Impacts of carbofuran on birds in Canada and the United State - Carbofuran and Wildlife Poisoning: Global Perspectives and Forensic Approaches - page 241

8.5 Evidence for secondary poisoning impacts with any
formulation type
Balcomb (1983) published the fi rst widely available report of a predator or scavenger dying after
eating a bird or mammal that had been poisoned by granular carbofuran. Until then, scientists
generally had not considered this hazard despite a few earlier indications that it was a problem. For
example, investigators had documented the deaths of an unidentifi ed hawk in the British Columbia
waterfowl kills (refer back to Section 8.2.2.2.3). Balcomb showed that the quantity of carbofuran
in the gastrointestinal tracts of songbirds killed by Furadan 10G (this was after in-furrow applica-
tion in maize) could be suffi cient to kill a larger-bodied predator or scavenger. Predators or scav-
engers that eat their prey whole or eat the viscera of their prey are at the greatest risk of consuming
unassimilated residues.
Mineau and colleagues (1999) inventoried documented kills of birds of prey from carbofuran that
occurred in the United States, Canada and the United Kingdom during 1985 to 1995. For the purpose
of their review, they defi ned secondary poisoning as the passing of residues from vertebrate to verte-
brate. This is a broader defi nition of secondary poisoning than that which was established from our
experience with persistent organochlorine pesticides. In that case, residues have resisted metabolism
and have been sequestered in fat deposits. In the case of organophosphorous and carbamate insecti-
cides, much of the potential for secondary poisoning lies in the ingestion of unassimilated residues
present in the gut of the prey. Despite restrictions, carbofuran was more frequently implicated in
secondary poisoning cases than any other cholinesterase-inhibiting insecticide. The likely route of
exposure was by scavengers eating gastrointestinal tract contents of songbirds or waterfowl.
Booth and colleagues (FMC 1983, described in Section 8.2.1.2) reported mortality of a north-
ern harrier and short-eared owl in their study of the granular formulation in maize. Littrell (1988)
reported a northern harrier and red-tailed hawk in association with the use of the 5G product in rice.
In one incident that involved the cultivation of winter wheat, it appeared that granules contaminating
an existing fox ( Vulpes sp.) carcass (the planting equipment likely ran over the carcass) subsequently
killed both a bald eagle and a red-tailed hawk.
California had a relatively steady occurance of secondary poisoning incidents from carbofuran in
birds of prey from the late 1980s to the early 1990s. Rice and grapes were the crops associated with
most of the incidents. Red-tailed hawks were the most commonly impacted species, accounting for
67% (14/21) of incidents. Most of the hawk crops analysed contained parts of passerine birds, or
more infrequently, waterfowl or rodents, confi rming secondary poisoning as the route of exposure
(CDFG 1985f; CDFG 1986f; CDFG 1990a; CDFG 1990e; CDFG 1990k; CDFG 1991c; CDFG
1991d, CDFG 1992a; CDFG 1992b; CDFG 1992c; CDFG 1993h).
The largest incidence of secondary poisoning occurred between 1989 and 1990 when investiga-
tors found about 15 or 16 bald eagles and four red-tailed hawks moribund or dead in the immediate
Richmond-Ladner area in the lower mainland of British Columbia (Mineau 1990; Elliott and Wilson
1993; Elliott, Langelier, Mineau et al. 1996). There have been several documented waterfowl kills
resulting from carbofuran use on root crops in this area (refer back to Section 8.2.2.2). Moribund
birds were typically lethargic, unable to stand, exhibited balance problems or lack of coordination,
had a fi xed or 'vacant' stare and constricted pupils, and a body temperature below normal (refer back
to Chapter 2). These signs are all consistent with acute poisoning with a cholinesterase-inhibiting
agent, and carbofuran was the principal insecticide in use in the root crops at the time. The birds had
full crops, a noticeable 'chemical' odour on the breath and in the crop contents, and an oily, reddish-
brown exudate in the mouth and crop. Balcomb (1983) reported that a red-shouldered hawk ( Buteo
lineatus ) secondarily poisoned by Furadan 10G salivated a 'brown fl uid'. All the hawks and eagles
were in good fl esh. Also, some cases were associated with the presence of waterfowl displaying
signs of toxicity.