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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
Guideline:
OECD Guideline 111 (Hydrolysis as a Function of pH)
Qualifier:
according to guideline
Guideline:
EU Method C.7 (Degradation: Abiotic Degradation: Hydrolysis as a Function of pH)
Version / remarks:
adopted, May 2008
GLP compliance:
yes (incl. QA statement)
Radiolabelling:
no
Analytical monitoring:
yes
Details on sampling:
The substance as an NLP contains different molecular weight fractions ( = NLP-fraction) which behave different in hydrolysis reaction. The hydrolysis rate constants and the half-life times at 25 °C and at pH 7 and pH 9 were calculated for six main NLP-fractions representing 96 % of the test item.
Only the main NLP-fractions representing 96 % of the test item were investigated in detail.
Buffers:
- Buffer pH 4: C6H8O7 / NaOH / NaCl, Riedel de Haen, Art.-No.: 33643
- Buffer pH 7: KH2PO4 / Na2HPO4, Fluka, Art.-No.: 33646
- Buffer pH 9: Na3BO3 · 10 H2O / hydrochloric acid, Riedel de Haën, Art.-No.: 33648
Estimation method (if used):
Arrhenius equation: to calculate the rate constants at other temperatures, when the rate constants are known for two or more temperatures (Further hydrolysis tests were conducted at 20 ° and 70 °C beside 50 °C).
Details on test conditions:
- Calibration:
Because the test item is an NLP and no standard compounds were available for the different fractions the test item was used as standard compound calculated with a stipulated overall content of 100 %. The calibration was only used to check the system suitability and to evaluate
the total water solubility. The hydrolysis tests itself were analyzed using the peak area and the total peak area of the fractions

- Preparation of the calibration stock solution:
Approx. 0.37 g of the test item were weighed into a 100 mL volumetric flask and dissolved and diluted to volume with acetonitrile (resulting concentration: approx. 3.7 g/l).

- Preparation of the calibration solutions:
Using the stock solution dilutions with acetonitrile were prepared to obtain six calibration solutions with concentrations between approx. 0.11 g /l and 1.84 g/l.

- Calculation:
The calibration was done by external standardization using the test item as standard compound. Because the test item is an NLP, the chromatogram shows several peaks. To calculate the response factor of the main NLP-fractions the initial weight of the test item in the standard solution was divided according the area-% share of the peaks determined in the corresponding calibration chromatogram.
Duration:
5 d
pH:
4
Temp.:
50
Initial conc. measured:
1.23 g/L
Duration:
30 d
pH:
7
Temp.:
20
Initial conc. measured:
1.15 g/L
Duration:
30 d
pH:
7
Temp.:
50
Initial conc. measured:
1.29 g/L
Duration:
15 d
pH:
7
Temp.:
70
Initial conc. measured:
1.28 g/L
Duration:
30 d
pH:
9
Temp.:
20
Initial conc. measured:
1.26 g/L
Duration:
15 d
pH:
9
Temp.:
50
Initial conc. measured:
1.22 g/L
Duration:
15 d
pH:
9
Temp.:
50
Initial conc. measured:
1.21 g/L
Duration:
4 d
pH:
9
Temp.:
70
Initial conc. measured:
1.27 g/L
Number of replicates:
1 replicate at pH 9
Preliminary study:
Prior to hydrolysis test a few experimental tests had to be done to define the solubility and the test concentration, an organic solvent additive if required, the analytical method and the test strategy. The preliminary test was performed at 50 ± 0.5 °C and pH 4.0, 7.0 and 9.0.

- Tier 1 (pH 4, 50 °C):
The test item was called to be stable at 50 °C at pH 4 and no half-life time and hydrolysis rate were calculated. Because no degradation was observed, no sterility test was performed in this case. Therefore no further tests at other temperatures were required for pH 4.

