Thallium [Tl, 81]

Thallium (Tl), a soft gray metal of group 13 in the periodic table of elements, is discolored when exposed to air. Thallium metal and its compounds are highly toxic and are strictly controlled to prevent a threat to humans and the environment. Radioisotope ²⁰¹Tl is used in medicine for scintigraphy and diagnosis of some diseases, including myocardial disorders and various cancer detections. The worldwide range of Tl in soils is 0.0014–2.8 mg/kg, at an average value of 0.5 mg/kg. The average concentration of thallium in seawaters is estimated within the range of 10–15 ng/L. Thallium contents of plants seem to be a function of its concentrations in soils, especially its mobile fractions. Thallium content in the human body is no more than 0.5 mg, and the level in the blood is 0.5 µg/L. Water-soluble Tl salts are readily absorbed by mucous membranes, such as the mouth, stomach, and intestines, and they can even penetrate trough the skin.