An element called Dolomite can turn anything black.
Theorhetically, yes. *note* This answer could be improved and took the place of an edit which violated the terms of service. If you think you can improve this answer, please contribute.
They could be a cause, but you should get checked. Black feces could mean internal bleeding
the element mercury can cause brain damage of kidney damage which could be fatal
no
well smoking could cause your lungs black
isn't that a disease?
That could be graphite, which is a natural allotrope of the element carbon.
when blood dries, it can get pretty dark and look black. and if its dirty it could look black.
If you mean something else, like- What can speed up a chemical reaction, that would be a catalyst. Or, you could say heat, though that is not an element.
If you have a copper float ball that will do it
cause he was black.
Not usually, but it could be an element of a set.