Prometryn

Phototransformation in soil

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

phototransformation in soil

Type of information:

experimental study

Adequacy of study:

supporting study

Study period:

6 Jul 1989 to 29 Nov 1989

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

Details on soil:

A sandy loam soil obtained from a field dissipation study site in California was used. The soil was received on April 25, 1988. The soil was stored in a refrigerator at about 4 °C. The soil was sieved sequentially through 2 mm and 1 mm sieves and the resulting fine (1 mm and less) soil was used for the preparation of soil plates and for the soil analyses.

Light source:

Xenon lamp

Remarks:

with irradiance values of 401.2 and 396.0 watts/m2

Light spectrum: wavelength in nm:

>= 300 - <= 450

Reference substance:

yes

Dark controls:

yes

DT50:

78 d

Test condition:

irradiated soil

DT50:

491 d

Test condition:

non-irradiated soil

Transformation products:

yes

No.:

#1

No.:

#2

- Non-Irradiated (Dark) Soil Plates: The mean recovery was 102.1 ± 1.8% of the applied radioactivity, with no noticeable contribution by the volatiles (less than 0.1%).

- Irradiated Soil Plates: The mean recovery was 102.7 ± 1.8% of the applied radioactivity, with no noticeable contribution by the volatiles (less than 0.1%).

- Characterization of 14C-labelled Residues: The mean Rf values for the test substance were 0.77 and 0.57 in the normal and reversed phase TLC systems respectively. Normal phase thin layer chromatographic analyses of the irradiated soil extracts revealed the parent and 2 other radioactive compounds. The latter two compounds were inconspicuous in the non-irradiated soil extracts. The separation was generally poor in the reversed phase TLC system and, therefore, not used for quantitative purposes. The resolution was adequate to evaluate the parent concentration at various sampling times during the 30-day study period.

- Radioactivity Recovered from Thin Layer Chromatograms: The mean recovery of the applied radioactivity was 99.1 ± 0.9%. These recovery levels indicate the absence of any volatile compounds in the soil extracts. This is not surprising in view of the fact that the volatile traps at the various sampling events did not contain any measurable radioactivity.

- Identification of 14C-Residues By GC-MS: The major single peak that was seen as the test substance on the thin layer chromatographic plates was confirmed by the GC-MS analyses. The 2 degradates mentioned previously were also observed by GC-MS analyses of the 30-day soil extract samples. They appear to be M4 and M13, formed by the successive loss of ethyl and isopropyl groups.

Validity criteria fulfilled:

not specified

Conclusions:

[Triazine(u)14-C]-labelled test substance showed some degree of degradation on a sandy loam soil maintained at 25 °C under irradiated conditions. The estimated half-life was 78 days. The net half-life that is attributable to photodegradation was 92 days. There was no noticeable breakdown of the parent under non-irradiated conditions. There were 2 minor degradates, identified as M4 and M13.

Executive summary:

The photodegradation of [triazine(U)-14C]-labelled test substance on soil was studied according to a protocol consistent with the EPA Pesticide Assessment Guidelines, Subdivision N, Section 161-3, and references contained therein. The study was carried out in compliance with GLP. The test compound was applied to 1 mm layer thick soil layers (on glass plates) at a rate of 9.5 - 10.6 ppm, based on soil dry weight. The soil plates were exposed to artificial sunlight intermittently (approximately 12 hr light and 12 hr dark) for a total period of 30 days. The temperature of the soil was maintained at 25 ± 1°C. Evolution of organic volatiles and production of 14CO2 was monitored. Control samples were treated in the same manner as the irradiated samples, but were incubated in the dark at 25 ± 1°C. The soil plates were sampled in duplicate at 0, 1, 3, 7, 14, 21 and 30 days of exposure.

The material balance was 102.1 ± 1.8% and 102.7 ± 1.8% of the applied dose in the non-irradiated and irradiated samples, respectively, with no significant contribution by the volatiles. The soil extracts were analyzed by 2 thin layer chromatographic systems for the parent and photoproducts. The identity of the parent and its degradates was confirmed by HPLC and GC-MS.

The estimated half-life under non-irradiated and irradiated conditions were 491 and 78 days, respectively. The net half-life that is attributable to photodegradation was calculated to be 92 days. There were no major degradates. There were 2 minor degradates, identified as M4 and M13.

Reference 2

Endpoint:

phototransformation in soil

Type of information:

experimental study

Adequacy of study:

supporting study

Study period:

3 Nov 1987 to 5 Dec 1987

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

Details on soil:

Sandy loam soil was passed through a 2 mm sieve, allowed to air dry, and sterilized by autoclaving. Sterilized soil (3.1 gm) was added aseptically to each of 34 sterile 50 mm petri dishes. Sterile distilled water (3.0 mL) was aseptically added to each dish and stirred into a slurry to form a 0.5 mm layer on the bottom surface of each petri dish. These were allowed to air dry one day prior to use.

