### Page 1 of 76 OFFICE OF CHEMICAL SAFETY

AND POLLUTION PREVENTION 

### UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, D.C. 20460

August 1 8 , 2015

PC Code s : 032201

MEMORAND UM DP Barcode: 427095

SUBJECT: Preliminary Ecological Risk Assessment for the Registration Review of Diquat

Dibromide

FROM: Elyssa Arnold, Biologist , Risk Assessment Process Leader James Lin, Environmental Engineer

Environmental Risk Branch 2

Environmen tal Fate and Effects Division ( 7507P)

THROUGH: Brian Anderson, Branch Chief

Environmental Risk Branch 2 Environmental Fate and Effects Division ( 7507P)

TO: Bonnie Adler , Chemical Review Manager

Jill Bloom , Team Leader Linda Arrington, Branch Chief Risk Management and Implementation Branch V

Pesticide Re

- evaluation Division (7508P)

This memorandum transmits the preliminary ecological risk assessment for the R egistration

R eview of diquat dibromide

. Based on currently registered uses and labeled rates, this preliminary assessment identifies potential risks to non

- target organisms

. This assessment is

focused on species that are not f ederally listed as threatened or endangered (referred to as “listed”) ; however, some general discussion of taxa for which “ no effect ” determin ations are expected is included. For taxa to which potential risk is identified , specific determinations for listed species are considered uncertain at this time. Currently labeled ra tes of diquat dibromide pose a potential risk of adverse effects

, i.e ., risk, to non

- target terrestrial and aquatic animals, including birds, reptiles, amphibians

, mammals, fish, and aquatic invertebrates

. In addition, diquat dibromide uses result in risks above levels of concern for terrestrial and aquatic plants. These risks may be reduced through label changes such as decrease s in maximum single application rates , decreases in the number of applications allowed per year, removal of aerial applications , u se of spray drift buffers and specification of coarse droplet spectrum to reduce spray drift.

### Page 2 of 76 

# Ecological Risk Assessment for the Registration Review of Diquat Dibromide

U

. S

. EPA PC CODE 032201

CAS No. 85

- 00

- 7

Prepared by : Elyssa Arnold

, Biologist

Jim Lin , Environmental Engineer

Reviewed by: Christine Hartless, Wildlife Biologist

R. David Jones, Senior Agronomist

Approved by:

Brian Anderson

, Branch Chief , Environmental Risk Branch 2

Environmental Fate and Effects Division

Office of Pesticide Programs U.S. Environmental Protection Agency 1200 Pennsylvania Avenue, NW Washington, D.C. 20460

August 1 8 , 2015

### Page 3 of 76 

## Table of Contents

1. Executive Summary

................................ ................................ ................................ ............ 4

1.1. Use Summary

................................ ................................ ................................ .......... 4

1.2. Predominant Risk Concerns

................................ ................................ .................... 4

1.3. Major uncertainties and Critical Data Gaps

................................ ............................ 6

1.4. Risk Reduction Options

................................ ................................ .......................... 7

2. Introduction

................................ ................................ ................................ ......................... 7

3. Problem Formulation Update

................................ ................................ .............................. 8

3.1. Chemical Identification and Mode of Action

................................ ......................... 8

3.2. Use Characterization

................................ ................................ ............................... 8

3.3. Label Uncertainties

................................ ................................ ............................... 12

4. Exposure Assessment

................................ ................................ ................................ ........ 13

4.1. E nvironmental Fate Summary

................................ ................................ .............. 13

4.2. Residues of Concern

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

4.3. Aquatic Exposures

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

4.4. Bioaccumulation

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

4.5. Mon itoring Data

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

4.6. Terrestrial Exposures

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

4.7. Spray Drift Transport

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

5. Effects Analysis

................................ ................................ ................................ ................ 25

5.1. Aquatic Toxicity Data

................................ ................................ ........................... 25

5.2. Terrestrial Toxicity Data

................................ ................................ ....................... 28

5.3. Incidents

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

5.4. Endocrine Disruptor Screening Program

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

6. Risk Characterization

................................ ................................ ................................ ........ 31

6.1. Aquatic Animals

................................ ................................ ................................ ... 31

6.2. Aquatic Plants

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

6.3. Ter restrial Animals

................................ ................................ ............................... 38

6.4. Terrestrial Plants

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

6.5. Risk Conclusions

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

7. Listed Species of Concern

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

7.1. Taxonomic Groups Potentially at Risk

................................ ................................ . 49

8. References

................................ ................................ ................................ ......................... 50

8.1. Cited Environmental Fate and Chemistry Studies

................................ ................ 52

8.2. Cited Ecotoxicity Studies

................................ ................................ ...................... 53 Appendix A. Risk Quadrant Figures and Tables

................................ ................................ .......... 56 Appendix B. SIP Output

................................ ................................ ................................ ............... 58 Appendix C. STIR Output

................................ ................................ ................................ ............ 59 Appe ndix D. SWCC Example Output

................................ ................................ .......................... 60 Appendix E. T

- REX Model Example Inputs

................................ ................................ ................ 62 Appendix F. TERRPLANT Model Example Inputs

................................ ................................ ..... 64 Appendix G. MCnest Output

................................ ................................ ................................ ........ 65 Ap pendix H. Ecotoxicity Data

................................ ................................ ................................ ...... 69

### Page 4 of 76 1. Executive Summary

Diquat dibromide is a non

- selective contact herbicide and desiccant used to control broadleaf and

grassy weeds i n terrestrial and aquatic areas, and as a desiccant in seed crops and potatoes. It is in the bipyridylium class. Diquat formulations contain diquat in the dibromide salt form

, which is the registered active ingredient (PC 032201)

. This assessment, c onsistent with previous assessments, focus es on th e cation form of diquat , referred to in this assessment as diquat (PC 032202)

. Diquat is persistent in the environment, binds strongly to soil and sediment, and is toxic to nearly all tested taxa.

1.1. Use Sum mary

Agricultural u se sites for diquat dibromide include alfalfa, canola, clover, and a large variety of fruit and vegetable crops. Diquat dibromide is used in agriculture for weed control as well as pre

harvest defoliation for seed crops and post

- harvest desiccation for some fruit and vegetable

crops. The most significant agricultural use by amount applied and percent crop treated is on potatoes (U.S. EPA, 2015 a ). Diquat dibromide is used a s a desiccant/defoliant for commercial greenhouses and nurseries, ornamental seed crops, and commerci al and residential landscaping. It is also used in aquatic environments to contro l algae and aquatic weeds, and t o control tree root intrusions in drainage systems. When used as a desiccant , diquat dibromide can be applie d

b y aircraft or ground equipment. In aquatic sites, diquat dibromide may be injected below the water surface for submerged weeds, or sprayed for weed control alo ng the edges of aquatic sites

.

While diquat dibromide is the registered active ingredient (a.i.), the active component of the compound is diquat cation. Therefore, all application rates, exposure estimates, and toxicity endpoints discussed in th is assessment are in units of diquat cation, referred to as diquat. Diquat

cation (184.24 g/mol) is 5 3.55% of diqu at dibromide (344.05 g/mol) by molecular mass

. The maximum treatment concentration for aquatic si tes is 1.47 ppm diquat

. The maximum single application rate for terrestrial sites i s 0.5 lb diquat /acre (A)

. The maximum annual application

rate is 3 lb diquat /A/yr for food uses and 6 lb diquat /A/yr for ornamentals.

1.2. Predominant Risk Concerns

Diquat dibromide is expected to be transported by spray drift and r unoff to non

- targeted areas. Since it binds strongly to soil and mainly to clay matter, diquat dibromide may also be transported to non

- target areas by eroded soil and transported dust . In addition, because available studies suggest that diquat dibromide degrades slowly, if at all, the potential for accumulation

exists in areas of co ntinual use. There were no major degradates identified in any of the environmental fate studies on diquat dibromide

.

Diquat dibromide exhibits acute and chronic toxicity to nearly all taxa tested, including fish, aquatic invertebrates, birds, mammals, and aquatic and terrestrial plants. Diquat dibromide is practically non

- toxic to adult honey bees ( Apis mellifera ) on an acute contact and oral exposure basis, however no data are available on chronic toxicity to adult honey bees or on acute or

chronic toxici ty to larval bees. Incidents have been reported involving aquatic invertebrates, fish, reptiles, and terrestrial plants.

### Page 5 of 76 Figure 1.1 and Table 1.1 give a broad overview of the potential risk concerns and supporting evidence for registered uses of diquat di bromide

. An explanation of these tools can be found in Appendix A

.

Figure 1.1. Graphic Summary of Potential Risks of Current Uses of Diquat DibromideCertainty



# Risk Diquat Dibromide

Terr. Plants

Fish Mammals Birds Aq. I nverts Aq. Plants

Terr. Inverts

### Page 6 of 76 Table 1.1. Evidence of Risk to Taxonomic Groups from Current Uses of Diquat Dibromide



### Predominant Evidence of Negligible Risk Predominant Evidence of Risk

N/A Diquat is expected to persist for extended periods in both terrestrial and aquatic environments.

Terrestrial Plants : RQs> LOC (up to 66 ) via spray drift

for listed and non

- listed dicots for all terrestrial uses and

for listed and non

- listed monocots for some use

scenarios . Multiple incidents reported.

Birds, Reptiles, and Terrestrial

- phase Amphibians : Acute and chronic RQs>LOC for all terrestrial uses. On e reptile incident reported.

Mammals : Acute and chronic RQs>LOC for all

terrestrial uses.

Aquatic Plants : RQs>LOC for listed and non

- listed

vascular and non

- vascular aquatic plants for nearly all use patterns. Consistent with use as an aquatic herbicide.

A quatic Invertebrates : Acute and chronic RQs>LOC for multiple uses for water column and benthic aquatic invertebrates. One mollusk incident reported.

Fish and Aquatic

- phase Amphibians : Acute RQ> LOC

for non

- listed freshwater fish following direct aquatic application. Acute RQs>LOC for listed freshwater fish

for one terrestrial use. No exceedances for estuarine/marine fish. Multiple incidents reported.



### Limited Evidence of Negligible Risk Limited Evidence of Risk

Terrestrial Invertebrates : No risks exceeding levels of concern for adult honey bee acute contact or oral

exposures . No chronic toxicity data or larval toxicity

data available. N/A



### 1.3. Major uncertainties and Critical Data Gaps

Uncertainties specific to this assessment include:

• There are n o chronic toxicity data available for estuarine/marine benthic

invertebrate s, only a 10

- day (subchronic) study on Leptocheirus plumulosus which

evaluated mortality. As reproductive toxicity but not lethality was observed for the freshwater amphipod, Hyalella azteca , there is uncertainty as to whether similar effects would be seen in a chronic study on L. plumulosus . D iquat is expected to partition to sediment in aquatic systems.

• While no risks of concern to terrestrial invertebrates are identified based on acute contact and oral exposure routes, no toxicity data are available with which to assess chronic exposure to a dult honey bees or acute or chronic exposure to larval bees. These exposure routes remain significant uncertainties for the assessment of the impact of diquat dibromide on pollinators. The problem formulation for diquat

### Page 7 of 76 dibromide was completed in 2010, pri or to the introduction of the requirements for chronic testing on honey bees (USEPA et al. , 2014). The Agency expects to publish additional guidance on addressing gaps in bee toxicity data for pesticides that have undergone Registration Review in the near future.

Data gaps include:

• Non

- guideline: Chronic sediment toxicity for estuarine/marine invertebrates

• Terrestrial invertebrate studies

o Non

- guideline (Tier 1): Honey bee larvae acute toxicity

o Non

- guideline (Tier 1): Honey bee adult chronic oral toxicity

o Non

- guideline (Tier 1): Honey bee larvae chronic toxicity

o Non

- guideline (Tier 2): Semi

- field testing for pollinators (tunnel or colony feeding studies)

o Non

- guideline (Tier 2): Field trial of residues in pollen and nectar

o OCSPP 850.3040 (Tier 3): Field test ing for pollina t ors

1.4. Risk Reduction Options

EFED has identified potential o ptions for reducing the risks identified in this assessment or the spatial extent of potential impacts; however, r isk management decisions will be based on an

assessment of both risks and benefits :

• Use of spray drift buffers, specification of medium to coarse droplet size , and/or further restriction of aerial applications to reduce exposure via spray drift.

• Restricting timing of applications to fall and winter to reduce reproductive risks to avian species.

• Reducing the maximum single application rate, decreasing the number of applications per year, and/or increasing application intervals to reduce overall exposure.

2. Introduction

Th is preliminary risk assessment (PRA) examines the potential ecological risks associated with

labeled uses of the herbicide diquat dibromide based on the best available scientific and commercial information on the use, environmental fate and transport, and effects of diquat

dibromide on non

- target organisms. This assessment is focused on species that are not federally listed as threatened or endangered (referred to as “listed”) ; however, some general discussion of

taxa for which “ no effect ” determinations are expected is included. For taxa to which potential

risk is identified , specific determinations for listed species are co nsidered uncertain at this time

. Methodology consistent with the r ecommendations of the April 2013 National Academy of Sciences (NAS) report 1 

### for evaluating risk to listed species is currently under development.

1 http://www.nap.edu/catalog.php?record_id=18344

### Page 8 of 76 3. Problem Formulation Update

A d etailed problem formulation for the registration review of diquat dibromide was completed in 2010 (USEPA, 2010a, 2010c). Since that time, an ecological risk assessment was conducted for a

Section 3 new use on canola at 0.5 lb diqu at /A (USEPA, 2010e) and an endangered species assessment was conducted for the federally threatened delta smelt (USEPA, 2010f). A drinking water memo in supp ort of the new use on canola referred to the previous assessment conducted for a higher use rate (USEPA, 2008, 2010d). The endangered species assessment concluded that diquat was “ likely to adversely affect ” the delta smelt (USEPA, 2010f). A number of ecotoxicity studies have been submitted to the Agency since 2010 and additional studies have been identified from the open literature. The results of these studies were incorporated into this assessment.

G uidance documents and models implemented by EFED since 2010 were also applied i n this

assessment. These include ecological risk assessment guidance for benthic invertebrates (USEPA, 2014c) , guidance for evaluating ecological toxicity data in the open literature (USEPA, 2011b) , the S urface W ater C oncentration C alculator (SWCC) (USEPA, 2014b)

, and the Markov Chain Nest Productivity Model ( MCnest ) ( USEPA , 2014 a )

.

Additionally, d rinking water and inhalation exposure pathways were screened using the SIP (Screening Imbibition Program) and STIR (Screen ing Tool for Inhalation Risk) screening

methods , which were not yet implemented at the time the problem formulation was written . SIP results indicated that drinking water exposure alone is a potential acute and chronic exposure pathway of concern for birds and mammals (see Appendix B ). STIR results showed that droplet inhalation may be a potential exposure pathway of concern for birds, but exposure via vapor inhalation is not likely to be significant (see Appendix C ). This is based on the highest single application rate ( 0.5 lbs diquat /A). SIP and STIR are described in detail at: http://www.epa.gov/oppefed1/models/terrestrial/index.htm

.

3.1. Chemical Identification and Mo de of Action

Diquat is a contact herbicide in the bipyridylium class. 2 

### The bipyridylium herbicides are quaternary ammonium salts. C ompounds in this group

, e.g. , diquat and paraquat, cause rapid disruption of cell membranes and very rapid death of plants

. Diquat penetrate s into the cytoplasm and cause s the formation of peroxides and free electrons (light is required) w hich destroy the cell membranes almost immediately. R apid destruction of cell membranes prevent s

tr anslocation to other regions of the plant. Severe injury is evident hours after application, first as

water

- soaked areas which later turn yellow or brown. Maximum kill is attained in a week or less. Partial coverage of a plant with spray results in spotting and/or pa rtial shoot kill. New growth on surviving plant s will be normal in appearance. Some translocation of d iquat can occur within a plant if a period of darkness follows application (Ashton and Crafts, 1973)

.

3.2. Use Characterization

Diquat dibromide is used as a nonselective contact herbicide for agricultural and non

- crop weed control, aquatic weed control, and as a plant regulator and desiccant for agricultural seed crops.

2 https://www.extension.purdue.edu/extmedia/WS/WS

- 23

- W.html

### Page 9 of 76 The most significant agricultural use is on potatoes, with an annual average of 200,000 l bs a.i. applied per year from 2004

- 2013, and an average of 35% and a maximum of 50% of the crop treated (U.S. EPA, 2015 a ). The quantity of diquat dibromide applied to potatoes during this period is approximately 100 times greater than that applied to any o ther agricultural crop , and the percent crop treated is approximately 10 times greater

.

Tables 3.1, 3.2, and 3.3 summarize the registered uses of diquat for agricultural, landscaping

, and aquatic uses, respectively. The diquat dibromide containing end

- use products include Reglone ® 

### Dessicant (EPA Reg. No. 100

- 1061), Reward ® 

### Landscape and Aquatic Herbicide ( EPA Reg. No. 100

- 1091)

, and Tribune ® 

### Herbicide (EPA Reg. No. 100

- 1390). These products

and their associated Section 24(c) labels are used as surrogates in this assessment to represent over 100 active Section 3 and Section 24(c) labels. All three of these end

- use products are formulated as SL (soluble liquid concentrate) with a concentration of 37.3% a.i. (formulated as 3.73 lbs diquat dibromide/gallon equivalent to 2 lb of the active ingredient diquat /gallon). Registe red application methods include foliar spr ays via ground (broadcast and hand

- held equipment) , aerial, and aquatic (boat) methods

. Diquat dibromide products include co

formulations with other herbicides including glyphosate, prodiamine, dicamba, fluazifop

- P

- butyl, oxyfluorfen, imazapic, and indaziflam. However, only risk from diquat dibromide exposure alone is assessed here.

Table 3.1. M aximum Use Patterns f or Reglone® Dessicant (EPA Reg. No. 100

- 1061 and Associated 24(c)

labels )

Site M ax Sin gle Applicati

on Rate (lb diquat /A) Max # Applica

tions

/Year Max Application

Rate per

year (lb diquat

/A/yr) Minimum

Retreat

ment

Interval

(days) Application Type Application Equipment

Application Timing

Geo Restrictions

Bearing Crops

Artichoke, Asparagus, Ginseng 0.5 3 1.5 5 Directed spray, foliage Ground boom Sprayer When emerged weeds are small

Canola 0.5 1 0.5 NA Broadcast, pre

- harvest foliage

Ground boom Sprayer, Aerial

boom Potato 0.5 2 1 5

Inter

- row Weed Control

Eggplant, Green Pepper, Tomato 0.5 6 3 5 Directed spray, row middle

weeds Ground boom Sprayer

Post

- directed prior to transplanting or as a post

directed hooded spray application when transplants are

well established. FL only

– Eggplant FL, PR only

– Green Pepper,

Tomato

Non

- bearing Crops (Small Fruits

– non

- bearing) Blackberry, Blueberry, Boysenberry, 0.5 1 0.5 NA Directed spray, foliage Ground boom Sprayer When emerged weeds are small

### Page 10 of 76 Cranberry, Dewberry, Gooseberry, Grapes, Huckleberry, Jojoba, Loganberry,

Raspberry

Non

- bearing Crops (Trees

– non

- bearing)
Acerola, Almonds, Apples, Apricots, Banana, Cherries, Coffee, Conifers, Crabapple, Dates,

Figs, Filberts, Grapefruits, Guava,

K iwi, Lemon, Lime, Macadamia, Mango,

Nectarines, Olive, Orange, Papaya,

Passion Fruit, Peaches, Pears, Pecan, Persimmons, Pistachios, Plantains, Plums, Pomegranates, Prunes, Tangelos, Tangerines, Walnuts 0.5 1 0.5 NA Directed spray, foliage

Ground boom Sprayer When emerged weeds are small

Non

- bearing Crops (Vines) Cantaloupe Vines 0.25 6 1.5 5

Post

- harves t Ground boom Sprayer

F L only, e xcept Tomato Vines for FL and SC only Cucumber Vines,

Squash, except
Acorn, Tomato Vines,

Watermelon Vines 0.38 6 2.28 5

Pepper Vines, Squash, Acorn 0.5 6 3 5

Non

- crop ped or Non

- planted Areas on Farms
Fence Lines, Farmyards, Farm Buildings, Fuel Storage Areas, Barrier Strips, Equipment Areas, Dry (non

- flooded areas) around ponds,

lakes and drainage

ditches on farms 0.5 NA 1.5 5 Broadcast, Spot treatment foliage Backpack Sprayer When emerged weeds are small

Seed Crops

Alfalfa seed crop, Clover seed crop 0.5 4 2 5 Broadcast, Pre

- harvest foliage Ground boom sprayer, Aerial

boom

Calendula, Carrots, Coriander, Radishes, except Daikon variety, Spinach, 0.5 1 0.5 NA Broadcast, Pre

- harvest foliage Ground boom sprayer, Aerial

boom 3 to 10 days before harvest prior to swathing

### Page 11 of 76 Sugar beets, Table

Beets, Turnips MN only

– Calendula WA only

– Spinach, Table beets

WA, O R only

- Sugar beets

WA, ID only

– Carrots, Coriander, Radishes, except

Daikon variety, Turnips

Table 3.2. Maximum Non

- Aquatic Use Patterns for Reward® Landscape and Aquatic Herbicide (EPA Reg.

No. 100

- 1091) and Tribune® Herbicide (EPA Reg. No. 100

- 1390)

Site Max Single Applica

tion Rate Max # Applica

tions

/Year Max Applica

tion Rate

per year (lb diquat

/A/yr) Minimum

Retreat

ment

Interval

(days) Application Type/ Application Equipment/

Application Timing/

Geo Restrictions

Commercial Greenhouse (beneath benches), ornamental field grown and

container stock

, and

other similar areas 1 0.5 lb diquat /A 12 6 28 Broadcast, foliage of target weed/ Ground boom sprayer, Backpack Sprayer/

Pre

- plant, Pre

- emergence or Post

- Emergence Dire cted Spray/ No pre

- emergence application on ornamental crops in CA

0.01 lb diquat /gal 12 NA 5 Spot

- Treatment, foliage target

weed/ Backpack sprayer/

Pre

- plant, Pre

- emergence or Post

- Emergence Directed Spray/ No preemergence application on

ornamental crops in CA

Ornamental Seed Crops 0.5 lb diquat /A 3 1.5 5 Broadcast, foliage of target weed/ Ground boom sprayer, backpack sprayer/

Pre

- harvest Desiccation/ Except CA.

