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Hydrolysis

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Reference
Endpoint:
hydrolysis
Type of information:
experimental study
Adequacy of study:
key study
Study period:
22-11-2011 till 01-03-2012
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:
yes
Remarks:
see "Principles of method if other than guideline" for deviations
Principles of method if other than guideline:
Based on the information of the sponsor the test substance was recommended to be stored at a temperature lower than 25°C. Therefore the screening hydrolysis study (Tier 1) was performed at a test temperature of 20°C instead of the required 50°C according to the guideline.

No Thymol was added to the buffer solutions as, based on microbiological experience, the addition of Thymol as a disinfectant is not necessary because the buffer solutions were also sterilized.

Only a screening hydrolysis study was performed in orderto determine if the half life would occur to be less than 12 hours and thus no water solubility testing would be required.
GLP compliance:
yes (incl. certificate)
Radiolabelling:
no
Analytical monitoring:
yes
Details on sampling:
At the moment the test substance was added to the buffer solutions the first sample was taken from a test vessel and analyzed using the analytical method described below. Subsequent samples were taken on different time intervals and analyzed to determine the percentage of hydrolysis.Samples were analyzed directly after sampling in order to prevent further hydrolysis.
Buffers:
Sterile test buffer solutions of pH 4.0, 7.0 and 9.0 were prepared according to the description in Annex 3 of OECD 111 and purged with nitrogen for at least 5 minutes. Sterilization of the buffer solutions was performed by autoclaving at 121°C for at least 20 minutes.
Details on test conditions:
Chemicals
All chemicals used were of reagent grade quality, unless stated otherwise.
Buffer solutions of the different pH values were prepared according to the information as described in Annex 3 of OECD 111.

Materials
All glassware and buffer solutions were sterilised. Buffer solutions were flushed with nitrogen to minimise oxidation. Test vessels were kept under dark conditions to avoid eventual photo degradation. A temperature controlled water bath was used; temperature was measured using a calibrated thermometer. pH was measured using a pH meter.


Duration:
5 d
pH:
7
Temp.:
20
Initial conc. measured:
1 314.3 mg/L
Duration:
5 d
pH:
9
Temp.:
20
Initial conc. measured:
1 256.9 mg/L
Positive controls:
no
Negative controls:
no
Preliminary study:
The screening hydrolysis test was performed separately for each pH value tested. The test substance showed hydrolysis at pH values 7 and 9, the hydrolysis rate increased at higher pH value. For pH value 4 the influence of buffer solution in the HPLC chromatogram was too high to detect reliable results.
The half-life for pH 7 was calculated to be far more than 12 hours, the limit for conducting a water solubility test according to the REACH guidance, whereas for pH 9 the half-life was calculated to be 12.5 hours. Overall it can be concluded that based on the hydrolysis rate a water solubility test still has to be conducted.
Transformation products:
not measured
Details on hydrolysis and appearance of transformation product(s):
pH value of 4
The temperature during the test varied between 19.8 and 20.1°C. The peak in the HPLC chromatogram for the test substance was completely overlapped by a huge peak for the buffer solution. Therefore it was not possible to calculate reliable results for this pH value.

pH value of 7
The temperature during the test varied between 19.7 and 20.1°C. It was observed that about 35% of the test substance was hydrolyzed after 5 days. Detailed results of the hydrolysis are displayed in table II and figure 1. Using the information gathered during the screening hydrolysis test also a calculation of the half-life (t ½) was determined by applying the Arrhenius relationship, the relation between the logarithmic value of the concentration of the test substance and the time. The half-life for the test substance was calculated to be 200 hours. Detailed results are displayed in figure 2 and calculations for the half-lives are given in table IV.

