A physiologically based model of chromium kinetics in the rat

A physiologically based model of chromium kinetics in rats has been developed. The general structure of the model is similar to that of a model of lead kinetics in rats. Like lead chromium exchanges between plasma and the bone surfaces in contact with plasma, and also like lead, although with much lower efficiency, it can become incorporated into actively mineralizing bone. Both processes are included in the model. Parallel absorption and disposition schemes for chromium(VI) and chromium(III) are linked in the model by reduction processes occurring throughout the body, including the lung and gastrointestinal tract. Examination of a number of data sets from studies in which chromium salts were administered to rats intravenously, orally, or by intratracheal instillation established that intravenous administration, on the one hand, and oral or pulmonary administration, on the other hand, result in different disposition patterns. The model was calibrated based on published oral and intratracheal kinetic studies in rats given soluble chromium(III) and chromium(VI) salts. In the most complete of these studies, chromium concentrations were monitored in individual tissues for 42 days following intratracheal administration of a soluble chromium(VI) salt. Inclusion in the model of a urinary excretion delay was necessary in order to fit excretion data from two other intratracheal studies. Model predictions of blood chromium concentrations are compared with the results of a published kinetic study in which rats were administered a soluble chromium(VI) salt by inhalation.