Modified respiratory tract model for uranium. Its implications on bioassay interpretations

The excretion of inhaled poorly transportable compounds of uranium relative to chest content has been measured in humans by a substantial number of measurements of urine, feces, and in vivo measurements over the chest. The use of these measurements have permitted us to compare the results predicted by the models with empirical observations in humans. The ICRP-30 model for inhaled class Y compounds of uranium along with the ICRP-30 systemic model, no matter what the particle size, grossly under predicts urinary excretion over time than that observed in human occupationally exposed to poorly transportable compounds of uranium by inhalation. Conversely, if urinary excretion were to be used to estimate the contents of poorly transportable uranium compounds in the lung using ICRP-30 models, the results would be significantly overestimated. The new ICRP (ICRP-66) respiratory tract model also grossly underestimates urinary excretion of inhaled poorly transportable uranium compounds and exacerbates the problem, at least for the default values of the parameters of the model. A lung model derived from the original ICRP-30 lung model, which is named 'modified,' has been proposed in this work. It predicts urinary excretion better, even though it is not entirely satisfactory in predicting urine/fecal ratio in excreta. (author). 19 refs., 11 figs