Last edited Thu Jan 29, 2026, 04:33 AM - Edit history (1)
simply separate. The nomenclature "ethylmercury" for what is actually diethylmercury is unfortunate, but deeply embedded in the language due to use by non-chemists, and obsolete nomenclature among chemists, particularly in industry. Diethylmercury, like other dialkylmercurys, is hightly toxic, and can diffuse through the skin. It is NOT added to any drugs or other products, though back in the 30s(?) and 40s it may have been used to kill microorganisms in certain settings; more usually, a derivative such as ethylmercury chloride (EtHgCl) was used. This use was banned after some poisoning events where EtHgCl-treated grain meant for planting was consumed by humans or pigs.
The compound (not mixture) used as an antibacterial and preservative is ethylmercurithiosalicylate, containing an ethylmercury group (with a +1 formal charge) bound to a water-soluble organic sulfide via a Hg-S bond. Mercury tends to form tight bonds with sulfur; cinnabar (HgS) is one of the least soluble salts known (Solubility 1.04×10−25 g/100 ml water (Ksp at 25 °C = 2×10−32)*). Thiols used to be referred to as "mercaptans" because of their ability to "capture" sulfur, which is why a raw egg (rich in thols and sulfide) is recommended as first aid in the event of ingesting mercury or its compounds. As the rest of the thimerosal molecule is metabolized, the ethylmercury cation can become separated, but tends to form the chloride salt (abbrec. EtHgCl) due to the strong Hg-Cl bond and the ubiquity of chloride in biological systems. The half-life for excretion of mercury from thimerosal is relatively short.
It would appear that the inventor of thimerosal made quite a lucky hit when he discovered this compound -- it's certainly conceivable that a randomly chosen organomercury compound would be horribly toxic, with all kinds of bad side effects, but despite decades of searching for bad effects due to low doses of thimerosal, none seem to have been found (in absurdly high doses, it is known to be quite toxic -- after all, if it didn't at least kill bacteria, it would be useless, so of course it has some toxicity). On the other hand, I don't know what other alternatives might have been tested -- if the methylmercury derivative had been used, instead of the ethylmercury one, the compound would certainly have been more toxic. In fact, many of the fears about thimerosal are based on extrapolation of data from methylmercury derivatives, and apparently have contributed to allowed exposures being set lower than necessary -- i.e. early estimates of thimerosal toxicity were probably too high.
* 10−12 would be one trillionth. 10−25 is 100 octillionths. i.e. these are very, very tiny numbers.
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