“ ' if?“ u - 1' .1 N» an} 9' .6 ma i' '. 3" _‘ '7... - in $25“ '33:}? & Ali-Cur"; V 'S’am .._.-.. 33% d t ‘r \ -_.....~._-- -——- -—---v ”vi—Mm“ .~A»~...W‘ O This is to certify that the dissertation entitled PHOTOCHEMISTRY OF FOUR SYMMETRYCAL TRIAZINES ON CLAY SURFACES presented by NGUESSAN ADRIAN TIBEBI has been accepted towards fulfillment of the requirements for MASTERS _ ENTOMOLOGY degree in %m{,. M Major pflsscr Date £67115; /74PJ MSU is an Affirmatiw Action/Equal Opportunity Institution 0—12771 )V1SSI_J RETURNING MATERIALS: Place in book drop to ”3353155 remove this checkout from _;—. your record. FINES will be charged if book is returned after the date stamped below. PHOTOCHEMISTRY OF FOUR SYMMETRICAL TRIAZINES 0N CLAY SURFACES By N'Guessan Adrian Tibebi A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Department of Entomology Pesticide Research Center 1983 ABSTRACT PHOTOCHEMISTRY OF FOUR SYMMETRICAL TRIAZINES 0N CLAY SURFACES N'Guessan Adrian Tibebi The photodegradation rate constant and half-life of four s-triazine herbicides at two different concentrations (0.13 and 0.23 uQ/cmz), two pH's (pH4 and pH7.8) and on three different clay surfaces (montmorillonite, attapulgite and kaolinite) were determined. The rate constants varied from 12.50 sec"1 x 10'7 (trietazine. 0.23 ug/cm2 on kaolinite at pH7 8) 1 to 63.75 sec' x 10'7 (simetryne, 0.13 ug/cm2 on montmorillonite at pH4) for the easily extractable fractions of the herbicides. 1 The rate constants ranged from 0.17 sec' x 10'7 (trietazine, 0.23 1 x 10'7 (simetryne, 0.13 ug/cm2 on kaolinite at pH7 8) to 0.63 sec— HST/cm2 on montmorillonite at pH4) for the tightly bound fraction. The total rate constants were approximately the same as those of 1 x 10'7 l the easily extractable portion, ranging from 12.70 sec" (trietazine. 0.23 ug/cm2 on kaolinite at pH708) to 64.40 sec" x 10'7 (simetryne, 0.13 ug/cm2 on montmorillonite at pH4). The rate constants decreased when the concentration of the s-triazines on the clay surfaces reached a certain level. They were faster at pH4 than at pH7.8 and decreased in the order: simetryne > simazine > atrazine > trietazine. The half-life times (t l/2) increased when the pH's of the clays decreased. They were faster on montmorillonite followed by attafipulgite, and kaolinite and decreasedin the order:.trietazine‘>»atrazine > simazine > simetryne. The mechanism for the variation of the rate constant is discussed from 3 viewpoints: 1) The thickness of the herbicide molecular layers on the clay surfaces. 2) The effect of molecular structure, and 3) The effect on absorption and adsorption of the protonated s-triazine in acidic condition. There were no significant relationships between extinction coefficient in 295-305 nm wavelength range and the photodegradation rates of the four s-triazines. ii It I ACKNOWLEDGEMENTS I extend my sincerest gratitude to my adivsor Dr. Mathew Zabik for his patience, and for giving me a chance to use his knowledge and experience to further my career and intensify my scientific curiosity. I would also like to thank the Government of Ivory Coast for its financial support, which has, in large part, allowed me to come this far. I would also like to extend my appreciation to Dr. Richard Leavitt for his help and encouragement, and Drs. George Bird, Donald Penner, and Stephen Boyd for serving on my graduate committee. I will always be greatful to my parents, Tibe Alphonse and Bouzie Henriette for their total sacrifices and understanding. Finally, it is with a warm heart and smile that I thank all of my special friends; Michelle Watkins, Bob Schultz, Bob Kon and Lester Geissel for special things we shared together. iv I! I' 1:9.ptl II TABLE OF CONTENTS Pages ACKNOWLEDGEMENTS .......................... iv LIST OF TABLES ........................... vii LIST OF FIGURES .......................... viii CHAPTER I: INTRODUCTION & HISTORICAL ............... 1 CHAPTER II: EXPERIMENTAL Equipment and reagents Chemicals .......................... 14 Clay_samples ......................... 14 Solvent ........................... 14 Photochemical equipment ................... 14 Glass reaction plates .................. .. 14 pH meter and establishment of pH4 and pH7.8 ......... 16 Analytical equipment .................... 16 Experimental Procedure Preparation of clay thin layer chromotography (TLC) ..... 16 Pesticide application .................... 17 Study % recovery ....................... 19 CHAPTER III: RESULTS AND DISCUSSION Effect of molecular structure and functional groups of s-triazines on photodegradation rates .................... 21 The influence of concentrations on the photodegradation ..... 22 Page Photodegradation rates as influenced by different type of Plays at p”4 and pH7 8 ..................... 23 Relationship between the photodegradation rates and the UV absorbance of the four s-triazines ............... 24 CHAPTER IV: CONCLUSIONS ..................... 66 LITERATURE CITED ......................... 67 vi Table II III IV VI VII VIII IX LIST OF TABLES Page Authentic s-triazines and Photoproducts .......... 4 Characteristics of Some Common Clay Minerals ....... 10 Structure and Constituents of 3 Clay Minerals ....... 15 Recovery of Four s-triazines from 3 Different Clay samples at pH4 a"d pH7.8 ................. 20 S-triazines Analysis Parameters .............. 25 Total Photodegradation Rate Consta’ntsfor Four s-triazines on Clay Surfaces at pH7.8 of (0.13 and 0.23 ug/cmz) Herbicides ........................ 26 Total Photodegradation Rate Constants for Fourrs-triazines on Clay Surfaces at pH4 of (0.13 and 0.23 ug/cmz) Herbicides ........................ 