Induced degradation of chlorpyrifos insecticide in simulated wastewater with advanced oxidation processes (AOPs), using ultraviolet irradiation (UV), ozonation and chemical oxidation using (sodium hypochlorite, calcium hypochlorite, monochloride-isocyanuric acid (MCICA), dichloroiso-cyanuric acid (DCICA), trichloroisocyanuric acid (TCICA) ) was studied. Chlorpyrifos and its degradation products were extracted using solid phase extraction (SPE) method, identified using GC-MS. Results showed that the degradation of chlorpyrifos in simulated wastewater followed the first order reaction, and its half life was 3.34, 5.64, 7.13 and 10.69h under ozonation, UV, 1.5%TCICA and 1.5%DCICA respectively when chlorpyrifos solutions treated for 12 h. The concentrations of chemical oxidative substances, active chlorine content and time of treatments had a significant effect on degradation rate of chlorpyrifos, which increased with increasing of each. The most enhancement of chlorpyrifos degradation was observed in treatment with ozonation, UV, TCICA and DCICA where the dissipations % of the parent compounds were 85.70, 57.71, 43.71 and 35.07 %, respectively. The intermediates products of chlorpyrifos degradation using chemical method were identified as O,O-Diethyl thiophosphate(DEP), 3,5,6-trichloro-2-pyridinol(TCP), 3,5,6-trichloro-2-methoxypyridine(TMP) and 2,3,5,6-tetrachloro-pyridine. UV leads to formation of O,O-Diethyl phosphate, TCP and Chlorpyrifos oxon. Ozonation leads to formation of O,O-Diethyl thiophosphate beside the UV degradation products.

1. App. Sci. Report.
15 (2), 2016: 63-73
© PSCI Publications
Applied Science Reports
www.pscipub.com/ASR
E-ISSN: 2310-9440 / P-ISSN: 2311-0139
DOI: 10.15192/PSCP.ASR.2016.15.2.6373
Degradation of an organophosphorus insecticide
(chlorpyrifos) in simulated wastewater using advanced
oxidation processes and chemical oxidation.
A.M Tony1
, M.S.A. EL – Geuindi 1
, Salah M. Hussein2
, Mohamed Z. Abd Elwahab1
Faculty of Engineering, Eng. Chemistry Dept. Minia Univ., Egypt
Faculty of Agriculture, Plant Protection Dept. Minia University
Corresponding author email: tonymoussa60@hotmail.com
Paper Information A B S T R A C T
Received: 21 February, 2016
Accepted: 28 May, 2016
Published: 2 July, 2016
Induced degradation of chlorpyrifos insecticide in simulated wastewater
with advanced oxidation processes (AOPs), using ultraviolet irradiation
(UV), ozonation and chemical oxidation using (sodium hypochlorite,
calcium hypochlorite, monochloride-isocyanuric acid (MCICA),
dichloroiso-cyanuric acid (DCICA), trichloroisocyanuric acid (TCICA) )
was studied. Chlorpyrifos and its degradation products were extracted
using solid phase extraction (SPE) method, identified using GC-MS.
Results showed that the degradation of chlorpyrifos in simulated
wastewater followed the first order reaction, and its half life was 3.34,
5.64, 7.13 and 10.69h under ozonation, UV, 1.5%TCICA and 1.5%DCICA
respectively when chlorpyrifos solutions treated for 12 h. The
concentrations of chemical oxidative substances, active chlorine content
and time of treatments had a significant effect on degradation rate of
chlorpyrifos, which increased with increasing of each. The most
enhancement of chlorpyrifos degradation was observed in treatment with
ozonation, UV, TCICA and DCICA where the dissipations % of the parent
compounds were 85.70, 57.71, 43.71 and 35.07 %, respectively. The
intermediates products of chlorpyrifos degradation using chemical method
were identified as O,O-Diethyl thiophosphate(DEP), 3,5,6-trichloro-2-
pyridinol(TCP), 3,5,6-trichloro-2-methoxypyridine(TMP) and 2,3,5,6-
tetrachloro-pyridine. UV leads to formation of O,O-Diethyl phosphate,
TCP and Chlorpyrifos oxon. Ozonation leads to formation of O,O-Diethyl
thiophosphate beside the UV degradation products.
