As for Agent Orange, just in case some people are unaware of its wicked pedigree, the petition helpfully explains that it "was the chemical defoliant used by the U.S. in Vietnam, and it caused lasting environmental damage as well as many serious medical conditions in both American veterans and the Vietnamese." No indication, though, of the fact that those medical conditions have been attributed to the other half of Agent Orange (the 2,4,5-T component) and its contaminant, dioxin.
The petition does say that "industry tests also show that 2,4-D is contaminated with dioxins," which is cause for concern, but again, there's no indication of how prevalent this contamination might be. To the extent that it is a concern, though, it's not specific to these GE crops. Why? Because 2,4-D is the world's most widely used herbicide—something the petition also neglects to mention.