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EC number: 219-787-9
CAS number: 2530-87-2
Approach to the Terrestrial Chemical Safety Assessment
No long-term terrestrial toxicity data are available with
(3-chloropropyl)trimethoxysilane (CAS 2530-87-2).
The registered substance will hydrolyse rapidly (half-life 4.5 hours at
pH 7 at 20°C) in contact with water and atmospheric moisture to
(3-chloropropyl)silanetriol and methanol. Therefore the terrestrial
chemical safety assessment for (3-chloropropyl)trimethoxysilane is based
on its hydrolysis products (3-chloropropyl)silanetriol and methanol.
These form the basis of the chemical safety assessment and are assessed
(3-Chloropropyl)silanetriol is highly water soluble, has low potential
for bioaccumulation and low potential for adsorption (based on log Kow <3
(-1.1) and log Koc 0.45) and there is no reason to expect any
specific mechanism of toxicity beyond narcosis.
In the context of the Integrated Testing Strategy for the terrestrial
compartment (ECHA guidance Chapter R.7c, terrestrial hazard
classification scheme, Table R.7.11-2) (ECHA 2017) the aquatic toxicity
tests do not indicate that the substance is very toxic (EC/LC50 >1
mg/l for algae, Daphnia and fish). However, despite rapid
degradation of the parent substance, the silanol hydrolysis product,
(3-chloropropyl)silanetriol, is not readily biodegradable and may
persist in the environment. The substance is therefore assigned to
Hazard Category 3.
In this situation, a screening approach is applied: a confirmatory
long-term terrestrial test is usually appropriate, in addition to the
equilibrium partitioning approach with an extra factor of ten, in order
to determine whether further full tests are necessary.
The PNECscreen(EQPM) for (3-chloropropyl)silanetriol is derived
from the long-term test results with algae and has a value of 0.37 mg/kg
dwt. For the purpose of the screening assessment comparison only, an
extra factor of ten is applied (PECx10/PNECscreen(EQPM)). Based on the
exposure assessment of (3-chloropropyl)trimethoxysilane (CAS 2530-87-2),
the highest terrestrial PECx10/PNECscreen(EQPM) for
(3-chloropropyl)silanetriol is 0.044 x 10 = RCR 0.44.
A confirmatory long-term terrestrial toxicity test is therefore
required in accordance with the recommendations for hazard category 3
In addition, toxicity was observed in the aquatic microorganism test,
read across from a structural analogue,
dichloro(3-chloropropyl)methylsilane (CAS 7787-93-1) (3 hour EC50 value
of 400 mg/l and EC10 value of 197 mg/l (ASRI) (Werner,
1997)). ECHA guidance Chapter R.7c states “Where inhibition of sewage
sludge microbial activity has been observed in Annex VIII testing, a
test on soil microbial activity will additionally be necessary for a
valid PNEC to be derived.” A toxicity to soil microorganisms test is
therefore also required.
However, prior to terrestrial toxicity tests being carried out,
the technical feasibility of testing the silanol hydrolysis product,
(3-chloropropyl)silanetriol, would need to be assessed. To achieve the
test concentrations required by terrestrial testing guidance (up to 1000
mg/kg), aqueous stock solutions would need to be prepared at very high
concentrations, well above 1000 mg/l. Silanetriols are susceptible to
condensation reactions. Condensation of (3-chloropropyl)silanetriol is
expected to become important at loadings above about 1000 mg/l causing
the formation of insoluble polymeric particles (sols) and gels over
time. It therefore may not be possible to test terrestrial organisms at
high enough test concentrations to meaningfully assess the terrestrial
toxicity of (3-chloropropyl)silanetriol. Prior to any testing, the
feasibility of dosing at concentrations up to 1000 mg/kg dw would have
to be assessed. Further details on technical feasibility of terrestrial
testing with silanetriol substances are given in Annex 5 of the CSR and
attached in Section 13 of IUCLID.
In addition, if a confirmatory long-term terrestrial test were to
be conducted, an assessment factor of 100 would be applied to derive
PNECsoil from one long-term test. For this value to be more conservative
than the PNECsoil derived by the equilibrium partitioning method, the
NOEC derived in the terrestrial test would have to be ≤37 mg/kg dw.
There is no basis to expect such toxicity for
(3-chloropropyl)silanetriol based on the absence of significant toxicity
observed in aquatic tests and the low potential for adsorption to and
bioaccumulation in soil.
In the case of (3-chloropropyl)silanetriol, the Registrant
considers that a long-term terrestrial study is unlikely to affect the
outcomes of the chemical safety assessment. As such the Registrant
proposes that further testing is currently not necessary.
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.
ECHA (2017). Guidance on Information Requirements and Chemical
Safety Assessment. Chapter R.7c: Endpoint specific guidance. Version 3.0
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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