poisoning of raptors with organophosphorus and carbamate ...

20 M•NE^U ET AL. VOL. 33, NO. 1
(1998) used radiotelemetry and pesticide-use data
correlated with foot-wash residues and plasma ChE
to assess the relative contributions of a number of
different OP pesticides to the 'effective' exposure
in Red-tailed and Red-shouldered Hawks using the
orchards. Of the pesticides studied (ethyl parathion,
diazinon, methidathion and chlorpyrifos),
parathion contributed the most to the measured
level of inhibition in the birds. Parathion use in
breeding, migration or wintering area).
There are other risk factors of overarching importance,
namely the toxicity of ChE inhibitors
and the relative sensitivity of raptors to OP and CB
pesticides.
Toxicity to Birds of In-use Pesticides. Poisoning
incidents occur frequently because many ChEdnhibiting
pesticides are acutely toxic to birds. Also,
the importance of cholinergic systems is such that,
even if exposure does not cause immediate death,
many sublethal manifestations of exposure to ChE
inhibitors can lead to reduced survival in exposed
individuals (Grue et al. 1991). Based on their review
of poisoning cases, Grue et al. (1983) concluded
that a large proportion of incidents can be
explained by toxicity and extent of use. Inherent
in their conclusion is that exposure is inevitable,
or at least difficult to limit in many cases. In light
of this, we compared the use of ChE-inhibiting pesticides
in the U.S. with that in the U.K since there
dormant-oil sprays was canceled in December
1991. In more recent years (1993-94), a number
of incidents have been associated with exposure of
birds to the other three OP insecticides (Hosea
pers. comm.). Most of the birds did not appear to
die from toxicosis. For most, trauma such as electrocution,
entanglement or impact was diagnosed
as the proximate cause of death. Based on depressed
ChE levels as well as pesticide residues extracted
from feathers or foot washes, pesticides
were frequently ascribed a contributory role only.
appears to be a dramatic difference in the relative
proportion of labeled-use cases to the total number
of cases in these two jurisdictions (Table 12). Unfortunately,
a similar comparison could not be
made with Canada because there were no comprehensive
statistics on pesticide use.
We assumed that the 1994 pesticide data were
representative of the 1985-95 period summarized.
It should be noted that pesticides not currently
used on crops such as famphur and fenthion were
Nevertheless, we included some of these incidents. excluded. We found that the use of ChE inhibitors
A good analogy from a human perspective would
be traffic accidents and impaired driving: the exact
circumstances surrounding accidents are varied,
yet the root cause is impairment. Continuing the
analogy, the situation is made more complex by
(expressed as tons of a.i./ha of cropland) was almost
three times higher in the U.S. than in the
U.K. For the U.K., six compounds accounted for
>85% of the total tonnage of ChE inhibitors used
(Garthwaite et al. 1994). Of these, only aldicarb
the fact that motor vehicle accidents occur even (8.2% of ChE-inhibiting tonnage) has an HD5
without alcohol. The role that ingesting contaminated
prey may play in some of these incidents has
not been assessed. Although foot and feather washes
are routinely analyzed, crop contents are not.
(Hazardous Doses) value (the avian LD50 value calculated
to be at the 5% lower tail of the distribution
of all avian LD50 values with a 50% probability
for that compound)