The past few years has seen an explosion of interest in silver nanoparticles.  Along with a plethora of products using the particles to imbue antimicrobial properties on everything from socks to toothpaste, nanometer scale silver particles have been under intense scrutiny from researchers and policy makers concerned that they present an emerging health and environmental risk.  But a paper published last month in the journal ACS Nano suggests that, contrary to popular understanding, we’ve been exposed to silver nanoparticles for as long as we have been using the metal.

I became aware of work in Jim Hutchison’s lab at the University of Oregon some months ago that showed nanoscale silver particles are readily released from larger particles and pieces of metal.  I remember the shiver (quite literally) as I saw data that seemed to challenge the current obsession with nanoscale silver as a possible new and unusual risk to people and the environment.  And at the time I wondered just how people would react when they discovered how ubiquitous exposure to nano-silver has probably been for the past few thousand years.

But rather than headlines screaming “feds invest millions in researching a centuries old non-problem” when the work was published last month, the response was rather muted.  Since publication, there has been a piece in Chemical & Engineering News, a long article written by Gwyneth Shaw in the New Haven Independent, a bizarrely headlined article claiming “Nanoparticles ‘no threat to health'” in TG Daily (as if the inverted commas justify the clearly unfounded statement)… and that’s about it.  And I’m not quite sure what to make of this deafening indifference.

From the paper in ACS Nano: Over a period of four weeks and in the presence of moisture, 75 nm silver particles became surrounded by large numbers of much smaller particles.

The research itself shows that under certain conditions, metallic silver will release large numbers of silver nanoparticles.  Researchers attached small silver particles to electron microscope grids and exposed them to moisture.  Over a period of weeks, the particles became surrounded by large numbers of much smaller particles – the silver was shedding silver nanoparticles (see images to the right).  Nanoparticle release was also seen when resting large silver objects on the grids.  And the effect wasn’t confined to silver – copper also released nanoparticles in the presence of moisture.  To be sure that this wasn’t a product of how the research was conducted, the researchers checked to make sure that the particles weren’t being produced because of conditions on the grid or in the electron microscope – they weren’t.

The implications of this work are quite stunning.  It implies – although verification is needed – that any object made out of silver or coated in silver will slowly release silver nanoparticles into the environment.  Silver jugs and cutlery – used since ancient times – will have been releasing silver nanoparticles into food and drink.  Silver jewelry will have been releasing silver nanoparticles onto wearer’s skin.  Silver tongue studs will have been releasing silver nanoparticles into people’s gastrointestinal tract.  As soon as you start to think about it, there are all sorts of places where people and the environment could have been coexisting with silver nanoparticles for some time!

Assuming that this is the case, what are the implications for current research on the health and environmental impacts of silver nanoparticles, of which there is rather a lot? (A search of the ICON nanoEHS Virtual Journal returns over 300 papers mentioning silver published since 2005).  Is nano silver a sufficiently unusual and potentially dangerous substance to justify millions of dollars being spent on researching its risks?  Does the new wave of nano silver products represent an emergent risk, or simply a repackaged old risk?  And if exposure to nano silver has been occurring for millennia, where is the evidence for harm associated with this exposure?

Of course, a critical factor here is how much stuff are people and the environment exposed to – how much nano silver will you be exposed to eating with premium silverware for instance, and how does this compare to wearing the latest offering of nano-silver socks?  It may be that the new interest in using nano silver in commercial products is leading to a significant jump in exposure.

Be that as it may, the most significant implication of the research to me is that it undermines the assumption that products carrying the “nanotechnology” label automatically present new and unusual risks.  Silver nanoparticles have been touted as a product of nanotechnology, and indeed they do fit the bill – intentionally engineered at the nanoscale to be used in unique ways.  And this association with nanotechnology has led to research and policy organizations to invest an awful lot of time and effort in them – from the Organization for Economic Cooperation and Development to the US Environmental protection Agency.  Yet from a health and environmental impact perspective, it is looking increasingly likely that many engineered silver nanoparticles are indistinguishable from those nanoparticles shed by every piece of silver and silver plated stuff in common use.

So where does this leave us?  Should we abandon research into the health and environmental impacts of silver nanoparticles?  Probably not, because we still need to understand the risks associated with what we intentionally use.  But we might want to ease back on the passion that seems to be driving interest in nano silver risks, almost to the exclusion of other materials.

And we might want to rethink framing nano silver as a new threat from an emerging technology – unless someone can convincingly demonstrate that the nanoparticles from my silver spoon are not as worrisome as those from my nano-engineered socks.

Andrew Maynard