Turf Grass: Pesticide Exposure Assessment and Predictive Modeling

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Chapter 9

Modeling Approach for Regulatory Assessment of Turf and Golf Course Pesticide Runoff James N. Carleton1, Cheryl Sutton2, James Lin2 and Mark Corbin2 1

Environmental Protection Agency, Office of Water, Office of Science and Technology 2 Environmental Protection Agency, Office of Pesticide Programs

The U.S. Environmental Protection Agency (EPA) uses the models PRZM (Pesticide Root Zone Model) and EXAMS (Exposure Analysis Modeling System) to estimate environmental concentrations (EEC) of pesticides for aquatic exposure assessments and the estimated drinking water concentrations (EDWC) of pesticides for human exposure assessments. To address turf chemicals, EPA has developed specific scenarios for PRZM-EXAMS that estimate runoff of pesticides from managed turf grass. This paper discusses these turf scenarios and associated adjustment factors that are applied to model outputs specifically for golf courses.

Objectives The Environmental Protection Agency, Office of Pesticide Program’s (EPA/OPP) “turf work group” was formed in 2000, for the purpose of developing a methodology for simulating runoff loadings of pesticides from turf-covered landscapes. The methodology would have the primary purpose of providing scientists in OPP with tools for assessing exposures to aquatic organisms, and to people who consume water impacted by runoff of turf-applied chemicals. For practical reasons, it was desirable that the methodology be implementable within the same essential modeling framework (i.e., using the current versions of PRZM and EXAMS) that is in routine use by OPP scientists U.S. government work. Published 2009 American Chemical Society

123

In Turf Grass: Pesticide Exposure Assessment and Predictive Modeling Tools; Nett, M., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2010.

124 to estimate pesticide runoff loadings from cropped agricultural land, and resulting concentrations in receiving waters.


Background Using NASA satellite data, researchers have estimated the area covered by turf grass in the continental United States to be about 63,000 square miles, or 1.9% of total area (1), which makes turf the largest irrigated “crop” in the continental U.S., with about three times the acreage of irrigated corn. America’s devotion to turf-covered landscapes exacts a high ecological toll in terms of lost habitat, and, perhaps more insidiously, in squandered opportunities to choose alternative vegetation to support struggling native fauna (e.g. bird) populations with food and shelter (2, 3). The energy and chemical inputs necessary to maintain turf grass covered landscapes may also induce environmental damage via nutrient and pesticide runoff (4, 5), and, perhaps, through emissions of the potent greenhouse gas nitrous oxide (N2O) (6). OPP is charged with assessing the health and ecological risks directly associated with the use of pesticides. For this purpose, OPP uses the Pesticide Root Zone Model (PRZM) to simulate pesticide runoff and leaching. PRZM simulates two zones in an agricultural field ⎯ the cropped zone and the soil zone. The cropped zone includes the region above the land surface. The soil zone includes the region below the land surface. Turf, unlike most agricultural crops, can have a third important zone: the thatch zone. The thatch zone is located between the cropped zone (foliage) and the soil. Thatch is made up of live as well as dead (undecomposed or partially decomposed) grass leaf and root material. Thatch is important in turf modeling because it possesses hydrologic and chemical properties which may differ significantly from the other two zones described above. The thatch zone may strongly influence movement of both water and pesticide from the surface into the soil. Correctly representing the properties of the thatch zone is therefore important to simulation of pesticide runoff and leaching from turf areas.

Scenario Development Approach In order to meet the short-term objectives described above, the team revisited an unpublished modeling approach developed by James Lin at Bayer in the early 1990's which employed the existing version of the model (PRZM 1). This involved adding thatch as a 2 cm. layer of “soil” on top of an actual soil profile, similar to an approach later used by Duborow et al. (7) to model pesticide runoff from turf. The following critical thatch properties needed to model it as soil were obtained from an associated laboratory study (unpublished) on Kentucky bluegrass thatch: field capacity = 0.47; wilting point = 0.27; organic carbon = 35.6%. A value for bulk density of 0.37 g/cm3 was obtained from a published study (8). Results from a small turf plot runoff study were used to back-calculate a curve number for the site, and PRZM was run to simulate the runoff of pesticides under the artificial rainfall conditions of the



