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

Ecotoxicological Summary

Hazard for aquatic organisms

Freshwater

Hazard assessment conclusion:

PNEC aqua (freshwater)

PNEC value:

0.016 mg/L

Assessment factor:

1 000

Extrapolation method:

assessment factor

PNEC freshwater (intermittent releases):

0.16 mg/L

Marine water

Hazard assessment conclusion:

PNEC aqua (marine water)

PNEC value:

0.002 mg/L

Assessment factor:

10 000

Extrapolation method:

assessment factor

STP

Hazard assessment conclusion:

PNEC STP

PNEC value:

76.3 mg/L

Assessment factor:

10

Extrapolation method:

assessment factor

Sediment (freshwater)

Hazard assessment conclusion:

PNEC sediment (freshwater)

PNEC value:

0.063 mg/kg sediment dw

Extrapolation method:

equilibrium partitioning method

Sediment (marine water)

Hazard assessment conclusion:

PNEC sediment (marine water)

PNEC value:

0.006 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:

0.004 mg/kg soil dw

Extrapolation method:

equilibrium partitioning method

Hazard for predators

Secondary poisoning

Hazard assessment conclusion:

no potential for bioaccumulation

Additional information

The registration substance [3‑(2,3‑epoxypropoxy)propyl]diethoxy(methyl)silane (CAS 2897-60-1) is a diethoxysilane with methyl and 3-(2,3-epoxypropoxy)propyl side-chains. It has predicted water solubility of 1200 mg/l and log K_ow of 2.7 at 20°C, a measured vapour pressure of 0.42 Pa at 25°C and predicted hydrolysis half-lives at 20-25°C of 0.4 hours at pH 4, 11.7 hours pH 7 and 0.2 hours at pH 9. [3‑(2,3‑Epoxypropoxy)propyl]diethoxy(methyl)silane will hydrolyse in contact with water and atmospheric moisture to [3-(2,3-epoxypropoxy)propyl]methylsilanediol (1 mole) and ethanol (2 moles).

However, regarding the predicted hydrolysis half-life, data for a structurally similar substance has shown that QSAR might underestimate the hydrolysis half-life as the QSAR values for this similar substance were predicted to be significantly lower than those from the respective measured OECD 111 hydrolysis rate study. Taking this into account, as well as the experimental fish, aquatic invertebrates and algal toxicity studies which estimated the hydrolysis half-life to be 2 -3 hours in the respective test media, it can be expected that hydrolysis half-life for the registered substance (pH7, 25°C) is indeed <12 h.

REACH guidance (ECHA 2016, R.16) states that “for substances where hydrolytic DT₅₀ is 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 2016) 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 silanol hydrolysis product, in accordance with REACH guidance. As described in Sections 1.3 and 4.1 of the CSR (4.8 and 5.1.2 of IUCLID), the silanol hydrolysis products may be susceptible to condensation reactions as well as subsequent hydrolysis reactions of the epoxide functional group.

The silanol hydrolysis product, [3-(2,3-epoxypropoxy)propyl]methylsilanediol, has a high predicted water solubility of 1E+06 mg/l, but this is limited to around 1000 mg/l by condensation reactions, low predicted log K_ow of -0.7 and low predicted vapour pressure of 2.8E-04 Pa. 

During the tests with the registration substance, [3-(2,3-epoxypropoxy)propyl]diethoxy(methyl)silane (CAS 2897-60-1), it is likely that the test organisms were exposed to a mixture of the hydrolysis products of the substance and the parent substance. The fish and invertebrate study reports conclude that the substance had a hydrolysis half-life of approximately 3 hours under the test conditions, attributed by the reviewer to the elevated pH conditions of the test media (pH 7.7 - 8.2). The stability analyses conducted in the algal test showed the test material to be unstable in culture medium over the 72-hour test period and that the half-life of the test material was determined to be approximately 2 hours, again attributed to the elevated pH (pH 7.8 - 8.2). It is reasonable to conclude, for the reasons discussed above, that the test organisms were predominantly exposed to the hydrolysis products of the test substance.

  

There are no reliable microorganism toxicity data available for [3-(2,3-epoxypropoxy)propyl]diethoxy(methyl)silane (CAS 2897-60-1), therefore good quality data for the structurally-related substance, [3-(2,3-epoxypropoxy)propyl]triethoxysilane (CAS 2602-34-8), have been read across. Both substances hydrolyse rapidly and have silanol hydrolysis products that share epoxide as a functional group; the justification for read across is discussed further in the IUCLID Section 6.1.7, Toxicity to Microrganisms, Endpoint Summary.

Conclusion on classification

The substance has reliable short-term E(L)C₅₀ values of 180 mg/l in fish, 20 mg/l in invertebrates and >32 mg/l in algae (139 mg/l, 15.5 mg/l and >25 mg/l, respectively, based on the hydrolysis product [3-(2,3-epoxypropoxy)propyl]methylsilanediol). It has a NOEC value of 3.2 mg/l, or 2.5 mg/l as [3-(2,3-epoxypropoxy)propyl]methylsilanediol, in algae.

The substance hydrolyses rapidly in water and is not readily biodegradable.

The hydrolysis product [3-(2,3-epoxypropoxy)propyl]methylsilanediol is susceptible to further hydrolysis reactions and the ultimate hydrolysis product 3-{3-[dihydroxy(methyl)silyl]propoxy}propane-1,2-diol is considered unlikely to exhibit significant ecotoxic effects based on QSAR estimated E(L)C₅₀s >>100 mg/l. The rate of reaction under environmental conditions is uncertain but the half-life is not expected to be more than a few days. It could be argued that [3-(2,3-epoxypropoxy)propyl]methylsilanediol meets the criteria of a ‘rapidly degradable’ substance in the context of classification and labelling for the environment; however, in the absence of definitive evidence, a precautionary approach has been applied.

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

Acute toxicity: Not classified.

Chronic toxicity: Category Chronic 3.