ToxFAQsTM for Iodine
Spanish: Yodo
CAS# 7553-56-2
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This fact sheet answers the most frequently asked health questions about iodine. For more information, you may call the ATSDR Information Center at 1-800-232-4636. This fact sheet is one in a series of summaries about hazardous substances and their health effects. It is important you understand this information because this substance may harm you. The effects of exposure to any hazardous substance depend on the dose, the duration, how you are exposed, personal traits and habits, and whether other chemicals are present.
Highlights
Iodine is a naturally occurring element that is required for good health. Exposure to high levels of stable or radioactive iodine can cause damage to the thyroid. This chemical has been found in at least 9 of the 1,636 National Priorities List sites identified by the Environmental Protection Agency (EPA).
What is iodine?
Iodine is a naturally occurring element
found in sea water and in certain rocks and sediments. There
are non radioactive and radioactive forms of iodine.
Iodine is used as a disinfectant for
cleaning surfaces and storage containers and is used in skin
soaps and bandages, and for purifying water. Iodine is also
added to some table salt to ensure that all people in the
United States have enough iodine in their diet.
Most radioactive iodine is manmade. It
is used in medical tests and to treat certain diseases. Most
radioactive forms of iodine change very quickly (seconds to
days) to stable elements that are not radioactive. However, 129I (read as iodine 129) changes very slowly (over millions
of years).
What happens to iodine when it enters the environment?
The primary source of nonradioactive
iodine is the ocean. It enters the air from sea spray or as
iodine gas. Once in the air, iodine can combine with water
or with particles in air and can enter the soil and surface
water, or land on vegetation when these particles fall to
the ground or when it rains. Iodine can remain in soil for
a long time. It can also be taken up by some plants that grow
in the soil, but plants are considered a poor source of dietary
iodine.
Small amounts of radioactive iodine are
produced from the operation of nuclear power plants, which
can release minor amounts to air and water. Large amounts
have been released during rare power plant accidents. Iodine
is also released from atomic bomb explosions. Very large amounts
are made in nuclear power plants for medical use. Once given
to the patient, most iodine decays in the body. The rest is
exhaled or excreted in the urine and decays naturally in the
environment.
How might I be exposed to iodine?
- The general population is exposed to low levels of iodine
in air, some food, and some beverages. Food (iodized salt,
salt water, bread, and dairy products) is the largest source
of exposure to iodine.
- The general population is rarely exposed to radioactive
iodine, unless they undergo certain medical tests or are
given it for the treatment of thyroid disease.
- People who work at facilities using radioactive iodine
may be exposed to higher than normal levels.
How can iodine affect my health?
Iodine has both beneficial and harmful
effects on human health. Iodine is needed by your thyroid
gland to produce thyroid hormones. However, exposure to unnecessarily
high levels of nonradioactive and radioactive iodine can damage
the thyroid. Damage to the thyroid gland can result in effects
in other parts of your body, such as your skin, lung, and
reproductive organs.
Radioactive iodine can be used by doctors
to check your thyroid for medical problems, and to cure thyroid cancer.
How likely is iodine to cause cancer?
Some human studies have found an increased
risk of thyroid cancer in certain populations, particularly
populations with iodine deficient diets receiving iodine supplements.
Other human studies have not found an association between
exposure to high levels of iodine and cancer risk. Exposure
to high levels of radioactive iodine may also increase the
risk of thyroid cancer. However, the evidence is inconclusive
for exposures in the United States.
How can iodine affect children?
Iodine is essential for the growth and
development of children. However, children are more sensitive
to the harmful effects of excessively high levels of stable
and radioactive iodine than adults because their thyroid glands
are still growing. If babies and children receive too much
iodine, they can develop an enlarged thyroid gland (called
a goiter), which does not produce enough thyroid hormone for
normal growth.
Radioactive iodine in food can be more harmful to babies and children than to adults. Because a child’s thyroid gland is smaller than that of an adult, a child’s thyroid gland will receive a higher radiation dose than the adult exposed to the same amount of iodine.
How can families reduce the risk of exposure to iodine?
We need iodine to maintain growth and
health, but we want to prevent exposure to too much iodine.
Foods are not normally expected to have enough iodine to harm
your health. Unless you are exposed to radioactive waste or
emissions, you generally do not have to worry about excessive
exposure.
Is there a medical test to show whether I've been exposed to iodine?
There are reliable tests that can measure
iodine in the blood, urine, and saliva. These tests are not
available at your doctor's office, but your doctor can
send the samples to a laboratory that can perform the tests.
However, these tests cannot predict whether you will experience
any health effects.
Two types of tests are available for
radioactive iodine. One is to see if you have been exposed
to a large dose of radiation, and the other is to see if iodine
is in your body. The first looks for changes in blood cell
counts or in your chromosomes that occur at 3 to 5 times the
annual occupational dose limit. It cannot tell if the radiation
came from radioactive iodine. The second type of test involves
examining your blood, feces, saliva, urine, and even your
entire body. It is to see if iodine is being excreted from
or remains inside your body. Either the doctor's office
collects and sends the samples to a special lab for testing,
or you must go to the lab for testing.
Has the federal government made recommendations to
protect human health?
The National Research Council has established a recommended dietary allowance (RDA) for iodine of 150 micrograms per day (150 Āµg/day), with additional allowances of 25 Āµg/day during pregnancy and 50 Āµg/day during nursing. These dietary intake levels are sufficient to satisfy the metabolic needs of the body.
The Nuclear Regulatory Commission (NRC) has set limits for radioactive iodine in workplace air of 2x10-8 microcurie per milliliter (ĀµCi/mL) for 131I. EPA has set an average annual drinking water limit of 3 pCi/L for 131I so the public radiation dose will not exceed 4 millirem.
References
Agency for Toxic Substances and Disease
Registry (ATSDR). 2004. Toxicological
Profile for iodine. Atlanta, GA: U.S. Department of Health
and Human Services, Public Health Service.
Where can I get more information?
If you have questions or concerns, please contact your community or state health or environmental quality department or:
For more information, contact:
Agency for Toxic Substances and Disease Registry
Office of Innovation and Analytics, Toxicology Section
4770 Buford Highway
Chamblee, GA 30341-3717
Phone: 1-800-CDC-INFO 888-232-6348 (TTY)
Email: Contact CDC-INFO
ATSDR can also tell you the location of occupational and environmental health clinics. These clinics specialize in recognizing, evaluating, and treating illnesses resulting from exposure to hazardous substances.