N-[2,5-dichloro-4-(1,1,2,3,3,3-hexafluoropropoxy)-phenyl-aminocarbonyl]-2,6-difluorobenzamide

Phototransformation in soil

Link to relevant study record(s)

Reference

Endpoint:

phototransformation in soil

Type of information:

experimental study

Adequacy of study:

key study

Study period:

12 Mar 1993 to 28 Feb 1994

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

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

Version / remarks:

October 18, 1982

Deviations:

not specified

GLP compliance:

yes (incl. QA statement)

Radiolabelling:

yes

Analytical monitoring:

yes

Analytical method:

high-performance liquid chromatography

Details on sampling:

For continuous exposure samples of one plate each were taken for analysis directly after the treatment and after 7, 10, 12, 14, and 17 days of exposure to continuous light. The latter time interval corresponded to 34 calendar days or to 23.94 Florida sunlight equivalents as calculated from the initial spectral energy distribution measurements. The trapping solutions were taken for analysis and replaced by fresh solutions at all sampling times of the plates. The dark control sample was analysed as well after 17 days of continuous exposure.
For the viable, moist soil experiment samples were taken after 0, 5, 9, 14, 19 and 26 days of exposure to light with a day night cycle of 12 hours. The latter sampling time corresponded to 26 calendar days or to 40.6 days Florida sunlight equivalents.

Details on soil:

Soil characteristics are provided in Table 1 in 'Any other information on materials and methods incl. tables'.
The study was performed with either dry or viable, moist (75%FC) Les Evouettes loam. The microbial biomass of the soil was determined prior to the start of the experiment. Before use, the soil was passed to a 2 mm sieve. Soil moisture of viable soil experiment was adjusted during the study at the sampling times.

Light source:

Xenon lamp

Light spectrum: wavelength in nm:

>= 290

Details on light source:

- Filters used: Filters to cut-off light of less than 290 nm wavelength
- Irradiation equipment: The spectral energy distribution (300 - 700 nm) of the light source, i.e. the incident light available at the soil level in all experiment were recorded using a portable spectroradiometer. A holographic grating monochromator and a Teon cosine diffuser either fixed or in combination with a glass fiber optic probe were used.

Details on test conditions:

An overvew of the experimental sampling is provided in Table 2 in 'Any other information on materials and methods incl. tables '
TEST SYSTEM
- Type, material and volume of test apparatus or thin layers: In order to control the temperature of the irradiated plates and to trap any volatile product formed, the plates were placed in the stainless steel cooling tank. The tank was then sealed with a quartz lid, using an appropriate sealing and placed beneath the Xenon burner.
- Method of application/ Application procedure: Two stock solutions of 14C-labelled test substance in 1.0 mL ethyl acetate were prepared and checked for concentration by liquid scintillation counting and anaylsed by TLC for radiochemical The amounts determined were 2.332 and 2.5597 mg for the dry soil and viable soil experiment, respectively. For application, 120 µL (=278.58 µg) stock solution I and 590 µL (=1574.71 µg) stock solution II were each made up to 1 mL with ethyl acetate thus giving treatment solutions I and II for the dry soil and moist soil experiment, respectively. Thereafter, 100 µL (= 27.86 µg) and 95 µL (=150 µg) of the corresponding application solutions were spotted uniformly over the soil surfaces of each plate (surface area 30 cm2). By this procedure a total of 7 plates was treated.
- Details of traps for volatile: Moistened air was sucked through the cooling tank and any volatile products formed were trapped. For the collection of volatiles an air flow through system was installed with a gas flow of about 5 mL/minute controlled by a peristaltic pump. The outlet was passed through three traps in the sequence ethylene glycol, 0.1 N H2SO4 and 2 N NaOH to absorb volatiles .
- Dark control: Dark control samples were incubated in the same way, with an identical gas flow system but maintained in darkness
- Irradiation: Irradiation was performed either continuously (experiment with dry soil) or with a 12 hours light/dark cycle (experiment with moist, viable soil).

