Background: The study investigated the distribution of silver after 28 days repeated oral administration of silver
nanoparticles (AgNPs) and silver acetate (AgAc) to rats. Oral administration is a relevant route of exposure because
of the use of silver nanoparticles in products related to food and food contact materials.
Results: AgNPs were synthesized with a size distribution of 14 ± 4 nm in diameter (90% of the nanoparticle volume)
and stabilized in aqueous suspension by the polymer polyvinylpyrrolidone (PVP). The AgNPs remained stable
throughout the duration of the 28-day oral toxicity study in rats. The organ distribution pattern of silver following
administration of AgNPs and AgAc was similar. However the absolute silver concentrations in tissues were lower
following oral exposure to AgNPs. This was in agreement with an indication of a higher fecal excretion following
administration of AgNPs. Besides the intestinal system, the largest silver concentrations were detected in the liver and
kidneys. Silver was also found in the lungs and brain. Autometallographic (AMG) staining revealed a similar cellular
localization of silver in ileum, liver, and kidney tissue in rats exposed to AgNPs or AgAc.
Using transmission electron microscopy (TEM), nanosized granules were detected in the ileum of animals exposed
to AgNPs or AgAc and were mainly located in the basal lamina of the ileal epithelium and in lysosomes of
macrophages within the lamina propria. Using energy dispersive x-ray spectroscopy it was shown that the granules
in lysosomes consisted of silver, selenium, and sulfur for both AgNP and AgAc exposed rats. The diameter of the
deposited granules was in the same size range as that of the administered AgNPs. No silver granules were
detected by TEM in the liver.
Conclusions: The results of the present study demonstrate that the organ distribution of silver was similar when
AgNPs or AgAc were administered orally to rats. The presence of silver granules containing selenium and sulfur in
the intestinal wall of rats exposed to either of the silver forms suggests a common mechanism of their formation.
Additional studies however, are needed to gain further insight into the underlying mechanisms of the granule
formation, and to clarify whether AgNPs dissolve in the gastrointestinal