CORRESPONDENCE/REBUTTAL pubs.acs.org/est
Comment on “120 Years of Nanosilver History: Implications for Policy Makers”
R
ecently, Environmental Science and Technology published a policy analysis paper by Nowack et al.1 showing that nanosilver has been in commerce for more than 100 years. The authors argued that because these silver-based products have been safely used in the past, it would be a mistake to ignore this historical information and treat nanosilver as a “new chemical with new and unknown risks.” This rebuttal contends that most of the historical data cited by Nowack et al. are of limited value for assessing new products containing nanosilver and, as a result, product specific information is required when evaluating the risk posed by using these products. Nowack et al. state that “The more than 50-year use of these nanosilver products presents a unique opportunity for environmental scientists to study the effects of the discharge of nanosilver...and epidemiologists could study populations of homeowners using silver-based algicides.” We find that only 7 of the 92 registered silver-based products presented in this analysis are confirmed to contain nanosilver (Table 1 in ref 1) and only two of these have been in use for more than 20 years (Table 2 in ref 1). Algaedyn was registered with the United States Environmental Protection Agency (USEPA) under the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) in 1954 as an algicide for residential swimming pools. However, because the silver content of this product is limited (i.e., 0.8%), the annual mass of silver released and the exposure from its use are limited. In another argument, Nowack et al. suggest that historical work on the health effects of colloidal silver products support the claim of no adverse effects for consumer products containing nanosilver. Regulatory agencies like the USEPA have considered data on colloidal silver in deriving toxicological end points for silver.2 However, it is unclear if observations for silver-based health supplements are applicable for evaluating the safety of nanosilver in consumer products such as clothing and bedding where the exposure routes (ingestion vs dermal), exposure duration (periodic vs prolonged), and population sizes (limited vs widespread) are different. We do not believe that observations for colloidal-silver based health supplements are applicable for evaluating the safety of micrometerscale-silica decorated with nanosilver3 or spray applied nanosilver4 due to differences in physical properties. We note that there are cases where adverse health effects for colloidal silver and nanosilver have been observed, albeit under extreme use conditions. One person was reported to have developed epileptic seizures and coma followed by irreversible neurological toxicity after daily ingestion of colloidal silver for 4 months.5 And there is one case where a burn patient treated with a nanosilver-coated wound dressing developed clinical signs of argyria and liver toxicity.6 In an effort to resolve uncertainty regarding the safety of nanosilver, key questions about nanosilver were recently posed to an independent peer-review scientific panel.7 The Panel concluded that since the effects of nanosilver are dependent on its physical properties, these nanomaterials should be evaluated on a r 2011 American Chemical Society
case-by-case basis.7 This conclusion is further supported by studies in the literature reporting that the toxicity of nanosilver depends on the morphology and surface properties of these nanoparticles.8 10 Even though nanosilver has been safely used in some consumer products, it should not necessarily be inferred that all types of nanosilver are safe for use. In the past decade, the number of synthesis methods for nanosilver has drastically increased.11 One can expect future developments in the manufacture of silver nanoparticles and the ability to engineer and tune their characteristics in order to fit a wide spectrum of applications. Thus, the evaluation of risk for each nanosilver product should consider the physical, chemical, and possibly toxic characteristics unique to that product. Jed Costanza,†,* Amro M. El Badawy,‡ and Thabet M. Tolaymat§ †
‡
U.S. Environmental Protection Agency, Office of Pesticide Programs, Arlington, Virginia Department of Civil & Environmental Engineering, University of Cincinnati, Cincinnati, Ohio
§
U.S. Environmental Protection Agency, Office of Research and Development, Cincinnati, Ohio
’ AUTHOR INFORMATION Corresponding Author
*E-mail:
[email protected]. Notes
The opinions expressed herein are those of the authors and have not been subjected to U.S. EPA review and therefore do not necessarily reflect the views of the U.S. EPA, and no official endorsement should be inferred.
’ REFERENCES (1) Nowack, B.; Krug, H. F.; Height, M. 120 years of nanosilver history: Implications for policy makers. Environ. Sci. Technol. 2011, 45, 1177–1183. (2) Health assessment information statement under Integrated Risk Information System. http://www.epa.gov/IRIS/subst/0099.htm (accessed February 25, 2011). (3) Egger, S.; Lehmann, R. P.; Height, M. J.; Loessner, M. J.; Schuppler, M. Antimicrobial properties of a novel silver-silica nanocomposite material. Appl. Environ. Microbiol. 2009, 75, 2973–2976. (4) External Review Draft, Nanomaterial Case Study: Nanoscale Silver in Disinfectant Spray, EPA/600/R-10/081; U.S. Environmental Protection Agency: Washington, DC, 2010. (5) Mirsattari, S. M.; Hammond, R. R.; Sharpe, M. D.; Leung, F. Y.; Young, G. B. Myoclonic status epilepticus following repeated oral ingestion of colloidal silver. Neurology 2004, 62, 1408–1410. (6) Trop, M.; Novak, M.; Rodl, S.; Hellbom, B.; Kroell, W.; Goessler, W. Silver-coated dressing Acticoat caused raised liver enzymes and argyria-like symptoms in burn patient. J. Traum. 2006, 60, 648–652. Published: August 05, 2011 7591
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CORRESPONDENCE/REBUTTAL
(7) FIFRA Scientific Advisory Panel Meeting held November 3 - 5, 2009 on the Evaluation of Hazard and Exposure Associated with Nanosilver and Other Nanometal Pesticide Products. http://www. epa.gov/scipoly/sap/meetings/2009/november/110309ameetingminutes.pdf (accessed February 25, 2011). (8) Carlson, C.; Hussain, S. M.; Schrand, A. M.; Braydich-Stolle, L. K.; Hess, K. L.; Jones, R. L.; Schlager, J. J. Unique cellular interaction of silver nanoparticles: Size-dependent generation of reactive oxygen species. J. Phys. Chem. B 2008, 112, 13608–13619. (9) Pal, S.; Tak, Y. K.; Song, J. M. Does the antibacterial activity of silver nanoparticles depend on the shape of the nanoparticle? A study of the gram-negative bacterium Escherichia coli. Appl. Environ. Microbiol. 2007, 73, 1712–1720. (10) El Badawy, A.; Silva, G.; Morris, B.; Scheckel, K.; Suidan, M.; Tolaymat, T. Surface charge dependent toxicity of silver nanoparticles. Environ. Sci. Technol. 2011, 45, 283–287. (11) Tolaymat, T. M.; El Badawy, A. M.; Genaidy, A.; Scheckel, K. G.; Luxton, T. P.; Suidan, M. An evidence-based environmental perspective of manufactured silver nanoparticle in syntheses and applications: A systematic review and appraisal of peer-reviewed scientific papers. Sci. Total Environ. 2010, 408, 999–1006.
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