120 Years of Nanosilver History: Implications for Policy Makers

Abstract

Nanosilver is one nanomaterial that is currently under a lot of scrutiny. Much of the discussion is based on the assumption that nanosilver is something new that has not been seen until recently and that the advances in nanotechnology opened completely new application areas for silver. However, we show in this analysis that nanosilver in the form of colloidal silver has been used for more than 100 years and has been registered as a biocidal material in the United States since 1954. Fifty-three percent of the EPA-registered biocidal silver products likely contain nanosilver. Most of these nanosilver applications are silver-impregnated water filters, algicides, and antimicrobial additives that do not claim to contain nanoparticles. Many human health standards for silver are based on an analysis of argyria occurrence (discoloration of the skin, a cosmetic condition) from the 1930s and include studies that considered nanosilver materials. The environmental standards on the other hand are based on ionic silver and may need to be re-evaluated based on recent findings that most silver in the environment, regardless of the original silver form, is present in the form of small clusters or nanoparticles. The implications of this analysis for policy of nanosilver is that it would be a mistake for regulators to ignore the accumulated knowledge of our scientific and regulatory heritage in a bid to declare nanosilver materials as new chemicals, with unknown properties and automatically harmful simply on the basis of a change in nomenclature to the term "nano".

When enough is enough

“…(This is partly because the solubility of nanosilver is not fully understood, and the solubility influences the bioavailability which, in turn, influences the sensitivity of silver-resistant and silver-sensitive bacteria 17 .) Finally, we predict that the SCENIHR will underline the importance of silver speciation as this has been a general theme in many previous reviews 3,11,14,16,[18][19][20][24][25][26] .…”

“…Two of the review articles in journals were also funded by the European Commission 14,16 . And 2011 saw the publication of five more review articles on nanosilver in scientific journals [21][22][23][24][25] , plus a 136-page report from the Danish Environmental Protection Agency (Danish EPA) about nanosilver and six other nanomaterials 26 .…”

“…Hence, we predict that the SCENIHR's upcoming review will consist of five main sections summarizing: the properties and uses of nanosilver; human and environmental toxicity; microbial resistance; risk assessment; and research needs 3,8,10,14,16,[18][19][20][24][25][26] . We also predict that the SCENIHR's report will say something along the following lines: "Nanosilver is reportedly one of the most widely used nanomaterials in consumer products today but the scale of production and use is unknown.…”

“…After reviewing the literature on human toxicity, there is a good chance that the SCENIHR will say that the toxicity of silver metal is generally considered to be relatively low, while noting that a non-life-threatening bluish-grey discolouring of the skin has been found only after high and repeated ingestion or inhalation of colloidal silver 2,3,10,20,21,24,26 . And the conclusions will probably echo those of the highly cited review published in Nanotoxicology in 2009 and several other recent reviews 6,14,20,23 by saying something along the following lines: the number of wellcontrolled studies on the potential toxicities of nanosilver as well as the current knowledge of the kinetics of nanosilver is too limited to provide a proper foundation of human risk assessment.…”

“…Moreover, because inhibition of nitrifying bacteria by nanosilver has been observed in the very few original studies that have been published, the SCENIHR will have to consider this topic under the heading of 'Other environmental, health and safety (EHS) issues' because this phenomenon might affect the proper functioning of wastewater treatment plants 20,23,26 . It remains uncertain whether nanosilver is more toxic than ionic silver, the report is likely to say, because the effects seen in many cases can be ascribed to ionic silver: however, some studies have documented a more pronounced effect associated with nanosilver, but the data is inconclusive 2,9,19,22,24,25 .…”