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Environmental fate & pathways

Hydrolysis

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Administrative data

Endpoint:
hydrolysis
Type of information:
experimental study
Adequacy of study:
key study
Study period:
2004-07-02 to 2004-11-25
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
2005
Report date:
2005

Materials and methods

Test guideline
Qualifier:
according to guideline
Guideline:
OECD Guideline 111 (Hydrolysis as a Function of pH)
Version / remarks:
12 May 1981.
GLP compliance:
yes (incl. QA statement)

Test material

Constituent 1
Chemical structure
Reference substance name:
1,4-dithiane-2,5-diol
EC Number:
254-751-6
EC Name:
1,4-dithiane-2,5-diol
Cas Number:
40018-26-6
Molecular formula:
C4H8O2S2
IUPAC Name:
1,4-dithiane-2,5-diol
Test material form:
solid: particulate/powder
Specific details on test material used for the study:
STABILITY AND STORAGE CONDITIONS OF TEST MATERIAL
- Storage condition of test material: approximately 4°C, in the dark

Radiolabelling:
no

Study design

Analytical monitoring:
yes
Details on sampling:
- Sampling intervals for the parent/transformation products: 0 h, 2.4 h, 24 h, 120 h
- Sampling method: Aliquots of the sample solutions were taken from the flasks at various times and the pH of each solution recorded. The concentration of the sample solution was determined by gas chromatography (GC).
Samples: Duplicate aliquots (A and B, 10 mL) were frozen and freeze dried. The residue was re-dissolved in 20 ml of derivatizing agent (Pyridine: hexamethylsilazane: chlorotrimethylsilane (10:2:1 v/v/v)) and allowed to stand for 30 minutes. The resulting solution was then centrifuged (6000 rpm, 10 minutes) and the supernatant solution taken for analysis. Standards: Duplicate standard solutions of test material were prepared in derivatizing agent (see above) at a nominal concentration of 750 mg/L.
- Sampling intervals/times for pH measurements: 0 h, 2.4 h, 24 h, 120 h
Buffers:
- pH: 1.2
- Type and final molarity of buffer:
- Composition of buffer: 5.04E-002 mol/L Potassium chloride, 6.48E-002 mol/L Hydrochloric acid
- pH: 4
- Type and final molarity of buffer:
- Composition of buffer: 0.01 mol/L Potassium hydrogen phthalate
- pH: 7
- Type and final molarity of buffer:
- Composition of buffer: 6.00E-003 mol/L Disodium hydrogen orthophosphate (anhydrous), 4.00E-003 mol/L Potassium dihydrogen orthophosphate, 4.00E-003 mol/L Sodium chloride
- pH: 9
- Type and final molarity of buffer:
- Composition of buffer: 0.01 (2.00E-003*) mol/L Disodium tetraborate, 0.02 (4.00E-003*) mol/L Sodium chloride
* lower concentration used for preliminary test only, as was found to be insufficient to hold samples at required pH.

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.
Details on test conditions:
TEST SYSTEM
- Type, material and volume of test flasks, other equipment used: stoppered glass flasks
- Sterilisation method: The buffer solutions were filtered through a 0.2 µm membrane filter to ensure they were sterile before commencement of the test.
- Lighting: none
- Measures taken to avoid photolytic effects: The solutions were shielded from light whilst maintained at the test temperature.
- If no traps were used, is the test system closed/open: closed

OTHER TEST CONDITIONS
- Preparation of samples: Sample solutions were prepared in stoppered glass flasks at a nominal concentration of 1.5 g/L in the three buffer solutions.
- Preliminary test: Sample solutions at pH 4, 7 and 9 were maintained at 50.0 ± 0.5°C for a maximum period of 120 hours.
- Hydrolysis of unstable substances: Results from the Preliminary test showed it was necessary to undertake further testing at pH 4, pH 7 and pH 9, with solutions being maintained at temperatures in the range of 40 to 70 ± 0.5°C for periods of up to 240 hours.
- Hydrolysis at pH 1.2: Results from testing at pH 4 showed it was necessary, in accordance with the guideline, to undertake a further test at pH 1.2 with solutions being maintained at 37.0 ± 0.5°C for a period of 24 hours.

Positive controls:
not specified
Negative controls:
not specified
Statistical methods:
Treatment of results
Graphs of the common logarithm of the concentration (g/L) versus time (hours) were plotted for pH 4, pH 7 and pH 9 at the various temperatures and the rate constant and half-life calculated using the equations indicated below.
By plotting the natural logarithm of the rate constants against the reciprocal of the temperature (K), the rate constant and half-lives at 25°C were obtained by extrapolation.


