Degradation of flumioxazin in illuminated water-sediment systems

Article abstract of DOI:10.1021/jf202542v

The aerobic aquatic metabolism of flumioxazin was studied in two water-sediment systems under illumination and in darkness to investigate its degradation profiles. ¹⁴C-Flumioxazin separately labeled at the 1- and 2-positions of the tetrahydrophthalimide moiety or uniformly labeled at the phenyl ring was applied to a overlying water at a rate equivalent to 600 g ai/ha by assuming uniform distribution in the water layer to a depth of 100 cm. Flumioxazin was rapidly degraded at 20 °C in the overlying waters irrespective of irradiation with half-lives of 0.1-0.4 day. Both various modes of liquid chromatography-mass spectrometry (LC-MS) and nuclear magnetic resonance (NMR) spectroscopy analyses showed four major degradates under irradiation. Two of them were formed via successive hydrolysis of the cyclic imide ring, and the others were 2-arizidinone derivatives via photoinduced rearrangement. The presence of sediment under illumination greatly reduced the formation of these degradates and accelerated their degradation. The partitions of flumioxazin and its degradates to the bottom sediment not only reduced their fractions in the water layer subjected to hydrolysis and photolysis but also enhanced their microbial degradation in the sediment. The illuminated water-sediment systems were considered to more adequately represent the behavior of flumioxazin and its degradates in the environment than the corresponding studies of aqueous photolysis and water-sediment in darkness.

Full text of DOI:10.1021/jf202542v

ARTICLE
pubs.acs.org/JAFC
Degradation of Flumioxazin in Illuminated WaterÀSediment Systems
Atsushi Shibata,* Rika Kodaka, Takuo Fujisawa, and Toshiyuki Katagi
Environmental Health Science Laboratory, Sumitomo Chemical Company, Ltd., Takatsukasa 4-chome, Takarazuka, Hyogo 665-8555,
Japan
S Supporting Information
b
ABSTRACT: The aerobic aquatic metabolism of flumioxazin was studied in two waterÀsediment systems under illumination and
in darkness to investigate its degradation profiles. 14C-Flumioxazin separately labeled at the 1- and 2-positions of the tetra-
hydrophthalimide moiety or uniformly labeled at the phenyl ring was applied to a overlying water at a rate equivalent to 600 g ai/ha
by assuming uniform distribution in the water layer to a depth of 100 cm. Flumioxazin was rapidly degraded at 20 °C in the overlying
waters irrespective of irradiation with half-lives of 0.1À0.4 day. Both various modes of liquid chromatographyÀmass spectrometry
(LC-MS) and nuclear magnetic resonance (NMR) spectroscopy analyses showed four major degradates under irradiation. Two of
them were formed via successive hydrolysis of the cyclic imide ring, and the others were 2-arizidinone derivatives via photoinduced
rearrangement. The presence of sediment under illumination greatly reduced the formation of these degradates and accelerated their
degradation. The partitions of flumioxazin and its degradates to the bottom sediment not only reduced their fractions in the water
layer subjected to hydrolysis and photolysis but also enhanced their microbial degradation in the sediment. The illuminated
waterÀsediment systems were considered to more adequately represent the behavior of flumioxazin and its degradates in the
environment than the corresponding studies of aqueous photolysis and waterÀsediment in darkness.
KEYWORDS: flumioxazin, waterÀsediment system, photodegradation, hydrolysis, natural water
’ INTRODUCTION
However, a limited number of studies have been conducted in
the latter case because a fixed test design is not yet available.12,13
Other than the data for official requirement, many researches
have conducted waterÀsediment studies in darkness and/or illu-
minated condition for various chemical classes of pesticides.14À25
Especially in clear and shallow water bodies, the degradation path-
way under illumination becomes very important for photolabile
compounds, and if excessive amounts of photounique products are
formed, their fate in the aqueous environment needs to be clarified
in relation to the ecotoxicological assessment.
The objective of this study is to clarify the effect of illumination
and bottom sediment on the dissipation of 1 and the possible
accumulation of its degradates using a waterÀsediment system
under illumination in comparison with those in the aqueous
photolysis in natural water and waterÀsediment in darkness. We also
identified the definitive structures of major photoproducts of 1 using
liquid chromatographyÀelectrospray ionizationÀmass spectro-
metry (LC-ESI-MS) and NMR spectroscopy in conjunction with
direct chromatographic comparison with the reference standards.
Flumioxazin (1), 2-[7-fluoro-3,4-dihydro-3-oxo-4-(2-propynyl)-
2H-1,4-benzoxazin-6-yl]-4,5,6,7-tetrahydro-1H-isoindole-1,
3-(2H)-dione, is a herbicide for pre-emergence control of a broad
spectrum of weeds in several crops such as soybean, peanut, and
fruit trees.1,2 The behavior of 1 has been intensively studied in
water,3,4 soil,5À7 and rat.8,9 The hydrolysis rate of 1 increased
with an increase in pH as its half-lives were 4.1 days, 16.1 h, and
17.5 min at pH 5.0, 7.0, and 9.0, respectively. The primary
product was an anilic acid derivative (2), which was subsequently
degraded to the corresponding dicarboxylic acid (3) and aniline
(4) via opening of the imide ring followed by cleavage of the
amide linkage.3 Kwon et al. have reported the photodegradation
of 1 with the respective half-lives of 41.5 and 4.9 h at pH 5 and 7,
and one unique photoproduct was suggested only by mass
spectrometry to be formed via hydrolytic cleavage of the amide
linkage in the benzoxiazinone ring.4 The moderate soil degrada-
tion of 1 was reported with the half-life of 12.9À17.9 days in the
laboratory experiments at 15 and 25 °C and 10.6À32.1 days in
the field site.5,6
Incidentally, pesticide applied to the agricultural fields may
reach various water bodies via spray-drift and runoff events and
successively undergoes degradation processes such as hydrolysis,
photolysis, and microbial transformations together with parti-
tioning to suspended matters and bottom sediment. To know the
behavior of pesticides in the aqueous environment, a waterÀ
sediment study in darkness is officially required in the European
Union (EU) registration of pesticide10 in accordance with Orga-
nisation for Economic Co-operation and Development (OECD)
Guideline 308,11 and the one under illumination is conditionally
required for a photolabile pesticide with direct photolysis half-
life of a few days and formation of a photoproduct above 10%.
