Lányi_K_PhD_theses_2002

Gas chromatographic and gas chromatographic – mass
spectrometric study of the photodegradation processes of
nitrogen-containing herbicides
PhD theses
Ms. Katalin Lányi
Supervisors:
Dr. Zoltán Dinya
Dr. Lajos Papp
University of Debrecen
Debrecen, 2002

2
1. INTRODUCTION AND OBJECTIVES
The chemistry of pesticides has evolved from some simple compounds like the arsenic,
lead and fluoride-compounds, and some naturally occurring organic materials, like pyrethrins
and rotenone, to the wide range of compounds used in these days covering almost everything
from the broad-spectrum effects to the very specific plant protection. In line with the
unexpected spread of new compounds, the demand arose for controlling the utilisation and
distribution of pesticides. After the pesticide gets into the soil, various physical and physico-
chemical processes, and chemical and biochemical reactions determine its fate.
Photodegradation processes are involved in dissipation of pesticides in water, soils and
plants. The relevance of photodegradation processes in the fate of the herbicides applied to the
soil is due to their high water solubility and moderate persistence, which indicate that it might
be found as an environmental contaminant in agricultural runoff waters, where photolysis
processes play an important role. Triazines, ureas and thiolcarbamates are among the most
used herbicides worldwide. Since they can be found in many environmental compartments,
their fate in ecosystems and the characterisation of their degradation pathways are to be
determined.
The aim of this study was to assess the characteristics of phototransformation processes of
nitrogen-containing herbicides (triazines: atrazine, cyanazine, terbuthylazine, and terbutryn;
ureas: diuron, fenuron, chloroxuron, and methabenzthiazuron; and thiolcarbamates: buthylate,
cycloate, EPTC, molinate, vernolate) in vivo. I aimed to determine the degradation rate of
individual pesticides, to compare the degradation rates of compounds belonging to the same
group in order to assess the structural effects, to find connection between the rate of
degradation and the chemical structure of chemicals, and to identify the degradation products.
Different additives were used to model the possible degradation pathways occurring within
natural circumstances under the sunlight. These additives were photosensitisers (H2O2, TiO2),
as well as, materials naturally occurring in the soils (montmorrilonite, humic acid). In order to
gain detailed information about the photoreaction taking place under these circumstances, I
conducted experiments for studying the charge transfer processes taking place in the presence
of benzophenone.

3
2. MATERIALS AND METHODS
The pesticide standards were dissolved in dichloro-methane, and illuminated by a high-
pressure mercury vapour lamp in a 1-cm silica cuvette equipped with Teflon cap. The
degrading energy was 125 W, the degradation of triazines was also conducted by a 15-W
mercury vapour lamp, in order to gain information on the effect of illuminating energy. By
regular intervals samples were taken from the reaction vessel, and the degradation process
was followed by consecutive GC measurements in order to determine the amount of
degradation products and the original substance. The completely degraded mixtures were
analysed by GC-MS in order to determine the chemical structure of the most important
degradation products.
3. NEW SCIENTIFIC RESULTS
3.1 Chemical structure of the main degradation products
The most significant processes of photodegradation of triazines are the partial or complete
loss of side-chains, or rather the substitution of the heteroatom-containing side-chain to
hydroxyl-group (figure 1.). Besides the consecutive processes, loss of the different side chains
takes also place parallely, thus, different metabolites will be formed having mixed side-
chains, until the cyanuric acid and 2-amino-4,6-dihydroxy-1,3,5-s-triazine formed by loosing
all the side-chains. The presence dimer products, which could be detected during the
degradation of all triazines proves the radical character of processes occurring during the
photodegradation.
The degradation rank of triazines was the following: terbutryn – cyanazine – atrazine –
terbuthylazine (figure 2.). The average degradation rate of individual compounds can be seen
in the table 1.

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Figure 1 - General photodegradation pathways of triazines
N
N
N
R3
NHNH
R1 R2
N
N
N
R3
NH2NH
R1
N
N
N
OH
NHNH
R1 R2
N
N
N
NH
NH
R3
R2
N
N
N
NH
NH
R3
R2
OHHO
OH
N
N
N
OHHO
R3
N
N
N
N
N
N
R3
NHH2N
R2
OHHO
NH2
N
N
N
Figure 2 - Degradation pattern of triazines at 125 W degrading energy
0,0
10,0
20,0
30,0
40,0
50,0
60,0
70,0
80,0
90,0
100,0
0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 110 115 120
Photodegradation (hours)
%
terbutryn
cyanazine
terbuthylazine
atrazine
Increasing the degradation energy (15 W → 125 W) has raised the degradation rate by 2-5
on the one hand, on the other hand, the chlorine containing metabolite – which appeared also
in the completely degraded mixture during the low-energy experiments – has completely
disappeared from the mixture, thus, the increased degrading energy favours the formation of
less dangerous, nature identical metabolites.

