mecoprop-P (ISO); (R)-2-(4-chloro-2-methylphenoxy)propionic acid

Phototransformation in soil

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

phototransformation in soil

Type of information:

experimental study

Adequacy of study:

key study

Study period:

05 October 1995 to 20 December 1995

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

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

Deviations:

no

GLP compliance:

yes

Radiolabelling:

yes

Analytical monitoring:

yes

Analytical method:

liquid chromatography

high-performance liquid chromatography

mass spectrometry

Details on soil:

COLLECTION AND STORAGE
- Geographic location: Timmerman, Washington on 5 May 1995.
- Collection procedures: Approximately 80 lbs of a coarse sandy loam soil was removed.
- Sampling depth: The soil used for this study was collected from the top 2 to 9 inches of the site.
- Storage and transport conditions: Stored in the dark in a walk-in refrigerator at a temperature of approximately 4 °C.
- Soil preparation: Upon receipt, the soil was sieved through a 2 mm stainless steel sieve.

PROPERTIES
- Soil texture: Sandy loam
- % sand: 66 %
- % silt: 27 %
- % clay: 7 %
- pH: 7.4
- Organic carbon (%): 0.9 %
- CEC (meq/100 g): 14.4
- Bulk density (g/cm³): 1.28 g/cc
- Microbial Viability in Soil: The soil microbial viability associated with the sandy loam soil was established prior to initiation of the preliminary and definitive studies and at termination of the definitive study. Soil samples (1 g) were extracted with 99 mL of sterile reagent water and the extract was serially diluted from 10^-1 to 10^7. A volume of 100 μL of each dilution was plated onto nutrient agar medium. Plates were incubated at a temperature of 35 to 37 °C for approximately 24 hours prior to counting colonies.

Light source:

Xenon lamp

Light spectrum: wavelength in nm:

>= 250 - <= 700

Details on light source:

Xenon arc lamp provided by a modified Heraeus Suntest Accelerated Exposure Unit. This accelerated exposure unit generates a radiation distribution similar to that of natural sunlight. The lamp was fitted with an additional glass filter that limited transmission of UV radiation to wavelengths greater than 300 nm. The light source was operated on an alternating 12-hour cycle to approximate natural light and dark cycles. In order to accommodate the physical dimensions of the photolysis module, the xenon arc lamp was removed from its housing within the Heraeus Unit and suspended directly above the test module at a height of approximately 12 inches.
- Spectral Profiles and Total Intensity Measurements of the Artificial Light Source as Compared to Natural Sunlight: Spectral profiles for the artificial light source and natural sunlight over the wavelength range of 250 to 700 nm was recorded with a Model IL-1700 Research Radiometer, Model IL-760D power supply, double monochromator, Model IL-791 and P2 Fiber Optic probe. The total integrated light intensity of the artificial light source and sunlight was measured using an SUD400W photodiode detector over the wavelength range of 250 to 700 nm. All components of the spectroradiometer were manufactured by International Light, Inc.
Sunlight measurements were recorded on 1 August 1995 at 12:17 p.m. on a clear, sunny day outside the Wareham, Massachusetts laboratory (42° North latitude). Outside measurements were obtained by positioning the fiber optic probe directly at the sun (55° from the horizontal measured with a protractor). Light intensity measurements for the artificial light were recorded directly under the lamp at a distance of 12.5 inches using the SUD400W. A Pyrex® plate was placed approximately 2 inches over the SUD400W detector. For spectral profile measurements, the fibre optic probe was positioned at a distance from the xenon lamp which was approximately the same distance as the soil samples to the light. A Pyrex® plate glass was also positioned approximately 2 inches above the fiber optic probe and approximately 10.5 inches from the xenon lamp. Additionally, spectral measurements to verify complete occlusion of light within the dark control test module were made by positioning the fiber optic probe beneath the black cloth used to occlude light.
Total light intensities of the artificial light source and natural sunlight were measured on 4 October 1995 and 1 August 1995, respectively. Total intensity measurements were 3.40 x 10^-3 and 1.67 x 10^-2 W/cm^2, respectively. The total intensity of the artificial light source was, therefore, approximately 20.4 % that of natural sunlight. Following termination of the study, total light intensity of the artificial light source (recorded on 27 November 1995) was 3.69 x 10^-3 W/cm^2, representing 22.1 % the intensity of natural sunlight.
These results indicate that the artificial light source was a reasonable model for sunlight and that the light intensity and spectral profile of the artificial light remained stable during the time of the study.

Details on test conditions:

PRELIMINARY STUDY
- A preliminary study using [14C]-test material was performed to establish appropriate sampling intervals for the definitive study (i.e., to establish an appropriate kinetic half-life for parent compound and patterns of formation and decline of major photodegradates) and to confirm the acceptability of the experimental procedures (e.g., extractions, volatile trapping, material balance at sampling intervals and chromatographic profiles).
- Preparation of Soil Plates: Twenty-seven 60 mm (diameter) thin-film soil samples in glass petri dishes were prepared using the sandy loam soil. Twelve dishes were designated as irradiated replicates, thirteen as dark control replicates and two as soil blanks. The blank samples were used for temperature measurement during irradiation (photolysis samples) and incubation (dark controls evaluating soil metabolism/abiotic degradation processes). The percent moisture was determined using a Sartorius Moisture Analyser. Approximately 5.9 g of soil (approximately equivalent to 5.4 g dry weight) was weighed into each dish. Based on the bulk density of the soil (1.28 g/cm^3) and the area of the bottom of the petri dish, this amount of soil provided a layer 1.5 mm in thickness. An equal volume of water was added to the measured soil placed in the petri dish, and the slurry was gently swirled until the soil was evenly distributed. The water was allowed to evaporate from the soil plates prior to dosing.
- Dosing: Five-hundred μL of the 0.0131 mg/mL [14C]-test material secondary stock solution, representing 1.54 μCi (3 417 210 dpm, equivalent to 6.85 μg test material based on radioassay and specific activity), was added to each soil replicate (5.43 g on a dry weight basis; except for the two soil blanks) to produce a concentration of 1.26 μg/g (ppm), (1.18 ppm target), approximating 2.4 lbs active ingredient/acre (the maximum seasonal application rate of the test material for turf). The experimental application rate was based on a calculation which assumed a soil bulk density of 1.5 g/cm^3 and test material incorporation 6" deep into the soil. Dosing of the test material was performed via dropwise addition of the dosing solution using a glass syringe, being careful to evenly distribute the solution over the surface of the soil. The solvent (acetonitrile) was allowed to evaporate from the soil for one hour at room temperature. The soil samples were remoisturised to 12.5 %, which was 75 ± 10 % of the field moisture capacity (FMC), based on the tare weight and the dry weight of soil added to each dish.
- Soil Extraction Procedure: Duplicate replicate samples were extracted and analysed on Day 0. Duplicate irradiated and dark control sample replicates were sampled on Days 1, 4 and 7 to quantify residual test material and major degradates. The individual soil samples were extracted in a graduated centrifuge tube with 3 x 10 mL of acetonitrile/ water/ acetic acid (8: 2: 0.1 v/v/v). Extraction was conducted by vortexing for three minutes, then shaking by hand for three additional minutes. The solvent was separated from the soil during each extraction by centrifugation (3 000 rpm for 20 minutes). The three extracts were combined, thoroughly mixed and the final volume recorded. Three 100 μL aliquots were radioassayed to quantify the overall extractable radioactivity. The total radioactivity in the combined extract from each soil plate was compared to the radioactivity applied to each plate to determine percent recovery. An aliquot of the combined soil extract was profiled by HPLC-RAM to quantify the remaining test material and to establish a degradate profile.
- Volatile Trapping Procedure: The polyurethane foam plugs, ethylene glycol and 10 % potassium hydroxide solutions were replaced and quantified by radioassay at each sampling interval, with the exception of Day 0. The total volumes of the ethylene glycol and potassium hydroxide solutions were measured and 1.0 mL and 0.5 mL aliquots radioassayed, respectively, after mixing with 15 mL of Monophase® scintillation cocktail. Overflow traps containing liquid were also radioassayed by LSC. The polyurethane foam plugs were extracted with two 5 mL portions of methanol by vortexing samples for several minutes and removing the solvent. Triplicate 1 mL aliquots of the combined extract were radioassayed, after mixing with 15 mL of Monophase scintillation cocktail.
- Combustion Analysis for Non-Extractable (Bound) Residues: The radioactivity associated with the post-extracted soil was quantified by placing the soil in a fume hood to dry, thoroughly mixing the soil with a spatula and transferring soil aliquots into burn cones for combustion. Recovery data for the oxidiser was determined prior to analysing each set of samples by combusting and counting the activity of a standard reference material (Spec-Chec™ [14C] standard) and comparing the measured value to that of a concurrently fortified Spec-Chec™ standard added directly to scintillation cocktail. Since the oxidiser recovery was typically greater than 98 %, experimental data were not corrected.

