Silver nanoparticles added to socks to kill the bacteria associated with smelly feet can easily leak into waste water during washing, a new study reveals.
The release of these particles could potentially disrupt helpful bacteria used in waste-water treatment facilities, say some researchers, or endanger aquatic organisms in lakes and streams.
In recent years, nanoparticles of silver 鈥� a metal known to have antibacterial properties 鈥� have been added to athletic wear, bandages and cleaning product.
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Of the more than 600 consumer products that contain nano materials, . Yet very little is known about where these particles end up when such products are put to use.
鈥淭he whole reason silver nanoparticles are used is because silver kills bacteria that cause foot odour,鈥� says Troy Benn, a researcher at in Tempe. 鈥淏ut if those nanoparticles are released into the environment you no longer have any control over what organisms they affect.鈥�
鈥楧igested鈥� socks
Benn and colleagues bought six brands of sock advertised as containing silver antibacterial nanoparticles. To find out how much silver each sock contained, they 鈥渄igested鈥� it in acid then used chemical spectroscopy to determine the amount of silver left in the digested solution.
Next, they washed fresh silver socks in jars of distilled water and used the same spectroscopy method to determine how much silver had been dissolved in the water.
Two brands of sock lost nearly 100% of their silver content within four washings, while two other brands lost less than 1% over the same number of washings.
The findings, presented on April 6 at a , will be published in the journal .
Toxic sludge
Modelling conducted by the researchers suggests that quantities of silver nanoparticles flowing out of water treatment facilities should be within safe levels set by the US .
However, they believe that sludge from such facilities may contain higher silver concentrations. This sludge is often sold as fertilizer for agricultural use, but higher concentrations of silver may make it too toxic for this purpose.
of Duke University in North Carolina says increased silver concentrations could harm the bacteria used in water treatment facilities to process waste.
鈥淲e have known since the Middle Ages that silver is toxic and anything that increases silver availability in the environment is going to be problematic,鈥� he says.
What is nano?
Wiesner says it could make sense to regulate materials like silver. 鈥淭here is a clear case where you can ban a material based on its toxicity, regardless of size,鈥� Wiesner says.
But he cautions against arbitrary bans on nanomaterials 鈥� defined as anything smaller than 100 nanometres in size 鈥� until more is known.
鈥淚f you are going to regulate nanomaterials, what we define as 鈥榥ano鈥� is somewhat arbitrary,鈥� he adds. 鈥淚s a 101 nm object dangerous and a 99 nm object made out of the same material not dangerous? Until we have a fundamental understanding of what it is that governs nano-material behaviour we can鈥檛 draw that line.鈥�
Journal Reference: (DOI: 10.1021/es7032718)
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