Lab mice fed Monsanto’s genetically modified corn and water exposed to their herbicide Roundup led to tumors and organ damage, reports a French study that could have resonance in the debate over GMOs.

The peer-reviewed study, the first of its kind to show potential damage from lifetime exposure to GMOs, appeared in the journal Food and Chemical Toxicology.

Gilles-Eric Seralini of the University of Caen and colleagues said rats fed on a diet containing NK603 – a seed variety made tolerant to dousings of 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.

Monsanto has tried to deflect the study by asserting that his longtime criticism of this researcher reflects a bias. But the study did get a peer review, though some independent scientists have criticized the study for using the wrong kind of rat.

The debate over GMOs moves into the political arena this year. A ballot measure in California, Prop 37, would mandate labeling of the presence of GMOs in all processed food products. GMO products have already been banned in France, and forcing labeling in the most populous state in the union would probably lead to that becoming industry standard for the US market. Retailers also face activist pressure to stop stocking GMO food on their shelves.

California Right to Know, the coalition supporting Prop 37, jumped on the lab mice study with this statement:

The results of this study are worrying. They underscore the importance of giving California families the right to know whether our food is genetically engineered, and to decide for ourselves whether we want to gamble with our health by eating GMO foods that have not been adequately studied and have not been proven safe.

Monsanto has already spent $7 million trying to stop Prop 37.