125 study. Differences between modeled total pesticide runoff loads and measured loads leaving the four plots ranged between -27.4% and 34.5%, indicating fair agreement between model predictions and data. A key consideration in modeling thatch as a soil layer is the selection of an appropriate value for % organic carbon (%OC). Although thatch has a very high organic carbon content, pesticide sorption to organic carbon in thatch is not well characterized by the results of sorption studies conducted in soils. Several studies that have examined and compared Koc values for pesticides in thatch and in soil have found lower Koc values in thatch (9, 10). This may be due to the relatively undecomposed nature of the organic matter in thatch, and resultant differences in hydrophobicity of carbon in thatch as compared to soil. Unfortunately, OPP does not typically have studies of pesticide sorption on thatch to develop model inputs and must use sorption coefficients derived from studies on soil. The approach adopted by the OPP Turf Work Group expanded on Dr. Lin’s basic approach, and in the absence of thatch-based Koc values, used soil-based Koc values (which are available in registrant-submitted environmental fate studies) to model thatch sorption. In this approach, PRZM was first calibrated via curve number adjustment so that modeled runoff matched the experimentally observed runoff response to a set of artificial rainfall events. Empirically-based adjustments to the %OC in modeled thatch were then made so that the sorptive behavior of studied pesticides (as reflected in the total mass of pesticide lost from the field in overland runoff) reasonably matched the results obtained in published small plot turf runoff studies. Small Plot Studies Used to Calibrate Effective %OC in Thatch The results of published studies conducted in the Piedmont Region of Georgia (11, 12) were found to contain sufficient detail to calculate a value for effective %OC in the thatch layer. These studies involved small-plot simulated golf course fairways (planted in bermuda grass) to which 2,4-D, dicamba, mecoprop, and dithiopyr were applied. The soil at the site was described as a Cecil sandy clay loam. Simulated rainfall of known volume (2.5 to 5 cm) was applied on days 1, 2, 4 and 8 after pesticide application. Total water volume leaving the plots after each artificial rainfall was reported in one study (12). Total pesticide load leaving the plots in runoff was reported in both studies. In order to simulate these applications and runoff events in a manner consistent with standard EPA approaches, the meteorological file that would ordinarily be used for modeling this specific region [Major Land Resource Area (MRLA) 136] was altered to include these “rainfall” additions on the specified dates. Extra rainfall was added to the file in arbitrarily-selected years 1956 and 1957, since the meteorological file did not include data for the time period after 1983, and the actual applications took place in 1993 and 1994. The soil profile in the PRZM input file was developed as described above, with soil layer thicknesses and properties for a Cecil sandy clay loam obtained from the Data Base Analyzer and Parameter Estimator (DBAPE) database (13), and a generic 2-cm thick layer of “thatch” on top as described above. Application rates and


126 dates were set to match those of the actual applications. The PRZM foliar extraction coefficient (0.5) and pesticide fate properties were set in accordance with existing OPP input parameter guidance. Maximum rooting depth was set at 3-cm, so that roots extended 1 cm below the thatch layer into the soil. The model was run for 1956, using various trial values of nominal curve number (CN2) until the total volume of runoff for the simulated events matched the observed volume reasonably well (Figure 1), which occurred with CN2 set to 93. This is is similar to the value of 91 that Durborrow et al. (7) found fit data from this site.

Percent runoff


80 70 60

observed

50

simulated

40 30 0

50

100

150

200

Hours After Treatment

Figure 1. Modeled vs. observed runoff at Georgia small plot turf runoff study, shown as a function of hour after treatment.

With the curve number set at 93, PRZM was then run for 1956 and 1957, using various trial values of %OC in the thatch layer, to model two compounds with high and low mobilities: 2,4-D (Koc=34.23) and dithiopyr (Koc=1920), respectively. By trial and error, a value of 7.5% OC was found to result in good agreement between model predictions and the runoff data for both compounds (Figures 2, 3, 4). Results for compounds modeled using Kd rather than Koc (dicamba, Kd=0.07 mL/g; and mecoprop, Kd=0.29 mL/g) also matched the GA data reasonably closely (Figures 5, 6). Note that because Kd was used instead of Koc to model these latter two compounds, sorption was modeled as independent of %OC, and the same results would have been obtained with any assumed %OC value for the “thatch” in the PRZM input file. This simply indicates that, for low-sorbing compounds, the chemical runoff algorithms already present in PRZM provide adequate representations of runoff in these particular small plot studies, without the need for pseudo-empirical adjustment of soil parameters to account for the presence of thatch.


