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Description of key information

No substance accumulation of synthetic amorphous silica was observed in tissues following oral administration of synthetic amorphous silica.

Key value for chemical safety assessment

Bioaccumulation potential:
no bioaccumulation potential

Additional information

The data base compiles 12 studies performed between 1963 and 2014 in rats. They used test substances of synthetic amorphous silica forms produced by different processes including untreated and surface-treated test material with the specific surface area (BET) ranging from 70-700 m2/g. Most of them meet the criteria of Klimisch score 2, four meet the criteria of Klimisch score 1.

In 6 studies, the test substance was applied by inhalation to rats. A high overall elimination of amorphous silica without accumulation in the lungs was found. These substances showed no bioaccumulation potential.

The absorption to inner organs was evaluated in rats feed with SAS for 1 month, which displayed no absorption of the substance in liver, kidney and spleen (no-Guideline study, 1968). In 1966 the excretion of SiO2was assessed in human probands. The urinary excretion of humans added up to less than 0.5% of the dose applied within 4 days. In 2012, as part of a CEFIC-LRI project, SAS was tested in an oral two-generation reproduction toxicity study according to OECD guideline 416. This material was used in 2018 for the evaluation of Si-distribution in organs and deposition-related tissue alterations. Dust particles remain located free on the surface of the gastrointestinal tract. There was no distribution to other organs found.

The literature describes synthetic amorphous silica as biosoluble and therefore not biopersistent (Sohal et al. 2018). Roelofs and Vogelsberger (2004) concluded that nanosized silica particles show an increased solubility. The existence of special surface-active components (surfactant) does not show a significant influence on the dissolution behaviour of such type of silica in biological-like media. Furthermore, the increased energy of these nano- particles is responsible for a relatively fast dissolution process and higher maximum silica concentrations observably. Lee et al. (2017) studied the solubility, absorption, tissue distribution and excretion kinetics of silicon dioxide (E 551) following single-dose oral administration to rats. The effect of the presence of food components, such as sugar and protein, on the absorption of nanoparticles was also evaluated by measuring silicon urinary excretion. Particle size was found to have no significant effect on in vivo dissolution, biodistribution or excretion kinetics. The absorption profile of silica nanoparticles was highly dependent on the presence of sugar or protein, showing an accelerated absorption rate in the presence of glucose, presumably due to a surface interaction on nanoparticles. In the scientific opinion “Re-evaluation of silicon dioxide (E 551) as a food additive“ the EFSA Panel on Food Additives and Nutrient Sources added to Food (ANS) reviewed studies limited on food grades silica. The Panel summarizes that by using different model fluids mimicking the various steps of the GIT, it was shown that the proportion of nanosized silicon dioxide which may be released from the food is dependent on the conditions in the GIT (pH, electrolyte concentration, etc.), on the initial content of nanoparticles in the sample added to the food, and on the form of the food (EFSA ANS Panel, 2018).

 

Conclusion:

The test substance, inhaled or received orally, is not absorbed in solid form from the body. It remains obviously at the position of its admission and gets not distributed nor metabolised. Applied via inhalation the lung burden increased quickly but reached a steady state soon. The test substance seems to be excreted mainly by mucociliar clearance like other natural dust particles. Applied orally the test substance seems to pass unmodified through the gastro-intestinal tract and gets excreted with the faeces.