’ MATERIALS AND METHODS
Chemicals. The nonradiolabeled authentic standards of flumioxazin
(1) and its degradates, N-[7-fluoro-3-oxo-4-(2-propynyl)-2H-1,4-ben-
zoxazin-6-yl]-3,4,5,6-tetrahydrophthalamic acid (2), 3,4,5,6-tetra-
hydrophthalic acid (3), and 6-amino-7-fluoro-4-(2-propynyl)-2H-1,
4-benzoxazin-3(4H)-one (4), were prepared in our laboratory according
Received: June 26, 2011
Revised:
September 12, 2011
Accepted: September 15, 2011
Published: September 15, 2011
r
2011 American Chemical Society
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Table 1. NMR Data for Degradate 5 in CD3CNa
C
1H (multiplicity, J)
13C
HÀH COSY correlated H
HMQC correlated C
HMBC correlated C
1
196.1
143.5
20.8
2
3
2.34 (m)
H-4
H-3
20.8
21.9
C-2, 4
C-2, 3
4
1.77 (br s)
21.9
5
113.3
6
152.6 (d, 1019)
35.1
7
3.59 (d, 23.2)
H-15
35.1
C-5, 6, 8
8
170.3
138.5
92.5
9
10
11
12
13
14
15
5.72 (m)
H-15
92.5
30.1
C-5, 6, 9
4.14 (d, 2.4)
30.1
H-13, 15
C-9, 12, 13, 14
77.2
2.63 (t, 2.4)
3.20 (br s)
73.9
H-11
C-11
166.1
43.8
H-7, 10, 11
43.8
C- 9, 10, 14
a 1H, HÀH COSY, HMQC, and HMBC NMR spectra are shown in the Supporting information (Figures S1ÀS4).
to the reported method.3 Degradate 5, N-(2-propynyl)-4-[4-carboxy-3-
fluoro-2-(3,4,5,6-tetrahydrophthalimido)-2-butenylidene]azetidine-2-one,
was photochemically prepared in our laboratory by using the following
method. A 50% aqueous acetontrile solution of 1 (260 mg) using 10 mM
acetic acid buffer at pH 5 was continuously irradiated under stirring for
7 days with a 500 W xenon arc lamp (UIV-5150XE, Usio, Japan). The
light intensity was maintained almost constant throughout the study
with its irradiance at 300À400 nm of 2.144 MJ/m2/day on average. After
removal of acetonitrile under reduced pressure, the aqueous layer was
extracted four times with 200 mL of ethyl acetate. The combined organic
phase was evaporated to dryness and purified by silica gel (Merck,
Darmstadt, Germany) column chromatography with chloroform/
methanol (9:1, 6:1, and 4:1, v/v) to obtain the fraction of 5 (total yield,
14.3%). The chemical structure of 5 was confirmed by LC-ESI-MS and
1H and 13C NMR spectroscopy with various pulse sequences (Table 1
and Supporting Information, Figures S1ÀS4). Degradate 6, N-(2-
propynyl)-4-[4-carboxy-3-fluoro-2-(2-carboxy-1-cyclohexenecarbonyl-
amino)-2-butenylidene]azetidine-2-one, was conveniently prepared by
hydrolysis of 5 in borate buffer at pH 9 for 24 h. Its chemical structure
was confirmed with LC-ESI-MS. The chemical purity of each nonra-
diolabeled standard was determined to be >96% by high-performance
Figure 1. Proposed degradation pathway of 1 in waterÀsediment
systems under illumination. / and 2 indicate the 14C-labeled positions
of 1.
liquid chromatography (HPLC). The chemical structures of 1 and its
potential degradates 2À6 are shown in Figure 1.
14C-1 separately labeled at the 1- and 2-positions of the tetrahy-
drophthalimide moiety ([THP-14C]-1) or uniformly labeled at the
phenyl ring ([Phe-14C]-1), as shown in Figure 1, was prepared in our
laboratory according to the reported method.3 Each labeled compound
was purified by TLC development in ethyl acetate/hexane (3:1, v/v)
prior to use. Radiochemical purity was >97% as determined by HPLC.
The specific activityies of [THP-14C]-1 and [Phe-14C]-1 were 13.2 and
12.6 MBq mgÀ1, respectively. Other reagents were of the purest grade
commercially available.
1
coherence spectoscopy (HMQC), and H-detected multiple-bond
heteronuclear multiple-quantum coherence spectrum (HMBC) NMR
spectra were measured with a Varian Unity 400 FT-NMR spectrometer
operating at 400.45 MHz with a 5 mm PFG ATB probe. LC-ESI-MS
spectra in positive and negative ion modes were obtained by a Waters
Micromass ZQ spectrometer equipped with Waters Separation Module
2695 and Photodiode Array Detector 2996 as liquid chromatograph.
