4. METHOD OF SOLUTION
The ICRP task group lung dynamics model, in which the respiratory tract is divided into four regions, is used for the estimation of exposure due to inhalation. In this model inhaled materials are deposited in the regions with various probabilities depending on the particle diameter. Deposited materials are excreted from the regions to the body fluids and to the gastro-intestinal tract, or exhaled with different removal rates depending on the solubility.
The simple ICRP Pub. 2 model is used for the estimation of ingestion exposure.
A four-compartment model is used to evaluate the internal exposure to the G.I. tract, i.e. the model considers the G.I. tract to be composed of the stomach, the small intestine, the upper and lower large intestine. Material that enters the G.I. tract through the stomach passes these compartments in turn and the absorption into the body fluids occurs only at the small intestine.