2-Pyridinecarboxylic acid, 4-amino-3,6-dichloro-

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:

6 October 2003 to 18 December 2003

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)

Deviations:

no

GLP compliance:

yes

Specific details on test material used for the study:

Purity: 99.9%

Radiolabelling:

yes

Analytical monitoring:

yes

Analytical method:

high-performance liquid chromatography

Details on sampling:

- Sampling intervals of soil samples: 0, 2, 7, 14, 26, 35 and 44 DAT, equivalent to 0, 1, 5, 9, 17, 23 and 28 days of summer sunlight at 40° N latitude
- Sampling method: Transfer soil from flask to centrifuge tube (dark controls already in tubes for extraction) Extract 3 times with 5 mL 90:10 Acetone:1.0 N HCl. Analyse aliquots by LSC and HPLC.
- Sampling method for CO2 and volatile organics: Separate silica gel and ascarite. Extract ascarite with water. Analyse aliquots by LSC.
- Sterility check, if any: not applicable
- Measurement of moisture content: 21, 35 DAT-irradiated samples only.
- Sample storage conditions before analysis: Sample extracts were analysed by LSC on the day of sacrifice. Organic extracts analysed by HPLC, initially, within one week of sacrifice. Actinometers, concentrated soil extracts, and ascarite trap extracts were stored refrigerated. Organic soil extracts were stored in freezer.

Details on soil:

COLLECTION AND STORAGE
This soil was selected as representative of pasture land regions of North America and Europe.
- Geographic location: Germany
- Collection procedures: Soils were collected following ISO 10381-6, Soil quality-Sampling.

PROPERTIES
- Soil texture: Silt loam
- % sand: 28
- % silt: 58
- % clay: 14
- pH: 7.7
- Organic matter (%)
- Organic carbon (%): 1.0
- CEC (meq/100 g): 8.1
- Water holding capacity: 19.9 % at 0.33 bar; 7.1 % at 15 bar
- Bulk density, disturbed (g/cm3): 1.18
- Initial soil biomass (µg/g): 40.6

PREPARATION OF SOIL
Prior to use, the moisture content of the soil was determined using a Denver IR Moisture Analyser. The moisture data were then used to calculate the amount of fresh soil required per biometer flask for 2.5 g dry weight of soil and the amount of water needed to achieve 75 % of 1/3 bar moisture.

Light source:

Xenon lamp

Details on light source:

Samples were irradiated using a 6500 W xenon arc lamp with an inner borosilicate filter and an outer Soda Lime filter (Atlas Electric Devices Company, Chicago, IL) in a temperature-controlled room. The wavelength distribution of the xenon lamp is similar to natural sunlight, making xenon a viable alternative to using sunlight in a photolysis study. The wavelength distribution of the lamp was determined prior to and after the study using an OL-754 spectroradiometer (Optronic Laboratories, Orlando, FL).
A chemical actinometer was used to determine the overall light intensity of the xenon lamp and to compare the light-energy emitted by the lamp with sunlight. An actinometer is a chemical that has a known quantum yield (ϕ), independent of wavelength. The actinometer used in conjunction with this study was p-nitroacetophenone (PNAP) and pyridine (pyr) in HPLC-grade water.

Details on test conditions:

TEST SYSTEM
- Type, material and volume of test apparatus: Quartz boiling flasks with a flat bottom (11.4 cm² surface area) were used for the irradiated samples. Amber-coloured Pyrex glass vials were used for the dark control samples.
- Experimental set-up: For the irradiated samples, approximately 2.5 g (oven dry basis) of soil was measured into flattened round-bottomed quartz flasks. Deionised water was added to the irradiated samples to adjust soil moisture to 75% of 1/3-bar moisture. Ascarite traps were connected to the flasks and the connection sealed with parafilm. The moist soil was maintained on the 12 hour light/dark cycle to simulate solar irradiation. The soil temperature was stabilised at 25 °C.
The experimental set-up was the same for the dark control samples except amber-coloured Pyrex glass vials with Teflon-lined screw caps were used as containers and the soil moisture was not adjusted. Dark controls were placed in a darkened incubator set at 25 °C.
- Details of traps for volatile, if any: The irradiated sample flasks were equipped with a trap containing a layer of 80:20 Silica Gel Grade 35, 12-42 mesh and a layer of glass wool, followed by Ascarite II, 20-30 mesh. The silica gel acted as a moisture barrier to prevent excess water vapour from reaching the ascarite layer, a CO₂ trap. The tops of the traps were covered with parafilm. The traps were then wrapped in aluminium foil to keep light exposure of the trapping material to a minimum.

