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Phototransformation in water

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Endpoint:
phototransformation in water
Type of information:
experimental study
Adequacy of study:
supporting study
Study period:
15 March 1991 to 31 July 1991
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
study well documented, meets generally accepted scientific principles, acceptable for assessment
Study type:
direct photolysis
Qualifier:
according to guideline
Guideline:
other: Test Guideline Phototransformation of Chemicals in Water, Part A: Direct Phototransformation, Berlin.
Version / remarks:
January 1990
Deviations:
no
GLP compliance:
yes
Radiolabelling:
no
Analytical method:
high-performance liquid chromatography
Light source:
other: 1 000 W Mercury lamp equipped with a grating monochromator (Schoeffel GM 250).
Light spectrum: wavelength in nm:
>= 290
Details on light source:
The UV-beam was collimated to the Quartz cuvette so that the solution was completely irradiated by UV-radiation of the wavelength chosen.
The output was calibrated using the ferrioxalate method (actinometer according to Parker).
Details on test conditions:
A solution containing 59.3 mg test material in 10 mL methanol was prepared. The UV-spectrum was measured using methanol in the reference cuvette. The absorption above 310 nm was found to be insignificant.

UV-ABSORPTION SPECTROPHOTOMETER
- The apparatus used was a HITACHI U-3200 Spectrophotometer. The cuvettes used were 1 cm Quartz cuvettes.

ACTINOMETRY
PRINCIPLE
The (chemical) actinometry is performed in order to determine how many photons of the wavelength chosen for performing the irradiation are provided by the irradiation unit (lamp + monochromator). The actinometer solution is contained in an identical cuvette as the one used for the actual irradiation experiment. All other conditions have to be identical, too. The actinometer solution contains a substance of known photochemical reaction products and quantum efficiency. The intensity of the light (photon irradiance) is determined by analysing the decrease in concentration of a known photochemically active substance. If the volume of the actinometer solution in the cuvette is not fully illuminated, a correction has to be applied which takes into account the fraction illuminated. The same is true if less than 100 % of the radiation at the wavelength used is absorbed by actinometer solution. In this case, the fraction absorbed (calculated from the absorption spectrum of the actinometer solution) has to be taken into account.

ACTINOMETRY ACCORDING TO THE FERRIOXALATE (PARKER'S) METHOD
Parker's method consists of irradiating a solution of potassium ferrioxalate in dilute sulfuric acid. The iron (II) ions formed by photochemical reduction of iron (III) are analysed spectrophotometrically using phenanthroline as chelating agent. At the wavelength used (304 nm) there is 100 % absorption, i.e., there is no correction needed for incomplete absorption. The quantum efficiency of the photoreduction is Φ = 1.24.

- Performance
A solution of 0.2984 g potassium ferrioxalate was dissolved in 80 mL Milli-Q-water, 10 mL 1N sulfuric acid was added and filled up with water to give 100 mL. 3 mL portions of this solution were irradiated at 304 nm for 15, 30 60, 90 and 120 min.
The measurement of the iron (II) content was performed by mixing 2 mL of the irradiated actinometer solution with 2 mL of the phenanthroline solution (0.1 g phenanthroline in 100 mL Millipore water), 1 mL of buffer solution (13.608 g sodium acetate in 100 mL Millipore water; 60 mL of this solution and 36 mL 1 N sulfuric acid were filled up to 100 mL Millipore water) in a 20 mL volumetric flask and diluting to volume with Millipore water.
The absorbance of this mixture at 510 nm is measured against a non-irradiated sample solution in the reference cuvette.
The preparation of calibration graph for the colorimetric method is described elsewhere. The calibration graph was found to remain constant during several years by using the spectrophotometer HITACHI U-3200.
The number of iron (II) ions formed during the irradiation were also given. The irradiance was calculated from these data taking into account the quantum efficiency of the photochemical reaction and the irradiated volume (3 mL). Since the cuvettes are quadratic, the total amount of photons had to be divided by 3 in order to obtain the photon irradiance in [photons/(s·cm^2 )]. In order to obtain the same quantity in Einsteins (mol photons), the number had to be divided by Avogadro's number.
The constancy of the photon irradiance as a function of time shows that the UV-lamp has a constant output, as required for irradiation experiments.

IRRADIATION OF TEST MATERIAL IN WATER
- Solution
25.3 mg of the test material was dissolved in 50 mL Milli-Q-water. The initial concentration is 0.506 g/L (C = 2.36·10^-3 mol/L). The absorbance (A) of this solution at 304 nm is calculated from the molar, decadic absorption coefficient (ε = 2.001 L/mol·cm) at 304 to be:
A = ε·C·l = 0.0047 (at a pathlength l = 1 cm).

- Irradiation at 304 nm
A 1 cm Quartz cuvette was filled with 3 mL of the solution and irradiated at 304 nm for 144 hours. The solution was completely illuminated, so that no correction had to be applied. The geometrical arrangement of lamp, monochromator and cuvette was identical to that used for the actinometry.
The concentration of the test material was measured by HPLC after 0, 1, 2, 3, 20, 22, 24, 26, 44, 46, 48, 51, 67, 69, 71, 138, 140, 143 and 144 hours of irradiation time.

CALIBRATION AND CALCULATIONS
The sizes of the peaks detected by the UV detector (areas) were measured with an integrator.
The corresponding amount of the test material was computed by comparison of the measured area to a calibration curve generated from the standard solutions.
The calibration curve obtained was linear within a concentration range of 2.2 to 440 ng per injection of 20 μL.
Duration:
144 h
Reference substance:
no
Dark controls:
no
Parameter:
max lambda
Value:
304 nm
Remarks on result:
not measured/tested
Key result
DT50:
> 144 h
Test condition:
Illuminated at 304 nm
Transformation products:
not measured
Details on results:
CONCENTRATION OF TEST MATERIAL DURING IRRADIATION
The average concentration measured (after dilution 1:500) amounts to:
Test material = 0.836 μg/mL

There is no significant decrease of the concentration during the irradiation time (correlation coefficient r = - 0.5 for a plot of ln c vs. time). The standard deviation of the average concentration amounts to ± 2.9 %.

ESTIMATION OF THE UPPER LIMIT OF THE QUANTUM EFFICIENCY
From the measured concentration, the upper limit of the quantum efficiency of direct photochemical transformation in water at 304 nm can be estimated. In order to perform this estimation, it is assumed that a 5.8 % decrease (twice the standard deviation) in concentration over the irradiation time (144 hours) would have been detected with certainty, given the accuracy of the analytical method applied (standard deviation 2.9 %).
Experimentally, an upper limit of k is obtained from first order kinetics:
C = C0 · e^-kt
ln C = ln C0 - k · t
k = (ln C0 – ln C) / t
Where:
C0: Concentration of substance at the beginning of the experiment (t = 0)
C: Concentration of substance at irradiation time t (t > 0)
t: Irradiation time t [s]
k: (Pseudo-) 1st order rate constant of direct photochemical transformation [s^-1]

For the test material in water, the following data are used for the calculation:
C0 = 0.836 μg/mL (average from n = 19 samples)
C = 0.788 μg/mL (= Co - 2 · standard deviation (5.8 %))
t = 5.184 · 10^5 s (144 h total irradiation time)

With these data and the equations above the following rate constant is calculated:
k ≤ 1.141 · 10^-7 s^-1

The quantum efficiency of direct photochemical transformation (Φ) is defined according to the equation:
Φ = Number of molecules disappeared (Nn) / Number of photons absorbed (N)

The number of photons absorbed per second (N/s) in 1 cm^3 of the irradiated solution is given by:
N/s = (I0 · %A) / 100
Where:
I0: Photon irradiance [photons/(cm^2·s)], as determined by actinometry
% A: Percentage of photons absorbed in the solution at the irradiation wavelength

%A = (1 – I/I0) · 100
Where:
I/I0 = Fraction of photons transmitted at the irradiation wavelength and at the thickness of the cuvette (d = 1 cm) = transparency T

The transparency T and, hence, % A is calculated according to the law of Lambert and Beer:
Log1/T = logI^0 / I = A = ε · C · d
Where:
A: Absorbance
ε: Molar decadic absorption coefficient [L/(mol·cm)]
C: Concentration of substance [mol/L]
d: Thickness of cuvette

% A = (1 – 10^εcd) · 100

For the test material, the following data are used for calculating % A:
ε (304 nm): 2.001 L/mol·cm
C = C0: 0.418 g/L / 214.6 g/mol = 1.95 · 10^-3 mol/L
d: 1 cm

%A = (1 – 10^2.001 · 0.00195 · 1) · 100 = 0.89 %

Using the equation given previously to determine the number of photons absorbed per second and square centimetre is obtained:
N/s = 3.74 · 10^11 photons/cm^2 · s

The total number of photons absorbed after the time τ = 1/k (N) is given by (N/s)·τ.
τ = 1/k = 8.764 · 10^6 s
N = 3.28 · 10^18 photon/cm^3

The number of molecules disappeared in 1 cm^3 after irradiation for a time τ (Nn) is given by:
Nn = (C0 – C0/e) · Na/1000
Where:
e: Euler's number (2.71828)
Na: Avogadro constant (6.0221 · 10^23

From this and the initial concentration (C0 = 1.95 · 10^-3 mol/L)
Nn = 7.42 · 10^17 molecules/ cm^3
disappeared after time τ (upper limit).

