Abstract. 1 Introduction

Transcription

1 Transactions on Ecology and the Environment vol 3, WIT Press, ISSN Isolating and representing processes affecting pesticide partitioning C.C. Truman, P. Steinberger, A. Klik*, & R.A. Leonard USDA-ARS, Southeast Watershed Research Laboratory, Tifton, Georgia 33, USA, and Universitaet fuer Bodenkultur Wien, Vienna, Austria ^Collaborator via a fellowship under the OECD Co-operative Research Programme. ctswrl@tifton. cpes.peachnet. edu Abstract We evaluated a laboratory technique to isolate intrinsic processes controlling pesticide partitioning between infiltration, runoff and sediment. The laboratory technique provided controlled test conditions and reproducible results on processes affecting partitioning of rainfall, runoff, and pesticides at the soil surface, and sediment and pesticide transport. Atrazine and chlorpyrifos half-life values determined prior to simulating rainfall from corresponding concentrations in the 0- cm soil layer were 30 and 0 d. Atrazine, chlorpyrifos, and 2,4-D concentrations remaining in the 0- cm surface layer decreased logarithmically with rainfall duration. Atrazine and 2,4-D concentrations in the 0- cm layer were positively correlated with those associated with splash (S), runoff (R), and sediment yield (E) (R^=0.6-0.). Relationships for all pesticide concentrations in the 0- cm layer and infiltration (INF) were negatively correlated. Relatively poor correlations (R^= ) were found between chlorpyrifos and corresponding concentrations in the surface layer even though positive correlations were found between R and E (R^=0.) and E and S,. (R^=0.). Methodologies described provide a means of evaluating how changes in pesticide concentrations in the surface layer and the thickness of that layer are influenced by soil, rainfall and pesticide characteristics, and desorption kinetics affects pesticide transport by runoff. Introduction Pesticide partitioning is important in determining the magnitude of pesticide loss associated with infiltration/leaching and/or runoff (water or sediment)

2 Transactions on Ecology and the Environment vol 3, WIT Press, ISSN Measurements and Modelling in Environmental Pollution from agricultural fields. This lab study isolates processes influencing pesticide partitioning and transport in runoff and on sediment. Soil, pesticide, and rainfall characteristics will influence timing and amount of pesticide losses and the dominant transporting agent of that pesticide. Research on pesticide partitioning and entrainment into runoff has shown that the apparent partitioning coefficient (K^ or K^) for pesticides between water and sediment in runoff increases with pesticide residence time (,0), apparently related to diffusion limited desorption from internal soil aggregate surfaces. This phenomenon and processes controlling water and pesticide partitioning are not well understood and have yet to be fully defined. The objective of this paper was to describe a laboratory technique for determining pesticide partitioning between infiltration, runoff, and sediment. 2 Materials and methods Soil from the Ap horizon (0-0 cm) of the Greenville sandy clay loam (clayey, kaolinitic, thermic Rhodic Kandiudult) was used, and physical and chemical properties of this soil were as follows: 64% sand; 2% clay; 2 g kg~* organic matter; ph (I^O) = 5; and cation exchange capacity = cmol kg. Soil was air-dried and sieved through a mm sieve. Soil (depth=0 cm) was placed over a 5 cm layer of sand in a.5 m^ stainless steel erosion pan with a 53 cm wide by 60 cm long by 5 cm deep central test area. Before simulating rainfall, three pesticides (Table ) were applied to the soil surface with a nozzle-type, laboratory sprayer. After atrazine [6-chloro-Nethyl-N'-(l-methylethyl)-l,3,5-triazme-2,4-diamine] and chlorpyrifos [0,0-diethyl-0-(3,5,6-trichloro-2-pyridinyl)-phosphorothioate] were applied, 4 d were allowed to elapse before simulating rainfall. For 2,4-D [2,4-dichlorophenoxyacetic acid, dimethylamine salt], we waited 24 h after the initial rainfall event, sprayed 2,4-D, waited d, then simulated rainfall. Pesticide concentrations in the 0- cm soil depth were determined, 3, and 4 d following pesticide application. The erosion pan was then placed at a % slope which corresponded to the slope found in the field. Table. Selected properties and application rates of three pesticides used. Property *l/2> d Atrazine 60 Chlorpvrifos 30 2,4-D 0 KOC> "d i~' Solubility, mg L Application rate, kg ai ha"* 3.5