27 Total Photodegradation Half-life for Four s-triazines on Clay Surfaces at pH7.8 and pH4 and at Plate Concentration of 0.13 pg/cm2 ........................ 28 Absorbance and Extinction Coefficient Values for Four s-triazines in MEOH .................... 29 vii Figure 10 11 LIST OF FIGURES Page Total Photolysis of thin film glass plate of montmorillonite pH7.8 of (0.23 ug/sz) s-triazines ............. 31 Total Photolysis of thin film glass plate of attapulgite pH7.8 of (0.23 ug/cmz) s-triazines ............. 33 Total Photolysis of thin film glass plate of kaolinite pH7.8 of (0.23 ug/cmz) s-triazines ............. 35 Total Phogolysis of thin film glass plate of montmorillonite pH4 of (0.23 ug/cmz) s-triazines .............. 37 Total Photolysis of thin film glass plate of kaolinite pH4 of (0.23 ug/cmz) s-triazines .............. 39 Total Photolysis of thin film glass plate of attapulgite pH4 of (0.23 ug/cmz) s-triazines .............. 41 Total Photolysis of thin film glass plate of montmorillonite pH7.8 of (0.13 ug/cmz) s-triazines ............. 43 Total Photolysis of thin film glass plate of kaolinite pH7.8 of (0.13 ug/cmz) s-triazines ............. 45 Total Photolysis of thin film glass plate of attapulgite pH7.8 of (0.13 ug/cmz) s-triazines ............. 47 Total Photolysis of thin film glass plate of montmorillonite pH4 of (0.13 ug/cmz) s-triazines .............. 49 Total Photolysis of thin film glass plate of attapulgite pH4 of (0.13 ug/cmz) s-triazines .............. 5l viii Figure 12 13 14 15 16 17 18 Total Photolysis of thin film glass plate of kaolinite pH4 of (0.13 ug/cmz) s-triazines ............. UV absorption of 20 ppm simetryne in MEOH ......... UV absorption of 20 ppm atrazine in MEOH ......... UV absorption of 20 ppm simazine in MEOH ......... UV absorption of 20 ppm trietazine in MEOH ........ UV absorption of 2 ppm simazine in MEOH at pH7.8 ..... UV absorption of 2 ppm simazine in MEOH at pH4.’ ..... ix Page 53 55 57 59 61 63 65 CHAPTER I: INTRODUCTION & HISTORICAL Triazine herbicides are important means of controlling weeds afflicting man's food crops. It is well understood that with the growing world food crises, triazine herbicides continue to be vital in the production of food and for the protection of man and animals from starvation. The more man's technology develops, the more important it becomes to study its influence on the environment: on the soil (including clays), water, and air, and on the flora and fauna. This is mainly a matter of public concern, questioning whether or not human habitats will not be changed too much by technology to allow healthy and worthwhile living. The technology for controlling weeds by chemical means instead of by expensive and tiresome mechanical and manual methods is of rather recent origin, especially the sophisticated use of the preventive application of herbicides on the still weed-free clay in the soil. Beneficial as the use of triazine herbicides is, it is not without risk since various types of these chemicals are being introduced into the environment. Introduction of a herbicide into the ecosystem subjects it to a variety of physico-chemical and biological processes which ultimately determine not only its persistence and fate, but also its degradation products. One of the more important environmental aspects that should be taken into account is the effect of sunlight. Irradiation by the sun may lead to various photoprocesses and thus to photoproducts which are different from the parent herbicides in their environmental properties and toxicological significance. The photochemical behavior of a triazine herbicide along with its properties must be viewed in light of its overall interaction with elements of the environment such as clay particles as related to behavior, transport and fate. Knowledge of the dynamics of the photochemistry of triazine herbicides on clay surfaces will lead not only to better understanding of the fate and behavior of chemicals in the clay environment, but will lead to development and improvement in technology for the use of these compounds. It should be mentioned as a factor which influences the various features responsible for safe, efficient, and economical performance of soil applied selective and nonselective herbicides such as: inactivation, positioning and persistence of the herbicide in the soil. Ultraviolet energy causes the chemical alteration of many pesticides under laboratory conditions (Mitchell, 1961). If such photodecomposition were to occur under field conditions the resu1t(s) might be of major importance in determining the environmental stability and agricultural use of these compounds. Evaluation of such naturally occurring photo- products and the investigation of their chemistry, photodegradative rate constants, and pharmacology would be necessary to evaluate the merit of their continued use. Any photochemical reactions in solution or solid adsorbed phases are governed by basic processes divided into two parts that should be understood. The primary photochemical process involves a series of events that start with the absorption of a quantum of radiation by a molecule and ends with the disappearance of that molecule or its conversion back to its initial ground state or to different excited states. The secondary reactions are those non-chemical processes that lead to chemical products. During the primary processes there are usually a variety of ways for molecular degradation or rearrangement. These paths can include formation of free radicals, ions, intramolecular rearrangements, and