More about nanosilver toxicology (see earlier posting about US EPA silver nanomaterials consultation) this week courtesy of an article by Michael Berger about a new report from a group of German researchers. From the article on Nanowerk,
Silver had already been recognized in ancient Greece and Rome for its infection-fighting properties but in modern times pharmaceutical companies made more money developing antibiotics. However, thanks to emerging nanotechnology applications, silver has made a comeback in the form of antimicrobial nanoparticle coatings for textiles, surgical instruments, lab equipment, floors or wall paints (see for instance: “Antibacterial nanotechnology multi-action materials that work day and night”).
The flip side of silver’s desired toxicity towards microbes is that it might have toxic effects for humans as well (“As nanotechnology goes mainstream, ‘toxic socks’ raise concerns”) and this has raised debate about the safety of nanosilver products. Although scientists have worked to reduce the toxicity of antimicrobial nanosilver in products, concerns remain.
Not helping to put these concerns to rest is a new report from a group of researchers in Germany that shows that toxicity of silver nanoparticles increases during storage because of slow dissolution under release of silver ions.
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According to Epple [Matthias Epple, a professor for inorganic chemistry at the University of Duisburg-Essen], there is a general agreement that dissolved silver ions are responsible for the biological action that is especially pronounced against microorganisms. The lethal silver concentration of silver nanoparticles for human mesenchymal stem cells is about three times higher than that of silver ions (in terms of the absolute concentration of silver in a given solution).
The report has been published by the American Chemical Society in Chemistry of Materials. You can find an abstrect here, the full article is behind a paywall.
I was interested to note that the focus for the report is on the dissolution of nanoscale silver in water. By contrast, the US EPA consultation uses, as its starting point for the case study, nanoscale silver in an antibacterial spray. While laboratory researchers tend to focus on specifics such as the dissolution of silver nanoparticles and ions, the EPA’s strategy allows for a 360o view. Theoretically, commenters could focus on anything from the production of the air spray, its own packaging, its use in various situations such as hospitals or food packaging, etc., and the various ways it dissipates into the environment, e.g. being washed off and ending up in the water supply. This can lead to a comprehensive framework for future research activities examining more specific questions which provide answers that fit back into the framework.
Berger’s article reminds me of an October 29, 2009 news item on Science Daily about Swiss researchers, clothes washers, and nanosilver,
Scientists in Switzerland are reporting results of one of the first studies on the release of silver nanoparticles from laundering those anti-odor, anti-bacterial socks now on the market. Their findings may suggest ways that manufacturers and consumers can minimize the release of these particles to the environment, where they could harm fish and other wildlife.
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They found that most of the released particles were relatively large and that most came out of the fabrics during the first wash. The total released varied from 1.3 to 35 percent of the total nanosilver in the fabric. Bleach generally did not affect the amount released. “These results have important implications for the risk assessment of silver textiles and also for environmental fate studies of nanosilver, because they show that under certain conditions relevant to washing, primarily coarse silver-containing particles are released,” the paper says.
The research report was published by the American Chemical Society’s Environmental Science and Technology journal. The abstract is available here, the full article is behind a paywall.