You might be interested in a response to a similar question from Andrew Kniss, associate professor of Weed Ecology & Management in the Department of Plant Sciences at the University of Wyoming. He addresses pesticide toxicity in his response, and an excerpt is below:
“…The most common pesticide incorporated into GMO crops are proteins that originate from Bacillus thuringiensis, commonly referred to as Bt crops. The nice thing about Bt proteins is that they are very specific in the types of organisms they are toxic to. The crops have been engineered to produce a Bt protein that is toxic only to certain types of insect pests (usually Coleoptera and Lepidoptera) that feed on the plants. This greatly reduces nontarget impacts by only exposing insect pests that feed on the crop. These Bt proteins are practically non-toxic to humans and other mammals. It has been well documented that the use of Bt crops has actually reduced pesticide spraying. So, in the case of GMO Bt crops, we have actually reduced the application of insecticides to the soil…”
You can view the full response here: http://gmoanswers.com/ask/how-can-adding-lot-toxic-poison-pesticides-ground-be-good. If you have any additional questions, please ask.