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Ecotoxicological information

Endpoint summary

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Additional information

Due to the rapid hydrolysis of the substance, the chemical safety assessment is based on the silanol hydrolysis product methylsilanetriol.

The very rapid initial hydrolysis of the parent substance is well proven and soil exposure to the parent is not expected. Hydrolysis of the intermediate substances is less well established. However, they all have log Kow <3 and react rapidly, so they are not of concern for the terrestrial compartment.

Testing considerations for toxicity to terrestrial organisms:

PNECsoil has been calculated from the aquatic data using the Equilibrium Partitioning Method. The risk characterisation ratios (RCR) based on the PNECsoil are <1: The quantitative chemical safety assessment (conducted according to Annex I of REACH) indicates that the Risk Characterisation Ratio (RCR) is well below 1, even with due consideration of contributing uncertainties, and therefore the risk is adequately controlled.

The hydrolysis product, methylsilanetriol, is not readily biodegradable but has low potential for bioaccumulation, low potential for adsorption and has low bioavailability (based on log Kow <3); partitioning to the terrestrial compartment is expected to be minimal. No toxicity was observed in aquatic tests conducted at high concentrations, and there is no reason to expect any specific mechanism of toxicity beyond narcosis. Therefore, the occurrence of more severe toxic effects in the terrestrial compartment that were not expressed in the aquatic studies would be considered unlikely. 

In addition, the substance is only used in industrial settings in closed systems under controlled conditions and emissions to surface waters are unlikely.

The Soil Hazard Category 3 (ECHA 2017, guidance part R7(c) Table R.7.11—2) has been derived for the substance due to the potential persistence of methylsilanetriol. In accordance with the screening assessment for Soil Hazard Category 3 substances, a PNECsoil has been calculated from the aquatic data on the basis of the equilibrium partitioning method. The PNEC calculated by Equilibrium Partitioning has been derived for the purpose of chemical safety assessment and the risk characterisation ratios are below 1. In addition, a confirmatory long-term soil toxicity test should be conducted.

Overall it is concluded that the risk characterisation conclusion is sufficiently conservative in respect of any uncertainties and therefore further in vivo testing is not considered necessary.  However, in order to comply with ECHA testing requirements for Soil Hazard Category 3 substances, a chronic earthworm reproduction test with methylsilanetriol is proposed.

Details on how the PNEC and the risk characterisation ratio have been derived can be found in IUCLID Section 6.0 and Chapters 9 and 10 of the Chemical Safety Report, respectively.