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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:
From 01 July 2015 to 26 July 2016.
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Reason / purpose:
reference to other study
Qualifier:
according to
Guideline:
EU Method C.7 (Degradation: Abiotic Degradation: Hydrolysis as a Function of pH)
Version / remarks:
2008
Deviations:
no
Qualifier:
according to
Guideline:
OECD Guideline 111 (Hydrolysis as a Function of pH)
Version / remarks:
2004
Deviations:
no
Qualifier:
according to
Guideline:
EPA OPPTS 835.2120 (Hydrolysis of Parent and Degradates as a Function of pH at 25°C)
Version / remarks:
2008
Deviations:
no
GLP compliance:
yes
Radiolabelling:
no
Analytical monitoring:
yes
Details on sampling:
-Samples for analysis were taken, from duplicate vessels, immediately after preparation (t=0) and after 5 days (Tier 1) or at several sampling points after t=0 (Tier 2).
-Samples taken from solutions with a temperature > 20°C were cooled to room temperature using running tap water, prior to further treatment/analysis.
-The samples were diluted to a concentration within the calibration range. End solution: 75/25 (v/v) acetonitrile/water.
-Pretreated test samples were analysed by single injection.
Buffers:
- Buffer pH 4, 0.01 M: aqueous solution of 16.7% 0.01 M sodium acetate and 83.3% 0.01 M acetic acid. The buffer contained 0.0009% (w/v) sodium azide.
- Buffer pH 7, 0.01 M: aqueous solution of 0.01 M potassium di-hydrogenphosphate adjusted to pH 7 using 1 N sodium hydroxide. The buffer contained 0.0009% (w/v) sodium azide.
- Buffer pH 9, 0.01 M: 1.2 -1.3 g Tris (hydroxymethyl) aminomethane in 1000 mL water, adjusted to pH 9 using 1 N hydrochloric acid.


Details on test conditions:
- Tier 1 preliminary test: at pH 4, 7 and 9 and 50°C.
- Tier 2 main study: at pH 4, 7 and 9. Three different temperatures for each pH.
- The buffers were filter-sterilised through a 0.2 µm FP 30/0.2 CA-S filter and transferred into sterile vessels.
- To exclude oxygen, nitrogen gas was purged through the solution for 5 minutes.
- The test substance was spiked to the solutions at a target concentration of 4 mg/L using a spiking solution in acetonitrile.
- Nominal concentrations were not corrected for the spiking volume (spiking volume was < 1% of sample volume).
- Sterile vessels (two for each sampling time) 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 was determined at each sampling point.
- Blank buffer solutions containing a similar content of blank spiking solution were treated similarly as the test samples and analysed at t=0. No test substance was detected in the blank buffer solutions.
Duration:
720.8 h
pH:
4
Temp.:
20 °C
Initial conc. measured:
3.95 mg/L
Remarks:
3.91 and 3.98 mg/L
Duration:
628.2 h
pH:
4
Temp.:
50 °C
Initial conc. measured:
4 mg/L
Remarks:
4.0 and 4.01 mg/L
Duration:
189.3 h
pH:
4
Temp.:
60 °C
Initial conc. measured:
3.79 mg/L
Remarks:
3.71 and 3.86 mg/L
Duration:
722.6 h
pH:
7
Temp.:
20 °C
Initial conc. measured:
4.24 mg/L
Remarks:
4.15 and 4.32 mg/L
Duration:
96 h
pH:
7
Temp.:
50 °C
Initial conc. measured:
4.02 mg/L
Remarks:
3.99 and 4.04 mg/L
Duration:
30.3 h
pH:
7
Temp.:
60 °C
Initial conc. measured:
4.12 mg/L
Remarks:
3.81 and 4.42 mg/L
Duration:
52.5 h
pH:
9
Temp.:
20 °C
Initial conc. measured:
4.04 mg/L
Remarks:
3.89 and 4.19 mg/L
Duration:
24 h
pH:
9
Temp.:
40 °C
Initial conc. measured:
4.61 mg/L
Remarks:
4.53 and 4.68 mg/L
Duration:
7 h
pH:
9
Temp.:
50 °C
Initial conc. measured:
3.93 mg/L
Remarks:
3.69 and 4.16 mg/L
Number of replicates:
Two
Positive controls:
no
Negative controls:
no
Preliminary study:
At pH 4, pH 7 and pH 9, a degree of hydrolysis of ≥ 10% was observed after 5 days at 50°C. According to the guideline, the higher Tier test was required to determine the half-life time of the substance.
Test performance:
Tier 2 recovery:
- Recovery is the concentration analysed at t=0 for the test sample relative to the nominal concentration.
- The mean recovery was calculated from duplicate samples.
- The mean recoveries at each pH and temperature are shown below.
- The mean recoveries fell within the criterion range of 90-110%.
- Concentrations analysed in the test samples were not corrected for recovery.

