pymetrozine (ISO); (E)-4,5-dihydro-6-methyl-4-(3-pyridylmethyleneamino)-1,2,4-triazin-3(2H)-one

Phototransformation in water

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

phototransformation in water

Type of information:

experimental study

Adequacy of study:

supporting study

Study period:

23 Feb 1993 to 17 May 1993

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:

other: UBA Draft Test Guideline "Phototransformation of Chemicals in Water, Part A, Direct Phototransformation", Berlin, FRG

Version / remarks:

January 1990

Deviations:

no

GLP compliance:

yes

Radiolabelling:

no

Analytical method:

high-performance liquid chromatography

other: UV/VIS-spectroscopy

Details on sampling:

IRRADIATION TIMES
- Test series 1 and 2 (with test solution C): 0, 1, 2, 5, 10, 20, 40, 80 minutes
- Test series 4 and 5 (with test solution C and D, resp.): 0, 60, 120, 180 minutes
- Test series 3 and 6 (with test solution C and D, resp.): 20 minutes

HPLC-analysis was done immediately after exposition ( with a lag time of about 5 minutes between end of photolysis and injection for HPLC) and repeated every 240 minutes for 4 times in order to evaluate the relaxation pattern. For a more thorough investigation of the reisomerization process after photolysis the samples of test series 3 and 6 were reanalysed every 20 minutes up to a final observation time of 380 minutes. For the time of reanalysis all samples were stored at 20° C in the thermostated autoinjector.

For 4-nitroanisole (used to determine the photon flux in the optical cells), the exposure times were 1, 15, 30, 60 and 120 minutes (for test solution E). HPLC analysis was also done directly after exposition.

Buffers:

For UV/VIS-Spectroscopy and photolysis a 0.01 molar buffer solution of pH 7 was prepared by diluting phosphate buffer containing 0.041 mol Na2HPO4 and 0.028 mol KH2PO4 with Millipore S.Q.S.-water in a ratio of 1:7.

Light source:

Xenon lamp

Light spectrum: wavelength in nm:

313

Details on light source:

The test solutions for exposure were irradiated on an optical bench system, fitted with a xenon arc light source and a monochromator with adjustable slits to supply monochromatic light of appropriate wavelength. The following operational conditions were used:
- Lamp current: 40 A (corresp. to 800 W power)
- Slit width: 1 mm (corresp. to 6.5 nm halfband width
- Light intensity: 0.0017 mol photons*L-1*h-1

The UV-beam was collimated orthogonal to the plane, polished surface of the cuvettes and the solutions were completely irradiated by the UV-radiation.

CHEMICAL ACTINOMETRY
The incident light available in the photolysis vessels was determined with test solution E by a light induced reaction between 4-nitroanisole and pyridine. The actinometric measurements were executed before, between and after the test series with the test substance.

Details on test conditions:

TEST SYSTEM
- Type, material and volume of test apparatus/vessels: Rectangular cuvettes (optical path length 1 cm, sample volume 1.5 mL), constructed entirely of Suprasil® quartz glass. The cuvettes were fitted tightly with Teflon stoppers.
- Sterilisation method: Because of the short reactions times there was no need to conduct the work under sterile conditions.

TEST MEDIUM
- Volume used/treatment: Sample volume was 1.5 mL
- Kind and purity of water: Millipore S.Q.S.-water
- Source of natural water (if applicable) in terms of geographical location, site characteristics and date of collection:

PREPARATION OF TEST SOLUTIONS
- Test solution A (for UVNIS-Spectroscopy): Exactly 2.5 mL of stock solution A was transferred into a 250 mL volumetric flask and made up with 0.01 molar buffer solution pH 7 to a final volume of 250 mL. The resulting concentration of a.i. was 1.9 ppm or 8.75E-06 mol/L.
- Test solution B (for UV/VIS-Spectroscopy): As another test solution for spectroscopy stock solution B was used without any further dilution. The concentration of a.i. was 19.52 ppm or 8.99E-05 mol/L.
- Test solution C (for photolysis of the test substance): Exactly 0.49 mL of stock solution A was transferred into a 250 mL volumetric flask and made up with 0.01 molar buffer solution pH 7 to a final volume of 250 mL. The resulting concentration of a.i. was 0.37 ppm or 1. 71E-06 mol/L.
- Test solution D (for photolysis of the test substance): Exactly 0.45 mL of stock solution A was transferred into a 250 mL volumetric flask and made up with 0.01 molar buffer solution pH 7 to a final volume of 250 mL. The resulting concentration of a.i. was 0.37 ppm or 1. 70E-06 mol/L.
- Test solution E (for photolysis of the 4-nitroanisole): Exactly 0.1 mL of stock solution D was transferred into a 100 mL volumetric flask and made up with 0.01 M pyridine to a final volume of 100 mL. The resulting concentration of a.i. was 0.61 ppm or 3.98E-06 mol/L.

SAMPLE IRRADIATION
The present construction of the optical bench system did not allow a simultanous irradiation of multiple samples; therefore the experiment was conducted in form of independent sequential time series. Pretests indicated a very rapid transformation of the parent molecule within the first 10 minutes of irradiation followed by a very slow further dissipation; addditionally a certain degree of reversabilty for the transformation was observed after storage of samples in the darkness. For these reasons three types of experiment were conducted:
- Two test series focussed on the initial transformation (test series 1 and 2)
- Two test series focussed on the long term degradation (test series 4 and 5)
- Two test series focussed on the relaxation process (test series 3 and 6)

For each sampling time one cuvette for photolysis and another one for dark control was used.

Duration:

16 h

Temp.:

20 °C

Initial conc. measured:

0.39 mg/L

Reference substance:

no

Dark controls:

yes

Computational methods:

The calculations were performed by a program for nonlinear curve fitting and parameter estimation

Parameter:

max lambda

Value:

297.5 nm

Parameter:

max epsilon

Value:

20 344 L/(mol cm)

Quantum yield (for direct photolysis):

0.31

Key result

DT50:

4.4 h

Test condition:

at 20 °C

Predicted environmental photolytic half-life:

The photochemical rate constants for the E-->Z-isomerization in shallow waters are estimated for midspring time at geographical latitudes of 50° N and 40° N which corresponds to locations such as Frankfurt or Winnipeg and Madrid or Denver respectively.
These rate constants, however, are not representative for the environmental half life of the test substance since the irreversible decay will be controlled by the thermal degradation of the Z-isomer. This thermal rate constant k Z-->Products is under all sun light conditions with 0.0026 [min-1] (at 20° C) much smaller than the photochemical rate constants kE-->Z for establishing the E/Zequilibrium (between 2.7E+05 [min-1] at 40° N and 2.0E+05 [min-1] at 50° N respectively) and represents thus the rate determining step. Assuming first order kinetics for this thermal degradation, a half life of 4.4 h is expected at 20° C which means a rapid degradation of the test substance in shallow surface waters.

Transformation products:

not measured

Details on results:

STABILITY OF THE TEST SUBSTANCE
The dark control samples of the test substance showed no degradation. Hence the compound was stable in its test solution for the duration of the experiments (See ‘Any other information on results incl. tables’).

UV/VIS-ABSORPTION SPECTRUM OF THE TEST SUBSTANCE
The test substance shows an absorption maximum at 297.5 nm with a decadic molar extinction coefficient of E = 20 344 L/mol/cm and at the irradiation wavelength of 313 nm still a value of E = 11 484 L/mol/cm. The spectrum levels out at 360 nm, indicating a large spectral overlap with sun light and thus a high interaction probability. The spectral data and the spectrum are represented in ‘Any other information on results incl. tables’.

1H-NMR-SPECTRA OF THE E- AND Z-ISOMERS OF THE TEST SUBSTANCE
A mixture of isomers was photochemically produced by irradiation of a saturated solution of the test substance in 3D-acetonitrile for 16 hours at 300 nm. Their existence and structures were confirmed by identical but field shifted 1H-NMR-spectra and the time dependent conversion of the resonance signals. Further on, the configuration of the Z-isomer was proven by absence of any nuclear overhauser effect between the 1H nuclear spins of the CH2 function of the triazine ring and N-N=CH-group which, in contrast, is observable for the E-isomer due to the close vicinity of both H-atoms in this configuration. Another support for the Z-configuration was derived from the J(CH) coupling constants between C-atom and H-atom of the N-N=CH-group with 174 Hz for the Z-isomer and 166 Hz for the E-isomer which is in good agreement with recent findings.

KINETICS OF THE PHOTOLYTIC AND THERMAL TRANSFORMATION OF THE TEST SUBSTANCE
A very rapid conversion of the test substance was observed for the first 10 minutes of irradiation at 313 nm, followed by a much less pronounced decline for the subsequent irradiation, reaching a level between 26% and 28% of the initial concentration after 180 minutes. However, after termination of light exposition and leaving the samples at 20°C in darkness for 16 hours, a relaxation up to a final value of 59% of the initial concentration occurred. Molecules like the test substance which are characterized by C=N bonds and large substituents on the carbon and nitrogen atoms, prefer for their ground-state the sterically less strained anti configuration. Further on, they are subject to photochemically and thermally controlled syn-anti isomerizations either by rotation around the C=N double bond or by linear inversion at the nitrogen. Especially irradiation of the E-isomer brings about the formation of the less thermodynamically stable Z-isomer which becomes subsequently reisomerized, establishing a photostationary ratio of both isomeres. It is, however, usually not possible to isolate the Z-isomer since it reverts easily by thermal conversion to the stable anti configuration (energy barriers around 58-75 k/mol).

The characterization of the ground state of the test substance being an E-configuration was supported by absence of any signal for the Z-isomer in HPLC before irradiation and by 1H-NMR analysis. Thus, at room temperature, the thermal E/Z-equilibrium is completely on side of the E-configuration. In the first stage of photolysis (partition A) the E-isomer becomes very rapidly converted into the Z-isomer until a photostationary equilibrium is established. This equilibrium is controlled by three processes, the photochemical E-->Z-isomerization, the photochemical Z-->E-isomerization and the thermal Z-->E-isomerization characterized by the rate constants k1, k2 and k5 respectively. These rate constants were calculated to be for k1 between 0.225 per minute and 0.240 per minute, for k2 about 0.149 per minute and for k5 between 0.0038 per minute and 0.0036 per minute in the independent irradiation experiments of series 1, 2 and 3, 6 respectively. After 20 minutes irradiation (partition B) the equilibrium concentration of E-isomer was about 36 % of the initial which means the equilibrium has been shifted strongly in favour of the Z-isomer. The equilibrium constants, calculated on basis of k1 and k2, are between 1.51 and 1.61 compared to the experimental observed values of 1.74 and 1.79 after 20 minutes irradiation. This difference between calculated and observed values can be attributed to the model assumption of a pure photochemical equilibrium which overestimates the photochemical Z-->E-isomerization in presence of a thermal Z-->E-isomerization.

