Registration Dossier

Administrative data

Key value for chemical safety assessment

Genetic toxicity in vitro

Description of key information

There are no genetic toxicity studies available for [3-(2,3-epoxypropoxy)propyl]dimethoxy(methyl)silane (CAS 65799-47-5).

Gene mutation (Bacterial reverse mutation assay / Ames test)

[3-(2,3-Epoxypropoxy)propyl]trimethoxysilane: positive with and without activation in TA97 and TA100 cells (similar to OECD TG 471) (Microtest Research Ltd., 1988).

[3-(2,3-Epoxypropoxy)propyl]diethoxy(methyl)silane: positive with and without activation in TA 100, TA 1535 and WP2 uvrA cells (similar to OECD TG 471) (BioReliance, 2000).

In vitro cytogenicity

[3-(2,3-Epoxypropoxy)propyl]diethoxy(methyl)silane: positive with and without metabolic activation in cultured human lymphocytes (OECD 473) GLP (SafePharm 2004c).

Mutagenicity in mammalian cells

[3-(2,3-Epoxypropoxy)propyl]trimethoxysilane: positive with and without metabolic activation in mouse lymphoma L5178Ycells (similar to OECD TG 476) (Litton Bionetics, 1983).

Endpoint conclusion
Endpoint conclusion:
adverse effect observed (positive)

Genetic toxicity in vivo

Description of key information

In vivo micronucleus assay: [3-(2,3-epoxypropoxy)propyl]diethoxy(methyl)silane was negative in mice (oral administration by gavage) (OECD 474) (Shin-Etsu, 2009).

Further information on [3-(2,3-epoxypropoxy)propyl]diethoxy(methyl)silane will be added when the comet assay has been completed.

Endpoint conclusion
Endpoint conclusion:
no adverse effect observed (negative)

Additional information

Data are read across from bacterial and mammalian mutagenicity studies for [3-(2,3-epoxypropoxy)propyl]trimethoxysilane (2530-83-8) and from bacterial and in vitro cytogenicity studies for [3-(2,3-epoxypropoxy)propyl]diethoxy(methyl)silane (2897-60-1).

The key study for bacterial mutagenicity for [3-(2,3-epoxypropoxy)propyl]trimethoxysilane (2530-83-8) is from a valid study conducted according to a protocol that is similar to OECD TG 471 and under GLP (Microtest Research Ltd., 1988). The test substance produced a five-fold increase in revertants in Salmonella typhimurium TA 100, and a two-fold increase in TA 97 with and without metabolic activation. The test substance is considered mutagenic in Salmonella typhimurium strains TA97 and TA100 both in the absence and presence of metabolic activation under the conditions of the test.

The key study for bacterial mutagenicity for [3-(2,3-epoxypropoxy)propyl]diethoxy(methyl)silane (2897-60-1) is from a valid bacterial reverse mutation assay conducted according to OECD TG 471 and under GLP, using Salmonella typhimurium TA98, TA100, TA1535 and TA1537 and Escherichia coli WP2uvrA (BioReliance, 2000). There was a positive, dose related increase in the number of revertant colonies in TA 100, TA 1535 and WP2 uvrA, with and without metabolic activation. The test substance is mutagenic in these tester strains. Appropriate positive and solvent controls were added and gave expected results. It is concluded that the test substance is positive for mutagenicity to bacteria under the conditions of the test.

The key study for in vitro cytogenicity for [3-(2,3-epoxypropoxy)propyl]diethoxy(methyl)silane (2897-60-1) is from a study conducted according to OECD 473, and in compliance with GLP (SafePharm 2004c). The test material induced a statistically significant dose-related increase in the frequency of cultured human blood lymphocytes with chromosome aberrations in the absence and the presence of metabolic activation. Appropriate positive and solvent controls were used and gave the expected results. The test material was therefore considered to be clastogenic to human lymphocytes in vitro.

The key study for mammalian mutagenicity for [3-(2,3-epoxypropoxy)propyl]trimethoxysilane (2530-83-8) is from a valid study conducted according to a protocol similar to OECD TG 476 and under GLP (Litton Bionetics, 1983). The substance induced mutations in mouse lymphoma L1578Y TK cells, both with and without metabolic activation, in a dose dependent manner. It is considered that the test substance is positive for the induction of mutations in mammalian cells under the conditions of this test.

