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 nontarget wildlife. We summarize 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 freshwater monitoring at Maungatautari, or in freshwater 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 present in marine shellfish sampled from Little Barrier, Rangitoto or Motutapu. A range of birds, including a kiwi from Little Barrier, were considered nontarget mortalities. Nine little blue penguins found dead on beaches outside the Rangitoto/Motutapu area after baiting were considered most likely to have died of starvation, despite the detection of brodifacoum in three birds. This result highlights the critical role of post-application environmental monitoring in rodent eradications, and information gaps regarding the movement, persistence, and effects of brodifacoum in the environment.

Migration of Brodifacoum and Diphacinone from Bait Pellets Into Topsoil at Palmyra Atoll National Wildlife Refuge

“…The results of this current study are in agreement with other findings (Morgan and Wright 1996, Ogilvie et al 1997, Orazio et al 2009) that suggest rodenticides used in broadcast eradications do not transfer high concentrations of toxicants to soil, even in warm, moist conditions where the degradation of bait matrices is rapid. The active ingredients in rodenticides are known for the potential to persist in the environment (Primus et al 2005, Sage et al 2007, Fisher et al 2011), but the low concentration used in bait pellets limits their potential for significant environmental contamination.…”

“…In one instance, residual concentrations of brodifacoum were detected in soil samples from forest and grassland sites following an aerial broadcast application off New Zealand. Detection levels decreased to near the limit of detection after 100 days (Fisher et al 2011). Information gaps exist around the physical and biological factors that enable toxicants like brodifacoum and diphacinone to persist under various environmental conditions.…”

“…Toxicants deployed during campaigns to control or eradicate invasive rodents may persist in the environment, creating potential exposure pathways for non-target organisms. Anticoagulants are the most widely used rodenticides worldwide (Eason et al 2002, Hoare andHare 2006); however, the migration of toxicants from the bait matrix into soil, and the persistence of toxicant in soil mediums, has rarely been studied in laboratory (Newby and White 1978, Jackson et al 1991, Hall and Priestly 1992, Jackson and Ashton 1992, or in natural settings (Ogilvie et al 1997, Orazio et al 2009, Fisher et al 2011.…”

Managing non-target wildlife mortality whilst using rodenticides to eradicate invasive rodents on islands

“…This may be appropriate for non-target species deemed at risk and present yearround. Examples of this tactic on previous projects include Northern tuatara (Sphenodon punctatus punctatus) on Little Barrier Island, New Zealand (Fisher et al 2011), two species of reptiles on Desecheo Island, Puerto Rico (Will et al 2019), and deer mice (Peromyscus maniculatus anacapae) on Anacapa Island, United States, where individuals of each species where captured, then housed in captivity during and after bait application (Howald et al 2009).…”

Managing non-target wildlife mortality whilst using rodenticides to eradicate invasive rodents on islands

“…This may be appropriate for non-target species deemed at risk and present yearround. Examples of this tactic on previous projects include Northern tuatara (Sphenodon punctatus punctatus) on Little Barrier Island, New Zealand (Fisher et al 2011), two species of reptiles on Desecheo Island, Puerto Rico (Will et al 2019), and deer mice (Peromyscus maniculatus anacapae) on Anacapa Island, United States, where individuals of each species where captured, then housed in captivity during and after bait application (Howald et al 2009). There are risks inherent in bringing wild-caught animals into captivity (Animal Care and Use Committee, American Society of Mammalogists 1998) and being able to adequately maintain them for a required duration.…”