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PUBLIC HEALTH STATEMENT 

Americium 

CAS#: 7440-35-9 

Division of Toxicology April 2004 

This Public Health Statement is the summary 

chapter from the Toxicological Profile for 

americium. 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 

americium 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. Americium 

has been found in at least 8 of the 1,636 current or 

former NPL sites. However, the total number of 

NPL sites evaluated for americium is not known. 

As more sites are evaluated, the sites at which 

americium is found may increase. This information 

is important because exposure to americium 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 

normally 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. However, since americium is 

radioactive, you can also be exposed to its radiation 

if you are near it. 

External or internal exposure to radiation may occur 

from natural or man-made sources. Naturally 

occurring sources of radiation are cosmic radiation 

from space or naturally occurring radioactive 

materials in our body or in soil, air, water, or 

building materials. Man-made sources of radiation 

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 americium, 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 or 

radioactive materials you’re exposed to and your 

age, sex, diet, family traits, lifestyle, and state of 

health. 

1.1 WHAT IS AMERICIUM? 

Americium (pronounced, 1am-c-0ris(h)-‘-cm) is a 

human-made, radioactive element. There are no 

naturally occurring or stable isotopes of americium. 

Pure americium is a silvery metal. There are two 

important isotopes of americium, americium 241 

and americium 243, also written as 241Am and 

243Am, and read as americium two-forty-one and 

americium two-forty-three. Both isotopes have the 

same chemical behavior in the environment. 

Quantities of americium, as well as other 

radioactive elements, can be measured in units of 

mass (grams), but are usually measured in terms of 

their radioactivity (curies or becquerels). Both the 

DEPARTMENT of HEALTH AND HUMAN SERVICES, Public Health Service
 

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__________________________________________________________________________________________ 

PUBLIC HEALTH STATEMENT 

Americium 

CAS#: 7440-35-9 

Division of Toxicology April 2004 

curie (Ci) and the becquerel (Bq) tell us how much 

a radioactive material decays every second. The 

becquerel is a new international unit and the curie is 

a traditional unit; both units are currently used in 

the United States. A becquerel is the amount of 

radioactive material in which 1 atom transforms 

every second, and a curie is the amount of 

radioactive material in which 37 billion atoms 

transform every second. 

Each radioactive isotope of an element, including 

americium, constantly gives off radiation, which 

changes it into an isotope of a different element or a 

different isotope of the same element. This newly 

formed nuclide may be stable or radioactive. This 

process is called radioactive decay. 241Am and 

243Am give off alpha particles (sometimes referred 

to as alpha radiation) and change into 

neptunium 237 (237Np) and neptunium 239 (239Np), 

respectively. Neptunium is also radioactive, so 

isotopes of this element also give off radiation and 

change into isotopes of other elements. This 

process continues and eventually ends when stable 

isotopes of bismuth and lead are formed. 

Half-life is the term that is used to describe the rate 

of the decay process. Specifically, the half-life is 

the time it takes for half of the atoms of a 

radionuclide to undergo radioactive decay and 

change it into a different isotope. The half-life of 

241Am is 432 years. The half-life of 243Am is 

7,370 years. 

Specific activity is a term that describes the relative 

rates of decay of the same mass of different 

radioactive materials. If you have 1 gram of each 

isotope of americium side by side, the specific 

activities would be 3.4 curies per gram for 241Am 

and 0.2 curies per gram for 243Am. Thus, for the 

same mass, 241Am is about 17 times more 

radioactive (i.e., its specific activity would be 

17 times higher) than that of 243Am. The higher the 

specific activity of a radioisotope, the faster it is 

decaying. 

The predominant commercial use of 241Am is in 

ionization-type smoke detectors. This application 

relies on the alpha particles that are produced when 

the isotope decays as an ionization source. A 

typical household smoke detector contains 

0.9 microcuries (μCi; a μCi is one millionth of a 

curie) or 33,000 Bq of 241Am, and 1 g of americium 

dioxide is sufficient to make 5,000 smoke detectors. 

