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PUBLIC HEALTH STATEMENT 

SELENIUM 

CAS#: 7782-49-2 

Division of Toxicology September 2003 

This Public Health Statement is the summary 

chapter from the Toxicological Profile for 

Selenium. 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 

selenium 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. Selenium has 

been found in at least 508 of the 1,623 current or 

former NPL sites. However, the total number of 

NPL sites evaluated for selenium is not known. As 

more sites are evaluated, the sites at which selenium 

is found may increase. This information is 

important because exposure to selenium at high 

levels may harm you and because these sites may be 

sources of exposure. A minimum dietary level of 

selenium is required for good health. 

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. 

If you are exposed to selenium, 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/them. 

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 SELENIUM? 

Selenium is a naturally occurring, solid substance 

that is widely but unevenly distributed in the earth's 

crust. It is also commonly found in rocks and soil. 

Selenium, in its pure form of metallic gray to black 

crystals, is often referred to as elemental selenium 

or selenium dust. Elemental selenium is 

commercially produced, primarily as a by-product 

of copper refining. Selenium is not often found in 

the environment in its elemental form, but is usually 

combined with other substances. Much of the 

selenium in rocks is combined with sulfide minerals 

or with silver, copper, lead, and nickel minerals. 

Selenium also combines with oxygen to form 

several substances that are white or colorless 

crystals. Some selenium compounds are gases. 

Selenium and its compounds are used in some 

photographic devices, gun bluing (a liquid solution 

used to clean the metal parts of a gun), plastics, 

paints, anti-dandruff shampoos, vitamin and mineral 

supplements, fungicides, and certain types of glass. 

For example, selenium sulfide is used in antidandruff shampoos by the common trade name 

Selsun Blue. Selenium is also used to prepare drugs 

and as a nutritional feed supplement for poultry and 

livestock. 

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 

SELENIUM 

CAS#: 7782-49-2 

Division of Toxicology September 2003 

1.2 WHAT HAPPENS TO SELENIUM WHEN 

IT ENTERS THE ENVIRONMENT? 

Selenium occurs naturally in the environment. As 

an element, selenium cannot be created or 

destroyed, although selenium can change forms in 

the environment. Weathering of rocks and soils may 

result in low levels of selenium in water, which may 

be taken up by plants. Weathering also releases 

selenium into the air on fine dust-like particles. 

Volcanic eruptions may release selenium in air. 

Selenium commonly enters the air from burning 

coal or oil. Selenium that may be present in fossil 

fuels combines with oxygen when burned, which 

may then react with water to form soluble selenium 

compounds. Airborne particles of selenium, such as 

in ash, can settle on soil or surface water. Disposal 

of selenium in commercial products and waste 

could also increase the amount of selenium in soil. 

The forms and fate of selenium in soil depend 

largely on the acidity of the surroundings and its 

interaction with oxygen. In the absence of oxygen 

when the soil is acidic, the amount of selenium that 

can enter plants and organisms should be low. 

Elemental selenium that cannot dissolve in water 

and other insoluble forms of selenium are less 

mobile and will usually remain in the soil, posing 

smaller risk of exposure. Selenium compounds that 

can dissolve in water are sometimes very mobile. 

Thus, there is an increased chance of exposure to 

these compounds. Selenium may enter surface 

water in irrigation drainage waters. Some evidence 

indicates that selenium can be taken up in tissues of 

aquatic organisms and possibly increase in 

concentration as the selenium is passed up through 

the food chain. Selenium concentrations in aquatic 

organisms have been a problem as a result of 

irrigation runoff in some dry areas of the United 

States. 

1.3 HOW MIGHT I BE EXPOSED TO 

SELENIUM? 

People are exposed to low levels of selenium daily 

through food, water, and air. Selenium is also an 

essential nutrient for humans and animals. 

However, selenium can be harmful when regularly 

taken in amounts higher than those needed for good 

health. People receive the majority of their daily 

intake of selenium from eating food, and to a lesser 

extent, from water intake. Estimates of the average 

intake of selenium from food for the U.S. 

population range from 71 to 152 millionths of a 

gram of selenium per person per day. Low levels of 

selenium can also be found in drinking water. 

Selenium levels are less than 10 parts of selenium in 

a billion parts of water (10 ppb) in 99.5% of 

drinking water sources tested. People may be 

exposed to higher-than-normal levels of selenium at 

hazardous waste sites by swallowing soil or water, 

or by breathing dust. In some parts of the United 

States, especially in the western states, some soils 

naturally have higher levels of selenium 

compounds. Some plants can build up selenium to 

levels that harm livestock feeding on them. In these 

areas, people could be exposed to too much 

selenium if they eat a lot of locally grown grains 

and vegetables or animal products that have built up 

high levels of selenium. People may also be 

exposed to selenium from industrial sources. 

