Dimethoxymethylvinylsilane

Endpoint summary

Description of key information

Acute oral LD50 values of greater than 5000 mg/kg or 7120 for males and 7236 mg/kg for females were derived for read-across substances triethoxy(vinyl)silane and trimethoxy(vinyl)silane respectively.
The acute inhaled LC50 was greater than 5000 mg/m3 for the registered substance, dimethoxy(methyl)vinylsilane.

Key value for chemical safety assessment

Acute toxicity: via oral route

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

LD50

Value:

5 000 mg/kg bw

Acute toxicity: via inhalation route

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

LC50

Value:

5 000 mg/m³ air

Acute toxicity: via dermal route

Endpoint conclusion

Endpoint conclusion:

no study available

Additional information

No acute oral toxicity data are available for the registered substance. However, reliable data are available for related alkoxysilane substances and these are used as weight of evidence.

In an acute oral toxicity study with triethoxy(vinyl)silane (WIL, 1998) an LD₅₀ in excess of 5000 mg/kg bw was identified. Five male and five female rats were treated by oral gavage with 3846 or 5000 mg/kg bw. At the higher dose 2/5 males and 1/5 females died, whereas at the lower dose 2/5 females were found dead. There was evidence of systemic toxicity at both doses including impaired muscle coordination, hypoactivity, tremors and clear ocular discharge. Mucoid faeces and laboured breathing were each noted for animals that died. All surviving animals appeared normal by day 13 of the observation period.

An acute oral toxicity study with trimethoxy(vinyl)silane (BRRC, 1984) gave LD₅₀ values of 7.34 ml/kg and 7.46 ml/kg in male and female rats, respectively. Deaths were noted at 8 or 16 ml/kg and clinical signs included sluggishness, red to brown discharge, lacrimation, pilo-erection, unkempt appearance, prostration, emaciation and unsteady gait. At necropsy, dark red kidney sections were observed in animals that died at 16 and 8 ml/kg. There were no gross necropsy findings in animals that survived to the end of the study. On the basis of a measured relative density of 0.97, the reported LD₅₀ values correspond to ca. 7120 and 7236 mg/kg for males and females respectively.

In the key inhaled acute study with the registered substance, dimethoxy(methyl)vinylsilane (DCC, 1996) there were no notable findings in animals exposed to 5 mg/L for 4 hours, therefore the LC₅₀ was considered to be greater than 5000 mg/m³.

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 acute toxicity relevant properties are structural similarity as well as physical-chemical and basic toxicological parameters 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 acute toxicity at the relevant dose levels based on publicly available information (OECD SIDS, 2004a and OECD 2004b). 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; at 37.5^oC and at pH 7 and 2 (relevant for conditions in the lung or stomach following inhaled or oral exposure) the predicted half-lives are 0.1 hours and 5 seconds respectively. 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, 0.9 hours at pH 7 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 half-life at 37.5ºC and pH 2 (relevant for conditions in the stomach following oral exposure) is approximately 5 seconds. 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 pH 2 are very rapid ( ≤ 0.1 hours) so all substances will be 90% hydrolysed to similar silicon-containing hydrolysis products after less than 20 minutes. Compared to the typical gastric emptying half-life for liquids in the order of 77 minutes in rats (RIVM, http://www.interspeciesinfo.com/Interspecies/Stomach), several hydrolysis half-lives would therefore have occurred and absorption in the intestine would almost exclusively relate to the final hydrolysis products. As a result, after oral administration, all three substances will hydrolyse rapidly in the stomach and systemic exposure will be to the similar hydrolysis products methylvinylsilanediol or vinylsilanetriol and methanol or ethanol. Therefore, read-across from triethoxy(vinyl)silane and trimethoxy(vinyl)silane to dimethoxy(methyl)vinylsilane for oral administration is considered to be 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) Similar toxicokinetics

When oral exposure takes place it can be assumed, except for the most extreme of insoluble substances, that uptake through intestinal walls into the blood occurs. Uptake from intestines can be assumed to be possible for all substances that have appreciable solubility in water or lipid. Other mechanisms by which substances can be absorbed in the gastrointestinal tract include the passage of small water-soluble molecules (molecular weight up to around 200) through aqueous pores or carriage of such molecules across membranes with the bulk passage of water (Renwick, 1993). The hydrolysis products of the registered and read-across substances are all highly water soluble and have molecular weights less than 200 so systemic exposure is very likely following oral exposure. Therefore in view of the rapid hydrolysis following oral dosing, it is appropriate to read-across the available oral data for the read-across substances trimethoxy(vinyl)silane and triethoxy(vinyl)silane which produce similar silicon-containing hydrolysis products to address the potential for acute toxicity.

(d) Acute Toxicity

The alkyl alkoxy silanes, including vinyls, generally have oral and dermal LD₅₀ values of greater than 2000 mg/kg bw and inhaled LC₅₀ values greater than the maximum achievable test concentration (PFA, 2015t).

(e) Discussion of the acute toxicity of the non-silanol hydrolysis products

Both methanol and ethanol have a low order of acute toxicity and are considered not to contribute to any effects noted at the doses used in the studies with the read-across substances (OECD SIDS, 2004a and OECD 2004b).

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.

PFA (2015t): Analogue report: Mammalian toxicity of alkyl alkoxysilanes and silanols; PFA.404.002.002 (October 2015)

Renwick A. G. (1993) Data-derived safety factors for the evaluation of food additives and environmental contaminants. Fd. Addit. Contam. 10: 275-305.

Justification for selection of acute toxicity – oral endpoint
Studies were conducted according to or similar to an appropriate OECD test guideline. One was conducted in compliance with GLP. The GLP status of the second study is uncertain. The oral LD50 value for triethoxy(vinyl)silane is used for CSA as it is the lower value.

Justification for selection of acute toxicity – inhalation endpoint
Study was conducting according to an appropriate guideline and in compliance with GLP.

Justification for classification or non-classification

Based on the available for the substance itself and for related alkoxysilanes, dimethoxy(methyl)vinylsilane does not require classification for acute toxicity according to Regulation (EC) 1272/2008.