Decomposition of 14C-fenitrothion under the influence of UV and sunlight under tropical and subtropical conditions

Article abstract of DOI:10.1016/j.chemosphere.2007.07.063

The decomposition of ¹⁴C-fenitrothion on silica gel chromatoplates as well as in polar and non polar solvents under sunlight and ultraviolet light was investigated, Its stability to sunlight on leaf surfaces of bean plants and on different surfaces (such as glass, quartz and plastic) was also determined. The main photoproducts were identified as carboxyfenitrothion, fenitrooxon, carboxyfenitrooxon and 3-methyl-4-nitrophenol and a small amount 3-caboxy-4-nitrophenol and methyl parathion. The addition of carbaryl and deltamethrin insecticides slightly accelerated the photodecomposition of fenitrothion on silica gel plates and in solution.

Full text of DOI:10.1016/j.chemosphere.2007.07.063

Available online at www.sciencedirect.com
Chemosphere 70 (2008) 1653–1659
www.elsevier.com/locate/chemosphere
1
4
Decomposition of C-fenitrothion under the influence of UV
and sunlight under tropical and subtropical conditions
S.M.A.D. Zayed, F. Mahdy *
Department of Applied Organic Chemistry, National Research Centre, Dokki, Cairo, Egypt
Received 4 April 2007; received in revised form 25 July 2007; accepted 25 July 2007
Available online 5 September 2007
Abstract
1
4
The decomposition of C-fenitrothion on silica gel chromatoplates as well as in polar and non polar solvents under sunlight and
ultraviolet light was investigated, Its stability to sunlight on leaf surfaces of bean plants and on different surfaces (such as glass, quartz
and plastic) was also determined. The main photoproducts were identified as carboxyfenitrothion, fenitrooxon, carboxyfenitrooxon and
3
-methyl-4-nitrophenol and a small amount 3-caboxy-4-nitrophenol and methyl parathion. The addition of carbaryl and deltamethrin
insecticides slightly accelerated the photodecomposition of fenitrothion on silica gel plates and in solution.
2007 Elsevier Ltd. All rights reserved.
ꢀ
Keywords: Fenitrothion; Photodecomposition; Sun and UV lights; Different surfaces; Different solvents
1
. Introduction
to control insects on rice, cereals, fruits, vegetables, stored
grains and cotton. It is applied in public health measures to
control flies, mosquitoes and cockroaches (WHO, 1992). It
has been also used for the control of stored product insect
pests in a number of countries (Snelson, 1987). The insecti-
cide is non-systemic and non-persistent (Spencer, 1981;
Hassall, 1990; Briggs and Council, 1992). The acute toxic-
ity of fenitrothion to mammal is considered to be low
(Spencer, 1981; Hayes, 1982; Hayes and Laws, 1990).
In Egypt, fenitrothion is used on cotton and other
plants. Cotton receives, other than fenitrothion, insecti-
cides such as carbaryl and deltamethrin, so the soil under
the plant usually contain a mixture of the used insecticides.
Therefore, we found it important to investigate the stability
of fenitrothion in presence of carbaryl and deltamethrin in
solution.
This paper studies the decomposition of fenitrothion by
ultraviolet (UV) and sun light on silica gel surface and on
bean foliage and when dissolved in organic solvents and
water. Also, the effect of some pesticide chemicals usually
used for spraying cotton plants (carbaryl and deltamethrin)
on the photodecomposition of fenitrothion and stability of
the insecticide fenitrothion on surfaces of glass, quartz and
plastic was examined.
Organophosphorus compounds have recently been used
as an alternative to organochlorine compounds for pest
control. The widespread use of organophosphorus insecti-
cides results in the release of their residues into natural
water, thus inducing an environmental problem (Derbalah
et al., 2004a).
Fenitrothion, first prepared by Sumitomo Chemical Co.
has the structural formula [O,O-dimethyl-O-(3-methyl-4-
nitrophenyl) phosphorothioate, I] is marketed under differ-
ent trade names, e.g., Sumithion, Novathion and Metathion.
