### U. S. ENVIRONMENTAL PROTECTION AGENCY Washington, D.C. 20460

OFFICE OF CHEMICAL SAFETY AND POLLUTION PREVENTION 

### Date: January 15, 2013 

### Chemical: Ethanaminium (2,4-D choline salt) 

### PC Code: 051505 

### DP Barcodes: 400223, 400230, 400234, 400237, 405028, 405812

### D~Cl**SION~** 

### 441'151)**44~:2.44}** 

## 4'5 775 5.} 4'5'='460 MEMORANDUM

SUBJECT:

TO:

FROM:

Approved By: EFED Environmental Risk Assessment of Proposed Label for Enlist (2,4-D Choline Salt), New Uses on Soybean with DAS 68416-4 (2,4-D Tolerant) and Enlist (2,4-D 

### + Glyphosate Tolerant) Corn and Field Corn

Michael Walsh, Risk Manager Reviewer Kathryn Montague, Risk Manager Dan Kenny, Branch Chief Registration Division (7505P)

Meghan Radtke, Ph.D., Biologist

# ~**~** Faruque Khan, Ph.D., Senior Scientist

### ~.:.__~ :;;;> 

### Environmental Risk Branch I Environmental Fate and Effects Division (7507P) 

## /1_/ 

# /71/ ( _/

# EdwardOdenkirchen,Ph.D.ActingBran~Chi**~~ \**  .;\ 0---- 

# I( 1 

# 5/ /)

Sujatha Sankula, Ph.D., Lead Biologist**~"'~** 

### '\ 1**~~** 

### Environmental Risk Branch I · Environmental Fate and Effects Division (7507P)

The Environmental Fate and Effects Division (EFED) has assessed the ecological risks to listed and non-listed species associated with the proposed new uses of2,4-D choline salt

on herbicide-tolerant com and soybean.

No direct risks from the proposed applications of2,4-D choline salt to herbicide-tolerant

com and soybeans were identified for the following:

• Birds (chronic)

• Aquatic plants

• Freshwater fish (acute and chronic)

1

### 2 • Estuarine/marine fish (acute and chronic)

• Freshwater invertebrates (acute and chronic)

• Estuarine/marine invertebrates (acute and chronic)

• Aquatic plants

• Terrestrial insects

The re was insufficient information to determine if the following groups are at direct risk from the proposed new uses of 2,4

- D choline salt :

• Mammals (acute and chronic)

• Birds , reptiles, terrestrial

- phase amphibians (acute)

• Terrestrial plants

In addition, t here was insufficient information for all taxa to determine if i ndirect effects are expected because of potential dependencies (e.g., food, shelter, habitat) on species that are directly affected

. Information, such as biological distribution, species biology, spray drift properties specific to the 2,4

- D choline formulations, and mitigation efforts in regions where the pesticide is used, could be used to reduce the uncertainty regarding potential direct and indirect effects.

A spray drift analysis using the AIXR 11004 nozzle and the GF2726 formulation indicated that buffers of 202 feet would reduce risk quotients for birds (acute), mammals (acute and chronic)

, and terrestrial plants below the Agency’s levels of concern. This buffer is only achieved through the combination of the AIXR 11004 nozzle and GF2726 formulation. The l ocations of the buffers would be dependent on species distribution, species biology, and any mitigation efforts proposed by the registrant.

The following major data gaps and uncertainties were identified in this assessment:

• Acute oral toxicity test for pa sserines (850.2100) is not available; data from bobwhite quail and mallard duck were used as surrogates.

• Estuarine/marine invertebrate chronic toxicity test (850.1350) is not available; an

acute

- to

- chronic ratio based on freshwater invertebrates was applie d.

• Terrestrial plant seedling emergence and vegetative vigor tests (850.4100, 850.4150) were not available for the 2,4

- D choline salt/glyphosate formulation; data from other 2,4

- D forms were used as surrogates. There is u ncertainty as to whether they acc urately represent the toxicity of a dual herbicide product to terrestrial plants.

• Vapor

- phase effects data on terrestrial plants were limited in scientific soundness; conservative assumptions were made to characterize the risk to terrestrial plants from va por

- phase drift.

Key Uncertainties and Information Gaps

A number of ecological and fate uncertainties were identified. Table 1 lists several studies that could be used to address these uncertainties.

Table 1. Fate and Ecological Toxicity Data Gaps for 2,4

- D Choline Salt

### 3 Guideline # Data Gap Justification

835.6100 Terrestrial Field Dissipation To conf i rm the bridging strate gy for the environment al fate behavior of 2,4

- D choline salt to 2,4

- D acid, a terrestrial field dissipation study would be needed

.

850

- 6100 Analytical method s for soil and water An environmental chemistry method (ECM) in soil and water would be used to support the terrestrial field dissipation stud y

. An independently validated environmental chemistry method as well as ECM in soil and water is necessary to evaluate the results of the terrestrial field dissipation study

.

850.2100 Avian Oral Toxicity Test for Passerines The CFR require s testing for one passerine species when a chemical is intended for outdoor use. The current method of calculating a weight

- adjusted LD 50 using bobwhite quail or mallard duck data may over

- or under

- estimate risks to passerines because these birds may metabolize the chemical differently. This study has already been requested through the Problem F ormulation of Registraton Review. A protocol for the study should be submitted to EPA for approval prior to study initiation.

850.4150 Terrestrial Plant Vegetative Vigor Test The CFR requires t ypical end

- use data for terrestrial plants. In the case of t he new 2,4

- D choline salt registrations, no information is available for the two 2,4

- D choline salt formulations, nor the EnlistTM formulation, which is a mixture with glyphosate. For the 2,4

- D choline salt

- glyphosate formulation, it is anticipated that th ere could be additional toxicological effects (synergistic or additive) because of the presence of two herbicides. This could change the outcome of the assessment by yielding more sensitive toxicity values for terrestrial plants, thus modifying minimum bu ffer distances.

Non

- guideline Terrestrial Plant Vegetative Vigor Test with Vapor Phase Exposure 2,4

- D is known to volatilize from the field and drift off site under certain environmental conditions. EFED evaluated a vapor

- phase study on grap es, cotton, soybean, and tomato ; however, the methodology did not include a control, did not measure growth/weight parameters, and was not well

- aligned with the 850.4150 protocol. Open literature studies and field data from the
vapor

- flux study suggest 20% plant dama ge corresponds to significant reductions in yield. A vapor

- phase study with vegetative vigor endpoints would confirm these conclusions

. At a minimum, grape and cotton should be tested as these were the most sensitive species in the submitted vapor

- phase study.



### Labeling Recommendations

According to the Label Review Manual, the following label statements are recommended for 2,4

- D choline formulations for ground boom application ( http://www.epa.gov/oppfead1/labeling/lrm/index.htm ):

Application Instructions

A combination of AIXR 11004 spray nozzle, GF

- 2 7 2 6 formulation, and appropriate pressure are required to be selected to provide ASABE Standard S571.1 droplet size category of coarse/very coarse (D V0.5 

### of ≥ 439μm) or coarser. Directions from the equipment manufacturer or vendor, pesticide registrant or a test facility using a laser

- based measurement instrument must be used to adjust

### 4 equipment to produce acceptable droplet size spectra. Application equipment must be tested at l east annually to confirm that pressure at the nozzle and nozzle flow rate(s) are properly calibrated”.

To add additional nozzles to the label, spray drift curves for the new nozzle and/or droplet spectrum information must document that the additional nozzle(s) is expected to perform similarily to the nozzles already specified on the label with the GF

- 2726 formulation.

Environmental Hazards

“ This pesticide is toxic to birds, mammals, fish, and aquatic invertebrates. Do not apply directly to water, or to areas where surface water is present or to intertidal areas below the mean high water mark. Do not contaminate water when disposing of equipment washwater or rinsate. ”

Groundwater Advisory

"2,4

- D, an anion of 2,4

- D choline is known to leach through soil into groundwater under certain conditions as a result of label use. This chemical may leach into groundwater if used in areas where soils are permeable, particularly wh ere the water table is shallow.”

Surface Water Label Advisories

“2,4

- D from 2,4

- D choline application may impact surface water quality through spray and runoff of rain water. This product has a high potential for runoff for several months or more after application. Poorly draining soils and soils with shallow water tables are more prone to produce runoff that contains this product. A level, well maintained vegetative buffer strip between areas to which this product is applied and surface water features such as ponds, streams, and springs will reduce the potential for contamination of water from rainfall

- runoff. Runoff of this product will be reduced by avoiding applications when rainfall is forecasted to occur within 48 hours.”

### 5 

## Ecological Risk Assessment for the Section 3 New Use Registration of 2,4

- D Choline Salt on Soybean with DAS 68416

- 4 (2,4

- D Tolerant) and 2,4

- D + Glyphosate Tolerant Corn and Field Corn

Team Members Meghan Radtke, Ph.D., Biologist Faruque Khan, Ph.D., Senior Scientist

Peer Reviewers Anita Ullagaddi, M.S., Biologist Stephen Wente, Ph. D

., Biologist

Acting Branch Chief Edward Odenkirchen , Ph.D.

Date of Approval January 15 , 2013

### 6 TABLE OF CONTENTS

1. Executive Summary

................................ ................................ ................................ ................. 9

1.1 Nature of the Chemical Stressor

................................ ................................ ........................... 9

1.2 Potential Risk to Non

- Target Organisms

................................ ................................ ........... 11

1.3 Listed Species Assessment

................................ ................................ ................................ . 11

1.4 Data Gaps and Uncertainties

................................ ................................ ............................... 12 2. Problem Formulation

................................ ................................ ................................ ............. 14

2.1 Nature of Regulatory Action

................................ ................................ ............................... 14

2.2 Stressor Source and Distribution

................................ ................................ ........................ 14

2.2.1 Nature of the Chemical Stressor

................................ ................................ ................. 14
2.2.2 Environment al Fate Bridging Strategy

. ................................ ................................ ...... 14

2.2.3 Environmental Fate and Transport

................................ ................................ ............. 15

2.2.4 Degradates

................................ ................................ ................................ .................... 1 9

2.2. 5 2,4

- D Choline Salt Use Characterization

................................ ................................ ... 20

2.3 Receptors

................................ ................................ ................................ .............................. 21

2.3.1 Aquatic and Terrestrial Receptors and Effects

................................ .......................... 21

2.3.2 Ecosystems Potentially at Risk

................................ ................................ ................... 21

2.4 Assessment Endpoints

................................ ................................ ................................ ......... 21 2.5 Conceptual Model

................................ ................................ ................................ ............... 22

2.5.1 Risk Hypothesis

................................ ................................ ................................ ........... 22

2.5.2 Conceptual Diagrams

................................ ................................ ................................ .. 22

2.6 Analysis Plan

................................ ................................ ................................ ....................... 24

2.6.1 Measures of Effect and Exposure

................................ ................................ ............... 25 3. Exposure Assessment

................................ ................................ ................................ ............. 27

3.1 Proposed 2,4

- D Choline Salt Application Information

................................ ..................... 27

3.2 Aquatic Exposure Modeling for 2,4

- D Choline Salt

................................ ......................... 29

3.2.1 PRZM

- EXAMS Model

................................ ................................ ............................... 29

3.2. 2 Model Inputs

................................ ................................ ................................ ................ 30

3.2. 3 Model Outputs: Aquatic Exposure Estimates

................................ ............................ 34

3 .3 Monitoring Data

................................ ................................ ................................ .................. 35

3. 4 Terrestrial Exposure Estimates for 2,4

- D Choline Salt

................................ ..................... 36

3.4 .1 Exposure Estimates for Birds and Mammals

................................ ............................. 37

3.4 .2 Exposure Estimates for Plants

................................ ................................ .................... 38 4. Ecological Effects Assessment

................................ ................................ .............................. 40

4.1 Aquatic Effects Summary

................................ ................................ ................................ ... 41

4.1.1 Toxicity Effects on Fish and Amphibians

................................ ................................ .. 41

### 7 4.1.2 Toxicity Effects on Invertebrates

................................ ................................ ............... 42

4.1.3 Toxicity Effects on Plants

................................ ................................ ........................... 43

4.2 Terrestrial Effects Summary

................................ ................................ ............................... 48

4.2.1 Toxicity Effects on Birds

................................ ................................ ............................ 44

4.2.2 Toxicity Effects on Mammals

................................ ................................ ..................... 45

4.2.3 Toxicity Effects on Non

- Target Insects

................................ ................................ ..... 46

4.2.4 Toxicity Effects on Plants

................................ ................................ ........................... 47

4.3 Incident Database Review

................................ ................................ ................................ ... 48 5. Risk Characterization

................................ ................................ ................................ ............ 51
5.1 Risk Estimation

................................ ................................ ................................ .................... 51

5.1.1 Summary of Aquatic Risk Quotients

................................ ................................ .......... 51

5.1.2 Summary of Terrestrial Risk Quotients

................................ ................................ ..... 55

5.2 Risk Description

................................ ................................ ................................ .................. 57

5.2 .1 Probit Slope Response Analysis of LOC Values and Acute RQ Values

................ 58

5.2 .2 AgDrift Analysis for Terrestrial Plants, Birds, and Mammals

................................ 58

5.2.3 Risk to Aquatic Vertebrates and Invertebrates

................................ .......................... 59

5.2.4 Risk to Terrestrial Animals

................................ ................................ ......................... 60

5.2.5 Risks to Terrestrial Plants

................................ ................................ ........................... 62

5.2.6 Risks to Aquatic Plants

................................ ................................ ............................... 65

5.3 Listed Species Assessment

................................ ................................ ................................ . 66
5.3.1 D ata Gaps and Uncertainties

................................ ................................ ....................... 67 6

. References

................................ ................................ ................................ .............................. 69 9 Appendix A

. Registrations and Uses for 2,4

- D Choline Salt

................................ .................... 71 Appendix B

. Major and Minor Degradates Identified in Environmental Fate Studies

................................ ................................ ................................ ................................ ................ 73 Appendix C . SIP and STIR Results for 2,4

- D Choline Salt

................................ ...................... 74 Appendix D . Examples of PRZM/EXAMS Outputs for 2,4

- D and 2,4

- DCP

......................... 77 Appendix E

. Avian and Mammalian Risk Quotient Calculations for 2,4

- D Choline Salt Based on T

- REX

................................ ................................ ................................ ....................... 82 Appendix F . Terrestrial Plant Risk Quotient Calculations for 2,4

- D Choline Salt Based on TerrPlant

................................ ................................ ................................ .......................... 84 Appendix G . Risk Quotient Method and Levels of Concern

................................ .................... 86 Appendix H

. Preliminary Volat ility Flux Data

................................ ................................ ........... 88 Appendix I

. Examp le of PERFUM Input and Output

................................ .............................. 94 Appendix J

. Spray Drift Deposit ion Curves

................................ ................................ ............. 103

### 8 Acknowledgement s

The 2,4

- D chemical team (Dr

. Meghan Rad t ke, Dr. Faruque Khan

, Dr. Sujatha Sankula, and Dr. Edward Odenkirchen) would like to acknowledge the contribution s and invaluable ass istance and technical support from the Plant Tech Team, Mr. Charles Peck, Mr. Gabe Rothman

, and Dr. James Hetrick in analyzing and model ing the spray drift and volatilization of 2,4

- D. This assessment has been peer reviewed in draft form by individuals chosen for their diverse perspectives and technical expertise. We wish to thank the following individuals for their peer review of this document: Mr. Nelso n Thurman, Dr. Katrina White, Ms . Elizabeth Riley, Mr. Reuben Ba ris, Dr. Stephe n Wente

, and Ms. Anita Ullagaddi.

### 9 

## 1. Executive Summary

2,4

- D choline salt is an herbicide in the phenoxy or phenoxyacetic acid family that is used pre plant, preemergence and postemergence for selective control of broadleaf weeds

. It is currently registered on a number of crops including: sugarcane, r ice, pome fruits, stone fruits, conventional corn and soybeans , fallow land, turf, and tree and brush control. Dow Agrosciences LLC, the manufacturer and registrant of 2,4

- D choline salt, submitted an application to the U.S. Environmental Protection Agenc y (EPA) to add the following

uses to the 2,4

- D choline salt label: 1) Enlist corn and field corn (con taining DAS 68416

- 4 trait), and 2) Enlist soybean (containing DAS 68416

- 4). All of these crops contain genetic traits that make them tolerant to the herb icide, 2,4

- D ; unless specifically stated, all mentions of corn and soybean in this assessment will refer to the 2,4

- D herbicide

tolerant varieties that are being assessed

. Two of the proposed registrations contain only 2,4

- D choline salt as the active ing redient whereas the other two labels are for a 2,4

- D

choline salt/glyphosate mixture. The latter would allow applications to herbicide

- tolerant corn and soybeans with resistance to both 2,4

- D choline salt and glyphosate.

2,4

- D choline salt has already been registered for use on c onventional corn and soybean

, but an ecological risk assessment was not performed on these crops. The proposed application rates and seasonal/annual maximums are similar to those tha t have been previously assessed for other cro ps ; however, the timing of the applications is different because of the herbicide tolerant trait in corn and soybeans. The trait allows for applications to herbicide

- tolerant corn and soybeans that are later in the growing season (later growth stages) tha n conventional varieties of these crops. G round boom application is the only recommended method for Enlist corn, field corn containing DAS 68416

- 4 trait

, and herbicide

- tolerant soybean.

1.1 Nature of the Chemical Stressor

2,4

- D choline salt is a quaternary ammonium salt that rapidly dissociates into a 2,4

- D anion and a choline cation

. 2,4

- D is a plant growth regulator (synthetic auxin herbicide) in the phenoxy or phenoxyacetic acid family that is used as a preplant, pre

- emergence, and post

- emergence herbicide for the selective control of broadleaf weeds

.
Based on the registrant

- submitted studies, the following conclusions were drawn regarding the environmental fate and ecological effects of 2,4

- D choline salt :

Fate

• The environmental fate strategy for 2,4

- D is based on bridging the degradation of 2,4

- D esters and 2,4

- D salts to 2,4

- D acid.

• 2,4

- D is an anionic (X

- COO

- H+) acid unde r most environmental conditions; it is expected to be mobile to moderately mobile. The vapor pressure (1.4 × 10 - 7 

### mm Hg) and Henry's Law Constant (8.56 x 10 - 6 

### atm

- m 3 

### /mol) indicate that 2,4

- D acid has a low volatility.

### 10 • The degradation of 2,4

- D appears to be dependent on oxidative microbially

mediated mineralization in the terrestrial environment and photod egradation in
water.

• Preliminary results from a field volatility study performed with 2,4

- D choline salt, 2,4

- D ethylhexyl ester (EHE), and 2,4

- D dimethylamine salt (DMA salt) suggest that the estimated volatility flux rate of 2,4

- D choline salt is lower than the amine and EHE formulations.

• Three major degradates were identified in the submitted envir onmental fate studies for 2,4

- D: 1,2,4

- benezenetriol (maximum formed = 37%); 2,4

- D

dichlorophenol (2,4

- DCP) (maximum formed = 32.6%); and chlorohydroquinon e (CHQ) (maximum formed = 16%)

.

• 2,4

- D is unlikely to bioaccumulate in fish given the low value of the log n

octanol/water partition coefficient (log K ow 

### = 0.18 at neutral pH).

Ecological

• Ecotoxicity studies for algae, freshwater fish, and honeybee support bridging 2,4

- D choline salt data to 2,4

- D acid data.

• On an acute basis, 2,4

- D acid is practically non

- toxic to freshwater fish, estuarine/marine fish, and amphibians; and slightly toxic to freshwater and estuarine/marine invertebrates

.

• NOAECs ar e available for freshwater fish (based on length), estuarine/marine fish (based on survival), and freshwater invertebrates (based on survival and reproduction).

• 2,4

- D acid i s more toxic to vascular aquatic plants than non

- vascular aquatic plants.

• 2,4

- D acid is more toxic to dicots than monocots

. Seedling emergence toxicity is based on shoot length whereas vegetative vigor toxicity is based on weight.

• 2,4

- D acid is slightly (based on dietary study) to moderately toxic (based on oral dose) to birds on a n acute basis. There were no observed chronic effects in the reproductive study.

• On an acute basis, 2,4

- D acid is slightly toxic to mammals. Chronic effects include: decreased female body weight gain, male renal tubule alteration, increased gestation length, and decreased pup body weight.

• 2,4

- D acid is practically non

- toxic to adult honeybees.

### 11 1.2 Potential Ri sk to Non

- Target Organisms

Ecological risks associated with the new uses of 2,4

- D choline salt are summarized below:

• Proposed 2,4

- D choline salt uses are not expected to directly adversely affect freshwater or estuarine/marine fish, and freshwater or estuarine/marine invertebrates.

• Proposed 2,4

- D choline salt uses are not expected to directly adversely affect aquatic vascular and non

- vascular plants

.

• B irds may be directly affected by the proposed uses of 2,4

- D choline salt on a n acute basis. C hronic effects are not expected.

• M ammals may be directly affected by the proposed uses of 2,4

- D choline salt on an acute and chronic basis.

• 

### T errestrial plants (monocots and dicots) may be directly affected by the proposed uses of 2,4

- D choline salt.

• The acute contact toxicity test on honey bees demonstrated that 2,4

- D choline salt is practically non

- toxic; however, the lack of direct effect s on terrestrial invertebrates does not preclude concerns for indirect effects.

1.3 Listed Species Assessment

The screening

- level analysis for 2,4

- D choline salt indicated that there was insufficient information to determine if there were direct effects to mammals ( acute and chronic ); birds, reptiles, and land

- phase amphibians (acute); and terrestrial plants . Indirect effects

are determined by assessing the potential for reduction of biologically mediated

resources, or habitat modification of listed tax a ; however, there was insufficient information to determine if there were indirect effects to any taxa (Table 2 ).

Table 2 . Listed Species Risks Associated with the Proposed New Uses for 2,4

- D Choline Salt

Listed Taxa Direct Effects Indirect Effects 1



### Terrestrial and semi

aquatic plants:

Monocots

Dicots Insufficient information Insufficient information Insufficient information Insufficient information

Birds Insufficient information

– Acute No

– Chronic Insufficient information

### 12 Listed Taxa Direct Effects Indirect Effects 1



### Terrestrial

- phase amphibians 2 

### Insufficient information

– Acute No

– Chronic Insufficient information

Reptiles 2 

### Insufficient information

– Acute No

– Chronic Insufficient information

Mammals Insufficient information

– Acute Insufficient information

– Chronic Insufficient information

Aquatic plants: Vascular Non

- vascular No No Insufficient information Insufficient information

Freshwater fish No

– Acute No

– Chronic Insufficient information

Aquatic

- phase

amphibians 3 

### No

– Acute No

– Chronic Insufficient information

Freshwater invertebrates No

– Acute No

– Chronic Insufficient information

Mollusks No

– Acute No

– Chronic Insufficient information

Marine/estuarine fish No

– Acute No

– Chronic Insufficient information

Marine/estuarine

invertebrates No

– Acute No

– Chronic Insufficient information

Terrestrial invertebrates No Insufficient information

1 

### Indirect effects to a li sted species occur when its resource base is reduced or habitat is modifi ed; indirect effects are possible for all taxa based on potentia l effects to terrestrial plants and obligate relationships with birds and/or mammals.
2 

### Birds are surrogates for reptiles and terrestrial

- phase amphibians.
3 

### Freshwater fish are surrogates for aquatic

- phase amphibians.

1.4 Data Gaps and Uncertainties

Avian Acute Oral Toxicity Test for Passerine s (850.2100) : The CFR require s data for one passerine species when a chemical is intended for outdoor use. The current method of calculating a weight

- adjusted LD 50 

### using bobwhite quail or mallard duck data may

over

- or under

- estimate risks to passerines because these birds may metabolize the chemical differently. This study has already been requested through Problem Formulation. A protocol for the study of passeri ne species should be submitted to EPA for approval prior to study initiation.

Estuarine/Marine Invertebrate Chron ic Toxicity Test (850.1350): No acceptable data are available for the chronic toxicity of 2,4

- D choline salt to marine/estuarine

### 13 invertebrate s. Currently, the toxicological effects for estuarine/marine invertebrates on a chronic basis remain uncertain for 2,4

- D choline salt , although this assessment estimated a chronic value based on an acute

- to

- chronic ratio using freshwater invertebrate data

. Additionally, chronic risk quotients for freshwater invertebrates did not come close to exceed ing the level of concern; thus increasing EFED’s confidence that the available aquatic invertebrate information is sufficient to evaluate risk.

Terrestrial Pl ant Seedling Emergence and Vegetative Vigor Tests (850.4100, 850.4150): Typical end

- use data are required for terrestrial plants. In the case of the new 2,4

- D choline salt registrations, no information is available for the two 2,4

- D choline salt formulat ions, nor the EnlistTM formulation, which is a mixture with glyphosate. For the 2,4

- D choline salt

- glyphosate formulation, it is anticipated that there could be additional toxicological effects (synergistic or additive) because of the presence of two herbicides. In lieu of these data, toxicity information from other 2,4

- D formulations were used as surrogates on an acid

- adjusted basis

.
Terrestrial Plant Vegetative Vigor Test with Vapor Phase Exposure (non

- guideline): 2,4

- D is known to volatilize from the field and drift off site under certain environmental conditions. EFED evaluated a vapor

- phase study on grapes, cotton, soybean, and tomato; however, the methodology did not include a control, did not measure growth/weight parameters, and was not well

- aligned with the 850.4150 protocol. A vapor

- phase study with vegetative vigor endpoints is being recommended to further characterize the risk to plants from this exposure route. Grape and cotton should be tested as these were the two most sensitive spec ies in the vapor

- phase study that was submitted.

Additionally, the following uncertainties were identified for this risk assessment:

• For terrestrial organisms, only dietary exposure to 2,4

- D choline salt was assessed.

• For freshwater fish, birds, and terrestrial insects, definitive acute toxicity data were not available. Acute data were presented as greater than values, making it possible to conservatively compare the toxicity value directly to the EECs to estimate potential risk.

• For terrestri al plants, vegetative vigor toxicity values for monocots were non

definitive. The EC 25 

### (a greater than value) was compared directly to the EECs to assess the likelihood of risk. The monocot vegetative vigor NOAEC was a less than value; however, given that seedling emergence data were more sensitive for dicots than the vegetative vigor data, the same pattern was assumed to hold true for monocots. Consequently, the monocot seedling emergence NOAEC was assumed to be the most sensitive monocot NOAEC and used to calculate risk quotients. If this assumption is false, the risk to listed monocots may have been under

- estimated.

### 14 • In the absence of chronic data for marine/estuarine invertebrates, an acute

- to

chronic ra tio was calculated to estimate the NOAEC for Eastern oyster

.

• This risk assessment only considered the most sensitive of the species evaluated in the registrant

- submitted studies. The position of the tested species relative to the distribution of all spec ies’ sensitivities to 2,4

- D choline salt is unknown. Extrapolating the risk conclusions from the most sensitive tested species to non

tested species may either underestimate or overestimate the potential risks to those species.

• 2,4

- D is currently underg oing a Tier I Endocrine Disruptor Screening as required by FFDCA section 408(p) . The results of the screening analysis are not yet available

.


## 2. Problem Formulation

The problem formulation provides the foundation for the ecological risk assessment being c onducted for the proposed new uses of the herbicide 2,4

- D choline salt . As such, it articulates the purpose and objectives of the risk assessment, evaluates the nature of the problem, and provides a plan for analyzing the data and characterizing the risk.

2.1 Nature of Regulatory Action

Under the authority of the Federal Insecticide, Fungicide and Rodenticide Act (FIFRA), D ow Agrosciences LLC is seeking registration for the new uses of 2,4

- D choline salt as a foliar spray for the control of broadleaf weeds in herbicide

- tolerant soybeans containing DAS

- 68416

- 4, and for the cont rol of annual and perennial weed s in herbicide

- tolerant EnlistTM corn and herbicide

- tolerant field corn ( Table 6 ). See Appendix A for a l ist of current uses and application information for 2,4

- D choline salt.

