2

Carfentrazone-ethyl (i.e., F8426) is the ethyl ester of carfentrazone (i.e., F8426-

chloropropionic acid). Carfentrazone-ethyl readily hydrolyzes to carfentrazone via aerobic 

microbial metabolism and alkaline hydrolysis (degradation by anaerobic microbial metabolism is 

uncertain). Carfentrazone, however, is not readily biodegraded and is stable to hydrolysis. 

Aqueous photolysis may be a dominant route of degradation of carfentrazone in clear, shallow 

waters (photolysis on soil is uncertain). Additional major routes of dissipation of carfentrazone 

include leaching and runoff, due to its mobility in soil. Carfentrazone and its ethyl ester have 

low volatility and are not expected to bioconcentrate in aquatic or terrestrial organisms.

Carfentrazone-ethyl is a triazolinone (mode-of-action group E/14) that inhibits the 

enzyme protoporphyrinogen oxidase (PPO), resulting in an accumulation of protoporphyrins 

that, in the presence of ultraviolet light, can be photoactivated into reactive oxygen radicals that 

have the potential to cause oxidative damage to cell membranes. This class of herbicides is 

referred to as light-dependent peroxidizing herbicides (LDPHs), which have enhanced toxicity in 

the presence of solar ultraviolet light. Although LDPH toxicity to fish appears to increase as 

light intensity increases, no definitive data have been submitted to allow for a determination 

regarding how much toxicity may increase in the presence of direct sunlight. The default 

toxicity factor is currently 29. 

Carfentrazone-ethyl is moderately toxic to fish and aquatic invertebrates on an acute 

basis. Some data are available to estimate chronic toxicity to fish (rainbow trout NOAEC = 118 

μg a.i./L); however, data have so far been inadequate to confidently estimate the light-dependent 

peroxidizing enhancement to toxicity. Carfentrazone-ethyl is very highly toxic to aquatic plants, 

which is expected given its herbicidal properties.

Carfentrazone-ethyl is practically non-toxic to terrestrial animals. However, toxicity data 

are not available for passerine bird species that may in some cases be more sensitive than the 

mallard and bobwhite that are currently tested. The chief terrestrial risk is to non-target plants. 

Incident reports confirm that carfentrazone-ethyl use may cause damage to non-target plants. 

Toxicity data using a typical end-use product is needed to adequately characterize risk to plants.
3

Problem Formulation for the Environmental Fate, 

Ecological Risk, Endangered Species, and Drinking 

Water Exposure Assessments in Support of the 

Registration Review of Carfentrazone-ethyl

Cl F

Cl

O

O

N

N

N

O

F

F

CAS Registry Number: 128639-02-1

PC Code: 128712

Prepared by:

Greg Orrick, Environmental Scientist

Donna R. Judkins, Ph.D., Biologist

U.S. Environmental Protection Agency

Office of Pesticide Programs

Environmental Fate and Effects Division

Environmental Risk Branch II

1200 Pennsylvania Ave., NW

Mail Code 7507P

Washington, DC 20460

Reviewed by:

R. David Jones, Ph.D., Senior Agronomist

Jean Holmes, DVM,MPH, Risk Assessment Process Leader

Brian Anderson, Branch Chief

March 8, 2011
4

Table of Contents

1. Purpose................................................................................................................................ 5

2. Problem Formulation .......................................................................................................... 5

2.1. Nature of Regulatory Action................................................................................................ 5

2.2. Previous Risk Assessments.................................................................................................. 5

2.2.1. Ecological Risk Assessments........................................................................................ 5

2.2.2. Drinking Water Exposure Assessments........................................................................ 7

2.2.3. Clean Water Act Programs ........................................................................................... 7

3. Stressor Source and Distribution ........................................................................................ 8

3.1. Overview of Pesticide Usage............................................................................................. 10

3.2. Environmental Fate and Transport .................................................................................... 11

4. Receptors........................................................................................................................... 15

4.1. Aquatic and Terrestrial Effects.......................................................................................... 16

4.2. Incident Database Review ................................................................................................. 25

4.3. Ecosystems Potentially at Risk .......................................................................................... 26

5. Assessment Endpoints ...................................................................................................... 26

6. Conceptual Model.............................................................................................................. 28

6.1. Risk Hypothesis................................................................................................................. 28

6.2. Conceptual Diagram .......................................................................................................... 29

7. Analysis Plan ..................................................................................................................... 31

7.1. Stressors of Concern .......................................................................................................... 32

7.2. Measures of Exposure........................................................................................................ 32

7.3. Measures of Effect............................................................................................................. 34

7.4. Integration of Exposure and Effects .................................................................................. 35

7.5. Endangered Species Assessments...................................................................................... 35

7.6. Drinking Water Assessment .............................................................................................. 36

7.7. Endocrine Disruptor Screening Program........................................................................... 36

7.8. Preliminary Identification of Data Gaps............................................................................ 37

7.8.1. Environmental Fate..................................................................................................... 37

7.8.2. Effects ......................................................................................................................... 39

8. References......................................................................................................................... 44

APPENDIX A: Carfentrazone-ethyl Eco Effects Bibliography .................................................. 48

APPENDIX B: Environmental Degradates of Carfentrazone-ethyl............................................ 54

APPENDIX C: Data Call-In Tables. ........................................................................................... 58
5

1. Purpose

The purpose of this problem formulation is to provide a better understanding of the 

environmental fate and ecological effects of carfentrazone-ethyl, considering its currently 

registered uses. Carfentrazone-ethyl is a triazolinone herbicide used to control broadleaf weeds 

and grasses in a wide range of agricultural crops, turfgrass, non-agricultural areas, and aquatic 

areas including water bodies and wetlands. It provides a plan for analyzing relevant data for 

carfentrazone-ethyl and conducting updated ecological risk and drinking water assessments for 

registered uses. Additionally, this problem formulation identifies remaining data gaps, 

uncertainties and potential assumptions used to address those uncertainties in characterizing the 

ecological risk associated with the registered uses of carfentrazone-ethyl.

2. Problem Formulation

2.1. Nature of Regulatory Action

This report summarizes the Environmental Fate and Effects Division‟s (EFED) Problem 

Formulation for the Registration Review of carfentrazone-ethyl. 

The Food Quality Protection Act of 1996 mandated the Environmental Protection Agency (EPA 

or the Agency) to implement a new program, i.e., registration review 

(http://www.epa.gov/oppsrrd1/registration_review/). All pesticides distributed or sold in the 

United States generally must be registered by the EPA. The decision to register a pesticide is 

based on the consideration of scientific data and other factors showing that it will not cause 

unreasonable risks to human health, workers, or the environment when used as directed on 

product labeling. The registration review program is intended to ensure that, as the ability to 

assess risk evolves and as policies and practices change, all registered pesticides continue to 

meet the statutory standard of no unreasonable adverse effects to human health and the 

environment. Changes in science, public policy, and pesticide use practices will occur over time. 

Through the new registration review program, the Agency periodically reevaluates pesticides to 

make sure that as change occurs, products in the marketplace can be used safely. 

As part of the implementation of the new Registration Review program pursuant to Section 3(g) 

of the Federal Insecticide, Fungicide and Rodenticide Act (FIFRA), the Agency is beginning its 

evaluation to determine whether carfentrazone-ethyl continues to meet the FIFRA standard for 

registration. This problem formulation for the environmental fate and ecological risk assessment 

chapter in support of the registration review is intended for the initial docket opening the public 

phase of the review process.

2.2. Previous Risk Assessments

2.2.1. Ecological Risk Assessments

Previous Assessments

The most recent risk assessments available in the docket which serve as the basis for this 

problem formulation include the following:
6

Experimental-use permits for F8426 Herbicide use on wheat, corn, soybeans and 

sorghum, 1995 and 1997 (DP 205680 and 221704)

New use assessment for sweet corn, sorghum and rice, 1999 (DP 261660)1

New use assessment for caneberries (raspberries and blackberries), turf and cotton, 2001 

(DP 272622, 272623, and 272733)2

Section 18 for use on sweet corn to control broadleaf weeks in Wisconsin, 2001 (DP 

265843).

Section 18 for use on hops for mildew control in Washington, Oregon and Idaho, 2001 

(DP 273524, 273680, and 273683)

Section 18 for use on fruiting vegetables in Florida for control of nightshade, purslane 

and morninglory, 2002 (DP 282105)

New use as an aquatic herbicide, 2004 (DP 294782)3

New use assessment (including drinking water and ecological assessment) for grapes, 

tobacco, citrus, pome and stone fruits, tree nuts including pistachio, and tuberous and 

corm vegetables, April 29, 2004 (DP 296368)4

Memo conveying Enumeration of Endangered Plant Species for Proposed Use of 

Carfentrazone-ethyl on Various Crops, August 2, 2004 (DP 299145)

August 5, 2004 memo (DP 293217) conveying the DER for MRID 46037001, accepting 

the rainbow trout early life-stage study under UVL conditions.

January 25, 2006 data call-in (DCI 128712-26285) asking for special LDPH study.

November 23, 2009 memo (DP 333793) reclassifies MRID 46037001 as “Supplemental, 

for qualitative use only” (does not satisfy DCI 128712-26285).

Label amendment assessment for rice, 2011 (DP 384371)

Several ecological risk assessments for carfentrazone-ethyl concluded risk and uncertainties in 

the following area:

risk to aquatic and terrestrial plants from many uses, especially aerial application to corn 

and sorghum; 

acute and chronic risk to fish, aquatic plants and shoreline terrestrial plants from use as an 

aquatic herbicide; and

chronic risk to fish from use on caneberries;

uncertainty in the degree to which toxicity may be increased in the presence of sunlight;

primary data gaps identified included a modified early life stage study in fish to evaluate 

enhanced toxicity in the presence of sunlight and terrestrial plant toxicity studies using a 

TEP. 

 

1 Carfentrazone-ethyl Herbicide Environmental Fate and Ecological Effects Assessment and Risk Characterization 

for a Section 3 for Use on Sweet Corn, Sorghum, and Rice (J. Carleton, N. Mastrota, 12/2/99; DP 261660).

2 New uses of Carfentrazone-ethyl on caneberry, cotton, and turf. 2001 (J. Carleton, R. Felthousen and W. Eckel DP 

272622, 272623 and 272733).

3 New use of carfentrazone-ethyl as an aquatic herbicide, July 1, 2004 (W. Erickson and W. Eckel, DP 294782).

4 Drinking Water and Ecological Assessment for Proposed New Uses of Carfentrazone-ethyl on Grapes, Tobacco, 

Citrus, Pome and Stone Fruits, Tree Nuts including Pistachio, and Tuberous and Corm Vegetables Subgroup., April 

29, 2004 (W. Erickson, DP 296368).
7

2.2.2. Drinking Water Exposure Assessments

A new chemical drinking water exposure assessment was conducted for carfentrazone-ethyl in 

November 1999 (DP barcode 240937). The use pattern of highest exposure estimates was rice, 

with acute and chronic total residue estimated drinking water concentrations (EDWC) in surface 

water of 205 μg/L and 7 μg/L, respectively. These values were based on field study data and a 

2x dilution factor rather than model estimates. Assumptions used in this drinking water 

assessment were later revised (DP barcode 384371, USEPA, 2011). Total residues included the 

parent compound, F8426-chloropropionic acid, F8426-cinnamic acid, F8426-propionic acid, 

F8426-benzoic acid, and 3-hydroxymethyl-F8426-benzoic acid. Surface water and ground water 

total residue EDWCs for use on sweet corn and sorghum were up to 1.7 μg/L and 6.6 μg/L, 

respectively. A Section 18 assessment conducted in May 2000 (DP barcode 265843) relied upon 

the 1999 DWA exposure estimates.

In February 2001, a drinking water exposure assessment was conducted for proposed new uses 

(DP barcode 271184+). Residues of concern were represented by modeling only the 

chloropropionic acid of carfentrazone-ethyl (i.e., carfentrazone acid). Surface water exposure 

estimates for acute and chronic exposure were 21 μg/L and 20 μg/L (56-day mean), respectively. 

The ground water EDWC was 13 μg/L.

A Section 18 assessment of use on fruiting vegetables in Florida was conducted the following 

year, in April 2002 (DP barcode 282105). In this assessment, caneberries remained the use of 

maximum exposure estimates (excluding use on rice). Once again, residues of concern were 

represented by modeling carfentrazone acid. Surface water exposure estimates for acute and 

chronic exposure were 34 μg/L and 19 μg/L (annual mean), respectively. The ground water 

EDWC was 13 μg/L. Assessments of multiple agricultural crops and aquatic uses conducted in 

October 2003 (DP barcode 293780+) and May 2004 (DP barcode 296368) relied upon the 

maximum exposure estimates of the 2002 Section 18 assessment for use in human health dietary 

risk assessment.

The most recent drinking water exposure assessment was conducted in 2011 for proposed label 

amendments to the current use on rice (DP barcode 384371). Carfentrazone-ethyl, its acid 

(carfentrazone), and its cinnamic acid were the residues of concern in drinking water. Surface 

water exposure was estimated with the Tier I Rice Model that was provisionally modified to 

estimate degradation using laboratory data. The proposed label amendments and the currently 

labeled use on rice resulted in similar surface water exposure estimates of 125-126 μg/L (peak 

exposure) and 48 μg/L (chronic exposure).

2.2.3. Clean Water Act Programs

Aquatic Life Criteria and Aquatic Life Benchmarks

The Clean Water Act requires the Agency to publish water quality criteria that accurately reflect 

the latest scientific knowledge on the kind and extent of all identifiable effects on health and 

welfare which might be expected from the presence of pollutants in any body of water, including 

ground water. While these recommended criteria do not, in themselves, impose any 
8

requirements, states and authorized tribes can use them to develop water quality standards. An 

Aquatic Life Ambient Water Quality Criteria document has not been published for 

carfentrazone-ethyl (refer to url: http://www.epa.gov/waterscience/criteria/).

Based on toxicity values revised by the EPA, the OPP publishes aquatic life benchmarks for 

freshwater species, based on the most sensitive species from the most recent risk assessments. 

For carfentrazone-ethyl, no aquatic life benchmarks have been published (see url: 

http://www.epa.gov/oppefed1/ecorisk_ders/aquatic_life_benchmark.htm#benchmarks).

Impaired Water Bodies

Carfentrazone-ethyl is not identified as a cause of impairment for any water bodies listed as 

impaired under section 303(d) of the Clean Water Act, based on information provided at 

http://iaspub.epa.gov/tmdl_waters10/attains_nation_cy.cause_detail_303d?p_cause_group_id=88

5. No Total Maximum Daily Load (TMDL) criteria have been developed for carfentrazoneethyl, based on information provided at

http://iaspub.epa.gov/tmdl_waters10/attains_nation.tmdl_pollutant_detail?p_pollutant_group_id

=885&p_pollutant_group_name=PESTICIDES. More information on impaired water bodies and 

TMDLs can be found at http://www.epa.gov/owow/tmdl/. The Agency invites submission of 

water quality data for this pesticide. To the extent possible, data should conform to the quality 

standards in Appendix A of the OPP Standard Operating Procedure: Inclusion of Impaired 

Water Body and Other Water Quality Data in OPP’s Registration Review Risk Assessment and 

Management Process (see: 

http://www.epa.gov/oppsrrd1/registration_review/water_quality_sop.htm), in order to ensure 

they can be used quantitatively or qualitatively in pesticide risk assessments.

3. Stressor Source and Distribution

Carfentrazone-ethyl is registered for use as an herbicide on a myriad of vegetable, field, orchard, 

and non-agricultural sites. Agricultural sites for which carfentrazone-ethyl is registered for use 

include those of the crop groups for root and tuber vegetables, bulb vegetables, leafy vegetables 

including brassica vegetables, legume vegetables, fruiting vegetables, cucurbit vegetables, citrus 

fruits, pome fruits, stone fruits, berries and small fruits, tree nuts, cereal grains, hay, and spices. 

Additional agricultural sites include cotton, dates, fallow land, figs, hops, okra, olives, peanuts, 

persimmons, pomegranates, sugarcane, sunflowers, tobacco, and other tropical and subtropical 

crops including avocados, bananas, cocoa, tea, Indian mulberries, vanilla, coconuts, palms, 

coffee, guayule, atemoyas, cherimoyas, biribas, canistels, feijoa, jaboticaba, longans, mangos, 

papayas, pulasans, rambutans, sapodillas, sapotas, soursops, star apples, and teosinte. Nonagricultural sites include ornamentals (including trees, grasses, and other plants), turf, grass 

grown for seed, uncultivated land, commercial areas including airports, farm premises, 

residential areas, recreational areas, pastures and rangeland, forests and tree plantations 

(including Christmas tree plantations), rights-of-way, paved areas, drainage systems, mine sites, 

and aquatic areas (including water bodies and wetlands). 

Table 3.1 lists the use patterns of maximum exposure for the current uses of carfentrazone-ethyl. 

