Literature Review on Residues of Anticoagulant Rodenticides in Non-Target Animals

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Anticoagulant rodenticides are the principal means of controlling pest rodents in the Nordic countries. Due to the intrinsic properties of second generation anticoagulants, i.e. extremely slow elimination from the body and high toxicity, they are prone to accumulate in the non-target species which consume poisoned rodents. Despite wide use there are no published studies on occurrence of residues of anticoagulant rodenticides in the non-target animals in the Nordic countries. This review of publicly available studies was aimed to find out which anticoagulant substances are found and in which species. The concentrations are reported as well as the proportion of exposed animals. We have further compiled a list of species that could potentially be exposed to anticoagulant rodenticides in the Nordic countries. The review shows that anticoagulant residues have been found everywhere they have been measured and secondary exposure to second generation anticoagulants is common among certain avian and mammalian predators. The results call for initiation of measurements of anticoagulant rodenticides also in the Nordic countries.




Residues of second generation anticoagulant rodenticides in wildlife have been found all around the world where the occurrence of residues has been investigated. Second generation anticoagulants, brodifacoum, bromadiolone, difenacoum, difethialone and flocoumafen, have been gradually introduced after the appearance of resistance to warfarin and other first generation substances. They are much more toxic and in particular more persistent in rodents and hence potent in accumulating in non-target species that feed on target and non-target rodents. Despite wide use of anticoagulants, there are relatively few studies where anticoagulant residues have been measured in non-target animals. More systematic incident studies have been done only in Britain and in some states of the US. In addition to Britain, published data on anticoagulant residues is available only in France in Europe. In Britain anticoagulant residues have been studied in particular in barn owl (Tyto alba) and in polecats (Mustela putorius). About one third of studied carcasses contained residues. In most cases, the residues were expected to be sublethal. No studies on the effects of the sublethal residues have been found. In the UK incident program other commonly exposed species were buzzard (Buteo buteo), red kite (Milvus milvus), and fox (Vulpes vulpes). In the US the commonly exposed species were great horned owls (Bubo virginianus), red-tailed hawks (Buteo jamaicensis), coyotes, foxes and raccoons. Anticoagulants are the dominant rodenticides in the Nordic countries, but no information is available on residues in non-target species. Information on residues is needed in order to judge whether the currently used risk mitigation measures are effective and whether further measures or restrictions should be considered.


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