Terrestrial Field Dissipation Studies - American Chemical Society

Downloaded via TUFTS UNIV on July 9, 2018 at 20:00:35 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.

Chapter 17

Experiments in a Volatilization Chamber under Simulated Outdoor Conditions: A Contribution to a Better Understanding of Field Dissipation Studies R. Kubiak State Institution for Research and Training in Agriculture, Viticulture and Horticulture, Ecology Department, Breitenweg 71, D-67435 Neustadt, Germany

A n experimental volatilization chamber is presented which allows for fall mass balance studies after application of C-labeled compounds to plants and/or soils. The design of this chamber allows for the control of environmental parameters which influence the metabolism and volatilization of pesti -cides; either standardized climatic conditions, or measured and recorded outdoor scenarios can be used. This paper provides the results of chamber studies using the pesticides fenpropi-morph and parathion-methyl, these results illustrate the repro -ducibility,exactness and with the example of parathion methyl the transferability of the data to field studies. 14

© 2003 American Chemical Society

Arthur et al.; Terrestrial Field Dissipation Studies ACS Symposium Series; American Chemical Society: Washington, DC, 2002.

257

258

Introduction

After the application of a pesticide in agriculture, a substantial fraction of the dosage applied may enter the atmosphere and may be transported over long distances (1). The rate and the extent of the emission after application depends on the physical and chemical properties of the pesticide, the application pa rameters, the climatic conditions during and after application as well as the char acteristics of the target. Vapor pressure and Henry's law constant as well as the kind of formulation used (2) are important parameters of the plant protection agent, and the droplet size as well as the water amount are application charac teristics to be taken into account. Furthermore, it is well known that volatiliza tion processes may be influenced by the relative humidity (3), air temperature (4), atmospheric pressure and wind velocity (5). Furthermore, irradiation may influence the metabolism of compounds via direct or indirect photolysis (6). Last but not least the sorption and desorption processes as well as transport to deeper soil layers and chemical and biological degradation in the soil may depend not only on soil characteristics such as structure, humus content and biological ac tivity but also on soil temperature, soil moisture and pH-value (7). Since plants have fewer sorption sites than soils, volatilization of applied compounds is nor mally higher from plant than from soil surfaces but also on plant surfaces the potential amount of volatilization may be reduced by uptake into the leaves or degradation processes on the plant surface (8). In field dissipation studies, espe cially the climatic conditions vary during the experimental time and between different experiments which makes field dissipation irreproducible. Furthermore, field studies are open experimental systems, i.e. a distinction between degrada tion processes, the formation of bound residues and volatilization of the pesticide sprayed or any metabolites formed is not possible. To contribute to a better interpretation of field dissipation studies a labora tory chamber was designed fulfilling the following requirements: 1. 2.

The use of formulated plant protection agents with the option of using Relabeled active ingredients A n application procedure, which is in accordance with agricultural practice as regards nozzle type, water amount ha" , spraying pressure and target dis tance A n experimental chamber in which the climatic parameters can be simulated that may influence the fate of the compound including volatilization A direct measurement of the volatile compound and the possibility of ob taining mass balances when using RC-labeled compounds. 1

3. 4.


259 To investigate the precision and the reproducibility of the results obtained from the chamber, experiments were carried out with different C-labeled com pounds. To investigate the transferability of the results obtained from these chamber experiments to the field, a comparative experiment was carried out with parathion-methyl. 14

Material and Methods

Design of the Application Chamber and Application Procedure In order to ensure well-controlled application conditions a computercontrolled spraying system was built which enables application amounts between 100 and 2000 L ha" , spraying pressures between 1.0 and 3.0 bar and driving speeds between 0.1 and 30 km h" . Nozzles licensed for agricultural use can be connected to this system in such a way that only the nozzle itself reaches into the application chamber. This chamber consists of stainless steel, can be closed with a door and an experimental platform containing bare soil or a plant/soil system can be introduced. The size of the experimental area is 0.5 m . It is fixed on a platform of variable height. Depending on the experiment, bare soil or plant stands of different heights can be sprayed with the correct distance between the nozzle and the target area (9). When using C-labeled active ingredients appli cation losses can be determined precisely by measuring the radioactivity re maining in the spray system and at the chamber walls which are covered with filter paper during application. Figure 1 shows the equipment. 1