Assessment of labeled uses on avocados and coffee will be used as a surrogate for assessment of 
9

the remaining labeled tropical and subtropical crops (i.e., bananas, cocoa, tea, Indian mulberries, 

vanilla, coconuts, palms, guayule, atemoyas, cherimoyas, biribas, canistels, feijoa, jaboticaba, 

longans, mangos, papayas, pulasans, rambutans, sapodillas, sapotas, soursops, star apples, and 

teosinte). The extent of production of many of these crops in the United States and its territories 

is unclear.

TABLE 3.1. Labeled Carfentrazone-ethyl Use Patterns of Maximum Exposure.

Use

Max. 

Single 

App. Rate

(lbs a.i./A)

Max. No. 

of App. 

per 

Season

Min. 

Reapp. 

Interval 

(d)

Max. 

Seasonal 

App. Rate 

(lbs a.i./A)

Max. No. 

of Seasons 

per Year A

Max. 

Annual 

App. Rate

(lbs a.i./A)

App. 

Type

Pastures, millet NS B NS NS NS TBD D TBD Aerial

Cotton NS NS 10 NS 1 NS Ground

Rice, wild rice 0.23 NS NS 0.35 1 0.35 Ground

Jerusalem artichokes 0.13 NS NS 0.038 TBD TBD Ground

Cane berries 0.12 NS 14 0.46 1 0.46 Ground

Potatoes 0.099 NS NS 0.21 1 0.21 Aerial

Ornamental turf 0.098 NS 14 NS 4 NS Ground

Fallow land, airports, commercial 

premises, forest/tree farms, golf 

course turf, residential premises, 

rights-of-way, uncultivated non-ag. 

areas, paved areas, water bodies

0.094 NS NS NS NA NS Aerial

Hay, grass for seed, rangeland, sod 

farms 0.092 1 NA 0.092 2 0.18 Aerial

Recreational areas 0.055 NS NS NS 4 NS Aerial

Cabbage, Christmas trees, 

commercial lawns, fencerows, 

industrial areas, ornamental trees 

and plants, residential lawns, 

sugarcane, tobacco

0.042 NS NS NS 4 NS Aerial F

Farm premises, mine sites 0.040 NS NS NS NA NS Aerial

Legume veg., sorghum 0.036 NS NS NS 1 NS Aerial

Grapes, hops, some vegetables, 

stone fruits, tree nuts 0.036 NS 14 0.14 1 0.14 Aerial G

Brassica veg., bush berries, 

cucurbit veg., spice crops, fruiting 

veg., leafy veg., root and tuber veg.

0.036 NS NS 0.11 3 0.33 Aerial

Cereal grains (barley, corn, oats, 

rye, rice, wild rice, buckwheat, 

teosinte, triticale, and wheat)

0.036 1 NA 0.036 3 0.11 Aerial

Tree nuts, stone fruits, citrus fruits, 

pome fruits, subtropical and 

tropical fruits such as avocados, 

bananas and coffee

0.031 NS 14 E0.20 1 0.20 Ground

Cranberries, mangos 0.031 NS NS 0.12 1 0.12 Ground

Recreational lawns 0.031 NS 14 0.093 3 0.28 Ground

Peanuts, sunflowers 0.028 NS NS NS 1 NS Aerial
10

Use

Max. 

Single 

App. Rate

(lbs a.i./A)

Max. No. 

of App. 

per 

Season

Min. 

Reapp. 

Interval 

(d)

Max. 

Seasonal 

App. Rate 

(lbs a.i./A)

Max. No. 

of Seasons 

per Year A

Max. 

Annual 

App. Rate

(lbs a.i./A)

App. 

Type

Bermuda grass 0.028 NS NS NS NA NS Ground

Artichokes, okra, bulb veg. 0.017 NS NS 0.52 3 1.6 Ground

Water, swamp, wetland, drainage 

system

0.54 lbs 

a.i./acre-ft NS 14 NS NA C NS Injection

0.20 lbs 

a.i./acre-ft NS 14 NS NA NS Boat, etc.

A

 Based on data regarding California agriculture provided in a memo from BEAD to EFED (USEPA, 2007).

B

 NS means “not stated”.

C

 NA means “not applicable”.

D

 TBD means “to be determined”.

E

 Reapplication interval is 14 days for a seasonal maximum application rate of 0.20 lbs a.i./A but is also not stated 

for some uses for a seasonal maximum application rate of 0.12 lbs a.i./A.

F

 Aerial application for cabbage, ground application for other uses.

G

 Aerial application for grapes, ground application for other uses.

Conservative assumptions will be made for maximum application rates (single, seasonal, or both) 

and minimum reapplication intervals (3 days is the default assumption) if they are not stated on 

the current labels.

3.1. Overview of Pesticide Usage

Based on a Screening Level Usage Analysis conducted by the Agency (USEPA 2010), using 

data from 2001 to 2007, roughly 46,000 pounds of carfentrazone-ethyl are applied annually to 

agricultural crops. Carfentrazone-ethyl usage is highest on cotton and rice, with annual averages

of 20,000 lbs and 10,000 lbs of active ingredient (lbs a.i.) applied, respectively (representing 

43% and 22% of the total use on agricultural crops, respectively). The crop with the highest 

average percent crop treated with carfentrazone-ethyl is caneberries (65%), followed by hops 

(60%). Estimates of non-agricultural uses are not readily available.

According to the United States Geological Survey‟s national pesticide usage data (based on 

information from 1999 to 2004), an average of 96,439 lbs of carfentrazone-ethyl per year are 

applied nationally to agriculture in the United States (see Figure 3.1). Based on these data, 

approximately 35% of the average pounds of carfentrazone-ethyl used per year is applied to 

corn, approximately 34% is applied to rice, and 29% is applied to cotton.
11

FIGURE 3.1. Estimated Usage of Carfentrazone-ethyl (USGS, 2010).

3.2. Environmental Fate and Transport

Carfentrazone-ethyl [ethyl α,2-dichloro-5-[4-(difluoromethyl)-4,5-dihydro-3-methyl-5-oxo-1H1,2,4-triazol-1-yl]-4-fluorobenzenepropanoate; CAS No. 128639-02-1; PC code 128712] is the 

ethyl ester of carfentrazone (CAS No. 128621-72-7), which is its chloropropionic acid (chemical 

names and structures are provided in Appendix B). Carfentrazone-ethyl readily hydrolyzes to 

carfentrazone via aerobic microbial metabolism and alkaline hydrolysis (anaerobic microbial 

metabolism is uncertain). Carfentrazone, however, is not readily biodegraded and is stable to 

hydrolysis. Aqueous photolysis may be a dominant route of degradation of carfentrazone in 

clear, shallow waters (photolysis on soil is uncertain). Additional major routes of dissipation of 

carfentrazone include leaching and runoff, due to its mobility in soil. Environmental fate and 

transport properties of carfentrazone-ethyl and carfentrazone are summarized in Tables 3.2 and 

3.3, respectively.
12

TABLE 3.2. General Physical/Chemical Properties and Environmental Fate Parameters of 

Carfentrazone-ethyl.

Parameter Value Reference

Physical/Chemical Parameters

Molecular mass 412.20 g/mol (Calculated)

Water solubility 12 mg/L (20°C)

22 mg/L (25°C)

MRID 43939203

Vapor pressure 5.4 x 10-8torr (20°C)

1.2 x 10-7torr (25°C)

Octanol-water partition 

coefficient (KOW)

2.3 x 103(log KOW = 3.36)

Henry‟s Law constant 2.4 x 10-9atm·m3/mol (20°C)

3.0 x 10-9atm·m3/mol (25°C)

Octanol-air partition coefficient 

(KOA)

2.3 x 1010 torr (20°C)

1.9 x 1010 torr (25°C)

(Calculated from P/C 

properties)

Dissociation constant (pKa) No dissociation MRID 43939203

Persistence in Water

Hydrolysis half-life No evidence of degradation (pH 5)

8.6 d (pH 7)

2.8 hrs (pH 9)

MRID 43189231

Aqueous photolysis half-life 9.5 d MRID 44934201

Aerobic aquatic metabolism halflife 2.3 hrs (clay loam sediment; pH 7.3-8.1)

2.7 hrs (silty clay loam sediment; pH 5.1-7.7)

MRID 44419016

Persistence in Soil

Aerobic soil metabolism half-life 12 ± 13 d (loamy sand; pH 4.5)

1.0 ± 0.1 d (Speyer 2.2 loamy sand; pH 5.8)

0.10 ± 0 d (silt loam; pH 5.6)

0.12 ± 0.01 d (sandy clay loam; pH 5.7)

MRID 44165034

Mobility

No acceptable soil mobility data because compound is not stable in soil.

Bioconcentration

Fish bioconcentration factor 49 (edible), ≤413 (inedible), ≤186 (whole fish) MRID 44165042

Field Dissipation

Terrestrial field dissipation DT50 2 d (KS sand)

5 d (MN silt loam)

(Parent detected 

≤20 cm deep.)

(MRID 44165039) A

Intervals were inadequate to establish 

a half-life (NC sandy loam)

1 d (IA clay loam)

(Parent detected 

≤10 cm deep.)

MRID 44419017

Aquatic field dissipation DT50 5 d (CA rice water; pH 7.3)

2 d (LA rice water; pH 6.1)

(MRID 44654701) B

0.3 d (6.2 hrs; FL pond; pH 7.9) MRID 46253901

A

Study results are uncertain because the analytical method used was not independently validated.

B

Study results are uncertain because storage stability data were not provided.
13

Mobility

Carfentrazone-ethyl is soluble in water up to 22 mg/L (at 25°C; MRID 43939203). 

Volatilization into air will be limited, with a relatively low vapor pressure (1.2 x 10-7torr at 

25°C) and Henry‟s Law Constant (3.0 x 10-9atm·m3/mol at 25°C). EpiSUITE (v4.0) estimates a 

half-life in air of 51 hours for carfentrazone-ethyl, which indicates that any volatilized residues 

will persist in air, which may result in long-range transport. However, long-range transport of 

carfentrazone-ethyl is not an exposure route of concern due to the compound‟s low volatility and 

low persistence in most environments following deposition from the air. The mobility of 

carfentrazone-ethyl in soil could not be measured due to its rapid degradation in soil.

The octanol-water (KOW) and octanol-air (KOA) partition coefficients of carfentrazone-ethyl (2.3 

x 103and 1.9 x 1010, respectively) were sufficiently high to investigate the compound‟s 

bioaccumulation potential. However, fish bioconcentration factors are ≤413, indicating that 

bioaccumulation of carfentrazone-ethyl residues is not a primary concern in aquatic organisms 

(MRID 44165042). Carfentrazone-ethyl is not expected to bioconcentrate in terrestrial 

organisms either due to its low bioconcentration in aquatic organisms and its low expected 

availability to terrestrial organisms due to its non-persistence in most environments.

Degradation

Carfentrazone-ethyl rapidly hydrolyzes in alkaline water (half-life of 2.8 hours at pH 9) and

readily hydrolyzes in neutral water (half-life of 8.6 days at pH 7). There is no evidence of 

degradation by hydrolysis in acidic water (pH 5; MRID 43189231). The compound is readily 

microbially metabolized in aerobic environments, with half-lives in soil ranging from 0.10 to 21

days (mean of 3.2±7.2; MRID 44165034) and half-lives in water of 2.3 to 2.7 hours (MRID 

44419016). The degradation half-lives in water, however, may have been shortened by

instability during sample processing and any storage prior to analysis. They also may reflect 

chemical hydrolysis as well as biodegradation since water pH values were up to 7.7 and 8.1 on 

study intervals when the test compound was detected; however, this is uncertain because 

degradation rates were similar between systems of predominantly acidic and alkaline pH. The 

biodegradation half-lives in soil and water only describe the initial degradation kinetics of 

carfentrazone-ethyl since the degradation kinetics were biphasic over time and not first-order. 

Low levels of the compound (generally less than 10% of the applied in soil and less in water) 

persisted over the duration of the studies. The biodegradation of carfentrazone-ethyl in 

anaerobic environments is uncertain because acceptable anaerobic biodegradation data have not 

been submitted.

Carfentrazone-ethyl undergoes aqueous photolysis, with a half-life of 9.5 days (MRID 

44934201). However, biodegradation and any neutral to alkaline hydrolysis, rather than 

photolysis, are expected to dominate degradation.

Transformation Products

The primary degradate of carfentrazone-ethyl is carfentrazone (i.e., carfentrazone acid, the 

chloropropionic acid of carfentrazone-ethyl; chemical names and structures are provided in 

Appendix B). Carfentrazone formed up to 99.7% of the applied radioactivity (% AR) by 14 days 
14

after treatment and was stable at each pH in the submitted hydrolysis study of the ethyl ester (MRID 

43189231). Carfentrazone also formed up to 90% AR (1.3 days after treatment) and 80% AR (1 or 7 

days after treatment) in the submitted aerobic soil metabolism and aerobic aquatic metabolism 

studies of the ethyl ester, respectively. Carfentrazone was persistent in some aerobic soils, with halflives of 31, 101, and 286 days (MRID 44165034), and persistent in some aerobic aquatic systems as 

well, with half-lives of 39 and 72 days in a submitted study of the ethyl ester (MRID 44419016, 

study in review). A review from the European Commission (2003) indicates that carfentrazone is 

persistent in anaerobic environments as well, with a DT50 greater than 100 days. Photolysis may be 

an important route of dissipation for carfentrazone, with half-lives in water of 5.4 to 10 days reported 

in the European Commission (2003) review.

As an anion (pKa of 2.66; Kemikalie-inspektionen, 2008), carfentrazone is mobile, with soil-water 

partition coefficients (Kd) ranging from 0.39 to 1.3 L/kg in five soils (MRID 43189233). 

Partitioning to soil was not correlated with the soil‟s fraction of organic carbon. Carfentrazone, as 

an anion, will not bioconcentrate in aquatic or terrestrial organisms.

Physicochemical properties of carfentrazone are uncertain. Studies have not been submitted or 

located on the water solubility, vapor pressure, octanol-water partition coefficient, or dissociation 

constant of carfentrazone. Estimates from EpiSUITE are uncertain, as the model was not 

designed to be accurate for ionic compounds. For example, EpiSUITE (v4.0) estimates a log 

KOW of 3.48 for carfentrazone, which is inaccurate (i.e., too high) for an anion. Values of log 

KOW for carfentrazone reported by some secondary sources (e.g., Kemikalie-inspektionen, 2008) 

appear to be similarly inaccurate at acidic pH values. Table 3.3 summarizes reported

environmental fate and transport properties of carfentrazone.

TABLE 3.3. General Physical/Chemical Properties and Environmental Fate Parameters of 

Carfentrazone Acid.

Parameter Value Reference A

Physical/Chemical Parameters

Molecular mass 384.14 g/mol (Calculated)

Dissociation constant (pKa) 2.66 (temperature not reported) Kemikalieinspektionen, 2008

Persistence in Water

Hydrolysis half-life No evidence of degradation (pH 5)

No evidence of degradation (pH 7)

No evidence of degradation (pH 9)

MRID 43189231

Aqueous photolysis half-life 5.4-10.4 d European 

Commission, 2003

Aerobic aquatic metabolism 

half-life 

39 d (silty clay loam sediment)

72 d (clay loam sediment)

MRID 44419016

Persistence in Soil

Aerobic soil metabolism halflife30.9 d (Speyer 2.2 loamy sand)

101 d (UK clay loam)

286 d (US Cosad loamy sand)

MRID 44165034

Anaerobic soil metabolism

DT50

>100 d (Speyer 2.2 loamy sand) European 

Commission, 2003
15

Parameter Value Reference A

Mobility

Soil-water partitioning 

coefficient (Kd)

0.39 (CA loamy sand; 0.23% o.c.)

1.05 (UK sandy clay loam; 3.4% o.c.)

1.11 (Speyer 2.2 loamy sand; 2.3% o.c.)

1.28 (NY loamy sand; 1.9% o.c.)

1.32 (UK silt loam; 2.7% o.c.)

MRID 43189233

A

Sources with no MRID have not been reviewed by the Agency.

Other major degradates of carfentrazone-ethyl in aerobic soil include its cinnamic acid (up to 

51% AR at 33 days), its propionic acid (up to 23% AR at 270 days), its benzoic acid (up to 22% 

AR at 365 days), 3-hydroxymethyl-F8426-benzoic acid (up to 24% AR at 365 days), and an 

unidentified compound, Unknown 7 (up to 18% AR at 365 days; MRID 44165034). In aerobic 

aquatic systems, the only major degradate of carfentrazone-ethyl other than carfentrazone acid 

was its cinnamic acid (up to 11% AR at 21 days); MRID 44416016, study in review). Major 

photolytic degradates of carfentrazone-ethyl included α,2,4-trihydroxy-F8426 (up to 18% AR at 

15 days), α-hydroxymethyl-2,4-dihydroxy-F8426 (up to 15% AR at 15 days), and α-hydroxyF8426 (up to 12% AR at 8 days; MRID 44934201). Major photolytic degradates of 

carfentrazone acid are uncertain because acceptable aqueous photolysis data on carfentrazone 

have not been submitted. Carbon dioxide and other volatile compounds formed no more than 

4.6% AR in any submitted study of carfentrazone-ethyl.

