Photolysis of methyl-parathion thin films: Products, kinetics and quantum yields under different atmospheric conditions

Article abstract of DOI:10.1016/j.jphotochem.2009.11.014

The present study focuses on the photodegradation of methyl-parathion thin films, an organophosphate insecticide, under different atmospheric conditions. The latter include nitrogenated, oxygenated and ozonated atmospheres, under low and high relative humidity conditions. Addition of oxygen to the atmospheric mixture did not seem to affect the reaction rates and quantum yields. Relative humidity affect was minor, with a small enhancement in reaction rate under 254. nm radiation. The addition of ozone (to either dry or humid atmosphere), at all concentrations tested, largely enhanced degradation rates. In the absence of ozone, the obtained quantum yields for photolysis of methyl-parathion thin films under 254 and 313. nm were 0.024 ± 0.007 and 0.012 ± 0.005, respectively. These values are higher than the values previously reported for solutions of methanol and water. Although the presence of molecular oxygen and water vapors did not seem to affect much the reaction rates, it did have a certain effect on the resulted products. More polar products were obtained under oxygenated and ozonated atmospheres, as well as dimers under ozone conditions. The reaction on thin films has yielded more toxic products than usually found in solutions, adding alkylphosphate esters in addition to the oxons formed normally.

Full text of DOI:10.1016/j.jphotochem.2009.11.014

Journal of Photochemistry and Photobiology A: Chemistry 209 (2010) 193–202
Contents lists available at ScienceDirect
Journal of Photochemistry and Photobiology A:
Chemistry
journal homepage: www.elsevier.com/locate/jphotochem
Photolysis of methyl-parathion thin films: Products, kinetics and quantum
yields under different atmospheric conditions
∗
Michal Segal-Rosenheimer , Yael Dubowski
Faculty of Civil and Environmental Engineering, Technion – Israel Institute of Technology, Technion City, Haifa 32000, Israel
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 12 August 2009
Received in revised form
The present study focuses on the photodegradation of methyl-parathion thin films, an organophosphate
insecticide, under different atmospheric conditions. The latter include nitrogenated, oxygenated and
ozonated atmospheres, under low and high relative humidity conditions. Addition of oxygen to the atmo-
spheric mixture did not seem to affect the reaction rates and quantum yields. Relative humidity affect
was minor, with a small enhancement in reaction rate under 254 nm radiation. The addition of ozone (to
either dry or humid atmosphere), at all concentrations tested, largely enhanced degradation rates. In the
absence of ozone, the obtained quantum yields for photolysis of methyl-parathion thin films under 254
and 313 nm were 0.024 ± 0.007 and 0.012 ± 0.005, respectively. These values are higher than the values
previously reported for solutions of methanol and water. Although the presence of molecular oxygen and
water vapors did not seem to affect much the reaction rates, it did have a certain effect on the resulted
products. More polar products were obtained under oxygenated and ozonated atmospheres, as well as
dimers under ozone conditions. The reaction on thin films has yielded more toxic products than usually
found in solutions, adding alkylphosphate esters in addition to the oxons formed normally.
1
2 November 2009
Accepted 21 November 2009
Available online 26 November 2009
Keywords:
Methyl-parathion
Photolysis
Quantum yields
Thin films
Atmospheric conditions
©
2009 Elsevier B.V. All rights reserved.
◦
1
. Introduction
parathion at 25 C), they are susceptible to reside on airborne
particles or deposited upon ambient surfaces [13]. Nevertheless,
photochemical degradation of OPs has been studied mainly in aque-
ous solutions (e.g., [14–17], and references therein). Fewer studies
were done involving OPs adsorbed onto soils [18–21], simulating
soil under atmospheric conditions [18] or using theoretical sim-
ulations of atmospheric conditions [22]. Field observations [7,11]
indicate that upon exposure to solar radiation and atmospheric oxi-
dants organophosphates quickly degrade (within a matter of hours
up to few days) from thion (P S) to the oxon (P O) active com-
pounds, which are usually more toxic and soluble [23]. Woodrow
et al. [24] exhibited a rapid conversion (within 2 min) of parathion
to paraoxon at midday when released in the field. However, on
testing parathion photochemical reaction in the gas-phase under
controlled conditions they have observed conversion only after
40 min, and with the addition of ozone this time was shorten to
half [25]. However, Winer and Atkinson [26] have shown that OPs
gas-phase reaction with ozone was negligible. Apparent from the
above, the radiation flux and the specific environmental conditions
can significantly affect lifetime of the investigated pesticides. More-
over, the above investigations were conducted in the gas-phase.
Hence, applying their findings to oxidation of sorbed semi-volatile
pesticides is very limited as the kinetics of gas-phase and analog
heterogeneous reactions can significantly differ [27,28]. The few
previous studies regarding heterogeneous photoxidation of OPs
indeed provided important information of relative reaction rates
For the last couple of decades organophosphate pesticides (OPs)
have been used abundantly on a vast range of insecticidal applica-
tions, from household and garden usage to commercial agricultural
applications mainly on orchards and cotton grows [1,2]. Although
their use has been decreased over the years, due to their high toxi-
city to mammals [3], OPs are still being used in large quantities. In
Israel, for example, a recently published pesticides survey [4] has
shown that OP usage has actually increased in 2006 in comparison
to 2003.
The atmosphere is considered an important transportation
medium for pesticides although most, including OPs, are semi-
volatile compounds in nature [5–7]. Their introduction to the
atmosphere is via drift during application, post-application
volatilization and dust erosion. The amount volatilized from agri-
cultural fields typically range between 20 and 50%, and sometime
can even reach 90% for soil fumigants [8]. In addition to its impor-
tance with regard to pesticide transport, the atmosphere is also
an important media for transformations of OPs [9–12]. As most
OPs have low vapor pressure (e.g., 1.7 × 10−5 mmHg for methyl-
∗ Corresponding author. Tel.: +972 4 8292808; fax: +972 4 8228898.
E-mail addresses: segalm@tx.technion.ac.il (M. Segal-Rosenheimer),
yaeld@tx.technion.ac.il (Y. Dubowski).