PREPARATION OF THIN-LAYER PLATES: Soil thin layes of 30 cm2 each were prepared by applying an aqueous slurry of soil to a glass or stainless steel plate (about 50 g soil mixed with 30 ml bidestilled water) so that a layer of about 1 mm thickness was formed. Thereafter, the layers were allowed to dry for 10 hours at room temperature (experiment with dry soil and continuous light) or for about 15 - 20 minutes (experiment with moist, viable soil and 12 hrs. day-night iradiation regimen) to reach a soil moisture of < = 75% FC.

REPLICATION (dry soil and moist soil)
- No. of replicates (dark control): 1
- No. of replicates (irradiated): 6 (one unexposed replicate)

MAINTENANCE OF TEST CONDITIONS SPECIFIED UNDER "DURATION"
- Temperature maintenance method: In order to control the temperature of the irradiated plates and to trap any volatile product formed, the plates were placed in the stainless steel cooling tank. Cooling water, at a pre-set temperature, was pumped through the base of the tank to control the temperature of the irradiated soil coated plates.
- Moisture maintenance method: Moistened air was sucked through the cooling tank.

Duration:

408 h

Temp.:

25 °C

Initial conc. measured:

0.5 kg/ha d.w.

Duration:

624 h

% Moisture:

75

Temp.:

24.5 °C

Initial conc. measured:

0.5 kg/ha d.w.

Reference substance:

not specified

Dark controls:

yes

Test performance:

The stability of the test compound was proven by analysis of an aliquot of the application solution of the test substance left at room temperature during treatment. Its purity was for the dry soil experiment still 97.7 % and for the moist soil experiment 97.8 % thus proving the stability of the test compound in the vehicle during treatment.

% Degr.:

14.54

Sampling time:

408 h

Test condition:

dry soil, irrad. continuous

% Degr.:

0.73

Sampling time:

408 h

Test condition:

dry soil, dark control

% Degr.:

9.95

Sampling time:

624 h

Test condition:

moist soil, irrad. 12:12 L:D

% Degr.:

2.17

Sampling time:

624 h

Test condition:

moist soil; dark control

Key result

DT50:

72.2 d

Test condition:

dry soil, irrad. continuous

Remarks on result:

other: equivalent to 119 days of latitude 40° N summer sunlight

Key result

DT50:

263 d

Test condition:

moist soil; irrad. 12:12 L:D;

Remarks on result:

other: equivalent to 379 days of latitude 40° N summer sunlight

Transformation products:

no

Details on results:

An overview of the results is provided in Table 3 – Table 6 in ‘Any other information on results inlc. tables’ 
- Recovery of Radioactivity: On the average, 102.19 ± 1.16 % and 100.72 ± 0.68 % of the radioactivity applied were recovered after the various exposure periods to artificial light for the continuous and light/dark experiment, respectively. For the dark control the recovery accounted for 100.93 – 100.35 %. By far the majority of the recovered radioactivity remained in the soil and consisted of extractable radioactivity. Non-extractable radioactivity amounted at the end of the study to 4.2 and 5.02 % for both experiments. In addition, volatile radioactivity in form of carbon dioxide was observed. At the end of the exposure period 7.79 and 1.76 % of the applied radioactivity was found to be carbon dioxide for the continuous and light/dark experiment, respectively, demonstrating that a small amount of the chlorophenyl-ring moiety was photolytically mineralized.
- Rate of Degradation of the Parent Molecule: When fitted to the exponential function given under 2.6.1 the compound showed under dry soil conditions a half-life of 72.2 calendar days when exposed to continuous light equivalent to 119 days of latitude 40° N summer sunlight with 95% confidence limits ranging between 105 and 135 days. At the end of the study, i.e. after 27.9 days latitude 40°N or 34 calendar days the parent molecule still amounted to 85.46 % of the radioactivity applied. No significant degradation occurred in the dark control, i.e. the parent molecule accounted after the same time for 99.27%. For the experiment performed with moist, viable soil under a light regimen of 12 hours light and dark the half-life was even longer representing 263 calendar days equivalent to 379 days of latitude 40° N summer sunlight. The 95% confidence limits were 321 to 463 Florida days. The reasons for the longer half-life are mainly due to the deeper penetration of the test compound into the moist soil and to its imobility in soil thus preventing the test compound from movement to the upper soil surface (evapotransport) and hence from degradation by light. However, at the end of the study, i.e. after 40.56 days latitude 30° or 26 calendar days the parent molecule still amounted to 90.05 % of the radioactivity applied. No significant degradation occurred in the dark control, i.e. the parent molecule accounted after the same time for 97.83%.
- Formation of Degradates: Analysis of extractable radioactivity showed no significant amounts of photolytic degradates. Radioactive fractions observed represented the original impurities observed

