Pesticide Residues in Birds and Mammals - Pesticides: Evaluation of Environmental Pollution - page 441

Recently, Watanabe et al. (2010) explained the apparent contradiction of the reported
high resistance (expressed as the LD 50 ) of some bird species (e.g., chickens, ring-necked
pheasants ( Phasianus colchicus ), and northern bobwhites ( Colinus virginianus )) to warfarin
when compared with brown rats and the fact that many observed cases of death episodes
in the wild occur in raptors. They found that there is a wide interspecies difference among
birds in xenobiotic metabolism and sensitivity to ARs based on vitamin K 2,3-epoxide
reductase kinetics and inhibition and warfarin metabolic activity.
Table 14.5 shows the levels of FGAR and SGAR residues determined in birds from differ-
ent periods of time, zones, and sources. Animals studied were usually found dead or mori-
bund in the wild, or captured, and, in a few cases, a veterinary diagnosis of anticoagulant
poisoning was eventually made.
In situations in which ARs are commonly used against different rodent pests, exposure
of raptors is usually more common than of other groups of birds. For example, in France,
a study carried out in the wetlands and marshes of Loire Atlantique's department where
ARs are employed to combat the large and semiaquatic rodent coypus ( Myocastor coypus ),
it was determined that from 30 raptors (11 common buzzards, 10 barn owls, 5 tawny owls,
and 4 European kestrels) and 29 waterbirds (15 mallards, 13 Eurasian coots ( Fulica atra ), and
1 common moorhen ( Gallinula chloropus )) found dead or moribund in the wild, 22 raptors
(73%) and only 4 waterfowl (14%) presented levels ≥0.008 μg/g WW of residues (Lambert
et al. 2007). In spite of this, even when rodent control campaigns using heavy doses of ARs
are performed in the field, an increase in the exposure of raptors is not expected to occur
if managed correctly, the results of nontarget exposures depending less on the amount of
bait used rather than on the way it is used (Shore et al. 2006a).
The Strigiformes is an order comprising some 200 species of birds of prey, and due to their
diet and feeding habits, some of their representatives have been used in many occasions
to monitor the exposure to the residues of ARs. Newton et al. (1990) detected brodifacoum
and difenacoum at medium-low concentrations (<0.52 and <0.11 μg/g WW, respectively)
in the livers of 15 (10.3%) out of 145 barn owls found dead in the United Kingdom and
submitted to their laboratory for a survey period of 7 years, between 1983 and 1989. Only
one bird was diagnosed postmortem as poisoned with brodifacoum (0.43 μg/g), while in
the rest of 144 animals, the cause of death was ascribed to trauma, starvation, or shot. In
fact, barn owls have been monitored in the United Kingdom since 1983 by the Predatory
Bird Monitoring Scheme (PBMS) (Newton et al. 1990; Walker et al. 2008a). The PBMS in
Britain covers a long-term monitoring program that examines the levels of pesticide and
other pollutant residues in selected avian wildlife species (Walker et al. 2008a). Analytical
methods have varied with the time passed, and currently the number of ARs determined
is higher and the limit of quantification (LoQ) is lower than in previous years. But, when
data were normalized for the four SGARs, brodifacoum, bromadiolone, difenacoum, and
flocoumafen and a common LoQ of 0.01 μg/g WW was applied to each, the percentage of
positive individuals for any SGAR plotted against time shows that exposure had increased
over time, from an almost undetectable proportion in 1983 to a maximum of 53% in 2003,
decreasing again to 30%-35% during the period from 2004 to 2006 (Walker et al. 2010).
The increase during this long period was driven by an augment of exposure mainly due
to bromadiolone and difenacoum, while brodifacoum and flocoumafen exposures were
more erratic and showed no clear trend. However, it should be stressed that when all the
AR residues determined were considered and more sensitive methods were used with
lower LoQs, the true level of exposure of barn owls in 2006 (n = 62) was 62.9% (6.4% to any
FGAR, 62.9% to any SGAR), with a total of 25.8% of the examined individuals exposed to
multiple rodenticides (Walker et al. 2010).