1

2

14

Figure 1. Application chamber for simulation offield application scenarios under controlled conditions. (Reproduced with permission of reference 10. Copyright 1999 Verlag Dr. Kôster)


260 Before application aliquots of the homogenized radioactive application so lution are measured using a liquid scintillation counter (LSC) and the total amount of radioactivity is calculated. A few minutes after application all fine droplets have reached the target and the chamber door is opened. The experi mental platform removed for installation in the experimental chamber. The re sidual volume of the solution in the spraying equipment is determined and the whole spraying system is extracted with a suitable organic solvent. The remain ing radioactivity is determined by measuring aliquots in a L S C . The paper, that covers the inner walls of the application chamber during application is removed and extracted with a suitable solvent. The volume is determined and aliquots are measured in a L S C . The total radioactivity which has not reached the target is calculated from these measurements and die amount is deducted from the total radioactivity measured in the spraying solution. The balance is the amount of C which has reached the target. This very precise result is the 100% basis for the mass balance of the experiment. Knowing the specific radioactivity of the la beled compound (kBq mg' ) and the percentage-value of the active ingredient in the formulation the exact amounts of radio-labeled compound and of formulated product applied can be calculated. i 4

1

Design of the Volatilization Chamber and its Possibilities After application, the experimental platform is introduced into the volatili zation chamber. This working step lasts only 1 to 2 minutes, thus avoiding con siderable C-losses via volatilization. At the bottom of the platform (5 cm deep for experiments with bare soil and 10 cm deep for experiments with plants) an irrigation system made of perforated tubes is installed and connected to a water tank and a pump outside the chamber to control soil moisture during the experi ments. The chamber equipment consists of an air conditioning system, suitable for the on-line production of air temperatures and humidities ranging from 10 to 30 °C and 35 to 95% rh, respectively. The conditioned air reaches an equalization chamber, where the turbulence caused by the transport blowers is calmed down and converted into two parallel air streams: a fast one, 10 cm in height, simulat ing outdoor wind speeds up to 3 m s" above plant stands or bare soil surfaces and a slow stream, 80 cm high, simulating air exchange rates in plant stands (up to 0.3 m s' ). As in the application chamber, the experimental platform is vari able in height and is fixed before the start of an experiment so that the surface area (bare soil or upper part of a plant stand) reaches into the fast air stream. During experiments with bare soil, the wind channel producing the slow wind speed is closed, so that real outdoor conditions can be simulated for a wide range of applications. 14

1

1


261 After having passed the chamber room, the two air streams reach mixing channels in which the air, which may now be loaded with volatile compounds, is homogenized. High-volume sampling systems are installed downstream which allow for a homogeneous isokinetic air sampling up to 10% of a total air volume per time unit. After that the mixing channels reach a filter system normally filled with activated carbon holding back volatile radioactive compounds. A second blower discharges the air from the system. The air pressure in the chamber is equal to the actual air pressure outside because a blower pressing air into the air conditioning system and the second blower pulling at the end compensate each other. Since irradiation may influence the fate of pesticides applied under field conditions, a metal halide lamp producing up to 1200 W m" on the plant or soil surface is installed above the chamber which is covered with a Sanalux® glass allowing for the transition of UV-light with small losses only. This lamp pro duces a wavelength distribution very similar to natural sunlight. The lamp is computer-controlled and its light intensity can simulate the solar intensities from sunrise to sunset. Figure 2 illustrates the complete volatilization chamber. 2

Figure 2. Design of the volatilization chamber. (Reproduced with permission of reference 10. Copyright 1999 Verlag Dr. Koster)

A i r Sampling and Analysis For exact investigation of the volatile radioactivity, the sampling systems downstream the isokinetic samplers consist of the following parts:


262 1.

