p-[4,5-dihydro-4-[[2-methoxy-5-methyl-4-[[2-(sulphooxy)ethyl]sulphonyl]phenyl]azo]-3-methyl-5-oxo-1H-pyrazol-1-yl]benzenesulphonic acid, sodium salt

Hydrolysis

Link to relevant study record(s)

Reference

Endpoint:

hydrolysis

Remarks:

in dependence of pH

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2020-05-08 to 2021-03-12

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

EU Method C.7 (Degradation: Abiotic Degradation: Hydrolysis as a Function of pH)

Version / remarks:

440/2008

Deviations:

no

Qualifier:

according to guideline

Guideline:

OECD Guideline 111 (Hydrolysis as a Function of pH)

Version / remarks:

2004

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Analytical monitoring:

yes

Details on sampling:

- Sampling intervals for the parent/transformation products:
preliminary test: Start and after 120 h incubation at 50 °C
definitive test: spaced sampling points (minimum of 8) until transformation of 90%; duplicates for pH 7, single replicates for pH 9 at each sampling interval
- Sampling method: Stabilization by adding 10 µL formic acid and direct analysis afterwards
- Sampling intervals/times for pH measurements: Check of the buffer solutions at test start and at the respective test temperatures
- Sampling intervals/times for sterility check: Once at thest end, determined for pH 7 from additional samples after incubation at 36 ± 1 °C for 48 hours and at 22 ± 1 °C for 72 hours. At pH 9 the study duration was ≤ 4 h, no sterility check was deemed to be necessary.
- Sample storage conditions before analysis: Ambient temperature at the autosampler of the analytical system;

Buffers:

Buffer solution pH 4
0.18 g of sodium hydroxide and 5.7555 g of mono potassium citrate were dissolved in 500 mL purified water.

Buffer solution pH 7
3.854 g of ammonium acetate were dissolved in 500 mL purified water.

Buffer solution pH 9
0.426 g sodium hydroxide, 1.8638 g potassium chloride and 1.5458 g boric acid were dissolved in 500 mL purified

Buffer solutions were prepared from chemicals with analytical grade or better quality following the composition guidance given in “KÜSTER-THIEL, Rechentafeln für die Chemische Analytik” and the OECD Guideline No. 111, respectively, by direct weighing of the buffer components. Buffers were purged with nitrogen for 5 min and then the pH was checked to a precision of at least 0.1 at the test temperatures. Buffers were sterilized by filtration through 0.2 µm.

Details on test conditions:

TEST SYSTEM
- Type, material and volume of test flasks, other equipment used: HPLC vials, brown glass, volume: 2 mL
- Sterilisation method: via autoclav
- Measures taken to avoid photolytic effects: Usage of brown glass vessels and opaque water baths
- Details of traps for volatile, if any: None
- If no traps were used, is the test system closed/open: closed
- Is there any indication of the test material adsorbing to the walls of the test apparatus? No
TEST MEDIUM
- Volume used/treatment: 1 mL
- Kind and purity of water: see "Buffers" above
- Identity and concentration of co-solvent: None was used

Duration:

120 h

pH:

4

Temp.:

50 °C

Initial conc. measured:

14.5 mg/L

Remarks:

preliminary test

Duration:

120 h

pH:

7

Temp.:

50 °C

Initial conc. measured:

15.4 mg/L

Remarks:

preliminary test

Duration:

120 h

pH:

9

Temp.:

50 °C

Initial conc. measured:

12.8 mg/L

Remarks:

preliminary test

Duration:

552 h

pH:

7

Temp.:

20 °C

Initial conc. measured:

15.4 mg/L

Duration:

168 h

pH:

7

Temp.:

30 °C

Initial conc. measured:

15.4 mg/L

Duration:

33.4 h

pH:

7

Temp.:

50 °C

Initial conc. measured:

15.6 mg/L

Duration:

301 min

pH:

9

Temp.:

20 °C

Initial conc. measured:

15.5 mg/L

Duration:

150 min

pH:

9

Temp.:

30 °C

Initial conc. measured:

15.3 mg/L

Duration:

22.7 min

pH:

9

Temp.:

50 °C

Initial conc. measured:

15.6 mg/L

Number of replicates:

Preliminary test: Duplicate at test start and end for each pH value
Definitive test: Duplicate at test start and each sampling interval for pH 7, single replicates at test start and each sampling interval for pH 9

Positive controls:

no

Negative controls:

no

Statistical methods:

Arrhenius calculation acc. to the guidelines for the definitive test results

Preliminary study:

In the preliminary test for the pH values 7 and 9 the test item was degraded after 120 hours more than 10%. For pH 4 no degradation was measured.