It is a broad-spectrum organophosphorus insecticide that has
been in use since 1959. It is considered to be a common river
water pollutant, and its residues in natural water undergo
photodegradation, resulting in the release of many toxic
metabolites, some being more toxic than the parent com-
pound to aquatic organisms (Eto, 1974; Amoros et al.,
2
000; Derbalah et al., 2004b).
Fenitrothion is considered somewhat toxic to fish
(
Thomson, 1989). And it is also employed in agriculture
*
Corresponding author. Tel./fax: +2023370931.
E-mail address: nrc-mahdy@hotmail.com (F. Mahdy).
0
045-6535/$ - see front matter ꢀ 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.chemosphere.2007.07.063

1654
S.M.A.D. Zayed, F. Mahdy / Chemosphere 70 (2008) 1653–1659
The photodecomposition of fenitrothion has been
phorylchloride in presence of triethylamine 0.81 ml
(0.006 M) and the mixture was stirred at 5–10 ꢁC for
30 min. After removal of the separated triethylamine
hydrochloride by filtration, the filtrate was evaporated in
a vacuum. The obtained (O,O-dimethylthiophosphoryl
chloride) in toluene was allowed to react with 0.58 g
(0.003 M) of potassium salt of 3-methyl-4-nitrophenol
while stirring for 30 min at room temperature. This mixture
was refluxed for 2–3 h at 60–80 ꢁC, cooled, diluted with
cold water and the organic layer was separated and dried
over anhydrous sodium sulphate. Under reduced pressure
the solvent was evaporated to give yellow-brown liquid
bp 140–145 ꢁC, 0.1 mmHg). The product was purified by
preparative thin layer chromatography (TLC) (Silica gel
60 F254 pre-coated plates 20 · 20 cm; layer thickness
reported by several authors (Durand et al., 1990, 1994;
Barcelo et al., 1993; Burrows et al., 2002; Sakellarides
et al., 2003; Matsushita et al., 2006). All these studies were
carried out in temperate regions. In the present work we
studied the photodecomposition under local conditions
which are almost tropical (or subtropical), where the tem-
perature reaches 37–41ꢁ in summer which is accompanied
with a high degree of relative humidity (90–100%).
2
. Materials and methods
2
.1. Chemicals
1
4
C-methanol was obtained from Amersham Interna-
1
4
0
.5 mm Art. 5744). The prepared C-fenitrothion had a
tional Corporation, United Kingdom. Thiophosphoryl-
chloride was obtained from Fluka AG. All solvents and
silica gel used were of chemical grades. (Merck Darmstadt,
Germany). Labelled fenitrothion I (Nishizawa et al., 1963)
Fenitrooxon II (Kim et al., 2000), 3-methyl-4-nitrophenol
III (Akintonwa and Hutson, 1967), carboxyfenitrothion
specific activity 2.96 MBq (0.08 lci/mg) and a radiometric
purity 98% (Nishizawa et al., 1963).
Non-labelled fenitrothion was prepared as described
above and its main degradation products were synthesized
in our laboratory according to known procedures for com-
parison purposes (Fig. 1).
(
(
IV) (Bowden et al., 1946) and carboxyfenitrooxon (V)
Greenhalgh and Marshall, 1976) were synthesized in the
laboratory according to the procedures indicated.
2.1.2. Synthesis of fenitrooxon (II)
Oxidation of fenitrothion was obtained by mixing feni-
2
.1.1. Synthesis of fenitrothion (I)
1
trothion solution (2 mM) in acetonitrile with a 10 times
excess of bromine solution (20 mM) in acetonitrile fol-
lowed by vortexing the mixture for a few seconds. The
completion of the reaction was checked by silica gel TLC
by using suitable mobile phases (Hexane: Benzene 1:2).
