Registration Dossier

Administrative data

Description of key information

Acute Oral:  Based on the mid-point range for each constituent of MS-Silane, compounds with known data account for approximately 57.5% (range 25-90%) of MS-Silane.  Acute oral LD50s for the 5 constituents tested range from 214-2190 mg/kg bw. Constituents of unknown toxicity make up approximately 57% of the mixture (30-84%) and are predicted to have acute oral LD50s between 1440 and 2230 mg/kg bw based on trend analysis.  No synergies that would increase toxicity should occur between the constituents.  Therefore, read-across from the most toxic constituents to the remainder of the mixture should overestimate the toxicity of the mixture and provide a conservative estimate of toxicity.  The 3 lowest acute oral LD50s are 214 mg/kg bw (chlorotrimethylsilane; 75-77-4), 238 mg/kg bw (tetrachlorosilane; 10026-04-7), and 250 mg/kg bw (dichloromethylsilane; 75-54-7).  The mean LD50 for these compounds is 234 mg/kg bw and was used as the read-across value for MS-Silane.
Acute Inhalation: Acute inhalation toxicity of chlorosilanes as a class of materials has shown a strong structure-activity relationship (r2 = .97) between chlorine content and LC50 values. Estimated LC50 values for mono-, di-, and trichlorosilanes were determined to be 3262, 1639, and 1066 ppm, respectively, utilizing this relationship and the lower limit of the 95% prediction interval (Jean, PA, RH Gallavan, GB Kolesar, WH Siddiqui, JA Oxley, and RG Meeks. 2006. Chlorosilane Acute Inhalation Toxicity and Development of an LC50 Prediction Model. Inhalation toxicology 18:515-522.). As a result, the LC50 for the most highly chlorinated constituent of MS-Silane (tetrachlorosilane) of 4,600 mg/m3 was used as the read-across value for MS-Silane.

Key value for chemical safety assessment

Acute toxicity: via oral route

Endpoint conclusion
Dose descriptor:
LD50
Value:
234 mg/kg bw

Acute toxicity: via inhalation route

Endpoint conclusion
Dose descriptor:
LC50
Value:
4 600 mg/m³

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.  The constituents are as follows:

 

75-78-5 dichloro(dimethyl)silane (20-35%)*

75-54-7 dichloromethylsilane (0-20%)*!

10026-04-7 tetrachlorosilane (0-15%)*!

75-77-4 chlorotrimethylsilane (0-5%)*!

1450-14-2 hexamethyldisilane (5-15%)*

4525-44-4 dichloroethylmethylsilane (5-15%)

1560-28-7 chloropentamethyldisilane (10-15%)

4342-61-4 1,2-dichlorotetramethyldisilane (8-12%)

13683-11-9, chloro(dimethyl)[(trimethylsilyl)methyl]silane (5-15%)

2401-73-2 1,3-dichloro-1,1,3,3-tetramethyldisiloxane (0-3)

2943-62-6 1-chloro-1,1,3,3,3-pentamethyldisiloxane (2-6%)

4518-94-9 dichloromethylpropylsilane (0-3%)

unknown CAS (dichloromethylsilyl)methyl trimethylsilane (0 -15%).

 

*acute oral LD50 test data and acute inhalation LC50 test data available

! most toxic constituents based on acute oral LD50 data

 

Acute Oral Toxicity

Data are available for 5 of the constituents. These compounds are rapidly hydrolyzed to their non-chlorinated form with the release of hydrochloric acid. Oral exposure is highly unlikely because the material is corrosive and handling is very controlled. If oral exposure did occur, exposure would be to the chlorinated form of the material. Therefore, acute oral testing was conducted for the chlorinated form of the compounds. Acute oral LD50s for the 5 constituents tested range from 214-2190 mg/kg bw. Test data are not available for the other 8 constituents. Due to the absence of data on some of the constituents and the variable nature of the composition, a toxic units approach to determining mixture toxicity cannot be reliably utilized. In addition, data and QSAR tools are currently insufficient to develop validated QSAR models to predict the toxicity of the constituents.

 

In lieu of a complete set of data, the most conservative approach is to use the toxicity for the most toxic members and assume that all other components of the UVCB are equally as toxic. This approach assumes that the mixture as a whole is not more toxic than the most toxic members for which data are available. Of the 5 constituents for which data are available, the 3 lowest acute oral LD50s are 214 mg/kg bw (chlorotrimethylsilane; 75-77-4), 238 mg/kg bw (tetrachlorosilane; 10026-04-7), and 250 mg/kg bw (dichloromethylsilane; 75-54-7). These constituents account for 0-40% of the MS-Silane. Dichloro(dimethyl)silane (75-78-5) is less toxic (595 mg/kg bw) and accounts for 20-35% of MS-Silane. Hexamethyldisilane (1450-14-2) accounts for 5-15% of the mixture and has a toxicity of 2190 mg/kg bw. Based on the mid-point range for each constituent, compounds with known data account for approximately 57.5% (range 25-90%) of MS-Silane.

 

Acute oral LD50 data were also obtained for 3 other silicones of similar chemistry (Reconsile silicone alliance report PFA:151.004.001). Acute oral toxicity LD50s for these compounds (chloromethyltrimethylsilane, 2344-80-1; triethylsilane, 617-86-7 and tetramethylsilane, 75-76-3) were all >2000 mg/kg bw.

Available data were input into the OECD QSAR Toolbox. The QSAR toolbox profiler did not identify a specific mode of action therefore non-polar narcosis was used for read-across and trend-analysis. A full description of the QSAR findings and plots is attached.

Acute Inhalation Toxicity

Acute inhalation toxicity of chlorosilanes as a class of materials has shown a strong structure-activity relationship (r2 = .97) between chlorine content and LC50 values. Estimated LC50 values for mono-, di-, and trichlorosilanes were determined to be 3262, 1639, and 1066 ppm, respectively, utilizing this relationship and the lower limit of the 95% prediction interval (Jean, PA, RH Gallavan, GB Kolesar, WH Siddiqui, JA Oxley, and RG Meeks. 2006. Chlorosilane Acute Inhalation Toxicity and Development of an LC50 Prediction Model. Inhalation toxicology 18:515-522.). The good correlation between chlorine content and LC50 provides a sound basis for estimation of LC50s for chlorosilanes not already evaluated.

In lieu of a complete set of data, the most conservative approach is to use the toxicity for the most toxic (and in this case most highly chlorinated) constituent and assume that all other components of the UVCB are equally as toxic. This approach assumes that the mixture as a whole is not more toxic than the most toxic members for which data are available. As a result, the LC50 for the most highly chlorinated constituent of MS-Silane (tetrachlorosilane) of 4,600 mg/m3 was used as the most conservative representative read-across value for MS-Silane.

Acute Dermal Toxicity

In accordance with Column 2 of REACH Annex VIII, the acute toxicity study via the dermal route (required in Section 8.5.2) does not need to be conducted as the substance is classified as corrosive.

Justification for classification or non-classification

According to the CLP, the test substance is classified as Acute Oral Category 3, "Toxic if swallowed" and Acute Inhalation Category 3, "Toxic if inhaled". This is based on: vapour inhalation (4 hour) 2.0 < LC50 </= 10 mg/L, and 50 < oral LD50 </= 300 mg/kg bw.