Cyclohexanone, peroxide

Hydrolysis

Link to relevant study record(s)

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

Guideline:

OECD Guideline 111 (Hydrolysis as a Function of pH)

Version / remarks:

Tier 1: Screening experiment

Deviations:

no

Principles of method if other than guideline:

There were three modifications to OECD guideline 111:
· No thymol was added to the buffer solutions as, based on microbiological experience, the addition of
thymol as a disinfectant is not necessary because the buffer solutions were sterilized also.
· A test temperature of 12°C was used. At the temperature of 50°C, as mentioned in OECD 111, the
test substance is thermally not stable.
· Only Tier 1 of the guideline was conducted in this screening study.

GLP compliance:

yes (incl. QA statement)

Radiolabelling:

no

Analytical monitoring:

yes

Details on sampling:

At the moment the test vials were placed in the water bath, the first sample was taken and analyzed. Subsequent samples were taken on different time intervals and analyzed to determine the percentage of hydrolysis. Samples were analyzed directly after sampling in order to prevent further hydrolysis.

Buffers:

Buffer solutions of the pH values 7 and 9 were prepared according to the buffer systems of CLARK and
LUBS and buffer solution pH 4 according KOLTHOFF and VLEESCHOUWER, as described in Annex 3 of
OECD guideline 111 (OECD, 2004).

Sterilization of the buffer solutions was performed by autoclaving at 121°C for 20 minutes.

Sterilised aqueous buffer solutions of different pH values (pH 4, 7 and 9) were spiked with the test
substance and incubated (12°C) in the dark under controlled laboratory conditions. After appropriate time
intervals, buffer solutions were analysed for the amount of test substance still available.

Details on test conditions:

Test vessels and buffer solutions were sterilised. Sterilization
of glassware was performed by heating at 180°C for at least 30 minutes.

Test solutions were flushed with nitrogen to minimise
oxidation. Test vessels were kept under dark conditions. A temperature-controlled water bath was used;
temperature was measured using a calibrated thermometer, pH was measured using a pH meter.

Duration:

5 d

pH:

4

Temp.:

12 °C

Initial conc. measured:

500 µg/L

Remarks:

The measured concs at the beginning of the test (± 500 μg/L) are higher than the nominal spiked conc of 400 μg/L. This is probably caused by matrix effect of the pH buffer, however this has no influence on the results of the hydrolysis rate.

Duration:

5 d

pH:

7

Temp.:

12 °C

Initial conc. measured:

500 µg/L

Remarks:

The measured concs at the beginning of the test (± 500 μg/L) are higher than the nominal spiked conc of 400 μg/L. This is probably caused by matrix effect of the pH buffer, however this has no influence on the results of the hydrolysis rate.

Duration:

5 d

pH:

9

Temp.:

12 °C

Initial conc. measured:

500 µg/L

Remarks:

The measured concs at the beginning of the test (± 500 μg/L) are higher than the nominal spiked conc of 400 μg/L. This is probably caused by matrix effect of the pH buffer, however this has no influence on the results of the hydrolysis rate.

Number of replicates:

Six for analytical repeatability (lowest and highest standard concentrations), one for half-life measurements at each pH

Positive controls:

no

Negative controls:

no

Statistical methods:

Table I: Summary of validation parameters of the analytical method
Parameter Limit Determined
Regression (R2 ≥ 0.99 0.996
Accuracy calibration standards (% recovery) 80 – 120 81.6 – 108.1
Quality control (% recovery) 80 – 120 83.7 – 100.3
Stability calibration standards (% recovery) 80 – 120 81.6 – 98.8
Repeatability (CV (%)) at lowest standard ≤ 20 0.6
Repeatability (CV (%)) at highest standard ≤ 20 0.2
LOQ (μg/L) 25
System stability (deviation % from initial) ≤ 10 -4.1 – 6.2
CV: Coefficient of variation
LOQ: Limit of quantification

Preliminary study:

The screening hydrolysis study was performed separately for each pH value tested. Results of the
different pH values are displayed below. The measured concentrations at the beginning of the test (±
500 μg/L) are higher than the nominal spiked concentration of 400 μg/L. This is probably caused by
matrix effect of the pH buffer, however this has no influence on the results of the hydrolysis rate. As the
rate of hydrolysis is calculated from the decreasing concentration compared to the initial measured
concentration (not based on nominal spiked concentration).

Transformation products:

not measured

Key result

pH:

4

Temp.:

12 °C

Hydrolysis rate constant:

0.002 h-1

DT50:

376 h

Key result

pH:

7

Temp.:

12 °C

Hydrolysis rate constant:

0.002 h-1

DT50:

376 h

Key result

pH:

9

Temp.:

12 °C

Hydrolysis rate constant:

0.002 h-1

DT50:

301 h

Details on results:

pH 4
The pH value at the start of the test was measured to be 4.0. The temperature during the test varied
between 12.0 and 12.1°C. It was observed that 21 % of the test substance was hydrolysed after 5 days.

pH 7
The pH value at the start of the test was measured to be 7.0. The temperature during the test varied
between 12.0 and 12.1°C. It was observed that 21 % of the test substance was hydrolysed after 5 days.

pH 9
The pH value at the start of the test was measured to be 9.0. The temperature during the test varied
between 12.0 and 12.1°C. It was observed that 25 % of the test substance was hydrolysed after 5 days.

Validity criteria fulfilled:

yes

Remarks:

The test temperature during the screening experiment at the different pH values was measured to be within the criteria, 12.0 ± 0.5°C. The respective pH values of the different buffer solutions were measured to be within the criteria, pH value ± 0.1.

Conclusions:

The results of a screening hydrolysis study are as follows:

Half-life at pH4 and pH7, 12 oC of 376 hours
Half-life at pH9, 12 oC of 301 hours

Executive summary:

The results of a screening hydrolysis study are as follows:

Half-life at pH4 and pH7, 12 oC of 376 hours

Half-life at pH9, 12 oC of 301 hours

Description of key information

The results of a screening hydrolysis study are as follows:

Half-life at pH4 and pH7, 12 oC of 376 hours

Half-life at pH9, 12 oC of 301 hours

Key value for chemical safety assessment

Half-life for hydrolysis:

376 h

at the temperature of:

12 °C