Sub-chronic toxicity study in rats orally exposed to nanostructured silica.

BACKGROUND: Synthetic Amorphous Silica (SAS) is commonly used in food and drugs. Recently, a consumer intake of silica from food was estimated at 9.4 mg/kg bw/day, of which 1.8 mg/kg bw/day was estimated to be in the nano-size range. Food products containing SAS have been shown to contain silica in the nanometer size range (i.e. 5-200 nm) up to 43% of the total silica content. Concerns have been raised about the possible adverse effects of chronic exposure to nanostructured silica. METHODS: Rats were orally exposed to 100, 1000 or 2500 mg/kg bw/day of SAS, or to 100, 500 or 1000 mg/kg bw/day of NM-202 (a representative nanostructured silica for OECD testing) for 28 days, or to the highest dose of SAS or NM-202 for 84 days. RESULTS: SAS and NM-202 were extensively characterized as pristine materials, but also in the feed matrix and gut content of the animals, and after in vitro digestion. The latter indicated that the intestinal content of the mid/high-dose groups had stronger gel-like properties than the low-dose groups, implying low gelation and high bioaccessibility of silica in the human intestine at realistic consumer exposure levels. Exposure to SAS or NM-202 did not result in clearly elevated tissue silica levels after 28-days of exposure. However, after 84-days of exposure to SAS, but not to NM-202, silica accumulated in the spleen. Biochemical and immunological markers in blood and isolated cells did not indicate toxicity, but histopathological analysis, showed an increased incidence of liver fibrosis after 84-days of exposure, which only reached significance in the NM-202 treated animals. This observation was accompanied by a moderate, but significant increase in the expression of fibrosis-related genes in liver samples. CONCLUSIONS: Although only few adverse effects were observed, additional studies are warranted to further evaluate the biological relevance of observed fibrosis in liver and possible accumulation of silica in the spleen in the NM-202 and SAS exposed animals respectively. In these studies, dose-effect relations should be studied at lower dosages, more representative of the current exposure of consumers, since only the highest dosages were used for the present 84-day exposure study.

Effects of silver nanoparticles (NM-300K) on Lumbricus rubellus earthworms and particle characterization in relevant test matrices including soil.

The impact of silver nanoparticles (AgNP; at 0 mg Ag/kg, 1.5 mg Ag/kg, 15.4 mg Ag/kg, and 154 mg Ag/kg soil) and silver nitrate (AgNO3 ; 15.4 mg Ag/kg soil) on earthworms, Lumbricus rubellus, was assessed. A 4-wk exposure to the highest AgNP treatment reduced growth and reproduction compared with the control. Silver nitrate (AgNO3 ) exposure also impaired reproduction, but not as much as the highest AgNP treatment. Long-term exposure to the highest AgNP treatment caused complete juvenile mortality. All AgNP treatments induced tissue pathology. Population modeling demonstrated reduced population growth rates for the AgNP and AgNO3 treatments, and no population growth at the highest AgNP treatment because of juvenile mortality. Analysis of AgNP treated soil samples revealed that single AgNP and AgNP clusters were present in the soil, and that the total Ag in soil porewater remained high throughout the long-term experiment. In addition, immune cells (coelomocytes) of earthworms showed sensitivity to both AgNP and AgNO3 in vitro. Overall, the present study indicates that AgNP exposure may affect earthworm populations and that the exposure may be prolonged because of the release of a dissolved Ag fraction to soil porewater.

Behaviour of silver nanoparticles and silver ions in an in vitro human gastrointestinal digestion model.

Oral ingestion is an important exposure route for silver nanoparticles (AgNPs), but their fate during gastrointestinal digestion is unknown. This was studied for 60 nm AgNPs and silver ions (AgNO3) using in vitro human digestion model. Samples after saliva, gastric and intestinal digestion were analysed with SP-ICPMS, DLS and SEM-EDX. In presence of proteins, after gastric digestion the number of particles dropped significantly, to rise back to original values after the intestinal digestion. SEM-EDX revealed that reduction in number of particles was caused by their clustering. These clusters were composed of AgNPs and chlorine. During intestinal digestion, these clusters disintegrated back into single 60 nm AgNPs. The authors conclude that these AgNPs under physiological conditions can reach the intestinal wall in their initial size and composition. Importantly, intestinal digestion of AgNO3 in presence of proteins resulted in particle formation. These nanoparticles (of 20-30 nm) were composed of silver, sulphur and chlorine.