Spectral and GC-MS analysis of phototransformation of herbicides in water

Article abstract of DOI:10.1134/S1070427209030100

The phototransformation of 2,4-dichlorophenoxyacetic and 2-methyl-4-chlorophenoxyacetic acids in water was studied using the KrCl*(λ_rad 222 nm) and XeBr*(λ_rad 283 nm) excilamps as UV radiation source.

Full text of DOI:10.1134/S1070427209030100

ISSN 1070-4272, Russian Journal of Applied Chemistry, 2009, Vol. 82, No. 3, pp. 396–401. © Pleiades Publishing, Ltd., 2009.
Original Russian Text © O.N. Chaikovskaya, I.V. Sokolova, E.A. Karetnikova, V.S. Mal’kov, S.V. Kuz’mina, 2009, published in Zhurnal Prikladnoi Khimii,
2009, Vol. 82, No. 3, pp. 404–409.
PHYSICOCHEMICAL STUDIES
OF SYSTEMS AND PROCESSES
Spectral and GC–MS Analysis
of Phototransformation of Herbicides in Water
O. N. Chaikovskaya, I. V. Sokolova, E. A. Karetnikova, V. S. Mal’kov, and S. V. Kuz’mina
Tomsk State University, Tomsk, Russia
Institute for Water and Ecological Problems, Russian Academy of Sciences, Far Eastern Branch, Khabarovsk, Russia
Received July 30, 2008
Abstract―The phototransformation of 2,4-dichlorophenoxyacetic and 2-methyl-4-chlorophenoxyacetic acids
in water was studied using the KrCl* (λrad ~222 nm) and XeBr* (λrad ~283 nm) excilamps as UV radiation
source.
DOI: 10.1134/S1070427209030100
Among a variety of herbicides used now all over
the world, 2,4-dichlorophenoxyacetic (2,4-D) and 2-
methyl-4-chlorophenoxyacetic (MCPA) acids occupy
the leading place in the production and application.
After dispersion, herbicides remain on the soil surface,
where they under degradation mainly by soil
microorganisms or are sorbed by organic particles. By
the literature data [1–5], 2,4-D may remain in the
environment from 1 to 6 months.
reagents in combination with UV radiation may make
reaction time shorter, however, these processes often
require the additional stage of the separation, which
increases the cost of the method.
Consequently, direct photodecomposition is a
possible alternative method to the decomposition by
ionizing radiation, because it uses simple apparatus, is
cheap, and, apart from this, allows radiation intensity
and wavelength to be easily controlled [13].
Incorrect use, loss, and inappropriate storage and
transportation of herbicides is dangerous, because their
concentration in aqueous medium may attain several
hundreds of ppm. Consequently, a necessary exists for
the development of efficient methods of herbicide
decomposition under various conditions.
This study is concerned with the phototrans-
formation of 2,4-dichlorophenoxyacetic and 2-methyl-
4-chlorophenoxyacetic acids exposed to the UV radia-
tion of exciplex lamps.
EXPERIMENTAL
Decomposition of 2,4-D was studied by means of
chemical treatment with the H2O2/Fe2+ system, by
photochemical treatment with the systems TiO2/UV
radiation/O3, Fe2+/UV radiation/О3, UV radiation/Fe2+
oxidation, microwave radiation/UV radiation, TiO2/
solar radiation, TiO2/UV radiation, TiO2/active carbon/
UV radiation, by means of photoelectrolytic treatment
[6–12]. The use of ionizing radiation in oxidative
decomposition of 2,4-D is also an efficient method,
which, on the one hand, does not require addition of
chemical reagents to aqueous solutions, but, on the
other hand, requires a complex control measuring
apparatus. As known, the use of catalysts and chemical
We used in the study 2,4-D (98%, Aldrich) and
МСРА (95%, Aldrich). Aqueous solutions of the
compounds under study were prepared by dissolving a
dry weighed portion. The dissolution of МСРА and
2,4-D to a 10–3-M concentration was made complete
by agitating a solution with an ultrasonic stirrer at 40°С
for 15 min. The working concentration of herbicides
was 10–4 M.
2,4-D and MCPA aqueous solutions were irradiated
in a 10×10×45-mm quartz cell or in a glass beaker at
room temperature. The irradiation time was from 1 to
60 min for both lamps. The distance from the
396