The cinnamic acid, propionic acid, and benzoic acid of carfentrazone-ethyl were persistent in 

aerobic soils, with respective half-life ranges of 65-430 days, 56-370 days, and 420-3300 days 

(MRID 44633504). All of these acids were mobile in soil, with respective Freundlich KOC value 

ranges of 44-333 L/kgOC (cinnamic acid), 27-260 L/kgOC (propionic acid), and 4-41 L/kgOC

(benzoic acid; MRID 44165036). The mobility in soil of 3-hydroxymethyl-F8426-benzoic acid 

was shown to be high, with Freundlich KOC values ranging from <0.3 to 9 L/kgOC (MRID 

44165037).

In summary, nine major degradates of carfentrazone-ethyl have been identified in submitted 

studies. Six degradates, including carfentrazone acid, form in aerobic soil. Three degradates are 

photoproducts that are not expected to be prominent in the environment due to biodegradation 

and alkaline hydrolysis processes dominating the degradation of carfentrazone-ethyl.

4. Receptors

Consistent with the process described in the Overview Document5, the risk assessment for 

carfentrazone-ethyl will rely on a surrogate species approach. Toxicological data generated from 

surrogate test species, that are intended to be representative of broad taxonomic groups, are used 

to extrapolate to potential effects on a variety of species (receptors) included under these 

taxonomic groupings. 

 

5Overview of the Ecological Risk Assessment Process in the Office of Pesticide Programs. Office of Prevention, 

Pesticides, and Toxic Substances. Office of Pesticide Programs. Washington, D.C. January 23, 2004.
16

Acute and chronic toxicity data from studies submitted by pesticide registrants along with the 

available open literature are used to evaluate the potential direct and indirect effects of 

carfentrazone-ethyl on aquatic and terrestrial receptors. Toxicity studies for the technical grade 

active ingredient (TGAI) and the typical end-use product (TEP) will all be considered in the 

ecological risk assessment. Open literature studies are identified using EPA‟s ECOTOX 

database6that employs a literature search engine for locating chemical toxicity data for aquatic 

life, terrestrial plants, and wildlife. Research papers accepted into the ECOTOX database are 

screened using standard procedures to ensure consistent, high quality information; these studies 

will be considered during the „Analysis‟ phase of risk assessment process. The Ecological 

Incident Information System (EIIS, version 2.17) that tracks incident reports submitted to EPA 

and the Avian Monitoring Information System (AIMS8) will be used to identify supportive, line 

of evidence information on exposure of aquatic and terrestrial receptors. Data from all of these 

sources can also provide insight into the direct and indirect effects of carfentrazone-ethyl on 

biotic communities from loss of species that are sensitive to the chemical.

4.1. Aquatic and Terrestrial Effects

Effects on Aquatic Organisms

Acute aquatic toxicity data are available for carfentrazone-ethyl; however, chronic toxicity data 

are incomplete, lacking freshwater life-cycle and saltwater early life-stage studies, which are 

needed due to potential direct application to water. Moreover, carfentrazone-ethyl‟s mode-ofaction (previously described) as a protoporphyrinogen oxidase inhibitor, raises substantial 

concerns for its LDPH toxicity to aquatic organisms. Table 4.1 provides a summary of the most 

sensitive data from taxonomic groups and the surrogate species used to characterize potential 

acute and chronic aquatic effects of carfentrazone-ethyl. A list of all submitted studies to date is 

found in Appendix A. 

TABLE 4.1. Aquatic toxicity profile for Carfentrazone-ethyl

Taxon Exposure 

Duration

Guideline

Most 

Sensitive 

Species 

Tested

Toxicity Value Acute Toxicity 

Category1 MRID

Freshwater 

Fish and 

AquaticPhase 

Amphibians

Acute 850.1075

Rainbow trout 

Oncorhynchus 

mykiss

LC50= 1.6 mg

a.i./L using 

TGAI (91.7% 

a.i.)

Moderately 

Toxic 43189228

Chronic

850.1400

850.1500

Rainbow trout 

ELS2 Test

Rainbow trout 

Life Cycle 

Test

NOAEC = 118 

μg a.i./L

LOAEC = 242 

μg a.i./L3

--

4

NA

44424201

--

 

6

http://www.epa.gov/ecotox

7

http://www.epa.gov/oppefed1/general/databasesdescription.htm

8 American Bird Conservency database, http://www.abcbirds.org/. 
17

Taxon Exposure 

Duration

Guideline

Most 

Sensitive 

Species 

Tested

Toxicity Value Acute Toxicity 

Category1 MRID

LDPH5

Study

No 

Guidelines 

(modified 

850.1400)

Rainbow trout

Rainbow trout

NOAEC = < 16.4 

μg a.i./L

LOAEC = 16.4 

μg a.i./L6

NOAEC = 22 μg 

a.i./L

LOAEC = 45 μg 

a.i./L7

NA

44963201

No NOAEC, 

dosing and 

dissolved oxygen 

problems.

46037001

Does not meet 

requirement for an 

LDPH study.

Estuarine/ 

Marine Fish

Acute 850.1075

Tidewater 

silverside

Menidia 

beryllina

LC50= 1.14 mg 

a.i./L using 

TGAI (90.3 % 

a.i.)

Moderately 

Toxic 44165005

Chronic 850.1400 -- No Data -- --

Freshwater 

Invertebrates

Acute

850.1010

Water flea 

Daphnia 

magna

EC50= >9.8 mg 

a.i./L 

Moderately 

Toxic 43189230

850.1735 Invertebrate 

Sediment Test

No Data -- --

Chronic 850.1300 Water flea -- NA --

Estuarine/ 

Marine 

Invertebrates

Acute

Mysid shrimp 

Mysidopsis 

bahia

LC50 = 1.16 mg 

a.i./L

Moderately 

Toxic 44165003

850.1740 Invertebrate 

Sediment Test

No Data -- --

Chronic 850.1350 -- No Data NA --

Vascular 

plant

Tier I and 

Tier II8 850.4400 Duckweed (Lemna gibba)

EC50 = 5.9 μg 

ai/L;

NOAEL = 2.2 

ppb

NA 43849603

Nonvascular 

plant

Tier I and 

Tier II8 850.5400

Freshwater 

diatom

(Navicula 

pelliculosa)

EC50 = 6.5 μg 

ai/L

NOAEL = 1.9 

ppb

NA 43849605

1 Categories of acute toxicity for aquatic organisms based on LC50 (mg/L): < 0.1 very highly toxic; 0.1-1 highly 

toxic; >1-10 moderately toxic; >10-100 slightly toxic; >100 practically nontoxic.

2 ELS = early life-stage

3

.Based on significant reductions in total length and wet weight of juvenile fish.

4 Missing Data.

5LDPH = Light-Dependant Peroxidizing Herbicide; Data Call In, GDCI 128712-26285, required FMC to submit a 

fish early life-cycle study (OPPTS guideline 850.1400) for carfentrazone-ethyl under ultraviolet light conditions. 

Though study is underway, data have not yet been submitted; therefore, a data gap still exists DCI 128712-26285.

6 Based on significant reductions in wet weight at lowest test concentration; length and survival also reduced at 34.6 

μg ai/L.

7 Based on larval survival, length at day 58 and terminal growth (length, wet weight, and dry weight)

8 Guideline specifies that if 50% effect is exceeded in Tier I, then Tier II data are also required.

The LC50 was 1.6 mg a.i./L for rainbow trout using technical grade carfentrazone-ethyl (MRID 

43189228). For estuarine/marine fish, the tidewater silverside LC50 was 1.14 mg a.i./L, also 

using technical grade (MRID 44165005). In an early life-stage study rainbow trout had 
18

significant reductions in total length and wet weight of juvenile fish at a concentration of 242 μg 

a.i./L (NOAEC = 118 μg a.i./L; MRID 44424201) under standard test conditions. However, 

attempts made to estimate the LDPH enhanced toxicity were unsuccessful (MRIDs 44963201

and 46037001). In the former study (MRID 44963201), dissolved oxygen problems were cited. 

The latter study (MRID 46037001) was initially classified as acceptable and later downgraded to 

supplemental for qualitative use because the lighting was not deemed adequate for an LDPH 

study; however this study did add a line of evidence showing that the LDPH toxicity appears to 

be on the order of five to ten times greater. The NOAEC for rainbow trout was <16.4 μg a.i./L

(44963201), but no endpoints were confirmed for use in risk assessment. This is a data gap.

Acute toxicity data are required per 40 CFR Part 158.630 for fish and aquatic invertebrates for 

all terrestrial and aquatic uses. Since carfentrazone-ethyl converts rapidly, 2.3-2.7 h, into 

carfentrazone acid, which has an aerobic aquatic half-life of 39-72 d, data on carfentrazone acid 

acute toxicity to fish and aquatic invertebrates will also be assessed. With the exception of 

saltwater fish and mollusk toxicity data, most of the needed data are available; see section below 

where the information is presented by taxonomic group. Acute saltwater fish and oyster shelldeposition studies with carfentrazone acid are needed; these are data gaps.

Since carfentrazone-ethyl may be directly applied to water, chronic toxicity data are required for 

both fish and aquatic invertebrates, both freshwater and saltwater. Though the aerobic aquatic 

half-life is 2.3-2.7 h (MRID 44419016), no acceptable anaerobic aquatic data are available and 

so, the persistence of carfentrazone-ethyl in anaerobic aquatic environments is unknown. The 

compound hydrolyzes quickly (t1/2 of 2.8 hrs) in alkaline waters and is stable in acidic waters. 

The main degradate, carfentrazone acid (Table 3.3), has an aerobic aquatic metabolism t1/2 of 39-

72 d. Because the pesticide may be applied directly to water and the estimated environmental 

concentration (EEC, 12 μg a.i./L from use as an aquatic herbicide) is ≥ 0.1 of the fish early lifestage study (NOAEC = 118 μg a.i./L; MRID 44424201 or <16.4 μg a.i./L from LDPH toxicity, 

MRID 44963201), the requirement for a fish life-cycle study is triggered using a freshwater fish 

species. A freshwater invertebrate life-cycle test using the TGAI is required for all terrestrial and 

aquatic uses. Since, however, the acid form is expected to be the dominant form after a few 

hours, this test is requested using carfentrazone acid, in lieu of parent. A fish early life-stage 

study and an invertebrate life-cycle study are both required for saltwater species due to the 

potential for direct application to saltwater. These studies should be conducted using species for 

which acute data are available. Chronic fish and aquatic invertebrate studies should be 

conducted using the degradate, carfentrazone acid, since this is the form expected in chronic 

aquatic exposure.

Acute sediment toxicity tests for freshwater and saltwater invertebrates are needed since:

the soil-water partition coefficient is unknown due to rapid degradation of the 

parent compound, and so the half-life for the parent plus acid is not a primary 

concern, even though the anaerobic aquatic half-life has not been determined; and 

the Koc is unknown; however, if it does hydrolyze to the acid quickly in aerobic 

and anaerobic water bodies, then the Koc of the acid would be more relevant. 

Being an ion, the acid is mobile to highly mobile with Koc values ranging from 6.3 

to 48 L/kg.
19

The core issue is whether the residues will partition to sediment. The parent's Kow is slightly 

greater than 1000, so it triggers acute sediment toxicity studies. But it is expected to be very 

short lived. The acid, on the other hand, will not primarily partition to sediment. Therefore, 

even though the acid may persist, it does not trigger the chronic sediment toxicity study because 

it will not partition to sediment. The parent half-life is <10 d in soil (aerobic aquatic half-life 

2.3-2.7 h, MRID 44419016) suggesting the need for acute, rather than chronic, sediment data. 

Therefore, acute sediment toxicity studies are needed for the parent only.

Carfentrazone-ethyl was very highly toxic to aquatic plants (EC50 = 6.5 μg a.i./L for a diatom 

and 5.9 μg a.i./L for duckweed). 

Data are available to assess toxicity to four degradation products [F8426-cinnamic acid, 

carfentrazone (F8426-chloropropionic acid), F8426-benzoic acid and F8426-proprionic acid]. 

These data are presented below by taxonomic group of test organisms.

Fish and Aquatic-Phase Amphibians

Since LC50's for the parent compound (Table 4.1) fall in the range of >1 to 10 ppm, 

carfentrazone-ethyl is classified as moderately toxic to freshwater and saltwater fish on an acute 

basis. Rainbow trout toxicity studies with four degradation products of carfentrazone-ethyl show 

that they are all slightly to practically nontoxic to fish (Table 4.2). Degradates tested were less 

toxic than parent to fish on an acute basis. 

TABLE 4.2. Acute Toxicity of Degradation Products of Carfentrazone-ethyl to the Rainbow 

Trout

Degradation 

product % ai

96-hour

LC50

(ppm)

Toxicity 

Category

MRID No.

Author/Year

Study 

Classification

F4826–chloropropionic 

acid (carfentrazone acid)

99.0 >99.2 Slightly toxic to 

Practically nontoxic

44165015 Acceptable

F4826-benzoic acid 99.0 >92.5 Slightly toxic to 

Practically nontoxic

44165009 Acceptable

F4826–cinnamic acid 96.6 >25.4 Slightly toxic to 

Practically nontoxic

44176105 Acceptable

F4826–proprionic acid 98.6 >95.6 Slightly toxic to 

Practically nontoxic

44165013 Acceptable

Aquatic Invertebrates

Since LC50's for the parent compound (Table 4.1) fall in the range of >1 to 10 ppm, 

carfentrazone-ethyl is classified as moderately toxic to aquatic invertebrates on an acute basis. 

Daphnid toxicity studies with four degradation products of carfentrazone-ethyl show that they

are all slightly to practically nontoxic to freshwater invertebrates (Table 4.3). Similarly, one test 

conducted with the mysid with one degradate shows it to be slightly to practically nontoxic. 
20

Therefore, degradates tested were less toxic than parent to aquatic invertebrates, both freshwater 

and saltwater, on an acute basis.

TABLE 4.3. Acute Toxicity of Degradation Products of Carfentrazone-ethyl to the Waterflea 

and the Mysid

Degradation 

product % ai

96-hour

EC50 

(ppm)

Toxicity 

Category MRID No.

Study 

Classification

Waterflea (Daphnia magna)

F4826–chloropropionic 

acid (carfentrazone acid)

99.0 >101 Practically nontoxic 44165016 Acceptable

F4826–benzoic acid 99.0 >92.8 Slightly toxic to 

Practically nontoxic

44165007 Acceptable

F4826–cinnamic acid 96.9 >10.7 Slightly toxic to 

Practically nontoxic

44176103 Acceptable

F4826–proprionic acid 98.6 >102 Practically nontoxic 44165011 Acceptable

Mysid (Mysidopsis bahia)

F4826–chloropropionic 

acid (carfentrazone acid)

99.0 >99.2 Slightly toxic to 

Practically nontoxic

44165015 Acceptable

Aquatic Plants

Aquatic plant and algae testing is required for any herbicide that has outdoor non-residential 

terrestrial uses that may move off-site by runoff (solubility >10 ppm in water), by drift (aerial or 

irrigation), or that is applied directly to aquatic use sites (except residential). Results of Tier II 

toxicity testing show that technical carfentrazone-ethyl exhibits considerable toxicity to aquatic 

plants, algae, and blue-green algae (Table Error! Reference source not found.4.1). The most 

sensitive aquatic plant tested is the vascular plant duckweed (EC50 = 5.9 μg a.i./L). The 

freshwater diatom is also highly sensitive to carfentrazone-ethyl (EC50 = 6.5 μg a.i./L).

TABLE 4.4. Acute Toxicity of Degradation Products of Carfentrazone-ethyl to Freshwater 

Green Algae (Pseudokirchneria subcapitata, formerly Selenastrum capricornutum).

Degradation product % ai

EC50

(ppb)

NOAEL

(ppb)

MRID No.

Author/Year

Study 

Classification

F8426 - Chloropropionic Acid

(carfentrazone acid) 98.6 534 405 44165014 Supplemental1

F8426 - Benzoic Acid 98.6 12,600 2,700 44165006 Supplemental1

F8426 - Cinnamic Acid 98.6 26.2 8.46 44176102 Supplemental1

F8426 - Propionic Acid 98.6 139 100 44165010 Supplemental1

1Only 72 h; Guideline 850.5400 specifies 120 h, but otherwise, scientifically sound.

Selenastrum capricornutum 
21

Algal toxicity studies with four degradation products of carfentrazone-ethyl show a broad range 

of toxicity to algae (Table 4.4), all less toxic than parent. Even though these studies were 

classified as supplemental, due to the short test duration (72 h, rather than the guideline 

requirement of 120 h), they can be compared to parent toxicity at 72 h by using MRID 44419005

(see Table 7.6), since this study also had only 72 h duration. This study showed parent to be 

more toxic than either degradate with a 72-h EC50 of 12.7 μg ai/L (as compared to 26.2-12,600) 

and NOAEC of 8.15 μg ai/L (as compared to 8.46-2700). Cinnamic acid was the most toxic 

degradation product to green algae, with toxicity approximately half that of the parent based on 

EC50 results, but very close based on the no-effect level.

