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Hydrolysis

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Reference
Endpoint:
hydrolysis
Type of information:
experimental study
Adequacy of study:
key study
Study period:
From June 20, 2006 to July 17, 2006
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
EU Method C.7 (Degradation: Abiotic Degradation: Hydrolysis as a Function of pH)
Deviations:
no
Qualifier:
according to guideline
Guideline:
OECD Guideline 111 (Hydrolysis as a Function of pH)
Deviations:
no
GLP compliance:
yes (incl. QA statement)
Radiolabelling:
no
Analytical monitoring:
yes
Details on sampling:
Preliminary tests:
pH 4.0 and 50°C: 2.4 and 120 h
pH 7.0 and 50°C: 2.4 and 120 h
pH 9.0 and 50°C: 2.4 and 120 h

Main test:
Test 1 at pH 7.0 and 50°C: 1.3, 2.6, 4.3, 6.1, 22 and 23 h
Test 1 at pH 7.0 and 70°C: 0.3, 0.4, 0.7, 0.9, 1.3, 1.7 and 2.0 h
Test 1 at pH 7.0 and 30°C: 19, 26.3, 43, 66.2, 89.9, 97.6 and 165.3 h

Buffers:
pH 4, 7 and 9
Details on test conditions:
Preparation of the Test Samples:
Solutions of the test item were prepared by weighing about 0.39 g to 0.45 g of the test item in 50 mL volumetric flasks and dissolving the test item in the relevant buffers. This preparation was done in a glove box filled with nitrogen.

Hydrolysis Procedure:
The flasks containing the hydrolysis mixtures were placed in a thermostatically controlled water bath at the selected temperature for the specified time.

METHOD
Pretests:
- The pretests were done at 50±0.5°C with buffers at pH 4, 7 and 9.

Test 1:
- At 50±0.5°C with buffer at pH 7. At least 6 aliquots were taken between a decomposition rate of 10 and 90%.
- At 70±0.5°C with buffer at pH 7. At least 6 aliquots were taken between a decomposition rate of 10 and 90%.
- At 30±0.5°C with buffer at pH 7. At least 6 aliquots were taken between a decomposition rate of 10 and 90%.

Each sample was measured twice.
Duration:
5 d
pH:
4
Temp.:
50 °C
Initial conc. measured:
7.89 g/L
Duration:
5 d
pH:
7
Temp.:
50 °C
Initial conc. measured:
8.29 g/L
Duration:
5 d
pH:
9
Temp.:
50 °C
Initial conc. measured:
7.67 g/L
Duration:
23 h
pH:
7
Temp.:
50 °C
Initial conc. measured:
8.12 g/L
Duration:
2 h
pH:
7
Temp.:
70 °C
Initial conc. measured:
8.32 g/L
Duration:
165.3 h
pH:
7
Temp.:
30 °C
Initial conc. measured:
8.4 g/L
Number of replicates:
Preliminary Test: All experiments were run in duplicates
Main test: All experiments were run in duplicates

Positive controls:
no
Negative controls:
no
Transformation products:
not measured
pH:
4
Temp.:
50 °C
DT50:
> 120 h
Remarks on result:
other: Based on the preliminary test, the degree of hydrolysis was <10 % within 120 h
pH:
7
Temp.:
50 °C
DT50:
> 2.4 - < 120 h
Remarks on result:
other: Based on the preliminary test, the degree of hydrolysis was 21.6% at 2.4 h and >99% at 121 h.
pH:
7
Temp.:
50 °C
Hydrolysis rate constant:
0.093 h-1
DT50:
7.4 h
Type:
(pseudo-)first order (= half-life)
Remarks on result:
other: Correlation coefficient (r) = 0.999
pH:
7
Temp.:
70 °C
Hydrolysis rate constant:
1.05 h-1
DT50:
0.7 h
Type:
(pseudo-)first order (= half-life)
Remarks on result:
other: Correlation coefficient (r) = 0.999
pH:
7
Temp.:
30 °C
Hydrolysis rate constant:
0.007 h-1
DT50:
97.1 h
Type:
(pseudo-)first order (= half-life)
Remarks on result:
other: Correlation coefficient (r) = 0.999
pH:
7
Temp.:
25 °C
Hydrolysis rate constant:
0.003 h-1
DT50:
204 h
Remarks on result:
other: Calculated by extrapolation. Correlation coefficient (r) = 0.999
pH:
9
Temp.:
50 °C
DT50:
< 2.4 h
Remarks on result:
other: Based on the preliminary test
Details on results:
- At pH 4, less than 10% of the reaction was observed after 120 h (5 d) at 50°C (half life >1 y). Thus the test substance was considered hydrolytically stable and according to the guidelines no additional testing was required.
- The decomposition at pH 7 was below 50% after 2.4 h at 50°C and above 10% after 120 h (5 d) at 50°C. Therefore, examination of the hydrolysis kinetics was essential. For pH 7 at 25°C, the half-life was determined by extrapolation of the results of the experiments at 30, 50 and 70°C, and was found to be 204 h (8.5 d).
- At pH 9, more than 50 % of the reaction was observed after 2.4 h at 50°C. Thus the test substance was considered hydrolytically unstable and according to the guidelines no additional testing was required.