3 Transactions on Ecology and the Environment vol 3, WIT Press, ISSN Measurements and Modelling in Environmental Pollution 453 Simulated rainfall was applied with a multiple-intensity rainfall simulator (3). The simulator uses 000 Veejet nozzles, was placed 3 m above the erosion pan, and the rainfall intensity was 44 mm h"\ Runoff (R), sediment yield (E), splash water (S^), splash sediment (Sg), and infiltration (INF) were measured at 5 min intervals during each rainfall event. Pesticides were measured in R, E, S^, Sg, and INF at every other 5 min interval. Pesticide concentrations were determined on soil samples taken from the 0- cm soil depth just before simulating rainfall and at times corresponding to pesticide runoff sample collection. Pesticide sample preparation and analysis Runoff and splash samples were immediately separated into water and sediment phases after collection by filtering each sample through a 0.45 micron filter paper. Water samples andfilters+sedimentswere stored at 4 C until analysis. Water volumes were determined, and pesticide samples associated with R, S^, and INF were prepared. Atrazine was analyzed with GC, chlorpyrifos with enzyme-linked immunosorbent assay (ELISA) and GC, and 2,4-D with ELISA method. All water samples and diluted soils/sediment extracts were analyzed for chlorpyrifos and 2,4-D using ELISA. Detection limits were 0. ug L~* for chlorpyrifos and 0. ug L~* for 2,4-D. GC/NPD analyses were performed on a Perkin Elmer Autosystem, and detection levels for atrazine and chlorpyrifos were 0.05 and 0.20 ug L"\ respectively. GC/ECD analyses were performed on a Hewlett Packard 50 GC equipped with an electron captor detector. Detection level for chlorpyrifos was 0.0 ug L"^. HPLC/UV analyses were performed on a Hewlett Packard 00 HPLC or a Hewlett Packard 050 HPLC, and detection limits for atrazine and chlorpyrifos were 0.20 and 0.30 ug L"\ respectively. Soil/sediment samples (soils before and during rainfall simulation event, E and S^) were first extracted by a microwave assisted extraction (MAE) procedure. Briefly, soils and sediments+0.45 micronfilterswere extracted with ml MEOH.^O (:) mixture at 00 C for 20 min at 00% power. After allowing extraction vessels to cool to room temperature, the supernatant was filtered through a 0.45 micron pore size puradisc. Extract was then placed in a vial for HPLC, GC/NPD, GC/ECD, and/or GC/MS analysis. 3 Experimental results and discussion Data collected in this study can be used to isolate processes controlling water and pesticide partitioning. Our purpose here is to show how such data can be used to study and isolate processes controlling water and pesticide partitioning. Questions addressed include: What were the degradation characteristics of atrazine and chlorpyrifos during the 4 d period?, How much of each pesticide remains in the 0- cm surface soil layer during the rainfall event?, Are pesticide concentrations in the 0- cm surface layer related to pesticide concentrations in INF, R, S^, Sg, and E?

4 Transactions on Ecology and the Environment vol 3, WIT Press, ISSN Measurements and Modelling in Environmental Pollution 3. Hydraulic losses and sediment yield Reproducible results were obtained for runoff (R), sediment yield (E), infiltration (INF), splash water (S^), and splash sediment (S^). Average water losses for INF, R, and S^ are given in Fig.. Infiltration (INF) began at min, and INF rates increased sharply to a maximum just less than the rainfall intensity by the end of thefirstrainfall duration. The Greenville sandy clay loam is not susceptible to surface sealing, therefore, it took well into the second rainfall duration for INF rates to steadily decrease (as R rates steadily increased). Sediment yield (E) rates increased during the first and second rainfall duration although never exceeding 0.02 and 0.4 kg m"^ h~*, respectively (Table 2) TIME (min) Figure. Average infiltration (INF), runoff (R), and splash water (S^) losses with time during the rainfall event (=44 mm h~*). 3.2 Pesticide degradation and losses associated with R and E Measured degradation rates for atrazine (Fig. 2) and chlorpyrifos were t^ = 30 and 0 d, respectively, which were significantly shorter than those listed in Table. Values in Table were "non-statistical averages" determined from values reported throughout the entire US (2). Values of t^ for this study were longer than other reported field t^ values for atrazine and chlorpyrifos in the southeastern US, and can be attributed to pesticides being applied to air-dried soils and keeping the erosion pans inside during the 4 d between pesticide application and simulating rainfall. Lack of water in air-dried soils reduces pesticide degradation rates by reducing microbial activity thus causing longer t^ values. By keeping the erosion pan inside during those 4 d,

