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Hydrolysis

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Endpoint:
hydrolysis
Type of information:
experimental study
Adequacy of study:
key study
Study period:
01.06.2017 - 31.07.2017
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)
Radiolabelling:
no
Analytical monitoring:
yes
Details on sampling:
Three samples were analysed at the start of the experiments. Two separate tubes were analysed at each analytical occasion of hydrolysis test. One sample was taken from the control vessels.
The whole amount of the vials was transferred to the SPE cartridges. The eluate was analysed by GC.
Buffers:
pH 4.0: 1 mL 0.2 M Sodium hydroxide and 125 mL 0.2 M Potassium hydrogen phthalate were diluted to 500 mL with ultra-pure water.
pH 7.0: 74 mL 0.2 M Sodium hydroxide and 125 mL 0.2 M Potassium dihydrogen phosphate were diluted to 500 mL with ultra-pure water.
pH 9.0: 54 mL 0.2 M Sodium hydroxide and 125 mL 0.2 M Boric acid and Potassium chloride were diluted to 500 mL with ultra-pure water.
The pH of each buffer solution was checked with a calibrated pH meter. The required amount of the buffer solutions was prepared according to the above ratios.
Details on test conditions:
TEST SYSTEM
- Equipment used: screw cap headspace vials
Balances: PG 203 S, Mettler Toledo, No.: 1122082152 BP210D, Sartorius, No.: 60602907
SPE cartridges: Discovery DSC-18, 3mL/500mg, No.: SP8914B
pH meter: InoLab pH Level 2, No.: 03260014
Ultrasonic bath: Branson 3210-E-MT, No.: A700343D
Water purification system: MILLIPORE, DIRECT Q5, No.: F0DA13956K
Thermostat: OMH 400, Heratherm, No.: 41865966
Hot air steriliser: M-53, Binder, No.: 910243
- Temperature: pH 4: 40, 50 and 60 ± 0.5 °C; pH 7: 30, 40 and 50 ± 0.5 °C; pH 9: 10, 20 and 30 ± 0.5 °C
- Lighting: no
- Measures taken to avoid photolytic effects: The hydrolysis reaction was carried out using a dark thermostat to avoid photolytic effects
- Measures to exclude oxygen: Nitrogen was bubbled into the water for five minutes before the preparation of the solutions in order to exclude oxygen.

TEST MEDIUM
- Volume used/treatment: 20 mL
- Kind and purity of water: ultra-pure water from water purification system
- Preparation of test medium: 201.65 mg of test item was dissolved in 10 mL of acetonitrile.
- Renewal of test solution: no

OTHER TEST CONDITIONS
- Adjustment of pH: yes, with Sodium hydroxide
Duration:
646 h
pH:
4
Temp.:
40 °C
Initial conc. measured:
187 mg/L
Duration:
525 h
pH:
4
Temp.:
50 °C
Initial conc. measured:
187 mg/L
Duration:
164 h
pH:
4
Temp.:
60 °C
Initial conc. measured:
186 mg/L
Duration:
495.5 h
pH:
7
Temp.:
30 °C
Initial conc. measured:
206 mg/L
Duration:
495.5 h
pH:
7
Temp.:
40 °C
Initial conc. measured:
206 mg/L
Duration:
164 h
pH:
7
Temp.:
50 °C
Initial conc. measured:
187 mg/L
Duration:
215 h
pH:
9
Temp.:
10 °C
Initial conc. measured:
189 mg/L
Duration:
72 h
pH:
9
Temp.:
20 °C
Initial conc. measured:
214 mg/L
Duration:
27 h
pH:
9
Temp.:
30 °C
Initial conc. measured:
233 mg/L
Number of replicates:
3
Positive controls:
no
Negative controls:
no
Statistical methods:
The pseudo-first order rate constant (kobs) for each test temperature was determined from the plots of the natural logarithm of the concentration versus time. Applying the Arrhenius equation the rate constant k and half-life were calculated at 20 °C from the plot of ln k versus 1/T.
Preliminary study:
Based on the results of the preliminary test (please refer to IUCLID section 5.1.2) the hydrolysis rate of the test substance was found to be 32 % at pH 4, 89 % at pH 7 and >99 % at pH 9 after 5 days at 50 °C. Based on the results obtained, the test substance was considered as hydrolytically unstable at pH 4, pH 7 and pH 9 under the conditions investigated and the subsequent full test was initiated.
Test performance:
Test solutions were prepared by adding 200 µL of Stock Solution II to 20 mL of the buffer solutions (pH = 4, pH = 7, pH = 9) in screw cap headspace vials. Before vials were closed oxygen was removed by blowing nitrogen into the tubes. Acetonitrile content of the test solutions was 1 % (v/v). Nominal starting concentration test item in the buffer solutions was 0.2 mg/mL around 1.5 mM.

