4,5-dihydro-5-oxo-4-[[4-[[2-(sulphooxy)ethyl]sulphonyl]phenyl]azo]-1-(4-sulphophenyl)-1H-pyrazole-3-carboxylic acid, sodium salt

Hydrolysis

Link to relevant study record(s)

Reference

Endpoint:

hydrolysis

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2018-02-08 to 2018-03-26

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

Deviations:

no

Qualifier:

according to guideline

Guideline:

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

Version / remarks:

2008

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Radiolabelling:

no

Analytical monitoring:

yes

Details on sampling:

- Sampling intervals for the parent/transformation products:
Preliminary Test (Tier 1):
pH 4 at 50 °C: sampling at 0, 0.5, 1, 1.5, 2, 2.5, 29 and 120 h;
pH 7 at 50 °C: sampling at 0, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5 h;
pH 9 at 50 °C: sampling at 0, 0.5, 1 h.

Main Test (Tier 2):
pH 7 at 20 °C: sampling at 0, 32, 48, 56, 72, 79, 96 h;
pH 7 at 35 °C: sampling at 0, 4, 8, 24, 28, 32, 48 h;
pH 7 at 50 °C: sampling at 0, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5 h

- Sampling method: At each sampling time 2 mL diluent were added (dilution factor 2). The samples were homogenised by shaking after recrimbing. Two vials were prepared for each pH and each sampling date.
- Sampling intervals/times for pH measurements: same as sampling intervals for content determination
- Sample storage conditions before analysis: directly used for analysis

Buffers:

- pH: 4, 7, 9
- Type and final molarity of buffer: The citrate buffer (pH 4), the phosphate buffer (pH 7), and the borate buffer (pH 9) were prepared in a concentration of 0.05 M on the basis of the undissociated acids.
- Composition of buffer:
Citrate buffer pH 4 (0.05 M): Per 1 L ultra-pure water about 10.505 g citric acid monohydrate was weighed and about 60 mL of sodium hydroxide solution (1 M) was added to reach pH 4.
Phosphate buffer pH 7 (0.05 M): Per 1 L ultra-pure water about 6.805 g potassium dihydrogenphosphate was weighed and about 30 mL of sodium hydroxide solution (1 M) was added to reach pH 7.
Borate buffer pH 9 (0.05 M): Per 1 L ultra-pure water about 3.902 g boric acid and about 3.728 g potassium chloride were weighed and 21 mL of sodium hydroxide solution (1 M) were added to reach pH 9.

Details on test conditions:

TEST SYSTEM
- Type, material and volume of test flasks, other equipment used: 6mL crimb vials
- Sterilisation method: Sterile buffer solutions used, sterilised by autoclaving
- Lighting: dark
- Measures taken to avoid photolytic effects: shaking in the dark
- Measures to exclude oxygen: degassing the buffers with argon for at least five minutes and purging the vessels with argon before preparing the test solution
- Test system: closed, with teflon sealed crimp caps

TEST PROCEDURE
- Test item preparation: weighed 110 mg into a 100 mL volumetric flask and then brought to volume with the corresponding buffer solutions.
- Test concentration: 1000 mg/L
- Preliminary Test (Tier 1): performed at 50 ± 0.5 °C at three pH values 4, 7 and 9
- Main Test (Tier 2): performed at pH 7 at 20 °C ± 0.5 °C, 35 °C ± 0.5 °C and 50 °C ± 0.5 °C.

Duration:

120 h

pH:

4

Temp.:

50 °C

Initial conc. measured:

1 000 mg/L

Remarks:

Preliminary Test (Tier 1)

Duration:

5 h

pH:

7

Temp.:

50 °C

Initial conc. measured:

1 000 mg/L

Remarks:

Preliminary Test (Tier 1)

Duration:

1 h

pH:

9

Temp.:

50 °C

Initial conc. measured:

1 000 mg/L

Remarks:

Preliminary Test (Tier 1)

Duration:

96 h

pH:

7

Temp.:

20 °C

Initial conc. measured:

1 000 mg/L

Remarks:

