September 1999 |
ToxFAQs™ |
for |
Uranium |
(Uranio) |
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This fact sheet answers the most frequently
asked health questions about uranium. For more information,
you may call the ATSDR Information Center at 1-888-422-8737.
This fact sheet is one in a series of summaries about hazardous
substances and their health effects. 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.
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HIGHLIGHTS: Uranium is a naturally
occurring chemical substance that is mildly radioactive.
Everyone is exposed to low amounts of uranium through
food, air, and water. Exposure to high levels of uranium
can cause kidney disease. It is not known to cause cancer,
but can decay into other radioactive materials that may.
Uranium above natural levels has been found in at least
54 of the 1,517 National Priorities List sites identified
by the Environmental Protection Agency (EPA). |
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What
is uranium? |
Uranium is a common naturally occurring
and radioactive substance. It is a normal part of rocks, soil,
air, and water, and it occurs in nature in the form of minerals
- but never as a metal. Uranium metal is silver-colored with
a gray surface and is nearly as strong as steel. Natural uranium
is a mixture of three types or isotopes called U-234 (234U),
U-235 (235U), and U-238 (238U).
All three are the same chemical, but they have different radioactive
properties.
Typical concentrations in soil are a
few parts per million (ppm). Some rocks contain high enough
mineral concentrations of uranium to be mined. The rocks are
taken to a chemical plant where the uranium is taken out and
made into uranium chemicals or metal. The remaining sand is
called mill tailings. Tailings are rich in the chemicals and
radioactive materials that were not removed, such as radium
and thorium.
One of the radioactive properties of
uranium is half-life, or the time it takes for half of the
isotope to give off its radiation and change into another
substance. The half-lives are very long (around 200,000 years
for 234U, 700 million years
for 235U, and 5 billion years
for 238U. This is why uranium
still exists in nature and has not all decayed away.
The isotope 235U
is useful as a fuel in power plants and weapons. To make fuel,
natural uranium is separated into two portions. The fuel portion
has more 235U than normal
and is called enriched uranium. The leftover portion with
less 235U than normal is called
depleted uranium, or DU. Natural, depleted, and enriched uranium
are chemically identical. DU is the least radioactive and
enriched uranium the most.
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What
happens to uranium when it enters the environment? |
- Uranium is already naturally present throughout the environment.
Human activities, wind, streams, and volcanoes can move
the uranium around and change the levels that you are exposed
to.
- Uranium is found in soil where it may stay for billions
of years.
- It exists as dust in the air and the dust settles onto
surface water, soil, and plants.
- Uranium enters water by dissolving soil, eroding soil
and rocks, or in releases from processing plants. Larger
particles settle into the bottom of lakes, rivers, and ponds
and join uranium that is there naturally.
- Some plants may absorb uranium or it may stick to the
root surface.
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How
might I be exposed to uranium? |
- Breathing air or drinking water in a place that has higher
than background levels of uranium.
- Eating food grown in areas with higher than background
levels of uranium.
- Working in factories that process uranium or with phosphate
fertilizers, or living near any type of mine.
- Living near a coal-fired power plant.
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How
can uranium affect my health? |
All uranium mixtures (natural, depleted,
and enriched) have the same chemical effect on your body.
Large amounts of uranium can react with the tissues in your
body and damage your kidneys. The radiation damage from exposure
to high levels of natural or depleted uranium are not known
to cause cancer (see next section).
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How
likely is uranium to cause cancer? |
Humans and animals exposed to high levels
of uranium did not have higher cancer rates. The Committee
on the Biological Effects of Ionizing Radiation (BEIR IV)
reported that eating food or drinking water that has normal
amounts of uranium will most likely not cause cancer.
Uranium can decay into other radioactive
substances, such as radium, which can cause cancer if you
are exposed to enough of them for a long enough period of
time. Studies have reported lung and other cancers in uranium
miners; however, the miners also smoked and were exposed to
other substances that cause cancer, such as radon and silica
dust.
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How
does uranium affect children? |
Like adults, children are exposed to
small amounts of uranium in air, food, and drinking water.
If children were exposed to very large amounts of uranium,
it is possible that they might have kidney damage like that
seen in adults. We do not know whether children differ from
adults in their susceptibility to the health effects of uranium
exposure.
It is not known if exposure to uranium
can affect the developing human fetus. In laboratory animals,
high doses of uranium in drinking water resulted in birth
defects and an increase in fetal deaths. Measurements of uranium
have not been made in pregnant women, so we do not know if
uranium can cross the placenta and enter the fetus. In an
experiment with pregnant animals, only a small amount of the
injected uranium reached the fetus.
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How
can families reduce the risk of exposure to uranium? |
If your doctor finds that you have been
exposed to significant amounts of uranium, ask whether your
children might also be exposed. Your doctor might need to
ask your state health department to investigate.
It is possible that higher-than-normal
levels of uranium may be in the soil at a hazardous waste
site. If you live near such a hazardous waste site, you should
prevent your children from eating dirt and make sure that
they wash their hands frequently and before eating. You should
also wash fruits and vegetables grown in that soil well, and
consider discarding the outside portion of root vegetables.
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Is
there a medical test to show whether I've been exposed to uranium? |
Uranium is in your normal diet, so there
will always be some level of uranium in all parts of your
body. Uranium is normally measured in a sample of urine collected
and sent to a laboratory. Blood, feces, and tissue samples
are rarely used. Because most uranium leaves the body within
a few days, higher than normal amounts in your urine shows
whether you have been exposed to larger-than-normal amounts
within the last week or so. Some highly sensitive radiation
methods can measure uranium levels for a long time after you
take in a large amount. Also, some radiation equipment can
tell if uranium is on your skin.
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Has the federal government made recommendations to protect human health? |
The EPA requires that spills or accidental
releases of uranium waste into the environment containing
0.1 curies or more of radioactivity must be reported to the
EPA.
The EPA is currently working to develop
an appropriate drinking water limit for uranium based on a
broad range of human and animal health studies.
The Occupational Safety and Health Administration
has set occupational exposure limits for uranium in breathing
air over an 8-hour workday, 40-hour workweek. The limits are
0.05 milligrams per cubic meter (0.05 mg/m³)
for soluble uranium dust and 0.25 mg/m³
for insoluble uranium dust.
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References |
Agency for Toxic Substances and Disease
Registry (ATSDR). 1999. Toxicological
Profile for uranium. Atlanta, GA: U.S. Department of Health
and Human Services, Public Health Service.
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Where can I get more information? |
ATSDR can tell you where to find occupational
and environmental health clinics. Their specialists can recognize,
evaluate, and treat illnesses resulting from exposure to hazardous
substances. You can also contact your community or state health
or environmental quality department if you have any more questions
or concerns. For more information, contact:
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Agency for Toxic Substances and Disease Registry
Division of Toxicology
1600 Clifton Road NE, Mailstop F-32
Atlanta, GA 30333
Phone: 1-888-42-ATSDR (1-888-422-8737)
FAX: (770)-488-4178
Email: ATSDRIC@cdc.gov
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