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PUBLIC HEALTH STATEMENT 

Iodine 

CAS#: 7553-56-2 

Division of Toxicology April 2004 

This Public Health Statement is the summary 

chapter from the Toxicological Profile for iodine. It 

is one in a series of Public Health Statements about 

hazardous substances and their health effects. A 

shorter version, the ToxFAQsTM, is also available. 

This information is important 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. For 

more information, call the ATSDR Information 

Center at 1-888-422-8737. 

This public health statement tells you about iodine 

and the effects of exposure. 

The Environmental Protection Agency (EPA) 

identifies the most serious hazardous waste sites in 

the nation. These sites make up the National 

Priorities List (NPL) and are the sites targeted for 

long-term federal cleanup activities. Iodine has 

been found in at least 8 sites. Radioactive iodine 

has been found at 9 sites, including iodine-129 (129I) 

in at least 3 sites, and iodine-131 (131I) in at least 6 

sites of the 1,636 current or former NPL sites. 

However, the total number of NPL sites evaluated 

for iodine is not known. As more sites are 

evaluated, the sites at which iodine is found may 

increase. This information is important because 

exposure to iodine may harm you and because these 

sites may be sources of exposure. 

When a substance is released from a large area, 

such as an industrial plant, or from a container, such 

as a drum or bottle, it enters the environment. This 

release does not always lead to exposure. You are 

exposed to a substance only when you come in 

contact with it. You may be exposed by breathing, 

eating, or drinking the substance, or by skin contact. 

External exposure to radiation may occur from 

natural or man-made sources. Naturally occurring 

sources of radiation are cosmic radiation from space 

or radioactive materials in soil or building materials. 

Man-made sources of radioactive materials are 

found in consumer products, industrial equipment, 

atom bomb fallout, and to a smaller extent from 

hospital waste and nuclear reactors. 

If you are exposed to either radioactive or stable 

iodine, many factors determine whether you’ll be 

harmed. These factors include the dose (how 

much), the duration (how long), and how you come 

in contact with it. You must also consider the other 

chemicals you’re exposed to and your age, sex, diet, 

family traits, lifestyle, and state of health. 

1.1 WHAT IS IODINE? 

Iodine is a naturally occurring element that is 

essential for the good health of people and animals. 

Iodine is found in small amounts in sea water and in 

certain rocks and sediments. Iodine occurs in many 

different forms that can be blue, brown, yellow, red, 

white, or colorless. Most forms of iodine easily 

dissolve in water or alcohol. Iodine has many uses. 

Its most important use is as a disinfectant for 

cleaning surfaces and storage containers. Iodine is 

also used in skin soaps and bandages, and for 

purifying water. Iodine is used in medicines. 

Iodine is added to food, such as table salt, to ensure 

that all people in the United States have enough 

iodine in their bodies to form essential thyroid 

hormones. Iodine is put into animal feeds for the 

same reason. Iodine is used in the chemical 

industry for making inks and coloring agents, 

chemicals used in photography, and in making 

batteries, fuels, and lubricants. Radioactive iodine 

also occurs naturally. Radioactive iodine is used in 

medical tests and to treat certain diseases, such as 

DEPARTMENT of HEALTH AND HUMAN SERVICES, Public Health Service
 

Agency for Toxic Substances and Disease Registry 

www.atsdr.cdc.gov/ Telephone: 1-888-422-8737 Fax: 770-488-4178 E-Mail: atsdric@cdc.gov 
 

 

 

 

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PUBLIC HEALTH STATEMENT 

Iodine 

CAS#: 7553-56-2 

Division of Toxicology April 2004 

over-activity or cancer of the thyroid gland. 

1.2 WHAT HAPPENS TO IODINE WHEN IT 

ENTERS THE ENVIRONMENT? 

The oceans are the most important source of natural 

iodine in the air, water, and soil. Iodine in the 

oceans enters the air from sea spray or as iodine 

gases. Once in the air, iodine can combine with 

water or with particles in the 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 because it 

combines with organic material in the soil. It can 

also be taken up by plants that grow in the soil. 

Cows or other animals that eat these plants will take 

up the iodine in the plants. Iodine that enters 

surface water can reenter the air as iodine gases. 

Iodine can enter the air when coal or fuel oil is 

burned for energy; however, the amount of iodine 

that enters the air from these activities is very small 

compared to the amount that comes from the 

oceans. 

Radioactive iodine also forms naturally from 

chemical reactions high in the atmosphere. Most 

radioactive forms of iodine change very quickly 

(seconds to days) to stable elements that are not 

radioactive. However, one form, 129I, changes very 

slowly (millions of years), and its levels build up in 

the environment. Small amounts of radioactive 

iodine, including 129I and 131I, can also enter the air 

from nuclear power plants, which form radioiodine 

from uranium and plutonium. Larger amounts of 

radioactive iodine have been released to the air from 

accidents at nuclear power plants and from 

explosions of nuclear bombs. 

