UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

WASHINGTON, D.C. 20460 

Date: August 8, 2013 

OFFICE OF CHEMICAL SAFETY 

AND POLLUTION PREVENTION 

Subject: 2,4-D. Occupational and Residential Exposure Assessment for a Proposed Use of 

2,4-D Choline on Herbicide-Tolerant Corn and Soybean 

PC Code: 03000 I, 05 1505 

Decision No.: ·q'l19fl 

Petition No.: NA 

Risk Assessment Type: OccupationaVResidential Exposure Assessment 

TXR No.: NA 

MRTD No.: NA 

From: Alexandra LaMay, Biologist 

Risk Assessment Branch VII 

DP Barcode: 0413002 

Registration No.: NA 

Regulatory Action: Section 3 

Case No.: NA 

CAS No.: 94-75-7 

40 CFR: 40 CFR 180.142 

Through: 

Health Effects Division (750

1

9P) 0--

Michael Metzger, Chief ' / J a# .J 

Risk Assessment Branch V tuf-. ( 

Health Effects Division (7 09P) 

and 

Matthew Crowley, Biologist 

Margarita Collantes, Biolbgis /)c?~ 

Exposure Science Advisory Committee (ExpoSAC) I HED 

To: Michael Walsh 

Registration Division (7505P) 

Introduction 

The Registration Division (RD) requested that the Health Effects Division (HED) conduct an 

exposure and risk assessment for the new use of2,4-D choline on herbicide-tolerant com and 

soybean. 

It is HED policy to use the best available data to assess exposure. Several sources of generic 

data were used in this assessment as surrogate data in the absence of chemical-specific data, 

Page I of35 
including Pesticide Handlers Exposure Database Version 1.1 (PHED 1.1 ); the Agricultural 

Handler Exposure Task Force (AHETF) database; the Outdoor Residential Exposure Task Force 

(ORETF) database; and the Residential SOPs. Some of these data are proprietary, and subject to 

the data protection provisions of the Federal Insecticide, Fungicide, and Rodenticide Act 

(FIFRA). 

Note: This memorandum was reviewed by the Exposure Science Advisory Committee 

(ExpoSAC) on June 13, 2013. 

Page 2 of35 
Page 3 of 35

Table of Contents

1.0 Executive Summary............................................................................................................. 4

2.0 Risk Assessment Conclusions and Recommendations........................................................ 5

2.1 Summary of Risk Estimates............................................................................................. 5

2.2 Label Recommendations from Occupational Assessment............................................... 5

2.3 Label Recommendations from Residential Assessment .................................................. 6

2.4 Data Deficiencies and Requirements ............................................................................... 6

3.0 Hazard Characterization....................................................................................................... 6

4.0 Use Profile ........................................................................................................................... 8

5.0 Residential Exposure and Risk Estimates............................................................................ 9

5.1 Residential Handler Exposure/Risk Estimates................................................................. 9

5.2 Residential Post-application Exposure/Risk Estimates.................................................. 11

5.2.1 Residential Post-application Exposure for Turf Use ................................................... 12

5.2.2 Residential Post-application Exposure for Aquatic Use.............................................. 13

5.3 Combined Residential Risk Estimates (Multiple Exposure Scenarios) ......................... 14

5.4 Residential Risk Estimates for Use in Aggregate Assessment ...................................... 14

5.5 Spray Drift...................................................................................................................... 17

5.6 Volatilization .............................................................................................................. 17

5.6.1 Flux Data................................................................................................................. 18

5.6.2 Volatilization Modeling and Risk Assessment....................................................... 18

5.6.3 Volatilization Risk Estimates.................................................................................. 19

6.0 Occupational Exposure and Risk Estimates ...................................................................... 21

6.1 Occupational Handler Exposure/Risk Estimates............................................................ 21

6.2 Occupational Post-application Exposure/Risk Estimates .............................................. 23

6.2.1 Occupational Post-application Inhalation Exposure/Risk Estimates...................... 24

6.2.2 Occupational Post-application Dermal Exposure/Risk Estimates.......................... 24

Appendix A. Summary of Occupational and Residential Non-cancer Algorithms..................... 25

Appendix B. Flux Rates and Flux Profiles ................................................................................... 34
Page 4 of 35

1.0 Executive Summary

2,4-Dichlorophenoxyacetic acid (2,4-D) is an alkylchlorophenoxy herbicide used to control a 

variety of broadleaf weeds. It is a longstanding active ingredient (ai) registered for a variety of 

food/feed uses. Permanent tolerances for 2, 4-D are established under 40 CFR 180.142 for a 

wide variety of crops and livestock commodities.

The proposed use is for 2,4-D choline use on herbicide-tolerant corn and soybean. These crops 

have a trait that that increases the herbicide tolerance of corn and soybean to 2,4-D via increased 

metabolism through a pathway involving the metabolite 2,4-dichlorophenol (2,4-DCP). 

For corn, the proposed use is for pre-plant, pre-emergence, or post-emergence (when corn is no 

later than the V8 growth stage or 48 inches tall) application to herbicide-tolerant field corn at a 

maximum single application rate of 1.0 lb acid equivalent (ae)/acre (A). For soybean, the 

proposed use is for pre-plant, pre-emergence, or post-emergence (when soybean is no later than 

the R2, or full flowering, growth stage) application to soybean at a maximum single application 

rate of 1.0 lb ae/A. For post-emergence applications for both crops, a maximum of two 

applications are permitted with a minimum of 12 days between applications. The maximum 

seasonal application rate is 3 lbs ae/A/season for both crops. The directions indicate no more 

than one pre-emergence application and no more than two post-emergence applications per use 

season. Applications are to be made using groundboom equipment. Aerial application and 

chemigation are prohibited. The proposed preharvest interval (PHI) for corn and soybeans is 30 

days. 

There are registered uses of 2,4-D on ornamental turf including golf courses and parks as well as 

aquatic uses; therefore, residential handler exposure and post-application exposure to treated turf 

is possible. As the Residential SOPs were updated in 2012, these scenarios have been reassessed. There is no potential hazard via the dermal route for 2,4-D, therefore the handler 

assessment included only the inhalation route of exposure and the post-application assessment 

included only the inhalation and incidental oral route of exposure. The residential handler and 

post-application risk estimates are not of concern for 2,4-D for all scenarios and all routes of 

exposure. 

An increase in use of 2,4-D is anticipated in the near future due to several factors (e.g., resistance 

traits in certain crops and weed resistance management). Exposure to drift and volatilization, 

and the appropriate available data, were considered in this assessment due to the anticipated 

market expansion. Concerning spray drift, the residential postapplication exposure assessment 

for registered use as direct application to turf is protective of potential deposition on turf from 

spray drift for the proposed use of 2,4-D choline on herbicide-tolerant corn and soybean. The 

potential exposure to vapor phase 2,4-D residues emitted from treated fields for the proposed 

uses of 2,4-D choline has been evaluated in this assessment. Volatilization modeling was 

completed using Probabilistic Exposure and Risk model for FUMigants (PERFUM) as well as 

chemical- and formulation-specific flux data. The results indicate that volatilization of 2,4-D

from treated crops does occur and could result in bystander exposure to vapor phase 2,4-D. 

Results of PERFUM modeling, however, indicate that airborne concentrations, even at the edge 

of the treated fields, are not of concern. 
Page 5 of 35

Occupational handlers may apply 2,4-D choline with groundboom equipment. There is no 

potential hazard via the dermal route for 2,4-D, therefore the occupational handler assessment 

included only the inhalation route of exposure. Occupational handler inhalation risk estimates 

are not of concern (i.e., MOEs > LOC of 300) for all scenarios for use of 2,4-D choline on 

herbicide-tolerant corn and soybean. At baseline PPE (i.e., no respirator), the occupational 

handler inhalation MOE is 4,900 for mixer/loaders and 3,200 for applicators using groundboom 

equipment. 

There is no potential hazard via the dermal route for 2,4-D; therefore, a quantitative occupational 

post-application dermal risk assessment was not completed. The minimum Worker Protection 

Standard (WPS) restricted entry interval (REI) of 48 hours is adequate to protect agricultural 

workers from post-application exposures to 2,4-D. 

Human Studies Review

This risk assessment relies in part on data from studies in which adult human subjects were 

intentionally exposed to a pesticide or other chemical. These data, which include studies from 

PHED 1.1; the AHETF database; the Outdoor Residential Exposure Task Force (ORETF) 

database; and the Residential SOPs, are (1) subject to ethics review pursuant to 40 CFR 26, (2) 

have received that review, and (3) are compliant with applicable ethics requirements. For certain 

studies, the ethics review may have included review by the Human Studies Review Board. 

Descriptions of data sources, as well as guidance on their use, can be found at the Agency 

website1. 

2.0 Risk Assessment Conclusions and Recommendations

2.1 Summary of Risk Estimates

The residential handler and post-application risk estimates are not of concern for 2,4-D for all 

scenarios and all routes of exposure. The residential postapplication exposure assessment for 

registered use as direct application to turf is protective of potential deposition on turf from spray 

drift. The volatilization assessment indicates there are no risks of concern for bystanders 

adjacent to treated fields.

Occupational handler inhalation risk estimates are not of concern (i.e., MOEs > LOC of 300) for 

all scenarios for use of 2,4-D choline on herbicide-tolerant corn and soybean. At baseline PPE 

(i.e., no respirator), the occupational handler inhalation MOE is 4,900 for mixer/loaders and 

3,200 for applicators using groundboom equipment. There is no potential hazard via the dermal

route for 2,4-D; therefore, a quantitative occupational post-application dermal risk assessment 

was not completed.

2.2 Label Recommendations from Occupational Assessment 

 

1

http://www.epa.gov/pesticides/science/handler-exposure-data.html and 

http://www.epa.gov/pesticides/science/post-app-exposure-data.html
Page 6 of 35

None.

2.3 Label Recommendations from Residential Assessment

None.

