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EC number: 231-130-8
CAS number: 7440-21-3
The effects of repeated exposure to silicon particles were recently investigated in a subchronic inhalation study. The results showed no signs of systemic toxicity. The main findings were very mild, local inflammatory effects observed in the lungs and lung-associated lymph nodes. No severe exposure-related effects were observed. No other studies on repeated dose toxicity of silicon were available. Repeated dose toxicity data on synthetic amorphous silicon dioxide and calcium silicate show that the silicon ion does not cause systemic target organ toxicity after oral exposure. The comparative in vitro data on the dissolution kinetics of silicon and synthetic amorphous silica in different artificial biological fluids show that the dissolution of silicon from silicon particles in vitro is similar or lower than that of synthetic amorphous silica. Therefore, the bioavailabity of silicon from silicon particles is likely to be similar or lower than that of synthetic amorphous silica. Based on read-across, no systemic toxicity is expected from oral exposure to silicon.
Repeated dose systemic toxicity
No systemic effects were observed after subchronic exposure of rats to
silicon particles by inhalation. Furthermore, repeated dose toxicity
data on synthetic amorphous silicon dioxide show that the silicon ion
does not cause systemic target organ toxicity after ingestion. The
comparative in vitro data on the dissolution kinetics of silicon and
synthetic amorphous silica in different artificial biological fluids
show that the dissolution of silicon from silicon particles in vitro is
similar or lower than that of synthetic amorphous silica. Therefore, the
bioavailabity of silicon from silicon particles is likely to be similar
or lower than that of synthetic amorphous silica. Also, repeated dose
toxicity data on calcium silicate do not show any systemic toxicity.
Calcium silicate can be used as a read-across substance for silicon
since it is a sparingly soluble silicon compound which releases silicon
in the body. Thus, based on read-across to amorphous silicon dioxide and
calcium silicate, no systemic toxicity is expected from oral exposure to
Repeated dose local toxicity
The main target organs for exposure to silicon by inhalation are the
lungs. Repeated exposure to silicon particles in the alveolar size range
at 16 mg/m3 resulted in very mild local inflammatory effects in the
lungs and lung-associated lymph nodes. No statistically significant
effects were observed at lower exposure doses.
Two epidemiological studies among the workers exposed to synthetic
amorphous silica did not show any effects on lung function (Wilson et
al. 1979; Choudat et al. 1990). Recent epidemiological studies from the
silicon/ferrosilicon industry suggest the increased prevalence of COPD
and decline in lung function (FEV1) of the exposed workers. The latest
studies by Johnsen and co-workers (e.g., Johnsen et al. 2010) correlate
these with cumulative dust exposure. The effect was seen both in FeSi/Si
and FeMn/SiMn/FeCr plants. Increasing evidence has accumulated showing
that COPD may be related to workplace exposure to dusts, fumes and gases
in general. It has been estimated that for COPD a population
attributable risk of 15-20% is caused by occupational dusts/fumes.
Therefore, the increased risk of COPD reported in the metallurgical
industry is likely to be a general dust/fume exposure-related phenomenon
rather than a specific effect of silicon or silica fumes formed during
the process. Since silicon particles are only a minor component of these
dusts present in silicon/ferrosilicon factories, no firm conclusions on
the inhalation toxicity of silicon can be made based on these studies.
In a 90-day inhalation toxicity study on silicon particles, no systemic
effects were observed. Very slight inflammatory effects in the lungs and
lung-associated lymph nodes were reported at the highest dose tested (16
mg/m3). These findings were considered not to support classification of
silicon since 1) the effects were rated as very slight in severity, 2)
were only observed at a dose leading to increased retention of particles
in the lungs (moderate lung overload), and 3) were clearly distinct from
the severe progressive inflammatory effects observed with quartz (1
mg/m3). The findings following inhalation exposure to silicon particles
are likely to be predominantly caused by general,
non-substance-specific, effects of poorly soluble particles at lung
burdens exceeding the capacity of the macrophage-mediated alveolar
No significant adverse effects have been reported for synthetic
amorphous silica after repeated oral exposure. Based on the knowledge
about the comparative dissolution kinetics of silicon from silicon
particles and from synthetic amorphous silica (see Chapter
'Toxicokinetics'), it can be concluded that silicon is also of low
toxicity after repeated oral exposure. Based on dissolution data,
metallic impurities of silicon are not likely to have an impact on the
toxicity of silicon (see Chapter 'Toxicokinetics').
No classification is suggested.
A detailed justification paper discussing the interpretation of the
90-day inhalation study results is attached in Section 13 of the Iuclid
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