Ethylmercury (sometimes ethyl mercury) is a cation composed of an ethyl group bound to a mercury(II) centre; its chemical formula is C2H5Hg+. Ethylmercury is sometimes used as a generic term to describe organomercury compounds which include ethylmercury such as ethylmercury chloride and ethylmercury urea.
Ethylmercury is one of the metabolites of thiomersal, which is used as a preservative in some vaccines. Thiomersal is the ethylmercury-releasing compound sodium ethylmercuric thiosalicylate, C9H9HgNaO2S, which is made from the combination of ethyl mercuric chloride, thiosalicylic acid, sodium hydroxide, and ethanol.
Unlike methylmercury, ethylmercury has not been found to bioaccumulate. The toxicity of ethylmercury is not well studied - exposure standards based on methylmercury (such as those currently recommended by the United States Environmental Protection Agency) have not been demonstrated to be equivalent for ethylmercury.