1
010-6030/$ – see front matter © 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.jphotochem.2009.11.014

1
94
M. Segal-Rosenheimer, Y. Dubowski / Journal of Photochemistry and Photobiology A: Chemistry 209 (2010) 193–202
Table 1
Summary of the different experimental set-ups.
lamp emitting at 185 and 254 nm (Jelight Inc., double bore 78-
2
046) and then was measured with an ozone monitor (InDevk, 2B
Treatment
Radiation (254/313 nm)
N2
O2
RHa
O3
Technologies). Working concentrations were between 7 × 10 and
12
14
3
2
× 10 molecules/cm , which corresponds to 300 ppb to 10 ppm.
a
b
c
d
e
f
+
+
+
+
+
+
−
−
−
−
+
+
+
+
+
+
+
+
+
+
−
+
−
−
+
−
−
−
−
+
High concentrations were used in some of the 254 nm experiments
for a better detection and identification of products, where lower
concentrations (∼300 ppb) were used under the 313 nm experi-
ments to resemble more closely atmospheric scenarios such as
heavily polluted atmosphere. Methyl-parathion film was deposited
directly on the ATR crystal by applying 100 ␮l of 3 mM solution of
the pure compound (Supelco, Neat grade) in ethanol (BioLab, ana-
lytical reagent) and allowing the solvent to evaporate (complete
removal of the solvent was confirmed by ATR spectra). The ATR
flow-through chamber was then sealed to ambient atmosphere.
Spectral measurements started simultaneously with the mount-
ing of the UV lamp on top of the chamber’s quartz window, while
the proper gas mixtures were flowing continuously through it.
Total flow was kept constant under all experimental conditions.
Radiometric readings were taken using 254 and 313 nm calibrated
sensors (UVX Radiometers by UVP), that were mounted (in sepa-
rate experiments) at the same location, distance and configuration
as the ATR crystal in the experimental system. Irradiance measure-
−
+
+
+
+
−
−
+
−
+
+
b
a
−
+
−
−
+
b
C
b
e
f
−
b
+
+
+
a
RH represents the conditions of high relative humidity during the experiment
values between 70 and 80% RH).
Represents blank set-up, according to similar set-up with radiation.
(
b
[
18] and possible surface products [29,30]. A new study regarding
the photodegradation of methyl-parathion in ice has shown higher
quantum yields compared to solutions [31]. Nevertheless, there is
still a need for a more comprehensive studies on photolysis and
quantum yields of surface bonded OPs, and of formation rates of
their degradation products left on the surface and released to the
air. Quantification of the photochemical processes under various
atmospheric conditions, and the knowledge of their degradation
products and formation rates will allow a better assessment of their
atmospheric fate, and the possible impact on air quality and human
health aspects.
Methyl-parathion (o,o-dimethyl o-p-nitrophenyl phosphoroth-
ioate) is an important member of the OP group, and was chosen
as a model compound for the present study. The fact that its con-
densed photochemical degradation products are known, and that
several investigations were made on it (mostly in aqueous phase)
2
ments gave 542 and 391 ␮W/cm , for the 254 and 313 nm lamps,
respectively.
Infrared absorbance spectra averaged 32 scans per spec-
−
1
trum at 2 cm
resolution over a spectral detection range of
−
1
4000–650 cm . Background was taken on a clean ATR crystal
under the corresponding experimental conditions.
Absorption cross-section of the methyl-parathion film was
determined by measuring its absorbance at varying surface con-
centrations. Films were deposited in a defined slot on a quartz slide,
and their absorbance was measured between 200 and 600 nm (res-
olution of 2 nm) using UV–vis spectrophotometer (Genesis 10 UV,
[
16,18,32–39], make it an ideal compound for investigation and
comparison.
The present work focuses on the investigation of photolysis
®
Thermo ).
of thin films of methyl-parathion under different atmospheric
conditions (e.g., humidity, oxygen level, and presence of ozone),
including reaction rates, quantum yields, and the formation rates
of its degradation products.
2.2. GC–MS analysis
Residue of the reacted methyl-parathion film was extracted at
the end of the experiments with 3 ml of ethanol (BioLab, analytical
reagent) and analyzed by gas chromatography–mass spectroscopy
(GC–MS) for the verification and identification of surface photo-
products. For identification, 5 ␮l samples were injected into the
GC–MS (Varian CP-3800 GC with MS trap detector Varian Sat-
2
. Experimental
2.1. Experimental set-up and procedures
◦
urn 2000, run in EI mode). Injector temperature was 240 C and
Detailed description of the experimental system is given else-
analysis was done using a capillary column (Varian DB-5 column;
30 m; 250 ␮m I.D.; film thickness 0.25 ␮m). The method started at
◦
where [40]. In brief, the system consists of a 45 Horizontal ZnSe
ATR crystal (HARTPlus, Pike Technologies Inc.) placed in a flow-
through homemade Stainless steal chamber with a quartz window
at its top. A mercury lamp (model 3UV lamp-38, 8 W UVP, Ltd.) was
placed on top the quartz window. Illumination central wavelengths
were at 254 or 313 nm.
◦
◦
◦
50 C, which was held for 2 min, then ramped to 100 C at a rate of
◦
◦
20 C/min, followed by an increase to 150 C at 5 C/min, and then
◦
◦
to 250 C at 10 C/min. The method used an initial splitless mode
and a split ratio of 1:10 after 1 min. Ions were collected in the range
of 40–300 m/z.
Photodegradation of methyl-parathion thin films was tested
under various conditions as summarized in Table 1. Settings ‘a–f’
has been conducted both under 254 and 313 nm radiations. A set
of blank experiments with no radiation was conducted under all
3. Results and discussion
3.1. Methyl-parathion photolysis rates under various
atmospheric conditions
b
b
b
selected gas mixtures as detailed in Table 1 (i.e., settings a , c , e ,
b
and f ). In the table, RH refers to high relative humidity atmosphere
(
i.e., 70–80% for high RH and below 5% otherwise). Humidifica-
tion was obtained by bubbling dry nitrogen gas through DI water
18.2 Mꢀ water, Millipore). Relative humidity and temperature of
Fig. 1 shows the spectral changes observed during photolysis
of methyl-parathion film under 254 nm irradiation and dry oxy-
genated atmosphere.
(
the gas flow were monitored in a mixing cell located just before
the reactor’s inlet, using AHLBORN Alemo® 2390-3 instrument.
