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EC number: 221-906-4
CAS number: 3277-26-7
Nominal conc. (mg/L)
Time weighted mean measured conc. (mg/L)
Dimethylsilanol: The endpoint is waived.
Dimethylsilanediol: Long-term toxicity to invertebrates: 21 day EC50
>12.6 mg/l mg/l and NOEC ≥12.6 mg/l (highest concentration tested) (OECD
guideline 211), read-across from data on the ultimate hydrolysis product
dimethylsilanediol (CAS 1066-42-8).
No data are available for the registered substance, 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).
Short- and long-term aquatic toxicity data are also available on
the ultimate hydrolysis product, where no effects were reported at the
highest concentrations tested, see details below.
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 invertebrates study because, as indicated in guidance
R.188.8.131.52 (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.
The intermediate hydrolysis product, dimethylsilanol, is
very water-soluble, has low bioavailability (based on log Kow <<3) and
there is no reason to expect any specific mechanism of toxicity beyond
narcosis. Therefore, the occurrence of toxic effects that were not
expressed in the existing short-term aquatic studies (conducted at
concentrations up to 1000 mg/l with trimethylsilanol) would be
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. 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 NOEC. For a narcotic chemical
without a specific mode of toxic action, it is unlikely that the aquatic
PNEC would be significantly over-estimated using this method.
In addition, dimethylsilanol is not likely to persist in the
environment because it is susceptible to hydrolysis, forming
dimethylsilanediol, for which long-term invertebrate toxicity data are
available (see below).
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.
A 21 day NOEC value of ≥12.6 mg/L and EC50
value of >12.6 mg/L (Time Weighted Average measured concentrations,
limit test) have been determined for the effects of dimethylsilanediol
(CAS 1066-42-8, the ultimate hydrolysis product) on survival,
reproduction and growth of Daphnia magna. 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 9 and 10 of the
Chemical Safety Report, respectively.
Information on Registered Substances comes from registration dossiers which have been assigned a registration number. The assignment of a registration number does however not guarantee that the information in the dossier is correct or that the dossier is compliant with Regulation (EC) No 1907/2006 (the REACH Regulation). This information has not been reviewed or verified by the Agency or any other authority. The content is subject to change without prior notice.Reproduction or further distribution of this information may be subject to copyright protection. Use of the information without obtaining the permission from the owner(s) of the respective information might violate the rights of the owner.
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