In the third stage of photolysis (partition C) a slow and nearly constant decline of E- and Z-isomer was observed. This decline was also present after relaxation and is thus irreversible. It can be characterized by first order rate constants of 0.0015 per minute and 0.0016 per minute for the duplicate irradiation series and represents the summary rate of all irreversible processes (Σ k(irrev) = k3 + k4 + k6 + k7). Above rate constants are mean values of the calculated slopes immediately after irradiation and after relaxation for 240, 480 and 720 minutes as well. After termination of light exposition a slow relaxation up to a 59 % of the initial value was observed after 16 hours at 20° C (partition D). This incomplete reversion of the Z-isomer implies an irreversible degradation of the test substance via its Z-isomer. A more detailed evaluation of this relaxation process with experimental series 3 and 6 (after 20 minutes irradiation) gave rate constants of 0.0038 per minute and 0.0036 per minute for the thermal Z-->E-isomerization (k5) and 0.0029 per minute and 0.0023 per minute for the irreversible thermal decay of Z-isomer (k6) respectively. This thermal rate constant k Z-->Products with a mean value of 0.0026 per minute is in fair agreement with the irreversible decline of the test substance at equilibrium state (partition C). Since the rate constant for the thermal degradation of Z-isomer covers already completely the decline of parent concentration during irradiation any direct photolytic degradation of E- and Z-isomer may be excluded (k3 = 0 and k4 = 0). The parameters for optimal fit deviate slightly from those experimental parameters which may be due to the simplified approach for the different transformation processes which, of course, cannot represent the whole complexity.

ACTINOMETRY WITH 4-NITROANISOLE
Applying first order kinetics, the light induced reaction between 4-nitroanisole and pyridine could be described by rate constants of 0.00330 per minute, 0.00323 per minute and 0.00292 per minute before, between and after the irradiation experiments with the test substance respectively, with a mean of0.00315 per minute. These data indicate a slight decrease in photon flux during the experiment, with a mean calculated to be about I(313)= 0.0017 mol photons/L/h.

CALCULATION OF THE QUANTUM YIELD
First step in the transformation of the test substance by direct photolysis in water is the conversion of its E-isomer into the Z-isomer. This isomerization is controlled by a quantum yield of ФE-->Z = 0.31 which means, under consideration of the big overlap between spectral absorption of the test substance and spectral irradiance of sun light, that the a.i. will be very efficiently isomerized into its Z-isomer under environmental conditions.

Table: UV/VIS-Absorption Spectrum of the test substance

Wavelength λ (nm)	mol. Extinction ԑ (I/mol/cm)
280.0	15031
282.5	16083
285.0	17063
287.5	18160
290.0	19198
292.5	19931
295.0	20306
297.5	20344
300.0	19940
302.5	19000
305.0	17620
307.5	15910
310.0	13935
312.5	11685
315.0	9201
317.5	6753
320.0	4647
323.1	2794
330.0	834
340.0	131
350.0	25
360.0	6
370.0	0
313.0	11484

 

Table: Photochemical and Thermal Transformation of the test substance

Test Series 1 and 4							Test Series 2 and 5
Time of	Relaxation			[min]			Relaxation [min]
Irradiation   [min]	0	240	480		720	960	0	240	480	720	960
0	0.39	0.39	0.39		0.39	0.39	0.39	0.39	0.39	0.39	0.39
1	0.31	0.35	0.36		0.36	0.36	0.32	0.35	0.36	0.37	0.36
2	0.27	0.32	0.34		0.34	0.34	0.26	0.33	0.34	0.34	0.34
5	0.19	0.28	0.31		0.31	0.31	0.18	0.28	0.30	0.31	0.32
10	0.16	0.27	0.29		0.30	0.30	0.16	0.27	0.29	0.30	0.30
20	0.14	0.25	0.28		0.29	0.29	0.14	0.26	0.28	0.29	0.30
40	0.13	0.24	0.27		0.28	0.28	0.13	0.25	0.27	0.28	0.28
60	0.12	0.24	0.26		0.27	0.27	0.12	0.24	0.27	0.27	0.28
80	0.14	0.24	0.26		0.26	0.26	0.12	0.23	0.26	0.26	0.26
120	0.12	0.22	0.24		0.25	0.25	0.11	0.22	0.24	0.24	0.24
180	0.11	0.20	0.22		0.23	0.23	0.10	0.20	0.22	0.23	0.23
	Values in ppm						Values in ppm
The 80 min.sample of test serie 1 has already experienced some relaxation since analysis was retarded by about 20 min.

Table: Dark control for the photolysis of the test substance

Test Series 1 and 4						Test Series 2 and 5
Time of	Relaxation [min]					Relaxation [min]
Irradiation [min]	0	240	480	720	960	0	240	480	720	960
0	0.39	0.39	0.39	0.39	0.39	0.39	0.39	0.39	0.39	0.39
1	n.a.	n.a.	n.a.	n.a.	n.a.	n.a.	n.a.	n.a.	n.a.	n.a.
2	n.a.	n.a.	n.a.	n.a.	n.a.	n.a.	n.a.	n.a.	n.a.	n.a.
5	n.a.	n.a.	n.a.	n.a.	n.a.	n.a.	n.a.	n.a.	n.a.	n.a.
10	0.39	0.39	0.39	0.39	0.39	0.39	0.39	0.39	0.39	0.39
20	0.39	0.39	0.39	0.39	0.38	0.39	0.39	0.39	0.39	0.39
40	0.39	0.39	0.39	0.38	0.38	0.39	0.39	0.39	0.39	0.39
60	0.39	0.39	0.39	0.39	0.39	0.39	0.39	0.39	0.39	0.39
80	0.39	0.39	0.39	0.39	0.38	0.39	0.39	0.39	0.39	0.39
120	0.39	0.39	0.39	0.39	0.39	0.39	0.39	0.39	0.39	0.39
180	0.39	0.39	0.39	0.39	0.39	0.39	0.39	0.39	0.39	0.39
	Values in ppm					Values in ppm
No significant dark reaction
n.a. means not analysed

                                                            

Table: E/Z isomerisation        

Exposition Time [min]	Serie 2/5 E / Z	Serie 1/4 E / Z	Mean E / Z
0	108.4 / 0.0	107.7 / 0.0	108.1 / 0.0
1	87.9 / 10.7	86.1 / 10.7	87.0 / 10.7
2	73.3 / 18.7	74.0 / 17.5	73.7 / 18.1
5	50.9 / 30.3	54.4 / 27.6	52.7 / 28.9
10	44.0 / 33.1	46.1 / 30.3	45.1 / 31.7
20	39.9 / 33.7	40.3 / 32.6	40.1 / 33.1
40	36.5 / 33.8	37.8 / 33.6	37.2 / 33.7
60	34.9 / 32.9	35.0 / 33.5	35.0 / 33.2
80	34.1 / 32.3	40.3 / 29.4	37.2 / 30.9
120	32.0 / 29.5	33.9 / 29.0	33.0 / 29.2
180	28.8 / 27.1	31.7 / 25.2	30.2 / 26.2
260	42.3 / 16.3	43.0 / 14.3	42.7 / 15.3
340	50.3 / 11.9	51.3 / 8.1	50.8 / 10.0
420	55.5 / 4.8	56.4 / 4.1	56.0 / 4.5
500	58.0 / 2.7	58.7 / 3.0	58.3 / 2.8
580	60.4 / 1.3	60.7 / n.d.	60.5 / 0.7
660	61.6 / n.d.	61.2 / n.d.	60.5 / n.d.
740	61.8 / n.d.	62.6 / n.d.	62.2 / n.d.
820	62.5 / n.d.	62.8 / n.d.	62.6 / n.d.
900	63.2 / n.d.	63.8 / n.d.	63.5 / n.d.
peak responses of the isomeres, observed values in [mV•s]
Photolysis was terminated at 180 minutes, subsequently thermal relaxation
n.d. means not detectable

Validity criteria fulfilled:

not specified

Conclusions:

Under sun light conditions, the thermally stable E-isomer of the test substance is with a quantum yield of 0.31 in a first transformation step very efficiently isomerized into its unstable Z-isomer. This isomere is subject to three further transformation steps:
- a photochemical and thermal reisomerization to the E-isomer
- a thermal, irreversible degradation
There was no evidence of direct photochemical degradation of the test substance but the photochemical transformation into its Z-isomer is a necessary prerequisite for further degradation of the compound; thus the environmental half life is estimated from the thermal degradation of the Z-isomer to be about 4.4 hours at 20° C water temperature.
At midspringtime and clear skies, the environmental half life in shallow waters in central europe is expected to be less than one day, even under consideration of decreased rate constants-at lower temperatures.
These findings, however, do not exclude the evolution of photolysis products upon extended irradiation which may be brought about by indirect photolysis or photochemical interactions with thermal degradation products.

Executive summary:

The photolytic degradation of the test substance was studied at a concentration of 0.37 ppm (1. 71E-6 mol/L) in aquous buffer of pH 7 containing 0.2% acetonitrile, using monochromatic light of 313 nm of a xenon arc lamp operated at 800 W. The incident light intensity was determined by chemical actinometry to be 0.0017 mol photons/L/h. The test substance does exist at ambient temperature only in form of its E-isomer which became under light exposition very quickly photoisomerized to the photochemically and thermally unstable Z-isomer up to an equilibrium ratio of about 1 to 1.8. This Z-isomer was subject to three further transformation processes:

- a photochemical and thermal reisomerization to the E-isomer

- a thermal, irreversible degradation

There was no evidence of direct photochemical degradation of the test substance but the photochemical isomerization into its Z-isomer seems to be a necessary prerequisite for further degradation of the compound. The calculated mean rate constants were 0.233 per minute for the E-->Z-isomerization (at 313 nm) and 0.0026 per minute for the irreversible thermal decay of Z-isomer which means a thermal half-life of 4.4 hours (at 20° C), assuming first order kinetics. The quantum yield of the photochemical E-->Z-isomerization was found to be 0.31 which means under consideration of the big overlap between spectral absorption of the test substance and spectral irradiance of sun light, that the a.i. will be very efficiently isomerized to its Z-isomer under environmental conditions. The half-time of E-->Z-conversion in shallow waters was estimated for midspringtime at geograhical latitudes of 50° N and 40° N which corresponds to locations such as Frankfurt or Winnipeg and Madrid or Denver respectively. Under clear sky conditions, half-times between 5 minutes (at 40 ° N) and 7 minutes (at 50° N) are expected which means that the test substance is very rapidly isomerized into its unstable Z-isomer which itself decays with a half-life of 4.4 hours at 20° C.

