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Due to the rapid hydrolysis of the substance, the chemical safely assessment is based on the silanol hydrolysis product 3-chloropropyl(methyl)silanediol.


Testing for toxicity to terrestrial organisms is not considered necessary because:

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 or 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 silanol hydrolysis product is not readily biodegradable but has low potential for bioaccumulation and low potential for adsorption (based on log Kow <3 (0.8) and low log Koc (1.4)); partitioning to the terrestrial compartment is expected to be minimal. Toxicity was only observed at very high concentrations in aquatic tests and there is no reason to expect any specific mechanism of toxicity beyond narcosis. 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-Chloropropyl(methyl)silanetriol 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. 

The PNECscreen (EQPM) for 3-chloropropyl(methyl)silanediol is derived from the short-term test result with algae and has a value of 0.22 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 of 3-chloropropyl(dimethoxy)methylsilane (CAS 18171-19-2), the highest PECx10/PNECscreen (EQPM) for 3-chlorpropyl(methyl)silanediol is (1.91E-3 x 10) / 0.22 = RCR 8.7E-2. The highest agricultural RCR is therefore well below 1 indicating that one confirmatory long-term terrestrial toxicity test is required according to ECHA guidance Chapter R.7c (ECHA 2017), and if toxicity is shown in the confirmatory test then full testing according to Annex X would be required.

However, in the event that terrestrial invertebrate and plant studies were 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).

Full testing in both terrestrial plants and invertebrates would result in a new value of 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 ≤11 mg/kg dw. There is no basis to expect such toxicity for 3-chloropropyl(methyl)silanediol based on the absence of significant toxicity observed in aquatic tests and the low potential for bioaccumulation.

In the case of 3-chloropropyl(methyl)silanediol, the Registrant considers that a long-term terrestrial study is unlikely to affect the outcomes of the chemical safety assessment. As such the Registrant proposes that further testing (including the confirmatory study) is not necessary.


Overall it is concluded that the risk characterisation conclusion is sufficiently conservative in respect of any uncertainties and therefore further in vivo 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 and Chapters 9 and 10 of the Chemical Safety Report, respectively.