Comparison of two different application routes of nanosilver in rats - evidence for nanoparticles after silver ion treatment

The unique properties of silver nanoparticles have a great potential to advance food safety and revolutionize food packaging. Despite these promising applications, there are concerns about the impact of silver nanoparticles on human health. Therefore, the tissue distribution and excretion of coated silver nanoparticles was investigated in rats after single oral administration including a 7-days post treatment observation time. The animals received silver nanoparticles at a dose of 20 mg/kg body weight and an equimolar dose of silver ions by gavage. The silver content was measured in different organs after days 1, 2, 3 and 7. To assess the effect of the intestinal passage on systemic bioavailability, an additional group of rats was intravenously administered with 4 mg/kg body weight silver nanoparticles and another group was treated with an equimolar dose of silver ions. The fate of the silver was compared after 24 h single intravenous administration. An accumulation of silver was observed in different organs. As expected, most of the nanosilver was excreted via feces and minor amounts were detected in intestine and colon. Orally administered ionic silver was detected in feces and additionally in the urine. Remarkably, also after intravenous injection of nanosilver, silver was found in feces, which suggests biliary excretion of silver nanoparticles. In addition to this, the formation of small Ag2S nanoparticles was observed after ionic administration. It is concluded that the oral resorption of nanosilver results in an accumulation of silver in different organs and feces. Results obtained after intravenous application suggest a biliary excretion. Formation of small Ag2S nanoparticles can be detected after ionic silver application.