Mercury (Amalgam) were usually in a tooth. A crown goes over the whole tooth and contacts the gums, therefore in contact with blood/tissue. I wouldn’t lower your eyebrows, and when you do, it won’t matter anyways.
Fear sells very well, scary movies, big foot, UFOs and Nessy.
For a reality check go to FDA.gov and read about the types of filling material available including silver amalgam and you will not be so afraid. Sorry, can not help you with the other scary items.