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Strontium
(chemical symbol Sr) is a silvery metal that rapidly turns yellowish in
air. Strontium is found naturally as a non-radioactive element.
Strontium has 16 known isotopes. Naturally occurring strontium is found
as four stable isotopes Sr-84, -86, -87, and -88. Twelve other isotopes
are radioactive. Strontium-90 is the most important radioactive isotope
in the environment, although strontium-89 can be found around reactors,
and strontium-85 is used in industry and medicine.
The Basics
Exposure to Strontium-90
Health Effects of Strontium-90
Protecting People From Strontium-90
The Basics
Who discovered strontium?
In 1790 Adair Crawford and William Cruikshank first
detected non-radioactive strontium in the mineral strontianite
in Scotland. Metallic strontium was isolated in 1808 by Sir Humphry
Davy.
Radioactive Sr-90, like many other radionuclides,
was discovered in the 1940s in nuclear experiments connected to
the development of the atomic bomb.
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Where does strontium-90 come from?
Strontium-90 is a by-product of the fission of uranium
and plutonium in nuclear reactors, and in nuclear weapons. Strontium-90
is found in waste from nuclear reactors. It can also contaminate
reactor parts and fluids. Large amounts of Sr-90 were produced
during atmospheric nuclear weapons tests conducted in the 1950s
and 1960s and dispersed worldwide.
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What are the properties of strontium-90?
Non-radioactive strontium and its radioactive isotopes
have the same physical properties. Strontium is a soft metal similar
to lead. Strontium is chemically very reactive, and is only found
in compounds in nature.
When freshly cut, it has a silvery luster, but rapidly
reacts with air and turns yellow. Finely cut strontium will burst
into flame in air. Because of these qualities, it is generally
stored in kerosene.
Strontium-90 emits a beta particle with, no gamma
radiation, as it decays to yttrium-90 (also a beta-emitter). Strontium-90
has a half-life of 29.1 years. It behaves chemically
much like calcium, and therefore tends to concentrate in the bones
and teeth.
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What is strontium-90 used for?
Strontium-90
is used as a radioactive tracer in medical and agricultural studies.
The heat generated by strontium-90's radioactive decay can be converted
to electricity for long-lived, portable power supplies. These are often
used in remote locations, such as in navigational beacons, weather
stations, and space vehicles.
Strontium-90 is also used in electron tubes, as a radiation source
in industrial thickness gauges, and for the treatment of eye diseases.
Controlled amounts of strontium-90 have been used as a treatment
for bone cancer.
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Exposure to Strontium-90
How does strontium-90 get into the environment?
Strontium-90 was widely dispersed in the 1950s and
1960s in fall out from atmospheric testing of nuclear weapons.
It has been slowly decaying since then so that current levels
from these tests are very low.
Strontium-90 is also found in waste from nuclear
reactors. It is considered one of the more hazardous constituents
of nuclear wastes. The accident at the Chernobyl nuclear power
plant also introduced a large amount of Sr-90 into the environment.
A large part of the Sr-90 was deposited in the Soviet Republics.
The rest was dispersed as fallout over Northern Europe and worldwide.
No significant amount of stronium-90 reached the U.S.
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How does strontium-90 change in the environment?
As strontium-90 decays, it releases radiation and
forms yttrium-90 (Y-90), which in turn decays to stable zirconium.
The half-life of Sr-90 is 29.1 years, and that of Yttrium-90 is
64 hours. Sr-90 emits moderate energy beta particles, and Y-90
emits very strong (energetic) beta particles. Strontium-90 can
form many chemical compounds, including halides, oxides, and sulfides,
and moves easily through the environment.
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How do people come in contact with strontium-90?
Everyone is exposed to small amounts of strontium-90,
since it is widely dispersed in the environment and the food chain.
Dietary intake of Sr-90, however, has steadily fallen over the
last 30 years with the suspension of nuclear weapons testing.
People who live near or work in nuclear facilities may have increased
exposure to Sr-90. The greatest concern would be the exposures
from an accident at a nuclear reactor, or an accident involving
high-level wastes.
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How does strontium-90 get into the body?
People may inhale trace amounts of strontium-90 as
a contaminant in dust. But, swallowing Sr-90 with food or water
is the primary pathway of intake.
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What does strontium-90 do once it gets into the body?
When people ingest Sr-90, about 70-80% of it passes
through the body. Virtually all of the remaining 20-30% that is
absorbed is deposited in the bone. About 1% is distributed among
the blood volume, extracellular fluid, soft tissue, and surface
of the bone, where it may stay and decay or be excreted.
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Health Effects of Strontium-90
How can strontium-90 affect people's health?
Strontium-90 is chemically similar to calcium, and
tends to deposit in bone and blood-forming tissue (bone marrow).
Thus, strontium-90 is referred to as a "bone seeker."
Internal exposure to Sr-90 is linked to bone cancer, cancer of
the soft tissue near the bone, and leukemia.
Risk of cancer increases with increased exposure
to Sr-90. The risk depends on the concentration of Sr-90 in the
environment, and on the exposure conditions.
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Is there a medical test to determine exposure to strontium-90?
The most common test for exposure to strontium-90
is a bioassay, usually by urinalysis. As with most cases of internal
contamination, the sooner the test is taken after ingesting or
inhaling the contaminant, the more accurate the results will be.
Most major medical centers should be capable of performing this
test.
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Protecting People from Strontium-90
How do I know strontium if I'm near strontium-90?
Although you are exposed to tiny amounts of strontium-90
from past accidents and weapons testing, you cannot sense its
presence. You need specialized equipment to detect Sr-90.
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What can I do to protect myself and my family from
strontium-90?
Strontium-90 dispersed in the environment, like that
from atmospheric weapons testing, is almost impossible to avoid.
You may also be exposed to tiny amounts from nuclear power reactors
and certain government facilities. The more serious risk to you
(though it is unlikely), is that you may unwittingly encounter
an industrial instrument containing a Sr-90 radiation source.
This is more likely if you work in specific industries:
- scrap metal sorting, sales and brokerage
- metal melting and casting
- municipal landfill operations.
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Orphan
Sources Initiative
This
site provides information on EPA's efforts to retrieve orphan sources
for proper disposal and to protect the public from them. |
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What is EPA doing about strontium-90?
EPA protects people and the environment from Sr-90
by establishing standards for the clean-up of contaminated sites,
by setting limits on the amount of Sr-90 (and other radionuclides)
that may be released to the air, and by setting limits on the
amount of strontium-90 (and other radionuclides) that may be present
in public drinking water.
EPA uses its authority under the Comprehensive
Environmental Response, Compensation, and Liability Act (commonly
known as "Superfund") to set standards for the clean-up
of existing contaminated sites. Cleanups must meet all environmental
requirements that are relevant or applicable, including state
regulations and regulations issued in connection with other federal
environmental laws.
When these types of regulations are unavailable,
or not protective enough, EPA sets site-specific cleanup levels.
Site-specific standards limit the chance of developing cancer
because of exposure to a site-related carcinogen (such as strontium-90)
to between one in 10,000 and one in 1,000,000.
EPA uses its Clean
Air Act authority to set limits on the amount of radionuclides,
such as Sr-90, that may be released to the air.
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RadNESHAPS
This site provides information on EPA's
National
Emission Standards for Hazardous Air Pollutants: Radionuclides. |
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EPA uses its Safe
Drinking Water Act authority to establish maximum contaminant
levels (MCLs) for beta emitters, such as strontium-90, in public
drinking water. The MCL for beta emitters is 4 millirem per year
or 8 picoCuries per liter of water.
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