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
The source - how the contaminant got into the environment
- The transport media - how the contaminant moves through the
- The exposure point - how people came in contact with the contaminant
- The exposure route - how the contaminant entered the body
- 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).
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contaminants and contaminant sources
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