The Lysimeter Concept - American Chemical Society

Chapter 9

Demonstration of the Functionality of a Self-Contained Modular Lysimeter Design for Studying the Fate and Transport of Chemicals in Soil Under Field Conditions Downloaded by UNIV MASSACHUSETTS AMHERST on September 29, 2012 | http://pubs.acs.org Publication Date: September 10, 1998 | doi: 10.1021/bk-1998-0699.ch009

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I. Van Wesenbeeck , D. J. Schabacker , K. Winton , L. Heim , M . W. Winberry , M . D. Williams , J. B. Weber , L. R. Swain , and R. Velagaleti 3,5

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DowElanco Environmental Fate Group, R&D Building 306, A-2, Room 730, 9330 Zionsville Road, Indianapolis, IN 46268 Novartis Crop Protection, 410 Swing Road, Greensboro, NC 27419 Analytical Bio-chemistry (ABC) Laboratories, Inc., Columbia, MO 65201 North Carolina State University, Raleigh, NC 27695 2

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Analytical Bio-Chemistry (ABC) Laboratories, Inc. has developed a modular lysimeter design and has instrumented and installed the lysimeters at four field sites in the United States: Missouri (MO), Iowa (IA), Illinois (IL), North Carolina (NC) and Ontario (ON), Canada. The modular lysimeter design consists of three components that are readily assembled and installed in the field; an intact soil core, a run-off (overflow) collection system, and a leachate collection system. In N C , the lysimeters were installed at the N C State University Experimental Station site in Clayton with a Novartis Crop Protection development compound, designated as C-XYZ for confidentiality reasons. The fate and transport of the chemical was studied over a period of 90 days using intact 90 cm deep, 15 cm diameter soil columns containing sandy soil. Parent compound degraded into an acid metabolite that was detected down to 60 cm in the soil profile. Parent compound was not observed at a soil depth below 15 cm. The decline of the parent compound coincided with the formation of the acid metabolite which degraded into four additional metabolites. Lysimeters 30 cm in diameter and 75-90 cm deep were instrumented and installed at four locations (MO, IA, IL, and ON) to study the fate and transport of a DowElanco development compound, designated as C-DEC for confidentiality reasons. In these experiments, the fate and transport of the test compound and a bromide tracer in the lysimeters were compared with that in the field plots for 12 months. Preliminary results from IA and M O suggest that degradation and solute transport processes were similar in the soil plots and lysimeters, and that the 30 cm diameter pipe lysimeters approach the representative elementary volume (REV) for solute transport processes at the IA site. The modular pipe lysimeter design offers significant advantages in terms of assessing solute mass balance, mobility, variability (through increased replication) and reduced cost of radioactive waste compared to soil plot studies. 14

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Current Address: Hoechst Marion Roussel, Inc., Kansas City, M O 64137.

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©1998 American Chemical Society

In The Lysimeter Concept; Führ, F., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1998.

Downloaded by UNIV MASSACHUSETTS AMHERST on September 29, 2012 | http://pubs.acs.org Publication Date: September 10, 1998 | doi: 10.1021/bk-1998-0699.ch009

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Evaluating the degradation, adsorption, run-off (overflow), and leaching of chemicals in soil under actual field conditions is important in predicting their movement to surface and ground water. Soil, surface water, and ground water are potential recipients of chemical contaminants and are the environmental matrices of concern from environmental and human health perspectives. Assessment of risk to the terrestrial and aquatic organisms and to humans often involves the use of data generated from in-situ field experiments and predictive modeling. Lysimeters have been used extensively for assessing the environmental fate and mobility of agricultural chemicals, and their use has been reviewed in detail by Winton and Weber (1996). The lysimeter design developed by A B C Laboratories, Inc. provides an opportunity to study the fate and transport of chemicals and to generate reliable data on degradation, adsorption, run-off (overflow), leaching, and surface overflow (run-off) of chemicals applied to soils. These data are useful in prediction of risks of chemicals to human and environmental health. Materials and Methods The Modular Experimental Design. The modular A B C lysimeter design (U.S. Patent No. #5,594,185) incorporates a soil column, a leachate collection component, and a run-off collection component. A l l three modules are assembled in the field and placed in the ground in direct contact with the surrounding soil, thus maintaining an in-situ field moisture, % humidity, and temperature profile. The run-off/overflow component of the design is to preserve mass balance, i.e. to keep radioactivity from running over the top edge of the column in the event of excessive rainfall. The selfcontained nature of these components enables conduct of studies using radiolabeled test substances without risk of contaminating the surrounding soil (Figure 1). The modular design can be adapted to field sites with varying climatic conditions. For example, in lysimeters installed in Ontario (ON), Canada, the soil core was anchored to concrete support pillars for stability during freezing winters, since the frost line in this area is deeper than the length of the soil column (Figure 2). Experiments Conducted in North Carolina. The degradation and mobility of the Novartis compound, X Y Z , and its degradation products was monitored under field conditions in Clayton, North Carolina (NC) using outdoor lysimeters. The control soil in the intact soil core was segmented and was characterized as a sandy loam transitioning to loamy sand with increasing depth. pH ranged from 5.0 to 6.3 and organic matter from 0.4 to 2.6% with increasing depth. Collection of Soil Cores, Instrumentation and Installation of Lysimeter. The 15 cm steel pipes were obtained commercially pre-cut to 100 cm in length. Steel hooks were welded to the steel pipes to facilitate installation of the lysimeters in the ground or their removal from the ground. The leachate and run-off (surface overflow) collection systems consisted of commercially available PVC pipes capped at one end.