The upper limit of the quantum efficiency of direct photochemical transformation (Φ) is obtained according to the equation given above and the data for Nn and N:
Φ (test material in water) ≤ 0.23

Since only this upper limit of the quantum efficiency could be measured, no attempt was made to measure the concentration dependence of the direct photochemical transformation (Φ), as required if C0 > 0.001 mol/L.

Summary of the Concentration of the Test Material after Irradiation at 304 nm

Irradiation Time

[h]

Concentration Sample

[µg/mL]

0

0.9

1

0.85

2

0.85

3

0.84

20

0.85

22

0.83

24

0.85

26

0.83

44

0.87

46

0.83

48

0.79

51

0.84

67

0.81

69

0.83

71

0.82

138

0.82

140

0.81

143

0.84

144

0.82

Average: 0.836 µg/mL

Standard deviation (n-1): 0.024

Rel. Standard deviation: 2.9 %

Validity criteria fulfilled:
not specified
Conclusions:
Under the conditions of the study, the upper limit of the quantum efficiency of direct photochemical transformation (Φ, test material in water) was found to be ≤ 0.23.
Executive summary:

The phototransformation of the test material in water was determined according to the UBA Test Guideline Direct Phototransformation under GLP conditions.

The test material is dissolved in water. The decrease in concentration of the test material under illumination with UV-radiation of 304 nm with time is followed by HPLC. The intensity of the UV-radiation (spectral photon irradiance) is measured using chemical actinometry. The quantum efficiency of the disappearance is calculated for the irradiation wavelength.

In order to enable calculation of the photochemical lifetime (or half-life) of the test material, the UV-absorption spectrum was measured in the range 290 to 400 nm.

An aqueous solution of the test material was illuminated at 304 nm for up to 144 hours without significant decrease in concentration.

Under the conditions of the study, the upper limit of the quantum efficiency of direct photochemical transformation (Φ, test material in water) was found to be ≤ 0.23.

Endpoint:
phototransformation in water
Type of information:
calculation (if not (Q)SAR)
Adequacy of study:
supporting study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
accepted calculation method
Study type:
direct photolysis
Qualifier:
no guideline followed
Principles of method if other than guideline:
The calculated environmental photolytic half-life can be used for a rough estimation of the persistence of the chemical being irradiated. The calculation carried out is valid for direct phototransformation in the top millimetres of a natural aquatic system.
The pseudo first-order constant for direct transformation (k) and thus the lifetime (τ) and half-life (t½) of a chemical in water can be computed from:
- The experimentally determined quantum yield of disappearance of the compound upon excitation;
- The experimentally determined light absorption spectrum of the compound in aqueous solution at above 290 nm, which is the lower spectral limit of sunlight reaching the earth’s surface;
- The solar light intensity available in the spectral range which coincides with the light absorption spectrum of the compound.
GLP compliance:
no
Remarks:
Calculation method.
Radiolabelling:
no
Computational methods:
CALCULATION OF THE LIFE-TIME AND HALF-LIFE FOR DIRECT PHOTOTRANSFORMATION
The pseudo first-order constant for direct transformation (k) and thus the lifetime (τ) and half-life (t½) of a chemical in water can be computed from:
- The experimentally determined quantum yield of disappearance of the compound upon excitation;
- The experimentally determined light absorption spectrum of the compound in aqueous solution at above 290 nm, which is the lower spectral limit of sunlight reaching the earth’s surface;
- The solar light intensity available in the spectral range which coincides with the light absorption spectrum of the compound.
t½ = ln2 x τ
τ = 1/k
k = ϕ x ka
ka = ∑^λ1 λ2 2303 x 10^3 x I0(λ) x Δλ x ε(λ)
Where:
t½ is the half-life (s)
τ is the lifetime (s)
k is the pseudo first-order rate constant for direct photolysis (s^-1)
ϕ is the quantum yield of disappearance upon excitation for the wavelength range λ1 to λ2 (mole x Einstein^-1)
ka is the pseudo first-order rate constant for light absorption (s^-1)
I0(λ) is the incident sunlight intensity at wavelength λ (Einstein x cm^-1 x s^-1 x nm^-1)
Δλ is the wavelength range (nm)
ε(λ) is the molecular extinction coefficient (litre^-1 x mole^-1 x cm^-1)
2303 is ln10, i.e. the factor for conversion of molecular extinction coefficient of the compound into a Naperian basis
10^3 is the factor for conversion of ε(λ) from litre^-1 x mole^-1 x cm^-1 into cm^3 x mole^-1 x cm^-1

In central Europe, variations of the solar irradiance are mainly caused by the climatic conditions and not by the geographical location. Therefore, it seems to be appropriate to use mean solar irradiances for the estimation of photochemical transformation rates. The data used for these estimations reflect the mean values of solar irradiance in Europe at 52 ° northern latitude. The calculation of these data based on the spectral solar irradiance outside the earth’s atmosphere depends on the zenith angle. For the performance of the calculations the zenith angle was set to noon minus ⅙ of daylight for each month. With this value the light attenuation due to light scattering and adsorption was calculated for the performance of the calculations. The calculated clear sky was finally corrected for the influence of clouds.
DT50:
6 593 h
Test condition:
Minimum environmental photolytic half-life of the test material in water estimated in July.
Predicted environmental photolytic half-life:
Quantum yield for the loss of the test material was estimated to be less than or equal to 0.23 mole x Einstein^-1. Molar extinction coefficients of the test material were obtained. From the upper limit of a quantum yield only a lower limit of the environmental half-life can be calculated.
Minimum environmental photolytic half-life of the test material in water can be estimated to 6 593 h in July.
Transformation products:
not measured
Validity criteria fulfilled:
not applicable
Conclusions:
Minimum environmental photolytic half-life of the test material in water can be estimated to 6593 h in July.
Executive summary:

The pseudo first-order constant for direct transformation (k) and thus the lifetime (τ) and half-life (t½) of a chemical in water can be computed from:

- The experimentally determined quantum yield of disappearance of the compound upon excitation;

- The experimentally determined light absorption spectrum of the compound in aqueous solution at above 290 nm, which is the lower spectral limit of sunlight reaching the earth’s surface;

- The solar light intensity available in the spectral range which coincides with the light absorption spectrum of the compound. 

In central Europe, variations of the solar irradiance are mainly caused by the climatic conditions and not by the geographical location. Therefore, it seems to be appropriate to use mean solar irradiances for the estimation of photochemical transformation rates. The data used for these estimations reflect the mean values of solar irradiance in Europe at 52 ° northern latitude. The calculation of these data based on the spectral solar irradiance outside the earth’s atmosphere depends on the zenith angle. For the performance of the calculations the zenith angle was set to noon minus ⅙ of daylight for each month. With this value the light attenuation due to light scattering and adsorption was calculated for the performance of the calculations. The calculated clear sky was finally corrected for the influence of clouds.

Quantum yield for the loss of the test material was estimated to be less than or equal to 0.23 mole x Einstein^-1. Molar extinction coefficients of the test material were obtained. From the upper limit of a quantum yield only a lower limit of the environmental half-life can be calculated.

Minimum environmental photolytic half-life of the test material in water can be estimated to 6 593 h in July.

Endpoint:
phototransformation in water
Type of information:
experimental study
Adequacy of study:
key study
Study period:
17 July 1995 to 17 December 1995
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Study type:
direct photolysis
Qualifier:
according to guideline
Guideline:
EPA Guideline Subdivision N 161-2 (Photodegradation Studies in Water)
Deviations:
no
GLP compliance:
yes
Specific details on test material used for the study:
TREATMENT OF TEST MATERIAL PRIOR TO TESTING
- Preparation of the Test Material Primary Stock Solution, Purification of the Radiolabelled Test Material and Radiopurity Analysis
The primary stock solution was prepared by transferring the entire contents of the received vial of [14C)-test material via repetitive rinsing with acetonitrile to a final volume of 60 mL. The stock solution was analysed by LSC and determined to have a concentration of 0.142 mg/mL (70 660 dpm/μL) based on a sponsor-supplied specific activity of 224.86 μCi/mg (499 189 dpm/μg; 8.32 MBq/mg). HPLC-RAM analysis revealed, however, that the [14C]-test material had a radiopurity of 94.5 %. Since it was below 95 %, the [14C)-test material primary stock solution was reduced to approximately 1 mL under nitrogen and purified by semi-preparative HPLC. The entire amount of impure [14C]-test material was injected (in approximate 200 μL portions) onto a semi-preparative C18 HPLC column and the eluting region, corresponding to the test material, was collected and pooled. Most of the acetonitrile (from the mobile phase) was removed under nitrogen, and 30 mL of reagent water was added to the remaining acidic water. After adjusting the pH to approximately 2 with acetic acid, the purified [14C]-test material was partitioned with 3 x 500 mL of methylene chloride. The methylene chloride was then removed with nitrogen and the sample was re-dissolved in 50 mL of acetonitrile. Three 5-μL aliquots of the purified stock solution were profiled by HPLC-RAM, establishing a radiopurity of 100 %. The purified test material primary stock solution was used to prepare stock solutions for testing.

