3-(dimethoxymethylsilyl)propyl methacrylate

Endpoint summary

Description of key information

The first key study was read across from the analogous substance (trimethoxysilyl)methyl methacrylate (CAS 54586-78-6). The test material was found not sensitising in a guideline study which was compliant with GLP (BSL Bioservice, 2003d). The study was conducted in accordance with OECD guideline and in compliance with GLP.

The second key study was read across from the analogous substance [dimethoxy(methyl)silyl]methyl methacrylate (CAS 121177-93-3)

The study was conducted in accordance with OECD guideline and in compliance with GLP (Bioservice, 2003e). The test material was reported to be not sensitising to guinea pigs.

The experimental work on a local lymph node assay (LLNA) for CAS 2530-85-0 is now complete and the reported result is negative. The study report is not yet finalised, therefore it is not included to the dossier at this stage.

Key value for chemical safety assessment

Skin sensitisation

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed (not sensitising)

Additional information:

The first key study for skin sensitisation found the test material, (trimethoxysilyl)methyl methacrylate (CAS 54586-78-6), to be not sensitising in a guideline study which was compliant with GLP (BSL Bioservice, 2003d).

Slight signs of erythema were recorded 24 h as well as 48 hours in all animals after first application. No other signs of irritation were observed in any other animal after the intradermal application (induction first stage). No signs of irritation were observed after the topical application (induction second stage).

The results of the test animals at the challenge phase were compared with the results of the control animals. No signs of irritation were observed after the challenge. The maximum percentage of animals sensitized was 0%. Animals of both groups survived throughout the test period. Animals of the test group showed no reduced weight gain as compared to historical data and the animals of the control group nor any other signs of toxicity.

The second key study for skin sensitisation found the test material, [dimethoxy(methyl)silyl]methyl methacrylate (CAS 121177-93-3), to be not sensitising in a guideline study which was compliant with GLP (BSL Bioservice, 2003e).

No signs of skin irritation were recorded in any of the test animals at induction or challenge any of the observations.

The maximum percentage of animals sensitized was 0%. Animals of both groups survived throughout the test period.

Read-across justification

There are no available measured data for 3-[dimethoxy(methyl)silyl]propyl methacrylate (CAS 14513-34-9) for skin sensitisation. Therefore, the Annex requirements are fulfilled by data on structurally analogous substances. This document describes the analogue approach for fulfilling this endpoint by read-across from two source substances, (trimethoxysilyl)methyl methacrylate (CAS 54586-78-6) and [dimethoxy(methyl)silyl]methyl methacrylate (CAS 121177-93-3), according to the Read-across Assessment Framework (RAAF) .

Read-across is proposed in accordance with RAAF Scenario 2: “This scenario covers the analogue approach for which the read-across hypothesis is based on different compounds which have the same type of effect(s). For the REACH information requirement under consideration, the effects obtained in a study conducted with one source substance are used to predict the effects that would be observed in a study with the target substance if it were to be conducted. The same type of effect(s) or absence of effect is predicted. The predicted strength of the effects may be similar or based on a worst case.”

The read-across justification is presented (Table 5.6.4) according to RAAF scenario 2 assessment elements (AE) as outlined in Table B1 of the RAAF1:

Table 1: RAAF scenario 2 assessment elements (AE) as given in Appendix B (Table B1) of the RAAF1

AE A.1	Characterisation of source substance
AE A.2	Link of structural similarity and differences with the proposed Prediction
AE A.3	Reliability and adequacy of the source study
AE 2.1	Compounds the test organism is exposed to
AE 2.2	Common underlying mechanism, qualitative aspects
AE 2.3	Common underlying mechanism, quantitative aspects
AE 2.4	Exposure to other compounds than to those linked to the prediction
AE 2.5	Occurrence of other effects than covered by the hypothesis and Justification
AE A.4	Bias that influences the prediction

1.AE A.1 Identity and characterisation of the source substance

The first source substance, (trimethoxysilyl)methyl methacrylate (CAS 54586-78-6), is a member of an analogue group of alkoxysilanes and silanols containing a methacrylate group. It has a silicon atom bound to three methoxy groups, and one methyl methacrylate group. Its predicted hydrolysis half-lives are 0.3 h at pH 4, 4.2 h at pH 7 and 0.1 h at pH 9 and 20-25°C.

At pH 5 (pH of skin), the hydrolysis rate is 0.3 h. The products of hydrolysis are (trihydroxysilyl)methyl methacrylate and methanol.  

