Tris(isopropenyloxy)vinylsilane

Ecotoxicological Summary

Additional information

The hydrolysis half-life of tris(isopropenyloxy)(vinyl)silane (CAS 15332-99-7) is ≤6.6 h at pH 7 and 20-25°C. The registration substance will hydrolyse in contact with water and atmospheric moisture to vinylsilanetriol and propen-2-ol. REACH guidance (ECHA 2012, 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”. TGD and ECHA guidance, (EC 2003, ECHA 2012) 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. Therefore, the environmental hazard assessment, is based on the properties of the silanol hydrolysis product, in accordance with REACH guidance. As described in Section 4.8 (water solubility), the silanol hydrolysis products may be susceptible to condensation reactions.

Consideration of the non-Si hydrolysis product propen-2-ol (CAS 29456-04-0) / acetone (CAS 67-64-1)

The hydrolysis of tris(isopropenyloxy)(vinyl)silane (CAS 15332-99-7) produces vinylsilanetriol and 3 molecules of propen-2-ol. Propen-2-ol is an enol type structure, which is in equilibrium with its keto tautomer, propanone (commonly called acetone). The equilibrium heavily favours the keto form at room temperature. Therefore, the properties of acetone as well as vinylsilanetriol are considered for the chemical safety assessment.

Measured data are available from the OECD SIDS for acetone (OECD 1999 SIDS for acetone, CAS 67-64-1).

Long- and short-term aquatic toxicity data show E(L)C₅₀ and NOEC values in excess of 1000 mg/l, and terrestrial tests report no effects seen at the maximum concentrations tested. Therefore, at the loading rates experienced in these tests it is unlikely that the presence of acetone would significantly affect the results of the tests.

READ-ACROSS JUSTIFICATION

In order to reduce testing, read-across is proposed to fulfil REACH Annex VII requirements for the registration substance from substances that have similar structure and physicochemical properties. Ecotoxicological studies are conducted in aquatic medium or in moist environments; therefore the hydrolysis rate of the substance is particularly important, because after hydrolysis has occurred, the resulting product has different structural features, physicochemical properties and behaviour.

The registration substance and the substance used as surrogate for read-across are part of a class of low-functionality compounds acting via a non-polar narcosis mechanism of toxicity. The group of organosilicon substances in this group contain alkyl, aryl, alkoxy or hydroxy groups attached to the silicon atom when present in aqueous solution. Secondary features may be present in the alkyl chain (e.g. halogen, nitrile, unsaturated bonds) that do not affect the toxicity of the substances. The silanol hydrolysis products may be susceptible to condensation reactions (see Section 4.8 (water solubility)).

The registration substance hydrolyses rapidly in water and therefore the selection of surrogate substance is based on log K_ow of the resulting silanols and the chemical groups present in them. Additional information is given in a supporting report (PFA 2016y) attached in Section 13.

In addition, the properties of the non-silanol hydrolysis product are reviewed in the following section.

In the following paragraphs the read-across approach for tris(isopropenyloxy)(vinyl)silane is assessed for the surrogate substance taking into account structure, hydrolysis rate and physicochemical properties. The table below presents relevant physicochemical properties and the available ecotoxicological data.

Table: Physicochemical parameters and ecotoxicity data for the registered and surrogate substance

