Document ID: EPA-HQ-OPP-2006-0703-0003
Agency: epa
Document Type: Supporting & Related Material
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Posted Date: 2007-08-28T04:00Z

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<p>Office of Pesticide Programs (OPP) Conference Room 4370<br />
2777 Crystal Drive - Potomac Yard One, South<br />
Arlington, VA 22202</p>

<p><strong>On this Page</strong></p>

<ul>
<li><a href="#attendees">Attendees</a></li>
<li><a href="#welcome">Welcome and Introductions</a></li>
<li><a href="#brief">Brief Updates</a></li>
<li><a href="#presentations">Major Presentations</a></li>
<li><a href="#wrap">Wrap up</a></li>
</ul>

<hr />

<h2 id="attendees">Attendees</h2>

<table class="table zebra" summary="Attendees">
<thead>
<tr>
<th scope="col">Name</th><th scope="col">Association</th></tr>
</thead>
<tbody>
<tr><td>Marija Arsenovic</td><td>	IR4	</td></tr>   
<tr><td>Lizanne Avon</td><td>	PMRA	   </td></tr>
<tr><td>Reuben Baris</td><td>	Environmental Turf Services	   </td></tr>
<tr><td>Michael Barrett</td><td>	OPP/EFED	   </td></tr>
<tr><td>Steve Bedosky</td><td>	LFR	   </td></tr>
<tr><td>Betsy Behl</td><td>	OPP/EFED	   </td></tr>
<tr><td>Jim Breithaupt</td><td>	OPP/EFED	   </td></tr>
<tr><td>Elizabeth Buckley</td><td>Pesticide and Toxic Chemical News</td></tr>
<tr><td>Katherine Carr</td><td>	Monsanto	   </td></tr>
<tr><td>Wenlin Chen</td><td>	Syngenta	   </td></tr>
<tr><td>James Cooper</td><td>Florida Dept. of Ag. and Consumer Svcs.</td></tr>
<tr><td>Mark Corbin</td><td>	OPP/EFED	</td></tr>   
<tr><td>Marietta Echeverria</td><td>	OPP/EFED</td></tr>	   
<tr><td>Tammara Estes</td><td>	Stone Environmental	</td></tr>   
<tr><td>Kris Garber</td><td>	OPP/EFED	   </td></tr>
<tr><td>Kurt Getsinger</td><td>	USACE	   </td></tr>
<tr><td>Cathleen Hapeman</td><td>	USDA-ARS	   </td></tr>
<tr><td>Paul Hendley</td><td>	Syngenta	   </td></tr>
<tr><td>Erin Henry</td><td>	OPP/EFED	   </td></tr>
<tr><td>Jim Hetrick</td><td>	OPP/EFED	   </td></tr>
<tr><td>Scott Jackson</td><td>	BASF	   </td></tr>
<tr><td>Russell Jones</td><td>	Bayer Crop Science</td></tr>	   
<tr><td>RDavid Jones</td><td>	OPP/EFED	   </td></tr>
<tr><td>Faruque Khan</td><td>	OPP/EFED	   </td></tr>
<tr><td>Brian Kiernan</td><td>	OPP/EFED	   </td></tr>
<tr><td>Jim Lin</td><td>	OPP/EFED	   </td></tr>
<tr><td>Qingli Ma</td><td>	Environmental Turf Services	   </td></tr>
<tr><td>Greg Malis</td><td>	PMRA	   </td></tr>
<tr><td>Keara Moore</td><td>	OPP/EFED	   </td></tr>
<tr><td>Andy Newcombe</td><td>	LFR	   </td></tr>
<tr><td>Greg Orrick</td><td>	OPP/EFED	   </td></tr>
<tr><td>Paul Paquin</td><td>	Hydroqual	   </td></tr>
<tr><td>Ron Parker</td><td>	OPP/EFED	   </td></tr>
<tr><td>Lucas Paz</td><td>	LFR	   </td></tr>
<tr><td>T.S. Ramanarayanan</td><td>	Bayer Crop Science	   </td></tr>
<tr><td>Amy Ritter</td><td>	Waterborne Environmental	   </td></tr>
<tr><td>Mohammed Ruhman</td><td>	OPP/EFED	   </td></tr>
<tr><td>Lucy Shanaman</td><td>	OPP/EFED	   </td></tr>
<tr><td>Donald Stubbs</td><td>	OPP/RD	   </td></tr>
<tr><td>Jane Tang	</td><td>Bayer Crop Science	   </td></tr>
<tr><td>Michelle Thomson</td><td>	Dupont	   </td></tr>
<tr><td>Nelson Thurman</td><td>	OPP/EFED	   </td></tr>
<tr><td>Jayne Walz</td><td>	Cerexagri	   </td></tr>
<tr><td>Tracy White</td><td>	OPP/RD	   </td></tr>
<tr><td>Marty Williams</td><td>	Waterborne Environmental</td></tr>
<tr><td>Dirk Young</td><td>	OPP/EFED	 </td></tr>

