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Runoff of 1,3-dichloropropene from field plot exposed to simulated and natural rainfall.

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Concern over runoff of surface-applied pesticides has resulted in significant research in the areas of runoff and modeling at the microplot, 1 - 10 [m.sup.2] (Baker and LaFlen 1979; Gaynor and van Wesenbeeck 1995), mesoplot, < 0.1 ha (Gaynor et al. 1992; Tan et al. 1993) and field scale, several ha to many [km.sup.2] (Cryer et al. 1999; Rhode et al. 1980). A review of studies assessing off-site movement of pesticides by water is given by wauchope et al. (1995). They define two categories of runoff studies, those that rely on natural rainfall and those that rely on simulated rainfall. Simulated rainfall studies are typically conducted at the microplot (1-10 [m.sup.2]) scale or the mesoplot (< 0.1 ha) scale, while natural rainfall studies are conducted with plot sizes up to the watershed scale. Most runoff research has been conducted with herbicides or insecticides that are soil or foliar applied and have the greatest potential for wash-off and subsequent transport via runoff or sorbed to sediments. Runoff pote ntial of a subsurface soil-injected volatile compound, such as the soil fumigant 1,3-dichloropropene (1,3-D), that diffuses rapidly through the soil profile, has not been studied for potential to contaminate surface water bodies beyond edge-of-field by runoff.

1,3-D is the active ingredient in the Dow AgroSciences plant protection product Telone II [R] soil fumigant. Telone II [R] is a pre-plant soil treatment used for protection of a variety of high-value crops and nursey stock from nematode and disease infestations. Telone II [R] is used Iin the southeastern United States in tobacco, sweet potatoes, tomatoes, peppers and a variety of fruit crops. In agricultural settings, Telone II(r) is typically injected into the soil at a depth of 30 to 45 cm using shanks set to the desired depth.

The primary objective of this study was to conduct a mesoplot scale (< 0.1 ha) field study using simulated rainfall to assess the potential for 1,3-D to reach the field edge via runoff under worst-case conditions in the southeastern United States. The study was designed to achieve worst-case conditions by selecting test site conditions that promote runoff (> 5% slope and high clay content) yet allow for flux of 1,3-D to the soil surface. Also, worst-case conditions were achieved by using simulated rainfall at a rate that exceeded a 1-in-25-year event and coincided with the time period that 1,3-D concentrations at the soil surface are at a maximum.

Methods and Materials

Properties of 1,3-D: Chemical and physical properties of 1,3-D are as follows:

Chemical name: 1,3-dichloropropene (CAS #542-75-6)

Common name: 1,3-D

Empirical formula: [C.sub.3][H.sub.4][Cl.sub.2]

Isomers: cis-l,3-dichloropropene trans-1,3-dichloropropene

Isomeric ratio: 51:49, cis:trans

Molecular weight: 110.98 g/mol

Density (25[degrees]C): 1.217 g/ml

Vapor pressure (25[degrees]C): 34.3 torr (cis); 23.0 torr (trans)

Water solubility (25[degrees]C): 2180 ppm (cis); 2320 ppm (trans)

Kow (25[degrees]C: 116 (cis); 107 (trans)

Henry's Law (25[degrees]C): 1.8([10.sup.-3] [m.sup.3] atm/gmol (cis) 1.05([10.sup.-3] [m.sup.3] atm/gmol (trans)

Environmental chemistry: 1,3-Dichloro-propene degrades readily in the soil environment. The compound degrades by hydrolysis (McCall 1987; Castro and Belser 1966), soil microbial metabolism (Van Dijk 1974), and other processes. Plants (bean, carrot, and tomato) grown on l,3-D treated soil rapidly metabolize the material. (Berry et al. 1980).

