Radium (chemical symbol Ra) is a naturally-occurring radioactive
metal. Its most common isotopes are radium-226, radium 224, and
radium-228. Radium is a radionuclide formed by the decay of uranium
and thorium in the environment. It occurs at low levels in virtually
all rock, soil, water, plants, and animals.
Who discovered radium?
Radium was discovered in 1898 by French physicist and Nobel laureate
Marie
Curie in pitchblende (a uranium and radium-bearing mineral).
There is about 1 gram of radium in 7 tons of pitchblende. Elemental
radium was isolated by Mme. Curie in 1911.
Where does radium come from?
Radium forms when isotopes of uranium or thorium decay in the
environment. Most radium (radium-226) originates from the decay
of the plentiful uranium-238.
In the natural environment, radium occurs at very low levels
in virtually all rock, soil, water, plants, and animals. When
uranium (or thorium) occurs in high levels in rock, radium is
often also found in high levels.
What are the properties of radium?
Radium is a naturally radioactive, silvery-white metal when freshly
cut. It blackens on exposure to air.
When purified, radium glows in the dark, a property once widely
exploited for clock dials and gauges before the risks of radium
exposure were understood.
Metallic radium is highly chemically reactive. It forms compounds
that are very similar to barium compounds, making separation of
the two elements difficult.
Radium originates from the radioactive decay of uranium and thorium.
Radium-226 is found in the uranium-238 decay series, and radium-228
and -224 are found in the thorium-232 decay series.
Radium-226, the most common isotope, is an alpha emitter, with
accompanying gamma radiation, and has a half-life of about 1600
years. Radium-228 is principally a beta emitter and has a half-life
of 5.76 years. Radium-224 has a half life of 3.66 days. Radium
decays to form isotopes of the radioactive gas radon, which is
not chemically reactive. Stable lead is the final product of this
lengthy radioactive decay series.
What is radium used for?
In the early 1900's, when it was newly discovered, no one understood
the dangers of radium. People were fascinated with its mysterious
properties, especially its luminescence. Industries sprang up
to manufacture hundreds of consumer products containing radium.
Advertisements proclaimed its special powers and unique effects
in such products such as hair tonic, toothpaste, ointments, and
elixirs. Glow in the dark watch and clock faces were immensely
popular.
Most of its original uses have been halted for health and safety
reasons, but its wide use in luminescent paints continued through
World War II, because the soft glow of radium's luminescence made
aircraft dials, gauges and other instruments visible to their
operators at night. Radium was also an early radiation source
for cancer treatment. Small seeds were implanted in tumors to
kill cancerous cells. Safer, more effective radiation sources,
such as cobalt-60 have mostly replaced it.
Radium is a radiation source in some industrial radiography devices,
a technology similar to x-ray imaging used in industry to inspect
for flaws in metal parts. When radium is mixed with beryllium
it becomes a good source of neutrons, useful in well logging devices
and research. Radium also has been added to the tips of lightening
rods, improving their effectiveness by ionizing the air around
it.
Radium occurs naturally in the environment. As a decay product
of uranium and thorium, it is common in virtually all rock, soil,
and water. Usually concentrations are very low. However, geologic
processes can form concentrations of naturally radioactive elements,
especially uranium and radium. Radium is soluble in water. As
a result, groundwater in areas where concentrations of radium
are high in surrounding bedrock typically has relatively high
radium content.
How does radium change in the environment?
All isotopes of radium are radioactive. As they decay, they emit
radiation and form new radioactive elements, until they reach
stable lead. Isotopes of radium decay to form different isotopes
of radon. For example, radium-226 decays to radon-222, and radium-228
goes through several decays to radium-224 before forming radon-220.
How do people come in contact with radium?
Since radium is present at low levels in the natural environment,
everyone has some minor exposure to it. However, individuals may
be exposed to higher levels of radium if they live in an area
where there is an elevated level of radium in the surrounding
rock and soil. Private well water in such areas can also be an
added source of radium.
The concentration of radium in drinking water is generally low,
but there are specific geographic regions in the United States
where higher concentrations of radium occur in water due to geologic
sources. Limited information is available about the amounts of
radium that are typically present in food and air, but they are
believed to be very low.
