Beyond the natural mercury emission to the atmosphere, the anthropogenic contribution mainly as Hg(II) has increased; consequently, the mercury content in natural waters increased as well. The main part of Hg(II) rapidly attaches to particulates in suspension found in water bodies, and then is deposited in sediments where covalent molecules are formed, such as HgCl and CH3Hg ; the latter forms dimethylmercury [Hg(CH3)2], a molecular volatile liquid. The formation of Hg(CH)2in natural waters is normally favored under anaerobic conditions, where microorganisms convert Hg(II) to Hg(CH3)2
. This fact occurs mainly in the first layers of sediments in rivers and lakes. Dimethylmercury is transformed under acidic or neutral conditions into the monomethylmercury and other forms, such as CH3Cl and CH3OH. Therefore, the
production of methylmercury in natural waters predominates over the formation of dimethylmercury. Methylmercury diffuses easier than Hg(II) salts into animal fatty
tissues and this characteristic facilitates its bioaccumulation. Once in the body, methylmercury may bind to sulfur-containing amino acids forming soluble compounds
in animal tissues. Due to these reasons, methylmercury is the most hazardous mercury form