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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:
2012-03-06 - 2012-04-25
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: Well-documented GLP Guideline study
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)
GLP compliance:
yes (incl. certificate)
Remarks:
The Department of Health of the Government of the United Kingdom
Specific details on test material used for the study:
Details on properties of test surrogate or analogue material:
No surrogate or analogue material was used.
Radiolabelling:
no
Analytical monitoring:
yes
Details on sampling:
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 GC.
- Samples: Duplicate aliquots (A and B) of each sample solution were diluted by a factor of 20 using MeCN.
- Standards: Duplicate standard solutions of test item were prepared in MeCN:relevant buffer solution (95:5 v/v) at a nominal concentration of 25 mg/L.
- Matrix blanks: MeCN:relevant buffer solution (95:5 v/v)
Buffers:
pH 4: Potassium hydrogen phthalate (0.005 mol dm-3)
pH 7: Disodium hydrogen orthophosphate (anhydrous, 0.003 mol dm-3), Potassium dihydrogen orthophosphate (0.002 mol dm-3), Sodium chloride (0.002 mol dm-3)
pH 9: Disodium tetraborate (0.001 mol dm-3), Sodium chloride (0.002 mol dm-3)
Estimation method (if used):
Not applicable.
Details on test conditions:
PREPARATION OF TEST SOLUTIONS
Sample solutions were prepared in stoppered glass flasks at a nominal concentration of 0.5 g/L in the three buffer solutions. A 1 % co-solvent of acetonitrile was used to aid solubility.
The concentration of each solution did not exceed the lesser of 0.01 mol/L or half the water solubility.
The test solutions were split into individual vessels for each data point.
The solutions were shielded from light whilst maintained at the tes test temperature.

PRELIMINARY TEST / TIER 1
An aliquot of test item (1.2523 g) was diluted to 25 mL with acetonitrile (MeCN). This solution was diluted by a factor of 100 in pH 4, 7 and 9 buffers to give a concentration of 501 mg/L.
Sample solutions at pH 4, 7 and 9 were maintained at 50 +/- 0.5 °C for a period of 5 days.

TIER 2
An aliqout of test item (0.5056 g) was diluted to 10 mL with MeCN. This solution was diluted by a factor of 100 in pH 9 buffer to give a concentration of 506 mg/L.
Sample solutions were maintained at 50 +/- 0.5 °C for a period of 7 days.
Duration:
5 d
pH:
4
Initial conc. measured:
501 mg/L
Duration:
5 d
pH:
7
Initial conc. measured:
501 mg/L
Duration:
5 d
pH:
9
Initial conc. measured:
501 mg/L
Duration:
7 d
pH:
9
Initial conc. measured:
506 mg/L
Number of replicates:
2
Positive controls:
yes
Remarks:
Standard Solution
Negative controls:
no
Statistical methods:
No statistical methods described.
Preliminary study:
Concerning pH 4 and 7 at a temperature of 50 +/- 0.5 °C, no further testing was required.
pH 9: Approximately 10 % hydrolysis after 5 days at 50 +/- 0.5 °C was determined, however, variability in the results from the 24 and 48 h timepoint had indicated hydrolysis greater than 10 %. A further test was therefore required.
Test performance:
Neither unusual observations were reported nor deviations from the test procedure as well as no further information affecting results.
Transformation products:
not measured
Details on hydrolysis and appearance of transformation product(s):
No details reported since the test substance is hydrolytically stable and no transformation products are build.
pH:
4
Temp.:
25 °C
DT50:
> 1 yr
Type:
other: Arrhenius relationship
Remarks on result:
other: As less than 10 % hydrolysis occurred after 5 d, no further testing to determine the rate constants was performed.
pH:
7
Temp.:
25 °C
DT50:
> 1 yr
Type:
other: Arrhenius relationship
Remarks on result:
other: As less than 10 % hydrolysis occurred after 5 d, no further testing to determine the rate constants was performed.
pH:
9
Temp.:
25 °C
DT50:
> 1 yr
Type:
other: Arrhenius relationship
Remarks on result:
other: As less than 10 % hydrolysis occurred after 5 d, no further testing to determine the rate constants was performed.
Other kinetic parameters:
Not relevant.
Details on results:
PRINCIPLE:
The concentration of the test item is determined as a function of time, using a suitable analytical method. In the case of decreasing concentrations, the logarithms of the concentrations are plotted against time (log10 (ct)). If the plot is a straight line, the reaction is considered to be of (pseudo-) first order. The rate constant and the half-life time are then calculated using the slope. From data generated at differing temperatures for any single pH, an estimation of the rate constant and half- life at 25 °C is determined by the use of the Arrhenius relationship.
VALIDATION:
The linearity of the detector response with respect to concentration was assessed over the following nominal concentration ranges: 7.15 to 57.2 mg/L in MeCN:pH4 buffer (95:5 v/v), 5.95 to 47.6 mg/L in MeCN:pH7 buffer (95:5 v/v) and 7.40 to 59.2 mg/L in MeCN:pH9 buffer (95:5 v/v). These were satisfactory with correlation coefficients of 0.999, 1.000 and 0.999 respectively being obtained.
GENERAL:
The tier 1 test at pH 9 showed a decrease in concentration of the test item over 48 hours to 84 % of the initial concentration which then increased to 89 % after 5 days. Therefore further investigation was required at this pH. During this second test at pH9, although the concentration decreased to less than 90 % of the initial concentration at the 48 hour timepoint, further samples taken after 5 and 7 days showed that there had in fact been no loss of test item over the entire test. Therefore the result for the 48 hour timepoint has been regarded as erroneous and overall the test item is stable in aqueous media at pH 9. As less than 10 % hydrolysis occurred after five days, no further testing to determine the rate constants was performed.