1.3 HOW MIGHT I BE EXPOSED TO 

IODINE? 

Iodine is a natural and necessary part of the food 

that you eat and the water that you drink. In the 

United States, most table salt contains iodine. 

Iodine is put into table salt to make sure that 

everyone has enough iodine in their bodies to form 

essential thyroid hormones. In the past, people in 

some areas of the United States did not get enough 

iodine in their diets. Iodine is in some breads 

because it is added to flour to condition bread 

dough for baking. Iodine is also in cow and goat 

milk. Iodine gets into milk when cows or goats eat 

iodine that is in their food and water. Iodine can 

also get into milk when iodine is used to clean 

milking machines and milk storage containers, and 

to clean the animals’ udders at dairy farms and 

dairies. Iodine is in ocean fish, shellfish, and 

certain plants that grow in the ocean (kelp). This is 

because there is iodine in sea water, and some sea 

plants and animals concentrate iodine in their 

tissues. Iodine can also be in the air. Iodine is in 

sea spray and mist, which are tiny drops of sea 

water. Iodine is in cleansers and medicines that are 

used to clean and bandage skin wounds (tincture of 

iodine). You can be exposed to these if they are 

placed on your skin. Some medicines have iodine 

in them. Iodine is used to treat water to make it safe 

for drinking. You can buy iodine water purifying 

tablets that you add directly to water. You can also 

buy water treatment cartridges for your home that 

have iodine in them. Some iodine will get into the 

water that you drink if you use these tablets or 

cartridges. 

People are almost never exposed to radioactive 

iodine, unless they work in a place where 

radioactive iodine is used or if they are given 

DEPARTMENT of HEALTH AND HUMAN SERVICES, Public Health Service
 

Agency for Toxic Substances and Disease Registry 

www.atsdr.cdc.gov/ Telephone: 1-888-422-8737 Fax: 770-488-4178 E-Mail: atsdric@cdc.gov 
 

 

 

 

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PUBLIC HEALTH STATEMENT 

Iodine 

CAS#: 7553-56-2 

Division of Toxicology April 2004 

radioactive iodine by their doctors. Radioactive 

iodine is used in certain medical tests and 

treatments. You might have these tests if your 

doctor needs to look for problems in your thyroid 

gland or if your doctor needs to treat you for a 

problem with your thyroid gland. In the past, 

people were exposed to radioactive iodine released 

from nuclear bomb tests, after accidental explosions 

and fires at nuclear power plants, or from facilities 

that processed or used nuclear fuel for power plants. 

1.4 HOW CAN IODINE ENTER AND 

LEAVE MY BODY? 

Most of the iodine that enters your body comes 

from the food that you eat. A smaller amount 

comes from the water that you drink. Iodine will 

enter your body if it is in the air that you breathe. 

Some forms of iodine can enter your body when 

placed on the skin. Iodine can also be injected into 

your blood by your doctor for special medical tests 

or treatments. Iodine that enters your body quickly 

goes into your thyroid gland, a small important 

organ in your neck. Iodine is used in the thyroid 

gland to make hormones that are needed for growth 

and health. Almost all of the iodine in your body is 

in your thyroid gland. Iodine that does not go into 

your thyroid gland leaves the body in your urine in 

a few weeks to months. Small amounts of iodine 

can also leave your body in sweat or in breast milk. 

Iodine that leaves your body each day is usually 

replaced by the iodine that you eat in your food, so 

that the amount of iodine in your body is just 

enough to keep you healthy. 

1.5 HOW CAN IODINE AFFECT MY 

HEALTH? 

Iodine is needed for your thyroid gland to produce 

thyroid hormones. You and your thyroid gland are 

healthy when there is just enough iodine in your 

body, about 10–15 milligrams, so that just the right 

amount of thyroid hormones are produced. This 

amount would look like much less than a pinch of 

table salt if placed in your hand. This amount of 

iodine is in most people when they eat the foods 

that people normally eat in the United States. Your 

thyroid gland can become unhealthy if more or less 

than this amount of iodine is in your body. An 

unhealthy thyroid gland can affect your entire body. 

If the thyroid gland cannot make enough hormone, 

then you would have to be given thyroid hormone 

in pills. If your thyroid gland makes too much 

hormone, then you would have to be given drugs to 

make your thyroid make less hormone. Radioactive 

iodine can also be unhealthy for your thyroid gland. 

If too much radioactive iodine enters your body, the 

radioactive iodine will destroy your thyroid gland 

so that the gland will stop making hormones. Too 

much radioactive iodine in your body can also cause 

thyroid nodules or cancer. 

