Environmental or occupational epidemiologists are often faced with chemical, physical, or biological contaminants that are more tangible but less concrete. The exposure pathways and media outlined in the slide here are provided to illustrate the complexity as well as the general scheme involved in assessing human exposure to environmental contaminants. (The interrelationships depicted in the slide here should become more apparent from materials presented in the next lecture.) The discussion that follows also explains why it appears to be more appropriate for epidemiologists to assess human exposure to this type of contaminants, than for scientists from other existing disciplines.

Exposures to environmental contaminants can occur via dermal contact, ingestion, dietary intake, and inhalation. The above flowchart also indicates that the contaminant can be available on foliar or structural surfaces, or in such commonly-encountered environmental media or compartments as food, air, soil, and drinking water. For some chemicals, some exposure routes and media may play a more significant role than others do. In this lecture, dietary intake and ingestion are considered different, although in both cases the route of exposure is oral. Dietary intake involves the exposure from daily food consumption, and frequently including drinking water as well. Ingestion is referred to here as any other oral intake, such as from hand-to-mouth by a toddler crawling on a treated carpet. The exposure scenarios that follow echo those presented in Dong and Ross (in press), and can serve to account for many common routes and media of exposure to environmental contaminants.