Results and discussion

Preliminary study:
Greater than 10% hydrolysis occured in 120 hours; the test material was therefore classified as ‘unstable’ as stated in Method 111 of the OECD Guidelines for Testing of Chemicals. Therefore further testing, conducted at 50, 60 and 70°C, was required to estimate the rate constant and half-life.
Transformation products:
not specified
Total recovery of test substance (in %)open allclose all
% Recovery:
28.1
pH:
1.2
Temp.:
37 °C
Duration:
24 h
% Recovery:
86.5
pH:
4
Temp.:
50 °C
Duration:
72 h
% Recovery:
79.1
pH:
4
Temp.:
50 °C
Duration:
96 h
% Recovery:
72.8
pH:
4
Temp.:
50 °C
Duration:
118.5 h
% Recovery:
67.7
pH:
4
Temp.:
50 °C
Duration:
144 h
% Recovery:
61.8
pH:
4
Temp.:
50 °C
Duration:
168 h
% Recovery:
49.8
pH:
4
Temp.:
60 °C
Duration:
72 h
Remarks on result:
other: Test A
% Recovery:
29.8
pH:
4
Temp.:
60 °C
Duration:
96 h
Remarks on result:
other: Test A
% Recovery:
30.3
pH:
4
Temp.:
60 °C
Duration:
120 h
Remarks on result:
other: Test A
% Recovery:
21.7
pH:
4
Temp.:
60 °C
Duration:
144 h
Remarks on result:
other: Test A
% Recovery:
17
pH:
4
Temp.:
60 °C
Duration:
168 h
Remarks on result:
other: Test A
% Recovery:
13.1
pH:
4
Temp.:
60 °C
Duration:
240 h
Remarks on result:
other: Test A
% Recovery:
42.1
pH:
4
Temp.:
60 °C
Duration:
72 h
Remarks on result:
other: Test B
% Recovery:
38.6
pH:
4
Temp.:
60 °C
Duration:
96 h
Remarks on result:
other: Test B
% Recovery:
23.8
pH:
4
Temp.:
60 °C
Duration:
120 h
Remarks on result:
other: Test B
% Recovery:
22.2
pH:
4
Temp.:
60 °C
Duration:
144 h
Remarks on result:
other: Test B
% Recovery:
28.3
pH:
4
Temp.:
60 °C
Duration:
168 h
Remarks on result:
other: Test B
Remarks:
Timepoint not used in further calculations, due to extraneous point obtained.
% Recovery:
7.23
pH:
4
Temp.:
60 °C
Duration:
240 h
Remarks on result:
other: Test B
% Recovery:
68.7
pH:
4
Temp.:
70 °C
Duration:
18 h
% Recovery:
64.3
pH:
4
Temp.:
70 °C
Duration:
21 h
% Recovery:
49.6
pH:
4
Temp.:
70 °C
Duration:
24 h
% Recovery:
43.2
pH:
4
Temp.:
70 °C
Duration:
42 h
% Recovery:
38.7
pH:
4
Temp.:
70 °C
Duration:
45 h
% Recovery:
29.4
pH:
4
Temp.:
70 °C
Duration:
48 h
% Recovery:
101
pH:
7
Temp.:
40 °C
Duration:
2 h
% Recovery:
95.8
pH:
7
Temp.:
40 °C
Duration:
4 h
% Recovery:
92.9
pH:
7
Temp.:
40 °C
Duration:
6 h
% Recovery:
58.6
pH:
7
Temp.:
40 °C
Duration:
22 h
% Recovery:
57.5
pH:
7
Temp.:
40 °C
Duration:
24 h
% Recovery:
52.1
pH:
7
Temp.:
40 °C
Duration:
26 h
% Recovery:
85.3
pH:
7
Temp.:
50 °C
Duration:
2 h
Remarks on result:
other: Test A
% Recovery:
79.3
pH:
7
Temp.:
50 °C
Duration:
3 h
Remarks on result:
other: Test A
% Recovery:
70
pH:
7
Temp.:
50 °C
Duration:
4 h
Remarks on result:
other: Test A
% Recovery:
59.4
pH:
7
Temp.:
50 °C
Duration:
5 h
Remarks on result:
other: Test A
% Recovery:
51.4
pH:
7
Temp.:
50 °C
Duration:
6 h
Remarks on result:
other: Test A
% Recovery:
45.7
pH:
7
Temp.:
50 °C
Duration:
7 h
Remarks on result:
other: Test A
% Recovery:
85.8
pH:
7
Temp.:
50 °C
Duration:
2 h
Remarks on result:
other: Test B
% Recovery:
76.8
pH:
7
Temp.:
50 °C
Duration:
3 h
Remarks on result:
other: Test B
% Recovery:
67
pH:
7
Temp.:
50 °C
Duration:
4 h
Remarks on result:
other: Test B
% Recovery:
62.4
pH:
7
Temp.:
50 °C
Duration:
5 h
Remarks on result:
other: Test B
% Recovery:
55.8
pH:
7
Temp.:
50 °C
Duration:
6 h
Remarks on result:
other: Test B
% Recovery:
49.1
pH:
7
Temp.:
50 °C
Duration:
7 h
Remarks on result:
other: Test B
% Recovery:
69.9
pH:
7
Temp.:
60 °C
Duration:
1 h
% Recovery:
55.5
pH:
7
Temp.:
60 °C
Duration:
1.5 h
% Recovery:
44.8
pH:
7
Temp.:
60 °C
Duration:
2 h
% Recovery:
33.8
pH:
7
Temp.:
60 °C
Duration:
2.5 h
% Recovery:
31
pH:
7
Temp.:
60 °C
Duration:
3 h
% Recovery:
23.4
pH:
