Vol.4, No.5B, 7-11 (2013) Agricultural Sciences
doi:10.4236/as.2013.45B002
The effects of ultrasonic irradiation in combination
with ozone on the reduction of residual ethion of
tangerine (Citrus reticulata Blanco cv. Sai Nam Pung)
fruit after harvest
Kanda Whangchai1,2,3*, Satit Phiyanalinmat4, Jamnong Uthaibutra1,2,3, Sarunya Pengphol5,
Nakao Nomura6
1Postharvest Technology Innovation Center, Commission on Higher Education, Bangkok, Thailand;
*Corresponding Author:
2Postharvest Technology Research Institute, Chiang Mai University, Chiang Mai, Thailand
3Postharvest Technology Research Institute, Chiang Mai University, Chiang Mai,Thailand
4Department of Industrial Chemistry, Faculty of Science, Chiang Mai University, Chiang Mai, Thailand
5Faculty of Agriculture and Industrial Technology,Nakonsawan Rajabhat University, Nakonsawan, Thailand
6Graduate School of Life and Environmental Science, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, lbaraki, Japan
Received 2013
ABSTRACT
Ethion residue removal efficiency using indi-
vidual and combined effects of ultrasonication
(US), ozonation (O3), ultrasonication and ozona-
tion (US/O3) was investigated. A 1 mg·L-1 stan-
dard ethion was subjected to an ultrasonic irra-
diation (3W input power) device with different
frequencies of 108, 400, 700, 1000 kHz, and to an
ozone with a concentr ation of 200 mg · mL-1 wi th
various exposure times (0, 15, 30, 45 and 60
minutes). Reduction of residual ethion was de-
termined by gas chromatography with flame
photometric detection (GC-FPD). It was found
that 1000 kHz ultrasonic irradiation for 60 min-
utes was the most effective treatment for re-
ducing ethion concentration. Additionally, ozone
could reduce the concentration of standard
ethion after 60 minutes of exposure. Ultrasonic
irradiation in combination with ozone had a
synergistic effect in reducing standard ethion
concentration, with the highest rate occurring
within the first 15 minutes. Ethion concentration
was reduced to 75.43% after ultrasonic irradia-
tion at 1000 kHz and ozone exposure for 60 min-
utes. The effectiveness of the combined scheme
for reducing of ethion re sidues on tangerine was
also determined by GC-FPD. The ethion residue
on fresh tangerines after ultrasonic irradiation
and ozone washing was reduced by 73.03% after
60 minutes. The present study demonstrates
that ultrasonic irradiation and ozone exposure
could be use d to re du ce e thi on resi du es in tre ate d
tangerine in order to meet the Standards for
Pesticide Residue Limit s.
Keywords: Tangerine; Ethion; Pesticide Residue;
Ozone; Ultrasonic Irradi ation
1. INTRODUCTION
The economical important pests in tangerine produc-
tion are Asian citrus psyllid (Diaphorina citri Kuwayama:
Psyllidae) the carrier of citrus greening disease (green-
ing), citrus aphid (Toxoptera sp.), chilli thrips (Scirto-
thrips dorsalis Hood: Thripidae), and the African red
mite (Eutetranychus africanus Tucker: Tetranychidae).
The pest feed on tangerine fruits and spread diseases
which in turn ruin the fruits’ appearance. To prevent
these growers, they have to apply a lot of chemical pesti-
cides every week, even at the harvesting time to improve
the tangerines’ aesthetic quality.
There were several batches of tangerine in one plant at
a time reported by Davis and Albrigo (1994) ]1[. There-
fore, in one batch, the chemical pesticides applied to the
tangerines, it would unavoidably affect other batches,
and led to the chemical residue problems. The insecti-
cides used for controlling thrips were ethion, abamectin,
imidacloprid, methomyl, and carbosulfan, respectively.
Ethion is an organophosphate pesticide for controlling
aphids, mites, and thrips. It inhibits the cholinesterase
enzyme in an insect’s nervous system. Currently, grow-
ers widely use ethion, which leaves the chemical residues
on the surface of fruits and vegetables, and sometimes
Copyright © 2013 SciRes. Openly accessible at http://www.scirp.org/journal/as/

K. Whangchai et al. / Agricultural Sciences 4 (2013) 7-11
8
absorbs into the plant tissues. It has been reported that
tangerines consisted of ethion concentrations above the
Maximum Residue Limits (MRL) level (1.0 mg·kg-1),
and 31.8% of the sampled fruits were contaminated with
ethion, cypermethrin, profenophos, carbaryl, chlopyrifos,
and carbosulfan residue below the tangerine MRL level.
