A couple of years ago now, we held a Cafe Scientifique with the topic 1080 – friend or foe? Topical then (it drew a large crowd, wtih people from both sides of the debate) & just as topical now. On the one hand, 1080 is promoted as our current best option for the control of possums, mustelids (mainly stoats & ferrets), rabbits, & rats. Those opposing its use describe it as contrary to our image as a clean, green nation; harmful to a range of non-target animals, & potentially a threat to water supplies.
1080 is sodium monofluoroacetate (FCH2COONa). The 1080 used in New Zealand, while manufactured in the lab, is chemically & toxicologically identical to the chemical produced in a range of plants as part of their anti-herbivore defenses. Sodium monofluoroacetate is found in around 40 Australian plant species & is the toxic agent in poisonous plants from India, Brazil & parts of Africa – apparently the highest known concentration is 8.0mg/g in the seems of a plant from South Africa. It’s also found in Camellia sinensis, but at very low concentrations (50-160 nanograms/g, in Ceylon tea, & up to 230 ng/g in green tea).
1080 kills by interrupting cellular respiration – possums die of heart failure within a few hours of eating carrot baits laced with the poison. Unfortunately it’s also highly toxic to domestic dogs (Eason, 2009a) - a risk that shouldn’t be trivialised – & may also kill other non-target species: it’s toxic to livestock, for example, & so will also kill feral deer & goats in forests. Although sub-lethal doses are rapidly broken down in an animal’s body, 1080 may persist for weeks in carcases & this poses the risk of secondary poisoning, both for dogs & for other species that may scavenge the bodies.
The key focus of its use in New Zealand is possums, which were introduced to New Zealand in the 1850s – they were intended to be the basis of a fur trade but, in the absence of natural predators & with an ample food supply, they spread quickly through our forests, to the extent that they’re now found in about 90% of our land area. They do a considerable amount of damage to native plants (& introduced plants as well, not being too fussy about what they eat) & we know that they also prey upon the eggs & chicks of native birds. Possums are also a vector for bovine tuberculosis, which they can spread to both cattle & deer (we have a fairly high proportion of Tb-infected cattle in NZ, which poses some risk to our export markets): while only a small proportion of possums may be infected at any one time, those animals are widely distributed. In other words, there are strong environmental and economic reasons for reducing the possum population in this country.
Several different poisons, plus trapping, are used to kill possums in New Zealand, although 1080 is perhaps the best-known & most widely-used of these. It’s applied using ground control baits and – more controversially – by aerial drops of carrot or cereal baits laced with 1080 over areas that are either difficult
& or expensive to get into on the ground. It is effective, reducing possum numbers in targeted areas with very positive effects on the prevalence of bovine Tb & on forest restoration (a pleasing outcome, given how fragmented & degraded much of our native forests have become since human settlement). For example, in the Waikato possum control (largely using 1080) reduced the number of Tb-infected dairy herds from >200 in 1995 to 5 in 2006. However, while modern GPS systems have improved the accuracy of the aerial drops, there are still significant public concerns to do with contamination of drinking water & deaths of non-target species.
With regard to waterways – the maximum acceptable level of sodium monofluoroacetate in NZ’s drinking water supplies is 2 parts per billion (ppb). There’s no disputing that 1080 drops have at times affected water-supply catchments, but at the same time there’s no evidence (eg Eason, 2002b) of long-term contamination of ground/surface waters or of reticulated supply. While 1080 is definitely highly toxic to humans, that needs to be put into perspective: we’d need to eat at least 100g of carrot baits (which are dyed bright green, so there’s not much chance of mistaking them for normal carrots), or eat at least 37kg of meat from a sheep that died of 1080 poisoning, or drink at least 5,000 litres of water from a heavily contaminated waterway (all at once, as otherwise it would be excreted before it could reach toxic levels in the body). Nonetheless, anyone handling 1080 or the poisoned baits has to take extensive safety precautions & be trained in safe storage and use of the chemical.
There have certainly been problems with 1080 killing non-target bird species, particularly when the baits have been small or contained a large proportion of chaff (Eason, 2002a). (Birds & reptiles are, however, less susceptible than mammals.) However, there’s also evidence that 1080 drops have a beneficial effect on bird numbers overall, through reducing predation by possums & rats, & also be reducing competition for food. For example, in 1990 the Department of Conservation used 1080 to eradicate possums & wallabies from Rangitoto Island in the Hauraki Gulf. Miller & Anderson (1992) monitored bird populations on Rangitoto for a year after the drop. They found that there "was no significant decline in bird numbers recorded immediately after poisoning, with four species increasing in abundance (P<0.001) [this included carrion feeders]. Twelve months after the operation the abundance of four species had increased significantly (P<0.001)" They concluded that the drop had no negative effect on the island’s bird populations. Similarly a combination of trapping & poisoning (1080, followed by brodifacoum) of rats & possums in Motatau, Northland, saw in increase in native pigeons & other bird species (Innes et al., 2004).
The eradication project described by Innes & his colleagues shows the range of chemical methods available to animal pest controllers: 1080, brodifacoum, cyanide & cholecalciferol among them. Traps, pest-proof fences, & shooting are other options. All these control methods have advantages & disadvantages to do with cost, effectiveness, safety of both operators & the public, persistence in the environment (eg while 1080 normally breaks down quickly in both water & soil, this is not the case in cold dry conditions), humaneness, & the risks they pose to non-target species. At the moment 1080 is the most widely-used method for large-scale pest control. It’s relatively cheap, & extremely effective in reducing the numbers of pest animals. But because of its toxicity, there are ongoing research programs studying other means of possum control – the most promising would seem to be some method of fertility control (Ji, 2009), perhaps using immunocontraception. This would essentially mean using a vector (eg a parasitic nematode specific to possums) to deliver a vaccine that would elicit an immune response towards sperm, rendering female possums infertile. While this sounds an elegant solution, nothing is as simple as it seems – in Australia, where possums are a protected species, there’s concern about the possibility of this sort of self-spreading biocontrol system crossing the ditch and affecting Australian possums. Ji (2009) suggests that the best option for New Zealand at present would be some combination of bait-delivered fertility control (still under development) and improved conventional methods, so it’s likely that 1080 & other chemical controls will be with us for a while yet.
Anyone interested in a more detailed statistical treatment of research investigating 1080 impacts on birds should read this post by statistician Ian Westbrooke.
C.Eason (2002b) Technical review of sodium monofluoroacetate (1080) toxicology. Animal Health Board & Landcare Research. ISBN 0-478-09346-2
J.Innes, G.Nugent, K.Prime & E.B.Spurr (2004) Responses of kukupa (Hemiphaga novaeseelandiae) and other birds to mammal pest control at Motatau, Northland. New Zealand Journal of Ecology 28(1): 73-81
W.Ji (2009) A review of the potential of fertility control to manage brushtail possums in New Zealand. Human-Wildlife Conflicts 3(1): 20-29
C.J.Miller & S.Anderson (1992) Impacts of aerial 1080 poisoning on the birds of Rangitoto Island, Hauraki Gulf, New Zealand. New Zealand Journal of Ecology 16(2): 103-107