Test performance:

None

Transformation products:

yes

No.:

#1

No.:

#2

No.:

#3

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

- Formation and decline of each transformation product during test: See tables below

- Pathways for transformation:
- Other:

% Recovery:

99

pH:

4

Temp.:

50 °C

Duration:

120 h

Remarks on result:

other: result of preliminary test

% Recovery:

34

pH:

7

Temp.:

50 °C

Duration:

120 h

Remarks on result:

other: result of preliminary test

% Recovery:

3

pH:

9

Temp.:

50 °C

Duration:

120 h

Remarks on result:

other: result of the preliminary test

% Recovery:

9.03

pH:

7

Temp.:

20 °C

Duration:

552 h

% Recovery:

10.58

pH:

7

Temp.:

30 °C

Duration:

168 h

% Recovery:

12.69

pH:

7

Temp.:

50 °C

Duration:

33.4 h

% Recovery:

11.35

pH:

9

Temp.:

20 °C

Duration:

301 min

% Recovery:

4.37

pH:

9

Temp.:

30 °C

Duration:

150 min

% Recovery:

2.68

pH:

9

Temp.:

50 °C

Duration:

22.7 min

Key result

pH:

7

Temp.:

20 °C

Hydrolysis rate constant:

0 s-1

DT50:

162 h

Type:

(pseudo-)first order (= half-life)

Key result

pH:

7

Temp.:

30 °C

Hydrolysis rate constant:

0 s-1

DT50:

52.2 h

Type:

(pseudo-)first order (= half-life)

Key result

pH:

7

Temp.:

50 °C

Hydrolysis rate constant:

0 s-1

DT50:

11.2 h

Type:

(pseudo-)first order (= half-life)

Key result

pH:

7

Temp.:

25 °C

Hydrolysis rate constant:

0 s-1

DT50:

93.1 h

Type:

other: calculated using Arrhenius equation

Key result

pH:

9

Temp.:

20 °C

Hydrolysis rate constant:

0 s-1

DT50:

1.67 h

Type:

(pseudo-)first order (= half-life)

Key result

pH:

9

Temp.:

30 °C

Hydrolysis rate constant:

0 s-1

DT50:

0.565 h

Type:

(pseudo-)first order (= half-life)

Key result

pH:

9

Temp.:

50 °C

Hydrolysis rate constant:

0.003 s-1

DT50:

0.071 h

Type:

(pseudo-)first order (= half-life)

Key result

pH:

9

Temp.:

25 °C

Hydrolysis rate constant:

0 s-1

DT50:

0.954 h

Type:

other: calculated using Arrhenius equation

Details on results:

TEST CONDITIONS
- pH, sterility, temperature, and other experimental conditions maintained throughout the study: Yes
- Anomalies or problems encountered (if yes): None

MAJOR TRANSFORMATION PRODUCTS

At pH7:
- Range of maximum concentrations in % of the applied amount and hours of incubation when observed:
#1:
20 °C: 9.63% (start); 30 °C: 9.63% (start); 50 °C: 11.6% (start)
#2:
20 °C: 24.9% (527 h); 30 °C: 27.2% (end); 50 °C: 24.0% (28.0 h)
#3:
20 °C: 57.2% (408 h); 30 °C: 60.4% (78.6 h); 50 °C: 58.6% (12.7 h)

- Range of maximum concentrations in % of the applied amount at end of study period:
#1:
20 °C: 3.82%; 30 °C: 4.03%; 50 °C: 3.35%
#2:
20 °C: 6.58%; 30 °C: 27.2%; 50 °C: 19.6%
#3:
20 °C: 36.1%; 30 °C: 47.7%; 50 °C: 18.9%

At pH9:
- Range of maximum concentrations in % of the applied amount and minutes of incubation when observed:
#1:
20 °C: 3.85% (10.1 min); 30 °C: 4.61% (121 min); 50 °C: 4.75% (1.50 min)
#2:
20 °C: 1.92% (start); 30 °C: 2.67% (start); 50 °C: 2.84% (start)
#3:
20 °C: 91.6% (end); 30 °C: 109% (end); 50 °C: 109% (end)

- Range of maximum concentrations in % of the applied amount at end of study period:
#1:
20 °C: 2.69%; 30 °C: 4.53%; 50 °C: 4.37%
#2:
20, 30 and 50 °C: not detectable
#3:
20 °C: 91.6%; 30 °C: 109%; 50 °C: 109%

