Degradation of fenitrothion by ultrasound/ferrioxalate/UV system

Article abstract of DOI:10.1016/j.ultsonch.2009.06.011

The sonochemical photodegradation of fenitrothion, which is one of phosphorothiate insecticides, was carried out in the presence of Fe(III) and oxalate. The degradation rate was strongly influenced by initial concentrations of Fe(III) and oxalate. An initial fenitrothion concentration of 10 mg L^-1 was completely degraded after 30 min at pH 6 under the optimum conditions. Therefore, the photo-Fenton reaction combined with sonication in the presence of oxalate was available around neutral pH. The decrease of TOC as a result of mineralization of fenitrothion was observed during ultrasound (US)/ferrioxalate/UV process. In addition, the formations of nitrite and sulfate ions as end-products were observed during this degradation system. The decomposition of fenitrothion gave two kinds of intermediate products. The degradation mechanism of fenitrothion was proposed on the base of the evidence of the identified intermediates. Based on these results, US/ferrioxalate/UV system could be useful technology for the treatment of wastewater containing fenitrothion.

Full text of DOI:10.1016/j.ultsonch.2009.06.011

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Ultrasonics Sonochemistry 17 (2010) 200–206
Contents lists available at ScienceDirect
Ultrasonics Sonochemistry
journal homepage: www.elsevier.com/locate/ultsonch
Degradation of fenitrothion by ultrasound/ferrioxalate/UV system
a
a
b
a
Hideyuki Katsumata a, , Toshiko Okada , Satoshi Kaneco , Tohru Suzuki , Kiyohisa Ohta
*
a Department of Chemistry for Materials, Graduate School of Engineering, Mie University, Tsu, Mie 514-8507, Japan
b Environmental Preservation Center, Mie University, Tsu, Mie 514-8507, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
The sonochemical photodegradation of fenitrothion, which is one of phosphorothiate insecticides, was
carried out in the presence of Fe(III) and oxalate. The degradation rate was strongly influenced by initial
concentrations of Fe(III) and oxalate. An initial fenitrothion concentration of 10 mg Lꢀ1 was completely
degraded after 30 min at pH 6 under the optimum conditions. Therefore, the photo-Fenton reaction com-
bined with sonication in the presence of oxalate was available around neutral pH. The decrease of TOC as
a result of mineralization of fenitrothion was observed during ultrasound (US)/ferrioxalate/UV process. In
addition, the formations of nitrite and sulfate ions as end-products were observed during this degrada-
tion system. The decomposition of fenitrothion gave two kinds of intermediate products. The degradation
mechanism of fenitrothion was proposed on the base of the evidence of the identified intermediates.
Based on these results, US/ferrioxalate/UV system could be useful technology for the treatment of waste-
water containing fenitrothion.
Received 18 March 2009
Received in revised form 8 June 2009
Accepted 12 June 2009
Available online 17 June 2009
Keywords:
Fenitrothion degradation
Sonication
Photo-Fenton reaction
Oxalate
Mineralization
Wastewater treatment
Ó 2009 Elsevier B.V. All rights reserved.
1. Introduction
at ambient temperature and pressure with low energy photons,
does not require expensive catalyst, and utilizes natural sunlight.
Organophosphorous insecticides have been widely used as an
alternative to organochlorine compounds for pest control. How-
ever, most of them are highly toxic, can exhibit chemical stability
and resistance to biodegradation [1–3] and, because of the proba-
bility of their being discharged into aquatic systems, great
attention has to be paid to their degradation, to diminish their
harmful effects on the environment.
Fenitrothion, an organophosphorus pesticide, is considered to
be a common river water pollutant, and is detected with high
frequency in river water all over Japan [4–6]. Furthermore, fenitro-
thion residues in natural water undergo photodegradation, result-
ing in the release of many toxic metabolites, some more toxic than
the parent compound, to aquatic organisms [7,8]. Moreover, feni-
trothion and its photoproducts are suspected endocrine disruptors
[8,9]. LC50 (48 h) of fenitrothion for carp, for example, is 4.1 mg Lꢀ1
[10]. Subsequently, the presence of fenitrothion and its metabolites
in natural water has led to a search for highly effective methods for
their removal or decomposition into environmentally compatible
compounds.
