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August 31, 2012
Case study on nano-silver disinfectants

               EPA’s Office of Research and Development (ORD) recently issued a case study on nano-silver in disinfectant spray products.  As with previous case studies the ORD has conducted on nano-chemicals, the current study recognizes that there is very little solid scientific information about how the interaction of nano-silver with people and the environment differs from effects associated with conventional silver. 
               Therefore, the study does not draw conclusions about potential risks.  Instead, it is intended to be used as part of a process to identify what is known and particularly what is unknown about nano-silver in a selected application and provide a starting point to identify and prioritize possible research directions to support future assessments of nano-silver.
               The nano-silver study is organized around the comprehensive environmental assessment (CEA) framework that structures available information pertaining to the product life cycle; environmental transport and fate; exposure dose in humans, ecological populations, and the environment; and potential impacts in these receptors. 
Selected comments
               Following are excerpts from the summary chapter of ORD’s 423-page document:

  • Currently available data indicate that over 300 consumer products on the market could contain nano-silver, suggesting that an understanding of aggregate exposure from numerous sources might be useful for accurately determining exposure pathways and estimating dose levels.
  • With a higher surface-to-volume ratio than larger, conventional silver particles, nano-silver could confer greater antimicrobial activity to spray disinfectants using this form of silver compared to conventional silver; several manufacturers have claimed that nano-silver disinfectant sprays kill 99 percent of bacteria on a variety of surfaces and prevents odor for long periods of time.
    • Currently there is no reliable way to differentiate between nano-silver and conventional silver in either the laboratory or the environment.
    • Nano-silver release scenarios include disposing of cloths used to wipe down surfaces sprayed with disinfectant; washing cleaning supplies or clothing with disinfectant on them; spraying sinks, bathtubs, and other surfaces near drains; laundering clothing treated with nano-silver; and disinfecting trash cans, furniture, and children’s toys.
    • In natural aquatic systems, the sensitivity of many organisms to silver ion means that the release of the ion from nano-silver during transport and transformation could have a large influence on exposure and toxicity.
    • The types of products claiming to contain nano-materials and the likely exposure scenarios for those products led one group of authors to suggest that, of all of the nano-materials considered, nano-silver has the highest potential to result in consumer exposure.  To that end, experts agree that use of cleaning products such as nano-silver disinfectant spray is likely to result in high exposure levels via inhalation and dermal pathways, particularly to consumers.
    • Several reports from national bodies such as the Scientific Advisory Panel for the Federal Insecticide, Fungicide, and Rodenticide Act, the Netherlands National Institute for Public Health and the Environment, and in peer-reviewed literature conclude that data on nano-silver exposure and potential toxicity are insufficient to reach meaningful conclusions about the material’s risk.
    • A single case study of nano-silver exposure in a teenage boy revealed elevated silver concentrations in blood and urine coupled with several symptoms, such as loss of appetite and elevated liver enzyme.  Blood and urine levels of silver were still elevated 7 weeks later, but returned to normal by 10 months’ postexposure.

               This is the third case study on nano-ingredients the ORD has released; the two others address nanoscale titanium dioxide used for drinking water treatment and in topical sunscreen products.  ORD’s next case study in its series addresses multiwalled carbon nanotubes in flame-retardant coatings applied to upholstery textiles.
               ORD’s case study is available at http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid=241665#Download.



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