Biological Half Life (T1/2) 02
Biological Half Life (T1/2) 02 : (a) The term which is used for the time required for the amount of a particular substance in a biological system to be reduced to one half of its value by biological processes when the rate of removal is approximately exponential. Substances with a long biological half_life will tend to accumulate in the body and are, therefore, particularly to be avoided. Substances with a short biological half_life may accumulate if some becomes tightly bound, even if most is cleared from the body rapidly. There is also the possibility of cumulative effects of chemicals which have a short residence time in the body. [Duffus, 2000: Univ. Edinburgh Med School On-line Chemical Safety Glossary]; (b) The time required for a biological system (such as a human or animal) to eliminate, by natural processes, half the amount of a substance (such as a radioactive material) that has been absorbed into that system. [SRA, 1999: Glossary of Risk Analysis Terms] [USDOE, 2000: RAIS Glossary] [Cf. Half-Life]
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