Photolysis of chlorpyrifos-methyl, chlorpyrifos-methyl oxon, and 3,5,6-trichloro-2-pyridinol

Article abstract of DOI:10.1002/poc.3957

The photodegradation of chlorpyrifos-methyl (1), and two of its photodegradation products, chlorpyrifos-methyl oxon (2), and 3,5,6-trichloro-2-pyridinol (3) was studied using low pressure Hg lamps irradiating at 254?nm either in pure acetonitrile (ACN) or in 10% ACN/H₂O. Experiments conducted in pure ACN allowed us to identify the photoproducts in the photolysis of 1, 2, and 3 both, in air saturated samples and in the absence of oxygen as analyzed by gas chromatography–mass spectrometry (GC-MS), high resolution mass spectrometry (HRMS), and phosphorus-31 nuclear magnetic resonance (³¹P NMR). Since 2 and 3 are products in the photodegradation of 1, their degradations in 10% ACN/H₂O were independently measured, and it was determined that 1 and 2 degrade at comparable rates. Instead, 3 does not interfere in the measurement since it degrades much faster, and their products do not absorb in the region of 1. Our results indicate that short wave photolysis could become a plausible detoxification mechanism.

Full text of DOI:10.1002/poc.3957

Received: 28 December 2018
DOI: 10.1002/poc.3957
Revised: 1 March 2019
Accepted: 6 March 2019
R E S E A R C H A R T I C L E
Photolysis of chlorpyrifos‐methyl, chlorpyrifos‐methyl oxon,
and 3,5,6‐trichloro‐2‐pyridinol
Virginia L. Lobatto1
| Gustavo A. Argüello2
| Elba I. Buján1
1 Instituto de Investigaciones en
Abstract
Fisicoquímica de Córdoba (INFIQC),
CONICET, Departamento de Química
Orgánica, Facultad de Ciencias Químicas,
Universidad Nacional de Córdoba, Haya
de la Torre y Medina Allende, Ciudad
Universitaria, Córdoba, Argentina
The photodegradation of chlorpyrifos‐methyl (1), and two of its
photodegradation products, chlorpyrifos‐methyl oxon (2), and 3,5,6‐trichloro‐
2‐pyridinol (3) was studied using low pressure Hg lamps irradiating at
254 nm either in pure acetonitrile (ACN) or in 10% ACN/H2O. Experiments
conducted in pure ACN allowed us to identify the photoproducts in the photol-
ysis of 1, 2, and 3 both, in air saturated samples and in the absence of oxygen as
analyzed by gas chromatography–mass spectrometry (GC‐MS), high resolution
mass spectrometry (HRMS), and phosphorus‐31 nuclear magnetic resonance
(31P NMR).
2 Instituto de Investigaciones en
Fisicoquímica de Córdoba (INFIQC),
CONICET, Departamento de
Fisicoquímica, Facultad de Ciencias
Químicas, Universidad Nacional de
Córdoba. Haya de la Torre y Medina
Allende, Ciudad Universitaria, Córdoba,
Argentina
Since 2 and 3 are products in the photodegradation of 1, their degradations in
10% ACN/H2O were independently measured, and it was determined that 1
and 2 degrade at comparable rates. Instead, 3 does not interfere in the mea-
surement since it degrades much faster, and their products do not absorb in
the region of 1.
Correspondence
Gustavo A. Argüello, Instituto de
Investigaciones en Fisicoquímica de
Córdoba (INFIQC), CONICET,
Departamento de Fisicoquímica, Facultad
de Ciencias Químicas, Universidad
Nacional de Córdoba. Haya de la Torre y
Medina Allende, Ciudad Universitaria,
X5000HUA, Córdoba. Argentina.
Email: gaac@fcq.unc.edu.ar
Our results indicate that short wave photolysis could become a plausible detox-
ification mechanism.
KEYWORDS
3,5,6‐trichloro‐2‐pyridinol, chlorpyrifos‐methyl, chlorpyrifos‐methyl oxon, photodegradation
Elba I. Buján, Instituto de Investigaciones
en Fisicoquímica de Córdoba (INFIQC),
CONICET, Departamento de Química
Orgánica, Facultad de Ciencias Químicas,
Universidad Nacional de Córdoba. Haya
de la Torre y Medina Allende, Ciudad
Universitaria, X5000HUA, Córdoba.