2.2 Stressor Source and Distribution

2.2.1 Nature of the Chemical Stressor

2,4

- D is a plant growth regulator (synthetic auxin herbicide) in the phenoxy or phenoxyacetic acid family. It is used as a preplant, pre

- emergence, and post

- emergence herbicide for the selective control of broadleaf weeds. 2,4

- D cause s disruption of multiple growth processes in susceptible plants by affecting proteins in the plasma membrane, interfering with R NA production, and changing the properties and integrity of the plasma membrane. Disruption of reproductive processes may occur resulting in sterile or multiple florets and nonviable seed production. Symptoms may appear on young growth almost immediately after application, but death may not occur for several weeks.

2. 2. 2

. Environmental Fate Bridging Strategy

The salt and ester forms of 2,4

- D are derivatives of 2,4

- D acid. The environmental fate

### 15 stra tegy for 2,4

- D is based on bridging the data on the degradation of 2,4

- D esters and 2,4

- D salts to 2,4

- D acid [Registration Standard for 2,4 Dichlorophenoxyacetic acid (2,4

- D), 1988, 540/RS

- 88

- 115]. The bridging data provide information on the time of dis sociation of 2,4

- D amine salts and the rate of hydrolysis of 2,4

- D esters. The c holine salt of 2,4

- D is also considered equivalent to 2,4

- D acid. The 2,4

- D c holine salt has been shown to dissociate rapidly ( within 6 seconds) in water (MRID 48260701). However, a field terrestrial study conducted with 2,4

- D choline is required to conf i rm the bridging strategy. Table 3 provide s sele cte d physico

- chemical properties of 2,4

- D choline salt. A detailed environmental fate data bridging strategy can be found in the 2005 Registration Eligibili ty Document (RED) for 2,4

- D (US EPA 2005).

Table 3

. Selected P hysical and Chemical Properties of 2,4

- D Choline S alt
Parameter Value Source

Chemical structure MRID 48260701

Molecular formula and weight (g/mol) C 13 H 19 Cl 2 NO 4 324. 2 MRID 48260701

Water s olubility (mg/L) Not applicable for end use product MRID 48208302
Density (g/cm 3 ) 1.21 MRID 482 08302 LogK OW Not applicable for end use product MRID 48208302 Vapor pressure (mm Hg@~25oC)



### 2. 2. 3. Environmental Fate and Transport

The physicochemical properties in Table 4 suggest that 2,4

- D acid is soluble in water (569 mg/L). The vapor pressure (1.4 × 10 - 7 

### mm Hg) and Henry's Law Constant (8.56 x 10 - 6 

### atm

- m 3 

### /mol) indicate that 2,4

- D acid has low volatility. The Agency r eceived a field volatility study (MRID 48862902) p erformed with 2,4

- D choline salt, 2,4

- D ethylhexyl ester (EHE), and 2,4

- D dimethylamine salt (DMA salt). This study is in review at this time; however, preliminary results suggest that the volatility rate of 2,4

- D from the choline salt is lower than the DMA and EHE formulations (Figure 1). Additional data and figures are provided in Appendix H

. 2,4

- D acid is unlikely to bioaccumulate in fish given the low value of the log n

- octanol/water partition coefficient (log K ow 

### 0.18 at neutral pH).

Table 4 also provides environmental fate properties of 2,4

- D acid, along with the major and minor degradates detected in the submitted environmental fate and transport studies. 2,4

- D acid is stable abiotic hydr olysis in buffered aqueous solutions at pH 4, 5, 7, and 9. The degradation of 2,4

- D acid appears to be dependent on oxidative microbially

mediated mineralization in the terrestrial environment and photodegradation in water. Results from laboratory studie s indicate rapid to moderately rapid degradation under aerobic soil conditions with half

- lives ranging from 1.4 days to 12.4 days and a median

### 16 half

- life of 2.9 day s. Only minor degradates, 2,4

- d ichlorophenol (2,4

- DCP) and 2,4

- dichloroanisol (2,4

- DCA), wer e identified in soils. The photodegradation half

- life of 2,4

- D acid was 12.9 days in a pH 5.0 buffer solution and a major degradate, 1,2,4

- benezenetriol (37% of applied) was identified. 2,4

- D acid was stable to photodegradation in soil.

2,4

- D acid was not stable in aerobic aquatic environments (t 1/2 

### =15.0 days) but was moderately persistent to persistent (t 1/2 

### =28.5 to 333 days) in anaerobic aquatic laboratory studies. The major degradates were chlorohydroquinone (CHQ) (maximum of 16.0 % of applied) in aerobic aquatic conditions and 2,4

- DCP (maximum of 32. 6 % of applied) under anaerobic aquatic environment.

The registrant conducted a total of 30 terrestrial field dissipation studies in CA, CO, NC, ND, NE, OH, and TX on bare g round plots as well as plots cropped with corn, pasture, turf, and wheat. The 2,4

- D acid half

- lives ranged from 1.1 to 42.5 days with a median half

- life of 6.1 days. These half

- lives reflect dissipation from the surface soil layer (0 to 6 inches). The d ata indicate a rapid to moderately rapid dissipation rate for 2,4

- D acid. The results of this study are also consistent with half

- lives from laboratory studies and confirm the conceptual model for 2,4

- D dissipation

. The half

- lives of 2,4

- D degradation
pr oducts (2,4

- DCP and 2,4

- DCA) were not estimated because of their sporadic occurrence patterns in surface soils. To address the behavior of 2,4

- D in aquatic water systems, a series of aquatic field dissipation studies were conducted. Three studies were

co nducted using 2,4

- D DMA while a fourth study was conducted using 2,4

- D BEE. In addition, two field dissipation studies using 2,4

- D DMA were also submitted to address forest field dissipation.

Table 4 . Physical Chemical and Environmental Fate Propertie s of 2,4

- D Acid

Parameter Value Source
Selected Physical/Chemical Parameters

Chemical Structure TOXNET

IUAPC Name (2,4

- dichlorophenoxy)acetic acid U.S. EPA, 2005 b

CAS Name (2,4

- dichlorophenoxy)acetic acid U.S. EPA, 2005 b

CAS No. 94

- 75

- 7 U.S. EPA, 2005 b
Molecular Weight (molecular formula) 221.04 g/mol (C 8 H 6 Cl 2 O 3 ) U.S. EPA, 2005 b

Smile s Code O=C(O)COc(c(cc(c1)Cl)Cl)c1 EPISUITE4.1 Vapor pressure (25°C) 1.4 x 10 - 7 mm Hg U.S. EPA, 2005 b

### 17 Parameter Value Source Aqueous solubility (20 ° C) 569 mg/L U.S. EPA, 2005 b

Dissociation constants (pKa ) in water (25°C) 2.60 MRID 471122

- 02

Henry’s Law Constant (25°C) 8.56 x10 - 6 atm

- m 3 /mol Rice et al, 1997 Log octanol

- to

- water partition coefficient (log K OW ) 2.14 @ pH 5.0 0.18 @ pH 7.0 0.10 @ pH 9.0 U.S. EPA, 2005 b

Persistence
Hydrolysis half

- life Stable MRID 41007301 Aqueous photolysis half

- life 12.98 days

Degradates 1 1,2,4

- benzenetriol (37% of applied) MRID 41125306

Soil photolysis half

- life Stable CO 2 (5% of applied) MRID 41125305

Aerobic soil metabolism half

- life (days) Catlin Silty clay loam

– 1.7 day

Commerce Loam

– 4.62 days Catlin Silty clay loam

– 1.4 days Fargo Clay

– 12.4 days Keith Clay loam

– 4.4 days Walla Walla silt loam

– 2.0 days Cecil Sandy loam

- 2.9 days Degradates 2,4

- DCP (3.5%) 2,4

- DCA (2.8%) MRID 43167501,

MRID 00116625

Anaerobic aquatic metabolism half

- life (total system) 333 days 28.5 days 41 .0 days

Degradates 2,4 DCP (Maximum 32.6% of applied) 4

- chloropheno xy acetic acid ( 4

- CPA)

< 2.0% of applied), 4

- chlorophenol ( 4

- CPP) < 2.0% of applied)

, 2,4

- DC A (<2% of applied) MRID 43356001 MRID 42979201 MRID 41557901

### 18 Parameter Value Source Aerobic aquatic metabolism half

- life (total system) 15 days Inconclusive 2

D egradates Chlorohydroquinone (CHQ) (maximum 16% of Applied) 2,4

- DCP (4.9 of applied) MRIDs 42045301 44188601

Mobility
Adsorption/desorption

K d

- ads / K d

- des (mL/g)

K

foc

- ads / (mL/g) Adsorption Freundlich adsorption K f

- ads values Sand 0.36 Sandy loam 0.17 Loam 0.28 Silty clay loam 0.52 Clay 1.27

Desorption Freundlich adsorption K f

- des values Sand 1.16 Sandy loam 0.87 Loam 1.58 Silty clay loam 1.99 Clay 1.64

Adsorption Freundlich adsorption K foc values Sand 76 Sandy loam 70 Loam 117 Silty clay loam 59 Clay 58.1 MRID 44117901 MRID 42045302

MRID 44117901

MRID 42045302

MRID 44117901

MRID 42045302

Leaching Thin Layer Chromatography (TLC) Retention Value (R f, unitless) (Un

- aged sample) Sand 1.0 Sandy loam 0.77 Silt loam 0.60 Loam 0.41

Column Study (Aged sample) Immobile MRID 00057313

MRID 00080124

### 19 Parameter Value Source
Field Dissipation
Terrestrial field dissipation half

- life The first order half

- lives ranged from 1.1 to 42.5 days with a median half

- life of 6.1 days MRID 43914701 MRID 43762401 MRID 43762402 MRID 43514601 MRID 43533401 MRID 43864001 MRID 43592801 MRID 43762403 MRID 43762404 MRID 43640601 MRID 43831702 MRID 43872703 MRID 43849102 MRID 43831701 MRID 43705202 Aquatic field dissipation half

- life Estimated dissipation half

- lives of 20.7 and 2.7 days from the North Carolina pond after the first and second applications, 14 days and 6.1 days in water from a North Dakota pond after the first and second applications, and 1.0 day in water from the Louisiana rice paddy after a single application MRID 439083 02 MRID 43491601

Forest Field Dissipation half

- life The estimated half lives for 2,4

- D were 59 days in exposed soil, 68 days in protected soil, 42 days on foliage, and 72 days on leaf litter. MRID 43954702

Field Volatility 3 Maximum Flux Rate (g/m 2

- s) 5.50E

- 09 (Farmland, IN) 1.53E

- 08 (Fowler, IN) 1.88E

- 08 (Little Rock, AR) 1. 4 8E

- 0 9 (Little Rock, AR) 4
1.48E

- 09 (Ty Ty, GA) 2.44 E

- 09 (Ty Ty, GA) 4 MRID 48862902 5

1 Structures of major and minor degradates of 2,4

- D a re provided in Appendix B
2 Half

- life cannot be calculated because study duration was insufficient
3 Agency estimated f lux rate based on 1.0 lb a.e./A of 2,4

- D choline salt
4 Flux study performed with 2,4

- D choline plus glyphosate
5 Study in review



### 2.2. 4 Degradates

There were three major degradates identified in the submitted environmental fate studies for 2,4

- D; 1,2,4

- benzenetriol (37% formed) , 2,4

- dichlorophenol (2,4

- DCP) (32.6% formed) , and chlorohydroquinone (CHQ) (16% formed)

. Minor degradates included 4

- chlorophenol, 4

- CPA and 2,4

- DCA (Table 4 )

. The major degradate, 1,2,4

- benzenetriol,

### 20 is a photodegradate that was observed under abiotic conditions and is less likely to occur under natural conditions where microbe

- mediated degradation occurs. The 1,2,4

- benzenetriol degrada te was eliminated from concern because it is formed only via aqueous photolysis. I t may be less likely to occur in many environments because degradation of 2,4

- D appears to be dependent primarily on oxidative microbial

- mediated mineralization. The exposu re of CHQ in the environment is likely to be low since it formed in aerobic aquatic environments to a significant extent only on day 27, and, from that point, dissipation was rapid (half

- life of 5 days). Although 2,4

- DCP is a minor degradate in the terres trial environment, it is a major degradate (<32%) under anaerobic aquatic conditions. There are some toxicity data for 2

- DCP available in the ECOTOX database 1 

### and the European Footprint database 2 

### that suggest it is more toxic than 2,4

- D for selected aquat ic organisms. Therefore, 2,4

- D as well as its degradate

, 2,4

- DCP, will be considered as independent stressor s of concern in ecological risk assessment.

Figure 1

. Volatility Flux Profile of 2,4

- D F ormulations

2.2. 5 2,4

- D Choline Salt Use Characterization

2,4

- D choline salt is a non

- selective herbicide for the control of broadleaf weeds. The proposed new uses for 2,4

- D choline salt include soybeans containing DAS

- 68416

- 4, EnlistTM corn, and field corn containing DAS

- 40278

- 9. The curre nt action refers to GF

2654 TS (soybean), GF

- 2654 TC (field corn), GF

- 2726 (EnlistTM corn), and GF

- 2727 (EnlistTM corn). GF

- 2726 and GF

- 2727 are products that contain both 2,4

- D choline salt and glyphosate. Table 6 shows the application rates for each use. All products are applied as a ground foliar spray. The herbicide

- tolerant trait allows for a later application in both soybean (R2 stage) and corn (V8 stage).

1 http://cfpub.epa.gov/ecotox/
2 http://sitem.herts.ac.uk/aeru/footprint/en/index.htm

### 21 2.3 Receptors

2.3.1 Aquatic and Terrestrial Receptors and Effects

The receptor is a biological entity that is exposed to a stressor (USEPA 1998) . Consistent with the process described in the Overview Document, this risk assessment uses a surrogate species approach in its evaluation of 2,4

- D choline salt (USEPA 2004)

. Toxicological data generated from surrogate test species, which are intended to be representative of broad taxonomic groups, are used to extrapolate the potential effects on a variety of species (receptors) included under these taxonomic groupings.

A cute and chronic toxic ity data from studies submitted by the pesticide registrant along with available open literature studies are used to evaluate potential direct effects of pesticides to the aquatic and terrestrial receptors. Open literature studies are identified through E PA’s ECOTOX database (http://cfpub.epa.gov/ecotox/), which employs a literature search engine for locating chemical toxicity data for aquatic and terrestrial flora and fauna. The evaluation of both sources of data provides insight into the direct and indi rect effects of pesticides on biotic communities from loss of species that are sensitive to the chemical and changes in structural and functional characteristics of the affected communities.

A search of the ECOTOX database on October 24, 2012 yielded no studies for 2,4

- D choline salt. Therefore, only studies submitted by the registrant were evaluated to determine the effects of 2,4

- D choline salt on non

- target organisms.

2.3.2 Ecosystems Potentially at Risk

The ecosystems at risk from exposure to a stressor are often extensive in scope; it may not be possible to identify specific ecosystems at the screening level. In general terms, terrestrial ecosystems potentially at risk could include the treated field and areas immediately adjacent to the treate d field that may receive drift or runoff. Areas adjacent to the treated field could include other cultivated fields, fencerows and hedgerows, meadows, fallow fields or grasslands, woodlands, riparian habitats, and other uncultivated areas.

Aquatic ecos ystems potentially at risk from a stressor include water bodies adjacent to or downstream from the treated field; impounded bodies such as ponds, lakes, and reservoirs; and flowing waterways such as streams or rivers. For uses in coastal areas, aquatic ha bitat also inclu des marine ecosystems and estuaries.

2.4 Assessment Endpoints

Assessment endpoints represent the actual environmental value that is to be protected, defined by an ecological entity (species, community, or other entity), and its attribute or characteristics (USEPA 1998, 2005 a ) . For 2,4

- D choline salt , the ecological entities include the following: birds, amphibians, reptiles, mammals, insects, freshwater fish and

### 22 invertebrates, estu arine/marine fish and invertebrates, and aquatic plants and algae. The attributes for each of these entities include survival, growth, and reproduction.

2.5 Conceptual Model

For a pesticide to pose an ecologica l risk, it must reach ecological receptors in biologically significant concentrations. An exposure pathway is the means by which a pesticide moves in the environment from a source to an ecological receptor. For an ecological pathway to be complete, it mu st have a source, a release mechanism, an environmental transport medium, a point of exposure for ecological receptors, and a feasible route of exposure.

A conceptual model is intended to provide a written description and visual representation of the pred icted relationships between the stressor, potential routes of exposure, and the predicted effects for the assessment endpoint. A conceptual model consists of two major components: the risk hypothesis and the conceptual diagram (USEPA 1998, 2005 a )

.

2.5.1 Risk Hypothesis

Based on the environmental fate characteristics and mode of action, it is presumed in this screening

- level assessment that 2,4

- D choline salt , when used in accordance with the label, has the potential to adversely affect survival, growth, and/or reproduction of both terrestrial and aquatic organisms.

B irds, mammals, amphibians, r eptiles, and non

- target insects may be exposed to 2,4

- D choline salt through direct ingestion of the pesticide on the dietar y items, incidental ingestion of contaminated soil, dermal contact with treated plant surfaces and soil during activities in the treated areas, direct impingement of sprayed material on the body at the time of application, preening activities, and ingestio n of drinking water contaminated by the pesticide

. 2,4

- D exposures to aquatic species may occur through spray drift, runoff, volatilization, wet/dry dep osition, and leaching to ground water

. The seedling emergence and vegetative vigor of non

- target terrestrial plants and growth and biomass accumulation of aquatic plants adjacent to the site of 2,4

- D choline salt application could be affected by runoff, drift, and volatilization from treated fields

.

2.5.2 Conceptual Diagram s
The potential exposure pathways and effects of 2,4

- D and its degradate s , 2,4

- dichlorophenol (2,4

- DCP )

, from appli cations of 2,4

- D choline salt on terrestrial and aquatic environments are depicted in Figure 2 . Solid arro ws represent the most likely routes of exposure and effects while dashed lines represent potential routes of exposure that are considered less likely for 2,4

- D choline salt and its degradates

.
Figure 2 . Conceptual Model for Exposure Routes for 2,4

- D and its Degradates

### 23 Stressors 2,4

- D choline salt products applied to use site

Transport Pathways Spray Drift

Exposure Media

Exposure Route Ingestion/ Inhalation Direct contact/ Root Uptake Direct contact/ Root Uptake Gill/ Integument Uptake

Receptors

Attribute Changes Birds/ Mammals/ Insects Terrestrial Plants

Acute Effects

• Mortality Aquatic Invertebrates Aquatic Vertebrates Amphibians Wetland/ Riparian Plants/Aquatic plant

Individual Plants

• Seedling emergence

• Vegetative vigor

Terrestrial
Aquatic Volatilization and
Atmospheric transport
and deposition Leaching to groundwater

Terrestrial Environment Aquatic Environment

Chronic Effects

• Reproduction

• Growth

• Survival Acute Effects

• Mortality Chronic Effects

• Reproduction

• Growth

• Survival Chronic Effects

• Reproduction

• Growth

• Survival Source/

In

- situ deposition
(Soil and Foliage)

Runoff

Air

plant transfer 

# Exposure Routes for 2,4

- D

### 24 The conceptual model used to depict the potential ecological risk associated with 2,4

- D choline salt (and the degrada te s of concern ) assumes that as an herbicide, 2,4

- D choline salt can affect terrestrial and aquatic organisms if environmental exposure is expected as a result of the proposed label uses. The use scenarios for 2,4

- D choline salt involve ground spray appli cat ions of the herbicide to herbicide

- tolerant corn and soybean foliage

. While 2,4

- D choline salt is already registered on conventional varieties of these crops, the herbicide

- tolerant varieties allow for the application of 2,4

- D choline salt at later dat es in the season. Altering the timing of 2,4

- D choline salt applications may change the window of exposure for non

- target vegetation. A variety of food types (e.g., short grass, long grass, broadleaf plants) will be assessed regardless of the type repres ented by the target crop, as a variety of food types exist on and off the treated field.

As there are multiple spray applications to foliage, degradation of the chemical on the foliage between applications is considered in the terrestrial assessments. A default foliar dissipation rate of 35 days will be used in the terrestrial risk assessments since no foliar dissipation studies are available ; this may be an over

- estimate . For aquatic assessments, the microbial degradation on foliage is assumed stable, b ut wash

- off of the foliage will be considered using the default wash

- off coefficient assumption of 0.5 cm - 1 

### . Spray drift will be considered in the aquatic assessments as a route of loading to the pond, with higher levels of spray drift for aerial applicat ions than ground spray applications.

2,4

- D choline salt will dissociate into its salt and 2,4

- D acid upon reaching a water body

. It is then partitioned between the water column, suspended sediment, and bed sediment at a ratio based on the pesticide’s physical/chemical properties. Degradation by abiotic hydrolysis, photolysis, and microbial mediated metabolism is taken into account.

2,4

- D choline salt is unlikely to bio

- accumulate in fish ; the study was waived because of the low Log K ow 

### .
For birds and mammals, only the dietary route of exposure is considered. Solubility information for 2,4

- D choline salt was not available, however; beca use it rapidly dissociates into 2,4

- D acid and the choline salt, it is appropriate to use 2,4

- D acid’s solubility. S creen ing for risks from drinking water was performed with the Screening Imbibition Program (SIP). The model identified that exposure throu gh drinking water may present acute and chronic concerns for birds and mammals (Appendix C ). The Screening Tool for Inhalation Risk (STIR ) did not identify concerns for birds or mammals (Appendix C )

. Other u ncertainties in this risk assessment include the lack of information on exposure from soil ingestion and dermal routes.

2.6 Analysis Plan

The first

- tier screening

- level risk assessment is used as the approach to determine risk to

non

- target organisms from the proposed new uses for 2,4

- D cho line salt . Measures of exposure and effect are used to evaluate the potential risk for a specific assessment endpoint. A risk quotient is obtained by dividing the measures of exposure for a particular assessment endpoint by the measures of effect for tha t endpoint. The risk quotient is a deterministic point

- estimate

- based approach and does not provide a

### 25 quantitative estimate of likelihood and/or magnitude of an adverse effect. Risk quotients are compared to specified levels of concern; if the risk quoti ent exceeds the level of concern, then the potential for risk exists.

Polychloro dibenzo

- p

- dioxin (PCDD) and polychloro dibenzo

- p

- furans (PCDF) may be formed during the manufacture of 2,4

- D and can remain in the products as impurities. According to 2,4

- D registrants, since the 1990’s, the manufacturing processes for 2,4

- D and its chemical intermediate, dichlorophenol, have been modified to reduce concentrations of PCDD and PCDF in the technical 2,4

- D products. The Agency reviewed recently submitted product chemistry data for the end

- use (product “GF

- 2654 TC” to evaluate toxic impurities in 2,4

- D choline formulation (U.S. EPA 2012, D405897

, C onfi dential Memo)

. No PCDD and PCDF were detected above 30% of the limit of quantitation (LOQ) in the register ed sources of the active ingredients for 2,4

- D choline. Assuming 30% of the LOQ, the toxicity equivalence (TEQ) of PCDD and PCDF was estimated using toxicity equivalence factors derived from the World Health Organization (WHO 2 005 3 

### ). The estimated TEQ of the technical product used in 2,4

- D choline is approximately 4.8 times lower than the the estimated TEQ calculated for the formulated products of 2,4

- dichlorophenoxyacetic acid (2,4

- D) and ethylhexyl dichlorophenoxyacetate (2,4

- D EHE) in a previous assessment (US EPA 2005, D 317729, Confidential Memo ). The previous assessment concluded that t he environmental loading of PCDD and PCDF from terrestrial and aquatic uses of 2,4

- D is not expected to pose a risk for reproductive effects to pi scivorous birds and mammals. Therefore, 2,4

- D choline salt use in corn and soybean is not expected to pose risk to terrestrial organisms since the TEQ for 2,4

- D choline is 4 .8 times lower than the formulated products of 2,4

- D acid and EHE

. N o ecological risk assessment is warranted for PCDD and PCDF for 2,4

- D choline salt formulations at this time.

The stressors of ecological concern for terrestrial and aquatic organisms are 2,4

- D acid and its degradates. However, as outlined in the degradate section a bove, all but 2,4

- DCP can be eliminated as likely degradates of concern. 2,4

- DCP is primarily formed in aquatic environments; it is only a minor degradate in terrestrial environments. Therefore, 2,4

- D and degradate 2,4

- DCP will be considered as stressors of concern in the aquatic analyses and only 2,4

- D will be considered for terrestrial environments

.

2.6.1 Measures of Effect and Exposure

The assessment will examine the effects of 2,4

- D choline salt (and 2,4

- DCP, when relevant) on aquatic and terrestrial environments primarily through the routes of spray drif and runoff. Model details are described later in this section. Sev eral other models are used to characterize effects from vapor exposures, buffer distances, and individual effects probabilities; these are included in the risk description section.

Table 5 lists the measures of environmental exposure and ecological effect s used to assess the potential risks of 2,4

- D choline salt to non

- target organisms. The methods

3 van den Berg et al., 2006

### 26 used to assess risks are consistent with those outlined in the Overview Document (USEPA 2004).

Table 5 . Measures of Effect and Exposure for 2,4

- D Choline Sal t

Assessment Endpoint Surrogate Species and Measures of Ecological Effect 1 

### Measures of Exposure

Birds 2 

### Survival Bobwhite quail oral LD 50 

### Bobwhite quail and m allard duck dietary LC 50



### Maximum residues on food items and soil Reproduction and growth Bobwhite quail reproduction N OAEC

Mammals Survival Laboratory rat oral LD 50



### Reproduction and growth Laboratory rat two

- generation NOAEC and NOAEL
Freshwater amphibians Survival Leopard frog LC 50 

### Peak EEC

Freshwater fish 3 

### Survival Rainbow trout LC 50 

### Peak EEC Reproduction and growth Fathead minnow NOAEC 60

- day average EEC

Estuarine/ marine fish Survival Tidewater silverside LC 50 

### Peak EEC Reproduction and growth Sheepshead minnow NOAEC 60

- day average EEC

Freshwater invertebrates Survival Water flea EC 50 

### Peak EEC

Reproduction and growth Water flea NOAEC 21

- day average EEC

Estuarine/ marine invertebrates Survival Eastern oyster LC 50 

### Peak EEC

Reproduction and growth Eastern oyster NOAEC 4 

### 21

- day average EEC

Terrestrial plants Seedling emergence and vegetative vigor Onion (monocot) Lettuce (dicot)

EC 25 

### and NOAEC Maximum residues on foliage and soil

### 27 Assessment Endpoint Surrogate Species and Measures of Ecological Effect 1 

### Measures of Exposure

Aquatic plants Survival and growth Vascular

– Duckweed Non

- vascular

– Freshwater diatom

EC 50 

### and NOAEC Peak EEC

Terrestrial insects Survival Honeybee acute LD 50 

### N/A

1 

### Risk assessment guidance indicates that the most sensitive species tested within a taxonomic group are to be used for screening level risk assessments.
2 

### Birds represent surrogates for reptiles and terrestrial

- phase amphibians.
3 

### Freshwater fish are surrogates for aquatic

- phase amphibians.
4 

### Based on acute

- to

- chronic ratio calculation

.



## 3. Exposure Assessment

3.1 Proposed 2,4

- D Choline Salt Application Information

Table 6 shows the maximum application rates for each new use of 2,4

- D choline salt

, based on the proposed labels. Uses are being expanded to include Enlist corn and soybean containing DAS

- 68416

- 4. Additional information regarding the proposed 2,4

- D choline salt uses can be found in Section 2.2.2.