</tbody>
</table>

<table class="table zebra">
<caption>Dial In Participants</caption>
<thead>
<tr>
<th scope="col">Name</th><th scope="col">Association</th></tr>
</thead>
<tbody>
<tr><td>Lars Anderson</td><td>	USDA-ARS</td></tr>
<tr><td>Kevin Armbrust</td><td>	State of MS	</td></tr>   
<tr><td>Monica Ball</td><td>	Dupont</td></tr>	   
<tr><td>Mark Bookbinder</td><td>	Bookbinder</td></tr>	   
<tr><td>Cecil Dharmasri</td><td>	Syngenta</td></tr>	   
<tr><td>Tony Fristachi</td><td>	USEPA-ORD</td></tr>	   
<tr><td>George Ghanem</td><td>	IECIS	</td></tr>   
<tr><td>Daniel Hass</td><td>	NYC health</td></tr>	   
<tr><td>Pat Haven</td><td>	Dow Agrosciences</td></tr>	   
<tr><td>Heather Johnson</td><td>	State of MN</td></tr>	   
<tr><td>Ian Kennedy</td><td>	PMRA</td></tr>	   
<tr><td>Jim Knuteson</td><td>	Dow Agrosciences	</td></tr>   
<tr><td>Bill Mahlburg</td><td>	Nufarm</td></tr>	   
<tr><td>Elise McCoy</td><td>	FMC	</td></tr>   
<tr><td>Roy Meyer</td><td>	NJDEP	</td></tr>   
<tr><td>Natalia Peranginangin</td><td>	Syngenta</td></tr>	   
<tr><td>George Sabbagh</td><td>	Bayer Crop Science</td></tr>	   
<tr><td>John Troiano</td><td>	CDPR</td></tr>	   
<tr><td>Katherine von Stackelburg</td><td>	Menzie-Cura	</td></tr> 

</tbody>
</table>

<p class="pagetop"><a href="#content">Top of page</a></p>
<hr />

<h2 id="welcome">Welcome and Introductions</h2>

<p>The Exposure Modeling Group hosts quarterly meetings that are open to the public to provide a forum for cooperative exchange of facts and technical information on technical issues related to pesticide exposure modeling between EFED and stakeholders with similar technical expertise. Keara Moore (OPP/EFED) chaired the meeting in the capacity of co-chair of the EFED Water Quality Tech Team (WQTT). </p>

<p>This meeting includes presentations which focused on exposure assessment for aquatic pesticides. All FIFRA EMWG agendas, minutes and presentations and be found at: <a href="http://www.epa.gov/oppefed1/models/water/emwg_top.htm">http://www.epa.gov/oppefed1/models/water/emwg_top.htm </a></p>

