A high-ranking New Zealand scientist is calling on our environmental regulators to recognise the possible cancer risk associated with the popular weed killer glyphosate.

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Massey University associate professor Andrea ‘t Mannetje sat on an elite World Health Organisation (WHO) working group in 2015, which found the chemical was a "probable carcinogen". But that report has been ignored by New Zealand regulators.

Glyphosate is the most widely used weed killer in the world and is the active ingredient in popular brands like Round Up.

The working group, which consisted of 18 expert scientists from all over the world, reviewed studies associated with weed killer and found there was "limited" evidence of cancer in humans exposed to the chemical, and "sufficient" evidence of cancer in experimental animals.

Speaking for the first time about her work on the subject, Ms 't Mannetje said the public has a right to know about the potential cancer concerns.

"The human evidence suggests from epidemiological studies that exposure to glyphosate, particularly long-term exposure over multiple years, is associated with Non-Hodgkin's lymphoma," she says.

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"I think people probably change their behaviour once they know there is concern about a specific chemical, and people have the right to know so that they can make their own decisions."

However, regulators at the New Zealand Environmental Protection Agency (EPA) have decided to ignore that report, and have commissioned their own study into the chemical.

That report, carried out by a single New Zealand scientist, Wayne Temple, concluded that glyphosate is "unlikely to be genotoxic or carcinogenic in humans".

The EPA put forward Clark Ehlers, their Acting General Manager of Hazardous Substances, to respond to the queries from 1 NEWS.

"The New Zealand EPA stance on that is that glyphosate is safe to use, provided the instructions on the labels are followed," he says.

"The WHO IARC report looked at the inherent properties of that chemical and did not really consider the use pattern or how glyphosate is generally used, and thinking about how people are exposed to glyphosate."

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While the New Zealand EPA has dismissed the WHO report and the chemical remains available for purchase and use, there has been plenty of action overseas, including bans, restrictions or other limitations in at least 30 countries, including the Netherlands, Portugal and Italy.

While in the US, several courts have ruled it does cause cancer, ordering the manufacturer to pay hundreds of millions of dollars in damages to claimants dying of Non-Hodgkin's lymphoma, and thousands of other cases are due to be heard on the same claim.

The manufacturer, Monsanto, now owned by German firm Bayer, continues to strenuously deny any cancer link and has appealed the court decisions.

Ms 't Mannetje continues to appeal to the EPA to change the chemical's classification.

"I think it would be good if the EPA classifies this chemical as a suspected carcinogen, because that really accurately reflects what the scientific evidence is for this chemical," she says.

"The New Zealand public has the right to know this."

That's not on the cards for now and with neither side backing down, the weed killer continues to fly off the shelves.