Arsenic is a metalloid widely distributed in the earth’s crust and present at an average concentration of 2 mg/kg. Arsenic can exist in four valency states: –3, 0, +3 and +5. Under reducing conditions, arsenite (As (III)) is the dominant form; arsenate (As (V)) is generally the stable form in oxygenated environments. Elemental arsenic is not soluble in water. Arsenic salts exhibit a wide range of solubilities depending on pH and the ionic environment.