<p class="pagetop"><a href="#content">Top of page</a></p>
<hr />

<h2 id="brief">Brief Updates</h2>

<ol>
<li><p><strong>New WQTT co-chairs</strong></p>
<p>Dirk Young and Greg Orrick will be the WQTT co-chairs for the upcoming year.</p>
</li>
<li><p><strong>PRZM3.12.2 Evaluation</strong></p>
<p>QA/QC of the new version of PRZM has been completed.  The report is being finalized to incorporate minor edits and will be released soon.  This update only addresses curve number and emergence dates issues.  QA/QC review of volatility/temperature issues will be handled as a separate project at a later date.  The new version of the EFED shell (PE5.pl) and the updated scenarios are ready and will be released when PRZM 3.12.2 is implemented. </p>
</li>
<li><p><strong>EXPRESS</strong></p>
<p>EFED is working with ORD on a QA/QC process for EXPRESS.  EXPRESS will be implemented when QA/QC is completed successfully. </p>
</li>
<li><p><strong>Rice Model</strong></p>
<p>T.S. Ramanarayanan asked about the status of the rice model and about the "interim" rice model.  Betsy Behl answered that the refined rice model development project was not completed due to EFED's increased workload to meet its reregistration deadlines.  The Agency agreed that the rice model has been "interim" for some time, and confirmed that it is the model that is used to assess aquatic exposure from pesticides used on rice.</p>
</li>
</ol>

<p class="pagetop"><a href="#content">Top of page</a></p>
<hr />

<h2 id="presentations">Major Presentations</h2>

<p><strong>Herbicides for Submersed Weed Control:  Understanding Aqueous Concentration and Exposure Time Relationships (Kurt Getsinger, U.S. Army Corp of Engineers)</strong></p>

<p>Invasive aquatic plants have a number of negative consequences such as impeding navigation, curtailing recreation, clogging water intakes, degrading fish and wildlife habitat, decreasing biodiversity, and harming threatened and endangered species.  Herbicide treatments for aquatic plants can be made as emergent applications, treating the leaf surface, or as submersed application, treating the water body.  Herbicide efficacy is dependent on dose and contact time, with lower doses requiring longer exposure times.  Concentration and exposure time relationships (CETs) are unique to both herbicide and plant.  Laboratories, growth chambers, greenhouses, outdoor tanks, and ponds are used to test the CETs.  Herbicides should be selected based on the CET relationship; to have acceptable control, you must identify the target plant, determine the proper exposure time required for the herbicide/plant combination, and understand the water exchange characteristics of the treatment site.  Treatment areas include spot treatments, partial lake treatments, and large blocks or whole lakes.  As the treated area increases, the application rate may possibly be reduced because of the ratio of treated: non-treated water.  Contact time of herbicides is influenced by water column distribution, which is affected by water exchange processes, including gravity flow, wind-generated currents, and temperature factors (isothermal and stratified conditions).  To achieve the optimal contact time when applying submersed herbicides, apply in static/quiescent water and low-wind conditions, inject below water surface with variable length hoses, and apply when the water column is close to isothermal conditions.  In flowing water environments, there are different factors affecting the CETs.</p>

<p><strong>Assessing Exposure to Aquatic Plant Pesticides (R David Jones & Nelson Thurman, USEPA - OPP/EFED)</strong></p>

<p>The United States Environmental Protection Agency (USEPA) Office of Pesticide Programs (OPP) conducts both ecological and human health risk assessments for pesticides applied directly to aquatic systems.  The Environmental Fate and Effects Division (EFED) of OPP has primary responsibility for estimating exposure in aquatic systems from the direct application of pesticides.  EFED attempts to answer several general questions when conducting exposure assessments for aquatic pesticides, including what is the maximum expected concentration as specified on the label, how long will the pesticide persist in these systems above levels of concern (LOC), how far will the pesticide travel from the site of application at concentrations above the LOC, and how sufficient is the available data to answer these questions.  Examples of direct applications to aquatic systems, which EFED typically has evaluated, include application to rice paddies, application to reservoirs and ponds, and application to irrigation canals.  Commonly applied pesticides include herbicides for control of native and invasive weeds, insecticides, and piscicides.  </p>

