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EC number: 215-710-8
CAS number: 1344-95-2
1. Toxicological endpoints
High doses of calcium silicate
(CS, >5000 mg/kg bw) failed to produce adverse effects after oral
ingestion in experimental animals.
No experimental data have been
located following acute inhalation exposure to CS. Aerosol
levels that were technically achievable under
experimental conditions with
synthetic amorphous silica (SAS) are acutely non-toxic and clearly
sub-lethal (=< 2 mg/L). This is also assumed for CS.
CS gave no evidence of a mutagenic
potential in various in-vitro and in-vivo studies, additionally
supported by negative results obtained with structure-analogous silica
in standard tests as well as in an in-vitro/ex-vivo assay for gene
mutation, following inhalation exposure of rats to SAS for 13 weeks.
CS provided no evidence of a
carcinogenic potential in a limited 2y feeding study in rats, consistent
with the negative results from longterm feeding studies in rat and mouse
using structure-analogous SAS. In a comparative life-span
carcinogenicity study using the intrapleural rat model, synthetic
amorphous sodium aluminium silicate (NAS), administered at a
cancer-producing dose for fibres, induced no mesotheliomas. In synopsis
of all genotoxicity, carcinogenicity along with various long-term
inhalation studies with CS, NAS, and SAS, it is concluded that there is
no evidence of a carcinogenic potential of synthetic amorphous CS after
oral ingestion or inhalation exposure.
CS did not induce adverse effects
on intra-uterine development in three animal species.
No impact on reproductive
parameters is expected by prolonged exposure to CS, given the inherent
properties of this substance class, and based on limited data from
synthetic amorphous silica (SAS), the parent substance of CS.
and oral exposure are
relevant toxicological issues, based on the inherent substance
properties and experimental evidence. The long-term
oral NOAEL value, the highest dose tested in a 2y feeding study in rats
receiving CS, was approx. 3000 mg/(kg bw*d).
inhalation exposure (readacross,
limited experimental data after prolonged exposure to calcium silicate
in rats and guinea pigs (up to 24 months) provides evidence that no
definite differences in effects exist between synthetic amorphous silica
(SAS) and calcium silicate (CS). However, no NOEC can be derived from
this study, as only one single high and adverse exposure concentration
was applied (Columbia 1966).
the analogy approach is adopt
by making use of experimental data obtained with SAS, in particular for
deriving the NOEC: The inhalation
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].
Experimental No-Observable-Adverse-Effect Concentration (NOAEC)
After 5 exposures (6 h/d) to
1 mg/m3 (respirable), no tissue reaction was
observed (see 7.5.3: ASASP 2003a, b, c). After 13 weeks at 1.3 mg/m3
(respirable), there was no morphological tissue effect that could
be considered as a pathological manifestation (slight reversible
collagen stimulation and no significant increase in lung weight) [see
7.5.3: Degussa 1987].
Based on the pathological
relevance of effects, 1 mg/m3 (respirable) was 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 SAS which appears to induce more marked tissue responses
than the precipitated SAS type.
The short-term LOAEC(5 d)
was 5.4 mg/m3for the pyrogenic SAS, but this concentration
was more of a NOAEC for the precipitated types [see 7.5.3: ASASP 2003
a,b,c]. The low exposure level did not provide any evidence of an
accumulation of adverse effects over time.
comparable test conditions, we expect that synthetic amorphous calcium
silicate shows the same behaviour.
Particle size distribution of the aerosols used in inhalation studies as
compared with dusts under technical application:
particle size and morphology rather than particle composition is the
determinant of inflammatory response in the lung.
respirable fractions of
the experimental SAS aerosols that consisted
of particles with aerodynamic diameters of =< 5 µm represented >= 50
consisting of particles with
aerodynamic diameters of =< 10 µm represented > 80 wt%.
In the commercial
products, that fraction of particles in the whole-size range of
air-borne particles according to EN/DIN 481 that is potentially able to
reach the thoracic and alveolar site (respirable fraction) is below
1 vol% (= wt%) (see: Endpoint
summary of 4. "Physical
chemical properties_Particle characteristics" and entries of chapter
of the DNEL(inhalation)
With reference to
the German OEL of 4 mg/m3 for
synthetic amorphous silicas (inhalable fraction) [stipulated
by entry into the TRGS]
is based on a scientific evaluation of the German scientific committee,
Senatskommission zur Prüfung gesundheitsschädlicher Arbeitsstoffe
("MAK-Kommission") (MAK Germany/Austria/Switzerland) [MAK 1994]. The
principles of this evaluation correspond to those published by the
European "Scientific Committee on Occupational Exposure Limits, SCOEL".
This procedure is in
compliance with the rules laid down in the CSA guidance, Chapter R 8
(ECHA 2008, R 8, Appendix R.8 -13).
MAK´s proposal for an OEL for synthetic amorphous silica:
The MAK Commission
clearly confined this OEL to highly disperse synthetic amorphous silica
(SAS) and excluded other forms of silicas that – although
radiographically amorphous – tend to exhibit a crystalline character:
these include tempered or calcinated amorphous silica, silica glasses,
silica fumes and similar types. They argue that these types show a
particle-size distribution generally different from that of SAS, while
the experimental toxicological response pattern resembles that of
crystalline silicas following inhalation. While deciding, the Commission
took into account that under occupational and use conditions SAS forms
aggregates and agglomerates with particle sizes of up to 100 µm, i.e.
representing a particle distribution distinctly beyond the critical
respirable fine-particle spectrum, and that the pulmonary effects showed
complete reversibility during a recovery period [MAK 1994]. The OEL
represents the inhalable fraction of dust, which is related to the
available epidemiological exposure data. Animal test results are related
to respirable dust fraction.
Arbeitsstoffe. Toxikologisch-arbeitsmedizinische Begründung von
MAK-Werten (Maximale Arbeitsplatz-Konzentrationen).Amorphe
Kieselsäuren, Deutsche Forschungsgemeinschaft (DfG),
closed 10 April 1989, VCH
mbH, Weinheim 1994
on information requirements and chemical safety assessment: Chapter R.8:
Characterisation of dose [concentration]-response for human health, May
oral and inhalation exposure
are not relevant toxicological issues, based on the inherent substance
properties and experimental evidence. Therefore, DNEL values are not
the general population.
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