Re: Japan - Trace Amounts of Plutonium found in soil at Fukushima Dai-ichi Nuclear Power Plant
from the Institute for Energy and Environmental Research:
Health Effects of Plutonium
Plutonium-239 is a very hazardous carcinogen which can also be used to make nuclear weapons. This combination of properties makes it one of the most dangerous substances. Plutonium-239, while present in only trace quantities in nature, has been made in large quantities in both military and commercial programs in the last 50 years. Other more radioactive carcinogens do exist, like radium-226, but unlike plutonium-239 cannot be used to make nuclear weapons, or are not available in quantity. Highly enriched uranium (HEU) can also be used to make nuclear weapons, but it is roughly one thousand times less radioactive than plutonium-239. The
danger is aggravated by the fact that plutonium-239 is relatively difficult to detect once it is outside of secure, well-instrumented facilities, or once it has been incorporated into the body. This is because its gamma ray emissions, which provide the easiest method of detection of radionuclides, are relatively weak.
The
main carcinogenic property of plutonium-239 arises from the energetic alpha radiation it emits. Alpha particles, being heavy, transfer their energy to other atoms and molecules within fewer collisions than the far lighter electrons which are the primary means of radiation damage for both gamma and beta radiation.1
Alpha particles travel only a short distance within living tissue, repeatedly bombarding the cells and tissue nearby. This results in far more biological damage for the same amount of energy deposited in living tissue. The relative effectiveness of various kinds of radiation in causing biological damage is known as "relative biological effectiveness" (RBE). This varies according to the type of radiation, its energy, and the organ of the body being irradiated. A simple factor, called quality factor, is used to indicate the relative danger of alpha, beta, gamma and neutron radiation for regulatory purposes. The International Commission on Radiation Protection currently recommends the use of a quality factor of 20 for alpha radiation relative to gamma radiation.2
Once in the body, plutonium-239 is preferentially deposited in soft tissues, notably the liver, on bone surfaces, in bone marrow and other non-calcified areas of the bone, as well as those areas of the bone that do not contain cartilage. Deposition in bone marrow can have an especially harmful effect on the blood formation which takes place there. By contrast, radium-226, another alpha emitter, is chemically akin to calcium and so becomes deposited in the calcified areas of bones.
When it is outside the body, plutonium-239 is less dangerous than gamma-radiation sources. Since alpha particles transfer their energy within a short distance, plutonium-239 near the body deposits essentially all of its energy in the outer dead layer of the skin, where it does not cause biological damage.
The gamma rays emitted due to plutonium-239 decay penetrate into the body, but as these are relatively few and weak,
a considerable quantity of plutonium-239 would be necessary to yield substantial doses from gamma radiation. Thus,
plutonium-239 can be transported with minimal shielding, with no danger of immediate serious radiological effects. The
greatest health danger from plutonium-239 is from inhalation, especially when it is in the common form of insoluble plutonium-239 oxide.
Another danger is absorption of plutonium into the blood stream through cuts and abrasions. The risk from absorption into the body via
ingestion is generally much lower than that from inhalation, because plutonium is not easily absorbed by the intestinal walls, and so most of it will be excreted.
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Experiments on beagles have shown that a very small amount of plutonium in insoluble form will produce lung cancer with near-one-hundred-percent probability. When this data is
extrapolated to humans, the figure for lethal lung burden of plutonium comes out to about 27 micrograms. Such an extrapolation from animals, of course, has some uncertainties. However, it is
safe to assume that several tens of micrograms of plutonium-239 in the lung would greatly increase the risk of lung cancer. Larger quantities of plutonium will produce health problems in the short-term as well
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One of the few attempts to analyze the effects of microgram quantities of plutonium on exposed human subjects was a long-term study of 26 "white male subjects" from the Manhattan Project exposed to plutonium at Los Alamos in 1944 and 1945, where the first nuclear weapons were made. These subjects have been followed for a long period of time, with the health status of the subjects periodically published. The most recent results were published in a study in 1991.3
The amounts of plutonium deposited in the bodies of the subjects were estimated to range from "a low of 110 Bq (3 nCi) ...up to 6960 Bq (188 nCi),"4 corresponding to a weight range of 0.043 micrograms to 3 micrograms. However, weaknesses in the study resulted in considerable uncertainties about the amount and solubility of plutonium actually incorporated at the time of exposure.5
Of the seven deaths by 1990, one was due to a bone cance (bone sarcoma).6 Bone cancer is rare in humans......
Read more at:
http://www.ieer.org/ensec/no-3/puhealth.html
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The article Sharon posted included this:
According to TEPCO, was detected, the companion of plutonium 239 and plutonium 238, near the ground in three cases it 240 per 238 kg of plutonium is one of them, was detected around 0.54 becquerels . This concentration is included in the normal soil level and national level, both about the same concentration of plutonium in Japan fell in the atmosphere by nuclear testing was done in the past, at a level that is harmful to human body that no.....
So, it sounds to me as if the detected level may in fact be safe at the moment, but long term exposure or higher doses - may be a different story.
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