Temperature ranged between 22.2 and 25.3 C. N2 and O2 (both,
3.1.1. Spectra interpretation
◦
Representative bands of the parent molecule are shown in
Fig. 1. The vibrational frequency of the P S band is usually
>99.999% Maxima) mixture at a ratio of 4:1, was used as a syn-
−
1
thetic atmosphere. Ozone was generated by irradiating a dry flow of
O2 and He (both >99.999%, Maxima) with a low-pressure mercury
about 675 cm . However, the symmetrical stretching frequency
of the PO3 group is known to interact mechanically with this

M. Segal-Rosenheimer, Y. Dubowski / Journal of Photochemistry and Photobiology A: Chemistry 209 (2010) 193–202
195
−
1
Fig. 1. Temporal changes of methyl-parathion film during photolysis under 254 nm in dry oxygenated atmosphere. Insert shows increase with time of the 2400–3600 cm
region. Methyl-parathion (solid black line) representative bands are shown in panel above. A detailed assignment for the functional groups is given in text.
band and obscure its specific location [41]. Following this, bands
photolysis rate constant kp for each setting. Temperature variation
during experiments was negligible (1 and 0.3 C over 4 h of irradi-
−1
−1
−1
◦
A (660 cm ), B (767 cm ), and C (835 cm ) were assigned,
respectively, to the P S stretch, PO3 symmetric stretch, and PO3
asymmetric stretch vibrations within the conjugated bond of
ation for 254 nm, and 313 nm light, respectively), and hence, was
not considered to affect evaporation rate. Photolysis rates and half-
lives for all tested conditions are summarized in Table 2. Half-lives
were calculated based on the first order photolysis rate constants
(t1/2 = ln2/kp). Photolysis rates under the 254 nm irradiation were
higher by a factor of two to three when compared to the rates under
313 nm light, at the same experimental conditions. Photolysis rates
under dry nitrogenated or oxygenated atmospheres did not show
significant difference. Previous investigations regarding parathion
photolysis [13] indicated that the presence of water can contribute
to the thion to oxon conversion via interaction of water molecules
with the synthesized parent molecule or with reactive interme-
diates. Comparison between the photolysis rates observed in the
present study under humid and dry conditions showed indeed a
small enhancement under humid nitrogenated atmosphere and
254 nm light. Under all other conditions the differences were within
experimental error.
−1
−1
O3P S. Bands D (926 cm ) and E (1033 cm ) were assigned to
the P–O stretch vibration of the P–O–Ar (Ar = aromatic ring) group,
and to the O–C stretch of the P–O–CH group, respectively. B and F
3
−1
(
1227 cm ) were assigned to the O–Ar stretch whereas bands G1
and G were assigned to the symmetric and asymmetric stretching
2
−1
of the NO group [42]. H band at 1488 cm represents the para sub-
2
stituted benzene ring, and finally, the I and I bands were assigned
1
2
to the stretch vibrations of the di-substituted benzene [41].
3.1.2. Kinetics
As exposure time increases, the absorbance at the bands
assigned to the parent molecule, as detailed above was decreas-
ing. It can be noticed that many of the original bands exist also in
the product molecules. Hence, methyl-parathion loss rate can be
−
1
extracted only from its unique bands at 767 and 660 cm (B and
A in Fig. 1). The latter, however, was not used as a proxy for the
reaction rate measurement due to its low intensity, and its higher
susceptibility to measurement noise (detection threshold of our IR
Although MPT is not very reactive towards ozone [26], the pres-
ence of ozone did seem to significantly enhance the photolysis rates
of methyl-parathion. In comparison to our blank experiments with
ozone (eb and fb in Table 1), direct reaction of MPT with ozone
could not explain the relatively high photolysis rates, both under
−
1
detector was at 650 cm ).
Photolysis rate constants were extracted from the fit of
−
1
b
temporal changes in absorbance peak area at the 767 cm
254 and 313 nm radiations (i.e., k[e ] + k[b] ꢀ k[e]), indicating a syn-
band. All the analyzed data fit an exponential decay model (p-
ergistic effect between UV and O3, as also observed by Kromer et
al. [18]. The enhanced rate can be a result of an indirect photolysis
pass involving the photochemical decomposition of ozone under
UV radiation (where wavelengths up to 313 nm are effective) to
value < 0.001), indicating first order kinetics. Blank experiments
b
(
noted as a–f in Table 1) revealed a certain amount of methyl-
parathion volatilization under the different experimental settings
and although methyl-parathion has a relatively low vapor pres-
sure, other investigations [18] also showed differing amounts of
volatilization under different conditions. In the present case, how-
ever, volatilization rates were similar under the different settings
1
molecular oxygen in its singlet state O2( ꢁg), and to electronically
1
excited oxygen O( D) [27]. Both species are reactive and can induce
the formation of carboxylic moieties and ketones from aromatic
alcohols. This assumption is supported later on by our spectral and
chromatographic product analysis. As no significant difference was
observed between dry and humid conditions in the presence of
−
1
(
0.0019 ± 0.0002 min ) and their averaged value was subtracted
from the observed decomposition rate constant to yield the net
Table 2
Methyl-parathion films photolysis rates (min−1) under the different experimental set-ups (half-lives in minutes are shown in parenthesis).
a
b
c
d
e
f
2
3
54 nma
13 nma
0.0027 ± 0.0007 (261)
0.0010 ± 0.0006 (702)
0.0025 ± 0.0004 (278)
0.0011 ± 0.0006 (630)
0.0032 ± 0.0009 (215)
0.0011 ± 0.0002 (630)
0.0021 ± 0.0008 (324)
0.0008 ± 0.0002 (880)
0.0038 ± 0.0003 (183)
0.0016 ± 0.0002 (437)
0.0038 ± 0.0003 (183)
0.0019 ± 0.0004 (358)
a
Radiation experiments under 254 nm were done in triplicates (n = 3), and under 313 in duplicates (n = 2) for each setting. Error values correspond to deviation between
replicates.

1
96
M. Segal-Rosenheimer, Y. Dubowski / Journal of Photochemistry and Photobiology A: Chemistry 209 (2010) 193–202
Fig. 2. Relative spectral responsivity curves of (a) 254 nm radiometer, (b) 313 nm radiometer, and the spectral illumination curves of (c) 254 UV lamp, (d) 313 UV lamp used
in the laboratory experiments, and (e) absorption cross-section curve of methyl-parathion thin film. UV lamps and radiometer responsivity curves are given in relative units.
ozone at 254 nm radiation, the existence of hydroxyl radicals was
considered to be of a minor effect.
The obtained photolysis rates and half-lives are difficult to com-
pare with other studies due to the large difference in reaction
conditions and set-ups. Hence, quantum yields were calculated for
the different experimental set-ups and were used for comparison.
parathion film (Iabs) is given by:
Iabs = I0 × ꢁεꢂ × [C]0
(3)
where [C]0 is the initial methyl-parathion thin film surface concen-
2
tration in molecules/cm . Similar film thickness was assumed on
both ATR experiments and on absorption cross-section measure-
ments.
