult
age-gender subgroups exceeded their relevant estimated average
requirements (EARs) of 65 µg/person/day for children 2 and 6 years, 73
µg/person/day for children 10 years, and 95 µg/person/day for the
remaining 10 age-gender subgroups.
The EARs are defined by NAS as the nutrient intake levels estimated
to meet the requirements of half the healthy individuals within a
particular age group. An AI is set by NAS when there is insufficient
evidence to determine an EAR and defined as the recommended average
daily intake level of a nutrient that is assumed to be adequate for a
group of apparently healthy individuals.
What is FDA recommending to consumers?
FDA is not recommending any changes to infants' and children's diets
and eating habits based on current perchlorate data. FDA continues to
recommend a healthy eating plan, consistent with the Dietary Guidelines
for Americans, that emphasizes fruits, vegetables, whole grains, and
fat-free or low-fat milk and milk products; includes lean meats,
poultry, fish, beans, eggs, and nuts; and is low in saturated fats,
trans fats, cholesterol, salt (sodium) and added sugars. Additionally,
adequate intake of iodine has previously been recognized as important
for healthy thyroid function .
FDA's 2004/2005 Exploratory Surveys
How did FDA conduct the exploratory surveys for perchlorate in 2004 and 2005?
During Fiscal Year 2004 (FY04), FDA conducted an initial exploratory
survey that involved the collection and analysis of samples of domestic
origin (i.e., bottled water, milk, lettuce, tomatoes, carrots, spinach,
cantaloupe). Produce samples (lettuce, tomatoes, carrots, spinach, and
cantaloupe) were collected particularly from regions (i.e., Southern
California and Arizona) where water sources were known to be
contaminated with perchlorate, based on a study report of detecting
perchlorate in winter lettuce grown in Southern California or Arizona
(Environmental Working Group. Suspect Salads: Toxic rocket fuel found in samples of winter lettuce. 2003.
). Bottled water and milk samples were collected from throughout the
country. Bottled water was selected for the survey to obtain an initial
assessment of perchlorate occurrence in source waters for bottling,
while milk was sampled as a follow up to a Texas Tech University study
that found perchlorate in a small number of milk samples from Texas
(Kirk et al., Perchlorate in Milk. Environ. Sci. Technol. 2003,
37:4979-4981). Produce samples (lettuce, tomatoes, carrots, spinach,
and cantaloupe) were selected for the survey based on their high water
content, relatively high consumption, and early indications of
perchlorate uptake by plants (when irrigated with
perchlorate-containing water or when grown in soil that naturally
contains perchlorate or that has been previously exposed to
perchlorate-containing water or fertilizer).
For FY05, FDA expanded the exploratory survey. In addition to
collecting further samples of tomatoes, carrots, spinach, and
cantaloupe, FDA collected samples of other high water content foods,
including fruits and fruit juices such as apples, oranges, and grapes;
vegetables such as cucumbers, green beans, and greens; and seafood such
as aquaculture fish and shrimp. In addition, grain products such as
wheat flour, cornmeal, and rice were sampled as a follow up to a Texas
Tech University study report that found perchlorate in wheat heads
(Jackson et al., Perchlorate Accumulation in Forage and Edible
Vegetation. J. Agric. Food Chem. 2005, 53:369-373). The FY05 samples
collected by FDA consisted of domestic products grown in a broader
range of locations within the U.S. (i.e., Florida, Georgia, Idaho,
Illinois, Iowa, Kansas, Louisiana, Maine, Mississippi, Missouri,
Montana, Nebraska, New Jersey, New Mexico, North Carolina, Ohio,
Oregon, Pennsylvania, South Carolina, Texas, Washington) to determine
if perchlorate occurs in foods from wider regions of the United States,
and not only from regions where water sources were known to be
contaminated with perchlorate. In FY05, FDA also collected and analyzed
a limited number of imported products commonly entering the U.S. market
(e.g., produce from Mexico, grapes from Chile, aquaculture salmon from
Canada, shrimp from Southeast Asia) that were available for sampling
Has FDA informed the public of the perchlorate levels that have been found in foods from the exploratory surveys?
Yes. The complete set of perchlorate data obtained from the FY04 and FY05 exploratory surveys is available on FDA's website.
What was the exposure estimate based on the exploratory surveys and how did it compare to EPA's RfD?
FDA's preliminary perchlorate exposure assessment (see "Preliminary Estimation of Perchlorate Dietary Exposure Based on FDA 2004/2005 Exploratory Data")
suggested that perchlorate levels found in the 27 foods and beverages
(milk, fruits and fruit juices, vegetables, grain products, aquaculture
fish and shrimp) are not likely to present a public health risk. Based
on perchlorate data obtained from FDA's FY04 and FY05 exploratory
surveys, the estimated total mean population (all persons aged 2 and
above) perchlorate exposure from the 27 foods and beverages was
determined to be 0.053 µg/kg bw/day, which is below the RfD of 0.7
µg/kg bw/day, the daily exposure level over a lifetime that is not
expected to cause adverse health effects, recommended by NAS and
adopted by EPA. FDA's preliminary exposure estimate was similar to the
geometric mean perchlorate dose of 0.066 µg/kg bw/day for the U.S.
population (males and females aged 20 years and older) estimated by
et al. in 2006 (Perchlorate Exposure of the US Population, 2001-2002. J Expo Sci Environ Epidemiol (2006), 1-8).
Did the perchlorate levels in the 27
foods and beverages analyzed from the exploratory surveys provide an
accurate measure of exposure to perchlorate?
There are uncertainties associated with the conclusions of FDA's
preliminary exposure assessment because the perchlorate levels in the
27 foods and beverages were exploratory data and consumption of the 27
foods and beverages represented only about 32 percent of the total diet
for the U.S. population, ages 2 years and older and 42 percent of the
total diet for children, 2-5 years.
At the time FDA conducted the preliminary exposure assessment based
on 2004/2005 exploratory perchlorate data, it did not have any
information on the distribution of perchlorate in foods that constitute
the remaining 68 percent of the total diet for U.S. population, ages 2
years and older and 58 percent of the total diet for children, 2-5
years. Therefore, the true average intake of perchlorate could be
higher than the average intake based on FDA's exploratory perchlorate
data for the 27 foods and beverages. Sampling of additional food types
to increase representation of the total U.S. diet and collection of
food types from wider regions of the country would better characterize
perchlorate distribution in the U.S. food supply that could provide a
more precise assessment of the scope of perchlorate exposure and the
public health implications for food with more reasonable certainty.
Therefore, FDA conducted a more comprehensive and nationally
representative exposure assessment based on perchlorate data obtained
from FY05 and FY06 Total Diet Study surveys (see questions 6-10 above).
FDA's Next Steps
What are FDA's next steps?
FDA is continuing to test additional food types for perchlorate. In
FY07, FDA tested additional samples of individual food products
collected through additional surveys, and during FY 08, additional TDS
samples will be analyzed for perchlorate. Information on the
distribution of perchlorate in a wider variety of foods obtained from
these surveys will further enhance FDA's ability to assess the dietary
exposure of U.S. consumers to perchlorate.
FDA will continue to inform the public of its findings as additional
data is collected. Other steps may include developing and fostering
public/private partnerships to gather scientific and technological
information and data for assessing the human exposure to perchlorate.
FDA is continuing to work with the Interagency Working Group on
Perchlorate, composed of other federal agencies, including USDA and
EPA, to evaluate the potential risk associated with perchlorate
For more information, read
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