Reaction mass of calcium disilicide and calcium silicide

Endpoint summary

Additional information

Silicon and calcium are practically taken always present in soil minerals and dissolved in soil pore water. Anthropogenic and potentially bioavailable silicon in soil is present in oxidized form as silica Si(OH)₄and calcium as ionized Ca (II).

Terrestrial toxicity of calcium and silica are expected to be low, since soil dwelling species are well adapted to the presence of these elements in soil and soil pore water. Some soil types may be very rich or almost entirely built from these minerals. Calcium is essential for all and silica is essential for some of soil living species.

No standard studies or information has been located showing toxicity of silica to soil dwelling species. Based on the results of short term pelagic tests (algae, fish) acute lethal effects might be avoided if the soil pore water concentration remains below the colloid forming/saturation concentration (> 160 mg/L (at 20-25°C)). It has been observed that normally the concentration of silica in soil pore water remains relatively constant and clearly below the saturation/polymerization concentrations. Long term effects data is not available.

Adaptation to high natural silica or calcium concentration may be species sensitive and the most tolerable species favor the extreme conditions. For instance, species may live in soil type called “diatomaceous earth” also known as “diatomite’ or “kieselgur’, which is a naturally occurring, siliceous (amorphous SiO₂> 90%) 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.

It has been observed that normally the concentration of silica in soil pore water 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 the 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.

Annex XI adaptation rules offer the possibility to apply weight of evidence approach instead of testing. In estimation of hazard of CaSi, the read across method may be utilized in the first hand by applying the already existing hazard data. Based on already existing information, it is currently not seen necessary to have any targeted ecotoxicological testing of CaSi in soil. All the main and minor constituent elements Ca, Si and Fe, Al, Ti are all very common elements present in soil minerals and soil (fine) particulate matter and generally these elements are not regarded specifically hazardous elements in soil environment and therefore hazard profile of these element is rather low. In addition, the manufacture and use categories indicate no direct and remarkable exposure to soil compartment (SU3, 14 PC 7,11, PROC 3, 4, 5, 8a, 8b, 9, 20, 21, 22).