PREPARATION AND APPLICATION OF TEST MATERIAL
- Preparation of Application Solutions
A stock solution was prepared by diluting test material in 2 mL of acetonitrile/methanol (1: 1). The stock solution was stored in a freezer when not in use.
The dosing solution was prepared prior to the day of sample treatment. The radiolabelled stock solution in acetonitrile/methanol (1/1) was removed from the freezer and allowed to warm to room temperature. The dosing solution was prepared by removing 1.50 mL and transferring to a 2-mL volumetric flask. The organic solvent was evaporated by gently blowing a stream of nitrogen on the liquid. HPLC-grade water was added to bring the solution to 2.0 mL volume. The solution was mixed by inverting the flask repeatedly. The final concentration of the dosing solution was 468 µg/mL, a.i. The radiochemical purity of the test material dosing solution was determined prior to sample treatment and again later in the study by HPLC.

- Application Procedures
Dosing solution (28 µL) was applied to each sample for a soil concentration of 5.24 µg/g a.i. A total of 13.1 µg was added to each sample flask. The dosing solution was applied with a positive displacement pipette uniformly over the soil surface.
The homogeneity and application rate of the test material dosing solution were determined by taking aliquots of the dosing solution periodically during treatment. These direct spikes were assayed by LSC.

- Evaporation Procedures
As the dosing solution was applied in water, no evaporation step was necessary.

REPLICATION
- No. of replicates (dark): 16
- No. of replicates (irradiated): 16

MAINTENANCE OF TEST CONDITIONS SPECIFIED UNDER "DURATION"
- Temperature maintenance method: The irradiated samples were placed under the xenon lamp in a temperature-controlled water bath in a temperature-controlled room. A thermocouple probe was submerged in untreated soil in a quartz flask. A circulating water bath attached to the probe was used to adjust the temperature of the soil. The probe was set to keep the soil temperature at 25 °C. The soil temperature was checked each work day. The entire system was maintained in a temperature-controlled room, also set at 25 °C. The lamp room temperature was monitored by the Camille alarm system that notified the Temperature Monitoring Coordinator when the lamp room temperature fell out of range for more than 1 hour.
The dark control samples were incubated in the dark in an incubator set at 25 °C. Incubator temperatures were monitored with the Camille temperature-monitoring system. The Temperature Monitoring Coordinator was alerted if any temperature controlled devices were out of the acceptable range for more than 1 hour.
- Moisture maintenance method: The soil moisture of the irradiated samples was adjusted to and maintained at approximately 75 % of 1/3 bar. Periodically the moisture lost from the flask was determined (gravimetrically) and HPLC grade water was added, when necessary, to return the test system to initial weight. Soil moisture content was checked for the light exposed samples at 22 and 35 DAT. Soil moisture throughout the study was adequate to maintain biological activity.
The soil moisture of dark control samples was not monitored nor adjusted during the study.

Duration:

28 d

Temp.:

25 °C

Reference substance:

yes

Remarks:

p-Nitroacetophenone (PNAP)pyridine (pyr)

Key result

DT50:

61 d

Transformation products:

no

Physical Conditions

Daily average temperatures were recorded for the lamp room and incubator chamber for the study. The soil temperatures were also manually recorded. The lamp was checked each work day to ensure it was following the correct on/off cycle. The actinometry data indicate that 1 DAT of exposure to the xenon lamp was equivalent to 0.65 days in the summer sun at 40° N latitude. Therefore, the sample exposure time of 2, 7, 14, 26, 35, and 44 DAT were converted to 1, 5, 9, 17, 23, and 28 days in the summer sun at 40° N latitude. These converted sampling times were used in the kinetics calculations for the irradiated samples.

