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Environmental fate & pathways

Hydrolysis

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Description of key information

Based on the results of QSAR calculations and taken into account that for the main components (chain lengths ≥ C12) the solubility in water is negligible, hydrolysis of Glycerides, C8-18 and C18-unsatd. mono- and di-, acetates (CAS No. 91052-13-0) is not a relevant degradation pathway in the environment.

Key value for chemical safety assessment

Additional information

The UVCB substance Glycerides, C8-18 and C18-unsatd. mono- and di-, acetates (CAS No. 91052-13-0) consists of triglyceride acetates in multiple forms, which covers mono- and di-acetate isomers with alkane chain lengths from C8 to C18, predominantly C12. The dissolution behaviour of each component in aqueous solution varies depending on its molecular structure instead of its quantity contained in the registered substance. The water solubility study presented in IUCLID section 4.8 exhibits that the tested substance is sparing soluble within water. Based on the total peak area of GC chromatogram, the water solubility was determined as 8.75 mg/L at 20 °C. However, the comparison of the GC chromatograms between the dissolved and standard test substance reveals that major peak being attributed to the glycerides, C8 mono- and di-acetate, as well as a number of other unidentified species of low molecular weight. These chemical compositions in the soluble fraction are either molecules present in the test substance as minor components, or the hydrolysis products at a very low concentration level. The solubility of main components with increased chain length (≥ C12) is negligible.

A testing of hydrolysis as a function of pH according to OECD Guideline 111 was initiated, but could not be successfully completed due to the limitation analytical determination. Anyway, the preliminary test made it clear that the true dissolution of the test substance as such was not feasible at a concentration at which robust analytical data were attainable due to the poor solubility of the higher molecular weight components present dominantly in the test substance. The hydrolysis analysis based on minor components is considered to be neither representative nor reliable for this UVCB substance.

In place of experimental data, hydrolysis half-lives data at pH 7 and 8 for three individual components of Glycerides, C8-18 and C18-unsatd. mono- and di-, acetates, (8:2:2; 12:2:2; 14:12:2), were calculated by using the computer program HYDROWIN from SRC. The estimated half-life for the different components at pH 7 ranges from 164 days (8:2:2) to 373 days (14:12:2) and at pH 8 from 16.4 to 37.3 days.

Considering the hydrolysis property at pH 4, which is not provided directly by HYDROWIN, additional calculations using the web-based calculator SPARC were performed. These calculations take into account the following representative components of the UVCB substance: (a) C8 fatty acid mono- and diacetates as molecular structures representing the lower molecular weight components; (b) C12 and (c) C14 fatty acid mono- and diacetates representing the molecular structures of the main components. Furthermore, all these components exist as different isomers. Therefore, the SPARC calculations were done for all the relevant isomers mentioned below (for details see the attached document in the relevant endpoint study record in section 5.1.2):

Isomer 1: Diacetate components containing one octanoate, dodecanoate or tetradodecanate group between two acetoxygroups groups.

Isomer 2: Diacetate components containing one octanoate, dodecanoate or tetradodecanoate group and two acetoxygroups side by side.

Isomer 3: Monoacetate components containing one acetoxygroup and two octanoate, dodecanoate or tetradodecanoate groups side by side.

Isomer 4: Monoacetate components containing one acetoxygroup between two octanoate, dodecanoate or tetradodecanoate groups.

 

The calculated DT50 are summarized in the following table:

pH 4

pH 7

pH 9

[days]

[days]

[days]

Isomer 1 of

C8 FA diacetate

3815

538

5.4

C12 FA diacetate

3816

539

5.4

C14 FA diacetate

3816

539

5.4

 

Isomer 2 of

C8 FA diacetate

5099

575

5.8

C12 FA diacetate

5101

575

5.8

C14 FA diacetate

5101

575

5.8

 

Isomer 3 of

C8/C8 FA monoacetate

5925

769

7.7

C12/C12 FA monoacetate

5929

770

7.7

C14/C14 FA monoacetate

5929

770

7.7

 

Isomer 4 of

C8/C8 FA monoacetate

9729

846

8.5

C12/C12 FA monoacetate

9743

847

8.5

C14/C14 FA monoacetate

9743

847

8.5

 

The results show that the hydrolysis potential of the components varies obviously along with the stereo structure of the molecules and the positions of the functional groups. The hydrolysis process of the diacetate components with two acetoxygroups placing side by side is slower than the ones with one alkoxycarbonylgroup (C8, C12, C14) in between. The hydrolysis potential of the monoacetate components with one acetoxygroup between two alkoxycarbonylgroups (C8, C12, C14) is slower than the ones with two alkoxycarbonylgroups (C8, C12, C14) side by side.

Furthermore, significant differences can be found over the typical environmental pH values (from pH 4 to pH 9). The half-lives decrease from 10-27 yr at pH 4 to 1.5-2.3 yr at pH 7, and further to 5.4-8.5 days at pH 9. These results are in line with the results of the HYDROWIN calculation.    

Based on the results of the QSAR calculations above and taken into account that for the main components (chain lengths ≥ C12) the solubility in water is negligible, except under the alkaline conditions, hydrolysis of Glycerides, C8-18 and C18-unsatd. mono- and di-, acetates (CAS No. 91052-13-0) is not a relevant degradation pathway in the environment according to ECHA guidance document R.7b (ECHA 2012).