GM Free Cymru

Mexico should reject the introduction of GM maize

Date Added to website 9th April 2014

Salk Institute scientist reveals why he opposes GMOs in a dramatic letter to the country's President

Lic. Enrique Peña Nieto
 Presidente de la República Mexicana
 Palacio Nacional Edif. 10 P.B. Col. Centro, Del. Cuauhtémoc, C.P. 06067 México, D.F.

Lic. Enrique Martínez y Martínez Secretario de Agricultura, Ganadería, Desarrollo Rural, Pesca y Alimentación
 Avenida Municipio Libre 377 Col. Santa Cruz Atoyac, Del. Benito Juárez, C.P. 03310 México, D.F.

Ing. Juan José Guerra Abud
 Secretario de Medio Ambiente y Recursos Naturales
 Blvd. Adolfo Ruiz Cortines 4209 Col. Jardines en la Montaña, Del. Tlalpan, C.P. 14210 México, D.F.

My name is David Schubert. I have a doctorate in immunology and serve as a Professor at the Salk Institute for Biological Studies in San Diego, California, considered one of the top medical research institutions in the world. As a member of this institution I actively work on the development of drugs to treat Alzheimer's and stroke. Therefore, I possess first-hand knowledge of molecular genetics, toxicology and safety testing involving new chemical and biological entities. I am also knowledgeable about the technology of genetically modified organisms (GMOs ) and have published articles in leading scientific journals on GM plants and their effect on human health.

Recently, I've written letters, like this one, that have contributed to the debate on the introduction of GM eggplant in India and Bangladesh. In both cases, the process of introduction [of the transgenic varieties] has been suspended. Since eggplant is native to these countries, just as corn is a native crop of Mexico, the situations and problems related to the use of GM technology in both regions are nearly identical.

Therefore, I am convinced of the need for Mexico to follow the advice of scientific panels of scientists and government review in India, Bangladesh, the European Union, Japan, South Korea and the vast majority of the free countries of the world, and reject the introduction of transgenic maize. This conclusion is based on several reasons discussed below.

Points 1 through 5 are exceptionally important but have been treated by other people. I will focus, then, on the impact of GM maize on human health, which falls within my area of ​​expertise. To my knowledge, the following statements are documented in scientific and government publications: 1) No necessity. The [diverse] corn crop [in Mexico] is not severely threatened by pest infestations.

2) High environmental risk. Corn is native to Mexico and transgenes will unquestionably pollute and degrade its natural populations. In addition, Mexico is the center of biodiversity and a global treasure of plant varieties capable of fighting disease and climate change. These capabilities would be diminished if GM seeds are introduced into their territory.

3) Higher costs. The annual purchase of seeds, as opposed to seed saving, will increase production costs at all levels of the food chain. Small farmers and peasants, who are the most important nodes of the agricultural production system in Mexico, will be most affected by the high costs and potential crop failures because some varieties of GM maize are not the most appropriate in all planting sites. The transgenes entering the local populations eventually contaminate all local varieties.

4) Social and political dependency. Once the foreign companies control the seed market for any plant [in Mexico] they will continue introducing GM seeds of other species and therefore wield enormous power through political processes over the peasants who constitute a large segment of the Mexican population. This has already happened in the U.S. where the seed companies are the main financial support of both political parties (Republicans and Democrats) and have designated persons in positions of high power to dictate national and international agricultural policies.

5) Irreversible. When GM maize is introduced into Mexico, even on a small scale, it will irreversibly contaminate native varieties. This is unequivocal and the only way to prevent it is to not allow GMO plantings.

6) Bt proteins pose human health risks. Transgenic corn expressing the Bt crystal proteins is also resistant to herbicides so the chemicals required for cultivation are compound the threat to the health of those who consume it. I delve into these issues that are of great importance for a country like Mexico where maize is consumed in large quantities and often un a manner involving little or no processing. However, I would first like to dispel some myths that are used by the proponents of GM maize to argue that this is harmless. It is claimed that, as there is no human illness associated with the consumption of Bt corn in the United States, it should be a safe food to eat. This conclusion is invalid for several reasons. In the first place, only a small fraction of Bt corn produced [in the U.S.] is consumed directly: the vast majority is used as livestock feed and to produce [vegetable] oil, high fructose syrup, and ethanol; none of these products contain the Bt proteins. The corn consumed that has Bt proteins is more than anything else likely to be eaten as an ingredient in a highly processed food, e.g., chips and other snacks that are not [supposed to be] important components of a [healthy] diet.

In contrast, the Bt proteins of GM maize cultivated in Mexico would be consumed directly and in larger quantities because corn is the staple food and is therefore an important element of the Mexican diet. Additionally, according to the richness of traditional food, GM maize will be prepared following an infinite number of recipes leading to potential chemical changes of Bt proteins and causing unknown toxicity and immunogenicity effects. In this regard, even if there have been some studies of GM maize food safety, these have not controlled for the health effects [we surmise may be associated] with different methods of food preparation [like we would expect to be the case in Mexico's more diverse recipes involving corn].

