Degradation behavior and products of malathion and chlorpyrifos spiked in apple juice by ultrasonic treatment

Article abstract of DOI:10.1016/j.ultsonch.2009.06.003

Apple juice (13 °Brix) spiked with malathion and chlorpyrifos (2-3 mg l^-1 of each compound) was treated under different ultrasonic irradiations. Results showed that ultrasonic treatment was effective for the degradation of malathion and chlorpyrifos in apple juice, and the output power and treatment time significantly influenced the degradation of both pesticides (p < 0.05). The maximum degradations were achieved for malathion (41.7%) and chlorpyrifos (82.0%) after the ultrasonic treatment at 500 W for 120 min. The degradation kinetics of both pesticides were fitted to the first-order kinetics model well (R² ≥ 0.90). The kinetics parameters indicated that chlorpyrifos was much more labile to ultrasonic treatment than malathion. Furthermore, malaoxon and chlorpyrifos oxon were identified as the degradation products of malathion and chlorpyrifos by gas chromatography-mass spectrometry (GC-MS), respectively. The oxidation pathway through the hydroxyl radical attack on the P{double bond, long}S bond of pesticide molecules was proposed.

Full text of DOI:10.1016/j.ultsonch.2009.06.003

Ultrasonics Sonochemistry 17 (2010) 72–77
Contents lists available at ScienceDirect
Ultrasonics Sonochemistry
journal homepage: www.elsevier.com/locate/ultsonch
Degradation behavior and products of malathion and chlorpyrifos spiked
in apple juice by ultrasonic treatment
Yuanyuan Zhang a, Zhiyong Xiao b, Fang Chen a, , Yiqiang Ge a,c, Jihong Wu a, Xiaosong Hu a,
*
*
a College of Food Science and Nutritional Engineering, Key Laboratory of Fruits and Vegetables Processing, Ministry of Agriculture, Engineering Research Centre for Fruits and
Vegetables Processing, Ministry of Education, China Agricultural University, Beijing 100083, China
b Beijing Agro-Environmental Monitoring Station, Beijing 100029, China
c China Rural Technology Development Center, Beijing 100045, China
a r t i c l e i n f o
a b s t r a c t
Apple juice (13 °Brix) spiked with malathion and chlorpyrifos (2–3 mg lÀ1 of each compound) was treated
under different ultrasonic irradiations. Results showed that ultrasonic treatment was effective for the
degradation of malathion and chlorpyrifos in apple juice, and the output power and treatment time sig-
nificantly influenced the degradation of both pesticides (p < 0.05). The maximum degradations were
achieved for malathion (41.7%) and chlorpyrifos (82.0%) after the ultrasonic treatment at 500 W for
120 min. The degradation kinetics of both pesticides were fitted to the first-order kinetics model well
(R2 P 0.90). The kinetics parameters indicated that chlorpyrifos was much more labile to ultrasonic treat-
ment than malathion. Furthermore, malaoxon and chlorpyrifos oxon were identified as the degradation
products of malathion and chlorpyrifos by gas chromatography–mass spectrometry (GC–MS), respec-
tively. The oxidation pathway through the hydroxyl radical attack on the P@S bond of pesticide molecules
was proposed.
Article history:
Received 8 February 2009
Received in revised form 18 May 2009
Accepted 2 June 2009
Available online 6 June 2009
Keywords:
Ultrasonic treatment
Malathion
Chlorpyrifos
Degradation
Apple juice
Reaction kinetics
Ó 2009 Elsevier B.V. All rights reserved.
1. Introduction
[14] and dimethoate [15] could be degraded by ultrasonic
treatment in aqueous solution. However, the effect of ultrasonic
The organophosphorus pesticides (OPPs) are a group of very
effective and widely used pesticides. It is well known that OPPs
have strong inhibitory activity to cholinesterase [1], reproductive
toxicity [2], cytotoxicity [3], immunotoxicity [4] and genotoxicity
[5]. They eventually become the health risk to human beings in
consequence of bioaccumulation through the food chain, although
the use of OPPs provides benefits for increasing agricultural pro-
duction. Therefore, the control of residual levels of OPPs in food
has become a public concern.
