ethyl 5,5-diphenyl-2-isoxazoline-3-carboxylate

Biodegradation in soil

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

biodegradation in soil: simulation testing

Type of information:

experimental study

Adequacy of study:

weight of evidence

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

comparable to guideline study

Qualifier:

according to guideline

Guideline:

other: United States Environmental Protection Agency (EPA) Pesticide Assessment Guidelines

Qualifier:

equivalent or similar to guideline

Guideline:

other: Canadian Guidelines for Determining Environmental Chemistry and Fate of Pesticides

Qualifier:

equivalent or similar to guideline

Guideline:

other: Society of Environmental Toxicology and Chemistry (SETAC - Europe) Procedures for Assessing the Environmental Fate and Ecotoxicology of Pesticides3 set forth in European Union Commission Directive 95/36/EC of 14 July 1995

GLP compliance:

yes (incl. QA statement)

Test type:

laboratory

Radiolabelling:

yes

Oxygen conditions:

aerobic

Soil classification:

USDA (US Department of Agriculture)

Soil no.:

#1

Soil type:

sandy loam

% Clay:

16.8

% Silt:

28.6

% Sand:

54.6

% Org. C:

2.8

pH:

7.25

CEC:

14.03

Bulk density (g/cm³):

1.27

Details on soil characteristics:

SOIL COLLECTION AND STORAGE
- Geographic location: Wonder Lake, Illinois, USA
- Soil preparation: 2 mm sieved; thoroughly mixed
- Storage conditions: 4 °C

Soil No.:

#1

Duration:

24 h

Soil No.:

#1

Duration:

126 d

Soil No.:

#1

Initial conc.:

7.75 other: µg per flask

Based on:

other: test mat. in the degradation rate experiment

Soil No.:

#1

Initial conc.:

6.74 other: µg per flask

Based on:

other: test. mat. in the metabolism study

Parameter followed for biodegradation estimation:

CO2 evolution

radiochem. meas.

Soil No.:

#1

Temp.:

25.0°C

Humidity:

75%

Microbial biomass:

245.8 µg carbon/g soil

Details on experimental conditions:

2. EXPERIMENTAL DESIGN
- Soil preincubation conditions: The environmental chamber was set to maintain 25 ± 1 °C, and a temperature recording device (Tempscribe®, Bacharach) was used to continuously record actual temperatures.
- Soil (g/replicate): 50 (dry weight basis)
- Test apparatus (Type/material/volume): Erlenmeyer test flasks were fitted to a carbon dioxide-free supply of humidified air within a dark environmental chamber for 6 days and 5 days prior to treatment in the kinetic and metabolism experiments, respectively. Positive pressure air flow through the flow-through test system was regulated by a uniform capillary flow cell. Ambient air passed through a container of 1 M sodium hydroxide to remove carbon dioxide and a container of distilled water to humidify the air. The humidified carbon dioxide-free air passed through an individual deionized water vessel immediately prior to entering each test flask to ensure that the air was saturated and would not cause the soil to dry.
- Details of traps for CO2 and organic volatile, if any: A polyurethane foam plug was fitted in the top of the flask as a trap for organic volatiles exiting the flask. After exiting the test flask, air passed through two additional polyurethane foam plugs to trap organic volatiles and then through an alkaline trap (ethanolamine or 1 M sodium hydroxide) to collect carbon dioxide.

Test material application
- Volume of test solution used/treatment: The amount of test substance added to flasks for the ethyl 5,5-diphenyl-2-isoxazoline-3-carboxylate degradation rate experiment was 3.275 x 106 dpm/flask or 7.75 ug ethyl 5,5-diphenyl-2-isoxazoline-3-carboxylate/per flask.The amount of test substance added to flasks for the metabolism portion of the study was 2.849 x 106 dpm/flask or 6.74 µg/per flask.

Experimental conditions (in addition to defined fields)
- Moisture maintenance method: Positive pressure air flow through the flow-through test system was regulated by a uniform capillary flow cell. Ambient air passed through a container of distilled water to humidify the air.
- Continuous darkness: Yes

3. OXYGEN CONDITIONS
- Methods used to create the aerobic conditions: Positive pressure air flow through the flow-through test system was regulated by a uniform capillary flow cell.

