Australia's top cancer body is calling for an independent review into the world's most popular weedkiller, which has been linked to non-Hodgkin's lymphoma.
Cancer Council Australia is concerned there has not been an independent or formal review of the chemical glyphosate - the active ingredient in Roundup - in more than two decades.
The chemical is the most widely used herbicide on the planet and is popular with home gardeners and farmers in Australia and New Zealand.
In 2015, the World Health Organisation body, the International Agency for Research on Cancer (IARC), classified glyphosate as "probably carcinogenic to humans".
"We are concerned that this issue's not being taken seriously enough in Australia, particularly by the agricultural industry," Cancer Council Australia chief executive Dr Sanchia Aranda said.
"The IARC report is independent and does suggest that there is absolutely a reason for concern."
Glyphosate was patented by Monsanto four decades ago, sparking a revolution in agriculture.
Instead of ploughing or tilling fields farmers started spraying glyphosate to kill weeds before planting their next crop.
Roundup was marketed to farmers and home gardeners across the world as safe and effective.
More than 500 glyphosate products are sold in Australia today.
"It is the safest herbicide that's ever been developed," said Scott Partridge, the vice-president of Bayer, the company which recently bought Monsanto for $US63 billion ($NZ98b).
School groundskeeper wins landmark case
In August, a jury in California awarded $US289 million to California man Dewayne Lee Johnson, who claims Monsanto's weedkiller was a substantial factor in causing his terminal cancer, and that the company failed to warn of the potential risk.
The trial blew the lid on a decades long campaign by Monsanto to protect its flagship product. A trove of company documents, known as the Monsanto Papers, reveals a history of the company ghost-writing articles in support of glyphosate, attempts to undermine the IARC finding, and internal concerns about the safety of Roundup.
In one email from 2003, Monsanto's lead toxicologist warns the company cannot say that Roundup is not a carcinogen because they have not done the necessary tests.
"For the last 20 or 30 years, Monsanto has engaged in a systematic and deliberate campaign to attack any science that says their product is not safe and to attack any scientist that has the courage to say something," said Brent Wisner, a lawyer on the legal team which won the landmark case.
"They have a corporate culture that has zero interest in safety. It has only an interest in maintaining the ability of them to sell this product."
Monsanto said the documents revealed in court were "cherry-picked" and insisted more than 800 studies and reviews showed glyphosate was safe.
The company is challenging the jury verdict.
In America, more than 9000 people are now suing, claiming Monsanto's Roundup products led to their cancer.
Retired farmer John Barton is one of them.
"Monsanto was telling us it was safe," he said.
Mr Barton has non-Hodgkin's lymphoma and believes it is the result of him spraying Roundup on his cotton farm in Bakersfield, California.
He believes Monsanto knew for decades that Roundup could present a potential cancer risk.
"I would like to see them admit that they had hidden this for a long time and that they realised it was not safe and that they should have warnings that let people make that decision for themselves whether they want to use that product or not," he said.
Australia's regulator, the Australian Pesticides and Veterinary Medicines Authority (APVMA), has not formally reviewed glyphosate since 1995.
The regulator did a scientific evaluation of the IARC report and decided there was no reason to formally review glyphosate.
"Glyphosate remains safe to use in the Australian environment," APVMA chief executive Dr Chris Parker said.
Concerns have been raised about the regulator's independence because it is primarily funded by the chemical companies it regulates.
"Governments have an obligation to fund these kinds of agencies with public money so that that transparency and independence can be assured," Dr Aranda said.
The APVMA insists it acts independently of industry.
"Our decisions are our decisions, they're not able to be influenced by politicians or industry," Dr Parker said.
What's in the Monsanto Papers?
The Monsanto Papers are millions of internal documents released as part of US lawsuits against the company over claims its flagship product, Roundup, causes cancer. This is what the papers reveal:
- Monsanto ran a long-standing, aggressive campaign to protect its flagship product, Roundup.
- The papers show Monsanto knew of the potential risk of Roundup's key ingredient, glyphosate, for decades.
- In 2003, Monsanto's lead toxicologist warned they could not say "Roundup is not a carcinogen" because they hadn't done necessary testing to prove that.
- Over the years Monsanto attempted to kill off independent assessments of glyphosate.
- Monsanto launched a PR campaign to undermine a World Health Organisation cancer agency study that classified glyphosate as a "probable human carcinogen".
- Monsanto ghost wrote a scientific paper and a magazine article in support of glyphosate and paid experts to appear on panels.
- Monsanto continues to insist Roundup is safe and they say that is backed by hundreds of scientific papers.