Simulated sunlight-induced photodegradations of triasulfuron and cinosulfuron in aqueous solutions

Article abstract of DOI:10.1021/jf010948s

To elucidate the photochemical behavior of two sulfonylureas (cinosulfuron and triasulfuron) for which the chemical formulas are relatively close, their photodegradation was studied in water. All experiments were carried out under laboratory conditions using a xenon arc lamp as the source of radiation to simulate environmental conditions. Polychromatic quantum efficiencies were calculated to determine the photochemical pesticide lifetimes at pH 7, and a comparison with hydrolysis lifetimes has been performed. The results obtained showed clearly that at pH 7, photodegradation becomes a more important pathway than chemical degradation. HPLC-DAD was used to study the kinetics for both sulfonylureas and their photoproducts, whereas HPLC-MS (ESI in positive and negative modes) was used to identify photoproducts. These results suggest that the photodegradation of these two sulfonylureas proceeds via a number of reaction pathways: (1) cleavage of the sulfonylurea bridge; (2) desulfonylation, which can proceed either by a carbon-sulfur cleavage or a nitrogen-sulfur cleavage; (3) O-demethylation of methoxy moieties present on the triazine ring; and (4) O-dealkylation of benzene derivatives. In addition, it was found that the desulfonylation represented the main step and that it was wavelength dependent.

Full text of DOI:10.1021/jf010948s

J. Agric. Food Chem. 2002, 50, 1081−1088 1081
Simulated Sunlight-Induced Photodegradations of Triasulfuron
and Cinosulfuron in Aqueous Solutions
†
†
‡
‡
E. VULLIET, C. EMMELIN, M. F. GRENIER-LOUSTALLOT, O. PA ¨I SS EÄ , AND
,
†
J. M. CHOVELON*
LACE, Laboratoire d’Application de la Chimie a` l’Environnement, UMR 5634,
CNRS 43 bld du 11 novembre 1918, 69622 Villeurbanne Cedex, France, and SCA Service Central
D’analyse, USR 059 CNRS, Echangeur de Solaise, B.P. 22, 69390 Vernaison, France
To elucidate the photochemical behavior of two sulfonylureas (cinosulfuron and triasulfuron) for which
the chemical formulas are relatively close, their photodegradation was studied in water. All experiments
were carried out under laboratory conditions using a xenon arc lamp as the source of radiation to
simulate environmental conditions. Polychromatic quantum efficiencies were calculated to determine
the photochemical pesticide lifetimes at pH 7, and a comparison with hydrolysis lifetimes has been
performed. The results obtained showed clearly that at pH 7, photodegradation becomes a more
important pathway than chemical degradation. HPLC-DAD was used to study the kinetics for both
sulfonylureas and their photoproducts, whereas HPLC-MS (ESI in positive and negative modes) was
used to identify photoproducts. These results suggest that the photodegradation of these two
sulfonylureas proceeds via a number of reaction pathways: (1) cleavage of the sulfonylurea bridge;
(2) desulfonylation, which can proceed either by a carbon-sulfur cleavage or a nitrogen-sulfur
cleavage; (3) O-demethylation of methoxy moieties present on the triazine ring; and (4) O-dealkylation
of benzene derivatives. In addition, it was found that the desulfonylation represented the main step
and that it was wavelength dependent.
KEYWORDS: Cinosulfuron; triasulfuron; photodegradation; quantum efficiency; HPLC-MS analysis
INTRODUCTION
accelerate chemical hydrolysis (photoassisted reaction) or form
new products. In this context, photochemical investigation may
contribute to a better understanding of pesticide behavior in the
environment.
This paper reports on the photochemical behavior in water
of two sulfonylureas (SAs), cinosulfuron (CS) and triasulfuron
Since the early 1980s, there has been a dramatic increase in
the number of as well as the use of sulfonylurea herbicides to
control broadleaf weeds and some grasses in cereal crops. Some
of the reasons for their rapid and good acceptance include low
application rates (∼2-75 g/ha), good crop selectivity, and very
low acute and chronic animal toxicity.
