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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:
24 Apr - 14 Jun 2002
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:
This procedure corresponds to test method C.7 for determination of abiotic degradation, EG-guideline 92/69.
Deviations:
no
GLP compliance:
yes (incl. QA statement)
Radiolabelling:
no
Analytical monitoring:
yes
Buffers:
pH: 9
buffer: borax / hydrochloric acid, Riedel de Haen Art. No. 33548, ready to use solution

pH:7
buffer: potassium dihydrogen phosphate / Di-sodium hydrogen phosphate, Riedel de Haen Art. No. 33546, ready to use solution

pH:4
buffer: citric acid / potassium hydroxide / sodium chloride, Riedel de Haen Art. No. 33543, ready to use solution
Duration:
5 d
pH:
4
Temp.:
50 °C
Remarks:
The initial test concentration is not stated.
Duration:
26 d
pH:
7
Temp.:
50 °C
Remarks:
The initial test concentration is not stated.
Duration:
3 d
pH:
7
Temp.:
65 °C
Remarks:
The initial test concentration is not stated.
Duration:
22 h
pH:
7
Temp.:
80 °C
Remarks:
The initial test concentration is not stated.
Duration:
41 h
pH:
9
Temp.:
50 °C
Remarks:
The initial test concentration is not stated.
Duration:
169 min
pH:
9
Temp.:
65 °C
Remarks:
The initial test concentration is not stated.
Duration:
56 min
pH:
9
Temp.:
80 °C
Remarks:
The initial test concentration is not stated.
Number of replicates:
None
Positive controls:
no
Negative controls:
no
Statistical methods:
The correlation coefficient for In k versus T^-1 was calculated for each measurement at pH 7 and 9.
Transformation products:
not measured
Key result
pH:
4
Temp.:
50 °C
Remarks on result:
hydrolytically stable based on preliminary test
Remarks:
Within 5 days the degradation was less than 10 %.
Key result
pH:
7
Temp.:
25 °C
Hydrolysis rate constant:
0 s-1
DT50:
25 220 h
Type:
(pseudo-)first order (= half-life)
Remarks on result:
other: The correlation coefficient for In k versus T^-1 was calculated; the value of -0.99237 proves the correctness of the results.
Key result
pH:
9
Temp.:
25 °C
Hydrolysis rate constant:
0 s-1
DT50:
1 051 h
Type:
(pseudo-)first order (= half-life)
Remarks on result:
other: The correlation coefficient for In k versus T^-1 was calculated; the value of-0.99869 proves the correctness of the results.

At pH value = 7 and 50 °C:
preliminary test (test 1):
The degradation reaction is given by pseudo-first order reaction (correlation coefficient 0.99887), the half-time and the rate constant (first order reaction) is given by:
t(1/2) = 873 hours
k = 2.20448E-07 1/s


At pH value = 7 and 65 °C:
test 3:
The degradation reaction is given by pseudo-first order reaction (correlation coefficient 0.99996), the half-time and the rate constant (first order reaction) is given by:
t(1/2) = 95.1 hours
k- 2.024 HE-06 1/s


At pH value = 7 and 80 °C:
test 3:
The degradation reaction is given by pseudo-first order reaction (correlation coefficient 0.99869), the half-time and the rate constant (first order reaction) is given by:
t(1/2) = 25.9 hours
k=7.43575E-06 1/s


 


At pH value = 9 and 50 °C:
preliminary test (test 1):
The degradation reaction is given by pseudo-first order reaction (correlation coefficient 0.99922), the half-time and the rate constant (first order reaction) is given by:
t(1/2) = 29.7 hours
k = 6.48474E-06 1/s


At pH value = 9 and 65 °C:
test 3:
The degradation reaction is given by pseudo-first order reaction (correlation coefficient 0.99973), the half-time and the rate constant (first order reaction) is given by:
t(1/2) = 3.73 hours
k = 5.16091E-05 1/s


At pH value = 9 and 80 °C:
test 3:
The degradation reaction is given by pseudo-first order reaction (correlation coefficient 0.99948), the half-time and the rate constant ( first order reaction) is given by:
t(l/2) = 0.763 hours
k = 2.52240E-041/s


 


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 HPLC 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): 4 measurements


pH 7 (50°C): 6 measurements


pH 9 (50°C): 5 measurements


Yes
The temperature, pH value, buffer composition and a table of all concentration-time data points shall be stated.

The temperature, pH value, buffer composition and a table of all concentration-time data points is stated for each test.


Yes

 

Validity criteria fulfilled:
yes
Remarks:
See 'Any other information on results incl. tables'
Conclusions:
pH4: hydrolytically stable (based on preliminary test)
pH7: hydrolytically stable (DT50 > 1 yr at 25 °C)
pH9: DT50 1015 h at 25 °C
Executive summary:

The hydrolytic degradation of 4,6-Dichlor-5-Fluorpyrimidine was investigated according to EU Method C.7 at pH4, pH7 and pH9. A preliminary test was performed first at a temperature of 50 °C. Based on the result the substance is considered hydrolytically stable at pH4.
A main test was performed at 65 and 80 °C for pH7 and pH9. The test resulted in hydrolytic half lives of 95.1 and 25.9 h for pH7 at 65 and 80 °C, respectively. At pH9 hydrolytic half lives of 3.73 and 0.763 h resulted at 65 and 80 °C, respectively. The half lives from the main test were re-calculated to an environmentally relevant temperature of 25 °C by using Arrhenius equation. The re-calculation indicated that the substance is hydrolytically stable at pH7 with a DT50 of > 1 yr (25220 h). For pH9 a slow hydrolytic degradation is indicated with a DT50 of 1051 h.

Description of key information

The hydrolytic degradation of 4,6-Dichlor-5-Fluorpyrimidine was investigated according to EU Method C.7 at pH4, pH7 and pH9. A preliminary test was performed first at a temperature of 50 °C. Based on the result the substance is considered hydrolytically stable at pH4.
A main test was performed at 65 and 80 °C for pH7 and pH9. The test resulted in hydrolytic half lives of 95.1 and 25.9 h for pH7 at 65 and 80 °C, respectively. At pH9 hydrolytic half lives of 3.73 and 0.763 h resulted at 65 and 80 °C, respectively. The half lives from the main test were re-calculated to an environmentally relevant temperature of 25 °C by using Arrhenius equation. The re-calculation indicated that the substance is hydrolytically stable at pH7 with a DT50 of > 1 yr (25220 h). For pH9 a slow hydrolytic degradation is indicated with a DT50 of 1051 h.

Key value for chemical safety assessment

Half-life for hydrolysis:
25 220 h
at the temperature of:
25 °C

Additional information