Humans are normally not exposed to large amounts 

of selenium in the air, unless selenium dust or 

volatile selenium compounds are formed in their 

workplace. Occupations in which humans may be 

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 

SELENIUM 

CAS#: 7782-49-2 

Division of Toxicology September 2003 

exposed to selenium in the air are the metal 

industries, selenium-recovery processes, paint 

manufacturing, and special trades. 

1.4 HOW CAN SELENIUM ENTER AND 

LEAVE MY BODY? 

Selenium from the environment mainly enters the 

body when people eat food containing selenium. 

The human body easily absorbs the organic 

selenium compounds (for example, selenoamino 

acids) when eaten, and makes them available where 

needed in the body. The selenium in drinking water 

is usually in the form of inorganic sodium selenate 

and sodium selenite; these forms of selenium are 

also easily absorbed from the digestive tract. The 

human body can change these inorganic selenium 

compounds into forms that it can use. Selenium in 

the air may also enter your body when you breathe 

it. 

Hazardous waste sites at which selenium is present 

could represent a major source of exposure. The 

way that selenium can enter the body from a 

particular site depends on such factors as whether 

vegetables are grown in soil in which selenium from 

the site has been deposited, whether water at the site 

contains selenium and is able to flow into drinking 

water supplies, and whether selenium dust blows 

into the air. As mentioned earlier, specific 

conditions at a site can greatly influence which 

selenium compounds form and whether they can 

move in the environment to places where people 

might be exposed. Therefore, it is important to 

know that the presence of selenium at a site does 

not necessarily mean that people are being exposed 

to it. Specific tests of locally grown food, drinking 

water, and air must be done to find out whether 

exposure is occurring. You should also be aware 

that selenium compounds, including those used in 

some medicated dandruff shampoos, are not easily 

absorbed through the skin. 

Most of the selenium that enters the body quickly 

leaves the body, usually within 24 hours. Beyond 

what the body needs, selenium leaves mainly in the 

urine, but also in feces and breath. Selenium in the 

urine increases as the amount of the exposure goes 

up. Selenium can build up in the human body, 

however, if exposure levels are very high or if 

exposure occurs over a long time. The amount that 

builds up in the body depends on the chemical form 

of the selenium. It builds up mostly in the liver and 

kidneys but also in the blood, lungs, heart, and 

testes. Selenium can build up in the nails and in 

hair, depending on time and amount of exposure. 

1.5 HOW CAN SELENIUM AFFECT MY 

HEALTH? 

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 hurt people is to 

learn how the chemical is absorbed, used, and 

released by the body; for some chemicals, animal 

testing may 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 

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 

SELENIUM 

CAS#: 7782-49-2 

Division of Toxicology September 2003 

scientists must comply with strict animal care 

guidelines. 

The general public rarely breathes high levels of 

selenium, although some people may be exposed to 

selenium dust and selenium compounds in 

workplace air. Dizziness, fatigue, and irritation of 

mucous membranes have been reported in people 

exposed to selenium in workplace air at 

concentrations higher than legal levels. In extreme 

cases, collection of fluid in the lungs (pulmonary 

edema) and severe bronchitis have been reported. 

The exact exposure levels at which these effects 

might occur are not known, but they become more 

likely with increasing amounts of selenium and with 

increasing frequency of exposure. 

The normal intake of selenium by eating food is 

enough to meet the Recommended Daily Allowance 

(RDA) for this essential nutrient. However, as 

discussed in Chapters 2 and 3 of this profile, 

selenium compounds can be harmful at daily dietary 

levels that are higher than needed. The seriousness 

of the effects of excess selenium depends on how 

much selenium is eaten and how often. Intentional 

or accidental swallowing of a large amount of 

sodium selenate or sodium selenite (for example, a 

very large quantity of selenium supplement pills) 

could be life-threatening without immediate 

medical treatment. Even if mildly excessive 

amounts of selenium are eaten over long periods, 

brittle hair and deformed nails can develop. In 

extreme cases, people may lose feeling and control 

in arms and legs. These health effects, called 

selenosis, were seen in several villages in China 

where people were exposed to foods high in 

selenium for months to years. No human 

populations in the United States have been reported 

with long-term selenium poisoning, including 

populations in the western part of the country where 

selenium levels are naturally high in the soil. 

