Pentapotassium bis(peroxymonosulphate) bis(sulphate)

Hydrolysis

Link to relevant study record(s)

Reference

Endpoint:

hydrolysis

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2007-02-14 - 2007-07-02

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: The raw data (i.e. the concentrations of KMPS triple salt in the different test solutions at the different time points) is not included in the original report, but was provided separately by the applicant.

Qualifier:

according to guideline

Guideline:

OECD Guideline 111 (Hydrolysis as a Function of pH)

Deviations:

no

GLP compliance:

yes

Radiolabelling:

no

Analytical monitoring:

yes

Details on sampling:

Sampling times were different for all test systems. Each test solutions was analysed in time intervals to provide at least six data points.

Buffers:

Exact composition is not indicated; preparation was made according to the guideline.

Details on test conditions:

TEST SYSTEM
Test solutions were filled in 4-oz amber bottles which were placed into ovens for incubation at different temperatures.

Tests were made at 20, 30 and 50°C

TEST MEDIUM
The preparation of buffer solutions corresponded to test method OECD 111. In addition, synthetic seawater and freshwater were prepared. A stock solution of the test substance was prepared in deionised water at a nominal concentration of 3 g/100mL. For the preparation of the test solutions, 25 mL of the stock solution was mixed with approximately 225 mL of the appropriate solution to be tested (i.e. buffer solution, seawater or freshwater, respectively).

Tables are presented under "Any other information on materials and methods incl. tables".

Duration:

836 h

pH:

4

Temp.:

20 °C

Initial conc. measured:

3 g/L

Duration:

739 h

pH:

4

Temp.:

30 °C

Initial conc. measured:

3 g/L

Duration:

431 h

pH:

4

Temp.:

50 °C

Initial conc. measured:

3 g/L

Duration:

720 h

pH:

7

Temp.:

20 °C

Initial conc. measured:

3 g/L

Duration:

335 h

pH:

7

Temp.:

30 °C

Initial conc. measured:

3 g/L

Duration:

23.1 h

pH:

7

Temp.:

50 °C

Initial conc. measured:

3 g/L

Duration:

75.2 h

pH:

9

Temp.:

20 °C

Initial conc. measured:

3 g/L

Duration:

22.7 h

pH:

9

Temp.:

30 °C

Initial conc. measured:

3 g/L

Duration:

20.5 h

pH:

9

Temp.:

50 °C

Initial conc. measured:

3 g/L

Number of replicates:

Two replicates per test solution and temperature.

Positive controls:

not specified

Negative controls:

not specified

Statistical methods:

Averages and least squares linear regression were employed.

Preliminary study:

Was not performed.

Test performance:

no remarks on test performance

Transformation products:

not measured

Details on hydrolysis and appearance of transformation product(s):

- Pathways for transformation:
Two decomposition pathways of KMPS (KHSO5) are important, namely hydrolysis to H2O2 and disproportionation to O2 (with sulfate also formed in each case). These pathways are described by the following reactions:
HSO5- + H2O -> HSO4- + H2O2 (hydrolysis)
HSO5- -> HSO4- + ½ O2 (disproportionation)
Although the present study describes the "hydrolysis" of KMPS (KHSO5) as a function of pH, it is actually the decomposition via disproportionation that is being monitored by the method. This is because the method is measuring a net loss in active oxygen by an iodometric titration. It can be seen from the pathways described above that the hydrolysis of HSO5- does not result in a net loss in active oxygen. Rather, the active oxygen is converted from HSO5- to H2O2, and the iodometric method does not distinguish between HSO5- and H2O2.

pH:

4

Temp.:

20 °C

DT50:

> 800 h

Remarks on result:

other: DT50 values were determined by visual examination of the plot ´ln (normalised % KMPS) vs time´

pH:

4

Temp.:

30 °C

DT50:

440 h

Remarks on result:

other: see above

pH:

4

Temp.:

50 °C

Hydrolysis rate constant:

1.58 d-1

DT50:

110 h

Remarks on result:

other: k and t1/2 values were determined by linear regression analysis

Key result

pH:

7

Temp.:

20 °C

DT50:

145 h

Remarks on result:

other: DT50 values were determined by visual examination of the plot ‘ln (normalised % KMPS) vs time’

pH:

7

Temp.:

30 °C

DT50:

53 h

Remarks on result:

other: see above

pH:

7

Temp.:

50 °C

Hydrolysis rate constant:

0.12 h-1

DT50:

6 h

Remarks on result:

other: k and t1/2 values were determined by linear regression analysis

pH:

9

Temp.:

20 °C

DT50:

2.8 h

Remarks on result:

other: DT50 values were determined by visual examination of the plot ‘ln (normalised % KMPS) vs time’

pH:

9

Temp.:

30 °C

Hydrolysis rate constant:

0.4 h-1

DT50:

1.72 h

Remarks on result:

other: k and t1/2 values were determined by linear regression analysis

pH:

9

Temp.:

50 °C

Hydrolysis rate constant:

0.68 h-1

DT50:

1 h

Remarks on result:

other: k and t1/2 values were determined by linear regression analysis

Other kinetic parameters:

Hydrolysis rate constants and dissipation times determined in freshwater and in seawater are given in table 7, which is presented under "Remarks on results including tables and figures"

Details on results:

TEST CONDITIONS
- pH, sterility, temperature, and other experimental conditions maintained throughout the study: Yes

TRANSFORMATION PRODUCTS AND PATHWAYS OF HYDROLYSIS:
- Description of pathways:
The dissipation of KHSO5 can be chemically described by two redox-reactions (formulae see above): the reaction of the monoperoxohydrogensulfate ion with H2O (hydrolysis; in which monoperoxohydrogensulfate is reduced to hydrogensulfate and water is oxidised to hydrogen peroxide) and the disproportionation of monoperoxohydrogensulfate to hydrogensulfate and oxygen. Like monoperoxohydrogensulfate, hydrogen peroxide and oxygen are chemically reactive species with a high oxidising potential. Compared to freshwater and the buffers, seawater has a higher concentration of chloride-ions. The faster dissipation of KHSO5 in seawater could therefore be explained by possible further reactions of monoperoxohydrogensulfate, hydrogen peroxide and oxygen with chloride yielding chlorine, hydrogensulfate, water and OH-.

The concentrations of KMPS triple salt in the different test solutions (pH 4, 7, 9, seawater and freshwater) at different time points are presented in table 4 (20°C), table 5 (30°C) and table 6 (50°C).The initial amount of KMPS triple salt detected at the first sampling immediately after application (t = 0) was set as 100 %. The concentrations found at the other time points were normalised to this initial concentration.

 

Hydrolysis rate constant (kh)

 

In the original report data analysis was performed by linear regression. Data were analysed by first normalising the % KMPS triple salt values at each time point to the initial concentration and obtaining the natural logarithm of the normalised values. The resulting ln (normalised % KMPS triple salt) were then plotted against time and the curves obtained were examined to see if they were linear down to at least two half-lives. If the curves were linear, regression analysis was used to compute the slope of the curve, which is the rate constant k. If the curve was non-linear, aDT50 value was obtained by determining where the curve reached the ln (normalised % KMPS triple salt) that corresponds to on half-life, which is 0.693. The rate constant and t1/2 (or DT50) values obtained for the two replicated were then averaged to give the reported value. Results are presented in table 7.

For the seawater and freshwater systems incubated at 20°C, the rate constants and the resulting DT50 values were re-calculated during dossier preparation using non-linear regression analysis. A first order multi compartment model was fitted to the data. Results are included in table 7.

Table 4: Hydrolysis of KMPS at 20°C (expressed as percentage of initial concentrations)

20°C, pH 4		20°C, pH 7		20°C, pH 9		20°C, Seawater		20°C, Freshwater
Time [h]	KMPS [%]	Time [h]	KMPS [%]	Time [h]	KMPS [%]	Time [h]	KMPS [%]	Time [h]	KMPS [%]
0	100.00	0	100.00	0	100.00	0	100.00	0	100.00
18.8	97.12	0.83	98.59	1.33	65.91	1.17	69.45	1	99.78
42.7	93.89	2.17	97.66	2.5	53.44	2.5	64.15	3.5	99.44
116	84.18	22.8	84.81	3.25	47.08	4.5	51.28	4.5	99.64
214	79.04	191	41.04	4	42.56	22.67	33.72	5.67	99.30
356	74.91	286	29.32	4.83	38.42	52.5	23.84	6.67	98.62
522	71.84	360	23.12	21.5	13.69	120	18.04	25.3	92.66
691	70.37	504	15.67	28.1	10.56	191	17.99	97.7	64.37
836	68.94	720	8.62	45.1	11.09	360	12.25	169	51.94
-	-	-	-	52.7	10.91	504	12.38	312	44.42
-	-	-	-	75.2	10.48	719	6.64	505	41.26
-	-	-	-	-	-	-	-	673	38.56
-	-	-	-	-	-	-	-	817	39.95

