Heavy metals Totally Explained

A heavy metal is any of a number of higher atomic weight elements, which has the properties of a metallic substance at room temperature. There are several different definitions concerning which elements fall in this class designation. Alternative terms are 'metal' or 'semi-metal' (according to the element in view). Some of the nearly 40 known definitions are:

According to one definition, heavy metals are a group of elements between copper and bismuth on the periodic table of the elements—having specific gravities greater than 4.0.

A more strict definition increases specificity to metals heavier than the rare earth metals, which are at the bottom of the periodic table. None of these are essential elements in biological systems and additionally, most of the better known elements are toxic in fairly low concentrations. Thorium and uranium are occasionally included in this classification as well, but they're more often referred to as "radioactive metals". See actinides in the environment for further details of these radioactive metals.

Also, often the elements beyond mercury, for example, the actinides such as uranium and plutonium, are not excluded from the heavy metals. In the context of nuclear power plants, tHM means tons of heavy metal.

In astronomy, which defines any element heavier than helium a metal, a heavy metal or heavy element includes all elements that were not formed in the big bang; all but hydrogen (and deuterium), helium, and lithium.

Any toxic metals may be called "heavy metals", whether or not they're heavy.

Relationship to living organisms

Living organisms require trace amounts of some heavy metals, including iron, cobalt, copper, manganese, molybdenum, vanadium, strontium, and zinc, but excessive levels can be detrimental to the organism. Other heavy metals such as mercury, lead and cadmium (with one exception for the latter

) are toxic metals — they've no known vital or beneficial effect on organisms, and their accumulation over time in the bodies of mammals can cause serious illness. The pathway for toxic effects on humans is normally:

for the entry of heavy metals into the atmosphere as industrial stack gas

to enter the soil as a soil contaminant

to enter groundwater as a water pollutant

to be deposited in ocean bottoms or bay mud, which materials at a later time be dredged to the surface In medical usage, the definition is considerably looser and includes all toxic metals irrespective of their atomic weight: "heavy metal poisoning" can include excessive amounts of iron, manganese, aluminium, or beryllium (the seventh-lightest metal) as well as the true heavy metals.
Heavy metals in a hazardous materials (or "hazmat") setting are for the most part classified in Misc. on the UN model hazard class but, they're sometimes labeled as a poison when being transported.

Sources

Kuhn, Karl F. and Koupelis, Theo (2004) In Quest of the Universe, Fourth Edition. Jones and Bartlett Publishers, Canada. ISBN 0-7637-0810-0

Duffus, J. H. (2002) "Heavy Metals" – A meaningless term? – Pure Appl. Chem., 74 (5): 793-807, 3 Abb., 4 Tab.; Oxford.

External results

Click here for more details on Heavy Metals

External Link Exchanges

Do you know how hard it is to get a link from a large encyclopaedia? Well we're different and will prove it. To get a link from us just add the following HTML to your site on a relevant page:

<a href="http://heavy_metals.totallyexplained.com">Heavy metals Totally Explained</a>

Then simply click through this link from your web page. Our crawlers will verify your link, extract the title of your web page and instantly add a link back to it. If you like you can remove the words Totally Explained and embed the link in article text.
As long as your link remains in place, we'll keep our link to you right here. Please play fair - our crawlers are watching. Your site must be closely related to this one's topic. Any kind of spamming, dubious practises or removing the link will result in your link from us being dropped and, potentially, your whole site being banned.