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On the other hand, radionuclides with very short radioactive half-lives have also very short effective half-lives. For example, tritium has the biological half-life about 10 days, while the radioactive half-life is about 12 years. Moreover, if t 1/2 is large in comparison to t b, the effective half-life is approximately the same as t b.
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If a radioactive compound with radioactive half-life (t 1/2) is cleared from the body with a biological half-life t b, the effective half-life (t e) is given by the expression:Īs can be seen, the biological mechanisms always decreases the overall dose from internal contamination. This means that a radioactive substance can be expelled before it has had the chance to decay.Īs a result, the biological half-life significantly influences the effective half-life and the overall dose from internal contamination. Radioactive isotopes that were ingested or taken in through other pathways will gradually be removed from the body via bowels, kidneys, respiration and perspiration. The biological half-life depends on the rate at which the body normally uses a particular compound of an element. Most radionuclides will give you much more radiation dose if they can somehow enter your body, than they would if they remained outside. The intake of radioactive material can occur through various pathways such as ingestion of radioactive contamination in food or liquids, inhalation of radioactive gases, or through intact or wounded skin. If the source of radiation is inside our body, we say, it is internal exposure. It is also very important in radiation protection, when considering internal exposure. The biological half-life (t biological) can be defined for metabolites, drugs, and other substances. An effective half-life of the radioactive substance will involve a decay constant that represents the sum of the biological and radioactive decay constants, as in the formula:īesides the radioactive half-life, the effective half-life is determined by the biological half-life, which is the time taken for the amount of a particular element in the body to decrease to half of its initial value due to elimination by biological processes alone, when the rate of removal is roughly exponential. This variable is widely used in radiation therapy. All rights reserved.In general, the effective half-life is the time taken for the amount of a specific radionuclide in the body to decrease to half its initial value from both elimination by biological processes and radioactive decay. Literature reports for the stability of other organophosphorus toxicants were summarized because our current studies suggest that other organophosphorus toxicants are also crosslinking agents.Ībsorbance spectra Chlorpyrifos oxon Extinction coefficient Half-life Stability.Ĭopyright © 2019 The Authors. The half-life of chlorpyrifos oxon was 20.9 days at pH 8 and 6.7 days at pH 9. The rate of conversion of chlorpyrifos oxon to 3,5,6-trichloro-2-pyridinol was measured at 23 ☌ in 20 mM TrisCl pH 8 and pH 9 by recording loss of absorbance at 290 nm for chlorpyrifos oxon and increase in absorbance at 320 nm for 3,5,6-trichloro-2-pyridinol. We undertook to determine the half-life of chlorpyrifos oxon in aqueous solution because literature values do not exist. Assays for protein crosslinking can avoid artifacts by using information on the stability of chlorpyrifos oxon in solution. Aqueous solutions of chlorpyrifos oxon are used to study the ability of chlorpyrifos oxon to catalyze protein crosslinking.