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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:
OECD Guideline 111 (Hydrolysis as a Function of pH)
Deviations:
no
Qualifier:
according to
Guideline:
EPA OPPTS 835.2120 (Hydrolysis of Parent and Degradates as a Function of pH at 25°C)
Deviations:
no
GLP compliance:
yes
Radiolabelling:
yes
Remarks:
labeled at pyridine-2,6-14C and fused pyrimidine-3-14C
Analytical monitoring:
yes
Duration:
5 d
pH:
4
Temp.:
50 °C
Initial conc. measured:
5 other: µg/mL
Duration:
5 d
pH:
7
Temp.:
50 °C
Initial conc. measured:
5 other: µg/mL
Duration:
5 d
pH:
9
Temp.:
50 °C
Initial conc. measured:
5 other: µg/mL
Number of replicates:
Two
Transformation products:
no
% Recovery:
>= 99.1 - <= 100.9
pH:
4
Temp.:
50 °C
Duration:
5 d
Remarks on result:
hydrolytically stable based on preliminary test
% Recovery:
>= 99.4 - <= 101.6
pH:
7
Temp.:
50 °C
Duration:
5 d
Remarks on result:
hydrolytically stable based on preliminary test
% Recovery:
>= 99.2 - <= 104.3
pH:
9
Temp.:
50 °C
Duration:
5 d
Remarks on result:
hydrolytically stable based on preliminary test
Key result
pH:
4
Temp.:
25 °C
DT50:
> 1 yr
Type:
other: hydrolytic half-life
Key result
pH:
7
Temp.:
25 °C
DT50:
> 1 yr
Type:
other: hydrolytic half-life
Key result
pH:
9
Temp.:
25 °C
DT50:
> 1 yr
Type:
other: hydrolytic half-life
Results with reference substance:
The amount of radioactivity recovered from LSC was compared with the amount of radioactivity injected to HPLC. The overall mean recovery of radioactivity from the analytical column was found to be 99.1%, within the acceptable limits of 90-110%.
Validity criteria fulfilled:
yes
Conclusions:
This study demonstrated that the test substance was hydrolytically stable at pH 4, 7, and 9. Hydrolysis did not occur for all pHs tested at 50°C. The hydrolytic half-life (t1/2) at 25°C is considered to be >1 year at pH 4, 7, and 9.
Executive summary:

The hydrolytic stability of 14C-test substance was investigated in sterile buffer solutions at pH 4, 7 and 9, which were incubated at 50 ± 0.5°C for 5 days according to the guidelines OECD 111 and U.S. EPA OPPTS 835.2120.

Solutions of 14C-test substance were prepared in 0.01 M acetate buffer (pH 4), 0.01 M phosphate buffer (pH 7) and 0.01 M borate buffer (pH 9) at a nominal test concentration of 5 µg/mL, which was less than one-half of the solubility of the test substance in each of these buffers.

At selected time intervals, samples were analyzed directly by LSC to determine the quantity of radioactivity present in each sample. Radioactivity was quantitatively recovered from each test solution, with recoveries ranging from 99.1 to 104.3%.

Test solutions were subjected to chromatographic analysis (HPLC) to investigate the nature of any hydrolysis products formed. The hydrolysis of the test substance at 50 ± 0.5°C after 5 days of incubation was <10% in pH 4, 7 and 9 buffer solutions.

The test substance was considered to be stable at pH 4, 7, and 9 and no further tests were performed.

Based on the results of this study, hydrolysis is not expected to be a route of degradation of the test substance in the environment.

Endpoint:
hydrolysis
Type of information:
experimental study
Adequacy of study:
supporting study
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to
Guideline:
other: OECD 507 Nature of the Pesticide Residues in Processed Commodities - High Temperature Hydrolysis (16 October 2007)
Deviations:
no
GLP compliance:
yes
Radiolabelling:
yes
Remarks:
Three radiolabelled forms of the test substance, [pyridine-2,6-14C], [fused pyrimidine-5-14C] and [methylene-14C] were tested.
Analytical monitoring:
yes
Details on sampling:
- Sampling intervals: pH 4: Samples heated for 20 min, then allowed to return to room temperature; pH 5: Samples heated for 60 min, then allowed to return to room temperature; pH 6: Samples heated for 20 min, then allowed to return to room temperature.
- Sample storage conditions before analysis: Samples analyzed on the same day. Sub-samples were stored frozen after the initial analysis at less than -10°C.
Buffers:
- pH: Aqueous buffers at pH 4, 5, and 6
- Type and final molarity of buffer: A final buffer concentration of 0.01 M was selected in order to minimize possible catalytic effects
- Composition of buffer: pH 4: 33 mL of 0.1 M citric acid solution and 17 mL of 0.1 M sodium citrate solution were added to a volumetric flask, and made up to 500 mL with Milli-Q water and mixed. This prepared buffer solution was sonicated for about 5 minutes and the pH of the prepared buffer solution was adjusted to 4.01 using a pre-calibrated pH meter by drop-wise addition of 0.1 M citric acid solution.
pH 5: 20.5 mL of 0.1 M citric acid solution and 29.5 mL of 0.1 M sodium citrate solution were added to a volumetric flask, and made up to 500 mL with Milli-Q water and mixed. This prepared buffer solution was sonicated for about 5 minutes and the pH of the prepared buffer solution was adjusted to 5.02 using a pre-calibrated pH meter by drop-wise addition of 0.1 M citric acid solution.
pH 6: 9.5 mL of 0.1 M citric acid solution and 41.5 mL of 0.1 M sodium citrate solution were added to a volumetric flask, and made up to 500 mL with Milli-Q water and mixed. This prepared buffer solution was sonicated for about 5 minutes and the pH of the prepared buffer solution was adjusted to 6.02 using a pre-calibrated pH meter by drop-wise addition of 0.1 M citric acid solution.
Details on test conditions:
TEST SYSTEM
- Type, material and volume of test flasks, other equipment used: Aqueous buffers at pH 4, 5, and 6 Amber glass vials/vessels
- Sterilisation method: Autoclaving for glasswar. All buffer solutions were sterilized by passing through a 0.2-µm sterilized filters. The experiment was performed in a laminar flow chamber under aseptic condition.
- Measures to exclude oxygen: The dissolved gases in the prepared buffer solutions were removed by sonicating the solutions for 5 minutes before adding the test substance
- Is there any indication of the test material adsorbing to the walls of the test apparatus: No significant loss of radioactivity due to adsorption to apparatus