When 1,3-D is injected into soil, physical and chemical partitioning occurs among soil components: air, mineral surfaces, organic matter, and water. Leistra (1970) estimated that 80% to 90% of the applied 1,3-D is associated with organic matter; 10% to 20% is associated with soil water; less than 1% is present in the soil air; and the amount sorbed to soil minerals is negligible. Thomason and McKenry (1974) found that warm, dry soil conditions resulted in greater 1,3-D vapor movement than if the same soils tested were cold and moist. 1,3-D is more mobile in the vapor phase in drier, low organic matter soils of coarse texture (Leistra 1972; Thomason and McKenry 1974). 1,3-D moves from the injection point by water and vapor transport. The method of application and mobility of 1,3-D creates a complex system of concentration gradients within soil. Therefore it is impractical to collect soil residue samples immediately after treatment for confirmation of application rate in field-scale studies. Gaseous diffusion through soil pore spaces and the upward movement of soil water in response to surface evaporation results in the loss of some 1,3-D to the atmosphere through the soil surface-air interface. In a study of 1,3-D flux from a field soil in the Imperial Valley of California, Knuteson et al. (1995) applied 137 kg/ha (12.1 gallon/acre) of 1,3-D via broadcast injection to a clay loam soil. About 11% of the applied 1,3-D volatilized during the eight-day study.

Test site: The study site is located in Montgomery County in southwest Virginia on the Prices Fork Agricultural Research Farm of Virginia Tech, about 10 kilometers west of Blacksburg, Virginia (17[degrees]12'40" latitude and 80[degrees]25'54" longitude). The site is in the ridge and valley physiographic province of southwest Virginia (USDA 1985). Plots were established on a Groseclose clay loam (clayey, mixed, mesic Typic Hapludults) with a relatively uniform slope of about 5%. Irrigation water was obtained from a pond in a different drainage basin. The Groseclose clay loam is in the hydrologic group C, with a moderate surficial permeability of 5-15 cm/hr (2.0-6.0 in/hr) and a slow subsurface permeability of 0.15-0.5 cm/hr (0.06-0.2 in/hr).The field site had been fallow for at least five years prior to use for this study.

An analysis of the 1992 National Resource Inventory database (USDA 1994) for tobacco crop use (primary Telone II(r) market) in the southeastern U.S. (North and South Carolina, Georgia, and Virginia) found slopes to range from 0 to 55% with all hydrologic soil groups represented. Further analysis revealed that only 2% of tobacco soils were hydrologic group D soils, while 23% of the soils were classified as hydrologic group C soils. About 24% of the area had slopes greater than or equal to 5%. The soil and topography of the selected site rank it in the higher percentiles of vulnerability for runoff.

The soil profile was characterized by analysis of six, 120 cm soil cores. Cores were segmented into eight 15 cm segments, which were analyzed separately. The surface layer (0-15 cm) had an organic matter content of 2.72%, pH of 6.48, cation exchange capacity of 7.17 meq/100 g, bulk density (disturbed) of 1.10 g/[cm.sup.3] and a textural classification of a loam to clay loam (sand 27-45%, silt 42-48%, and clay 11-21%). Soil characteristics below 15 cm ranged as follows: organic matter, 0.98-0.20%; pH 6.58-4.95; cation exchange capacity 11.38-6.47 meq/100 g; bulk density (disturbed), 1.17-0.98 g/[cm.sup.3;] and textural classification, loam, clay loam, or clay (sand 19-31%, silt 8-46%, and clay 15-67%).

Plot layout and construction: Three 0.04 ha (0.1 acre) plots (Table 5) were established at the study site. Figure 1 shows the plot topography after site preparation. Average plot slopes were 4.7%, 4.9%, and 5.5 % for Plots 1, 2, and 3, respectively. For soil and air sampling, each plot was further divided into three suhplots that were further gridded into 18 sampling locations. Plot borders were installed to isolate each plot and to direct runoff downslope for flow measurement and sample collection (Figure 1). Border installation was begun immediately after chemical application. Borders along the sides and upslope end of each plot were 30-cm high plywood strips. Side and top borders were buried about 10 to 15 cm below the ground surface. Each joint was sealed with silicon caulk and held together with wood screws.

At the downslope end of the plot, V-shaped borders directed runoff to measurement and sampling instrumentation. The V-shaped borders were constructed of 45 cm high sections of plywood, buried at least 15 cm below the ground surface. Joints between the V-shaped borders and side border, as well as joints between the V-shaped borders and flume support, were covered with metal flashing and sealed with silicon caulk to ensure that all runoff passed through the flume.