They analyzed the peel and flesh of 50 tangerine fruits
collected from the growers, local market and super mar-
ket in Chiang Mai, Lamphun, and Lampang from No-
vember 2008 to December 2009. They found that pesti-
cide residue content, i.e. ethion, profenofos, and triazofos
were higher than the MRL level. An average ethion con-
centration of 1.14 mg·kg-1, it was found in 92% of the
peel samples. Moreover, 50% of tangerine flesh samples
were found to contain an average concentration of 0.01
mg·kg-1 ethion [2].
Ultrasonic irradiation technology effectively reduces a
variety of organic and inorganic contaminants and its
acoustic cavitations generate many hot spots with high
temperatures and pressures those cause the sonolysis of
H2O molecules. Consequently, radical species H, ●OH,
●OOH are formed which lead to a direct destruction of
chemicals in aqueous solution [3]. Hoffman et al.(1996)
reported that ultrasonication at the frequency of 20 to
500 kHz was the effective method in the rapid destruc-
tion of organic contaminants in water [4]. In addition,
Wang et al. (2000) indicated that methyl parathion could
be degraded using ultrasonication at a frequency of 40
kHz [5]. While Song et al. (2007) reported that ultra-
sonication at 200 kHz for 240 seconds effectively to sink
Microcystis surface scum and could be used to reduce
mycrocystin toxin and musty odor substances in aquaculture
pounds [6]. There was no report on the treatment with
ultrasonication and ozonation especially on tangerine.
Ozonation is a promising method to reduce chlopyrifos
in the pericarp and aril of fresh lychee [7]. Furthermore,
Inan et al.(2007) reported the reduction of aflatoxin B1
content in flaked and chopped red peppers (Capsicum
annuum) by 80 and 93% at the rate of 33 and 66 mg·L-1,
respectively after 6 hours of ozone exposure [8]. Wu et
al. (2007) demonstrated that using dissolved ozone (1.4
mg· L -1) for 60 minutes was the effective method to re-
duce 60% - 99% of methyl-parathion, cypermethrin,
parathion and diazinon in aqueous solution [9]. This re-
search mainly studied the effectiveness of ultrasonic ir-
radiation and ozone on the reduction of standard ethion
and residual ethion on tangerine.
2. MATERIAL AND METHODS
Ethion standard was purchased from Sigma-Aldrich
Laborchemikalien GmbH (Stienheim, Germany) with a
99.9% purity (ethion structure is shown in Figure 1).
Ethion stock solution (1000 mg·L-1) was prepared for the
pesticide residue analysis using acetone as the solvent for
high-performance liquid chromatography (HPLC) grade
99.9%, from RCI Labscan Ltd. (Bangkok, Thailand).
The solution was diluted with deionized distilled water to
the appropriate concentrations.
Ultrasonic devices, with an input power of 3 watts and
4 varying frequencies; 108, 400, 700, 1000 kHz and
made by Honda Electronics Company (Toyohashi, Aichi,
Japan), were utilized for three replications. A polyethyl-
ene cylinder reactor 10 cm in diameter, equipped with a
transducer at the lower part was used. Standard ethion
(25 mL) or KI solution in a flask was sonicated in an
ultrasonic reactor.
Ozone gas produced by an ozone generator (Ozonizer,
Sky zone model S05AE) was bubbled into ethion solu-
tion in a flask. The ozone gas was bubbled with a flow
rate of 25 ml·min-1. Dissolved ozone was determined by
the indigo colorimetric method [11].
The treatments that shown good results in ethion deg-
radation from above experiment was used for combina-
tion of ultrasonication and ozone treatment. The ethion
standard was prepared in the ultrasonic reactor mention
ealier. The solution was bubbled with ozone gas from
ozone generator. Samples were collected for the deter-
mination of ethion concentration using GC-FPD (Agilent
Technologies Model 6890) and percentage of removal
rate of the ethion were calculated as the degradation per-
centage.
2.1. Study of Optimum Frequency of
Ultrasonic Irradiation and Ozone
Treatment for Liberation of Iodine and
Reducing Standard Ethion Solution at
Different Times
Standard ethion concentration of 1 mg·L-1 or 2% KI
solution was prepared in a flask and then placed inside
the ultrasonic reactor mentioned earlier and subjected to
different frequencies at 108, 400, 700, and 1000 kHz. A
200 mg·L-1 ozone gas was bubbled for 15, 30, 45 and 60
minutes through the ethion solution or KI. The concen-
tration of iodine liberation from 2% potassium iodine
with different times, was measured at 354 nm using
spectrophotometer. Finally, three replicates of ethion
samples were analyzed by a gas chromatograph equipped
with a flame photometric detector (GC-FPD). Then, the
O
O
P
S
S
O
O
PS
S
H
H
H
H
H
HH
H
H
H
H
H
HH
HH
H
HH
HH
H
Figure 1. The chemical structure of ethion [10].
