Roundup Ready Corn May Cause Tumors in Rats: Is Monsanto’s Genetically Modified Corn Hazardous to Your Health?

French researchers at the University of Caen have published a study showing that rats fed on Monsanto’s NK603 genetically modified (GM) Roundup Ready corn, or exposed to the Roundup weed-killer itself, developed massive tumors and suffered major organ damage over time. The highly controversial study, published on Sept. 19 in the peer-reviewed journal Food and Chemical Toxicology, has caused both intense outrage amongst GM supporters and a sense of fierce justification within the anti-GM community.

NK603, a GM corn developed by Monsanto to withstand high levels of Roundup, contains a glyphosphate (Roundup’s main active ingredient)-tolerant enzyme called EPSPS, derived from the bacteria Agrobacterium tumefaciens. Under normal conditions, glyphosphate inactivates this enzyme, thus preventing the production of the amino acids tyrosine, phenylalanine, and tryptophan in plants. EPSPS is present in plants, bacteria, and fungi, but not in mammals, which are incapable of synthesizing their own aromatic amino acids. NK603 is marketed for consumption by both humans and livestock.

Gilles-Eric Séralini and colleagues fed groups of rats on a diet containing various amounts of NK603—grown with or without Roundup—or with water containing Roundup at levels permitted in the U.S. The researchers showed that 50 percent of males and 70 percent of females died prematurely, as opposed to only 30 percent and 20 percent in the control groups (fed only non-GM corn), respectively. Additionally, animals on the GM corn diet developed tumors, and suffered severe liver and kidney damage more frequently than control animals.

In other studies, Séralini showed that in vitro, Roundup decreased testosterone production in rat testicular cells treated with the weed-killer at “the range in some human urine and in environment to agricultural levels.” While only high doses were found to be toxic, low doses did result in an endocrine impact. In another study on three microorganisms used in the dairy industry, Séralini showed that while glyphosphate alone seemingly had no effect on the microorganisms, the full Roundup formulation, which includes multiple adjuvants, had an “inhibitory effect on microbial growth and a microbicide effect at lower concentrations than those recommended in agriculture.”

France has ordered a review of Séralini’s most recent study by its National Agency for Health Safety (ANSES), and has sent the research to the European Union’s food safety agency (EFSA). A joint statement by France’s health, environment, and farm ministries said that, “Based on the conclusion… the government will ask the European authorities to take all necessary measures to protect human and animal health, measures that could go as far as an emergency suspension of imports of NK603 maize in the European Union.”

While the study’s results have already had a global impact, there is also significant criticism of the scientific and statistical methods employed by the researchers.

The language of the report was not entirely scientific, and apparently, “All data cannot be shown in one report, and the most relevant are described here.” While this is not an unusual statement, in this case, relevant data did not seem to include proper reporting of results from control groups, or analyses showing statistically significant differences between control and experimental groups.

“The photographs are very graphic, but do not include a control,” stated Professor Maurice Moloney, Institute Director and Chief Executive at the U.K.’s Rothamsted Research.

Sprague-Dawley rats, the animals used in Gilles-Eric’s study, are frequently used in cancer research due to their propensity to naturally develop tumors. Professor David Spiegelhalter, Winton Professor of the Public Understanding of Risk at the University of Cambridge stated, “All the comparisons are made with the ‘untreated’ control group, which only comprised 10 rats of each sex, the majority of which also developed tumors… there is no proper statistical analysis, and the numbers are so low they do not amount to substantial evidence.”

“Ten rats per group is a small number. For example, is the death of three out of ten controls compared to five out of ten males in the treated group statistically significant?” said Dr. Wendy Harwood, a senior scientist at the U.K.’s John Innes Centre. Given the sizes of some of the rats’ tumors, some scientists also criticized the study as inhumane.

Other researchers claimed the study was designed to look for specific outcomes, rather than to objectively test for all possible outcomes. Much of this criticism stemmed from the fact that Séralini is a well-known GMO opponent whose scientific objectivity has been called into question in the past.

However, while the study certainly has holes, it also demonstrates the real possibility that Monsanto’s Roundup Ready GMO corn, and the Roundup chemical itself, may damage mammalian health in the long term, even at low doses. Rats in the experimental groups still fared worse than control animals. And while Monsanto and other GM supporters claim that there is no evidence of harm due to GM foods in humans, we haven’t had enough time to truly draw conclusions—GM food has really only been in our diets for the past 15 years.

In a statement that seems to mirror much of Europe’s opinions of GM agriculture, France’s Jose Bove, vice-chairman of the European Parliament’s commission for agriculture, said, “This study finally shows we are right and that it is urgent to quickly review all GMO evaluation processes.”


By Genevieve Weber



–        Gilles-Eric Séralini, et al. 2012 study published in Food and Chemical Toxicology: Long term toxicity of a Roundup herbicide and a Roundup-tolerant genetically modified maize

–        The reactions of various experts to GM maize causing tumors in rats

–        NK603 information from Monsanto


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