heavy metal definition

[Gregg Cohen]

We got into a discussion today that asked the question:

"What is the definition of a 'heavy metal', and which
metals fulfill these requirements?

We just couldn't find an 'official' definition.

Thanks

gc

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Gregg Cohen, Ph.D. 130 Radnor-Chester Rd.
Scientist Suite 100
Picker International, Inc. St. Davids, PA 19087
CT Visualization (216)473-4323
gco...@stdavids.picker.com

[bro...@vms1.bham.ac.uk]

In article <1993Dec8.1...@picker.com>, gco...@stdavids.picker.com (Gregg Cohen) writes:
> We got into a discussion today that asked the question:
>
> "What is the definition of a 'heavy metal', and which
> metals fulfill these requirements?
>
> We just couldn't find an 'official' definition.
>

This is a term that chemists don't seem to like to use even thought the rest
of us do (as microbiologists rarely use 'germ'). It is too non-specific.
Varying definitions exist, for example:

1. Those elements in the lower part of the periodic groups which are metals
(metals are another problem in chemical defintion). This might exclude the top
row of transition elements, for example (Ti to Zn), but include Cs and Ba.

2. The soft 'b' class metals (see Frausto da Silva and Williams 'The Biological
Chemistry of the Elements', Pergamon Press, 1991; or Nieboer and Richardson,
Environ. Pollution (ser B) 1, 3-26, 1980). The latter paper is an attempt to
replace the term with something which is chemically and biologically
significant.

Both classifications split many commonly accepted 'heavy metals' between
classes. Numerous other working definitions exist, but are not chemically
and/or biologically rigorous.

I hope that helps. We work on heavy metals in bacteria, and haven't got a good
definition. We always seem to find exceptions. Maybe you should put the
same question to a chemical list.

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[David E Salt]

When the term heavy metal is used in conection with biolological processes
then a definition based on the preference for donor atoms in ligands is
the most applicable. Most 'traditional' heavy metals have a donor atom
preference of S>N>O which puts them in class b or borderline based on the
definition of Nieboer and Richardson, Environmental Pollution (series B)
1, 3-26, 1980.

I hope this helps

David Salt