Reaction mass of 4,4,13,13-tetraethoxy-3,14-dioxa-8,9-dithia-4,13-disilahexadecane and 4,4,14,14-tetraethoxy-3,15-dioxa-8,9,10-trithia-4,14-disilaheptadecane

Endpoint summary

Additional information

The registration substance is a reaction mixture comprising approximately 60% w/w of 4,4,13,13 -tetraethoxy-3,14-dioxa-8,9-dithia-4,13-disilahexadecane (S2 constituent) and 40% w/w of 3,15 -dioxa-8,9,10-trithia-4,14-disilaheptadecane,4,4,14,14-tetraethoxy- (S3 constituent).

No data are available for short- or long-term toxicity of the registration substance to aquatic organisms. These endpoints are therefore addressed by weight of evidence from data for two related substances; 4,4,13,13-tetraethoxy-3,14-dioxa-8,9-dithia-4,13-disilahexadecane (S2 constituent, CAS 56706-10-6) and polysulfides, bis[3-(triethoxysilyl)propyl] (containing S2, S3 and S4 constituents, CAS 211519-85-6).

Reliable short-term toxicity tests results are available for freshwater fish (Danio rerio), invertebrates (Daphnia magna) and algae (Desmodesmus subspicatus) for 4,4,13,13-tetraethoxy-3,14-dioxa-8,9-dithia-4,13-disilahexadecane (S2) (CAS 56706-10-6). The relevant short-term values are:

Fish: LC₅₀ (96 h): >1000 mg/l

Daphnia: EC₅₀ (48 h): <1 mg/l

Daphnia: EC₅₀ (48 h): 4 mg/l;

Algae: EC₅₀ (72 h): >500 mg/l; NOELR: 32 mg/l

It is likely that the Daphnia magna and algae were subject to physical effects of undissolved test substance (or precipitated cross-linked oligomers of the silanol) and the results of these tests therefore need to be treated with caution. The substance itself appears to be non-toxic at the solubility limit; this interpretation is supported by QSAR, which predicts that no short-term or long-term ecotoxic effects would be expressed in fish, invertebrates or algae in either short- or long-term tests at the limit of solubility of the substance.

Reliable short-term toxicity tests results are available for freshwater fish (Danio rerio), invertebrates (Daphnia magna) and algae (Desmodesmus subspicatus) for polysulfides, bis[3-(triethoxysilyl)propyl] (CAS 211519-85-6). The relevant short-term values are:

Fish: LC₅₀ (96 h): >10000 mg/l; NOELR: ≥10000 mg/l

Daphnia: EC₅₀ (48 h): >10 mg/l; NOELR: ≥10 mg/l

Algae: EC₅₀ (72 h): 700 mg/l; EC₁₀: 60 mg/l

It is likely that, because of the prolonged test medium preparation phases, the test organisms were predominantly exposed to a mixture of undissolved parent substance, silanol hydrolysis product and precipitated oligomeric or cross-linked condensation products. Physical effects are likely to have had a role in the studies that showed effects.

The data have been obtained with test media that are likely to have contained the test substance at its solubility limit and the hydrolysis products of the substances. Nominal concentrations (saturated test media) were applied as well as WAFs prepared. The lowest LL₅₀/EL₅₀ values that are adjudged not to have been influenced by the presence of undissolved material in the test media have been chosen to describe the hazard properties of the registration substance.

The hydrolysis products are freely soluble at low concentrations. It is therefore appropriate to base PNECs for the hydrolysis products on the loading rates used in the preparation of the test media. The parent substance itself appears to be non-toxic at the solubility limit.

Based on this approach the following data are considered appropriate for assessing the registration substance.

Fish 96-hour LL₅₀: >1000 mg/l (nominal) (read across from CAS 56706-10-6)

Invertebrate 48-hour EL₅₀: >10 mg/l (nominal) (read across from CAS 211519-85-6)

Algae 96-hour EC₅₀: 700 mg/l and NOEC: 60 mg/l (nominal) (read across from CAS 211519-85-6)

Data waivers are applicable to long-term fish and invertebrate toxicity endpoints based on the absence of short-term aquatic toxicity at the limit of solubility, and the difficulty in preparing the test media in aqueous solutions.

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