Plutonium toxicity

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> 
>               PLUTONIUM'S RISK TO HUMAN HEALTH DEPEND ON ITS FORM
> 
>    In a nuclear explosium, plutonium-239 fissions and releases a huge
>    amount of energy and radiation. But plutonium itself is a highly toxic
>    element that requires a great deal of care in handling.
> 
>    Experts agree that the silvery, unstable metal plutonium-239, with a
>    half-life of 24,000 years, is hazardous and sould be isolated from the
>    biosphere. However, the risks posed to workers and communities by
>    stored plutonium depend on the route of exposure as well as the
>    particle size, isotope, and chemical form.
> 
>    Weapons-grade plutonium outside the body presents little risk unless
>    exposures are frequent and extensive. It emits primarily alpha
>    particles, which cannot penetrate skin, clothing, or even paper.
>    Nearly all the energy from plutonium is deposited on the outer,
>    nonliving layer of the skin, where it causes no damage. The neutrons
>    and the relatively weak gamma photons it emits can penetrate the body,
>    but large amounts of weapons-grade plutonium would be needed to yield
>    substantial doses.
> 
>    Workers wearing only lead aprons can handle steel drums containing
>    solid plutonium metal with no immediate untoward effects. However, as
>    weapons-grade plutonium ages, it becomes more dangerous because some
>    of the contaminating plutonium-241 is converted via beta decay to
>    americium-241, which emits far stronger gamma radiation.
> 
>    On the other hand, plutonium inside the body is highly toxi. Solid
>    plutonium metal is neither easily dispersed nor easily inhaled or
>    absorbed into the body. But if plutonium metal is exposed to air to
>    any degree, it slowly oxidizes to plutonium oxide (PuO2), which is a
>    powdery, much more dispersable substance. Depending on the particle
>    size, plutonium-239 oxide may lodge deep in the alveoli of the lung
>    where it has a biological half-life of 500 days, and alpha particles
>    from the opxide can cause cancer. Also, fractions of the inhaled
>    plutonium oxide can slowly dissolve, enter the bloodstream, and end up
>    primarily in bone or liver.
> 
>    Plutonium oxide is weakly soluble in water. If it is ingested in food
>    or water, only a small fraction (4 parts per 10,000) is absorbed into
>    the gastrointestinal tract. However, it may take just a few millionths
>    of a gram to cause cancer over time. In animals, small doses induce
>    cancer, especially in lung and bone.
> 
>    In published studies of plutonium's effects on humans, most subjects
>    were exposed to multiple sources of radiation. Some researchers say
>    the available health data on plutonium workers have not yet been used
>    to do careful epidemiological studies, because researchers have been
>    denied access to much of the data on workers and military personnel
>    exposed to plutonium. In the studies done so far, plutonium workers do
>    not show major excesses of any type of cancer.
> 
>    Becuase of the relative lack of human data, the risks of chronic
>    exposure to plutonium are uncertain. Exposure standards in the U.S.
>    are based partly on studies of survivors of Hiroshima and Nagasaki and
>    partly on animal experiments. A 1991 White House Office of Science &
>    Technology Policy studye says that "sufficient human data are not
>    available to provide accurate risk assessment of exposure."


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