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EC number: 231-130-8
CAS number: 7440-21-3
A 90-day nose-only inhalation study with silicon particles (MMAD 2.6 um)
was performed in Wistar rats according to OECD 413 (Fraunhofer ITEM
2014), with exposures 6 hours/day, 5 days/week during 13 weeks. The
doses used in the test were 1, 4 and 16 mg/m3 of silicon and they were
selected on the basis of a range-finding study. Quartz DQ12 (1 mg/m3)
was used as a positive control. The rats were exposed nose-only six
hours/day, five days/week during 13 weeks. All groups were examined on
day 1 after end of exposure (day 1). In addition, animals exposed to 16
mg/m2 silicon or 1 mg/m3 quartz were examined after recovery periods of
13 weeks (day 91), 26 weeks (day 182) and 52 weeks (day 365). The
highest silicon exposure concentration (16 mg/m3) resulted in moderate
The results showed no effects indicating systemic toxicity in animals
exposed to silicon and all statistically significant local effects
observed were of minimal/very slight severity. Silicon caused no
significant effects on body weight, haematology or clinical chemistry.
Lung weights were significantly increased on day 1 in males of the 16
mg/m3 silicon group and in the quartz group and among females in the 4
and 16 mg/m3 silicon groups and in the quartz group. During the recovery
period, significantly increased lung weights were only seen in the
No statistically significant effects were observed in the 1 and 4 mg/m3
groups at the end of the exposure period.
One day after the end of exposure, alveolar granulocyte infiltration and
interstitial mononuclear cell infiltration, indicating very slight
(minimal) inflammatory effects, were observed in the 16 mg/ m3 group.
The inflammation persisted during the recovery period.
A statistically significant increase of polymorphonuclear neutrophils in
bronchoalveolar lavage fluid was observed in animals of the 16 mg/m3
group at the end of exposure. 13 weeks later, neutrophils were still
observed, but at decreasing concentrations. In addition, upon 13 weeks
of recovery, two cases of very slight interstitial fibrosis were
observed in the lungs of rats from the 16 mg/m3 group. After 26 weeks of
recovery, fibrosis was detected in six rats. One year after the end of
the exposures, the statistically significant findings in the 16 mg/m3
recovery group included interstitial mononuclear cell infiltration
(observed in all animals; very slight (minimal) inflammatory effects),
interstitial fibrosis (very slight) of the lungs, granulomatous
inflammation of the bronchus-associated lymphoid tissue (very slight to
slight) and of the lung-associated lymph nodes (slight to severe), and
fibrosis of the lung-associated lymph nodes (slight to moderate). In
addition, very sight pleural fibrosis was observed in five animals (out
of 20 examined rats; not statistically significant from control group).
The effects observed in the quartz DQ12 group (1 mg/m3) were much more
severe than in the silicon 16 mg/m3 group. Fibrosis, hypertrophy, and
alveolar lipoproteinosis occurred already at day 1 after the end of the
exposure, and progressed within the one-year recovery period. In
addition to the effects detected earlier, necrosis was observed in the
lung-associated lymph nodes of animals examined 26 and 52 weeks after
the end of the exposure.
The NOAEC for silicon was 4 mg/m3and
the LOAEC 16 mg/m3.
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