PATHWAYS OF HYDROLYSIS
- Description of pathwayS:
- Figures of chemical structures attached: Yes/No

Hydrolysis Results for the Test Item at pH 7 and 20 °C

Hydrolysis Time	Concentration	Ln Concentration
[h]	[mg/L]
0.00	15.4	2.73
26.3	13.6	2.61
32.3	13.4	2.60
45.8	12.6	2.53
98.7	9.23	2.22
168	7.06	1.95
240	5.17	1.64
312	3.21	1.16
408	2.75	1.01
527	1.73	0.547
552	1.39	0.326

 

Formation of the Transformation Products T1, T2 and T3 at pH 7 and 20 °C

Hydrolysis Time	[% of test item]
[h]	T1	T2	T3
0.00	9.63	2.28	3.13
26.3	3.91	1.21	16.7
32.3	4.35	1.22	17.6
45.8	3.34	1.11	23.0
98.7	7.11	1.22	26.0
168	6.10	0.990	40.5
240	8.32	4.43	48.4
312	6.09	9.77	48.2
408	5.80	13.4	57.2
527	4.03	24.9	56.2
552	3.82	6.58	36.1

 

Hydrolysis Results for the Test Item at pH 7 and 30 °C

Hydrolysis Time	Concentration	Ln Concentration
[h]	[mg/L]
0.00	15.4	2.73
6.72	14.0	2.64
25.9	10.4	2.34
28.4	9.87	2.29
32.3	9.51	2.25
45.8	7.91	2.07
51.1	7.33	1.99
54.9	7.08	1.96
72.8	5.56	1.72
78.6	5.09	1.63
168	1.63	0.487

 

Formation of the Transformation Products T1, T2 and T3 at pH 7 and 30 °C

Hydrolysis Time	[% of test item]
[h]	T1	T2	T3
0.00	9.63	2.28	3.13
6.72	9.60	1.95	11.4
25.9	3.54	0.847	37.4
28.4	3.59	0.778	39.0
32.3	3.73	0.873	42.1
45.8	3.48	0.193	50.4
51.1	3.53	1.71	55.2
54.9	3.15	1.87	56.9
72.8	3.04	3.69	60.0
78.6	3.02	5.43	60.4
168	4.03	27.2	47.7

 

Hydrolysis Results for the Test Item at pH 7 and 50 °C

Hydrolysis Time	Concentration	Ln Concentration
[h]	[mg/L]
0.00	15.6	2.75
0.917	13.9	2.63
1.87	12.9	2.55
3.25	10.1	2.31
4.72	8.31	2.12
6.72	7.56	2.02
8.72	6.30	1.84
10.7	5.38	1.68
12.7	4.50	1.50
28.0	2.11	0.748
33.4	1.98	0.684

 

Formation of the Transformation Products T1, T2 and T3 at pH 7 and 50 °C

Hydrolysis Time	[% of test item]
[h]	T1	T2	T3
0.00	11.6	0.573	1.24
0.917	11.5	0.103	7.73
1.87	8.93	-	19.4
3.25	5.54	-	30.0
4.72	5.45	0.496	39.0
6.72	3.94	0.901	49.0
8.72	4.35	2.69	54.9
10.7	4.23	5.18	57.7
12.7	3.42	9.48	58.6
28.0	3.83	24.0	24.9
33.4	3.35	19.6	18.9

 

Hydrolysis Results for the Test Item at pH 9 and 20 °C

Hydrolysis Time	Concentration	Ln Concentration
[min]	[mg/L]
0.00	15.5	2.74
10.1	14.2	2.65
20.3	13.4	2.59
30.2	12.8	2.55
45.1	11.3	2.43
60.1	10.5	2.36
75.1	9.68	2.27
90.4	8.43	2.13
120	6.97	1.94
151	6.12	1.81
201	3.93	1.37
251	2.96	1.09
301	1.76	0.564

 

Formation of the Transformation Products T1, T2 and T3 at pH 9 and 20 °C

Hydrolysis Time	[% of test item]
[min]	T1	T2	T3
0.00	2.69	1.92	3.33
10.1	3.85	1.21	8.80
20.3	2.60	1.13	16.5
30.2	3.19	1.09	21.5
45.1	2.44	0.965	30.2
60.1	2.90	0.662	36.5
75.1	2.72	0.329	43.2
90.4	2.68	0.276	46.7
120	2.93	0.194	58.9
151	2.94	-	71.4
201	2.72	-	74.1
251	2.74	-	86.1
301	2.69	-	91.6

 

