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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:
February 2018 to May 2018
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to
Guideline:
OECD Guideline 111 (Hydrolysis as a Function of pH)
Version / remarks:
2004
Deviations:
no
GLP compliance:
yes
Radiolabelling:
no
Analytical monitoring:
yes
Details on sampling:
- Sampling intervals for the parent/transformation products: The test was sampled periodically to provide at least 6 data-points between 10% and 90% hydrolysis for each replicate (Days 1, 3, 6, 8, 14, 22, 28, 30)
- Sampling method: Two vials(replica) for each day of sampling and each pH were prepared using three different head stock solutions with different buffers; 1.5 ml of each bottle series was transferred into each GC vials
- Sample storage conditions before analysis: Samples were analysed as soon as practicable once obtained from the reaction vessels by comparison of blank and test solution absorbances at 200 nm. If immediate analysis of test samples was not possible, samples were placed in cold storage (≤5 °C) to prevent further hydrolysis.
Buffers:
pH 4: 9 ml of 0.1M NaOH + 50 ml of 0.1M Potassium citrate monobasic
pH 7: 29.63 ml of 0.1M NaOH + 50 ml of 0.1M monopotassium phosphate
pH 9: 21.3 ml of 0.1M NaOH + 50 ml of 0.1M boric acid
All buffers were made up to 100 ml with deionised water. Buffers were sterilised by filtering to 0.2μm.
Details on test conditions:
TEST SYSTEM
- Amber vials and incubators were chosen to ensure that the hydrolysis reactions were carried out in the dark to avoid photolytic effects;
- Measures to exclude oxygen: Oxygen was excluded from the system by passing nitrogen into the headspace prior to sealing;

TEST MEDIUM
- Preparation of test medium: To prepare the treatments, approximately 2.5g of test material was made up to 50ml of Acetonitrile in a volumetric flask. 100µL of this solution was added to 100ml of each buffer (made to volume in a volumetric flask). Blank solutions consisted of non-spiked buffer media used to make the test solutions.
- Renewal of test solution: no

OTHER TEST CONDITIONS
- Adjustment of pH: The pH was controlled at the start of the test for each buffer with a calibrated pH meter.
Duration:
28 d
pH:
4
Temp.:
15 °C
Initial conc. measured:
50 mg/L
Duration:
28 d
pH:
7
Temp.:
50 °C
Initial conc. measured:
50 mg/L
Duration:
28 d
pH:
9
Temp.:
70 °C
Initial conc. measured:
50 mg/L
Positive controls:
no
Negative controls:
no
Preliminary study:
The OECD guideline states that 'for each buffered system if less than 10% hydrolysis is observed after 5 days the chemical is considered to be hydrolytically stable (t½>1 year) and no further testing is required'. This was not observed, initial results indicated that the test item had hydrolysed >10% after 5 days at all three pH conditions, therefore a tier 2 test was performed.
Test performance:
As per guideline, using the buffers recommended in OECD testing guideline 111
Transformation products:
yes
No.:
#1
% Recovery:
ca. 11
pH:
9
Temp.:
70 °C
Duration:
30 d
% Recovery:
ca. 27
pH:
9
Temp.:
50 °C
Duration:
30 d
% Recovery:
ca. 19
pH:
9
Temp.:
15 °C
Duration:
30 d
% Recovery:
ca. 45
pH:
7
Temp.:
70 °C
Duration:
30 d
% Recovery:
ca. 40
pH:
7
Temp.:
50 °C
Duration:
30 d
% Recovery:
ca. 2
pH:
7
Temp.:
15 °C
Duration:
28 d
% Recovery:
ca. 7
pH:
4
Temp.:
70 °C
Duration:
30 d
% Recovery:
ca. 7
pH:
4
Temp.:
50 °C
Duration:
30 d
% Recovery:
ca. 7
pH:
4
Temp.:
15 °C
Duration:
8 d
Key result
pH:
4
Temp.:
15 °C
DT50:
3.1 d
Type:
(pseudo-)first order (= half-life)
Key result
pH:
4
Temp.:
50 °C
DT50:
3.8 d
Type:
(pseudo-)first order (= half-life)
Key result
pH:
4
Temp.:
70 °C
DT50:
2.8 d
Type:
(pseudo-)first order (= half-life)
Key result
pH:
7
Temp.:
15 °C
DT50:
1.4 d
Type:
second order
Key result
pH:
7
Temp.:
50 °C
DT50:
11.1 d
Type:
second order
Key result
pH:
7
Temp.:
70 °C
DT50:
10 d
Type:
second order
Key result
pH:
9
Temp.:
15 °C
DT50:
11.4 d
Type:
(pseudo-)first order (= half-life)
Key result
pH:
9
Temp.:
50 °C
DT50:
11.7 d
Type:
(pseudo-)first order (= half-life)
Key result
pH:
9
Temp.:
70 °C
DT50:
7.3 d
Type:
(pseudo-)first order (= half-life)
Results with reference substance:
No reference substance used
Validity criteria fulfilled:
yes
Conclusions:
The substance is susceptible to hydrolysis under environmental conditions (pH 4 -9). Hydrolysis is more rapid in neutral and acidic conditions
Executive summary:

A GLP study was conducted in accordance with OECD test guideline 111 using non-radiolabelled test material. The definitive test was conducted at 15, 50 and 70 °C at pH values of 4, 7 and 9. The hydrolysis of the substance was pH dependent. At pH 4 and pH 9 a first order reaction was found; the reaction at pH 7 was second order. The hydrolysis reaction was much more related to the pH than to the temperature.

Description of key information

The substance is susceptible to hydrolysis under environmental conditions (pH 4 -9). Hydrolysis is more rapid in neutral and acidic conditions.

Key value for chemical safety assessment

Half-life for hydrolysis:
1.4 d
at the temperature of:
15 °C

Additional information