3-(trimethoxysilyl)propylamine

Endpoint summary

Additional information

Approach to the Terrestrial Chemical Safety Assessment

The hydrolysis half-life of 3-(trimethoxysilyl)propylamine (CAS 13822-56-5, EC 237-511-5) is 2.6 hours at pH 7 and 25°C. The registered substance will hydrolyse in contact with water and atmospheric moisture to form 3-aminopropylsilanetriol and methanol. The chemical safety assessment for the terrestrial compartment is therefore based on the silanol hydrolysis product, 3-aminopropylsilanetriol.

In accordance with Column 2 of REACH Annex IX, there is no need to further investigate the effects of this substance in long-term terrestrial toxicity studies because, as indicated in guidance R.7.11.6 (ECHA 2016), the quantitative chemical safety assessment (conducted according to Annex I of REACH) indicates that the Risk Characterisation Ratio is well below 1, and therefore the risk is already adequately controlled and further testing is not justifiable.

The silanol hydrolysis product, 3-aminopropylsilanetriol, upon which the chemical safety assessment is based, is highly water soluble and has a low log K_owvalue and therefore, exposure of the soil compartment is expected to be low.

The substance is not adsorbing (based on log K_oc-0.6), has low bioavailability (based on log K_ow<3 (-2.0)) and low toxicity was observed in short- and long-term aquatic tests. Therefore, the occurrence of more severe toxic effects in the terrestrial compartment that were not expressed in the aquatic studies would be considered unlikely.

3-Aminopropylsilanetriol classed as hazard category 3 for the terrestrial environment (Table R.7.11-2 of ECHA guidance R7.c, 2017) based on potential for high persistence (DT50 > 180 days), lack of ready biodegradability and low toxicity to aquatic organisms (EC/LC50 not <1 mg/l).    In this situation, a screening approach is applied: a confirmatory long-term terrestrial test is usually appropriate, in addition to the equilibrium partitioning approach with an extra factor of ten, in order to determine whether further full tests are necessary.    

The PNECscreen(EQPM) for 3-aminopropylsilanetriol is derived from the short-term key aquatic invertebrates EC₅₀, generating a PNECsoil value of 0.069 mg/kg dwt. For the purpose of the screening assessment comparison only, an extra factor of ten is applied to the predicted environmental concentration (PEC) to derive the screening risk characterisation ratio (RCR) (PECx10/PNECsoil(EQPM)). Based on the exposure assessment for 3-aminopropylsilanetriol, the highest agricultural soil RCR is 0.252, which has a corresponding PEC of 0.017 mg/kg dw. The screening RCR ((PECx10)/PNECsoil(EQPM)) for 3-aminopropylsilanetriol is therefore (0.017 * 10)/0.069 = screening RCR 2.46. 

Long-term terrestrial toxicity testing is therefore required in accordance with the recommendations for hazard category 3 substances. If long-term terrestrial tests were to be conducted, an assessment factor of 10 would be applied to derive PNECsoil from three long-term tests. Long-term tests with terrestrial plants, invertebrates and soil microorganisms would result in a new value for PNECsoil. This value could only be more conservative than the value of PNECscreen(EQPM) in the situation that standard testing in terrestrial plants or invertebrates exhibited a dose response with a NOEC/EC10 = 6.9 mg/kg dw (and applying an assessment factor of 100). There is no basis to expect such toxicity for 3-aminopropylsilanetriol based on the absence of significant toxicity observed in aquatic tests (all E(L)C50 values >100 mg/l).    

In the case of 3-aminopropylsilanetriol, the registrants consider that a long-term terrestrial study is unlikely to affect the outcomes of the chemical safety assessment. As such the registrants propose that further testing is not necessary. 

The PNEC calculated by the Equilibrium Partitioning Method has been determined for the purpose of deriving a chemical safety assessment and the risk characterisation ratios are below 1.

It is recognised that the aquatic PNEC used in the EQPM does not take into account any indicator for effects in aquatic microorganisms. However, according to REACH guidance, Chapter R.7c (ECHA, 2017), where inhibition of sewage sludge microbial activity has been observed, a test on soil microbial activity will additionally be necessary for a valid PNEC to be derived. A sewage treatment plant microorganisms toxicity test has been conducted with an analogue substance. Some inhibition of microbial activity was observed at concentrations below 100 mg/l but above 1 mg/l (EC10 13 mg/l). Significant toxicity to soil microorganisms is therefore not expected and it is unlikely that the PNECsoil based on aquatic ecotoxicity test results would not be protective for terrestrial microorganisms, therefore testing with soil microorganisms is not necessary.

Overall it is concluded that the risk characterisation conclusion is sufficiently conservative in respect of any uncertainties and therefore further in is not considered necessary.

Details on how the PNEC and the risk characterisation ratio have been derived can be found in IUCLID Section 6.0 and Chapters 9 and 10 of the Chemical Safety Report, respectively.