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Table 1 - Connection between the degradation rate of triazines and the degradation
energy
Average degradation rate (v), if the degradation energy is
15 W 125 WCompound
µg·ml-1
·h-1
rel.*
µg·ml-1
·h-1
rel.*
v125W/v15W
atrazine 20,6 2,73 45,4 1,30 2,20
cyanazine 17,1 2,28 81,5 2,34 4,77
terbuthylazine 7,6 1,00 34,8 1,00 4,58
terbutryn 63,6 8,48 280,0 8,04 4,40
*
: compared to the degradation rate of terbuthylazine, which has the slowest degradation
Loss and oxidation of the alkyl-chains are the dominant processes also during the
degradation of ureas (figure 3.). Besides that, the substitution of halogen atom to a hydroxyl-
group, and hydroxylation of the aromatic ring are the secondary processes. The high ratio of
dimer products suggests that in the photodegradation of ureas the radical processes dominate.
The well known carcinogenity of azo-compounds assigns outstanding importance to this fact.
Figure 3 - General photodegradation pathways of ureas
R3
NH N
R2
R1
O
R3'
NH NH2
O
(HO)n
H2N NH
R1
O
H2N N
R2
R1
O
R3
NH N
R2'
R1'
O
HO
OH
R3
NH NH2
O
R3
R2
NH NH
R2
O
R3
NH NH
R2
O
N N R3R3
The degradation rate of ureas was the following: methabenzthiazurone – chloroxuron –
fenuron – diuron (figure 4.). The average degradation time of individual compounds can be
seen in the table 2.

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Table 2 - Average degradation rates of ureas
Average degradation rate (v)Compound
µg·ml-1
·h-1
rel.*
diuron 31,0 1,00
fenuron 55,7 1,80
chloroxuron 164,5 5,31
methabenzthiazurone 766,7 24,73
*
: compared to the degradation rate of diuron, which has the slowest degradation
Figure 4 - Degradation pattern of ureas at 125 W degrading energy
0,0
10,0
20,0
30,0
40,0
50,0
60,0
70,0
80,0
90,0
100,0
0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170
Photodegradation (hours)
%
diuron
fenuron
chloroxuron
methabenzthiazuron
In the case of thiolcarbamates, the most frequent processes are the α- and β-oxidation of
alkyl-groups connecting to the nitrogen atom. In the most cases, the N-formyl and N-
dealkylated products were identified in the degradation mixture (figure 5.). The thiol-
derivatives were formed in very small amounts. Vernolate is the only studied thiolcarbamate
having thiopropil-group instead of thioetil connected to the carbonyl-C. The N-dealkylation
and oxidation of the CH2-group connected to the nitrogen occur in this case, too. It can be
stated based on the experiments, that the tioalkyl-group shows fair stability under the
circumstances of photodegradation. Its partly or completely degraded products can not be
detected, or represent only very small part of the mixture.

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Figure 5 - General photodegradation pathways of thiolcarbamates
R2
N
R3
C S R1
O
N
C
C S R1
O
R3'
O
R2
NH C S R1
O
R2
R2
N
R3'''
C S R1
O
OHC
R2
N
R3
C S R1'
O
CHO
R2
N
R3
C SH
O
R2
N
CH2
C S R1
O
C
R3''
O
R2
N
OHC
C S R1
O
The degradation rate of thiolcarbamates was the following: butylate – EPTC – vernolate –
molinate – cycloate (figure 6.). The average degradation time of individual compounds can be
seen in the table 3.
Table 3 - Average degradation rates of thiolcarbamates
Average degradation rate (v)Compound
µg·ml-1
·h-1
rel.*
butylate 625,0 2,50
cycloate 250,0 1,00
EPTC 438,5 1,75
molinate 277,8 1,11
vernolate 312,5 1,25
*
: compared to the degradation rate of cycloate, which has the slowest degradation
In the case of experiments with additives, the charge transfer complex formed between the
herbicide molecule and benzophenone is expected to promote the degradation, since it
increases the efficiency of energy transfer. The results of experiments supported this
expectation, since the degradation methabenzthiazurone was the fastest in the presence of
benzophenone. H2O2 can have two different effects: it initiates the formation of hydroxyl-
radicals, but it also consumes them. At lower concentrations the earlier process dominates, at
higher concentrations the latter. The H2O2 concentration used in my experiments (70 µl·ml-1
)
belongs clearly to the second category.