3
.2. Methyl-parathion quantum yields under various
Since photodegradation rates of methyl-parathion was rela-
tively similar under the different atmospheric conditions (except
under ozonated atmosphere), the obtained quantum yields are
given as an averaged value (with their standard deviation) for each
radiation wavelength. Values obtained following the above calcu-
lations yielded quantum yields of 0.024 ± 0.007 and 0.012 ± 0.005
for 254 and 313 nm radiations, respectively. These values are an
order of magnitude higher than the values published by Wan et
al. [17] for methyl-parathion in methanol (data available only for
atmospheric conditions
Quantum yields were calculated by using the following equa-
tion:
dC/dt
˚
=
(1)
Iabs
where dC/dt is the observed initial photodegradation rate (the
extracted kp), and Iabs is the light flux absorbed by the methyl-
parathion film. Iabs is a function of both the incident light flux
2
54 nm radiation), and are 50 times higher than the corresponding
values of methyl-parathion quantum yields in water (both for 254
and 313 nm radiations). Nevertheless, the relative ratio between
the 254 and 313 nm quantum yields in the present study (∼2) cor-
responds well with the ratio published by Wan et al. for aqueous
solution [17]. Recent values published by Weber et al. [31] has
shown that quantum yields in ice were at least 6 times higher than
the values obtained by Wan et al. in aqueous solutions [17], with
no apparent difference between aerated and degassed conditions.
(
(
I ) and the average absorption cross-section coefficient
cm /molecule). I0 was calculated from the light flux measured
ε
0
2
using the specific radiometers for each lamp and a correction fac-
tor compensating for the differences between spectral illumination
curves of the UV lamps and the spectral responsivity curves of
the corresponding radiometers (see detailed explanation in Segal-
Rosenheimer and Dubowski [40]).
spectral range of the radiometers (ꢂ –ꢂ2 were in the ranges of
ε
was calculated over the
◦
Their values were obtained at the low temperatures of −20 C, in
1
comparison to the present study, which was held under ambient
2
54–370 and 266–370 nm, for the 254 and 313 nm UV lamps,
◦
temperatures (∼25 C).
respectively) according to:
According to the quantum yield obtained under 313 nm light,
the outdoor half-life of methyl-parathion films can be evaluated. It
appears that the flux of solar radiation greatly affect this environ-
mental parameter, which range between 80 min, at a solar zenith
ꢀ
ꢂ
2
I(ꢂ) × ε(ꢂ)dꢂ
ꢂ
1
ꢁεꢂ =
ꢀ
(2)
ꢂ
2
I(ꢂ)dꢂ
ꢂ
1
◦
angle (SZA) of 10 (corresponding to midsummer at our location,
◦
◦
where I(ꢂ) represents the lamp spectral output function (see Fig. 2)
and ε(ꢂ) is the measured absorption cross-section of methyl-
parathion film at wavelength ꢂ, as shown in Fig. 2. Following
the above, the actual light flux initially absorbed by the methyl-
32 N,) to 30 h (1.3 days) for SZA of 86 . Such half-lives and wide
fluctuations were observed previously in many outdoor and labora-
tory investigations regarding the photolysis of OPs and are detailed
in a review paper by Floesser-Mueller and Schwack [13]. The fact

M. Segal-Rosenheimer, Y. Dubowski / Journal of Photochemistry and Photobiology A: Chemistry 209 (2010) 193–202
197
that observed degradation rates could vary between hours to days
and even weeks, further emphasize the importance of obtaining
quantum yields rather than half-lives. The large variability in the
basic radiation conditions (throughout the day), accompanied by
different environments (different humidity, ozone levels, different
surfaces, etc.) can indeed cause large differences in final half-lives
obtained in the field. Chukwudebe et al. [29] have found that 70% of
methyl-parathion thin films were degraded under solar radiation
after 14 h. However, they did not supply any information regard-
ing the time of year or of the total radiation flux to allow proper
comparison with our current results. In comparison to a former
investigation done by our group on the photolysis of cypermethrin
[
40] (an insecticide of the pyrethroid family), it was shown that
◦
under SZA of 10 the half-life of this compound will be around
1
9 h. Although quantum yields for methyl-parathion were found
to be lower than for cypermethrin, its absorption spectrum has
higher overlap with solar spectrum, grading it as a more sensitive
compound to photolysis in comparison to cypemethrin.
3
3
.3. Photoproducts
.3.1. Products identification by GC–MS
Many investigations have shown that the formed degradation
products of organophosphates, especially of parathion ([13] and
references therein) were not affected by the UV radiation wave-
lengths used (254 or 313 or 365 nm). Indeed, our results support
this observation as same products were identified on both radia-
tions used in the present study.
Two surface products, methyl paraoxon (MPO) and o,o,s
trimethyl-thiophosphate (OTT) were identified by our GC–MS anal-
ysis under all experimental conditions, with lower OTT to MPO
ratio when O3 was also present (i.e., settings e and f). MPO is a
well documented photoproduct of methyl-parathion (e.g., [13,16]
and references therein), while OTT is the methyl analog of one
of the well known photoproducts of ethyl-parathion [13], o,o,s
triethyl-thiophosphate, and was also detected as a main photo-
product of methyl-parathion thin films under sunlight and UV
radiation [29]. In addition to these two surface products other prod-
ucts were found under specific conditions (see also Scheme 2).
Methanecarbothiolic acid (MCA) was detected under all conditions,
except for dry nitrogen (setting a). Additional polar products were
observed under humid and oxygenated conditions, including: the
aliphatic acid 2-propionic acid, 2 methyl (AA), propanoic acid (PA),
and alcohols (2-propyl 1-pentanol, 2PP). Diethyl-phthalate (DiePH)
and dimethyl phthalate (DimPH) were detected after irradiation
under dry oxygen and dry ozone, respectively. Furthermore, p-
Fig. 3. Spectra of the photolysis reaction of methyl-parathion under various atmo-
spheric settings (b–f, as detailed in Table 1) at the end of each experiment for the
−
1
−1
spectral ranges of (A) 650–1900 cm and (B) 2800–3800 cm . Initial spectrum of
methyl-parathion is shown as red solid line at the bottom of each panel. Standard
spectra (taken from NIST spectral library) of the photoproducts of methyl-parathion
that were used for spectral analysis are shown in the upper part of each panel.
Spectra were shifted for clarity.
conditions. This region represents carbonyl absorption bands asso-
ciated with aldehydes, ketones and carboxylic acids, and hence
increase more prominent under oxygenated conditions (ozone or
oxygen, with higher intensity under ozonated conditions) in com-
parison to only nitrogen atmospheres (spectrum not shown). The
−
1
PO symmetric stretch of the O P O band (791 cm ), and the P
O
3
3
−
1
band stretch (1294 cm ) can be associated to methyl paraoxon
(MPO, spectrum I in upper panel in Fig. 3A), and the latter also to
o,o,s trimethyl-thiophosphate (OTT). Since reference standard or
library spectrum of OTT was not available, the spectrum of o,o,o
trimethyl-phosphate (OTP) was selected to spectrally represent
it (spectrum III in upper panel of Fig. 3A). Both compounds are
almost similar, apart from the difference in their P–S (OTT) and P–O
(
2,2,4-trimethyl-4-chromaryl) phenol (TCP) was detected only in
the presence of O3 (i.e., settings e and f).
