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EC number: 215-710-8
CAS number: 1344-95-2
a 2-year feeding study on rats receiving various high levels of calcium
silicate, terminal (24-months), Si tissue-levels were significantly
increased in kidney and liver at dietary levels of 5 % [= NOEL] and
higher, while at 1 % a positive trend was
only distinguishable in the kidneys of male rats. No interim
measurements had been performed, neither are there data
about excretion [Columbia 1956].
absorption of structure-analoguous SAS* appears to be insignificant as
compared to the high doses applied in animals
and humans: In the acute human oral ingestion test, the small apparent
increases in the urine output of human volunteers –
if any at all - were remarkably low as compared with the high dose of
2500 mg SiO2 applied (0.5 % within 4 days p.a.) [Lang
1966: see Degussa 1966].
experimental data about particle distribution and inhalation of calcium
silicate is available. Based on structure-analogy, it is concluded that
- under normal handling and intended use - particulate calcium silicate
in air is hardly respirable and that inhaled particle will efficiently be
cleared from the lung. Experimental
information about SAS is summarised below:
Particle size distribution of the aerosols used in inhalation studies as
compared with dusts under technical application:
respirable fractions of the experimental SAS aerosols that
consisted of particles with aerodynamic diameters of =<5 µm represented
>=50 wt%, those consisting of particles with aerodynamic diameters of
=<10 µm represented >80 wt%.
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 is below 1 vol%
(see: 4. Physical chemical properties_Particle characteristics; Chapter
Deposition in and elimination from lung tissue / NOAEC
data on the kinetics of silica deposition in the lung of experimental
animals during and after prolonged exposure to respirable silica are
exposure concentrations of up to 30 mg/m3 for prolonged
time, the initial uptake phase is characterized by relatively high
deposition followed by a phase of low increase; there is no evidence of
Si accumulation in the lung tissue.
amorphous silicas are rapidly eliminated from the lung tissue: after an
exposure period of 13 weeks (rat, 35 mg/m3), the elimination
half-life from lung tissue can be estimated to be equal or less than 7
weeks [Degussa 1987].
the other hand, crystalline silica - although inhaled at a more than
10fold lower concentration - persisted in the lung with no substantial
decrease post-exposure [Johnston et al. 2000].
the experimental NOAECof 1 mg SAS/m3(rat, 13 wk), 6/20
rats, about 30 %, showed a slight, but measurable increase in Si in the
lung tissue 1 week post-exposure [see Degussa 1987]. With the
elimination characteristics in mind, no accumulation during chronic
exposure is supposed to occur.
The efficient clearance may also be explained by the limited, but
significant water solubility of amorphous silicas
[see 4.8: READACROSS_Vogelsberger 2003/2004_SAS_solub,37°C,RL1]. The
clearance of SAS by dissolution is estimated to be at
least 20 times faster than particulate clearance by macrophages [see ECETOC
2006, Chapter 7, p. 79]. This can be assumed to apply for
calcium silicate, too, which also shows significant but limited
solubility in water.
(2006): Synthetic Amorphous Silica (CAS No. 7631-86-9). JACC Report No.
51, European Centre for Ecotoxicology and Toxicology of Chemicals,
Brussels, September 2006
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