Pesticide Residues in Birds and Mammals - Pesticides: Evaluation of Environmental Pollution - page 434

second-generation ARs, or SGARs (and sometimes described also as “superwarfarins” or
as long-acting anticoagulant rodenticides (LAARs)). The pharmacological target molecule,
vitamin K 2,3-epoxide reductase, and the mode of action of SGARs are the same as those
of the FGAR type (Pelfrène 2010; Watanabe et al. 2010).
However, there are some important differences between the two groups. FGARs are
characterized by moderate toxicity in terms of LD 50 (see Table 14.1 ) and often need continu-
ous exposure to the bait to be effective in rodent control. SGARs are much more acutely
toxic, generally providing a lethal dose after a single feeding, and tend to have longer
half-lives and thus a considerably higher persistence in animal tissues. For example,
Vandenbroucke et al. (2008) determined the comparative pharmacokinetics in mice ( Mus
musculus ) of eight freely available ARs in the Belgian market after a single oral dose, and
the shortest elimination half-lives in the plasma were found for the FGARs coumatetralyl
(0.52 days), chlorophacinone (11.7 days), and warfarin (14.9 days), while the longest were
for the SGARs brodifacoum (91.7 days), difethialone (38.9 days), and bromadiolone (33.3
days). Moreover, due to the great affinity to the binding sites in the liver, the elimination
half-lives in this organ were found to range from 15.8 days for coumatetralyl to 307.4 days
for brodifacoum.
Owing to its extensive use, poisoning in domestic and farm animals or wild birds and
mammals may occur in cases of direct intentional or accidental ingestion of the poisoned
baits (Stone et al. 1999; Mineau and Tucker 2002; Berny et al. 2005, 2010; Guitart et al. 2010b).
After an aerial baiting operation with brodifacoum to eradicate rats and mice and reduce
rabbit numbers on Motuihe Island, New Zealand, in groups of pukekos ( Porphyrio porphy-
rio ) and paradise shelducks ( Tadorna variegata ) that were being monitored, mortalities of
48/98 (49%) and 31/52 (60%) were observed, respectively (Dowding et al. 1999). A recent
case of mass poisoning occurred in Spain in 2007 when an outbreak of common voles
( Microtus arvalis ) causing potentially severe crop damage was inappropriately treated
with large-scale application of wheat grain treated with 0.005% chlorophacinone in the
open field, causing the death of dozens of individuals of domestic pigeons ( Columba livia ),
a mostly granivorous species in the wild (Sarabia et al. 2008; Olea et al. 2009). The poi-
soning of game animals such as pigeons or white-tailed deers, which can potentially be
exposed to high doses of ARs due to the direct ingestion of poisoned baits, has raised con-
cerns regarding the potential health effects if these animals are hunted and consumed by
humans (Stone et al. 1999; Olea et al. 2009).
On the other hand, the delayed action of such compounds, with mortality in rodents
occurring days or even weeks after initial bait consumption, together with the high tox-
icity and long elimination half-lives especially observed with the SGARs, has resulted
in secondary exposure and even lethal poisoning of various nontarget animals, mainly
affecting the populations of birds of prey and carnivorous mammals worldwide who
feed on poisoned rodents (Newton et al. 1990; Berny et al. 1997; Howald et al. 1999; Shore
et al. 2003; Murray and Tseng 2008; Dowding et al. 2010). However, any animal, includ-
ing an invertebrate, which has consumed the rodenticide bait, could potentially serve
as a source of secondary exposure for a predator or a scavenger (Eason and Spurr 1995;
Howald et al. 1999; Thorsen et al. 2000; Spurr et al. 2005; Hoare and Hare 2006; Dowding
et al. 2010).
Massive mortality has been barely described in the literature after secondary poisoning.
For example, 28 animals, principally red foxes and buzzards ( Buteo buteo ), were recovered
from a single area in France, near the Swiss border, where bromadiolone was applied to
carrot baits at a dose of 100 mg/kg for the control of European water voles ( Arvicola ter-
restris ) (Berny et al. 1997). A similar episode was reported by Kupper et al. (2006), when