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Ecotoxicological information

Sediment toxicity

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Reference
Endpoint:
sediment toxicity: long-term
Data waiving:
study scientifically not necessary / other information available
Justification for data waiving:
other:

Description of key information

Key value for chemical safety assessment

Additional information

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

The very rapid initial hydrolysis of the parent substance is well proven and sediment 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 sediment compartment.

Testing for toxicity to sediment dwelling organisms is not considered necessary because:

PNECsediment has been calculated from the aquatic data using the Equilibrium Partitioning Method. The risk characterisation ratios (RCR) based on the PNECsediment are <1.

In accordance with Column 2 of REACH Annex X, there is no need to further investigate the effects of this substance in a sediment toxicity study because, as indicated in guidance R.7.11.6 (ECHA 2016), 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 already adequately controlled and further testing is not justifiable.

The substance 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 sediment 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 sediment compartment that were not expressed in the aquatic studies would be considered unlikely. 

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.      

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.

In addition, the substance is only used in industrial settings in closed systems under controlled conditions and emissions to surface waters are unlikely. Therefore, further studies are not scientifically justified.