Samples dissolved in acetonitrile were manually injected into an ioniza-
tion source through a Sumipax ODS A-212 column (150 mm  6 mm
Spectroscopy. 1H and 13C and, for two-dimensional experiments,
HÀH correlated spectroscopy (COSY), 1H-detected multiple-quantum
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Table 2. Characteristics of Bottom Sediments and Overlying
Water Used in This Study
Kasai pond,
Calwich Abbey Lake,
Derbyshire, U.K.
location
sediment
Hyogo, Japan
USDA textural class
sand %
silty clay loam
silt loam
14
56
27
68
5
silt %
clay %
30
organic carbon %
pH (H2O)
1.9
6.8
4.9
7.9
overlying natural water
suspended solids (mg LÀ1
pH
)
42.9
6.9
16.2
7.9
i.d., 5 μm, SCAS Co., Ltd., Japan) at a flow rate of 1.0 mL minÀ1 using
the following gradient system with acetonitrile (A) and 0.05% formic
acid in water (B): 0 min, % AÀ% B, 20À80; 40 min, % AÀ% B, 60À40;
50 min, % AÀ% B, 95À5; 51 min, % AÀ% B, 20À80.
Figure 2. Compartment model used for kinetic analysis of degradation
of [THP-14C]-1 (a) and [Phe-14C]-1 (b) under illumination and in
darkness (c).
HPLC Analysis. HPLC was carried out by using a Shimadzu LC-
20AT pump linked in series with a SPD-20A UVÀvis detector and a
Perkin-Elmer Radiomatic 150TR radiodetector equipped with a 500 μL
liquid cell. An Ultima-Flo AP (Packard Instrument Co.) was utilized as a
scintillator. A Sumipax ODS A-212 column was employed for an
analytical purpose at a flow rate of 1.0 mL minÀ1. The following gradient
systems were used for the analysis: (method 1) acetonitrile (A) and
5 mM tetrabutylammonium phosphate (PIC-A reagent, Waters) (B),
0 min, % AÀ% B, 5À95; 20 min, % AÀ% B, 50À0; 45 min, % AÀ% B,
90À10; 53 min, % AÀ% B, 5À95; (method 2) acetonitrile (solvent A)
and 0.01% trifluoroacetic acid (solvent B), 0 min, % AÀ% B, 20À80; 40
min, % AÀ% B, 60À40; 50 min, % AÀ% B, 95À5; 51 min, % AÀ% B,
20À80. Retention times of 1 and its degradates 2À6 in methods 1 and 2
were as follows: 33.3 and 38.6 min (1); 25.4 and 23.4 min (2); 20.3 and
7.7 min (3); 24.9 and 15.7 min (4); 26.5 and 27.8 min (5); 24.1 and
12.1 min (6), respectively.
including each waterÀsediment system was immersed in a water bath
maintained at 20 ( 2 °C and set on an orbital shaker (MK-200D,
Yamato Scientific, Japan) at 20 rpm to moderately mix the water phase
without disturbance of the sediment. Humidified air was continuously
passed over the water surface to ethylene glycol and alkaline traps in
sequence for collection of organic volatiles and carbon dioxide, respec-
tively, in the same manner as previously reported.19,22 Each vessel was
irradiated using a 2 kW xenon arc lamp (UXL-25SC, Usio, Japan) set
above the vessels, and UV light with wavelengths below 290 nm was cut
off by a Pyrex glass plate. The light intensity was maintained almost
constant throughout the study with its irradiance at 300À400 nm of
0.672 MJ/m2/day on average. Illumination was continued for 8 h per day
during the experiment, which was equivalent to the daily irradiance of
natural sunlight in Tokyo (35° N, AprilÀJune). In the case of dark
control, the system was set on an orbital shaker (SCS-20N, Sanki Seiki
Co., Ltd., Japan) and maintained at 20 ( 2 °C in an incubator (SR-
30VE2, Nagano Science Co., Ltd., Japan) without illumination.
The overlying water and associated sediment were separately ana-
lyzed in duplicate at days 0, 1, 3, 7, 14, and 30 for [THP-14C]-1 and at
days 0, 3, 7, 14, and 30 for [Phe-14C]-1 after application. At each
sampling, the pH and oxidationÀreduction potential (ORP) values of
the water and sediment layers were individually monitored by an F-22
pH-meter equipped with pH and ORP electrodes (Horiba, Ltd., Japan).
In addition, the dissolved oxygen content (DO) in the water layer was
measured with a DO-8F DO-meter (Horiba, Ltd.). The overlying water
was collected by decantation and directly radioassayed by LSC, followed
by HPLC cochromatography with the corresponding nonradiolabeled
reference standards. The sediment was stepwise extracted three times
with acetone/water (5:1, v/v) and then with acetone/0.1 M HCl (9:1, v/v)
by a mechanical shaker for 10 min. The portion of each combined extract
was individually radioassayed by LSC and concentrated in vacuo for
HPLC analysis. The chemical identity of each radiolabeled compound
was confirmed by comparing its HPLC retention time with those of
the nonradiolabeled reference standards. The unextractable sediment
residues were air-dried and combusted for radioassay. The selected
unextractable residues were further fractionated by alkaline for char-
acterization of radioactivity.
