Updated 10.22am: Infant formula exporters are doubtful police will ever catch the person behind the so-called 1080 threat.

Today's the day someone says they will start putting the poison in infant formula, if the Government hasn't stopped using the pesticide to kill possums.

Police are investigating letters sent to Federated Farmers and Fonterra, from a person warning they'll contaminate infant formula if the government doesn't stop using 1080 pesticide.

Infant Formula Exporters' Association Chairman Michael Barnett is confident in the security around New Zealand's plants and processes.

But he's not holding out hope for an arrest.

"I'd be surprised if they do, I think anybody can make a threat the way that this person has, they've got the publicity that they want for the issue but nevertheless the chances of catching these sorts of nutters is pretty remote."

Deputy Commissioner Mike Clements says there's no lack of suspects.

"People who are of interest in the investigation, and they number in the hundreds, in fact nearly 2000 of them."

But Mike Clements concedes it's a possibility the culprit will never be found.

He says police are aware it could have been a hoax and aren't seeing anything at the moment that could change that.

"We've by necessity had to treat it as a serious threat. We have and we will continue to do so."

Barnett is reiterating New Zealand has sound processing systems and good security.

"I think that the public and consumers should feel pretty safe that, yes there's a threat, and no I don't think that anybody could get through the security that we have."