There are three classes of mercury: metallic elemental mercury (quicksilver, Hg 0 ), inorganic mercurial salts (e.g., Hg 2 Cl 2 , Hg + , HgCl 2 , Hg +2 ), and organic mercurials (e.g., methylmercury, phenylmercury). Adverse effects from exposure to mercury differ depending on the form and the route of exposure..