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EC number: 231-130-8
CAS number: 7440-21-3
The surface of silicon is composed of a thin oxidized silicon
layer resembling the surface of amorphous silicon dioxide. Both silicon
and amorphous silica release silicon from particles in the form of
monosilicic acid. The available in vitro data on the dissolution
kinetics of silicon in different artificial biological fluids show that
the dissolution pattern of silicon from silicon particles in synthetic
biological fluids is slightly slower when compared to pyrogenic
amorphous silica (Aerosil Ox50) (Herting et al. 2009a,b). This lower
dissolution can be explained by lower specific surface area, which is
higher in the case of synthetic amorphous silica. Based on these in
vitro dissolution data, the bioavailabity of silicon from silicon
particles is similar or slightly lower than from synthetic amorphous
silica, and it is justified to use read-across from amorphous silicon
dioxide to silicon. A detailed description of the justifications for
read-across is available in Section 13 of the Iuclid dossier.
After ingestion, amorphous silicon dioxide has insignificant
effect on tissue or urinary silicon levels. Since silicon in different
forms is ubiquitous in the environment, various foods, drinking water
and beverages contain silicon. Our normal dietary intake of silicon is
between 20-50 mg Si/day and the silicon in diet seems to be in highly
bioavailable form, as shown by a high proportion of dietary silicon
excreted in the urine. The differences in dietary intake are likely to
explain the variability in urine levels of silicon between different
individuals. Although in neutral solutions elemental silicon and
amorphous silicon dioxide are slowly dissolved, in acidic solutions is
significantly lower. Thus, e.g. in the stomach, the release of silicon
from silicon particles is likely to be low, which is likely to affect
the absorption from the gastrointestinal tract.
Metallurgical silicon may contain small amounts of impurities,
mainly iron (up to 3%), aluminium and calcium (up to 1.5%). In vitro
dissolution data show that the release of these metals from silicon is
at the same level as the release from pyrogenic silica particles
(Aerosil Ox50). Therefore, these minor impurities of silicon are
unlikely to hamper the read-across from amorphous silicon.
A subchronic inhalation study with silicon particles (MMAD 2.6 µm)
was performed in Wistar rats according to OECD 413 (Fraunhofer ITEM
2014). The doses used in the test were 1, 4 and 16 mg/m3of
silicon. The results showed that subchronic exposure by inhalation
resulted in an overload effect in rat lungs at the highest dose level
(16 mg/m3). The calculated half-times for silicon after
exposure at 16 mg/m3were 128 days for male and 119 days for
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