7
Temp.:
60 °C
Duration:
3.5 h
% Recovery:
89.2
pH:
9
Temp.:
30 °C
Duration:
1 h
Remarks on result:
other: Test A
% Recovery:
78
pH:
9
Temp.:
30 °C
Duration:
2 h
Remarks on result:
other: Test A
% Recovery:
68.5
pH:
9
Temp.:
30 °C
Duration:
3 h
Remarks on result:
other: Test A
% Recovery:
58.3
pH:
9
Temp.:
30 °C
Duration:
4 h
Remarks on result:
other: Test A
% Recovery:
48.8
pH:
9
Temp.:
30 °C
Duration:
5 h
Remarks on result:
other: Test A
% Recovery:
46.5
pH:
9
Temp.:
30 °C
Duration:
6 h
Remarks on result:
other: Test A
% Recovery:
80
pH:
9
Temp.:
30 °C
Duration:
1 h
Remarks on result:
other: Test B
% Recovery:
63.5
pH:
9
Temp.:
30 °C
Duration:
2 h
Remarks on result:
other: Test B
% Recovery:
49.5
pH:
9
Temp.:
30 °C
Duration:
3 h
Remarks on result:
other: Test B
% Recovery:
42
pH:
9
Temp.:
30 °C
Duration:
4 h
Remarks on result:
other: Test B
% Recovery:
35.8
pH:
9
Temp.:
30 °C
Duration:
5 h
Remarks on result:
other: Test B
% Recovery:
30.8
pH:
9
Temp.:
30 °C
Duration:
6 h
Remarks on result:
other: Test B
% Recovery:
59.3
pH:
9
Temp.:
40 °C
Duration:
1 h
Remarks on result:
other: Test A
Remarks:
Samples for this test were run incorrectly on the instrument, meaning sample A and B had to be calculated separately for each timepoint. This error was considered to have had a negligible effect on the study. Percent of initial calculated from the mean initial concentration.
% Recovery:
59.5
pH:
9
Temp.:
40 °C
Duration:
1 h
Remarks on result:
other: Test B
Remarks:
see above
% Recovery:
41.5
pH:
9
Temp.:
40 °C
Duration:
2 h
Remarks on result:
other: Test A
Remarks:
see above
% Recovery:
42.1
pH:
9
Temp.:
40 °C
Duration:
2 h
Remarks on result:
other: Test B
Remarks:
see above
% Recovery:
29.5
pH:
9
Temp.:
40 °C
Duration:
3 h
Remarks on result:
other: Test A
% Recovery:
31.3
pH:
9
Temp.:
40 °C
Duration:
3 h
Remarks on result:
other: Test B
% Recovery:
21.8
pH:
9
Temp.:
40 °C
Duration:
4 h
Remarks on result:
other: Test A
% Recovery:
22.3
pH:
9
Temp.:
40 °C
Duration:
4 h
Remarks on result:
other: Test B
% Recovery:
15.9
pH:
9
Temp.:
40 °C
Duration:
5 h
Remarks on result:
other: Test A
% Recovery:
16.4
pH:
9
Temp.:
40 °C
Duration:
5 h
Remarks on result:
other: Test B
% Recovery:
13.8
pH:
9
Temp.:
40 °C
Duration:
6 h
Remarks on result:
other: Test A
% Recovery:
14.2
pH:
9
Temp.:
40 °C
Duration:
6 h
Remarks on result:
other: Test B
Dissipation DT50 of parent compoundopen allclose all
Key result
pH:
4
Temp.:
25 °C
Hydrolysis rate constant:
0 s-1
DT50:
ca. 179 d
Type:
(pseudo-)first order (= half-life)
Key result
pH:
7
Temp.:
25 °C
Hydrolysis rate constant:
0 s-1
DT50:
ca. 272 h
Type:
(pseudo-)first order (= half-life)
Key result
pH:
9
Temp.:
25 °C
Hydrolysis rate constant:
0 s-1
DT50:
6.08 h
Type:
(pseudo-)first order (= half-life)
Other kinetic parameters:
After 24 hours at pH 1.2 and 37°C, 28.1% of the test material remained.

The kinetics of the study have been determined to be consistent with that of a pseudo-first order reaction as the graphs of log10 concentration versus time are straight lines.
It has been observed that the rate of hydrolysis increases with an increase in pH.
Details on results:
MAJOR TRANSFORMATION PRODUCTS
none determined

Applicant's summary and conclusion

Validity criteria fulfilled:
yes
Remarks:
please refer to Overall remarks
Conclusions:
The rate constant and estimated half-life at 25°C of the test material are:
4.47E-008/ sec at pH 4, corresponding to an estimated half-life of 179 days at pH 4; 7.07E-007/ sec at pH 7, corresponding to an estimated half-life of 272 hours at pH 7; 3.17E-005/ sec at pH 9, corresponding to an estimated half-life of 6.08 hours at pH 9.
After 24 hours at pH 1.2 and 37°C, 28.1% of the test material remained.