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Figure 1. A Graphic Representation of Design Used at the North Carolina Field Site.

Figure 2. A Graphic Representation of Design Used at Field Sites in Missouri, Iowa, Illinois, and Canada. The concrete pillar as a base support was only used in Canada.



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This collection system was connected to the soil column via teflon tubing between corresponding holes in the soil column and leachate component. Similarly, the leachate collection system was connected to the base of the soil column via teflon tubing between two sets of corresponding holes in the soil column. The leachate and run-off collection systems were fitted with an appropriate size PVC cap to prevent entry of direct rainfall. Intact soil cores were collected from the Agricultural Experimental Station of North Carolina State University in Clayton, N C by pressing a 100 cm long and 15 cm diameter steel pipe into the ground using a backhoe. Core integrity was monitored by visually examining the soil compaction (< 5 cm acceptable), as well as leaching of water through selected soil cores prior to treatment with the test substance. The pipes containing soil cores were subsequently lifted from soil. Approximately 10 cm of the soil was removed from the bottom of the intact soil core, creating the leachate collection area and freeing the two holes designated for the leachate collection system. A wire mesh held in place by a metal tripod was placed at the bottom of the core to support the soil column. The bottom of the soil core (leachate collection area) was sealed with an aluminum flashing tightly banded and caulked to the bottom of the soil core. The soil core was then instrumented with the run-off and leachate collection systems. The run-off and leachate collection modules contained a silanized glass vessel to collect run-off or leachate as it was produced. A teflon tube was placed in the silanized glass vessel and ran down the length of the leachate collection module for leachate sampling. The lysimeter clusters were buried in the soil back to soil surface level and allowed to acclimate to the surrounding environment for approximately three weeks before application of the test substance. Seven XYZ-treated lysimeters and one untreated control lysimeter were used for the study. Over the duration of the study, daily rainfall amounts, air and soil temperatures, and pan evaporation were obtained from the nearest National Océanographie and Atmospheric Association (NOAA) recording station in Raleigh, NC. Rainfall during the test period was 135% of the 10-year average amount of rainfall. Application of Test Substance. The surface of each soil core was dosed at a nominal concentration of 3.65 kg ai/ha (3 lbs ai/A) of the radiolabeled test substance (specific activity = 12.3 ^Ci/mg). The dose solution was prepared by dissolving 55.2 mg of X Y Z in 4 mL of acetonitrile:acidified water (8:2, v:v). Approximately 0.45 mL of dose solution in acetonitrile: acidified water (8:2, v.v) containing -9.7 μθ/mg (4,500 dpm/g) of radioactivity was applied to each lysimeter in a manner to ensure even coverage to the exposed surface of the intact soil core of each of the seven treated lysimeters. A n irrigation volume of -30 mL of de-ionized (DI) water was added to each treated lysimeter immediately following application. Sampling and Analysis. Visual observations of leachate and surface overflow were made on a weekly basis or after heavy rainfall, and leachate and surface overflow were collected when present. Leachates were collected by attaching a pipetter vacuum pump to the end of the sampling tubes and withdrawing entire



