As silver nanoparticles (AgNPs) are used in a wide array of commercial products and can enter the human body through oral exposure, it is important to understand the fundamental physical and chemical processes leading to changes in nanoparticle size under the conditions of the gastrointestinal (GI) tract. Rapid AgNP growth was observed using nanoparticle tracking analysis with 30 s resolution over a period of 17 min in simulated gastric fluid (SGF) to explore rapid kinetics as a function of pH (SGF at pH 2, 3.5, 4.5 and 5), size (20 and 110 nm AgNPs), and nanoparticle coating (citrate and PVP). Growth was observed for 20 nm AgNP at each pH, decreasing in rate with increasing pH, with the kinetics shifting from second-order to first-order. The 110 nm AgNP showed growth at ≤3.5 pH, with no growth observed at higher pH. This behavior can be explained by the generation of Ag+ in acidic environments, which precipitates with Cl−, leading to particle growth and facilitating particle aggregation by decreasing their electrostatic repulsion in solution. These results highlight the need to further understand the importance of initial size, physicochemical properties, and kinetics of AgNPs after ingestion to assess potential toxicity.

Consumer exposure to silver nanoparticles (AgNP) via ingestion can occur due to incorporation of AgNP into products such as food containers and dietary supplements. AgNP variations in size and coating may affect toxicity, elimination kinetics or tissue distribution. Here, we directly compared acute administration of AgNP of two differing coatings and sizes to mice, using doses of 0.1, 1 and 10 mg/kg body weight/day administered by oral gavage for 3 days. The maximal dose is equivalent to 2000× the EPA oral reference dose. Silver acetate at the same doses was used as ionic silver control. We found no toxicity and no significant tissue accumulation. Additionally, no toxicity was seen when AgNP were dosed concurrently with a broad-spectrum antibiotic. Between 70.5% and 98.6% of the administered silver dose was recovered in feces and particle size and coating differences did not significantly influence fecal silver. Peak fecal silver was detected between 6- and 9-h post-administration and <0.5% of the administered dose was cumulatively detected in liver, spleen, intestines or urine at 48 h. Although particle size and coating did not affect tissue accumulation, silver was detected in liver, spleen and kidney of mice administered ionic silver at marginally higher levels than those administered AgNP, suggesting that silver ion may be more bioavailable. Our results suggest that, irrespective of particle size and coating, acute oral exposure to AgNP at doses relevant to potential human exposure is associated with predominantly fecal elimination and is not associated with accumulation in tissue or toxicity.

Due to their widespread incorporation into a range of biomedical and consumer products, the ingestion of silver nanoparticles (AgNPs) is of considerable concern to human health. However, the extent to which AgNPs will be modified within the gastric compartment of the gastrointestinal tract is still poorly understood. Studies have yet to fully evaluate the extent of physicochemical changes to AgNPs in the presence of biological macromolecules, such as pepsin, the most abundant protein in the stomach, or the influence of AgNPs on protein structure and activity. Herein, AgNPs of two different sizes and surface coatings (20 and 110 nm, citrate or polyvinylpyrrolidone) were added to simulated gastric fluid (SGF) with or without porcine pepsin at three pHs (2.0, 3.5, and 5.0), representing a range of values between preprandial (fasted) and postprandial (fed) conditions. Rapid increases in diameter were observed for all AgNPs, with a greater increase in diameter in the presence of pepsin, indicating that pepsin facilitated AgNPs aggregation. AgNPs interaction with pepsin only minimally reduced the protein’s proteolytic functioning capability, with the greatest inhibitory effect caused by smaller (20 nm) particles of both coatings. No changes in pepsin secondary structural elements were observed for the different AgNPs, even at high particle concentrations. This research highlights the size-dependent kinetics of nanoparticle aggregation or dissolution from interaction with biological elements such as proteins in the gastrointestinal tract. Further, these results demonstrate that, in addition to mass, knowing the chemical form and aggregation state of nanoparticles is critical when evaluating toxicological effects from nanoparticle exposure in the body.