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Environmental fate & pathways

Hydrolysis

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Endpoint:
hydrolysis
Type of information:
experimental study
Adequacy of study:
weight of evidence
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)
Version / remarks:
2004-11-23
Deviations:
no
GLP compliance:
no
Remarks:
In-house quality and environmental management system in place. Certified in accordance with ISO 9001:2015 and ISO 14001:2015.
Radiolabelling:
no
Analytical monitoring:
yes
Remarks:
Ion chromatography
Buffers:
1) pH-4 buffer solution:
20.43 g potassium hydrogen phthalate were dissolved in 1 L distilled water at 20 °C. To 500 mL of that solution 4.0 mL NaOH 0.1 M and water are added to an overall volume of 1.0 L.

2) pH-7 buffer solution:
13.61 g potassium hydrogen phosphate were dissolved in 1 L distilled water at 20 °C. To 500 mL of that solution 296.3 mL NaOH 0.1 M and water are added to an overall volume of 1.0 L.

3) pH-9 buffer solution:
6.19 g boric acid were dissolved in 1 L distilled water at 20 °C. To 500 mL of that solution 213.0 mL NaOH 0.1 M and water are added to an overall volume of 1.0 L.
Details on test conditions:
TEST SYSTEM
- Type, material and volume of test flasks, other equipment used: standard laboratory glassware
- Sterilisation method: none
- Lighting: darkness
- Measures taken to avoid photolytic effects:yes, the test was performed unter total darkness.
- Measures to exclude oxygen: none.

TEST MEDIUM
- Volume used/treatment: 50 mL
- Kind and purity of water: distilled water

OTHER TEST CONDITIONS
- Adjustment of pH: none
Duration:
4 d
pH:
9
Temp.:
60 °C
Duration:
4 d
pH:
7
Temp.:
60 °C
Duration:
4 d
pH:
4
Temp.:
60 °C
Duration:
32 d
pH:
9
Temp.:
25 °C
Duration:
32 d
pH:
7
Temp.:
25 °C
Duration:
32 d
pH:
4
Temp.:
25 °C
Duration:
31 d
pH:
9
Temp.:
10 °C
Duration:
31 d
pH:
7
Temp.:
10 °C
Duration:
31 d
pH:
4
Temp.:
10 °C
Number of replicates:
2
Positive controls:
no
Negative controls:
no
Preliminary study:
The preliminary hydrolysis test was performed at 50 °C at pH values of 4, 7 and 9. The samples were incubated for five days and analyzed afterwards.

S2O8[2-] (t = 0) S2O8[2-] (t = 5 days)
pH 4 88.21 7.77
pH 7 84.93 13.37
pH 9 97.45 12.33

The persulfate was hydrolyzed to similar degrees at all tested pH values. Given the fact, that in each case the amount of hydrolyzed substance is more than 10 %, the substance cannot be considered hydrolytically stable. Thus, an in-detail study was conducted.
Transformation products:
not specified
Key result
pH:
7
Temp.:
12 °C
Hydrolysis rate constant:
0 h-1
DT50:
1 698.18 h
Type:
(pseudo-)first order (= half-life)
Key result
pH:
4
Temp.:
60 °C
Hydrolysis rate constant:
0.025 h-1
DT50:
27.7 h
Type:
(pseudo-)first order (= half-life)
pH:
7
Temp.:
60 °C
Hydrolysis rate constant:
0.019 h-1
DT50:
36.5 h
Type:
(pseudo-)first order (= half-life)
pH:
9
Temp.:
60 °C
Hydrolysis rate constant:
0.019 h-1
DT50:
36.5 h
Type:
(pseudo-)first order (= half-life)

As the APS was found to be unstable at all tested pH values, advanced tests were conducted for all three conditions. The buffered APS solutions were thermostated at 10, 25, as well as 60 °C, respectively.

Hydrolysis at 10 °C

Table 1: Analytic results of the hydrolysis of APS at 10 °C and pH = 4.