Rainfall simulator: The rainfall simulator described by Dillaha et al. (1988) was placed over each plot after border installation was complete. Water was supplied to the rainfall simulator from a nearby pond that was filled with rain and well water. The rainfall simulator was designed to simulate an intense rainfall event of about 5 cm/hr (2 in/hr). The uniformity of the simulator was assessed during the study by placing 81 rain gauges throughout each plot. Average rainfall volume across test plots was 9.75 [+ or -] 1.02 cm. Rainfall volume in plots 1, 2, and 3 was 9.53 [+ or -] 0.91, 9.40 [+ or -] 0.94, and 10.36 [+ or -] 0.97 cm, respectively. Quantity of surface-applied pesticide in the aqueous phase of runoff is primarily related to antecedent water content and time between chemical application and rainfall event (Wauchope 1978; Gaynor et al. 1992, 1995; Moorman et al. 1989; Jaynes et al. 1999). Pantone et al. (1992) reported greater runoff losses and associated higher herbicide concentrations in one day compared with 30 days after herbicide application. However, for this study, because the material is injected 30 cm below the soil surface, a rainfall occurring immediately after an application would be a less vulnerable situation than a rainfall occurring when the peak mass flux of 1 ,3-D is occurring at the soil surface, Thus, simulated rainfall for this study was timed to coincide with the expected period of peak mass flux of 1,3-D at the soil surface. Based on field volatility studies conducted with 1,3-D, peak flux for a 30 cm injection on test site soils should occur at about 3 days after application (Knuteson et al., 1995).

Test substance application: The Telone II[R] application was made using a 7 shank broadcast applicator on July 9, 1999. Each shank was spaced 30 cm (12 inches) apart. Prior to application, both the tractor speed and the flow from the applicator were calibrated. Application area included the test plot area (36 m x 37.2 in), plus 3 m wide application buffer areas on the west, east and south sides of the plot. Buffer areas were added to allow the applicator to stop and start the injectors between application passes and to ensure an even application in the test plot area. The Telone II[R] was injected at a depth of 30 cm (12 inches). Final application rate was measured (total mass applied to the measured area) to be 367 kg/ha (32.4 gallons/acre). This high application rate was used to meet EPA requirements of conducting the study under worst-case conditions for potential runoff. However, in the southeast United States, the majority of Telone II[R] is used for tobacco production at rates of 102-136 kg/ha (9-12 ga llons/acre). Immediately after application, the soil surface of each test plot was disked across the slope followed by packing up-slope (worst-case runoff scenario) with a cultipacker to seal the plot surface and maximize the retention of 1,3-D within the soil profile. The final pass with the culti-packer left a series of small ridges, further increasing the worst-case runoff scenario.

Air sampling: Air samples were taken at 15 cm and 90 cm heights above the surface of each subplot (Figure 1) at 12-hour intervals from the time of application to assess the amount of 1,3-D volatilized from each plot. Air samples were also taken at about two-hour intervals before, during, and after the simulated rainfall event. Air was drawn through an activated charcoal air monitoring tube at a rate of 1.5-L/min using a calibrated battery operated pump. Air trapping was initiated as soon as possible after chemical application and continued until 12 hours after the simulated rainfall event. After each air- sampling interval, sample tubes were labeled, sealed, and stored frozen until shipment to the laboratory.

Meteorological data: An on-site automated Campbell Scientific 21X weather station (Campbell Scientific Inc., Logan, Utah) was installed near the northwest corner of Plot 3 (Figure 1) to measure and record meteorological parameters. Soil temperature (maximum, minimum, average daily, and average hourly at depths of 2.5 cm, 10 cm, and 50 cm), rainfall (total precipitation hourly and daily), relative humidity (%, average hourly and daily), and air temperature (maximum, minimum, average daily, and average hourly) were recorded. Wind speed (maximum and average) and direction (degrees from north) and solar radiation (k W/[m.sup.2], average hourly and daily) were also recorded.

Runoff and rainfall monitoring and sampling: A total of 81 manual rain gauges were placed in the study plots (nine rain gauges randomly placed in each subplot) to quantify amount and uniformity of simulated rainfall. They were emptied immediately before the start of the event, and measurements were recorded immediately after the end of the event.

Three test plots were each instrumented with calibrated flow measurement and automatic sample collection devices. Overland flow was diverted from each test plot to a 15 cm h-flume with an approach sloped at 8%. Each flume had a stilling well with a float and pulley, mechanical FW1 paper chart type stage recorder, equipped with a potentiometer attached to the pulley that enabled the electronic measurement of stage by a Campbell 21X data-logger. Electronic measurements were used in calculations of stage and flow, whereas paper charts served as a backup data source and provided calibration values.