DEFINITIVE STUDY
TEST SYSTEM
- Type, material and volume of test apparatus or thin layers: The experimental set-up consisted of two custom-designed soil photolysis modules constructed of stainless steel with inlet and outlet ports for the trapping of volatile products. Two complete test modules were used, one for the irradiated samples and one for the dark controls. The upper compartment of each module housed the test material-fortified soil samples. The lower compartment of each test module was designed for cooling by recirculating an "antifreeze" solution containing 15 % ethylene glycol and 85 % reagent water. The soil photolysis modules for the irradiated and dark control test systems were fitted with a Pyrex® glass plate. The seal between the glass plate and the stainless steel ledge at the top of each module was made using 1/4 inch silicone foam strips and was secured with C-clamps.
Sterile, hydrated CO2-free air was pulled slowly and continually through each module at an approximate flow rate of 10 mL/minute with a vacuum pump to aerate the soil, as well as trap any volatile degradates. The inlet port of each module was connected to a flask containing a 10 % potassium hydroxide solution, which acted as a carbon dioxide scrubber so as not to saturate the in-line potassium hydroxide trapping solutions. The outlet port of each module was connected to a trapping train comprised of the following media, in series: Two polyurethane foam plugs in succession, ethylene glycol, and two traps each containing 10 % potassium hydroxide. A single volatile trapping train was connected to each test module and served as a collective trap for all irradiated soil samples or for the samples incubated in the dark.
- Application procedure: Thin-layer soil samples containing [14C]-test material at the maximum seasonal application rate (equivalent to 2.4 lbs. active ingredient/acre) were exposed to a xenon arc lamp provided by a modified Heraeus Suntest Accelerated Exposure Unit. This accelerated exposure unit generates a radiation distribution similar to that of natural sunlight. The lamp was fitted with an additional glass filter that limited transmission of UV radiation to wavelengths greater than 300 nm. The light source was operated on an alternating 12-hour cycle to approximate natural light and dark cycles. In order to accommodate the physical dimensions of the photolysis module, the xenon arc lamp was removed from its housing within the Heraeus Unit and suspended directly above the test module at a height of approximately 12 inches.
- Volume of test solution used/treatment: The maximum seasonal application rate, equivalent to 2.4 lbs. active ingredient/acre.
- Method of application: Exactly 500 μL of the 0.0131 mg/mL [14C]-test material secondary stock solution, representing 1.54 μCi, was added to each soil replicate, except for the two soil blanks, to produce a concentration of 1.26 ppm. Dosing of the test material was performed as previously described for the preliminary study.
- Details of traps for volatile, if any: Volatiles were purged from the headspace of each test module and captured by continually drawing air into a series of traps using a vacuum pump at a flow rate of approximately 10 mL/minute. Each trap consisted of a scintillation vial equipped with an open-top cap and a Teflon®-coated septum. The trapping train consisted of: (1) two polyurethane foam plugs in succession, (2) an empty trap, (3) ethylene glycol, (4) an empty trap, (5) two vials of 10 % potassium hydroxide in succession and (6) an empty trap. Traps were connected in series through Teflon® tubing acting as a collective trap for all soil samples being irradiated or incubated in the dark. Carbon dioxide from the air was scrubbed with a 10% potassium hydroxide solution so as not to saturate the potassium hydroxide trap solutions. Traps were analysed and replaced at each sampling interval.
In order to determine the trapping efficiency of 14CO2 in the trapping system, 3 mL of a 0.0312 mg/mL [14C]sodium bicarbonate primary stock solution in 0.1 N NaOH was added to an empty glass petri dish (60 mm in diameter). The dish was placed in the photolysis module and the glass plate was attached (sealed) to the stainless steel module. The outlet of the test module was connected to a trapping train consisting of polyurethane foam, ethylene glycol, and two 10 % potassium hydroxide solutions in succession. Immediately after beginning the purge, via vacuum, of the headspace of the test module, the sodium bicarbonate was converted to radiolabeled carbon dioxide by the addition of 2 mL of 6 M hydrochloric acid. The addition of the acid was made by positioning a syringe under the silicone foam strip used to secure the glass plate. The headspace of the module was allowed to purge at approximately 20 mL/minute for 27.8 hours. Upon completion of the purge, the final volume of each trap was measured and aliquots of the ethylene glycol and potassium hydroxide traps were radioassayed by LSC to determine recovery. The foam plugs were extracted twice with 5-mL portions of methanol, and aliquots were radioassayed to determine additional recovery. The radioactivity recovered from each trap solution, the methanol extract of the foam plugs and the radioactivity remaining in the acidified bicarbonate solution were used to determine overall radioactive recovery and the trapping efficiency of the test system. After purging the test module, 104 % of the applied radioactivity was recovered in the potassium hydroxide trapping solutions. No additional radioactivity was found in the acidified sodium bicarbonate solution. The results were:
Ethylene glycol: < minimum detection limit, 0 % applied radioactivity.
KOH-1: 13 246 118 dpm, 100.4 % applied radioactivity.
KOH-2: 440 611 dpm, 3.34 % applied radioactivity
Acidified NaH^14CO3: 1 881 dpm, 0.014 % applied radioactivity
Total radioactivity: 13 688 610 dpm, 103 % applied radioactivity.
Applied radioactivity (NaH^14CO3 in 0.1 M NaOH) = 13 198 815 dpm.
The results of the trapping experiment, therefore, demonstrated that the trapping system was efficient for capturing 14CO2.
- Volatile trapping procedures: The polyurethane foam plugs, ethylene glycol and 10 % potassium hydroxide solutions were analysed and replaced at each sampling interval, except Day 0, according to the method described for the preliminary study.
- Indication of test material adsorbing to the walls of test apparatus: Humic Acid, Fulvic Acid and Humin Fractionation of Bound Residues: Since the radioactivity associated with the post-extracted soil was greater than 10 % of the applied dose, a humic acid/fulvic acid/humin fractionation procedure was performed using the Day 30 replicates. These samples were chosen because bound residues were maximal. The post-extracted soil (approximately 5 g) was transferred to a centrifuge tube with 25 mL of 0.1 N sodium hydroxide and approximately 0.025 g of CaCl2. The test samples were vigorously shaken, further mixed on a vortex mixer and centrifuged at 3 000 rpm for 20 minutes. The supernatant was removed with a volumetric pipet and the volume transferred to a graduated cylinder. The remaining soil was subsequently combusted to quantify radioactivity associated with the humin fraction. Approximately 10 drops of concentrated hydrochloric acid was added to the supernatant to adjust the pH to approximately 1.
The solution was stored in a centrifuge tube in the refrigerator for the weekend to allow sufficient time for the precipitation of the humic acid fraction. The contents of the tube were vacuum filtered and the supernatant (fulvic acid fraction) was decanted. Radioassay was performed on the fulvic acid fraction (3 x 0.5 mL), the humic acid fraction (combustion of filter paper) and the humin fraction (3 x 0.5 g combustions of sodium hydroxide-extracted soil). Additionally, aliquots of air-dried soil (5 x 0.1 g) were dosed with 50 μL of a diluted [14C]-test material stock solution and combusted to determine the efficiency of combustion. The efficiency was determined by comparing the results of combustions to a stock check. Combustion efficiency was determined to be 90.2 % and applied to the humin fraction results.

