Scientists have hit back against the criticism levelled at the research linking the world’s best-selling weedkiller and a strain of GM maize – both developed by Monsanto – with tumours, multiple organ damage and premature death in rats.

The peer-reviewed paper, published yesterday in Food & Chemical Toxicology Journal, was the first to examine the long-term effects of Roundup and Roundup resistant NK603. Scientists from the University of Caen, France, found that rats exposed to even the smallest amounts developed  mammary tumours and severe liver and kidney damage as early as four months in males, and seven months for females, compared with 23 and 14 months respectively for a control group.

Other scientists were quick to question the methodology used by the team of researchers, led by Prof Gilles-Eric Séralini, with criticism centring on the size of the control group and the breed of the rat used in the study.

Now Dr Michael Antoniou, a reader in molecular genetics and member of Criigen – the Committee of Research & Independent Information on Genetic Engineering – has vigorously refuted questions raised by fellow scientists about the robustness of the study.

Researchers had come under fire from Prof Tom Saunders, head of the nutritional sciences research division at King’s College London, who said the breed of rats used in the study, the Sprague-Dawley, was very prone to mammary tumours – particularly when food intake is not restricted.

“The SD rat was used in the original glyphosate toxicity studies,” Antoniou said.

“In addition, many studies – including many from industry – on GM foods use SD rats. Based on this history of use, it was appropriate to use this strain too. If it was the wrong strain to use here then it was wrong in many previous GM food safety feeding studies conducted by industry and upon which marketing approval was granted.”

He continued: “The key is that there were both quantitative and qualitative differences in the tumours arising in control and test groups. In the former they appeared much later and at most there was one tumour per animal, if at all.

“In the latter case, the tumours began to be detected much earlier (4 months in males; 7 months in females), grew much faster and many animals had two or even three tumours.

“Many animals in the test groups had to be euthanised for welfare legal reasons due to the massive size of the tumours; none of the control animals had to be euthanised but died in their own time. One should not ignore these biological facts.”

Regarding the rats’ diets, Antoniou said the animals had unrestricted access to food and water, and there was no difference in consumption or drinking levels between controls and test groups, apart from the group exposed to the highest Roundup concentration drank less.

Further criticism centred on the size of the control groups. Anthony Trewavas, professor of cell biology at the University of Edinburgh, said the control group was inadequate to make any deduction, and were of no value without knowing the degree of variation in a control group of 90 or 180 rodents.

“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,” he warned. “To be frank, it looks like random variation to me in a rodent line likely to develop tumours anyway.”

But Antoniou said the two-year experiment followed international OECD guidelines. The rodents in the experiment were divided into 10 groups of 20 animals, with nine of those groups exposed to Roundup or NK603. “Standard practice is for the control group to be matched in size to the experimental groups. The experimental groups were 20 animals and therefore the control group should be 20 animals.

“Trewava’s statement is not correct. From the 20-animal control, you can get a measure of tumour frequency in the control group. You don’t need to look at hundreds of animals. If he believes this, then he should also agree that the studies done by others – including industry – are also invalid.

“The key thing is that there are big differences between the tumour frequencies in the control and the experimental groups. Claims that the results are just the result of random variation in a rat line that has a high frequency of tumours is not valid.

“The evidence for this is that the differences between the groups are much larger than the standard deviations of the two groups. In Seralini’s study, the differences are so large that it is not necessary to use a statistical test. It is obvious.

“This study used more rats in test groups, for a far longer duration than any previous investigation employed by industry to obtain approval for this and other GM crop products.”

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