Exposure to silver nanoparticles may be more common than we thought

by Andrew Maynard on November 7, 2011

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.

1 Hilary Sutcliffe November 8, 2011 at 5:30 am

Very interesting. As you say, there is still much knowledge to be gained as to the effect of silver from whatever source. But silver was chosen for good reason, and we shouldn’t be too hard on ourselves for taking significant steps to understand the impacts. However the point of adaptive governance is to make changes based on new knowledge, when the studies already commissioned have been completed and we have a richer picture of the effect of silver then a better decision on where to put scarce resources can be made.

2 Andrew Maynard November 8, 2011 at 8:19 am

Absolutely agree on the adaptive governance front. But I do worry about research and policy making inertia, and that the state of knowledge is developing faster than people can respond to it. What do you do if you have a 5 year plan for a major research or policy initiative, and half way through the justification begins to slip through your fingers? The wise answer would be to change course in response to the evidence, but I know of very few policy or even research organizations that are adept at doing that.

3 Renzo Dalla Via November 9, 2011 at 8:20 am

Many interesting points there Andrew. I can only reflect on the fact that we have not completely tied all current health issues with a cause. So, is it our nano silver off spoons adding to neural illness, inbalance of body flora, epigenetic changes, etc etc, etc.
Oh my, seems there are more questions and cases out there than anwers and the more we see connections the more we see issues.
Renzo

4 Simon Brown November 9, 2011 at 8:54 pm

This is an interesting paper but there is a perhaps surprising issue that I don’t believe was addressed in this research – it is possible that the nanoparticles that are shed are actually made of silver oxide. We have recently published a paper [Applied Physics Letters 99, 171914 (2011)] that shows that silver alloy particles (85% Ag, 15%Au) are transformed over a few weeks through formation of oxides. In some of our unpublished work we see particles similar to those in the Hutchinson group’s work – while we are still attempting to get unambiguous results we are pretty confident that are AgO rather than Ag. If we are right, then this means that the conclusion that we don’t need to worry about silver nanoparticles because they have been around us for years is incorrect – we may have been surrounded by silver oxide nanoparticles for years, and we may therefore still need to do a lot of work to understand the properties of silver particles.

5 Mike February 3, 2012 at 7:27 am

Let’s not forget the very important environmental issue of chem-trail spraying by the government. It’s been going on for 50+ years and lat year the US gov admitted that it was doing it to save the earth!! They refuse to elaborate because of “National Security”.. This frightens me!
Now these particles are showing up in the soil and plant life!!

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