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Short-term toxicity to fish

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Description of key information

Short-term toxicity to fish: 96 hour EC50 >100 mg/l (nominal): (highest concentration tested) (OECD Guideline 203 (Fish, Acute Toxicity Test)), read-across from an analogous/structurally related substance, trimethoxysilane (CAS 2487-90-3). The EC50 is equivalent to >78.64 mg/l when expressed in terms of the silanol hydrolysis product, monosilicic acid.
A 96 hour LC50 of >245 mg/L and a NOEC of ≥245 mg/L have been determined for the effects of tetraethyl orthosilicate, CAS 78-10-4 on mortality of Brachydanio rerio (now renamed as Danio rerio). It is likely that the test organisms were exposed to the hydrolysis products of the substance.

Key value for chemical safety assessment

Additional information

There are no reliable short-term data available for hexachlorodisilane (CAS 13465-77-5), therefore good quality data for appropriate structural analogues, trimethoxysilane (CAS 2487-90-3) and tetraethyl orthosilicate (CAS 78-10-4), have been read across. All substances share the same silanol hydrolysis products, monosilicic acid. The other hydrolysis products are hydrogen chloride for hexachlorodisilane, methanol for trimethoxysilane and ethanol for tetraethyl orthosilicate.

A 96-h LC50 value of >100 mg/l and NOEC of ≥100 mg/l (nominal) (highest concentration tested) have been determined for the effects of trimethoxysilane (CAS 2487-90-3) on mortality of Oncorynchus mykiss. In view of the test media preparation method/exposure regime it is likely that the test organisms were exposed predominantly to the hydrolysis products of the tested substance. The results may be expressed in terms of concentration of the hydrolysis product, monosilicic acid, by applying a molecular weight correction: (MW of silanol = 96.1 / MW of parent = 122.2) * >100 = >79 mg/l.

A 96-h LC50 value of >245 mg/l and NOEC of ≥245 mg/l (mean measured) (highest concentration tested) have been determined for the effects of tetraethyl orthosilicate (CAS 78-10-4) on mortality of Danio rerio. In view of the test media preparation method/exposure regime it is likely that the test organisms were exposed predominantly to the hydrolysis products of the tested substance. The results may be expressed in terms of concentration of the hydrolysis product, monosilicic acid, by applying a molecular weight correction: (MW of silanol = 96.1 / MW of parent = 208.33) * >245 = >113 mg/l.

 

Refer to the discussion in the Section 6 endpoint summary (Section 7.0 of CSR) for further discussion on the approach to chemical safety assessment for this registration substance, and justification for read-across used.