In Vitro Solubility of Uranium Tetrafluoride with Oxidizing Medium Compared with in Vivo Solubility in Rats

Summary

A simple in vitro solubility test for uranium tetrafluoride (UF₄) was developed to investigate the effects of addition of enzymes, proteins or gases such as O₂ to synthetic biological fluid or Gamble solvent. The tests were conducted concomitantly with an in vivo inhalation experiment using male rats. In the presence of Gamble solvent alone, UF₄ exhibited class Y behaviour with a dissolution half-time of 300–500 days. However, when oxygen or carbonates were added to the Gamble solvent, UF₄ displayed class W behaviour, with a half-time of 25–50 days. Lastly, in the presence of oxygen and pyrogallol, which simulates the action of the enzyme NADPH, the superoxide ion (O⁻₂) was formed, which appears to have a dominant role in the oxidation of U⁴⁺ to U⁶⁺. Under these conditions UF₄ behaved like a class D compound, and had a dissolution half-time of only 2–3 days. These latter results correlated with those of the inhalation experiment in which the dissolution half-time was calculated to be between 2·5 and 5·2 days. The data are also in agreement with urine monitoring data obtained for workers exposed to UF₄ over a 20-year period.