Voodoo and Mercury
Mercury is believed to attract love, luck or riches and can protect against evil. It is also known to cause permanent damage to developing children's brains and have numerous harmful effects on the nervous system of adults.
Its uses in religious practices can be debated under First Amendment, but its dangers should not. A good starting point for education about the safe limits of mercury is EWG's tuna calculator where personalized information about safe levels of tuna is available.