Radioassay. Radioactivity in aqueous solution and sediment ex-
tracts was determined by liquid scintillation counting (LSC) with a
PerkinElmer model 3110TR liquid scintillation spectrometer equipped
with an automatic external standard in low-potassium glass vials, using
10 mL of Emulsifier Scintillator Plus (Perkin-Elmer Inc.). Unextractable
sediment residues were air-dried at room temperature and then pow-
dered by a mill mixer MM301 (Retsh, Germany), and its portion was
combusted using a PerkinElmer model 307 Sample Oxidizer prior to
LSC measurements, as described previously.19,22
Metabolism Study. Two types of bottom sediment and overlying
water were individually collected from Kasai pond (Hyogo, Japan) and
Calwich Abbey Lake (Derbyshire, U.K.) and stored in a refrigerator at
4 °C until use. Their physical and chemical properties are summarized in
Table 2. The waterÀsediment samples of Kasai (pH 6.9) and Calwich
Abbey (pH 7.9) were chosen to clarify differences in the behavior of 1 in
relation to the pH of the overlying water. Each sample of water and
sediment was passed through 0.2 and 2 mm sieves prior to use, respectively.
A sediment sample equivalent to approximately 12 g on a dry weight
basis was taken into a two-necked cylindrical glass vessel (4.4 cm i.d.) to
a depth of 2 cm, and then the overlying water was added to each vessel to
a depth of 6 cm. After a preincubation period of at least 2 weeks,
approximately 20 μL of 14C-1 acetonitrile solution was applied to the
water surface in each vessel at a rate of 5.47 μg/vessel, using a micro-
syringe, which is equivalent to the field application rate of 600 g ai/ha
by assuming its uniform distribution in the water layer to a depth of
100 cm.11 To investigate the effect of illumination, the glass vessel
To examine the effect of sediment on the photolytic and hydrolytic
profiles of 1, its behavior in the corresponding overlying water was exam-
ined in the presence and absence of illumination by using [THP-14C]-1
under conditions identical to the above. The overlying water was ana-
lyzed in duplicate up to 30 days after application. At each sampling, the
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Figure 3. Degradation of [THP-14C]-1 in natural water under illumination (a) and in darkness (b): (]) Kasai; (ƒ) Calwich Abbey.
Table 3. DT50 and DT90 Values of 1 in Natural Water and WaterÀSediment Systemsa
illumination
darkness
DT50 (days)
DT90 (days)
χ2
DT50 (days)
DT90 (days)
χ2
Kasai
THP
Phe
natural water only
0.3
1.5
2.6
0.9
1.6
0.9
5.1
8.5
3.1
5.3
6.6
1.2
0.4
1.1
2.3
2.1
3.6
1.2
3.8
9.5
10.3
21.3
4.2
overlying water in wÀs system
total wÀs system
overlying water in wÀs system
total system
5.6
7.6
3.3
6.9
11.9
11.9
21.4
Calwich Abbey
THP
natural water only
0.1
0.2
0.2
0.2
0.5
0.7
2.2
0.0
5.7
0.1
0.2
0.2
0.2
0.5
0.7
12.8
3.9
overlying water in wÀs system
total wÀs system
19.3
a The data were fitted to single first-order equations using FOCUS_DEGKIN version 2. DT50 value = 0.693/dissipation rate constant (k), DT90 value =
2.303/dissipation rate constant (k).
pH, ORP, and DO values were individually measured. The overlying
water was directly radioassayed by LSC and HPLC cochromatography.
Calculations. The dissipation rate constant, half-life (DT50), and
period of 90% dissipation (DT90) of 1 were estimated assuming single
first-order kinetics by using the FOCUS degradation kinetics software
FOCUS_DEGKIN version 2.26 χ2 tests were used to evaluate differ-
ences between observed and calculated values for the SFO fit. By taking
into account the previous hydrolytic degradation of 13 and the chemical
structures of photodegradates 5 and 6, a kinetic analysis for degradates
based on the assumed compartments was conducted using the Model-
Maker program (version 4, ModelKinetix, U.K.), as shown in Figure 2.
The data were fitted to single first-order equations, and the coefficients
of determination (r2) were obtained from the regression analysis.
Under illumination, the maximum amounts of 2, 3, 5, and 6 were
80.3, 59.1, 11.0, and 50.8% AR for the Kasai water and 82.4, 57.4,
2.1, and 48.5% AR for the Calwich Abbey water, respectively.
2 was a major degradate in the first three days and, thereafter, 5
and 6 were formed to their maxima at 7À14 days with a
concomitant decrease of 2. The photodegradates 5 and 6
gradually decreased toward the end of the study. More rapid
conversion of 1 to 6 at a higher pH in the Calwich Abbey water
resulted in less formation of 5. The amount of 3 gradually
increased during the studies to 46.9À59.1% AR at 30 days after
treatment. Detailed kinetic analysis on the equilibrium between 1
and 2, that is, opening and recyclization of the imide ring, has
clarified that two opposite reactions proceed in relatively similar
rates at pH 7.0À8.03 and, thus, it was considered difficult to
precisely estimate the rates of forward and back reactions
between 1 and 2 or between 5 and 6 for the tested waters at
pH 6.8 and 7.9. Therefore, we conveniently allocated each of the
two related compounds to the single compartments as (1 + 2)
and (5 + 6) for the irradiated samples (Figure 2). The half-lives
under illumination for the compartments (1 + 2), 3, and (5 + 6)
were individually estimated for Kasai and Calwich Abbey waters
as 2.7/2.3, 38.4/18.2, and 12.4/2.5 days, respectively (Table 4).
In the dark control, 2 and 3 were the major degradates with
maximum amounts of 93.9À95.6 and 10.3À35.9% AR at 1À3
and 30 days, respectively, and each half-life was estimated to be
’ RESULTS
Photolysis and Hydrolysis in Natural Water. The degrada-
tion of [THP-14C]-1 in the two natural waters is shown in
Figure 3. [THP-14C]-1 rapidly dissipated in both natural waters
with half-lives of 0.1À0.3 day under illumination and 0.1À0.4 day
in darkness, respectively (Table 3). The formation and decline
of the major degradates are shown in Figure 4 (distribution 14C,
Supporting Information, Tables S1 and S2). Degradates 2 and 3
were detected as the major ones irrespective of illumina-
tion, whereas 5 and 6 were detected only under illumination.
