Implementation of Vegetative Buffer Strip 

Effectiveness in Removing Pesticides in 

Regulatory Assessments

Bjoern Roepke, Russell L. Jones and 

George Sabbagh

Presentation to the EMPM

March 19, 2013 
2

Outline

 Introduction

 Chronology of Industry Research

 Implementation in Europe

 Current activities in the U.S.

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Introduction

 Vegetative buffer strips 

are a mitigation practice 

commonly used to reduce 

the effects of pesticide 

runoff

 Used for many years to 

prevent soil erosion

 Also provide other benefits, such as reduction of 

runoff and nutrients, wildlife habitat improvement, 

and streambank protection

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Introduction

 Industry scientists in Europe and the United States 

for many years have been interested in vegetative 

buffer strips for removal of pesticides in runoff 

water

 Also interested in quantifying the effectiveness of 

this mitigation practice

 Ultimate goal is to implement a successful risk 

mitigation practice and to have this reflected in 

regulatory risk assessments

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Early Industry Collaboration in the U.S. 

 Collaboration with

USDA on guidance

document issued in

2000

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Early Industry Collaboration in the U.S.

 Early 2000s-Industry funded the compilation and 

analysis of available published data on vegetative 

buffer strip efficiency compiled and analyzed at Iowa 

State (eventually published as Arora, 2010)

 This work was of considerable use in later projects in 

both the U.S. and Europe

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Early Industry Collaboration in Europe

 Product specific runoff studies conducted in 1991-

1992 in collaboration with the University of 

Karlsruhr in the Weiherbach region of Germany

 Joint collaboration on runoff studies in France and 

Germany beginning in early to mid-1990s

 Work by national industry association in Germany 

to quantify effectiveness of buffer strips as part of 

assessments for national registrations

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Early Industry Collaboration in Europe

 Participation of industry in FOCUS groups dealing 

with surface water assessments

 Surface Water Scenarios (2003)

 Landscape and Mitigation (2005)

The information from the literature compilation from 

the Iowa State project was included in the final report

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Industry Activities

 Two developments led to an increased need for 

industry to have quantitative assessments of the 

efficacy of buffer strips for removing pesticides

 The work at Iowa state was unsuccessful in 

developing a quantitative model for estimating the 

efficacy of vegetative buffer strips for removing 

pesticides

 The simple estimates proposed by the FOCUS 

Landscape and Mitigation Group were rejected as 

being unsuitable for regulatory assessments

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Industry Research Chronology

 In late 2007, scientists in the CropLife America 

Environmental Risk Assessment Committee 

requested scientists in member companies to 

explore ways to characterize the effectiveness of 

buffer strips

 George Sabbagh of Bayer working together with 

Garey Fox and A. Kamanzi, supported by Bayer 

scientists, developed an equation predicting 

pesticide removal as a function of the infiltration of 

water in the buffer and the amount of sediment 

removal using the Iowa State data base

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Pesticide Trapping Equation

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Predicted vs. measured reductions in pesticide transfer 

across vegetated filter strips (Sabbagh et al., 2009): 

- development (n=47; left-hand figure)

- evaluation (n=120; right-hand figure) datasets
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Industry Research Chronology

 The equation of Sabbagh et al. did a good job of 

predicting pesticide removal but infiltration and 

sediment reduction are a function of the specific 

event runoff event and buffer design

 In 2008 Sabbagh and Fox worked with MunozCarpena (University of Florida) to incorporate the 

pesticide trapping equation into Munoz-Carpena’s 

buffer strip model VSFMOD

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Other Buffer Strip Modeling Research

 Other organizations also started to develop buffer 

strip models or expand nutrient models to 

pesticides. Some examples

 APEX: USDA-ARS

 REMM: Texas Blacklands Research and Extension

 PRZM-BUFF: Waterborne Environmental

 SWAT: USDA-ARS

 CropLife America (CLA) funded a comparison of 

these models along with VSFMOD (presented at 

the EMPM in 2008)-did not include a comparison 

on common data sets

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Industry Research

 The European Crop Protection Association 

(ECPA) wanted to consider buffer strip models in 

their program on Advancing Intelligent Mitigation 

(AIM)

 Wanted to determine which buffer strip model 

seemed to be providing the most realistic conditions

 ECPA and several U.S. companies sponsored a 

comparison on three U.S. and European data sets

 Results presented at an EMPM meeting in 2010

 ECPA chose VSFMOD for their work in Europe 

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Model Comparison Study Results Summary

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Model APEX PRZM 

BUFF REMM VSFMOD

Pesticide 15.6 (10) 16.3 (14) 31.2 (31) 8.5 (8)

Runoff 30.4 (20) 36.9 (28) 34.5 (32) 12.3 (9)

Sediment 19.4 (17) 31.0 (31) 30.3 (24) 12.2 (17)

Number in parentheses is the standard deviation

Ranking by Mean Absolute Error (%)
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Implementation into EU Assessments

 Needs regulatory acceptance

 FOCUS Landscape and Mitigation

 PPR opinion on FOCUS LM 

 Clear principles for implementation

 Mitigation measures must be effective and practical

 Needs to be an accepted approach to be 

incorporated into the estimate of exposure

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Implementation Procedure

 Conduct sensitivity analysis to determine 

important parameters

 Define runoff buffer scenarios for each of the four 

FOCUS runoff scenarios

 Incorporate scenarios into modeling software

 An effort involving a number of organizations

 ECPA

 University of York and FERA

 Università Cattolica del Sacro Cuore

 University of Florida

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Sensitivity Analysis

 Analysis based on field experiments reported in 

the literature

 Two soil types and six pesticides with a range of 

different properties

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Sensitive Parameters Insensitive Parameters