5 Transactions on Ecology and the Environment vol 3, WIT Press, ISSN Measurements and Modelling in Environmental Pollution 455 pesticides were not exposed to direct sunlight (lack of photo-degradation), wind, or humidity (lack of volatilization). Pesticide concentrations associated with R rates decreased from their initial maximum to a steady-state concentration (Table 2). Decreases in atrazine and 2,4-D concentrations in R with time were similar in that their concentrations at 5 min were extremely high followed by a sharp decrease in concentrations to steady-state levels. Similar event-based results for atrazine, 2,4-D and other relatively soluble herbicide concentrations have been observed by other researchers (2,,,2,3,4). Chlorpyrifos showed similar responses in terms of concentrations in R, were relatively low. Majority of chlorpyrifos losses were associated with sediment due to its relatively high equilibrium (about 6000) value..0 QL a. g H- LJ o 0000 z o CJ LdzN Event, k=-0.02 Event 2, k= B 0 2 TIME (days) Figure Atrazine concentrations in the 0- cm application. soil layer versus days after As sediment yield (E) rates increased, pesticide concentrations decreased to steady-state levels (Table 2). Relatively large chlorpyrifos concentrations were found in sediments, and generally decreased with time during the rainfall event. However, atrazine concentrations associated with E were also relatively large early in the event, and declined rapidly toward the end of the event. Also, atrazine concentrations associated with E were greater than those associated with R. Atrazine transport by sediment can be significant, especially during a time period immediately following pesticide application (,4,6). Pantone and associates reported atrazine concentrations associated with sediments to be one to two orders of magnitude greater than that associated with runoff water (,). These studies attributed greater atrazine concentrations in sediments than runoff to soils with high organic matter

6 456 Measurements and Modelling in Environmental Pollution Table Runoff (R), sediment yield (E), and associated pesticide losses. Time min R mm, /h Atrazine Chlorpyrifos ppb ,4-D E kg/m^/h i Atrazine n, Chlorpyrifos ppb ,4-D Not Applied Transactions on Ecology and the Environment vol 3, WIT Press, ISSN

7 Transactions on Ecology and the Environment vol 3, WIT Press, ISSN Measurements and Modelling in Environmental Pollution 45 contents, high-intensity rainfall events shortly after atrazine application, and/or when the time period between atrazine application and thefirstrainfall event was a week or longer. 3.3 Pesticide losses vs 0- cm soil concentrations Pesticide losses are, in part, a function of the amount of pesticide remaining in the soil surface. A better understanding of pesticide losses in runoff, sediment yield, and/or infiltration will be obtained if we understand factors or processes affecting pesticide amounts remaining in the surface soil layer. Atrazine concentrations in the 0- cm surface soil layer decreased logarithmically with time during the rainfall event (R^=0.0) (Fig. 3). Similar relationships were obtained for chlorpyrifos and 2,4-D. Relationships between pesticide losses associated with S, R and E and pesticide amounts in the 0- cm soil layer for atrazine and 2,4-D were positively correlated (R^=0.6-0.). Relationships between all pesticides in INF and corresponding amounts in the 0- cm depth were negatively correlated. Poor correlations (R^= ) were obtained for chlorpyrifos even though quite strong correlations were found between R vs E (R =0.) and E vs S^ (R^ = 0.). Given the large K^ value for chlorpyrifos, one would not expect chlorpyrifos losses to be correlated with 0- cm amounts only, but rather need a detachment and transport component to increase the correlation coefficient describing the delivery of this sediment-transported pesticide. Q. Q. Event aaaaa Event O O O Y = In X R*=0.0. n= TIME (mm) Figure 3. Atrazine concentrations in the 0- cm versus time during the rainfall event. soil layer