PREPARATION OF SOIL PLATES: Twenty-six 60-mm (diameter) soil samples in glass petri dishes were prepared using the sandy loam soil. Twelve dishes were designated as irradiated replicates, twelve as dark control replicates and two as soil blanks. The blank samples were used for temperature measurement during light-exposure and incubation in the dark. Percent moisture was determined using a Sartorius Moisture Analyser. Approximately 5.9 g of soil (approximately 5.4 g dry weight) was weighed into each dish. Based on the bulk density of the soil (1.28 g/cm^3) and the area of the bottom of the petri dish, this weight provided a soil layer 1.5 mm in thickness. An equal volume of water was added to the soil in each petri dish, and the slurry was gently swirled until the soil was evenly distributed. The water was allowed to evaporate from the samples prior to dosing.

REPLICATION
- No. of replicates (dark): One for the dark controls
- No. of replicates (irradiated): One for the irradiated samples

MAINTENANCE OF TEST CONDITIONS SPECIFIED UNDER "DURATION"
- Temperature maintenance method: Temperature of the soil samples was monitored throughout exposure by placing the probe of a min-max thermometer into an unfortified soil sample. The soil dish, containing the thermometer probe, was placed into the module with the fortified soil samples. During the definitive study, temperature control of both the irradiated and dark control modules was maintained by adjusting the temperature of the circulating water bath/chiller during light and dark periods. For the preliminary photolysis study, the dark control test module was placed in a separate environmental chamber, controlled at a temperature of approximately 25 °C and covered with a black cloth to prevent light exposure.
- Moisture maintenance method:

OTHER
- Reference Standards: Reference standards were received from commercial sources for identification of potential photodegradates. The reference standards (neat) were stored either at room temperature, in a refrigerator (approximately 4 °C; 4-methoxybenzyl chloride) or under nitrogen (4-chlorophenol).
Once reference standard stock solutions were prepared, they were stored in a freezer at -20 °C.
A sample of [14C]sodium bicarbonate with a specific activity of 5.80 mCi/mmol as reported by the supplier, was stored frozen (-10 °C).
- Standard Reagents: All aqueous solutions were prepared using reagent water (meeting ASTM Type IIA requirements) obtained with a Sybron/Bamstead NANOpure® II system. The filter-sterilised water typically has greater than 16. 7 Mohm-cm resistivity and a total organic carbon concentration below the 1 mg/L detection limit.
- Primary Stock Solutions: A radiolabelled test material primary stock solution was prepared by transferring the entire amount of the purified [14C]- test material via repetitive rinsing with acetonitrile into a 50 mL volumetric flask and diluting to volume. The primary stock solution was analysed by liquid scintillation counting (LSC) to have a mean measured concentration of 0.131 mg/ml (6.53 mg [14C]- test material), based on the radioactivity and the specific activity (224.86 uCi/mg). The radiopurity of this primary stock solution was determined to be 100 % by HPLC-RAM. This primary stock was used to prepare a secondary stock solution for fortification of the soil samples.
A radiolabelled sodium bicarbonate primary stock solution was prepared by transferring the entire contents of the bottle via repetitive rinsing with 0.1 N NaOH into a 100 mL volumetric flask and diluting to volume. The primary stock solution was analysed by LSC to have a mean measured concentration of 0.0312 mg/mL (3.12 mg [14C]NaHCO3), based on the radioactivity and the specific activity. This stock solution was used for determination of the trapping efficiency.
- Secondary Stock Solution: For the preliminary and definitive studies, separate secondary radiolabelled stock solutions were prepared by diluting 1.4 mL of the 0.131 mg/mL [14C]- test material primary stock solution to a final volume of 14 mL with acetonitrile. This produced stock solutions with a concentration of 0.0131 mg/mL. An aliquot of the secondary stock solution was profiled by HPLC-RAM prior to initiation of the preliminary study.

- Soil extraction procedure: Duplicate fortified replicates were analysed on Day 0. Duplicate irradiated and dark control replicates were analysed on Days 5, 11, 15, 22 and 30 to quantify residual test material and degradates. The soil samples were extracted, quantified and chromatographically profiled as described in the preliminary study.
- Combustion Analysis for Non-Extractable (Bound) Residues: The radioactivity associated with the post-extracted soil was quantified by placing the soil in a fume hood to dry, thoroughly mixing the soil with a spatula and transferring soil aliquots into burn cones for combustion. Recovery data for the oxidiser was determined prior to analysing each set of samples by combusting and counting the radioactivity of a standard reference material (Spec-Chec™ [14C] standard) and comparing the measured value to that of a fortified Spec-Chec™ standard added directly to scintillation cocktail. Since the oxidiser recovery was typically greater than 97 %, experimental data were not corrected. In addition, at each sampling interval, except on Day 0, air-dried aliquots of soil (3 x 0.1 g) were dosed with 50 μL of a diluted [14C]-testmaterial stock solution and combusted to determine the efficiency of soil combustion. The efficiency was determined by comparing the results of combustions to 50 μL aliquots of the diluted [14C]test material stock solution quantified by direct LSC. Combustion efficiency ranged from approximately 89 % to 100 % throughout the study. Because efficiency of combusting soil was considered acceptable throughout the definitive study, bound residue results were not corrected for soil combustion efficiency.

CALCULATIONS
During this study, calculations were performed using the following formulas.
Determining radioactivity (and percent of applied dose) in a combined soil extract:
(dpm in aliquot / volume (mL) of aliquot) x volume of extract (mL) = dpm in extract

Example: Day 15, irradiated sample:

(9 451.982 dpm / 0.1 mL) x 27 mL = 2 552 035.14 dpm

Percent of applied dose:
(2 552 035.14 dpm / 3417210 dpm/ soil plate) x 100 = 74.7 %

Determining radioactivity in an individual volatile trap (e.g. KOH 1):

(dpm in aliquot / volume (mL) of aliquot) x volume of trap (mL) = dpm in trap

Example: Day 15, irradiated sample

(2 935.580 dpm / 0.5 mL) x 14 mL = 82 196.24 dpm

Percent of applied dose:
(82 196.24 dpm / ((3417210 dpm/soil plate) + (7 plates))) x 100 = 0.344 %

Determining radioactivity in volatile traps (cumulative):

(dpm in all traps (Day 5) / number of samples) + (dpm in all traps (Day 11) / number of samples) + (dpm in all traps (Day 15) / number of samples) + etc.