5. SAMPLING DETAILS
- Sampling intervals: Degradation study: 0, 1, 4, 5, 7 and 24 hours after treatment; metabolism study: Days 0, 1, 3, 7, 15, 24.
- Method of collection of CO2 and volatile organic compounds: volatile traps with sodium hydroxide and ethanolamine

Soil No.:

#1

% Recovery:

94.95

Remarks on result:

other: 94 to 95.9% in the degradation rate experiment

Soil No.:

#1

% Recovery:

97.1

Remarks on result:

other: 87.4 to 106.8 % in the metabolism study

Soil No.:

#1

DT50:

0.1 d

Type:

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

Temp.:

25 °C

Soil No.:

#1

DT50:

0.3 d

Type:

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

Temp.:

12 °C

Remarks on result:

other: recalculated from 25°C to 12°C

Transformation products:

yes

No.:

#1

Evaporation of parent compound:

yes

Volatile metabolites:

yes

Residues:

yes

Details on results:

TEST CONDITIONS
- Aerobicity, moisture, temperature and other experimental conditions maintained throughout the study: Yes
- Anomalies or problems encountered: temperature deviated; see above

The safener ethyl 5,5-diphenyl-2-isoxazoline-3-carboxylate rapidly degrades to its hydrolytic metabolite 5,5-diphenyl-2-isoxazoline-3-carboxylic acid in soil under aerobic conditions (DT90 <1 day). The degradation of the metabolite 5,5-diphenyl-2-isoxazoline-3-carboxylic acid was also rapid (DT50 and DT90 of 6.5 and 21 days, respectively). Mineralization to carbon dioxide was substantial, accounting for 65% of applied radioactivity after 126 days in this study.

Reference 2

Endpoint:

biodegradation in soil: simulation testing

Type of information:

experimental study

Adequacy of study:

weight of evidence

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

comparable to guideline study

Qualifier:

according to guideline

Guideline:

other: United States Environmental Protection Agency (EPA) Pesticide Assessment Guidelines, Subdivision N, 162-1

Qualifier:

equivalent or similar to guideline

Guideline:

other: Canadian Guidelines for Determining Environmental Chemistry and Fate of Pesticides, PMRA: T-1 -255

Qualifier:

equivalent or similar to guideline

Guideline:

other: Society of Environmental Toxicology and Chemistry (SETAC —Europe) Procedures for Assessing The Environmental Fate and Ecotoxicology of Pesticides set forth in European Union Commission Directive 95/36/EC of 14 July 1995 amending EC Directive 91/414/EEC

GLP compliance:

yes

Test type:

laboratory

Radiolabelling:

yes

Oxygen conditions:

aerobic

Soil classification:

USDA (US Department of Agriculture)

Soil no.:

#1

Soil type:

sandy loam

% Clay:

6.8

% Silt:

17.2

% Sand:

76

% Org. C:

1.72

pH:

5.2

CEC:

5.37 meq/100 g soil d.w.

Bulk density (g/cm³):

1.3

Soil no.:

#2

Soil type:

clay loam

% Clay:

32.2

% Silt:

38

% Sand:

29.8

% Org. C:

1.99

pH:

7.5

CEC:

7.99 meq/100 g soil d.w.

Bulk density (g/cm³):

1.09

Soil no.:

#3

Soil type:

clay loam

% Clay:

37.2

% Silt:

37.7

% Sand:

25.1

% Org. C:

4.09

pH:

6.2

CEC:

13.77 meq/100 g soil d.w.

Bulk density (g/cm³):

0.98

Details on soil characteristics:

SOIL COLLECTION AND STORAGE
- Geographic location: 1) Münster, Germany, 2) clay loam soil: Orainville, France, 3) clay loam soil Chantepie, France
- Soil preparation: screening through a 2 mm sieve, thorough mixing before use in the study

PROPERTIES OF THE SOILS (in addition to defined fields)
- Moisture at 1/3 atm (%): 9.83

Soil No.:

#1

Duration:

120 d

Soil No.:

#2

Duration:

120 d

Soil No.:

#3

Duration:

120 d

Soil No.:

#1

Initial conc.:

17.7 other: µg/mL

Based on:

test mat.