other excited molecules which may then react in secondary processes to form new products. The nonchemical primary processes include radiative and nonradiative physical processes which lead to a net chemical change. Therefore, the photochemical reaction of many pesticides involves two operations: (1) absorption of energy leading to excited states and (2) the transformation of the various electronically excited states to chemical products. The effects of ultraviolet light on herbicides have been investigated by several researchers. Crosby and Tutass (1966) reported that 2,4- dichlorophenoxycetic acid (2,4-D) decomposed rapidly in the presence of water and natural sunlight to yield 2,4-dichlorophenol, 4-chloro- catechol, 2-hydroxy-4-ch1orophenoxyacetic acid, 1,2,3-benzenetriol, and polymeric humic acids. Rosen and Strusz (1968) found that 3-(p- bromophenyl)-1-methoxy-l-methy1urea underwent a photolysis reaction when exposed to natural sunlight in aqueous solution. The major product was 3-(p-hydroxy-pheny1)-l-methoxy-l-methylurea. Changes in the UV spectra of photolysed solutions and decreases in the phytotoxicity of the unidentified product mixture have been reported (Comes and Timmons, 1965; Jordan et al., 1963, 1965). Jordan et al., 1970, summarized the literature prior to 1970 on s-triazine TABLE I: AUTHENTIC S-TRIAZINES AND PHOTOPRODUCTS 2 ,r A ' Substitution on Triazine Rings at Positions Common 2 4 6 Designation Atrazine Cl NHCZH5 NHiC3H7 I Propaaine C1 NH1C3H7 NH1C3H7 II Sima21ne Cl NHCZH5 NHCZH5 III Trieta21ne Cl NHC2H5 N(C2H5)2 IV Hydroxy-Atrazine 0H NHCZH5 NHiC3H7 V Hydroxy-Propazine OH NHiC3H7 NHiC3H7 VI Hydroxy-Simazine 0H NHC2H5 NHC2H5 VII Hydroxy-Trietazine OH NHCZH5 N(C2H5)2 VIII Atratone OCH3 NHCZH5 NHiC3H7 IX Promometone OCH3 NH1C3H7 NH1C3H7 X Simetone OCH3 NHCZH5 NHCZH5 XI Iodo-Atrazine I NHC2H5 NHiC3H7 XII Iodo-Propazine I NHiC3H7 NHiC3H7 XIII Iodo-Simazine I NHC2H5 NHC2H5 XIV Ametryne SCH3 NHC2H7 NHiC2H7 XV Prometryne SCH3 NHiC3H7 NHiC3H7 XVI Simetryne SCH3 NHC2H5 NHCZH5 XVII NHCZH5 NHCZH5 XVIII NH1C3H7 NHCZH5 XIV NH1C3H7 NH1C3H7 XX photodecomposition. Recently, Plimmer and co-workers studied the photolysis of simazine (III) and simetone (XI) at 220 nm in methonal solution by combined glpc- mass spectrometry. Simazine (III) yielded XI and other methylated products (Plimmer, personal communication). Plimmer, et al., 1969, also reported the conversion of Simetryne (XVII) to (XVIII) as the result of irradiation of the solid material (Table I). Pape and Zabik (1970, 1972), in recent investigation have demon- strated the generality of the photochemical solvolysis of 2-chloro-s- triazines in alcohols, water between 253.7 and 300 nm. Photolysis of I, II, and III in methanol and water yielded XI, X, XI and V, VI, VIII in hydrocarbon, alcoholic, or aqueous solution resulted in the formation of the 4,6-di(alkylamino)-s-triazines XIX, XX and XVIII, respectively (Table I). In early studies, Jordan et a1. (1964) adsorbed simazine [2-chloro- 4,6-bis(ethylamino-s-triazine)], atrazine [2-ch1oro-4-ethylamino-6- isoproxylamino-s-triazines] and ametryne [2-methylthio-4-ethylamino- 6-isoproxylamino-s-triazine], on filter paper which was then exposed to ultraviolet light and sunlight. The ultraviolet spectrum showed progressive changes indicating the photodecomposition of these 5- triazine herbicides. The photodegradation of the halogenated triazine herbicides involve the replacement of the halogen with the solvent molecule followed by dealkylation reactions as shown by Plimmer and Kingebiel (1968) and Pape and Zabik (1972a). Apparently the use of 254 nm and 300 nm ultraviolet radiation affects more the reaction rate than the reaction products (Pape and Zabik, 1972a). The rate of photoreaction is dependent on at least three factors: the first is the nature of halogen substituted as the K decreases rapidly in the order I > Br > C1 > F. These results are in agreement with the known dissociation energies of the corresponding carbon halogen bonds and to their ability to undergo valency shell expansion mainly in the excited state. The second is the effect of the N-alkyl substituents. S-triazines with ethyl substituents with the 4 and 6 positions show a greater K value than those with isopropylgroups. This effect is mainly due to differences in size of the alkyl groups as steric effects are known to disturb the geometry of an excited state (Ruzo et al., 1973). Until now, photolysis in solution was by far the most thoroughly studied process. Unfortunately for environmental photochemists, the substrates of interest are often found as solids or in the absorbed or adsorbed phase; thus it becomes necessary to carry out studies on soil and plant surfaces. It has been shown that the absorption spectrum is shifted when certain compounds are adsorbed on silica gel, for example, trifluralin has a maximum at 375 nm in cyclohexane but at 435 nm on silica gel (Plimmer, 1978). It has been reported that absorption of pesticides on soils decreases their reaction quantum yields (Hautala, 1976). This effect also has been observed where the pesticide interacts with sediment, probably as a result of decreased light availability. Much speculative attention has been given to the influence of light in the deactivation of s-triazine herbicides on the soil (clay included); but little critical research has been conducted on actual losses from photodecomposition. Nevertheless, sufficient research has been carried out to demonstrate that photodecomposition does occur with some s-triazine herbicides. Usually the silt loam or sandy loam varieties are used as