I don't understand how you can say GMO food is safe, when farmers are spraying glyphosate on their crops. Glyphosate becomes systemic in the plant and cannot be washed off, and recent studies show a strong link between glyphosate and breast cancer. http://www.ncbi.nlm.nih.gov/pubmed/23756170 Furthermore, glyphosate is a chelating agent, which means it is binding to key nutrients in the soil, making them unavailable for the crops that are being grown. Therefore, those crops are going to be deficient in those nutrients, as proven in studies that have compared the nutritional values of GM corn and nonGM corn. Glyphosate also destroys the beneficial bacterial environment of the soil so that plants have a weakened immune response to diseases. All of this translates to inferior nutritional quality of GM crops. http://www.naturalnews.com/040210_gm_corn_march_against_monsanto_glyphosate.html So my question again, how can you say that GM foods are safe and nutritionally identical to nonGM foods??

Expert response from Marian Bleeke, P.h.D.

Global Residue and Exposure Strategy Lead, Bayer Crop Science

Friday, 08/11/2013 20:04

Your first question involves breast cancer, and I’d recommend you review a response that my colleague John Swarthout provided to a similar question posed on this site.

Regarding your other question, it is true that glyphosate is a chelating agent, but that does not imply that it makes nutrients “unavailable in the soil.” Let me explain why. First, chelation is a natural and important process in soil.  Metals are mostly present in soil as solids and need to be dissolved to be taken up by a plant. Chelation increases the solubility of metal ions, reduces their toxicity, and makes them available for uptake by plants.  Organic acids and amino acids, such as citric acid and glycine, are naturally occurring chelators that are present in soil and play an important role in micronutrient uptake.  Plants also exude strong chelators that bind to micronutrients and make them available for update.  It all makes for a complex mixture in soil of metals and chelators, of which glyphosate is just one small component. 

The degree to which metals and chelators bind depends on the relative strength of their interaction and their concentrations, and it adjusts as the mixture changes. In other words, binding does occur but it is not permanent and each molecule can bind only a specific number of ions at any one time.  For instance, one glyphosate molecule will bind no more than one manganese ion. So amounts of glyphosate and metal ions are important parts of the equation. Glyphosate primarily stays in the top 6–12 inches of soil, with maximum concentrations in that zone of several parts per million (ppm), and declines over time, with a typical half-life of about a month.  In contrast, the concentrations of micronutrient metal ions in soil are much higher. Metals such as iron and aluminum are in the range of 7,000–300,000 ppm or higher; others, such as manganese (20–3,000 ppm) and zinc (10–300 ppm), are present in lower concentrations but still significantly higher than those of glyphosate.  Because metal ion concentrations are so much higher than glyphosate's, with much of it in insoluble soil particles, glyphosate binds tightly to soil and shows very little uptake into plants or movement through soil.

There is not any indication that these low levels of glyphosate are having an impact on the uptake of metal ion micronutrients into crops.  All studies comparing GM crops to their non-GM counterparts to date have shown no biologically relevant differences in micronutrient levels.  One excellent review publication from multiple public-sector scientists can be found here. The authors concluded most of the literature available indicates that mineral nutrition in glyphosate-resistant crops is not affected either by the glyphosate-resistance trait or by application of glyphosate, and that yield data on glyphosate-resistant crops do not support the hypotheses that there are substantive mineral nutrition or disease problems that are specific to glyphosate-resistant crops.

I realize that this accusation about nutrient deficiencies with GM crops is readily found on the Internet. These allegations are not, however, backed by a credible data set.  (See a response from Kevin Folta here.)

There are many environmental studies related to glyphosate, and there is no indication of harm to microbial structure of the soil.  Remember that microbes are ubiquitous, and each type responds to changes in the environment.  For instance, they would undoubtedly be different between a location with loamy soil that is irrigated and in a higher average daily temperature than one with clay soil not being irrigated and with a lower average temperature.  So be careful when you hear about changes in microbes. Furthermore, if plants were weakened, then high yields would not be sustainable.  But we also have data. All plants are evaluated for germination characteristics, crop growth and development from emergence to maturity, including vegetative and reproductive stages, crop yield and crop response to abiotic stressors, diseases and arthropods.  For example, for corn from our phenotypic study, we commonly evaluate:

Finally, a comprehensive paper was published in 2012 by Dr. Duke (USDA) on these glyphosate topics; it can be found at J. Agric. Food Chem 60 (2012): 10375–97.