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

Phototransformation in water

Link to relevant study record(s)

Reference

Endpoint:

phototransformation in water

Type of information:

experimental study

Adequacy of study:

key study

Study period:

15 January 2002 - 10 December 2003

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

test procedure in accordance with national standard methods

Study type:

direct photolysis

Qualifier:

according to guideline

Guideline:

EPA OPPTS 835.2210 (Direct Photolysis Rate in Water by Sunlight)

Deviations:

no

Qualifier:

according to guideline

Guideline:

EPA Guideline Subdivision N 161-2 (Photodegradation Studies in Water)

Deviations:

no

Qualifier:

according to guideline

Guideline:

other: SETAC-Europe Procedures for Assessing the Environmental Fate and Ecotoxicity of Pesticides, Part 1, Section 10.0

Deviations:

no

GLP compliance:

yes

Radiolabelling:

yes

Analytical method:

other: Liquid scintillation counting (LSC) and high performance liquid chromatography with a radioactive detector (HPLC/RAM) along with fraction collection and offline liquid scintillation counting.

Details on sampling:

STERILITY AND pH CHECK SAMPLES
Surrogate samples were prepared for pH and sterility check for the buffered water, only. To analyse for sterility, a trypticase soy broth was prepared and sterilised according to package instructions for determination of the sterility of the kinetics samples. Immediately upon removal of the surrogate samples from the photolysis chamber, an aliquot of the surrogate was spiked into a culture tube containing soy broth. The culture tubes were placed in a 25 °C incubator for a minimum of 5 days. A sterile check sample remained clear amber throughout the study period. A non-sterile check of soy broth that had been deliberately contaminated was also incubated throughout the study period. The non-sterile check was cloudy. The sterility of the sample was confirmed if, after the incubation period the soy broth continued to be a clear amber solution.

SAMPLING INTERVALS
For the buffered water samples a light-exposed and dark control sample of each label were taken at 4, 7, 11, 14 and 18 days after treatment (DAT). Actinometer samples were taken at the same sampling interval, except no actinometers were taken at 18 DAT. For the natural water samples a light-exposed and dark control sample for each label were taken at 0.5, 1.5, 3.5, 7, 10.5, and 15 DAT. Actinometer samples were taken at the same sampling interval. The lamp was set to irradiate continuously during the treatment intervals.

SAMPLE STORAGE CONDITIONS
Samples were analysed for activity by LSC the day of sampling. HPLC was typically conducted on test samples within two days of sampling. All samples were stored refrigerated. Actinometer solutions were stored refrigerated.

SAMPLE PREPARATION AND PROCESSING
The samples were removed and the pH of each sample was adjusted to approximately pH 9.0 using 0.5 N NaOH. To assist with solubility, 12.0 mL of acetone was added to the sample vial and the total sample was transferred to a graduate cylinder. The total volume was measured and aliquots removed for LSC. Sub-samples were taken for HPLC analysis. The remaining samples were stored refrigerated.

Buffers:

Buffered water was prepared at a concentration of 0.05 M (HEPES) made in Milli-Q water. Buffered water was prepared by adding approximately 11.9 g of HEPES in 1000 mL of Milli-Q water. The pH was adjusted to pH 7.0 using 1.0 N NaOH. The buffer was then sterilised by autoclaving for a minimum of 15 minutes at 120 °C. No change in the pH was observed after sterilisation. Before aliquoting the sterilised buffered water into individual vials for the photolysis study, 1 % acetonitrile was added.