TEST MEDIUM
- Volume used/treatment: 4.5 mL of sterile pH 4, 5, or 6 buffer containing approximately 5 μg/mL test substance
- Kind and purity of water: Milli-Q water
- Preparation of test medium: Test solutions were prepared by adding 3 aliquots of 83 µL each of the pyridine-2,6-14C, 3 aliquots of 88 µL each of fused pyrimidine-3-14C and methylene-14C of 14C-test substance stock solutions into nine 25 mL volumetric flasks. The contents of each flask were evaporated to dryness using a gentle stream of nitrogen. About 15 mL aliquot of the respective buffer solutions were added to each flask. Each flask was then sonicated for a minute and then brought to volume using the respective buffer solutions of pH 4, 5, and 6. The flasks were stoppered and mixed thoroughly.
- Identity of co-solvent: Acetonitrile

OTHER TEST CONDITIONS
- Adjustment of pH: The pH of each buffer solution was measured at the time of preparation and after addition of the test substance.
Duration:
20 min
pH:
4
Temp.:
90 °C
Initial conc. measured:
5 other: µg/mL
Duration:
60 min
pH:
5
Temp.:
100 °C
Initial conc. measured:
5 other: µg/mL
Duration:
20 min
pH:
6
Temp.:
120 °C
Initial conc. measured:
5 other: µg/mL
Number of replicates:
Three
Transformation products:
no
Details on hydrolysis and appearance of transformation product(s):
The test substance is hydrolytically stable, therefore no hydrolysis pathway is proposed.
% Recovery:
>= 97.2 - <= 103.1
pH:
4
Temp.:
90 °C
Duration:
20 min
% Recovery:
>= 97.5 - <= 101.1
pH:
5
Temp.:
100 °C
Duration:
60 min
% Recovery:
>= 101 - <= 103.4
pH:
6
Temp.:
120 °C
Duration:
20 min
Details on results:
TEST CONDITIONS
- pH, sterility, temperature, and other experimental conditions maintained throughout the study: Yes

UNIDENTIFIED RADIOACTIVITY
- at pH5: An unknown peak was observed in the pyridine labeled test substance at a level of 1.2 and 1.1% AR at ‘0’ hour and after 60 minutes of incubation, respectively. An unknown peak was observed in the fused pyrimidine labeled test substance at a level of 1.1% AR after 60 minutes of incubation. No other radiolabeled components were detected in methylene label test substance.
Results with reference substance:
The amount of radioactivity recovered from LSC was compared with the amount of radioactivity injected to HPLC. The overall mean recovery of radioactivity from the analytical column was found to be 94.4%, within the acceptable limits of 90-110%.
Validity criteria fulfilled:
yes
Conclusions:
This study demonstrated that the test substance was hydrolytically stable under conditions representative of pasteurization (pH 4, 90 ± 5ºC, for 20 min.), baking (pH 5, 100 ± 5ºC, for 60 min.) and sterilization (pH 6, 120 ± 5ºC at 15 psi, for 20 min.).
Executive summary:

The hydrolytic stability of 14C-test substance was investigated in sterile buffer solutions at pH 4, 5, and 6, which were incubated at 90°C for 20 min (pH 4), 100°C for 60 min (pH 5) and 120°C under pressure (15 psi) for 20 min (pH 6) to represent pasteurization, baking/brewing/boiling and sterilization, respectively. This hydrolysis study was conducted to investigate the nature of potential residues in processed commodities under these conditions in accordance with the OECD Test Guideline 507.

Three radiolabelled forms of the test substance, [pyridine-2,6-14C]-test substance, [fused pyrimidine-5-14C]-test substance and [methylene-14C]-test substance were tested. Solutions of each radiolabel were prepared in 0.01M citrate buffer (pH 4, 5 and 6) at a nominal test concentration of 5 µg/mL, which is not more than one-half of the water solubility of the test substance.

At the end of the incubation period, samples were analyzed directly by LSC to determine the quantity of radioactivity present in each sample. Radioactivity was quantitatively recovered from each test solution. The mass balance is 99.7, 100.1 and 102.4%AR for the solutions under conditions representative of pasteurization (pH 4, 90ºC, for 20 min.), baking (pH 5, 100ºC, for 60 min.) and sterilization (pH 6, 120ºC at 15 psi, for 20 min.).

Test solutions were subject to chromatographic analysis (HPLC) to investigate the nature of any hydrolysis products formed. In all samples, the applied radioactivity was recovered as the test substance.

This study demonstrated that the test substance was hydrolytically stable under conditions representative of pasteurization (pH 4, 90ºC, for 20 min.), baking (pH 5, 100ºC, for 60 min.) and sterilization (pH 6, 120ºC at 15 psi, for 20 min.).

Description of key information

In a study conducted under OECD guideline 111, the test substance was hydrolytically stable at pH 4, 7, and 9. Hydrolysis did not occur for all pHs tested at 50°C. The half-life was considered to be > 1 year at 25°C.

Key value for chemical safety assessment

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

Additional information