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Environmental fate & pathways

Hydrolysis

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Reference
Endpoint:
hydrolysis
Type of information:
experimental study
Adequacy of study:
key study
Study period:
2001-01-23 till 2001-01-30
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to
Guideline:
EU Method C.7 (Degradation: Abiotic Degradation: Hydrolysis as a Function of pH)
Version / remarks:
31st July 1992
Deviations:
no
GLP compliance:
not specified
Radiolabelling:
no
Analytical monitoring:
yes
Details on sampling:
The concentration of the test substance in the solution was determined in duplicate, after:
- 0, 45.25, 48, 54 and 70 hours (pH 4.0)
- 0, 48 and 51 hours (pH 7.0)
- 0, 48 and 51 hours (pH 9.0)
Buffers:
Buffer solutions at pH 4.0, 7.0 and 9.0 were prepared. The pH of each buffer solution was checked before use. In addition each buffer solution was degassed using nitrogen. For each buffer solution, one replicate was performed in which an aliquot (0.0296 g for pH 4.0. 0.0291 g for pH 7.0 and 0.0302 g for pH 9.0) of the test substance was dissolved in 2.5 mL of methanol and make up to 250 mL with the buffer solution in a test bottle protected from light.
Estimation method (if used):
Arrhenius plot of Ln k versus 1/T (T expressed in Kelvin) was constructed from the data.
Duration:
70 h
pH:
4
Temp.:
60 °C
Initial conc. measured:
101 ng/L
Duration:
70 h
pH:
7
Temp.:
60 °C
Initial conc. measured:
98.9 ng/L
Duration:
70 h
pH:
9
Temp.:
60 °C
Initial conc. measured:
103 ng/L
Number of replicates:
2
Positive controls:
not specified
Negative controls:
not specified
Preliminary study:
The abiotic degradation was estimated in a preliminary test. The determination was undertaken at three pH levels (pH 4.0, 7.0 and 9.0). The test was performed at 50°C and 75 °C under sterile conditions and protected from light. During the preliminary test the degradation, at each pH value indicated an hydrolysis lower than 50% after 2.4 hours and higher than 10% after 3 days. The test item was considered as hydrolytically unstable.
Test performance:
First determination (test 1) was performed at 50°C to cover approximately 20-70% hydrolysis. As the results of this test indicated a pseudo-first order reaction kinetic, the final test (test 3) was performed at 60°C and 75°C.
Transformation products:
not measured
% Recovery:
38
pH:
4
Temp.:
60 °C
Duration:
70 h
% Recovery:
31
pH:
7
Temp.:
60 °C
Duration:
51 h
% Recovery:
36
pH:
9
Temp.:
60 °C
Duration:
51 h
pH:
4
Temp.:
25 °C
Hydrolysis rate constant:
0.001 h-1
DT50:
680 h
Type:
(pseudo-)first order (= half-life)
Key result
pH:
7
Temp.:
25 °C
Hydrolysis rate constant:
0.008 h-1
DT50:
82.9 h
Type:
(pseudo-)first order (= half-life)
pH:
9
Temp.:
25 °C
Hydrolysis rate constant:
0.004 h-1
DT50:
178 h
Type:
(pseudo-)first order (= half-life)
Details on results:
Please see the tables below for details.

Table 1: Hydrolysis as a function of pH (pH 4.0 at 60°C)

Sampling Time (hours)

Measured pH

Measured concentration (µg/mL)

First assay

Second assay

Mean

Remaining concentration (%)

0

3.97

102

99.5

101

100

45.25

3.92

59.5

60.0

59.8

59

48

3.95

51.5

44.2

47.9

47

54

3.92

42.6

42.7

42.7

42

70

3.90

38.6

38.9

38.8

38

 

Table 2: Hydrolysis as a function of pH (pH 7.0 at 60°C)

Sampling Time (hours)

Measured pH

Measured concentration (µg/mL)

First assay

Second assay

Mean

Remaining concentration (%)

0

6.95

98.4

99.3

98.9

100

48

6.92

41.0

38.6

39.8

40

51

6.92

31.9

30.1

31.0

31

 

Table 3: Hydrolysis as a function of pH (pH 9.0 at 60°C)

Sampling Time (hours)

Measured pH

Measured concentration (µg/mL)

First assay

Second assay

Mean

Remaining concentration (%)

0

8.97

103

103

103

100

48

8.97

49.2

49.7

49.5

49

51

8.95

38.8

33.0

35.9

36

Validity criteria fulfilled:
yes
Conclusions:
Following advanced tests results according to EU Method C.7, the test item can be considered as hydrolytically unstable with: t1/2 = 680 h at 25°C for pH 4.0, t1/2 = 82.9 h at 25°C for pH 7.0 and t1/2 = 178 h at 25°C for pH 9.0.
Executive summary:

The determination of the hydrolysis as a function of pH was based on the EEC-Directive 92/69 EEC, Part C, Methods for the determination of Ecotoxicity, C.7: “Abiotic degradation: Hydrolysis as a function of pH”. The test item was determined to be not hydrolytically stable at pH 4, 7 or 9 in the preliminary test.During the preliminary test the degradation, at each pH value indicated an hydrolysis lower than 50% after 2.4 hours and higher than 10% after 3 days. The hydrolysis rate was then determined at three different temperatures. First determination (test 1) was performed at 50°C to cover approximately 20-70% hydrolysis. As the results of this test indicated a pseudo-first order reaction kinetic, the final test (test 3) was performed at 60°C and 75°C. The values of the hydrolysis rate constant and t1/2 at 25°C for each pH were obtained by extrapolation. The values were found to be: hydrolysis rate constant = 0.00102 h-1 and t1/2= 680 h at 25°C for pH 4.0; hydrolysis rate constant = 0.00836 h-1 and t1/2= 82.9 h at 25°C for pH 7.0; hydrolysis rate constant = 0.00389 h-1 and t1/2=178 h at 25°C for pH 9.0.

Description of key information

Following advanced tests results according to EU Method C.7, the test item can be considered as hydrolytically unstable with: t1/2 = 680 h at 25°C for pH 4.0, t1/2 = 82.9 h at 25°C for pH 7.0 and t1/2 = 178 h at 25°C for pH 9.0 (reference 5.1.2 -1).

Key value for chemical safety assessment

Half-life for hydrolysis:
82.9 h
at the temperature of:
25 °C

Additional information

The determination of the hydrolysis as a function of pH was based on the EEC-Directive 92/69 EEC, Part C, Methods for the determination of Ecotoxicity, C.7: “Abiotic degradation: Hydrolysis as a function of pH”. The test item was determined to be not hydrolytically stable at pH 4, 7 or 9 in the preliminary test.During the preliminary test the degradation, at each pH value indicated an hydrolysis lower than 50% after 2.4 hours and higher than 10% after 3 days. The hydrolysis rate was then determined at three different temperatures. First determination (test 1) was performed at 50°C to cover approximately 20-70% hydrolysis. As the results of this test indicated a pseudo-first order reaction kinetic, the final test (test 3) was performed at 60°C and 75°C. The values of the hydrolysis rate constant and t1/2at 25°C for each pH were obtained by extrapolation. The values were found to be: hydrolysis rate constant = 0.00102 h-1 and t1/2= 680 h at 25°C for pH 4.0; hydrolysis rate constant = 0.00836 h-1 and t1/2= 82.9 h at 25°C for pH 7.0; hydrolysis rate constant = 0.00389 h-1 and t1/2=178 h at 25°C for pH 9.0 (reference 5.1.2 -1).