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There are no reliable aquatic toxicity data available for hexachlorodisilane (CAS 13465-77-5), therefore good quality data for the structurally-related substances, trimethoxysilane (CAS 2487-90-3) and tetraethyl orthosilicate (CAS 78-10-4), have been read across.

 

Reliable short-term toxicity tests results are available for freshwater fish (Oncorynchus mykiss), invertebrates (Daphnia magna) and algae (Pseudokirchneriella subcapitata) for trimethoxysilane (CAS 2487-90-3). The relevant short-term values are:

Fish: LC50 (96 h): >100 mg/l; NOEC: ≥100 mg/l (nominal) (LC50 >79 mg/l and NOEC ≥79 mg/l when expressed in terms of concentration of the hydrolysis product, monosilicic acid).

Daphnia: EC50 (48 h): >100 mg/l; NOEC: ≥100 mg/l (nominal) (EC50 >79 mg/l and NOEC ≥79 mg/l when expressed in terms of concentration of the hydrolysis product, monosilicic acid).

Algae: EC50 (72 h): >100 mg/l; NOEC: <6.3 mg/l (nominal) (EC50 >79 mg/l and NOEC <5 mg/l when expressed in terms of concentration of the hydrolysis product, monosilicic acid).

 

The very rapid hydrolysis of trimethoxysilane (CAS 2487-90-3) (half-life <0.3 minutes at pH 7 and 20-25°C) indicate 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. Silanetriol may be formed as an intermediate hydrolysis product.

 

 

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

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

Daphnia: EC50 (48 h): >844 mg/l; NOEC: ≥844 mg/l (nominal) (EC50 >389 mg/l and NOEC ≥389 mg/l when expressed in terms of concentration of the hydrolysis product, monosilicic acid).

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).

 

The rapid hydrolysis of tetraethyl orthosilicate (CAS 78-10-4) (half-life 4.4 hours at pH 7 and 20-25°C) indicate 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.

 

Refer to Section 7.0 for further discussion of the approach to chemical safety assessment and justification for read across.