1,4-Benzenediol, 2-(6-oxido-6H-dibenz[c,e][1,2]oxaphosphorin-6-yl)-

Hydrolysis

Link to relevant study record(s)

Reference

Endpoint:

hydrolysis

Type of information:

experimental study

Adequacy of study:

key study

Study period:

May 2021-May 2022

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

EU Method C.7 (Degradation: Abiotic Degradation: Hydrolysis as a Function of pH)

Deviations:

yes

Remarks:

Please see field principals methods other than the guideline

Qualifier:

according to guideline

Guideline:

OECD Guideline 111 (Hydrolysis as a Function of pH)

Deviations:

yes

Remarks:

Please see field principals methods other than the guideline

Principles of method if other than guideline:

The following deviations from the guidelines were documented:
 The study was performed at temperature 49.1 – 49.4°C (pH 7 and pH 4) resp. at 49.2
– 49.4 °C (pH 9) instead of at 49.5 – 50.5 °C due to an error. This was stated as uncritical,
because the result after 5 days was definite.
The deviation was signed and assessed by the study director on 21. Mar. 2022.
 For the measurements in buffer pH9 concentrations down to 10% of the initial concentration
could not be determined. This was due to the solubility of the test item in
buffer pH 9, determined during this study, was lower than expected from the validation
results. Also the measured test item concentration in this buffer was lower than
the nominal concentration, probably due to immediately after preparation of the solution
starting hydrolysis.
This was stated as uncritical, because the result after tier 1 was definite (decrease
after 5 days at 50 °C ≥ 10%).
The deviation was signed and assessed by the study director on 25. Mar. 2022.
 After five days (120 hours), the concentrations of the test item lay below 90% of the
nominal start concentration at all three pH values. Therefore, tier 2 should have been
conducted, but was not conducted on demand of the sponsor.

GLP compliance:

yes (incl. QA statement)

Radiolabelling:

no

Analytical monitoring:

yes

Remarks:

HPLC

Details on sampling:

Aqueous samples were diluted with an equal amount of methanol (dilution factor 2) and
acidified immediately after sampling with 1% 2 M hydrochloric acid (final content).
500 μL test solution was mixed with 500 μL methanol and 10 μL 2 M hydrochloric acid each.
The resulting dilution factor was 2.02.
For each sampling time, two fresh vessels were used to avoid microbial contamination and
contact with oxygen.

Buffers:

The composition was taken from the annex of the OECD method (buffer solutions 7 and 9)
resp. Küster et al. (buffer solution 4). All chemicals used were of analytical grade. The pH
was measured with a pH-meter with an uncertainty of 0.01 units and pH was adjusted to the
nominal pH value ± 0.02 units.

Buffer-Solution, pH 4
Parameter Amount
CH3COOH, 2 M 80 mL
CH3COONa, 1 M 40 mL
Demineralised water ad 1000 mL
pH was measured with 4.02.

Buffer-Solution, pH 7
Parameter Amount
KH2PO4 8.7085 g
Demineralised water 500 mL
NaOH, 2 M 14.9 mL
Demineralised water Ad 1000 mL
pH was adjusted using NaOH to 7.01.

Buffer-Solution, pH 9
Parameter Amount
H3BO3 3.0934 g
KCl 3.7293 g
Demineralised water 500 mL
NaOH, 2 M 10.75 mL
Demineralised water Ad 1000 mL
pH was measured with 9.00.

Details on test conditions:

Mixtures with not more than half of the saturation concentration of test item in the hydrolysis
buffer/water mixtures (50/50 % (v/v)) pH 4, pH 7 and pH 9 were prepared.
Temperature was held constant to 49.1 – 49.4 °C. All tests were conducted protected from
light and air. The test vessels and buffer solutions were sterilised before preparing the test
vessels. Cooled buffers were introduced into the test vials. Then, they were spiked with test
item to avoid loss of test item during preparation of the test vials. This was due to the test
item being expected to be hydrolysed fast. After spiking, the amount of solvent did not exceed
1 % v/v.
The test vessels were purged with argon (oxygen-free) before the test and were closed using
Teflon seals.
Two vessels were analysed directly, the others were stored at the test temperature in an
incubation chamber.

Duration:

5 d

pH:

4

Temp.:

49.4 °C

Initial conc. measured:

>= 0.187 - <= 0.212 mg/L

Duration:

5 d

pH:

7

Temp.:

49.4 °C

Initial conc. measured:

>= 0.21 - <= 0.239 mg/L

Duration:

5 d

pH:

9

Temp.:

49.4 °C

Initial conc. measured:

>= 0.044 - <= 0.078 mg/L

Number of replicates:

2 for each concentration

Positive controls:

no

Negative controls:

no

Preliminary study:

Tier 1 was started for pH 9 twice, because the first performance showed a start concentration
of 0.031 mg/L instead of 0.08 mg/L.
To verify the initial concentration at pH 9, 500 μL buffer 1:1, pH 9, was mixed with
500 μL methanol, 10 μL 2M HCl and 5 μL spiking solution. Two replicates were prepared.
For the solutions with nominal concentration 0.08 mg/L the concentrations 0.0720 resp.
0.0709 mg/L were obtained. The loss of 10.7% is probably due to immediately starting hydrolysis
at this pH.
Tier 1 was repeated for pH 9, and only this data is used for evaluation, because the first
performance was interrupted. All data of this study are stored together in the GLP archive
of the laboratory.

Transformation products:

not measured

% Recovery:

< 10

pH:

4

Temp.:

49.4 °C

Duration:

120 h

% Recovery:

< 10

pH:

7

Temp.:

49.4 °C

Duration:

120 h

% Recovery:

0

pH:

9

Temp.:

49.4 °C

Duration:

120 h

Remarks on result:

other: because no signals were detected after 120 h

Key result

pH:

4

Temp.:

49.4

DT50:

< 120 h

Remarks on result:

not measured/tested

Key result

pH:

7

Temp.:

49.4 °C

DT50:

< 120 h

Remarks on result:

not measured/tested

Key result

pH:

9

Temp.:

49.4

DT50:

< 120 h

Remarks on result:

not measured/tested

Details on results:

No signals were detected after 5 days. At pH 9 due to fast hydrolysis differing start concentrations
were measured. This was stated as uncritical, because the result is definite.
After five days (120 hours), the concentrations of the test item lay below 60% of the nominal
start concentration at all three pH values therefore tier 2 had to be conducted.

Validity criteria fulfilled:

yes

Conclusions:

After five days (120 hours), the concentrations of the test item lay below 60% of the nominal
start concentration at all three pH values therefore tier 2 should have been conducted.
No signals were detected after 5 days. At pH 9 due to fast hydrolysis differing start concentrations were measured. This was stated as uncritical, because the result is definite.
Tier 2 and tier 3 were not performed on demand of the sponsor.

Key value for chemical safety assessment

Half-life for hydrolysis:

120 h

at the temperature of:

49.4 °C