thin film on glass plates. Studies of fluchloralin and bentazon (Nilles and Zabik, 1974) and of pydrin (Holmstead et al., 1978) serve as guide-light. Gast (1962) reported losses in activity for simazine and atrazine after exposure to ultraviolet (UV) and infrared light radiation, particularly if the herbicides were applied to a dry surface. Dewey (1960) found a decrease in simazine activity after the herbicide was irradiated with a mercury vapor high-pressure lamp. Sheets and Danielson (1961) irradiated simazine on filter paper with UV light, but their results were not conclusive. Jordan et al. (1965) studied the effect on simazine and atrazine of UV light sources with peak emission of 254, 311, and 360 mu respectively, representing far, middle, and near UV light. The two herbicides were deposited on aluminum planchets and irradiated for periods up to 400 hours. The absorption of simazine and atrazine under UV is greater at 220 mu. Following irradiation, absorbance decreased. The greatest decrease occurred after irradiation with 254 muand the least with 360 mu. Loss of simazine and atrazine was rapid during the initial period of irradiation, but as time progressed the rate of loss decreased. As a continuation of the photochemistry of pesticides in solid phase we examined the photodegradation of four s—triazine herbicides on three different clay surfaces. To fully understand the_photo- chemical behavior of chemicals on clays, it is necessary to know the structures and properties of the clays used and their different power of adsorption at different pHs. The term clay, refers to the layered aluminosilicate minerals which are considered to be colloidal (less than about one to two u in diameter). A large number of different types of clay minerals have been found in nature. Each clay mineral has a specific crystalline structure. All of the layered aluminosilicate clays have a common property: they are made of sheets of tetrahedra of silicon oxide and sheets of octahedra of aluminum oxides and hydroxides. A silicon tetrahedron is formed when the small silica atom is surrounded by four oxygen atoms. An aluminum octahedron is formed when six oxygens or hydroxyls surround a large atom like aluminum. Some clays are made up of alternating sheets of silica tetrahedra and aluminum octahedra. The ratio of tetrahedral sheets to octahedral sheets is 1:1, and these are called the 1:1 clays. Kaolinite is the best known member of this type. In other clays, the unit layer is made up of two sheets of silica tetrahedra enclosing a sheet of aluminum octahedra. The ratio of tetrahedral sheets to octahedra sheets is 2:1, thus are called 2:1 clays. As unit layers are combined, two tetrahedral sheets lie next to each other. In many cases, the two identical sheets do not attract each other by chemical bonds, but only by relatively week Van der Naals forces, and can be readily separated by water molecules. Such clays therefore have the ability to swell on wetting and to shrink on drying. Montmorillonite is probably the best of these types. Sometimes aluminum replaces silicon in the tetrahedral while iron, magnesium, manganese and a few other cations of similar size may replace aluminum in the octahedra. This replacement of ions has been termed "isomorphous substitution". The valance of the replacing cations in many cases is lower than that of the original ions. This means that some of the negative valences of the oxygen atoms are not satisfied internally and this creates an overall net negative charge on the clay surface. This total negative charge has to be neutralized by cations, thus cations such as sodium, potassium, calcium, and hydrogen are attracted to the clay surfaces. These ions may be replaced by other cations in the soil environment and are known as "exchangeable cations", and the amount of exchangeable cations that a clay can retain is known as the clay's "cation exchange capacity" or CEC. In the 1:1 clays, exchangeable cations are adsorbed only on the exterior surfaces, but in 2:1 clays the cations may also be adsorbed on the interior surfaces. For some of the 2:1 clays, potassium atoms are located between the neighboring tetrahedral sheets and hold the sheets tightly together with electrostatic bonds. Consequently these clays do not shrink or swell and are termed the "nonexpanding" 2:1 clays. Attapulgite illustrates that type of clay. Expanding 2:1 clays have a much greater specific surface area and C.E.C. than the nonexpanding 2:1 clays. Some of the characteristics of selected clay minerals are given in Table II. The expanding 2:1 clays, because of their‘ 10 greater surface area and CEC, adsorb the triazines to a greater extent, followed by 2:1 nonexpanding and finally l:l clays. The degree of association and dissociation is determined by the pH. Tab1e II: CHARACTERISTICS OF SOME COMMON CLAY MINERALS CHARACTERISTICS MONTMORILLONITE VERICULITE ATTAPULGITE KAOLINITE Type of layering 2:1 2:1 2:1 1:1 Type of swelling Expanding Limited Non- Non- Expanding Expanding Expanding CEC (meg./g.) 80-150 120-200 10-40 2-10 Specific surface 700-750 500-700 75-25 25-50 (sq. m./g.) Bailey et al. (1968) found that regardless of the chemical character of the adsorbate, adsorption occurred to the greatest extent on the highly acid hydrogen montmorillonite (pH6.8)' The same author concludes that the magnitude of adsorption of organic compounds with widely different chemical characters is governed by three factors: (1) pH of the clay systems, (2) water solubility, and (3) the dissociation constant of the adsorbate. In this research, our attention was focused on the pH's because the s-triazines undergo acid-base reactions as a function of pH. These workers also found that the adsorption of acidic type compounds was dependent upon the pH of the suspension. For weekly basic herbicides like the s-triazines, surface activity is probably the most important property of the soil or colloid system in determining the extent and the nature of adsorption and desorption. 