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Figure 4. Formation and decline of degradates 2À6 in Kasai and Calwich Abbey natural waters under illumination (a and c) and in darkness (b and d):
(b) 2; (2) 3; (0) 5; (O) 6.
Table 4. DT50 Values (Days) of 1 and Its Degradates 2À6 in Natural Water and WaterÀSediment Systemsa
illumination
darkness
1 + 2
3
4
5 + 6
r2
1
2
3
4
r2
Kasai
THP
Phe
natural water only
2.7
2.2
4.0
2.1
3.4
38.4
0.6
1.1
na
na
na
12.4
10.2
7.1
0.986
0.972
0.985
0.994
0.992
0.4
1.4
2.2
2.5
3.7
38.7
3.5
7.2
2.4
6.4
87.5
0.7
1.5
na
na
na
0.991
0.883
0.863
0.834
0.874
overlying water in wÀs system
total wÀs system
overlying water in wÀs system
total system
na
na
0.1
0.6
4.9
0.3
0.8
na
3.2
na
Calwich Abbey
THP
natural water only
2.3
2.1
3.0
18.2
2.7
na
na
na
2.5
1.8
2.3
0.977
0.921
0.962
0.1
0.3
0.2
62.4
16.0
35.0
5.6
0.5
1.3
na
na
na
0.858
0.986
0.993
overlying water in wÀs system
total wÀs system
4.3
a The DT50 values were estimated with ModelMaker program version 4, by assuming the first-order kinetics for each reaction in each compartment
model. DT50 value = 0.693/rate constant (k). Compartment models a and b were used for the illuminated conditions with THP and Phe labels,
respectively, and compartment model c was used for the dark conditions, as shown in Figure 2. na, not applicable.
38.7À62.4 and 5.6À87.5 days. There were several unknown
fractions in “others”, but none exceeded 9.1% AR (Supporting
Information, Tables S1 and S2), and 14CO2 gradually increased
to 9.0À14.8% AR at 30 days under illumination, whereas
negligible amounts of other unknowns and CO2 were produced
in darkness.
Degradation in the WaterÀSediment Systems under Illu-
mination and in Darkness. The measured values of pH, ORP,
and DO in the overlying water or sediment throughout the
studies are listed in Tables 5À7. The pH values of both phases
did not significantly change during the incubation period in each
system. Aerobicity of the water phase and anaerobicity of the
sediment phase were demonstrated to be mostly maintained
from the results of ORP and DO values. The distribution of 14C
in the waterÀsediment systems under both illumination and
darkness is summarized in Tables 5 and 6 for Kasai systems and
in Table 7 for Calwich Abbey ones. Under illumination, [14C]-1
rapidly dissipated with half-lives of 0.9À1.5 and 0.2 days for the
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Table 5. Distribution of [THP-14C]-1 and Its Degradates 2À6 in the Kasai WaterÀSediment System under Illumination and in
Darknessa
% of the applied radioactivity
illumination
7 days
darkness
3 days
0 days
1 day
3 days
14 days
30 days
1 day
30 days
volatiles (CO2)
na
90.4
87.1
3.3
nd
nd
78.5
54.5
14.3
5.6
0.3
60.9
23.2
17.2
10.9
5.4
4.2
40.7
3.4
8.3
12.6
1.1
24.0
7.7
nd
nd
78.9
53.3
21.3
3.9
0.1
74.2
11.9
55.9
6.4
8.3
24.1
0.5
water phase
1
2
5.3
0.0
5.6
nd
15.5
5.7
3
9.4
5.4
5
nd
2.6
10.2
9.8
2.6
nd
nd
nd
nd
6
nd
0.5
3.3
2.7
1.7
nd
nd
nd
nd
other unknowns
nd
1.1
0.7
2.6
0.8
0.4
nd
2.4
sediment phase
7.9
7.1
nd
22.1
15.5
2.0
38.7
18.7
4.4
48.0
9.8
71.1
5.0
10.9
5.7
1.8
1.2
nd
19.2
14.4
1.0
25.6
12.9
7.3
53.9
6.7
1
2
4.0
5.9
6.5
3
nd
nd
0.6
0.9
nd
nd
nd
2.5
5
nd
nd
0.7
2.0
2.0
nd
nd
nd
6
nd
nd
nd
0.3
0.9
0.2
1.9
48.0
90.6
nd
nd
nd
other unknowns
bound residues
total
0.3
0.6
98.3
nd
0.4
4.0
3.7
1.1
nd
1.2
4.0
13.8
99.9
27.0
92.9
53.6
92.0
2.0
4.1
36.9
86.2
100.6
98.1
99.9
water phase
pH
6.7
7.6
6.7
6.0
6.9
6.2
6.6
6.7
6.8
5.6
6.8
5.9
6.8
6.6
7.0
6.1
6.9
5.4
DO (mg/L)
ORP (mV)
sediment phase
pH
187
160
151
147
190
205
163
119
119
6.7
6.5
6.8
6.5
6.7
6.7
6.8
6.9
6.7
ORP (mV)
À209
À220
À237
À222
À227
À213
À181
À178
À215
a Each value is described as the mean value of duplicate samples. na, not analyzed; nd, not detected. Data of 0, 7, and 14 days in darkness are not shown
(full data are shown in the Supporting information, Table S5).
water phase and 1.6À2.6 and 0.2 days in the total system of Kasai
and Calwich Abbey, respectively, with corresponding total
recoveries of 89.6À100.6 and 80.9À97.7% AR (Tables 5À7).