APS (10 °C, pH = 4)

Day

Sample-ID

weighed-in
sample [g]

S2O82- [%]

pH

SO42-

 

 

 

 

 

 

Sample 1

Sample 2

 

 

 

 

1

0 (Start)

0.1171

85.40

85.35

4.03

 

4

1

0.1151

85.91

85.71

4.05

 

8

2

0.1142

85.99

85.43

4.10

 

11

3

0.1157

87.98

88.00

4.08

 

15

4

0.1142

88.54

88.39

4.10

 

18

5

0.1162

88.65

87.68

3.97

 

22

6

0.1147

90.90

92.08

3.90

 

25

7

0.1149

91.79

92.33

4.08

 

29

8

0.1143

92.38

92.47

4.10

 

31

9

0.1182

94.54

94.78

4.06

0.5

APS is hydrolytically stable at 10 °C and pH=4. Interestingly, the measured APS content was found to increase over the measurement period. The sulfate content of the final sample 9 was determined to be 0.5 %, further confirming the stability of APS under these conditions.

Table 2: Analytic results of the hydrolysis of APS at 10 °C and pH = 7.

APS (10 °C, pH = 7)

Day

Sample-ID

weighed-in
sample [g]

S2O82- [%]

pH

SO42-

 

 

 

 

 

 

Sample 1

Sample 2

 

 

 

 

1

0 (Start)

0.1201

85.53

85.06

6.97

 

4

1

0.1148

86.40

84.98

6.97

 

8

2

0.1143

85.85

86.16

7.03

 

11

3

0.1142

88.27

88.29

7.04

 

15

4

0.1177

88.94

88.00

7.05

 

18

5

0.1155

89.37

87.87

6.96

 

22

6

0.1165

91.54

91.77

6.88

 

25

7

0.1159

82.02

91.78

7.00

 

29

8

0.1160

92.56

93.17

7.00

 

31

9

0.1185

94.89

93.52

6.96

0.1

The results from the study at pH = 4 can be confirmed for pH = 7. APS is hydrolytically stable under these conditions (10 °C and pH=7) as well. Likewise, the measured APS content was found to increase over the measurement period. The sulfate content of the final sample 9 was determined to 0.1 %, confirming the stability of APS under these conditions.

Table 3: Analytic results of the hydrolysis of APS at 10 °C and pH = 9.

APS (10 °C, pH = 9)

Day

Sample-ID

weighed-in
sample [g]

S2O82- [%]

pH

SO42-

 

 

 

 

 

 

Sample 1

Sample 2

 

 

 

 

1

0 (Start)

0.1155

84.05

84.16

8.86

 

4

1

0.1148

84.80

85.16

8.75

 

8

2

0.1152

85.95

85.25

8.80

 

11

3

0.1149

88.24

88.60

8.86

 

15

4

0.1161

88.60

88.14

8.86

 

18

5

0.1176

89.19

87.77

8.85

 

22

6

0.1166

90.30

91.72

8.70

 

25

7

0.1151

91.07

92.13

8.80

 

29

8

0.1145

92.56

92.68

8.70

 

31

9

0.1183

93.78

93.52

8.75

0.6

The results from the study at pH = 4 and 7 can be confirmed for pH = 9 as well. APS is hydrolytically stable under these conditions (10 °C and pH=9) as well. Likewise, the measured APS content was found to increase over the measurement period. The sulfate content of the final sample 9 was determined to 0.6 %, confirming the stability of APS under these conditions.

Hydrolysis at 25 °C

Table 4: Analytic results of the hydrolysis of APS at 25 °C and pH = 4.

APS (25 °C, pH = 4)

Day

Sample-ID

weighed-in sample [g]

S2O82- [%]

pH

SO42-

Sample 1

Sample 2

1

0 (Start)

0.1117

85.66

85.95

4.08

 

5

1

0.1133

85.62

85.57

4.09

 

8

2

0.1128

85.57

85.40

4.05

 

12

3

0.1180

85.95

86.14

3.94

 

15

4

0.1121

85.21

85.41

4.03

 

19

5

0.1138

85.20

85.40

4.01

 

22

6

0.1125

84.72

84.21

4.05

 

26

7

0.1123

84.45

84.39

3.99

 

29

8

0.1142

77.80

78.07

3.81

 

32

9

0.1121

68.94

68.82

3.82

3.22

APS is hydrolytically stable until after sample 7 (after approx. 3 weeks). Afterwards, the APS content was found to decrease significantly. Likewise, the pH value drops to 3.8 indicating that the buffer is used up at this point. The sulfate content was analysed to 3.2% which is a lower value than anticipated from the decreased amount of persulfate. This might be explained by the fact that persulfates can decompose via a different pathway in the acidic milieu and form monoperoxosulfate SO52- as an intermediate decomposition product which was not determined analytically during this study.

