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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
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)
GLP compliance:
yes (incl. certificate)
Radiolabelling:
no
Analytical monitoring:
yes
Details on sampling:
Duplicate sample solutions were taken initially and from the waterbath at various time points. The pH of each solution was recorded. The concentration of test item in the sample solutions was determined by high performance liquid chromatography (HPLC).
Samples
An aliquot of the pH 4 and 7 sample solutions were basified with drops of triethylamine to improve their peak shape. An aliquot of the pH 9 sample solution was analysed without further treatment.
Buffers:
The test system consisted of a pH 4 buffer solution and purified water which was adjusted to pH 7 and 9 after addition of the test item.
Duration:
24 h
pH:
4
Temp.:
50 °C
Initial conc. measured:
193 mg/L
Duration:
120 h
pH:
4
Temp.:
50 °C
Initial conc. measured:
193 mg/L
Duration:
24 h
pH:
7
Temp.:
50 °C
Initial conc. measured:
211 mg/L
Duration:
24 h
pH:
7
Temp.:
50 °C
Initial conc. measured:
209 mg/L
Duration:
120 h
pH:
7
Temp.:
50 °C
Initial conc. measured:
211 mg/L
Duration:
120 h
pH:
7
Temp.:
50 °C
Initial conc. measured:
209 mg/L
Duration:
24 h
pH:
9
Temp.:
50 °C
Initial conc. measured:
222 mg/L
Duration:
24 h
pH:
9
Temp.:
50 °C
Initial conc. measured:
220 mg/L
Duration:
120 h
pH:
9
Temp.:
50 °C
Initial conc. measured:
222 mg/L
Duration:
120 h
pH:
9
Temp.:
50 °C
Initial conc. measured:
220 mg/L
Duration:
670 h
pH:
9
Temp.:
50 °C
Initial conc. measured:
222 mg/L
Duration:
670 h
pH:
9
Temp.:
50 °C
Initial conc. measured:
220 mg/L
Number of replicates:
2
Positive controls:
no
Negative controls:
no
Transformation products:
not measured
Details on hydrolysis and appearance of transformation product(s):
Due to additional peaks forming in the chromatography when the test was performed with pH 7 and pH 9 buffers, the test was repeated with the stock solutions being prepared in purified water followed by pH adjustment. Although the pH 7 samples maintained the required pH (± 0.1), the pH 9 samples did drop to approximately pH 8.5 for the 477¼ and 670 Hours’ time points. This was possibly a consequence of the reaction of the test item over time. It was considered that this did not have a significant effect on the test as the rate of hydrolysis was not calculated. Significant changes in pH would probably affect the hydrolytic rate as the pH drifts. In contrast, the pH 4 buffer did not form significant additional peaks in the chromatography and was therefore used in the test.
The samples and standards were prepared in plastic vessels because the test item readily absorbed to the surface of glass vessels, including after silanizing the glass.
The addition of triethylamine to the pH 4 and pH 7 samples was to basify them and improve the peak shape as they had a tendency to tail/broaden. This was successful for pH 7 but not completely so for pH 4. In contrast, the standards being prepared in just purified water were already basic due to the test item.
No significant peaks were observed at the approximate retention time of the test item on analysis of the matrix blank solution. Therefore blank subtraction was not performed.
From the result it can be clearly seen that the concentration at pH 9 decreases over time. However the decrease is not linear as would usually be expected for hydrolysis as water is always in significant excess and isn’t a rate limiting step. Additionally, the main components of the test item had no functional groups that were expected to hydrolyse under conditions of the test. Oxidation with dissolved oxygen is a possibility, but this would be expected to be too low in concentration to be responsible for the decrease in concentration of the test item. Reaction with itself could be possible but this was not confirmed.
% Recovery:
100
pH:
4
Temp.:
50 °C
Duration:
24 h
% Recovery:
95.8
pH:
4
Temp.:
50 °C
Duration:
120 h
% Recovery:
99.1
pH:
7
Temp.:
50 °C
Duration:
24 h
% Recovery:
98.1
pH:
7
Temp.:
50 °C
Duration:
120 h
% Recovery:
89.7
pH:
9
Temp.:
50 °C
Duration:
24 h
% Recovery:
79.7
pH:
9
Temp.:
50 °C
Duration:
120 h
% Recovery:
65.7
pH:
9
Temp.:
50 °C
Duration:
477.25 h
% Recovery:
62.3
pH:
9
Temp.:
50 °C
Duration:
670 h
pH:
4
Temp.:
50 °C
DT50:
> 1 yr
Type:
not specified
pH:
7
Temp.:
50 °C
DT50:
> 1 yr
Type:
not specified
pH:
9
Temp.:
50 °C
Remarks on result:
not determinable
Validity criteria fulfilled:
yes
Conclusions:
The estimated half-life at 25 °C of the test item has been shown to be greater than 1 year at pH 4 and 7. For pH 9, 38% was lost in 28 days at 50 °C; however, it was considered that although the concentration of test item reduced over time it was most probably not due to hydrolysis.
Executive summary:

The estimated half-life at 25 °C of the test item has been shown to be greater than 1 year at pH 4 and 7. For pH 9, 38% was lost in 28 days at 50 °C; however, it was considered that although the concentration of test item reduced over time it was most probably not due to hydrolysis.

Description of key information

The estimated half-life at 25 °C of the test item has been shown to be greater than 1 year at pH 4 and 7. For pH 9, 38% was lost in 28 days at 50 °C; however, it was considered that although the concentration of test item reduced over time it was most probably not due to hydrolysis.

Key value for chemical safety assessment

Half-life for hydrolysis:
1 yr
at the temperature of:
50 °C

Additional information