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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
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: Guideline study with GLP.
Qualifier:
according to guideline
Guideline:
EU Method C.7 (Degradation: Abiotic Degradation: Hydrolysis as a Function of pH)
Deviations:
no
GLP compliance:
yes
Radiolabelling:
no
Analytical monitoring:
yes
Details on sampling:
According to the EC-method.
Buffers:
Buffer pH 4: 500 mL 0.1 mol/L potassium hydrogenphthalate and 4 ml 0.1 mol/L sodium hydroxide filled up to 1000 mL with deionised water.
Buffer pH 7: 500 mL 0.1 mol/L potassium dihydrogenphosphate and 296.4 mL 0.1 mol/L sodium hydroxide filled up to 1000 mL with deionised water.
Buffer pH 9: 500 mL 0.1 mol/L boric acid in 0.1 mol/L potassium chloride and 213 mL 0.1 mol/L sodium hydroxide filled up to 1000 mL with deionised water.
The deionised water was boiled for 15 minutes and kept in a refrigerator before use. Each buffer solution was degassed with helium for 5 minutes.
Estimation method (if used):
Solutions of the test substance in buffers with pH values of 4, 7 and 9 were kept at 50 °C and the concentration of 7-AMCA was determined after various times up to a maximum of 5 days. It was the aim to find out:
• Are less than 10% of the test substance hydrolysed in 5 days? In this case the half-life at 25 °C is greater than one year according to the guideline and the substance is classified as stable to hydrolysis.
• Are more than 50% of the test substance hydrolysed in 2.4 hours? In this case the half-life at 25 °C is lower than one day according to the guideline and the test substance is classified as easily hydrolysable.
If the rate of hydrolysis is between these limits, a main test has to be performed.
Portions of 4.3, 4.8 and 5.1 mg of the test substance were weighed in flasks and dissolved in 100 ml of the appropriate buffer.
The solutions were kept in a water bath at the test temperature in the dark. Portions of the solutions were taken from the flasks, and the concentration of the test substance was analysed by HPLC.
Readings of temperatures (calibrated glass/mercury thermometer) and pH (pH-meter) were recorded at each analysis.
Details on test conditions:
In the main test solutions of approx. 50 % saturation of the test substance in buffers with pH of 4, 7 and 9 were kept at 65 °C and 75 °C and the concentrations of 7-AMCA were determined at different times.
The test was performed in duplicates for each temperature and each pH.
Portions of 3.7, 3.7 and 4.0 mg of the test substance at 65 °C and portions of 4.4, 4.3 and 4.4 mg at 75 °C were weighed in flasks, dissolved in 100 ml of the appropriate buffer each and divided into two 50 mL portions. The solutions were kept in a water bath at the test temperature in the dark.
Duration:
5.2 h
pH:
3.95
Initial conc. measured:
0.035 - 0.035 g/L
Duration:
3.7 h
pH:
3.95
Temp.:
75 °C
Initial conc. measured:
0.043 - 0.043 g/L
Duration:
30.8 h
pH:
6.96
Temp.:
65 °C
Initial conc. measured:
0.036 g/L
Duration:
25.4 h
pH:
6.98
Temp.:
75 °C
Initial conc. measured:
0.042 g/L
Duration:
4.98 h
pH:
9
Temp.:
65 °C
Initial conc. measured:
0.039 g/L
Duration:
2.8 h
pH:
9.02
Temp.:
75 °C
Initial conc. measured:
0.044 - 0.044 g/L
Number of replicates:
2.
Positive controls:
no
Negative controls:
no
Statistical methods:
At each test temperature and each pH in the main test the hydrolysis of the test substance followed a first order kinetic (linear relation of ln c versus time).
Rate constants at 25 °C were calculated by the equation of Arrhenius.
Preliminary study:
The preliminary test showed that half-life of the test substance at 25 °C will be greater than 1 day and less than 1 year. Therefore the main test was performed, according to the guideline.
Transformation products:
not measured
Details on hydrolysis and appearance of transformation product(s):
The hydrolysis of 7-AMCA follows a pseudo first order kinetic at each pH.
7-AMCA is more stable in neutral than in acidic and alkaline solutions. The calculated half life times at 25 °C were 28.8 h at pH 4, 2100 h at pH 7 and 280 h at pH 9.
pH:
4
Temp.:
75 °C
Hydrolysis rate constant:
0.271 h-1
DT50:
2.56 h
Type:
(pseudo-)first order (= half-life)
pH:
4
Temp.:
65 °C
Hydrolysis rate constant:
0.177 h-1
DT50:
3.93 h
Type:
(pseudo-)first order (= half-life)
pH:
4
Temp.:
25 °C
Hydrolysis rate constant:
0.024 h-1
DT50:
28.8 h
Type:
(pseudo-)first order (= half-life)
pH:
7
Temp.:
75 °C
Hydrolysis rate constant:
0.04 h-1
DT50:
17.4 h
Type:
(pseudo-)first order (= half-life)
pH:
7
Temp.:
65 °C
Hydrolysis rate constant:
0.017 h-1
DT50:
40.4 h
Type:
(pseudo-)first order (= half-life)
pH:
7
Temp.:
25 °C
Hydrolysis rate constant:
0 h-1
DT50:
2 100 h
Type:
(pseudo-)first order (= half-life)
pH:
9
Temp.:
75 °C
Hydrolysis rate constant:
0.342 h-1
DT50:
2.03 h
Type:
(pseudo-)first order (= half-life)
pH:
9
Temp.:
65 °C
Hydrolysis rate constant:
0.144 h-1
DT50:
4.82 h
Type:
(pseudo-)first order (= half-life)
pH:
9
Temp.:
25 °C
Hydrolysis rate constant:
0.003 h-1
DT50:
280 h
Type:
(pseudo-)first order (= half-life)
Validity criteria fulfilled:
not applicable
Conclusions:
7-AMCA is more stable in neutral than in acidic and alkaline solutions. The calculated half life times at 25 °C were 28.8 h at pH 4, 2100 h at pH 7 and 280 h at pH 9.
Executive summary:

The rate of hydrolysis of 7 -AMCA as a function of pH was determined according to the methods described in Directive 92/69/EEC method C.7. The rate constants at pH 4, pH 7 and pH 9 were determined at 50 °C (preliminary test), and at 65 °C and 75 °C (main test). From the data of the main test the rate constants at 25 °C were calculated.

Results:

The hydrolysis of 7-AMCA follows a pseudo first order kinetic at each pH.

7-AMCA is more stable in neutral than in acidic and alkaline solutions. The calculated half life times at 25 °C were 28.8 h at pH 4, 2100 h at pH 7 and 280 h at pH 9.

Description of key information

The hydrolysis of 7-AMCA follows a pseudo first order kinetic at each pH.
7-AMCA is more stable in neutral than in acidic and alkaline solutions.

The calculated half life times at 25 °C were 28.8 h at pH 4, 2100 h at pH 7 and 280 h at pH 9.

Key value for chemical safety assessment

Half-life for hydrolysis:
2 100 h
at the temperature of:
25 °C

Additional information