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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:
22 Jul - 02 Oct 2015
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
OECD Guideline 111 (Hydrolysis as a Function of pH)
Qualifier:
according to guideline
Guideline:
EU Method C.7 (Degradation: Abiotic Degradation: Hydrolysis as a Function of pH)
GLP compliance:
yes (incl. QA statement)
Radiolabelling:
no
Analytical monitoring:
yes
Details on sampling:
- Sampling intervals for the parent/transformation products: samples were taken at test start (0 h) and at 9 to 10 spaced points (between 10 and 90% of hydrolysis) until test end, at each test temperature
- Sampling intervals/times for temperature measurements: every hour
- Sampling intervals/times for sterility check: sterility was checked at test end by colony forming units determination with Water Plate Count Agar from additional samples of the advanced test by incubation at 36 ± 1 °C for 48 h and at 22 ± 1 °C for 72 h
- Sample storage conditions before analysis: all test item containing samples were prepared immediately (if possible less than 30 min until start of enrichment, but at least not more than 5% of the total study time)
Buffers:
- pH: 4, 7, 9
- Composition of buffer: according to guideline 111
- Buffer solution pH 4: NaOH and mono potassium citrate were dissolved in double distilled water.
- Buffer solution pH 7: NaOH and KH2PO4 were dissolved in double distilled water.
- Buffer solution pH 9: NaOH, KCI and H3BO3 were dissolved in double distilled water.
Details on test conditions:
TEST SYSTEM
- Type, material and volume of test flasks, other equipment used: sterile headspace flasks, volume: 119 mL, with aluminium tops with PTFE seals, test volume: 50 mL
- Sterilisation method: autoclaving
- Temperatures: 20, 30, 50 °C
- Measures taken to avoid photolytic effects: avoidance of direct sunlight and the use of opaque water baths
- Measures to exclude oxygen: buffers were purged with nitrogen for 5 min and subsequently pH was checked to a precision of 0.1 at the test temperature
- If no traps were used, is the test system closed/open: closed

TEST MEDIUM
- Kind and purity of water: double distilled water
- Identity and concentration of co-solvent: acetonitrile, =< 1% (v/v)
Duration:
30 d
pH:
4
Initial conc. measured:
>= 3.98 - <= 4.29 mg/L
Remarks:
Test was performed at 20, 30 and 50 °C.
Duration:
30 d
pH:
7
Initial conc. measured:
>= 3.98 - <= 4.29 mg/L
Remarks:
Test was performed at 20, 30 and 50 °C.
Duration:
30 d
pH:
9
Initial conc. measured:
>= 3.98 - <= 4.29 mg/L
Remarks:
Test was performed at 20, 30 and 50 °C.
Number of replicates:
Duplicates per pH value and sampling date.
Positive controls:
no
Negative controls:
yes
Remarks:
Buffer solutions (pH value 4, 7 and 9)
Preliminary study:
In the preliminary test, more than 10% of the test item was degraded after 120 h at pH 4, 7 and 9 (24, 11 and 78%, respectively).
Transformation products:
yes
No.:
#1
Details on hydrolysis and appearance of transformation product(s):
- Other: transformation product was quantified for all temperature conditions at pH 9
% Recovery:
90.6
pH:
9
Temp.:
20 °C
Duration:
28.5 h
% Recovery:
85
pH:
9
Temp.:
20 °C
Duration:
71.9 h
% Recovery:
72.5
pH:
9
Temp.:
20 °C
Duration:
723 h
% Recovery:
78.5
pH:
9
Temp.:
30 °C
Duration:
47.7 h
% Recovery:
52.8
pH:
9
Temp.:
30 °C
Duration:
338 h
% Recovery:
38.4
pH:
9
Temp.:
30 °C
Duration:
506 h
% Recovery:
28.1
pH:
9
Temp.:
30 °C
Duration:
723 h
% Recovery:
52.4
pH:
9
Temp.:
50 °C
Duration:
28.6 h
% Recovery:
36.3
pH:
9
Temp.:
50 °C
Duration:
53.4 h
% Recovery:
10.3
pH:
9
Temp.:
50 °C
Duration:
170 h
pH:
4
Temp.:
30 °C
Hydrolysis rate constant:
0 s-1
DT50:
12 132 d
Type:
(pseudo-)first order (= half-life)
Remarks on result:
other: Number of data points: 11, slope of regression graph: not significantly non zero
pH:
4
Temp.:
50 °C
Hydrolysis rate constant:
0 s-1
DT50:
63.9 d
Type:
(pseudo-)first order (= half-life)
Remarks on result:
other: Number of data points: 11, slope of regression graph: significantly non zero
pH:
7
Temp.:
20 °C
Hydrolysis rate constant:
0 s-1
DT50:
415 d
Type:
(pseudo-)first order (= half-life)
Remarks on result:
other: Number of data points: 11, slope of regression graph: not significantly non zero
pH:
7
Temp.:
30 °C
Hydrolysis rate constant:
0 s-1
DT50:
566 d
Type:
(pseudo-)first order (= half-life)
Remarks on result:
other: Number of data points: 11, slope of regression graph: not significantly non zero
pH:
7
Temp.:
50 °C
Hydrolysis rate constant:
0 s-1
DT50:
89 d
Type:
(pseudo-)first order (= half-life)
Remarks on result:
other: Number of data points: 11, slope of regression graph: significantly non zero
pH:
7
Temp.:
25 °C
Hydrolysis rate constant:
0 s-1
DT50:
451 d
Type:
(pseudo-)first order (= half-life)
Remarks on result:
other: values calculated via Arrhenius equation
pH:
9
Temp.:
20 °C
Hydrolysis rate constant:
0 s-1
DT50:
72.9 d
Type:
(pseudo-)first order (= half-life)
Remarks on result:
other: Number of data points: 11, slope of regression graph: significantly non zero
pH:
9
Temp.:
30 °C
Hydrolysis rate constant:
0 s-1
DT50:
17.3 d
Type:
(pseudo-)first order (= half-life)
Remarks on result:
other: Number of data points: 11, slope of regression graph: significantly non zero
pH:
9
Temp.:
50 °C
Hydrolysis rate constant:
0 s-1
DT50:
2.24 d
Type:
(pseudo-)first order (= half-life)
Remarks on result:
other: Number of data points: 10, slope of regression graph: significantly non zero
pH:
9
Temp.:
25 °C
Hydrolysis rate constant:
0 s-1
DT50:
29 d
Type:
(pseudo-)first order (= half-life)
Remarks on result:
other: values calculated via Arrhenius equation
Details on results:
TEST CONDITIONS
- pH, sterility, temperature, and other experimental conditions maintained throughout the study: no (for more information see any other information on results)

