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Hydrolysis

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Reference
Endpoint:
hydrolysis
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
OECD Guideline 111 (Hydrolysis as a Function of pH)
Deviations:
no
Qualifier:
according to guideline
Guideline:
EU Method C.7 (Degradation: Abiotic Degradation: Hydrolysis as a Function of pH)
Deviations:
no
GLP compliance:
yes (incl. QA statement)
Specific details on test material used for the study:
Batch: CDD-005
Radiolabelling:
no
Analytical monitoring:
yes
Details on sampling:
For both the tier 1 and 2 tests, the concentration of the sample solutions was determined by high performance liquid chromatography (HPLC).
Buffers:
- pH: 4
- Type and final molarity of buffer: 0.006, 0.004 and 0.007 mol/dm^-3 for the 3 components below respectively.
- Composition of buffer: Citric acid, sodium chloride and sodium hydroxide.

- pH: 7
- Type and final molarity of buffer: 0.003, 0.002 and 0.002 mol/dm^-3 for the 3 components below respectively.
- Composition of buffer: Disodium hydrogen orthophosphate (anhydrous), Potassium dihydrogen orthophosphate and sodium chloride.

- pH: 9
- Type and final molarity of buffer: 0.001 and 0.002 mol/dm^-3 for the 2 components below respectively.
- Composition of buffer: Disodium tetraborate and sodium chloride.
Details on test conditions:
Tier 1 study: Sample solutions were prepared in stoppered glass flasks at a nominal concentration of 4.0 g/L in the three buffer solutions. A 1% co-solvent of acetonitrile was used to aid solubility. The concentration of each solution did not exceed the lesser of 0.01 mol/L or half the water solubility. The test solutions were split into individual vessels for each data point. The solutions were shielded from light whilst maintained at the test temperature. Sample solutions prepared at pH 4, 7 and 9 were maintained at 50.0 ± 0.5 °C for a period of 120 hours.


Tier 2 study: Results from the tier 1 test showed it was necessary to undertake further testing at pH 4, pH 7 and pH 9, with solutions being maintained at 50.0 ± 0.5°C, 60.0 ± 0.5°C and 70.0 ± 0.5°C for a period of 407, 383 and 144 hours respectively. The further testing was required due to hydrolysis from tier 1 testing being greater than 10% after 5 days (120 hours).

Duration:
407 h
pH:
4
Temp.:
50 °C
Initial conc. measured:
4 mg/L
Duration:
407 h
pH:
7
Temp.:
50 °C
Initial conc. measured:
4 mg/L
Duration:
407 h
pH:
9
Temp.:
50 °C
Initial conc. measured:
4 mg/L
Duration:
383 h
pH:
4
Temp.:
60 °C
Initial conc. measured:
4 mg/L
Duration:
383 h
pH:
7
Temp.:
60 °C
Initial conc. measured:
4 mg/L
Duration:
383 h
pH:
9
Temp.:
60 °C
Initial conc. measured:
4 mg/L
Duration:
144 h
pH:
4
Temp.:
70 °C
Initial conc. measured:
4.06 mg/L
Duration:
144 h
pH:
7
Temp.:
70 °C
Initial conc. measured:
4.06 mg/L
Duration:
144 h
pH:
9
Temp.:
70 °C
Initial conc. measured:
4.06 mg/L
Number of replicates:
2 per concentration
Positive controls:
no
Negative controls:
no
Preliminary study:
Results from the tier 1 testing showed it was necessary to undertake further tier 2 testing as hydrolysis was observed to be >10% after 120 hours.

Tier 1 testing provided an approximate half life of 380 hours, therefore testing at temperatures of lower than 25 °C was not carried out as there would be an insufficient rate of hydrolysis to complete testing within the recommended 30 days testing within the guidelines. Therefore the temperatures of 50 °C, 60 °C and 70 °C were chosen to maintain testing within the timeframe.
Transformation products:
not measured
Key result
pH:
4
Temp.:
25 °C
Hydrolysis rate constant:
0 s-1
DT50:
765 d
Type:
(pseudo-)first order (= half-life)
Key result
pH:
7
Temp.:
25 °C
Hydrolysis rate constant:
0 s-1
DT50:
666 d
Type:
(pseudo-)first order (= half-life)
Key result
pH:
9
Temp.:
25 °C
Hydrolysis rate constant:
0 s-1
DT50:
600 d
Type:
(pseudo-)first order (= half-life)
Details on results:
The kinetics of the study have been determined to be consistent with that of a pseudo-first order reaction as the graphs of log10 concentration versus time are straight lines.

No significant peaks were observed at the approximate retention time of the test item on analysis of any matrix blank solutions.

It has been observed that the rate of hydrolysis increases with an increase in pH.

The rate constant and estimated half-life at 25 °C of the test item are shown in the following

table:

pH

Rate constant (s-1)

Estimated half-life at 25°C (hours)

Estimated half-life at 25°C (days)

4

1.05 x 10-8

1.84 x 104hours

765

7

1.20 x 10-8

1.60 x 104hours

666

9

1.34 x 10-8

1.44 x 104hours

600

Validity criteria fulfilled:
yes
Conclusions:
Under the conditions of this study, the rate constants and estimated half-lives of the test material can be seen in the table of the 'any other information on results incl. tables' field. This provided a half life of between 600 and 765 days in a pH range of 4-9.

Description of key information

One experimental study was conducted (according to OECD testing guideline 111) to determine the hydrolytic-stability of the test substance at varying pH.

Key value for chemical safety assessment

Half-life for hydrolysis:
666 d
at the temperature of:
25 °C

Additional information

Under the conditions of this study, the rate constants and estimated half-lives of the test material can be seen in the following table:

pH

Rate constant (s-1)

Estimated half-life at 25°C (hours)

Estimated half-life at 25°C (days)

4

1.05 x 10-8

1.84 x 104hours

765

7

1.20 x 10-8

1.60 x 104hours

666

9

1.34 x 10-8

1.44 x 104hours

600

This provided a half life of between 600 and 765 days in a pH range of 4-9.

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