To protect the public from the harmful effects of 

toxic chemicals and to find ways to treat people 

who have been harmed, scientists use many tests. 

One way to see if a chemical will harm people is to 

learn how the chemical is absorbed, used, and 

released by the body. In the case of a radioactive 

chemical, it is also important to gather information 

concerning the radiation dose and the dose rate to 

the body. For some chemicals, animal testing may 

DEPARTMENT of HEALTH AND HUMAN SERVICES, Public Health Service
 

Agency for Toxic Substances and Disease Registry 

www.atsdr.cdc.gov/ Telephone: 1-888-422-8737 Fax: 770-488-4178 E-Mail: atsdric@cdc.gov 
 

 

 

 

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PUBLIC HEALTH STATEMENT 

Iodine 

CAS#: 7553-56-2 

Division of Toxicology April 2004 

be necessary. Animal testing may also be used to 

identify health effects such as cancer or birth 

defects. Without laboratory animals, scientists 

would lose a basic method to get information 

needed to make wise decisions to protect public 

health. Scientists have the responsibility to treat 

research animals with care and compassion. Laws 

today protect the welfare of research animals, and 

scientists must comply with strict animal care 

guidelines. 

1.6 HOW CAN IODINE AFFECT 

CHILDREN? 

This section discusses potential health effects from 

exposures during the period from conception to 

maturity at 18 years of age in humans. 

Babies and children need iodine to form thyroid 

hormones, which are important for growth and 

health. If infants and children do not have enough 

iodine in their bodies, their thyroid glands will not 

produce enough thyroid hormone and they will not 

grow normally. If they have too much iodine in 

their bodies, they may develop an enlarged thyroid 

gland (goiter), which may not produce enough 

thyroid hormone for normal growth. We also need 

just the right amount of iodine from our mothers 

before we are born. Too much iodine from the 

mother can cause a baby’s thyroid gland to be so 

large that it makes breathing difficult or impossible. 

Not enough iodine from the mother can cause a 

baby to not produce enough thyroid hormone, 

which can affect growth and mental development of 

the baby. Radioactive iodine in food can be more 

harmful to babies and children than to adults. When 

radioactive iodine is in the air, it can get onto the 

grass and water that the cows eat and drink. Infants 

and children drink a lot more milk than most adults. 

If there is radioactive iodine in the milk that a child 

or infant drinks, more iodine will enter the thyroid 

gland of the child than of an adult who drinks less 

milk. In addition, because the thyroid gland of a 

child or infant is smaller than that of an adult, a 

child’s thyroid gland will receive a higher radiation 

dose than an adult. Children are more sensitive to 

the harmful toxic effects of iodine and radioactive 

iodine than adults because their thyroid glands are 

still growing and the thyroid gland tissues are more 

easily harmed by radioactive iodine, and because 

children need a healthy thyroid gland for normal 

growth. 

1.7 HOW CAN FAMILIES REDUCE THE 

RISK OF EXPOSURE TO IODINE? 

We all are exposed to iodine in the food that we eat 

and in the water that we drink. Iodine is needed for 

your good health. We do not want to prevent 

exposure to iodine, but we do want to try to prevent 

exposure to too much iodine. This is not likely to 

happen from eating a normal diet in the United 

States or from drinking water or breathing air. It 

could happen if you were careless about storing 

soaps or cleansers or medicines that have iodine in 

them. For example, a child could swallow 

medicines that contain iodine. People are rarely 

exposed to radioactive iodine, unless they work in a 

place where radioactive iodine is used or if they are 

given radioactive iodine by their doctors for certain 

medical tests or treatments. 

If your doctor finds that you have been exposed to 

significant amounts of iodine, ask whether your 

children might also be exposed. Your doctor might 

need to ask your state health department to 

investigate. 

DEPARTMENT of HEALTH AND HUMAN SERVICES, Public Health Service
 

Agency for Toxic Substances and Disease Registry 

www.atsdr.cdc.gov/ Telephone: 1-888-422-8737 Fax: 770-488-4178 E-Mail: atsdric@cdc.gov 
 

 

 

 

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PUBLIC HEALTH STATEMENT 

Iodine 

CAS#: 7553-56-2 

Division of Toxicology April 2004 

1.8 IS THERE A MEDICAL TEST TO 

DETERMINE WHETHER I HAVE 

BEEN EXPOSED TO IODINE? 

