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Environmental fate & pathways

Hydrolysis

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Reference
Endpoint:
hydrolysis
Type of information:
experimental study
Adequacy of study:
key study
Study period:
1993-12-06 to 1994-04-20
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:
(1992)
Deviations:
no
GLP compliance:
yes (incl. QA statement)
Remarks:
signed 1994-03-16
Radiolabelling:
no
Analytical monitoring:
yes
Details on sampling:
- Sampling intervals for the Preliminary test/Test 1: 0 h (test start), 2.4 h, 24 h, 72 h, 96 h, and 120 h
- Sampling intervals for the Test 3: 0 h (test start), 24 h, 70, 94, 144 h
- Sampling method: test material was monitored by GC-FID
- Sample storage conditions before analysis:
Preliminary test/Test 1: at 50 °C in each buffer solution;
Test 3: at 25 °C in pH 9 buffer, at 70 °C and 60 °C in pH 7 buffer
Buffers:
- pH 4, 7 and 9 in Preliminary test/Test 1 and pH 9 and pH 7 in Test 3
- Temperature: 50 °C in Preliminary test/Test 1 and 25 °C for pH 9, and 60 and 70 °C for pH 7 in Test 3
- Composition of buffer:
Buffer solution pH 4: 0.05 mol/dm³ citric acid, 0.10 mol/dm³ sodium hydroxide, 0.05 mol/dm³ hydrochloric acid.
Buffer solution pH 7: 0.04 mol/dm³ disodium hydrogen orthophosphate, 0.03 mol/dm³ potassium dihydrogen orthophosphate.
Buffer solution pH 9: 0.05 mol/dm³ disodium tetraborate, 0.02 mol/dm³ hydrochloric acid.
Estimation method (if used):
A logarithmic graph of the concentration against time was plotted for each test and an estimate of the rate constant and the half-life was directly determined at 25 °C for pH 9. The Arrhenius relationship of the rate constant at higher temperatures was used for pH 7.
Details on test conditions:
TEST MEDIUM
- Standards: Standard solutions were prepared in hexane at a nominal concentration of 500 mg/L.
Duration:
120 h
pH:
4
Temp.:
50 °C
Initial conc. measured:
78.2 mg/L
Duration:
120 h
pH:
7
Temp.:
50 °C
Initial conc. measured:
84.3 mg/L
Duration:
120 h
pH:
9
Temp.:
50 °C
Initial conc. measured:
58.8 mg/L
Duration:
144 h
pH:
9
Temp.:
25 °C
Initial conc. measured:
40.9 mg/L
Duration:
144 h
pH:
7
Temp.:
60 °C
Initial conc. measured:
35.9 mg/L
Remarks:
Test A
Duration:
144 h
pH:
7
Temp.:
60 °C
Initial conc. measured:
42.2 mg/L
Remarks:
Test B
Duration:
144 h
pH:
7
Temp.:
70 °C
Initial conc. measured:
33 mg/L
Number of replicates:
Single replicates except for Test 3 in pH 7 buffersolution at 60 °C which was performed in duplicates.
Positive controls:
not specified
Negative controls:
not specified
Statistical methods:
no data
Preliminary study:
- In the preliminary test/test 1, the test item was found to ungergo less than 10 % hydrolysis after 5 days at 50 °C in pH 4 buffer solution. At 50 °C in pH 7 and pH 9 buffer solution, the test item was found to undergo greater than 10 % hydrolysis after 5 days but less than 50 % hydrolysis after 2.4 hours.

- Estimated rate constant and half-life was estimated for pH 7 buffer solution at 50 °C to be 0.00162 per hour and 428 hours, respectively.
Test performance:
No unusual observations during test performance.
Transformation products:
not measured
Details on hydrolysis and appearance of transformation product(s):
not applicable
% Recovery:
99
pH:
4
Temp.:
50 °C
Duration:
120 h
% Recovery:
82.5
pH:
7
Temp.:
50 °C
Duration:
120 h
% Recovery:
0.32
pH:
9
Temp.:
50 °C
Duration:
96 h
Remarks on result:
other: after 120 h none detected
% Recovery:
46.5
pH:
9
Temp.:
25 °C
Duration:
144 h
% Recovery:
51.6
pH:
7
Temp.:
60 °C
Duration:
144 h
Remarks on result:
other: test A
% Recovery:
53.9
pH:
7
Temp.:
60 °C
Duration:
144 h
Remarks on result:
other: test B
% Recovery:
32.8
pH:
7
Temp.:
70 °C
Duration:
94 h
Key result
pH:
4
Temp.:
25 °C
DT50:
> 1 yr
Key result
pH:
7
Temp.:
25 °C
Hydrolysis rate constant:
0 h-1
DT50:
7 420 h
Key result
pH:
9
Temp.:
25 °C
Hydrolysis rate constant:
0.005 h-1
DT50:
133 h
Type:
(pseudo-)first order (= half-life)
Other kinetic parameters:
no data
Details on results:
RESULTS
- At pH 7 and pH 9: t1/2 (25 °C) for pH 7 = 7.42*10^3 hours, t1/2 (25 °C) for pH 9 = 133 hours
- At pH 4: stable at pH 4 at 20 °C (t1/2 > 1 a)
Validity criteria fulfilled:
yes
Conclusions:
In the preliminary test (50 °C), the test item was found to be stable at pH 4, but at pH 7 and pH 9 a decrease of the test concentration greater than 10 % was observed after 5 days. In further tests, the half-life of the reactions at 25 °C have been estimated to be 7420 h and 133 h for pH 7 and pH 9, respectively.
Executive summary:

The hydrolysis of the test item was investigated as a function of pH at 50 °C and pH 4, 7, and 9 according to Directive 92/69/EEC, Method C.7 (1992). The test item was hydrolytically stable at pH 4 (<10 % decrease in 5 days). At pH 7 the rate constant and half-life of the reactions at 25 °C have been estimated to be 0.0000935 h-1 and 7420 h, respectively. At pH 9 the rate constant and half-life of the reactions at 25 °C have been estimated to be 0.00521 h-1 and 133 h, respectively.

Description of key information

pH 4: stable

pH 7: half-life of the reactions at 25 °C: 7420 h

pH 9: half-life of the reactions at 25 °C: 133 h

Key value for chemical safety assessment

Half-life for hydrolysis:
7 420 h
at the temperature of:
25 °C

Additional information

The hydrolysis of the test item was investigated as a function of pH at 50 °C and pH 4, 7, and 9 according to Directive 92/69/EEC, Method C.7 (1992). The test item was hydrolytically stable at pH 4 (<10 % decrease in 5 days). At pH 7 the rate constant and half-life of the reactions at 25 °C have been estimated to be 0.0000935 h-1and 7420 h, respectively. At pH 9 the rate constant and half-life of the reactions at 25 °C have been estimated to be 0.00521 h-1and 133 h, respectively.