© 2016 PSCI Publisher All rights reserved.
Key words:
Introduction
Organophosphorus insecticides are a group of chemical compounds which worldwide used in agricultural to
prevent bad effects of insects and other pests to increase the yields of the crops. Chlorpyrifos in Egypt has a significant
importance due to its wide distribution, persistence and extensive use. Chlorpyrifos led to contamination of soil, surface,
air, and groundwater in many parts of the world (Randhawa et al. 2007), which in turn has resulted in undesirable side
effects such as acute toxicity and chronic toxicity i.e. teratogenicity, carcinogenicity and mutagenicity (Juraske, et al.,
2007). Their residues are presented in different environmental compartment: soil, air, Food and water (Ioannidou et al.,
2010, Hussein et al. 2015). The contamination of surface and ground water by pesticides is an important issue so as the
scientists are dealing with over the years to prevent accumulation or contamination (Hussein et al. 2002). Since the
presence of pesticides in water can cause serious problems in both the environment and human being, their removal from
water is often required. Water treatment methods include precipitation, coagulation/flotation, sedimentation, filtration,
membrane process, electrochemical techniques, ion exchange, biological process, adsorption onto activated carbon and
chemical process were used for removing pesticides from water ( Miltner et al., 1985; Pirbazari et al., 1984 and EL –
Geuindi et al., 2005). Each method has its own merits and limitations in applications. Among chemical treatments,
physicochemical and biological treatments are generally referred to as advanced oxidation processes (AOPs), which
include UV irradiation, photo-catalysis (hydrogen peroxide and ozone), chemical oxidation (Briceño et al., 2012) and
biodegradation (Hussein et al., 2002, Singh et al., 2004, Burrows et al., 2002). Chemical degradation process is one of the
most powerful methods to change the structure molecule of insecticide and change it to nontoxic compounds with a beam
of accelerated electrons or chemical catalysis was employed for decomposition of various pollutants. Many publications
were devoted to the degradation of organic compounds by oxidation compounds and ionizing radiation (Cooper et al.,
1989, Basfar et al., 2007 and Mohamed et al., 2009).The aim of this study is to degrade organophosphorus insecticide

2. App. Sci. Report. 15 (2), 2016: 63-73
64
chlorpyrifos by using chemical oxidation using (NaOCl, Ca(OCl)2, MCICA, DCICA, TCICA), UV and ozone in
simulated wastewater to select method which can remove chlorpyrifos with maximum percent in the minimum time.
Materials And Experimental Methods
Chlorpyrifos insecticide used in this experiment was active ingredient materials 97.9 % and Dursban 48% EC
formulation was supplied from Central Laboratory of Residue Analysis of Pesticides (Egypt). Chemicals used for
chemical degradation were NaOCl, Ca(OCl)2, (MCICA), (DCICA) and (TCICA) in which supplied from ISIPAC
company (Egypt) with 90%, 70%, 98%, 99%, 98% purity respectively. All chemical reagents used were analytical grade.
Dichloromethane (CH2Cl2), methanol (CH3OH) and ethyl acetate (CH3COOC2H5) of HPLC quality were purchased from
Sigma-Aldrich, Chlorpyrifos (O, O-diethyl O-(3, 5, 6- trichloro-2-pyridyl)-phosphorothioate).
Chemical formula C9H11Cl3NO3PS
Physical properties of Chlorpyrifos are as follows: Density, 1.398g/cm3
, Melting point 42°C, Boiling point 160°C, Molar
mass, 350.59 g/mol, LD50, 202 mg/kg.
Stock solutions
Individual stock solutions at 14 µg/ml (ppm) of the chlorpyrifos were prepared in 10-mL dark volumetric flasks
with dichloromethane (DCM) and stored at −20 °C and from it working standard sets were prepared using the serial
dilution method chlorpyrifos (Barr et al., 2006). These standards were used to calculate calibration curve, limits of
detection (LOD), limits of quantification (LOQ) and the recovery %. The retention time (RT) and the area of standards
were calculated, and their concentrations were automatically calculated according to the standard. Peak area against
concentration was plotted to draw calibration curve using Excel program.