Argentina..
Email: elba@fcq.unc.edu.ar
Funding information
Consejo Nacional de Investigaciones
Científicas y Técnicas, Grant/Award
Number: PIP 112‐21501‐00242 CO;
Universidad Nacional de Córdoba, Grant/
Award Number: SECyT 366/2016 and
113/17
J Phys Org Chem. 2019;e3957.
wileyonlinelibrary.com/journal/poc
© 2019 John Wiley & Sons, Ltd.
1 of 8
https://doi.org/10.1002/poc.3957

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LOBATTO ET AL.
water solubility and vapor pressure than chlorpyrifos,[8]
is one of the most widely used insecticides in the world.[3]
It is classified as class III, slightly hazardous,[7] and regis-
tered in Argentina for use in the control of insects on
stored grains and complementary treatments of storage
and transport facilities.[9]
In an attempt to find an efficient method of degrading
organophosphorus insecticides, we have previously stud-
ied the reactivity of 1 with hydroxyl and perhydroxyl ions
as well as the effect of cyclodextrins on these reactions.[10]
Besides, the hydrolysis of chlorpyrifos‐methyl oxon was
studied through the use of high performance liquid chro-
matography (HPLC)‐MS/MS methods, and its degrada-
tion products were also determined.[11] We are
presenting now our results on the photodegradation of 1
and the two direct products Chlorpyrifos‐methyl oxon 2
and 3,5,6‐trichloro‐2‐pyridinol 3 (Scheme 1), using low
pressure Hg lamps as light source for a detoxification
process.
Previous reports on the photodegradation of 1 are lim-
ited. Photodegradation of 1 as well as of chlorpyrifos in
virgin olive oil using UV lamps[12,13] emitting at 200 to
280 nm, studies on the atmospheric degradation,[3,14]
and quantum yield measurements in aqueous solution
at 254 nm for 1 and chlorpyrifos of 0.013 and 0.016,
respectively, have been reported.[15] The latter results
came after the work by Dilling et al[16] who had measured
the quantum yield for chlorpyrifos and for 3 at 313 nm in
aqueous solutions.
Kamiya had studied the effect of humic substances on
the photodegradation of chlorpyrifos[17] and the effect of
cyclodextrins[18] and metal ions[19] on that reaction.
Ukpebor et al[20] studied the degradation of chlorpyrifos
exposed to direct sunlight in aqueous solutions at differ-
ent pHs. Finally, also degradation of chlorpyrifos has
been recently studied by photoreactive TiO2 nanoparti-
cles.[21] None of these papers investigated the photoprod-
ucts. Bavcon Kralj et al[22] found chlorpyrifos oxon and 3
as photodegradation products when an aqueous‐ethanol
solution of chlorpyrifos was irradiated with a 125 W
xenon parabolic lamp. The same photoproducts, among
others, were found by irradiation at 254 nm of a solution
of chlorpyrifos in methanol.[23] There are also some
reports on the photocatalytic degradation of chlorpyri-
fos.[21,24,25] Shemer et al[26] had measured the degradation
rate and quantum yield of 3 in aqueous solution without
analyzing the products. Feng et al[27] had investigated 3
by photolytic and microbial degradation at 254 nm in
phosphate buffer (pH 7). They had proposed a mecha-
nism of degradation of 3 that ends up in ammonium, car-
bon dioxide, and water after having formed different
aromatic products. In addition, Devi et al[24] proposed
that 3, formed in the photocatalytic degradation of
1 | INTRODUCTION
Agrochemicals are intensely used as part of current inte-
grated pest management in order to protect crops and
vegetables.[1] International statistics indicate that pests
take off 42% of the total potential production of foodstuff
even with the use of agrochemicals; nevertheless, without
them, the loss would rise to 70%.[2] On the other hand,
when pesticides are applied in the field, they can contam-
inate the soil, water, and atmosphere producing an
important environmental impact.[3]
Organophosphorus pesticides are extensively used in
different applications and have replaced the use of organ-
ochlorine pesticides since the second half of last century
because they are less persistent in the environment.[4]
The toxicity of organophosphorus insecticides results from
the
inhibition
of
acetylcholinesterase
(AChE).