4
C-fenitrothion labelled at the carbon atoms of the
methyl groups was synthesized by a single vesseled reaction
that involved the condensation of 0.28 ml (0.007 M) of C-
methanol in toluene with 0.315 ml (0.003 M) of thiophos-
1
4
*
S
P
*
Et N
3
CH O
3
PSCl3 + 2 CH OH
3
Cl
*
CH O
3
KO
NO2
S
P
*
CH O
CH3
3
O
NO2
CH3
*
Reflux, 2-3 hrs
CH O
3
Fenitrothion [I]
CH3
NO2
COOH
S
S
P
S
CH3O
CH3O
CH3O
CH O
3
P
O
O
NO2
P
O
NO2
CH3O
3
CH O
[I]
[
IV]
[VII]
CH3
NO2
CH3
NO2
COOH
NO2
COOH
NO2
O
O
P
CH3O
CH3O
CH3O
CH3O
HO
P
O
O
HO
[II]
[
V]
[III]
[VI]
14
Fig. 1. Synthesis of C-fenitrothion and its main degradation products by photodecomposition.

S.M.A.D. Zayed, F. Mahdy / Chemosphere 70 (2008) 1653–1659
1655
Isolation of the product was achieved by preparative TLC
silica gel) using the same mobile phases as used in analy-
tical TLC (Kim et al., 2000). It gave colorless liquid
bp 146.5–148 ꢁC, 0.7 mmHg).
(Rayoner chamber photo reactor with a wave length
(6 · 3000 ꢁK lamp, Ca. 800 w, 300 ± 10 nm).
(
The temperature of the chromatoplates irradiated with
˚
(
UV light was elevated to about 30 C. Experiments in the
dark were carried out alongside as controls. All glass ves-
sels used were pyrex.
2
.1.3. Synthesis of 3-methyl-4-nitrophenol (III)
One gram of pure fenitrothion was dissolved in 10 ml of
% alcoholic potassium or sodium hydroxide and heated
5
2.2.2. Effect of sunlight
on water bath for 30 min. After removal of the solvent,
few drops of water were added and the undesirable materi-
als were extracted with ether. After acidification of phenol
salt with 2 N HCl, the solution was cooled over night and
the pure phenol was obtained by crystallization from water
The other series of degradation experiments of the
radio-insecticide in the same above solutions were studied
following exposure to sunlight as follows: water solution
for 1, 6, 12, 24 h and other solutions for 1, 6, 12, 24 h
and two weeks.
(
mp 125–128 ꢁC) (Akintonwa and Hutson, 1967).
Fenitrothion on silica plates (16 lg) were exposed to
sunlight for 1, 3, 7, 15 days. Corresponding experiments
in the dark were also carried out to serve as controls. Pos-
sible degradation products were investigated using thin
layer chromatography.
2
.1.4. Synthesis of formylfenitrothion
Formylfenitrothion [O,O-dimethyl-O-(4-nitro-m-form-
ylphenyl) phosphorothioate] was prepared by the dropwise
addition of dimethyl chlorothiophosphate in dry acetone to
an ice cold equimolar solution of 5-hydroxy-2-nitrobenzal-
dehyde in benzene containing 1.1 equiv of NaOH. The
reaction mixture, maintained in an atmosphere of nitrogen,
was allowed to come to room temperature when the addi-
tion was complete and then was refluxed for 8 h. The sol-
vent was removed; the residues were cautiously
suspended in water and then extracted three times with
chloroform. The combined organic washes were dried
2.2.3. Stability of fenitrothion on surfaces of glass, quartz
and plastic
A solution of one mg of radioactive fenitrothion in hex-
ane (2 ml) was allowed to evaporate in a Pyrex Petri dish.
In a similar manner solution one mg of insecticide was
placed on a quartz surface and on a plastic surface and
then exposed to sunlight for two weeks.
(
sodium sulfate), filtered and the solvent was removed to
2.2.4. Effect of various pesticides on fenitrothion
photodecomposition
yield a pale yellow oil (Greenhalgh and Marshall, 1976).
