Radioactivity after ingestion

While adequate Intestinal absorption Is clearly required to maintain zinc sufficiency, a number of different methods are presently used for Its measurement. Intestinal absorption has been measured by clinical balance studies, tracers (using both stable and radioactive Isotopes) and serum levels after Ingestion of pharmacologic doses of stable zinc compounds. Each can be useful, but each also has limitations and It Is Important to note that different methods. In reality, measure different aspects of absorption. While results are often reported as absorption, specific nomenclature has been developed to specify the results from each method of measurement(13,14). 

The feces in the high-dose animals had 35%, 58%, and 80% ofthe total recovered radioactivity after 24 hours, 48 hours, and 7 days, respectively. The amount of radioactivity excreted in urine was about 10% of amount excreted in feces. A elimination half-life of about 30 hours was estimated for benzo[a]pyrene. The data are limited because the exposed area of skin was not reportedly covered or collars were not employed to prevent ingestion of test compound by the animal. In guinea pigs, 73% of the dose was excreted 7 days after low-level (0.28 mg) exposure to benzo[a]pyrene (Ng et al. 1992). 

Relatively little Pu, Pu, Pu, americium and curium are formed in the irradiation of thorium-uranium fuel with fissUe makeup. However, when plutonium is used as fissile makeup for a thorium fuel cycle, considerable quantities of americium and curium are formed. As discussed in Sec. 2.4, these are the radionuclides that are the greatest contributors to radioactivity and ingestion toxicity after about 600 years of waste isolation, when the fission products have decayed. 

Figure 23.17 After ingesting Na % the uptake of the radioactive iodine by the thyroid giand in a patient is monitored with a scanner. The photos show a normai thyroid giand (ieft) and an eniarged thyroid giand (right).

Human metabolism of l- C-diethylpropion has been described. 8 Twenty-one metabolites have been Identified. The major metabolite, hippuric acid, represented about 27% of the radioactivity excreted in the urine between 8 and 12 hours after ingestion of the drug. 

Hackett and coworkers [26] showed that after ingestion of 2 g of purified C-labeled catechin, plasma radioactivity peaked at a level corresponding to 40 pmol/L catechin. Most of the catechin was present as metabolites 12.5% was in the native form. Half of the dose was excreted in urine, mainly as 3 -... 

After ingestion, an absorption of about 2% has been found in animals, " whereas an average absorption of about 6% was noted in five human beings given single doses of radioactive cadmium. Calcium, iron, or protein deficiency increases the retention rate. ""... 

Experiments with rats given oral doses of tritiated food-grade mineral oil provide supporting evidence that the absorption of hydrocarbons in mineral oils is limited. Five hours after dosing with 0.66 mL/kg of tritiated mineral oil ("liquid petrolatum U.S.P."), -75% of the administered radioactivity remained in the alimentary tract, and only 3% of the administered radioactivity was accounted for by radioactivity in other parts of the rat carcass (Ebert et al. 1966). About 80% of the administered radioactivity was recovered in feces during the first 2 days after treatment, and over 90% of the radioactivity in the feces was in the form of mineral oil. These data are consistent with the hypothesis that ingested mineral oil was poorly absorbed. Neither biliary excretion nor enterohepatic circulation of mineral oils was measured in this study, and thus, any quantitative estimates of the extent of absorption based on these data should be viewed as tentative. 

Three treated cats were sacrificed 0.5, 1, 2, 5, and 10 days after treatment. Radioactivity in urine and feces collected over the 10-day period accounted for 28% and 19% of the applied dose, respectively, but no radioactivity was detected in expired air. Radioactivity in analyzed tissues reached maximal levels at 24 hours (accounting for 8.7% of the applied dose). These data are inadequate for quantitative measurements of the extent of dermal absorption of TOCP, because a significant traction of the applied radioactivity was not accounted for in the analysis, and some of the TOCP may have been ingested by the cats during grooming. 

Fig. 17. Biological model recommended for describing the uptake and retention of cerium by humans after inhalation or ingestion. Numbers in parentheses give the fractions of the material in the originating compartments which are cleared to the indicated sites of deposition. Clearance from the pulmonary region results from competition between mechanical clearances to the lymph nodes and gastrointestinal tract and absorption of soluble material into the systemic circulation. The fractions included in parentheses by the pulmonary compartment indicate the distribution of material subject to the two clearance rates however, these amounts will not be cleared in this manner if the material is previously absorbed into blood. Transfer rate constants or functions, S(t), are given in fractions per unit time. Dashed lines indicate clearance pathways which exist but occur at such slow rates as to be considered insignificant compared to radioactive decay of the cerium isotopes.

Peak plasma levels are reached about 1.5 h after oral ingestion, the maximum concentrations being in the order of 2 - 3 ng equivalents/ml (parent drug + metabolites) for an oral 1 mg dose. The elimination from the plasma is biphasic and proceeds with mean half-lives of 6 h (a-phase) and 50 h ((3-phase). Similar elimination half-lives are obtained from the urinary excretion. The cumulative renal excretion is practically the same after oral and intravenous administration and amounts to 6 - 7 % of the radioactivity dosed. The main portion of the dose, either oral or intravenous, is eliminated by the biliary route into the faeces. The kinetics of bromocriptine has been demonstrated to be linear in the oral dose range from 2.5 to 7.5 mg. 

Radioactivity results when some part of an atom is unstable. The instability exists because the orbital electrons or the nucleus contain too much energy. Radioactive atoms are called radionuclides. They release excess energy by emitting radiation. The type of radiation released (alpha, beta, or gamma particles) may be more or less hazardous to humans, depending on the location of the radioactive materials. Exposure to radioactive materials outside the body poses external hazards. Radioactive materials may also be hazardous when ingested, inhaled, or injected and thus pose internal hazards. The sections below describe the characteristics of radiation particles as external or internal hazards and as they may be encountered after a terrorist attack. Chapter 3 provides additional details and addresses health effects associated with exposure to radiation. 

No studies were located in humans regarding the distribution of 1,2-dibromoethane after oral exposure. In humans intentionally ingesting 1,2-dibromoethane, kidney lesions and centrilobular necrosis of the liver were found (Olmstead 1960 Saraswat et al. 1986). This is indirect evidence of distribution of 1,2-dibromoethane. The tissue distribution of 1,2-dibromoethane has been studied in rats following exposure by the oral route. Although retention was limited, the kidneys, liver, and spleen appear to retain the highest amounts of the administered dose (Plotnick et al. 1979) as illustrated in Table 2-4. Rats received an oral dose of 15 mg/kg/day of labeled 1,2-dibromoethane in corn oil. Twenty-four hours later 3% of radioactivity was detected in fat, brain, kidney, liver, spleen, testes, blood, and plasma, 72.38% in the urine, and 1.65% in the feces (Plotnick et al. 1979). By 48 hours after administration, 73% of the radiolabeled dose was accounted for in the urine, 1.1% in the liver, and 2.4% in the feces. Total recovery was 77.8% of the administered radioactivity. 

Allowance should be provided for as long a time period as possible after processing before the sterilized food is ingested in order to permit the induced radioactivities to decay. 

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