Registration Dossier

Environmental fate & pathways

Endpoint summary

Administrative data

Description of key information

Additional information

Abiotic degradation

Chlorosilanes hydrolyse very rapidly to silanols and hydrogen chloride. The half-life for dichloro(dimethyl) silane has been estimated as 0.3 min at pH 7 and 1.5oC. This gives a half-life of ca. 0.002 h at pH 7 and 12oC using the conversion DT50 (XoC) = DT50 (t) x e(0.08(T-X)) (ECHA Guidance R16). The rate is then ln2 / 0.002 = 300 h-1. Other chlorosilanes with measured data have half lives of ca. 0.2 min at pH 7 and 1.5oC. Their rates adjusted to ln2 / 0.0014 = 495 h-1.

Biotic degradation

No ready biodegradation tests are available for MS-Silane, its constituents or their silanol hydrolysis products. Read-across from an OECD 310 study for the related substance trimethylsilanol, and category-based considerations, indicate that MS-Silane will not biodegrade in water.

Several soil studies are available for the silanol hydrolysis product of dichloro(dimethyl) silane, which is used as weight of evidence that degradation in soil does occur but not to a significant extent. Initial rates of degradation in soil simulation tests ranged from 0.16 to 2.1% per month.

The chemical safety assessment indicates that it is not necessary to obtain further information on biodegradation via simulation tests in water or sediment.

Degradation rates of MS-Silane:

 

Degradation rate in water:

Rapid hydrolysis is expected. On the basis ofread-across and category-based considerations, MS-Silane is not expected to biodegrade in water

Degradation rate in sediment:

On the basis ofread-across and category-based considerations, MS-Silane is not expected to biodegrade in sediment

Degradation rate in soil:

Initial rates of degradation for dimethyl(silane) in soil simulation tests ranged from 0.16 to 2.1% per month.

Degradation rate in air:

Reaction with water vapour, rather than photolysis, is expected to be the primary degradation process of MS-Silane constituents. Calculated half-life of dimethylsilanediol for reaction with hydroxyl radicals is 2.2 days; measured half-life is 20 days. Measured half lives for other silanols range from 2-9 days.