Radiopathology of americium 241. I. Distribution of americium in adult mice.
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A retention-excretion model for americium in humans.
This paper discusses current information on the biological behavior of americium and describes a biokinetic model for americium in humans. Emphasis is on the time-dependent distribution and excretion of systemic americium in the adult, but potential differences with age in parameter values are addressed, and predictive models of absorption of americium to blood from the respiratory and gastrointestinal (GI) tracts are provided in an appendix. The analysis builds on the author's previous biokinetic model for plutonium in humans and recent analyses and/or models of other authors regarding the behavior of americium and related elements in humans and laboratory animals. Compared with the retention model for americium implied in ICRP Publication No. 48, the present model, as applied to adults, yields reasonably similar whole-body retention of americium at all times, much less retention in the liver after a few months, somewhat greater retention in the total skeleton after a few years, and very similar long-term integrated activities of long-lived americium isotopes on bone surfaces. Compared with a previous model of Durbin and Schmidt, the present model, as applied to adults, predicts very similar retention in the liver at all times, somewhat smaller retention in the total skeleton after a few years, and somewhat greater urinary excretion rates at all times after acute uptake to blood.
Americium↗
The absorption of ingested neptunium, plutonium and americium in newborn hamsters.
Hamsters aged 1, 4, 7, 22 and 30 days were given oral doses of either plutonium-239 citrate or americium-241 nitrate. The values of gastrointestinal absorption obtained were 3.5, 1.4, 0.04, 0.007 and 0.003 per cent, respectively, for plutonium and 4.5, 1.7, 0.5, 0.006 and 0.02 per cent, respectively, for americium, compared with values in adults of 0.01 per cent for plutonium and 0.05 per cent for americium. The absorption of neptunium was measured in hamsters aged 2 and 4 days and values of 2.3 and 1.7 per cent, respectively, were obtained for 239Np as the nitrate and 5.5 and 2.1 per cent, respectively, for 239Np as the bicarbonate compared with the values in adults of 0.02 per cent for both chemical forms. Thus, the absorption of plutonium, americium and neptunium at 1-2 days of age was about 100 times greater than in adults. The results for plutonium and americium show that absorption decreased rapidly with age over the suckling period. The values of absorption obtained at the time of weaning at 22 days were lower than in adults.
Aging↗
[Role of biocomponents of the bile and excreta in the elimination of plutonium and americium from the body].
A study was made of the role of biocomponents of bile, urine and feces in the elimination of plutonium and americium from the organism. Plutonium 239 and americium 241 were separated in bile due to higher tropism of plutonium to low molecular weight ligands, and of americium, to a protein-containing fraction. The status of plutonium excreted in feces was the same as the physicochemical status of americium. Plutonium 239 and americium 241 eliminated in urine were in a completely ultrafiltered state.
Americium↗
The distribution of 137Cs, plutonium and Americium in sheep.
Radiochemical measurements on tissues taken from sheep from the Cumbrian and Lancashire coast have given data which allow the tissue distribution and body content of plutonium isotopes, americium-241 and caesium-137 to be calculated. The data are particularly useful as the concentrations in lung confirm that for these animals the main route of intake is from the diet and not from inhalation. Plutonium and americium concentrate in the liver and skeleton. Caesium-137 was, as expected, found mainly in the meat of the animals. Additionally a controlled feeding experiment has been conducted to determine the gastrointestinal absorption of plutonium and americium from contaminated vegetation. A value of 0.01% for plutonium and 0.005% for americium was determined.
Americium↗
Transfer of environmental plutonium and americium across the human gut: a second study.
A follow-up to our previous study is described on human gut transfer factors for plutonium and americium in winkles harvested from the shoreline near the British Nuclear Fuels plc Sellafield reprocessing plant. Six male and two female adult volunteers ate single quantities of shellfish; samples of their urine before and after consumption were analysed. As in the previous study, the plutonium and americium excreted were difficult to detect, and counting times of approximately 8 weeks were employed. Results are presented in detail to allow further interpretation, but preliminary assessment has been carried out on the basis of published data for excretion following transfer to blood. The mean and range obtained for the gut transfer for plutonium was 1.3 (0.2-3.2) x 10(-4); for americium the result was 0.8 (0.4-1.7) x 10(-4). Combined with the results of the previous study when interpreted on the same basis, the results were 1.7 (0.2-4.9) x 10(-4) and 0.9 (0.3-2.8) x 10(-4), respectively. No significant evidence was revealed in this study for differences in gut transfer between males and females, nor for seasonal differences, e.g. due to differences in form of incorporation of actinides in shellfish. For realistic assessments of doses due to shellfish consumption near Sellafield, to assess compliance with criteria recommended by the International Commission on Radiological Protection (ICRP), a suitable value for the gut transfer factor of both plutonium and americium might be 2 x 10(-4). A value of 5 x 10(-4) would appear to be cautious.
