(chloromethyl)triethoxysilane

Endpoint summary

Additional information

Valid short term measured data for the registered substance are available for fish and algae.

A 96-hour LC₅₀value of >100 mg/l and NOEC value of 100 mg/l have been determined for the effects of the test substance on mortality of Oncorhynchus mykiss and a 72-hour ErC₅₀value of >100 mg/l and NOEC value of 50 mg/l have been determined for the effects of the test substance on Pseudokirchneriella subcapitata, both results based on nominal concentration of the substance.

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.

The hydrolysis half-life of (chloromethyl)triethoxysilane (CAS No. 15267-95-5) is approximately 2.5 h at 20-25°C and pH 7; the substance will therefore undergo rapid hydrolysis in contact with water to form (chloromethyl)silanetriol and ethanol.

REACH guidance (ECHA 2016, R.16) states that “for substances where hydrolytic DT₅₀ is less than 12 hours, environmental effects are likely to be attributed to the hydrolysis product rather than to the parent itself”. TGD guidance, (European Commission, 2003) and R.16 (ECHA, 2016) also suggests that when the hydrolysis half-life is less than 12 hours, the breakdown products, rather than the parent substance, should be evaluated for aquatic toxicity. Therefore, the environmental hazard assessment, including sediment and soil compartments due to water and moisture being present, is based on the properties of the silanol hydrolysis product in accordance with REACH guidance. As described in Section 1, condensation reactions of the silanols are possible.

READ-ACROSS JUSTIFICATION

In order to reduce animal testing read-across is proposed to fulfill up to REACH Annex IX requirements for the registered substance from substances that have similar structure and physicochemical properties. Ecotoxicological studies are conducted in aquatic medium or in moist environments; therefore the hydrolysis rate of the substance is particularly important since after hydrolysis occurs the resulting product has different physicochemical properties and structure.

In moist medium, (chloromethyl)triethoxysilane hydrolyses rapidly (half-life 2.5 h at 20-25°C and pH 7) to (chloromethyl)silanetriol. The non-silanol hydrolysis product ethanol is not expected to contribute to any adverse effects at the relevant dose levels. This is discussed further below.

In the following paragraphs the read-across approach for (chloromethyl)triethoxysilane is assessed for each surrogate substance taking into account structure, hydrolysis rate and physicochemical properties.

Read-across from triethoxy(methyl)silane (CAS No. 2031-67-6) to (chloromethyl)triethoxysilane (CAS No. 15267-95-5):

Measured data was not available for chloromethyl)triethoxysilane (CAS No. 15267-95-5) therefore read across from the comparable substances, triethoxy(methyl)silane (CAS No. 2031-67-6) was used to fill the data gap for invertebrates.

The registration and read-across substances are structurally similar;the only difference is switching a Cl for a H on the methyl group. The substances hydrolyse rapidly to produce the structurally analogue silanol hydrolysis products, (chloromethyl)silanetriol and (methyl)silanetriol, respectively.

The registered substances are part of an analogue group of chloroalkoxysilane substances containing chloroalkyl and alkoxy groups (III-15). The read-across substances is part of an analogue group of triethoxysilanes hydrolysing rapidly at pH 7 (I-2-T-Et-H) and is selected asthe most appropriate based on chemical structure and similar physic-chemical properties. Both substances have similarlog K_owvalues (2.5and 2.2, respectively) and comparable molecular weights. A similar environmental behavior of the silanol hydrolysis products is also expected, as their molecular weights and log K_oware comparable and due to the fast hydrolysis, the hydrolysis products of these substances are also of relevance in the chemical safety assessment.

For the following endpoints read-across data from the structural related substance triethoxy(methyl)silane were used for the assessment of the aquatic toxicity. Reliable short-term toxicity test result with freshwater organisms is available for invertebrates. A 48-hour EC₅₀value of >500 mg/l and NOEC of ≥500 mg/l have been determined for the effects of the test substance on mobility of Daphnia magna based on nominal concentration of the substance. However, it is likely that the test organisms were primarily exposed to the hydrolysis products of the substance.

Additional information is given in a supporting reports PFA (2016) also attached in Section 13 of the IUCLID dossier.

Table7.1.1 Key physicochemical parameters and ectoxicological data for the registered and surrogate substances.

CAS Number	15267-95-5	2031-67-6
Chemical Name	(chloromethyl)triethoxysilane	triethoxy(methyl)silane
Si hydrolysis product	(chloromethyl)silanetriol	(methyl)silanetriol
Molecular weight (parent)	212.75 g/mol	178.31
Molecular weight (hydrolysis product)	128.6	94.14
log Kow(parent)	2.5	2.2
log Kow(silanol hydrolysis product)	-2.1	-2.4
Water sol (parent)	1100 mg/l at 20°C	2900 mg/l at 20°C
Water sol (silanol hydrolysis product))	1E+06 mg/l at 20°C	1E+061 mg/l at 20°C
Vapour pressure (parent)	6.5 Pa at 25°C	100 Pa at 25°C
Vapour pressure (hydrolysis product)	2.1E-03 Pa at 25°C (QSAR)	5.20E-02 Pa at 25°C
Hydrolysis t1/2at pH 7 and 20°C-25°C	2.5 h	5.5 h
Hydrolysis t1/2at pH 4 and 25°C	0.2 h	0.3 h
Hydrolysis t1/2at pH 9 and 25°C	0.1 h	0.1 h
Short-term toxicity to fish (LC50)	>100 mg/l	>500 mg/l
Short-term toxicity to aquatic invertebrates (EC50)	n/a	>500 mg/l
Algal inhibition (ErC50and NOEC)	>100 mg/l	>500 mg/l
Long-term toxicity to aquatic invertebrates (NOEC)	n/a	n/a