Carbofuran: Toxicity, diagnosing poisoning and rehabilitation of poisoned birds - Carbofuran and Wildlife Poisoning: Global Perspectives and Forensic Approaches - page 32

were reported. These had between 1 and 5.4 granule equivalents in them. One red-shouldered hawk
( Buteo lineatus ), collected moribund and sacrifi ced, had 1.5 granule equivalents in its stomach con-
tents and the same amount in its digestive tract tissue (from the ingestion of contaminated prey). Ten
common grackles nesting near the treated fi elds were not exhibiting any toxicosis, but were none-
theless collected and analysed. Nine had measurable carbofuran residue levels. The mean for all 10
birds was 0.87 ppm. All carcass collections were made 72 hours post carbofuran fi eld treatment, but
exposure could have occurred at any point up to the time of collection given that granules can persist
for some time on the soil surface.
As noted, the spontaneous postmortem reactivation of cholinesterase enzymes is known to take
place following carbofuran exposure (as is the case for most carbamates). For example, Ludke, Hill
and Dieter (1975) fed three week old Japanese quails a diet contaminated with 600 ppm carbofuran
for 4 hours then allowed the carcasses to age before carrying out analysis. Reactivation, though not
complete, but was certainly well underway after 24 hours at 35°C. Reactivation was slight after two
days at room temperature. Reactivation of brain samples was noted but was not complete in a study
by Bunyan and Jennings (1976), who were able to diagnose brain ChE inhibition despite 5 days aging
at room temperature. They warned that the very large doses used on the birds may have been suffi -
cient to mask/prevent spontaneous reactivation. The defi nitive study, however, was that of Hill (1989)
who showed a clear temperature-dependant reactivation of samples from birds killed by carbofuran.
Hunt, Hooper and Littrell (1995) reported on the reactivation of ChE in brain samples from several
heron species killed by aquatic runoff containing carbofuran in a vineyard. Reactivation was slower
than expected, suggesting that there may be interspecies differences in the speed of reactivation,
or that any unbound insecticide in the samples could interfere with reactivation. Elliott, Langelier,
Mineau et al. (1996) and Mineau and Tucker (2002) also described one case where spontaneous
recovery was only possible after residual insecticide had been removed from the sample with a gel
permeation column. Hunt and Hooper (1993) have provided guidance on various aspects of sample
reactivation, including variations in relation to temperature, dilution, solvents used, and regarding the
solid phase extraction of unbound pesticides from samples. Other examples/guidance regarding
reactivation assays can be found in Smith, Thomas and Hulse (1995).
Analytical data showing carbofuran is present in a carcass is usually a fi nding of signifi cance.
However, we should caution that increased analytical sensitivity now means that modern equipment
can detect very low/trace levels, and that such levels may be of questionable physiological signifi -
cance (particularly in large birds like goose or grouse species that may inhabit farmland). Carbofuran
is readily absorbed from the avian digestive system (Hicks 1970), is then readily metabolised, and can
easily degrade within samples. In a study by FMC (the primary manufacturer of carbofuran), investi-
gators were unable to detect the insecticide in many of the bird carcasses they had spiked (i.e., delib-
erately treated the carcasses with carbofuran) in the fi eld (see Chapter 8, Section 8.4.1.3.) although
this may have been related to a fault within the techniques used, either low levels of spiking or
inadequate analytical methods. Mineau and Tucker (2002) have reviewed the carbofuran levels found
in the gastrointestinal tracts of birds determined to have been poisoned by carbofuran. They found that
values ranged from < 0.1 ppm to > 1 000 ppm, i.e., by four orders of magnitude. Values at the upper
end of this range (e.g., > 100 ppm) were typically associated with baiting and cases of criminal
poisoning. However, there was signifi cant overlap between cases of abusive poisoning and cases of
poisoning caused by registered use, with the majority of data falling between 1 and 100 ppm, for both
types of incident. Authors of Chapter 5 (see Section 5.5.3) describe how inexperienced poisoners use
an enormous amount of poison while 'professional poisoners' use very small amounts which makes
it more diffi cult to detect.
A promising forensic technique may involve the extraction of bound residues from bird feet.
Vyas and colleagues (2005) placed eastern screech-owls ( Megascops asio ) on a piece of deer car-
cass contaminated with fl owable carbofuran for 40 minutes, to mimic a malicious baiting situation.
They euthanised the owls, and placed their feet outdoors at temperatures ranging from 13 to 30°C