 

 

 

Table 5: Hydrolysis of KMPS at 30°C (expressed as percentage of initial concentrations)

30°C, pH 4		30°C, pH 7		30°C, pH 9		30°C, Seawater		30°C, Freshwater
Time [h]	KMPS [%]	Time [h]	KMPS [%]	Time [h]	KMPS [%]	Time [h]	KMPS [%]	Time [h]	KMPS [%]
0	100.00	0	100.00	0	100.00	0	100.00	0	100.00
2.25	99.40	1	98.54	0.5	79.27	0.33	86.72	0.75	100.00
19.6	90.06	2.25	95.92	1	62.33	1.5	57.63	3.75	97.85
92	71.71	3.5	93.38	2.75	30.99	2.83	47.87	4.75	96.37
164	62.34	4.25	91.41	3.5	24.98	4	39.97	5.83	95.72
262	56.46	4.75	89.28	4.25	21.26	4.5	41.84	6.83	92.05
404	51.47	5.25	89.44	5.25	17.45	5	38.62	25	71.34
571	46.58	22.7	66.93	22.7	7.98	22	21.14	97.2	37.86
739	42.54	47.3	53.17	-	-	45.6	17.13	125	34.36
-	-	120	25.49	-	-	119	11.85	196	30.26
-	-	217	14.13	-	-	191	9.65	337	25.39
-	-	287	10.12	-	-	-	-	504	23.90
-	-	335	8.15	-	-	-	-	673	22.45
-	-	-	-	-	-	-	-	817	21.89

 

 

Table 6: Hydrolysis of KMPS at 50°C (expressed as percentage of initial concentrations)

50°C, pH 4		50°C, pH 7		50°C, pH 9		50°C, Seawater		50°C, Freshwater
Time [h]	KMPS [%]	Time [h]	KMPS [%]	Time [h]	KMPS [%]	Time [h]	KMPS [%]	Time [h]	KMPS [%]
0	100.00	0	100.00	0	100.00	0	100.00	0.00	100.00
1	100.20	1	96.11	1	47.02	1	55.17	1.08	99.51
4	96.89	2	86.99	1.75	30.36	1.5	49.29	2.42	92.74
20.5	84.47	3	76.23	2	25.51	2.75	29.04	3.83	77.65
46.5	71.59	4.75	59.80	2.25	22.40	3.5	23.89	4.67	70.14
71.5	62.50	6.25	50.09	2.5	20.28	4	21.14	5.42	63.97
97	53.65	6.5	47.87	2.75	18.33	5.25	16.31	22.0	19.44
172	33.71	23.1	8.83	3.5	15.34	22.8	9.57	28.5	13.31
240	18.73	-	-	4.75	13.11	-	-	46.1	7.21
335	13.47	-	-	20.5	11.24	-	-	-	-
431	4.55	-	-	-	-	-	-	-	-

 

 

 

Table 7:  Hydrolysis rate constants and dissipation times

Temperature	DT50 [h] a)	k [h-1] b)	t1/2 [h] b)
pH 4
20	> 800	n.d.	n.d.
30	440	n.d.	n.d.
50	n.d.	0.0066	110
pH 7
20	145	n.d.	n.d.
30	53	n.d.	n.d.
50	n.d.	0.12	6.0
pH 9
20	2.8	n.d.	n.d.
30	n.d.	0.4	1.72
50	n.d.	0.68	1.0
Seawater
20	5.6	n.d.	n.d. / 5.2 c)
30	2.5	n.d.	n.a.
50	1.4	n.d.	n.a.
Freshwater
20	215	n.d.	n.d. / 202 c)
30	65	n.d.	n.d.
50	8.7	n.d.	n.d.

a)    DT50values were determined by visual examination of the plot `ln (normalised % KMPS) vs time´

b)    k and t1/2values were determined by linear regression analysis                                                                               

c)    t1/2 values were calculated by non-linear regression analysis applying a first order multi compartment model with the software ModelMaker Version 4.0

n.d. not determined

Validity criteria fulfilled:

yes

Conclusions:

The abiotic decomposition of KMPS triple salt in aqueous solutions depends both on the pH value and the temperature. DT50 values decrease with increasing pH value and increasing temperature.
Two decomposition pathways of KHSO5 are important, namely hydrolysis to H2O2 and disproportionation to O2 (with sulfate also formed in each case). These pathways are described by the following reactions:
HSO5- + H2O -> HSO4- + H2O2 (hydrolysis)
HSO5- -> HSO4- + ½ O2 (disproportionation)
Although the present study describes the "hydrolysis" of KMPS (KHSO5) as a function of pH, it is actually the decomposition via disproportionation that is being monitored by the method. This is because the method is measuring a net loss in active oxygen by an iodometric titration. It can be seen from the pathways described above that the hydrolysis of HSO5- does not result in a net loss in active oxygen. Rather, the active oxygen is converted from HSO5- to H2O2, and the iodometric method does not distinguish between HSO5- and H2O2.