The key study for in vivo cytogenicity for  [3-(2,3-epoxypropoxy)propyl]diethoxy(methyl)silane: [3-(2,3-epoxypropoxy)propyl]diethoxy(methyl)silane (2897-60-1) is from a study conducted according to OECD 474, and in compliance with GLP (Shin-Etsu, 2009). No evidence for a test substance induced increase in the incidence of micronucleated polychromatic erythrocytes in mice bone marrow was observed when tested up to the limit concentration. No clinical signs of toxicity were observed following oral administration of 500, 1000 and 2000 mg/kg of test material to mice. Appropriate positive and vehicle controls were included and gave the expected results. It is concluded that the test substance does not cause damage to chromosomes under the conditions of the test.

It should be noted that the PCE / NCE ratio was unchanged in treated animals, so there is no evidence that the test substance reached the target tissue. However, the available information on the toxicokinetics suggests that the registered substance will hydrolyse very rapidly in the acidic milieu of the stomach (hydrolysis half-life at 37.5°C and pH 2 is 5 seconds). The hydrolysis product, [3-(2,3-epoxypropoxy) propyl]methylsilanediol is water soluble (1.0E+06 mg/l) and has a favourable molecular weight (192.28) for absorption so systemic exposure is likely. Although the parent substance has a molecular weight which is not favourable for uptake (248.4) it is water soluble (1200 mg/l), so some systemic exposure is possible if unhydrolysed parent compound is left in the stomach. It is therefore concluded based on the result of the study that the test substance is negative for the induction of micronuclei under the conditions of the test.

Further testing has been contracted for [3-(2,3-epoxypropoxy)propyl]diethoxy(methyl)silane to further evaluate the potential for genetic toxicity. A comet assay has been approved by the ECHA and the study will be added to this dossier when it becomes available.

Read-across justification

There are no available measured data [3-(2,3-epoxypropoxy)propyl]dimethoxy(methyl)silane (CAS 65779-47-5) for genetic toxicity. Therefore, the Annex requirements are fulfilled with data on structural analogue substances. This document describes the analogue approach for fulfilling this endpoint by read-across from two source substances, [3‑(2,3‑epoxypropoxy)propyl]trimethoxysilane, (2530-83-8), and [3‑(2,3‑epoxypropoxy)propyl]diethoxy(methyl)silane, (2897-60-1), according to the Read-across Assessment Framework (RAAF)[1].

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, [3-(2,3-epoxypropoxy)propyl]trimethoxysilane, (2530-83-8) is a trimethoxysilane with a 3-(2,3-epoxypropoxy)propyl side-chain. It hydrolyses to [3-(2,3-epoxypropoxy)propyl]silanetriol (1 mole) and methanol (3 moles). Its measured hydrolysis half lives are: 0.15 hours at pH 5, 6.5 hours at pH 7, 0.13 hours at pH 9 and 24.5°C (OECD 111) At 37°C, close to physiological temperature, half-lives of 0.087 hours at pH 5, 3.3 hours at pH 7 and 0.053 hours at pH 9 were determined for the substance. At physiological temperature 35ºC and pH 2 (relevant for conditions in the stomach following oral exposure), the hydrolysis half-life is approximately 5 seconds.

At 37.5ºC and pH 5.5 (relevant for dermal exposure), the hydrolysis half-life will be in between the half-lives at pH 5 and pH 7 at 37.5ºC, i.e. between 0.087 hours and 3.3 hours. The hydrolysis half-life at pH 7 and 37.5°C (relevant to the lungs and blood) is predicted to be 3.3 hours. The products of hydrolysis are [3-(2,3-epoxypropoxy)propyl]silanetriol (1 mole) and methanol (3 moles). The source substance has log Kow of 0.5 at 20°C (estimated), predicted water solubility of 1.1E+05 at 23°C and predicted vapour pressure of 1.1 Pa at 25°C.

The second source substance [3‑(2,3‑epoxypropoxy)propyl]diethoxy(methyl)silane, (2897-60-1) is a diethoxysilane with methyl and 3-(2,3-epoxypropoxy)propyl side-chains. Its estimated hydrolysis half-lives at 20-25°C 0.4 hours at pH 4, 0.5 hours at pH 5, 11.7 hours pH 7 and 0.2 hours at pH 9. The calculated half-life at pH 2 and 35°C (relevant for conditions in the stomach following oral exposure) is approximately 5 seconds. At 37.5ºC and pH 5.5 (relevant for dermal exposure), the hydrolysis half-life will be less than 0.5 hours. The hydrolysis half-life at pH 7 and 37.5°C (relevant to the lungs and blood) is predicted to be 4.4 hours. The products of hydrolysis are [3-(2,3-epoxypropoxy)propyl]methylsilanediol (1 mole) and ethanol (2 moles). The source substance has log Kow of 2.7 at 20°C (estimated), predicted water solubility of 1200 and measured vapour pressure of 0.42 Pa at 25°C.

