1.1 What is americium? |
1.2 What happens to americium when it
enters the environment? |
1.3 How might I be exposed to americium? |
1.4 How can americium enter and leave
my body? |
1.5 How can americium affect my health? |
1.6 How can americium affect children? |
1.7 How can families reduce the risk of
exposure to americium? |
1.8 Is there a medical test to determine
whether I have been exposed to americium? |
1.9 What recommendations has the federal
government made to protect human health? |
1.10 Where can I get more information? |
References |
|
|
|
April 2004 |
Public Health Statement |
for |
Americium |
(Americio) |
|
|
|
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 ToxFAQs™,
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, am--'ris(h)--m)
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 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.
|
back to top |
|
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, 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.
|
back to top |
|
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.
|
back to top |
|
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 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.
|
back to top |
|
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.
|
back to top |
|
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.
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.
|
back to top |
|
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.
|
back to top |
|
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 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.
|
back to top |
|
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
contains other alpha emitters, such as uranium, thorium, and
radium.
|
back to top |
|
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
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
|
back to top |
|
References |
Agency for Toxic Substances and Disease
Registry (ATSDR). 2004. Toxicological
profile for americium. Atlanta, GA: U.S. Department of
Health and Human Services, Public Health Service.
|
back to top |
|
|
|