Light source:

Xenon lamp

Light spectrum: wavelength in nm:

>= 290 - <= 800

Details on light source:

- Irradiance Source: Samples were irradiated using a 6500 W Xenon lamp (Atlas Electronic Devices Company, Chicago, IL), in a temperature-controlled room.
- Emission wavelength spectrum: With the filters used, the wavelength distribution of xenon light is similar to natural sunlight. The wavelength distribution of the lamp was determined prior to and after the study using an OL-754 spectroradiometer (Optronics Laboratories, Orlando, FL). A representative graphical depiction of the wavelength distribution was collected, which ranged from 290 to 800 nm.
- Filters used and their purpose: The lamp was equipped with both inner and outer filters to simulate the irradiance from natural sunlight. The inner filter was a CIRA filter, a borosilicate glass filter designed to block light below 285 nm. The outer filter was a soda lime filter, to block light below 300 nm.
- Other: 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. The actinometer used in conjunction with this study was p-nitroacetophenone (PNAP) and pyridine (pyr) in water.

CHARACTERISATION OF LIGHT SOURCE
The wavelength distribution, measured by spectroradiometer, of the xenon lamp effectively simulates summer sunlight. However, the intensity, or quantity of light energy incident on a surface varies with distance from the lamp. Therefore, if the spectroradiometer probe is not at the exact distance from the lamp as the photolysis samples, it will not receive the same amount of light energy as the samples. Additional difficulties are incurred while trying to use a spectroradiometer to quantify the light energy received by photolysis samples. First, it is difficult to obtain a continuous radiometer reading from the light source. Also, the energy readings have to be converted from irradiance through air (Jλ values), which the probe reads, to energy through water (Lλ xenon) in which the compound of interest is dissolved. Therefore, the amount of light samples received (Lλ xenon) was calculated based on both the spectroradiometer Jλ values (as a measure of the relative intensity of light at each wavelength) and actinometery data (as a measure of the overall quantity of irradiance received by the samples).

Details on test conditions:

NATURAL WATER
In addition to in buffered water, the photolysis was also conducted in natural water collected from the White River located in Indianapolis, Indiana. After arrival at the testing facility, the river water sample was stored in an incubator set at 20 °C for approximately two weeks prior to use.

DESCRIPTION OF EXPERIMENTAL SET-UP
All samples were incubated in quartz round bottom flasks except for the dark control actinometers, which were incubated in amber glass vials. All dark samples were stored in a cardboard box covered with aluminium foil in the photolysis chamber.

PREPARATION AND APPLICATION OF TEST MATERIAL
- Preparation of Application Solutions
Stock solutions of the aniline and benzoyl labelled materials were prepared in acetonitrile to an appropriate concentration for application. Acetonitrile was used to ensure that the carrier solvent did not act as a photosensitizer. The concentrations of the application solution added to 48 mL of the buffer test system were 91 and 100 ng/µL, for the aniline and benzoyl label, respectively.
The concentrations of the application solution added to 48 mL of the natural water test system were 84 and 92 ng/µL, for the aniline and benzoyl label, respectively. Aliquots of the application solution (30 µL) were added to 48 mL of the buffer test system, and 30 µL aliquots of the application solutions were added to the natural water (48 mL).
- Application Procedures
Sterilised buffer or natural water was added to silanised quartz round bottom flasks. Aliquots of the dosing solutions were removed before, during, and after dosing to determine the application rate and the uniformity of the dosing solution.
After dosing, the flasks were capped and placed in the photolysis chamber. The lamp light source was programmed for continuous exposure. The dark control samples were stored in the photolysis chamber inside a cardboard box and covered with aluminium foil.
Analysis of the Day 0 samples began immediately after dosing.
- Control Materials Application
A chemical actinometer solution was used to determine the irradiance received during the study and a PNAP/pyr actinometer was chosen.
The quantum yield for a PNAP/pyr actinometer is independent of wavelength and adjusted by concentration of pyridine, as stated in the equation:
Φ = 0.0169[pyr]
The concentration of pyridine used in the actinometer solution was 5.1 x 10^-³ M for buffered water and 6.2 x 10^-³ M for natural water.
A stock solution of PNAP/pyridine/water was prepared by combining an aliquot of PNAP stock solution and 208 µL of pyridine for the buffered water and 500 µL of pyridine for the natural water in a 500 mL and in a 1 L volumetric flask for the natural water and for the buffered water, respectively, and bringing to volume with HPLC grade water. Forty-eight mL aliquots were added to quartz flasks (irradiated) and 16 mL aliquots were added to amber-coloured pyrex glass tubes (dark controls).
The samples for irradiation were fitted with a glass stopper. The samples were then placed in the xenon lamp room with the dosed buffered or natural water samples. The samples for dark control were capped with a Teflon-lined screw-cap and placed in the photolysis chamber in a cardboard box wrapped with aluminium foil.