Transformation products:
not specified
% Recovery:
99
pH:
4
Temp.:
20 °C
% Recovery:
100
pH:
4
Temp.:
50 °C
% Recovery:
95
pH:
4
Temp.:
60 °C
% Recovery:
106
pH:
7
Temp.:
20 °C
% Recovery:
100
pH:
7
Temp.:
50 °C
% Recovery:
103
pH:
7
Temp.:
60 °C
% Recovery:
101
pH:
9
Temp.:
20 °C
% Recovery:
115
pH:
9
Temp.:
40 °C
% Recovery:
98
pH:
9
Temp.:
50 °C
pH:
4
Temp.:
20 °C
Hydrolysis rate constant:
0 h-1
DT50:
369 d
Type:
other: see 'Details on results'
Remarks on result:
other: y= 4.78E-05 + 1.97 (r=0.179)
pH:
4
Temp.:
50 °C
Hydrolysis rate constant:
0.004 h-1
DT50:
7.1 d
Type:
(pseudo-)first order (= half-life)
Remarks on result:
other: y= -1.77E-03 + 1.90 (r=0.942)
pH:
4
Temp.:
60 °C
Hydrolysis rate constant:
0.013 h-1
DT50:
2.2 d
Type:
(pseudo-)first order (= half-life)
Remarks on result:
other: y= -5.66E-03 + 1.94 (r=0.990)
pH:
7
Temp.:
20 °C
Hydrolysis rate constant:
0.001 h-1
DT50:
23 d
Type:
(pseudo-)first order (= half-life)
Remarks on result:
other: y= -5.43E-04 + 1.94 (r=0.845)
pH:
7
Temp.:
50 °C
Hydrolysis rate constant:
0.031 h-1
DT50:
23 h
Type:
(pseudo-)first order (= half-life)
Remarks on result:
other: y= -1.33E-02 + 2.03 (r=0.996)
pH:
7
Temp.:
60 °C
Hydrolysis rate constant:
0.09 h-1
DT50:
7.7 h
Type:
(pseudo-)first order (= half-life)
Remarks on result:
other: y= -3.89E-02 + 2.02 (r=0.997)
pH:
9
Temp.:
20 °C
Hydrolysis rate constant:
0.048 h-1
DT50:
15 h
Type:
(pseudo-)first order (= half-life)
Remarks on result:
other: y= -2.07E-02 + 2.01 (r=0.995)
pH:
9
Temp.:
40 °C
Hydrolysis rate constant:
0.162 h-1
DT50:
4.3 h
Type:
(pseudo-)first order (= half-life)
Remarks on result:
other: y= -7.03E-02 + 2.00 (r=0.994)
pH:
9
Temp.:
50 °C
Hydrolysis rate constant:
27.1 h-1
DT50:
2.6 h
Type:
(pseudo-)first order (= half-life)
Remarks on result:
other: y= -1.18E-01 + 2.03 (r=0.996)
Details on results:
The hydrolysis rate constant and half-life time of the test item at each temperature was obtained and the Arrhenius equation was used to determine the rate constant and half-life time at 25°C. The slope for hydrolysis at pH 4 at 20°C was positive, which means that there was no degradation by hydrolysis at the given conditions. Therefore it was not possible to take this slope into account for determination of half-life time at 25°C. Based on this, half-life time at 25°C was determined by extrapolation of the values obtained for 50°C and 60°C. Half-life at 20°C was also extrapolated in the same way

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

pH

Temp.

Hydrolysis rate constant

Half-life

 

 

 

 

4

25°C

0.00016

180 days

7

25°C

0.00223

13 days

9

25°C

0.0656

11 hours

 

 

 

 

 

 

Conclusions:
Hydrolysis of the test substance at pH 4-9 shows a pseudo-first order behaviour.
-Half-life time at 25°C and pH 4 was determined to be 180 days.
-Half-life time at 25°C and pH 7 was determined to be 13 days.
-Half-life time at 25°C and pH 9 was determined to be 11 hours.




Executive summary:

The rate of hydrolysis of the substance at pH values normally found in the environment (pH 4-9) was determined in a GLP-compliant Tier 2 study according to EC C.7, OECD 111 and EPA OPPTS 835.2120 guidelines. Hydrolysis rates of the substance at three different temperatures were determined from which the hydrolysis rate at 25°C was calculated. Quantification was based on the main constituent of the substance. The constituent was shown to degrade by a pseudo-first order behaviour. Half-life times at 25°C and pH 4, pH 7 and pH 9 were determined to be 180 days, 13 days and 11 hours, respectively.

Description of key information

Tier 2 hydrolysis study (EC C.7, OECD 111, OPPTS 830.2120) at pH 4, 7 and 9. Quantification was based on the main constituent of the substance.

The constituent was shown to degrade by a pseudo-first order behaviour. Half-life times at 25°C and pH 4, pH 7 and pH 9 were determined to be 180 days, 13 days and 11 hours, resp.

Key value for chemical safety assessment

Additional information