Radioactive materials excretion

Microbiological estimations of Bi in urine have limited value. Ideally the urine should be frozen and estimations of Bn should be made without delay. The least fecal contamination of urine and any bacterial prolifera tion may lead to grossly inaccurate results. After oral administration relatively little vitamin B12 appears in the urine, and serum levels are a much better indication of amounts absorbed. Vitamin Bn tolerance tests based on determinations of urinary excretion of the vitamin after intramuscular injection are described by Estrada et al. (1954). E. L. Smith (1953) found that most of the radioactive material excreted in the urine by a human subject after an oral dose of labeled vitamin B12 was not present as microbiologically active cobalamin. A urinary excretion test with radioactive vitamin B12 is discussed on page 159. 

The large discrepancy between the estimates of intake calcrrlated on the basis of the direct thyroid measirrement and of the measuremerrt of radioactive material excreted in trrine suggests that at least one of the default assirmptions used to derive these estimates is not correct. Although there are significant individiral differences in iodine uptake and metabolism, these differences cannot generally account for a discrepancy of a factor of nearly ten. On the other hand, the rate of excretion of... 

Only 6% of the radioactivity from radiolabeled ( "C) heptachlor was found in the urine while 60% was found in the feces of male rats 10 days after a single oral dose indicating that most of the radioactive material was not absorbed and was excreted in the feces (Tashiro and Matsumura 1978). These data strongly suggest that a large percentage of heptachlor is absorbed from the gastrointestinal tract and eliminated via the bile into the feces. More than 72% of the radioactivity eliminated in the feces was present as metabolites of heptachlor (heptachlor epoxide, 13.1% H-2, < 0.1% 1-OH-chlordene, 19.5% 1-OH-chlordene epoxide, 17.5% 1,2-OH-chlordene, 3.5% H-6, 19.0%). 

The dose of radiation delivered by an internally deposited radionuclide depends on the quantity of radioactive material residing in situ. This quantity decreases as a function of the physical half-life of the radionuclide and the rate at which the element is redistributed or excreted (i.e., its biological half-life). Because the physical half-life is known precisely and the biological half-life can be characterized within limits for most radionuclides, the dose to a tissue that will ultimately be delivered by a given concentration of a radionuclide deposited therein can be predicted to a first approximation. The collective dose to a population that will be delivered by the radionuclide—the so-called collective dose commitment—serves as the basis for assessing the relevant long-term health effects of the nuclide. 

The test can be repeated, giving intrinsic factor orally together with the radioactive vitamin B12 - if the impaired absorption was because of a simple lack of intrinsic factor, and not to antiintrinsic factor antibodies in saliva or gastric juice, then a normal amount of the radioactive material should be absorbed and excreted. 

Mathematical models are used to describe the various processes involved in the internal deposition and retention of radionuclides and the associated radiation doses received by various organs and tissues in the body. In models of this type, the body is viewed as a series of compartments into which the radioactive materials enter and exit at various rates, ultimately being removed from the system by some form of excretion, by radioactive decay, or both. 

A. A radioactive material must be eliminated from the body to remove its hazard. Detoxification, which is effective against chemical hazards, will not be effective since radioactivity is not modified by chemical changes. The methods of elimination include renal excretion for most soluble materials, elimination in the feces for materials that are retained in the gut or which can be secreted in the bile, and exhalation for volatile materials and gases. Chelating agents, e.g., calcium or zinc DTPA (diethylenetriamine pentaacetic acid), if administered soon after exposure, are effective in enhancing the elimination of certain radioisotopes. These materials are not very effective for radioisotopes that have been incorporated and fixed in organs and tissues, e.g., bone. 

Bioassav - Radiological bioassay is the determination of the kind, quantity, or concentration and location of radioactive material in the human body by direct measurement or analysis of materials excreted or removed from the body. 

After intravenous administration, 46-63 per cent of radioactive indomethacin is rapidly excreted in the bile of dogs, guinea-pigs and monkeys. Radioactive material in the bile is largely reabsorbed in the intestine of the guinea-pig and monkey, but not of the dog . Renal clearance of the compound and its metabolites is the important excretory route in most species, except in the dog in which faecal excretion is high and urinary clearance negligible . 

Water-Soluble Metabolites. Administering unidentified metabolites from plants to animals is difficult to conduct due to practical considerations. The concentration of enough radioactive material in a sufficiently small volume to administer is difficult to achieve. Enough radioactivity is needed to provide sufficient radioactivity to determine excretion patterns and rate and for identifying metabolites, difficulty of too little activity is enhanced if metabolites in tissues, eggs, or milk must be identified. Unless the specific activity is in the 20-25 mCi/mmole range, the identification of further metabolites in animals would be difficult due to losses normally encountered during extraction and purification procedures. 

