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Environmental fate & pathways

Phototransformation in water

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Reference
Endpoint:
phototransformation in water
Type of information:
experimental study
Adequacy of study:
key study
Study period:
20 April 2009 to 3 May 2013
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Study type:
direct photolysis
Qualifier:
according to guideline
Guideline:
OECD Guideline 316 (Phototransformation of Chemicals in Water - Direct Photolysis)
Version / remarks:
October 2008
Qualifier:
according to guideline
Guideline:
other:
Version / remarks:
EPA Test Guideline OPPTS 835.2240, Photodegradation in Water (October 2008)
GLP compliance:
yes (incl. QA statement)
Radiolabelling:
yes
Analytical method:
high-performance liquid chromatography
other: Liquid scintillation counting (LSC)
Buffers:
Buffer solutions (0.02M) at pH 7
Light source:
Xenon lamp
Light spectrum: wavelength in nm:
>= 300 - <= 400
Relative light intensity:
20.93
Details on light source:
- Emission wavelength spectrum: 300-400 nm
- Filters used and their purpose: Hanau Suntest accelerated exposure machines were used as the light source and filtered radiation from a xenon burner to remove light below 290 nm to give ultra-violet and visible light with a spectral distribution close to that of natural sunlight.
- Light intensity at sample and area irradiated: 20.93 Watts/m2
- Relative light intensity based on intensity of sunlight: 25.13 Watts/m2/day
Details on test conditions:
TEST SYSTEM
- Type, material and volume of test apparatus/vessels: irradiated-Borosilicate glass cuvettes, quartz lids; darkness-Borosilicate glass cuvettes
- Sterilisation method: autoclaving.
- Details of traps for volatile, if any: Vessels with side arms were used for this study in order to trap volatiles. All samples containing radiolabelled test item were equipped with bacterial air filters, polyurethane bungs and two 2M sodium hydroxide traps. Humidified (sterile) air was pulled over the irradiated samples and through the traps.
- Indication of test material adsorbing to the walls of test apparatus: no