(TS). The quantum efficiency has also been calculated and the
kinetics followed. The different photoproducts have been
identified and compared with those obtained in the literature
for chemical hydrolysis, and a pathway of photochemical
degradation has been proposed.
Their mode of action consists of the inhibition of acetolactate
synthase (ALS), a key enzyme in the biosynthetic pathway of
branched-chain amino acids (leucine, isoleucine, and valine) in
the plant.
Although it is claimed that chemical hydrolysis and microbial
degradation represent the main degradation pathways of sulfo-
nylureas (1, 2), several papers indicate that photodegradation
is an alternative pathway to chemical hydrolysis (3-6). Indeed,
the chemical degradation rates of sulfonylureas are pH depend-
ent, and generally these compounds are more susceptible to
chemical hydrolysis at acidic rather than at neutral or weakly
basic pH (7, 8). Therefore, we can easily imagine that at neutral
pH, photodegradation can become an important pathway. In
addition, it is known that photodegradation processes can
MATERIALS AND METHODS
Chemicals. Cinosulfuron [CAS Registry No. 94593-91-6, 1-(4,6-
dimethoxy-1,3,5-triazin-2-yl)-3-[(2-methoxyethoxy)phenyl]urea] and
triasulfuron [CAS Registry No. 82097-50-5, [2-(6-methoxy-4-methyl-
1,3,5-triazin-2-yl)-1-[2-(2-chloroethoxy)phenylsulfonyl]urea]] were pur-
chased from Riedel De Ha e¨ n and were used as received. Their limits
-
1
-1
of solubility in water are 815 mg L for CS and 4000 mg L for TS
at pH 7 and 25 °C. 2-Amino-4-methoxy-6-methyl-1,3,5-triazine was
purchased from Aldrich and (2-chloroethoxy)benzene from Fluka. For
photodegradation experiments, pesticides were solubilized in phosphate
-
3
buffer (K
2
4
HPO /KH
2
PO
4
5 × 10 M), whereas for hydrolysis studies
three buffers were used: acetate buffer for pH 5, phosphate buffer for
pH 7, and borate buffer for pH 9. The water used for LC mobile phase
and buffer preparation was purified with a Millipore system (Milli-Q-
50 18 MΩ).
*
Author to whom correspondence should be addressed [telephone (33)
0
4.72.43.26.38; fax (33) 04.72.44.81.14; e-mail chovelon@univ-lyon1.fr].
†
LACE.
‡
SCA.
1
0.1021/jf010948s CCC: $22.00 © 2002 American Chemical Society
Published on Web 02/01/2002

1082 J. Agric. Food Chem., Vol. 50, No. 5, 2002
Vulliet et al.
2
-1
Table 1. Rate Constant (× 10 h ) for Hydrolysis of Cinosulfuron and
Triasulfuron at Different pH Values and in Pure Water
kdark (CS)
kdark (TS)
pure water
pH 5
pH 7
0.01
0.05
NE
0.06
0.1
0.002
0.003
a
pH 8.9
0.009
a
Not estimated because the hydrolysis proceeded at a much slower rate.
Figure 2. Conversion rate of cinosulfuron ([) and triasulfuron (9) during
suntest irradiation.
Table 3. Triasulfuron and Cinosulfuron Kinetic Data and Quantum
Efficiencies Obtained in Water
ksuntest
t1/2,suntest
(h)
Φ molecules/
photon
τsunlight
lifetime (days)
t1/2,sunlight
(days)
-
1
(
h
)
-
2
2
CS 3.65 × 10
TS
19
45
0.071
0.079
25
30
17.3
20.8
-
1.53 × 10
Figure 1. UV spectra of cinosulfuron (- - -) and triasulfuron (s) in
phosphate buffer.
Table 2. Energy of Singlet (ES1) and Triplet (ET1) States
CS
TS
ES1 (kJ/mol)
ET1 (kJ/mol)
408.3
302.8
409.7
304.4
Spectrometer Apparatus. The absorption spectra were recorded
with a double-beam UVIKON 930 spectrophotometer (Kontron Instru-
ments), whereas fluorescence and phosphorescence spectra were
recorded on a Kontron SFM 25 fluorometer. Fluorescence was measured
in a phosphate buffer, whereas phosphorescence was measured in EPA,
a mixture made up of isopentane (18%), ethanol (41%), and diethyl
ether (41%).
