Re:

"This means that nearly anything can displace it such as calcium, potassium, sodium, etc. "


That's clearly nonsense to any second year chemistry student who's learnt the strong affinity the sulfur atom (the sulfurs in body protein) has for all heavy metals, including mercury - the Hg to sulfur bonds in the body's proteins is almost impossible to break unless a more powerful chelating substance is present. Its why many metal ores (minerals) are able to exist on the earth as sulfides (cinnabar, pyrite) and remain stable for eons.

Definitely not readily displaceable by alkali metals or alkaline earth metals. Tweet