organisms are exposed to environmental hazards via several possible
pathways. Pathways trace the route
that the contaminant travels from its source to the living organism (the
receptor). Health Canada’s scheme
divides exposure pathways in to three sets of factors that include:
source: this is the ultimate origin of a contaminating substance.
media: are the elements through which the contaminant travels and that
represent the points at which humans become exposed. Water, air, soil and food are the main
|3) Routes of
exposure: are the means by which contaminants are then transferred to, or
absorbed by the human body. These may
include any or all of inhalation, skin absorption or ingestion, depending
upon the media.
|The degree to
which a chemical is absorbed by the body depends mainly upon the physical and
chemical properties of the substance, as well as the nature of the exposure
route and the exposure amount.
|The main portals
of entry, the lungs, digestive system and skin, may in the case of some
substances, effectively inhibit absorption.
If a substance does pass into the body it may be metabolized in the
liver and excreted as a waste product although this does not necessarily mean
that the body tissues will fully escape the harmful effects of that
substance. Some chemicals are not
readily excreted but become stored in the body. For example, chemicals that are fat soluble
are not only easily absorbed, but also become stored in the body’s fatty