Extraction of pesticide from water
Chlorpyrifos from water were extracted using Environmental Protection Agency (EPA) method (525.2) using
Thermo Scientific Dionex AutoTrace 280 Solid-Phase Extraction (SPE) instrument. The recovery % was 80.3 – 94.6%
with relative standard deviations 6.02 -12 %. The recoveries obtained are within the EPA recommendations (from 65 to
115%).
LOD were calculated as follows:
LOD = 3.3 * Sd / b and LOQ = 10* Sd / b (Dolan, 2005)
Where Sd= standard deviation of calibration curve, b= slope of calibration curve.
Mass spectrometer configuration
Detection and calibration curve of insecticide and its degradation products were done using an Agilent 5975T
LTM GC/MSD gas chromatograph equipped with a mass spectrometer. The GC column was a fused silica capillary
column HP-5MS, 5% phenyl methylpolysiloxane, with the dimensions of 20 m × 0.18 mm i.d. and a 0.18 μm film
thickness (Agilent Technologies). A purified helium carrier gas was used at a constant flow. The MS was operated in
electron impact (EI) ionization mode at an EM voltage of 1811.8 volts (injection volume 1.0 μl in split less mode) with no
solvent delay. The total ion current (TIC) chromatograms were recorded between 50-800 m/z, at a rate of 37 scans per
second. EI mass spectrum database searches were carried out in a mass spectral library National Institute of Standard
Technology (NIST) search program version 1.5, Gaithersburg, MD, USA.
To measure the molecular weight by the GC device access to the mass spectrometer, the Mass spectrum of a
sample of a certain material compared with the standard mass spectrum and then definition of unknown components.
(Singha et al., 2004).
The temperature program used was as follows:
Initial temperature, 80˚ C held for 1 min, then at the rate of 20˚ C /min to 150˚C, rate 10˚C/min to 210 ˚C, 10˚C
/min to 280˚C and then maintaining this temperature for 5 min. The temperature of the injection port was 220˚C and a 1µl
volume was injected. The temperatures of ionization source were kept at 210˚C. For identification, the major ions (m/z) and
retention times both were considered.
Degradation of pesticide using chemical method
Oxidation of chlorpyrifos was achieved by preparing a stock solution of 26 liters 14 ppm commercial chlorpyrifos
EC in deionized water for preparation of simulated wastewater. Then transfer 250 ml of stock solution to thirty dark 250
ml bottle. NaOCl, Ca(OCl)2, (MCICA), (DCICA) and (TCICA) were added to chlorpyrifos EC with six different

3. App. Sci. Report. 15 (2), 2016: 63-73
65
concentrations varies from (0.3% to 1.8%) in three replicates and left at room temperature in dark room, and stir well for
about 50 minutes to let the reaction takes place. After 24 hours three samples 250 ml volume of each treatment were
extracted using SPE technique using different solvents as Ethyl acetate (EtOAc), Methylene chloride (CH2Cl2) and
Methanol (MeOH). These solvents were used for extraction and then analyzed on GC/MS. LT50 and removal percent of
pesticide was calculated from peak area of pesticide.
Degradation of pesticide using ultraviolet irradiation (UV)
The used UV Photolytic reactor was dark cylindrical shape having dimensions of 27 cm length, 2.5 cm diameter
and made up of stainless steel. The photo reactor filled with 250 ml of 14 ppm chlorpyrifos EC solution. The source of UV
light is a 10 W high-pressure mercury lamp (mean wavelength 254 nm). Irradiation interval was from 2 to 12 hours. Then
extracted using SPE and analyzed on GCMS.
Degradation of pesticide using ozone (O3)
Ozonation experiments were carried out using ozone generator model 1KNT-24 (ENALY Co. China). By
bubbling gaseous ozone of 5mg/l concentration and constant flow rate of 80 ml/min into a 500 ml round dark bottom flask
connected with gas dark scrubber with a disperser at the column bottom. The volume of 250 ml chlorpyrifos (initial
concentration: 14 ppm) was ozonated for different time periods (from 2 to 12 hours). The excess gaseous ozone was
trapped in 2% potassium iodide (KI) solution.
