Report from the Sub-comittee on the environment and health

Relationship between
pesticides and cancer not
documented
Hormonal toxicity
Developmental toxicity
though <strong>the</strong> exposure to DDT was considerably greater (Krieger et al.
1994). A third major American study was unable to establish any
relationship between <strong>the</strong> blood content of organochlorine compounds and
<strong>the</strong> risk of breast cancer. However, <strong>the</strong> follow-up period was short, and
problems with confounder correction resulted in statistical weakness
(Hunter et al. 1997). Lastly, a recently published Danish study showed a
statistically significant dose-related correlation between <strong>the</strong> blood
content of dieldrin and <strong>the</strong> risk of breast cancer (Høyer et al. 1998). The
o<strong>the</strong>r relationships between risk of cancer and blood content of betahexachlorocyclohexane,
DDT and PCB were not statistically significant.
As <strong>the</strong> results of <strong>the</strong> above-mentioned epidemiological studies indicate,
<strong>the</strong>re are data that show that exposure to organochlorine compounds can
be connected with an increased risk of breast cancer, although without
sufficient, clear grounds to deduce <strong>the</strong> significance for <strong>the</strong> general
population. A scientific panel appointed by <strong>the</strong> National Cancer Institute
of Canada came to a similar conclusion in a review of studies of mainly
occupational exposure and risk of cancer (Ritter 1997). The panel
concluded that <strong>the</strong>re was insufficient scientific evidence that pesticides
contributed significantly to total cancer mortality.
It is well documented that a number of persistent chemicals can affect <strong>the</strong>
endocrine system by affecting <strong>the</strong> hormones in <strong>the</strong> body that are
responsible for maintaining homeostasis and regulating <strong>the</strong>
developmental processes (Gray, Ostby 1998; Kavlock et al. 1996; Tilson,
Kavlock 1997; Porter et al. 1993). Endocrine disruptors have been
broadly defined as exogenous substances that disrupt production, release,
transport, metabolism, sorption, action or elimination of <strong>the</strong> body’s
natural hormones (Kavlock et al. 1996; Tilson, Kavlock 1997). Some of
<strong>the</strong>se substances can induce <strong>the</strong> cytochromal P450 systems in <strong>the</strong> liver.
This can affect <strong>the</strong> metabolism of steroid hormones (including sex
hormones) and thyroid hormones, whereby secondary effects can be
induced in hormone-dependent organs.
However, too little is known about endocrine disruptors, and <strong>the</strong>
designation has in some cases been used where <strong>the</strong> biological
relationship is far <strong>from</strong> clarified. The suspicion about <strong>the</strong> very persistent
substances DDT, DDE and PCB is warranted in view of <strong>the</strong> effects <strong>the</strong>se
substances have on wild animals (e.g. seals, otters and alligators). For <strong>the</strong>
endocrine disruptors, too, <strong>the</strong>re are problems in extrapolating <strong>from</strong>
studies of test animals with relatively high exposures to <strong>the</strong> relatively low
exposures that occur in <strong>the</strong> environment and <strong>the</strong> very small amounts that
humans are exposed to. These endocrine disruptions cannot be
demonstrated in present test systems, but work is going on under OECD
to improve <strong>the</strong> test programme for new chemicals, so that animal tests
are better able to document such effects.
Developmental effects are effects that occur in <strong>the</strong> individual during
development as a result of exposure prior to conception, in <strong>the</strong> foetal
existence or postnatally until <strong>the</strong> individual is fully developed. The result
of <strong>the</strong> developmental disturbances can be death, structural abnormalities,
inhibited growth or functional disturbances. However, it is often difficult
to determine whe<strong>the</strong>r miscarriage or stillbirth is due to reproductive or
developmental effects.
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