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

Endpoint summary

Additional information

There are no reliable aquatic toxicity data available for N-(dimethylvinylsilyl)-1,1-dimethyl-1-vinylsilylamine (CAS 7691-02 -3).

For aquatic toxicity endpoints good quality weight of evidence data for the structurally-related substance 1,1,1,3,3,3-hexamethyldisilazane (CAS 999-97-3) and the silanol hydrolysis product’s analogue substance trimethylsilanol (CAS 1066-40-6) have been read across. In addition, supporting data have been read across from trimethoxy(vinyl)silane (CAS 2768-02-7) to provide evidence of low toxicity from the vinyl group of the registered substance and the data for ammonia required to derive the chemical safety assessment for the ammonium hydrolysis product are also presented.

For the activated sludge respiration inhibition endpoint, microorganisms toxicity data have been read across for the structurally-related substance dichloro(methyl)(vinyl)silane (CAS 124-70-9), which derives a 3-hour ASRI EC₁₀value of >100 mg/l (loading rate).

The data from the read-across substances, 1,1,1,3,3,3-hexamethyldisilazane (CAS 999-97-3) and trimethylsilanol (CAS 1066-40-6), are presented below.

 

• 1,1,1,3,3,3-Hexamethyldisilazane (CAS 999-97-3)

Reliable short-term toxicity tests results are available for freshwater fish (Brachydanio rerio), invertebrates (Daphnia magna) and algae (Scenedesmus subspicatus) for 1,1,1,3,3,3-hexamethyldisilazane (CAS 999-97-3). The relevant short-term values are:

Fish: LC₅₀ (96 h): 88 mg/l; NOEC: 56 mg/l (the LC₅₀ is equivalent to 49 mg/l in terms of concentration of the hydrolysis product, trimethylsilanol and 9.3 mg/l in terms of NH₃)

Daphnia: EC₅₀ (48 h): 80 mg/l; NOEC: 25 mg/l (the EC₅₀ is equivalent to 45 mg/l in terms of concentration of the hydrolysis product, trimethylsilanol and 8.4 mg/l in terms of NH₃)

Algae: EC₅₀ (72 h): 50 mg/l; NOEC: 7.5 mg/l (equivalent to 28 and 4.2 mg/l respectively in terms of concentration of the hydrolysis product, trimethylsilanol and equivalent to 5.2 mg/l and 0.8 mg/l respectively in terms of NH₃)

   

The very rapid hydrolysis of 1,1,1,3,3,3-hexamethyldisilazane (CAS 999-97-3), (half-life <<1 min at pH 7 and 20-25 °C) means it is likely that the test organisms in each test were exposed primarily to the hydrolysis products, trimethylsilanol and ammonia. In the aqueous phase, trimethylsilanol (TMS) can react with itself in a condensation reaction to form hexamethyldisiloxane (HMDS, CAS 107-46-0) and water, which is discussed further below.

 

• Trimethylsilanol (CAS 1066-40-6)

Reliable data have been read across from the silanol hydrolysis product's analogous substance, trimethysilanol (CAS 1066-40-6).

Reliable short-term toxicity tests results are available for freshwater fish (Oncorhynchus mykiss), invertebrates (Daphnia magna) and algae (Selenatrum capricornutum, new name: Pseudokirchneriella subcapitata) with trimethylsilanol (CAS 1066-40-6). The relevant short-term values are:

Fish: LC₅₀ (96 h): 271 mg/l; NOEC: 100 mg/l

Daphnia: EC₅₀ (48 h): 124 mg/l; NOEC: <60 mg/l

Algae: EC₅₀ (72 h): >684 mg/l; NOEC: 44 mg/l

 

It should be noted that trimethylsilanol (TMS) in the aqueous phase can react with itself in a condensation reaction to form hexamethyldisiloxane (HMDS, CAS 107-46-0) and water. In an aqueous solution, an equilibrium is established between TMS (monomer) and HMDS (dimer). The equilibrium of the reaction is in favour of TMS, particularly at low concentrations. The condensation reactions of TMS are reversible unless the concentration of HMDS exceeds its solubility; in this case, HMDS forms a separate phase, driving the equilibrium towards HMDS. At a loading of 100 mg/l, >99.9% TMS is expected. At loadings above about 500-1000 mg/l the concentration of HMDS is predicted to exceedits solubility, resulting in formation of a separate phase.

Hexamethyldisiloxane (HMDS) is classified for the environment as Aquatic Acute 1 and Aquatic Chronic 2 according to Regulation (EC) No 1272/2008. Therefore it is possible that the outcome of the studies with trimethylsilanol were affected by the formation of HMDS in the test system and subsequent exposure of this to test organisms. However, the use of the available studies to assess dimethylvinylsilanol is considered to be a conservative approach.

Therefore, the data for trimethylsilanol used as read-across are considered to be a reliable worst-case scenario.

• Trimethoxy(vinyl)silane (CAS 2768-02-7)

In addition, reliable data have been read across from trimethoxy(vinyl)silane (CAS 2768-02-7) as supporting evidence for low toxicity from the vinyl group of the registered substance.

Toxicity tests results are available for freshwater fish (Oncorhynchus mykiss), invertebrates (Daphnia magna) and algae (Pseudokirchneriella subcapitata). Given the rapid hydrolysis rate of the substance (half-life at 20-25°C of 5.5 hours at pH 7) and the test methods, it is likely that the test organisms were exposed predominantly to the silanol hydrolysis products vinylsilanetriol and methanol. The relevant value are:

Fish: LC₅₀ (96 h): 191 mg/l; NOEC: 128 mg/l

Daphnia: EC₅₀ (48 h): 169 mg/l; NOEC: <60 mg/l

Daphnia: NOEC (21 d): 28 mg/l; EC₅₀: 119 mg/l

Algae: EC₅₀ (72 h): >89 mg/l; NOEC: ≥89 mg/l

• Ammonia

Ecotoxicity data for ammonia has been reviewed by various regulatory programmes. Toxicity of ammonia is dependent on the degree of ionization and, therefore, is highly pH dependent and also dependent on temperature.

Reliable long and short-term test results are available for ammonia sourced from the Environment Agency Proposed EQS for Water Framework Directive Annex VIII Substances: Ammonia (un-ionized) 2007.

In the short-term tests the most sensitive species to ammonia was found to be fish (pink salmon), with an LC₅₀ of 0.083 mg un-ionised NH₃/l (Rice and Bailey, 1980). Long-term test results also showed fish as the most sensitive species with a NOEC of 0.014 mg un-ionised NH₃/l for rainbow trout (Solbe et al, 1989).

 

Refer to IUCLID Section 6 endpoint summary (CSR Section 7.0) for further discussion of the approach to chemical safety assessment and justification for read across.