UNLABELLED: Uranium trioxide, produced industrially, was administered to rats either by inhalation or direct injection of an aqueous suspension into the lungs. THE RESULTS: show that uranium was cleared rapidly from the lungs, mainly to the blood; show that distribution of uranium among body tissues, and the fraction of the systemic content excreted in urine, was similar to that obtained for other transportable hexavalent uranium compounds; suggest that urine monitoring data would be of more value than lung radioactivity counting measurements for assessing occupational human exposure; indicate that for setting exposure limits by inhalation the uranium trioxide should be considered a highly transportable compound. Thus intakes by workers should be restricted to those recommended for short-term exposures and not those based on an annual limit.
UNLABELLED: Uranium trioxide, produced industrially, was administered to rats either by inhalation or direct injection of an aqueous suspension into the lungs. THE RESULTS: show that uranium was cleared rapidly from the lungs, mainly to the blood; show that distribution of uranium among body tissues, and the fraction of the systemic content excreted in urine, was similar to that obtained for other transportable hexavalent uranium compounds; suggest that urine monitoring data would be of more value than lung radioactivity counting measurements for assessing occupational human exposure; indicate that for setting exposure limits by inhalation the uranium trioxide should be considered a highly transportable compound. Thus intakes by workers should be restricted to those recommended for short-term exposures and not those based on an annual limit.