MAJOR TRANSFORMATION PRODUCTS

At pH 9 and 20 °C:
- Maximum concentrations in % of the parent substance and day(s) of incubation when observed: 100% at 0 h
- Maximum concentration in % of the parent substance at end of study period: 72.5% at 723 h

At pH 9 and 30 °C:
- Maximum concentrations in % of the parent substance and day(s) of incubation when observed: 100% at 0 h
- Maximum concentration in % of the parent substance at end of study period: 28.1% at 723 h

At pH 9 and 50 °C:
- Maximum concentrations in % of the parent substance and day(s) of incubation when observed: 100% at 0 h
- Maximum concentration in % of the parent substance at end of study period: 10.3% at 170 h

The test item showed a moderate hydrolysis rate (t1/2 =< 30 d) at pH 9 at 30 and 50 °C.

At pH 4 and 7, 50 °C and pH 9, 20 °C only a slow hydrolysis (t1/2 > 30 d) was observed.

At pH 4 and 7, 20 and 30 °C the half-lives were > 1 year indicating no significant hydrolysis of the test item.

Table 1: pH values in the test system measured before start of hydrolysis.

Test Intended pH-value Measured pH-value at 20 °C Measure pH-value at 30 °C Measured pH-value at 50 °C
Advanced 4.0 ± 0.1 4.02/4.03 4.03/4.02 4.03/4.02
7.0 ±0.1 6.98 / 6.99 6.98/6.99 6.98/7.00
9.0 ±0.1 9.03 / 9.03 9.03/9.03 9.03/9.02

Table 2: Mean, maximum and minimum values of temperature measured in the test system.

Test pH value Intended Temperature Measured Temperature 
Mean ± SD  Min. / Max.
Preliminary 4, 7, 9 50.0 ± 0.5 50.0 ± 0.07 49.6 / 50.3
Advanced 20.0 ± 0.5 20.0 ±0.1 19.7/20.6*
30.0 ± 0.5 30.0 ±0.1 29.3/30.4*
50.0 ±0.5 50.0 ± 0.2 47.6 / 50.5**

* Temperature out of range for 0.1% of the total run time

** Temperature out of range for 1.4% of the total run time

No significant colony forming units were found during CFU-determination, confirming the sterility of the test solutions.

Validity criteria fulfilled:
yes
Conclusions:
The test item showed a moderate hydrolysis rate (t1/2 =< 30 d) at pH 9 at 30 and 50 °C.
At pH 4 and 7, 50 °C and pH 9, 20 °C only a slow hydrolysis (t1/2 > 30 d) was observed.
At pH 4 and 7, 20° and 30 °C the half-lives were > 1 year indicating no significant hydrolysis of the test item.
The transformation product was 3,3,5-Trimethylcyclohexanol which was identified via co-chromatography.

Description of key information

The test substance is hydrolytically stable under environmental conditions at pH 4 and pH 7. For pH 9 a DT50 of 29 d was calculated at 25 °C (Arrhenius equation).

Key value for chemical safety assessment

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

Additional information

One experimental study is available investigating the hydrolytic properties of the substance. The study was performed according to OECD 111 (GLP). A preliminary test with a concentration of 5 mg/L was performed at three different pH values (pH 4, 7 and 9) and 50 °C. The test substance was found to be hydrolytically unstable (degradation > 10%) under the conditions of the preliminary test after 120 h. Thus, a main test with a maximum duration of 30 d was performed for pH 4, 7 and 9 at 20, 30 and 50 °C (initial test substance concentration: 3.98 - 4.29 mg/L). The results from GC/MS analysis indicated that the test substance is hydrolytically stable at pH 4 with a DT50 > 1 year at 30 °C and a DT50 of 63.9 d at 50 °C. A comparable result was observed at pH 7 with a DT50 of > 1 year at 20, 30 (regression analysis) and 25 °C (calculated using Arrhenius equation). The fastest hydrolysis was recorded at pH 9 with a DT50 of 72.9 d at 20 °C, 17.3 d at 30 °C and 2.24 d at 50 °C based on regression analysis. Applying the Arrhenius equation a DT50 of 29 d resulted at 25 °C. 3,3,5-trimethylcyclohexanol was identified by co-chromatography as the major transformation product during hydrolysis at pH 9. All validity criteria of the study were met.