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Are There Pesticides in Some GMOs?

GMO Myth 3: GM Crops Contain Poisonous Insecticides


Silverije via Wikipedia

It is often claimed that food made from genetically modified crops contains harmful insecticides which cause health problems when ingested. Is there any truth to this claim? Does eating genetically modified organisms (GMOs) expose you to pesticides?

Which GMOs Allegedly Have Insecticides?

The first thing to consider in addressing this question is to determine what GMOs this claim refers to. As noted in a previous article, GMOs are not a single category. Describing a plant as a GMO doesn’t really tell you anything substantial. It is just refers to the technique to make the crop strain. It doesn't provide any of the important information describing how the genetics have been altered and what makes the genetically modified crop different from other varieties of the same plant.

The specifics about the modifications are essential since each GMO is unique. This insecticide claim may be valid in reference to one GM-variety but not to another. In fact, there may also be similar concerns with some non-GMO strains too. It's simply not clear without the specifics. Details matter.

What Are Bt-GMOs?

The concern about insecticides refers specifically to Bt-GMOs, for example, Bt-corn and Bt-soy. These GM strains have been genetically engineered to express one of the Cry genes from Bacillus thuringiensis (Bt), a bacteria that lives in the dirt and is toxic to certain insect larvae.

Bt bacteria have actually been used as an insecticide in organic farming for decades. Since the Cry protein, naturally expressed by these bacteria, is lethal to many insect larvae, the bacteria can just be sprinkled over crops to fight infestations. Of course, bacteria present on the outside of the crops can mostly be washed off before eating. With Bt-modified crops, however, the plant itself produces the insecticide so there is no way to remove it. This is the root of the concern about Bt-modified GMOs.

Engineered to Express Bt Insect Toxin

In essence, then, there is truth to the claim that some GMOs contain an insecticide. Some GM-crops have been genetically engineered to express a naturally occurring bacterial insect toxin often referred to as Bt-toxin. Is this protein safe for human consumption? Actually, overwhelming evidence shows that it is.

First of all, it is important to note that we regularly eat the bacteria Bacillus thuringiensis (Bt) that produces the Cry protein daily. Significant levels have been found in a wide range of fruits and vegetables and even processed foods such as pasturized milk, ice cream, and tea beverages. The ubiquitous presence of Bt isn't surprising due to its wide use as a pesticide, especially in organic farming.

Also, as UC Berkeley genomics researcher Michael Eisen notes in his blog on the Bt-crops, many kinds of biological insecticides exist naturally in plants. As a result of the evolutionary arms war between plants and animals, "natural pesticides have been found in every plant in which they have been sought….Wheat makes a family of proteins lethal to hessian flies, peas contain the insecticidal protein PA1b, tomatoes tomatine, and so on." As a matter of fact, all corn contains the insecticide maysin. There are hundreds of natural insecticides we routinely ingest, including the Bt-Cry protein.

It obviously isn't enough just to note that the Bt-insectide is generally present, however, to ensure the safety of Bt-GMOs. It's certainly important to evaluate the safety of GM-plants expressing the Cry protein. In the late 1990s the Environmental Protection Agency (EPA) did this, and its report released in 2000 noted, "no unreasonable adverse effects from these products." In coming to this conclusion, they noted that Bt-based "microbial pesticides have a long history of safe use without adverse health or environmental effects." Further, they evaluated studies showing that the Cry protein expressed in GMOs, "behaves as would be expected of a dietary protein breaking down rapidly in digestive fluids…is not structurally related to any known food allergen or protein toxin; and…does not display any oral toxicity when administered at high doses."

The potential allergenicity of Bt-GMOs have also been evaluated. No Bt-specific responses were observed. Also, allergy testing is required for approval of each new GMO used in food, so this testing is repeated with each new variety.

What About Studies Showing Negative Effects of Bt-GMOs?

Most of the claims about the negative effects of Bt-GMOs cite two scientific studies. Before going into detail about these two studies, it is important to note that there have been a couple thousand studies on GMOs and, of these, only a few have found possible negative health issues. So, these studies are outliers.

One study published in 2011 in Reproductive Toxicology reported that 93 percent of pregnant women in Eastern Quebec had significant levels of the Bt-Cry protein in their blood. The concern they speculated about is that this protein may negatively affect fetal development.

In fact, though, the study provides no data or references that the Bt-protein actually has any effect on fetal development at all. Further, as mentioned above, Bt is found in all types of food so there is no reason to think the Bt-Cry protein detected in this study is mostly from GMOs. While there are some methodological criticisms of the work, even if the results are assumed correct, they really seem to suggest that the Bt-toxin is common and harmless to humans. You can read a more detailed review of the publication by David Tribe on the Biology Fortified website.

The other study commonly cited to show the dangers of Bt-GMOs was published by Gilles-Eric Seralini, et al. in 2012 in the Journal of Food and Chemical Toxicity. This report was widely criticized immediately on release for its poor methodology and inconclusive analysis. The data provided simply do not support the study's conclusions that Bt-corn correlated with tumor formation in rats. After a year-long investigation, the publisher concluded the study did not meet the minimal scientific standards of the journal and so retracted it. References to this study as supporting evidence that Bt-GMOs cause cancer demonstrate either ignorance or indifference to the scientific evidence.

But Some GMOs Do Contain an Insecticide

In the end, though, it is true that GMOs modified to express Bt-Cry proteins do, in fact, express an insecticide. In fact, as mentioned above, they express many insecticides. The Bt-Cry is just another one. As a result, there is a rationale for the concern and it certainly makes sense to investigate the safety of Bt-modified GMOs. For over 15 years, though, these studies have been done. No negative effects have been identified. While it is impossible to prove anything is absolutely safe under all circumstances, any health risks from Bt-GMOs seem very low to negligible.

Of course, some very cautious individuals may still not be reassured by this vast amount of work, and may still prefer to avoid Bt-GMOs. That is an understandable position. What is not reasonable, though, is to generalize this concern about one type of GMO to pan all genetically modification of crops as possibly dangerous. GMOs are not all equal and genetic engineering has proven a highly useful tool to improve food crops in numerous ways. Bt-producing GMOs are just one variety. Distinctions matter.

(Published: Dec 30, 2013)

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