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My intuition tells me that organic mercury compounds are absolutely toxic. Unimaginably, fundamentally, extremely and uncompromisingly toxic.

I know that is not true for all doses.

Thiomersal is the organomercury compound that was used in vaccines as preservative. It's use has been controversial outside of the scientific community.

I am not asking whether the use in vaccines is dangerous, to be clear:

The use of mercury as Thiomersal in vaccines it is not dangerous.

That is well-established beyond reasonable doubt. Far beyond.

My intuition tells me that any organomercury compound it so mind-blowingly toxic that I feel cognitive dissonance if I try to accept that, at some dose, it's not.

I'm totally aware that toxicity depends on dose, that the compound is toxic at higher doses, and the dose used is just low enough that it is not toxic.

But the dose used is still antiseptic and antifungal, and having anything in my body that contains mercury and carbon in a dose high enough to kill a form of life feels just not right.

I would not worry at all to get vaccinated with a vaccine containing Thiomersal, and if a physician would ask me whether I prefer a vaccine with or without it, I would answer "Whatever you think is best."

But still, on the abstract level, the feeling of "That can't be right" to have an organomercury compound in my body it pretty strong.

I know it is not dangerous, but:

How is that even possible?

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    $\begingroup$ How is it possible to have highly toxic chemicals like sodium and chlorine in the body? Or how can harmless carbon and nitrogen form highly toxic cyanide? $\endgroup$ – jamesqf Dec 31 '19 at 2:14
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    $\begingroup$ @jamesqf I understand what you mean, and my intuition has no problem with that, even cyanide itself can be used as medical drug. But organomercury compounds are much worse than even cyanide: For example, methylmercury goes into the brain and stays there, going on to kill brain cells until there are not enough to live, some month later. Cyanide makes getting oxygen not work, either you die, or feel bad until the next day and all is fine, roughly. Methylmercury is just unimaginable toxic. $\endgroup$ – Volker Siegel Dec 31 '19 at 2:28
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    $\begingroup$ I think you missed my point, which is that chemical compounds have chemical properties that are usually entirely unrelated to the properties of the elements that compose them. The properties of CN, including its toxicity, are nothing like those of elemental C or N. NaCl (necessary for life) is nothing like elemental Na (probably bursts into flame in contact with body fluids) or Cl (used in WWI as a poison gas). So why should any particular mercury compound be toxic? See answer regarding the difference between ethylmercury & methylmercury. $\endgroup$ – jamesqf Dec 31 '19 at 19:01
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    $\begingroup$ You might also ask why it is that literally hundreds of millions of people can spend large parts of their lives with mercury-containing dental amalgams in their teeth, without showing any sign of mercury poisoning. $\endgroup$ – jamesqf Dec 31 '19 at 19:04
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    $\begingroup$ @CJDennis - Yes, it is not about mercury in general, but about organic compounds containing it. (I know somebody who ate metallic mercury just for bragging.) Exposure to metallic mercury is over longer time because it vaporizes slowly. I think the problem with fillings is different: The filling is created using a mercury alloy, which is eutectic. That means the amounts of the alloyed metals have a specific relation. If one of the metals is too much, it stays unalloyed as particles in the alloy bulk. If the mixture contained minimally to much mercury, that can diffuse out over long time. $\endgroup$ – Volker Siegel Jan 1 at 9:36
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Thiomersal is broken down into two compounds, thiosalicylate and ethylmercury (Ensink 2015). The thiosalicylate it is relatively non-toxic, and there is even some evidence that this compound could counteract some of the effects of mercury poisoining (Asadi et al 2010), though the mechanism of this inhibition has yet to be elucidated.

Although they have similar names, methylmercury and ethylmercury have very different levels of toxicity. Methylmercury has long been known to be highly toxic, producing high levels of cell death in the brain, particularly in the cerebellum and the visual cortex (Ceccatelli et al 2010).

Unlike methylmercury, ethylmercury appears unable to cross the blood-brain barrier as fast as it is eliminated in the stool. Consequently, small quantities of ethylmercury have been shown to be non-toxic, resulting in the relative non-toxicity of thiomersal (Pichichero et al 2002).


