Metabolism of an Industrial Uranium Trioxide Dust after Deposition in the Rat Lung

Uranium trioxide, produced industrially, was administered to rats either by inhalation or direct injection of an aqueous suspension into the lungs. The results: 1 show that uranium was cleared rapidly from the lungs, mainly to the blood; 2 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; 3 suggest that urine monitoring data would be of more value than lung radioactivity counting measurements for assessing occupational human exposure; 4 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.