Thiophosphate insecticides are transformed to the corre-
sponding phosphate in the target organism by the action
of cytochrome P450 resulting in a toxic bioactivation.[4]
Because of the environmental impact of agrochemicals
and their global use, it is necessary to find efficient ways
to minimize their negative impacts. The ideal result would
be the complete mineralization, obtaining nontoxic simple
compounds. Conventional methodologies as adsorption of
pesticides, biodegradation, ozonation, and chlorination
were used in natural environmental media, although the
results were rather discouraging. Methods based on the
utilization of light radiation as the source of energy were
used as an alternative to conventional methods. They are
based on the use of natural solar light or an external ultra-
violet (UV) light, like Xe or Hg lamps. These methods
include direct and indirect photolysis as well as other more
complex treatments like photolysis combined oxidants,
photo‐Fenton processes, photo‐catalysis, photosensitized
oxidation, and photoelectrocatalytic oxidation.[5]
The most used insecticide in Argentina is chlorpyrifos
(O,O‐diethyl
O‐(3,5,6‐trichloro‐2‐pyridinil)‐phosphoro-
thioate),[6] an organophosphorus compound classified as
moderately hazardous (class II) by the World Health
Organization.[7]
Chlorpyrifos‐methyl
(O,O‐dimethyl
O‐(3,5,6‐trichloro‐2‐pyridinil)‐phosphorothioate),
(Scheme 1), with similar molecular structure but higher
1
SCHEME 1 Structures of chlorpyrifos‐methyl (1), chlorpyrifos‐
methyl oxon (2), and 3,5,6‐trichloro‐2‐pyridinol (3)

LOBATTO ET AL.
3 of 8
chlorpyrifos, ends in ammonium hydroxide, carbon diox-
ide, and water. In contrast, Žabar et al[28] found by irradi-
ation at 315 nm in an aqueous solution of 3, different
products such as a substituted pyrrol structure with car-
boxylic groups and 5,6‐dichloro‐2,3‐dihydroxypyridine.
The results that we present here include the identifica-
tion of photoproducts of the photolysis of 1, 2, and 3, as
well as the lifetimes associated whit their
photodegradation in aqueous solution.
250 mL were irradiated, and samples were taken at differ-
ent times to be analyzed by 31P NMR. See Data S1 for
more details.
Although we were not able to achieve the complete
isolation of the photoproducts via preparative chromatog-
raphy, the analysis of the different fractions obtained,
either by NMR, GC‐MS, or HRMS allowed us to arrive
at conclusive identifications without mishaps.
2.3 | Experimental analyses
2 | MATERIALS AND METHODS
2.1 | Materials
UV‐Vis spectra were recorded on a Multispec‐1800
Shimadzu using a quartz cell of 1‐cm path length.
Kinetics experiments were followed with the same appa-
Chlorpyrifos‐methyl PESTANAL (1) (FLUKA) and
chlorpyrifos‐methyl oxon (2) (Supelco) were characterized
by 1H, 13C, and phosphorus‐31 nuclear magnetic
resonance (31P NMR), ultraviolet‐visible (UV‐Vis) spectro-
photometry, gas chromatography–mass spectrometry
(GC‐MS) and high resolution mass spectrometry (HRMS).
3,5,6‐Trichloro‐2‐pyridinol (3) (Sigma‐Aldrich) was char-
acterized by 1H and 13C NMR, UV‐Vis spectrophotometry,
GC‐MS and HRMS. Acetonitrile (ACN) (Baker, HPLC
grade) and chemicals were used as received. Water was
purified with a Millipore Milli‐Q apparatus.
1
ratus. H, 13C, and 31P NMR spectra were obtained in
CDCl3 at 400, 101, and 121 MHz, respectively, with a
Bruker Avance II 400 spectrometer. The identification of
the photoproducts was conducted with GC‐MS analyses
performed on a Varian Saturn 2200 GC/MS equipment.
