A recent study by two Arizona State University researchers found that socks made of fabric incorporating nanoscale silver may potentially release that silver into wash-water.
T. Benn, et al., "Nanoparticle Silver Release into Water from Commercially Available Sock Fabrics," Environmental Science & Technology, Vol. 42, at 4133-4139 (2008).
Why put silver in your socks? Because it is a well-known antimicrobial agent and microbes cause sock odor. Kill the microbes, and your feet smell fresh. At least that’s the marketing angle.
Several environmental NGOs, however, are concerned with whether silver might be released from the socks, enter the wash-water and waste-water streams, and keep on killing microbes. While you may not want microbes in your socks, they are a vital part of the ecosystem. The authors theorize that "[t]he ubiquitous use of commercial products containing n-Ag could potentially compromise the health of many ecosystems." (This is yet another twist to the Samsung Silver Care washing machine controversy a couple of years ago).
As for the socks themselves, the researchers selected pairs from Sharper Image, Fox River, Arctic Shield, Zeusah, and AgActive "based on the manufacturers’ claims that the socks contained nanoparticles of silver. " We checked the advertising for ourselves, and only Arctic Shield and AgActive London actually make nanosilver claims, while Fox River and Zeusah make general silver and/or silver ion claims. As for the Sharper Image socks, the company is in the final stages of bankruptcy and is closing its stores. Its new owner may or may not continue direct sales through its catalog and the internet. No work on whether they will continue to sell socks at all.
Perhaps the most interesting thing about the advertising was efficacy claims:
"Your feet feel and smell fresher for longer."
"Stay fresh no matter how long you wear them."
"You can wear our socks for days on end and they won’t smell."
"Just by wearing [our] socks we guarantee no more foot odor."
Testimonial: "I bought some of [your] socks for my nephew when he came to stay with me for the holiday. His feet always smelled but with the new socks, the smell is all gone. I am very happy."
Testimonial: "I wore them three days and there was no smell at all."
Regarding the test itself, the socks were first analyzed for their nanosilver content. Three of the six socks contained silver particles in the 100-500 nm range; only one contained silver particles in the traditional nanoscale range (under 100 nm). The socks were then washed three times in ultra-pure distilled laboratory water for 24 hour or 1 hour periods using an orbital shaker/agitator. No soaps or detergents were used. The researchers analyzed the resulting wash-water.
To cut a long story short, the researchers found that "at least some of the n-Ag is released into the wash-water as nanoparticles; not just as dissolved ionic silver."
As for total silver release, three of the six socks were found to have leached silver into the wash-water. (Sharper Image, Fox River, AgActive London). During the three 24 hour tests, the AgActive socks released a total of 19 of their 20 micrograms of silver, the Fox River socks released 165 of their 31,241 micrograms of silver, and the Sharper Image socks released 1578 of their 1845 micrograms of silver. In the three, one hour tests, the Sharper Image socks released 1020 micrograms of silver, and the Fox River socks released 390 micrograms of silver.
Interestingly, socks washed in plain old tap water did not release near as much silver as those washed in the ultra-pure, distilled, laboratory water.