Heavy metals

Heavy metals is a controversial and ambiguous term for <a href="/facts/Metal/pqQVs8QU">metallic</a> elements with relatively high <a href="/facts/Density/92p6hh9I">densities</a>, <a href="/facts/Atomic_weight/A3vbuz2n">atomic weights</a>, or <a href="/facts/Atomic_number/bgAr581S">atomic numbers</a>. The criteria used, and whether <a href="/facts/Metalloid/uMFVXuTq">metalloids</a> are included, vary depending on the author and context and it has been argued that the term "heavy metal" should be avoided. A heavy metal may be defined on the basis of density, atomic number or <a href="/facts/Chemical_property/uMVxKspS">chemical behaviour</a>. More specific definitions have been published, none of which have been widely accepted. The definitions surveyed in this article encompass up to 96 out of the 118 known <a href="/facts/Chemical_element/0jducgWD">chemical elements</a>; only <a href="/facts/Mercury_(element)/WlxfoHva">mercury</a>, <a href="/facts/Lead/EYljasJN">lead</a> and <a href="/facts/Bismuth/75FLjkoX">bismuth</a> meet all of them. Despite this lack of agreement, the term (plural or singular) is widely used in science. A density of more than 5 g/cm3 is sometimes quoted as a commonly used criterion and is used in the body of this article.
The earliest-known metals—common metals such as <a href="/facts/Iron/DkICCKIC">iron</a>, <a href="/facts/Copper/I8PEE8oX">copper</a>, and <a href="/facts/Tin/vxbbBgNz">tin</a>, and precious metals such as <a href="/facts/Silver/xXe41BGg">silver</a>, <a href="/facts/Gold/1znknojp">gold</a>, and <a href="/facts/Platinum/qJC6lQf7">platinum</a>—are heavy metals. From 1809 onward, <a href="/facts/Light_metal/EnY70VxC">light metals</a>, such as <a href="/facts/Magnesium/XyIhd2FG">magnesium</a>, <a href="/facts/Aluminium/7wmR8jYE">aluminium</a>, and <a href="/facts/Titanium/53ArnDoy">titanium</a>, were discovered, as well as less well-known heavy metals including <a href="/facts/Gallium/EucevDs9">gallium</a>, <a href="/facts/Thallium/v35pGMJB">thallium</a>, and <a href="/facts/Hafnium/rBNnlxDS">hafnium</a>.
Some heavy metals are either essential nutrients (typically iron, <a href="/facts/Cobalt/gqhScEw4">cobalt</a>, copper and <a href="/facts/Zinc/80b1qgk3">zinc</a>), or relatively harmless (such as <a href="/facts/Ruthenium/uzCm4ufn">ruthenium</a>, silver and <a href="/facts/Indium/zRq3stVb">indium</a>), but can be toxic in larger amounts or certain forms. Other heavy metals, such as <a href="/facts/Arsenic/k1c4f44D">arsenic</a>, <a href="/facts/Cadmium/wXkV2eIX">cadmium</a>, mercury, and lead, are highly poisonous. Potential sources of heavy metal poisoning include <a href="/facts/Mining/g6uDIFab">mining</a>, <a href="/facts/Tailings/g7TtDIJR">tailings</a>, <a href="/facts/Smelting/Ghdvhlga">smelting</a>, <a href="/facts/Industrial_waste/3Q8pUT8Q">industrial waste</a>, <a href="/facts/Agricultural_runoff/zPxoaA0D">agricultural runoff</a>, <a href="/facts/Chemical_hazard/9dBLejnB">occupational exposure</a>, <a href="/facts/Environmental_impact_of_paint/AlhprtEe">paints</a> and <a href="/facts/Treated_wood/eLLDnkbE">treated timber</a>.
Physical and chemical characterisations of heavy metals need to be treated with caution, as the metals involved are not always consistently defined. As well as being relatively dense, heavy metals tend to be less <a href="/facts/Chemical_reaction/GpqWlKrz">reactive</a> than lighter metals and have far fewer <a href="/facts/Solubility/kLE9h3Jb">soluble</a> <a href="/facts/Sulfide/d8YMjLeu">sulfides</a> and <a href="/facts/Hydroxide/zW0wxpWD">hydroxides</a>. While it is relatively easy to distinguish a heavy metal such as <a href="/facts/Tungsten/WYwbNDYX">tungsten</a> from a lighter metal such as <a href="/facts/Sodium/eYuSPu2V">sodium</a>, a few heavy metals, such as zinc, mercury, and lead, have some of the characteristics of lighter metals; and lighter metals such as <a href="/facts/Beryllium/dv295voP">beryllium</a>, <a href="/facts/Scandium/TJRt1chg">scandium</a>, and titanium, have some of the characteristics of heavier metals.
Heavy metals are relatively rare in the <a href="/facts/Structure_of_the_Earth/678dYXU7">Earth's crust</a> but are present in many aspects of modern life. They are used in, for example, <a href="/facts/Golf_club/e10LtRMx">golf clubs</a>, <a href="/facts/Cars/I1IsH8IK">cars</a>, <a href="/facts/Antiseptic/ua05WK9M">antiseptics</a>, <a href="/facts/Self-cleaning_oven/56maIKKY">self-cleaning ovens</a>, <a href="/facts/Plastic/Kla5QItn">plastics</a>, <a href="/facts/Solar_panel/gufbEu8n">solar panels</a>, <a href="/facts/Mobile_phone/H3EcqD9h">mobile phones</a>, and <a href="/facts/Particle_accelerator/Pkuc08xC">particle accelerators</a>.

Heavy metals open-in-new

Heavy metals