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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:
June 7, 1999 to Aug. 23, 1999
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
GLP compliance:
yes
Analytical monitoring:
yes
Details on sampling:
-Pretests:
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 4.0 and 50°C: 6.50, 9.00, 15.30, 20.20 and 24.40 h
Test 1 at pH 7.0 and 50°C: 2.00, 3.00, 3.50, 4.50 and 5.50 h
Test 3 at pH 4.0 and 60°C: 0.17, 4.00, 7.50, 17.70 and 19.40 h
Test 3 at pH 4.0 and 70°C: 0.08, 4.50, 5.00 and 6.00 h
Test 3 at pH 7.0 and 60°C: 0.17, 0.75, 1.50 and 2.50 h
Test 3 at pH 7.0 and 70°C: 0.08, 0.33 and 0.50 h
Buffers:
- pH: pH 4, 7 and 9
-pH 4:
21.008 g citric acid monohydrat were dissolved in 200 mL sodium hydroxide solution (c=1 mole/L). This solution was filled up to a volume of 1,000 mL with distilled water. 44 mL of hydrochloric acid (c=1 mole/L) were added to 560 mL of this solution and filled up to a volume of 1,000 mL with distilled water. For performing the hydrolysis the solution was refluxed and the pH value was adjusted to pH 4 for the each hydrolysis temperature.

- pH 7:
13.61 g potassium dihydrogen phosphate were dissolved in 1,000 mL distilled water. 29.63 mL of sodium hydroxide solution (c=1 mole/L) were added to 500 mL of this solution and filled up to a volume of 1,000 mL with distilled water. For performing the hydrolysis the solution was refluxed and the pH value was adjusted to pH 7 for each hydrolysis temperature.

- pH 9:
7.46 g potassium chloride and 6.184 g boric acid were dissolved in 1,000 mL water. 500 mL of this solution were added to 21.3 mL sodium hydroxide (c=1 mole/L) and filled up to a volume of 1,000 mL with water. For performing the hydrolysis the solution was refluxed and the pH value was adjusted to pH 9.0 for the each hydrolysis temperature.
Details on test conditions:
Choice of Concentration:
The optimal concentration of the test substance required for the analysis varied between 136 and 257 mg/L. This value is less than half of the solubility in water and thus satisfies the requirements of the guidelines.

Preparation of Test Samples:
Solutions of the test substance were prepared by weighing between 7 and 13 mg of the test substance in a 50 mL volumetric flask and dissolving in the relevant buffer. The resulting solution was subjected immediately to the hydrolysis procedure.

Preparation of the Standards:
The calculation standards were freshly prepared by weighing between 7 and 13 mg of the standard test substance in a 50 mL volumetric flask and dissolving in the buffer pH 4 or pH 7.

Hydrolysis Test Procedure:
The flask containing the hydrolysis mixture was placed in a thermostatically controlled water bath at the selected temperature for the specified time. Thereafter it was cooled immediately. The pH was controlled. The HPLC analysis of the unhydrolysed test substance (main compound) was performed without any delay.
Positive controls:
no
Preliminary study:
The decomposition at pH 9 was higher than 50% after 2.4 h at 50°C. Thus the test substance was considered hydrolytically instable at pH 9. According to the guideline a half-life period of less than 1 d under environmental conditions (25°C) was estimated. The pretests at pH 4 and at pH 7 indicated that an examination of the hydrolysis kinetics is essential.
Transformation products:
not specified
% Recovery:
>= 93.4 - <= 94
St. dev.:
0.3
pH:
4
Temp.:
50 °C
Duration:
2.4 h
% Recovery:
>= 7.1 - <= 7.7
St. dev.:
0.3
pH:
4
Temp.:
50 °C
Duration:
5 d
% Recovery:
>= 65.4 - <= 66.3
St. dev.:
0.4
pH:
7
Temp.:
50 °C
Duration:
2.4 h
% Recovery:
>= 0.7 - <= 1.3
St. dev.:
0.3
pH:
7
Temp.:
50 °C
Duration:
5 d
% Recovery:
>= 0.45 - <= 0.46
St. dev.:
0.1
pH:
9
Temp.:
50 °C
Duration:
2.4 h
% Recovery:
>= 0.06 - <= 0.36
St. dev.:
0.2
pH:
9
Temp.:
50 °C
Duration:
5 d
pH:
4
Temp.:
50 °C
Hydrolysis rate constant:
0.025 h-1
DT50:
27.63 h
Type:
(pseudo-)first order (= half-life)
pH:
4
Temp.:
60 °C
Hydrolysis rate constant:
0.056 h-1
DT50:
12.45 h
Type:
(pseudo-)first order (= half-life)
pH:
4
Temp.:
70 °C
Hydrolysis rate constant:
0.133 h-1
DT50:
5.21 h
Type:
(pseudo-)first order (= half-life)
pH:
7
Temp.:
50 °C
Hydrolysis rate constant:
0.186 h-1
DT50:
3.73 h
Type:
(pseudo-)first order (= half-life)
pH:
7
Temp.:
60 °C
Hydrolysis rate constant:
0.637 h-1
DT50:
1.08 h
Type:
(pseudo-)first order (= half-life)
pH:
7
Temp.:
70 °C
Hydrolysis rate constant:
1.634 h-1
DT50:
0.42 h
Type:
(pseudo-)first order (= half-life)
Key result
pH:
4
Temp.:
25 °C
DT50:
12.9 d
Type:
(pseudo-)first order (= half-life)
Remarks on result:
other: extrapolated according to the Arrhenius equation
Key result
pH:
7
Temp.:
25 °C
DT50:
3.4 d
Type:
(pseudo-)first order (= half-life)
Remarks on result:
other: extrapolated according to the Arrhenius equation
Key result
pH:
9
Temp.:
25 °C
DT50:
< 1 d
Remarks on result:
other: based on preliminary study

