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Long-term toxicity to fish

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Description of key information

Key value for chemical safety assessment

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The registered substance, hexamethylcyclotrisiloxane (D3, CAS 541-05-9; EC No. 208-765-4), hydrolyses rapidly (23 minutes at pH 7 and 25°C) to an initial intermediate hydrolysis product, 1,1,3,3,5,5-hexamethyltrisiloxane-1,5-diol (L3-diol; CAS 3663-50-1; EC No. 222-920-3), followed by further hydrolysis (>200 hours at pH 7 and 25°C) to the ultimate hydrolysis product dimethylsilanediol (DMSD, CAS 1066-42-8; EC No. 213-915-7).

The initial hydrolysis product, the L3-diol, is therefore the relevant chemical species for assessment of environmental toxicity.

A long-term toxicity to aquatic invertebrates study with the L3-diol has been proposed. The decision to waive or conduct a study for the long-term fish endpoint will be made after the results of the long-term toxicity to aquatic invertebrates study are available.

Short-term and long-term aquatic toxicity data are also available on the ultimate hydrolysis product dimethylsilanediol, where no effects were reported at the highest concentrations tested. A 32-day EC10 of >12 mg/l has been determined for the effects of dimethylsilanediol (CAS 1066-42-8) on larval development of Pimephales promelas based on mean measured concentrations. The data are used to derive indicative sediment and soil PNECs for the ultimate hydrolysis product, using the Equilibrium Partitioning Method.

Details on how the PNEC and the risk characterisation ratio have been derived can be found in IUCLID Section 6.0 and Chapters 7, 9 and 10 of the Chemical Safety Report.