Analytical Methodology

Verification of Extraction Procedures

The efficiency of the extraction procedure was shown by the organic extraction results on 0 day. Since 100 % of the applied radioactivity was extractable, the extraction method was determined to be sufficient.

Verification of Chromatographic Procedures

HPLC column recoveries were determined by directly counting an aliquot of each sample analysed by HPLC and comparing to the sum of the radioactivity eluted from the column. HPLC recoveries were between 90 and 110 %.

Material Balance

The mass balance was 100.1 ± 4.4 % and 93.8 ± 7.3 % in the dark and irradiated samples, respectively. Over time the material balance of the irradiated samples decreased. The test apparatus relied on passive trapping of CO₂ and acid gases in the ascarite traps; therefore, a volatile could have been lost when the sample was opened to adjust the soil moisture. The material balance of the dark control samples remained between 90 and 110 % of applied radiocarbon throughout the study.

Distribution and Compositions of Residues

The distribution of the residues in the irradiated samples shifted during the study. Extractable 14C residues in the soil decreased from 104.7 % at Day 0 to 73.9 % of the applied radioactivity at the end of the irradiation period. Non-extractable 14C residues in the soil increased from 0.6 % at Day 0 to 8.0 % of the applied radioactivity at study termination. At the end of the study 3.3 % of the applied radioactivity was present in the ascarite traps.

The amount of test material extractable from irradiated soil samples decreased from 104.2 % at Day 0 to 69.3 % of the applied radioactivity at study termination. At the end of the study, greater than 90 % of the radioactivity present in the extract was still parent test material. No photodegradates of greater than 3.8 % of applied were observed.

For the dark control soil system, the distribution of the residues remained fairly constant throughout the study. Extractable 14C residues in the soil decreased from 104.7 % at Day 0 to 93.3 % of the applied radioactivity at the end of the incubation period. Non-extractable 14C residues in the soil increased from 0.6 % at Day 0 to 3.8 % of the applied radioactivity at study termination.

For the dark control samples, extractable test material decreased from 104.2 % at Day 0 to 92.4 % of the applied radioactivity at study termination. Only parent test material was observed in the organic extracts.

Test material degraded into non-extractable residues in both the irradiated and dark control samples. Characterisation of these residues from irradiated samples shows that approximately 64 % of the 14C non-extractable residues were associated with the fulvic acid fraction (acid and base soluble). Approximately 14 % and 18 % of the 14C non-extractable residues were associated with the humic acid and humin fractions, respectively.

Identification and Characterisation of Transformation Products

Parent test material accounted for greater than 90 % of the radioactivity present in any HPLC chromatogram of the organic extracts. A small amount of radioactivity (3 % of applied at the end of the irradiation period) was recovered from the ascarite traps. As this pool of radioactivity never reached concentrations greater than 5 % of the applied radiocarbon, no further characterisation was conducted. No degradation products other than NER and volatile materials were observed in this study.

Kinetic Analysis of Data

Kinetics of Parent Compound Degradation

First-order, non-linear rate constants of the test material were calculated to be 0.0130 and 0.0016 days-1 for the irradiated and dark control soils, respectively. The kinetics of test material degradation for the irradiated and dark control samples were found to be non-linear, and first-order. These rate constants were then used to calculate the photolysis rate constant; the k(photolysis) was 0.011 days^-1. The half-life and DT90 values for phototransformation were 61 and 203 days, respectively.

Decline of Metabolites

No metabolites, other than NER and a small amount of volatile material were observed.

Degradation Pathway

The test material photodegraded into non-extractable residue and volatile material in the Parabraun Erde silt loam soil.

