(Beyond Pesticides, March 7, 2012) Researchers in Europe have found that the insecticide Bacillus thuringiensis (Bt) when incorporated into genetically engineered (GE) plants, and the herbicide glyphosate, used widely with GE glyphosate-tolerant crops, are toxic to human cells, disputing commonly held assertions by regulators and the chemical industry that these substances are entirely harmless to humans. The research team, led by scientists at the University of Caen in France, says that at very high doses Bt is toxic to human cells, and glyphosate, when formulated as the product Roundup, manufactured by Monsanto Co., damages human cells, even in extremely low doses. The findings of the study have been published online in the Journal of Applied Toxicology.
Bt is a commonly used least-toxic insecticide which is available in several different strains, each toxic to a different range of insects. The substance is a naturally occurring soil bacterium that has been harnessed and enhanced to make it more effective as a pesticide product. Crops such as corn and cotton are also often genetically engineered (GE) to produce Bt proteins so that insects are infected with the toxin when they feed on the plant. The French researchers suggest that it may be this enhancement that lends the substance its toxicity to human cells. By introducing the modified toxin gene into the plants, the structure of the toxins is modified and may thereby cause different effects. The content of the Bt proteins within the plants is highly variable. Many genetically engineered plants contain several Bt toxins at the same time. For example, SmartStax, developed collaboratively by Monsanto and Dow AgroSciences, produces six different Bt toxins and therefore has a higher overall content of the proteins. SmartStax is also an example of a product with â€śstackedâ€ť GE traits, because not only does it contain Bt, it is also engineered to be resistant to spraying with Roundup. Before this study, there had been no investigation of the combined effects of these toxins and residues from spraying, or their potential risks for human health, which was considered unlikely. The researchers have now shown that interactivity does occur between Bt and glyphosate when formulated as Roundup. They stated that further investigations are necessary to examine other potential combined effects under varying conditions. In concluding the studyâ€™s abstract, the authors say that, â€śIn these results, we argue that modified Bt toxins are not inert on nontarget human cells, and that they can present combined side-effects with other residues of pesticides specific to [genetically modified] plants.â€ť
Glyphosate is a general herbicide used for eradication of broadleaf weeds. It has previously been linked to a number of serious human health effects, including increased cancer risk, neurotoxicity, and birth defects, as well as eye, skin, and respiratory irritation. One of the inert ingredients in product formulations of Roundup, polyoxyethyleneamine (POEA), kills human embryonic cells. It is also of particular concern due to its toxicity to aquatic species as well as instances of serious human health effects from acute exposure. The French study shows that Roundup causes necrosis and apoptosis in human cells at 50 parts per million, well below levels commonly found in agricultural formulations.
â€śWe were very much surprised by our findings. Until now, it has been thought almost impossible for Bt proteins to be toxic to human cells. Now further investigations have to be conducted to find out how these toxins impact the cells and if combinatorial effects with other compounds in the food and feed chain have to be taken into account,â€ť says Gilles-Eric SĂ©ralini from the University of Caen, who supervised the experiments. â€śIn conclusion, these experiments show that the risks of Bt toxins and of Roundup have been underestimated.â€ť
In their investigations, the researchers examined several products, including the Cry1Ab and Cry1Ac Bt toxins developed by Monsanto for inclusion in GE crops, as 