Each plot was equipped with a system to collect automatic flow-proportional composite samples. Each sampling system contained an ISCO auto-sampler (ISCO Inc., Lincoln, Nebraska) with a composite sample kit activated by the 21X data-logger. Each data-logger calculated cumulative flow and initiated a sample after the specified flow volume of 1.33 [m.sup.3] (40 cu. ft.) was reached. The date, time, potentiometer mV, stage (ft), flow rate (cfs), and cumulative flow (cu. ft.) were recorded at each sample time. Flow composite runoff samples were collected in 40-mL volatile organic analysis (VOA) vials and immediately chilled on wet ice.

Time-based runoff collection samples from natural rainfall were collected at half-hour increments starting at 8 a.m. and ending at 1 p.m. Runoff samples from simulated rainfall were collected at ten-minute increments starting around 2 p.m. and ending after 4 p.m. All samples were collected in duplicate into 40-mL VOA vials and immediately chilled on wet ice.

Soil sampling: Two 60 cm cores from each subplot were collected to measure distribution of 1,3-D in the soil profile. After each core was collected, holes were backfilled with bentonite. Each core was subdivided into 15-cm segments, starting from the top. For each segment, the acetate liner was cut open and immediately re-cored by removing two 5 g subsamples of the soil cores and placing them into separate pre-weighed 40-mL purgeable VOA vials. Collection of a sub-sample was accomplished by using a plastic 10 cc syringe with the end cut off to remove 5 g (soil drawn into the syringe approximately to the 5 cc mark)

of soil. All samples in VOA vials were capped and frozen in a cooler with dry ice immediately after collection. Soil surface (0-2.5 cm) were collected using the modified 10 cc syringes (as described above) to "plug" the surface soil directly. Two 5 g subsamples were collected and placed into separate pre-weighed 40-mL VOA vials. Surface soil samples were collected just before and after the simulated rainfall event. Surface samples were collected within three randomly chosen grid blocks within each subplot.

Specific samples were collected from test plots before the simulated rainfall event for purposes of determining the antecedent water content. Because of preceding natural rainfall, the surface profile of the soil was near saturation, and as a result, the moisture measurements were not meaningful and are not reported.

Sample analysis: Individual concentrations of cis- and trans-1,3-D were measured and summed for the total 1,3-D concentration for each matrix (soil, air, and water). Water samples were analyzed for residues of 1,3-D by gas chromatography with mass selective detection (GC/MSD) using a purge and trap concentrator. Limit of detection (LOD) for water analysis was 0.015 ppb and limit of quantitation (LOQ) was 0.05 ppb. Soil samples were analyzed for residues of 1,3-D by methanol extraction and subsequent measurement by GC/MSD using a purge and trap concentrator. The LOD and LOQ for soil analyses were 0.30 ppb and 1.00 ppb, respectively. Air monitoring tubes were analyzed for residues of cis- and trans-1,3-D from the charcoal by acetone extraction and subsequent measurement by gas chromatography using electron capture detection (GC/ECD). The LOD and LOQ for charcoal tube analyses were 0.03 [mu]g/tube and 0.10 [mu]g/tube, respectively.

Results and Discussions

Meteorological conditions: On the day of application and the day after application, air and soil temperatures were warm, with air temperatures ranging from 15.9[degrees]C to 31.5[degrees]C and soil temperature ranging from 17.2[degrees]C to 35.9[degrees]C as shown in Table 1. The second day after application and the day of simulated rainfall, both air and soil temperatures were cooler, with air temperatures ranging from 16.4[degrees]C to 20.1[degrees]C and soil temperatures ranging from 19.2[degrees]C to 24.7[degrees]C. The day of simulated rainfall was also cool, with air temperatures ranging from 12.6[degrees]C to 15.1[degrees]C and soil temperatures in the range of 15.4[degrees]C to 17.4[degrees]C.

On the day of the simulated rainfall, 3,4 cm of natural rainfall preceded the simulated rainfall. Natural rainfall also occurred during the simulated event. Even though natural rainfall was not planned, the simulated rainfall event was continued because the timing needed to coincide with the expected period of maximum 1,3-D flux. Total rainfall during the simulated event averaged 9.4 cm (4.7 cm/hr). This intensity was representative of a 1-in-50-year, two-hour duration storm for Blacksburg, Virginia (Herschfield 1961). The combined natural rainfall and simulated rainfall was 12.8 cm with a 10-hour duration (1.28 cm/hr), which is representative of a l-in-l0-year storm for most of Virginia and North Carolina, and representative of a 1-in-5-year storm for Eastern North Carolina (Herschfield 1961). The significant storm return period for the two-hour simulated rainfall, along with the preceding natural rainfall, induced conditions that were representative of high runoff potential events.