Example: Irradiated samples through Day 15:

(328 869.6 dpm / 11) + (173 496.8 dpm / 9) + (98 327.3 dpm / 7) = 63 221.4 dpm

Percent of applied:
(63 221.4 dpm / 3417210 dpm) x 100 = 1.85 %

Determining radioactivity in bound residues:
(dpm in combusted aliquot / weight of aliquot (g)) x soil sample (g) = dpm in bound residue

Example: 76 977.984 dpm/g x 5.43 g = (417 990.451 dpm / sample)

Percent of applied dose: (417 990.451 dpm / 3 417 210 dpm) x 100 = 12.2 %

Determining material balance during analysis of a soil sample:
((dpm in combined extracts + dpm (cumulative) in volatile traps + dpm in bound residues) / applied dose) x 100

Example: Day 15, irradiated sample:

((2 552 035.14 dpm + 63 221.41 dpm + 512 501 dpm) / 3 417 210 dpm) x 100 = 91.5 %

Determining residual percent test material at a sampling interval:
% test material of HPLC x % extractable

Example: Irradiated soil extract:
74.7 % of applied radioactivity was extractable
The test material represented 96.5 % of HPLC profile
Therefore, 74.7 % x 96.5 % = 72.1 % test material

Half-life determination:
At each sampling interval, the remaining percent test material in the irradiated and dark control solutions was determined in duplicate by HPLC-RAM analysis. The photolytic rate constant (k) and the first-order half-life (t½) of the test material were calculated by plotting the natural logarithm of the percent test material remaining versus time (in days). The resulting line indicating the best fit of the data was established using linear regression analysis. The photolytic rate constant was calculated from the following equation, based on apparent first-order kinetics:

Ln (% test material remaining = k . t

Where:
k = rate constant (day^-1)
t = time (day)

The half-life (t½) in days was calculated from the following equation:

t½ = 0.693 / [k]

Duration:

30 d

% Moisture:

75

Temp.:

25 °C

Initial conc. measured:

2.4 other: lb/acre

Reference substance:

yes

Dark controls:

yes

Preliminary study:

Results of the preliminary study indicated that the test material degraded in both irradiated and dark control soils. Material balances during the 7-day study ranged from 93.5 to 106 % and from 89.9 to 103 % of the applied radioactivity in irradiated and dark control samples, respectively. As indicated, the only significant extractable radioactive compound corresponded to the test material. For irradiated and dark control samples, respectively, non-extractable (bound) radioactive residues accounted for an average of 10.4 and 10.6 % of the applied radioactivity at Day 7. Volatiles accounted for 1.0 and 2.4 % of the applied radioactivity, respectively, at Day 7. First-order half-lives were calculated to be 23.1 days (r^2 = 0.916) and 13.9 days (r^2 = 0.970). Based on the results of the preliminary study, the definitive study was conducted over a 30-day exposure period with sampling intervals at Day 0, 5, 11, 15, 22 and 30.

% Degr.:

0

Sampling time:

30 d

Test condition:

In the absence of irradiation

Remarks on result:

other: Standard deviation not reported.

Key result

DT50:

16 d

Test condition:

Environmentally relevant sunlight, 2.4 lbs active ingredient/acre

Transformation products:

yes

No.:

#1

Details on results:

DISTRIBUTION OF RADIOACTIVE RESIDUES (MATERIAL BALANCE)
Extractable residues from the irradiated samples decreased during the study, from an average of 92.8 % to 74.3 % of the applied radioactivity. Concomitantly, there was a steady increase in non-extractable residues for irradiated samples, reaching a maximum average of 14.9 % of applied radioactivity in the Day 30 samples. In contrast, extractable radioactivity from the dark controls remained essentially constant, between 90 and 97 % of the applied radioactivity, throughout the 30-day incubation period, with no more than 4.3 % of applied radioactivity associated with the soil after extraction. For both irradiated and dark control samples, production of volatiles was minimal and totaled 2.55 % and 0.913 % of applied radioactivity, respectively at Day 30. Material balances ranged from 88. 7 to 95.4 % of the applied radioactivity and from 92.3 to 101 % in irradiated and dark controls samples, respectively, during the 30-day study.

HPLC PROFILING AND QUANTITATION OF DEGRADATES THROUGHOUT THE STUDY
The HPLC chromatograms of soil extracts from both Day 0 samples (Replicate 1 and 2) are indicate that the test material was the sole radioactive residue extractable from soil. Minimal extractable degradates were observed in irradiated samples; none for dark controls. The minor photodegradate with a retention time of 37.40 minutes, accounting for 4.6 % of the chromatogram radioactivity (3.2 % of applied radioactivity), was tentatively identified as 4-chloro-2-methylphenol, based on its similar retention time to the authentic reference standard. Its identity was confirmed by 2D-TLC.

2D-TLC CONFIRMATION OF THE TEST MATERIAL AND 4-CHLORO-2-METHYLPHENOL IN A DAY 30 IRRADIATED SOIL EXTRACT
The identities of residual test material and 4-chloro-2-methylphenol, extracted from a Day 30 irradiated soil sample replicate, were confirmed by another chromatographic method, 2D-TLC. The location of the standards in two dimensions, as well as in each individual dimension, was determined by the quenching of short-wavelength UV light. The major radioactive spot, accounting for 90.2 % of the radioactivity on the plate, corresponded to the test material reference standard. The spot accounting for 3.5 % of the detected radioactivity on the plate corresponded to the 4-chloro-2-methylphenol reference standard. The spot accounting for 0.8 % of the radioactivity on the plate appeared to correspond to the 4-chloro-2-methylanisole reference standard. However, this minor product was not detectable with HPLC profiling. There was also 5.6 % of the detected radioactivity remaining at the origin of the TLC plate. Since this radioactivity was not apparent in the HPLC profile it most likely resulted from air oxidation at the silica gel surface, after application and prior to development.

LC-(ELECTROSPRAY) MS CONFIRMATION OF TEST MATERIAL IN A DAY 30 IRRADIATED SOIL EXTRACT
The identity of residual test material in a Day 30 irradiated soil extract was also confirmed by LC-(electrospray) MS. The total ion chromatogram (TIC) and negative ion mass spectrum of the reference standard and the Day 30 irradiated soil extract are quite similar in both chromatographic retention time and in mass spectra, confirming the identity of the test material.

KINETICS
Based on the assumption of first-order kinetics, the half-life of the test material in irradiated samples was calculated to be 79.9 days (r^2 = 0.699). Since the artificial light source represented approximately 20 % of natural sunlight, the environmentally relevant half-life of the test material on soil is probably closer to 16 days. Degradation in soil in the absence of artificial light was not apparent in the definitive study. This is most likely because of the minimal retention of soil moisture in both irradiated and dark control samples, in spite of initially providing moisture at 75 % of FMC and continuously aerating samples with hydrated air. That is, the thin soil layer (1.5 mm) with a large surface area in the petri dish rapidly lost associated water through evaporation in spite of efforts to maintain a moisture level optimal for microbial processes. However, since both irradiated and dark control samples were kept under essentially identical conditions, the difference in half-lives is thought to be influenced only by the effect of the artificial light source. Furthermore, the experimental set-up relating to soil moisture was directly modeled after the most recent guidance on this subject provided in the EPA Pesticide Reregistration Rejection Rate Analysis - Environmental Fate (U.S. EPA, 1993).

FRACTIONATION OF SOIL-BOUND RESIDUES
The nature of the non-extractable (soil-bound) residues in a Day 30 irradiated replicate was determined, based on a conventional humic acid/ fulvic acid/ humin fractionation procedure. For this sample, bound residues represented 13.0 % of the applied radioactivity. After fractionation, humic acid, fulvic acid and humin represented 2.96, 21.6 and 80.8 % of the bound residue, respectively. Overall recovery during the fractionation was 105 %. These results indicated that the test material degradates (phenols and other reactive entities) were incorporated into all three organic soil components, albeit in somewhat different proportions.

