Laundered Gym Clothes Don't Leach Much Nanosilver

A portion of the silver nanoparticles embedded in certain types of athletic clothing to prevent body odor comes off during the wash cycle—but they retain their microbial effect even at low concentrations, researchers have concluded.

Scientists report in the American Chemical Society journal Environmental Science & Technology that while silver nanoparticles and coatings leach from commercially available garments during laundering, the levels are insufficient to keep the nanoparticles from doing their intended job—nor to render the wastewater toxic. Nonetheless, they recommend keeping the initial metal concentrations in these products low, as the remaining silver is likely to leach out over time when the clothes are discarded in landfills.

Thanks to their antimicrobial properties, silver nanoparticles are found in an increasing array of products such as food packaging, bandages and textiles. At the same time, scientists have been studying the possible effects that silver nanoparticles might have on the environment and human health. Generally, those studies have shown that the particles can be toxic, but their safety is dependent on a number of factors, such as size and dose.

Paul Westerhoff, professor and senior advisor on science and engineering at Arizona State University, and colleagues, however, wanted to see how the design of antimicrobial clothes affects how well they stand up to washing and their potential to leach silver into the environment.

The researchers tested commercial athletic shirts in which the silver nanoparticles were incorporated in any of four different ways. Washing the shirts released a range of silver concentrations, depending on how the nanoparticles were attached. But overall the resulting toxicity of the wastewater due to its silver content was negligible to zebrafish embryos—a model animal used in toxicity studies.

As to clothes washing's effect on antimicrobial efficacy, testing demonstrated greater than 99.9% inhibition of E. coli growth—even for textiles that retained as little as 2 μg/g silver after washing. "This suggests that very little nanosilver is required to control bacterial growth in textiles," the researchers conclude.