Effects on Terrestrial Organisms

Laboratory and field toxicity studies are available for characterization of the effects of 

carfentrazone-ethyl to birds (also surrogate for terrestrial-phase amphibians and reptiles) and 

mammals. Table 4.5 provides a summary of the most sensitive species tested for each terrestrial 

taxonomic group; see Appendix A for a complete list of submitted studies to date. 

TABLE 4.5. Terrestrial toxicity profile for carfentrazone-ethyl

Taxon Exposure 

Duration

Guideline Most Sensitive 

Species Tested Toxicity Value

Acute Toxicity 

Category MRID

Mammals

Acute 850.2400

Norway Rat

Rattus 

norvegicus

LD50 = >5000

mg/kg bw

Practically 

Nontoxic 43189207

Chronic

870-3800

(83-4 two 

gen.

repro.)

Norway Rat

NOAEL = 142 

mg/kg/d (1500 

ppm)

LOAEL = 387 

mg/kg/d for

females (4000 

ppm)1

NA 44165026

Birds, 

Reptiles and 

TerrestrialPhase 

Amphibians

Acute Oral 850.2100

Northern 

Bobwhite 

Colinus 

virginianus

Passerine

LD50= >2250 mg 

ai/Kg bw, 

NOAEL = 810 

mg/kg bw2

Data Gap

Practically 

Nontoxic

--

43189225

--

Sub-acute 

Dietary 850.2200

Northern 

bobwhite

and 

Mallard duck 

Anas 

platyrhynchos

LC50= >5620 mg 

ai/kg 

NOAEC = 5620

mg ai/kg3

Practically 

Nontoxic

43189226

43189227

Chronic

Reproduction 850.2300 Mallard duck

NOAEC = 1000

mg ai/kg

LOAEC = >1000 

mg ai/kg4

NA 44419003

Terrestrial 

Invertebrates Acute 850.3020 Honey Bee

Apis mellifera

LD50= >27.9 μg 

a.i./bee, NOAEC = 

27.9 μg a.i./bee5

Practically 

Nontoxic 44633502
22

Taxon Exposure 

Duration

Guideline Most Sensitive 

Species Tested Toxicity Value

Acute Toxicity 

Category MRID

Nonguideline

Earthworm, 

Eisenia foetida

EC50 >820 = mg 

ai/kg, NOAEC =

820 mg ai/kg

Practically 

Nontoxic 44176101

Terrestrial 

Plants

Tier II Plant 

Studies 

with TGAI

850.4100

Seedling 

Emergence

Monocot:

Onion

Allium cepa

Dicot:

Cabbage

Brassica 

oleraceae

EC25= >0.009 lb 

a.i./A, NOAEC = 

0.002 lb a.i./A

6

EC25= 0.017 lb 

a.i./A, NOAEC = 

0.007 lb a.i./A

7

NA 43939204

850.4150 

Vegetative 

Vigor

Monocot:

Onion

Dicot:

Tomato

Solanum 

esculentum

EC25= 0.012 lb 

a.i./A, NOAEC = 

0.006 lb a.i./A8

EC25= 0.0012 lb 

a.i./A, NOAEC = 

0.0006 lb a.i./A

NA 43892716

1Based on decreased pup body weights in both sexes of the F2 generation

2The NOEL of 810 mg/kg is based upon the slight reduction in body weight gain noted among birds at the 1350 and 

2250 test levels.

3No effects seen at the highest concentration tested.

4No observed reproduction impairment at the highest concentration tested.

5No observed reproduction impairment at the highest concentration tested.

6Based on shoot weight.

7Based on shoot length

8Based on weight.

Acute toxicity to terrestrial animals is categorized using the classification system shown in Table 

4.6 (USEPA, 2004). Toxicity categories for terrestrial plants have not been defined.

TABLE 4.6. Categories of Acute Toxicity for Avian and Mammalian Studies

Toxicity Category Oral LD50 Dietary LC50

Very highly toxic < 10 mg/kg < 50 ppm

Highly toxic 10 - 50 mg/kg 50 - 500 ppm

Moderately toxic 51 - 500 mg/kg 501 - 1000 ppm

Slightly toxic 501 - 2000 mg/kg 1001 - 5000 ppm

Practically non-toxic > 2000 mg/kg > 5000 ppm

Mammals, Birds, Terrestrial-Phase Amphibians and Reptiles

Carfentrazone-ethyl is categorized as practically nontoxic toxic to birds (surrogate for terrestrialphase amphibians and reptiles), mammals, and terrestrial insects on an acute basis (LD50 = 

>5000 mg a.i./kg and >2250 mg a.i./kg based on body weight of the rat and quail; respectively,

and >200 mg/bee; MRIDs 43189207, 43189225 and 44176108). Acceptable acute avian oral 

toxicity data have not been submitted for a passerine species, which is now required under the 40 

CFR Part 158 (2008) data requirements for conventional pesticides.
23

Carfentrazone-ethyl affected mammalian development, causing decreased pup body weights in 

both sexes of the F2 generation in a two-generation reproduction study with the rat at a dietary 

concentration of 1500 ppm (MRID 4416526). 

Two avian subacute dietary toxicity studies were submitted, one with Northern bobwhite (MRID 

43189226) and one with mallards (MRID 43189227). Both studies found the dietary LC50 to be 

>5620 mg a.i./L. Both studies show that carfentrazone-ethyl is practically nontoxic to birds on a

subacute basis.

Results of avian reproduction studies using the TGAI showed that dietary concentrations up to 

1000 ppm caused no observed reproduction impairment in either quail or mallards. Dietary 

exposure to 1000 ppm caused reduction in body weight in adult bobwhite. Results were 

uncertain in the bobwhite reproduction study due to problems with health of test birds, but results 

are sufficient to conclude that use of carfentrazone-ethyl has low chronic toxicity to birds. 

Therefore, this study does not need to be repeated. Based on the application rates approved for 

carfentrazone-ethyl, EECs are not expected to approach levels that showed potential effects in 

the reproduction toxicity studies. 

Terrestrial Invertebrates

A honey bee acute contact study was performed using TGAI (92.2% a.i.) resulting in 48-h acute 

contact LD50 of >27.9 μg a.i./bee (MRID 44633502, Table 4.5). This study was classified as 

acceptable, indicating that carfentrazone-ethyl is practically nontoxic to terrestrial invertebrates.

9

Earthworm subchronic (14-d) toxicity tests are available for the parent compound and four 

degradates (Table 4.7). No significant effects were seen at the top test concentration, which was 

1000 mg a.i./kg in all studies. The differences in EC50s and NOAELs represents mean measured 

concentrations in all except MRID 44176104 (data is not available for measured concentrations 

in this study). These studies indicate that carfentrazone-ethyl and its major degradates are 

practically non-toxic to earthworms.

TABLE 4.7. Acute Toxicity of Degradation Products of Carfentrazone-ethyl to

Earthworms, (Eisenia foetida).

Degradation product % ai

EC50

(ppm ai)

NOAEL

(ppm ai)

MRID No.

Author/Year

Study 

Classification

F4826–cinnamic acid 96.9 >100011000144176104 Supplemental2

F4826–chloropropionic acid

(carfentrazone acid) 99.0 >756 756 4416501744409007 Supplemental2

F4826–benzoic acid 99 >753 753 44165008

44419009 Supplemental2

F4826–proprionic acid 98.6 >846 846 44165012

44419008 Supplemental2

1No measured concentrations were reported in this study, 1000 mg ai/kg was the top nominal concentration in all studies 

presented in this table; therefore, cinnamic acid is not necessarily less toxic than the other degradates or parent, this information 

is needed to be able to make a comparison.

2 No approved guideline currently exists for this study, but otherwise, it is scientifically sound.

 

9

http://www.epa.gov/oppefed1/ecorisk_ders/toera_analysis_eco.htm
24

Terrestrial Plants (Guideline 850.4100 and 850.4150) using TEP

For effects on seedling emergence, onion was the most sensitive species with an EC25 of >0.009

lb a.i./A and a NOAEL of 0.002 lb a.i./ A.. For effects on vegetative vigor, tomato was the most 

sensitive species with an EC25 of 0.0012 lb a.i./A and an NOAEL of 0.0006 lb a.i./A. 

Available terrestrial plant toxicity studies were classified supplemental because the test 

substance was technical product; guidelines require that plant testing be conducted using a 

typical enduse product, TEP. The proposed rule establishing use of the TEP for vegetative vigor 

and seedling emergence studies states, “The TEP that contains the highest percentage of active 

ingredient, and/or is the most commonly used, would be required.” (FR Vol. 70 No. 47; March 

11, 2005; 12289). Tier II seedling emergence and vegetative vigor studies on all plants tested 

(see Tables 4.8 and 4.9) should be repeated using TEP. This is a data gap.

TABLE 4.8. Seedling emergence toxicity of nontarget terrestrial plant (Tier II)

Species % ai EC25 (lb ai/A) NOAEL (lb ai/A)

Corn (monocot) 91.7 >0.063 0.063

Onion (monocot) 91.7 >0.009 0.002

Ryegrass (monocot) 91.7 >0.063 0.063

Wheat (monocot) 91.7 >0.063 0.063

Cabbage (dicot) 91.7 0.022 0.007

Cucumber (dicot) 91.7 >0.063 0.021

Lettuce (dicot) 91.7 0.026 0.006

Radish (dicot, root crop) 91.7 0.023 0.007

Tomato (dicot) 91.7 0.037 0.021

Soybean (dicot) 91.7 >0.063 0.063

TABLE 4.9. Vegetative vigor toxicity of nontarget terrestrial plant (Tier II)

Species % ai EC25 (lb ai/A) NOAEC (lb ai/A)

Corn (monocot) 91.7 >0.063 0.063

Onion (monocot) 91.7 0.012 0.006

Ryegrass (monocot) 91.7 >0.063 0.063

Wheat (monocot) 91.7 >0.063 0.063

Cabbage (dicot) 91.7 0.0019 0.0005
25

TABLE 4.9. Vegetative vigor toxicity of nontarget terrestrial plant (Tier II)

Species % ai EC25 (lb ai/A) NOAEC (lb ai/A)

Cucumber (dicot) 91.7 0.0025 0.0008

Lettuce (dicot) 91.7 0.0023 0.0004

Radish (dicot, root crop) 91.7 0.0027 0.0004

Tomato (dicot) 91.7 0.0012 0.0006

Soybean (dicot) 91.7 >0.019 0.006

The potential for effects to non-target plants has been demonstrated in the field (see Section 4.2. 

Incident Database Review below) although the magnitude is uncertain. 

4.2. Incident Database Review 

An incident review was made on October 27, 2010 by querying the Ecological Incident 

Information System (EIIS, version 2.1) and the Avian Montoring Information System (AIMS), 

for more information, see Receptors section, above. Reported ecological incidents from the EIIS 

database associated with the use of carfentrazone-ethyl are summarized in Table 4.10; no bird 

incidents were found in the AIMS database. 

TABLE 4.10. Summary of Reported Incidents Involving Carfentrazone-ethyl

Taxon

Number of Incidents Involving Carfentrazone-ethyl

Registered 

Use/Misuse, 

(Undetermined)

Likelihood, 

Highly 

Probable

Likelihood, 

Probable

Likelihood, 

Possible

Likelihood, 

Not Likely

Terrestrial 

Vertebrates 0/0 -0- -0- -0- -0-

Terrestrial 

Invertebrates 0/0 -0- -0- -0- -0-

Terrestrial 

Plants 2/6 (2) 3 2 3 2

Aquatic 

Animals 0/0 -0- -0- -0- -0-

Ten incidents involving carfentrazone-ethyl have been reported so far, seven in Washington and 

three in California. All reported incidents involved plant damage; no animal incidents have been 

reported. The two incidents (I014796-001 and I014796-002) from registered use of 

carfentrazone-ethyl were both from use on sweet corn in 2003, and involved extensive damage 

(145 and 515 acres, respectively); however, both were determined “not likely” to have been 

caused by carfentrazone-ethyl. These two incidents, submitted by EPA Region 10, were from 

Dept. of Agriculture, State of Washington from investigations of damage to corn. In both cases, 

Atrazine 4F (I014796-002 report merely specifies Atrazine), Outlook and Aim (active ingredient 
26

is carfentrazone-ethyl) were applied in accordance with labels. Laboratory analysis in both 

cases, however, did not detect any of the ingredients applied. Investigators speculated that there 

was an adverse reaction from Outlook to the variety of sweet corn grown, caused by weather and 

irrigation conditions for the crop. Laboratory analysis also showed MCPA residues (another 

herbicide), which was allegedly not applied at the time of the incident but is not normally found 

long after an application. 

Two incidents classified as “highly probable” for attribution to carfentrazone-ethyl were both 

due to misuses, one intentional (I0210998-028). Of the two incidents classified “probable,” one 

was deemed accidental (I020725-055), but one was undetermined (I019519-043), and therefore, 

may have been due to a registered use; both of these occurred in California. Similarly, of the 

three incidents classified as “possible” two were determined to be from misuse (one accidental) 

of carfentrazone-ethyl, while the legality of use for the other was undetermined, and therefore, 

may have been due to a registered use. Overall, available incident data indicate that exposure 

pathways for carfentrazone-ethyl are complete and that exposure levels may be sufficient to 

result in field-observable effects.

4.3. Ecosystems Potentially at Risk 

Carfentrazone-ethyl may be applied as an aerial or ground spray herbicide to terrestrial habitats 

for agricultural uses, and as a spot treatment for non-agricultural and residential areas or directly 

to water. The ecosystems potentially at risk are often extensive in scope; therefore, it may not be 

possible to identify specific ecosystems during the development of a nation-wide ecological risk 

assessment. However, in general terms, terrestrial ecosystems potentially at risk could include 

the treated field and immediately adjacent areas that may receive drift or runoff. Areas adjacent 

to the treated field could include cultivated fields, fencerows and hedgerows, meadows, fallow 

fields or grasslands, woodlands, riparian habitats, and other uncultivated areas. Due to the 

persistence of carfentrazone-ethyl, it is expected to drift and/or runoff due to application to food 

crops, resulting in possible exposure to aquatic ecosystems. Aquatic ecosystems potentially at 

risk due to the use of carfentrazone-ethyl include water bodies adjacent to, or downstream from, 

the treated field and might include impounded bodies such as ponds, lakes and reservoirs, or 

flowing waterways such as streams or rivers. For uses in coastal areas, aquatic habitat also 

includes marine ecosystems, including estuaries. When applied directly to water, aquatic 

animals and plants, as well as shoreline terrestrial plants, are at risk.

5. Assessment Endpoints

Assessment endpoints are defined as “explicit expressions of the actual environmental value that 

is to be protected.” Defining an assessment endpoint involves two steps: 1) identifying the 

valued attributes of the environment that are considered to be at risk; and 2) operationally 

defining the assessment endpoint in terms of an ecological entity (i.e., a community of fish and 

aquatic invertebrates) and its attributes (i.e., survival and reproduction). Therefore, selection of 

the assessment endpoints is based on valued entities (i.e., ecological receptors), the ecosystems 

potentially at risk, the migration pathways of pesticides, and the routes by which ecological 

receptors are exposed to pesticide-related contamination. The selection of clearly defined 

assessment endpoints is important because they provide direction and boundaries in the risk 
27

assessment for addressing risk management issues of concern. Changes to assessment endpoints 

are typically estimated from the available toxicity studies, which are used as the measures of 

effects to characterize potential ecological risks associated with exposure to a pesticide, such as 

carfentrazone-ethyl.

In its ecological risk assessments, the Agency does not routinely include an evaluation of 

mixtures of active ingredients, either those mixtures of multiple active ingredients in product 

formulations or those in the applicator‟s tank. In the case of the product formulations of active 

ingredients (that is, a registered product containing more than one active ingredient), each active 

ingredient is subject to an individual risk assessment for regulatory decision regarding the active 

ingredient on a particular use site. If effects data are available for a formulated product 

containing more than one active ingredient, the data may be used qualitatively or quantitatively 

in accordance with the Agency‟s Overview Document and the Services‟ Evaluation 

Memorandum (USEPA, 2004 and USFWS/NMFS/NOAA, 2004).

Available toxicity data for environmental mixtures of carfentrazone-ethyl with other pesticides 

will be presented as part of the ecological risk assessment. It is expected that the toxic effect of 

carfentrazone-ethyl, in combination with other pesticides used in the environment, is likely to be 

a function of many factors including but not necessarily limited to: (1) the exposed species, (2) 

the co-contaminants in the mixture, (3) the ratio of carfentrazone-ethyl and co-contaminant 

concentrations, (4) differences in the pattern and duration of exposure among contaminants, and 

(5) the differential effects of other physical/chemical characteristics of the receiving waters (e.g.

organic matter present in sediment and suspended water). Quantitatively predicting the 

combined effects of all these variables on mixture toxicity to any given taxa with confidence is 

beyond the capabilities of the available data and methodologies. However, a qualitative 

discussion of implications of the available pesticide mixture effects data on the confidence of 

risk assessment conclusions will be addressed as part of the uncertainty analysis.

