Triethoxy(3-thiocyanatopropyl)silane

Endpoint summary

Additional information

No terrestrial toxicity data are available for the registered substance.

Triethoxy(3-thiocyanatopropyl)silane has a half-life of 23 hours at pH 7 and 25 °C, which indicates that the substance will be completely hydrolysed to triethoxy(3-thiocyanatopropyl)silanetriol and ethanol by the time the substance reaches the terrestrial compartment. Therefore, the terrestrial assessment is based on the hydrolysis products.

Consideration of the Si hydrolysis product: triethoxy(3-thiocyanatopropyl)silanetriol

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 degradation of the parent substance, the silanol hydrolysis product may persist in the environment. The substance is therefore assigned to Hazard Category 3.

In this situation, a screening approach is applied, where the equilibrium partitioning risk assessment approach is applied with an extra factor of ten and, in addition, a confirmatory long-term terrestrial test is to be conducted:

PEC/PNECscreen:

The PEC × 10 / PNECscreen based on the equilibrium partitioning method (EPM) indicates the substance will have a risk characterisation ratio (RCR) >1. The highest terrestrial RCR is 8.48 in agricultural soil.

Confirmatory long-term test:

An OECD 222 study with earthworms is proposed with the registered substance.

In addition, ECHA guidance Chapter R.7c, Table R.7.11—2 states the following: "If PEC/PNECscreen > 1 or indication of risk from confirmatory long-term soil toxicity test: Conduct long-term toxicity tests according to the standard information requirements Annex IX or X (invertebrates and plants), choose lowest value for derivation of PNECsoil". The PEC/PNECscreen is >1, which indicates that standard information requirements according to Annex IX or X should be conducted. However, a long-term aquatic toxicity study with invertebrates, OECD 211, is proposed, which is likely to affect the PEC/PNECscreen. Therefore, it is proposed to review the results of the screening assessment once the OECD 211 and 222 study results are available, before concluding on the need to conduct an OECD 208 long-term toxicity to terrestrial plants study.

Furthermore, toxicity was observed in the aquatic microorganism test (3 hour EC₅₀ 130 mg/L; EC₁₀ 4.3 mg/L (activated sludge respiration inhibition)). 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 soil microorganisms nitrogen inhibition test (OECD 216) is therefore also proposed.

In the meantime, a PNEC and the risk characterisation ratio have been derived based on EPM, details of which can be found in IUCLID Section 6.0 and Chapters 9 and 10 of the Chemical Safety Report, respectively.

Consideration of the non-Si hydrolysis product: ethanol

Due to the volatile nature of ethanol, it is considered unlikely that it would reach the terrestrial compartment. In addition, ethanol is considered to be of low toxicity to terrestrial organisms in the public domain literature and is not hazardous at the concentrations relevant to the studies relevant to Annex IX requirements. Some studies also indicate potentially stimulating effects to plants - although the significance of the studies is doubtful (OECD 2004 SIDS for ethanol, CAS 64-17-5).