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Please be aware that this old REACH registration data factsheet is no longer maintained; it remains frozen as of 19th May 2023.

The new ECHA CHEM database has been released by ECHA, and it now contains all REACH registration data. There are more details on the transition of ECHA's published data to ECHA CHEM here.

Diss Factsheets

Ecotoxicological information

Long-term toxicity to fish

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fish early-life stage toxicity
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study scientifically not necessary / other information available
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Description of key information

Key value for chemical safety assessment

Additional information

The constituents of the substance hydrolyse rapidly, therefore the environmental aspects of chemical safety assessment are based on the hydrolysis products Silanol HP-W, HP-X, HP-Y and HP-Z. However, due to the uncertainty around hydrolysis rates of some of the constituents, the parent substance, divided into Blocks, is also assessed.

For assessment of the parent substance constituents, the data relevant to the corresponding silanol hydrolysis product are used.

Testing for long-term toxicity to fish is not considered necessary because:


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 further testing is not justified for the following reasons:  


The substance has acute toxicity data available for three trophic levels for each silanol assessment entity, as well as chronic invertebrate and algal toxicity data for silanol assessment entities HP-X and HP-Z.

For Silanol HP-X there were no effects observed at the highest concentrations tested, even when the substance was tested at high nominal concentrations of 500 mg/l.


For Silanol HP-Z, based on the available aquatic data the most sensitive trophic level in the short-term tests was invertebrates, but the most sensitive trophic level in the long-term tests was for algae. Furthermore, no effects were observed in the short-term toxicity to fish test even when the substance was tested at high nominal concentrations approaching 1000 mg/l.


For Silanols HP-X and HP-Z, no PNECs have been derived because no hazard is identified.


For Silanols HP-W and HP-Y, short-term toxicity of the test substance and degradation products to fish is low and the most sensitive species was algae. An assessment factor of 1000 was applied to derive the freshwater PNEC, this high assessment factor to derive the predicted no-effect level already reflects the typically higher value of a short-term EC50 compared to a long-term EC10. It is unlikely that the aquatic PNEC would be significantly over-estimated using this high assessment factor.


PNECs have been derived for the purpose of chemical safety assessment and the risk characterisation ratios for Silanols HP-W and HP-Y are below 1.

In addition, Silanols HP-Y and HP-W make up only a small proportion of the substance, therefore a large proportion of the substance is covered by the existing data. To achieve a concentration of silanols HP-Y and HP-W, equivalent to the lowest effect concentration of 36 mg/l used to derive PNEC for Silanol HP-Y and HP-W, a loading of more than 100 mg/l of whole substance would be needed.


Please see the attached document in IUCLID Section 13, which gives details on structure and properties of the parent substance and its hydrolysis products, as well as the amount of each hydrolysis product produced per kg of parent substance.

All the silanol hydrolysis products are highly water-soluble and have low potential for bioaccumulation based on log Kow <3.

Assessment of parent substance

The constituents of the parent substance have been divided into seven Blocks, A to G.

The approach of assessing only the hydrolysis product for constituents C-G is not supported based on uncertainty in the hydrolysis rates and current ECHA guidance. However, testing of this UVCB substance would be technically difficult and could not provide information useful for setting PNECs for the constituents. It is also unlikely to be possible to separate individual constituents for testing. In addition, there are no data available for read across to the parent substance.

For assessment of the parent substance, PNECs have therefore been derived for each Block using the data read across to the silanol hydrolysis products, but without molecular weight correction where applicable. The risk characterisation ratios derived using this approach are all <1.

Please refer to the discussion in IUCLID Section 6, Ecotoxicological Information, and CSR Section 7.0 for further information of the technical infeasibility of testing the parent substance.


Overall it is concluded that the risk is adequately assessed using the existing short-term data and the long-term invertebrate tests, and that in vivo testing on vertebrate animals 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 7, 9 and 10 of the Chemical Safety Report.