1. Development and Application of a Modeling Approach for Predicting Pyrethroid Residues in Residential Water Bodies for Use in Environmental Risk Assessments
Michael Winchell, Stone Environmental
Lauren Padilla, Stone Environmental
Scott Jackson, BASF
On Behalf of the Pyrethroid Working Group
CLA-RISE Spring Conference
April 11th, 2014
4/11/ Slide

2. © 2013 by Pyrethroid Working Group. All rights reserved
Background
Use of pyrethroid insecticides in urban environments and detections of these pyrethroids in some urban drainage systems has led to the evaluation of urban exposure potential as part of a national risk assessment.
Supported by existing monitoring datasets, simulation modeling may be used to estimate pesticide concentrations in urban drainage systems.
The use of modeling in a national risk assessment requires:
A validated modeling approach
Regionally specific model inputs or a validated worst-case scenario
Apr 2014 Slide
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Challenges
Pesticide use in urban residential environments is complex!
Multiple potential use sites each with different characteristics.
Apr 2014 Slide
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Objectives
Develop a residential pyrethroid exposure scenario that:
Captures the heterogeneity in use sites found in a residential environment.
Accounts for the hydrologic processes in residential watersheds.
Allows the flexibility of modifying pyrethroid use assumptions to regional variations in climate and use practices.
Calibrate and validate the model exposure scenario using a robust monitoring dataset.
Develop regional model parameterizations representing:
Regionally specific pyrethroid use patterns
Local climate conditions
Apply the residential exposure model scenario for use in a pyrethroid environmental risk assessment to predict regionally specific residential aquatic EECs.
Apr 2014 Slide
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Discussion Topics
Residential pyrethroid use data
Model selection
Residential scenario development
Residential scenario calibration
Regional residential parameterizations
Model application for residential aquatic exposure assessment
Don’t read each one … provide overview
Apr 2014 Slide
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6. Residential Pyrethroid Use Data: Background on Pyrethroid Use Surveys
The PWG has commissioned two residential use surveys in the past 5 years:
California survey (PWG, 2010)
US regional survey (Northwest, North Central, Northeast, Mid Atlantic, South Central, Southeast) (Winchell and Cyr, 2013; Winchell 2013)
The primary survey objectives were:
To understand any regional differentiation in pyrethroid use characteristics for parameterization of residential exposure models
To understand relative significance of different pyrethroids to support product specific assessments in these regions
Data collected by the surveys included:
The fraction of households receiving treatments
The types of sites/surfaces receiving treatments
The relative significance of different pyrethroid products for each use site
The seasonal frequency of applications on different types of surfaces
Apr 2014 Slide
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7. Residential Pyrethroid Use Data: Specific Use Sites for Exposure Model
Focus on quantifying application practices for:
Building foundation perimeters
Patios and walkways (away from garage door/wall)
Driveways (away from garage door/wall)
Lawns/landscape areas
Driveway has shown to be most significant
Apr 2014 Slide
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8. Residential Pyrethroid Use Data: Use Quantification for Exposure Model
Fraction of neighborhood households receiving outdoor insecticide treatments
Fraction of use sites treated with each active ingredient
Seasonal frequency of applications made to each use site
Percentage of a use site’s surface area that is treated
Make verbal comment on why yellow lines are treated
Apr 2014 Slide
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9. Residential Pyrethroid Use Data: Primary Findings
Residential pyrethroid use is greater in California than in other regions of the United States.
Outside of California, pyrethroid use is generally higher in the southern regions than the northern regions.
Pyrethroid use is most prevalent for the building foundation perimeter and lawn/landscape area use sites.
The variability in use prevalence (as selection of product) among the different pyrethroid active ingredients is low, with the exception of bifenthrin, which has estimated use of 2 to 10 times as frequent use as the other pyrethroids.
The surface area treated for patios/walkways, driveways away from the building perimeter is low, most commonly <= 10%.
Don’t say details on bifethrin
Apr 2014 Slide
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10. Model Selection: SWMM and AGRO Models
Storm Water Management Model (SWMM): US EPA
Watershed scale, urban/residential water quantity and quality model
Strength in handling of sub-hourly runoff and flow routing
Able to model multiple surface types (lawn, driveway, etc.)
AGRO: Canadian Center for Environmental Modeling (CEMC)
Water Quality Model: Quantitative Water, Air, Sediment Interaction (QWASI) Fugacity model (Mackay, 2001).
