The Mercury Rating is based on the occurence and concentration of mercury in components of prodcuts. Levels below 40 ppm were assigned a LOW level. Products with mercury between 41 and 100 ppm were assigned a MEDIUM level of mercury. U.S. and European Union packaging standards limit mercury to an upper limit of 100 ppm in packaging. The European RoHS directive sets a limit of 100 ppm. Products with mercury above 100 ppm were assigned a HIGH level of mercury. Mercury, depending on the level of exposure and the form of mercury, has been linked to kidney damage, and is toxic to the nervous system.
Note: The European toy standard (for migration from toys) for mercury is 60 ppm. The U.S. voluntary toy standard (ASTM F973-07 for migration from toys) is 60 ppm. On February 10, 2009 the CPSC adopted the ASTM F973-07 limits for mercury and other metals(view ASTM standard) as a mandatory standard.