4-aminophenol

Hydrolysis

Link to relevant study record(s)

Reference

Endpoint:

hydrolysis

Type of information:

experimental study

Adequacy of study:

key study

Study period:

From 2017-11-02 to 2018-01-22

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 111 (Hydrolysis as a Function of pH)

Deviations:

yes

Remarks:

conducted in sterile natural water at 12 and 25°C

Principles of method if other than guideline:

The hydrolytic stability of the test item was investigated in sterile natural water at two different temperatures. The target concentration in the test was 10 mg/L and was below half of the water solubility of the test item.

GLP compliance:

yes (incl. QA statement)

Radiolabelling:

no

Analytical monitoring:

yes

Details on sampling:

- Sampling intervals for the parent/transformation products:
- Sampling method:
Sampling Intervals – Preliminary Test: Duplicate samples were taken immediately after treatment (time 0), after 17 hours, 19 hours and 24 hours of incubation at 25 °C and 12 °C.
Sampling Intervals – Main Test: Based on the results of the preliminary test, the main test was conducted for 25 °C with intervals of 0, 1, 1.75, 2.75, 3.25, 3.75, 4.25, 5, 5.75 and 6.75 hours. For 12 °C samples were taken after 0, 1, 2, 3, 4, 5, 6, 7, 9, 12 and 24 hours.
- Sampling methods for the volatile compounds, if any: Since the test systems were tightly closed, evaporation was not an issue and had not to be corrected.
- Sampling intervals/times for pH measurements: pH were verified at each measurements intervals.
- Sampling intervals/times for sterility check: Aliquots of 1 mL of sterilized river water used for the study, sterilized purified water, and tap water (positive control) were uniformly distributed onto the surface of agar plates (Merck, CASO-Agar Caseinpepton-Sojamehlpepton-Agar for Microbiology) and incubated in the dark at room temperature for up to 7 days. The colonies that developed on these plates at the end of the respective exposure period were counted.
- Sample storage conditions before analysis: the samples were stabilized with 0.5 mL of acetonitrile containing 2 % HFBA. This led to a sample preparation factor of 1.05. The samples were measured directly after preparation using HPLC with UV detection.
- Other observation, if any (e.g.: precipitation, color change etc.): none specified

Buffers:

No buffer, sterile natural river water (pH 8.18) was used.

Estimation method (if used):

Degradation rates of the test item were calculated according to the FOCUS Guidance (2006) on estimating persistence and degradation kinetics from Environmental Fate Studies using the software tool CAKE (version 3.2, Release). According to the Guidance, if degradation rates for use in modelling can be described by Single First-Order (SFO) kinetics, no other models need to be calculated. In this study, SFO met the requirements in all cases. Thus the SFO model output was selected and is presented in this study.

Details on test conditions:

TEST SYSTEM
- Type, material and volume of test flasks, other equipment used: glass vessels containing 9.5 mL test solutions. Hydrolysis was performed at 25 °C and 12 °C. Samples were incubated under constant shaking (100 rpm) using a thermostated incubator (Infors HT Multitron Pro) at the desired temperature.
- Sterilisation method: To minimise the process of microbial degradation during incubation, all glass equipment (including the incubation vessels) was sterilized by an autoclave prior to use.
All treatments were performed in a sterile bench under laminar flow conditions.
Total plate counts (bacteria) were determined for the test solutions immediately after sterilization at the end of the incubation period.
Natural water was collected in Mumpf (Switzerland). It was sterilized by a “NALGENE” Rapid Flow disposable filter with PES membrane (pore size 0.2 µm).
- Lighting: test performed in the dark (to avoid photolytic effects)
- Measures to exclude oxygen: no
- is the test system closed/open : closed
- Is there any indication of the test material adsorbing to the walls of the test apparatus? No
TEST MEDIUM
- Volume used/treatment 9.5 mL
- Kind and purity of water: Natural water was collected in Mumpf (Switzerland).
- Preparation of test medium:
Preliminary Test: River water was spiked with the test item. The test item (50.2 mg) was dissolved in acetonitrile and made up to the mark in a 50 mL volumetric flask to prepare a stock solution with a concentration of 1004 mg/L. A stock solution aliquot of 0.095 mL was diluted to 9.5 mL with river water to obtain river water samples with a concentration of 10.0 mg test item/L. The experimental value for the water solubility of the test item provided by the sponsor is 6500 mg/L at 25°C. The test item concentration is thus far below the half of the water solubility as requested by the OECD Guideline.
Main Test: The test item (47.6 mg) was dissolved in acetonitrile and made up to the mark in a 50 mL volumetric flask to prepare a stock solution with a concentration of 952 mg/L. A stock solution aliquot of 0.1 mL was diluted to 9.5 mL with river water to obtain river water samples with a concentration of 10.0 mg test item/L.
In parallel, two samples were prepared by diluting 0.1 mL from the stock solution in 10 mL acetonitrile/water (5/95, v/v) containing 0.1% HFBA, resulting in solutions with test item concentration of 9.52 mg/L. These samples were measured directly after preparation to verify the concentration of the stock solution.

