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Approach to the Terrestrial Chemical Safety Assessment

The registered substance will hydrolyse rapidly (half-life 0.025 hours at pH 7 at 25°C) in contact with water and atmospheric moisture to N-(3-(trihydroxysilyl)propyl)ethylenediamine and methanol. REACH guidance (ECHA 2016, R.16) states that “for substances where hydrolytic DT50 is less than 12 hours, environmental effects are likely to be attributed to the hydrolysis product rather than to the parent itself”. ECHA Guidance Chapter R.7b (ECHA, 2017) states that where degradation rates fall between >1 hour and <72 hours, testing of parent and/or degradation product(s) should be considered on a case-by-case basis. Therefore, in accordance with REACH guidance, the environmental hazard assessment, including sediment and soil compartments due to water and moisture being present, is based on the properties of the hydrolysis products, in accordance with REACH guidance.

Therefore, in accordance with REACH guidance, the terrestrial chemical safety assessment for N-(3 -(trimethoxysilyl)propyl)ethylenediamine is based on both the silanol hydrolysis product N-(3-(trihydroxysilyl)propyl)ethylenediamine. The non-silanol hydrolysis product, methanol, is not expected to contribute to toxicity to terrestrial organisms. 


Hydrolysis product: N-(3-(trihydroxysilyl)propyl)ethylenediamine

In accordance with Column 2 of REACH Annex IX, there is no need to further investigate the effects of this substance in a long or short-term terrestrial toxicity to invertebrates/higher plants study because, as indicated in guidance R.7.11.6 (ECHA 2017), the quantitative chemical safety assessment (conducted according to Annex I of REACH) indicates that the Risk Characterisation Ratio is below 1 and therefore the risk is already adequately controlled and further testing is not justifiable.


The substance is highly water soluble and is not readily biodegradable but has low bioavailability and low potential for adsorption (based on log Kow <3 (-4) and log Koc -0.7). Low toxicity was observed in short-term aquatic tests and the occurrence of more severe toxic effects in the terrestrial compartment that were not expressed in the aquatic studies would be considered unlikely.


N-(3-(Trihydroxysilyl)propyl)ethylenediamine is 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.


In the event that terrestrial invertebrate and plant studies need to be conducted, the definitive terrestrial risk characterisation would use a PNECsoil based on the lower of the two test results with an assessment factor of 50 (unless soil microorganism data are available as well, in which case, the assessment factor would be 10).


A confirmatory test would be conducted with the most sensitive organism group based on short-term aquatic testing. For this substance, algae were the most sensitive organisms in the long-term tests, indicating a preference to conduct a confirmatory test with terrestrial plants.


The PNECscreen(EQPM) for N-(3-(trihydroxysilyl)propyl)ethylenediamine is derived from the long-term test results with algae and has a value of 0.00687 mg/kg dwt. For the purpose of the screening assessment comparison only, an extra factor of ten is applied (PECx10/PNECscreen(EQPM)). Based on the exposure assessment, the highest agricultural soil RCR available for the silanol hydrolysis product, N-(3-(trihydroxysilyl)propyl)ethylenediamine is 0.959, with a corresponding Predicted Environmental Concentration (PEC) of 0.00659 mg/kg dwt. The (PECx10)/PNECscreen(EQPM) for N-(3-(trihydroxysilyl)propyl)ethylenediamine is (0.00659*10)/ 0.00687 = screening RCR 9.59.


A confirmatory long-term terrestrial toxicity test is therefore required in accordance with the recommendations for hazard category 3 substances. If a confirmatory long-term terrestrial test were to be conducted, an assessment factor of 100 would be applied to derive PNECsoil from one long-term test. A confirmatory test with either terrestrial plants or invertebrates 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 ≤ 0.687 mg/kg dw (and applying an assessment factor of 100). There is no basis to expect such toxicity for N-(3-(trihydroxysilyl)propyl)ethylenediamine based on the absence of significant toxicity observed in aquatic tests.


In the case of N-(3-(trihydroxysilyl)propyl)ethylenediamine, 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 (including the confirmatory study) is not necessary.


Additionally, no toxicity was observed in a short-term toxicity to soil macroorganisms except arthropods study for the effects of the registration substance on the mortality of Eisenia fetida (14-day LC50 >810 mg/kg dry weight, expressed in terms of the concentration of the silanol hydrolysis product, N-(3-(trihydroxysilyl)propyl)ethylenediamine).

Overall, it is concluded that the risk characterisation conclusion is sufficiently conservative 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 IUCLID Section 6.0, CSR Section 7, and Chapters 9 and 10 of the Chemical Safety Report, respectively.