Because most people in the United States eat foods 

produced in many different areas, overexposure to 

selenium in food is unlikely to occur. 

In some regions of China where soil levels of 

selenium are very low, not eating enough selenium 

has resulted in health effects. Selenium is used by 

the body in antioxidant enzymes that protect against 

damage to tissues done by oxygen, and in an 

enzyme that affects growth and metabolism. Not 

eating enough selenium can cause heart problems 

and muscle pain. Muscle pain has also been noted in 

people fed intravenously for a long time with 

solutions that did not contain selenium. Babies born 

early may be more sensitive to not having enough 

selenium, and this may contribute to lung effects. In 

the United States, selenium in food is sufficient to 

meet the RDA and prevent harmful effects from not 

enough selenium. 

Upon contact with human skin, industrial selenium 

compounds have been reported to cause rashes, 

redness, heat, swelling, and pain. Brief, acute 

exposure of the eyes to selenium dioxide as a dust 

or fume in workplace air may result in burning, 

irritation, and tearing. However, only people who 

work in industries that process or use selenium or 

selenium compounds are likely to come into contact 

with levels high enough to cause eye irritation. 

Studies of laboratory animals and people show that 

most selenium compounds probably do not cause 

cancer. In fact, some studies of cancer in humans 

suggest that lower-than-normal selenium levels in 

the diet might increase the risk of cancer. Other 

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 

SELENIUM 

CAS#: 7782-49-2 

Division of Toxicology September 2003 

studies suggest that dietary levels of selenium that 

are higher than normal might reduce the risk of 

cancer in humans. However, taking selenium so that 

your daily amount is greater than that required 

might just increase your risk of selenium poisoning. 

Based on studies done until 1987, the International 

Agency for Research on Cancer (IARC) determined 

that selenium and selenium compounds could not be 

classified as to their ability to cause cancer in 

humans. However, since then, the EPA has 

determined that one specific form of selenium, 

called selenium sulfide, is a probable human 

carcinogen. Selenium sulfide is the only selenium 

compound shown to cause cancer in animals. Rats 

and mice that were fed selenium sulfide daily at 

very high levels developed cancer. Selenium sulfide 

is not present in foods, and it is a very different 

chemical from the organic and inorganic selenium 

compounds found in foods and in the environment. 

Also, if introduced into the environment, selenium 

sulfide does not dissolve readily in water and would 

probably bind tightly to the soil, further reducing 

any chance of exposure. Because selenium sulfide is 

not absorbed through the skin, the use of antidandruff shampoos containing selenium sulfide is 

generally considered safe. 

Very high amounts of selenium have caused 

decreased sperm counts, increased abnormal sperm, 

changes in the female reproductive cycle in rats, 

and changes in the menstrual cycle in monkeys. The 

relevance of the reproductive effects of selenium 

exposure in animals studied to potential 

reproductive effects in humans is not known. 

Selenium compounds have not been shown to cause 

birth defects in humans or in other mammals. 

1.6 HOW CAN SELENIUM AFFECT 

CHILDREN? 

This section discusses potential health effects from 

exposures during the period from conception to 

maturity at 18 years of age in humans. 

Children living near selenium waste sites or coal 

burning plants are likely to be exposed to higher 

environmental levels of selenium through breathing, 

touching soil, and eating contaminated soil. 

Children living in areas of China with high 

selenium in the soil had higher levels of selenium in 

the blood than adults from that area. Very few 

studies have looked at how selenium can affect the 

health of children. Children need small amounts of 

selenium for normal growth and development. 

Children will probably show the same sort of health 

effects from selenium exposure as adults, but some 

studies suggest that they may be less susceptible to 

health effects of selenium than adults. 

We do not know if exposure to selenium could 

result in birth defects in people. Selenium 

compounds have not been shown to cause birth 

defects in humans or in other mammals. We have 

no information to suggest that there are any 

differences between children and adults in where 

selenium is found in the body or in how fast it 

enters or leaves the body. Studies in laboratory 

animals have shown that selenium crosses the 

placenta and enters the fetus. Studies in humans 

show that infants are supplied with selenium 

through breast milk, and therefore, women who 

were exposed to selenium by living near a waste 

site might transfer selenium to their babies. 

However, babies in areas of China with high 

selenium in the soil did not show any signs of health 

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 

SELENIUM 

CAS#: 7782-49-2 

Division of Toxicology September 2003 

effects due to selenium, even though some of their 

parents did. 

