Environmental Health Criteria 214

HUMAN EXPOSURE ASSESSMENT
quantitatively. In most cases, biomarkers of exposure provide a
semi-quantitative or qualitative indication of exposure.
10.3.4 Normative data
Currently many biological markers are being developed for
research purposes (Schulte, 1987; Kelsey, 1990; Bond et al., 1992;
Fowle & Sexton, 1992). However, collecting population baseline data on
these markers is necessary before they can be useful for monitoring
and surveillance purposes. Longitudinal and cross-sectional
information on normal ranges and correlation with environmental
exposures and demographic characteristics are required. Reference
ranges are available for some biological markers. For example, blood
concentration data for a number of pesticides and metals were
collected in a representative sample of the US population in the
National Health and Nutrition Evaluation Survey (NHANES IV) and the
German Environmental Survey (Krause et al., 1992). The ranges may vary
in different exposed populations owing to differing residual levels in
the environment (Grandjean, 1986; Alessio, 1993). Data from specimen
banks are beginning to provide some exposure information on geographic
and demographic parameters (Kemper, 1993).
10.4 Advantages of biological markers for exposure assessment
Biological markers integrate over all sources of exposure, which
allows for efficient characterization of exposure to multiple sources
and evaluation of past exposures (US NRC, 1991a; Sim & McNeil, 1992).
When contaminants are found in many environmental media, biological
monitoring can be the most effective way to determine an individual's
total exposure. Biological markers may also indicate the presence of
additional exposures; for example, biological markers used in
occupational settings have been applied to determine if
non-occupational exposures to similar agents are occurring (Lauwerys,
1983). Some biological markers (e.g., PCB concentrations in breast
milk) represent cumulative exposure to environmental contaminants.
Markers which integrate over long periods of time can be used to
evaluate past exposure in a much more accurate manner than historical
record review and exposure reconstruction (DeRosa et al., 1993;
Sampson et al., 1994). Biological markers can also be the best way to
measure recent exposures, especially those where dermal contact is the
primary route of entry. Table 34 summarizes the advantages and
limitations of using biological markers in exposure assessment.
Table 34. Advantages and limitations of biological markers for environmenta
exposure assessment
Advantages Limitations
Demonstrate exposure has occurred source and route identification
Integration over all exposure routes kinetics and timing of exposure
Characterization of individual biological variability and confounding
exposure-doses
Inclusion of internal sources altered response as a result of
multiple exposure
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