MODIFIED RESPIRATORY-TRACT MODEL FOR URANIUM - ITS IMPLICATIONS ON BIOASSAY INTERPRETATIONS

The excretion of inhaled poorly transportable compounds of uranium rel ative to chest content has been measured in humans by a substantial nu mber of measurements of urine, feces, and in vivo measurements over th e chest. The use of these measurements have permitted us to compare th e results predicted by the models with empirical observations in human s. The ICRP-30 model for inhaled class Y compounds of uranium along wi th the ICRP-30 systemic model, no matter what the particle size, gross ly underpredicts urinary excretion over time than that observed in hum an occupationally exposed to poorly transportable compounds of uranium by inhalation. Conversely, if urinary excretion were to be used to es timate the contents of poorly transportable uranium compounds in the l ung using ICRP-30 models, the results would be significantly overestim ated. The new ICRP (ICRP-66) respiratory tract model also grossly unde restimates urinary excretion of inhaled poorly transportable uranium c ompounds 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 no t entirely satisfactory in predicting urine/fecal ratio in excreta.