N-[3-(trimethoxysilyl)propyl]butylamine

Endpoint summary

Description of key information

In accordance with REACH Annex XI, Section 3, there is no need to further investigate the effects of the silanol hydrolysis product 3-(N-butylamino)propylsilanetriol in short- or long-term terrestrial toxicity studies because exposure of terrestrial organisms to 3-(N-butylamino)propylsilanetriol is not significant (RCR < 1).

Additional information

The expected hydrolysis half-life of the registration substance is 4.0 h at pH 7 and 20-25 °C. Therefore, the hazard assessment for the terrestrial compartment is based on the silanol hydrolysis product 3-(N-butylamino)propylsilanetriol. The other hydrolysis product, methanol, is known for its absence of environmental toxicity at concentration levels relevant to the herein conducted studies (OECD SIDS, 2004).

 

In accordance with REACH Annex XI, Section 3, there is no need to further investigate the effects of the silanol hydrolysis product 3-(N-butylamino)propylsilanetriol in short- or long-term terrestrial toxicity studies because exposure of terrestrial organisms to 3-(N-butylamino)propylsilanetriol is not significant (RCR < 1). The hazard assessment based on acute aquatic toxicity data with the parent compound shows no toxicity toward aquatic organisms of all three trophic levels (all acute effect values, i.e. E(L)C50s were > 1 mg/L). However, the tested concentrations were well below the predicted solubility of the substance (1.3E+04 mg/L) and therefore do not provide an accurate representation of the likely toxicity of the substance. Thus, it was considered appropriate to read across from the structurally analogue substance, N-ethyl-3-trimethoxysilyl-2-methylpropanamine (CAS No. 227085-51-0). The source substance is also expected to hydrolyse rapidly in the aquatic environment (DT50 = 4.7 h at pH 7 and 20-25 °C, QSAR) to form a structurally similar silanol hydrolysis product, N-ethyl-3-trihydroxysilyl-2-methylpropanamine, and the common alcohol hydrolysis product methanol. Short-term aquatic toxicity data is available for all three trophic levels. No short-term toxicity effects up to the highest concentrations tested were observed in any of the three organism groups (EC/LC50 > 100 mg/L, equivalent to > 81 mg/L based on molecular weight corrections). However, for the purpose of exposure-based adaptation as in the present endpoint, PNECs were derived in the Chemical Safety Report (CSR, Chapters 9 and 10) for the required risk characterization even though no hazard was identified in the available aquatic toxicity studies. The PNECs aqua (freshwater/marine water) were derived using a worst-case threshold value of 100 mg/L (equivalent to 81 mg/L based on molecular weight corrections) in combination with the standard assessment factors of 1000 and 10000, respectively, as outlined in ECHA guidance R.10 (2008).

Due to the fast hydrolysis half-life of the parent source compound and the duration of the standard acute aquatic toxicity tests (48 up to 96 hours), the organisms can be assumed to be predominantly exposed to the hydrolysis products. The silanol hydrolysis product of the target compound is well soluble and thus, greater toxicity in long-term tests is unlikely. Therefore, the risk is already adequately controlled and further testing is not necessary.

 

In addition, testing for toxicity to terrestrial organisms is not considered necessary because:

-The silanol hydrolysis product, 3-(N-butylamino)propylsilanetriol, upon which the chemical safety assessment for the terrestrial compartment is based, is highly water-soluble and has a low expected log D (pH 7) value (-3.91, QSAR) and therefore, exposure of the soil compartment is expected to be low.  

- 3-(N-butylamino)propylsilanetriol has a low potential for adsorption (log Koc = 1.19; QSAR) and low potential for bioaccumulation (based on log D < 3) and there is no reason to expect any specific mechanism of toxicity beyond narcosis.

-Terrestrial testing is technically difficult for trialkoxysilanes in general due to condensation reactions at high test-concentrations. A feasibility study is currently ongoing. For further information, please see attached justification IUCLID chapter 13.

-No toxicity towards sludge microorganism was observed in the aquatic mircroorganisms test (OECD 209) on the analogue source substance N-[3-(trimethoxysilyl)propylcyclohexylamine] (CAS No. 3068-78-8) and in the toxicity control of the ready biodegradation test (OECD 301 B), therefore a toxicity test on soil microorganisms is not required.

 

Overall, it is concluded that the risk characterisation conclusion is sufficiently conservative in respect of any uncertainties and therefore further testing is not considered necessary. Details on how the PNEC and the risk characterisation ratio have been derived can be found in chapters 7, 9 and 10 of the Chemical Safety Report.

 

References:

OECD, 2004: SIDS Initial Assessment Report for Methanol, SIAM 19, Berlin, Germany, 19-22 October 2004, Methanol, CAS 67-56-1