### 28 Table 6 . Proposed 2,4

- D Choline Salt Uses

Proposed Label Use Active Ingredients Method Maximum Application Rate (Interval)
GF

- 2726 , GF

- 2727

EnlistTM corn 2,4

- D choline salt

Glyphosate G round broadcast spray Preplant (Burndown) Single application at 1 lb ae /A

Preemergence Single application at 1 lb ae/A

Postemergence (up to V8 stage

- 48 inches) Maximum s ingle application at 1 lb ae/A

2 applications, maximum (12 days)

Seasonal maximum of 3 lb ae /A

GF

- 2654 TC

Field corn containing DAS

40278

- 9 2,4

- D choline salt Ground broadcast spray Preplant Single application at 1 lb ae/A

Preemergence Single application at 1 lb ae/A

Postemergence (up to V8 stage

- 48 inches) Maximum s ingle application at 1 lb ae/A

2 applications, maximum (12 days)

Seasonal maximum of 3 lb ae /A
GF

- 2654 TS

### 29 Proposed Label Use Active Ingredients Method Maximum Application Rate (Interval)

Soybeans containing DAS

- 68416

- 4 2,4

- D choline salt Ground broadcast spray Preplant Single application at 1 lb ae/A

Preemergence Single application at 1 lb ae/A

Postemergence (up to R2 stage ) Maximum single application at 1 lb ae/A

2 applications, maximum (12 days)

Seasonal maximum of 3 lb ae /A

3.2 Aquatic Exposure Modeling for 2 , 4

- D Choline Salt

A Tier II screening

- level surface water exposure for aquatic risk assessment was conducted for the Section 3 proposed new use registration. Modeled application rates represent the maximum use pattern s of the proposed label s for use on herbicide

- tolerant

c orn and soybean. Since the 2,4

- D choline salt dissociates rapi dly in less than 6 seconds in the environme nt (MRID 48260701), the aquatic exposure was based on the 2,4

- D acid equivalent. Aquatic exposure was also modeled for its major degradate 2,4

- DCP, w hich is more toxic than 2,4

- D for selected aquatic organisms ( http://cfpub.epa.gov/ecotox/ ) using the highest exposure scenario for 2,4

- D ( i.e.

, MS Corn S TD )

. An a dditional PRZM/EXAMS model run w as performed to estimate the no drift exposure using MS Corn STD scenario for 2,4

- D to determine the contribution of spray drift in surface water.

3.2.1 PRZM

- EXAMS Model

T he Pesticide Root Zone Model, (PRZM, Carsel et al ., 1997) and the Exposure Analysis Modeling System (EXAMS, Burns, 1997) were used in tan dem to generate aquatic estimated environmental concentrations (EECs). PRZM (3.12.2 dated May 12, 2005) simulates fate and transport on the agricultural field whereas EXAMS (2.98.04.06, dated April 25, 2005) simulates the fate and resulting daily concentr ations in the water body. Simulations are carried out with the linkage program shell, PE5V01.pl (dated November 15, 2006), which incorporates the standard agricultural and non

- agricultural scenarios developed by EFED. Simulations are run for multiple (us ually 30) years, and the EECs represent peak values that are expected once every ten years based on the thirty years of daily values generated during the simulation. Additional information on these models can be found at: http://www.epa.gov/oppefed1/mode ls/water /index.htm

.
The aquatic exposure is estimated for the maximum application pattern to a 10

- ha field bordering a 1

- ha pond, 2

- m deep (20,000 m 3 

### ) with no outlet. Exposure estimates generated using this standard pond are intended to represent a wide variety of vulnerable

### 30 water bodies that occur at the top of watersheds including prairie pot holes, playa lakes, wetlands, vernal pools, man

- made and natural ponds, and intermittent and first

- order streams. As a group, there are factors that make these w ater bodies more or less vulnerable than the standard surrogate pond. Static water bodies that have larger ratios of pesticide

- treated drainage area to water body volume would be expected to have higher peak EECs than the standard pond. These water bodie s will be either smaller in size or have large drainage areas. Smaller water bodies have limited storage capacity and thus may overflow and carry pesticide in the discharge, whereas the standard pond has no discharge. As watershed size increases beyond 1 0

- ha, it becomes increasingly unlikely that the entire watershed is planted with a non

- major single crop that is all treated simultaneously with the pesticide. Headwater streams can also have peak concentrations higher than the standard pond, but they lik ely persist for only short periods of time and are then carried and dissipated downstream.

Standard PRZM crop scenarios, which consist of location

- specific soils, weather, and cropping practices, were used in the simulations to represent proposed labeled uses of 2,4

- D choline salt

. Standard corn scenarios are available for Illinois , Indiana, Iowa, Kansas, Minnesota, Mississippi, North Carolina, Nebraska, Ohio, and Pennsylvania. A single standard scenario, Mississippi , is available for so ybean

. The propo sed label recommends applying 2,4

- D choline salt on corn th rough the V8 stage (48 inches tall )

. Applications to soybeans can occur up to the R2 stage (full bloom). 2,4

- D choline salt application dates were chosen based on the geographical location of the crop and explored the extended application time period.

2,4

- D choline salt labels have a recommendation to use the 2,4

- D c holine product with an ASABE S

- 572 droplet size classification of coarse/coarser (D v0.5 

### of ≈ 439 μm) spray quality. Given the limited option for droplet size in the current AgDRIFT ground module, the droplet size of D v0.5 

### of 341μm option was used as the nearest label recommended coarse/coarser droplet size. Maximum spray drift fractions (0.017) using a droplet size of Dv0.5 of 341μm as well as no spray drift fraction were evaluated to account for the spray drift contribution in the E EC s. Table 9 presents all simulated surface water concentrations of 2,4

- D for corn and soybean.

3.2.2 Model Inputs

Input parameters for the PR ZM/EXAMS models are listed in Table 7 and Table 8 for 2,4

- D and 2,4

- DCP respectively

. Explanations of the various model input parameters are discussed below. Since 2,4

- DCP is a major degradate (32.6%) formed in the aquatic environment but only 3. 5 % formed in the terrestrial environment, two application rates were used in PRZM/EXAMS modeling to account contribution from terrestrial via runoff/erosion of parent as well as 2,4

- DCP and direct deposition from spray drift. 2,4

- DCP exposures were modeled f or the highest EECs from the parent (MS corn scenario). Using these contribution s in tandem requires post

- processing of the modeled output to derive a weighted EEC that represent s the contribution of runoff/ erosion from the terrestrial environment and dir ect deposition of spray drift to an aquatic environment

. A Microsoft Excel spreadsheet was used that allows for the weighting and aggregation of exposure from both scenarios. The daily time series from each model run was copied

### 31 from the times series file (*_TS.out) generated from the PRZM into the EXCEL spreadsheet

. Rolling averages for the relev ant durations of exposure (4, 14, 21 , and 60 day averages) were estimated using Table 20 of PRZM/EXAMS

. Example PRZM/EXAMS model outpu t s of 2,4

- D and post

- processed 2,4

- D CP EECs were provided in Appendix D

.

Table 7

. PRZM/EXAMS Input Parameter Values for 2,4

- D

Parameter Value Source Comments

Maximum application

Rate lb a.e. /A (kg

a.e. /ha) Corn and Soybean: 1.0 (1.12) GF

- 2654 TC 2,4

- D (56.3%) Application rate for GF

- 2654 for corn and soybean are much higher than GF

- 2726 (24.4% of 2,4

- D,). Therefore no exposure assessment was performed for GF

- 2726.

Number of Applications 3 GF

- 2654 TC 2,4

- D (56.3%) 1 application for p re

- emergence 1 application on emergence date

1 application for post emergence

Minimum Application Intervals (days) 12 (Pre emergence)
12, 21 and 28 (Post emergence) GF

- 2654 TC 2,4

- D (56.3%) Minimum application interval before emergence

A

pplication intervals for post

emergence

Scenario and Application Date 2 IA Corn

- 13

- 05 1
IL Corn 19

- 04 2
IN Corn 03

- 05 1
KS Corn 28

- 04 2
MN Corn 03

- 05 1
MS Corn 29

- 03 2 MS Soybean 04

- 04 2
NC Corn 03

- 03 1
NE Corn 13

- 05 2
OH Corn 19

- 04 2
PA Corn 04

- 04 1 Based on PRZM/EXAMS Scenarios 12 days before crop emergence

12

- 28 days from the date of crop emergence in the scenario

Depth of Incorporation (inches) 0 GF

- 2654 TC 2,4

- D (56.3%) For foliar application according to Input parameter guidance (USEPA 2009)

Method of Application Ground spray GF

- 2654 TC 2,4

- D (56.3%) ---

Application Efficiency Ground: 0.99 Input parameter guidance (USEPA, 2009) Default values for ground spray

Spray Drift Fraction 0.017 3 Estimated Based on nearest droplet size specification in the submitted labels
Molecular Mass (g/mol) 221.04 USEPA 2005 Product chemistry data

Vapor Pressure (Torr) 1.4 x 10 - 7 USEPA 2005 Product chemistry data
Henry’s Law Constant (atm m3/mol) 8.56 x 10 - 6 Rice et al., 1997 Measured value

### 32 Parameter Value Source Comments

Solubility in Water (mg/L) 569 USEPA 2005

---

Hydrolysis t 1/2 at pH 7.0 (days) 0 MRID 41007301 Stable to hydrolysis @ pH 7.0

Aquatic Photolysis t 1/2 (days) 12.98 MRID 41125306 ---

Aerobic Soil Metabolism t 1/2 (d) 6.92 MRID 43167501 MRID 00116625 90 th percentile upper confidence bound on the mean half

- life of 2,4

- D
Aerobic Aquatic Metabolism t 1/2 (d) 15 x 3 4 MRID 420445301 Input parameter guidance (USEPA 2009)

Anaerobic Aquatic Metabolism t 1/2 (d) 321 MRID 43356001 MRID 42979201 MRID 41557901 90 th percentile upper confidence bound on the mean half

- life of 2,4

- D
Soil Partitioning Coefficient (K oc ; ml/g oc ) 76.02 MRID 44117901 MRID 42045302 Represent average K foc from 5 soils

1 = PRZM/EXAMS simulation s w ere performed with a single post

- emergence crop scenario (12 days after crop emergence)

2
= PRZM/EXAMS simulation s w ere performed with varied post

- emergence crop scenario s (12, 21 a n d 28 days after crop emergence)

3 = Spray drift fraction was estimated using AgDRIFT 2.1.1 model

– Tier I Ground scenario (High boom, D V 0.5 341 μm and 90 th percentile data )

4 = Due to reported half

- life for a single aerobic aquatic metabolism study, the input half

- life was multiplied by 3 according to g uidance for selecting input parameters in modeling for environmental fate and transport of pesticides. Version 2.1 October 22, 2009.



### Ta ble 8

. PRZM/EXAMS Input Parameter Values for 2,4

- DCP

Parameter Value Source Comments

Scenario and Application Date MS Corn 1 Based on PRZM/EXAMS Scenario

. 12 days before crop emergence. 12days from the date of crop

emergence in the scenario Spray Drift Fraction 1.0 Assumed To evaluate 2,4

- DCP contribution from 2,4

- D spray drift

2,4

- DCP mass/acre from r u noff contribution of parent ( lb a.e. /A ) 0.02 4 Estimated 2 To evaluate 2,4

- DCP contribution from 2,4

- D runoff (10%) based on PRZM manual 3

Molecular Mass (g/mol) 162.9 USEPA 2005 Product chemistry data

### 33 Parameter Value Source Comments

Maximum application

Rate lb a.e. /A ( kg a.e./ha ) Corn

0.02 6 (0.02 9 ) 4

0.028 (0.031 ) 5 Estimated See calculations in footnotes 3and 4

Number of Applications 3 GF

- 2654 TC 2,4

- D (56.3%) 1 application for p re

- emergence 1 application on emergence date

1 application for post emergence

Method of Application Ground Assumed 2,4

- DCP from post

- application parent degradation in terrestrial environment

Direct Application Assumed 2,4

- DCP c ontributions from spray drift and 10% of parent from runoff were simulated as a direct application via spray drift into surface water body

Depth of Incorporation (inches) 0 Assumed For ground application according to Input parameter guidance (USEPA 2009)

Application Efficiency 1.0 Assumed To evaluate 2,4

- DCP contribution from runoff and erosion

0 Assumed 2,4

- DCP ontributions from spray drift and 10% of parent from runoff were simulated via spray drift as a direct application into surface water body
Solubility in Water (mg/L) 4500 TOXNET 6 Open literature value

Hydrolysis t 1/2 at pH 7.0 (days) 0 Assumed No Data

Aquatic Photolysis t 1/2 (days) 0 Assumed No Data

Aerobic Soil Metabolism t 1/2 (d) 75 x 3 7 EPISUITE 8 Single v alue multiplied by 3 according to the Inp ut parameter guidance (USEPA 2009)

Aerobic Aquatic Metabolism t 1/2 (d) 35.5 x 3 7 EPISUITE 8 Single v alue multiplied by 3 according to the Input parameter guidance (USEPA 2009)

Anaerobic Aquatic Metabolism t 1/2 (d) 337.5 x 3 7 EPISUITE 8 Single v alue multiplied by 3 according to the Input parameter guidance (USEPA 2009)
Soil Partitioning Coefficient (K oc ; ml/g oc ) 609 EPISUITE 8

---

### 34 Parameter Value Source Comments

1 P RZM/EXAMS simulation w as performed only for MS Corn based on highest E ECs observed in 2,4

- D
exposure 2 2,4

- D application rate (1.0 lb a.e/A) x [(0. 1

, runoff contribution of 2,4

- D) x (0.326, the maximum conversion rate from the anaerobic aquatic degradation of 2,4

- D to 2,4

- DCP in laboratory studies) x (0.74, the molecular weight ratio of 2,4

- D to 2,4

- DCP)]
3 http://www.epa.gov/ceampubl/gwater/przm3/przm3123.html
4 2,4

- D application rate (1.0 lb a.e/A) x [(0.035, the maximum conversion rate f or the terrestrial degradation of 2,4

- D in the terrestrial environment to 2,4

- DCP in laboratory stu dies) x (0.74, the molecular weight ratio of 2,4

- D to 2,4

- DCP)]
5 2,4

- D application rate (1.0 lb a.e/A) x [(0.017, spray drift contribution of 2,4

- D) x (0.326, the maximum conversion rate from the anaerobic aquatic degradation of 2,4

- D to 2,4

- DCP in labo ratory studies) x (0.74, the molecular weight ratio of 2,4

- D to 2,4

- DCP) + 0.024 lbof runoff contribution ]
6 http://toxnet.nlm.nih.gov/cgi

- bin/sis/search/f?./temp/~nU3WAu:1
7 Due to reported half

- life for a single value, the input half

- life wa s multiplied by 3 according to g uidance for selecting input parameters in modeling for environmental fate and transport of pesticide s. Version 2.1 October 22, 2009
8 http://www.epa.gov/oppt intr/exposure/pubs/episuite.htm



### 3.2. 3 Model Outputs: Aquatic Exposure Estimates

The Mississippi scenario that modeled three applications of 2,4

- D choline salt at 1 lb

a e

/A produced the highest EECs for herbicide

- tolerant corn. This same scenario was also modeled without spray drift. In general, r esults suggest that the E EC s for the droplet size of D v0.5 

### of 341μm are slightly higher (≤ 4%) as compared to the no spray drift fraction (Table 9 )

, w hich indicates that most of the aquatic exposure is driven by runoff. EECs for the 2,4

- DCP degradate were also modeled for Mississippi and were much lower than those for 2,4

- D acid ( e.g. 6.4 versus 58 μg ae/L for peak EEC; Table 9 ).

Table 9

. Range of Estimated Environmental Concentrations (EECs) of 2,4

- D and 2,4

- DCP for Surface Water Drinking Water Source (model) Use Scenario (modeled rate) Peak EEC ( μg ae /L ) 21

- Day EEC ( μg ae /L ) 60

- Day EEC ( μg ae /L )

Surface Water (PRZM/EXAMS) Aquatic Exposure for 2,4

- D ( Parent )

Corn : IA Corn STD IL Corn STD IN Corn STD KS Corn STD MN Corn STD MS Corn STD NC Corn STD NE Corn STD OH Corn STD PA Corn STD ( 3 app. X 1.0 lbs a.e./acre ) 26.5

- 21.9 30.1

- 24.4 26.5

- 24.5 28.3

- 23.5 16.0

- 14.1 58.0

- 57.8 28.0

- 21.0 40.8

- 36.6 26.8

- 16.7 11.8

- 10.9 23.8

- 20.2 26.6

- 21.9 25.3

- 22.1 20.9

- 18.7 15.1

- 12.8 41.6

- 41.0 26.5

- 19.7 36.4

- 33.1 19.3

- 11.7

9.6

- 8.9 19.1

- 16.7 22.7

- 20.0 20.9

- 18.9 13.7

- 12.5 13.6

- 11.7 29.2

- 26.4 23.2

- 17.5 28.9

- 27.9 11.4

- 8.8 6.6

- 6.6

### 35 Drinking Water Source (model) Use Scenario (modeled rate) Peak EEC ( μg ae /L ) 21

- Day EEC ( μg ae /L ) 60

- Day EEC ( μg ae /L ) Soybean : MS Soybean STD ( 3 app. X 1.0 lbs a.e./acre ) 42.8

- 42.8 32.5

- 32.5 21.4

- 21.3

Corn : MS Corn STD 1 ( 2 app. @ 1.0 lbs and 2 App @0.50 lb a.e./acre ) 57.8 41.3 27.3

Corn : MS Corn STD 2 ( 3 app. X 1.0 lbs a.e./acre ) 56.5 40.1 25.3

Aquatic Exposure for 2,4

- DCP (Degradate)

Corn : MS Corn STD 3 ( 3 app. x 0.026 lbs a.e./acre ) 4 and 3 app. x 0.0 28 lbs a.e./acre ) 5 4.66 6 3.84 6 3.62

1 Post Emergence 2 a pplications at 0.50 lb a.e./A
2 PRZM/EXAMS simulated EECs without spray drift fraction to evaluate spray drift contribution
3 P RZM/EXAMS simulation w as performed only for MS Corn based on highest EECs observed in 2,4

- D exposure
4 = 2,4

- D application rate (1.0 lb a.e/A) x [(0.035, the maximum conversion rate f or the terrestrial degradation of 2,4

- D in the terrestrial environment to 2,4

- DCP in laboratory studies) x (0.74, the molecular weight ratio of 2,4

- D to 2,4

- DCP)]
5
= Sum of 0.02 4 lb from runoff contribution and 0.004 lb from spray drift ]
6 = Reported values are based on combi ni ng exposures from terrestrial runoff/erosion and spray drift contribution using post processing



### 3.3 Monitoring Data

Monitoring data considered in the previous assessment (US EPA 2004) were the United States Geological Survey’s (USGS) National Water Quality Assessment Program (NAWQA) groundwater and surface water database, USGS/EPA reservoir monitoring database, National Drinking Water Contaminant Occurrence Database (NCOD), and US EPA’s Storage and Retrieval environmental data system (STORET). Review of these databases was conducted to provide peak and median concentrations. Additionally, the quality of data was evaluated for targeting pesticide use areas, detection limits, and analytical recoveries. The mo nitoring data indicate that 2,4

- D is detected in groundwater and surface water. The highest time

- weighted annual mean (TWAM) concentration was 1.45 μg/L from the NAWQA database containing non

- targeted data reflecting pesticide concentrations in flowing wa ter as opposed to more stationary bodies of water such as ponds, lakes, and reservoirs. A lso, 2,4

- D is detected in treat ed (finished) drinking water.

### 36 Maximum concentrations of 2,4

- D in surface source water and ambient groundwater are 58 μ g/L and 14.8 ug/L, respectively.

Monitoring data from the USGS NAWQA program were accessed o n September 21, 2012 to evaluate the current trend of 2,4

- D concentration s in surface water and groundwater. All data of filtered s urface water and groundwater were downloaded since the drinking water memorandum was issued in 2004. For surface water, a total of 931 water samples were analyzed for 2,4

- D. 2,4

- D was detected in 47.0 % (i.e. 434 sam ples from a total national data set of 931 samples). The maximum concent rations of 2,4

- D ranged from 0.008 μg/l to 8.7 00 μg/L. Even though the maximum concentration of 8.7 μg/L is lower than the previously reported value of 15 μg/L, 2,4

- D was detected at a higher percentage in surface water sampled after 2003 as compared to t he 23.5% (i.e. 1030 sam ples from a total national data set of 4377) reported in the previou s drinking water memorandum (US EPA 2004). For groundwater, a total of 1184 water samples were analyzed for 2,4

- D. 2,4

- D was detected in 1.0% of the samples (i.e. 12 sam ples from a total national data set of 1184 samples). The maximum concentrations of 2,4

- D ranged from 0.008 μg/L to 1.4 μg/L. Percent of detection and the reported concentration are lower than in the previously reported drinking water memorandum (US EP A 2004). Several mitigation measures may have contributed to the lower concentrations of 2,4

- D in NAWQA surface water and ground water monito ring in the years since the RED was issued ( 2005 )

. The following mitigation measures were placed in the RED to reduce 2,4

- D loading in the environment (US EPA 2005) :

• The application rate was reduc ed f rom 2.0 to 1.5 lb ae/A per year for turf uses.

• Master label rates were lower than the existing labels rates for various use s. All registrants must conform use rates to those set forth in the 2,4

- D master label and reflected in the 2,4

- D RED label table.

• Measures to control spray drift described in the “Spray Drift Management” section in the RED to reduce the risk of 2,4

- D to no n

- target plants.

3.4 Terrestrial Exposure Estimates for 2,4

- D Choline Salt

The Terrestrial Exp osure (T

- REX) model (Version 1.5 .1), an EFED computer model that uses a first

- order dissipation relationship to account for residue dissipation between applications, was used to estimate exposure concentrations of 2,4

- D to terrestrial wildlife. The T

- REX simulation model incorporates th e Kenaga nomogram (Fletcher et al. 1994; Hoerger and Kenaga 1972; Pfleeger et al. 1996) (relationship between the amount of pesticide applied and the amount of pesticide residue present on a given food item). The model also calculates the peak concentrati on of pesticide residues on each food item on a daily interval for one year using a first order decay function based on the concentrations present from both the initial and additional applications. In addition to exposure concentrations (dose and diet

- bas ed), the T

- REX model calculates risk quotients based on food items for mammals and birds, including herbivores, insectivores, and granivores. For dose

- based exposures, three weight classes of mammals (15, 35, and 1000 g) and birds (20, 100, and 1000 g) ar e considered.

### 37 A default foliar dissipation half

- life of 35 days was used in this assessment. Example i nput parameters, such as application rate, interval, and number of applications, used in the T

- REX model are presented with corresponding EECs in Tabl es 10 and 11 ( also Appendix E ).

3.4 .1 Exposure Estimates for Birds and Mammals

The estimated e xposure concentrations of 2,4

- D choline salt for birds and mammals are presented in Tables 10 and 11 , respectively. These estimates are based on the upper

bound Kenaga dose and the assumption that the species in question eat one type of food item and forage only in the treated and/or overspray areas.

EECs ranged from 26 to 578 mg ae/kg

- diet for dietar y exposures (birds and mammals). Avian dose

- based EECs ranged from 2.34 to 659 mg ae/kg

- bw while mammalian dose

based EECs ranged from 1.23 to 552 mg ae/kg

- bw (Tables 10 and 11 )

.

Table 10 . Avian Exposure Concentration Estimates for Foliar Applications

Feeding Category Dietary

based EECs (mg/kg

- food item) Dose

- based EECs (mg/kg

- bw)

Small (20 g) Medium (100 g) Large (1000 g)

2,4

- D choline salt on herbicide

- tolerant corn and soybean

– 3 applications at 1 lb ae/A (12 day interval) Short grass 578.44 658.79 375.67 168.19 Tall grass 265.12 301.94 172.18 77.09 Broadleaf plants 325.37 370.57 211.31 94.61 Fruits/pods 36.15 41.17 23.48 10.51 Arthropods 226.56 258.03 147.14 65.88 Seeds 36.15 9.15 5.22 2.34

Table 11 . Mammalian Exposure Concentration Estimates for Foliar Applications

Feeding Category Dietary

based EECs (mg/kg

- food item) Dose

- based EECs (mg/kg

- bw)

Small (15 g) Medium (35 g) Large (1000 g)

2,4

- D choline salt on herbicide

- tolerant corn and soybean

– 3 applications at 1 lb ae/A (12 day interval) Short grass 578.44 551.50 381.16 88.37 Tall grass 265.12 252.77 174.70 40.50 Broadleaf plants 325.37 310.22 214.40 49.71 Fruits/pods 36.15 34.47 23.82 5.52 Arthropods 226.56 216.00 149.29 34.61 Seeds 36.15 7.66 5.29 1.23

### 38 3.4 .2 Exposure Estimates for Plants

TerrPlant 1.2.2 (10/29/09) was used as a Tier 1 model for screening level assessments of pesticides. The model provides estimates of exposure to terrestrial plants from single pesticide applications; however, the model does not consid er exposures to plants from multiple pesticide applications. TerrPlant derives pesticide EECs in runoff and in spray drift, and develops risk quotients for non

- listed and listed species of monocots and dicots inhabiting dry an d semi

- aquatic areas (Appendi x F ).

The estimated e xposure concentrations of 2,4

- D choline salt for terrestrial plants are presented below (Table 12 ) . The most protective application scenario for each use was selected, based on information from the label. EECs ranged from 0.01 (spray drift) to 0.51 (total for semi

- aquatic areas )

.

Table 12 . Terrestrial Plant Exposure Concentration Estimates Description Equation EEC (lb ae /A) 2,4

- D Choline Salt and EnlistTM on Corn and Soybeans

– single ground application at 1 lb ae /A
Runoff to dry areas (A/I)*R 0.05 Runoff to semi

- aquatic areas (A/I)*R*10 0.5 Spray drift A*D 0.01 Total for dry areas ((A/I)*R)+(A*D) 0.06 Total for semi

- aquatic areas ((A/I)*R*10)+(A*D) 0.51

Atmospheric Concentration Analysis

Henry's Law constant of 8.56 x10 - 6 

### atm

- m 3 

### /mol indicates that 2

, 4

- D is expected to volatilize from moist soil and water surfaces. The Probablistic Exposure and Risk Model for Fumigants (PERFUM

, v. 2.5.1, 7/2/2008) is used in estimating the vapor phase (secondary drift) of 2,4

- D in the atmosphere

. T he PERFUM model is a processor of the ISCST3 model (Reiss and Griffin 2008 4 

### ), which has been developed from EPA’s Office of Air Quality Planning and Standards 5 

### . PERFUM can calculate upper

- bound EECs in air near the edge of a field or at a downwind distance of a treated field

. PERFUM incorporates actual weather data and flux distribution estimates, and then accounts for changes and altering conditions. Analyses based on a variety of model outputs can be used to compare the potential r isks at a range of distances. The PERFUM model and users manual are public and can be downloaded at http://www.epa.gov/opp00001/science/models_pg.htm

.

