Ingestion, both intentional and inadvertent, represents a major route of exposure to environmental contaminations. Ingestion of drinking water and foodstuffs containing environmental contaminants can result in significant exposure to many compounds with known adverse health effects. The gastrointestinal system offers an important protective mechanism to preclude absorption of harmful contaminants but, by its essential processes, affords other mechanisms that allow passage of possibly harmful materials into the body. In this chapter we will assess this route of exposure. We begin with a brief discussion of the physiology of the gastrointestinal system contrasting it with the other barriers to absorption: the lung epithelium and the skin. This is followed by a discussion of the primary pathways of ingestion exposure: water ingestion, food ingestion, and ingestion of nondietary items. At each stage, we will call upon current scientific work to address specifics of these issues. Since the mechanisms for ingestion and absorption of inorganic and organic compounds
are different, we will investigate each separately. Further, we will use typical values of dietary and nondietary intake to calculate the likely exposure and intake of specific chemical compounds in water, food, and in nondietary items. These calculations, done for both children and adults, give insight into the levels of contaminants taken into the body through this route.