The concentrated apple juice (CAJ) has been an economically
important food product in China, where export of CAJ accounts
for nearly 50% of the world export volume [6]. However, the appli-
cation of OPPs has resulted in pesticide residues in fruit and dete-
rioration of CAJ quality. Several methodologies have been
developed for dissipation of OPPs residues in CAJ, including the
post-harvest storage [7], as well as chlorine and ozone washes
and resin adsorption during processing [8,9]. During the past dec-
ade, a number of studies have used the physical and chemical (son-
ochemistry) effects generated by acoustic cavitation for the
degradation of organic pollutants [10,11]. In the case of OPPs, sev-
eral results showed that parathion [12], dichlorvos [13], diazinon
treatment on the dissipation of pesticides in fruit juice, to the best
of our knowledge, has not been reported.
In the present study, malathion (S-[1,2-bis(carbethoxy)ethyl]-
O,O-dimethyl dithiophosphate) and chlorpyrifos (O,O-diethyl-O-
(3,5,6-trichloro-2-pyridyl)phosphorothioate), which are often used
to protect apple trees and fruits from the aphid and acarid, were
chosen as representative examples. The objectives of this study
are to investigate the degradation behavior and kinetics of mala-
thion and chlorpyrifos spiked in apple juice treated by ultrasonic
and to identify the degradation products of malathion and
chlorpyrifos.
2. Experimental
2.1. Materials
Malathion (99.5%; CAS Registry No. 121-75-5) and chlorpyrifos
(99.0%; CAS Registry No. 2921-88-2) were purchased from Dr.
Ehrenstorfer (Augsburg, Germany). Acetonitrile and sodium chlo-
ride were analytical grade and obtained from Beijing Beihua Fine
Chemicals Co. (Beijing, China). Acetonitrile was redistilled before
use. HPLC-grade acetone was purchased from Tianjin
Concord Technology Co. Ltd. (Tianjin, China). CAJ at 78 °Brix was
* Corresponding authors. Tel./fax: +86 10 62737645x18.
E-mail addresses: chenfangch@sina.com (F. Chen), huxiaos@263.net (X. Hu).
1350-4177/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.ultsonch.2009.06.003

Y. Zhang et al. / Ultrasonics Sonochemistry 17 (2010) 72–77
73
manufactured by a local factory and diluted to 13 °Brix (similar to
raw apple juice, pH 3.86) for ultrasonic treatment. Individual pes-
ticide stock solutions (200–300 mg lÀ1) were prepared in acetone
and stored in glass-stoppered flasks at À18 °C. The stock solutions
were added to the reconstituted apple juice with final pesticide
increase at 8 °C minÀ1 up to 280 °C, held for 14.25 min. The mass
spectrometer was operated in electron impact (EI) ionization mode
at 70 eV and the temperatures of the transfer line, ion source, and
quadrupole were set as 200, 250 and 250 °C, respectively. The total
ion current (TIC) chromatograms were recorded between m/z 33
and 400 at a rate of 40 scans per second. EI mass spectrum data-
base searches were carried out in a mass spectral library (National
Institute for Standard Technology (NIST), search program version
1.5, Gaithersburg, MD, USA). Simultaneously, the unspiked apple
juice was used as the blank control to eliminate those peaks com-
ing from the sample preparation procedure and chromatographic
system.
concentrations as 2–3 mg lÀ1
.