TEST SYSTEM MAINTENANCE
- Experimental Conditions and Monitoring
The irradiated samples were placed under the lamp in a temperature-controlled room on a turntable. A fan was used to help circulate the air in the room. The room temperature was set at 25 °C during the incubation of the buffered water samples and 19 °C during the incubation of the natural water samples.
The dark control samples were incubated in the same temperature controlled room in a cardboard box covered with aluminium foil.

PREPARATION OF SAMPLES FOR PHOTOTRANSFORMATION PRODUCT IDENTIFICATION
For LC/MS analysis by reverse phase chromatography, samples, one of each label, were prepared by liquid/liquid extraction with dichloromethane and diethyl ether. Samples were initially extracted with dichloromethane and the supernatant removed. This was performed three times and the resulting organic phases were pooled. Sample pH of the aqueous phase was adjusted to pH 5.0 and salted using NaCl. Liquid/liquid extraction was then preformed three times using diethyl ether. The dichloromethane and diethyl ether extracts were combined and reduced to near dryness under nitrogen. Samples were brought up in acetonitrile and submitted for LC/MS.
For LC/MS analysis by HILIC, irradiated buffered water samples 18 DAT for each label were concentrated. Samples were reduced under nitrogen in a TurboVap using acetone as an azeotrope to remove the majority of the water. Aliquots were taken for pH, HPLC and LSC analysis.
For normal phase HPLC analysis, irradiated buffered water samples 11 DAT were concentrated. Samples were reduced under nitrogen in a TurboVap using methanol as an azeotrope to remove the water. Mobile phase of chloroform:methanol:acetic acid was added to the samples. Aliquots were taken for HPLC and LSC analysis. Additional samples were treated similarly for TLC analysis.

PREPARATION OF EXAGGERATED RATE SAMPLES FOR PHOTOTRANSFORMATION PRODUCT CHARACTERISATION
Additional samples were dosed at exaggerated rate for phototransformation characterisation. For the ¹⁴C-aniline-Iabelled material, the majority of the remaining dosing solution (6.2 mL in acetonitrile, approximately 57 µg) was concentrated to approximately 2 - 3 mL under a gentle stream of nitrogen (without heat). HPLC-grade water (48 mL) was added and 5 % co-solvent (acetonitrile) added and the solution was mixed well. The majority of the ¹⁴C-benzoyl-labelled material (6.0 mL in acetonitrile, approximately 57 µg) was concentrated then diluted in the same manner. Aliquots (3 x 20 µL) of each solution were analysed by LSC to determine the concentration. The samples were placed in the photolysis room and exposed for approximately 19 days under xenon light.
At 19 DAT, the samples were removed from the light source for characterisation of the polar phototransformation product. An aliquot of the exaggerated rate samples (40 mL) was purified through a C₁₈ SPE to separate the polar unknowns from the parent. The sample was acidified to contain 0.1 % acetic acid, then added to a conditioned SPE (C₁₈, Waters, 0.5 g). The column was rinsed with water containing 1 % acetic acid (10 mL) which was combined with the load volume. The SPE was then eluted with 80:20 water:acetonitrile, both containing 1 % acetic acid (10 mL), then eluted with acetonitrile containing 1 % acetic acid (2 x 10 mL, combined).
The volumes of the load and elution fractions were recorded, and aliquots were analysed by LSC and HPLC. The exaggerated rate ¹⁴C-aniline C₁₈ SPE load fraction (40 mL) was concentrated (rotary evaporator, 50 °C water bath) using acetone to azeotrope to concentrate to approximately 1 mL. Acetonitrile (2.0 mL) was used to rinse the glassware, then added to the concentrate.