Most physicians do not test for iodine in their 

offices, but can collect samples and send them to 

special laboratories. They can also feel the thyroid 

for lumps that may have been caused by disease or 

past exposure to radioactive iodine, but the results 

do not tell the cause. Every person’s body contains 

a small amount of iodine, but normally not 

radioactive iodine (such as 131I). Iodine can be 

measured in the blood, urine, and saliva. The 

amount is normally measured by its mass (in 

grams). If the iodine is radioactive, it can be 

measured by its mass or by its radiation emissions. 

These emissions are used to tell the amount of 

radioactive iodine (in curies or becquerels) and the 

radiation dose it gives to your body (in sieverts or 

rem). 

Radiation detectors can measure radioactive iodine 

inside your body using the radiation coming from 

the thyroid gland in your neck. This is useful only 

if you recently inhaled or ingested some, or if your 

physician recently gave you some for medical 

purposes. Your body quickly eliminates iodine and 

radioactive iodine, so tests should be done shortly 

after exposure. 

1.9 WHAT RECOMMENDATIONS HAS 

THE FEDERAL GOVERNMENT 

MADE TO PROTECT HUMAN 

HEALTH? 

The federal government develops regulations and 

recommendations to protect public health. 

Regulations can be enforced by law. Federal 

agencies that develop regulations for toxic 

substances include the Environmental Protection 

Agency (EPA), the Occupational Safety and Health 

Administration (OSHA), the Food and Drug 

Administration (FDA), the Department of Energy 

(DOE), and the U.S. Nuclear Regulatory 

Commission (USNRC). 

Recommendations provide valuable guidelines to 

protect public health but cannot be enforced by law. 

Federal organizations that develop 

recommendations for toxic substances include the 

Agency for Toxic Substances and Disease Registry 

(ATSDR), the National Institute for Occupational 

Safety and Health (NIOSH), and the FDA. 

Regulations and recommendations can be expressed 

in not-to-exceed levels in air, water, soil, or food 

that are usually based on levels that affect animals; 

then they are adjusted to help protect people. 

Sometimes these not-to-exceed levels differ among 

federal organizations because of different exposure 

times (an 8-hour workday or a 24-hour day), the use 

of different animal studies, or other factors. 

Recommendations and regulations are also 

periodically updated as more information becomes 

available. For the most current information, check 

with the federal agency or organization that 

provides it. Some regulations and 

recommendations for iodine include the following: 

The National Research Council has established a 

Recommended Dietary Allowance for iodine of 

150 micrograms per day (μg/day), with additional 

allowances of 25 μg/day during pregnancy and 

50 μg/day during nursing. The EPA has established 

regulations that limit releases of certain forms of 

radioactive iodine to the environment and require 

that industries report releases of certain forms of 

radioactive iodine. NIOSH has established 

DEPARTMENT of HEALTH AND HUMAN SERVICES, Public Health Service
 

Agency for Toxic Substances and Disease Registry 

www.atsdr.cdc.gov/ Telephone: 1-888-422-8737 Fax: 770-488-4178 E-Mail: atsdric@cdc.gov 
 

 

 

 

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PUBLIC HEALTH STATEMENT 

Iodine 

CAS#: 7553-56-2 

Division of Toxicology April 2004 

recommendations for limits of worker exposures to 

iodine and radioactive iodine. The Nuclear 

Regulatory Commission, the National Council of 

Radiation Protection and Measurements (NRCP) 

and the International Commission of Radiological 

Protection (ICRP) have established recommended 

limits for worker exposures to radioactive iodine 

and for releases of radioactive iodine to the 

environment. 

1.10 WHERE CAN I GET MORE 

INFORMATION? 

If you have any more questions or concerns, please 

contact your community or state health or 

environmental quality department, your regional 

Nuclear Regulatory Commission office, or contact 

ATSDR at the address and phone number below. 

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. 

Toxicological profiles are also available on-line at 

www.atsdr.cdc.gov and on CD-ROM. You may 

request a copy of the ATSDR ToxProfiles CDROM by calling the information and technical 

assistance toll-free number at 1-888-42ATSDR (1­

888-422-8737), by email at atsdric@cdc.gov, or by 

writing to: 

Agency for Toxic Substances and Disease Registry 

Division of Toxicology 

1600 Clifton Road NE 

Mailstop F-32 

Atlanta, GA 30333 

Fax: 1-770-488-4178 

For-profit organizations may request a copy of final 

profiles from the following: 

National Technical Information Service (NTIS) 

5285 Port Royal Road 

Springfield, VA 22161 

Phone: 1-800-553-6847 or 1-703-605-6000 

Web site: http://www.ntis.gov/ 

DEPARTMENT of HEALTH AND HUMAN SERVICES, Public Health Service
 

Agency for Toxic Substances and Disease Registry 

www.atsdr.cdc.gov/ Telephone: 1-888-422-8737 Fax: 770-488-4178 E-Mail: atsdric@cdc.gov