Improved model for uranium metabolism in the primate

The proposed model divides the human body into different compartments: red cell, short-term bone, long-term bone, kidney, and urine. The rate of transfer between compartments is assumed to be governed by 1st order kinetics. Transfer from plasma to the other compartments is considered as instantaneous. Feedback from bone compartments and red cells to plasma is taken into account. An exact analytical solution to the model was proposed that can be solved for any kind of time dependent exposure to uranium. This methodology is unique to this model and represents a significant change in analytical solutions that have been proposed in the literature. Specific analytical solutions for the more common cases of uranium exposure were derived. These include: (1) single injection dose to the blood; (2) exposure to background levels of natural uranium by ingestion; (3) exposure through inhalation during working hours for uranium workers; (4) single inhalation dose (most probable case for accidents); (5) constant inhalation exposure during a finite interval of time; (6) single ingestion dose.For the experimental part of the study, five baboons were injected intravenously with uranium nitrate. The partition of uranium between plasma and red cells was studied. The half-life in short-term bone was derived. The distribution of uranium in soft tissues four days after injection was studied: the kidney was seen to be the main organ for uranium deposition. The concentration in human skeleton was found equal to 0.02 μgU/g ash. For this concentration in skeleton the gastrointestinal absorption factor was calculated as 23% and the daily excretion as 0.24 μgU/day. This model is suitable for deriving dose limits and determining body burdens from standard bioassay information