Impact of - IDL-BNC @ IDRC - International Development Research ...

The pyrethroid, cypermethrin, is moderately hazardous (class II) orally and
slightly hazardous (class III) when absorbed through the skin. NOAELs in the
90-day and chronic feeding studies are 10 times those of dichiorvos and 100
times higher than those of dieldrin. Metabolism and excretion are rapid and
other toxicity parameters are also favourable. The lower toxicity of pyrethroids,
combined with their slow skin penetration make them safer to use.
Skin sensations (tingling) that occur with overexposure usually disappear
within a few hours and leave no aftereffects. These sensations act as a warning
signal that exposure should be better controlled.
Reported cases of occupational systemic poisoning with pyrethroids are rare.
However, He et al. (1989) reported 229 cases in China, 2 of which were fatal.
The explanation was a failure to observe basic principles of industrial hygiene
(He et al. 1988, 1989). With respect to health and safety, however, the development
and use of the pyrethroids was an improvement over the more toxic
organophosphates.
Flocoumafen, a representative of the latest generation of anticoagulants, was
included in this overview to illustrate that extreme toxicity according to the
WHO classification, does not necessarily mean a high risk to human health.
Although flocoumafen is classified as extremely hazardous (class IA), it is also
an extremely efficient rodenticide. The oral and dermal LD50 values of 0.25 and
0.54 mg/kg, respectively, and a 90-day NOAEL apply to the pure substance,
but the formulation used to poison bait is almost nontoxic because it contains
only 50 ppm' (w/w) of the active ingredient. In addition, during product
development, a deliberate effort was made to make poisoned bait unattractive
to nontarget species by incorporating it into wax blocks with a deterrent colour
(blue) and a bitter taste. These measures have rendered a potentially hazardous
product safe for practical use. In the unlikely event of an intoxication, a
specific antidote (vitamin K) is available. No cases of human intoxication have
been reported.
Conclusion
Pesticides must meet many requirements, the most important of which is
efficacy. Therefore, selection always begins with efficacy testing. If results are
promising, additional work will be carried out to test for human and environmental
safety. Commercial and technical requirements must also be met.
Progress in increasing specificity and improving efficacy has made possible
dramatically lower application rates, resulting in a major reduction in exposure
of people applying the substances. In a number of cases, a reduction in
intrinsic toxicity for mammals has also been achieved.
Guided by better understanding of intrinsic toxicity and data on personal
exposure during application, product development and product stewardship
can contribute to safety through improved formulations and packaging and
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