Tetramethylsilane

Ecotoxicological Summary

Hazard for aquatic organisms

Freshwater

Hazard assessment conclusion:

PNEC aqua (freshwater)

PNEC value:

0.002 mg/L

Assessment factor:

1 000

Extrapolation method:

assessment factor

PNEC freshwater (intermittent releases):

0.019 mg/L

Marine water

Hazard assessment conclusion:

PNEC aqua (marine water)

PNEC value:

0 mg/L

Assessment factor:

10 000

Extrapolation method:

assessment factor

STP

Hazard assessment conclusion:

PNEC STP

PNEC value:

1.71 g/L

Assessment factor:

10

Extrapolation method:

assessment factor

Sediment (freshwater)

Hazard assessment conclusion:

PNEC sediment (freshwater)

PNEC value:

0.054 mg/kg sediment dw

Extrapolation method:

equilibrium partitioning method

Sediment (marine water)

Hazard assessment conclusion:

PNEC sediment (marine water)

PNEC value:

0.005 mg/kg sediment dw

Extrapolation method:

equilibrium partitioning method

Hazard for air

Air

Hazard assessment conclusion:

no hazard identified

Hazard for terrestrial organisms

Soil

Hazard assessment conclusion:

PNEC soil

PNEC value:

0.036 mg/kg soil dw

Extrapolation method:

equilibrium partitioning method

Hazard for predators

Secondary poisoning

Hazard assessment conclusion:

no potential for bioaccumulation

Additional information

The registered substance, tetramethylsilane (CAS 75-76-3; EC No. 200-899-1), is a volatile liquid at standard temperature and pressure, with a vapour pressure of approximately 79500 Pa at 20°C. The high volatility of the substance makes water-based properties difficult to measure. However, the substance has a predicted log K_ow of 2.7 at 20°C (QSAR) and a predicted water solubility of 19.6 mg/l at 20°C. In addition, reliable analytical measurements of the substance were carried out in ecotoxicological test media. In the algal study (Springborn Smithers 2010), the maximum achievable exposure concentration under testing conditions (standard closed system, minimal headspace, 23°C) was 0.078 mg/l at test start and 0.0079 mg/l geometric mean over 72 hours.

In the acute fish study (Springborn Smithers 2010), the maximum achievable exposure concentration under testing conditions (specially designed closed system, zero headspace, 14°C) was reported as 3.6 mg/l.

In contact with water, tetramethylsilane is not susceptible to hydrolysis due to the presence of stable Si-C and C-H bonds.

 

The high volatility of the substance (boiling point = 27°C, measured; vapour pressure = 79500 Pa at 20°C) and its slight solubility in water (water solubility = 19.6 mg/l (estimated)) indicate that exposure of the aquatic and terrestrial compartments 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 aquatic compartment will be minimal.

 

Short term aquatic toxicity data are available for the substance. The tests were designed as closed systems in order to minimize losses through volatilisation. No long-term aquatic tests nor terrestrial tests are available.

Conclusion on classification

Tetramethylsilane (CAS 75-76-3; EC No. 200-899-1) has reliable short-term E(L)C₅₀ values of 1.9 mg/l in fish, >103 mg/l in invertebrates and >0.0079 mg/l in algae, as well as an algal NOEC value of ≥0.0079 mg/l.

The substance is not biodegradable and may persist in the environment.

These data are consistent with the following classification under Regulation (EC) No 1272/2008 (as amended) (CLP):

Acute toxicity: Not classified.

Chronic toxicity: Chronic Category 2, H411: Hazardous to the aquatic environment.