Table 5: Analytic results of the hydrolysis of APS at 25 °C and pH = 7.

APS (25 °C, pH = 7)

Day

Sample-ID

weighed-in sample [g]

S2O82- [%]

pH

SO42-

Sample 1

Sample 2

1

0 (Start)

0.1122

84.63

84.97

7.03

 

5

1

0.1135

85.64

85.77

6.99

 

8

2

0.1158

86.19

86.12

6.96

 

12

3

0.1157

86.50

86.69

6.93

 

15

4

0.1183

86.78

86.84

6.97

 

19

5

0.1134

86.67

86.57

6.94

 

22

6

0.1122

87.95

87.67

7.00

 

26

7

0.1113

87.95

88.00

6.93

 

29

8

0.1170

82.39

82.82

6.85

 

32

9

0.1136

82.98

83.43

6.81

2.40

The results from the study at pH = 7 indicate that almost no hydrolysis was observed under these conditions. After one month the persulfate content was reduced by approx. 2.5 %. The analysed amount of SO42- in the terminal sample was 2.40 % which is in good accordance to the decomposed amount of persulfate. Analogous to the study at pH = 4 the final pH-value of the sample is slightly lower than the original sample at the beginning of the measurement indicating that the buffer was at its limit.

Table 6: Analytic results of the hydrolysis of APS at 25 °C and pH = 9.

APS (25 °C, pH = 9)

Day

Sample-ID

weighed-in sample [g]

S2O82- [%]

pH

SO42-

Sample 1

Sample 2

1

0 (Start)

0.1130

85.66

85.95

8.76

 

5

1

0.1121

85.77

85.99

8.72

 

8

2

0.1144

86.51

86.43

8.71

 

12

3

0.1130

86.49

86.52

8.69

 

15

4

0.1144

86.75

87.00

8.71

 

19

5

0.1146

87.46

87.09

8.67

 

22

6

0.1122

87.07

86.94

8.70

 

26

7

0.1121

87.46

87.21

8.68

 

29

8

0.1135

82.07

82.77

8.51

 

32

9

0.1124

83.00

82.58

8.52

2.94

The results from the study at pH = 9 is very similar to the result obtained at pH = 7. APS is hydrolytically stable under these conditions as well. After one month the persulfate content was reduced by approx. 3 %. The analysed amount of SO42- in the terminal sample was 2.94 % which is in good accordance to the decomposed amount of persulfate. Analogous to the study at pH = 4 the final pH-value of the sample is slightly lower than the original sample at the beginning of the measurement indicating that the buffer was at its limit.

Hydrolysis at 60 °C

Table 7: Analytic results of the hydrolysis of APS at 60 °C and pH = 4.

APS (60 °C, pH = 4)

Date, Time

Sample-ID

weighed-in
sample [g]

S2O82- [%]

pH

SO42-

Sample 1

Sample 2

2019-03-25, 07:00

0 (Start)

0.1138

84.48

84.37

4.09

 

2019-03-25, 15:00

1

0.1127

59.51

59.42

3.83

 

2019-03-26, 06:00

2

0.1136

37.68

38.58

3.60

 

2019-03-26, 11:00

3*

0.1138

28.74

28.76

3.47

 

2019-03-26, 15:00

4*

0.1134

28.56

28.94

3.46

 

2019-03-27, 06:00

5*

0.1130

20.00

19.09

3.43

 

2019-03-27, 13:00

6*

0.1134

15.97

15.82

3.42

 

2019-03-28, 06:00

7**

0.1150

11.06

11.05

3.35

 

2019-03-28, 13:00

8**

0.1123

10.45

10.43

3.36

 

2019-03-29, 06:00

9**

0.1130

7.53

7.53

3.36

81.87***

* dilution factor for ion chromatographic analysis = 8000

** dilution factor for ion chromatographic analysis = 4000

*** dilution factor for ion chromatographic analysis = 80000

APS decomposes rather quickly under the test conditions. After approx. 4 days less than 10 % of the original content was found in the respective samples. The amount of sulfate detected in the terminal sample is in good agreement with that finding. At this temperature it was not possible to hold the pH value of the buffered solutions at 4. It drifted steadily to 3.36 throughout the study.