- Primary Stock Solution Preparation
A non-radiolabelled racemic test material stock solution was prepared by dissolving and diluting 0.0251 g of non-radiolabelled test material with acetonitrile/reagent water (1:1) to volume in a 50 mL flask, producing a concentration of 0.502 mg/mL. This stock solution was used to fortify solutions for determining an appropriate test concentration based on the ultraviolet spectrum of the test material.
The [14C]-test material primary stock solution (prepared and purified as above) was analysed by liquid scintillation counting (LSC) to have a mean measured concentration of 0.131 mg/mL (total of 6.53 mg [14C]-test material), based on the radioactivity and the sponsor-supplied specific activity. The radiopurity (100 %) of this primary stock solution was confirmed by HPLC-RAM using HPLC system #1. This primary stock was used to prepare the dosing solution.
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) for the primary stock solution, based on the radioactivity and the specific activity. This stock solution was used for determination of trapping efficiency of 14CO2.

- Concentration, Radiopurity and Specific Activity Determination of the Dosing Solution
For the preliminary and definitive study, a dosing solution was prepared by combining 1.54 mL of the 0.131 mg/mL radiolabelled primary stock solution and 9.9 mg of non-radiolabelled test material and diluting to a final volume of 10 mL with acetonitrile. This produced a calculated concentration of 1 mg/mL. The specific activity determination of the dosing solution was performed using HPLC. The total concentration of test material (sum of radiolabelled and non-labelled) was determined by HPLC-UV analysis at a detection wavelength of 230 nm.
Quantitation was achieved using external calibration methods using an authentic standard for the test material at various dilutions to serve as calibration standards. The radiochemical purity of the dosing solution was determined by HPLC-RAM. The total radioactivity per microlitre (dpm/μL) of the dosing solution was determined by LSC analysis. Using this procedure, the concentration of the test material dosing solution was experimentally determined to be 0.959 mg/mL, the radiopurity was 100 % and the specific activity was 10 718 dpm/μg.

- Test Solutions
A nominal 1 0 mg/L test material solution for preliminary testing was prepared using 200 mL of the pH 7 buffer solution. In a sterile 200 mL volumetric flask, exactly 2.00 mL of the radiolabelled test material dosing solution at 0.959 mg/mL in acetonitrile was diluted to volume with pH 7 buffer solution. The ratio of acetonitrile to buffer solution was 1 % (v/v).
Each nominal 10 mg/L test material test solution concentration for definitive testing was prepared using 200 mL of pH 5, pH 7 and pH 9 buffer solutions. In sterilised 200 mL volumetric flasks, exactly 2.00 mL of the radiolabelled test material secondary stock solution at a concentration of 0.959 mg/mL in acetonitrile was diluted to volume with the appropriate buffer solution. The acetonitrile, used as a co-solvent, represented 1 % on a volume to volume basis and is not a known photosensitiser.
Radiolabelling:
yes
Analytical method:
high-performance liquid chromatography
other: LSC
Buffers:
BUFFER SOLUTION PREPARATION
All buffer solutions were autoclaved at 121 °C for 30 minutes and allowed to cool to room temperature. Prior to use, the buffers were saturated with bacteria-free air for approximately 20 minutes. A general method of preparation for pH 5, pH 7 and pH 9 buffer solutions is as follows:
- pH 5: A volume of 200 mL of 0.010 M sodium acetate was combined in a graduated cylinder with 200 mL of 0.010 M acetic acid and diluted to 600 mL with reagent water. The pH was measured to be approximately 5.0.
- pH 7: A volume of 300 mL of 0.010 M potassium phosphate, monobasic was combined in a graduated cylinder with 300 mL of 0.010 M potassium phosphate, dibasic and diluted to 675 mL with reagent water. The pH was measured to be approximately 7.0.
- pH 9: A volume of 100 mL of 0.010 M HCI was combined in a graduated cylinder with 375 mL of 0.010 M sodium tetraborate decahydrate and diluted to 675 mL with reagent water. The pH was measured to be approximately 9.0.
Light source:
Xenon lamp
Light spectrum: wavelength in nm:
>= 250 - <= 700
Details on light source:
The artificial light source used for this study was provided by a Heraeus Suntest Accelerated Exposure Unit utilising xenon arc irradiation. The xenon arc lamp was removed from the Heraeus Unit and suspended directly above the racks holding the test vessels.
Samples (irradiated and dark controls) were placed in random order (based on a random number generator computer program, i.e., Microsoft® Excel) under the light on black, non-reflective racks at approximately 45° to the table surface at either 6 or 10.5 inches from the lamp.
- Emission wavelength spectrum: The lamp was fitted with a filter that prevents transmission of light below 300 nm. Spectral profiles for the artificial light source and sunlight over the wavelength range of 250 to 700 nm were recorded with a Model IL-1700 Research Radiometer, a Model IL-760D power supply, a double monochromator, a Model IL-791 and a P2 Fibre 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.
- Light intensity at sample and area irradiated: Spectral profiles for the artificial light source and for natural sunlight were recorded on 4 May 1995 and 1 August 1995, respectively. Sunlight measurements were recorded at 12:17 p.m. on a clear, sunny day outside the Wareham, Massachusetts laboratory (42° North latitude). Measurements were obtained by positioning the fibre optic probe directly at the sun. The light intensity measurements for the artificial light were recorded at two representative positions on the stainless-steel rack which was used to hold samples during the exposure. Thus, the fibre optic probe was placed at 6 and 10.5 inches from the xenon arc lamp and light measurements were recorded.
- Relative light intensity based on intensity of sunlight: Total integrated light intensities of the artificial light source and sunlight were measured with the SUD400W detector on 4 May 1995 and 1 August 1995, respectively. The light intensity received by samples at two different distances from the xenon arc lamp (6 and 10.5 inches, representing two different shelves where samples were irradiated) ranged from 36.5 to 49.7 % of natural sunlight. Therefore, based on spectral profiles and total light intensity, the artificial light source represented an acceptable model for mimicking natural sunlight.
Additionally, total intensity and spectral profiles for the artificial light source were measured upon completion of the definitive study (12 October 1995) as described above.
Artificial light values are comparable to those recorded prior to study initiation, thereby indicating a consistent artificial light source during the 30-day light-exposure period.
- Duration of light/darkness: The light was operated on a 12 hour on/off cycle to simulate natural light cycles.
Details on test conditions:
PRELIMINARY STUDY
A preliminary photolysis test using [14C]-test material in pH 7 buffer solution was conducted to estimate the rate of test material photolysis and to set appropriate sampling intervals for the definitive study. Twenty-four vials were prepared, with twelve designated as light-exposed replicates. The remaining twelve vials were designated as dark control replicates. Aliquots (8 mL) of the 10 mg/L test solution were transferred to individual clear borosilicate glass vials (approximately 19 x 65 mm) with Teflon®-lined septa and plastic open-top screw caps for the light-exposed and dark control replicates. The dark control replicates were wrapped with aluminium foil.
Two additional samples for both the light-exposed and dark controls were prepared and connected to the trapping system for the collection of volatiles. Additionally, the weight of these vessels was recorded on Day 0 for comparison to determine any loss due to evaporation at subsequent sampling intervals. When necessary, test vessels were remoisturised to the weight measured on Day 0 by addition of sterile reagent water in a laminar flow hood to maintain sterility. Samples for irradiation were placed on photolysis racks at approximately 25 °C throughout exposure. The dark controls were placed upright in racks within an environmental chamber maintained at approximately 25 °C.
Duplicate vials of light-exposed and dark control test solutions were sampled after 1, 3 and 7 days of intermittent light (12 hours on/12 hours off) to monitor test material loss. At time 0, duplicate samples were removed directly from the volumetric flask. At each interval, the total volume of each sample solution was measured. Triplicate 0.1 mL aliquots were removed from each test solution, radioactivity quantified by LSC analysis and the aliquots compared to the 0.1 mL aliquots radioassayed at time 0 to determine radiometric mass balance at each sampling interval. The test material in all samples was quantified by HPLC-RAM analysis.
The ethylene glycol and 10 % potassium hydroxide trapping solutions from the volatile collection samples (also referred to as aerated samples) were replaced and quantified by radioassay at each sampling interval except for Day 0. The total volumes of the ethylene glycol and potassium hydroxide solutions were measured and 1 mL aliquots were radioassayed after mixing with 15 mL of Monophase® scintillation cocktail. Overflow traps containing liquid were also radioassayed by LSC. The 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 were radioassayed, after mixing with 15 mL of Monophase® scintillation cocktail.
At each sampling interval, the aerated vessels were weighed on an analytical balance and sterile reagent water was added via sterile pipet under the laminar flow hood to return the weight to that measured on Day 0. At test termination (Day 7), the aerated vessels for both the light-exposed and dark controls were sampled and analysed in a manner similar to the non-aerated test vessels.

