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Short-term toxicity to aquatic invertebrates

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Description of key information

Short-term toxicity to invertebrates: 48 hour EC50 >100 mg/l (nominal) (highest concentration tested) (OECD Guideline 202 (Daphnia sp. Acute Immobilisation Test)), read-across from an analogous/structurally related substance, trimethoxysilane (CAS 2487-90-3). The EC50 is equivalent to >79 mg/l when expressed in terms of the silanol hydrolysis product.

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 48-h EC50 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 mobility of Daphnia magna. 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 48-h EC50 value of >844 mg/l and NOEC of ≥844 mg/l (nominal) (highest concentration tested) have been determined for the effects of tetraethyl orthosilicate (CAS 78-10-4) on mobility of Daphnia magna. 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) * >844 = >389 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.