What chemical compounds might be present in drinking water?
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# 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?

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Video 7 A comparison of some reactions of thallium(I) and potassium ions.
Transcript

## Answer

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.

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