Ethoxytrimethylsilane

Endpoint summary

Additional information

The registered substance ethoxytrimethylsilane (CAS 1825-62-3) hydrolyses rapidly in contact with water (DT50 = 2.2 min at pH 7 and 25 °C, EU method C.7) to form the hydrolysis products trimethylsilanol 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. Therefore, the assessment of aquatic toxicity has been based on the silanol hydrolysis product trimethylsilanol (CAS 1066-40-6). The second hydrolysis product ethanol is known for its overall low environmental hazard profile and thus is not considered to contribute to the overall aquatic toxicity of the parent compound (OECD SIDS, 2004). In consequence, data for the alcohol hydrolysis product is not presented specifically for each environmental toxicity endpoint within this dossier. Additional information is given in a supporting report attached in IUCLID Section 13 (PFA, 2016).

Acute toxicity studies evaluating the short-term toxicity of the silanol hydrolysis product trimethylsilanol (CAS 1066-40-6) to aquatic organisms are available for all three trophic levels. All studies were performed according to international standard guidelines and GLP. No short-term toxicity effects were observed towards the tested organisms of all three trophic levels below a concentration of 100 mg/L. The lowest EC50 value was obtained in the study with aquatic invertebrates (EC50 (48 h) = 124 mg/L). A NOEC (72 h) value of 44 mg/L (initial measured concentration) was measured in algae based on the inhibition of growth. The toxicity of the silanol hydrolysis product to activated sludge microorganisms was assessed in a study according to ISO 8192 and OECD guideline 209. The EC50 was found to be 6670 mg/L.

Table 1: Overview on aquatic effects for ethoxytrimethylsilane and its hydrolysis products.

	Parent	Silanol hydrolysis product	Other hydrolysis product*
CAS	1825-62-3	1066-40-6	64-17-5
	ethoxytrimethylsilane	trimethylsilanol	Ethanol
Acute fish (LC50)	RA CAS 1066-40-6	271 mg/L	> 1100 mg/L
Acute Invertebrates (EC50)	RA CAS 1066-40-6	124 mg/L	12340 mg/L
Algae (ErC50)	RA CAS 1066-40-6	> 684 mg/L	10000 mg/L^a
Algae (NOErC)	RA CAS 1066-40-6	44 mg/L	No data
Toxicity to microorganisms (EC50)	RA CAS 1066-40-6	6670 mg/L	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

 

Reference:

OECD (2004): SIDS Initial Assessment Report for SIAM 19, Berlin, Germany, 19-22 October 2004, Ethanol, CAS 64-17-5.