STORAGE STABILITY
Soil extracts were profiled by HPLC within 9 days of obtaining the extract. Subsequent 2D-TLC (for confirming test material and 4-chloro-2-methylphenol) and LC (electrospray) MS (for-confirming the test material) analyses were conducted approximately 2 and 1.3 months after extraction, respectively. For LC-MS analysis, a reanalysis of the Day 30 irradiated replicate showed essentially the same chromatographic profile as observed earlier, thereby confirming stability during storage. For 2D-TLC analysis, the quantitative contribution of the test material and 4-chloro-2-methyl phenol (90.2 and 3.5 %) was comparable to contributions provided by the original HPLC-RAM analysis (92.7 and 4.56 % for the test material and 4-chloro-2-methylphenol, respectively). Samples were stored in the freezer at less than -10 °C.

Summary of the Distribution of Radioactive Residues (as % of Applied) During the 30-day Photolysis Study (Material Balance Summary).

Sampling Interval	Sample Description	% Extractable	% Bound Residues	% Volatiles (Cumulative)	Total Material Balance (% of Applied)
Day 0	Replicate A	91.4	0.93	NA	92.3
Day 0	Replicate B	94.2	1.10	NA	95.3
Day 5	Light replicate A	84.8	9.72	0.87	95.4
Day 5	Light replicate B	85.3	8.81	0.87	95.0
Day 5	Dark replicate A	92.4	2.21	0.05	94.7
Day 5	Dark replicate B	92.5	20.4	0.05	94.6
Day 11	Light replicate A	73.4	16.9	1.43	91.7
Day 11	Light replicate B	79.5	13.0	1.43	93.9
Day 11	Dark replicate A	90.9	4.09	0.071	95.1
Day 11	Dark replicate B	94.3	3.39	0.071	97.8
Day 15	Light replicate A	74.7	12.2	1.84	88.8
Day 15	Light replicate B	71.9	15.0	1.84	88.7
Day 15	Dark replicate A	91.6	3.05	0.0813	94.7
Day 15	Dark replicate B	90.0	3.18	0.0813	93.3
Day 22	Light replicate A	76.9	14.4	2.55	93.8
Day 22	Light replicate B	76.1	15.1	2.55	93.7
Day 22	Dark replicate A	95.8	4.33	0.0893	100
Day 22	Dark replicate B	93.0	3.81	0.0893	96.9
Day 30	Light replicate A	70.9	16.8	2.55	90.2
Day 30	Light replicate B	77.7	13.0	2.55	93.2
Day 30	Dark replicate A	97.0	3.05	0.913	101
Day 30	Dark replicate B	94.7	2.99	0.913	98.6

NA- Not applicable; volatile traps not measured on Day 0. Aeration started on Day 0.

Calculations were performed using actual unrounded analytical data, not the rounded values presented in this table. Minor discrepancies may be attributed to rounding.

 

Summary of Degradate Quantitation During 30-Day Study (Based on HPLC-RAM).

Sampling Interval	Condition	% of Applied in Soil Extract	% Unknown #1*	% Unknown #1**	% CMP†	% CMP‡
Day 0	NA	91.4	ND	ND	ND	ND
Day 0	NA	94.2	ND	ND	ND	ND
Day 5	Light	84.8	ND	ND	2.14	1.81
Day 5	Light	85.3	ND	ND	2.93	2.50
Day 5	Dark	92.4	ND	ND	ND	ND
Day 5	Dark	92.5	ND	ND	ND	ND
Day 11	Light	73.4	ND	ND	2.38	1.75
Day 11	Light	79.5	ND	ND	2.43	1.93
Day 11	Dark	90.9	ND	ND	ND	ND
Day 11	Dark	94.3	ND	ND	ND	ND
Day 15	Light	74.7	ND	ND	3.48	2.60
Day 15	Light	71.9	ND	ND	2.45	1.76
Day 15	Dark	91.6	ND	ND	ND	ND
Day 15	Dark	90	ND	ND	ND	ND
Day 22	Light	76.9	ND	ND	2.4	1.85
Day 22	Light	76.1	ND	ND	3.01	2.29
Day 22	Dark	95.8	ND	ND	ND	ND
Day 22	Dark	93	ND	ND	ND	ND
Day 30	Light	70.9	1.45	1.03	4.56	3.23
Day 30	Light	77.7	< 1	< 1	3.35	2.60
Day 30	Dark	97	ND	ND	ND	ND
Day 30	Dark	94.7	ND	ND	ND	ND

ND - Not detected

CMP - 4-Chloro-2-methylphenol

* Percent of HPLC; retention time 3.60 minutes

** Percent of applied; retention time 3.60 minutes

† Percent of HPLC; retention time 37.30 - 37.90 minutes

‡ Percent of applied; retention time 37.30 - 37.90 minutes

 

Summary of Degradate Quantitation During 30 -Day Study (Based on HPLC-RAM) Continued.

Sampling Interval	Condition	% of Applied in Soil Extract	% Test Material*	% Test material **	% Unknown#2†	% Unknown #2‡
Day 0	NA	91.4	100	91.4	ND	ND
Day 0	NA	94.2	100	94.2	ND	ND
Day 5	Light	84.8	97.9	83.0	ND	ND
Day 5	Light	85.3	97.1	82.8	ND	ND
Day 5	Dark	92.4	100	92.4	ND	ND
Day 5	Dark	92.5	100	92.5	ND	ND
Day 11	Light	73.4	97.6	71.7	ND	ND
Day 11	Light	79.5	97.6	77.6	ND	ND
Day 11	Dark	90.9	100	90.9	ND	ND
Day 11	Dark	94.3	100	94.3	ND	ND
Day 15	Light	74.7	96.5	72.1	ND	ND
Day 15	Light	71.9	97.6	70.1	ND	ND
Day 15	Dark	91.6	100	91.6	ND	ND
Day 15	Dark	90	100	90.0	ND	ND
Day 22	Light	76.9	96.8	74.4	< 1	< 1
Day 22	Light	76.1	96.2	73.2	< 1	< 1
Day 22	Dark	95.8	100	95.8	ND	ND
Day 22	Dark	93	100	93.0	ND	ND
Day 30	Light	70.9	92.7	65.7	1.30	ND
Day 30	Light	77.7	94.4	73.3	1.66	ND
Day 30	Dark	97	100	97.0	ND	ND
Day 30	Dark	94.7	100	94.7	ND	ND

ND - Not detected

* Percent of HPLC; retention time 39.00 - 39.70 minutes

** Percent of applied; retention time 39.00 - 39.70 minutes

† Percent of HPLC; retention time 43.70 - 43.90 minutes

‡ Percent of applied; retention time 43.70 - 43.90 minutes

Validity criteria fulfilled:

not specified

Conclusions:

Test material applied to the surface of a thin layer of a sandy loam soil (at a concentration of 1.26 ppm approximating 2.4 lbs a.i./acre, the maximum seasonal application rate) was found to slowly photolyse under an artificial light source (xenon-arc radiation) with a calculated first-order half-life of 79.9 days. The test material in the same soil, in the absence of radiation, showed no apparent degradation in the definitive study. The artificial light source had a spectral profile similar to natural sunlight. The total intensity of the artificial light source was approximately 20 % of natural sunlight in early August in Wareham, Massachusetts, making it a reasonable model for simulating light. However, since the artifical light source was approximately 1/5 of natural sunlight, the environmentally relevant half-life of the test material in soil is estimated at 16 days.
In irradiated samples throughout the study, most of the extractable radioactivity corresponded to the test material. Its identity was confirmed by its HPLC retention time as compared to the authentic reference standard, as well as its Rf values in 2D-TLC and its LC-(electrospray) mass spectrum. A photodegradate accounting for an average of 2.92 % of the applied radioactivity in the Day 30 irradiated soil replicate samples was initially identified as 4-chloro-2-methyl phenol by HPLC profiling (when compared to the authentic reference standard) and later confirmed by 2D-TLC.
Based on the results of this study, the test material is expected to pholyse on the uppermost surface of soils.

