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Hydrolysis

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Reference
Endpoint:
hydrolysis
Type of information:
experimental study
Adequacy of study:
key study
Study period:
From 7 June, 2012 to 18 Oct, 2012
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to
Guideline:
OECD Guideline 111 (Hydrolysis as a Function of pH)
Deviations:
yes
Remarks:
During the main test at 20°C at pH 4 and pH 7, the temperature was not controlled within ± 0.5°C. However, study integrity was not adversely affected by this deviation.
Qualifier:
according to
Guideline:
EU Method C.7 (Degradation: Abiotic Degradation: Hydrolysis as a Function of pH)
Deviations:
yes
Remarks:
During the main test at 20°C at pH 4 and pH 7, the temperature was not controlled within ± 0.5°C. However, study integrity was not adversely affected by this deviation.
Qualifier:
according to
Guideline:
EPA OPPTS 835.2120 (Hydrolysis of Parent and Degradates as a Function of pH at 25°C)
Deviations:
yes
Remarks:
During the main test at 20°C at pH 4 and pH 7, the temperature was not controlled within ± 0.5°C. However, study integrity was not adversely affected by this deviation.
GLP compliance:
yes (incl. certificate)
Radiolabelling:
no
Analytical monitoring:
yes
Details on sampling:
Samples for analysis were taken immediately after preparation (t=0) and at several sampling points after t=0. The samples taken after t=0 were cooled to room temperature using running tap water (except for the samples in the 20°C environment).
Buffers:
-Acetate buffer pH 4, 0.01 M: solution of 16.7% 0.01 M sodium acetate and 83.3% 0.01 M acetic acid.
-Phosphate buffer pH 7, 0.01 M: solution of 0.01 M potassium di-hydrogenphosphate adjusted to pH 7 using 1 N sodium hydroxide.
-Borate buffer pH 9, 0.01 M: solution of 0.01 M boric acid and 0.01 M potassium chloride adjusted to pH 9 using 1 N sodium hydroxide.

The buffers contain 0.0009% (w/v) sodium azide.

Details on test conditions:
- Tier 1 preliminary test was performed at pH 4, 7 and 9 and 50.1 ± 0.2°C.
- Tier 2 main study was performed at pH 4, 7 and 9. At each pH hydrolysis at three different temperatures was followed.
- The test at pH 9 and 40°C was performed in duplicate.
- The buffer solutions were filter-sterilised through a 0.2 µm filter and transferred into sterile vessels.
- To exclude oxygen, nitrogen gas was purged through the solution for 5 min.
- The test substance was spiked to the solutions at a target concentration of 50 µg/L using a spiking solution in acetonitrile. .
- The spiking volume was < 1% of the sample volume. Nominal concentrations were not corrected for the spiking volume.
- For each sampling time, duplicate sterile vessels under vacuum were filled with 6 mL test solution and placed in the dark in a temperature controlled environment.
- The pH of the test solutions at pH 4, 7 and 9 was determined at t=0 and at each sampling point after t=0. Actual pH : 3.9-4.1, 6.9-7.1 and 9.0.
- Blank buffer solutions containing a similar content of blank spiking solution were treated similarly as the test samples and analysed at t=0.
Duration:
766.5 h
pH:
4
Initial conc. measured:
ca. 33 - ca. 33.5 µg/L
Duration:
768 h
pH:
4
Initial conc. measured:
ca. 40.4 - ca. 44.8 µg/L
Duration:
720 h
pH:
4
Initial conc. measured:
ca. 35.3 - ca. 37.3 µg/L
Duration:
745.77 h
pH:
7
Initial conc. measured:
ca. 35.2 µg/L
Duration:
725.08 h
pH:
7
Initial conc. measured:
ca. 32.8 - ca. 38.3 µg/L
Duration:
171.25 h
pH:
7
Initial conc. measured:
ca. 31.5 - ca. 31.7 µg/L
Duration:
478 h
pH:
9
Initial conc. measured:
ca. 43.9 - ca. 49.2 µg/L
Duration:
94.08 h
pH:
9
Initial conc. measured:
ca. 27.7 - ca. 40.5 µg/L
Duration:
63.58 h
pH:
9
Initial conc. measured:
ca. 34.2 - ca. 35 µg/L
Duration:
26.07 h
pH:
9
Initial conc. measured:
ca. 32.8 - ca. 57.7 µg/L
Number of replicates:
Two
Positive controls:
no
Negative controls:
no
Preliminary study:
A small test substance peak was detected in the blank buffer solution at pH 4, which was below the lowest standard (0.01 μg/L) after a dilution by a factor of 2. The mean recovery of the test substance containing buffer solutions at pH 7 and pH 9 for t=0 were slightly out of the acceptable range of 70-110% for non-labelled chemicals. Since a hydrolysis study focuses on the relative concentration decrease of the test substance in time, the mean recoveries were considered acceptable and the analytical method was considered adequate for supporting the hydrolysis study on the test substance. A degree of hydrolysis of the major component of the test substance of ≥ 10% was observed at pH 4, pH 7 and pH 9 after 5 d. According to the guideline, the higher tier test was required to determine the half-life time of the test substance.
Test performance:
RECOVERIES (Tier 2)
- Recovery is the concentration analysed at t=0 relative to the nominal concentration.
- Mean recovery in the table below is the mean of duplicate test samples.
- The mean recoveries of the test at pH4/20°C, pH 7/40°C and pH 9/40°C (both tests) were slightly outside the acceptable range of 70-110%. Since a hydrolysis study focusses on the relative concentration decrease of the test substance in time, the above mentioned mean recoveries were considered acceptable and the analytical method was considered adequate for support the hydrolysis study on the test substance.