2.4 Data Deficiencies and Requirements

Turf Transferable Residue (TTR): In accordance with the updated Part 158 data requirements 

(2007), a TTR study is required for all occupational (e.g., sod farms, golf courses, parks, and 

recreational areas) or residential turf uses. Acceptable TTR data are available for 2,4-D. There 

is no potential hazard via the dermal route for 2,4-D.

Dislodgeable Foliar Residue (DFR): In accordance with the updated Part 158 data requirements 

(2007), one or more DFR studies are required when a pesticide has residential or occupational 

uses that could result in post-application dermal exposure. A DFR study is not required for 2,4-

D at this time since there is no potential hazard via the dermal route for 2,4-D. 

3.0 Hazard Characterization

Acute Toxicity

Table 3.0.1 - Acute Toxicity Categories for 2,4-D

2

Acid

Acute Oral (870.1100) III

Acute Dermal (870.1200) III

Acute Inhalation (870.1300) III

Primary Eye Irritation (870.2400) I

Primary Skin Irritation (870.2500) IV

Dermal Sensitization (870.2600) Not a dermal sensitizer 

Toxicological PODs Used for Risk Assessment

Table 3.0.2 Summary of Toxicological Doses and Endpoints for 2,4-D for Use in Occupational and NonOccupational Human Health Risk Assessments

Exposure/ 

Scenario

Point of 

Departure

Uncertainty/FQ

PA Safety 

Factors

RfD, PAD, 

Level of 

Concern for 

Risk 

Assessment

Study and Toxicological Effects

Acute Dietary 

(General 

Population, 

including 

Infants and 

Children)

NOAEL = 67 

mg/kg/day

UFA= 10x

UFH=10x

FQPA SF= 1x

aRfD=aPAD = 

0.67 

mg/kg/day

Acute Neurotoxicity Study – Rat

MRID 43115201 (1994)

LOAEL = 227 mg/kg/day based on slight 

gait abnormalities (forepaw flexing and 

knuckling) and increased incidence of 

incoordination.

 

2 ORE Assessment for RED. D316596. T. Dole. 5/4/05.
Page 7 of 35

Table 3.0.2 Summary of Toxicological Doses and Endpoints for 2,4-D for Use in Occupational and NonOccupational Human Health Risk Assessments

Exposure/ 

Scenario

Point of 

Departure

Uncertainty/FQ

PA Safety 

Factors

RfD, PAD, 

Level of 

Concern for 

Risk 

Assessment

Study and Toxicological Effects

Incidental 

Oral (1-30 

days and 1-6 

months)

NOAEL = 21 

mg/kg/day 

UFA= 10x

UFH=10x

FQPA SF= 1x

Residential 

LOC for MOE 

= 100

Extended 1-generation reproduction 

(Crl:CD(SD) rat)

MRID 47972101 (2010)

LOAEL=800/600 ppm (males 55.6 mkd; 

females 46.7 mkd), based on kidney 

toxicity manifested as increased kidney 

weights and increased incidence of 

degeneration of the proximal convoluted 

tubules, and for offspring based on 

decreased body weight observed 

throughout lactation. 

Dermal 

Short- and 

IntermediateTerm (1-30 

days and 1-6 

months)

No potential hazard via the dermal route, based on the lack of systemic effects following repeat 

dermal exposure of rabbits at dose levels up to 1000 mg/kg/day. Although developmental toxicity 

was not assessed in the dermal study, clear NOAELs (dermal equivalent doses of 250 and 300 

mg/kg/day) were determined; the developmental effects occurred at dose levels that exceed renal 

clearance mechanism (dermal equivalent doses of 750 and 900 mg/kg/day); dose levels required to 

exceed the renal clearance mechanism would not be attained following dermal exposure to humans.

Inhalation 

Short- and 

IntermediateTerm (all 

durations)

LOAEL = 0.05 

mL/kg/day

HEC=0.013 

mg/L/dayA

(residential)

HEC= 0.056 

mg/L/dayA

(occupational)

HED=1.9 

mg/kg/dayB

(residential)

HED= 2.68 

mg/kg/dayB

(occupational)

UFA = 3x

UFH = 10x

FQPA SF = 

1xLOAEL→NOAEL

= 10x

Residential 

and 

Occupational 

LOC for MOE 

= 300

Subchronic inhalation toxicity study (SD 

CD rat)

MRID 47398701 (2008)

LOAEL = 0.05 mg/L/day, based on 

portal-of-entry effects

(squamous metaplasia and epithelial 

hyperplasia with increased mixed 

inflammatory cells within the larynx); not 

totally resolved following a 4-week 

recovery period.

Cancer (oral, 

dermal, 

inhalation)

Classification: Group D – not classifiable as to human carcinogenicity

Point of Departure (POD) = A data point or an estimated point that is derived from observed dose-response data and 

used to mark the beginning of extrapolation to determine risk associated with lower environmentally relevant human 

exposures. NOAEL = no observed adverse effect level. LOAEL = lowest observed adverse effect level. UF = 

uncertainty factor. UFA = extrapolation from animal to human (interspecies). UFH = potential variation in 

sensitivity among members of the human population (intraspecies). UFL = use of a LOAEL to extrapolate a 

NOAEL. UFS = use of a short-term study for long-term risk assessment. UFDB = to account for the absence of key 

data (i.e., lack of a critical study). FQPA SF = FQPA Safety Factor. PAD = population adjusted dose (a = acute, c 

= chronic). RfD = reference dose. MOE = margin of exposure. LOC = level of concern. N/A = not applicable.

1 The HEC used for risk assessment is the most sensitive one derived from the nasal degeneration effects.

A Residential HEC (portal of entry endpoint) = rat POD * (daily duration adjustment) * weekly duration adjustment * RDDR
Page 8 of 35

= 0.05 mg/L * (6 hrs/24 hrs) * (5 days/7 days) * Tracheobronchial RDDR (1.49) = 0. 013 mg/L

Occupational HEC (portal of entry endpoint) = rat POD * (daily duration adjustment) * weekly duration adjustment * RDDR

= 0.05 mg/L * (6 hrs/8 hrs) * (5 days/5 days) * Tracheobronchial RDDR (1.49) = 0.056 mg/L

B Residential HED (portal of entry endpoint) = HEC * human specific conversion factor * daily duration 

= HEC (0.013 mg/L) * 6.0 L/hr/kg * 24 hrs= 1.9 mg/kg/day

Occupational HED (portal of entry endpoint) = HEC * human specific conversion factor * daily duration

= HEC (0.056 mg/L) *6.0 L/hr/kg * 8 hrs= 2.68 mg/kg/day

Absorption

Since the short- and intermediate-term inhalation PODs were based on route-specific toxicity 

studies, no absorption factors were necessary to estimate inhalation exposure.

Body Weight

The standard body weight for the general population (80 kg) was used for all inhalation exposure 

scenarios covered in this risk assessment since the endpoints selected were not developmental 

and/or fetal effects.

4.0 Use Profile 

For corn, the proposed use is for pre-plant, pre-emergence, or post-emergence (when corn is no 

later than the V8 growth stage or 48 inches tall) application to herbicide-tolerant field corn at a 

maximum single application rate of 1.0 lb acid equivalent (ae)/acre (A). For soybean, the 

proposed use is for pre-plant, pre-emergence, or post-emergence (when soybean is no later than 

the R2, or full flowering, growth stage) application to soybean at a maximum single application 

rate of 1.0 lb ae/A. For post-emergence applications for both crops, a maximum of two 

applications are permitted with a minimum of 12 days between applications. The maximum 

seasonal application rate is 3 lbs ae/A/season for both crops. The directions indicate no more 

than one pre-emergence application and no more than two post-emergence applications per use 

season. Applications are to be made using groundboom equipment. Aerial application and 

chemigation are prohibited. The proposed preharvest interval (PHI) for corn and soybeans is 30 

days. The 2,4-D product labels direct mixers, loaders, applicators and other handlers to wear 

long-sleeved shirt and long pants, shoes plus socks, chemical-resistant gloves, and protective 

eyewear; a chemical-resistant apron is required when mixing or loading, cleaning up spills or 

equipment, or otherwise exposed to the concentrate.

Table 4.1. Summary of Proposed Directions for Use of 2,4-D Choline.

Applic. Timing, 

Type, and 

Equip.

Formulation 

[EPA Reg. 

No.]

Applic. 

Rate (lb 

ae/A)

Max. No. 

Applic. per 

Season

Max. 

Seasonal 

Applic. Rate 

(lb ai/A)

PHI 

(days)

Use Directions and 

Limitations

Herbicide-Tolerant Soybeans 

Groundboom 

equipment only

Preplant, 

Preemergence, 

and 

Postemergence 

Application

Liquid

[62719-

AUU]

1 lb 

ae/acre 3

3 lb ae/acre 

per use 

season

30

Do not apply this product 

through any type of 

irrigation system. Do not 

aerially apply this product. 

Do not apply more than 

one preemergence 

application and no more 

than two postemergence 
Page 9 of 35

Table 4.1. Summary of Proposed Directions for Use of 2,4-D Choline.

Applic. Timing, 

Type, and 

Equip.

Formulation 

[EPA Reg. 

No.]

Applic. 

Rate (lb 

ae/A)

Max. No. 

Applic. per 

Season

Max. 

Seasonal 

Applic. Rate 

(lb ai/A)

PHI 

(days)

Use Directions and 

Limitations

applications per use season. 

Do not apply to soybeans 

later than the R2 stage.

Herbicide-Tolerant Corn

Groundboom 

equipment only

Preplant, 

Preemergence, 

and 

Postemergence 

Application

Liquid

[62719-

AGO]

1 lb 

ae/acre 3

3 lb ae/acre 

per use 

season

Forage: 

30

Do not apply this product 

through any type of 

irrigation system. Do not 

aerially apply this product. 

Do not apply more than 

one preemergence 

application and no more 

that two postemergence 

applications per use season. 

