"This bridge can't accommodate your ridiculous treat-truck and we will fine you if you break it."
Pickup owners: "tHiS iS a ScAm"
I bet these same people post comments like "fuck around, find out" and "should have listened" on videos of people getting shot by the cops for not following their orders one hundred percent.
Not only would it take a long time, I imagine the results would be extremely random to the point it would be unreliable as an execution method. Carcinogens, and the way each person's body reacts to them, are highly unpredictable. That's why health disclaimers on carcinogenic products say "may cause cancer" and not "will cause cancer."
It would be far easier to just shoot or stab the target and make it look like a robbery gone bad or something.
Reminds me of that scene from Austin Powers where they parody those intricate death traps in James Bond films...