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Environmental fate & pathways

Hydrolysis

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Description of key information

Hydrolysis half-life: >200 -2000 hour at pH 7, 1.9 -6.6 h pH 4, and 2.0 -13.9 h pH 9 at 20 - 25°C (QSAR)

Key value for chemical safety assessment

Half-life for hydrolysis:
200 h
at the temperature of:
20 °C

Additional information

The requirement to conduct a hydrolysis study for the substance is waived in accordance with column 2 of REACH Annex VIII because the substance is insoluble in water. A measured water solubility of <10 ng/l at 20°C was determined for the substance.

Half-life values at 20-25°C of > 200 - 2000 h at pH 7, 1.9 – 6.6 h at pH 4, and 2.0 – 13.9 h at pH 9 were obtained for 3,3-bis[(dimethylvinylsilyl)oxy]-1,1,5,5-tetramethyl-1,5-divinyltrisiloxane using accepted validated QSAR methods. The result is considered to be reliable and has been used for assessment purposes.

The products of hydrolysis are dimethylvinylsilanol and silicic acid.

Hydrolysis of the read-across substance phenyl silsesquioxanes (EC 939-487-8)

Data for the substance phenyl silsesquioxanes (EC -939-487-8) are read-across to the submission substance for appropriate endpoints (see Section 1.4).The structural similarity and the siloxane hydrolysis half-life of the read-across substance to the submission substance is relevant to this read-across, as discussed in the appropriate Sections of the CSR for each endpoint.

No measured hydrolysis data is available for phenyl silsesquioxanes (EC -939-487-8); predicted half-lives of 1.9 -3.3 h at pH 4, 200 - 630 h at pH 7 and 2.0 - 5.3 h at pH 9 and 20 -25°C are calculated for this substance.

Under laboratory conditions, the likely final products of hydrolysis are phenylsilanetriol and trimethylsilanol.

Hydrolysis of the read-across substance 1,1,1,5,5,5-hexamethyl-3-phenyl-3-[(trimethylsilyl)oxy]trisiloxane (CAS 2116-84-9)

Data for the substance1,1,1,5,5,5-hexamethyl-3-phenyl-3-[(trimethylsilyl)oxy]trisiloxane (CAS 2116-84-9) are read-across to the submission substance for appropriate endpoints (see Section 1.4 of the CSR). Hydrolysis half-lives of 1.9 -3.6 h at pH 4, 200 - 630 h at pH 7 and 2.0 -5.3 h at pH 9 and 20-25°C were determined for the substance using a validated QSAR estimation method. The stated half-life is for removal of the registration substance due to hydrolysis. The products of this reaction are also unstable in water, and so further hydrolysis reactions will follow, the ultimate products being phenylsilanetriol (1 mole) and trimethylsilanol (3 moles) per mole of parent substance.

 

Hydrolysis of the read-across substance decamethylcyclopentasiloxane (CAS 541-02-6)

Data for the substance decamethylcyclopentasiloxane (CAS 541-02-6) are read-across to the submission substance,3,3-bis[(dimethylvinylsilyl)oxy]-1,1,5,5-tetramethyl-1,5-divinyltrisiloxane for appropriate endpoints (see Section 1.4).The rate of hydrolysis of the two substances is relevant to this read-across.

For decamethylcyclopentasiloxane, hydrolysis half-lives at 25°C of 9.3 h at pH 4, 1590 h at pH 7 and 24.8 – 31.6 h at pH 9 were determined in accordance with OECD 111 (Durham 2006). 

The ultimate products of hydrolysis are dimethylsilanediol and trimethylsilanol. 

 

Hydrolysis of the read-across substance dodecamethylcyclohexasiloxane (CAS 540-97-6)

Data for the substance dodecamethylcyclohexasiloxane (CAS 540-97-6) are read-across to the submission substance for appropriate endpoints (see Section 1.4).The rate of hydrolysis of the two substances is relevant to this read-across.

For dodecamethylcyclohexasiloxane (CAS 540-97-6), hydrolysis half-lives at 25°C of 22.3 h at pH 4, >1 year at pH 7 and 96 h at pH 9 were determined. 

The ultimate products of hydrolysis are dimethylsilanediol and trimethylsilanol. 

 Hydrolysis of the read-across substance hexamethyldisiloxane (L2, CAS No. 107-46-0)

Data for the substance hexamethyldisiloxane (L2, CAS No. 107-46-0) are read-across to the submission substance for appropriate endpoints (see CSR Section 1.4). The silanol hydrolysis product of the two substances is relevant to this read-across, as discussed in the appropriate Sections of the CSR for each endpoint.

For hexamethyldisiloxane, hydrolysis half-lives of 1.4 h at pH 5, 116 h at pH 7 and 12.4 h at pH 9 at 25°C were determined in accordance with OECD 111 (Dow Corning Corporation 2006a).

The half-lives at pH 7, pH 5.5 and pH 2 and 37.5°C have been calculated as for the target substance above. This gives half-lives at 37.5°C of 57 h at pH 7, 2.2 h at pH 5.5 and 5 s at pH 2.

The ultimate hydrolysis product is trimethylsilanol (2 moles per mole of parent).