Expert response from David Tribe Ph.D.
Senior Lecturer, Agriculture and Food Systems/Microbiology and Immunology, University of Melbourne, Parkville, Australia
Friday, 07/03/2014 11:53
Dr. David Tribe, Senior Lecturer on Agriculture and Food Systems and Microbiology and Immunology at the University of Melbourne, Parkville, Australia, addressed the study conducted by Aziz Aris and Samuel Leblanc in an article on the Biofortified Blog. The full article is posted below.Here are a few key points:
- “The authors of the study claim to have detected the Cry1Ab protein in the blood of pregnant and nonpregnant Canadian women, and in umbilical cord blood of fetuses.”
- "A number of methodological and interpretive limitations of this paper limit the relevance of the reported findings and conclusions about food safety.”
- “The authors do not provide any evidence that GM foods are the source of the [Cry1Ab] protein. No information was gathered on the diet of any individual in the study, so the assertion that the detection of Cry1Ab is linked to ingested GM food is, at best, speculative.”
A recent publication by Aziz Aris and Samuel Leblanc in the journal Reproductive Toxicology (“Maternal and fetal exposure to pesticides associated to genetically modified foods in eastern townships of Quebec, Canada”) claims to have detected traces of herbicides (used on herbicide-tolerant “genetically modified” plant varieties) or their major metabolite and the insecticidal protein Cry1Ab (produced by certain varieties called Bt-resistant insect pests) in the blood of Canadian women, pregnant or not pregnant, and in umbilical cords.
Th[e Kuntz] site will publish any credible information about the validity of these claims, and this article will be updated periodically.
A publication lacking credibility
Only claims of Aris and Leblanc on Cry1Ab are discussed here for the time being.
The Cry1Ab protein is produced by some Bt cotton and corn (e.g., MON810).
Aris and Leblanc claim they detected this protein in 93 percent of pregnant women and 69 percent of nonpregnant women tested and believe that this is linked to the consumption of foods derived from Bt varieties, which in Canada must mean corn, rather than cottonseed oil.
Surprisingly, the authors do not consider that the origin of Cry1Ab could be food from organic farming (which sprays Cry1Ab, or bacteria producing it, on fruit or vegetable crops) or from its use in gardening (CryA1b is part of available “natural insecticide” formulations).
If we examine the possibility of a Bt corn food origin for Cry1Ab, since these proteins do not bioaccumulate, it is necessary to consider recent consumption.
First question: Do 93 percent of pregnant women in Canada actually consume corn almost daily?
Second question: Are the values in blood reported by Aris and Leblanc consistent with the levels present in Bt corn kernels?
The answer is no. Here’s why:
The authors reported average values of 0.19 nanograms per milliliter (ng/ml) of blood from pregnant women. Knowing that, in corn MON810, for example, levels of Cry1Ab in the grain are between 190 and 390 ng/g fresh weight, assuming that 1 percent will pass into the blood (which is on the high side, taking into account losses during corn storage, cooking and gastric digestion and the intestinal barrier), this would require a woman of 60 kg to consume 120 g of corn (for the mean blood value of 0.19 ng/ml, assuming a plasma volume of 2.5 liters) and about 1.5 kg (for the maximum reported blood values of 2.28 ng/ml), which seems unrealistic—and even more if one takes into account all extracellular fluids (10 liters, which would imply an average consumption of 490 g of corn and 5.8 kg in order to reach the maximum value in blood).
Third question (which follows logically the above-mentioned findings): Is the Cry1Ab detection method used by Aris and Leblanc reliable?
Note first that the test used, marketed by Agdia, is claimed to detect the protein Cry1Ab from 1 ng/ml (read the introduction to this article), while Aris and Leblanc claim to have detected average concentrations lower than the detection limit, e.g., 0.04 ng/ml in umbilical cords!
One can cite the publication by Lutz et al. (J. Agric. Food Chem. 2005, 53 (5): 1453–6) showing that the ELISA test used by Aris and Leblanc is not sufficient to guarantee the identity of positive signals (to avoid misinterpretation, samples tested positive for Cry1Ab protein by ELISA should be reassessed by another technique).
Note that Aris and Leblanc did not discuss this issue, nor the results of Chowdhury et al. (J. Animal Sci. 2003, 81: 2546–51), which indicate that these ELISAs do not work for blood (from pigs).
Moreover, they do not cite the publication by Paul et al. (Analytica Chimica Acta 2008, 607: 106–13) that discusses the validity of the tests available on the market. (Provisional) answers to the questions that arise: in the absence of the validation of the detection of Cry1Ab, it is likely that the authors incorrectly conclude that any signal was indicative of the presence of the Cry1Ab protein, whereas they most likely correspond to false positives.
