[3-(2,3-epoxypropoxy)propyl]triethoxysilane

Ecotoxicological Summary

Hazard for aquatic organisms

Freshwater

Hazard assessment conclusion:

PNEC aqua (freshwater)

PNEC value:

0.1 mg/L

Assessment factor:

1 000

Extrapolation method:

assessment factor

PNEC freshwater (intermittent releases):

1 mg/L

Marine water

Hazard assessment conclusion:

PNEC aqua (marine water)

PNEC value:

0.01 mg/L

Assessment factor:

10 000

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:

1.5 mg/kg sediment dw

Extrapolation method:

equilibrium partitioning method

Sediment (marine water)

Hazard assessment conclusion:

PNEC sediment (marine water)

PNEC value:

0.15 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:

0.24 mg/kg soil dw

Extrapolation method:

equilibrium partitioning method

Hazard for predators

Secondary poisoning

Hazard assessment conclusion:

no potential for bioaccumulation

Additional information

[3-(2,3-epoxypropoxy)propyl]triethoxysilane hydrolyses in the presence of water, including atmospheric moisture, to ultimately yield 2,3-dihydroxypropoxypropylsilanetriol and ethanol. The hydrolysis half-life is12 –36 hours at pH 7 and 25⁰C. However the ecotoxicity studies that are available for the registered substance were conducted at pH 8. At this pH the hydrolysis rate is expected to be 5 to 10 times faster and it is therefore likely that, under the static and semi-static exposure conditions of the aquatic toxicity tests reported in the following sections, the test organisms will have been predominately exposed to the hydrolysis products of the registered substance.

The properties of ethanol have been discussed extensively in the public literature. Ethanol is considered to be non-toxic to aquatic organisms at the concentrations at which it would have been present in the tests reviewed in this assessment; the short-term EC₅₀ and LC₅₀ values for ethanol are in excess of 1000 mg/l (OECD 2004a - SIDS for ethanol, CAS 64-17-5).

As a consequence of the above, the environmental hazard assessments that follow (including those for sediment and soil compartments) are based on the assumption that any observed effects are the result of exposure to a mixture of the registered substance, [3-(2,3-epoxypropoxy)propyl]triethoxysilane, the intermediate hydrolysis product [3-(2,3-epoxypropoxy)propyl)silanetriol and the ultimate silanol hydrolysis product, 2,3-dihydroxypropoxypropylsilanetriol.

There are two characteristics of the substance that are thought to confer toxicity to the substance: the presence of the epoxy group in the molecular structure and the log K_ow of the substance. Hydrolysis of the substance can occur at the epoxy group and at the alkoxy group. The hydrolysis of the epoxy group will result in an open ring, which is less reactive and less toxic. The hydrolysis of the alkoxy group will generate a silanetriol with a lower log K_ow and thus a less bioavailable form of the substance. The intermediate hydrolysis product 3-(2,3-epoxypropoxy)propyl)silanetriol is expected to be less toxic than the parent substance because even though the epoxy ring is still present it has a lower log K_ow value. Likewise, it is expected to be more toxic than the ultimate hydrolysis product because the epoxy ring is absent from the ultimate hydrolysis product and it has a lower log K_ow value. 

Conclusion on classification

Data available for structural analogue short-term toxicity to aquatic organisms show LC₅₀/EC₅₀ values to be in the range 1 to 10 mg/l. The hydrolysis product may persist in the environment, however the log K_ow values of the parent substance and its hydrolysis products are <3. It is therefore proposed that the substance is classified as Aquatic Chronic Category 2 according to Regulation (EC) No. 1272/2008.