1

Environmental Fate, Ecological Risk and 

Endangered Species Assessment

in Support of the Registration Review of 

Fomesafen Sodium (PC123802)

O

F3C

Cl

NO2

H

N

S

O

O O

CH3

Prepared by:

Paige D. Doelling, PhD, Fisheries Biologist

Stephen P. Wente, PhD, Biologist

Reviewed by:

Faruque Khan, PhD, Senior Fate Scientist

U. S. Environmental Protection Agency

Office of Pesticide Programs

Environmental Fate and Effects Division

Environmental Risk Branch I

1200 Pennsylvania Ave., NW

Mail Code 7507P

Washington, DC 20460

December 2008
2

Table of Contents

1.0 Executive Summary................................................................................................ 6

1.1 Nature of Stressor ............................................................................................... 6

1.2 Potential Risk...................................................................................................... 6

1.3 Endangered Species Assessment ........................................................................ 7

2.0 Problem Formulation .............................................................................................. 9

2.1 Stressor Description............................................................................................ 9

2.2 Environmental Fate Summary ............................................................................ 9

2.3 Mode of Action................................................................................................. 10

2.4 Use Characterization......................................................................................... 10

2.5 Assessment Endpoints ...................................................................................... 12

2.5.1 Ecosystems Potentially at Risk ................................................................. 13

2.5.2 Ecological Effects..................................................................................... 13

2.5.2.1 Direct......................................................................................................... 13

2.5.2.2 Indirect ...................................................................................................... 13

2.6 Risk Hypotheses................................................................................................ 15

2.7 Results of Previous Assessments...................................................................... 15

2.8 Analysis Plan .................................................................................................... 16

3.0 Exposure Assessment............................................................................................ 17

3.1 Label Application Rates and Intervals.............................................................. 17

3.2 Aquatic Exposure.............................................................................................. 18

3.2.1 PRZM-EXAMS Modeling Inputs and Scenario Selection ....................... 18

3.2.2 PRZM-EXAMS Modeling Output............................................................ 19

3.2.3 Registrant-submitted Aquatic Exposure Modeling................................... 20

3.2.4 SCIGROW Modeling for Ground Water.................................................. 20

3.2.5 Soil Accumulation .................................................................................... 21

3.3 National Surface Water Monitoring Data ......................................................... 23

3.3.1 Surface Water............................................................................................ 23

3.3.2 Ground Water............................................................................................ 23

3.4 Bird and Mammal Exposure (TREX)............................................................... 24

3.5 Terrestrial Invertebrate Exposure ..................................................................... 26

3.6 Terrestrial Plant Exposure (TerrPlant & AgDrift)............................................ 27

3.6.1 TerrPlant ................................................................................................... 27

3.6.2 AgDrift...................................................................................................... 28

4.0 Effects Assessment ............................................................................................... 30

4.1 Specific Toxicological Concerns Associated with this Chemical .................... 30

4.2 Aquatic Hazard Summary................................................................................. 31

4.3 Summary of Aquatic Ecotoxicity Studies......................................................... 33

4.3.1 Aquatic Guideline Data............................................................................. 33

4.3.2 Aquatic Data from ECOTOX ................................................................... 33

4.4 Terrestrial Hazard Summary............................................................................. 35

4.5 Summary of Terrestrial Ecotoxicity Studies..................................................... 36

4.5.1 Avian and Small Mammal Guideline Data............................................... 36

4.5.2 Terrestrial Plant Data ................................................................................ 36

4.5.2.1 Guideline Studies...................................................................................... 36
3

4.5.2.2 Additional Registrant-Submitted Data...................................................... 37

4.5.3 Terrestrial Insect Data............................................................................... 38

4.5.4 ECOTOX Data.......................................................................................... 38

4.5.4.1 Biochemical Endpoints............................................................................. 38

4.5.4.2 Aquatic Community-Level ....................................................................... 39

4.5.5 Carcinogenicity, Mutagenicity, and Endocrine Disruption ...................... 40

4.5.6 Toxic Effects of Multi-Active Ingredient Labeled Products .................... 40

4.6 Incident Database Review................................................................................. 41

5.0 Risk Estimation..................................................................................................... 42

5.1 Aquatic RQ Summary....................................................................................... 43

5.2 Terrestrial RQ Summary................................................................................... 44

5.2.1 Terrestrial Plants....................................................................................... 44

5.2.1.1 TerrPlant ................................................................................................... 44

5.2.1.2 AgDrift...................................................................................................... 46

5.2.2 Avian RQ Summary.................................................................................. 47

5.2.3 Small Mammal RQ Summary................................................................... 48

5.2.4 Terrestrial Invertebrate Summary............................................................. 48

6.0 Risk Description.................................................................................................... 50

6.1 Aquatic Risk...................................................................................................... 50

6.2 Terrestrial Risk.................................................................................................. 53

6.2.1 Birds, Reptiles, and Amphibians .............................................................. 53

6.2.2 Mammals................................................................................................... 54

6.2.3 Terrestrial Invertebrates............................................................................ 54

6.2.4 Plants......................................................................................................... 56

6.3 Endangered Species.......................................................................................... 58

6.3.1 Aquatic Listed Species.............................................................................. 58

6.3.2 Terrestrial Listed Species.......................................................................... 59

6.3.3 Plants......................................................................................................... 65

6.3.4 Action Area............................................................................................... 66

6.3.5 Probability of Individual Effects............................................................... 68

6.4 Risk Conclusions .............................................................................................. 70

7.0 Uncertainties......................................................................................................... 72

7.1 Exposure Assessment Uncertainties................................................................. 72

7.1.1 Aquatic Exposure...................................................................................... 72

7.1.1.1 Modeling Assumptions............................................................................. 72

7.1.1.2 Monitoring Data........................................................................................ 72

7.1.1.3 Impact of Vegetative Setbacks on Runoff ................................................ 72

7.1.1.4 PRZM Modeling Inputs and Predicted Aquatic Concentrations .............. 73

7.1.2 Terrestrial Exposure Uncertainties ........................................................... 73

7.1.2.1 Residue Levels Selection .......................................................................... 74

7.1.2.2 Dietary Intake............................................................................................ 74

7.2 Effects Assessment Uncertainties..................................................................... 75

7.2.1 Age Class and Sensitivity of Effects Thresholds...................................... 75

7.2.2 Use of Surrogate Species Data.................................................................. 75

7.2.3 Extrapolation of Effects............................................................................ 75

7.2.4 Acute LOC Assumptions.......................................................................... 75
4

References......................................................................................................................... 76

Guideline Study References.............................................................................................. 76

ECOTOX References........................................................................................................ 81

Appendix A – Exposure and Modeling

Appendix B – Ecological Effects

Appendix C – ECOTOX Bibiligraphy

Appendix D – RQ Method and LOCs

Appendix E – Analysis Summary

Appendix F – LOCATES (Endangered Species)

Appendix G – Spray Drift Analysis 

Table of Figures

Figure 1 Chemical structure of fomesafen.......................................................................... 9

Figure 2 Conceptual model for fomesafen effects............................................................ 14

Figure 3. Estimate of Fomesafen Loading in the Surface Soil ......................................... 23
5

Table of Tables

Table 1 Summary of Direct and Indirect Effects............................................................... 8

Table 2 Current Fomesafen Registrations........................................................................ 11

Table 3 Summary of Assessment Endpoints and Measures of Ecological Effect ........... 12

Table 4 Label Application Rates and Intervals for Fomesafen Use on Soybeans, Cotton, 

Snap Beans and Dry Beans1........................................................................................... 17

Table 5 Label Application Rates and Intervals for Section 24c Uses of Fomesafen....... 18

Table 6. Input Parameters for PRZM-EXAMS Modeling of Fomesafen on Cotton, 

Soybeans, Dry Beans, and Snap Bean ........................................................................... 19

Table 7. PRZM-EXAMS Aquatic EECs for Fomesafen ................................................. 20

Table 8 PRZM-EXAMS EECs for Fomesafen at 0.50 lb ai/A........................................ 20

Table 9. Input Parameters for SCIGROW Modeling for Fomesafen .............................. 21

Table 10 Label Application Rates and Intervals for Fomesafen Use on Soybeans, Cotton, 

Snap Beans, and Dry Beans

1

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

Table 11 Input Parameters for TREX Modeling.............................................................. 24

Table 12 Bird Dose Estimates.......................................................................................... 25

Table 13 Mammal Dose Estimates.................................................................................. 26

Table 14 Terrestrial Invertebrate Exposure ..................................................................... 26

Table 15 Terrestrial Plant Exposure ................................................................................ 27

Table 16 Drift Deposition from Ground Applications..................................................... 29

Table 17 Drift Depostion from Aerial Applications........................................................ 29

Table 18 Aquatic Toxicity Profile for Fomesafen ........................................................... 32

Table 19 Terrestrial Toxicity Profile for Fomesafen ....................................................... 35

Table 20 Drift Deposition from Aerial Applications....................................................... 46

Table 21 Drift Deposition from Ground Applications..................................................... 46

Table 22 Avian RQ Summary.......................................................................................... 47

Table 23 Small Mammal RQ Summary........................................................................... 48

Table 24 Terrestrial Invertebrate RQ Summary .............................................................. 49

Table 25 Summary of Risk to Non-listed Aquatic Organisms........................................ 52

Table 26 Comparison of Chronic Data for Acifluorfen, Fomesafen, and Oxyfluorfen... 54

Table 27 Summary of Risk to Non-Listed Terrestrial Animals....................................... 55

Table 28 Summary of Risk to Non-listed Terrestrial Plants............................................ 57

Table 29 Summary of Risk to Listed Aquatic Organisms............................................... 58

Table 30 Summary of Risk to Listed Terrestrial Animals............................................... 60

Table 31. Listed birds potentially at risk from fomesafen............................................... 62

Table 32. Listed reptiles and amphibians potentially at risk from fomesafen ................. 63

Table 33 Summary of Risk to Listed Plants .................................................................... 64

Table 34 Endangered Plants by Crop and State............................................................... 67

Table 35 Probability of Individual Effects....................................................................... 69

Table 36 Summary of Direct and Indirect Effects........................................................... 71
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1.0 Executive Summary

1.1 Nature of Stressor

Fomesafen is an herbicide. It is applied as a foliar spray (both pre-emergent and postemergent) for control of broad-leaved weeds, grasses, and sedges. Mode of action is via 

cellular membrane disruption. It is highly persistent in soil (aerobic soil metabolism halflives of 29-99 weeks, dependent on soil type) resulting in a potential for accumulation in 

terrestrial environments. The label suggests not planting sensitive crops in a fomesafentreated field for a 3-18 month period, due to the persistence of fomesafen in the soil. 

Additionally, it is highly mobile, and is expected to leach into groundwater and be 

transported from the site via runoff into surface waters. Based on physical properties, 

bioaccumulation and long-range transport are not expected to be of concern. It is 

extremely toxic to terrestrial plants, especially dicots, but of fairly low acute toxicity to 

fish and wildlife. Some chronic reproductive effects have been noted in mammals, and 

may also occur in birds. No major degradates of toxicological concern have been 

identified.

1.2 Potential Risk 

Chemical Properties 

Fomesafen is highly persistent and mobile in soil. These environmental fate properties 

are expected to promote year-to-year accumulation in soil as well as off-site movement 

by leaching and runoff. Because fomesafen is spray applied, there is a potential for drift 

onto non-target plants. Prolonged phytotoxic effects on non-target plants are expected 

based on the persistence of fomesafen. EFED has no data from which to determine how 

long it may be toxic, but the labels recommend not planting sensitive crops in the use site 

for 3 to 18 months following treatment.

Ecological Risk Conclusions

Ecologically, the organisms most at risk from fomesafen are terrestrial plants, especially 

dicots. Because terrestrial plants are important both ecologically (they provide a critical 

part of both the structure and function that defines “habitat”) and economically (nearby 

non-target, non-treated crop plants may be affected), these potential impacts are an 

important consideration. No LOCs were exceeded for aquatic endpoints except the listed 

species LOC for freshwater non-vascular plants. At the time of this assessment, there 

were no listed non-vascular freshwater plants, and no listed species had been identified as 

having an obligate relationship with freshwater non-vascular plants. For terrestrial 

organisms, chronic LOCs were exceeded for birds (and by extension, reptiles and 

amphibians) at all but the lowest application rate. Chronic LOCs were exceeded for 

mammals only for small herbivorous mammals at the highest application rate. These 

LOC exceedences apply to both listed and non-listed species. Based on spray drift 

estimations, clearance distances for chronic exceedences are well within the clearance 

distances for terrestrial plants, thus if terrestrial plants are protected, then by virtue of 

sensitivity, other vulnerable organisms should be protected as well. Clearance distances 

for chronic effects on birds, reptiles, amphibians, and mammals are 10 ft from the 
7

application source for ground applications (based on low boom estimates) and 100 ft for 

aerial applications (based on application parameters used in AgDrift Tier I estimates). 

For terrestrial plants, using drift estimates based on the more sensitive dicots, effects 

should be anticipated as far as 850 ft for ground applications, and 1,000 ft for aerial 

applications.

1.3 Endangered Species Assessment

For listed animals, both aquatic and terrestrial, the primary risk posed by use of 

fomesafen as currently registered under Section 3 is due to potential degradation of plant 

communities providing food, shelter, or protection from predators. On the basis of these 

indirect effects and the anticipated magnitude of such effect, an overall determination of 

may affect, likely to adversely affect applies to all listed species located with 850 ft of the 

application location. The action area, based on the furthest extent at which an LOC is 

exceeded (dicots), is 1,000 ft away from agricultural land in geographic areas where 

fomesafen is registered for use. A list of potentially affected species is included as 

Appendix F. No direct effects are anticipated for aquatic organisms, constituting a no 

effect determination for these organisms on the basis of direct effects. Based on available 

data, there is a chronic risk to birds, reptiles, and terrestrial-phase amphibians. The 

Agency is unable to evaluate the potential magnitude of these chronic effects, thus the 

overall determination for these taxa is may affect, likely to adversely affect.
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Table 1 Summary of Direct and Indirect Effects

Evaluation 

Organism

LOCATES 

Category Direct Effects Indirect Effects Critical HabitatEffects

Monocots Monocots

Yes

Ground ≤100 ft

Aerial ≤100 ft

from point of 

application

No?

(only listed monocot 

affected is aquatic)

Other1

No

(No potentially 

affected species 

have designated 

critical habitat)

Dicots

Dicots

Yes

Ground ≤300 ft

Aerial ≤900 ft

from point of 

application

Yes

Potential for effects 

on other plants in 

the community. 

Alteration of habitat 

may create 

environment 

unsuitable to the 

listed species.

Effects may occur 

up to

Ground ≤300 ft

Aerial ≤900 ft

from point of 

application

Yes

(6 potentially 

affected species 

have designated 

critical habitat)

Birds

Reptiles

Birds Terrestrial 

Phase 

Amphibians

Mammals Mammals

Yes

Chronic 

Exceedences

Ground ≤10 ft

Aerial ≤100 ft

from point of 

application

FW Aquatic 

Plants2

FW Aquatic 

Plants

SW Aquatic 

Plants

SW Aquatic 

Plants

FW

Crustacea

FW Bivalves FW Aquatic 

Invertebrates FW

Gastropods

FW Fish

FW Fish Aquatic 

Phase 

Amphibians

SW

Crustacea

SW Bivalves SW Aquatic 

Invertebrates SW

Gastropods

SW Fish SW Fish

No

No LOC 

exceedences

Yes

Potential for effects 

on other plants in 

the community. 

Alteration of habitat 

may create 

environment 

unsuitable to the 

listed species.

Effects may occur 

up to

Ground ≤300 ft

Aerial ≤900 ft

from point of 

application

Yes

Potential for effects 

on other plants in 

the community. 

Alteration of habitat 

may create 

environment 

unsuitable to the 

listed species.

Effects may occur 

up to

Ground ≤300 ft

Aerial ≤900 ft

from point of 

application

1 Cycads, Conifers, Fern Allies. These genera have no direct corollary test organism, and have 

been evaluated based on the most sensitive plant endpoint.

2

Evaluated based on both non-vascular plants (algae) and vascular plants (duckweed)
9

2.0 Problem Formulation

Problem formulation provides a strategic framework for the risk assessment. By

identifying the important components of the problem, it focuses the assessment on the 

most relevant chemical properties, exposure routes, and endpoints.

2.1 Stressor Description

Fomesafen is applied as a pre-plant, pre-emergence, and post-emergence herbicide in 

soybeans, snap beans, dry beans, and cotton for control of broadleaf weeds, grasses, and 

sedges. Fomesafen can be applied via ground and aerial sprays. Because fomesafen is 

persistent in soil (aerobic soil degradation t1/2 = 29 to 99 weeks at 0.50 lb ai/A application 

rate; MRID 00135660), residual in soil of the treated field is considered in this risk 

assessment as a secondary source.

O

F3C

Cl

NO2

H

N

S

O

O O

CH3

Figure 1 Chemical structure of fomesafen

Empirical formula: C15H10ClF3N2O6S

Molecular weight: 438.77 g/mole

CAS Registry Nos.: 72178-02-0

Chemical Class: Diphenyl ether

2.2 Environmental Fate Summary

Major routes of fomesafen dissipation are leaching, runoff, and microbial degradation. 

Because fomesafen is persistent and mobile in soil, it is expected to move from the 

application site into groundwater and surface water. Additionally, off-site movement of 

fomesafen is expected through spray drift from aerial and ground spray. The high 

persistence of fomesafen is expected to contribute to year-to-year accumulation in 

terrestrial and aquatic environments. 

Fomesafen is stable to abiotic hydrolysis. It undergoes slow photodegradation in water

(t1/2 = 49 to 289 days). Fomesafen is persistent (aerobic soil t1/2 = 29 to 99 weeks) in

aerobic soil and aquatic environments. However, it degrades rapidly (t1/2 <20 days) in 

anaerobic environments. The major degradation product of fomesafen is 5-(2-chloroa,a,a-trifluoro-p-tolyloxy)-N-methylsulphonyl-panthranilamide (fomesafen amine). A 

minor degradation product is 5-(2-chloro-a,a,a-trifluoro-p-tolyloxy) anthranilic acid 

(fomesafen amino acid). Neither degradate has been identified as a toxicological concern. 
10

Fomesafen is expected to be very mobile in soil. Simple partitioning coefficients range 

from 0.51 in loamy coarse sand to 2.45 in sandy clay loam soil. Regression analysis 

indicates fomesafen sorption is not dependent on soil organic matter content. Aged soil 

column leaching studies indicate degradation products of fomesafen are not mobile in 

soils; less than 0.06% of applied radioactivity was detected in the leachate samples.

Field dissipation studies in NC, IL, MS, AR, AL, TX, LA, SD, MN, KY, IA, and MO 

indicate fomesafen is moderately persistent to persistent (t1/2 = 50 to 150 days ) in surface 

soils under actual use conditions. Fomesafen was detected at depths up to 30 inches in the 

soil profile. Fomesafen amine was the only degradation product identified in field 

dissipation studies. Prospective ground water monitoring in NC indicates fomesafen 

moved through the soil profile into medium and deep ground water.

Fomesafen has a low potential for bioaccumulation in fish tissues. Bioaccumulation 

factors for fosmesafen were 0.7 for whole fish, 0.2 for edible tissues, and 5.2 for 

nonedible tissue. Bioaccumulated residues decreased by 95% during a 14-day depuration 

period.

2.3 Mode of Action

Fomesafen is a diphenyl ether. It disrupts the cell membrane of the plant 

(www.syngentacroprotection-us.com) by penetrating into the cytoplasm and causing 

formation of peroxides and free electrons (http://www.ces.purdue.edu/extmedia/WS/WS23-W.html). The specific mode of action is inhibition of protoporphyrinogen oxidase 

(Roberts 1998). Fomesafen generally acts quickly, and does not translocate. It has both 

foliar and soil activity. Other herbicides in this group include aciflourfen, lactofen, and 

oxyfluorfen.

2.4 Use Characterization

Fomesafen is used primarily as a pre-plant, pre-emergence, and post-emergence herbicide 

to control broadleaf weeds, grasses, and sedges in soybeans, snap beans, dry beans, and 

cotton. Methods of application are ground spray and aerial spray (maximum 0.375 lb 

ai/A, soybeans, dry beans, snap beans, and cotton). Application is limited to once a year, 

or in alternate years, depending on location. Application rates are regionally specific.