To examine the effect of various pesticides on fenitrothi-
on photodecomposition, each of the pesticide (carbaryl and
deltamethrin) chemicals was added on silica gel plate and/
or added to fenitrothion solution as follows:
1. On silica gel
2
.1.5. Synthesis of carboxyfenitrothion (IV)
Carboxyfenitrothion [O,O-dimethyl-O-(4-nitro-m-car-
boxyphenyl) phosphorothioate] (IV) was obtained by oxi-
dation of formyl-fenitrothion with 1.2 equiv of chromium
trioxide/sulfuric acid in acetone (Bowden et al., 1946).
50 lg of each pesticide dissolved in methonal was spotted
1
4
at the baseline of TLC plate and C-fenitrothion (5 lg in
methanol) was overspotted at the same position. The chro-
matoplates were exposed to sunlight for 2 days and then
developed by the solvent systems. The percent of individual
products was determined by LSC of radioactive gel regions.
2. In solution
2
.1.6. Synthesis of carboxyfenitrooxon (V)
Carboxyfenitrooxon [O,O-dimethyl-O-(4-nitro-m-car-
boxyphenyl) phosphate] (V) was prepared by oxidation of
IV in acetone with an excess of potassium permanganate/
magnesium sulfate at room temperature. The reaction
was essentially complete after 15 min. Filtration of the
crude reaction mixture and removal the solvent yielded a
white crystalline material which can recrystallized from
ether: mp 114–115 ꢁC (Greenhalgh and Marshall, 1976).
(a) 10 lg fenitrothion was dissolved in water (5 ml),
(b) 10 lg fenitrothion + 1 mg carbaryl were dissolved
in 5 ml water,
(c) 10 lg fenitrothion + 1 mg deltamethrin were dis-
2
2
.2. Photodecomposition of fenitrothion
solved in 5 ml water.
.2.1. Effect of Ultraviolet Light
Fenitrothion solutions in distilled water at 14 ppm, 1.0%
The three solutions were exposed to sunlight for one
week (in July).
in 50% aqueous methanol, 1.0% in methanol, 1.0% fenitro-
thion in benzene and 1.0% in acetone were used.
2.2.5. Photodecomposition of fenitrothion deposits on bean
leaves
Fenitrothion was individually spotted on silica gel plate
1
4
(
10 lg) (without fluorescent indicator) and then exposed to
C-Fenitrothion (84.5 lg) in 50 ll of hexane was applied
short UV-light (310 nm) for 15, 30, 60, 90 min at a distance
of 25 cm. The photodecomposition was investigated in a
glass apparatus with Quartz vessel used for irradiation
to the upper surface of each primary leaf by a micropepitte.
After treatment, the plants were placed in a protected area
for about 8 h each day. The residual radioactivity after

1656
S.M.A.D. Zayed, F. Mahdy / Chemosphere 70 (2008) 1653–1659
various time intervals (1, 3, 6, 12 d) was removed by wash-
ing with two separate (50 ml) portions of methanol. The
leaves after washing were frozen and then extracted twice
with 10 ml of methanol. Extracts were subjected to LSC
for the determination of the radioactivity and to TLC for
the analysis of the radioactive products. The extracted res-
idues were combusted using a Harvey Biological Oxidizer
posed upon UV-irradiation showing variable rates of pho-
todecomposition. The rate of degradation in polar
solutions decreased in the order: water solution > 50%
methanol > acetone and methanol solutions. In benzene
solution, on the other hand, the insecticide decomposed less
1
4
readily. When C-fenitrothion in acetone solution was irra-
diated with UV at 310 nm six products, in addition to par-
ent compound, were detected. The nature and percentage of
(
(
Model-OX-600) followed by Liquid Scintillation Counting
LSC). For radio-thinlayer chromatography measurement,
1
4
the products are listed in Table 2. On exposure of C-feni-
trothion to sunlight in water solution, the insecticide disap-
peared rapidly and Table 3 shows the percentage of the
individual degradation products. Carboxyfenitrothion was
the main product.
1
cm zones of the plates were scrapped, mixed with scintil-
lator and counted.