It is worth noting that our GC analysis is likely to underestimate
the formation of carboxylic acids and aldehydes since no derivati-
zation was used.
−
1
(
OTP) bonds that have spectral contribution around 613–440 cm
,
3
.3.2. Spectral product identification and reaction trends
Spectral analysis of the temporal changes during reaction
out of our measure spectral range [41]. The relatively broad band
−
1
increase at the 800–880 cm emerging together with the decrease
of the representative bands of the parent molecule can explain the
increase of both MPO and OTT. Although OTP was not detected in
our GC analysis, it is also known as one of the possible photoprod-
revealed some additional insights regarding products formation,
and supported some of our GC–MS analysis results. Fig. 3 shows
the spectral changes occurred during photolysis under the oxy-
genated conditions (settings b and d–f, the other conditions are
not shown for clarity). Fig. 3A focuses on the spectral region
between 650 and 1900 cm , and Fig. 3B focuses on the region
of 2800–3800 cm . Upon exposure to UV light, under all tested
gas mixtures, increased absorbance was observed in the fol-
−
1
ucts of methyl-parathion [29]. The 1297, 1640, and the 1700 cm
bands in the photolyzed MPT film can be associated to the aliphatic
acid detected (AA) (spectrum V). Although not detected by our
GC–MS analysis, the signature of hydroquinone (HQ, spectrum
IV) can also be detected in the spectrum of photolyzed MPT film
−1
−1
−
1
−1
−1
lowing bands (Fig. 3A lower part): 791 cm , between 800 and
8
1
(Fig. 3A), both at the broad 1200 cm band and at the 1488 cm
−
1
−1
80 cm , 1200 cm
(broad increase including 1187, 1263, and
band, which represents para substituted benzene rings [41]. Also,
−
1
−1
−1
294 cm bands), 1488, 1524 cm , and the bands between 1640
its contribution can be seen at the 3000–3400 cm OH band stretch
−1
and 1780 cm . The latter are especially enhanced under ozonated
(Fig. 3B). The fact that 4-nitrophenol (4NP, spectrum II) was not

1
98
M. Segal-Rosenheimer, Y. Dubowski / Journal of Photochemistry and Photobiology A: Chemistry 209 (2010) 193–202
Fig. 4. Reaction progress plots of methyl-parathion and its products using the
inverse model” calculations, as detailed in the text (y-axis represents relative
“
progress, and hence is unit less). Panel (A) represents reaction progress under dry
oxygenated atmosphere and panel (B) is under dry ozonated atmosphere.
detected in the GC–MS and spectral analyses of the films’ residue
at the end of the experiments may in part be a result of its sus-
ceptibility to direct photolysis [13]. Indeed, as will be shown later
(
Fig. 4), the continuous FTIR analysis does show its build-up and
Fig. 5. Experimental spectra of the initial methyl-parathion film (solid blue line)
and final residue after photolysis at 254 nm (dotted red line) at dry oxygenated
atmosphere (A) and dry ozonated atmosphere (B). Black lines represent the recon-
struction error as detailed in text. (For interpretation of the references to color in
this figure legend, the reader is referred to the web version of the article.)
loss during the reaction. The recent study by Weber et al. [31] also
mentioned its relatively low formation yields and its susceptibility
to photolysis, making it difficult to trace it at the end of reaction.
Upon photolysis an increase in the OH associated band
−1
(
3000–3600 cm ) is observed as well as a smaller increase at the
−1
2
800–3200 cm region. Comparing the different experiments, it
Furthermore, enhanced water uptake by the oxidized film may also
affect this spectral region.
seems that under dry oxygen conditions, the broadening occurs
mainly in the 2800–3200 cm range, while under humid condi-
tions, the OH broadening is up to 3400 cm . Similar behavior is
seen upon irradiation in the presence of ozone, when dry atmo-
sphere results in a broadening up to 3400 cm
atmosphere results in a very broad peak up to 3600 cm . These
trends probably represent both the formation of acid products
(
in surface hygroscopicity following the formation of more polar
photoproducts. In the presence of ozone, photo-oxidation results
in even higher water uptake (under high RH experiment), which
−1
The five products shown in Fig. 3 were used to reconstruct
the temporal reaction spectra, using the “inverse method”, as
described in Segal-Rosenheimer and Dubowski [40]. In short, the
obtained temporal spectra are assumed to be superposition of both
the parent material (i.e., methyl-parathion), and its photodegra-
dation products. A linear decomposition was obtained over the
−1
−
1
and a humid
−
1
−
1
mainly under humid oxygenated atmosphere) and an increase
“fingerprint” spectral range of 650–1900 cm using least square
minimization to find the best fit of the spectral contribution of par-
ent material and its products at each time point. This analysis gave
an insight on the changes of the parent material and its products
with time, as shown in Fig. 4. The amount of each component is
described as the ratio relative to its reference spectral signature,
and the trend in time can be quantified to give the formation or
loss rates. Decrease rates of methyl-parathion calculated this way
correlated quite well with its decomposition rates calculated based
−
1
increases absorbance in the bulk water band of 3400 cm
.
−
1
The contribution of the OTT/OTP band at around 3000 cm
can be seen under all experimental settings. Also, HQ contribution
seems to be more prominent under humid conditions. The spec-
tral signature of 4NP, which acts more as an intermediate, cannot
be seen clearly in the presented end-of-experiment spectra. The
broadening of the absorption bands around 3200–3400 cm under
settings b, d and e could be explained quite well with the identified
products. However, the large broadening under setting f (humid
ozonated atmosphere) could not be attributed to the known spec-
tral features of the detected and postulated products. As mentioned
earlier, additional products were found to prevail under ozonated
conditions (e.g., TCP), but their reference spectra were not available.
−
1
on the 767 cm band. The general trends of the reaction progress
under all conditions were very similar. The loss rates of MPT were
similar to obtained formation rates for OTT but slower than the
calculated formation rates of MPO. This is not too surprising consid-
ering that the latter was estimated based on the absorbance band
−
1
associated with the O (P–O )–Ar, and it is likely that additional
3
unaccounted products with similar functional group (and spec-
tral signatures) are present and resulted in overestimation of MPO

M. Segal-Rosenheimer, Y. Dubowski / Journal of Photochemistry and Photobiology A: Chemistry 209 (2010) 193–202
Scheme 1. Pathways of the main three photoproducts for methyl-parathion photolysis on thin films.
Scheme 2. Secondary photoproducts formation under the different experimental atmospheric settings.