TEST SYSTEM
- Type, material and volume of test apparatus/vessels: The reaction vessels for the irradiated replicates consisted of clear, borosilicate glass vials (approximately 19 x 65 mm) with a Teflon®-lined septum and a plastic open-top screw cap. Dark control solutions were prepared in similar borosilicate vials, wrapped with aluminium foil and incubated in the same environmental chamber as the irradiated samples (definitive study).
- Sterilisation method: The test vessels and buffer solutions were autoclaved prior to the addition of test solution to minimise the possibility of microbial transformations occurring during the exposure or incubation period.
- Details of traps for volatile, if any: Yes.
Collection of Volatiles:
Volatiles were swept from the headspace of a pair of test vessels for each buffered test solution 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) sulfuric acid 0.5 M;
(4) an empty trap;
(5) ethylene glycol;
(6) an empty trap;
(7) two vials of 10 % potassium hydroxide in succession;
(8) an empty trap.
For the definitive study, an additional trap solution of 0.5 M sulfuric acid was included in series between the polyurethane foam plugs and the ethylene glycol and potassium hydroxide trapping media to collect any basic volatiles produced during irradiation/incubation. Traps were connected in series through silicone tubing and received volatiles from individual samples using gang valves as splitters. Carbon dioxide from the incoming 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.
- 14CO2 Trapping Efficiency:
In order to determine the trapping efficiency of 14CO2 in the trapping system, 1 mL of a 0.032 mg/mL [14C]sodium bicarbonate primary stock solution in 0.1 N NaOH was added to an empty vial (approximately 19 x 65 mm) through the Teflon®-lined septum. The vial 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 vial containing the [14C]sodium bicarbonate, the [14C]sodium bicarbonate was converted to [14C]carbon dioxide by the addition of 0.5 mL of 6 M hydrochloric acid. The addition of the acid was made through the septum via syringe. The headspace of the vial was allowed to purge at a flow rate of approximately 20 mL/minute for 20 hours. Upon completion of the purge, aliquots of the ethylene glycol and potassium hydroxide traps were radioassayed by LSC to determine recovery. The polyurethane foam plugs were extracted twice with 5 mL portions of methanol, and aliquots radioassayed to determine additional recovery. The radioactivity quantified from each trap was used to determine overall radioactive recovery and the trapping efficiency of the experimental set-up.
After the 20-hour purge of the test vial containing the acidified [14C]sodium bicarbonate, 95.7 % of the added radioactivity was recovered in the potassium hydroxide trapping solutions. Approximately 0.06 % of the applied radioactivity remained in the acidified sodium bicarbonate solution. The results of the trapping experiment, therefore, demonstrated that the trapping system was efficient for capturing 14CO2.
Two additional aerated samples for both the light-exposed and dark controls for each solution (pH 5, 7 and 9) were prepared and connected to the trapping system described above. Volatiles were trapped by continually drawing air through the headspace of the samples into the series of trapping media. The weight of these vessels was recorded on Day 0 and used as a comparison for remoisturisation at subsequent sampling intervals.

REPLICATION
- No. of replicates: Seventy-two samples were prepared, twenty-four for each buffer solution at pH 5, 7 and 9. Twelve tubes of each buffer solution containing 10 mg/L [14C-]test material were designated as light-exposed samples and twelve were used as dark controls.

OTHER
- The sample racks were constructed of stainless steel with internal copper coils, allowing for the circulation of a chilled refrigerant/water solution to cool the samples resting on the racks. A refrigerated/circulating bath containing approximately 15 % ethylene glycol: 85 % water maintained the temperature of the samples on the photolysis racks at approximately 25 °C throughout exposure.
Temperature was measured throughout exposure by placing the probe of a min-max thermometer into a clear borosilicate glass vial (19 x 65 mm) containing approximately 8 mL of reagent water. The vial, containing the thermometer probe, was placed on the photolysis racks with the test vessels.
- Test solutions were transferred in 8 mL aliquots to individual 19 mm x 65 mm borosilicate glass vials with Teflon®-lined septa and open-top screw caps. The test vessels for the dark controls were covered with aluminium foil.
Duplicate vials of irradiated and dark control test solutions were sampled after 1, 3, 7, 14 and 30 days of intermittent light (12 hours on/12 hours off) to establish the time course of test material loss and the pattern of formation and decline of significant degradates. At time 0, duplicate samples (approximateIy 2 mL) of each buffer containing the [14C]-test material solution were removed directly from the respective volumetric flask for HPLC-RAM and LSC analysis. At all other sampling intervals, duplicate samples from each buffer solution were removed from the photolysis racks and the total volume of each sample was measured. Aliquots (approximately 2 mL) were transferred from the appropriate vials into amber vials and chromatographically profiled by HPLC-RAM. Triplicate 0.1 mL aliquots were also removed from each sample and the amount of radioactivity present was quantified by LSC analysis and compared to the 0.1 mL aliquots radioassayed at time 0 to determine radiometric mass balance at each sampling interval.
Samples for initial analysis were stored either refrigerated or frozen for no more than 4 days prior to chromatographic analysis. After analysis, samples were stored frozen. In some instances, samples were re-chromatographed as long as 8 months after the initial analyses. In those instances, stability was established by first chromatographing the freezer-stored samples under the original conditions to allow comparison to the original analysis. Profiles of stored samples were nearly identical to those obtained initially, indicating long-term freezer storage stability.
The polyurethane foam plugs, ethylene glycol, sulfuric acid and 10 % potassium hydroxide trapping solutions were replaced and quantified by radioassay at each sampling interval except for Day 0. The total volumes of the ethylene glycol, sulfuric acid and potassium hydroxide solutions were recorded. Duplicate 1 mL aliquots of ethylene glycol and sulfuric acid solution and 0.5 mL of the potassium hydroxide traps were radioassayed after mixing with either 15 mL of Monophase® (ethylene glycol and KOH) or lnstagel (sulfuric acid) scintillation cocktail. Overflow traps containing liquid were also radioassayed by LSC. The foam plugs were extracted with two 5 mL portions of methanol by vortexing samples for several minutes and removing the solvent. Duplicate 1 mL aliquots were removed from the combined solvent and radioassayed after mixing with 15 mL of Monophase® scintillation cocktail.

- Confirmation of Trapped 14CO2 From Irradiated (Day 30) Samples by Barium Precipitation
Trapped 14CO2 in the potassium hydroxide trapping solution for a Day 30, pH 7 irradiated sample was confirmed by barium precipitation. A mixture of 5.0 mL of the potassium hydroxide trapping solution and 5.0 mL of a saturated barium hydroxide (Ba(OH)2) solution were combined in an 12 mL Nalgene® centrifuge tube. The contents of the tube were vortexed and the precipitate was allowed to settle overnight. The contents of the tube were centrifuged at 10 000 rpm for 15 minutes and the supernatant was decanted into a separate vial. The precipitate was dried under a gentle stream of nitrogen. Radioactivity in the supernatant was quantified by LSC analysis. Radioactivity in the precipitate was quantified by combustion analysis using a sample oxidiser.

- Ultra-Violet/Visible Spectral Analysis
Prior to test initiation, duplicate 10 mg/L solutions of test material in pH 5, 7 and 9 buffer solutions were prepared and UV-visible absorption spectra were recorded over the wavelength range of 280 to 900 nm using a Perkin Elmer Lambda 6 Spectrophotometer. No absorption exceeding 0.05 absorbance units at any wavelength longer than 290 nm was observed.

- Microbial Plate Counts to Verify Sterility of Test Solutions During Exposure (Irradiated Samples) and Incubation (Dark Controls)
The maintenance of sterility of test solutions (pH 5, 7 and 9) during the 30-day exposure (irradiated samples) and incubation (dark controls) was established by a standard plate count methodology. Pour plates were prepared by adding 100 μL of test solution (pH 5, 7 or 9 test solutions on Day 0 and pH 5, 7 or 9 irradiated and dark control samples on Day 30) to the centre of an empty plate along with approximately 15 to 20 mL of molten nutrient agar (45 to 50 °C). The plate was swirled on a level surface to homogeneously distribute the sample aliquot within the microbial medium. Colonies were counted on the plates after incubating at 35 ± 2 °C for 24 – 72 hours. Total counts for Day 0 and Day 30 at all pHs tested indicated no more than 60 colony forming units/mL (only in Day 30, pH 5 samples; no counts in all others), confirming that sterility had been maintained throughout the 30-day definitive study.
Duration:
30 d
Temp.:
25 °C
Initial conc. measured:
10 mg/L
Reference substance:
no
Dark controls:
yes
Computational methods:
- CALCULATIONS
During this study, calculations were performed using the following formulae:

- Initial (time 0) dpm per test vessel: (dpm in aliquot of dosing solution / aliquot size (mL)) x total volume of sample (mL)

Example: pH 7
Replicate 1: (10 308.045 dpm / 0.1 mL) x 8.0 mL = 824 643.6 dpm
Replicate 2: (10 111.482 dpm / 0.1 mL) x 8.0 mL = 808 918.56 dpm

(824 643.6 dpm + 808 918.56 dpm) / 2 = 816 781.08 dpm / test vessel

- Percent of applied radioactivity in test solution at a given sampling interval:
[((dpm in measured aliquot / aliquot size (mL)) x test volume (mL)) / initial time (time 0) dpm per test vessel] x 100

Example: pH 7, irradiated Replicate, Day 14:
[((9933.302 dpm / 0.1 mL) x 8.0 mL) / 816 781.08 dpm] x 100 = 97.3 %

- Determining volatile production (cumulative):
(mean dpm in measured aliquot (Day 1) / size of aliquot (mL)) x measured volume of trap (mL) +
(mean dpm in measured aliquot (Day 3) / size of aliquot (mL)) x measured volume of trap (mL) + etc.