Table 1: Summary and extrapolation of the hydrolysis results at pH 4

 Temperature  Half life  Experiment
 50°C  27.63 h  test 1
 60°C  12.45 h  test 3
 70°C  5.21 h  test 3
 25°C  310.4 h = 12.9 d  extrapolation

           

 Table 2: Summary and extrapolation of the hydrolysis results at pH 7

Temperature  Half life  Experiment
 50°C  3.73 h  test 1
 60°C  1.08 h  test 3
 70°C  0.42 h  test 3
 25°C  82.1 h = 3.4 d  extrapolation
Validity criteria fulfilled:
yes
Conclusions:
Under the test conditions, the extrapolated half-life for hydrolysis of the test substance was found to be 12.9 and 3.4 d at pH 4 and at pH 7, respectively.
Executive summary:

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

Based on the results of a preliminary test which demonstrated test substance decomposition to be higher than 50% after 2.4 h at pH 9 and 50°C, the test substance was considered hydrolytically instable at pH 9. According to the guideline a half-life period of less than 1 d under environmental conditions (25°C) was estimated at pH 9. The pretests at pH 4 and at pH 7 indicated that examination of the hydrolysis kinetics was essential. Hence a main study was conducted at pH 4 and 7.

 

At pH 4 the half-life period was determined by extrapolating the results of the experiments at 50, 60 and 70°C to a temperature of 25°C. It was found to be 12.9 d. At pH 7 the extrapolated half-life at the temperature of 25°C was found to be 3.4 d.

 

Under the test conditions, the extrapolated half life for hydrolysis of the test substance was found to be 12.9 and 3.4 d at pH 4 and at pH 7 respectively.

Description of key information

Under the test conditions, at pH 4 the half-life period was determined by extrapolating the results of the experiments at 50, 60 and 70°C to a temperature of 25°C. It was found to be 12.9 d. At pH 7 the half-life period was determined by extrapolating the results of the experiments at 50, 60 and 70°C to a temperature of 25°C. It was found to be 3.4 d.

Key value for chemical safety assessment

Half-life for hydrolysis:
3.4 d
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 EU Method C.7 and in compliance with GLP. Based on the results of a preliminary test which demonstrated test substance decomposition to be higher than 50% after 2.4 h at pH 9 and 50°C, the test substance was considered hydrolytically instable at pH 9. According to the guideline a half-life period of less than 1 d under environmental conditions (25°C) was estimated at pH 9. The pretests at pH 4 and at pH 7 indicated that examination of the hydrolysis kinetics was essential. Hence a main study was conducted at pH 4 and 7. At pH 4 the half-life period was determined by extrapolating the results of the experiments at 50, 60 and 70°C to a temperature of 25°C. It was found to be 12.9 d. At pH 7 the extrapolated half-life at the temperature of 25°C was found to be 3.4 d. Under the test conditions, the extrapolated half life for hydrolysis of the test substance was found to be 12.9 and 3.4 d at pH 4 and at pH 7 respectively.

(Muhlberger, 1999).