Reference 2

Endpoint:

phototransformation in water

Type of information:

experimental study

Adequacy of study:

supporting study

Study period:

24 Feb 1994 to 27 Aug 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)

Version / remarks:

October 1992

Deviations:

no

Qualifier:

according to guideline

Guideline:

other: Biologische Bundesanstalt fur Land- und Forstwirtschaft (BBA, Germany) Guideline: Phototransformation of Chemicals in Water

Version / remarks:

January 1990

Deviations:

no

GLP compliance:

yes

Radiolabelling:

yes

Remarks:

[14C]-labelled at position 6 of the triazine ring

Analytical method:

high-performance liquid chromatography

mass spectrometry

other: Thin-layer chromatography (TLC), Liquid scintillation counting (LSC)

Details on sampling:

- Sampling intervals: Two test vessels were taken for analysis immediately after test substance addition. Duplicate irradiated test vessels were taken for analysis at 0.5, 1, 2, 4, 7 and 15 days after test substance addition. Duplicate dark control test vessels were taken at 2, 7 and 15 days after test substance addition. Trapping solutions associated with vessels which were taken for analysis were radioassayed (and replaced with fresh solutions where applicable) at the sampling times as appropriate.

- Storage of samples: Radioassay of each test solution, measurement of pH and removal of a subsample for microbiological examination were all carried out on the day of sampling. Quantitative HPLC analysis and two-dimensional TLC analysis, and HPLC and TLC co-chromatography with non-radiolabelled reference substances, were also carried out on the day of sampling. HPLC co-chromatography with a previously isolated photoproduct was carried out 4 weeks after sampling. When not being analysed, test solutions were stored at <-20°C. The unlabelled reference standards were also stored, as neat compounds, at -20°C during the course of the study. In addition to spectroscopic analysis, their stability was also assessed chromatographically during the course of the study: in all cases essentially only one HPLC UV peak or TLC UV spot was observed. Their stability was further confirmed by HPLC towards the end of the study. In this figure, the individual chromatograms of the three reference substances were obtained in April 1995 as part of another study; the chromatogram of the mixture of the reference substances, including non-radiolabelled test substance, was obtained in May 1995, just prior to the irradiation period in this study. Chromatograms which were obtained during the study, further testify to the stability of the reference substances.

Buffers:

- Buffer solution preparation: Potassium dihydrogen orthophosphate (2.722 g) was dissolved in ca 1900 mL water and the pH adjusted to 7.0 with a potassium hydroxide solution. The solution was then made up to volume in a 2 L volumetric flask and the pH checked. No further adjustment of pH was necessary.
- pH measurements: Measurements of the pH of test buffer solutions were made using a model 3030 pH meter. The meter was calibrated prior to each measurement using pH 4 and pH 7 standard buffer solutions.

Light source:

Xenon lamp

Light spectrum: wavelength in nm:

>= 290 - <= 400

Relative light intensity:

>= 1.2 - <= 1.34

Details on light source:

- Source: The study was conducted using a Suntest accelerated exposure unit fitted with a xenon arc light source. A special system of mirrors and filters prevented infra-red and ultra-violet radiation with a wavelength of less than 290 nm from reaching the test solutions. Hence the emission spectrum produced was similar to that of natural sunlight.
- Measurement of light intensities: The spectral energy distributions of the lamp source and natural sunlight were measured using a Spectrad system incorporating a model 1680B double spectrometer
- Comparison of the artificial light source and natural sunlight: Light intensity measurements were made at each test sample position in the Suntest apparatus at the beginning and the end of the study. Intensity measurements were made at 1 nm intervals over the wavelength range 290 - 400 nm. A plastic template was used to position the integrating sphere of the spectrometer at the correct position under the Suntest light source and at the same distance from it as the surface of the test solutions during the study. The incident light was measured through the top part of a test vessel identical to those used in the study. Light intensity measurements (290 - 400 nm) were also made of natural sunlight on 30 January 1995, 25 April 1995 and 3 August 1995 at the test facility (latitude 52° 21 'N, longitude 0° 15'W). The measurements of April 1995 were used to calculate the equivalent duration of natural sunlight received by each test solution. The remaining measurements were used to estimate confidence limits for these calculated values. The light intensity measurements were integrated to provide the total light intensity over the wavelength range 290 - 400 nm. For each position in the Suntest apparatus, the average intensity over the irradiation period was calculated from the starting and finishing values, assuming that any change in intensity during the study occurred in a linear fashion. This average intensity for each position was then used to calculate the equivalent time of irradiation of natural sunlight received by each test solution. Additionally, intensity measurements between 250 and 700 nm were made at the central position under the Suntest light source, and also of natural sunlight at test facility.

Details on test conditions:

TEST SYSTEM
- Test vessels: The test vessels were constructed of borosilicate glass and were cylindrical in shape, of internal diameter 2.5 cm and height 8.0 cm. They were each fitted with two entry ports, near the top, to allow for the collection of volatiles, and for the addition and removal of test solution. Vessels for irradiation were placed in individual sockets in a water-cooled steel block, positioned in the Suntest unit. The cooling block also incorporated magnetic field switching devices to drive Teflon-coated magnetic stirrer bars in the test solutions. Dark control solutions were placed on an oscillating shaker which was kept in darkness in a temperature-controlled room.
- Incubation conditions: Irradiated test solutions were maintained at ca 25°C and were stirred continuously with magnetic stirrer bars. These solutions were irradiated continuously. Control vessels were maintained in darkness at ca 25°C and were oscillated continuously.
- Sterilisation method: The test vessels and glassware were sterilised by autoclaving at 121 °C for 20 minutes. Treated buffer solution was sterilised by filtration through a 0.2 μm cellulose acetate filter. Addition of the radiolabelled test substance solution to the buffer solution, filtration of the treated buffer solution and dispensing of treated buffer solution into test vessels were carried out in a laminar flow cabinet. Samples of test solutions were taken for microbiological examination at each sampling interval.
- Details on traps: All test vessels (with the exception of those taken for time zero analysis) were incorporated into gas-flow systems, such that groups of two to four
vessels were connected, via sterile tubing, to each other in series. For each series, air was drawn, at a flow rate of ca 5 mL/minute, through a water trap (for humidification), a microbial filter (0.2 μm) the headspaces of the test vessels, another filter, then through an empty trap, and then through a series of Dreschel bottle traps containing ethyl digol (trap 1) or 1M aqueous potassium hydroxide solution (traps 2 and 3).

TEST MEDIUM
- Kind and purity of water: HPLC grade
- Preparation of test medium: The radiolabelled test substance was used as supplied, without any radiodilution. A stock solution of the radiolabelled test substance in methanol was prepared at a concentration of 1.46 mg/mL. An aliquot (3.5 mL) of this solution was transferred to a glass beaker and evaporated to dryness under a stream of nitrogen. Buffer solution (500 mL) was then added to the beaker to dissolve the solid. Dissolution of the solid was aided by sonication. After mixing, and filtration, triplicate aliquots (100 μL) of the treated buffer solution were taken for radioassay. From these measurements the concentration of the test substance in the treated buffer solution was 10.5 mg/L. Portions (20 mL) of treated buffer solution were aseptically transferred to pre-weighed test vessels, which were then re-weighed. Twelve vessels for irradiation were established, and a further six to act as dark controls. All of these allowed for the collection of volatile radioactivity. Two further vessels were established which were taken immediately for analysis (time zero analysis).
- Note: vessels which were destined for sampling at 0.5 and 1 day after addition of treated buffer solution were established 5 days after the start of irradiation of the other vessels. A portion of unfiltered treated buffer solution was stored in darkness at +4 °C during this period. This was then filtered, and radioassayed as described above. The measured concentration of the test substance in the solution was 10.2 mg/L. The radiochemical purity of the radiolabelled test substance was measured in the methanol stock solution (98.0%) and in the treated buffer solutions following addition to the test vessels (97.4% and 97.3% (0.5 and 1 day vessels)).

TEMPERATURE RECORDING
The temperature of the irradiated solutions was recorded using an indwelling thermocouple probe, positioned in a test vessel containing untreated buffer solution. The thermocouple was connected to a monitoring system manufactured at the test facility. The temperature of the room containing the dark control solutions was measured using a thermometer located in the room. Temperatures of irradiated and of dark control solutions were recorded twice daily. Throughout the study the mean recorded temperatures were 24.9°C (± 0.3°C) (irradiated vessels) and 25.0°C (± 0.4°C) (dark control vessels). The temperature ranges were 24.2 - 25.5°C (irradiated vessels) and 24.2 - 25.5°C (dark control vessels)

MICROBIAL EXAMINATION OF TEST SOLUTIONS
Using aseptic procedures, aliquots (1 mL) of each test solution were used to prepare Tryptone Soya Agar pour-plates in duplicate. The plates were incubated at 32 ± 1°C for 5 days. After incubation the plates were examined for bacterial and fungal growth and the results recorded

REPLICATION
- No. of replicates (dark): 2
- No. of replicates (irradiated): 2

Duration:

15 d

Temp.:

25 °C

Initial conc. measured:

10 mg/L

Reference substance:

no

Dark controls:

yes

Computational methods:

The line of best fit for the calculation of the half-life was calculated using a computer software package.

Key result

DT50:

6.8 d

Test condition:

at pH 7 and at 25°C, irradiated with 40°N summer sunlight.