Example: pH 7, irradiated, aerated samples during 30-day exposure (KOH-1 traps):
((< MDL* (Day 1) / 0.5 mL) x 13.0 mL) + ((53.4 dpm (Day 3) / 0.5 mL) x 13.0 mL) + ((< MDL* (Day 7) / 0.5 mL) x ~15.0 mL) + ((970.429 dpm (Day 14) / 0.5 mL) x 15.0 mL) + ((2167.884 dpm (Day 30) / 0.5 mL) x 12 mL) = 82 530 dpm

(82 530 dpm / 816 781.08 dpm) x 100 = 10.1 % of applied radioactivity

* < MDL = less than minimum detection limit

- Determining percent test material remaining (for kinetic analysis) at a given sampling interval:
(% of applied radioactivity in test solution of time t x % of HPLC profile contributed by test material) / 100

Example: Day 14, pH 7, irradiated sample:
(97.3 % x 31.7 %) / 100 = 30.8 % test material

HALF-LIFE DETERMINATION
At each sampling interval, the residual percentage of test material relative to time 0 in the irradiated and dark control solutions was determined in duplicate by HPLC-RAM analysis. The photolytic rate constant (k) and half-life (t½) of the test material were calculated at each pH tested by plotting the natural logarithm of the residual percentage of the test material versus time, using linear regression analysis. The photolytic rate constant was calculated from the following equation, based on apparent first-order kinetics:
Ln (test material at time t [relative to time 0]) = kt
Where:
k = rate constant (day^-1)
t = time (day)

The linear regression of Ln (test material % at a given sampling interval [relative to time 0]) versus time was determined with the slope of the regression line equal to k, the kinetic rate constant.

The half-life (t½) in days was calculated from the following equation:
t½ = 0.693 / |k|
Preliminary study:
A preliminary study in which 14C-test material in pH 7 buffer was irradiated for 7 days was conducted to establish appropriate sampling intervals for the definitive study, as well as to confirm the validity of the experimental study design.
Material balance ranged from 95.4 to 100 % and 94.8 to 103 % in non-aerated (volatiles not collected) irradiated and dark control samples, respectively. In aerated samples, where volatiles were trapped, material balance after 7 days averaged 89.4 and 101 % for irradiated and dark control replicates, respectively. A first-order kinetic plot of the chromatographic data (quantifying loss of the test material over the 7-day study) indicated half-lives of 5.28 and 406 days in irradiated and dark control samples, respectively. As a result of these data, sampling intervals for the definitive study were chosen to be Day 0, 1, 3, 7, 14 and 30.
Key result
DT50:
7.16 d
Test condition:
10 mg/L exposed to an artificial light source for 12 continuous hours per day
Transformation products:
yes
No.:
#1
No.:
#2
Details on results:
HALF-LIFE
For the irradiated samples, half-lives were calculated based on apparent first-order kinetics. For pH 7 irradiated samples, the half-life was calculated to be 7.16 days. Dark controls showed no significant degradation over the 30-day incubation period. The coefficient of determination of the linear regression was calculated to be 0.946, indicating an excellent fit of the data.
Additional exposures at pH 5 and 9 provided irradiated sample half-lives of 4.91 and 6.93 days, respectively. Coefficients of determination were calculated to be 0.971 and 0.919, respectively, indicating an excellent fit of the data. Dark controls at pH 5 and pH 9 showed no appreciable degradation of the test material.
The results of this study indicate that the test material readily undergoes photodegradation under artificial sunlight conditions. The lack of degradation in the dark controls indicates that the test material is hydrolytically stable between pH 5 and 9.

TEST CONDITIONS
- pH, sterility, temperature, and other experimental conditions maintained throughout the study: Measurement of pH in the buffer solutions during the study indicated that specified pH values had been maintained and that buffer capacities had not been exceeded for most samples. The material balances for non-aerated, pH 7 irradiated and dark control samples over the 30-day study ranged from 75.6 to 103 % and 94.4 to 103 %, respectively. Recovery in Day 30 aerated (i.e., volatile collection) samples averaged 77.9 and 97.8 % for irradiated and dark control samples, respectively.
Although not the primary focus of the study, additional exposures were also conducted at pH 5 and 9. The material balances for non-aerated, pH 5 irradiated and dark control samples ranged from 73.6 to 100 % and 94.3 to 100 %, respectively. Recovery in Day 30 aerated samples averaged 64.1 and 98.5 % for irradiated and dark controls, respectively. Material balances for nonaerated, pH 9 irradiated and dark control samples ranged from 95.6 to 103 % and 98.8 to 104 %, respectively. Recovery in Day 30 aerated pH 9 samples averaged 83.1 and 102 % for irradiated and dark controls, respectively.

MAJOR TRANSFORMATION PRODUCTS
The test material began to photodegrade primarily to more polar products as early as Day 1 of the light exposure. The polar degradates (represented by retention times from 3.60 to 12.8 minutes) were quantitatively substantial by Day 14, representing 67 % of the HPLC profile. To better resolve these photodegradates into individual components, chromatographic conditions were modified (using HPLC System #4) at the Day 14 sampling interval to provide a more gradual gradient elution program.
The Day 30 replicate sample was additionally profiled using HPLC System #5. As indicated, using the modified conditions to achieve better peak resolution, no individual photodegradate in the Day 14 (based on HPLC System #4) and the Day 30 (based on HPLC System #5) sample exceeded 10 % of the Day 0 radiocarbon, except for the photodegradate which was subsequently identified as o-cresol. The representative HPLC chromatograms of dark control samples from Day 14 and Day 30 (HPLC System #4) illustrate the hydrolytic stability of the test material.
Although originally profiled in HPLC System #3, one of the two replicate irradiated samples from Day 0, 1, 3 and 7 were re-chromatographed using HPLC #4. This was acceptable since after re-chromatographing these samples in HPLC System #3 after approximately 8 months of freezer storage, their profiles were essentially the same as when first chromatographed. This-indicated that the samples had remained stable during freezer storage.
The identification of o-cresol as a major photoproduct of the test material was initially accomplished by comparison of its HPLC retention time to that of the authentic reference standard which was purchased commercially. The retention time of the reference standard was 30.73 minutes (based on UV detection at 220 nm) compared to a 31.1-minute retention time of the radiolabelled photodegradate (based on radiometric detection). The 0.63 minute difference was due to the UV detector being placed first, in series, with the radiometric flow detector.
Structural confirmation of the photodegradate as o-cresol was accomplished by GC-MS. The major photodegradates in the Day 14 sample had nearly identical chromatographic retention time and electron impact mass spectrum as the authentic reference standard.

VOLATILISATION
Volatile photodegradates captured in the potassium hydroxide trapping solution (pH 7 aerated, irradiated samples) accounted for an average of 11.0 % of the applied radioactivity after the 30-day exposure. Trapped 14CO2 in the form of HCO3^- and CO3^-2 was confirmed by barium precipitation of an aliquot of a Day 30 irradiated sample potassium hydroxide trap. The precipitated Ba14CO3 was quantified by combustion to account for 69 % of the radioactivity present in the aliquot of the potassium hydroxide sample prior to barium addition.
In an additional experiment to characterise the nature of the radioactivity in the potassium hydroxide trapping solution, another aliquot (1 mL) of the pH 7 Day 30 potassium hydroxide solution was acidified to approximately pH 3 and radioassayed by LSC. One hour after acidification, no detectable radioactivity remained in the solution, confirming that all of the captured radioactivity in KOH was [14CO2].
The material balances at Day 30 in the pH 7 aerated and irradiated replicate samples were lower than in the non-aerated replicate samples. This was attributed to the difficulty in maintaining the efficiency of the volatile trapping system over a 30-day purging period.

SUPPLEMENTARY RESULTS:
- Confirmation of Residual Test Material In a Day 14 Irradiated Sample: The identification of residual test material in a Day 14 irradiated sample was confirmed by LC-(electrospray) mass spectrometry. The chromatographic retention times (10.73 versus 10.88 minutes) and mass spectra for the test material reference standard and the putative test material in the sample were nearly identical.
- HPLC Profiles in pH 5 and 9 Buffers: Although not the primary focus of the study, the photodegradate profiles in these buffers are similar to the photodegradate profiles in the pH 7 buffer. The test material is also hydrolytically stable at both pHs, based on HPLC chromatograms in the dark controls.
- HPLC Profiles In Aerated (Volatile Collection) Samples: The chromatographic profile of the aerated 30-day irradiated sample is qualitatively similar to the non-aerated sample The aerated 30-day dark control sample confirms the hydrolytic stability of the test material when not exposed to artificial light.
Validity criteria fulfilled:
not specified
Conclusions:
Under the conditions of the study first-order photolytic half-lives of the test material at pH 5, 7 and 9 were determined to be 4.91, 7.16 and 6.93 days, respectively. Based on the results of this study, the test material is not expected to persist in surface waters.
Executive summary:

A 30-day aqueous photolysis study of the test material was conducted according to the Pesticide Assessment Guidelines, Subdivision N Chemistry: Environmental Fate § 161-2 under GLP conditions.