SPECTRAL AND GC–MS ANALYSIS
397
Table 1. Spectral characterization of herbicides in water
excilamps to the irradiated solution was 5 cm. During
irradiation, a solution under study absorbed the energy
E = 0.5–3 1 J cm–3. The installation was cooled with an
air ventilator to protect the solution from overheating.
Absorption, nm
Fluorescence,
Sample
λ
max, nm
λ1max
284
278
λ2max
228
226
In photochemical study, unique excilamps, KrCl*
(λra ~222 nm) and XeBr* (λrad ~283 nm), with Δλ = 5–
10 nm, Wpeak = 18 mW cm–2, f = 200 kHz, and a pulse
length of 1 µs [14–17] were used as UV radiation
sources.1 These lamps were chosen because the UV
radiation with λrad~222 nm is absorbed by higher-lying
electronically excited states of molecules under study.
From these states, a passage can occur into the
photodissociative states participating in photocleavage
of О–Н, С–С, and С–Cl bonds. As a consequence, the
efficiency of the molecular phototransformations
increases [18–22]. The irradiation at λrad ~283 nm
allows direct population of the photodissociaive state
participating in photocleavage of C–Cl bond.
2,4-D
310
310
MPCA
measured. The toxicity of the solutions was estimated
by the ratio BI = I/I0 of the bioluminescence intensity
of bacteria in a herbicide solution to that of the
reference [23]. According to the world practice,
solutions are ranked in the following order with respect
to their toxicity: nontoxic (I/I0 = 1), weakly toxic (I/I0 >
0.7), medium-toxic (I/I0 = 0.5), and extremely toxic
(I/I0 < 0.3).
The spectral characteristics of the studied mole-
cules in water are given in Table 1. The 2,4-D and
MCPA absorption spectra contain two characteristic
bands. Noteworthy, the fluorescence intensity of 2,4-D
is lower by a factor of 200 in comparison with MCPA.
The spectral and luminescence characteristics of
initial and irradiated 2,4-D and MCPA solutions were
recorded with an UNICAM/Thermo Evolution 600
UV-Visible Spectrophotometer (USA) and a Varian
Cary Eclipse spectrofluorimeter (Austria).
The intensity decrease around 228 nm and the
intensity increase in the region 240–260 nm were
observed in the absorption spectra of 2,4-D exposed to
KrCl* (λrad ~222 nm) or XeBr* (λrad ~283 nm) excilamp
radiation. The above changes are due to the molecular
phototransformations and formation of photoproducts.
As the time of the UV irradiation increases to 60 min,
the secondary photoproducts are observed in the
absorption spectra at λ > 350 nm. Similar changes,
occurring however after shorter irradiation time, were
also found in the MPCA spectra (Fig. 1). Therefore,
we may conclude that 2,4-D is more stable to
photodegradation than MCPA. Yet, the data on the
GC–MS analysis show that the degree of conversion of
To determine the concentration of 2,4-D and
МСРА after the photolysis, samples were preliminarily
acidified with HCl to рН 1 and extracted with diethyl
ether. Then, the extracts were evaporated in an airflow
to a volume of 0.5 ml. The chromatography-mass spec-
trometry analysis of samples was done on a Finnigan
Trace DSQ instrument (Thermo Electron Chromato-
graphy-Mass Spectrometry Division, USA). The
conditions of the analysis were as follows: Trace TR-
5MS column, 100°C (5 min), 10 deg min–1 to 180°С
(5 min), 100 deg min–1 to 300°С (1 min), MS detector,
carrier gas helium.
The toxicity of aqueous solutions was evaluated in
biological test (lowest organisms, Photobacterium
phosphoreum luminescent bacteria) [23]. We used in
the analysis 109 bacterial cells ensuring the averaged
statistically confident toxicity evaluation. The bio-
luminescence was measured on an “Angstrem” chemi-
luminometer equipped with a cooled photomultiplier,
an amplifier, and a thermostatically controlled eight-
position cell compartment. The total radiation intensity
within 400–700 nm in the photon counting mode was
Fig. 1. Absorption spectra of MCPA in water (c = 10–3 M)
(1) before and (2) after 60 min of exposure to UV radiation
of (2) XeBr* and (3) KrCl* excilamp; the same for Figs. 2–
5. (D) Optical density (rel. units) and (λ) wavelength (nm).
1
The lamps were developed under the supervision of V.F. Tarasenko
at the High Current Electronics Institute, Russian Academy of
Sciences, Siberian Branch, Tomsk, Russia).
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398
CHAIKOVSKAYA et al.
Fig. 2. Fluorescence spectra of 2,4-D aqueous solution (c =
10–3 M) (1) before and (2) after exposure to UV radiation
of a KrCl* excilamp at different fluorescence excitation
