ABSTRACT
The discussion of variability in the previous chapter presumes that each individual exposed to the same amount of chemical received the same dose of chemical at the site in the body where the toxic effect occurred, e.g., the lungs. However, it has been shown experimentally that this is not the case. One of the main factors that influences the dose at the site of action, or the "effective dose," is the route of exposure or how the individual was exposed. The three main routes of exposure are inhalation (breathing in the material), ingestion (eating or drinking the substance), and dermal contact (entry through the skin). From this simple analysis, it might appear that the most dangerous chemicals to the lungs are those that are inhaled; to the digestive system, those that are ingested; and to the skin, those that are touched. This fairly obvious conclusion is generally appropriate, however, only for local effects which often occur soon after exposure has occurred.
