Environmental Engineering Reference
In-Depth Information
On the other hand, the indirect effects are subtler, because the pesticides exert their
effects without the necessity of exposure of the affected individuals (lethal effects can
occur, but not related to direct pesticide poisoning), and take place when the use of certain
chemicals has effects on plants or prey and thus on the diet of their natural consumers
(Freemark and Boutin 1995; Mañosa et al. 2001; Sullivan and Sullivan 2003; Boatman et al.
2004; Morris et al. 2005).
14.1.1.1 Indirect Effects
It is well known that the density and reproduction of specialist carnivorous species are
intimately linked to the population dynamics of their prey, affecting productivity or sur-
vival. Indirect effects have been demonstrated, for example, in the treatments with roden-
ticides in England (Brakes and Smith 2005), intended to eradicate rats (
Rattus
spp.), which
also affected the populations of nontarget small mammals such as European wood mice
(
Apodemus sylvaticus
), bank voles (
Clethrionomys glareolus
), and field voles (
Microtus agres-
tis
). These animals are important in the diet of many species such as barn owls (
Tyto alba
),
long-eared owls (
Asio otus
), short-eared owls (
Asio flammeus),
), tawny owls (
Strix aluco
), hen
harriers (
Circus cyaneus
), European kestrels (
Falco tinnunculus
), stouts (
Mustela erminea
), and
weasels (
Mustela nivalis
), species that were in turn indirectly affected by the use of the pes-
ticides through the reduction of available food.
A more recent example of indirect effects was reported in France (Poulin et al. 2010) and
was related to the use of the microbial insecticide
Bacillus thuringiensis
var.
israelensis
(Bti),
considered the most selective and least toxic pesticide currently available worldwide to
control mosquitoes. House martins (
Delichon urbicum
) in Bti-treated zones were adversely
affected in their clutch size (2.3 vs. 3.2 chicks produced per nest) and in the number of
young that actually fledged, both smaller than in the control zones. The explanation was
related to the diet: small prey (<2.5 mm), such as flying ants, were consumed in greater
proportion in treated areas by house martins, while large prey (<7.5 mm), such as midges,
mosquitoes, dragonflies, and spiders, dominated in the control ones.
14.1.1.2 Direct Effects
Lethal poisoning in nontarget birds and mammals due to significant exposures to pesti-
cides are not uncommon (Fleischli et al. 2004; Kwon et al. 2004; Wang et al. 2007; Berny et al.
2010; Guitart et al. 2010a,b). However, most of the reported mortalities are due to intentional
poisonings, which are frequently a result of acute exposure to a restricted number of well-
known and, sometimes, easily available poisonous pesticides, mainly organophosphorus
(OP) and carbamate (CB) insecticides, strychnine, and anticoagulant rodenticides (ARs)
(de Snoo et al. 1999; Berny 2007; Wang et al. 2007; Muzinic 2007; Hernández and Margalida
2008; Martínez-Haro et al. 2008). When pesticides are used in a deliberate or illegal attempt
to poison animals, secondary poisonings, whereby a predator or scavenger consumes the
flesh of primarily exposed species, can easily occur because of the high doses of pesticides
usually employed (Wobeser et al. 2004; Martínez-Haro et al. 2008).
Accidental lethal poisonings are a less common observable event if pesticides are used
in accordance with the manufacturer instructions and governmental regulations, and
most episodes are related to the use of treated seed, bait, or wood preservatives and the
spraying of grasslands (Berny et al. 1997; de Snoo et al. 1999; Fleischli et al. 2004; Pain
et al. 2004). However, when pesticides are misused or when registered products are not
applied to the approved target and at the proper application rate indicated on the product
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