Nanosilver Toxicity

A number of articles in C&EN in recent years imply that nanosilver metal particles are toxic (most recently, C&EN Online Latest News, Aug. 8). In fact, nanosilver particles are no more toxic in natural environments than other forms of silver metal. The fundamental chemistry of silver and its compounds does not change as a function of size.

What does change is the kinetics of reaction because the higher surface area of smaller particles allows more rapid reactivity. In almost all natural environments, silver will react rapidly with sulfur-containing ligands to form innocuous silver sulfide, and this occurs without the release of highly oxidizing ionic silver species. Where nanosilver has been demonstrated as cytotoxic is exclusively in artificial in vitro environments. Extensive data provided from the photoprocessing industries and from recent studies all attest to the benign nature of silver and its chemistry in naturally occurring environments.

Unfortunately, since February 2008, the Environmental Protection Agency has put a moratorium on registering all products containing nanosilver and other nanomaterials that are claimed to have pesticide use. During this period, the Silver Nanotechnology Working Group and the Silver Institute have engaged in extensive work focusing on reviewing the science on nanosilver appearing in peer-reviewed journals and on preparing well-thought-out scientific submissions to EPA in response to, among others, the EPA Office of Pesticide Programs’ proposed nanopesticide policy (Fed. Reg.2011,76, 35383) and the FIFRA Scientific Advisory Panel recommendations (SAP Minutes No. 2010-01, Jan. 26, 2010).

These organizations have interacted with EPA in challenged exchanges on how best to regulate nanopesticides, leading to a clear and reasonable path for registration. It is hoped that EPA and other agencies will ultimately no longer impose unwarranted barriers to these emerging nanotechnology industries but will instead nourish the benefits these can provide while screening on a case-by-case basis for any environmental risk.

We need a sensible path forward for registering nanopesticides that is not burdensome for either the government or industry.

By Rosalind Volpe
Durham, NC