On 2002-06-27 17:50, ChrisA wrote:
Uhm, the dental amalgam is non-toxic because the silver and the mercury bind to each other tighter than the acids in you can break them apart.
This is not correct. According to Pauling, mercury is considered relatively unreactive. The amalgam forms as metals, e.g. gold, silver, tin, <i><b>dissolve</b></i> in the liquid mercury. Amalgam is a solution, not a compound, and, in any event, how could metals which only exist in the positive valence state ( Au, Ag, Hg ) be expected to form a chemical bond with one another?
Prospectors at one time used mercury to concentrate the fine gold they found in their pans by simply pouring the mercury in and sloshing it about until the gold was dissolved. The gold was recovered by placing the mercury in a distillation apparatus made of iron ( because mercury does not wet iron ). On heating, the more volatile mercury was driven off and condensed for re-use, while the refractory gold, silver, etc., were left behind in the retort. The miner who discribed this process to me suggested it was best to retire a good deal upwind until the process was completed.
If you swallowed drops of un-mixed mercury, it would assuredly not be harmless, nor does it need to occur only in compounds to be harmful... the vapors of liquid mercury were quite harmful to the historic (and immortalized by Lewis Carroll) hatter. It does, however, take a good deal of exposure to damage you.
What you point up here is the difference between acute and chronic exposure. Acute exposure can cause such things as skin irritation, or metal-fume fever if the vapors are inhaled. Chronic exposure -- repeated over long periods of time -- can produce much more serious effects, as you point out.
Mercury is also a cumulative toxin... once it's in you, it doesn't leave, so while you might not be harmed by ingesting, say, a milligram of mercury, you would be eventually if you ingested a milligram annually... (I don't, offhand, know how much it actually takes to cause brain damage).
This isn't quite correct. Mercury is excreted from the body, just at a rather slow rate. If exposure exceeds the excretion rate, then it will accumulate, otherwise not. The brief exposure in the dentist's chair is presumably sufficiently low-level and infrequent that serious effects are avoided and the body can recover. I understand, however, that dentists themselves must be very careful because their exposure is very long-term.
Not to say that organic compounds containing mercury are harmless, either... I strongly recommend against eating locoweed!
According to references I have seen the active ingredient in locoweed isn't mercury, but an alkaloid toxin.
