Environmental Health Criteria 214

HUMAN EXPOSURE ASSESSMENT
to be caused by such exposures. It is a scientific tool that can
sometimes detect environmentally induced health effects in
populations, and it may offer opportunities to link actual exposures
with adverse health outcomes (US NRC, 1991c, 1994; Matanoski et al.,
1992; Beaglehole et al., 1993).
Exposure assessment methods can be used for identifying and
defining the low or high exposure groups. They can also be used for
devising more accurate exposure data from measured environmental
contaminant levels and personal questionnaire or time-activity diary
data, or estimating population exposure differences between days of
high and low pollution, or between high and low pollution in
communities using measured environmental and population behavioural
data (see also Chapters 3 and 5).
In particular, to establish long-term health effects of "low
dose" environmental exposures, epidemiological methods are the
predominant, if not only, tools at hand for health-effect assessment.
However, the excess risk of most environmentally related health
effects is small, with relative risks and odds ratios usually being
less than 2 across the observed range of exposure experienced by
populations. Furthermore, there are usually no "non-exposed"
comparison groups, and the factors contributing to the development of
diseases are numerous. As a consequence, environmental epidemiology
faces considerable methodological challenges. Adequate exposure
assessment is one key issue, as well as the need for studies conducted
with large populations.
2.3 Human exposure information in risk assessment
Risk assessment is a formalized process for estimating the
magnitude, likelihood and uncertainty of environmentally induced
health effects in populations. Exposure assessment (e.g., exposure
concentrations and related dose for specific pathways) and effects
assessment (i.e., hazard identification, dose-response evaluation) are
integral parts of the risk assessment process. The goal is to use the
best available information and knowledge to estimate health risks for
the subject population, important subgroups within the population
(e.g., children, pregnant women and the elderly), and individuals in
the middle and at the "high end" of the exposure distribution (US NRC,
1983; Graham et al., 1992; Sexton et al., 1992).
Environmental health policy decisions should be based on
established links among emission sources, human exposures and adverse
health effects. The chain of events depicted in Fig. 4 is an
"environmental health paradigm": a simplified representation of the
key steps between emission of toxic agents into the environment and
the final outcome as potential disease or dysfunction in humans. This
sequential series of events serves as a useful framework for
understanding and evaluating environmental health risks (Sexton, 1992;
Sexton et al., 1992, 1993). It is directly related to the risk
assessment process.
* Exposure assessment in the risk assessment framework focuses on
the initial portion of the environmental health paradigm: from
sources, to environmental concentrations, to exposure, to dose. The
major goal of exposure assessment is to develop a qualitative and
quantitative description of the environmental agent's contact with
(exposure) and entry into (dose) the human body. Emphasis is placed
on estimating the magnitude, duration and frequency of exposures,
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