Second, it is logically false to assert that since there is no evidence of disease related to the consumption of GM products, that these are therefore safe for human health. [This is not a scientific statement and] Making such an assertion requires a well-designed experiment with proper controls [and has not been done.] Moreover, this problem is more serious because the foods derived from GM crops will not be labeled as such [so controlled studies are nearly impossible].

Therefore, perhaps the greatest concern about the introduction of any GM product on the market should be that, even when it causes harm to human health, it would be impossible to detect due to the lack of epidemiological studies and technical limitations. For example, to detect a disease epidemic requires an incidence of at least twice the normal rate. If the GM maize was harmful and caused a disease like Parkinson's, which has an incidence rate of almost 20 new cases per year per 100,000 people, then in Mexico some 25,000 annual new cases would be diagnosed and tabulated to identify a significant increase and yet there is no way to associate the disease directly with some GM crop consumption.

Furthermore, the symptoms of many diseases related to environmental factors take decades to appear [and are therefore cumulative effects]. Clearly, once the GM maize is released commercially there will be no way to monitor adverse health effects caused by the product itself. Biotech companies are aware that for this reason they will never be held accountable for the damage to human health that their products might cause.

Most varieties of GM maize are modified to be insect-resistant (Bt varieties) or herbicide-resistant (e.g., glyphosate). Bt protein and glyphosate have been documented to cause damage to human health which will be discussed separately [for each transgenic technology] in the following paragraphs.

Bt Corn and Human Health

The Environmental Protection Agency (EPA) of the United States recommended extensive testing on the safety of Bt crops [1], but due to lack of federal laws that require rigorous safety tests for GM foods in the U.S. this has never been undertaken [2]. The United States does not require any proof that GM food is safe for human consumption before marketing.

There are at least four mechanisms by which introduction of the Bt gene in the maize genome may cause damage. These include: (1) random insertion of transgenes in plant DNA and resulting unintended consequences [3]; (2) alterations in plant metabolism because of the inserted protein which results in new toxic products; (3) direct toxicity of the Bt proteins; and (4) the immune response obtained by the [presence of the] Bt protein. Documented scientific evidence for all four of these mechanisms exists. An example of the first is the discovery of unintended alterations, such as the synthesis of nine known carcinogens in GM tobacco plants [4]. For the second mechanism, studies have documented abnormal levels of production of a molecule called Bt lignin [5]. This feature was discovered thanks to the dramatic changes that began to be observed in the hardness of the stem of this [GMO] plant. Many varieties of Bt corn possess this characteristic so it is likely that the increase in the production of lignin is related to the expression of the Bt protein itself and not due to [random] mutations caused by the same genetic modification process [2]. There are probably more unforeseen changes in GM crops, and many of them have already been registered [6]. The direct toxic and immunological dangers of Bt proteins are discussed next.

Allergies are complex responses of the immune system to foreign substances, and its symptoms can vary unpredictably from one individual to another. Bt toxins, for their part, have been used for some time as aerosol insecticide sprays for many crops, but [the toxin] can be washed off the plant and contain[s] a less toxic form of the protein than that produced by the GM plant – in which the toxin is in all consumable parts of the plant [and not just the surface]. The aerosol spore consists of Bt toxin that must be activated in the digestive tract of insects. In contrast, the Bt toxin produced in maize is an activated form of the protein that does not require any modification to become toxic. Therefore, it is much more powerful than the variety used in aerosols.

On the other hand, there is strong evidence that the Bt proteins have provoked strong immune reactions in some farm workers [7], probably because these are composed of amino acid sequences that are homologous to certain well-known allergens [ 8, 9 ]. Moreover, the concentration and quantity of active Bt toxins people would be consuming by eating Bt corn is much higher than the levels of exposure agricultural workers are subjected to.

In support of the results found among humans, when [other] animals are exposed to Bt toxins, these also act as a potent 'immunogen', triggering immune system responses in the blood and intestine [10, 11, 12 ]. More recently, there was a long-term feeding study in the U.S. with pigs, which have a resemblance to the human digestive system. The pigs were fed a mixed diet that included GM maize Bt proteins. After five months, drastic stomach inflammation levels in were found in the GM-fed pigs were found and females had heavier uteri than those given the no GM diet [13].

Additional studies with animals have shown that Bt toxins cause direct tissue damage. For example, Fares and El- Sayed proved that mice fed Bt potato had abnormal intestinal cells structure [14 ]. Other studies reported histopathological changes in both liver and kidney in rats consuming Bt corn [15], and changes in the levels of urea and urine proteins of rats fed Bt rice [16].

