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

ingredient/ha ranged from 17 to 181 ppm. Yet, well-tended turf is as uniform
and structurally simple a "crop" as one is likely to encounter in a hazard
evaluation.
The relation between the intended rate of application and the likely exposure
of wildlife species is, therefore, complex and difficult to predict accurately
even when the route of exposure is known. This is an especially serious
problem for acutely toxic products with low margins of safety.
Persistence of pesticides
Most nonorganochiorine pesticides are relatively short lived, at least in plant
and animal tissue. They are more likely to persist in abiotic components of the
environment, such as soil, aquatic sediments, or groundwater. The rapid
disappearance and lack of bioaccumulation characteristic of organophosphate
and carbamate insecticides made these classes an attractive alternative when
the persistence problems associated with organochiorine insecticides became
widely known.
A recent compilation of residue dissipation rates from plant surfaces (Willis
and McDowell 1987) cites average half-lives of 3.0 days and 2.4 days for
organophosphates and carbamates, respectively. However, there are sitespecific
examples of long environmental half-lives about which generalizations
must be made with caution. For example, the relatively lipophilic
organophosphate, fenitrothion, has been found to persist at low levels bound
to the waxy epicuticle of conifer needles (Sundaram 1987) and these residues
may persist from one spray season to the next.
A proper evaluation of the persistence of a particular pesticide requires exact
knowledge of the conditions under which it is to be used. For example, Getzin
(1973) reported that the persistence of carbofuran was 7- to 10-fold greater in
acidic soils (pH 4.3-6.8) than in alkaline soil (pH 7.9). The stability of carbofuran
granules under acidic conditions has been identified as a factor in
large kills of waterfowl in Canada. Carbofuran granules remain toxic to
waterfowl throughout the autumn and winter when fields are often flooded
and attractive to birds.
Examples of problem pesticides
or problem situations
Organochiorine insecticides
It is beyond the scope of this paper to review the evidence of ecological damage
resulting from the use of persistent organochiorines. The use of most of these
products has been cancelled or significantly curtailed in most developed
countries; DDT, aldrin, dieldrin, endrin, chiordane, heptachlor, toxaphene,
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