TABLE 1: PRELIMINARY TEST

 

Test conditions

Time point (h)

% hydrolysis

Comment

Test at pH 4.0 and 50°C

2.4

-

Further testing not required as the degree of hydrolysis was lower than 10% within 120 h.

120

5.07

Test at pH 7.0 and 50°C

2.4

21.6

Further testing necessary as the degree of hydrolysis was lower than 50% within 2.4 h and higher than 10% within 120 h.

120

>99.0

Test at pH 9.0 and 50°C

2.4

>99.0

No further testing necessary as the degree of hydrolysis was higher than 50% within 2.4 h.

120

>99.0

 

 

 TABLE 2: MAIN TEST

 

Test conditions

Kobs

t1/2

Comment

Test 1 at pH 7.0 and 50°C

0.093 h-1

7.4 h

Results indicated a pseudo first order reaction.

Test 1 at pH 7.0 and 70°C

1.05 h-1

0.7 h

 Results indicated a pseudo first order reaction.

Test 1 at pH 7.0 and 30°C

0.0071 h-1

97.1 h

Results indicated a pseudo first order reaction.

 

Validity criteria fulfilled:
yes
Conclusions:
Under the conditions of the study, the half-life of the test substance at pH 7 was found to be 7.4 h, 0.7 h and 97.1 h at 50, 70 and 30°C, respectively. 
From these results, the rate constant at pH 7 and 25°C was calculated to be 0.0034 h-1, leading to a half-life of 204 h.
Executive summary:

A study was conducted to determine hydrolysis as a function of pH for the test substance according to EU Method C.7 and OECD Guideline 111, in compliance with GLP.

 

Based on the results of a preliminary test which demonstrated >50% hydrolysis within 2.4 h at pH 9.0 and <10% hydrolysis within 120 h (5 d) at pH 4.0, additional testing was only required at pH 7. Results of the main test (Test 1) at pH 7 demonstrated a pseudo first order reaction at 30, 50 and 70°C. From the results, the rate constant (Kobs) and the half-life (t1/2) of the test substance were derived or calculated for different temperatures at pH 7.

Under the conditions of the study, the half-life of the test substance at pH 9 was <2.4 h and at pH 4 was >120 h. The half-life of the test substance at pH 7 was found to be 7.4 h, 0.7 h and 97.1 h at 50, 70 and 30°C, respectively.

From these results, the rate constant at pH 7 and 25°C was calculated to be 0.0034 h-1, leading to a half-life of 204 h.

Description of key information

The rate constant for hydrolysis at pH 7 and 25°C was calculated to be 0.0034/h, leading to a half-life of 204 h.

Key value for chemical safety assessment

Half-life for hydrolysis:
204 h
at the temperature of:
25 °C

Additional information

A study was conducted to determine hydrolysis as a function of pH for the test substance according to EU Method C.7 and OECD Guideline 111, in compliance with GLP. Based on the results of a preliminary test which demonstrated >50% hydrolysis within 2.4 h at pH 9.0 and <10% hydrolysis within 120 h (5 d) at pH 4.0, additional testing was only required at pH 7. Results of the main test (Test 1) at pH 7 demonstrated a pseudo first order reaction at 30, 50 and 70°C.From the results, the rate constant (Kobs) and the half-life (t1/2) of the test substance were derived or calculated for different temperatures at pH 7. Under the conditions of the study, the half-life of the test substance at pH 9 was <2.4 h and at pH 4 was >120 h. The half-life of the test substance at pH 7 was found to be 7.4 h, 0.7 h and 97.1 h at 50, 70 and 30°C, respectively. From these results, the rate constant at pH 7 and 25°C was calculated to be 0.0034 h-1, leading to a half-life of 204 h (Moller, 2006a).