Soil No.:

#2

Initial conc.:

17.8 other: µg/mL

Based on:

test mat.

Soil No.:

#3

Initial conc.:

17.8 other: µg/mL

Based on:

test mat.

Parameter followed for biodegradation estimation:

CO2 evolution

radiochem. meas.

Soil No.:

#1

Temp.:

20.0 °C

Humidity:

40 %

Microbial biomass:

190 µg microbial C/g dry soil

Soil No.:

#2

Temp.:

20.0 °C

Humidity:

40 %

Microbial biomass:

370 µg microbial C-g dry soil

Soil No.:

#3

Temp.:

20.0 °C

Humidity:

40 %

Microbial biomass:

910 µg microbial C/g dry soil

Details on experimental conditions:

2. EXPERIMENTAL DESIGN
- Soil preincubation conditions: Soil moisture was adjusted to approximately 40% of water holding capacity at ambient pressure by the addition of deionized water. Soil moisture was maintained through the study. The flasks were fitted to a humidified air supply within a dark environmental chamber at 20 ± 1 °C for at least two days prior to treatment.
- Soil (g/replicate): 50 (dry weight basis)
- Control conditions, if used (present differences from other treatments): 1 sterile control from Münster soil. Several flasks containing Münster soil were fitted with bacterial air vents. The flasks were then sterilized by gamma irradiation
- Test apparatus (Type/material/volume): Erlenmeyer flasks; Flasks fitted to a humidified air supply for at least two days prior to treatment.
- Details of traps for CO2 and organic volatile, if any: Air flow was regulated by a uniform capillary flow cell. Flow rates: 2.4 to 3.8 mL/min. After exiting the test flask, air ppassed through an ehylene glycol trap to collect organic volatiles and an ethanolamine trap to collect carbon dioxide. The traps and test system were interconnected with glass and Tygon tubing.

Test material application
- Volume of test solution used/treatment: 435 µL (Münster soil), 432 µL (Orainville and Chantepie soils)
- Application method: The preincubated soil was treated at a nominal concentration of 0.154 mg per kg dry soil.

Experimental conditions (in addition to defined fields)
- Moisture maintenance method: humidified air supply fitted: continuous passing through deionized water prior to entering the treatment flask
- Continuous darkness: Yes

3. OXYGEN CONDITIONS
- Methods used to create the an/aerobic conditions: air flow by uniform capillary flow cell

5. SAMPLING DETAILS
- Sampling intervals: Sampling on days 3, 7, 15, 21, 28, 56, 85, and 119 after treatment
- Sampling method for soil samples: whole flasks sacrificed
- Method of collection of CO2 and volatile organic compounds: volatile traps with ethylene glycol and ethanolamine
- Sampling intervals/times for:
> Sterility check, if sterile controls are used: days 1, 15, 29, 57, 120 after treatment

Soil No.:

#1

Remarks on result:

other: 84.2 to 105.9 % in the Münster soil

Soil No.:

#2

Remarks on result:

other: 87.6 to 108.6 % in the Orainville soil

Soil No.:

#3

Remarks on result:

other: 83.0 % to 104.8 % in the Chantepie soil

Soil No.:

#1

DT50:

0.72 d

Type:

other: bi-exponential

Temp.:

20 °C

Soil No.:

#2

DT50:

1.13 d

Type:

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

Temp.:

20 °C

Soil No.:

#3

DT50:

0.59 d

Type:

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

Temp.:

20 °C

Soil No.:

#1

DT50:

1.5 d

Type:

other: bi-exponential

Temp.:

12 °C

Remarks on result:

other: recalculated from 20°C to 12°C

Soil No.:

#2

DT50:

2.4 d

Type:

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

Temp.:

12 °C

Remarks on result:

other: recalculated from 20°C to 12°C

Soil No.:

#3

DT50:

1.3 d

Type:

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

Temp.:

12 °C

Remarks on result:

other: recalculated from 20°C to 12°C

Transformation products:

yes

No.:

#1

No.:

#2

No.:

#3

Details on transformation products:

