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of the risk is a quantitative issue; lifetime risks of cancer of 102 and 1O are
entirely different and would produce markedly diverging consequences in
terms of risk management. Furthermore, high-low dose extrapolation with
mathematical models has very weak scientific support and tends to be an
administrative procedure rather than a real scientific evaluation of the risk.
Discussion highlighted the importance of data on personal exposure doses. In
terms of information, an epidemiological study in a small cohort with accurate
personal-exposure data may be equal or even better than one in a large cohort
with poorly defined personal exposures.
Currently, health-risk assessment of human exposure to pesticides is mainly
based on data from experiments on animals. Little information is available
about effects on humans because of the lack of "strong" data from epidemiological
studies. This problem may be overcome by applying a more scientific
approach in health-risk assessment. Knowledge of the pharmacokinetics and
pharmacodynamics of a compound in different species must be increased by
carrying out studies on the mechanism of action.
To obtain "good" human data, investigators should critically review the
protocol for future epidemiological studies and address the question of
whether the effort required in such a study is proportioial to the possible
outcome. Specific questions should be addressed, such as the possibility of
accurate exposure measurements, the selection of a suitable control group in
case-control studies, and the feasibility of collecting accurate data on health
status of exposed and unexposed people.
Cohort studies of factory workers who manufacture pesticides can minimize
these problems. In these studies, controls can be selected among unexposed
workers in the same factory or nearby factories where workers are exposed to
different chemicals or processes. Employment records can be used to obtain
dates of employment and job titles and, thereby, identify those who had the
opportunity to be exposed and the duration of exposure. If subgroups of
workers are exposed to only a few pesticides or chemicals used in production,
then it is possible to relate excess incidence or mortality to a particular
exposure. Such studies often suffer from having a very small sample size;
evaluation of workers in more than one factory and in more than one country
where the same pesticides are produced may be necessary.
In choosing a reference group, using two similar industrial populations for
comparison eliminates the healthy-worker effect, which may appear when
using the whole general population. One should, in such cases, select a second
industry with workers of similar social and economic backgrounds so that
diet, physical demands, and other life-style factors are likely to be similar.
One way to handle the comparison problem is the selection of the unexposed
or lowest exposed group within the cohort as an internal reference. When this
is done, care should be taken to assure similarities in duration of follow-up
and in the size of the groups. In case-control studies, controls may come either
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