Executive summary:

A soil photolysis study of 14C-[UL-phenyl]-test material was conducted according to a general protocol following U.S. EPA (FIFRA) Pesticide Assessment Guidelines, Subdivision N Chemistry: Environmental Fate § 161-3 and in compliance with GLP. Its objective was to establish the significance of soil surface photolysis under simulated sunlight (xenon arc) as a route of degradation and to identify and quantify any significant degradates formed.

The artificial light source was a modified Heraeus Suntest Accelerated Exposure Unit, utilising xenon radiation. The spectral profile of the simulated sunlight was compared to the spectral profile of natural sunlight during August, 1995. Outside measurements were taken adjacent to the laboratory which is located at 42 ° North latitude. Over the wavelength range of 250 to 700 nm, the spectral profile of the simulated sunlight source (fitted with an additional glass filter that limited transmission of UV radiation to wavelengths greater than 300 nm) was similar to the spectral profile of natural sunlight. Total intensity measurements over the same wavelength range indicated that the simulated sunlight source represented about 20 % of the total intensity of sunlight. Thus, the simulated sunlight source (xenon arc) was considered to be an acceptable model for natural sunlight.

A 7-day preliminary study was conducted to obtain an estimate of the photolytic half-life of [14C]-test material and thereby establish appropriate sampling intervals for the definitive study. First-order half-lives were calculated to be 23.1 days (r^2 = 0.916) and 13.9 days (r^2 = 0.970) in irradiated and dark control samples, respectively. Based on the results of the preliminary study, the definitive study was conducted over a 30-day exposure period with sampling intervals on Days 0, 5, 11, 15, 22 and 30.

The sandy loam soil used in this study was shown to be microbially viable, based on standard plate counts. Quantitation of colony forming units/gram of soil was determined prior to and following the definitive study. Enumeration was essentially constant and of a magnitude which was consistent with other soil photolysis and soil metabolism studies performed by the Test Facility.

In the definitive study, the first-order half-life of test material was calculated to be 79.9 days (r^2 = 0.699) in irradiated samples. Since the artificial light source represented approximately 20 % of natural sunlight, the environmentally relevant half-life of test material on soil was estimated to be 16 days. Degradation was not apparent in the absence of light. This was most likely because of the minimal retention of soil moisture in both irradiated and dark control samples, in spite of initially providing moisture at 75 % of field moisture capacity and continuously aerating samples with hydrated air. That is, the thin soil layer (1.5 mm) with a large surface area within the petri dish rapidly lost associated water through evaporation in spite of efforts to maintain a moisture level optimal for microbial processes. However, since both irradiated and dark control samples were kept under essentially identical conditions, the difference in half-lives was thought to be influenced only by the effect of the artificial light source. Furthermore, the experimental set-up relating to soil moisture was modeled directly after the most recent guidance on this subject, provided in the EPA) Pesticide Reregistration Rejection Rate Analysis - Environmental Fate (U.S. EPA, 1993).

Material balances at sampling intervals throughout the 30-day definitive study ranged from 88.7 to 95.4 % and from 93.3 to 101 % of applied radioactivity in the irradiated and dark control samples, respectively.

Radioactive residues identified in soil extracts included test material (in irradiated and dark control samples) and 4-chloro-2-methylphenol (maximum of 3.2 % of applied radioactivity, and only detected in irradiated samples). The identity of test material was accomplished by comparing its chromatographic (HPLC, 2D-TLC) and mass spectral (LC-[electrospray] MS) properties to the test material reference standard (identical in chromatography and mass spectral properties to test material under conditions employed in this study). The identity of 4-chloro-2-methylphenol was accomplished by comparing its chromatographic (HPLC, 2D-TLC) properties to the authentic reference standard.

During the 30-day study, there was a steady decrease in extractable residues in the irradiated samples, from an average of 92.8 to 74.3 % of the applied radioactivity. Concomitantly, there was a steady increase in non-extractable (bound) residues in the irradiated samples, reaching a maximum average of 14.9 % of applied radioactivity by Day 30. In contrast, extractable radioactivity from the dark controls remained essentially constant, between 90.0 and 97.0 %, throughout the 30-day incubation with no more than 4.3 % of applied radioactivity associated with the soil after extraction. For both irradiated and dark control samples, production of volatiles was measurable, albeit minimal, and totaled 2.55 and 0.912 % of applied radioactivity, respectively, after 30 days of incubation.

Based on identification of radioactive residues in soil extracts, as well as quantifying volatiles and soil-bound residues, a postulated photolytic pathway of test material suggests a slow degradation to 4-chloro-2-methylphenol followed by binding of the phenol(s) to soil with slow microbially mediated turnover (mineralisation) to carbon dioxide.

Reference 2

Endpoint:

phototransformation in soil

Type of information:

other: Re-analysis of study data according to the latest guidelines.

Adequacy of study:

supporting study

Study period:

not applicable

Reliability:

4 (not assignable)

Rationale for reliability incl. deficiencies:

secondary literature

Reason / purpose for cross-reference:

reference to same study

Reason / purpose for cross-reference:

reference to same study

Reason / purpose for cross-reference:

reference to same study

Qualifier:

no guideline followed

Principles of method if other than guideline:

The report considers three degradation kinetics studies. The first is the degradation of the test material and metabolites in four aerobic soils (Schocken 1997), the second is the degradation of the test material and metabolites due to photolysis in soil (Connor 1996a) and the third is the degradation of the test material and its metabolites due to photolysis in water (Connor 1996b).
This study summary specifically relates to the degradation kinetics study to re-assess the degradation of the test material and metabolites due to photolysis in soil, as reported in Connor (1996a), using FOCUS (2006, 2014). SFO kinetics were used in the first instance (most appropriate for use in environmental fate modelling), with FOMC and DFOP used to determine trigger values for additional studies where biphasic kinetics were observed. CAKE 3.1 was used to perform the kinetics fitting procedure, with the OLS optimiser. The IRLS optimiser was used where confidence limits with the initial OLS fit were unreliable (predominantly for metabolites).

GLP compliance:

no

Remarks:

Summary of data

DT50:

14.8 d

Test condition:

DT50 as a trigger for further studies (d)

DT50:

14.8 d

Test condition:

DT50 for modelling (d)

Transformation products:

yes

Remarks:

PCOC ( 4-chloro-o-cresol)

No.:

#1

Kinetics Fitting to the Test Material and Metabolite PCOC Due to Photolysis in Soil

- Test Material Degradation Kinetics Via Soil Photolysis

SFO provided a reasonable visual fit to the data, though there was a slight ‘wave’ to the residuals, whilst the statistical tests were passed for both the degradation constant and the X-error value. FOMC provided a good visual fit to the data, however the confidence interval for β did include zero. The SFO fit is accepted as providing a reliable fit to the degradation of the test material in this soil via photolysis and DFOP kinetics were not performed as this was unnecessary.

The artificial light used in this study was recorded as approximately the same as that expected naturally at 42°N latitude in the autumn but 20 % of that expected naturally during the summer. Therefore, the DT50 values produced from this analysis were corrected with a factor of 0.2 to make these laboratory values more applicable to field conditions in the summer.