241Am is also used for industrial gauging 

applications and in medical diagnostic devices. 

There are research applications, but no commercial 

applications for 243Am. This will change if the 

United States and Russia turn nuclear warheads into 

power reactor fuel by making a mixed oxide fuel of 

uranium and plutonium. This fuel, called MOX, 

will contain both 241Am and 243Am, and the plan is 

to use it to make electricity. Once used, the spent 

nuclear fuel is to be sent for disposal. 

1.2 WHAT HAPPENS TO AMERICIUM 

WHEN IT ENTERS THE 

ENVIRONMENT? 

241Am can be released to the environment from 

nuclear reactors, nuclear explosions, and accidents, 

as well as from manufacturing products containing 

americium (such as smoke detectors). Americium 

is a byproduct of plutonium production. 241Am is 

formed from the radioactive decay of plutonium 

241 (241 Pu), which itself is produced from uranium 

238 (238U) while it is inside an operating nuclear 

reactor. In the absence of clean-up procedures, 

DEPARTMENT of HEALTH AND HUMAN SERVICES, Public Health Service
 

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__________________________________________________________________________________________ 

PUBLIC HEALTH STATEMENT 

Americium 

CAS#: 7440-35-9 

Division of Toxicology April 2004 

radioactive decay is the only way for decreasing the 

amount of americium in the environment. Because 

241Am has a long half-life, it will be present in the 

environment for a long time. Since 241Pu can be 

released along with 241Am in the decay process, the 

amount of 241Am will slowly increase for decades, 

even in the absence of additional 241Am releases, 

and then slowly decrease. 

241Am released to the atmosphere will be associated 

with particles and will settle to earth or be washed 

from the air in precipitation (e.g., rain, snow). 

241Am from atmospheric nuclear weapons tests may 

remain in the atmosphere for decades before settling 

to earth. For example, 241Am released in nuclear 

accidents, like the accident at Chernobyl, will stay 

in the lower atmosphere and begin to settle to earth 

near the site from which it was released. Larger 

particles will settle out more quickly and over a 

smaller area; smaller particles may remain in the 

atmosphere for several months and travel far from 

where they were released. Precipitation removes 

particles from the air more rapidly. 

241Am released into water from nuclear facilities 

will tend to stick to particles in the water or the 

sediment. 241Am deposited on soil is so strongly 

attached to soil particles that it does not travel very 

far into the ground. Ultimately, most americium 

ends up in soil or sediment. 

While plants may take up 241Am from the soil, the 

amount taken up is small, especially in the parts of 

the plant that are most often eaten (i.e., the fruit, 

grain, and seeds). While fish may take up 241Am, 

the amount that builds up in the flesh is very small. 

Most of the 241Am found in shellfish like shrimp or 

mussels is contained in the shell, rather than in the 

edible parts of the animal. 

1.3 HOW MIGHT I BE EXPOSED TO 

AMERICIUM? 

You may be exposed to 241Am by breathing air, 

drinking water, or eating food containing 241Am; 

however, the levels of 241Am in air, water, soil, and 

food are generally very low, and of little health 

consequence. 

People working at sites where nuclear waste is 

stored, in nuclear power plants, or in other nuclear 

facilities that handle 241Am may be exposed to 

higher levels of americium than the general 

population. People living near these sites also may 

be exposed to elevated levels of americium. People 

who produce or handle 241Am in smoke detectors or 

other devices may be exposed to higher levels. In 

the case of a nuclear accident, exposure could occur 

by breathing or eating dust containing 241Am. Even 

at sites that contain measurable levels of radioactive 

contamination, the amount of 241Am that is taken up 

into plant and animal tissue is so small that it is of 

little concern. 

1.4 HOW CAN AMERICIUM ENTER AND 

LEAVE MY BODY? 