Hydrolysis Results for the Test Item at pH 9 and 30 °C

Hydrolysis Time	Concentration	Ln Concentration
[min]	[mg/L]
0.00	15.3	2.73
1.00	15.4	2.74
4.02	14.4	2.67
8.02	13.2	2.58
11.7	12.3	2.51
18.0	10.5	2.36
25.0	9.17	2.22
43.5	6.12	1.81
48.0	5.56	1.72
60.0	4.16	1.43
75.1	3.51	1.26
90.2	2.84	1.04
121	1.32	0.279
150	0.669	-0.402

 

Formation of the Transformation Products T1, T2 and T3 at pH 9 and 30 °C

Hydrolysis Time	[% of test item]
[min]	T1	T2	T3
0.00	4.33	2.67	7.59
1.00	4.26	2.64	8.17
4.02	4.42	2.60	14.9
8.02	4.41	2.43	22.8
11.7	4.40	2.11	30.2
18.0	4.39	1.83	41.1
25.0	4.37	1.52	49.6
43.5	4.48	1.01	71.4
48.0	4.27	0.855	73.7
60.0	4.34	0.763	83.7
75.1	4.55	0.639	87.7
90.2	4.45	0.574	92.6
121	4.61	-	103
150	4.53	-	109

 

Hydrolysis Results for the Test Item at pH 9 and 50 °C

Hydrolysis Time	Concentration	Ln Concentration
[min]	[mg/L]
0.00	15.6	2.75
1.07	12.4	2.52
1.50	13.2	2.58
2.02	11.2	2.41
2.53	11.3	2.43
3.00	10.0	2.30
4.05	8.06	2.09
5.00	7.02	1.95
7.00	4.53	1.51
9.02	3.92	1.37
12.0	3.11	1.14
16.0	0.862	-0.148
22.7	0.418	-0.873

 

Formation of the Transformation Products T1, T2 and T3 at pH 9 and 50 °C

Hydrolysis Time	[% of test item]
[min]	T1	T2	T3
0.00	4.34	2.84	8.63
1.07	4.13	2.02	26.3
1.50	4.75	2.11	35.2
2.02	4.34	1.60	43.8
2.53	4.33	1.81	42.0
3.00	4.36	1.46	49.3
4.05	4.14	1.13	56.8
5.00	4.70	0.873	75.2
7.00	4.43	-	86.1
9.02	4.59	-	92.8
12.0	4.38	-	94.8
16.0	4.62	-	109
22.7	4.37	-	109

Validity criteria fulfilled:

yes

Conclusions:

The test item showed a moderate hydrolysis rate (2.4 h ≤ t1/2 ≤ 30 d) for pH 7 at 20, 30 and 50 °C and a fast hydrolysis (t1/2 ≤ 2.4 h) for pH 9 at 20, 30 and 50 °C.
At pH 4, no significant reduction of the test item concentration was observed in the preliminary test and therefore the test item was considered as hydrolytically stable under this condition and a half-life of > 1 year could be assumed for environmental typical temperatures (25 °C).

Executive summary:

Reaction Rate Constants and Half-Lives at pH 7

	pH 7
	20 °C	30 °C	50 °C	25 °C ^1)
Reaction rate constant kobs [1/s]	1.19 · 10^-6	3.69 · 10^-6	1.72 · 10^-5	2.07 · 10^-6
Half-life T½ [h]	162	52.2	11.2	93.1
Half-life T½ [d]	6.76	2.18	0.466	3.88
Number of data points	11	11	11	EA = 6.92 · 10^4J * mol^-1
Slope of regression graph	significantly non-zero

1) = values calculated via Arrhenius equation
EA = activation energy

 

Reaction Rate Constants and Half-Lives at pH 9

	pH 9
	20 °C	30 °C	50 °C	25 °C ^1)
Reaction rate constant kobs [1/s]	1.16 · 10^-4	3.41 · 10^-4	2.72 · 10^-3	2.02 · 10^-4
Half-life T½ [h]	1.67	0.565	0.0708	0.954
Half-life T½ [d]	0.0694	0.0235	0.00295	0.0398
Number of data points	13	14	13	EA = 8.30 · 10^4J * mol^-1
Slope of regression graph	significantly non-zero

1) = values calculated via Arrhenius equation
EA = activation energy

Description of key information

The substance is expected to hydrolyse under normal environmental conditions. Experimental studies on hydrolytic effects demonstrated that the substance does undergo hydrolysis at environmentally relevant pH’s, with a half life of 6.75 days at pH 7 (20°C).

Key value for chemical safety assessment

Half-life for hydrolysis:

6.75 d

at the temperature of:

20 °C