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Approach to the Terrestrial Chemical Safety Assessment

The registered substance will hydrolyse moderately rapidly (half-life 35 hours at pH 7 at 25°C) in contact with water and atmospheric moisture to (3-chloropropyl)silanetriol and ethanol. 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 both the parent substance, (3-chloropropyl)triethoxysilane and the silanol hydrolysis product, (3-chloropropyl)silanetriol, in accordance with REACH guidance.

Therefore, in accordance with REACH guidance, the terrestrial chemical safety assessment for (3-chloropropyl)triethoxysilane is based on both the registration substance and its silanol product (3-chloropropyl)silanetriol. The non-silanol hydrolysis product, ethanol, is not expected to contribute to toxicity to terrestrial organisms. 

 

Parent: (3-chloropropyl)triethoxysilane

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 2016), 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 water soluble and is not readily biodegradable, and has some bioavailability and potential for adsorption (based on log Kow >3 (3.13) and log Koc 1.7). 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.

 

(3-Chloropropyl)triethoxysilane is classed as hazard category 1 for the terrestrial environment (Table R.7.11-2 of ECHA guidance R7.c, 2017) based on no potential for adsorption (log Kow < 5), no potential for high persistence (DT50 < 180 days) and low toxicity to aquatic organisms (EC/LC50 not <1 mg/l). Therefore, the approach for screening assessment for the parent substance is to conduct a PEC/PNECscreen based on the Equilibrium Partitioning Method. The PNEC calculated by the Equilibrium Partitioning Method for the parent substance generates a risk characterisation ratio that is below 1. Terrestrial testing is therefore not required with the parent substance, (3-chloropropyl)triethoxysilane (CAS 5089-70-3).

Additionally, short-term tests conducted with fish and algae (according to OECD 203 and 201, respectively) are ongoing. Once the results of these studies have become available, long-term aquatic testing with the most sensitive trophic level (either Daphnia or fish) will be proposed with the parent substance. The PNECsoil value, based on the equilibrium partitioning method, will be revised once the new aquatic data become available.

 

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.

 

Hydrolysis product: (3-chloropropyl)silanetriol

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 2016), 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 (-1.1) and log Koc 0.45). 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.

 

(3-Chloropropyl)silanetriol 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.

 

The PNECscreen(EQPM) for (3-chloropropyl)silanetriol is derived from the long-term test results with algae and has a value of 1.534 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 (PECx10)/PNECscreen(EQPM) for (3-chloropropyl)silanetriol is (0.167*10)/1.534 = 1.09.

In addition, 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 = 153.4 mg/kg dw (and applying an assessment factor of 100). There is no basis to expect such toxicity for (3-chloropropyl)silanetriol based on the absence of significant toxicity observed in aquatic tests.

In the case of (3-chloropropyl)silanetriol, 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.

In addition, prior to terrestrial toxicity tests being carried out, the technical feasibility of testing the silanol hydrolysis product, (3-chloropropyl)silanetriol, would need to be assessed. To achieve the test concentrations required by terrestrial testing guidance (up to 1000 mg/kg), aqueous stock solutions would need to be prepared at very high concentrations, well above 1000 mg/l. Silanetriols are susceptible to condensation reactions. Condensation of (3-chloropropyl)silanetriol is expected to become important at loadings above about 1000 mg/l causing the formation of insoluble polymeric particles (sols) and gels over time. It therefore may not be possible to test terrestrial organisms at high enough test concentrations to meaningfully assess the terrestrial toxicity of (3-chloropropyl)silanetriol. Prior to any testing, the feasibility of dosing at concentrations up to 1000 mg/kg dw would have to be assessed. Further details on technical feasibility of terrestrial testing with silanetriol substances are attached in Section 13 of IUCLID.

 

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.