Landscape, Industrial, Commercial,

Residential and

Public Areas 0.5 lb diquat / A 3 1.5 28 Broadcast, foliage of target weed/ Ground boom sprayer/

As needed for control of undesired foliage

0.01 lb diquat / gal 3 NA 5 Spot

- Treatment, undesired target

weed/ Backpack sprayer/

As needed for control of undesired foliage

Turf Renovation 0.5 lb diquat /A 2 1 28 Broadcast, undesired turf/ Ground boom sprayer/

As needed

Dormant Established

Turf Grass 0.5 lb diquat /A 2 1 28 Broadcast, to desired turf/ Ground boom sprayer/ Apply when turf grass is do r mant

1 Use inside g reenhouse s is considered an indoor use and will not be assessed. Ornamental field grown and container

stock and “other similar areas” is considered an outdoor use.

### Page 12 of 76 Table 3. 3 . Maximum Direct Aquatic Use Patterns for Reward® Landscape and Aquatic Herbicide (EPA Reg.

No. 100

- 1091) and Tribune® Herbicide (EPA Reg. No. 100

- 1390 and Associated 24(c) Labels )

Site Max Single Application Rate Max # Appli

cations

/Year Max Application

Rate per year (lb diquat / A/yr) Minimum

Retreat

ment

Interval

(days) Application Type/ Application Equipment/

Application Timing/

Geo Restrictions

Floating and

Marginal

Weeds 4 lb diquat /

Surface Acre/1 ft (1.47 ppm diquat ) 12 NA 14 Broadcast, foliage of the target weed species/ Backpack, airboat, spray handgun, helicopter, airplane, or

similar application equipment

results in thorough spray coverage/

As needed/

Not for use in NY without

supplemental labeling

0.04 lb diquat /gal 12 NA 14 Spot

- Treatment, foliage of target weed species/ Backpack, spray handgun, or similar application equipment

results in thorough spray coverage/

As needed/ Not used on Frog's Bit ( Limnobium spongia ) in CA

1. Submersed

Weeds.

2. Standing and Flowing Water

- Submerged

Weeds 4 lb diquat /

Surface A c r e/4 ft (0.37 ppm)
12 NA 14 Broadcast to water surface or

below water surface to contact foliage of weed species./ Backpack, airboat, spray handgun, helicopter, airplane, or

similar application equipment

results in thorough spray coverage/

As needed. 2. FL, ID, AL, GA only 3.NY only 3. Still Water

-

Submerged

Weeds 4 lb diquat /

Surface Acre/1 ft (1.47 ppm)

Still Water

- Floating Weeds 1.5 lb diquat /

Surface Acre/1 ft (0.55 ppm) 12 NA 14 Broadcast, foliage of the target weed species/ Backpack, airboat, spray handgun, or similar application equipment results in thorough

spray coverage/

As needed/

NY only Still Water

- Duckweed,

Cattails 2 lb diquat /

Surface Acre/1 ft (0.74 ppm) 12 NA 14

Note: Treat only 1/3 to 1/2 of water body area at one time and wait 14 days between treatments to prevent oxygen loss from decomposition dead weeds which may cause fish suffocation.



### 3.3. Label Uncertainties

Three diquat dibromide end

- use products and their associated Section 24(c) labels are used as surrogates in this assessment to represent over 10 0 active Section 3 and Section 24(c) labels. These labels are representative of most diquat dibromide uses ( U.S. EPA, 2015b). For the

### Page 13 of 76 assessed labels, missing information such as maximum number of applications per year, maximum annual application rate, and minimum retreatment interval was reconciled through communication with the registrant. For other diquat dibromide labels, ambiguities in this type of information may remain. The degree to which this risk assessment is protective of aquatic and terrestrial organisms depends on the extent to which the assessed labels represent the maximu m use patterns allowed across all the labels

.

4. Exposure Assessment

EFED used standard available models to evaluate potential exposures to aquatic a nd terrestrial organisms as described at http://www.epa.gov/pesticides/science/models_db.htm

. Aquatic exposure was estimated using the SWCC. Terrestrial exposure was estimated using the

Te rrestrial Residue Exposure Model (T

- REX) v.1.5.2 for animals and TERRPLANT v.1.2.2 for plants. Spray drift exposure was estimated using AgDRIFT v2.1.1. Estimates of chronic risk to birds were refined using the MCnest model.

4.1. Environmental Fate Summary

Di quat dibromide has a high water solubility (700,000 mg/L at pH 7) and a low vapor pressure (1

x 10

- 7 

### mmHg at 20 o 

### C). The calculated Henry's Law Constant of 1.4 x 10

- 1 3 

### atm

- m3/mol)

indicates that diquat dibromide is not expected to be volatile under field co nditions or from

water. In laboratory batch equilibrium studies, d iquat dibromide was shown to be immobile with

Freundlich K ads 

### of 15

– 42 in sand sediment and two sand soils and Freundlich K ads 

### values of

1882

– 10740 i n sandy loam, sandy clay loam, and loam soils

. Diquat dibromide binds strongly to clay particles. Due to its low BCF values ( 0.7X for edible, 2.5x for nonedible, and 1.03x for whole fish)

, fish bioaccumulation is not likely to occur.

The primary route of environmental dissipation of diquat dib romide is strong adsorption to soil

par ticles. Diquat dibromide does not hydrolyze or photodegrade and is resistant to microbial degradation under aerobic and anaerobic conditions. Reinert and Rodgers (1987) studied various sediment types and found that un bound, biologically available diquat dibromide can be biodegraded by bacteria in the laboratory. However, because of the rapid adsorption of diquat

dibromide to sediments in the environment which may render it less a vailable to biodegradation, Reinert and Rodgers (1987) suggested that the opportunity for microbial decomposition of sorbed diquat dibromide is reduced

.

When used as an aquatic herbicide, diquat dibromide is removed from the water column by adsorption to sediments, aquatic vegetatio n, and organic matter. Adsorbed diquat dibromide is persistent and immobile, and is not expected to be a ground water contaminant. The available environmental fate data for diquat dibromide are summarized in Table 4.1

. First order

d egradation calculations w ere used to determine the half

- lives in this table.

### Page 14 of 76 Table 4.1

. Chemical Properties and Environmental Fate Parameters of Diquat Dibromide

Parameter Value Source

Selected Physical/Chemical Parameters

Molecular mass (molecular formula) 344.05 g/mol ( C 12 H 12 Br 2 N 2 ) (Calculated)

Vapor pressure (20°C) < 1 x 10

- 7 torr Product Chemistry

Aqueous solubility (20 ° C, pH 7) 700, 000 mg/L

Henry’s Law Constant (20°C) 1.4 x10

- 1 3 atm

- m 3 /mol (Calculated)

Log octanol

- to

- water partition coefficient (log K ow )
(20 ° C, pH 7) - 4.6 MRID 00138928

Persistence in Water

Hydrolysis half

- life (20 ° C) (pH 5, 7, 9) stable MRID 4 0418801

Aqueous photolysis half

- life (20 ° C) (pH 7) 74 days MRID 40418801

Persistence in Soil

Photodegradation half

- life on soil stable MRID 40246101

Aerobic soil metabolism half

- life (20°C) stable MRID 40972301

Aerobic aquatic metabolism half

- life (20 o C) stable MRID 40927601

Anaerobic aquatic metabolism half

- life (20°C) stable M RID 40972302

Mobility

Freundlich Adsorption coefficient (K

a d s ) (mL/g) 15

- 42 (sand sediment and soil)

1882

- 10740 (sandy loam, sandy clay loam and loam soils) MRID 40348601

Field Dissipation

Aquatic Field Dissipation half

- life 1

– 2 days (removed by adsorption) MRID 409 1 7 403

Terrestrial Field Dissipation half

- life stable MRID 42060301

MRID 42060302

Fish Bioconcentration

Bioconcentration Factor (BCF) 0.7X (edible), 2.5x (nonedible), 1.03x (whole fish). Rapid depuration (50% in 3 days) MRID 40326901



### 4.2. Residues of Concern

There were no major degradates isolated from any of the standard environmental fate studies , so no degradates of concern for diquat dibromide have been identified . The aqueous photolysis study included a test system without sediment, which resulted in a half

- life of 74 days and breakdown to the major degradate 1,2,3,4

- tetrahydro

- 1

- oxopyrido (1,2

- a) pyrazin

- 5

- ium ion. However, in an aquatic environment with sediment ( i.e. , natural aquatic environment) photolysis

is not expected to be a significant route of diquat d egradation

.

### Page 15 of 76 4.3. Aquatic Exposures

The available physical/chemical and environmental fate propert ies of diquat dibromide were

us ed to calculate exposure model input parameters to estimate potential environmental

concentrations

. The exposure modelin g for aquatic environments was done separately for

terrestrial and aquatic uses.

4.3.1. Aquatic Modeling for Terrestrial Uses

The expected environmental concentrations ( EEC s ) for diquat dibromide in surface water and

sediment were generated based on maximum application rates ( Table 3.1 and 3.2)

. Simulations were conducted using the SWCC model (v 1.106, May, 2014)

. Sample m odel inputs and output

are in Appendix D . The SWCC simulates pesticide runoff from a treated area to an adjacent water body following appli cations, in addition to loadings that occur directly to the water as a consequence of spray drift. The SWCC scenarios assume a standard 1

- hectare, 2

- meter depth pond (static water body) into which a 10

- hectare field drains (see http://www.epa.gov/oppefed1/models/water/ )

.

The SWCC modeling scenarios are presen ted in Table 4.2

. For each modeling scenario, the maximum single and annual application rate s , the maximum number of applications per year
,

an d the minimum retrea tment interval are listed

. The application timing is determined according to the label directions and the crop stage timing of the modeling scenarios.

Table 4.2 . SWCC Scenarios and Input Parameters Describing Maximum Patterns of Diquat Use on Representative Terrestrial Use Sites

Use Sites Max Single Application Rate (lb diquat /A) Max # Applications / yr Max Applicat ion Rate per year (lb diquat /A/yr)

Minimum Retre atment Interval (days) SWCC Model Scenarios / 1 st application date / Aerial (12.5% drift) or Ground (6.2% drift) Applications

(Inter

- row Weed Control) Eggplant, Green Pepper, Tomato 0.5

6

3

5 CA Tomato / May 1 st / Ground FL Tomato / April 22 nd /Ground

PA Tomato / July 10 th / Ground

Non

- bearing Crops (Vines)

– Cucumber Vines, Squash, except
Acorn, Tomato Vines,

Watermelon Vines 0.38

6

2.28

5 FL Cucumber / December 20 th / Ground

Non

- bearing Crops

(Vines)

– Pepper Vines, Squash, Acorn 0.5

6

3

5 FL Pepper / December 10 th / Ground

(Seed Crops) Alfalfa seed crop, Clover seed

crop 0.5

4

2

5 CA Alfalfa (OP) / December 30 th /Aerial MN Alfalfa (OP) / August 25 th / Aerial

NC Alfalfa (OP) / June 1 st / Aerial PA Alfalfa (OP) / October 31 st / Aerial

Ornamental f ield grown and container 0.5

12

6 CA Nursery / February 25 th / Ground FL Nursery / January 15 th / Ground MI Nursery / January 15 th / Ground

### Page 16 of 76 stock and other similar

areas 28 NJ Nursery / January 15 th / Ground OR Nursery / January 15 th / Ground

TN Nursery / Apri l 1 st / Ground

(Bearing Crops) Artichoke, Asparagus, Ginseng 0.5

3

1.5

5 CA Row

- Crop / March 1 st / Ground MI Asparagus / July 1 st / Ground

(Bearing Crops)

Canola 0.5

1

0.5

NA ND Canola / June 1 st / Aerial

(Bearing Crops) Potato 0.5

2

1

5 ID Potato / June 15 th / Aerial ME Potato / August 1 st / Aerial

Non

- bearing Crops (Small Fruits, Trees)* 0.5

1

0.5

NA MI Cherries / June 1 st / Ground GA Peaches / April 15 th / Ground

GA Pecans / June 1 st / Ground

(Seed Crops) Calendula, Carrots, Coriander, Radishes, except Daikon variety, Spinach, Sugar B eets, Table Beets, Turnips 0.5

1

0.5

NA FL Carrots / November 1 st / Ground MN Sugarbeets / July 1 st / Ground

Ornamental Seed Crops, Landscape, Industrial, Commercial,

Residential and Public

Areas 0.5

3

1.5

5 CA Residential / March 1 st / Ground

Residential BSS / March 1 st / Ground

Turf Renovation,

Dormant Established

Turf Grass 0.5

2

1

28 PA Turf / April 10 th / Ground FL Turf / February 10 th / Ground CA Turf / January 15 th / Ground



### * Refers to maximum use table ( Table 3.1 )



### For aquatic exposure, modeling was conducted for parent diquat dibromide only . Half

- lives used for modeling are presented in Table 4. 3 . Ap plication parameters were chosen based on the likely method of application at the maximum application rate as indicated in the label instructions. Chemical propert ies and model input valu es were c hosen according to the current Input

Parameter G uidance (USEPA, 2009).

Table 4.3

. Chemical Input Parameters for Diquat Aquatic Exposure Modeling

Parameter Value Source

Molecular Weight (g/mol) 344.05 Calculated

Water Solubility (mg/L) 700,000 Product Chemistry

Vapor Pressure (torr) 1 x 10

- 7

Hydrolysis half

- life (day s ) @pH 7 0 (stable) MRI D 40418801

Aqueous photolysis half

- life (day s ) 74 days M RID 40418801

Aerobic soil metabolism half

- life (day s ) 0 (stable) MRID 40972301

### Page 17 of 76 Parameter Value Source

Aerobic aquatic metabolism half

- life (day s ) 0 (stable) MRID 40927601

Anaerobic aquatic metabolism half

- life (day s ) 0 (stable) MRID 40972302

Adsorption coefficients (K d ) 5839 ( mean ) MRID 40348601



### The EECs liste d in Table 4.4 and 4.5 reflect dail y 1

- in

- 10 year return frequency surface water

concentrations in the water column and in benthic environments, respectively, based on maximum application rates for label ed uses of diquat dibromide. The nursery modeling scenarios generally produce the highe st aquatic EECs due to the high annual application rate s for this use

.

Table 4.4

. Aquatic Water Column Exposure Estimates for Diquat Terrestrial Uses

Use Sites SWCC Scenario 1

- in

- 10

- year Peak Exposure (μg/L) 1

- in

- 10

- year 21

- day Average Exposure (μg/L) 1

- in

- 10

- year 60

- day Average Exposure (μg/L)

(Inter

- row Weed Control) Eggplant, Green Pepper, Tomato CA Tomato 5.05 2.94 2.88

FL Tomato 19.1 12.3 12.2

PA Tomato 22.4 12.8 12.7

Non

- bearing Crops (Vines)

– Cucumber Vines, Squash, except Acorn, Tomato Vines,

Watermelon Vines FL Cucumber 13.6 9.24 9.18

Non

- bearing Crops (Vines)

– Pepper Vines, Squash, Acorn FL Pepper 17.7 11.8 11.8

(Seed Crops) Alfalfa seed crop, Clover seed

crop CA Alfalfa 6.69 4.18 4.12

MN Alfalfa 4.37 1.96 1.86

NC Alfalfa 6.93 3.48 3.38

PA Alfalfa 11.3 6.42 6.30

Ornamental f ield grown

and container stock and

other similar areas CA Nursery 52.6 23.3 23.1

FL Nursery 36.6 22.2 22.1

MI Nursery 34.5 20.0 19.9

NJ Nursery 41.7 23.1 22.4

OR Nursery 13.0 9.75 9.70

TN Nursery 34.4 22.1 21.9

(Bearing Crops) Artichoke, Asparagus, Ginseng CA Row

- Crop 8.52 4.14 4.09

MI Asparagus 16.4 4.30 3.83

(Bearing Crops) Canola ND Canola 4.37 1.69 1.66

(Bearing Crops) Potato ID Potato 4.63 2.16 2.13

ME Potato 8.19 4.66 4.60

Non

- bearing Crops (Small Fruits, Trees) MI Cherries 5.03 2.17 2.17

GA Peaches 6.17 1.89 1.88

### Page 18 of 76 Use Sites SWCC Scenario 1

- in

- 10

- year Peak Exposure (μg/L) 1

- in

- 10

- year 21

- day Average Exposure (μg/L) 1

- in

- 10

- year 60

- day Average Exposure (μg/L)

G A Pecans 4.01 2.07 2.06

(Seed Crops) Calendula, Carrots, Coriander,

Radishes, except Daikon variety, Spinach, Sugar B eets, Table Beets, Turnips FL Carrots 3.37 1.99 1.98

MN Sugarbeets 3.47 1.49 1.48

Ornamental Seed Crops,

Landscape, Industrial, Commercial,

Residential and Public

Areas CA Residential 2.51 1.26 1.22

Residential BSS 4.08 1.91 1.87

Turf Renovation,

Dormant Established

Turf Grass PA Turf 4.04 1.57 1.55

FL Turf 2.22 0.870 0.859

CA Turf 2.05 0.771 0.760

Bolded values indicate the highest EECs for the use pattern

Table 4.5. Aquatic Benthic Exposure Estimates for Diquat Terrestrial Uses

Use Sites SWCC Scenario 1

- in

- 10

- year Peak

Pore Water

Exposure

(μg/L) 1

- in

- 10

- year 21

- day Average

Pore Water

Exposure

(μg/L) 1

- in

- 10

- year Peak

Total / Dry

Sediment

(μg/ kg ) 1

- in

- 10

- year 21

- day Average

Total / Dry

Sediment

(μg/ kg )

(Inter

- row Weed Control) Eggplant,

Green Pepper,

Tomato CA Tomato 2.86 2.86 16702 16702

FL Tomato 12.2 12.2 71248 71248

PA Tomato 12.7 12.7 74168 74168

Non

- bearing Crops (Vines)

– Cucumber Vines, Squash, except Acorn, Tomato Vines,

Watermelon Vines FL Cucumber 9.17 9.15 53553 53436

Non

- bearing Crops

(Vines)

– Pepper Vines, Squash, Acorn FL Pepper 11.7 11.7 68328 68328

(Seed Crops)

Alfalfa seed crop, Clover seed crop CA Alfalfa 4.12 4.10 24060 23944

MN Alfalfa 1.80 1.80 10512 10512

NC Alfalfa 3.34 3.35 19506 19564

PA Alfalfa 6.24 6.24 36442 36442

Ornamental field grown and container

stock

, and other

similar areas CA Nursery 23.1 23.1 134904 134904

FL Nursery 22.0 22.0 128480 128480

MI Nursery 19.9 19.9 116216 116216

NJ Nursery 22.4 23.0 130816 134320

OR Nursery 9.69 9.69 56590 56590

### Page 19 of 76 Use Sites SWCC Scenario 1

- in

- 10

- year Peak

Pore Water

Exposure

(μg/L) 1

- in

- 10

- year 21

- day Average

Pore Water

Exposure

(μg/L) 1

- in

- 10

- year Peak

Total / Dry

Sediment

(μg/ kg ) 1

- in

- 10

- year 21

- day Average

Total / Dry

Sediment

(μg/ kg )

TN Nursery 21.9 21.9 127896 127896

(Bearing Crops) Artichoke, Asparagus, Ginseng CA Row

- Crop 4.10 4.09 23944 23886

MI Asparagus 3.80 3.80 22192 22192

(Bearing Crops)

Canola ND Canola 1.64 1.64 9578 9578

(Bearing Crops)

Potato ID Potato 2.12 2.12 12380 12380

ME Potato 4.60 4.50 26864 26806

Non

- bearing Crops (Small Fruits, Trees) MI Cherries 2.04 2.17 11914 12673

GA Peaches 1.87 1.87 10921 10921

G A Pecans 2.06 2.06 12030 12030

(Seed Crops) Calendula, Carrots, Coriander, Radishes, except Daikon variety, Spinach, Sugar

B eets, Table Beets, Turnips FL Carrots 1.97 1.97 11504 11504

MN Sugarbeets 1.47 1.47 8585 8585

Ornamental Seed Crops, Landscape, Industrial, Commercial,

Residential and

Public Areas CA Residential 1.20 1.20 7008 7008

Residential BSS 1.85 1.85 10804 10804

Turf Renovation,

Dormant

Established Turf

Grass PA Turf 1.55 1.55 9052 9052

FL Turf 0.851 0.851 4970 4970

CA Turf 0.751 0.750 4385 4380

Bolded values indicate the highest EECs for the use pattern



### 4.3.2. Aquatic Modeling for Aquatic Uses

T h e maximum single application rate for the di rect aquatic use is 4 lb diquat /surface a c re/ft (see Table 3.3) . The labels also specify to treat only 1⁄3 to 1⁄2 of water body area at one time with a minimum retreatment interval of 14 days. Considering the receiving water body as the standard

1

- hectare ( i.e. , 2.47 acre), 2

- meter ( i.e. , 6 .56 ft) depth pond, the initial loading of diquat is shown

below:

4 lb diquat /surface a cre /ft x 1⁄2 x 6.56 ft x 2.47 acre = 32.4 lb diquat

F actor ing in the volume of the pond, the initial concentration in the pond after the first treatment will be 0.735 mg/L (ppm). Considering the minimum retreatment interval of 14 days, the diquat concentrations in the pond following the re peated treatments are shown in Figure 4.1

, based on

### Page 20 of 76 the aquatic field dissipation half

- life of 2 days. The maximum 21

- day average concentration is 0.133 mg/L, and the maximum 60

- day average concentration is 0.116 mg/L. For reference

purpose s , all these expected values are h igher tha n the drinking water MCL of 0.02 mg/L.

Figure 4.1. Diquat Concentration in the Standard Pond Following Aquatic Applications



### The results of SWCC runs were used to estimate the sediment and pore water concentrations. In a total of 30 SWCC runs, the range for the ratios between the peak water concentrations to the peak pore water concentrations is from 23.1% to 74.54% with the average of 50.36%. Similarly, the range for the ratios between 21

- day average water concentrations to the 21

- day average pore

wate r concentrations is from 88.37% to 100% with the average of 97.8%. Using the average values to derive the pore water concentrations, the peak water concentration of 0.735 mg/L would yield a value of 0.370 mg/L for peak pore water concentration. The 21

- da y average pore water concentration will be 0.130 mg/L (based on the water concentration of 0.133 mg/L). The

results for sediment concentrations of all the 30 SWCC runs show a conversion factor of

0.0171% ; this factor was used to derive the sediment concen trations in terms of μg/kg

. Based on

this conversion factor, the peak sediment concentration is 2161733 μg/kg ( 0.370 mg/L * 1000 μg/mg ÷ 0.0171%) and the 21

- day average value is 760124 μg/kg. The 21

- day average sediment EEC is compared to the chronic sediment toxicity endpoints.

4.4. Bioaccumulation

Based on the low BCF val u es (see Table 4.1 ) , bioaccumulation is not a concern for diquat

dibromide

.

4.5. M onitoring Data

No surface water or groundwat er monitoring data for diquat were found from searches of the

E PA Pesticides in groundwater database (1994) or the USGS National Water

- Quality Assessment Program (NAWQA). 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

0 10 20 30 40 50 60 70 

### Diquat Conc. (mg/L) in the Pond with Time

### Page 21 of 76 Surface and ground water monitoring data are available for diquat from the South Florida Wa ter Management District (SFWMD) and the EPA Office of Water. An MCL of 0.02 mg/L (20 ppb)

was established for diquat in 1999 , and the Florida Department of Environmental Protection (FDEP) has accepted this standard.

