The Environmental Protection Authority is shrugging off criticism of its processes by a group of mainly Wellington scientists.
Writing in the latest edition of the New Zealand Medical Journal, the scientists argued the authority used unsound methodology in its comments on the herbicide Glyphosate, which is used in many weedkillers including Roundup.
It had been criticised as probably carcinogenic by a specialist agency of the World Health Organisation.
This was rebutted in a report by the authority.
The scientists writing in today's publication say this rebuttal was unsound.
Massey University's Professor Jeroen Douwes said the herbicide should be restricted.
"I don't think that for private use we actually need Glyphosate, and I think for private use we could in fact introduce a ban, whether city councils should be using Glyphosate, I'm not sure, but there are alternatives. I think a ban could be considered."
But the authority says the scientists themselves have produced a deficient argument.
In a statement, the Environmental Protection Authority said the article contained very little new information, and relied significantly on media references and opinion.
It acknowledged public concern around glyphosate, but said as a scientific organisation its decisions must be based on evidence and data.
"EPA's decision-making processes are more extensive and complex than implied in the commentary. The Hazardous Substances and New Organisms Act requires us to follow a set process when considering chemicals for reassessment, which is costly.
"The process ensures we spend taxpayers' money wisely, and that we address those chemicals which present the biggest threat to human health and our environment, in priority order," the statement said.
The authority added glyphosate was on a watchlist, but other chemicals remained more dangerous.
"For example, paraquat (a weed killer) is currently undergoing reassessment, to be followed by chlorpyrifos (a pesticide), because both chemicals are determined to be considerably more harmful to people and our environment than glyphosate at the present time. This reflects the EPA's commitment to protecting human health and environmental safety."