1,3-D in soil and air: Data in Table 2 show that 1 ,3-D concentrations in the soil profile of the three test plots averaged 8,981, 11,098, 2,316, and 836 [mu]g/kg at the 0-15, 15-30, 30-45, and 45-60 cm intervals, respectively. Results indicate that 1,3-D was distributed throughout the top 30 cm of the soil profile. The average 1,3-D concentration in the top 2 cm of the three test plots was 1,980 [mu]/kg before simulated rainfall (Table 2). This suggests about 0.1% of the applied 1,3-D (equivalent to about 0.37 kg/ha) was in the top 2 cm and potentially available for runoff. After the simulated rainfall event, the surface concentration of 1,3-D averaged 1,800 [mu]/kg (Table 2). Given the variation of 1,3-D concentrations measured in the surface soil samples (Table 2), there was no statistical difference in the pre- and post-rainfall concentrations.

Air concentrations after chemical application ranged from below the limit of detection (0.028 [mu]g/[m.sup.3]) to 1,181 [mu]g/[m.sup.3]. In general, concentrations were higher at 15 cm than 90 cm above the soil surface and concentrations tended to be higher at night than during the day Concentrations at the 15 cm height increased through the first 24 hours then fluctuated until the sharp decline on day 2 because of 0.7 cm of precipitation and cooler air temperatures. On the day of the simulated rainfall, air concentrations were low (< LOD to 8 [mu]g/[m.sup.3] because of natural precipitation and cool air temperatures. The 1,3-D air concentrations observed at 15 cm and 90 cm heights over the plot before natural and simulated rainfall events were similar in magnitude to those observed in previous field volatility studies conducted under similar conditions (Knuteson et al. 1995). However, the concentrations observed in pre-rain air samples and the analysis of the top 2 cm of soil indicate that levels of 1,3-D a vailable for runoff were typical of worst-case conditions.

Runoff measurements: Two periods of rainfall and runoff occurred on July 12, 1999. Figure 2 shows at about 8 a.m., natural rainfall caused runoff that was followed by a simulated rainfall event starting at about 2 p.m. Table 3 shows that a large percentage of the simulated rainfall (62.1 to 80.8%) ran off.

Runoff was evaluated from natural and simulated rainfall. Table 4 and Figure 3 show that 1,3-D concentrations ranged from 0.653 to 5.47, 0.649 to 7.97, and 1.30 to 6.88 ppb for plots 1, 2, and 3, respectively, for the natural rainfall runoff event. Total 1,3-D mass losses caused by runoff from plots 1, 2, and 3 were 8.25, 19.3, and 14.8 mg, respectively (Figure 3 and Tables 4). Maximum concentrations during the natural rainfall runoff event were associated with the first small peak in flow rate.

Table 4 and Figure 3 show that concentration of 1,3-D from simulated rainfall ranged from 4.17 to 12.1, 3.56 to 12.2, and 7.32 to 17.2 ppb for plots 1,2, and 3, respectively. Peak concentrations for plots 1 and 2 occurred early in the event, and decreased during the event. Plot 3 had fluctuations in concentrations with no specific times for peak values. Total l,3-D mass losses caused by runoff from the simulated rainfall event for plots 1, 2, and 3 were 211, 252, and 406 rag, respectively as shown in Figure 3 and Table 4.

When natural and simulated runoff events were combined, the masses of 1,3-D in runoff from plots 1, 2, and 3 were 220, 271, and 421 mg, respectively (Figure 3 and Table 4). Total mass of 1,3-D in runoff was equivalent to about 0.002% of the applied 1,3-D (Table 5).