Remarks on result:

other: assuming first order kinetics

Remarks:

The rate constant (k) was calculated to be 0.0992 - 0.1077/day

Predicted environmental photolytic half-life:

Light in the wavelength range 290 - 400 nm is most likely to cause photochemical reactions and so this range was chosen for comparative purposes. To relate the light intensity of the xenon arc source to natural summer sunlight (latitude 40°N) various corrections were necessary. The sunlight measurements relate to sunlight on 25 April 1995 at latitude 52°N. Published data (Mill et al 1982) indicate that the measured intensity on this day would be about 75 % of the midday midsummer intensity at latitude 40°N. Additionally it was assumed that the average daily radiation intensity from the sun is about 75 % of the peak intensity over a 12-hour period, whereas the radiation in the Suntest was of constant intensity

The ratios (r) for different positions in the Suntest apparatus were in the range 1.20 - 1.34 with a mean value of 1.25 (unrounded ratios were used in the formula). Calculated equivalent sunlight times are shown in ‘Any other information on results incl. tables’. The coefficients of variation of intensity measurements at different positions were 3% (pre-study) and 5% (post-study).

Transformation products:

yes

Details on results:

TEST CONDITIONS
- pH: The pH ranged from 6.96 – 7.06 throughout the test
- Sterility: Microbiological examination showed that sterility had been maintained in all test solutions

RECOVERIES
The total recovery of radioactivity from all test solutions (including volatile radioactivity) was in the range 96.7 - 102.9% of the amount initially applied (See 'Any other information on resutls incl. tables'). In calculating the recoveries of radioactivity, allowance was made for the changes (reductions) in the weights of the test vessels (+ solutions) before and after irradiation. Very little volatile radioactivity was evolved from irradiated solutions (2.6% after 15 days). This was distributed between the ethyl digol and potassium hydroxide solutions. Hardly any volatile radioactivity was evolved from dark control solutions (ca 0.1 % after 15 days).

DEGRADATION OF THE TEST SUBSTANCE
The test substance was rapidly and extensively degraded in irradiated test solutions. The half-life of the test substance, calculated assuming first-order kinetics, was equivalent to 6.8 days of latitude 40 °N summer sunlight. The test substance was hardly degraded at all in dark control solutions, such that the proportion of the test substance remaining had declined to about 95 % applied radioactivity after 15 days.

TRANSFORMATION PRODUCTS
- M2: Quantification the test substance and its photodegradation products was achieved using HPLC. Three components were separated by the method used, in addition to the test substance itself. The major component corresponded chromatographically to the reference substance M2. The levels of M2 rose to 71 % of the applied radioactivity after irradiation equivalent to 18 days of latitude 40°N summer sunlight, and then declined thereafter.

- M11: Reference substance M11 corresponded chromatographically to a photodegradation product representing up to 21 % applied radioactivity after 38 days equivalent summer sunlight. A third component, representing up to about 9 % applied radioactivity, was shown, after isolation of the eluate solution and re-chromatography (TLC), to be comprised of a number of components. In a 15-day irradiated solution (4R), in which the proportion of this component was the greatest, none of these represented more than about 6 % applied radioactivity. A smeared region of radioactivity in the HPLC radiochromatograms which eluted between about 13 and 17 minutes (zone a) represented a maximum of 8.4 % applied radioactivity in a 15-day irradiated solution. This smeared zone did not contain any discrete peaks of radioactivity in any test solution.

- M5: Selected solutions were also analysed chromatographically using TLC to provide supporting quantitative and qualitative data. The proportions of the test substance, M2 and M11 in these solutions, as determined by this method, were in reasonable agreement with those obtained by HPLC. A minor component in irradiated solution, which was resolved by the two-dimensional TLC system, corresponded to the reference substance M5 In the HPLC system, this reference substance chromatographed very close to the main degradate peak (ie M2). Where M5 was quantified though, using TLC, it represented about 1 % applied radioactivity.

The characterisation of the test substance, M2, M11 and M5 in incubated solutions was achieved by co-chromatography of selected test solutions with mixtures of the authentic unlabelled reference substances. In addition, M2 and M11 have already been identified, by mass spectrometry, as photodegradation products of the test substance in a previous study (Hawkins et al 1993). One of these previously isolated photodegradation products (M2) was co-chromatographed (HPLC) with a selected irradiated test solution, further confirming its presence as a photoproduct in this study.

Table: Light intensity measurements for each irradiated test solution. Results are expressed as light energy (µW/cm2) over the wavelength range 290 – 400 nm

Nominal duration of irradiation (days)	Pre-study	Post-study	Mean	Ratio of mean intensity to sunlight intensity
0.5 0.5	3200 3110	3010 3210	3129 3147	1.20 1.21
1	3240	3340	3277	1.26
1	3350	3310	3335	1.28
2	3180	3150	3178	1.22
2	3250	3330	3255	1.25
4	3350	3310	3345	1.28
4	3190	3030	3169	1.21
7	3170	3380	3218	1.23
7	3470	3570	3493	1.34
15	3250	3320	3285	1.26
15	3210	3390	3300	1.26

 

Table: Duration of irradiation periods for each irradiated test solution

Nominal duration of irradiation (days)	Actual duration of irradiation (hours)	Equivalent time of latitude 40°N summer sunlight (days)(a)
0.5	12.35	1.23
0.5		1.24
1	24.08	2.52
1		2.56
2	47.56	4.83
2		4.94
4	93.17	9.95
4		9.43
7	164.15	16.87
7		18.31
15	357.86	37.53
15		37.71

a) The time varied between samples due to different intensities at each position in the apparatus

 

Table: Recoveries of radioactivity from irradiated test solutions after addition of the radiolabelled test substance at a nominal concentration of 10 mg/L. Results are expressed in % applied radioactivity.

Time after treatment (days)	Equivalent time of latitude 40°N summer sunlight (days)	Test solution	Volatiles	Total
0	-	100.5	-	100.5
	-	99.9	-	99.9
0.5	1.23	101.6	<0.2	101.6
	1.24	101.9	<0.2	101.9
1	2.52	101.0	<0.2	101.0
	2.56	101.2	<0.2	101.2
2	4.83	99.2	<0.1	99.2
	4.94	99.2	<0.1	99.2
4	9.95	99.4	0.3	99.7
	9.43	99.3	0.3	99.6
7	16.87	98.8	0.8	99.6
	18.31	99.2	0.8	100.0
15	37.53	99.9	2.6	102.5
	37.71	100.3	2.6	102.9

 

Table: Recoveries of radioactivity from dark control test solutions after addition of the radiolabelled test substance at a nominal concentration of 10 mg/L. Results are expressed in % applied radioactivity.

Time after treatment (days)	Test solution	Volatiles	Total
0	100.5	-	100.5
	99.9	-	99.9
2	96.7	<0.2	96.7
	99.2	<0.2	99.2
7	99.5	0.1	99.6
	99.3	0.1	99.4
15	100.5	<0.2	100.5
	100.4	<0.2	100.4

 

Table: Production of volatile radioactivity from irradiated test solutions after addition of the radiolabelled test substance at a nominal concentration of 10 mg/L. Results are expressed as % applied radioactivity

Time after treatment (days)	Trapping solution		Total	Cumulative total
	Ethyl digol (trap 1)	1M KOH (trap 2 and 3)
0 - 0.5	<0.05	<0.16	<0.21	<0.21
0 - 1	<0.04	<0.16	<0.20	<0.20
0 - 2	<0.02	<0.08	<0.10	<0.10
2 - 4	0.17	0.11	0.28	0.28
0 - 7	0.31	0.51	0.82	0.82
7 - 15	0.49	1.26	1.75	2.57

 

Table: Production of volatile radioactivity from dark control test solutions after addition of the radiolabelled test substance at a nominal concentration of 10 mg/L. Results are expressed as % applied radioactivity

Time after treatment (days)	Trapping solution		Total	Cumulative total
	Ethyl digol (trap 1)	1M KOH (trap 2 and 3)
0 - 2	< 0.03	< 0.15	<0.18	<0.18
0 - 7	0.08	< 0.15	0.08	0.08
0 - 15	< 0.05	< 0.15	<0.20	<0.20

 

Table: Proportions of test substance remaining in irradiated and dark control test solutions. The concentrations were determined by HPLC. Results are expressed as % applied radioactivity.

Time after treatment (days)	Irradiated		Dark control
	Equivalent time of latitude 40°N Vessel summer sunlight number (days)	Test substance	Test substance
0	-	97.4	97.4
	-	96.6	96.6
0.5	1.23	82.7	NS
	1.24	82.8
1	2.52	72.6	NS
	2.56	69.6
2	4.83	52.2	94.1
	4.94	51.5	96.4
4	9.95	23.0	NS
	9.43	26.8
7	16.87	9.6	94.5
	18.31	8.3	93.9
15	37.53	2.4	95.5
	37.71	2.3	95.0

 

Table: Proportions of radioactive components in irradiated test solutions. Components were resolved and quantified using two-dimensional TLC. Results are expressed as % applied radioactivity.

Time after treatment (days)	0		0.5		1		2		4		7		15
Equivalent time of latitude 40°N summer sunlight (days)(a)	-	-	1.23	1.24	2.52	2.56	4.83	4.94	9.95	9.43	16.87	18.31	37.53	37.71
Component
Unknown 1(b)	0.2	0.2	0.7	0.9	0.9	1.2	1.5	1.6	2.8	2.6	3.9	5.0	8.3	10.6
M2	0.2	0.2	14.0	14.0	21.6	25.8	38.4	39.5	61.2	58.5	70.2	70.7	57.6 (48.3)	56.2
M11	0.4	0.4	1.3	1.2	2.4	1.6	3.3	3.1	6.7	5.7	8.1	7.7	20.8 (13.4)	21.6
Zone a(c)	0.8	1.0	0.9	1.0	1.4	1.1	1.9	1.8	4.0	3.6	5.0	5.2	8.4	6.9
Test substance	97.4	96.6	82.7	82.8	72.6	69.6	52.2	51.5	23.0	26.8	9.6	8.3	2.4 (1.0)	2.3
Diffuse radioactivity(d)	1.5	1.5	1.9	1.9	2.0	1.8	2.0	1.7	1.9	2.2	2.0	2.3	2.4	2.5

a) Light intensity measurements were made at individual positions in the Suntest apparatus

b) In the 15-day irradiated solution 4R, this fraction comprised at least four components, none of which represented more than 6.3 % applied radioactivity.

c) Region of the chromatogram between M11 and the test substance. This region did not contain any discrete radioactive components

d) Radioactivity not associated with any of the components listed in the table

Values in parentheses were obtained by two-dimensional TLC. 2D-TLC of the solution from one vessel on the day of sampling was unsuccessful and no meaningful quantitative data could be obtained. Mean proportions are tabulated in the table below.

