4-(5-(3,5-dichloro-4-fluorophenyl)-5-(trifluoromethyl)-4,5-dihydro-1,2-oxazol-3-yl)-N-(2-ethyl-3-oxo-1,2-oxazolidin-4-yl)-2-methylbenzamide

Phototransformation in soil

Link to relevant study record(s)

Reference

Endpoint:

phototransformation in soil

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

other: EPA OPPTS 835.2410

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Radiolabelling:

yes

Analytical monitoring:

yes

Analytical method:

liquid chromatography

high-performance liquid chromatography

mass spectrometry

other: liquid scintillation

Details on sampling:

Duplicate samples from all irradiated and dark control plots were taken at 0, 1, 3, 7, 12 and 17 days after treatment.

Details on soil:

The soil used for the study was a sandy loam collected from East Anglia, Norfolk, United Kingdom on May 17, 2016. Upon arrival at the test facility, the soil was sieved through a 2 mm sieve. Thereafter, the soil was stored under moist aerobic conditions at a temperature of 4°C until use.
The soil moisture content was determined by an infrared drying unit (Mettler Toledo MJ33 compact moisture analyzer).
Air-dried soil (1.6 g) was transferred into glass vessels (4.9 cm inner diameter). On the day prior to treatment, the dry soil samples were moistened with 1.6 mL purified water, after which the soil layers were allowed to air-dry overnight. Subsequently, the air-dried soil layers were checked for potential soil cracks prior to treatment.
For the moist soil experiment, air-dried soil (3.2 g) was transferred into glass vessels (4.9 cm inner diameter). Two days prior to treatment, the dry soil samples were moistened with 3.2 mL of purified water, after which the soil layers were allowed to air-dry for two days. Purified water (1024 μL) was added to give a soil moisture content of pF 2. The soil moisture content of the samples was checked and adjusted if needed.

Light source:

Xenon lamp

Light spectrum: wavelength in nm:

>= 290 - <= 800

Relative light intensity:

>= 400 - <= 765

Details on light source:

- Emission wavelength spectrum: similar spectral distribution compared to natural sunlight
- Filters used and their purpose: UV filter to cut off wavelengths below 290 nm

Details on test conditions:

Test apparatus (irradiated/dark controls): glass vessels with quartz lids, individually connected to volatile traps
Traps for CO2 and organic volatiles: one ethylene glycol (organic volatiles) and one 2M NaOH (CO2)
Solvent: 7-23% acetonitrile in methanol
Volume of test solution in dry soil test: 100 μL (MP label), 115 μL (HP label), 105 μL (Oxo label)
Volume of test solution in moist soil test: 110 μL (MP label), 135 μL (HP label), 130 μL (Oxo label)
Application: by Hamilton glass syringe with subsequent evaporation of solvent
Temperature: 20 ± 2 °C
Continuous irradiation (treatment)
Continuous darkness (dark control)
Moisture content: pF 2 for the moist soil experiment, not determined for dry soil experiment
Moisture maintenance: daily adjustment (based on weight) for the moist soil experiment

Duration:

17 d

Temp.:

20 °C

Initial conc. measured:

16.675 mg/kg soil d.w.

Duration:

17 d

Temp.:

20 °C

Initial conc. measured:

15.18 mg/kg soil d.w.

Duration:

17 d

Temp.:

20 °C

Initial conc. measured:

14.641 mg/kg soil d.w.

Duration:

17 d

% Moisture:

33.2

Temp.:

20 °C

Initial conc. measured:

13.951 mg/kg soil d.w.

Duration:

17 d

% Moisture:

33.2

Temp.:

20 °C

Initial conc. measured:

9.181 mg/kg soil d.w.

Duration:

17 d

% Moisture:

33.2

Temp.:

20 °C

Initial conc. measured:

9.029 mg/kg soil d.w.

Reference substance:

no

Dark controls:

yes

Computational methods:

The rate of degradation of 14C-labelled test substance, based on experimental days, was calculated using single first-order (SFO) kinetics (CAKE v. 3.1). All three labels were fitted together. As the substance did not degrade significantly in the dark control samples, no compensation for degradation in the dark controls was made for this compound.

Key result

DT50:

85.1 d

Test condition:

Irradiated dry soil, calculated for natural sunlight at latitude of 30 to 50° N

Key result

DT50:

111.6 d

Test condition:

Irradiated moist soil, calculated for natural sunlight at latitude of 30 to 50° N

DT50:

45.8 d

Test condition:

Irradiated dry soil

DT50:

61.2 d

Test condition:

Irradiated moist soil

DT50:

511 d

Test condition:

Dark control dry soil

DT50:

556 d

Test condition:

Dark control moist soil

Transformation products:

yes

No.:

#1

Details on results:

Recovery at start for irradiated soil and dark control (dry soil):
MP label: 100.9 to 101.7% of applied radioactivity (average 101.3%)
HP label: 103.2 to 104.3% of applied radioactivity (average 103.9%)
Oxo label: 99.4 to 101.2% of applied radioactivity (average 100.3%)