Table 1: Preliminary test results

Solution

Mean Peak Area

Standard 25.1 mg/L

3.29 x106

Standard 25.5 mg/L

3.67 x106

Initial Sample A, pH 4

3.20x106

Initial Sample B, pH 4

2.82 x106

Standard 25.0 mg/L

3.33x 106

Standard 25.5 mg/L

3.40 x106

Initial Sample A, pH 7

3.27x 106

Initial Sample B, pH 7

3.26 x106

Standard 25.5 mg/L

3.18 x106

Standard 25.5 mg/L

3.13 x106

Initial Sample A, pH 9

3.30 x106

Initial Sample B, pH 9

3.20x 106

Standard 25.5 mg/L

3.22 x106

Standard 26.6 mg/L

3.24x 106

24 Hour Sample A, pH 4

2.93x 106

24 Hour Sample B, pH 4

3.38 x106

Standard 25.5 mg/L

3.23x 106

Standard 26.6 mg/L

3.40x 106

24 Hour Sample A, pH 7

3.15x 106

24 Hour Sample B, pH 7

3.17 x106

Standard 25.5 mg/L

3.17 x106

Standard 26.6 mg/L

3.39x 106

24 Hour Sample A, pH 9

2.78x 106

24 Hour Sample B, pH 9

3.15 x106

Standard 25.5 mg/L

3.01x106

Standard 26.6 mg/L

3.43x 106

48 Hour Sample A, pH 4

3.10 x106

48 Hour Sample B, pH 4

2.97 x106

Standard 25.5 mg/L

3.12x 106

Standard 26.6 mg/L

3.46 x106

48 Hour Sample A, pH 7

2.99 x106

48 Hour Sample B, pH 7

2.26x 106

Standard 25.5 mg/L

3.27x106

Standard 26.6 mg/L

3.22x 106

48 Hour Sample A, pH 9

2.72x 106

48 Hour Sample B, pH 9

2.63x 106

Standard 25.5 mg/L

3.35x 106

Standard 26.6 mg/L

3.50x 106

120 Hour Sample A, pH 4

2.98x 106

120 Hour Sample B, pH 4

3.24x 106

Standard 25.5 mg/L

3.69x106

Standard 26.6 mg/L

3.71x 106

120 Hour Sample A, pH 7

3.40x 106

120 Hour Sample B, pH 7

2.78x 106

Standard 25.5 mg/L

3.47x 106

Standard 26.6 mg/L

3.56x106

120 Hour Sample A, pH 9

3.06 x106

120 Hour Sample B, pH 9

3.06x 106

Table 2: pH 4 at 50 +/- 0.5 °C

 

Time (Hours)

 

 

0(A)

0(B)

24(A)

24(B)

48(A)

48(B)

120(A)

120(B)

Concentration (g/L)

0.500

0.493

.0.472

0.545

0.503

0.480

0.454

0.493

Log10 [concentration (g/L)]

-0.301

-0.307

-0.326

-0.263

-0.299

-0.318

-0.343

-0.307

Mean concentration (g/L)

0.497

0.509

0.492

0.474

% hydrolysis

-

-

4.87

-9.80

-1.27

3.23

8.55

0.748

Table 3: pH 7 at 50 +/- 0.5 °C

 

Time (Hours)

0(A)

0(B)

24(A)

24(B)

48(A)

48(B)

120(A)

120(B)

Concentration (g/L)

0.493

0.491

0.495

0.498

0.474

0.358[1]

0.478

0.392[2]

Log10 [concentration (g/L)]

-0.307

-0.309

-0.305

-0.303

-0.324

-

-0.320

-

Mean concentration (g/L)

0.492

0.497

 

 

% hydrolysis

-

-

-0.618

-1.13

3.73

-

2.84

-

Table 4: pH 9 at 50 +/- 0.5 °C

 

Time (Hours)

0(A)

0(B)

24(A)

24(B)

48(A)

48(B)

120(A)

120(B)

Concentration (g/L)

0.511

0.510

0.441

0.501

0.436

0.423

0.453

0.453

Log10 [concentration (g/L)]

-0.292

-0.292

-0.356

-0.301

-0.360

-0.374

-0.343

-0.344

Mean concentration (g/L)

0.511

0.471

 

 

