2,4-Hexadienoic acid, 3-(trimethoxysilyl)propyl ester, (2E,4E)-

Ecotoxicological Summary

Hazard for aquatic organisms

Freshwater

Hazard assessment conclusion:

PNEC aqua (freshwater)

PNEC value:

0.019 mg/L

Assessment factor:

1 000

Extrapolation method:

assessment factor

PNEC freshwater (intermittent releases):

0.19 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:

1.7 mg/L

Assessment factor:

10

Extrapolation method:

assessment factor

Sediment (freshwater)

Hazard assessment conclusion:

PNEC sediment (freshwater)

PNEC value:

0.069 mg/kg sediment dw

Extrapolation method:

equilibrium partitioning method

Sediment (marine water)

Hazard assessment conclusion:

PNEC sediment (marine water)

PNEC value:

0.007 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 for bioaccumulation

Additional information

The hydrolysis half-life of 3-(trimethoxysilyl)propyl-(2E,4E)-hexa-2,4-dienoate is 4.7 h at pH 7 and 25°C. It has a measured water solubility of 442 mg/l and log K_ow of 3.09. The registration substance will hydrolyse in contact with water and atmospheric moisture to 3-(trihydroxysilyl)propyl-(2E,4E)-2,4-hexadienoate and methanol.

 

3-(Trihydroxysilyl)propyl-(2E,4E)-2,4-hexadienoate has a high predicted water solubility of 1.0E+06 mg/l, limited to approximately 1000 mg/l by condensation reactions, and a low predicted log K_ow of -0.3.

 

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 Section 4.8, the silanol hydrolysis products may be susceptible to condensation reactions.

 

Consideration of the non silanol hydrolysis product methanol

Methanol is well characterised in the public domain literature and is not hazardous at the concentrations relevant to the studies; the short-term EC₅₀ and LC₅₀ values for this substance is in excess of 1000 mg/l (OECD 2004 - SIDS for methanol, CAS 67-56-1). Therefore, at the loading rates experienced in these tests it is unlikely that the presence of methanol would significantly affect the results of the tests.

Conclusion on classification

The substance has reliable short-term E(L)C₅₀ values of 19 mg/l in fish, >22 mg/l in invertebrates and >76 mg/l in algae expressed in terms of the hydrolysis product 3-(trihydroxysilyl)propyl-(2E,4E)-2,4-hexadienoate. It has reliable a NOEC of 76 mg/l in algae and reliable a long-term EC₁₀ of 1.9 mg/l in Daphnia, also expressed in terms of the hydrolysis product 3-(trihydroxysilyl)propyl-(2E,4E)-2,4-hexadienoate.

The substance hydrolyses rapidly in water and is not readily biodegradable. The log K_ow of the silanol hydrolysis product is -0.3.

The most sensitive species tested was fish. The long-term data do not represent this species, therefore it may be concluded that adequate chronic toxicity data are not available. This would lead to the following classification, using the LC₅₀ value obtained in the short-term fish study of 19 mg/l, under Regulation (EC) No 1272/2008 (as amended) (CLP):

Acute toxicity: Not classified.

Chronic toxicity: Category Chronic 3.

(Under GHS outside the EU, an acute toxicity classification (Category Acute 3) may be applied.)