The aim of this opinion is to assess whether the use of nanosilver, in particular in medical care and in consumer products, could result in additional risks compared to more traditional uses of silver and whether the use of nanosilver to control bacterial growth could result in resistance of micro-organisms.
SCENIHR concludes that the widespread (and increasing) use of silver containing products implicates that both consumers and the environment are exposed to new sources of silver. Human exposure is direct (food, hand-to-mouth contact, skin) and may be life long; while in the environment silver nanoparticles may be a particularly effective delivery system for silver to organisms in soil, water and sediment and may act as sources of ionic silver over extended periods of time. Therefore, additional effects caused by widespread and long term use of silver nanoparticles cannot be ruled out.
Regarding the hazard associated with the dissemination of the resistance mechanism following the use of silver nanoparticles, no studies are available at this moment, representing a serious gap of knowledge. Since other nanoparticles have been shown to substantially increase the horizontal gene transfer between bacteria – which is extremely relevant for developing resistance – the potential of silver nanoparticles to induce similar effects should be given particular attention.
More data are needed to better understand bacterial response to ionic silver and silver nanoparticles exposure. Since the mechanisms resulting in silver nanoparticles resistance are not well understood, it is not possible to estimate at this time whether or not resistance of microorganisms will increase and spread in view of a more widespread use of silver nanoparticles in products.