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There are no reliable aquatic toxicity data available for trichlorosilane (CAS 10025-78-2), therefore good quality data for the structurally-related substance trimethoxysilane (CAS 2487-90-3) have been read across. Both substances rapidly hydrolyse to the intermediate hydrolysis product silanetriol, followed by further rapid hydrolysis to monosilicic acid and another non-silanol hydrolysis product.

 

The hydrolysis rate of trimethoxysilane (CAS 2487-90-3) (half-life ≤0.3 min at pH 7 and 2 °C) and test media preparation methods (overnight mixing of test solutions and static regime) mean it is likely that the test organisms in each test were exposed primarily to the hydrolysis products, monosilicic acid and methanol.

The relevant short-term values are:

Fish: LC50 (96 h): >100 mg/l (nominal), or >79 mg/l expressed in terms of concentration of the hydrolysis product monosilicic acid (Springborn Smithers, 2004a).

Invertebrates: Daphnia: EC50 (48 h): >100 mg/l (nominal), or >79 mg/l expressed in terms of concentration of the hydrolysis product monosilicic acid (Springborn Smithers, 2004b).

Algae: ErC50 (72 h): >100 mg/l and NOEC <6.3 mg/l (nominal), or >79 mg/l and <5 mg/l respectively, expressed in terms of concentration of the hydrolysis product monosilicic acid (Springborn Smithers, 2004c).

 

To support the available reliable short-term toxicity tests that have been read-across from trimethoxysilane (CAS 2487-90-3), data have also been read across from the analogous substance tetraethyl orthosilicate (CAS 78-10-4) which also hydrolyses rapidly to monosilicic acid and ethanol.

Reliable short-term toxicity tests results are available for freshwater fish (Danio rerio), invertebrates (Daphnia magna) and algae (Pseudokirchneriella subcapitata) read across from tetraethyl orthosilicate (CAS 78-10-4). The relevant short-term values are:

Fish: LC50 (96 h): >245 mg/l (measured) (>113 mg/l when expressed in terms of concentration of the hydrolysis product, monosilicic acid) (Hüls, 1993).

Daphnia: EC50 (48 h): >75 mg/l (measured concentration) (>35 mg/l when expressed in terms of concentration of the hydrolysis product, monosilicic acid) (Springborn Smithers Laboratories, 2006).

Algae: EC50 (72 h): >100 mg/l; NOEC: ≥100 mg/l (nominal) (EC50 >46 mg/l and NOEC ≥46 mg/l when expressed in terms of concentration of the hydrolysis product, monosilicic acid) (Springborn Smithers, 2008).

 

The rapid hydrolysis of tetraethyl orthosilicate (CAS 78-10-4) (half-life 4.4 hours at pH 7 and 20-25°C) indicates that, under conditions relevant to ecotoxicity assessment, it will hydrolyse to monosilicic acid over the course of the tests and therefore the test organisms in each test were exposed primarily to the hydrolysis products. 

 

No reliable data are available for toxicity to microorganisms; a 3-hour EC50 value of >100 mg/l is read-across from tetraethyl orthosilicate (CAS 78-10-4) (Desmares-Koopmans, 2010).

 

Refer to IUCLID Section 6, CSR Section 7, and the ecotoxicity RAAF report attached in IUCLID Section 13 or as an Annex in the CSR, for further discussion of the approach to chemical safety assessment and justification for read across.