Table 3.Balance of Radioctivity after Exposure of [U-14C] dichlorophenylring labelled test substance on dry Soil Surfaces to artificial Light (exposure to continuous light)

	Irradiation Time (hrs. cont. light)						Dark control
	0	168	240	288	336	408	408
Extractables	100.41	93.60	93.64	92.20	91.26	91.73	99.99
CH2C12-phase	99.55	92. 69	92.60	91.64	90. 57	91.20	99.27
Water-phase	0.86	0.90	1.05	0.56	0.69	0.53	0.72
Non-extractables	0.06	4.91	4.62	4.1 1	5.15	4.20	0.93
C02	0.00	3.17	4.24	5.34	6.47	7.79	0.00
Ethylene glycol	0.00	0.02	0.03	0.04	0.05	0.07	0.00
Total	100.46	101.70	102.54	101.69	102.93	103.80	100.93

Average recovery irrad. Samples	102.19
StDev	1.16

 

Table 4. Balance of Radioactivity after Exposure of [U-14C] dichlorophenylring labelled test substance on moist Soil Surfaces to artificial Light (Exposure to a light regimen of 12 hours light and dark)

	Irradiation Time (hrs. day/night cycle)						Dark control
	0	120	216	336	456	624	624
Extractables		98.15	97.10	96.39	95.41	94.34	99.93
CH2C12-phase	99.14	97.91	96.84	95. 79	94.59	91.23	87.78
Water-phase	0.21	0.24	0.27	0.60	0.82	3.10	12.14
Non-extractables	0.05	2.56	3.18	4.04	4.1 1	5.02	0.42
C02	0.00	0.27	0.55	0.85	1.19	1.76	0.00
Ethylene glycol	0.00	0.00	0.00	0.00	0.00	0.00	0.00
Total	99.40	100.97	100.84	101.28	100.71	101.12	100.35

Average recovery irrad. Samples	100.72
StDev	0.68

 

Table 5. Formation of Photolytic Degradates after Exposure of [U-14C] dichlorophenyl-ring labelled test substance on dry Soil Surfaces to artificial Light (Exposure to continuous light)

Irradiation Time (hrs. cont. light)	Partent substance	Fraction 1	Fraction 2	NA	Total
	Retention Time(min.)
	15.20	14.40	13.20
0	99.55	0.00	0.00	0.86	100.41
168	91.21	0.00	1.48	0.90	93.60
240	87.97	2.78	1.85	1.05	93.64
288	88.71	1.92	1.01	0.56	92.20
336	85.23	3.80	1.54	0.69	91.26
408	85.46		2.28	0.53	91.73
(Dark control) 408	99.27	0.00	0.00	0.72	99.99

NA: Aqueous phases not analysed

Table 6. Formation of Photolytic Degradates after Exposure of [U-14C] dichlorophenyl-ring labelled test substance on moist Soil Surfaces to artificial Light (Exposure to a light regimen of 12 hours light and dark)