<p>Examples discussed in the presentation included application of fipronil to rice paddies for insect control, 2,4-D to reservoirs for weed control, xylene and acrolein to irrigation canals for weed control, and rotenone to ponds for control of invasive or undesirable fish.  The first examples of assessment techniques presented included the calculation of pesticide concentrations in rice paddy water at the point of release to surface water streams.  Comparison of predicted fipronil concentration in release water compared favorably with available monitoring data.  For 2,4-D, an assessment of potential setback distances between application for aquatic weed control and drinking water intakes was discussed.  In this example, a simple advection/dispersion model was used to evaluate an appropriate setback distance for labeling.  Using a simple model accounting for dilution, degradation and volatilization, Xylene was assessed to determine how long it would persist above the LOC after discharge from an irrigation system.  Rotenone was presented as an example of an assessment approach for a piscicide with limited fate data.  The intention of the assessment was to determine how long after treatment could native fish species be re-introduced to both lakes/reservoirs and streams/rivers.  Acrolein was another herbicide used in irrigation canals presented as an assessment example.  In this example, acrolein is applied to irrigation systems and is not intended to reach surface waters beyond the canal systems.  A proposed approach was presented for assessing under what conditions acrolein would not be expected to reach surface waters.  Finally, the presentation summarized future goals for EFED to develop new approaches for assessing other aquatic use scenarios, including a higher level rice model, cranberries and watercress, mosquito larvacides, and more advanced approaches for assessing piscicides.</p>

<p><strong>Use of Visual PLUMES and EXAMS in the Development and Field Evaluation of Aquatic Herbicides (Scott Jackson, BASF)</strong></p>

<p>Hydrilla was presented as an example of an invasive species. This plant is very difficult to control because it lives in a wide variety of water bodies and tolerates a wide variety of   salinity, temperature, nutrient and light conditions. The project evaluated the use of models on two types of systems: semi-static systems such as lakes and ponds and flowing systems such as streams, ditches and canals.</p>

<p>Because contact time is critical with chemical control techniques for plants, there is a time/concentration element required to effectively use aquatic herbicides. Because concentration must be maintained for a period of time, flowing water and stratified water bodies may become a complex challenge.</p>

<p>This evaluation project has been using two models in tandem to assess both risk and efficacy challenges for aquatic herbicides. They are the Exposure Analysis Modeling System (EXAMS) for semi-static systems and the EPA/ORD model, Visual PLUMES for flowing systems. EXAMS is an interactive software application for formulating aquatic ecosystem models and rapidly evaluating the fate, transport, and exposure concentrations of synthetic organic chemicals. The Visual Plumes model system is a Windows-based software application for simulating surface water jets and plumes. It also assists in the preparation of mixing zone analyses, Total Maximum Daily Loads (TMDLs), and other water quality applications. </p>

<p>Presently there are five models built into Visual Plumes platform. These are DKHW, NRFIELD/FRFIELD, UM3, PDSW, and DOS PLUMES. Although all the models have features that make them useful, the evaluation project focused on the UM3 model. Application inputs to the model are port diameter, elevation, vertical and horizontal angle, number, spacing and depth plus the acute/chronic mixing zone and effluent flow and concentration of the active ingredient. Ambient inputs include E-fate property information, speed and direction of the current, salinity, ambient temperature, background concentration, decay rate and far-field diffusion. The model uses a representative meteorological file for rainfall. The pond has turnover and outflow.</p>

<p>Visual Plumes and EXAMS allow straightforward determination of drinking water setback distances, calculation of eco exposure EEC values, calculation of human health EDWC values for dietary assessment and water holding times to estimate acceptable non-target plant exposure. Recent developments to the model include the ability to use daily meteorology data to more realistically simulate volume change and water body turn over,  which are important for calculating herbicide/plant contact time.</p>

<p><strong>A 2-Dimensional Modeling Approach to Estimate Holding Time and Setback Distances in Generalized Canal and Lake Settings (Lucas W. Paz, Ph.D., LFR Inc./Syngenta)</strong></p>

