A new study shows tiny doses of best-selling weedkiller Roundup raise the chances of cancer in rats. What are the implications?

The GM debate was reignited this week with the publication of the world’s first long-term peer-reviewed study into the health impacts of a genetically-modified maize crop together with the world’s most popular weedkiller, Roundup.

Scientists at the University of Caen fed rats varying doses of Monsanto’s NK603 maize, which is resistant to Roundup, as well as water that contained traces of Roundup at levels deemed safe by European and US authorities. The rats developed cancer much earlier than the control group, their tumours were larger, and there were more of them. Female rats were affected the most - up to 80% had developed mammary tumours by the end of the trial.

“All the previous studies, which only went up to 90 days, missed the impact completely,” says Dr Michael Antoniou, reader in molecular genetics at King’s College London.

The study drew criticism from some scientists who said a control group of 20 rats was not big enough. Monsanto was more cautious, promising to review the study, while pointing to EU research which concluded “there is no scientific evidence associating GMOs with higher risks for the environment or for food and feed safety.”

In the US, where 70% of processed foods contain GM material, the study’s findings will be seized upon by the anti-GM lobby. In the UK, use of GM crops is limited to GM-based animal feed, and the study is most likely to maintain public opposition despite growing industry calls for a re-examination of GM’s merits.

The more immediate impact may revolve around a reassessment of the potential risks of glyphosate-based pesticides, including Monsanto’s Roundup. The world’s best-selling herbicide, Roundup is extensively used by British farmers, and widely available in UK garden centres. It was recommended by Gardeners’ Question Time as recently as last week.

Maybe it shouldn’t be. The University of Caen team found rats that ate conventionally-grown maize but whose drinking water contained even a tiny proportion of Roundup developed tumours at the same rate as those who ate larger quantities of NK603 and drank larger doses of Roundup.

EU safety levels for glyphosate, the active ingredient in Roundup, are 10,000 times higher than the lowest dose tested in the study (50 nanograms per litre).

“The results of the study clearly demonstrate that lower levels of complete agricultural glyphosate herbicide formulations, at concentrations well below officially set safety limits, induce severe hormone-dependent mammary, hepatic [liver] and kidney disturbances,” the scientists concluded.

The researchers pointed out that it is glyphosate itself which has been approved for commercial use, and not Roundup, which includes other ingredients to help it penetrate plants more efficiently.

Defra does not monitor glyphosate levels in drinking water, leaving it up to the UK’s 26 water boards to decide whether monitoring is necessary and to conduct tests only if they think it is. Eleven currently test for glyphosate, feeding back their results to Defra’s drinking water inspectorate. The DWI said this week that all 11 boards have reported levels within EU safety limits.

What makes the study so potentially significant is that it calls the safety levels themselves into question. “If not restricted, Roundup should certainly be re-evaluated. I’ve taken enough of a message from this paper to say we should take it seriously,” says Mustafa Djamgoz, professor of cancer biology and Imperial College, who was not involved in the study.

Patrick Holden, founding director of the Sustainable Food Trust agrees. “It’s calling into question the world’s most popular herbicide and the effectiveness of the regulatory process. It’s one of those landmark pieces of research which could shift public attitudes,” he says.

None of this, of course, helps farmers who desperately need to increase production to feed a world population that will have grown to nine billion by 2050, according to the UN. “Roundup is an essential part of modern agriculture, removing previously highly labour-intensive tasks,” says NFU combinable crops advisor James Mills. “The merits of questioning the validity of such a readily-available product are debatable.”