Environmental Health Criteria 214

HUMAN EXPOSURE ASSESSMENT
By their very nature, bioaerosols have compositions and
concentrations that are highly variable. The conditions favourable for
growth, reproduction and dispersion vary within a wide range of
temperature, moisture and nutrient conditions. These same factors
influence by interactions with human and animal activities. Mechanical
systems and machines can cause amplification and distribution of
biological aerosols. As a result personal exposures are quite
variable; this, in turn, has led many investigators to rely on area
air sampling and/or bulk sampling of materials. For example, it is
recommended that a surrogate measure of mite allergen exposure is
derived from bedding and floor dust samples. Home samples, whether air
or dust is sampled, are often the "exposure" value used in
epidemiological investigations.
Finally, the advancement of aerobiological exposure assessment to
eventual use in quantitative risk assessment will require better
understanding of relevant dose to cause sensitization and reactivity
for many different organisms and/or agents.
10. ASSESSING EXPOSURES WITH BIOLOGICAL MARKERS
10.1 Introduction
This chapter presents a summary of the major concepts,
definitions, advantages, limitations, sampling, media and uses of
biological markers as applied for exposure assessment to environmental
contaminants. These exposures are frequently characterized by low
contaminant concentrations, multiple sources and multiple types of
chemicals. Use of biological markers has been extensively reviewed
from both epidemiological and occupational monitoring perspectives as
well as their use in risk assessment (Bernard & Lauwerys, 1986; Harris
et al., 1987; US NRC, 1987; Hulka & Wilcosky, 1988; Cullen, 1989;
Griffith et al., 1989; Henderson et al., 1989; Monster & Zielhuis,
1991a,b; Schulte, 1991; Hulka & Margolin, 1992; IPCS, 1993; Aitio,
1994; Grandjean et al., 1994; Silbergeld & Davis, 1994). The reader
should refer to the research literature for a comprehensive and
detailed understanding of the complex issues relevant to the
development, validation, and application of biomarkers in studies of
human exposure. The specific issue of using biological markers in
occupational settings is beyond the scope of this chapter.
It is important to indicate that, to date, very few biomarkers
can be effectively used for quantitative estimation of prior
environmental exposure to contaminants (e.g., carbon monoxide or
lead). In most cases, there are qualitative or semi-quantitative
indicators for monitoring such exposures. However, as the field
evolves, and knowledge of the pharmacokinetics and pharmacodynamics of
xenobiotics develops, the number of quantitatively validated
biomarkers of exposure will also increase.
Biological markers present unique advantages as tools for
multimedia exposure assessment. They are highly sensitive indices of
an individual's exposure to chemicals, since they provide a measure of
the internal dose, account for all routes of exposure and integrate
over a variety of sources of exposure (Friberg, 1985; Baselt, 1988;
Sim & McNeil, 1992). Therefore, they can represent past exposure
(e.g., the presence of lead in shed teeth), recent exposure to an
external source (e.g., VOCs in exhaled breath) and even future
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