A search of OPPIN on 4/24/2008 (PDD) located 20 active Section 3 and Section 24 

registration numbers associated with the active ingredient fomesafen. Of these, 5 were 

end-use products, 4 were technicals or formulation intermediates (with no associated 

crops), and 11 were state-specific special local needs (Sec. 24c), all of which were 

associated with a single parent Section 3 label. Only 2 registrants (Syngenta and BASF) 

hold current fomesafen registrations, and as of this writing, BASF has submitted a 

Request for Voluntary Cancellation for its fomesafen containing products. Three of the 

end-use products include a second active ingredient.
11

Table 2 Current Fomesafen Registrations

Product Name

(Registrant)

EPA Registration 

Number

(latest label date)

Active Ingredients

(% w/w) Crops

Section 3 End Use Products

Reflex

(Syngenta)

Emulsifiable concentrate

100-993

(02/08/08) Fomesafen 22.8% Cotton, dry beans, snap beans, soybeans

Flexstar

(Syngenta)

Emulsifiable concentrate

100-1101

(03/20/07) Fomesafen 22.1% Soybeans

Prefix

(Syngenta)

Emulsifiable concentrate

100-1268

(4/13/07)

Fomesafen 10.2%

s-metolachlor 46.4% Soybeans

BAS 530 04

(BASF)

Soluble concentrate

7969-82

10/22/97

Fomesafen 12.9%

Bentazon 29% Soybeans

Faster

(BASF)

Soluble concentrate

7969-83

10/22/97

Fomesafen 7.2%

Bentazon 29.8% Soybeans

Section 24 Registrations

AL030003 

AR030006 

GA880005 

MS980002 

NC950010 

SC030006 

TX040002

Pine seedlings in 

nurseries

NC870005

SC900004

Soybeans, idle 

cropland

SC900004

Soybeans, idle 

cropland, non cropland

(USDA eradication 

program only)

NE060002 Dry beans

Reflex

(Syngenta)

Emulsifiable concentrate

AR080004

Fomesafen 22.8%

Cotton

Section 3 Technicals and Formulation Intermediates

Fomesafen paste 100-1016

Fomesafen technical 100-1017

Fomesafen salt aqueous 100-1092

concentrate 100-1103

Manufacturing intermediates with no registered 

crop uses. Not anticipated to be 

environmentally relevant except in case of spill.
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2.5 Assessment Endpoints

Assessment endpoints are selected based on ecosystems typically at risk from pesticide 

applications. Specific ecological effects are evaluated based on toxicity information from 

guideline tests and open literature data, and focus on the general categories of survival, 

growth, and reproduction. Information regarding sub-lethal effects, if available, is 

discussed in the risk characterization. EFED assesses behavioral or biochemical 

endpoints if they are quantitatively linked to effects on survival or fecundity.

Table 3 Summary of Assessment Endpoints and Measures of Ecological Effect

Assessment Endpoint Measures of Ecological Effecta

Aquatic Environments

1. Survival, growth, and reproduction of fish 

and aquatic phase amphibians

Freshwater

1a. Rainbow trout acute LC50

1

1b. NOAEC estimated from sheepshead minnow 

ACR1

Saltwater

1c. Sheepshead minnow acute LC50

1

1d. Sheepshead minnow chronic NOAEC

2. Survival, growth, and reproduction of 

aquatic invertebrates

Freshwater

2a. Water flea EC50

1

2b. Water flea chronic NOAEC1

Saltwater

2c. Mysid shrimp acute EC50

1

2d. Mysid shrimp chronic NOAEC1

3. Survival, growth, and reproduction of 

aquatic plants

Freshwater

3a. Non-vascular plant (freshwater algae) acute 

EC50

1

and NOAEC1

3b. Non-vascular plant (freshwater algae) acute 

EC50

2

and NOAEC

Saltwater

3c. Non-vascular plant (saltwater diatom) acute 

EC50

2

and NOAEC3

Terrestrial Environments

4. Survival, growth, and reproduction of 

mammals

4a. Guinea pig acute LC50

1

4b. Rat chronic NOAEC1

5. Survival, growth, and reproduction of 

birds, terrestrial phase amphibians, and 

reptiles

5a. Mallard duck acute oral LC50

1

5b. Mallard duck acute dietary LC50

1

5c. Mallard duck chronic NOAEC1

6. Survival, growth, and reproduction of 

terrestrial invertebrates 6a. Honey bee acute contact LC50

7. Survival, growth, and reproduction of 

terrestrial plants

7a. Monocot (onion) seedling emergence EC25

1

7b. Dicot (radish) vegetative vigor EC25

1

a

All toxicity data reviewed for this assessment are tabulated in Appendix B.

1 Guideline study

2 ECOTOX study
13

2.5.1 Ecosystems Potentially at Risk

For typical fomesafen applications, the ecosystem at risk is the application site itself, 

including organisms that might be sprayed during application, organisms affected by 

residual fomesafen in the soil; and the adjacent aquatic and terrestrial environments 

affected due to runoff, spray drift, or groundwater contamination. In water bodies 

receiving runoff from the treatment site, fish, aquatic-phase amphibians, aquatic 

invertebrates, and aquatic vascular and non-vascular plants are considered. Terrestrial 

organisms assessed include non-target plants, insects, amphibians, reptiles, birds, and 

mammals. Because fomesafen is an herbicide, potential affects on non-target plants have 

been addressed at length. 

2.5.2 Ecological Effects

Evaluation of ecological effects focuses initially on direct effects to the groups of 

organisms residing in the ecosystems at risk, based on ratios (risk quotients) of the 

estimated environmental concentration (EEC) to a designated toxicity endpoint for a 

surrogate test organism. If pre-established levels of concern (LOCs) are exceeded for 

direct effects, indirect effects to endangered species (e.g., food chain, decrease in 

community diversity) are evaluated based on the group of organisms exceeding the LOC. 

Details on the RQ method and LOCs are in Appendix G. 

2.5.2.1 Direct

Direct effects evaluated are the survival, growth, and reproduction of various taxa of 

organisms potentially exposed to fomesafen. Taxonomic groups evaluated include 

aquatic plants (algae and vascular), aquatic invertebrates, aquatic vertebrates, terrestrial 

plants, terrestrial invertebrates, birds, and mammals. There are currently no guideline 

tests for reptiles or amphibians, so these taxa are evaluated using bird data as a surrogate 

for reptiles and terrestrial phase amphibians, and fish as a surrogate for aquatic phase 

amphibians. Both acute and chronic effects are considered.

2.5.2.2 Indirect

When herbicides are applied, indirect effects may include a decline in primary

productivity, or change in composition of plant communities proximate to the treated area 

or systems (wetlands and water bodies) receiving runoff from the site. If LOCs are 

exceeded for any taxa, potential indirect effects to endangered species are assessed.
14

Figure 2 Conceptual model for fomesafen effects

Stressor Fomesafen applied to crop

Source Direct application Spray drift Runoff

Receptors

Birds and 

Mammals

Terrestrial 

insects

Individual organisms

Reduced survival

Reduced growth

Reduced reproduction

Food chain

Reduction in primary productivity

Reduction in prey

Shift in community composition

Habitat integrity

Reduced cover

Community change

Attribute

Change

Aquatic 

plants

invertebrates

vertebrates

Terrestrial 

plants

Soil accumulation, 

leaching and runoff

Soil 

invertebrates
15

2.6 Risk Hypotheses

· Fomesafen transported in runoff from treated areas may affect the survival, 

growth, or reproduction of aquatic plants, aquatic invertebrates, aquatic-phase 

amphibians or fish.

· Fomesafen may affect the survival, growth, or reproduction of non-target plants

proximate to the treatment site.

· Fomesafen residues in plant and animal dietary sources may affect growth, 

survival, or fecundity of birds, terrestrial-phase amphibians, or small mammals ingesting 

these materials.

· Fomesafen residues on plants may affect survival of terrestrial invertebrates.

2.7 Results of Previous Assessments

A Section 3 new use ecological risk assessment was conducted for fomesafen in 2006 

(DP302766) when it was proposed for use on cotton, dry beans, and snap beans. Two 

proposed rates (0.5 lb ai/A, ground only) and 0.375 lb ai/A (ground and aerial) were 

evaluated. An alternative lower rate (0.2 lb ai/A) was also evaluated.

Key findings of this assessment included:

· The greatest acute risk associated with fomesafen use was for non-target 

terrestrial plants. 

· The persistence and mobility of fomesafen in soil and the persistence in aquatic 

environments is a concern. 

· Accumulation in the soil of a field repeatedly treated with fomesafen may

adversely affect crops subsequently planted in the field. Effects from a single treatment 

may persist for 3-18 months.

· Concentrations of fomesafen in shallow groundwater used for irrigation purposes 

may be high enough to adversely affect crops subsequently planted in the field.

· Fomesafen is practically non-toxic to slightly toxic to aquatic animals, both 

freshwater and estuarine/marine. No adverse effects to aquatic animals are anticipated 

based on proposed application rates.

· Fomesafen does exert toxic effects on aquatic plants but risk quotients (RQs) for 

the scenarios modeled were below the level of concern (LOC).
16

· Fomesafen is practically non-toxic to slightly toxic to birds and mammals on an 

acute basis. Chronic reproductive effects were noted in rats. A chronic LOAEC for birds 

was not established. No acute risk LOCs were exceeded, but acute endangered species 

LOCs were exceeded for small mammals at application rates of 0.5 and 0.375 lb ai/A.

Some chronic RQs for both birds and mammals exceeded the LOC at all application 

rates. The meaning of the exceedence for birds is uncertain, as the guideline study 

submitted did not determine a LOAEC. Better data may significantly affect the chronic 

risk picture for birds.

Endangered Species

· Based on LOC exceedences, the following taxa of endangered species were 

identified as potentially being at risk from fomesafen use: amphibians (terrestrial phase), 

birds, dicotyledon plants, mammals, monocotyledon plants, and reptiles

· Fomesafen is likely to affect plants near the treated areas, with potential effects 

extending to >900 ft away from the treatment source in the case of aerial application. 

Direct effects (reduction of growth, survival, or fecundity) may occur for endangered 

plants in the drift zone. Effects on non-endangered plants in the drift zone may constitute 

indirect effects (reduction of food or cover) to endangered animals.

Fomesafen was registered for use on all proposed crops, with a maximum application of 

0.375 lb ai/A via both aerial and ground applications.

2.8 Analysis Plan

This assessment was conducted in accordance with the methods, and using the models 

described in the Overview Document (USEPA 2004). Some additional methods were 

used to more specifically determine which listed species might be at risk as a result of 

fomesafen use. These methods build on existing models and were as follows:

● Terrestrial animals were grouped into “Kenaga categories” based on diet and size 

information available in the natureserve database (www.natureserve.org) and species 

recovery plans developed by the Services in order to determine which animals were 

likely to be at risk.1

● The AgDrift model was used to determine how far away from the point of 

application that estimated fomesafen concentrations on terrestrial food items were high 

enough for RQs to exceed LOCs. The point at which the concentration is low enough 

that the RQ drops below the LOC is referred to as the “clearance estimate” and is 

presented in the appropriate tables.

1 The classification is currently undergoing the QA/QC process within EFED.
17

3.0 Exposure Assessment

EFED conducted the exposure assessment using standard exposure modeling methods, as 

described in the Overview Document (USEPA 2004).

3.1 Label Application Rates and Intervals

Fomesafen is registered under Section 3 as a pre-plant, pre-emergence, and postemergence herbicide for control of broadleaf weeds, grasses, and sedges in soybeans, 

cotton, snap beans, and dry beans. Additional uses covered under Section 24c (special 

local needs, or SLN) registrations are for use on pine seedlings in nurseries (AL, AR, 

GA, MS, NC, SC, TX), for control of weeds in dry beans in Nebraska, and for control of 

witchweed in soybeans and idle cropland in North Carolina and South Carolina. Use in 

South Carolina also includes non-cropland, although the South Carolina uses are limited 

to areas included in the USDA witchweed eradication program.

Section 3 labels belonging to the primary registrant, Syngenta, include regionally specific 

application rates, shown in Table 1. Based on these labels, fomesafen can be applied via 

aerial and ground spray at a maximum application rate of 0.375 lbs ai/A. Section 3 labels 

belonging to BASF do not provide regionally specific application rates, but “are intended 

for use” in the areas included in Regions 1-4, and application rates (0.19- 0.23 lb ai/A) 

are lower than those on the Syngenta labels.

Table 4 Label Application Rates and Intervals for Fomesafen Use on Soybeans, Cotton, 

Snap Beans and Dry Beans1

Region States in Region App Rate (lbs/A) Application Interval

1

AL, AR, GA, LA, MS, MO2, 

NC, OK2, SC, TN, TX2 0.375 1 year

2

DC, DE, IL2, IN2, KY, MD, , 

OH2, PA3, WV, VA, 

0.375 2 year

3

CT, IA, ME, MA, MI3, NH, 

NJ, NY, PA3, RI, WI, VT

0.312 2 year

4

KS2, MI3, MN2, ND3, NE2

SD3, WI2 0.25 2 year

5 ND3

, MN3, SD3

0.170 2 year

1REFLEX 2.5 Gallonâ (EPA Reg. No. 100-993)

2Does not include entire state

3

Portions of state are in multiple regions

Application rates on some of the Section 24c labels (pine seedling use, also belonging to 

the primary registrant) are slightly higher, with a maximum application rate of 0.5 lbs 

ai/A for pre-emergence applications. The higher rate does not apply in all states. States 

included under pine seedling uses are in Region 1 as defined on the parent label, although 

the Section 24c label for Texas is assumed to include the entire state. 
18

Table 5 Label Application Rates and Intervals for Section 24c Uses of Fomesafen

Use Site States Application 

Technique

Max App Rate 

(lbs ai/A)

Application 

Interval

Pine seedlings AR, GA, MS, NC, SC, Aerial or Ground 0.5 1 year

in nurseries AL, TX Aerial or Ground 0.375 1 year

Soybeans, idle 

cropland, noncropland

SC (Horry and 

Marion counties) Aerial or Ground 0.375 1 year

Soybeans, idle 

cropland

NC (Robeson, 

Cumberland, 

Sampson, Bladen, 

and Pender counties)

Aerial or Ground 0.375 1 year

Dry beans NE Aerial or Ground 0.25 2 years

1 Based on areas currently infested with witchweed, as noted on 

www.ncagr.com/plantindustry/plant/weed/witchnc.htm, accessed May 16, 2008

3.2 Aquatic Exposure

Tier II EFED aquatic exposure modeling uses the linked Pesticide Root Zone Model and 

Exposure Analysis Model System (PRZM/EXAMS). PRZM uses the chemical’s 

physical and environmental fate properties and the site characteristics to predict the 

concentration of pesticide in runoff and entrained sediment from the field. EXAMS 

estimates the concentration of pesticide in an edge-of-field small water-body receiving 

runoff from the field. The water-body has a constant volume (20 million liters) with no 

outflow and is intended to represent an upper-end occurrence concentration.

3.2.1 PRZM-EXAMS Modeling Inputs and Scenario Selection

The aquatic exposure assessment for fomesafen was conducted to assess use on soybeans, 

dry beans, snap beans, and cotton. The Mississippi soybeans scenario was used as both a 

scenario representing MS soybeans as well as a surrogate for dry beans and snap beans, 

as EFED currently has no standard scenarios for these crops in this region. Standard 

scenarios were selected to assess runoff potential from vulnerable use sites in MS 

(soybean and cotton), NC (cotton), and TX (cotton). The MI beans scenario from region 

4 was selected to provide more geographical balance to the analysis since all of the other 

scenarios occur in region 1. No other EFED scenarios had combinations of crop and 

location relevant to this assessment. Input parameters for fomesafen were selected 

according to EFED Input Parameter Guidance for PRZM/EXAMS1. Input parameters are 

shown in Table 6.

1 Guidance for Selecting Input Parameters in Modeling the Environmental Fate and Transport of Pesticides. 

Version II, 2/28/02.
19

Table 6. Input Parameters for PRZM-EXAMS Modeling of Fomesafen on Cotton, Soybeans, 

Dry Beans, and Snap Bean

Parameter Value Comments Source

Application Rates (kg ai/ha) 0.19 - 0.56 Varies by Region Label1

Molecular Weight (grams/mole) 420 EPA 2020220

Solubility (mg/L) 1200 @pH = 7; 200c MRID 45048207

Vapor Pressure (torr) <7.5 × 10-7 @ 50oC HSDB

Henry’s Constant (atm m3/mol) 7.5 × 10-13 Estimated HSDB

Kd (L/kg) 0.68 Lowest non-sand Kd Acc. No. 259413

Aerobic Soil Metabolism Half-life 

(days) 511 Upper 90th percentile of mean2

Acc. No. 071059

Acc. No. 00135660

Aerobic Aquatic Metabolism Halflife (days) 129.4 Upper 90th percentile 

of mean3

Acc. No. 72158

Anaerobic Aquatic Metabolism 

Half-life (days) 1000 Conservative Assumption 

No Data Available

Photodegradation in Water (days) 289 @pH = 7 MRID 40451101

Hydrolysis Half-life (days) Stable @pH = 7 Acc. No. 071059

1 Reflect application rates on the REFLEX 2LC, REFLEX 2.5, and REFLEX labels

2 Calculated from half-lives of 187.6, 630, 57, 693, 349.3, 527.1, 207 days using a mean of 387.84 days and 

standard deviation of 242.90 days.

3 Calculated from half-lives of 139.9, 60.9, 92.4, and 115.5 days using a mean of 102 days and standard 

deviation of 33.44 days.

The MI beans scenario from region 4 was selected to provide more geographical balance 

to the analysis since all of the other scenarios occur in region 1. No other EFED scenarios 

had combinations of crop and location relevant to this assessment. Because applications 

in Region 4 are restricted to every other year, a modified copy of the PE5 shell was 

created to only apply the pesticide in alternate years (odd years). This can be seen in the 

Appendix A PRZM/EXAMS outputs for Michigan beans in which the even year EECs 

are always lower than the odd years.

3.2.2 PRZM-EXAMS Modeling Output

For aerial applications (Table 7), peak 1 in 10 year estimated environmental

concentrations (EECs) ranged from 2.3 ppb (beans, MI) to 12.0 ppb (cotton, TX). 

Chronic 1-in-10 year (21-day average and 60-day average) EECs ranged from 1.7 ppb 

(beans, MI, 60-day average) to 11.4 ppb (cotton, MS &TX, 21-day average).
20

Table 7. PRZM-EXAMS Aquatic EECs for Fomesafen

Peak 21 days 60 days

Region Crop State

App. 

Date

Aerial/

Ground mg/L (ppb)

Region 1: Annual Applications at 0.375 lb a.i/A

A 8.99 8.57 7.74 1 Soybean MS 5/1 G 8.19 7.77 6.95

A 11.83 11.37 10.07 1 Cotton MS 5/15 G 11.20 10.79 9.56

A 8.99 8.72 8.03

1 Cotton NC 5/10 G 8.20 7.96 7.34

A 11.96 11.39 10.31 1 Cotton TX 5/10 G 11.44 10.90 9.85

Region 4: Every-other-year Applications at 0.28 lb a.i/A

A 2.27 2.15 1.94

4 Beans MI 6/15 G 2.37 2.25 2.02

Peak 1-in-10 year EECs for ground spray applications (Table 8) ranged from 10.9 ppb 

(cotton, NC) to 15.3 ppb (cotton, TX). Chronic 1 in 10 year (21-day average and 60-day

average) concentrations ranged from 9.8 ppb (cotton, NC, 60-day average) to 14.5 ppb 

(cotton, TX, 21-day average).

Table 8 PRZM-EXAMS EECs for Fomesafen at 0.50 lb ai/A

Peak 21 days 60 days Region Crop State App. 