Adult↗
[Determination of americium-241 in urine].
A technique has been developed for the determination of americium 241 in urine by a radiochemical purification of the nuclide from uranium (upon co-precipitation of americium 241 with calcium and lanthanum), plutonium, thorium, and polonium 210 (upon co-precipitation of these radionuclides with zirconium iodate). alpha-Radioactivity was measured either in a thick layer of the americium 241 precipitate with a nonisotope carrier or in thin-layer preparations after electrolytic precipitation of americium 241 on a cathode.
Americium↗
[Assessment of the distribution in the body and the dose on the respiratory tract and organs after single, short-term and long-term inhalation of americium-241].
On the basis of comparison of publications on accidental human intake of americium-241 and animal experimental studies dosimetric characteristics were obtained reflecting the dynamics of accumulation, formation of the dose on the organs and parts of the respiratory tract, as well as of the 24-hour elimination from the organism of the mentioned radionuclide following single, short- and long-term administration of americium-241 from the air. Results were obtained with the use of computers for quantitative modelling of the most complete metabolic transport scheme of americium.
Americium↗
Transfer of environmental plutonium and americium across the human gut.
Data on gut transfer factors for environmental forms of radionuclides are essential for estimates of public radiation exposures following ingestion, and thus in decisions on controlling waste discharges. Dose estimates for transuranic nuclides are particularly sensitive to uncertainties stemming from gut transfer data being related to non-environmental forms and/or derived from animal experiments. We have measured human gut transfer factors for plutonium and americium in two experiments using marine foods obtained near Sellafield, Cumbria. Firstly, the urine of volunteer members of the critical group of shellfish consumers was analysed for transuranics and the results related to their consumption rates. Secondly, remotely-based volunteers ate single quantities of shellfish obtained near Sellafield, and their urine was analysed. An overall result for the gut transfer factor for environmental plutonium of 0.8 X 10(-4) indicates no need to increase the value of 1 X 10(-4), currently used by the International Commission on Radiological Protection (ICRP) for soluble forms. Results for americium show that the ICRP value of 5 X 10(-4) is maximising, and that a value of 1 X 10(-4) would be supportable. The results from the study of critical group members provide confidence in our habits survey techniques and reassurance that there are no significant pathways for intake of transuranics by these people that have not been recognised.
Adult↗
Plutonium and americium uptake in rats fed with Cumbrian shellfish--implications for estimates of dose to man.
Winkles (Littorina littorea) and mussels (Mytilus edulis) collected on the Cumbrian coast contain americium-241 and isotopes of plutonium discharged from the nuclear-fuel reprocessing plant at Sellafield. Shellfish have been fed to rats and measurements made of the gastrointestinal absorption of the actinides. For shellfish collected over a 1-year period from March 1983 to February 1984, the average values for the fractional absorption of plutonium and americium were 9 x 10(-4) and 3 x 10(-4), respectively, for winkles and 1.5 x 10(-3) and 6 x 10(-4), respectively, for mussels. Comparisons with results for winkles collected in December 1981 and mussels collected in July 1982 suggest that there may be considerable seasonal variation in the availability of the actinides for absorption. The results suggest that in calculations of doses to individuals consuming shellfish in west Cumbria, it may be prudent to examine the effect of using the new ICRP gut transfer factor of 1 x 10(-3) for both actinides, in comparison with the value of 5 x 10(-4) recommended previously by NRPB. The use of 1 x 10(-3) would increase the estimate of the committed effective dose equivalent for 1985 intakes, from the value of 0.73 mSv calculated by the Ministry of Agriculture, Fisheries and Food, to 1.29 mSv. However, taking into account up-to-date estimates of the retention of the actinides in liver and bone would reduce this value to 1.07 mSv. If, in addition, allowance is made for the effect of the burial and recycling of actinides in bone, a significant reduction in the dose estimate could result; for example, the use of one proposed dynamic bone model would reduce the value from 1.07 to 0.54 mSv.
Americium↗
The biodistribution and toxicity of plutonium, americium and neptunium.