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

The target substance, [3-(2,3-epoxypropoxy)propyl]dimethoxy(methyl)silane (CAS 65779-47-5) is a dimethoxysilane with a methyl and a 3-(2,3-epoxypropoxy)propyl side-chains.

The first source substance, [3-(2,3-epoxypropoxy)propyl]trimethoxysilane, (2530-83-8) is a trimethoxysilane with a 3-(2,3-epoxypropoxy)propyl side-chain.

The second source substance, [3-(2,3-epoxypropoxy)propyl]diethoxy(methyl)silane, (2897-60-1) is a diethoxysilane with a methyl and a 3-(2,3-epoxypropoxy)propyl side-chains.

The target and source substances are all alkoxysilanes with a 3-(2,3-epoxypropoxy)propyl side-chain. They have the general structural formula shown in Figure 1 (attached).

For the target substance:                         R1 is methyl,      R2 is methyl.

For the source substance 2530-83-8:        R1 is methoxy,  R2 is methyl.

For the source substance 2897-60-1:        R1 is methyl,      R2 is ethyl.

Therefore, all structural features of the target substance (3-(2,3-epoxypropoxy)propyl side-chain, dialkoxy(methyl)silane, methoxysilane) are present in one or both of the source substances.

The target substance and the source substance 2530-83-8 are both methoxysilanes with a 3-(2,3-epoxypropoxy)propyl side-chain. The difference between these substances is that one of the three methoxy groups in the source substance is replaced by a methyl group in the target substance.

The target substance and the source substance 2897-60-1 are both dialkoxysilanes with methyl and 3-(2,3-epoxypropoxy)propyl side-chains. The difference between these substances is that the two alkoxy groups are ethoxy for the source substance and methoxy for the target substance.

The three substances all have similar moderate molecular weight (220-248) and low vapour pressure (0.4-3 Pa at 25°C). They all have low log Kow (0.5-2.7) and moderate to high water solubility (1200 – 110000 mg/l), with the target substance being in between the two source substances. All the substances hydrolyse rapidly, with half-lives of <12 hours at pH 7 and 25°C and 5 s at pH 2 and 37.5°C.

Table 2: Physicochemical properties

Property

Target substance

Source substance

Source substance

CAS

65799-47-5

2530-83-8

2897-60-1

Type

Dimethoxy

Trimethoxy

Diethoxy

Name

[3-(2,3-epoxypropoxy)propyl]dimethoxy(methyl)silane

[3-(2,3-epoxypropoxy)propyl]trimethoxysilane

[3-(2,3-epoxypropoxy)propyl]diethoxy(methyl)silane

Hydrolysis products

[3-(2,3-epoxypropoxy)propyl]methylsilanediol (1 mole) and methanol (2 moles)

[3-(2,3-epoxypropoxy)propyl]silanetriol (1 mole) and methanol (3 moles)

[3-(2,3-epoxypropoxy)propyl]methylsilanediol (1 mole) and ethanol (2 moles)

MW

220.34

236.34

248.4

WS / mg/l

1.2E+04

1.1E+05

1200

Log Kow

1.7

0.5

2.7

Hydrolysis half-life at pH 7 and 25°C

1.6 hours

6.5 hours (measured)

11.7 hours

Hydrolysis half-life at pH 7 and 37.5°C

0.6 hours

3.3 hours (measured)

4.4 hours

Hydrolysis half-life at pH 2 and 37.5°C

5 s

5 s

5 s

VP at 25°C / Pa

3.0

1.1

0.42 (measured)

HP MW

192.29

194.26

192.29

HP WS / mg/l

1E+06 (limited to around 1000 mg/l by condensation reactions)

1E+06 (limited to around 1000 mg/l by condensation reactions)

1E+06 (limited to around 1000 mg/l by condensation reactions)

HP Log Kow

-0.7

-2.6

-0.7

HP VP at 25°C / Pa

2.8E-04

1.7E-05

2.8E-04

 

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

3-(2,3-Epoxypropoxy)propyltrimethoxysilane:

Gene mutation (Bacterial reverse mutation assay / Ames test) positive with and without activation in TA97 and TA100 cells (similar to OECD TG 471) (Reliability 2) (Microtest Research Ltd., 1988).

Mutagenicity in mammalian cells: positive with and without metabolic activation in mouse lymphoma L5178Ycells (similar to OECD TG 476) (Reliability 2) (Litton Bionetics, 1983).