Date mg/L 

1 Cotton MS 5/15 14.9 14.4 12.7

1 Cotton NC 5/10 10.9 10.6 9.8

1 Cotton TX 5/10 15.3 14.5 13.1

1- Concentrations were derived for 0.50 lb ai/A using ground spray 

3.2.3 Registrant-submitted Aquatic Exposure Modeling

The registrant submitted Tier II PRZM/EXAMS modeling assessments for fomesafen use 

on cotton and soybeans (MRID 450482-04, 450482-05, 450482-06). The modeling 

scenarios used were developed to assess fomesafen runoff from vulnerable use sites 

(Hydrologic D soils) with high rainfall. Selected scenarios represent sites in Tensas 

County, LA (MRLA 131) for cotton; Leflore, MS (MRLA 131) for soybeans; and Dodge, 

NE (MRLA 102B) for soybeans, and Sheboygan, WI (MRLA 95B). Maximum 

application rates were 0.31 lbs for snap beans, 0.5 lbs ai/A for cotton, and 0.375 lbs ai/A 

for soybeans. Only ground spray was considered, although the labels allow aerial spray. 

The sources (study identification numbers) of environmental fate data are not reported. 

Additionally, there are no explanations for selection of the environmental fate data in the 

exposure assessment. The registrant estimated environmental concentrations are similar 

in magnitude to, but slightly higher than, those calculated by EFED.

3.2.4 SCIGROW Modeling for Ground Water

Because fomesafen is mobile and persistent in soil, a screening level groundwater 

assessment using SCIGROW (ver. 2.3) was conducted to estimate the concentration of 

fomesafen in shallow groundwater, which could potentially be used for crop irrigation. 

Input parameters for SCIGROW are listed in Table 10.
21

Table 9. Input Parameters for SCIGROW Modeling for Fomesafen

Parameter Value Comments Source

Application Rate (kg ai/ha)- Cotton 0.375 – 0.17 Varies by Region Label1

Koc (L/kg) 68 Estimated2Acc No. 259413

Aerobic Soil Metabolism Half-life 

(days)

387.84 Mean3Acc No. 071059

Acc. No. 00135660

1-Reflect maximum application rates on the REFLEX 2LC, REFLEX 2.5 and REFLEX labels

2-Koc estimated using Kd/SOC=Koc; where Kd=0.68 and SOC=1% SOC percentage

3-Calculated from half-lives of 187.6, 630, 57, 693, 349.3, 527.1, 207 days using a mean of 387.84 days and standard deviation of 

242.90 days. 

Based on the SCIGROW estimate, the concentration of fomesafen in shallow ground 

water in sand soils (Table 10) is not expected to exceed 5.01 mg/L (Region 1).

Table 10 Label Application Rates and Intervals for Fomesafen Use on Soybeans, Cotton, 

Snap Beans, and Dry Beans1

Region Application Rate (lbs/A)

(Application Interval)

SCIGROW-estimated 

Groundwater 

Concentrations (μg/L)

Fomesafen Application 

Due Solely to Irrigation 

(lbs ai/A)

1 0.375 (1 year) 5.01 2.27 × 10-3

2 0.375 (2 year) 2.5 1.13 × 10-3

3 0.312 (2 year) 2.08 9.42 × 10-4

4 0.25 (2 year) 1.67 7.56 × 10-4

5 0.17 (2 year) 1.14 5.16 × 10-4

1REFLEX 2.5 Gallonâ (EPA Reg. No. 100-993)

Because fomesafen is expected to leach to groundwater, EFED has calculated the 

maximum application rate of fomesafen from two inches of irrigation water. This 

calculation assumes that two inches of irrigation water is required for optimum plant 

growth. The application rate of fomesafen in terms of lbs ai/A in 2 inches of 

groundwater is calculated as follows:

10 μg g 454g / lbs

μg L

12in ft

43,560ft A 2in 28.32L ft lbs ai/A 6

2 3

 ́

 ́

 ́  ́

=

EEC fomesafen

where: 

fomesafen is the estimated application rate of fomesafen in lbs ai/A in 2 in/A of 

groundwater; and

EEC is the region-specific SCIGROW EEC in groundwater from Table 5.

Based on two inches of irrigation and the SCIGROW estimate, the application rate of 

fomesafen is estimated to vary from 0.00227 to 0.000516 lbs ai/A.

3.2.5 Soil Accumulation

Because of the persistence of fomesafen in soil, a screening level assessment was

conducted to quantify the accumulation of fomesafen residues in soil. This screeninglevel assessment does not consider loss of pesticide to run-off and leaching (only

degradation by aerobic soil metabolism is considered). A first-order decay model was 
22

used to estimate fomesafen soil concentrations over 20 years. This model is based on 

first-order decay of a single application:

kt A A e-

= 0

where: A is the soil fomesafen concentration at any point in time; A0 is the original soil 

fomesafen concentration at the time that it was applied; k is the upper 90th percentile of 

the mean aerobic soil metabolism half-life (t1/2 = 511 days; k = 1.356452 × 10-3days

-1

), 

which was used to represent the microbial mediated decay rate of fomesafen in soil; and t

is the time since the fomesafen application.

Because multiple applications occur over this 20 year timeframe, this equation is 

modified to account for multiple applications:

å=

-

=

n

i

kt

i

i A A e

1

0,

where: i is a counter variable that denotes the first fomesafen application when i = 1 and 

the second when i = 2, etc.; n is the last application; A0,i is the soil fomesafen 

concentration contributed by the i

th application; and ti is the time since the ith fomesafen 

application.

The soil fomesafen concentration contributed to the upper 15 cm of soil by the i

th

application (A0,i) in mg/Kg is calculated as:

0, 2 2 2 3

10 000 m /ha 10 000 cm /m 15 cm g/cm

lbs ai/A 454 g/lbs 2 47105381A/ha 1000 mg/g 1000 g/Kg

, , density

AppRate .

A i

 ́  ́  ́

 ́  ́  ́  ́

=

where: AppRate is the regional maximum application rate from Table 3 and density is the 

bulk density of soil. The bulk density of soil varies from 1.0 g/cm3for clay soils to 1.8 

g/cm3for sandy or compacted soils 

(http://www.cdpr.ca.gov/docs/emon/pubs/sops/fsso001.pdf). The modeling scenario 

assumes that 100% of fomesafen residue is applied to the soil as recommended for a preemergent application. The model scenario also assumes that microbial degradation is the 

only route of dissipation from the application site. These assumptions are expected to 

exaggerate predicted formesafen soil concentrations.

Figure 3 illustrates the fomesafen concentrations in soil reach a plateau after

approximately 10 years regardless of the application rate or soil bulk density. An 

application rate of 0.375 lbs/A applied every year (Region 1) can theoretically result in a 

maximum fomesafen concentration of 0.71 mg/kg in soils with a low bulk density (1.0 

g/cm3). The same application rate (0.375 lbs ai/A applied every year) can theoretically 

result in a maximum fomesafen concentration of 0.4 mg/kg in soils with a high bulk 

density (1.8 g/cm3). Applying fomesafen every other year (Region 2 to 5) and at lower 

application rates also reduces residual soil fomesafen concentrations.
23

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0 5 10 15 20

Years

Soil Concentration (mg/Kg)

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0 5 10 15 20

Years

Soil Concentration (mg/Kg)

Region 1 Region 2

Region 3 Region 4

Region 5

Figure 3. Estimate of Fomesafen Loading in the Surface Soil (0-15 cm depth) in Clay Soils 

(a; bulk density = 1.0 g/cm3) and Sandy or Compacted Soils (b; bulk density = 1.8 g/cm3) of 

Regions 1 through 5.

3.3 National Surface Water Monitoring Data

3.3.1 Surface Water

The USGS National Water Quality Assessment (NAWQA) database was accessed 

(6/9/08, SPW). No data for fomesafen was located in the database, but this appears to be 

because fomesafen is not included in the schedules of chemicals quantified by the 

laboratory. Therefore, a lack of data should not be construed as meaning there are no 

detectable fomesafen residues in surface waters.

3.3.2 Ground Water

A groundwater monitoring study was submitted (MRID 42247001), but the shallow 

groundwater wells were dry during the study. Fomesafen was detected in soil porewater 

at concentrations ranging from 1 mg/L (at 4 months) to 17 mg/L (at 1 month). It was 

detected at a concentration of 1 mg/L in the medium- to deep-depth wells.

These observed porewater concentrations are much higher than the SCIGROW EECs for 

groundwater. Using the porewater concentrations of 1 mg/L and 17mg/L (from the 

groundwater study) as outer bounds of the fomesafen groundwater concentrations that 

might be applied in irrigation water, concentrations of fomesafen in irrigation water could 

range from 0.45 to 7.7 lbs ai/A, respectively.

a b
24

3.4 Bird and Mammal Exposure (TREX)

EFED estimates exposure of birds and mammals using the Terrestrial Exposure Model 

(TREX). TREX uses the Kenaga nomagram, as modified by Fletcher et al (1994) to 

determine pesticide residues on several categories of food items, then calculates the 

potential dose an organism might receive from ingesting contaminated items using 

allometric equations. Dose estimates are based on the upper bound dose and assumptions 

that the organism exclusively eats one type of food item and forages only in the treated 

and/or overspray areas.

Table 11 Input Parameters for TREX Modeling

Input Parameters Value Source

Application Rate

0.5 lb ai/A

0.375 lb ai/A

0.312 lb ai/A

0.25 lb ai/A

0.17 lb ai/A

Label

Reflex

100-993

Foliar Half-life 35 days EFED Default

Number of Applications 1 per year

Label

Reflex

100-993

Avian LD50 5,000 mg/kg bw (mallard duck) MRID 163168

Avian LC50 20,000 mg/kg diet (mallard duck) MRID 163381

Avian NOAEC 46 mg/kg diet (mallard duck) MRID 135639

Mammal LD50 607 mg/kg bw (guinea pig) MRID 164901

Mammal NOAEC 1,000 mg/kd diet (rat) MRID 144862

For birds, dose estimates for the 0.50 lb ai/A application rate range from 2.1 mg/kg bwt 

(1000 g frugivores, granivores, and insectivores) to 134.0 mg/kg bwt (20 g herbivores). 

At the 0.375 lb ai/A application rate, estimated doses range from 1.6 mg/kg bwt (1000 g 

frugivores, granivores, and insectivores) to 102.5 mg/kg bwt (1000 g fruit and pods). 

Dose estimates for the 0.17 lb ai/A application rate range from 0.7 mg/kg bwt (1000 g 

frugivores, granivores, and insectivores) to 46.5 mg/kg bwt (20 g herbivores).
25

Table 12 Bird Dose Estimates

Kenaga Upper Bound Dose (mg/kg bwt)

Feeding Categories Small

(20 g)

Medium 

(100 g)

Large

(1000 g)

0.50 lb ai/A Application Rate(pine seedlings, Region 1)

Short grass 133.93 76.38 34.19

Tall grass 61.39 35.01 15.67

Broadleaf plants/small insects 75.34 42.96 19.23

Fruits/pods/seeds/large insects 8.37 4.77 2.14

0.375 lb ai/A Application Rate (Region 1 & 2)

Short grass 102.5 58.45 26.17

Tall grass 46.98 26.79 11.99

Broadleaf plants/small insects 57.66 32.88 14.72

Fruits/pods/seeds/large insects 6.41 3.65 1.64

0.17 lb ai/A Application Rate (Lowest Rate, Region 5)

Short grass 46.47 26.50 11.86

Tall grass 21.30 12.14 5.44

Broadleaf plants/small insects 26.14 14.90 6.67

Fruits/pods/seeds/large insects 2.90 1.66 0.74

For mammals dose estimates for the 0.50 lb ai/A application rate range from 0.25 mg/kg 

bwt (1000 g granivore) to 112 mg/kg bwt (20 g short grass). At the 0.375 lb ai/A 

application rate, estimated doses range from 0.2 mg/kg bwt (1000 g granivore) to 85.8 

mg/kg bwt (20 g short grass). Dose estimates for the 0.17 lb ai/A application rate range 

from 0.1 mg/kg bwt (1000 g granivore) to 38.9 mg/kg bwt (20 g short grass).
26

Table 13 Mammal Dose Estimates

Kenaga Upper Bound Dose (mg/kg bwt)

Feeding Categories Small

(15 g)

Medium 

(35 g)

Large

(1000 g)

0.50 lb ai/A Application Rat e(Pine seedlings, Region 1)

Herbivores/Insectivores

Short grass 112.12 77.49 17.97

Tall grass 51.39 35.52 8.23

Broadleaf plants/small insects 63.07 43.59 10.11

Fruits/pods/seeds/large insects 7.01 4.84 1.12

Granivores

Fruits/pods/seeds/large insects 1.56 1.08 0.25

0.375 lb ai/A Application Rate (Region 1,2)

Herbivores/Insectivores

Short grass 85.81 59.30 13.75

Tall grass 39.33 27.18 6.30

Broadleaf plants/small insects 48.27 33.36 7.73

Fruits/pods/seeds/large insects 5.36 3.71 0.86

Granivores

Fruits/pods/seeds/large insects 1.19 0.82 0.19

0.17 lb ai/A Application Rate (Lowest Rate, Region 5)

Herbivores/Insectivores

Short grass 38.90 26.88 6.23

Tall grass 17.83 12.32 2.86

Broadleaf plants/small insects 21.88 15.12 3.51

Fruits/pods/seeds/large insects 2.43 1.68 0.39

Granivores

Fruits/pods/seeds/large insects 0.54 0.37 0.09

3.5 Terrestrial Invertebrate Exposure

Exposure of terrestrial invertebrates was estimated using the dietary-based EECs 

produced by TREX for the two insect categories (small and large). The value produced 

by TREX, mg ai/kg insect, is equivalent to mg ai/g insect. The fomesafen residue for a 

bee (μg ai/bee) is calculated by multiplying the residue by the assumed weight of a honey

bee (0.128 g) to establish a dose per bee. This method assumes that contact is the 

relevant route of exposure, rather than ingestion. This method of estimation is believed 

to be adequate for fomesafen.

Table 14 Terrestrial Invertebrate Exposure

Application Rate

(lb ai/A)

Insect Size 

Category

EECs 

(mg ai/kg insect)

Dose per Bee

(mg ai/bee)

0.50 Small insects 67.50 8.64

(Pine seedlings, Region 1) Large insects 7.50 0.96

0.375 Small insects 50.63 6.48

(Regions 1,2) Large insects 5.63 0.72

0.017 Small insects 22.95 2.94

(Region 5) Large insects 2.55 0.32
27

3.6 Terrestrial Plant Exposure (TerrPlant & AgDrift)

Currently, EFED uses the TerrPlant Model (Version 1.2.1) to evaluate exposure of 

terrestrial plants to pesticides applied on agricultural fields. In cases where spray drift 

may be of concern in the risk assessment EFED also uses the AgDrift model.

3.6.1 TerrPlant

TerrPlant has two basic exposure scenarios. The first is an adjacent upland area, which is 

exposed to the pesticide via drift and dissolved concentrations in sheet runoff. The 

second is an adjacent semi-aquatic (wetland) area, which is exposed to the pesticide via 

drift and to dissolved concentrations in channelized runoff. Drift is calculated as a 

percentage of the application rate (1% for ground and 5% for aerial, airblast, or spray 

chemigation) and is not adjusted for distance from the application site. The amount of 

dissolved pesticide in the runoff component is estimated based on solubility of the active 

ingredient. 

Table 15 Terrestrial Plant Exposure

Total Loading (Runoff + Drift) (lb ai/A) Drift EEC (lb ai/A) Application Method Upland Areas Wetland Areas All Areas

Application Rate 0.5 lb ai/A (Pine seedlings, Region 1)

Aerial 0.05 0.275 0.025

Ground 0.03 0.255 0.005

Application Rate 0.375 lb ai/A (Region 1 & 2)

Aerial 0.0375 0.20625 0.01875

Ground 0.0225 0.19125 0.00375

Application Rate 0.312 lb ai/A (Region 3)

Aerial 0.0312 0.1716 0.0156

Ground 0.01872 0.15912 0.00312

Application Rate 0.25 lb ai/A (Region 4)

Aerial 0.025 0.1375 0.0125

Ground 0.015 0.1275 0.0025

Application Rate 0.17 lb ai/A (Region 5)

Aerial 0.017 0.0935 0.0085

Ground 0.0102 0.0867 0.0017
28

3.6.2 AgDrift

Because of concerns about effects on non-target plants located in the overspray or spray

drift area, EFED elected to perform an analysis of potential deposition of fomesafen 

using AgDrift modeling software. AgDrift was developed using extensive fieldmeasured data sets, and provides a method of estimating deposition of the compound of 

concern at a specified distance away from the application source. Deposition is heavily

dependent on the method of application and droplet size. 

The AgDrift modeling reported in Table 16 and Table 17 is AgDrift Tier I, with 

associated defaults. It should be completely reproducible by anyone else using the model 

with the same settings, as the only required inputs are the application rate and distance 

from the field. Please note, however, that “fraction of applied” results were put

into an Excel spreadsheet in order to more efficiently calculate RQs for different 

endpoints and application rates. Some of the values being calculated are based on very 

low concentrations of fomesafen, and there could be minor variations in output 

depending on how values for the input or from the output are rounded. 

The Tier I modeling extends to approximately 1,000 ft away from the point of 

application. At this point, the mathematical curve that represents the deposition is 

asymptotic. Thus, evaluations past this point were not performed. It is possible to 

estimate deposition at longer distances using higher tiers of AgDrift, but the greater 

distances add substantial uncertainty. For aerial applications, the deposition at 950 ft 

ranges from 0.3% to 4%, depending on droplet size. Deposition was estimated in 50 ft 

increments for droplet spectrums ranging from very fine to very coarse (ASTM standard 

designation, 4 different ranges as implemented in the modeling software). For ground 

applications, estimates were done every 10 ft for the first 100 ft and at 50 ft increments 

thereafter. Estimates were done for both high and low boom application methods, in the 

2 droplet ranges implemented in AgDrift (very fine to fine, fine to medium, ASTM 

standard designation). All values reported are based on the 90th percentile estimate. 

Complete modeling output is included in Appendix G. 

Values in the table are reported at the distance where deposition is slightly lower than the 

NOAEC for the most sensitive plant, or at the limit of the Tier I modeling, designated as 

>950 ft. The actual furthest extent of the Tier I model varies slightly depends on the 

method of application and droplet size.
29

Table 16 Drift Deposition from Ground Applications

Low Boom High Boom

Very Fine to Fine Fine to Medium Medium to Coarse Coarse to Very Coarse Application 

Rate 

(lb ai/A) Distance

(ft)

Deposition

(lb ai/A)

Distance

(ft)

Deposition

(lb ai/A)

Distance

(ft)

Deposition

(lb ai/A)

Distance

(ft)

Deposition

(lb ai/A)

0.5 300 0.0018 150 0.0017 450 0.0020 250 0.0017

0.375 200 0.0019 80 0.0020 400 0.0020 150 0.0019

0.312 200 0.0016 70 0.0020 350 0.0019 150 0.0016

0.25 150 0.0017 50 0.0019 300 0.0019 90 0.0019

0.17 80 0.0020 30 0.0019 250 0.0016 60 0.0018

Table 17 Drift Depostion from Aerial Applications

Very Fine to Fine Fine to Medium Medium to Coarse Coarse to Very 

Coarse Application 

Rate 

(lb ai/A) Distance

(ft)

Deposition

(lb ai/A)

Distance

(ft)

Deposition

(lb ai/A)

Distance

(ft)

Deposition

(lb ai/A)

Distance

(ft)

Deposition

(lb ai/A)

0.5 950 0.0214 950 0.0060 950 0.0028 700 0.0020

0.375 950 0.0161 950 0.0045 950 0.0021 550 0.0019

0.312 950 0.0134 950 0.0037 950 0.0021 550 0.0019

0.25 950 0.0107 950 0.0030 600 0.0019 350 0.0020

0.17 950 0.0073 950 0.0020 400 0.0019 250 0.0019
30

4.0 Effects Assessment

Toxicity endpoints are established based on data generated from guideline studies 

submitted by the registrant, and from open literature studies that meet the criteria for 

inclusion into the ECOTOX database maintained by EPA/ORD. EFED policy is to use 

the effects endpoint from the most sensitive tested species for each taxa evaluated. In 

aquatic systems, taxa evaluated include aquatic plants, invertebrates, and fish. Fish serve 

as a surrogate for aquatic-phase amphibians when amphibian data are unavailable or 

unacceptable for quantitative use. Where data are available, separate endpoints are used 

for freshwater and estuarine/marine organisms. In terrestrial systems, taxa evaluated 

include birds and mammals. Bird endpoints are generally derived from guideline studies 

on bobwhite quail and/or mallard duck. Bird data are used as a surrogate for reptiles and 

terrestrial-phase amphibians when data for these taxa are unavailable or unacceptable for 

quantitative use. Mammal data are derived from guideline studies conducted on 

laboratory rats, mice, or rabbits.

