Environmental Engineering Reference
In-Depth Information
in agricultural and urban areas or wild lands. The majority of rodenticide-related expo-
sures involved long-acting ARs (Poppenga and Oehme 2010).
Historically, many natural (mineral and toxin) poisonous and nonselective substances
have been used for this purpose; fortunately most of them are now prohibited in many
countries and/or applications. However, prohibition does not mean that exposition (usu-
ally in criminal acts) cannot occur. This is the case of thallium sulfate, once widely used
as a rodenticide, for which poisoning cases are still seen (Volmer et al. 2006). But the
most striking case is that of strychnine, an extremely poisonous alkaloid obtained from
the seeds of the plant
Strychnos nux-vomica
. It is a fast-acting product, so it is unexpected
that living vertebrate animals may carry or accumulate residues of strychnine in their
bodies. Cases of domestic and wildlife poisonings are described frequently in European
Laboratories of Toxicology (Martínez-López et al. 2006; Wang et al. 2007; Hernández
and Margalida 2008; Martínez-Haro et al. 2008; Berny et al. 2010; Guitart et al. 2010b).
Interestingly, Martínez-López et al. (2006) were able to detect strychnine residues by GC/
MS in the carcass of a Bonelli's eagle (
Hieraaetus fasciatus
) found in the field, which had
died 20-45 days before.
14.6.1 Zinc Phosphide and Phosphine
Zinc phosphide (Zn
3
P
2
) acts through the release of phosphine gas (PH
3
) (Plumlee 2004). It
is a rodenticide considered relatively safe for nontarget animals, as secondary poisoning
of scavenger species is unlikely (Sterner and Mauldin 1995). However, direct ingestion
of zinc phosphide baits or the consumption of the digestive tracts of poisoned animals
poses a risk for many domestic and wildlife species (Mauldin et al. 1996; Drolet et al. 1996;
Poppenga et al. 2005). Aluminum phosphide (AlP) is used more as an insecticide for stored
cereal grains and can also generate phosphine gas (Proudfoot 2009).
14.6.2 Anticoagulant Rodenticides
ARs are vitamin K antagonists that prevent the synthesis of functionally active blood-
clotting factors II, VII, IX, and X, and therefore, kill rodents by predisposing them to fatal
hemorrhage (Murphy 2007). These compounds are, at present, some of the preferred meth-
ods of controlling rodent infestations worldwide.
Chemically, ARs are classified into two classes: 4-hydroxycoumarin derivatives (brodi-
facoum, bromadiolone, difenacoum, warfarin, and some others belong to this group),
and 1,3-indanedione derivatives (with chlorophacinone and diphacinone being the most
prominent examples) (Murphy 2007; Pelfrène 2010). However, from the clinical point of
view, both types of chemical classes produce similar basic symptomatology and require
comparable treatment, based on the use of vitamin K
1
as antidote (Plumlee 2004; Pelfrène
2010).
More practical and environmentally useful is the classification based on the toxicolog-
ical properties (Murphy 2007). Warfarin, the first AR introduced in the market shortly
after the end of World War II, and others such as chlorophacinone, coumatetralyl, or
diphacinone are called first-generation ARs or FGARs. They were so successful and thus
so extensively used in the following years that it led to the development of rodent resis-
tance to their effects (Pelz et al. 2005; Ishizuka et al. 2007), the first population of warfarin-
resistant brown rats (
Rattus norvegicus
) being discovered in a Scottish farm in 1958 (Boyle
1960). This prompted the introduction of new products in the 1970s and 1980s, such as
brodifacoum, bromadiolone, difenacoum, difethialone, or flocoumafen, now defined as
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