Radioactive cesium and thallium, whether ingested or inhaled, will end up in the intestines. Prussian blue traps these materials in die intestines and keeps them from being absorbed by the body. The radioactive materials then move through the intestines and are excreted in bowel movements. Prussian blue reduces the biological half-life of cesium in the body from about 115 days to about 40 days. Prussian blue reduces the biological half-life of thallium from about 8 days to about 3 days. Because Prussian blue reduces the time that radioactive cesium and thallium stay in the body, it helps limit the amount of time the body is exposed to radiation. 

Dogs, rats, and rabbits metabolize fluoroacetate compounds to nontoxic metabolites, and excrete fluoroacetate and fluorocitrate compounds peak rate of excretion occurs during the first day after dosing and drops shortly thereafter. Rats dosed with radiolabeled 1080 at 5.0 mg/kg BW had 7 different radioactive compounds in their urine. Monofluoroacetate comprised oifly 13% of the urinary radioactive material, fluorocitrate oifly 11%, and an unidentified toxic metabolite 3% 2 nontoxic metabolites accounted for almost 73% of the urinary radioactivity. Animal muscle usually contained nondetectable residues of any 1080 component within 1-5 days of treatment. Defluorination occurred in the liver by way of an enzymic glutathione-dependent mechanism which in the brush-tailed opossum resulted in the formation of 5 -carboxymethylcysteine and free fluoride ion. A rapid rate of defluorination together with a low reliance on aerobic respiration favored detoxification of fluoroacetate rather than its conversion into fluorocitrate, and may account for the resistance of reptiles to 1080 when compared to mammals. 

Only individuals likely to receive within 1 year more than 10% of the allowable dose limits are required to be monitored by the licensee. However, unless the dose is monitored, it is difficult to establish with certainty that an active user of radioisotopes may not have exceeded the 10% limit. Many licensees do monitor most users of radioactive materials by providing personnel dosimeters to measure external exposures, excluding those who only work with weak beta emitters. In order to monitor internal exposures, the licensee can perform measurements of (1) concentrations of radioactive materials in the air in the workplace, (2) quantities of radionuclides in the body, (3) quantities of radionuclides excreted from the body, or (4) combinations of these measurements. 

An internal radiation hazard may arise if radioactive material gets inside the body. This could occur if radioactive gases or particles are breathed into the lungs if radioactive material in any form is transferred to the mouth if it is injected or enters through a cut or graze or if the material is in a particular form that is absorbed through the intact skin. Clearly, once the radioaaive material is inside the body it is in direct contact with tissues and cells and will continue to irradiate them until the radioactivity decays or the material is excreted from the body. 

Urinalysis is perhaps the most common form of bioassay measurement. It is routinely performed as part of periodic bioassay program even when intakes are not suspected due to the relative cost and quickness of this type of bioassay. Fecal analyses are generally only performed when an intake is suspected because the excretion of radioactive material in the feces is highest in the first few days immediately following the incident. After that, urinary excretion is more common and more likely to detect an intake. 

The radiation dose received through the intake of radioactive material depends on the mode of intake, the quantity involved, the organs in which the material becomes deposited, the rate at which it is eliminated (by radioactive decay and excretion) and the radiations emitted. 

Because the water produced is not radioactive, methyl acetate foms by the first reaction, where all of the oxygen-18 ends up in methyl acetate. 55. 2 neutrons 4 / particles 57. Strontium. Xe is chemically unreactive and not readily incorporated into the body. Sr can be easily oxidized to Si +. Strontium is in the same family as calcium and could be absorbed and concentrated in the body in a fashion similar to Ca. The chemical properties determine where radioactive material may be concentrated in the body a how easily it may be excreted. 59. a. unstable beta production b. stable c. unstable positron production or electron capture d. unstable, positron production, electron capture, or alpha production. 61. 3800 decays/s 63. The third-life will be the time required for the number of nuclides to reach one-third of the original value (No/3). The third-life of this nuclide is 49.8 years. 65. 1975 67. 900 g 5u 69. 7 X 10 m/s 8 X 10- J/nu-clei 71. All evolved 02(g) comes from water. 79. 77% and 23% 81. Assuming that (1) the radionuclide is long lived enough that no signiheant decay occurs during the time of the experiment, and (2) the total activity is uniformly distributed only in the rat s blood, V = 10. mL. 83. a. 1 C b. N, c, N, UQ, and =N c. -5.950 X 10 J/mol H 85. 4.3 X 10- 87.-H Ne - g Bh -H 4 Jn 62.7 s [Rn 7 5f 6d ... 

Internal doses carmot be measured directly they can otrly be inferred from measured qrrantities such as body activity content, excretion rates or airborne concentrations of radioactive material. Section 7 provides an illustration of the assessment of doses from such measurements. 

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