Copyright © 2013 SciRes. Openly accessible at http://www.scirp.org/journal/as/

K. Whangchai et al. / Agricultural Sciences 4 (2013) 7-11 9
Copyright © 2013 SciRes. Openly accessible at http://www.scirp.org/journal/as/
percent removal of the ethion was calculated at each col-
lection time to compare the best method.
2.2. Reduction of Ethion on Harvested
Tangerine using Ultrasonic Irradiation
and Ozone
An ultrasonic device volume 55 L equipped with eight
transducers and ultrasonic frequency at 1000 kHz 24 W
was used in large-scale application. The ultrasonic device
was also made by Honda Electronics Company (Toyo-
hashi, Aichi, Japan). Tangerine samples were treated with
ethion 1 day before harvesting. The fruits were immersed
in distilled water and subjected to washing using ultra-
sonic reactor, ozone and their combination while wash-
ing using only distilled water was employed as the con-
trol. The 5 g of chopped tangerine was extracted with
acetone and methylene chloride homogenized at 13,000
rpm for 1 minute and dried using rotary vacuum evapo-
ration at 340 mbar [12]. The final solvent was HPLC
grade of acetone. Then the samples were analyzed ethion
residue using GC-FPD as previous report [13].
2.3. GC-FPD Instrument and Conditions
The GC-FPD analysis was performed with an Agilent
Technologies (Wilmington, DE) model 6890 gas chro-
matograph equipped with a flame photometric detector.
The GC was carried out using a fused silica capillary
column HP-5, 5% Phenyl Methyl Siloxane, with dimen-
sions of 30 m × 0.32 mm i.d. and a 0.25 μm film thick-
ness (Agilent Technologies). The temperature was pro-
grammed at 10℃·min-1 from the initial temperature at
100℃ to 200℃. And then at 4℃·min-1, it increased to
the final temperature of 220℃. A purified He carrier gas
was used with the flow rate of 3.6 mL·min-1. The detec-
tor temperature was set at 250℃. Those sample solutions
(1.0 µL) were injected in splitless mode, and the quanti-
fication of ethion was performed using ethion standard as
a reference .
2.4. Statistical Analysis
All experiments were replicated three times and evalu-
ated with a regression procedure using the SPSS version
17. Duncan’s Multiple Range Test (*P ≤ 0.05) was per-
formed to determine the significant difference among
various treatments.
3. RESULTS AND DISCUSSION
3.1. Study of Optimum Frequency and Time
for Iodine Liberation and Reducing
Standard Ethion Solution by Ultrasonic
Irradiation and Ozone Treatment
Iodine production was a direct measurement of soni-
cation and ozonation effects. Iodine yield increased with
increasing ultrasonic frequencies directly and it reached
the highest value of iodine production rate (absorbance
of OD 354) when ultrasonic frequency was 1000 kHz
with ozone exposure for 60 minutes (Figure 2) These
results indicated that ultrasonic irradiation generated
highly active hydroxyl radicals, which reacted with po-
tassium iodide to release iodine in the process [14].
The effectiveness of ultrasonic irradiation to reduce
the concentration of standard ethion solution (1 mg·L-1)
was also investigated. It was found that the ethion con-
centration was significantly reduced with prolonged ul-
trasonic exposure time. Moreover, ultrasonic irradiation
at 1000 kHz for 60 minutes was the most effective treat-
ment for reducing ethion concentration (Figure 3). The
advantage effect of high ultrasonic frequency may be due
to the increasing cavitational activity which led to a
higher number of collapsing cavities directly influencing
Exposure time(m in)
0 102030405060
O D 354 nm of 2% KI
0
2
4
6
8
10
12
Control
108kHz
400kHz
700kHz
100kHz
O3
100kHz+O3
400kHz+O3
700kHz+O3
1000kHz+O3
Figure 2. Changes of KI absorbance at 354 nm after exposed to
ultrasonic irradiation and ozone treatment.
Exposure time(min)
0 102030405060
% degradation of ethion
0
20
40
60
80
100
control
108Hz
400Hz
700Hz
1000Hz
Figure 3. Percent removal of ethion standard solution using
ultrasonic irradiation with various frequencies.

K. Whangchai et al. / Agricultural Sciences 4 (2013) 7-11
10
Copyright © 2013 SciRes. Openly accessible at http://www.scirp.org/journal/as/
relevant report of Yao et al.(2010) that the optimal fre the
reduction rate of ethion. This evidence followed the
quency for parathion degradation occurred at 600 kHz
and it attributed to the much higher ●OH yield compared
to treatments at 200 kHz[15].
