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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:
Testing was conducted between 04 January 2012 and 09 June 2012.
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: see 'Remark'
Remarks:
Study conducted in compliance with agreed protocols, with no or minor deviations from standard test guidelines and/or minor methodological deficiencies, which do not affect the quality of the relevant results. The study report was conclusive, done to a valid guideline and the study was conducted under GLP conditions.
Qualifier:
according to
Guideline:
OECD Guideline 111 (Hydrolysis as a Function of pH)
Deviations:
no
Qualifier:
according to
Guideline:
EU Method C.7 (Degradation: Abiotic Degradation: Hydrolysis as a Function of pH)
Deviations:
no
Principles of method if other than guideline:
Performed at 15°C due to instability of the test item at the Sponsor's request. Rather than a result at 25°C as specified in the guidelines.
GLP compliance:
yes
Radiolabelling:
no
Analytical monitoring:
yes
Details on sampling:
Preparation of samples
Stock Sample solutions were prepared in glass flasks at a nominal concentration of 0.015 mg/l in the three buffer solutions that had been equilibrated to 10°C. A 1% co-solvent of acetonitrile was used to aid dissolution. The stock solutions were split into individual vessels for each data point. The solutions were shielded from light whilst maintained at the test temperature.

Testing at 15°C
Sample solutions at pH 4, 7 and 9 were maintained at 15.0 ± 0.5°C.

Analysis of sample solutions
The sample solutions were taken from the waterbath at various times and the pH of each solution recorded.
The concentration of the sample solution was determined by high performance liquid chromatography – mass spectrometry (HPLC-MS).

Samples
An aliquot (20 ml) was passed through a previously primed* (* The cartridges were primed with tetrahydrofuran, acetonitrile and methanol followed by reverse osmosis water.) Strata X solid phase extraction cartridge. The cartridge was dried with nitrogen and the analyte eluted with 2 ml of acetonitrile.

Standards
Duplicate standard solutions of test item were prepared in acetonitrile at a nominal concentration of 0.25 mg/l.

Matrix blanks
An aliquot of relevant buffer (20 ml) was treated as per the samples.
Acetonitrile.


Buffers:
Buffer Solution (pH 4)
Components: Potassium hydrogen phthalte
Concentration (mol dm-3): 0.005

Buffer Solution (pH7)
Components: Disodium hydrogen orthophosphate (anhydrous), Potassium dihydrogen orthophosphate, Sodium chloride
Concentration (mol dm-3): 0.003, 0.002, 0.002

Buffer Solution (pH9)
Components: Disodium tetraborate, Sodium chloride
Concentration (mol dm-3): 0.001, 0.002

The buffer solutions were filtered through a 0.2 µm membrane filter to ensure they were sterile before commencement of the test. Also these solutions were subjected to ultrasonication and degassing with nitrogen to minimise dissolved oxygen content.

Estimation method (if used):
Not used.
Details on test conditions:
Refer to details on sampling and analytical methods.
Duration:
28 h
pH:
4
Initial conc. measured:
0 other: g/L - Sample A
Duration:
28 h
pH:
4
Initial conc. measured:
0 other: g/L - Sample B
Duration:
28 h
pH:
7
Initial conc. measured:
0 other: g/L - Sample A
Duration:
28 h
pH:
7
Initial conc. measured:
0 other: g/L - Sample B
Duration:
28 h
pH:
9
Initial conc. measured:
0 other: g/L - Sample A
Duration:
28 h
pH:
9
Initial conc. measured:
0 other: g/L - Sample B
Number of replicates:
.
Positive controls:
no
Negative controls:
no
Statistical methods:
Not specified.
Preliminary study:
The mean peak heights relating to the standard and sample solutions are shown in table 4.2 (please see remarks on results including tables and figures section).
Test performance:
Validation
The linearity of the detector response with respect to concentration was assessed over the nominal concentration range of 0 to 0.4 mg/l. These were prepared by dissolving an aliquot of test item (0.1027 g) in acetonitrile and performing serial dilutions with acetonitrile. This was satisfactory with a correlation coefficient of 0.999 being obtained. Please see Attachment 5 for Figure 4.4 - Linearity graph.

Recovery of analysis of the sample procedure was assessed and proved adequate for the test, as the hydrolysis rate is determined by the change in sample concentrations and not the absolute concentrations. Therefore, a 100% recovery is not essential, but consistency is preferential. At a nominal concentration of 1.6 x 10-2 mg/l, a mean percentage recovery of 57.5 % was obtained. See Table 4.6 for individually sample recovery percentages (please see remarks on results including tables and figures section).

The test sample concentrations have not been corrected for recovery of analysis.
Transformation products:
not specified
pH:
4
Temp.:
15 °C
DT50:
< 24 h
pH:
7
Temp.:
15 °C
DT50:
< 24 h
pH:
9
Temp.:
15 °C
DT50:
< 24 h
Other kinetic parameters:
None.
Details on results:
The half-life at 15°C of the test item at pH 4, 7 and 9 was estimated to be less than 24 hours.