SPE tubes were conditioned with 3 mL of tetrahydrofuran, then 3 mL methanol and 3 mL ultrapure water. Then 20 mL of the test solution (the whole amount of the vial) was loaded to the packing together with 0.5 mL Internal Standard Stock Solution. Then it was dried. The cartridges were washed with 1 mL ultrapure water. The test item was eluted with 5 mL of acetonitrile. The eluate was analysed by GC.
Transformation products:
not measured
% Recovery:
51
pH:
4
Temp.:
40 °C
Duration:
646 h
% Recovery:
27
pH:
4
Temp.:
50 °C
Duration:
525 h
% Recovery:
21
pH:
4
Temp.:
60 °C
Duration:
164 h
% Recovery:
27
pH:
7
Temp.:
30 °C
Duration:
495.5 h
% Recovery:
3
pH:
7
Temp.:
40 °C
Duration:
495.5 h
% Recovery:
6
pH:
7
Temp.:
50 °C
Duration:
164 h
% Recovery:
15
pH:
9
Temp.:
10 °C
Duration:
215 h
% Recovery:
21
pH:
9
Temp.:
20 °C
Duration:
44.1 h
% Recovery:
15
pH:
9
Temp.:
30 °C
Duration:
27 h
Key result
pH:
4
Temp.:
20 °C
Hydrolysis rate constant:
0 h-1
DT50:
8 122 h
Type:
(pseudo-)first order (= half-life)
Key result
pH:
7
Temp.:
20 °C
Hydrolysis rate constant:
0.001 h-1
DT50:
784 h
Type:
(pseudo-)first order (= half-life)
Key result
pH:
9
Temp.:
20 °C
Hydrolysis rate constant:
0.022 h-1
DT50:
32 h
Type:
(pseudo-)first order (= half-life)
Details on results:
TEST CONDITIONS
- pH, sterility, temperature, and other experimental conditions maintained throughout the study: Yes

MAJOR TRANSFORMATION PRODUCTS
- Transformation products were not investigated

Measured data at pH 4


 






























































































































































































Temperature



Sampling time (hours)



Concentration
(mg/L)
n = 2



Hydrolysis
(%)



Measured pH



40 °C



Control buffer



-



-



4.00



Start



187 (n = 3)



-



4.01



22



184



2



4.02



120



158



16



4.00



166



158



15



4.03



222



140



26



4.02



239



141



25



4.01



311



134



28



4.04



484



105



44



4.00



646



95



49



4.01



50 °C



Control buffer



-



-



4.02



Start



187 (n = 3)



-



3.98



22



181



4



4.01



70



154



18



3.99



120



131



30



4.00



166



116



38



4.02



239



93.5



50



4.01



311



80.9



57



4.00



381



70.4



62



3.98



525



51.2



73



4.04



60 °C



Control buffer



-



-



4.03



Start



186 (n = 3)



-



4.02



3



188



0



4.02



20



166



11



4.02



29



139



25



4.01



52



121



35



4.02



75



95.3



49



4.03



92



83.2



55



4.02



164



39.8



79



4.01



 


Measured data at pH 7


 










































































































































































































Temperature



Sampling time (days)



Concentration
(mg/L)
n = 2



Hydrolysis
(%)



Measured pH



30 °C



Control buffer



-



-



7.04



Start



206 (n = 3)



-



7.02



15.5



190



8



7.04



47.5



178



14



7.00



88.5



163



21



6.97



160.5



140



32



7.03



230.5



104



49



7.04



333.5



92.9



55



7.04



423.5



71.2



65



7.03



495.5



56.3



73



7.00



40 °C



Control buffer



-



-



7.02



Start



206 (n = 3)