4.1 Specific Toxicological Concerns Associated with this Chemical

Fomesafen is a diphenyl-ether, one of a class of herbicides sometimes referred to as lightdependent peroxidizing herbicides (LDPHs), which have enhanced toxicity in the 

presence of solar ultra-violet radiation. Because toxicity of the LDPHs is affected by the 

presence of ultraviolet (UV) radiation, toxicity tests used in this assessment, which were 

conducted under standard laboratory lighting conditions, may underestimate the toxicity

of fomesafen to some taxa under natural sunlight conditions. The Agency is currently in 

the process of developing a protocol for aquatic studies that evaluate the effect of UV 

light on the toxicity of these herbicides, but at the time of this assessment, it had not been 

finalized (EFED 2007). Preliminary studies have been submitted for some chemicals, but 

not fomesafen. Fish early life-cycle studies on oxyfluorfen conducted under UV light 

indicate larval fish LD50s are approximately an order of magnitude lower than LD50s 

based on standard lighting conditions (MRID 46585104). In this study, the larval fish 

appeared to hatch prematurely compared to the controls, and then die. Based on the 

mode of action, it is possible that disruption of the egg cell membrane caused the 

premature hatch. The extent to which UV light enhances the toxicity of fomesafen is 

unknown. However, existing studies may underestimate the toxicity. Potential impacts 

of the underestimation are discussed in the Risk Description (Section 6).

Fomesafen, along with other chemicals in this class have been associated with 

peroxisome proliferation, which can induce hepatocellular carcinomas in rodents. (Smith 

and Elcombe 1989, Ashby et al as cited in Krijt et al 1999. A discussion of potential for 

carcinogenicity, based on EFED’s review of open literature information and the HED’s 

review of mammalian guideline studies, is included in the terrestrial effects section.
31

4.2 Aquatic Hazard Summary

Fomesafen was originally registered for use in the 1980s. Guideline studies from that 

time were available for aquatic invertebrates and fish, both freshwater and 

marine/estuarine. Although some of the studies were conducted on formulated product, 

and would not be acceptable under current standards, they were classified as core or 

supplemental under the guidelines at the time they were submitted, and have been used in 

this assessment. When necessary, endpoints for these tests were re-calculated and/or data 

were converted to express toxicity on the basis of active ingredient. Overall, fomesafen 

is slightly toxic to practically nontoxic to invertebrates and practically non-toxic to fish 

on an acute basis. Chronic tests were conducted under standard laboratory lighting, and 

as noted in Section 4.1, may underestimate toxicity by approximately an order of 

magnitude.
32

Table 18 Aquatic Toxicity Profile for Fomesafen

Assessment 

Endpoint

Surrogate 

Species Toxicity Value Used Source Citation Comments

Freshwater

Acute Toxicity 

to Fish and 

Aquatic-phase 

Amphibians

Rainbow trout

LC50=126 mg/L

95%CI=117-135 mg/L

Slope=14.6

MRID

103023

Formulation1,2

(practically nontoxic)

Chronic 

Toxicity 

Fish and 

Aquatic-phase 

Amphibians

Calculated 

based on ACR

(Sheepshead 

minnow/sheeps

-head minnow

LC50=9.4 mg/L

(ACR=13.4) Estimated

Estimated from 

formulation data.

Daphnia ACR=7.5

Mysid ACR=35.7

Acute Toxicity 

to Aquatic 

Invertebrates

Water flea

LC50=376 mg/L

95%CI=323-437 mg/L

Slope=5.6

MRID 

1631169

Formulation1,2

(practically nontoxic)

Chronic 

Toxicity 

Aquatic 

Invertebrates

Water flea NOAEC=50 mg/L

LOAEC=100 mg/L

MRID

135642

Formulation1,2

Reduced growth, and 

# of offspring

Acute Toxicity 

to Aquatic 

Plants 

(non-vascular)

Green alga LC50=0.092 mg/L3

NOAEC=0.010 mg/L3

MRID 

46673804

Technical

Biomass most 

sensitive endpoint

Acute Toxicity 

to Aquatic 

Plants 

(vascular)

Duckweed LC50= 0.210 mg/L

NOAEC=0.064 mg/L

MRID

46673803

Technical

Dry weight most 

sensitive endpoint

Saltwater

Acute Toxicity 

to Fish

Sheepshead 

minnow

LC50= >163mg/L

95%CI=ND

Slope=ND

MRID

135651

Formulation1,2

(practically nontoxic)

Chronic 

Toxicity to 

Fish 

Sheepshead 

minnow

NOAEC=12.2 mg/L

LOAEC=20.1 mg/L

MRID

135644

Formulation1,2

Reduced larval 

survival

Acute Toxicity 

to Aquatic 

Invertebrates

Mysid shrimp

LC50=25 mg/L

95%CI=19-38 mg/L

Slope=ND

MRID

135647

Formulation1,2

(slightly toxic)

Chronic 

Toxicity

Aquatic 

Invertebrates

Mysid shrimp NOAEC=0.70 mg/L

LOAEC=1.7 mg/L

MRID 

135648

Formulation1,2

Parental mortality

Acute Toxicity 

to Aquatic 

Plants 

SW diatom LC50= 1.51 mg/L

NOAEC=0.94 mg/L

MRID 

46673806

Technical

Biomass most 

sensitive endpoint

1 Data are from studies originally reviewed and classified in 1984, some of which used formulated 

product. 2For purposes of this risk assessment, test concentrations were adjusted for percent ai if 

necessary, and endpoints were re-calculated using TOXANAL software. 3Endpoints have been 

revised since those reported in problem formulation, which were based on provisional data. NDnot determined.
33

4.3 Summary of Aquatic Ecotoxicity Studies

4.3.1 Aquatic Guideline Data

Fomesafen was originally registered for use in the 1980s. Guideline studies from that 

time were available for aquatic invertebrates and fish, both freshwater and 

marine/estuarine. Although some of the studies were conducted on formulated product, 

and would not be acceptable under current standards, they were classified as core or 

supplemental under the guidelines at the time they were submitted. When necessary, 

endpoints were re-calculated and/or data were converted to express toxicity on the basis 

of active ingredient. Aquatic plant data are from studies conducted on the technical 

ingredient. Acute toxicity (LC50s) for fish and invertebrates ranges from 25 mg ai/L 

(mysid shrimp, MRID 135647) to 1,507 mg/L (bluegill, MRID 163169). No sub-lethal 

effects were reported in the acute studies. Overall, fomesafen is slightly toxic to 

practically nontoxic to invertebrates and practically non-toxic to fish on an acute basis. 

Chronic toxicity (NOAECs) for fish and invertebrates range from 0.7 mg ai/L (mysid 

shrimp, parental mortality, MRID 1354648) to 50 mg ai/L (Daphnia magna, reduced 

growth, total number of offspring, MRID 1354642). Because of fomesafen’s low toxicity

to aquatic animals based on the available data, additional studies were not requested at 

the time of problem formulation, and this risk assessment was conducted using existing 

data. More recent studies on aquatic plants were conducted on the technical active 

ingredient (ai). LC50s for aquatic plants range from 0.092 mg ai/L (green alga, MRID 

46673804) to 71 mg ai/L (bluegreen alga, MRID 46673807). NOAECs range from 

0.0095 mg ai/L (green alga, MRID 46673804) to 27.3 mg ai/L (bluegreen alga, MRID 

46673807). 

4.3.2 Aquatic Data from ECOTOX

Several studies were available in ECOTOX evaluating the effects of fomesafen on 

aquatic organisms, including mesocosm studies that addressed effects on community 

structure and primary productivity (Caquet et al 2005 (E87334) and Caquet 2006 

(E95935); Perschbacher et al 1997 (E53095)). Other studies evaluated effects on the 

hematocytes of snail exposed to fomesafen in solution Russo et al (2007) (E95100) and 

Russo and Medec (2007) (E95590).

Taken together, Caquet et al (2005) (E87334) and Caquet (2006) (E95935) show that 

fomesafen applied to mesocosms in aquatic concentrations of approximately 30-60 mg/L 

can cause perturbations in the ecosystem. These perturbations appear to be mostly

associated with shifts in species composition and abundance, rather than reductions in 

overall primary productivity and biomass (of either plants or animals). Stable isotope 

analysis of predators in the system, nymphs of the common backswimmer (Notonecta 

glauca L.), confirm there are some modifications in both trophic level and initial carbon 

source when treatments were compared to controls. Treatments with a nonylphenolcontaining surfactant, Agral 90, and fomesafen (applied at the same nominal 

concentration as the fomesafen only treatment) produced slightly different effects on the 

mesocosms. Based on the structure of the experiments and the data presented in the 
34

papers, it cannot be determined if differences in response were associated with the 

surfactant alone or some interactive effect between fomesafen and the surfactant. 

Application of the fomesafen-surfactant mixture reduced water concentrations of 

fomesafen in the mesocosoms. At termination of treatment, fomesafen concentrations 

were given by authors as 62.5 ±5.3 mg/L (mean) in the fomesafen-only ponds and as 19.4 

±7.6 mg/L (mean) in the fomesafen-Agral 90 ponds. The authors make no mention of 

measuring concentrations in other compartments in the mesocosm or performing any

mass balance calculations to determine fate of fomesafen in the mixture mesocosms, 

although they speculate (Caquet et al 2005) it may have accumulated at the interfaces.

Currently, the EFED assumption for spray drift in aerial applications is 5%, and it is 

assumed to be the product (or whatever application mix) deposited directly on the surface 

of a water body adjacent to a treated field. Study authors have essentially made the same 

assumption, and evaluated the short-term effects (deposition-72 hrs) of a 1% and 10% 

drift rate associated with aerial application to soybeans on the phytoplankton community

of a small (500-L) pond. Based on this work, one could interpret that short-term effects 

on the phytoplankton abundance and production from concentrations of fomesafen ≤0.06 

mg/L are not anticipated. This should be caveated with the fact that the community was 

dominated by cyanobacteria (which appear to be less sensitive to fomesafen than green 

algae). Also, measurement endpoints reported by authors evaluate overall primary 

productivity of the system, rather than community structure, which may be more 

responsive.

Authors noted statistically significant increases in production of reactive oxygen species 

(ROS) in snails exposed to water concentrations of fomesafen ≥10 mg/L (Russo et al

2007). Cellular membrane permeability was increased at exposure concentrations of ≥10 

mg/L (Russo et al 2007, Russo and Madec 2007). Increased cellular permeability may

lead to higher percentages of apoptotic and necrotic cells in the population of circulating 

hemocytes in the snails, but these cells do not necessarily proceed to death (Russo and 

Madec 2007). Responses vary across the time course of exposure (24-504 hours) with a 

lower response generally noted at 504 hours (Russo et al 2007, Russo and Madec 2007). 

It is unclear in both works whether the reduced response is due to a compensatory

response by the cells, or overwhelming of cellular processes following extended 

exposure. At concentrations of ≤270 mg/L for durations ≤504 hours (21 days) there was 

no observable abnormal behavior, mortality, or reduction of hemocyte cell viability in the 

snails (Russo et al 2007, Russo and Madec 2007). Based on this work, it appears that 

fomesafen induces an immune response in freshwater snails at concentrations that may

occur in the environment, but how these responses translate to measurable effects at an 

organism level (e.g., reduced growth, tumor activation, increase susceptibility to disease) 

are unknown.
35

4.4 Terrestrial Hazard Summary

Guideline studies evaluating effects on birds, mammals, and terrestrial invertebrates were 

available for fomesafen. Several ECOTOX studies suitable for risk assessment purposes 

were available. On an acute basis, fomesafen is slightly toxic to mammals and practically

non-toxic to birds and honeybees. Open literature studies indicate fomesafen may induce 

homolysis and formation of hepatic carcinomas in some strains of mice, but these occur 

at concentrations and durations of exposure far higher than likely to occur in the 

environment based on current registrations. HED (USEPA 2006) has determined

fomesafen is neither mutagenic nor carcinogenic for humans, nor does it appear to be 

associated with endocrine-disrupting effects.

Table 19 Terrestrial Toxicity Profile for Fomesafen

Assessment 

Endpoint

Surrogate 

Species Toxicity Value Used Source Citation Comments

Vertebrates

Acute Risk to 

Mammals Guinea pig

LC50=607 mg/kg

95%CI=ND

Slope=ND

MRID 

164901 Slightly toxic

Chronic Risk to 

Mammals Rat NOAEC=1,000 mg/kgLOAEC=ND

MRID 

144862

No reproductive 

effects

Mallard duck

(oral dose)

LC50=>5,000 mg/kg

95%CI=ND

Slope=ND

MRID 

163168 Practically non-toxic

Acute Risk to 

Birds, 

Terrestrialphase 

Amphibians, 

and Reptiles

Mallard duck 

(dietary)

LC50=>20,000 mg/kg

NOAEC=20,000 mg/kg

MRID

163384 Practically non-toxic

Chronic Risk to 

Birds, 

Terrestrial 

phase 

Amphibians, 

and Reptiles

Mallard duck NOAEC=46 mg/kg

LOAEC=>46 mg/kg

MRID 

135639

No endpoints 

affected

Invertebrates

Acute Risk to 

Invertebrates

Honey bee

(acute contact) LD50=>100 mg/bee MRID 135651 Practically non-toxic

Plants

Acute Risk to 

Monocots

Onion

(seedling 

emergence)

EC25= 0.084 lb ai/A

NOAEC=0.030 lb ai/A

MRID 

46673801

Acute Risk to 

Dicots

Lettuce

(vegetative vigor)

EC25= 0.002 lb ai/A

NOAEC=<0.002 lb ai/A

MRID 

46673802

Formulation

(Reflex 2 LC)
36

4.5 Summary of Terrestrial Ecotoxicity Studies

4.5.1 Avian and Small Mammal Guideline Data

Guideline acute toxicity studies were available for birds (both dose and dietary), and 

small laboratory mammals (dose). The oral LD50 for mallard ducks was greater than the 

highest dose tested (LD50>5,000 mg/kg, MRID163168). Sub-acute dietary LC50s for 

both mallards and bobwhite quail were also greater than the highest dose tested (>20,000

mg/kg, MRIDs 163384, 164901) Acute oral dose LD50s were available for guinea pigs (F 

607 mg/kg, MRID 164901), mice (F 745 mg/kg, M 766 mg/kg, MRID164901) and rats 

(F 1499 mg/kg, M 1858 mg/kg, MRID 164901). On the basis of both dose and dietary

values, fomesafen is practically non-toxic to birds and slightly toxic to mammals. 

Endpoints for female guinea pigs and mallard ducks were the most sensitive and were 

used to develop risk quotients.

Chronic guideline studies were available for birds (mallard duck, MRID 135639) and 

small laboratory mammals (rat, MRID 144862). The bird guideline study did not 

establish a LOAEC, only determining that there were no effects at the highest (meanmeasured) concentration tested for birds. No sub-lethal effects were noted. Lack of a 

LOAEC contributes significant uncertainty to the evaluation of chronic risk to birds. The 

mallard duck NOAEC (46 ppm) is used in the determination of chronic risk to birds, but 

it may over-estimate the risk to birds. In some cases, calculated exposure is near or 

above the maximum tested concentration. In the rat study, no treatment related 

reproductive parameters were affected at the highest dose tested, resulting in a 

reproductive NOAEC of 1,000 mg/kg (MRID 144862). Changes in the liver 

histopathology of both the parents and the offspring were noted at 1,000 mg/kg. 

Histology changes are difficult to link with the assessment endpoints of growth, survival 

and fecundity evaluated by the Agency. The reproductive NOAEC of 1,000 mg/kg was 

used to develop endpoints for mammals.

Because of fomesafen’s low toxicity to terrestrial organisms based on the available data, 

additional studies were not requested at the time of problem formulation, and this risk 

assessment was conducted using existing data.

4.5.2 Terrestrial Plant Data

4.5.2.1 Guideline Studies

Terrestrial plant guideline studies were available. Fomesafen is effective, both pre- and 

post-emergent, against a variety of plants, although dicots appear to be more sensitive 

than monocots for both endpoints (seedling emergence and vegetative vigor). The 

product is marketed as a control for broad-leafed weeds.

Guideline studies for seedling emergence (MRID 46673801, acceptable) and vegetative 

vigor (MRID 46673802, acceptable) were available at the time of this assessment. Both 

studies evaluated the effects of fomesafen formulated product (REFLEX 2LC) on 10 

plant species. Species tested included 4 monocots (onion, barnyard grass, corn, and oats) 
37

and 6 dicots (radish, lettuce, tomato, soybean, oilseed rape, and sugarbeet). Two 

concentrations were tested: 0.25 lb ai/A and 0.50 lb ai/A. For monocots, the seedling 

emergence EC25s ranged from 0.084 lb ai/A to >0.48 lb ai/A (no effect at highest 

concentration tested). Dicots were more sensitive, with the seedling emergence EC25s 

ranging from 0.005-0.35 lb ai/A, with the exception of soybeans, with an EC25 of >0.48 

lb ai/A (no effect at highest concentration tested). Currently, soybeans are the crop for 

which fomesafen is most commonly used. For dicots, the sensitivity range for the 

vegetative vigor endpoint is similar to the seedling emergence endpoint. EC25s for the 

dicot vegetative vigor endpoint range from 0.002-0.24 lb ai/A, with the exception of 

soybeans, with an EC25 of >0.47 lb ai/A (no effect at highest concentration tested). For 

monocot vegetative vigor endpoint EC25s ranged from 0.29 lb ai/A to >0.47 lb ai/A (no 

effect at highest concentration tested). Based on this data, dicots appear more sensitive 

than monocots, and the vegetative vigor and seedling emergence endpoints appear to be 

equally sensitive.

4.5.2.2 Additional Registrant-Submitted Data

Efficacy data (MRID 135656) were part of the data package submitted for the original 

registration of fomesafen, and were considered in this assessment. The efficacy data 

included pre-emergence and post-emergence treatment of 24 plant species, at two 

concentrations (0.25 and 1.0 kg ai/ha, or when converted, 0.42 and 0.54 lb ai/A). The 

two concentrations are greater than most currently registered rates. The plant species 

tested included both monocots (11 species) and dicots (13 species). Both crop (7 species) 

and non-crop (17 species) plants were evaluated. With the exception of soybeans, all 

plants tested experienced >20% “damage” when treated pre-emergence, with a significant 

number (65%) experiencing >80% damage when treated with the lower concentration 

(0.25 kg ai/ha). Applied post-emergence, fomesafen is slightly less effective, with 

“damage” typically in the 0-40% range for monocots and 40-80% range for dicots. The 

report did not specify how damage was quantified.

Additional plant data was submitted by the registrant during the registration review 

process (MRID 47587101). This submission was not reviewed by EPA for acceptability, 

and raw data were not included, thus values reported herein do not represent anything 

statistically generated by the Agency. Inclusion of these data is intended to provide a 

broader view of potential effects on plants than is provided by guideline data alone. 

These data do not represent a regulatory endpoint.

The submission included an estimation a 10th percentile EC25, based on EC25s for a range 

of plant species tested by the registrant. The registrant’s database included 210 efficacy 

tests addressing 35 common crop and weed, with multiple application rates ranging from 

0.01-0.45 lb ai/A. Effects on the plants are rated on a visual scale of 1 to 10 compared to 

control plants, then converted to a percent effects scale (0%=no damage, 100%=complete 

efficacy). 
38

4.5.3 Terrestrial Insect Data

Guideline tests for honeybees were submitted (MRID 135651, Core), as was a field 

chronic effects study on earthworms (MRID 135652). The acute oral LD50 for honeybees 

was >50 mg ai/bee, and the acute contact LD50 was >100 mg ai/bee. The field test for 

earthworms included two applications of fomesafen, applied at one-year intervals. Fields 

were treated with 0.5 kg ai/ha and 5.0 kg ai/ha. No adverse effects on total numbers, total 

weights, or numbers of individual species were noted at the 0.5 kg ai/ha treatment level. 

