Ivan Anderson wrote: > Dear MAMA2BEAR, > > The designation 'heavy metal' is an arbitrary label, usually meaning > 'toxic metal'. > > All metals are toxic in sufficient doses, silver is less toxic than > most. > > Here are some references which demonstrate the arbitrary nature of > 'heavy metals'. > > Regards > Ivan. > > What is a heavy metal? > > "Turning to regular dictionaries (as opposed to chemical dictionaries): > Webster (3) gives "A metal of high specific gravity; esp: a metal having > a specific gravity of 5.0 or over." > > All the metals that I think of as heavy metals have densities above 5 > g/cm3, while no metals with densities below 5 have heavy metal > chemistry. This supports Webster's definition, but it is deceptive. > Being a heavy metal has little to do with density, but rather concerns > chemical properties.
How about iron. It is essential for life, and comprises much of the hemoglobin of the blood. It has a density of 7.8. > > > The metals that I have seen referred to as heavy metals comprise a block > of all the metals in Groups 3 to 16 that are in periods 4 and greater. > This seems to be a definition that should be generally useful. It may > also be stated as the transition and post-transition metals." > [silver is a transition metal - Ivan] > http://jchemed.chem.wisc.edu/Journal/Issues/1997/Nov/abs1374.html > This is the chemistry definition, and appears to be pretty consistant. > > "heavy metal > > In the human health context, heavy metals are transition metal elements > in the sixth and heavier periods [ silver is in the fifth period - > Ivan ], which should be present only in small quantities. Like lead Pb) > and mercury (Hg), for instance. > In microelectronics, heavy metals are period four and six transition > metals that are troublesome contaminants because of their electrical > properties. Au (see Gold) and Pt are lifetime killers in Si. Fe, Cu, Ni, > and Cr, in period IV, have atomic weights in the range 51 to 63, or > about twice that of Si. They're at the top of the famous curve of > (nuclear) binding energy, so they're rather common. > > Because the conventional definitions include only transition metals, > they exclude, amusingly, barium (Ba), whose name means heavy." > http://www.plexoft.com/SBF/H01.html > > "The term heavy metal has apparently arisen as a convenience among > policy makers for referring to metals with potential toxicity. Cadmium, > mercury, lead and bismuth are often mentioned, partly because human > activities have increased their concentration in the environment. Other > metals are also associated with health problems. On the other hand, all > are not, gold being an example because it cannot be easily absorbed by > the body. Moreover, even light metals may cause health problems. > > A scientific definition of heavy metal might be based on whether a metal > has a lower or higher density than its oxide. The dividing line in the > periodic table will then go through titanium, which has several oxides, > some of which are heavier and some lighter than pure titanium. That puts mercury as lower, but close to the definition of at weight 200 being the dividing line. > Another > approach defines heavy metal as one that has a density greater that 6.0 > grams per cubic centimetre. Thereby, metals heavier than vanadium would > be heavy metals [ silver is heavier than vanadium, as is magnesium, > copper, iron, zinc and other essential metals - Ivan ], thus including > most of the commercial metals." > http://206.191.21.210/icme/q&as/qav5n4.htm As well as iron. I don't think even the FDA would consider iron supplements as heavy metal. Marshall
