Biokinetics and absorption of actinides in human volunteers: a review.

Experiments that have been described in the literature are reviewed, with emphasis on the techniques that have been used, rather than a critical appraisal of the results obtained.

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.

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).

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.

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 gastrointestinal absorption and retention of niobium in adult and newborn guinea pigs.

The gastrointestinal absorption of 95Nb ingested in milk by adult guinea pigs on a milk-supplemented diet was estimated as 0.8 +/- 0.2% (SEM; n = 4) and a value of 1.4 +/- 0.2% was obtained for guinea pigs fasted for 24 h before and 2 h after the oral administration of 95Nb in a citrate solution. The absorption in 2-day-old animals given the 95Nb-citrate solution was estimated as 1.5 +/- 0.2% (SEM; n = 3). These results support the values currently used for radiological protection purposes to calculate doses from the ingestion of niobium isotopes; these are 1% for adults and 2% for infants in the first year of life. Intestinal retention of niobium in newborn guinea pigs was low, unlike retention in other species, but consistent with observations of the retention of other elements in guinea pigs. It is considered that retention in human neonates is likely to be most similar to that in guinea pigs. Whole-body retention of 95Nb after systemic administration in citrate solution was slightly lower in 2-day-old guinea pigs than in adults, with rapid excretion of about 50% over the first day compared with 40% in adults. Subsequent clearance was similar in the two age groups with a retention half-time of about 30 days.

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.

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.

The effect of concentration and chemical form on the gastrointestinal absorption of neptunium.

The gastrointestinal absorption of neptunium at low mass concentrations as 239Np nitrate (0.5-1 ng Np; 2-5 micrograms l-1) has been found to be 0.03, 0.02 and 0.18 per cent in adult rats, hamsters and rabbits, respectively. Administration as 239Np bicarbonate increased uptake in the rat to 0.15 per cent but had no significant effect on uptake in either the hamster or the rabbit. Absorption in the rat was also increased to 0.14 per cent for 239Np citrate but not for either 239Np phytate (0.04 per cent) or 239Np incorporated into rat liver (0.01 per cent). The fasting of rats for 8 hours increased their subsequent absorption of 239Np as the bicarbonate to 0.25 per cent. The absorption of neptunium at high mass concentrations as 237Np nitrate (0.5 mg Np, 5 g l-1) was increased to 0.26 per cent in the rat compared with the value of 0.03 per cent for 239Np (0.5 ng, 5 micrograms l-1) but a similar effect of concentration was not observed in the hamster. The results support the use of a value of absorption of 0.1 per cent instead of 1 per cent in calculations of annual limits on intake of radioisotopes of neptunium by workers and in estimates of radiation doses resulting from the ingestion of contaminated food and water by adult members of the public.

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.

Radioactivity in environmental samples taken in the Sellafield and Ravenglass areas of West Cumbria, 1977-1982.

Terrestrial foodstuffs and other materials of agricultural importance have been analyzed for fission products and actinides discharged in waste from the Sellafield processing works in west Cumbria . Results obtained between 1977 and 1982 are summarized and it is concluded that the internal radiation exposure of the general public due to consumption of locally produced food in no instance amounts to more than a small fraction of recommended limits. Deposition of seaborne sediment is shown to be the main route by which radionuclides of Sellafield origin reach grazing land bordering a nearby tidal estuary.