Duration:

18 d

Temp.:

25 °C

Initial conc. measured:

53 other: ng/mL; Buffred water

Duration:

15 d

Temp.:

19 °C

Initial conc. measured:

40 other: ng/mL; Natural water

Reference substance:

yes

Remarks:

PNAP/pyr

Dark controls:

yes

Quantum yield (for direct photolysis):

0.001

Predicted environmental photolytic half-life:

- Theoretical Half-life of the Test Material in Buffered Water: t½ = 153 days
- Observed Half-Life of the Test Material in Natural Water: t½ = 41 days

Transformation products:

yes

No.:

#1

Details on results:

SAMPLE PH AND STERILITY
Surrogate samples for the buffered water were removed at each interval and checked for sterility and pH. Sterility was maintained throughout the study. The pH varied slightly over the course of the study, (6.7 - 7.1) but did not have an impact on the results of the study. No pH or sterility measurements were made on the natural water samples.

MATERIAL BALANCE
The material balance for the individual samples irradiated in buffered water ranged from 86.7 to 100.7 % of applied radioactivity and average % of applied radioactivity for the irradiated buffered water samples ranged from 91.5 to 96.7 %. The material balance for the individual dark control samples in buffered water ranged from 78.3 to 102.7 % of applied radioactivity, and average % of applied radioactivity for the dark control buffered water samples ranged from 88.3 to 96.5 %. The material balance indicates that volatile photoproducts were not generated during the study.
The material balance for the individual samples irradiated in natural water ranged from 82.6 to 105.0 % of applied radioactivity, and average % of applied radioactivity for the irradiated buffered water samples ranged from 92.1 to 103.0 %. The material balance for the individual dark control samples in buffered water ranged from 91.8 to 114.5 % of applied radioactivity, and average % of applied radioactivity for the dark control buffered water samples ranged from 94.7 to 110.2 %. The material balance indicates that volatile photoproducts were not generated during the study.

DISTRIBUTION AND IDENTIFICATION OF TRANSFORMATION PRODUCTS
A transformation product with a retention time of 8.0 minutes in the benzoyl-labelled samples was identified as the 2,6-difluorobenzamide degradate by LC/MS. This product reached a maximum of 18.1 % of applied radioactivity at 18 DAT. A peak eluting with the solvent front (5 minutes) was observed in both the aniline (maximum 16.3 % AR) and the benzoyl (maximum 18.1 % AR) labels.
In the natural water five transformation products were observed. The transformation product observed at a retention time of 8.0 minutes in the benzoyl-labelled samples was identified as the 2,6-difluorobenzamide. This product reached a maximum of 21.1 % of applied at 10.5 DAT.
The concentration of four transformation products remained below 10 % of applied radioactivity (maximum 8.5 %).
Additional separation methods were used to attempt to identify the polar transformation products. Initially, samples were analysed by a Polar RP column developed by Phenomenex to maximize the retention and selectivity of polar or aromatic compounds. Separation of the five minute peak away from the solvent front or into multi-components was not achieved using this column.
Normal phase separation was attempted on several samples to attempt to separate the polar transformation product into multiple peaks. Chromatography was poor and the entire sample eluted at the solvent front.
HILIC chromatography was attempted with LC/MS detection on kinetic samples. Using an improved separation technique it was anticipated that the resolution of the polar transformation product would improve and allow for detection by MS. However, HILIC may not have worked properly due to the highly aqueous sample and the results were inconclusive.

