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Now I (and most of us here, I guess) have grown up around "Mercury's toxic! Avoid handling it! Do NOT screw around with this thing, if you value your life" and other equally heartening pieces of advice regarding mercury. Apparently mercury poisoning makes you, really lose it.

Now a while back I chanced upon a video on Youtube (I checked today, and now there're multiple videos on the same thing) where someone was messing around with elemental mercury … with his/her (I don't remember) bare hands.

Naturally I was taken aback. A quick check provided sufficient evidence to ascertain that he/she hadn't died as a result.

Now I posed this to a teacher of mine, and after some deliberation, he concluded that it isn't the mercury metal that's toxic. He told me that it's the various compounds of mercury that are formed by elemental mercury once it gets in your system (i.e- once you drink it) which are responsible for the toxicity. So apparently touching metallic mercury with your bare hands isn't an issue, since the metal isn't subjected to all those metabolic reactions that go on inside the body; heck you can even gargle it and live (provided you spit it out afterwards) since mercury's fairly inert.

So what I'd like to know is

Is it true that metallic mercury by itself, isn't toxic?


*Spin-off questions:

Is there any substance to my teacher's claim? How come those asses that performed this mundane task survived and now live (seemingly) normal lives without going insane? Were they already insane prior to touching the mercury? Should I just go and touch some mercury, partly to discover if it is indeed possible to touch metal mercury safely (and partly just to let out all the stress that built up while typing out this question)?

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  • $\begingroup$ Mercury is toxic. This person is jeopardizing his/her health, or it's not mercury. $\endgroup$ – Zhe Oct 19 '16 at 17:22
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    $\begingroup$ Have a look at this wikipedia page, especially the paragraph "Elemental mercury". $\endgroup$ – Philipp Oct 19 '16 at 17:34
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    $\begingroup$ Elemental mercury is toxic but the main exposure route is through inhalation of mercury vapors more than skin exposure to the metallic form (see for instance the Wikipedia page en.wikipedia.org/wiki/Mercury_poisoning). On the initial question: the problem with the initial question regarding toxicity is that in itself the affirmation that (elemental) mercury is toxic does not indicate at which doses and through which type of exposure it is the case. $\endgroup$ – PLD Oct 19 '16 at 17:37
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    $\begingroup$ Metallic mercury is less toxic to the touch than people seem to assume. Also, human skin is surprisingly durable, and you can safely hold pretty crazy stuff in your hands for a short while, especially if you wash them soon afterwards. Not that I recommend doing it, though. Indeed, some compounds can fatally poison you upon touching. Metallic mercury is not one of them. $\endgroup$ – Ivan Neretin Oct 19 '16 at 21:23
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    $\begingroup$ The trouble with holding globs of mercury, especially in a classroom, is that someone is sure to drop it. The little globules skitter into nooks and crannies and are very difficult to completely remove (or cover with sulfur). While in a well-ventilated room that is not immediately hazardous, over years mercury accumulates from such demos. $\endgroup$ – DrMoishe Pippik Oct 19 '16 at 21:44
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Mercury is toxic, but you need to carefully define what you mean by toxic or you draw incorrect conclusions

Toxic is a broad term. It means a lot of different things. The timescale matters. Some toxic things take years to exhibit their effects; others act instantly.

A binary distinction between toxic and not-toxic is pretty meaningless: you need to define the context and the timescale of the toxicity.

Mercury metal and mercury compounds are usually considered toxic. But their effects are varied in time and degree. Mercury metal is pernicious but only if you are exposed to it over a long time period. In fact you could probably drink it with few ill effects. The body just doesn't absorb it quickly. What is dangerous about mercury is not short term exposure to the metal but long term exposure to the vapour. This is why people don't suffer immediate ill effects when handling the metal even without skin protection.

Mercury vapour is readily absorbed in the body and will accumulate in tissue causing a variety of long term effects. This was discovered by mercury miners who often developed long term problems from their exposure. And it was documented for science by some chemists who started to suffer effects after working with the metal over long periods of time and managed to document their own decline (see Stock's work, for example). Mercury metal is often widely used in laboratories to provide a limited overpressure for gas distribution (you allow the gas to bubble through a mercury manometer).

Since the toxicity was recognised, chemists have been a lot more careful and always avoid vapour buildup by working in well ventilated spaces and making sure that manometers containing mercury are vented safely to the outside (via scrubbing filters) along with other potentially toxic vapours.

