Shape and size of SAS
Depending upon the manufacturing process, SAS can exist in various types and sizes, all of which can be used as E551. These different types can have different surface-specific characteristics and can each have a different impact on the uptake and distribution of SAS in the body as well as its hazard potential. This increases the complexity of the SAS risk assessment.
Under the conditions present in the gastrointestinal tract, SAS particles can clump together and subsequently degrade into particles, many of which are then silica nanoparticles. In other words, if SAS powder consists of larger aggregated and agglomerated particles, these can still fall apart and result in nanoparticles to which the consumer will then be exposed.
The effects of SAS in case of a realistic, long-term, low level of exposure via food consumption are not clear. However, previous research in mice has shown that the consumption of very large quantities of SAS can cause liver damage. If SAS is injected directly into the bloodstream, even small quantities are harmful. There are also indications that SAS can accumulate in tissues. Such accumulation does not automatically imply a health risk, but it does indicate that additional studies are needed.
In 2014 RIVM National Institute for Public Health and the Environment performed a computer model simulation based on information on the uptake and distribution of SAS in the human body and data from a laboratory animal study. The conclusion was that after oral consumption leading to a low uptake in the body, SAS particles can still accumulate in the liver. Based on the effects in the liver (fibrosis) of laboratory animals, the distribution in the body and the estimated consumption, RIVM had previously concluded that health effects resulting from SAS could not be excluded.
In order to enable a clear assessment of the potential health risks, detailed information is needed on the degree to which silica nanoparticles are absorbed in the body via food. The same applies to the degree to which the substance can potentially accumulate in tissues and to information on the various types of SAS that are used in foods.
Reassessment by EFSA
In 2018, the European Food Safety Authority published the reassessment of silicon dioxide (E551) as a food additive. In this reassessment, attention was paid to the potential risks for humans associated with nanoparticles in E551. Although there is insufficient information available to determine safe levels for daily consumption, EFSA concluded that there are no indications that a risk exists at the current level of use of SAS in foods. RIVM comes to a different conclusion: health effects as a result of SAS in food cannot be excluded. The difference between these two conclusions is a result of the fact that, in its risk assessment, RIVM took the accumulation of SAS in organs into account in a different way. The risk assessment by RIVM is based on the concentration of SAS in the organs resulting from the amount of silica ingested on a daily basis throughout the entire life span, in contrast with only using the daily intake of silica.
Computer modelling of the accumulation of SAS particles in the liver (van Kesteren et al., 2015):
Solubility and hazard potential of different silica particles (Dekkers et al., 2013):
Behaviour of SAS in the intestines (Peters et al., 2012; RIKILT):
Presence of SAS and risks in food (Dekkers et al., 2011): https://doi.org/10.3109/17435390.2010.519836
Letter to Parliament follow-up study on SAS (in Dutch)