Executive summary:

Materials and methods

The aqueous hydrolysis test was conducted according to test method OECD 111. KMPS triple salt was dissolved in buffer solutions of pH 4, 7 and 9 as well as in synthetic seawater and freshwater. The test solutions were incubated at 20, 30 and 50°C. The concentration of KMPS triple salt in the test solutions was determined at different time intervals by titration with sodium thiosulfate.

 

Results and discussion

kH

Please refer to Table 7.

KMPS data were analysed by plotting the ln (normalised % KMPS triple salt) against time. For several test systems the plotted curves were not linear. However, regression analysis is only possible for linear curves. For those test systems where no linearity could be observed, KMPS triple salt data were evaluated by visual examination. In those cases no hydrolysis rate constants could be determined.

 

DT50

The dissipation times of KMPS triple salt in aqueous solutions depend both on the pH value and the temperature. DT50 values decrease with increasing pH values. In buffered solutions, the fastest dissipation is observed at pH 9 with DT50values of 2.8 hours at 20°C and 1 hour at 50°C. In seawater, dissipation of KHSO5 at 20°C is much faster with a DT50 of 5.2 hours than in freshwater with a DT50 of 202 hours. As both types of water have similar pH values (around pH 8) the salinity of the seawater seems to have an important influence on the dissipation of KHSO5.

The dissipation of KHSO5 can be chemically described by two redox-reactions (formulae see under "Conclusion"): the reaction of the monoperoxohydrogensulfate ion with H2O (hydrolysis; in which monoperoxohydrogensulfate is reduced to hydrogensulfate and water is oxidised to hydrogen peroxide) and the disproportionation of monoperoxohydrogensulfate to hydrogensulfate and oxygen. Like monoperoxohydrogensulfate, hydrogen peroxide and oxygen are chemically reactive species with a high oxidising potential. Compared to freshwater and the buffers, seawater has a higher concentration of chloride-ions. The faster dissipation of KHSO5 in seawater could therefore be explained by possible further reactions of monoperoxohydrogensulfate, hydrogen peroxide and oxygen with chloride yielding chlorine, hydrogensulfate, water and OH-.

Description of key information

The hydrolysis of KMPS (triple salt) was investigated in one key study and two supporting studies. The key study is in accordance with the OECD Test Guidelines 111. However, as mentioned above organic materials present in water significantly influcene the rate of hydrolysis. Therefore, to realistically reflect environmental scenarios the hydrolysis rate in soil was used for chemical safety assessment (see IUCLID section 5.2.3).

Key value for chemical safety assessment

Half-life for hydrolysis:

145 h

at the temperature of:

20 °C

Additional information

In the hydrolysis study, the degradation of KMPS was measured by determining the loss of active oxygen by iodometric titration.

The degradation of KMPS in aqueous solution is pH and temperature dependant. Degradation is accelerated with increasing temperature and increasing pH. While KMPS has a half-life of above 800 h (at 20°C) in a buffered solution of pH 4, the half-life at pH 7 is 145 hours and only 2.8 hours at pH 9. Degradation in seawater is considerably faster (DT50= 5.5 hours, pH 8.0-8.2, 20°C) than in freshwater (DT₅₀= 215 hours, pH 7.8-8.2, 20°C).

Since the titration method would also detect other peroxide species and a loss of active oxygen was observed it can be concluded that no other peroxide species is built upon hydrolysis.

The reason for the faster degradation of KMPS in seawater is the so-called Haber-Will-Statter Reaction. In this, the sodium chloride of the seawater is oxidised by KMPS so that chlorine is released.

HSO₅^-+2Cl-+ 2H+ àHSO₄-+ Cl₂+H₂O

The chlorine reacts with water to form hypochlorous acid:

Cl₂+H₂OàHOCl +HCl

Hypochlorous acid (HOCl) is only of transient nature, hypochlorous acid is extremely rapidly eliminated in the environment due to reaction with ammonia and organic material which act as reductants.