TEST MEDIUM
- Volume used/treatment: 80 to 100 μL

REPLICATION
- No. of replicates (dark): 2
- No. of replicates (irradiated): 2
Duration:
35 d
Temp.:
25 °C
Reference substance:
yes
Dark controls:
yes
Computational methods:
- Calculation of molar absorption coefficients: The rate of degradation of fluazifop-P was estimated using KinGUI 1.1 software. The rate of degradation was estimated by fitting single first-order kinetics (SFO) to the data.
- Half-lives or DT50, DT75, and DT90 values and appropriate associated confidence intervals: The degradation times DegT50 and DegT90 (time until 50 or 90% degradation) were calculated by the software from the optimized kinetic parameters.
% Degr.:
3.6
Sampling time:
0 d
Remarks on result:
other:
Remarks:
average % of applied radioactivity of [Pyridinyl-14C]Fluazifop-P for two replicates
% Degr.:
12.5
Sampling time:
3 d
Remarks on result:
other: average % of applied radioactivity of [Pyridinyl-14C]Fluazifop-P for two replicates
% Degr.:
16.2
Sampling time:
5 d
Remarks on result:
other: average % of applied radioactivity of [Pyridinyl-14C]Fluazifop-P for two replicates
% Degr.:
18.9
Sampling time:
8 d
Remarks on result:
other: average % of applied radioactivity of [Pyridinyl-14C]Fluazifop-P for two replicates
% Degr.:
31.8
Sampling time:
15 d
Remarks on result:
other: average % of applied radioactivity of [Pyridinyl-14C]Fluazifop-P for two replicates
% Degr.:
51.7
Sampling time:
28 d
Remarks on result:
other: average % of applied radioactivity of [Pyridinyl-14C]Fluazifop-P for two replicates
% Degr.:
50.9
Sampling time:
30 d
Remarks on result:
other: average % of applied radioactivity of [Pyridinyl-14C]Fluazifop-P for two replicates
% Degr.:
1.2
Sampling time:
35 d
Remarks on result:
other: average % of applied radioactivity of [Pyridinyl-14C]Fluazifop-P for two dark control replicates
% Degr.:
0
Sampling time:
0 d
Remarks on result:
other: average % of applied radioactivity of [Phenyl-14C]Fluazifop-P for two replicates
% Degr.:
20
Sampling time:
3 d
Remarks on result:
other: average % of applied radioactivity of [Phenyl-14C]Fluazifop-P for two replicates
% Degr.:
25.2
Sampling time:
5 d
Remarks on result:
other: average % of applied radioactivity of [Phenyl-14C]Fluazifop-P for two replicates
% Degr.:
38
Sampling time:
8 d
Remarks on result:
other: average % of applied radioactivity of [Phenyl-14C]Fluazifop-P for two replicates
% Degr.:
54.1
Sampling time:
18 d
Remarks on result:
other: average % of applied radioactivity of [Phenyl-14C]Fluazifop-P for two replicates
% Degr.:
67
Sampling time:
21 d
Remarks on result:
other: average % of applied radioactivity of [Phenyl-14C]Fluazifop-P for two replicates
% Degr.:
73.2
Sampling time:
35 d
Remarks on result:
other: average % of applied radioactivity of [Phenyl-14C]Fluazifop-P for two replicates
% Degr.:
0
Sampling time:
35 d
Remarks on result:
other: average % of applied radioactivity of [Phenyl-14C]Fluazifop-P for two dark control replicates
Key result
DT50:
16.7 d
Remarks on result:
other: Photodegradation kinetics (in Days Summer Sunlight (30, 40 and 50°N in Europe and North America) for combined [phenyl-14C] and [pyridinyl-14C]fluazifop-P
Transformation products:
yes
No.:
#1
No.:
#2
No.:
#3
No.:
#4
Details on results:
TEST CONDITIONS
- pH, sterility, temperature, and other experimental conditions maintained throughout the study: Yes
MAJOR TRANSFORMATION PRODUCTS (distinguish between dark and irradiated samples)
- Range of maximum concentrations in % of the applied amount and day(s) of incubation when observed:
[Pyridinyl-14C]Fluazifop-P
- Transformation product #1: 1.8-21.5% of Applied Radioactivity during 0-30 d (DAT) with maximum concentration at DAT 28.
- Transformation product #4: ND-13.4% of Applied Radioactivity during 0-30 d (DAT) with maximum concentration at DAT 28/30.
[Phenyl-14C]Fluazifop-P in pH 7 Buffer
- Transformation product #1: ND-31.4% of Applied Radioactivity during 0-30 d (DAT) with maximum concentration at DAT 21.
- Transformation product #2: ND-12.7% of Applied Radioactivity during 0-30 d (DAT) with maximum concentration at DAT 8.
MINOR TRANSFORMATION PRODUCTS (distinguish between dark and irradiated samples)
[Pyridinyl-14C]Fluazifop-P
- Transformation product #2: 0.7-7.8% of Applied Radioactivity during 0-30 d (DAT) with maximum concentration at DAT 28.
- Transformation product #3: 0.1-1.1% of Applied Radioactivity during 0-30 d (DAT) with maximum concentration at DAT 30.
[Phenyl-14C]Fluazifop-P in pH 7 Buffer
- two unknown transformation products each accounting for < 10% applied radioactivity
TOTAL UNIDENTIFIED RADIOACTIVITY (RANGE) OF APPLIED AMOUNT (distinguish between dark and irradiated samples):
[Pyridinyl-14C]Fluazifop-P
- a total unknown transformation products ranges from 1.0% to 4.9% of Applied Radioactivity during 0-30 d (DAT) with maximum concentration at DAT 30.
[Phenyl-14C]Fluazifop-P in pH 7 Buffer
- two unknown transformation products (A & C) each accounting for < 10% applied radioactivity
- a total other unknown transformation products on the two unknown (A & C) ranges from ND to 23.4% of Applied Radioactivity during 0-30 d (DAT) with maximum concentration at DAT 30.