Table 8: Analytic results of the hydrolysis of APS at 60 °C and pH = 7.

APS (60 °C, pH = 7)

Date, Time

Sample-ID

weighed-in
sample [g]

S2O82- [%]

pH

SO42-

Sample 1

Sample 2

2019-03-25, 07:00

0 (Start)

0.1146

85.23

85.19

7.05

 

2019-03-25, 15:00

1

0.1123

74.68

74.19

6.96

 

2019-03-26, 06:00

2

0.1128

53.73

54.32

6.63

 

2019-03-26, 11:00

3*

0.1138

49.63

48.97

6.57

 

2019-03-26, 15:00

4*

0.1143

46.77

46.95

6.55

 

2019-03-27, 06:00

5*

0.1129

32.42

32.33

6.41

 

2019-03-27, 13:00

6*

0.1128

30.41

30.42

6.40

 

2019-03-28, 06:00

7**

0.1139

22.69

22.90

6.21

 

2019-03-28, 13:00

8**

0.1127

20.82

21,06

6.20

 

2019-03-29, 06:00

9**

0.1158

14.29

14.22

6.06

72.04***

* dilution factor for ion chromatographic analysis = 8000

** dilution factor for ion chromatographic analysis = 4000

*** dilution factor for ion chromatographic analysis = 40000

APS decomposes rather quickly at these conditions, however somewhat slower than at pH = 4. The amount of sulfate detected in the terminal sample (72.04 %) is in good agreement with the corresponding APS content. As for the previous study at pH = 4 it was also not possible to keep the pH value of the buffered solutions at 7. It drifted steadily to a final value of 6.06 during the study.

Table 9: Analytic results of the hydrolysis study of APS at 60 °C and pH = 9.

APS (60 °C, pH = 9)

Date, Time

Sample-ID

weighed-in
sample [g]

S2O82- [%]

pH

SO42-

Sample 1

Sample 2

2019-03-25, 07:00

0 (Start)

0.1160

85.86

85.77

8.88

 

2019-03-25, 15:00

1

0.1165

69.94

70.58

8.71

 

2019-03-26, 06:00

2

0.1122

50.78

51.25

8.34

 

2019-03-26, 11:00

3*

0.1116

45.03

44.50

8.19

 

2019-03-26, 15:00

4*

0.1136

43.53

43.38

8.16

 

2019-03-27, 06:00

5*

0.1130

35.42

35.33

7.68

 

2019-03-27, 13:00

6*

0.1143

31.89

31.59

7.60

 

2019-03-28, 06:00

7**

0.1117

21.52

21.65

7.00

 

2019-03-28, 13:00

8**

0.1165

19.21

19.26

3.30

 

2019-03-29, 06:00

9**

0.1159

13.60

12.93

2.93

78.17***

* dilution factor for ion chromatographic analysis = 8000

** dilution factor for ion chromatographic analysis = 4000

*** dilution factor for ion chromatographic analysis = 40000

APS decomposes at 60 °C and pH=9 with a similar rate compared to the study at pH = 7. The amount of sulfate detected in the terminal sample is again in good agreement with the corresponding APS content. As for the previous studies at 60 °C it was also not possible to keep the pH value of the buffered solutions at 9. Especially close to the end of the study the pH value of the sample fell rapidly to a final value of 2.93.

Validity criteria fulfilled:
yes
Conclusions:
APS was shown to be hydrolitically stable at 10 °C and pH 4, 7 and 9, a minor hydrolysis was observed at 25 °C, whereas, a very strong hydrolysis at 60 °C was observed within 4 days. The DT50 at pH 4 and 60 °C was determined to be 27.2 h, at pH 7 and 9 and 60 °C the DT50 was determined to be 36.5 h. The DT50 at environmentally relevant temperature (12 °C) and pH 7 was extrapolated to be 1698.18 h (70.76 d).
Executive summary:

A study according to OECD TG 111 was performed to determine the hydrolysis potential of the test item. Inittialla, a Tier 1 tests at for 5 days at 50 °C and H 4, 7 and 9 was performed. Hydrolisys of more than 10 % was observed at all pH levels. Thus, a Tier 2 hydrolysis test was conducted at 10, 25 and 60 °C and pH 4, 7 and 9. Hydrolysis studies at 10 and 25 °C run for ca. 30 days, while at 60 °C the hydrolysis process was finished after 4 days. APS was shown to be hydrolitically stable at 10 °C and pH 4, 7 and 9, a minor hydrolysis was observed at 25 °C, whereas, a very strong hydrolysis at 60 °C was observed within 4 days. The DT50 at pH 4 and 60 °C was determined to be 27.2 h. The DT50 at environmentally relevant temperature (12 °C) was extrapolated to be 1288.76 h (53.7 d).