Kinetic studies
The degradation rate of chlorpyrifos was calculated mathematically according to (Timme et al., 1980), that
degradation behavior of pesticide residues can be described mathematically as a pseudo-first order reaction, rate of
degradation (K) could be calculated using common logarithms from the following equation:-
Log R = log R0 – 0.434Kt
where R0: residue level at the initial time (zero time), R: residue level at interval in days after application.
Kt: degradation rate constant at the successive intervals in days, K: mean of Kt.
Chlorpyrifos half-life value (RL50) was calculated mathematically according to (Moye et al., 1987) from the following
equation:-
K
Ln
RL
2
50 
Detection of chlorine content of oxidant
Detection of chlorine content of each treatment was done using Egyptian standard test method (ES: 1462/2008) as
follows:
Available chlorine content = (3.545 x N x V)/ W
Where N is the normality of sodium thiosulfate, V is the final volume taken from burette and W is the weight of
treatment.
Statistical analysis
Data analysis was performed using Costat software. Insecticide data removal was analyzed in different chemical
agent samples via one-way
ANOVA and LSD (least significant difference) test at p < 0.05 levels.
Figure1 . Calibration curve of Chlorpyrifos
Several trials had been done to reach to optimum detection of insecticide and its degradation products on gas
chromatograph instrument. Figure (1) shows good sensitivity and repeatability obtained with detection limits of 0.097-
0.15 ppm. LOD and LOQ were 0.36ppm, 1.09ppm respectively. Correlation coefficient was 0.9994

4. App. Sci. Report. 15 (2), 2016: 63-73
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Results And Discussion
Degradation of chlorpyrifos using chemical method
Oxidation Products of chlorpyrifos at using chemical oxidants (NaOCl, Ca(OCL)2, MCICA, DCICA, TCICA) is
shown in fig.(2) in which peak no.1 was DEP (O,O-Diethyl thiophosphate), peak no.2 was TCP (3,5,6-trichloro-
2pyridinol), peak no.3 was TCMP (3,5,6-trichloro-2-methoxypyridine), peak no.4 was (2,3,5,6-tetrachloropyridine), peak
no.5 was Chlorpyrifos using National Institute of Standards and Technology (NIST) library.
Figure 2. Total ion chromatogram (TIC) of chlorpyrifos degradation products using chemical method
Fig. (3) Shows main fragment ions of peak No.1 at m/z 47, 98, 106, 142, 169,188 and 210 comparing with NIST
library gave good matching quality about 96.9% for DEP (O,O-Diethyl thiophosphate).
Figure 3. Main fragments of peak1
Fig. (4) shows main fragment ions of peak No.2 at m/z 39, 66, 94, 148 and 211 comparing with NIST library gave good
matching quality about 97.8% for TCP (3,5,6-trichloro-2pyridinol).
Figure 4. Main fragments of peak2
DEP
tetrachloropyridine
TCP
TCMP
Chlorpyrifos

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67
Fig. (5) shows main fragment ions of peak No.3 at m/z 98, 107, 148, 170, 176,183 and 211 comparing with NIST
library gave good matching quality about 98.3% for TCMP (3,5,6-trichloro-2-methoxypyridine).
Figure 5. Main fragments of peak3
Fig. (6) shows main fragment ions of peak No.4at m/z 75, 144, 180, 184, 212 and 221 comparing with NIST
library gave good matching quality about 97.5% for 2,3,5,6-tetrachloropyridine.
Figure 6. Main fragments of peak 4
Figure (7) shows main fragment ions of peak No.5 at m/z 98, 106, 142, 169, 188 and 210 comparing with NIST
library gave good matching quality about 99.2% for Chlorpyrifos
Figure 7. Main fragments of peak 5

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68
Based upon the identification of degradation products of chlorpyrifos, the oxidation pathway of chlorpyrifos
using chemical method were assumed in table (1).
