Given that external application means it can be largely washed off; yet a possibly lesser amount may be required for GMOs, in which scenario do we consume more?
How would you have a chance to find that out without long-term testing?
Is this just blatantly incorrect, based on outdated science (given that it was published so long ago), or is it not the whole story?
[1]: http://www.iatp.org/news/poison-risk-is-greater-from-organic...
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When ingested, the bacterium produces endotoxins which attack the walls of the insects' guts. In mammals, they can cause death from septic shock."
We have to make the difference between Bt bacteria, and Bt toxin. Bt toxin is a protein produced by the Bt bacteria. As far as I understand, the professor here is talking about spraying the crop with live Bt bacteria, and apparently the bacteria can produce other toxins than just Bt proteins.
You are referring to GMO varieties of potato, corn, cotton and soybean. These plants have been engineered to produce Bt Cry proteins.
These proteins become toxic in the alkaline (basic, pH > 7) digestive systems of certain insects [1]. No signs of toxicity has ever been found for these proteins in the acidic (pH < 7) digestive systems of mammals, including humans [2].
Also, these Bt toxins are naturally produced by a species of bacteria, Bacillus thuringiensis. And either bacterial spores or extracted Bt toxins have been used as pesticides in agriculture since the 1920s. Also, as the Bt toxin is produced by bacteria, not a chemical factory, it is considered a natural product and is approved and widely used as a pesticide in organic farming [3].
Your fear of GMO based Bt-producing crops as "plants which produce chemicals" is wrong and misguided in two levels. Bt is not toxic to humans, and you cannot avoid digesting some Bt proteins by avoiding just GMO crops, as Bt is also used in non-GMO farming and also in organic farming.
[1] https://en.wikipedia.org/wiki/Bacillus_thuringiensis#Mechani...
[2] https://en.wikipedia.org/wiki/Bacillus_thuringiensis#Safety_...
[3] https://en.wikipedia.org/wiki/Bacillus_thuringiensis#Use_of_...