2.2. Ultrasonic treatment
Ultrasonic treatment was performed with a high-intensity
ultrasonic probe type (Ningbo Scientz Biotechnology Co. Ltd., Ning-
bo, China) equipped with a diameter of 6.0 mm microtip. The max-
imum output power and frequency are 650 W and 25 kHz,
respectively. An aliquot of apple juice (100 ml) was added to a con-
ical flask (150 ml) and irradiated through dipping the microtip in
the juice 10 mm below the surface. The treatment times were set
as 15, 30, 45, 60, 75, 90, 105 and 120 min and the treatment pow-
ers were set as 100, 300 and 500 W. A thermostatic circulator HX-
1050 (Beijing Detianyou Technology Development Co. Ltd., Beijing,
China) was used to maintain the temperature of samples at 15 °C
( 2 °C). All the treated samples were stored at 4 °C for a maximum
of 24 h for analysis. Each treatment was conducted in triplicate.
2.6. Statistical analysis
Data were analyzed using the SAS 8.0 software (Statistical Anal-
ysis System Inc., Cary, NC, USA). The effects of ultrasonic power and
treatment time on the degradation of malathion and chlorpyrifos
in apple juice were evaluated by analysis of variance (ANOVA), fol-
lowed by Duncan’s test. ANOVA was based on a significance level
of p = 0.05.
3. Results and discussion
2.3. Extraction
3.1. Determination and recovery of malathion and chlorpyrifos
The extraction of pesticides is a modification of the standard
method established by Ministry of Agriculture of China [16]. An ali-
quot of apple juice (20.0 ml) was mixed with 50.0 ml of acetonitrile
in a conical flask (100 ml). The mixture was shaken vigorously for
15 min and filtered through Whatman No. 1 filter paper into a
measuring cylinder (100 ml) containing 10.0 g sodium chloride.
The mixture was centrifuged at 2000g for 5 min after mixing thor-
oughly. A portion (10.0 ml) of the upper acetonitrile layer was
carefully transferred to a glass test tube and evaporated to dryness
under a stream of nitrogen in a water bath at 40 °C. The residue on
the wall of glass tube was re-dissolved in 2.0 ml of acetone and
transferred to vials for gas chromatography (GC) and gas chroma-
tography–mass spectrometry (GC–MS) analysis.
The quantification of malathion and chlorpyrifos was performed
by GC through the external standard method. The good linearity
was obtained in the concentration range of 0.25–5.00 mg lÀ1 for
both pesticides (R2 > 0.98). Limits of detection (LOD) were calcu-
lated as 0.008 mg lÀ1 for malathion and 0.005 mg lÀ1 for chlorpyri-
fos by using a signal-to-noise ratio of 3. In addition, the recoveries
of method ranged from 84% to 103% for malathion and 86% to 103%
for chlorpyrifos at various concentration levels, which were within
the range of 60–140% for routine pesticide residue analyses recom-
mended by Putnam et al. [17]. The relative standard deviations
(RSDs) were from 5.1% to 13.6% for malathion and 3.4% to 12.8%
for chlorpyrifos, the values being within the accepted range for res-
idue determinations.
2.4. GC Analysis of malathion and chlorpyrifos in apple juice
3.2. Effect of ultrasonic irradiation on the degradation of malathion
and chlorpyrifos
GC analysis was conducted with a Fuli GC 9790 (Fuli Analytical
Instrument Co. Ltd., Zhejiang, China) equipped with a HP-5 fused
silica capillary column (30 m  0.53 mm, 1.5
lm, Hewlett Packard,
The changes in concentrations of malathion and chlorpyrifos
during ultrasonic treatment were shown in Fig. 1. The ANOVA re-
sults indicated that the degradation of both pesticides increased
significantly with the ultrasonic power and treatment time
(p < 0.05). The degradation rates of malathion and chlorpyrifos
after the treatment at 500 W for 15 min were 2.8 and 2.3 times
greater than that of treated at 100 W for 15 min, respectively. Sim-
ilar results have been reported in previous research in which the
degradation rate of dichlorvos treated at 161 W was higher than
that of treated at 86 W in aqueous solution under ultrasonic treat-
ment for 30 min [13]. Similarly, the degradation rates of malathion
and chlorpyrifos after the treatment at 100 W for 120 min were 4.0
and 3.8 times as compared with that at 100 W for 15 min, respec-
tively. Among all treatments, the maximum degradation rate for
malathion (41.7%) and chlorpyrifos (82.0%) were achieved after
the ultrasonic treatment at 500 W for 120 min. Some evidence sup-
ported the positive effect of increased output power and treatment
time on the degradation of both pesticides [15,18]. On one hand,
more energy was provided to the samples when output power ele-
vated, resulting in the more rapid occurrence of the formation and
collapse of cavitation bubble. The higher concentration of hydroxyl
radical formed correspondingly and reacted with more pesticides
Avondale, USA) and flame photometric detector operating with an
optical filter selective for phosphoric compounds (passing band
centered at 526 nm). Nitrogen carrier gas was used at the constant
pressure of 0.05 MPa. The temperature program was as follows:
initial temperature isothermal at 120 °C for 1 min, then from 120
to 240 °C at 10 °C minÀ1, and held 7 min at 240 °C. The injector
and detector temperatures were set at 250 and 260 °C, respec-
tively. Sample solution (1.0 ll) was injected in splitless mode.
