Sodium monofluoroacetate (1080) is a white, odourless, tasteless powder. It is highly soluble in water but relatively insoluble in organic solvents such as alcohol or acetone. Before issue to Pastures Protection Boards, a blue-black dye is incorporated in the powder. The powder itself is very dangerous and has to be handled with great care. However, before use it is dissolved in water to make a 3.33% solution of 1080 and this is used to poison baits. Aqueous solutions of 1080 decrease in toxicity on storage. Chenoweth (1949).
CONTROL OVER USE
The use of 1080 in New South Wales is controlled by the Department of Agriculture and it is restricted to licensed operators who have successfully completed a training course conducted by the Department. In addition, trained operators such as Rangers and Rabbit Inspectors of P.P. Boards are required to attend refresher courses from time to time. The Department exercises control over the type and size of the bait material used, the concentration of 1080 applied to the bait and the distribution of the poisoned bait. The Department also supervises the storage and handling of 1080 by Board staff.
OCCURRENCE IN NATURE
1080 occurs in nature in some plants and in South Africa in 1944 it was identified as the toxic principle in a poisonous plant known ac gifblaar (Dichapetalum cymosum) which had long been recognised as the cause of poisoning in sheep, Marais (1944). Since then 1080 has been isolated from a number of other plants, including several from Australia. For example, Acacia Georginae common name 'Gidgee' or 'Georgine Gidyea'. This is a large shrub or small tree, which is confined to the Georgina river basin of Queensland and adjacent eastern areas of Northern Territory. This plant has caused heavy losses in both sheep and cattle from fluoroacetic acid poisoning, mostly in dry seasons when other feed is scarce, Whittem & Murray (1963). Another plant found in Northern Australia which has caused serious losses in livestock is Gastrolobium grandiflorum, or heart leaf poison bush. McEwan (1964) isolated monofluoroacetic acid.
MODE OF ACTION
Sodium monofluoroacetate is not poisonous in itself but is converted in the body to fluorocitrate which blocks a vital biochemical system known as the Tricarboxylic Acid Cycle involved with energy production in cells. This causes the energy supply to cells to be reduced to a point where they lose function.
Toxic effects do not appear immediately after ingestion, even with massive doses of 1080, as time is required for conversion of the fluoroacetate to fluorocitrate. In dogs this lag period usually varies from 15 minutes to two hours but can be somewhat longer.
The damage to body cells manifests itself clinically in disturbances to the central nervous system and/or heart.
Death may result from:
a). Ventricular fibrillation of the heart.
b). Progressive central nervous system depression with either heart or respiratory failure.
c). Respiratory arrest after severe convulsions.
SUSCEPTIBILITY TO 1080 POISONING - SPECIES VARIATION
There is considerable variation in susceptibility between various species of animals.
In general, amongst the warm blooded species primates and all types of birds are the least susceptible, whereas carnivora and wild rodents appear to be particularly sensitive. Cold blooded animals, such as reptiles, fish and amphibians, are more resistant still. Chenoweth (1949).
Dogs are the most susceptible of all animals to 1080. The following table illustrates the relative susceptibility of the various species of animals. McIntosh (1964).
|ANIMAL||Quantity of 1080 to kill in mg/kg liveweight||Relative Resistance|
|Man||2.0 - 5.0||25 - 60|
|Mallard Duck||8.0 - 16.0||100 - 200|
Work has been done in several species of birds of prey and scavengers in U.S.A. It has been reported that the lethal dose for three species of hawks and one species of owl is about 10 mg/kg, and one species of vulture about 15 mg/kg, Atzert (1971). This is much the same level as in the domestic fowl which is well over 100 times as resistant as a dog.
