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Some people blame the preservative thiomersal in vaccines for all kinds of illnesses, but mainly for autism. As thiomersal is a mercury compound, there is some plausibility in suspecting it may cause some damage, but is there some hard data on how dangerous it really is?

How comparable are the effects of thiomersal to equal amounts of elementary mercury or methyl mercury? Is there evidence that the amount that was typically used in vaccines (it is seldom used now) is harmful?

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It also was used in saline solution for contact-lens wearers quite some time ago. I stopped wearing them in the mid-90s, and my saline had been thimerosal-free for some time. – David Thornley Mar 11 '11 at 3:09
up vote 26 down vote accepted

Thiomersal itself is toxic in quantity, degrading to ethylmercury (C2H5Hg+).

As a vaccine preservative, however, it is harmless. (Global Advisory Committee on Vaccine Safety (2006-07-14): "Thiomersal and vaccines".) This hasn't stopped anti-vaccine activists claiming that the Hg+ atom has nigh-magical powers of autism-causing evil, however, despite no link whatsoever having been found with much research.

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How does ethyl mercury compare in toxicity to methy mercury? Some anti-vaccine activists use the methyl mercury uptake recommendations to argue against thiomersal, are they comparable in toxicity? – Mad Scientist Feb 25 '11 at 0:06
The answer is "it doesn't matter, because the quantities in the vaccine are ridiculously tiny by comparison." They are seeing an Hg+, assuming Wakefield wasn't a proven fraud and assuming it must cause autism even if they haven't got a mechanism as yet. – David Gerard Feb 25 '11 at 0:16
Any comment regarding this recent news article? – user2813274 May 26 '15 at 16:57

Thimersal does not cause autism. The only study indicating such was proven to be not just shoddy, but an actual fraud committed for the purpose of profiting on the legal fees from ensuing lawsuits. There have been many studies across multiple countries using different vaccine preservatives which show that there's no link between autism and any vaccine.

Thimersal is the poster child for correlation != causation. Just because kids happen to become symptomatic for autism at the same time they get vaccines, people swallowed the bait - hook, line, and sinker.

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Can you provide links to the fraud finding? – morganpdx Feb 24 '11 at 23:55
@morganpdx Russel is certainly refering to Andrew Wakefield, see this link for some information on that:… . Brian Deer has written a lot about that case, if you're interested. – Mad Scientist Feb 24 '11 at 23:58
Godlee F., Smith J., Marcovitch H. "Wakefield’s article linking MMR vaccine and autism was fraudulent." BMJ 2011; 342:c7452 doi: 10.1136/bmj.c7452 (Published 5 January 2011) – David Gerard Feb 24 '11 at 23:59
@Fabian, @David Very nice. Thank you! – morganpdx Feb 25 '11 at 0:22
Actually, that's not correlation != causation, because there isn't even a correlation. What we have here is observation bias, where people who's kids coincidentally became symptomatic after vaccines assume correlation, because they're not looking at the vast number of kids where it didn't happen. When you vaccinate a million kids a year, some of them will have diseases or conditions manifest at nearly the same time. – John Rhoades Jul 14 '11 at 19:36

Thiomersal is toxic, in much higher dosages than found in vaccines.

Here is some safety information about thiomersal.

Its OEL (occupational exposure limit) is 0.05 mg/m3. (Ibid)

[And the autism link, is of course, fraudulent nonsense.]

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