Carfentrazone-ethyl is a triazolinone herbicide that belongs to the mode-of-action group E/14 

that inhibits the enzyme protoporphyrinogen oxidase (PPO). This class of herbicides is referred 

to as light-dependent peroxidizing herbicides (LDPH), which have enhanced toxicity in the 

presence of solar ultraviolet light. LDPHs target PPO specifically, which is present in the heme 

and chlorophyll biosynthetic pathways of animals and plants, respectively. Inhibition of PPO in 

animals and plants leads to an accumulation of phototoxic heme and chlorophyll precursors 

called protoporphyrins, which, in the presence of ultraviolet light, produce activated oxygen 

radicals that can rapidly disrupt cellular function via oxidative damage to cell membranes. Some 

chemicals in this class have also 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). Other example registered herbicides in this group include oxyfluorfen, 

acifluorfen, lactofen, nitrofen, and fomesafen.

To estimate exposure concentrations, the ecological risk assessment considers applications at 

maximum rates. If multiple applications are allowed, the maximum amount per application and 

minimum interval between applications are used – provided that maximum total annual 

application amounts are also included in this configuration. Several EFED exposure models 

(e.g., PRZM-EXAMS, T-REX) are used to estimate likely high-end exposure to carfentrazone-
28

ethyl. The most sensitive toxicity endpoints are used from surrogate test species to estimate 

treatment-related direct effects on acute mortality and chronic reproductive, growth and survival 

assessment endpoints. Toxicity tests are intended to determine effects of pesticide exposure on 

birds, mammals, fish, terrestrial and aquatic invertebrates, and plants. These tests include shortterm acute, sub-acute, and reproduction studies and are typically arranged in a hierarchical or 

tiered system that progresses from basic laboratory tests to applied field studies. The toxicity 

studies are used to evaluate the potential of a pesticide to cause adverse effects, to determine 

whether further testing is required, and to determine the need for precautionary label statements 

to minimize the potential adverse effects to non-target animals and plants.

6. Conceptual Model

For a chemical to pose an ecological risk, it must reach ecological receptors in biologically 

significant concentrations. An exposure pathway is the means by which a pesticide moves in the 

environment from a source to an ecological receptor. For an ecological exposure pathway to be 

complete, it must have a source, a release mechanism, an environmental transport medium, a 

point of exposure for ecological receptors, and a feasible route of exposure.

A conceptual model provides a written description and visual representation of the predicted 

relationships between carfentrazone-ethyl, potential routes of exposure, and the predicted effects 

for the assessment endpoint. A conceptual model consists of two major components: risk 

hypothesis and a conceptual diagram (USEPA, 1998).

6.1. Risk Hypothesis

Risk hypotheses are specific assumptions about potential adverse effects (i.e., changes in 

assessment endpoints) and may be based on theory and logic, empirical data, mathematical 

models, or probability models (USEPA, 1998). For this assessment, the risk is stressor-initiated, 

where the stressor is the release of carfentrazone-ethyl into the environment. The following risk 

hypotheses are presumed for this screening-level assessment:

Carfentrazone-ethyl, when used in accordance with registered labels, will lead to off-site 

movement of the compound’s residues via runoff, spray drift, and eroded soil leading to 

exposure of nontarget plants and animals Based on information on the environmental 

fate, mode of action, direct toxicity, and potential indirect effects of the compound’s 

residues, the registered uses of carfentrazone-ethyl cause reduced survival, growth, and 

reproduction to non-target terrestrial and aquatic animals and plants.

Carfentrazone-ethyl, when applied directly to water in accordance with current labels, 

will result in exposure of non-target aquatic plants and animals, which will result in 

adverse effects upon the survival, growth, and/or reproduction of non-target aquatic 

animals and plants.
29

6.2. Conceptual Diagram

The conceptual site model is a generic graphic depiction of the risk hypothesis, and assumes that 

the herbicide, carfentrazone-ethyl, having multiple outdoor agricultural and non-agricultural 

uses, is capable of affecting aquatic and terrestrial animals provided that environmental 

concentrations are sufficiently elevated as a result of proposed label uses. Based on an 

examination of the physicochemical properties of carfentrazone-ethyl, the fate and disposition in 

the environment, and mode of application, a conceptual model was developed that represents the 

possible relationships between the stressors, ecological receptors, and the assessment endpoints. 

Through a preliminary iterative process of examining available data, the conceptual model (i.e., 

the representation of the risk hypothesis) may be refined to reflect the likely exposure pathways 

and the organisms that are most relevant and applicable to this assessment (see Figure 6.1 and 

Figure 6.2 below). They include the parent compound, or stressor (carfentrazone-ethyl), the 

sources, transport pathways, exposure media and exposure points, biological receptor types, and 

attribute changes.

In order for a chemical to pose an ecological risk, it must reach ecological receptors in 

biologically significant concentrations. An exposure pathway is the means by which a pesticide 

moves in the environment from a source to an ecological receptor. For an ecological exposure 

pathway to be complete, it must have a source, a release mechanism, an environmental transport 

medium, a point of exposure for ecological receptors, and a feasible route of exposure. In 

addition, the potential mechanisms of transformation (as well as which transformation products 

may form in the environment, in which media, and how much) must be understood, especially if 

the chemical‟s transformation products are of greater toxicological concern than the parent 

compound. In this case, only the parent compound is examined, since major degradates are less 

toxic than parent. The assessment of ecological exposure pathways, therefore, includes an 

examination of the source and potential migration pathways, and the determination of potential 

exposure routes for carfentrazone-ethyl.

Under the possible uses of carfentrazone-ethyl, the sources and mechanisms of release of the 

compound are from ground or aerial spray applications to agricultural and non-agricultural areas. 

Surface runoff from the areas of application is assumed to depend on factors such as topography, 

irrigation, and rainfall events. Direct deposition may result in contamination of food items that 

may be consumed by terrestrial organisms. Spray drift results in contaminated adjacent areas, 

including bodies of water. As mentioned in Section 3 above, carfentrazone-ethyl‟s tendency to 

move from soil to surface water is unknown and it has little tendency to leach to ground water

due to its quick degradation to carfentrazone acid. Due to the low potential for volatilization, 

atmospheric transport of carfentrazone-ethyl is unlikely.

For aquatic receptors, the major point of exposure is through direct contact with the water 

column, sediment, and pore water (gill/ integument) contaminated from either direct application,

spray drift (from spray application), and/or runoff from treated areas. Indirect effects to aquatic 

organisms (both fish and aquatic invertebrates) can also occur through impact to various food 

chains (bioaccumulation/ bioconcentration). The representative aquatic receptors are certain 

freshwater and estuarine/ marine fish, invertebrates, and, in certain cases, aquatic plants. The 

major point of exposure for terrestrial animals is consumption of food contaminated with 
30

residues such as grass, foliage, and small insects. For plants, the point of exposure is direct 

contact or root uptake. The representative terrestrial receptors are mammals, birds and terrestrial 

plants. The attribute changes used to assess risk to terrestrial receptors depend on the type of test 

(e.g., reduced survival, growth, or reproduction for animals and seedling emergence and 

vegetative vigor for plants). It should be noted, that these species do not cover all the possible 

species in the animal and plant kingdoms; certain taxa are considered as surrogates for other 

taxa. For example, fish may be considered surrogates for aquatic phase amphibians.

This conceptual model also shows details about biomagnification for a chemical (see piscivorous 

birds and mammals in (Figure 6.1). Carfentrazone-ethyl has a log KOW and log KOA (2.3 x 103

and 1.9 x 1010, respectively) that indicate that bioconcentration in aquatic and terrestrial 

organisms should be investigated. However, fish bioconcentration factors are ≤413, indicating 

that carfentrazone-ethyl residues will not bioconcentrate in aquatic organisms (MRID 

44165042). And the compound is not expected to be available to bioconcentrate in terrestrial 

organisms due to its non-persistence and its low bioconcentration observed in aquatic organisms.

FIGURE 6.1. Conceptual model depicting stressors, exposure pathways, and potential 

effects to aquatic organisms from the use of carfentrazone-ethyl on agricultural and certain 

non-agricultural sites. Dotted lines indicate exposure pathways that have a low likelihood 

of contributing to ecological risk.

**Route of exposure includes only ingestion of fish and aquatic inverts.

Stressor

Source

Receptors

Attribute

Change

Carfentrazone-ethyl applied to agricultural or non-agricultural use site

Direct Application or 

Spray drift

Aquatic animals

Invertebrates 

Vertebrates

**Piscivorous mammals 

 and birds 

Individual organisms

Reduced survival

Reduced growth

Reduced reproduction

Food chain

Reduction in algae and 

 vascular plants

Reduction in prey

availability

Habitat integrity

Reduction in primary

productivity

Reduced cover

Surface water/

Sediment

Runoff

Aquatic Animals

Invertebrates

Vertebrates

Exposure

Media

Uptake/gills

or integument

Ingestion Ingestion

Atmospheric 

transport

Wet/dry deposition

Soil Leaching to

Groundwater

Uptake/gills

or integument

Aquatic Plants

Non-vascular

Vascular

Uptake/cell, 

roots, leaves Riparian plants

terrestrial 

exposure 

pathways; see 

Figure 6.1b
31

FIGURE 6.2. Conceptual model depicting stressors, exposure pathways, and potential 

effects to terrestrial organisms from the use of carfentrazone-ethyl on agricultural and 

certain non-agricultural sites. Dotted lines indicate exposure pathways that have a low 

likelihood of contributing to ecological risk.

Drinking water exposure of carfentrazone-ethyl to avian and mammalian species will be 

screened to determine if this is a potential pathway of concern. The Screening Imbibition 

Program (SIP v.1.0, Released Jun. 15, 2010) will be used to calculate an upper bound estimate of 

exposure using carfentrazone-ethyl‟s solubility, the most sensitive acute and chronic avian 

toxicity endpoints, and the most sensitive acute and chronic mammalian toxicity endpoints.

7. Analysis Plan

In registration review, pesticide ecological risk assessments will follow the Agency‟s Guidelines 

for Ecological Risk Assessment, will be in compliance with the paper titled “Overview of the 

Ecological Risk Assessment Process in the Office of Pesticide Programs, U.S. Environmental 

Protection Agency” (USEPA, 2004), and will be done in accordance with Section 7 of the 

Endangered Species Act.

Stressor

Source

Attribute

Change

Carfentrazone-ethyl applied to agricultural or non-agricultural terrestrial use 

site

Direct

application Spray drift

Terrestrial 

vertebrates

Terrestrial 

invertebrates

Individual 

organisms

Reduced survival

Reduced growth

Reduced reproduction

Food chain

Reduction in prey and food

Habitat integrity

Reduction in primary productivity

Reduced cover

Terrestrial plants

grasses/ forbs, fruit, seeds 

(trees, shrubs)

Runoff

Terrestrial 

vertebrates 

Exposure Media 

& Receptors Soil

Ingestion

Ingestion

Ingestion

Dermal uptake/Ingestion

Atmospheric 

transport

Root uptake/contact

Wet/dry deposition

Ingestion

Leaching to

Groundwater

Irrigation 

water
32

Previously completed screening level risk assessments and exceedances of Agency levels of 

concern indicate a need to further examine and refine risk. Analysis of potential indirect effects 

on listed species is also required. This analysis plan will be revisited and may be revised 

depending upon the data available in the open literature and the information submitted by the 

public in response to the opening of the Registration Review docket.

Use information will be retrieved from registration labels and used as inputs for estimating 

exposure concentrations from the various use scenarios. Carfentrazone-ethyl‟s use patterns 

suggest potential risk concerns to aquatic and terrestrial organisms. The range of potential 

exposure to carfentrazone-ethyl to non-target terrestrial organisms can vary on application 

method (aerial or ground), application rate, and use pattern. 

7.1. Stressors of Concern

The focus of this assessment is solely on carfentrazone-ethyl because ecotoxicity data indicate 

that carfentrazone acid and other transformation products are much less toxic to aquatic 

organisms than the parent compound. Toxicity data on pesticide mixtures (products containing 

multiple active ingredients) and environmental mixtures of carfentrazone-ethyl with other 

pesticides (those mixtures occurring in the environment following application), if available, may 

be discussed as part of the ecological risk assessment. Carfentrazone-ethyl may be applied in 

tank mixtures with other products approved for use on registered crops. It is expected that the 

toxic effect of carfentrazone-ethyl, in combination with other pesticides used in the environment, 

is likely to be a function of many factors including, but not necessarily limited to: (1) the 

exposed species, (2) the co-contaminants in the mixture, (3) the ratio of carfentrazone-ethyl and 

co-contaminant concentrations, (4) differences in the pattern and duration of exposure among 

contaminants, and (5) the differential effects of other physical/ chemical characteristics of the 

receiving waters (e.g. organic matter present in sediment and suspended water). Quantitatively 

predicting the combined effects of all these variables on mixture toxicity to any given taxa with 

confidence is beyond the capabilities of the available data and methodologies. However, a 

qualitative discussion of implications of the available pesticide mixture effects data on the 

confidence of risk assessment conclusions will be addressed as part of the uncertainty analysis.

7.2. Measures of Exposure

In order to estimate risks of carfentrazone-ethyl exposures in aquatic and terrestrial 

environments, all exposure modeling and resulting risk conclusions will be made based on 

maximum application rates for the current use patterns. Measures of exposure are based on 

aquatic and terrestrial models that predict estimated environmental concentrations of 

carfentrazone-ethyl using maximum labeled application rates and methods, as well as any 

mitigation measures specifically indicated on the label. The models used to predict aquatic 1-in10 year EECs are the Tier I Rice Model and the Tier II coupled models Pesticide Root Zone 

Model and EXposure Analysis Model System (PRZM/EXAMS). The model used to predict 

terrestrial exposure is T-REX. The model used to derive EECs relevant to terrestrial and wetland 

plants is TerrPlant. These models are parameterized using relevant reviewed registrantsubmitted environmental fate and transport data.
33

PRZM (v.3.12.2, May 12, 2005) and EXAMS (v.2.98.4.6, April 25, 2005) are the current 

screening simulation models coupled with the graphical user interface, PE (v5.0, November, 

2006) to generate daily exposures and 1-in-10 year EECs of carfentrazone-ethyl that may occur 

from spray drift and runoff to surface water bodies adjacent to application sites. PRZM 

simulates pesticide application, movement and transformation on an agricultural field and the 

resultant pesticide loadings to a receiving water body via runoff, erosion and spray drift. 

EXAMS simulates the fate of the pesticide and resulting concentrations in the water body. The 

standard scenario used for ecological pesticide assessments assumes application to a 10-hectare 

agricultural field that drains into an adjacent 1-hectare water body that is 2 meters deep (20,000 

m

3

volume) with no outlet. The composite model PRZM/EXAMS is used to estimate screeninglevel exposure of aquatic organisms to stressors.

The Tier I Rice Model (v1.0; May 8, 2007) relies on an equilibrium partitioning concept to 

provide conservative estimates of EECs resulting from application of pesticides to rice paddies. 

When a pesticide is applied to a rice paddy, the model assumes that it will instantaneously 

partition between a water phase and a sediment phase. The model does not account for pesticide 

degradation, mass transfer between the aqueous phase and the sediment, volatilization, dilution, 

or other dissipation processes. The Tier I Rice Model was calibrated to generate estimates that 

are consistent with or conservative for dissolved concentrations measured within rice paddies 

and in discharged paddy water. The model was not evaluated or calibrated for concentrations 

measured in sediment and does not account for residues bound to suspended sediment. The Tier 

I Rice Model may be provisionally refined to account for degradation, as was done in a recent 

drinking water exposure assessment (DP 384371; USEPA, 2011).

The measure of exposure for aquatic species is the 1-in-10 year return peak or rolling mean 

concentration. The 1-in-10 year peak is used for estimating acute exposures of direct effects to 

aquatic organisms. The 1-in-10-year 60-day mean is used for assessing chronic exposure to fish 

and aquatic-phase amphibians. The 1-in-10-year 21-day mean is used for assessing aquatic 

invertebrate chronic exposure.

Given the aquatic toxicity of carfentrazone-ethyl, its potential for direct application to water and 

the unknown degradation of parent under anaerobic conditions, the Agency will also consider the 

potential exposures resulting from benthic/sediment concentrations (EECs). Pore water 

concentrations are commonly used to predict toxicity of non-ionic substances in sediments and 

characterize exposure to organisms that spend time in or near sediments (Di Toro et al., 1991; 

USEPA, 2002). PRZM/EXAMS estimates 1-in-10-year peak and 21-day mean EECs for pore 

water.

Exposure estimates for terrestrial animals assumed to be in the target area are derived using the 

T-REX model (version 1.3.1, 12/07/2006). For pesticides such as carfentrazone-ethyl, which can 

be applied as a dust, this includes the amount of pesticide per square foot, used in LD50 per 

square foot risk assessment calculations. EECs for terrestrial plants inhabiting dry and wetland 

areas are derived using TerrPlant (version 1.2.2, 12/26/2006). This model uses estimates of 

pesticides in runoff and in spray drift to calculate EECs. EECs are based upon solubility, 

application rate and minimum incorporation depth.
34

7.3. Measures of Effect

Ecological effects data are used as measures of direct and indirect effects to biological receptors. 