wavelengths. (I) Intensity (rel. units) and (λ) wavelength
(nm); the same for Figs. 3–5. λ (nm): (1) 260, (2) 400, (3)
350, (4) 330, (5) 310, (6) 300, (7) 280, and (8) 260.
Fig. 3. Fluorescence spectra of 2,4-D aqueous solution (c =
10–3 M) (1) before and (2) after exposure to UV radiation
of a XeBr* excilamp at different excitation wavelengths. λ
(nm): (1, 2) 260, (3) 280, (4) 300, (5) 330, (6) 350, and
(7) 400.
analysis, 2,4-D exposed to KrCl* (λrad ~222 nm, Е =
1.92 J cm–3) excilamp radiation is most probably
converted to 2,4-dichlorophenol, in line with the
literature data [24]:
these molecules reaches 99% after 30 min of UV
irradiation by these lamps.
The fluorescence analysis of 2,4-D subjected to UV
irradiation revealed several fluorescent photoproducts
(Figs. 2, 3). However, not all of them were detected by
GC–MS method. When KrCl* excilamp is used for the
irradiation, approximately six fluorescent products of
2,4-D photolysis appear. Their fluorescence in the
regions peaking at 430, 475, and 525 nm coincides
with the fluorescence of products formed after the
XeBr* excilamp irradiation. No photolysis product
emitting in the region 400 nm (Table 1) was recorded
after the XeBr* excilamp irradiation, contrary to a
KrCl irradiation. By the data of the chromatographic
CH2COOH
O
OH
Cl
Cl
Cl
Cl
2,4-D
2,4-Dichlorophenol
Table 2. Maxima of fluorescence bands of herbicides in
water exposed to UV radiation of exciplex lamps
λmax, nm
Fluorescence
excitation
KrCl*
XeBr*
KrCl*
XeBr*
370
wavelength, nm
2,4-D
MPCA
260
350
370
290
280
300
310
330
350
400
330
330
400
430
475
525
320
320
–
330
330
–
330
330
–
Fig. 4. Fluorescence spectra of MCPA aqueous solution
(c = 10–3 M) (1) before and (2) after exposure to UV
radiation of a KrCl* excilamp at different fluorescence
excitation wavelengths. λ (nm): (1) 260, (2) 280, and
(3) 330.
430
475
525
410
460
500
430
460
500
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SPECTRAL AND GC–MS ANALYSIS
399
Table 3. Toxicity of 10–4 M aqueous solutions of MCPA
Scheme 1.
and 2,4-D before and after UV irradiation
CH2COOH
Cl
O
OH
Irradiation
Test
CH3
Sample
time, min, and
Toxicity
no.
energy, E, J cm–3
1
2
3
4
5
6
7
МСРА
МСРА+KrCl*
–
Medium
Cl
OH
15/1.5
30/3
15/0.5
30/1
–
''
MCPA
2-Methylphenol
OH
CH3
OH
''
МСРА+XeBr*
''
2-Methylresorcinol
Extremal
Medium
''
2,4-D
2,4-D+KrCl*
O
CH3
15/1.5
O
CH3
8
9
30/3
''
''
''
OH
2,4-D+XeBr*
15/0.7
30/1.44
2-Methyl-p-benzoquinone
2-Methylhydroquinone
10
The GC–MS analysis of 2,4-D aqueous solution
exposed to a XeBr* radiation (λrad ~283 nm, Е =
1.73 J cm–3) revealed neither 2,4-D, nor products of its
conversion. Apparently, to do this, sample preparation
and conditions of the analysis should be changed. By
the data of GC–MS, MCPA (с = 2×10–4 M) exposed to
KrCl* excilamp radiation (E = 1.95 J cm–3) decom-
poses by the Scheme 1.
Scheme 2.
OH
OH
O
CH3
CH3
O
According to the fluorescence analysis, three main
photolysis products are present (Fig. 4). The fluore-
scent compounds in the regions 460 and 500 nm
appear at longer irradiation times (Table 2). The
transformation scheme for MCPA (c = 2×10-4 M)
exposed to a XeBr* excilamp radiation (E = 1.6 J cm–3)
is given in Scheme 2.
2-Methylhydroquinone
2-Methyl-p-benzoquinone
COOH
CH2
O
OH
OH
Cl
CH3
CH3
CH3
Presence of different products was also con-
firmed by the fluorescence spectra (Fig. 5). As seen
from these spectra, the mechanism of the MCPA
photolysis is multichannel and involves breaking of
both С–Cl and O–C bonds.
OH
MCPA
2-Methyl-4-chorophenol 2-Methylphenol
The toxicity of the 2,4-D and MCPA aqueous
solution exposed to a KrCl* excilamp radiation does
not exceed the medium value, i.e., no photolysis
products increasing toxicity of the medium are formed
(Table 3, tests nos. 2, 3, 7, 8). In the given case, the
detoxication effect following the irradiation is not
observed. The toxicity of the MCPA solutions exposed
to a XeBr* excilamp radiation ranks as “extremely”
toxic (Table 3, test no. 5). This may be due to
CH2CH3
OH
O
CH3
CH3
Cl
Cl
OH
Ethoxybenzene 2-Methyl-4,6-dichlorophenol
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 82 No. 3 2009

400
CHAIKOVSKAYA et al.
(Scientific-Educational Center, Tomsk State University,
Tomsk, Russia) for the assistance in the chromato-
graphy-mass spectrometry analysis of photolysis
products of herbicides.
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(1) It was found that the degradation of herbicides
(2,4-dichlorophenoxyacetic and 2-methyl4-chlorophe-
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