How 'heavy' should an element be, to be a "Heavy Metal"? I've come across the term "Heavy metals" innumerable times in articles, mostly pertaining to environmental issues.

Is there a weight range (of sorts) against which an element (metal) is classified as a "Heavy metal"?

Often I see "Heavy metals" refer to Cadmium (Atomic number 48), Mercury (Atomic number 80) and Lead (Atomic number 82), but does this term also apply to metals of intermediate atomic masses [such as Tungsten (Atomic number 50), Gold (Atomic number 79) and Tin (Atomic number 81)]?

I can't seem to find any chemical literature that deals with this, so I suspect that the term "Heavy metal" has no real serious scientific definition.
There is no true, accepted definition of heavy metal. I was taught to apply the option a metal that has density equal to or over $5.0\ \mathrm{g/cm^3}$.

Other variants include a different density range, specific gravity over density, environmental impact, atomic number, toxicity, or atomic mass, even chemical properties. See here$^{[1]}$ for further information and references.




$[1]$ John H. Duffus. '"Heavy metals"—a meaningless term?'. IUPAC technical report. Pure and Applied Chemistry, $(2002)$, 74(5), pp 793$-$807.