The SFWMD data base contained a total of 42 samples taken from April 1992 to November 2000

at approximately a 1

- 3 month interval. For diquat, the only detection observed in surface water was 0.0045 ppm in 1994 (2.4% detection frequency) . Further monitoring beyond 1994 has

shown no detection s in surface water. Also in the SFWMD, diquat was detected in 9 sediment samples out of 17 sediment samples total taken from canals with a maximum concentration of 3.1 ppm (LOD of 0.25 ppm ; Miles and Pfeuffer, 1997)

.

The EPA Office of Water has also collected monitoring data for diquat at intake pumps of drinking water utilities th at use surface water and ground water, provided by community water

system s. Monitoring was conducted in 14 states over many years. However, data from only eight

states i n the years 1993

- 19 97 were included in the report. In these eight states, the percent of

co mbined surface water and ground water systems reporting exceed a nces of the 20 ppb MCL was 0.06 %, resultin g in a n exceedance for 0.27 % of the population ( USEPA , 2000 ).

4.6. Terrestrial Wildlife Exposures

4.6.1. Birds and Mammals

Dietary EECs for birds and mammals were calculated using T

- REX v.1.5.2 . EECs are based on

the application rates, number of applications, and retreatment intervals presented in Table s 3.1

and 3.2

. A foliar dissipation rate of 35 days (default value) was used for this analysis to estimate dissipation after each application. Model inputs are detailed in Appendix E

. Resulting upper bound exposure estimates to birds and mammals are in Table 4.6

. Use pat terns with the same application rate, number of applications, and application intervals are combined in the table below because they result in identical EECs in T

- REX.

Terrestrial exposure via drinking water may result from the aquatic uses outlined in Ta ble 3.3

, however those uses are not addressed in this section. See Section 3 and Appendix B for discussion of the drinking water exposure pathway for birds and mammals. See Section 3 and Appendix C for discussion of the inhalation exposure pathway for bird s and mammals.

Table 4. 6 . T

- REX Calculated EECs as Food Residues for Terrestrial Animals from Diquat Terrestrial Uses

Food Type Dietary

- Based EEC (ppm) (Mammals and Birds) Dose

- Based EEC for Birds (mg/kg

- bw) Dose

- Based EEC for Mammals (mg/kg

- bw)

All Size Classes Small (20 g) Medium (100 g) Large (1000 g) Small (15 g) Medium (35 g) Large (1000 g)

1. (Inter

- row Weed Control) Eggplant, Green Pepper, Tomato

2. Non

- bearing Crops (Vines)

– Pepper Vines, Squash, Acorn Use pattern: 0.5 lb diquat /A, 6 applications, 5 day retreatment interval Short grass 570 649 370 16 6 54 4 37 6 87 Tall grass 261 298 170 7 6 249 172 40

### Page 22 of 76 Food Type Dietary

- Based EEC (ppm) (Mammals and Birds) Dose

- Based EEC for Birds (mg/kg

- bw) Dose

- Based EEC for Mammals (mg/kg

- bw)

All Size Classes Small (20 g) Medium (100 g) Large (1000 g) Small (15 g) Medium (35 g) Large (1000 g) Broadleaf plants 321 365 208 93 30 6 211 4 9 Fruits/pods 36 41 23 10 34 23 5 .4 Arthropods 223 254 145 65 213 147 3 4

Seeds 3 6 9.0 5.1 2.3 7.6 5.2 1.2

Non

- bearing Crops (Vines)

– Cucumber Vines, Squash, except Acorn, Tomato Vines, Watermelon Vines Use pattern: 0.38 lb diquat /A, 6 applications, 5 day retreatment interval Short grass 433 49 4 2 81 126 413 28 6 6 6 Tall grass 19 9 226 1 29 5 8 189 13 1 30 Broadleaf plants 24 4 27 8 1 58 7 1 232 16 1 37 Fruits/pods 27 3 1 1 8 7. 9 2 6 1 8 4.1 Arthropods 1 70 193 110 49 16 2 11 2 26

Seeds 27 6 .9 3.9 1.8 5.7 3.97 0.92 (Seed Crops) Alfalfa seed crop, Clover seed crop Use pattern: 0.5 lb diquat /A, 4 applications, 5 day retreatment interval Short grass 416 474 270 121 39 7 274 6 4 Tall grass 19 1 217 124 55 18 2 12 6 29 Broadleaf plants 234 267 152 68 223 154 3 6 Fruits/pods 26 30 17 7.6 2 5 17 4.0 Arthropods 163 186 106 47 15 5 107 2 5

Seeds 26 6.6 3.8 1.7 5.5 3.8 0.88

Ornamental field grown and container stock

, and other similar areas Use pattern: 0.5 lb diquat /A, 12 applications, 28 day retreatment interval Short grass 281.56 32 1 18 3 8 2 26 8 18 6 4 3 Tall grass 129.05 14 7 8 4 3 8 123 85 20 Broadleaf plants 158.38 180 10 3 4 6 151 104 24 Fruits/pods 17.60 20 1 1 5.1 17 1 2 2.7 Arthropods 110.28 12 6 7 2 3 2 105 7 3 1 7

Seeds 17.60 4. 5 2.5 1.1 3.7 2.6 0.60

1. (Bearing Crops) Artichoke, Asparagus, Ginseng

2. Ornamental Seed Crops, Landscape, Industrial, Commercial, Residential and Public Areas Use pattern: 0.5 lb diquat /A, 3 applications, 5 day retreatment interval Short grass 327 37 3 212 95 312 21 6 50 Tall grass 1 50 17 1 97 4 4 14 3 9 9 2 3 Broadleaf plants 184 2 1 0 1 20 5 4 175 121 2 8 Fruits/pods 20 23 13 5 .9 19 13 3 .1 Arthropods 128 14 6 83 37 122 84 20

Seeds 20 5 .2 2.9 1 .3 4.33 3.0 0.69

1. (Bearing Crops) Canola

2. Non

- bearing Crops (Small Fruits, Trees)

3. (Seed Crops) Calendula, Carrots, Coriander, Radishes, except Daikon variety, Spinach, Sugar Beets, Table Beets, Turnips Use pattern: 0.5 lb diquat /A, 1 application Short grass 120 137 78 35 114 79 1 8 Tall grass 55 63 36 16 52 36 8.4 Broadleaf plants 6 8 77 44 20 64 44 1 0 Fruits/pods 7.5 8.5 4.9 2.2 7.2 4.9 1. 2 Arthropods 47 54 31 14 45 3 1 7. 2

Seeds 7.5 1.9 1.1 0.48 1. 6 1 .1 0.25

### Page 23 of 76 Food Type Dietary

- Based EEC (ppm) (Mammals and Birds) Dose

- Based EEC for Birds (mg/kg

- bw) Dose

- Based EEC for Mammals (mg/kg

- bw)

All Size Classes Small (20 g) Medium (100 g) Large (1000 g) Small (15 g) Medium (35 g) Large (1000 g) (Bearing Crops) Potato Use pattern: 0.5 lb diquat /A, 2 applications, 5 day retreatment interval Short grass 22 9 260 14 9 66 218 15 1 3 5 Tall grass 10 5 119 68 30 100 69 16 Broadleaf plants 12 9 14 7 8 4 37 0 12 3 8 5 20 Fruits/pods 14 16. 9 .3 4. 2 1 4 9 .4 2. 2 Arthropods 90 102 58 26 85 59 1 4

Seeds 14 3 .6 2.1 0.92 3.0 2. 1 0.49
Turf Renovation, Dormant Established Turf Grass Use pattern: 0.5 lb diquat /A, 2 applications, 28 day retreatment interval Short grass 18 9 215 12 3 5 5 180 124 2 9 Tall grass 8 7 9 9 56 25 8 3 57 13 Broadleaf plants 106 121 69 3 1 101 70 16 Fruits/pods 12 13 7. 7 3.4 11 7

. 8 1.8 Arthropods 7 4 84 48 2 2 7 1 4 9 11

Seeds 1 2 3.0 1.7 0.76 2.5 1.7 0.40



### 4.6.2. Terrestrial Invertebrates

The Guidance for Assessing Pesticide Risks to Bees (USEPA et al. , 2014) provides equations for

the calculation of EECs for bees. The Tier I exposure method is intended to account for the major routes of pesticide exposure that are relevant to bees ( i.e. , through diet and contact). Exposure routes for bees differ based on application type. B ees foraging in a field treated with a pesticide through foliar spray , such as diquat, could potentially be exposed to the pesticide through direct spray as well through consuming contaminated food. Foraging honey bees may

also be exposed to pesticides via consumption of water from surface water, puddles, dew droplet

formation on leaves

, and guttation fluid; however, the Tier I exposure method does not include quantification of exposures via these routes.

The EECs for a single f oliar application of diquat at the maximum application rate are calculated

below. 3



### Adult Contact EEC = 0.5 0 lbs diquat /A * 2.7 μg diquat /bee = 1.35 μg diquat cation /bee

Adult Dietary EEC = 0. 50 lbs diquat /A * 110 μg diquat /g * 0.292 g/day = 1 6

. 1 μg diquat

cation /bee/day

Larval Dietary EEC = 0. 50 lbs diquat /A * 110 μg diquat /g * 0.124 g/day = 6.82 μg diquat /bee/day

3 Based on food consumption rates for larvae (0.124 g/day) and adult (0.292 g/day) worker bees and concentration in pollen and nectar.

### Page 24 of 76 4.6.3. Terrestrial Plants

EECs for terrestrial plants were calculated using TERRPLANT v.1.2.2. TERRPLANT inputs are

detailed in Appendix F

. Resulting upper bound exposure estimates to terrestrial and semi

aquatic (wetland) plants are in Table 4. 7

. EECs are based on the maximum single application

rate for terrestrial uses , solubility, and spray drift fraction

. The default spray drift assumption s in the model were updated to reflect the most recent spray drift modeling guidance with 6% drift for ground applications and 12% drift for aerial applications , consistent with the SWCC modeling for aquatic exposure via spray drift (USEPA, 2013).

Table 4.7 . Calculated EECs for Terrestrial and Semi

- Aquatic Plants near Diquat Terrestrial Use Areas

Crop Single Max. Application

Rate (lbs diquat /A) EECs (lbs diquat /A)

Ground Aerial

Dry

Areas (Total) Semi

Aquatic

Areas (Total) Spray

Drift Dry

Areas (Total) Semi

Aquatic

Areas (Total) Spray

Drift

Non

- bearing Crops (Vines)

– Cucumber Vines, Squash, except Acorn, Tomato Vines,

Watermelon Vines 0.38 0.042 0.21 0.023 0.065 0.24 0.046

All other terrestrial use

s ites 0.50 0.055 0.28 0.030 0.085 0.31 0.060



### 4.7. Spray Drift Transport

Exposure via spray drift was assessed using AgDRIFT v2.1.1. Spray drift deposition as a fraction

of the on

- field application rate varies by distance from the field and by droplet size ( Figure 4.2 )

, and is not dependent on the active ingredient applied . The AgDRIFT Tier 1 model estimates deposition up to 1,000 ft from a treated field. Figure 4.2 depicts spray drift deposition for the first 100 ft. Spray drift exposure can impact both terrestrial and aquatic taxa.

### Page 25 of 76 DSD = Droplet Size Distribution Figure 4.2

. Spray Drift Deposition Fractions at Varying Distance from a Treated Field



### 5. E ffects Analysis

Summaries of the most sensitive aquatic and terrestrial toxicity data for diquat are provided in

Table s 5.1 and 5.2 , respectiv ely

. A full list of toxicity studies considered can be found in Appendix H

. All toxicity endpoints are presented in units of diquat cation.

5.1. Aquatic Toxicity Data

Diquat is slightly to highly toxic to freshwater and estuarine/marine fish on an acute exposure
basis. The most sensitive freshwater fish acute endpoint is from an open literature study on several age classes of walleye ( Stizostedion vitreum ) identified in the ECOTOX database (Paul et
al. , 1994; MRID 49611201; E14903). Diquat dibromide (tested as the end

- use product Diquat HA) had an LC 50 

### of 0.75 mg diquat /L in 8

- 10 day old walleye. While many acute toxicity studies for freshwater fish are available (see Table A

- 1 in Appendix H ), no ne of t hem were conducted using the technical grade active ingredient (TGAI). Therefore, the endpoint used for risk

estimation is based on end

- use product testing (referred to as TEP, typical end

- use product)

. The

most sensitive estuarine/marine fish acute endpoi nt is 51.1 mg diquat /L for the sheepshead

m innow ( Cyprinodon variegatus ) (MRID 40316101 ); however, this endpoint may be an

underestimate of the true toxicity due to the presence of precipitate in the test system. Chronic exposure studies on freshwater and estuarine/marine fish demonstrated effects on fish growth at 0.316 mg diquat/L (NOAEC = 0.122 mg diquat/L) and 7.7 mg diquat/L (NOAEC = 3.0 mg diquat/L), respectively (MRIDs 40380703, 49095901). 0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00

0 10 20 30 40 50 60 70 80 90 100Deposition Fraction

Distance from Edge of Treated Field (ft)

Aerial Spray, Fine to Medium DSD Ground Spray, Very Fine to Fine DSD

Aerial Spray, Medium to Coarse DSD Ground Spray, Fine to Medium/Coarse DSD

### Page 26 of 76 A 4

- day study on the African clawed frog ( Xenopus laevis ) resulted in mortality of 20% at 0.5 0

mg diquat /L, 45% at 0.75 mg diquat /L, 75 % at 1.00 mg diquat /L, and 10 0% at 1.2 5, 1.50, and

2

. 00 mg diquat /L (MRID 05005290). Inhibition in growth and pigmentation was seen in

sur vivors a f t er day 3 and distortion in body shape was observed at 1.5 mg diquat /L.

Diquat is slightly to very highly toxic to freshwater and estuarine/marine invertebrates on an acute exposure basis. The most sensitive species tested is Hyalella azteca with an LC 50 

### of 0.09

mg diquat /L (MRID 48826701). The most sensitive chronic aquatic invertebrate endpoint is from an open literature study identified in the ECOTOX database evaluating the toxicity of diquat dibromide to great pond snails ( Lymnaea stagnal is ) (Ducrot et al ., 2010; MRID 49613201; E168652). Over the full snail lifecycle, diquat exposure impacted development and food consumption at 0.0032 mg diquat /L (NOAEC = 0.0011 mg diquat /L). Hatching rate and mortality were impacted at 0.0067 mg diquat /L. The study simulated exposure from four aquatic applications of diquat dibromide (tested as the end

- use product Reglone 2). Recovery was observed following transfer of surviving snails to clean water on day 168 of the study

. The most

sensitive chronic aqua tic invertebrate endpoint from a study using TGAI is on Daphnia magna

, with a NOAEC of 0.036 and a LOAEC of 0.057 mg diquat/L based on survival (MRID 40380702).

Because diquat binds strongly to sediment, tests on benthic invertebrates were also required. A

42

- day lifecycle test on the freshwater amphipod Hyalella azteca showed that diquat exposure significantly impacted reproduction at 11 mg diquat /kg sediment or 0.043 mg diquat /L pore water (MRID 49262901). A 63

- day lifecycle test on the freshwater midge Chironomus dilutus showed no effects on survival, growth, or reproduction up to 37 mg diquat /kg sediment or 0.54

mg diquat /L pore water (MRID 49261902)

. A 10

- day test on the marine amphipod Leptocheirus plumulosus measured only impacts on survival, and found no effect at 110 mg diquat /kg sediment (MRID 49584101). Diquat was not detected above the LOQ in pore water (0.0048 mg diquat /L on Day 0 and 0.0043 mg diquat /L on Day 10) in that study.

In tests with vascular and non

- vascular aquatic plants, s ignificant toxic effects including decreases in biomass, growth rate, and frond number (for Lemna gibba ) were observed

. EC 50 

### values for aquatic plants range from 0.00070 to 102 mg diquat/L (see Table A

- 1 1 in Appendix

H ).

Table 5.1. Most Sensitive Toxicity Endpoints for Aquatic Organisms Exposed to Diquat

Taxonomic

Group Study Type Test

Substance (% diquat ) Test Species Toxicity Value

measured mg diquat /L (Acute Toxicity Category or Most Sensitive Endpoints ) MRID and Study

Classification

Aquatic Vertebrates

Freshwater

fish 1 Acute TEP ( 240 g diquat /L ) Walleye ( Stizostedion vitreum) 96

- hr LC 50 = 0.75 ( Highly toxic) 49611201 Quantitative

Chronic (Early

- l ife

Stage) TGAI (21.1%) Fathead minnow ( Pimephales promelas ) 34

- d NOAEC = 0.122

34

- d LOAEC = 0.316 (Growth) 40380703 Acceptable

### Page 27 of 76 Taxonomic

Group Study Type Test

Substance (% diquat ) Test Species Toxicity Value

measured mg diquat /L (Acute Toxicity Category or Most Sensitive Endpoints ) MRID and Study

Classification

Estuarine/

marine fish Acute TGAI (21.1%) Sheepshead Minnow ( Cyprinodon variegat u s ) 96

- hr LC 50 = 51.1 (Slightly toxic) 40316101 Acceptable

Chronic TGAI (21.5%) Sheepshead Minnow 34

- d NOAEC = 3.0

34

- d LOAEC = 7.7 (Growth) 49095901 Acceptable

Aquatic Invertebrates in Water Column

Freshwater

invertebrates Acute TGAI (23.6%) Hyalella azteca 96

- hr EC 50 = 0.09 (Very highly toxic) 48826701 Acceptable

Chronic TEP (16.7%) Great Pond Snail ( Lymnaea stagnalis ) 168

- d NOAEC = 0.0011

168

- d LOAEC = 0.0032

(Development, Food consumption) 49613201 Quantitative

TGAI (21.1%) Daphnia magna 21

- d NOAEC = 0.036

21

- d LOAEC = 0.057 (Survival) 40380702 Acceptable

Estuarine/

marine

invertebrates Acute TGAI (21.1%) Mysid Shrimp ( Americamysis bahia ) 96

- hr LC 50 = 0.42 ( Highly toxic ) 40315701 Acceptable

Chronic TGAI (21.5%) Mysid Shrimp 31

- d NOAEC = 0.052

31

- d LOAEC = 0.104 (Female dry weight) 49095902 Acceptable

Benthic Invertebrates

Freshwater

invertebrates Chronic TGAI (21.5%) Hyalella azteca 42

- d NOAEC = 11 mg/kg sed. = 0.043 mg/L pore water 2

42

- d LOAEC = 23 mg/kg sed.

= 0.037 mg/L pore water 2 (Reproduction) 49261901 Acceptable

Estuarine/

marine

invertebrates Sub

chronic TGAI (22.2%) Leptocheirus plumulosus 10

- d NOAEC = 110 mg/kg

sed.

10

- d LOAEC >110 mg/kg sed. (No effects) 3 49584101 Acceptable

Aquatic Plants

Aquatic plants and algae Vascular 4 TGAI (22.4%) Duckweed ( Lemna gibba ) 14

- d NOAEC = 0.0012

14

- d EC 50 = 0.0047

(Frond number) 48784007 Acceptable

Non

vascular TGAI (20.5%) Freshwater Diatom ( Navicula pelliculosa ) 120

- hr NOAEC = 0.00033

120

- hr EC 50 = 0.00070 (Yield) 48784008 Supplemental

1 F ish are used as surrogate species for aquatic

- phase amphibians.

2 Due to the relatively high 0

- hour recovery of pore water co ncentration at the 11 mg diquat /kg level, the TWA calculated concentration at this level exhibited a shift in order, i.e. , was higher than the TWA

- calculated pore water concentration for the hig her nominal level, 23 mg diquat /kg.

3 Pore water concentrations w ere below the LOQ (0.0048 mg diquat /L on Day 0 and 0.0043 mg diquat /L on Day

10 ). Survival was the only endpoint measured.

4 A non

- guideline Tier III study cited in previous assessments (MRID 41883002 ) provided an EC 50 of 0.00075 mg diquat /L for giant duckweed ( Spirodela punctata ) based on decrease in dry weight. This endpoint will be used for

additional risk characterization.

### Page 28 of 76 5.2. Terrestrial Toxicity Data

Diquat is moderately to highly toxic to birds on an acute exposure basis. When the LD 50 

### values

for the mallard duck ( Anas platyrhynchus ) (60.6 mg diquat /kg

- bw; MRID 00106559) and zebra

finch ( Taeniopygia guttata ) (28.9 mg diquat /kg

- bw; MRID 49095903) are scaled by body weight using the Mineau scaling factor of 1.15, they are equivalent. Diquat is moderately toxic to birds

on a sub

- acute dietary exposure basis. In chronic studies on the mallard duck, effects on egg laying have been observed as low as 24 mg diquat /kg

- diet (NOAEC=4.2 mg diquat /kg

- diet) ( MRID 00116565 )

. Additional studies have demonstrated that varying the window of exposure during the egg laying period can result in higher LOAECs (MRIDs 48784012, 48784013 ). One study demonstrated full recovery of egg production during a post

- treat ment recovery period (MRID 48784014).

Diquat is moderately toxic to mammals on an acute exposure basis (MRID 00081506) . In a 2

- generation reproduction study on laboratory rats ( Rattus norvegicus ), the number of pups/litter and pup body weight were affect ed by exposure to diquat at 12 mg diquat /kg

- bw, equivalent to 240 mg diquat /kg

- diet (NOAEC=4 mg diquat /kg

- bw, equivalent to 80 mg diquat /kg

- diet) (MRID 41531301)

.

Diquat is practically non

- toxic to adult honey bees ( Apis mellifera ) on an acute contact and oral exposure basis. No data are available on chronic toxicity to adult honey bees or on acute or

chronic toxicity to larval bees.

No effects on seedling emergence were observed following diquat application to terrestrial plant species (MRID 40165101). T oxicity wa s observed in studies of diquat’s effects on vegetative vigor (MRID 49141801), with greater impacts to dicots than to monocots. This comports with diquat ’ s mode of action as a contact herbicide.