The photolysis was studied in a 0.01 M phosphate buffer (pH 7) at 25 ± 1 °C. Test material samples (10 mg/L) were exposed to an artificial light source (xenon arc lamp) which had a spectral profile similar to natural sunlight The integrated light intensity of the artificial light (over the wavelength range of 250 to 700 nm) was determined to be approximately 30 to 50 % of the integrated light intensity of sunlight in August in Wareham, Massachusetts (42 ° North latitude). Therefore, the artificial light source was considered to be a suitable simulation model for natural sunlight.

First-order photolytic half-lives of the test material at pH 5, 7 and 9 were determined to be 4.91, 7.16 and 6.93 days, respectively. Coefficients of determination of the linear regressions were calculated to be 0.971, 0.946 and 0.919, respectively, indicating an excellent fit of the data at all three pHs. The test material did not appreciably degrade in the dark, indicating hydrolytic stability at pH 5 through 9.

Photodegradates were nearly all chromatographically more polar than the test material. When profiled with a gradual gradient elution program using reversed-phase (C18) HPLC, the major photodegradate (identified as o-cresol) accounted for as much as 30.4 % of the initial concentration in a Day 30, pH 7, irradiated replicate sample. The o-cresol photodegradate was identified initially by its chromatographic retention time as compared to the authentic reference standard. The identification was confirmed by comparing the gas chromatography/electron impact mass spectrum

Under the conditions of the study first-order photolytic half-lives of the test material at pH 5, 7 and 9 were determined to be 4.91, 7.16 and 6.93 days, respectively. Based on the results of this study, the test material is not expected to persist in surface waters.

Endpoint:
phototransformation in water
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
Study type:
other: kinetic analysis
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 water, as reported in Connor (1996b), 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:
3.5 d
Test condition:
DT50 as a trigger for further studies.
DT50:
3.5 d
Test condition:
DT50 for modelling
Transformation products:
yes
Remarks:
O-cresol
No.:
#1

Kinetics Fitting to the Test Material and Metabolite O-Cresol Due to Photolysis in Water

- Test Material Degradation Kinetics Via Aqueous Photolysis

SFO provided a good visual fit to the data and 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 α and β did include zero. The SFO fit is accepted as providing a reliable fit to the degradation of the test material in this study 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 in the autumn at 42°N latitude but 50 % of that expected naturally in the summer. Therefore, the DT50 values produced from this analysis were corrected with a factor of 0.5 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 7.0 days

o DT90 for use as trigger value 23.4 days

o DT50 for use in modelling 7.0 days

- Corrected (correction for light intensity in the summer)

o DT50 for use as trigger value 3.5 days

o DT90 for use as trigger value 11.7 days

o DT50 for use in modelling 3.5 days

- O-Cresol Degradation Kinetics Via Aqueous 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 good visual fits for the metabolite. All statistical tests passed, including the t-test which passed for the metabolite degradation constant and the confidence limits of ffM did not include zero. The X-error for the metabolite was 9.81 %. FOMC + SFO kinetics for the parent and metabolite respectively once again provided a good visual fit for the metabolite. However, the t-test failed for the metabolite degradation constant and confidence limits for α and β both included zero. Therefore, the SFO + SFO kinetics fit can be considered to provide reliable values for the formation and degradation of the o-cresol metabolite via aqueous photolysis.

The artificial light used in this study was recorded as approximately the same as that expected naturally at 42ºN latitude but 50 % of that expected naturally in the summer. Therefore, the DT50 values produced from this analysis were corrected with a factor of 0.5 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 62.3 days

o DT90 for use as trigger value is 207 days

o DT50 for use in modelling is 62.3 days

o ffM for use in modelling is 0.38

- Corrected values (correction for light intensity in the summer):

o DT50 for use as trigger value is 31.2 days

o DT90 for use as trigger value is 104 days

o DT50 for use in modelling is 31.2 days

o ffM for use in modelling is 0.38

The calculated values for the test material and the metabolite o-cresol for degradation via photolysis in water are presented below.

Summary of Fitted Parameters for the Decline of the Test Material and the Production and Decline of O-Cresol for Degradation Via Photolysis in Water.

Compound

Kinetic Model

Fitted Parameters

Aqueous Photolysis

Test material

SFO

M0(%)

99.63

k1(d-1)

0.098

FOMC

M0(%)

100.7

α

5.71

β

51.98

DFOP

 

Not required

o-cresol

SFO + SFO

M0(%)

99.52

k1(d^-1)

0.098

km(d^-1)

0.011

ffM

0.378

FOMC + SFO

M0 (%)

100.7

α

5.48

β

49.82

km(d^-1)

0.008

ffM

0.361

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 data-set is useful for the calculation of the appropriate kinetic parameters for the test material and the metabolite o-cresol in water due to photolysis. Kinetics for the parent test material could be fitted to the data-set, providing reliable kinetics parameters. O-cresol was only identified at relevant concentrations in the aqueous photolysis study where reliable kinetics parameters could be determined using an SFO + SFO kinetics fit.

A summary of the key parameters for the test material and o-cresol following photolysis in water are shown below. The (corrected) aqueous photolysis DT50 for the test material of 3.5 days is rather shorter than the 40 days in the peer review (EC 2003). However, the kinetics fit was well supported by both visual assessment and the statistics and therefore the use of this value appears reasonable. The aqueous photolysis (corrected) DT50 for o-cresol of 31.2 days and the formation fraction of 38 % is supported by visual assessment and the statistics of the fitting procedure making their use acceptable in risk assessment. However, o-cresol is considered of only slight toxic concern (PAN 2015) as it has lost the chlorine atom from the aromatic carbon ring (therefore losing the toxophore from the parent compound, Sinclair 2009). It should be noted that these corrected degradation values are relevant to light intensity at roughly 42°N in summer conditions; relevant for southern and central zones, but perhaps not as reliable for modelling in the northern zone. Use of the uncorrected DT50 values may be appropriate when considering autumn applications.

Summary of Fitting Parameters for the Decline of the Test Material and O-Cresol Following Photolysis in Water

Endpoint

Test 

Material

O-Cresol

Temperature correction

Light intensity correction (for summer conditions)

0.5

0.5

Kinetic model for use to trigger studies

SFO

SFO + SFO

DT50 trigger (uncorrected) (days)

7.0

62.3

DT90 trigger (uncorrected) (days)

23.4

207

DT50 trigger (corrected) (days)

3.5

31.2

DT90 trigger (corrected) (days)

11.7

104

Kinetic model for use in modelling

SFO

SFO + SFO

DT50 modelling (uncorrected) (days)

7.0

62.3

DT50 modelling (corrected) (days)

3.5

31.2

Formation Fraction

0.38

Kinetics were fitted to both the test material and o-cresol data from a aqueous 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): 3.5

- DT90 as a trigger for further studies (d): 11.7

- DT50 for modelling (d): 3.5

O-Cresol:

- DT50 as a trigger for further studies (d): 31.2

- DT90 as a trigger for further studies (d): 104

- DT50 for modelling (d): 31.2

- Formation fraction (%): 38

Validity criteria fulfilled:
not applicable
Conclusions:
Kinetics were fitted to both the test material and o-cresol data from a aqueous 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): 3.5
- DT90 as a trigger for further studies (d): 11.7
- DT50 for modelling (d): 3.5
O-cresol:
- DT50 as a trigger for further studies (d): 31.2
- DT90 as a trigger for further studies (d): 104
- DT50 for modelling (d): 31.2
- Formation fraction (%): 38
Executive summary:

This study summary relates to the degradation kinetics study to re-assess the degradation of the test material and metabolites due to photolysis in water, as reported in Connor (1996b), 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 o-cresol data from a aqueous 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): 3.5

- DT90 as a trigger for further studies (d): 11.7

- DT50 for modelling (d): 3.5

O-cresol:

- DT50 as a trigger for further studies (d): 31.2

- DT90 as a trigger for further studies (d): 104

- DT50 for modelling (d): 31.2

- Formation fraction (%): 38

Endpoint:
phototransformation in water
Type of information:
experimental study
Adequacy of study:
supporting study
Study period:
Not reported
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
study well documented, meets generally accepted scientific principles, acceptable for assessment
Study type:
direct photolysis
Qualifier:
no guideline followed
Principles of method if other than guideline:
The test material was irradiated under various conditions of pH, oxygenation and wavelengths in order to study the reactions involved in the aqueous phototransformation.
GLP compliance:
not specified
Specific details on test material used for the study:
- Purity: 96 %
The commercial product, which was slightly coloured, was purified by recrystallisation from water + ethanol (1 + 1 by volume) and obtained as colourless needles. Its purity was confirmed by NMR and high performance liquid chromatography (HPLC) analyses.
Radiolabelling:
no
Analytical method:
gas chromatography
high-performance liquid chromatography
mass spectrometry
other: UV-VIS and fluorescence spectrophotometry, NMR
Buffers:
To compare the photochemical behaviour of both forms of test material, solutions were irradiated either at pH 2.15 (in the presence of hydrochloric acid) or at pH 5.5 (phosphate buffer).
Light source:
other: Xenon lamp, Mercury lamp, Fluorescent lamps, Lamps (Philips HPW 125), Natural sunlight
Details on light source:
Several devices were used for the irradiation of solutions. For the determination of quantum yields, solutions were irradiated at 280 nm with a xenon lamp (1 600 W) equipped with a Schoeffel monochromator providing a parallel beam. Band width at mid-height was about 10 nm. The photon flow was evaluated at 3.7 x 10^14 photons/cm^2/s with potassium ferrioxalate.
Solutions were irradiated at 254 nm in a device consisting of a cylindrical mirror with an elliptic base, a low-pressure mercury lamp ('Germicide Lamp') located along one of the focal axes and a quartz cylindrical reactor (2 cm ID) located along the other focal axis. The average photon flow received in 30 mL was evaluated as 2.1 x 10^17 photons/s, using uranyl oxalate as the chemical actinometer. In order to isolate photoproducts, a solution (100 mL) was irradiated with six low pressure mercury lamps surrounded by a cylindrical mirror. The photon flow in 100 mL was evaluated at 2.8 x 10^18 photons/s with uranyl oxalate.
Two other devices were used to study the influence of irradiation wavelength. One consisted of six fluorescent lamps (Duke GL 20W) emitting at wavelengths longer than 275 nm with a maximum near 310 nm. Mercury lines at 365, 405 and 436 nm were also emitted, but were not involved in the direct phototransformation of the test material. The quartz reactor was placed along the symmetry axis. The photon flow received in 21.5 mL was evaluated at 9.9 x 10^16 photons/s; this value is lower than the total photon flow emitted by the lamp, since the actinometer absorbs only a low percentage of the energy emitted on lines 405 nm and 436 nm, but slightly higher than the photon flow really absorbed by the solution of test material.
In the other device, solutions were irradiated with lamps (Philips HPW 125) and maintained at room temperature with a cooling jacket. These lamps were medium pressure mercury lamps fitted with a black bulb in order to select the line at 365 nm. About 85, 6 and 2 % of the light was emitted at 365 nm, 334 nm and 313 nm respectively. With this device the photon flow was evaluated at 2.4 x 10^17 photons/s in 20 mL using the chemical actinometer Aberchrome 540. Potassium ferrioxalate is too sensitive in these conditions and uranyl oxalate is not sufficiently absorbing at 365 nm.
Solutions were also exposed in natural sunlight in a 'Pyrex' vessel. Experiments were carried out in Clermont-Ferrand (latitude 46 ° N, altitude 420 m) in September.




Details on test conditions:
- Deoxygenation
In order to study the influence of oxygen, solutions were deoxygenated by argon bubbling for 50 min. The reactor was closed with a septum and samples were collected with a syringe at different stages of the photochemical transformation.
Reference substance:
not specified
Dark controls:
yes
Computational methods:
Not reported
Transformation products:
yes
No.:
#1
No.:
#2
No.:
#3
No.:
#4
Details on results:
- UV absorption
Molecular and anionic forms of the test material have similar UV spectra. They absorb at wavelengths shorter than 310 nm. The maximum of absorption of both forms is located at 280 nm, but the molar absorption coefficient is slightly higher for the anionic form (ε = 1 604 M^-1cm^-1) than for the molecular form (ε = 1 390 M^-1 cm^-1) . The absorption spectrum of the test material overlaps with that of sunlight in summer, since the wavelength of sunlight starts at about 295 nm at sea level. The overlap is smaller, but not negligible, in winter. It is shown experimentally that the test material may be phototransformed in September. However, in environmental conditions some induced photoreactions may also be involved.

- Irradiation of the anionic form
A solution 4.94 x 10^-4 M of test material buffered at pH 5.5 was irradiated at 254 nm in the presence and in the absence of oxygen. Similar UV spectra were observed in both cases. The absorption increases and a weak absorption band appears between 300 and 400 nm. In both cases two photoproducts appear on the HPLC chromatogram.
The same photoproducts are formed when solutions are irradiated between 275 and 350 nm in the presence or in the absence of oxygen. Thus the formation of products is affected neither by oxygen nor by the irradiation wavelength between 254 nm and 350 nm. (Absorption is very low at λ > 310 nm).
2-(4-hydroxy-2-methylphenoxy)propionic acid is clearly the main primary photoproduct. Its UV spectrum, obtained on a photodiode array detector, is similar to the spectrum of the test material. It was isolated by preparative HPLC and identified by MS and 1H NMR.

- Induced phototransformation
Fe(III) salts absorb in the range 300 - 400 nm and may induce the photooxidation of organic substrates present in the solution. Several processes may be involved, depending on the substrate. In the present work, Fe(III) perchlorate (10^-3 M) was used to induce the degradation of the test material in acidic solution (5.03 x 10^-4 M; pH 2.15) irradiated at 365 nm. The acidification was necessary to prevent the precipitation of Fe(III) hydroxide. After 30 min about 83 % of test material was transformed, whereas direct photolysis is negligible under these conditions. The main product is 4-chloro-o-cresol that accumulates in the solution.
Methanol was used as a quencher of ·OH to identify the role of these radicals in the reaction. In the presence of methanol (20 mL/L, about 0.49 M) transformation is inhibited by about 80 %, whereas about 99 % of ·OH is quenched. (Evaluated from the rate constant 9.7 x 10^8 M^-1 s^-1 for the reaction ·OH + CH3OH). It was deduced that hydroxyl radicals contribute to the formation of 4-chloro-o-cresol, but probably another pathway is also involved.
Nitrite and nitrate ions are also photochemical sources of hydroxyl radicals.
The quantum yield of photolysis is significantly higher with HNO2 (about 0.45) than with NO2- (0.015 - 0.07 according to the wavelength) and NO3- (0.009 - 0.017). Nitrite ions were preferred to nitrate ions in the present work since they absorb at longer wavelengths (maximum at 352 nm) than nitrate ions (maximum at 302 nm) and it is possible to excite them selectively at 365 nm in the presence of test material. A further advantage is that nitrite ions have a higher molar absorption coefficient and higher quantum yield, but unfortunately NO2- ions are good ·OH quenchers and the production of ·OH in a solution is only efficient at low concentrations of nitrite.
A 5.0 x 10^-4 M solution of test material with 5 x 10^-4 M sodium nitrite and acidified at pH 2.15 was irradiated at 365 nm. Several photoproducts were formed but only 4-chloro-o-cresol accumulated in the solution. The efficiency increased with increasing irradiation time and it may be assumed that 4-chloro-o-cresol is not only formed as a primary photoproduct. By comparison with a solution kept in the dark it was established that this transformation did not result from a thermic reaction of HNO2. The rate of formation of 4-chloro-o-cresol was significantly higher at pH 2.15 than at pH 5.15, due to the fact that the photolysis of HNO2 is more efficient than the photolysis of NO2-.







Validity criteria fulfilled:
not applicable
Conclusions:
The formation of the main primary photoproducts resulting from the phototransformation of the test material is not influenced either by oxygen or by wavelength in the range 254 - 310 nm, but depends on pH (different photochemical behaviour of molecular and anionic forms): Heterolytic photohydrolysis is the main reaction observed with the anionic form, whereas a photochemical rearrangement is the main pathway with the molecular form. A number of other photoproducts were identified: o-cresol, 4-chloro-o-cresol and quinonic derivatives. The photoreactivity of the molecular form is interesting for comparison with other chloroaromatic pesticides, but generally it plays a minor role under environmental conditions.
Different photochemical reactivity was observed when solutions were irradiated in sunlight or near­UV light. Under these conditions 4-chloro-o-cresol is formed as the main photoproduct. This phenomenon confirms the wavelength effect previously reported in the case of 4-chloro-2-methylphenoxyacetic acid. It is attributed to reactions induced by quinonic compounds formed as intermediates.
The transformation of the test material can be induced by Fe(III) salts and nitrite ions, leading to the formation of 4-chloro-2-methylphenol as the main product. An oxidation of the acetic moiety by hydroxyl radicals may be suggested.
The test material does not accumulate in environmental conditions and induced reactions play a major role in the phototransformation.
Executive summary:

The test material was irradiated under various conditions of pH, oxygenation and wavelengths in order to study the reactions involved in the phototransformation. Four main photoproducts were identified: 2-(4-hydroxy-2-methylphenoxy)propionic acid, o-cresol, 2-(5-chloro-2-hydroxy-3- methylphenyl)propionic acid, and 4-chloro-o-cresol. When the anionic form of the test material was irradiated between 254 nm and 310 nm (UV-C or UV-B), 2-(4-hydroxy-2-methylphenoxy)propionic acid was the main photoproduct. At 254 nm its formation initially accounted for more than 80 % of the transformation. The reaction results from a heterolytic photohydrolysis. O-cresol accounted for only a low percentage of the transformation. The stoichiometry was different with the molecular form: The main photoproduct, 2-(5-chloro-2-hydroxy-3- methylphenyl)propionic acid, resulted from a rearrangement after a homolytic scission. Products 2-(4-hydroxy-2-methylphenoxy)propionic acid, o-cresol and 4-chloro-o-cresol were also formed as minor photoproducts. Some other minor photoproducts were also identified. In contrast, 4-chloro-o-cresol was the main photoproduct under sunlight irradiation or when solutions were irradiated in near-UV light (UV-A). This wavelength effect is attributed to the involvement of an induced phototransformation; 4-chloro-o-cresol is also the main photoproduct when the phototransformation is induced by Fe(III) perchlorate or nitrite ions. In usual environmental conditions the excitation of the molecular form is negligible and the phototransformation is mainly due to induced photoreactions.

