from inhaled radon. The PBPK model appears to provide reasonable predictions of retained radon, and its physiological basis provides the basis of the distribution of radon among the organs of the body.
As seen from table 4.4, the dose to the stomach depends strongly on whether radon is considered to move into the stomach wall, presumably by diffusion. Alpha particles emitted within the contents of the stomach cannot penetrate the mucus layer lining the epithelium and cannot reach the stem cells at risk (the range of alpha particles in tissue is about 50–60 µm). This mucus layer is thought to be important in minimizing the exposure of the stomach epithelium to the acidic environment of the gastric lumen (Livingston and Engel 1995) and possibly acts as a barrier to the gastric absorption of drugs (Larhed and others 1997). The layer is composed primarily of mucin mol-