Over the past several years, there has been an increasing interest
in use of ultrasonic (US) irradiation to treat organic contaminants
in aqueous solutions [17]. The sonochemical reaction pathways
for the degradation of organic compounds involve the reaction
with hydroxyl radicals and a thermal reaction. The hydroxyl radi-
cals are produced by the sonolysis of water as the solvent inside
the collapsing cavitation bubbles under extremely high-tempera-
ture and pressure [18]. The hydroxyl radicals generated can react
with organic compounds or occur the recombination to H2O2
inside the cavitation bubble and at its interfacial region. Alterna-
tively, organic compounds in the vicinity of a collapsing bubble
may undergo pyrolytic decomposition due to the high local tem-
perature and pressure [19]. US action can be affected in several
ways. Frequency, power, and nature of the dissolved gas(es) have
important effects on reaction product distribution and reaction
rate [20–22]. Furthermore, previous studies have demonstrated
that the addition of chemicals, such as iron ions or ozone, or com-
bination with UV radiation, can amplify ultrasonic action [23,24].
Among these combination methods, photo-Fenton process can
be expected to an efficient method for wastewater treatment and
promotes the rate of degradation of various organic pollutants.
However, Fenton systems have a disadvantage in which the appli-
cable pH range is restricted at pH around 3 because of large
production of iron sludge. It is expected that the production of iron
precipitation can be prevented and the applicable pH of Fenton
reaction can be expanded by the presence of suitable ligands. Fur-
thermore, Fe(III) complexes have been known to play an important
A variety of effective treatment methods have been reported for
the degradation of fenitrothion, e.g., photolysis [11,12], photocatal-
ysis [13–15] and photo-Fenton [16] processes. Among these meth-
ods, photocatalytic one is highly promising because it can operate
* Corresponding author. Tel./fax: +81 59 231 9425.
E-mail address: hidek@chem.mie-u.ac.jp (H. Katsumata).
1350-4177/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.ultsonch.2009.06.011

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H. Katsumata et al. / Ultrasonics Sonochemistry 17 (2010) 200–206
201
role in producing oxidants because of its high molar absorptivity
and quantum yield. For example, several attempts have been made
to apply ferrioxalate as a photochemical method in the treatment
of polluted water, using artificial or solar light [25,26].
Concentration of Fe(II) formed during the degradation process
was determined by the phenanthroline (phen) method. The absor-
bance of Fe(II)-phen complex was taken at 510 nm (e510
=
nm
1.118 ꢂ 104 L molꢀ1 cmꢀ1). The hydroxyl radical concentration
was estimated using a deoxyribose method [27]. Deoxyriobose
(3.5 mM) was reacted with OHꢀ radicals generating by the opti-
mized ultrasound/ferrioxalate/UV system. The reaction was
stopped by addition of 5 mL thiobarbituric acid (1% w/v in
50 mM NaOH) and 5 mL of trichloroacetic acid (2.8% w/v). The mix-
ture was heated at 80 °C for 30 min. The product of the reaction
was quantified at 532 nm using a Shimadzu UV-1650PC double-
beam spectrometer. The concentration of OHꢀ radicals was equated
with thiobarbituric acid active substances using an extinction coef-
In the present study, we have investigated the degradation and
mineralization of fenitrothion in water using of US/ferrioxalate/UV
process. The initial concentrations of Fe(III) and oxalate affected on
the degradation were evaluated. The progress of mineralization of
fenitrothion was monitored by total organic carbon (TOC) content
and ionic chromatography. Furthermore, the intermediate prod-
ucts of fenitrothion during this sono-photocatalytic process have
been identified by gas chromatography–mass spectrometry (GC/
MS). The degradation pathway was proposed on the basis of inter-
mediates formed.
ficient, e .
532 nm, of 153 mMꢀ1 cmꢀ1
The intermediate products during degradation of fenitrothion
were extracted with dichloromethane (2 mL ꢂ 3). The combined
organic fraction was dried by Na2SO4, and concentrated under N2
flow. A GC/MS (Shimadzu GC–MS 5050A) was used for separation
and detection of the intermediate products. The GC was equipped
with a HP-5 capillary column (30 m ꢂ 0.25 mm i.d.) in helium car-
rier gas (1.5 mL minꢀ1) and with splitless injection system. The GC
oven temperature was programmed to hold 50 °C for initial 3 min,
to increase from 50 to 280 °C at a rate of 15 °C minꢀ1 and to hold at
280 °C for 3 min. The injector and interface temperatures were
kept at 280 °C. Mass spectra were obtained by the electron-impact
(EI) mode at 70 eV using the full scan mode.