Do not apply to corn later 

than the V8 stage or corn 

more than 48 inches tall.

5.0 Residential Exposure and Risk Estimates

There are registered residential uses of 2,4-D for use on ornamental turf, including parks, sports 

fields, and golf courses, as well as aquatic uses; these uses have been assessed previously and 

there are no new residential uses proposed. The existing residential uses that have been 

reassessed in this document to reflect updates to HED’s 2012 Residential SOPs3along with 

policy changes for body weight assumptions. The revision of residential exposures will impact 

the human health aggregate risk assessment for 2,4-D.

5.1 Residential Handler Exposure/Risk Estimates

HED uses the term “handlers” to describe those individuals who are involved in the pesticide 

application process. HED believes that there are distinct tasks related to applications and that 

exposures can vary depending on the specifics of each task. Residential handlers are addressed 

somewhat differently by HED as homeowners are assumed to complete all elements of an 

application without use of any protective equipment.

The quantitative exposure/risk assessment developed for residential handlers is based on the 

following scenarios: 

Mixing/Loading/Applying Liquid/WP/DF to Lawns/Turf with Hose-End Sprayer

Mixing/Loading/Applying Liquid/WP in WSP to Lawns/Turf/Aquatic Sites with 

Manually-pressurized handwand

Mixing/Loading/Applying Ready-to-Use/WP in WSP to Lawns/Turf with Hose-End 

Sprayer

Mixing/Loading/Applying Liquid to Lawns/Turf/Aquatic Sites with Backpack

 

3 Available: http://www.epa.gov/pesticides/science/residential-exposure-sop.html
Page 10 of 35

Mixing/Loading/Applying Liquid/WP/DF to Lawns/Turf with Manually-pressurized 

handwand or backpack

Mixing/Loading/Applying Granule to Lawns/Turf with Push-type spreader, Belly 

Grinder, Spoon, Shaker Can, Cup or Hand dispersal

Residential Handler Exposure Data and Assumptions

A series of assumptions and exposure factors served as the basis for completing the residential 

handler risk assessments. Each assumption and factor is detailed below.

Application Rate:

The maximum application rate for lawns/turf is 1.45 lb ae/acre for registered uses.

Unit Exposures and Area Treated or Amount Handled:

Unit exposure values and estimates for area treated or amount handled were taken from HED’s 

2012 Residential SOPs4.

Exposure Duration: 

Residential handler exposure is expected to be short-term in duration. Intermediate-term 

exposures are not likely because of the intermittent nature of applications by homeowners.

Residential Handler Non-Cancer Exposure and Risk Estimate Equations

The algorithms used to estimate exposure and dose for residential handlers can be found in 

Appendix A and/or the 2012 Residential SOPs5.

Combining Exposures/Risk Estimates:

There is no potential hazard via the dermal route for 2,4-D. Only inhalation risk estimates were 

quantitatively assessed. 

Summary of Residential Handler Non-Cancer Exposure and Risk Estimates

The residential handler risk estimates are not of concern for 2,4-D (MOEs are greater than the 

level of concern of 300 for inhalation) for all scenarios.

Table 5.1.1. Residential Handler Non-cancer Exposure and Risk Estimates for 2,4-D.

Exposure Scenario Level of Concern Inhalation Unit 

Exposure (mg/lb ai)

Maximum 

Application 

Rate1

Area Treated or 

Amount 

Handled Daily2

Inhalation

Dose

(mg/kg/day)3

MOE4

(LOC = 300)

Mixer/Loader/Applicator

Lawns/Turf, Liquid/ 

WP/DF, Hose-end sprayer

Inhalation = 300

0.022 1.5 lb ae/acre 0.5 acres 0.00021 9,200

Lawns/Turf/ Aquatic Sites, 

Liquid/WP in WSP, 

Manually-pressurized 

handwand

0.018 0.06 lb 

ae/gallonA 5 gallons 0.000068 28,000

Lawns/Turf, Ready-touse/WP in WSP, Hose-end 0.034 1.5 lb ae/acre 0.5 acres 0.00032 6,000

 

4 Available: http://www.epa.gov/pesticides/science/residential-exposure-sop.html

5 Available: http://www.epa.gov/pesticides/science/residential-exposure-sop.html
Page 11 of 35

Table 5.1.1. Residential Handler Non-cancer Exposure and Risk Estimates for 2,4-D.

Exposure Scenario Level of Concern Inhalation Unit 

Exposure (mg/lb ai)

Maximum 

Application 

Rate1

Area Treated or 

Amount 

Handled Daily2

Inhalation

Dose

(mg/kg/day)3

MOE4

(LOC = 300)

sprayer

Lawns/Turf/ Aquatic Sites, 

Liquid, Backpack 0.14 0.06 lb ae/gallonA 5 gallons 0.00053 3,600

Lawns/Turf, WP/DF, 

Manually-pressurized 

handwand or Backpack

1.1 0.06 lb 

ae/gallonA 5 gallons 0.0041 460

Lawns/Turf, Granule, Pushtype spreader 0.0026 1.5 lb ae/acre 0.5 acres 0.000024 78,000

Lawns/Turf, Granule, Belly 

Grinder 0.039 0.0000344 lb ai/ft2,B 1200 ft2

0.00002 94,000

Lawns/Turf, Granule, Spoon 0.087 0.0000344 lb 

ai/ft2,B 100 ft2

0.0000037 510,000

Lawns/Turf, Granule, Cup/ 

Shaker Can 0.013 0.0000344 lb ai/ft2,B 100 ft2

0.00000056 3,400,000

Lawns/Turf, Granule, Hand 

Dispersal 0.38 0.0000344 lb ai/ft2,B 100 ft2

0.000016 120,000

1 Based on registered or proposed label.

2 Based on HED’s 2012 Residential SOPs (http://www.epa.gov/pesticides/science/residential-exposure-sop.html).

3 Inhalation Dose = Inhalation Unit Exposure (mg/lb ai) × Application Rate (lb ai/acre or gal) × Area Treated or Amount 

Handled (A/day or gallons/day) ÷ BW (kg).

4 Inhalation MOE = Inhalation POD (mg/kg/day) ÷ Inhalation Dose (mg/kg/day).

A 1.5 lb ai per acre with minimum of 25 gallons used per acre = 0.06 lb ai/gal

B 1.5 lb ai/acre * 1 acre/43560 ft2= 0.0000344 lb ai/ft2

5.2 Residential Post-application Exposure/Risk Estimates

There is the potential for post-application exposure for individuals exposed as a result of being in 

an environment that has been previously treated with 2,4-D. The quantitative exposure/risk 

assessment for residential post-application exposures is based on the following scenarios: 

As a result of existing residential uses:

Incidental ingestion (i.e., hand-to-mouth, object-to-mouth, soil ingestion exposure) from 

contact with treated turf (children 1 < 2 years old only)

Episodic granular ingestion on treated turf (children 1 < 2 years old only)

Incidental ingestion of water during recreational swimming (both adults and children 3 < 

6 years old).

Assessment of post-application exposure to turf treated with liquid formulations is protective of 

exposure to solid formulations.

The lifestages selected for each post-application scenario are based on an analysis provided as an 

Appendix in the 2012 Residential SOPs6. These lifestages are not the only lifestages that could 

be potentially exposed for these post-application scenarios; however, the assessment of these 

 

6 Available: http://www.epa.gov/pesticides/science/residential-exposure-sop.html
Page 12 of 35

lifestages is health protective for the exposures and risk estimates for any other potentially 

exposed lifestages.

5.2.1 Residential Post-application Exposure for Turf Use

Residential Post-application Exposure Data and Assumptions for Turf Use

A series of assumptions and exposure factors served as the basis for completing the residential 

post-application risk assessment. Each assumption and factor is detailed in the 2012 Residential 

SOPs6.

Chemical-specific TTR Data 

There are three transferable turf residue studies available for 2,4-D, MRIDs 45033101, 

44655703, and 44655702. These studies have been determined to be acceptable for risk 

assessment purposes. The highest predicted day 0 TTR value is 0.28 μg/cm2(from MRID 

44655703, TRT3, North Carolina, application rate of 1.79 lb ae/acre). For risk assessment 

purposes, this residue value is scaled to the 1.45 lb ae/acre application rate; the residue value for 

risk assessment is 0.23 μg/cm2on day 0.

Residential Post-application Non-Cancer Exposure and Risk Equations

The algorithms used to estimate residential post-application exposure and dose can be found in 

Appendix A and/or the 2012 Residential SOPs6.

Combining Exposure and Risk Estimates

There is no potential hazard via the dermal route for 2,4-D. Only incidental oral risk estimates 

were quantitatively assessed. The incidental oral scenarios (i.e., hand-to-mouth and object-tomouth) should be considered inter-related and it is likely that they occur interspersed amongst 

each other across time. Combining these scenarios would be overly-conservative because of the 

conservative nature of each individual assessment. The granular ingestion scenario is not 

combined as this exposure would not occur as a result of routine behavior and is considered an 

episodic event related to poisoning. Therefore, no post-application exposure scenarios were

combined for children 1 < 2 years old. 

Summary of Residential Post-application Non-Cancer Exposure and Risk Estimates for Turf Use

The residential post-application risk estimates are not of concern for 2,4-D (MOEs are greater 

than the level of concern of 100) for all incidental oral scenarios.

Table 5.2.1. Residential Post-application Non-cancer Exposure and Risk Estimates for 2,4-D.

