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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
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
Reason / purpose for cross-reference:
read-across source
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
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:
55 h
pH:
7
Temp.:
60 °C
Duration:
31 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 SPS, 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:
502.475 h
Type:
(pseudo-)first order (= half-life)
Key result
pH:
4
Temp.:
60 °C
Hydrolysis rate constant:
0.115 h-1
DT50:
6 h
Type:
(pseudo-)first order (= half-life)
pH:
7
Temp.:
60 °C
Hydrolysis rate constant:
0.064 h-1
DT50:
10.8 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 SPS at 25 °C and pH = 4.















































































































SPS (25 °C, pH = 4)



Day



Sample-ID



weighed-in sample [g]



S2O82- [%]



pH



SO42-



Sample 1



Sample 2



1



0 (Start)



0.1182



79.59



79.79



4.03



 



4



1



0.1188



80.12



79.66



4.03



 



7



2



0.1196



78.77



78.95



4.02



 



11



3



0.1184



78.69



78.37



4.02



 



14



4



0.1179



78.56



78.64



4.01



 



18



5



0.1186



77.87



77.86



3.97



 



21



6



0.1198



77.94



78.29



4.04



 



25



7



0.1189



77.31



76.94


4.01

 



28



8



0.1191



75.96



75.74



3.97



 



32



9



0.1191



74.79



74.60



3.91



7.32



SPS is hydrolytically stable until after sample 7 (after approx. 3 weeks). Afterwards, the SPS content was found to decrease more significantly. The pH value was stable over the study. The sulfate content was analyzed to be 7.32 %, which matches the reduced persulfate content within the margin of error.


Hydrolysis at 60 °C


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

























































SPS (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)



0.1199



80.37



80.37



4.01



 



2020-07-20, 15:00



1



0.1183



34.75



35.18



3.54



 



2020-07-21, 06:00



2*



0.1179



6.41



6.41



3.21



 



2020-07-21, 14:00



3**



0.1174



2.29



2.28



3.21



82.03***



* dilution factor for ion chromatographic analysis = 8000


** dilution factor for ion chromatographic analysis = 4000


*** dilution factor for ion chromatographic analysis = 80000


SPS decomposes rather quickly under the given test conditions. After approx. 24 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 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 = 0.115 h-1. The respective half-life value was calculated to be 6.0 h.


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











































































SPS (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)



0.1181



81.31



81.53



7.00



 



2020-07-27, 13:00



1



0.1196



70.52



70.42



6.93



 



2020-07-28, 06:00



2



0.1190



28.64



28.30



6.57



 



2020-07-28, 13:00



3*



0.1171



17.59



18.13



6.27



 



2020-07-29, 06:00



4*



0.1197



5.90



5.87



6.27



 



2020-07-29, 14:00



5**



0.1172



2.18



2.20



6.21



76.04***



* dilution factor for ion chromatographic analysis = 10000


** dilution factor for ion chromatographic analysis = 1000


*** dilution factor for ion chromatographic analysis = 80000


SPS decomposes rather quickly under the 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 6.21 throughout the study.


The decomposition of SPS 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 = 97.5 % to a value of k = 0.064 h-1. The respective half-life value was calculated to be 10.8 h.

Validity criteria fulfilled:
yes
Conclusions:
SPS 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 6.0 h and at pH 7 and 60 °C the DT50 was determined to be 10.8 h. The DT50 at environmentally relevant temperature (12 °C) and pH 7 was extrapolated to be 502.5 h (20.9 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 SPS 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 SPS. The test at 25 °C run for ca. 30 days, while at 60 °C the hydrolysis process was finished after 2 - 4 days. SPS 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 6.0 h and at pH 7 and 60 °C the DT50 was determined to be 10.8 h. The DT50 at environmentally relevant temperature (12 °C) and pH 7 was extrapolated to be 502.5 h (20.9 d).

Description of key information

SPS 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 6.0 h and at pH 7 and 60 °C the DT50 was determined to be 10.8 h. The DT50 at environmentally relevant temperature (12 °C) and pH 7 was extrapolated to be 502.5 h (20.9 d).

Key value for chemical safety assessment

Half-life for hydrolysis:
20.9 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 SPS 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 SPS. The test at 25 °C run for ca. 30 days, while at 60 °C the hydrolysis process was finished after 2 - 4 days. SPS 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 6.0 h and at pH 7 and 60 °C the DT50 was determined to be 10.8 h. The DT50 at environmentally relevant temperature (12 °C) and pH 7 was extrapolated to be 502.5 h (20.9 d).