<p>Lucas Paz of LFR Inc. presented a 2-dimensional modeling approach to estimate holding time and setback distances at which compound concentrations in canals and lakes reach acceptable background levels.  The approach uses the Enhanced RMA Model Suite, which consists of RMA-GEN, a graphically interactive finite element geometric model; RMA-10, a finite element hydrodynamic model; RMA-11, a linked water quality model; and RMA-PLT, a post-processing module.  The methodology was conducted over sixty model runs that included five application rates and six treatment areas for two scenarios (canals and lakes). Results from each of the sixty model runs were evaluated separately by monitoring selected nodes at downstream intervals and by evaluating the detailed graphical output associated with each model run. A simplified file naming convention was established in accordance with the five application rates (L1-L5) and the six types of percent area applications (P5, P10, P20, P30, P40, and P50) for each scenario. The evaluation indicated that application rates/loading regimes and geometries as well as key physical and chemical input parameters strongly influence modeled results.  Estimates of holding time (T_e), at which concentrations are no longer of concern at loaded elements, were significantly longer than estimates of time to maximum downstream distance traveled by concentrations of concern (T_d) for canal scenario runs.  However, T_e estimates were significantly shorter than T_d estimates for most lake runs.  Detailed examination of graphical output files reveal that the downstream longitudinal extent of the canal plumes begin  to contract before the plume core leaves the application area (the loaded elements).  This difference in canal plume behavior was found to be primarily caused by larger canal dispersion coefficients, restricted canal geometry, and greater total mass loading for the lake scenario.  The presentation concluded with 1-minute animations of modeled concentration estimates over time in the canal and lake scenarios.</p>

<p><strong>Dissipation of Aquatic Herbicides in Flowing Water - Lars Anderson, USDA-ARS Exotic and Invasive Weed Research, Davis, California</strong></p>

<p>The United States Department of Agriculture (USDA) Agricultural Research Service (ARS) is responsible for conducting research into the effective methods for control of aquatic plants, including aquatic herbicides.  Aquatic herbicides are typically applied as either a foliar, aerial application or as a subsurface injection.  Aerial or surface applications are designed to control emerged aquatic plants, which can either be floating with roots in the water column, or plants which are rooted in the bottom of the system but with foliage emergent above the water surface.  Subsurface injection is intended to control submersed plants, which are typically rooted in bottom sediments.  When designing an aquatic herbicide application program, it is critical to understand the nature of the target plant.  In addition, an aquatic weed control program must be designed with optimal conditions for efficacy.  Key factors are correct placement of the pesticide, obtaining the proper pesticide concentration in the target zone, and insuring the appropriate contact time between the pesticide and the target plant.  Estimation of the necessary contact time is critical to understanding what concentration should be applied.  Studies have shown that increasing contact time can dramatically reduce the needed concentration to achieve efficacy.  In order to understand the appropriate contact time, the study design must take into account factors that could reduce or remove pesticide from the target zone.  Important factors to consider include diffusion (dilution), degradation, plant uptake, non-target organism uptake, adsorption, and interaction with other chemicals, volatilization, and currents in the system.  The geometry and nature of the target zone can have a profound influence on the potential removal of the pesticide from the desired application area.  Physical interaction of the target system can result in significant changes in flow through the target area.  Applications in flowing systems need to be targeted to the specifics of the system.  An understanding of the needed duration of exposure is critical to a successful treatment.  Specific examples of copper applications in flowing systems, including tidally influenced systems, were presented.  The conclusion of these specific examples is that dissipation can be reasonably predicted in "clean" conduits, but that plants, vertical mixing, and other variables of hydraulic condition can influence transport rates, and hence dissipation from a target zone.</p>

<p><strong>Three Approaches to Modeling Dispersion of Aquatic Herbicides (Marty Williams and Amy Ritter, Waterborne Environmental)</strong></p>

<p>Marty Williams of Waterborne Environmental presented several approaches to model dispersion of aquatic herbicides to estimate setback distances and timing restrictions in different environments.  In a canal environment, they used RIVWQ, a link-node finite dispersion model that simulates transport driven by river driven flows and dispersion processes.  The model was developed to fill a niche left by other commonly used models, which are steady state or not convenient for large modeling.  It can simulate a parent compound and up to four degradates in a variety of transformation processes.  Validation against field test results showed that the model reproduced observed concentrations well.  To model a lake environment, Waterborne used EXAMS, a surface water model developed by  EPA.  Instead of using it as a single compartment model, as EFED does for exposure assessment, they used a segment/compartment approach where the system is divided into a number of discrete volumes connected by advective and dispersive fluxes.  This model can simulate a large range of usage environments and conditions and can be used to graphically represent results for different areas of a system.  To model an estuary environment, Waterborne used the Environmental Fluid Dynamics Code (EFDC), a hydrodynamic model based on equations of unsteady flow.  EFDC includes a sophisticated sediment transport model to handle partitioning to sediment and can give spatial and temporal output.  Model selection is often a trade-off between the difficulty in obtaining a solution and the risk of not representing the system.  If modeling is accepted by regulatory agencies, it can be useful to discuss novel approaches in advance and to include field studies in the data package.</p>