Lifestage

Post-application Exposure 

Scenario Application 

Rate1

Dose 

(mg/kg/day)2 MOEs3 Combined Routes

Combined 

MOEs Use Site Route of Exposure

1 to <2 years Turf

Hand-to-Mouth

1.45 lb 

ae/acre

0.0315 670

NA NA

Object-to-Mouth 0.00096 22,000

Soil Ingestion 4.9x10-5 430,000

Episodic Granular 

Ingestion

3% ai; 1.5 lb 

ae/acre 0.14 490A

1 Based on registered or proposed label.

2 Dose equations can be found in Appendix A.

3 MOE = POD (mg/kg/day) / Dose (mg/kg/day).

4 Combined MOE = NA.

A Ingestion of granules is considered episodic in nature; MOE was calculated using the acute dietary endpoint and POD
Page 13 of 35

5.2.2 Residential Post-application Exposure for Aquatic Use

2,4-D can be used for aquatic weed control of surface and submerged weeds. According to the 

2005 RED for 2,4-D, the target concentration in the water column surrounding submerged weeds 

is 2 to 4 ppm. Although many treatments are applied to aquatic areas where recreational 

swimming is not likely to occur, some subsurface treatments are made at recreational lakes. As a 

result, individuals can be exposed to 2,4-D residues in water by entering these areas if they have 

been previously treated. A 24 hour swimming restriction was also added to the master label 

according to the RED. Of the possible post-application exposures, swimming in treated water is 

considered by HED to be worse case and is used as a surrogate for all other possible postapplication exposures. The extent of exposure during recreational swimming is assumed to be 

short-term in duration. Risks estimates were calculated for post-application incidental oral 

ingestion while swimming in treated lakes or ponds. Inhalation exposure is expected to be 

negligible for swimmers; therefore, a post-application inhalation assessment was not conducted. 

Furthermore, the inhalation assessment for residential handlers is expected to be protective of 

potential post-application exposure and risk.

Residential Post-application Exposure Data and Assumptions for Aquatic Use

A series of assumptions and exposure factors served as the basis for completing the residential 

post-application risk assessment for the swimmers scenario and can be found in Appendix A. 

Inhalation exposure from swimming is expected to be negligible, especially in compared to 

ingestion. Furthermore, 2,4-D will exist primarily in anion form in the environment; therefore, 

significant volatilization from water surfaces is not anticipated because anions are not expected 

to volatilize.

The Agency considered residential post-application exposure for different segments of the 

population. The lifestages selected for each post-application scenario are based on an analysis 

provided as an Appendix in the 2012 Residential SOPs7. These lifestages are not the only 

lifestages that could be potentially exposed for these post-application scenarios; however, the 

assessment of these lifestages is health protective for the exposures and risk estimates for any 

other potentially exposed lifestages. 

The scenarios, routes of exposure and lifestages assessed include ingestion of water during 

recreational swimming (both adults and children 3 < 6 years old).

The swimmer calculations have been updated from the previous assessment to reflect the revised 

body weights for adults and children. Also the water ingestion rates and the time spent in the 

water have been revised to correspond with the 2012 Residential SOPs. A body weight of 80 kg 

is used for assessing incidental oral ingestion for adults since the toxicity endpoint selected is not 

based on a developmental study where developmental and/or fetal effects were observed. The 

level of concern for adults and children (3 to < 6 years old) for short-term incidental oral 

exposures is MOEs < 100.

 

7 Available: http://www.epa.gov/pesticides/science/residential-exposure-sop.html
Page 14 of 35

Residential Post-application Non-Cancer Exposure and Risk Equations

The equations and inputs are generally derived from SWIMODEL 3.0, developed by EPA as a 

screening tool to conduct exposure assessments of pesticides found in swimming pools and spas. 

It uses well-accepted screening exposure assessment equations to calculate the high end exposure 

for swimmers expressed as a mass-based intake value (mg/event). The model focuses on 

potential chemical intakes only and does not take into account metabolism or excretion of the 

chemical of concern. Detailed information and the algorithms used to estimate residential postapplication exposure from uses of 2,4-D for aquatic application are presented in Appendix A of 

this document.

Summary of Residential Post-application Exposure and Risk Estimates for Aquatic Use

Table 5.2.5 presents the post-application incidental oral ingestion MOE values calculated for 

adults and children 3 to <6 years old after aquatic applications of 2,4-D. 

Post-application risk estimates do not exceed HED’s level of concern for any of the scenarios 

assessed. 

Table 5.2.2. Residential Post-application Non-cancer Exposure and Risk Estimates for 2,4-

D (Swimmer Scenario)

Exposure Scenario Level of 

Concern

Maximum 

Concentration 

in Water 1

(mg/L)

Exposure Dose

(mg/kg/day) 2

Short-term 

MOE 3

Ingestion of water, 

Adult

100 4

0.0039 5,300

Ingestion of water,

Child 3<6 years 

0.0306 690

1. Maximum concentration in water = 4 mg/L (4 ppm) based on maximum application rate for 

 aquatic weed control: 10.8 lb ae/acre-foot. It is possible that the concentration may exceed this value immediately after 

application before mixing. However it is conservative to assume exposure to this concentration for a short-term duration

(1 to 30 days) as well as considering the 24 hour swimming restriction on the master label.

2. Exposure dose (mg/kg/day) = Refer to Appendix A.

3. MOE = NOAEL/Exposure dose. The level of concern for adults and children (3< 6 years old) is MOEs < 100.

5.3 Combined Residential Risk Estimates (Multiple Exposure Scenarios)

There are no combined residential exposure scenarios.

5.4 Residential Risk Estimates for Use in Aggregate Assessment

Table 5.4 reflects the residential risk estimates that are recommended for use in the aggregate 

assessment for 2,4-D.

Inhalation exposures are not included in the aggregate assessment since effects from the 

inhalation endpoint are not systemic

Post-application granular pesticide exposure following applications to lawns and turf are not 

included in the aggregate assessment as this exposure would not occur as a result of routine 

behavior and is considered an episodic event related to poisoning

The recommended residential exposure for use in the adult aggregate assessment reflects 

incidental oral exposure from post-application exposure swimmer scenario
Page 15 of 35

The recommended residential exposure for use in the children 1<2 years old aggregate 

assessment reflects hand-to-mouth exposures from post-application turf scenario (i.e., 

post-application exposure to turf applications)
Page 16 of 35

Table 5.4.1. Recommendations for the Residential Exposures for the 2,4-D Aggregate Assessment.

1

Lifestage

Residential Handler Residential Post-application 

Dose (mg/kg/day)2 MOE3 Dose (mg/kg/day)4 MOE5

Dermal Inhalation Total Dermal Inhalation Total Dermal Inhalation Oral Total Dermal Inhalation Oral Total

Short-Term

Adult NA NA NA NA NA NA NA NA 0.0039 NA NA NA 5,300 NA

Child N/A NA NA 0.0315 NA NA NA 670 NA

1 Bolded risk estimates should contribute to the residential exposure portion of the aggregate assessment. 

2 Residential Handler Dose = the highest handler dose for each applicable lifestage of all scenarios assessed from Table 5.1.1. 

3 Residential Handler MOE = the lowest MOEs identified in Table 5.1.1. 

4 Residential Post-application Dose = the highest post-application dose for each applicable lifestage of all scenarios assessed. 

5 Residential Post-application MOE = the MOEs associated with the highest doses identified. 
Page 17 of 35

5.5 Spray Drift

Off-target movement of pesticides can occur via many types of pathways and it is governed by a 

variety of factors. Sprays that are released and do not deposit in the application area end up offtarget and can lead to exposures to those it may directly contact. They can also deposit on 

surfaces where contact with residues can eventually lead to indirect exposures (e.g., children 

playing on lawns where residues have deposited next to treated fields). The potential risk 

estimates from these residues can be calculated using drift modeling coupled with methods 

employed for residential risk assessments for turf products.

The approach to be used for quantitatively incorporating spray drift into risk assessment is based 

on a premise of compliant applications which, by definition, should not result in direct exposures 

to individuals because of existing label language and other regulatory requirements intended to 

prevent them.8 Direct exposures would include inhalation of the spray plume or being sprayed 

directly. Rather, the exposures addressed here are thought to occur indirectly through contact 

with impacted areas, such as residential lawns, when compliant applications are conducted. 

Given this premise, exposures for children (1 to 2 years old) and adults who have contact with 

turf where residues are assumed to have deposited via spray drift thus resulting in an indirect 

exposure are the focus of this analysis analogous to how exposures to turf products are 

considered in risk assessment. 

Several 2,4-D products have existing labels for use on turf, thus it was considered whether the 

risk assessment for that use may be considered protective of any type of exposure that would be 

associated with spray drift. If the maximum application rate on crops adjusted by the amount of 

drift expected is less than or equal to existing turf application rates, the existing turf assessment

is considered protective of spray drift exposure. The proposed maximum single application rate

of 2,4-D choline on herbicide-tolerant corn and soybean is 1 lb ae/acre. This is less than the 

registered application rate on turf of 1.5 lb ae/acre, which has been previously assessed and 

which was updated based on the revised SOPs for Residential Exposure Assessment (i.e., see 

above in Section 5.2). Thus, even if 100% of the application rate on herbicide-tolerant corn and 

soybean is deposited on an adjacent lawn, calculated risk estimates from drift would not be of 

concern. This again is because all existing registered uses on lawns have been previously

assessed and no risks of concern were identified. 

The registered residential uses on turf result in exposure greater than potential exposure from 

spray drift; therefore, no new residential assessment needs to be completed. 

5.6 Volatilization 

The potential exposure to bystanders from vapor phase 2,4-D residues emitted from treated fields 

has been evaluated for the proposed use of 2,4-D choline on herbicide-tolerant corn and soybean. 

Bystander exposure from 2,4-D emitted from treated fields depends on two main factors: 1) the 

rate at which these chemicals come off a treated field (described as the off-gassing, emission or 

flux) and 2) how those vapors are dispersed in the air over and around the treated field. 

 

8 This approach is consistent with the requirements of the EPA’s Worker Protection Standard.
Page 18 of 35

Volatilization can occur during the application process or thereafter. It can result from aerosols 

evaporating during application, while deposited sprays are still drying (e.g., possibly via codistillation), or after as dried deposited residues volatilize. This assessment uses an analysis after 

sprays have dried.