127

Percent applied 2,4-D

8 6 observed

4

simulated

2 0 50

100

150

200


Figure 2. Modeled vs. observed 2,4-D runoff loading at Georgia small plot turf runoff study, shown as a function of hour after treatment.

Percent applied dithiopyr, 1st application


0

1.0 0.8 0.6

observed

0.4

simulated

0.2 0.0 0

3

6

9

12

Days After Treatment

Figure 3. Modeled vs. observed dithiopyr runoff loading at Georgia small plot turf runoff study (first application), shown as a function of days after treatment.


Percent applied dithiopyr, 2nd application

128 1.0 0.8 0.6

observed

0.4

simulated

0.2 0.0 3

6

9

12

Days After Treatment

Figure 4. Modeled vs. observed dithiopyr runoff loading at Georgia small plot turf runoff study (second application), shown as a function of days after treatment.

Percent applied dicamba


0

12 10 8 observed

6

simulated

4 2 0 0

50

100

150

200


Figure 5. Modeled vs. observed dicamba runoff loading at Georgia small plot turf runoff study, shown as a function of hours after treatment.


Percent applied mecoprop

129 12 10 8 observed

6

simulated

4 2 0


0

50

100

150

200


Figure 6. Modeled vs. observed mecoprop runoff loading at Georgia small plot turf runoff study, shown as a function of hours after treatment.

Summary of Approach The approach developed by OPP for constructing turf runoff modeling scenarios was to select soils (and their properties) for the region to be modeled, just as one would do to develop an agricultural runoff scenario. A 2-cm deep layer of “thatch” was then added on top of the modeled soil profile, posessing the following properties: bulk density = 0.37; field capacity = 0.47; wilting point = 0.27; organic carbon = 7.5%. Curve numbers were selected based on “good condition” open space areas as specified in TR-55 (8), that is, 39, 61, 74, and 80 for hydrologic soil groups A, B, C, and D, respectively. A 2-cm layer of thatch is typical for golf course fairways, but is probably thicker than average for golf course greens (Mike Kenna, personal communication; Research Director, United States Golf Association Green Section). Modern greens built according to current USGA specifications are designed to rapidly infiltrate water, and are built upon sand/peat mixtures, with tile underdrainage. However, a large fraction of the greens in the United States are of the old-style “push-up” variety, composed essentially of existing soil from the site, and lacking underdrainage. In the interests of simplicity, transparency, and implementability, turf was considered to be essentially generic, with no distinction made between fairways, greens, tees, or residential lawns. For chemicals applied to golf courses, the fraction of the total area composed of greens, tees, and fairways may be used to modify the results of a modeling run, somewhat in the fashion of a percent cropped area (PCA) adjustment for agricultural chemicals.