The Agency estimated the volatility flux from a submitted field volatility study performed with 2,4

- D choline as well as 2,4

- D dimethylamine salt (DMA) and 2,4

- D ethylhexyl ester (EHE) at four different sites ( MRID 48862902 )

. This study is in review

4 http://www.exponent.com/
5 The ISCST3 model documentation can be accessed on

- line at: http://www.epa.gov/scram001/ dispersion_alt.htm

### 39 at this time and preliminary flux profiles are provided in Appendix H

. The Agency

estimated highest volatility flux of 1.88 x 10 - 8 

### g/m 2

- 

### s from Little Rock, AR was used in the PE RFUM modeling. Atmospheric concentration s at the 90 th 

### percentile of 2,4

- D for

corn are depicted at various distances in Figure 3

. An example of the input for t he PERFUM model is provided in Appendix I

.
Figure 3. Estimated 90 th 

### Percentile of 2,4

- D C oncentration s in the A tmosphere

Since the PE RFUM model is limited to vapor drift estimation, the AERSCREEN model is used to calculate wet and dry deposition in the environment. AERSCREEN is a screening model, based on the US EPA AERMOD model

, d esigned to produce estimates of "worst

- case" 1

- hour concentrations for a single source without the need for hou rly meteorological data (US EPA 2011). Details of the AERSC R EEN model can be obtained from the cited URL 6 

### below

. The highest volatility flux of 1.88 x 10 - 8 

### g/m 2

- 

### s from Little Rock, AR was also used in the AERSCREEN modeling. Table 1 3 provides maximum wet and dry deposition s of 2,4

- D

. The estimated w et and dry depositions were negligible (≤ 9.60 x 10 - 4 

### lb a.e/A)

. E x ample s of input and output of the AERSCREEN model are provided in Appendix I

.

Table 13 . Daily AERSCREEN 2,4

- D Maximum Total 24

- Hour Deposition Results

Time Period (Hours) Total Field Emissions (lb a.i./A) Total Field Emissions

(% of applied) Total Dry Deposition (lb a.i./A) Total Wet Deposition (lb a.i./A) Total Deposition (lb a.i./A) Total Deposition (% of applied) Total Deposition (% of emitted)

Choline Formulation, Corn and Soybeans (EPA Field Emissions) 1

0

- 5 1.20 x 10 - 2 1.204% 1.05 x 10 - 3 5.00 x 10 - 5 1

. 1 0 x 10 - 3

- - 5

– 10 8.43 x 10 - 5 0.008% 5.00 x 10 - 5 0 5.00 x 10 - 5

- -

6 http://www.epa.gov/ttn/scram/models/screen/aerscreen_userguide.pdf )

### 40 Time Period (Hours) Total Field Emissions (lb a.i./A) Total Field Emissions

(% of applied) Total Dry Deposition (lb a.i./A) Total Wet Deposition (lb a.i./A) Total Deposition (lb a.i./A) Total Deposition (% of applied) Total Deposition (% of emitted)

10

- 16 1.59 x 10 - 5 0.002% 0 0 0

- - 16

- 23 7.30 x 10 - 6 0.001% 0 0 0

- - 23

- 24 4.90 x 10 - 5 0.005 % 2 .00 x 10 - 5 0 2 .00 x 10 - 5

- - Total 1.22 x 10 - 2 1.220 % 9.60 x 10 - 4 5.00 x 10 - 5 1.1 7 x 10 - 3 0.117 % 9.48%
1 Deposition values for corn and soybeans the same despite 50 cm and 15 cm release heights modeled, respectively



### Atmos p h e ric Monitoring Data

Data collected in the 1960s and 1970s, and summarized in Majewski and Capel (1995), indicate that 2,4

- D has been detected in rainwater samples at concentrations between 50 nanograms per liter (ng/L) and 204,000 ng/L, while 2,4

- D was detected in air samples at concentrations between 1.15 nanograms per gram (ng/g) and 1410 ng/g. Majewski and Capel noted that the higher concentrations were infrequently detected, and the authors also noted that the high detections were located near areas where pesticides were applied and may have resulted from unusual conditions. More recent data reported by Anderson et al. (2002) on water and rainfall samples in a wetland environment in Alberta, Canada indicate that 2,4

- D was one of the most frequently detected pesticides in rainfall samples with a f requency of detection of 65%; h owever, concentrations did not exceed 1 μg/L . In a study conducted in southern Manitoba by Rawn et al. (1999), 2,4

- D was detected in rainfall at concentrations less than 1 μg/L and was detected in air as both vapor and particle phase at a maximum concentration of 3500 picograms per cubic meter (pg/ m 3 

### ). Both rainfall and air detections were closely associated with local use; however, the authors noted that the relative contribution of these compartments to surface water was low compared to runoff.



## 4. Ecological Effects Assessment

Eco toxicity data are available for 2,4

- D choline salt for a limited number of taxa (acute freshwater fish, acute honeybee, acute freshwater invertebrate, and green algae). These studies support the bridging strategy that has been used for other forms of 2,4

- D; 2,4

- D toxi city is usually reported in “acid equivalents” so that toxicity data can be compared among forms. For this assessment, 2,4

- D choline salt specific data , when available, will be discussed as well as the most sensitive 2,4

- D acid equivalent data (the 2005 R ED can be consulted for a complete listing of 2,4

- D data

– USEPA 2005b). Only the most sensitive 2,4

- D toxicity value from the broader 2,4

- D dataset will be used in risk quotient calculations . Given that there is a difference between the toxicity of este rs and amines/salts/acid in aquatic systems, only toxicity data from the latter will be considered for aquatic exposures , unless it is unavailable. Ester data will be used in the absence of salt/amine/acid data . For terrestrial scenarios, the most sensit ive 2,4

- D toxicity value will be used, regardless of the chemical form.

### 41 A search of the ECOTOX database on October 24 , 201 2 did not yield any 2,4

- D choline toxicity studies . Therefore, only studies submitted by the registrant were evaluated to determine the effects of 2,4

- D choline salt on non

- target organisms. The Ecological Incident Information System (EIIS) was also reviewed to provide a refined characterization of the ecological effects for 2,4

- D. The ECOTOX database and European Footprint database yielded toxicological information for aquatic organisms indicating that 2,4

- DCP, a major degradate of 2,4

- D, is more toxic than 2,4

- D. References from the Footprint database were not available for review

. ECOTOX sources were not formally reviewed; howeve r the implication of 2,4

- DCP’s higher toxicity is incorporated into the risk characterization section of the document.

4.1 Aquatic Effects Summary

2,4

- D choline salt’s effects on aquatic fauna were determined by evaluating freshwater and estuarine/marine fish and invertebrates, and freshwater amphibians. A cute and chronic studies were submitted for freshwater fish, freshwater invertebrates , and estuarine/marine fish, whereas only acute studies were submitted for estuarine/marine invertebrates and freshwa ter amphibians. In general, 2,4

- D choline salt is slightly toxic to fish and invertebrates, and practically non

- toxic to aquatic

- phase amphibians, on an acute basis.

4.1.1 Toxicity Effects on Fish and Amphibians

An acute freshwater fish limit test for 2 ,4

- D choline salt was available. Neither mortalities nor sub

- lethal effects were observed. This study yielded the lowest registrant

submitted endpoint to date for 2,4

- D moieties and classifies 2,4

- D choline salt as “slightly toxic” to freshwater fish

. Acute and chronic studies for other fish and amphibians were not available for 2,4

- D choline salt; however, data were available for other 2,4

- D forms. The lowest chronic endpoint for freshwater fish was in an early life stage study with the fathead minnow . The study found a decrease in length (most sensitive endpoint) as well as mortality at the highest two concentrations (98.1 and 62.9 mg ae/L) and weight loss at 37.6 mg ae/L. An acute estuarine/marine fish study with the tidewater silverside classified 2,4

- D as “slightly toxic” to estuarine/marine fish. No mortalities or sub

- lethal effects were observed. Chronic estuarine/marine fish endpoints were only available for ester forms of 2,4

- D. The lowest endpoint was based on survival of sheepshead minnow in an early life study. Other effects included a reduction of hatchability at the two highest concentrations (287 and 194 μg ae/L), and reduced length and weight (133 μg ae/L). An acute study with the leopard frog suggests that 2,4

- D is “practically non

- toxic” to freshwater amphibians. No sub

- lethal effects were observed. The study was classified as “supplemental” because it was a non

- guideline study; however, it is considered scientifically sound and appropriate for use in risk assessments (Table 14 ).

### 42 Table 14 . Toxic Effects in Fish and Amphibians
Test Species 2,4

- D Form Tested Toxicity Value (mg ae/L) Study Classification MRID #

Acute Freshwater Fish Rainbow
trout (Oncorhynch

us mykiss ) 2,4

- D choline salt 96

- h LC 50 

### > 48 Acceptable 48892401

Chronic Freshwater Fish (early life cycle) Fathead minnow ( Pimphales promelas ) Dimethylamine salt of 2,4

- D NOAEC = 14.2 * Based on

length Acceptable 41767701

Acute Estuarine/ Marine Fish Tidewater silverside ( Menidia beryllina ) Diethanolamine salt of 2,4

- D 96

- h LC 50 

### > 80.24 Acceptable 42018301

Chronic Estuarine/ Marine Fish Sheepshead minnow ( Cyprinodon variegatus ) Butoxyethyl ester of 2,4

- D NOAEC = 0.05554 * Based on survival Acceptable 41345701

Acute Freshwater Amphibians Leopard frog tadpoles

( Rana pipiens ) Dimethylamine salt of 2,4

- D 96

- h LC 50 

### = 278* Supplemental 44517306

*Denotes value used for calculating risk quotients

4.1.2 Toxicity Effects on Invertebrates

An acute freshwater invertebrate limit test for 2,4

- D choline salt was available using the water flea

. One mortality was reported; however, it was considered incidental and not related to the treatment. No sub

- lethal effects were observed. The most sensitive endpoint for acute exposures to freshwater invertebrates occurred in a wat er flea study conducted with 2,4

- D acid ( M R ID 41158301)

. Sub

- lethal effects were not reported for this study; the study classifies 2,4

- D as “slightly toxic” to freshwater invertebrates on an acute basis. A freshwater invertebrate chronic study with the w ater flea yielded endpoints based on survival and reproduction (number of neonates produced, number of broods produced per daphnid, and brood size) . No other effects were observed. An acute study with the eastern oyster classified 2,4

- D as “slightly” tox ic to estuarine/marine invertebrates. One mortality occurred at the highest treatment level (155 mg ae/L) and reduced feeding was also observed at this concentration. Shell growth reduction was noted in the other concentrations and the EC 50 

### was based on this parameter (Table 15 )

.
Estuarine/marine invertebrate chronic toxicity data were not available. A toxicity value can be estimated based on the assumption that the acute

- to

- chronic ratio (ACR) for freshwater invertebrates applies to estuarine/marine invertebrates also. Thus, the

### 43 following equation w as used to estimate a NOAEC for eastern oyster , the most sensitive estuarine/marine species on an acute basis (Table 15 )

.

E C 50( oyster ) 

### = EC 50 (waterflea) 

### = 49.6 = 2 5 = 31.8 = NOAEC (oyster ) 

### NOAEC (oyster ) 

### NOAEC (waterflea) 

### X 16.05

Table 15

. Toxic Effects in Invertebrates

Test Species 2,4

- D Form Tested Toxicity Value (mg ae/L) Study Classification MRID #

Acute Freshwater Invertebrates Water flea ( Daphnia

magna ) 2,4

- D choline salt 48

- h EC 50 

### > 40.7 Acceptable 48892402

Acute Freshwater Invertebrates Water flea ( Daphnia

magna ) 2,4

- D acid 48

- h LC 50 

### = 25 * Acceptable 41158301

Chronic Freshwater Invertebrates Water flea ( Daphnia

magna ) Diethanolamine salt of 2,4

- D NOAEC = 16.05* Based on survival and reproduction Acceptable 42018303

Acute Estuarine/

Marine Invertebrates Eastern oyster ( Crassostr

ea virginica ) Isopropylamine salt of 2,4

- D 96

- h EC 50 

### = 49.6* Acceptable 41429003

Chronic Estuarine/

Marine Invertebrates Eastern oyster ( Crassostr

ea virginica ) ACR NOAEC = 31.8* Based on ACR ACR ACR

*Denotes value used for calculating risk quotients

4.1.3 Toxicity Effects on Plants

A non

- vascular aquatic plant study for 2,4

- D choline salt was available using green algae

. Yield and growth rates were affected at the 23.3 mg ae/L treatment. The most sensitive endpoint for non

- vascular plants was derived from a freshwater diatom study and was based on growth inhibition. An aquatic vascular plant study with duckweed was avail able. The most sensitive endpoints were a reduction in frond number and plant number. At the two highest treatment levels (2.11 and 1.03 mg ae/L), colony break up and root destruction were observed; there was a statistically significant increase in frond chlorosis as well (Table 1 6 ).

### 44 Table 1 6 . Toxic Effects in Aquatic Plants

Test Species 2,4

- D Form Tested Toxicity Value (mg ae /L) Study Classification MRID #

Non

- Vascular Aquatic Plant Green algae ( Pseudokirc

hneriella subcapitata ) 2,4

- D choline salt 72

- h IC 50 

### > 45.85

NOAEC = 23.3 Acceptable 48892 405

Non

- Vascular Aquatic Plant Freshwater diatom ( Navicula pelliculosa ) Dimethylam ine salt of

2,4

- D EC 50 

### = 3.88* Acceptable 41505903

Vascular Aquatic Plant Duckweed ( Lemna gibba ) Diethanola mine salt of 2,4

- D EC 50 

### = 0.2992* Acceptable 42712204

*Denotes value used in risk quotient calculations

4.2 Terrestrial Effects Summary

2,4

- D choline salt’s effects on terrestrial organisms were determined by evaluating toxicity data for birds, mammals, insects, and terrestrial plants. Acute and chronic studies were submitted for birds and mammals; acute contact data were available for honeybees. V egetative vigor and seedling emergence data were available for plants. In general, 2,4

- D choline salt is practicall y non

- toxic to terrestrial insects, slightly toxic to mammals

, and moderately toxic to birds, on an acute basis. Terrestrial dicots appear to be more sensitive than monocots.

4.2.1 Toxicity Effects on Birds

2,4,

- D choline salt’s toxicity to birds was evaluated through acute oral exposure, acute dietary exposure, and chronic dietary exposure. Birds are considered a surrogate for terrestrial

- phase amphibians and reptiles, in the absence of taxa

- specific data.

The acute oral toxic ity study was conducted with the northern bobwhite quail and resulted in a classification of “moderately toxic” to birds on an acute oral basis. Toxic symptoms prior to death were lethargy, reduced reaction to external stimuli, depression, lower limb weak ness, wing droop, prostrate posture, loss of righting reflex, and a ruffled appearance. Sub

- lethal effects includ ed a drop in body weight at two of the treatment levels (218.7 and 135 mg ae/kg

- bw) . There was also a decrease in food consumption at the 21 8.7 mg ae/kg

- bw treatment level during the first 3 days after dosing, but this was compensated for by a 2

- 3 times higher food consumpt ion rate from days 4 through 14 (Table 17 ).

Two acute dietary studies were available, classifying 2,4

- D choline salt as “ practically

non

- toxic” on an acute dietary basis to birds. No mortalities occurred in either study.

### 45 The northern bobwhite quail study exhibited a slight decrease in body weight gain at the 3035 and 1706 mg ae/kg

- diet treatment levels. The mallard duck s tudy exhibited a decrease in body weight gain and feed consumption, but only at the highest treatment level (3035 mg ae/kg

- diet) (Table 17 ).

The chronic reproduction study was performed with the northern bobwhite quail. Two mortalities occurred, but they were considered incidental and not related to the treatment. No sub

- lethal effects were observed.

Table 17. Toxic Effects in Birds

Test Species 2,4

- D Form Tested Toxicity Value Study Classification MRID #

Acute Oral

Toxicity No r thern bobwhite quail (Colinius virginianus ) Triisopropanol amine salt of 2,4

- D LD 50 

### = 218.7 mg ae/kg

- bw *

NOAEL = 67.5 mg ae/kg

- bw Acceptable 41644401

Acute Dietary Toxicity Northern bobwhite quail (Colinius virginianus ) Triisopropanol amine salt of 2,4

- D LC 50 

### > 3035
mg a e /kg

- diet

NOAEL = 961 mg ae/kg

- diet Acceptable 41644402

Acute Dietary Toxicity Mallard Duck ( Anas platyrhynchos ) Triisopropanol amine salt of 2,4

- D LC 50 

### > 3035
mg ae /kg

- diet

NOAEL =

1706 mg ae/kg

- diet Acceptable 41644403

Chronic Reproduction Northern bobwhite quail ( Colinius virginianus ) 2,4

- D acid LOAEC > 962 mg ae/kg

- diet

NOAEC = 962 mg ae/kg

- diet *

No effects Acceptable 45336401

*Denotes value used for risk quotient calculation

4.2.2 Toxicity Effects on Mammals

The acute toxicity of 2,4

- D choline salt to mammals was assessed using the oral gavage study conducted on laborato ry rat . Based on the LD 50 

### , 2,4

- D choline salt is moderately toxic to mammals on an acute basis . The two

- generation chronic study with the

### 46 laboratory rat indicated sever al endpoints in parents and offspring growth (see Table 1 8 ) to be the most sensitive. Some reproductive effects were also identified (Table 18 ).

Table 18 . Toxic Effects in Mammals from Acute Oral Exposure to 2,4

- D Choline Salt
Test Species 2,4

- D Form Tested Toxicity Value Study Classification MRID #

Acute Oral Rat ( Rattus norvegicus ) Triisopropanol amine salt of 2,4

- D LD 50 

### = 441 mg ae/kg

- bw* Acceptable 41413501

Chronic

Two

Generation Reproduction

Rat ( Rattus norvegicus ) 2,4

- D acid Parental NOAEL = 5 mg ae/kg

- bw Based on decreased female weight gain (F 1 

### )

and male renal tubule alteration (F 0 

### and F 1 

### )

Reproductive NOAEL = 20 mg ae/kg

- bw Based on increase in gestation length

Offspring NOAEL = 5 mg ae/kg

- bw Based on decreased pup body weight Acceptable 00 150557 00163996

*Denotes value used for calculating risk quotients

4.2.3 Toxicity Effects on Non

- Target Insects

There are contact toxicity data for 2,4

- D choline salt. The study had several incidental deaths in the control and four of the five treatment groups; none were considered statistically significant. Three bees were observed to be either apathetic (slow response to stimuli) or affected (reduced c oordination), but the effects were not dose responsive. The most sensitive 2,4

- D toxicity value is derived from a honeybee study with 2

- ethylhexyl ester of 2,4

- D. It classifies 2,4

- D as “practically non

- toxic” to honeybees on an acute contact basis. Sub

- lethal signs of toxicity included lethargy, immobility, loss of equilibrium and hyper excitability (Table 19 ).

### 47 Table 1 9

. Toxic Effects in Honeyb ee ( Apis mellifera )

Test 2,4

- D Form Tested Toxicity Value (μg ae /bee) Toxicity Classification Study Classification MRID #

Contact Toxicity 2,4

- D choline salt LD 50 

### > 89.4 NOAEL = 89.4 Practically

non

- toxic Acceptable 48892404

Contact Toxicity 2

- ethylhexyl ester of 2,4

- D LD 50 

### > 66 NOAEL = 33 Practically

non

- toxic Acceptable 43982101

4.2.4 Toxicity Effects on Plants

Typical end

- use product data are not available for the 2,4

- D choline salt. Given that a dual herbicide product is being registered

– 2,4

- D choline salt/glyphosate

– data for this herbicide combination are necessary for a thorough toxicol ogical assessment. The stress of simultaneous exposure to two herbicides may cause additive or synergistic effects in terrestrial plants and lead to increased toxicity. Conversely, the herbicides could interfere with each other and cause a decrease in th e toxicity of the product. Finally, the herbicides may operate independently and the observed toxicity may be equivalent to the more toxic of the two chemicals.

For this risk assessment , data from other forms of 2,4

- D were used as surrogates for the 2,4

- D choline salt and 2,4

- D choline salt/glyphosate products . For seedling emergence, onion was the most sensitive monocot and lettuce was the most sensitive dicot. Shoot length was the most sensitive parameter for both species, as well as for four of the o ther species that were tested (tomato, cucumber, soybean, turnip). Seedling emergence was the most sensitive parameter for one species (cabbage) and other toxicological observations included chlorosis and leaf curl. Onion and lettuce were also the most

s ensitive species for the vegetative vigor test. The most sensitive parameter for onion was fresh weight. Leaf distortion and necrosis were also observed. The most sensitive parameter for lettuce was dry weight. Chlorosis, necrosis, leaf curl, stem curl , wilt, and adventitious growth were also reported as effects. Overall, the vegetative vigor and seedling emergence studies indicate that 2,4

- D choline salt is slightly more toxic to dicots than monocots ( Table 20 )

.

Table 20 . Toxic Effects in Terrestrial Vascular Plants
Test Species 2,4

- D Form Tested Toxicity Value (lb ae/A) Study Classification MRID #
Seedling Emergence Monocot = Onion ( Cepa allium)

Dicot = Lettuce ( Lactuca sativa ) Isopropylamine salt of 2,4

- D Monocot EC 25 

### = 0.010*

NOAEC = 0.005628* Based on shoot length

Dicot EC 25 

### = 0.00081* NOAEC = 0.00047* Acceptable 43982101

### 48 Test Species 2,4

- D Form Tested Toxicity Value (lb ae/A) Study Classification MRID #

Based on shoot length Vegetative Vigor Onion ( Cepa allium ) 2,4

- D acid EC 25 

### > 0.0075 NOAEC < 0.0075

Based on fresh weight Acceptable 42416801

Vegetative Vigor Lettuce ( Lactuca sativa ) 2

- ethylhexyl ester of 2,4

- D EC 25 

### = 0.0 021* N OAEC = 0.001 67* Based on dry weight Acceptable 47106004

*Denotes value used for calculating risk quotients

4.3 Incident Database Review

The Environmental Protection Agency maintains an incident database system called the Ecological Incident Information System (EIIS) to track and evaluate accidental kills associated with pesticide use. Based on the information contained in the incident report, the likelihoo d of a particular pesticide causing the incident is classified as highly probable, probable, possible, or unlikely. If there are incidents, this information will be reviewed and considered in conjunction with the degree to which the levels of concern

were exceeded, information on sales, local use practices, and monitored levels in the environment to determine whether the predicted effect based on the labeled use of the product is likely to occur or not.

A search of the EIIS , Avian Incident Monitoring Syst em, and the Incident Database System on October 31 , 201 2 did not identify any ecological incidents attributed to 2,4

- D choline salt. Although incident reporting is required under FIFRA Section 6(a)(2), the absence of additional reports in EIIS does not i ndicate that the chemical has no effects on wildlife; rather, it is possible that incidents have gone unreported. Registrations for 2,4

- D choline salt are relatively recent (first registration occurred March 2011), thus, the time frame for collecting inci dents is short. Given that 2,4

- D choline salt is similar in its toxicity and mode of action to other 2,4

- D forms, the full suite of 2,4

- D incidents was considered in this risk assessment. The 2,4

- D Problem Formulation contains a comprehensive list of all incidents reported in the EIIS as of August 6, 2012 (USEPA 2012). The database c ontained approximately 4 60 plant incidents

, 22 fish incidents

, 2

non

- specified aquatic incidents, 4 mammal incidents, 4 bird incidents, and 1 honeybee incident

.

Given that 2,4

- D is an herbicide, it is not surprising that the vast number of reported incidents are related to plants. Many of these were lawn/turf grass incidents where browning or mortality occurred as a result of the application (some applications were conside red “misuse,” but many were registered uses). In agricultural settings, direct treatment and spray drift were commonly cited as the cause of damage. Overall, the diversity and number of reported plant incidents supports the premise that 2,4

- D has the potential to affect non

- target plants.

### 49 Many of the other incidents (fish, aquatics, bird, mammals, honeybee) involved other chemicals in ad dition to 2,4

- D. The presence of more than one pesticide, especially if 2,4

- D is not explicitly tested for and detected, increases the uncertainty of the cause of the incident. Below is a list of the incidents that were most likely caused by 2,4

- D (Table 21 ). These incidents demonstrate that registered uses of 2,4

- D may have adverse effects

on non

- target fish and birds.

### 50 Table 21 . Selected Ecological Incidents A ssociated with 2,4

- D from the EIIS Database

Incident Number (Source) Taxa Magnitude Year State Use Legality of Use Certainty Category 2,4

- D Residues Other Chemicals Involved Comments

2,4

- D I000636

- 017 Catfish Several 1987 MO Home/ lawn Registered High probability N/R No Mortality caused by runoff into a pond

2,4

- D I000799

- 003 Turkey Cardinal Blackbird Duck Bream Bass Duck, Bream, Bass

– hundreds All others

– Unknown 1991 NC Home/lawn Not determined Probable 2,4

- D tested for in duck and blackbird tissue; 2,4

- D detected in
water

– 1 ppb Dicamba Mecoprop Carbaryl Diazinon Pentachlorophenol Oxamyl Mortality caused by ingestion (birds) and runoff into stream (fish)

2,4

- D B0000

- 300

- 37 Drum Bream Croaker 100 fish each 1984 SC N/R Not determined Probable N/R No Mortality caused by ingestion

2,4

- D I000925

- 001 Unknown fish 23000 1993 WV Right

- of

- way, rail Registered High probability Confirmed in water, concentration
not reported Triclopyr Mortality caused by drift into
stream

### 51 

## 5. Risk Characterization

Risk characterization is the integration of exposure and effects to determine the ecological risk associated with the proposed new uses for 2,4

- D choline salt . The risk characterization provides estimates and descriptions of the risk; articulates risk

ass essment assumptions, limitations, and uncertainties; synthesizes an overall conclusion; and provides risk managers with information to make regulatory decisions.

5.1 Risk Estimation

The risk quotient method was used to determine if 2,4

- D choline salt has the poten tial to cause adverse effects to non

- target organisms. In the risk quotient method, the estimated environmental concentrations (EECs) are divided by acute and chronic toxicity values. The resulting unit

- less risk quotients are compared to t he Agency’s levels of concern to determine the need f or regulatory action (Appendix G ).

5.1.1 Summary of Aquatic Risk Quotients

5.1.1.1 Risk Quotients for Fish

Risk qu otients were calculated for acute effects on freshwater amphibians and chronic effects on freshwater and estuarine/marine fish (Table 22 ) . Acute risk quotients for freshwater amphibians and fish ranged from <0.001 to 0.001 and did not exceed the acute listed or non

- listed species LOCs (0.05 and 0.1, respectively). Likewise, the chronic LOC of 1 was not exceeded for freshwater fish (range of < 0.001 to 0.002 ) or estuarine/marine fish (range of 0.09 to 0.53).