People can also be exposed to radium if it is released into the
air from the burning of coal or other fuels. Certain occupations
can also lead to high exposures to radium, such as working in
a uranium mine or in a plant that processes ores. Phosphate rocks
typically contain relatively high levels of both uranium and radium
and can be a potential source of exposure in areas where phosphate
is mined.
In some parts of the country, former radium processing plants
exist that were highly contaminated with radium. However, most
of these have been cleaned up and do not pose a serious health
threat any longer.
Radium emits several different kinds of radiation, in particular,
alpha and gamma
radiation. Alpha radiation is only a concern if radium is taken
into the body through inhalation or ingestion. Gamma radiation,
or rays, can expose individual even at a distance. As a result,
radium on the ground, for example, can expose individuals externally
to gamma rays or be inhaled or ingested with contaminated food
or water. The greatest health risk from radium in the environment,
however, is actually its decay product radon, which can collect
in buildings.
How does radium get into the body?
People may swallow radium with food and water, or may inhale
it as part of dust in the air. Radium can also be produced in
the body from "parent" radionuclides (uranium and thorium)
that have been inhaled or swallowed, but this is not a significant
source.
What does radium do once it gets into the body?
Most radium that is swallowed (about 80%) promptly leaves the
body through the feces. The other 20% enters the bloodstream and
accumulates preferentially in the bones. Some of this radium is
excreted through the feces and urine over a long time. However,
a portion will remain in the bones throughout the person's lifetime.
Radium emits several different kinds of radiation, in particular,
alpha particles and gamma rays. Alpha particles are generally
only harmful if emitted inside the body. However, both internal
and external exposure to gamma radiation is harmful. Gamma rays
can penetrate the body, so gamma emitters like radium can result
in exposures even when the source is a distance away.
Long-term exposure to radium increases the risk of developing
several diseases. Inhaled or ingested radium increases the risk
of developing such diseases as lymphoma, bone cancer, and diseases
that affect the formation of blood, such as leukemia and aplastic
anemia. These effects usually take years to develop. External
exposure to radium's gamma radiation increases the risk of cancer
to varying degrees in all tissues and organs.
However, the greatest health risk from radium is from exposure
to its radioactive decay product radon. It is common in many soils
and can collect in homes and other buildings.
Is there a medical test to determine exposure to radium?
There are tests that can determine exposure to radium or other
radioactive substances. For example, a whole body count can measure
the total amount of radioactivity in the body, and urine and feces
can be tested for the presence of radionuclides.
These tests are not routinely performed in a doctor's office
because it requires special laboratory equipment. There is no
test that can detect external exposure to radium's gamma radiation,
unless the doses were very high, and cellular damage is detectable.
You need special equipment to detect the presence of radium.
However, you can buy radon detection kits at most hardware stores.
What is EPA doing about radium?
The U.S. Congress passes laws that authorize EPA and other federal
agencies, to protect public health and the environment from radium
and other radioactive materials. EPA has issued a variety of regulations
that limit the release of radium and other radionuclides to the
environment. For example, Congress passed the Uranium Mill Tailings
Radiation Control Act (UMTRCA). EPA has established standards
for cleaning up and managing leftover uranium ore at inactive
ore-processing plants under the authority of UMTRCA. The U.S.
Department of Energy is responsible for conducting the cleanups,
and the U.S. Nuclear Regulatory Commission oversees and manages
them.
Complementing these efforts, EPA's Superfund program identifies
abandoned industrial sites contaminated with radium and other
radionuclides and chemicals. It then assesses the health and environmental
risks the sites pose, and assigns priorities for cleaning them
up based on those risks. Superfund regulations require sites to
be cleaned up to the point that people living on the sites after
cleanup would have no more than a 1-in-10,000 to a 1-in-1,000,000
increased risk of developing cancer from exposure to contaminants.
Other laws passed by Congress address specific environmental
media. The Clean Air Act authorizes EPA to establish annual limits,
known as National Emission Standards for Hazardous Air Pollutants,
for the maximum amount of radium and other radionuclides that
may be released to the air. For radium the "NESHAP"
is 10 millirem. The Safe Drinking Water Act authorizes EPA to
limit the Maximum Contaminant Levels of radium and other radionuclides
in publicly supplied drinking water. For 226 and 228 radium, the
MCL is 5 picocuries per liter and for 224 radium it is 15pCi/l.
Both the air and water standards limit the increased lifetime
cancer risk to about 2 in 10,000.
