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Glyphosate and GMO Testing of Maseca Flours: Results and Relevancy

Editor's note: Read this article in Spanish here.

On October 9, 2018, Organic Consumers Association (OCA) reported the presence of the chemical glyphosate and AMPA, its main metabolite, in Maseca-brand white and yellow corn flour samples purchased in different regions of Mexico. Some flour samples tested as high as 94.15 percent for the presence of genetically modified organisms (GMO).

Testing was conducted by Health Research Institute (HRI) in Fairfield, Iowa (U.S.), on behalf of Organic Consumers Association Mexico (ACO). HRI  specializes in detecting and quantifying substances in food, water, soils and even the human body. Tests are performed using accredited standards, rigorous quality assurance processes and advanced technologies.

Testing methodology

HRI used the following methodology to test samples of Maseca corn flour:

• HRI TM #8 "Glyphosate and AMPA Detection by LC-MS/MS"

• Sample preparation employed a modification of the method described in Chamkasem, Narong, Cynthia Morris, and Tiffany Harmon. 2016. “Direct Determination of Glyphosate, Glufosinate, and AMPA in Milk by Liquid Chromatography/tandem Mass Spectrometry.” Journal of Regulatory Science 3 (2): 20–26.

• LC-MS/MS analysis employed a modification of the method described in Jensen, Pamela K., Chad E. Wujcik, Michelle K. McGuire, and Mark A. McGuire. 2016. “Validation of Reliable and Selective Methods for Direct Determination of Glyphosate and Aminomethylphosphonic Acid in Milk and Urine Using LC-MS/MS.” Journal of Environmental Science and Health, Part B 51 (4): 254–59. doi:10.1080/03601234.2015.1120619.

• Limit of Quantitation (LOQ) and Limit of Detection (LOD) are sub-part per billion for this method and are determined for each sample.

• Effective Glyphosate Level was calculated according to Food and Agriculture Organization (FAO) method where total glyphosate residue is the sum of the weight of glyphosate + 1.5 × the weight of its metabolite AMPA.

• HRI TM #30 "GMO Detection by PCR"

• Analysis quantitates total of all GMO corn varieties available since 1997. LOQ is 0.01%

Maseca flour test results

HRI analyzed nine products chosen from different regions of Mexico and four products from the U.S. The brands, products and origin, as well as the results reported by the laboratory are the following:

Table 1

ND- non detectable

Table 1. Results


Understanding the results

A clear correlation was observed between the presence of GMOs and glyphosate. The higher the concentration [%] of GMO, the higher the concentration of glyphosate.

In the case of the Maseca flours purchased in Mexico, three of the nine products tested contained high concentrations of GMO and glyphosate. The remaining samples showed very low or no detectable values. This is worrisome for consumers, who have no way of knowing which batches of flour are contaminated.

The concentrations of GMOs detected in the samples are so high that, for example, in Europe these products would have to be labeled as genetically modified foods (the threshold value is 1 percent).

Concerning the presence of glyphosate, the concentrations found are below the threshold proposed by U.S. and EU government regulatory agencies. However, this does not mean that they are safe. In fact, some claim there cannot be safe levels for glyphosate consumption because diseases such as cancer are multifactorial, depending on sensitivity, predisposition and other individual and environmental characteristics that can make a person ill. The problem is that even official “safe” thresholds levels are too high.

The following table presents reference thresholds for the presence of glyphosate in foods.

Table 2

Table 2. Reference thresholds on the presence of glyphosate in food


As can be seen on Table 2, according to the U.S. Environmental Protection Agency (EPA), it is safe for a person who weighs 154 lb. to consume 122.5 mg/glyphosate per day. The EU is more conservative. The EU’s chronic reference dose for a 154-lb. person is 21 mg glyphosate per day. California is more conservative yet, setting a “No Significant Risk Level” of 1.1 mg/day for a person weighing 154 lb.

The Environmental Working Group recently conducted an analysis of the safety question and concluded that a level that is protective to children, who are more vulnerable, would be 0.01 mg per day for a 154-lb. person.

The thresholds proposed by these organizations range from 0.01 to 122.5 mg of glyphosate consumption in one day for a 154-lb person. The range between the extremes is very large and could be larger if the most recent studies on the toxicity of glyphosate are considered.

A study published in 2017 by Mesnage et al. found that a dose of only 700 ng/day would trigger early stages of non-alcoholic fatty liver disease in a 154-lb. person. This, assuming people would respond to glyphosate at doses similar to rats.

A relevant question is what is the basis of government decisions to set such high “safety” thresholds for glyphosate. Two arguments for explaining this can be made:

Related to crop production. The threshold values established by U.S. and EU agencies were initially much lower than the current ones. In some cases, regulators have been influenced more by the needs of agrochemical companies to sell their products than by the need to protect the health of the public.

For instance, a paper by Bohn, et al. (2014) states the following: “The legally acceptable level of glyphosate contamination in food and feed, i.e. the maximum residue level (MRL) has been increased by authorities in countries where Roundup-Ready GM crops are produced, or where such commodities are imported. In Brazil, the MRL in soybean was increased from 0.2 mg/kg to 10 mg/kg in 2004—a 50-fold increase—but only for GM-soy. The MRL for glyphosate in soybeans has been increased also in the U.S. and Europe. In Europe, it was raised from 0.1 mg/kg to 20 mg/kg (a 200-fold increase) in 1999, and the same MRL of 20 mg/kg was adopted by the U.S. In all of these cases, MRL values appear to have been adjusted, not based on new scientific evidence, but pragmatically in response to actual observed increases in the content of residues in glyphosate-tolerant GM soybeans.”