A possible validation, which, surprisingly, is lacking in the work of Aris and Leblanc, is the electrophoretic separation of plasma proteins and immunodetection of the protein Cry1Ab (“Western blot,” a common laboratory technique).
It therefore appears that this publication, in its present state, is of insufficient quality to be convincing. It has not undergone a proper review process according to the standards of a scientific journal, which would have required the validation of the results and their discussion in relation to available literature.
FSANZ response to study linking Cry1Ab protein in blood to GM foods. Accessed May 30, 2011.
There has been some media speculation about a recent paper published by Aziz Aris and Samuel Leblanc titled “Maternal and fetal exposure to pesticides associated to genetically modified foods in eastern townships of Quebec, Canada” (Reproductive Toxicology, 2011).
What is the paper about?
The paper deals with two herbicides, glyphosate and glufosinate ammonium, that are sprayed on both genetically modified (GM) and non-GM crops, and an insecticidal protein, Cry1Ab, that is produced by the naturally occurring soil bacterium Bacillus thuringiensis subsp. kurstaki (Btk). The gene encoding this protein has been used to genetically modify some crops so that they contain the protein and are thus protected against certain insect pests. The protein is also extensively used in organic and conventional farming as a direct-application pesticide.
The authors of the study claim to have detected the Cry1Ab protein in the blood of pregnant and nonpregnant Canadian women, and in umbilical cord blood of fetuses.
What are the concerns about the paper?
A number of methodological and interpretive limitations of this paper limit the relevance of the reported findings and conclusions about food safety. The key limitations include insensitivity of the assay method used and unsubstantiated and invalid assumptions regarding the source of the Cry1Ab protein in the diets of test subjects. Media speculation arising from this paper has also presented conclusions about the human-health relevance of this paper that are not supported by either the paper itself or the broader scientific literature. These issues are discussed in more detail below.
The assay method
The assay method (ELISA) used for Cry1Ab protein was not tested (validated) for its suitability to measure Cry1Ab in human blood. Other reports in the scientific literature have shown that the ELISA assay is not suitable for this purpose.
In mammals, the Cry1Ab protein is degraded in the stomach. If any fragments of the Cry1Ab protein were to pass through into the bloodstream, they would be present at levels much lower than could be quantified by the assay method used in the study.
The assumption that GM foods are the source of the Cry1Ab protein
The authors do not provide any evidence that GM foods are the source of the protein. No information was gathered on the diet of any individual in the study, so the assertion that the detection of Cry1Ab is linked to ingested GM food is, at best, speculative.
Several insecticidal formulations (e.g., Delfin, Dipel) contain a blend of crystallised proteins (including Cry1Ab and living Btk spores) that germinate into the bacterium that then produces the proteins. These formulations have been applied worldwide, including in Australia, for decades. They are applied to crops such as broccoli, cauliflower, celery, melons, potatoes, spinach, tomatoes, cucumbers, turnip, grapes, kiwifruit, citrus and avocados. They are used both commercially and by home gardeners and are permitted for use on organically certified crops.
In comparison, the consumption of food derived from GM corn containing the Cry1Ab protein (no other currently commercialised GM crop species contains this gene) is recent and relatively minor. The corn lines containing the Cry1Ab protein are used mostly for animal feed and for processing into refined products, such as corn syrup and cornstarch, which, because of processing, contain negligible levels of any protein. None of the GM corns produced so far is from the popcorn or sweet-corn lines and is therefore not consumed directly. Therefore, ingestion of Cry1Ab by humans via GM corn is not likely to be significant compared with conventional and organic produce sources.
Interpretation by the media that Cry1Ab protein is a human safety issue
There have been claims in the media that the paper proves that GM foods are not safe for human consumption.
However, the paper does not discuss the safety implications of finding Cry1Ab in the human body, and the authors make no mention of any abnormalities in either the subjects or, in the case of those who were pregnant at the time of the study, the subsequent process of birth or the health of the mothers and babies postpartum.
The Cry1Ab protein, whether ingested via Btk-sprayed conventional or organic crops or via GM corn products containing the protein, is safe for human consumption at the levels likely to be found in these sources.
For more information, see this report, prepared under the auspices of the World Health Organization. It is about Bacillus thuringiensis (Bt), the organism used in the spray formulations, and from which various genes have been isolated for use in genetically modified crops. Chapter 7 deals with a whole range of exposures to the organism (and, hence, the proteins produced by it) and their effects in humans.
If you have any additional questions after reviewing this response, please ask.
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