France 24 reports that “France has asked its national health body to verify a study released this week linking Monsanto’s NK603 genetically modified corn to cancer in rats, saying the results of the probe could lead to an ’emergency suspension’ of NK603 imports.” NK603 is modified to be resistant to Monsanto’s popular herbicide Roundup (glyphosate), thus allowing farmers to use the product as a post-emergencce herbicide without damaging feral crops.
The results of this study are inherently controversial. Regulators have set relatively high tolerances for it because few biological effects have previously been observed even at very high doses. For example, EPA’s Reference Dose (RfD) for glyphosate is 0.1 mg/kg/day, a factor of 10 below the highest No Observed Exposure Level (NOEL). The NOEL applies to biological effects that are generally agreed to be non-adverse, not cancer.
EPA also has set a primary drinking water standard, called a Maximum Contaminant Level ([MCL), of 700 parts per billion (ppb). This level is precautionary; according to EPA, “Some people who drink water containing glyphosate in excess of the MCL over many years could experience problems with their kidneys or reproductive difficulties.” The multiple qualifications in this statement (some people, over many years, could experience) hint at the extent of this precaution.
How could a chemical that has been shown to be relatively benign cause cancer?
According to France 24:
French scientists led by Gilles-Eric Seralini at the University of Caen in Normandy unveiled a study that said rats fed with NK603 corn or exposed to the weedkiller used with it developed tumors…
The study, published in the peer-reviewed journal Food and Chemical Toxicology, says it is the first to look at rats over their normal lifespan of two years.
This is not true, however. EPA’s Reference Dose, published in 1987, was based on several studies in animals conducted over their 2-year lifetimes. With respect to cancer, a 2-year study was performed and it revealed virtually no tumorigenic effects, even at very high doses:
Charles River CD-1 mice (50/sex/dose level) were fed diets containing glyphosate at dose levels of 0, 1000, 5000, or 30,000 ppm for 24 months. The incidence of renal tubule adenomas observed in the male mice exceeded that of the controls (0/49 controls; 0/49 low-dose; 1/50 mid-dose; 3/50 high-dose).
Note that the highest dose — 1,000 ppm — is almost 1,500 times greater than than the MCL.
A re-evaluation of the renal tumor slides prepared from the male mice indicated the presence of an additional adenoma in the control group and malignant tumors in the two higher dose groups. Therefore, the incidences of the reevaluated data are 1/49 control adenoma; 0/49 low; 1/50 mid, carcinoma; 3/50 high, 1 adenoma, 2 carcinomas. It was the judgment of two reviewing pathologists that the renal tumors were not treatment-related. In addition, the inclusion of a tumor in the control group eliminated statistical significance for the high-dose group.
EPA, which by policy and practice errs on the side of classifying substances as carcinogens if even benign tumors are observed in animals subjected to very high doses that humans will never experience, nonetheless deemed the evidence inadequate to determine whether glyphosate could cause cancer in animals.
The French paper is published here.