The column was a nonpolar phase HP5‐MS from Agilent
(95% dimethylpolysiloxane‐5% phenyl), 30 m long, and
with an internal diameter of 0.25 mm. The elution gas
was Helium with a flux of 1 mL min−1. The injector
and ion trap temperatures were 250°C and 200°C, respec-
tively, the oven heating ramp was 15°C min−1 from 80°C
up to 280°C, and the interface temperature was 250°C.
The pressure in the MS instrument was 10−5 Torr, pre-
cluding ion‐molecule reactions from taking place, and
MS recordings were made in the electron ionization mode
(EI) at 70 eV with an emission current of 10 μA and a
maximum ionization time of 25 000 μs. The mass interval
swept ranged from 40 to 650 m/z. HRMS were recorded
with a Bruker, Micro TOF Q II equipment, operated with
an ESI source in (positive/negative) mode, with use of
nitrogen as nebulizing and drying gas and sodium for-
mate (10 × 10−3 M) for internal calibration.
2.2 | Irradiation methods
Irradiation was conducted using four low pressure mer-
cury lamps (Philips G6T5, 6W) emitting at 254 nm, placed
inside a metal box. The temperature inside the box when
all the lamps were on was 36°C. A 1‐cm path length
quartz cuvette or a round‐bottom quartz flask (250 mL)
sealed with Teflon caps were used for the different
experiments.
For the kinetics measurements, solutions of 1, 2, and 3
(2 × 10−5 M) in 10% ACN/H2O were poured separately in
the 1‐cm quartz cuvette and irradiated at 254 nm. The rel-
ative changes of absorbance vs time data were fitted with
a simple exponential function.
For product analysis, air equilibrated solutions of 1
(51.7 × 10−3 M), 2 (3.7 × 10−3 M), or 3 (52.4 × 10−3 M)
were poured separately in the 1‐cm quartz cuvette and
irradiated at 254 nm using pure ACN because of solubil-
ity issues. In the case of 1 and 2, the irradiation time
was 235 minutes while only 30 minutes were needed for
3. In the absence of oxygen (N2 bubbled solutions), solu-
tions of 1 (53.8 × 10−3 M) or 2 (15.0 × 103 M) in ACN
were irradiated at 254 nm for 240 minutes. The resultant
solutions were analyzed by GC‐MS and HRMS. Addition-
ally, rather dilute solutions of 1 (1.04 × 10−3 M) and 2
(7.47 × 10−4 M) in a round‐bottom quartz flask of
3 | RESULTS AND DISCUSSION
3.1 | Photoproducts analyses
Natural environmental degradation, as well as bulk
detoxification processes generally occur in water bodies.
In this medium, the solubility of the studied compounds
is rather low. For this reason, in laboratory assays, pure
ACN was used. In order to identify the photoproducts, 1
and 2 were photolized both, in air saturated samples
and in the absence of oxygen. In the case of 3, it was stud-
ied only in air saturated samples. The crude of the reac-
tions were analyzed by GC‐MS, HRMS, and 31P NMR.
From the results obtained, that we describe below, we

4 of 8
LOBATTO ET AL.
propose the photodegradation pathways depicted in
Scheme 2.
GC‐MS showed the presence of 2, 6, and one of the
three possible isomers of 9 coming from degradation of
1; in the case of 2, we observed the presence of 7 and
two of the three possible isomers of 8.
3.1.1 | Analysis in air saturated samples
Given these results, it seems that there is no special
involvement of dissolved molecular oxygen in the mecha-
nism of degradation, that is, there seems to be no partic-
ipation of reactive oxygen species (ROS) in the
mechanism of degradation. There is still, of course, oxy-
gen available for the P=S to P=O interchange reaction
that takes place when no dissolved oxygen is present.
This supply is believed to come from the water content
of the solvent. It is nevertheless worth to be known that
no special reactions are to be expected because of the
ubiquitous presence of oxygen in the environment.
The analytical techniques used allowed us to get an
almost complete scan of the products of degradation.
