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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 20 February 1995 to 15 July 1995
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
comparable to guideline study with acceptable restrictions
Remarks:
The study is deemed scientifically valid even though some information were not reported, such as the repeatability and sensitivity of analytical method and the characteristics of water used. Also no positive or negative control was used and the no sterility check was reported.
Qualifier:
equivalent or similar to
Guideline:
OECD Guideline 111 (Hydrolysis as a Function of pH)
Deviations:
no
Principles of method if other than guideline:
Not applicable
GLP compliance:
yes (incl. certificate)
Specific details on test material used for the study:
- Storage condition of test material: room temperature
Radiolabelling:
no
Analytical monitoring:
yes
Details on sampling:
- Sampling method: an aliquot of each sample solution (100 mL) was extracted using three portions (3 x 25 mL) of dichloromethane. The extracts were passed through anhydrous sodium sulphate, combined and evaporated to dryness. The residue was dissolved in hexane (4.0 mL).

- Sampling intervals for the parent/transformation products:
# Preliminary Test (Test1): 0, 2.4, 48, 120 and 288 hours
# Test 3: 0, 24, 166, 243, 337 and 411 hours
Buffers:
pH 4:
- Composition of buffer:
Citric acid: 0.05 mol/L
Sodium hydroxide: 0.10 mol/L
Hydrochloric acid: 0.05 mol/L

pH 7:
- Composition of buffer:
Disodium hydrogen orthophosphate: 0.04 mol/L
Potassium dihydrogen orthophosphate: 0.03 mol/L

pH 9:
- Composition of buffer:
Disodium tetraborate: 0.05 mol/L
Hydrochloric acid: 0.0192 mol/L
Estimation method (if used):
None
Details on test conditions:
TEST SYSTEM
- Type, material and volume of test flasks, other equipment used: glass flasks
- Measures taken to avoid photolytic effects: protected from light
- Measures to exclude oxygen: stoppered flasks
- If no traps were used, is the test system closed/open: closed system (stoppered flasks)
- Is there any indication of the test material adsorbing to the walls of the test apparatus? no

TEST MEDIUM
- Volume used/treatment: 1000 mL
- Kind and purity of water: not mentioned
- Preparation of test medium: A stock solution of the test material was prepared in acetonitrile at a concentration of 150 mg/L. Aliquots (10.0 mL) of the stock solutions were added to each buffer solutions (1000 mL) to give a nominal concentration of 1.5 mg/L
- Renewal of test solution: no
Duration:
288 h
pH:
4
Temp.:
50 °C
Initial conc. measured:
ca. 1.52 mg/L
Duration:
288 h
pH:
7
Temp.:
50 °C
Initial conc. measured:
ca. 1.59 mg/L
Duration:
120 h
pH:
9
Temp.:
50 °C
Initial conc. measured:
ca. 1.86 mg/L
Duration:
411 h
pH:
9
Temp.:
25 °C
Initial conc. measured:
ca. 1.61 mg/L
Number of replicates:
1
Positive controls:
no
Negative controls:
no
Statistical methods:
Log10 regression
Preliminary study:
No hydrolysis was measured in pH4 and pH7 buffer solutions at 50°C. Greater than 10% hydrolysis was observed after 5 days at 50°C in pH9 buffer solution.
Test performance:
None
Transformation products:
not measured
Details on hydrolysis and appearance of transformation product(s):
Not applicable
% Recovery:
ca. 93.8
pH:
9
Temp.:
25 °C
Duration:
ca. 24 h
% Recovery:
ca. 72.6
pH:
9
Temp.:
25 °C
Duration:
ca. 166 h
% Recovery:
ca. 45
pH:
9
Temp.:
25 °C
Duration:
ca. 243 h
% Recovery:
ca. 37.2
pH:
9
Temp.:
25 °C
Duration:
ca. 337 h
% Recovery:
ca. 30
pH:
9
Temp.:
25 °C
Duration:
ca. 411 h
Key result
pH:
4
Temp.:
25 °C
DT50:
> 1 yr
Type:
not specified
Key result
pH:
7
Temp.:
25 °C
DT50:
> 1 yr
Type:
not specified
Key result
pH:
9
Temp.:
25 °C
Hydrolysis rate constant:
ca. 8.6 s-1
DT50:
ca. 224 h
Type:
(pseudo-)first order (= half-life)
Remarks on result:
other: r2=0.987
Other kinetic parameters:
None
Details on results:
TEST CONDITIONS
- pH, sterility, temperature, and other experimental conditions maintained throughout the study: not reported

Table 5.1.2/1: Preliminary test (test 1) results

Time (hours) pH4 pH7 pH9
Concentration (mg/L) % recovery (expressed as % of initial) Concentration (mg/L) % recovery (expressed as % of initial) Concentration (mg/L) % recovery (expressed as % of initial)
Initial 1.52 - 1.59 - 1.86 -
2.4 1.35 88.8 1.52 96.0 1.32 70.6
24 1.31 86.4 1.24 18.4 0.634 34.1
48 1.1 72.3 1.25 79.1 0.292 15.7
120 1.22 80.2 1.28 81.0 0.0221 1.19
288 1.46 96.0 1.29 81.5    

The log10 regressions at pH 9 50°C and pH 9 25°C are presented in attached figure.

Validity criteria fulfilled:
yes
Conclusions:
The rate constant of hydrolysis of the test substance at pH9 and at 25°C has been determined to be 8.60 x 10-7 s-1 (half-life = 224 hours). At pH 4 and 7 the half-life is estimated to be superior to 1 year.
Executive summary:

A study was performed to assess the abiotic degradation of the test substance, according to a method equivalent to OECD Guideline 111 (Hydrolysis as a Function of pH). No major deviation was observed even though some information are lacking such as the repeatability and sensitivity of analytical method.

 

The transformation products were not identified.

 

Hydrolysis was evaluated in a preliminary test and then in a main test. In the preliminary test the substance failed to hydrolyse at pH 4 and pH 7 (at 50°C) while more than 10% hydrolysis was observed after 5 days in pH 9 (at 50°C).

Therefore the main test was performed at pH 9 and directly at 25°C.

 

The Log10regressions suggest that the reactions are pseudo-first order because Log10 concentration versus time is linear (r2> 0.98).

The rate constant at pH 9 and 25°C was measured at 8.60 x 10-7s-1, which corresponds to a half-life of 224 hours.

The rate constant at pH 9 and 50°C was measured at 3.58x 10-2h-1, which corresponds to a half-life of 19.4 hours.

Description of key information

Method equivalent to OECD Guideline 111, GLP, key study, validity 2:

Half-life = 224 hours (pH 9; 25°C)

Key value for chemical safety assessment

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

Additional information

One valid key study is available to assess the abiotic degradation of the registered substance. This study was performed according to a method equivalent to OECD Guideline 111 with GLP statement. No major deviation was observed even though some information are lacking such as the repeatability and sensitivity of analytical method.

Hydrolysis was evaluated in a preliminary test and then in a main test. In the preliminary test the substance failed to hydrolyse at pH 4 and pH 7 (at 50°C) while more than 10% hydrolysis was observed after 5 days in pH 9 (at 50°C). Therefore the main test was performed at pH 9 and directly at 25°C. The Log10regressions suggest that the reactions are pseudo-first order because Log10 concentration versus time is linear (r2> 0.98). The rate constant at pH 9 and 25°C was measured at 8.60 x 10-7s-1, which corresponds to a half-life of 224 hours. The rate constant at pH 9 and 50°C was measured at 3.58x 10-2h-1, which corresponds to a half-life of 19.4 hours. The transformation products were not identified.