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Valid short term measured data for the registered substance itself are not available. A 48-hour EC50 of > 100 mg/l was determined according to OECD 202 with the read accross substance (chloromethyl)trimethoxysilane CAS RN 5926-26-1 and a 72-hour ErC50 of >100 mg/l and a NOEC of 50mg/l was derterminde for algae, OECD201 with the read accross substance (Chloromethyl)triethoxysilane CAS RN 15267-95-5.

As the substance is subject to rapid hydrolysis, it is therefore likely that the test organisms were primarily exposed to hydrolysis product retained in the test media.

6.1.3) Read-across justification for aquatic invertebrates

 

There is no measured data available for (Chloromethyl)diethoxymethylsilane (CAS 2212-10-4) for short term toxicity testing to aquatic invertebrates. This document describes the analogue approach for fulfilling this endpoint by read-across from a source substance (Chloromethyl)trimethoxysilane (CAS 5926-26-1), 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 source substance, (Chloromethyl)trimethoxysilane (CAS RN 5926-26-1) contains a chloromethyl silane group in addition with methoxy moieties. (Chloromethyl)trimethoxysilane hydrolyses rapidly to form (chloromethyl)silanetriol (1 moles) and methanol (3 moles) under conditions relevant in the environment or in vivo, with a half-life of 28 to 504 min. A half-life value of approximately 28 to 504 min at 20-25°C and pH 7 was obtained using an accepted using HYDROWIN v2.00.

The source substance has log Kow of -0.42 at 20°C (QSAR), water solubility of 1.4E+05 mg/l at 20°C (QSAR) and vapour pressure of 340 Pa at 25°C (QSAR).

 

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

The registration substance, (Chloromethyl)diethoxymethylsilane (CAS 2212-10-4), and the read-across substance, (Chloromethyl)trimethoxysilane (CAS RN 5926-26-1), are structurally similar. (Chloromethyl)trimethoxysilane (CAS RN 5926-26-1) contains a chloromethyl silane group in addition to three methoxy-groups attached to the Si atom, while in (Chloromethyl)diethoxymethylsilane (CAS 2212-10-4) two ethoxy-groups are attached to the Si atom of the chloromethyl silane group and the third ethoxy group is substituted by a methyl group.

This structural difference remains in the Si-containing hydrolysis product for the target and source substance. The Si hydrolysis product for the target substance is (chloromethyl)methylsilanediol while the Si hydrolysis product for the source substance is chloromethylsilanetriol.

 

Table 2: Physico-chemical properties

 

Property

 

Target substance

 

Source substance

 

Substance name

 

(Chloromethyl)diethoxymethylsilane  

 

(Chloromethyl)trimethoxysilane  

 

CAS number

 

2212-10-4

 

5926-26-1

 

Hydrolysis half-life at pH 4 and 20 - 25°C

 

1.1 – 24 min (QSAR)

 

1.1 – 24 min (QSAR)

 

Silanol hydrolysis product

 

(chloromethyl)methylsilanediol

 

chloromethylsilanetriol

 

Non-Si hydrolysis product

 

Ethanol

 

Methanol

 

LogKow Value

 

1.82 (QSAR)

 

-0.42 (QSAR)

 

Vapour pressure

 

25.2 hPa at 25°C (measured)

 

340 Pa at 25°C (QSAR)

 

Water solubility

 

1487 mg/L at 25°C (QSAR)

 

1.4 E+05 mg/l at 20°C (QSAR)

 

 

 

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

 

In an acute toxicity of (Chloromethyl)trimethoxysilane to Daphnia magna in a 48-hour Immobilization Test according to OECD Guideline 202 evaluate the influence of the test item on the mobility respectively survival of Daphnia magna was evaluated.Young Daphnia were exposed in a static test for 48 hours to an aqueous test medium containing the test item at the concentration of nominal 100 mg/L. This limit test was performed in compliance with the test guidelines to demonstrate whether the test item has a toxic effect on Daphniaup to at least this concentration. Since the test item hydrolyses in water very quickly, in the present test the hydrolysis products of the test item were tested.

The test item was mixed into test water at a concentration of 100 mg/L and was stirred for 24 hours. Thus, the main part of the test item at the start of the test were hydrolysis products. At the start of the test just before introduction of the Daphnia 98 - 99 % of nominal were found. After 48 hours test duration between 70 % and 83 % of the nominal value were determined. Thus, during the test period of 48 hours the Daphniawere exposed to the hydrolysis products of a mean of 88 mg test item/L. Since in the mean 88%of nominal were found, the reported results are related to the nominal concentration of 100 mg test item/L, the 48-hour EC50 and EC100 were clearly higher than 100 mg/L, the NOEC may even be higher than 100 mg/L.