	Parent substance	Fraction 1	Fraction 5	Fraction 3	Fraction 4	Fraction 2		NA		Total
	Retention time (min)
	15.44	14.56	14.20	17.00	17.48	13.36
0	96.95	0.99	0.00	0.00	1.19	0.00	0.21		99.35
120	93.99	1.76	0.98	0.00	0.88	0.29	0.24		98.15
216	93.25	1.74	0.39	0.97	0.00	0.48	0.27		97.10
336	91.76	1.44	0.57	1.25	0.00	0.77	0.60		96.39
456	90.90	1.70	0.57	0.00	0.85	0.57	0.82		95.41
624	90.05	1.92	0.64	0.46	0.36	0.91	0.00		94.34
(Dark control) 624	97.83	0.97	0.00	0.48	0.65	0.00	0.00		99.93

NA: Aqueous phases not analysed

Validity criteria fulfilled:

yes

Conclusions:

In a phototransformation in soil study that was performed in accordance with EPA 161-3 guideline, the test substance was very slowly degraded by light when applied to soil surfaces with half-lifes of 72.2 days (dry soil; continuous light) and 263 days (moist soil; 12 hours light and dark cycle). These values are equivalent to 119 days (dry soil; continuous light) and 379 days (moist soil; 12 hours light and dark cycle) under summer sunlight at latitude 40° N.

Executive summary:

The photolytic behaviour of 14C-dichlorophenyl ring-labelled test substance was investigated on the surface of a dry sterile and a moist viable loam soil (Les Evouettes). The study followed EPA guideline 161 -3 and was in compliance with GLP criteria. The dry and the moist soils were exposed to a continuous light or a 12 hours light regime experiment, respectively. The artificial light source used was a Xenon arc lamp (average 19 W/m2) in a Suntest unit ( λ > 290 nm). The resulting radiation had a spectral distribution comparable to natural sunlight in intensity and wavelengths. The experiments were run for 34 (continuous light experiment) and 26 (experiment with 12 hrs. light-dark cycle) calendar days corresponding to 28 and 37.5 days latitude 40°N. The dry soil test was conducted with a slurry of sieved soil and water, applied to glass or stainless steel plates forming a layer 1 mm deep and 30 cm2 in area. The plates were allowed to dry for ten hours at room temperature and then dosed with radiolabelled test substance at 0.5 kg/ha. The samples were irradiated continuously at 25 ± 0.3°C for up to 17 days. Samples were taken at 0, 7, 10, 12, 14 and 17 days. The moist soil test was conducted with a slurry of sieved soil and water, applied to glass or stainless steel plates forming a layer 1 mm deep and 30 cm2 in area. The plates were allowed to dry to approximately 75% field moisture capacity and then dosed with radiolabelled test substance at 0.5 kg/ha. The samples were irradiated continuously at 24.5 ± 0.3°C for up to 17 days. Samples were taken at 0, 5, 9, 14, 19 and 26 days. One dark control plate was prepared per experiment. Control samples were treated in the same way as irradiated samples, except that they were kept in the dark. For analysis, the supernatants were concentrated, partitioned with dichloromethane and the radioactivity in each phase quantified by LSC. Characterisation and quantification of the photodegradation products were conducted by HPLC.

The percentage recovery of the applied radioactivity was in a range of 99.4-103.8%. The recovery from the dark control plates was > 99% at the end of the study. The amounts of parent substance recovered from the dry soil decreased very slowly from 99.6% AR to 85.5% AR after 17 days of continuous irradiation (34 days on a 12 hour light/dark cycle basis). In the moist soil exposed on a 12 hour light/dark cycle the amount of AR decreased from 97.0% to 90.0% in 26 days. The majority of the recovered radioactivity that remained in the soil consisted of extractable radioactivity. Analysis of extractable radioactivity showed no significant amounts of photolytic degradates, i.e., unknown metabolites were low with no single component exceeding 3.8% AR at any sampling interval. Non-extractable radioactivity accounted at the end of the study to 4.2 and 5.02 % for both experiments. At the end of the exposure period 7.8 and 1.8 % AR was found to be CO2 for the continuous and light/dark experiment, respectively, demonstrating that a small amount of the dichlorophenyl ring moiety was photolytically mineralized. No significant degradation occurred also in the dark control, i.e. the parent molecule accounted after the same time for 99.3 %(dry soil; continuous light) and 97.8% (moist soil; 12 hours light and dark cycle).

