destillation fraction of chlorosilanes

Endpoint summary

Description of key information

There are no adequate data regarding the repeated dose toxicity of MS-Silane or its constituents via the oral route, therefore data from the hydrolysis product of two structurally similar constituents of MS-Silane [dichloro(dimethyl)silane, CAS 75-78-5; 20 - 35% in MS-Silane and dichloro(methyl)silane; CAS 75-54-7; 0 - 20% in MS-Silane] has been used to read-across.  In the OECD 422 study on dimethylsilanediol (DMSD, CAS 1066-42-8), Sprague-Dawley rats in the toxicity phase of the study were dosed for 28/29 days. The NOAEL was based on hepatic protoporphyrinosis in males at the higher dose of 500 mg/kg bw/day. As has been demonstrated by the acute toxicity and irritation/corrosion data, there would also be corrosive local effects from HCl if MS-Silane were to be administered. 
There are no adequate data regarding the repeated dose toxicity of MS-Silane or its constituents via the inhalation route, therefore data from the hydrolysis product of a constituent of MS-Silane [chlorotrimethylsilane, CAS 75-77-4; 0 - 5% in MS-Silane] has been used to read across.   In the OECD 422 study on trimethylsilanol (CAS 1066-40-6) Sprague-Dawley rats were treated by vapour inhalation.  No adverse effects were observed at the highest dose tested (600 ppm, equivalent to 2666 mg/m3) thus the NOAEC for trimethylsilanol was at least 600 ppm (2666 mg/m3).
There are no adequate data regarding the repeated dose toxicity of MS-Silane or its constituents via the dermal route.

Key value for chemical safety assessment

Repeated dose toxicity: via oral route - systemic effects

Endpoint conclusion

Dose descriptor:

NOAEL

250 mg/kg bw/day

Study duration:

subacute

Species:

rat

Repeated dose toxicity: inhalation - systemic effects

Endpoint conclusion

Dose descriptor:

NOAEC

2 666 mg/m³

Study duration:

subacute

Species:

rat

Additional information

MS-Silane is a UVCB comprised of 13 constituents. They are a structurally similar group of silanes with varying levels of carbon, oxygen and chlorine substitution.

There are no reliable repeated dose toxicity data on the MS-Silane, so good quality data from the most representative hydrolysis products, dimethylsilanediol (CAS 1066-42-8) and trimethylsilanol (CAS 1066-40-6) are used for read across to assess the general systemic toxicity of MS-Silane. An additional study was available for tetraethylorthosilicate (TEOS) which reported NOAELs of 50 - 100 mg/kg bw/day; however, the results from this study were not felt to be as representative of MS-Silane as a whole due to the hydrolysis products of TEOS being ethanol and silicic acid.

In an OECD 422 study with dimethylsilanediol, Sprague-Dawley rats were dosed for 28/29 days in the toxicity phase of the study. The NOAEL was determined to be 250 mg/kg/day, based on hepatic protoporphyrinosis in males at the higher dose of 500 mg/kg bw/day.    Further, it was considered appropriate to use the NOAELs from this OECD 422 study on dimethylsilanediol as the starting point to quantify systemic DNELs for MS-Silane as this provided the most conservative DNEL of the four MS-Silane constituents that were registered in 2010 [i.e., dichloro(dimethyl)silane, dichloromethylsilane, chlorotrimethylsilane, and tetrachlorosilane].

Local corrosive effects can be attributed to formation of hydrochloric acid (HCl). The local effects of inhalation exposure to chlorosilane are adequately addressed by the existing data and Indicative Occupational Exposure Limit (IOEL) for HCl. Appropriate operational conditions and risk management measures are required to maintain compliance with the existing IOEL for HCl. This is already explained in the CSR.

Repeated dose toxicity: via oral route - systemic effects (target organ) digestive: liver

Justification for classification or non-classification

The available read-across data on dimethylsilanediol suggest that the key systemic effect (hepatic protoporphyrinosis) was only observed at a dose greater than 250 mg/kg bw/day in a sub-acute oral toxicity study. In addition, no adverse effects were observed at the highest dose tested (600 ppm, equivalent to 2666 mg/m3) in a 28 -day inhalation study on trimethylsilanol, thus the NOAEC was at least 600 ppm (2666 mg/m3). Therefore there is no justification to classify for repeated dose systemic toxicity.