Data are typically obtained from registrant-submitted studies or from literature studies identified 

by ECOTOX. The ECOTOX database provides more ecological effects data in an attempt to 

bridge existing data gaps. ECOTOX is a source for locating single chemical toxicity data and 

potential chemical mixture toxicity data for aquatic life, terrestrial plants, and wildlife.

ECOTOX was created and is maintained by the USEPA, Office of Research and Development, 

and the National Health and Environmental Effects Research Laboratory's Mid-Continent 

Ecology Division.

The acute measures of effect used for animals in this assessment are the LD50, LC50 and EC50 for 

the most sensitive species measured for each assessed group. The assessed groups are, freshwater 

fish, freshwater invertebrates, estuarine\marine fish, estuarine/marine invertebrates, mammals, 

birds, terrestrial invertebrates, aquatic plants, and terrestrial plants. LD stands for "Lethal Dose", 

and LD50 is the amount of a material, given all at once, that is estimated to cause the death of 

50% of the test organisms. LC stands for “Lethal Concentration” and LC50 is the concentration 

of a chemical that is estimated to kill 50% of the test organisms. EC stands for “Effective 

Concentration” and the EC50 is the concentration of a chemical that is estimated to produce a 

specific effect in 50% of the test organisms. Endpoints for chronic measures of exposure for 

listed and non-listed animals are the NOAEL and NOAEC. NOAEL stands for “No ObservedAdverse-Effect-Level” and refers to the highest tested dose of a substance that has been reported 

to have no harmful (adverse) effects on test organisms. The NOAEC (i.e., “No-ObservedAdverse-Effect-Concentration”) is the highest test concentration at which none of the observed 

effects were statistically different from the control. For non-listed plants, only acute exposures 

are assessed (i.e., EC25 for terrestrial plants and EC50 for aquatic plants); for listed plants either 

the NOAEC or EC05 is used.

Information on the potential effects of carfentrazone-ethyl on non-target animals is also collected 

from the Ecological Incident Information System (EIIS). The EIIS is a database containing 

adverse effect (typically mortality) reports on non-target organisms where such effects have been 

associated with the use of pesticides. Information on incidents involving avian species is also 

provided through the Avian Monitoring Information System (AIMS), which is maintained by the 

American Bird Conservancy. 

Where available, sub-lethal effects observed in both registrant-submitted and open literature 

studies will be evaluated qualitatively. Such effects may include behavioral changes (e.g., 

lethargy and changes in coloration). Quantitative assessments of risks, though, are limited to 

those endpoints that can be directly linked to the Agency‟s assessment endpoints of impaired 

survival, growth and reproduction.

The assessment of risk for direct effects to non-target organisms makes the assumption that the 

toxicity of carfentrazone-ethyl to birds is similar to terrestrial-phase amphibians and reptiles. 

The same assumption is made for fish and aquatic-phase amphibians.
35

Several toxicity studies are needed to better assess the potential risk of carfentrazone-ethyl

exposure to non-target organisms, including:

terrestrial plant toxicity studies using a TEP;

passerine acute oral toxicity;

acute toxicity to mollusks using carfentrazone acid;

chronic fish and aquatic invertebrate toxicity using carfentrazone acid;

acute sediment toxicity; and

light-dependent peroxidizing herbicide (LDPH) toxicity.

7.4. Integration of Exposure and Effects

Risk characterization is the integration of exposure and ecological effects characterization to 

determine the potential ecological risk from the use of pesticides and the likelihood of direct and 

indirect effects to non-target organisms in aquatic and terrestrial habitats. The exposure and 

toxicity effects data are integrated in order to evaluate the risks of adverse ecological effects on 

non-target species. For the assessment of risks, the risk quotient (RQ) method is used to 

compare exposure and measured toxicity values. EECs are divided by acute and chronic toxicity 

values. The resulting RQs are then compared to the Agency‟s Levels of Concern (LOCs) 

(USEPA, 2004). These criteria will be used to indicate when carfentrazone-ethyl‟s uses, as 

directed on the label, have the potential to cause adverse direct or indirect effects to non-target 

organisms. In addition, incident data from the EIIS will be considered as part of the risk 

characterization.

7.5. Endangered Species Assessments

Consistent with the Agency‟s responsibility under the Endangered Species Act (ESA), the 

Agency will evaluate risks to Federally-listed threatened and/or endangered (listed) species from 

registered uses of carfentrazone-ethyl. This assessment will be conducted in accordance with the 

Overview Document (USEPA, 2004), provisions of the ESA, and the Services‟ Endangered 

Species Consultation Handbook (USFWS/NMFS, 1998).

The assessment of effects associated with the registration of carfentrazone-ethyl is based on an 

action area. The action area is considered to be the area directly or indirectly affected by the 

federal action, as indicated by the exceedance of Agency Levels of Concern (LOCs) used to 

evaluate direct or indirect effects. The Agency‟s approach to defining the action area under the 

provisions of the Overview Document (USEPA, 2004) considers the results of the risk 

assessment process to establish boundaries for that action area with the understanding that 

exposures below the Agency‟s defined LOCs constitute a no-effect threshold. For the purposes 

of this assessment, attention will be focused on the footprint of the action (i.e., the area where 

carfentrazone-ethyl application occurs), plus all areas where offsite transport may result in 

potential exposure that exceeds the Agency‟s LOCs. Specific measures of ecological effect that 

define the action area for listed species include any direct and indirect effects and/ or potential 

modification of its critical habitat, including reduction in survival, growth, and reproduction as 

well as the full suite of sub-lethal effects available in the effects literature. Therefore, the action 

area extends to a point where environmental exposures are below any measured lethal or sublethal effect threshold for any biological entity at the whole organism, organ, tissue, and/ or 
36

cellular level of organization. In situations where it is not possible to determine the threshold for 

an observed effect, the action area is not spatially limited and is assumed to be the entire United 

States.

Probit Analysis

Analysis of raw data from the aquatic acute toxicity studies for carfentrazone-ethyl will be used 

to estimate probabilities of effects to aquatic and terrestrial animals. Slope estimates along with 

95% conficence intervals will be used. When slope data is unavailable, a default slope of 4.5 is 

used with confidenct intervals of 2 and 9 (Urban and Cook, 1986).

7.6. Drinking Water Assessment

A drinking water assessment will be conducted to support future human health risk assessments 

of carfentrazone-ethyl. The drinking water assessment will incorporate model estimates of 

carfentrazone-ethyl residues of concern in surface and ground waters. The MARC determined 

that the residues of concern in water are carfentrazone-ethyl, its acid (carfentrazone), and its 

cinnamic acid (USEPA, 1998a). Concentrations in surface waters will be estimated using the 

Tier I models FQPA Index Reservoir Screening Tool (FIRST, v.1.1.1, Dec. 18, 2007) and Tier I 

Rice Model (v1.0, May 8, 2007) followed, if necessary, by the Tier II linked models Pesticide 

Root Zone Model (PRZM v3.12.2, May 12, 2005) and EXposure Analysis Modeling System 

(EXAMS v2.98.4.6, Apr. 25, 2005). Ground water estimates of concentrations will be estimated 

using the Tier I model Screening Concentration in Ground Water (SCI-GROW v2.3, Jul. 29, 

2003) followed by a higher tier model if necessary. The drinking water assessment will also 

include a summary of available surface and ground water monitoring data.

7.7. Endocrine Disruptor Screening Program

As required under FFDCA section 408(p), EPA has developed the Endocrine Disruptor 

Screening Program (EDSP) to determine whether certain substances (including pesticide active 

and other ingredients) may have an effect in humans or wildlife similar to an effect produced by 

a “naturally occurring estrogen, or other such endocrine effects as the Administrator may 

designate.” The EDSP employs a two-tiered approach to making the statutorily required 

determinations. Tier 1 consists of a battery of 11 screening assays to identify the potential of a 

chemical substance to interact with the estrogen, androgen, or thyroid (E, A, or T) hormonal 

systems. Chemicals that go through Tier 1 screening and are found to have the potential to 

interact with E, A, or T hormonal systems will proceed to the next stage of the EDSP where EPA 

will determine which, if any, of the Tier 2 tests are necessary based on the available data. Tier 2 

testing is designed to identify any adverse endocrine related effects caused by the substance, and 

establish a dose-response relationship between the dose and the E, A, or T effect.

Between October 2009 and February 2010, EPA issued test orders/data call-ins for the first 

group of 67 chemicals, which contains 58 pesticide active ingredients and 9 inert ingredients. 

This list of chemicals was selected based on the potential for human exposure through pathways 

such as food and water, residential activity, and certain post-application agricultural scenarios. 

This list should not be construed as a list of known or likely endocrine disruptors. 
37

Carfentrazone-ethyl was not included in the list. Test orders were issued in November, 2009. 

Carfentrazone-ethyl is not among the group of 58 pesticide active ingredients on the initial list to 

be screened under the EDSP. Under FFDCA sec. 408(p) the Agency must screen all pesticide 

chemicals. Accordingly, EPA anticipates issuing future EDSP test orders/data call-ins for all 

pesticide active ingredients.

For further information on the status of the EDSP, the policies and procedures, the list of 67 

chemicals, the test guidelines and the Tier 1 screening battery, please visit our website: 

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

7.8. Preliminary Identification of Data Gaps

The Agency needs additional environmental fate and ecological effects studies prior to 

conducting the planned assessments. Data gaps, uncertainties and potential paths forward for the 

assessments of carfentrazone-ethyl are described below.

7.8.1. Environmental Fate

The studies submitted to fulfill environmental fate data requirements for carfentrazone-ethyl are 

not sufficient for exposure assessment. The submitted anaerobic aquatic metabolism study was 

conducted on one soil with HPLC water; pH and dissolved oxygen were not reported; and 

sampling intervals were inadequate to describe the decline of the parent compound (MRID 

44165035). Therefore, a guideline-compliant study is requested of acidic sediments and their 

associated waters.

Aqueous photolysis may be an important degradation route for carfentrazone acid. The 

submitted aqueous photolysis study on carfentrazone acid was unacceptable because the sterility 

of the samples was not determined during the study and material balances were poor in some 

samples, showing a pattern of decline over time (MRID 44165032). Therefore, a new study is

requested in order to describe the environmental fate of carfentrazone in clear, shallow, sun-lit 

surface waters.

The submitted soil photolysis study of carfentrazone-ethyl is unacceptable (MRID 44165033). 

However, this data gap does not need to be filled because biodegradation rates are expected to 

outpace photolysis rates in soil. A column leaching study of carfentrazone-ethyl is unacceptable 

(MRID 44165038) and a batch equilibrium study was not submitted. However, the compound is 

too short-lived in soil to allow for a successful batch equilibrium study. Batch equilibrium data 

are available for the major identified degradates in aerobic soil, carfentrazone, F8426-cinnamic 

acid, F8426-propionic acid, F8426-benzoic acid, and 3-hydroxymethyl-F8426-benzoic acid

(MRID 43189233, 44165036, 44165037). Therefore, batch equilibrium data on carfentrazoneethyl are not requested.

A submitted analytical method in soil (MRID 44165040 and used in MRID 44165039) is

upgradeable without an independent laboratory validation (ILV) report. MRID 44165043 was 

submitted as an ILV for MRID 44165039/44165040. However, the method validated in MRID 

44165043 was described in MRID 44419018 and not used in MRID 44165039. Therefore, the 
38

analytical method in soil described in MRID 44419018 is acceptable, based on the ILV, and the 

terrestrial field dissipation study in MRID 44165039 is not acceptable (i.e., is upgradeable) 

without independent validation of the analytical method in soil used in the study (independent 

validation of analytical methods used in field studies was required for studies submitted on and 

after April 19, 1996, twelve months after publication of 60 FR 19589; Apr. 19, 1995). An ILV 

of the analytical method used in MRID 44165039 (MRID 44165040) is requested to support the 

field dissipation study.

Frozen storage stability data are needed to upgrade an aquatic field dissipation study (MRID 

44654701) to an acceptable classification. These data are requested.

Tables 7.1, 7.2, and 7.3 identify studies by MRID that offer data for each guideline requirement, 

as well as study classifications and whether or not further data are needed in order to support risk 

assessment. Draft Data Call-In (DCI) tables for requested data are provided in APPENDIX C.

TABLE 7.1. Submitted Environmental Fate Data for Carfentrazone-ethyl.

Guideline Data 

Requirement

Submitted 

Studies (MRID)

Classification Data 

Needed?

Comments

835.2120 Hydrolysis 43189231 Acceptable No. --

835.2240 Aqueous 

photolysis

44165031 Unacceptable No. --

44934201 Acceptable

835.2410 Soil photolysis 44165033 Unacceptable Currently, 

no.

Biodegradation rates are expected to 

outpace photolysis rates.

835.4100 Aerobic soil 

metabolism

43189232 Upgradeable No. --

44165034 Supplemental

835.4200 Anaerobic soil 

metabolism

(None) (Not applicable) Currently, 

no.

These data are not expected to change 

pending exposure assessments.

835.4300 Aerobic aquatic 

metabolism

44419016 Supplemental No. --

835.4400 Anaerobic aquatic 

metabolism

44165035 Unacceptable Yes. A guideline-compliant study conducted 

in acidic systems is requested.

835.1230

835.1240

Adsorption/ 

desorption and 

leaching

44165038 Unacceptable Currently, 

no.

Carfentrazone-ethyl was too shortlived in soil to conduct a batch 

equilibrium study.

835.6100 Terrestrial field 

dissipation

44165039 Upgradeable Yes. MRID 44165039 is upgradeable 

without independent validation of the 

analytical method in soil used in the 

study (MRID 44165040). MRID 

44419017 may be upgradeable with 

acceptable soil characterization and 

storage stability data of sufficient 

duration. Submitted analytical 

methods are upgradeable if not 

independently validated.

44419017 Supplemental

Storage stability 44165049 Acceptable

Analytical method 

in soil

44165040, 

44165039

Upgradeable

44419018

(ILV: 44165043)

Acceptable
39

Guideline Data 

Requirement

Submitted 

Studies (MRID)

Classification Data 

Needed?

Comments

835.6200 Aquatic field 

dissipation

44419019 Unacceptable Yes. Frozen storage stability data are needed 

to upgrade MRID 44654701 to an 

acceptable classification.

44654701 Upgradeable

46253901 Supplemental

Storage stability (None) (N/A)

Analytical method 

in water

44165002 Acceptable

850.1730 Fish BCF 44165042 Acceptable No. --

TABLE 7.2. Submitted Environmental Fate Data for Carfentrazone Acid.

OCSPP

Guideline

Data 

Requirement

Submitted 

Studies (MRID)

Classification Data 

Gap?

Comments

835.2240 Aqueous 

photolysis

44165032 Unacceptable Yes. A guideline-compliant study conducted 

in sterilized water is requested.

835.4100 Aerobic soil 

metabolism

44633504 Supplemental No. --

835.1230

835.1240

Adsorption/ 

desorption and 

leaching

43189233 Supplemental No. --

TABLE 7.3. Submitted Environmental Fate Data for Degradates of Carfentrazone-ethyl 

and Carfentrazone Acid.

OCSPP

Guideline

Data 

Requirement

Submitted 

Studies (MRID)

Classification Data 

Gap?

Comments

835.4100 Aerobic soil 

metabolism

44633504 Supplemental No. --

835.1230

835.1240

Adsorption/ 

desorption and 

leaching

44165036 Supplemental No. --

44165037 Supplemental

7.8.2. Effects

Although many submissions have been made to provide data on the effects of carfentrazoneethyl to aquatic and terrestrial organisms, data gaps still exist (Tables 7.4-7.6). Data gaps 

include the following: avian acute oral toxicity on a passerine species; terrestrial plant toxicity 

studies using a TEP; aquatic invertebrate life cycle toxicity; and full life-cycle fish toxicity.

These data gaps are discussed below. 
40

TABLE 7.4. Available Ecological Effects Data for Aquatic Animals Exposed to 

Carfentrazone-ethyl and Remaining Data Gaps. 

Guideline Description MRID/ 

Accession Classification Data Gap? Comments

850.1010

Freshwater 

invertebrates –

Acute toxicity

43189230 Acceptable

No

--

44165004 Acceptable

45168001 In Review Mixture: Carfentrazoneethyl/Metsulfuron-methyl test.

850.1025

850.1035

Saltwater 

invertebrates –

Acute toxicity

44165003 Acceptable

Yes, mollusk 

data for 

carfentrazone 

acid

--

850.1075 Freshwater fish –

Acute toxicity

43189228 Acceptable

No --

43189229 Acceptable

850.1075 Saltwater fish –

Acute toxicity 44165005 Acceptable

Yes, for 

carfentrazone 

acid

--

850.1300

Freshwater 

invertebrate –

life cycle test

44419006 Invalid Yes Guideline-compliant studies 

are requested for both 

freshwater and saltwater 

invertebrates, with 

carfentrazone acid.. 850.1350

Saltwater 

invertebrates –

life cycle test

-- -- Yes

850.1400 Freshwater fish –

early life stage test 44424201 Acceptable No --

850.1400

modified

Light-Dependent 

Peroxidizing 

Herbicide (LDPH) 

Fish ELS Study

44963201 Supplemental 

Yes

Modified protocol: “Early 

Life-Stage Toxicity Test with 

Fathead Minnow (Pimephales 

promelas) Under High Light 

Conditions Following FIFRA 

Guideline 72-4 and OPPTS 

Draft Guideline 850.1400.” 