Photodegradation Equipment. A solar simulator (Suntest CPS+,
Heraeus), equipped with a 1.5 kW xenon arc lamp, protected with an
adequate filter to simulate the solar spectrum between 290 and 800
nm, was used, and the experiments were carried out in ordinary
atmosphere at 20 °C.
Kinetics of Photodegradation. Phosphate buffer solutions of SAs
(0.09 mM for cinosulfuron and 0.01 mM for triasulfuron) were
irradiated for 500 and 700 h, respectively. This buffer was chosen as
no absorption in the wavelength range studied was found and no shift
of absorbance spectrum bands occurred. At selected time intervals,
samples were collected and analyzed directly (without preconcentration),
using HPLC-DAD.
HPLC Conditions for Kinetic Studies. HPLC analyses were
performed with a Shimadzu VP series HPLC system equipped with a
photodiode array detector (DAD). A Hypersil BDS C18 column (5 µm,
Figure 3. Evolution of principal photoproducts during (a) cinosulfuron and
b) triasulfuron suntest irradiation. In these figures, (C2) and (T2) areas
were divided by 10 and 3, respectively. Area determination at λ ) 220
(
1
(
25 × 4 mm) was used with a gradient elution of (A) methanol and
B) water (pH was set up at 2.80 with phosphoric acid). The gradient
used was 95% (B) at t ) 0, to 50% (B) at t ) 30 min, and 50% (B)
nm.
-
1
(SPE) cartridge Isolute ENV+ (50 mg, 6 mL). The solid phase was
first conditioned with 3 mL of methanol and then 6 mL of deionized
water. Afterward, the pesticides were eluted with 0.5 mL of methanol
and then analyzed by HPLC-MS.
HPLC-MS Identification. The identification of photoproducts was
performed using HPLC-MS equipment (Hewlett-Packard HP 1100
series LC-MSD). The stationary phase consisted of a Hypersil HP Elite
during 10 min. The flow rate was set at 1 mL min , and the injection
volume was 20 µL.
Photoproduct Identification. A phosphate buffer solution of SAs
was irradiated for 150 h, and samples were taken at regular intervals.
As photoproducts were obtained at very low concentrations, a precon-
centration step was required to perform HPLC-MS analysis. In this
context, 5 mL of each sample was extracted on a solid phase extraction

Photodegradation of Triasulfuron and Cinosulfuron
J. Agric. Food Chem., Vol. 50, No. 5, 2002 1083
Figure 4. HPLC chromatograms of (A) non-irradiated and (B) irradiated solutions of (a) cinosulfuron and (b) triasulfuron. Irradiation times were 260 and
00 h for CS and TS, respectively. Detection at λ ) 220 nm.
3
column (5 µm, 150 × 3 mm) and a precolumn thermostated at 40 °C.
The mobile phases were composed of (A) methanol and (B) 10
shows the rate constant in the dark at different pH values for
CS and TS. From these results we can see that the best stability
is obtained for neutral or weakly basic solutions, which is in
agreement with those reported by Braschi (8). To reduce
chemical hydrolysis, the photolysis experiments were performed
at pH 7 (phosphate buffer) for which both selected herbicides
are predominantly anionic.
-
3
M
ammonium formate + formic acid, the pH of which was set to 2.91,
and the gradient used was the same as previously described. The
injection volume was 2 µL. MS detection was performed with
electrospray ionization (ESI), in positive and negative modes. Operating
conditions for nebulization were as follows: capillary potential, 4000
-
1
2
V; auxiliary gas, N ; flow rate, 12 L min ; pressure, 55 psig.
Calculation of the Quantum Efficiencies. The quantum efficiencies
Φ) were calculated using custom application software Photon (9), and
their values have been defined using the equation
Spectrometric Results. SAs have been found to be composed
of two very weakly coupled chromophores (11), the first one
corresponding to benzene derivatives and the second to triazine
derivatives.