A significant change in numbers of one species of earthworm (Allolobophura nocturna) 

was noted at the higher treatment level, but authors attributed this to modifications in 

grass cover caused by the herbicide treatment rather than direct toxic effects.

Studies were also submitted (MRID 135656) for eight species of invertebrates, from the 

orders Acarina, Hemiptera, Diptera, Lepidoptera, Coleoptera, and Nemotoda. Fomsafen 

was applied to multiple life stages at concentrations of 250 and 500 ppm. The greatest 

level of mortality in these tests was 9%. Aphids (Aphis fabae) experienced mortality

rates of 9% at concentrations of 250 ppm and 500 ppm.

4.5.4 ECOTOX Data

Some information regarding toxicity of fomesafen was available in the open litereature. 

Full reviews of studies with endpoints potentially useful for this risk assessment are 

located in Appendix B. No studies contained endpoints lower than those derived from 

guideline studies. Summaries of studies evaluating biochemical and community-level 

endpoints are presented below.

4.5.4.1 Biochemical Endpoints

Several studies (Krijt et al 1993 (E95026); Krijt et al 1994a (E95399); Krijt et al 1994b 

(E95589); Krijt et al 1999 (E95400); Krijt et al 2003 (E95588)) evaluating the effects of 

fomesafen on mammalian hematocytes were located and reviewed. The work of Krijt et

al demonstrates that fomesafen ingested by mice at concentrations ranging from 100-

2,500 ppm diet for 10 days causes elevated liver and fecal porphyrins, primarily via 

inhibition of the 7th enzyme of the heme biosynthesis protoprophyrin III oxidase (Krijt et

al 1993). Body weight gain is statistically significantly affected when fomesafen is 

administered at concentrations of 2,500 ppm in diet for 10 days (Krijt et al 1993). The 

treatment groups in all investigations are small (n=3 or 4). Mice used in the experiments 

were generally in the size range of 30-35 grams. In some cases, fomesfen may also 

inhibit uroporphyrinogen III decarboxylase, but specific biochemical responses may vary

dependent on the strain of mouse (Krijt et al 1994m, Krijt et al 2003). Consumption of 

high doses (2,300-3,000 ppm) for extended periods of time (50 weeks to 14 months) 

caused development of precancerous cells in the liver (Krijt et al 1999). Even with 

extended exposure, mice appeared to recover following a period of clean diet (3months) 

with liver porphyrins decreasing, and liver histology not noticeably different from 

controls (Krijt et al 1999). In both studies that included a recovery period, liver 

porphyrin concentrations decreased rapidly following withdrawal from fomesafen, but 

did not return to the same levels as controls during the observation period (Krijt et al

1999). 
39

Two studies described the effects of fomesafen on the hemocytes of the freshwater snail 

Lymnaea stagnalis (Russo et al 2007, Russo and Madec 2007). Authors noted 

statistically significant increases in production of reactive oxygen species (ROS) in snails 

exposed to water concentrations of fomesafen (≥10 mg/L) (Russo et al 2007). Cellular 

membrane permeability was increased at exposure concentrations of ≥10 mg/L (Russo et

al 2007, Russo and Madec 2007). Increased cellular permeability may lead to higher 

percentages of apoptotic and necrotic cells in the population of circulating hemocytes in 

the snails, but these cells do not necessarily proceed to death (Russo and Madec 2007). 

Responses vary across the time course of exposure (24-504 hours) with a decrease 

response generally noted at 504 hours as compared to 24 hours (Russo et al 2007, Russo 

and Madec 2007). It is unclear in both works whether the reduced response is due to a 

compensatory response by the cells, or overwhelming of cellular processes following 

extended exposure. At concentrations of ≤270 mg/L for durations ≤504 hours (21 days),

there was no observable abnormal behavior, mortality, or reduction of hemocyte cell 

viability in the snails (Russo et al 2007, Russo and Madec 2007). Based on this work, it 

appears that fomesafen induces an immune response in freshwater snails at 

concentrations that may occur in the environment, but how these responses translate to 

measurable effects at an organism level (e.g., reduced growth, tumor activation, increase 

susceptibility to disease) are unknown.

4.5.4.2 Aquatic Community-Level

Mesocosm studies (Caquet et al 2005, Caquet 2006) show that fomesafen applied in

concentrations of approximately 30-60 mg/L can cause perturbations in the ecosystem. 

These perturbations appear to be mostly associated with shifts in species composition and 

abundance, rather than reductions in overall primary productivity and biomass (of either 

plants or animals). Stable isotope analysis of predators in the system, nymphs of the 

common backswimmer (Notonecta glauca L.), confirm there are some modifications in 

both trophic level and initial carbon source when treatments were compared to controls. 

Treatments with a nonylphenol-containing surfactant, Agral 90, and fomesafen (applied 

at the same nominal concentration as the fomesafen only treatment) produced slightly

different effects on the mesocosms. Based on the structure of the experiments and the 

data presented in the papers, it cannot be determined if differences in response were 

associated with the surfactant alone or some interactive effect between fomesafen and the 

surfactant. Application of the fomesafen-surfactant mixture reduced water concentrations 

of fomesafen in the mesocosoms. At termination of treatment, fomesafen concentrations 

were given by authors as 62.5 ±5.3 mg/L(“maximum mean”) in the fomesafen only ponds 

and as 19.4 ±7.6 mg/L (“maximum mean”) in the fomesafen-Agral 90 ponds 

Pershbarger et al (1997) examines the effect of spray drift on aquatic mesocosms. Study

authors evaluated the short-term effects (deposition to 48 hrs) of a 1% and 10% drift rate 

associated with aerial application to soybeans on the phytoplankton community of a small 

(500-L) pond. Based on this work, one could interpret that short-term effects on the 

phytoplankton abundance and production from concentrations of fomesafen ≤0.06 mg/L 

are not anticipated. This should be caveated with the fact that the mesocosm community

was dominated by cyanobacteria (which appear to be less sensitive to fomesafen than 
40

green algae based on registrant-submitted studies: MRID 46673806, green alga EC50 92 

mg/L; MRIDs 46673807, blue-green alga EC50 710 mg/L). Also, measurement endpoints 

reported by authors evaluate overall primary productivity of the system, rather than 

community structure, which may be more responsive.

4.5.5 Carcinogenicity, Mutagenicity, and Endocrine Disruption

Based on data submitted for use in human health risk assessments, the Health Effects 

Division (HED) evaluates potential for carcinogenicity. Fomesafen was classified as “not 

likely to be carcinogenic to humans.” This decision was “based on the weight-ofevidence which supports activation of peroxisiome proliferator-activated alpha (PPARa) 

as the mode of action for fomesafen-induced hepatocarcinogeneisis in mice. The data did 

not support either mutagensis or cytotoxicity followed by regenerative proliferation as 

alternative modes of action.” (USEPA 2006).

EPA is required under the FFDCA, as amended by FQPA, to develop a screening 

program to determine whether certain substances (including all pesticide active and other 

ingredients) “may have an effect in humans that is similar to an effect produced by a 

naturally occurring estrogen, or other such endocrine effects as the Administrator may 

designate.” Following the recommendations of its Endocrine Disruptor Screening and 

Testing Advisory Committee (EDSTAC), EPA determined that there were scientific 

bases for including, as part of the program, androgen and thyroid hormone systems, in 

addition to the estrogen hormone system. EPA also adopted EDSTAC’s recommendation 

that the Program include evaluations of potential effects in wildlife. When the 

appropriate screening and/or testing protocols being considered under the Agency’s 

Endocrine Disrupter Screening Program (EDSP) have been developed and vetted, 

fomesafen may be subjected to additional screening and/or testing to better characterize 

effects related to endocrine disruption.

4.5.6 Toxic Effects of Multi-Active Ingredient Labeled Products 

Mammalian toxicity data were available for several formulated products, including one 

containing only fomesafen and all those containing multiple active ingredients. Based on 

female guinea pig data (used as the assessment endpoint LD50 = 607 mg/kg bw), rats are 

less sensitive to fomesafen (female LD50 = 1,499 mg/kg bw). For the formulations, rat 

data was compared to minimize variability associated with interspecies variation.

Flexstar (reg#100-1101), which contains only fomesafen (22.1%) has an LD50 of 3863 

mg/kg (female, 95% CI not reported, MRID44030101). Prefix (reg #100-1268), which 

contains both fomesafen and s-metolachlor (10.1% and 46.5% respectively) has an LD50

of 5,000 mg/kg (combined, 95% CI 2,865-8,390, MRID46952103). Metolachlor has an 

LD50 of 2780 mg/kg (combined, 95% CI 2,180-3,545, MRID00015523). Formulations 

containing bentazon (BAS 530 04 (29%), reg#7969-82 and Faster (29.8%), reg#7969-83) 

have an LD50 of >1210 mg/kg and 1470 mg/kg (95% CI 1,000-2,160, MRIDs 40340502,

40031302). Bentazon has an LD50 of 1480 mg/kg (MRIDs 92065, 64314).
41

Although guideline studies are not designed to elucidate such effects, there do not appear 

to be additive or synergistic acute toxicity effects between fomesafen and any of the 

currently co-formulated active ingredients based on available data. Toxic effects to 

mammals from ingestion of the formulated products containing fomesafen alone or 

fomesafen in conjunction with s-metolachlor or bentazon are not anticipated to exceed 

toxic effects estimated based on the technical active ingredient (Appendix H).

4.6 Incident Database Review

EFED maintains EIIS, a database containing reported incidents of damage to non-target 

species caused by pesticide use. There are a total of 65 reported incidents (Appendix F) 

for fomesafen, 64 of which are damage to agricultural crops. Incidents reported cover a 

range of 13 years (1992-2005), but many of them (83%) were reported in 2001-2003. 

Corn was the crop most frequently reported damaged, accounting for 86% of the total 

plant damage reports. The most frequently reported routes of exposure for corn were 

direct treatment, drift, and carryover. In many cases (36%) the legality was classified as

registered use. In other cases (55%), the legality of application is unknown. The 

certainty that the incident was related to fomesafen use was generally classified as 

probable. Other crops damaged included green peas, cotton, and soybeans under 

registered use conditions. Only 5 cases of misuse or accidental misuse were reported.

There is one report of a fish kill (I007601-001). In this incident, there was a report of 

approximately 200 fish (channel catfish, crappie, largemouth bass, and redear sunfish) 

dying following a legal application to a soybean site. The certainty of the kill being 

related to fomesafen runoff is classified as possible. Application was in accordance with 

registered use.
42

5.0 Risk Estimation

Risk is estimated by calculating the ratio of the expected environmental concentration 

and the appropriate toxicity endpoint. This value is the risk quotient (RQ), which is then 

compared to pre-established levels of concern (LOC) for each category evaluated. The 

RQ methodology, LOCs, and specific details of calculation are contained in Appendix G. 

The highest EECs and most sensitive endpoints are used to determine the screening level 

RQ. Using these two values, theoretically, results in a conservative estimate of risk.
43

5.1 Aquatic RQ Summary

Based on scenarios modeled for Section 3 label rates (0.17-0.375 lb ai/A) and existing 

Section 24 label rates, no acute or chronic RQs for animals exceeded any LOCs. Acute 

RQs for freshwater and saltwater fish and invertebrates ranged from <0.01 to 0.02. 

Chronic RQs for freshwater and saltwater fish and invertebrates were ≤0.02. Acute risk 

RQs for fresh-and saltwater plants, both vascular and non-vascular, ranged from <0.01 to 

0.16. In no cases did RQs for plants exceed the acute risk LOC. Listed species RQs for 

fresh- and saltwater aquatic plants ranged from <0.01 to 1.6. At the 0.5 lb ai/A 

application rate, RQs for freshwater non-vascular plants exceed the listed species LOC. 

For some, but not all of the scenarios modeled, RQs for freshwater non-vascular plants 

exceed the listed species LOC at the application rate of 0.375 lb ai/A (RQs for all 

scenarios modeled are included in Appendix A). In no cases did the modeled 

concentrations of fomesafen exceed the LOAEC for freshwater non-vascular plants. 

Fomesafen appears to pose very low risk to aquatic ecosystems based on the data 

currently available.

Table 21 Summary of Aquatic RQs

Taxa Acute RQ Chronic RQ1 Endangered 

Species RQ2

Highest Section 24 Use on Cotton at 0.5 lb ai/A (MS scenario, ground application)

FW Aquatic Plants (algal) 0.16 NA11.6 a

FW Aquatic Plants (vascular) 0.07 NA10.24

FW Aquatic Invertebrates <0.01 <0.01 <0.01

FW Fish <0.01 NC <0.01

SW Aquatic Plants 0.01 NA10.02

SW Aquatic Invertebrates <0.01 <0.01 <0.01

SW Fish <0.01 <0.01 <0.01

Highest Section 3 EEC: Use on Cotton at 0.375 lb ai/A (TX scenario, aerial application)

FW Aquatic Plants (algal) 0.13 NA11.2a

FW Aquatic Plants (vascular) 0.06 NA10.19

FW Aquatic Invertebrates <0.01 <0.01 <0.01

FW Fish <0.01 <0.01 <0.01

SW Aquatic Plants <0.01 NA10.01

SW Aquatic Invertebrates <0.01 0.02 <0.01

SW Fish <0.01 <0.01 <0.01

Lowest EEC: Use on Beans at 0.17 lb ai/A (MI scenario, aerial application)

FW Aquatic Plants (algal) 0.03 NA10.24

FW Aquatic Plants (vascular) 0.01 NA10.04

FW Aquatic Invertebrates <0.01 <0.01 <0.01

FW Fish <0.01 <0.01 <0.01

SW Aquatic Plants <0.01 NA1<0.01

SW Aquatic Invertebrates <0.01 <0.01 <0.01

SW Fish <0.01 <0.01 <0.01

1 There are no chronic aquatic plants tests. 2 Endangered species RQ for plants are calculated 

based on NOAEC. Endangered species RQs for animals are calculated in the same way as 

acute risk values, but compared to a different LOC. NA – not applicable, NC – Not calculated, 

data not available. aExceeds endangered species LOC.
44

5.2 Terrestrial RQ Summary

5.2.1 Terrestrial Plants

Risk quotients were calculated based on the exposures estimated by both TerrPlant and 

AgDrift. Calculations were made using data from both types of guideline studies 

(vegetative vigor and seedling emergence). Evaluations were done for both monocots 

and dicots. The most sensitive endpoint was dicot vegetative vigor (EC25=0.0016 lb ai/A, 

NOAEC=0.00098 lb ai/A). For the seedling emergence tests, calculated EC05 was 

unavailable, and the reported NOAEC was greater than the calculated EC25, so the EC25

was used as the toxicity endpoint for the endangered species analysis.

5.2.1.1 TerrPlant

Because fomesafen is highly toxic to terrestrial plants, RQs for all application rates, both 

aerial and ground, are presented below. It is especially toxic to dicots, and RQs exceed 

the LOC for both non-listed and listed species of plants in upland and wetland areas, as 

well as on the basis of spray drift alone. RQs for non-listed dicots range from 4.3 (drift 

only, 0.17 lb ai/A) to 59.8 (wetland, 0.5 lb ai/A). RQs for listed dicots range from >0.85 

(drift only, 0.17 lb ai/A) to 59.8 (wetland, 0.5 lb ai/A). For non-listed monocots, RQs 

exceed the LOC only in the wetland area. Non-listed monocot RQs range from <0.1 

(drift only, 0.17 lb ai/A) to 3.3 (wetland, 0.5 lb ai/A). RQs for listed monocots range 

from <0.1 (drift only, 0.17 lb ai/A) to 3.3 (wetland, 0.5 lb ai/A).
45

Table 22 Terrestrial Plant Risk Quotients Based on TerrPlant

Total Loading RQ

(Seedling Emergence)

Total Loading RQ

(Seedling Emergence)

Drift Only

(Vegetative Vigor)

Upland Areas Wetland Areas Drift Only

Application 

Rate

(lb ai/A) Monocot Dicot Monocot Dicot Monocot Dicot

Aerial Applications Non-listed Plants

0.5

Region 1 pine 0.60 10.87a

3.27a59.78a0.30 12.50a

0.375

Region 1 & 2 0.45 8.15a

2.66a44.84a0.22 9.38a

0.312

Region 3 0.37 6.78a

2.04a37.30a0.19 7.80a

0.25

Region 4 0.30 5.43a

1.64a29.89a0.15 6.25a

0.17

Region 5 0.20 3.70a

1.11a20.33a0.10 4.25a

Ground Applications Non-listed Plants

0.5

Region 1 pine 0.36 6.52a

3.04a55.43a<0.1 2.50a

0.375

Region 1 & 2 0.27 4.89a

2.28a41.58a<0.1 1.88a

0.312

Region 3 0.22 4.07a

1.87a34.59a<0.1 1.56a

0.25

Region 4 0.18 3.26a

1.52a27.72a<0.1 1.25a

0.17

Region 5 0.12 2.22a

1.03a18.85a<0.1 0.85

Aerial Applications Listed Plants

0.5

Region 1 pine 1.67a

10.87a9.17a59.78a0.83 >12.50a

0.375

Region 1 & 2 1.25a

9.87a6.88a54.28a0.63 >9.38a

0.312

Region 3 1.04a

8.21a5.72a45.16a0.52 >7.80a

0.25

Region 4 0.83 6.58a

4.58a36.18a0.42 >6.25a

0.17

Region 5 0.57 4.47a

3.12 24.61a0.28 >4.25a

Ground Applications Listed Plants

0.5

Region 1 pine 1.00a

7.89a8.50a67.11a0.17 >2.50a

0.375

Region 1 & 2 0.75 5.92a

6.38a50.33a0.13 >1.88a

0.312

Region 3 0.62 4.93a

5.30a41.87a0.10 >1.56a

0.25

Region 4 0.50 3.95a

4.25a33.55a<0.1 >1.25a

0.17

Region 5 0.34 2.68a

2.89a22.82a<0.1 >0.85

a Exceeds or equals LOC of 1
46

5.2.1.2 AgDrift

Acute risk RQs and listed species RQs were calculated for aerial and ground applications 

(low boom and high boom) using the EC25 and NOAEC for the most sensitive dicot 

(lettuce EC25 0.0002 lb ai/A, NOAEC <0.00019 lb ai/A). As the endpoints are so similar, 

RQs presented below apply to both listed and non-listed species. Because the droplet 

size is an important parameter in determining spray drift, clearance distances and RQs 

were calculated for all droplet spectrum available in AgDrift. The maximum extent of 

AgDrift Tier I modeling is approximately 1,000 ft from point of application for aerial 

applications, but the specific distance varies slightly dependent on the droplet spectrum. 

For the sake of consistency, modeling was terminated at 950 ft for all spectra. At this 

distance, the mathematical curve which describes the deposition is asymptotic, there are 

only small declines for greater linear distances. 

For aerial applications, fomesafen applied with a very fine to fine or fine to medium 

droplet spectrum exceeds the terrestrial plant LOC at all application rates. For coarser 

droplet spectra, RQs range from 0.96 to 1.4, and clearance distances range from 250 ft to 

>950 ft. Ground applications require a narrower buffer to clear the LOC, especially a 

low boom. Clearance distances for ground applications range from 30 ft to 450 ft.