Another way of looking at the relative susceptibility of various species is by comparing the amount of standard 1080 poisoned carrot bait which would have to be eaten to cause toxicity and death. A rabbit would only have to eat 0.083 of an ounce of bait, however, a human would have to eat somewhere between 12 ounces to 4 pounds 3 ounces. Three ounces of bait would be toxic to a pig, a sheep one ounce, a rat 1/7 ounce and a dog 2/7 ounce. Since the average weight of a dog is about 40 lbs and a rat about 12 lbs, and they both require the same amount of carrot bait, this illustrates the great variability that can occur between species.
The relative resistance of humans is illustrated by a report that Prof. E.D. Adrian took a dose of fluoroacetate sufficient to produce urine toxic to guinea pigs, (Peters 1954).
This variation in the susceptibility of the various species of animals is taken into account when poisoning noxious animals. Studies on the behaviour and habits of animals have shown still further means of protecting non-target species from accidental poisoning.
Some of the factors taken into consideration are:—
a). The nature of the bait material - e.g., diced carrot or apple is very acceptable to rabbits and safer on non-target species than grain. Baits for feral pig control are restricted to grain and pellets.
b). The colour of the bait - most animals cannot see colours; just black and white and the various intermediate shades. Birds see colours and some colours such as yellow and more particularly green are less attractive to them. Thus, bait material such as grain dyed green is largely avoided by birds.
c).The size of the bait - Since 1080 is applied to the surface of the bait material, it is obvious that there will be a greater amount of 1080 per pound weight of bait if the bait is cut finely, due to the greater surface area. Thus, carrot baits should be from ¼ to ½ inch in diameter and meat baits for dingoes about ½ lb. in size. As far as possible, baits laid should be uniform in size to ensure an even distribution of the poison.
d). Placement of the bait - Rabbit baits are placed in freshly dug furrows. This fresh disturbance of earth appears to attract rabbits. When the poisoning is finished it can easily be seen if any uneaten bait is left and this can be picked up or buried. Possums are quite susceptible to 1080 and their poisoning can be avoided if trails are placed well away from clumps of trees. Wild pig baits are placed in shallow holes which should be covered during the day. It is important to locate bait stations or trails on feeding areas of the target species. Proper placement means less poisoned bait is needed and reduces risk to non-target species. Free feeding techniques using non-poisoned bait are used to entice target species to the bait stations or trails. The amount of bait needed to kill the target species should be carefully calculated to avoid use of excessive poisoned material.
THE QUESTION OF PAIN
The question of pain is often raised during discussion on 1080 poisoning, particularly in regard to dogs where central nervous effects predominate.
The symptoms shown in poisoned dogs are certainly spectacular and distressing to observers, as illustrated in the classical description by Foss (1948) and no doubt familiar to many rural veterinarians. 'A quiet period is followed by hyper-excitability with loud barking and wild, inco-ordinate, impulsive activity, associated with incontinence of urine and faeces. Retching and vomiting may occur before this stage. The excitable stage suddenly merges into one convulsion. At first tonic and extensor, with dilated pupils and brick reflexes, later the fits are clonic with champing of the jaws and inco-ordinate arrhythmic running movements of all four limbs. After a brief respite with heavy panting, the whole pattern is repeated at intervals of 1-2 minutes until death occurs, once again from respiratory failure'.
Several human cases of 1080 poisoning, some of which have recovered, have been studied overseas. Although humans show severe epileptiform convulsions as well as cardiac effects, no pain has ever been reported. It is reasonable to assume that a similar lack of pain would be experienced by other animals. Also due to derangement of cells in the central nervous system, the reception of pain stimuli would be decreased. From a humane point of view, 1080 compares very favourably with other commonly used poisons such as arsenic, phosphorus, strychnine and organo-phosphates.
EFFECTS OF 2080 ON ANIMAL POPULATIONS
The target species of animals for 1080 poisoning are the rabbit, fox, wild pig and dingo. All except the dingo are species introduced into Australia by European settlers. Also in New South Wales it has been reported that a large percentage of the dingo population is no longer pure bred, but is the result of cross breeding with domestic dogs.
