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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:
2010-05-21 to 2010-08-04
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)
Version / remarks:
2004
Deviations:
no
Qualifier:
according to
Guideline:
EU Method C.7 (Degradation: Abiotic Degradation: Hydrolysis as a Function of pH)
Version / remarks:
2008
Deviations:
no
GLP compliance:
yes (incl. certificate)
Radiolabelling:
no
Analytical monitoring:
yes
Details on sampling:
The samples were measured by the previously validated reverse phase HPLC method using UV detection .
Buffers:
- pH 4: 3 mL 0.2 M Sodium hydroxide and 375 mL 0.2 M Potassium hydrogen phthalate were diluted to 1500 mL with ultra-pure water,
- pH 7: 221.7 mL 0.2 M Sodium hydroxide and 375 mL 0.2 M Potassium dihydrogen phosphate were diluted to 1500 mL with ultra-pure water,
- pH 9: 160.5 mL 0.2 M Sodium hydroxide and 375 mL 0.2 M Boric acid and Potassium chloride were diluted to 1500 mL with ultra-pure water.
Details on test conditions:
TEST SYSTEM
- Measures taken to avoid photolytic effects: The hydrolysis reaction was carried out using a dark thermostat to avoid photolytic effects.
- Measures to exclude oxygen: Nitrogen was bubbled into the water for five minutes before the preparation of the solutions in order to exclude oxygen.

TEST SOLUTION
Stock solution (~5 mg/mL): ca.50 mg of the test item was dissolved in acetonitrile to a total volume of 10 mL. The test solutions were prepared by dilution of the “stock solutions for the hydrolysis test” with the corresponding buffer solutions, just before analysis and start of the storage. 1500 mL sterile solutions were prepared at pH 4, 7 and 9. Solutions were transferred into ~22 mL screw-cap glass tubes with PTFE septa. The solution was analysed at the start of the tests and then at appropriate time intervals: in order to get at least six other data points in the range of 10 to 90 % hydrolysis. The test solutions were prepared by five-hundred fold dilution of the “stock solutions for the hydrolysis test” with the corresponding buffer solutions.
Duration:
5 d
pH:
4
Initial conc. measured:
ca. 22 mg/L
Duration:
5 d
pH:
7
Initial conc. measured:
ca. 22 mg/L
Duration:
5 d
pH:
9
Initial conc. measured:
ca. 22 mg/L
Number of replicates:
2
Negative controls:
yes
Remarks:
control buffer
Statistical methods:
No statistical method performed.
Preliminary study:
Based on the results of the preliminary test the hydrolysis rate of TBPEH was found to be 70 % at pH 4 and 75 % at pH 7 and 84 % at pH 9 after 5 days at 50 degree C.
Transformation products:
no
Details on hydrolysis and appearance of transformation product(s):
The decomposition of the substance was monitored by HPLC-UV. The decomposition of the test substance TBPEH is well known and results in the formation of tert-butanol and 2-ethylhexanoic acid as the main compounds. However, these degradation products can not be detected under the given validated test method neither from the decomposition chromatograms nor by using the corresponding reference substances.
The LCQ analyse of the decomposition solution did not provide any additional information on the degradation products.