Table 5. 2 . Most Sensitive Toxicity Endpoints for Terrestrial Animals Exposed to Diquat

Taxonomic

Group Study Type Test

Substance (% diquat) Test Species Toxicity Value

measured diquat (Acute Toxicity Category or Most Sensitive Endpoints ) MRID and Study

Classifi cation

Birds 1 Acute Oral TGAI (21.5%) Zebra finch ( Taeniopygia

guttata ) LD 50 = 28.9 mg/kg

- bw (Highly toxic) 49095903 Supplemental

Sub

- acute

dietary TGAI (18.9%) Bobwhite quail ( Colinus virginianus ) LC 50 = 540 mg/kg

- diet (Moderately toxic) 00116565 Supplemental

Chronic TGAI (19.6%) Mallard duck NOAEC = 4.2 mg/kg

- diet LOAEC = 24 mg/kg

- diet (Eggs laid) 00114230 Acceptable

Mammals 2 Acute Oral TEP (19.3%) Laboratory rat ( Rattus norvegicus ) LD 50 = 120 mg/kg

- bw (Moderately toxic) 00081506 Acceptable

Acute

Inhalation TEP (19.5%) LC 50 = 0.19 mg/L (Toxicity Category III) 00162046 Acceptable

### Page 29 of 76 Taxonomic

Group Study Type Test

Substance (% diquat) Test Species Toxicity Value

measured diquat (Acute Toxicity Category or Most Sensitive Endpoints ) MRID and Study

Classifi cation

Chronic (2

- generation reproduction) TGAI (21.1%) NOAEC = 80 mg/kg

- diet = 4 mg/ kg

- bw/day

LOAEC = 240 mg/kg

- diet = 12 mg/kg

- bw/day (F1 pups/litter; F1 body weight gain during lactation) 41531301 Acceptable

Insects Acute

contact TGAI Honey bee ( Apis mellifera ) 48

- hr LD 50 >100 μg/bee (Practically non

- toxic) 00072012 Acceptable

Acute oral TEP (16.7%) 48

- hr LD 50 = 47 μg/bee (Practically non

- toxic) 40208001 Acceptable

Terrestrial

Plants Seedling Emergence TEP Monocots & Dicots NOAEC = 4.65 lb /A

IC 25 >4.65 lb /A

(No effects) 40165101 Acceptable

Vegetative Vigor TGAI (21.5) Monocot: Corn ( Zea mays ) NOAEC = 0.027 lb /A

IC 25 = 0.059 lb /A

(Dry weight) 4914180 1 Supplemental Dicot: Cabbage ( Brassica oleracea ) NOAEC = 0.00091 lb /A

IC 25 = 0.0022 lb /A (Dry weight)

1 Bi rds are used as surrogate specie s for terrestrial

- phase amphibians and reptiles.

2 Mammalian toxicity endpoints provided and reviewed by the U.S. EPA Office of Pesticide Programs Health Effects

Division (HED).



### 5.3. Incidents

A review of the Ecological Incident Information System (EIIS, version 2.1 .1 ), the ‘Aggregate Incident Reports’ database, and the Avian Monitoring Information System (AIMS) for e cological incidents involving diquat dibromide was completed on April 21, 2015 using PC c ode s 032201 (diquat dibromide) and 032202 (diquat).

Eight aquatic incidents classified as ‘possible,’ ‘probable,’ or ‘highly probable’ were reported in

EIIS. All eight incidents were as a result of direct application of diquat dibromide to a water body. Reported effects for all incidents were mortality, with species including clams, fish, frogs

, turtles, and alligators . Of these eight reported incidents, two were m isuse s
, four were registered uses, and two were of unknown legality of use. For three of the incidents that were associated

with registered uses, the cause of death was reported as likely to be due to low dissolved oxygen following a large die

- off of aquat ic plants . No further information regarding cause of mortality was provided for the fourth registered use incident or the two unknown use incidents.

Thirteen terrestrial plant incidents classified as ‘possible,’ ‘probable,’ or ‘highly probable’ are report ed in EIIS. Three of the 1 3 incidents were recorded in EIIS as misuses, four were recorded as registered uses, and the remaining six were recorded as unknown legality. Exposures were recorded as direct spray or spray drift. Reported effects were plant dama ge and plant mortality to species including alfalfa, strawberry, ornamental plants, grapes, spinach,

and wildflowers

.

### Page 30 of 76 In the Aggrega te Incident Reports database, 29 fish and wildlife incidents, 4 7 plant incidents,

and three other non

- target incidents were reported. As no additional information on these aggregated incidents is available , they are assumed to be representative of registered uses of diquat dibromide

.

No avian incident reports for diquat or diquat dibromide were identified in the AIMS database.

A lack of reported incidents does not necessarily mean that such incidents have not occurred. In addition, incident reports for non

- target plants and animals typically provide information on

acute mortali ty events only. Reports for other adverse effects, such as reduced growth or impaired reproduction, are rarely received.

5.4. Endocrine Disruptor Screening Program

As required by FIFRA and FFDCA, EPA reviews numerous studies to assess potential adverse

outco m es from exposure to chemicals. Collectively, these studies include acute, subchronic and chronic toxicity, including assessments of carcinogenicity, neurotoxicity, developmental, reproductive, and general or systemic toxicity. These studies include endpoi nts which may be susceptible to endocrine influence, including effects on endocrine target organ histopathology, organ weights, estrus cyclicity, sexual maturation, fertility, pregnancy rates, reproductive los s, and sex ratios in offspring. For ecological hazard assessments, EPA evaluates acute tests and chronic studies that assess growth, developmental and reproductive effects in different taxonomic groups. As part of the Preliminary Problem Formulation for Registration Review (DP

Barcode 365771 ), EPA revi ewed these data and selected the most sensitive endpoints for

relevant risk assessment scenarios fro m the existing hazard database. However, as required by FFDCA section 408(p), diquat dibromide is subject to the endocrine screening part of the

Endocrine D isruptor Screening Program (EDSP).

EPA has developed the EDSP to determine whether certain substances (including pesticide active and other ingredients) may have an effect in humans or wildlife similar to an effect produced by a “naturally occurring estr ogen, or other such endocrine effects as th e Administrator may designate.” The EDSP employs a two

- tiered approach to making the statutorily required determinations. Tier 1 consists of a battery of 11 screening assays to identify the potential of a

chemical substance to interact with the estrogen, androgen, or thyroid (E, A, or T) hormonal systems. Chemicals that go through Tier 1 screening and are found to have the potential to interact with E, A, or T hormonal systems will proceed to the next stage of the EDSP where EPA will determine which, if any, of the Tier 2 tests are necessary based on the available data. Tier 2 testing is designed to identify any adverse endocrine

- related effects caused by the substance, and

establish a dose

- response relationship bet ween the dose and the E, A, or T effect.

Under FFDCA section 408(p), the Agency must s creen all pesticide chemicals. Between October 2009 and February 2010, EPA issued test orders/data call

- ins for the first group of 67 chemicals, which contains 58 pesti cide active ingre dients and 9 inert ingredients. A second list of chemicals identified for EDSP screening was published on June 14, 2013 4 

### and includes some pesticides

4 See http://www.regulations.gov/#!documentDetail;D=EPA

- HQ

- OPPT

- 2009

- 0477

- 0074 for the final second list of

chemicals.

### Page 31 of 76 scheduled for registration review and chemicals found in water

. Neither of these lists should be construed as a list of known or likely endocrine disruptors.

For further information on the status of the EDSP, the policies and procedures, the lists of chemicals, future lists, the test guidelines and the Tier 1 screen ing battery, please visit our

website. 5



### 6. Risk Characterization

For this risk assessment of diquat dibromide , the deterministic RQ method was used to provide a metric of potential risks. The RQ is a comparison of exposure estimates to toxicity endpoints ( i .e. , RQ = EEC/toxicity endpoint)

. The resulting RQs are compared to the Agency’s risk levels of concern (LOC), which are the Agency’s interpretive policy such that when acute or chronic

risk LOCs are exceeded, the need for regulatory action may be consider ed. These criteria are used to indicate when the use of a pesticide, as directed on the label, has the potential to cause

adverse ef fects to non

- target organisms. For acute and chronic risks to animals, the LOCs are 0.5 and 1.0, respectively

, and for plant s, the LOC is 1.0. The LOC for terrestrial invertebrates is 0.4.

For li sted aquatic animals, the acute LOC is 0.05 and for listed terrestrial animals the acute LOC

is 0.1. For each taxa, RQs are generated and risks are discussed. Risk characterization includes

consideration of calculated RQs as well as additional data and lines of evidence.

6.1. A quatic Animals

6.1.1. Fish

The acute risk to non

- listed species LOC (0.5) is exceeded for freshwater fish following direct aquatic use of diquat at an application rate of 4 lb diquat /surface a c re/ft

. The chronic RQ for freshwater fish (0.95) is very close to the chronic risk LOC (1.0) for direct aquatic use of diquat.

N o terrestrial uses result in LOC exceedances for non

- listed freshwater fish, and no aquatic or

terrest rial uses result in LOC exceedances for estuarine/marine fish ( Table 6.1 ). The acute risk LOC (0.05) for listed freshwater fish is exceeded for one terrestrial use pattern s in addition to the direct aquatic use

, field grown and container stock of ornamenta ls

.

Freshwater fish are used as surrogate species for aquatic

- phase amphibians. A n acute toxicity study with diquat on the African clawed frog ( Xenopus laevis ) (MRID 05005290) demonstrates similar toxicity levels as studies on freshwater fish. In this study, 50% mortality was observed at 1.0 mg diquat /L ( most sensitive freshwater fish LC 50 

### =0.75 mg diquat /L , MRID 49611201 ) and inhibition of growth was seen at th e lowest conc entration tested, 0.5 mg diquat /L ( most sensitive freshwater fish NOAEC=0.122 mg diquat /L , MRID 40380703 ) . This study provides evidence that the use of freshwater fish as surrogate species for aquatic

- phase amphibians is appropriate

for assess ing risk from diquat exposure.

There are five fish kill incidents reported in EIIS that are attributed to diquat exposure. One incident was a misuse, involving dumping of a diquat product into a storm drain. Another

5 http://www.epa.gov/endo/

### Page 32 of 76 incident in a creek was attributed to t he use of diquat and malathion in or near the creek. The remaining three incidents were fish kills in golf course ponds that were directly treated with diquat. In these incidents, it was not clear whether the fish kills were the result of direct toxicity

o f diquat or a decrease in dissolved oxygen following the application from the decomposition of the targeted aquatic weeds

. Affected species included bream, carp, bass, and suckermouth

catfish. There was also one frog incident reported in EIIS attributed to diquat exposure. Few details are available for this incident, which was reported by a concerned citizen who observed animal and plant deaths in a creek following municipal spraying of diquat dibromide into the water body. Additionally, 29 fish and wildlif e incidents were reported in aggregate incident

reports.

The water monitoring data available for diquat are very limited, and unlikely to represent high

end exposures. The se data do not represent aquatic applications. The single surface water

detection v alue of 0.0045 mg diquat/L in South Florida is approximately 10 times lower than the concentrations predicted to result in acute or chronic risk concerns for fish. The MCL of 0.02 mg diquat/L is approximately half the concentration predicted to result in a cute or chronic risk

concerns for fish.

Based on the lines of evidence above, direct aquatic use of diquat dibromide poses acute risks of concern to freshwater fish and aquatic

- phase amphibians. Terrestrial uses of diquat dibromide do not pose risk s of co ncern to non

- listed fish but may pose risks of concern to listed freshwater

fish.

Table 6.1. Acute and Chronic Fish Risk Quotients for Aquatic and Terrestrial Uses of Diquat Dibromide

Use Sites Freshwater Estuarine/Marine

Acute Chronic Acute Chronic

LC 50 = 0.75 mg diquat /L NOAEC = 0.122 mg diquat /L LC 50 = 51.1

mg diquat /L NOAEC = 3.0 mg diquat /L

(Inter

- row Weed Control) Eggplant, Green Pepper, Tomato 0.030 0.10 0.0004 0.004

Non

- bearing Crops (Vines)

- Cucumber Vines, Squash, except Acorn, Tomato Vines,

Watermelon Vines 0.018 0.075 0.0003 0.003

Non

- bearing Crops (Vines)

- Pepper Vines, Squash, Acorn 0.024 0.10 0.0003 0.004

(Seed Crops) Alfalfa seed crop, Clover seed

crop 0.015 0.052 0.0002 0.002

Ornamental field grown and container stock,

and other similar areas 0.070 0.19 0.001 0.008

(Bearing Crops) Artichoke, Asparagus, Ginseng 0.022 0.034 0.0003 0.001

(Bearing Crops) Canola 0.006 0.014 0.0001 0.001
(Bearing Crops) Potato 0.011 0.038 0.0002 0.002

Non

- bearing Crops (Small Fruits, Trees) 0.007 0.018 0.0001 0.001

### Page 33 of 76 (Seed Crops) Calendula, Carrots, Coriander, Radishes, except Daikon variety, Spinach, Sugar beets, Table Beets, Turnips 0.005 0.016 0.0001 0.001

Ornamental Seed Crops, Landscape, Industrial, Commercial, Residential and Public

Areas 0.005 0.015 0.0001 0.001

Turf Renovation, Dormant Established Turf

Grass 0.005 0.013 0.0001 0.001

Aquatic Use 0.98 0.95 0.014 0.039

Bolded values exceed the LOC for non

- listed species of 0.5 for acute risk or 1.0 for chronic risk.

Shaded values exceed the LOC for listed species of 0.05 for acute risk

. The LOC of 1.0 for chronic risk to listed species is not exceeded in any of the scenarios in this table

.



### 6.1.2. Aquatic Invertebrates

– Water Column

Acute and chronic risk LOCs are exceeded for non

- listed and listed freshwater and estuarine/marine invertebrates following direct aquatic use of diquat. The acute risk LOC is also

exceeded for non

- listed freshwater invertebrates for one of the mo deled terrestrial use patter ns, field grown and container stock of ornamentals

. For listed species, t he acute risk LOC is

ex ceeded for eight of the 12 terrestrial use patterns for freshwater invertebrates and for two of the terrestrial use patterns for estuarine/marine invertebrates

. The chronic risk LOC is exceeded for all use patterns for non

- listed and listed freshwater invertebrates when the most sensitive TEP endpoint is used, but only for direct aquatic use when the most sensitive TGAI endpoint is used

. Chronic risk for estuarin e/marine invertebrates exceed s the LOC only for direct aquatic use ( Table 6.2 )

.

Chronic risk to freshwater invertebrates was assessed using a NOAEC of 0.0011 mg diquat/L (as TEP) from an open literature study on great pond snails ( Lymnaea stagnalis ) (Ducrot et al

., 2010; MRID 49613201; E168652). This species was affected by diquat exposure at concentrations an order of magnitude lower than the NOAEC for the standard test species, Daphnia magna

. If the NOAEC from the Daphnia study (NOAEC=0.036 mg diqu at /L; MRID 40380702) is used to calculate RQs, the chronic risk LOC is exceeded for direct aquatic use only

. While the endpoint for the great pond snail was derived from a study using TEP while the endpoint for D. magna was derived from a study using TGAI, it is likely that the difference in sensitivity is due primarily to the differences between mollusks and daphnids rather than the different test substances. However, exposure to a formulated product is generally expected only from spray drift, not from ru noff. Any toxicity due to the formulation rather than the active ingredient may be alleviated when exposure is via runoff only.

There is one mollusk incident reported in EIIS that is attributed to diquat exposure. F or two consecutive years, f ollowing trea tment of a large lake with diquat dibromide and copper sulfate,

thousands of dead clams were observed in the lake. It is not known whether the clam mortality was the result of direct toxicity of diquat or cop per sulfate or due to a decrease in dissolved

ox ygen from the decomposition of the targeted aquatic weeds.

The monitoring data available for diquat are very limited, and unlikely to represent high

- end exposures. The data available also do not represent aquatic applications. The single surface water

det ection value of 0.0045 mg diquat/L in South Florida is approximately 10 times lower than the

### Page 3 4 of 76 concentrations predicted to result in acute or chronic risk concerns for aquatic invertebrates. The MCL of 0.02 mg diquat/L is approximately half the concentration predicted to result in acute or chronic risk concerns for aquatic invertebrates.

Based on the lines of evidence above, direct aquatic use of diquat dibromide poses acute and

chronic risks of concern to freshwater and estuarine/marine invertebrates. Terrestrial uses of diquat dibromide pose acute and chronic risks of concern to non

- listed and listed freshwater invertebrates. Terrestrial uses also pose acute risks of concern to listed estuarine/marine

invertebrates.

Table 6.2. Acute and Chronic Aquatic Water Column Invertebrate Risk Quotients for Aquatic and Terrestrial Uses of Diquat Dibromide

Use Sites Freshwater Estuarine/Marine

Acute Chronic Acute Chronic

LC 50 = 0.09 mg diquat/L NOAEC = 0.0011 mg diquat/L (TEP, snail) NOAEC = 0.036 mg diquat/L (TGAI, daphnid) LC 50 = 0.42

mg diquat/L NOAEC = 0.052 mg diquat/L

(Inter

- row Weed Control) Eggplant, Green Pepper, Tomato 0.25 12 0.36 0.053 0.25

Non

- bearing Crops (Vines)

- Cucumber Vines, Squash, except Acorn, Tomato Vines,

Watermelon Vines 0.15 8.4 0.26 0.032 0.18

Non

- bearing Crops (Vines)

- Pepper Vines, Squash, Acorn 0.20 11 0.33 0.042 0.23

(Seed Crops) Alfalfa seed crop, Clover seed crop 0.13 5.8 0.18 0.027 0.12

Ornamental field grown and container stock, and other similar

areas 0.58 21 0.65 0.13 0.45

(Bearing Crops) Artichoke, Asparagus, Ginseng 0.18 3.9 0.12 0.039 0.083

(Bearing Crops) Canola 0.049 1.5 0.047 0.010 0.033
(Bearing Crops) Potato 0.091 4.2 0.13 0.020 0.090

Non

- bearing Crops (Small Fruits, Trees) 0.056 2.0 0.060 0.012 0.042

(Seed Crops) Calendula, Carrots,

Coriander, Radishes, except Daikon variety, Spinach, Sugar

beets, Table Beets, Turnips 0.039 1.8 0.055 0.008 0.038

Ornamental Seed Crops,

Landscape, Industrial, Commercial, Residential and

Public Areas 0.045 1.7 0.053 0.010 0.037

Turf Renovation, Dormant

Established Turf Grass 0.045 1.4 0.044 0.010 0.030

Aquatic Use 8.2 121 3.7 1.75 2.6

Bolded values exceed the LOC for non

- listed species of 0.5 for acute risk or 1.0 for chronic risk.

Shaded values exceed the LOC for listed species of 0.05 for acute risk or 1.0 for chronic risk.

### Page 35 of 76 6.1.3. Aquatic Invertebrates

– Benthic

The a cute risk LOC is exceeded for non

- listed freshwater benthic invertebrates for direct aquatic

use only. The chronic risk LO C is exceeded for listed and non

- listed freshwater benthic

invertebrates for nine of the 12 terrestrial uses ( Table 6.3 )

. The chronic risk LOC may be exceeded for estuarine/marine benthic invertebrates for one or more uses, however this is an uncertainty d ue to the lack of effects in the 10

- day study and the lack of available growth and reproductive data. Diquat is expected to bind strongly to sediment in aquatic systems.

LOC exceedances are seen for freshwater benthic invertebrates based on acute water column exposure as well as chronic exposure via sediment or pore water. The most sensitive freshwater organism tested was the amphipod Hyalella azteca , which experienced decreases in reproduct ive output with chronic exposure to diquat. In a chronic test with the freshwater midge Chironomus

dilutus , no effects on growth or reproduction were observed up to 37 mg diquat/kg sediment, 0.54 mg diquat/L pore water (MRID 49261902) . These results likely indicate differential sensitivity to diquat among benthic invertebrate families.

While there are two LOC exceedance s for estuarine/marine invertebrates based on the NOAEC

from a 10

- day sub

- chronic study of effects of diquat on survival of the amphipod L eptocheirus plumulosus , no effects were observed in this study. The NOAEC for this study is the highest concentration tested. Because a chronic study measuring growth and reproduction was not conducted, whether diquat impacts reproduction in L. plumulosus as it does in the freshwater amphipod H. azteca is unknown. Pore water RQs are n ot reported for L. plumulosus because pore water measurements of diquat in that study were <LOQ (0.0048 mg diquat /L on Day 0 and 0.0043 mg diquat /L on Day 10)

.

As noted above , aquatic monitoring data for diquat are very limited, are unlikely to represent high

- end exposures, and do not represent aquatic applications. The highest sediment detection

value of 3.1 mg diquat/kg in South Florida is one

- third of the lowest modeled sediment EEC and approximately one

- third of the lowest concentration predicted to result in a chronic risk concern

for benthic aquatic invertebrates.

Based on the lines of evidence above, terrestrial and aquatic uses of diquat dibromid e may pose acute and chronic risks of concern to both non

- listed and listed freshwater and estuarine/marine

benthic invertebrates.

Table 6.3. Chronic Aquatic Benthic Invertebrate Risk Quotients for Terrestrial Uses of Diquat Dibromide

Use Sites Freshwater Estuarine/Marine

Pore Water

Acute Pore Water

Chronic Sediment

Chronic Sediment

Sub

- chronic

LC 50 = 0.09

mg diquat /L NOAEC = 0.043 mg diquat /L NOAEC = 11 mg diquat /kg

sediment NOAEC = 110 mg diquat /kg

sediment

(Inter

- row Weed Control) Eggplant, Green Pepper, Tomato 0.14 0.30 6.7 0.67

### Page 36 of 76 Non

- bearing Crops (Vines)

- Cucumber Vines, Squash, except Acorn, Tomato Vines,

Watermelon Vines 0.10 0.21 4.9 0.49

Non

- bearing Crops (Vines)

- Pepper Vines, Squash, Acorn 0.13 0.27 6.2 0.62

(Seed Crops) Alfalfa seed crop, Clover seed

crop 0.069 0.15 3.3 0.33

Ornamental field grown and container stock,

and other similar areas 0.26 0.54 12 1.2

(Bearing Crops) Artichoke, Asparagus, Ginseng 0.046 0.10 2.2 0.22

(Bearing Crops) Canola 0.018 0.038 0.87 0.087

(Bearing Crops) Potato 0.051 0.10 2.4 0.24

Non

- bearing Crops (Small Fruits, Trees) 0.023 0.048 1.1 0.11

(Seed Crops) Calendula, Carrots, Coriander, Radishes, except Daikon variety, Spinach, Sugar beets, Table Beets, Turnips 0.022 0.046 1.0 0.10

Ornamental Seed Crops, Landscape, Industrial, Commercial, Residential and

Public Areas 0.021 0.043 0.98 0.098

Turf Renovation, Dormant Established Turf

Grass 0.017 0.036 0.82 0.082

Aquatic Use 4.1 3.0 69 6.9

Bolded values exceed the LOC for non

- listed species of 0.5 for acute risk or 1.0 for chronic risk.

Shaded values exceed the LOC for listed species of 0.05 for acute risk or 1.0 for chronic risk.