It is concluded that the test substance was very slowly degraded by light when applied to soil surfaces with half-lifes of 72.2 (dry soil; continuous light) and 263 days (moist soil; 12 hours light and dark cycle). These values are equivalent to 119 days (dry soil; continuous light) and 379 days (moist soil; 12 hours light and dark cycle) under summer sunlight at latitude 40° N.

Description of key information

All available data was assessed and the study representing the worst-case effects was included as key study. Other studies are included as supporting information. The effect value which is considered to be the worst-case is selected for the CSA.

DT50 = 263 days, irradiation with 12 hours light-dark cycle by Xenon arc lamp (wavelength >= 290 nm), 25 °C, EPA 161 -3, Dichlorophenyl-labelled test substance, Ellgehausen 1994a

Key value for chemical safety assessment

Half-life in soil:

263 d

Additional information

Two studies on photodegradation in soil are available, exposing the Les Evouettes soil (loam) to 14C-labelled test substance. Both of the studies are Reliability 1 studies, which followed EPA 161-3 guideline and met the GLP criteria. The study representing the worst-case effect (i.e. showed higher DT50 value) was included as key study. The effect value (DT50 = 263 days) from the key study was selected in CSA.

The 14C-dichlorophenyl- labelled test substance was used in the key study. This study was performed according to EPA guideline 161 -3 and in compliance with GLP criteria. In this study,14C-dichlorophenyl ring-labelled test substance was investigated on the surface of a dry sterile and a moist viable loam soil (Les Evouettes). The dry and the moist soils were exposed to a continuous light and to a 12 hours light regime experiment, respectively. The artificial light source used was a Xenon arc lamp (average 19 W/m2) in a Suntest unit ( λ > 290 nm). The experiments were run for 34 (continuous light experiment) and 26 (experiment with 12 hrs. light-dark cycle) calendar days corresponding to 28 and 37.5 days latitude 40°N. The dry soil test was conducted with a slurry of sieved soil and water, applied to glass or stainless steel plates forming a layer 1 mm deep and 30 cm2 in area. The plates were allowed to dry for ten hours at room temperature and then dosed with radiolabelled test substance at 0.5 kg/ha. The samples were irradiated continuously at 25 ± 0.3°C for up to 17 days. Samples were taken at 0, 7, 10, 12, 14 and 17 days. The moist soil test was conducted with a slurry of sieved soil and water, applied to glass or stainless steel plates forming a layer 1 mm deep and 30 cm2 in area. The plates were allowed to dry to approximately 75% field moisture capacity and then dosed with radiolabelled test substance at 0.5 kg/ha. The samples were irradiated continuously at 24.5 ± 0.3°C for up to 17 days. Samples were taken at 0, 5, 9, 14, 19 and 26 days. One dark control plate was prepared per experiment. Control samples were treated in the same way as irradiated samples, except that they were kept in the dark. The results show that the test substance was very slowly degraded by light when applied to soil surfaces with half-lifes of 72.2 (dry soil; continuous light) and 263 days (moist soil; 12 hours light and dark cycle). These values are equivalent to 119 days (dry soil; continuous light) and 379 days (moist soil; 12 hours light and dark cycle)under summer sunlight at latitude 40° N.

In the supporting study, the 14C-difluorophenyl-labelled test substance treated soil was incubated under continuous light (14.28 W/cm2) at 25 °C for 18.9 days. The test substance showed a half-life of 107 days under continuous light (equivalent to 165.3 days under summer sunlight at latitude 40° N).