11 Infrared studies reported by Russel et al. (1968b), Cruz et a1. (1968), and Bailey et a1. (1970) clearly show that various s-triazines are protonated on montmorillonite surfaces in the presence of a variety of different cations. Weber (1966) in an adsorption study of 13 related s-triazines by montmorillonite found that the maximum adsorption of all the compounds occurred at a pH in the vicinity of the dissociation constant of each compound. A further lowering of the pH resulted in some desorption of each of the adsorbed triazines. He attributed this to the competition of hydrogen ions for exchange sites at low pH levels. This result is directly opposite of that found by Frissel and Bolt (1962) for the adsorption of chloro-s-triazines. They found that about three to four pH units above the dissociation constant,adsorption started to increase as pH decreases down to pH one. Nearpass (1967), studying the effect of the predominant cation on the adsorption of simazine and atrazine by soils, found that the adsorption of simazine and atrazine is governed largely by the hydrogen ion activity relationship which occurred between the solution and the solid phase of the soil. At equal concentrations atrazine was less strongly adsorbed than simazine. Frissel (1961) studied the effect of suspension pH and electrolyte concentration on the adsorption of 14 organic compounds, including the chloro—s-triazines (simazine, chlorazine, and trietazine) on the clay minerals illite, montmorillonite and kaolinite. He found that the adsorption process was pH dependent and postulated that the triazines were adsorbed as neutral molecules in neutral and basic environments and as positively charged ions in acidic solutions. Montmorillonite 12 adsorbed greater amounts of the triazines than illite, attapulgite and kaolinite, respectively. Harris and Warren (1964) studied the adsorption from aqueous solution of several herbicides, including atrazine and simazine, by bentonite clay. Adsorption of atrazine by bentonite was much greater at pH4.1 than pH8.2. The higher adsorption at low pH was attributed to the triazines molecule with protons on the clay surface as suggested by Frissel. Simazine was adsorbed in greater amount than atrazine by bentonite at pH8.5. The adsorption from aqueous solution (pH7 saturated calcium hydroxide) of five s-triazines on 25 soil types, four clay minerals, was determined by Talbert and Fletchall (1965). In almost all cases, adsorption decreased in the order: prometryne > prometone > atrazine > propazine. Adsorption from aqueous solutions of the 13 triazines by Na- montmorillonite clay showed that adsorption was dependent upon the molecular structure of the compound and the pH of the system (Weber, 1966). The key to the amount of adsorption was the molecular structure of the compounds. Decreased adsorption resulted as the 2-substituent was changed in the following order; -SCH3 > OCH3 > -OH > -C1. The purpose of the present inveStigation was to extend the knowledge of the photochemistry of symmetrical substituted triazines on solid surfaces. In this study the solid phases used were montmorillonite, attapulgite, and kaolinite. The specific objectives were to: 1) Develop a comparative study of the photodegradative rate constant of each triazine herbicide in relationship with concentrations, pH's, and clay type. 13 Use the rate constants to calculate the half-life time (t 1/2) for the various triazines. Establish if possible, relatiohship between the photodegradative rate constants and the absorbance of the four s-triazines. CHAPTER II: EXPERIMENTAL Equipment and reagents Chemicals: All the s-triazines were analytical standards, obtained from Geigy Agricultural Chemicals, Division of Geigy Chemical Co., Saw Hill River Road, N.Y. and used without further purification. The purities were greater than 98%. Clay samples: The clay samples were Kaolinite and Attapulgite respectively from Macon Attapulgus, Georgia and Montmorrillonite from Rockville, Mississippi. Solvent: Methanol used in photochemical reactions was glass distilled. (Burdick and Jackson Laboratories, Inc.; Muskegon, MI). Photochemical equipment: The photodegradative experiments were carried out in a Rayonet Photochemical Reactor (The Southern N.E. Ultra- violet Co., Middletown, Conn.) fitted with RUL 3000 lamp having peak energy output at 300 nm. Glass reaction plates: Glass plates were obtained from the Division of American Hospital Supply Corporation. The size of plate was 6.0 x 2.5 cm. (Model Number M6130). 14 15 4>wrm HHH" qucnacxm >2c nozmqucmzqm om 412mm nr>< 3H2mm>rm mink Axum xmoflszddm >nnmocdcdam zozflaowdddosddm mmmmmmmmm Aozvmmsp>d AOIVNmemS AozvnmflmA>dw.wazo.mmvomo nmo» Asmm\doo av wndm Neuwo moudmo mc-fianm mama AA2N\QV 3-80 Sm-smm moo-moo mamamznm mmom pm.mo mm.ow mo.mo Emouw ww.o~ do.m¢ am.do mmmow o.mw w.mw p.dw mmo o.om t--- u--- zoo o.pu Ao.no h.dm nmo o.m~ nun: m.dm xmo o.po o.¢u o.dm zmmo o.wm I--- o.dw adom d.mm nun- o.mo Imon d.mm o.uu am.mm Imo+ dw.