Wednesday, 17 July 2013

Nanosilver: the future may be tiny and shiny, but is it safe?

A few years' ago I bought some socks containing nanosilver in the hope of reducing foot odour - or more specifically a lingering smell in shoes - I am not proud. Strangely, moving to a warmer, more humid climate since then has greatly reduced the problem, rather more so than the nanosilver, which was frankly useless. But soon after buying the less-than-super socks I started thinking about just what I had done. After all, you don't usually consider yourself in close proximity to amounts of silver around one billionth or so of a metre in size...

In the case of nanosilver, it has long been recognised as an anti-bacterial agent and fungicide too, hence the sock idea. I've already discussed smart materials elsewhere but felt this particular example deserved a post by itself. So just how efficient was the nanosilver anyway? According to studies in 2008 and 2009, up to one third of the metal is washed out at the first laundering. Hardly a long-term solution then! So what happens to the silver that disappears down the washing machine waste pipe? Could the nanoparticles get into the water supply if not removed in treatment plants, evading capture due to the minuteness of their size? I just had to find out!

It seems that silver-impregnated socks are just the tip of the iceberg, with all sorts of products in recent years taking advantage of its anti-bacterial capability. Everything from washing machines to vacuum cleaners has appeared, some removed from the market, if only a temporary basis, due to growing health concerns. But is the use of nanosilver just a fad, with little scientific evidence to support its alleged efficacy? In 2006 the New Zealand manufacturer Fisher and Paykel announced that there was no point incorporating nanosilver into their washing machines since a 20 degrees Celsius wash cycle using detergent would remove over 99 per cent of bacteria anyway! The same, year, the US Environmental Protection Agency claimed that it would introduce some nanotechnology-related legislation, although there seems to have been limited action in the meantime, to say the least.

Meanwhile other nations carry on regardless and allow if anything a greater than ever range of products with little attempt to investigate either their efficacy or ecological impact. Although found in some genuine anti-bacterial medical products, colloidal silver (that is, 1-1000 nanometre-sized silver particles in solution) is now being aggressively marketed after several decades in the doldrums. Claims for its use range from the mildly optimistic (in, for example, toothbrushes) to obvious quackery (a cure for AIDs, would you believe?) Clearly the manufacturers of alternative medicines have found a new weapon for their arsenals. But since gold is the only inert metal when it comes to ingestion - think gold flakes in vodka - just how safe is silver in any form of consumed product?

Starting with the assumption that there are no known cases of death by 'medicinal' products containing silver it might appear that consumers are just wasting their money, but there are plenty of other issues if you consider the bigger picture. Which in this case is the planetary ecosystem. Firstly, any overuse of household antibacterial agents can reduce children's immunity, although silver-based products are probably small fry compared to the myriad of cleaning sprays, gels and wipes aimed to keeping the family home 'safe from germs'. And since silver cannot differentiate between useful/symbiotic and harmful/disease-causing bacteria, the application is more akin to machine gun fire - with its consequences of 'collateral damage' - than a precision-targeted solution.

Next, the natural variation in the bacterial gene pool can lead to the sort of problems that hospitals are now facing with the likes of the MRSA 'superbug', namely that killing 99.9% of bacteria leaves the remaining 0.1% to form the one hundred per cent of the next, completely immune generation. A perfect example of inadvertent natural selection. Or should that be unintended artificial selection? However you define it, we are now starting to pay the price for thoughtless use (and frequent overuse) of our war against microbes.

Finally, back to my original question as to what happens to the ever-increasing amount of nanosilver washed down the drains from the likes of our socks (and the washing machines themselves). According to recent Swiss research, circa 95% of waste water nanosilver ends up as silver sulphide and is therefore relatively harmless. So need I have worried about where the material was ending up? Well, 5% on a global scale could still be considered a substantial amount, and since sewage sludge can end up being dumped on farm land - 3 to 4 million tonnes per year in the UK alone - could there be residual consequences on the soil bacteria, fungi, earthworms and of course farm produce destined for human consumption? Even a subtle shift in the microbial population could have a profound effect on the ecosystem and therefore the human food chain, if you want to be purely selfish about it.

This latter may sound like unsubstantiated scaremongering, but considering the history of research, often industry-sponsored, that has downplayed or even denied the dangers of nicotine, leaded petrol, DDT and various others, might it be too soon to say that the risk is non-existent? The lack of scientific evidence, combined with the poor efficacy of products such as my impregnated socks, suggest that fashionable capitalism is the primary reason behind much of the use of nanosilver. As we all know, mindlessly following others can lead to all sorts of problems. If there's a lesson here, it’s think before you shop: if you want to buy something small, shiny and made of silver, there are plenty of tried and trusted alternatives!