Registration Dossier

Environmental fate & pathways

Endpoint summary

Administrative data

Description of key information

Hydrolysis: Weigh of evidence: Based on read-across approach from experimental results on analogue substances VAC3, MAC3 and propyltriacetoxysilane, the test item is determined to be hydrolytically unstable (half-life < 12hours).

Biodegradation in water: Screening test: Key study: Based on read-across approach from experimental results on analogue butan-2-one O,O',O''-(methylsilanetriyl)oxime, the test item was determined not to be readily biodegradable. This result was supported by EPI-Suite, EPA (USA) / BIOWIN v4.10 calculation method.

Biodegradation in water and sediment: Simulation tests: Data waiving (other justification): In accordance with column 2 of REACH Annex IX, the study does not to be conducted since direct and indirect exposure of sediment is unlikely.

Biodegradation in soil: Data waiving (other justification): In accordance with column 2 of REACH Annex IX, the study does not to be conducted since direct and indirect exposure of sediment is unlikely.

Bioaccumulation: aquatic/sediment: Based on the read-across approach from analogue butanone oxime, the substance butan-2-one O,O',O''-(vinylsilanetriyl)oxime was determined to have a low bioconcentration potential.

Adsorption: Key study: Soil adsorption for butan-2-one O,O',O''-(vinylsilanetriyl)oxime was estimated by KOCWIN v2.00, MCI method and was determined to be: Koc = 5.933E+005 L/kg and Log Koc = 5.773.

Additional information

Monomeric silicon chemicals are known as silanes. A silane that contains at least one silicon carbon bond, (e.g -Si-CH3) is an organosilane. They normally contain two different types of reactive groups: the hydrolysable groups such as methoxy, ethoxy or acetoxy groups and the organo-functional group, such as epoxy, amino, methacryloxy, or sulfido. It is well known that the Si-OR bonds hydrolyse readily with water, even if only with moisture absorbed on the surface, to form silanol Si-OH groups. These silanol groups can then condense with each other to form polymeric structures with very stable siloxane Si-O-Si bonds.

Previously, to confirm that hydrolysis of silanes is fast, several hydrolysis tests have been conducted in analogue silanes. In the hydrolysis test performed on propyltriacetoxysilane, the process was very fast. The half-life at different pH of test item was determined to be < 37.5 seconds since it completely hydrolysed at 150 seconds after the initial contact with water.

Moreover, the hydrolysis test performed on two acetone oxime silanes, more than 50% of the components hydrolysed in less than 0.75hafter starting the dissolution of the test substance at 25 ºC and independently of the pH.

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 hydrolysis test performed with propyltriacetoxysilane, 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).

The results for environmental fate and pathways are as follows:

Hydrolysis: Weigh of evidence: Based on read-across approach from experimental results on analogue substances VAC3, MAC3 and propyltriacetoxysilane, the test item is determined to be hydrolytically unstable (half-life < 12hours).

Biodegradation in water: Screening test: Key study: Based on read-across approach from experimental results on analogue butan-2-one O,O',O''-(methylsilanetriyl)oxime, the test item was determined not to be readily biodegradable. This result was supported by EPI-Suite, EPA (USA) / BIOWIN v4.10 calculation method.

Biodegradation in water and sediment: Simulation tests: Data waiving (other justification): In accordance with column 2 of REACH Annex IX, the study does not to be conducted since direct and indirect exposure of sediment is unlikely.

Biodegradation in soil: Data waiving (other justification): In accordance with column 2 of REACH Annex IX, the study does not to be conducted since direct and indirect exposure of sediment is unlikely.

Bioaccumulation: aquatic/sediment: Based on the read-across approach from analogue butanone oxime, the substance butan-2-one O,O',O''-(vinylsilanetriyl)oxime was determined to have a low bioconcentration potential.

Adsorption: Key study: Soil adsorption for butan-2-one O,O',O''-(vinylsilanetriyl)oxime was estimated by KOCWIN v2.00, MCI method and was determined to be: Koc = 5.933E+005 L/kg and Log Koc = 5.773.