1 Exposure Modeling Public Meeting (EMPM)

March 20, 2012
Agenda and Abstracts

Time Presentation Number and Title Presenter

9:00

– 9:10 Welcome and Introductions Marietta Echeveria, Dirk

Young, and Katrina White

9:10

– 9:40 1

‐ NAFTA Guidance for Calculating Degradation

Kinetics in Environmental Media Dirk Young and Ian Kennedy

9:40

– 10:10 2

‐ Update: Implementation of PRZM

‐ GW Reuben Baris, Michael Barrett,

Rochelle F. H. Bohaty, Marietta

Echeverria, Ian Kennedy, Greg
Malis, Dirk Young, and James

Wolf

10:10

– 10:30 Break

10:30

– 11:00 3

‐ Measuring and Estimating Concentrations in
Drinking Water: A Historical Perspective Russell L. Jones

11:00

– 11:30 4

‐ Improved Characterization of the Temporal and
Spatial Variability of Potential Surface Water Drinking

Water Exposure by Using Environmental and Historic

Monitoring Databases Paul Hendley, Wenlin Chen,

Robert Joseph, Ron Williams,

Chris Harbourt & Paul Miller

11:30

– 12:00 5

‐ Estimating Upper Centile Pesticide Concentrations

and Sample Size Requirement Wenlin Chen, Paul Mosquin

12:00

– 1:00 Lunch

1:00

– 1:30 6

‐ Estimation of Upper Percentiles of Chlorpyrifos

Surface Water Concentration from Yearly Monitoring

Program Data Paul L. Mosquin, G. Gordon

Brown, Roy W. Whitmore, Nick

Poletika

1:30

– 2:00 7

‐ Sampling Plans for Water Quality Assessment John W. Green

2:00

– 2:30 8

‐ Update on Development of Drinking Water Intake

Watershed PCAs Jim Carleton, Rochelle Bohaty,

Marietta Echeverria, Nelson

Thurman, Michelle Thawley,

Katrina White, Mohammed

Ruhman

2:30

– 2:45 Break

2:45

– 3:15 9

‐ Exposure Assessment for Pronamide Drinking

Water Residues in California Central Coast Lettuce

Production Areas Nick Poletika, Brian Bret, Mike

Winchell

3:15

– 3:45 10 ‐ Hybrid PRZM:"Filling in the gaps" in Field
Sampling Data Using Realistic Simulation Modeling Paul Miller, Chris Harbourt,

William J. Northcott,

Paul Hendley, and

Jessie J. Prenger

3:45

– 4:00 Meeting Wrap

‐ Up2 

## Abstracts

1. NAFTA Guidance for Calculating Degrad ation Kinetics in Environmental Media
Dirk Young 1 , Ian Kennedy 2

1 Environmental Fate and Effects Division. United States Environmental Protection
Agency

2 Health Canada

The USEPA and Health Canada (NAFTA pa rtners) have developed guidance for
calculating degradation rates for transport model inputs (i .e., PRZM and EXAMS). The
NAFTA guidance specifies the conditions under which a first-order model can be used
to represent pesticide degradation data in NAFTA assessments and provides a
procedure to determine a representative rate when the data deviate from a first-order
concept. The NAFTA guidance is based on t he premise that ther e is no "correct"

transformation of non-first-order data into fi rst-order model paramet ers; therefore, any
parameter transformation will require a subjective dec ision based on an agreed-upon
level of protectiveness. The emphasis of the NAFTA procedure is therefore on
standardization of a process rath er than on statistics of determi ning "best fit" models. In
this regard the NAFTA group has arrived at a comparatively simple method that has
preserved some standard assumptions used by FOCUS such as use of a DT90 as a
reference point.

2. Update: Implementation of PRZM-GW
Reuben Baris, Michael Barrett, Rochelle F. H. Bohaty, Marietta Echeverria, Ian Kennedy, Greg Malis, Dirk Young, and James Wolf

Environmental Fate and Effects Division. United States Environmental Protection
Agency, Arlington, VA

Estimation of pesticide concentrations in gr oundwater is one of t he considerations as part of the exposure assessment in the pesticide registration process. For this reason,

Canada and the United States combined effo rts as part of the North American Free Trade Agreement (NAFTA) to develop a har monized groundwater modeling protocol. This included the development of a comm on conceptual groundwater modeling scenario for regulatory purposes designed to be protective of even the most vulnerable drinking water supplies. The Pesticide Root Zone Model (PRZM) was selected as the NAFTA regulatory tool. Evaluation of PRZM was co mpleted by comparing simulated pesticide concentrations to available targeted and non-t argeted monitoring data . For the majority of chemicals tested, PRZM-predict ed pesticide concentrations represent upper bound estimates of exposure in groundwater w hen conservative input parameters are used (e.g., maximum application rates, annua lly repeated applications, conservative degradation assumptions). There are some pesti cide detections in monitoring data that are not captured by PRZM model estimate s. This may be a result of physical processes that are not accounted for in PRZM (e.g., preferen tial flow or macroparticle3 transport). With site specific adjustments to the PRZM input values estimated pesticide concentrations compare very well to monitori ng data (the same order or within an order of magnitude). The evaluation de monstrates that PRZM is a versatile assessment tool that can be used both as a screening tool a nd a refined site-specific tool in risk

assessment.