TABLE 10 A Comparison of the Radioactive Residues in Irradiated pH 7 Buffer Determined by HPLC and TLC after Treatment with [14C]Fluazifop-P

Sample

Radiolabel

Timepoint (DAT)

%AR Analysed

Technique

Fluazifop-P

CGA142110

CGA181847

SYN546933

R201189

Origin

Unknowns

A214 Ext 1

Pyridinyl

28

97.5

TLC

HPLC

50.5

48.1

1.1

1.2

19.0

18.9

10.6

16.1

5.8

6.5

5.8

NA

ND

3.9

A216

Ext 1

Pyridinyl

30

92.6

TLC

HPLC

44.5

39.6

0.7

1.1

24.1

23.4

7.7

14.1

5.0

6.3

5.4

NA

0.7

5.3

C7

Ext 1

phenyl

8

100

TLC

TLC*

HPLC

60.9

58.2

59.0

NA

NA

NA

24.6

22.2

19.1

NA

NA

NA

8.1

11.3

12.9

5.0

6.6

NA

1.1

0.4

8.0

DAT – Experimental Days After Treatment

NA - Not applicable

* TLC performed using 1D TLC system

Validity criteria fulfilled:
yes
Executive summary:

Study Design

The aqueous phototransformation of [pyridinyl-14C]fluazifop-P and [phenyl-14C]fluazifop-P was studied at 25 ± 2ºC in sterile aqueous phosphate buffer (pH 7). The initial concentration of fluazifop-P (R156172, the free acid form of fluazifop-P-butyl) was 5 μg ai/mL and samples were continuously irradiated for up to 35 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 (300 – 400 nm), 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. Samples were analysed at intervals of 0, 3, 5, 8, 15, 28 and 30 days after treatment (DAT) for [pyridinyl-14C]fluazifop-P and 0, 3, 5, 8, 18, 21 and 35 DAT for [phenyl-14C]fluazifop-P. Dark controls were analysed at 35 DAT for both labels.

Results

In the definitive tests, the mean mass balance for the irradiated samples ranged from 96.9 to 103.0% and for the dark controls ranged from 101.9 to 106.1%. Maximum levels of volatile compounds were 3.8% and 15.1% of applied radioactivity for the

pyridinyl label and phenyl label, respectively. The nature of the radioactivity trapped in the sodium hydroxide traps for the [phenyl-14C]fluazifop-P label was confirmed as carbon dioxide by barium carbonate precipitation.

No notable degradation of either radiolabel occurred during the 35 days incubation in the dark. In addition to parent fluazifop-P, four known degradates were identified. There were three degradates present at 10% of applied radioactivity, #1 (up to 31.4% at 21 DAT), #4 (up to 13.4% at 28 and 30 DAT) and R201189 (up to 12.7% at 8 DAT). Parent and these degradates were confirmed by HPLC and TLC co-chromatography with reference standards and by LC-MS.

A number of minor degradates, including #3, were also observed, however levels of individual degradates accounted for < 5% of applied radioactivity, with the exception of an unknown degradate in the phenyl radiolabel samples which occurred at > 5% at one

timepoint only.

The DegT50 value, derived from Single First-Order (SFO) kinetics for both radiolabels and applicable to Europe and North America (latitudes 30°, 40° and 50°), wasca17 days at pH 7.

SFO

DegT50(days)

Chi²

Prob > t

16.7

13.68

0.8338

4.7 x 10-10

 

Conclusion

Fluazifop-P was extensively degraded under simulated sunlight.

The three main photodegradation products were transformation product #1,#2 and #4. Initial photodegradation resulted in the formation of #2 with further photodegradation to #1. Another route of photodegradation resulted in cleavage of the ring systems and formation of #3 from the pyridinyl ring system and minor degradation products and carbon dioxide from the phenyl ring system. #3 levels remained low (ca 1%) as it underwent rearrangement of the pyridinyl ring system to form #4. Some of the radiolabel in both ring systems was ultimately mineralised to carbon dioxide.

DegT50 value applicable to Europe and North America (latitudes 30°, 40° and 50°) was ca 17 days in pH 7 buffer.

Description of key information

The aqueous phototransformation of [pyridinyl-14C]fluazifop-P and [phenyl-14C]fluazifop-P

was studied at 25 ± 20C in sterile aqueous phosphate buffer (pH 7). Fluazifop-P was extensively degraded under simulated sunlight with three main photodegradation products. DegT50 value applicable to Europe and North America was ca 17 days in pH 7 buffer.

Key value for chemical safety assessment

Half-life in water:
16.7 d

Additional information