(
dc/dt
Figure 1 shows the UV spectra of cinosulfuron (CS) and
triasulfuron (TS) in phosphate buffer. Both molecules presented
three absorption maxima below 290 nm but also a measurable
absorption tail up to 300 nm. According to an EC (94/37/CE)
directive, phototransformation must be taken into account if the
Φ )
3
∑Pabs
(t,λ)(∆λ × 10 )
where dc denotes the variation of the concentration of the substance
for time t and Pabs is the absorbed light for the same time in the
wavelength range studied. The summation must be performed at
appropriate intervals ∆λ (2.5 nm) in the absorption range of the
substance.
-
1
-1
molar extinction coefficient is >10 L mol cm for λ g 290
-
1
-1
nm. For CS and TS, ꢀ ) 2401 and 1487 L mol cm ,
respectively, at λ ) 290 nm, meaning that the photolytic
degradation pathway should not be neglected.
RESULTS AND DISCUSSION
The energy of the first excited singlet state and that of the
lowest excited triplet state (cf. Table 2) were calculated from
fluorescence and phosphorescence spectra. Both SAs exhibit a
low emission band, at 312 and 310 nm for CS and TS,
respectively (λexc ) 280 nm for both SAs), in the fluorescence
spectra and an emission band at 395 and 393 nm for CS and
TS, respectively, in the phosphoresence spectra (λexc ) 280 nm
for both SAs).
Aqueous Stability. It is known that the stability of sulfonyl-
urea in aqueous solution is markedly influenced by pH (8),
which can act on the structures of these compounds. In aqueous
solution, SAs exist primarily in neutral form at pH values below
their pKa values and in anionic form at pH levels above the
pKa [pKa ) 4.7 for CS and pKa ) 4.6 for TS (10)]. Table 1

1084 J. Agric. Food Chem., Vol. 50, No. 5, 2002
Vulliet et al.
Table 4. Retention Times, Mass Spectra, and UV Data of Photoproducts of Cinosulfurona
a
Irradiations have been performed with a suntest lamp in a phosphate buffer.
Kinetic Studies. Photodegradation Rates. The kinetic studies
were performed at pH 7 using HPLC-DAD analysis. Figure 2
represents conversion rate curves of both SAs. These results
clearly show that the photodegradation is faster for CS than for
TS (after 100 h, the conversion rates were 90 and 60% for CS
and TS, respectively). A pseudo-first-order reaction for the
photodegradation has been found, and kinetic data and quantum
efficiencies for these reactions are given in Table 3. Because
the hydrolysis rate constants are far lower than the photolysis
ones, their contribution will be negligible.
Indeed, the photoreaction values of k and t1/2 cannot be
directly compared with those obtained for the hydrolysis because
they depend on our individual experimental conditions (lamp
power, photoreactor geometry, etc). For direct comparison, the

Photodegradation of Triasulfuron and Cinosulfuron
J. Agric. Food Chem., Vol. 50, No. 5, 2002 1085
Table 5. Retention Times, Mass Spectra, and UV Data of Photoproducts of Trisulfuron
a
Irradiations have been performed with a suntest lamp in a phosphate buffer.
photolytic parameters under sunlight should be assessed. Such
an assessment is possible if the quantum efficiency, the molar
extinction coefficient, and the intensity of the solar spectrum
in a given area are taken into account. [Zepp and Cline (12)
give the intensity of the solar spectrum in North America).] In
these conditions, the lifetime can be calculated by the following
equation (a solution of low absorbance is required, in which
the absorbed light intensity is proportional to the concentration)
and the very low hydrolysis values, ka can be expressed as
3
ka ) 2.303 × 10 [Po(λ)∆λꢀ(λ)]
∑
where Po(λ) represents the solar intensity for wavelength λ [table
in Zepp and Cline (12)] and ꢀ(λ) the molar extinction coefficient
at these wavelengths.
Table 3 summarizes these results, which can be compared
to those obtained from the chemical degradation. For example,
for TS at pH 7, Brashi et al. (8) have found a half-life of 422
days, Weiss et al. (13) have not estimated it as it proceeded at
a much slower rate, and from our own experiments a value of
1444 days has been found.
