One of the trampers affected by a 1080 poison drop on a track in the Marlborough Sounds says the incident could threaten New Zealand's clean, green image.
Simon Caley and his wife were walking the Nydia Track on Saturday when 1080 pellets started to fall around them.
Mr Caley says they read a warning sign about the drop before they started on their hike, but a Department of Conservation employee reassured them that they would be fine. The couple was told that the helicopters wouldn't be dropping near the track itself because an exclusion zone was in place.
But Mr Caley says one of the pellets landed next to his wife's foot and she smelt a strong smell of cinnamon - used to repel birds - and felt dust in her mouth.
He says cases like this could really damage New Zealand's 100% pure image and it was downright dangerous.
"If I'd been a foreign tourist - particularly one with a fairly litigious nature - right now I could be filing a lawsuit. And think of the damage this could do to our tourist industry here. I'm not going to do that, but I am concerned that this sort of thing can happen and it's just unbelievable.
"We should be able to walk through our forest without being dumped on by chemical toxins, it's just ridiculous."
Mr Casey says he expects a full apology from Conservation Minister Nick Smith.
Dr Smith says the error is regrettable and the Conservation Department will investigate how it happened. However, the minister says he is in favour of the bait used to trap possums and stoats and what happened to the couple on Saturday is an isolated incident.
"I remain a very firm supporter of 1080 as an essential tool for dealing with pests and ensuring the survival of our native species and I don't consider this to be a particularly significant or worrying element.
"When you are doing tens of thousands of hectares, it is inevitable there will be some errors. The important thing is, there is no risk to public health."
DoC's Sounds area manager Roy Grose says the error was most unfortunate and the department deeply regrets it.
The Medical Officer of Health for Nelson-Marlborough, Ed Kiddle, says the incident is of concern, as the pellet drop was in breach of its conditions specifying a 20-metre exclusion area along the track.
"It's a poisonous substance and so hence it's used with a number of controls. The risk varies, the highest risk is if the pellets are eaten or ingested."
However, Dr Kiddle says in this case, he believes the risk to have been relatively small.