Report from the Sub-comittee on the environment and health

O<strong>the</strong>r sources of error
No conclusive evidence
Reproductive toxicity
conditions of life cover a very large number of factors and too little is
known about <strong>the</strong>ir effect on <strong>the</strong> development of disease.
Lack of big differences in exposure in <strong>the</strong> population group studied can
be a problem in studies of <strong>the</strong> effect of pesticides on public health. The
sources of error mentioned above are just a few of <strong>the</strong> inherent sources of
error in epidemiological studies. The uncertainty concerning, for
example, intake of pesticides is a particular problem when <strong>the</strong>re is only a
small variation in intake in <strong>the</strong> population group studied. While <strong>the</strong> true
difference in risk of, say, cancer between a lower and upper level of a
narrow intake interval is probably small, <strong>the</strong> observed difference
decreases with increasing uncertainty of <strong>the</strong> analytical measurements. A
negative result, i.e. a lack of relationship between exposure to a pesticide
and <strong>the</strong> risk of disease can <strong>the</strong>refore not be taken to mean that such a
relationship does not exist.
For a more detailed discussion of confounding and o<strong>the</strong>r sources of error
in epidemiological intake/exposure studies, see Tarasuk, Brooker 1997.
It cannot be proven on <strong>the</strong> basis of epidemiological studies that
pesticides, in <strong>the</strong> quantities to which <strong>the</strong> general population is exposed,
for example, via diet, are harmful to health. Conversely, one can never
completely prove scientifically that a pesticide cannot cause a health risk.
One can, however, show, with greater or lesser (un)certainty, <strong>the</strong>
probability or lack of probability of a health risk. This applies to all
scientific work, including tests carried out on animals.
6.2.6 Long-term effects of low-dose exposure
Low-dose exposure implies lengthy, continued or occasional exposure to
low levels of pesticides. With this form of exposure <strong>the</strong> body slowly
accumulates a quantity of one or more pesticides that is sufficient to
produce undesirable effects in <strong>the</strong> body. Unlike <strong>the</strong> health effects of
occupational exposure to pesticides (see section 6.1), <strong>the</strong>re are very few
epidemiological studies of <strong>the</strong> relationship between exposure of <strong>the</strong>
general population and <strong>the</strong> risk of developing a disease. In <strong>the</strong> following,
we sum up <strong>the</strong> findings <strong>from</strong> existing studies of <strong>the</strong> effect of pesticides
on reproduction, <strong>the</strong> hormonal system, cancer, <strong>the</strong> nervous system and
<strong>the</strong> immune system. For fur<strong>the</strong>r amplification of <strong>the</strong> existing knowledge,
readers are referred to Skadhauge (1998).
Toxic effects on reproduction can take <strong>the</strong> form of difficulty in
conceiving (reduced fertility or unrecognised early miscarriage),
infertility, miscarriage and stillbirth (Smith et al. 1997). In women, <strong>the</strong>
effects can also manifest <strong>the</strong>mselves in <strong>the</strong> form of paramenia (as a
consequence of changes in <strong>the</strong> neuro-endocrine function in <strong>the</strong>
hypothalamus, <strong>the</strong> pituitary gland and <strong>the</strong> ovaries) and, in men, in <strong>the</strong>
form of a low sperm count or changes in <strong>the</strong> mobility or appearance of
<strong>the</strong> sperm.
In animal tests, several pesticides have shown toxic effects on
reproduction (Traina et al. 1994). Particular attention has been paid to
pesticides with hormone-like() effects, but, in animal tests, a number of
o<strong>the</strong>r chemical substances have proved able to affect <strong>the</strong> reproductive
system, resulting in, for example, reduced quality of semen and
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