Metals are probably the oldest toxins known to humans.
Lead usage may have begun prior to 2000 BC in the smelting of silver. The environmental metals of greatest concern are lead, mercury, arsenic, and cadmium. Mercury is a contaminant of our water ways. Humans are exposed to mercury in the fish they eat as well as in the amalgam fillings in their teeth. Arsenic is found naturally in high concentration in drinking water in various parts of the world.