Environmental Health Criteria 214

HUMAN EXPOSURE ASSESSMENT
of the environmental health paradigm also showing the role of exposure
is depicted in Fig. 2. The role of exposure assessment in the risk
assessment framework applied by EU and US EPA is shown in Fig. 3.
The release of an agent into the environment, its ensuing
transport, transformation and fate in various environmental media, and
its ultimate contact with people are critical events in understanding
how and why exposures occur. Definitions for key events in the
continuum are summarized below. They were compiled from three sources:
Ott (1990); US EPA (1992a); Sexton et al. (1995a).
* Sources. The point or area of origin for an environmental agent
is known as a source. Agents are released into the environment from
a wide variety of sources, which are often categorized as
primary sources including point sources (e.g., incinerator)
versus area sources (e.g., urban runoff), stationary sources (e.g.,
refinery) versus mobile sources (e.g., automobile) and
anthropogenic sources (e.g., landfill) versus non-anthropogenic
sources (e.g., natural vegetation) and secondary sources
including condensation of vapours into particles and chemical
reactions of precursors producing new pollutants.
* Exposure pathway. An exposure pathway is the physical course
taken by an agent as it moves from a source to a point of contact
with a person. The substance present in the media is quantified as
its concentration.
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