~u do.dw u.mu Hoa>r doo.ou mo.mm doo.mo »omn u nmamo: mxozmscm nmumnsfik 16 pH Meter and establishment of pH4 and pH7 8: An Altex 70 pH meter Beckman Instruments, fitted with on Altex combination pH Electrode 531822 was used to measure pH. To obtain clay at pH4, 1.25 N HCl was added to different clay slurries while 1 N NOH was used in the same way to obtain a pH7 8' Analytical equipment: GC analyses were performed on a Tracor 560 chromotograph equipped with NP detector. Ultraviolet and visible spectra adsorption determination were performed on a Gilford UV-Vis 2600 spectophotometer interfaced to an HP 7225A Plotter (Hewlett-Packard Corp.) and a PDP-11/40 RSTS/E Computer System (Digital Equipment Corp.). Experimental procedures Preparation of clay thin-layer chromatography (TLC): Each clay was ground, using Arthur H. Thomas Co. Scientific Apparatus, Philadelphia, PA., and a mesh of 106 um opening or 0.0041 inch from USA-Standard Testing Sieve Soiltest, Inc., 2205 Lee Streer Evanston, Ill. 60202 to obtain uniform clay which would adhere to the glass plates. A solution of 3 N sodium chloride (3 N NaCl) was used to obtain the Na-Saturated clay. The different clay solutions were then washed with distilled water to remove excess sodium chloride and with methanol which was the solvent used for the pesticide solution. The clays were dried in a vaccuum oven at 49°C to remove the solvent. A slurry in distilled water was made and pH4 and pH7.8 were established. The overall solutions were dried in the oven at 110°C oVernight. Again 17 the grinder and mesh of 106 um opening were used to make thin particles. After that stage aqueous slurries were prepared in distilled water and .75 mm thick layer was spread using TLC apparatus. The clay TLC plates were stored in an oven at 110°C overnight and then in the drawers in the dark until they were applied. It is impor- tant to mention that due to the expansion of montmorillonite, it was very difficult to obtain uniform plates comparable to the kaolinite and attapulgite. Pesticide application and extraction: Four pesticides belonging to the s-triazine group were then chosen for photochemical investigation. S-triazine solutions, containing 2 and 3.5 ug were placed on the clay glass slide plates by 1 m1 pipette, so that the surface concentration would be 0.133 and 0.233 ug per cm2 respectively, after solvent evapor- ation. A small amount of solvent was added to each clay TLC plate to cover the surface uniformly when 1 ml of s-traizine solution was not sufficient to cover the whole plate. After the solvent evaporated, a glass cover plate was added and the edges taped to minimize pesticide evaporation. The plates were placed in the photochemical reactor for 4, 8, 12, 24, and 48 hr. periods and were irradiated perpendicular to the light tubes. The irradiation chamber temperature was 34°C-36°C. Each treatment was associated with a dark control. After irradiation, the plates were washed with 5 ml of methanol into scintillation vials for the easily extractable fraction. Anhydrous sodium sulfate was added to dry the methanol solution and a rotavapor was used to reduce the volume to 0.1 ml which was used in the final quantitation. One ul was injected into the Tracor 560-GC. 18 The bound fraction of the pesticides was obtained by treatment of the plates with ammonium acetate (NH4oAc) followed by extraction twice with 5 ml methylene chloride (CH2C12). This fraction was again dried with anhydrous sodium sulfate. The total volume was reduced to dryness and then made up to a (1) m1 volume with (CH30H) for injection into the Tracor 560 GC. To compensate for a small amount of pesticide disappearance by evaporation, identically prepared plates were placed in the same photoreactor the top of which was covered by a dark colored wool cloth to prevent exposure to room light, but still allow air flow past the plates. A heating mantle was used to maintain the temperature within the range of 34°C-36°C for these dark controls. The amount of pesticide remaining on the plates, bound or nonbound to the clay samples was quantitated by GC. The values obtained from the irradiated plates were corrected relative to the amount of pesticide which had disappeared from evaporation and/or reactions as shown by the dark controls. The photodegradative rate constants (K) were determined by least squares analysis (for both the bound and easily extractable fractions and then for the total.) of log (amount pesticides remaining) vs. irradiation time plots. The half-time (t 1/2) were calculated from (K) Using the following standard equation: t 1/2 = 9;%2§ For the purpose of estimating the relationship between the photo- degradative rate and the absorbance, the maximum absorbance for each pesticide was measured between 295-305 nm and the extenction coefficient was calculated. 19 Study of % recovery: Amount of pesticides obtained X 100 Amount of pesticides added % recovery = Three (3) ml of 3.5 ppm solution of the s-triazines was added to 10 g of each clay sample to obtain a concentration of 1.05 (21 ppm). The solutions were shaken and kept overnight to allow the adsorption of the herbicides and the evaporation of the methanol used as the solvent. The next morning, the whole samples were treated twice with 40 m1 of 3 N ammonium acetate, followed by extraction three times with 30 ml of methylene chloride. The total volume was reduced to dryness and then made up to 1 ml volume with methanol. One ul of the solution was injected into the Tracor 560 GC. By the comparison to the standard curves the results in Table IV were obtained. These results were used to show how good the standards recovered from the different clays and not as correction factors. 20 TABLE IV: RECOVERY OF FOUR TRIAZINES FROM THREE DIFFERENT CLAY MINERALS AT pH4 and pH7.8 Average % Recovery s-Triazines Ph7.8 pH4 Clay Type Atrazine 82 99 E Z . . 