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Adjustments for Golf Course Turf OPP uses a tiered system for drinking water exposure assessments. At Tier I, screening-level models are used to assess pesticide concentrations in drinking water. Tier I is designed to screen out chemicals with low potential risk for posing a drinking water concern. If the Tier I exposure estimates are determined to represent unacceptable exposure, then a more refined Tier II assessment is conducted which provides more site-specific, refined estimates by taking into account additional environmental fate parameters, specific soil data, weather information, and management practices to estimate daily concentrations of pesticides in water for an extended period of time (up to 30 years). In both Tier I and Tier II assessments, surface water results are adjusted for a PCA factor which takes into account the fact that only a portion of the watershed being modeled may be planted to the specific crop being modeled. However, PCAs are only applicable to agricultural crops, not to non-food use crops such as turf. In cases where a pesticide is used only on golf course turf, additional adjustment factors were needed to account for the percent acreage of a golf course (and, thus, a watershed made up entirely of golf course land) that is not treated with a pesticide. The Golf Course Adjustment Factor (GCAF) was used to refine surface water EDWCs and EECs generated by OPP’s aquatic exposure models for golf course turf scenarios. Golf course facilities consist of separate playing areas that are classified as tees, greens, practice greens, fairways, driving ranges, and roughs, in addition to “unmanaged grounds” where lakes, ponds, out-of-play areas, conservation areas, and buildings are located. Depending on the playing area, management practices and intensity can vary in these facilities. When an individual pesticide is used, for example, only on tees and greens, or tees and greens plus fairways, if it is assumed in the modeling scenario that the entire golf course is treated, this assumption can lead to overestimation of the EDWCs and EECs. The use of the GCAF to refine those values can correct for this by quantitatively discounting the percentage of managed land area on a golf course that is not treated with a pesticide. Background Information Based on the World Golf Foundation’s “The Golf 20/20 Industry Report for 2002,” (15), there were about 15,827 golf facilities in the United States as of March 2003. An average-sized 18-hole golf facility is about 150 acres of total land (including water bodies, hard structures and out-of-play areas), of which ca. two-thirds are maintained turf (16). A typical urban golf course is only 110-120 acres, and courses in resort areas may be 170-190 acres (Greg Lyman, personal communication 11/19/04; Director of Environmental Programs, Golf Course Superintendents Association of America). Generally, pesticides are not applied to entire golf courses, but rather to some holes and some parts of the course (e.g., tees, greens, and/or fairways). They may be applied as spot treatments or to an entire portion of a course, although pesticide labels are rarely specific on the usage details. Tees and greens are typically the most intensively managed



131 areas, and tend to receive higher pesticide inputs compared with fairways and roughs. In determining EDWCs for a drinking water assessment, OPP utilizes a standard EXAMS scenario referred to as the “index reservoir” in Tier II modeling with PRZM/EXAMS. OPP’s Tier I model FIRST (FQPA Index Reservoir Screening Tool) also uses the index reservoir scenario, which simulates a 172.8-ha field (watershed) draining into a 5.3-ha reservoir. For agricultural crops, a PCA is used to adjust the EDWCs to account for the portion of a drinking water watershed containing fields planted with a specific crop. PCAs have been developed for only a few agricultural crops to date, largely limited by availability of crop acreage data at the required scale. At the present time, data are not available at the scale needed to finalize development of the non-agricultural equivalent of a PCA for golf course uses. For agricultural and non-agricultural crops, it is assumed that the entire field is treated. While this is often the case for agricultural crops, it is not typically the case for golf courses. Thus, for a drinking water exposure assessment, the GCAF is used to adjust the EDWCs to account for the percentage of the field that is not treated. This, in effect, makes the GCAF a “percentage land area treated” adjustment, characteristic of land use on a golf course. This adjustment is applied to both Tier I and Tier II modeling outputs for use in a drinking water assessments. In determining EECs for an aquatic ecological exposure assessment, OPP uses a standard EXAMS scenario referred to as the “small static pond” in Tier II modeling with PRZM/EXAMS. Scenarios simulate a 10-hectare field draining into a 1-hectare static pond that is 2-meters deep and does not have an outlet. The pond serves as a surrogate for the range of small, sensitive water bodies that can be found in the headwaters of a watershed, including low-order streams. It is assumed that runoff is equally likely to flow into the pond from all areas of the treated field, and that the entire field is treated. With the small pond and turf scenarios, OPP concluded that EECs were representative of a subset of ponds that occur on golf courses, given their configuration, the size of the ponds and their drainage areas. Thus, a GCAF is not used with Tier I EECs from GENEEC2 (Generic Estimated Environmental Concentration Model, v. 2.0), the Tier I model used to determine pesticide concentrations in surface water for aquatic ecological exposure assessments. It is only used after Tier II (unadjusted) EECs result in relevant Level of Concern (LOC) exceedences. If there are no exceedences, then only the risk quotients (RQs) derived from nonmodified EECs are reported in the risk assessment. For ecological exposure modeling, a GCAF is only used to refine the Tier II EECs. In this case, both the adjusted and unadjusted Tier II EECs are reported in the ecological risk assessment. This approach differs from that used in estimating drinking water exposure because, for drinking water, effects are integrated over a watershed of larger spatial scale and estimated concentrations are generally accepted as reasonably conservative.


