decachlorotetrasilane

Toxicity to aquatic algae and cyanobacteria

Description of key information

Toxicity to algae: 72 hr EC50 >100 mg/l (nominal) (highest concentration tested) and NOEC <6.3 mg/l (nominal) (OECD Guideline 201 (Alga, Growth Inhibition Test)), read-across from an analogous/structurally related substance, trimethoxysilane (CAS 2487-90-3). The EC50 is equivalent to >79 mg/l and the NOEC as <5 mg/l when expressed in terms of the silanol hydrolysis product.

Additional information

There are no reliable short-term data available for decachlorotetrasilane (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 product, monosilicic acid. The other hydrolysis products are hydrogen chloride for decachlorotetrasilane, methanol for trimethoxysilane and ethanol for tetraethyl orthosilicate.

 

A 72-h EC₅₀ value of >100 mg/l (nominal) (highest concentration tested) and NOEC of <6.3 mg/l (nominal) have been determined for the effects of trimethoxysilane (CAS 2487-90-3) on growth rate and biomass of Pseudokirchneriella subcapitata. 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: EC₅₀: (MW of silanol = 96.1 / MW of parent = 122.2) * >100 = >79 mg/l; NOEC: (MW of silanol = 96.1 / MW of parent = 122.2) * <6.3 = <5 mg/l.

Examination of the growth inhibition data for all replicates indicates that inhibition was <10% at all test concentrations, with no clear dose-response, so that it is likely that the EC10 would be greater than the highest test concentration and the apparent effect on growth is considered not to indicate a hazard for this endpoint.

 

A 72-h EC₅₀ value of >100 mg/l and NOEC of ≥100 mg/l (nominal) (highest concentration tested) have been determined for the effects of tetraethyl orthosilicate (CAS 78-10-4) on growth rate and biomass of Pseudokirchneriella subcapitata. 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: EC₅₀: (MW of silanol = 96.1 / MW of parent = 208.33) * >100 = >46 mg/l; NOEC: (MW of silanol = 96.1 / MW of parent = 122.2) * ≥100 = ≥46 mg/l.

 

Refer to the Ecotoxicological Information Discussion for further discussion on the approach to chemical safety assessment for this registration substance, and justification for read-across used.