2. Experimental
2.1. Reagents
Fenitrothion was supplied by Wako Pure Chemical Industries
(Osaka, Japan) and was used as received. Analytical grade ferric
chloride hexahydrate (FeCl3ꢁ6H2O) and sodium oxalate were pur-
chased from Nacalai Tesque (Kyoto, Japan). All other chemicals
and solvents were of the purest grade commercially available
and were used without further purification. All aqueous solutions
were prepared with ultrapure water obtained from an ultrapure
water system (Advantec MFS Inc., Tokyo, Japan) resulting in a
resistivity > 18 MX cm.
3. Results and discussion
2.2. Ultrasonic degradation procedure
3.1. Effect of variables on the degradation of fenitrothion
Sonochemical experiments were conducted in duplicates using
an ultrasonic generator (150 W, 20 kHz, ultrasonic homogenizer
UH-150, SMT Co. Ltd., Tokyo, Japan) equipped with a titanium
oscillator (12 mm of diameter). Experiments were conducted in a
200 ml Pyrex glass cell. One hundred milliliter of fenitrothion solu-
tion and the precise amounts of iron(III) and oxalate was added
into the reaction cell. The pH of the sample solution was adjusted
with HCl and/or NaOH solution. The initial concentration of feni-
trothion in all experiments was 10 mg Lꢀ1 (3.6 ꢂ 10ꢀ5 mol Lꢀ1).
Reaction temperature was kept at 25 1 °C with a water bath.
The sample solution was irradiated with a black light (Toshiba
Lighting & Technology Co.). The beam was parallel and the distance
between lamp and the reactor wall was 10 cm. The lamp was
warmed up for 10 min to reach constant output. In this case, the
short UV radiation (k < 300 nm) was filtered out by the vessel wall.
The intensity of the light was measured by a UV radio meter (UVR-
400, Iuchi Co.) with a sensor of 320 to 410 nm wavelength. The
radio meter was set up at the same position as the reactor.
Effect of ligand on the degradation of fenitrothion by US/Fe(III)/
UV system was examined. Ligands studied were oxalate, malonate
and acetate. These results are shown in Fig. 1. The degradation per-
centage of fenitrothion was 55% after 30 min in the absence of li-
gands because much precipitation of Fe(OH)3 was observed
during the process. Malonate and acetate gave a no ligand effect
for the degradation of fenitrothion although iron precipitation
was not observed. This would be because of low quantum yield
for ferrous ion reproduction [28]. On the other hand, oxalate gave
a positive effect for the degradation of fenitrothion, that is, fenitro-
thion degradation was 65% after 30 min in the presence of oxalate.
2.3. Analyses
The progress in the degradation of fenitrothion was followed
with a HPLC (GL Science Co., Tokyo, Japan) equipped with a GL-
7450 UV detector (GL Science Co.) and a Inertsil ODS-2 separation
column (150 mm ꢂ 4.6 mm i.d., GL Science Co.). The elution was
monitored at 250 nm. The mobile phase was a mixture of acetoni-
trile and water (65/35, v/v), and was pumped at a flow rate of
1.0 mL minꢀ1
.
The progress of mineralization of fenitrothion was monitored
by measuring the TOC. TOC of the sample solution was measured
with a Shimadzu TOC analyzer (TOCꢀVE) based on CO2 quantifica-
tion by non-dispersive infrared analysis after high-temperature
catalytic combustion. The formation of anions was analyzed by io-
nic chromatography using a Metrohm Compact IC 7611 equipped
with a Shodex anionic column (IC SI-90 4E).
Fig. 1. Effect of ligand kind on the degradation of fenitrothion by use of US/Fe(III)/
UV system, (d): absence of ligand; (N): malonate; (j): oxalate; (.): acetate
([Fe(III)]0 = 1 ꢂ 10ꢀ5 M; [ligand]0 = 5 ꢂ 10ꢀ5 M; pH 6.0; ultrasonic power = 150 W;
light intensity = 1.0 mW cmꢀ2).

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H. Katsumata et al. / Ultrasonics Sonochemistry 17 (2010) 200–206
Therefore, the following experiments were conducted in the pres-
ence of oxalate.
