The Department of Conservation (DOC) said it was deeply apologetic if members of the public were exposed to pellets from one of its 1080 drops.
The Medical Officer of Health, DOC, and the Environmental Protection Agency were all investigating a complaint from trampers that they were hit with the toxic pellets on the Nydia track in the Marlborough Sounds.
A condition of consent was a 20 metre exclusion zone on both sides of the track.
Conservation services manager for the Sounds Roy Grose said they were still unsure whether it was a technical malfunction, or weather that may have caused the pellets to fall in that area.
"There were baits that went on the tracks so obviously we did not do that well and for that we apologise.
"I'm not exactly sure the legal ramifications, obviously if we've breached the condition of our consent then that's a major concern for us."