Heavy Metal Definition and List

Mercury droplets on surface

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A heavy metal is a dense metal that is (usually) toxic at low concentrations. Although the phrase "heavy metal" is common, there is no standard definition assigning metals as heavy metals.

Key Takeaways: Heavy Metal Definition and List

  • There is no consensus on the definition of a heavy metal. It is either a metal of high density or a toxic, relatively dense metal.
  • Some metals, such as lead and mercury, are both dense (heavy) and toxic. Lead and mercury are universally agreed to be heavy metals.
  • Other metals, such as gold, are dense yet not particularly toxic. Some people classify these metals as "heavy" based on their density, while others exclude them from a list of heavy metals because they do not pose a major health hazard.

Characteristics of Heavy Metals

Some lighter metals and metalloids are toxic and, thus, are termed heavy metals though some heavy metals, such as gold, typically are not toxic. ​

Most heavy metals have a high atomic number, atomic weight and a specific gravity greater than 5.0 Heavy metals include some metalloids, transition metals, basic metals, lanthanides, and actinides. Although some metals meet certain criteria and not others, most would agree the elements mercury, bismuth, and lead are toxic metals with sufficiently high density.

Examples of heavy metals include lead, mercury, cadmium, sometimes chromium. Less commonly, metals including iron, copper, zinc, aluminum, beryllium, cobalt, manganese and arsenic may be considered heavy metals.

List of Heavy Metals

If you go by the definition of a heavy metal as a metallic element with a density greater than 5, then the list of heavy metals is:

  • Titanium
  • Vanadium
  • Chromium
  • Manganese
  • Iron
  • Cobalt
  • Nickel
  • Copper
  • Zinc
  • Gallium
  • Germanium
  • Arsenic
  • Zirconium
  • Niobium
  • Molybdenum
  • Technetium
  • Ruthenium
  • Rhodium
  • Palladium
  • Silver
  • Cadmium
  • Indium
  • Tin
  • Tellurium
  • Lutetium
  • Hafnium
  • Tantalum
  • Tungsten
  • Rhenium
  • Osmium
  • Iridium
  • Platinum
  • Gold
  • Mercury
  • Thallium
  • Lead
  • Bismuth
  • Polonium
  • Astatine
  • Lanthanum
  • Cerium
  • Praseodymium
  • Neodymium
  • Promethium
  • Samarium
  • Europium
  • Gadolinium
  • Terbium
  • Dysprosium
  • Holmium
  • Erbium
  • Thulium
  • Ytterbium
  • Actinium
  • Thorium
  • Protactinium
  • Uranium
  • Neptunium
  • Plutonium
  • Americium
  • Curium
  • Berkelium
  • Californium
  • Einsteinium
  • Fermium
  • Nobelium
  • Radium
  • Lawrencium
  • Rutherfordium
  • Dubnium
  • Seaborgium
  • Bohrium
  • Hassium
  • Meitnerium
  • Darmstadtium
  • Roentgenium
  • Copernicium
  • Nihonium
  • Flerovium
  • Moscovium
  • Livermorium

Tennessine (element 117) and oganesson (element 118) have not been synthesized in sufficient quantities to know their properties for certain, but tennessine is likely either a metalloid or a halogen, while oganesson is a (probably solid) noble gas.

Keep in mind, this the list of heavy metals includes both natural and synthetic elements, as well as elements that are dense, but necessary for animal and plant nutrition.

Noteworthy Heavy Metals

While the classification of certain dense metals as heavy metals is debatable, others are noteworthy heavy metals because they are both heavy, toxic, and pose a health risk because of extensive use in society.

  • Chromium: The two common oxidation states of chromium are 3+ and 6+. The 3+ oxidation state is essential, in minute amounts, for human nutrition. Hexavalent chromium, on the other hand, is highly toxic and is a known human carcinogen.
  • Arsenic: Technically, arsenic is a metalloid rather than a metal. But, it is toxic. Arsenic readily binds to sulfur, disrupting enzymes used in metabolism.
  • Cadmium: Cadmium is a toxic metal that shares common properties with zinc and mercury. Exposure to this element can lead to a degenerative bone disease.
  • Mercury: Mercury and its compounds are toxic. Mercury forms organometallic compounds that pose an even greater health risk than its inorganic forms. Mercury primarily causes central nervous system damage.
  • Lead: Like mercury, lead and its compounds damage the nervous system. There is no "safe" exposure limit to either mercury or lead.

Sources

  • Baldwin, D. R.; Marshall, W. J. (1999). "Heavy metal poisoning and its laboratory investigation". Annals of Clinical Biochemistry. 36(3): 267–300. doi:10.1177/000456329903600301
  • Ball, J. L.; Moore, A. D.; Turner, S. (2008). Ball and Moore's Essential Physics for Radiographers (4th ed.). Blackwell Publishing, Chichester. ISBN 978-1-4051-6101-5.
  • Emsley, J. (2011). Nature's Building Blocks. Oxford University Press, Oxford. ISBN 978-0-19-960563-7.
  • Fournier, J. (1976). "Bonding and the electronic structure of the actinide metals." Journal of Physics and Chemistry of Solids. 37(2): 235–244. doi:10.1016/0022-3697(76)90167-0
  • Stankovic, S.; Stankocic, A. R. (2013). "Bioindicators of toxic metals" in E. Lichtfouse, J. Schwarzbauer, D. Robert (2013). Green materials for energy, products and depollution. Springer, Dordrecht. ISBN 978-94-007-6835-2.
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Helmenstine, Anne Marie, Ph.D. "Heavy Metal Definition and List." ThoughtCo, Oct. 4, 2021, thoughtco.com/definition-of-heavy-metal-605190. Helmenstine, Anne Marie, Ph.D. (2021, October 4). Heavy Metal Definition and List. Retrieved from https://www.thoughtco.com/definition-of-heavy-metal-605190 Helmenstine, Anne Marie, Ph.D. "Heavy Metal Definition and List." ThoughtCo. https://www.thoughtco.com/definition-of-heavy-metal-605190 (accessed October 16, 2021).