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One short-term study with terrestrial plants is available for tetramethylsilane (TMS, CAS 75-76-3; EC No. 200-899-1).

 

A NOEC value of 10 ppm (by volume) has been determined for the effects of tetramethylsilane on growth of Avena sativa and Lepidium sativum. 17-day EC40 and EC53 values of 124 ppm have also been determined for effects on growth of the two species. The test organisms were exposed to the substance in gaseous phase using gaseous exposure chambers.

 

No data are available for the toxicity of the substance to terrestrial invertebrates or soil microorganisms. Testing for toxicity to soil organisms is not considered necessary because:

 

In accordance with Column 2 of REACH Annex X, there is no need to further investigate the effects of this substance in a terrestrial toxicity 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 Ratios (RCRs) are well below 1, even with due consideration of contributing uncertainties, and therefore the risk is already adequately controlled and further testing is not justifiable.

 

The substance is not readily biodegradable but has a low log Kow value <3 (2.7), therefore, partitioning to the terrestrial compartment is expected to be minimal.

 

Tetramethylsilane (CAS 75-76-3; EC No. 200-899-1) is highly volatile with a boiling point of 27°C and a vapour pressure of 79500 Pa at 20°C indicating that exposure of the terrestrial compartment will be minimal. Distribution modelling of the substance in a sewage treatment plant (STP) indicates that tetramethylsilane will partition mostly to air. In addition, tetramethylsilane has a calculated Henry’s Law constant of 2.4E+5 Pa m3mol-1 suggesting that air will be the main compartment to which it partitions, therefore exposure of the terrestrial compartment will be minimal.

It would be extremely challenging to maintain meaningful concentrations of the test substance in terrestrial test systems. Tetramethylsilane has a Kair-soil value of 3.6 at 12°C (4.2 at 25°C) and a vapour pressure of 79500 Pa at 20°C.

Soil testing according to guideline methods does not allow for re-application of test substance to the soil. OECD 222 earthworm toxicity guidance suggests cut-off values of Kair-soil = 1 and a vapour pressure of 300 Pa before testing is technically not feasible. Conducting terrestrial ecotoxicity tests with this substance would therefore present considerable technical challenges due to the extreme volatility of the substance and the need for closed systems.

In addition, the substance is highly volatile and extremely flammable and therefore conducting terrestrial testing could be considered to present too much of a risk.