Similarly to the aqueous photolysis, the degradation rates of 1 in
the Calwich Abbey system were faster than those in the Kasai
one. Degradates 2, 3, 5, and 6 were detected as major degradates
with their maximum amounts (total system) of 32.8, 11.5, 12.2,
and 17.7% AR individually at 3, 3, 7, and 7 days in the case of the
Kasai system, but they markedly decreased to 7.4, 1.2, 0.7, and
1.9% AR at the end of the study. In the Calwich Abbey system, 2,
3, and 6 were produced at 70.8, 30.8, and 13.4% AR at 1, 7, and 3
days, each of which decreased to 3.2, 12.4, and 0% AR at 30 days.
The half-lives of each compartment (1 + 2), 3, 4, and (5 + 6)
were estimated, as listed in Table 4. Overall, compared to the
photodegradation in the natural waters, the presence of the
bottom sediment greatly retarded the formation of 5 and 6 in the
water phase from 50.6À61.8 to 7.0À24.6% AR in total after
7 days. Incidentally, the total recovery in darkness was 86.2À
101.0% AR for the Kasai system and 94.1À98.5% AR for the
Calwich Abbey system. The half-lives of 1 were 0.2À2.1 days in
the water phase and 0.2À3.6 days in the total system. Degradates
2 and 3 formed via hydrolysis were dominantly detected with the
maximum amounts (total system) of 44.4À88.9 and 4.4À10.3%
AR at 3À14 and 14 days, respectively. The estimated half-lives of
2, 3, and 4 based on the compartment model are listed in Table 4.
The unknown fractions in “others” exceeded neither 10% AR nor
>5% AR in at least two sequential measurements under any
conditions tested in this study. The volatile 14C was detected
only in the alkaline trap as 14CO2, which gradually increased to
7.5À24.5% AR at day 30 under illumination and to 2.5À8.3%
AR at day 30 in darkness. The bound residues gradually
increased to 40.4À55.3 and 15.8À61.4% AR at the end of the
study under light and dark conditions, respectively. The alkaline
fractionation of the bound residues showed that the radioactivity
was mainly distributed in the fluvic acid and humic acid fractions
under both light and dark conditions for the Kasai systems,
whereas no similar trend was observed for the Calwich Abbey
ones (Supporting Information, Table S6).
Identification of Photoproducts 5 and 6. The chemical
structure of one major photoproduct has been previously pro-
posed in the photodegradation of 1 in buffers at pH 5 and 74 to be
[4-(cyclohex-1-ene-1,2-dicarboxyimido)-3-fluoro-6-(N-prop-2-
ynylamino)phenoxy]acetic acid, possibly via hydrolytic cleavage
of the amide linkage in the benzoxiazinone ring. Because this
chemical structure was proposed only on the basis of its molecular
weight of 372 obtained with LC-ESI-MS, we have attempted to
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Journal of Agricultural and Food Chemistry
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Table 6. Distribution of [Phe-14C]-1 and Its Degradates 2À6 in the Kasai WaterÀSediment System under Illumination and in
Darknessa
% of the applied radioactivity
illumination
7 days
darkness
14 days
0 days
3 days
14 days
30 days
3 days
30 days
volatiles (CO2)
na
95.3
91.6
2.3
nd
1.7
64.1
9.1
7.4
43.0
2.6
8.8
30.3
nd
24.5
3.8
nd
0.3
56.4
30.6
17.3
4.9
1.1
37.6
2.7
2.5
4.4
nd
water phase
1
2
27.9
1.2
6.1
nd
nd
33.9
nd
3.7
0.7
nd
4
0.8
nd
nd
5
nd
9.4
7.2
1.7
nd
nd
nd
6
nd
11.1
5.4
17.4
8.9
6.7
nd
nd
nd
nd
other unknowns
1.4
2.1
2.0
nd
21.9
50.5
4.2
3.8
68.6
3.6
2.1
nd
3.6
1.0
nd
sediment phase
34.0
13.4
4.9
45.2
8.4
44.3
8.5
61.2
13.5
10.5
3.3
89.7
16.9
5.6
3.1
nd
1
2
3.8
2.9
18.6
1.1
4
nd
0.9
2.5
2.0
5
nd
1.2
1.4
nd
0.7
0.2
6.6
55.3
96.9
nd
nd
6
nd
nd
0.3
nd
nd
nd
nd
other unknowns
bound residues
total
nd
1.9
4.1
5.7
1.8
3.6
2.8
61.4
96.6
0.1
97.4
11.8
99.8
24.7
95.6
35.6
89.6
14.4
101.0
30.3
99.9
water phase
pH
6.7
5.3
6.7
5.3
6.9
5.8
7.0
5.1
6.2
5.0
6.8
5.1
6.7
6.2
6.2
5.5
DO (mg/L)
ORP (mV)
sediment phase
pH
268
245
179
160
229
260
160
217
6.5
6.5
6.8
6.6
6.3
6.8
6.1
5.3
11
ORP (mV)
À254
À255
À239
À221
À152
À363
À115
a Each value is described as the mean value of duplicate samples. na, not analyzed; nd, not detected. Data of 0 and 7 days in darkness are not shown (full
data are shown in the Supporting information, Table S6).
confirm the chemical identification of photochemically prepared
77.2 ppm and C-13 at 73.9 ppm (Table 1 and Supporting
Information, Figures S3 and S4). These results strongly sug-
gested the structure originating from the phenyl ring cleavage
followed by formation of the new four-member ring, 2-arizidi-
none. Because 6 could be produced by mild alkaline hydrolysis
of 5, its chemical structure was determined as the anilic acid
derivative of 5, which was formed by the opening of cyclic imide.