[3-(2,3-epoxypropoxy)propyl]diethoxy(methyl)silane:

Gene mutation (Bacterial reverse mutation assay / Ames test): positive with and without activation in TA 100, TA 1535 and WP2 uvrA cells (similar to OECD TG 471) (Reliability 1) (BioReliance, 2000).

In vitro cytogenicity: [3-(2,3-epoxypropoxy)propyl]diethoxy(methyl)silane: positive with and without metabolic activation in cultured human lymphocytes (OECD 473) GLP (Reliability 1) (SafePharm 2004c).

In vivo cytogenicity: [3-(2,3-epoxypropoxy)propyl]diethoxy(methyl)silane: negative in mice following oral (gavage) administration (OECD 474) GLP (Reliability 1) (Shin-Etsu, 2009).

4.  AE A.4 Bias that influences the prediction

Data on the source substances [3-(2,3-epoxypropoxy)propyl]trimethoxysilane and [3‑(2,3‑epoxypropoxy)propyl]diethoxy(methyl)silane were read-across to the registered (target) substance [3-(2,3-epoxypropoxy)propyl]dimethoxy(methyl)silane. The source substances and the target substance have similar chemical structure and physicochemical properties. All three substances hydrolyse at comparable rates and produce similar silicon-containing hydrolysis products. One source substance gives the same silanol hydrolysis product as the target substance, [3-(2,3-epoxypropoxy)propyl]diethoxy(methyl)silane and a different non-silanol hydrolysis product, ethanol. The other source substance gives a similar silanol hydrolysis product as the target substance, [3-(2,3-epoxypropoxy)propyl]silanetriol, and the same non-silanol hydrolysis product as the target substance, methanol. All structural features of the target substance (3-(2,3-epoxypropoxy)propyl side-chain, dialkoxy(methyl)silane, methoxysilane) are present in one or both of the source substances. All substances show similar predicted toxicity profiles using the OECD QSAR Toolbox v. 4.1, and have the same structural alerts for genetic toxicity. Therefore, their toxicological properties are expected to be similar, with similar genetic toxicity. No other data for relevant substances were available. These substances are the closest structural analogues to the target substance.

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

The source substances as well as the target substance hydrolyse at similar rate in contact with water under conditions relevant for oral exposure. Therefore, the test organism could possibly be exposed to the parent substance and their hydrolysis products, [3-(2,3-epoxypropoxy)propyl]silanetriol or [3-(2,3-epoxypropoxy)propyl]methylsilanediol and methanol or ethanol. 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 three substances have structural alerts for genotoxic carcinogenicity and they are all predicted to be Class III High hazard.

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

No genetic toxicity data are available for the target substance [3-(2,3-epoxypropoxy)propyl]dimethoxy(methyl)silane, therefore data are read-across from the structurally analogous substances [3-(2,3-epoxypropoxy)propyl]trimethoxysilane, (2530-83-8) and [3‑(2,3‑epoxypropoxy)propyl]diethoxy(methyl)silane, (2897-60-1). These three substances hydrolyse at comparable rates to produce one mole of a [3-(2,3-epoxypropoxy)propyl silanol. The non-silanol hydrolysis products are methanol and ethanol, which are of known toxicity and not expected to contribute to the effects observed for this endpoint. Moreover, they have similar predicted physicochemical properties, and are predicted by QSAR Toolbox to be subject to similar metabolic processes. 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

The registration substance, [3-(2,3-epoxypropoxy)propyl]dimethoxy(methyl)silane, has a reported purity of 98 %.

Neither the target substance nor the source substances have impurities of toxicological concern.

The purity of test substance in the genetic toxicity studies with the source substance, [3-(2,3-epoxypropoxy)propyltrimethoxysilane, was not reported. However, the Substance Identity Profile for the REACH Registration of this substance indicates that it has a purity of >98% and no impurities are present at >1%.

The purity of test substance in the genetic toxicity studies with the source substance, [3-(2,3-epoxypropoxy)propyl]diethoxy(methyl)silane, was 97.7% (bacterial mutagenicity assay) and 98.7% (in vitro cytogenicity.

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

Not relevant.


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

Justification for classification or non-classification

The available information for the substance indicates that, based on read-across data, [3-(2,3-epoxypropoxy)propyl]dimethoxy(methyl)silane is mutagenic to bacteria and mammalian cells and causes an increase in chromosome aberrations in vitro. Data from an in vivo micronucleus assay with the surrogate substance, [3-(2,3-epoxypropoxy)propyl]diethoxy(methyl)silane, indicate that the clastogenic effects observed in vitro are not observed in vivo. Further testing of the surrogate substance is being undertaken to evaluate the potential for mutagenicity in vivo.