Sodium monofluoroacetate, commonly known as 1080, is a fine white powder. It has a slight odour and taste, is stable under normal storage conditions, and is highly soluble in water. While manufactured 1080 is a highly lethal poison to many species, the active ingredient, fluoroacetate, is chemically identical to the fluoroacetate that occurs naturally in many poisonous plants. These poisonous plants occur in Brazil, South and West Africa, and Australia, especially Western Australia, where some 40 plant species produce it. Plants with high concentrations are potentially hazardous if eaten.
History and extent of use
1080 has been used in New Zealand for pest control since the mid-1950s and is the only poison registered for aerial application. 1080 was first registered as a pesticide for control of vertebrate pests in 1964, under the now repealed Pesticides Act. Its toxicity was well recognised at that time and hence it was classified as a “controlled pesticide”, which means that 1080 is available only to licensed operators.
In addition to New Zealand, 1080 is used in Australia, USA, Mexico and Israel. In the USA, 1080 use is restricted to a livestock collar to protect livestock such as sheep and goats from coyotes. (Coyotes attack livestock around the throat and bite on a lethal dose of 1080 contained in the collar.)
In Australia, 1080 was first used in rabbit control programmes in the early 1950s, where it is regarded as having “a long history of proven effectiveness and safety”8. It is seen as a critical component of the integrated pest control programmes for rabbits, foxes, wild dogs and feral pigs. Since 1994, broad-scale fox control using 1080 meat baits in Western Australia has significantly improved the population numbers of several native species and led, for the first time, to three species of mammals being taken off the state’s endangered species list. In Australia, minor direct mortality of native animal populations from 1080 baits is regarded as acceptable, compared to the predatory and competitive effects of those introduced species being managed using 1080.
Why does New Zealand use more 1080 than other countries?
New Zealand uses approximately 80% of the world’s production of manufactured 1080. In the period 1 July 2002 to 30 June 2003, this amounted to 2.3 tonnes of raw powder.
Mode of action
Although animals vary widely in their sensitivity to 1080 (discussed in the following sections), the basic mode of action of the poison is the same in all animals. 1080 acts by disrupting the “Krebs cycle”, the complex metabolic pathway that breaks down food providing energy for cells to function. Once the energy reserves are depleted, death occurs fairly quickly from heart or respiratory failure. Possums become lethargic and usually die within 6-18 hours from cardiac failure. This is the most common cause of death in herbivores poisoned by 1080. Carnivores experience central nervous system disturbances and convulsions as their energy supplies are exhausted, and then die of respiratory failure. Animals that eat sub-lethal doses may show mild signs of poisoning, but the 1080 is metabolised and excreted within one to four days and the animal recovers. All traces of 1080 are, therefore, likely to be eliminated within one week9.
Laboratory-based regulatory toxicology studies are required to characterise the toxicity of a chemical to target organs, as well as a chemical’s potential to cause genetic or foetal abnormalities. Such tests define No Observable Effect Levels (NOELs) that form the basis for setting limits on acceptable exposure levels for the chemical, for example, in drinking water or other media. Evaluation and interpretation of toxicology data in New Zealand is generally in accordance with internationally accepted methods specified by the OECD, US EPA or WHO. A series of regulatory toxicology studies on 1080 were conducted in the USA in the early 1990s and are summarised in the proceedings of a 1993 science workshop10. This workshop, convened by The Royal Society of New Zealand, brought together scientists from New Zealand, Australia, the United States and South Africa to review national and international research on 1080 and identity further research needs.
In addition to these studies, a demand for more information on the potential risk from regular, low level exposure to 1080, and on the potential of 1080 to cause cancer or birth defects, led to further studies being commissioned and directed by New Zealand scientists.
As described above, 1080 acts by disrupting the Krebs cycle, and animals receiving a lethal dose die from respiratory or heart failure. Studies on rats and sheep indicate that the target organs for sub-lethal 1080 poisoning are the heart and the testes, which are both tissues with high metabolic needs. In other words, the heart and testes need lots of energy to function normally.
When rats were given doses of 1080 (0.25 mg/kg-day), which are close to levels that can cause rat mortality (see Table 1), and over a long period of time (90 days), there was damage to the male gonadal tissue and sperm were significantly affected. Sperm showed reduced concentration and less motility, and a higher percentage were abnormal. There were no 1080-related effects on the same measures of sperm condition (concentration, motility, abnormality) at two lower dosage levels of 0.025 mg/kg-day and 0.075 mg/kg-day after 90 days11. The 0.075 mg/kg-day dosage level is the NOEL for repeat exposures in rats given 1080 orally, over a 90-day period. These physical effects occurred as the result of relatively high and prolonged sub-lethal exposure to 1080.