 

4. AE A.4 Bias that influences the prediction

 

Data on the source substance (Chloromethyl)trimethoxysilane (CAS RN 5926-26-1) were read-across to the registered (target) substance (Chloromethyl)diethoxymethylsilane (CAS 2212-10-4). The source substance and the target substance have similar chemical structure and physico-chemical properties. Both substances hydrolyse at similar rate to a similar Si-containing hydrolysis product, chloromethylsilanetriol resp. (chloromethyl)methylsilanediol. The non-silanol hydrolysis product is the same, ethanol. Due to that, their ecotoxicological properties are expected to be similar, with similar acute toxicity to aquatic invertebrates. No other data for relevant substances were available.

 

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

 

Both substances hydrolyse very rapidly in contact with water under conditions relevant for this endpoint. Therefore, the test organism is mainly exposed to their hydrolysis products, (chloromethyl)methylsilanediol, resp. chloromethylsilanetriol. The source and target substances have been profiled using the OECD QSAR Toolbox v. 4.1. The two substances and their silanol hydrolysis products show similar profiles for all toxicological endpoints. No alert for acute toxicity for aquatic invertebrates was detected by OECD QSAR Toolbox v.4.1.

 

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 (Chloromethyl)diethoxymethylsilane (CAS 2212-10-4), therefore data are read-across from the structurally analogous substance (Chloromethyl)trimethoxysilane (CAS RN 5926-26-1). Both substances hydrolyse at similar rate to a similar Si-containing hydrolysis product, chloromethylsilanetriol resp. (chloromethyl)methylsilanediol. The non-silanol hydrolysis products, ethanol and methanol respectively, are not expected to be relevant for this endpoint. Moreover, they have similar physico-chemical properties. Thus, both substances are expected to have similar toxicity profiles.

 

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

 

The target substance, (Chloromethyl)diethoxymethylsilane (CAS 2212-10-4), does not have any impurities of toxicological concern. The source substance, (Chloromethyl)trimethoxy-silane (CAS RN 5926-26-1), has a named impurity of approx. 1.5% which is (Chlormethyl)dimethoxymethylsilan (CAS RN 2212-11-5). It is not expected that this impurity that will release (Chloromethyl)methylsilandiol as the target substance upon hydrolysis will contribute to the short-term toxicity to aquatic invertebrates of the source substance. The test substance in the study with the source substance, (Chloromethyl)trimethoxysilane (CAS RN 5926-26-1), had a purity of 97.2%.

 

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.

6.1.5) Read-across justification for algae and cyanobacteria

 

There is no measured data available for (Chloromethyl)diethoxymethylsilane (CAS 2212-10-4) for the biodegradation. This document describes the analogue approach for fulfilling this endpoint by read-across from a source substance (Chloromethyl)trimethoxysilane (CAS 5926-26-1), 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 source substance, (Chloromethyl)trimethoxysilane (CAS RN 5926-26-1) contains a chloromethyl silane group in addition with methoxy moieties. (Chloromethyl)trimethoxysilane hydrolyses rapidly to form (chloromethyl)silanetriol (1 moles) and methanol (3 moles) under conditions relevant in the environment or in vivo,with a half-life of 28 to 504 min. A half-life value of approximately 28 to 504 min at 20-25°C and pH 7 was obtained using an accepted using HYDROWIN v2.00.

The source substance has log Kow of -0.42 at 20°C (QSAR), water solubility of 1.4E+05 mg/l at 20°C (QSAR) and vapour pressure of 340 Pa at 25°C (QSAR).

 

 

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

The registration substance, (Chloromethyl)diethoxymethylsilane (CAS 2212-10-4), and the read-across substance, (Chloromethyl)trimethoxysilane (CAS RN 5926-26-1), are structurally similar. (Chloromethyl)trimethoxysilane (CAS RN 5926-26-1) contains a chloromethyl silane group in addition to three methoxy-groups attached to the Si atom, while in (Chloromethyl)diethoxymethylsilane (CAS 2212-10-4) two ethoxy-groups are attached to the Si atom of the chloromethyl silane group and the third ethoxy group is substituted by a methyl group.

