Registration Dossier

Administrative data

Description of key information

No sensitisation data are available for the registered substance. Data are available for the structural analogue, tetramethylsilane (CAS 75-76-3), from a skin sensitisation study, conducted in accordance with OECD 406 (Buehler method) and in compliance with GLP. Tetramethylsilane was not sensitising in the guinea pig (Hüls, 1998). No skin reactions were observed at challenge.

Information on tetramethylsilane is included for completeness only.

Key value for chemical safety assessment

Skin sensitisation

Endpoint conclusion
Endpoint conclusion:
no adverse effect observed (not sensitising)
Additional information:

There are no measured data available to assess the skin sensitisation potential of trimethylsilane, and testing is not technically feasible because the substance is a gas. Therefore data for the structural analogue substance tetramethylsilane (CAS 75-76-3) has been used to assess its skin sensitisation potential. Tetramethylsilane was not sensitising (Hüls, 1998) when tested in the guinea-pig Buehler assay (OECD 406).

Information on tetramethylsilane is included for completeness only.

Read-across justification

To reduce animal testing REACH recommends to make use of a read-across approach where appropriate based on the high accordance in properties relevant for the specific endpoint. In the case of irritation the relevant properties are structural similarity as well as physical-chemical properties in the same range. In the following paragraphs the proposed read-across from triethylsilane to trimethylsilane is discussed. A report considering read across for all endpoints is attached in Section 13.

Read-across hypothesis

The hypothesis is that source and target substances have similar toxicological properties because they are structurally similar and have similar physicochemical properties. Trimethylsilane has a half-life in water of days and tetramethylsilane is hydrolytically stable, so reaction products do not need to be considered for the human health hazard assessment of these substances.

(a) Structural similarity

The registration and read-across substances are structurally similar and are members of an analogue group of alkylsilanes. The substances contain a silicon atom to which is attached three or four alkyl (methyl/ethyl) groups. For the registered substance there are three methyl groups, for tetramethylsilane there are four methyl group. The registered substance also has an Si-H group. There is no evidence that the Si-H group is sensitising.

(b) Similar physicochemical characteristics

The key physicochemical parameters are summarised below.

-

 

Target (registration substance)

 

Source (read-across substance

)

CAS number

993-07-7

75-76-3

EC number

213-603-0

200-899-1

Chemical Name

Trimethylsilane

Tetramethylsilane

Molecular weight
 (gmol-1)

74.20

88.23

log Kow

2.2 at 20°C

2.7 at 20°C

Water solubility at 20°C

Estimated to be 1400 mg/l at 20°C, in practice the concentration is not expected to be achieved due to very high volatility of the substance

19.6 mg/l at 25°C

Vapour pressure

Not applicable (substance is a gas), expected to be greater than 1.0E+05 Pa

79 000 Pa at 20°C

 

Respiratory sensitisation

Endpoint conclusion
Endpoint conclusion:
no study available

Justification for classification or non-classification

Based on a reliable in vivo study on tetramethylsilane, trimethylsilane is not classified as a skin sensitiser according to Regulation (EC) No 1272/2008.

There are no data to suggest that trimethylsilane is a respiratory sensitiser.

To reduce animal testing REACH recommends to make use of a read-across approach where appropriate based on the high accordance in properties relevant for the specific endpoint. In the case of sensitisation, the relevant properties are physicochemical properties and structural similarity. In the following paragraphs the proposed read-across from tetramethylsilane to trimethylsilane is discussed. A report considering read across for all endpoints is attached in Section 13.

Read-across hypothesis

The hypothesis is that source and target substances have similar toxicological properties because they are structurally similar and have similar physicochemical properties. The substances are hydrolytically stable in the context of toxicological testing (trimethylsilane and tetramethylsilane have half-lives in water of days), so reaction products do not need to be considered for the human health hazard assessment of these substances.

Read-across justification

(a)  The registration and read-across substances are structurally similar and are members of an analogue group of alkylsilanes. Both contain a silicon atom to which is attached three or four methyl groups. For the registered substance there are three methyl groups, for the read-across substance there are four. The registered substance also has an Si-H group. There is no evidence that the Si-H group is sensitising. It is therefore not considered likely that replacing Si-H with Si-CH3would be likely to confer additional skin sensitising properties on the registration substance; however, this cannot be demonstrated experimentally due to the physical state of trimethylsilane at ambient temperature and pressure.

(b)  The key physicochemical parameters are summarised below.

Table: Key physicochemical parameters

 

Target (registration substance)

Source substance (read-across)

CAS number

000993-07-7

000075-76-3

EC number

213-603-0

200-899-1

Chemical Name

Trimethylsilane

Tetramethylsilane

Molecular weight (gmol-1)

74.20

88.23

log Kow (parent)

2.2

2.7

Water solubility (parent)

Estimated to be 1400 mg/l (QSAR), limited by condensation reactions following abiotic reaction to silanol

19.6 mg/l

Vapour pressure (parent)

Not applicable (substance is a gas)

79000 Pa at 20°C