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Hydrolysis

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Reference
Endpoint:
hydrolysis
Type of information:
experimental study
Adequacy of study:
key study
Study period:
04 May to 17 August 2012
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: see 'Remark'
Remarks:
Study conducted in compliance with agreed protocols, with no or minor deviations from standard test guidelines and/or minor methodological deficiencies, which do not affect the quality of the relevant results. The study report was conclusive, with experiments conducted according to appropriate and valid guidelines and conducted under GLP conditions.
Qualifier:
according to guideline
Guideline:
OECD Guideline 111 (Hydrolysis as a Function of pH)
Deviations:
no
Qualifier:
according to guideline
Guideline:
EU Method C.7 (Degradation: Abiotic Degradation: Hydrolysis as a Function of pH)
Deviations:
no
Qualifier:
according to guideline
Guideline:
EPA OPPTS 835.2120 (Hydrolysis of Parent and Degradates as a Function of pH at 25°C)
Deviations:
no
GLP compliance:
yes
Radiolabelling:
no
Analytical monitoring:
yes
Details on sampling:
- Sampling intervals for the parent products: Samples were collected on Day 0, immediately after preparation, and then after Day 5.
- Sampling method: Samples collected on Day 5 were cooled to room temperature, using tap water. Samples were diluted with 0.1 M NaAc + acetonitrile: water (30:70, v/v) to yield concentrations within the calibration range.
- Sampling intervals/times for pH measurements: Day 0 and 5.
- Sampling intervals/times for blanks: Day 0 and 5.
Buffers:
- pH: 4
- Type and final molarity of buffer: 0.1 M Acetate buffer
- Composition of buffer: solution of 16.7% 0.1 M sodium acetate and 83.3% 0.1 M acetic acid. The buffer contains 0.0009% (w/v) sodium azide.

- pH: 7
- Type and final molarity of buffer: 0.1 M Phosphate buffer
- Composition of buffer: solution of 0.1 M potassium di-hydrogenphosphate adjusted to pH 7 using 10 N sodium hydroxide. The buffer contains 0.0009% (w/v) sodium azide.

- pH: 9
- Type and final molarity of buffer: 0.1 M Borate buffer
- Composition of buffer: solution of 0.1 M boric acid and 0.1 M potassium chloride adjusted to pH 9 using 10 N sodium hydroxide. The buffer contains 0.0009% (w/v) sodium azide.
Details on test conditions:
TEST SYSTEM
- Concentration: Test solutions were prepared in the buffer solutions at a target concentration of 10 mg/L
- Sterilisation method: Each solution was filter-sterilised through a 0.2 µm filter.
- Lighting: Test vessels were incubated in the dark.
- Measures taken to avoid photolytic effects: Vessels were kept in the dark.
- Measures to exclude oxygen: Test vessels were purged with nitrogen through the solution for 5 minutes.

TEST MEDIUM
- Preparation of stock solutions: The test material was prepared in acetonitrile:water (30:70, v/v) at concentrations of 2010 - 2723 mg/l. In order to dissolve the test material the solutions were ultrasonicated for 5 minutes.
- Preparation of test solutions: Test solutions were prepared in buffer solution at a nominal concentration of 10 mg/L.
- Volume used/treatment: 6 mL of test solution.
Duration:
5 d
pH:
4.1
Initial conc. measured:
13.1 - 13.2 mg/L
Duration:
5 d
pH:
7
Initial conc. measured:
13.9 mg/L
Duration:
5 d
pH:
9
Initial conc. measured:
14.1 mg/L
Number of replicates:
Each concentration was performed in duplicate.
Positive controls:
no
Negative controls:
yes
Remarks:
Blank buffer control solutions
Statistical methods:
CALCULATIONS

Response (R) Peak area of the test substance [units]

Calibration curve
R = aCN + b
where:
CN = nominal concentration [mg/L]
a = slope [units × L/mg]
b = intercept [units]

Analysed concentration (CA)
CA = [(R - b)/a]x d [mg/L]
where:
d = dilution factor

Recovery
= (CA/CN) x 100%
where:
CN = nominal concentration [mg/L]

