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EC number: 252-558-1
CAS number: 35435-21-3
No sediment toxicity data are available for the registration substance. Testing
for toxicity to sediment organisms is not considered necessary because:
hydrolysis half-life of the registration substance is approximately 43
hours at neutral pH. The sediment is exposed to the substance in the
environment via the effluent water released from the wastewater
treatment plant (WWTP). The sediment will therefore be exposed to the
same species as the receiving waters initially. As the substance resides
and settles in the sediment compartment, it will be susceptible to
further hydrolysis. Although significant hydrolysis is expected before
the sediment is exposed to the substance, the parent substance has a
much higher log Kow than the silanol hydrolysis product and is therefore
more likely to partition to the sediment. In addition, the parent
substance is expected to be more toxic than the silanol hydrolysis
product. However, as the sediment can act as a sink for chemicals, and
the silanol hydrolysis product, (2,4,4-trimethylpentyl)silanetriol, is
not readily biodegradable, it may persist in the sediment compartment
for longer than the parent substance. Accordingly, exposure and chemical
safety of the sediment should
be based on both
the parent substance and the hydrolysis products.
Currently, the available data assess the toxicity of the silanol
In accordance with Column 2
of REACH Annex X, there is no need to further investigate the effects of
the substance in a long-term sediment 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 is below 1, and therefore the risk is
already adequately controlled and further testing is not justifiable.
The silanol hydrolysis
product is not readily biodegradable but has low potential for
bioaccumulation and low bioavailability (based on log Kow <3
(0.9)), and there is no reason to expect any specific mechanism of
toxicity beyond narcosis.
Long-term toxicity testing
to aquatic invertebrates has been carried out with the registered
substance as well as a structural analogue. During these tests, it is
likely that organisms were exposed to the hydrolysis products of the
test substance. The occurrence of more severe toxic effects in the
sediment compartment that were not expressed in these aquatic studies
(conducted at concentrations up to 100 mg/l) would be considered
The PNEC calculated by
Equilibrium Partitioning has been derived for the purpose of chemical
safety assessment and the risk characterisation ratios are below 1.
Overall it is concluded that
the risk characterisation conclusion is sufficiently conservative in
respect of any uncertainties and therefore further testing is not
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.
aquatic toxicity tests are being conducted in accordance with ECHA Final
Decision TPE-D-2114455990-41-01/F. The OECD TG 210 Fish, Early
Life-Stage Toxicity test and the OECD TG 211 Daphnia Reproduction
test are currently ongoing. The substance dataset and risk assessment
will be updated once results of the chronic aquatic studies are
available and the studies are finalised. An update is planned to be
completed within three months from when the last final report is
received. The draft reports are expected in January/February 2021, with
the final reports following in March/April 2021.
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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