As a quite separate question, tests have recently been carried out to see whether 1080 could interfere with specific mechanisms of the endocrine system. Some long-lived chemicals that can accumulate in the body, unlike 1080, have been found to act as endocrine disruptors in humans and wildlife. Endocrine disrupting chemicals can be described as external chemicals that interfere in various ways with natural hormones that are responsible for maintaining homeostasis, as well as reproduction, development and some behaviours. Recently, laboratory tests were carried out to assess the ability of 1080 or fluorocitrate to mimic or interfere with the normal action of the female sex steroid 17ß-oestradiol, using an in vitro assay12. The results indicated that 1080 and fluorocitrate are unlikely to act as endocrinedisrupting chemicals through this particular mechanism. Additional testing is underway to find out whether 1080 can interfere with the actions of the male hormone, androgen.
Three different, complementary genetic toxicity tests were commissioned to determine whether 1080 alters genetic material, and therefore has the potential to cause cancer. The results of all three studies indicate that 1080 is not genotoxic, and provide strong evidence that it is not carcinogenic12.
Tests have also been undertaken to determine the developmental toxicity of 1080, that is, the effect on embryo development during pregnancy. In studies conducted on rats, mild skeletal defects were observed in 20% of the litters of female rats exposed to relatively high doses of 108013. However, no effects were observed at doses below 0.1 mg/kg-day13, a dose rate similar to the NOEL for organ toxicity in rats (of 0.075 mg/kg-day, described above).
Comparison of species sensitivity
In general, 1080 is extremely toxic to animals. However species vary widely in their sensitivity to 1080. Comparisons can be made using a measure of the lethal dose called the LD50. The LD50 is defined as the dose of 1080, expressed in milligrams of 1080 per kilogram of body weight (mg/kgbw), which will theoretically kill 50% of the test subjects of a specific population, under specified conditions. The lower the LD50 value, the more sensitive the species is to 1080.
The following table shows that dogs are particularly sensitive to 1080 poisoning, as are most other carnivores. Herbivores and birds are less sensitive, and reptiles and amphibians are less sensitive again. There is little LD50 data on New Zealand’s native insectivorous birds, but data for Australian insectivorous birds indicate the LD50 ranges from 3.4 to over 18 milligrams per kilogram of body weight14.
Table 1. Oral toxicity of 1080
||0.3 - 0.35
||0.25 - 0.64
||0.3 - 0.7
|Pig – feral pig
||0.4 - 1.0
||0.2 - 3.0
|South African clawed toad
Fish and other aquatic fauna (including invertebrates) generally have very low sensitivity to 1080. Toxicity tests have been conducted in the USA on bluegill sunfish, rainbow trout and the freshwater invertebrate Daphnia magna10. Tests at different 1080 concentrations on sunfish (for four days) and Daphnia (two days) showed that 1080 is “practically non-toxic” (a US EPA classification) to both these species10. Rainbow trout were also tested over four days at four concentrations ranging from 39 to 170 mg 1080 per litre. From these results an LC50 can be calculated, which is the concentration of 1080 per litre of water which theoretically kills 50% of the test fish. The LC50 for rainbow trout was calculated to be 54 mg 1080/litre, making 1080 “slightly toxic” to rainbow trout according to the US EPA classification system10.
How does this compare with the highest levels of 1080 found in water samples following 1080 aerial operations? Chapter 5.5 notes that only five water samples out of almost 1650 samples tested so far have reported 1080 levels of greater than 0.002 mg/litre or 2 parts per billion (ppb). This concentration is 27,000 times lower than the LC50 for rainbow trout. It is also 6,500 times lower than the concentration of 13 mg 1080/litre at which no mortality or sub-lethal effects were observed in trout after four days10. It is, therefore, reasonable to conclude that 1080 is most unlikely to cause mortality in freshwater species.
Estimates have been made of 1080 toxicity to humans, in the absence of formal toxicity testing. Indications are that an equivalent LD50 for humans is in the range of 2.0-10.0 mg 1080/kgbw15, indicating that 1080 is as toxic to humans as to many other species.
