Half-life, biological

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The period during which a biological system, for instance a human being or animal, naturally excretes half of the absorbed quantity of a certain substance from the body or a specific organ. For adults the following biological half-lives apply:

• Tritium (whole body): 10 days,

• Caesium (whole body): 110 days,

• Iodine (thyroid gland): 80 days,

• Plutonium: 20 years (liver), 50 years (skeleton).

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