199

2
00
M. Segal-Rosenheimer, Y. Dubowski / Journal of Photochemistry and Photobiology A: Chemistry 209 (2010) 193–202
formation rate. Degradation products with such functional group
although not identified in the present study) can be attributed
cases by the direct decomposition of aromatic-nitro groups [31],
which are present here. Under non-humid conditions (N2 and
N /O atmospheres), the reaction progresses via a pathway a in
(
to denitroparaoxon, and o-methyl, o,o-bis(4-nitrophenyl) phos-
phate, as were suggested in the past [13,30,43]. 4NP seems to be
formed and degrade during reaction, which can explain its absence
at the end of reaction from the IR spectrum and from the GC chro-
matogram. Also, it can be noticed that like for MPT, the degradation
of 4NP under radiation and ozone (Fig. 4B) occurs faster than in the
absence of ozone (Fig. 4A). Initial formation rate of 4NP was slower
than the decrease rate of methyl-parathion (MPT), which supports
its formation as a secondary product. Formation rate of HQ was
also slower than MPT degradation rate and supports its formation
as a secondary product, most probably of 4NP photolysis [16]. HQ
build-up was noted to increase faster when ozone was present.
Spectral reconstruction was obtained to test the accuracy of
the “inverse model” solutions. The reconstructed spectrum was
based on the coefficients extracted via the least square fit to yield a
calculated spectrum. Then, at each time point, the calculated spec-
trum was subtracted from the measured spectrum. Fig. 5A and B
presents the results of this procedure for the same experiments
shown in Fig. 4 (oxygenated and ozonated, respectively). The main
deviations can be observed around the 800, 1290, 1000–1200, and
2
2
Scheme 2, similar to the description of the pathway under degassed
non-protic media [13], involving the initially produced alkoxy rad-
icals (a and d in Scheme 1). Under oxygenated atmosphere the
additional formation of peroxy radicals may occur, which then yield
additional polar degradation products (pathway a1 in Scheme 2).
In our observations, oxygenated atmosphere did not affect the
reaction rate, but have added the additional oxygenated products.
Addition of water vapor seemed to result in the production of
carboxylic acid moieties. Also, under oxygenated and ozonated con-
ditions, the formation of larger molecules, such as DiePH, DimPH,
and TCP can be the result of the combination of two monomers
on the surface. In the case of ozonated atmosphere (pathway c
in Scheme 2), the initial excitation step is postulated to yield the
alkoxy radicals (a and d in Scheme 1). However, as ozone undergoes
photolysis to produce singlet oxygen and excited oxygen atom [27],
it may accelerate reactions following the first excitation step due to
additional production of peroxy and secondary hydroxyl radicals
(formed mainly via secondary reactions). It is interesting to note
that increasing ozone levels did not affect significantly the over-
all reaction rate, strengthening the conclusion that ozone does not
react directly with the MPT molecule, but only via its role in the for-
mation of secondary radicals. Surface ozone coverage was probably
at saturation under all ozone concentrations used in the present
study (≥300 ppb). The observed lack of dependency of degrada-
tion kinetic on gaseous ozone level also suggests that photolysis of
gaseous ozone followed by atomic oxygen chemistry was of less
importance than the photolysis of adsorbed ozone, at the limit of
saturated surface coverage. Indeed, Kromer et al. [18], who worked
with lower ozone levels (85–200 ppb), did report an increase in
reactivity towards higher levels of ozone. The high formation of
radicals (under relatively high ozone levels) can also result in an
increasing rate of terminating reactions.
−1
1
650–1750 cm
absorption bands, where the negative error in
the first two indicate an overestimation of the products absorbing
at this location (i.e., methyl paraoxon). In general, Fig. 5A, which
represents the reconstruction error under oxygenated conditions,
shows smaller deviations when compared to Fig. 5B (ozonated
atmosphere). A larger positive reconstruction error is shown under
−
1
ozone atmosphere, especially at the 1650–1750 cm , and the
1
−1
000–1200 cm band regions. The above regions are associated
with carbonyl functional groups, and ether–ester moieties, respec-
tively. Their positive deviation implies that there are still additional
compounds which were not accounted for in the reconstruction
procedure and enhances our assumption that our GC analysis did
not result in the full assembly of photoproducts. Also, as postu-
lated previously [44], the increased absorbance between 1100 and
−
1
1
200 cm can represent dimmer formation due to surface radical
reactions.
IR analysis of the gas downstream the reaction cell indicated
4. Conclusions
the presence of carbon dioxide, carbon monoxide (CO), and un-
identified gas products containing carbonyl groups.
Although post-application photolysis of MPT is expected to
occur mainly when it is adsorbed at the solid–air interface, quan-
titative information on this heterogeneous process is scarce. The
present study investigates the photolysis of methyl-parathion thin
films under various atmospheric conditions. The chemical changes
in the film upon irradiation were monitored in real-time using
ATR-FTIR spectroscopy, providing information on the kinetics and
surface product formation. To the best of our knowledge, this is the
first time quantum yield values are reported for photolysis of MPT
sorbed on inert surfaces. The obtained quantum yields were almost
insensitive to the different atmospheric conditions tested (nitro-
gen or oxygenated, under dry or humid conditions), suggesting
that the same value can be used for estimating the photodegra-
dation of sorbed MPT over a relatively wide range of ambient
atmospheric conditions. Although the obtained quantum yields of
MPT films were higher than previously reported in solutions, the
ratio between 254 and 313 nm quantum yields were shown to be
similar.
3.4. Suggested reaction pathways
Photolysis mechanisms of OPs, especially of aromatic thiophos-
phates, were investigated (to the best of our knowledge) only in
solutions [13]. The two known mechanisms are related to different
types of solvents; polar and non-polar; the former involves ionic
interactions, while the latter involves radical reactions. In our case,
as thin films are involved, the basic mechanism is postulated to be
controlled by radical reactions. The alkoxy radicals formed upon
the breakage of the exited MPT molecule may react (see Scheme 1)
with the parent molecule or its fragments and lead to the forma-
tion of MPO, 4NP, and OTT (see the three paths in Scheme 1). The
production of OTT is postulated to result from the interaction of
the initial photolysis fragments of MPT and MPO [13], as shown in
Scheme 1.
Under various atmospheres different products emerge
Scheme 2) due to secondary reactions involving MPO, 4NP
It was also shown that ozone significantly affects the overall
photolysis pathway. As the direct reaction of ozone with parent
material is slow, the observed synergistic effect of ozone and UV is
attributed to enhanced secondary reactions due to the formation
of peroxy radicals. The presence of ozone also contributes to the
formation of polar products (ketones, aldehydes, and carboxylic
acids), which in turn results in higher water uptake of the film,
as suggested by the enhanced absorbance in the broad OH bands
(
and OTT. The three suggested pathways support the formation of
the three main photoproducts under all atmospheric conditions,
as indeed was shown in our analysis.
