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Environmental fate & pathways

Hydrolysis

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Reference
Endpoint:
hydrolysis
Type of information:
experimental study
Adequacy of study:
key study
Study period:
05 May - 15 October 2008
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
Radiolabelling:
no
Analytical monitoring:
yes
Details on sampling:
Preliminary test - Tier 1
Test substance solutions were prepared in the buffer solutions at a nominal concentration of approximately 2400 mg/l. Each solution was filter-sterilised through a 0.2 µm membrane filter and transferred into a sterile glass vessel. To exclude oxygen, nitrogen gas was purged through the solution for 5 minutes. For each sampling time, vessels were filled in duplicate with 3 ml test solution, sealed and placed in the dark in a temperature controlled environment at 50.07°C +/- 0.05°C.
The concentration of the test substance in the test samples was determined immediately after preparation (t=0) and after 5 days. The samples taken at t=5 days were cooled to room temperature using running tap water. The samples were diluted in a 3:1 (v:v) ratio with methanol, 25-times further diluted with 25/75 (v/v) methanol/water and analysed.
Blank buffer solutions were treated similarly as the test samples and analysed at t=0.
The pH of each of the test solutions (except for the blanks) was determined at each sampling time.

Main study - Tier 2
Test substance solutions were prepared in the buffer solution pH 9 at a nominal concentration of approximately 2400 mg/l. Each solution was filter-sterilised through a 0.2 µm membrane filter and transferred into a sterile glass vessel. To exclude oxygen, nitrogen gas was purged through the solution for 5 minutes. For each sampling time, vessels were filled in duplicate with 4 ml test solution, sealed and placed in the dark in a temperature controlled environment. The study was performed at the following temperatures:
Temperature I: 20.0°C +/- 0.7°C
Temperature II: 49.9°C +/- 0.1°C
Temperature III: 59.8°C +/- 0.2°C

The concentrations of the test substance were determined immediately after preparation (t=0) and at several sampling points after t=0. The samples taken at t > 0 were cooled to room temperature using running tap water. The samples were diluted in a 3:1 (v:v) ratio with methanol and further diluted with 25/75 (v/v) methanol/water to obtain concentration within the calibration range.
The samples not analysed on the sampling day were stored in the freezer. Storage stability under these conditions was determined by the analysis of additional accuracy samples prepared at half the nominal concentration of the test samples (results are archived in the raw data). On the day of analysis, the frozen samples were defrosted at room temperature, treated and analysed.
Blank buffer solutions were treated similarly as the test samples and analysed at t=0.
The pH of each of the test solutions (except for the blanks) was determined at each sampling time.
With a sterility confirmation test at the end of the study it was demonstrated that the rate of hydrolysis of the test substance was determined accordingly.
Buffers:
Acetate buffer pH 4, 0.05 M
solution of 16.6% 0.05 M sodium acetate and 83.4% 0.05 M acetic acid.

Phosphate buffer pH 7, 0.05 M
solution of 0.05 M potassium dihydrogenphosphate adjusted to pH 7 using 1 N sodium hydroxide.

Borate buffer pH 9, 0.05 M
solution of 0.05 M boric acid and 0.05 M potassium chloride adjusted to pH 9 using 1 N sodium hydroxide
Number of replicates:
Calibration solutions were injected in duplicate. Test samples were analysed by single injection.
Positive controls:
no
Negative controls:
yes
Remarks:
Blank buffer solutions
Preliminary study:
At pH 4 and pH 7 a degree of hydrolysis of < 10% was observed after 5 days. It demonstrated that the half-life time of the test substance at 25°C is > 1 year. According to the guideline, no further tests were required.

At pH 9 a degree of hydrolysis of 93% after 5 days was observed. According to the guideline, the higher Tier test was required to determine the half-life time of the test substance.

A small response at the retention time of the test substance was observed in the chromatograms of the blank buffer solutions. It was considered to derive from the matrixes since it was not observed in the analytical blanks of 25/75 (v/v) methanol/water. The maximum contribution of the response to the peak area of the test substance was 0.11%. Based on this it was not considered to significantly interference the responses of the test substance.

The mean recoveries of the buffer solutions fell well within the criterion range of 90-110%. It demonstrated that the analytical method was adequate to support the hydrolysis study on the test substance.
Transformation products:
no
Key result
pH:
4
Temp.:
25 °C
DT50:
> 1 yr
Type:
(pseudo-)first order (= half-life)
Key result
pH:
7
Temp.:
25 °C
DT50:
> 1 yr
Type:
(pseudo-)first order (= half-life)
Key result
pH:
9
Temp.:
20 °C
DT50:
91 d
Type:
(pseudo-)first order (= half-life)
Key result
pH:
9
Temp.:
25 °C
DT50:
43 d
Type:
(pseudo-)first order (= half-life)
Key result
pH:
9
Temp.:
50 °C
DT50:
1.5 d
Type:
(pseudo-)first order (= half-life)
Key result
pH:
9
Temp.:
60 °C
DT50:
12 h
Type:
(pseudo-)first order (= half-life)
Other kinetic parameters:
For testing of pseudo-first order kinetics the mean logarithms of the relative concentrations between 10% and 90% were plotted against time. At all temperatures linear relationships were obtained. The half-life times of the test substance were determined according to the model for pseudo-first order reactions.
Details on results:
A small response at the retention time of the test substance was observed in the chromatograms of the blank solutions. It was considered to derive from the matrixes since it was not observed in the analytical blanks of 25/75 (v/v) methanol/water. It did not affect the results of the main test since matrix-matched calibration solutions were applied.

The mean recoveries of the buffer solutions fell well within the criterion range of 90-110%. It demonstrated that the analytical method was adequate to support the hydrolysis study on the test substance.
Validity criteria fulfilled:
yes
Conclusions:
The preliminary test (Tier 1) and main study (Tier 2) were performed for the determination of the rate of hydrolysis of the test substance at pH values normally found in the environment (pH 4-9). The half-life times of the test substance were:
Hydrolysis at pH 4: t½ > 1 year at 25°C
Hydrolysis at pH 7: t½ > 1 year at 25°C
Hydrolysis at pH 9:
t½ = 91 days at 20°C
t½ = 43 days at 25°C
t½ = 1.5 days at 50°C
t½ = 12 hours at 60°C

Description of key information

The preliminary test (Tier 1) and main study (Tier 2) were performed for the determination of the rate of hydrolysis of the test substance at pH values normally found in the environment (pH 4-9). The half-life times of the test substance were:

Hydrolysis at pH 4: t½ > 1 year at 25°C

Hydrolysis at pH 7: t½ > 1 year at 25°C

Hydrolysis at pH 9:

t½ = 91 days at 20°C

t½ = 43 days at 25°C

t½ = 1.5 days at 50°C

t½ = 12 hours at 60°C

Key value for chemical safety assessment

Half-life for hydrolysis:
1 yr
at the temperature of:
25 °C

Additional information