The yellow, sometimes orange, hue is a common sight on Hawke's Bay paddocks.

It's from glyphosate, the active ingredient in a weed spray used in New Zealand for 42 years, usually under the brand Roundup.

But its safety was called into question after a jury in the United States ordered Roundup manufacturer Monsanto to pay $NZ440 million in damages to a school caretaker who always used Roundup, and is now dying of cancer.

Monsanto strongly disputes any link with cancer, saying glyphosate only affects plants, does not persist in the environment and does not bio accumulate.


It said glyphosate breaks down quickly and harmlessly in the soil, but not everyone agrees because of an unusual chemical bond between phosphorus and carbon.

"The breakdown of glyphosate into actual harmless mineral salts requires the presence of an extremely rare bacteria in the soil, because the bond in glyphosate it a really unusual one," Hawke's Bay eco-nutritionist Phyllis Tichinin said.

Federated Farmers Hawke's Bay President Jim Galloway said glyphosate was central to farming systems and when applied correctly was harmless.

He said it was also greener than traditional spray-free farming systems.

"It reduces our carbon footprint and helps water quality by using it," he said.

"When you work ground up there is a release of carbon dioxide into the atmosphere."

There are many studies suggesting glyphosate is safe, but an International Agency for Research on Cancer report said glyphosate was a probable cause of cancer, though its findings have been widely criticised.

Massey University weed scientist Dr Kerry C Harrington said there was "a compelling case" that there was no issue with Roundup.


"It seems very unlikely that glyphosate causes cancer, bearing in mind there has just been a court case in America that said 'yes it does'," he said.

"But that is a jury case with members of the public. They get very confused when complicated toxicology concepts are put across."

But Tichinin said many of the positive studies could not be trusted.

"We are not actually getting objective science for most of the safety studies for glyphosate.

"The companies that want to register chemicals are allowed to submit their own data and studies for safety.

"They pay for those studies and then the US Environmental Protection Agency and other environmental agencies around the world do not have the staff, the funding or the political will to actually evaluate those studies," she said.

"And they are under time constraints, so things get slipped through.

"So basically we are dealing with bought science. We are dealing with tobacco science.

"These studies, when they are released which is infrequently, for actual objective, non-funded evaluation by toxicologists and scientists, they are being found to be faulty."

Both sides of the debate criticise the cancer research agency's findings, though for different reasons.

Tichinin said the report did not go far enough in saying glyphosate was definitely a carcinogen in animals.

"We base most of our assumptions about carcinogenicity on animal studies," she said.

"So how is it, it can be a proven carcinogen in animals but we still think it doesn't cause cancer in humans?

"We are not being consistent."

However the agency was found to have excluded from its final report multiple scientists' conclusion that there was no link between glyphosate and cancer in laboratory animals.

Here in New Zealand, a government-commissioned review found glyphosate was not a food safety issue for consumers, in agreement with a chorus of bodies such as the European Food Safety Authority.

Late last year the multi-agency US Agricultural Health Study was published. It tracked 52,000 spray applicators and 32,000 of their spouses for 20 years and found no link between glyphosate and cancer.

Monsanto's Roundup has long been on the radar of anti-GE activists, because it was the spray genetically-altered crops were designed to resist.

GE-Free NZ Hawke's Bay spokesman Adrian White said independent research is needed.

He said while many farmers were tied to the economics of glyphosate in their farming systems, there was an economic advantage should the nation distance itself from glyphosate.

"New Zealand's record now of exporting organic produce is going pretty well and we're getting a good reputation in lots of markets for both horticulture and beef and lamb," he said.

"If glyphosate was wound back, that reputation would grow."

But if glyphosate was banned, it could be replaced by sprays that are proven poisons. And with its use so obvious in our fields, more research is needed to remove the cloud of confusion over its safety.

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