pH value of 9
The temperature during the test varied between 19.7 and 20.1°C. It was observed that more than 92% of the test substance was hydrolyzed in 2 days. Detailed results of the hydrolysis are displayed in table III and figure 3. Using the information gathered during the screening hydrolysis test also a calculation of the half-life (t ½) was determined by applying the Arrhenius relationship, the relation between the logarithmic value of the concentration of the test substance and the time. The half-life for the test substance was calculated to be 12.5 hours. Detailed results are displayed in figure 4 and calculations for the half-lives are given in table IV.
pH:
7
Temp.:
20 °C
Hydrolysis rate constant:
0 min-1
DT50:
200 h
Type:
(pseudo-)first order (= half-life)
Remarks on result:
other: regression equation: y=3E-05x+3.1079; r2=0.9829
pH:
9
Temp.:
20 °C
Hydrolysis rate constant:
0.001 min-1
DT50:
12.5 h
Type:
(pseudo-)first order (= half-life)
Remarks on result:
other: regression equation: y=-0.0004x+3.0914; r2=0.9986

Results screening hydrolysis, pH 7

 

Sample

Time
 from start test

Conc.
(Ct)

Hydrolysis

Log Ct

 

min.

mg/l

%

 

pH 7,t=0 min.

3

1314.3

0.0

3.12

pH 7,t=2 hr

120

1283.9

2.3

3.11

pH 7, t=4 hr

240

1268.9

3.5

3.10

pH 7, t=1 day

1440

1143.3

13.0

3.06

pH 7, t=2 days

2880

1064.3

19.0

3.03

pH 7, t=5 days

7200

857.0

34.8

2.93

Results screening hydrolysis, pH 9

Sample

Time
 from start test

Conc.
(Ct)

Hydrolysis

Log Ct

 

min.

mg/l

%

 

pH 9, t=0min.

3

1256.9

0.0

3.10

pH 9, t=2 hr

120

1107.4

11.9

3.04

pH 9, t=4 hr

240

1002.9

20.2

3.00

pH 9, t=1 day

1440

303.2

75.9

2.48

pH 9, t=2 days

2880

89.3

92.9

1.95

pH 9, t=5 days

7200

< LOD

100.0

n.a.

n.a. not applicable

 

Calculation hydrolysis: 

{[Ct(t=0) - Ct(t=x)] / Ct(t=0)} x 100%

Calculation half-lives

 

 

Kobs

t1/2

 

slope

(min-1)

(min)

(hrs)

pH 7

-2.51234E-05

5.78487E-05

11982

200

pH 9

-0.000401381

0.000924213

750

12.5

Summary of method validations analytical method

Validation

Parameter

Result

Requirement

Linearity               

R squared

R2=0.997
(lowest value)

R2≥ 0.98

Reproducibility
(10 mg/L)

Coefficient of variation

15.9%

< 20%

Reproducibility
(1000 mg/L)

Coefficient of variation

6.9%

< 20%

Limit of detection

 

1.2 mg/L
(highest value)

 

Recovery pH 7

Mean

132.0%

70 – 110%

Standard deviation

6.0%

< 20%

Recovery pH 9

Mean

106.1%

70 – 110%

Standard deviation

5.1%

< 20%

System stability

Deviation control stand. from expected value

-0.9 to -9.8%

< 10%

Validity criteria fulfilled:
yes
Conclusions:
At a pH value of 7 the half-life (t½) for 2,4-pentanedione peroxide at a temperature of 20°C was calculated to be 200 hours.
At a pH value of 9 the half-life (t½) for 2,4-pentanedione peroxide at a temperature of 20°C was calculated to be 12.5 hours.
At pH value 4 no reliable results were observed so no information on hydrolysis can be given.
Based on the calculated half-lives it can be concluded a water solubility test for the test substance still has to be conducted.

Description of key information

At a pH value of 7 the half-life (t½) for 2,4-pentanedione peroxide at a temperature of 20°C was calculated to be 200 hours.

At a pH value of 9 the half-life (t½) for 2,4-pentanedione peroxide at a temperature of 20°C was calculated to be 12.5 hours.

At pH value 4 no reliable results were observed so no information on hydrolysis can be given.

Key value for chemical safety assessment

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

Additional information