 

Table: Mean proportions of radioactive components in irradiated test solutions. Components were resolved and quantified using HPLC. Results are expressed as % applied radioactivity. 

Time after treatment (days)	0	0.5	1	2	4	7	15
Mean equivalent time of latitude 40°N summer sunlight (days)(a)	-	1.24	2.54	4.89	9.69	17.59	37.62
Component
Unknown 1	0.2	0.8	1.1	1.6	2.7	4.5	9.5
M2	0.2	14.0	23.7	39.0	59.9	70.5	56.9
M11	0.4	1.3	2.0	3.2	6.2	7.9	21.2
Zone a (b)	0.9	1.0	1.3	1.9	3.8	5.1	7.7
Test substance	97.0	82.8	71.1	51.9	24.9	9.0	2.4
Diffuse radioactivity(c)	1.5	1.9	1.9	1.9	2.1	2.2	2.5

a) Light intensity measurements were made at individual positions in the Suntest apparatus

b) Region of the chromatogram between M11 and the test substance. This region did not contain any discrete radioactive components

c) Radioactivity not associated with any of the components listed in the table

 

Table: Mean proportions of radioactive components in dark control test solutions. Components were resolved and quantified using HPLC. Results are expressed as % applied radioactivity. 

Time after treatment (days)	0	2	7	15
Component
Unknown 1	0.2	0.4	0.7	1.0
M2	0.2	0.4	1.6	1.8
M11	0.4	0.5	0.3	0.5
Zone a(a)	0.9	0.3	0.6	0.3
Test substance	97.0	95.3	94.2	95.3
Diffuse radioactivity(b)	1.5	1.4	2.0	1.6

a) Region of the chromatogram between M11 and the test substance. This region did not contain any discrete radioactive components

b) Radioactivity not associated with any of the components listed in the table

 

Validity criteria fulfilled:

not specified

Conclusions:

The test substance is rapidly photodegraded in aqueous solution at pH 7 and at 25°C with a half-life equivalent to 6.8 days of latitude 40°N summer sunlight. One major photoproduct was formed, which represented up to about 71 % of the initial radioactivity after irradiation equivalent to about 18 days of natural sunlight. This product was identified, chromatographically, as M2. Another product, which represented up to about 21% of the initial radioactivity after about 38 equivalent days, corresponded to M11. These substances have been isolated and identified, by mass spectrometry, as photoproducts of the test substance in a previous study. Only trace amounts of volatile products, including CO2, were formed. The test substance was only slightly degraded in dark control solutions.

Executive summary:

The aqueous photolysis of the test substance, has been studied in a GLP-compliant study according to EPA Subdivision N Guideline 161-2. The test substance, labelled with carbon-14 in its triazine ring was used, at an initial concentration in solution of 10 mg/L. The study was conducted in aqueous solution buffered to pH 7, conditions under which the test substance is hydrolytically stable. A xenon arc simulated sunlight source was used and irradiation was continuous over time. Irradiated and dark control solutions were maintained at ca 25°C at all times. In irradiated solution the test substance was degraded with a half-life equivalent to 6.8 days of natural summer sunlight at latitude 40°N, assuming 12 hours of daylight. Recoveries of radioactivity from all solutions (irradiated and dark control) lay in the range 97 -103% of the applied amounts. Very little volatile radioactivity (2.6% applied radioactivity) was evolved from solutions after irradiation equivalent to about 38 days of natural sunlight. A number of photodegradation products of the test substance were separated by high performance liquid chromatography and thin-layer chromatography of irradiated test solutions. Two were of quantitative significance and have been isolated and identified by mass spectrometry in a previous study (Hawkins et al 1993). These structures were identified to be M2 and M11. The test substance was very slightly degraded in dark control solutions to ca 95 % applied radioactivity after about 38 days equivalent of natural sunlight.

Reference 3

Endpoint:

phototransformation in water

Type of information:

experimental study

Adequacy of study:

supporting study

Study period:

10 May 1994 to 30 Jan 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)

Version / remarks:

October 1992

Deviations:

no

Qualifier:

according to guideline

Guideline:

other: Biologische Bundesanstalt fur Land- und Forstwirtschaft (BBA, Germany) Guideline: Phototransformation of Chemicals in Water

Version / remarks:

January 1990

Deviations:

no

GLP compliance:

yes

Radiolabelling:

yes

Remarks:

[14C]-labelled at position 5 of pyridine ring

Analytical method:

high-performance liquid chromatography

mass spectrometry

other: Thin-layer chromatography (TLC), Liquid scintillation counting (LSC)

Details on sampling:

- Sampling intervals: Two test vessels were taken for analysis immediately after test substance addition. Duplicate test vessels (2 each of irradiated and dark control) were taken for analysis at 1, 2, 4, 7, 15 and 30 days after test substance addition. Trapping solutions associated with vessels which were taken for analysis were radioassayed (and replaced with fresh solutions where applicable) at the sampling times as appropriate.

- Storage of samples: Radioassay of each test solution, measurement of pH and removal of a subsample for microbiological examination were all carried out on the day of sampling. Quantitative HPLC analysis and two-dimensional TLC analysis, and HPLC and TLC co-chromatography with non-radiolabelled reference substances, were also carried out on the day of sampling. HPLC co-chromatography with a previously isolated photoproduct was carried out upto 7 months after sampling. When not being analysed, test solutions were stored at <-20°C. The unlabelled reference standards were also stored, as near compounds, at <-20°C during the course of the study. In addition to spectroscopic analysis at the end of the study, their stability was also assessed by chromatographic analysis during the course of the study: in most cases essentially only one HPLC UV peak or TLC UV spot was observed, although by the end of the study M3 also contained a significant proportion of the corresponding acid, M5. The presence of the acid was also apparent from the mass spectrum.

Buffers:

- Buffer solution preparation: Potassium dihydrogen orthophosphate (2.722 g) was dissolved in ca 1900 mL water and the pH adjusted to 7.0 with a potassium hydroxide solution. The solution was then made up to volume in a 2 L volumetric flask and the pH checked. No further adjustment of pH was necessary.
- pH measurements: Measurements of the pH of test buffer solutions were made using a model 3030 pH meter. The meter was calibrated prior to each measurement using pH 4 and pH 7 standard buffer solutions.

Light source:

Xenon lamp

Light spectrum: wavelength in nm:

>= 290 - <= 400

Relative light intensity:

>= 1.53 - <= 1.89

Details on light source:

- Source: The study was conducted using a Suntest accelerated exposure unit fitted with a xenon arc light source. A special system of mirrors and filters prevented infra-red and ultra-violet radiation with a wavelength of less than 290 nm from reaching the test solutions. Hence the emission spectrum produced was similar to that of natural sunlight.
- Measurement of light intensities: The spectral energy distributions of the lamp source and natural sunlight were measured using a Minimate-2 model 1681A monochromator fitted with 1.25 mm slits, a 300 nm blaze diffraction grating and a model 85T Teflon cosine diffuser linked to an Optronic Laboratories model 730 radiometer. A blocking filter was used at wavelengths greater than 550 nm.
- Comparison of the artificial light source and natural sunlight: Light intensity measurements were made at each test sample position in the Suntest apparatus at the beginning and the end of the study. Intensity measurements were made at 5 nm intervals over the wavelength range 290 - 400 nm. A plastic template was used to position the cosine diffuser on the monochromator at the correct position under the Suntest light source and at the same distance from it as the surface of the test solutions during the study. The incident light was measured through the top part of a test vessel identical to those used in the study.
Light intensity measurements (290 - 400 nm) were also made of natural sunlight at midday on 13 June 1989, 21 September 1993 and 19 October 1993 at the test facility (latitude 52° 21 'N, longitude 0° 15'W). Measurements were also made on 24 June 1994 (ie during the study) at teh test facility: these measurements were in close agreement with those of September 1993, but to be consistent with previous studies , the measurements of September 1993 were used to calculate the equivalent duration of natural sunlight received by each test solution. The remaining measurements were used to estimate confidence limits for these calculated values.
The light intensity measurements were integrated to provide the total light intensity over the wavelength range 290 - 400 nm. For each position in the Suntest apparatus, the average intensity over the irradiation period was calculated from the starting and finishing values, assuming that any change in intensity during the study occurred in a linear fashion. This average intensity for each position was then used to calculate the equivalent time of irradiation of natural sunlight received by each test solution.
Additionally, intensity measurements between 250 and 700 nm were made at the central position under the Suntest light source, and also of natural sunlight at the test facility (midday, 24 June 1994).

Details on test conditions:

TEST SYSTEM
- Test vessels: The test vessels were constructed of borosilicate glass and were cylindrical in shape, of internal diameter 2.5 cm and height 8.0 cm. With the exception of those vessels to be used for time zero analysis (which had only one entry port), they were each fitted with two entry ports, near the top, to allow for the collection of volatiles, and for the addition and removal of test solution. Vessels for irradiation were placed in individual sockets in a water-cooled steel block, positioned in the Suntest unit. The cooling block also incorporated magnetic field switching devices to drive Teflon-coated magnetic stirrer bars in the test solutions. Dark control solutions were placed on an oscillating shaker which was kept in darkness in an incubator.
- Incubation conditions: 'Irradiated' test solutions were maintained at ca 25°C and were stirred continuously with magnetic stirrer bars. These solutions were irradiated for the first 12 hours in every 24-hour period and kept in darkness for the remaining 12 hours. The duration of each light and dark phase was recorded. Control vessels were maintained in darkness at ca 25 °C and were oscillated continuously.
- Sterilisation method: All test vessels, glassware and buffer solutions were sterilised by autoclaving at 121 °C for 20 minutes. Buffer solution was divided into two portions (650 ml each) which ere autoclaved separately. After cooling, the pH of one portion was measured. No further adjustment of pH was found to be necessary and the other portion of the buffer solution was used for the study. Addition of the radiolabelled test substance solution to the buffer solution and dispensing of treated buffer solution into test vessels were carried out in a laminar flow cabinet. Samples of test solutions were taken for microbiological examination at each sampling interval.
- Details on traps: All test vessels (with the exception of those taken for time zero analysis) were incorporated into gas-flow systems, such that groups of four to six vessels were connected, via sterile tubing, to each other in series. For each series, air was drawn, at a flow rate of ca 5 mL/minute, through a water trap (for humidification), a microbial filter (0.2 μm, cellulose acetate), the headspaces of the test vessels, another filter, then through an empty trap, and then through a series of Dreschel bottle traps containing ethyl digol (trap 1) or 1M aqueous potassium hydroxide solution (traps 2 and 3).

