3-chloropropyltrimethoxysilane

Endpoint summary

Additional information

Approach to the Terrestrial Chemical Safety Assessment

 

No long-term terrestrial toxicity data are available with (3-chloropropyl)trimethoxysilane (CAS 2530-87-2).

The registered substance will hydrolyse rapidly (half-life 4.5 hours at pH 7 at 20°C) in contact with water and atmospheric moisture to (3-chloropropyl)silanetriol and methanol. Therefore the terrestrial chemical safety assessment for (3-chloropropyl)trimethoxysilane is based on its hydrolysis products (3-chloropropyl)silanetriol and methanol. These form the basis of the chemical safety assessment and are assessed separately.

 

(3-Chloropropyl)silanetriol:

 

(3-Chloropropyl)silanetriol is highly water soluble, has low potential for bioaccumulation and low potential for adsorption (based on log K_ow <3 (-1.1) and log K_oc 0.45) and there is no reason to expect any specific mechanism of toxicity beyond narcosis.

 

In the context of the Integrated Testing Strategy for the terrestrial compartment (ECHA guidance Chapter R.7c, terrestrial hazard classification scheme, Table R.7.11-2) (ECHA 2017) the aquatic toxicity tests do not indicate that the substance is very toxic (EC/LC₅₀ >1 mg/l for algae, Daphnia and fish). However, despite rapid degradation of the parent substance, the silanol hydrolysis product, (3-chloropropyl)silanetriol, is not readily biodegradable and may persist in the environment. The substance is therefore assigned to Hazard Category 3.

 

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)silanetriol is derived from the long-term test results with algae and has a value of 0.37 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)trimethoxysilane (CAS 2530-87-2), the highest terrestrial PECx10/PNECscreen(EQPM) for (3-chloropropyl)silanetriol is 0.044 x 10 = RCR 0.44.

A confirmatory long-term terrestrial toxicity test is therefore required in accordance with the recommendations for hazard category 3 substances.

In addition, toxicity was observed in the aquatic microorganism test, read across from a structural analogue, dichloro(3-chloropropyl)methylsilane (CAS 7787-93-1) (3 hour EC₅₀ value of 400 mg/l and EC₁₀ value of 197 mg/l (ASRI) (Werner, 1997)). ECHA guidance Chapter R.7c states “Where inhibition of sewage sludge microbial activity has been observed in Annex VIII testing, a test on soil microbial activity will additionally be necessary for a valid PNEC to be derived.” A toxicity to soil microorganisms test is therefore also required.

  

However, 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 given in Annex 5 of the CSR and attached in Section 13 of IUCLID.

 

In addition, 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. For this value to be more conservative than the PNECsoil derived by the equilibrium partitioning method, the NOEC derived in the terrestrial test would have to be ≤37 mg/kg dw. There is no basis to expect such toxicity for (3-chloropropyl)silanetriol based on the absence of significant toxicity observed in aquatic tests and the low potential for adsorption to and bioaccumulation in soil.  

 

In the case of (3-chloropropyl)silanetriol, 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 is currently not necessary.

 

Details on how the PNEC and the risk characterisation ratio have been derived can be found in IUCLID Section 6.0, and Chapters 7, 9 and 10 of the Chemical Safety Report.

 

 

References

ECHA (2017). Guidance on Information Requirements and Chemical Safety Assessment. Chapter R.7c: Endpoint specific guidance. Version 3.0 June 2017.