### 52 Table 22

. Acute Risk Quotients for Freshwater Amphibians and Chronic Risk Quotients for Freshwater Fish and Estuar ine/Marine Drinking Water Source (model) Use Scenario (modeled rate) Chronic risk to freshwater fish

60

- day EEC/ NOAEC

( NOAEC =

142 00 μg

ae/L) Acute risk to freshwater amphibians

Peak EEC/LC 50 (LC 50 = 278000 μg ae/L) Chronic risk to estuarine/ marine fish

60

- day EEC/ NOAEC

( NOAEC = 55.4 μg ae/L)

Surface Water (PRZM/EXAMS) Aquatic Exposure for 2,4

- D ( Parent )

Corn : IA Corn STD IL Corn STD IN Corn STD KS Corn STD MN Corn STD MS Corn STD NC Corn STD NE Corn STD OH Corn STD PA Corn STD ( 3 app. X 1.0 lbs a.e./acre ) 0.00 1

- 0.00 1 0.00 1

- 0.00 2 0.00 1

- 0.00 2 0.00 1

- 0.001 0.001

- 0.001 0.00 2

- 0.00 2 0.00 1

- 0.00 2 0.002

- 0.002 0.00 1

- 0.00 1

< 0.00 1

- < 0.001 <0.001

- <0.001 <0.001

- <0.001 <0.001

- <0.001 <0.001

- <0.001 <0.001

- <0.001 <0.001

- <0.001 <0.001

- <0.001 <0.001

- <0.001

< 0.001

- <0.001 <0.001

- <0.001 0.34

- 0.30 0.41

- 0.36 0.38

- 0.43 0.25

- 0.23 0.25

- 0.21 0.53

- 0.48 0.42

- 0.32 0.52

- 0.50 0.21

- 0.16 0.12

- 0.12

Soybean : MS Soybean STD ( 3 app. X 1.0 lbs a.e./acre ) 0.00 2

- 0.00 2 <0.001

- <0.001 0.39

- 0.38

Corn : MS Corn STD 1 ( 2 app. @ 1.0 lbs and 2 App @0.50 lb a.e./acre ) 0.00 2 <0.001 0.49

Corn : MS Corn STD 2 ( 3 app. X 1.0 lbs a.e./acre ) 0.00 2 <0.001 0.46

1 Post Emergence 2 applications at 0. 50 lb a.e./A
2 PRZM/EXAMS simulated EECs without spray drift fraction to evaluate spray drift contribution
3 P RZM/EXAMS simulation w as performed only for MS Corn based on highest EECs observed in 2,4

- D exposure
4 = 2,4

- D application rate (1.0 lb a.e/A) x [(0.035, the maximum conversion rate f or the terrestrial degradation of 2,4

- D in the terrestrial environment to 2,4

- DCP in laboratory studies) x (0.74, the molecular weight ratio of 2,4

- D to 2,4

- DCP)]
5
= 2,4

- D application rate (1.0 lb a.e/A) x [(0.017, spray drift con tribution of 2,4

- D) x (0.326, the maximum conversion rate from the anaerobic aquatic degradation of 2,4

- D to 2,4

- DCP from laboratory studies) x (0.74, the molecular weight ratio of 2,4

- D to 2,4

- DCP)]

### 53 5.1.1.2 Risk Quotients for Aquatic Invertebrates

A summary of risk quotients for acute and chronic exposures of 2,4

- D choline salt to freshwater and estuarine/marine invertebrates is presented in Table 2 3

, below

. R isk quotients ranged from <0.001 to 0.002 ( acute) and < 0.001 to 0.00 3 ( chronic ) for freshw ater invertebrates

. Risk quotients ranged from <0.001 to 0.001 (acute and chronic) for estuarine/marine invertebrates. None of the LOCs were exceeded for any scenario (acute listed = 0.05; acute non

- listed = 0.1; chronic = 1).

Table 23

. Acute and Chr onic Risk Quotients for Aquatic Invertebrates Exposed to 2,4

- D Choline Salt in Surface Water Drinking Water Source (model) Use Scenario (modeled rate) Acute risk to freshwater invertebrates

Peak EEC/LC 50 (LC 50 = 25000 μg ae/L) Chronic risk to freshwater invertebrates

21

- day EEC/NOAEC

(NOAEC = 16050 μg ae/L) Acute risk to estuarine/

marine invertebrates

Peak EEC/EC 50 (EC 50 = 49600 μg ae/L) Chronic risk to estuarine/ marine invertebrates

21

- day EEC/NOAEC

(NOAEC =

31800 μg

ae/L)

Surface Water (PRZM/EXAMS) Aquatic Exposure for 2,4

- D ( Parent )

Corn : IA Corn STD IL Corn STD IN Corn STD KS Corn STD MN Corn STD MS Corn STD NC Corn STD NE Corn STD OH Corn STD PA Corn STD ( 3 app. X 1.0 lbs a.e./acre ) 0.001

- 0.001 0.001

- 0.001 0.001

- 0.001 0.001

- 0.001 0.001

- 0.001 0.002

- 0.002 0.001

- 0.001 0.002

- 0.001 0.001

- 0.001 <0.001

- <0.001 0.001

- 0.001 0.002

- 0.001 0.002

- 0.001 0.001

- 0.001 <0.001

- <0.001

0.003

- 0.003 0.002

- 0.001 0.002

- 0.002 0.001

- 0.001 0.001

- 0.001 0.001

- <0.001 0.001

- <0.001 0.001

- <0.001 0.001

- <0.001

< 0.001

- <0.001 0.001

- 0.001 0.001

- <0.001 0.001

- 0.001 0.001

- <0.001 <0.001

- <0.001 0.001

- 0.001 0.001

- 0.001 0.001

- 0.001 0.001

- 0.001 <0.001

- <0.001

0.001

- 0.001 0.001

- 0.001 0.001

- 0.001 0.001

- <0.001 <0.001

- <0.001

Soybean : MS Soybean STD ( 3 app. X 1.0 lbs a.e./acre ) 0.002

- 0.002 0.002

- 0.002 0.001

- 0.001 0.001

- 0.001

Corn : MS Corn STD 1 ( 2 app. @ 1.0 lbs and 2 App @0.50 lb a.e./acre ) 0.002 0.003 0.001 0.001

Corn : MS Corn STD 2 ( 3 app. X 1.0 lbs a.e./acre ) 0.002 0.002 0.001 0.001

### 54 Drinking Water Source (model) Use Scenario (modeled rate) Acute risk to freshwater invertebrates

Peak EEC/LC 50 (LC 50 = 25000 μg ae/L) Chronic risk to freshwater invertebrates

21

- day EEC/NOAEC

(NOAEC = 16050 μg ae/L) Acute risk to estuarine/

marine invertebrates

Peak EEC/EC 50 (EC 50 = 49600 μg ae/L) Chronic risk to estuarine/ marine invertebrates

21

- day EEC/NOAEC

(NOAEC =

31800 μg

ae/L)

1 Post Emergence 2 applications at 0.50 lb a.e./A
2 PRZM/EXAMS simulated EECs without spray drift fraction to evaluate spray drift contribution
3 P RZM/EXAMS simulation w as performed only for MS Corn based on highest EECs observed in 2,4

- D
exposure 4 = 2,4

- D application rate (1.0 lb a.e/ A) x [(0.035, the maximum conversion rate f or the terrestrial degradation of 2,4

- D in the terrestrial environment to 2,4

- DCP in laboratory studies) x (0.74, the molecular weight ratio of 2,4

- D to 2,4

- DCP)]
5
= 2,4

- D application rate (1.0 lb a.e/A) x [(0.017, spray drift contribution of 2,4

- D) x (0.326, the maximum conversion rate from the anaerobic aquatic degradation of 2,4

- D to 2,4

- DCP from laboratory studies) x (0.74, the molecular weight ratio of 2,4

- D to 2 ,4

- DCP)]



### 5.1.1.3 Risk Quotients for Aquatic Plants

A summary of risk quotients for acute and chronic exposures of 2,4

- D choline salt to freshwater and estuarine/marine invertebrates is presented in Table 24 , below

. R isk quotients ranged from 0.002 to 0. 015 for non

- vascular aquatic plants and 0.021 to 0.194 for vascular aquatic plants. None of the risk quotients exceeded the LOC of 1 for aquatic plants.

Table 24

. Risk Quotients for Aquatic Plants Exposed to 2,4

- D Choline Salt in Surface Water Drinking Water Source (model) Use Scenario (modeled rate) Risk to non

- vascular plants

Peak EEC/EC 50 (EC 50 = 3880 μg ae/L) Risk to aquatic vascular plants

Peak EEC/EC 50 (EC 50 = 299.2 μg ae/L)

Surface Water (PRZM/EXAMS) Aquatic Exposure for 2,4

- D ( Parent )

Corn : IA Corn STD IL Corn STD IN Corn STD KS Corn STD MN Corn STD MS Corn STD NC Corn STD NE Corn STD OH Corn STD PA Corn STD ( 3 app. X 1.0 lbs a.e./acre ) 0.007

- 0.006 0.008

- 0.006 0.007

- 0.006 0.007

- 0.006 0.004

- 0.004 0.015

- 0.015 0.007

- 0.005 0.011

- 0.009 0.007

- 0.004 0.003

- 0.003 0.089

- 0.073 0.101

- 0.082 0.089

- 0.082 0.095

- 0.079 0.053

- 0.047 0.194

- 0.193 0.094

- 0.070 0.136

- 0.122 0.090

- 0.056 0.039

- 0.036

### 55 Drinking Water Source (model) Use Scenario (modeled rate) Risk to non

- vascular plants

Peak EEC/EC 50 (EC 50 = 3880 μg ae/L) Risk to aquatic vascular plants

Peak EEC/EC 50 (EC 50 = 299.2 μg ae/L) Soybean : MS Soybean STD ( 3 app. X 1.0 lbs a.e./acre ) 0.011

- 0.011 0.143

- 0.143

Corn : MS Corn STD 1 ( 2 app. @ 1.0 lbs and 2 App @0.50 lb a.e./acre ) 0.015 0.193

Corn : MS Corn STD 2 ( 3 app. X 1.0 lbs a.e./acre ) 0.015 0.189

1 Post Emergence 2 a pplications at 0.50 lb a.e./A
2 PRZM/EXAMS simulated EECs without spray drift fraction to evaluate spray drift contribution
3 P RZM/EXAMS simulation w as performed only for MS Corn based on highest EECs observed in 2,4

- D exposure
4 = 2,4

- D application rate (1.0 lb a.e/A) x [(0.035, the maximum conversion rate f or the terrestrial degradation of 2,4

- D in the terrestrial environment to 2,4

- DCP in laboratory studies) x (0.74, the molecular weight ratio of 2,4

- D to 2,4

- DCP)]
5
= 2,4

- D application rate (1.0 lb a.e/A) x [(0.017, spray drift con tribution of 2,4

- D) x (0.326, the maximum conversion rate from the anaerobic aquatic degradation of 2,4

- D to 2,4

- DCP from laboratory studies) x (0.74, the molecular weight ratio of 2,4

- D to 2,4

- DCP)]



### 5.1.2 Summary of Terrestrial Risk Quotients

5.1.2.1 Avian and Mammalian Risk Quotients

Acute toxicity risk quotients were based on the oral toxicity study for the northern bobwhite quail. Risk quotients ranged from 0.01 to 4.18. “Seeds” was the only dietary item that did not yield a risk quotient that ex ceeded the listed species LOC (0.1). The

non

- listed species LOC (0.5) was exceeded for small and medium birds consuming short grass, tall grass, broadleaf plants, and arthropods; and for large birds consuming short grass. The listed species LOC was excee ded for all of these scenarios as well as small and medium birds consuming fruits/pods; and large birds consuming tall grass, broadleaf plants, and arthropods. The chronic risk quotients ranged from 0.04 to 0.60 and did not exceed the chronic LOC of 1 (Ta ble 25 )

.

### 56 Table 2 5

. Summary of Avian Acute and Chronic Risk Quotients (RQs) for 2,4

- D Choline Salt for Foliar Applications

Feeding Category Chronic (d ietary

based ) RQs Acute (d ose - based ) RQs Small (20 g) Medium (100 g) Large (1000 g) 2,4

- D choline salt on herbicide

- tolerant corn and soybean

– 3 applications at 1 lb ae/A (12 day interval) Short grass 0.60 4.18** 1.87** 0.59** Tall grass 0.28 1.92** 0.86** 0.27* Broadleaf plants 0.34 2.35** 1.05** 0.33* Fruits/pods 0.04 0.26* 0.12* 0.04 Arthropods 0.24 1.64** 0.73** 0.23* Seeds 0.04 0.06 0.03 0.01 *Exceeds listed species LOC of 0.1 **Exceeds non

- listed species LOC of 0.5

The dose

- based acute mammalian risk quotients ranged from <0.01 to 0.57. The listed species LOC (0.1) was exceeded for small, medium, and large mammals consuming short grass, tall grass, broadleaf plants, and arthropods. In addition, small mammals consuming short grass also exceeded the non

- listed species LOC (0.5). Ch ronic dose

based risk quotients ranged from 0.32 to 50.2. The chronic LOC of 1 was exceeded for all size classes of mammals consuming all food items except for seeds. Chronic dietary

based risk quotients ranged from 0.36 to 5.78. The chronic LOC of 1 wa s exceeded for diets of short grass, tall grass, broadleaf plants, and arthropods (Table 2 6 ).

Table 2 6 . Summary of Mammalian Acute and Chronic Risk Quotients (RQs) for 2,4

- D Choline Salt Foliar Applications Risk Quotients Based on Kenaga Upper Bound EEC Dose

- Based RQs Chronic Dietary

Based RQs 15 g 35 g 1000 g

Acute Chronic Acute Chronic Acute Chronic

2,4

- D choline salt on herbicide

- tolerant corn and soybean

– 3 applications at 1 lb ae/A (12 day interval) Short grass 0.57** 50.2*** 0.49* 42.9*** 0.26* 23

. 0 *** 5.78*** Tall grass 0.26* 23.0*** 0.22* 19.7*** 0.12* 10.5*** 2.65*** Broadleaf plants 0.32* 28.2*** 0.27* 24.1*** 0.15* 12.9*** 3.25*** Fruits/pods 0.04 3.14*** 0.03 2.68*** 0.02 1.44*** 0.36 Arthropods 0.22* 19.7*** 0.19* 16. 8 *** 0.10* 9.00*** 2.27*** Seeds 0.01 0.70 0.01 0.60 <0.01 0.32 0.36 *Exceeds the acute listed species LOC of 0.1 **Exceeds the acute non

- listed species LOC of 0.5

*** Exceeds chronic LOC of 1.0

### 57 5.1.2.2 Plant Risk Quotients

Risk quotients exceeded the LOC (1) for all exposure scenarios . Risk quotients ranged from 1 to 90.62 for monocots and 12.35 to 1085.11 for dicots. Risk was attributed to both spray drift a nd runoff from treated fields (Table 2 7 ).

Table 2 7

. Summary of Risk Quotient s for Terrestrial Plants Exposed to 2,4

- D Choline Salt through Runoff and/or Spray Drift Plant Type Listed Status Dry Semi

- Aquatic Spray Drift 2,4

- D Choline Salt and EnlistTM on Corn and Soybeans

– single ground application at 1 lb ae/A
Monocot non

- listed 6.00* 51.00* 1.00* Monocot listed 10.66* 90.62* 1.78* Dicot non

- listed 74.07* 629.63* 12.35* Dicot listed 127.66* 1085.11* 21.28*

* Exceeds LOC of 1.

5.1.2.3 Non

- Target Insect Risk Quotients

Currently, EFED does not routinely quantify potential risks of pesticides to terrestrial

non

- target adult insects. Based on the acute contact data submitted for honeybee s , 2,4

- D choline salt is practically non

- toxic (LD 50 

### > 66 μg ae /bee). Bees or other b eneficial insects could be exposed to 2,4

- D choline salt through residues left on foliage or direct contact during the foliar spray application. Current data indicate that it is unlikely that such exposures would be lethal, although some sub

- lethal effect s were noted in the study (lethargy, immobility, loss of equilibrium, and hyper excitability ). While the honeybee is used as a surrogate for all terrestrial insects, there is uncertainty in this assumption in that

some other species of insects may be more sensitive to 2,4

- D choline salt

.

5.2 Risk Description

The results of this screening

- level risk assessment indicate that direct effects are not expected for aquatic organisms; birds, reptiles, and land

- phase amphibians (chronic), and terrestrial insects. There is insufficient information to determine how the proposed new uses of 2,4

- D choline salt will direct ly affect mamm als (acute and chronic), birds (acute)

, and terrestrial plants , and indirectly affect all taxonomic groups

. The registrant submitted

a stewardship plan (MRID 48862903) that is undergoing evaluation by the Biological Economics and Analysis Division. In addition, two risk assessment documents were supplied by the registrant and considered by EFED (MRIDs 48897101, 48897102). The risk asses sments focused on listed species in the six “launch” states; however, the methodology employed was not in line with methods used by the Agency (i.e., fitted spray drift curve, no air analysis, species sensitivity distributions). The following sections dis cuss the results of the risk quotient analysis, implications of incident data, and explore several additional analyses to further characterize the risks and elucidate potential mitigation options.

### 58 5.2 .1 Probit Slope Response Analysis of LOC Values and Ac ute RQ Values

As part of the risk estimation, the probability of mortality associated with the listed acute LOC values is estimated along with the probability of acute mortality occurring if exposure at the EEC actually occurs. The probability of mortalit y calculations are based on the probit slope dose

- response relationship. The probability of mortality for an exposed individual is calculated using an Excel spreadsheet tool IECV1.1 (Individual Effect Chance Model Version 1.1) developed by the U.S. EPA, O PP, Environmental Fate and Effects Division (June 22, 2004).

The model provides the option of inserting taxa

- specific probit slopes and confidence intervals. If specific information is not available, the model uses a default value of 4.5 for the probit s lope and 2 and 9 for the upper and lower 95% confidence interval bounds. For 2,4

- D choline salt , taxa

- specific data were only available for birds ; default values were used for mammals

.
Probabilities of mortality were only calculated for scenarios where the risk quotient exceeded the acute listed species LOC. For 2,4

- D choline salt, there were two groups that met this criterion

– birds and mammals (Table 2 8 ).

Table 2 8 . Probability of M ortality for an I ndividual B ird or M ammal for 2,4

- D Choline S alt RQ (range) Slope 95% Confidence Interval Odds (1 in...)
Birds 4.18

– 0.12 6.4 2.7 and 10.1 1

– 528,000,000 Mammals 0.57

– 0.10 4.5 2 and 9 7.35

– 294,000

5.2 .2 AgDrift Analysis for Terrestrial Plants, Birds, and Mammals

Applied 2,4

- D choline can drift from the treated area and still be present at concentrations that exceed acute levels of concern for birds, mammals, and terrestrial plants. Buffers may offer a potential mitigation st rategy to reduce the concentration of 2,4

- D choline salt that reaches non

- target organisms. 2 ,4

- D choline labels have a recommendation to use the 2,4

- D choline product with an ASABE S

- 572 droplet size classification of coarse/coarser spray quality. Given the limited option for droplet size in the current AgDRIFT ground module, the drop let size distribution of fine to medium/coarse ( D v0.5 

### of 341μm ) option with 90 th 

### data percentile and high boom w as used to estimate spray drift buffer distance s

. The results indicate that buffers could be set to mitigate adverse effects from spray drift
to non

- target monocots, mammals, and birds. Buffers for dicots would need to be greater than 1000 ft to mitigate the risk from spray drift, which is probably not a practical solution (Table 29).

The Agency explored an alternative approach to determine buffer distances using the label

- recommended droplet spectrum. The r egistrant submitted a spray drift field study (MRID 48844001, in review) with various drift red uction nozzles and formulations for spray drift management. A cursory review of the study showed that the combination of

### 59 an AIXR 11004 nozzle and the GF2726 formulation may be a feasible alternative for off

site drift management. The Agency considered th is specific combination of nozzle and formulation to determine the potential for off

- target movement of the 2,4

- D choline salt

. The deposition data show a biphasic dist ribution (Figure J

- 1, Appendix J ) with a bias toward near field deposition. To determine far

- field deposition, the Agency truncated the deposition data from 0 to10 feet and used 90 th 

### percentile data from 25 to 400 feet to dete rmine buffer distances (Figure J

- 2, Appendix J ). The d eposition curve was developed using Exponential Decay, Double, 4 Parameter equation using SigmaPlot version 10.0. The Exponential Decay, Double, 4 Parameter (EDDP) and various coefficients are listed below :

f= 25 (ft) + a*exp(

- b*x)+c*exp(

- d*x) Where : 25 ft represents 0 distance for the deposition curve

a = 0.0013

, b = 0.0388

, c = 0 .0 006 , and d = 0.0012

Table 29 shows that the buffer distances for dicots are shorter (62 to 202 ft) when estimated using the above equation as compared with the AgDRIFT model.

Table 29. Spray Drift Buffer Distances for 2,4

- D Choline Salt for Birds, Mammals, and Terrestrial P lants

Use

– herbicide

- tolerant soybean and corn Single application rate (lb ae /A) Fraction of

a

pplied Buffer distance (ground application) (ft) AgDRIFT 1 ED D P 2

Listed monocots 1 0.005628 135 NA Non

- listed monocots 1 0.010 66 NA Listed dicots 1 0.00047 >1000 202 Non

- listed dicots 1 0.00081 961 62 Listed mammals 1 0.175 3 NA Non

- listed mammals 1 0.877 3 NA Listed birds 1 0.024 23 NA Non

- listed birds 1 0.120 7 NA

1 AgDRIFT ground boom scenario with fine to medium/coarse droplet, high boom (50 inches), and 90 th data percentile
2 Represent deposition data (25 to 400 ft) from AXIR11004 nozzle and GF2726 formulation at boom height of 50 inches with 7mph (MRID 4884001) N A

- Not applicable due to truncated data.



### 5.2. 3 Risk to Aquatic Ve r tebrates and Invertebrates

The proposed uses of 2,4

- D choline salt did not exceed any levels of concern for chronic exposures to freshwater fish and estuarine/marine fish. Likewise, risk quotients for freshwater and estuarine/marine invertebrates did not e xceed acute or chronic LOCs

. Risk quotients could not be calculated for acute effects to freshwater and estuarine/marine fish because the toxicological values were non

- definitive. Thus, the

non

- definitive values were compared directly with the EECs. The highest peak EEC (MS Corn Sce nario = 58 μg ae/L) is less than the freshwater fish LC 50 

### (LC 50 

### > 48000 μg ae/L) and the estuarine/marine fish LC 50 

### (LC 50 

### > 80240 μg ae/L). This suggests that the

### 60 concentration of 2,4

- D in aquatic environments as a result of the proposed new uses on

corn and soybean is not high enough to result in acute adverse effects to freshwater and estuarine/marine fish.

Data from the European Footprint database and ECOTOX database indicate that 2,4

- DCP, a major degradate of 2,4

- D, is more toxic to fish and inverte brates than 2,4

- D. Footprint database toxicity values could not be evaluated because the Agency did not have access to the actual studies. Likewise, the open literature studies from the ECOTOX database were not reviewed in

- depth. However, based on the a quatic EECs for 2,4

- DCP that were generated from the new uses on herbicide

- tolerant corn and soybean, it is unlikely to pose a problem for fr eshwat er fish and invertebrates. In all cases, the EECs for 2,4

- DCP are much lower than the reported toxicity valu es (Table 30 )

.

Table 30

. 2,4

- DCP Toxicity Values and Toxicity Thresholds for Fr eshwater Fish and Invertebrates Reported acute value Acute EEC s Reported chronic value Chronic EECs

Freshwater fish 1000 μg/L 2 

### 4.66 μg/L 290 μg/L 2 

### 3.84 μg/L

Freshwater invertebrates 1400 μg/L 1,2 

### 4.66 μg/L 210 μg/L 2 

### 3.62 μg/L

1 

### European Footprint Database
2 

### ECOTOX Database

Incident data suggest registered uses of 2,4

- D result in mortality and toxic effects in freshwater fish. However, the application rate may have been higher than those of the proposed new uses. Given that the risk quotients, which were modeled with the hi ghest application rates for herbicide

- tolerant corn and soybean, were far below the LOCs, it is not expected that aquatic organisms will be at direct risk from these proposed new uses.

The proposed 2,4

- D choline salt formulations for registration are repo rted to maintain some properties that may reduce spray drift to non

- target areas. While EFED has received some information regarding these properties, the full suite of data necessary to analyze these properties is not available. Given that these data an d other potential mitigation options are not finalized, EFED has determined that insufficient information is available to make an effects call for indirect effects to aquatic invertebrates and fish.

5.2.4 Risk to Terrestrial Animals

Mammals Risk quotients for mammals exceeded the Agency’s LOCs for mammals for acute dose

based exposure and chronic dose

- based and dietary

- based exposure. The listed species LOC was exceeded for small, medium, and large mammals consuming short grass, tall grass, broadleaf plants , and arthropods; small mammals consuming short grass exceeded the non

- listed species LOC. The chronic dose

- based LOC was exceeded for all si ze

### 61 classes of mammals consuming all food items except for seeds. The chronic dietary

based LOC was exceeded for diets of short grass, tall grass, broadleaf plants, and arthropods for mammals. Thus, the risk quotient analysis predicts direct risks are
exp ected for listed mammals.

Likewise, indirect effects are predicted for mammals based on the risk quotients that exceeded the non

- listed mammal LOC

, terrestrial plants

, and birds. Indirect effects may occur when mammals depend on a terrestrial plant, bi rd, or other mammal that is adversely affected by 2,4

- D choline salt. Terrestrial plants provide food and habitat for mammals. Birds and other mammals may be food sources for listed species as well.

For acute exposures, the probit slope response analysi s indicated a 1 in 7.35 chance of an individual mammal being affected at the highest RQ and a 1 in 294,000 chance of an individual mammal being affected at the lowest RQ that exceeded the LOC.

2 ,4

- D is currently undergoing a Tier I Endocrine Disruptor Scr eening as re quired by FFDCA section 408(p). Effects noted in the two

- generation rat reproduction study included decreased female weight gain (F 1 

### ) and male renal tubule alteration (F 0 

### and F 1 

### ) in the parental generations. An increase in gestation length wa s documented as a reproductive effect and pup body weight was decreased compared with the controls.

The proposed 2,4

- D choline salt formulations for registration are reported to maintain some properties that may reduce spray drift to non

- target areas. While EFED has received some information regarding these properties, the full suite of data necessary to analyze these properties is not available. Given that these data and other potential mitigation options are not finalized, EFED has determined that in sufficient information is available to make an effects call for direct and indirect effects to mammals.

Birds, Reptiles, and Terrestrial

- Phase Amphibians Avian risk quotients exceeded the LOC for acute exposures. The non

- listed species LOC was exceeded for small and medium birds consuming short grass, tall grass, broadleaf plants, and arthropods; and for large birds consuming short grass. The listed species LOC was exceeded for all of these scenarios as well as small and medium birds consuming fruits/pods; and large birds consuming tall grass, broadleaf plants, and arthropods. Thus, the risk quotient analysis indicates that direct effects are predicted for birds on an acute basis ; no chronic risks are expected . Incident data also support this conclusion. Several incidents (~4) involving birds have been reported to the Agency. In particular, one incident involved four species of birds (blackbird, cardinal, duck, and turkey. 2,4

- D acid was applied to a lawn and an unkno wn number of birds were reported to have died via ingestion of the pesticide. 2,4

- D was detected in surface water at the site; however it was not specifically detected in any of the bird tissues that were sampled. An additional uncertainty is the applica tion of six other pesticides in a similar time frame (dicamba, mecoprop, carbaryl, diazinon, pentachlorophenol, and oxamyl).

Based on the risk quotient analysis, i ndirect effects from the proposed 2 ,4

- D choline salt uses are predic ted for birds. Several non

- listed bird LOCs were exceeded. Birds that

### 62 depend on terrestrial plants, mammals, or other birds for habitat and food may be affected

as the risk quotient analysis predicts risks to these groups.

Effects that may be seen in birds prior to death ar e lethargy, reduced reaction to external stimuli, depression, lower limb weakness, wing droop, prostrate posture, loss of righting reflex, and a ruffled appearance. Other effects may include a drop in body weight and food consumption ; however, in laborat ory studies, the birds began to recover several days after the acute exposure had taken place.

The proposed 2,4

- D choline salt formulations for registration are reported to maintain some properties that may reduce spray drift to non

- target areas. While EFED has received some information regarding these properties, the full suite of data necessary to analyze these properties is not available. Given that these data and other potential mitigation options are not finalized, EFED has determined that insuffic ient information is available to make an effects call for direct (acute only) and indirect effects to birds, reptiles, and terrestrial

- phase amphibians.

Terrestrial insects were not identified to be at risk from the proposed new uses of 2,4

- D choline salt , based on honey bee toxicity data

.

5.2. 5 Risks to Terrestrial Plants

All terrestrial plant ri sk quotients exceeded the LOC; r isk was a result of spray drift and runoff. Thus, the risk quotient analysis indicates that direct effects are predic ted from the proposed new uses of 2,4

- D choline salt to terrestrial plants. Incident data support this conclusion as the majority of incidents reported to the agency were for plants (~460)

. 2,4

- D choline salt is an herbicide, thus it is not unexpected that even s mall amounts of spray drift or runoff could cause adverse effects in non

- target species. It should be noted that none of these incidents were specifically for 2,4

- D choline salt as the initial registration for this chemical is relatively new; all the inci dents were all for other older forms of 2,4

- D.

