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EC number: 231-130-8
CAS number: 7440-21-3
Silicon is practically taken always present in soil minerals and
dissolved in soil pore water. If elemental silicon “metal” is released
to the soil the surfaces of silicon particles are normally already
oxidized or will be oxidized rapidly. The actual rate of oxidization is
highly dependent on particle size and environmental conditions.
Transformation/dissolution studies have shown that at least the tested
silicon powder samples did not react rapidly in contact with water. The
highest transformation/dissolution rate was 58 % in one week test period
(100 mg/l load in saline water at pH 7.4). Anthropogenic and potentially
bioavailable silicon in soil is therefore present in oxidized form as
silica and not at the elemental stage. Soil living species are primarily
exposed to dissolved silica which is present in soil pore water. The
maximum solubility of silica in water is limited by intrinsic physical
chemical properties of silicon (polymerization/colloids
forming). Short term acute aquatic tests have shown that at
a concentration > 160 mg/L (at 20-25°C),
SiO2solid colloids are being formed that are responsible for
the toxic effect.Colloid forming takes place at lower
concentration at reduced and therefore environmentally more relevant
It has been observed that the concentration of silica in soil pore
water normally remains relatively constant and clearly below the
saturation/polymerization concentrations. Adsorption of soluble silica
to soil minerals is a more favorable fate process than remaining in the
aqueous phase in high concentrations. On the other hand the dynamic
equilibrium helps in keeping concentrations relatively stable since
desorption may rapidly increase the soil pore water concentration to
some extent. Ultimately it is the mineral composition of soil in a
geological area that in the long term determines the concentration
levels of dissolved silica found regionally.
Terrestrial toxicity of silica is expected to be low since soil
living species are well adapted to the presence of silica in soil and
soil pore water. Silica is also essential for some soil-living species.
No studies or information has been located showing toxicity of silica to
soil-living species. Based on the results of short term pelagic tests
(algae, fish) acute lethal effects can be avoided if the soil pore water
concentration remains below the colloid forming/saturation
concentration. Adaptation to high natural silica concentration may be
species sensitive and the most tolerable species favors the extreme
conditions. In extreme cases, species may live in soil type called
“diatomaceous earth” also known as “diatomite’ or “kieselgur’, which is
a naturally occurring, siliceous sedimentary soil type and mineral. It
has a particle size ranging from less than 1 micron to more than 1
millimeter, but typically 10 to 200 microns. The typical chemical
composition of oven dried diatomaceous earth is 80 to 90% amorphous
silica, with 2 to 4% alumina (attributed mostly to clay minerals) and
0.5 to 2% iron oxide.
Information on Registered Substances comes from registration dossiers which have been assigned a registration number. The assignment of a registration number does however not guarantee that the information in the dossier is correct or that the dossier is compliant with Regulation (EC) No 1907/2006 (the REACH Regulation). This information has not been reviewed or verified by the Agency or any other authority. The content is subject to change without prior notice.Reproduction or further distribution of this information may be subject to copyright protection. Use of the information without obtaining the permission from the owner(s) of the respective information might violate the rights of the owner.
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