Takeaways From Mexico’s Final Rebuttal on the USMCA GM Corn Case

By Timothy Wise

Mexico’s closing argument in its ongoing dispute with the United States over its restrictions on genetically modified (GM) corn and glyphosate residues in tortillas was published in translation June 19. The government argues persuasively in the 264-page document that it has the right to take such precautionary measures under the trade agreement, that the measures have had minimal impacts on U.S. corn exporters and that its restrictions are indeed based on peer-reviewed science documenting the risks of consuming GM corn with glyphosate residues. These risks are particularly elevated for Mexicans, who consume more than 10 times the corn consumed in the U.S. and do so in minimally processed preparations, such as tortillas. 

Mexico refutes the U.S. rebuttal, which failed to acknowledge or rebut that evidence, relying instead on outdated studies that do not take Mexican consumption patterns into account and are often corrupted by conflicts of interest with biotechnology companies. As Mexico states in its accessible four-page introduction:

“Mexico has demonstrated throughout this controversy that there are legitimate concerns related to risks to human health and the diversity of native maize derived from the consumption of GM maize and has presented the scientific basis for these concerns, which will be addressed in detail throughout this paper. Mexico is protecting its population, which basically subsists on corn, as it is legally obliged to do so. The United States superficially analyzes and criticizes the evidence and risk assessment prepared by Mexico, but in its criticisms, it does not present arguments backed by science to support its position, but simply disqualifies with adjectives.” (paragraph 4)

“It is truly astonishing that the United States makes a plethora of superficial, false, contradictory claims and, above all, that it fails to present the technical-scientific evidence on which its claims are based - most likely because it does not exist.” (paragraph 13)

A readers’ guide

Following is a “readers’ guide” to the document in which I focus primarily on Mexico’s defense of the scientific foundations of its policies. Quotes are from the Mexican rebuttal itself, with paragraph numbers cited in parentheses for easy reference between the Spanish and English versions of the document.

The four-page introduction to the 264-page document presents a clear summary of Mexico’s main arguments, and the detailed table of contents offers a guide to the factual and legal fallacies in the U.S. arguments. All are well-documented, with 460 references in addition to an extensive set of case-law references.

The rebuttal is supported by two appendices that refute in detail the critiques offered by the U.S. as “scientific annexes” to its own rebuttal, which were widely criticized for being incomplete and lacking scientific evidence.

The rebuttal also is supported by written testimonies from four outside experts invited to contribute:

• Dr. Michael Antoniou, on toxicology 
• Dra. Ana Laura Wegier Briuolo, on maize biodiversity and gene flow 
• Dr. Eckart Boege Schmidt, on the importance of maize in Indigenous communities 
• Dra. Dulce Espinosa De la Mora, on the cultural importance of maize in Mexico

(I have not yet reviewed their written testimonies, though some are quoted in the document.)

The factual arguments are straightforward. “Mexico explains that the United States has ignored the relevant information in the evidence presented by Mexico regarding the risks to human health, biodiversity, and the diversity of corn. Mexico correctly characterizes Decree 2023, and explains that, in fact, U.S. imports have not been affected by Decree 2023.” (16)

Mexico argues that its decree is not merely a Sanitary and Phytosanitary measure but has broader goals, including protecting the diversity of its native maize. “Mexico is protecting this gene pool along with its cultural heritage, including traditional Mexican gastronomy, which is recognized by UNESCO as a world heritage site, and safeguarding the indigenous and peasant communities of Mexico, who maintain the gene pool in a complex system of constant domestication that faces risks posed by GM maize.” (7)

Mexico again points out that the U.S. incorrectly characterizes the measures in the decree as trade restrictions. “The United States continues to erroneously refer to certain provisions of Executive Order 2023 as the ‘Tortilla Corn Ban’ and the ‘Substitution Instruction.’ In the interest of non-repetition, Mexico refers to its explanation in its Initial Submission, and merely notes that there is no ban at all, but rather an End-Use Limitation on corn; and that no action has been taken to implement the Gradual Substitution Instruction.” (9)

Mexico points out that it complied with the U.S.-Mexico-Canada Agreement (USMCA) mandate to use the “least trade-distorting measure” available to achieve a desired policy. “The measures have not affected trade between the two countries at all, since, among other things, in 2024 there has been an increase in imports of white maize from the United States.” (10) Mexico documents this in a short section of the rebuttal (pp. 182-214), noting that:

• The drop in U.S. white corn exports to Mexico in 2023 was not because of the decree but because U.S. lost market share to South Africa when Mexico eliminated tariffs to fight food inflation.
• U.S. white corn exports to Mexico increased 62% in the first four months of 2024 compared to 2023 after tariffs on South African white corn were reinstated. (211)
• Total U.S. corn exports to Mexico continue to increase, despite the decree, undermining the U.S. argument that the so-called Substitution Instruction for GM feed corn is having a chilling effect on U.S. exports. (214)

The legal arguments are more extensive. “Mexico refutes the alleged incompatibilities of Decree 2023 with the USMCA, and explains that, in any case, the measures would be exempted by the exceptions included in the Treaty itself.” (17)

Mexico points out that the U.S. declined to respond in any way to the eight written submissions by non-governmental organizations, including IATP, despite being given the opportunity to do so. “In addition, Mexico notes that, on May 3, 2024, the date on which comments to the NGO Written Opinions were due, the United States decided not to respond to the NGO Written Opinions by not submitting any documents. Perhaps this is because, for the most part, the arguments made by the NGOs are forceful and emphasize that ‘there are significant concerns based on scientific facts and 'lessons learned' in an industry that has been at best very lightly regulated.’” (11)

U.S. ignores the evidence presented by Mexico on the risks to human health, biodiversity and native maize

“Instead of refuting the evidence presented by Mexico, the United States merely characterizes it as a ‘[s]harp turn away from legitimate science,’ based on isolated statements, unsubstantiated disqualifications, and irrelevant evidence. The truth is that the United States fails to refute that Mexico clearly identified the risks associated with GM corn and glyphosate.” (20)

Mexico cites U.S. NGO submissions, especially Friends of the Earth (FOE), on the inadequacy of U.S. approvals for Mexican consumption levels. “In any case, the safety assessments made by regulatory authorities in the United States and other countries are irrelevant to the extent that they do not take into account the level of protection that Mexico has identified, nor do they consider the high consumption of corn in the Mexican diet and traditional agricultural practices in Mexico.” (27).