Biodistribution and toxicity of antimicrobial ionic silver (Ag+) and silver nanoparticle (AgNP+) species after oral exposure, in Sprague-Dawley rats

Abstract

Although antimicrobial nanosilver finds numerous applications in the health and food industries, the in vivo toxicity of positively charged silver nanoparticles (AgNPs⁺) and relevant controls are largely unexplored. This study investigates the relationship between the biodistribution and toxicity of the well-known cetyltrimethylammonium bromide (CTAB)-capped AgNPs⁺ in 6-weeks old female Sprague-Dawley rats, at sublethal doses. Amounts comparative to those leaked from food products or considered for animal feed were administered through daily water intake, for an 18-day period: AgNPs⁺ (40 μg mL^-1), Ag⁺ (40 μg mL^-1), antimicrobial CTAB⁺ (24 μg mL^-1) and tap water. All exposures except for the water control had adverse effects on the health and systemic functions of rats (e.g., lethargy, hepatomegaly, splenomegaly, impediment of bone development, and/or heightened immune response). Although the total Ag accumulation in tissues (1.4-1.6 μg of Ag/g of liver, spleen, jejunum, and brain) was comparable for the two Ag species, AgNPs⁺ were generally more toxic than Ag⁺, particularly in spleen (0.8 μg Ag/g). Significantly reduced euthanasia time, alopecia, inflammatory responses in spleen, fragile veins, and enhanced lymphocytosis were observed only for AgNPs⁺. Overall, this study raises health concerns about the ingestion of capped-AgNPs⁺ or Ag⁺ by first-hand consumers and industry workers.

Keywords: Atomic absorption spectroscopy; Histopathology; Raman spectroscopy; Rats; Silver ions; Silver nanoparticles.