Hazard and Risk of Anticoagulant Rodenticides to Predatory and Scavenging Wildlife

Science Center Objects

Invasive mammalian predators are the most damaging group of animals affecting global biodiversity.  When introduced on remote islands, alien rodent species can devastate local biota and have been linked to approximately 30% of all extinctions. In addition, rodents can also consume and spoil crops, and serve as disease vectors that affect humans.  Starting in the 20th century, rodenticides were developed and introduced for the control of these commensal species.  Regrettably, some rodenticides pose a significant hazard to target wildlife.

The Challenge: While anticoagulant rodenticides revolutionized the rodent pest control industry, they are hazardous to non-target predatory and scavenging birds on a global scale. Second-generation compounds, like brodifacoum, can have prolonged effects in non-target species that increase toxicity of subsequent exposures.  Restrictions on the sale, distribution and packaging of some second- generation anticoagulant rodenticides (e.g., brodifacoum, difethialone, bromadiolone and difenacoum) have been instituted by the US EPA, but do not seem to have successfully reduced exposure and effects in non-target predatory wildlife. The risk posed by anticoagulant rodenticides to wildlife is inadequately characterized.  Data are needed to better evaluate the threat of these compounds to non-target organisms, and new safer compounds are needed to mitigate risk. 

The Science: Data on the toxicity of chlorophacinone, diphacinone and brodifacoum have been collected in American kestrels and Eastern screech-owls (e.g., blood clotting time, hematocrit, histopathological lesions, overt signs of distress). Findings are being employed in both deterministic and probabilistic risk assessments, and in the generation of dietary- and tissue residue-based toxicity reference values.  A pharmacokinetic model for diphacinone in various species of wild birds is under development in predatory birds and will assist in further evaluating the hazard of this rodenticide.  Studies evaluating the potential hazard of rapidly metabolized anticoagulant rodenticide diastereoisomers in target species are being planned.

The Future: Results of recent studies with brodifacoum now indicate the potential for latent and protracted effects of combinations of anticoagulant rodenticides encountered by free-ranging raptors residing at the urban-agricultural interface.  Efforts are underway to study new “eco-friendly” rodenticides that could potentially mitigate risk to non-target organisms.