EXAGGERATED RATE SAMPLES FOR PHOTOTRANSFORMATION PRODUCT CHARACTERISATION
Additional samples were dosed with both radiolabelled test materials. The concentration of test material in the exaggerated rate samples was approximately 1.1 µg/mL, which is approximately five times the aqueous solubility, achievable due to the concentration of co-solvent (approximately 5 %). Analysis of the exaggerated rate samples using HPLC program D indicated an increase in phototransformation products produced over time, with 6 - 12 % degradation by 18 DAT. This rate was slower than the kinetic samples and may have been due to the higher concentration of co-solvent, the higher concentration of test material in the system and the placement of the samples in the photolysis chamber. Phototransformation product profile was similar during the exaggerated rate study as was observed during the kinetics study.
Standards were run utilising the YMC ODS-AQ column on the Waters system to ensure that retention times matched standards from system to system.
Analysis of the exaggerated rate ¹⁴C-benzoyl sample indicated the presence of primarily test material and up to 11 % phototransformation product eluting at approximately 6 minutes using HPLC program D. The 6-minute phototransformation eluted with the 2,6-difluorobenzamide standard, which had previously been identified in this system. There was also a component eluting at the solvent-front (4.0 minutes), which accounted for no more than 1 % of the applied radioactivity in the exaggerated rate sample.
Analysis of the exaggerated rate ¹⁴C-aniline sample also indicated the presence of primarily parent by HPLC program D. In addition, two poorly resolved polar components were detected, at 4.0 minutes (solvent front, up to 4.9 % AR), and 6.0 minutes (up to 2.3 % AR). These polar components correspond to those at 5.0 and 8.0 minutes detected in the kinetics portion of the study.
In order to isolate the polar component of the exaggerated rate samples the following method was performed. The sample was loaded on to a C₁₈ solid phase extraction (SPE) cartridge. The C₁₈ SPE load sample contained 2.7 % of the radioactivity that was not retained on the SPE cartridge. Subsequently, 10 mL of 80:20 water:acetonitrile was added to the cartridge and the sample eluted. The elution contained 0.4 % of the applied radioactivity. A second elution was performed with acetonitrile and contained 88.2 % of the applied radioactivity, for a total recovery of 91.3 %. The C₁₈ SPE load fraction was analysed by HPLC using an aqueous hold at the beginning of the run (XTERRA MS column, 15 minutes with 100 % water containing 1 % acetic acid). The C₁₈ SPE load fraction contained two components, the major one eluted at the solvent front.
For further analysis the SPE load fraction was concentrated by rotoevaporation. Concentration recovery of the C₁₈ SPE load sample was only 67 %, with the majority of the outstanding radioactivity recovered in the condensate (18 %) that was trapped in the rotoevaporator. Analysis of the concentrated C₁₈ SPE load fraction by HILIC chromatography demonstrated the multicomponent nature of the concentrated fraction. The chromatogram of the SPE load fraction was shown to contain up to 18 peaks. The range of radioactivity applied was between 1.7 to 25.4 % injected. In the kinetics portion of the study, the polar unknown accounted for up to 16 % AR in the ¹⁴C-aniline samples. However, the multi-component nature of the fraction demonstrates that no individual component would represent greater than 5 % of the applied radioactivity.

EQUIVALENT IRRADIANCE TO NATURAL SUNLIGHT
- Buffered Water
The quantum yield and rate constant values for PNAP incubated with the buffered water solution were 8.69 x 10^-5 and 0.120 DAT^-1, respectively, to give a xenon day-averaged light absorption rate constant of 1385 DAT^-1. From Leifer (The Kinetics of Environmental Aquatic Photochemistry: American Chemical Society, 1988) at 40° N latitude summer sun the day-averaged light absorption rate constant for PNAP was 532 days^-1, which indicates that 1 DAT of the exposure in the xenon lamp during the buffered water solution experiment was equivalent to 2.60 days (1385 DAT^-1/532 days^-1) in the summer sun. Therefore, 14 days of continuous exposure was equivalent to 36 days in the summer sun at 40° N latitude for the buffered water sample set.
- Natural Water
The quantum yield (Φa) and rate constant values for PNAP incubated with the natural water solution were 1.05 x 10^-4 and 0.076 DAT^-1, respectively, to give a xenon day-averaged light absorption rate constant of 721 DAT^-1. From Leifer at 40° N latitude summer sun the day-averaged light absorption rate constant for PNAP is 532 days^-1, which indicates that 1DAT of exposure in the xenon lamp was equivalent to 1.4 days (721 DAT^-1/532 days^-1) in the summer sun. Therefore, 15 days of continuous exposure was equivalent to 21 days in the summer sun at 40° N latitude for the natural water sample set.

