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.
The normal dietary and fluid intake and urinary and fecal excretion of 234U and 238U were determined in humans under strictly controlled conditions in the Metabolic Research Ward at Hines Hospital. These values formed the basis of the metabolic balances of these uranium isotopes. The major pathway of 234U and of 238U excretion was via the intestine while the urinary 234U and 238U were very low, averaging 2% of the total excretion. The uranium balances were roughly in equilibrium. These data were used in combination with measurements of tissue concentrations of uranium from nonoccupationally exposed humans to calculate steady-state uptake factors for environmental exposure to uranium isotopes during baseline conditions of a normal dietary intake.
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