There is little immediate risk when working with metallic mercury as long as you don't spill it somewhere where it will collect and allow vapour to build up in the atmosphere.

Mercury compounds are a bigger risk. Some are readily absorbed into the body. The worst sort are mercury organometallic which are both volatile and penetrate the skin quickly. If you work with those you need to take extreme precautions. Even experienced chemists have been killed by accidents involving things like methyl mercury (see this tragic story).

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Quoting matt_black's answer:

In fact you could probably drink it with few ill effects.

Indeed, as described here (link is to a PDF), there are documented cases where individuals consumed appreciable quantities of mercury metal and did not suffer dramatic long-term medical consequences (citation markers removed here and in all quotes below):

Herewith, it is useful to recall two rather bizarre examples of oral intake of liquid mercury, confirming that the risk of acute poisoning is indeed minimal. First, it is a story of unlucky love in the former Czechoslovakia, when a desperate girl voluntarily swallowed several grams of mercury. Instead of the expected death, she had recovered soon and, since then, became the wanted object of exhibition at medical faculties for several years, when the students and other university staff could observe under a roentgen irradiation how the mercury circulated in her blood system, including its passage through the pumping heart. The second case is then a criminalistic legend from the old Austro-Hungarian Empire, when a (never-revealed) joker had injected liquid mercury into bonbons that were subsequently distributed among the VIPs attending the famous ball at Vienna's Opera. According to the contemporary press, almost every infected victim had suffered from a strong diarrhea (almost demolishing the toilets), but no-one died or being otherwise seriously endangered.

The above PDF link also corroborates matt_black's and Brace's arguments about the primary mechanism of toxicity deriving from the vapor, not the liquid, of elemental mercury:

Inhalation of $\ce{Hg}$-vapors by lungs is practically complete. The acute inhalation of high concentrations of metallic $\ce{Hg}$-vapors may cause severe chemical pneumonitis and noncardiogenic pulmonary edema.

Chronic intoxication from inhalation of mercury vapor produces a classic triad of tremor, neuropsychiatric disturbances, and gingivostomatitis.

Due to high solubility in fats, $\ce{Hg}$-vapors come into brain circulation in few minutes. They cross hematoencephalic barrier, acting neurotoxically. It is expected that, in brain tissue, elemental mercury is oxidized to $\ce{Hg^{II}}$ and these species cross the hematoencephalic barrier being then accumulated in cortex and basal ganglions. Similarly, mercury can be transformed by catalase to $\ce{Hg^{II}}$ in erythrocytes and this divalent form is then distributed into tissues, interacting readily with the $\ce{–SH}$ groups in the enzymes. The highest depot is present in kidneys; usually, in adrenals. The kidneys tissue reacts by producing metallothioneins (MTs; cysteine-rich proteins) which effectively bind mercury. As a consequence, kidney-namely: proximal tubulus and glomerulus-are badly damaged after such saturation.

The Wikipedia page on mercury poisoning linked to by Phillipp in a comment to the question does also have some further elaboration of the topic:

Quicksilver (liquid metallic mercury) is poorly absorbed by ingestion and skin contact. Its vapor is the most hazardous form. Animal data indicate less than $0.01\%$ of ingested mercury is absorbed through the intact gastrointestinal tract, though it may not be true for individuals suffering from ileus. Cases of systemic toxicity from accidental swallowing are rare, and attempted suicide via intravenous injection does not appear to result in systemic toxicity, though it still causes damage by physically blocking blood vessels both at the site of injection and the lungs. Though not studied quantitatively, the physical properties of liquid elemental mercury limit its absorption through intact skin and in light of its very low absorption rate from the gastrointestinal tract, skin absorption would not be high. Some mercury vapor is absorbed dermally, but uptake by this route is only about $1\%$ of that by inhalation.

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Mercury is very toxic, but, for a number of reasons, it isn't absorbed through the skin very well at all. The main danger from dealing with Mercury, as with most toxic liquids, are the vapours. Also even though it is mostly inert at room temperature, it will react with Nitric Acid, hot Sulfuric Acid, and Ammonia (in the presence of Oxygen), and all of these compounds will readily absorb into your skin, giving you Mercury poisoning. If you want to learn more about Mercury, TAOFLEDERMAUS and Cody's Lab are both great YouTube channels that work with Mercury a lot. Cody on Cody's Lab actually just got his Blood Mercury Concentration tested after he stuck his whole forearm into mercury in a recent experiment.

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