Protocol has been approved 

and study is in progress

46037001 Supplemental

850.1400 Saltwater fish –

early life stage test -- -- Yes

A guideline-compliant study is 

requested using an estuarine/ 

marine fish (a species for 

which acute toxicity data are 

available) with carfentrazone 

acid.

850.1500 Fish life cycle test -- -- Yes

A guideline-compliant study is 

requested using a freshwater 

fish (a species for which acute 

toxicity data are available) 

with carfentrazone acid.
41

Guideline Description MRID/ 

Accession Classification Data Gap? Comments

850.1735

Whole Sediment: 

acute freshwater 

invertebrates

-- -- Yes --

850.1740

Whole Sediment: 

acute marine 

invertebrates

-- -- Yes --

TABLE 7.5. Available Ecological Effects Data for Terrestrial Animals Exposed to 

Carfentrazone-ethyl and Remaining Data Gaps.

Guideline Description MRID/

Accession

Classification Data 

Gap?

Comments

850.2100 Avian acute oral 

toxicity:

Bobwhite quail

Passerine Species

43189225 Acceptable Yes

A dosing study with a passerine 

species is now required

(protocol to be submitted for

approval).

-- --

850.2200 Avian sub-acute 

dietary toxicity:

Bobwhite quail

Mallard

43189226 Acceptable No

--

43189227 Acceptable

850.2300 Avian 

reproduction:

Bobwhite quail

Mallard

44419002 Supplemental No

Quail study (44419002) was 

compromised by the death and 

injury of birds caused by a 

commotion but able to show no 

significant treatment-related 

effects and does not have to be 

repeated. 44419003 Acceptable

850.3020 Honeybee acute 

contact toxicity 44176108 Supplemental

No

44176108 - Study scientifically 

sound but only 24h; guideline 

specifies 48-h. 24-h NOAEL 

was 200 ug a.i./bee, highest 

level tested.

44633502 Acceptable

NonGuidleline14-d Toxicity to 

the Earthworm, 

Eisenia foetida

44165008

Propionic Acid Supplemental

No

44165008, 44165012,

44165017, 44176101 and 

44176104 were supplemental 

because no approved 

guidelines. This deviation does

not impact study results, data 

may be used in risk assessment.

For 44176101, LC50 was 

44419009

Addendeum to 

44165008 with test 

concentration 

measurements

Supplemental

44165012

Proprionic Acid Supplemental
42

Guideline Description MRID/

Accession

Classification Data 

Gap?

Comments

44419008

Addendeum to 

44165012 with test 

concentration 

measurements

Supplemental

>820 mg ai/kg and NOAEC 

was 820 mg ai/kg (highest 

conc. tested) –Tested on F8426 

Technical (95.0% purity). 

Another study 44176104 was 

tested on F8426-Cinnamic 

Acid (96.9% purity) and used 

nominal, rather than measured 

concentrations. The nominal 

concentrations were the same 

and the results the same in that 

there were no effects in the 

highest treatment tested 1000 

mg ai/kg. If these two studies 

were to be compared, measured 

concentrations would be 

needed for 44176104.

Addenda were sent (44419007, 

44419008 and 44419009) 

which defined the highest test 

concentrations for 44165008, 

44165012 and 44165017, 

respectively, as 753, 846 and 

756 mg ai/kg.

44165017

Chloropropionic 

Acid

Supplemental

44419007

Addendeum to 

44165012 with test 

concentration 

measurements

Supplemental

44176101

TGAI Supplemental

44176104

Cinn Acid Supplemental

TABLE 7.6. Available Ecological Effects Data for Plants Exposed to Carfentrazone-ethyl

and Remaining Data Gaps.

Guideline Description MRID Classification Data 

Gap? Comments

850.4100 Terrestrial Plant toxicity: 

Tier I seedling emergence 43939204 Supplemental No These studies were originally classified as acceptable, but 

later downgraded to 

supplemental due to use of 

TGAI (F8426 Technical 

91.7% purity), rather than the 

required TEP. Data on TEP 

toxicity to terrestrial plants is 

needed.

45626901 test with mixture: 

Parent plus two metabolites.

44419005 had 72h duration, 

rather than guideline 120h, 

otherwise scientifically sound.

850.4100 Terrestrial Plant toxicity: 

Tier 2 seedling emergence

43939204 Supplemental Yes, for 

TEP

850.4150 Terrestrial Plant toxicity: 

Tier I vegetative vigor 43892716 Supplemental No

850.4150 Terrestrial Plant toxicity: 

Tier 2 vegetative vigor

43939204 Supplemental Yes, for 

43892716 Supplemental TEP

850.4400 Aquatic Plant Growth: 

vascular plants

43849603 Acceptable

No

45626901 In Review

850.5400 Aquatic Plant Growth: algae

43829717 Acceptable No

43849603 Acceptable

43849604 Acceptable

43849605 Acceptable

43849606 Acceptable

44419005 Supplemental
43

Acceptable acute toxicity studies were submitted for freshwater and saltwater fish (MRIDs

43189228 and 44165005). Due to carfentrazone-ethyl‟s previously recognized LDPH toxicity, a 

DCI was issued in 2006 (DCI 128712-26285) asking for a special LDPH study. However, 

attempts made to estimate the LDPH toxicity were unsuccessful (MRIDs 44963201 and 

46037001) due to problems with dissolved oxygen and inadequate lighting. Although the 

toxicity appears to be on the order of five to ten times greater, no endpoints were confirmed for 

use in risk assessment. Since carfentrazone-ethyl converts rapidly to carfentrazone acid acute 

data are also needed on this degradate; data are available for rainbow trout (MRID 44165015), 

daphnids and mysids (MRIDs 44165016 and 44165015) but not for saltwater fish or mollusks. 

These are data gaps.

One acceptable early life-stage study is available for freshwater fish but no acceptable chronic 

toxicity data are available for estimating the chronic effects of carfentrazone-ethyl or its acid to 

invertebrates, in freshwater or saltwater, by water column or sediment exposure. Since 

carfentrazone-ethyl may be applied directly to water, and the expected EEC is > 0.1 of the early 

life stage NOAEC for rainbow trout (i.e., <16.4 μg a.i./L, based on LDPH toxicity, MRID 

44963201), chronic data are required per 40 CFR Part 158.630. Chronic studies using saltwater 

fish and both freshwater and saltwater invertebrates are needed with carfentrazone acid due to 

the rapid conversion. Without this data, risk would have to be assumed but would not be 

quantifiable.

Acceptable acute avian oral toxicity data were submitted for exposures of bobwhite quail and 

mallard duck to carfentrazone-ethyl; however, data are not available for passerines, which are 

required under the new 40 CFR Part 158 (Oct. 26, 2007) data requirements for conventional 

pesticides (72 FR 60934; USEPA 2007d). The new Part 158 data requirements specify that acute 

avian oral toxicity data be submitted for either a mallard duck or bobwhite quail and a passerine 

species. Therefore, an avian oral toxicity test (OCSPP Guideline 850.2100) is required for 

passerine birds, as specified in 40 CFR Part 158 (Oct. 26, 2007). EFED recommends that the 

Pesticide Re-evaluation Division (PRD) request submission of a passerine study protocol for 

review by the Agency prior to initiation of this study. If oral acute toxicity data are not 

submitted for passerines, EFED will assume acute risk for passerine species.

Studies submitted for terrestrial plants were originally categorized as acceptable, but later 

downgraded to supplemental since they were conducted using TGAI, rather than TEP. Since 

guidelines specify the use of TEP, all plant species tested should be retested using TEP. 

After evaluation of the available data for carfentrazone-ethyl, the effects data gaps for 

registration review are (additional information is in Appendix C):

Guideline Number: 850.1025, Oyster acute toxicity with carfentrazone acid.

Guideline Number: 850.1075, Fish acute toxicity (saltwater) with carfentrazone acid.

Guideline Number: Both 850.1300 and 850.1350, Aquatic Invertebrate Life Cycle 

Toxicity (freshwater and estuarine/marine) with carfentrazone acid.

Guideline Number: 850.1400, Early Life-Stage Toxicity (saltwater fish) with 

carfentrazone acid.
44

Guideline Number: 850.1400 Using Modified Protocol for Light-Dependent 

Peroxidizing Herbicide (LDPH) ELS Toxicity (freshwater fish) with TGAI.

Guideline Number: 850.1500, Full Life Cycle Fish Test (freshwater) with

carfentrazone acid.

Guideline Numbers: 850.1735 and 850.1740, Acute Whole Sediment Toxicity with 

TGAI (freshwater and saltwater).

Guideline Number: 850.2100, Study Title: Acute Avian Oral Toxicity Test using a 

Passerine species with TGAI.

Guideline Numbers: 850.4100 and 850.4150, Tier 2 Seedling Emergence and 

Vegetative Vigor with TEP.

Additional information can be found in Appendix C.

8. References

Di Toro, D. M., Zarba, C. S., Hansen, D. J., Berry, W. J., Schwartz, R. C., Cowan, C. E. 1991. Technical basis for 

establishing sediment quality criteria for nonionic organic chemicals using equilibrium partitioning. 

Environmental Toxicology and Chemistry, 10, 1541-1586.

European Commission. 2003. Review report for the active substance carfentrazone-ethyl. European Commission, 

Health & Consumer Protection Directorate-General. April 10, 2003. Online at: 

http://ec.europa.eu/food/plant/protection/evaluation/newactive/list1-19_en.pdf

Kemikalieinspektionen (Swedish Chemicals Agency). 2008. Sammanställning av protokoll om riktvärden för 

växtskyddsmedel i ytvatten (Summary of minutes on benchmarks for pesticides in surface water). 

Kemikalieinspektionen, Bekämpningsmedel och biotekniska produkter. April 29, 2008. Online at: 

http://www.kemi.se/upload/Bekampningsmedel/Vaxtskyddsmedel/Protokoll_riktvarden_vaxtskyddsmedel.

pdf

Krijt, J., Stranska, P., Sanitrak, J., Chlumska, A., and Fakan, F. 1999. Liver preneoplastic changes in mice treated 

with the herbicide fomesafen. Hum. Exp. Toxicol. 18: 338-344. (EcoReference No.: 95400)

Smith L.L. and C.R. Elcombe. 1989. Mechanistic studies and their role in the toxicological evaluation of pesticides. 

Food Addit. Contam. 6 Suppl. 1, pp. S57-S65.

Urban, J.D., and N.J. Cook. 1986. Ecological Risk Assessment: Standard Evaluation Procedures. Report No. EPA 

540/9-85-001. U.S. Environmental Protection Agency, Hazard Evaluation Division, Washington, D.C. 

Available from NTIS (National Technical Information Service), Springfield, Virginia 22161, as PB 86-247-

657. 

U.S. Environmental Protection Agency (USEPA). 1998. Guidelines for Ecological Risk Assessment, United States 

Environmental Protection Agency, Washington, D.C.: Government Printing Office. Available at 

http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid=12460 (Accessed June 19, 2009).

USEPA. 1998a. Carfentrazone-ethyl: Metabolism Assessment Review Committee (MARC) Memorandum. 

PP#7F4795. U.S. Environmental Protection Agency, Office of Pesticide Programs, Health Effects 

Division. Jun. 19, 1998. 

USEPA. 2004. Overview of the Ecological Risk Assessment Process in the Office of Pesticide Programs, United 

States Environmental Protection Agency, Washington, D.C.: Government Printing Office. Available at 

http://www.epa.gov/espp/consultation/ecorisk-overview.pdf (Accessed June 19, 2009).
45

USEPA. 2010. Screening Level Usage Analysis (SLUA): Carfentrazone-ethyl (128712). U.S. Environmental 

Protection Agency, Office of Chemical Safety and Pollution Prevention, Biological and Economic Analysis 

Division. Jul. 21, 2010.

USEPA. 2011. Orrick, G. Carfentrazone-ethyl: Drinking Water Exposure Assessment of Proposed Label 

Amendments for Use on Rice. DP barcode 384371. U.S. Environmental Protection Agency, Office of 

Chemical Safety and Pollution Prevention, Environmental Fate and Effects Division. Memorandum to 

Health Effects Division and Registration Division. Feb. 16, 2011.

U.S. Fisheries and Wildlife Service and National Marine Fisheries Service (USFWS/NMFS). 1998. Endangered 

Species Consultation Handbook: Procedures for Conducting Consultation and Conference Activities Under 

Section 7 of the Endangered Species Act. Final Draft, United States Fish and Wildlife Service (USFWS) 

and National Marine Fisheries Service (NMFS), Washington, D.C.: Government Printing Office. Available 

at http://www.fws.gov/endangered/consultations/s7hndbk/s7hndbk.htm (Accessed June 19, 2009).

U.S. Fisheries and Wildlife Service, National Marine Fisheries Service and National Oceanic and Atmospheric 

Administration (USFWS/NMFS/NOAA). 2004. 50 CFR Part 402. Joint Counterpart Endangered Species 

Act Section 7 Consultation Regulations; Final Rule. Federal Register Volume 69, Number 20, Pages 

47731-47762. August 5, 2004.

U.S. Geological Survey (USGS). 2010. 2002 Pesticide Use Maps. U.S. Geological Survey, National WaterQuality Assessment (NAWQA) Program, Pesticide National Synthesis Program. Accessed on Dec. 14, 

2010. Online at: http://water.usgs.gov/nawqa/pnsp/usage/maps/compound_listing.php?year=02

SUBMITTED ENVIRONMENTAL FATE STUDIES

MRID

43189231

Citation

Willut, J. (1993) Hydrolysis of F8426 at 25 degree C: Revised Report: Lab Project Number: 

842E1193E1: P/2887. Unpublished study prepared by FMC Corp. 59 p.

43189232 Goodyear, A. (1994) (Carbon 14) F8426: Aerobic Soil Metabolism and Degradation: Final Interim 

Report: Lab Project Number: 573/2: 573/ 2/1015: PC/0197. Unpublished study prepared by Hazleton 

Europe. 152 p.

43189233 Voelkl, S. (1994) Adsorption/Desorption of (carbon 14)-F8426- Chloropropionic Acid on Five Soils: 

Lab Project Number: 346173: 842I3293E1: PC/0202. Unpublished study prepared by RCC 

Umweltchemie AG. 166 p.

44165002 Wenger, K. (1996) F8426 Technical: Analytical Method Validation in Filtered and Unfiltered 

Saltwater: Lab Project Number: V96-0046: J9602001D: FMC/SWMV/F8426. Unpublished study 

prepared by Toxikon Environmental Sciences. 32 p.

44165031 Willut, J. (1994) Photodegradation of (carbon 14)-F8426 in Buffered Aqueous Solution at pH 5 by 

Artificial Sunlight: Revised: Lab Project Number: P-2884: 842E1293E1. Unpublished study prepared 

by FMC Corp. 133 p.

44165032 Willut, J. (1995) Photodegradation of (carbon 14)-F8426-chloropropionic Acid in Buffered Aqueous 

Solution by Simulated Sunlight: Lab Project Number: P-3051: 842E1294E1. Unpublished study 

prepared by FMC Corp. 175 p.

44165033 Willut, J. (1994) Photodegradation of (carbon 14)-F8426 in Soil by Simulated Sunlight: Lab Project 

Number: P-2915: 842E1393E1. Unpublished study prepared by FMC Corp. 64 p.

44165034 Goodyear, A. (1995) (Carbon 14)-F8426: Aerobic Soil Metabolism and Degradation: Final Report: Lab 

Project Number: PC-0227: 842I2193E1: 573/2. Unpublished study prepared by Corning Hazleton 

Europe. 241 p.
46

44165035 Goodyear, A. (1995) (Carbon 14)-F8426: Anaerobic Soil Metabolism and Degradation: Final Report: 

Lab Project Number: PC-0241: 842I2594E1: 573/4. Unpublished study prepared by Corning Hazleton 

Europe. 128 p.

44165036 Gravelle, W. (1995) Adsorption/Desorption of (carbon 14)-F8426-benzoic Acid, (carbon 14)-F8426-

cinnamic Acid, and (carbon 14)-F8426-propionic Acid on Five Soils: Lab Project Number: P-3070: 

842I3295E1. Unpublished study prepared by FMC Corp. 127 p.

44165037 Varanyak, L. (1996) Adsorption/Desorption of (carbon 14)-F8426-benzoic Acid on Five Soils: Lab 

Project Number: P-3139: 842E3296E1. Unpublished study prepared by FMC Corp. 80 p.

44165038 Voelkl, S.; Morgenroth, U. (1995) Leaching Characteristics of Aged Residues of (carbon 14)-F8426 in 

Five Soils under Laboratory Conditions: Lab Project Number: PC-0210: 842I3193E1: 345284. 