A further uncertainty is attached to the 2,4

- D choline salt/glyphosate product. The product contains two herbicides with different modes of action; however, no terrestrial plant data for this formulation are available. It is unknown if such a formula tion will have additive or synergistic effects (increased toxicity) or interference effects (decrease d toxicity) on terrestrial plants. Taking a con servative approach, it is possible that the 2,4

- D choline salt/glyphosate formulation will be more to xic to pla nts than the single active ingredient products.

The risk quotient analysis predicted i ndirect effects for terrestrial plants. Plants may depend on other plants to modify the environment so that they can grow (e.g., succession in a field). Plants may als o rely on birds and mammals for pollinator a nd seed dispersal services; the risk quotient analysis suggests that birds and mammals may be at direct risk from the proposed 2,4

- D choline salt new uses.

### 6 3 Based on the risk quotient analysis, dicots were more sensitive to 2,4

- D choline salt than monocots. The spray drift analysis, using the AIXR 11004 nozzle and the GF2726 formulation , indicates that buffers of 62 feet (non

- listed) and 202 feet (listed) is sufficient to protect dicots from exposures of 2,4

- D choline salt that exceed the Agency’s levels of

concern.

In addition to death, effects seen in plants may include decreased st em growth, decreased weight, necro sis, leaf and stem curl, wilting, and adventitious root growth.

Potential effects from the volatilization of 2,4

- D choline salt after application to fields were also considered. A plant vapor study was submitted to evalu ate the effects that 2,4

- D vapor from a treated field may have on neighboring non

- target species (MRID 48911801). The study did not use controls and presented qualitative observations on the percent of visual plant damage (necrosis, cupping of leaves at m argins, epinasty, twising of foliage, swelling or increased growth on the main stem at petiole attachment) for grapes, cotton, tomato, and soybeans. Grape was the most sensitive species followed by cotton, tomato, and then soybean. Plant damage endpoints are not normally used quantitatively in risk assessments and their sensivity, compared with growth/weight endpoints , is unknown.

In addition to the laboratory study, the registrant submitted several field studies that related plant damage in grape, cotto n, and soybean to growth or yield endpoints (Table 31 ). The studies were all con sidered scientifically sound and appropriate for qualitative incorporation into a risk assessment. All were field studies and there was variation in the methodology and timin g of measur emen ts. Crop y ields were measured at the end of the growing season or harvest . The height endpoint was measured at 14 and 28 days after treatment, but only the 14 day value is presented here as this corresponds to the vegetative vigor guidelin e study. In addition to variation in field sites (location, year, month), some fields also received applications of pesticides (not herbicides) to control insects and other pests. These variables introduce some uncertainty into the studies; however, they do simulate real

- life field conditions. Consequently, the results of the studies are considered appropriate for risk characterization.

Tabl e 31. Percent of Plant Damage Producing Significant Effects in Growth/Yield for Grape, Cotton, and S oybean Species Percent Damage Endpoint Citation

Grape 20% Growth/Yield Ogg et al. 1991 Cotton 58% Yield Marple et al. 2008 Cotton 62

- 66% Yield Everitt and Keeling 2009 Soybean 35% Yield Robinson et al. unpublished Soybean 35% Yield Andersen et al. 2004

### 64 Soybean 52% Height/Yield Kelley et al. 2005

Information regarding the effects of vapor phase 2,4

- D on grapes and cotton was also contained within the vapor

- flux study (MRID 48862902). In this study, fields were treated with a 2,4

- D choline salt formulation at an application rate of 5 lb ae/A. Plants were placed near a series of air monitoring stations approximately 1 hour after the herbicide was applied; this ensured that all of the effects were the result of vapor

- phase exposures rather than sp ray drift. Air monitoring stations were set at 5 and 15 m beyond the field’s edge and several sets were located along each side of the field to capture air concentrations that differed as a result of wind direction. Plants were also placed directly on th e field; no air monitoring station was associated with these plants. Plants were left in the field for 3 days after treatment and then removed to a greenhouse where they were observed for 27 days. Phytotoxic effects (qualitative) were scored on a scale o f 0 (no damage) to 100% (dead plant) and compared with controls. The only plants to show outward signs of damage were the grape (0.6% damage) and cotton (40% damage) plants located directly on the field. This study suggests that at 5 m from the edge of t he field, plants do not sustain damage from the revolatilization of 2,4

- D choline salt on the treated field.

Considering the results from the plant damage studies, the vapor

- flux study, and the laboratory vapor

- phase study, a conservative approach was tak en in selecting endpoints to characterize risk from vapor

- phase transport. At 20% physical damage, the grape had the lowest damage rate that resulted in statistically significant reductions in yield/growth. Grape was also the most sensitive species teste d in the laboratory vapor

- phase study. Using the percent of visual injury for grape, an endpoint of 1.9 μg ae/m 3 

### per hour was visually identified as the concentration that produced 20% physical damage.

The PERFUM model was used to estimate the off

- field distances for various concentrations of 2,4

- D as predicted from the vapor flux data (see Section 3.2.4 for more detail). Plant endpoints were selected based on three possible exposure periods: 1 hour, 4 hours, and 8 hours. These durations were selected based on the data in the vapor

- phase study (see above). To achieve a concentration of 1.9 μg ai/m 3 

### per hour in one hour, the atmospheric concentratio n of 2,4

- D would need to be 1.9 μg ai/m 3 

### per hour. To achieve the same concentration over a 4 hour perio d, the concentration of 2,4

- D would need to be 0.475 μg ai/m 3 

### per hour (1.9 / 4 hours). Likewise, the air concentration for an 8 hour exposure period is 0.238 μg ai/m 3 

### per hour (1.9 / 8 hours). The following graph (Figure 4) shows the vapor phase curves for the three different exposure durations. Horizontal line s mark the endpoint (1 hour = 1.9; 4 hours = 0.475; and 8 hours = 0.238 μg ai/m 3 

### per hour). The model predicts no adverse damage to plants off

- field for any of the exposure scenarios.

### 65 Figure 4. Vapor Phase Curves for Various Exposure Durations of 2,4

- D

The risk quotient analysis indicates there may be risks to terrestrial plants from runoff and spray drift; however, the proposed 2,4

- D choline salt formulations for registration are reported to maintain some properties that may reduce spray drift to non

- target areas. While EFED has received some information regarding these properties, the full suite of data necessary to analyze these properties is not available. Given that these data and
ot her potential mitigation options are not finalized, EFED has determined that insufficient information is available to make an effects call for direct and indirect effects to terrestrial plants.

5.2.6 Risks to Aquatic Plants

Aquatic vascular and non

- vasc ular plants yielded risk quotients below the LOC for 2,4

- D

. Risks from 2,4

- DCP were dismissed as a preliminary scan of the open literature indicates it is less toxic to vascular and non

- vascular plants than 2,4

- D. Based on the risk quotient analysis, direct risks to aquatic plants are not expected.

The proposed 2,4

- D choline salt formulations for registration are reported to maintain some properties that may reduce spray drift to non

- target areas. While EFED has received some information regarding these properties, the full suite of data necessary to analyze these properties is not available. Given that these data and other potential

### 66 mitigation options are not finalized, EFED has determined that insufficient inf ormation is available to make an effects call for indirect effects to aquatic plants.

5.3 Listed Species Assessment

The screening

- level analysis for 2,4

- D choline salt indicated that there was insufficient information to determine if there were direct effe cts to mammals (acute and chronic); birds, reptiles, and land

- phase amphibians (acute); and terrestrial plants . Indirect effects

are determined by assessing the potential for reduction of prey base or habitat modification of listed taxa ; however, there wa s insufficient information to determine if there were indirect effects to any taxa (Table 32 ).

Table 32

. Listed Species Risks Associated with the Proposed New Uses for 2,4

- D Choline Salt

Listed Taxa Direct Effects Indirect Effects 1



### Terrestrial and semi

aquatic plants:

Monocots

Dicots Insufficient information Insufficient information Insufficient information Insufficient information

Birds Insufficient information

– Acute No

– Chronic Insufficient information

Terrestrial

- phase amphibians 2 

### Insufficient information

– Acute No

– Chronic Insufficient information

Reptiles 2 

### Insufficient information

– Acute No

– Chronic Insufficient information

Mammals Insufficient information

– Acute Insufficient information

– Chronic Insufficient information

Aquatic plants: Vascular Non

- vascular No No Insufficient information Insufficient information

Freshwater fish No

– Acute No

– Chronic Insufficient information

Aquatic

- phase

amphibians 3 

### No

– Acute No

– Chronic Insufficient information

Freshwater invertebrates No

– Acute No

– Chronic Insufficient information

Mollusks No

– Acute No

– Chronic Insufficient information

Marine/estuarine fish No

– Acute No

– Chronic Insufficient information

### 67 Listed Taxa Direct Effects Indirect Effects 1



### Marine/estuarine

invertebrates No

– Acute No

– Chronic Insufficient information

Terrestrial invertebrates No Insufficient information

1 

### Indirect effects to a listed species occur when its prey base is reduced or habitat is modified; indirect effects are assumed for all taxa based on potential effects to terrestrial plants and obligate relationships with birds and/or mammals.
2 

### Birds are surrogates for reptiles and terrestrial

- phase amphibians.
3 

### Freshwater fish are surrogates for aquatic

- phase amphibians.

5.3. 1 Data Gaps and Uncertainties

Avian Acute Oral Toxicity Test for Passerines (850.2100): Data are required for one passerine species when a chemical is intended for outdoor use. The current method of calculating a weight

- adjusted LD 50 

### using bobwhite quail or mallard duck data may over

or under

- estimate risks to passerines because these birds may metabolize the chemical differently. A protocol for the study should be submitted to EPA for approval prior to study initiation. This study has also been identified as a gap in the 2,4

- D Problem Formulation (USEPA 2012, D402410).

Estuarine/Marine Invertebrate Chron ic Toxicity Test (850.1350): No acceptable data are available for the chronic toxicity of 2,4

- D choline salt to marine/estuarine invertebrates. Currently, the toxicological effects for estuarine/marine invertebrates on a chronic basis remain unknown for 2,4

- D choline salt, although this assessment estimated a chronic value based on an acute

- to

- chronic ratio using freshwater invert ebrate data. The 2,4

- D Problem Formulation identifies this as a gap, but concludes that chronic effects are unlikely, given the degradation rate of 2,4

- D acid in water (USEPA 2012, D402410). The acute

- to

- chronic ratio method was considered valid and prot ective in lieu of actual data.

Terrestrial Plant Seedling Emergence and Vegetative Vigor Tests (850.4100, 850.4150): Typical end

- use data are required for terrestrial plants. In the case of the new 2,4

- D choline salt registrations, no information is ava ilable for the two 2,4

- D choline salt formulations, nor the EnlistTM formulation, which is a mixture with glyphosate. For the 2,4

- D choline salt

- glyphosate formulation, it is anticipated that there could be additive

, synergistic, or interference between th e two herbicides, which could cause increased or decreased toxicological effects than are predicted by single ai data. In lieu of these data, toxicity information from other 2,4

- D formulations was used as a surrogate ; however
t hese surrogat es did not cont ain glyphosate. This represents a point of uncertainty regarding the effects to terrestrial plants in the current analysis.

Terrestrial Plant Vegetative Vigor Test with Vapor Phase Exposure (non

- guideline): 2,4

- D is known to volatilize from the field an d drift off site under certain environmental conditions. EFED evaluated a vapor

- phase study on grapes, cotton, soybean, and tomato;

### 68 however, the methodology did not include a control, did not measure growth/weight parameters, and was not well

- aligned with the 850.4150 protocol. As such, the results from the current vapor

- phase study are of very limited value; however, they represent the best information available at the time the risk assessment was prepared. Thus, the data were used in the risk descripti on section to characterize potential risk from 2,4

- D vapor coming off of fields. A vapor

- phase study with vegetative vigor endpoints is being recommended to further characterize the risk to plants from this exposure route.

Additionally, the following u ncertainties were identified for this risk assessment:

• For terrestrial organisms, only dietary exposure to 2,4

- D choline salt was assessed.

• The studies with vapor

- phase data yielded opposite conclusions regarding the potential for effects to terrestrial plants. Neither study measured quantitative endpoints and the laboratory study did not use a control. There remains uncertainty regarding the effects of vapor

- phase exposures on non

- target plants.

• For freshwater fish, birds, and terrestrial insects, definitive acute toxicity data were not available. Acute data were presented as greater than values, making it possible to conservatively compare the toxicity value directly to the EECs to estimate potential risk.

• For terrestrial plants, vegetative vig or toxicity values for monocots were non

definitive. The EC 25 

### (a greater than value) was compared directly to the EECs to assess the likelihood of risk. The monocot vegetative vigor NOAEC was a less than value; however, given that in dicots, seedling eme rgence data were more sensitive than the vegetative vigor data, the same pattern was assumed to hold true for monocots. Consequently, the monocot seedling emergence NOAEC was assumed to be the most sensitive monocot NOAEC and used to calculate risk quotie nts. If this assumption was false, then the analysis may have under

estimated the risk to listed monocots.

• In the absence of chronic data for marine/estuarine invertebrates, an acute

- to

chronic ratio was calculated to estimate the NOAEC for Eastern oyste r.

• This risk assessment only considered the most sensitive of the species evaluated in the registrant

- submitted studies. The position of the tested species relative to the distribution of all species’ sensitivities to 2,4

- D choline salt is unknown. Extra polating the risk conclusions from the most sensitive tested species to non

tested species may either underestimate or overestimate the potential risks to those species.

• 2,4

- D is currently undergoing a Tier I Endocrine Disruptor Screening as required by FFDCA section 408(p) . The results of the screening analysis are not yet available

.

### 69 

## 6

. References

Andersen, S.M., S.A. Clay, L.J. Wrage, and D. Matthees. 2004. Soybean foliage residues of dicamba and 2,4

- D and correlation to application rates and yield. Agronomy Journal , 96:750

- 760.

Anderson, A.M, Byrtus, G., Thompson J., Humphries, D., Hill, B., a nd Bilyk, M., 2002. Baseline Pesticide Data for Semi

- Permanent Wetlands in the Aspen Parkland of Alberta. Albeta Environment, Publication No. T/673.

Everitt, J.D. and J.W. Keeling. 2009. Cotton growth and yield response to simulated 2,4

- D and dicamba drift. Weed Technology , 23:503

- 506.

Fletcher, J.S., J.E. Nellsen, T.G. Pfleeger. 1994. Literature review and evaluation of the EPA food

- chain (Kenaga ) nomogram, an instrument for estimating pesticide residues on plants. Env. Toxicol. Chem. 13:1381

- 1391.

Hoerger, F. and E. E. Kenaga. 1972. Pesticide residues on plants: correlation of representative data as a basis for estimation of their magnitude in the environment. in : F. Coulston and F. Korte (editors), Environmental Quality and Safety: Chemistry, Toxicology, and Technology. Vol I. Georg Thieme Publishers, Stuttgart, West Germany, pp. 9

- 28.

Kelley, K.B., L.M. Wax, A.G. Hager, and D.E. Riechers. 20 05. Soybean response to plant growth regulator herbicides is affected by other postemergence herbicides. Weed Science, 53:101

- 112.

Majewski , M.S. and P.D. Capel. 1995. Pesticides in the atmosphere: distribution, trends, and governing factors. Ann Arbor Press, Inc. Chelsea, MI.

Marple, M.E., K. Al

- Khatib, and D.E. Peterson. 2008. Cotton injury and yield as affected by simulated drift of 2,4

- D and dicamba. Weed Technology , 22:609

- 614.

Ogg, A.G. Jr., M.A. Ahmedullah, and G.M. Wright. 1991. Infl uence of repeated applications of 2,4

- D on yield and juice quality of concord grapes ( Vitis labruscana ). Weed Science , 39(2):284

- 295.

Pfleeger, T.G., A. Fong, R. Hayes, H. Ratsch and C. Wickliff. 1996. Field evaluation of the EPA (Kenaga) nomogram, a m ethod for estimating wildlife exposure to pesticide residues on plants. Env. Toxicol. Chem. 15:535

- 543, 1996. U.S. Environmental Protection Agency. 1998. Guidelines for Ecological Risk Assessment. Risk Assessment Forum, Office of Research and Develo pment, Washington, D.C. EPA/630/R

- 95/002F. April 1998.

Robinson, A.P., V.M. Davis, D.M. Simpson, and W.G. Johnson. In review . Response of soybean yield components to 2,4

- D. Weed Science

.

### 70 U.S. Environmental Protection Agency. 2003. 2,4

- D: Health E ffects Division (HED) Metabolism Assessment Review Committee (MARC) decision document. DP Barcodes D293119 and D293128. Chemical ID Number 030001. Case Number 0073.

US EPA. 2004. Revised 2,4

- D Drinking Water Assessment for the Health Effects Division (HED) Reregistration Eligibility Decision Document. (DP 286666).

U.S. Environmental Protection Agency. 2004. Overview of the Ecological Risk Assessment Process in the Office of Pesticide Programs, U.S. Environmental Protection Agency. Listed and Threatened Species Effects Determinations. Office of Prevention, Pesticides and Toxic Substances, Office of Pesticide Programs, Washington, D.C. January 23, 2004.

U.S. Environmental Pr otection Agency. 2005 a . Generic Format and Guidance for the Level I Screening Ecological Risk Assessments Conducted in the Environmental Fate and Effects Division. Office of Pesticide Programs, Washington, D.C. January 24, 2005.

U.S. Environmental P rotection Agency. 2005b. Reregistration eligibility decision for 2,4

- D. Office of Prevention, Pesticides, and Toxic Substances, (7508C) EPA 738

- R

- 05

- 002. June 2005.

U.S. Environmental Protection Agency. 2005c. Revised screening level ecological risk assessment of polychlorinated dibenzodioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) contaminants from technical products of 2,4

- dichlorophenoxyacetic acid (2,4

- D). Confidential memo.

U.S. Environmental Protection Agency. 2011. AERSCREEN Use r’s Guide ( EPA

- 454/B

- 11

- 001)

. Office of Air Quality Planning and Standards, Air Quality Assessment Environmental Fate and Effects Division, Office of Pesticide Programs, Research Triangle Park, North Carolina

.


### U.S. Environmental Protection Agency. 2012. EFED Registration review problem formulation for 2,4

- D. Environmental Fate and Effects Division, Office of Pesticide Programs, Washington, D.C.

van den B. M. Birnbaum, L.S., Denison, M, De vito, M, Farland, W, Feeley, M, Fiedler, H, Hakansson, H., Hanb erg,A., Laurie Haws, L., h Martin Rose, M Stephen Safe, S., Dieter Schrenk, D., Tohyama, C, Angelika Tritscher,A., Tuomisto, J., Tysklind, M., Nigel Walker, N., and Peterson, R.E. 2006. Review

- The 2005 World Health Organization Reevaluation of Human and Mammalian Toxic Equivalency Factors for Dioxins and Dioxin

- Like Compounds . Toxicological Sci. 93: 223

- 241.

### 71 

## Appendix A. Registrations and Uses for 2,4

- D Choline Salt

Use Max. Single App. Rate (lbs ae/A) Max. No. of App. per Year Min. Reapp. Interval (d) Max. Annual App. Rate (lbs ae/A) App. Method

Cereal grains 1.25 1 post

emergence 1 preharvest NS A 1.75 Ground or aerial spray Broadcast

Field corn and
pop corn 1 (preplant or preemergence) 0.5 (postemergence) 1.5 (preharvest)

(3 total) 1 application per crop stage NS 3 Ground or aerial spray Broadcast Directed band

Sweet corn 1 (preplant or preemergence) 0.5 (post emergence)

(1.5 total) 1 application per crop stage 21 1.5 Ground or aerial spray Broadcast Directed band

Grain or forage sorghum 1 (amines, acid, salts) 0.5 (esters)

(1.5 total) 1 NR B 1 (amines, acid, salts) 0.5 (esters) Ground or aerial spray Broadcast Directed band

Soybeans 1 1 NR 1 Ground or aerial spray Broadcast

Sugarcane 2 (preemergence) 2 (postemergence)

(4 total) 1 application per crop stage NS 4 Ground or aerial spray Broadcast or band

Rice 1 (preplant) 1.5 (postemergence)

(2.5 total) 1 application per crop stage NS 1.5 Ground or aerial spray Broadcast or

s pot treatment

Pome fruits 2 2 75 4 Broadcast ground or spot
treatment

Stone fruits 2 2 75 4 Broadcast ground or spot
treatment
Nut orchards, pistachios 2 2 30 4 Broadcast ground or spot
treatment Established grass pastures, rangeland, and perennial grasslands not in agricultural 2 2 30 4 Ground or aerial spray Broadcast or spot

### 72 

## Appendix A. Registrations and Uses for 2,4

- D Choline Salt

Use Max. Single App. Rate (lbs ae/A) Max. No. of App. per Year Min. Reapp. Interval (d) Max. Annual App. Rate (lbs ae/A) App. Method

production

Ornamental turf 1.5 2 NS 3 Broadcast ground or spot
treatment Grass (turf) grown for seed and sod 2 2 21 4 Broadcast ground or spot
treatment Fallow land and crop stubble 2 2 30 4 Ground or aerial spray Broadcast Forest site preparation, forest roadsides, brush control, established conifer release 4 1 NR 4 Ground or aerial spray Broadcast

Tree and brush control 8 lb ai/100 gal (basal spray, cut surface

– stumps, frill) 2 ml of 4 lb ae/ injection site (injection) 1 NR 4 (broadcast only) Ground or aerial spray Broadcast, spot, basal, frill, cut stump or injection

Non

- cropland 4 2 30 4 Ground or aerial spray Broadcast or spot Aquatic weed control (irrigation ditch bank application) 2 2 30 (broadcast only) 4 Boat or aerial
spray Broadcast or spot Aquatic weed control (surface application for floating and emergent weeds) 4 2 21 (broadcast only) 8 Boat or aerial
spray Broadcast or spot

Aquatic weed control (surface application or subsurface injection for submersed weeds) 4 ppm ae/A (10.8 lb ae/Acre foot) 2 21 10.8 lb ae/Acre foot Boat or aerial
spray Broadcast or spot

A NS means “not stated.”

B NR means “not relevant.”

### 73 Appendix B. Major and Minor Degradates Identified in Environmental Fate Studies

Chemical Name (CAS No.) Molecular Formula Molecular wt .: g/mol e Chemical Structure Maximum Formed

2,4

- Dichlorophenol [ 2,4

- DCP ] (120

- 83

- 2) C 6 H 4 Cl 2 O 163.0 32. 6 % of applied in Anaerobic aquatic study

Chlorohydroquinone [CHQ] (615

- 67

- 8) C 6 H 3 (OH) 2 Cl 144.56 16.0 % of applied in aerobic aquatic study

1,2,4

- benezenetriol (533

- 73

- 3) C 6 H 6 O 3 126.11 37 .0 % formed of applied in aquatic photo

- degradation study

4

- chlorophenol (106

- 48

- 9) C 6 H 5 ClO 128.56 <2.0% formed of applied in anaerobic aquatic metabolism study [Intermediate degradate]

2,4

- dichloroanisol [ 2,4

- DCA ] (553

- 82

- 2) C 7 H 6 Cl 2 O 177.03 <2.0% formed of applied in aerobic soil metabolism study

4

- Chlorophenoxyacetic acid [ 4

- CPA] (122

- 88

- 3) C 8 H 7 ClO 186.59 <2.0% formed of applied in an aerobic aquatic metabolism study

### 74 

## Appendix C

. SIP and STIR Results for 2,4

- D Choline Salt

SIP

Table 1. Inputs Parameter Value Chemical name 2,4

- D choline salt Solubility (in water at 25 o C; mg/L) 569

Mammalian LD 50 (mg/kg

- bw) 441 Mammalian test species laboratory rat Body weight (g) of "other" mammalian species

Mammalian NOAEL (mg/kg

- bw) 5 Mammalian test species laboratory rat Body weight (g) of "other" mammalian species

Avian LD 50 (mg/kg

- bw) 218.7 Avian test species northern bobwhite quail Body weight (g) of "other" avian species Mineau scaling factor 1.15

Mallard NOAEC (mg/kg

- diet) Bobwhite quail NOAEC (mg/kg

- diet) 962 NOAEC (mg/kg

- diet) for other bird species Body weight (g) of other avian species NOAEC (mg/kg

- diet) for 2nd other bird species Body weight (g) of 2nd other avian species

Table 2. Mammalian Results Parameter Acute Chronic Upper bound exposure (mg/kg

- bw) 97.8680 97.8680 Adjusted toxicity value (mg/kg

- bw) 339.1998 3.8458 Ratio of exposure to toxicity 0.2885 25.4480

Conclusion* Exposure through drinking water alone is a potential concern for mammals Exposure through drinking water alone is a potential concern for mammals

Table 3. Avian Results

### 75 Parameter Acute Chronic Upper bound exposure (mg/kg

- bw) 460.8900 460.8900 Adjusted toxicity value (mg/kg

- bw) 157.5579 102.2590 Ratio of exposure to acute toxicity 2.9252 4.5071

Conclusion* Exposure through drinking water alone is a potential concern for birds Exposure through drinking water alone is a potential concern for birds

*Conclusion is for drinking water exposure alone. This does not combine all routes of exposure. Therefore, when aggregated with other routes ( i.e ., diet, inhalation, dermal), pesticide exposure through drinking water may contribute to a total exposure that has potential for effects to non

target animals.



