Thallium

Thallium is a metallic chemical element that does not freely occur in nature. It is a grey colored metal that is highly toxic and has been behind numerous fatal poisoning. Mere contact with thallium can cause poisoning as it is highly soluble in water and can easily pass through the skin. Prussian blue is used to remove thallium from the body. It is also a suspected carcinogen. Saddam Hussein, the former president of Iraq, is alleged to have used it to murder his political opponents.