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Short-term toxicity to fish

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Description of key information

Short-term toxicity to fish: 96-hour LC50 >500 mg/L (Silanol HP1, read across from a structural analogue); >934 mg/L (Silanol HP2, read across from a structural analogue); >200 mg/L, >100 mg/L and 130 mg/L (Silanol HP3, read across from two structural analogues as weight of evidence).      

The four major constituents of the registration substance undergo hydrolysis in water, with a half-life <12 h at pH 7 and 25°C in all cases. Therefore to support the chemical safety assessment of the hydrolysis products, short-term toxicity tests for fish have been read-across from structural analoguous substances which degrade to produce the same or similar silanols in solution.

Key value for chemical safety assessment

Additional information

The REACH data requirements are fulfilled by consideration of the three silanol hydrolysis products of the major constituents, which are based on studies with analogous test materials under conditions in which test organisms were exposed predominantly to the same (or structurally similar) silanol molecules due to hydrolysis of the tested substances under the conditions of the test.

Silanol HP1: A 96-hour LC50 value of >500 mg/L (nominal) has been read-across from a structural analogue, triethoxy(methyl)silane, CAS 2031-67-6, for effects on mortality of Danio rerio (tested as Brachydanio rerio). The study was conducted according to a standard guideline (EU Method C.1) and GLP. It is likely that the test organisms were exposed predominantly to the hydrolysis products of the substance, methylsilanetriol (1 mole) and ethanol (three moles). Ethanol is not likely to have contributed to toxicity at the tested concentrations. The LC50 value expressed in terms of methylsilanetriol is >500 x (94.14/178.31) = >264 mg/l.

Silanol HP2: A 96-hour LC50 of >934 mg/L and NOEC of ≥934 mg/L have been read across from a structural analogue, 3-aminopropyltriethoxysilane (CAS 919-30-2), for effects on mortality of Brachydanio rerio. The study was conducted according to a standard guideline (OECD TG 203) and GLP. It is likely that the test organisms were exposed predominantly to the hydrolysis products of the substance, 3-aminopropylsilanetriol (1 mole) and ethanol (three moles). Ethanol is not likely to have contributed to toxicity at the tested concentrations. The LC50 value expressed in terms of 3-aminopropylsilanetriol is >934 x (137.21/221.37) = >579 mg/l.

Silanol HP3: The short-term toxicity of Silanol HP3 in fish is based on weight of evidence from two read-across studies.

A 96-h LC50 value of >200 mg/L and a NOEC of ≥200 mg/L (nominal) have been read across from a structural analogue,  bis(triethoxysilylpropyl)amine (CAS 13497-18-2) for effects on mortality of the marine fish species Scophthalmus maximus. The study was conducted according using a standard method (OSPAR PARCOM protocol, similar to OECD TG 203) and GLP. It is likely that the test organisms were exposed predominantly to the hydrolysis products of the substance, bis(trihydroxysilylpropyl)amine (1 mole) and ethanol (six moles). Ethanol is not likely to have contributed to toxicity at the tested concentrations. The LC50 value expressed in terms of bis(trihydroxysilylpropyl)amine is >200 x (257.39/425.72) = >121 mg/l.

A 96-hour LC50 value of 130 mg/l and NOEC value of 100 mg/l (nominal) have been read across from a structural analogue, bis(trimethoxysilylpropyl)amine (CAS 82985-35-1), for effects on mortality of Salmo gairdneri (new name Oncorhynchus mykiss). The study was conducted according to a standard guideline (OECD Method 203) and GLP. It is likely that the test organisms were exposed predominantly to the hydrolysis products of the substance, bis(trihydroxysilylpropyl)amine (1 mole) and methanol (six moles). Methanol is not likely to have contributed to toxicity at the tested concentrations. The LC50 value expressed in terms of bis(trihydroxysilylpropyl)amine is 130 x (257.39/341.56) = 98.0 mg/l.

A 96-hour LC50 value of >100 mg/l (nominal) has been read across from a structural analogue bis(trimethoxysilylpropyl)amine (CAS 82985-35-1), for effects on mortality of Oryzias latipes under conditions where pH is controlled. The LC50 was 57 mg/l (nominal) under conditions where pH variation in the test media was not corrected. This value would not be representative of natural waters and so the LC50 with pH correction is taken forward in the chemical safety assessment. It is likely that the test organisms were exposed predominantly to the hydrolysis products of the substance, bis(trihydroxysilylpropyl)amine (1 mole) and methanol (six moles). Methanol is not likely to have contributed to toxicity at the tested concentrations. The LC50 value expressed in terms of bis(trihydroxysilylpropyl)amine is >100 x (257.39/341.56) = >75.3 mg/l.