Endpoint:
phototransformation in water
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
supporting study
Justification for type of information:
Please see the read-across justification report in IUCLID Section 13.
Reason / purpose for cross-reference:
read-across source
Transformation products:
yes
No.:
#1
No.:
#2
No.:
#3
No.:
#4

Description of key information

Connor (1996b)

Under the conditions of the study first-order photolytic half-lives of the test material at pH 5, 7 and 9 were determined to be 4.91, 7.16 and 6.93 days, respectively. Based on the results of this study, the test material is not expected to persist in surface waters.

Supporting Study: Klӧpffer (1991)

Under the conditions of the study, the upper limit of the quantum efficiency of direct photochemical transformation (Φ, test material in water) was found to be ≤ 0.23.

Supporting Study: Maestracci (1992)

Minimum environmental photolytic half-life of the test material in water can be estimated to 6 593 h in July

Supporting Study: Hazlerigg & Garrett (2015)

Kinetics were fitted to both the test material and o-cresol data from a aqueous 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): 3.5

- DT90 as a trigger for further studies (d): 11.7

- DT50 for modelling (d): 3.5

O-cresol:

- DT50 as a trigger for further studies (d): 31.2

- DT90 as a trigger for further studies (d): 104

- DT50 for modelling (d): 31.2

- Formation fraction (%): 38

Read-Across Substance: Meunier & Boule (2000)

The formation of the main primary photoproducts resulting from the phototransformation of the test material is not influenced either by oxygen or by wavelength in the range 254 - 310 nm, but depends on pH (different photochemical behaviour of molecular and anionic forms): Heterolytic photohydrolysis is the main reaction observed with the anionic form, whereas a photochemical rearrangement is the main pathway with the molecular form. A number of other photoproducts were identified: o-cresol, 4-chloro-o-cresol and quinonic derivatives. The photoreactivity of the molecular form is interesting for comparison with other chloroaromatic pesticides, but generally it plays a minor role under environmental conditions.

Different photochemical reactivity was observed when solutions were irradiated in sunlight or near­UV light. Under these conditions 4-chloro-o-cresol is formed as the main photoproduct. This phenomenon

confirms the wavelength effect previously reported in the case of 4-chloro-2-methylphenoxyacetic acid. It is attributed to reactions induced by quinonic compounds formed as intermediates.

The transformation of the test material can be induced by Fe(III) salts and nitrite ions, leading to the formation of 4-chloro-2-methylphenol as the main product. An oxidation of the acetic moiety by hydroxyl radicals may be suggested.

The test material does not accumulate in environmental conditions and induced reactions play a major role in the phototransformation.

Key value for chemical safety assessment

Half-life in water:
7.16 d

Additional information

Connor (1996b)

A 30-day aqueous photolysis study of the test material was conducted according to the Pesticide Assessment Guidelines, Subdivision N Chemistry: Environmental Fate § 161-2 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 photolysis was studied in a 0.01 M phosphate buffer (pH 7) at 25 ± 1 °C. Test material samples (10 mg/L) were exposed to an artificial light source (xenon arc lamp) which had a spectral profile similar to natural sunlight The integrated light intensity of the artificial light (over the wavelength range of 250 to 700 nm) was determined to be approximately 30 to 50 % of the integrated light intensity of sunlight in August in Wareham, Massachusetts (42 ° North latitude). Therefore, the artificial light source was considered to be a suitable simulation model for natural sunlight.

First-order photolytic half-lives of the test material at pH 5, 7 and 9 were determined to be 4.91, 7.16 and 6.93 days, respectively. Coefficients of determination of the linear regressions were calculated to be 0.971, 0.946 and 0.919, respectively, indicating an excellent fit of the data at all three pHs. The test material did not appreciably degrade in the dark, indicating hydrolytic stability at pH 5 through 9.

Photodegradates were nearly all chromatographically more polar than the test material. When profiled with a gradual gradient elution program using reversed-phase (C18) HPLC, the major photodegradate (identified as o-cresol) accounted for as much as 30.4 % of the initial concentration in a Day 30, pH 7, irradiated replicate sample. The o-cresol photodegradate was identified initially by its chromatographic retention time as compared to the authentic reference standard. The identification was confirmed by comparing the gas chromatography/electron impact mass spectrum

Under the conditions of the study first-order photolytic half-lives of the test material at pH 5, 7 and 9 were determined to be 4.91, 7.16 and 6.93 days, respectively. Based on the results of this study, the test material is not expected to persist in surface waters.

Supprting Study: Klӧpffer (1991)

The phototransformation of the test material in water was determined according to the UBA Test Guideline Direct Phototransformation under GLP conditions. The study was awarded a reliability score of 2 in accordance with the criteria set forth by Klimisch et al. (1997).

The test material is dissolved in water. The decrease in concentration of the test material under illumination with UV-radiation of 304 nm with time is followed by HPLC. The intensity of the UV-radiation (spectral photon irradiance) is measured using chemical actinometry. The quantum efficiency of the disappearance is calculated for the irradiation wavelength.

In order to enable calculation of the photochemical lifetime (or half-life) of the test material, the UV-absorption spectrum was measured in the range 290 to 400 nm.

An aqueous solution of the test material was illuminated at 304 nm for up to 144 hours without significant decrease in concentration.

Under the conditions of the study, the upper limit of the quantum efficiency of direct photochemical transformation (Φ, test material in water) was found to be ≤ 0.23.

Supporting Study: Maestracci (1992)

The calculated environmental photolytic half-life can be used for a rough estimation of the persistence of the chemical being irradiated. The calculation carried out is valid for direct phototransformation in the top millimetres of a natural aquatic system. The study was awarded a reliability score of 2 in accordance with the criteria set forth by Klimisch et al. (1997).

The pseudo first-order constant for direct transformation (k) and thus the lifetime (τ) and half-life (t½) of a chemical in water can be computed from:

- The experimentally determined quantum yield of disappearance of the compound upon excitation;

- The experimentally determined light absorption spectrum of the compound in aqueous solution at above 290 nm, which is the lower spectral limit of sunlight reaching the earth’s surface;

- The solar light intensity available in the spectral range which coincides with the light absorption spectrum of the compound. 

In central Europe, variations of the solar irradiance are mainly caused by the climatic conditions and not by the geographical location. Therefore, it seems to be appropriate to use mean solar irradiances for the estimation of photochemical transformation rates. The data used for these estimations reflect the mean values of solar irradiance in Europe at 52 ° northern latitude. The calculation of these data based on the spectral solar irradiance outside the earth’s atmosphere depends on the zenith angle. For the performance of the calculations the zenith angle was set to noon minus ⅙ of daylight for each month. With this value the light attenuation due to light scattering and adsorption was calculated for the performance of the calculations. The calculated clear sky was finally corrected for the influence of clouds.

Quantum yield for the loss of the test material was estimated to be less than or equal to 0.23 mole x Einstein^-1. Molar extinction coefficients of the test material were obtained. From the upper limit of a quantum yield only a lower limit of the environmental half-life can be calculated.

Minimum environmental photolytic half-life of the test material in water can be estimated to 6593 h in July.

Supporting Study: Hazlerigg & Garrett (2015)

This study summary relates to the degradation kinetics study to re-assess the degradation of the test material and metabolites due to photolysis in water, as reported in Connor (1996b), 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 o-cresol data from a aqueous 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): 3.5

- DT90 as a trigger for further studies (d): 11.7

- DT50 for modelling (d): 3.5

O-cresol:

- DT50 as a trigger for further studies (d): 31.2

- DT90 as a trigger for further studies (d): 104

- DT50 for modelling (d): 31.2

- Formation fraction (%): 38

Read-Across Substance: Meunier & Boule (2000)

The test material was irradiated under various conditions of pH, oxygenation and wavelengths in order to study the reactions involved in the phototransformation. The study was awarded a reliability score of 2 in accordance with the criteria set forth by Klimisch et al. (1997). Four main photoproducts were identified: 2-(4-hydroxy-2-methylphenoxy)propionic acid, o-cresol, 2-(5-chloro-2-hydroxy-3- methylphenyl)propionic acid, and 4-chloro-o-cresol. When the anionic form of the test material was irradiated between 254 nm and 310 nm (UV-C or UV-B), 2-(4-hydroxy-2-methylphenoxy)propionic acid was the main photoproduct. At 254 nm its formation initially accounted for more than 80 % of the transformation. The reaction results from a heterolytic photohydrolysis. O-cresol accounted for only a low percentage of the transformation. The stoichiometry was different with the molecular form: The main photoproduct, 2-(5-chloro-2-hydroxy-3- methylphenyl)propionic acid, resulted from a rearrangement after a homolytic scission. Products 2-(4-hydroxy-2-methylphenoxy)propionic acid, o-cresol and 4-chloro-o-cresol were also formed as minor photoproducts. Some other minor photoproducts were also identified. In contrast, 4-chloro-o-cresol was the main photoproduct under sunlight irradiation or when solutions were irradiated in near-UV light (UV-A). This wavelength effect is attributed to the involvement of an induced phototransformation; 4-chloro-o-cresol is also the main photoproduct when the phototransformation is induced by Fe(III) perchlorate or nitrite ions. In usual environmental conditions the excitation of the molecular form is negligible and the phototransformation is mainly due to induced photoreactions.