- Tier 1 (pH7 and 9, 50 °C):
The overall degradation of the test item observed at 50 °C at pH 7 after 5 days (120 h) was greater than 10 %. Therefore the pretest was extended. After 30 days (720 h) a degradation of approx. 45 % was observed and the hydrolysis test aborted. Even the overall degradation of the test item observed at 50 °C and pH 9 after 5 days (120 h) was greater than 10 %, too. Therefore the pretest was extended. After 7 days (170 h) a degradation of greater than 90 % was observed. The hydrolysis test was aborted after 15 days (360 h).

Sterility test were in compliance and showed no microbes (colonies). Therefore biotic degradation could be excluded. Further hydrolysis tests at 20 °C and 70 °C had to be performed in the second tier for pH 7 and 9.
Test performance:
The main test (second tier) was performed at pH 7 and 9 at 20 °C and 70 °C, values at which the test substance was found to be unstable as defined by the preliminary test above. The overall degradation of the test item observed at 20 °C and pH 9 after 30 days (720 h) was approx. 32 % and the overall degradation of the test item at 70 °C and pH 9 after 1 day (approx. 22 h) was 90 %. Both hydrolysis tests were aborted. A sterility test was in compliance and showed no microbes (colonies). Therefore biotic degradation could be excluded.

Test Conditions:
- 0.01 mol/l-solution of the test item according to OECD Guideline 111 (approx. 3.7 g/l) the solubility in different solvents and buffers was tested by visual investigation
- 0.01 mol/L aqueous solution was turbid, therefore the content of the test item in this aqueous solution was analyzed to estimated the solubility of the test item in water
- a half-saturated solution according to OECD-guideline was prepared (approx. 1.2 g/l), which was slightly turbid again
- the solution was filtered to get a clear solution
- the residue was determined gravimetrically to determine the amount of the precipitation
Transformation products:
not specified
Remarks:
Mass spectral data for transformation products are only available at pH 9 and could usually not be identified unambiguously.
Details on hydrolysis and appearance of transformation product(s):
- to avoid a 30 % content of organic solvent additive and although the 0.01 mol/L aqueous solution was turbid, the hydrolysis study was only performed with the soluble parts of the test item after filtration.
- aqueous solutions without organic solvent additive, concentration: approx. 1.2 g/l (approx. 3.3·10-3 mol/l)
- because the test item is an NLP containing different molecular weight fractions which probably behave different the NLP-fractions and the different peaks observed were investigated separately
- the overall hydrolysis was investigated using the total peak area of the main starting peaks which represent main NLP-fractions




% Recovery:
> 90
pH:
4
Temp.:
50 °C
Duration:
5 d
% Recovery:
> 90
pH:
7
Temp.:
20 °C
Duration:
30 d
% Recovery:
ca. 45
pH:
7
Temp.:
50 °C
Duration:
30 d
% Recovery:
10
pH:
7
Temp.:
70 °C
Duration:
15 d
% Recovery:
68
pH:
9
Temp.:
20 °C
Duration:
30 d
% Recovery:
6.3 - 6.8
pH:
9
Temp.:
50 °C
Duration:
15 d
% Recovery:
ca. 10
pH:
9
Temp.:
70 °C
Duration:
22 h
pH:
4
Temp.:
25 °C
DT50:
> 1 yr
Remarks on result:
other: The overall degradation of the test item observed at 50 °C at pH 4 after 5 days (120 h) is lower than 10 %. Therefore it can be assumed that the test item is also stable at 25 °C and no half-life time and hydrolysis rate were calculated.
pH:
7
Temp.:
25 °C
DT50:
573 d
Type:
(pseudo-)first order (= half-life)
Remarks on result:
other: Hydrolysis rate constant k [s-1]: 1.60 · 10E-8
pH:
9
Temp.:
25 °C
DT50:
15 d
Type:
(pseudo-)first order (= half-life)
Remarks on result:
other: Hydrolysis rate constant k [s-1]: 6.38 · 10E-7
Details on results:
At pH 9 insolube parts of 2.5 and 3.2 % parts were determined at 50 °C and of 2.2 % at 70 °C.