3. Measuring and Estimating Concentrations in Drinking Water: A Historical Perspective

Russell L. Jones BayerCrop Science

After the adoption of the F ood Quality Protection Act in 1996, risk assessments for registration had to include the contribution of residues in drinking water to dietary assessments. This triggered work modeli ng and monitoring work by both EPA and industry to determine satisfac tory methods for estimating and measuring concentrations in drinking water from both ground and surfac e water. This presentation reviews the developments in modeling and monitoring of dr inking water from surface water over the past 15 years, including identific ation of the most sensitive drinking water intakes, SWMI, WARP, and the Index Reservoir as we ll as the evolution in surface water monitoring studies. The results of the pas t research will be used to suggest potential approaches to obtaining appropriate estimate s of drinking water based on either modeling or monitoring.

4. Improved Characterization of the Temporal and Spatia l Variability of Potential Surface Water Drinking Water Exposure by Using Environmental and Historic Monitoring Databases Paul Hendley 1

, Wenlin Chen 1 , Robert Joseph 1 , Ron Williams 1 , Chris Harbourt 2 &

Paul Miller 2

1 Syngenta Crop Protecti on LLC, Greensboro, NC

2 Waterborne Environmental Inc., Champaign, IL

The extensive atrazine surface water moni toring database totals over 300,000 samples including ~120,000 drinking water samples from high frequency seasonal monitoring programs covering more than 15 years and >210 Community Water Systems (CWS). This wealth of frequent monitoring data samp led across a wide range of years and sites

allows for robust conclusions to be drawn wit h very high statistical certainty regarding the highest centiles of potential atrazine ex posures. To complement the monitoring data, site-specific details have also been accumulated on CWS watersheds, source waters and water handling procedures; this information has been used to better understand the expected temporal concentrati on patterns at individual CWS. We will outline how these and related data (e.g. daily flow and chemical monitoring data from Heidelberg University) have been used to ex amine approaches for optimizing sampling strategies for assessing potential drinking water concentrations in surface water. Scenarios with different sampling frequencies have been simulated and the results have been compared to measured data for each year and site. This talk will demonstrate how4 lower frequency monitoring data can be used to estimate potential maximum shorter

duration concentrations.

5. Estimating Upper Centile Pesticid e Concentrations and Sample Size Requirement

Wenlin Chen 1 , Paul Mosquin 2

1 Syngenta Crop Protection, LLC

2 RTI International

A survey sampling approach is presented fo r estimating upper centiles of aggregate distributions of surface water pesticide co ncentrations obtained from monitoring with large sample sizes but variable sampling frequency. It is applied to three atrazine monitoring programs of Community Water Syst ems (CWS) that used surface water as their drinking water source: 1. the nationwide Sa fe Drinking Water Act (SDWA) data, 2.the Syngenta Voluntary Monitoring Program (VMP), and 3. the Atrazine Monitoring Program (AMP). Requisite sample sizes are determined using statistical tolerance
limits, relative standard error, and the Woodru ff interval sample size criterion. These analyses provide 99.9% confiden ce that the existing data in clude the 99.9th centile

atrazine concentration for CWS raw and finis hed water in the Midwest atrazine high-use

areas and in the nationwide SDWA dat aset, assuming no bias due to nonrandom selection of CWS and monitored days during t hese years. The general validity of these approaches is established by a simulation that shows estimates to be close to target quantities for weights based on sampling pr obabilities or time intervals between samples.