Main Test (Tier 2)

Duration:

48 h

pH:

7

Temp.:

35 °C

Initial conc. measured:

1 000 mg/L

Remarks:

Main Test (Tier 2)

Duration:

5 h

pH:

7

Temp.:

50 °C

Initial conc. measured:

1 000 mg/L

Remarks:

Main Test (Tier 2)

Number of replicates:

2

Positive controls:

no

Negative controls:

no

Preliminary study:

At pH 4 about 100 % of the initial test item concentration was detected after 120 hours (t0.5 (25°C) > 1 year), therefore the test substance can be considered hydrolytically stable and no additional testing is required.
At pH 7 and pH 9 more than 10 % of the test item were hydrolysed within 5 hours (for pH 7), 1 hour (for pH 9) at 50 °C, respectively. It was decided to perform a Tier 2 study at pH 7. Since the hydrolysis at pH 9 was so fast, no Tier 2 test was conducted. Instead it is concluded that the degradation half-life is < 1 day at 25°C and pH 9.

Transformation products:

not measured

% Recovery:

66.1

pH:

7

Temp.:

20 °C

Duration:

96 h

% Recovery:

20.1

pH:

7

Temp.:

35 °C

Duration:

48 h

% Recovery:

38

pH:

7

Temp.:

50 °C

Duration:

5 h

Key result

pH:

7

Temp.:

20 °C

Hydrolysis rate constant:

-0.002 h-1

DT50:

161.5 h

Type:

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

Key result

pH:

7

Temp.:

35 °C

Hydrolysis rate constant:

-0.015 h-1

DT50:

20.5 h

Type:

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

Key result

pH:

7

Temp.:

50 °C

Hydrolysis rate constant:

-0.085 h-1

DT50:

3.7 h

Type:

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

Details on results:

TEST CONDITIONS
- pH, temperature maintained throughout the study: Yes
- Others: The hydrolysis at pH 9 was very fast. Approximately 5 % of the initial concentration was remaining after 0.5 hours at 50°C. Therefore the corresponding half-life time can be estimated to be much lower than one day at 25 °C. Because of the clear result of the preliminary test and the resulting short sampling intervals no Tier 2 test was performed.

Time course of test concentration at pH 7 at 20 °C:

Sampling time [h]	Concentration [mg/L]	Mean Concentration [mg/L]	% of initial concentration [%]	log[c(t)/c(0)]	pH
0	1003.56	1003.5	100	0	7.11
	1003.5
32	850.98	852.7	85	-0.07072	7.06
	854.38
48	784.47	786.9	78.4	-0.1056	7.09
	789.28
56	770.33	770.6	76.8	-0.11469	7.09
	770.8
72	733.29	734.3	73.2	-0.13564	7.1
	735.26
79	717	718	71.5	-0.14539	7.07
	719.09
96	660.42	662.9	66.1	-0.18007	7.08
	665.39

Time course of test concentration at pH 7 at 35 °C:

Sampling time [h]	Concentration [mg/L]	Mean Concentration [mg/L]	% of initial concentration [%]	log[c(t)/c(0)]	pH
0	1003.56	1003.5	100	0	7.11
	1003.5
4	879.9	882.4	87.9	-0.0559	7.08
	884.92
8	776.09	777.3	77.5	-0.1109	7.07
	778.46
24	431.85	432.1	43.1	-0.3659	7.06
	432.36
28	380.45	380.8	37.9	-0.4208	7.05
	381.05
32	341.54	342.3	34.1	-0.4671	7.07
	343.13
48	202.12	202.2	20.1	-0.6957	7.06
	202.35

Time course oftestconcentration at pH 7 at 50 °C:

Sampling time [h]	Concentration [mg/L]	Mean Concentration [mg/L]	% of initial concentration [%]	log[c(t)/c(0)]	pH
0	987.12	986.7	100	0	7.06
	986.25
0.5	927.03	921.4	93	-0.0297	7.09
	915.67
1	836.36	836.1	85	-0.0719	7.1
	835.79
1.5	773.04	772.5	78	-0.1063	7.09
	771.88
2	705.46	700.8	71	-0.1486	7.08
	696.2
2.5	635.21	635.7	64	-0.1909	7.08
	636.23
3	568.64	569.8	58	-0.2385	7.08
	570.91
3.5	521.33	522	53	-0.2765	7.06
	522.68
4	465.03	465.8	47	-0.326	7.07
	466.52
4.5	410.65	410.5	42	-0.3809	7.07
	410.35
5	373.69	374.6	38	-0.4206	7.06
	375.48

Degradation endpoint for hydrolysis of the test item:

Test-temperature	pH value	Kinetic model	Slope a [h^-1]	Y-axis intercept b	DT50 [h]	DT50 [d]
20 °C	pH 7	SFO	-0.001812	-0.008309	161.5	6.73
35 °C	pH 7	SFO	-0.014665	-0.000654	20.5	0.85
50 °C	pH 7	SFO	-0.085462	0.014573	3.7	0.15

Validity criteria fulfilled:

yes

Conclusions:

The test item is hydrolytically stable at pH 4. At pH 7 a Tier 2 study was performed. The determined degradation half-life values at pH 7 are 161.5, 20.5, 3.7 h for 20 °C, 35 °C, 50 °C, respectively. At pH 9 the hydrolysis is very fast and it is assumed that the half-life at 25°C is much lower than 1 day.

Executive summary:

The abiotic degradation of test item as a function of pH in aqueous solution was determined according to OECD guideline 111 and EC method C.7 (440/2008). 

First a preliminary test (Tier 1) was performed. The rate of hydrolysis at 50°C was assessed for pH 4, 7 and 9. The hydrolysis of test item was negligible at pH 4. The degradation of test item was less than 10 % at pH 4 at 50 °C over a period of 120 hours. Therefore the corresponding half-life time can be estimated to be longer than one year at 25 °C. The hydrolysis of test item was more than 10 % at pH 7 and pH 9 at 50 °C over a period of 1 hour.

The hydrolysis at pH 9 was very fast. Approximately 5 % of the initial concentration was remaining after 0.5 hours at 50 °C. Therefore the corresponding half-life time can be estimated to be much lower than one day at 25 °C. Because of the clear result of the preliminary test and the resulting short sampling intervals no Tier 2 test was performed at pH 9.

A Tier 2 test at 20 °C, 35 °C and 50 °C was performed at pH 7. The determined degradation half-life values at pH 7 are 161.5, 20.5, 3.7 h for 20 °C, 35 °C, 50 °C, respectively.

Description of key information

For this endpoint only one test is available. The abiotic degradation of test item as a function of pH in aqueous solution was determined according to OECD guideline 111 and EC method C.7 (440/2008). Hydrolysis was assessed at 3 pH values: pH 4, 7 and 9.

The hydrolysis of test item was negligible at pH 4. At pH 7 the determined degradation half-life values are 161.5, 20.5 and 3.7h at 20, 35 and 50 °C respectively. At pH 9 hydrolysis was very fast: lower than 1 day at 25°C.

Key value for chemical safety assessment

Half-life for hydrolysis:

161.5 h

at the temperature of:

20 °C

Additional information

The hydrolysis of test item was negligible at pH 4. The degradation of test item was less than 10 % at pH 4 at 50 °C over a period of 120 hours. Therefore the corresponding half-life time can be estimated to be longer than one year at 25 °C.

The hydrolysis of test item was more than 10 % at pH 7 and pH 9 at 50 °C over a period of 1 hour. The hydrolysis at pH 9 was very fast. Approximately 5 % of the initial concentration was remaining after 0.5 hours at 50 °C. Therefore the corresponding half-life time can be estimated to be much lower than one day at 25 °C. Because of the clear result of the preliminary test and the resulting short sampling intervals no Tier 2 test was performed at pH 9.

A Tier 2 test at 20 °C, 35 °C and 50 °C was performed at pH 7. The determined degradation half-life values at pH 7 are 161.5, 20.5, 3.7 h for 20 °C, 35 °C, 50 °C, respectively.