2.

polyurethane foams for adsorption of non-polar volatile compounds. Ex traction efficiency and break-through of the compounds is tested separately before the start of an experiment. The trap for sampling any C 0 which might have been formed as a result of mineralisation of the C-labeling position. This trap is a mixture of ethanolamine, 2-phenylethylamine, diethylengycolmonobutylether and ethylenglycole (1:1:1:1, vol: vol: vol: vol). A freezing trap, collecting the air moisture, which can be investigated quantitatively for any polar compounds by L S C . 1 4

2

l4

3.

Together with the investigation of the soil and/or plant material at the end of an experiment a total balance of the applied pesticide can be determined.

Table I. Active Ingredients used for the Experiments

(±)-cis-4-[3-4(tert-butylphenyl)-2-methylpropyl] • 2,6-dimethylmorpholin C H 3NO 303.5 3.5 χ 10" 4.3 1.0 x l O 4.1 [U- C]benzolring 30-75

Parathion-methyl 0,0-dimethyl-0-4nitrophenyl-phosphorusthioate CsH NO PS 263.2 1.29 x l O ' 55.0 2.5 χ ΙΟ" 3.0 [U- C]phenylring 420

EC 750

WP 200

Fenpropimorph IUPAC-name

Sum formula Molar mass [g mol ] Vapor pressure [Pa] Water sol. [mg L" ] Henry's law constant Log Pow C-labeling position Specific radioactivity [kBqmg'] Formulation type A.I amount [g ha" ] -1

1

14

1

22

3

3

7

14

10

5

3

6

14

Pesticides used and experiments carried out Experiments were carried out using the active ingredients described in Table I. A loamy sand (sand: > 70%, clay: < 10%, Corg: < 1.5%) was used for the ex periments. French beans in the 10-20 leaf stage just before blossom and barley just before ear emergence, grown under greenhouse conditions were used for the studies. To distinguish exactly between volatilization from plants and soil in case of plant experiments the soil was covered with filter paper during application. This paper was removed before the start of the experiment and the amount of C 1 4


263 was determined after extraction and combustion of the filter paper. A survey of the experiments carried out is given in Table II.

Table II. Experiments carried out AI

No. of Target replicates Parathion-methyl 2 French beans Parathion-methyl 1 French beans Fenpropimorph

Climate

Simulated day Simulated day without irradiation Simulated day Soily^ar^y^

3

Duration [hi 24 24 96

Sample work-up and analysis procedure The PU-foams were changed after 1, 3, 6 and 24 h and in case of the ex periments with fenpropimorph in addition after 48, 72 and 96 h. The freezing and C0 -traps were changed every 24 h. After 24 h (parathion-methyl) or after 96 h (fenpropimorph) the experiments were stopped, the plants were harvested and the soil was taken out for homogenization. 100 g samples were taken from the homogenized soil for extraction and C-measurement. Extraction o f fen propimorph and metabolites from soil was carried out using chloroform and a Bleidner-apparatus (11) using a method described by Heizler (12). Plants were extracted with methanol. In the case of parathion-methyl extraction was carried out using acetone. For chromatographic characterization radio-HPLC (fenpropi morph) or radio-TLC (parathion-methyl) was used (13, 14). A l l P U foams were extracted following a procedure described by Niehaus (15) and aliquots of the frozen air humidity and the C0 -traps were measured using suitable scintilla tors. 14

2

14

14

2

Results

Experiments with Parathion-methyl Parathion-methyl experiments were carried out for 24 h simulating a meas ured weather scenario in May in Germany. In two experiments the irradiation influence was taken into account and in one additional experiment it was not. Figure 3 shows the measured and simulated scenarios.


to

ON



Figure 3. Measured (—) and simulated (—) air temperature (a), air humidity (b), wind velocity above the plant stand (c) and irradiation (d). (Reproduced with permission of reference 10. Copyright 1999 VerlagDr. Kôster)