Through 31P NMR, the photolysis of 1 yielded 2 and
dimethyl phosphate (4), the latter also detected in the
degradation of 2. Using HRMS, we found compounds
2, 3, 4, O,O‐dimethyl phosphoro thioate (5), O,O‐
dimethyl O‐(dichloro‐2‐pyridinil)‐phosphoro thioate (6)
and O,O‐dimethyl O‐(dichloro‐2‐pyridinil)‐phosphate (7)
in the photolysis of 1; compounds 3, 4, 7, and O,O‐
dimethyl O‐(chloro‐2‐pyridinil)‐phosphate (8) in the pho-
tolysis of 2; but no degradation products were observed
for compound 3 by this technique, which could be taken
as an indication that mineralization could be occurring.
Should this happen, the products would not be detected
because the mass interval of the spectrometer starts
above 50 m/z.
The analysis of the products by GC‐MS showed inter-
esting features since we were able to detect the presence
of the three possible isomers of O,O‐dimethyl O‐(chloro‐
2‐pyridinil)‐phosphoro thioate (9), the three possible iso-
mers of 8, and two of the three possible isomers of
dichloro‐2‐pyridinol (10), in photolyzed solutions of 1, 2,
and 3, respectively. Besides, in the case of 1, the presence
of 3 and 6 was also observed, and in the case of 2, we
could identify 3 and 7.
3.2 | Irradiation with UV light
In order to assess whether the reaction observed only
depends on the absorption of light, one experiment was
run in the dark at 36°C, the temperature inside the box
when the lamps are irradiating. No reaction was observed
by UV‐Vis spectrometry up to 900 minutes indicating that
there are no thermal contributions.
A solution of 1 (2 × 10−5 M) in 10% ACN/H2O in the
quartz cuvette of 1 cm path length placed inside the metal
box was irradiated at 254 nm for a total of 350 minutes.
The UV‐Vis spectrum of the solution was taken before
irradiation and at different irradiation times. The insecti-
cide has two absorption bands at 229 and 289 nm. Upon
irradiation, both bands decreased indicating its consump-
tion (Figure 1A). When a rather concentrated solution of
1 (9.5 × 10−5 M) in pure ACN was irradiated during
100 minutes, the two absorption bands disappeared
(attributed to the consumption of 1), and one new band
3.1.2 | Analysis in the absence of oxygen
By HRMS we found compounds 2, 3, and 6 in the photol-
ysis of 1, and compounds 3 and 7 in the photolysis of 2.
SCHEME 2 Proposed
photodegradation pathways of 1

LOBATTO ET AL.
5 of 8
FIGURE 1 Spectra of 1 at different irradiation times. A, in 10% acetonitrile (ACN)/H2O, [1]0 = 2 × 10−5 M, optical path = 1 cm; B, in
acetonitrile (ACN), [1]0 = 9.5 × 10−5 M, optical path = 5 cm
was observed at 288 nm that later grew with continued
irradiation for 290 minutes (attributed to the formation
of 2) (Figure 1B). For these reasons, in order to calculate
the decay for the photodegradation of 1 in 10%
ACN/H2O, only the first points were taken into account,
and the lifetimes we arrived at were 2.59 and 2.27 hours
for 229 and 289 nm, respectively.
Nevertheless, as chlorpyrifos‐methyl oxon (2) and
3,5,6‐trichloro‐2‐pyridinol (3) were found among the
products, and their UV absorption bands lie in close
proximity to the bands of the parent molecule, we per-
formed independent degradation studies of these com-
pounds under the same conditions of the
photodegradation of 1.
The UV‐Vis spectrum of 2 (2 × 10−5 M) in 10%
ACN/H2O shows two absorption bands at 227 and
288 nm; these bands decreased with time as the solution
was irradiated up to 1240 minutes without noticeable
new bands formed (Figure 2). The lifetimes calculated at
the two maxima were around 7.2 hours.
FIGURE 2 Spectra of 2 in 10%
acetonitrile (ACN) at different irradiation
times. [2]0 = 2 × 10−5 M. Optical
path = 1 cm

6 of 8
LOBATTO ET AL.
The UV‐Vis spectrum of 3 (2 × 10−5 M) in 10%
would not be seen through chromatographic techniques
as experimentally proved.