1.7 HOW CAN FAMILIES REDUCE THE 

RISK OF EXPOSURE TO SELENIUM? 

If your doctor finds that you have been exposed to 

significant amounts of selenium, ask whether your 

children might also be exposed. Your doctor might 

need to ask your state health department to 

investigate. 

Since selenium occurs naturally in the environment, 

we cannot avoid exposure to it. Certain dietary 

supplements and anti-dandruff shampoos contain 

selenium in high levels. You should not exceed the 

recommended dosages when using these products. 

Children living near selenium waste sites or coal 

burning plants are likely to be exposed to higher 

environmental levels of selenium through breathing, 

touching soil, and eating contaminated soil. Some 

children eat a lot of dirt. You should discourage 

your children from eating dirt. Make sure they wash 

their hands frequently and before eating. 

Discourage your children from putting their hands 

in their mouths or from other hand-to-mouth 

activity. 

The primary route of human exposure to selenium is 

through eating food. People who irrigate their home 

gardens with groundwater containing high levels of 

selenium may grow and eat plants that contain high 

levels of selenium because this element is taken up 

in some plants. Fishermen and hunters of waterfowl 

who regularly eat fish and game from waterways 

with high selenium content may also consume 

above average levels of selenium. To reduce your 

family's exposure to selenium, obey any wildlife 

advisories issued by your state. Information on fish 

and wildlife advisories in your state is available 

from your state public health or natural resources 

department. 

1.8 IS THERE A MEDICAL TEST TO 

DETERMINE WHETHER I HAVE BEEN 

EXPOSED TO SELENIUM? 

Selenium can be measured in the blood, urine, and 

fingernails or toenails of exposed individuals. 

However, since selenium is an essential nutrient 

normally present in foods, low levels of selenium 

are normally found in body tissues and urine. Tests 

for selenium are most useful for people who have 

recently been exposed to high levels. Samples of 

blood, urine, or nails can be properly collected in a 

physician's office and sent to a laboratory that has 

the special equipment needed to measure selenium. 

Urine can be used to determine short-term exposure. 

Because red blood cells last about 120 days before 

they are replaced by newly made red blood cells, 

the presence of selenium in red blood cells can 

show whether a person was exposed to selenium 

during the 120 days before testing, but not if 

exposed more than 120 days before testing. Toenail 

clippings can be used to determine longer-term 

exposure. 

Many methods are available to measure selenium 

levels in human tissue and the environment. 

However, none of the methods that are routinely 

available can measure or detect each selenium 

compound in one test, and better tests that measure 

lower levels of different selenium compounds are 

needed. Also, these tests cannot determine the exact 

levels of selenium you may have been exposed to or 

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 

SELENIUM 

CAS#: 7782-49-2 

Division of Toxicology September 2003 

predict whether health effects will occur, even 

though very high amounts of selenium in blood are 

clearly related to selenosis. Some human as well as 

animal studies suggest that when people are 

exposed over a long period to higher-than-normal 

amounts of selenium, their bodies adjust to the 

higher amounts. 

The length of time that selenium stays in the body 

after exposure stops depends on the form of 

selenium to which the person was exposed. Thus, it 

is difficult to predict how useful a test will be if 

some time has gone by since exposure stopped. 

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), and the Food and Drug 

Administration (FDA). 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) and the National 

Institute for Occupational Safety and Health 

(NIOSH). 

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 selenium include the following: 

The EPA Office of Drinking Water regulates the 

amount of selenium allowed in drinking water. 

Public water supplies are not allowed to exceed 50 

ppb total selenium. 

The FDA regulations allow a level of 50 ppb of 

selenium in bottled water. OSHA is responsible for 

setting regulations on selenium levels allowable in 

the workplace. The exposure limit for selenium 

compounds in the air for an 8 hour period is 0.2 mg 

selenium/m3. 

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 or: 

Agency for Toxic Substances and Disease Registry 

Division of Toxicology 

1600 Clifton Road NE, Mailstop F-32 

Atlanta, GA 30333 

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 

SELENIUM 

CAS#: 7782-49-2 

Division of Toxicology September 2003 

Information line and technical assistance: 

Phone: 888-422-8737 

FAX: (770)-488-4178 

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. 

To order toxicological profiles, contact: 

National Technical Information Service 

5285 Port Royal Road 

Springfield, VA 22161 

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

Reference 

Agency for Toxic Substances and Disease Registry 

(ATSDR). 2003. Toxicological profile for selenium. 

Atlanta, GA: U.S. Department of Health and 

Human Services, Public Health Service. 

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