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EC number: 215-710-8
CAS number: 1344-95-2
In a 2-y feeding study, calcium silicate produced no significant adverse effects. Inhalation exposure to calcium silicate: Target organ is the lung. Based on results from synthetic amorphous silica (SAS), the parent substance, low exposure concentration of respirable dust particles provokes an inflammation response, which is reversible. No histopathological manifestations following exposure of 13 weeks to 1.3 mg/m3. An experimental NOAEC (acute to subchronic) of 1 mg/m3 (respirable) was established for SAS aerosol.
and oral exposure
are not relevant toxicological issues, based on the inherent substance
properties and experimental evidence. In a 2-y feeding
study, calcium silicate produced no significant adverse effects in rats,
the NOEL is considered to be approx. 3000 mg/kg bw [Columbia 1956].
No robust experimental data
about inhalation toxicity is available for the target compound, calcium
silicate (CS). The only long-term inhalation study in rats and guinea
pigs provides evidence that no definite differences in effects exist
between SAS and CS [Columbia 1966]. Yet,
from this comparative study conducted only at one high exposure level of
CS and SAS, a NOAEL cannot be derived.
Therefore, the analogy approach will be adopted, using data obtained
The inhalation of respirable
particles of synthetic amorphous silica (SAS) produces a time- and
dose-related inflammation response of the lung tissue in animal studies.
Progressive events following excess exposure are characterised as
"interstitial fibrosis/early nodular fibrosis/incipient fibrosis”.
However, a progression process of any lesion has not been observed like
that seen after quartz exposure, i.e. all observations suggest
reversibility. There are no signs of classical nodular silicosis or a
lymphatic-type pneumoconiosis. On the other hand, crystalline silica
produces persistent lung inflammation even at much lower exposure levels
[Johnston et al. 2000].
exposure to an average concentration of 1.3 mg/m3 of a
pyrogenic SAS resulted in mild reversible pro-inflammatory cell
proliferation rather than a pathologically relevant tissue change. Given
the low-grade severity of this common lung-tissue response, 1 mg/m3
can be established as NOAEC and LOEC (sub-chronic, 13 weeks). The LOAEC
was 5.9 mg/m3, the mid concentration, which produced clear
signs of histopathological adverse effects (stimulation of collagen
production, increase in lung weight, incipient interstitial fibrosis in
the lung, slight focal atrophy in the olfactory epithelium). All these
effects were reversible following discontinuation of exposure [Degussa
No lung-tissue effects were
observed following exposure of 5 days to 1 mg/m3 of the same
silica [NOEC (short-term)]; the LOAEC (5 d) was 5.4 mg/m3 [ASASP
2003 a,b,c]. Measurements of the particle-size
distributions under experimental conditions revealed, the exposure
aerosol was practically fully respirable.
Based on the pathological
relevance of effects after inhalation, 1 mg/m3(respirable)
could be established as NOEC(short-term) and NOAEC(sub-chronic). This
appears to be justified also in light of the fact that the sub-chronic
study was conducted with a pyrogenic synthetic amorphous silica (SAS)
which appears to induce more marked tissue responses than the
precipitated SAS type.
The low exposure level did
not provide any evidence of an accumulation of adverse effects over
time. Therefore, the NOAEC of SAS of 1 mg/m3 is considered to
apply also for prolonged/chronic exposure.
Based on the structural similarity as well as properties between
synthetic amorphous silica (SAS) and synthetic amorphous silicates, the
NOAEC of SAS is also adopted for calcium silicate.
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