Triethoxysilane

Ecotoxicological Summary

Hazard for aquatic organisms

Freshwater

Hazard assessment conclusion:

PNEC aqua (freshwater)

PNEC value:

0.96 mg/L

Assessment factor:

50

Extrapolation method:

assessment factor

PNEC freshwater (intermittent releases):

2.75 mg/L

Marine water

Hazard assessment conclusion:

PNEC aqua (marine water)

PNEC value:

0.79 mg/L

Assessment factor:

500

Extrapolation method:

assessment factor

STP

Hazard assessment conclusion:

PNEC STP

PNEC value:

580 mg/L

Assessment factor:

10

Extrapolation method:

assessment factor

Sediment (freshwater)

Hazard assessment conclusion:

PNEC sediment (freshwater)

PNEC value:

3.6 mg/kg sediment dw

Extrapolation method:

equilibrium partitioning method

Sediment (marine water)

Hazard assessment conclusion:

PNEC sediment (marine water)

PNEC value:

2.9 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:

0.63 mg/kg soil dw

Hazard for predators

Secondary poisoning

Hazard assessment conclusion:

no potential for bioaccumulation

Additional information

Measured short-term data at three trophic levels are available for triethoxysilane and the structurally analogous substance trimethoxysilane; with exposure being to the hydrolysis products of the substances. However, these are limit values only, showing no effects at the highest concentration tested. This means that a true PNEC cannot be calculated; only a value indicative of the lower limit of possible values for PNEC can be derived.

The rapid hydrolysis of triethoxysilane (half-life 1 h) means that environmental exposure assessment needs to be carried out for the hydrolysis products rather than the substance. Therefore, value of PNEC_aquatic(freshwater) for the hydrolysis product is needed. REACH guidance (ECHA 2010A, R.16) states that “for substances where hydrolytic DT₅₀is less than 12 hours, environmental effects are likely to be attributed to the hydrolysis product rather than to the parent itself”. TGD and ECHA guidance (EC 2003, ECHA 2010A) also suggest that when the hydrolysis half-life is less than 12 hours, the breakdown products, rather than the parent substance, should be evaluated for aquatic toxicity. Therefore, the environmental hazard assessment, including sediment and soil compartments due to water and moisture being present, is based on the properties of the hydrolysis products, in accordance with REACH guidance.

Triethoxysilane hydrolyses to form both silanetriol and ethanol. As silanetriol will break down further into inorganic, naturally occurring substances such as silica and silica acid, it is more appropriate to base the hazard assessment on ethanol as it is a still a conservative approach to use the effect concentrations of the hydrolysis product ethanol for derivation of PNECs.

The SIDS for ethanol (CAS 64-17-5) provides an in-depth review of the data available on the substance. The short term data reviewed in the SIDS indicates that all three taxonomic groups exposed to ethanol produced L(E)C₅₀values of ≥1000 mg/l. For fish a short term toxicity value of >100 mg/l is also available, however, this was a static test which is not recommended for a volatile substance such as ethanol. Additionally, >100 mg/l is a limit value and other short term toxicity studies conducted in flow-through test systems indicate LC₅₀values to be in the range 11 200-14 200 mg/l. It is therefore plausible to expect the LC₅₀value in the static test to have been in excess of 1000 mg/l should the range of exposure concentrations have been higher. Therefore, the most susceptible groups were equally invertebrates and algae with L(E)C₅₀values of 1000 mg/l.

The lowest reliable long term toxicity data reported in the SIDS for ethanol and on the ECHA homepage (Ethanol dossier) are a 10 d NOEC 9.6 mg/l and a 7 d NOEC 280 mg/l with invertebrates and higher vascular plants respectively.

The 9.6 mg/l NOEC is used to derive a PNEC with an assessment factor (AF) of 10 since long term toxicity data with the three taxonomic groups are available. Therefore, a PNEC_{aqua freshwater}of 0.96 mg/l is determined.

Data for saltwater species (NOEC of 79 mg/l for Palaemonetes pugio) were also available for ethanol and were used for the PNEC_{marine water}.

The documented PNECs are considered adequate for the present REACH risk characterisation. They have been calculated using the current ECHA guideline, including the most conservative assessment factors.

Conclusion on classification

Measured short-term data at three trophic levels are available for triethoxysilane and the structurally analogous substance trimethoxysilane; with exposure being to the hydrolysis products of the substances. These results, showing no effects at the highest concentration tested.According to Directive 67/578/EEC and Regulation (EC) No 1272/2008 classification criteria, no classification is required for triethoxysilane because the short-term toxicity data available on the substance indicate that EC/LC₅₀are in excess of 100 mg/l. The substance hydrolyses rapidly to silanetriol and ethanol. Silanetriol is an inorganic substance which is expected to enter natural biogeochemical cycles; Silanetriol will break down further into inorganic, naturally occurring substances such as silica and silica acid. Ethanol is known to biodegrade rapidly. The log K_owof the hydrolysis products is low and bioaccumulation is not expected.