The feral cat, which is also affected by 1080 poisonings is very destructive of native wild life, particularly ground birds and small marsupials.
It has been generally reported that there has been a build-up in native species such a wallabies, koalas and ground birds in areas of forest land where dingo populations have been reduced by poisoning.
In developed land, proper use of 1080 has not caused any significant issues in native fauna.
Giles (1975) in commenting on the use of 1080 for feral pig control, stated that there has been no evidence of damage to native fauna from 1080 poisoned pig baits, despite the abundance of macropods and seed eating birds in the areas in which it was used.
Mortalities in wild birds are frequently reported and 1080 is usually wrongly blamed. In the Armidale district where we have investigated complaints we have found losses are usually associated with the use of organo-phosphate insecticides for poisoning carcases for crows and eagle control, or grain for protection of crops. This was not unexpected as 1080 has a particularly low toxicity to avifauna and birds are particularly susceptible to organo-phosphates.
TRANS LOCATION AND PERSISTENCE IN SOILS
1080 is very soluble and is readily leached out of baits.
Hilton et al. (1969) noted that salts of monofluoroacetic acid exhibit a high degree of absorption to root tissues as well as other cellulosic materials; therefore, any sodium monofluoroacetate which is leached from baits is not likely to be carried far by the leaching water but to be held in the upper soil layers.
David & Gardiner (1966) demonstrated that monofluoroacetate breaks down in soil. They used both 20 ppm, and 50 ppm of the compound. Both steam sterilised and unsterilised soil samples were used. At the lower level no toxicity from monofluoroacetate could be detected after two weeks in unsterilised soil and at 50 ppm a lower level of toxicity was detected at 9 weeks but not in the 11th week or later. In sterilised garden soil at both dosage levels, toxicity was still evident at the end of 17 weeks when the tests were concluded.
The authors concluded'...there seems to be no grounds for condemning its use because of the fear it might leave a persistent harmful residue in the soil'.
Atzert (1971) commenting on these results stated that they were not entirely unexpected as it seemed likely that naturally occurring organisms capable of degrading monofluoroacetate should exist since several toxic plants normally synthesise monofluoroacetic acid.
Several workers, including Kelly (1965) and Goldman (1965) have isolated soil bacteria able to decompose monofluoroacetate. The organism responsible appears to be a pseudomonad which can utilise fluoroacetate as a sole carbon source. In other words, 1080 is biodegradable.
DANGER TO WATER STORAGES
Since 1080 is readily taken up by soil and plants and broken down it is not likely to be moved far by leaching water. Saito et al., (1966) monitored streams draining an area treated with 1080 rodent baits for five months after the advent without finding a trace of 1080 in the water.
BREAKDOWN IN PLANTS
Since 1080 which is leached from poison baits may be taken up by plants before breakdown by soil bacteria it is important to know its fate in plants. Preuss & Wenstein (1968) showed that plants contain an enzyme which can decompose sodium monofluoroacetate by cleaving the carbon-fluorine bond.
SUMMARY AND CONCLUSIONS
1080 is a very useful poison for the destruction of noxious animals. Nobody is compelled to use 1080 on their property. Alternative methods of control of noxious animals are available, however they are more costly, time consuming and generally less effective. In most instances, the alternate methods are also less humane than 1080 poisoning.
Due to the present high cost of labour, many landowners could not control their rabbits without 1080. The withdrawal of 1080 would almost certainly see a return to the rabbit plagues such as occurred following the last war, when rural labour was not available. This would lead to loss of production and damage to land by erosion.
Also, if 1080 were not available it is certain that other poisons would be used by landholders. These poisons such as arsenic, phosphorus, and strychnine and organo-phosphates cause more suffering than 1080 and would be more dangerous to non-target species.
1080 is strictly controlled and the poison is not available to the general public.
The use of 1080 does not cause a build-up of toxic residues in soil, water or plants.
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