# Does Nanosilver Have a Pronounced Toxic Effect on Humans?
## 3 Experimental Research Conducted by the Authors of the Review  
### Main Direction of Research and General Idea of Industrial Nanotoxicology  
Since NPs can penetrate the blood-brain barrier, for production workers and employees of other organizations where long-term contact with NPs is possible (scientific laboratories, medical organizations), there is a potential danger of the development of previously unknown nosological forms of neurological and mental diseases [52]. Inhalation and oral administration of NPs into animals are suitable for modeling chronic daily contact with NPs. However, it is difficult to conduct a long-term controlled study when choosing an inhalation contact, as it is necessary to constantly maintain the required content of NPs in the air of the inhalation chamber, preventing them from settling. To date, there are practically no reliable methods for monitoring the concentration of NPs in the air; however, when administrated orally, the concentration of NPs in a solution can be controlled with greater precision. These studies are simpler, cheaper, safer for researchers; therefore, in our studies, prolonged chronic contact with NPs by replacing drinking water to animals with a colloidal solution of AgNPs was chosen as the main mode of introducing AgNPs.  
Experimental mice drank a solution of AgNPs of a selected concentration for 1-4 months, which, at an average mouse life expectancy of 1.5-2 years, corresponds to approximately 3-12 years of the daily human consumption of NPs. Further, the accumulation of AgNPs in the brain and other organs of the animals (for comparison) was evaluated using neutron activation analysis (NAA). The presence and nature of cognitive impairments in experimental animals, compared with control ones, were evaluated using behavioral tests. The methodology of the experiments and the conditions for keeping the animals in the vivarium of M.F. Vladimirskiy Moscow Regional Research and Clinical Institute were approved by the institutional ethics committee and are consistent with the requirements of Directive 2010/63/EU of the European Parliament and of the Council of 22 September 2010 on the protection of animals used for scientific purposes. The methodology of cognitive tests in the Morris water maze was published in our earlier study [52]. A short description of the performed experiments and the effect of AgNPs on the objects of study are summarized in Table 2.  
\begin{table}
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Besides water, NPs can enter the body with food. In one of our studies, rats were administrated with unmodified and functionalized _Spirulina platensis_ biomass AgNPs for 28 days. As in the above-described experiments, the silver content in the organs of control and experimental animals was assessed by NAA. In animals administrated with both types of NPs (unmodified and modified), the highest content of silver was determined in the brain. At the same time, the hematological and biochemical indices of the rats did not change significantly under the action of AgNPs, except for the content of reticulocytes and eosinophils, which increased considerably [59].