July 1999 |
ToxFAQs™ |
for |
Thorium |
(Torio) |
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This fact sheet answers the most frequently
asked health questions about thorium. 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: Thorium is a radioactive
substance that occurs naturally in the environment. It
has been shown to cause an increase in cancers of the
lung, pancreas, and blood in workers exposed to high levels
of it in the air. This chemical has been found in at least
16 of the 1,177 National Priorities List sites identified
by the Environmental Protection Agency (EPA). |
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What
is thorium? |
Thorium is a naturally occurring, radioactive
substance. In the environment, thorium exists in combination
with other minerals, such as silica. Small amounts of thorium
are present in all rocks, soil, water, plants, and animals.
Soil contains an average of about 6 parts of thorium per million
parts of soil (6 ppm).
More than 99% of natural thorium exists
in the form of thorium-232. It breaks down into two parts-a
small part called "alpha" radiation and a large part called
the decay product. The decay product is also not stable and
continues to break down through a series of decay products
until a stable product is formed. During these decay processes,
radioactive substances are produced. These include radium
and radon. These substances give off radiation, including
alpha and beta particles, and gamma radiation.
Some rocks in underground mines contain
thorium in a more concentrated form. After these rocks are
mined, thorium is usually concentrated and changed into thorium
dioxide or other chemical forms. After most of the thorium
is removed, the rocks are called "depleted" ore or tailings.
Thorium is used to make ceramics, gas
lantern mantles, and metals used in the aerospace industry
and in nuclear reactions. Thorium can also be used as a fuel
for generating nuclear energy.
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What
happens to thorium when it enters the environment? |
- Thorium is a natural part of the environment.
- Thorium changes extremely slowly into other radioactive
substances.
- It takes about 14 billion years for half of the thorium-232
to change into new forms.
- As rocks are broken up by wind and water, the thorium
and all other components of the rocks become part of the
soil.
- Thorium in soil can be washed into rivers and lakes.
- Windblown dust and volcanic eruptions are natural sources
of thorium in the air.
- Burning coal may release small amounts of thorium into
the air.
- Mining thorium or making products that contain it may
also release thorium into the environment.
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How
might I be exposed to thorium? |
- Just by being alive, everyone is exposed to small amounts
of thorium in air, water, and food.
- Breathing air near facilities where uranium, phosphate,
or tin ore is processed.
- Living in homes built on soil with high levels of thorium.
- Working in the uranium, thorium, tin, and phosphate mining,
and gas mantle production industries may expose you to higher
levels of thorium.
- Living near radioactive waste disposal sites.
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How
can thorium affect my health? |
Studies on thorium workers have shown
that breathing high levels of thorium dust results in an increased
chance of getting lung disease. Liver diseases and effects
on the blood were found in people injected with thorotrast,
a thorium compound injected into the body as a radiographic
contrast medium between the years 1928 and 1955. Animal studies
have shown that breathing thorium may result in lung damage.
Studies on exposed human populations
have not reported any birth defects or effects on a person's
ability to have children.
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How
likely is thorium to cause cancer? |
Workers who had high exposures to cigarette
smoke, radon gas, and thorium had cancers of the lung, pancreas,
and blood. People who had large amounts of thorium injected
into their blood for special x-ray tests had more than the
usual number of liver tumors, cancers of the blood, such as
leukemia, and tumors of the bone, kidney, spleen, and pancreas.
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Is
there a medical test to show whether I've been exposed to thorium? |
Special tests that measure the level
of radioactivity from thorium in your urine and feces, and
radon gas in the air you exhale can determine if you have
been exposed to thorium. These tests are only useful if done
within several days to a week after exposure. The tests cannot
tell you if your health will be affected by the exposure.
They require special equipment and are probably not available
at your local clinic or hospital.
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Has the federal government made recommendations to protect human health? |
The EPA has set a drinking water limit
of 15 picocuries per liter (15 pCi/L) of water for gross alpha
particle activity and 4 millirems per year for beta particles
and photon activity (for example, gamma radiation and x-rays).
The federal recommendations have been
updated as of July 1999.
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Glossary |
CAS: Chemical Abstracts Service.
National Priorities List: A list of the
nation's worst hazardous waste sites.
Millirem (mrem): A unit used to measure
radiation dose.
Picocurie (pCi): A unit used to measure
the intensity of radiation.
ppm: Parts per million.
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References |
Agency for Toxic Substances and Disease
Registry (ATSDR). 1990. Toxicological Profile for thorium. 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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