Small risks

Valued for it’s antibacterial and odour-fighting properties, nanoparticle silver is becoming the star attraction in a range of products from socks to bandages. But now, two US researchers are recommending a closer examination of its consequences to the environment.

'The general public needs to be aware that there are unknown risks associated with the products they buy containing nanomaterials,' said Arizona State University researchers Paul Westerhoff and Troy M. Benn.

Westerhoff and Benn report that ordinary laundering can wash off substantial amounts of the nanosilver particles from socks impregnated with the material. The researchers suggest that the particles, intended to prevent foot odour, could travel through a wastewater treatment system and enter natural waterways where they might have unwanted effects on aquatic organisms living in the water and possibly humans, too.

A report on their findings is scheduled to be presented at the 235th national meeting of the American Chemical Society (ACS).

'This is the first report of anyone looking at the release of silver from this type of manufactured clothing product,' the researchers claimed.

Behind the researchers' concerns lies a very simple experiment. Benn and Westerhoff bought six pairs of name brand anti-odour socks impregnated with nanosilver. They soaked them in a jar of room temperature distilled water, shook the contents for an hour and tested the water for two types of silver - the harmful 'ionic' form and the less-studied nanoparticle variety.

'Different socks released silver at different rates, suggesting that there may be a manufacturing process that will keep the silver in the socks better,' said Benn. 'Some of the sock materials released all of the silver in the first few washings, others gradually released it. Some didn’t release any silver.' The researchers will present the specific brands they studied at their ACS presentation.

If sufficient nanosilver leeches out of these socks and escapes waste water treatment systems into nearby lakes, rivers and streams, it could damage aquatic ecosystems, said Benn. Ionic silver, the dissolved form of the element, does not just attack odour-causing bacteria. It can also hijack chemical processes essential for life in other microbes and aquatic animals.

'If you start releasing ionic silver, it is detrimental to all aquatic biota. Once the silver ions get into the gills of fish, it’s a pretty efficient killer,' said Benn. Ionic silver is only toxic to humans at very high levels. The toxicity of nanoparticle silver, said Westerhoff, has yet to be determined.

Westerhoff and Benn did not intend to establish the toxicity of silver. 'The history of silver and silver regulation has been set for decades by the US Environmental Protection Agency - we’re not trying to reexamine or reinvent that,' said Westerhoff.

They do hope to spark a broader examination of the environmental and health consequences of nanomaterials, as well as increasing awareness of nanotechnology’s role in everyday consumer goods.

Silver has been used historically since ancient Roman times, though its nanoparticle form has only recently appeared in consumer products. Beyond socks, nanosilver appears in certain bandages, athletic wear and cleaning products. Benn suggested that most consumers are unaware of these nano-additions.

To that end, the researchers suggest that improved product labelling could help. Westerhoff proposes that clothing labels could become like the back of a food packaging, complete with a list of 'ingredients' like nanosilver.

Westerhoff and Benn expect to expand their leeching experiments to other consumer products imbued with nanomaterials. They hope to find the moment in each product’s lifecycle when nanomaterials could be released into the environment, as well as developing better detection methods to characterise nanoparticles in water and air samples.