This assessment employs approaches EPA has used previously to assess inhalation exposures to 

fumigant pesticides9and is also consistent with the recommendations of the December 2009 

Federal Insecticide, Fungicide, and Rodenticide Act Scientific Advisory Panel (SAP)10 meeting 

on the scientific issues associated with field volatilization of conversional (semi-volatile) 

pesticides.

5.6.1 Flux Data

Flux data for 2,4-D were submitted and reviewed by the Agency11. The study measured the flux 

rates of 2,4-D ethylhexyl ester (EHE), 2,4-D dimethylamine salt (DMA salt) and the 2,4-D 

choline salt. 2,4-D choline is the form proposed for use on herbicide-tolerant corn and soybean. 

According to the registrant, 2,4-D choline has a reduced potential for volatility. Treatments of 

the three forms were applied to tilled bare soil plots in Fowler, IN and to mature soybeans 

approximately 30 cm high with 80% canopy in Farmland, IN. Treatments of the three forms plus 

a formulation with 2,4-D choline plus glyphosate were also applied to growing soybeans

approximately 12-15 cm high with 15% canopy cover in Little Rock, AR and to cotton plants

approximately 50 cm high with 40% canopy in Ty Ty, GA. Air samplers were placed in a wheel 

and spoke design at 5 and 15 meters from each treated field edge. Samplers were placed at a 

height of 30 cm in Fowler, at 50 cm in Farmland, at 15 cm in Little Rock, and at 50 cm in Ty Ty. 

2,4-D choline was applied at a rate of 4 lb ae/acre in Farmland, Little Rock, and Ty Ty; and at a

rate of 5 lb ae/acre in Fowler. Flux was calculated using the indirect method based on the study 

design. For this assessment, the data from the 2,4-D choline applications only were used as this 

action specifically seeks registration for 2,4-D choline product use in conjunction with the use of 

soybean and corn with resistance traits. 

The flux profiles used for the assessment can be found in Appendix B. Flux rates are adjusted to

the proposed application rate (i.e., 1 lb ae/acre) from the application rates in the flux study. This 

type of adjustment is done routinely for this type of data and analyses.

Quantitative analysis using flux rates derived from this study are described below.

 

5.6.2 Volatilization Modeling and Risk Assessment

Volatilization modeling for a single day was completed using Probabilistic Exposure and Risk 

model for FUMigants (PERFUM). There are a variety of factors that potentially affect the 

 

9 U.S. EPA 2004d. FIFRA Science Advisory Panel Meeting Minutes - Fumigant Bystander Exposure Model 

Review: Probabilistic Exposure and Risk Model for Fumigants (PERFUM) Using Iodomethane as a Case Study. 

Available at http://www.epa.gov/scipoly/sap/meetings/2004/august1/august2425minutes.pdf

10 U.S. EPA 2009. FIFRA Science Advisory Panel Meeting Minutes - Scientific Issues Associated with Field 

Volatilization of Conventional Pesticides. Available at 

http://www.epa.gov/scipoly/sap/meetings/2009/december/120309meetingminutes.pdf

11 MRID 48862902. Field Volatility of Different 2,4-D Forms. June 15, 2012. Dow AgroSciences LLC. 
Page 19 of 35

emission rates of 2,4-D and subsequent offsite transport including: field condition (bare soil, 

growing or mature crop canopy), field parameters (soil type, moisture, etc.), formulation type, 

meteorological conditions, and application scenario (rate, method ). To the extent possible, based 

on the limited information available and a lack of intentional statistical design to quantitatively 

evaluate such factors, the impact of these variables was considered. Flux estimates from all 

monitored trials, a number of field sizes, and various meteorological data were used with 

PERFUM to estimate risk based on the 2,4-D field volatility study summarized in Section 5.6.1 

and Appendix B. The PERFUM modelling results are based on Bradenton, FL; Yakima, WA; 

Flint, MI; and Ventura, CA weather datasets which have been used in the past for other 

volatilization analyses and represent a range of conditions including those which have 

consistently provided the highest risk estimates. The results of this analysis have been 

summarized for a 40, 80, and 120 acre field using the flux data submitted for 2,4-D choline and 

each source of weather data. The short-term residential inhalation endpoint was used in the 

volatilization assessment; it is a conservative assumption to compare the day 1 volatilization 

exposure to a short-term HEC. Furthermore, a 6-hour exposure averaging period was used in the 

model; it is a conservative assumption to compare the 6 hour average exposure from the model to 

the HEC calculated for 24 hours of exposure especially since the 6 hour exposure period used as 

the basis for the comparison represents the peak emissions period after application.

All of the files associated with the use of PERFUM in this assessment can be provided upon 

request. These files could be used to examine the detailed input and output files for each 

permutation of the model completed for this analysis. 

5.6.3 Volatilization Risk Estimates

The field volatility study suggests that volatilization of 2,4-D from treated crops does occur and 

could result in bystander exposure to vapor phase 2,4-D. Results of PERFUM modeling, 

however, indicate that airborne concentrations, even at the edge of the treated fields, are not of 

concern. The maximum proposed application rate of 1 lb a.e./A was assessed. There were no 

whole field and maximum field buffers estimated using PERFUM for any field size (i.e., risks 

were acceptable at all percentiles of exposure at the edge of a treated field). 

Table 5.6.3. Comparison of Results For 2,4-D Choline PERFUM Buffer Distributions 

Based On Flux Studya, b

Percentiles

Field 1: Farmland, IN

Meteorological Station Location

Bradenton, FL Flint, MI Ventura, CA Yakima, WA

Max

Bufferc

(ft)

Whole

Field

Bufferd

(ft)

Max

Bufferc

(ft)

Whole

Field

Bufferd

(ft)

Max

Bufferc

(ft)

Whole

Field

Bufferd

(ft)

Max

Bufferc

(ft)

Whole

Field

Bufferd

(ft)

40 A, 1 lb a.e/A

50 0 0 0 0 0 0 0 0

75 0 0 0 0 0 0 0 0

90 0 0 0 0 0 0 0 0

95 0 0 0 0 0 0 0 0

99 0 0 0 0 0 0 0 0

80 A, 1 lb a.e/A

50 0 0 0 0 0 0 0 0
Page 20 of 35

75 0 0 0 0 0 0 0 0

90 0 0 0 0 0 0 0 0

95 0 0 0 0 0 0 0 0

99 0 0 0 0 0 0 0 0

120 A, 1 lb a.e/A

50 0 0 0 0 0 0 0 0

75 0 0 0 0 0 0 0 0

90 0 0 0 0 0 0 0 0

95 0 0 0 0 0 0 0 0

99 0 0 0 0 0 0 0 0

Percentiles

Field 2: Fowler, IN

Meteorological Station Location

Bradenton, FL Flint, MI Ventura, CA Yakima, WA

Max

Bufferc

(ft)

Whole

Field

Bufferd

(ft)

Max

Bufferc

(ft)

Whole

Field

Bufferd

(ft)

Max

Bufferc

(ft)

Whole

Field

Bufferd

(ft)

Max

Bufferc

(ft)

Whole

Field

Bufferd

(ft)

40 A, 1 lb a.e/A

50 0 0 0 0 0 0 0 0

75 0 0 0 0 0 0 0 0

90 0 0 0 0 0 0 0 0

95 0 0 0 0 0 0 0 0

99 0 0 0 0 0 0 0 0

80 A, 1 lb a.e/A

50 0 0 0 0 0 0 0 0

75 0 0 0 0 0 0 0 0

90 0 0 0 0 0 0 0 0

95 0 0 0 0 0 0 0 0

99 0 0 0 0 0 0 0 0

120 A, 1 lb a.e/A

50 0 0 0 0 0 0 0 0

75 0 0 0 0 0 0 0 0

90 0 0 0 0 0 0 0 0

95 0 0 0 0 0 0 0 0

99 0 0 0 0 0 0 0 0

Percentiles

Field 3: Little Rock, AR

Meteorological Station Location

Bradenton, FL Flint, MI Ventura, CA Yakima, WA

Max

Bufferc

(ft)

Whole

Field

Bufferd

(ft)

Max

Bufferc

(ft)

Whole

Field

Bufferd

(ft)

Max

Bufferc

(ft)

Whole

Field

Bufferd

(ft)

Max

Bufferc

(ft)

Whole

Field

Bufferd

(ft)

40 A, 1 lb a.e/A

50 0 0 0 0 0 0 0 0

75 0 0 0 0 0 0 0 0

90 0 0 0 0 0 0 0 0

95 0 0 0 0 0 0 0 0

99 0 0 0 0 0 0 0 0

80 A, 1 lb a.e/A

50 0 0 0 0 0 0 0 0

75 0 0 0 0 0 0 0 0

90 0 0 0 0 0 0 0 0

95 0 0 0 0 0 0 0 0

99 0 0 0 0 0 0 0 0

120 A, 1 lb a.e/A
Page 21 of 35

50 0 0 0 0 0 0 0 0

75 0 0 0 0 0 0 0 0

90 0 0 0 0 0 0 0 0

95 0 0 0 0 0 0 0 0

99 0 0 0 0 0 0 0 0

Percentiles

Field 4: Ty Ty, GA

Meteorological Station Location

Bradenton, FL Flint, MI Ventura, CA Yakima, WA

Max

Bufferc

(ft)

Whole

Field

Bufferd

(ft)

Max

Bufferc

(ft)

Whole

Field

Bufferd

(ft)

Max

Bufferc

(ft)

Whole

Field

Bufferd

(ft)

Max

Bufferc

(ft)

Whole

Field

Bufferd

(ft)

40 A, 1 lb a.e/A

50 0 0 0 0 0 0 0 0

75 0 0 0 0 0 0 0 0

90 0 0 0 0 0 0 0 0

95 0 0 0 0 0 0 0 0

99 0 0 0 0 0 0 0 0

80 A, 1 lb a.e/A

50 0 0 0 0 0 0 0 0

75 0 0 0 0 0 0 0 0

90 0 0 0 0 0 0 0 0

95 0 0 0 0 0 0 0 0

99 0 0 0 0 0 0 0 0

120 A, 1 lb a.e/A

50 0 0 0 0 0 0 0 0

75 0 0 0 0 0 0 0 0

90 0 0 0 0 0 0 0 0

95 0 0 0 0 0 0 0 0

99 0 0 0 0 0 0 0 0

a.Short-term Residential HEC 13000 μg/m3, UF = 300, target concentration 43.3 μg/m3

b.Registrant study conducted using 2,4-D Choline

c.Max buffers are the largest buffer estimated from any given direction away from the field.

d. Whole field buffers are the average buffer estimated for an entire field (average for all directions)

6.0 Occupational Exposure and Risk Estimates

6.1 Occupational Handler Exposure/Risk Estimates

HED uses the term handlers to describe those individuals who are involved in the pesticide 

application process. HED believes that there are distinct job functions or tasks related to 

applications and exposures can vary depending on the specifics of each task. Job requirements

(amount of chemical used in each application), the kinds of equipment used, the target being 

treated, and the level of protection used by a handler can cause exposure levels to differ in a 

manner specific to each application event. 

