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EC number: 219-784-2
CAS number: 2530-83-8
The hydrolysis half-life of [3-(2,3-epoxypropoxy)propyl]trimethoxysilane
(CAS 2530-83-8) is 6.5 h at pH 7 and 24.5°C. This half-life reflects
hydrolysis of the methoxy groups. It is considered that the epoxide ring
opening is not significant for the exposure assessment at any relevant
pH, and the chemical safety assessment considers the hydrolysis products
[3-(2,3-epoxypropxy)propyl]silanetriol and methanol. This is a
conservative position in the absence of clear evidence, as the epoxide
structural feature is likely to be more toxic than the corresponding
diol (this is discussed further below).
The registered substance will hydrolyse in contact with water and
atmospheric moisture to [3-(2,3-epoxypropoxy)propyl]silanetriol and
methanol. REACH guidance (ECHA 2016, R.16) states that “for substances
where hydrolytic DT50 is less than 12
hours, environmental effects are likely to be attributed to the
hydrolysis product rather than to the parent itself”. ECHA Guidance
Chapter R.7b (ECHA, 2017) states that where degradation rates fall
between >1 hour and <72 hours, testing of parent and/or degradation
product(s) should be considered on a case-by-case basis.
[3-(2,3-epoxypropoxy)propyl]trimethoxysilane has a measured degradation
half-life of 6.5 hours at pH 7 and 24.5°C, as indicated above. The
substance will be exposed to the environment through waste-water
treatment plant (WWTP) effluent only. The residency time in the
waste-water treatment plant is approximately 15 hours with an average
temperature of 15°C (assumed to be at neutral pH). Significant
degradation by hydrolysis would be expected before the substance is
released to the receiving waters. The aquatic exposure and chemical
safety assessment therefore focus on the degradation products
[3-(2,3-epoxypropxy)propyl]silanetriol and methanol.
The proportion of the substance that adsorbs to the WWTP sludge will
either be burnt or spread on soil, depending on the practices of the
WWTP. The sediment is exposed to the substance in the environment via
the effluent water released from the WWTP. The sediment will therefore
be exposed to the same species as the receiving waters. Accordingly,
exposure and chemical safety of the sediment is based on the hydrolysis
Exposure of soil is via the partitioning of the substance to the WWTP
sludge. The sludge may then be spread onto soil, depending on the
practices of the WWTP. The substance will have undergone significant
hydrolysis by the time it reaches the soil, therefore exposure and
chemical safety assessment of soil is based on the degradation products.
Consideration of the non-Si hydrolysis product
The non-silicon-containing hydrolysis product of
[3-(2,3-epoxypropoxy)propyl]trimethoxysilane is methanol. Methanol is
well characterised in the public domain literature and is not hazardous
at the concentrations relevant to the aquatic toxicity studies; the
short-term EC50 and LC50 values for the substance
are in excess of 1000 mg/l (OECD, 2004a - SIDS Initial Assessment Report
for SIAM 19, Berlin, Germany, 18 -20 October 2004, Methanol, CAS
In conclusion, the environmental hazard assessment, including sediment
and soil compartments due to water and moisture being present, is based
on the properties of the silanol hydrolysis product, in accordance with
REACH guidance. As described in Sections 4.8 and 5.1.2 of IUCLID, the
silanol hydrolysis products may be susceptible to condensation reactions
as well as subsequent hydrolysis reactions of the epoxide functional
The registration substance [3-(2,3-epoxypropoxy)propyl]trimethoxysilane
(CAS 2530-83-8) has a predicted water solubility of 1.1E+05 mg/L and
predicted log Kow of 0.5.
There are two characteristics of
[3-(2,3-epoxypropoxy)propyl]trimethoxysilane that are thought to confer
toxicity to the substance: the presence of the epoxy group in the
molecular structure and the log Kow of the
substance. Hydrolysis of the substance can occur at the methoxy group
and the epoxy group. The hydrolysis of the methoxy group will generate a
silanetriol with a lower log Kow than the
parent and thus a less bioavailable form of the substance. The epoxy
group will still be present as the methoxy group will hydrolyse more
quickly than the epoxy group. The hydrolysis of the epoxy group will
result in an open ring, which is less reactive and less toxic.
The intermediate hydrolysis product
3-(2,3-epoxypropoxy)propyl)silanetriol is expected to be less toxic than
the parent substance because even though the epoxy ring is still present
it has a lower log Kow value. Likewise, it
is expected to be more toxic than the ultimate hydrolysis product
because the epoxy ring is absent from the ultimate hydrolysis product.
Consideration of the intermediate hydrolysis product
[3-(2,3-Epoxypropoxy)propyl]silanetriol has a low log Kow of
-2.6 and a high predicted water solubility of 1E+06 mg/L, although this
is limited by condensation reactions (see section 4.8 of the IUCLID),
and a molecular weight of 194.26. The substance contains an epoxy group
which is a chemical structure that might confer toxicity (REACH
guidance, ECHA 2008, R.10). However, this intermediate hydrolysis
product is expected to be less toxic than the parent substance, because
even though the epoxy ring is still present, the substance has a lower
log Kow value.
Consideration of the final hydrolysis product
3-[3-(trihydroxysilyl)propoxy]propane-1,2-diol is the final silanol
hydrolysis product of [3-(2,3-epoxypropoxy)propyl]trimethoxysilane. It
has a molecular weight of 212.28, a predicted log Kow of
-3.8 and predicted water solubility of 1E+06 mg/L. It is expected to be
less toxic than the parent substance and the intermediate hydrolysis
product, because the epoxy ring is absent and the log Kow is
The substance has reliable short-term E(L)C50values of
55 mg/l in fish, 324 mg/l in invertebrates and 350 mg/l in algae. It has
a reliable NOEC of 130 mg/l in algae and reliable long-term NOEC of >100
mg/l in Daphnia. The substance hydrolyses rapidly in water and is
not readily biodegradable but the log Kow of the hydrolysis
product is very low.
According to Regulation (EC) No 1272/2008 (as amended) (CLP),
where adequate chronic toxicity data are not available for three trophic
levels, classification should be based on the most stringent outcome of
the criteria set out in Table 4.1.0(b)(i) or (ii), and Table
4.1.0(b)(iii) of the Regulation. In this case, the lowest acute E(L)C50
is between >10 and =100
mg/L, and the substance is not rapidly biodegradable.
These data are therefore consistent with the following
classification under Regulation (EC) No 1272/2008 (as amended) (CLP):
Acute toxicity: Not classified
Chronic toxicity: Classified as Aquatic Chronic 3, H412: Harmful
to aquatic life with long lasting effects.
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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