- Kinetic model for modelling and trigger values is SFO

- Uncorrected values (applicable to the autumn):

o DT50 for use as trigger value 73.8 days

o DT90 for use as trigger value 245 days

o DT50 for use in modelling 73.8 days

- Corrected values (for full intensity of natural light in the summer):

o DT50 for use as trigger value 14.8 days

o DT90 for use as trigger value 49.0 days

o DT50 for use in modelling 14.8 days

- PCOC Degradation Kinetics Via Soil Photolysis

The OLS had difficulty in securing confidence limits for kinetics fitting to this soil data-set and therefore the IRLS optimiser was used as a refinement.

SFO + SFO kinetics for both parent and metabolite provided reasonable visual fits for the metabolite, though the final time-point is under-estimated. The t-test passed on the metabolite degradation constant and the confidence limits of ffM did not include zero. The X-error for the metabolite was 16.3 % (in exceedance of the 15 % recommended by FOCUS 2006, 2014), though this can be considered acceptable given the reasonable visual fit. FOMC + SFO kinetics for the parent and metabolite respectively once again provided a good visual fit for the metabolite and the confidence limits of ffM did not include zero, however the t-test failed for the metabolite degradation constant and the confidence limits of β did include zero. Therefore, the SFO + SFO kinetics fit can be considered to provide reliable values for the formation and degradation of the PCOC metabolite via photolysis in soil.

The artificial light used in this study was recorded as approximately the same as that expected naturally at 42°N latitude in the autumn but 20% of that expected naturally in the summer. Therefore, the DT50 values produced from this analysis were corrected with a factor of 0.2 to make these laboratory values more applicable to field conditions in the summer.

- Kinetic model for modelling and trigger values is SFO + SFO

- Uncorrected values (applicable in the autumn):

o DT50 for use as trigger value is 3.1 days

o DT90 for use as trigger value is 10.4 days

o DT50 for use in modelling is 3.1 days

o ffM for use in modelling is 0.775

- Corrected values (for full intensity of natural light in the summer):

o DT50 for use as trigger value is 0.6 days

o DT90 for use as trigger value is 2.1 days

o DT50 for use in modelling is 0.6 days

o ffM for use in modelling is 0.775

The calculated values for the test material and the metabolite PCOC for degradation via photolysis in soil are presented below.

Summary of Fitted Parameters for the Decline of the Test Material and the Production and Decline of PCOC for Degradation Via Photolysis Both Soil.

Compound	Kinetic Model	Fitted Parameters	Soil Photolysis
Test material	SFO	M0(%)	87.8
		k1(d^-1)	0.009
	FOMC	M0(%)	92.96
		α	0.102
		β	1.786
	DFOP		Not required
PCOC	SFO + SFO	M0(%)	87.35
		k1(d^-1)	0.009
		km(d^-1)	0.221
		ffM	0.775
	FOMC + SFO	M0(%)	93.48
		α	0.081
		β	0.858
		km(d^-1)	0.005
		ffM	0.122
	FOMC + DFOP		Not required

The most appropriate optimisations for risk assessment (either trigger values for further studies, modelling end-points or both) are highlighted in bold.

Taken as a whole, this sequence of data-sets is useful for the calculation of the appropriate kinetic parameters for the test material and its metabolite PCOC in soil due to photolysis. Kinetics for the parent test material could be fitted to the data-set, providing reliable kinetics parameters. Reliable kinetic parameters for the PCOC metabolite could be fitted in the soil photolysis study.

A summary of the key parameters for the test material and PCOC following photolysis in soil are shown below. The (corrected) soil photolysis DT50 for the test material of 14.8 days is rather shorter than the 50 days in the peer review (EC 2003). However, this is likely a difference in the reference light intensity used for the EU when correcting the uncorrected value of 73.8 days (which is applicable to autumn conditions). The (corrected) soil photolysis DT50 for PCOC of 0.6 days is not directly comparable to a value presented in the peer review (UNEP 1998). Whilst supported by the statistics and visual assessment of the kinetics fit, the use of this end-point should be considered with care to ensure the appropriate correction factor has been used. The formation factor of 77.5 % is far higher than that expected from discussion in the peer review (UNEP 1998). This may be a result of the relatively low degradation rate of the parent in the study where there was still around 70 % of the parent left at the end of the study.

Summary of Fitting Parameters for the Decline of the Test Material and PCOC Following Photolysis in Soil

Endpoint	Test  Material	PCOC
Temperature correction	-	-
Light intensity correction (for summer conditions)	0.2	0.2
Kinetic model for use to trigger studies	SFO	SFO + SFO
DT50 trigger (uncorrected) (days)	73.8	3.1
DT90 trigger (uncorrected) (days)	245	10.4
DT50 trigger (corrected) (days)	14.8	0.6
DT90 trigger (corrected) (days)	49	2.1
Kinetic model for use in modelling	SFO	SFO + SFO
DT50 modelling (uncorrected) (days)	73.9	3.1
DT50 modelling (corrected) (days)	14.8	0.6
Formation Fraction	-	0.775

 

Kinetics were fitted to both the test material and PCOC data from a soil photolysis study. SFO kinetics fitted the data for all of the data-sets well. The critical degradation end-points for these substances were as follows:

Test material:

- DT50 as a trigger for further studies (d): 14.8

- DT90 as a trigger for further studies (d): 49.0

- DT50 for modelling (d): 14.8

PCOC:

- DT50 as a trigger for further studies (d): 0.6

- DT90 as a trigger for further studies (d): 2.1

- DT50 for modelling (d): 0.6

- Formation fraction (%): 77.5

Validity criteria fulfilled:

not applicable

Conclusions:

Kinetics were fitted to both the test material and PCOC data from a soil photolysis study. SFO kinetics fitted the data for all of the data-sets well. The critical degradation end-points for these substances were as follows:
Test material:
- DT50 as a trigger for further studies (d): 14.8
- DT90 as a trigger for further studies (d): 49.0
- DT50 for modelling (d): 14.8
PCOC:
- DT50 as a trigger for further studies (d): 0.6
- DT90 as a trigger for further studies (d): 2.1
- DT50 for modelling (d): 0.6
- Formation fraction (%): 77.5

Executive summary:

This study summary specifically relates to the degradation kinetics study to re-assess the degradation of the test material and metabolites due to photolysis in soil, as reported in Connor (1996a), using FOCUS (2006, 2014). SFO kinetics were used in the first instance (most appropriate for use in environmental fate modelling), with FOMC and DFOP used to determine trigger values for additional studies where biphasic kinetics were observed. CAKE 3.1 was used to perform the kinetics fitting procedure, with the OLS optimiser. The IRLS optimiser was used where confidence limits with the initial OLS fit were unreliable (predominantly for metabolites).

Kinetics were fitted to both the test material and PCOC data from a soil photolysis study. SFO kinetics fitted the data for all of the data-sets well. The critical degradation end-points for these substances were as follows:

Test material:

- DT50 as a trigger for further studies (d): 14.8

- DT90 as a trigger for further studies (d): 49.0

- DT50 for modelling (d): 14.8

PCOC:

- DT50 as a trigger for further studies (d): 0.6

- DT90 as a trigger for further studies (d): 2.1

- DT50 for modelling (d): 0.6

- Formation fraction (%): 77.5

Description of key information

Connor (1996a)

Test material applied to the surface of a thin layer of a sandy loam soil (at a concentration of 1.26 ppm approximating 2.4 lbs a.i./acre, the maximum seasonal application rate) was found to slowly photolyse under an artificial light source (xenon-arc radiation) with a calculated first-order half-life of 79.9 days. The test material in the same soil, in the absence of radiation, showed no apparent degradation in the definitive study. The artificial light source had a spectral profile similar to natural sunlight. The total intensity of the artificial light source was approximately 20 % of natural sunlight in early August in Wareham, Massachusetts, making it a reasonable model for simulating light. However, since the artifical light source was approximately 1/5 of natural sunlight, the environmentally relevant half-life of the test material in soil is estimated at 16 days.

