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NEWS & INFORMATION HPS
Newsletter October 2002
Specialists
in Radiation Safety Potassium
Iodide (KI) HEALTH
PHYSICS SOCIETY FACT SHEET What
is it?
Potassium
iodide (KI) is a salt, similar to sodium chloride (NaCI), normal table salt. KI
is available in pill form or dissolved in water as a supersaturated potassium
iodide (SSKI) solution. The pills contain a daily adult (children's doses range
from 16-65 mg depending on their size and age) dosage of 130 milligrams (mg).
Several drops of the SSKI in juice or water will also provide a daily dosage of
130 mg. What
is KI used for?
The
thyroid gland needs iodine to carry out its hormone production function. The
gland is constantly removing iodine from the bloodstream. Iodine normally enters
the bloodstream from the food we eat. For decades it has been known that 130 mg
KI was enough iodine to totally satisfy an adult's thyroid gland's desire for
iodine for a day or so. If 130 mg of KI is taken shortly before radioactive
iodine enters the body, the thyroid gland will have already been totally
satisfied and will not absorb radioactive iodine from the bloodstream. Thus, the
body will eliminate the radioactive iodine, primarily by way of the urine, over
a period of a week or two and the thyroid will not absorb and store the
radioactive iodine. Taking KI is a method of shutting down the thyroid
absorption of iodine (a process called "blocking") until the body rids
itself of any radioactive iodine. Where
does radioactive iodine come from? Radioactive
iodine is a fission product, one of about 200 different radioactive atoms (radionuclides)
that can be produced when uranium atoms fission or split apart upon being struck
by a neutron. For example, radioactive iodine is created through the process of
using nuclear reactors to supply the heat used to produce electricity or as the
result of the detonation of an atomic bomb. The major isotopes of radioactive
iodine produced in the fissioning process have a short half-life. Therefore,
they only exist while the nuclear reactor is operating and producing electricity
or for a few days following the reactor shutdown or atomic bomb detonation. It
is not a concern, for example, in spent fuel from nuclear reactors. Radioactive
iodine is also made for medical purposes under controlled conditions using an
accelerator. Is
radioactive iodine hazardous? Radioactive
iodine can be hazardous if we are exposed to enough of it. Radioactive iodine
undergoes radioactive decay, releasing both beta and gamma rays. If we are close
to radioactive iodine or if we take radioactive iodine into our bodies, our
bodies will be exposed to its beta and gamma rays. If radioiodine is removed
from the bloodstream and stored in the thyroid gland, the thyroid gland and the
rest of the body will receive higher radiation doses than they would if the
radioiodine simply passed through the body. This removal and storage can be
prevented by the appropriate use of KI. Are
there any beneficial uses of radioactive iodine? Radioactive
iodine has been used for the past half century for diagnostic and therapeutic
purposes in medicine. In smalJ amounts it is used to determine whether or not
the thyroid gland is functioning normally. When tagged to certai11
pharmaceuticals, it can be used to create images of certain organs of the body.
When administered in larger doses it can lower the activity of an overactive
thyroid gland and cause it to function normally. In even higher doses it has
been proven to be a very effective cure for thyroid cancer. Is
KI a "magic bullet" to be used in the event of a nuclear accident? There
are many radioactive nuclides (atoms) that can be released to the environment in
the event of a severe nuclear accident. Radioactive iodine may be one of them
depending on the circumstances of the accident. For example, there was
essentially no radioactive iodine released into the environment during the Three
Mile Island (TMI) reactor accident while there was a large amount released from
Chernobyl. KI, if taken properly and in a timely fashion, can provide some Is
KI a "magic bullet" to be used in the event of a "dirty
bomb"? A
"dirty bomb" is a conventional explosive device incorporating
radioactive material. It is designed to produce contamination with the
radioactive material and instill fear and panic in people near the explosion. It
is extremely unlikely for radioiodine to be used in a "dirty bomb" due
to its short half-life and low radiotoxicity compared to other radioactive
materials that are more likely to be used. Therefore, KI would have no
protective value from a "dirty bomb." Are there any hazardous side effects associated with taking KI? While
there have been minimal side effects observed in large populations administered
KI (such as after the Chernobyl Accident), KI is a pharmaceutical that should be
taken only on the advice of health-care advisers. A small number of people have
an allergic reaction to iodine, which can cause hazardous side effects in them.
Since there is a possibility of side effects, national scientific organizations
and the Environmental Protection Agency (EPA) have established recommendations
for thyroid doses following an accident involving radioactive iodine at which
administering KI should be considered. If the potential exposure to the thyroid
is below these dose levels they consider the risk from effects of radioiodine in
the thyroid gland are not great enough to warrant the risk of a side effect. The
current EP A recommendation for State Health Officials is to consider
administering KI to the population if the thyroid has the potential to exceed a
dose of 25 rem. What
are the effects of radioiodine in the thyroid gland? Radioiodine
in the thyroid gland can lead to increased radiation dose to the thyroid gland
and to the rest of the body. Radiation to the thyroid gland of children
increases their risk of developing thyroid cancer later in life. Large amounts
of radioiodine in the adult thyroid gland can lead to a reduced functioning of
the gland and additional radiation dose to the rest of the body. Is
there an alternative to taking KI pills? The
absolute best protection is to not get exposed to ANY unjustified radiation.
This includes radiation from radioiodine and the many other radionuclides that
could be released from a nuclear accident. The primary protective action in
State emergency response plans is evacuation and sheltering. Administration of
KI is a supplemental action when it is warranted. If advised by State Health
Officials to evacuate or shelter, this should be done immediately. Are
we now better prepared to deal with nuclear emergencies? We learned a lot from the accidents at TMI and Chernobyl. This
information has been incorporated into our emergency plans that are now designed
to get people out of harm' s way in a timely fashion and assure that they
receive no or minimal radiation exposure. One of the lessons from Chernobyl,
for example, is that administration of KI is an appropriate protective action
when the situation warrants. In the event of any nuclear emergency, the best
procedure to follow is to tune into the emergency radio and television channels
and follow the advice given by those in charge of our safety in an emergency. _________________________________ The Health Physics Society is a nonprofit scientific professional organization whose mission is excellence in the science and practice of radiation safety. Since its formation in 1956, the Society has grown to approximately 6,000 scientists, physicians, engineers, lawyers, and other professionals representing academia, industry, government, national laboratories, the Department of Defense, and other organizations. Society activities include encouraging research in radiation science, developing standards, and disseminating radiation safety information. Society members are involved in understanding, evaluating, and controlling the potential risks from radiation relative to the benefits. Official position statements are prepared and adopted in accordance with standard policies and procedures of the Society. The Society maybe contacted at 1313 Dolley Madison Blvd. , Suite 402, Mclean, V A22101; phone: 703-790-1745; fax: 703-790-2672; email: hps@burkinc.com |
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