I would tend to agree. If one knows any agronomists or those experienced with commercial ag sprayers, herbicides and pesticides are diluted with water to crazy small concentrations. I think most laymen would be shocked at how little herbicide/pesticide etc goes into each acre.
It's true, farming is not rocket science, but these days those in the industry do work very hard at getting the volumes exactly right to maximize absorption and minimize runoff. Now I can see why the chemicals could be dangerous in their bulk form because they are generally highly concentrated in their commercial form.
Improper handling and disposal (you try not to "dispose" any, instead using your entire inventory as it is intended and directed in the field over time) would definitely be where I would look. Improper handling and disposal is a very serious crime, but it is relatively hard to police in a preventative or timely manner. There are tests that can be done after the fact, of course, but obviously that is problematic.