-



7.02



15.5



182



12



7.00



47.5



148



28



7.02



71.5



121



41



6.99



88.5



112



46



7.02



160.5



68.7



67



7.02



230.5



45.4



78



7.01



333.5



14.1



93



7.04



423.5



9.65



95



7.03



495.5



6.72



97



6.99



50 °C



Control buffer



-



-



7.04



Start



187



-



7.00



3



188



0



7.02



20



137



27



7.00



29



114



39



7.01



51.5



84.1



55



7.02



75



52.0



72



7.02



92



38.6



79



7.02



114



28.7



85



7.01



164



11.1



94



7.02



 


Measured data at pH 9


 












































































































































































Temperature



Sampling time (hours)



Concentration
(mg/L)
n = 2



Hydrolysis
(%)



Measured pH



10 °C



Control buffer



-



-



9.03



Start



189 (n = 3)



-



9.02



46



135



29



8.99



76



112



41



9.01



94



101



47



9.01



144



76.7



59



9.00



175



63.3



66



9.01



215



47.1



75



9.02



20 °C



Control buffer



-



-



9.00



Start



214



-



9.03



7



192



10



8.99



21



128



40



9.03



31



106



50



9.01



48



73.0



66



8.99



56



63.2



70



9.00



72



44.1



79



9.01



30 °C



Control buffer



-



-



8.98



Start



233



-



9.00



1.5



202



14



9.01



3



171



26



9.02



4.5



160



31



8.98



6



150



36



9.03



7.5



130



44



9.01



11.5



103



56



9.01



22



50.6



78



9.02



27



34.2



85



8.99



 


 



















































































Rate constants and half-lives based on the measured data



pH



Temperature



Slope



kobs, 1/h



t1/2



Regression Coefficient



4



40 °C



-0.00109



0.00109



639 h



0.984



50 °C



-0.00251



0.00251



276 h



0.992



60 °C



-0.00946



0.00946



73.3 h



0.996



7



30 °C



-0.00251



0.00251



276 h



0.992



40 °C



-0.00718



0.00718



96.6 h



0.991



50 °C



-0.01723



0.01723



40.2 h



0.999



9



10 °C



-0.00624



0.00624



111 h



0.997



20 °C



-0.02206



0.02206



31.4 h



0.997



30 °C



-0.06860



0.06860



10.1 h



0.998



 


 










































































































































Estimation of the half lives of the reaction at 20 °C



Temperature



1/T



pH 4



pH 7



pH 9



°C



(1/K)



kobs



ln k-



t1/2, h



kobs



ln k



t1/2, h



kobs



ln k



t1/2, h



10



0.00353



-



-



-



-



-



-



0.0062



-5.08



111



20



0.00341



-



-



-



-



-



-



0.0221



-3.81



31.4



30



0.00330



-



-



-



0.0025



-5.99



276



0.0686



-2.68



10.1



40



0.00319



0.0011



-6.83



639



0.0072



-4.94



96.6



-



-



-



50



0.00309



0.0025



-5.99



276



0.0172



-4.06



40.2



-



-



-



60



0.00300



0.0095



-4.66



73.3



-



-



-



-



-



-



20 (calculated)



 



8.5E-5



-9.37



8122



0.00088



-7.03



784



0.0217



-3.83



32



Constant



29.1



25.2



31.3



X coefficient



-11263



-9438



-10294



R Squared



0.979



0.999



1.000


Validity criteria fulfilled:
yes
Conclusions:
The calculated half lives of the hydrolysis reactions at pH 4, pH 7 and pH 9 are as follows:
t 1/2 at pH 4 and 20 °C: 8122 h
t 1/2 at ph 7 and 20 °C: 784 h
t 1/2 at pH 9 and 20 °C: 32 h
Executive summary:

A study was conducted according to Regulation (EC) No 440/2008 Part C.7 and OECD test guideline 111 to determine the hydrolysis of the test substance as a function of pH. The tier 1 test according to guideline was conducted and revealed that the test item is hydrolytically not stable at pH 4, 7 and 9. Thus, the subsequent Tier 2 test for the determination of the hydrolysis half-life was conducted. Hydrolysis was examined at three different pH values 4, 7 and 9 at three different temperatures: pH 4: 40, 50 and 60 ± 0.5 °C; pH 7: 30, 40 and 50 ± 0.5 °C; pH 9: 10, 20 and 30 ± 0.5 °C . The hydrolysis reaction was carried out using a dark thermostat to avoid photolytic effects. Three samples were analysed at the start of the experiments. Two separate tubes were analysed at each analytical occasion of hydrolysis test. One sample was taken from the control vessels. Samples are diluted or concentrated on SPE cartridges and then analysed by a GC – FID method in the presence of benzonitrile internal standard. The pseudo-first order rate constant (kobs) for each test temperature was determined from the plots of the natural logarithm of the concentration versus time. Applying the Arrhenius equation the rate constant k and half-life were calculated at 20 °C for pH 4 = 8.5E-5 h-1 and 8122 h, respectively, for pH 7 = 8.8E-4 h-1 and 784 h, respectively and for pH 9 = 0.0217 h-1 and 32 h, respectively.