### 6.2. Aquatic Plants

LOCs are exceeded for risk to non

- listed and listed vascular and non

- vascular aquatic plants following aquatic applications and nearly all terrestrial uses of diquat ( Table 6.4 ). D iquat appears to be more toxic to non

- vascular than to vascular aquatic plants. However, a non

guideline Tier III study c ited in previous assessments (MRID 41883002) provided an EC 50 

### of 0.00075 mg diquat /L for giant duckweed ( Spirodela punctata ) based on decrease in dry weight. If this endpoint is used for characterization of risk to non

- listed vascular aquatic plants, the

t oxicity and risk estimation would be equivalent to that for non

- vascular aquatic plants. The Tier III study was an outdoor, microcosm study conducted in sediment

- water systems. Due to the multitude of variables in this study, a more recent acceptable guideline study was considered more appropriate for the calculation of RQs in this assessment. However, the Tier III study provides useful supplemental information, demonstrating that some vascular aquatic plants may

be as sensitive as non

- vascular plants to diquat exposure. This study also demonstrates that the toxicity to aquatic plants from diquat exposure observed in guideline laboratory studies is also seen in more complex systems.

As an aquatic herbicide, risks of concern to aquatic plants as a resul t of exposure to diquat are expected. Consistent with its mode of action, diquat’s toxicity appears to be non

- selective across a variety of species of vascular and non

- vascular aquatic plants (see Appendix H , Table A

- 11 ). One study on green algae, Pseudoki rchneriella subcapitata , demonstrated decreased toxicity in the presence of sediment (MRID 48784011) , suggesting that binding of diquat to sediment in

### Page 37 of 76 aquatic systems may decrease the toxicity to plants in the water column.

Spray drift buffer widths that would be needed to reduce risk s below the LOCs can be calculated to inform potential risk mitigation options. Table s 6.5 and 6.6 below show the calculated buffer

widths for reducing risks below levels of concern for aquatic plants from ground and aerial ( terrestrial ) applications of diquat dibromide at a rate of 0.50 lb diquat /A, which is the maximum single application rate for 11 of the 12 diquat use patterns modeled in this assessment. For diquat

dibromide , a quatic plants are the most sensitive aquatic taxa, so the calculated buffers would also be protective of other aquatic species.

As shown, f or aerial applications with droplet size distribution of fine to medium , buffers of 275

or 900 ft are estimated to reduce risk s to below levels of concern for non

- listed and listed aquatic plant species, respectively. For ground applications with droplet size distribution in the very fine

to fine range and high boom height (50 in or 4.2 ft) , buffer widths are calculate d as 30 or 120 ft

for non

- listed and listed aquatic plant species, respectively. These droplet size distributions are the default s modeled when labels do not specify required droplet size distributions. Buffer widths for alternative droplet size spectra ar e provided in Tables 6.5 and 6.6 for comparison. The buffer

width s in Table s 6.5 and 6.6 are calculated for single application s only. If a water body receives exposure from multiple applications in one treatment area

, risks may be underestimate d

.

Table 6 .4. Aquatic Plant Risk Quotients for Aquatic and Terrestrial Uses of Diquat Dibromide

Use Sites Vascular Non

- vascular

Non

- listed Listed Non

- listed Listed

I C 50 = 0.0047

mg diquat /L NOAEC = 0.0012 mg diquat /L I C 50 = 0.00070

mg diquat /L NOAEC = 0.00033 mg

diquat /L
(Inter

- row Weed Control) Eggplant, Green Pepper, Tomato 4.8 19 32 68

Non

- bearing Crops (Vines)

- Cucumber Vines, Squash, except Acorn, Tomato Vines, Watermelon

Vines 2.9 11 19 41

Non

- bearing Crops (Vines)

- Pepper Vines, Squash, Acorn 3.8 15 25 54

(Seed Crops) Alfalfa seed crop, Clover seed crop 2.4 9.4 16 34

Ornamental field grown and container stock, and other similar

areas 11 44 75 159

(Bearing Crops) Artichoke, Asparagus, Ginseng 3.5 14 23 50

(Bearing Crops) Canola 0.93 3.6 6.2 13
(Bearing Crops) Potato 1.7 6.8 12 25

Non

- bearing Crops (Small Fruits, Trees) 1.1 4.2 7.2 15

(Seed Crops) Calendula, Carrots, Coriander, Radishes, except Daikon variety, Spinach, Sugar beets, Table Beets, Turnips 0.74 2.9 5.0 11

### Page 38 of 76 Ornamental Seed Crops, Landscape, Industrial, Commercial, Residential

and Public Areas 0.87 3.4 5.8 12

Turf Renovation, Dormant

Established Turf Grass 0.86 3.4 5.8 12

Aquatic Use 156 613 1050 2227

Bolded values exceed the LOC of 1.0.

Table 6.5. Spray Drift Buffer Distances to Reduce Risk to Aquatic Plants below Levels of Concern, Derived using AgDRIFT v2.1.1 for Aerial Spray at 0.5 lb diquat /A

Droplet Size Buffer Distance for no LOC Exceedance (ft)

Vascular Aquatic Plants Non

- vascular Aquatic Plants

Non

- listed Listed Non

- listed Listed

Coarse to Very Coarse 0 20 60 155

Medium to Coarse 0 55 115 275

Fine to Medium 0 130 275 900

Very Fine to Fine 70 840 >1,000 >1,000

Bolded rows are the recommended default assumptions for AgDRIFT modeling if droplet size is not otherwise specified on the label.

Table 6.6

. Spray Drift Buffer Distances to Reduce Risk to Aquatic Plants below Levels of Concern, Derived using AgDRIFT v2.1.1 for Ground Spray at 0.5 lb diquat /A

Droplet Size Boom Height Buffer Distance for no LOC Exceedance (ft)

Vascular Aquatic Plants Non

- vascular Aquatic

Plants

Non

- listed Listed Non

- listed Listed

Fine to Medium/Coarse Low 0 0 0 0

High 0 0 0 4

Very Fine to Fine Low 0 0 4 17

High 0 7 30 120

Bolded rows are the recommended default assumptions for AgDRIFT modeling if droplet size or boom height are not otherwise specified on the label.



### 6.3. Terrestrial Animals

6.3.1. Birds

Acute and chronic LOCs are exceeded across all terrestrial use patterns for both non

- listed and

liste d bird species. In this assessment, birds are used as surrogate species for terrestrial

- phase amphibians and reptiles. RQs calculated using T

- REX based on various dietary items are presented in Table 6. 7

.

The chronic RQs in Table 6. 7 are calculated using the NOAEC of 4.2 mg/kg

- diet from a guideline avian reproduction study with the mallard duck (MRID 00114230 , test concentrations 4.2, 24, and 98 mg/kg

- diet ). The only endpoint a ffected in the study was number of eggs laid. Subsequent studies demonstrated t hat beginning exposure to diquat later in the reproductive period than is done in the guideline study may result in higher NOAECs for this endpoint, although reductions in egg laying were seen consistently across all reproduction studies with the

### Page 39 of 76 mallard. A study that began exposure at photostimulation (when the period of light and dark is adjusted to stimulate egg production) and continued for 9 weeks resulted in a NOAEC of 19.2 mg/kg

- diet based on reductions in egg laying (MRID 48784012). A study that beg an exposure after egg laying was already underway and continued for 6 weeks resulted in a NOAEC of 33.8 based on the same endpoint (MRID 48784013). If either of these NOAECs are used to calculate RQs, the LOC is still exceeded for every use pattern and foo d item, with the exception of some seed

- eating birds ( granivores ) for some use patterns. Another study demonstrated that recovery of normal egg production is possible following cessation of a 6 week exposure (MRID 48784014). Overall, these studies demonstr ate that a real decrease in egg production is likely to occur following exposure of birds to diquat through food items. The severity of the reduction and its impact on the population may vary by the timing and duration of the exposure. The impacts of

these factors may also vary between different species of birds. While full recovery is possible

after exposure to diquat dibromide ends, there is likely to be considerable variability based on the timing of the laying period relative to the cessation of exposure . Prolonged exposure to diquat is likely if a bird population remains in the same location ( e.g. , during nesting season)

, due to diquat’s persistence in the environment.

The MCnest model was used to further evaluate the impact of diquat exposure on avian reproduction. The MCnest model estimates the number of broods per female expected in one

year for 60 bird species following a pesticide application based on the application ra te and avian toxicity values (USEPA, 2014a). The model was run a total of 12 times. S ingle application s of 0.5 lb diquat /A on March 1, June 1, September 1, and December 1 were simulated

. A t each of these time points , the model was run using the three toxic ity thresholds ( NOAEC s) for egg production discussed in the previous paragraph ( i.e. , 4.2, 19.2, and 33.8 mg/kg

- diet )

. The results show substantial decreases in broods per female across nearly all 60 species for applications on

March 1 and June 1 for all t hree toxicity thresholds

. F all and winter applications had much less impact on number of broods per female . There were only four species impacted by a diquat application in September , with equal impact across the three toxicity levels, and none impacted by an application in December. This reflects the fact that the majority of b ird species breed in spring and summer months. As shown in Table 4.2 , diquat applications may occur throughout the year for various uses. The higher toxicity thresholds impacted resu lts for some species following a spring or summer application. This demonstrates that the window of exposure during the reproductive cycle does make a difference in the impact of diquat on avian reproduction in these cases. However, the overall picture sho ws that substantial impacts on avian reproduction would be experienced by the majority of species modeled even with a shorter window of exposure during egg laying.

The use of only one application in these model simulations underestimates the potential impact

for use patterns that allow for multiple applications of diquat. Some use patterns allow for up to 6 consecutive applications with only 5 day intervals, consider ably prolonging exposure to nearby nesting bird populations. An example of graphical output from MCnest depicting a June 1 application is in Figure 6.1 ; full graphical output is in Appendix G

.

A n a dditional acute and chronic exposure pathway of concern fo r birds may include consumption of diquat

- contaminated drinking water (see Appendix B ). However, th e potential

risk from that exposure pathway is not quantified here. Exposure via drinking water may be

### Page 40 of 76 mitigated by the strong binding of diquat to sediment in aquatic systems, removing it from the

water , if the birds do not consume that sediment while drinking

. Similarly, exposure via inhalation of droplets following aerial or ground applications of diquat may contribute to potential risk for birds.

There is one reptile incident reported in EIIS attributed to diquat exposure with probable certainty and considered to be an accidental misuse. After application of diquat dibromide to a pond at three times the labeled rate, 400 turtles and 3 alligators died. No i ncidents were reported

with birds.

Based on these lines of evidence, terrestrial uses of diquat dibromide pose acute and chronic

risks of concern to non

- listed and listed birds, reptiles, and terrestrial

- phase amphibians.

Table 6. 7 . Upper Bound Kenaga, A cute and Chronic Avian Dose

- and Dietary

- Based Risk Quotients for Terrestrial Uses of Diquat Dibromide

Dietary item Avian RQs

Acute Dose

- based Size Classes Acute Dietary

based Chronic Dietary

based 20 g 100 g 1000 g

Adjusted LD 50 =

31 mg/kg

- bw Adjusted LD 50 = 39 mg/kg

- bw Adjusted LD 50 = 55 mg/kg

- bw LC 50 = 540 ppm NOAEC = 4.2 ppm
1. (Inter

- row Weed Control) Eggplant, Green Pepper, Tomato

2. Non

- bearing Crops (Vines)

– Pepper Vines, Squash, Acorn
Short grass 21 9.5 3 .0 1.1 136
Tall grass 9.7 4.4 1.4 0.48 62
Broadleaf plants 12 5.3 1.7 0.59 76
Fruits/pods 1.3 0.59 0.19 0.066 8.5
Arthropods 8.3 3.7 1.2 0.41 53

Seeds 0.29 0.13 0.042 0.066 8.5

Non

- bearing Crops (Vines)

– Cucumber Vines, Squash, except Acorn, Tomato Vines, Watermelon Vines
Short grass 16 7.2 2.3 0.8 0 103
Tall grass 7.4 3.3 1 .0 0.37 47
Broadleaf plants 9 .1 4.1 1.3 0.45 58
Fruits/pods 1 .0 0.45 0.14 0.05 0 6.4
Arthropods 6.3 2.8 0.9 0 0.31 40

Seeds 0.22 0.1 0 0.032 0.05 0 6.4 (Seed Crops) Alfalfa seed crop, Clover seed crop
Short grass 15 6.9 2.2 0.77 99
Tall grass 7.1 3.2 1.0 0.35 45

Broadleaf plants 8.7 3.9 1.2 0.43 56

Fruits/pods 0.97 0.43 0.14 0.048 6.2
Arthropods 6.1 2.7 0.86 0.30 39

Seeds 0.22 0.1 0.031 0.048 6.2

Ornamental field grown and container stock

, and other similar areas

Short grass 10 4.7 1.5 0.52 67
Tall grass 4.8 2.1 0.68 0.24 31
Broadleaf plants 5.9 2.6 0.84 0.29 38
Fruits/pods 0.65 0.29 0.093 0.033 4.2

### Page 41 of 76 Arthropods 4.1 1.8 0.58 0.20 26

Seeds 0.15 0.065 0.021 0.033 4.2
1. (Bearing Crops) Artichoke, Asparagus, Ginseng 2. Ornamental Seed Crops, Landscape, Industrial, Commercial, Residential and Public Areas

Short grass 12 5.4 1.7 0.61 78
Tall grass 5.6 2.5 0.79 0.28 36
Broadleaf plants 6.8 3.1 0.97 0.34 44
Fruits/pods 0.76 0.34 0.11 0.038 4.9
Arthropods 4.8 2.1 0.68 0.24 31

Seeds 0.17 0.076 0.024 0.038 4.9

1. (Bearing Crops) Canola

2. Non

- bearing Crops (Small Fruits, Trees) 3. (Seed Crops) Calendula, Carrots, Coriander, Radishes, except Daikon variety, Spinach, Sugar beets, Table Beets, Turnips

Short grass 4.5 2.0 0.63 0.22 29
Tall grass 2.0 0.92 0.29 0.10 13
Broadleaf plants 2.5 1.1 0.36 0.13 16
Fruits/pods 0.28 0.12 0.04 0.014 1.8
Arthropods 1.7 0.8 0.25 0.087 11

Seeds 0.06 0.028 0.009 0.014 1.8 (Bearing Crops) Potato
Short grass 8.5 3.8 1.21 0.42 54
Tall grass 3.9 1.75 0.55 0.19 25
Broadleaf plants 4.8 2.1 0.68 0.24 31
Fruits/pods 0.53 0.24 0.075 0.026 3.4
Arthropods 3.3 1.5 0.47 0.17 21

Seeds 0.12 0.053 0.017 0.026 3.4
Turf Renovation, Dormant Established Turf Grass
Short grass 7.0 3.1 1.0 0.35 45
Tall grass 3.2 1.44 0.46 0.16 21
Broadleaf plants 4.0 1.8 0.56 0.20 25
Fruits/pods 0.44 0.2 0.062 0.022 2.8
Arthropods 2.8 1.2 0.39 0.14 18

Seeds 0.10 0.044 0.014 0.022 2.8

Bolded values exceed the LOC for non

- listed species of 0.5 for acute risk or 1.0 for chronic risk.

Shaded values exceed the LOC for listed species of 0.1 for acute risk or 1.0 for chronic risk.

### Page 42 of 76 Figure 6.1. Modeled Number of Broods by Species for Varying NOAEC s using the MCnest Model

for a June 1 Diquat Application (30 of 60 modeled species presented)



### 6.3.2. Mammals

Acute and chronic LOCs are exceeded for most terrestrial use patterns for both non

- listed and

listed mammal ian species ( Table 6. 8 ) . The only exception is for acute risk to non

- listed mammals for the use pattern s with a single application of diquat at 0.5 lb diquat /A (these include (1) c anola, (2) non

- bearing small fruits and trees , and (3) seed crops of calendula, carrots, coriander, radishes, spinach, sugar beets, table beets, and t urnips)

. Additionally, acute and chronic risks do not exceed levels of concern for granivorous mammals for any use pattern.

An a dditional acute and chronic exposure pathway of concern for mammals may be realized through consumption of diquat

- contaminated drinking water (see Appendix B ). However, the potential risk from this exposure pathway is not quantified here. Exposure via drinking water may be mitigated by the strong binding of diquat to sediment in aquatic systems, removing it

from the water , if the mammals do not consume that sediment while drinking

. Inhalation is not an exposure pathway of concern for mammals.

No incidents have been reported involving diquat and mammals, however th is does not necessarily mean that no incidents have occurred.

Based on these lines of evidence, terrestrial uses of diquat dibromide pose acute and chronic

risks of concern to non

- listed and listed mammals. 0 0.5

1 1.5

2 2.5

3House sparrowMourning doveHorned LarkAmerican robinHouse finchChipping sparrowAmerican goldfinchCedar waxwingNorthern mockingbirdHouse wrenBarn swallowDark-eyed juncoWood thrush (contiguous)White-winged doveLark sparrowGrasshopper sparrowBoat-tailed grackleBlack-capped chickadeeNorthern cardinalAmerican kestrelWood thrush...Carolina chickadeeYellow warblerCommon grackleRed-winged blackbirdCanada goose (giant)Blue JayDickcisselNorthern bobwhiteMallard 

## Number of Broods Expected Following a June 1 Diquat Application of 0.5 lb diquat cation/A

Baseline (No diquat exposure) NOAEC = 33.8 mg/kg-diet (6 mg/kg-bw/d)

NOAEC = 19.2 mg/kg-diet (3.2 mg/kg-bw/d) NOAEC = 4.2 mg/kg-diet (0.412 mg/kg-bw/d)

### Page 43 of 76 Table 6. 8 . Upper Bound Kenaga, Acute and Chroni c Mammalian Dose

- and Dietary

- Based Risk Quotients for Terrestrial Uses of Diquat Dibromide

Dietary item Mammalian RQs

Acute Dose

- based Size Classes Chronic Dose

- based Size Classes Chronic Dietary

based 15 g 35 g 1000 g 15 g 35 g 1000 g

Adjusted

LD 50 = 264 mg/kg

- bw Adjusted

LD 50 = 213 mg/kg

- bw Adjusted

LD 50 = 92 mg/kg

- bw Adjusted

NOAEL

= 8.8 Adjusted

NOAEL

= 7.1 Adjusted

NOAEL

= 3.1 NOAEC = 80 ppm

1. (Inter

- row Weed Control) Eggplant, Green Pepper, Tomato

2. Non

- bearing Crops (Vines)

- Pepper Vines, Squash, Acorn

Short grass 2.1 1.8 0.94 62 53 28 7.1

Tall grass 0.94 0.81 0.43 28 24 13 3.3

Broadleaf plants 1.2 0.99 0.53 35 30 16 4.0

Fruits/pods 0.13 0.11 0.059 3.9 3.3 1.8 0.45

Arthropods 0.81 0.69 0.37 24 21 11 2.8

Seeds 0.029 0.024 0.013 0.86 0.73 0.39 0.45

Non

- bearing Crops (Vines)

- Cucumber Vines, Squash, except Acorn, Tomato Vines, Watermelon Vines

Short grass 1.6 1.3 0.72 47 40 22 5.4

Tall grass 0.72 0.61 0.33 22 18 10 2.5

Broadleaf plants 0.88 0.75 0.40 26 23 12 3.0

Fruits/pods 0.098 0.084 0.045 2.9 2.5 1.3 0.34

Arthropods 0.61 0.52 0.28 18 16 8.4 2.1

Seeds 0.022 0.019 0.010 0.65 0.56 0.30 0.34

(Seed Crops) Alfalfa seed crop, Clover seed crop

Short grass 1.5 1.3 0.69 45 39 21 5.2

Tall grass 0.69 0.59 0.32 21 18 9.5 2.4

Broadleaf plants 0.8 5 0.72 0.39 25 22 12 2.9

Fruits/pods 0.09 0.08 0.043 2.8 2.4 1.3 0.33

Arthropods 0.59 0.5 0.27 18 15 8.1 2.0

Seeds 0.021 0.018 0.01 0.63 0.54 0.29 0.33

Ornamental f ield grown and container stock

, and other similar areas

Short grass 1.0 0.87 0.47 31 26 14 3.5

Tall grass 0.47 0.40 0.21 14 12 6.4 1.6

Broadleaf plants 0.57 0.49 0.26 17 15 7.9 2.0

Fruits/pods 0.064 0.054 0.029 1.9 1.6 0.87 0.22

Arthropods 0.40 0.34 0.18 12 10 5.5 1.4

Seeds 0.014 0.012 0.006 0.42 0.36 0.19 0.22

1. (Bearing Crops) Artichoke, Asparagus, Ginseng 2. Ornamental Seed Crops, Landscape, Industrial, Commercial, Residential and Public Areas

Short grass 1.2 1.0 0.54 35 30 16 4.1

### Page 44 of 76 Tall grass 0.54 0.46 0.25 16 14 7.4 1.9

Broadleaf plants 0.67 0.57 0.30 20 17 9.1 2.3

Fruits/pods 0.074 0.063 0.034 2.2 1.9 1.0 0.26

Arthropods 0.46 0.40 0.21 14 12 6.4 1.6

Seeds 0.016 0.014 0.008 0.49 0.42 0.23 0.26
1. (Bearing Crops) Canola

2. Non

- bearing Crops (Small Fruits, Trees) 3. (Seed Crops) Calendula, Carrots, Coriander, Radishes, except Daikon variety, Spinach, Sugar beets, Table Beets, Turnips
Short grass 0.43 0.37 0.20 13 11 6.0 1.5

Tall grass 0.20 0.17 0.091 6.0 5.1 2.7 0.69

Broadleaf plants 0.24 0.21 0.11 7.3 6.3 3.4 0.84

Fruits/pods 0.027 0.023 0.012 0.81 0.69 0.37 0.094

Arthropods 0.17 0.15 0.078 5.1 4.4 2.3 0.59

Seeds 0.006 0.005 0.003 0.18 0.15 0.083 0.094

(Bearing Crops) Potato

Short grass 0.83 0.71 0.38 25 21 11 2.9

Tall grass 0.38 0.32 0.17 11 9.7 5.2 1.3

Broadleaf plants 0.47 0.40 0.21 14 12 6.4 1.6

Fruits/pods 0.052 0.044 0.024 1.6 1.3 0.71 0.18

Arthropods 0.32 0.28 0.15 9.7 8.3 4.4 1.1

Seeds 0.011 0.010 0.005 0.34 0.29 0.16 0.18

Turf Renovation, Dormant Established Turf Grass

Short grass 0.68 0.58 0.31 20 18 9.4 2.4

Tall grass 0.31 0.27 0.14 9.4 8.0 4.3 1.1

Broadleaf plants 0.38 0.33 0.18 12 10 5.3 1.3

Fruits/pods 0.043 0.036 0.020 1.3 1.1 0.59 0.15

Arthropods 0.27 0.23 0.12 8.0 6.9 3.7 0.9

Seeds 0.009 0.008 0.004 0.28 0.24 0.13 0.15

Bolded values exceed the LOC for non

- listed species of 0.5 for acute risk or 1.0 for chronic risk.