2
.3. Characterization of radioactive residues
Okowa et al. (1974) showed that photolysis involved
oxidation of the aryl methyl group to give carboxyfenitro-
thion. The rate of photodecomposition of the insecticide
varies according to the solvent used but not the nature of
the products. Solvents polarity affected both the rate and
the nature of products formed. Irradiation of fenitrothion
in non polar solvents appeared to favor oxidation of the
P@S to P@O, whereas in polar solvents oxidation occurred
at the aryl methyl group (Kormali et al., 2004).
Residues were characterized by TLC on silica gel plates
using toluene:ethyl acetate:acetic acid 5:7:1 (system 1) and
toluene:acetic acid (7:1) (system 2).
Identification of substances was made by comparison
with authentic reference samples, their R values and reten-
f
tion time are shown in Table 1. Analysis of fenitrothion
and its degradation products was performed by high per-
formance liquid chromatography (HPLC).
Spots were made visible by spraying the plates with van-
illin/sulfuric acid reagent (2.5%), followed by heating at
Fenitrothion residues in natural water undergo photo-
degradation, resulting in the release of several toxic meta-
bolites, some being more toxic to aquatic organisms than
˚
1
10 C for 3 min. Fenitrothion and its metabolites gave dif-
ferent colours (pink and blue). Authentic samples were
used for characterization of the residues.
Analysis by high performance liquid chromatography
Table 2
1
4
Photodecomposition of C-fenitrothion in acetone solution irradiated
with UV light
(
HPLC) was done on a Helwtt Packard (1100 USA)
equipped with gradient system pumping, solvent pro-
gram-mmer, the stainless steel column (125 · 4 mm I.D)
was packed with 5 lm ODS-Hypersil, variable-wavelength
UV detector operated at 254 nm. The mobile phase con-
sisted of a mixture of acetonitrile: water (1:1 v/v).
Photoproduct
% of recovered radiocarbon as indicated
products
Irradiation time (min)
15
30
60
90
30
Fenitrothion [I]
Fenitrooxon [II]
85
0.8
70
1
48
1.0
3
. Results and discussion
1.5
3
-Methyl- 4-nitrophenol [III] Detected by colour
Carboxyfenitrothion [IV]
Carboxyfenitrooxon [V]
5
0
10
2
20
3.5
25
6
3
.1. Photodecomposition products from irradiation of
C-fenitrothion in various solutions with UV light
1
4
3
-Carboxy-4-nitrophenol [VI] Detected by colour
Methylparathion [VII]
Unknown (origin)
Total
0
5
95.8
0
8
91
0.5
15
88
1
18
81.5
Fenitrothion dissolved in various solutions was found to
be relatively stable when kept in the dark. It readily decom-
Table 1
Table 3
f t
TLC solvent systems and R values and retention time (R ) for fenitrothion
1
4
Photodecomposition of C-fenitrothion in water solution exposed to
sunlight
and its photoproducts
Compounds
R
f
values
R
t
Photoproduct
% of recovered radiocarbon as indicated
products
A
B
C
Fenitrothion [I]
Fenitrooxon [II]
0.92
0.67
0.80
0.60
0.15
0.37
0.92
0.75
0.40
0.35
0.22
0.08
0.05
0.75
9.32
2.47
2.24
–
–
–
Exposure time (h)
1
6
12
24
Dark
3-Methyl- 4-nitrophenol [III]
Carboxyfenitrothion [IV]
Carboxyfenitrooxon [V]
Fenitrothion [I]
Fenitrooxon [II]
88
1
75
3
50
5
20
7
95
0.4
3-Carboxy-4-nitrophenol [VI]
3-Methyl- 4-nitrophenol [III] Detected by colour
Methylparathion [VII]
–
Carboxyfenitrothion [IV]
2
8
15
28
0.3
3
-Carboxy-4-nitrophenol [VI] Detected by colour
Solvent system A = toluene:ethylacetate:acetic acid (5:7:1).
B = toluene:acetic acid (7:1).
C = HPLC: UV detector 254 nm, mobile phase acetonitrile:water (1:1).
