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Environmental fate & pathways

Hydrolysis

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Administrative data

Link to relevant study record(s)

Reference
Endpoint:
hydrolysis
Type of information:
experimental study
Adequacy of study:
key study
Study period:
31 Oct - 22 Dec 1995
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)
Version / remarks:
92/69/EEC
Deviations:
no
GLP compliance:
yes (incl. QA statement)
Radiolabelling:
no
Analytical monitoring:
yes
Remarks:
GC
Details on sampling:
- Sampling intervals for the parent compound:
pH 7, 9 at 60 °C: 0, 16, 20, 24, 40, 44, 48 and 64 h (2 replicates)
pH 7, 9 at 80 °C: 0, 0.5, 1, 2, 3, 4, 5 and 6 (1 replicate)
- Sampling method: For determination of the initial test substance concentration three 2-ml aliquots were removed from the hydrolysis solutions and each extracted and analyzed by GC.
- Sampling intervals/times for pH measurements: same as for sampling
Buffers:
pH4:
- 0.05 M acetate buffer solution pH 4:
0.74 g = 0.009 mol sodium acetate p.a. Merck Art. 6268 (M = 82.03 g/mol) and
2.5 ml = 0.041 mol acetic acid 100 % p.a. (Merck Art. 63 E)
were dissolved to 1000 ml with double distilled water.
The pH value was adjusted to 4.00 with acetic acid 100 %.

pH7:
- 0.05 M phosphate buffer solution pH 7:
4.34 g = 0.031 mol disodium hydrogen phosphate Merck Art. 6589 (M = 141.96 g/mol) and
2.64 g = 0.019 mol potassium dihydrogen phosphate Merck Art. 4881 ( M = 136.09 g/mol)
were dissolved to 1000 ml with double distilled water.

pH9:
- 0.05 M borate buffer solution pH 9:
4.76 g = 0.012 mol disodium tetraborate decahydrate Merck Art. 6315 (M = 381.37 g/mol)
and 46 ml = 0.0046 mol hydrochloric acid Titrisol Merck Art. 9944 (0.1 M)
were dissolved to 1000 ml with double distilled water.
Details on test conditions:
TEST SYSTEM
- Type, material and volume of test flasks, other equipment used: 5 mL vials closed with screw caps, thermostatic bath made of stainless steel with a metal cover
- Sterilization method: All experiments were conducted using sterilized glassware, sample vials equipment and buffer solutions (method used for sterilization not specified).
- Measures taken to avoid photolytic effects: possible photolytic degradation of the test substance was prevented by exclusion of light .
- Measures to exclude oxygen: buffer solutions had been equilibrated at 50 °C for one hour followed by purging with nitrogen to remove dissolved oxygen.
- If no traps were used, is the test system closed/open: closed

TEST MEDIUM
- Kind and purity of water: double distilled water
- Preparation of test medium: Three test solutions buffered to pH 4, 7 or 9 were prepared by adding a stock solution of the test substance in the corresponding buffer solution to a volumetric flask containing the appropriate buffer solution.

OTHER TEST CONDITIONS
- Adjustment of pH: according to buffer solutions
- Dissolved oxygen: removed by purging with nitrogen
Duration:
6 h
pH:
9
Temp.:
80 °C
Initial conc. measured:
100 mg/L
Duration:
64 h
pH:
9
Temp.:
60 °C
Initial conc. measured:
100 mg/L
Remarks:
Solution I and Solution II
Duration:
6 h
pH:
7
Temp.:
80 °C
Initial conc. measured:
100 mg/L
Duration:
64 h
pH:
7
Temp.:
60 °C
Initial conc. measured:
100 mg/L
Remarks:
Solution I and Solution II
Duration:
168 h
pH:
9
Temp.:
50 °C
Initial conc. measured:
100 mg/L
Remarks:
preliminary test
Duration:
168 h
pH:
7
Temp.:
50 °C
Initial conc. measured:
100 mg/L
Remarks:
preliminary test
Duration:
2 h
pH:
4
Temp.:
50 °C
Initial conc. measured:
100 mg/L
Remarks:
preliminary test
Number of replicates:
pH 4: 1 replicate
pH 7: 2 replicate (60 °C, Solution I and II) and 1 replicate (80 °C)
pH 9: 2 replicate (60 °C, Solution I and II) and 1 replicate (80 °C)
Positive controls:
no
Negative controls:
no
Statistical methods:
The hydrolysis rate constants of the test substance at pH 7 and 9 were calculated under application of the Arrhenius equation with estimated values for A und E. The estimation of the parameters A, E and co (co = initial concentration at temperature T) was conducted by nonlinear regression using the data (hydrolysis times and measured concentrations) from the hydrolysis experiment at 50 °, 60 ° and 80 °C by a combination of direct search algorithms and the Marquardt algorithm. The software used for this calculation (PC program KIM) is based on TopFit 2.0, a kinetic data analysis program.
Preliminary study:
A preliminary study was performed at pH 4, 7 and 9. The data for the hydrolysis solution at pH 4 show that significantly more than 50% of the test substance were degraded within 2.4 hours at 50 ± 0.1 °C. Therefore, according to guideline no further experiments were necessary at this pH value. At pH 7 and pH 9 less than 50 % decay of the test substance was observed within 2.4 hours, but more than 10 % degradation occurred within 5 days at 50 ± 0.1 °C. Therefore hydrolysis experiments at two elevated temperatures with replication at the lower of those two temperatures.
Transformation products:
not specified
% Recovery:
48
St. dev.:
1.8
pH:
9
Temp.:
60 °C
Duration:
6 h
% Recovery:
21.5
St. dev.:
8.9
pH:
9
Temp.:
60 °C
Duration:
64.3 h
% Recovery:
20.6
St. dev.:
2.2
pH:
9
Temp.:
60 °C
Duration:
64.5 h
% Recovery:
25.1
St. dev.:
3.8
pH:
7
Temp.:
80 °C
Duration:
6 h
% Recovery:
12.6
St. dev.:
1.5
pH:
7
Temp.:
60 °C
Duration:
48 h
% Recovery:
11.2
St. dev.:
18.3
pH:
7
Temp.:
60 °C
Duration:
48 h
pH:
9
Temp.:
80
Hydrolysis rate constant:
0.111 h-1
DT50:
6.25 h
Type:
(pseudo-)first order (= half-life)
pH:
9
Temp.:
60
Hydrolysis rate constant:
0.024 h-1
DT50:
28.38 h
Type:
(pseudo-)first order (= half-life)
pH:
9
Temp.:
50
Hydrolysis rate constant:
0.011 h-1
DT50:
64.86 h
Type:
(pseudo-)first order (= half-life)
pH:
7
Temp.:
80
Hydrolysis rate constant:
0.225 h-1
DT50:
3.08 h
Type:
(pseudo-)first order (= half-life)
pH:
7
Temp.:
60
Hydrolysis rate constant:
0.042 h-1
DT50:
16.5 h
Type:
(pseudo-)first order (= half-life)
pH:
7
Temp.:
50
Hydrolysis rate constant:
0.017 h-1
DT50:
41.29 h
Type:
(pseudo-)first order (= half-life)
Key result
pH:
9
Temp.:
25
Hydrolysis rate constant:
0.001 h-1
DT50:
27.2 d
Type:
(pseudo-)first order (= half-life)
Remarks on result:
other: extrapolation to the hydrolysis rate constant and half-life at 25 °C was conducted by applying the Arrhenius equation.
pH:
7
Temp.:
25
Hydrolysis rate constant:
0.001 h-1
DT50:
22.3 d
Type:
(pseudo-)first order (= half-life)
Remarks on result:
other: extrapolation to the hydrolysis rate constant and half-life at 25 °C was conducted by applying the Arrhenius equation.
pH:
4
Temp.:
25
Hydrolysis rate constant:
> 5.1 h-1
DT50:
< 1 d
Type:
(pseudo-)first order (= half-life)
Remarks on result:
other: extrapolation to the hydrolysis rate constant and half-life at 25 °C was conducted by applying the Arrhenius equation.
Details on results:
TEST CONDITIONS
- pH, sterility, temperature, and other experimental conditions maintained throughout the study: Yes

