Assessment of uranium tetrafluoride dissolution in the lung by in vivo and in vitro methods

The data acquired over the past twenty years concerning the solubility of uranium tetrafluoride (UF4) are contradictory. To check the validity of this compound's W classification by the ICRP, we investigated its in vivo dissolution in rats and baboons and compared it to the in vitro dissolution obtained either with alveolar macrophages in culture or with a serum simulant fluid. We studied daily urinary excretion of uranium in rats and baboons and U tissue distribution in rats after inhalation of raw UF4 powder or intratracheal instillation of a UF4 particle suspension. Alveolar macrophages from 4 rats and 2 baboons were tested for their ability to dissolve UF4. Since UF4 dissolution in the lung may be influenced by oxidation to the very soluble form UO2F2, we performed in vitro dissolution with a serum simulant fluid bubbled with either pure oxygen or argon. There was good agreement between the in vivo and in vitro results for both rats and baboons. Our results support the view that dissolution of UF4 in the lung is fast, and that this compound is more soluble than expected. (author)