HQ is postulated to be formed either by the photolysis of 4NP
leading to unimolecular cleavage of the C–N aromatic bond, fol-
lowed by reaction with H O or with OH radicals [13,45]. The latter
2
−
1
can be generated here via secondary radical reactions, or in some
around 3400–3600 cm following photo-oxidation under humid

M. Segal-Rosenheimer, Y. Dubowski / Journal of Photochemistry and Photobiology A: Chemistry 209 (2010) 193–202
201
conditions. Under dry conditions, the bounded OH region was con-
centrated mainly at the region up to 3200 cm , and was attributed
to the formation of carboxylic acids.
[12] P.S. Honaganahalli, J.N. Seiber, Measured and predicted airshed concentrations
of methyl bromide in an agricultural valley and applications to exposure assess-
ment, Atmospheric Environment 34 (2000) 3511–3523.
−
1
[
13] H. Floesser-Mueller, W. Schwack, Photochemistry of organophosphorus insec-
ticides, Reviews of Environmental Contamination and Toxicology 172 (2001)
Using a linear combination of the IR spectra of the parent
compound and of the identified products, the observed temporal
spectra were reconstructed. These reconstructed spectra allowed
us to continuously follow the formation and loss rates of the parent
compound and its photoproducts. The largest error in the recon-
struction spectra was identified under ozone conditions supporting
our assumption that our GC–MS analysis underestimated certain
photo-oxidation products, such as carbonyls, esters, and possible
129–228.
[
14] S. Bondarenko, J.Y. Gan, Degradation and sorption of selected organophos-
phate and carbamate insecticides in urban stream sediments, Environmental
Toxicology and Chemistry 23 (2004) 1809–1814.
[15] M. Franko, P. Trebse, L. Pogacnik, Laser-induced degradation of organophos-
phates and monitoring of their toxicity by cholinesterase biosensors, Critical
Reviews in Analytical Chemistry 33 (2003) 285–290.
[16] E. Moctezuma, L. Elisa, P. Gabriela, H. de Las, Photocatalytic degradation of
methyl parathion: reaction pathways and intermediate reaction products, Jour-
nal of Photochemistry and Photobiology A: Chemistry 186 (2007) 71–84.
−
1
surface dimmers (absorbing around 1100–1200 cm ). Neverthe-
less, under all other tested conditions, reconstruction error was
relatively small; up to 10% at all times, suggesting that the identi-
fied photoproducts(based onGC–MSand infrared spectral analysis)
are the predominant species for the investigated reaction.
[
17] H.B. Wan, M.K. Wong, C.Y. Mok, Comparative-study on the quantum yields of
direct photolysis of organophosphorus pesticides in aqueous-solution, Journal
of Agricultural and Food Chemistry 42 (1994) 2625–2630.
[
18] T. Kromer, H. Ophoff, A. Stork, F. Fuhr, Photodegradation and volatility
of pesticides—chamber experiments, Environmental Science and Pollution
Research 11 (2004) 107–120.
Relative humidity seemed to have a minor effect in the present
investigation. Although it did seem to slightly enhance reaction
rates under nitrogenated atmosphere, as was reported previously
[19] N. Mikami, K. Imanishi, H. Yamade, J. Miyamoto, Photodegradation of fenitroth-
ion in water and on soil surface, and its hydrolysis in water, Nippon Noyaku
Gakkaishi 10 (1985) 263–272.
[
20] J. Miyamoto, Degradation of Fenitrothion in Terrestrial and Aquatic Environ-
ments Including Photolytic and Microbial Reactions, 1977, pp. 105–134.
21] T.M. Sakellarides, M.G. Siskos, T.A. Albanis, Photodegradation of selected
organophosphorus insecticides under sunlight in different natural waters and
soils, International Journal of Environmental Analytical Chemistry 83 (2003)
33–50.
[
13], the mutual effect of both oxygen and high relative humidity
[
did not seem to yield higher rates.
One of the major concerns regarding the environmental fate of
OP pesticides is their toxicity and the toxicity of their degradation
products. Most studies of photochemical degradation of methyl-
parathion in aqueous solution indicated 4-nitrophenol and methyl
paraoxon as the major photoproducts. The present work, like pre-
vious studies on photolysis of sorbed MPT (e.g., Sakellarides et al.
and Chukwudebe et al. [21,29]) indicate significant formation of
additional surface products; including trimethylphosphorothioate
esters that are known to have delayed toxic effect.
[22] Q.Z. Zhang, X.H. Qu, W.X. Wang, Mechanism of OH-initiated atmospheric pho-
tooxidation of dichlorvos: a quantum mechanical study, Environmental Science
&
Technology 41 (2007) 6109–6116.
[23] L.S. Aston, J.N. Seiber, Fate of summertime airborne organophosphate pesticide
residues in the Sierra Nevada mountains, Journal of Environmental Quality 26
(
1997) 1483–1492.
[
24] J.E. Woodrow, D.G. Crosby, T. Mast, K.W. Moilanen, J.N. Seiber, Rates of trans-
formation of trifluralin and parathion vapors in air, Journal of Agricultural and
Food Chemistry 26 (1978) 1312–1316.
[
[
25] J.E. Woodrow, D.G. Crosby, J.N. Seiber, Vapor-phase photochemistry of pesti-
cides, Residue Reviews 85 (1983) 111–125.
26] A.M. Winer, R. Atkinson, Atmospheric reaction pathways and lifetimes for
organophosphorous compounds, in: K. Da (Ed.), Long Range Transport of Pes-
ticides, Chelsea, 1990, pp. 115–127.
Acknowledgments
This research was funded by Marie Currie International Rein-
tegration grant, as part of the sixth framework programme of the
European Commission, and the Israeli Ministry of science, through
the Levi Eshkol fellowship.
[
27] B.J. Finlayson-Pitts, J.N. Pitts, Chemistry of the Lower and Upper Atmosphere,
2000.
[28] N.-O.A. Kwamena, M.G. Staikova, D.J. Donaldson, I.J. George, J.P.D. Abbatt, Role
of the aerosol substrate in the heterogeneous ozonation reactions of surface-
bound PAHs, Journal of Physical Chemistry A 111 (2007) 11050–11058.
[
29] A. Chukwudebe, R.B. March, M. Othman, A.T.R. Fukuto, Formation of trialkyl
phosphorothioate esters from organophosphorus insecticides after exposure
to either ultraviolet light or sunlight, Journal of Agricultural Food Chemistry 37
References
(
1989) 539–545.
[
1] V. Feigenbrugel, A. Le Person, S. Le Calve, A. Mellouki, A. Munoz, K. Wirtz,
Atmospheric fate of dichlorvos: photolysis and OH-initiated oxidation studies,
Environmental Science & Technology 40 (2006) 850–857.