Table 20 Drift Deposition from Aerial Applications

Very Fine to Fine Fine to Medium Medium to Coarse Coarse to Very 

Application Coarse

Rate 

(lb ai/A)

Clearance 

Distance

(ft)

RQ

unitless

Clearance 

Distance

(ft)

RQ

unitless

Clearance 

Distance

(ft)

RQ

unitless

Clearance 

Distance

(ft)

RQ

unitless

0.5 >950 10.7 >950 3.0 >950 1.4 700 0.98

0.375 >950 8.0 >950 2.3 >950 1.1 550 0.94

0.312 >950 6.7 >950 1.9 >950 1.1 550 0.94

0.25 >950 5.4 >950 1.5 600 0.96 350 0.98

0.17 >950 3.6 >950 1.0 400 0.94 250 0.96

Bold designates an exceedence (LOC=1)

Table 21 Drift Deposition from Ground Applications

Low Boom High Boom

Very Fine to Fine Fine to Medium Medium to Coarse Coarse to Very 

Coarse Application 

Rate 

(lb ai/A) Clearance 

Distance

(ft)

RQ

unitless

Clearance 

Distance

(ft)

RQ

unitless

Clearance 

Distance

(ft)

RQ

unitless

Clearance 

Distance

(ft)

RQ

unitless

0.5 300 0.88 150 0.83 450 0.98 250 0.83

0.375 200 0.96 80 0.98 400 0.95 150 0.96

0.312 200 0.80 70 0.90 350 0.97 150 0.85

0.25 150 0.83 50 0.93 300 0.94 90 0.95

0.17 80 0.98 30 0.93 250 0.79 60 0.88
47

5.2.2 Avian RQ Summary

For birds, no acute LOCs were exceeded at any application rates.

Chronic RQs are reported as <RQ, due to the fact that the NOAEC established in the 

guideline study was not definitive. At the application rate of 0.5 lb ai/A, chronic LOCs 

for birds in three out of the four food categories (short grass, tall grass, and broadleaf 

plants/small insects) were exceeded. At the application rate of 0.375 lb ai/A, chronic 

LOCs for birds consuming the food categories of short grass and broadleaf plants/small 

insects were exceeded. At the application rate of 0.17 lb ai/A, chronic LOCs for birds in 

the short grass food category were exceeded.

Table 22 Avian RQ Summary

Acute dose-based RQs1 Acute dietarybased RQs1Chronic 

RQs Risk quotients based on 

Kenaga upper bound EECs 20g 100g 1000g All birds All birds

Maximum Application Rate 0.5 lb ai/A (pine seedlings, states in region 1)

Short grass 0.05 0.02 0.01 0.01 <2.61c

Tall grass 0.02 0.01 <0.01 <0.01 <1.20c

Broadleaf plants/small insects 0.03 0.01 <0.01 <0.01 <1.47c

Fruits/pods/seeds/lg insects <0.01 <0.01 <0.01 <0.01 <0.16

Common Application Rate 0.375 lb ai/A (all crops, regions 1, 2)

Short grass 0.04 0.02 0.01 <0.01 <1.96c

Tall grass 0.02 0.01 <0.01 <0.01 <0.90

Broadleaf plants/small insects 0.02 0.01 <0.01 <0.01 <1.10c

Fruits/pods/seeds/lg insects <0.01 <0.01 <0.01 <0.01 <0.12

Minimum Application Rate 0.17 lb ai/A (all crops, region 5)

Short grass 0.02 0.01 <0.01 <0.01 <0.89c

Tall grass 0.01 <0.01 <0.01 <0.01 <0.41

Broadleaf plants/small insects 0.01 <0.01 <0.01 <0.01 <0.50

Fruits/pods/seeds/lg insects <0.01 <0.01 <0.01 <0.01 <0.06

a

exceeds acute risk LOC (0.5)

b exceeds endangered species acute risk LOC (0.1)

c

exceeds chronic risk LOC (1.0)
48

5.2.3 Small Mammal RQ Summary

For mammals, no acute LOCs were exceeded at any application rates. The chronic LOC 

was exceeded only for small (15g) mammals eating short grass at the highest rate (0.5 lb 

ai/A, pine seedlings in AR, GA, MS, NC, and SC).

Table 23 Small Mammal RQ Summary

Acute 

dose-based RQs

Chronic 

dose-based RQs

Chronic 

dietarybased RQsRisk Quotients based 

on Kenaga 

upper bound EEC 15 g 35 g 1000 g 15 g 35 g 1000 g All 

mammals

Maximum Application Rate 0.5 lb ai/A (pine seedlings, states in region 1)

Short grass 0.09 0.07 0.04 1.04 c0.89 0.48 0.48

Tall grass 0.04 0.03 0.02 0.48 0.41 0.22 0.22

Broadleaf plants/

small insects 0.05 0.04 0.02 0.59 0.50 0.27 0.27

Fruits/pods/seeds/

lg insects

0.01 <0.01 <0.01 0.07 0.06 0.03 0.03

Seeds (granivores) <0.01 <0.01 <0.01 0.01 0.01 0.01 NA

Common Application Rate 0.375 lb ai/A (all crops, regions 1&2)

Short grass 0.06 0.05 0.03 0.78 0.67 0.36 0.36

Tall grass 0.03 0.03 0.01 0.36 0.31 0.16 0.17

Broadleaf plants/

small insects 0.04 0.03 0.02 0.44 0.38 0.20 0.20

Fruits/pods/seeds/

lg insects <0.01 <0.01 <0.01 0.05 0.04 0.02 0.20

Seeds (granivores) <0.01 <0.01 <0.01 0.01 0.01 <0.01 NA

Minimum Application Rate 0.17 lb ai/A (all crops, region 5)

Short grass 0.03 0.02 0.01 0.35 0.30 0.16 0.16

Tall grass 0.01 0.01 0.01 0.16 0.14 0.07 0.07

Broadleaf plants/

small insects 0.02 0.01 0.01 0.20 0.17 0.09 0.09

Fruits/pods/seeds/

lg insects <0.01 <0.01 <0.01 0.02 0.02 0.01 0.01

Seeds (granivores) <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 NA

a

Equals or exceeds acute risk LOC (0.5)

b Equals or exceeds listed species acute risk LOC (0.1)

c

Equals or exceeds chronic risk LOC (1.0)

5.2.4 Terrestrial Invertebrate Summary

Fomesafen appears to be of relatively low toxicity to bees, based on submitted guideline 

tests. Estimated dose per bee for an organism in the treatment area ranged from 0.96 mg 

ai/bee (based on large insect estimator, 0.5 lb ai/A) to 8.64 mg ai/bee (based on small 

insect estimator). Using the acute contact LD50 of >100 mg ai/bee, anticipated exposure 

at the treatment site would not be greater than approximately 9% of the LD50. RQs 

calculated on this basis are shown below. At the time of this assessment, OPP has an 

interim listed species acute risk LOC for terrestrial insects, but does not have a 

corresponding LOC for non-listed species.
49

Table 24 Terrestrial Invertebrate RQ Summary

Application Rate

(lb ai/A)

Insect Size 

Category RQ Dose per Bee

(mg ai/bee)

Small insects <0.09 a0.50 8.64

(Pine seedlings, Region 1) Large insects <0.01 0.96

Small insects <0.07 a0.375 6.48

(Regions 1, 2) Large insects <0.01 0.72

0.017 Small insects <0.03 2.94

(Region 5) Large insects <0.01 0.32

a

Equals or exceeds interim listed species acute risk LOC (0.05)

Non-guideline field tests on earthworms submitted by the registrant showed that 

fomesafen did not have observable adverse effects on total numbers, total weights, or 

numbers of individual species at a treatment level of 0.45 lb ai/A. Decline in the 

population of one species of earthworms in the test plots was attributed to the change in 

plant cover on the plot as a result of the herbicide application.
50

6.0 Risk Description

6.1 Aquatic Risk

Based on currently available data, fomesafen appears to be of relatively low toxicity to 

aquatic animals in freshwater and estuarine/marine systems. Both acute and chronic 

effects were considered. Fomesafen is a light-dependent peroxidizing herbicide (LDPH), 

and may be more toxic under conditions of natural sunlight than in laboratory lighting

(Matringe 1989). The Agency has proposed testing this class of compounds under ultraviolet (UV) light conditions (EFED 2007), but as of the time of this risk assessment, such 

data were not available for fomesafen. Based on fish early-life cycle tests submitted for 

oxyfluorfen, another chemical in this class, UV light conditions appear to increase the 

toxicity by approximately an order of magnitude (MRID 46585104). To evaluate the 

effect of this increase in toxicity, fish early life cycle endpoints were adjusted by an order 

of magnitude and RQs were recalculated for all scenarios modeled. In all cases, RQs 

were <0.015. It should be noted, however, that the freshwater fish early life cycle 

endpoint was based on an ACR calculated from the saltwater fish studies, thus 

considerable uncertainty surrounds this endpoint. Based on the effects noted in the 

oxyfluorfen study (decreased hatching time and reduced larval survival) and the mode of 

action of LDPHs, it seems possible that oxyfluorfen may have affected the viability of the 

egg cell membrane surrounding the larva. Given this possibility, extrapolation of the 

enhanced toxicity to the fish life stages used in the acute toxicity tests was not judged to 

be appropriate. No tests conducted under UV light conditions were available for aquatic 

invertebrates, thus the type or magnitude of phototoxic effects on these types of 

organisms is unknown. Given that many zooplankters have translucent bodies, and are 

present in the surface layers of water bodies where UV rays might penetrate (Barron et al 

2000, Diamond et al 2005), photoenhanced toxicity to these taxa is a possibility.

In aquatic ecosystems, aquatic plants are the taxa most sensitive to fomesafen. Aquatic 

plants (both vascular and non-vascular) are the primary producers, and may serve as the 

primary energy base in some aquatic systems either via consumption by herbivores or 

energy input to the detrital food web. Perturbations to the base of the food chain have the 

potential to modify community structure and/or productivity of the affected system.

There are no acute risk LOC exceedences for any application rates. RQs exceed the 

listed species LOC for freshwater non-vascular plants for the application rate of 0.375 lb 

ai/A in some scenarios modeled, and for the application rate of 0.5 lb ai/A in all scenarios 

modeled. However, EECs (2-25 mg/L) do not exceed the LOAEC (23 mg/L), which is 

based on a 9% inhibition in biomass (MRID46673804). Mesocosm studies (Caquet et al

2005, Caquet 2006) show that fomesafen concentrations of 30-60 mg/L can cause 

perturbations in the system, but these perturbations are primarily associated with shifts in 

species composition and abundance rather than primary productivity. Mesocosm studies 

conducted by Pershbarger et al (1997) indicate short-term effects on phytoplankton 

abundance and composition from concentrations of fomesafen ≤60 mg/L are not 

measurable, but it must be noted that their experimental system was dominated by bluegreen alga (EC50 = 71,000 mg/L, MRID 46673807), which are less sensitive to fomesafen 
51

than the green alga (EC50 = 92 mg/L, MRID 46673804). The mesocosm studies were 

both conducted outdoors under natural sunlight conditions, thus any photoenhancement 

of fomesafen toxicity for these taxa would be implicitly incorporated into study results.

Measurable differences in the algal composition and productivity of water bodies 

receiving runoff from fields treated with fomesafen at the application rates evaluated in 

this document are not anticipated. At the time of this assessment, there were no listed 

freshwater non-vascular plants, and no indications of any obligate relationships between a 

listed species and freshwater algae. 

Fomesafen may indirectly affect aquatic systems by damaging plants in adjacent wetland 

or riparian zones. Modification of the vegetation in wetlands or riparian zones could 

cause decreased allochthonous input, increased sediment input, destabilization of the 

stream bank, or changes in the structural components (plant). Effects on waterbody 

associated plant communities can be minimized by ensuring an adequate offset distance 

is maintained between the application site and the wetland or riparian zone. Appropriate 

offset distances are discussed in the terrestrial plants section.
52

Table 25 Summary of Risk to Non-listed Aquatic Organisms

Assessment 

Endpoint Crops Estimator LOC Exceedence

Freshwater

Acute Toxicity to 

Fish and Aquaticphase Amphibians

Pine seedlings

Cotton, Beans (soy, snap, dry)

Cotton, Beans (soy, snap, dry)

MS cotton (0.5lb ai)

TX cotton (0.375 lb ai)

MI beans (0.375 lb ai)

No

No

No

Chronic Toxicity 

Fish and Aquaticphase Amphibians

Pine seedlings

Cotton, Beans (soy, snap, dry)

Cotton, Beans (soy, snap, dry)

MS cotton (0.5lb ai)

TX cotton (0.375 lb ai)

MI beans (0.375 lb ai)

No

No

No

Acute Toxicity to 

Aquatic 

Invertebrates

Pine seedlings

Cotton, Beans (soy, snap, dry)

Cotton, Beans (soy, snap, dry)

MS cotton (0.5lb ai)

TX cotton (0.375 lb ai)

MI beans (0.375 lb ai)

No

No

No

Chronic Toxicity 

Aquatic 

Invertebrates

Pine seedlings

Cotton, Beans (soy, snap, dry)

Cotton, Beans (soy, snap, dry)

MS cotton (0.5lb ai)

TX cotton (0.375 lb ai)

MI beans (0.375 lb ai)

No

No

No

Acute Toxicity to 

Aquatic Plants 

(non-vascular)

Pine seedlings

Cotton, Beans (soy, snap, dry)

Cotton, Beans (soy, snap, dry)

MS cotton (0.5lb ai

TX cotton (0.375 lb ai)

MI beans (0.375 lb ai)

No

No

No

Acute Toxicity to 

Aquatic Plants 

(vascular)

Pine seedlings

Cotton, Beans (soy, snap, dry)

Cotton, Beans (soy, snap, dry)

MS cotton (0.5lb ai

TX cotton (0.375 lb ai)

MI beans (0.375 lb ai)

No

No

No

Saltwater

Acute Toxicity to 

Fish

Pine seedlings

Cotton, Beans (soy, snap, dry)

Cotton, Beans (soy, snap, dry)

MS cotton (0.5lb ai)

TX cotton (0.375 lb ai)

MI beans (0.375 lb ai)

No

No

No

Chronic Toxicity to 

Fish 

Pine seedlings

Cotton, Beans (soy, snap, dry)

Cotton, Beans (soy, snap, dry)

MS cotton (0.5lb ai)

TX cotton (0.375 lb ai)

MI beans (0.375 lb ai)

No

No

No

Acute Toxicity to 

Aquatic 

Invertebrates

Pine seedlings

Cotton, Beans (soy, snap, dry)

Cotton, Beans (soy, snap, dry)

MS cotton (0.5lb ai)

TX cotton (0.375 lb ai)

MI beans (0.375 lb ai)

No

No

No

Chronic Toxicity

Aquatic 

Invertebrates

Pine seedlings

Cotton, Beans (soy, snap, dry)

Cotton, Beans (soy, snap, dry)

MS cotton (0.5lb ai)

TX cotton (0.375 lb ai)

MI beans (0.375 lb ai)

No

No

No

Acute Toxicity to 

Aquatic Plants 

Pine seedlings

Cotton, Beans (soy, snap, dry)

Cotton, Beans (soy, snap, dry)

MS cotton (0.5lb ai)

TX cotton (0.375 lb ai)

MI beans (0.375 lb ai)

No

No

No
53

6.2 Terrestrial Risk

In general, fomesafen presents low risk to terrestrial animals on an acute basis, with no 

acute LOC exceedences for either birds or mammals. However, there are chronic LOC 

exceedences for both birds and mammals at all application rates. Fomesafen poses a risk 

to terrestrial plants, especially dicots, in areas which may be subject to drift or runoff 

from the application site. Due to the sensitivity of dicots to fomesafen, effect from drift 

may occur as far away from the use site as 1,000 ft for aerial applications and 300 ft for 

ground applications.

6.2.1 Birds, Reptiles, and Amphibians

In the avian reproduction study on mallard ducks (MRID 135639), no endpoints were 

affected, thus the NOAEC was established as the highest dose tested (46 mg/kg diet). No 

LOAEC was determined, so based on the available data, the meaning of the chronic LOC 

exceedences for birds is difficult to interpret, either in terms of which endpoints might be 

affected, or if chronic exposure to fomesafen is at levels that would trigger these effects. 

It should also be noted that generally bobwhite quail, which were not tested for 

fomesafen, are more sensitive than mallard ducks. Avian data for fomesafen and several 

structurally similar compounds, acifluorfen (PCs 114401-114404), oxyfluorfen (PC 

111601), and lactofen (PC 128888), is presented below. The data available for the other 

chemicals suggests reproductive effects of fomesafen may include reduction in embryo 

survival, number of hatchlings, and/or number of eggs laid. The data also suggests that 

bobwhite quail are the more sensitive species for this class of chemicals, thus the mallard 

data used in the risk assessment may underestimate the risk to more sensitive species.

Mammalian data were also considered in an attempt to characterize the potential chronic 

toxicity for birds. Reproductive effects were noted in the lactofen and oxyfluorfen tests.

Because the reported NOAECs and LOAECs are in part an artifact of the test 

concentrations selected and sufficient data points are not available to generate chronic 

dose-response curves, no specific conclusions should be drawn regarding relative toxicity

of the compounds. In the absence of more definitive chronic avian data for fomesafen, 

the Agency concludes that there is a chronic risk to insectivorous or herbivorous birds, 

reptiles, and/or terrestrial-phase amphibians foraging in or near the treated area for all 

application rates. Potential effects on the fecundity of frugivorous birds foraging in or 

near the treated area should be anticipated for the 0.5 lb ai/A application rate.
54

Table 26 Comparison of Chronic Data for Acifluorfen, Fomesafen, and Oxyfluorfen.

Chemical Test Organism NOAEC

(mg/kg diet)

LOAEC

(mg/kg diet) Endpoints Affected

Avian

Bobwhite quail

(MRID 107491) 20 100 Reduced number of 

Acifluorfen embryos

(PC114401) Mallard duck

(MRID 107492) 100 >100 No endpoint affected

Fomesafen Mallard duck

(MRID 135639) 46 >46 No endpoint affected

Lactofen

(PC128888) No chronic data available

Bobwhite quail

(MRID 46070102) 124 256

Survivor weight, embryo 

survival, number of 

Oxyfluorfen hatchlings

(PC111601) Mallard duck

(MRID 46070101) 506 751

Eggs laid, embryo 

survival, number of 

hatchlings

Mammalian

Acifluorfen

(PC114401)

Rat

(MRID155548) 2500 ND No reproductive effects

Fomesafen Rat

(MRID144862) 1000 ND No reproductive effects

Lactofen

(PC128888)

Rat

(AC73859) 50 500 Reduced pup weight

Oxyfluorfen

(PC111601)

Rat

(MRID42014901) 400 1600 Decreased body weight, # live pups/litter

6.2.2 Mammals

For mammals, no acute LOCs were exceeded at any application rate. The chronic LOC 

was exceeded only for small (15g) mammals eating short grass at the highest application 

rate (0.5 lb ai/A, pine seedlings in AR, GA, MS, NC, and SC). Thus effects on the 

endpoints of growth, survival, and fecundity are not anticipated at the 0.375 lb ai/A 

application rate.

Open literature data demonstrated elevated levels of liver and fecal porphyrins in mice 

fed 100 mg/kg diet for 10 days (Krijt et al 1994b). Based on TREX estimates of dietary

EECs, only the 0.5 lb ai/A rate exceeds 100 mg/kg rate. Given the existing body of data 

regarding fomesafen effects on the liver porphyrins of small mammals, effects on this 

biochemical endpoint appear unlikely, although there is a difference in sensitivity

amongst strains of mice (Krijt et al 1994a). Where laboratory mice strains are in a 

species sensitivity distribution as compared to small wild mammals is unknown.