In irradiated samples throughout the study, most of the extractable radioactivity corresponded to the test material. Its identity was confirmed by its HPLC retention time as compared to the authentic reference standard, as well as its Rf values in 2D-TLC and its LC-(electrospray) mass spectrum. A photodegradate accounting for an average of 2.92 % of the applied radioactivity in the Day 30 irradiated soil replicate samples was initially identified as 4-chloro-2-methyl phenol by HPLC profiling (when compared to the authentic reference standard) and later confirmed by 2D-TLC.

Based on the results of this study, the test material is expected to pholyse on the uppermost surface of soils.

Supporting Study: Hazlerigg & Garrett (2015)

Kinetics were fitted to both the test material and PCOC data from a soil photolysis study. SFO kinetics fitted the data for all of the data-sets well. The critical degradation end-points for these substances were as follows:

Test material:

- DT50 as a trigger for further studies (d): 14.8

- DT90 as a trigger for further studies (d): 49.0

- DT50 for modelling (d): 14.8

PCOC:

- DT50 as a trigger for further studies (d): 0.6

- DT90 as a trigger for further studies (d): 2.1

- DT50 for modelling (d): 0.6

- Formation fraction (%): 77.5

Additional information

Connor (1996a)

A soil photolysis study of 14C-[UL-phenyl]-test material was conducted according to a general protocol following U.S. EPA (FIFRA) Pesticide Assessment Guidelines, Subdivision N Chemistry: Environmental Fate § 161-3 and in compliance with GLP. Its objective was to establish the significance of soil surface photolysis under simulated sunlight (xenon arc) as a route of degradation and to identify and quantify any significant degradates formed. The study was awarded a reliability score of 2 in accordance with the criteria set forth by Klimisch et al. (1997).

The artificial light source was a modified Heraeus Suntest Accelerated Exposure Unit, utilising xenon radiation. The spectral profile of the simulated sunlight was compared to the spectral profile of natural sunlight during August, 1995. Outside measurements were taken adjacent to the laboratory which is located at 42 ° North latitude. Over the wavelength range of 250 to 700 nm, the spectral profile of the simulated sunlight source (fitted with an additional glass filter that limited transmission of UV radiation to wavelengths greater than 300 nm) was similar to the spectral profile of natural sunlight. Total intensity measurements over the same wavelength range indicated that the simulated sunlight source represented about 20 % of the total intensity of sunlight.Thus, the simulated sunlight source (xenon arc) was considered to be an acceptable model for natural sunlight.

A 7-day preliminary study was conducted to obtain an estimate of the photolytic half-life of [14C]-test material and thereby establish appropriate sampling intervals for the definitive study. First-order half-lives were calculated to be 23.1 days (r^2 = 0.916) and 13.9 days (r^2 = 0.970) in irradiated and dark control samples, respectively. Based on the results of the preliminary study, the definitive study was conducted over a 30-day exposure period with sampling intervals on Days 0, 5, 11, 15, 22 and 30.

The sandy loam soil used in this study was shown to be microbially viable, based on standard plate counts. Quantitation of colony forming units/gram of soil was determined prior to and following the definitive study. Enumeration was essentially constant and of a magnitude which was consistent with other soil photolysis and soil metabolism studies performed by the Test Facility.

In the definitive study, the first-order half-life of test material was calculated to be 79.9 days (r^2 = 0.699) in irradiated samples. Since the artificial light source represented approximately 20 % of natural sunlight, the environmentally relevant half-life of test material on soil was estimated to be 16 days. Degradation was not apparent in the absence of light. This was most likely because of the minimal retention of soil moisture in both irradiated and dark control samples, in spite of initially providing moisture at 75 % of field moisture capacity and continuously aerating samples with hydrated air. That is, the thin soil layer (1.5 mm) with a large surface area within the petri dish rapidly lost associated water through evaporation in spite of efforts to maintain a moisture level optimal for microbial processes. However, since both irradiated and dark control samples were kept under essentially identical conditions, the difference in half-lives was thought to be influenced only by the effect of the artificial light source. Furthermore, the experimental set-up relating to soil moisture was modeled directly after the most recent guidance on this subject, provided in the EPA) Pesticide Reregistration Rejection Rate Analysis - Environmental Fate (U.S. EPA, 1993).

Material balances at sampling intervals throughout the 30-day definitive study ranged from 88.7 to 95.4 % and from 93.3 to 101 % of applied radioactivity in the irradiated and dark control samples, respectively.

Radioactive residues identified in soil extracts included test material (in irradiated and dark control samples) and 4-chloro-2-methylphenol (maximum of 3.2 % of applied radioactivity, and only detected in irradiated samples). The identity of test material was accomplished by comparing its chromatographic (HPLC, 2D-TLC) and mass spectral (LC-[electrospray] MS) properties to the test material reference standard (identical in chromatography and mass spectral properties to test material under conditions employed in this study). The identity of 4-chloro-2-methylphenol was accomplished by comparing its chromatographic (HPLC, 2D-TLC) properties to the authentic reference standard.

During the 30-day study, there was a steady decrease in extractable residues in the irradiated samples, from an average of 92.8 to 74.3 % of the applied radioactivity. Concomitantly, there was a steady increase in non-extractable (bound) residues in the irradiated samples, reaching a maximum average of 14.9 % of applied radioactivity by Day 30. In contrast, extractable radioactivity from the dark controls remained essentially constant, between 90.0 and 97.0 %, throughout the 30-day incubation with no more than 4.3 % of applied radioactivity associated with the soil after extraction. For both irradiated and dark control samples, production of volatiles was measurable, albeit minimal, and totaled 2.55 and 0.912 % of applied radioactivity, respectively, after 30 days of incubation.

Based on identification of radioactive residues in soil extracts, as well as quantifying volatiles and soil-bound residues, a postulated photolytic pathway of test material suggests a slow degradation to 4-chloro-2-methylphenol followed by binding of the phenol(s) to soil with slow microbially mediated turnover (mineralisation) to carbon dioxide.

Supporting Study: Hazlerigg & Garrett (2015)

This study summary specifically relates to the degradation kinetics study to re-assess the degradation of the test material and metabolites due to photolysis in soil, as reported in Connor (1996a), using FOCUS (2006, 2014). SFO kinetics were used in the first instance (most appropriate for use in environmental fate modelling), with FOMC and DFOP used to determine trigger values for additional studies where biphasic kinetics were observed. CAKE 3.1 was used to perform the kinetics fitting procedure, with the OLS optimiser. The IRLS optimiser was used where confidence limits with the initial OLS fit were unreliable (predominantly for metabolites). The study was awarded a reliability score of 4 in accordance with the criteria set forth by Klimisch et al. (1997).

Kinetics were fitted to both the test material and PCOC data from a soil photolysis study. SFO kinetics fitted the data for all of the data-sets well. The critical degradation end-points for these substances were as follows:

Test material:

- DT50 as a trigger for further studies (d): 14.8

- DT90 as a trigger for further studies (d): 49.0

- DT50 for modelling (d): 14.8

PCOC:

- DT50 as a trigger for further studies (d): 0.6

- DT90 as a trigger for further studies (d): 2.1

- DT50 for modelling (d): 0.6

- Formation fraction (%): 77.5