Pyrasulfotole

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:

05 May 2003 - 05 Apr 2004

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)

GLP compliance:

yes

Radiolabelling:

yes

Analytical monitoring:

yes

Analytical method:

high-performance liquid chromatography

Details on sampling:

- Sampling intervals of soil samples: 0, 1, 3, 6, and 9 days post-application
- Sampling method: Two duplicate test systems were removed from the Suntest and incubator units for each sampling interval except for Day 0, where two test systems were shared. The samples were transferred to 11-mL ASE cells and extracted with methanol and water.
- Sampling method for CO2: No traps were used and the system was closed; no volatile components
- Sampling intervals/times for
- Sterility check, if any: none
- Measurement of moisture content: 0, 1, 3, 6, and 9 days post-application
- Sample storage conditions before analysis: All samples were analyzed within 24 hours of extraction

Details on soil:

COLLECTION AND STORAGE
- Geographic location: Grand Forks, North Dakota, USA
- Pesticide use history at the collection site: pesticides were not used
- Collection procedures: Soil thawed and sampled with spade.
- Sampling depth (cm): 0-15 cm
- Storage and transport conditions: Stored under alfalfa cover in greenhouse; Shipped in a 5 gallon bucket.
- Storage length: Stored under alfalfa cover in green house from 11 Feb 2003 to 25 Apr 2003 (total 73 days).
- Soil preparation (e.g.: 2 mm sieved; air dried etc.): Air-dried, plant material removed, sieved using 2 mm mesh, acclimated to study temperature, soil moisture determined

PROPERTIES
- Soil classification system and year: USDA
- Soil texture
- % sand: 19
- % silt: 62
- % clay: 19
- pH: 7.4 in CaCl2
- Organic carbon (%): 4.1%
- CEC (meq/100 g): 26 meq/100 g
- Field moisture capacity at 0.33 bar: 46.2%
- Bulk density (g/cm3): 0.90
- Initial microbial biomass/microbial population (unit): 1.397 mg microbial C/kg soil

Light source:

Xenon lamp

Light spectrum: wavelength in nm:

>= 290 - <= 750

Details on light source:

- Emission wavelength spectrum: < 290 nm
- Filters used and their purpose: Suprex (DSET) filter to limit emission wavelength to < 290 nm
- Light intensity at sample and area irradiated: 680 W/cm²
- Relative light intensity based on intensity of sunlight: Considering light intensity of an artificial light source calculated for 300-3000 nm, 58% of the light intensity is in the range of 300 to 800 nm.From the total radiant exposure measurement of 29.5 MJ/m², 17.1 MJ/m² was determined to be the daily irradiance (<800 nm) on June 23rd, 1988, in Phoenix, AZ (29.5 MJ/m² x 0.58 = 17.1 MJ/m²). Since the ozone layer effectively attenuates UV irradiation (< 290 nm) in the atmosphere, and only the UV/visible absorption region is believed to be intense enough to drive photolytic reactions thus, the absorption region of interest is narrowed to 290-750 nm. The Suntest unit was operated at approximately 680 W/m2 (290-800 nm) to simulate highly photoreactive conditions. At this intensity it would take 7.0 hours in the Suntest unit to equal one solar day. Since 7.0 hours represents 1 environmental day, 212 hours of continuous irradiation at 680 W/m² is equivalent to 30.3 environmental days (212 hours / 7.0 hours per day).
- Duration of light/darkness: 210 h (continuous)

Details on test conditions:

TEST SYSTEM
- Type, material and volume of test apparatus or thin layers: 4 cm diameter quartz glass vessels with ground glass stoppers in place of traps for the collection of CO2.
- Application procedure: The test systems were treated with the appropriate application solution using a 250 μL Hamilton syringe. The solutions were applied evenly across the surface of the soil. The ACN was allowed to evaporate off the soil and the test systems were shaken slightly to disperse the a.i. throughout the matrix after the drying process.
- Volume of test solution used/treatment: 140 µL
- Method of application: 250-μL syringe, evenly onto soil surface, evaporated and mixed
- Details of traps for volatile, if any: No volatility indicated.
- If no traps were used, type of test system: closed
- Indication of test material adsorbing to the walls of test apparatus: no

PREPARATION OF THIN-LAYER PLATES: Prior to sealing each test system, the soil moisture was adjusted to approximately 75% of 1/3-bar water holding capacity by the addition of 93 μL of Milli-Q ® water. After sealing each test system with a thin layer of stopcock grease, weights of each system were recorded.

