Environmental Health Criteria 214

HUMAN EXPOSURE ASSESSMENT
internal exposure sources (e.g., pesticides in adipose tissue).
Furthermore, their use may result in improved monitoring of total
population exposure, characterization of individual and population
exposures and evaluation of internal sources of exposure. These
markers are also useful surveillance tools for monitoring chemical
exposure in both individuals and populations over time.
Use of biological markers of exposure can improve the risk
assessment process by providing a critical link between chemical
exposure, internal dose and health impairment (IPCS, 1993). Biological
markers of exposure can improve clinical diagnoses where there is a
well-established relationship between biological marker and outcome.
10.2 General characteristics
Biological markers represent events or changes in human
biological systems as a result of exposure or disease (US NRC, 1991b).
They are classified as markers of exposure, effect, and susceptibility
and are considered to represent events along a theoretical continuum
from causal exposure to resulting health outcome (US NRC, 1987;
Schulte, 1989). A biological marker of exposure is defined as a
xenobiotic substance or its metabolite(s) or the product of an
interaction between a xenobiotic agent and some target molecule(s) or
cell(s) that is measured within a compartment of an organism (US NRC,
1989; IPCS, 1993). Biological markers of effect are measurable
biochemical, physiological, behavioural or other alterations within an
organism that, depending upon the magnitude, can be recognized as
associated with an established or possible health impairment or
disease (IPCS, 1993). Biological markers of susceptibility are
indicators of inherent or acquired abilities of an organism to respond
to the challenge of exposure to a specific xenobiotic substance (IPCS,
1993). Although the distinction between some biological markers of
exposure and effect may be overlapping, this chapter will focus on
those biological markers which can be applied to environmental
exposure assessment.
10.3 Considerations for use in environmental exposure assessment
The use of biological markers for exposure assessment represents
a different perspective for evaluation of human exposure to a
contaminant than traditional exposure assessment. Biological markers
of exposure are considered measures of internal dose, whereas exposure
is frequently defined as the concentration of an agent at the boundary
between an individual and the environment multiplied by time (US NRC,
1991b; IPCS, 1993). Owing to long-term storage of specific
contaminants in biological tissues (e.g., bone and fat), some
biological markers are markers of both cumulative dose and future
internal exposure.
Biological markers of exposure have been used most frequently in
industrial hygiene and occupational medicine (Elkins, 1954, 1967;
Lauwerys, 1983; Schulte, 1991). Before widespread application of
biological markers for exposure assessment of the general population
can occur, it is important to consider the situations which are best
suited for biological monitoring. Ideally, a biological marker of
exposure should be chemical-specific, detectable in trace quantities,
available by non-invasive techniques and inexpensive to assay. Also,
it must relate consistently and quantitatively to the extent of
exposure and ideally also integrate the exposure over time (Bond et
al., 1992). Currently there are very few biological markers that
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