The molecular weight of 6 was determined to be 390 by LC-MS
analysis in both positive and negative ion modes with its pseudo
ions detected at 389 [M À H]À and 391 [M + H]+.
1
5 by using not only LC-MS but also H and 13C NMR with
various pulse sequences. As a result, the chemical structure of 5
was determined to be N-(prop-2-ynyl)-4-[4-carboxy-3-fluoro-
2-(3,4,5,6-tetrahydrophthalimido)-2-butenylidene]azetidine-2-
one, as shown in Table 1. The pseudo ion of 5 was observed at
371 [M À H]À and 373 [M + H]+ in negative and positive ion
modes, respectively, which were identical to the ones previously
reported.4 The comparison between 1H and 13C NMR spectra of
1 and 5 clarified the tetrahydrophthalimide and prop-2-ynyl
moieties remained intact, whereas drastic changes occurred in
the phenyl ring as the signals of C-7, C-8, C-9, and C-10 shifted
toward a higher magnetic field (Supporting Information, Figure
S1). With regard to the phenyl ring, C-8 with no protons in the
HMQC spectrum was most likely to be assigned as a carboxyl
carbon from its chemical shift at 170.3 ppm suggesting the phenyl
ring cleavage between C-8 and C-9, and a comprehensive analysis
of the HMBC spectrum established the chemical structure of the
fragment consisting of C-8ÀC-7ÀC-6ÀC-5ÀC-10ÀC-9. Further-
more, in the HMBC spectrum, the olefinic C-9 at 138.5 ppm and
amide C-14 at 166.1 ppm both showed crosspeaks to two
different methylene protons H-11 and H-15 and, additionally,
the proton H-11 show crosspeaks to acetylene carbons C-12 at
’ DISCUSSION
The half-lives of 1 in the overlying water in the presence and
absence of sediment were 0.2À1.5 and 0.1À0.3 days under
illumination and 0.2À2.1 and 0.1À0.4 days in darkness, respec-
tively, which suggested the insignificant contribution to the
dissipation of 1 due to its rapid hydrolysis (Table 3), whereas
the degradation profiles were greatly dependent on illumination.
The faster degradation of 1 in Calwich Abbey than Kasai samples
could be explained from higher alkalinity of the water layer,
because hydrolysis of the imide linkage is a predominant process
irrespective of light or sediment. The degradation pathway of 1 in
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Journal of Agricultural and Food Chemistry
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Table 7. Distribution of [THP-14C]-1 and Its Degradates 2À6 in the Calwich Abbey WaterÀSediment System under Illumination
and in Darknessa
% of the applied radioactivity
illumination
7 days
darkness
3 days
0 days
1 day
3 days
14 days
30 days
1 day
30 days
volatiles (CO2)
na
95.4
86.0
6.4
nd
nd
79.3
1.1
60.9
2.9
nd
0.4
71.1
nd
2.1
57.1
nd
7.2
39.5
nd
7.5
17.3
nd
nd
81.1
0.9
0.1
82.4
1.2
7.8
41.3
nd
water phase
1
2
30.1
15.9
nd
6.4
1.9
0.8
7.9
nd
75.8
nd
76.1
0.9
33.9
nd
3
28.8
nd
23.0
nd
5
nd
nd
nd
nd
6
nd
9.9
4.5
16.3
2.3
9.9
nd
11.6
13.5
25.9
2.1
7.0
1.7
nd
nd
nd
nd
other unknowns
nd
14.9
33.4
1.8
12.8
43.1
1.2
8.7
56.1
nd
4.4
4.2
7.4
sediment phase
2.3
2.2
nd
14.7
1.8
16.0
0.8
46.5
6.5
1
2
12.3
0.5
5.8
nd
2.4
4.5
nd
11.2
nd
12.8
nd
20.4
0.3
3
nd
2.0
6.6
5
nd
nd
nd
nd
nd
nd
nd
nd
6
nd
1.1
1.4
1.7
95.6
1.8
1.7
6.2
nd
nd
nd
nd
other unknowns
bound residues
total
nd
3.1
5.1
2.9
8.7
40.4
80.9
0.9
1.4
3.5
0.1
97.7
6.2
16.9
92.5
26.2
89.8
0.7
1.1
15.8
95.6
97.5
95.8
98.5
water phase
pH
7.9
4.9
7.9
2.6
83
7.8
2.1
8.0
2.9
87
8.4
6.0
96
8.2
2.9
7.9
4.5
31
8.0
2.6
70
8.1
4.9
90
DO (mg/L)
ORP (mV)
sediment phase
pH
106
103
115
7.4
7.5
7.3
7.7
7.7
7.7
7.5
7.5
7.6
ORP (mV)
À246
À272
À265
À273
À259
À302
À245
À263
À313
a Each value is described as the mean value of duplicate samples. na, not analyzed; nd, not detected. Data of 0, 7, and 14 days in darkness are not shown
(full data are shown in the Supporting information, Table S7).
