Nanosilver: New Name but Well-Known Effects

Nanosilver is not a new discovery by nanotechnologists it has been used in various products for more than hundred years, as is shown by a new Empa study. The antimicrobial effects of minute silver particles, which were then known as "colloidal silver," were known from the earliest days of its use. As early as the 19th century minute silver particles were used, for example, in antibacterial water filters.

Numerous nanomaterials are currently at the focus of public attention. In particular, silver nanoparticles are being investigated in detail, both by scientists as well as by regulatory authorities. The assumption behind this interest is that they are dealing with a completely new substance; however, Empa researchers Bernd Nowack and Harald Krug, together with Murray Heights of the company HeiQ, have shown in a paper recently published in the journal Environmental Science & Technology that nanosilver is by no means the discovery of the 21st century. Silver particles with diameters of seven to nine nm were mentioned as early as 1889. They were used in medications or as biocides to prevent the growth of bacteria on surfaces, for example in antibacterial water filters or in algaecides for swimming pools.

The nanoparticles were known as "colloidal silver" in those days, but what was meant was the same then as now extremely small particles of silver. The only new aspect is the use today of the prefix "nano." "However," according to Nowack, "nano does not mean something new, and nor does it mean something that is harmful."

When "colloidal silver" became available on the market in large quantities in the 1920s it was the topic of numerous studies and subject to appropriate regulation by the authorities. Even in those days the significance of the discovery of nanoparticles and how they worked was realized.

"That is not to say that the possible side-effects of nanoparticles on humans and the environment should be played down or ignored," adds Nowack. It is important to characterize in exact detail the material properties of nanosilver and not just to believe unquestioningly the doubts and reservations surrounding the product.

The term nanoparticle is understood to refer to particles whose dimensions are less than 100 nm. Because of their minute size nanoparticles have different properties than those of larger particles of the same material. For example, for a given volume nanoparticles have a much greater surface area, so they are frequently much more reactive than the bulk material. In addition, even in small quantities nanosilver produces more silver ions than solid silver. These silver ions are toxic to bacteria. Whether or not nanosilver represents a risk to humans and the environment is currently the subject of a great deal of investigation.

Reference: 120 Years of Nanosilver History: Implications for Policy Makers, Bernd Nowack, Harald F. Krug, Murray Height, Environ Sci Technol, 2011, DOI: 10.1021/es103316q