Honestly, yes, you can find trace amounts of toxic chemicals in plants grown in "toxic" chemical based fertilizers. Of course, the catch 22 of the situation is that you can also find trace amounts of toxic chemicals in plants grown in cow-crap. You see, the air we breathe, the water we drink, and the earth we walk upon has been so innundated with toxic crap for the last couple of centuries that we can't avoid it, no matter how clean we live.
Is it something to concern one's self about? Certainly. I know I'm not the only person who thinks this has more to do with the steady and marked increase in cancers, circulatory and pulmonary diseases than tobacco or trans-fats. Is this a reason to put my pipes away? Hell no. I wouldn't be surprised to learn that I inhale more toxic crap letting my truck idle to warm in the -15c winter mornings (and I'm not giving that up either).