Environmental Health Criteria 214

HUMAN EXPOSURE ASSESSMENT
operations will be familiar with and use the same procedures.
QC refers specifically to the quality of the laboratory results.
It has two components. Internal QC is a set of procedures used by
staff of a laboratory for continuously assessing results as they are
produced. External QC is a system for objective checking of laboratory
performance by an independent agency. Internal QC includes displaying
results of control samples in control charts (e.g., Shewhard and cusum
charts), and use of control limits as criteria for signalling the need
for action, or for judging whether a set of data does or does not
include a state of statistical control. External QC, on the other
hand, provides independent evidence of the quality of laboratory
performance and individual analyst proficiency. Usually, a
coordinating laboratory distributes samples of known concentration to
the participating laboratories. Participating laboratories examine the
reference samples and submit the results to the coordinating
laboratory for performance evaluation.
Reference samples used in internal and external QC should have a
matrix and pollutant concentration which is similar to the real
sample. In addition, for several substances it is necessary to take
into consideration the chemical form in which they may exist.
Finally, interactions with human populations present a unique set
of study design and QA considerations that should be carefully
evaluated together with the conventional issues of sampling analysis
and procedures.
12. EXAMPLES AND CASE STUDIES OF EXPOSURE STUDIES
12.1 Introduction
Exposure studies have helped to establish a subdiscipline of
environmental science. Exposure analysis is now essential to
environmental epidemiology and quantitative risk assessment. Exposure
studies have called attention to practices, locations and populations
subjected to higher risk owing to environmental contamination.
However, the full promise of exposure analysis has not been realized.
Exposure information can influence public opinion and policy and offer
cost-effective innovative strategies for those looking for
alternatives to current regulatory approaches. Our current practice is
to partition problems into specific media (air, water, soil and food)
and structure our management as restrictive commands limiting
discharge. Exposure analysis is an integrated and more comprehensive
approach for dealing with risk management.
Kirk Smith discusses the potential of human exposure assessment
for air pollution regulation (in WHO, 1995a). He argues that for
developing countries, without the investment in monitoring, regulation
and control infrastructures, exposure reduction strategies "may
provide a much more efficient pathway of control over time than the
path followed by the currently developed countries". Structuring a
regulatory control programme that bases performance on the reduction
of human exposure while also considering cost should appeal to market
economies in both developed and developing countries. In order to
implement such strategies effectively one must have the ability to
quantitatively assess the relative contribution of various sources to
human exposure and risk by measurement or modelling. With the
development of exposure science, trading exposures among sources and
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