Environmental Health Criteria 214

HUMAN EXPOSURE ASSESSMENT
Improved health effects investigations invasive sampling
Improved population risk availability of human samples
assessment/risk management
specificity/sensitivity
Validation of exposure models lack of normative values for comparison
10.4.1 Characterizing inter-individual variability
A fundamental issue in the quantitative aspect of exposure
assessment is the characterization of inter-individual variability in
exposure. The pattern of exposure may differ within individuals,
groups or populations. For example, workers in the same factory may
have different exposures as a result of differing work habits
(Rappaport et al., 1993); families living in very airtight houses may
have greater exposure to indoor contaminants than families living in
draughty homes. Biological markers represent one strategy to assess
inter-individual variation in exposures, when measured environmental
concentrations do not differ between individuals. Genotype, dietary
habits, body size, state of health, lifestyle habits (e.g., smoking)
and behaviour may all play a role in determining an individual's
exposure (Bernard & Lauwerys, 1986). Biological markers of
susceptibility may also be used to explore biological variation in
response to exposure. For example, phenotypic differences in
Delta-aminolaevulinic acid dehydratase (ALAD) may influence both blood
lead levels and the health effects of lead (Wetmur, 1994;
Milkovic-Kraus et al., 1997). Incorporation of biological markers of
both exposure and susceptibility into biological monitoring studies
may result in further insight into inter-individual variability.
10.4.2 Efficacy of use
In some situations, biological markers can be more efficacious
tools than external exposure measurements for monitoring human
exposure in population studies. For example, participant burden may be
lower than in traditional monitoring schemes for some activities
(e.g., motor vehicle repair) and for some subjects (e.g., children and
the elderly) wearing a personal monitor may not be a practical
strategy to monitor a subject's exposure. For some exposure routes
such as dermal exposure, there is no adequate way to determine the
extent of exposure using non-biological methods (Ward et al., 1986;
Fiserova-Bergerova, 1987; Hemminki, 1992; Levesque et al., 1994). For
example, chloroform in exhaled breath has been used as a biological
marker to evaluate dermal exposure while swimming and showering
(Levesque et al., 1994). Under certain conditions, wearing a sampling
device alters behaviours that may, in turn, affect exposures as
measured by a sampling device. Wearing a sampling device may be unduly
burdensome in certain populations. Finally, monitoring devices may not
exist to evaluate these exposures. In these cases, biological markers
could be a preferred method to evaluate exposure.
Biological markers can improve the evaluation of human health
effects associated with environmental exposure to contaminants
(Schulte, 1987; US NRC, 1987; Hulka, 1991; Hulka & Margolin, 1992).
These markers have been advocated as a means to reduce measurement
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