Shaded values exceed the LOC for listed species of 0.1 for acute risk or 1.0 for chronic risk.



### 6.3.3. Terrestrial Invertebrates

The acute oral toxicity endpoint for honey bees is 47 μg diquat /bee and the EEC for adult dietary exposure is 16.1 μg diquat /bee/day. The acute contact RQ for honey bees is 0.34, slightly below the LOC of 0.4 (USEPA et al. , 2014).

The acute contact toxici ty endpoint for honey bees is non

- definitive. Therefore, an RQ value is not calculated for acute risk to terrestrial invertebrates via contact exposure. However, even if the

EEC of 1.35 μg diquat /bee is compared to the highest concentration tested, 100 μg diquat /bee, for the honey bee acute contact study, the RQs would be 0.014, over 10 times lower than the

### Page 45 of 76 acute risk LOC of 0.4 for bees (USEPA et al. , 2014)

.

No toxicity data are available for calculation of chronic RQs for adult bees or for acute or

chro nic RQs for bee larvae. Therefore, there is uncertainty regarding the potential acute and chronic effects of diquat on honey bee larvae as well as potential for chronic effects on adult bees. While diquat is not a systemic compound, r esidues from sub

- letha l concentrations of spray

drift on plants may be present in pollen and/or nectar and represent a route of exposure for bees through both contact and ingestion. Therefore, additional data on pollinators are needed to fully

characterize the risk associated w ith diquat use to all developmental stages of honey bees, as sensitivity may vary according to life

- stage and length of exposure (adult vs. larval and acute vs. chronic, respectively). These data are recommended under the Guidance for Assessing Pesticide Risks to Bees (USEPA et al. , 2014). The Agency expects to publish additional guidance on addressing gaps in bee toxicity data for pesticides that have undergone Registration Review in

the near future.

No incident s associated with diquat involving terrestrial invertebrates, such as bee kills, have been reported to the Agency.

6.4. Terrestrial Plants

LOCs are exceeded for risk to non

- listed and listed dicots following a single ground or aerial application of diquat at 0.38 or 0.50 lb diquat /A as a result of spray drift ( Table 6. 9 ). At 0.38 lb diquat /A, LOCs are exceeded for risk to listed monocots following aerial application of diquat as a result of spray drift . At 0.50 lb diquat /A, LOCs are additionally exceeded for risk to listed monocots following ground application and for risk to non

- listed monocots following aerial application of diquat as a result of spray drift

.

As a means of understanding the potential impact of s pray drift buffers on risk s to terrestrial pl ants , EFED has evaluated buffer widths for various droplet size spectra for ground and aerial applications at 0.50 lb diquat /A, the maximum single application rate for 11 of the 12 diquat use patterns modeled in this assessment ( Table s 6. 10 and 6.11 )

. Based on these evaluations, f or aerial applications, buffer width s of 610 to >1,000 ft would reduce risks below levels of concern

for non

- listed and listed dicot species , depending on droplet size

. F or ground applications, buffer

distances of 100 to 850 ft would reduce risks below levels of concern for non

- listed dicot species, depending on droplet size and boom height . Monocots are relatively less sensitive than dicots to diquat exposure and buffer widths for monocots are therefore smaller

.

The se modeled buffer widths are for a single application only. Risks associated with multiple applications may be greater

.

Exposures from r unoff alone do not result in LOC exceedances for any of the application scenarios modeled. This is due to the lack of toxicity i n the seedling emerg ence study using diquat (MRID 4 0 1 65101) , which simulates exposure in the soil from runoff . Diquat binds strongly to soil particles and is expected to be present in runoff primarily bound to eroded soil rather than freely dissolved in ru noff water. As a non

- systemic contact herbicide, this exposure pathway is not expected to result in toxicity exceeding risk levels of concern to terrestrial plants.

### Page 46 of 76 There are 13 terrestrial plant incidents reported in EIIS that were attributed to diquat e xposure. Three of the 1 3 incidents were misuses. The remaining 9 incidents all resulted from e xposure via direct spray or spray drift. Reported effects were pl ant damage and mortality ; affected species included strawberries, spinach, alfalfa, grapes, and ornamentals . Additionally , 4 7 plant

incidents were reported in aggregate incident reports

. As no additional information on these aggregated incidents is available , they are assumed to be representative of registered uses of diquat dibromide

.

Based on thes e lines of evidence, use s of diquat dibromide on terrestrial sites pose s risks of

concern to non

- listed and listed terrestrial plants. Aquatic uses are assumed to result in minimal exposure to terrestrial plants, although any overspray or spray drift from aquatic applications onto terrestrial sites could pose the same risks as spray drift resulting from terrestrial uses.

Table 6

. 9 . Terrestrial Plant Risk Quotients for Terrestrial Uses of Diquat Dibromide

Type of Plant Ground spray Aerial Spray

Dry Areas Semi

Aquatic

Areas Spray Drift Only Dry Areas Semi

Aquatic

Areas Spray Drift Only

Non

- bearing Crops (Vines)

– Cucumber Vines, Squash, except Acorn, Tomato Vines, Watermelon Vines

0.38 lb diquat /A

Monocot Non

listed <0.1 <0.1 0.39 <0.1 <0.1 0.77

Listed <0.1 <0.1 0.84 <0.1 <0.1 1. 7

Dicot Non

listed <0.1 <0.1 10 <0.1 <0.1 2 1

Listed <0.1 <0.1 25 <0.1 <0.1 50

All other terrestrial uses 0.50 lb diquat /A

Monocot Non

listed <0.1 <0.1 0.51 <0.1 <0.1 1.0

Listed <0.1 <0.1 1.1 <0.1 <0.1 2.2

Dicot Non

listed <0.1 <0.1 1 4 <0.1 <0.1 27

Listed <0.1 <0.1 3 3 <0.1 <0.1 6 6

Bolded RQ values exceed the LOC of 1.0.

Table 6. 10

. Spray Drift Buffer Distances to Reduce Risk to Terrestrial Plants below Levels of Concern, Derived using AgDRIFT v2.1.1 for Aerial Spray at 0.5 lb diquat /A

Plant Type Droplet Size Buffer Distance for no LOC Exceedance (ft)

Non

- listed Species Listed Species

Dicot Coarse to Very Coarse 610 >1,000

Medium to Coarse >1,000 >1,000

Fine to Medium >1,000 >1,000
Very Fine to Fine >1,000 >1,000

Monocot Coarse to Very Coarse 35 75

Medium to Coarse 50 110

Fine to Medium 80 170
Very Fine to Fine 250 670

### Page 47 of 76 Bolded rows are the recommended default assumptions for AgDRIFT modeling if droplet size is not otherwise specified on the label.

Table 6. 11

. Spray Drift Buffer Distances to Reduce Risk to Terrestrial Plants below Levels of Concern

, Derived using AgDRIFT v2.1.1 for Ground Spray at 0.5 lb diquat /A

Plant Type Droplet Size Boom Height 1 Buffer Distance for no LOC Exceedance (ft)

Non

- listed Species Listed Species

Dicot Fine to Medium/Coarse Low 100 320
High 180 470

Very Fine to Fine Low 240 570
High 460 850

Monocot Fine to Medium/Coarse Low 4 7
High 7 10

Very Fine to Fine Low 10 20
High 25 50

Bolded rows are the recommended default assumptions for AgDRIFT modeling if droplet size or boom height are not otherwise specified on the label.

1 Low boom height = 20 in, high boom height = 50 in.



### 6.5. Risk Conclusions

Risks exceeding levels of concern as a result of labeled diquat dibromide uses are identified for all assessed taxa with the exception of terrestrial invertebrates (for which critical toxicity data are lacking) . The specific risks identified for aquatic and terr estrial uses are listed below. Incidents attributed to diquat have been reported involving aquatic invertebrates, fish, reptiles, and terrestrial plants.

Risks exceeding levels of concern for aquatic uses:

• Acute risk to freshwater fish and aquatic

- phase amphibians.

• Acute and chronic risk to freshwater and estuarine/marine invertebrates.

• Risk to vascular and non

- vascular aquatic plants.

Aquatic uses are assumed to result in minimal exposure to terrestrial p lants and animals, although any overspray or spray drift from aquatic applications onto terrestrial sites could pose the same risks as spray drift resulting from terrestrial uses.

Risks exceeding levels of concern for terrestrial uses:

• Acute risk to fresh water fish (listed species only).

• Acute and chronic risk to water column and benthic freshwater invertebrates.

• Acute risk to water column estuarine/marine invertebrates (listed species only) and

acute and chronic risk to benthic estuarine/marine invertebra tes.

• Risk to vascular and non

- vascular aquatic plants.

• Acute and chronic risk to birds, reptiles, and terrestrial

- phase amphibians.

• Acute and chronic risk to mammals.

• Risk to terrestrial plants.

### Page 48 of 76 While no risks to terrestrial invertebrates are identified a bove concern levels based on acute contact and oral exposure routes, no toxicity data are available with which to assess chronic exposure to adult honey bees or acute or chronic exposure to larval bees.

7. Listed Species of Concern

Consistent with EPA’s responsibility under the Endangered Species Act (ESA), the Agency will evaluate risks to federally listed threatened and endangered (listed) species from registered uses of pesticides in accordance with the Joint Interim Approaches de veloped to implement the recommendations of the April 2013 National Academy of Sciences (NAS) report, Assessing Risks to Endangered and Threatened Species from Pesticides

. The NAS report 6 

### ou tlines recommendations on specific scientific and technical issues related to the development of pesticide risk assessments that EPA and the Services must conduct in connection with their obligations under the ESA and FIFRA. EPA will address concerns specific to diquat dibromide in connection with the development of its final registration review decision for diquat dibromide

.

In November 2013, EPA, the U.S. Fish and Wildlife Service, National Marine Fisheries (the Services), and USDA released a white paper containing a summary of their joint Interim Approaches for asse ssing risks to l isted species from pesticides. These Interim Approaches were developed jointly by the agencies in response to the NAS recommendations, and reflect a common approach to risk assessment shared by the agencies as a way of addressing scientific

differences bet ween the EPA and the Services. Details of the joint Interim Approaches are contained in the November 1, 2013 white pape r 7



### , Interim Approaches for National

- Level Pesticide Endangered Species Act Assessments Based on the Recommendations of th e National Academy of Sciences April 2013 Report.

Given that the agencies are continuing to develop and work toward implementation of the Interim Approaches to assess the potential risks of pesticides to listed species and their designated critical habitat, this ecological risk assessment supporting the r egistration review of diquat dibromide does not describe the specific ESA analysis, including effects determinations for specific listed species or designated critical habitat, to be conducted. While the agencies continue to develop a common method for ESA analysis, t his risk assessment for the registration

review of diquat dibromide describe s only the level of ESA analysis completed at this time . This

assessment allow s EPA to focus its future evaluations on the types of species where the potential

for effe cts exists, once the scientific methods being developed by the agencies have been fully vetted. Once the agencies have fully developed and implemented the scientific methods necessary to complete risk assessments for listed species and their designated cri tical habitats, these methods will be applied to subsequent analyses of diquat dibromide as part of completing this registration review.

6 http://www.nap.edu/catalog.php?record_id=18344

7 http://www.epa.gov/espp/2013 /nas.html

### Page 49 of 76 7.1. Taxonomic Groups Potentially at Risk

Based on this screening

- level assessment, there are potential risks of direct effects to listed and

non

- listed terrestrial plants from the use of diquat dibromide on all of its registered use sites. Listed species of all taxa may also be affected through indi rect effects because of the potential

direct effects on listed and non

- lis ted species. Potential direct effects on listed and non

- listed terrestrial plants , aquatic plants, birds, mammals, fish, and aquatic invertebrates from the use of diquat dibromide may be associated with modification of primary constituent elements of desig nated critical habitats, where such designations have been made. However, a t this current stage of the Registration Review process, it is premature to make effects determinations for listed species until fu rther refinements are conducted, based on recommen dations received from the National Academy of Sciences’ (NAS) National Research Council (NRC) April 2013 report 8



### . The NAS report outlines recommendations on specific scientific and technical issues related to the development of pesticide risk assessments t hat are compliant with the ESA and FIFRA.

To make effects determinations for individual listed species, useful refinements may include, but are not limited to, analyses of: 1) more detailed, species

- specific ecological and biological data; 2) more detailed and accurate information on diquat dibrom ide use patterns; and 3) sub

- county level spatial proximity data for the co

- occurrence of potential effects areas and listed species and any designated critical habitat. Examples of such refinements are described below.

The refinements based on individual species data; additional, detailed usage information, when available; and recommendations from the NRC report are expected to help to more accurately identify potential areas of effect and to better inform effects and habitat determinations for listed

spe cies and a ny designated critical habitats.

Table 7. 1 . Potential Effects to Federally

- List ed Taxa Associated with Direct Effects from the Labeled Uses of Diquat

Listed Taxon Direct Effects 1 Uses of Concern Yes/No Acute/Chronic

Terrestrial and semi

- aquatic plants

- monocots Yes NA All terrestrial uses

Terrestrial and semi

- aquatic plants

- dicots Yes NA All terrestrial uses

Terrestrial invertebrates No 2 NA None

Birds Yes Acute and Chronic All terrestrial uses

Terrestrial

- phase amphibians Yes Acute and Chronic All terrestrial uses Reptiles Yes Acute and Chronic All terrestrial uses

Mammals Yes Acute and Chronic All terrestrial uses

Aquatic plants Yes NA All terrestrial uses Direct aquatic use

Freshwater fish Yes Acute Ornamental field grown and container stock Direct aquatic use

Aquatic

- phase amphibians Yes Acute Ornamental field grown and container stock Direct aquatic use

Freshwater invertebrates Yes Acute and Chronic All terrestrial uses

Direct aquatic use

Marine/estuarine fish No NA None

8 http://www.nap.edu/catalog.php?record_id=18344

### Page 50 of 76 Listed Taxon Direct Effects 1 Uses of Concern Yes/No Acute/Chronic

Marine/estuarine

invertebrates 3 Yes Acute and Chronic (Inter

- row Weed Control) Eggplant, Green Pepper, Tomato Ornamental field grown and container stock Direct aquatic use

1 If direct effects are identified to any taxon, indirect effects or effects to designated critical habitat may occur for all

other taxa.

2 Based on acute toxicity data only. Presumed direct effects for larval and chronic toxicity.

3 Based on acute and chronic water column toxicity data and on 10

- day benthic toxicity data. Chronic benthic toxicity data may reveal additional terrestrial uses of concern.



### 8. References

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Reinert, K.H. and J.H. Rodgers. 1987. Fate and persistence of aquatic herbicides. Rev

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.

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USEPA. 2008. Abdel

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.

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at: http ://www.epa.gov/oppefed1/models/water/input_parameter_guidance.htm

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. Apr. 20, 2010

.

### Page 51 of 76 USEPA . 2010 b . Abdel

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Dibromide PF: Docket ID# EPA

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and Effects Division. Memorandum to the Special Review and Reregistrat ion Division . Apr. 20, 2010.

USEPA. 2010 c . Davy, M. Addendum to Diquat Dibromide Problem Formulation for Registration Re view. DP Barcode 365771. U.S. Environmental Protection Agency, Office of Pesticide Programs, Environmental Fate and Effects Division. M emorandum to the Product Reregistration Division . Jun. 7, 2010.

USEPA. 2010 d . Abdel

- Saheb, I. Drin king Water Assessment for Diquat Dibromide (Reglone®) Use on Canola Desiccant. DP Barcode 372018. U.S. Environmental Protection Agency,

Office of Pesticide Programs, Environmental Fate and Effects Division. Memorandum to the Registration Division. Apr. 13, 2010.

USEPA. 2010 e . Davy, M. And I. Abdel

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Dibromide for use on Canola. DP Barcode 372017. U.S. Environmental Protection Agency, Office of Pesticide Programs, Environmental Fate and Effects Division. Memorandum to the Registration Division . May 11, 2010.

USEPA. 2010 f . Hartless, C. and J. Lin. Risks of Diquat Dibromide use to the Federally Threatened Delta Smelt ( Hypomesus transpacificus ). U.S. Environmental Protection Agency, Office of Pesticide Programs, Environmental Fate and Effects Division. Dec. 17, 2010.

USEPA. 2011 a . Hartless, C. and J. Lin. Justification for Changes to D CI for Diquat Dibromide. DP Barcode 384111. U.S. Environmental Protection Agency, Office of Pesticide Programs,

Environmental Fate and Effects Division. Memorandum to the Pesticide Re

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Division . Feb. 9, 2011.

USEPA. 2011 b

. Evaluation Guidelines for Ecological Toxicity D ata in the Open Literature

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Effects Division. Available at http://www.epa.gov/pesticides/science/efed/policy_guidance/team_authors/endangered_speci

es_ reregistration_workgroup/esa_evaluation_open_literature.htm

.

USEPA. 2013. Guidance on Modeling Offsite Deposition of Pesticides via Spray Drift for Ecological and Drinking Water Assessments . U.S. Environmental Protection Agency, Office of Pesticide Progr ams, Environmental Fate and Effects Division, December 20, 2013.

USEPA. 2014a. Implementation of Markov Chain Nest Productivity Model (MCnest)

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

Effects Division. Av ailable at http://www.epa.gov/med/Prods_Pubs/mcnest.htm

.

### Page 52 of 76 USEPA. 2014b. Surface Water Concentration Calculator. U.S. Environmental Protection Agency, Office of Pesticide Programs, Environmental Fate and Effects Division. Available at http://www.epa.gov/oppefed1/models/water/index.htm#swcc

USEPA. 2014c. Toxicity Testing and Ecological Risk Assessment Guidance for Benthic

Invertebrates

. U.S. Environmental Protection Agency, Office of Pesticide Pro grams, Environmental Fate and Effects Division. Available at http://www.epa.gov/pestic ides/science/efed/policy_guidance/team_authors/aquatic_biology_t ech_team/ToxTesting_EcoRiskAssessmentForBenthicInvertebrates.pdf

USEPA . 2015 a . Alsadek, J. Updated Screening Level Usage Analysis (SLUA) Report for Diquat

dibromide PC #032201. U.S. Environme ntal Protection Agency, Office of Pesticide Programs, Biological and Economic Analysis Division. Memorandum to the Pesticide Re

evaluation Division

. Aug. 13, 2015

.

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. Jul. 2, 2015

.

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CA. June 23, 2014.

8.1. Cited Environmental Fate and Chemistry Studies

MRID Citation

00138928 McAllister, W.; Franklin, L.; Cohle, P.; et al. (1984) Uptake, Depuration and Bioconcentration of

14C

- R

- 40244 by Bluegill Sunfish (Lepomis macrochirus): ABC Final Report #30973; T

- 11414. (Un

- published study received Feb 1, 1984 under 476

- EX

- 104; prepared by Analytical Bio

Chemistry Laboratories, Inc., submitted by Stauffer Chemical Co., Richmond, CA; CDL:252340

- A)

40246101 Joseph, R.; Skidmore, M. (1987) Diquat: Photolytic Stability on Soil Surfaces: Lab Project ID: RJ0573B. Unpublished study prepared by ICI Agricultural Experiment Station. 50 p.

40326901 Hamer, M.; Farrelly, E.; Hill, I. (1987) Diquat: Investigation of Accumulation in Bluegill Sunfish

in a Flow

- through System: Lab. Proj. ID RJ0608B. Unpublished study prepared by Imperial Chemical Industries, PLC. 33 p.

40348601 Pack, D. (1987) Freundlich Soil Adsorption Coefficients of Diquat: L aboratory Project I.D: MEF

0069/8716930. Unpublished study prepared by Chevron Chemical Co. 41 p.

40418801 Tegala, B.; Skidmore, M. (1987) Diquat: An Aqueous Photolysis Study: Laboratory Project ID: RJ 0613B. Unpublished study prepared by Imperial Chemica l Industries, PLC. 54 p.

40917403 Fujie, G. (1988) Aquatic Field Dissipation Studies for Aquatic Uses and Aquatic Impact Uses: Laboratory Project ID: R10/1642AQDISS. Unpublished study prepared by Chevron Chemical Co. 183 p.

40927601 Johnston, J. (1988) Aerobic Aquatic Metabolism of Diquat: Laboratory Project ID MEF

- 0073. Unpublished study prepared by Chevron Chemical Co. 116 p.

40972301 Johnston, J. (1988) Aerobic Soil Metabolism of Diquat: Project ID: MEF

- 0071. Unpublished study prepared by Chevron Che mical Co. 116 p.

### Page 53 of 76 40972302 Johnston, J. (1988) Anaerobic Aquatic Metabolism of Diquat: Project ID: MEF

- 0072. Unpublished study prepared by Chevron Chemical Co. 129 p.

42060301 Fujie, G. (1991) Diquat Cation Soil Dissipation Study on Potatoes in New York: Supplement to: Lab Project Number: R010/7059SOILF. Data submitted as alternate to Craven Laboratories generated data. Unpublished study prepared by A&S Environmental Testing, Inc. 465 p.

42060302 Fujie, G. (1991) Diquat Cation Soil Dissipation Study on Potatoes in Idaho: Supplement to: Lab Proje ct Number: R010/7060SOILF. Data submitted as alternate to Craven Laboratories generated data|. Unpublished study prepared by A&S Environmental Testing, Inc. 320 p.



### 8.2. Cited Ecotoxicity Studies

MRID Citation

00072012 Kimura, E.T.; Young, P.R.; Staniszewski, K. (1959) Gibberellic acid: Toxicologic

and pharmacologic studies. American Pharmaceutical Association Journal XLVIII(2):127

- 129. (Also i n unpublished submission received Jan 31, 1977 under 275

- 32; submitte d by Abbott Laboratories, North Chicago, Ill.; CDL: 095795

- D)

00081506 Rittenhouse, J.R. (1979) The Acute Oral Toxicity of Diquat Water Weed Killer: SOCAL 1396/37:67 (S

- 1431). (Unpublished study received Sep 14, 1979 under 239

- 22 47; submitted by

Chevron Chemi cal Co., Richmond, Calif.; CDL:098973

- B)

00106559 Fink, R.; Beavers, J.; Joiner, G.; et al. (1982) Final Report: Acute Oral LD50

-- Mallard Duck: Diquat Technical (SX

- 1260): Project No. 162

- 131. Rev. (Unpublished study received May 13,

1982 under 239

- 1 663; prepared by Wildlife International Ltd. and Washington College, submitted by Chevron Chemical Co., Richmond, CA; CDL:247503

- A)

00114230 Fink, R.; Beavers, J.; Joiner, G.; et al. (1982) One

- generation Reproduction

-- Mallard Duck: Diquat Technical (SX

- 1 306): Project No. 162

- 143; S

- 2069. Final rept. (Unpublished study received Sep 3,

1982 under 239

- 1663; prepared by Wildlife International Ltd., submitted by Chevron Chemical Co., Richmond, CA; CDL: 248290

- D)

00116565 Fink, R.; Beavers, J.; Joiner, G.; et al. (1981) Subacute Feeding

-- Reproduction Screening

Bioassa y

-- Bobwhite Quail: Diquat Tech nical (SX

- 1306): Project No. 162

- 137; S

- 1984. Final rept. (Unpublished study received Sep 3, 1982 under 239

- 1663; prepared by Wildlife International Ltd.,

submitted b y Chevron Chemical Co., Richmond, CA; CDL:248290

- B)

00162046 Bruce, E. (1985) The Acute Inhalation Toxicity of Diquat Water Weed Killer (SX

- 1574) in Rats: SOCAL 2353. Unpublished study prepared by Chevron Environmental Health Center. 67 p.

