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

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: Directives 95/36/EC (1995), SETAC: Society of Environmental Toxicity and Chemistry "Procedures for Assessing the Environmental Fate and Ecotoxicology of Pesticides".

Qualifier:

equivalent or similar to guideline

Guideline:

EPA Guideline Subdivision N 161-3 (Photodegradation Studies on Soil)

GLP compliance:

yes

Radiolabelling:

yes

Analytical monitoring:

yes

Analytical method:

high-performance liquid chromatography

other: LSC

Details on sampling:

- Sampling intervals of soil samples: 0, 0.08, 0.17, 1, 3, 7, 14, 22 d
- Sampling method: soil scrapped off from the glass plates
- Sampling methods for the volatile compounds, if any: volatile traps: ethylene glycol and 2N NaoH
- Sample storage conditions before analysis: air-dried at room temperature in the dark.

Details on soil:

COLLECTION AND STORAGE
- Geographic location: New York
- Pesticide use history at the collection site: The soil has not been subjected to any pesticide and fertiliser since arrival at RCC.
- Storage and transport conditions: stored air dried, sieved to 2 mm equivalent diameter in closed plastic or glass container at room temperature in the dark
- Soil preparation: air dried, sieved to 2 mm equivalent diameter

PROPERTIES
- Soil classification system and year: USDA
- Soil texture: sandy loam
- % sand: 55.6
- % silt: 29.6
- % clay: 14.8
- pH: 6.7
- Organic carbon (%): 2.41
- CEC (meq/100 g): 14.44
- Initial moisture at 1/3 atm (%): 19.2
- Initial microbial biomass/microbial population (unit): 292553 and 345745 *10^3 (colonies per g dry soil)
- Final microbial biomass/microbial population (unit): > 6465517*10^3 (colonies per g dry soil)

PREPARATION OF SOIL
- Air dried / fresh: air dried

Light source:

Xenon lamp

Light spectrum: wavelength in nm:

> 290

Details on light source:

- Emission wavelength spectrum: > 290 nm wavelength
- Filters used and their purpose: filters to cut off light of less than 290 nm wavelength
- Light intensity at sample and area irradiated: 21.2 W/m²
- Relative light intensity based on intensity of sunlight: SUNTEST/sunlight intensity of 1.205 (intensity of summer daylight vertical incidence, cloudless day, 17.6 W/m²)
- Duration of light/darkness: 12 hours light/dark cycle

Details on test conditions:

TEST SYSTEM
- Type, material and volume of test apparatus or thin layers: Soil thin layers were prepared in duplicate by applying an aqueous slurry of soil to a glass plate (about 350 g soil mixed with 150-170 ml bidistilled water) so that a layer of < 2 mm thickness was formed.
- Application procedure: Hamilton Dispenser PB600 and a connected 100 µL syringe. On each treatment soil layer the 47 µL application solution was brought on the surface in drops of 2 µL each.
- Details of traps for volatile, if any: For the collection of volatiles an air flow through system was installed with a constant gas flow. The outlet air passed two traps for absorbing volatiles in sequence, containing ethylene glycol and 2N NaOH.

PREPARATION OF THIN-LAYER PLATES:

REPLICATION
- No. of replicates (dark): duplicate
- No. of replicates (irradiated): duplicate

MAINTENANCE OF TEST CONDITIONS SPECIFIED UNDER "DURATION"
- Temperature maintenance method: water cooling
- Moisture maintenance method: soil moisture of the irradiated plates was adjusted every 20 min during the first day. Thereafter, It was adjusted
two to three times during the irradiation period.

Duration:

22 d

% Moisture:

75

Temp.:

20 °C

Reference substance:

yes

Remarks:

Batch R001427

Dark controls:

yes

DT50:

6 h

Test condition:

experimental in the irradiated treatments; first order reaction kinetics. Since the same DT50 was measured for the dark control, this degradation was not photolysis but rather hydrolysis. But the first metabolite degraded differently in light & dark.

Transformation products:

yes

No.:

#1

Details on results:

HALF-LIFE

TEST CONDITIONS
- Moisture, temperature, and other experimental conditions maintained throughout the study: Yes
- Anomalies or problems encountered (if yes): Due to the repeated adjustment of the soil moisture content of the irradiated samples, for some plates, the radiaoctivity in soil moved from one treatment area to the other one. For these samples the extracts from the duplicate were pooled before analysis.

The degradation of the test substance on soil was significantly due to its rapid hydrolysis. No difference was observed for the irradiated and dark control samples. The DT-50 and DT-90 values of disappearance of Ethyl 5,5-diphenyl-2-isoxazoline-3-carboxylate were determined to be about 6 and 20 hours.

Ethyl 5,5-diphenyl-2-isoxazoline-3-carboxylate-[phenyl-U-14C] was degraded mainly to 5,5-diphenyl-2-isoxazoline-3-carboxylic acid. The rate of photolysis of this first metabolite on soil was slow but significant compared to the degradation in the dark. The DT-50 values for this metabolite degradation were calculated to be 131 days (irradiated) and 722 days (control).

The photolytic DT-50 value obtained for 5,5-diphenyl-2-isoxazoline-3-carboxylic acid corresponds to 201 days of Florida summer sunlight.

Validity criteria fulfilled:

not applicable

Description of key information

Photodegradation of the test substance on soil surfaces is not a significant route for the elimination of this compound from the environment.

Additional information

The phototransformation of the radiolabeled test substance was studied on a sandy loam soil (pH 6.7, organic carbon 2.41%) from New York, USA, with the substance being exposed in a rate equivalent to a projected application rate of 150 g/ha, for 22 days.

The degradation of the test item on soil was significantly due to its rapid hydrolysis. No difference was observed for the irradiated and dark control samples. For the irradiated soil, parent substance decreased rapidly from 100.3% of radioactivity applied on day 0 to 2.9% on day 3 On day 22, the test substance represented only 0.2% of the radioactivity applied. A half-life of 6 hours and a DT-90 value of 20 hours were calculated assuming first order reaction kinetics. The same results were observed for the samples incubated under the same conditions but in the dark. The parent substance represented 3.1% and 0.9% of the applied radioactivity after 3 and 22 days, respectively.

 

From this study, it is evident that photo-degradation of the test substance on soil surfaces is not a significant route for the elimination of this compound from the environment. Metabolites formed due to photolysis alone were negligible and only appeared in the 22 day samples, not the 0, 1, 24 hour samples.