- Renewal of test solution: No
- Identity and concentration of co-solvent: The concentration of the co-solvent acetonitrile in the test solution was 1% and in agreement with the OECD Guideline.
OTHER TEST CONDITIONS
- Adjustment of pH: no

Duration:

24 h

pH:

8.26

Temp.:

12 °C

Initial conc. measured:

10 mg/L

Duration:

24 h

pH:

8.26

Temp.:

25 °C

Initial conc. measured:

10 mg/L

Number of replicates:

At each sampling interval, duplicate samples per temperature were taken.

Positive controls:

no

Negative controls:

no

Preliminary study:

The test item degraded rapidly at 25 °C and 12 °C, representing after 17 hours 1.6 % at 25 °C and 7.4 % at 12 °C of the initially measured test item concentration. Corresponding amounts after 19 hours were 1.3 % and 7.0 % and the last measurements after 24 hours at 25 °C were 1.2 % of the concentration initially measured and 5.8 % at 12 °C. The main test study design was adapted, based on these results to assure the measurement of at least 5 intervals between 90 and 10 % of the test item concentration initialy measured.

Test performance:

Based on the results of the preliminary test, the main test was conducted for 25 °C with intervals of 0, 1, 1.75, 2.75, 3.25, 3.75, 4.25, 5, 5.75 and 6.75 hours. For 12 °C samples were taken after 0, 1, 2, 3, 4, 5, 6, 7, 9, 12 and 24 hours. The test item degraded rapidly at 25 °C, representing 2.3 % of the applied amount after 6.75 hours. At 12 °C the test item degraded slower than at the higher temperature representing 31 % after 6 hours. After 24 hours of incubation, the test item amounted to 4.7 % of the initially measured concentration.

Transformation products:

not measured

% Recovery:

4.7

pH:

8.18

Temp.:

12 °C

Duration:

24 h

% Recovery:

2.3

pH:

8.33

Temp.:

25 °C

Duration:

6.75 h

Key result

pH:

8.27

Temp.:

25 °C

Hydrolysis rate constant:

0.61 h-1

DT50:

1.14 h

Type:

(pseudo-)first order (= half-life)

Remarks on result:

other: Model: SFO Parent, M0: 100.5, k = 0.6099, χ2-error: 2.33, r2: 0.9994

Remarks:

; CI (95%): 1.12-1.16

Key result

pH:

8.11

Temp.:

12 °C

Hydrolysis rate constant:

0.165 h-1

DT50:

4.21 h

Type:

(pseudo-)first order (= half-life)

Remarks on result:

other: Model: SFO Parent, M0: 89.85, k = 0.1646, χ2-error: 10.1, r2: 0.9560

Remarks:

; CI (95%): 3.71-4.89

Other kinetic parameters:

DT90 at 25°C: 3.78 hours (CI (95%): 3.71-3.85); DT90 at 12°C: 14 hours (CI (95%): 12.3-16.2)

Details on results:

TEST CONDITIONS
- pH, sterility, temperature, and other experimental conditions maintained throughout the study: Yes
pH: 8.26-8.18 at 12°C, 8.26-8.33 at 25°C
No colonies of bacteria formed on the agar plates treated with the samples from the end of the incubation period (performed with sterile natural water). These solutions were therefore considered to be sterile during the study. A positive control with tap water and under similar test conditions showed contamination proving the validity of the method.
The mean temperatures throughout the experiment were:
Pretest 25 °C: 25.0 ± 0.0 °C.
Pretest 12 °C: 12.0 ± 0.1 °C.
Main Test 25 °C: 25.0 ± 0.0 °C.
Main Test 12 °C: 12.0 ± 0.2 °C.

