Environmental Monitoring for Brodifacoum Residues after Aerial Application of Baits for Rodent Eradication

Abstract

Aerial application of brodifacoum bait for eradication of invasive rodents from islands raises concerns about environmental contamination and adverse effects on non-target wildlife. We summarise results of environmental monitoring for brodifacoum residues after New Zealand eradications in a fenced reserve at Maungatautari and on the offshore islands Little Barrier, Rangitoto and Motutapu. Brodifacoum was not detected in extensive fresh water monitoring at Maungatautari, or in fresh water samples from Little Barrier Island. Residual concentrations were present in soil samples from underneath degrading bait pellets on Little Barrier, and decreased to near the limit of detection by C. 100 days after application. No brodifacoum was detected in marine shellfish sampled from Little Barrier, Rangitoto or Motutapu. A range of birds, including a kiwi from Little Barrier, were considered non-target mortalities. Residual brodifacoum concentrations detected in three of nine little blue penguins found dead on beaches outside the Rangitoto/ Motutapu area after baiting were considered to represent sublethal exposure, with starvation considered the likely cause of death. This result highlights the crucial role of post-application environmental monitoring in rodent eradications, in addressing community concerns and filling information gaps regarding the movement, persistence and effects of brodifacoum in the environment.