Hydrolysis was observed and calculated using the peak area of the different peaks and the total peak area of the main starting peaks which represent the main NLP-fractions. The peak identification (identification of NLP-fractions and hydrolysis products) were done by interpretation of HPLC-MS mass spectra. Chromatograms from the start and the end of the hydrolysis tests at pH = 9 were analyzed in positive and negative ionization mode. The test item is an NLP containing different molecular weight fractions (= NLP-fraction) which were not individually identified. The chemical composition of the starting material exists mainly of 2-benzofuran-1,3-dione, addition product with 2-(2-hydroxyethoxy)ethanol, ethoxylated. The NLP consists of molecules having different chain lengths even at the different carboxylic acid groups within the same molecule. A hydrolysis reaction of an NLP is very complex. The NLP molecules having different chain lengths may hydrolyse following different reaction kinetics. Shorter chain molecules could be already part of the NLP and could also be newly built by hydrolysis of longer chain molecules. These shorter chains may hydrolyse also. All these effects were observed during the hydrolysis of the test item.

Validity criteria fulfilled:
yes
Remarks:
A plate count tests according to prEN ISO 7218 (2005) was performed at the end of the tests. No microbes (colonies) were detected. Therefore biotic degradation could be excluded.
Conclusions:
The recovery and the repeatability were checked during the hydrolysis study by analyzing a solution of the test item in acetonitrile on every day of application (system suitability test). The recovery was between 90 % und 110 % and met the requirements of OECD 111. The method was sensitive enough to determine hydrolysis rates of greater than 90 %. The results of both hydrolysis tests at pH = 9 and 50 °C were identical. This demonstrates that the method and the procedure worked reproducible.
Executive summary:

The stability of the substance was determined according to the OECD guideline 111 and the EU method, C.7 (Currenta, 2009). Based on kinetic parameters, the following dissipation half-lives for a temparature of 25 °C were extrapolated based on the Arrhenius equation:

pH 4 (25 °C): > 1 year

pH 7 (25 °C): 573 days

pH 9 (25 °C): 15 days.

Description of key information

The stability of the substance was determined according to the OECD guideline 111 and the EU method, C. 7 (Currenta, 2009). Based on kinetic parameters, the following dissipation half-lives for a temperature of 25 °C were extrapolated based on the Arrhenius equation:
pH 4 (25 °C): > 1 year
pH 7 (25 °C): 573 days
pH 9 (25 °C): 15 days.

Key value for chemical safety assessment

Half-life for hydrolysis:
573 d
at the temperature of:
25 °C

Additional information

The hydrolysis behaviour of the substance was assessed in a study conducted to a high standard, in full compliance with all three tiers of the OECD guideline 111 and the EU method C.7. The kinetic parameters were followed using a HPLC/UV method. As the substance is a NLP containing different molecular weight fractions (= NLP-fraction) which were not completely individually identified, half-life determinations were calculated for six main NLP-fractions representing 96 % of the test item. The stability of the test item is found to decrease with increasing pH-value. At pH 4 and 50 °C the substance is found to be stable. Therefore it can be assumed that the substance is also stable at 25 °C and no half-life time and hydrolysis rate were calculated. The half-life time for the substance at pH 7 is 573 days and at pH 9 is 15 days, both at 25 °C.  

As the hydrolysis reaction of a NLP is very complex, resulting in a sum of hydrolysis products, a clear identification of the hydrolysis products is complicated. The NLP molecules having different chain lengths even at the different carboxylic acid groups within the same molecule and may hydrolyse following different reaction kinetics. Shorter chain molecules could be already part of the NLP and could also be newly built by hydrolysis of longer chain molecules. These shorter chains may hydrolyse also.

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