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Short-term toxicity to fish. Weight of evidence: LC50 (96h) = 192.34 mg/L (based on mortality) (read-across from supporting substance acetic acid).

Short-term toxicity to aquatic invertebrates: Weight of evidence: EC50 (48h) = 158.26 mg/L (based on mobility, without pH adjustment) (read-across from supporting substance acetic acid).

Toxicity to aquatic algae: Key study: EC50 (72h) = 28.75 mg/L and NOEC (72h) = 21.20 (based on growth rate, without pH adjustment) (read-across from analogue substance propyltriacetoxysilane).

Toxicity to microorganisms: Key study: NOEC (28 days) = 132.76 mg/L (based on biodegradation) (read-across from analogue substance methyltriacetoxysilane).

Based on the results from the aquatic toxicity (at least one value between 10 and 100 mg/L) but since the substance is readily biodegradable and according to CLP Regulation 1272/2008, the substance triacetoxyvinylsilane is not classified for aquatic toxicity.

Additional information

It is well known that triacetoxisilane undergoes rapid hydrolysis in aqueous or moist environments to acetic acid and trisilanol.

The confirm that hydrolysis of acetoxysilanes is fast, the test of hydrolysis of propyl triacetoxysilane in water was performed. It was measured, that the process was very fast. The half-life at different pH of propyltriacetoxysilane was determined to be < 37.5 seconds since the test item was completely hydrolysed at 150 seconds after the initial contact with water.

As it is stated in different publications, silanols hydrolyse well in water and the carbon- bounded substituents can have profound effects on the rate of hydrolysis. (Arkles B., Chemtech 1977; Pluddemann E.P., Plenum Press NY, 1982; Kay, B.D. and Assink R.A, J. Non-Cryst. Solids, 1988).

The rates of hydrolysis of the alkoxy groups are generally related to their steric bulk: CH3O>C2H5O> t-C4H9O and a methoxysilane hydrolyzes at 6-10 times rate of an ethoxysilane. Smith (Smith K. J. Org. Chem 1986) proved that increased organic substitution enhances the hydrolysis rate Me3SiOMe> Me2Si(OMe)2> MeSi(OMe)3.

During the performed hydrolysis test, the condensation and polimerysation of the molecules formed in hydrolysis were observed too. It was observed as the phase separation. Unfortunately, this phase separation caused the technical difficulties of the determination of the molecular weight of larger condensation products. It was possible to determined MW of smaller condensates which still are in solutions. Their average MW were between 604-695.

This phase separation as a result of condensation was described by Arkles. The hydrolysis of propyltrimetoxysilane showed that oligomers are formed and branched structures presages phase separation (Arkles B. et al, Silanes and Coupling Agents, 1992).

Taking in account both, the hydrolysis and condensation, it is expected that the observed in the hydrolysis test phase changed product contains large chain polymers with MW>1000.

Authors showed that molecules of MW>1000 cannot be biologically available (Van Gestel et a, Reg. Toxicol. and Pharmacol., 1985, 5, 422-31 and Zitko V, Handbook of Environmental Chemistry, v. 2 221-29).

A stated before, diacetoxysilane is not stable when exposed to water or moisture and undergo rapid hydrolysis. The hydrolysis produces 2 moles of acetic acid and the silanediol which condensate to higher weight siloxanes. The polymerization products are considered biologically unavailable and the toxicity is driven by acetate anion.

The toxicity of Diacetoxydi-tert-butoxysilane should be evaluated as the toxicity of acetic acid.

The results from aquatic toxicity studies for diacetoxydi-tert-butoxysilane are as follow:

- Short-term toxicity to fish. Weight of evidence: LC50 (96h) = 192.34 mg/L (based on mortality) (read-across from supporting substance acetic acid).

- Short-term toxicity to aquatic invertebrates: Weight of evidence: EC50 (48h) = 158.26 mg/L (based on mobility, without pH adjustment) (read-across from supporting substance acetic acid).

- Toxicity to aquatic algae: Key study: EC50 (72h) = 28.75 mg/L and NOEC (72h) = 21.20 (based on growth rate, without pH adjustment) (read-across from analogue substance propyltriacetoxysilane).

- Toxicity to microorganisms: Key study: NOEC (28 days) = 132.76 mg/L (based on biodegradation) (read-across from analogue substance methyltriacetoxysilane).

Based on the results from the aquatic toxicity (at least one value between 10 and 100 mg/L) but since the substance is readily biodegradable and according to CLP Regulation 1272/2008, the substance triacetoxyvinylsilane is not classified for aquatic toxicity.

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