To obtain the optimal initial Fe(III) and oxalate concentrations,
the investigations were carried out in the ranges of 0–1 ꢂ 10ꢀ3 and
0–5 ꢂ 10ꢀ3 M, respectively, at pH 6.0. As shown in Fig. 2, the deg-
radation rate of fenitrothion increased with increasing initial Fe(III)
and oxalate concentrations. The highest degradation was obtained
with 5 ꢂ 10ꢀ4 M Fe(III) and 5 ꢂ 10ꢀ3 M oxalate. Further increases
in Fe(III) initial concentration showed no further activity due to
the direct reduction of OHꢀ radicals by the metal ions [29]. The deg-
radation percentage of fenitrothion was almost constant over the
range of 2.5 ꢂ 10ꢀ3–5 ꢂ 10ꢀ3
M oxalate initial concentration.
Therefore, further increases in oxalate concentration would not
be able to be expected for the significant improvement of the deg-
radation rate of fenitrothion. The optimum concentration of oxa-
late was selected as 5 ꢂ 10ꢀ3 M in this study.
Fig. 3 shows fenitrothion degradation under ultrasonic or UV
irradiation and by the combination of the processes. The degrada-
tion rate for US/ferrioxalate/UV process was fastest in all ones.
After 30 min, fenitrothion was completely degraded using US/ferri-
oxalate/UV system, whereas 87% was decomposed with ferrioxa-
late/UV and 40% with ultrasonic. The primary degradation
reaction was estimated to follow a pseudo first-order kinetic law.
In order to obtain the pseudo first-order rate constant, ꢀLn(C/C0)
Fig. 3. Time profiles of fenitrothion degradation by different systems, (d): US; (j):
ferrioxalate/UV; (d): US/ferrioxalate/UV ([Fe(III)]0 = 5 ꢂ 10ꢀ4 M; [oxalate]0 = 5 ꢂ
10ꢀ3 M; pH 6.0; ultrasonic power = 150 W; light intensity = 1.0 mW cmꢀ2).
was plotted as a function of irradiation time. As a result, the degra-
dation rate constant in US/ferrioxalate/UV process (0.143 minꢀ1
)
was about 12 and 2.5 times greater than that in ultrasonic alone
(0.0117 minꢀ1 and ferrioxalate/UV process (0.0559 minꢀ1),
)
respectively. Furthermore, the rate constant in US/ferrioxalate/UV
process was about 2 times greater than the sum of the rate con-
stants in ferrioxalate/UV and US irradiation due to some synergetic
effects between the both processes. Therefore, ultrasonic process
combined with ferrioxalate/UV system is very useful for the degra-
dation of fenitrothion.
At the same time, the concentration of Fe(II) formed during the
process was measured using phenanthroline method (Fig. 4). The
concentration of Fe(II) in the reaction mixture increased up to
2 ꢂ 10ꢀ5 M, decreasing for reaction time above 5 min, and then it
reached a relatively stable value. This plateau value reached after
about 60 min of reaction time while the degradation of fenitrothi-
on and its by-products keeps going on. This plateau can be as-
signed to a photostationary equilibrium between Fe(II) and Fe(III)
that regenerates the absorbing species and gives an interesting cat-
alytic aspect [30,31].
Fig. 2. Degradation of fenitrothion by use of US/ferrioxalate/UV system after 15 min
at different concentrations of (a) Fe(III) ([oxalate]0 = 2.5 ꢂ 10ꢀ3 M) and (b) oxalate
([Fe(III)]0 = 5 ꢂ 10ꢀ4 M); pH 6.0; ultrasonic power = 150 W; light intensity =
Fig. 4. Formation of Fe(II) during US/ferrioxalate/UV process as
a function of
reaction time. ([Fe(III)]0 = 5 ꢂ 10ꢀ4 M; [oxalate]0 = 5 ꢂ 10ꢀ3 M; pH 6.0; ultrasonic
1.0 mW cmꢀ2
.
power = 150 W; light intensity = 1.0 mW cmꢀ2).

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H. Katsumata et al. / Ultrasonics Sonochemistry 17 (2010) 200–206
203
The US/ferrioxalate/UV system produced OHꢀ radical during
the reaction. The radical is a strong oxidizing agent that reacts
with fenitrothion and causes its degradation. The concentration
of OHꢀ radical increased up to 6 ꢂ 10ꢀ5 M a plateau value reached
after about 3 h of reaction time that lasted at least 5 h (Fig. 5).
The OHꢀ radical was thus produced during the whole reaction
time (5 h), which was confirmed by prolonged incubation with
deoxyribose. Accordingly, a continuous formation of OHꢀ radical
is observed allowing the complete mineralization of fenitrothion.