Endpoint:
hydrolysis
Type of information:
read-across based on grouping of substances (category approach)
Adequacy of study:
weight of evidence
Justification for type of information:
READ ACROSS CATEGORY APPROACH
A category group was formed with dipotassium peroxodisulphate (KPS), disodium peroxodisulphate (SPS) and diammonium peroxodisulphate (APS). Several physico-chemical, fate, ecotoxicological and toxicological endpoints were assessed using the category approach. Please refer to the read across justification in chapter 13 for further information.
Transformation products:
not specified
Key result
pH:
7
Temp.:
12 °C
Hydrolysis rate constant:
0 h-1
DT50:
1 698.18 h
Type:
(pseudo-)first order (= half-life)
Key result
pH:
4
Temp.:
60 °C
Hydrolysis rate constant:
0.025 h-1
DT50:
27.7 h
Type:
(pseudo-)first order (= half-life)
pH:
7
Temp.:
60 °C
Hydrolysis rate constant:
0.019 h-1
DT50:
36.5 h
Type:
(pseudo-)first order (= half-life)
pH:
9
Temp.:
60 °C
Hydrolysis rate constant:
0.019 h-1
DT50:
36.5 h
Type:
(pseudo-)first order (= half-life)
Endpoint:
hydrolysis
Type of information:
experimental study
Adequacy of study:
weight of evidence
Study period:
from 2020-07-03 to 2020-08-26
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)
Version / remarks:
2004-11-23
Deviations:
no
GLP compliance:
no
Remarks:
In-house quality and environmental management system in place. Certified in accordance with ISO 9001:2015 and ISO 14001:2015.
Radiolabelling:
no
Analytical monitoring:
yes
Remarks:
Ion chromatography
Buffers:
1) pH-4 buffer solution:
20.43 g potassium hydrogen phthalate were dissolved in 1 L distilled water at 20 °C. To 500 mL of that solution 4.0 mL NaOH 0.1 M and water are added to an overall volume of 1.0 L.

2) pH-7 buffer solution:
13.61 g potassium hydrogen phosphate were dissolved in 1 L distilled water at 20 °C. To 500 mL of that solution 296.3 mL NaOH 0.1 M and water are added to an overall volume of 1.0 L.
Details on test conditions:
TEST SYSTEM
- Type, material and volume of test flasks, other equipment used: standard laboratory glassware
- Sterilisation method: none
- Lighting: darkness
- Measures taken to avoid photolytic effects:yes, the test was performed unter total darkness.
- Measures to exclude oxygen: none.

TEST MEDIUM
- Volume used/treatment: 50 mL
- Kind and purity of water: distilled water

OTHER TEST CONDITIONS
- Adjustment of pH: none
Duration:
31 h
pH:
7
Temp.:
60 °C
Duration:
55 h
pH:
4
Temp.:
60 °C
Duration:
32 d
pH:
4
Temp.:
25 °C
Number of replicates:
2
Positive controls:
no
Negative controls:
no
Preliminary study:
A preliminary hydrolysis test was performed at 50 °C at pH values of 4, 7 and 9 with the category member APS. The samples were incubated for five days and analyzed afterwards.