05005290 Anderson, R.J.; Prahlad, K.V. (1976) The deleterious effects of fungicides and herbicides on Xenopus laevis embryos. Archives of Environmental Contamination and Toxicology 4(3):312

- 323.

40165101 Shilling, D. (1987) The Influence of Preemergence Applied Di quat in the Germination and Emergence o f Selected Plant Species: Labo ratory Project ID: 8704721. Unpublished study prepared by Univ. of Florida, Dept. of Agronomy. 11 p.

40208001 Gough, H.; Collins, I.; Jackson, D.; et al. (1987) Diquat: Acute 5

- day Contact and Oral Toxicity to Honey Bees (Apis mellifera): Laboratory Project ID: RJ055B. Unpublished study prepared by Imperial Chemicals Industries. 39 p.

40315701 Hoberg, J. (1987) Acute Toxicity of Diquat Concentrate to Mysid Shrimp (Mysidopsis bahia): Laboratory Project Identification: S

- 2910: 981.0287.6111.510. Unpublished study prepared by Springborn Life Sciences, Inc. 52 p.

40316101 Nicholson, R. (1987) Acute Toxicity of Diquat Concentrate to Sheepshead Minnow (Cyprinodon variegatus): Laboratory P roject ID: S

- 2909: 981.0287.6110.500. Unpublished study prepared by Springborn Life Sciences, Inc. 55 p.

40380702 Surprenant, D. (1987) The Chronic Toxicity of Diquat Conc. to Daphnia magna under Flow

through Conditions: Lab. Proj. ID. 87

- 8

- 2473. Unpubli shed study prepared by Springborn Life Sciences, Inc. 67 p.

40380703 Surprenant, D. (1987) The Toxicity of Diquat Conc. to Fathead Minnow (Pimephales promelas) Embryo and Larvae. Unpublished study prepared by Springborn Life Sciences, Inc. 64 p.

41531301 Hodge, M. (1990) Diquat: Multigenera tion Study in the Rat: Lab Pro ject Number: CTL/P/2462: RRO393. Unpublished study prepared by ICI Central Toxicology Laboratory. 2174 p.

### Page 54 of 76 41883002 Bellet, E. (1990) Effect of Diquat o n Aquatic Plants

- A Tier 3 Study : Lab Project Number: DQ

124

- 2. Unpublished study prepared by Chevron Chemical Co. 272 p.

43532703 Smyth, D.; Tapp, J. (1988) Diquat: Determination of Toxicity to the Green Alga Selenastrum capricornutum: Lab Project Numbers: FT51/88: BL/B/3271. Unpublished study prepared by ICI PLC. 18 p.

48784007 Magor, S.; Shillabeer, N. (2001) Diquat Dibromide

- Toxicity to Duckweed (Lemna gibba): Final Report. Project Number: BL6966/B, TK0025805. Unpublished study prepared by AstraZeneca UK, Ltd. 25p.

48784008 Kent, S. (1998) Diquat

- Toxicity to the Freshwater Diatom Navicula pelliculosa: Final Report. Project Number: BL6150/B, TK0117407. Unpublished study prepared by AstraZeneca UK, Ltd. 25p.

48784009 Kent, S. (1998) Diquat

- Toxicity to the Marine Alga Skeletonema costatum: Final Report. Project Number: BL6149/B, TK0117408. Unpublished study prepared by AstraZeneca UK, Ltd. 24p.

48784010 Kent, S. (1998) Diquat

- Toxicity to the Blue

- Green Alga Anabaena flos

- aquae: Final Report. Project Number: BL6148/B, TK0117409. Unpublished study prepared by AstraZeneca UK, Ltd. 26p.

48784011 Shillabeer, N. (1998) Diquat

- Toxicity to the Marine Alga Selenastrum capricornutum in the Presence of Sediment: Final Report. Project Number: BL6471/B, TK0117406. Unpublished study

prepare d by AstraZeneca UK, Ltd. 23p.

48784012 Temple, D.; Martin, K.; Beavers, J.; et al. (2004) Diquat

- An Egg Production Study with the Mallard: Final Report. Project Number: 528/158, TK0025806. Unpublished study prepared by Wildlife International, Ltd. 82p.

48784013 Temple, D.; Martin, K.; Beavers, J.; et al. (2004) Diquat

- An Egg Production Study with the Mallard (6 Weeks Exposure during Egglaying): Final Report. Project Number: 528/174, TK0025807. Unpublished study prepared by Wildlife International, Ltd. 106p.

48784014 Temple, D.; Martin, K.; Beavers, J.; et al. (2009) Diquat

- A Reproduction Study with the Mallard to Evaluate Reversibility in Effects following Withdrawal of Dietary Exposure: Final Report. Project Number: 528/273, T001762/08. Unpubli shed study prepared by Wildlife International, Ltd. 127p.

48826701 Bender, E. (2006) Diquat Technical

- Acute Toxicity to Hyalella azteca Under Static Conditions: Final Report. Project Number: TK0120969, 1666/CRA/510/05, 1666/CRC/510/05. Unpublished study prepared by Bioensaios Analises e Consultoria Ambiental Ltda. 23p.

49095901 Minderhout, T.; Kendall, T.; Gallagher, S.; et al. (2012) Diquat Dibromide

- An Early Life

- Stage Toxicity Test with the Sheepshead Minnow (Cyprinodon variegatus): Final Report. P roject Number: 528A/232, TK0175769. Unpublished study prepared by Wildlife International, Ltd. 77p.

49095902 Claude, M.; Kendall, T.; Gallagher, S.; et al. (2013) Diquat Dibromide

- A Flow

- Through Life

Cycle Toxicity Test with the Saltwater Mysid (America mysis bahia): Final Report. Project Number: 528A/240A, TK0024700. Unpublished study prepared by Wildlife International, Ltd. 94p.

49095903 Hubbard, P.; Martin, K.; Beavers, J. (2013) Diquat Dibromide

- An Acute Oral Toxicity Study

with the Zebra Finch Usi ng a Sequential Testing Procedure: Final Report. Project Number: 528/366, TK0024765. Unpublished study prepared by Wildlife International, Ltd. 98p. Relates to

L0001544.

49141801 Martin, J. (2013) Diquat Dibromide

- Evaluation of the Phytotoxicity to Non

- Target Terrestrial Plants Vegetative Vigor Test: Final Report. Project Number: 1787.6872. Unpublished study prepared by Syngenta Crop Protection, LLC. 347p. Relates to L0001563.

49262901 Daun, C. (2013) Enforcement Analytical Method: Maquat 86

- M. Unpu blished study prepared by Mason Chemical Company. 8p.

49261902 Bradley, M. (2013) Final Report: Diquat Dibromide

- Life Cycle Toxicity Test Exposing Midges (Chironomus dilutus) to Diquat Dibromide Applied to Sediment Under Static

- Renewal Conditions

Follow ing EPA Test Methods. Project Number: 1781/6869. Unpublished study prepared by Smithers Viscient Laboratories. 143p.

49584101 Bradley, M. (2015) Diquat Dibromide: 10

- Day Toxicity Test Exposing Estuarine Amphipods (Leptocheirus plumulosus) to Diquat Dibrom ide Applied to Sediment Under Static Conditions:

### Page 55 of 76 Final Report. Project Number: 1781/7059, TK0024762. Unpublished study prepared by Smithers Viscient Laboratories. 98p.

49611201 Paul, E.; Simonin, H.; Symula, J.; et al. (1994) The Toxicity of Diquat, Endot hall, and Fluridone to the Early Life Stages of Fish. Journal of Freshwater Ecology. 9(3).

49613201 Ducrot, V.; Pery, A.; Lagadic, L. (2010) Modelling Effects of Diquat under Realistic Exposure Patterns in Genetically Differentiated Populations of the Gastropod Lymnaea stagnalis. Philosophical Transactions of the Royal Society (365):3485

- 3494.

### Page 56 of 76 Appendix A. Risk Quadrant Figures and Tables

Risk quadrant figures and tables are a tool for use by EFED to better communicate with risk managers, who need to know which taxa have greater or lower risk and the certainty of the risk conclusions. The risk quadrant figure is extremely summarized to display the seven assessed taxa in one of four quadrants, whichever quadrant represents the highest risk for the tax on. The risk quadrant table summarizes the rationales for the placement of the taxa in the figure, as succinctly as possible. A taxon is only discussed once in the table: in the quadrant matching its location in the figure.

For example, if there are chronic risks of concern to mammals and acute risks to mammals are not of concern, then the term “Mammals” appears in the upper

- right quadrant of the figure and the table. The table summarizes (under the “Mammals” heading) the chronic RQ range and any

oth er salient lines of evidence for chronic risks of concern. In this example, the figure and table do not directly indicate low acute risks to mammals; it is implied by the absence of discussion. Only the rationales for the location of the taxa in the figu re are discussed in the table, with one exception: No Effect Determinations are summarized in the upper

- left quadrant of the table (not the figure).

The risk versus certainty quadrants are represented as four color

- coded categories, as represented

in the examples below. The left quadrants represent no risks of concern ( i.e. , no LOC exceedances). The right quadrants represent a risk of concern ( i.e. , at least one LOC exceedance). The upper quadrants represent higher certainty ( i.e. , a relatively complete data set and/or multiple lines of evidence support the risk conclusions). The lower quadrants represent lower certainty ( i.e. , a relatively limited data set and/or lines of evidence are limited or conflicting).

While communication of ris k is inherently subjective, use of subjective terminology or risk management values should be avoided. The intent of the risk quadrant figure is to simply display for the risk manager which taxa are of concern and the degree of confidence in the risk

conclusions. The in tent of the risk quadrant table is to simply explain the supporting evidence for the placement of taxa in the figure and serves essentially like a key to the figure. The table

should not summarize all of the risk conclusio ns, just the conclusions that sup port the placement of taxa in the figure.

The risk quadrant figure and table are placed in an assessment’s Executive Summary, the risk transmittal memo, or may be used for formal or informal communications with risk managers. A key to the placement of t axa in the figure and graph is placed in an appendix, as follows:

### Page 57 of 76 Key to Four Color

- Coded Categories in Risk Quadrant Figures and Tables : Green: Greater Certainty of Negligible Risk Red: Greater Certainty of Risks of Concern

• No LOC e xceedance with relatively complete data s et

or risks have been mitigated

• High confidence in data

• Fate and ecot ox profiles clearly support lack of a risk

concern • Multiple line s of evidence predict effects will occur

• LOC exceedances, fate, and ecotox profile should be

cons idered

• Exposure is expected to occur based on fate profile

and uses

• Probable or highly probable cause of incident(s)



### Yellow: Lower Certainty of Negligible Risk Orange: Lower Certainty of Risks of Concern

• No LOCs exceeded but other non

- compelling

circumstances suggest that there may be issues

• Possible cause of incident(s)

• Missing endpoints, poorly spaced test concentrations,

low confidence in data showing low toxicity

• An LOC exceedance is judged to not be of concern

due to use pattern or other cir cumstances that limit exposure potential

• Low risk c alls based on extrapolated data • LOCs exceeded; however, lines of evidence predicting risk are either limited or conflicting

• Possible cause of incident(s)

• Chronic risk called for non

- persistent chemical

• Risk calls based on lack of data without other lines of

evidence available

• Risk calls based on uncertain extrapolation methods

or conflicting data

• Missing endpoints, poorly spaced test concent rations,

low confidence in data

### Page 58 of 76 Appendix B

. SIP Output

Table 1. Inputs

Parameter Value

Chemical name Diquat

Solubility (in water at 25 o C; mg/L) 700000

Mammalian LD 50 (mg/kg

- bw) 120

Mammalian test species laboratory rat
Body weight (g) of "other" mammalian species

Mammalian NOAEL (mg/kg

- bw) 4

Mammalian test species laboratory rat
Body weight (g) of "other" mammalian species

Avian LD 50 (mg/kg

- bw) 28.9

Avian test species other
Body weight (g) of "other" avian species 13.6

Mineau scaling factor 1.15

Mallard NOAEC (mg/kg

- diet) 4.2
Bobwhite quail NOAEC (mg/kg

- diet)
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) 120400.0000 120400.0000
Adjusted toxicity value (mg/kg

- bw) 92.2993 3.0766
Ratio of exposure to toxicity 1304.4524 39133.5714

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

Parameter Acute Chronic
Upper bound exposure (mg/kg

- bw) 567000.0000 567000.0000
Adjusted toxicity value (mg/kg

- bw) 30.6212 0.2084
Ratio of exposure to acute toxicity 18516.6131 2721084.9932

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.

### Page 59 of 76 Appendix C

. STIR Output



## Input

Application and Chemical Information

Enter Chemical Name Diquat

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) 184.25
Enter Chemical Vapor Pressure (mmHg) 1.00E

- 07
Enter Application Rate (lb a.i./acre) 0.5

Toxicity Properties

**Bird**

Enter Lowest Bird Oral LD 50 (mg/kg bw) 28.9
Enter Mineau Scaling Factor 1.15
Enter Tested Bird Weight (kg) 0.0136

**Mammal**

Enter Lowest Rat Oral LD 50 (mg/kg bw) 120

Enter Lowest Rat Inhalation LC 50 (mg/L) 0.19

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 ) 9.92E

- 04

Maximum 1

- hour Vapor Inhalation Dose (mg/kg) 1.25E

- 04

Adjusted Inhalation LD 50 3.75E

- 01

Ratio of Vapor Dose to Adjusted Inhalation LD 50 3.32E

- 04 Exposure not Likely Significant

Maximum Post

- treatment Spray Inhalation Dose (mg/kg) 4.80E

- 02 Ratio of Droplet Inhalation Dose to Adjusted Inhalation

LD 50 1.28E

- 01 Proceed to Refinements



### Results Mammalian (0.015 kg ) Maximum Vapor Concentration in Air at Saturation (mg/m 3 ) 9.92E

- 04

Maximum 1

- hour Vapor Inhalation Dose (mg/kg) 1.57E

- 04

Adjusted Inhalation LD 50 1.13E+01

Ratio of Vapor Dose to Adjusted Inhalation LD 50 1.39E

- 05 Exposure not Likely Significant

Maximum Post

- treatment Spray Inhalation Dose (mg/kg) 6.04E

- 02 Ratio of Droplet Inhalation Dose to Adjusted Inhalation

LD 50 5.34E

- 03 Exposure not Likely Significant

### Page 60 of 76 Appendix D

. SWCC Example Output

Summary of Water Modeling of Diquat and the USEPA Standard Pond

Estimated Environmental Concentrations for Diquat are presented in Table 1 for the USEPA standard pond with the CAnurserySTD_V2 field scenario. A graphical presentation of the year

to

- year peaks is presented in Figure 1. These values were generated with the Surface Water Concentration Calculator (SWCC Version 1.106). Critical input values for the model are

summarized in Tables 2 and 3. This model estimates that about 4.7% of Diquat app lied to the field eventually reaches the water body. The main mechanism of transport from the field to the water body is by erosion (85.9% of the total transport), followed by spray drift (13.2%) and runoff (0.91%). In the water body, pesticide dissipates with an effective water column half

- life of 10888.7 days. (This value does not include dissipation by transport to the benthic region; it includes only processes that result in removal of pesticide from the complete system.) The main source of dissipation in the water column is photolysis (effective average half

- life = 10888.8 days) followed by volatilization (5.844262E+09 days). In the benthic region, pesticide is stable. The vast majority of the pesticide in the benthic region (99.99%) is sorbed to sedim ent rather than in the pore water.

Table 1. Estimated Environmental Concentrations (ppb) for Diquat.

Peak (1

- in

- 10 yr) 52.6

4

- day Avg (1

- in

- 10 yr) 24.7

21

- day Avg (1

- in

- 10 yr) 23.3

60

- day Avg (1

- in

- 10 yr) 23.1

365

- day Avg (1

- in

- 10 yr) 22.8

Entire Simulation Mean 12.0

Table 2. Summary of Model Inputs for Diquat.

Scenario CAnurserySTD_V2

Cropped Area Fraction 1

Koc (ml/g) 5839

Water Half

- Life (days) @ 25 °C 0

Benthic Half

- Life (days) @ 25 °C 0

Photolysis Half

- Life (days) @ 25

°Lat 74

Hydrolysis Half

- Life (days) 0

Soil Half

- Life (days) @ 25 °C 0

### Page 61 of 76 Foliar Half

- Life (days) 0

Molecular Wt 344.05

Vapor Pressure (torr) 1e

- 7

Solubility (mg/l) 700000

Table 3. Application Schedule for Diquat.

Date (Mon/Day) Type Amount (kg/ha) Eff. Drift

2/25 Ground 0.56 0.99 0.062

3/28 Ground 0.56 0.99 0.062

4/25 Ground 0.56 0.99 0.062

5/23 Ground 0.56 0.99 0.062

6/17 Ground 0.56 0.99 0.062

7/15 Ground 0.56 0.99 0.062

8/12 Ground 0.56 0.99 0.062

9/9 Ground 0.56 0.99 0.062

10/7 Ground 0.56 0.99 0.062

11/5 Ground 0.56 0.99 0.062

12/3 Ground 0.56 0.99 0.062

12/31 Ground 0.56 0.99 0.062

Figure 1. Yearly Peak Concentrations

### Page 62 of 76 Appendix E. T

- REX Model Example Inputs

TREX MODEL INPUTS

These values will be used in the calculation of exposure estimates for foliar, granular, liquid and/or

seed applications of pesticides.

Chemical Identity and Application Information

Chemical Name: Diquat

Seed Treatment? (Check if yes) FALSE

Use: (Seed Crops) Alfalfa seed crop, Clover seed crop

Product name and form: % A.I. (leading zero must be entered for formulations <1% a.i.): 100.00%

Application Rate (lb ai/acre) 0.5

Half

- life (days): 35

Application Interval (days): 5

Number of Applications: 4

Are you assessing applications with variable
rates or intervals? no

Assessed Species Inputs (optional, use defaults for RQs for national level assessments)

What body weight range is assessed (grams)? Birds Mammals

Small 20 15

Medium 100 35

Large 1000 1000

### Page 63 of 76 Endpoints

Avian

Endpoint Toxicity value Indicate test species below Optional

Test Organism Body weight (g) Optional

Test Species

Name Toxicity

Value
Referenc e (MRID)

LD50 (mg/kg

- bw)

28.90 3

13.60 zebra
finch 49095903

LC50 (mg/kg

diet) 540.00 1 116565 NOAEL (mg/kg

bw) 1
NOAEC (mg/kg

diet) 4.20 2 114230

Enter the Mineau et al. Scaling Factor 1.15



### Mammalian

Acute Study Chronic Study

Size (g) of mammal used in toxicity study Default rat body weight is 350 grams 350 350

Endpoint Toxicity value Reference (MRID) LD50 (mg/kg

bw) 120.00 81506 LC50 (mg/kg

diet)

Reported

Chronic Endpoint 4.00

1 41531301 Is dietary

concentration

(mg/kg

- diet) reported from

the available

chronic

mammal study? (yes or no) yes

41531301

Enter dietary

concentration

(mg/kg

- diet) 80.00

### Page 64 of 76 Appendix F . TERRPLANT Model Example Inputs

TerrPlant v. 1.2.2 Green values signify user inputs (Tables 1, 2 and 4).

Table 1. Chemical Identity.

Parameter User Inputs

Chemical Name Diquat

PC code 32201

Use Many Application Method Broadcast

Application Form liquid Solubility in Water (ppm) 700000

Table 2. Input parameters used to derive EECs.

Input Parameter Symbol Value (user inputs) Units

Application Rate A 0.5 lb a.i./A

Incorporation I 1 none
Runoff Fraction R 0.05 none

Drift Fraction D 0.12 none

Table 3. EECs for Diquat. Units in lb a.i./A.

