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to demonstrate the causal relation between herbicide use and the decline in
populations of Partridge (Perdix perdix and Alectoris rufa). Much of the research
into the long-term ecological effects of modern (i.e., nonorganochiorine)
pesticides is in its infancy. For this reason, much of the following account deals
only with the direct effect of pesticide use on wildlife.
Theoretical consideration of the hazards
posed by pesticides
In the absence of comprehensive field-testing of a pesticide submitted for
registration in Canada or other developed countries, regulations require that
the potential environmental hazard be estimated on the basis of toxicity to a
few test species and on the projected use of the product. This hazard assessment
often follows a "quotient" method, whereby levels that are toxic or cause
mortality in test species are compared to predicted levels of exposure. In
theory, safety factors are introduced into this calculation to allow for errors in
estimation or extrapolation. In practice, the level of uncertainty isso high that
most of the acutely toxic pesticides, such as organophosphates and carbamates,
cannot adequately be assessed without field-testing.
Because of the importance of the pesticide market in the USA and because US
registration is highly desirable to pesticide manufacturers, environmental
toxicology data required by the US Environmental Protection Agency (EPA)
are usually available for most of the pesticides registered worldwide (Table 1).
Canada currently accepts all environmental toxicology data generated to US
Table 1. Environmental toxicology information, at the tier I and 2 levels,
required for most pesticides used in the field.
Vertebrate tests
Avian single-dose oral LDa
Avian dietary LCso
Wild-mammal toxicity test (seldom available, data on laboratory rodents used
instead)
Acute toxicity test for freshwater fish
Avian reproduction test
Fish early life-stage test
Invertebrate tests
Acute toxicity test for freshwater invertebrates
Honey bee: contact LD50 and toxicity of foliage residues
Aquatic invertebrate life-cycle test
Note: Supplementary tests on estuarine and marine fish and invertebrates are also requested
where relevant.
a LDso = lethal dose to 50% of animals tested; LC5O = lethal concentration to 50% of organisms
tested.
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