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Development of safe chemical pesticides
W.F. Tordoir
Occupational Health and Toxicology, Health, Safety and Environment
Division, Shell International Petroleum,
The Hague, Netherlands
Pesticides must meet many requirements, of which efficacy is fundamental.
Product selection, therefore, always begins with efficacy testing; if
these results are promising, additional work is carried out to check for
human and environmental safety. However, commercial and technical
requirements must also be met. Progress has been made in both increasing
the selectivity (i.e., restricting the pesticidal activity to target species) and
in improving efficacy. This has made dramatically lower application rates
possible. In a number of cases, a reduction in intrinsic toxicity for
mammals has also been achieved. Guided by a better understanding of
intrinsic toxicity and good data on personal exposure during application,
product development and product stewardship can contribute to safety
through improved formulations, packaging, and advice on handling and
personal protection. A comparison of three insecticides as representatives
of organochiorines, organophosphates, and pyrethroids shows that, with
the development of the pyrethroids, a major step forward has been made
in the creation of safe pesticides. Similarly, the example of a highly toxic
rodenticide demonstrates that a high efficacy and sophisticated product
development can compensate for high toxicity.
It is only logical that in the history of the development of chemical pesticides,
nearly all attention was focused initially on the ability of a substance to kill
pests; concern for safety was secondary and followed somewhat later. The
drive to develop safe pesticides is reflected in the introduction of pesticide
registration and the increasingly stringent requirements to meet registration
criteria. In 1950, only acute toxicity tests and a 30- to 90-day feeding study
using rats were required for registration. By 1960, a 2-year study of effects on
rats and a 1-year study using dogs were necessary. By 1970, most current
requirements were in place (Table 1). The need for registration, combined with
requirements for toxicity testing and restrictions for marketing certain pesticides,
have, in turn, had a positive effect on the development of safe pesticides.
("Safe" is used here in relation to effects on human health.)
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