Overall recovery for irradiated soil (dry soil):
MP label: 94.2 to 102.5% of applied radioactivity (average 99.6%)
HP label: 103.2 to 109.1% of applied radioactivity (average 106.2%)
Oxo label: 91.9 to 104.9% of applied radioactivity (average 99.0%)

Overall recovery for dark control (dry soil):
MP label: 93.6 to 103.3% of applied radioactivity (average 99.6%)
HP label: 102.8 to 108.2% of applied radioactivity (average 105.3%)
Oxo label: 98.4 to 108.8% of applied radioactivity (average 102.5%)

Mean total extractable residues (dry soil) at start of experiment
MP label: 101.3% (irradiated and dark control)
HP label: 103.9% (irradiated and dark control)
Oxo label: 100.2% (irradiated and dark control)

Mean total extractable residues (dry soil) at end of experiment
MP label: 90.5% (irradiated) and 95.7% (dark control)
HP label: 100.7% (irradiated) and 105.6% (dark control)
Oxo label: 76.2% (irradiated) and 99.1% (dark control)

Mean total non-extractable residues (dry soil) at end of experiment
MP label: 3.3% (irradiated) and 0.4% (dark control)
HP label: 2.7% (irradiated) and 0.3% (dark control)
Oxo label: 5.7% (irradiated) and 0.4% (dark control)

Mean total carbon dioxide evolved (dry soil) at end of experiment
MP label: 1.8% (irradiated) and <0.1% (dark control)
HP label: 2.4% (irradiated) and <0.1% (dark control)
Oxo label: 10.5% (irradiated) and <0.1% (dark control)

<0.1% for all labels for other volatile degradation products (dry soil)


Recovery at start for irradiated soil and dark control (moist soil):
MP label: 103.8 to 104.1% of applied radioactivity (average 103.9%)
HP label: 107.2 to 108.5% of applied radioactivity (average 107.9%)
Oxo label: 101.0 to 101.4% of applied radioactivity (average 101.2%)

Overall recovery for irradiated soil (moist soil):
MP label: 101.2 to 110.8% of applied radioactivity (average 105.9%)
HP label: 97.8 to 108.5% of applied radioactivity (average 102.5%)
Oxo label: 101.0 to 108.8% of applied radioactivity (average 103.7%)

Overall recovery for dark control (moist soil):
MP label: 102.1 to 107.4% of applied radioactivity (average 104.7%)
HP label: 99.6 to 108.5% of applied radioactivity (average 104.8%)
Oxo label: 99.4 to 109.8% of applied radioactivity (average 102.5%)

Mean total extractable residues (moist soil) at start of experiment
MP label: 103.9% (irradiated and dark control)
HP label: 107.8% (irradiated and dark control)
Oxo label: 101.1% (irradiated and dark control)

Mean total extractable residues (moist soil) at end of experiment
MP label: 98.5% (irradiated) and 106.5% (dark control)
HP label: 96.6% (irradiated) and 103.3% (dark control)
Oxo label: 90.5% (irradiated) and 99.2% (dark control)

Mean total non-extractable residues (moist soil) at end of experiment
MP label: 6.5% (irradiated) and 0.5% (dark control)
HP label: 5.0% (irradiated) and 1.1% (dark control)
Oxo label: 9.1% (irradiated) and 1.1% (dark control)

Mean total carbon dioxide evolved (dry soil) at end of experiment
MP label: 0.6% (irradiated) and <0.1% (dark control)
HP label: 0.4% (irradiated) and <0.1% (dark control)
Oxo label: 3.3% (irradiated) and 0.5% (dark control)

<0.1% for all labels for other volatile degradation products (dry soil)

Results with reference substance:

Not applicable

Validity criteria fulfilled:

yes

Conclusions:

The substance degraded slowly under continuous irradiation in dry and moist soil layers.

Executive summary:

