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Hydrolysis

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Reference
Endpoint:
hydrolysis
Type of information:
experimental study
Adequacy of study:
key study
Study period:
07 June 2017 to 15 November 2017
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)
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
Qualifier:
according to guideline
Guideline:
other: REACH Regulation (EU) No 1907/2006 of the European Parliament and of the Council.
Deviations:
no
GLP compliance:
yes (incl. QA statement)
Radiolabelling:
no
Analytical monitoring:
yes
Details on sampling:
- At each sampling time, two samples were removed from the bath and an aliquot (1 mL) of each was diluted to volume (10 mL) with mobile phase for analysis by high performance liquid chromatography (HPLC).
- Extended testing at pH 9: Duplicate samples were taken immediately to serve as t0 samples, and then several pairs of samples were analysed in the range 10 to 90 % hydrolysis to test for pseudo-first order behaviour.
Buffers:
Buffer solutions were prepared as follows:
- pH 4: 0.2 M aqueous potassium dihydrogen orthophosphate (110 mL) was mixed with 0.07 M aqueous disodium hydrogen orthophosphate dodecahydrate (250 mL) and purified water (640 mL). The pH was adjusted to 4.0 ± 0.05 with orthophosphoric acid.
- pH 7: 0.2 M aqueous potassium dihydrogen orthophosphate (250 mL) was mixed with 1 M sodium hydroxide (30 mL) and purified water (720 mL). The pH was adjusted to 7.0 ± 0.05 with 1 M hydrochloric acid.
- pH 9: 0.1 M boric acid in 0.1 M aqueous potassium chloride (500 mL) was mixed with 1 M sodium hydroxide (21 mL) and purified water (480 mL). The pH was adjusted to 9.0 ± 0.05 with 1 M hydrochloric acid.
Details on test conditions:
PRELIMINARY TEST
The following procedure was carried out at each of pH 4, 7 and 9:
- Aliquots (0.1 mL) of a stock solution in purified water (3 g/L) were added to separate Wheaton vials containing buffer solution (10 mL), which had been purged with nitrogen and pre-equilibrated at test temperature (50 ± 0.5 °C).
- The samples, of nominal concentration 30 mg/L, were placed in a 50 °C water bath in the dark until sampling was required (immediately, and then after 2.4, 24 and 120 hours).
- At each sampling time, two samples were removed from the bath and an aliquot (1 mL) of each was diluted to volume (10 mL) with mobile phase for analysis by high performance liquid chromatography (HPLC).
- Sample pH and incubation temperature were monitored over the period of the test.

EXTENDED TESTING AT PH 9
- Separate tests were conducted at temperatures of 50, 60 and 70 °C in the dark, and the procedure followed was as detailed for the preliminary test. Duplicate samples were taken immediately to serve as t0 samples, and then several pairs of samples were analysed in the range 10 to 90% hydrolysis to test for pseudo-first order behaviour.
Duration:
120 h
pH:
4
Temp.:
50 °C
Initial conc. measured:
28.5 mg/L
Duration:
120 h
pH:
7
Temp.:
50 °C
Initial conc. measured:
31.7 mg/L
Duration:
120 h
pH:
9
Temp.:
50 °C
Initial conc. measured:
29.7 mg/L
Duration:
480 h
pH:
9
Temp.:
50 °C
Initial conc. measured:
31.84 mg/L
Duration:
168 h
pH:
9
Temp.:
60 °C
Initial conc. measured:
29.26 mg/L
Duration:
64 h
pH:
9
Temp.:
70 °C
Initial conc. measured:
28.91 mg/L
Number of replicates:
The test was performed in duplicate
Positive controls:
no
Negative controls:
no
Preliminary study:
- The preliminary study showed that at pH 4 and pH 7 and 50 ± 0.5 ºC, less than 10 % hydrolysis had occurred after 120 hours (5 days), equivalent to an environmental (25 °C) half-life (te½) of greater than 1 year. No further testing was therefore necessary at these pH values.
- At pH 9 and 50 ± 0.5 ºC, however, more than 10 % hydrolysis had occurred after 120 hours (5 days), indicating a te½ value of less than 1 year. This necessitated proceeding to definitive testing at this pH value.
Test performance:
LINEARITY
Under the conditions described, the calibration of the test material was found to be linear over the range 0 to 5 mg/L with a regression coefficient of 1.0000. It was considered that the analytical method was sufficiently sensitive to quantify test material concentrations down to 10 % or less of the initial concentration.

PH OF TEST SOLUTIONS
- The results show that there were no significant changes in pH with time.
Transformation products:
not specified
Key result
pH:
4
Temp.:
25 °C
DT50:
> 1 yr
Remarks on result:
hydrolytically stable based on preliminary test
Key result
pH:
7
Temp.:
25 °C
DT50:
> 1 yr
Remarks on result:
hydrolytically stable based on preliminary test
Key result
pH:
9
Temp.:
25 °C
Hydrolysis rate constant:
0 h-1
DT50:
398 d
Type:
(pseudo-)first order (= half-life)
Details on results:
EXTENDED TESTING AT PH 9
- At pH 9, definitive tests were conducted at temperatures of 50, 60 and 70 °C, and the hydrolysis rate constant (k) and te½ at 25 °C were extrapolated from
the measured values of log10k at the selected temperatures using the Arrhenius relationship. A te½ value of 398 days was obtained at this pH value.
- The hydrolysis reactions for the test material at pH 9 were shown to follow pseudo-first order behaviour.

