Non-Lethal Dose-Response Models Replace Lethal Bioassays for Predicting the Hazard of Para-Aminopropiophenone to Australian Wildlife

Simple Summary Para-aminopropiophenone (PAPP) is registered as bait poison for the humane control of red foxes and wild dogs in Australia. To classify the relative hazard of poisons, regulatory bodies have historically demanded LD50 values (the dose lethal to 50% of an animal population) to define the comparative sensitivity of pest and wildlife species. Instead, we developed a replacement assay that used non-lethal dose-response methods to assess the sensitivity of 12 wildlife species and laboratory rats to PAPP that did not require death to be used as an experimental outcome. By establishing the relationship between non-lethal doses of PAPP and the formation of methaemoglobin (MetHb), we found that we could accurately predict doses likely to be lethal. Our estimates very closely approximated existing LD50 values determined for PAPP. We argue that laboratory-based lethal-dose bioassays are unsuited to assessing the comparative hazard of toxicants to wildlife species. In contrast, non-lethal assays that use biologically relevant measures can provide much more robust and meaningful indications of relative hazard even in species of high conservation value, where lethal experimentation can rarely be justified. Para-aminopropiophenone (PAPP) is a potent methaemoglobin (MetHb) forming agent used for the lethal control of exotic carnivores and mustelids. To assess the sensitivity of Australian wildlife to PAPP we developed an in vivo assay that did not use death as an endpoint. Sub-lethal dose-response data were modelled to predict PAPP doses required to achieve an endpoint set at 80% MetHb (MetHb(80)). The comparative sensitivity of non-target mammals referenced to this endpoint was found to be highly variable, with southern brown bandicoots (Isoodon obesulus) the most sensitive species (MetHb(80) = 6.3 mg kg(-1)) and bush rats (Rattus fuscipes) the most tolerant (MetHb(80) = 1035 mg kg(-1)). Published LD50 estimates were highly correlated with PAPP doses modelled to achieve the MetHb(80) endpoint (r(2) = 0.99, p < 0.001). Most dose-response data for native mammals were collected in the field or in semi-natural enclosures, permitting PAPP and placebo dosed animals to be fitted with tracking transmitters and transponders and released at their point of capture. A protracted morbidity and mortality was observed only in Australian ravens (Corvus coronoides). The combination of sub-lethal dose-response assay and survival data collected in the field provided more relevant information about the actual hazard of pest control agents to non-target wildlife species than laboratory-based lethal-dose bioassays. We discuss the need to replace lethal-dose data with biologically meaningful insights able to define a continuum of toxicological hazards that better serve the needs of conservation and veterinary scientists and wildlife managers.

Automated summary

Para-aminopropiophenone (PAPP) is used in Australia for the humane control of red foxes and wild dogs. Instead of using lethal dose bioassays, a non-lethal assay was developed to assess the sensitivity of wildlife species to PAPP, providing more meaningful indications of relative hazard. The study suggests the need for biologically relevant insights to define the toxicological hazards and protect non-target wildlife species.