<p><strong>Exposure Modeling Approaches for Terrestrial and Aquatic Uses of Copper  (Jim Hetrick and Paige Doelling-Brown, USEPA - OPP/EFED)</strong></p>

<p>Jim Hetrick, Senior Physical Scientist of the Environmental Fate and Effects Division, presented key highlights of the exposure modeling approach for the terrestrial and aquatic uses of copper.  The work was done for the ecological risk assessment conducted in support of the Coppers Registration Eligibility Decision (RED) and was harmonized with the Office of Water's approach for setting "aquatic life criteria."

A spatially-explicit risk assessment was conducted using site-specific USGS water quality monitoring data in conjunction with modeling.  For estimating potential exposures for terrestrial and aquatic uses, PRZM/EXAMS or EXAMS was used to simulate concentrations of total Cu.  The Office of Water's Biotic Ligand Model (BLM), an aqueous speciation model, was used to predict site-specific Cu<sup>2+</sup> activity and site-specific toxicity endpoints (LC<sub>50</sub>s) using median water quality data from 811 USGS monitoring sites.   For indirect aquatic uses (e.g., "root killers"), the Office of Pollution Prevention and Toxics' Exposure and Fate Assessment Screening Tool (E-FAST) was used to estimate concentrations of total Cu, EPISuite was used to estimate a water treatment removal efficiency, and flow assumptions (7Q10 or 30Q5) were used to estimate concentrations in flowing water bodies.  In summary, the assessment demonstrated that sites with low pH, low DOC and/or low alkalinity were vulnerable to adverse effects to aquatic organisms from applications of copper.    </p>

<p><strong>Field and Modeling Support for Aquatic Pesticide Registrations (Jim Knuteson and Pat Havens, Dow AgroSciences)</strong></p>

<p>Jim Knuteson of Dow AgroSciences presented field studies and modeling conducted in support of registration of the aquatic herbicide triclopyr.  Field dissipation studies in large lake environments found bulk dissipation rates of 0.5 to 4.8 days, while in whole pond environments, dissipation rates ranged from 5.9 to 7.5 days.  In one of these studies, rhodamine dye was applied as well as triclopyr, and the results were used to validate an EXAMSII modeling approach.  Measured dye concentrations were used to calibrate longitudinal dispersion and water velocity inputs.  The model was run using those inputs along with the environmental fate parameters for triclopyr.  Simulated dissipation was compared to the measured dissipation, and it was concluded that EXAMSII can be used to predict aquatic dissipation.  Dow also developed a shoreline model with EXAMS to examine triclopyr movement with scenarios representative of lakes and reservoirs and varying dispersion coefficients, application areas, and water velocities.  The model predicted setback distances, where the long-term annual average concentration would be below the level of concern, of 300 to 600 m.  EFED had an alternative approach for modeling setback distances using a Python program based on the analytical solution to the one-dimension convection-dispersion equation.  Modeling a water body based on the Index Reservoir with conservative assumptions about environmental parameters led to setback distances of 300 to 792 m for the same situations previously modeled with EXAMS.  The Python model is useful for Tier I modeling of simple chemical transport in slow moving water with minimum dispersion.  More advanced flow modeling needs to be attempted for more refined assessment.</p>

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<h2 id="wrap">Wrap up</h2>

<p><strong>Next Meeting</strong></p>

<p>EFED is looking into dates for the next meeting and will announce the date through the list server.  </p>

<p>EFED is considering holding EMWG meetings three times a year instead of quarterly.  Comments were generally supportive of the change.  An official announcement will be made through the listserver if this change is adopted.  </p>

<p>Paul Hendley suggested that meetings covering a range of general topics should be included as well as meetings focusing on particular themes. </p>

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