CAS Number	15332-99-7	2768-02-7
Chemical Name	Tris(isopropenyloxy)(vinyl)silane	Trimethoxy(vinyl)silane
Si hydrolysis product	Vinylsilanetriol	Vinylsilanetriol
Molecular weight (parent)	226.35 g/mol	148.24 g/mol
Molecular weight (hydrolysis product)	106.15 g/mol	106.15 g/mol
log Kow (parent) at 20°C	3.8 (QSAR prediction)	1.1 (QSAR predicton)
log Kow (silanol hydrolysis product) at 20°C	-2.0 (QSAR prediction)	-2.0 (QSAR prediction)
Water sol (parent) at 20°C	130 mg/l (QSAR prediction)	30000 mg/l (QSAR prediction)
Water sol (silanol hydrolysis product) at 20°C	1.0E+06 mg/l (limited to about 1000 mg/l by condensation reactions) (QSAR prediction)	1.0E+06 mg/l (limited to about 1000 mg/l by condensation reactions) (QSAR prediction)
Vapour pressure (parent)	5.3 Pa at 25°C(QSAR prediction)	1190 Pa at 20°C (measured)
Vapour pressure (hydrolysis product)	0.017 Pa at 25°C(QSAR prediction)	0.017 Pa at 25°C (QSAR prediction)
Hydrolysis t1/2 at pH 7 and 20-25°C	≤6.6 h (20-25°C) (QSAR prediction)	0.1 h (QSAR prediction)
Hydrolysis t1/2 at pH 4 and 20-25°C	≤0.3 h (20-25°C) (QSAR prediction)	0.04 h (QSAR prediction)
Hydrolysis t1/2 at pH 9 and 20 -25°C	≤0.1 h (20-25°C) (QSAR prediction)	0.004 h (QSAR prediction)
Short-term toxicity to fish (LC50)	n/a	191 mg/l
Short-term toxicity to aquatic invertebrates (EC50)	n/a	169 mg/l
Algal inhibition (ErC50and NOEC)	n/a	7 d ErC50: 210 mg/l and NOEC 25 mg/l 72 h EC50 >89 mg/l and NOEC ≥89 mg/l
Long-term toxicity to fish (NOEC)	n/a	n/a
Long-term toxicity to aquatic invertebrates (NOEC)	n/a	21 d NOEC: 28 mg/l
Long-term sediment toxicity (NOEC)	n/a	n/a
Short-term terrestrial toxicity (L(E)C50)	n/a	n/a
Long-term terrestrial toxicity (NOEC)	n/a	n/a
Toxicity to microorganisms (EC50, EC10, NOEC)	n/a	oxygen consumption (P. putida) 5hr EC10 1.1 ml/L

 

 

•            Read-across from trimethoxy(vinyl)silane to tris(isopropenyloxy)(vinyl)silane

Tris(isopropenyloxy)(vinyl)silane (CAS 15332-99-7) and trimethoxy(vinyl)silane (CAS 2768-02-7) both hydrolyse rapidly in contact with water (≤6.6 h at pH 7 and 0.1 h at pH 7 at 20-25°C respectively). Tris(isopropenyloxy)(vinyl)silane and trimethoxy(vinyl)silane share the same organosilicon hydrolysis product, vinylsilanetriol; the non-silicon hydrolysis products are acetone and methanol, respectively . They also share similar physicochemical properties: high water solubility, log K_ow <4 (3.8 and 1.1 respectively) and low molecular weight (226.35 g/mol and 148.24 g/mol respectively).

Short-term toxicity data to invertebrates and algae endpoints for trimethoxy(vinyl)silane are read-across to the submission substance. E(L)C₅₀ values of 169 and 210/>89 mg/l, respectively, have been determined. NOEC values of approximately 25/>=89 mg/l were determined in the algae test. Trimethoxy(vinyl)silane is also used to read-across to the long-term toxicity to invertebrates endpoint, with a NOEC value of 28 mg/l.

The aquatic toxicity data for the surrogate substance indicates that it is not acutely toxic to aquatic organisms.

               

•            Considerations on the non-silanol hydrolysis product of the surrogate substance:

Methanol

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

References:

ECHA 2012: European Chemicals Agency. Guidance on information requirements and chemical safety assessment Chapter R.16: Environmental Exposure Estimation. Version: 2.1, October 2012 (Section R.16.5.4.1. Hydrolysis).

OECD 1999 SIDS Initial Assessment Report (SIAR) for the 9th SIAM, Paris, France, 29 -30 June 1999, Acetone, CAS 67-64-1.

OECD 2004 SIDS Initial Assessment Report SIAM 19, Berlin, Germany, 18 -20 October 2004, Methanol, CAS 67-56-1.

Conclusion on classification

Based on the available read-across data the substance has reliable short-term E(L)C₅₀ values of 169 mg/l for invertebrates and 210 and >89 mg/l for algae, read across from structural analogue trimethoxy(vinyl)silane. It has reliable NOEC values of 25 and >=89 mg/l in algae and a reliable long-term NOEC of 28 mg/l in Daphnia, also read across from trimethoxy(vinyl)silane.

The substance hydrolyses rapidly in water and the silanol hydrolysis product, vinylsilanetriol, has low predicted log K_ow (-2.0) but is not readily biodegradable.  

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