In 2011 there was some media speculation about a 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, in press, 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 thuringiensissub sp.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 non-pregnant Canadian women, and in umbilical cord blood of foetuses.
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 which 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 blood stream, 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 livingBtkspores 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, kiwi-fruit, citrus, 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 contain this gene) is recent and relatively minor. The corn lines containing the Cry1Ab protein are mostly used for animal feed and for processing into refined products such as corn syrup and corn starch which, because of processing, contain negligible levels of any protein. None of the GM corns produced so far are popcorn or sweetcorn lines and are therefore not consumed directly. Therefore, ingestion of Cry1Ab by humans via GM corn is not likely to be significant compared to 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 is proof 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 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, 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.