Page 149 - Materials Chemistry, Second Edition

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4.5 EXPOSURE ASSESSMENT
Exposure assessment is the determination of the concentration/doses to which human
populations or environmental compartments are or may be exposed. An exposure
assessment is designed to estimate the magnitude of actual and potential receptor
exposures to environmental contaminants, as well as the frequency and duration of
these exposures, the nature and size of the populations potentially at risk (i.e., the
risk group), and the pathways by which the risk group are or may be exposed.
The following steps must be taken in a typical exposure analysis for an envi-
ronmental contamination problem:

• Determination of the concentrations of the chemicals of concern in each
medium to which potential receptors are or may be exposed
• Estimation of the intakes of the chemicals of concern, using the appro-
priate case-specific exposure parameter values

The exposure assumptions election can be very difficult and is one of the critical
elements of an ERA. Efforts have been made to standardize the process of exposure
assessment, but the best approach remains to tailor the exposure assessment to the
particular characteristics of the study. For instance, risk experts should visit the study
area if possible and contact relevant agencies and individuals to assemble information
regarding the habits and activities of local populations.

4.5.1 EXPOSURE ASSESSMENT DATA
One of the most important steps in the ERA process is the determination of
potential exposure. Exposure estimation involves combining predicted concentra-
tions for target chemicals with certain assumptions about the environmental fate of
these chemicals and activity patterns of the receptors. Subsequently, the results of
the exposure assessment include toxicity and epidemiologist information to provide
a quantitative estimate of risk. Therefore the exposure assessment is based on
representative monitoring data and/or on model calculations. Appropriate informa-
tion on substances with analogous use and exposure patterns or analogous properties
will be taken into account when available. However, the availability of representative
and reliable monitoring data or the amount and detail of the information necessary
to derive realistic exposure levels by modeling will vary.
4.5.1.1 Environmental Monitoring
Whenever possible, high-quality and relevant measured exposure data should be
used in risk characterization. Measured exposure data may be available for existing
substances, but are unavailable for new substances. The latter may be obtained from
industry monitoring programs, particularly for occupational exposure, or other mon-
itoring studies.
As a first step, the available data must be assessed with regard to their reliability.
The confidence in measured exposure concentrations is determined by the adequacy
of techniques, strategies and quality standards applied for sampling analysis and
protocol.

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