The crops in question are engineered to carry pesticide-producing genes from the bacterial species Bacillus thuringiensis (Bt). In recent years, companies have increasingly turned to crossbreeding different varieties of Bt crops, producing crops that now carry numerous different strains of Bt toxin at once. These "stacked-trait" crops are being approved for planting and sale, based on several false assertions made by the genetically modified (GM) crop industry, the study found.
Hiding toxic effects
One such assertion is that each individual Bt toxin affects only a small number of insect pests, and has no effects on other species such as beneficial insect predators ("non-target" species). But the researchers found numerous studies showing the opposite to be true.According to lead researcher Angelika Hilbeck, companies hide the truth by defining non-target effects in a highly narrow fashion: a "quick kill."
"This is an economic concept: you want a quick kill for economic reasons, to save the crop from pest-induced damage," Hilbeck said. "But Bt toxins are not fast-acting toxins. Even in target pests, Bt toxins don't kill quickly – it takes most susceptible insects a day or more to die. The Bt toxin in GM crops is expressed in the crop plant for months at a time. Residues linger in soil and aquatic systems.
"Regulatory tests need to look at long-term and sublethal effects, because that is what non-target organisms are likely to be exposed to. Currently these tests are not required. Yet we found a lot of evidence in the scientific literature that non-target organisms such as ladybirds, water fleas, lacewings and even slugs are adversely affected by Bt toxins."
The review also turned up evidence that Bt toxins may have long-term, toxic effects in mammals – including, potentially, in humans who eat GM crops.
The uncertainty around the safety of stacked-trait Bt crops is only worsened, the researchers noted, by the fact that scientists do not even understand how Bt toxins function. The formerly accepted model has been widely discredited due to new research, and the revelation of scientific misconduct and data tampering by the researchers who first proposed it.
More dangerous than single pesticides
Another false industry claim is that use of Bt crops reduces pesticide use. But the review found that the total pesticide load in stacked-trait Bt crops often exceeded the typical amount of pesticide used in a non-GM field. For example, SmartStax GM corn contains six different Bt toxins and two herbicide tolerant traits. The total Bt toxin load in this crop is 19 times the average 2010 pesticide application rate!Perhaps the most glaring regulatory failing uncovered by the review, is the acceptance of industry claims that stacked-trait crops should be approved on the basis of tests conducted on single-trait crops. Yet the review uncovered numerous studies showing that stacked-trait crops caused biological effects not produced by any of the individual toxins alone. The same thing occurred when Bt toxins were mixed with neonicotinoid insecticides, as commonly occurs in the field.
The review also found that industry dossiers seeking stacked-trait approval consistently failed to mention the studies that contradicted their false assumptions. Regulators did not require any further safety testing of stacked-trait crops, beyond a few short-term insect feeding trials.
Instead, the researchers said, regulators should require long-term mammal feeding trials, as a minimum.
Furthermore, Hilbeck said, "We have to extend the definition of 'effect' from the economic to the ecological."
Sources for this article include:
GMWatch.org
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