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Supporting Data for Recommended GCAF Values In developing this GCAF guidance, two independent sources of data were reviewed. Additional information/data searching was conducted by personal communication and by consulting research reported on golf organization Web sites (e.g., Golf Course Superintendents Association of America at www.GCSAA.org and the United States Golf Association at www.USGA.org. The data obtained from the GCSAA, presented in Table 1, were utilized to develop the recommended GCAFs. The data from a USGA survey (which was an internal survey for use by pesticide registrants) were not used to develop the GCAFs, as the results were based on information for a smaller sample of golf courses and percentages were calculated based on total facility acreage, including non-turfgrass areas. The survey data provided by the GCSAA was based on the survey responses from 741 GCSAA members submitted over two years. Responses represented multiple course types including private, semi-private, daily fee, municipal, resort, and other. The majority of the courses were 18-hole facilities (572); others that were represented included 9-hole (79) and >19-hole (90) facilities. Respondents were from eight USGA regions of the country: Northeast (90), Mid-Atlantic (58), Southeast (73), Florida (45), Mid-Continent (150), North Central (163), Northwest (36) and Southwest (122). The distribution of responses matched the distribution of GCSAA members by course type, size and USGA region. Survey data used to develop the GCAFs are presented in Table I. Table I. Golf Course Superintendent Association of America Golf Course Acreage Survey Data Use Type Tees Greens Fairways Roughs Practice Greenc Driving Ranged

Average Number of Acresa 2.7 2.9 31.9 66.8 0.2 7.1

Percentage of Courseb (%) 2.4 2.6 28.6 60.0 0.018 6.4

a

Based on personal communication with Greg Lyman, GCSAA, 11/19/2004, these data represent the final results of the GCSAA 1999-2000 survey for golf course size. b Percentage represents course subtype divided by total maintained turf acreage of 111.5 acres. Acreage in lakes, ponds, out-of-play areas and hard structure acreage is not included; when included, the average size of a golf course is closer to 150 acres. c Practice green acreage is managed similar to greens and is accounted for in the recommended GCAF for tees and greens. d Driving range acreage is managed similar to roughs and is accounted for in the recommended GCAF for roughs.


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OPP Procedure for Use of Adjustment Factors Specific to Golf Course Turf on Tees, Greens, Fairways and Roughs This procedure describes how OPP adjusts EDWCs (drinking water assessment; both Tier I and Tier II) and refines EECs (ecological exposure assessments; Tier II only) resulting from pesticide use on golf course turf. This modification of estimated concentrations, using OPP aquatic exposure models, accounts for the percentage of the total golf course acreage that actually receives pesticide treatment. For pesticides applied only to tees and greens, the FIRST or PRZM/EXAMS output values are multiplied by 0.05 to modify the EDWCs (surface water only) and Tier II EECs, and the resulting values are reported as the adjusted EDWCs or EECs. For applications to fairways only, the output values are multiplied by 0.29. When tees, greens, and fairways are all treated, the output values are multiplied by 0.34. If tees, greens, fairways and roughs are all treated, a GCAF is not utilized, as the output values are “multiplied by” a factor of 1. For EECs, adjusted and unadjusted concentrations are both reported. The GCAFs are summarized in Table II. Table II. Recommended Golf Course Adjustment Factors by Turf Type Treated Areas of Course (Turf Type) Tees & Greens (includes practice green) Fairways Roughs (includes driving range) Tees & Greens & Fairways Tees & Greens & Fairways & Roughs