HYDROLYSIS RATE (Tier 2):
For testing of pseudo-first order kinetics the mean logarithms of the relative concentrations between 10% and 90% were plotted against time. Linear relationships were obtained at all temperatures.

For each temperature and pH, the logarithms of all relative concentrations were correlated with time using linear regression analysis. The half-life times (and rate constants) of the substance were determined according to the model for pseudo-first order reactions. The Arrhenius equation was used to calculate the rate constant and half-life time at 25°C.
Transformation products:
not measured
% Recovery:
67
pH:
4
Temp.:
20 °C
% Recovery:
85
pH:
4
Temp.:
50 °C
% Recovery:
73
pH:
4
Temp.:
70 °C
% Recovery:
70
pH:
7
Temp.:
20 °C
% Recovery:
71
pH:
7
Temp.:
50 °C
% Recovery:
63
pH:
7
Temp.:
70 °C
% Recovery:
93
pH:
9
Temp.:
20 °C
% Recovery:
ca. 68 - ca. 69
pH:
9
Temp.:
40 °C
% Recovery:
91
pH:
9
Temp.:
50 °C
pH:
4
Temp.:
20 °C
Hydrolysis rate constant:
0 h-1
DT50:
242 d
Type:
(pseudo-)first order (= half-life)
Remarks on result:
other: y= -5.18E-5x + 1.99; r=0.314
pH:
4
Temp.:
50 °C
Hydrolysis rate constant:
0.001 h-1
DT50:
41.7 d
Type:
(pseudo-)first order (= half-life)
Remarks on result:
other: y= -3.00E-4x + 1.78; r=0.703
pH:
4
Temp.:
70 °C
Hydrolysis rate constant:
0.001 h-1
DT50:
28.8 d
Type:
(pseudo-)first order (= half-life)
Remarks on result:
other: y= -4.36E-4x + 1.99; r=0.961
pH:
7
Temp.:
20 °C
Hydrolysis rate constant:
0 h-1
DT50:
114 d
Type:
(pseudo-)first order (= half-life)
Remarks on result:
other: y= -1.10E-4 + 1.97; r=0.558
pH:
7
Temp.:
50 °C
Hydrolysis rate constant:
0.003 h-1
DT50:
10.5 d
Type:
(pseudo-)first order (= half-life)
Remarks on result:
other: y= -1.19E-3x + 1.85; r=0.966
pH:
7
Temp.:
70 °C
Hydrolysis rate constant:
0.018 h-1
DT50:
38.6 h
Type:
(pseudo-)first order (= half-life)
Remarks on result:
other: y= -7.8E-3x + 2.02; r=0.987
pH:
9
Temp.:
20 °C
Hydrolysis rate constant:
0.005 h-1
DT50:
143 h
Type:
(pseudo-)first order (= half-life)
Remarks on result:
other: y= -2.11E-3x + 1.88; r=0.985
pH:
9
Temp.:
40 °C
Hydrolysis rate constant:
0.004 h-1
DT50:
15.9 h
Type:
(pseudo-)first order (= half-life)
Remarks on result:
other: y= -1.90E-2x + 1.97; r=0.989
pH:
9
Temp.:
50 °C
Hydrolysis rate constant:
0.098 h-1
DT50:
7.05 h
Type:
(pseudo-)first order (= half-life)
Remarks on result:
other: y= -4.27E-2x + 1.88; r=0.965

Table 1: Hydrolysis rate constants and half-life times at 25°C (pH 4, 7 and 9)

 

pH

Temp.

Hydrolysis rate constant

Half-life

4

25°C

1.69E-4

171 d

7

25°C

3.80E-4

76.0 d

9

25°C

8.62E-3

80.4 h

 

 

Validity criteria fulfilled:
not specified
Conclusions:
Hydrolysis of di-TMPTTA shows a pseudo-first order behavior. Half-life times at 25°C and pH 4, 7 and 9 were determined to be 171 d, 76 d and 80 h, respectively.





Executive summary:

The rate of hydrolysis of di-TMPTTA at pH values normally found in the environment (pH 4-9) was determined according to EU Method C.7, OECD Guideline 111 and EPA Guideline OPPTS 835.2120. Hydrolysis rates of the substance at 20, 50 and 70°C (pH 4 and 7) or 20, 40 and 50°C (pH 9) were determined from which the hydrolysis rate at 25°C was calculated. The test substance was shown to degrade by a pseudo-first order behavior. Half-life times at 25°C and pH 4, 7 and 9 were determined to be 171 d, 76 d and 80 h, respectively (Lammers, 2013).

Description of key information

Hydrolysis of test substance shows a pseudo-first order behaviour. Half-life times at 25°C and pH 4, 7 and 9 were 171 d, 76 d and 80 h, respectively.

Key value for chemical safety assessment

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

Additional information

The rate of hydrolysis of di-TMPTTA at pH values normally found in the environment (pH 4-9) was determined according to EU Method C.7, OECD Guideline 111 and EPA Guideline OPPTS 835.2120. Hydrolysis rates of the substance at 20, 50 and 70°C (pH 4 and 7) or 20, 40 and 50°C (pH 9) were determined from which the hydrolysis rate at 25°C was calculated. The test substance was shown to degrade by a pseudo-first order behavior. Half-life times at 25°C and pH 4, 7 and 9 were determined to be 171 d, 76 d and 80 h, respectively (Lammers, 2013).