Summary and Conclusions

Runoff of 1,3-D was evaluated in a worst-case scenario that included a soil susceptible to runoff (5% slope with hydrologic group C soils), intense simulated (and natural) rainfall, up-slope tillage practices, and high 1,3-D application rate (367 kg/ha, 32.4 gallons/acre). Under these severe conditions, total mass of 1,3-D discharged in runoff averaged 0.002% of the applied chemical. The maximum 1,3-D concentration observed in runoff was 17.2 ppb, which is more than one order of magnitude below the lowest aqueous toxicological level of concern of 280 ppb (five day EC50 for freshwater diatom). In addition, rapid 1,3-D hydrolysis (11 days @ 20[degrees]C) further diminishes the possibility of 1,3-D having any environmental effects in surface water from field runoff (McCall, 1987). If results from this mesoplot study (< 0.1 ha) represent field scale conditions and processes, then our results indicate that the use of 1,3-D as a soil fumigant does not pose an environmental risk to offsite surface waters caused by runoff from treated fields.

[Figure 2 omitted]

[Figure 3 omitted]
Table 1

Summarized meteorological data.

                             Air Temp.       Soil
                                          temperature
                                          ([degrees]C
                                             ) at
                                            various
                                            depths
Operation/day               ([degrees]C)   2.5 cm

Application (Day 0)          15.9-31.5    17.2-35.9
Instrumentation (Day 1)      21.4-29.0    21.2-32.9
Instrumentation (Day 2)      16.4-20.1    19.2-24.7
Simulated rainfall (Day 3)   12.6-15.1    15.4-17.4

                            Soil temperature ([degrees]C) at various
                                             depths
Operation/day                10 cm

Application (Day 0)         21.0-30.2
Instrumentation (Day 1)     23.1-28.0
Instrumentation (Day 2)     21.2-23.2
Simulated rainfall (Day 3)  17.5-19.6

                               Soil
                            temperature
                            ([degrees]C
                               ) at
                              various
                              depths
Operation/day                 50 cm

Application (Day 0)         23.5-24.5
Instrumentation (Day 1)     23.5-24.0
Instrumentation (Day 2)     22.7-23.7
Simulated rainfall (Day 3)  21.1-22.5
Table 2

Soil concentrations of 1,3-D before and after the simulated
rainfall event.

                                Plot 1        Plot 2        Plot 3
                             ([micro]/kg)  ([micro]/kg)  ([micro]/kg)

           Depth
(before simulated rainfall)

          0-2 cm                  1895          1998          2047
          0-15 cm                 9446          9271          8225
         15-30 cm                12029         11831          9435
         30-45 cm                 3631          1679          1639
         45-60 cm                  151           158          2200

           Depth
(after simulated rainfall)

          0-2 cm                  1261          2500          1638

                             Average [+ or -] SD
                                ([micro]/kg)       CV

           Depth
(before simulated rainfall)

          0-2 cm              1980 [+ or -] 78      4
          0-15 cm             8981 [+ or -] 660     7
         15-30 cm            11098 [+ or -] 1443   13
         30-45 cm             2316 [+ or -] 1139   49
         45-60 cm              836 [+ or -] 1181  141

           Depth
(after simulated rainfall)

          0-2 cm              1800 [+ or -] 635    35
Table 3

Runoff volumes from each plot.

         Total runoff   Total runoff    Total rainfall       Runoff
             (L)            (cm)             (cm)        (% of rainfall)

Plot 1      32577      7.80 (3.07 in.)  12.5 (4.94 in.)       62.1
Plot 2      41742      10.0 (3.95 in.)  12.4 (4.89 in.)       80.8
Plot 3      37841      9.25 (3.64 in.)  13.4 (5.27 in.)       69.1

Average     37387      9.02 (3.55 in.)  12.8 (5.04 in.)       70.7
SD           4599      1.12 (0.45 in.)  0.55 (5.03 in.)       9.45
Table 4

Runoff, 1,3-concentrations and sediment loads from natural and
simulated runoff.

Natural rainfall

                                             Discrete 1,3-D
Sampling               Runoff                      concentration
  times               flow (L)                         (ppb)
            Plot 1    Plot 2    Plot 3         Plot 1       Plot 2

  8:08       120       91.9      311            1.97         1.73
  8:39       60.9      76.7      125           0.653        0.649
  9:09       146       220       221            1.23         1.83
  9:40       396       662       608            5.47         7.97
  10:09      563       922       862            3.46         5.70
  10:39      311       577       276            2.37         3.33
  11:10      217       457       181            1.79         2.52
  11:48      98.8      222       122            2.61         2.10
  12:12      465       700        65            3.80         4.36
  12:43      38.0      688       329            1.44         2.32

           Discrete               Cumulative                Sediment
            1,3-D
Sampling  concentrat              1,3-D mass                  load
             ion
  times     (ppb)                    (mg)                   (% w:w)
          Plot 3       Plot 1     Plot 2    Plot 3      Plot 1

