EtHg

EtHg is the shorthand for ethylmercury, an organomercury compound in which an ethyl group is bound to a mercury atom (Et-Hg). In practice, EtHg often appears in compounds such as thimerosal (also known as thiomersal), a mercury-containing preservative used in some medical preparations. Thimerosal is the ethylmercury thiosalicylate salt, historically employed to prevent microbial growth in multi-dose vials of vaccines and certain ophthalmic solutions.

Chemically and pharmacologically, EtHg belongs to organomercury species that can release mercury within biological systems. Ethylmercury is typically absorbed and distributed differently than methylmercury, with ongoing research describing its toxicokinetics, tissue distribution, and excretion. In general, ethylmercury is thought to be cleared from the bloodstream more quickly than methylmercury and is more rapidly excreted by the kidneys, though high exposures can still pose toxic risks, particularly to the nervous system. The potential for neurotoxicity is recognized at sufficient doses, and regulatory agencies emphasize that risk is related to dose and exposure duration.

Uses and regulation vary by country and over time. Thimerosal has been largely removed or reduced to trace amounts in most pediatric vaccines in many regions, including the United States and the European Union, though small amounts may remain in some multi-dose vaccine vials or in certain non-vaccine products. Public health authorities generally consider the low levels used in approved products to be safe, and extensive studies have found no causal link between thimerosal-containing vaccines and autism or other chronic neurodevelopmental disorders.