The use of commercial products containing
engineered nanomaterials
in realistic scenarios may lead to the accumulation of exogenous particles
in brain tissues. In this study, we simulated the use of silver (Ag)
nasal spray in humans using Sprague–Dawley rats at 0.04 mg/kg/day.
Silver-containing particles were explicitly identified in the rat
brain after the administration of nasal sprays containing colloidal
Ag or silver ions (Ag+) for 2 weeks using multiple methods.
The accumulation of Ag-containing particles showed a delayed effect
in different brain regions of the rats, with the mass concentration
of particles increasing continuously for 1–2 weeks after the
termination of administration. The size of the observed Ag-containing
particles extracted from the brain tissues ranged from 18.3 to 120.4
nm. Further characterization by high-resolution transmission electron
microscopy with energy-dispersive spectroscopy showed that the nanoparticles
comprised both Ag and sulfur (S), with Ag/S atomic ratios of 1.1–7.1,
suggesting that Ag-containing particles went through a series of transformations
prior to or during their accumulation in the brain. Collectively,
these findings provide evidence for the accumulation and transformation
of Ag-containing particles in the rat brain, indicating a realistic
risk to brain health resulting from the application of Ag-containing
commercial products.