Table 1. oxidation products using chemical method
Peak no. Chemical name Structure
RT
(min)
Mwt Molecular formula
1 DEP (O,O-Diethyl thiophosphate) 7.2 170.17 C4H11O3PS
2 TCP (3,5,6-trichloro-2-pyridinol) 11.2 198.43 C5H2Cl3NO
3
TCMP (3,5,6-trichloro-2-
methoxypyridine)
12.5 212.46 C6H4Cl3NO
4 2,3,5,6-tetrachloro-pyridine 16.3 216.89 C5HCl4N
5 Chlorpyrifos 22.1 350.59 C9H11Cl3NO3PS
Figure (9) shows the degradation trend of chlorpyrifos at using different oxidant. At using NaOCl with
concentration (0.3 – 1.8) % leads to degradation (1.82 – 14.12) %. At using Ca(OCl)2 with concentration (0.3 – 1.8) %
leads to degradation (3.89 – 18.41)%. At using MCICA with concentration (0.3 – 1.8) % leads to degradation (7.41 –
23.49) %. At using DCICA with concentration (0.3 – 1.8) % leads to degradation (12.24 – 35.29) %. At using TCICA with
concentration (0.3 – 1.8) % leads to degradation (17.58 – 46.05) %. From these results it is clear that at oxidant percent
increase leads to increase degradation of chlorpyrifos, due to increase the chlorine content.
The optimum oxidation of chlorpyrifos achieved after treatment with 1.5% (TCICA) reaching 45.67 % removal.
While at using 1.8% (TCICA) gave better oxidation 46.05 % than that of 1.5% (TCICA) but treatment with 1.8% gave
precipitation of (TCICA) due to saturation of the solution. Half life time of chlorpyrifos using DCICA was 10.7 hours
while at using TCICA was 7.1 hours as shown in table (4).
Figure 8. Oxidation trend of chlorpyrifos using different oxidants after 24h

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69
Figure 9.Kinetic trend of chlorpyrifos using different oxidants after 12h
Figure 10. Bar chart showing the degradation percent of chlorpyrifos
Figure (10) shows that at chlorine content increase, the degradation percent of chlorpyrifos increased. At using
TCICA (25.28% chlorine) the degradation was 46.05%, while at using NaOCl (6.92% chlorine) degradation was 14.12%.
TCICA has found applications as a chlorination, oxidizing agent and as a mild homogeneous catalyst in organic chemistry
and also disinfectant (Paseta et al, 2016). Figure ( 11 ) shows chemical formula of (TCICA) and its reactions in water
producing first cyanuric acid (C3H3N3O3) and hypochlorous acid (HClO) and then Cl2 upon oxidation of HClO.
Figure 11. Reaction of (TCICA) in water.
Effect of ultraviolet irradiation of insecticide
Exposure of chlorpyrifos to different time interval from 1 hr to 12 hrs using high-pressure mercury lamp (254 nm)
leads to degradation of insecticide. Chlorpyrifos EC (14 ppm) was oxidized to O,O-Diethyl phosphate, TCP and
Chlorpyrifos oxon. Percent removal of chlorpyrifos reaches 57.71% at exposure of 12 hours as shown in figure (16). Half
life time of chlorpyrifos using ultraviolet irradiation was 5.6 hrs as shown in table (4).
Figure 12. TIC of degradation products of chlorpyrifos using UV
O,O-Diethylphosphate
TCP
Chlorpyrifos
Chlorpyrifosoxon

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Fig.(12) shows the total ion chromatogram of oxidation products of Chlorpyrifos using UV in which peak no.1
was O,O-Diethyl phosphate, peak no.2 was TCP, peak no.3 was Chlorpyrifos oxon, peak no.4 was Chlorpyrifos
Figure 13. Shows main fragment ions of peak No.1 at m/z 45, 81, 99, 109, 127 and 155 comparing with NIST library gave good
matching quality about 98.2% for O,O-Diethyl phosphate.
Figure 14. shows main fragment ions of peak No.3 at m/z 18, 29, 81, 109, 197 and 270 comparing with NIST library gave good
matching quality about 97.3% for chlorpyrifos oxon.
Table 2. chemical structure of chlorpyrifos oxidation using UV
Peak
no.
