The source of contamination is where the chemicals originate or are released.

Examples are landfills, drums, or emission stacks.

The environmental medium through which contaminants travel describes what media
(e.g., water, soil, air, or biota) are affected by chemicals and how chemicals move from one
media to another.

Examples are chemicals leaving a landfill in leachate and entering streams or chemicals released in air emissions and depositing on soil.

The point of exposure is the location where people contact a chemical in the environment.

Examples are drinking water taps or recreational areas where chemicals have migrated.

The route of exposure describes how the chemical enters a person’s body.

  Examples are eating (ingestion) or breathing (inhalation).

The exposed population is the individual or group of people who are contacting the chemical from
the source.

Examples include the residents who use contaminated drinking water or people swimming and wading in contaminated streams.