Are Bt Toxins Safe to Eat?

Anne Sherrod

The pesticides Bt and Roundup loom large amongst the many concerns regarding genetically modified (GM) foods. The bacterium Bacillus thuringiensis (Bt) was once hailed as a completely natural, safe insecticide, because it produces toxic substances that target certain insects, but do not affect animals or humans. But are the toxins safe for humans to eat? That is the question that arose when agrochemical companies set about modifying and transferring genes from the bacterium into food plants, which then make their own version of the insecticide.

Once used in Canada as a roadside weed killer, Roundup is now sprayed on crops that have been genetically engineered to tolerate it, so the fields can be chemically weeded. This trait, too, is produced by modifying and transplanting genes from bacteria to food plants. Though the crops survive the Roundup, they also absorb it, so it enters our food.

Today in Canada, corn, soybeans, canola, and sugar beets are said to be the only genetically modified foods on the market. However, GM seeds for other grains and vegetables have been registered and approved for consumption by Health Canada.

The main active ingredient in Roundup is the herbicide glyphosate. Many animal studies since the 1980s have demonstrated birth defects and other reproductive problems from glyphosate and Roundup. Most recently, a study published in 2010 reported birth defects in frog and chicken embryos from exposure at doses much lower than those used in agricultural spraying.1

In recent years a research team at the University of Caen (France), working with human cells cultured in the laboratory, has been steadily documenting damage to DNA, cell respiration and cell membranes, as well as endocrine disruption, due to glyphosate and Roundup. In some cases, these effects were observed at concentrations similar to what is allowed in food. For instance, endocrine disruption began at a concentration of 0.5 parts per million, but the US Environmental Protection Agency allowed 400 parts per million in some food and animal feed.2

Now, in 2012, the University of Caen team, led by Professor Gilles-Eric Séralini, has published research showing that a modified Bt toxin from GM foods, called Cry1Ab, kills human cells.3 Another modified Bt toxin in the same experiment, Cry1c, did not kill the cells.

This study was the first to use the modified Bt toxins from genetically modified plants. Previous studies had all been carried out on the toxins produced naturally by the bacteria. “The toxin gene is modified in all GMOs before the genetic construction – truncated, mutated, and thus it is never exactly the wild toxin,” says Professor Séralini.4

The researchers say that more experiments are needed to determine how these effects on cells in the laboratory relate to actual people. Such studies are desperately needed. Recently medical researchers at Sherbrooke Hospital in Quebec found the Cry1Ab toxin in the bloodstream of 55 out of 69 pregnant and non-pregnant women they tested.5 Eighty per cent of the fetal blood samples from the expectant mothers contained Cry1Ab. How did it get there? Neither the women tested nor their partners had been in direct contact with pesticides. The doctors state in their report: “Given the widespread use of GM foods in the local daily diet (soybeans, corn, potatoes), it is conceivable that the majority of the population is exposed through their daily diet … trace amounts of the Cry1Ab toxin were detected in the gastrointestinal contents of livestock fed on GM corn, raising concerns about this toxin in insect-resistant GM crops … there may be a high risk of exposure through consumption of contaminated meat.”

The Quebec medical researchers also tested for glyphosate in the above-mentioned blood samples, but found none. The University of Caen researchers tested four Roundup formulations, and found they were all more toxic than glyphosate alone. This implicated various additives in Roundup that have previously been claimed to be “inert.” At least one of them, POEA, is not only toxic in itself, but also increases the toxicity of glyphosate in several ways.

GM foods have been on the market in Canada since 1995. While there have been earlier studies showing the potential for serious health effects, it has taken this long to start tracking down some of the mechanisms involved. Meanwhile our government agencies waltz the public around with studies that are too few, too short-term, based on sloppy assumptions and too often purveyed by the very merchants of these artificialized foods.

Resistant weeds and insects mean increased exposure to toxins

Weeds and crop-eating insects in fields of genetically modified crops are getting hammered with the same pesticides year after year. The result, since about 2005, has been fields choked with glyphosate-tolerant weeds, and the onslaught of a voracious Bt-resistant corn rootworm.

Many farmers have responded by using more and more Roundup, or adding more toxic herbicides such as 2,4-D. So much Roundup is being used that in 2011 the US Geological Survey reported that glyphosate can be found in rain and rivers in agricultural areas of the Mississippi River watershed, and even in the air where it is heavily used.

The response of the GMO industry has been to develop seeds with new and more implanted genes. Right now in Canada, corn seeds are available that contain two modified Bt genes, as well as the modified gene for Roundup tolerance. GM crops with tolerance to 2,4-D herbicide are said to be on the way.

Researchers at the University of Caen emphasize that multiple modifications in GM foods, and the substances they produce, interact with each other. The effects cannot be known unless they are studied in the same mixtures that occur in GM foods. The Caen team has already discovered interactions between the Bt toxins and Roundup, but for the most part, the ballooning mixtures in GM foods remain unstudied and their effects unknown.


Anne Sherrod is a Director of the Valhalla Wilderness Society.

[From WS Summer 2012]


1.       Paganelli A, Gnazzo V, Acosta H, López, SL Carrasco AE, “Glyphosate-Based Herbicides Produce Teratogenic Effects on Vertebrates by Impairing Retinoic Acid Signaling, Chem Res Toxicol, Aug 9, 2010.


2.       Gasnier C, Dumont C, Benachour N, Clair E, Chagnon M-C, Séralini, G-E, “Glyphosate-based herbicides are toxic and endocrine disruptors in human cell lines,” Toxicology 262

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