REAKTIVE GELB F 97494

Hydrolysis

Link to relevant study record(s)

Reference

Endpoint:

hydrolysis

Type of information:

experimental study

Adequacy of study:

key study

Study period:

December 19, 2001 to May 02, 2002

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:

1992

Qualifier:

according to guideline

Guideline:

OECD Guideline 111 (Hydrolysis as a Function of pH)

Version / remarks:

1995

GLP compliance:

yes

Radiolabelling:

no

Analytical monitoring:

yes

Details on sampling:

The samples were injected into the HPLC system without further pretreatment. Some of them were diluted with water. Approximately 25 mg of the test substance were dissolved in 100 mL of water and used as an external standard. The results of the tests were not corrected for the purity of the test substance.

PRELIMINARY TEST: Samples were collected at 0 h, 2.4 h and 120 h. To stop the reaction after sampling, the samples were cooled with ice. They were stored at <0°C if they could not be analysed immediately. For the calculation of the degree of hydrolysis, the mean values of both measurements at 0 h were taken.

MAIN TEST: Samples were collected at the following time points - 0, 6, 24, 27.5 and 31 h from the test systems incubated at 50°C (Test 1); and at 0, 26, 44.5 and 117 h from test systems incubated at 38°C (Test 3)

Buffers:

Standard buffer solution (pH 4, 7 and 9) were used.

Details on test conditions:

PRELIMINARY TESTS

Preparation of test solutions:
A known concentration of the test substance was dissolved in 2000 mL standard buffer pH 4 (measured 3.8 - 3.9), or standard buffer pH 7 (measured 6.8 - 6.9), or standard buffer pH 9 (measured 8.7 - 8.8) tempered at 50±0.5°C in special reaction flasks.

Sampling:
A sample of each solution was taken and the start concentrations were determined. The reaction flasks were then protected from light. Samples were again taken after 2.4 and 120 h. To stop the reaction after sampling the samples were cooled with ice. They were stored at <0°C if they could not be analysed immediately. All samples were injected twice. The pH values of the buffer solutions were measured at the beginning and at the end of the experiments. For the calculation of the degree of hydrolysis, the mean values of both measurements at 0 h were taken.

MAIN TESTS

Test 1:
Preparation of test solutions:
A known concentration of the test substance was dissolved in 2000 mL standard buffer pH 4 (measured 4.0 - 4.2) or standard buffer pH 7 (measured 6.9 - 7.2) tempered at 50°C in special reaction flasks.

Test 3:
Preparation of test solutions:
A known concentration of the test substance was dissolved in 2000 mL standard buffer pH 4 (measured 4.0 - 4.0) or standard buffer pH 7 (measured 7.0 - 7.1) tempered at 38°C in special reaction flasks.

Sampling:
A sample of each solution was taken and the start concentrations were determined. The reaction flasks were then protected from light. Samples were taken after appropriate times. To stop the reaction after sampling the samples were cooled with ice. They were stored at <0°C if they could not be analysed immediately. All samples were injected twice. The pH values of the buffer solutions were measured at the beginning and at the end of the experiments. For the calculation of the degree of hydrolysis the mean values of both measurements at 0 h were taken.

Duration:

48 h

pH:

4

Temp.:

50 °C

Initial conc. measured:

506 mg/L

Duration:

117 h

pH:

4

Temp.:

38 °C

Initial conc. measured:

482.5 mg/L

Duration:

31 h

pH:

7

Temp.:

50 °C

Initial conc. measured:

509.5 mg/L

Duration:

117 h

pH:

7

Temp.:

38 °C

Initial conc. measured:

515.5 mg/L

Number of replicates:

No experimental replicates were performed. However, each sample was analyzed twice.

Positive controls:

no

Negative controls:

no

Preliminary study:

As result from the preliminary tests additional testing at pH 9 was not required because the degree of hydrolysis was higher than 50 % within 2.4 hours. Additional testing at pH 4 and 7 was required because the degree of hydrolysis was lower than 50 % within 2.4 hours and higher than 10 % within 5 days.

Transformation products:

not measured

pH:

4

Temp.:

50 °C

Hydrolysis rate constant:

0.025

DT50:

27.2 h

Type:

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

Remarks on result:

other: Correlation coefficient ‘r’ = 0.9998

pH:

4

Temp.:

38 °C

Hydrolysis rate constant:

0.006

DT50:

109.24 h

Type:

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

Remarks on result:

other: Correlation coefficient ‘r’ = 0.9949

pH:

4

Temp.:

25 °C

Hydrolysis rate constant:

0.001

DT50:

564 h

Remarks on result:

other: Calculated.

pH:

7

Temp.:

50 °C

Hydrolysis rate constant:

0.04

DT50:

17.26 h

Type:

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

Remarks on result:

other: Correlation coefficient ‘r’ = 0.9982

pH:

7

Temp.:

38 °C

Hydrolysis rate constant:

0.007

DT50:

101.08 h

Type:

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

Remarks on result:

other: Correlation coefficient ‘r’ = 0.9895

pH:

7

Temp.:

25 °C

Hydrolysis rate constant:

0.001

DT50:

801 h

Remarks on result:

other: Calculated.

pH:

9

Temp.:

50 °C

DT50:

< 2.4 h

Remarks on result:

other: Based on the preliminary test.

pH:

9

Temp.:

25 °C

DT50:

< 24 h

Remarks on result:

other: Calculated.