ACN/H2O shows two absorption bands at 239 and
320 nm. After 1 minute of irradiation, these two bands
disappeared, and two new bands were observed at 262
and 348 nm that later decreased with continued irradia-
tion for 16 minutes (Figure 3). From the decay in absor-
bance at these wavelengths, we could estimate a
residence time of 5.4 minutes for the band at 262 nm that
could be attributed to 10 because when exchanging a
chlorine atom by a hydrogen atom in one of the three
positions of the aromatic ring of 3, the maximum wave-
length should change. The residence time for the other
compound resulted of the order of 1.7 minutes.
An analysis of the values obtained shows that the deg-
radation of 3 does not complicate the measurement of the
degradation rate of 1 since it is much faster, and the prod-
ucts do not absorb in the region of 1. In the case of 2, the
degradation rate is of the order (actually it is slightly
slower) than that of the parent molecule, and thus it
could contaminate the value if no care is taken when
determining the degradation rate.
3.3 | Photodegradation pathway
Andre et al[29] studied the photolysis of pyridine in
aqueous solution with a germicidal lamp. They observed
the disappearance of the band corresponding to pyridine
(λmax 250 nm) and the formation of the compound 5‐
amino‐2,4‐pentadienal (λmax 360 nm) over time. The
band observed at 348 nm in the photolysis of 3
(Figure 3) shows the same profile as that of 5‐amino‐
2,4‐pentadienal and resembles the characteristic n‐π*
enamine aldehyde transition indicative of the opening
of the pyridine ring.[29] The difference of the maxima of
absorption might be because of the fact that our com-
pound has substituents in the ring of the pyridine. The
disappearance of this band might indicate the existence
of a route to the mineralization of 3, whose products
The experimental evidence led us to propose the
photodegradation pathway shown in Scheme 2, which is
also consistent with previous results in the literature.
Compounds 2, 3, 4, and 5 were found in the atmospheric
degradation[3] of 1. Among the products of the
photodegradation of chlorpyrifos, Slotkin et al[23] found
3, the diethylated analogous of 2, 4, and 5 and 3,6‐
dichloro‐2‐[pyridinyl‐O, O‐ethyl] thiophosphate, an anal-
ogous of 6. Devi et al[24] proposed the formation of
chlorpyrifos‐oxon and 3 by photocatalytic degradation of
chlorpyrifos; they also proposed the formation of 10 from
3 in the reaction medium, and that the final products of
the decomposition of 3 were ammonium hydroxide,
FIGURE 3 Spectra of 3 in 10%
acetonitrile (ACN) at different irradiation
times. [3]0 = 2 × 10−5 M. Optical
path = 1 cm

LOBATTO ET AL.
7 of 8
TABLE 1 Parameters regulated to some species of animals according to the Pesticide Properties Data Base[30]
Ecotoxicology
1
2
3
Mammals (rat)—acute oral LD50 (mg kg‐1)
Birds (Colinus virginianus)—acute LD50 (mg kg‐1)
Fish (Oncorhynchus mykiss)—acute 96 hour LC50 (mg L‐1)
Aquatic invertebrates (Daphnia magna)—acute 48 hour EC50 (mg L‐1)
5000a (low)
869b (moderate)
34.75c (high)
>0.0024d (high)
‐
3129a (low)
>2000a (low)
923a (moderate)
0.41a (moderate)
0.0006a (high)
>12.6a (moderate)
10.4a (moderate)
aEU Regulatory & Evaluation Data as published by EC, EFSA (RAR, DAR & Conclusion dossiers), EMA (eg) EU Annex III PIC DGD (For example, see http://
ec.europa.eu/sanco_pesticides/public/index.cfm or EFSA Scientific Publications https://www.efsa.europa.eu/en/publications).
bChemID Online Databases (See http://chem.sis.nlm.nih.gov/chemidplus/) /IPCS INCHEM (See http://www.inchem.org/).
cPeer Reviewed Scientific Publications.
dU.S. EPA ECOTOX Database (see http://cfpub.epa.gov/ecotox/) /U.S. EPA Pesticide Fate Database (See http://cfpub.epa.gov/pfate/home.cfm) /Miscellaneous
WHO documents.
