France will seek an immediate EU ban on imports of a genetically-modified corn made by Monsanto if a study linking it to cancer in rats is deemed credible, Prime Minister Jean-Marc Ayrault said Thursday.
But the French scientist leading the study said he would not let the European Union's food safety watchdog, EFSA, verify his results because it had approved the NK603 corn in the first place.
Scientists at France's University of Caen found that rats fed on NK603 or exposed to the weedkiller Roundup used with it, also made by Monsanto, developed tumours.
The authors of the study billed the findings as "extremely worrying," but their methodology and results and their relevance to humans have been questioned by other experts in the field.
"I've demanded a rapid procedure, in the order of a few weeks, which will allow us to establish the scientific validity of this study," Ayrault said.
"If the results are confirmed (agriculture minister) Stephane Le Foll will seek a European ban on these GMOs (Genetically Modified Organisms)."
However Gilles-Eric Seralini told a press conference at the European parliament that "It's out of the question that those who authorised NK603 carry out a counter-study of our findings as there'd be a conflict of interest."
EFSA, which authorises the sale and planting of GMOs, was asked by the EU executive Wednesday for an opinion as soon as possible, hopefully by year's end, on the study headed by Seralini.
But for EFSA to rule on the findings, it would need to see the study's original data.
NK603 is a type of corn, or maize, that has been engineered to make it resistant to Roundup and is used by farmers to maximise yields.
The authors of the study said it was the first experiment in GM food that followed rats throughout their lifespan, as opposed to just 90 days.
Premature death and tumours were far higher among rats, especially females, that had been fed the GM corn or given ordinary corn supplemented by water to which low concentrations of Roundup had been added, they said.
At the 14-month stage of experiment, no animals in the control groups showed any signs of cancer, but among females in the "treated" groups, tumours affected between 10 and 30 percent of the rodents, the study said.
"By the beginning of the 24th month, 50-80 percent of female animals had developed tumours in all treated groups, with up to three tumours per animal, whereas only 30 percent of controls were affected," it said.
Males which fell sick suffered liver damage, developed kidney and skin tumours and digestive problems.
But other scientists said the study was too underpowered, had questionable gaps in the data and raised doubts more about Roundup than the NK603 corn itself.
It entailed 200 rats divided into 10 experimental groups, of which only 20 were "controls" fed ordinary corn and plain water.
This sample size is too small to rule out statistical quirks, especially as the rats were of the "Sprague-Dawley" laboratory strain, which is notoriously susceptible to mammary tumours, said Maurice Moloney, research director at Britain's Rothamsted agricultural research station.
"The first thing that leaps to my mind is why has nothing emerged from epidemiological studies in the countries where so much GM has been in the food chain for so long" Mark Tester, a professor at the Australian Centre for Plant Functional Genomics, University of Adelaide, told the news site Science Media Centre.
"If the effects are as big as purported, and if the work really is relevant to humans, why aren't the North Americans dropping like flies?! GM has been in the food chain for over a decade over there—and longevity continues to increase inexorably."
Explore further: France orders probe after rat study links GM corn, cancer (Update)