Registration Dossier

Administrative data

Endpoint:
hydrolysis
Type of information:
experimental study
Adequacy of study:
key study
Study period:
26 March to 09 November 1998
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: Compliant to GLP and testing guideline, adequate coherence between data, comments and conclusions

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
1998
Report Date:
1998

Materials and methods

Test guideline
Qualifier:
according to
Guideline:
EU Method C.7 (Degradation: Abiotic Degradation: Hydrolysis as a Function of pH)
Version / remarks:
1981
Deviations:
no
GLP compliance:
yes (incl. certificate)

Test material

Reference
Name:
Unnamed
Type:
Constituent
Radiolabelling:
no

Study design

Analytical monitoring:
yes
Details on sampling:
- Sampling method: An aliquot (5 mL) of the aqueous is withdrawn from the flask. 2.0 mL of the water phase is introduced in a 50 ml volumetric flask. After addition of 1 ml of internal standard solution, the volume is adjusted with methanol and the resulting solution is analysed by glc/ms.
Buffers:
- pH: 4
- Type and final molarity of buffer: Phthalate buffer
- Composition of buffer: Potassium hydrogen phthalate was dissolved into 250 ml of water in a 500 ml volumetric flask. A Sodium hydroxide 0.1 N solution was prepared by diluting 2,0 g of pure sodium hydroxide pellets into 500 ml of water. 2 ml of this NaOH solution was added to the volumetric flask. The volume was adjusted to 500 ml with purified water.


- pH: 7
- Type and final molarity of buffer: Phosphate buffer
- Composition of buffer: Potassium dihydrogenphosphate was dissolved into 250 ml of purified water in a 500 ml volumetric flask. 148 ml of sodium hydroxide 0.1 N solution was added to this solution and the volume was made up to 500 ml with purified water.


- pH: 9
- Type and final molarity of buffer: Borate buffer
- Composition of buffer: Boric acid and potassium chloride were dissolved into water and the volume was made-up to 250 ml. 106 ml of sodium hydroxide 0.1 N solution was added to this solution and the volume was made up to 500 ml with purified water.

The buffer solutions were incubated in the water bath at the test temperature and their pH were adjusted to the nominal value.
Details on test conditions:
NEH test solution was prepared by adding an aliquot of a NEH working solution in methanol to the buffer solution. The concentration of the methanolic working solution of NEH was chosen to obtain a NEH concentration of 6 mg/l in the test solution and a final methanol concentration of approximately 1 %.

Tests solutions were incubated at the test temperature in borosilicate glass bottles of nominal volume close to the initial volume of the test solution. The bottles were closed with teflon lined screw caps.
The incubation of the test solutions was performed in a water bath equilibrated at the test temperature. The temperature was monitored with a PT 100 probe.
Duration of testopen allclose all
Duration:
0 min
pH:
4
Temp.:
50 °C
Initial conc. measured:
3.8 mg/L
Duration:
144 min
pH:
4
Temp.:
50 °C
Initial conc. measured:
3.52 mg/L
Duration:
5 d
pH:
4
Temp.:
50 °C
Initial conc. measured:
0.07 mg/L
Duration:
0 min
pH:
7
Temp.:
50 °C
Initial conc. measured:
3.31 mg/L
Duration:
144 min
pH:
7
Temp.:
50 °C
Initial conc. measured:
3.09 mg/L
Duration:
5 d
pH:
7
Temp.:
50 °C
Initial conc. measured:
0.11 mg/L
Duration:
0 min
pH:
9
Temp.:
50 °C
Initial conc. measured:
3.47 mg/L
Duration:
144 min
pH:
9
Temp.:
50 °C
Initial conc. measured:
3.27 mg/L
Duration:
5 d
pH:
9
Temp.:
50 °C
Initial conc. measured:
0.18 mg/L

Results and discussion

Preliminary study:
- Less than 50 % hydrolysis occurs within the first 2.4 hours of the test for each of the pH tested.
- More than 10 % hydrolysis occurs after 5 days of incubation in the test conditions.

This information may be roughly interpreted as an ambient temperature stability of NEH between one day and one year. Additional experiments are needed to determine the order and rated of the hydrolysis reaction.
Test performance:
According to the conclusion of preliminary test and test 1 the study needs to be completed by test 3.
Transformation products:
not measured
Identity of transformation productsopen allclose all
Details on hydrolysis and appearance of transformation product(s):
Unfortunately no attempt was wade to identity the hydrolysis products. It was, maybe, with some reason assumed that there is no doubt that the primary breakdown products will be the substances listed above (2-Ethylhexan-1-ol and the Nitrate anion).
Total recovery of test substance (in %)open allclose all
% Recovery:
92.6
pH:
4
Temp.:
50 °C
Duration:
144 min
% Recovery:
2
pH:
4
Temp.:
50 °C
Duration:
5 d
% Recovery:
93.4
pH:
7
Temp.:
50 °C
Duration:
144 min
% Recovery:
3
pH:
7
Temp.:
50 °C
Duration:
5 d
% Recovery:
94.2
pH:
9
Temp.:
50 °C
Duration:
144 min
% Recovery:
5
pH:
9
Temp.:
50 °C
Duration:
5 d
Dissipation DT50 of parent compoundopen allclose all
pH:
4
Temp.:
50 °C
Hydrolysis rate constant:
0.001 min-1
DT50:
1 225 min
Type:
(pseudo-)first order (= half-life)
pH:
7
Temp.:
50 °C
Hydrolysis rate constant:
0 min-1
DT50:
1 475 min
Type:
(pseudo-)first order (= half-life)
pH:
9
Temp.:
50 °C
Hydrolysis rate constant:
0 min-1
DT50:
1 702 min
Type:
(pseudo-)first order (= half-life)
pH:
4
Temp.:
25 °C
Hydrolysis rate constant:
>= 0.002 - <= 0.003 min-1
DT50:
>= 241 - <= 370 h
Type:
(pseudo-)first order (= half-life)
pH:
7
Temp.:
25 °C
Hydrolysis rate constant:
0.004 min-1
DT50:
157 h
Type:
(pseudo-)first order (= half-life)
pH:
9
Temp.:
25 °C
Hydrolysis rate constant:
>= 0.004 - <= 0.006 min-1
DT50:
>= 108 - <= 148 h
Type:
(pseudo-)first order (= half-life)
Details on results:
The hydrolysis test was thus repeated as described above by incubating test solutions at the temperature of 25 °C (Test 3). Duplicate determinations were run for each pH value; however, for pH 7.0 the second determination gave irrelevant values compared to the other determinations, thus this second determination should probably be rejected.
NEH was shown to hydrolyse in each of the pH conditions tested following a pseudo-first order reaction. Half-life of the hydrolysis reaction at 25 °C ranged from 370 hours (pH 4.0) to 108 hours (pH 9.0).
The variability of the determination seems to be rather high owing to the results presented. However, one has to consider the fact that the solubility of the compound is rather low, meaning that the concentrations determined in the test solutions are close to the limit of determination of the analytical method thus leading to some degree of uncertainty.
Variability as high as 126 % coefficient of variation have been reported in the literature (OECD guidelines for the testing of chemicals, Method 111).

Applicant's summary and conclusion

Validity criteria fulfilled:
yes
Conclusions:
The test item was shown to hydrolyse in each of the pH conditions tested following a pseudo-first order reaction. Half-life of the hydrolysis reaction at 25 °C ranged from 370 hours (pH 4.0) to 108 hours (pH 9.0).