ABSTRACT
Apart from local effects at the site of contact, a toxicant can cause injury only after it is absorbed by the organism. Absorption can occur through the skin, the gastrointestinal tract, the lungs, and several minor routes. Furthermore, the nature and intensity of the effects of a chemical on an organism depend on its concentration in the target organs. The concentration depends not only on the administered dose but also on other factors, including absorption, distribution, binding, and excretion. For a chemical to be absorbed, distributed, and eventually excreted, a toxicant must pass through a number of cell membranes. A cell membrane generally consists of a biomolecular layer of lipid molecules with proteins scattered throughout the membrane (Fig. 1).
