Registration Dossier

Ecotoxicological information

Toxicity to aquatic algae and cyanobacteria

Currently viewing:

Administrative data

Link to relevant study record(s)

Description of key information

Toxicity to algae: 72-hour ErC50 >500 mg/l (Silanol HP1, read across from a structural analogue); >1000 mg/l (Silanol HP2, read across from a structural analogue); >125 mg/l (Silanol HP3, read across from a structural analogue).      

The four major constituents of the registered substance undergo hydrolysis in water, with a half-life <12 h at pH7 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 72-hour ErC50 value of >500 mg/l and NOErC of ≥500 mg/l (nominal) have been read-across from a structural analogue, triethoxy(methyl)silane, CAS 2031-67-6, for effects on growth rate of Pseudokirchneriella subcapitata (tested as: Selenastrum capricornutum). The study was conducted according to a standard guideline (EU Method C.3) 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 ErC50 value expressed in terms of methylsilanetriol is >500 x (94.14/178.31) = >264 mg/l.

Silanol HP2: A 72-hour ErC50 value of >1000 mg/L and ErC10 of 321 mg/l (nominal) have been determined for the effects of the test substance on growth rate of the freshwater algae Scenedesmus subspicatus. A 72-hour EbC50 of 603 mg/L and EbC10 of 38 mg/l have been determined for effects on biomass. The NOEC in the study was 1.3 mg/L (for effects on growth rate and/or biomass; no growth rate-specific NOEC is derived) (derived in an extension to the above study and under consistent conditions). In a separate test, a 72 hour ErC50 value of 863 mg/L and NOEC of 40 mg/L have also been determined for the effect of the test substance on growth rate of the marine algae Skeletonema costatum. It is likely that the test organisms were exposed to the hydrolysis products of the substance. The NOEC in Scenedesmus subspicatus is not representative of the inhibition of growth rate, as the EC10 values for growth rate and biomass make clear. It is not appropriate to derive PNEC based on biomass effects in the absence of effects on growth rate. Excluding this result, the NOEC in the Skeletonema costatum study is the most appropriate starting value for the derivation of PNEC. 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 ErC50 value expressed in terms of 3 -aminopropylsilanetriol is >1000 x (137.21/221.37) = >620 mg/l.

Silanol HP3: A 72-h ErC50 value of 125 mg/l (nominal); 118.3 mg/l (measured, DOC) and NOErC of 51 mg/l (nominal); 58.5 mg/l (measured, DOC) have been read across from a structural analogue,  bis(triethoxysilylpropyl)amine (CAS 13497-18-2) for the effect of the test substance on growth rate of the marine alga Phaeodactylus tricornutum. The study was conducted according using a standard method (ISO standard 10235, similar to OECD TG 201) 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 ErC50 value expressed in terms of bis(trihydroxysilylpropyl)amine is 125 x (257.39/425.72) = 75 mg/l.

A 72-hour ErC50 value of 36 mg/l and NOErC of 8.3 mg/l (nominal) have been read across from a structural analogue bis(trimethoxysilylpropyl)amine (CAS 82985-35-1), for effects on growth rate of Pseudokirchneriella under conditions where pH is controlled at around 8.0. The ErC50 was 31 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 ErC50 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 ErC50 value expressed in terms of bis(trihydroxysilylpropyl)amine is 36 x (257.39/341.56) = 27.1 mg/l.