Based on the anticipated use patterns and current labeling, types of equipment and techniques 

that can potentially be used, occupational handler exposure is expected from the proposed uses. 

The quantitative exposure/risk assessment developed for occupational handlers is based on the 

following scenarios: 

Mixing/Loading Liquid for Groundboom Application
Page 22 of 35

Applying Spray by Groundboom Equipment

Occupational Handler Exposure Data and Assumptions

A series of assumptions and exposure factors served as the basis for completing the occupational 

handler risk assessments. Each assumption and factor is detailed below on an individual basis.

Application Rate: 

The proposed maximum single application rate on herbicide-tolerant corn and soybean is 1 lb 

ae/acre.

Unit Exposures: It is the policy of HED to use the best available data to assess handler exposure. 

Sources of generic handler data, used as surrogate data in the absence of chemical-specific data, 

include PHED 1.1, the AHETF database, the Outdoor Residential Exposure Task Force 

(ORETF) database, or other registrant-submitted occupational exposure studies. Some of these 

data are proprietary (e.g., AHETF data), and subject to the data protection provisions of FIFRA. 

The standard values recommended for use in predicting handler exposure that are used in this 

assessment, known as “unit exposures”, are outlined in the “Occupational Pesticide Handler Unit 

Exposure Surrogate Reference Table12”, which, along with additional information on HED 

policy on use of surrogate data, including descriptions of the various sources, can be found at the 

Agency website13.

Area Treated or Amount Handled: 

Area treated or amount handled includes:

Groundboom equipment: 200 acres per day for high-acreage field crops 

Exposure Duration: 

HED classifies exposures from 1 to 30 days as short-term and exposures 30 days to six months 

as intermediate-term. Exposure duration is determined by multiple factors, including the 

exposed population, the use site, the pest pressure triggering the use of the pesticide, and the 

cultural practices surrounding that use site. For most agricultural uses, it is reasonable to believe 

that occupational handlers will not apply the same chemical every day for more than a onemonth time frame; however, there may be a large agribusiness and/or commercial applicators 

who may apply a product over a period of weeks (e.g., completing multiple applications for 

multiple clients within a region). 

For 2,4-D, based on the proposed use, short- and intermediate-term exposures are anticipated for 

the following reasons: (1) the product can be applied multiple times per year (2) the product can 

be applied to multiple application sites and (3) there may be a large agribusiness and/or 

commercial applicators who may apply a product over a period of weeks.

Mitigation/Personal Protective Equipment: Estimates of inhalation exposure are calculated for 

various levels of personal protective equipment (PPE). Results are presented for “baseline,” 

defined as a single layer of clothing consisting of a long sleeved shirt, long pants, shoes plus 

 

12 Available: http://www.epa.gov/opp00001/science/handler-exposure-table.pdf

13 Available: http://www.epa.gov/pesticides/science/handler-exposure-data.html
Page 23 of 35

socks, no protective gloves, and no respirator. The 2,4-D product labels direct mixers, loaders, 

applicators and other handlers to wear long-sleeved shirt and long pants, shoes plus socks, 

chemical-resistant gloves, and protective eyewear; a chemical-resistant apron is required when 

mixing or loading, cleaning up spills or equipment, or otherwise exposed to the concentrate.

Occupational Handler Non-Cancer Exposure and Risk Estimate Equations

The algorithms used to estimate non-cancer exposure and dose for occupational handlers can be 

found in Appendix A.

Combining Exposures/Risk Estimates:

There is no potential hazard via the dermal route for 2,4-D; therefore, only occupational handler 

inhalation exposures are quantitatively assessed.

Summary of Occupational Handler Non-Cancer Exposure and Risk Estimates

Occupational handler risk estimates are not of concern (i.e., MOEs > LOC of 300) for all 

scenarios for use of 2,4-D choline on herbicide-tolerant corn and soybean. At baseline PPE (i.e., 

no respirator), the occupational handler inhalation MOE is 4,900 for mixer/loaders and 3,200 for 

applicators using groundboom equipment. 

Table 6.1.1. Occupational Handler Non-Cancer Exposure and Risk Estimates for 2,4-D.

Exposure Scenario Crop or 

Target

Inhalation Unit 

Exposure (μg/lb 

ai)1

Maximum

Application 

Rate2

Area 

Treated 

Daily3

Inhalation

Mitigation Level: 

No respirator

Dose 

(mg/kg/day)4 MOE5

Mixer/Loader

Mixer/Loader, 

Liquid, Groundboom

High Acreage 

Crop 0.219 1 lb ae/acre 200 acres 0.000548 4,900

Applicator

Applicator, Spray, 

Groundboom

High Acreage 

Crop 0.34 1 lb ae/acre 200 acres 0.00085 3,200

1 Based on the “Occupational Pesticide Handler Unit Exposure Surrogate Reference Table” (March 2013); Level of mitigation: Baseline.

2 Based on proposed labels.

3 Exposure Science Advisory Council Policy #9.1.

4 Inhalation Dose = Dermal Unit Exposure (μg/lb ai) × Conversion Factor (0.001 mg/μg) × Application Rate (lb ai/acre or gal) × Area Treated or 

Amount Handled Daily (A or gal/day) ÷ BW (kg).

5 Inhalation MOE = Inhalation NOAEL (mg/kg/day) ÷ Inhalation Dose (mg/kg/day).

6.2 Occupational Post-application Exposure/Risk Estimates

HED uses the term post-application to describe exposures that occur when individuals are 

present in an environment that has been previously treated with a pesticide (also referred to as reentry exposure). Such exposures may occur when workers enter previously treated areas to 

perform job functions, including activities related to crop production, such as scouting for pests 

or harvesting. Post-application exposure levels vary over time and depend on such things as the 

type of activity, the nature of the crop or target that was treated, the type of pesticide application, 

and the chemical’s degradation properties. In addition, the timing of pesticide applications, 

relative to harvest activities, can greatly reduce the potential for post-application exposure.
Page 24 of 35

6.2.1 Occupational Post-application Inhalation Exposure/Risk Estimates

Based on the Agency's current practices, a quantitative occupational post-application inhalation 

exposure assessment was not performed for 2,4-D at this time primarily because of the low acute 

inhalation toxicity (Toxicity Category III) and vapor pressure (1.4 x 10-7 mm Hg at 25°C for 2,4-

D acid). However, there are multiple potential sources of post-application inhalation exposure to 

individuals performing post-application activities in previously treated fields. These potential 

sources include volatilization of pesticides and resuspension of dusts and/or particulates that 

contain pesticides. The Agency is in the process of evaluating available post-application 

inhalation exposure data generated by the ARTF and may, as appropriate, develop policies and 

procedures, to identify the need for and, subsequently, the way to incorporate occupational postapplication inhalation exposure into the Agency's risk assessments. If new policies or 

procedures are put into place, the Agency may revisit the need for a quantitative occupational 

post-application inhalation exposure assessment for 2,4-D.

Although a quantitative occupational post-application inhalation exposure assessment was not 

performed, an inhalation exposure assessment was performed for occupational/commercial 

handlers. Handler exposure resulting from application of pesticides outdoors is anticipated to 

result in higher exposure than post-application exposure. Therefore, it is expected that these 

handler inhalation exposure estimates would be protective of most occupational post-application 

inhalation exposure scenarios. Furthermore, a quantitative volatilization inhalation exposure 

assessment was assessed for bystanders in Section 5.6 and indicates no risk of concern for 

bystanders.

6.2.2 Occupational Post-application Dermal Exposure/Risk Estimates

Occupational Post-application Dermal Exposure

There is no potential hazard via the dermal route for 2,4-D; therefore, a quantitative occupational 

post-application dermal risk assessment was not completed.

Restricted Entry Interval

The REI specified on the proposed label is based on the acute toxicity of 2,4-D. 2,4-D is 

classified as Toxicity Category III via the dermal route, Toxicity Category IV for skin irritation 

potential, and Toxicity Category I for eye irritation. It is not a skin sensitizer. Under 40 CFR 

156.208 (c) (2) (iii), ai’s classified as Acute Toxicity Category I for acute dermal, eye irritation 

or primary skin irritation are assigned a 48-hour REI. Therefore, the [156 subpart K] Worker 

Protection Statement interim REI of 48 hours is adequate to protect agricultural workers from 

post-application exposures to 2,4-D. 
Page 25 of 35

Appendix A. Summary of Occupational and Residential Non-cancer Algorithms

Residential Non-cancer Handler Algorithms

Dermal and Inhalation Handler Exposure Algorithm

Daily dermal and inhalation exposure (mg/day) for residential pesticide handlers, for a given 

formulation-application method combination, is estimated by multiplying the formulationapplication method-specific unit exposure by an estimate of the amount of active ingredient 

handled in a day, using the equation below:

E = UE * AR * A

where:

E = exposure (mg/day);

UE = unit exposure (mg/lb ai);

AR = application rate (e.g., lb ai/ft2, lb ai/gal); and

A = area treated or amount handled (e.g., ft2/day, gal/day).