Unknown (origin)
Total
3
6
13
83
28
75
0.1
95.8
94
92

S.M.A.D. Zayed, F. Mahdy / Chemosphere 70 (2008) 1653–1659
1657
the parent compound (Eto, 1974; Amoros et al., 2000; Der-
balah et al., 2004b).
The results obtained show that fenitrothion when irradi-
ated with UV or sunlight undergoes the following photo-
chemical reactions:
photoproducts (Brewer et al., 1974). In the dark, at room
temperature, the hydrolysis of fenitrothion proceeded very
slowly (Greenhalgh et al., 1980).
1
3.3. C-Fenitrothion on glass, quartz and plastic
4
(
1) oxidation of the P@S group to P@O group, (2) oxida-
tion of m-methyl group to carboxyl group, (3) cleavage of
P–O-aryl linkage to give the corresponding phenol. The
photodecomposition pathways of fenitrothion deduced
from the identified photoproducts are shown in Fig. 1.
According to Kormali et al. (2004) fenitrothion is
photodegraded very slowly in absence of catalysts. It is
effectively photodecomposed upon photolysis with near
Solid fenitrothion on glass, quartz and plastic surfaces is
readily decomposed after exposure to sunlight for two
weeks.
According to Fukushima and Katagi, 2006, silica gel
provides a photo reactive environment of fenitrothion
where a number of unknown polar products were obtained.
Simple aliphatic organic solvents, inert surfaces such as
glass, octadecylsilane and poly (tetrafluoroethylene) and
reactive silica gel were not appropriate for a model surface
of a plant (Fukushima and Katagi, 2006).
À3
visible and UV light, in presence of either PW O40 or
1
2
TiO , fenitrothion disappeared within 30–40 min in the
2
À3
presence of PW O , whereas less than 20 min are
1
2
40
required in the presence of TiO (Kormali et al., 2004).
2
Table 5
1
4
Distribution of C-fenitrothion at different time after application to beans
leaves
1
.2. Photodecomposition of C-fenitrothion on silica gel
4
3
chromatoplates
1
4
Fraction
Recovery of applied C-fenitrothion %
Days after application
Table 4 shows photodecomposition of fenitrothion on
silica gel chromatoplates when exposed to UV light or sun-
light. The half-life of the insecticide was calculated to be
approximately 15 min with UV and around one week when
exposured to sunlight. The Carboxyfenitrothion, fenitroo-
xon, carboxyfenitrooxon and 3-methyl-4-nitro-phenol rep-
resented the main products in each case and a small
amount of 3-carboxy-4-nitrophenol was also formed dur-
ing the exposure of fenitrothion to sunlight (Fig. 1). On
the other hand, fenitrothion was found to suffer no change
on silica gel plates when kept in the dark within two weeks.
Addison (1981) reported on the photolysis of fenitrothion
by UV radiation (200–400 nm) from a xenon lamp in the
vapour phase (10–15 mg/50–1 reaction chamber) at 85–
1
3
6
12
Surface wash
Methanol extract
Residues
43
25
2
10
20
1.5
31.5
7
2
12
0.8
14.8
15
1.3
23.3
Total
70
Table 6
14
Photodegradation products formed on bean leaves treated with C-
fenitrothion on exposure to sunlight
photoproduct
% of recovered radiocarbon as indicated
products
Days after application
1
3
6
12
Fenitrothion [I]
Fenitrooxon [II]
3
40
1.1
4.5
1.5
3
0.5
0.3
0.1
9
6
0 ꢁC and computed the disappearance half life to be
1 ± 11 min and 24 ± 3 min in the absence or presence of
-Methyl- 4-nitrophenol [III] Detected by colour
Carboxyfenitrothion [IV]
-Carboxy-4-nitrophenol [VI] Detected by colour
3
ozone (0.7–0.9 ± 1 mg/m ), respectively (Addison, 1981).