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leachate into a silylated amber sample bottle. The sample bottle was removed, capped, labeled, and shipped frozen to A B C Laboratories for radioassay and component analysis. Surface overflow collection bottles were accessed by hand and shipped in the same manner. A single treated lysimeter was removed randomly from the field at day 0,1 ,3, 14, 30, 62, and 90 following the application of the test substance. The control lysimeter was taken at day 90. The leachate and run-off7overflow units were disassembled from the soil core unit in the field. The intact soil cores were capped at both ends and immediately placed in a cooler with dry ice and shipped to A B C Laboratories. After they were received and logged at A B C Laboratories, the soil cores were stored frozen (-20°C) until analysis. The frozen soil cores were sectioned into 0-7.5, 7.5-15,15-30, 30-45,45-60, 60-75 and 75-90 cm segments with a power saw. Soils from each segment were homogenized and ground with dry ice. Following at least 24 hours of freezer storage to remove the dry ice, the total mass of the homogenized soil in each segment was determined. Nine aliquots (-500 mg wet weight basis) of each soil were combusted to determine the total amount of C residues in each soil segment. Soil segments containing or approaching 10% of the applied radioactivity were extracted and analyzed by HPLC to determine the concentration of the parent compound and its degradation products. 1 4

Experiments Conducted in Missouri and Iowa. The degradation and the mobility of two labels of the DowElanco C - D E C test compound was compared between lysimeters and field plots at two locations; one located on a silty loam overlying a silty clay loam soil [pH=6, Organic Matter (OM)=2.5%] at the A B C Laboratories site in Columbia, Missouri (MO), and the other located on a loam overlying a sandy loam/loamy sand (pH=6.5, OM=3%) soil in Cedar Falls, Iowa (IA). At each site two1 m χ 5 m bordered plots were instrumented with run-off/overflow collection systems and were treated with one of the two labeled test materials. An untreated control plot (2.4 m χ 3 m) was located approximately 5 m upwind from the treated plots and was treated with potassium bromide (KBr) tracer. Nine 30 cm diameter steel pipe lysimeters were installed adjacent to the soil plots to a depth of 90 cm at each site. The lysimeters were installed in the fall, approximately six months prior to application to allow acclimation to the surrounding soil environment. Eight lysimeters were treated with the test compound (4 with each label) and with the bromide tracer. One control lysimeter was treated with bromide only. Analysis of the DowElanco test compound is currently in progress, thus only a description of the bromide tracer mobility is described in this manuscript. 14

Collection of Soil Cores, Instrumentation and Installation of Lysimeters. The 30 cm diameter, 100 cm deep steel pipes used to collect the intact soil core were obtained pre-cut from a commercial supplier in Columbia, MO. Steel hooks were welded to the top of the lysimeter to facilitate installation or removal of steel pipes into and from soil, respectively. The run-off/overflow collection component was a metal canister open at the top end and sealed at the bottom. The runoff/overflow



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collection modules were tightly banded to the soil column with metal clamps to prevent movement during freeze and thaw. The leachate collection component was a PVC pipe capped at the bottom with a glass collection jar. The run-off/overflow collection system was connected to the soil column via teflon tubing between corresponding holes in the soil column and run-off/overflow component. Similarly, the leachate collection system was connected to the base of the soil column via teflon tubing between two sets of corresponding holes in the soil column and leachate component. The leachate and run-off components were fitted with PVC caps of appropriate dimension in order to prevent rain water from directly entering (Figure 2). The cap of the leachate component was fitted with U-shaped vent tube to ensure that an atmospheric pressure boundary condition was maintained at the bottom of the lysimeter. The collection of soil cores and installation of the lysimeters was similar to that described for North Carolina. Plot Preparation and Maintenance. The plant cover in the control plot and lysimeters was removed prior to the bromide tracer application and was maintained under bare soil condition for the duration of the study. Weeds growing in the plots and lysimeters were removed after application by cutting them at the soil surface and placing the back into the plot. Climatological data. An automated weather station was installed at both test sites. The weather station recorded precipitation (rain and snow), air temperature, soil temperature (2.5,10, 50 cm), wind speed and direction and solar irradiance. A Time Domain Reflectometry (TDR) system was installed in the control plot at each site to monitor volumetric soil water content at the 15,30,45,60 and 90 cm depths. Irrigation. Irrigation was applied to the plots and lysimeters during the growing season to ensure that total precipitation plus irrigation amounted to at least 125% of the 30 year monthly average rainfall amounts reported by the nearest NO A A site. Irrigation rate was not allowed to exceed the infiltration rate to prevent ponding. In the field plot irrigation amounts were measured by the use of rain gauges placed at various points on the plot. The lysimeters were irrigated separately using a perforated container that covered the surface area of the lysimeter and allowed irrigation water to drip uniformly across the soil surface. Application of the Bromide Tracer. KBr was broadcast sprayed on the control plot and treated lysimeters at a rate of 150 kg/ha (15 g/m ), after the test substance had been applied. Approximately 5 mm of water was added to the plots and lysimeters after application of the test substance and the KBr. 2