- Formation and decline of each transformation product during test: The formation and decline of 5,5-diphenyl-2-isoxazoline-3-carboxylic acid was well described by an assumption of first-order kinetics especially in the Orainville and Chantepie clay loam soils. In the Münster soil a retardation of the degradation of 5,5-diphenyl-2-isoxazoline-3-carboxylic acid was observed, similar to that with the parent compound, giving further evidence to the argument that the reduction in microbial activity of this soil with time influenced the rate of degradation. DT50 values in the three soils ranged from 3.2 days to 11.4 days. 5,5-diphenyl-2-isoxazoline-3-carboxylic acid was not degraded in sterile soil.
- Description of biotransformation pathway: The primary route of degradation in soil was via hydrolysis to 5,5-diphenyl-2-isoxazoline-3-carboxylic acid, which has also been shown to be the principal aqueous hydrolysis product of ethyl 5,5-diphenyl-2-isoxazoline-3-carboxylate. Further degradation of 5,5-diphenyl-2-isoxazoline-3-carboxylic acid occurred in this study as indicated by the high amount of mineralization (75.7% after Day 119 in Chantepie soil). No mineralization of 5,5-diphenyl-2-isoxazoline-3-carboxylic acid was observed in sterile soil, where this degradate was persistent. Intermediate transient degradates involving opening of the isoxazole ring of ethyl 5,5-diphenyl-2-isoxazoline-3-carboxylate were detected. These were the 3-hydroxynitrile 3-hydroxy-3,3-diphenylpropanenitrile and its partial hydrolysis product, the amide 3-hydroxy-3,3-diphenylpropanamide.

Evaporation of parent compound:

yes

Volatile metabolites:

yes

Residues:

yes

The results from this study indicate that ethyl 5,5-diphenyl-2-isoxazoline-3-carboxylate rapidly hydrolyzes in a wide range of soil conditions to 5,5-diphenyl-2-isoxazoline-3-carboxylic acid with a DT50 value of ca. 1 day.

The metabolite 5,5-diphenyl-2-isoxazoline-3-carboxylic acid is also readily metabolized and proceeds with significant mineralization to CO2 as well as association with non-extractable residue.

DT50 values for this compound range from 3.2 days to 11.4 days. Because of the significant dissipation by mineralization under aerobic conditions in soil, ethyl 5,5-diphenyl-2-isoxazoline-3-carboxylate and 5,5-diphenyl-2-isoxazoline-3-carboxylic acid will not persist in soil under actual use conditions.

Reference 3

Endpoint:

biodegradation in soil: simulation testing

Type of information:

experimental study

Adequacy of study:

weight of evidence

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

comparable to guideline study

Qualifier:

equivalent or similar to guideline

Guideline:

other: Canadian Guidelines for Determining Environmental Chemistry and Fate of Pesticides; PMRA: T-1-255

Qualifier:

equivalent or similar to guideline

Guideline:

other: Society of Environmental Toxicology and Chemistry (SETAC - Europe) Procedures for addressing the environmental fate and ecotoxicology of pesticides ; Annex II, Point 7.1.1.1

GLP compliance:

yes

Test type:

laboratory

Radiolabelling:

yes

Oxygen conditions:

aerobic

Soil classification:

USDA (US Department of Agriculture)

Soil no.:

#1

Soil type:

sandy loam

% Clay:

6.8

% Silt:

17.2

% Sand:

76

% Org. C:

1.72

pH:

5.2

CEC:

5.37 meq/100 g soil d.w.

Bulk density (g/cm³):

1.3

Details on soil characteristics:

SOIL COLLECTION AND STORAGE
- Geographic location: Münster, Germany
- Soil preparation: 2 mm sieved; thoroughly mixed

PROPERTIES OF THE SOILS (in addition to defined fields)
- Moisture at 1/3 atm (%): 40

Soil No.:

#1

Duration:

120

Soil No.:

#1

Initial conc.:

38.5 other: µg/cm

Based on:

test mat.

Parameter followed for biodegradation estimation:

CO2 evolution

radiochem. meas.