Soil Vegetation

 -saturated hydraulic conductivity -spacing of stems

 -saturated water content -height

Sediment -hydraulic resistance

 -average diameter of particles

 -organic carbon content

 -clay content Muñoz-Carpena et al. (2010). JEQ 39:630-641
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Parameter Definition

 Insensitive parameters

 Assess likely range across the EU

 Propose default values 

Appropriate level of conservatism

Documentation to justify selection from literature

 Sensitive parameters

 GIS analysis within each scenario

 Generate distributions for each parameter

Support selection of conservative values

Facilitate higher-tier modelling (e.g. Probabilistic)

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Probability Distributions for Ksat

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R1 R2 R3

R4

 N for each R scenario small

 Hydraulic parameters strongly 

correlated

scenario n mean st.dev.

R1 348 23.1 20.3

R2 69 98.6 77.5

R3 171 49.5 59.5

R4 222 53.9 56.3

Lognormal distribution

ks as variable and area as density
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Deriving Conservative Values for Ksat & θsat

 Separate simulations for:

 The four FOCUS R scenarios (n = 69 – 348)

 Storm events with 30 mm rain over 1 hour or 8 hours

 Pesticides with Koc of 100 L/kg or 10,000 L/kg

 Each run reads Ksat, θsat and θfc for one soil 

unit

 θfc used as fixed (and correlated) input for initial water 

content

 All other parameters held at constant values

relevant to the FOCUS R scenario

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Deriving Conservative Values for Ksat & θsat

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0

10

20

30

40

50

60

70

80

90

100

40 50 60 70 80 90 100

Percentile of the frequency distribution

% pesticide removal

8 hour event, 

Koc=10,000

8 hour event, 

Koc = 100

1 hour event, 

Koc = 10,000

1 hour event, 

Koc = 100

R3
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Note 

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The efficiency in removing pesticide varies with 

properties of soil, pesticide and runoff event

The relative vulnerability of different soils is 

independent of pesticide and event properties

but
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90th Percentile Worst-Case Values in the VFS

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Parameter R1 R2 R3 R4

Ks (m s-1) 7.04 x 10-7 2.79 x 10-6 9.25 x 10-7 1.52 x 10-6

θs (cm3 cm-3) 0.447 0.403 0.472 0.420

θfc (cm3 cm-3) 0.395 0.312 0.385 0.372
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Changes to Ksat and θsat in the VFS

 Data from SEISMIC (LandIS data, NSRI) for soil 

series in England and Wales

 SEISMIC reports Ksat and θsat for each soil 

series and distinguishes between permanent 

grassland and arable land

 Use information to estimate Ksat and θsat for 

grassed buffer strips from the field Ksat and θsat

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Ksat and θsat in the VFS

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y = 1.1058x

R2 = 0.2344

35

40

45

50

55

60

65

70

35 40 45 50 55 60 65 70

Theta sat (cm/day) Permanent grassland

Theta sat (cm/day) Arable land

Theta sat

-15

-10

-5

0

5

10

15

40 45 50 55 60 65

Residuals (Pred - Obs)

Theta sat (cm/day)

Worst-case assumption as default:

Hydraulic properties equal to those in arable field
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Determination of Sediment Particle Size

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0

100

200

300

400

500

600

0 50 100 150 200 250 300

d50 sediment (μm)

d50 parent soil (μm)

Elliot

Chisci & Martinez

Slattery & Burt

0

5

10

15

20

25

30

0-20

20-4040-6060-80

80-100

100-120120-140140-160160-180180-200200-220220-240240-260260-280280-300300-320320-340340-360360-380380-400400-420420-440440-460460-480480-500500-520520-540

% of samples

d50 range (μm)

Mean particle size of 

eroded sediment:

 Worst-case value as

 default (30 μm)
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Software Development

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FOCUS 

PRZM VFSMOD-W FOCUS 

TOXSWA

SWAN

Edge-of- field 

runoff

Interception in 

VFS

Fate in 

surface water
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Example Result

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66% reduction

80% reduction

Red = no mitigation

Blue = 5m buffer

Green = 10m buffer
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European Status 

 Scenario Development report available at: 

www.york.ac.uk/environment/pesticide

 SWAN software including vegetative buffer strip 

modeling as a mitigation measure now available

 Training conducted for European regulators in 

Paris on October 10, 2012

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Conclusions

 Develop of the mitigation practice of removal of 

pesticides by vegetative buffer strips and 

quantifying its effectiveness has been a multi-step 

process involving many scientists over a period of 

about 25 years

 Built on previous work for use in removing sediment 

 Current a procedure for quantifying the 

effectiveness of vegetative buffer strips is being 

adopted in European regulatory risk assessments

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Conclusions

 The process for potential implementation in 

regulatory assessments in the U.S. continues

 Next step is a workshop sponsored by the Soil and 

Water Conservation Society on April 17

Participants will include scientists from USDA, EPA, 

universities, and industry

March 19, 2013