Sampling and Analysis for Bromide Tracer. Cores for bromide analysis were taken from the field plots on day 0, and 2, 4, 10 and 21 weeks after treatment (WAT). Samples were taken at 0-15 cm depth only on day 0. For subsequent intervals cores for bromide analysis were taken from 0-90 cm using a 3 stage probe with diameters of 7.5, 5, and 2.5 cm respectively for the 0-15, 15-45, and 45-90 cm



128 stage. As each stage was completed, a steel casing remained in the hole to prevent contamination of deeper depths. Soil cores for bromide analysis were sectioned every six inches and composited by A B C Laboratories before being shipped to DowElanco. Soil cores were also taken from two of the lysimeters at 14 W A T and from the 6 remaining lysimeters at the termination of the study (52 WAT) and shipped to DowElanco for analysis of the bromide tracer. Run-off/overflow and leachate were collected from the lysimeters weekly, or after significant run-off/overflow or leaching events. Soil, leachate, and run-off/overflow samples were frozen and shipped to DowElanco for the test substance and bromide tracer analysis. For the Br" analysis, soil samples from the field were weighed, mixed, and a 5 g subsample was extracted using 20 mL of DI water. Soil extracts and leachate water were analyzed for bromide concentration using a bromide specific electrode with a limit of detection (LOD) of 0.3 ppm. Modeling of Bromide Leaching. The pesticide leaching model (PLM) incorporates the pesticide adsorption and degradation routines from the C A L F model (Walker and Barnes, 1981; Nicholls, Walker and Baker, 1982) into the solute leaching model (SLM; Hall, 1993). P L M divides the soil profile into 5 cm layers between which soil solution is exchanged to simulate internal drainage and soil drying by evaporation. Soil solution is partitioned into mobile and immobile components, within each layer, with only the mobile components being displaced during drainage. Solute is permitted to diffuse between the two components. The program operates on a daily time step and is driven by the inputs of rainfall, évapotranspiration and maximum and minimum air temperatures. Since most soils drain rapidly to field capacity which has been defined by a matric potential of -5 kPa (Webster and Beckett, 1972), the volume of pores available for mobile water is estimated to be equal to the volume of pores air filled at -5 kPa potential. The volume of pores available to the immobile component is equal to the volume of pores water-filled at the same potential. The mobile phase is sub-divided into "fast" and "slow" domains which are empirically determined for the soils tested. Essentially this becomes a calibration factor for predicting hydrology for a particular site. Additional details of the model can be obtained from the P L M user's manual. For the IA study, actual soil and weather data at the site were available as model inputs. Initial runs were conducted and compared to the bromide leaching data in order to obtain (calibrate) the relative proportions of the "fast" and "slow" mobile phase. Once the model was calibrated for the bromide data, and therefore adequately describing the site hydrology, it can be used to predict test substance movement.


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Results and Discussion


North Carolina Site. Mobility of the Test Substance. Movement of the radioactivity through the soil core was observed with time. However, the vast majority of the radioactivity was found in the top 30 cm. Radioactivity was also detected in the 30-45 cm and 45-60 cm segments during the course of the study, but did not exceed 5% of the applied dose. No radioactivity above the minimum quantifiable limit (MQL) was observed in the 60-75 cm or 75-90 cm segments during the course of the study (Figure 3). Radioactivity was detected in the leachate only at a few sampling times. The highest amount of radioactivity observed in the leachate was 0.014% of the applied dose at day 30 sampling. Minor amounts of radioactivity were also observed in the surface overflow samples in the day 60 and 90 samplings. The amount of radioactivity in the run-off/overflow never exceeded 0.01% of the applied dose at any single event. The approximate M Q L in soil by combustion radioanalysis was 2 χ 10" mg/kg (ppm) while the M Q L in the leachate and overflow was 7.5 x1ο" mg/mL. The difference in M Q L between soil and water justifies the presence of C-activity in the leachate with no radioactivity observed in the lower soil core segments at specific sampling times. 3

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Degradation and Depletion of the Test Substance. The parent compound decreased rapidly during the first 30 days of the study ranging from 102.9% of the applied dose at day 0 to 16.3% of the applied dose at day 30. The amount of the parent compound at study termination (90 days) was 16.4% of the applied activity and was primarily observed in the 0-7.5 cm segment. Only minor amounts of the parent compound were observed in the segments below 7.5 cm (

The Lysimeter Concept - American Chemical Society

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