the illuminated waterÀsediment system was proposed, as shown
in Figure 1. 1 underwent hydrolytic opening of the imide ring to
form 2 followed by cleavage of the amide linkage to produce 3
and 4. Direct photolysis is considered to operate in the formation
of 5 and 6 because 1 and 2 individually have an absorption maxi-
mum in water at 290 and 297 nm, with its shoulder extending
above 300 nm (Supporting Information, Figure S8). It is suggested
that the photoexcited 1 and 2 in water react with a hydroxyl ion at
the C-8 carbon on the phenyl ring, which simultaneously induces
its cleavage with subsequent molecular rearrangement to form
the four-member ring, 2-arizidinone. Because 2, having an
absorption maximum similar to that of 1, was rapidly formed
by hydrolysis of 1, 6 may be dominantly produced by the above
photoreaction directly from 2. Some pesticides are known to be
susceptible to photolysis, forming a product having a very unique
chemical structure via bond cleavage and rearrangement by
direct and indirect photolysis.27,28 The fission of the phenyl ring
and successive rearrangement to produce the five-member ring
have been reported in the photolysis studies of halogenated
phenols and attributed to photooxidation and photoreduc-
tion.27,29 There is a possibility that indirect photolysis with
activated oxygen species such as hydroxyl radical produced
by humic substances and clay mineral in natural water30,31 is
involved to some extent in the formation of 5 and 6, but it was not
confirmed in this study.
With regard to the major degradates, 2, 3, 5, and 6 were much
less produced in the overlying water in the waterÀsediment
system under illumination (Tables 5À7) than observed in
natural water under light. The maximum amounts of 2, 3, 5,
and 6 produced in the former test system as compared with those
in the latter one were lower by factors of 0.35, 0.18, 0.90, and 0.34
for Kasai, and those of 2, 3, and 6 were 0.74, 0.50, and 0.24 for
Calwich Abbey, respectively. With respect to the dissipation rate,
2, 3, 5, and 6 degraded more quickly in the overlying water in the
waterÀsediment system under illumination than observed in the
natural water under irradiation (Table 4). The presence of
sediment under illumination accelerated the degradation of the
compartment (5 + 6) in the total system by a factor of 1.1À1.7 as
compared with the water-only system, whereas much faster
dissipation of 3 by a factor of 4.2À35.0 was observed. The
partition to the bottom sediment and microbial degradation
therein were most likely to be involved for less production of
degradates and their acceleration on dissipation in the systems,
which can be precisely confirmed by comparing the dark control
results between the natural water and waterÀsediment. As
expected, less production of 2 and 3 in the overlying water by
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Journal of Agricultural and Food Chemistry
ARTICLE
factors of 0.60À0.79 and 0.29À0.33 and more rapid degradation in
the total system by factors of 1.8À5.4 and 4.3À58.0, respectively,
were obtained. It has been reported that the faster dissipation of
pesticide in a water layer resulted from the increase of organic matter
content in sediment,21 and partition of the compounds between the
water and sediment phase depended on their partition coefficient
(Koc) values.23 In this study, although two sediments with different
organic carbon contents were used, large differences in the parti-
tioning trend of 1and its degradates were not observed. This may be
due to rapid hydrolysis of 1 producing the degradates with low Koc
values, which will be less affected with respect to the partitioning to
the sediment. The Koc value of 1is in the range of 116À200 by batch
equilibrium method,5 whereas the Koc values of its degradates of 2, 3,
5, and 6 are estimated to be 18, 27, 319, and 512, respectively, by the
EPI-Suite program.32 In addition, the enhancement on decomposi-
tion of the degradates by illumination can be suggested from the
increase of radioactivity transformed to sediment-bound residue and
carbon dioxide in comparison with the dark condition. All of the
above consequences clearly indicated that the balance between the
partitioning and abiotic/biotic degradation is deeply involved in the
contribution of reducing the production of each degradate. Inciden-
tally, aniline compound 4 was scarcely detected in the system
according to the results of the Kasai waterÀsediment system treated
with[Phe-14C]-1(Table 6), whereas the corresponding degradate 3
produced by the complete cleavage of the imide ring amounted to
its total maximum of 11.5% AR for the one using [THP-14C]-1
(Table 5). To the contrary, other minor unknowns reached 27.6%
AR at maximum in the phenyl label treated system after 14 days and
decreased to 10.4% AR with a concomitant increase of bound acti-
vity, which indicated the rapid transformation of 4 to various kinds
of minor degradates followed by their binding to the sediments.
These degradation processes may proceed via oxidation of the
amino group followed by polymerization, as typically known for an
aniline,33 and in such a case, the quantity of each degradate produced
will be variable on each occasion but relatively in low amount.
In conclusion, the results in our illuminated waterÀsediment
study are considered to represent the fate of 1 and its degradates
in the aqueous environment where various important phenom-
ena in nature are more precisely included in the test system than
the individual aqueous photolysis and waterÀsediment study in
darkness. Our results suggest that 1 and its degradates are rapidly
degraded with half-lives of less than several days and do not
persist in the aqueous environment.
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’ ASSOCIATED CONTENT
Supporting Information. Full data of the 14C distribution
S
b
in natural water (Tables S1 and S2), in waterÀsediment systems in
darkness (Tables S3ÀS5), the radioactivity in the bound residues
(Table S6), 1H and 13C NMR spectra with various pulse sequences
NMR spectra of 5 (Figures S1ÀS4), representative HPLC radio-
chromatograms of water layer and sediment extracts in metabolism
study (Figures S5ÀS7), and UVÀvisible absorption spectra of 5
and 6 (Figure S8). This material is available free of charge via the
Internet at http://pubs.acs.org.
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’ AUTHOR INFORMATION
Corresponding Author
*Phone: +81 797 74 2073. Fax: +81 797 74 2132. E-mail:
shibataa@sc.sumitomo-chem.co.jp.
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Journal of Agricultural and Food Chemistry
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