Report from the Sub-comittee on the environment and health

Syn<strong>the</strong>tic pesticides have
changed molecular
properties
Conclusion concerning
coformulants
Conclusion concerning
natural substances
compared with pesticides
142
insects and has a low potential for producing toxicity in humans. If
injected directly into <strong>the</strong> blood, <strong>the</strong> substance has a highly toxic effect on
mammals. The normally low toxicity is due to slow absorption through
<strong>the</strong> skin or in <strong>the</strong> gastrointestinal tract in mammals. Pyrethrins are very
unstable and break down almost instantaneously in sunlight. The effect
of this mixture is increased in <strong>the</strong> spray product by adding a synergist,
piperonylbutoxide. This substance is only slightly toxic in itself, but
impedes <strong>the</strong> enzyme systems that break pyrethrins down, enabling <strong>the</strong>m
to act for a longer period of time in insects.
One of <strong>the</strong> main groups of modern syn<strong>the</strong>tic pesticides is <strong>the</strong> so-called
pyrethroids, which contain <strong>the</strong> same chemical, active group as
pyrethrum, but in which <strong>the</strong> molecule has been made more stable by use
of aromatic structures, halogenation or reaction with cyanide. This
considerably increases <strong>the</strong> toxic effect on insects – 1000 times, for
instance, for deltamethrin compared with naturally occurring pyrethrins.
The increased stability of <strong>the</strong> molecules at <strong>the</strong> same time gives a risk of
dispersal in <strong>the</strong> atmosphere and to surface water and ground water. The
pyrethroid example illustrates <strong>the</strong> fact that syn<strong>the</strong>tic pesticides usually
contain chemical structures that are seldom found in nature. The physical
and chemical properties of <strong>the</strong> molecule, and thus its toxicity, are <strong>the</strong>reby
changed. This effect depends particularly on changes in <strong>the</strong> direction of
lower degradability, greater persistence, changed solubility and increased
penetration in membranes.
7.4 The sub-committee’s conclusions and recommendations
Coformulants, which are added to pesticide formulations, are not covered
by an authorisation scheme of <strong>the</strong> same scope as for active pesticide
chemicals. Coformulants are a very broad and extensive group of
substances, <strong>the</strong> composition of which can vary within <strong>the</strong> individual
product or type of product. The coformulants are normally less harmful
to <strong>the</strong> environment and health than <strong>the</strong> active ingredient, but often occur
in large concentrations, and substances that are harmful to <strong>the</strong>
environment and/or health can be used – e.g. substances that produce
acute or chronic toxicity. Some of <strong>the</strong> substances can thus be more
harmful to <strong>the</strong> environment or health than <strong>the</strong> active ingredient to which
<strong>the</strong>y are added. A few of <strong>the</strong> substances feature in DEPA’s list of
undesirable substances.
All plants contain varying concentrations of toxic substances to protect
<strong>the</strong>mselves against attack by viruses, microorganisms and herbivores.
Most herbivores eat only specific food plants. Humans thus eat only a
limited number of plant species – less than 100 – that have been selected
and used for many generations as components in human food. Therefore,
even though crop plants contain substances that have a toxic effect on
certain o<strong>the</strong>r groups of organisms, in most cases <strong>the</strong>y produce very little
toxicity in humans. Unlike pesticides, <strong>the</strong> toxic natural substances are
inside <strong>the</strong> plant and only exhibit <strong>the</strong>ir toxic effect when o<strong>the</strong>r organisms
approach it, touch it or eat it. Pesticides, on <strong>the</strong> o<strong>the</strong>r hand, are normally
spread over larger areas of land, with <strong>the</strong> aim of knocking out pests –
often with around 90% effect in <strong>the</strong> entire area. All organisms in <strong>the</strong> area
in question are thus exposed to and hit by <strong>the</strong> pesticide or later eat plant