Results

Testing at 15°C

The mean peak areas relating to the standard and sample solutions are shown in the following table:

Table 4.2

Solution

Mean Peak Area (Total Ion Count)

Standard 0.211 mg/l

8.288 x 105

Standard 0.210 mg/l

9.163 x 105

Initial Sample A, pH 4

3.087 x 105

Initial Sample B, pH 4

3.011 x 105

2 Hour Sample A, pH 4

4.025 x 105

2 Hour Sample B, pH 4

1.960 x 105

4 Hour Sample A, pH 4

3.178 x 105

4 Hour Sample B, pH 4

2.097 x 105

6 Hour Sample A, pH 4

4.052 x 105

6 Hour Sample B, pH 4

2.249 x 105

Standard 0.207 mg/l

1.392 x 107

Standard 0.212 mg/l

9.960 x 106

22 Hour Sample A, pH 4

1.278 x 106

22 Hour Sample B, pH 4

1.211 x 106

28 Hour Sample A, pH 4

1.722 x 106

28 Hour Sample B, pH 4

-3.528 x 105*

Standard 0.211 mg/l

6.490 x 105

Standard 0.210 mg/l

6.922 x 105

Initial Sample A, pH 7

3.246 x 105

Initial Sample B, pH 7

2.193 x 105

2 Hour Sample A, pH 7

1.318 x 105

2 Hour Sample B, pH 7

1.608 x 105

4 Hour Sample A, pH 7

1.884 x 105

4 Hour Sample B, pH 7

1.552 x 105

6 Hour Sample A, pH 7

2.505 x 105

6 Hour Sample B, pH 7

2.325 x 105

 

Table 4.2 continued

Solution

Mean Peak Area (Total Ion Count)

Standard 0.207 mg/l

8.247 x 106

Standard 0.212 mg/l

6.376 x 105

22 Hour Sample A, pH 7

2.746 x 105

22 Hour Sample B, pH 7

1.239 x 105

28 Hour Sample A, pH 7

9.739 x 105

28 Hour Sample B, pH 7

3.496 x 105

Standard 0.211 mg/l

4.542 x 105

Standard 0.210 mg/l

4.449 x 105

Initial Sample A, pH 9

1.373 x 105

Initial Sample B, pH 9

1.691 x 105

2 Hour Sample A, pH 9

6.367 x 104

2 Hour Sample B, pH 9

1.046 x 105

4 Hour Sample A, pH 9

1.311 x 105

4 Hour Sample B, pH 9

1.554 x 105

6 Hour Sample A, pH 9

2.132 x 105

6 Hour Sample B, pH 9

1.242 x 105

Standard 0.207 mg/l

3.834 x 106

Standard 0.212 mg/l

3.978 x 106

22 Hour Sample A, pH 9

3.623 x 105

22 Hour Sample B, pH 9

1.911 x 105

28 Hour Sample A, pH 9

2.219 x 105

28 Hour Sample B, pH 9

-1.553 x 105*

  *The sample peak area was less than blank peak area that was subtracted.


 

The test item concentrations at the given time points are shown in the following tables:

Table 4.3      pH 4 at 15.0 ± 0.5ºC

Time (Hours)

Concentration (g/l)

Log10[concentration (g/l)]

% of initial concentration

A

B

A

B

A

B

0

7.45 x 10-6

7.26 x 10-6

-5.13

-5.14

-

-

2

9.71 x 10-6

4.73 x 10-6

-5.01

-5.33

132

64.3

4

7.67 x 10-6

5.06 x 10-6

-5.12

-5.30

104

68.8

6

9.77 x 10-6

5.43 x 10-6

-5.01

-5.27

133

73.8

22

2.24 x 10-6

2.12 x 10-6

-5.65

-5.67

30.4

28.8

28

3.02 x 10-6

n/a*

-5.52

n/a*

41.0

n/a*

Result:          Slope    =   -1.98x 10-2(see Figure 4.1)
kobs        =   4.56x 10-2hour-1
              =   1.27x 10-5second-1
t½          =   15.2 hours

Table 4.4      pH 7 at 15.0 ± 0.5ºC

Time (Hours)

Concentration (g/l)

Log10[concentration (g/l)]

% of initial concentration

A

B

A

B

A

B

0

1.02 x 10-5

6.88 x 10-6

-4.99

-5.16

-

-

2

4.14 x 10-6

5.05 x 10-6

-5.38

-5.30

48.4

59.1

4

5.91 x 10-6

4.87 x 10-6

-5.23

-5.31

69.3

57.1

6

7.86 x 10-6

7.30 x 10-6

-5.11

-5.14

92.1

85.5

22

7.86 x 10-7

3.55 x 10-7

-6.11

-6.45

9.20

4.15

28

2.79 x 10-6

1.00 x 10-6

-5.56

-6.00

32.6

11.7

Result:          Slope    =   -3.33x 10-3(see Figure 4.2)
kobs        =   7.68x 10-2hour-1
              =   2.13x 10-5second-1
t½          =   9.03 hours