0 Swan ne 89 96 E Simetryne 86 75 g: '— Trietazi ne 89 82 g Atrazine 93 86 :3 Simazi ne 98 86 5 5’ Simetryne 79 82 3: [-— Trietazi ne 86 75 E Atrazine 89 96 Simazi ne 93 98 E E Simetryne 93 96 ES :5 Trietazine 82 71 CHAPTER III: RESULTS AND DISCUSSION Effect of Molecular Structure and Functional Group of s-triazines on Photodegradation Rates The photodegradation results of four s-triazine herbicides at concentrations (0.13 and 0.23 ug/cmz) showed that plots of log (amount pesticide remaining) versus time of irradiation where linear, indicating first-order reaction kinetics (Figures l-12). There were not large differences in the photodegradation rates among the four herbicides, varying from 12.50 to 10'7 sec'1 (trietazine, 0.23 ug/cm2 on kaolinite at pH7.8) to 63.80 x 10"7 sec"1 (simetryne, 0.13 ug/cm2 on montmorillo- nite at pH4 (Tables XI, XII). For different groups of herbicides, differences due to functional group with substituents in the 2-position and ethyl substituents in the 4- and 6-N positions (simetryne) showed greater K value, and decreased in the order: R1 = R2 = C2H5 and R3 = SCH3 (simetryne) > R1 = R2 = C2H5 and R3 = Cl (simazine) > R1 = C2H5, R2 = i-C3H7, and R3 = Cl (atrazine) > R1 = CZHS’ R2 = (C2H5)2 and R = 3 Cl (trietazine). This is true for the easily extractable fraction, the tightly bound, and the total amount of s-triazines at different pH's. This sequence is in good agreement with the solution photodegradation results of Ruzo, et al. (1973), and long, et al. (1983). The greater K value with ethyl substituents in the 4 and 6 positions than those with isopropyl groups was mainly due to differences in size of the alkyl 21 22 groups as steric effects are known to disturb the geometry of an excited state (Ruzo, et al., 1973). Influence of Concentration on the Photodegradation Two different concentrations were irradiated for each s-triazine. Plots of log (herbicide disappearance concentration) versus time, were linear but had different slopes depending on initial concentration. Tables VI and VII of the total photodegradation rates for the four 5- triazines on thin film glass plates of the different clay samples at pH4 and pH7.8 showed that the higher the concentration, the slower the photodegradation rate constants. The apparent decrease in rate constant is probably due to the fact that at higher concentration the herbicides were distributed in thicker layers on the clay surfaces, with the upper layers playing a protective role over the lower layers. Thus, the over- all degradation rates decrease as the concentration increases. This is in good agreement with the result of long, et a1. (1983). The estimation of molecular size by means of the stereomodel methods indicates that the molecular size of the various pesticides varies between 6.3 - 16.0 A x 6.0 - 7.5 A, with the thickness varying between 1.5 A to 2.5 A. The calculation using the above value indicates that the number of molecular layers on the clay surfaces in the 0.13 ug/cm2 was approximately 7. There were about 12 layer in the .231gg/cm2 treatment. J. A. Kitchener (1946) estimated that about 98% of the radiation, of wave- length less than the absorption threshold, which enters a typical crystal may be absorbed within a distance of 10'6 cm. If we assume that every molecular layer is 2 A in thickness, then the molecular layer for the .13, and .23],g/cm2 would be 14 and 24 A respectively, 23 that shows the molecular layer of pesticides. in high concentration is thicker to permit radiation to penetrate into the layer, so photodegradation is only in the upper herbicides layers. Consequently, the rate constants decreased. Photodegradation Rates as Influenced by Clays at pH4 and pH7 8 The photodegradation rates of the easily extractable (non-bound) fractions were faster at pH4 than at pH7.8 and decreased in the order: montmorillonite > attapulgite > kaslinite. At pH4 there is protonation of the s-triazines on clay surfaces, Russel, et al. (1968b); Cruz, et al., (1968); Bailey, et al., (1970); and Frissel and Bolt (1968). The effect of the protonation leads to a comple formation, changing the structure 415%E1fl regardless of the type of of the s- -triazines and become [:. s- -triazine. This complex seems to4 adsorb more UV light than s-triazine adsorbed in neutral or basic conditions (i.e. on clays at pH7.8). If so, the rate constants at pH4 should be faster than those at pH7.8. This assumption was verified by the following supplementary experiment: we determined the UV spectra of 2 ppm solutions of simazine at pH4 and pH7.8. The absorbance and thus the extention coefficients was higher at pH4 than at pH7.8 (Figures 17 & 18). Therefore, at pH4 the complex absorbs more than at pH7.8° Consequently, the photodegradation rates were higher. As for the tightly bound fractions (bound fractions) the photo- degradation rates did not fluctuate much. At pH4 and pH7 8 they -1 -7 -1 -7 differed by .01 to .02 sec x 10 , varying from .17 sec x 10 (trietazine, on kaolinite) to .625 sec.1 x 10'7 (simetryne on the same 24 kaolinite). This was due to the fact that little reaction took place, illustrated by low photodegradation rates. The total photodegradation rate constants for the easily extractable fraction and the tightly ones, were approximately the same as the non- bound portion. Once again, most of the reactions took place with the loosely bound fraction. Relationship Between the Photodegradation Rate and the UV Absorbance of the Four-Triazines The maximum energy output of the irradiation source was 300 nm and environmental photodegradation occurs at wavelengths above 290 nm, Since the earth's ozone layer absorbs most of the sun's electromagnetic radiation below that wavelength, we‘ have: estimated the maximum absorbance of the test compounds in 210-340 nm and 295-305 nm regions. 