TEST MEDIUM
- Kind and purity of water: HPLC grade
- Preparation of test medium: The radiolabelled test substance was used as supplied, without any radiodilution. A stock solution of the radiolabelled test substance in methanol was prepared at a concentration of 1.25 mg/L. An aliquot (4.8 mL) of this solution was added to the second 650 mL portion of pH 7 buffer solution. After mixing, triplicate aliquots (100 μL) of the treated buffer solution were taken for radioassay. From these measurements the concentration of test substance in the treated buffer solution was 9.15 mg/L. The concentration of the methanol co-solvent was 0. 74 % by volume. Portions (20 mL) of treated buffer solution were aseptically transferred to pre-weighed test vessels, which were then re-weighed. Fourteen vessels for irradiation were established (to include two spares), and a further fourteen to act as dark controls (to include two spares). All of these allowed for the collection of volatile radioactivity. Two further vessels (not fitted for volatiles collection) were established which were taken immediately for analysis (time zero analysis).

TEMPERATURE RECORDING
The temperature of the irradiated solutions was recorded using an indwelling thermocouple probe, positioned in a test vessel containing untreated buffer solution. This vessel was placed in the central position of the cooling block. The thermocouple was connected to a monitoring system manufactured at the test facility, employing an Acom microcomputer and data handling system. The temperature of the incubator containing the dark control solutions was measured using a thermometer located in the incubator. Temperatures of irradiated and of dark control solutions were recorded twice daily. Throughout the study the mean recorded temperatures were 24.5°C (± 0.7°C) (irradiated vessels) and 24.8°C (±0.5°C) (dark control vessels). The temperature ranges were 19.8 - 25.7°C (irradiated vessels, although all except six readings were 24.0 - 25.7°C) and 23.5 - 27.0°C (dark control vessels, all except two readings were 24.2 - 26.0°C).

MICROBIAL EXAMINATION OF TEST SOLUTIONS
Using aseptic procedures, aliquots (1 mL) of each test solution were used to prepare Tryptone Soya Agar pour-plates in duplicate. The plates were incubated at 32 ± 1°C for 5 days. After incubation the plates were examined for bacterial and fungal growth and the results recorded.

REPLICATION
- No. of replicates (dark): 2
- No. of replicates (irradiated): 2

Duration:

30 d

Temp.:

25 °C

Initial conc. measured:

10 mg/L

Reference substance:

no

Dark controls:

yes

Computational methods:

The line of best fit for the calculation of the half-life was calculated using a computer software package.

Key result

DT50:

4.3 d

Test condition:

at pH 7 and at 25°C, irradiated with 40°N summer sunlight.

Remarks on result:

other: assuming first order kinetics

Remarks:

The rate constant (k) was calculated to be 0.1441 - 0.2577/day

Predicted environmental photolytic half-life:

Light in the wavelength range 290 - 400 nm is most likely to cause photochemical reactions and so this range was chosen for comparative purposes. To relate the light intensity of the xenon arc source to natural summer sunlight (latitude 40°N) various corrections were necessary. The sunlight measurements relate to midday sunlight on 21 September 1993 at latitude 52°N. Published data (Mill et al 1982) indicate that the measured intensity on this day would be about 55% of the midday midsummer intensity at latitude 40°N. Additionally it was assumed that the average daily radiation intensity from the sun is about 75% of the peak intensity over a 12-hour period, whereas the radiation in the Suntest was of constant intensity.

The ratios (r) for different positions in the Suntest apparatus were in the range 1.53 - 1.89 with a mean value of 1.71 (unrounded ratios were used in the formula). Calculated equivalent sunlight times are shown in ‘Any other information on results incl. tables’. The coefficients of variation of intensity measurements at different positions were 7% (pre-study) and 5% (post-study).

Transformation products:

yes

Details on results:

TEST CONDITIONS
- pH: The pH values of all test solutions at the time of sampling, were in the range 7.02 - 7.19, with most values in the range 7.0 - 7.1.
- Sterility: Microbiological examination showed that sterility had been maintained in all test solutions.

RECOVERIES
The total recovery of radioactivity from all test solutions (including volatile radioactivity, see below) was in the range 92.3 - 100.3% of the amount initially applied. In calculating the recoveries of radioactivity, allowance was made for the changes (reductions) in the weights of the test vessels ( + solutions) before and after irradiation, which became more significant with time. Very little volatile radioactivity was evolved from irradiated solutions. This amounted to 0.5 % applied radioactivity after 15 days although anomalously low levels (0.01 %) were detected from the 30-day irradiated solutions. Similarly, in the dark control solutions, volatile radioactivity amounted to 0.2 % applied radioactivity after 15 days.

DEGRADATION OF THE TEST SUBSTANCE
The test substance was rapidly and extensively degraded in irradiated test solutions. The half-life of the test substance, calculated assuming first order kinetics, was equivalent to 4.3 days of latitude 40°N summer sunlight.
Also shown in this figure are upper and lower estimates of the line of best fit, based upon alternative sunlight intensity measurements made at HRC. the test substance was much more slowly degraded in dark control solutions, such that the proportion of test substance remaining had declined to about 90% applied radioactivity after 30 days.

TRANSFORMATION PRODUCTS
On the whole, the proportions of the test substance and its photoproducts, as determined by HPLC and TLC, were in reasonable agreement; in the following discussion the proportions as determined by HPLC are used. Two components were separated by both HPLC and TLC in addition to the test substance itself (HPLC also separated a very minor component, AP2; this did not account for more than 1 % applied radioactivity). The major component corresponded, chromatographically, to the reference substance of M3. The level of this product rose to about 92 % of the initial radioactivity after irradiation equivalent to 32 days of latitude 40°N summer sunlight. Reference substance of M10 corresponded, chromatographically, to a photodegradation product representing up to about 4% applied. M3 was the major degradation product in dark control test solutions. The characterisation of the test substance. M3 and M10 in irradiated solution, and of the test substance in dark control solution, was achieved by co-chromatography of selected test solutions with the authentic unlabelled reference standards. Co-chromatography was performed after up to 7 months of freezer storage of the test solutions. Storage of the samples resulted in a shift of equilibrium between the test substance and its initial hydrolysis products, M3 and M2 (the triazine-ring product). The equilibrium shift resulted in quantitative differences only in the proportions of the test substance and M3; qualitatively the samples were the same. The identities of both the test substance and M3 in irradiated solution were further confirmed by mass spectrometry. The spectra of the isolated products were essentially similar to those of the respective reference substances.

Table: Light intensity measurements for each irradiated test solution (Results are expressed as light energy (µW/cm2) over the wavelength range 290 – 400 nm)

Nominal duration of irradiation (days)	Pre-study	Post-study	Mean	Ratio of mean intensity to sunlight intensity
1	1972	1903	1971	1.74
1	1873	1683	1871	1.64
2	2012	1892	2009	1.78
2	1786	1743	1785	1.58
4	2047	1855	2035	1.80
4	1947	1884	1943	1.72
7	2171	1873	2137	1.89
7	1888	1768	1874	1.66
15	2095	1875	2040	1.80
15	2144	1896	2082	1.84
30	1712	1763	1738	1.54
30	1825	1635	1730	1.53

 

Table: Duration of irradiation periods for each irradiated test solution

Nominal duration of irradiation (days)	Actual duration of irradiation (hours) (a)	Equivalent time of latitude 40°N summer sunlight (days)(b)
1	8.54	0.91
1	8.54	0.86
2	20.74	2.25
2	20.74	2.00
4	44.85	4.93
4	44.85	4.71
7	80.53	9.30
7	80.53	8.15
15	174.85	19.27
15	174.85	19.67
30	347.69	32.65
30	347.69	32.50

a) Vessels were irradiated for approximately 12 hours in each 24-hour period

b) The time varied between replicate samples due to different intensities at each position in the Suntest apparatus

 

Table: Recoveries of radioactivity from irradiated test solutions after addition of the radiolabelled test substance at a nominal concentration of 10 mg/L (Results are expressed in % applied radioactivity.

Time after treatment (days)	Equivalent time of latitude 40°N summer sunlight (days)	Test solution	Volatiles	Total
1	0.91	98.2	<0.1	98.2
	0.86	99.1	<0.1	99.1
2	2.25	99.4	<0.1	99.4
	2.00	99.4	<0.1	99.4
4	4.93	99.4	<0.1	99.4
	4.71	99.4	<0.1	99.4
7	9.30	95.0	0.2	95.2
	8.15	97.6	0.2	97.8
15	19.27	92.9	0.5	93.4
	19.67	91.8	0.5	92.3
30	32.65	97.9	<0.1	97.9
	32.50	98.4	<0.1	98.4

 

Table: Recoveries of radioactivity from dark control test solutions after addition of the radiolabelled test substance at a nominal concentration of 10 mg/L. Results are expressed in % applied radioactivity.

Time after treatment (days)	Test solution	Volatiles	Total
0	99.3	-	99.3
	99.3	-	99.3
1	99.2	<0.1	99.2
	99.1	<0.1	99.1
2	99.9	<0.1	99.9
	100.1	<0.1	100.1
4	100.1	0.2	100.3
	99.8	0.2	100.0
7	99.8	0.1	99.9
	99.1	0.1	99.2
15	99.4	0.2	99.6
	99.4	0.2	99.6
30	98.5	<0.1	98.5
	99.2	<0.1	99.2

 

Table: Production of volatile radioactivity from irradiated test solutions after addition of the radiolabelled test substance at a nominal concentration of 10 mg/L. Results are expressed as % applied radioactivity.