GCAF (0.024 + 0.026) = 0.05 0.29 0.66 (0.05 + 0.29) = 0.34 (0.05 + 0.29 + 0.66 ) = 1.0

Use/Guidance Restrictions The assumption that the entire watershed of a drinking water reservoir is comprised of golf course land, and that all of this land is treated, is a conservative simplification that is necessary given land use and pesticide application data limitations. With approximately 15,827 golf facilities in the United States, the co-occurrence of golf courses and other crops treated with the same pesticide in the same watershed cannot be discounted. OPP’s default PCA of 0.87 for agricultural crops cannot be used to refine EDWCs for golf course or other turf uses because the number was derived without including turf acreage. The current default PCA is based on the highest percentage of agricultural land in any United States Geological Survey (USGS) 8-digit Hydrologic Unit Code (HUC) in the conterminous United States. More data at a relevant spatial scale are necessary before OPP can develop PCAs for turf grass or other nonagricultural uses, including golf courses. The GCAF is different from the PCA factor, which is applicable only to agricultural crops and refers to the fraction of a watershed that is planted with a



134 particular crop. Instead, it is a correction factor used to account for the partial land area treated relative to the total golf course acreage. The GCAF is applied to model estimates for drinking water assessments. For ecological exposure modeling, the GCAF is only used to refine the Tier II EECs if Tier II (unadjusted) EECs result in exceedences of relevant LOCs. The GCAF is not used for Tier I EECs from GENEEC2. If there are no exceedences in Tier II modeling, then only the RQs derived from non-modified EECs are reported in the risk assessment. If there are exceedences in Tier II modeling, both the adjusted and unadjusted Tier II EECs are reported in the ecological risk assessment, and the differences are described in the risk characterization. The GCAF is not applied to groundwater values determined using the Tier 1 model SCI-GROW (Screening Concentration in Ground Water), which is based on a treated field rather than a watershed. The adjustment factor is only applicable to golf course use scenarios, and is not used for other turf use scenarios, such as sod farm, residential, right-of-ways, (other) recreational or any other turf uses. If other uses are permitted on the label(s), the adjustment factor is used only to modify, as appropriate, the values reported for golf course turf use. If there are any turf uses on the label other than golf course turf (for example, if the use is for “undifferentiated turf” or “sod farms”), the unadjusted values are reported to represent those uses, in addition to the adjusted values representing golf course use. Additionally, when used for modifying EECs, both the initial Tier II EEC and adjusted/refined Tier II EEC values are reported in the risk assessment. Remaining Uncertainties While a GCAF allows the user to modify the EDWCs and EECs determined by aquatic exposure models for a golf course turf use scenario, it does not take into account all uncertainties involved in estimating surface water concentrations associated with the use of a pesticide on a golf course. There are several aspects of pesticide use on golf course turf that may result in the model scenario underestimating surface water concentrations. Golf courses are commonly built near water; many are near wetlands. Golf courses are typically designed to drain water, incorporating a mix of areas with higher slopes, depressions, and tile drainage systems. These drains rapidly transport water that infiltrates to discharge points in nearby surface water bodies. Currently, neither the Tier I nor the Tier II aquatic exposure models used by OPP can account for subsurface drainage on golf courses. The turf standard scenario used in the Tier II model is a general one that is not specific to golf courses. The GCAF takes into account the fact that not all of the turf is treated; thus, it only allows for a “percentage land area treated” adjustment. The GCAF does not account for the fact that, for drinking water, it is highly unlikely that an entire drinking water watershed would be comprised of golf course turf. Additional data, analogous to the data used to develop PCA factors, are needed to address this issue. The values utilized to develop the GCAF represent average values, as data


135 were not available to represent higher percentile values. Also, the use of the GCAF assumes that the estimated surface water concentrations will be reduced in equal proportion to the reduced level of acreage treated; supporting data for this assumption are not available. Future research needs to help address some of these uncertainties include review of reliable pesticide monitoring data from golf courses, with adequate ancillary data to allow comparison with initial and refined EECs. The results of this research and additional data may lead to revised scenarios in the future.


Acknowledgements We are grateful to John Ravenscroft, Dana Spatz, Ron Parker, R. David Jones and Elizabeth Behl for their contributions.

Disclaimer Any opinion, findings, conclusions or recommendations expressed in this manuscript are those of the authors alone, and do not necessarily reflect the views of U.S. Environmental Protection Agency or the U.S. Government. Mention of trade names or commercial products does not constitute endorsement or recommendation for use.

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Turf Grass: Pesticide Exposure Assessment and Predictive Modeling

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