Chemical name Structure
RT
(Min)
Mwt Molecular formula
1
O,O-Diethyl
phosphate
5.8 154.10 C4H11O4P
2 TCP 11.2 198.43 C5H2Cl3NO
3 Chlorpyrifos oxon 18.1 334.52 C9H11Cl3NO4P
4 Chlorpyrifos 22.1 350.59 C9H11Cl3NO3PS

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Based upon the identification of degradation products of chlorpyrifos, the oxidation pathway of chlorpyrifos
using Ultraviolet irradiation were assumed in table (2). These oxidation products were agreed with (Slotkin et al., 2009).
Effect of ozonation of insecticide
Exposure of chlorpyrifos to different time interval from 1 to 12 hours using ozonation leads to degradation of
insecticide. Chlorpyrifos EC (14 ppm) was oxidized to O,O-Diethyl phosphate, O,O-Diethyl thiophosphate, TCP, and
Chlorpyrifos oxon. Percent removal of insecticide varies from 0 % to 85.70% at exposure of 12 hours as shown in figure
(16). Half life time of chlorpyrifos using ozonation process was 3.3 hours as shown in table (4).
Figure 15. TIC of degradation products of chlorpyrifos using ozone
Fig.(15) shows the total ion chromatogram of oxidation products of chlorpyrifos using ozone in which peak 1 is
O,O-Diethyl phosphate, peak2 O,O-Diethyl thiophosphate, peak3 TCP, peak4 Chlorpyrifos oxon, peak5 Chlorpyrifos.
Table 3. chemical structure of chlorpyrifos oxidation using ozone
Peak
no.
Chemical name Structure
RT
(min)
Mwt Molecular formula
1
O,O-Diethyl
phosphate
5.8 154.10 C4H11O4P
2
O,O-Diethyl
thiophosphate
7.2 170.17 C4H11O3PS
3 TCP 11.2 198.43 C5H2Cl3NO
4 Chlorpyrifos oxon 18.1 334.52 C9H11Cl3NO4P
5 Chlorpyrifos 22.1 350.59 C9H11Cl3NO3PS
Based upon the identification of degradation products of chlorpyrifos, the oxidation pathway of chlorpyrifos
using ozone were assumed in table (3). These oxidation products were agreed with (El Masri et al. 2014).
O,O-Diethylphosphate
TCP
Chlorpyrifos
Chlorpyrifosoxon
O,O-Diethylthiophosphate

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Figure 16. Removal % of chlorpyrifos (EC) versus time using UV and O3
Table 4. Chlorpyrifos removal percent after treatment with UV, O3 and 1.5%chemicals
Time
(hour)
Chlorpyrifos degradation%
NaOCl Ca(OCl)2 MCICA DCICA TCICA UV O3
0 0.00 0.00 0.00 0.00 0.00 0.00 0.00
2 4.93 6.64 14.86 21.57 31.57 33.36 39.36
4 7.86 10.43 19.93 29.43 39.71 47.00 59.21
6 9.71 12.93 21.43 31.14 42.36 51.71 72.70
8 11.64 15.21 21.86 31.71 43.00 54.29 80.40
10 12.21 15.93 22.71 31.79 43.43 56.79 84.80
12 12.71 16.29 22.93 32.07 43.71 57.71 85.70
K 0.02 0.02 0.04 0.06 0.10 0.12 0.21
LT50 >12 >12 >12 10.69 7.13 5.64 3.34
LT50: Half-life value, K: Degradation rate constant
Ozone selectively reacts with compounds containing heteroatoms such as S, N, O, and Cl via two different
pathways, namely direct molecular and indirect radical chain-type reactions (Gottschalk et al., 2000). Thus,
pesticides, which usually have some heteroatoms on the molecules, are often expected to be destroyed by
ozonation (Reynolds et al., 1989). However, as has been found by many researchers, the reactivity of pesticides
with ozone varies largely due to their diverse structural features (Reynolds et al., 1989 and David et al., 1991) the
characteristics of the wastewater to be treated, i.e., pH, concentration of ozone decomposition initiators, promoters and
scavengers in the reacting medium (Glaze et al., 1987) Similar type of products were reported by (Briceño et al. 2012
and Randhawa et al. 2007)
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