Degree of hydrolysis
= [(mean C0 – Ct) / mean C0] x 100%
where:
C0 = concentration at t=0
Ct = concentration at t=5 days
Transformation products:
not measured
Details on hydrolysis and appearance of transformation product(s):
Degree of hydrolysis: At each pH the degree of hydrolysis by Day 5 was < 10%.
% Recovery:
104
pH:
4
Duration:
5 d
% Recovery:
100
pH:
7
Duration:
5 d
% Recovery:
100
pH:
9
Duration:
5 d
Key result
pH:
4
Temp.:
25 °C
DT50:
> 1 yr
Type:
(pseudo-)first order (= half-life)
Key result
pH:
7
Temp.:
25 °C
DT50:
> 1 yr
Type:
(pseudo-)first order (= half-life)
Key result
pH:
9
Temp.:
25 °C
DT50:
> 1 yr
Type:
(pseudo-)first order (= half-life)
Details on results:
TEST CONDITIONS
- pH, sterility, temperature, and other experimental conditions maintained throughout the study: Yes
- Blank Controls: The test material was not detected in the blank controls.
- Viability of the test method: Percentage recoveries ranged from 90 to 110%, demonstrating that the analytical method was adequate to support the study.

Table 1. Hydrolsis of the Test Material at pH 4, 7 and 9

pH

Sampling Time

Analysed Concentration (mg/L)

Degree of Hydrolysis (%)

Actual pH

Individual

Mean

4

0 hours

13.2

 

 

4.1

13.1

 

4.1

5 days

13.3

-1.2

-0.8

4.2

13.2

-0.3

4.2

7

0 hours

13.9

 

 

7.0

13.9

 

7.0

5 days

14.0

-0.7

-0.3

7.0

13.9

0.1

7.0

9

0 hours

14.1

 

 

9.0

14.1

 

9.0

5 days

14.2

-1.3

-1.2

9.0

14.2

-1.2

9.0

Table 2. Percentage Recoveries

pH

Nominal Concentration (mg/L)

Analysed Concentration (mg/L)

Recovery (%)

Mean Recovery (%)

4

12.7

13.2

104

104

12.7

13.1

104

7

13.9

13.9

100

100

13.9

13.9

100

9

14.0

14.1

100

100

14.0

14.1

100

Validity criteria fulfilled:
yes
Conclusions:
Under the conditions of the test, the test material was shown to undergo hydrolysis after 5 days incubation to a degree of less than 10% at each pH level. The half life was determined to be > 1 year at 25 ºC.
Executive summary:

The half life of the test material was determined in a hydrolysis as a function of pH study performed according to the HPLC method. The study was performed in line with GLP and to the standardised guidelines OECD 111, EU method C.7 and EPA OPPTS 835.2120.

Stock solutions were prepared in duplicate over a range of pH levels, samples were collected for analysis immediately after preparation on Day 0, and then again after 5 Days of incubation. The range of pH values were produced using buffer solutions and were monitored at each time point, where selected pH levels were based on those normally found in the environment; pH 4, 7 and 9. The test material was quantified at each time point, by HPLC, and the degree of hydrolysis calculated.

The percentage recovery of each duplicate was recorded on Day 0, yielding mean percentage recoveries of 100 to 104 %, values which demonstrate the viability of the analytical method.

The degree of hydrolysis was calculated to be < 10%, thus according to the study guidelines the second Tier test was not required.

Under the conditions of the test, the half live of the test material at pH 4, 7 and 9 was determined in a Tier 1 test to be > 1 year at 25 ºC.

Description of key information

The half-life for hydrolysis was determined to be > 1 year at 25 ºC for 3,5-Dimethylpyrazole from pH 4 to 9. This was determined in a key study (Baltussen, 2012) which was performed in line with GLP and to the standardised guidelines OECD 111, EU method C.7 and EPA OPPTS 835.2120.

Key value for chemical safety assessment

Half-life for hydrolysis:
1 yr
at the temperature of:
25 °C

Additional information

The half life of the test material was determined in a hydrolysis as a function of pH study performed according to the HPLC method.

Under the conditions of the test, the half live of the test material at pH 4, 7 and 9 was determined in a Tier 1 test to be > 1 year at 25 ºC. The degree of hydrolysis after 5 Days of incubation was calculated to be < 10%.

The study was conducted according to the GLP and standardised guidelines, with sufficient level of reporting. Therefore the study was assigned a reliability score of 1, according to the principles for assessing data quality as outlined in Klimisch (1977).

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