Americium can enter your body from the air you 

breathe, the food you eat, or the water you drink, or 

from contact with your skin. If you breathe in air 

that contains americium, some forms of americium 

that dissolve, easily in lung fluid stay in your lungs 

for hours or days. Other forms that do not dissolve 

easily in lung fluid might stay in your lungs for 

months or years. Some americium that enters your 

lungs may get into your blood. If you swallow 

americium, a very small amount of what enters your 

DEPARTMENT of HEALTH AND HUMAN SERVICES, Public Health Service
 

Agency for Toxic Substances and Disease Registry 

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__________________________________________________________________________________________ 

PUBLIC HEALTH STATEMENT 

Americium 

CAS#: 7440-35-9 

Division of Toxicology April 2004 

digestive tract may also enter your blood. Most of 

the americium entering your blood leaves your body 

in your urine and feces. Of the small amount that 

stays in your body, most goes to your bones, where 

it can remain for many decades; a smaller amount 

goes into your liver and other organs, where it may 

remain for a few years as the body clears it. 

1.5 HOW CAN AMERICIUM 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. In the case of a radioactive 

chemical, it is also important to gather information 

concerning the radiation dose and dose rate to 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 

scientists must comply with strict animal care 

guidelines. 

In the process of radioactive decay, americium 

releases alpha particles and gamma rays. Alpha 

particles are relatively high energy particles, but 

travel only extremely short distances and do not 

penetrate the skin. However, if americium is taken 

into the body and enters body tissues, alpha 

particles may produce damage to nearby cells. 

Gamma rays can travel much greater distances and 

can penetrate the entire body. Since alpha particles 

do not penetrate the skin and the gamma rays 

released from americium sources are relatively low 

in energy, external exposure to americium is not 

usually considered to be a danger to your health. 

The radiation from americium is the primary cause 

of adverse health effects from absorbed americium. 

Upon entering the body by any route of exposure, 

americium moves relatively rapidly through the 

body and is deposited on the surfaces of the bones 

where it remains for a long time. As americium 

undergoes radioactive decay in the bone, alpha 

particles collide with nearby cell matter and give all 

of their energy to this cell matter. The gamma rays 

released by decaying americium can travel much 

farther before hitting cellular material, and many of 

these gamma rays leave the body without hitting or 

damaging any cell matter. The dose from this alpha 

and gamma radiation can cause changes in the 

genetic material of these cells that could result in 

health effects such as bone cancers. Exposure to 

extremely high levels of americium, as has been 

reported in some animal studies, has resulted in 

damage to organs such as the lungs, liver, kidneys, 

and thyroid. It is rare, however, that a person would 

be exposed to amounts of americium large enough 

to cause harmful effects in these organs. 

1.6 HOW CAN AMERICIUM AFFECT 

CHILDREN? 

This section discusses potential health effects from 

exposures during the period from conception to 

maturity at 18 years of age in humans. 

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 
__________________________________________________________________________________________ 

PUBLIC HEALTH STATEMENT 

Americium 

CAS#: 7440-35-9 

Division of Toxicology April 2004 

Americium accumulates in human bones and 

remains there for a long time. Americium emits 

radioactive alpha particles in the bone that can 

cause damage to the surrounding tissue. The body 

normally repairs all of the damage, but if it fails, 

bone cancer could result after many years. If 

americium exposure to children occurs, the 

exposure to the radiation from americium may be 

for a longer period of time, causing a larger 

radiation dose over their lifetime and increasing the 

likelihood of producing cancer. However, there are 

no published data showing that children are more 

susceptible than adults to radiation-induced 

americium toxicity. A developing baby is expected 

to have some americium in its body. It could be 

affected by this americium while in the womb if the 

pregnant mother has high enough levels of 

americium in her blood. 

1.7 HOW CAN FAMILIES REDUCE THE 

RISK OF EXPOSURE TO 

AMERICIUM? 

If your doctor finds that you have been exposed to 

significant amounts of americium, ask whether your 

children might also be exposed. Your doctor might 

need to ask your state health department to 

investigate. 

