3-(triethoxysilyl)propyl methacrylate

Ecotoxicological Summary

Additional information

The hydrolysis half-life of 3-(triethoxysilyl)propyl methacrylate is 0.6 h at pH 4, 23.9 h at pH 7 and 0.3 h at pH 9 and 20-25°C (QSAR) (for reaction of ethoxysilane groups). The registration substance will hydrolyse at a moderate rate under neutral conditions in contact with water and atmospheric moisture to 3-(trihydroxysilyl)propyl methacrylate and ethanol. REACH guidance (ECHA 2016b, 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 substance itself”. TGD and ECHA guidance, (EC 2003, ECHA 2016c, R.7b) also suggest that when the hydrolysis half-life is less than 12 hours, the breakdown products, rather than the parent substance, should be evaluated for aquatic toxicity. Within the normal pH range relevant to the environment, extensive hydrolysis could be anticipated, although at pH7 the half-life is predicted to be longer than 12 hours.

Therefore, it is appropriate to conduct the environmental hazard assessment to assess both the registration substance and its hydrolysis products for the aquatic compartment.

As described in Section 4.8 of the IUCLID dossier, the silanol hydrolysis products may be susceptible to condensation reactions.

Read-across from 3-trimethoxysilylpropyl methacrylate CAS no. 2530-85-0 to 3-(triethoxysilyl)propyl methacrylate CAS No. 21142-29-0

3-(Triethoxysilyl)propyl methacrylate (CAS 21142-29-0) and 3-trimethoxysilylpropyl methacrylate (CAS 2530-85-0) both hydrolyse, moderately and rapidly respectively, in contact with water (half-life 23.9 h at pH 7 and 20-25°C and 1.7 h at pH 7 and 20-25°C respectively). Both substances share the same silanol hydrolysis product, 3-(trihydroxysilyl)propyl methacrylate. The aquatic toxicity data for the surrogate substance indicates that the silanol hydrolysis product is not acutely toxic to aquatic organisms. The study results, adjusted to reflect the concentration of 3-(trihydroxysilyl)propyl methacrylate, are read across to provide evidence for the aquatic toxicity assessment of the silanol hydrolysis product of the registration substance.

The non-silanol hydrolysis products of the target and source substances are ethanol and methanol, respectively.

 

Considerations on the non-silanol hydrolysis products:

Ethanol and methanol are well-characterised in the public domain literature and are not hazardous at the concentrations relevant to the studies; the short-term EC₅₀ and LC₅₀ values for these substances are in excess of 1000 mg/l (OECD, 2004a - SIDS for methanol, CAS 67-56-1, OECD 2004b - SIDS for ethanol, CAS 64-17-5). Therefore, at the loading rates experienced in these read-across tests it is unlikely that the presence of methanol would significantly affect the results of the tests.

 

 

Table: comparison of properties of registration substance and read-across substance

 

CAS Number	21142-29-0	2530-85-0
Chemical Name	3-(Triethoxysilyl)propyl methacrylate	3-Trimethoxysilylpropyl methacrylate
Si hydrolysis product	3-(Trihydroxysilyl)propyl methacrylate	3-(Trihydroxysilyl)propyl methacrylate
Molecular weight (parent)	290.43 g/mol	248.35 g/mol
Molecular weight (hydrolysis product)	206.27 g/mol	206.27 g/mol
log Kow (parent)	3.6	2.1
log Kow (silanol hydrolysis product)	-0.9	-0.9
Water sol (parent)	63 mg/l at 20°C	2200 mg/l at 20°C
Water sol (silanol hydrolysis product))	limited to about 1000 mg/l by condensation reactions	limited to about 1000 mg/l by condensation reactions
Vapour pressure (parent)	0.05 Pa at 25°C	2.3 Pa at 25°C
Vapour pressure (hydrolysis product)	1.2E-05 Pa at 25°C	1.2E-05 Pa at 25°C
Hydrolysis t1/2 at pH 7 and 25°C	23.9 h	1.7 h
Hydrolysis t1/2 at pH 4 and 25°C	0.6 h	0.3 h
Hydrolysis t1/2 at pH 9 and 25°C	0.3 h	0.1 h
Short-term toxicity to fish (LC50)	4.7 mg/l (ECOSAR prediction)	LC50 (96 h): >100 mg/l and >1042 mg/l (in terms of parent substance)
Short-term toxicity to aquatic invertebrates (EC50)	>75.3 mg/l	EC50 (48 h): >100 mg/ l and >876 mg/l   (in terms of parent substance)
Algal inhibition (ErC50 and NOEC/EC10)	ErC50 36.2 mg/l; ErC10 9.39 mg/l	EC50 (72 h): >100 mg/l and >536 mg/l; NOEC: ≥100 mg/l and 322 mg/l   (in terms of parent substance)

Conclusion on classification

Reliable, measured data are available for Daphnia and algae, determining EC₅₀ values of >75.3 mg/l and 36.2 mg/l, respectively. An ErC₁₀ value of 9.39 mg/l was also determined in the algal test. No measured data are available for the toxicity of the substance to fish. A reliable short-term LC₅₀ for fish of 4.7 mg/l has been estimated by QSAR, although the experimental evidence with Daphnia and algae suggest that this value may be conservative.

The substance hydrolyses at a moderate rate in water and is considered to be readily biodegradable, failing the 10 -day window, although the silanol hydrolysis product would not be considered as readily biodegradable. However, the silanol hydrolysis product does not fulfil the criteria for classification as hazardous to the aquatic environment.

These data are consistent with the following classification under Regulation (EC) No 1272/2008 (as amended) (CLP):

Acute toxicity: Not classified.

Chronic toxicity: Not classified.