Soil No.:

#1

Temp.:

10±1°C

Humidity:

40 %

Microbial biomass:

190 µg microbial C/g dry soil

Details on experimental conditions:

2. EXPERIMENTAL DESIGN
- Soil preincubation conditions: Soil moisture was adjusted to approximately 40% of water holding capacity at ambient pressure by the addition of deionized water. Soil moisture was maintained through the study. The flasks were fitted to a humidified air supply within a dark environmental chamber at 10 ± 1 °C for at least two days prior to treatment.
- Soil (g/replicate): 50 (dry weight basis)
- Control conditions, if used (present differences from other treatments): 1 sterile control. Several flasks were fitted with bacterial air vents. The flasks were then sterilized by gamma irradiation.
- Test apparatus (Type/material/volume): Erlenmeyer flasks; Flasks fitted to a humidified air supply for at least two days prior to treatment.
- Details of traps for CO2 and organic volatile, if any: Air flow was regulated by a uniform capillary flow cell. Flow rates: 1.8 to 2.4 mL/min. After exiting the test flask, air ppassed through an ehylene glycol trap to collect organic volatiles and an ethanolamine trap to collect carbon dioxide. The traps and test system were interconnected with glass and Tygon tubing.

Test material application
- Volume of test solution used/treatment: 17.94 µg/mL

Experimental conditions (in addition to defined fields)
- Moisture maintenance method: humidified air supply fitted: continuous passing through deionized water prior to entering the treatment flask
- Continuous darkness: Yes

3. OXYGEN CONDITIONS
- Methods used to create the an/aerobic conditions: air flow by uniform capillary flow cell

5. SAMPLING DETAILS
- Sampling intervals: 3, 7, 14, 21, 28, 56, 84
- Sampling method for soil samples: whole flasks sacrificed
- Method of collection of CO2 and volatile organic compounds: volatile traps with ethylene glycol and ethanolamine
- Sampling intervals/times for:
> Sterility check, if sterile controls are used: 3, 14, 28, 56, 119

Soil No.:

#1

Remarks on result:

other: More than 99.9 % of the detected volatile radioactivity was found in the ethanolamine in all cases, suggesting that the recovered volatile radioactivity was entirely carbon dioxide

Soil No.:

#1

DT50:

0.95 d

Type:

other: bi-exponential

Temp.:

10 °C

Soil No.:

#1

DT50:

0.8 d

Type:

other: bi-exponential

Temp.:

12 °C

Remarks on result:

other: recalculated from 10°C to 12°C

Transformation products:

yes

No.:

#1

No.:

#2

No.:

#3

Details on transformation products:

- Formation and decline of each transformation product during test: The predominant compound detected in soil extracts was 5,5-diphenyl-2-isoxazoline-3-carboxylic acid at every time point after Day 0.5,5-diphenyl-2-isoxazoline-3-carboxylic acid is known to be rapidly formed from ethyl 5,5-diphenyl-2-isoxazoline-3-carboxylate by hydrolysis. AE C637375 (3-hydroxy-3,3-diphenylpropanenitrile) was identified at levels up to 7.5% of applied radioactivity. The only other identified metabolite was 3-hydroxy-3,3-diphenylpropanamide which did not exceed 2.7% of applied. No other single metabolite exceeded 1.3%.
- Description of biotransformation pathway: ethyl 5,5-diphenyl-2-isoxazoline-3-carboxylate dissipated rapidly, initially resulting in 5,5-diphenyl-2-isoxazoline-3-carboxylic acid, with 5,5-diphenyl-2-isoxazoline-3-carboxylic acid degrading to 24% or less in non-sterile soil by Day 119. Calculated DT50 and DT90 values based on first-order kinetics are given in the table below.

Evaporation of parent compound:

yes

Volatile metabolites:

yes

Residues:

yes

The results from this study indicate that ethyl 5,5-diphenyl-2-isoxazoline-3-carboxylate rapidly hydrolyzes at 10 °C to 5,5-diphenyl-2-isoxazoline-3-carboxylic acid with a DT50 value of 1 day even under low pH conditions. The first metabolite 5,5-diphenyl-2-isoxazoline-3-carboxylic acid is also readily metabolized and proceeds with significant mineralization to CO2 as well as association with non-extractable residue. Because of the significant dissipation by mineralization under aerobic conditions in soil, ethyl 5,5-diphenyl-2-isoxazoline-3-carboxylate and 5,5-diphenyl-2-isoxazoline-3-carboxylic acid will not persist in soil under actual use conditions.