While discharges from nuclear waste sites, nuclear 

reactors, or plants that manufacture ionization 

smoke detectors or gauges containing americium 

are regulated, it is possible that higher-than-normal 

levels of americium may be in soil near a nuclear 

waste site, nuclear reactor, or plant that 

manufactures ionization smoke detectors or gauges 

containing americium. If you live near any of these 

types of nuclear or manufacturing sites, discourage 

your children from putting their hands in their 

mouths and engaging in other hand-to-mouth 

activities. 

Discharge water and air emissions from facilities 

that make americium smoke detectors or gauges or 

produce plutonium for nuclear weapons may 

contain some americium. These operations are 

strictly regulated, but you can check local health 

advisories before consuming fish or other food from 

these waters. Nuclear reactors are not expected to 

discharge measurable amounts of americium. 

Ionization smoke detectors that contain americium 

are safe when installed; however, you should not 

allow your children to play with these detectors. If 

the detectors are damaged or are no longer being 

used, they should be promptly returned to the 

manufacturer for disposal. 

1.8 IS THERE A MEDICAL TEST TO 

DETERMINE WHETHER I HAVE BEEN 

EXPOSED TO AMERICIUM? 

Physicians do not test for americium in their offices, 

but they can collect samples and send them to 

special laboratories or request that you be sent to 

such a laboratory. If you are exposed to a large 

dose of radiation from americium, your blood can 

be tested for signs of damage to the cell 

chromosomes. If americium were to enter your 

body from contaminated air, food, or water, the 

amount of americium (in Ci or Bq) can be estimated 

by measuring the radiation given off by the 

americium present in samples of blood, urine, teeth, 

or tissue. If in the lungs, the amount of americium 

can be estimated by measuring the americium 

gamma radiation that exits the body. Radiation 

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 
__________________________________________________________________________________________ 

PUBLIC HEALTH STATEMENT 

Americium 

CAS#: 7440-35-9 

Division of Toxicology April 2004 

detector systems used for these purposes are at a 

limited number of locations. The amount in your 

lungs and excretions falls sharply after exposure, so 

tests should be done as soon as possible. 

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), 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 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 americium include the 

following: 

The USNRC established radiation dose limits to the 

public and to workers. To ensure that these limits 

are met, USNRC also set concentration limits for 

241Am in air, water, and sewer discharge that can be 

released from licensed facilities. This ensures that 

the annual radiation dose will not exceed 0.1 rem 

(0.001 sievert) to the public, or 5 rem (0.05 sievert) 

to the worker or 50 rem (0.5 sievert) to their bones. 

The concentration limits are 

0.00000000000002 microcurie per milliliter 

(2x10-14 μCi/mL) for air, 0.00000002 microcurie 

per milliliter (2x10-8 μCi/mL) for water, and 

0.0000002 microcurie per milliliter (2x10-7 μCi/mL) 

for releases to sewers. The USNRC requires that 

intake of americium not exceed the specified annual 

limits on intake (ALI) for inhalation or oral routes 

of exposure. The occupational exposure limits are 

6x10-3 μCi (ALI) for workers inhaling 241Am and 

8x10-1 μCi (ALI) for ingestion of 241Am. The level 

of 241Am in workplace air, specified as the derived 

air concentration (DAC), is not to exceed 

3x10-12 μCi/mL (which can be adjusted to account 

for work weeks shorter or longer than 40 hours). 

The FDA has set a food contamination guideline of 

2 Bq/kg per kilogram (5.4x10-5 μCi/kg) for 241Am 

to protect 3-month-old children. This is the 

population group that would receive the highest 

radiation dose from eating food that contains 

americium. The EPA has established a public 

drinking water limit of 15 picocurie per liter 

(pCi/L). This is for the sum of all radioactive 

materials that give off alpha radiation. 241Am and 

243Am are examples, but drinking water normally 

DEPARTMENT of HEALTH AND HUMAN SERVICES, Public Health Service
 

Agency for Toxic Substances and Disease Registry 

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__________________________________________________________________________________________ 

PUBLIC HEALTH STATEMENT 

Americium 

CAS#: 7440-35-9 

Division of Toxicology April 2004 

contains other alpha emitters, such as uranium, 

thorium, and radium. 

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 

CD-ROM 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