G.J. Ham

Gastrointestinal absorption of neptunium and curium in humans

The gastrointestinal absorption of Np and Cm has been determined in five male adult volunteers. The Np and Cm, which were in citrate solution, were taken with food. An initial experiment with each individual determined the fraction of each element excreted in the urine following intravenous administration. Subsequently, the results for urinary excretion for the two routes of administration were used to calculate the fractional absorption (f1) of ingested Np and Cm. The mean f1 values were: Np (2.0 +/- 0.2) X 10(-4), range (1.2-2.9) X 10(-4), and Cm (1.7 +/- 0.3) X 10(-4), range (0.95-3.0) X 10(-4), the quoted uncertainties being the standard error of the means. Currently, the International Commission on Radiological Protection recommends a value of 10(-3) for both elements. Cumulative urinary excretion over 1 wk after intravenous injection accounted for about 20%-40% of administered Np and 7%-10% of Cm. At the conclusion of the experiment, the total committed effective dose equivalent for each volunteer was calculated to be in the range 130-250 microSv, based on the individual f1 values, and, in some cases, a knowledge of the rate of clearance of 239Np through the gut as measured by whole-body counting.

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.

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.

Plutonium and Cs-137 in autopsy tissues in Great Britain

Tissues removed at autopsy from members of the general public contain significantly higher concentrations of plutonium and 137Cs in west Cumbrians than in people from three other regions of Great Britain. Several autopsy cases from Cumbria showed unusually high values of plutonium. Subsequently it was found that the subjects had been former employees of British Nuclear Fuels.

Determination of actinides in environmental materials using extraction chromatography

The determination of actinides at low level in environmental materials has always been a time-consuming and difficult task. The trivalent actinides in particular require lengthy separation methods that often use large amounts of hazardous materials, producing a waste disposal problem. In the last 10 years extraction chromatography (reversed phase partition chromatography) of the actinides has undergone considerable development. The technique uses an inert polymeric support which is impregnated with a selective extractant to form a solid sorbent in the extraction column. Extractants have been developed by Horowitz and co-workers to give very specific adsorption of actinides in the presence of other elements. These resins are now commercially available, making possible their use in routine analysis. The difficulty in applying this technique to environmental sample analysis is that, as the materials are expensive, only small columns are used. This means that preconcentration techniques must be used to allow the sample to be presented to the extraction column in a sufficiently small volume. The preconcentration steps used, must be chosen to lower the concentration of interfering elements to an acceptable level while giving a high yield of the required analyte and not making the method unduly long. This paper describes the methods used in our laboratories and current operating experience of them.

Radioactivity in environmental samples taken in the Sellafield, Ravenglass and Morecambe Bay areas of west Cumbria

Seaborne sediments deposited in the estuaries of the Esk, Duddon, Leven and Kent have been analysed for fission products and actinides discharged in waste from the Sellafield processing works in west Cumbria, and the values compared with the generally expected values due to fallout from atmospheric nuclear weapons tests. Analyses of tissues from sheep grazing the marshes of these estuaries show that the internal radiation dose of the general public through eating mutton or liver from these animals would be at most a few percent of recommended limits. Analytical data are presented on the actinide content of beef cattle, and on potato crops grown under field conditions; these data show that, as with the sheep data, the radiation dose to the consumer would be small.

The gastrointestinal absorption of neptunium, plutonium and americium in a primate (C. jacchus)

Mixtures of Np, Pu and Am were administered to primates (C. jacchus) by gastric intubation to measure their fractional gastrointestinal absorption (f1 values). The values obtained were about 2 x 10(-3) and 1 x 10(-3), respectively, for Np and Pu administered as the citrate, and 2 x 10(-3) and 6 x 10(-4), respectively, for Pu and Am in potato. The significance of these values in terms of absorption in humans is discussed.

Speciation of plutonium in potato and the gastrointestinal transfer of plutonium and americium from potato.

Complexation of Pu(IV) and Am(III) by naturally occurring agents such as citrate and phytate might enhance their uptake from the digestive tract. However, the extent to which they enhance the gastrointestinal uptake of actinides from foodstuffs is far from resolved, as this study shows. Investigations of the chemical forms of Pu(IV) and Am(III), by gel permeation chromatography, in simulated digests of potato tubers naturally radiolabelled with 239Pu(IV) and 241Am(III) have shown that neither citrate nor phytate appear to determine their chemical forms. Therefore, it is possible that these are not the complexing anions which determine the gastrointestinal transfer of these radioelements from potato meal. Isotachophoretic analyses of the juices pressed from tubers and solutions prepared by simulated digestion of potato tubers have demonstrated the presence of several low molecular weight anions. These anions might be complexing agents because they possess an isotachophoretic mobility similar to that of citrate; some of these anions remain unidentified. Whereas 239Pu and 241Am were used in the foregoing studies, 238Pu and 241Am were used to produce either in vitro or naturally radiolabelled potatoes for gastrointestinal transfer measurements using rats and hamsters. Gastrointestinal transfer values of 0.13 +/- 0.05% (mean +/- standard error of mean) and 0.16 +/- 0.06% were determined with rats for the uptake of 238Pu and 241Am, respectively, from naturally labelled potato meal. Higher gastrointestinal transfer values were obtained for hamsters: for 238Pu and 241Am the transfer values from naturally labelled meal were 0.25 +/- 0.08% and 0.33 +/- 0.07%, respectively. Similar values were observed for uptake from in vitro labelled potato meal. On the basis of the similarity of the values for the naturally labelled potato meal and for the spiked potato meal it would appear that biological incorporation is not necessary for the binding of the actinides to the ligands which will determine gastrointestinal transfer.

The gastrointestinal absorption of ‘biologically incorporated’ plutonium-239 in the rat

Growing potatoes have been labelled by foliar applications of plutonium citrate. Approximately 0.4% of the radioactivity was taken up by the tubers. The potatoes were fed to rats and the gastrointestinal uptake of plutonium was estimated to be 0.34%. The significance of these results in relation to the uptake by humans is discussed.

Measurements of actinide gut-transfer factors in humans.

Measurements have been made of the gastrointestinal absorption in humans of 239Np and 242Cm administered together in citrate media. Using five volunteers, consistent results of (2.0 +/- 0.2) x 10(-4) and (1.7 +/- 0.3) x 10(-4) were obtained for Np and Cm respectively; the quoted uncertainties are the standard errors of the means. A progress report is given of work to measure the f1 value for Pu in humans. Early work suggests an f1 value of 2 x 10(-4).