Environmental Health Criteria 214

HUMAN EXPOSURE ASSESSMENT
10.7 Summary
Biological markers represent a means to monitor environmental
exposure by characterizing an individual's total dose of a contaminant
from all sources of exposure. The main advantage of this strategy is
in evaluation of an individual's total exposure using a measure which
integrates over all exposure sources and is influenced by human
behaviour. Biological markers are also believed to be more predictive
of health effects than external measures of exposure. They address
several exposure assessment needs:
* characterizing an individual's or a population's exposure
* generating population distributions of dose
* identifying the environmental and demographic determinants of
exposure.
The main disadvantage of biological markers is the difficulty in
characterizing the individual sources which contribute to the
subject's total exposure. When developing and utilizing biological
markers, understanding the toxicokinetics of the contaminant in the
system is crucial to characterize the biological variability and to
determine whether the biological marker is valid for exposure
assessment purposes at the concentration of interest. Biological
markers have been crucial in improving our understanding of human
exposure to certain contaminants, such as lead. Numerous non-invasive
methods are available for biological monitoring, and exposure
assessors should try to include these when developing environmental
monitoring protocols.
11. QUALITY ASSURANCE IN EXPOSURE STUDIES
11.1 Introduction
Human exposure studies are complex and often utilize specialized
instrumentation and management of large amounts of data. Consequently,
quality assurance (QA) should be applied to all aspects of an exposure
study, including its design, implementation and reporting, to ensure
the reliability and reproducibility of the results. A successful QA
programme will monitor occurrence of potential errors in various
components of the study and establish protocols for remedying such
errors. In this chapter, important types of potential error in
exposure results are described, and tools for identifying them are
introduced.
Exposure studies involve evaluations and comparison of exposures
over time, geographical locations and populations. It is important
that the results of the study accurately represent the exposures,
rather than reflecting bias or error introduced by the study design or
method. The reader is referred to the previous chapters on strategies
and designs for exposure studies (Chapter 3) and related statistical
concepts (Chapter 4) with respect to the principles of designing a
high quality exposure study.
The reader is also referred to Environmental Health Criteria
141: Quality Management for Chemical Safety Testing (IPCS, 1992) a
monograph which deals explicitly with the organization of a QA
programme. A prerequisite for producing data of good quality in
exposure studies is the availability of adequate facilities,
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