KINETIC ANALYSIS OF DATA
- Kinetics of Parent Compound Degradation
The rate constant of the test material under study conditions was 0.0150 DAT^-1 in buffered water and 0.0174 DAT^-1 in natural water. Dark controls were stable over the photolysis period, indicated by statistical analysis using a t-test. This indicated that hydrolysis was not a major factor in test material degradation.
- Actinometer Kinetics
The degradation rate constant for PNAP (Ka) was determined experimentally for each test system. The PNAP rate constant was found to be -0.120 DAT^-1 for the buffered water and -0.076 DAT^-1 for the natural water. Actinometer dark controls were stable over the study period.
- Quantum Yield of Actinometer
The quantum yield of a PNAP actinometer is dependent only upon the concentration of pyridine.The concentration of pyridine in the actinometer for the buffered water was 5.14 x 10^-3 M.
Therefore the quantum yield of PNAP was
Φa = 0.0169 [pyr] = 0.0169 [5.14 x 10^-3 M] = 8.69 x 10^-5
Where:
Φa = quantum yield of the actinometer
[pyr] = concentration of pyridine in the actinometer solution
A degradation rate constant (Ka) of 0.120 DAT^-1 was determined for the PNAP actinometer. The actinometer quantum yield and degradation rate constant were used to calculate:
ΣεaλLλ = 1385
Where:
εaλ = molar absorptivity of PNAP actinometer at each wavelength
Lλ = wavelength distribution of xenon lamp

-Calculation of Lλ for the Xenon Lamp
Using the Solver function of Excel™ the molar absorptivity of the PNAP actinometer at each wavelength (εaλ) and the wavelength distribution measured from the xenon lamp, Lλ, can be calculated at each wavelength.
Multiplying the molar absorptivity of the test material (εaλ) at each wavelength by Lλ, the term ΣεcλLλ was calculated as 13 day^-1. The test material degradation rate constant (Kc) was calculated as 0.0150 days^-1. The quantum yield for the test material can then be calculated:
Φc = Kc / ΣελLλ = 1.15 x 10^-3

- Theoretical Half-life of the Test Material in Buffered Water
Once a quantum yield is determined, it can then be used to calculate the theoretical half-life at any latitude for any season. Lλ values can be multiplied by the molar absorptivity of the test material to calculate ΦcΣεcλLλ at various latitudes and seasons. In buffered water the term ΣεcλLλ is equal to 4 at 40° N latitude under summer sunlight. Using the quantum yield of the test material (1.15 x 10^-3) and ΣεcλLλ , at heoretical photolytic half-life of the test material in buffered water is calculated as:
t½ = ln 2 / ΣελLλ = ln 2 / (1.15 x 10^-3 x 4) = 153 days

- DT90 values
Once the quantum yield and half-life is determined the theoretical DT90 can be calculated based on the rate constant (Kc). The DT90 was calculated for the buffered water according to the following equation:
DT90= In(10) / Kc
For example, in the buffered water the rate constant is equal to 0.0045 days^-1 at 40° N latitude under summer sunlight. The theoretical DT90 was calculated as 509 days.

OBSERVED HALF-LIFE OF THE TEST MATERIAL IN NATURAL WATER
The rate constant calculated in natural water was used to calculate the half-life and DT90. The half-life was calculated using the following equation:
t½ = In 2 / 0.017 = 41 days
DT90= In 10 / 0.017 = 135 days

STORAGE STABILITY
Kinetic samples were analysed for activity by LSC within two days of sampling. HPLC analysis was run within one week of sampling; therefore, determination of storage stability was unnecessary. Actinometer dark control samples acted as storage stability samples for the exposed actinometers.

