Tuatara poison to be reassessed
An over-the-counter rat poison that indirectly killed four tuatara at Nelson’s Natureland is a ‘‘priority’’ for review, the Environmental Protection Agency says.
The tuatara were exposed to chronic low levels of brodifacoum, a poison well known and controversial for its use in aerial drops on offshore islands or inside nature sanctuaries with predator-proof fences.
The exposure at Natureland was not through aerial drops, however. The tuatara died after years of eating an unknown number of cockroaches that were carrying a deadly lunch of a common over-the-counter rat poison that contains brodifacoum.
EPA general manager for hazardous substances and new organisms Clark Ehlers said the substance was ‘‘one of a number of VTAs (vertebrate toxic agents) on our priority chemicals list’’.
The list, available online, identifies about 40 chemicals the EPA believes are most in need of review.
‘‘Protection of the unique nature of the New Zealand environment is at the core of what we do at the EPA, and we give regard specifically to protection of our native and taonga species during our risk assessment process,’’ Ehlers said.
He said secondary poisoning of non-target animals, by eating either the carcasses of poisoned animals or live organisms that were carrying the poison, like the cockroaches at Natureland, was a ‘‘well-documented characteristic’’ of VTAs.
Ehlers said the use of VTA products was regulated and had ‘‘a range of controls’’ to limit the risk of secondary poisoning.
Brodifacoum is included on the agency’s priority list for review because of its high risk to both human health and the environment, and its availability
‘‘Reports such as that of the deaths of the tuatara at Natureland . . . play an important role in our assessment.’’ Clark Ehlers, Environmental Protection Agency
for home use.
‘‘Reports such as that of the deaths of the tuatara at Natureland, plus other data and research, play an important role in our assessment of these substances,’’ Ehlers said.
‘‘Factors evaluated include the nature and persistence of the active substance, metabolism of the target organism, the method and frequency of delivery, target species, and how other non-target vector organisms might be exposed to the VTA.’’
Ehlers did not give a timeline for when the review of brodifacoum would take place.
The EPA issued a caution notice for the use of VTA products in 2017, to outline best practice for many available rodent poisons. The notice warns users not to place the poisons where children or non-target animals could access them, but focuses on animals like cats or dogs rather than insects or other pests.
Natureland director Grant Abel said in his report into the deaths that Natureland had been using the Pestoff brand of rat poison ‘‘in accordance with the directions for use’’ since August 2015.
The first death linked to the poison’s use was two years later, in August 2017.
‘‘The Pestoff label clearly states that bait stations should be located in areas where rodents are likely to be active, and bait replenished daily until the baits cease to be eaten . . . The label includes clear warnings about toxin accumulation and secondary poisoning risks, but not in the context of live invertebrates that may be eaten by insectivorous birds and reptiles.’’
Abel also noted in the report that the risk of secondary poisoning from rodenticides was not mentioned in the Tuatara Husbandry Manual used ‘‘by all zoos and tuatara holders’’.
He said Pestoff’s manufacturer had been proactive, reaching out to him in the wake of his report and indicating a potential change to the product’s labelling.