Endpoint:
hydrolysis
Type of information:
experimental study
Adequacy of study:
supporting study
Study period:
2017-02 to 2017-4
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)
Qualifier:
according to guideline
Guideline:
EU Method C.7 (Degradation: Abiotic Degradation: Hydrolysis as a Function of pH)
GLP compliance:
yes (incl. QA statement)
Specific details on test material used for the study:
The test item was dissolved in acetonitrile.
Radiolabelling:
no
Analytical monitoring:
yes
Details on sampling:
- Sampling intervals: at start and at the end of test (5 days)
- Sampling method: grab samples
- Sampling times for pH measurements: at start and at the end of the test
Buffers:
- pH: 4
- Composition of buffer: 1 mL 0.2 M Sodium hydroxide and 125 mL 0.2 M Potassium hydrogen phthalate were diluted to 500 mL with ultra-pure water.

- pH: 7
- Composition of buffer: 74 mL 0.2 M Sodium hydroxide and 125 mL 0.2 M Potassium dihydrogen phosphate were diluted to 500 mL with ultra-pure water.

- pH: 4
- Composition of buffer: 54 mL 0.2 M Sodium hydroxide and 125 mL 0.2 M Boric acid and Potassium chloride were diluted to 500 mL with ultra-pure water.
Details on test conditions:
TEST SYSTEM
- Equipment used: screw cap headspace vials
Balances: PG 203 S, Mettler Toledo, No.: 1122082152 BP210D, Sartorius, No.: 60602907
SPE cartridges: Discovery DSC-18, 3mL/500mg, No.: SP8914B
pH meter: InoLab pH Level 2, No.: 03260014
Ultrasonic bath: Branson 3210-E-MT, No.: A700343D
Water purification system: MILLIPORE, DIRECT Q5, No.: F0DA13956K
Thermostat: OMH 400, Heratherm, No.: 41865966
Hot air steriliser: M-53, Binder, No.: 910243
- Temperature: 50 ° ± 0.5 °C
- Lighting: no
- Measures taken to avoid photolytic effects: The hydrolysis reaction was carried out using a dark thermostat to avoid photolytic effects
- Measures to exclude oxygen: Nitrogen was bubbled into the water for five minutes before the preparation of the solutions in order to exclude oxygen.

TEST MEDIUM
- Volume used/treatment: 20 mL
- Kind and purity of water: ultra-pure water from water purification system
- Preparation of test medium: 201.65 mg of test item was dissolved in 10 mL of acetonitrile.
- Renewal of test solution: no

OTHER TEST CONDITIONS
- Adjustment of pH: yes, with Sodium hydroxide
Duration:
5 d
pH:
4
Temp.:
50 °C
Initial conc. measured:
> 197 - < 212 mg/L
Duration:
5 d
pH:
7
Temp.:
50 °C
Initial conc. measured:
> 213 - < 222 mg/L
Duration:
5 d
pH:
9
Temp.:
50 °C
Initial conc. measured:
> 188 - < 219 mg/L
Number of replicates:
6
Positive controls:
no
Negative controls:
no
Statistical methods:
The chromatograms were evaluated with the help of TotalChrom™ chromatography software. Ratio of the peak areas (the test item and the internal standard) was calculated and used for the computations. Calculations were carried out using “EXCEL for Windows".
Preliminary study:
pH 4: 32 % hydrolysis
pH 7: 89 % hydrolysis
pH 9: >99 % hydrolysis
Transformation products:
no
% Recovery:
68
St. dev.:
2.9
pH:
4
Temp.:
50 °C
Duration:
5 d
% Recovery:
11
St. dev.:
0.46
pH:
7
Temp.:
50 °C
Duration:
5 d
% Recovery:
< 0.6
pH:
9
Temp.:
50 °C
Duration:
5 d
Remarks on result:
other: below limit of quantification
Details on results:
TEST CONDITIONS
- pH and temperature maintained throughout the study: Yes

At pH 4:
- Range of maximum concentrations at end of study period:
At the end of the study period, the concentrations were 131 - 147 mg/L.

