Rats fed a lifelong diet of one of the bestselling strains of genetically modified corn suffered tumours and multiple organ damage, according to a controversial French study published today.
The report is set to reignite the debate over whether GM crops are safe.
It has already sparked a major row with scientist who claims the study has 'no value'.
Gilles-Eric Seralini of the University of Caen and colleagues said rats fed on a diet containing NK603 - a seed variety from crop giant Monsanto made tolerant to dousings of the bestselling weedkiller Roundup - or given water containing Roundup at levels permitted in the United States died earlier than those on a standard diet.
The animals on the GM diet suffered mammary tumours, as well as severe liver and kidney damage.
The researchers said 50 percent of males and 70 percent of females died prematurely, compared with only 30 percent and 20 percent in the control group.
Seralini was part of a team that flagged previous safety concerns based on a shorter rat study in a scientific paper published in December 2009 but this takes things a step further by tracking the animals throughout their two-year lifespan.
Monsanto said at the time of the earlier research that the French researchers had reached 'unsubstantiated conclusions.'
Monsanto was not immediately available for comment but the group has in the past repeatedly said its products are safe and there is no credible evidence of any health risk to humans or animals from consuming GM crops.
Seralini believes his latest lifetime rat tests give a more realistic and authoritative view of risks than the 90-day feeding trials that form the basis of GM crop approvals, since three months is only the equivalent of early adulthood in rats.
However, in an unusual move, the research group behind the research did not allow reporters to seek outside comment on their paper before its publication in the peer-reviewed journal Food and Chemical Toxicology.
It is expected to create particular waves in France, where fierce opposition to genetically modified organisms (GMOs) led to a ban on growing such plants.
France's Jose Bove, vice-chairman of the European Parliament's commission for agriculture and known as a fierce opponent of GM, called for an immediate suspension of all EU cultivation and import authorisations of GM crops.
'This study finally shows we are right and that it is urgent to quickly review all GMO evaluation processes,' he said in a statement.
'National and European food security agencies must carry out new studies financed by public funding to guarantee healthy food for European consumers.'
However, scientists from around the world have questioned the validity of the research.
Ottoline Leyser, Associate Director of the Sainsbury Laboratory, University of Cambridge, said: 'Like most of the GM debate, this work has very little to do with GM.
'The authors of the paper do not suggest that the effects are caused by genetic modification.
'They describe effects of the roundup herbicide itself and effects that they attribute to the activity of the enzyme introduced into the roundup resistant maize.
'There is good evidence that introducing genes in to crops using GM techniques results in fewer changes to the crops than introducing them using conventional breeding.
'This is unfortunately rather a subtle point and is somewhat tangential to the immediate issue.'
Anthony Trewavas, Professor of Cell Biology, University of Edinburgh, said: 'The control group is inadequate to make any deduction.
'Only 10 rodents so far as I can see and some of these develop tumours. Until you know the degree of variation in 90 or 180 (divided into groups of ten) control rodents these results are of no value.
'That is what should have been done and no doubt reflects the predetermined bias of the experimenters and the funding groups that they don’t appreciate that a control group was essential for each treatment.
'These figures for normal appearance of tumours in these rodent lines are surely available and using a line which is very susceptible to tumours can easily bias any result.
'To be frank it looks like random variation to me in a rodent line likely to develop tumours anyway.'
The French team has also been accused of making their research difficult to analyse.
Alan Boobis, Professor of Biochemical Pharmacology, Imperial College London, said: 'Some of the effects are presented in a way that makes it difficult to evaluate their significance.
'For example, there does not appear to be a statistical analysis of the mammary tumours.
'These occur quite often in untreated animals.
'One would usually also take into account the historical controls in the testing lab, in reaching a conclusion.
'The pesticide itself has been subject to long term studies in rodents by others.'
Mark Tester, Research Professor, Australian Centre for Plant Functional Genomics, University of Adelaide, said: '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?
'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!
'And if the effects are as big as claimed, why have none of the previous 100+ plus studies by reputable scientists, in refereed journals, noticed anything at all?' /dailymail.co.uk/