% Recovery:
87
pH:
4
Temp.:
25 °C
Duration:
5 d
% Recovery:
85
pH:
7
Temp.:
25 °C
Duration:
5 d
% Recovery:
92
pH:
9
Temp.:
25 °C
Duration:
5 d
Key result
pH:
4
Temp.:
15 °C
Hydrolysis rate constant:
0.007 h-1
DT50:
104 h
Type:
(pseudo-)first order (= half-life)
pH:
4
Temp.:
37 °C
Hydrolysis rate constant:
0.017 h-1
DT50:
41 h
Type:
(pseudo-)first order (= half-life)
pH:
4
Temp.:
60 °C
Hydrolysis rate constant:
0.042 h-1
DT50:
17 h
Type:
(pseudo-)first order (= half-life)
Key result
pH:
7
Temp.:
15 °C
Hydrolysis rate constant:
0.008 h-1
DT50:
86 h
Type:
(pseudo-)first order (= half-life)
pH:
7
Temp.:
37 °C
Hydrolysis rate constant:
0.012 h-1
DT50:
60 h
Type:
(pseudo-)first order (= half-life)
pH:
7
Temp.:
60 °C
Hydrolysis rate constant:
0.041 h-1
DT50:
17 h
Type:
(pseudo-)first order (= half-life)
Key result
pH:
9
Temp.:
15 °C
Hydrolysis rate constant:
0.005 h-1
DT50:
152 h
Type:
(pseudo-)first order (= half-life)
pH:
9
Temp.:
37 °C
Hydrolysis rate constant:
0.008 h-1
DT50:
84 h
Type:
(pseudo-)first order (= half-life)
pH:
9
Temp.:
60 °C
Hydrolysis rate constant:
0.061 h-1
DT50:
11 h
Type:
(pseudo-)first order (= half-life)
Details on results:
No further details

No other information

Validity criteria fulfilled:
yes
Conclusions:
The calculated half lives of the hydrolysis reactions at pH 4, pH 7 and pH 9 are as follows:
t 1/2 at pH4 and 15 degree C: 104 h, 37 degree C: 41 h, 60 degree C: 17 h;
t 1/2 at ph7 and 15 degree C: 86 h, 37 degree C: 60 h, 60 degree C: 17 h;
t 1/2 at pH9 and 15 degree C: 152 h, 37 degree C: 84 h, 60 degree C: 11 h.
Based on the results obtained, test substance tert.-Butylperoxy- 2-ethylhexanoat is hydrolytically unstable at pH 4, pH 7 and pH 9 under the conditions investigated.
Executive summary:

The hydrolysis of tert.-Butylperoxy- 2-ethylhexanoat in different pH buffer solutions was investigated according to OECD Guideline No. 111 and EU method C.7. The analysis of tert.-Butylperoxy- 2-ethylhexanoat was carried out with a HPLC method using UV detection. Sterile aqueous buffer solutions of different pH values (pH 4, 7, 9) were prepared with the test substance solutions and buffer solutions. The hydrolysis of TBPEH was examined at pH 4, 7 and 9 at three temperatures: 15 ± 0.5 degree C, 37 ± 0.5 degree C and 60 ± 0.5 degree C. TBPEH concentrations in the buffer solutions were: ca. 22 mg/L (ca. 0.1 mM). The calculated half lives of the hydrolysis reactions at pH 4, pH 7 and pH 9 are given in the following table:

Buffer solution

Temperature, °C

t1/2, hours

pH 4

15

104

25

67

37

41

60

17

pH 7

15

86

25

67

37

60

60

17

pH 9

15

152

25

103

37

84

60

11

Based on the results obtained, test substance tert.-Butylperoxy- 2-ethylhexanoat hydrolytically unstable at pH 4, pH 7 and pH 9 under the conditions investigated.

Description of key information

The hydrolysis of TBPEH was determined at various pH values and temperatures. The rate of hydrolysis decreased with increasing pH and temperature. Hydrolysis increased with temperature and decreasing pH. From values obtained in the key study, the environmentally relevant rate of hydrolysis at pH 7 and 12 °C was calculated using the Arrhenius equation and resulted in a hydrolysis rate of 1.84E 03 h 1 and a DT50 of 376.3 h (15.68 days).

Key value for chemical safety assessment

Half-life for hydrolysis:
15.8 d
at the temperature of:
12 °C

Additional information

The hydrolysis behaviour of TBPEH was assessed in two studies according to EU method C.7 and OECD guideline no. 111. From values obtained in the key study, the environmentally relevant rate of hydrolysis at pH 7 and 12 °C was calculated using the Arrhenius equation and resulted in a hydrolysis rate of 1.84E 03 h 1 and a DT50 of 376.3 h (15.68 days).