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Short-term toxicity to fish

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Description of key information

Short-term toxicity to fish: 96 h LC50 ca. 180 mg/l (nominal), 32 mg/L (geometric mean) (OECD 203), 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 139 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 fish

Fresh water fish
Effect concentration:
139 mg/L

Additional information

There are no reliable short-term fish 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 96 h LC50 value of ca. 32 mg/l geometric mean of the parent substance, and 180 mg/l nominal, has been reported for the effects of [3-(2,3-epoxypropoxy)propyl]diethoxy(methyl)silane (CAS 2897-60-1) on the mortality of the freshwater fish O. mykiss. 50% mortality was achieved at the highest concentration tested (180 mg/L) however, the test medium was observed to increase in turbidity with increasing concentration from 48 h.

The reviewer of the report considers the turbidity to be caused by the formation of less soluble oligomers or polymers in solution.

Due to behavioural effects being observed from 3 h (consistent with known effects of epoxides in fish, as report e.g. by Lipnick (1991)) and mortalities being recorded from 29 h, it is thought that the effects are due to the toxicity of the substance rather than physical effects associated with undissolved materials. This is the only study available for this substance and has been chosen as key. The study report discusses the potential for two hydrolysis reactions of the different functional groups and concludes that the substance had a hydrolysis half-life for removal of parent 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 7.7-8.2). 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) * 180 mg/l = 139 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.

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