Rodenticides: the good, the bad, and the ugly

Shore, R.F.. 2017 Rodenticides: the good, the bad, and the ugly. In: DellaSala, Dominick A.; Goldstein, Michael I., (eds.) Encyclopedia of the Anthropocene. Vol. 5, Contaminants. Oxford, Elsevier, 155-160.

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Rodents are controlled because of the human health and economic threats they pose. Anticoagulant rodenticides (ARs) are the most widely used control agent and work by interrupting the vitamin K cycle, ultimately impairing blood clotting. Various “first-generation anticoagulant rodenticides” (FGARs) were developed in the 1950s and 1960s but, following the development of resistance in rats and mice, have been superseded in many countries by second-generation anticoagulant rodenticides (SGARs), to which there is currently only limited resistance. Collectively, SGARs are the most widely used chemicals for rodent control throughout the world, although FGAR use still remains. AR use is regulated in many countries, not least because it poses an environmental risk. This is because ARs are toxic to all vertebrates, including nontargets—species not subject to control campaigns. Exposure occurs typically as a result of ingestion, consumption either of bait (primary exposure) or of live or dead (target or nontarget) prey species that have fed on baits (secondary exposure). Animals most at risk of primary exposure include invertebrates, reptiles, birds and mammals, and granivorous (grain-feeding) species are the most likely to be attracted to and feed on grain-based baits. Most environmental studies have focused on secondary exposure to SGARs; the greater acute toxicity and persistence in (prey) body tissues of these compounds, compared with FGARs, enhances the likelihood of secondary exposure and poisoning. Such exposure is often detected from the presence of liver residues and indicates occurrence of one or more exposure events. Many studies on secondary exposure have been conducted and collectively show that exposure is widespread among predatory and scavenging species throughout the world. In some species, almost all individuals in a population may have liver residues, and detection of multiple compounds is common. This suggests predators and scavengers commonly experience repeated, sublethal, exposures, and ARs are transferred through multiple food webs. The amount of use, baiting practices, dietary preferences, the presence of resistance, and competition for food resources, are some of the factors that influence the likelihood of exposure. A critical question is what are the effects of exposure in nontarget individuals and populations? Most information is available about acute mortalities in vertebrates, although definitive attribution of cause of death to ARs, based on necropsy sign and the presence of chemical residue, is challenging. Despite such diagnostic uncertainties, there is evidence that use of ARs does result in some wildlife mortalities, although the extent of these varies between species, location, and baiting practices. It is documented that primary poisoning has caused reductions in population numbers in some cases. Although secondary AR poisonings can sometimes involve large numbers of individuals, there is no clear evidence to date of direct AR-mediated population declines in predators although mortalities may be a significant additional population stressor. While most concern has focused on lethal poisoning, the widespread secondary exposure that occurs in predators may possibly be associated with sublethal effects, although the extent and importance of any such effects are poorly understood and represent a major knowledge gap. Overall, the wide-scale exposure of wildlife to ARs, particularly the diverse and wide-scale secondary exposure of predators and scavengers, has led to initiatives aimed to restrict sales or implement other mitigation measures around AR use. These are intended to reduce exposure and risk among nontarget species, although their success has yet to be determined.

Item Type: Publication - Book Section
Digital Object Identifier (DOI):
UKCEH and CEH Sections/Science Areas: Pollution (Science Area 2017-)
ISBN: 9780128096659
Additional Keywords: anticoagulant rodenticide, bait, coagulation, FGARs, hemorrhage, mitigation, nontargets, poisoning, population effects, predators, primary and secondary exposure, rat and mouse control, resistance, SGARs, sublethal effects, wildlife mortalities
NORA Subject Terms: Ecology and Environment
Date made live: 19 Mar 2018 13:51 +0 (UTC)

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