Validity criteria fulfilled:

yes

Conclusions:

The photodegradation rate of the test material was 0.011 days-1 with a half-life of 61 days. Only a small amount of volatile material and non-extractable residues were observed as a result of test material photodegradation. In irradiated samples, 3 % of the applied radioactivity was recovered in the ascarite traps by the end of the study period. Up to 8 % of the applied radioactivity was present as NER.
It can therefore be concluded that photodegradation of the test material on soil surfaces occurs at a moderate rate. No unique photo products are formed.

Executive summary:

The phototransformation of the test material on soil was investigated in a study which was conducted under GLP conditions and in accordance with the EPA Pesticide Registration Guidelines, Subdivision N, § 161-3, and SETAC-Europe Procedures for Assessing the Environmental Fate and Ecotoxicity of Pesticides, Section 2.0 guidelines.

During the study the phototransformation of 14C-test material was studied on a silt loam soil (pH 7.7, organic carbon 1.0 %) from Germany at 25 °C and 75 % of 1/3 bar moisture using a xenon lamp as a light source. Samples, fortified at approximately 5.2 mg a.i./kg soil, were irradiated for up to the equivalent of 28 days of summer sunlight at 40 °N latitude.

14C-test material was applied in water on the soil surface by positive displacement pipette. The treated samples were irradiated by intermittent irradiation using a 6500W xenon arc lamp, with an inner borosilicate filter and an outer Soda Lime filter. The intermittent irradiation consisted of a 12 hour irradiation/12 hour dark cycle to imitate regular sunlight patterns. Irradiated test vessels were connected to traps containing ascarite for the collection of CO₂ and acidic volatiles. Dark control samples were maintained in a dark incubator set at 25 °C. Samples were taken at 0, 2, 7, 14, 26, 35, and 44 days after treatment for the determination of the parent compound and transformation products. The soil samples were extracted with 90:10 acetone: 1.0 N HCl and the 14C-test material residues were analysed by HPLC. Extracted, air-dried soil samples were combusted to determine the amount of non-extractable residues. Non-extractable residues were characterised by partitioning into fulvic acid, humic acid, and humin pools. Radioactive material in solution was quantified by a liquid scintillation counter. Radioactive material remaining in the soil pellet after extraction was quantified by oxidative combustion.

A PNAP/pyridine (p-nitroacetophenone/pyridine) chemical actinometer solution was used to quantitate the amount of light that the samples received. Based on the PNAP/pyr actinometer data, 44 DAT of irradiation was equivalent to 28 days of irradiation in the summer sun at 40° N latitude.

The mass balance was 100.1 ± 4.4 % and 93.8 ± 7.3 % in the dark and irradiated samples, respectively. At the test termination, approximately 92 % of the applied 14C remained as the parent test material in the dark samples. No transformation occurred in the dark samples.

In the irradiated samples, concentration of the parent test material decreased from 104.2 % at day 0 to 69.3 % of the applied amount at test termination. Since the degradates formed in the irradiated samples were less than 5 % of applied, they were not conclusively identified. In irradiated samples, at the end of the study, up to 3.3 % of the applied radioactivity was present in the ascarite traps as evolved CO₂ and acid gases.

Extractable 14C residues decreased from 104.7 % of the applied amount at day 0 to 93.3 % and 73.9 % of the applied amount at termination in the dark and irradiated samples, respectively. In the irradiated samples, non-extractable 14C residues increased from 0.6 % of the applied amount at day 0 to 8.0 % of the applied at study termination. Non-extractable residues in the dark samples were 0.6 % of the applied amount at day 0, and 3.8 % of the applied amount at test termination. The test material degraded into non-extractable residues and volatiles.

The degradation rate constants of the test material in the dark and irradiated samples were 0.002 and 0.013 days^-1, respectively. These values result in a k(photolysis) of 0.011 days^-1 , with a DT50 of 61 days and a DT90 value of 203 days.

