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Long-term toxicity to fish

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fish early-life stage toxicity
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other justification
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Endpoint waived

Key value for chemical safety assessment

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No data are available for the registered substance 1,1,3,3-tetramethyldisiloxane (CAS 3277-26-7), which hydrolyses very rapidly to dimethylsilanol during the intermediate hydrolysis. The substance further hydrolyses to dimethylsilanediol (CAS 1066-42-8), however the final hydrolysis rate is >48 hours, therefore as indicated by the REACH guidance (ECHA 2016, R.16), the aquatic chemical safety assessment and PNECs are based on the intermediate hydrolysis product, for which short-term aquatic toxicity data have been read across from the structural analogue trimethylsilanol (CAS 1066-40-6) (structural analogue of dimethylsilanol).

Based on the short-term aquatic data set on trimethylsilanol, the most sensitive trophic level is invertebrates, although no toxicity was observed below 100 mg/l. For the purpose of chemical safety assessment, a freshwater PNEC has been derived by applying an assessment factor of 1000 to the short-term data.

Short-term aquatic toxicity data are also available on the ultimate hydrolysis product dimethylsilanediol, where no effects were reported at the highest concentrations tested.

In accordance with Column 2 of REACH Annex IX, there is no need to further investigate the effects of this substance in a long-term aquatic toxicity to fish study because, as indicated in guidance R. (ECHA 2016), the quantitative chemical safety assessment (conducted according to Annex I of REACH) indicates that the Risk Characterisation Ratio is below 1 and therefore the risk is already adequately controlled and further testing is not justifiable.

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 or justified on ethical grounds.   

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.   

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