Triethoxy(vinyl)silane

Endpoint summary

Additional information

The registered substance triethoxy(vinyl)silane (CAS No. 78-08-0) hydrolyses rapidly in contact with water (DT50 = 0.9 h at pH 7 and 20 – 25 °C, QSAR) to vinylsilanetriol and ethanol. REACH guidance R.16 states that “for substances where hydrolytic DT50 is less than 12 h, environmental effects are likely to be attributed to the hydrolysis product rather than to the parent itself” (ECHA, 2016). TGD (EC, 2003) and REACH guidance R.16 (ECHA, 2016) also suggest that when the hydrolysis half-life is less than 12 h, the breakdown products, rather than the parent substance, should be evaluated for aquatic toxicity testing.

Because there is no data available on the aquatic toxicity of the registered substance or its silanol hydrolysis product, the aquatic toxicity was assessed based on read-across to a structural similar analogue substance trimethoxy(vinyl)silane (CAS No. 2768-02-7). The source substance hydrolyses rapidly in the aquatic environment (DT50 = 0.1 h at 20 -25 °C and pH 7, QSAR) to form the same silanol hydrolysis product as the target substance, vinylsilanetriol, and the alcohol hydrolysis product methanol instead of ethanol, which is formed as the second hydrolysis product of the target substance. Additional information is given in a read-across justification attached in IUCLID section 13.

 

Acute toxicity studies evaluating the short-term toxicity of the source substance to aquatic organisms are available for all three trophic levels. All studies were performed according to accepted standard guidelines and GLP. No acute effects were observed towards the tested organisms of all three trophic levels up to the highest concentration tested. Chronic toxicity data of the source substance is available for aquatic invertebrates and algae. In Algae no effects were seen up to the highest tested concentration. For aquatic invertebrates a 21-day NOEC of 28.1 mg/L (measured, time-weighted average) was obtained.

For the toxicity in aquatic microorganism, data was read across for the source substance of a reliable biodegradation study conducted according to OECD 301 F and GLP conditions. The biodegradation rate in the toxicity control shows a similar course of biodegradation as the two controls containing the reference item only. Within 14 days of exposure, a biodegradation of 64 % was observed. Thus, according to guideline the test item shows no inhibitory effect on activated sludge microorganisms up to a concentration of 100 mg/L. The NOEC of 100 mg/L can be used for the PNEC derivation. On this basis, no toxic effects are anticipated by the target substance and the degradation process in sewage treatment plants is not considered to be inhibited.

The second hydrolysis products of source and target substance methanol and ethanol are 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 both alcohol hydrolysis products are in excess of 1000 mg/l (see Table 1) (OECD SIDS, 2004; OECD SIDS, 2004). Thus, methanol and ethanol are not considered to contribute to the overall aquatic toxicity of the source and target substance, respectively. In consequence, data for the alcohol hydrolysis products are not presented specifically for each environmental toxicity endpoint within this dossier.

Table 1: Overview on aquatic effect values for Triethoxy(vinyl)silane and its hydrolysis products.

	Source	Parent	Silanol hydrolysis product	Other hydrolysis product*
				Source	Parent
CAS	2768-02-7	78-08-0		67-56-1	64-17-5
	Trimethoxy(vinyl)silane	Triethoxy(vinyl)silanol	vinylsilanetriol	Methanol	Ethanol
Acute fish (LC50)	> 100 mg/L	RA CAS 2768-02-7	RA CAS 2768-02-7	> 15000 mg/L	> 1100 mg/L
Acute Invertebrates (EC50)	168.7 mg/L	RA CAS 2768-02-7	RA CAS 2768-02-7	>10000 mg/L	12340 mg/L
Chronic aquatic invertebrates (NOEC)	28.1 mg/L	RA CAS 2768-02-7	RA CAS 2768-02-7	No data	No data
Algae (ErC50)	> 89 mg/L	RA CAS 2768-02-7	RA CAS 2768-02-7	Ca. 22000 mg/L	10000 mg/L^a
Algae (NOErC)	89 mg/L	RA CAS 2768-02-7	RA CAS 2768-02-7	No data	No data
Toxicity to microorganisms (NOEC)	100 mg/L	RA CAS 2768-02-7	RA CAS 2768-02-7	No data	6500 mg/L^b

* Source = OECD SIDS (2004)

^a: 96-h EC50 for Selenastrum capricornumtum also known as Pseudokirchneriella subcapitata

^b: 16-hour toxicity threshold using Pseudomonas putida

 

References:

OECD SIDS, 2004. Ethanol - SIDS Initial Assessment Report For SIAM 19, Berlin, Germany: UNEP Publications.

OECD SIDS, 2004. Methanol - SIDS Initial Assessment Report For SIAM 19, Berlin, Germany: UNEP Publications.