8 Transactions on Ecology and the Environment vol 3, WIT Press, ISSN Measurements and Modelling in Environmental Pollution 4 Summary and conclusions We developed and evaluated a laboratory technique to determine pesticide partitioning and transport between and into infiltration, runoff, and sediment. A sandy clay loam was exposed to simulated rainfall (44 mm h"*) 4 d after applying atrazine (3.0 kg ai ha"*) and chlorpyrifos (.5 kg ai ha~*) and d after applying 2,4-D (.0 kg ai ha"*) to determine pesticide partitioning and transport between and into infiltration, runoff and sediment. The following conclusions can be made:. Atrazine and chlorpyrifos t^ values determined from corresponding concentrations in the 0- cm soil layer were 30 and 0 d. Concentrations of atrazine, chlorpyrifos and 2,4-D remaining in the 0- cm layer decreased logarithmically with time during simulated rainfall events. Relationships between pesticide concentrations in the 0- cm surface layer and pesticide concentrations associated with R, S and E were positively correlated for atrazine and 2,4-D (R^=0.6-0.), whereas those relationships for all pesticides and INF were negatively correlated. Relatively poor correlations (R^= ) were found between chlorpyrifos and corresponding concentrations in the surface layer even though correlations were found between R and E (R^ = 0.) and E and S^ (R% = 0.). 3. The laboratory technique described provided controlled test conditions and reproducible information on processes affecting: partitioning of rainfall, runoff and pesticides at the soil surface, soil detachment and sediment and pesticide transport. This technique also provides a means of evaluating changes in pesticide concentrations in the 0- cm surface layer and thickness of that layer as a function of soil, rainfall and pesticide characteristics, and effects of non-equilibrium desorption conditions on pesticide transport via runoff as related to assumed equilibrium conditions. This information increases our understanding of how factors or processes affect pesticide partitioning and transport, and our ability to develop process-based models to predict pesticide fate and transport for event-based storms. References. Baker, J.L., & Johnson, H.P. The effect of tillage systems on pesticides in runoff from small watersheds. Trans. ASAE,, 22, Baker, J.L., & Laflen, J.M. Runoff losses of surface applied herbicides as affected by wheel tracks and incorporation. J. Environ. OuaL,, Foster, G.R., Neibling, W.H., & Nattermann, R.A. A programmable rainfall simulator, 2, ASAE Paper No

9 Transactions on Ecology and the Environment vol 3, WIT Press, ISSN Measurements and Modelling in Environmental Pollution Hall, J.K. Erosional losses of s-triazine herbicides. J. Environ. Qual., 4, 3, Hall, J.K., Pawlus, M., & Higgins, E.R. Losses of atrazine in runoff water and soil sediment. J. Environ. QuaL, 2,, Leonard, R.A., & Wauchope, R.D. The pesticide submodel. pp.- In W.G. Knisel (Editor) Model documentation. Vol.. CREAMS: A field scale model for chemicals, runoff, and erosion from agricultural management systems. USDA Conserv. Res. Rep. 26. U.S. Gov. Print. Office, Washington, DC, 0.. Pantone, D.J., Young, R.A., Buhler, D.D., Eberlein, C.P., Koskinen, W.C., & Forcella, F. Water quality impacts associated with pre- and postemergence applications of atrazine in maize. J. Environ. Qual.,2, 2, Pantone, D.J., Potter, K.N., Torbet, H.A. & Morrison, I.E. Atrazine loss in runoff from no-tillage and chisel-tillage systems on a Houston black clay soil. J. Environ. QuaL, 25:52-5, 6.. Smith, C.N., Bailey, G.W., Leonard, R.A., & Langdale, G.W.. Transport of agricultural chemicals from small upland piedmont watersheds. Environmental Research Laboratory Office of Research and Development, U.S. Environmental Protection Agency, Athens, Georgia. EPA-600/ May,. pp Triplett, G.B., Conner, B.J., & Edwards, W.M. Transport of atrazine and simazine in runoff from conventional and no-tillage com. J. Environ. QuaL,,, -4.. Wauchope, R.D., & Leonard, R.A. Maximum pesticide concentrations in agricultural runoff: a semi-empirical prediction formula. J. Environ. Qual, 0,, White, A.W., Bamett, A.P., Wright, B.C., & Holladay, J.H. Atrazine losses from fallow land caused by runoff and erosion. Environ. Sci. Tech., 6,, White, A.W., Asmussen, L.E., Hauser, E.W., & Turnbull, J.W. Loss of 2,4-D in runoff from plots receiving simulated rainfall and from a small agricultural watershed. J. Environ. Qual, 6, 5, This paper is a U.S. Government publication subject to copyright rules pertaining to all U.S. Government publications