Accounts for chemical mass exchange between water column (dissolved and sorbed compartments), benthic layer (dissolved and sorbed compartments), and air.
Simulation of sediment dynamics, including handling of incoming sediment; important for high Koc pyrethroids.
AGRO-2014 (Padilla and Winchell, 2013) includes improvement in parameterization based on comparison with micro-cosm study data.
Don’t give details on AGRO … just that it was chosen for receiving water
Apr 2014 Slide
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11. Residential Scenario Development: Study Location
Aliso Viejo, Orange County, CA
Part of CA DPR / UC Riverside monitoring program
Drainage area: 67.2 acres
307 homes
Dwelling unit density: 4.6 units/acre.
Watershed boundary delineated during multi-year monitoring study. (Haver, 2012a)
Apr 2014 Slide
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12. Residential Scenario Development: Conceptual Model
Aliso Viejo neighborhood was spatially delineated.
Particular attention to impervious use sites.
Lower driveway
Upper driveway (within 5 ft)
Garage door
Impervious within 5-ft foundation perimeter
Patios/walkways away from building
Impervious areas near lawns (1.5 ft) receive irrigation.
A fraction of impervious surfaces (other than driveway) flow into adjacent lawns.
Emphasize complexity of scenario
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13. Residential Scenario Development: Conceptual Model, Continued
Each landscape element in the model can be sub-divided into portions receiving pyrethroid applications and portions not receiving applications.
Further splitting can be made to allow multiple application frequencies (every 6 weeks, and every 12 weeks).
The watershed is divided into “sub-watersheds”:
Allows for more accurate routing
Allows model to build in variability in pyrethroid application timing
Apr 2014 Slide
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14. Residential Scenario Development: Pyrethroid Use Assumptions
A best estimate of the extent and frequency of actual pyrethroid use in California was required for the scenario.
Bifenthrin was chosen based on its relatively extensive use and frequency of detections in monitoring data.
Key assumptions include:
75.9% of households use outdoor insecticides (Winchell, 2013)
Some households are treated every 6 weeks, and some every 12 weeks
Fraction of use sites treated with bifenthrin (of households using insecticides) at these intervals was estimated from survey data and were set as follows:
Use Site
Estimated Total Percent Treated (%)
Estimated Percent Treated Every 6 Weeks (%)
Estimated Percent Treated Every 12 Weeks (%)
Foundation Perimeter
25.7
13.1
12.6
Patios/Walkways
24.9
12.7
12.2
Driveways
24.1
10.6
13.5
Lawns
24.4
5.4
18.9
Apr 2014 Slide
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15. Residential Scenario Calibration: Calibration Approach
The monitoring study led by Oki and Haver (2011) provided the following datasets for calibration of the Aliso Viejo scenario:
Daily and hourly flow from the stormwater outfall (Haver, 2012b)
30 bifenthrin concentration analyses from both wet and dry periods
Estimated weekly and annual pyrethroid mass load
Flow calibrated through adjustment of:
Irrigation practices
Hydrologic connectivity of impervious surfaces
Subsurface flow contributions
Routing parameterization
Bifenthrin mass and concentrations calibrated by adjusting:
Washoff parameters
Don’t read sub-bullets
Apr 2014 Slide
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16. Residential Scenario Calibration: Hydrology Calibration
Mean daily flows and hourly flows are well simulated:
Flow Bias: -2%
Daily NSE (Nash Sutcliffe Efficiency): 0.83 (Nash and Sutcliffe, 1970)
Hourly NSE: 0.57
Surface runoff rarely occurs from lawns.
Mention hourly; mention lawns
Apr 2014 Slide
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Residential Scenario Calibration: Bifenthrin Calibration, Cumulative Mass
The simulated cumulative bifenthrin mass load over 1 year was compared to the observed mass load.
Over the 1 year period, the model predicted 10% more mass load than observed.
Given high bias in simulated mass, calibration is conservative.
Conservative
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SWMM/AGRO-2014 Application: California, Historical vs. Current Practices
Current pyrethroid labels (as of ~2010) limit applications on hard surfaces to crack and crevice applications.
Bifenthrin EEC distributions show a reduction in annual maximum EECs of ~10x after incorporating new label restrictions into the residential scenario.
Results in this comparison assumed that the bifenthrin use extent was equal to that of all pyrethroids combined.