Residential Non-cancer Post-application Algorithms

Turf/Physical Activities on Turf

Post-application Dermal Exposure Algorithm – Physical Activities on Turf

*The dermal exposure is necessary to address the hand-to-mouth exposure scenario

Exposure resulting from contacting previously treated turf while performing physical activities is 

calculated as shown below. Residential post-application exposure assessment must include 

calculation of exposure on the day of application. Therefore, though an assessment can present 

exposures for any day “t” following the application, it must include “day 0” exposure.

E = TTRt * CF1 * TC * ET

where:

E = exposure (mg/day);

TTRt = turf transferable residue on day t (μg/cm2);

CF1 = weight unit conversion factor (0.001 mg/μg);

TC = transfer coefficient (cm2/hr); and

ET = exposure time (hr/day).

If chemical-specific TTR data are available, then surface residues from the day of application 

should be used (assume that individuals could be exposed to residues immediately after 

application). However, if data are not available, then TTRt can be calculated using the following 

formula:
Page 26 of 35

TTRt= AR * F * (1-FD)t * CF2 * CF3

where:

TTRt = turf transferable residue on day t (μg/cm2);

AR = application rate (lbs ai/ft2or lb ai/acre);

F = fraction of ai as transferable residue following application (unitless);

FD = fraction of residue that dissipates daily (unitless);

t = post-application day on which exposure is being assessed;

CF2 = weight unit conversion factor (4.54 x 108μg/lb); and

CF3 = area unit conversion factor (1.08 x 10-3ft2/ cm2or 2.47 x 10-8acre/cm2).

Dermal absorbed doses are calculated as:

BW

E AF D*

where:

D = dose (mg/kg-day);

E = exposure (mg/day);

AF = absorption factor (dermal); and

BW = body weight (kg).

Table A-1: Turf (Physical Activities) -- Inputs for Residential Post-application Dermal Exposure

Algorithm Notation Exposure Factor

(units) Point Estimate(s)

AR Application rate

(mass active ingredient per unit area) 1.5 lb ae/acre

F

Fraction of AR as TTR 

following application (if 

chemical-specific data is 

unavailable)

L/WP/WDG 0.01

Granules 0.002

FD

Daily residue dissipation 

(if chemical-specific data 

is unavailable)

(fraction)

L/WP/WDG 0.1

Granules 0.1

TC

Transfer 

Coefficient 

(cm2/hr)

L/WP/WDG

Adults 180,000

Children 1 < 2 years old 49,000

Granules

Adults 200,000

Children 1 < 2 years old 54,000

ET Exposure Time

(hours per day)

Adults 1.5

Children 1 < 2 years old 1.5

BW Body Weight

(kg)

Adults 80

Children 1 < 2 years old 11

L/WP/WDG = Liquids/Wettable Powders/Water-dispersible Granules

Post-application Hand-to-Mouth Exposure Algorithm– Physical Activities on Turf
Page 27 of 35

Exposure from hand-to-mouth activity is calculated as follows (based on the algorithm utilized in 

the SHEDS-Multimedia model):

E = [HR * (FM * SAH) * (ET * N_Replen) * (1- (1- SE)

(Freq_HtM/N-Replen))]

where:

E = exposure (mg/day);

HR = hand residue loading (mg/cm2);

FM = fraction hand surface area mouthed / event (fraction/event);

SAH = typical surface area of one hand (cm2);

ET = exposure time (hr/day);

N_Replen = number of replenishment intervals per hour (intervals/hour);

SE = saliva extraction factor (i.e., mouthing removal efficiency); and

Freq_HtM = number of hand-to-mouth contacts events per hour (events/hour).

and

SA * 2

Fai *DE

HR

H

hands

where:

HR = hand residue loading (mg/cm2);

Faihands = fraction ai on hands compared to total surface residue from dermal transfer coefficient 

study (unitless);

DE = dermal exposure (mg); and

SAH = typical surface area of one hand (cm2).

Dose, normalized to body weight, is calculated as:

BW

E

D

where:

D = dose (mg/kg-day);

E = exposure (mg/day); and

BW = body weight (kg).

Table A-2: Turf (Physical Activities) – Inputs for Residential Post-application Hand-to-Mouth Exposure 

Algorithm 

Notation

Exposure Factor

(units) Point Estimate(s)

Faihands

Fraction of ai on hands 

from dermal transfer 

coefficient study

(unitless)

Liquid formulations 0.06

Granular formulations 0.027
Page 28 of 35

Table A-2: Turf (Physical Activities) – Inputs for Residential Post-application Hand-to-Mouth Exposure 

Algorithm 

Notation

Exposure Factor

(units) Point Estimate(s)

DE Dermal exposure (mg) Calculated

SAH

Typical surface area of one hand (cm2), children 1 < 

2 years old 150

AR Application rate

(mass active ingredient per unit area) 1.5 lb ae/acre

HR Residue available on the hands (mg/cm2) Calculated via (DE * Faihands)/SAH

FM

Fraction hand surface area mouthed

(fraction/event) 0.127

N_Replen Replenishment intervals per hour

(intervals/hr) 4

ET Exposure time 

(hrs/day) 1.5

SE Saliva extraction factor

(unitless) 0.48

Freq_HtM Hand-to-mouth events per hour

(events/hr) 13.9

BW Body Weight

(kg) Children 1 < 2 years old 11

Post-application Object-to-Mouth Exposure Algorithm– Physical Activities on Turf

Exposure from object-to-mouth activity is calculated as follows (based on the algorithm utilized 

in SHEDS-Multimedia):

E = [OR* CF1 * SAMO * (ET * N_Replen) * (1- (1- SEO)

(Freq_OtM/N_Replen))]

where:

E = exposure (mg/day);

OR = chemical residue loading on the object on day “t” (ug/cm2);

CF1 = weight unit conversion factor (0.001 mg/μg);

SAMO = area of the object surface that is mouthed (cm2/event);

ET = exposure time (hr/day);

N_Replen = number of replenishment intervals per hour (intervals/hour);

SEO = saliva extraction factor (i.e., mouthing removal efficiency); and

Freq_OtM = number of object-to-mouth contact events per hour (events/hour).

and

OR = AR * FO * CF2 * CF3

where:

OR = chemical residue loading on the object (μg/cm2);

AR = application rate (lbs ai/ft2or lb ai/acre);

FO = fraction of residue available on the object (unitless);
Page 29 of 35

CF2 = weight unit conversion factor (4.54 x 108μg/lb); and

CF3 = area unit conversion factor (1.08 x 10-3ft2/cm2or 2.47 x 10-8acre/cm2).

Dose, normalized to body weight, is calculated as:

BW

E

D

where:

D = dose (mg/kg-day);

E = exposure (mg/day); and

BW = body weight (kg).

Table A-3: Turf (Physical Activities) – Inputs for Residential Post-application Object-to-Mouth Exposure 

Algorithm 

Notation

Exposure Factor

(units) Point Estimate(s)

AR Application rate (to turf)

(mass active ingredient per unit area) 1.5 lb ae/acre

FO Fraction of AR as OR following application 10.01

SAMO

Surface area of object mouthed 

(cm2/event) 10

N_Replen Replenishment intervals per hour (intervals/hour) 4

SEO

Saliva extraction factor

(fraction) 0.48

ET Exposure time 

(hours per day) 1.5

Freq_OtM Object-to-mouth events per hour (events/hr) 8.8

BW Body Weight (kg) Children 1 < 2 years old 11

1 This SOP assumes that all of the residue on the turf could be transferred to the object (e.g., object residue is 

equal to turf transferable residue).

Post-application Incidental Soil Ingestion Exposure Algorithm– Physical Activities on Turf

Exposure from incidental soil ingestion is calculated as follows:

E = SRt * SIgR * CF1

where:

E = exposure (mg/day);

SRt = soil residue on day "t" (μg/g);

SIgR = ingestion rate of soil (mg/day); and

CF1 = weight unit conversion factor (1 x 10-6g/μg).

and

SRt = AR * FS * (1-FD)

t

* CF2 * CF3 * CF4

where:
Page 30 of 35

SRt = soil residue on day "t" (μg/g);

AR = application rate (lbs ai/ft2or lb ai/acre);

FS = fraction of ai available in uppermost cm of soil (fraction/cm);

FD = fraction of residue that dissipates daily (unitless);

T = post-application day on which exposure is being assessed;

CF2 = weight unit conversion factor (4.54 x 108μg/lb);

CF3 = area unit conversion factor (1.08 x 10-3ft2/cm2 or 2.47 x 10-8acre/cm2); and

CF4 = soil volume to weight unit conversion factor (0.67 cm3/g soil).

Dose, normalized to body weight, are calculated as:

BW

E

D

where:

D = dose (mg/kg-day);

E = exposure (mg/day); and

BW = body weight (kg).

Table A-4: Turf (Physical Activities) – Inputs for Residential Post-application Incidental Soil Ingestion 

Exposure 

Algorithm 

Notation

Exposure Factor

(units) Point Estimate(s)

AR Application rate

(mass active ingredient per unit area) 1.5 lb ae/acre

FS Fraction of AR available in uppermost 1 cm of soil

(unitless) 1

FD

Daily residue dissipation

(fraction) 0.1

SIgR Soil ingestion rate (mg/day) 50

BW Body weight (kg) Children 1 < 2 years old 11

Post-application Episodic Granular Ingestion Exposure Algorithm– Physical Activities on Turf

Exposure from incidental ingestion of pesticide pellets or granules is calculated as follows:

 E = GIgR* FD * CF1

where:

E = exposure (mg/day);

GIgR = ingestion rate of dry pesticide formulation (g/day);

FD = fraction of ai in dry formulation (unitless); and

CF1 = weight unit conversion factor (1,000 mg/g).

