The gastrointestinal (GI) absorption factors and the biological retention times for polonium were determined for a group of 14 volunteers--seven men and seven women--from Saskatoon, Saskatchewan, Canada. Each volunteer consumed 2.0 kg of caribou meat containing known amounts of naturally occurring 210Po. Urine and faecal samples were collected for up to 65 days after meat consumption and analysed for 210Po. The average GI absorption factor for the 14 volunteers was 56 +/- 4% (range = 31-71%), not significantly different from the ICRP value of 50%. About 3% of absorbed polonium underwent prompt excretion by the urinary pathway. The remainder was retained by the body with a half-time >100 days, compared to the ICRP value of 50 days. The effect of these findings increases the dose estimate for ingestion of 210Po in food by a factor of 1.5 to 3.5. Thus, background doses to people consuming caribou and reindeer may be higher than previously thought.
The daily intake of long-lived alpha-emitting members of the U, Th and Ac series by New York City residents has been estimated from measurements of diet, water and air samples. The total daily intakes from inhalation, food and water consumption in mBq are 18 (234U), 0.7 (235U), 16 (238U), 6 (230Th), 4 (232Th) and 52 (226Ra). From this, we infer that the total daily intakes of 228Th and 228Ra are 4 and 35 mBq, respectively.
Measurements of the environmental and metabolic behaviour of the naturally occurring radionuclides have provided necessary information on the behaviour of stable elements and have been useful analogues in the study of man-made radionuclides. Uranium has been studied primarily because of its role in the nuclear industry and its possible effects as a heavy metal in occupational exposure cases. There is abundant literature dealing with uranium studies in animals, and some literature on human studies with chronically ill patients. Relatively few data are available which document the uranium concentrations in humans under chronic, low level environmental conditions. Some recent bone measurements performed at the US Department of Energy, Environmental Measurements Laboratory are presented. For comparison, a summary of published information on uranium concentrations in blood, soft tissues and bones of humans is also presented. These data are selected to eliminate results from areas of known elevated natural radionuclide levels and occupational or controlled experimental exposure cases. From the measurements of the uranium concentration in bone from 12 countries, it is possible to derive a cumulative frequency distribution for the sampled populations.
Specimens of lung, liver, kidney and vertebrae from New York City autopsy cases were measured for naturally occurring U. An age dependency in U concentration was found in lung and vertebrae. The bone concentration was found to be a factor of 10 lower than previously reported for this tissue, thus the skeletal burden of U is estimated to be factor of 10 lower than that suggested in ICRP Publication 23.
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