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Please be aware that this old REACH registration data factsheet is no longer maintained; it remains frozen as of 19th May 2023.

The new ECHA CHEM database has been released by ECHA, and it now contains all REACH registration data. There are more details on the transition of ECHA's published data to ECHA CHEM here.

Diss Factsheets

Environmental fate & pathways

Endpoint summary

Administrative data

Description of key information

Tetraethyl orthosilicate (TEOS, CAS 78-10-4, EC No. 201-083-8) hydrolyses rapidly to form monosilicic acid (CAS 10193-36-9; EC No. 233-477-0) and ethanol (CAS 64-17-5; EC No. 200-578-6). Monosilicic acid exists only in dilute aqueous solutions and readily condenses at concentrations above approximately 100-150 mg/L as SiO2 to give a dynamic equilibrium between monomer, oligomers and insoluble amorphous polysilicic acid.

Monosilicic acid and its condensation products are inorganic and enter natural biogeochemical cycles. Monosilicic acid and its condensation products are ubiquitous in the environment.

A comparison of the total flux of dissolved silica into rivers can be compared with the input from manufacture and use of tetraethyl orthosilicate (refer to CSR Section 9) and indicates that the input is considered negligible in comparison with the natural flux of silica/silicic acid in the environment. The global natural flux of dissolved silicic acids into rivers has been estimated as 5.6 Tmol Si/y, a fraction (20%) originating from temperate regions. Western Europe represents 6.5% of the temperate regions, the dissolved quantity of monosilicic acid in European rivers is estimated to be 0.073 Tmol Si/y or 4374 Kt SiO2/y. In the environment, typical concentrations of monosilicic acid are up to 75 mg SiO2/L in river water and up to 14 mg SiO2/L in seawater (ECETOC 2006).

Therefore, it is not appropriate to calculate Predicted Environmental Concentrations (PECs) for the hydrolysis product monosilicic acid.


ECETOC (2006). Synthetic Amorphous Silica, SAS (CAS 7631-86-9). JACC No. 51. September 2006.

Additional information