Description of key information

DT50 = 61 days; DT90 = 203 days (silt loam soil (pH 7.7, organic carbon 1.0 %) from Germany at 25 °C and 75 % of 1/3 bar moisture using a xenon lamp as a light source), EPA Pesticide Registration Guidelines, Subdivision N, § 161-3, and SETAC-Europe Procedures for Assessing the Environmental Fate and Ecotoxicity of Pesticides, Section 2.0 guidelines, Rutherford (2004)

Key value for chemical safety assessment

Half-life in soil:

61 d

Additional information

The phototransformation of the test material on soil was investigated in a study which was conducted under GLP conditions and in accordance with the EPA Pesticide Registration Guidelines, Subdivision N, § 161-3, and SETAC-Europe Procedures for Assessing the Environmental Fate and Ecotoxicity of Pesticides, Section 2.0 guidelines. The study was awarded a reliability score of 1 in accordance with the criteria set forth by Klimisch et al. (1997).

During the study the phototransformation of 14C-test material was studied on a silt loam soil (pH 7.7, organic carbon 1.0 %) from Germany at 25 °C and 75 % of 1/3 bar moisture using a xenon lamp as a light source. Samples, fortified at approximately 5.2 mg a.i./kg soil, were irradiated for up to the equivalent of 28 days of summer sunlight at 40 °N latitude.

14C-test material was applied in water on the soil surface by positive displacement pipette. The treated samples were irradiated by intermittent irradiation using a 6500W xenon arc lamp, with an inner borosilicate filter and an outer Soda Lime filter. The intermittent irradiation consisted of a 12 hour irradiation/12 hour dark cycle to imitate regular sunlight patterns. Irradiated test vessels were connected to traps containing ascarite for the collection of CO₂ and acidic volatiles. Dark control samples were maintained in a dark incubator set at 25 °C. Samples were taken at 0, 2, 7, 14, 26, 35, and 44 days after treatment for the determination of the parent compound and transformation products. The soil samples were extracted with 90:10 acetone: 1.0 N HCl and the 14C-test material residues were analysed by HPLC. Extracted, air-dried soil samples were combusted to determine the amount of non-extractable residues. Non-extractable residues were characterised by partitioning into fulvic acid, humic acid, and humin pools. Radioactive material in solution was quantified by a liquid scintillation counter. Radioactive material remaining in the soil pellet after extraction was quantified by oxidative combustion.

A PNAP/pyridine (p-nitroacetophenone/pyridine) chemical actinometer solution was used to quantitate the amount of light that the samples received. Based on the PNAP/pyr actinometer data, 44 DAT of irradiation was equivalent to 28 days of irradiation in the summer sun at 40° N latitude.

The mass balance was 100.1 ± 4.4 % and 93.8 ± 7.3 % in the dark and irradiated samples, respectively. At the test termination, approximately 92% of the applied 14C remained as the parent test material in the dark samples. No transformation occurred in the dark samples.

In the irradiated samples, concentration of the parent test material decreased from 104.2 % at day 0 to 69.3 % of the applied amount at test termination. Since the degradates formed in the irradiated samples were less than 5 % of applied, they were not conclusively identified. In irradiated samples, at the end of the study, up to 3.3 % of the applied radioactivity was present in the ascarite traps as evolved CO2 and acid gases.

Extractable 14C residues decreased from 104.7 % of the applied amount at day 0 to 93.3 % and 73.9 % of the applied amount at termination in the dark and irradiated samples, respectively. In the irradiated samples, non-extractable 14C residues increased from 0.6 % of the applied amount at day 0 to 8.0 % of the applied at study termination. Non-extractable residues in the dark samples were 0.6 % of the applied amount at day 0, and 3.8 % of the applied amount at test termination. The test material degraded into non-extractable residues and volatiles.

The degradation rate constants of the test material in the dark and irradiated samples were 0.002 and 0.013 days^-1, respectively. These values result in a k(photolysis) of 0.011 days^-1, with a DT50 of 61 days and a DT90 value of 203 days.