6.2.3 Terrestrial Invertebrates

Based on available data, effects on terrestrial invertebrates, while possible, do not appear 

likely. Lack of indicated toxicity in guideline bee studies, guideline aquatic invertebrate 

studies, and non-guideline studies on soil invertebrates, arthropods, and in aquatic 

mesocoms support this conclusion.
55

Table 27 Summary of Risk to Non-Listed Terrestrial Animals

Clearance estimate

Assessment 

Endpoint

Application 

Rate

lb ai/A

Size Class

(g) LOC Exceedence1

Distance 

from site 

(ft)

Rate

(lb ai/A)

Vertebrates

0.5

15

35

1000

No

No

No

Clears at current rate

0.375

15

35

1000

No

No

No

Clears at current rate Acute Risk to 

Mammals

0.17

15

35

1000

No

No

No

Clears at current rate

0.5

15

35

1000

Yes (SG)

No

No

Aerial 02

Ground 10

0.473

Clear

Clear

0.375

15

35

1000

No

No

No

Clears at current rate Chronic Risk to 

Mammals

0.17

15

35

1000

No

No

No

Clears at current rate

0.5

20

100

1000

No

No

No

Clears at current rate

0.375

20

100

1000

No

No

No

Clears at current rate

Acute Risk to 

Birds, 

Terrestrialphase 

Amphibians, 

and Reptiles 0.17

20

100

1000

No

No

No

Clears at current rate

0.5 All Yes (SG, TG, BL, SL) Aerial 100

Ground 10 0.192

0.375 All Yes (SG, BL) Aerial 100

Ground 10 0.192

Chronic Risk to 

Birds, 

Terrestrialphase 

Amphibians, 

and Reptiles 0.17 All Yes (SG) Aerial 100

Ground 10 0.192

Invertebrates

Acute Risk to 

Invertebrates All rates All Risk appears unlikely Not applicable

1 LOC exceedences using more conservative dose-based estimates

2 AgDrift clearance estimate is ~45% deposition directly below aircraft

3 Clearance level is for short grass estimate 

4 OPP does not currently have an acute risk LOC for non-listed terrestrial invertebrates

Feeding categories: short grass (SG), tall grass (TG), broadleaf plants, small insects (BL), seeds, 

large insects (SL), granivore-mammals only (G)

NA – Not applicable
56

6.2.4 Plants

The non-target organisms of greatest concern for fomesafen are plants in the overspray, 

runoff, and spray drift zones. Fate data do not indicate fomesafen is likely to be subject 

to long-range atmospheric transport, thus this route of exposure has not been addressed in 

the assessment. It is, however, persistent in soil, and may affect plants growing in the 

soil of treated fields or overspray areas for an extended period (approximately a year) 

following application. Because of the persistence, it is also likely to accumulate in fields 

repeatedly treated with fomesafen, even if the field is only treated in alternate years. The 

theoretical maximum concentration occurs in about 10 years if the field is treated in 

alternate years. Maximum residual concentration for an application rate of 0.375 lb ai/A 

is 0.29 lb ai/A, and for an application rate of 0.5 lb ai/A is 0.38 lb ai/A. These 

concentrations are greater than the seedling emergence EC25s of the most sensitive dicot 

(tomato, EC25 0.005 lb ai/A) and the most sensitive monocot (onion, EC25 0.084 lb ai/A).

Shallow groundwater used for irrigation of agricultural fields could potentially contain 

sufficient fomesafen to affect some crops. Based on estimated concentrations delivered 

to a field receiving 2 inches of irrigation water (0.0004-0.0077 lbs ai/A, based on 

application rate of 0.5 lb ai/A to field), sensitive crop species such as radish, lettuce, 

oilseed rape, and tomato (EC25s of 0.002-0.008 lb ai/A) could be affected. How long 

fomesafen will persist in the groundwater is not well defined. 

Fomesafen has the potential to adversely affect plant communities of concern beyond the 

edges of the treated field. Plants potentially affected by fomesafen include crops in 

neighboring fields, hedgerows, riparian zones, and wetlands. Using AgDrift (Tier 1), 

EFED was unable to calculate the distance required for the acute plant risk to fall below 

the LOC for aerial applications, with toxicity predicted to occur at least to 900 ft beyond 

the application point for aerial applications and 300 ft for ground applications. Potential 

runoff effects to wetlands near the treatment site are difficult to evaluate, as the amount 

of runoff is greatly influenced by slope, presence of buffers, and degrees of 

channelization in runoff swales. Wetlands receiving direct runoff from treated sites are 

likely to be affected.

Because fomesafen is an herbicide, it may affect the primary productivity, community

composition, and/or structure of herbaceous communities located near the margins of the 

treated fields. EFED has no data with which to evaluate the potential effect on woody

plants, although given the mode of action for fomesafen (cell membrane disruption), 

woody plants may be more resistant. Modifications to the plant community may have 

significant effects on the populations of animals dependent on those communities.
57

Table 28 Summary of Risk to Non-listed Terrestrial Plants

Clearance estimate1

Assessment 

Endpoint

Type of 

Plant

Application 

Rate

lb ai/A

LOC Exceedence2

Distance 

from site 

(ft)

Rate

(lb ai/A)

Aerial Application

0.5 No

0.375 No

0.312 No

0.25 No

Upland

0.17 No

Clears at current rate

(Based on 

runoff and drift)

0.5 Yes

0.375 Yes

0.312 Yes

0.25 Yes

Wetland

0.17 Yes

100 0.084

Ground Application

0.5 No

0.375 No

0.312 No

0.25 No

Upland

0.17 No

Clears at current rate

(Based on 

runoff and drift)

0.5 Yes

0.375 Yes

0.312 Yes

0.25 Yes

Acute Risk to 

Monocots

Wetland

0.17 Yes

10 0.084

Aerial Application

0.5 Yes

0.375 Yes

0.312 Yes

0.25 Yes

Upland

0.17 Yes

0.5 Yes

0.375 Yes

0.312 Yes

0.25 Yes

Wetland

0.17 Yes

>900 0.002

Ground Application

0.5 Yes 300

0.375 Yes 200

0.312 Yes 200

0.25 Yes 150

Upland

0.17 Yes 80

0.5 Yes 300

0.375 Yes 200

0.312 Yes 200

0.25 Yes 150

Acute Risk to 

Dicots

Wetland

0.17 Yes 80

0.002

1

Based on drift estimates from AgDrift, does not include runoff
58

6.3 Endangered Species 

6.3.1 Aquatic Listed Species

No aquatic endangered species are at risk for direct effects from fomesafen. Although 

there are listed species LOC exceedences for freshwater non-vascular plants, there were 

no listed freshwater non-vascular plants at the time of this assessment. Additionally, no 

listed species have been identified as having an obligate relationship with freshwater nonvascular plants. This results in a determination of no effect for aquatic organisms on the 

basis of direct effects. Indirect effects to aquatic organisms are possible, based on 

potential effects on riparian and wetland plant communities. For an evaluation of indirect 

effects, please see the section on endangered plants.

Table 29 Summary of Risk to Listed Aquatic Organisms

Assessment 

Endpoint Crops Estimator LOC Exceedence

Freshwater

Acute Toxicity to 

Fish and Aquaticphase Amphibians

Pine seedlings

Cotton, Beans (soy, snap, dry)

Cotton, Beans (soy, snap, dry)

MS cotton (0.5lb ai)

TX cotton (0.375 lb ai)

MI beans (0.375 lb ai)

No

No

No

Chronic Toxicity 

Fish and Aquaticphase Amphibians

Pine seedlings

Cotton, Beans (soy, snap, dry)

Cotton, Beans (soy, snap, dry)

MS cotton (0.5lb ai)

TX cotton (0.375 lb ai)

MI beans (0.375 lb ai)

No

No

No

Acute Toxicity to 

Aquatic 

Invertebrates

Pine seedlings

Cotton, Beans (soy, snap, dry)

Cotton, Beans (soy, snap, dry)

MS cotton (0.5lb ai)

TX cotton (0.375 lb ai)

MI beans (0.375 lb ai)

No

No

No

Chronic Toxicity 

Aquatic 

Invertebrates

Pine seedlings

Cotton, Beans (soy, snap, dry)

Cotton, Beans (soy, snap, dry)

MS cotton (0.5lb ai)

TX cotton (0.375 lb ai)

MI beans (0.375 lb ai)

No

No

No

Acute Toxicity to 

Aquatic Plants 

(non-vascular)

Pine seedlings

Cotton, Beans (soy, snap, dry)

Cotton, Beans (soy, snap, dry)

MS cotton (0.5lb ai)

TX cotton (0.375 lb ai)

MI beans (0.375 lb ai)

Yes

Yes

No

Acute Toxicity to 

Aquatic Plants 

(vascular)

Pine seedlings

Cotton, Beans (soy, snap, dry)

Cotton, Beans (soy, snap, dry)

MS cotton (0.5lb ai)

TX cotton (0.375 lb ai)

MI beans (0.375 lb ai)

No

No

No

Saltwater

Acute Toxicity to 

Fish

Pine seedlings

Cotton, Beans (soy, snap, dry)

Cotton, Beans (soy, snap, dry)

MS cotton (0.5lb ai)

TX cotton (0.375 lb ai)

MI beans (0.375 lb ai)

No

No

No

Chronic Toxicity to 

Fish 

Pine seedlings

Cotton, Beans (soy, snap, dry)

Cotton, Beans (soy, snap, dry)

MS cotton (0.5lb ai)

TX cotton (0.375 lb ai)

MI beans (0.375 lb ai)

No

No

No

Acute Toxicity to 

Aquatic 

Invertebrates

Pine seedlings

Cotton, Beans (soy, snap, dry)

Cotton, Beans (soy, snap, dry)

MS cotton (0.5lb ai)

TX cotton (0.375 lb ai)

MI beans (0.375 lb ai)

No

No

No

Chronic Toxicity

Aquatic 

Invertebrates

Pine seedlings

Cotton, Beans (soy, snap, dry)

Cotton, Beans (soy, snap, dry)

MS cotton (0.5lb ai)

TX cotton (0.375 lb ai)

MI beans (0.375 lb ai)

No

No

No

Acute Toxicity to 

Aquatic Plants 

Pine seedlings

Cotton, Beans (soy, snap, dry)

Cotton, Beans (soy, snap, dry)

MS cotton (0.5lb ai)

TX cotton (0.375 lb ai)

MI beans (0.375 lb ai)

No

No

No
59

6.3.2 Terrestrial Listed Species

There are no listed species acute risk LOC exceedences for birds or mammals. Chronic 

risk LOCs were exceeded for herbivorous birds at all application rates except the 0.17 lb 

ai/A rate (Region 5). Chronic risk LOCs were exceeded for insectivorous birds at 

applications rates of 0.375 lb ai/A and higher (Region 1 & 2). As birds are the surrogate 

for reptiles and terrestrial-phase amphibians, these exceedences also apply to those taxa. 

Exceedences are based on a non-definitive endpoint from a guideline study, and thus may 

overestimate risk. In absence of a definitive endpoint, the Agency assumes effects may

occur at any exposure concentrations about the established NOAEC. The AgDrift model 

was used to estimate the distances from the application site for exposure to drop below 

the level of concern based on the most conservative estimator (short grass). The resulting 

clearance distances were 10 ft for ground applications and 100 ft for aerial applications. 

Thus, for listed insectivorous and herbivorous birds, reptiles, or amphibians nesting or 

foraging within 100 ft of the application source, the direct effects determination is may

affect, likely to adversely affect. For organisms located greater than 100 ft away from the 

field, the direct effects determination is no effect. Table 31 and Table 32 show which 

species have been identified as potentially at risk, based on application rate, geographic 

location, and dietary habits. Indirect effects on listed birds, reptiles, and terrestrial-phase 

amphibians are possible, based on potential effects on plant communities and/or 

designated habitat. For an evaluation of indirect effects, please see the section on 

endangered plants.

For mammals, there were no listed species acute risk LOC exceedences or chronic risk 

LOC exceedences for any of the existing Section 3 application rates. For application 

rates of 0.375 lb ai/A or less, the effects determination for mammals is no effect. Chronic 

risk LOCs were exceeded for the small herbivorous mammals (15g) at the 0.5 lb ai/A 

application rate, which applies only to pine seedlings in AR, GA, MS ,NC, and SC.

Based on the available data (LOCATES and dietary information), no listed small 

herbivorous mammals occur in these locations.
60

Table 30 Summary of Risk to Listed Terrestrial Animals

Clearance estimate

Assessment 

Endpoint

Application 

Rate

lb ai/A

Size 

Class

(g)

LOC Exceedence1

Distance 

from site 

(ft)

Rate

(lb ai/A)

Vertebrates

0.5

15

35

1000

No

No

No

Clears at current rate

0.375

15

35

1000

No 

No

No

Clears at current rate Acute Risk to 

Mammals

0.17

15

35

1000

No

No

No

Clears at current rate

0.5

15

35

1000

Yes (SG)

No

No

Aerial 02

Ground 10

0.473

Clear

Clear

0.375

15

35

1000

No

No

No

Clears at current rate Chronic Risk to 

Mammals

0.17

15

35

1000

No

No

No

Clears at current rate

0.5

20

100

1000

No

No

No

Clears at current rate

0.375

20

100

1000

No

No

No

Clears at current rate

Acute Risk to 

Birds, 

Terrestrialphase 

Amphibians, 

and Reptiles 0.17

20

100

1000

No

No

No

Clears at current rate

0.5 All Yes (SG, TG, BL, SL) Aerial 100

Ground 10 0.192

0.375 All Yes (SG, BL) Aerial 100

Ground 10 0.192

Chronic Risk to 

Birds, 

Terrestrialphase 

Amphibians, 

and Reptiles 0.17 All No Clears at current rate

Invertebrates

0.5 All Yes

0.375 All Yes

Aerial 0

Ground 10 Acute Risk to 0.28

Invertebrates 0.17 All No Clears at current rate

1 LOC exceedences using more conservative dose-based estimates

2 AgDrift clearance estimate is ~45% deposition directly below aircraft

3 Clearance level is for short grass estimate 

4 OPP does not currently have an acute risk LOC for non-listed terrestrial invertebrates

Feeding categories: short grass (SG), tall grass (TG), broadleaf plants, small insects (BL), seeds, 

large insects (SL), granivore-mammals only (G)
61

Indirect Effects and Critical Habitat Effects (Birds, Reptiles, Amphibians, and Mammals)

The most likely indirect effect on listed animals is modification of habitat as a result of 

damage to plants. The habitat modification could include reduced food supply, locations 

for nesting or burrowing, and/or reduced cover for predator avoidance. Both monocots 

and dicots are affected by fomesafen, although based on available data, effects on 

sensitive species of dicots occur at lower concentrations. The assessment endpoint used 

for non-listed plant species is the EC25, a measure of a 25% reduction in the most 

sensitive endpoint for the most sensitive plant. Although plant sensitivity to fomesafen 

varies, determining the range of sensitivities in plant communities near application sites 

is beyond the scope of this assessment. For fomesafen, the most sensitive endpoints are 

typically biomass and percent survival. While it is difficult to predict community-level 

effects on the plant community supporting the listed plants, a 25% reduction in these

endpoints is likely to reduce the viability of any affected population. Degradation of 

habitat could indirectly affect listed species in a number of ways. Thus, for purposes of 

this assessment, exceedence of the non-listed plant LOC is considered a “may affect, 

likely to adversely affect” for listed animals, and has the potential to modify designated 

critical habitat for habitat located within 1,000 ft of aerial applications and 850 ft of 

ground applications.

Potential mitigation measures include but are not limited to: 1) restricting applications of 

fomesafen within 1,000 ft of populations of endangered plants, and 2) restricting 

applications of fomesafen at sites where runoff to wetland areas is likely. Removal of 

aerial application methods from the label is another possibility. However, in light of the 

fact that anticipated effects zones are almost as wide for ground applications, this may 

not be the most beneficial mitigation.
62

Table 31. Listed birds potentially at risk from fomesafen

Common 

Name

Scientific 

Name Pine Soybean Cotton Dry Beans

Snap 

Beans

Flycatcher, 

Southwestern 

Willow

Empidonax 

trailii extimus R1 R1 R1

Plover, Piping Charadrius 

melodus R1 R1, R2 R1, R2 R1, R2 R1, R2

Tern, 

California 

Least

Sterna 

antillarum 

browni

R1 R1 R1

Tern, Interior 

Least

Sterna 

antillarum R1 R1, R2 R1 R1, R2

Warbler, 

Bachman’s

Vermivora 

bachmanii R1 R2 R1, R2

Warbler, 

Goldencheeked

Dendroica 

chrysoparia R1 R1 R1 R1 R1

Warbler, 

Kirtland’s

Dendroica 

kirtlandii R1 R1, R2 R1 R1, R2

Woodpecker, 

Red-cockaded

Picoides 

borealis R1 R1, R2 R1, R2 R1 R1, R2

Woodpecker, 

Ivory-billed

Campephilus 

principalis R2 R2
63

Table 32. Listed reptiles and amphibians potentially at risk from fomesafen

Common 

Name

Scientific 

Name Pine Soybean Cotton Dry Beans

Snap 

Beans

Frog, Dusky 

Gopher

Rana capito 

sevosa

R1 R1

Salamander, 

Cheat 

Mountain

Plethodon 

nettingi R2 R2

Salamander, 

Flatwoods

Ambystoma 

cingulatum R1 R1 R1 R1

Salamander, 

Red Hills

Phaeognathus 

hubrichti R1 R1 R1 R1

Salamander, 

Shenandoah

Plethodon 

shenandoah R2 R2

Toad, Houston Bufo 

houstonensis R1 R1 R1 R1 R1

Tortoise, 

Gopher

Gopherus 

polyphemus R1 R1 R1 R1 R1

Turtle, 

Alabama Redbellied

Pseudemys 

alabamensis R1 R2 R1 R1

Turtle, 

Northern Bog

Clemmys 

muhlenbergii R1 R2 R2

Turtle 

Flattened 

Musk

Sternotherus 

depressus R1 R3 R1 R1 R1

Turtle 

Plymouth Redbellied

Pseudemys 

rebriventris 

bangsi

R3

Turtle, Ringed 

Sawback

Graptemys 

oculifera R1 R1 R1 R1 R1

Turtle, Yellowblotched Map

Graptemys 

flavimaculata R1 R2 R1 R1 R1
64

Table 33 Summary of Risk to Listed Plants

Clearance estimate1

Assessment 

Endpoint Type

Application 

Rate

lb ai/A

LOC Exceedence2

Distance 

from site 

(ft)

Rate

(lb ai/A)

Aerial Application

0.5 Yes

0.375 Yes

0.312 Yes

100 0.03

0.25 No

Upland

0.17 No Clears at current rate

0.5 Yes

0.375 Yes

0.312 Yes

0.25 Yes

100 0.03 Wetland

0.17 No Clears at current rate

Ground Application

0.5 Yes 20 0.03

0.375 No

0.312 No

0.25 No

Upland

0.17 No

Clears at current rate

0.5 Yes 20

0.375 Yes

0.312 Yes

0.25 Yes

Acute Risk to 

Monocots

Wetland

0.17 Yes

10 0.03

Aerial Application

0.5 Yes

0.375 Yes

0.312 Yes

0.25 Yes

Upland

0.17 Yes

0.5 Yes

0.375 Yes

0.312 Yes

0.25 Yes

Wetland

0.17 Yes

>900 <0.002

Ground Application

0.5 Yes 300

0.375 Yes 200

0.312 Yes 200

0.25 Yes 150

Upland

0.17 Yes 80

0.5 Yes 300

0.375 Yes 200

0.312 Yes 200

0.25 Yes 150

Acute Risk to 

Dicots

Wetland

0.17 Yes 80

<0.002
65

6.3.3 Plants

Using LOCATES, a list of plants co-occurring with labeled crops was generated. For 

crops listed only on Syngenta labels, which contain wording such that application outside 

the designated regions would be considered misuse2, search parameters were constrained 

to only states listed on the label. BASF labels (soybeans only) contained less specific 

language, thus the search was nationwide, resulting in the inclusion of Florida and 

Hawaii. Table 30 shows the number of species potentially affected by crop and state. 

Numbers of monocots and dicots are shown separately. Ferns, cycads, and lichens, for 

which no data were available, are listed with dicots, which are more sensitive to 

fomesafen.

Direct Effects

Exceedences of endangered species LOC (based on NOAECs) for the most sensitive 

plants tested constitute a “may affect” determination. Based on this definition, use of 

fomesafen may affect listed plants of all varieties located near the application site. Spray

drift analysis using AgDrift (Tier I, Terrestrial Assessment, Point Deposition, ASAE fine 

to medium spray) resulted in clearance distances of approximately 1,000 ft for dicots, and 

200 ft for monocots for aerial applications at a maximum rate of 0.375 lb ai/A. For 

ground applications, clearance distances were estimated at 850 ft for dicots and 20 ft for 

monocots. As no data are available to evaluate the sensitivity of endangered plants to 

fomesafen, all are conservatively assumed to be as sensitive as the most sensitive species 

tested.

While plants are not subject to the same “take” definitions as animals, the dicot listed 

species clearance distances for fomesafen are approximately the same as the dicot 

clearance distances for non-listed species, which are based on a 25% reduction in the 

most sensitive endpoint for the most sensitive plant. For fomesafen, the most sensitive 

endpoints are typically biomass and percent survival. While it is difficult to predict 

community-level effects on the plant community supporting the listed plants, a 25% 

reduction in these endpoints is likely to reduce the viability of any affected population.

