Nano-silver: Old problems or new challenges?

by Andrew Maynard on September 9, 2008

Project on Emerging Nanotechnologies

The blogging community is no stranger to the use (and possible abuse) of nanometre-scale silver—products ranging from silver-enhanced socks and toothpaste to plush toys and cure-alls have all appeared in the spotlight recently. With each passing month, the number of nano-silver gizmos on the market is growing.

Back in March 2006 when the Project on Emerging Nanotechnologies Consumer Products Inventory was launched, there were 25 products claiming to use nanoscale silver. In contrast, the August 2008 update of the inventory brought the number of nano-silver containing products to 235—an increase of nearly ten times over two and a half years!

This fashion for a splash of silver in consumer products has quite naturally led to questions being asked—how much silver is being used, where does it go, and what harm does it do (if any) when it gets there? Unfortunately, answers to these questions have been less than forthcoming; leading to a lot of speculation and rather less science in the ensuing discussions. But this is hopefully about to change…

Some time ago, the Project on Emerging Nanotechnologies asked Dr. Sam Luoma—an internationally respected expert on silver in the environment—to turn his thoughts to the possible impacts of nano-silver. The result—just published—is a thorough exposition of what is known about silver in the environment, how this applied to nanoscale silver, what new potential challenges the use of nano-silver raises, and how these challenges might be addressed.

The report (available here. PDF, 1.1 MB), which includes a highly recommended foreword by J. Clarence Davies on the policy implications arising from Sam’s science-based analysis, is probably the most comprehensive assessment to date of the current state of knowledge on silver and nano-silver in the environment. By my reckoning it covers everything you ever wanted to know about silver, and then some…

Luoma starts off by looking at what is already known about silver in the environment; what happens to it, where it accumulates, its bioavailability, and its toxicity. He then goes on to ask how much of this can be applied to nanoscale silver, and where the nanoscale form of the material leads to new behaviour and new challenges.

The discussion follows a logical progression, using the “source-pathway-receptor-impact” principle for risk assessment suggested by Richard Owen and Richard Handy in 2007 (PDF, 428 KB). In essence, this deals with the questions:

  • Where does the silver come from?
  • Where does it go and how does it get there?
  • What is exposed to it? And
  • What happens then?

This turns out to be a smart move, because when the discussion moves from silver (about which we know quite a bit) to nanoscale silver (about which we know not a lot), a clear framework has been established for thinking about where nano-silver can probably be treated as other forms of silver, where its “nano-ness” likely leads to shifts in behaviour away from the established baseline, and where the critical data gaps and challenges lie.

This is a report that has to be read from cover to cover to get the full flavour of Luoma’s analysis. Fortunately, the 60 pages (72 with foreword, appendix and references) are written in a highly accessible style—never have marine clams been so engaging! However, here are a few things in particular that struck me as I read through the work:

  • First, Sam eloquently establishes that we know a lot about silver in the environment; we are not starting from zero knowledge, but have a solid baseline from which to build on. This is a timely reminder that dealing with nanotech risks will often mean building on existing knowledge, rather than starting from scratch.
  • Second, the physical, chemical and biological behaviour of silver in the environment is complex—this is not a substance that can be dealt with through sweeping generalizations. The transport, bioavailability and toxicity of the material depends to a significant degree on the chemistry of the environment it is within, and the potential to cause harm may decrease as well as increase depending on this environment. There is no reason to believe that things get any simpler when dealing with nanoscale silver.
  • Third, while somewhat speculative, it is possible to imagine scenarios where the distributed use and release of nanoscale silver could lead to relevant environmental loadings. In other words, just because the individual release rates from one washing machine or a single pair of nano-silver socks are extremely low, does not mean that the cumulative release rates from many nano-silver products will not be important. While I suspect that some of the usage figures in Sam’s scenarios may be on the high side of realistic, it is possible to show that the widespread use of nano-silver containing products could lead to environmental contamination levels comparable with those associated with the analogue photographic industry at its peak.
  • Fourth, silver nanoparticles could conceivably act as a “Trojan horse” for getting toxic silver ions into cells—essentially increasing the toxicity of the material by transporting it to places that are normally off-limits.
  • And finally, there are sufficient gaps in our knowledge over the release, fate and impact of nano-silver that, when coupled with what is known, demand strategic research into potential risks and their management at a level which currently does not exist.

But these are fleeting impressions that do not do the report justice, and are certainly no substitute for reading the report itself.

I suspect that nano-silver is here to stay—the value it adds to products is too real to ignore. But its safe use will depend on grappling with the new challenges it presents. And Luoma’s report provides what is probably the most thorough resource to date for identifying these challenges, and developing a plan of action for dealing with them.

Clearly, essential reading for anyone with a stake in ensuring a responsible and successful nano-silver business!

____________________________

Notes

The report “Silver Nanotechnologies and the Environment: Old Problems or New Challenges?” (PEN 15) is freely available at www.nanotechproject.org/publications/archive/silver/

In the spirit of full disclosure, I could be accused of having a biased perspective on this report; having worked closely with Sam through its development. So you probably shouldn’t take too much notice of me when I claim that this is a seminal report on nano-silver in the environment, and one that is destined to become the reference work in the field for some years.

Sam’s report is augmented by a database of silver nanotechnology used in commercial products, published on the Project on Emerging Nanotechnologies website (available here). This was compiled by Emma Fauss at the University of Virginia, and complements the PEN Consumer Product Inventory by including more extensive information on the use of nanoscale silver in products.

__________________________________________________________________

This post first appeared on the SAFENANO blog in September 2008

Comments on this entry are closed.