An experimental test of the toxicity of cereal pellets containing brodifacoum to the snails of Henderson Island, South Pacific

Abstract

Context Cereal pellets containing the anti-coagulant poison brodifacoum at 20 ppm are routinely used to rid islands of invasive rodents. The impact, if any, of the poison on invertebrates is not well understood. This is problematic because many of the islands targeted for treatment harbour endemic invertebrate species, including snails where available information about brodifacoum impact is equivocal. Aims Combining field tests and subsequent laboratory analysis, the present study investigated the effect of brodifacoum on the snails of Henderson Island, South Pacific. Methods In the field, we housed snails in plastic boxes for up to 10 days to compare the survival of those kept with and without access to brodifacoum cereal pellets. Subsequently, we analysed brodifacoum levels in those kept with access to poisoned pellets, according to whether they survived or died. Key results There were no detectable differences in the survival between the captive snails kept with and those kept without access to brodifacoum. Among those with access, there were no significant differences in brodifacoum concentrations between the minority that died and the majority that survived. In fact, brodifacoum was detected in only a few samples. Conclusions Brodifacoum appears not to pose a risk to the snails of Henderson Island. Implications Although it would be prudent to test the impact of brodifacoum on the resident snails before proceeding with a rodent eradication on other islands, we suspect the Henderson results can be extended to other sites.