Comment submitted by Maira Powell, PhD, Nanotechnology Citizen Engagement Organization

I recommend that as risk assessors and regulators consider hazards related to ?nano? forms of silver, they review the available literature on all forms of silver, as well as the growing number of recent scientific studies that focus on ?nano? silver forms. As an increasing number of products with engineered nanosilver enter the market, more silver?in a large variety of forms, some nano-sized and some not?will end up in workplaces, homes, and the environment, resulting in human, animal and ecosystem exposures. In the last two years, I have reviewed hundreds of papers about environmental health and safety issues related to silver, including nano-sized forms. Several are attached. Yet several United States regulatory reviews to date have relied heavily on surprisingly few of these studies to make important decisions about silver. Human health risk assessments on silver, for example, still rely heavily on two extremely old and methodologically limited studies: Gaul & Staud (1935) and Hill & Pillsbury (1939). Based largely on these two very outdated reviews, silver is widely considered to be ?innocuous? to humans other than argyria. This assumption seems to have contributed to the ubiquitous use of silver and nanosilver in numerous consumer products, as well as commercial and industrial applications. Yet there is considerable research and clinical evidence that silver is not innocuous to humans (although there is a clear lack of adequate long-term studies for human health risk assessments related to silver exposures). Further, it is well known that silver, especially in ionic forms, is a potent environmental toxin at relatively low levels. Recent studies on nanoparticulate forms of silver suggest that it can be even more potent toxicologically than larger forms in some circumstances, and may pose new mechanisms of toxicity based on small size, surface area, morphology, surface chemistry, and other characteristics. Sincerely, Maria Powell, PhD