[3-(trimethoxysilyl)propyl]urea

Endpoint summary

Additional information

The registered substance 1-[3-(trimethoxysilyl)propyl]urea (CAS No. 23843-64-3) hydrolyses rapidly in contact with water (estimated DT50 = 2.8 h) to [3-(trihydroxysilyl)propyl]urea and methanol. It is therefore very likely that the test organisms in the toxicity tests were predominantly exposed to the hydrolysis products. 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.

 

Suitable experimental data testing the toxicity of the registered (parent) substance to fish, aquatic invertebrates and algae were not available. Therefore, it was considered appropriate to read across from the structurally analogous substance ureidopropyltrialkoxysilane, mixed methoxy and ethoxy esters (CAS No. 116912-64-2). Both substances share the same silanol hydrolysis product (i.e. [3-(trihydroxysilyl)propyl]urea), the other hydrolysis products are methanol and ethanol, respectively. Both substances are expected to hydrolyse within the timescale of aquatic toxicity tests. Further information on the read across approach can be found in IUCLID Section 13.

 

An acute fish toxicity study conducted with the analogue substance is available (OECD 203), in which Cyprinus carpio was exposed under static conditions for 96 h to the single nominal test item concentration of 100 mg/L. No toxic effects were observed in the study resulting in an LC50 (96 h) of > 100 mg/L (nominal). In the short-term toxicity study with the analogous substance and aquatic invertebrates (OECD 202), Daphnia magna was exposed under static conditions for 48 h to a single nominal test item concentration of 100 mg/L (nominal). No toxic effects were observed in the study resulting in an EC50 (48 h) of > 100 mg/L (nominal). The influence of the read across substance on the growth of the freshwater algae species Pseudokirchneriella subcapitata was investigated in a 72 h static test according to OECD 201 guidance. Test item concentrations of 0 (control), 10, 22, 46, 100 and 220 mg/L were used. The study resulted in an ErC50 of > 220 mg/L and a NOErC (72 h) of 10 mg/L. In all studies a static system was used, due to the high rate of hydrolytical degradation of the substance. With a static system an exposure to both the parent and the hydrolysis products was achieved.

 

The hydrolysis products methanol and ethanol 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). 

 

References:

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

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