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Figure 6 - Degradation pattern of thiolcarbamates at 125 W degrading energy
0,0
10,0
20,0
30,0
40,0
50,0
60,0
70,0
80,0
90,0
100,0
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Fotobontás (óra)
%
butylate
cycloate
EPTC
molinate
vernolate
On the score of this, it can be stated that – since radical processes play important role in the
photodegradation of studied herbicides – presence of radical-trap compounds – especially in
higher amounts – can significantly increase the residence time of these xenobiotics in the
environment.
TiO2, montmorrilonite and humic acid sensitize by adsorbing the herbicides on their
surface, and loosening their bonds. The various, composite aromatic compounds of humic
acid, as polyphenols, organic acids, etc. – similarly to the benzophenone – can also form
charge transfer complexes with the organic compounds, further sensitizing them for the
photodegradation. At the same time, these additives – since they form heterogeneous system
with the sample – can also have inhibiting effect, since the grains can absorb the light, thus
decreasing the amount of degrading energy on the examined molecule. The overall effect
depends on the compositions of examined compound, montmorrilonite, or humic acid, and
since these latter two are multiparameter attributes, it is hard to predict the effect to be
experienced.
The overall effect of humic acid utilised in my experiments was the moderate inhibition,
thus, the adsorption effect exceeded the sensitizing effect. Since the humic acid – herbicide
ratio occurring in the soils falls to the same magnitude as utilised in this experiments,
presumably this kind of effect can take place in the soils, too. TiO2 and montmorrilonite have

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slightly increased the rate of degradation, however, in the case of TiO2 this effect can not be
considered significant (figure 7.).
Figure 7 – Photodegradation of methabenzthiazurone in the presence of various
additives
0,000
0,150
0,300
0,450
0,600
0,750
0,900
1,050
1,200
0 0,3 0,6 0,9 1,2 1,5 1,8 2,1 2,4 2,7 3 3,3 3,6 3,9 4,2
Óra fotobontás
MBTA[mg·ml-1
]
hydrogen-peroxyde
humic acid
control
charge transfer complex
montmorrilonite
titanium-dioxyde
The experiments carried out with additives led to an other important consequence: these
materials changed not only the time-course of degradation, but there was also a dramatic shift
in the ratio of metabolites. In the presence of additives, the emphasis is on the metabolites of
greater size instead of the smaller compounds.
The experiments carried out without additives suggested a reassuring picture that the
studied herbicides have dominantly natural identical metabolites with low ecotoxicology. The
ratio of metabolites representing high toxicity, carcinogenity or other kind of risks was
infinestimal, or they were not stable enough for remaining in the reaction mixture. However,
the experiment with the additives showed clearly, that the natural or artificial additives can
shorten the time of degradation, but their presence can lead to the formation and persistence
of less degraded, toxic materials more extraneous for the environment.
Moreover, under natural circumstances, many other processes can occur in the soil, on the
effect of microbiological processes N-oxidation can occur on the nitrogen atom of the studied
compound. On the one hand, this leads directly to the formation of nitroso-compounds, which

10
have high toxicity and carcinogenity. The nitrite- and nitrate-ions of soil can react with these
nitroso-compounds, thus forming N-nitroso-amines, which are even more toxic and
carcinogen, that the nitroso-compounds. In the European Union the quantity and quality of N-
nitroso-amines shall be strictly checked in food and raw materials. Resulting from the tight
connection between the plant and the soil, the measurement of N-nitroso-amines in the soils is
inevitable. Since these processes are dependent on the soil type, local level investigations
shall be carried out.
In the case of these kind of knowingly utilised xenobiotics – like the pesticides – in vivo
experiments are required for analysing the environmental effect (water, soil, and
microorganisms). since the in vitro experiments leave open too much question about the real
fate of the compounds in the environment. Since these, this research shall be continued in
order to gain more detailed information about the transformation, reactions, metabolites, and
derivatives of the nitrogen containing herbicides.