Similar results obtained for the ozone-treated standard
solution of ethion. Reduction of ethion concentration was
directly proportional to increase in ozone exposure time.
At 60 minutes exposure, ethion concentration decreased
by 66.85% (Figure 4). Ozone is a strong oxidant and it
could possibly degrade the ethion. As reported by Ku et
al. (1998) the diazinon degradation occurred within 1
hour of ozone treatment [16]. These results agreed well
with the previous studies on the reduction of carbamate
pesticides and some organic phosphorus in water solu-
tion after ozone treatment with the same range of contact
times [17].
The ethion solution treated with ultrasonication in
combination with ozone (US/O3) showed the improved
rate of ethion degradation, with the highest degradation
rate took place after the first 15 minutes. This may be
due to the synergistic effect of ultrasonic-ozone treatment,
degraded and oxidized ethion structure. Moreover, the
combination (US/O3) scheme for 60 minutes with 1000
kHz US, its exposure time reduced the ethion concentra-
tion by 75.43%, which is significantly (*P < 0.05) higher
compared with other treatments (Figure 4). Therefore,
ultrasonication and ozonation in combination exhibited a
promising treatment for residual ethion removal that ac-
complished by ozone or ultrasonication alone. Thus,
there was a synergistic effect to use ultrasonic and ozone
treatments together. This followed the similar findings by
Weaver et al. (1998) who reported the importance of the
rapid degradation of organic contaminants using ozone
and ultrasonic irradiation (20 kHz) resulting in an in-
crease of hydroxyl radicals[3].
Exposure time( min)
0 102030405060
% degradation of ethion
0
20
40
60
80
100
Control
O3
108kHz+O3
400kHz+O3
700kHz+O3
1000kHz+O3
Figure 4. Percent removal of ethion standard solution using the
combinations of ultrasonic irradiation and ozone treatment.
3.2. Reduction of Ethion on Harvested
Tangerine Using Ultrasonic Irradiation
and Ozone
Tangerine fruits were immersed in an ultrasonic reac-
tor with the frequency of 1000 kHz and combined with
ozone treatment in order to reduce residual ethion. It was
found that the ethion residue on fresh tangerine showed
the lowest level (0.03 ppm) or 73.07% of removal rate
when the ultrasonic frequency was 1000 kHz and com-
bined with the ozone treatment for 60 minutes with sig-
nificant (*P < 0.05) different when compared with an
individual treatment and the control, which was im-
mersed in distilled water (Figure 5). This tendency could
be explained by the reaction of ultrasonic frequencies
with exposure ozone producing the ●OH radical, which
effectively decomposed ethion residue on the tangerine
surface. Similarly, Wenrong et al. (2002) reported that
the decomposition rate of arsenazo treated by ozone or
ultrasonic was more rapid than that treated by ozone
alone and the structure of arsenazo was decomposed
more completely[18]. In addition, Wu et al.(2007) also
indicated that ozone water treatment could effectively
reduce pesticides (methyl-parathion, parathion, diazinon
and cypermethrin) residue on Pak Choi (Brassica rapa)
surface [9].
4. CONCLUSIONS
The concentration of ethion was reduced after using
ultrasonic or ozone treatment. The reduction could in-
crease with increasing contact time directly. The higher
the ultrasonic frequencies, the greater the percent re-
moval could achieve. The combined ultrasonic and ozone
treatments had a synergistic effect on ethion degradation
controlO3US US+O3
Ethion concentration(ppm)
0.0
.2
.4
.6
.8
1.0
0.8
0.6
0.4
0.2
Treatment
c
bb
a
Figure 5. Ethion residue in tangerine after washing in the com-
bination of ultrasonication and ozonation. Error bars denote
standard deviations. Different letters indicate significant dif-
ferences by Duncan’s multiple range test (p ≤ 0.05).

K. Whangchai et al. / Agricultural Sciences 4 (2013) 7-11
Copyright © 2013 SciRes. http://www.scirp.org/journal/as/
11
in both aqueous solution and ethion treated tangerines.
Therefore, further studies to reduce the toxicity of pesti-
cides contaminated agricultural products are also re-
quired.
Openly accessible at
5. ACKNOWLEDGEMENTS
This research was supported by the Postharvest Technology Innova-
tion Center, Commission on Higher Education, Bangkok. The authors
are also grateful to the Faculty of Science and Postharvest Technology
Research Institute, Chiang Mai University, Thailand for providing the
laboratory facilities and to Honda Electronics Company Toyohashi,
Aichi, Japan for ultrasonic device support.
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