Light source:

sunlight

Light spectrum: wavelength in nm:

>= 220 - <= 400

Reference substance:

yes

Dark controls:

yes

% Degr.:

3.45

Sampling time:

30 d

Test condition:

irradiated soil

Remarks on result:

other: degradated to M2

DT50:

> 30 d

Test condition:

irradiated soil

Transformation products:

yes

No.:

#1

- Radiochemical Purity: The radiochemical purity was determined by HPLC analysis to be 98.5%.

-Temperature: The mean temperature throughout the study was 22.0 ± 0.2 °C.

- Light intensity: Light intensity data are presented as minimum and maximum intensity and total cumulative energy for each study day. The mean total energy per study day was 16.0 ± 5.3 W min/cm2.

- Material Balance: The mean extraction efficiency was 100.9 ± 6.5% and the mean total recovery was 102.6 ± 7.9%. The total radiocarbon present in extracted soil solids ranged from 0.2% to 3.8%.

- Quantitative Characterization of [14C]-labelled test substance and Its Degradation Products: All soil sample extracts were subjected to HPLC analysis to determine the quantitative nature of residues present. In all cases greater than 95 percent of the total extracted radiocarbon was identified as [14C]-labelled test substance. The only degradation product detected was M2. This characterization was confirmed with a representative sample (Day 30, Irradiated Sample Replicate 2) using thin-layer chromatographic analysis.

- Photodegradation of the test substance: Because less than 10% degradation was observed over the 30-day exposure period, the test substance is considered to be photolytically stable on soil. Total extractable radiocarbon when subjected to HPLC indicated 96.55% was [14C]-labelled test substance and 3.45% was M2 in samples irradiated 30 days. The total extractable radiocarbon was 100% [14C]-labelled test substance in those samples maintained 30 days in the dark. This indicates that the reaction was photochemically mediated. The half-life was greater than 30 days. Over the 30 day period an increase in bound residues in both the irradiated and dark control samples was observed, although there appeared to be no difference in increase between the two.

Conclusions:

The half-life for the photochemical reaction in natural sunlight is greater than 30 days. The only photoproduct identified was M2 which comprised 3.45% of the total recovered radiocarbon in irradiated samples. Because less than 10% degradation was observed over the 30-day exposure period, the test substance is considered to be photolytically stable on soil.

Executive summary:

The photodegradation of [14C]-labelled test substance on soil was studied according to a protocol consistent with the EPA Pesticide Assessment Guidelines, Subdivision N, Section 161-3. The study was carried out in compliance with GLP. [14C]-labelled test substance was applied as a thin film to the surface of sterilized sandy loam soil and exposed to natural sunlight for 30 days. All samples were irradiated exclusively with natural sunlight at this location (Latitude - 38.05 N; Longitude - 84.30 W). The mean total energy per study day was 16.0 ± 5.3 W min/cm2. All soil chambers were oriented in the same manner such that the chambers were facing south perpendicular to the sun's path. Sandy loam soil was passed through a 2 mm sieve, allowed to air dry, and sterilized by autoclaving. Test material was prepared such that each test plate was theoretically dosed with 9.21 x 106 dpm (142.9 µg) or 46.1 ppm. Duplicate light exposed and dark control plates were removed from their respective soil chambers at the following times - Day 0, 5, 10, 15, 20, and 30. The mean temperature throughout the study was 22.0 ± 0.2 °C.

The radiochemical purity was determined by HPLC analysis to be 98.5%. The mean extraction efficiency was 100.9 ± 6.5% and the mean total recovery was 102.6 ± 7.9%. The total radiocarbon present in extracted soil solids ranged from 0.2% to 3.8%.In all cases greater than 95 percent of the total extracted radiocarbon was identified as [14C]-labelled test substance. The only degradation product detected was M2. This characterization was confirmed with a representative sample using thin-layer chromatographic analysis. Total extractable radiocarbon when subjected to HPLC indicated 96.55% was [14C]-labelled test substance and 3.45% was M2 in samples irradiated 30 days. The total extractable radiocarbon was 100% [14C]-labelled test substance in those samples maintained 30 days in the dark. This indicates that the reaction was photochemically mediated.

Because less than 10% degradation was observed over the 30-day exposure period, the test substance is considered to be photolytically stable on soil. The half-life was greater than 30 days. Over the 30 day period an increase in bound residues in both the irradiated and dark control samples was observed, although there appeared to be no difference in increase between the two.

Description of key information

Photolysis is not expected to be a significant degradation process of the test substance in soil. It may slightly accelerate its degradation in summer.