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.



Conclusions and implications to the Nordic countries

The existence of substantial incident data along with liver-residue analyses confirms that birds and non-target mammals are being exposed to anticoagulant rodenticides all around the world. The fact that numerous species of birds and mammals, including predators and scavengers have been exposed to these substances indicates that both primary and secondary exposure is occurring. Exposure of non-target animals is likely to be more widespread than the number of reported incidents suggests. Most surveys have been based on the activity of the general public who has sent carcasses to analysis when they have suspected poisoning. In many situations carcasses might not be detected, death may be attributed to natural mortality, or an incident may not be reported for a variety of reasons. In conclusion, studies made on secondary exposure reveal only the top of the iceberg. Residues found in predators and scavengers show that predominantly the second generation substances, i.e. brodifacoum, bromadiolone, difenacoum, flocoumafen and difethialone, cause secondary exposure. There were not many incidents where first generation anticoagulants were involved. The frequency of incidents is assumed to correlate to the use volumes of the substances. Unfortunately we have not found published data on sale volumes that could be compared to the number of incidents in the UK and US where most incident data are available. The statistics on sale volumes or use frequencies would enable the comparison of the likelihood or potency of the substances in causing the secondary poisoning. Due to lack of resources and/or ignorance of the potential risk measurements have been made only in few countries, and the incidents are likely to be much more widespread than reported here.


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