Details on results:

In the main tests for test 1 (pH 4 and 7 at 50 °C) a linear dependence on time of degradation and the logarithm to base ten of the test item concentration was obtained which means that the hydrolysis reaction was a pseudo first order reaction.
Because of these results further tests at pH 4 and 7 according to test 3 were performed at 38 °C. From the measured results the rate constants (Kobs) and the half-life (t 1/2) of the test item were calculated

TABLE 1: PRELIMINARY TEST

 

Test conditions	Time point (h)	% hydrolysis	Comment
Test at pH 4.0 and 50°C	2.4	-1.50	Further testing necessary as the degree of hydrolysis was lower than 50% within 2.4 h and higher than 10% within 120 h.
	120	95.38
Test at pH 7.0 and 50°C	2.4	6.17	Further testing necessary as the degree of hydrolysis was lower than 50% within 2.4 h and higher than 10% within 120 h.
	120	70.25
Test at pH 9.0 and 50°C	2.4	68.77	No further testing necessary as the degree of hydrolysis was higher than 50% within 2.4 h.
	120	53.16

 

 

 

TABLE 2: MAIN TEST

 

Test conditions	Kobs	t1/2	Comment
Test 1 at pH 4.0 and 50°C	0.0255 h^-1	27.20 h	Results indicated a pseudo first order reaction. Test 3 was therefore performed at 38°C.
Test 3 at pH 4.0 and 38°C	0.0063 h^-1	109.24h
Test 1 at pH 7.0 and 50°C	0.0401 h^-1	7.26h	Results indicated a pseudo first order reaction. Test 3 was therefore performed at 38°C.
Test 3 at pH 7.0 and 38°C	0.0069 h^-1	101.08 h

 

Validity criteria fulfilled:

yes

Conclusions:

Under the conditions of the study, the half-life of the test substance at pH 9 was considered to be < 2.4 h. The half-life of the test substance at pH 4 and 7 were determined to be 27.20 and 17.26 h, respectively, at 50°C, and 109.24 and 101.08 h, respectively, at 38°C. From the Arrhenius equation, the rate constant at 25°C were calculated to be 0.00124 and 0.00086 at pH 4 and 7, respectively, and the corresponding half-lives were 564 and 801 h.

Executive summary:

A study was conducted to determine hydrolysis as a function of pH for the test substance according to OECD Guideline 111 and EU Method C.7, in compliance with GLP.

Based on results of the preliminary tests which demonstrated >50% hydrolysis within 2.4 h at pH 9.0, additional testing was only required at pH 4 and 7. Results of the main test (Test 1) at pH 4 and 7 at 50°C demonstrated a pseudo first order reaction. Therefore, further testing at pH 4 and 7 at 38°C was carried out according to 'Test 3'. From the results the rate constant (K_obs) and the half-life (t_1/2) of the test substance were derived or calculated for different temperatures and pH conditions.

Under the conditions of the study, the half-life of the test substance at pH 9 was considered to be < 2.4 h. The half-life of the test substance at pH 4 and 7 were determined to be 27.20 and 17.26 h, respectively, at 50°C, and 109.24 and 101.08 h, respectively, at 38°C. From the Arrhenius equation, the rate constant at 25°C were calculated to be 0.00124 and 0.00086 at pH 4 and 7, respectively, and the corresponding t_1/2were 564 and 801 h.

Description of key information

Under the conditions of the study, the half-life of the test substance at pH 9 was considered to be < 2.4 h. The half-life of the test substance at pH 4 and 7 were determined to be 27.20 and 17.26 h, respectively, at 50°C, and 109.24 and 101.08 h, respectively, at 38°C. From the Arrhenius equation, the rate constant at 25°C were calculated to be 0.00124 and 0.00086 at pH 4 and 7, respectively, and the corresponding half-lives were 564 and 801 h.

Key value for chemical safety assessment

Half-life for hydrolysis:

801 h

at the temperature of:

25 °C

Additional information

A study was conducted to determine hydrolysis as a function of pH for the test substance according to OECD Guideline 111 and EU Method C.7, in compliance with GLP. Based on results of the preliminary tests which demonstrated >50% hydrolysis within 2.4 h at pH 9.0, additional testing was only required at pH 4 and 7. Results of the main test (Test 1) at pH 4 and 7 at 50°C demonstrated a pseudo first order reaction. Therefore, further testing at pH 4 and 7 at 38°C was carried out according to 'Test 3'. From the results the rate constant (K_obs) and the half-life (t_1/2) of the test substance were derived or calculated for different temperatures and pH conditions.