## STIR



## Input

Application and Chemical Information
Enter Chemical Name 2,4

- D Choline salt Enter Chemical Use herbicide Is the Application a Spray? (enter y or n) y If Spray What Type (enter ground or air) air Enter Chemical Molecular Weight (g/mole) 324.7 Enter Chemical Vapor Pressure (mmHg) 1.40E

- 07 Enter Application Rate (lb a.i./acre) 1

Toxicity Properties

**Bird** Enter Lowest Bird Oral LD 50 (mg/kg bw) 218.7 Enter Mineau Scaling Factor 1.15 Enter Tested Bird Weight (kg) 0.178 **Mammal**
Enter Lowest Rat Oral LD 50 (mg/kg bw) 441
Enter Lowest Rat Inhalation LC 50 (mg/L) 0.78 Duration of Rat Inhalation Study (hrs) 4 Enter Rat Weight (kg) 0.35


## Output Results Avian (0.020 kg ) Maximum Vapor Concentration in Air at Saturation (mg/m 3 ) 2.45E

- 03 Maximum 1

- hour Vapor Inhalation Dose (mg/kg) 3.08E

- 04 Adjusted Inhalation LD 50 2.16E+00

Ratio of Vapor Dose to Adjusted Inhalation LD 50 1.43E

- 04 Exposure not Likely Significant Maximum Post

- treatment Spray Inhalation Dose 9.61E

- 02

### 76 (mg/kg)

Ratio of Droplet Inhalation Dose to Adjusted Inhalation LD 50 4.45E

- 02 Exposure not Likely Significant



### Results Mammalian (0.015 kg ) Maximum Vapor Concentration in Air at Saturation (mg/m 3 ) 2.45E

- 03 Maximum 1

- hour Vapor Inhalation Dose (mg/kg) 3.87E

- 04 Adjusted Inhalation LD 50 4.64E+01

Ratio of Vapor Dose to Adjusted Inhalation LD 50 8.32E

- 06 Exposure not Likely Significant Maximum Post

- treatment Spray Inhalation Dose (mg/kg) 1.21E

- 01

Ratio of Droplet Inhalation Dose to Adjusted Inhalation LD 50 2.60E

- 03 Exposure not Likely Significant

### 77 

## Appendix D

. Examples of PRZM/EXAMS Outputs for 2,4

- D and 2,4

- DCP

2,4

- D

stored as MSCornAT1.out Chemical: 2 4 D choline PRZM environment: MScornSTD.txt; modified Tueday, 29 May 2007 at 13:57:40 EXAMS environment: pond298.exv;modified Tueday, 26 August 2008 at 06:14:08 Metfile: w03940.dvf;modified Tueday, 26 August 2008 at 06:14:14

Water segment concentrations (ppb)
Year Peak 96 hr 21 Day 60 Day 90 Day Yearly 1961 16.9 15.9 14.0 10.3 8.1 2.3
1962 48.0 46.1 37.3 24.1 18.4 5.0 1963 4.9 4.6 4.1 2.8 2.2 0.6 1964 30.5 28.1 23.6 16.4 12.1 3.2 1965 38.6 37.0 28.9 17.8 13.1 3.4
1966 10.6 9.8 7.4 4.7 3.6 1.0 1967 12.7 11.8 9.4 6.3 4.8 1.3 1968 13.4 12.9 10.9 8.7 6.6 1.8
1969 13.4 12.5 10.6 6.8 5.0 1.4 1970 6.0 5.6 4.3 3.5 2.7 0.7 1971 49.3 46.2 36.9 22.7 17.3 4.8 1972 5.4 5.1 4.0 2.8 2.3 0.6
1973 29.1 27.7 23.5 14.7 11.0 3.0 1974 38.4 35.7 31.8 20.1 14.8 4.0 1975 9.7 9.1 7.3 5.4 4.4 1.2 1976 33.8 31.6 25.1 17.7 13.5 3.7
1977 15.8 14.8 13.4 10.1 7.5 2.0 1978 7.3 6.9 6.2 4.8 3.7 1.0 1979 93.4 88.6 75.4 50.6 38.9 10.8
1980 98.3 94.1 83.9 61.1 48.9 13.6 1981 10.8 10.1 8.8 5.9 4.4 1.2 1982 10.4 9.7 8.6 5.5 4.2 1.2 1983 58.9 54.9 42.1 26.7 20.1 5.4
1984 9.8 9.2 8.3 6.7 5.1 1.4 1985 8.9 8.5 6.8 5.5 4.2 1.1 1986 3.3 3.1 2.7 1.9 1.5 0.4
1987 4.1 3.8 3.2 2.7 2.2 0.6 1988 38.5 36.2 28.4 22.4 17.6 4.8 1989 18.4 17.2 14.5 11.7 9.2 2.5 1990 11.7 11.0 8.5 5.2 4.0 1.1

Sorted results

### 78 Prob. Peak 96 hr 21 Day 60 Day 90 Day Yearly 0.03 98.27 94.09 83.86 61.11 48.91 13.55
0.06 93.43 88.55 75.44 50.64 38.87 10.83 0.10 58.93 54.93 42.07 26.65 20.08 5.38 0.13 49.28 46.21 37.29 24.05 18.36 4.98 0.16 48.03 46.11 36.94 22.69 17.61 4.85
0.19 38.64 36.99 31.77 22.35 17.25 4.77 0.23 38.50 36.23 28.93 20.14 14.81 3.97 0.26 38.40 35.70 28.36 17.80 13.50 3.66
0.29 33.75 31.55 25.10 17.66 13.05 3.44 0.32 30.52 28.12 23.59 16.39 12.14 3.19 0.35 29.13 27.74 23.51 14.69 10.99 2.98 0.39 18.37 17.22 14.52 11.67 9.16 2.51
0.42 16.85 15.89 14.01 10.32 8.08 2.27 0.45 15.81 14.79 13.43 10.05 7.52 2.00 0.48 13.42 12.86 10.90 8.68 6.57 1.76 0.52 13.36 12.52 10.58 6.79 5.12 1.39
0.55 12.67 11.77 9.35 6.70 5.02 1.35 0.58 11.67 10.95 8.82 6.33 4.83 1.33 0.61 10.75 10.13 8.65 5.92 4.44 1.24
0.65 10.57 9.76 8.50 5.53 4.42 1.22 0.68 10.36 9.66 8.31 5.49 4.25 1.18 0.71 9.83 9.20 7.40 5.41 4.23 1.14 0.74 9.67 9.14 7.28 5.22 4.02 1.13
0.77 8.86 8.46 6.79 4.82 3.67 1.01 0.81 7.34 6.90 6.23 4.73 3.56 0.99 0.84 5.97 5.58 4.34 3.47 2.66 0.74
0.87 5.38 5.05 4.06 2.84 2.26 0.65 0.90 4.95 4.62 4.02 2.83 2.20 0.62 0.94 4.07 3.83 3.19 2.66 2.18 0.60 0.97 3.28 3.08 2.75 1.94 1.53 0.42

0.10 57.97 54.06 41.59 26.39 19.91 5.34 Average of yearly
averages

: 2.84

Inputs generated by pe5.pl

- Novemeber 2006

Data used for this run: Output File: MSCornAT1 Metfile: w03940.dvf
PRZM scenario: MScornSTD.txt

### 79 EXAMS environ
ment file: pond298.exv

Chemica l Name: 2 4 D choline

Descripti

on Variable Name Value Units Comments

Molecul

ar weight mwt 221.4 g/mol

Henry's Law Const. henry 8.56E

- 06 atm

- m^3/mol

Vapor Pressure vapr 1.40E

- 07 torr

Solubilit
y sol 569 mg/L

Kd Kd mg/L
Koc Koc 61.7 mg/L Photolys is half

life kdp 13 days Half

- life

Aerobic Aquatic Metaboli

sm kbacw 45 days Halfife

Anaerob ic Aquatic Metaboli

sm kbacs 321 days Halfife

Aerobic Soil Metaboli

sm asm 6.9 days Halfife

Hydroly sis: pH 7 0 days Half

- life

Method: CAM 2 integer See PRZM manual Incorpor ation Depth: DEPI cm

Applicat ion Rate: TAPP 1.12 kg/ha

Applicat ion Efficienc
y: APPEFF 0.99 fraction

Spray Drift DRFT 0.017 fraction of application rate applied to pond

### 80 Applicat ion Date Date 29

- 03 dd/mm or dd/mmm or dd

- mm or dd

- mmm

Interval 1 interval 12 days Set to 0 or delete line for single app.

app. rate 1 apprate kg/ha

Interval 2 interval 12 days Set to 0 or delete line for single app.

app. rate 2 apprate kg/ha

Record 17: FILTRA

IPSCND 1
UPTKF Record 18: PLVKR T 0.079

PLDKR T FEXTR C 0.5

Flag for Index Res. Run IR EPA Pond

Flag for runoff calc. RUNOF F none none, monthly or total(average of entire run)



### P re Process 2,4

- DCP PRZM/EXAMS Output s for Terrestrial and Spray Drift

date Terrestrial EEC Spray Drift EEC Percent Terr Percent Spray Drift % Treated Adjusted EEC

1/1/1961 0.00E+00 0.00E+00 1.00E+00 1.00E+00 1.00E+00 0.00E+00

1/2/1961 0.00E+00 0.00E+00 1.00E+00 1.00E+00 1.00E+00 0.00E+00

1/3/1961 0.00E+00 0.00E+00 1.00E+00 1.00E+00 1.00E+00 0.00E+00

1/4/1961 0.00E+00 0.00E+00 1.00E+00 1.00E+00 1.00E+00 0.00E+00

1/5/1961 0.00E+00 0.00E+00 1.00E+00 1.00E+00 1.00E+00 0.00E+00

1/6/1961 0.00E+00 0.00E+00 1.00E+00 1.00E+00 1.00E+00 0.00E+00

1/7/1961 0.00E+00 0.00E+00 1.00E+00 1.00E+00 1.00E+00 0.00E+00

1/8/1961 0.00E+00 0.00E+00 1.00E+00 1.00E+00 1.00E+00 0.00E+00

1/9/1961 0.00E+00 0.00E+00 1.00E+00 1.00E+00 1.00E+00 0.00E+00

1/10/1961 0.00E+00 0.00E+00 1.00E+00 1.00E+00 1.00E+00 0.00E+00

1/11/1961 0.00E+00 0.00E+00 1.00E+00 1.00E+00 1.00E+00 0.00E+00

1/12/1961 0.00E+00 0.00E+00 1.00E+00 1.00E+00 1.00E+00 0.00E+00

1/13/1961 0.00E+00 0.00E+00 1.00E+00 1.00E+00 1.00E+00 0.00E+00

1/14/1961 0.00E+00 0.00E+00 1.00E+00 1.00E+00 1.00E+00 0.00E+00

1/15/1961 0.00E+00 0.00E+00 1.00E+00 1.00E+00 1.00E+00 0.00E+00

1/16/1961 0.00E+00 0.00E+00 1.00E+00 1.00E+00 1.00E+00 0.00E+00

### 81 1/17/1961 0.00E+00 0.00E+00 1.00E+00 1.00E+00 1.00E+00 0.00E+00

. . . . . . .

. . . . . . .

. . . . . . .

. . . . . . .

. . . . . . . 12/27/1990 7.18E

- 05 2.26E

- 04 1.00E+00 1.00E+00 1.00E+00 2.98E

- 04
12/28/1990 7.12E

- 05 2.24E

- 04 1.00E+00 1.00E+00 1.00E+00 2.95E

- 04
12/29/1990 7.06E

- 05 2.22E

- 04 1.00E+00 1.00E+00 1.00E+00 2.93E

- 04
12/30/1990 7.00E

- 05 2.20E

- 04 1.00E+00 1.00E+00 1.00E+00 2.90E

- 04
12/31/1990 6.94E

- 05 2.19E

- 04 1.00E+00 1.00E+00 1.00E+00 2.88E

- 04

1/1/1991 6.89E

- 05 2.17E

- 04 1.00E+00 1.00E+00 1.00E+00 2.86E

- 04



### Post Process 2,4

- DCP PRZM/EXAMS Outputs for Terrestrial and Spray Drift Outputs
Year Max Peak 4

- day Max 14 day Max 21 day Max 30 day Max 60 day Max 90 day Annual 2.0E+03 3.7E

- 03 3.5E

- 03 3.1E

- 03 3.0E

- 03 2.8E

- 03 2.5E

- 03 2.1E

- 03 1.1E

- 03 2.0E+03 4.4E

- 03 4.3E

- 03 3.9E

- 03 3.7E

- 03 3.6E

- 03 3.0E

- 03 2.5E

- 03 1.1E

- 03 2.0E+03 3.7E

- 03 3.6E

- 03 3.1E

- 03 2.9E

- 03 2.8E

- 03 2.3E

- 03 2.0E

- 03 9.3E

- 04 2.0E+03 4.2E

- 03 4.0E

- 03 3.7E

- 03 3.5E

- 03 3.3E

- 03 2.7E

- 03 2.3E

- 03 9.3E

- 04 2.0E+03 3.7E

- 03 3.6E

- 03 3.1E

- 03 2.9E

- 03 2.8E

- 03 2.3E

- 03 2.0E

- 03 8.4E

- 04 2.0E+03 3.8E

- 03 3.6E

- 03 3.3E

- 03 3.0E

- 03 2.8E

- 03 2.5E

- 03 2.1E

- 03 8.7E

- 04 2.0E+03 3.5E

- 03 3.4E

- 03 3.2E

- 03 3.2E

- 03 3.0E

- 03 2.6E

- 03 2.2E

- 03 9.0E

- 04 2.0E+03 3.8E

- 03 3.6E

- 03 3.3E

- 03 3.1E

- 03 3.0E

- 03 2.5E

- 03 2.2E

- 03 8.8E

- 04 2.0E+03 4.4E

- 03 4.2E

- 03 3.7E

- 03 3.5E

- 03 3.3E

- 03 2.7E

- 03 2.2E

- 03 8.9E

- 04 2.0E+03 3.6E

- 03 3.4E

- 03 3.0E

- 03 2.8E

- 03 2.7E

- 03 2.3E

- 03 1.9E

- 03 9.4E

- 04 2.0E+03 4.6E

- 03 4.4E

- 03 4.0E

- 03 3.8E

- 03 3.6E

- 03 3.0E

- 03 2.5E

- 03 1.0E

- 03 2.0E+03 3.5E

- 03 3.4E

- 03 3.1E

- 03 2.9E

- 03 2.7E

- 03 2.4E

- 03 2.0E

- 03 9.0E

- 04 2.0E+03 4.5E

- 03 4.4E

- 03 3.9E

- 03 3.7E

- 03 3.5E

- 03 2.9E

- 03 2.4E

- 03 9.5E

- 04 2.0E+03 4.4E

- 03 4.2E

- 03 3.7E

- 03 3.5E

- 03 3.3E

- 03 2.7E

- 03 2.3E

- 03 9.1E

- 04 2.0E+03 3.6E

- 03 3.5E

- 03 3.3E

- 03 3.2E

- 03 3.0E

- 03 2.6E

- 03 2.2E

- 03 9.6E

- 04 2.0E+03 3.9E

- 03 3.8E

- 03 3.4E

- 03 3.2E

- 03 3.1E

- 03 2.8E

- 03 2.5E

- 03 1.1E

- 03 2.0E+03 4.2E

- 03 4.0E

- 03 3.6E

- 03 3.3E

- 03 3.2E

- 03 2.6E

- 03 2.2E

- 03 9.8E

- 04 2.0E+03 3.8E

- 03 3.6E

- 03 3.3E

- 03 3.2E

- 03 3.0E

- 03 2.6E

- 03 2.3E

- 03 1.2E

- 03 2.0E+03 5.6E

- 03 5.5E

- 03 5.0E

- 03 4.8E

- 03 4.7E

- 03 4.0E

- 03 3.4E

- 03 1.5E

- 03 2.0E+03 5.7E

- 03 5.6E

- 03 5.3E

- 03 5.0E

- 03 4.9E

- 03 4.2E

- 03 3.6E

- 03 1.5E

- 03 2.0E+03 3.8E

- 03 3.6E

- 03 3.2E

- 03 3.0E

- 03 2.9E

- 03 2.5E

- 03 2.2E

- 03 1.2E

- 03 2.0E+03 4.2E

- 03 4.0E

- 03 3.6E

- 03 3.3E

- 03 3.1E

- 03 2.5E

- 03 2.2E

- 03 1.1E

- 03 2.0E+03 5.0E

- 03 4.7E

- 03 4.2E

- 03 4.1E

- 03 3.9E

- 03 3.4E

- 03 2.9E

- 03 1.2E

- 03 2.0E+03 3.8E

- 03 3.6E

- 03 3.3E

- 03 3.1E

- 03 2.9E

- 03 2.5E

- 03 2.1E

- 03 9.5E

- 04 2.0E+03 3.6E

- 03 3.5E

- 03 3.1E

- 03 2.9E

- 03 2.8E

- 03 2.3E

- 03 1.9E

- 03 8.4E

- 04 2.0E+03 3.6E

- 03 3.5E

- 03 3.1E

- 03 2.8E

- 03 2.7E

- 03 2.4E

- 03 2.1E

- 03 9.0E

- 04 2.0E+03 3.7E

- 03 3.5E

- 03 3.2E

- 03 3.0E

- 03 2.9E

- 03 2.4E

- 03 2.1E

- 03 9.5E

- 04 2.0E+03 4.4E

- 03 4.2E

- 03 3.8E

- 03 3.6E

- 03 3.3E

- 03 2.8E

- 03 2.4E

- 03 1.0E

- 03 2.0E+03 3.8E

- 03 3.6E

- 03 3.4E

- 03 3.3E

- 03 3.2E

- 03 2.8E

- 03 2.4E

- 03 1.0E

- 03 2.0E+03 3.6E

- 03 3.5E

- 03 3.3E

- 03 3.1E

- 03 2.9E

- 03 2.6E

- 03 2.2E

- 03 1.1E

- 03

90th % (ppm) 0.00 0.00 0.00 0.00 0.00 0.00 0.00

90th % (ppb) 4.66 4.05 3.84 3.62 3.01 2.55 1.17

### 82 

## Appendix E

. Avian and Mammalian Risk Quotient Calculations for 2,4

- D Choline Salt Based on T

- REX

Applications to herbicide

- tolerant soybean and corn at 1 lb ae/A, 3 applications that are 12 days apart

Upper Bound Kenaga, Acute Avian Dose

- Based Risk Quotients

Size Class (grams) Adjusted LD50 EECs and RQs

Short Grass Tall Grass Broadleaf Plants Fruits/Pods/Seeds Arthropods Granivore

EEC RQ EEC RQ EEC RQ EEC RQ EEC RQ EEC RQ

20 0.00 658.79 #DIV/0! 301.94 #DIV/0! 370.57 ### 41.17 #DIV/0! 258.03 # ## 9.15 ###

100 0.00 375.67 #DIV/0! 172.18 #DIV/0! 211.31 ## # 23.48 #DIV/0! 147.14 ### 5.22 ###

1000 0.00 168.19 #DIV/0! 77.09 #DIV/0! 94.61 # ## 10.51 #DIV/0! 65.88 ### 2.34 ###

Upper Bound Kenaga, Subacute Avian Dietary Based Risk Quotients

LC5

0 EECs and RQs

Short Grass Tall Grass Broadleaf Plants Fruits/Pods/Seed

s Arthropods

EEC RQ EEC RQ EEC RQ EEC RQ EEC RQ

0 5 78.4 4 #DIV/0 ! 265.1 2 #DIV/0 ! 325.3 7 #DIV/0 ! 36.15 ##### 226.5 6 #DIV/0 !

Size class not used for dietary risk quotients

Upper Bound Kenaga, Chronic Avian Dietary Based Risk Quotients

NOAEC (ppm) EECs and RQs

Short Grass Tall Grass Broadleaf Plants Fruits/Pods/Seed

s Arthropods

EEC RQ EEC RQ EEC RQ EEC RQ EEC RQ

962 578.44 0.6 0 265.12 0.2 8 325.37 0.34 36.15 0.04 226.56 0.2 4 Size class not used for dietary risk quotients

Upper Bound Kenaga, Acute Mammalian Dose

- Based Risk Quotients

Size Adjusted EECs and RQs

### 83 Class (grams) LD50

Short Grass Tall Grass Broadleaf Plants Fruits/Pods/ Seeds Arthropods Granivore

EEC RQ EEC RQ EEC RQ EEC RQ EEC RQ EEC RQ

15 969.24 551.50 0.57 252.77 0.26 310.22 0.32 34.47 0.04 216.004 0.2229 7.6597 0.0079

35 784.22 381.16 0.49 174.70 0.22 214.40 0.27 23.82 0.03 149.288 0.1904 5.2939 0.0068

1000 339.20 88.37 0.26 40.50 0.12 49.71 0.15 5.52 0.02 34.6129 0.102 1.2274 0.0036

Upper Bound Kenaga, Acute Mammalian Dietary Based Risk Quotients

LC50 (ppm) EECs and RQs

Short Grass Tall Grass Broadleaf Plants Fruits/Pods/See ds Arthropods

EEC RQ EEC RQ EEC RQ EEC RQ EEC RQ

0 5 78.4 4 #DIV/0 ! 265.1 2 #DIV/0 ! 325.3 7 #DIV/0 ! 36.15 ##### 226.5 6 #DIV/0 !

Size class not used for dietary risk quotients

Upper Bound Kenaga, Chronic Mammalian Dietary Based Risk Quotients

NOAEC (ppm) EECs and RQs

Short Grass Tall Grass Broadleaf Plants Fruits/Pods/Seeds/Larg e Insects Arthropods

EEC RQ EEC RQ EEC RQ EEC RQ EEC RQ

100 578.4 4 5.7 8 265.1 2 2.6 5 325.3 7 3.2 5 36.15 0.36 226.5 6 2.2 7 Size class not used for dietary risk quotients

Upper Bound Kenaga, Chronic Mammalian Dose

- Based Risk Quotients

Size Class (grams) Adjusted NOAEL EECs and RQs

Short Grass Tall Grass Broadleaf Plants Fruits/Pods/ Seeds Arthropods Granivore

EEC RQ EEC RQ EEC RQ EEC RQ EEC RQ EEC RQ

15 10.99 551.50 50.19 252.77 23.00 310.22 28.23 34.47 3.14 216.00 19.66 7.66 0.70

35 8.89 381.16 42.87 174.70 19.65 214.40 24.11 23.82 2.68 149.29 16.79 5.29 0.60

1000 3.85 88.37 22.98 40.50 10.53 49.71 12.93 5.52 1.44 34.61 9.00 1.23 0.32

### 84 

## Appendix F . Terrestrial Plant Risk Quotient Calculations for 2,4

- D Choline Salt Based on TerrPlant

2,4

- D choline salt application to herbicide

- tolerant corn and soybean at 1 lb ae/A

Table 1. Chemical Identity.

Parameter User Inputs
Chemical Name 2,4

- D Choline Salt PC code 52505 Use Herbicide

- tolerant corn and soybean Application Method foliar spray

Application Form liquid Solubility in Water (ppm) 569

Table 2. Input parameters used to derive EECs.

Input Parameter Symbol Value (user inputs) Units Application Rate A 1

Incorporation I 1 none Runoff Fraction R 0.05 none

Drift Fraction D 0.01 none

Table 3. EECs for 2,4

- D Choline Salt. Units in . Description Equation EEC Runoff to dry areas (A/I)*R 0.05 Runoff to semi

- aquatic areas (A/I)*R*10 0.5 Spray drift A*D 0.01 Total for dry areas ((A/I)*R)+(A*D) 0.06 Total for semi

- aquatic areas ((A/I)*R*10)+(A*D) 0.51

Table 4. Plant survival and growth data used for RQ derivation. Units are in . All values are user inputs Seedling Emergence Vegetative Vigor Plant type EC 25 NOAEC EC 25 NOAEC

Monocot 0.01 0.005628 x x

Dicot 0.00081 0.00047 0.0021 0.00167

Table 5. RQ values for plants in dry and semi

- aquatic areas exposed to 2,4

- D Choline Salt through runoff and/or spray drift.*

### 85 Plant Type Listed Status Dry Semi

- Aquatic Spray Drift

Monocot non

- listed 6.00 51.00 1.00 Monocot listed 10.66 90.62 1.78

Dicot non

- listed 74.07 629.63 12.35 Dicot listed 127.66 1085.11 21.28 *If RQ > 1.0, the LOC is exceeded, resulting in potential for risk to that plant group.

### 86 

## Appendix G . Risk Quotient Method and Levels of Concern

The Risk Quotient Method is the means by which the Environmental Fate and Effects Division (EFED) integrates the results of exposure and ecotoxicity data. In this method, both acute and chronic risk quotients are calculated by dividing exposure estimates by the most sensitive ecotoxicity values derived f rom the studies. Calculated risk quotients are then compared to OPP's levels of concern. The levels of concern are the criteria used by OPP to indicate potential risk to non

- target organisms and the need to consider regulatory action. EFED has defined le vels of concern for acute risk, potential restricted use, and for listed species. Risk presumptions, along with the corresponding risk quotients and levels of concern are summarized in the table below.

Table G

- 1. Levels of Concern for Assessed Taxa

Risk Presumption Risk Quotient Level of Concern

Birds

Acute Risk EEC/LC 50 

### or LD 50 

### /sqft or LD 50 

### /day 0.5

Acute Restricted Use EEC/LC 50 

### or LD 50 

### /sqft or LD 50 

### /day (or LD 50 

### < 50 mg/kg) 0.2

Acute Listed Species EEC/LC 50 

### or LD 50 

### /sqft or LD 50 

### /day 0.1

Chronic Risk EEC/NOAEC 1

Mammals

Acute Risk EEC/LC 50 

### or LD 50 

### /sqft or LD 50 

### /day 0.5

Acute Restricted Use EEC/LC 50 

### or LD 50 

### /sqft or LD 50 

### /day (or LD 50 

### < 50 mg/kg) 0.2

Acute Listed Species EEC/LC 50 

### or LD 50 

### /sqft or LD 50 

### /day 0.1

Chronic Risk EEC/NOAEC 1
Aquatic Animals

Acute Risk EEC/LC 50 

### or EC 50 

### 0.5

Acute Restricted Use EEC/LC 50 

### or EC 50 

### 0.1
Acute Listed Species EEC/LC 50 

### or EC 50 

### 0.05

Chronic Risk EEC/NOAEC 1

Terrestrial and Semi

- Aquatic Plants

Acute Risk EEC/EC 25 

### 1
Acute Listed Species EEC/EC 05 

### or NOAEC 1

### 87 Risk Presumption Risk Quotient Level of Concern
Aquatic Plants

Acute Risk EEC/EC 50 

### 1
Acute Listed Species EEC/EC 05 

### or NOAEC 1

### 88 

## Appendix H : Preliminary Volatility Flux Data

Table X

- 1. 2,4

- D volatility flux rate from soybean at Farmland, IN

Period 1 Flux Rate (g/m 2

- s)
Unadjusted Flux Rate **2** Adjusted Flux Rate 3

EPA Registrant EPA Registrant Field 1 (2,4 D choline)

1 2.20E

- 08 1.80E

- 10 5.50E

- 09 4.50E

- 11

2 2.90E

- 10 1.60E

- 11 7.25E

- 11 4.00E

- 12

3 8.30E

- 12 1.40E

- 11 2.08E

- 12 3.50E

- 12

4 5.80E

- 12 5.00E

- 12 1.45E

- 12 1.25E

- 12

5 5.10E

- 10 3.50E

- 11 1.28E

- 10 8.75E

- 12

6 4.80E

- 11 1.50E

- 10 1.20E

- 11 3.75E

- 11

7 5.90E

- 10 1.60E

- 10 1.48E

- 10 4.00E

- 11

8 6.00E

- 11 1.10E

- 10 1.50E

- 11 2.75E

- 11 Field 2 (2,4

- D DMA)

1 6.00E

- 08 1.30E

- 08 3.00E

- 08 6.50E

- 09
2 1.60E

- 09 2.50E

- 11 8.00E

- 10 1.25E

- 11
3 2.20E

- 10 1.20E

- 10 1.10E

- 10 6.00E

- 11
4 8.00E

- 11 8.40E

- 11 4.00E

- 11 4.20E

- 11
5 1.20E

- 09 7.00E

- 10 6.00E

- 10 3.50E

- 10
6 1.50E

- 10 2.60E

- 10 7.50E

- 11 1.30E

- 10
7 3.40E

- 10 3.50E

- 10 1.70E

- 10 1.75E

- 10
8 1.40E

- 10 1.50E

- 10 7.00E

- 11 7.50E

- 11 Field 3 (2,4

- D EHE)

1 7.80E

- 08 7.60E

- 08 7.80E

- 08 7.60E

- 08

2 5.10E

- 08 4.00E

- 08 5.10E

- 08 4.00E

- 08

3 3.40E

- 09 5.40E

- 09 3.40E

- 09 5.40E

- 09

4 6.90E

- 09 2.80E

- 09 6.90E

- 09 2.80E

- 09

5 2.80E

- 08 2.50E

- 08 2.80E

- 08 2.50E

- 08

6 6.60E

- 09 2.70E

- 09 6.60E

- 09 2.70E

- 09

7 1.50E

- 08 4.40E

- 09 1.50E

- 08 4.40E

- 09

8 2.50E

- 09 3.20E

- 09 2.50E

- 09 3.20E

- 09

1 = Air Monitoring Period (varies

- 2 to 11 hours)

2 Flux rate based on application rate used in study
3 = Flux rate based on 1.0 lb a.e./A

Table X

- 1. 2,4

- D volatility flux rate from Bare field. Fowler, IN

Period 1 Flux Rate (g/m2

- s)
Unadjusted Flux Rate 2 Adjusted Flux Rate 3

EPA Registrant EPA Registrant

### 89 Field 1 (2,4

- D Choline)