266 14

Table III. Volatile radioactivity after application of C-parathion-methyl to French beans. Experimental Conditions without irradiation with irradiation (1 repl.) with irradiation (2 repl. )

lh 15.9 15.3 19.9

st

nd

Volatilization 2h 40.5 45.6 49.9

i

after 6h 53.4 60.2 56.1

24h 77.2 65.9 65.3

^radioactivity applied = 100 % 14

Under these conditions 15.3 % to 19.9 % of the C-parathion-methyl ap plied volatilized during the first hour after application. After 3 hours already 40.5 % and 49.9 % had volatilized. These processes continued, and after 24 hours more than 60 % of the radioactivity applied was determined in the P U foams of the trap system in the 3 experiments (13). Table III shows the volatili zation kinetics of both experiments under the influence of simulated sunlight and the kinetics of the volatilization of radioactivity in the dark. At this time, the 3 experiments were stopped, the plant material was har vested, extracted and analyzed. Table IV provides the mass balances.

14

Table IV. Mass Balances of Experiments with C-Parathion methyl Kind of experiment

Volatilized Extracted Not extracted Mass after 24 h from plants from plants balance [%]' [%]' l%f [%]'

Simulated outdoor conditions including irradiation (1 repl.) Simulated outdoor conditions including irradiation (1 repl.) Simulated outdoor conditions without irradiation

65.9

20.9

8.0

94.8

65.3

19.4

8.4

93.1

77.2

17.3

3.0

97.5

st

st

l

: radioactivity applied = 100 % 1 4

The radioactivity extracted from plants as well as the amount of C volatil ized and sorbed on the PU-foams were further investigated by T L G . The results showed that more than 99 % of the volatilized C represented still unchanged parathion-methyl in all experiments. Furthermore, more than 99 % of the radio activity extracted from the French beans was still the A . I. whereas under the influence of simulated sunlight more than 50 % of the radioactivity extracted were polar metabolites so that the amount of parathion-methyl still available on the plants was reduced (10). 1 4


267 Experiments with fenpropimorph For the fenpropimorph experiments a typical four-day German weather sce nario was recorded outside and programmed. Figure 4 shows the measured and simulated data. 1 4

Figure 5 characterizes the results of the volatilization kinetics of C fenpropimorph from the plant/soil systems. The volatilization rate was rapid within the initial 24 hours after application in the three experiments. Subse quently volatilization rate decreased and was nearly complete after 4 days.

14

Table V . Mass Balance of Experiments with C-Fenpropimorph Experiment Volatile C Volatile C 0 Extracted from plants Not extracted from plants Extracted from soil Not extracted from soil Mass balance 1 4

1 4

2

]

// [%]'

U%f 48.1 1.8 15.8 6.5 12.1 6.2 90.5

46.1 1.1 15.2 8.2 15.3 4.0 89.9

III[%]' 60.3 0.0 14.5 3.9 24.8 1.5 105.0

: radioactivity applied = 100 %

The mass balance in these experiments consisted of the extractable radio activity in soil and in plants and the volatile compounds. In addition to the vola tile compounds determined in the PU-foams in two of the three experiments small amounts of C 0 were detected in the C 0 traps. Table V shows the de tails of the results obtained. Most of the C-labeled residues recovered were extractable from plant and soil. The results obtained from H P L C investigation showed that at least 60 % of the radioactivity extracted from plants consisted of the metabolite fenpropimorph acid and other polar metabolites (11). In the soil extracts, however, only the un changed fenpropimorph was determined (14). 1 4

2

2

14

Discussion The application equipment presented here provided for an application pro cedure similar to agricultural practice. This was shown by determination of de viations of spraying amount per 100 cm to be 9 %, i.e., an equal distribution of the spray volume in this equipment is possible with nozzles licensed for agricul tural use (16). In the same paper, the wind profile in the chamber was investi2


as oo Arthur et al.; Terrestrial Field Dissipation Studies ACS Symposium Series; American Chemical Society: Washington, DC, 2002.


1,50

i 1

!—I

48 60 72 Hours after appl.

84

I %

12

24

36 48 60 72 Hours after appl.

