according to the history channel ,during lewis and clark exposition a long time ago murcury was used to fight off certain illnesses ,parasites ,researchers could trace there route by maps , but the strange thing was that they found high mercury levels at all there camp sights probably from human waste and urin ,so the half life of mercury is much more than we have been told , we have been told 30 years but if they are finding mercury readings from hundreds of years ago this is not a good thing ,just glad all my amalgams are out!!!!!!!!!!!!!