The susceptibility of (or risk to) different animals during 1080 poisoning operations depends on how much 1080 they eat. Susceptibility is also affected by body size (see Susceptibility to 1080). The likelihood of a particular individual or species encountering 1080 poison will depend on the amount and type of bait used, its pattern of distribution, and the population densities and movements of the animals in and around the baited area26. Actual susceptibility to 1080 can only be accurately measured in field studies, which can be difficult to carry out due to the large number of variables involved. Field studies on the impact of 1080 poisoning operations indicate that estimates of potential susceptibility may overemphasise the actual risk faced by many non-target species26. Nonetheless, these estimates are useful for assessing risks for rare and endangered species and can be used in designing operations to minimise the estimated risks. The outcomes of 1080 operations for bird populations and other native animals are described in Chapter 5.1 and Chapter 5.2.
Breakdown of 1080 in animals
Over the past 50 years, studies in laboratory animals of how 1080 is absorbed, metabolised and excreted, show that sub-lethal amounts are excreted unchanged and as less toxic compounds. Studies of the rate of 1080 elimination in mammals such as mice, goats, sheep and rabbits indicate that sub-lethal doses of 1080 are likely to be metabolised and excreted, so that no 1080 is detectable in tissues within approximately seven days27. By contrast, anticoagulant rodent poisons, such as brodifacoum, are extremely persistent in animal tissues. This comparatively rapid metabolism and excretion of 1080 from animals means that 1080 does not bioaccumulate (build up) in the food chain through sub-lethal doses.
1080 degrades more slowly in carcasses, where it might persist for some months. In colder temperatures, 1080 degradation is slowed even further. In these circumstances, 1080 poses a risk to dogs if they feed on tainted carcasses. Most dog deaths occur as a result of the dog scavenging on poisoned possums, particularly if they eat the stomach of the carcass.
Degradation of 1080 in the environment
Studies show that micro-organisms in New Zealand soils will degrade 1080. The degradation occurs by enzymes defluorinating fluoroacetate (removing the fluorine atom). Ultimately, enzyme intermediates and non-toxic products are formed, such as glycolate9. Common soil fungi can also defluorinate 108028.
In laboratory experiments, the amount of 1080 remaining in soils was reduced to 50% after 10 days at 23°C, 30 days at 10°C and 80 days at 5°C29. Leaching experiments in soil showed that traces of 1080 might be leached through soil, particularly if heavy rainfall occurred shortly after 1080 was applied. These experiments indicate that 1080 does not persist long enough in the environment to have detrimental effects. The conclusion from a range of studies into the fate of 1080 in New Zealand soils is that “most New Zealand soils can be expected to contain micro-organisms with the ability to rapidly develop enzymes capable of degrading 1080”28. This means that any 1080 that leaches from baits or carcasses should have little persistence in our soils.
Bio-degradation of 1080 in the environment occurs even more rapidly in water. At 21°C, micro-organisms in water degrade 1080 in two to six days29. At lower temperatures, microbial action is slower and degradation might take one to two weeks, or longer, at temperatures below 7°C. Aquatic plants can also significantly affect 1080 degradation rates. In laboratory experiments, the presence of a native aquatic plant (Myriophyllum triphyllum) reduced concentrations of 1080 below detectable levels within one day (at 23°C) and within three days (at 7°C)30.
The solubility of 1080 means that it is also rapidly diluted in water. This dilution effect, especially in flowing waterways, is more important in quickly reducing the level of 1080 to insignificant concentrations, than the rate of breakdown by micro-organisms.
In Western Australia the natural levels of fluoroacetate in plants may be several hundred times the concentration applied in 1080 aerial operations in New Zealand. No fluoroacetate has been found in water samples taken from the Perth water supply and catchment, despite the presence of some Gastrolobium species with higher concentrations of fluoroacetate in the leaves than in the 1080 baits used here.
Susceptibility to 1080
Other factors beside sensitivity to 1080 can determine the effect of 1080 poisoning operations on animal populations. Body size is particularly important. For example, Table 1 shows that silvereye and Australian magpie have similar sensitivities to 1080. However, a magpie (at 320 g average weight) is about 23 times heavier than a silvereye (of average weight 14 g) and, therefore, would need to eat about 23 times as much 1080 as a silvereye to receive the equivalent of an LD50. The silvereye is, therefore, much more susceptible to 1080 poisoning than the magpie. Similarly, although a possum is much more sensitive to 1080 than a silvereye, its much larger size means it would need to eat at least 16 times more 1080 than a silvereye to receive the equivalent of an LD50. Hence, the ranking list in Table 1 is not the same as a ranking list of susceptibility when body weight is considered. This means the very small insectivorous birds tend to be the most susceptible, or “at risk” species.
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