Time after treatment (days)	Trapping solution		Total	Cumulative total
	Ethyl digol (trap 1)	1M KOH (trap 2 and 3)
0 - 1	<0.01	<0.01	<0.02	<0.02
1 – 2	<0.01	<0.03	<0.04	<0.06
0 – 4	<0.01	<0.01	<0.02	<0.02
4 – 7	0.01	0.15	0.16	0.16
7 - 15	0.02	0.33	0.35	0.51
0 - 30	<0.01	0.01	0.01	0.01

 

Table: Production of volatile radioactivity from dark control test solution after addition of the radiolabelled test substance at a nominal concentration of 10 mg/L. Results are expressed as % applied radioactivity.

Time after treatment (days)	Trapping solution		Total	Cumulative total
	Ethyl digol (trap 1)	1M KOH (trap 2 and 3)
0 – 1	<0.01	0.01	0.01	0.01
1 – 2	<0.01	<0.01	<0.02	0.01
0 – 4	<0.01	0.22	0.22	0.23
4 - 7	<0.01	0.14	0.14	0.14
7 - 15	<0.01	0.04	0.04	0.18
0 - 30	<0.01	0.02	0.02	0.02

Table: Proportions of test substance remaining in irradiated and dark control test solutions. The concentrations were determined by HPLC. Results are expressed as % applied radioactivity.

Time after treatment (days)	Irradiated		Dark control
	Equivalent time of latitude 40°N Vessel summer sunlight number (days)	Test substance	Test substance
0	0	94.5	94.5
	0	95.1	95.1
1	0.91	77.1	93.7
	0.86	77.4	94.1
2	2.25	59.2	96.2
	2.00	58.9	96.5
4	4.93	31.0	95.7
	4.71	31.2	95.6
7	9.30	10.1	93.3
	8.15	12.3	94.0
15	19.27	1.5	92.8
	19.67	0.8	92.9
30	32.65	0.6	89.0
	32.50	0.8	91.1

Mean proportions are tabulated in the table below.

 

Table: Mean proportions of radioactive components in irradiated test solutions. Components were resolved and quantified using HPLC. Results are expressed as % applied radioactivity.

Time after treatment (days)	0	1	2	4	7	15	30
Mean equivalent time of latitude 40°N summer sunlight (days)(a)	-	0.89	2.1	4.82	8.73	19.47	32.58
Component
M10	0.1	0.1	0.2	0.5	1.2	3.3	4.2
Peak AP2	c	0.1	0.1	c	0.1	0.3	0.6
M3	2.8	19.3	37.6	66.6	82.9	86.8	91.8
Test substance	94.8	77.3	59.1	31.1	11.2	1.2	0.7
Diffuse radioactivity (b)	1.7	2.1	1.6	1.2	1.1	1.0	1.0

a) Light intensity measurements were made at individual positions in the Suntest apparatus

b) Radioactivity not associated with any of the components listed in the table

c) Not present as a discrete component; included in ‘Diffuse radioactivity’

 

Table: Mean proportions of radioactive components in dark control test solutions. Components were resolved and quantified using two-dimensional TLC. Results are expressed as % applied radioactivity. 

Time after treatment (days)		1	2	4	7	15	30
Mean equivalent time of latitude 40°N summer sunlight (days)(a)		0.89	2.13	4.82	8.73	19.47	32.58
Component	Typical RfS(b)
Test substance	0.36/0.59	79.4	64.3	38.4	14.9	1.1	1.3
M3	0.58/0.68	15.0	32.4	59.3	79.2	84.3	83.1
M10 Origin Remainder	0.33/0.74 0 - 0.1/0 -	c 0.3 4.0	c 0.2 2.6	c 0.2 1.7	c 0.2 2.1	1.6 0.3 5.3	3.3 0.4 10.1

a) Light intensity measurements were made at individual positions in the Suntest apparatus

b) The first value refers to the first dimension and the second value to the second dimension

c) Not apparent; included in 'Remainder'

 

Table: Mean proportions of radioactive components in dark control test solutions. Components were resolved and quantified using HPLC. Results are expressed as % applied radioactivity

Time after treatment (days)	0	1	2	4	7	15	30
Component
M10	0.1	0.1	0.1	0.4	0.5	0.5	0.4
Peak AP2	b	0.1	0.3	b	0.1	0.1	0.1
M3	2.8	3.1	1.7	1.9	3.4	4.1	6.0
Test substance	94.8	93.9	96.4	95.7	93.7	92.9	90.1
Diffuse radioacitvity(a)	1.7	2.0	1.6	2.1	2.0	2.0	2.5

a) Radioactivity not associated with any of the components listed in the table

b) Not present as a discrete component; included in 'Diffuse radioactivity'

Validity criteria fulfilled:

not specified

Conclusions:

The test substance is rapidly photodegraded in aqueous solution at pH 7 and at 25°C with a half-life equivalent to 4.3 days of latitude 40°N summer sunlight. One major photodegradation product was formed, which represented up to about 92% of the initial radioactivity after irradiation equivalent to about 32 days of natural sunlight. This product was identified, chromatographically (HPLC and TLC) and spectroscopically, as M3. Another photoproduct, which represented up to about 4% of the initial radioactivity, corresponded to M10. Only trace amounts of volatile products, including CO2, were formed. The test substance was only slightly degraded in dark control solutions.

Executive summary:

The aqueous photolysis of the test substance, has been studied in a GLP-compliant study according to EPA Subdivision N Guideline 161-2. The test substance, labelled with carbon-14 in its pyridine ring, was used at an initial concentration in solution of 10 mg/L. The study was conducted in aqueous solution buffered to pH 7, conditions under which the test substance is hydrolytically stable. A xenon arc simulated sunlight source was used and irradiation was for the first 12 hours in each 24-hour period. Irradiated and dark control solutions were maintained at ca 25°C at all times. In irradiated solution, the test substance was degraded with a half-life equivalent to 4.3 days of natural summer sunlight at latitude 40°N, assuming 12 hours of daylight. Recoveries from all solutions (irradiated and dark control) lay in the range 92 - 100% of the applied amounts. Very little volatile radioactivity (up to 0.5% applied radioactivity) was evolved from irradiated solutions. Only one major photoproduct of the test substance was formed in irradiated solutions. This corresponded, using high performance liquid chromatography and thin-layer chromatography, to M3. This represented up to about 92% of the initial radioactivity after irradiation equivalent to about 32 days of natural sunlight. The identities of this photoproduct and of unchanged test substance in irradiated solution were further confirmed by mass spectrometry. Another photoproduct, which represented up to about 4% applied radioactivity, was chromatographically identified as M10.The test substance was slightly degraded (mainly to M3) in dark control solutions to ca 90% applied radioactivity.

Reference 4

Endpoint:

phototransformation in water

Type of information:

experimental study

Adequacy of study:

supporting study

Study period:

23 Jul 1996 to 06 Jan 1997

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)

Version / remarks:

18 October 1982

Deviations:

no

Qualifier:

according to guideline

Guideline:

other: Biologische Bundesanstalt für Land- und Forstwirtschaft (BBA, Germany): Phototransformation of Chemicals in Water

Version / remarks:

January 1990

Deviations:

no

GLP compliance:

yes

Radiolabelling:

yes

Remarks:

[14C]-labelled at position 6 of triazine ring

The rate of degradation of the test substance (DT50) in this study was determined to be 6.2 days. In this study the identities of two major photoproducts were confirmed, by co-chromatography of irradiated solutions with authentic reference standards, M2 and M5. To this end, two dissimilar chromatographic systems were employed, reversed phase high performance liquid chromatography and two-dimensional normal phase thin-layer chromatography. No other photodegradation product represented more than 10 % of the initial radioactivity. 

Conclusions:

The rate of degradation of the test substance (DT50) in this study was determined to be 6.2 days.

Executive summary:

The photodegradation in water of the test substance was investigated in accordance to EPA Guideline Subdivision N 161-2 and in compliance with GLP criteria. The test substance, radiolabelled at its triazine ring, was added to sterile aqueous buffer solution, pH 7.0, at a nominal concentration of 10 mg/L which is below its reported water solubility of 270 mg/L. Solutions were irradiated continuously with a xenon arc light source at a temperature of ca 25°C for periods of up to 15 days. The spectral energy distribution of the light source over the wavelength range 290 - 400 nm was measured and compared with the distribution of natural sunlight over the same range. The maximum duration of irradiation was equivalent to about 40 days of natural summer sunlight at latitude 40°N. Further samples of buffer solution treated with the radiolabelled test substance were incubated in darkness at ca 25°C over the same periods of time. All test solutions were analysed for pH, total radioactivity concentration and the relative proportions of the test substance and any radiolabelled degradation products present.

The rate of degradation of the test substance (DT50) in this study was determined to be 6.2 days. In this study the identities of two major photoproducts were confirmed, by co-chromatography of irradiated solutions with authentic reference standards, M2 and M5. To this end, two dissimilar chromatographic systems were employed, reversed phase high performance liquid chromatography and two-dimensional normal phase thin-layer chromatography. No other photodegradation product represented more than 10 % of the initial radioactivity. 

Reference 5

Endpoint:

phototransformation in water

Type of information:

experimental study

Adequacy of study:

supporting study

Study period:

24 Mar 2003 to 12 Aug 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:

OECD Guideline 316 (Phototransformation of Chemicals in Water - Direct Photolysis)

Version / remarks:

Draft, August 2000

Qualifier:

according to guideline

Guideline:

other: Japanese Ministry of Agriculture, Forestry and Fisheries, Test Data for Registration of Agricultural Chemicals, 12 Nohsan No. 8147: Photodegradation in Water (2-6-2)

Version / remarks:

24 November 2000, revised 26 June 2001

GLP compliance:

yes (incl. QA statement)

Radiolabelling:

yes

Remarks:

[14C]-labelelled at position 2 of pyridine ring

DT50:

15.1 d

Test condition:

At ~ 25 °C; light intensity at 300 - 400 nm of the Xenon arc source was determined to be on average 44.2 ± 1.9 W/m2.

Remarks on result:

other: The value is expressed in calendar days. This figure corresponded to 22.6 ± 0.8 days of natural midsummer sunlight at latitudes 30 to 50°N.