In the nuclear fuel cycle the transuranic radionuclides plutonium-239, americium-241 and neptunium-237 would probably present the most serious hazard to human health if released into the environment. Despite differences in their solution chemistry the three elements exhibit remarkable similarity in their biochemical behaviour, apparently sharing similar transport pathways in blood and cells. After entering the blood the elements deposit predominantly in liver and skeleton, where retention appears to be prolonged, with half-times of the order of years. The principal late effects of all three radionuclides are the induction of cancers of bone, lung or liver. For the latter tumours the induction risk per unit radiation dose appears similar for the three radionuclides. But in bone there are indications that, due to microscopic differences in the distribution of the alpha-particle radiation dose, the efficiency of bone cancer induction may increase in the order americium-241 less than plutonium-239 less than neptunium-237. No case of human cancer induced by these radionuclides is known.
Americium↗
The gastrointestinal absorption of plutonium and americium in the hamster.
Plutonium-239 and americium-241 were administered to adult hamsters in various chemical forms and their absorption from the gut was measured. The results have been compared with published data on other species in order to derive values for the estimated absorption of these actinides in man. On the basis of current knowledge, the best values for adults would appear to be: 0.05% for americium, 0.01% for plutonium ingested in soluble form, and 0.0001% for plutonium ingested as the dioxide. Plutonium dioxide should be considered as soluble if a significant proportion (greater than 5%) of the activity is in particles less than 25 nm in diameter.
Administration, Oral↗
Metabolism of americium-241 in man: an unusual case of internal contamination of a child and his father.
The metabolism of americium-241 has been studied during an 8-year period in an adult male and his son who, at the ages of 50 and 4 years, respectively, were accidentally and unknowingly contaminated within their home by means of inhalation. Chelation therapy with calcium trisodium pentetate was more effective in enhancing the removal of americium-241 from the child than from the father.
Age Factors↗
The movement of plutonium, americium, and curium through the food chain.
The actinides, plutonium, americium and curium, are being produced in increasing quantites as the nuclear programme is expanded. As these alpha-particle-emitting elements are hazardous to man there is considerable concern about the movement of these elements through the environment; The uptake of these elements from soil into the plants is low, as is the gastrointestinal concentration factor. Although there are complexing agents in the environment which have been shown to complex these elements there is no evidence that these complexing agents might bring about a concentration of actinides in the food chain of man.
Actinoid Series Elements↗
The uptake of plutonium-238, 239, 240, americium-241, strontium-90 and caesium-137 into potatoes.
Transfer factors have been measured for 239 Pu + 240 Pu, 241 Am, 90 Sr and 137 Cs into potatoes grown in a blend of soil which included silt polluted with radioactive waste discharged into the Irish Sea. The experiment has been carried out over four seasons and attempts to assess the radiological consequences to the consumer which would arise if potatoes were to be grown in land heavily contaminated with the silt. During the course of the experiment plutonium and americium became less available for uptake, 90 Sr became slightly more available and 137 Cs remained nearly constant in its availability. The values of the transfer factors are among the lowest reported for these radionuclides into potatoes.
Americium↗
1976 Hanford americium exposure incident: medical management and chelation therapy.
A chronological account is given of the general medical management of a patient involved in an americium exposure incident.
Accidents, Occupational↗
1976 Hanford americium exposure incident: external decontamination procedures.
An accident resulted in the deposition on an injured workman's skin surfaces, in acid-burned areas and in lacerations, of something in excess of 6 mCi 241Am. This paper describes the external decontamination procedures used, the change in americium content of the skin during the course of treatment, and some of the unusual problems encountered from the extrusion of foreign material and flaking of skin and scar tissue.
Accidents, Occupational↗
1976 Hanford americium exposure incident: in vivo measurements.
Detailed external measurements were made of internally deposited 241Am in a nuclear chemical operator involved in an americium exposure accident at the Hanford plant. Despite some interference from high-level external contamination, quantitative measurements of the 241Am content in the lung, liver and bones were made starting on the third day after the accident. The rate of excretion of 241Am from these organs was determined. The 241Am embedded in the skin of the face and head was carefully mapped. The distribution over the total length of the body was also determined. Linear and rectilinear scanners, gamma cameras, large and small scintillation detectors, proportional counters, and Si(Li) and intrinsic germanium detectors were used to evaluate the internal deposition. Methods of calibration for quantitative measurement included simulation of the 241Am activity in both phantom and cadaver parts.
Absorption↗