Related to crop consumption. Threshold levels have been based on outmoded models of toxicology and biochemistry that failed to take into account the properties of endocrine/hormone disruptors such as glyphosate, which can have health damaging effects at even the very low levels. Safety studies are also likely to be underestimating glyphosate toxicity because these studies usually examine the effects of glyphosate alone, while in practice it is always used in combination with surfactants that significantly increase toxicity (Annett et al 2014, Moore et al 2012). Another factor to consider is that most safety testing examines a single endpoint, most commonly cancer. There are many other disease states that are highly debilitating, such as NAFLD, that could easily be missed all-together in current safety assessment protocols.

Taking all of these considerations together, we can conclude that the “safety” thresholds set by governments around the world, even well-intentioned governments like that of California and organizations like the Environmental Working Group, grossly underestimate the toxicity of glyphosate. Further, more conservative thresholds such as the level reported to trigger NAFLD should be used as the threshold for what could be considered safe exposure to this chemical.


In the case of glyphosate concentrations found in Maseca flours and, having as background the previous discussion on safety thresholds, we can conclude that the Maseca products OCA and HRI analyzed are potentially hazardous to human health.

OCA tested a total of 13 masa flour and tortilla samples, finding as much as 30 ng glyphosate per gram in some masa flour samples. The average content was 5.0 ng/g.

A typical tortilla weighs about 30g. Thus, on average a tortilla will contain 30 x 5.0 = 150 ng glyphosate. A typical diet might include at least six tortillas per day, containing a total of 912 ng glyphosate. Thus, through tortilla consumption alone, a person could potentially consume 132% per day of the glyphosate needed to trigger Non-Alcoholic Fatty Liver Disease.

Additional research is needed to assess this more fully, but current evidence points to a clear health hazard associated with the consumption of Maseca corn flour. this. The levels of glyphosate designated as safe by the U.S. EPA, the EU and even the California authorities are unrealistically high. The safety assurances associated with these thresholds do not serve the public, but create a false sense of security and thus create a hazard to the public for the benefit of agrochemical companies.

There is growing evidence that regulators both in the U.S. and Europe have been unduly influenced by Monsanto and more broadly by the chemical and ag-biotech industry (Baum Hedlund, 2018). This financial benefit for agro-chemical companies is gained at the expense of the public’s health.

There is another core issue, in addition to health and safety: It is of great concern that glyphosate is present at any level in masa flour. It was found in five out of the 13 samples tested. The widespread presence of agrochemicals in masa flour indicates that this brand is not using “natural” methods, but is using instead industrial / chemical farming methods with all of their associated social, environmental and health impacts.

As consumers, we must demand the differentiation of the flour, masa and tortilla in terms of the corn with which it is made: with or without GMO and glyphosate.

“Yo quiero mi tortilla 100% nixtamalizada” — “I want my tortilla 100% nixtamalized”

ACO’s  campaign for healthy, high-quality tortillas was launched in 2017. Through the campaign we expect to:

• Contribute to the protection of the nixtamalized tortilla and the recognition and inclusion of the communities that produce the nixtamalized tortilla.

• Advocate for of the exercise of the full Right to Food (in Mexican law) through the consumption of nixtamalized tortilla.

• Provide enough information for consumers to make decisions in benefit of their health while being aware about the characteristics of low quality corn flour industrialized tortilla.

As a result of the in-depth study of the corn-tortilla system, it became clear that we had to discuss other essential quality criteria in tortillas, in addition to nixtamalization. Thus, the campaign also promotes tortillas made from Mexican, criollo, pesticide-free corn. This is why we performed tests on Maseca, the leading brand worldwide selling industrialized corn flour and tortillas.

For suggestions on how to avoid Maseca and other contaminated corn flours, read this.


Annett, R., Habibi, H. R. and Hontela, A. 2014. Impact of glyphosate and glyphosate-based herbicides on the freshwater environment. – Journal of Applied Toxicology DOI 10.1002/jat.2997.

Bøhn, T., Cuhra, M., Traavik, T., Sanden, M., Fagan,, J., Primicerio, R.: Compositional differences in soybeans on the market: Glyphosate accumulates in Roundup Ready GM soybeans. Food Chemistry 153: 207–215, 2014.

Mesnage R, et al, “Multiomics reveal non-alcoholic fatty liver disease in rats following chronic exposure to an ultra-low dose of Roundup herbicide.” Scientific Reports (a Nature publication). doi:10.1038/srep39328, Jan. 2017.

Moore, L. J., Fuentes, L., Rodgers, J. H., Bowerman, W. W., Yarrow, G. K., Chao, W. Y. and Bridges, W. C. 2012. Relative toxicity of the components of the original formulation of Roundup (R) to five North American anurans. – Ecotoxicology and Environmental Safety 78: 128-133.

Baum Hedlund, 2018. Monsanto Papers. Consulted: September 2018.

Mariana Ortega is campaign director for Organic Consumers Association Mexico (ACO), a project of US-based Organic Consumers Association (OCA). OCA is a US-based 501(c)(3) nonprofit consumer advocacy organization focused on food, agriculture and environmental issues. To keep up with this campaign and other consumer news and alerts, sign up for our newsletter.