Ethylmercury is one of the metabolites of thiomersal, which is used as a preservative in some vaccines. For this application, the ethylmercury salt sodium ethylmercuric thiosalicylate is used. Thiomersal (C9H9HgNaO2S) 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, but exposure standards based on methylmercury (such as those currently recommended by the EPA) are not demonstrated to be equivalent for ethylmercury.