S2O8[2-] (t = 0) S2O8[2-] (t = 5 days)
pH 4 88.21 7.77
pH 7 84.93 13.37
pH 9 97.45 12.33

The persulfate was hydrolyzed to similar degrees at all tested pH values. Given the fact, that in each case the amount of hydrolyzed substance is more than 10 %, the substance cannot be considered hydrolytically stable. Thus, an in-detail study was conducted.
Test performance:
The category member APS was determined to be hydrolitically stable at 10 °C and pH 4, 7 and 9. Similar stability was observed in the tests at 25 °C. To adequatelly represent the hydrolysis behaviour of KPS, only pH 4 was tested at 25 °C. If any hydrolyses was observed at pH 4 and 25 °C, further measurements at higher pH-values (7 and/or 9) would have been performed at this temperature.
Transformation products:
not specified
Key result
pH:
7
Temp.:
12 °C
Hydrolysis rate constant:
0.001 h-1
DT50:
558.3 h
Type:
(pseudo-)first order (= half-life)
Key result
pH:
4
Temp.:
60 °C
Hydrolysis rate constant:
0.098 h-1
DT50:
7.1 h
Type:
(pseudo-)first order (= half-life)
pH:
7
Temp.:
60 °C
Hydrolysis rate constant:
0.058 h-1
DT50:
12 h
Type:
(pseudo-)first order (= half-life)

Hydrolysis tests were conducted at 25 °C, pH = 4, as well as 60 °C, pH = 4 and 60 °C, pH = 7.


 


Hydrolysis at 25 °C


Table 1: Analytic results of the hydrolysis of KPS at 25 °C and pH = 4.















































































































KPS (25 °C, pH = 4)



Day



Sample-ID



weighed-in sample [g]



S2O82- [%]



pH



SO42-



Sample 1



Sample 2



1



0 (Start)



0.1355



70.50



70.62



4.02



 



4



1



0.1356



70.58



70.47



4.02



 



7



2



0.1355



69.50



69.61



4.02



 



11



3



0.1344



68.74



68.52



4.03



 



14



4



0.1344



68.64



68.52



4.03



 



18



5



0.1346



68.73



68.35



3.99



 



21



6



0.1378



68.59



68.67



4.05



 



25



7



0.1355



67.92



68.12



4.02



 



28



8



0.1356



66.16



66.45



4.00



 



32



9



0.1352



64.65



64.91



3.98



7.02



KPS is hydrolytically stable until after sample 7 (after approx. 3 weeks). Afterwards, the KPS content was found to decrease significantly. The pH value was stable over the study. The final sulfate content was analyzed to be 7.02 % matching the reduced persulfate content within the margin of error.


 


Hydrolysis at 60 °C


Table 2: Analytic results of the hydrolysis of APS at 60 °C and pH = 4.

























































KPS (60 °C, pH = 4)



Date, Time



Sample-ID



weighed-in
sample [g]



S2O82- [%]



pH



SO42-



Sample 1



Sample 2



2020-07-20, 07:00



0 (Start)



0.1363



71.45



71.41



4.02



 



2020-07-20, 15:00



1



0.1355



32.03



31.62



3.55



 



2020-07-21, 06:00



2*



0.1344



7.25



7.22



3.20



 



2020-07-21, 14:00



3**



0.1346



3.48



3.48



3.21



70.05***



* dilution factor for ion chromatographic analysis = 8000


** dilution factor for ion chromatographic analysis = 4000


*** dilution factor for ion chromatographic analysis = 80000


 


KPS decomposes rather quickly under the given test conditions. After approx. 24 hours less than 10 % of the original content was found in the respective samples. The amount of sulfate detected in the terminal sample is in good agreement with that finding. At this temperature it was not possible to hold the pH value of the buffered solutions at 4. It drifted steadily to 3.21 throughout the study.


 


The decomposition of PPS follows a first order kinetic under these conditions. The rate constant (inverse of the trend line’s slope) can be obtained with a coefficient of determination of R2 = 99.9 % to a value of k = 0.098 h-1. The respective half-life value was calculated to be 7.1 h.


 


Table 3: Analytic results of the hydrolysis of KPS at 60 °C and pH = 7.











































































KPS (60 °C, pH = 7)



Date, Time



Sample-ID



weighed-in
sample [g]



S2O82- [%]



pH



SO42-



Sample 1



Sample 2



2020-07-27, 07:00



0 (Start)



0.1346



73.05



72.27



7.02



 



2020-07-27, 13:00



1



0.1348



63.33



63.03



6.98



 



2020-07-28, 06:00



2



0.1348



28.20



28.07



6.56



 



2020-07-28, 13:00



3*



0.1357



18.35



18.47



6.55



 



2020-07-29, 06:00



4*



0.1360



6.14



6.26



6.31



 



2020-07-27, 14:00



5**



0.1372



3.05



3.03



6.26



68.13***



* dilution factor for ion chromatographic analysis = 10000


** dilution factor for ion chromatographic analysis = 1000


*** dilution factor for ion chromatographic analysis = 80000


 


APS decomposes rather quickly under the given test conditions, however significantly slower than at pH = 4. After approx. 48 h less than 10% of the original content was found in the respective samples. The amount of sulfate detected in the terminal sample is in good agreement with that finding. At this temperature, it was also not possible to hold the pH value of the buffered solutions at 7. It drifted steadily to 6.26 throughout the study.


