Whenever the environuts want to ban or restrict something it becomes the “most toxic substance on the planet. If they want to shutdown coal fired power plants the most toxic substance is mercury, if they want to stop duck hunting it is lead. Well sorry neither one is the most toxic substance on the planet.
"Thallium is frequently referred to as the poison of choice: Only a gram of the colorless, odorless, water-soluble heavy metal can kill. It is as toxic as arsenic, and even more so than lead."
Read more: http://www.answers.com/topic/thallium#ixzz1pHyrbH1U
I am pretty sure that certain snake and spider venoms are much more toxic than Thallium.
I remember reading decades ago (back when the population of the earth was “only” 2 billion) that a water-glass full of pure botulism toxin, properly distributed, could kill the entirety of humanity.