Description Equation EEC

Runoff to dry areas (A/I)*R 0.025

Runoff to semi

- aquatic areas (A/I)*R*10 0.25 Spray drift A*D 0.06 Total for dry areas ((A/I)*R)+(A*D) 0.085

Total for semi

- aquatic areas ((A/I)*R*10)+(A*D) 0.31

Table 4. Plant survival and growth data used for RQ derivation. Units are in lb a.i./A

Seedling Emergence Vegetative Vigor
Plant type EC 25 NOAEC EC 25 NOAEC

Monocot 4.65 4.65 0.059 0.027

Dicot 4.65 4.65 0.0022 0.00091

Table 5. RQ values for plants in dry and semi

- aquatic areas exposed to Diquat through runoff and/or spray drift.*

Plant Type Listed Status Dry Semi

- Aquatic Spray Drift

Monocot non

- listed <0.1 <0.1 1.02

Monocot listed <0.1 < 0.1 2.22

Dicot non

- listed <0.1 <0.1 27.27

Dicot listed <0.1 <0.1 65.93

### Page 65 of 76 Appendix G . MCnest Output

Figure F

- 1. Modeled Number of Broods by Species for Varying NOAECs using the MCnest Model for a March 1 Diquat Application

### Page 66 of 76 Figure F

- 2

. Modeled Number of Broods by Species for Varying NOAECs using the MCnest Model for a June 1 Diquat Application

### Page 67 of 76 Figure F

- 3

. Modeled Number of Broods by Species for Varying NOAECs using the MCnest Model fo r a September 1 Diquat Application

### Page 68 of 76 Figure F

- 4

. Modeled Number of Broods by Species for Varying NOAECs using the MCnest Model for a December 1 Diquat Application

### Page 69 of 76 Appendix H

. Ecotoxicity Data

1. Toxicity to Aquatic Organisms

1.1. Aquatic Vertebr ate Toxicity

1.1.1. Freshwater Fish Toxicity

Table A

- 1. Acute Toxicity of Diquat Cation to Freshwater Fish

Species 1,2 % Diquat

C ation 96

- hour LC 50 (ppm diquat

c ation) Toxicity Category MRID No. Author, Year Study

Classification

Black bullhead ( Ameiurus melas ) 18 6 94 Slightly toxic 40098001 Mayer and Ellersick, 1986 Supplemental

Bluegill sunfish ( Lepomis macrochirus ) 19.8 3 14 Slightly toxic 00138962 Thompson et al. , 1980 Supplemental

Bluegill sunfish 18 4 33 5
(72

- hr) Slightly toxic 00115572 McCann, 1967 Supplemental

Bluegill sunfish 18 6 79 Slightly toxic 40098001 Mayer and Ellersick, 1986 Supplemental

Bluegill sunfish 18 6 92 Slightly toxic 40098001 Mayer and Ellersick, 1986 Supplemental

Bluegill sunfish 18 6 107 Practically non

- toxic 40098001 Mayer and Ellersick, 1986 Supplemental

Bluegill sunfish 18 6 227 Practically non

- toxic 40098001 Mayer and Ellersick, 1986 Supplemental

Bluegill sunfish 18 6 243 Practically non

- toxic 40098001 Mayer and Ellersick, 1986 Supplemental

Bluegill sunfish 18 6 >107 Practically non

- toxic 40098001 Mayer and Ellersick, 1986 Supplemental

Bluegill sunfish 18 6 >241 Practically non

- toxic 40098001 Mayer and Ellersick, 1986 Supplemental

Bluegill sunfish 18 6 >386 Practically non

- toxic 40098001 Mayer and Ellersick, 1986 Supplemental

Brown trout ( Salmo trutta ) 18 4 17.8 Slightly toxic 00115858

Simonin et al. , 1977 Supplemental

Goldfish ( Carassius auratus auratus ) 18 6 >54 Slightly toxic 40098001 Mayer and Ellersick, 1986 Supplemental

Largemouth bass ( Micropterus salmoides ) 240 g/L 4.9 Moderately toxic 49611201 ( E014903)

Paul et al. , 1994 Quantitative

Rainbow trout ( Oncorhynchus mykiss ) 19.8 3 14.8 Slightly toxic 00138961 Thompson et al. , 1980 Supplemental

Rainbow trout 18 6 >54 Slightly toxic 40098001 Mayer and Ellersick, 1986 Supplemental

Smallmouth bass ( Micropterus dolomieu ) 240 g/L 3.9 Moderately toxic 49611201 ( E014903)

Paul et al. , 1994 Quantitative

Walleye ( Stizostedion

vitreum ) 240 g/L 0.75 Highly toxic 49611201 ( E014903)

Paul et al. , 1994 Quantitative

Yellow perch ( Perca flavescens ) 18 6 32 Slightly toxic 40098001 Mayer and Ellersick, 1986 Supplemental

Bolded value s indicate the endpoints used for risk estimation

. 1 In previous risk assessments for diquat dibromide, an acute toxi city study for goldfish (LC50 > 5000 mg/L, MRID 00059586) was listed. This study was conducted with dikegulac sodium (PC code 109601) and will not be included in this or future risk assessments for diquat dibromide.

2 In previous risk assessments for diquat dibromide, an acute study for striped bass ( Roccus saxatilis , MRID 00028002, Wellborn, 1969) was listed. This study is reclassified as Unacceptable (previously classified Supplemental). Reasons for the reclassifi cation include no raw data, not recommended test species, formulated product, laboratory method concerns as study author noted issues with aquaria containing residue from previous toxicity tests.

### Page 70 of 76 3 Test substance: Diquat 2 Spray.

4 Test substance was an unspecified EUP

. 5 This endpoi nt is based on a 72

- hr tes t. Previous EFED risk assessments indicated the LC 50 was 64.6 mg/L; this value is correct for mg a .i./L. The LC 50 when calculated in terms of cation is 33 mg cation/L.

6 Product tested was described as a ‘Liquid Concentrate’ in summary tables and as Reglo ne (an EUP) in some raw data sheets.

Table A

- 2. Chronic Toxicity of Diquat Cation to Freshwater Fish

Species % Diquat

C ation NOAEC /

LOAEC (ppm diquat

c ation) Most Sensitive Endpoint MRID No. Author, Year Study

Classification

Fathead minnow ( Pimephales promelas ) 21.1 0.122 / 0.316 Wet weight 40380703 Surprenant, 1987 Acceptable



### 1.1.2. Estuarine/Marine Fish Toxicity

Table A

- 3. Acute Toxicity of Diquat Cation to Estuarine/Marine Fish

Species % Diquat

C ation 96

- hour LC 50 (ppm diquat

c ation) Toxicity Category MRID No. Author, Year Study

Classification

Longnose killifish ( Fundulus

similis ) 20 >20 (48

- hr) Slightly toxic 40228401 Mayer, 1986 Supplemental

Sheepshead m innow ( Cyprinodon variegatus ) 21.1 51.1 1 Slightly toxic 40316101
Nicholson, 1987 Acceptable

1 Slope = 2.14

Table A

- 4. Chronic Toxicity of Diquat Cation t o Estuarine/Marine Fish

Species % Diquat

C ation NOAEC /

LOAEC (ppm diquat

c ation) Most Sensitive Endpoint MRID No. Author, Year Study

Classification

Sheepshead m innow 21.5 3.0 / 7.7 Length and w et weight 49095901

Minderhout et al. , 2012 Acceptable



### 1.1.3. Amphibian Toxicity

Table A

- 5. Toxicity of Diquat Cation t o Amphibians

Species % Diquat

C ation Toxicity Description MRID No. Author, Year Study

Classification

African clawed frog

( Xenopus laevis ) TGAI Mortality a t Day 3:

90% at 1. 5 and 1. 2 5 ppm diquat; 50% at 1.0 ppm; 20% at 0.5 ppm

I nhibition in growth and pigmentation for survivors starting at Day 3

Distortion in body shape observed at 1.5 ppm 05005290

Anderson et al. , 1976 Supplemental

### Page 71 of 76 1.2. Aquatic Invertebrate Toxicity

1.2.1. Freshwater Invertebrate Toxicity

Table A

- 6

. Acute Toxicity of Diquat Cation to Freshwater Invertebrates

Species % Diquat

C ation 48

- hour LC 50 (ppm diquat

c ation) Toxicity Category MRID No. Author, Year Study

Classification

Apple snail (Family: Ampullariidae ) 18 5 1.1 (9 6

- hr) Moderately toxic 40098001 Mayer and Ellersick, 1986 Supplemental

Gammarus fasciatus 18 5 > 54 (24

- hr) Slightly toxic 40098001 Mayer and Ellersick, 1986 Supplemental

Freshwater amphipod

( Hyalella azteca ) 23.6 0.09 (96

- hr) Very highly toxic 48826701 Bender, 2006 Acceptable

Freshwater amphipod

( Hyalella azteca ) Unknown 1 0.14 Highly toxic 00115862

Nicholson et al. , 1974 Supplemental

Water flea ( Daphnia magna ) 17.9 2 0.77 Highly toxic 00115577

Wheeler et al. , 1978 Supplemental

Water flea 46.6 1.17 3 Moderately toxic 00115576

Wheeler et al. , 1978 Acceptable

Water flea TGAI 7.1 (26

- hr) 4 Moderately toxic 05001465 Crosby et al. , 1966 Supplemental

Bolded value s indicate endpoints used for risk estimation

. 1 Test substance: Ortho EUP

2 Test substance: Diquat Water Weed Killer

3 Slope = 5.7

4 1 ppm of non

- ionic surfactant Tween 20 added to test system

5 Product tested was described as a ‘Liquid Concentrate’ in summary tables and as Reglone (an EUP) in some raw data sheets.

Table A

- 7

. Chronic Toxicity of Diquat Cation to Freshwater Invertebrates

Species % Diquat

C ation NOAEC /

LOAEC (ppm diquat

cation ) Most Sensitive Endpoint MRID No. Author, Year Study

Classification

Great Pond Snail ( Lymnaea stagnalis ) 16.7 0.00 11 /

0.00 32 Embryonic stage duration, Age at first

spawning, Food

consumption 49613201 (E168652)

Ducrot et al. , 2010 Quantitative

Water flea 21.1 0.036 / 0.057 Survival 40380702 Surprenant, 1987 Acceptable



### 1.2.2. Estuarine/Marine Invertebrate Toxicity

Table A

- 8. Acute Toxicity of Diquat Cation to Estuarine/Marine Invertebrates

Species % Diquat

C ation 96

- hour LC 50 (ppm diquat

c ation) Toxicity Category MRID No. Author, Year Study

Classification

Eastern Oyster ( Crassostrea virginica ) 21.1 >54.9 1 Slightly toxic 40316001 Dionne, 1987 Acceptable

Eastern Oyster 21.1 >0.50 (48

- hr) Highly toxic 40228401 Mayer, 1986 Supplemental

Mysid Shrimp ( Americamysis bahia ) 21.1 0.42 2 Highly toxic 40315701 Hoberg, 1987 Acceptable

Pink Shrimp ( Penaeus duorarum ) 21.1 >20 (48

- hr) Slightly toxic 40228401 Mayer, 1986 Supplemental

1 28% reduction in shell growth at 54.9 ppm diquat cation

2 Slope = 5. 4

### Page 72 of 76 Table A

- 9. Chronic Toxicity of Diquat Cation to Estuarine/Marine Invertebrates

Species % Diquat

C ation NOAEC /

LOAEC (ppm C ation) Most Sensitive Endpoint MRID No. Author, Year Study

Classification

Mysid Shrimp 21.5 0.052 / 0.104 Female dry weight 49095902

Claude et al. , 2013 Acceptable



### 1.2.3. Benthic Invertebrate Toxicity

Table A

- 10

. Toxicity of Diquat Cation to Benthic Invertebrates

Species % Diquat

C ation NOAEC /

LOAEC (ppm diquat

cation ) Most Sensitive Endpoint MRID No. Author, Year Study

Classification

Freshwater amphipod

( Hyalella azteca ) 21.5 Sediment: 11 / 23 mg/kg

Pore water:

0.043 / 0.037 mg/L 1 Reproduction (42

- day test) 49261901 Bradley, 2013 Acceptable

Freshwater amphipod

( Hyalella azteca ) 21.5 Sediment:

47 / >47 mg/kg None (28

- day test) 2 48784016 Bender, 2006 Supplemental

Midge ( Chironomus dilutus ) 21.5 Sediment: 37 / >37 mg/kg

Pore water:

0.54 / >0.54 mg/L None (63

- day test) 49261902 Bradley, 2013 Acceptable

Midge ( Chironomus dilutus ) 22.4 Sediment:

100 / >100

mg/kg None (20

- day test) 3 48784015 Ashwell, 1999 Supplemental

Saltwater amphipod ( Leptocheirus plumulosus ) 22.2 Sediment:

110/>110

mg/kg None (10

- day test) 4 49584101 Bradley, 2015 Acceptable

1 Due to the relatively high 0

- hour recovery of pore water concentration at the 11 mg diquat cation/kg level, the TWA calculated concentration at this level exhibited a shift in order, i.e. , was higher than the TWA

- calculated pore water concentration for th e higher nominal level, 23 mg diquat cation/kg.

2 Reproduction not assessed

3 OECD 218 method, endpoint measured: emergence

4 Endpoint measured: survival only. Pore water concentrations we re below the LOQ ( 0.0048 mg diquat cation /L on Day 0 and 0.0043 mg d iquat cation/L on Day 10 ).



### 1.3. Aquatic Plant Toxicity

Table A

- 11. Toxicity of Diquat Cation to Aquatic Plants

Species % Diquat

C ation EC 50 (ppm diquat

cation ) EC 05 or NOAEC (ppm diquat

cation ) MRID No. Author, Year Study

Classification

Duckweed ( Lemna gibba ) 22.4 0.0047 (14

- d) 0.0012 48784007 Magor and Shillabeer, 2001 Acceptable

Green algae ( Pseudokirchneriella subcapitata ) 26.8 0.0094 (96

- hr) 0.0068 43532703 Smyth and Tapp,

1988 Acceptable

Green algae ( Pseudokirchneriella subcapitata ) 20.5 >0.30 0.30 48784011 Shillabeer, 1998 Supplemental 1

### Page 73 of 76 Species % Diquat

C ation EC 50 (ppm diquat

cation ) EC 05 or NOAEC (ppm diquat

cation ) MRID No. Author, Year Study

Classification

Blue

- green Algae ( Anabaena flos

- aquae ) 20.5 0.0087 (120

- hr) 0.0013 48784010 Kent, 1998 Acceptable

Freshwater Diatom ( Navicula pelliculosa ) 20.5 0.00070 (120

- hr) 0.00033 48784008 Kent, 1998 Supplemental

Marine Diatom ( Skeletonema costatum ) 20.5 0.011 (120

- hr) 0.00057 48784009 Kent, 1998 Supplemental

Marine diatom ( Isochryris galbana ) 20 7.6 (240

- hr) No data 40228401 Mayer, 1986 Supplemental

Marine diatom ( Phaeodactylum

tricornutum ) 20 7.6 (240

- hr) No data 40228401 Mayer, 1986 Supplemental

Marine algae ( Dunaliella tertiolecta ) 20 16 (240

- hr) No data 40228401 Mayer, 1986 Supplemental

Green algae ( Chlorococcum sp. ) 20 102 (240

- hr) No data 40228401 Mayer, 1986 Supplemental

Giant duckweed ( Spirodela punctata ) 35.3 0. 000 75 3 No data 41883002 Bellet, 1990 Supplemental 2

Water h yacinth ( Eichhornia crassipes ) 35.3 0.014 4 No data 41883002 Bellet, 1990 Supplemental 2

Water l ettuce ( Pistia stratiotes ) 35.3 0.0158 5 No data 41883002 Bellet, 1990 Supplemental 2

Watershield ( Brasenia schreberi ) 35.3 No data 6 No data 41883002 Bellet, 1990 Supplemental 2

Torpedograss ( Panicum repens ) 35.3 3

. 513 7 No data 41883002 Bellet, 1990 Supplemental 2

Bahiagrass ( Paspalum notatum ) 35.3 No data 8 No data 41883002 Bellet, 1990 Supplemental 2

Hydrilla ( Hydrilla verticillata ) 35.3 0.00 9 9 No data 41883002 Bellet, 1990 Supplemental 2

Azolla ( Azolla caroliniana ) 35.3 0.011 6 9 No data 41883002 Bellet, 1990 Supplemental 2

Bolded value s indicate endpoints used for risk estimation

. 1 Study conducted with sediment present in the test vessels

2 Tier III outdoor study

3 Giant duckweed EC 50 with foliar application: 0.0036 lb cation /A

4 Water hyacinth EC 50 with foliar application: 0.0198 lb cation /A

5 Water lettuce EC 50 with foliar application: 0.1067 lb cation /A

6 Watershield EC 50 with foliar application: 3.5900 lb cation /A

7 Torpedograss EC 50 with foliar application: 3.6391 lb cation /A

8 Bahiagrass EC 50 with foliar application: 14.409 lb cation /A

9 Azolla EC 50 with foliar application: 0.0277 lb cation /A



### 2. Toxicity to Terrestrial Organisms

2.1. Avian Toxicity

Table A

- 1 2

. Acute Oral Toxicity of Diquat Cation to Birds

### Page 74 of 76 Species % Diquat

C ation LD 50 (mg diquat

cation /kg

- bw) Toxicity Category MRID Author, Year Study

Classification

Mallard duck ( Anas platyrhynchus ) 45.6 60.6 1 Moderately toxic 00106559

Fink et al. , 1982 Acceptable

Mallard duck 30 90.7 Moderately toxic 00160000

Tucker et al. , 1970 Supplemental 2

Zebra finch ( Taeniopygia guttata ) 21.5 28.9 3 Highly toxic 49095903

Hubbard and Beavers, 2013 Supplemental

1 Slope = 4 .2

2 Test substance: formulated product. Only male birds tested.

3 Slope = 4 .82

Table A

- 13. Sub

- acute Dietary Toxicity of Diquat Cation to Birds

Species % Diquat

C ation LC 50 (mg diquat

cation /kg

- diet) Toxicity Category MRID Author, Year Study

Classification

Japanese quail ( Coturnix coturnix japonica ) 37 264 1 ,5 Highly toxic 00022923, 00008595

Heath et al. , 1972 Supplemental

Mallard duck 37 >981 5 Moderately toxic 00022923, 00008595

Heath et al. , 1972 Supplemental

Northern bobwhite quail

(Colinus virginianus) 18.9 540.4 2 Moderately toxic 00116565

Fink et al. , 1982 Supplemental

Northern bobwhite quail 37 575 3 ,5 Moderately toxic 00022923, 00008595

Heath et al. , 1972 Supplemental

Ring

- necked Pheasant ( Phasianus colchicus ) 37 734 4 ,5 Moderately toxic 00022923, 00008595

Heath et al. , 1972 Supplemental

1 Slope = 4 .8

2 Egg production was significantly affected from 215 to 1000 ppm cation.

3 Slope = 7.6

4 Slope = 7.5

5 Calculated in units of diquat cation based studies conducted with a 37% diquat dibromide formulation.

Table A

- 14. Chronic Toxicity of Diquat Cation to Bi rds

Species % Diquat

C ation NOAEC / LOAEC (mg diquat

cation /kg

- diet) Most Sensitive Endpoint MRID No. Author, Year Study

Classification

Mallard duck 19.6 4.2 / 24 Eggs laid 1 00114230

Fink et al. , 1982 Acceptable

Mallard duck 22.7 19.2 / 36.9 Eggs laid and female body weight gain 2 48784012 Temple et al. , 2004 Supplemental

Mallard duck 22.7 33.8 / 74.5 Eggs laid 3 48784013 Temple et al. , 2004 Supplemental

Mallard duck 22.0 <71.8 / 71.8 (treatment phase) 152 / >152 (post

treatment phase) E ggs laid

, hatchling weight,

and mean food consumption 4 48784014 Temple et al. , 2009 Supplemental

Northern bobwhite quail 19.6 100 / >100 None 0011 9988

Fink et al. , 1982 Supplemental

1 At 24 mg cation/kg

- diet, a marked reduction was observed in the numbers of eggs laid (376 total = 31 per pen ), normal hatchlings (153 total = 13 per pen ), and 14

- day old survivors (151 total = 13 per pen ) when compared to the control group (49 8

total = 42 per pen , 261 total = 22 per pen , and 256 total = 21 per pen

, respectively). These differences, although not statistically

significant, were considered treatment

- related and biologically meaningful. Statistical power was limited due to the use of only 12 pairs of birds per treatment group. A t 98 mg cation/kg

- diet, a statistically

- significant reduction was observed in the numbers

### Page 75 of 76 of eggs laid, eggs set, ratio of eggs set to eggs laid, viable embryos, live embryos, number of normal hatchlings, and 14

- day old survivors when compared to the control group.

2 Study with 9 weeks of exposure beginning at photostimulation to induce egg production. Egg production and egg weight were the only reproductive parameters measured.

3 Study with 6 weeks of exposure beginning 5 weeks into the egg laying period. Egg production and egg w eight were the only reproductive parameters measured.

4 Study with 6 weeks of exposure beginning at start of egg laying period (treatment phase) and a 6

- week recovery period immediately following the exposure period (post

- treatment phase).



### 2.2. Mammalian Toxi city

Table A

- 15. Acute Oral Toxicity of Diquat Cation to Mammals

Species % Diquat

C ation LD 50 (mg diquat

cation /kg

- bw) Toxicity Category MRID Author, Year Study

Classification

Laboratory rat ( Rattus norvegicus ) 19.3 120 Moderately toxic 00081506 Rittenhouse, 1979 Acceptable

Table A

- 16. Acute Inhalation Toxicity of Diquat Cation to Mammals

Species % Diquat

C ation 4

- hr L C 50 (mg diquat

cation / L ) Toxicity Category MRID Author, Year Study

Classification

Laboratory rat 19.5 0.19 Toxicity category

III 00162046 Bruce, 1985 Acceptable

Table A

- 17. Acute Oral Toxicity of Diquat Cation to Mammals

Species % Diquat

C ation NOAEC / LOAEC (mg diquat

cation /kg

- bw) Most Sensitive Endpoint MRID Author, Year Study

Classification

Laboratory rat 21.1 4 / 12 1 F1 pups/litter; F1 body weight gain during lactation 41531301 Hodge, 1990 Acceptable

1 LOAEC / NOAEC = 80 / 240 mg/kg

- diet



### 2.3. Terrestrial Invertebrate Toxicity

Table A

- 18. Acute Toxicity of Diquat Cation to Honey Bees

Species % Diquat

C ation 48

- hr LD 50 (μ g diquat

cation / bee ) Toxicity Category MRID Author, Year Study

Classification

Honey bee ( Apis mellifera ) TGAI >100 (contact) Practically non

toxic 00131562 Atkins, 1983 Acceptable

Honey bee 16.7 47 (oral) Practically non

toxic 40208001 Gough, 1987 Acceptable



### 2.4. Terrestrial Plant Toxicity

Table A

- 19. Tier I Seedling Emergence Toxicity of Diquat Cation

Type of Study Species Crop IC 25 (lbs diquat

cation /A) NOAEC

or IC 05 (lbs diquat

cation /A) Most Sensitive Endpoint MRID Author, Year Study

Classification

Monocots Barnyard grass >4.65 4.65 None 40165101 Shilling, 1987 Corn >4.65 4.65 None

### Page 76 of 76 Onion >4.65 4.65 None Acceptable

Rye >4.65 4.65 None

Dicots Jimson weed >4.65 4.65 None Morning glory >4.65 4.65 None

Potato >4.65 4.65 None Sicklepod >4.65 4.65 None Soybean >4.65 4.65 None

Sunflower >4.65 4.65 None

Table A

- 20. Tier II Vegetative Vigor Toxicity of Diquat Cation

Type of Study Species Crop IC 25 (lbs diquat

cation ./A) NOAEC

or IC 05 (lbs diquat

cation /A) Most Sensitive Endpoint MRID Author, Year Study

Classification

% diquat cation

Monocots Corn 0.059 0.027 Dry weight

49141801 Martin, 2013 Supplemental

21.5% Oat >0.24 0.24 None

Onion 0.12 0.075 Dry weight Ryegrass 0.15 0.075 Dry weight

Dicots Cabbage 0.0022 0.00091 Dry weight

Carrot 0.013 0.00091 Dry weight Oilseed Rape 0.0075 0.0027 Dry weight

Soybean 0.010 0.0027 Dry weight Sugarbeet 0.0042 0.00091 Dry weight

Sunflower 0.0042 0.0027 Dry weight

Monocots Corn 0.011 0.037 Height

41883001 Bellet, 1990 Supplemental

35.3% Onion 0.18 0.037 Height

Dicots Sunflower 0.049 0.020 Height

Cotton 0.0047 0.020 Height

Yellow nutsedge 0.14 0.037 Height

Soybean 0.0074 0.020 Dry weight

Monocots Sweet corn 0.023 0.017 Dry weight 44755601

Porch and Krueger, 1999 Supplemental

35.9% Dicots Wheat 0.091 0.070 Dry weight

Bolded values indicate the most sensitive endpoints.