Environmental Health Criteria 214

HUMAN EXPOSURE ASSESSMENT
limited. Of particular concern is uncharacterized biological
variability which may influence uptake, distribution, metabolism or
excretion of the contaminant of interest and, therefore, the internal
dose. Some authors consider that the influence of genetic variation is
limited in comparison to the impact of other susceptibility factors
(Perera & Weinstein, 1982). During validation studies, it is necessary
to gather information on potential confounding factors. Baseline data
on pre-exposure biological marker concentrations and demographic
variables should be obtained to assess inter-individual biological
variability more accurately.
Previous exposure and pathophysiological states can change the
biological response to current exposure. This is of particular concern
in cross-sectional investigations or in studies of individuals with
previous or long-term exposure. Previous or concurrent exposure to
agents that elicit similar responses to the contaminant of interest
may alter metabolic activity in response to exposure. These
alterations may lead to an increase or decrease in the rate of
metabolism or excretion, or a change in the type or amount of
metabolites formed, which thereby alters the internal dose and
potentially, the biologically effective dose. Interactions between the
exposure of interest and other environmental exposures, diet,
medication use, cigarette smoking and alcohol consumption may affect
the outcome of the exposure and the interpretation of the biological
monitoring results.
In some cases, exposure to chemicals can cause maladaptive
changes and the biological markers of exposure may represent
subclinical disease. For example, long-term exposure to metals at high
concentrations can result in kidney damage and thereby alter the
processing of metals in the kidney. This results in potentially low
excretion of metals in urine and subsequent underestimation of
exposure (Lauwerys, 1983). In some situations, clinical tests can be
conducted at the same time to address issues such as reduced kidney
function. Conversely, individuals with long-term exposure may
represent those individuals who are least susceptible to the agent's
effects; this may be problematic when using workers to validate
biological markers at high levels of exposure (Hauser et al., 1995).
10.5.3 Participant burden
Collection of biological media presents challenges different from
collection of environmental samples. At the minimum, it requires
active participation on the part of the study subject. In designing
studies, it is critical to recognize that collection of biological
samples can be invasive. Some routine medical procedures, such as
collection of a small vial of blood, may be more acceptable to
participants than more involved, yet non-invasive, sampling methods
such as collection of a 24-h urine specimen or wearing an air sampling
pump for a day. Other sampling strategies, such as fat biopsies or
collection of large volumes of blood, may be impractical for
environmental exposure assessments because of excessive participant
burden. Ethical considerations also include how participants should be
informed about their results.
10.5.4 Biosafety
Biological media can serve as vectors of infectious disease, such
as AIDS and hepatitis. Because of this hazard, special procedures must
be used when collecting, transporting, storing, analysing and
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