Validity criteria fulfilled:

yes

Conclusions:

The test material photodegraded in buffered water and natural water with a theoretical half-life of 153 and 41 days, respectively, under summer sunlight at 40° N latitude. The test material degraded to 2,6- difluorobenzamide and multiple polar photodegradates, none of which exceeded 5 % of the applied radioactivity.
The low water solubility and the use pattern reduce the probability of the compound being introduced into an aqueous environment. If introduced into an aqueous environment, photolysis will contribute to the dissipation of the compound.

Executive summary:

The potential of the tets material to undergo photolysis was investigated in a study conducted in accordance with the standardised guidelines with the US EPS 161-2, SETAC-Europe Procedures for Assessing the Environmental Fate and Ecotoxicity of Pesticides, Part 1, Section 10.0 and OPPTS 835.2210 under GLP conditions.

The aqueous phototransformation of radiolabelled test material was studied at approximately 25 °C in sterile aqueous HEPES buffer solution at pH 7.0 and at approximately 19 °C in natural water. The initial concentration in the buffered water was approximately 53 ng/mL and the initial concentration in the natural water was approximately 40 ng/mL. Samples were irradiated in quartz containers under continuous exposure using a xenon light source. Actinometers were irradiated along with the test material samples to characterise the light source. Irradiation under the xenon light is equivalent to 36 days, and 21 days summer sunlight at 40° N latitude for the buffered water and natural water, respectively. Dark control samples were wrapped in foil and incubated concurrently in the photolysis chamber.

Samples in buffer solution were analysed at 0, 4, 7, 11, 14 and 18 DAT (days after treatment). Samples in natural water were analysed at 0, 0.5, 1.5, 3.5, 7, 10.5, and 15 DAT. The samples were analysed by LSC and HPLC/RAM along with fraction collection and offline liquid scintillation counting. Identification of the transformation products was done by LC/MS and by co-chromatography.

For buffer solution photolysis samples, the mass balance was 88.3 to 96.5 % (average of replicates) and 91.5 to 96.7 % (average of replicates) of the applied radioactivity in the dark and the irradiated samples, respectively. At test termination 89.3 and 93.7 % of the applied radioactivity of the aniline and the benzoyl labels, respectively, remained as the parent in the dark samples. No transformation occurred in the dark samples.

For natural water photolysis samples, the mass balance was 94.7 to 110.2 % (average of replicates) and 92.1 to 103.0 % (average of replicates) of the applied radioactivity in the dark and the irradiated samples, respectively. At test termination 109.8 and 100.5 % of the applied radioactivity of the aniline and the benzoyl labels, respectively, remained as the parent in the dark samples. No transformation occurred in the dark samples.

A quantum yield of 1.5 x 10^-3 was calculated in buffered water. Using the quantum yield the theoretical half-life at 40° N latitude during the summer was found to be 153 days in buffered water and the corresponding DT90 value was 509 days. Natural water observed half-life was 41 days and the DT90 was 135 days.

The phototransformation product 2,6-difluorobenzamide was observed in the benzoyl label of the test material in buffered water (up to 18.1 % applied radioactivity (AR)) and natural water (up to 21.0 % AR) and was confirmed by LC/MS. A polar phototransformation product was observed in both labels in buffered water (16.3 % AR aniline label, 8.1 % AR benzoyl label) and natural water (12.3 % AR aniline label, 11.8 % AR benzoyl label). Further investigation using exaggerated rate aniline-labelled samples indicated that the polar peak contained up to 18 peaks. The range of radioactivity was between 1.7 to 25.4 % injected on the LC. In the kinetics portion of the study, the polar unknown accounted for up to 16 % AR in the ¹⁴C-aniline samples. However, the multi-component nature of the fraction demonstrates that no individual component would represent greater than 5 % of the applied radioactivity.