 Table 4.5      pH 9 at 15.0 ± 0.5ºC

Time (Hours)

Concentration (g/l)

Log10[concentration (g/l)]

% of initial concentration

A

B

A

B

A

B

0

6.43 x 10-6

7.92 x 10-6

-5.19

-5.10

-

-

2

2.98 x 10-6

4.90 x 10-6

-5.53

-5.31

41.6

68.3

4

6.14 x 10-6

7.28 x 10-6

-5.21

-5.14

85.6

101

6

9.99 x 10-6

5.82 x 10-6

-5.00

-5.24

139

81.1

22

1.94 x 10-6

1.03 x 10-6

-5.71

-5.99

27.1

14.3

28

1.19 x 10-6

n/a*

-5.92

n/a*

16.6

n/a*

Result:          Slope    =   -2.91x 10-2(see Figure 4.3)
kobs        =   6.71x 10-2hour-1
              =   1.86x 10-5second-1
t½          =   10.3 hours

*Data not applicable due to a negative peak area

Table 4.6      Recoveries

Sample

Recovery (%)

A

57.4

B

57.3

C

57.9

As a comparison, the recovery percentages of the 0 hour timepoints based on the ‘as weighed in’ concentration of 1.66 x 10-5g/L are shown in the following table:

Table 4.7      Recoveries

pH

Recovery (%)

A

B

4

44.8

43.7

7

61.4

41.4

9

38.7

47.7

Validity criteria fulfilled:
yes
Remarks:
The linearity of the detector response with respect to concentration was assessed over the nominal concentration range of 0 to 0.4 mg/l. This was satisfactory with a correlation coefficient of 0.999 being obtained.
Conclusions:
The half-life at 15°C of the test item at pH 4, 7 and 9 was estimated to be less than 24 hours.
Executive summary:

The determination was carried out using a procedure based on Method C7 Abiotic Degradation, Hydrolysis as a Function of pH of Commission Regulation (EC) No 440/2008 of 30 May 2008 and Method 111 of the OECD Guidelines for Testing of Chemicals, 13 April 2004.

Discussion

The study was performed at 15°C at the request of the Sponsor due to the known thermal instability of the test item. The buffers were equilibrated prior to initial sample preparation to a sub-test temperature of 10°C to assist in stability of the test item prior to starting the test period and extraction of the initial samples.

Although the standard matrix blank contained no peak at the retention time of the test item, the sample matrix blank did. The peak in the sample blanks was subtracted from their relevant samples.

Sample results were seen to be variable. This will partly have been due to sensitivity/detection variability with the analytical method, but the stability of the test item could also significantly affect the sample results. The test concentration was very close to the detection limit of the analytical method, so direct analysis was not possible. Hence, the samples were extracted to concentrate up and dissolve in a solvent the test item was substantially more hydrolytically stable in. The time it took to extract the samples may also have been critical and contributed to variability.

Even so, it was evident that the test item could be extracted from the samples and on reviewing all the results, it can be suggested that the test item degraded significantly throughout the test. Although, it could not be concluded that all the degradation was due to hydrolysis or a combination of both hydrolysis and thermal degradation. The uncertainty of exact sample concentrations and variability meant an accurate half-life result could not be measured. The results also showed no definitive evidence of different hydrolytical rates for the pHs tested. Therefore a half-life of less than 24 hours will be used for all three pHs.

Conclusion

The half-life at 15°C of the test item at pH 4, 7 and 9 was estimated to be less than 24 hours.

Description of key information

The half-life at 15°C of the test item at pH 4, 7 and 9 was estimated to be less than 24 hours as an absolute worst case. Measured data in the 
hydrolysis test as well as the measured data in the ecotoxicity tests suggest this occurs somewhat faster however.

Key value for chemical safety assessment

Half-life for hydrolysis:
24 h
at the temperature of:
15 °C

Additional information

The assessment of hydrolytic stability was carried out at 15°C using a procedure based on Method C7 Abiotic Degradation, Hydrolysis as a Function of pH of Commission Regulation (EC) No 440/2008 of 30 May 2008 and Method 111 of the OECD Guidelines for Testing of Chemicals, 13 April 2004 and determined the half-life at 15°C of the test item at pH 4, 7 and 9 was estimated to be less than 24 hours. Due to hydrolysis and thermal degradation taking place as well as the low levels at which the analytical method needed to operate the accuracy of the results was limited and can therefore the result can only be concluded as <24 hours. At environmentally relevant pH's the half-life was between 9 and 10 hours but due to variation in the measurements the plotted regression curve was not 100% conclusive. 24 hours was therefore reported as a worst case. Measured ecotoxicity data suggests that hydrolysis occurs faster however. It is still possible to conclude that the test substance will only be present for a short period of time in the environment before degrading. Consideration to the breakdown products should be given during risk assessment.