Credit: © 2008 ACS

Certain brands of socks now contain silver nanoparticles to prevent the growth of bacteria that can cause unpleasant odours. However, little is known about what happens to the silver when these socks are washed. Now researchers at Arizona State University1 have shown that colloidal and ionic silver can leach out during washing.

To wash the socks, Troy Benn and Paul Westerhoff agitated them in glass bottles containing ultrapure water for 1 and 24 hours to both simulate the washing machine cycle and to allow sufficient time for the silver to leach out of the socks. The water left behind was then examined for silver using electron microscopy, energy dispersive X-ray analysis and an ion-selective electrode in combination with a pH meter. They found that the original amount of silver per gram of material in the socks ranged from levels that were too small to detect up to 1,360 micrograms, and that the leaching rate also varied considerably from brand to brand.

Benn and Westerhoff suggest that manufacturing processes of the socks can affect the rate at which the silver is released. However, washing the socks in tap water seemed to strip less silver from the fabric, suggesting that experiments in ultrapure water may overestimate the amount of silver that could be leached out.