For the Pre-Test, mean recoveries of total radioactivity during the 7-day incubation period were 100.4% ± 1.1 % and 99.8% ± 1.3% for irradiated and dark control samples, respectively. The results of the Pre-Test showed that the test substance significantly photodegraded with an estimated half-life of 12.9 calendar days. In the dark control samples, the test compound was stable (98.3% on day 7). Based on these findings the exposure time and the sampling intervals of the main test were selected. For the Main Test, the total mean recovery from the irradiated solutions during the 29-day incubation period amounted to 100.4% ± 1.2%. For the dark control samples, the mean recovery was 102.4% ± 1.6%. The test substance showed significant photo-degradation in sterile pond water. After 10 and 29 days of irradiation, the test substance represented 63.0% and 27.7% of the applied radioactivity, respectively. Besides the test substance, one major radioactive fraction was detected (M3) reaching a maximum of 70.7% of the applied radioactivity at the end of the study (day 29). In addition only one minor degradate (M10) was detected at the end of the study amounting to 0.9% of the radioactivity applied. Little (≤0.2%) volatile radioactivity in the form of carbon dioxide was found.

 

No degradation of the test substance was observed in the pond water samples incubated under the same conditions but in the dark. Between days 0 and 29 of incubation, the test substance represented 100% and 104.6% of the applied radioactivity. The rate of photolytic degradation of the radiolabelled test substance, was described assuming first order reaction kinetics. The experimental half-life (DT50) was determined to be 15.1 calendar days. This figure corresponded to 22.6 ± 0.8 days of natural midsummer sunlight at latitudes 30 to 50°N. When related to Tokyo spring time, a half-life of 42.9 days is obtained. In conclusion, the test substance was degraded by direct photolysis with a half-life of 22.6 ± 0.8 days natural midsummer sunlight at latitudes 30 to 50°N corresponding to 42.9 days Tokyo spring time. Only one major photo-degradate (M3) was formed reaching at the end of the study 70.7%. No degradation of the test substance was observed under dark control conditions.

Validity criteria fulfilled:

not specified

Conclusions:

The experimental half-life (DT50) was determined to be 15.1 calendar days.

Executive summary:

The rate of photochemical degradation of the radiolabelled test substance has been investigated under simulated sunlight in sterile natural pond water in accordance with JMAFF Agchem Test Guidelines 12 Nohsan N. 8147 and in compliance with GLP criteria. For this purpose, the pyridine-radiolabelled test substance was dissolved in the test medium and aliquots of 15 ml were exposed to artificial light (Xenon light) in 25 mL incubation tubes constructed entirely of borosilicate glass and covered with borosilicate lids. The concentration of the test substance in the test medium amounted to about 5 mg/L. Irradiation was carried out for an initial period of 7 calendar days (Pre-Test) in cycles of 12h light/12h dark followed by a Main Test of 29 calendar days. All samples were exposed at a constant temperature of 24.8 ± 0.9 °C. The integral of light intensity at 300 - 400 nm of the Xenon arc source was determined to be on average 44.2 ± 1.9 W/m2. Corresponding control samples were incubated under the same conditions but in the dark. Duplicate samples were taken for analysis at regular intervals over the incubation periods. Dark control samples (single: Pre-Test or duplicate: Main Test) were taken at the same intervals as for the irradiated samples.

For the Pre-Test, mean recoveries of total radioactivity during the 7-day incubation period were 100.4% ± 1.1 % and 99.8% ± 1.3% for irradiated and dark control samples, respectively. The results of the Pre-Test showed that the test substance significantly photodegraded with an estimated half-life of 12.9 calendar days. In the dark control samples, the test compound was stable (98.3% on day 7). Based on these findings the exposure time and the sampling intervals of the main test were selected. For the Main Test, the total mean recovery from the irradiated solutions during the 29-day incubation period amounted to 100.4% ± 1.2%. For the dark control samples, the mean recovery was 102.4% ± 1.6%. The test substance showed significant photo-degradation in sterile pond water. After 10 and 29 days of irradiation, the test substance represented 63.0% and 27.7% of the applied radioactivity, respectively. Besides the test substance, one major radioactive fraction was detected (M3) reaching a maximum of 70.7% of the applied radioactivity at the end of the study (day 29). In addition only one minor degradate (M10) was detected at the end of the study amounting to 0.9% of the radioactivity applied. Little (≤0.2%) volatile radioactivity in the form of carbon dioxide was found.

 

No degradation of the test substance was observed in the pond water samples incubated under the same conditions but in the dark. Between days 0 and 29 of incubation, the test substance represented 100% and 104.6% of the applied radioactivity. The rate of photolytic degradation of the radiolabelled test substance, was described assuming first order reaction kinetics. The experimental half-life (DT50) was determined to be 15.1 calendar days. This figure corresponded to 22.6 ± 0.8 days of natural midsummer sunlight at latitudes 30 to 50°N. When related to Tokyo spring time, a half-life of 42.9 days is obtained. In conclusion, the test substance was degraded by direct photolysis with a half-life of 22.6 ± 0.8 days natural midsummer sunlight at latitudes 30 to 50°N corresponding to 42.9 days Tokyo spring time. Only one major photo-degradate (M3) was formed reaching at the end of the study 70.7%. No degradation of the test substance was observed under dark control conditions.

Reference 6

Endpoint:

phototransformation in water

Type of information:

experimental study

Adequacy of study:

supporting study

Study period:

29 Jul 2010 to 05 Jan 2011

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 316 (Phototransformation of Chemicals in Water - Direct Photolysis)

Version / remarks:

October 2008

Deviations:

yes

Remarks:

no definitive test was performed

Qualifier:

according to guideline

Guideline:

other: EPA Guideline OPPTS 835.2240 Photodegradation in water

Version / remarks:

October 2008

Deviations:

yes

Remarks:

no definitive test was performed

Qualifier:

according to guideline

Guideline:

other: JMAFF 12 Nohsan No 8147

Version / remarks:

24 November 2000, revised 26 June 2001

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Radiolabelling:

yes

Remarks:

[14C]-labelled at position 5 of pyridine ring or position 6 of triazine ring

DT50:

1 d

Test condition:

25 °C; light intensity of ~ 25 W/m2 (at 290 nm)

Remarks on result:

other: for both the pyridine and triazine radiolabelled test substance

The mean mass balance from the irradiated samples was in the range 95.5 – 98.6% AR (applied radioactivity) and from the dark controls was 98.4 – 98.6% AR. There was no detectable volatile radioactivity present in the sodium hydroxide traps for either label. Low levels (≤0.3% AR) of volatile radioactivity were recovered from the foam bungs attached to light irradiated and dark units treated with pyridine-labelled test substance. The level of parent compound decreased over the 2 day incubation period from 94.8 - 96.3% AR to 22.6 -23.2 % AR for irradiated samples. In addition to the test substance, one known degradate was identified for samples treated with the pyridine-labelled test substance. This degradate, M3, was present at 71.6% AR (at Day 2). In addition to the test substance, two known degradates were identified for samples treated with the triazine-labelled test substance. There was one degradate present at 66.8% AR at 2 DAT, namely M2. A minor degradate, M11, was present at 2.3% AR (at 2 DAT). No significant degradation was apparent in any ‘dark control’, indicating that the degradation in irradiated samples was due to photodegradation only. The test substance degraded relatively rapidly under irradiated conditions. The DegT50 and DegT90 values were estimated using non-linear regression using single-phase first-order (SFO) kinetics. The test substance degraded under simulated sunlight at an estimated DegT50 equivalent to ca 1.0 days of UK/US summer sunlight. Rates expressed in days after treatment (DAT) are equivalent to summer sunlight DAT, as no correction factor was required.

 

On exposure to artificial sunlight, the test substance was considered to undergo cleavage of the ring systems with formation of M2 and M11 from the triazinyl ring system and M3 from the pyridinyl ring system. The major degradation products observed were M2 and M3, reaching levels of 66.8 and 71.6% AR (2 DAT), respectively. Another minor product identified was M11 at a level of 2.3% AR (2 DAT). No other single degradate was observed at > 3.3% AR.

Validity criteria fulfilled:

not specified

Conclusions:

The test substance degraded under simulated sunlight at an estimated DegT50 equivalent to ca 1.0 days of UK/US summer sunlight.

Executive summary:

The aqueous phototransformation of pyridine- and triazine-radiolabelled test substance was investigated at 25 ± 1ºC in sterile, aqueous phosphate buffer (pH 7) in accordance to OECD 316 and in compliance with GLP criteria. The initial concentration of the test substance was 5 mg ai/L and the samples were continuously irradiated for up to 2 days using light from xenon lamps in Suntest instruments filtered to remove wavelengths below 290 nm. The light intensity of the Suntests was set to give ca 25 W/m2, which was approximately equivalent to 1 day of UK/US summer sunlight for 24 hours continuous irradiation. Irradiated test vessels were connected to traps for the collection of carbon dioxide. Irradiated and dark control samples were analysed at 0 and 2 days. Identification and quantification of the test substance and its degradates was analysed by liquid scintillation counting (LSC), HPLC, thin layer chromatography (TLC) and liquid chromatography-mass spectroscopy (LC-MS).

The mean mass balance from the irradiated samples was in the range 95.5 – 98.6% AR (applied radioactivity) and from the dark controls was 98.4 – 98.6% AR. There was no detectable volatile radioactivity present in the sodium hydroxide traps for either label. Low levels (≤0.3% AR) of volatile radioactivity were recovered from the foam bungs attached to light irradiated and dark units treated with pyridine-labelled test substance. The level of parent compound decreased over the 2 day incubation period from 94.8 - 96.3% AR to 22.6 -23.2 % AR for irradiated samples. In addition to the test substance, one known degradate was identified for samples treated with the pyridine-labelled test substance. This degradate, M3, was present at 71.6% AR (at Day 2). In addition to the test substance, two known degradates were identified for samples treated with the triazine-labelled test substance. There was one degradate present at 66.8% AR at 2 DAT, namely M2. A minor degradate, M11, was present at 2.3% AR (at 2 DAT). No significant degradation was apparent in any ‘dark control’, indicating that the degradation in irradiated samples was due to photodegradation only. The test substance degraded relatively rapidly under irradiated conditions. The DegT50 and DegT90 values were estimated using non-linear regression using single-phase first-order (SFO) kinetics. The test substance degraded under simulated sunlight at an estimated DegT50 equivalent to ca 1.0 days of UK/US summer sunlight. Rates expressed in days after treatment (DAT) are equivalent to summer sunlight DAT, as no correction factor was required.

Description of key information

Information on this endpoint is not part of Annex VIII data requirements; all included studies are marked as supporting information and considered in the CSA.