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 source substance has LogKow of 1.2 at 20°C (QSAR), water solubility of 23000 mg/l at 20°C (QSAR) and vapour pressure of 8 Pa at 25°C (QSAR).

The second source substance [dimethoxy(methyl)silyl]methyl methacrylate (CAS 121177-93-3), has a silicon atom bound to two methoxy groups, one methyl group and one methyl methacrylate group. Its predicted hydrolysis half-lives are 1.8 h at pH 7, 0.2 h at pH 4, 0.04 h at pH 9 and 25°C.

At pH 4 (the closest to the known pH of skin, 5.5), the hydrolysis rate is approximately 0.2 h. At pH 7 (the pH of eye), the hydrolysis rate is 1.8 h.

The hydrolysis products in this case are [dihydroxy(methyl)silyl]methyl methacrylate and methanol. The source substance has a LogKow of 2.4 at 20°C, vapour pressure of 37 Pa at 25°C and water solubility of 2500 mg/l.

2.AE A.2 Link of structural similarities and differences with the proposed prediction

The registration and the first read-across substance, (trimethoxysilyl)methyl methacrylate (CAS 54586-78-6), are structurally similar and are members of an analogue group of alkoxysilanes and silanols containing a methacrylate group. The registration substance has a propyl methacrylate side-chain attached to the silicon atom, while the source substance has a methyl methacrylate side-chain.

In addition to the propyl methacrylate or methyl metacrylate side-chains, the target substance has two methoxy groups and one methyl group bound to silicon while the source substance has three methoxy groups bound to a silicon. Therefore, the differences between the two structures is that one of the three methoxy groups in the source substance is replaced by a methyl group in the target substance and the registration substance has a propyl methacrylate side-chain attached to the silicon atom, while the source substance has a methyl methacrylate side-chain. The silanol hydrolysis products are 3-[dihydroxy(methyl)silyl]propyl methacrylate and (trihydroxysilyl)methyl methacrylate for the registered substance and read-across substance, respectively. The common non silanol hydrolysis product is methanol.

The source substance, [dimethoxy(methyl)silyl]methyl methacrylate (CAS 121177-93-3), and the target substance, 3-[dimethoxy(methyl)silyl]propyl methacrylate (CAS 14513-34-9), are structurally similar. They are both dimethoxy silanes with one methyl group. The difference is that the source substance has a methyl methacrylate side-chain attached to the silicon atom, while the target substance has a propyl methacrylate side-chain instead.

These two substances both hydrolyse in similar rate to a disilanol (1 mole) and methanol (2 moles). The hydrolysis products of these two substances are structurally similar in the same way. They are both disilanols with one methyl side-chain. The difference is that the source substance has a methyl methacrylate side-chain, whereas the target substance has propyl methacrylate side-chain (see Table 1).

Table 2: Physico-chemical properties

Property		Target substance		Source substance		Source substance
Substance name		3-[Dimethoxy(methyl)silyl]propyl methacrylate		(trimethoxysilyl)methyl methacrylate)		[dimethoxy(methyl)silyl]methyl methacrylate
CAS number		14513-34-9		54586-78-6		121177-93-3
Hydrolysis half-life at pH 5and 25ºC		0.2 hours (QSAR)		0.3 hours (QSAR)		unknown
Silanol hydrolysis product		3-[dihydroxy(methyl)silyl]propyl methacrylate		(trihydroxysilyl)methyl methacrylate		[dihydroxy(methyl)silyl]methyl methacrylate
Non-Si hydrolysis product		methanol		methanol		methanol
LogKow value		3.4 at 20°C (QSAR)		1.2 at 20°C (QSAR)		2.4 at 20°C (QSAR)
Vapour pressure		1.3 Pa at 25°C (QSAR)		8.0 Pa at 25°C (QSAR)		37 Pa at 25°C (QSAR)
Water solubility		240 mg/L at 20°C (QSAR)		23000 mg/l at 20°C (QSAR)		2500 mg/l

3.AE A.3 Reliability and adequacy of the source study

The first key study for skin sensitisation found the test material, (trimethoxysilyl)methyl methacrylate (CAS 54586-78-6), to be not sensitising in a guideline study which was compliant with GLP (BSL Bioservice, 2003d).

Slight signs of erythema were recorded 24 h as well as 48 hours in all animals after first application. No other signs of irritation were observed in any other animal after the intradermal application (induction first stage). No signs of irritation were observed after the topical application (induction second stage).