[
[
[
[
[
30] R.L. Joiner, K.P. Baetcke, Identification of the photoalteration products formed
from parathion by ultra violet light, Journal of the Association of the Official
Analytical Chemistry 57 (1974) 408–415.
31] J. Weber, R. Kurková, J. Klánová, P. Klán, C.J. Halsall, Photolytic degradation of
methyl-parathion and fenitrothion in ice and water: implications for cold envi-
ronments, Environmental Pollution (2009), doi:10.1016/j.envpol.2009.05.045.
32] T.W. Chou, R. Spanggord, E. Shingai, N. Bohonos, Fate of methyl parathion
in freshwater systems. 3. Biodegradation studies, Abstracts of Papers of the
American Chemical Society 172 (1976) 62–162.
33] N.O. Crossland, D. Bennett, Fate and biological effects of methyl parathion in
outdoor ponds and laboratory aquaria. 1. Fate, Ecotoxicology and Environmen-
tal Safety 8 (1984) 471–481.
34] S.V. Dzyadevych, J.M. Chovelon, A comparative photodegradation studies of
methyl parathion by using Lumistox test and conductometric biosensor tech-
nique, Materials Science & Engineering C: Biomimetic and Supramolecular
Systems 21 (2002) 55–60.
[
2] E.D. Richter, P. Chuwers, Y. Levy, M. Gordon, F. Grauer, J. Marzouk, S. Levy, S.
Barron, N. Gruener, Health effects from exposure to organophosphate pesti-
cides in workers and residents in Israel, Israel Journal of Medical Sciences 28
(
1992) 584–598.
[
[
[
3] T.R Fukuto, Mechanism of action of organophosphorous and carbamate insec-
ticides, Environmental Health Perspectives 87 (1990) 245–254.
4] Y. Bar-Ilan, G. Malman, Usage Survey of Pesticides in the Lake Kinneret
Basin—2006 Period, 2007, pp. 1–92.
5] H. de-ruiter, H.J. Holterman, C. Kempenaar, H.J.L. Mol, J.J. de-Vlieger, J.C.V. de-
Zande, Influence of Adjuvants and Formulations on the Emission of Pesticides
to the Atmosphere, Plant Research International B.V., 2003.
[
6] M. Harnly, R. McLaughlin, A. Bradman, M. Anderson, R. Gunier, Correlating
agricultural use of organophosphates with outdoor air concentrations: a par-
ticular concern for children, Environmental Health Perspectives 113 (2005)
[
[
[
[
35] Z. Gerstl, C.S. Helling, Fate of bound methyl parathion residues in soils
as affected by agronomic practices, Soil Biology & Biochemistry 17 (1985)
1
184–1189.
[
[
[
7] M.S. Majewski, M.M. McChesney, J.E. Woodrow, J.H. Prueger, J.N. Seiber, Aero-
dynamic measurements of methyl-bromide volatilization from tarped and
nontarped fields, Journal of Environmental Quality 24 (1995) 742–752.
8] F. Van den Berg, R. Kubiak, W.G. Benjey, M.S. Majewski, S.R. Yates, G.L. Reeves,
J.H. Smelt, A.M.A. van der Linden, Emission of pesticides into the air, Water Air
and Soil Pollution 115 (1999) 195–218.
6
67–673.
36] S.S. Lee, B.R. Holt, B.E. Suta, D.H. Liu, Fate of methyl parathion in freshwater
systems. 4. Environmental fate assessment, Abstracts of Papers of the American
Chemical Society 172 (1976) 63–163.
37] W.R. Mabey, A. Baraze, B.Y. Lan, H. Richardson, D.G. Hendry, T. Mill, Fate of
methyl parathion in freshwater systems. 2. Hydrolysis and photolysis, Abstracts
of Papers of the American Chemical Society 172 (1976) 61–161.
38] H.K. Rotich, Z.Y. Zhang, Y.S. Zhao, J.C. Li, The adsorption behavior of three
organophosphorus pesticides in peat and soil samples and their degradation
in aqueous solutions at different temperatures and pH values, International
Journal of Environmental Analytical Chemistry 84 (2004) 289–301.
39] J.H. Smith, D.C. Bomberger, D.L. Haynes, D.F. Stivers, M.E. Zinnecker, Fate of
methyl parathion in freshwater systems. 1. Introduction and physical transport
processes, Abstracts of Papers of the American Chemical Society 172 (1976)
9] J. Seiber, S. Datta, J. Woodrow, Transport and fate of pesticides in fog in Califor-
nia’s Central Valley, Abstracts of Papers of the American Chemical Society 215
(
1998) U37–U137.
[
[
10] J. Seiber, J. LeNoir, C. Wujcik, J. Woodrow, Atmospheric deposition or organic
contaminants in the Sierra Nevada mountains and the Great Basin, Abstracts
of Papers of the American Chemical Society 214 (1997) 82–90.
11] J.N. Seiber, B.W. Wllson, M.M. McChesney, Air and fog deposition residues
of four organophosphate insecticides used on dormant orchards in the San
Joaquin Valley, California, Environmental Science & Technology 27 (1993)
[
6
0–160.
2
236–2243.

2
02
M. Segal-Rosenheimer, Y. Dubowski / Journal of Photochemistry and Photobiology A: Chemistry 209 (2010) 193–202
[
40] M. Segal-Rosenheimer, Y. Dubowski, Photolysis of thin films of cypermethrin
using in situ FTIR monitoring: products, rates and quantum yields, Journal of
Photochemistry and Photobiology A: Chemistry 200 (2008) 262–269.
41] D Lin-Vien, N.B. Colthup, W.G. Fateley, J.G. Grasselli, The Handbook of Infrared
and Raman Frequencies of Organic Molecules, Academic Press, 1991.
42] M. Janotta, K. Manfred, F. Vogt, B. Mizaikoff, Sol–gel based mid-infrared evanes-
cent wave sensors for detection of organophosphate pesticides in aqueous
solution, Analytica Chimica Acta 496 (2003) 339–348.
[43] S. Buckland, R. Davidson, The photodegradation of parathion and chlormephos,
Pesticide Science 19 (1987) 61–66.
[44] M. Segal-Rosenheimer, Y. Dubowski, Heterogeneous ozonolysis of cyperme-
thrin using real-time monitoring FTIR techniques, Journal of Physical Chemistry
C 111 (2007) 11682–11691.
[45] N. Daneshvara, M.A. Behnajadyb, Y.Z. Asgharb, Photooxidative degradation of
4-nitrophenol (4-NP) in UV/H2O2 process: influence of operational parameters
and reaction mechanism, Journal of Hazardous Materials 139 (2007) 275–279.
[
[