 


The decomposition of PPS follows a first order kinetic under these conditions. The rate constant (inverse of the trend line’s slope) can be obtained with a satisfactory coefficient of determination of R2 = 98.5 % to a value of k = 0.058 h-1. The respective half-life value was calculated to be 12.0 h.

Validity criteria fulfilled:
yes
Conclusions:
KPS showed minor hydrolysis at 25 °C, which was not continuously, but only towards the end of the monitored timeframe. Whereas at 60 °C strong hydrolysis (faster at acidic than at neutral pH values) was observed. The DT50 at pH 4 and 60 °C was determined to be 7.1 h and at pH 7 and 60 °C the DT50 was determined to be 12 h. The DT50 at environmentally relevant temperature (12 °C) and pH 7 was extrapolated to be 558.3 h (23.3 d).
Executive summary:

A study according to OECD TG 111 was performed to determine the hydrolysis potential of the test item. Initially, a Tier 1 tests at for 5 days at 50 °C and pH 4, 7 and 9 were performed with the category member APS. Hydrolisys of more than 10 % was observed at all pH levels. Thus, a Tier 2 hydrolysis test was conducted at 10, 25 and 60 °C and pH 4, 7 and 9 with APS. It was shown that the persulfate is hydrolytically stable at 10 °C and different pH-levels, therefore, hydrolysis studies with KPS were performed only at the relevant test conditions. Hydrolysis studies at 25 °C and pH 4 and 60 °C and pH 4 and 7 were conducted with KPS. The test at 25 °C run for ca. 30 days, while at 60 °C the hydrolysis process was finished after 2 - 4 days. KPS showed minor hydrolysis at 25 °C, which was not continuously, but only towards the end of the monitored timeframe. Whereas at 60 °C strong hydrolysis (faster at acidic than at neutral pH values) was observed. The DT50 at pH 4 and 60 °C was determined to be 7.1 h and at pH 7 and 60 °C the DT50 was determined to be 12 h. The DT50 at environmentally relevant temperature (12 °C) and pH 7 was extrapolated to be 558.3 h (23.3 d).

Endpoint:
hydrolysis
Type of information:
experimental study
Adequacy of study:
disregarded due to major methodological deficiencies
Study period:
1951
Reliability:
3 (not reliable)
Rationale for reliability incl. deficiencies:
significant methodological deficiencies
Remarks:
publicly available literature
Qualifier:
equivalent or similar to
Guideline:
OECD Guideline 111 (Hydrolysis as a Function of pH)
Deviations:
yes
Remarks:
The decomposition rates of potassium persulfate in water were investigated at various pH values, ranging from 1 to 10. Assessments were limited to a temperature of 50 °C.
GLP compliance:
no
Radiolabelling:
no
Analytical monitoring:
not specified
Details on sampling:
No information available
Buffers:
Carbonate buffer; phosphate buffer
Details on test conditions:
In the kinetics experiments 100 mL-portions of persulfate and buffer solution were placed in separate vessels and brought to the desired temperature in a thermostat and then mixed. Samples were withdrawn periodically by pipette and were added to a tenfold excess of water at room temperature to practically stop the reaction. Gelatin and supporting electrolyte were then added and the solution was diluted for a known volume. Samples were then analysed using polarographic analysis.
Number of replicates:
NA
Positive controls:
not specified
Negative controls:
not specified
Statistical methods:
NA
Transformation products:
not specified
pH:
1
Temp.:
50 °C
Hydrolysis rate constant:
0.035 h-1
DT50:
20 h
Type:
(pseudo-)first order (= half-life)
pH:
1.6
Temp.:
50 °C
Hydrolysis rate constant:
0.011 h-1
DT50:
65 h
Type:
(pseudo-)first order (= half-life)
pH:
3
Temp.:
50 °C
Hydrolysis rate constant:
0.006 h-1
DT50:
120 h
Type:
(pseudo-)first order (= half-life)
Key result
pH:
7
Temp.:
50 °C
Hydrolysis rate constant:
0.005 h-1
DT50:
130 h
Type:
(pseudo-)first order (= half-life)
pH:
10
Temp.:
50 °C
Hydrolysis rate constant:
3.3 h-1
DT50:
210 h
Type:
(pseudo-)first order (= half-life)