2.5. GC–MS analysis of degradation products of malathion and
chlorpyrifos
Degradation products of malathion and chlorpyrifos were iden-
tified with a Shimadzu GC/MS-QP2010 Plus (Shimadzu Co., Kyoto,
Japan) configured with a programmed temperature vaporization
injector (Shimadzu Co., Kyoto, Japan). The sample solution was in-
l) with an AS 2000 autosampler (Shimadzu Co., Kyo-
to, Japan). An Rxi -5 ms fused silica capillary column
jected (10.0
l
TM
(30 m  0.25 mm, 0.25
lm; Restek International, Bellefonte, USA)
was used in GC separation. Helium was used as the carrier gas with
flow rate of 1.75 ml minÀ1. The GC temperature program consisted
of the initial temperature of 82 °C, held for 5 min, followed by the

74
Y. Zhang et al. / Ultrasonics Sonochemistry 17 (2010) 72–77
Treatment time (min)
45 60 75
2.2
2.0
1.8
1.6
1.4
1.2
a
0
15
30
90
105 120
a
100W
300W
500W
0.0
-0.1
-0.2
-0.3
-0.4
-0.5
-0.6
100W
300W
500W
Linear fit for 100W
Linear fit for 300W
Linear fit for 500W
0
15
30
45
60
75
90
105 120
Treatment time(min)
45 60 75
Treatment time (min)
0
15
30
90
105
120
b
0.0
-0.2
-0.4
-0.6
-0.8
-1.0
-1.2
-1.4
-1.6
-1.8
2.8
2.4
2.0
1.6
1.2
0.8
0.4
b
100W
300W
500W
100W
300W
500W
Linear fit for 100W
Linear fit for 300W
Linear fit for 500W
Fig. 2. The first-order kinetics model of malathion (a) and chlorpyrifos (b).
0
15
30
45
60
75
90
105 120
Treatment time (min)
Fig. 1. The changes of concentration of malathion (a) and chlorpyrifos (b) in apple
juice under different ultrasonic conditions.
as that at 100 W, and the t1/2 values at 500 W were half of that
at 100 W. In addition, the difference in the values of kinetics
parameters between both pesticides was significant. The k values
of chlorpyrifos were 2.7–3.6 times higher than those of malathion,
indicating that chlorpyrifos is much more labile to ultrasonic treat-
ment than malathion. This could be explained by the Henry’s con-
stant of chlorpyrifos and malathion. Henry’s constant characterizes
the relative amount of a substrate that will enter the vapor bub-
bles, and it has been demonstrated that the compounds with high-
er Henry’s constants are more prone to diffusing into the cavitation
bubbles and degraded more rapidly compared with the com-
pounds with lower Henry’s constant under the same sonication
condition [19]. Therefore, chlorpyrifos (Henry’s constant is
6.76 Â 10À1 Pa m3 molÀ1) degrades more rapidly than malathion
(Henry’s constant is 1.21 Â 10À2 Pa m3 molÀ1) [20]. In addition,
in samples [18]. On the other hand, due to the ultrasonic secondary
mechanical effects such as stirring and oscillation when the output
power and treatment time enhanced, mixing of samples was im-
proved and the degradation of pesticides was accelerated [15].