1
Φka
τ )
where τ denotes the lifetime and ka is the pseudo-first-order
rate constant of direct photolysis in the range of wavelength
These results confirm that for neutral pH, direct photodeg-
radation becomes a more important pathway than for pure
chemical degradation.
(290-800 nm) studied and for the outset of the experiment
degradation rate < 8 h). Due to the short period of time selected
(

1086 J. Agric. Food Chem., Vol. 50, No. 5, 2002
Vulliet et al.
Figure 5. General scheme of photodegradation for CS and TS.
Kinetics of the Main Photoproducts. Figure 3 represents
kinetic curves of the five main photoproducts. For both SAs,
only the more representative photoproducts are shown, although
others have also been identified (cf. Tables 4 and 5). Among
them, certain are only intermediates as they will in turn be
transformed into new photoproducts.
C13 photoproducts.
Identification of the Photoproducts. Many photoproducts
of more or less large concentrations have been tentatively
identified using the following.
HPLC-UV Data. Commercial 2-amino-4-methoxy-6-methyl-
1
,3,5-triazine (AMMT) and (2-chloroethoxy)benzene (CEBS)
are representative of the two chromophoric groups present on
these two SAs. Spectral data of AMMT exhibit two bands (195
and 210 nm) in the UV region, whereas those of CEBS show
three bands (202, 222, and 280 nm). Therefore, the presence of
benzenic groups has been easily recognizable in the photoprod-
ucts C6-C13 and T5-T10. The very close spectral data of T3
Aromatic hydroxylated photoproducts give mass spectra for
which the molecular ions are 16 amu more than the parent
compounds (C11, C12, C13, T9, and T10).
The following positive fragments have been identified as
originating from several photoproducts
(
clearly identified as the AMMT by comparison with the
standard product) and C3 indicate that T3 and C3 must have
nearly the same structures. C3 has thus been identified as
2
-amino-4,6-dimethoxy-1,3,5-triazine. In the same way, com-
parison of the spectral data of CEBS with T5 and C6 has allowed
us to identify T5 as 2-(2-chloroethoxy)benzensulfonamide and
C6 as the 2-(methoxyethoxy)benzensulfonamide.
HPLC-MS Data on the Basis of Pseudomolecular Ions ([M
+
-
+
H] and [M - H] ) and Fragments. Photoproducts contain-
ing an unchanged triazine ring exhibit an ion fragment m/z 141
(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino], according to
[
results obtained by Marek and Koskinen (14). The fragment
m/z 167 has been identified (14) as [[(4-methoxy-6-methyl-1,3,5-
triazin-2-yl)amino]carbonyl] and comes from the fragmentation
of photoproducts T2, T4, and T8. By analogy, a fragment at
m/z 183 is obtained for CS for C2, C5, C8, C10, C11, C12, and

Photodegradation of Triasulfuron and Cinosulfuron
J. Agric. Food Chem., Vol. 50, No. 5, 2002 1087
MS data are collected in Tables 4 and 5, whereas characteristic
HPLC-UV chromatograms are presented in Figure 4. Several
peaks of ammonium and sodium adducts were detected during
analyses but have not been reported in these tables. These data
allow us to propose chemical formulas as well as photodegra-
dation schemes.
The main steps of the degradation include (cf. Figure 5) the
cleavage of the sulfonylurea bridge to give photoproducts A
(C6, T5) and B (C3, T3). This step, which corresponds to a
hydrolysis mechanism, is the typical degradation pathway of
SA herbicides and occurs also for chemical degradation (8).
Meanwhile, at pH 7, pure chemical degradation occurs very
slowly, suggesting that this hydrolysis reaction is indeed
photoassisted (photohydrolysis). Products A are not represented
in the kinetic photoproducts as they are rapidly photodegraded
in turn. On the contrary, the concentration of B increases
steadily.
Also included in degradation is the photodesulfonylation,
which proceeds either by a homolytic nitrogen-sulfur cleavage
or by a homolytic carbon-sulfur cleavage (a free radical
mechanism). Such reactions have only been observed via
photodegradation mechanisms.