Half-lives of potassium persulfate at 50 °C as a function of pH were calculated from data in the Kolthoff and Miller report.

pH-value

1.0

1.6

 3.0

 7.0

 10.0

Half-life (hours)

20

65

120

130

210

DT50 at pH 7: 130 h (5.4 d) at 50 °C = 1929.6 h (80.4) d at 12 °C (Arrhenius equation)

Validity criteria fulfilled:
not applicable
Conclusions:
Potassium persulfate hydrolyses in water, forming potassium ions and persulfate anions. The persulfate anions further oxidize water producing oxygen, sulphate ions and hydrogen ions.
Executive summary:

Hydrolysis: In alkaline, neutral and dilute acid solutions persulfate decomposes according to reaction (1), while in strongly acid solutions reactions (2) and (3) occur:

S2O82-+ H2O --> 2 HSO4- + ½ O2 (1)

H2S2O8+ H2O --> H2SO5 + H2SO4 (2)

H2SO5 + H2O --> H2O2 + H2SO4 (3)

All degradation products are ubiquitous to the natural environment. The rates of decomposition increased with decreasing pH ranging from 0.035 h-1 at pH 1 to 3.3 h-1 at pH 10, respectively DT50 of 20 hour to DT50 of 21 hour. The rate of hydrolysis at pH 7 and 12 °C was calculated using the Arrhenius equation resulting in 3.6E-04 h-1 and DT50 = 1929.6 h (80.4 days).

Description of key information

KPS showed minor hydrolysis at 25 °C, which was not continuously, but only towards the end of the monitored timeframe. Whereas at 60 °C strong hydrolysis (faster at acidic than at neutral pH values) was observed. The DT50 at pH 4 and 60 °C was determined to be 7.1 h and at pH 7 and 60 °C the DT50 was determined to be 12 h. The DT50 at environmentally relevant temperature (12 °C) and pH 7 was extrapolated to be 558.3 h (23.3 d).

Key value for chemical safety assessment

Half-life for hydrolysis:
23.3 d
at the temperature of:
12 °C

Additional information

A study according to OECD TG 111 was performed to determine the hydrolysis potential of the test item. Initially, a Tier 1 tests at for 5 days at 50 °C and pH 4, 7 and 9 were performed with the category member APS. Hydrolisys of more than 10 % was observed at all pH levels. Thus, a Tier 2 hydrolysis test was conducted at 10, 25 and 60 °C and pH 4, 7 and 9 with APS. It was shown that the persulfate is hydrolytically stable at 10 °C and different pH-levels, therefore, hydrolysis studies with KPS were performed only at the relevant test conditions. Hydrolysis studies at 25 °C and pH 4 and 60 °C and pH 4 and 7 were conducted with KPS. The test at 25 °C run for ca. 30 days, while at 60 °C the hydrolysis process was finished after 2 - 4 days. KPS showed minor hydrolysis at 25 °C, which was not continuously, but only towards the end of the monitored timeframe. Whereas at 60 °C strong hydrolysis (faster at acidic than at neutral pH values) was observed. The DT50 at pH 4 and 60 °C was determined to be 7.1 h and at pH 7 and 60 °C the DT50 was determined to be 12 h. The DT50 at environmentally relevant temperature (12 °C) and pH 7 was extrapolated to be 558.3 h (23.3 d).


In a disregarded study from 1951 on the hydrolysis of KPS at pH levels from 1 to 10, the rates of decomposition of KPS increased with decreasing pH ranging from 0.035 h-1 at pH 1 to 3.3 h-1 at pH 10, respectively, DT50 of 20 hour to DT50 of 21 hour. The rate of hydrolysis at pH 7 and 12 °C was calculated using the Arrhenius equation resulting in 3.6E-04 h-1 and DT50 = 1929.6 h (80.4 days).