The answer to whether or not silver is, indeed, a heavy metal, is not as easy to answer as would first appear. This document looks at the legal, medical, and scientific qualifications of the term "heavy metals", and questions both the common belief and relevancy of the term "heavy metal". Certain groups of people try to classify silver as a heavy metal such as cadmium and mercury, in order to promote fear mongering regarding the use of silver in medicine. This document serves to debunk such a claim, and educate interested individuals about the truth of this classification, and it's relevance to silver use by people.
in the News...
The FDA has cleared another silver-based
product. The AlphaSan® antimicrobial additive ( CAS Number: 265647-11-8
) is a zirconian phosphate-based ceramic ion-exchane resin made with
silver, and has been cleared by the FDA as an acceptable food contact
"On surfaces treated
with AlphaSan antimicrobial, bacteria still find their way. However,
they get an extra special dose of silver ions." - Milliken Corp.
Read more: FDA clears silver-based antimicrobial additive...
There is No Scientific of Medically Significant Basis to Classify Silver as a Heavy Metal
There is no Consensus on a Scientifically Valid Definition of Heavy Metal
"There is a tendency, unsupported by the facts, to assume that all so-called “heavy metals” and their compounds have highly toxic or ecotoxic properties. This has no basis in chemical or toxicological data. Thus, the term “heavy metals” is both meaningless and misleading."
- John H. Duffus, The Edinburgh Centre for Toxicology, Scotland, "Pure and Applied Chemistry" 74, 793–807
Bjerrum’s Inorganic Chemistry contains the earliest reference to the term "Heavy Metals" in chemistry, published in 1936. Bjerrum defined heavy metals based on density. Any metal with a density greater than 4 g/cm3 was thus considered to be a heavy metal. However, Bjerrum's definition was never accepted, nor used as a formal or official definition of a heavy metal.
However, there is no relationship between density and any reactive properties associated with metals, or any other element in the periodic table. Heavy metals were redefined based on a gram atomic weight, and also by the atomic number on the periodic table ( with many variations in "opinion" of the starting number ). By some of these "official" definitions of what a heavy metal is, both Magnesium and Potassium are classified as heavy metals.
The most widely used toxicology reference, Casarett and Doull’s Toxicology, never uses the term “heavy metal”, but only references toxic metals. This is most likely due to the fact that the heavy metal classification, in any historical or modern form, lacks scientific validity.
A few thoughts by Stephen J. Hawkes of Oregon State University, Department of Chemistry, demonstrate an interesting perspective:
"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. These acquired the name heavy metals because they all have high densities, but the usefulness of the term is related to their chemistry, not their density. It is not necessary to decide whether semimetals should be included as heavy metals, which is fortunate, since it is unlikely that any decision would be generally agreeable."
From a chemical standpoint, the above definition is satisfactory. However, it is clear that this definition of "heavy metal" may not in any way be related with suspected toxicity, but has meaning only pertaining to specific chemical properties.
Hawkes also places the whole "controversy" in rather comical perspective by sharing a chemistry teacher's answer to the question: What is a Heavy Metal?
"I asked this question of my introductory chemistry teacher over 50 years ago. He replied rather hesitantly, "A metal that behaves in a heavy metal manner." A vague term requires a vague definition, but just what is a 'heavy metal manner'?"
Medically & Legally: Classification of Heavy Metals is Dependent on Regulatory Agencies
Silver, medically, does not share the toxicology associated with what are commonly described as heavy metals, and technically referred to as "toxic metals", such as mercury, cadmium, arsenic and lead.
Legally, the definition of what is or is not a heavy metal varies depending on which regulatory agency one queries.
As an example, According to SIGNA's medicare qualification documents, silver is not classified as a heavy metal. The most logical explanation for this is simple: Silver does not pose the same health risks as toxic metals, and there is no medical regularatory agency in the world which claims that it does.
Is silver a heavy metal?
Silver, medically, does not share the toxicology associated with what are commonly described as heavy metals. Legally, the definition of what is or is not a heavy metal varies depending on which regulatory agency one queries. According to SIGNA's medicare qualification documents, silver is not a heavy metal.
The term heavy metal is not truly a scientific term, and there has never been consensus on the meaning of this term in the scientific community. Classification of "heavy metal" has never been scientifically based on any actual quality associated with any element, although many adaptations to the periodic table have been attempted.
There is no basis from a biological standpoint, a chemical standpoint, or any other scientifically demonstrable standpoint including any medical significance that would suggest any actual significant meaning for the term heavy metal as applied to silver, or any other metal.
Please see the following references for further details:
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