# Guidance on Modeling Offsite Deposition of Pesticides via Spray Drift

Exposure Modeling Public Meeting (EMPM) March 24, 2014

Environmental Fate and Effects Division Office of Pesticide Programs U.S. Environmental Protection Agency 

## Katrina White, Faruque Khan, Marietta Echeverria, Chuck Peck

# Purpose of Guidance

 

## Establish default assumptions for modeling spray drift for agricultural uses

 

## Spray drift in terrestrial risk assessments

 

## Spray drift in aquatic risk assessments

 

## How to characterize effect of buffers on risk

http://www.etsprayers.com/2013/05/12/5

- things

- you

- should

- consider

- to

- avoid

- spray

- drift/

### PRZM/EXAMS Inputs for Spray Drift Fraction for Applications of Liquids Without Any Spray Drift Limitations (Estimated using AgDRIFT Version 2.1.1)

Type of Application Spray Drift Fraction for Runoff and Drift
EEC Without Buffer Previous Default Inputs Ecological Risk Assessment Using EPA Farm Pond

Aerial 0.125 0.05
Ground 0.062 0.01
Airblast 0.042 0.03 Drinking Water Assessments Using Index Reservoir

Aerial 0.135 0.16
Ground 0.066 0.064
Airblast 0.048 0.063

Granular applications: spray drift fraction = 0 application efficiency = 1

If there is a buffer distance, use AgDRIFT to determine the appropriate spray drift
fraction.

# AgDRIFT: Default Input Parameters (Agricultural Uses)

 

# Tier I Aerial

 

### Use ASAE Fine to Medium DSD unless the evidence indicates that use of Very Fine to Fine DSD is likely

 

### 10 mph wind speed, 10 ft. release height

 

### 60

- foot swath width

 

# Tier I Ground

 

### Boom Height = High Boom

 

### Data Percentile = 90th Percentile

 

### DSD = ASAE Very fine to Fine

 

# Tier I Airblast

 

### Sparse (Young/Dormant)

 

### Estimates a 50 th 

### percentile drift due to limitations in data Except for the Tier I aerial assumption, the scenarios result in the highest exposure
estimate

If a label specifies something
different from the default assumptions, the label specifications are used in modeling.

# Spray Drift and Terrestrial Exposure

Egrets, herons, and
other birds
in wild rice
field.

http://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=9373

# Terrestrial Animal Exposure off the Field

 

## Estimate Risk at a Distance from the Edge of the Field (Use AgDRIFT and TREX)

 

### Enter distance from the edge of the field as the buffer distance in AgDRIFT to get the ‘Fraction of Applied’

 

### Fraction of Applied x Application Rate = Application rate in TREX to estimate risk at the specified distance from the edge of the field

 

## Applications directly to water and bare ground

 

### Assume exposure at the edge of the field will be identical to exposure on water body or field (e.g., use full application rate in TREX and assess exposure to terrestrial organisms)

 

## For bare ground application

 

### EECs for seeds and insects reflect exposure on the field

 

### EECs for residues on plants will mainly occur at the edge of the field

## Spray Drift Distance: Distance from the edge of the field where exposure is at levels where LOCs could be exceeded

# Terrestrial Spray Drift Distance

- Animals

 

# Estimate the ‘Fraction of Applied’ and Enter into AgDRIFT

 

## Fraction of applied = fraction of application rate that is expected to result in some effect

 

# Fraction of Applied = LOC/RQ ratio

 

## Acute and chronic terrestrial animal RQs

 

## Use LOC relevant to organisms (listed or nonlisted) analyzed

 

## Use RQ based on maximum number of applications and
maximum use rateOutput

– Drift Distance

Input Select

# Terrestrial Spray Drift Distance

- Plants

 

## Plant exposure models are not currently available that examine exposure due to multiple applications

 

## Include uncertainty language a.i./A lbs in Rate n Applicatio Maximum a.i/A lbs in plants listed for 05 NOAEC/EC or plants nonlisted for 25 EC 

# Fraction of Applied for Plants =

# Spray Drift and Aquatic Exposure

# Estimate Spray Drift Fraction for PRZM/EXAMs using AgDRIFT for Ecological and Drinking Water

Assessments

Do not use the default inputs (e.g., 0.01, 0.05, 0.16, 0.064)

## Ecological Risk:

EPA Pond Human Health Drinking Water:

Index Reservoir

10 hectare agricultural field

1 ha pond • 173 ha watershed

• 5.3 ha reservoir

• 1500 m x 4 m of stream with
4 m bufferSelect

Input the Buffer Distance

Output: Spray
Drift Fraction for

PRZM/EXAMs Ecological
Assessment 

# Spray Drift For Ecological
Assessments

# Calculating Spray Drift for Index Reservoir

Normalized Spray Drift Fraction for Streams (unitless) = Spray Drift Fraction for Streams x SA of Streams/SA of Reservoir



# Adjusted Spray Drift Fraction for Index Reservoir (unitless) =

Normalized Spray Drift Fraction for Streams + Spray Drift Fraction

for Reservoir

### PRZM/EXAMS Inputs for Spray Drift Fraction for Applications of Liquids Without Any Spray Drift Limitations (Estimated using AgDRIFT Version 2.1.1)

Type of Application Spray Drift Fraction for Runoff and Drift
EEC Without Buffer Previous Default Inputs Ecological Risk Assessment Using EPA Farm Pond

Aerial 0.125 0.05
Ground 0.062 0.01
Airblast 0.042 0.03 Drinking Water Assessments Using Index Reservoir

Aerial 0.135 0.16
Ground 0.066 0.064
Airblast 0.048 0.063

Granular applications: spray drift fraction = 0 application efficiency = 1

If there is a buffer distance, use AgDRIFT to determine the appropriate spray drift
fraction.

