4.1.4 Toxicity of thallium(I) compounds
Another Group 13 element thallium, and especially thallium(I), is extremely poisonous. Thallium poisoning has been linked to industrial emissions from the burning of coal and the smelting of thallium-rich sulfide ores. Consequently the United States Environmental Protection Agency sets the safe level of thallium in drinking water at 0.5 ppb. When ingested, thallium seems to follow potassium in its metabolism, and it probably interferes with vital roles played by potassium in the nervous system. Note the ionic radius of Tl+ (160 pm) resembles that of K+ (152 pm). Again, this supports the general explanation of toxicity: the nervous system mistakenly accepts thallium(I) instead of potassium ions. Essential biological processes are then blocked because thallium(I) is an inadequate substitute.
How similar is the chemistry of thallium(I) and potassium ions shown in Video 7?
Download this video clip.Video player: Video 7Transcript: Video 7 A comparison of some reactions of thallium(I) and potassium ions.
End transcript: Video 7 A comparison of some reactions of thallium(I) and potassium ions.NARRATORFirst, aqueous sodium hydroxide is added to a solution of potassium sulfate. And then to a solution of thallium(I) sulfate. Now, an aqueous carbonate solution is added to potassium sulfate. And then to thallium sulfate. The hydroxide and carbonate of thallium(I) are soluble, like those of potassium. This is unusual.Soluble metal hydroxides and carbonates are rare. Potassium also forms an insoluble tetraphenylborate. Will thallium resemble it in this respect? The tetraphenylborate is added first to potassium sulfate. And then to thallium sulfate. The tetraphenylborates are insoluble. These experiments point to a resemblance between potassium and thallium.Video 7 A comparison of some reactions of thallium(I) and potassium ions.Interactive feature not available in single page view (see it in standard view).Like potassium, thallium forms, unusually, a soluble, alkaline carbonate and hydroxide, Tl2CO3 and TlOH. Both ions also form a precipitate with the addition of a solution containing the tetraphenylborate anion, BPh4− where Ph = phenyl.