Heavy metals

Heavy metals are metals or chemical compounds containing metals with relatively high density, high atomic weights, or atomic numbers. 

This might mean up to 96 out of the 118 known chemical elements.  Mercury, lead and bismuth are examples. The term is widely used in science. They have a density of more than 5 g/cm3.Sengupta 2002, pp. 1–2  All of them are denser than iron 

The term is sometimes used for any toxic metal, or metalloid such as arsenic,Kumar, Abbas & Aster 2013, p. 276 regardless of density.Duffus 2002; Newman & Unger 2003, pp. 21–2 

The term heavy metals includes chromium, cobalt, nickel, copper, zinc, arsenic, silver, gold, cadmium, antimony, mercury, thallium, tungsten, platinum and lead. 

The heaviest metal by density is osmium. Although most heavy metals are toxic, not all of them are. For example, gold, which is one of the heaviest metals, is non-toxic and chemically inert in the body. Some gold compounds are toxic, however. More specific definitions of a heavy metal have been proposed but none is widely used. One common definition of a heavy metal is that it has a density and/or atomic number higher than iron.

Heavy metals are scarce in the Earth's crust because most have sunk into the Earth's core. Many are used in modern life. They are used, for example, in golf clubs, cars, antiseptics, self-cleaning ovens, plastics, solar panels, mobile phones, and particle accelerators.

References

 Kumar V, Abbas AK & Aster JC 2013, 'Environmental and nutritional diseases,' in V Kumar, AK Abbas & JC Aster (eds), Robbins basic pathology, 9th ed, Elsevier, Philadelphia, PA. 
 Newman MC & Unger MA 2003. Fundamentals of ecotoxicology, 2nd ed. Lewis, Boca Raton, FL. 
 Sengupta AK 2002, 'Principles of heavy metals separation', in AK Sengupta (ed), Environmental separation of heavy metals: engineering processes, Lewis, Boca Raton, FL. 

 Related pages 
Hyperaccumulator
Category:Metals