  8:08     1.78        0.238      0.159     0.554       0.624
  8:39     1.95        0.277      0.208     0.797        1.50
  9:09     1.30        0.457      0.612      1.08        2.15
  9:40     6.88         2.62       5.89      5.26        2.29
  10:09    6.08         4.57       11.1      10.5        1.09
  10:39    2.87         5.31       13.1      11.3       0.554
  11:10    1.99         5.70       14.2      11.7        4.32
  11:48    1.48         5.92       14.7      11.8       0.439
  12:12    2.71         7.69       17.7      13.6       0.993
  12:43    3.47         8.25       19.3      14.8       0.439

                Sediment
Sampling          load
  times         (% w:w)
          Plot 2    Plot 3

  8:08    0.577     0.670
  8:39     1.57      1.34
  9:09     2.77      2.98
  9:40     2.38      2.33
  10:09   0.970     0.508
  10:39   0.485     0.439
  11:10   4.300      4.27
  11:48   0.692     0.254
  12:12   0.947     0.831
  12:43   0.462     0.716

Simulated rainfall

                                             Discrete 1,3-D
Sampling               Runoff                      concentration
  times               flow (L)                         (ppb)
            Plot 1    Plot 2    Plot 3         Plot 1       Plot 2

  14:00      1213      1739      2095           10.1         10.2
  14:10      2323      2999      2922           12.1         12.2
  14:20      2436      3019      2911           9.00         9.39
  14:30      2549      3060      2930           8.72         7.56
  14:40      2561      3064      2931           8.38         7.54
  14:50      2647      3182      3011           5.98         6.36
  15:00      2693      3289      2983           6.79         6.58
  15:10      2639      3289      2976           6.03         5.82
  15:20      2564      3288      2977           5.66         4.56
  15:30      2648      3288      3018           5.58         4.81
  15:40      2630      3289      3015           4.21         3.56
  15:50      2516      3289      2948           4.17         3.88
  16:00      735       1092      743            5.03         4.80
  16:10      201       240       141            6.14         4.74

           Discrete               Cumulative                Sediment
            1,3-D
Sampling  concentrat              1,3-D mass                  load
             ion
  times     (ppb)                    (mg)                   (% w:w)
          Plot 3       Plot 1     Plot 2    Plot 3      Plot 1

  14:00    9.00         20.5       37.0      33.6       0.924
  14:10    11.7         48.7       73.6      67.8        1.22
  14:20    10.2         70.6       102       97.6       0.947
  14:30    8.46         92.9       125       122        0.855
  14:40    11.2         114        148       155        0.739
  14:50    12.4         130        168       192        0.855
  15:00    13.2         148        190       232        0.716
  15:10    14.2         164        209       274        0.878
  15:20    17.2         179        224       325         1.46
  15:30    10.0         194        240       356        0.647
  15:40    10.8         205        252       388         1.11
  15:50    7.32         215        264       410        0.577
  16:00    12.2         219        270       419        0.577
  16:10    15.6         220        271       421        0.185

                Sediment
Sampling          load
  times         (% w:w)
          Plot 2    Plot 3

  14:00   0.855      1.02
  14:10   0.855     0.855
  14:20   0.808     0.993
  14:30   0.808     0.693
  14:40   0.901      1.32
  14:50   0.647     0.831
  15:00   0.554     0.762
  15:10   0.577     0.924
  15:20   0.901     0.716
  15:30   0.601      1.15
  15:40   0.647     0.647
  15:50   0.739     0.670
  16:00    1.04     0.346
  16:10   0.277     0.370
Table 5

Percent of applied 1,3-D in runoff.

                      Total 1,3-D                   Percent of
          Plot area     applied    Total 1,3-D in  applied 1,3-D
         ([m.sup.2])   (g/plot)      runoff (g)      in runoff

Plot 1       423        15,017         0.220          0.0015%
Plot 2       426        15,076         0.271          0.0018%
Plot 3       425        15,061         0.421          0.0028%

Average      425        15,051         0.304          0.0020%
  SD           2            31         0.104          0.0007%


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LUCAS G. Heim, Nathan J. Snyder, and Ian J. van Wesenbeeck are with the Dow AgroSciences Global Environmental Chemistry Laboratory in Indianapolis, Indiana.
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