The photolysis of 14C-radio-labelled substance was investigated under GLP on dry and moist soil layers to EPA OPPTS guideline 835.2410. Radiolabel was applied at three positions of the molecule (methylphenyl (MP), halophenyl (HP), and oxoisoxazolidinyl (OXO), and the test substance was applied at rates equivalent to 150 g ai/ha to 1 mm soil layers (dry soil) and 2 mm soil layers (moist soil) of East Anglia soil (sandy loam) in individual glass vessels. The treated soils were continuously irradiated using a Suntest XLS+, (Atlas Material Testing Solutions, Germany) equipped witha xenon arc lamp. The emitted light was filtered to give a spectral distribution close to that of natural sunlight with mean light intensites ranging from 45.6 W/m2 to 48.3 W/m2. The samples were maintained at 20 °± 2 °C and irradiated for a period of 17 days, which is equivalent to approximately 31 to 33 days of summer sunlight at latitudes of 30 to 50° N.
Duplicate samples per label were taken for analysis across 6 time intervals during irradiation. ‘Dark control’ samples were also prepared and maintained under similar conditions as irradiated soils. Dark control samples were taken for analysis at intervals equivalent to that of the irradiation tests.
At each sampling interval, the samples were extracted using acetonitrile/water, tetrahydrofuran or isohexane. The extracts were analysed by LSC and radio-HPLC to quantify the amount of parent and degradation products present. The identity of the components was confirmed by TLC and LC-MS-MS. Any volatile radioactivity was continuously flushed from the vessels, collected in traps and analysed via Liquid Scintillation Counting (LSC). Remaining unextracted radioactivity was quantified by combustion and a mass balance was determined for each sample.
Dry soil
The mass balances ranged from 91.9% to 109.1% applied radioactivity (AR) for the irradiated soils (all labels) and from 93.6% to 108.8% AR for the corresponding dark controls. The total extractable radioactivity remained at about 90-100% of AR for the MP and HP labels, but decreased to 76.2% for the Oxo label over the study period.
Non-extractable radioactivity for all three labels remained low. The formation of carbon dioxide was low for the MP and HP labels and reached 10.5% AR at 17 DAT for the Oxo label. The amount of organic volatiles trapped in the ethylene glycol traps was negligible throughout the study (≤ 0.1% AR). The extractability in the dark controls for all labels ranged from 108.2 to 95.7% AR for the duration of the study. Non-extractable radioactivity did not exceed 0.4% AR and carbon dioxide and organic volatiles remained ≤ 0.1% AR.
Degradation in irradiated dry soil layers was slow and the substance concentration decreased to 81.8%, 88.2% and 62.9% AR for the MP, HP and OXO labels, respectively, by day 17. The relatively low value observed with the OXO label is partly due to the relatively low recovery of radioactivity (92.5%) when compared with the previous intervals. One significant degradation product was observed for each radiolabel, 4-[5-(3,5-dichloro-4-fluorophenyl)-5-(trifluoromethyl)-4,5-dihydro-1,2-oxazol-3-yl]-2-methylbenzamide, which increased throughout the study reaching mean maximum levels of 6.5% and 6.3% AR in the MP and HP labels, respectively. Degradation in dark control samples was minimal.
Moist soil
The mass balance ranged from 97.8% to 110.8% AR for all irradiated soils and from 99.4% to 109.8% AR for the corresponding dark controls. The total extractable radioactivity in irradiated samples declined only slightly over time to 98.5%, 96.6% and 90.5% AR for the MP, HP and OXO labels, respectively, by day 17. Non-extractable radioactivity for all three labels was <10% AR throughout incubation. Formation of carbon dioxide was lower than observed in the dry soil experiment, representing a maximum of 3.3% AR at 17 DAT for the OXO label and ≤ 0.6% AR in the MP and HP labels. Again, the presence of other organic volatiles remained negligible in all labels throughout the study. The extractability in the dark controls for all labels ranged from 98.6 to 107.8% AR for the duration of the study. Non-extractable radioactivity did not exceed 1.1% AR, carbon dioxide did not exceed 0.5% AR and organic volatiles remained below 0.1% AR.
In irradiated moist soil layers, substance levels decreased to 84.6%, 80.6% and 83.0% AR for the MP, HP and OXO labels, respectively, by day 17. Under irradiated moist layer conditions, up to eight degradates were detected for each radiolabel. The predominant degradate observed in the MP and HP labels was 4-[5-(3,5-dichloro-4-fluorophenyl)-5-(trifluoromethyl)-4,5-dihydro-1,2-oxazol-3-yl]-2-methylbenzamide, which increased throughout the study reaching mean levels of 5.1% AR (MP label) and 6.1% AR (HP label) by 17 DAT. No significant (> 5%) degradates were observed in the OXO label. Degradation in dark control samples was minimal.
In dry soil the substance degraded with a half-life of 45.8 days under artificial sunlight, which is equivalent to 85.1 days for natural sunlight at 30° N to 50° N. Degradation in moist soil was slightly longer, with a half-life of 61.2 days under artificial sunlight, corresponding to 111.6 days days for natural sunlight at 30° N to 50° N.

 

Description of key information

The photolysis of the substance in dry and moist soil was studied under GLP following the EPA-OPPTS 835.2410 guideline. The molecule was separately radio-labelled at the methylphenyl, halophenyl or oxoisoxazolidinyl positions, and applied at rates equivalent to 150 g/ha to 1 mm dry soil layers or 2 mm moist soil layers of East Anglia sandy loam. The treated soils were irradiated continuously with light coming from a xenon arc lamp over a period of 17 days. The light was filtered to give a spectral distribution close to that of natural sunlight. The substance degraded slowly in irradiated dry and moist soil, whereas minimal degradation was observed in the dark controls. The half-life in dry soil was determined to be 45.8 days for artificial sunlight, which is equivalent to 85.1 days for natural sunlight at 30 to 50° N. Degradation in moist soil was slightly longer, with a half-life of 61.2 days for artificial sunlight, which is equivalent to 111.6 days for natural sunlight at 30 to 50° N.

Key value for chemical safety assessment

Half-life in soil:

111.6 d