%hydrolysis

-

-

13.7

1.98

14.6

17.2

11.2

11.2

Table 5: Mean peak areas relating to the standard and sample solutions

Solution

Mean Peak Area

Standard 25.9 mg/L

3.53 x 106

Standard 26.7 mg/L

3.80 x 106

Initial Sample A, pH 9

3.45 x 106

Initial Sample B, pH 9

3.82 x 106

Standard 25.9 mg/L

3.31 x 106

Standard 26.7 mg/L

3.12 x 106

48 Hour Sample A, pH 9

2.75 x 106

48 Hour Sample B, pH 9

2.84 x 106

Standard 25.9 mg/L

3.03 x 106

Standard 26.7 mg/L

3.59 x 106

120 Hour Sample A, pH 9

3.16 x 106

120 Hour Sample B, pH 9

3.39 x 106

Standard 25.9 mg/L

2.08 x 106

Standard 26.7 mg/L

1.91 x 106

168 Hour Sample A, pH9

2.47 x 106

168 Hour Sample B, pH9

2.17 x 106

Table 6: pH 9 at 50 +/- 0.5 °C, Tier 2

 

Time (Hours)

0(A)

0(B)

   24(A)

24(B)

48(A)

48(B)

120(A)

120(B)

Concentration (g/L)

0.494

0.546

0.499

0.464

0.501

0.538

0.649

0.569

Log10 [concentration (g/L)]

-0.306

-0.263

-0.348

-0.333

-0.300

-0.269

-0.187

-0.245

Mean concentration (g/L)

0.520

0.457

 

 

%hydrolysis

-

-

13.8

10.7

3.63

-3.38

-24.8

-9.42

Table 7: Estimated half-lives at 25 °C of the test item

pH

Estimated half-life at 25 °C

4

> 1 year

7

> 1 year

9

> 1 year

Validity criteria fulfilled:
yes
Remarks:
Validation criteria are fulfilled.
Conclusions:
The study is regarded as a valid guideline study with certificated GLP compliance. At pH 4, 7 and 9 (Tier 2 necessary ) the test substance can be regarded as hydrolytically stable at an ambient temperature of 25 °C (half-life greater than 1 year).
Executive summary:

The potential of the test substance to hydrolyse under environmental conditions was investigated according to OECD Guideline 111 under certificated GLP compliance (Tarran, 2012). The test substance is dissolved in an aqueous solution at pH 4, 7 and 9 and incubated in the dark at 50 +/- 0.5 °C. The concentration of the test item is determined as a function of time. The estimation of the half-life at 25 °C for any single pH was determined by the use of the Arrhenius relationship. The test substance was diluted to 25 mL with acetonitrile (MeCN). This solution was diluted by a factor of 100 in pH 4, 7 and 9 buffers, resulting in a concentration of 501 mg/L. Concerning pH 4 and 7, the preliminary experiment over a period of 5 days was sufficient to conclude, that the substance is stable at ambient temperature, since the half-lifes will be greater than 1 year, respectively. A further test was required at pH 9, since approximately 10 % hydrolysis after 5 days at 50 °C, however, variability in the results form the 24 and 48 h timepoints indicated higher hydrolysis rates. In the Tier 2 testing, the sample solutions (diluted to 10 mL with MeCN, concentration of 506 mg/L) were maintained at the same temperature for a period of 7 days. Since less than 10 % hydrolysis was observed after this testing period, also at pH 9 the substance can be regarded as hydrolytically stable at ambient temperature. As less than 10 % hydrolysis occurred after five days, no further testing to determine the rate constants was performed.

Description of key information

Hydrolysis, as a function of pH, EU Method C.7: hydrolytically stable compound (at pH 4, 7 and 9) and the half-life at 25 °C will be greater than 1 year 

Key value for chemical safety assessment

Half-life for hydrolysis:
1 yr
at the temperature of:
25 °C

Additional information

The potential of the test substance to hydrolyse under environmental conditions was investigated according to OECD Guideline 111 under certificated GLP compliance (Tarran, 2012). The test substance was dissolved in an aqueous solution at pH 4, 7 and 9 and incubated in the dark at 50 +/- 0.5 °C. The concentration of the test item is determined as a function of time. The estimation of the half-life at 25 °C for any single pH was determined by the use of the Arrhenius relationship. The test substance was diluted to 25 mL with acetonitrile (MeCN). This solution was diluted by a factor of 100 in pH 4, 7 and 9 buffers, resulting in a concentration of 501 mg/L. Concerning pH 4 and 7, the preliminary experiment over a period of 5 days was sufficient to conclude, that the substance is stable at ambient temperature, since the half-lifes will be greater than 1 year, respectively. A further test was required at pH 9, since approximately 10 % hydrolysis after 5 days occurred at 50 °C, however, variability in the results from the 24 and 48 h timepoints indicated higher hydrolysis rates. In the Tier 2 testing, the sample solutions (diluted to 10 mL with MeCN, concentration of 506 mg/L) were maintained at the same temperature for a period of 7 days. Since less than 10 % hydrolysis was observed after this testing period, also at pH 9 the substance can be regarded as hydrolytically stable at ambient temperature. As less than 10 % hydrolysis occurred after five days, no further testing to determine the rate constants was performed.