The European Commission’s (EC) Scientific Committee on Emerging and Newly Identified Health Risks (SCENIHR) has published its final opinion on the risk assessment of nanosilver in Nanosilver: safety, health and environmental effects and role in antimicrobial resistance. The Committee was asked by the EC ‘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’. All comments, including those by NIA, have now been made available publicly.
SCENIHR states that no conclusive proof can be given on the risk of exposure to nanosilver – traditionally ‘no clear adverse health effects have been associated with silver exposure in general’, and while some studies indicate there is a risk to humans through direct contact, and that exposure to it could ‘be lifelong’, ‘no information can be found on long-term (low) exposure to silver or silver-containing products in the general population’. Similarly ‘it is unclear how population of bacteria … will change in the presence of low, but significant, amounts of silver and how resistance to silver can become established’, and whether ionic silver will have a significant impact on the environment.
The opinion is based around four terms of reference – they, and SCENIHR’s corresponding responses to them, are provided below:
- ‘What may be the implications of the widespread use of nanosilver for human health and the environment? Please consider direct as well as indirect effects occurring via the distribution into the environment. Does this change the existing assessments for silver in general?’
SCENIHR notes that while ‘human and environmental effects of silver are mainly linked to silver ions’, silver is ‘effectively detoxified’ in the environment as ‘large fractions of the silver reaching the environment will precipitate as silver sulphide’, which ‘is very stable and does not release ionic silver’. Furthermore ‘it is important to note that nanosilver represents probably less than 50% of the silver used as a biocide in consumer products’, that ‘the total amount of silver released from consumer products is generally rather low’, and that ‘nanosilver is only a small fraction of the total amount of silver entering the environment’.
Nevertheless the committee concluded that ‘the widespread (and increasing) use of silver containing products implicates that both consumers and the environment are exposed to new sources of silver’, and that ‘additional effects caused by widespread and long-term use of Ag-NPs cannot be ruled out’.
It mentions that the best described example of exposure to silver in humans is argyria, which is ‘in general considered to be relatively harmless’, but that ‘in vivo and in vitro studies have now indicated that nanosilver exposure leads possibly to genotoxicity, changes in [the] activity of the immune system, and an accumulation of silver in [the] spleen, liver and testes’. Human exposure, SCENIHR notes, ‘may be lifelong’.
With regards to 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’. Furthermore ‘it has been observed that Ag-NPs act as a source of bioavailable silver, and it cannot be excluded that Ag-NPs represent a new source of environmental exposure to silver that delivers to organisms in a way that is not effective for other forms of silver’.
- ‘Could the widespread use of nanosilver, in particular in medical care and in consumer products, increase the risk of selecting Ag resistance micro-organisms? Could the widespread use of nanosilver create cross-resistance in micro-organisms?’
SCENIHR comments that ‘there is a paucity of information’ on this topic and that more information is needed to better understand it. It notes that ‘no documentation is available’ on the ‘hazard associated with the dissemination of the resistance mechanisms’, which represents ‘a serious gap of knowledge’. The committee does caution that ‘since other NPs have been shown to substantially increase the horizontal gene transfer between bacteria, which is extremely relevant for developing resistance’, particular attention should be made to study whether silver nanoparticles do the same.
- ‘To what extent may the widespread use of nanosilver and the possible increase of resistant micro-organisms reduce the nanosilver’s efficacy?’
The committee notes that there is not enough information to ‘allow for the formulation of a definite answer’. Furthermore as ‘the mechanisms resulting in Ag-NPs resistance are not well understood, it is not possible at this time to estimate whether or not resistance will increase and spread in view of a more widespread use of nanosilver in products’.
- ‘Are there any other safety, health and environmental effects of nanosilver?’
SCENIHR states that, on the one hand, ‘no clear adverse health effects have been associated with silver exposure in general’, but on the other, ‘no information can be found on long-term (low) exposure to silver or silver-containing products in the general population’. Similarly for bacteria, ‘it is unclear how population of bacteria … will change in the presence of low, but significant, amounts of silver and how resistance to silver can become established’.
Follow this link to read the full SCENIHR opinion on nanosilver, and this to read comments submitted by external organisations, including by NIA, on drafts of the opinion.