Table 1: Preliminary test results for hydrolysis of the test material

pH

Concentration of the test material in solution at time th (in hours) (mg/L)

t0h

t2.4h

t24h

t120h

Measured

Mean

Measured

Mean

Measured

Mean

Measured

Mean

4

28.7, 28.3

28.5

29.3, 29.3

29.3

28.2, 28.1

28.2

28.8, 28.9

28.8

7

32.2, 31.3

31.7

31.5, 31.5

31.5

30.6, 30.8

30.7

30.5, 31.1

30.8

9

28.9, 30.6

29.7

30.7, 30.4

30.5

30.4, 29.7

30.1

23.8, 24.1

23.9

 

Table 2: Results for hydrolysis of the test material at pH 9 and 50 °C

Time (hours)

Concentration (mg/L)

Mean concentration (mg/L)

log10Ct

0

31.93, 31.74

31.84

1.503

72

28.84, 28.60

28.72

1.458

144

25.57, 25.56

25.57

1.408

216

22.23, 23.18

22.71

1.356

336

18.20, 18.36

18.28

1.262

408

16.30, 17.04

16.67

1.222

480

14.83, 15.25

15.04

1.177

Exponential regression, log10Ct= 1.505 - 0.00069t

                                                       r = -0.9992

rate constant, kobs= -slope x 2.303 = 0.001598 hour-1

 

Table 3: Results for hydrolysis of the test material at pH 9 and 60 °C

Time (hours)

Concentration (mg/L)

Mean concentration (mg/L)

log10Ct

0

29.54, 28.97

29.26

1.466

24

25.95, 25.93

25.94

1.414

48

22.28, 22.86

22.57

1.354

72

20.34, 21.18

20.76

1.317

120

16.68, 16.39

16.54

1.218

144

14.86, 15.37

15.12

1.179

168

13.51, 13.45

13.48

1.130

Exponential regression, log10Ct= 1.459 - 0.00197t

                                                       r = -0.9989

Rate constant, kobs= -slope x 2.303 = 0.004548 hour-1

 

Table 4: Results for hydrolysis of the test material at pH 9 and 70 °C

Time (hours)

Concentration (mg/L)

Mean concentration (mg/L)

log10Ct

0

28.79, 29.02

28.91

1.461

7

25.98, 26.26

26.12

1.417

16

20.96, 20.97

20.97

1.321

31

18.76, 18.91

18.84

1.275

40

15.19, 15.09

15.14

1.180

55

12.60, 13.23

12.92

1.111

64

12.58, 12.35

12.47

1.096

Exponential regression, log10Ct= 1.445 - 0.00588t

                                                       r = -0.9872

Rate constant, kobs= -slope x 2.303 = 0.01354 hour-1

Validity criteria fulfilled:
yes
Conclusions:
Under the conditions of this study, the test material was determined to be hydrolytically stable under acidic and neutral conditions, but to hydrolyse slowly under basic conditions with a half-life of 398 days.
Executive summary:

The rate of hydrolysis of the test material as a function of pH was investigated in accordance with the standardised guidelines OECD 111 and EU Method C.7., under GLP conditions.

The preliminary study showed that at pH 4 and pH 7 and 50 ± 0.5 °C, less than 10 % hydrolysis had occurred after 120 hours (5 days), equivalent to an environmental (25 °C) half-life (te½) of greater than 1 year. No further testing was therefore necessary at these pH values.

At pH 9 and 50 ± 0.5 °C, however, more than 10 % hydrolysis had occurred after 120 hours (5 days), indicating a te½ value of less than 1 year. This necessitated proceeding to definitive testing at this pH value.

The hydrolysis reactions for the test material were shown to follow pseudo-first order behaviour in definitive testing at pH 9. Definitive tests were conducted at temperatures of 50, 60 and 70 °C, and the hydrolysis rate constant (k) and te½ at 25 °C were extrapolated from the measured values of log10k at the selected temperatures using the Arrhenius relationship. A te½ value of 398 days was obtained at pH 9.

Under the conditions of this study, the test material was determined to be hydrolytically stable under acidic and neutral conditions, but to hydrolyse slowly under basic conditions with a half-life of 398 days.

Description of key information

Under the conditions of this study, the test material was determined to be hydrolytically stable under acidic and neutral conditions, but to hydrolyse slowly under basic conditions with a half-life of 398 days.

Key value for chemical safety assessment

Half-life for hydrolysis:
398 d
at the temperature of:
25 °C

Additional information

The rate of hydrolysis of the test material as a function of pH was investigated in accordance with the standardised guidelines OECD 111 and EU Method C.7., under GLP conditions.

The preliminary study showed that at pH 4 and pH 7 and 50 ± 0.5 °C, less than 10 % hydrolysis had occurred after 120 hours (5 days), equivalent to an environmental (25 °C) half-life (te½) of greater than 1 year. No further testing was therefore necessary at these pH values.

At pH 9 and 50 ± 0.5 °C, however, more than 10 % hydrolysis had occurred after 120 hours (5 days), indicating a te½ value of less than 1 year. This necessitated proceeding to definitive testing at this pH value.

The hydrolysis reactions for the test material were shown to follow pseudo-first order behaviour in definitive testing at pH 9. Definitive tests were conducted at temperatures of 50, 60 and 70 °C, and the hydrolysis rate constant (k) and te½ at 25 °C were extrapolated from the measured values of log10k at the selected temperatures using the Arrhenius relationship. A te½ value of 398 days was obtained at pH 9.

Under the conditions of this study, the test material was determined to be hydrolytically stable under acidic and neutral conditions, but to hydrolyse slowly under basic conditions with a half-life of 398 days.

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