carbon dioxide, and water, that is, complete mineraliza-
tion. Meanwhile, Farner Budarz et al[21] assumed that
chlorpyrifos‐oxon and 3 are produced in the primary pho-
todissociation of chlorpyrifos and studied only the kinet-
ics of disappearance.
and 2, respectively. Experiments conducted in pure
ACN allowed us to identify essentially all the photoprod-
ucts. These include 2, 3, the phosphate 4, and
thiophosphate 5 and compounds where one or two chlo-
rine atoms are removed from 1, 2, or 3.
Although, we could not make a total quantification of
the products, by following the photodegradation of 1 by
31P NMR, we could observe that after 416 minutes of irra-
diation, the most abundant P containing product was
compound 4 (Figure S18); therefore, if around 10% of
the reaction goes through the direct formation of 2, as
roughly quantified from 31P NMR, it seems necessary to
have also a direct sulfur‐oxygen interchange for the 90%
coming from 5 to form compound 4, a reaction path that
remains open even in the absence of dissolved oxygen.
Although the most abundant product indicates the break-
ing of a C‐O bond, dechlorination reactions are also
important and take place both from the reactant itself
as well as from the pyridine ring as seen by the products
formed.
Compounds 1, 2, and 3 are described in the Pesticide
Data Base of the University of Hertfordshire, and some
of their parameters for mammals, fish, birds, and aquatic
invertebrates are listed[30] in Table 1. It is observed that
the toxicity of 1 is low in mammals, moderate in birds
and fish, and high in aquatic invertebrates. For 2 is mod-
erate in mammals and high in birds and fish; and for 3 is
low in mammals and birds and moderate in fish and
aquatic invertebrates.
Regarding compound 4, we could not see the forma-
tion of phosphoric acid as postulated in the paper by
Borras et al.[3] In that publication, they did not provide
detailed mechanisms, so we believe that in our system,
there will probably be an available channel that provides
the hydrogen interchange more easily since we have an
ACN solution.
Compounds 3, 4, and 5 are products of the metabolism
of chlorpyrifos as well as of its environmental degrada-
tion. They are used as biomarkers of exposure to the
insecticide by measuring its concentration in urine. In
experiments conducted by Timchalk et al[31] where some
rats were administered equal molar doses of chlorpyrifos,
3, 4, or 5, observable cholinergic effects were noted only
in those animals treated with chlorpyrifos. This can be
taken as an indication that 4 and 5 are less toxic than
chlorpyrifos. We could identify compound 10 as the only
product after irradiation of 3; thus, considering the results
of Devi et al,[24] we think that mineralization to ammo-
nium hydroxide, carbon dioxide, and water could occur.
Under the light of these results, we believe that, irradi-
ation with UV light might be a useful method for detoxi-
fication of chlorpyrifos‐Me solutions.
A coarse comparison about these different species let
us to conclude that a detoxification process seems to pose
no risk to the environment.
FUNDING INFORMATION
This research was supported in part by Consejo Nacional
de Investigaciones Científicas y Técnicas. Argentina
(CONICET) (PIP 112‐21501‐00242 CO), and Universidad
Nacional de Córdoba, Argentina (SECyT 366/2016 and
113/17). V. L. L. is a CONICET fellow, and G. A. A. and
E. I. B. are members of the research career, CONICET
(Argentina).
4 | CONCLUSIONS
The photodegradation at 254 nm of 1, 2, and 3 was stud-
ied. The kinetics of the degradation in 10% ACN/H2O
presented an average value of 2.38 and 7.2 hours for 1

8 of 8
LOBATTO ET AL.
[16] W. L. Dilling, L. C. Lickly, T. D. Lickly, P. G. Murphy, R. L.
ORCID
McKellar, Environ. Sci. Techno 1984, 18, 540.
Virginia L. Lobatto https://orcid.org/0000-0002-4242-2231
Gustavo A. Argüello
8493
[17] M. Kamiya, K. Kameyama, Chemosphere 1998, 36, 2337.
https://orcid.org/0000-0002-3044-
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