Under the conditions of this study, the test material photodegraded in buffered water and natural water with a theoretical half-life of 153 and 41 days, respectively, under summer sunlight at 40° N latitude.

Description of key information

The test material photodegraded in buffered water and natural water with a theoretical half-life of 153 and 41 days, respectively, under summer sunlight at 40° N latitude

Key value for chemical safety assessment

Half-life in water:

41 d

Additional information

The potential of the test material to undergo photolysis was investigated in a study conducted in accordance with the standardised guidelines with the US EPS 161-2, SETAC-Europe Procedures for Assessing the Environmental Fate and Ecotoxicity of Pesticides, Part 1, Section 10.0 and OPPTS 835.2210 under GLP conditions. The study was awarded a reliability score of 1 in accordance with the criteria set forth by Klimisch et al. (1997).

The aqueous phototransformation of radiolabelled test material was studied at approximately 25 °C in sterile aqueous HEPES buffer solution at pH 7.0 and at approximately 19 °C in natural water. The initial concentration in the buffered water was approximately 53 ng/mL and the initial concentration in the natural water was approximately 40 ng/mL. Samples were irradiated in quartz containers under continuous exposure using a xenon light source. Actinometers were irradiated along with the test material samples to characterise the light source. Irradiation under the xenon light is equivalent to 36 days, and 21 days summer sunlight at 40° N latitude for the buffered water and natural water, respectively. Dark control samples were wrapped in foil and incubated concurrently in the photolysis chamber.

Samples in buffer solution were analysed at 0, 4, 7, 11, 14 and 18 DAT (days after treatment). Samples in natural water were analysed at 0, 0.5, 1.5, 3.5, 7, 10.5, and 15 DAT. The samples were analysed by LSC and HPLC/RAM along with fraction collection and offline liquid scintillation counting. Identification of the transformation products was done by LC/MS and by co-chromatography.

For buffer solution photolysis samples, the mass balance was 88.3 to 96.5 % (average of replicates) and 91.5 to 96.7 % (average of replicates) of the applied radioactivity in the dark and the irradiated samples, respectively. At test termination 89.3 and 93.7 % of the applied radioactivity of the aniline and the benzoyl labels, respectively, remained as the parent in the dark samples. No transformation occurred in the dark samples.

For natural water photolysis samples, the mass balance was 94.7 to 110.2 % (average of replicates) and 92.1 to 103.0 % (average of replicates) of the applied radioactivity in the dark and the irradiated samples, respectively. At test termination 109.8 and 100.5 % of the applied radioactivity of the aniline and the benzoyl labels, respectively, remained as the parent in the dark samples. No transformation occurred in the dark samples.

A quantum yield of 1.5 x 10^-3was calculated in buffered water. Using the quantum yield the theoretical half-life at 40° N latitude during the summer was found to be 153 days in buffered water and the corresponding DT90 value was 509 days. Natural water observed half-life was 41 days and the DT90 was 135 days.

The phototransformation product 2,6-difluorobenzamide was observed in the benzoyl label of the test material in buffered water (up to 18.1 % applied radioactivity (AR)) and natural water (up to 21.0 % AR) and was confirmed by LC/MS. A polar phototransformation product was observed in both labels in buffered water (16.3 % AR aniline label, 8.1 % AR benzoyl label) and natural water (12.3 % AR aniline label, 11.8 % AR benzoyl label). Further investigation using exaggerated rate aniline-labelled samples indicated that the polar peak contained up to 18 peaks. The range of radioactivity was between 1.7 to 25.4 % injected on the LC. In the kinetics portion of the study, the polar unknown accounted for up to 16 % AR in the ¹⁴C-aniline samples. However, the multi-component nature of the fraction demonstrates that no individual component would represent greater than 5 % of the applied radioactivity.

Under the conditions of this study, the test material photodegraded in buffered water and natural water with a theoretical half-life of 153 and 41 days, respectively, under summer sunlight at 40° N latitude.