Toxic effects or damage, however, were not observed. It has not been investigated yet whether particles are transported via the blood-brain barrier. During studies dealing with the damage caused to nerves by silver (not explicitly nanosilver particles), silver was detected in the region of the blood-brain barrier but was not found to have passed it.

Literatur:

1. Wijnhoven, S et al 2009, Nanotoxicology, 3:2,109-138
2. Lansdown AB 2007, Crit Rev Toxicol 37:237-250.

Uptake of silver particles in the cells has been proved within the framework of in vitro studies ^[1]. Particles or small agglomerates are mostly taken up through phagocytosis or pinocytosis and can be detected by means of electron microscopy in cell inclusions (the so-called vesicles). The special uptake mechanisms valid for silver nanoparticles have not been analyzed so far.

Literatuer:

1. Gaiser et al 2009, Environ Health. 21;8 Suppl 1:S2
   

An important aspect of the behaviour of nano silver in the environment is the solubility of the particles in the presence of oxygen. Probably there is always, at least temporarily, a mixture of both particles and ions. It is unclear whether the particles released are stable in the environment or dissolve completely in a certain time or under certain conditions. It is known that the solubility of the particle depends on the one hand on particle size and on the other on the external conditions. At high pH and in the presence of oxygen the proportion of dissolved silver increases [1]. If many salts are present, larger units of nanoparticles are formed, which sink to the ground because of their size ^[1].
Various silver nanoparticles examined showed a very low or slow dissolution with only about 1% of free silver ions in the solution ^{[2, 3]}. These nanoparticles, however, had a surface coating that could affect the solubility. The presence of dissolved organic components binding to the silver nanoparticles can prevent leaching of Ag-ions ^{[1, 4]}. Conversely, this process may, depending on the nature of the organic component, also favor an extraction of ions.
Undeniably, however, is that silver ions are released, although their quantity and speed of extraction from the particle can vary widely, depending on external conditions (composition of the surrounding solution) and possible particle coatings.
The behaviour of silver ions in the environment is well known. Only a small proportion of the dissolved ions are free, the majority binds rapidly to clay minerals, iron or manganese dioxide and sulphur compounds, and is deposited in the sediment. Especially silver sulphide is a poorly soluble compound.
A study on the behaviour of silver nanoparticles in salt water showed a deposition of particles in the upper layers of the sediment. The remaining silver ions are probably bound very fast by the chloride salt in the salt water ^[5].

A degradation, so a reduction in the environment is generally not occurring for metals such as silver. However, pure silver may be converted by e.g. salts present in the environment or the water into forms which may have other effects. In addition to the water, much of the silver is expected in soils ^[6]. In summary, the environmental behavior of nano-silver has received relatively little attention and in terms of solubility and the whereabouts of undissolved particles, there is still much more research needed.
 

Literature

1. Lok, C.-N. et al. (2007), Journal of Biological Inorganic Chemistry 12, 527.
2. Navarro, E. et al. (2008), Environ Sci & Technol 42, 8959-8964.
3. Geranio, L. et al. (2009), Environ Sci Technol 43, 8113-8118.
4. Gao, J. et al. (2009), Environ Sci & Technol 43, 3322-3328.
5. Bradford, A. et al. (2009) Environ Sci Technol 43, 4530-4536.  
6. Benn, T. M.Westerhoff, P. (2008), Environ Sci & Technol 42, 4133.