Validity criteria for the hydrolysis study:

























Target condition according to guideline:Actual condition according to the study:Validity criteria met:
The analytical method used will depend on the nature of the substance and must be sufficiently precise and sensitive to detect a reduction of 10 % of the initial concentration.Analysis via GC-FID is senstive enough to detect a reduction of 10% of the initial concentration.Yes
A sufficient number of samples (not less than four) should be chosen to cover the range 20 to 70 % of hydrolysis to test for pseudo-first order behaviour at the specified pH values.

pH 4 (50°C): 7 measurements (50% degradation within 2.4 h)


pH 7 (50-80°C): 5-7 measurements


pH 9 (50-80°C): 4-7 measurements


 


yes
Confidence intervals should be computed and presented for all regression coefficients, rateconstants, half-lives, and any other kinetic parameters (e.g. DT50).

All relevant parameters are reported within the study. 


Yes
Validity criteria fulfilled:
yes
Remarks:
See 'Any other information on results incl. tables'
Conclusions:
Based on experimental data, the hydrolytical half-lives at 25 °C were extrapolated and accounted to <1 d (pH 4), 22.3 d (pH 7) and 27.2 d (pH 9).
Executive summary:

The study was performed to determine the hydrolysis of the test stubstance as a functon of pH according to EU guideline 92/69/EEC C.7. A preliminary study was performed at pH 4, 7 and 9. The data for the hydrolysis solution at pH 4 show that significantly more than 50% of the test substance were degraded within 2.4 hours at 50 °C. Therefore, according to guideline no further experiments were necessary at this pH value. The extrapolation to the hydrolysis rate constant and half-life at 25 °C was conducted by applying the Arrhenius equation and respective half-life was <1 d. At pH 7 and pH 9 less than 50 % decay of the test substance was observed within 2.4 hours, but more than 10 % degradation occured within 5 days at 50 °C. Therefore hydrolysis experiments at two elevated temperatures (60 °C and 80°C) with replication at 60 °C. Based on experimental data, the hydrolytical half-lives for pH 7 and pH 9 at 25 °C were extrapolated and accounted to 22.3 d (pH 7) and 27.2 d (pH 9).

Description of key information

The study was performed to determine the hydrolysis of the test stubstance as a functon of pH according to EU guideline 92/69/EEC C.7. A preliminary study was performed at pH 4, 7 and 9. The data for the hydrolysis solution at pH 4 show that significantly more than 50% of the test substance were degraded within 2.4 hours at 50 °C. Therefore, according to guideline no further experiments were necessary at this pH value. The extrapolation to the hydrolysis rate constant and half-life at 25 °C was conducted by applying the Arrhenius equation and respective half-life was <1 d. At pH 7 and pH 9 less than 50 % decay of the test substance was observed within 2.4 hours, but more than 10 % degradation occured within 5 days at 50 °C. Therefore hydrolysis experiments at two elevated temperatures (60 °C and 80°C) with replication at 60 °C. Based on experimental data, the hydrolytical half-lives for pH 7 and pH 9 at 25 °C were extrapolated and accounted to 22.3 d (pH 7) and 27.2 d (pH 9).

Key value for chemical safety assessment

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

Additional information