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The Speciation of Silver Nanoparticles in Antimicrobial Fabric Before and After Exposure to a Hypochlorite/Detergent Solution

U.S. Environmental Protection Agency-National Risk Management Research Lab., 26 West Martin Luther King Dr., Cincinnati, OH 45268

^* Corresponding author (tolaymat.thabet{at}epa.gov).

Received for publication August 27, 2008. Because of their antibacterial properties, silver nanoparticles are often used in consumer products. To assess environmental and/or human health risks from these nanoparticles, there is a need to identify the chemical transformations that silver nanoparticles undergo in different environments. Thus an antimicrobial sock material containing Ag nanoparticles was examined by X-ray absorption spectroscopy to identify the speciation of Ag. The material was exposed to a hypochlorite/detergent solution and subjected to agitation. An elemental Ag nanopowder was also exposed to the hypochlorite/detergent solution or to a 1 mol L^–1 NaCl solution. Results showed that the sock material nanoparticles consisted of elemental Ag. After exposure to the hypochlorite/detergent solution, a significant portion (more than 50%) of the sock nanoparticles were converted, in situ, to AgCl. Results from exposures to elemental Ag nanopowder suggest that an oxidation step is necessary for the elemental Ag nanoparticles to transform into AgCl as there was no evidence of AgCl formation in the presence of chloride alone. As a result, if Ag ions leach from consumer products, any chloride present may quickly scavenge the ions. In addition, the efficacy of Ag, as an antimicrobial agent in fabrics, may be limited, or even negated, after washing in solutions containing oxidizers as AgCl is much less reactive than Ag ion.

Abbreviations: eV, electron volt • K_sp, solubility constant • LCF, linear combination fitting • MRCAT, materials research collaborative access team • WWTP, wastewater treatment plant • XANES, x-ray absorption near edge spectroscopy • XAS, x-ray absorption spectroscopy