5 M and 93 x 10"6 At 94 x 10- M simetryne and atrazine did not give a measurable absorption. There was no significant relationship between the extinction coefficients and the rate constants of the triazines (Table IX). 25 TABLE V: TRIAZINES ANALYSIS PARAMETERS Extraction Instrument Column Retention s-Triazine Solvent Detector.l Packing2 Column, 0C3 Time, min Trietazine Methanol NP A 200 2.00 Atrazine Methanol NP A 200 1.90 Simazine Methanol NP A 200 1.90 Simetryne Methanol NP A 200 2.90 1NP = Nitrogen-Phosphorus detector 2A = 6' x 2 mm i.d. glass containing 3% silicone SE 30 on 80/100 chromosorb N-HP 3For GC-NP detector and injector temperature were 250°C 26 TABLE VI: TOTAL PHOTODEGRADATION RATE CONSTANTS FOR FOUR TRIAZINES 0N CLAY SURFACES AT pH OF (1.3 and 0.23 ug/cmz) HERBICIDES 7.8 Rate Constant (sec.1 x 10'7) s-Triazines 0.13 ug/cm2 0.23 ug/cm2 Clay Type LIJ Trietazine 17.751 .2232 17.903 13.051 .1932 14.603 53 O Atrazine 38.07 .326 38.47 31.08 .215 31.50 .3 Ci Simazine 40.50 .441 40.95 33.70 .34 34.10 g 2 Simetryne 58.16 .602 59.00 53.20 .556 53.80 ‘2’ Trietazine 16.21 .218 16.50 12.70 .185 12.90 “J [.— Atrazine 37.75 .2741 37.98 31.01 .207 31.30 {3* :3 Simazine 39.50 .442 39.95 32.20 .238 32.60 g [— Simetryne 57.01 .601 58.01 52.79 .545 52.98 <= Trietazine 16.01 .198 16.39 12.50 .174 12.70 Atrazine 35.49 .253 35.70 30.33 .204 30.65 E; Z Simazine 39.50 .430 39.96 32.10 .336 32.50 g; Simetryne 56.60 .601 57.20 52.44 .543 52.90 :5 1Easily extractable fraction 2Tightly bound fraction 3Total amount of l and 2 27 TABLE v11: TOTAL PHOTODEGRADATION RATE CONSTANTS 0N CLAY SURFACES FOR FOUR TRIAZINES AT pH4 OF (0 13 and 0.23 pg/cmz) HERBICIDES Rate Constant (sec:T x 10'7) s-Triazine 0.13 ug/cm2 0.23 ug/cm2 Clay Type Trietazine 19.011 .232 19.20 14.501 .1982 15.05 E. Atrazine 40.37 .401 40.82 33.05 .240 33.08 3 Simazine 42.97 .403 42.06 35.01 .345 35.40 g Simetryne 63.75 .625 64.40 55.44 .563 55.99 5:: Trietazine 18.50 .224 18.72 14.01 .185 14.20 1.. Atrazine 39.50 .402 39.91 32.80 .2399 33.11 g Simazine 39.85 .386 39.99 34.85 .343 35.90 3: Simetryne 63.50 .607 64.11 54.05 5674 54.66 FF Trietazine 18.10 .222 18.30 13.78 .179 13.89 Atrazine 39.40 .343 39.74 32.73 .238 32.97 E Simazine 39.90 .355 40.30 34.70 .340 35.06 g Simetryne 63.01 .615 63.78 53.60 .5520 54.16 E 1 2 3 Tightly bound fraction Total amount of l and 2 Easily extractable fraction 28 TABLE VIII: TOTAL PHOTODEGRADATION HALF-LIFE FOR FOUR TRIAZINES 0N CLAY SURFACES AT pH7 8 AND pH4 AND AT PLATE CONCENTRATION OF .13 ug/sz Half-Life, hr s-Triazines pH7.8 pH4 Clay Types LLJ Atrazine 50 47 t: Z O Simazine 47 45 j o: Simetryne 33 30 E Z Trietazine 107 100 g Atrazine 51 48 E Simazine 48 48 5 5’ Simetryne 33 30 E I'— Trietazine 117 103 < Atrazine 54 48 LL] Simazine 48 48 L‘. E Simetryne 34 30 g Trietazine 117 105 29 we «00. mmw—N om.~ m.m¢m mm wcwumpmvgh o o nuom— mw.P m.n¢m mm mchwLp< mmm mmo. ommmp ww.~ m.m¢m mm mchmem o o mpmow om.~ o.wv~ em w:»gpmswm he: mom-mmmv fie: mom-mmmv so 6_oz\S mocmncown< 5: 2 8-0? mcw~6wcp-m Eu mFoE\4 mucwncoma< xmz m Ezswxmz :umcmpm>mz cowpmcpcmucou xmz m Ezswxmz mucmncomn< :omz zH mmzHN HzmHuHmumou onHquhxm oz< muzCDZJOLDID" p.00 w.mm ..+_____0 _ -+-H -— -—-—+——-—-———+——.——— Ho Hm . C< >mmomh4Hoz on ma mm: mHIqummDmHu4HDZ on Na Hun: >4m>~HZm HZ ImOI M M > 4 b D 1 4 4 a a 31 o i» 1 NDImmHulmw DHCuomO Nana >4m>NHzm ma Hum: Hz ImOI - ~+-——-—+—- —-——+—--—~—+-— —- -—+———- -—(> VA. ’4 )«o a. I v S (>mmomm> 5.00 w. mo .7 H.D..wJ Tux. WHO Hmnc< >mmDmHu4Hoz DH... MG 201 mHz>NHzm HZ meI ’ I! b O D 1 A! 4 F L 1T > M anmmvlmw oHrHuomD Mama mHI>NHzm ma HuHur Hz ImOI ._+-—--— ~-—1> +__ -H. HH+ H__ H. HH+H._._ _ L .__T_ 0 00 «.6 S e 9 (>CDZJOUTQ3> an Hm . C< >mmomw4Hoz on ma wt: qum4>NHzm Hz IMQI #.8$fil o o 4? 0 1A J» 0 0 o b . moummvnmw nHrnomo mama «mHm4>~Hzm mm 60: Hz zmox w.mo M m w Hm H H m.33 . . H m mm + r e 6.0 90 S.» <>mmwp4Hoz OH... N pp: wHI>NH2m Hz ImOI >4 HUI... m F 5 L b P P b ‘ 1‘ NQImmpumw oHrnomD mmmm H, mHz>NHzm m to: H2 xmox. 0:1 . . H w + a m . H H . .. w H _ _ H L. 0 >1 8 4 o 41 11 4 11H m m w m m m m m w m a 1. A. . a m m 2 m m m m a m u. 218. BB (>(UHHZ34C Z! 64 Figure 17: UV absorption Of 2 ppm simazine in MEOH at pH7.8 n3NEH mrmdma HFNNNG p.286 65 Uiriz > w miatncncnz> n.92HH 9.9Nfiu .leNNG .JFHKHU .Herflm flHo Hm .C< >mmomp4Hoz on N pp: mHI>NH «o ‘ v 1 4 2m 3 pl» Hz :3: thmm61mw ermomo.mmso Eidzm m 63.. Hz :8:ka 218.88 ZELBB 238.88 1 (P w m m m t> simazine > atrazine > trietazine, (2) the effect of initial concentration on the rate constants due to the distribution of the herbicides in thicker layers on clay surfaces at higher concentration, the upper layers playing a protective role over the lower layers, (3) the effect of protonation of s-triazines in acid condition leading to the formation of a complex with higher extinction coefficient. (4) the determination of the half-life times of the four triazines on clay surfaces at different pHs (5) the lack of consistent relationship between the photodegradation rates and the extinction coefficient. 66 67 LITERATURE CITED LITERATURE CITED Bailey, G. W., and Rotherg, T (l968) Adsorption of organic herbicides by montmorillonite. Role of pH and chemical character by adsorbate. Soil Sci. Soc. Amer. Proc. 32, 222. Bailey, G. W., and White, J. L. 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