Reference 4

Endpoint:

biodegradation in soil: simulation testing

Type of information:

experimental study

Adequacy of study:

weight of evidence

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

other: United States Environmental Protection Agency (EPA) Pesticide Assessment Guidelines

Qualifier:

equivalent or similar to guideline

Guideline:

other: Canadian Guidelines for Determining Environmental Chemistry and Fate of Pesticides

Qualifier:

equivalent or similar to guideline

Guideline:

other: Society of Environmental Toxicology and Chemistry (SETAC - Europe) Procedures for Assessing the environmental fate and ecotoxicology of pesticides

GLP compliance:

yes

Test type:

laboratory

Radiolabelling:

yes

Oxygen conditions:

anaerobic

Soil classification:

USDA (US Department of Agriculture)

Soil no.:

#1

Soil type:

sandy loam

% Clay:

6.8

% Silt:

17.2

% Sand:

76

% Org. C:

1.72

pH:

5.2

CEC:

5.37 meq/100 g soil d.w.

Bulk density (g/cm³):

1.3

Details on soil characteristics:

SOIL COLLECTION AND STORAGE
- Geographic location: Münster, Germany
- Soil preparation: 2 mm sieved; thoroughly mixed

Soil No.:

#1

Duration:

132 d

Soil No.:

#1

Initial conc.:

17.8 other: µg/mL

Based on:

test mat.

Parameter followed for biodegradation estimation:

CO2 evolution

radiochem. meas.

Soil No.:

#1

Temp.:

19.96±0.42°C

Humidity:

100%

Microbial biomass:

190 µg microbial C/g dry soil

Details on experimental conditions:

2. EXPERIMENTAL DESIGN
- Soil preincubation conditions: Deionized water (50 mL) was added to each flask to give a water layer of approximately 1cm. The flasks were fitted to a nitrogen supply within a dark environmental chamber at 20 ± 1 °C for 32 days prior to treatment to establish anaerobic conditions before addition of test substance. To help establish reducing conditions, 250 mg of powdered alfalfa pellets were added to
each flask. Eh ranges for aerobic microbial respiration have been reported to be between approximately 200 mV to 850 mV. For this study, anaerobic condition was defined as being below the lower reported aerobic Eh value of < 200 mV in the surface water.
- Soil (g/replicate): 50 (dry weight basis)
- Test apparatus (Type/material/volume): Erlenmeyer flasks; Flasks fitted to a humidified nitrogen supply for 32 days prior to treatment.
- Details of traps for CO2 and organic volatile, if any: Air flow was regulated by a uniform capillary flow cell. Flow rates: 2.4 to 5.4 mL/min. After exiting the test flask, the nitrogen passed through an ehylene glycol trap to collect organic volatiles and an ethanolamine trap to collect carbon dioxide. The traps and test system were interconnected with glass and Tygon tubing

Test material application
- Volume of test solution used/treatment: 455 µL
- Application method : The preincubated soil was treated at a nominal concentration of 0.154 mg per kg dry soil.

Experimental conditions (in addition to defined fields)
- Moisture maintenance method: humidified air supply fitted: continuous passing through deionized water prior to entering the treatment flask
- Continuous darkness: Yes

3. OXYGEN CONDITIONS
- Methods used to create the an/aerobic conditions: nitrogen flow by uniform capillary flow cell
- Evidence that an/aerobic conditions were maintained during the experiment: Eh and pH measurements prior to harvesting and on day 2, 7, 14, 21, 27, 55, 91, 119, 132

5. SAMPLING DETAILS
- Sampling intervals: days 3, 7, 14, 21, 28, 55, 91, 119, 132
- Sampling method for soil samples: whole flasks sacrificed
- Method of collection of CO2 and volatile organic compounds: volatile traps with ethylene glycol and ethanolamine

Soil No.:

#1

Remarks on result:

other: 85.9 to 105.2 %

Soil No.:

#1

DT50:

0.02 d

Type:

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

Temp.:

20 °C

Soil No.:

#1

DT50:

0.042 d

Type:

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

Temp.:

12 °C

Remarks on result:

other: recalculated from 20°C to 12°C

Transformation products:

yes

No.:

#1

No.:

#2

Evaporation of parent compound:

yes

Volatile metabolites:

yes

Residues:

yes

Details on results:

TEST CONDITIONS
- Aerobicity, moisture, temperature and other experimental conditions maintained throughout the study: Yes

The results from this study indicate that ethyl 5,5-diphenyl-2-isoxazoline-3-carboxylate rapidly hydrolyzes under anaerobic conditions at 20 °C to 5,5-diphenyl-2-isoxazoline-3-carboxylic acid with at DT50 value <0.1 day. The metabolite 5,5-diphenyl-2-isoxazoline-3-carboxylic acid is also readily metabolized to 3-hydroxy-3,3-diphenylpropanenitrile (DT50 = 13.9 days). Metabolism proceeds with minimal mineralization to CO2 as well as little association with non-extractable residues.

3-hydroxy-3,3-diphenylpropanenitrile accumulates under anaerobic conditions. However, when the soil is converted to aerobic conditions, 3-hydroxy-3,3-diphenylpropanenitrile is rapidly mineralized to CO2 without significant accumulation of intermediates. This indicates that, although 3-hydroxy-3,3-diphenylpropanenitrile may accumulate under flooded conditions in the field, its degradation would resume when the land is drained.

Description of key information

DT50 = 0.8 - 2.4 days (US EPA 162 -1, Society of Environmental Toxicology and Chemistry (SETAC - Europe) Procedures for addressing the environmental fate and ecotoxicology of pesticides ; Annex II, Point 7.1.1.1.), under aerobic conditions, recalculated to 12 °C.

DT50 = 0.042 days ( US EPA Pesticide Assessment Guidelines) under anaerobic conditions, recalculated to 12 °C.

Additional information

The degradation of the substance isoxadifen-ethyl in soil has been investigated in several studies. The objective of the studies was to determine the metabolic pathway, degradation rate and half-life of the substance under aerobic and anaerobic conditions in soil. For this purpose, the concentrations of the substance and its metabolites in soil, their rate of formation and degradation and their identity were determined with radioactive labelled test item under laboratory conditions. Additionally, volatile metabolites including 14CO2 and bound residues were quantified to establish material balances.

An aerobic soil environment will have a significant contribution to the overall degradation of the substance. The parent substance rapidly hydrolyzes in a wide range of soil conditions to the metabolite 5,5-diphenyl-2-isoxazoline-3-carboxylic acid. The half lives in aerobic soils (DT50) of the parent substance were between 0.8 – 2.4 days (recalculated from the different incubation temperatures to 12°C) in the different soils (4 EU soils and 1US soil). The metabolite 5,5-diphenyl-2-isoxazoline-3-carboxylic acid is also readily metabolized and proceeds with significant mineralization to CO2 as well as association with non-extractable residue. DT50 values for this metabolite range from 3.2 days to 11.4 days. Because of the significant dissipation by mineralization under aerobic conditions in soil, ethyl 5,5-diphenyl-2-isoxazoline-3-carboxylate ethyl 5,5-diphenyl-2-isoxazoline-3-carboxylate and 5,5-diphenyl-2-isoxazoline-3-carboxylic acidw ill not persist in soil under actual use conditions.

 

An additional study investigated the biotic degradation under anaerobic conditions. This laboratory study showed that the parent substance was rapidly degraded (DT50 = 0.042 d, recalculated to 12°C).

The metabolite 5,5-diphenyl-2-isoxazoline-3-carboxylic acid is also readily metabolized to 3-hydroxy-3,3-diphenylpropanenitrile (DT50 = 13.9 days). Metabolism proceeds with minimal mineralization to CO2 as well as little association with non-extractable residues.

3-hydroxy-3,3-diphenylpropanenitrile accumulates under anaerobic conditions. However, when the soil is converted to aerobic conditions, 3-hydroxy-3,3-diphenylpropanenitrile is rapidly mineralized to CO2 without significant accumulation of intermediates. This indicates that, although 3-hydroxy-3,3-diphenylpropanenitrile may accumulate under flooded conditions in the field, its degradation would resume when the land is drained.

Overall, a persistence in soil of the parent compound and its metabolites is not expected under aerobic conditions due to transformation and further mineralization to CO2.