Interestingly, the concentration of malathion declined more
slowly than that of chlorpyrifos under the same treatment condi-
tions. The degradation rate of chlorpyrifos (48.4%) was 2.1 times
higher than that of malathion (22.6%) after the treatment at
500 W for 30 min. This indicated that malathion was more resis-
tant to ultrasonic treatment than chlorpyrifos. Therefore, it is nec-
essary to determine the degradation kinetics to describe the
degradation behavior of both pesticides.
3.3. Degradation kinetics of malathion and chlorpyrifos
Table 1
The first-order kinetic model fitted to the degradation of malathion and chlorpyrifos
and deduced parameters.
The plots of ln(Ct/C0) vs. irradiation time for both pesticides
were given in Fig. 2, and the deduced parameters for different
treatments were listed in Table 1. The linear relationship between
ln(Ct/C0) and irradiation time indicated that the degradation fol-
lowed a first-order kinetics well (R2 P 0.9). This was in accordance
with the description in degradation kinetics of dichlorvos by ultra-
sonic treatment in aqueous solution [13]. Moreover, there was a
similar increase of k values and a similar decline of t1/2 values for
both pesticides when the output power was enhanced from 100
to 500 W. For example, the k values at 500 W were twice as large
Power (W) Regression equation R2
p Value k (minÀ1
)
t1/2 (min)
Malathion
100
300
500
ln(Ct/C0) = À0.0024 t 0.96 <0.0001 0.0024 0.0001 292.5
ln(Ct/C0) = À0.0039 t 0.99 <0.0001 0.0039 0.0001 178.2
ln(Ct/C0) = À0.0050 t 0.90 0.0006
0.0050 0.0004 138.6
Chlorpyrifos
100
300
ln(Ct/C0) = À0.0065 t 0.97 <0.0001 0.0065 0.0002 105.9
ln(Ct/C0) = À0.0091 t 0.95 <0.0001 0.0091 0.0004
ln(Ct/C0) = À0.0138 t 0.94 <0.0001 0.0138 0.0007
76.0
50.2
500

Y. Zhang et al. / Ultrasonics Sonochemistry 17 (2010) 72–77
75
the chemical structures of both pesticides were considered to be
related to the degradation behavior. This also has been proposed
in the biodegradability of organophosphorus pesticides in soil
[21] and in water [22].
was shown in Fig. 3. Positively confirmed by the NIST Mass Spec-
tral Library with high spectrographic fit (>89%), malaoxon and
chlorpyrifos oxon were found as the products of malathion and
chlorpyrifos, respectively. Simultaneously, this result was con-
firmed by the mass spectra of malaoxon and chlorpyrifos oxon
(Fig. 4 and Fig. 5). In the mass spectra of malaoxon (Fig. 4), the
fragment ion at m/z 268 was formed by the successive losses
of ethoxy group and H from the molecular ion at m/z 314 (the
response was low and not labeled). Next, loss of CO from the
fragment ion at m/z 268 yielded fragment ion at m/z 240. In
3.4. Identification of degradation products of malathion and
chlorpyrifos
The apple juice after the ultrasonic treatment at 500 W for
120 min was analyzed with GC–MS and the TIC chromatogram
Fig. 3. TIC chromatogram of both pesticides and their degradation products in apple juice treated by ultrasonic at 500 W for 120 min malaoxon (1), malathion (2),
chlorpyrifos oxon (3) and chlorpyrifos (4).
%
a
127
100.0
75.0
50.0
99
25.0
142
143
173
268
195
79
159
239
93
100.0
212
224
315
285
275.0 300.0 325.0
65
255
0.0
75.0
125.0
150.0
175.0
200.0
225.0
250.0
b
Inten.