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Publication of Ms. Katalin Lányi (born Katalin Varró):
Referenced publications:
1. Z. Dinya, Gy. Litkei, J. Jekő, K. Varró, S. Antus: GC-LC-MS Studies of the Extracts of
Buds of Populus Nigra. In: Flavonoids and Bioflavonoids 1995 [Proceedings of the
International Bioflavonoid Symposium. 9th
Hungarian Bioflavonoid Symposium] (Editors: S.
Antus, M. Gábor and K. Vetschera) Akadémiai Kiadó, Budapest, 1996
2. Z. Dinya, F. Sztaricskai, E. Horváth, J.B. Schaág, K. Varró: Studies of the components of
Desertomycin complex by means of electrospray and MALDI mass spectrometric techniques.
Rapid Communications in Mass Spectrometry Vol. 10. 1439-1448 (1996)
3. Katalin Lányi; Enikő Varga: Elaboration and use of a double channel detection ion
chromatographic method in determining ions in aqueous samples. Chromatographia
Supplement, Vol. 51. (2000).
4. Katalin Lányi, Zoltán Dinya: Gas Chromatographic Method for Studying the
Photodegradation Rate of Some Nitrogen Containing Pesticides. Chromatographia (közlés
alatt)
Presentations and other publications:
1. Varró Katalin: Szerves és szervetlen mikroszennyezők meghatározása természetes vizekben
HPLC-s és ionkromatográfiás módszerrel. MSc theses, 1993.
5. Dragan Drinic, Zsuzsanna Flachner, Zigrida Shperlina, Nadya Sozonova, Demi Theodori,
Katalin Varró: The future of international negotiations on Long Range Transboundary Air
Pollution in the light of a Combined Emission Reduction protocol. EPCEM project riport, 1994.
6. Katalin Varró: Literature study on TRE and TIE methods. EPCEM szakmai gyakorlat
riportja az AquaSense BV-nek, Amsterdam, the Netherlends, 1994.
7. Z. Dinya, Gy. Litkei, J. Jekő, K. Varró, S. Antus: GC-LC-MS Studies of the Extracts of
Buds of Populus Nigra. International Bioflavonoid Symposium (9th
Hungarian Bioflavonoid
Symposium), Vienna, Austria, 1995
8. Zoltán Dinya, László Somsák, Erzsébet Sós, Zoltán Györgydeák, Katalin Varró and J-P.
Praly: Stereochemical effects in the EI and CI mass spectra of anomerically disubstituted

12
monosaccharide derivatives. 5th
International Conference on Chemical Synthesis of
Antibiotics and Related Microbial Products, Debrecen, 1996
9. Z. Dinya, L. Somsák, E. Sós, Z. Györgydeák, P. Benke and K. Varró: Stereochemical
effects in the spectra of anomerically disubstituted monosaccharide derivatives. 14th
International Mass Spectrometry Conference, Tampere, Finland, 1997
10. Lányi Katalin, Lányi István: Helyszíni mérések jelentősége és lehetőségei vizes
környezetben. Alföldi Tudományos Tájgazdálkodási Napok, Mezőtúr, 1997
11. Katalin Lányi, Enikő Varga: Double channel detection ion chromatographic method for
determination of ions in aqueous samples. Advances in Chromatography and Electrophoresis
(ACE) Symposium, 1998, Szeged
12. Lányi Katalin, Dinya Zoltán: Oxigéntartalmú heterociklusos vegyületek fragmentációs
sémájának tanulmányozása. 42. Magyar Spektrokémiai Vándorgyűlés, 1999, Veszprém
13. Katalin Lányi; Enikő Varga: Elaboration and use of a double channel detection ion
chromatographic method in determining ions in aqueous samples. Balaton Symposium ’99 On
High-Performance Separation Methods, 1999, Siófok
14. Katalin Lányi; Zoltán Dinya: Gas chromatographic - mass spectrometric method for
studying the photodegradation processes of some commonly used pesticides. Balaton
Symposium ’99 On High-Performance Separation Methods, 1999, Siófok
15. Lányi Katalin: A novel approach for studying the mixability of various pesticides in order
to promote new plant growing technologies. II. Alföldi Tudományos Tájgazdálkodási Napok,
1999, Mezőtúr
16. Lányi Katalin, Dinya Zoltán: Nitrogén tartalmú herbicidek fotodegradációs folyamatainak
vizsgálata GC-MS módszerrel. 44. Magyar Spektrokémiai Vándorgyűlés, 2001, Baja
17. Katalin Lányi, Zoltán Dinya: Gas Chromatographic Method for Studying the
Photodegradation Rate of Some Nitrogen ContainingHerbicides. Balaton Symposium ’01 On
High-Performance Separation Methods, 2001, Siófok

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