The government's proposal to treat grain free of charge using bromadiolone has prompted mixed reactions from industry groups, with the Nature Conservation Council today opposing plans to use the poison.
Council spokesperson James Tremain said they are concerned the poison, not currently licensed for use in wide-spread agricultural settings, will make its way through the eco-system via birds and insects who eat the dead mice.
"It goes right through the food chain," Mr Tremain said. "It accumulates into insects which will then bio-accumulate through the food chain. These things can be very dangerous."
Farmers said the use of the strong poison is warranted to deal with the plague though cast doubt on the availability of enough stock to treat significant areas.
So what sets the so-called 'napalm' of rodenticides, as the Agriculture Minister called it, apart from the current poison used, and why is it so controversial?
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CSIRO researcher Steve Henry explained bromadiolone is an anticoagulant bait which stops the animal's blood from clotting and causes internal bleeding.
"It takes a period of up to three days to kill the animal and during that time the toxins are coming through its faeces, so any animal that eats those feces is potentially exposed to the toxin," Mr Henry said.
"Also, after the animal dies the toxin doesn't break down in the animal, so any animal that comes along and eats that animal is then subject to be poisoned by the poison still in the mouse or rat."
Zinc phosphide is the only poison currently approved for agricultural use and doesn't leave intoxicated corpses behind, Mr Henry explained.
"When an animal is poisoned by zinc phosphide, the phosphide is converted to phosphene in the mouse's stomach and that phosphene gets triggered up into the blood and goes off and damages the major organs and the animal dies," he explained.
"Most phosphene is used up in the act of doing that damage to the major organs and what isn't used up dissipates out into the environment as a gas after the animal dies."
"So the chances of secondary poisoning with zinc phosphide are very, very low."
The gas, phosphene, that poisons the animal and can be released after it dies is seriously harmful to humans in large quantities, and is therefore not appropriate for domestic use in confined spaces.
Bromadiolone on the other hand has not been allowed to be used in primary production since 2017 when its former permit wasn't renewed because of the poison's impact on non-target species.
An emergency permit submitted by the government is under review by the APVMA to allow the poison to be used in the grain treatment plan.
The association said in a statement that they are assessing the potential impacts of the use of bromadiolone, including considering its effect on non-target species as it continues to deliberate.
The NSW government intends to use both a double dose of zinc phosphide and the bromadiolone to tackle the plague which has devastated crops.
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