Controversy has erupted over new French scientific research claiming that genetically modified corn and the herbicide Roundup increases the chance of lab rats developing tumours and dying prematurely.
The paper, published by journal Food and Chemical Toxicology overnight, prompted the French government to ask a health watchdog to investigate whether the strain of GM corn posed a threat to human health and imports should be suspended.
But independent scientists criticised the researchers for conducting the tests on rats highly prone to tumours and using an unconventional analysis described by one academic as a "statistical fishing trip".
The paper found low levels of both GM corn strain known as NK603 and Roundup — the world's best selling weed-killer — could cause severe health effects over a rats' 2-year life-time, including mammary tumours and kidney and liver damage.
Up to 50 per cent of males and 70 per cent of females tested in the study died prematurely, compared with 30 per cent of rats in a control group.
The engineered corn, which is resistant to Roundup, and the herbicide itself are both products of agricultural biotechnology multi-national Monsanto.
But critics pointed to a 1979 study on the same type of rat that found an overwhelming proportion developed tumours before the age of two, even if otherwise healthy.
They questioned the researchers failure to use a standard statistical analysis to examine whether the results differed from what might be expected through random variation.
The French government responded to the paper by asking the National Agency for Health Safety to investigate the finding.
"Depending on [its] opinion, the government will urge the European authorities to take all necessary measures to protect human and animal health," three ministers said in a statement.
In a press conference at the University of Caen in Normandy, lead scientist Gilles-Eric Seralini said the study was the first look at rats over their normal lifespan of two years.
"For the first time ever, a GM organism and a herbicide have been evaluated for their long-term impact on health, and more thoroughly than by governments or the industry," he said. "The results are alarming."
Professor Seralini is a long-time critic of genetically modified foods and has previously attacked Australian authorities for failing to get independent assessments of GM foods.
Earlier this year he drew criticism for posting on his website a certificate declaring he had been named the International Scientist of the Year 2011.
The certificate was removed from his website after it was revealed it was issued by the International Biographical Centre of Cambridge, which invites scientists and professionals to buy certificates declaring they are world leaders.
The strain of GM corn at the centre of the new study is sold, but not grown, in Australia. It is used in products such as corn oil, corn syrup and cornflour.
Regulator Food Standards Australia and New Zealand has approved more than 50 GM products to be imported into the two countries. Farmers in some Australian states — particularly Western Australia, but also Victoria and NSW — grow GM cotton and canola.
Scott Kinnear, director of GM-sceptic organisation the Safe Food Foundation, said the new research exposed a critical deficiency in the local regulatory process.
"To ensure that the public is protected against further exposure, there is an urgent need for a fundamental overhaul of the regulatory framework," he said.
"I think before we dismiss Seralini's research it is important for him to have an opportunity to come back against his critics. It is far too easy to just dismiss it."
Food Standards Australia New Zealand said it had not seen compelling evidence of a safety risk.
FSANZ chief scientist Paul Brent said it would look at any new research, but its confidence in the safety of GM products was backed by regulatory counterparts in the US, Canada, Japan and Europe.
GM crops are widely grown in the US, Brazil and China but remains a hot-button issue in some European countries.
"As far as I am concerned there has never been a study that has shown in any way that there is a safety concern," Dr Brent said.
"There is no plausible scientific reason to think something is going to happen. You look at a comparison of GM food and non-GM food and they are almost exactly the same."