At pH 7:
- Range of maximum concentrations at end of study period:
At the end of the study period, the concentrations were 22 - 25 mg/L.

At pH 9:
- Range of maximum concentrations at end of study period:
At the end of the study period, the concentrations were below the LOQ of 1.3 mg/L.
Validity criteria fulfilled:
yes
Conclusions:
Based on the results of the preliminary test the hydrolysis rate of test item was found to be 32 % at pH 4, 89 % at pH 7 and >99 % at pH 9 after 5 days at 50 °C. Based on the results obtained, test item can be considered as hydrolytically unstable at pH 4, pH 7 and pH 9 under the conditions investigated.
Executive summary:

The hydrolysis of the test item was assessed in accordance with the OECD guideline 111 and the EU method C.7 in a preliminary test. The hydrolysis of the test item in different aqueous buffer solutions (pH = 4, 7 and 9) at 50 °C was investigated using GC. The content of test item in the different pH buffer samples was determined at the beginning and the end of the test periods. Six samples were analysed at the start of the study. Based on the measured concentration the hydrolysis of the test item was determined to be 32 % at pH = 4; 89 % at pH = 7 and >99 % at pH = 9. Based on the results obtained, test item can be considered as hydrolytically unstable at pH 4, pH 7 and pH 9 under the conditions investigated. No observations were made which case doubt on the validity of the study results.

Description of key information

The rate constant k and half-life were determined at 20 °C for pH 4 = 8.5E-5 h-1 and 8122 h respectively, for pH 7 = 8.8E-4 h-1 and 784 h, respectively and for pH 9 = 0.0217 h-1 and 32 h, respectively.

Key value for chemical safety assessment

Half-life for hydrolysis:
784 h
at the temperature of:
20 °C

Additional information

Key study


A study was conducted according to Regulation (EC) No 440/2008 Part C.7 and OECD test guideline 111 to determine the hydrolysis of the test substance as a function of pH. The tier 1 test according to guideline was conducted and revealed that the test item is hydrolytically not stable at pH 4, 7 and 9. Thus, the subsequent Tier 2 test for the determination of the hydrolysis half-life was conducted. Hydrolysis was examined at three different pH values 4, 7 and 9 at three different temperatures: pH 4: 40, 50 and 60 ± 0.5 °C; pH 7: 30, 40 and 50 ± 0.5 °C; pH 9: 10, 20 and 30 ± 0.5 °C . The hydrolysis reaction was carried out using a dark thermostat to avoid photolytic effects. Three samples were analysed at the start of the experiments. Two separate tubes were analysed at each analytical occasion of hydrolysis test. One sample was taken from the control vessels. Samples are diluted or concentrated on SPE cartridges and then analysed by a GC – FID method in the presence of benzonitrile internal standard. The pseudo-first order rate constant (kobs) for each test temperature was determined from the plots of the natural logarithm of the concentration versus time. Applying the Arrhenius equation the rate constant k and half-life were calculated at 20 °C for pH 4 = 8.5E-5 h-1 and 8122 h, respectively, for pH 7 = 8.8E-4 h-1 and 784 h, respectively and for pH 9 = 0.0217 h-1 and 32 h, respectively.


 


Supporting study


The hydrolysis of the test item was assessed in accordance with the OECD guideline 111 and the EU method C.7 in a preliminary test. The hydrolysis of the test item in different aqueous buffer solutions (pH = 4, 7 and 9) at 50 °C was investigated using GC. The content of test item in the different pH buffer samples was determined at the beginning and the end of the test periods. Six samples were analysed at the start of the study. Based on the measured concentration the hydrolysis of the test item was determined to be 32 % at pH = 4; 89 % at pH = 7 and >99 % at pH = 9. Based on the results obtained, test item can be considered as hydrolytically unstable at pH 4, pH 7 and pH 9 under the conditions investigated. No observations were made which case doubt on the validity of the study results.