N-(dimethylvinylsilyl)-1,1-dimethyl-1-vinylsilylamine

Long-term toxicity to aquatic invertebrates

Link to relevant study record(s)

Reference

Endpoint:

long-term toxicity to aquatic invertebrates

Data waiving:

study scientifically not necessary / other information available

Justification for data waiving:

other:

Description of key information

The endpoint is waived.

Additional information

A study is available with the read-across substance trimethoxy(vinyl)silane (CAS 2768-02-7). The registration substance and the read across substance, trimethoxy(vinyl)silane, are structurally similar, as they both have a vinyl side chain and have low log K_owvalues (<3). The data are considered as supporting.

A 21-day NOEC value of 28.1 mg/l has been determined for the effects of the read-across substance trimethoxy(vinyl)silane on survival and reproduction of Daphnia magna when expressed in terms of measured concentrations. Due to the rapid rate of hydrolysis the concentration was based on the measured concentration of the hydrolysis product, methanol. The NOEC is equivalent to 20.1 mg/l when expressed in terms of the silanol hydrolysis product of the tested substance, vinylsilanetriol. This value is read across to dimethylvinylsilanol, the hydrolysis product of the registered substance.

However the data are not used to derive the PNEC because ammonia and log K_ow are thought to drive the toxicity of the registered substance. The chemical safety assessment is based on the production of ammonia by reading-across from 1,1,1,3,3,3-hexamethyldisilazane and on the log Kow of the silanol hydrolysis product by reading-across from trimethylsilanol.

Reliable long-term data are available sourced from the Environment Agency Proposed EQS for Water Framework Directive Annex VIII Substances: Ammonia (un-ionised) 2007. A 29-d NOEC of 0.066 mg NH₃/l has been reported for toxicity of ammonia to the aquatic invertebrate Deleatidium sp. (Champ et al, 1977).

Testing for long-term toxicity to invertebrates is not considered necessary because:

No data are available for the registered substance, which rapidly hydrolyses to dimethylvinylsilanol and ammonia. Chemical safety assessment and PNECs are based on these hydrolysis products. Data have been read across from structural analogues 1,1,1,3,3,3-hexamethyldisilazane (CAS 999-97-3), which produces ammonia and trimethylsilanol (structural analogue of dimethylvinylsilanol), and trimethylsilanol.

 

Ammonia is assessed separately to dimethylvinylsilanol and the data waiver is based on the silanol hydrolysis product.

 

In accordance with Column 2 of REACH Annex IX, there is no need to further investigate the effects of this substance in a long-term aquatic toxicity to invertebrates study because, as indicated in guidance R.7.8.4.3 (ECHA 2016), the quantitative chemical safety assessment (conducted according to Annex I of REACH) indicates that the Risk Characterisation Ratio is below 1 and therefore the risk is already adequately controlled and further testing is not justifiable.

 

The substance is highly water-soluble, has low bioavailability (based on log K_ow <3 (1.5)) and there is no reason to expect any specific mechanism of toxicity beyond narcosis. Therefore, the occurrence of toxic effects that were not expressed in the existing short-term aquatic studies (conducted at concentrations up to 500 mg/l with 1,1,1,3,3,3-hexamethyldisilazane and 1000 mg/l with trimethylsilanol) would be considered unlikely.

 

Based on the short-term aquatic data set, the most sensitive trophic level is algae according to data read across from 1,1,1,3,3,3-hexamethyldisilazane, where ammonia is present to drive toxicity. Toxicity was observed below 100 mg/l. When reading across from trimethylsilanol only (structural analogue of the silanol hydrolysis product of the registered substance), the most sensitive trophic level is invertebrates. However, based only on the results from trimethylsilanol, no toxicity was observed below 100 mg/l.

 

A PNEC has been derived for the purpose of chemical safety assessment. An assessment factor of 1000 was applied to derive the freshwater PNEC; this high assessment factor to derive the predicted no-effect level already reflects the typically higher value of a short-term EC₅₀ compared to a long-term EC₁₀. For a narcotic chemical without a specific mode of toxic action, it is unlikely that the aquatic PNEC would be significantly over-estimated using this method.

Also, as long-term data are available for the effects of ammonia on fish (the most sensitive trophic level in acute toxicity studies) and ammonia is considered the cause of toxicity in studies conducted with the registration substance, the PNEC based on this data is considered protective of the long-term effects to invertebrates.

 

Overall it is concluded that the risk characterisation conclusion is sufficiently conservative in respect of any uncertainties and therefore further in vivo testing is not considered necessary.

 

Details on how the PNEC and the risk characterisation ratio have been derived can be found in IUCLID Section 6.0, CSR Section 7, and Chapters 9 and 10 of the Chemical Safety Report, respectively.

Ammonia:

Data and PNEC derivation for ammonia have been taken from published sources.

For the hydrolysis by-product, ammonia, reliable chronic data are presented in the CSR Section 7.0.