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Short-term toxicity to aquatic invertebrates

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Description of key information

Short-term toxicity to invertebrates: 48 h EC50 value of 20 mg/l (nominal) 3.1-9.5 mg/L (geometric mean) (OECD 202), read-across from an analogous/structurally related substance, [3-(2,3-epoxypropoxy)propyl]diethoxy(methyl)silane (CAS 2897-60-1). The LC50 is equivalent to 15.5 mg/l when expressed in terms of the silanol hydrolysis product of the tested substance, [3-(2,3-epoxypropoxy)propyl]methylsilanediol. This value is read across to 2-(3,4-epoxycyclohexyl)ethylsilanetriol.

Key value for chemical safety assessment

Fresh water invertebrates

Fresh water invertebrates
Effect concentration:
15.5 mg/L

Additional information

There are no reliable short-term invertebrate toxicity data available for 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane (CAS 3388-04-3), therefore good quality data for an appropriate structural analogue, [3-(2,3-epoxypropoxy)propyl]diethoxy(methyl)silane (CAS 2897-60-1), have been read across. Both substances are susceptible to rapid hydrolysis and have similar silanol hydrolysis products in terms of the presence of the toxicologically active epoxide functional group, and similar physicochemical properties. The other hydrolysis products are methanol and ethanol, respectively.

A reliable 48 h EC50 value of 20 mg/l (nominal), equivalent to 3.1-9.5 mg/l parent substance (geometric mean), has been determined for the effects of [3-(2,3-epoxypropoxy)propyl]diethoxy(methyl)silane (CAS 2897-60-1) to the freshwater invertebrate Daphnia magna. The test substance hydrolyses rapidly while the hydrolysis product is also subject to further hydrolysis (epoxy ring opening). Therefore the organisms were exposed to a mixture of the test substance and the hydrolysis product. The study report discusses the two hydrolysis steps and concludes that the substance had a hydrolysis half-life of approximately 3 hours under the test conditions. This is attributed by the reviewer to the reaction of alkoxy groups under elevated pH conditions of the test media (pH 8.0 - 8.1). Therefore the effects seen in the test are attributed to [3-(2,3-epoxypropoxy)propyl]methylsilanediol. In view of the fact that the analytical results are for parent substance, it is appropriate to interpret the results in terms of nominal concentration.

The results may be expressed in terms of concentration of the hydrolysis product of the tested substance, [3-(2,3-epoxypropoxy)propyl]methylsilanediol, by applying a molecular weight correction: (MW of silanol=192.29 / MW of parent=248.40) * 20 mg/l = 15.5 mg/l.

2-(3,4-Epoxycyclohexyl)ethylsilanetriol is susceptible to further hydrolysis reactions and the ultimate hydrolysis product 2-(3,4-dihydroxycyclohexyl)ethylsilanetriol is considered unlikely to exhibit significant ecotoxic effects based on QSAR estimated E(L)C50 values >>100 mg/l (ECOSAR). The rate of reaction under environmental conditions is uncertain but the half-life is not expected to be more than a few days.