Dose, normalized to body weight, are calculated as:

BW

E

D
Page 31 of 35

where:

D = dose (mg/kg-day);

E = exposure (mg/day); and

BW = body weight (kg).

Table A-5: Turf (Physical Activities) – Inputs for Residential Post-application Episodic Granular 

Ingestion Exposure 

Algorithm 

Notation

Exposure Factor 

(units) Point Estimate(s)

FD Fraction of active ingredient in dry formulation 3%

AR Application rate (lbs/A or lbs/1,000 ft2) 1.5 lb ae/acre

GIgR Granule ingestion rate per day

(g/day) 1 0.05

BW Body Weight (kg) Children 1 < 2 years old 11

1

See discussion below on how this value is adjusted.

Post-application granular pesticide exposure following applications to lawns and turf would not 

occur as a result of routine behavior and is considered an episodic event related to poisoning.

The default ingestion rate for dry pesticide formulations (e.g., pellets and granules) is 0.3 

gram/day for children 1 < 2 years old. It is assumed that if 150 pounds of product were to be 

applied to a 1⁄2 acre lawn, the amount of product per square foot would be approximately 3 g/ft2

and a child would consume one-tenth of the product available in a square foot. According to the 

2012 Residential SOP, if product-specific information is available, the granular ingestion rate 

may be adjusted to reflect the amount of product applied on a per area basis if it is less or more 

than 150 pounds to a 1⁄2 acre lawn. For instance, if 50 pounds of product is meant to treat a 1⁄2 

acre lawn, then the ingestion rate should be reduced by a third to 0.1 grams/day. As the 

maximum application rate for 2,4-D on lawns is 1.5 lb ae/acre, and the maximum percent of 

active ingredient in dry formulation is 3%, the maximum amount of product to treat an acre is 50 

pounds; or a maximum of 25 pounds of product to treat a half-acre. Therefore, the point estimate 

for granular ingestion rate (GIgR) has been adjusted to 0.05 grams/day.

Swimming

The algorithms and their inputs and assumptions used to estimate residential post-application 

exposure and dose for the proposed/ registered use of 2,4-D for aquatic application are outlined 

below. 

There is the potential for post-application incidental oral (water ingestion) exposures to 2,4-D

residues in water following treatment to control aquatic weeds. Exposures during recreational 

swimming are assumed to be short-term in duration. The equations and inputs are generally 

derived from SWIMODEL 3.0, developed by EPA as a screening tool to conduct exposure 

assessments of pesticides found in swimming pools and spas. It uses well-accepted screening

exposure assessment equations to calculate the high end exposure for swimmers expressed as a 

mass-based intake value (mg/event). The model focuses on potential chemical intakes only and 

does not take into account metabolism or excretion of the chemical of concern. Detailed 
Page 32 of 35

information and the downloadable executable file are available at 

http://www.epa.gov/oppad001/swimodel.htm, however, some of the inputs and parameters have 

been updated and are outlined below. The equations as provided in the SWIMODEL User's 

Manual (version 3.0) were used in a spreadsheet format to estimate the exposures.

Ingestion of Water while Swimming

The equation below taken from SWIMODEL 3.0 is used to calculate post application ingestion 

exposures while swimming. Exposure from incidental ingestion of treated water is calculated as 

follows:

Where:

E = exposure (mg/day),

Cw = chemical concentration in water (mg/L),

IgR = ingestion rate of water (L/hr),

ET = exposure time (hrs/day).

Dose, normalized to body weight, is calculated as:

where:

D = dose (mg/kg-day);

E = exposure (mg/day);

BW = body weight (kg).

Table A-6: Swimming – Inputs for Residential Post-application Incidental Oral Exposure 

Algorithm 

Notation

Exposure Factor

(units)

Point Estimate(s)

Cw Chemical concentration in water

(mg/L)

4 ppm

IgR Water ingestion rates (L/hr)

are based on the 2011 

Exposure Factors Handbook 

(USEPA, 2011), Table 3-5.

Adult 0.021

Children 3 < 6 years old 0.049

ET Exposure time (hours per 

day) for recreational 

activities in water is based on 

the 2011 Exposure Factors 

Handbook (USEPA, 2011) 

data on average time spent in 

a pool, river, or lake (Tables 

16-19 and 16-20).

Adult 3.7

Children 3 < 6 years old 3

BW Body Weight (kg) based on 

the 2011 Exposure Factors 

Handbook (USEPA, 2011).

Adults 80

Children 3 < 6 years old 19
Page 33 of 35

Occupational Non-cancer Handler Algorithms

Potential daily exposures for occupational handlers are calculated using the following formulas:

where:

E = exposure (mg ai/day),

UE = unit exposure (μg ai/lb ai),

AR = maximum application rate according to proposed label (lb ai A or lb ai/gal), and

A = area treated or amount handled (e.g., A/day, gal/day).

The daily doses are calculated using the following formula:

where:

ADD = average daily dose absorbed in a given scenario (mg ai/kg/day),

E = exposure (mg ai/day),

AF = absorption factor (dermal and/or inhalation), and

BW = body weight (kg).

Margin of Exposure: Non-cancer risk estimates for each application handler scenario are 

calculated using a Margin of Exposure (MOE), which is a ratio of the toxicological endpoint to 

the daily dose of concern. The daily dermal and inhalation dose received by occupational 

handlers are compared to the appropriate POD (i.e., NOAEL) to assess the risk to occupational 

handlers for each exposure route. All MOE values are calculated using the following formula:

where:

MOE = margin of exposure: value used by HED to represent risk estimates (unitless),

POD = point of departure (mg/kg/day), and

ADD = average daily dose absorbed in a given scenario (mg ai/kg/day).
Page 34 of 35

Appendix B. Flux Rates and Flux Profiles

Flux Rates for 2,4-D Choline

Period Hours After Treatment

2,4-D Choline

Flux

(μg/m

2

-s)

Rate Adj. Flux

(μg/m

2

-s)

Field 1- Farmland, IN

1 3 2.2E-2 5.5E-3

2 9 2.9E-4 7.25E-5

3 15 8.3E-6 2.08E-6

4 21 5.8E-6 1.45E-6

5 34 5.1E-4 1.28E-4

6 45 4.8E-5 1.2E-5

7 58 5.9E-4 1.48E-4

8 69 6.0E-5 1.5E-5

Field 2- Fowler, IN

1 5 7.7E-2 1.53E-2

2 11 9.3E-4 1.85E-4

3 17 6.2E-4 1.23E-4

4 23 6.9E-3 1.37E-3

5 34 2.6E4 5.16E-5

6 47 1.6E-6 3.17E-7

7 59 5.2E-6 1.03E-6

8 70 3.3E-6 6.55E-7

Field 3- Little Rock, AR

1 5 7.5E-2 1.88E-2

2 10 2.1E-3 5.25E-4

3 16 3.3E-4 8.25E-5

4 23 1.3E-4 3.25E-5

5 36 6.1E-3 1.53E-3

6 47 2.1E-4 5.25E-5

7 60 2.0E-4 5.0E-5

8 71 1.2E-4 3.0E-5

Field 4- Ty Ty, GA

1 4 1.17E-2 1.48E-3

2 10 2.83E-3 3.58E-4

3 16 1.25E-3 1.58E-4

4 22 3.16E-4 4.0E-5

5 36 4.84E-4 6.13E-5

6 47 1.1E-4 1.39E-5

7 60 2.94E-4 3.72E-5

8 71 9.87E-5 1.25E-5
Page 35 of 35

Flux Profile Used in PERFUM Analysis 

Time (hr)

2,4-D choline (only)a

μg/m2/sec

Field 1: Farmland, 

IN Field 2: Fowler, IN Field 3: Little Rock, AR Field 4: Ty Ty, GA

Crop: Soybean Tilled Bare Soil Crop: Soybean Crop: Cotton

Day 1- App. Start 

Time 10:00 

Day 1- App. Start 

Time 9:00

Day 1- App. Start 

Time 7:00

Day 1- App. Start 

Time 9:00

1 1.45E-06 1.23E-04 3.25E-05 2.90E-05

2 1.45E-06 1.37E-03 3.25E-05 2.90E-05

3 1.45E-06 1.37E-03 3.25E-05 2.90E-05

4 1.45E-06 1.37E-03 3.25E-05 2.90E-05

5 1.45E-06 1.37E-03 3.25E-05 2.90E-05

6 1.45E-06 1.37E-03 1.53E-03 2.90E-05

7 1.28E-04 1.37E-03 1.88E-02 1.38E-04

8 1.28E-04 5.16E-05 1.88E-02 1.38E-04

9 1.28E-04 1.53E-02 1.88E-02 2.63E-03

10 5.50E-03 1.53E-02 1.88E-02 2.63E-03

11 5.50E-03 1.53E-02 1.88E-02 2.63E-03

12 5.50E-03 1.53E-02 5.25E-04 2.63E-03

13 7.25E-05 1.53E-02 5.25E-04 2.53E-04

14 7.25E-05 1.85E-04 5.25E-04 2.53E-04

15 7.25E-05 1.85E-04 5.25E-04 2.53E-04

16 7.25E-05 1.85E-04 5.25E-04 2.53E-04

17 7.25E-05 1.85E-04 8.25E-05 2.53E-04

18 7.25E-05 1.85E-04 8.25E-05 2.53E-04

19 2.08E-06 1.85E-04 8.25E-05 7.78E-05

20 2.08E-06 1.23E-04 8.25E-05 7.78E-05

21 2.08E-06 1.23E-04 8.25E-05 7.78E-05

22 2.08E-06 1.23E-04 8.25E-05 7.78E-05

23 2.08E-06 1.23E-04 3.25E-05 7.78E-05

24 2.08E-06 1.23E-04 3.25E-05 7.78E-05

a.Flux profile uses rate adjusted flux (i.e., scaled down to the proposed maximum single broadcast application rate

of 1 lb a.e./A). Period 1 flux corresponds to start time in the flux profile.