84

Figure 4. Measured (—) and simulated (—) air temperature (a), humidity (b), wind velocity (c) and irradiation (d) during the experimental period of 4 days. (Reproduced with permission of reference 10. Copyright 1999 Verlag Dr. Kôster)

1

36

24

Τ ι

12

2

200 H

400

600

800-1

Wm

270 l4

% C 100 C Z J volatilized C in exp. I EMI volatilized C in exp. II • i volatilized C in exp. I l l 14

14

80

14

46-60 60

i

40 20

1

3

6

24

48

96

72

Hours after application

Figure 5. Kinetics of volatile radioactivity after application of Cfenpropimorph to barley/soil (Reproduced with permission of reference 10. Copyright 1999 VerlagDr. Kôster) gated. Therefore, the wind speed was measured at different heights at the cham ber front, in the middle and in the back of the chamber, aspiring a speed of l m s " at a height of 80 to 90 cm and an air exchange rate of 0.1 to 0.2 m s" at the chamber bottom. The results showed, that the wind speeds were uniform at each point and were rapidly reduced in the transition zone (area of plant stand sur face). These conditions were also measured in fields with barley and wheat (10). Since it is well known that results of laboratory experiments do not reflect the real outdoor conditions in detail, (17) the volatilization chamber presented here cannot simulate a field experiment but rather the parameters which have an important influence on the metabolism and volatilization of compounds applied in agriculture. This is the air temperature, the wind velocity, the relative air hu midity and the irradiation. It could be shown that the outdoor scenarios recorded and programmed were simulated very well and were reproduced exactly. The only restrictions are that wind velocities near calm can not be simulated because the online air condition system requires a minimum of air exchange, and that the intensity of the metal halide lamp can be adjusted only stepwise (10). The results obtained with C-parathion-methyl and C-fenpropimorph showed that volatilization may be a rapid and decisive process immediately after application and may be of importance for the interpretation of residue analysis in field dissipation studies. The experiments with C-parathion-methyl indicated that the influence of irradiation may be of importance already after application because photolytical processes of the compounds sorbed on the target can ap pear. Photolytical reactions of volatilized compounds in the atmosphere can not be simulated in this chamber which is another restriction of the system. This is due to the fact that the time the volatilized chemicals stay in the chamber is too short for photodegradation. 1

1

l4

14

14


271 In recent years several attempts were made to measure volatile compounds directly in the atmosphere after their application to the field. Therefore mete orological distribution models (18, 19) are used. It was already shown that these models may be used for a mass balance, however, with the restriction that these experiments require enormous preparations and special environmental condi tions, e.g., concerning the wind direction, which are often not available in the field. Therefore, the volatilization chamber described here provides an easy-touse experimental tool which supplies exact and reproducible information about the further fate of a pesticide after application taking into account mass balance, degradation and transport. In order to investigate whether the results from the volatilization chamber reflect the field conditions, an experiment was started where a wettable powder formulation of parathion-methyl was applied to French beans (20). Directly after application and after 1, 3, 6 and 24 hours randomized plant sampling was carried out and the parathion-methyl concentration was de termined. The environmental conditions during the experiment were measured and recorded and used for a parallel experiment with C-parathion-methyl in which the application conditions as well as the weather conditions during the experiments were repeated exactly. Volatile C-parathion-methyl was measured after PU-foam extraction as described above. The results showed that the lack of plant residues compared with the initial value determined in the field experiment by residue analysis after 1, 3, 6 and 24 hours were in good accordance: After 1 hour 86.1 % of the initial value were determined in the field experiment and 15.9 % volatilization were measured in the corresponding chamber experiment. After 3 hours 48.6 % of the initial value were determined on the plants in the field whereas 41.4 % volatilization were measured in the laboratory. Six hours after application 29.8 % had remained in the field and 53.4 % had volatilized in the chamber. After 24 hours all plants were harvested and analyzed. At this time 25.9 % of the initial value were determined in the field and 77.2 % of the C applied had volatilized in the laboratory. Together with the extractable and nonextractable residues in the plants the mass balance of the chamber experiment was 97.5 %. 14

14

1 4

Experiments in the volatilization chamber can also contribute to a better in terpretation of field dissipation studies if not only volatilization occurs but also mineralisation. This was demonstrated in an experiment with C-dimethoate after application to soil (20). After an experimental time of 24 hours, 7.9 % C 0 appeared in the C0 -traps of the chamber resulting from an intensive biodegradation by soil microorganisms. Another 7.8 % were no longer extractable from soil, 10.5 % were metabolites and only 1.3 % were determined as volatile dimethoate. Together with the extractable dimethoate residues (75.4 %) a mass balance of 102.9 % was obtained. The results presented here show that the volatilization chamber can reflect the field situation concerning the parameters important for the fate of pesticides. It provides detailed information for a better understanding, the results are repro ducible and mass balances can be prepared when using C-labeled compounds . 14

l 4

2

2

14


272

References 1. 2. 3. 4. 5. 6. 7.