Sources:

  • Asadi S, Zhang B, Weng Z, Angelidou A, Kempuraj D, Alysandratos KD, Theoharides TC. 2010. Luteolin and thiosalicylate inhibit HgCl(2) and thimerosal-induced VEGF release from human mast cells. Int J Immunopathol Pharmacol 23(4): 1015-1020.

  • Ceccatelli S, Daré E, Moors M. 2010. Methylmercury-induced neurotoxicity and apoptosis. Chemico-Biological Interactions 188(2): 301-308. doi:10.1016/j.cbi.2010.04.007

  • Ensink E. 2015. Preservative or poison? The science behind Thimerosal. The Substrate (online): http://substrate.asbmb.org/2015/05/15/preservative-or-poison-the-science-behind-thimerosal/

  • Pichichero ME, Cernichiari E, Lopreiato J, Treanor J. 2002. Mercury concentrations and metabolism in infants receiving vaccines containing thiomersal: a descriptive study. The Lanclet 360(9347): 1737-1741. doi:10.1016/S0140-6736(02)11682-5

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    $\begingroup$ is the toxicity of mercury in general primarily focused on its effects in the brain, then? $\endgroup$ – Michael Dec 31 '19 at 0:20
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    $\begingroup$ So its still nasty stuff but we simply poop it out fast enough to survive? $\endgroup$ – PTwr Dec 31 '19 at 2:20
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    $\begingroup$ @PTwr That really describes a very large number of toxins. Everything has some minimum dose required for it to actually be dangerous, and below that it's usually a case of the body getting rid of it (either through excrement or through some form of decomposition) faster than it can do anything dangerous. $\endgroup$ – Austin Hemmelgarn Dec 31 '19 at 3:22
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    $\begingroup$ Just as a curiosity - what prevents the body from breaking it down into the more toxic or the two, or one being converted into another (like how Ureic Acid breaking down into ammonia) by the body? $\endgroup$ – Pureferret Dec 31 '19 at 10:55
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    $\begingroup$ @Pureferret If you examine the structures of thimerosal, ethylmercury and methylmercury, you'll discover that breaking thimerosal down into methylmercury doesn't make sense, structurally; you'll also discover that reactions that turn ethylmercury into methylmercury don't really make sense energetically. $\endgroup$ – Williham Totland Dec 31 '19 at 23:03
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There is a considerable number of toxins that work by building strong complexes with vital molecules or cell mechanisms. If you start out with already complete complexes that the body will neither break up or accumulate, the toxicity is, so to say, already exhausted. Cyanide is like that: it builds strong complexes with iron, but something like potassium ferrocyanide is even commonly added to table salt.

Things are different with enzymatic poisons like Amatoxins or Botulism toxin since their toxicity is not used up while they are effecting their damage.

"Not being used up" refers to the idea that the toxins are active and can cause damage catalytically, over and over. Consider diphtheria toxin, which enzymatically inactivates proteins necessary for protein synthesis. Even a single molecule of that toxin (well, technically it's a complex of more than one) can kill a single cell by inactivating every single one of its targets and causing protein synthesis to grind to a halt. Cyanide, on the other hand, binds to its target and doesn't let go, so one molecule of cyanide can inactivate one molecule of (say) cytochrome c oxidase (complex IV).

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    $\begingroup$ The case of "toxicity not used up" is interesting. $\endgroup$ – Volker Siegel Dec 31 '19 at 16:48
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    $\begingroup$ @VolkerSiegel "Not being used up" refers to the idea that the toxins are active and can cause damage catalytically, over and over. Consider diphtheria toxin, which enzymatically inactivates proteins necessary for protein synthesis. Even a single molecule of that toxin (well, technically it's a complex of more than one) can kill a single cell by inactivating every single one of its targets and causing protein synthesis to grind to a halt. Cyanide, on the other hand, binds to its target and doesn't let go, so one molecule of cyanide can inactivate one molecule of (say) cytochrome c. $\endgroup$ – forest Jan 1 at 9:00
  • $\begingroup$ Thanks, that's worth adding it to the answer - which I just did. $\endgroup$ – Volker Siegel Jan 1 at 9:05

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