This structural difference remains in the Si-containing hydrolysis product for the target and source substance. The Si hydrolysis product for the target substance is (chloromethyl)methylsilanediol while the Si hydrolysis product for the source substance is chloromethylsilanetriol.

 

Table 2: Physico-chemical properties

 

Property

 

Target substance

 

Source substance

 

Substance name

 

(Chloromethyl)diethoxymethylsilane  

 

(Chloromethyl)trimethoxysilane  

 

CAS number

 

2212-10-4

 

5926-26-1

 

Hydrolysis half-life at pH 4 and 20 - 25°C

 

1.1 – 24 min (QSAR)

 

1.1 – 24 min (QSAR)

 

Silanol hydrolysis product

 

(chloromethyl)methylsilanediol

 

chloromethylsilanetriol

 

Non-Si hydrolysis product

 

Ethanol

 

Methanol

 

LogKow Value

 

1.82 (QSAR)

 

-0.42 (QSAR)

 

Vapour pressure

 

25.2 hPa at 25°C (measured)

 

340 Pa at 25°C (QSAR)

 

Water solubility

 

1487 mg/L at 25°C (QSAR)

 

1.4 E+05 mg/l at 20°C (QSAR)

 

 

 

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

 

The ready biodegradability of (chloromethyl)trimethoxysilane (CAS RN 5926-26-1) was assessed in a manometric respirometry test according to OECD Guideline 301 F. The test item was investigated over a period of 28 days. The biodegradation was followed by the oxygen uptake of the microorganisms during exposure. As a reference item Aniline was tested simultaneously under the same conditions as the test item and functioned as a procedure control. After correction of the mean biochemical oxygen demand of the inoculum controls on day 2 of exposure 19% and 20% biodegradation were determined. At the end of the 10-day window, on day 12 biodegradation rates of 52 % and 53 % were measured. At the end of the 28-day exposure period degradation rates of 44 % and 52 % were found. The percentage biodegradation did not exceed 60 % within the 10- day window. The test item can therefore be considered to be not readily biodegradable.

 

4. AE A.4 Bias that influences the prediction

 

Data on the source substance (Chloromethyl)trimethoxysilane (CAS RN 5926-26-1) were read-across to the registered (target) substance (Chloromethyl)diethoxymethylsilane (CAS 2212-10-4). The source substance and the target substance have similar chemical structure and physico-chemical properties. Both substances hydrolyse at similar rate to a similar Si-containing hydrolysis product, chloromethylsilanetriol resp. (chloromethyl)methylsilanediol. The non-silanol hydrolysis product is the same, ethanol. Due to that, their ecotoxicological properties are expected to be similar. No other data for relevant substances were available.

 

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

 

Both substances hydrolyse very rapidly in contact with water under conditions relevant for this endpoint. Therefore, the test organism is mainly exposed to their hydrolysis products, (chloromethyl)methylsilanediol, resp. chloromethylsilanetriol. The source and target substances have been profiled using the OECD QSAR Toolbox v. 4.1. The two substances and their silanol hydrolysis products show similar profiles for all toxicological endpoints. No alert for biodegradation was detected by OECD QSAR Toolbox v.4.1. No classification for sensitization has been assigned to the substance.

 

 

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 (Chloromethyl)diethoxymethylsilane (CAS 2212-10-4), therefore data are read-across from the structurally analogous substance (Chloromethyl)trimethoxysilane (CAS RN 5926-26-1). Both substances hydrolyse at similar rate to a similar Si-containing hydrolysis product, chloromethylsilanetriol resp. (chloromethyl)methylsilanediol. The non-silanol hydrolysis products, ethanol and methanol respectively, are not expected to be relevant for this endpoint. Moreover, they have similar physico-chemical properties. Thus, both substances are expected to have similar toxicity profiles.

 

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

 

The target substance, (Chloromethyl)diethoxymethylsilane (CAS 2212-10-4), does not have any impurities of toxicological concern. The source substance, (Chloromethyl)trimethoxy-silane (CAS RN 5926-26-1), has a named impurity of approx. 1.5% which is (Chlormethyl)dimethoxymethylsilan (CAS RN 2212-11-5). It is not expected that this impurity that will release (Chloromethyl)methylsilandiol as the target substance upon hydrolysis will contribute to biodegradation of the source substance. The test substance in the study with the source substance, (Chloromethyl)trimethoxysilane (CAS RN 5926-26-1), had a purity of 97.2%.

 

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.