In addition, the concentration of OHꢀ radical by US/ferrioxalate/
UV system was 4.6 and 1.7 times higher than those of US and
ferrioxalate/UV, respectively, after 5 h. These results are in accor-
dance with the degradation rate of fenitrothion by these systems
(Fig. 3).
100
80
60
40
20
3.2. Mineralization
0
30
60
90
120
Reaction time (min)
When the total mineralization of fenitrothion proceeds stoi-
chiometrically using oxygen as oxidizing agent, the mineralization
reaction can be estimated as follows:
Fig. 6. Formation of nitrite ion from fenitrothion degradation during US/ferrioxa-
late/UV process. ([Fe(III)]0 = 5 ꢂ 10ꢀ4 M; [oxalate]0 = 5 ꢂ 10ꢀ3 M; pH 6.0; ultrasonic
power = 150 W; light intensity = 1.0 mW cmꢀ2).
2C9H12NO5PS þ 27O2 ! 2HNO3 þ 2H3PO4 þ 2H2SO4
þ 18CO2 þ 6H2O
ð1Þ
100
80
60
40
20
It should be remarked that nitrogen released has been mea-
sured as a combination of ammonia, nitrite and nitrate, but ammo-
nia and nitrite can be oxidized to nitrate after long irradiation time
[32,33].
The formation of nitrite, nitrate and ammonium ions during the
degradation reaction as a function of reaction time are presented in
Fig. 6. Both nitrate and ammonium ions were not detected during
the reaction time. The concentration of nitrite ion quickly in-
creased with increasing the reaction time, suggesting a very fast re-
lease of nitrogen atoms from fenitrothion. 100% conversion of
fenitrothion nitrogen content was achieved after 2 h of the reaction
time. Therefore, nitrogen atoms from fenitrothion could be com-
pletely mineralized by US/ferrioxalate/UV system. The formation
of sulfate ion from fenitrothion degradation was also investigated.
These results are shown in Fig. 7. The conversion percentage of
fenitrothion sulfur atoms to sulfate ions increased with increasing
the reaction time in which ca. 60% of the initial S was detected as
sulfate ion after 12 h. By comparing the formation rates of nitrite
0
3
6
9
12
Reaction time (h)
Fig. 7. Formation of sulfate ion from fenitrothion degradation during US/ferriox-
alate/UV process. ([Fe(III)]0 = 5 ꢂ 10ꢀ4 M; [oxalate]0 = 5 ꢂ 10ꢀ3 M; pH 6.0; ultra-
sonic power = 150 W; light intensity = 1.0 mW cmꢀ2).
6
4
2
and sulfate ions, it was found that the release of nitrogen from feni-
trothion happened more easily than that of sulfur in US/ferrioxa-
late/UV system. In addition, phosphate ion was not detected at
all during the reaction time. The results revealed that phosphoric
acid dimethyl (methyl) ester and/or thiophosphoric acid dimethyl
(methyl) ester remained in the solution after 12 h of the reaction
time.
The progress of the mineralization of the fenitrothion solution
was monitored by measuring the TOC. At the same time the de-
crease of TOC for oxalate alone was also investigated because oxa-
late is organic compound and contributes to TOC value. As shown
in Fig. 8, TOC for the mixture of fenitrothion and oxalate rapidly de-
creased with increasing the reaction time up to 6 h, and then
showed a constant TOC value although the complete mineraliza-
tion could not achieve after 12 h. Similarly, mineralization of oxa-
late quickly proceeded up to 6 h. However, subtraction of TOC for
the mixture of fenitrothion and oxalate to TOC for oxalate alone de-
creased initial 4 mg C/L to 1 mg C/L after 12 h and would show the
TOC changes for original fenitrothion. Therefore, the mineraliza-
tion of fenitrothion could take place by US/ferrioxalate/UV system.
0
1
2
3
4
5
Reaction time (h)
Fig. 5. Formation of OHꢀ radicals during US, ferrioxalate/UV and US/ferrioxalate/UV
processes as a function of reaction time, (h): US alone; (4): ferrioxalate/UV; (d):
US/ferrioxalate/UV ([Fe(III)]0 = 5 ꢂ 10ꢀ4 M; [oxalate]0 = 5 ꢂ 10ꢀ3 M; pH 6.0; ultra-
sonic power = 150 W; light intensity = 1.0 mW cmꢀ2).