Exposure Pathways

Chemicals can be released into the soil, water or air from spilled or leaking containers, leaking landfills or dumps, through spraying, or released from smokestacks. These chemicals follow a pathway, or a route from the time of release to the point of human contact. When a substance enters the ecosystem where it is not normally found, it is called a contaminant. Humans become exposed to these contaminants by touching, breathing, or ingesting substances that contain the chemical (ATSDR, 1993).

To determine if human health is at risk of disease from contaminants, two things must occur: there must be an exposure to a contaminant; and the contaminant must be toxic. A complete exposure pathway must be present for disease to occur. The elements of an exposure pathway are:

  1. The source - how the contaminant got into the environment
  2. The transport media - how the contaminant moves through the environment
  3. The exposure point - how people came in contact with the contaminant
  4. The exposure route - how the contaminant entered the body
  5. The receptor population - how susceptible the population is to the contaminant (adapted from ATSDR, 1994).

Additionally, whether the exposure causes disease depends on the dose (how much), the duration (how long you are exposed), the route of exposure (breathing, eating, or through the skin), other chemicals to which you are exposed, and individual characteristics such as age, sex, nutritional status, genetic traits, lifestyle and general health condition (ATSDR, 1993).

Analyzing the exposure pathway at a contaminated site is an important challenge. Consideration must be given to how the chemical behaves in various kinds of environments (soil, air, water, sediment, biota). Some contaminants disperse quickly and others are very tenacious. For example, if drinking water is contaminated, individuals can be exposed to the contaminant not only by drinking but by showering through skin absorption and through inhaling droplets in the air. Or, if surface water is contaminated with a chemical that clings to soil particles, individuals may be exposed as the chemical makes its way through the food chain when animals ingest contaminants in soil and sediment. Learning what chemicals are present and how they "behave" are critical steps in understanding risk.

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