"But that said in concentrated doses it does have the power to kill and that is frightening for parents that buy milk formula to feed their children.''
The owner of Hamills, a Tauranga fishing and hunting store, described it as "disgusting".
"We're not fans of 1080 here at all but that's not the way to operate," owner Stacy Whiteman said.
"That's completely disgusting. There's no justification for anything like that.
"We absolutely do not condone that sort of thing."
Police today said the person or people who wrote the letters threatened to make their threat public if the Government did not meet their demand by the end of this month.
Police National Headquarters said a full investigation began in November, with an Auckland-based team called Operation Concord involving up to 36 police staff.
Mike Clement, Police deputy commissioner of national operations, said although it was possible the threat was a hoax, it must be treated seriously. He encouraged the person or group to make themselves known.
"The letter writer may not have really considered the implications of their actions when this communication was drafted," Mr Clement said.
Several specialist groups and support agencies, including MPI, were involved.
Federated Farmers was also helping with the investigation.
Mr Clement said authorities were using all available resources to resolve the issue but wanted the public's help.
"You might be aware of someone who has strong views [about] 1080 and has made threats," Mr Clement said. "Please make contact with us."
"This criminal threat is designed to cause fear in order to generate a domestic policy outcome," Ministry for Primary Industries deputy director general Scott Gallagher said.
Yet he said he was confident New Zealand infant and other formula was "just as safe today" as it was before the threat was made.
"This type of threat does occur from time to time internationally," he said.
However, it was the first such threat received in New Zealand.
Mr Gallagher said Kiwis could be proud of the country's food safety model, which was among the world's best.
"Since this threat was made, security and vigilance has been significantly increased," he added.
He said "all the relevant players in the supply chain" had strengthened security after the threat.
He said MPI and industry partners confirm "there is no 1080 in infant and other formula."
Mr Gallagher said a new testing regime enhanced already strong testing and food safety measures.
He said industry partners including retailers had strengthened food safety since the threat.
Mr Clement said police treated the incident as a "crime of blackmail" rather than a terrorist act.
No particular brand or company's formula was targeted.
Mr Clement said the investigation commenced in secret but it was time to ask for the public's help, and police also believed the threat was low, so there was no need to go public before.
He said police had always treated the case "very seriously" despite starting inquiries out of the public eye.
"There are many other factors to consider, one of which has been food safety."
Mr Clement would not say where the threat was sent.
Fonterra chief executive Theo Spierings said the dairy industry had thrown its full weight behind the police and Government investigation.
He said the threat was a "despicable act".
His main priority was to protect consumers and "robust" testing had not shown any sign of the chemical.
"Our product is safe, as an industry we will be continually working together."
