Plutonium is a very dense metal, radioactive, man-made during the past sixty years as part of its activities involving fissile material. Plutonium isotopes are radioactive. The most abundant isotopes are the 238, 239, 240 and 241. These four radionuclides have radioactive periods or half-lives ranging from 14.1 to 24,000 years. Apart plutonium-241,(*)these isotopes are alpha emitters.
The fissile property of plutonium-239 and the ability to produce with reactors relatively large amounts of it has led to its use for nuclear weapons and nuclear energy. In reactors, plutonium-239, like uranium-235 captures neutrons and undergoes fission. Plutonium fission provide about one third of the energy produced in conventional reactors. It is not necessary to extract this plutonium which is produced in the nuclear fuelbecause.
The U.S. has recovered or acquired between 1944 and 1994 approximately 110 tons of plutonium with 100 tons in inventory. About 80% is military grade, mainly plutonium-239, derived from the production reactors at the sites of Hanford and Savannah River.
Atomic weapon tests have dispersed up to 1980s about 10 tons of plutonium into the atmosphere. The level of fallout on the ground is between 10 and 100 picocurie per kilogram (0.37 and 3.7 Bq / kg). Accidents and releases nearby weapon tests facilities have caused locally more important contaminations.
Plutonium occurs most commonly in the form of highly insoluble oxide. It remains in the first centimeters of the ground surface. In water, plutonium is found in the upper layer of sediment to which it strongly adheres. Typically, only one part out of 2000 is dissolved. In soil, chemical or biological processes can make soluble a small fraction of plutonium. But while plutonium may be accumulated in aquatic organisms, there is no accumulation in the food chain.
A radiotoxic element
Because of its lack of mobility, medical data do not confirm the reputation of plutonium as the most deadly substance known to man. It is not as immediately harmful as many chemicals. The danger resulting from its alpha radiation does not become effective unless plutonium is present in the human body after inhalation or ingestion.
When plutonium is inhaled, a significant fraction can pass from the lungs into the bloodstream and other organs depending on the solubility of the compound. If plutonium is ingested, the digestive system will only absorbs about 0.05% of it. Very little is absorbed through contact with skin. Plutonium present in the blood is deposited in the liver and skeleton with biological retention periods between respectively 20 and 50 years.
Inhalation of contaminated dust and aerosols is the main risk of cancer resulting from alpha of plutonium, well before the risk in case of ingestion.
Laboratory studies on animals have shown that exposure to high levels of plutonium caused respiratory diseases, cancers and reduced life expectancy. The tissues affected are the lungs, liver, lymph nodes and bones. However, these results have not been corroborated by epidemiological studies on humans exposed to low levels of plutonium
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