Exposure of non-target small mammals to anticoagulant rodenticide during chemical rodent control operations
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The extensive use of anticoagulant rodenticides (ARs) results in widespread unintentional exposure of non-target rodents and secondary poisoning of predators despite regulatory measures to manage and reduce exposure risk. To elucidate on the potential vectoring of ARs into surrounding habitats by non-target small mammals, we determined bromadiolone prevalence and concentrations in rodents and shrews near bait boxes during an experimental application of the poison for 2 weeks. Overall, bromadiolone was detected in 12.6% of all small rodents and insectivores. Less than 20 m from bait boxes, 48.6% of small mammals had detectable levels of bromadiolone. The prevalence of poisoned small mammals decreased with distance to bait boxes, but bromadiolone concentration in the rodenticide positive individuals did not. Poisoned small mammals were trapped up to 89 m from bait boxes. Bromadiolone concentrations in yellow-necked mice (Apodemus flavicollis) were higher than concentrations in bank vole (Myodes glareolus), field vole (Microtus agrestis), harvest mouse (Micromys minutus), and common shrew (Sorex araneus). Our field trials documents that chemical rodent control results in widespread exposure of non-target small mammals and that AR poisoned small mammals disperse away from bating sites to become available to predators and scavengers in large areas of the landscape. The results suggest that the unintentional secondary exposure of predators and scavengers is an unavoidable consequence of chemical rodent control outside buildings and infrastructures.
KeywordsRodent control Anticoagulant rodenticides Non-target exposure Secondary poisoning Rodent dispersal Insectivores
Jennifer Lynch, Jens Peder Hounisen, and Lars Haugaard provided invaluable technical and field assistance. We thank Charlotte Dahl Schiødt and Ellen Christiansen for laboratory assistance and the Danish Nature Agency for access to the field sites. We also thanks the reviewers for valuable comments on an earlier draft of the manuscript.
The study was funded by research grants from the Danish Environmental Protection Agency (MST 667-00100 and MST 667-00112).
Compliance with ethical standards
The field trials were done in accordance with a permit issued to the Department of Bioscience by the Danish Nature Agency: SN302-009SEI.
Conflict of interest
The authors declare that they have no conflict of interest.
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