8. 9. 10.

11. 12.

13. 14. 15. 16. 17. 18. 19. 20.

Gath, B.; Jaeschke,W.;Kubiak, R.; Ricker, R.; Schmider, F.; Zietz, E. Nachrichtenbl. Deutscher Pflschtzd. 1993, 45, 134-143 Wienhold, B. J.; Gish, T. J. J. Environm.Qual.1994, 23, 292-298 Harper,L.Α.;White,A.W.;Bruce, R. R.; Thomas,A.W.;Leonard, A. A. J. Environm.Qual.1976, 5, 236-242 Guenzi,W.D.;Beard, W. E. Soil Sci. Soc. Am. Proc. 1970, 34, 443-447 Grass, B.; Wenzlawik, B. W.; Rüdel, Η. Chemosphere. 1994, 28, 491-499 Hock, B.; Fedtke, C.; Schmidt,R.R.Herbizide: Entwicklung, Anwendung, Wirkungen, Nebenwirkungen; Thieme-Verlag: Stuttgart, GE, 1995 Van den Berg, F.; Kubiak, R.; Benjey, W. G.; Majewski, M. S.; Yates, S. R.; Reeves,G.L.;Smelt,J.H.;Van der Linden,A.M.A.In The Fate of Pesticides in the Atmosphere; Van Dijk, H. F. G., Van Pul, A. J., De Voogt, P.; Kluwer Academic Publishers: Dordrecht, NE, 1999, 195-218 Breeze,V.G.;Fowler, A. T. New Phytol. 1992, 120, 389-396 Kubiak, R.; Maurer, T.; Eichhorn, K. W. Sci. Of Total Environm., 1993, 132, 115-123 Kubiak, R. Praxisrelevante Untersuchungen zum Verhalten von Pflanzen -schutzmittelnin der Umwelt; Schriftenreihe Agrarwissenschaft Band 6; Verlag Dr. Köster, Berlin, GE, 1999, 1-155 Staimer, N.; Müller, T.; Kubiak, R. Int.J.Environm.Anal.Chem. 1996, 65, 183-191 Heizler, W. Methodensammlung zur Rückstandsanalytik von Pflanzen -schutzmitteln;Deutsche Forschungsgemeinschaft; Verlag Chemie; Wein -heim,GE,1991 Müller, T.; Maurer, T.; Kubiak, R. Environm. Monitoring and Assessment. 1997, 44, 541-547 Müller, T.; Staimer, N.; Kubiak, R. Pestic. Sci. 1998, 53, 245-251 Niehaus, R.; Scheulen, B.; Durbeck,H.W.Sci. Of Total Environm. 1990, 99, 163-172 Maurer, T.; Kubiak, R. Ecoinforma. 1994, 9, 567-579 Kubiak, R.; Führ, F.; Mittelstaedt,W.;Hansper, M.; Steffens, W. Weed Sci. 1988, 36, 514-518 Majewski, M. S.; Desjardins, R.; Rochette, P.; Pattey, E.; Seiber,J.N.; Glotfelty, D. E. Environm. Sci. Technol. 1993, 27, 121-128 Majewski, M. S.; Glotfelty, D. E.; Paw,K.T.;Seiber, J. N. Environm. Sci. Technol. 1990, 24, 1490-1497 Kubiak, R.; Müller, T.; Maurer, T.; Eichhorn, K. W. Int.J.Environm. Anal. Chem. 1995, 58, 349-358


Terrestrial Field Dissipation Studies - American Chemical Society

Recommend Documents