Thus, fomesafen is likely to adversely affect dicots up to 1,000 ft away from the 

application point, and likely to adversely affect monocots up to 100 ft away from the 

application point for aerial applications, based on the maximum application rate of 0.375 

lb ai/A. For ground applications, the respective distances would be 850 ft for dicots, and 

10 ft for monocots.

Note that spray drift estimates do not take into the account the effects of runoff from the 

treated site. Because runoff conditions and the quality of vegetated buffers vary widely 

from site to site, these effects are difficult to estimate in a general sense. However, 

except in cases of extreme channelization or nearly bare ground, runoff across a 1,000 ft 

2 Clarification of label language provided in email from James Stone, Registration Division, OPP on May 

1, 2008. BASF labels (7969-82, 7969-83) contain the phrase “intended for use” in certain geographic 

areas, which is too vague for use outside the listed areas to be construed as misuse.
66

buffer is likely to be low. Because fomesafen is less toxic to monocots, a grassy buffer 

would likely be more effective.

Potential mitigation measures include but are not limited to: 1) restricting applications of 

fomesafen within 1,000 ft of populations of endangered plants, and 2) restricting

applications of fomesafen at sites where runoff to wetland areas is likely. Removal of 

aerial application methods from the label is another possibility. However, in light of the 

fact that anticipated effects zones are almost as wide for ground applications, this may 

not be the most beneficial mitigation.

Indirect Effects

Pesticide-mediated indirect effects to plants are usually the loss of an important pollinator 

or dispersal species. Given the relatively low toxicity of fomesafen to animals in general, 

the likelihood of these types of effects appears to be extremely low. Some endangered 

plant species may require the presence of other non-endangered plant species to create a 

suitable habitat. Fomesafen effects on the habitat plants could constitute an indirect 

effect, but without detailed information on the plant’s life history and distribution, EFED 

is unable to even qualitatively evaluate this type of effect.

6.3.4 Action Area

The action area is determined based on the furthest range of anticipated effects. Based on 

the work of Russo et al (2007) and Russo and Madec (2007), it appears that fomesafen 

induces an immune response in freshwater snails and no definitive NOEC for this effect 

has been experimentally determined. Therefore for purposes of the ESA, the action area 

is considered to be the entire U.S.

Other than this sub-lethal snail immune response, the most sensitive organisms evaluated 

are terrestrial dicots. Based on an analysis with AgDrift, deposition from aerial 

applications at the highest Section 3 rate (0.375 lb ai/A) at 950 ft away from the point of 

application will be 0.004 lb ai/A. The most sensitive endpoint is the dicot NOAEC of 

0.002 lb ai/A. At approximately 1,000 ft, the decline curve in AgDrift based empirical 

measurements is asymptotic. For a fine-to-medium droplet size spray, only 1.2% of 

applied will be deposited on the downwind side of the field, presuming no interception.

Thus, for practical reasons, the extent of these dicot effects is estimated at 1,000 ft from 

point of application. This applies to all agricultural land in the regions where fomesafen 

is registered for use under the existing Syngenta labels.
67

Table 34 Endangered Plants by Crop and State

Pine Soybeans Cotton Dry Beans Snap Beans State

Monocot Dicot1 Monocot Dicot1 Monocot Dicot1 Monocot Dicot1 Monocot Dicot1

AL 3 13 3 11 3 13 1 1 3 12

AR 0 3 0 2 0 3

CT 1 0 0 2 1 1

DC 2 0

DE 2 0 2 0

GA 6 12 6 12 4 12 6 11

IA 2 4 2 3 2 4

IL 2 7 1 7

IN 1 4 0 1 1 4

KS 1 1 1 1 1 1

KY 0 10 0 9

LA 0 2 0 2

MA 1 0 1 0 2 1

ME 2 1 2 1 2 1

MD 2 4 1 2 2 4

MI 3 3 3 2 3 5

MN 2 1 1 2 2 2

MO 1 7 0 3 0 1 2 2

MS 0 3 0 3 0 3 0 1 0 3

NC 5 21 5 21 3 16 1 5 5 22

ND 1 0 1 0 1 0

NE 1 1 1 2 1 0

NH 1 0 1 1

NJ 3 2 3 0 3 2

NY 1 5 1 5 1 5

OH 2 4 1 1 2 4

OK 2 0 2 0

PA 2 0 2 0 2 0

RI 0 1 1 1

SC 6 14 6 14 3 11 1 5 6 14

SD 1 0 1 0 1 0

TN 2 18 0 5 1 3

TX 2 5 2 14 2 24 2 11 2 13

VA 1 3 2 7 0 1 4 13

VT 0 1 0 1

WI 2 4 2 4

WV 0 1 1 4

BASF Labels only (soybeans nationwide)

FL 1 25

HI 11 74

Dicot1 This category also includes fern, lichens, and cycads, which are reported separately in 

LOCATES.

Blank rows or section of rows indicate that crop does not co-occur with any endangered plants in 

that state.
68

6.3.5 Probability of Individual Effects

Generally, available toxicity data provides an LC50 or an EC50, (the concentration at 

which 50% of the test population exhibits the designated endpoint, usually mortality). 

Because the Endangered Species Act (ESA) requires determination of potential effects at 

an individual level, this information must be extrapolated from existing data. The Agency

uses the probit dose response relationship as a tool for deriving the probability of effects 

on a single individual (U.S. EPA, 2004). The individual effects probability associated 

with the acute RQ is based on the mean estimate of the probit dose response slope and an 

assumption that that probit model is appropriate for the data set. In some cases, probit is 

not the appropriate model for the data, and EFED has low confidence in extrapolations 

from these types of data sets. In addition to a single effects probability estimate based on 

the mean, upper, and lower estimates of the effects probability are also provided to 

account for variance in the slope, if available. The upper and lower bounds of the effects 

probability are based on available information on the 95% confidence interval of the 

slope. Individual effect probabilities are calculated based on an Excel spreadsheet tool 

IECV1.1 (Individual Effect Chance Model Version 1.1) developed by the U.S. EPA, 

OPP, Environmental Fate and Effects Division (June 22, 2004).

Probability of individual effects for the various assessment endpoints, if the acute RQ 

equals the endangered species LOC, is provided below in Table 35. Probablity of 

individual effects is only evaluated for animals on an acute basis. For plant endangered 

species risk quotients and animal chronic risk quotients, the endpoint used is a no effect 

level, thus an evaluation of the probability of individual effects is not applicable.
69

Table 35 Probability of Individual Effects

Assessment 

Endpoint

Surrogate 

Species LC50 and Slope Fits Probit

Chance of 

Individual 

Effect

Acute Toxicity to 

FW Fish

Rainbow 

trout

126 mg/L and 9.7 (lower bound)

126 mg/L and 14.6

126 mg/L and 19.5 (upper bound)

At LOC of 0.05

Yes

<1 in 1016

<1 in 1016

<1 in 1016

1 in 4.2×108

Acute Toxicity to 

FW Aquatic 

Invertebrates

Water flea

376 mg/L and 3.9 (lower bound)

376 mg/L and 5.6

376 mg/L and 7.3 (upper bound)

At LOC of 0.05

Yes

1 in 5.1x106

1 in 6.3x1012

<1 in 1016

1 in 4.2×108

Acute Toxicity to 

SW Fish

Sheepshead 

minnow

>163 mg/L and 4.5 (default slope)

At LOC of 0.05 No 1 in 2.9x105NA

Acute Toxicity to 

SW Aquatic 

Invertebrates

Mysid 

shrimp

>163 mg/L and 4.5 (default slope)

At LOC of 0.05 No 1 in 2.9x105NA

Acute Toxicity to 

Mammals Guinea pig 607 mg/kg and 4.5 (default slope)

At LOC of 0.1

No 1 in 2.9x105

1 in 2.9×105

Acute Toxicity to 

Birds, Terrestrial 

phase 

Amphibians and 

Reptiles

Mallard 

duck

Dose

>5,000 mg/kg and 4.5(default slope)

At LOC of 0.1

Diet

>20,000 mg/kg and 4.5(default slope)

At LOC of 0.1

No

1 in 2.9x105

NA

1 in 2.9x105

NA

N.A. – Non-definitive endpoint.
70

6.4 Risk Conclusions

Fomesafen is persistent in surface and ground water, and has high potential to leach to 

ground water, given its mobility in soil. Ecologically, the organisms most at risk from 

fomesafen are terrestrial plants, especially dicots. Because terrestrial plants are important 

both ecologically (they provide a critical part of both the structure and function that 

defines “habitat”) and economically (nearby non-target, non-treated crop plants may be 

affected), these potential impacts are an important consideration. No LOCs were 

exceeded for aquatic endpoints except the listed species LOC for freshwater non-vascular 

plants. At the time of this assessment, there were no listed non-vascular freshwater 

plants, and no listed species had been identified as having an obligate relationship with 

freshwater non-vascular plants. For terrestrial organisms, chronic LOCs were exceeded 

for birds (and by extension, reptiles, and amphibians) at all but the lowest application 

rate. Chronic LOCs were exceeded for mammals only for small herbivorous mammals at 

the highest application rate. These LOC exceedences apply to both listed and non-listed 

species. Based on spray drift estimations, clearance distances for chronic exceedences 

are well within the clearance distances for terrestrial plants, thus if terrestrial plants are 

protected, then by virtue of sensitivity, other vulnerable organisms should be protected as 

well. Clearance distances for chronic effects on birds, reptiles, amphibians, and 

mammals are 10 ft from the application source for ground applications (based on low 

boom estimates) and 100 ft for aerial applications (based on application parameters used 

in AgDrift Tier I estimates). For terrestrial plants, using drift estimates based on the 

more sensitive dicots, effects should be anticipated as far as 850 ft for ground 

applications, and 1,000 ft for aerial applications.
71

Table 36 Summary of Direct and Indirect Effects

Evaluation 

Organism

LOCATES 

Category Direct Effects Indirect Effects Critical HabitatEffects

Monocots Monocots

Yes

Ground ≤100 ft

Aerial ≤ 100ft

from point of 

application

No?

(only listed monocot 

affected is aquatic)

Other1

No

(No potentially 

affected species 

have designated 

critical habitat

Dicots

Dicots

Yes

Ground ≤300 ft

Aerial ≤ 900ft

from point of 

application

Yes

Potential for effects 

on other plants in 

the community. 

Alteration of habitat 

may create 

environment 

unsuitable to the 

listed species.

Effects may occur 

up to

Ground ≤300 ft

Aerial ≤ 900ft

from point of 

application

Yes

(6 potentially 

affected species 

have designated 

critical habitat

Birds

Reptiles

Birds Terrestrial 

Phase 

Amphibians

Mammals Mammals

Yes

Chronic 

Exceedences

Ground ≤10 ft

Aerial ≤ 100ft

from point of 

application

FW Aquatic 

Plants2

FW Aquatic 

Plants

SW Aquatic 

Plants

SW Aquatic 

Plants

FW

Crustacea

FW Bivalves FW Aquatic 

Invertebrates FW

Gastropods

FW Fish

FW Fish Aquatic 

Phase 

Amphibians

SW

Crustacea

SW Bivalves SW Aquatic 

Invertebrates SW

Gastropods

SW Fish SW Fish

No

No LOC 

exceedences

Yes

Potential for effects 

on other plants in 

the community. 

Alteration of habitat 

may create 

environment 

unsuitable to the 

listed species.

Effects may occur 

up to

Ground ≤300 ft

Aerial ≤ 900ft

from point of 

application

Yes

Potential for effects 

on other plants in 

the community. 

Alteration of habitat 

may create 

environment 

unsuitable to the 

listed species.

Effects may occur 

up to

Ground ≤300 ft

Aerial ≤ 900ft

from point of 

application

1 Cycads, Conifers, Fern Allies. These genera have no direct corollary test organism, and have 

been evaluated based on the most sensitive plant endpoint.

2

Evaluated based on both non-vascular plants (algae) and vascular plants (duckweed)
72

7.0 Uncertainties

Risk assessment, by its very nature, is not exact, and requires the risk assessor to make 

assumptions regarding a number of parameters, to use data which may or may not 

accurately reflect the species of concern, and to use models which are a simplified 

representation of complex ecological processes. In this risk assessment, EFED has 

attempted to locate the best available data regarding use and toxicity of fomesafen. 

Frequently, such information are better expressed as ranges rather then points, and when 

this is the case, EFED has opted to make use of the end of range which would result in a 

conservative estimate of risk. These uncertainties, and the directions in which they may 

bias the risk estimate, are described below.

7.1 Exposure Assessment Uncertainties

7.1.1 Aquatic Exposure

Overall, the uncertainties inherent in the aquatic exposure assessment tend to result in 

over-estimation of exposures. This is apparent when comparing modeling results with 

monitoring data. Estimated peak exposures are generally 1-2 orders of magnitude above 

the highest detections in the monitoring data. In general, the monitoring data should be 

considered a lower bound on exposure, while modeling represents an upper bound. The 

modeling conservatively assumes that the receiving water body and the application site 

are adjacent.

7.1.1.1 Modeling Assumptions

The uncertainties incorporated in the exposure assessment cannot be quantitatively

characterized. However, given the available data and EFED’s policy to rely on 

conservative modeling assumptions, it is expected that the modeling results in an overprediction in exposure. Qualitatively, conservative assumptions which may affect 

exposure include the following: 

· The assessment assumes all applications within the modeled watersheds 

occur concurrently (same time and same day) at the maximum application 

rate.

· The assessment assumes all applications are at maximum label rate.

7.1.1.2 Monitoring Data

No surface water monitoring data was identified for fomesafen.. Groundwater data was 

only available from the registrant submitted prospective groundwater study.

7.1.1.3 Impact of Vegetative Setbacks on Runoff

EFED does not currently have an effective tool to evaluate the impact of vegetative 

setbacks on runoff and pesticide loadings. The effectiveness of such setbacks is highly 

dependent on the condition of the vegetative strip. A well-established, healthy vegetative 
73

setback can be a very effective means of reducing runoff and erosion from agricultural 

fields and may substantially reduce loading to aquatic ecosystems. However, a setback 

that is narrow, of poor vegetative quality, or channelized is likely to be ineffective at 

reducing loadings. The presence and quality of setbacks are site-specific, and may vary

widely, even within a small geographic area. EFED does not currently incorporate any 

“buffer reduction” in its runoff exposure estimates. Until such time as quantitative 

methods to estimate the effect of vegetative setbacks of various conditions on pesticide 

loadings become available, EFED’s aquatic exposure predictions are likely to 

overestimate exposure where healthy vegetative setbacks exist and may underestimate 

exposure where poorly developed, channelized or no setbacks exist.

7.1.1.4 PRZM Modeling Inputs and Predicted Aquatic Concentrations

EFED used the linked PRZM/EXAMS model in this assessment, which produces 

estimated aquatic concentrations based on site conditions and historical meteorological 

files (generally 30-year). The “peak” pesticide concentration used in the assessment is 

probability-based, and is expected to be exceeded once within a ten-year period. PRZM 

is a process-based "simulation" model, which calculates what happens to a pesticide in a 

farmer's field on a day-to-day basis. It considers factors such as rainfall and plant 

transpiration of water, as well as how and when the pesticide is applied. The two major 

components are hydrology and chemical transport. Water movement in and off the field 

is simulated by the use of generalized soil parameters, including field capacity, wilting 

point, and saturation water content. Soils in each scenario are selected to represent high 

availability conditions for the pesticide. The chemical transport component simulates the 

method of pesticide application on the soil or on the plant foliage and the environmental 

processes acting on the pesticide. Dissolved, adsorbed, and vapor-phase concentrations 

in the soil are estimated by simultaneously considering the processes of pesticide uptake 

by plants, surface runoff, erosion, decay, volatilization, foliar wash-off, advection, 

dispersion, and retardation. 

Uncertainty associated with each of these individual components adds to the overall 

uncertainty of the modeled concentrations. Equations in the model have not been shown 

to exert any directional bias. Model inputs from the required environmental degradation

studies are chosen to represent the upper confidence bound of the mean, and are not 

expected to be exceeded in the environment 90% of the time. Mobility input values are 

selected to be representative of conditions in the open environment. Natural variation in 

soils adds to the uncertainty of modeled values. Factors such as application date, crop 

emergence date, and canopy cover can affect estimated concentrations. Ambient 

environmental factors, such as soil temperatures, sunlight intensity, antecedent soil 

moisture, and surface water temperatures may cause actual aquatic concentrations to 

differ from the modeled values.

7.1.2 Terrestrial Exposure Uncertainties

For terrestrial exposure estimates, the T-REX model is used to estimate exposure and 

calculate RQs.
74

7.1.2.1 Residue Levels Selection

The Agency relies on the work of Fletcher et al (1994) for setting the assumed pesticide 

residues in wildlife dietary items. These residue assumptions are believed to reflect a 

realistic upper-bound residue estimate, although the degree to which this assumption 

reflects a specific percentile estimate is difficult to quantify. It is important to note that 

the field measurement efforts used to develop the Fletcher estimates of exposure involve 

highly varied sampling techniques. It is possible that much of these data reflect residues 

averaged over entire above ground plants in the case of grass and forage sampling.

7.1.2.2 Dietary Intake

It was assumed that ingestion of food items in the field occurs at rates commensurate 

with those in the laboratory. Although the screening assessment process adjusts dryweight estimates of food intake to reflect the increased mass in fresh-weight wildlife food 

intake estimates, it does not allow for gross energy differences. Direct comparison of a 

laboratory dietary concentration- based effects threshold to a fresh-weight pesticide 

residue estimate would result in an underestimation of field exposure by food 

consumption by a factor of 1.25–2.5 for most food items. 

Differences in assimilative efficiency between laboratory and wild diets suggest that 

current screening assessment methods do not account for a potentially important aspect of 

food requirements. Depending upon species and dietary matrix, bird assimilation of wild 

diet energy ranges from 23 – 80%, and mammal’s assimilation ranges from 41 – 85% 

(U.S. Environmental Protection Agency, 1993). If it is assumed that laboratory chow is 

formulated to maximize assimilative efficiency (e.g., a value of 85%), a potential for 

underestimation of exposure may exist by assuming that consumption of food in the wild 

is comparable with consumption during laboratory testing. In the screening process, 

exposure may be underestimated because metabolic rates are not related to food 

consumption.
75

7.2 Effects Assessment Uncertainties

7.2.1 Age Class and Sensitivity of Effects Thresholds

It is generally recognized that test organism age may have a significant impact on the 

observed sensitivity to a toxicant. For guideline tests, young (and theoretically more 

sensitive) organisms are used. Testing of juveniles may overestimate toxicity at older age 

classes for active ingredients of pesticides which act directly (without metabolic 

transformation) on the organism, because younger age classes often have not developed 

enzymatic systems associated with the detoxification of xenobiotics. When the available 

toxicity data provides a range of sensitivity information with respect to age class, the risk 

assessors use the most sensitive life-stage information as measures of effect.

7.2.2 Use of Surrogate Species Data

Currently, there are no FIFRA guideline toxicity tests for amphibians or reptiles. 

Therefore, in accordance with EFED policy, data for the most sensitive freshwater fish 

are used as a surrogate for aquatic-phase amphibians, and data for the most sensitive bird 

are used as a surrogate for terrestrial-phase amphibians and reptiles. Use of data from the 

most sensitive organism is assumed to be protective of the majority of other organisms 

which may encounter the pesticide.

7.2.3 Extrapolation of Effects

Length of exposure and concurrent environmental stressors will likely affect the response 

of the organism to fomesafen. Because of the complexity of an organism’s response to 

multiple stressors, the overall direction of the response is unknown. Additional 

environmental stressors may decrease or increase the sensitivity to the herbicide. Timing, 

peak concentration, and duration of exposure are critical in terms of evaluating effects, 

and these factors will vary both temporally and spatially. Overall, the effect of this 

variability may result in either an overestimation or underestimation of risk

7.2.4 Acute LOC Assumptions

The risk characterization section of this assessment includes an evaluation of the potential 

for individual effects. The individual effects probability associated with the acute RQ is 

based on the assumption that the dose-response curve fits a probit model. It uses the 

mean estimate of the slope and the LC50 to estimate the probability of individual effects.
76

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77

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80

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