127
1000
750
500
250
0
O
S
O
O
O
O
99
P
O
55
O
79
110
142
195
47
71
75.0
268
173
175.0
155
87
239
222
50.0
100.0
125.0
150.0
200.0
225.0
250.0
m/z
Fig. 4. GC/MS spectra of malaoxon obtained from apple juice treated by ultrasonic irradiation at 500 W for 120 min (a) and NIST library (b).

76
Y. Zhang et al. / Ultrasonics Sonochemistry 17 (2010) 72–77
addition, the cleavage of the C–S bond of the molecular ion affor-
ded the ions at m/z 173 and m/z 142, which was in accordance
with the explanation on the mass spectra of malathion with
GC–MS in negative chemical ionization performed by Amendola
et al. [23]. Furthermore, fragment ion at m/z 173 yielded ethyl
oxonium ion at m/z 127 by the successive losses of C2H4 and
H2O, intramolecular cyclization and rearrangement. Subse-
quently, the fragment ion at m/z 99 was formed by the loss of
C2H4 from the fragment ion at m/z 127. For the mass spectra
of chlorpyrifos oxon (Fig. 5), molecular ion at m/z 335 was ob-
served. The fragment ion at m/z 298 was corresponded to
[MÀCl]+, and fragment ions at m/z 270 and 242 occurred due
to the loss of one and two ethylene from the fragment ion at
m/z 298, respectively. The fragment ions at m/z 109 and 81 were
produced from the cleavage of P–O bond and corresponded to
the side chain released from the ring of the fragment ions at
m/z 270 and 242, respectively. In addition, the fragment ion at
m/z 197 was yielded from the molecular ion by the loss of the
side chain. The ion at m/z 29 was the base peak and it was the
response of ethylene molecules released from the ion of m/z 298.
%
a
109
100.0
81
270
75.0
242
298
197
50.0
91
25.0
169
260
333
180
65
134
207
144
150.0
226
290
125
308
0.0
75.0
29
100.0
125.0
175.0
200.0
225.0
250.0
275.0
270
300.0
325.0
Inten.
b
1000
750
500
250
0
O
81
109
O
P
N
197
O
O
Cl
242
298
Cl
Cl
201
169
161
47
133
335
65
15
50
100
150
200
250
300
m/z
Fig. 5. GC/MS spectra of chlorpyrifos oxon obtained from apple juice (a) treated by ultrasonic irradiation at 500 W for 120 min and NIST library (b).
a
S
O
O
O
O
S
P
O
O
P
O
O
O
S
S
O
O
O
O
oxidation
malaoxon
Cl
malathion
Cl
b
S
Cl
Cl
Cl
O
O
N
P
N
O
O
Cl
P
oxidation
S
O
O
O
chlorpyrifos
chlorpyrifos oxon
Fig. 6. Ultrasonic oxidation pathways of malathion (a) and chlorpyrifos (b).

Y. Zhang et al. / Ultrasonics Sonochemistry 17 (2010) 72–77
77
Based upon the identification of degradation products of mala-
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The present study demonstrated that ultrasonic irradiation is a
promising process for the removal of malathion and chlorpyrifos
from apple juice, and the ultrasonic power and treatment time
have significant effects on their degradation (p < 0.05). The degra-
dation kinetics of both pesticides could be described by the first-
order kinetics model, but chlorpyrifos is shown to be much more
labile to ultrasonic irradiation than malathion. Malaoxon and
chlorpyrifos oxon were identified as the main degradation prod-
ucts of malathion and chlorpyrifos, and the oxidation pathway
through the hydroxyl radical attack on the P@S bond of pesticide
molecules was proposed.
Acknowledgements
The work was supported by the task of China Critical Project of
Agro-processing (2006BAD05A13) and The Fortieth Science Foun-
dation for Postdoctoral.