The research cited above demonstrates that the family of Bt proteins may act as allergen or toxicant in animals and some humans. This is of great importance to the health of the Mexican population because, if the introduction of Bt corn is approved since there will be such a huge [unparalleled] number of people who will consume Bt toxin at levels many thousands of times higher than ever before in the short history of GM technology.

As genetics and the health status of an individual determines the response to foreign proteins such as the Bt toxin, and Mexicans represent a very heterogeneous population with different genetic composition, age, and health, the consequences of using Bt maize will be unpredictable. The sickest people will undoubtedly be the most vulnerable to the toxic and immunological reactions. Since the ability of Bt toxin to cause allergic responses in some individuals is ambiguous, it is virtually certain that within the Mexican population, a large number of people consuming GM maize will develop such severe allergies and even immune responses resulting in anaphylaxis and possible death.

The number, however, cannot be predicted and, as there is no system to track this type of adverse reactions within a population, if Bt maize is grown commercially, their genetic presence in a food that is calorie source basic for a major section of Mexico will be irreversible. The introduction of this transgenic crop, therefore, must be prevented.


In addition to high levels of Bt toxins, most GM maize varieties have also been modified to be resistant to herbicides. While a large number of herbicides are in use the most studied is glyphosate since it is the active ingredient in so many different products. If corn or soybeans GMOs are introduced in Mexico, there will be a huge increase in the use of this herbicide in Mexico; after the introduction of GM crops in the United States, glyphosate use increased tenfold between 1996 and 2009 (from 27 million to 250 million pounds)[17]. A similar increase was observed in Argentina [18].

The relevance of this is that contrary to the assertions of its producers, glyphosate and its active formulation are harmful to human health. Like many environmental toxins, many years passed before we could identify the problems it causes, but these are now being documented in various scientific publications in the public domain. Some important risks are discussed immediately below along with other facts that are rarely included in the debate.

1) Glyphosate spray contains more than the herbicide and instead includes a mixture of compounds that help glyphosate to penetrate all the tissues of the plant including those we eat. Additional compounds called surfactants are not disclosed (and remain as trade secrets) and therefore do not undergo safety tests nor are they monitored on plants or in human drinking water. This is the case despite the fact that the surfactants are much more abundant in the formulation of the herbicide than the glyphosate itself. These, then, are not assessed chemicals whose human and animal consumption will increase dramatically once the GM maize is introduced in Mexico [19]. In the U.S., the EPA frequently performed tests to detect glyphosate in drinking water and groundwater, but it has then several times increased the allowable limits of these residues in food at the request of chemical producers.

2) The herbicide spray applied and all its components remain inside the plant and are consumed. They are not washed away!

3) Within 10 to 15 years, the weeds will be more resistant to glyphosate, so that even more toxic herbicides will be required for the production of GM corn. The next in line is the herbicide 2,4-D, a known carcinogen [20, 21].

4) Evidence of glyphosate found in the urine of several people in certain areas [22].

5) Part of the increased levels of glyphosate in drinking water, food and animal feed is due to the fact that it is now used as a drying agent, which is applied directly on the plants before harvest [23].

6) Some of the toxic effects of glyphosate that have been published are listed below, and all of them can or have been extrapolated as a serious risk to human health:

a. When ingested in food or water, glyphosate kills bacteria that form part of the beneficial intestinal microbiota, resulting in the growth of pathogenic microbes[24]. b . In support of the first point, for nine months when pigs were fed transgenic food treated with glyphosate increased intestinal inflammation compared to control animals was observed [13]. c . A large increase in tumor formation was documented in rats fed for two years with herbicide resistant GM maize [25]. d . More and more cases of human illness related to glyphosate exposure are being reported in countries like Argentina [18]. e . Even in small interventricular concentrations, glyphosate causes defects in embryonic development of amphibians and chickens; defects similar to those observed in studies of Argentine human populations [18, 26, 27]. f . Glyphosate has negative effects on testosterone production in rats [28, 29], and promotes the growth of cancer even in human cells in concentration at levels that are below detectable in the blood and urine of some individuals [30].

The publications cited above represent only a fraction of the extensive evidence that on the whole demonstrate real and projected harmful effects of glyphosate on human health. Glyphosate levels will quickly increase in food and the environment if GM maize is introduced to Mexico. Nothing will have served its purpose if, within 10 to 15 years, glyphosate is no longer an effective herbicide as different weeds develop resistance, as has occurred in different regions of the planet. Is it worth it, then, to take this type of risk in a country like Mexico?

My conclusion is therefore that GM maize is of no benefit to your country, but rather a great danger to the health of Mexicans.

It would be a profound mistake if GM maize was approved to enter the food supply in Mexico.


Professor Dr. David Schubert Salk Institute for Biological Studies La Jolla , California 92037


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