Apr 2014 Slide
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19. SWMM/AGRO-2014 Application: Regional Model Parameterization
Regional parameterizations of weather and treatment characteristics were developed for the Southeast (Orlando), South Central (Houston), Northwest (Seattle), North Central (Chicago), Northeast (Boston), and Mid-Atlantic (Philadelphia)
Weather:
30-year time series of hourly precipitation
30-year time series of daily average temperature
Monthly average evaporation
Irrigation:
Irrigation schedules for the California scenario were calibrated based on observed flow data.
Irrigation schedules for other regions were modified to achieve a similar amount of irrigation relative to plant evapotranspiration demands of the regional climate.
Pyrethroid Applications: Derived from survey data
The parameterization of the California residential scenario was modified to represent these regionally specific characteristics.
Apr 2014 Slide
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20. SWMM/AGRO-2014 Application: Regional Pyrethroid Use Frequency
The frequency of pyrethroid applications (number of times a household use site is treated annually) varied by region and use site.
Foundation perimeters are treated most frequently.
The highest number of applications is in California.
The lowest number of applications is in the Northeast.
Apr 2014 Slide
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21. SWMM/AGRO-2014 Application: Comparison of Regional Parameterizations
Annual maximum 24-hour EEC distributions were simulated using SWMM/AGRO-2014 for 7 regional parameterizations and 7 pyrethroids.
The overall EEC distribution for California was higher than the other 6 regions.
The Northeast and Mid-Atlantic had the lowest EECs.
All pyrethroids showed similar patterns across regions.
Apr 2014 Slide
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22. Summary and Conclusions
A SWMM/AGRO-2014 residential pyrethroid exposure modeling scenario was developed, calibrated, and parameterized for 7 different geographic regions.
The scenario’s conceptual model, based on a high density California neighborhood, accounts for pyrethroid application practices for a diverse set of residential use sites.
In California, EECs based on historical pyrethroid labels (pre-2010) were over 10x higher than EECs based on current labels.
As part of an environmental risk assessment, EECs in California were found to be higher than in any of the other 7 regions.
The urban residential modeling approach developed can be used for exposure assessments of other pesticide classes.
Make statement that CA represents a reasonable worst case scenario.
Apr 2014 Slide
© 2014 by Pyrethroid Working Group. All rights reserved

23. For Further Information on the Urban Exposure Modeling Approach …
“Development and Application of a Higher Tier Urban Modeling Approach for Estimating Pyrethroid Concentrations in Static Water Bodies Using SWMM and AGRO-2014”, Winchell, Padilla, and Jackson (2014), PWG-ERA-11
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24. © 2014 by Pyrethroid Working Group. All rights reserved
References
Haver, D. 2012a. Watershed Boundary for Aliso Viejo Subdivision. Personal Communication, Darren Haver, South Coast Research & Extension Center.
Haver, D. 2012b. Hourly Flow Data for Aliso Viejo Subdivision. Personal Communication, Darren Haver, South Coast Research & Extension Center.
Mackay, D Multimedia Environmental Models: The Fugacity Approach - Second Edition. Lewis Publishers, Boca Raton, pp
Oki, L, and D. Haver Evaluating Best Management Practices (BMPs) Effectiveness to Reduce Volumes of Runoff and Improve the Quality of Runoff from Urban Environments.
Nash, J. E. and Sutcliffe, J. V River flow forecasting through conceptual models, Part I - A discussion of principles. J. Hydrol. 10: 282–290.
Padilla, L. E., & Winchell, M. F Development And Testing Of An Improved Agro Model (AGRO-2014) For Use In Predicting Aquatic And Benthic Pesticide Concentrations In Ponds. PWG Report - PWG-ERA-03b. Stone Environmental Inc.
PWG (Pyrethroid Working Group) California 2009 Urban Pesticide Use Pattern Study. US EPA MRID Number
Winchell, M.F., M.J. Cyr Residential Pyrethroid Use Characteristics in Geographically Diverse Regions of the United States. PWG-ERA-02a.
Winchell, M.F Pyrethroid Use Characteristics in Geographically Diverse Regions of the United States: Parameterization of Estimated Pyrethroid Treatment Extent and Frequency for Urban Exposure Modeling. PWG-ERA-02b. Stone Environmental Inc.
Apr 2014 Slide
© 2014 by Pyrethroid Working Group. All rights reserved