The results of the test animals at the challenge phase were compared with the results of the control animals. No signs of irritation were observed after the challenge. The maximum percentage of animals sensitized was 0%. Animals of both groups survived throughout the test period. Animals of the test group showed no reduced weight gain as compared to historical data and the animals of the control group nor any other signs of toxicity.

The second key study for skin sensitisation found the test material, [dimethoxy(methyl)silyl]methyl methacrylate (CAS 121177-93-3), to be not sensitising in a guideline study which was compliant with GLP (BSL Bioservice, 2003e).

No signs of skin irritation were recorded in any of the test animals at induction or challenge any of the observations.

The maximum percentage of animals sensitized was 0%. Animals of both groups survived throughout the test period.

4.AE A.4 Bias that influences the prediction

Data on the source substances (trimethoxysilyl)methyl methacrylate (CAS 54586-78-6) and [dimethoxy(methyl)silyl]methyl methacrylate (CAS 121177-93-3) were read-across to the registered (target) substance 3-[dimethoxy(methyl)silyl]propyl methacrylate (CAS 14513-34-9). The source substances and the target substance have similar chemical structure and physico-chemical properties. All three substances hydrolyse at similar rate, and produce 3-[dihydroxy(methyl)silyl]propyl methacrylate, (trihydroxysilyl)methyl methacrylate or [dihydroxy(methyl)silyl]methyl methacrylate, as the silicon-containing hydrolysis products. They share a common non-silanol hydrolysis products methanol. Therefore, their toxicological properties are expected to be similar, with similar genotoxic effects. No other data for relevant substances were available.

5.AE A.2.1 Compounds the test organism is exposed to

The source substances as well as the target substance hydrolyse very rapidly in contact with water. Therefore, the test organism is mainly exposed to their hydrolysis products, 3-[dihydroxy(methyl)silyl]propyl methacrylate, (trihydroxysilyl)methyl methacrylate or [dihydroxy(methyl)silyl]methyl methacrylate  and methanol.  The source and target substances have been profiled using the OECD QSAR Toolbox v. 4.1. The three substances and their silanol hydrolysis products show similar profiles for all toxicological endpoints. All show alerts associated with skin and respiratory sensitisation, due to the presence of the (meth)acrylate groups.

Ophthalmologic changes and acidosis are described as typical primary effects in humans following exposure to methanol. Methanol is known to be a mild to moderate eye and skin irritant. The sensitisation potential of the non-silanol hydrolysis product, methanol, has not been reported in a guinea pig maximisation test (OECD 2004). At the doses of parent substance, the methanol toxicity is not expected to be relevant.

6.AE A.2.2 and A.2.3 Common underlying mechanism, qualitative and quantitative aspects

No toxicity data are available for the target substance 3-[dimethoxy(methyl)silyl]propyl methacrylate, therefore data are read-across from the structurally analogous substances (trimethoxysilyl)methyl methacrylate (CAS 54586-78-6) and [dimethoxy(methyl)silyl]methyl methacrylate (CAS 121177-93-3). These three substances hydrolyse at similar rate to a disilanol (1 mole) or a trisilanol (1 mole) and methanol (2 moles). The non-silanol hydrolysis product, methanol, is not expected to be relevant for this endpoint. Moreover, they have similar physico-chemical properties. Thus, all three substances are expected to have similar toxicity profiles.

7.AE 2.4 Exposure to other compounds than to those linked to the prediction

Neither the target substance, 3-[dimethoxy(methyl)silyl]propyl methacrylate, nor the source substances, (trimethoxysilyl)methyl methacrylate (CAS 54586-78-6)  and [dimethoxy(methyl)silyl]methyl methacrylate (CAS 121177-93-3), have impurities of toxicological concern.

The test substance in the study with the first source substance, (trimethoxysilyl)methyl methacrylate (CAS 54586-78-6), has a purity of 97.8%.

The test substance in the study with the second source substance, [dimethoxy(methyl)silyl]methyl methacrylate (CAS 121177-93-3), has a purity of 96.8%.

The target substance, 3-[dimethoxy(methyl)silyl]propyl methacrylate (CAS 14513-34-9), has a purity of >98% and no impurities are present at >1%.

8.AE 2.5 Occurrence of Other Effects than Covered by the Hypothesis and Justification

Not relevant

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

European Chemicals Agency (ECHA) (2015) Read-across Assessment Framework. Appendix B, Scenario 2

Respiratory sensitisation

Endpoint conclusion

Endpoint conclusion:

no study available

Justification for classification or non-classification

Based on the read-across available data, no classification is required for skin sensitisation in accordance with Regulation (EC) No. 1272/2008.