### Estimated Amount of the EEC That Is Due to Runoff (The Higher the Percentage the Less the EEC was Influenced by Spray Drift)

Scenario Peak Run

- off only EECs
Peak Run

- off + Drift EECs (Percent)

CAnurserySTD 98%

CAForestryRLF 95%

CAcornOP At Plant 94%

CAColeCropRLF 81%

CAcotton_WirrigSTD 66%

CAsugarbeet_WirrigOP
At Plant 43%

CAtomato_WirrigSTD 30%

CAfruit_WirrigSTD 12%

CAMelonsRLF 6% Log Kow =6

# Aquatic Spray Drift Distance/Buffer Distance

 

## Method 1: Considering Exposure to Spray Drift Only (use AgDRIFT and acute aquatic endpoints)

 

## This is needed for all assessments with all LOC exceedances because the drift distance may be greater than the terrestrial drift distance. If it is, it would establish the baseline potential area of effect

 

## Method 2: Considers Exposure to Both Spray Drift and Runoff

 

## Estimate spray drift fraction that will eliminate LOC exceedance by adjusting spray drift fraction input in PRZM/EXAMS using trial and error

 

## Find corresponding drift distance in AgDRIFT using Tables in Guidance or AgDRIFT

 

## Considers both acute and chronic riskDetermine PRZM/EXAMs
EECs without drift

a. Do not calculate a

spray drift distance
because there is no risk

c. Calculate a spray drift distance that considers risk due to exposure to

both runoff and spray. Estimate spray drift distances using Method 1

(acute endpoint and AgDRIFT) and Method 2 (AgDRIFT and PRZM/EXAMS). Runoff only EEC does not result in
LOC exceedance but the EEC that
considers both drift and runoff does result in an LOC exceedance No LOC
Exceedance
Runoff only EEC

r esults in LOC

exceedance

b. Risk cannot be mitigated using a spray drift buffer; however, any buffer used will help to
reduce risk. Estimate a spray drift distance using Method 1 (acute

endpoint, AgDRIFT) Determine PRZM/EXAMS EECS with Drift

Calculate RQs and Compare to LOCs LOC
Exceedance

# Calculating the Aquatic Spray Drift

Distance: Method 1

Input in AgDRIFT is the Initial Average Concentration

 

## Represents the average concentration within a defined water body, in ng/L

 

## Average concentration in a defined water body in ng/L that will not result in LOC exceedance

Initial Average Concentration

 

## Aquatic Organisms:

= LC 50 

## × LOC

 

## Aquatic plants:

= EC 50 

## × 1 (for non

- listed plants)

= EC 05 

## or NOAEC × 1 (for listed plants)

# Calculating the Aquatic Spray Drift :Example of Method 2

Example 1: Esfenvalerate, CACole crop, 2 applications, 0.06 kg/ha, 7 day interval Acute nonlisted LOC = 0.5, Acute listed LOC = 0.05, Chronic LOC = 1

Scenario Buffer Spray
Drift

Fraction peak EEC LC50 RQ Chronic

EEC NOAEC RQ PRZM/EXAMS EEC

with drift and runoff 0 0.24 0.50 3.00 0.17 0.07 0.04 2.00 PRZM/EXAMS EECs

without drift 0 0.00 0.03 3.00 0.01 0.01 0.04 0.26

PRZM/EXAMS EECs

with drift and runoff
with a buffer 800

- 997 0.04 0.09 3.00 0.03 0.02 0.04 0.53

600

- 750 0.05 0.11 3.00 0.04 0.02 0.04 0.61

450

- 550 0.06 0.13 3.00 0.04 0.02 0.04 0.69

350

- 400 0.07 0.15 3.00 0.05 0.03 0.04 0.76

# Spray Drift Fraction : EPA pond

Distance from edge of field to water body (feet) Fraction of Applied or Spray Drift Fraction Ground Application Aerial Application

ASAE very
fine to fine ASAE fine to
medium/coarse ASAE very
fine to fine ASAE fine to
medium ASAE
medium to

coarse 0 0.06 0.02 0.24 0.13 0.09
1 0.06 0.01 0.24 0.12 0.09
5 0.05 0.01 0.23 0.12 0.08
10 0.04 0.01 0.23 0.11 0.07
25 0.03 0.01 0.21 0.09 0.06
50 0.02 0.01 0.18 0.07 0.04
100 0.01 0.00 0.15 0.05 0.03
150 0.01 0.00 0.12 0.04 0.02
200 0.01 0.00 0.10 0.03 0.02
250 0.01 0.00 0.09 0.03 0.01
300 0.01 0.00 0.08 0.02 0.01
350 0.00 0.00 0.07 0.02 0.01
400 0.00 0.00 0.07 0.02 0.01
450 0.00 0.00 0.06 0.02 0.01
500 0.00 0.00 0.06 0.02 0.01
550 0.00 0.00 0.06 0.02 0.01
600 0.00 0.00 0.05 0.01 0.01
650 0.00 0.00 0.05 0.01 0.01
700 0.00 0.00 0.05 0.01 0.01
750 0 00 0 00 0.05 0 01 0 01

# Questions?

Katrina White
703

- 308

- 4536 White.Katrina@epa.gov

Published as Federal Registry Notice: http://www.regulations.gov/#! docketDetail;D=EPA

- HQ

- OPP

- 2013

- 0676

Comments accepted through end of April