Carbon-Sulfur CleaVage. The carbon-sulfur cleavage of CS
and TS gives the main photoproducts C (C2 and T2) (cf. Figure
3
, in which the C2 and T2 areas were divided by 10 and 3,
respectively). In this reaction, the photogenerated sulfonyl
•
radical (O2S R) is transformed into RSO3H. Curiously, these
photoproducts have never been reported, even by Pusino et al.
(15), who observed a C-S cleavage with the TS. These results,
as well as the fact that these molecules are composed of two
weak chromophores, suggest that the observed photoproducts
depend strongly on experimental conditions. In our experiments,
we have always used wavelengths >290 nm (Pusino et al.
worked with lower wavelengths). This is a very important fact
considering that when the UV characteristics of the C2 and T2
photoproducts (Tables 4 and 5) are examined, no photodegra-
dation can be expected when λ > 290 nm, as their absorbance
spectral range is far below this limit. To confirm this result, an
additional experiment using a quartz photoreactor and an HPK
lamp (results given elsewhere) was performed. It appears that
at the very beginning of the experiment, the concentration of C
increases but, after a while, decreases to zero due to the N-S
bond cleavage, which yields other byproducts such as B (C3,
T3) or D (C5, T4).
Figure 6. Comparison between the kinetic curves of the main photo-
products: (a) photoproducts C2 and T2; (b) photoproducts T4 and C5;
(c) photoproducts T3 and C3.
derivatives have wavelengths higher than >270 nm), but mass
spectroscopy results do not allow us a certain identification.
To summarize, we can say that the o-O substituent weakens
the C-S bond, which can be photochemically fragmented to
yield sulfonyl derivatives. The resulting photoproducts can in
turn be phototransformed by an N-S cleavage into further
photoproducts, if wavelengths are sufficiently energetic, for
example, capable of being absorbed by the triazine cycle. Solar
radiations (λ > 290 nm, 412 kJ/mol) are not sufficiently
energetic to provoke this second N-S cleavage, and the sulfonyl
derivative (HO3S-R) therefore becomes the more important
photoproduct.
Nitrogen-Sulfur CleaVage. In the nitrogen-sulfur cleavage,
the fragmentation is followed by an H abstraction from water,
which leads to photoproduct D (C4, T4). This reaction is far
less important than the carbon-sulfur cleavage, as shown in
Figure 5. Indeed, it has been shown (11) that this bond was
cleaved following excitation transfer from the triazine chro-
mophore to the sulfonylurea bridge. In our case, as the
wavelengths used do not allow an efficient excitation of the
triazine chromophore, it is quite normal that this reaction
represents only a minor route.
It is also interesting to note that ring substituents can
significantly affect the photolysis reaction in terms of C-S bond
stability. For example, Yang et al. (16) have found that the
o-chloro group reinforced the photochemical stability, in terms
of the C-S bond, whereas Weiss et al. (13) have found the
same for the p-amino group, presumably because these substit-
uents change the nature of the excitation process. This is why
such a reaction does not represent an important pathway for
them, but for Pusino et al. as well as for our case the o-O group
present on the benzene ring weakens the C-S bond, which will
be more easily cleaved. On the contrary, Choudhury and Dureja
(4) have found this reaction to be only a minor step using
chlorimuron-ethyl.
It is worthy of note that photoproducts originating from the
second part of the cleavage (RO-benzene radical) have not been
clearly identified, whereas Pusino et al. (15) identified one of
them (ClCH2CH2O-C6H5) with an authentic standard. Indeed,
starting from the UV spectrum, the C4 photoproduct might be
one of them (in Tables 4 and 5, absorption peaks for benzene

1088 J. Agric. Food Chem., Vol. 50, No. 5, 2002
Vulliet et al.
The O-demethylation of the methoxy moiety of the triazine
ring gives a hydroxytriazine E (C7, T7). According to the kinetic
curves, its concentration increases steadily to a maximum and
then decreases thereafter, meaning that these photoproducts are
only intermediates and degrade further through different path-
ways. This step has also been observed in the case of the
hydrolysis reaction (8, 17).
generated by sunlight, it is necessary to work with wavelengths
>290 nm.