The vapour phase photolysis of fenitrothion at 313 nm
UV radiations was also studied where 3-methyl-4-nitrophe-
nol and an unidentified product were detected as primary
0.3
0.5
0.5
0.1
3
Unknown (origin)
Total
1.6
43
3.5
10
3
7
1.5
2
Table 4
1
4
Photodecomposition of C-fenitrothion on silica gel chromatoplates irradiated with UV light and exposed to sunlight
Photoproduct
% of recovered radiocarbon as indicated products
irradiated UV)
% of recovered radiocarbon as indicated products
(exposed to sunlight)
(
Irradiation time (min)
Days after application
1
5
30
60
25
90
18
1
3
7
15
Fenitrothion [I]
Fenitrooxon [II]
50
6
40
5
80
2
70
4
50
6
30
8
3.5
2.5
3-Methyl-4-nitrophenol [III]
Detected by colour
Detected by colour
Carboxyfenitrothion [IV]
Carboxyfenitrooxon [V]
2.5
0.5
4.0
1.0
2.3
0.7
1.2
0.1
1.0
1.2
3
1.5
5
2
6
2.1
3-Carboxy-4-nitrophenol [VI]
Detected by colour
Detected by colour
Unknown (origin)
Total
15.0
74
10.0
60
8.0
39.5
6.5
28.3
10. 5
94.7
6.9
85.4
7.5
70.5
11.0
57.1

1658
S.M.A.D. Zayed, F. Mahdy / Chemosphere 70 (2008) 1653–1659
Table 7
Effect of carbaryl and deltamethrin on the photodecomposition of C-fenitrothion exposed to sunlight in solution and on silica gel
1
4
Pesticide chemical
% of recovered radiocarbon as indicated products
I
II
A
III
A
IV
A
V
A
Origin
A
Total
A
A
B
B
B
B
B
B
B
Fenitrothion
Fenitrothion + carbaryl
Fenitrothion + deltamethrin
54
46
40
70
60
45
10
5
5
4
3
5
Detected by colour
5
3
5
3
1.5
4
2
3
2
3
2
2
10
15
20
7
12
18
81
72
72
87
78.5
74
A = spotted on silica gel.
B = in solution.
I = fenitrothion.
II = fenitrooxon.
III = 3-methyl-4-nitrophenol.
IV = carboxyfenitrothion.
V = caroxyfenitrooxon.
1
.4. Exposure of C-fenitrothion deposition on bean leaves
4
3
to sunlight
It should be stressed that some photolysis products
obtained in the present study e.g., Oxon and 3-methyl-4-
nitrophenol and carboxyfenitrothion were reported in
other studies (Okowa et al., 1974; Mikami et al., 1985;
Durand et al., 1992, 1994; Castillo et al., 1997; Sakellarides
et al., 2003; Kormali et al., 2004). On the other hand, the
previously reported denitration products and the S-methyl
isomers of fenitrothion (Barcelo et al., 1993; Durand et al.,
1994; Sakellarides et al., 2003) could not be
detected.
It seems that, under tropical conditions, fenitrothion
suffers oxidation of the methyl group in solution (water,
acetone) to a considerable extent under the influence of
UV or sunlight (25–28%). Under the experimental condi-
tions used, the percentage of fenitooxon and carboxyfeni-
trothion is also relatively high.
As shown in Table 5 the radiocarbon applied was rap-
idly lost from leaf surfaces. The surface wash after different
time intervals contained a relatively small percentage of
applied radioactivity. The main metabolites were identified
by TLC using the authentic compounds e.g., carboxyfeni-
trothion, fenitrooxon, 3-methyl-4-nitrophenol and 3-car-
boxy-4-nitrophenol. The relative amounts of these
products are shown in Table 6.
Epicuticular waxes of fruits and vegetables can affect the
photodegradation rate and photoproducts that are formed.
Pesticides decay rates can be increased, decreased or
unchanged by waxes (Cabras et al., 1997; Pirisi et al.,
1
998, 2001).
It can be stated that oxidation processes dominate in
photolysis of fenitrothion under tropical conditions
1
.5. Effect of carbaryl and deltamethrin on C-fenitrothion
4
3
photodecomposition
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