1 7.70E

- 08 2.00E

- 08 1.53E

- 08 3.97E

- 09

2 9.30E

- 10 1.20E

- 09 1.85E

- 10 2.38E

- 10

3 6.20E

- 10 1.60E

- 10 1.23E

- 10 3.17E

- 11

4 6.90E

- 09 3.20E

- 09 1.37E

- 09 6.35E

- 10

5 2.60E

- 10 2.30E

- 10 5.16E

- 11 4.56E

- 11

6 1.60E

- 12 4.60E

- 12 3.17E

- 13 9.13E

- 13

7 5.20E

- 12 2.50E

- 11 1.03E

- 12 4.96E

- 12

8 3.30E

- 12 2.80E

- 12 6.55E

- 13 5.56E

- 13 Field 2 (2,4

- D DMA)

1 1.20E

- 07 5.60E

- 08 4.56E

- 08 2.13E

- 08
2 4.00E

- 09 5.40E

- 09 1.52E

- 09 2.05E

- 09
3 2.60E

- 10 3.50E

- 10 9.89E

- 11 1.33E

- 10
4 8.50E

- 09 4.80E

- 09 3.23E

- 09 1.83E

- 09
5 5.30E

- 10 3.30E

- 10 2.02E

- 10 1.25E

- 10
6 2.10E

- 12 9.00E

- 13 7.98E

- 13 3.42E

- 13
7 2.00E

- 11 6.40E

- 11 7.60E

- 12 2.43E

- 11
8 0.00E+00 1.00E

- 12

--- 3.80E

- 13 Field 3 (2,4

- D EHE)

1 2.50E

- 08 3.60E

- 08 2.50E

- 08 3.60E

- 08

2 5.20E

- 09 5.70E

- 09 5.20E

- 09 5.70E

- 09

3 8.50E

- 10 1.10E

- 09 8.50E

- 10 1.10E

- 09

4 4.80E

- 09 5.50E

- 09 4.80E

- 09 5.50E

- 09

5 8.10E

- 09 3.20E

- 09 8.10E

- 09 3.20E

- 09

6 1.40E

- 09 6.20E

- 10 1.40E

- 09 6.20E

- 10

7 1.30E

- 09 2.30E

- 09 1.30E

- 09 2.30E

- 09

8 7.80E

- 11 2.30E

- 11 7.80E

- 11 2.30E

- 11

1 = Air Monitoring Period (varies

- 5 to 11 hours)

2
= Flux rate based on application rate used in study

3 = Flux rate based on 1.0 lb a.e./A

Table 3. 2,4

- D volatility flux rate from soybean at Little Rock, AR

Period 1 Flux Rate (g/m2

- s) Unadjusted Flux Rate 2 Adjusted Flux Rate 3

EPA Registrant EPA Registrant

Field 1 (2,4

- D Choline)

1 7.50E

- 08 1.50E

- 08 1.88E

- 08 3.75E

- 09

2 2.10E

- 09 2.70E

- 09 5.25E

- 10 6.75E

- 10

3 3.30E

- 10 4.00E

- 10 8.25E

- 11 1.00E

- 10

4 1.30E

- 10 1.40E

- 10 3.25E

- 11 3.50E

- 11

5 6.10E

- 09 6.60E

- 10 1.53E

- 09 1.65E

- 10

6 2.10E

- 10 2.40E

- 10 5.25E

- 11 6.00E

- 11

### 90 Table 3. 2,4

- D volatility flux rate from soybean at Little Rock, AR

Period 1 Flux Rate (g/m2

- s) Unadjusted Flux Rate 2 Adjusted Flux Rate 3

EPA Registrant EPA Registrant

7 2.00E

- 10 2.50E

- 10 5.00E

- 11 6.25E

- 11

8 1.20E

- 10 1.40E+10 3.00E

- 11 3.50E+09 Field 2 (2,4 D choline plus glyphosate DMA)

1 2.00E

- 08 6.00E

- 08 2.44E

- 09 7.31E

- 09
2 3.40E

- 09 6.00E

- 09 4.14E

- 10 7.31E

- 10
3 4.40E

- 10 6.40E

- 10 5.36E

- 11 7.80E

- 11
4 1.80E

- 10 2.00E

- 10 2.19E

- 11 2.44E

- 11
5 3.90E

- 09 2.30E

- 09 4.75E

- 10 2.80E

- 10
6 1.20E

- 10 1.60E

- 10 1.46E

- 11 1.95E

- 11
7 3.00E

- 10 4.20E

- 10 3.65E

- 11 5.12E

- 11
8 9.80E

- 11 1.50E

- 10 1.19E

- 11 1.83E

- 11 Field 3 ( 2,4 D DMA)

1 3.70E

- 08 3.00E

- 08 9.02E

- 08 7.32E

- 08

2 3.00E

- 09 4.00E

- 09 7.32E

- 09 9.76E

- 09

3 3.40E

- 10 6.10E

- 10 8.29E

- 10 1.49E

- 09

4 9.10E

- 11 1.70E

- 10 2.22E

- 10 4.15E

- 10

5 3.70E

- 09 6.50E

- 10 9.02E

- 09 1.59E

- 09

6 1.60E

- 10 1.50E

- 10 3.90E

- 10 3.66E

- 10

7 1.30E

- 10 1.90E

- 10 3.17E

- 10 4.63E

- 10

8 8.30E

- 11 9.30E

- 11 2.02E

- 10 2.27E

- 10 Field 4 ( 2,4 D EHE)

1 3.50E

- 08 1.70E

- 07 8.54E

- 08 4.15E

- 07

2 2.60E

- 08 6.70E

- 09 6.34E

- 08 1.63E

- 08

3 2.60E

- 09 5.80E

- 10 6.34E

- 09 1.41E

- 09

4 1.20E

- 09 1.90E

- 09 2.93E

- 09 4.63E

- 09

5 9.60E

- 09 3.60E

- 09 2.34E

- 08 8.78E

- 09

6 7.20E

- 09 1.30E

- 09 1.76E

- 08 3.17E

- 09

7 5.80E

- 10 6.20E

- 10 1.41E

- 09 1.51E

- 09

8 7.30E

- 10 3.70E

- 10 1.78E

- 09 9.02E

- 10

1 Air Monitoring Period (varies

- 5 to 11 hours)

2 = Flux rate based on application rate used in study

3 = Flux rate based on 1.0 lb a.e./A

Table 4. 2,4

- D volatility flux rate from cotton field at Ty Ty, Ga

Period 1 Flux Rate (g/m2

- s)

### 91 Unadjusted Flux Rate 2 Adjusted Flux Rate 3

EPA Registrant EPA Registrant
Field 1 (2,4 D choline plus glyphosate DMA))

1 1.17E

- 08 6.00E

- 10 1.48E

- 09 7.59E

- 11

2 2.83E

- 09 5.00E

- 09 3.58E

- 10 6.33E

- 10

3 1.25E

- 09 6.00E

- 10 1.58E

- 10 7.59E

- 11

4 3.16E

- 10 1.00E

- 10 4.00E

- 11 1.27E

- 11

5 4.84E

- 10 8.00E

- 10 6.13E

- 11 1.01E

- 10

6 1.10E

- 10 1.00E

- 10 1.39E

- 11 1.27E

- 11

7 2.94E

- 10 5.00E

- 10 3.72E

- 11 6.33E

- 11

8 9.87E

- 11 1.00E

- 10 1.25E

- 11 1.27E

- 11 Field 2 (2,4 D choline

1 1.05E

- 08 3.00E

- 09 2.63E

- 09 7.50E

- 10

2 1.01E

- 09 7.00E

- 10 2.53E

- 10 1.75E

- 10

3 3.11E

- 10 3.00E

- 11 7.78E

- 11 7.50E

- 12

4 1.16E

- 10 7.50E

- 11 2.90E

- 11 1.88E

- 11

5 5.50E

- 10 2.00E

- 10 1.38E

- 10 5.00E

- 11

6 2.76E

- 10 3.50E

- 11 6.90E

- 11 8.75E

- 12

7 5.38E

- 10 2.50E

- 10 1.35E

- 10 6.25E

- 11

8 8.83E

- 11 5.50E

- 11 2.21E

- 11 1.38E

- 11 Field 3 ( 2,4 D DMA)

1 1.23E

- 08 1.00E

- 08 3.00E

- 08 2.44E

- 08

2 5.85E

- 09 1.00E

- 08 1.43E

- 08 2.44E

- 08

3 8.65E

- 10 3.50E

- 10 2.11E

- 09 8.54E

- 10

4 1.38E

- 10 1.50E

- 10 3.37E

- 10 3.66E

- 10

5 6.35E

- 11 3.50E

- 10 1.55E

- 10 8.54E

- 10

6 7.50E

- 11 7.50E

- 11 1.83E

- 10 1.83E

- 10

7 2.75E

- 10 4.00E

- 10 6.71E

- 10 9.76E

- 10

8 7.33E

- 11 8.00E

- 11 1.79E

- 10 1.95E

- 10 Field 4 ( 2,4 D EHE)

1 5.88E

- 09 3.00E

- 09 1.43E

- 08 7.32E

- 09

2 4.29E

- 08 3.00E

- 08 1.05E

- 07 7.32E

- 08

3 2.05E

- 08 5.00E

- 09 5.00E

- 08 1.22E

- 08

4 8.10E

- 09 3.00E

- 09 1.98E

- 08 7.32E

- 09

5 1.38E

- 08 7.00E

- 09 3.37E

- 08 1.71E

- 08

6 1.39E

- 09 3.50E

- 10 3.39E

- 09 8.54E

- 10

7 2.02E

- 09 1.20E

- 09 4.93E

- 09 2.93E

- 09

8 8.50E

- 10 4.00E

- 10 2.07E

- 09 9.76E

- 10

1 Air Monitoring Period (varies

- 3 to 13 hours)

2 = Flux rate based on application rate used in study

3 = Flux rate based on 1.0 lb a.e./A

### 92 Agency Estimated Volatility Flux Profiles of Various 2,4

- D Formulations

### 93 1.00E

- 12 1.00E

- 11 1.00E

- 10 1.00E

- 09 1.00E

- 08 1.00E

- 07 1.00E

- 06

1 2 3 4 5 6 7 8Volatility Flux (μg/m2-s)



### Monitoring Period 

# Ty Ty, GA (Cotton)

Choline
Choline+Glyphosate

Amine

Ester

### 94 

## Appendix I

Example of PERFUM Input and Output

****************************************************** ** PERFUM Output File

******************************************************

Version 2.5.1

- compiled on 7/2/2008 Run finished on: 11/14/2012 at 13:03

****************************************************** ** Basic information about the model run

************************** **************************** Scenario Type: GRN

Source of flux data: Application Rate Source of meteorological data: Peoria, IL ISCST3 meterological file: .. \ PERFUM2 \ MET \ IL14842.MET Field size (acres) : 79.969 Length in x

- direction (m): 569.00 Length in y

- direction (m): 569.00 Grid density: FINE

****************************************************** ** Toxicity Inputs

******************************************************

Human Equivalent Conc (ug/m3) : 120.0 Uncertainty factor: 1.0 Threshold (ug/m3): 120.0

****************************************************** ** Exposure Assumptions

******************************************************

Exposure averaging period (hours): 1 Distribution averaging time (hours): 1

****************************************************** ** Time Assumptions

******************************************************

Starting year: 1984 Ending year: 1988 Application Start Hour: 7

****************************************************** ** Additional assumptions for greenhouse scenario

### 95 ****************************************************** Greenhouse source type: Area Height of greenhouse + stack (m): 0.0 Greenhouse height (m): 0.5 Adjusted greenhouse height (m): 0.5 Source of flux data: Manually entered by user

****************************************************** ** Fumigant Flux Profiles

******************************************************

Flux rates for day number: 1

HOUR Flux Rate

_______________________ 1 0.032 2 0.032 3 0.032 4 0.032 5 0.032 6 0.032 7 18.8 00 8 18.800 9 18.800 10 18.800 11 18.800 12 18.800 13 0.525 14 0.525 15 0.525 16 0.525 17 0.525 18 0.525 19 0.082 20 0.082 21 0.082 22 0.082 23 0.082 24 0.082

Flux rates for day number: 2

HOUR Flux Rate

_______________________ 1 0.052 2 0.052 3 0.052 4 0.052 5 0.052 6 0.052 7 1.530 8 1.530 9 1.530 10 1.530

### 96 11 1.530 12 1.530 13 1.530 14 1.530 15 1.530 16 1.530 17 1.530 18 1.530 19 1.530 20 0.052 21 0.052 22 0.052 23 0.052 24 0.052

Flux rates for day number: 3

HOUR Flux Rate

_______________________ 1 0. 030 2 0.030 3 0.030 4 0.030 5 0.030 6 0.030 7 0.050 8 0.050 9 0.050 10 0.050 11 0.050 12 0.050 13 0.050 14 0.050 15 0.050 16 0.050 17 0.050 18 0.050 19 0.050 20 0.030 21 0.030 22 0.030 23 0.030 24 0.030

** All flux rates in micrograms per meter squared per second

----- Number of Periods with Buffer Length Estimates

-----

Period Valid Periods Calm Periods

_______________________________________ 1 1694 131 2 1658 167 3 1647 178 4 1639 186

### 97 5 1631 194 6 1622 20 3 7 1615 210 8 1609 216 9 1604 221 10 1597 228 11 1584 241 12 1565 260 13 1517 308 14 1446 379 15 1393 432 16 1357 468 17 1315 510 18 1281 544 19 1243 582 20 1214 611 21 119 4 631 22 1172 653 23 1146 679 24 1122 703

*** Due to some large buffers distances, estimates are valid only at or below the following percentiles

Period Maximum Percentile

___________________________ 1 99.525 2 99.854 3 99.978 4 99.996 5 99.990 6 99.989 7 100.000 8 100.000 9 100.000 10 100.000 11 100.000 12 100.000 13 100.000 14 100.000 15 100.000 16 100.000 17 100.000 18 100.000 19 100.000 20 100.000 21 100.000 22 100.000 23 100.000 24 100.000

------- Definition of Flux Averaging Periods

---------- Period 1: Hours 7 to 7 Period 2: Hours 8 to 8 Period 3: Hours 9 to 9

### 98 Period 4: Hours 10 to 10 Period 5: Hours 11 to 11 Period 6: Hours 12 to 12 Period 7: Hours 13 to 13 Period 8: Hours 14 to 14 Period 9: Hours 15 to 15 Period 10: Ho urs 16 to 16 Period 11: Hours 17 to 17 Period 12: Hours 18 to 18 Period 13: Hours 19 to 19 Period 14: Hours 20 to 20 Period 15: Hours 21 to 21 Period 16: Hours 22 to 22 Period 17: Hours 23 to 23 Period 18: Hours 24 to 24 Period 19: Hours 1 to 1 Period 20: Hours 2 to 2 Period 21: Hours 3 to 3 Period 22: Hours 4 to 4 Period 23: Hours 5 to 5 Period 24: Hours 6 to 6

--------- PERFUM Model Results

-----------
Concentration distribution results for rings the field

Ring No. Dist ance (meters)

____________________________________

1 5. 2 7. 3 10. 4 15. 5 20. 6 30. 7 50. 8 70. 9 80. 10 90. 11 100. 12 120. 13 150. 14 180. 15 210. 16 240. 17 270. 18 300. 19 360. 20 420. 21 480. 22 540. 23 600. 24 720. 25 840. 26 960.

### 99 27 1080. 28 1200. 29 1320. 30 1440.



### Table I

- 1 . AERSCREEN Inputs for 2,4

- D Air Modeling Runs
Input Parameter 

### Option/Value
Source Parameters Source Type Area

Maximum Field Emission Rate 1 Choline Formulation, Corn and Soybean Crops: 1.88 x 10 - 8 g/m 2

- s (EPA Value)

Field Size and Dimensions 80 acres (569 meters x 569 meters)
Height of Release Corn (Choline): 50 cm Soybean (Choline): 15 cm
Land Surface Parameters
Local Seasonal Characteristics 1

– Midsummer with lush vegetation Land Surface Characteristics 2

– Agricultural Lands Albedo Corn and Soybean Crops: 0.17 Bowen Ratio Corn and Soybean Crops: 0.4 Aerodynamic Surface Roughness Length Corn and Soybean Crops: 0.25 m

Geochemical and Resistance Parameters
Diffusion in Air Coefficient 2 0.06 cm 2 /s Diffusion in Water Coefficient 2 0.57 cm 2 /s Bulk Canopy Cuticular Resistance Parameter 3 2.08 s/cm
Henry’s Law Constant 4 0.867 Pa·m 3 /mol Atmospheric Half

- Life 5 69,732 seconds Meteorological Parameters Wind Speed Range 0.5

- 18 m/s Hourly Precipitation Amount 2 mm (0.08 inches) Temperature Range 288K

– 311K Surface Atmospheric Pressure 1013 hPa Cloud Cover 5/10 Relative Humidity 75% Output Parameters Averaging Period 1

- hour

Downwind Distances 6 0 m

– 100 m: Every 10 meters 100 m

- 3,000 m: Every 100 meters 3,000 m

– 10,000 m: Every 500 meters 10,000 m

– 20,000 m Every 5,000 meters Receptor Height 0 m (Ground

- level)

1. Maximum flux rates in field volatility studies scaled to labeled maximum application rate from MRID No. 48862902: EPA maximum identified from 2,4

- D Choline formulation corn crops flux rate based on its application to soybeans in Little Rock, AR. 7.50 x 10 - 8 g/m 2

- s fl ux rate deter mined from study at 4.0 lbs. ae ./A scaled to value in table at 1 lb. ae /A.
2. Diffusion in air coefficient and diffusion in water coefficient for 2,4

- D retrieved from Appendix C of, “AERMOD Deposition Algorithms

– Science Document (Revised Draft) ”, from EPA Office of Air Quality Planning and Standards.
3. Cuticular resistance parameter for 2,4

- D retrieved from Appendix D of, “AERMOD

### 100 Input Parameter 

### Option/Value Deposition Algorithms

– Science Document (Revised Draft)”, from EPA Office of Air Quality Planning and Standards.
4. Table 8
5. Atmospheric half

- life of 2,4

- D retrieved from hydroxyl radicals rate constant EpiSuite AOPWIN v. 1.92.
6. Distances referenced from the center of the treated field. The edge of the field is at a downwind distance of 1333.3 feet (402.3 m).



## Example output of AERSCREEN

AERSCREEN 11076 / AERMOD 09292 11/15/12 09:12:09 TITLE: soybean

----------------------------------------------------------------------------- ****************************** AREA PARAMETERS ******* *********************

----------------------------------------------------------------------------- SOURCE EMISSION RATE: 0.609E

- 02 g/s 0.483E

- 01 lb/hr AREA EMISSION RATE: 0.188E

- 07 g/(s

- m2) 0.149E

- 06 lb/(hr

- m2)
AREA HEIGHT: 0.01 meters 0.05 feet AREA SOURCE LONG SIDE: 569.00 meters 1866.80 feet AREA SOURCE SHORT SIDE: 569.00 meters 1866.80 feet INITIAL VERTICAL DIMENSION: 0.00 meters 0.00 feet
RURAL OR URBAN: RURAL INITIAL PROBE DISTANCE = 5000. meters 16404. feet

----------------------------------------------------------------------------- *********************** BUILDING DOWNWASH P ARAMETERS **********************

----------------------------------------------------------------------------- BUILDING DOWNWASH NOT USED FOR NON

- POINT SOURCES

-----------------------------------------------------------------------------

***************** ********* FLOW SECTOR ANALYSIS *************************** 25 meter receptor spacing: 1. meters

- 5000. meters

----------------------------------------------------------------------------- MAXIMUM IMPACT RECEPTOR Zo SURFACE 1

- HR CONC RADIAL DIST TEMPORAL SECTOR ROUGHNESS (ug/m3) (deg) (m) PERIOD

----------------------------------------------------- 1* 0.250 11.28 45 400.0 ANN * = worst case diagonal

----------------------------------------------------------- ------------------ ********************** MAKEMET METEOROLOGY PARAMETERS *********************

----------------------------------------------------------------------------- MIN/MAX TEMPERATURE: 297.0 / 299.0 (K)

MINIMUM WIND SPEED: 0.5 m/s
ANEM OMETER HEIGHT: 10.000 meters
SURFACE CHARACTERISTICS INPUT: USER ENTERED ALBEDO: 0.17 BOWEN RATIO: 0.40 ROUGHNESS LENGTH: 0.250 (meters)
METEOROLOGY CONDITIONS USED TO PREDICT OVERALL MAXIMUM IMPACT

------------------------------------------------------------- YR MO DY JDY HR

-- -- -- --- -- 10 01 10 10 01 H0 U* W* DT/DZ ZICNV ZIMCH M

- O LEN Z0 BOWEN ALBEDO REF WS

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

- 0.63 0.027

- 9.000 0.020

- 999. 10. 2.9 0.250 0.40 0.17 0.50
HT REF TA HT

- - - - - - - - - - -

10.0 299.0 2.0
METEOROLOGY CONDITIONS USED TO PREDICT AMBIENT BOUNDARY IMPACT

------------------------------------------------------ --------

### 101 YR MO DY JDY HR

-- -- -- --- -- 10 01 10 10 01 H0 U* W* DT/DZ ZICNV ZIMCH M

- O LEN Z0 BOWEN ALBEDO REF WS

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

- 0.63 0.027

- 9.000 0.020

- 999. 10. 2.9 0. 250 0.40 0.17 0.50
HT REF TA HT

- - - - - - - - - - -

10.0 299.0 2.0

----------------------------------------------------------------------------- ************************ AERSCREEN AUTOMATED DISTANCES **********************
OVERALL MAXIMU M CONCENTRATIONS BY DISTANCE

----------------------------------------------------------------------------- MAXIMUM MAXIMUM DIST 1

- HR CONC DIST 1

- HR CONC

(m) (ug/m3) (m) (ug/m3)

--------------------- --------------------- 1.00 8.800 2524.99 1.565 25.00 8.990 2550.00 1.552 50.01 9.180 2575.00 1.540 75.00 9.363 2 600.00 1.527 100.00 9.541 2625.01 1.515 125.00 9.713 2650.00 1.503 150.01 9.880 2675.00 1.491 174.99 10.04 2700.00 1.480 200.00 10.20 2725.01 1.468 225.00 10.35 2749.99 1.457 250.00 10.51 2775.00 1.446 274.99 10.65 2800.00 1.435 300.00 10.80 2825.00 1.424 325.00 10.94 2849.99 1.415 350.00 11.07 2875.00 1.404 375.01 11.16 2900.00 1.394 400.00 11.28 2925.00 1.384 425.00 8.361 2950.01 1.374 450.00 7.399 2975.00 1.364 475.01 6.780 3000.00 1.355 500.00 6.250 3025.00 1.345 525.00 5.909 3050.01 1.336 550.00 5.620 3075.00 1.326 575.01 5.367 3100.00 1.317 599.99 5.145 3125.00 1.308 625.00 4.946 3150.00 1.300 650.00 4.767 3174.99 1.290 675.00 4.604 3200.00 1.281 699.99 4.456 3225.00 1.272 725.00 4.319 3250.00 1.264 750.00 4.193 3274.99 1.255 775.00 4.075 3300.00 1.246 800.01 3.966 3325.00 1.238 825.00 3.864 3350.00 1.230 850.00 3.769 3375.01 1.222 875.00 3.678 3400.00 1.214 900.01 3.593 3425.00 1.206 924.99 3.513 3450.00 1.198 950.00 3.437 3475.01 1.190 975.00 3.365 3499.99 1.182 1000.00 3.296 3525.00 1.175 1024.99 3.231 3550.00 1.168 1050.00 3.1 69 3575.00 1.160 1075.00 3.109 3599.99 1.153 1100.00 3.052 3625.00 1.146 1125.01 2.997 3650.00 1.139 1150.00 2.945 3675.00 1.132 1 175.00 2.895 3700.01 1.125 1200.00 2.846 3725.00 1.118 1225.01 2.800 3750.00 1.111
1250.00 2.755 3775.00 1.105 1275.00 2.712 3800.01 1.098 1300.00 2.671 3825.00 1.091 1325.01 2.630 3850.00 1.085

### 102 1349.99 2.592 3875.00 1.079 1375.00 2.554 3900.00 1.072 1400.00 2.518 3924.99 1.066 1425.00 2.483 3950.00 1.060 1449.99 2.449 3975.00 1.054 1475.00 2.416 4000.00 1.048 1500.00 2.384 4024.99 1.042 1525.00 2.352 4050.00 1.036 1550.01 2.321 4075.00 1.030 1575.00 2.292 4100.00 1.025 1600.00 2.264 4125.01 1.019 1625.00 2.236 4150.00 1.014 1650.01 2.209 4175.00 1.008 1674.99 2.182 4200.00 1.003 1700.00 2.157 4225.01 0.9972 1725.00 2.132 4249.99 0.9918 1750.00 2.107 4275.00 0.9865 1774.99 2.084 4300.00 0.9813 1800.00 2.060 4325.00 0.9761 1825.00 2.038 4349.99 0.9710 1850.00 2.016 4375.00 0.9659 1875.01 1.994 4400.00 0.9608 1900.00 1.973 4425.00 0.9558 1925.00 1.952 4450.01 0.9509 1950.00 1.932 4475.00 0.9460 1975.01 1.912 4500.00 0.9411 1999.99 1.893 4525.00 0.9363 2025.00 1.874 4550.01 0.9316 2050.00 1.856 4575.00 0.9269 2075.00 1.837 4600.00 0.9222 2099.99 1.820 4625 .00 0.9176 2125.00 1.802 4650.00 0.9130 2150.00 1.785 4674.99 0.9085 2175.00 1.769 4700.00 0.9040 2199.99 1.752 4725.00 0.8996 2225.00 1.736 4750.00 0.8951 2250.00 1.720 4774.99 0.8907 2275.00 1.705 4800.00 0.8864 2300.01 1.690 4825.00 0.8821 2325.00 1.675 4850.00 0.8779 2350.00 1.660 4875.01 0.8737 2375.00 1.646 4900.00 0.8695 2400.01 1.632 4925.00 0.8654 2424.99 1.618 4950.00 0.8612 2450.00 1.604 4975.01 0.857 2 2475.00 1.591 4999.99 0.8532 2500.00 1.578

----------------------------------------------------------------------------- ********************** AERSCREEN MAXIMUM IMPACT SUMMARY *********************

------------------------ ----------------------------------------------------- 3

- hour, 8

- hour, and 24

- hour scaled concentrations are equal to the 1

- hour concentration as referenced in SCREENING PROCEDURES FOR ESTIMATING THE AIR QUALITY IMPACT OF STATIONARY SOURCES, REVISED (Section 4.5.4) Report number EPA

- 454/R

- 92

- 019 http://www.epa.gov/scram001/guidance_permit.htm under Screening Guidance
MAXIMUM SCALED SCALED SCALED SCALED 1

- HOUR 3

- HOUR 8

- HOUR 24

- HOUR ANNUAL
CALCULATION CONC CONC CONC CONC CONC PROCEDURE (ug/m3) (ug/m3) (ug/m3) (ug/m3) (ug/m3)

--------------- ---------- ---------- ---------- ---------- ----------

FLAT TERRAIN 11.29 11.29 11.29 11.29 N/A DISTANCE FROM SOURCE 402.00 meters
IMPACT AT THE AMBIENT BOUNDARY 8.800 8.800 8.800 8.800 N/A DISTANCE FROM SOURCE 1.00 meters

### 103 

## Appendix J Spray Drift Deposition Curves

Figure J

- 1

Figure J

- 2 90th Percentile Depostion Curve of AIXR Nozzle for GF-2726 2,4-D Choline Formulation

Distance (FT) 0 100 200 300 400 500Fraction of Applied

0.0 0.2 0.4 0.6 0.8 1.0 1.2