When freshly exposed to air, thallium exhibits a metallic luster, but soon develops a bluish-gray tinge, resembling lead in appearance. A heavy oxide builds up on thallium if left in iar, and in the presence of water the hydroxide is formed. The metal is very soft and malleable. It can be cut with a knife.
The element and its compounds are toxic and should be handled carefully. Contact of the metal with the skin is dangerous, and when melting the metal adequate ventilation should be provided. Exposure to Thallium (soluble compounds) - skin, as Tl, should not exceed 0.1 mg/M3. Thallium is suspect of carcinogenic potential for man.
A dose of 15 mg of Thallium to a 70 kg man can be fatal.