Dimethoxymethylvinylsilane

Endpoint summary

Key value for chemical safety assessment

Skin sensitisation

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed (not sensitising)

Additional information:

No skin senstisation data are available for the registered substance. Reliable data from related alkoxysilanes are therefore read across as weight of evidence.

A Guinea Pig Maximisation study that was conducted using the Magnusson and Kligmann (1970) protocol (Hill Top Biolab Inc., 1988) concluded triethoxy(vinyl)silane to be mildly sensitising. However, in OECD Test Guideline 406 a positive response rate of 30% must be met for a substance to be concluded to be a mild/moderate sensitiser. In this test the positive response rate was 20%, and therefore according to current criteria was considered negative. In addition the control animal mean scores were not significantly different to those of the test substance.

The guinea pig maximisation study for trimethoxy(vinyl)silane study for skin sensitisation found the test material not sensitising (WIL 2000). The reported sensitization incidence index for the test group was 0% (0/20) following challenge.

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 sensitisation 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 trimethoxy(vinyl)silane and triethoxy(vinyl)silane to dimethoxy(methyl)vinylsilane is evaluated point by point.

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 hydrolyse to similar silicon-containing hydrolysis products. The non-silanol hydrolysis products, methanol and ethanol, do not contribute to any adverse effects for sensitisation at the relevant concentrations based on publicly available information (OECD SIDS, 2004). This is discussed further below.

Read-across justification

The predicted hydrolysis half-lives of the registered substance, dimethoxy(methyl)vinylsilane, are 18.3 minutes at pH 7, <2 minutes at pH 2, and 0.7 minutes at pH 9, all at 25^oC. The products of hydrolysis are methylvinylsilanediol and methanol.

The read-across substance triethoxy(vinyl)silane has predicted hydrolysis half-lives at 20-25°C of 0.1 hours at pH 4, 0.2 hours at pH 5 and 0.02 hours at pH 9. As the hydrolysis reaction may be acid or base catalysed, the rate of reaction is expected to be slowest at pH 7 and increase as the pH is raised or lowered. The hydrolysis products are vinylsilanetriol and ethanol.

The read-across substance trimethoxy(vinyl)silane has predicted hydrolysis half-lives at 25°C of 0.1 hours at pH 7, 0.04 hours at pH 4, and 0.004 hours at pH 9. The hydrolysis products are vinylsilanetriol and methanol.

Therefore, the predicted half-lives for the registration and read-across substances at physiological pH are generally comparable so during dermal exposure similar levels of parent and hydrolysis products will be present and so read-across from triethoxy(vinyl)silane and trimethoxy(vinyl)silane to dimethoxy(methyl)vinylsilane for sensitisation is valid.

Analogue approach justification

(a) Structural similarity

The registration and read-across substances are structurally similar and are members of an analogue group of methylvinyl silane substances. All contain a silicon atom to which is attached to a vinyl group which is identical for all three. The registered substance has two alkoxy groups bound to silicon, the read-across substances have three. For the registered substance the two alkoxy groups are methoxy, the read-across substance trimethoxy(vinyl)silane has three such groups, while for the other read-across substance triethoxy(vinyl)silane, the three alkoxy groups are ethoxy. All hydrolyse rapidly to produce the similar silicon-containing hydrolysis products, methylvinylsilanediol or vinylsilanetriol and methanol or ethanol.

(b) Similar physicochemical characteristics

The key physicochemical parameters are summarised below.

Table: Key physicochemical parameters

	Target (registration substance)	Source (read-across substance	Source (read-across substance
CAS number	016753-62-1	000078-08-0	002768-02-7
EC number	240-816-6	201-081-7	220-449-8
Chemical Name	dimethoxy(methyl)vinylsilane	triethoxy(vinyl)silane	trimethoxy(vinyl)silane
Molecular weight  (gmol^-1)	132.23	190.31	148.23
log Kow(parent)	2.3	3	Not applicable
log Kow(silicon-containing hydrolysis product)	-0.1	-2.0	-2.0
Water solubility (parent)	3000 mg/L	930 mg/L	3E+04 mg/L
Water solubility (silicon-containing hydrolysis product)	5E+05 mg/L	1E+06 mg/L	1E+06 mg/L
Vapour pressure (parent)	3000 Pa	304 Pa	1190 Pa
Vapour pressure (silicon-containing hydrolysis product)	2.1 Pa	0.02 Pa	0.02 Pa

(c) Discussion of irritation properties of the non-silanol hydrolysis products

The non-silanol hydrolysis products, methanol and ethanol, do not contribute to any sensitisation effects at the relevant concentrations based on publicly available information.

Methanol and ethanol are not classified for sensitisation in Annex VI of Regulation (EC) No 1272/2008

OECD (2004): SIDS Initial Assessment Report for SIAM 19, Berlin, Germany, 18-20 October 2004, Methanol, CAS 67-56-1.

OECD (2004): SIDS Initial Assessment Report for SIAM 19, Berlin, Germany, 19-22 October 2004, Ethanol, CAS 64-17-5.

Migrated from Short description of key information:
The guinea pig maximisation tests for skin sensitisation conducted with trimethoxy(vinyl)silane and triethoxy(vinyl)silane found them to be non-sensitising.

Justification for selection of skin sensitisation endpoint:
The studies were conducted according to, or to a design comparable with, an appropriate guideline, and in compliance with GLP.

Respiratory sensitisation

Endpoint conclusion

Endpoint conclusion:

no study available

Justification for classification or non-classification

Based on the available read-across data from trimethoxy(vinyl)silane and triethoxy(vinyl)silane, dimethoxy(methyl)vinylsilane does not require classification for sensitisation according to Regulation (EC) 1272/2008.