6. Estimation of Upper Percentiles of Chlorpyrifos Surface Water Concentration from Yearly Monitoring Program Data Paul L. Mosquin 1 , G. Gordon Brown 1 , Roy W. Whitmore 1 , Nick Poletika 2

1 RTI International, Department of Statistics & Epidemiology, Research Triangle Park, NC, 27709, United States

2 Dow AgroSciences LLC, Department of Fi eld Exposure and Effects, Indianapolis, IN, 46268, United States

This talk presents a finite popul ation method to estimate annual 95 th , 99 th and 99.9 th

centiles of surface water chlorpyrifos concentrations and associated confidence intervals using historical surface water pesticide monitoring programs with large number

of measurements. The method provides reliable estimate s, accounting for infrequent sample collection, measurements below repo rting limits, and the strong seasonality present in these datasets. Data from thr ee monitoring programs are considered: the USGS National Water-Quality Assessment Program (NAWQA), the Heidelberg University National Center for Water Qua lity Research (NCWQR) monitoring data, and the Washington State Department of Agriculture/ Department of Ecology surface water monitoring program. Results for temporal trends will be provided, including a comparison of estimates before and after ch lorpyrifos was withdrawn from residential

use in 2001.5 7. Sampling Plans for Water Quality Assessment John W. Green, Ph.D. DuPont Applied Statistics Group

Sampling plans for monitoring chemical concent rations in rivers were investigated for two California streams of differing order to assess the relative merits of daily sampling versus less frequent sampling. The assessments were based on the ability to estimate time-weighted total and peak concentrations on a monthly or annual basis and to detect the presence of spikes in these concentra tions. A secondary purpose was to determine the feasibility of predicting spikes in chem ical concentrations from the river discharge rate. In these streams, some less frequent sampling plans were shown to provide almost the same utility as daily sampling for the first purpose and discharge rate was

shown to have little correlation with chemical concentration.

8. Update on Development of Drin king Water Intake Watershed PCAs Jim Carleton, Rochelle Bohaty, Marietta Echeverria, Nelson Thurman, Michelle Thawley, Katrina White, Mohammed Ruhman

Environmental Fate and Effects Division. United States Environmental Protection Agency, Arlington, VA

EFED uses percent crop area (PCA) adjus tment factors in its drinking water

assessments to account for the fact that watersheds supplying surface drinking water sources may not be devoted entirely to agricul ture. The first PCAs were developed in the late 1990s and mid 2000s, based on cropped ac reage within 8-digit HUCs. More recently, EFED has developed delineations fo r watersheds associated specifically with drinking water intakes that supply community water systems. EFED is planning to use this new dataset to develop drinking water in take watershed-specific PCAs. This talk will discuss this intake watershed dataset and PCA development methodologies in general terms, along with unique issues and c hallenges associated with the use of these new data for PCA development.

9. Exposure Assessment for Pronamide Drinking Water Residues in California Central

Coast Lettuce Production Areas

Nick Poletika 1 , Brian Bret 2 , Mike Winchell 3

1 Dow AgroSciences LLC

2 Dow AgroSciences LLC, Regulator y and Government Affairs NAFTA

3 Stone Environmental, Inc. Applied Information Management

Regulatory pesticide human exposure m odels are intentionally designed to be protective of individuals in populati ons. Consequently, they tend to be quite conservative in early assessment tiers, and predictions are generally refined with data in subsequent assessments. For drinking wate r obtained from surface water, pesticide exposure model concentration estimates for agricultural use generally are in the μg L -1
to tens of μg L -1 range, which can lead to concern if human health endpoints for a specific pesticide are low values. Cu rrently US EPA OPP accepts only targeted monitoring studies for refinement of model estimated concentrations. We present an6 alternative assessment method to target ed monitoring for a pesticide with a limited range of label crops and geographi c regions of use that relie s on proximity analysis of use sites and drinking water intakes. We al so address national security issues related

to sensitive intake location data and c onsider the general utility of the approach.

10. Hybrid PRZM:”Filling in the Gaps” in Field Sampling Data using Realistic Simulation Modeling
Paul Miller, PhD 1 , Chris Harbourt, PhD 1 , William J. Northcott, PhD 1 , Paul Hendley,

PhD 2 , and Jessie J. Prenger 1

1 Waterborne Environmental, Inc.

2 Syngenta

The Hybrid-PRZM approach can be used to combi ne observations from field monitoring with results from simulation modeling based on local rainfall for the same period to “fill in” gaps between sampling occasions. The appr oach uses Pesticide Root Zone Model (PRZM) simulations based on local rainfall data together with site-specific watershed soil and agronomic characteristics. The model is used to estimate edge-of-field atrazine concentrations occurring on days with rainfall; the simulation results are scaled to

watershed conditions without calibration. T he PRZM model results supplement field monitoring data with estimates of potentia l runoff events on days when runoff inducing rain falls in a watershed between sampling occasions. This technique captures the strengths of field and simulati on approaches to develop conservative daily time series using quality sampling results and appropriate simulation assumptions. Significant developments are presented here that result in improved exposure si mulation results;

these include the use of NEXRAD local precipitation data combined with a land workability algorithm to devel op appropriate distributions of application dates across a

watershed.