- Anomalies or problems encountered (if yes): No

Description of pathways: From the structure of the test item, hydrolysis is not to be expected but the disappearance could be related to auto-oxidation processes.

Validity criteria fulfilled:

not applicable

Conclusions:

Following a single first order reaction, test item degraded rapidly in sterile natural river water with half-lives of 1.14 hours and 4.21 hours at 25 °C and 12 °C, respectively.

Executive summary:

The purpose of the study was to determine the degradation rate of the test item under GLP based on OECD guideline No. 111 (modified as described below).

The hydrolytic stability of the test item was investigated in sterile natural river water at two different temperatures in the dark. The target concentration in the test was 10 mg/L and was below half of the water solubility of the test item (the experimental value for the water solubility of the test item provided by the sponsor is 6500 mg/L at 25°C).

Initially, a preliminary test was performed with the test item for up to 24 hours at 25 °C and 12 °C in the dark, using sterilized natural river water. The aim of the preliminary test was to estimate the degradation rate of the test item and to determine reasonable sampling intervals for the main test. The test item degraded rapidly at 25 °C and 12 °C, representing after 24 hours at 25 °C 1.2 % of the concentration initially measured and 5.8 % at 12 °C. The main test study design was adapted, based on these results to assure the measurement of at least 5 intervals between 90 and 10 % of the test item concentration initially measured.

In the main test, the test item degraded rapidly at 25 °C, representing 2.3 % of the initially measured concentration after 6.75 hours. At 12 °C the test item degraded proportionally slower still representing 31 % after 6 hours and decreasing to 4.7 % of the initially measured concentration after 24 hours of incubation.

Following a single first order reaction, the test item degraded rapidly in sterile natural river water with half-lives of 1.14 hours (CI (95%): 1.12-1.16) and 4.21 hours (CI (95%): 3.71-4.89) at 25 °C and 12 °C, respectively.

Description of key information

The purpose of the study was to determine the degradation rate of the test item under GLP based on OECD guideline No. 111 (modified as described below).

The hydrolytic stability of the test item was investigated in sterile natural river water at two different temperatures in the dark. The target concentration in the test was 10 mg/L and was below half of the water solubility of the test item (the experimental value for the water solubility of the test item provided by the sponsor is 6500 mg/L at 25°C).

Initially, a preliminary test was performed with the test item for up to 24 hours at 25 °C and 12 °C in the dark, using sterilized natural river water. The aim of the preliminary test was to estimate the degradation rate of the test item and to determine reasonable sampling intervals for the main test. The test item degraded rapidly at 25 °C and 12 °C, representing after 24 hours at 25 °C 1.2 % of the concentration initially measured and 5.8 % at 12 °C. The main test study design was adapted, based on these results to assure the measurement of at least 5 intervals between 90 and 10 % of the test item concentration initially measured.

In the main test, the test item degraded rapidly at 25 °C, representing 2.3 % of the initially measured concentration after 6.75 hours. At 12 °C the test item degraded proportionally slower still representing 31 % after 6 hours and decreasing to 4.7 % of the initially measured concentration after 24 hours of incubation.

Following a single first order reaction, the test item degraded rapidly in sterile natural river water with half-lives of 1.14 hours and 4.21 hours at 25 °C and 12 °C, respectively.

Key value for chemical safety assessment

Half-life for hydrolysis:

4.21 h

at the temperature of:

12 °C

Additional information

From the structure of the test item, hydrolysis is not to be expected but the disappearance could be related to auto-oxidation processes.