Triethylsilane

Ecotoxicological Summary

Hazard for aquatic organisms

Freshwater

Hazard assessment conclusion:

PNEC aqua (freshwater)

PNEC value:

0.001 mg/L

Assessment factor:

500

Extrapolation method:

assessment factor

PNEC freshwater (intermittent releases):

0.012 mg/L

Marine water

Hazard assessment conclusion:

PNEC aqua (marine water)

PNEC value:

0 mg/L

Assessment factor:

5 000

Extrapolation method:

assessment factor

STP

Hazard assessment conclusion:

PNEC STP

PNEC value:

100 mg/L

Assessment factor:

10

Extrapolation method:

assessment factor

Sediment (freshwater)

Hazard assessment conclusion:

PNEC sediment (freshwater)

PNEC value:

0.012 mg/kg sediment dw

Extrapolation method:

equilibrium partitioning method

Sediment (marine water)

Hazard assessment conclusion:

PNEC sediment (marine water)

PNEC value:

0.001 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:

0.003 mg/kg soil dw

Extrapolation method:

equilibrium partitioning method

Hazard for predators

Secondary poisoning

Hazard assessment conclusion:

no potential to cause toxic effects if accumulated (in higher organisms) via the food chain

Additional information

The registration substance triethylsilane (CAS No. 617-86-7) has a predicted log K_ow of 3.6, a predicted water solubility of 2 mg/l at 20°C and a low molecular weight (116.28 g/mol). The hydrolysis half-life of triethylsilane is approximately 377 h at pH 7 and 20˚C. The substance will react in water to form triethylsilanol and hydrogen. Triethylsilanol has a high predicted water solubility of 1E+06 mg/l, though this may be limited by condensation reactions, and low predicted log K_ow of 2.6.

Triethylsilane (CAS No 617-86-7) is a silane with three ethyl groups bound to the silicon atom. The environmental hazard assessment, including sediment and soil compartments, is primarily based on the properties of the registration substance, in accordance with REACH guidance (ECHA 2016). As described in Section 4.8 of IUCLID and 1.3 of the CSR, the silanol hydrolysis product may be susceptible to condensation reactions.

The registration substance is part of a class of low-functionality compounds acting via a non-polar narcosis mechanism of toxicity. The group of organosilicon substances in this group contain alkyl, aryl, alkoxy or hydroxy groups attached to the silicon atom when present in aqueous solution. Secondary features may be present in the alkyl chain (e.g. halogen, nitrile, unsaturated bonds) that do not affect the toxicity of the substances.

 

Consideration of the non-silanol hydrolysis product:

The other hydrolysis product hydrogen gas, is a ubiquitous element present in the atmosphere at 0.55 ppmV. Any anthropogenic contribution of hydrogen gas to the atmosphere from hydrolysis of trimethylsilanol is negligible therefore the substance is not considered in the risk assessment.

Conclusion on classification

The substance has reliable short-term E(L)C₅₀ values of >0.263 mg/l in fish, 0.577 mg/l in invertebrates and 1.14 mg/l in algae. It has a reliable NOEC of 0.127 and EC₁₀ of 0.636 mg/l in algae.

The substance hydrolyses slowly in water and is not readily biodegradable. It has a log K_ow of 3.6.

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

Acute toxicity: Category Acute 1; M-factor of 1

Chronic toxicity: Category Chronic 1; M-factor of 1

The classification of Chronic Category 1 is derived from the short-term data in accordance with CLP guidance Table 4.1.0 b iii:

Substances for which adequate chronic toxicity data are not available...and the substance is not rapidly degradable...Category Chronic 1: E(L)₅₀ <=1 mg/l.

Because the most sensitive species in the short-term tests was Daphnia, the algal NOEC is not deemed "adequate" chronic toxicity data and the classification is based on the Daphnia EC₅₀ of 0.566 mg/l.

An M-factor of 1, using the acute toxicity value, has been applied.