A complementary study using molecular modeling will be
performed to better understand the photochemical behavior of
SAs and also to try to forecast their photodegradation mecha-
nisms.
LITERATURE CITED
The O-dealkylation of lateral chains of the benzene ring leads
to the products F (C8, T8). It appears that these photoproducts
have never been observed by hydrolysis; these photoproducts
are also intermediate species.
Comparison between the Two SAs. The two SAs differ first
by the lateral chain borne by the benzene ring and second by
the OCH3 or CH3 moieties borne by the triazine ring. These
differences do not seem to overly influence quantum yield
values, which are similar for both cases.
Comparison of the absorption peaks at λ ) 234-236 nm in
aqueous buffers showed that the molar extinction coefficient is
higher for CS (Figure 1) than for TS. However, because the
lowest wavelength used during experiments is 290 nm, it is
unlikely that the photodegradation is strongly influenced.
Figure 5 shows a comparison between the kinetic curves of
the main photoproducts with semiquantification obtained by
expressing the ratio of photoproduct area/SA area (HPLC-UV
analysis). By comparing the photoproducts C2 and T2 (Figure
(1) Fredrickson, D. R.; Shea, P. J. Weed Sci. 1986, 34, 328-332.
(
2) Beyer, E. M.; Duffy, M. J.; Hay, J. V.; Schlueter, D. D.
Sulfonylureas in Herbicides: Chemistry, Degradation and Mode
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York, 1987; pp 117-189.
(3) Harvey, J. J.; Dulka, J.; Anderson, J. J. J. Agric. Food Chem.
1
985, 33, 590-596.
(
4) Choudhury, P. P.; Dureja, P. J. Agric. Food Chem. 1996, 44,
3379-3382.
(
(
5) Choudhury, P. P.; Dureja, P. Pestic. Sci. 1997, 51, 201-205.
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Pestic. Sci. 1999, 55, 955-961.
(7) Berger, B. M.; Wolfe, N. L. EnViron. Toxicol. Chem. 1996,
1
500-1507.
(
8) Braschi, I.; Calamai, L.; Cremonini, M. A.; Fusi, P.; Gessa, C.;
Pantani, O.; Pusino, A. J. Agric. Food Chem. 1997, 45, 4495-
4499.
(9) Guitonneau, S.; Maestracci, M.; M e´ allier, P.; Mouti e´ , E.
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Publications: Cambridge, U.K. 1994.
6a) it seems that the desulfonylation via the C-S bond cleavage
(
(
(
is more efficient for CS than for TS. As this step is the most
important one, it confirms that the conversion rate for CS is
faster than that for TS. On the contrary, the photohydrolysis
step (Figure 6b, T4 and C5) and the desulfonylation one via
the S-N bond cleavage (Figure 6c, C3 and T3) are more
efficient for TS than for CS, even if at the beginning of the
photoreaction, the kinetics are nearly the same. As these
photoproducts are formed to a lesser extent than the C-S bond
cleavage, they do not affect the values of the conversion rates
too greatly.
11) Caselli, M.; Ponterini, G.; Vignali, M. J. Photochem. Photobiol.
A 2001, 138, 129-137.
12) Zepp, R. G.; Cline, D. M. EnViron. Sci. Technol. 1977, 11, 359-
3
66.
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(
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Conclusion. This study confirms earlier findings that pho-
todegradation can no longer be neglected for a good understand-
ing of the evolution of environmental pollutants. We have shown
in particular that their lifetimes could be much more important
with regard to hydrolysis and that specific byproducts could
appear.
7
51-754.
17) Sarmah, A. K.; Kookana, R. S.; Duffy, M. J.; Alston, A. M.;
Harch, B. D. Pest. Manag. Sci. 2000, 56, 463-471.
Received for review July 20, 2001. Revised manuscript received
November 14, 2001. Accepted November 14, 2001.
Furthermore, the importance of the choice of the irradiation
wavelength is clear. If one wishes to identify photoproducts
JF010948S