Steffan Browning relaxes on the Picton foreshore. The former Green MP's long-term battle against the use of weedkiller glyphosate may be vindicated by a EU decision this week.

The European Union this week refused to renew the license for a weedkiller that has been in widespread use in New Zealand for the past 40 years.

The key ingredient in chemical giant Monsanto's Roundup, glyphosate is the most widely used weedkiller in history. The 15-year European license for glyphosate expired in 2016 and the EU has knocked back a temporary five-year license extension.

More than 1.3 million people from seven countries had petitioned the European Union for a moratorium on the use of glyphosate based on its links to cancer.

Glyphosate's pervasive residues were often found at more than legal limits in soils, common food products and even people across the UK and Europe.

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The EU is close to a total ban, a huge step resisted by Monsanto and many of the world's farmers who claim there is no viable alternative in weed control.

Monsanto's Roundup weedkiller has leaped off shop shelves for 40 years. An EU decision could bring a ban on the glyphosate ingredient key to its popularity.

Prompted by concerns from local authorities about the use of glyphosate in weed management, the New Zealand Environmental Protection Authority last year commissioned a report into its possible cancer links.

Poisons expert Dr Wayne Temple and his colleague from the National Poisons Centre, Michael Beasley, gave its use a green light. They said glyphosate was "unlikely" to be carcinogenic and should not be classified as a mutagen or carcinogen under the HSNO Act.

In a public health report tabled just before the election, then Marlborough Green list MP Steffan Browning claimed New Zealand's environment protection authorities had failed the country with shoddy research into glyphosate.

"New Zealand authorities appear to be ignoring the evidence, which raises serious questions about government systems and risk assessment processes," Browning and fellow researcher Jodi Bruning said in the report.

Browning said authorities tasked with regulating harmful products should heed the best science, such as findings by the International Agency for Research on Cancer (IARC). The IARC had determined glyphosate products were a probable human carcinogen.

"The IARC is the world's leading authority on cancer, which the NZ EPA cites as an authority," Browning said.

He said the EPA appeared to ignore its own terms of reference for evidence review, and an Official Information request showed the NZ EPA Review was significantly edited by NZ EPA and Ministry for Primary Industries (MPI) staff.

EPA communications advisor Michael Pearson said glyphosate was on the EPA's reassessment "watch list".

"This means we are constantly monitoring its status and international developments," Pearson said.

New Zealand's arable and horticulture industries were highly dependant on the use of glyphosate. Federated Farmers arable industry group chairman Guy Wigley said if a ban were to occur in New Zealand, it would jeopardise the country's ability to be competitive, particularly in grain and seed production.

"It would be a huge loss to New Zealand if for some vague off-chance it was seen as questionable if that wasn't founded in fact," Wigley said.

"There's a bit of argy-bargy between the Europeans and Americans around genetic qualification and glyphosate has probably got caught up in some of the politics," he said.

"It's not used here in the same way it is in America where glyphosate is sprayed over genetically modified crops. We don't use it in that way, we use it between one crop and the next, generally. It's very effective and very safe, so far, and for a chemical that's so widely used you'd think there would be a definitive answer whether it was safe or not."

Wigley said alternative chemicals were less user-friendly, more expensive and "a backward step".

Christchurch has ended the use of glyphosate in its parks and reserves. There has been heated public debate at Waiheke and Nelson over its use by contractors working for local authorities.

Earlier this month, local boards in Auckland were given the ability to intervene under new contracts to make children's parks and playgrounds free of glyphosate.

Marlborough District Council reserves and amenities manager Jane Tito said a range of herbicides including glyphosate were used by contractors on reserves and waterways to control weeds.

"We will be interested in the decision in Europe," Tito said, "and we will be guided by what the EPA decides."