REPLICATION
- No. of replicates (dark): 8
- No. of replicates (irradiated): 12 + 3 for identification of metabolites

MAINTENANCE OF TEST CONDITIONS SPECIFIED UNDER "DURATION"
- Moisture maintenance method: Maintained constant weight (if change >10%) of test system by periodically adding water as needed.

Duration:

9 d

% Moisture:

35

Temp.:

25 °C

Initial conc. measured:

0.51 mg/kg soil d.w.

Reference substance:

no

Remarks:

Reference substances were not utilized because no significant degradation was observed from the parent compound

Dark controls:

yes

Preliminary study:

No volatiles were found in the preliminary test.

DT50:

309 d

Remarks on result:

other: solar days in New River, AZ, USA; organic carbon: 4.1%

DT50:

173 d

Remarks on result:

other: solar days in New River, AZ, USA; organic carbon: 1.2%

Transformation products:

not measured

Remarks:

No degradates were formed greater than 1%; identification measures were not taken.

Details on results:

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

MAJOR TRANSFORMATION PRODUCTS (distinguish between dark and irradiated samples)
- No degradates were formed greater than 1%.

MINOR TRANSFORMATION PRODUCTS (distinguish between dark and irradiated samples)
- Two minor transformation products, Unknown A (irradiated test systems) and Unknown B (non-irradiated test systems) occurred at very low levels (approximately 1% of the applied radioactivity). No identification measures or kinetics calculations were done for these minor degradates.

Phototransformation of test item, expressed as ppm (ion of test item, expressed as ppm (μg/g) parent equivalents under irradiated and dark soil photolytic conditions.

		Sampling Times [days]
		Day 0	Day 1	Day 3	Day 6	Day 9
[^14C] test item	Irradiated Mean	0.5	0.5	0.4	0.4	0.4
	Dark Mean	0.5	0.5	0.5	0.5	0.4
Unknown A	Irradiated Mean	0.0	0.0	0.0	0.0	0.0
	Dark Mean	0.0	0.0	0.0	0.0	0.0
Unknown B	Irradiated Mean	0.0	0.0	0.0	0.0	0.0
	Dark Mean	0.0	0.0	0.0	0.0	0.0
Total Extractable Radioactivity	Irradiated Mean	0.5	0.5	0.5	0.4	0.4
	Dark Mean	0.5	0.5	0.5	0.5	0.5
Bound Residue	Irradiated Mean	0.0	0.0	0.0	0.0	0.0
	Dark Mean	0.0	0.0	0.0	0.0	0.0
Total % Recovery	Irradiated Mean	0.5	0.5	0.5	0.5	0.5
	Dark Mean	0.5	0.5	0.5	0.5	0.5

Validity criteria fulfilled:

not applicable

Description of key information

DT50: 309 solar days (New River, AZ, USA; organic carbon 4.1%)

DT50: 173 solar days (New River, AZ, USA; organic carbon: 1.2%)

Key value for chemical safety assessment

Half-life in soil:

309 d

Additional information

One study is available investigating the phototransformation of the test item in soil (M-062841-01-1). The phototransformation of the test item was studied (according to EPA Guideline N 161-3) in Horse Camp Bridge (HCB) soil, a silt loam from Grand Forks County, North Dakota, USA at 25 ± 1 °C and moisture of 35% (75% of 1/3-bar water holding capacity). The test substance was applied directly to the surface of the soil at an initial concentration of 0.51 µg/g of soil and continuously irradiated for 9 d (30 environmental days at New River, AZ) under artificial light (xenon lamp with <290 nm cut-off filter used) with intensity 680 W/m². Test vessels consisted of 4-cm diameter quartz glass containers. A preliminary study demonstrated that no volatiles were formed during photolysis. Therefore, test vessels were not connected to traps for the collection of CO2 and organic volatiles. Duplicate test systems were analyzed at 0, 1, 3, 6, and 9 d after application. The soil samples were extracted twice with methanol:water (8:2 and 7:3) on a Accelerated Solvent Extractor 200 (ASE). The radioactive residues were analyzed by HPLC. Since the organic carbon of the HCB soil was high (4.1%), the phototransformation of the substance was studied in the same way in a second soil from Pikeville, NC which had an organic carbon content of 1.2%. The test item remained relatively stable throughout the study in both non-irradiated and irradiated soil test systems. The phototransformation DT50 in HCB silt loam was 90 experimental days, which is equivalent to 309 solar days in New River, AZ (USA). The DT90 was 209 days (1027 solar days). The DT50 in Pikeville loamy sand was 50.6 experimental days, equivalent to 173 solar days in New River, AZ (USA). The DT90 was 168 days (576 solar days). No major degradation products were observed in both soil types.