Unpublished study prepared by RCC Umweltchemie AG. 223 p.

44165039 Jang, D. (1996) Terrestrial Field Dissipation--Carfentrazone-ethyl (F8426) 50 DF Herbicide: Lab 

Project Number: RAN-0270: 842E4194E1. Unpublished study prepared by FMC Corp. 286 p.

44165040 Jang, D. (1996) Analytical Methodology for the Determination of Carfentrazone-ethyl (F8426) and Its 

Metabolites in/on Bare Soil: Lab Project Number: RAN-0270M: 842E4194E1. Unpublished study 

prepared by FMC Corp. 101 p.

44165042 Schocken, M. (1995) F8426 Flow-Through Bioconcentration and Metabolism Study with Rainbow 

Trout (Oncorhynchus mykiss)...: Final Report: Lab Project Number: PC-0236: 94-8-5403: 

842E5493E1. Unpublished study prepared by Springborn Labs, Inc. 179 p.

44165043 Bixler, T. (1996) Independent Method Validation: Determination of F8426 and Its Metabolites in/on 

Soil: Lab Project Number: RC-0058: 842MVL96R1: A005.005. Unpublished study prepared by Maxim 

Technologies, Inc. 87 p.

44165049 Starner, K. (1996) Cold Storage Stability of Significant F8426 Environmental Degradates on Soil: 

F8426-propionic Acid, F8426-cinnamic Acid, F8426-benzoic Acid, and F8426-chloropropionic Acid: 

Lab Project Number: RAN-0285: 842CSS95R1. Unpublished study prepared by FMC Corp. 104 p.

44419016 Elmarakby, S. (1997) Aerobic Aquatic Metabolism of (carbon 14)-F8426: Lab Project Number: 

842E2296E1: P-3266: F97092-801. Unpublished study prepared by FMC Corp. 194 p.

44419017 Schreier, T. (1997) Terrestrial Field Dissipation--F8426 50 DF Herbicide: Lab Project Number: 

842E4195E1: RAN-0301. Unpublished study prepared by FMC Corp. 183 p.

44419018 Hubbard, H. (1997) Analytical Methodology for the Determination of Carfentrazone-Ethyl and its 

Metabolites on Soil: Lab Project Number: RAN-0301M: 842E4195E1. Unpublished study prepared by 

FMC Corp. 49 p.

44419019 Summer, S.; Saxena, A. (1997) Carfentrazone-ethyl (F8426) Herbicide--Aquatic Field Dissipation: Lab 

Project Number: N002159A: 842E4296E1: PC-0281. Unpublished study prepared by Battelle. 185 p.

44633504 George, M. (1997) Aerobic Soil Degradation of the F8426 Acid Metabolites, F8426-chloropropionic 

acid, F8426-propionic acid, F8426-cinnamic acid, and F8426-benzoic acid: Lab Project Number: 

842I2195E1: RAN-0276: 540W. Unpublished study prepared by FMC Corporation and PTRL West. 

219 p.

44654701 Holihan, J. (1998) F8426 40 DF Herbicide-Aquatic Field Dissipation: Lab Project Number: 

842E4297E1: P-3311. Unpublished study prepared by FMC Corporation. 150 p.

44934201 Concha, M. (1999) Photodegradation of (carbon-14)F8426 in Buffered Aqueous Solution at pH 5 under 

Artificial Light: Lab Project Number: 832W: 842E1299E1: PC-0294. Unpublished study prepared by 

PTRL West, Inc. 128 p.
47

46253901 Dow, K. (2004) F8426 Aquatic Herbicide Dissipation Following Treatment of a Pond. Project Number: 

842E4203E1, P/3657. Unpublished study prepared by FMC Corp. and NDR Research and Stone 

Environmental, Inc. 129 p.

SUBMITTED EFFECTS STUDIES CITED (See Appendix A for eco citations)

43189207

43189225

43189226

43189227

43189228

43189230

43829717

43849603

43849604

43849605

43849606

43892716

43939204

44165003

44165004

44165005

44165006

44165007

44165008

44165009

44165010

44165011

44165012

44165013

44165014

44165015

44165015

44165016

44165017

44165026

44176101

44176102

44176103

44176104

44176105

44176108

44409007

44419002

44419003

44419005

44419006

44419007

44419008

44419009

44424201

44633502

44963201

46037001

Mammalian Studies Cited:

44165026 Barton, S. (1994) F8426: Dose Range Finding Reproduction Study in Rats: Revised Final Report: Lab 

Project Number: A93-3759: 490835: 11056. Unpublished study prepared by Inveresk Research 

International. 162 p. 

43189207 Freeman, C. (1994) Acute Oral Toxicity Study in Rats: F8426 Technical: Lab Project Number: 

A92/3632. Unpublished study prepared by FMC Corp. 26 p. 
48

APPENDIX A: Carfentrazone-ethyl Eco Effects Bibliography

71-1 Avian Single Dose Oral Toxicity

MRID Citation Reference

43189225 2013852 Campbell, S.; Beavers, J. (1994) F8426 Technical: An Acute Oral Toxicity 

Study with the Northern Bobwhite: Lab Project Number: 104/175: A93/3769. 

Unpublished study prepared by Wildlife International Ltd. 18 p. 

71-2 Avian Dietary Toxicity

MRID Citation Reference

43189226 2013850 Campbell, S.; Beavers, J. (1994) F8426 Technical: An Dietary LC50 Study 

with the Northern Bobwhite: Lab Project Number: 104/ 173: A93/3770. 

Unpublished study prepared by Wildlife International Ltd. 35 p. 

43189227 2013851 Campbell, S.; Beavers, J. (1994) F8426 Technical: A Dietary LC50 Study with 

the Mallard: Lab Project Number: A93/3768: 104/174. Unpublished study 

prepared by Wildlife International Ltd. 36 p. 

71-4 Avian Reproduction

MRID Citation Reference

44419002 2013839 Pedersen, C. (1997) Avian Reproductive Toxicity Study with F8426 Technical 

in Bobwhite Quail: Lab Project Number: 112-013-07: A96-4402: 112S39A-2. 

Unpublished study prepared by Bio-Life Associates, Ltd. 459 p. 

44419003 2013835 Pedersen, C. (1997) Avian Reproductive Toxicity Study with F8426 Technical 

in Mallard Ducks: Lab Project Number: 112-014-08: A96-4403: 112S40. 

Unpublished study prepared by Bio-Life Associates, Ltd. 539 p. 

72-1 Acute Toxicity to Freshwater Fish

MRID Citation Reference

43189228 2082306 Sword, M.; Bucksath, J.; Bussard, J. (1994) Acute Flow-Through Toxicity of 

F8426 Technical to Rainbow Trout (Oncorhynchus mykiss): Final Report: Lab 

Project Number: A93/3758: 40960. Unpublished study prepared by ABC Lab., 

Inc. 240 p. 

43189229 2082307 Sword, M.; Bucksath, J.; Bussard, J.; et al. (1994) Acute Flow-Through 

Toxicity of F8426 Technical to Bluegill (Lepomis macrochirus): Final Report: 

Lab Project Number: 40961: A93/3757. Unpublished study prepared by ABC 

Lab., Inc. 191 p. 
49

44165009 2013828 Ward, T.; Magazu, J.; Boeri, R. (1995) Acute Toxicity of F8426-Benzoic Acid 

to the Rainbow Trout, Oncorhynchus mykiss: (Final Report): Lab Project 

Number: A95-4210: 786-FM. Unpublished study prepared by T. R. Wilbury 

Labs, Inc. 35 p. 

44165013 2034176 Ward, T.; Kowalski, P.; Boeri, R. (1995) Acute Toxicity of F8426-Propionic 

Acid to the Rainbow Trout, Oncorhynchus mykiss: (Final Report): Lab Project 

Number: A95-4214: 789-FM. Unpublished study prepared by T. R. Wilbury 

Labs, Inc. 35 p. 

44165015 2013830 Ward, T.; Kowalski, P.; Boeri, R. (1995) Acute Toxicity of F8426-

Chloropropionic Acid to the Rainbow Trout, Oncorhynchus mykiss: (Final 

Report): Lab Project Number: A95-4216: 782-FM. Unpublished study prepared 

by T. R. Wilbury Labs, Inc. 35 p. 

44176105 2013819

2013823

Cunningham, F. (1995) F8426-Cinnamic Acid: Acute Toxicity to Rainbow 

Trout, Oncorhynchus mykiss, Under Static Test Conditions: Lab Project 

Number: A95-4222: J9506003B: FMC/E103. Unpublished study prepared by 

Toxikon Environmental Sciences. 45 p. 

72-2 Acute Toxicity to Freshwater Invertebrates

MRID Citation Reference

43189230 2013849 Hicks, S.; Murrell, H.; Bucksath, J. (1994) Acute Flow-Through Toxicity of 

F8426 Technical to Daphnia magna: Final Report: Lab Project Number: 40962: 

A93/3800. Unpublished study prepared by ABC Lab., Inc. 292 p. 

44165007 2013821 Ward, T.; Magazu, J.; Boeri, R. (1995) Acute Toxicity of F8426-Benzoic Acid 

to the Daphnid, Daphnia magna: (Final Report): Lab Project Number: A95-

4208: 785-FM. Unpublished study prepared by T. R. Wilbury Labs, Inc. 36 p. 

44165011 2013822 Ward, T.; Kowalski, P.; Boeri, R. (1995) Acute Toxicity of F8426-Propionic 

Acid to the Daphnid, Daphnia magna: (Final Report): Lab Project Number: 

A95-4212: 788-FM. Unpublished study prepared by T. R. Wilbury Labs, Inc. 

37 p. 

44165016 2013818 Ward, T.; Kowalski, P.; Boeri, R. (1995) Acute Toxicity of F8426-

Chloropropionic Acid to the Daphnid, Daphnia magna: (Final Report): Lab 

Project Number: A95-4217: 781-FM. Unpublished study prepared by T. R. 

Wilbury Labs, Inc. 35 p. 

44176103 2013832 Cunningham, F. (1995) F8426-Cinnamic Acid: Acute Toxicity to the Water 

Flea, Daphnia magna, Under Static Test Conditions: Lab Project Number: A95-

4220: J9506003A: FMC/E101. Unpublished study prepared by Toxikon 

Environmental Sciences. 44 p. 

45168001 Mixture Samel, A. (2000) Carfentrazone Ethyl/Metsulfuron Methyl (DPX-KW025) 

50 WG (4:1): Static, Acute, 48-Hour, Toxicity Test to Daphnia magna: Lab 

Project Number: 13204: 241: DUPONT-4145. Unpublished study prepared by 

E.I. du Pont de Nemours and Company. 38 p. 
50

72-3 Acute Toxicity to Estuarine/Marine Organisms

MRID Citation Reference

44165003 2013824 Dunham, M.; Cunningham, F. (1996) F8426 Technical: Acute Toxicity to the 

Mysid (Mysidopsis bahia) Under Flow-Through Test Conditions: (Final 

Report): Lab Project Number: A96-4377: J9602001A: 

FMC/F8426/MYSIDOPSIS BAHIA/FT ACUTE. Unpublished study prepared 

by Toxikon Environmental Sciences. 45 p. 

44165004 2013825 Cunningham, F. (1996) F8426 Technical: Acute Effects on New Shell Growth 

of the Eastern Oyster (Crassostrea virginica): (Final Report): Lab Project 

Number: A96-4378: J9602001C: FMC/F8426/OYSTER/GROWTH. 

Unpublished study prepared by Toxikon Environmental Sciences. 46 p. 

44165005 2013826 Dunham, M.; Cunningham, F. (1996) F8426 Technical: Acute Toxicity to the 

Tidewater Silverside (Menidia beryllina) Under Flow-Through Conditions: 

(Final Report): Lab Project Number: A96-4376: J9602001B: 

FMC/F8426/MENIDIA BERYLLINA/FT ACUTE. Unpublished study 

prepared by Toxikon Environmental Sciences. 45 p. 

72-4 or 850-1400 Fish Early Life Stage/Aquatic Invertebrate Life Cycle 

Study

MRID Citation Reference

44419006 2013838

2013840

Knacker, T.; Schallnas, H.; Weidenauer, M. (1992) A Study on the Chronic 

Toxicity of F8426 Technical to Daphnia magna: Lab Project Number: A96-

4547: 91186-FMC: A-17-95-35. Unpublished study prepared by ECT 

Oekotoxikologie GmbH and Battelle. 148 p. 

44424201 2013834

2034173

Liu, H.; Kranzfelder, J.; Groetsch, K. (1997) Carfentrazone-ethyl (F8426) 

Technical: Toxicity to Embryos and Larvae of the Rainbow Trout, 

Oncorhynchus mykiss, Under Flow-Through Test Conditions: Lab Project 

Number: A96-4528: J9609004A: FMC/F8426/RT ELS. Unpublished study 

prepared by Toxikon Environmental Sciences. 121 p. 

44963201 2013845 Ellenberg, W.; Rielly, P.; Glover, S. (1999) Carfentrazone-ethyl (F8426) 

Technical: Toxicity to Embryos and Larvae of the Rainbow Trout, 

Oncorhynchus mykiss, Under Flow-Through Conditions: Lab Project Number: 

99J0001: A99-4961: FMC/F8426/RT ELS. Unpublished study prepared by 

Toxikon Corporation. 148 p. 

46037001 2016951 Ross, T.; Kendall, T.; Krueger, H. (2003) F8426: An Early Life-Stage Toxicity 

Test with the Rainbow Trout (Oncorhynchus mykiss) Under Ultraviolet Light 

Conditions: Final Report. Project Number: 104A/107, A2001/5397. 

Unpublished study prepared by Wildlife International, Ltd. 72 p.
51

122-2 Aquatic plant growth

MRID Citation Reference

44419004 2013836 Ward, T.; Kowalski, P.; Boeri, R. (1997) Growth and Reproduction Toxicity 

Test with F8426 Cinnamic Acid and the Freshwater Alga, Selenastrum 

capricornutum: Lab Project Number: A96-4468: 1068-FM. Unpublished study 

prepared by T.R. Wilbury Labs., Inc. 41 p. 

123-1 Seed germination/seedling emergence and vegitative vigor

MRID Citation Reference

43829716 2034151 Feutz, E. (1994) Evaluating the Effects of F8426 on the Germination, 

Emergence, and Vegetative Vigor of Non-Target Terrestrial Plants: Final 

Report: Lab Project Number: 41031: PC-0209: 842E7393E1. Unpublished 

study prepared by ABC Labs, Inc. 365 p. 

43939204 2013858 Feutz, E. (1996) Evaluating the Effects of F8426 on the Germination, 

Emergence, and Vegetative Vigor of Non-Target Terrestrial Plants: Supplement 

to Final Report: Lab Project Number: 41031: 842E7393E1: PC-0209. 

Unpublished study prepared by ABC Labs, Inc. 253 p. 

123-2 Aquatic plant growth

MRID Citation Reference

43829717 2013856 Hicks, S.; Bussard, J. (1994) Acute Toxicity of F8426 Technical to 

Selenastrum capricornutum Printz: Final Report: Lab Project Number: 40964: 

A93-3801. Unpublished study prepared by ABC Labs, Inc. 397 p. 

43849603 2013857 Forbis, A.; Ziegler, T.; Veltri, J. (1995) Acute Toxicity of F8426 Technical to 

Lemna gibba G3: Final Report: Lab Project Number: 42391: A94-4112: ABC 

42391. Unpublished study prepared by ABC Labs, Inc. 85 p. 

43849604 2013855 Forbis, A.; Ziegler, T.; Bucksath, J. (1995) Acute Toxicity of F8426 Technical 

to Skeletonema costatum: Final Report: Lab Project Number: 42388: A94-

4113: ABC 42388. Unpublished study prepared by ABC Labs, Inc. 82 p. 

43849605 2013853 Forbis, A.; Ziegler, T.; Bucksath, J. (1995) Acute Toxicity of F8426 Technical 

to Navicula pelliculosa Final Report: Lab Project Number: 42389: A94-4114: 

ABC 42389. Unpublished study prepared by ABC Labs, Inc. 82 p. 

43849606 2013854 Forbis, A.; Ziegler, T.; Bucksath, J. (1995) Acute Toxicity of F8426 Technical 

to Anabaena flos-aquae Final Report: Lab Project Number: 42390: A94-4115: 

ABC 42390. Unpublished study prepared by ABC Labs, Inc. 81 p. 

44165006 2013820 Ward, T.; Magazu, J.; Boeri, R. (1995) Acute Toxicity of F8426-Benzoic Acid 

to the Freshwater Alga, Selenastrum capricornutum: (Final Report): Lab 

Project Number: A95-4140: 708-FM. Unpublished study prepared by T. R. 

Wilbury Labs, Inc. 38 p. 
52

44165010 2013829 Ward, T.; Kowalski, P.; Boeri, R. (1995) Acute Toxicity of F8426-Propionic 

Acid to the Freshwater Alga, Selenastrum capricornutum: (Final Report): Lab 

Project Number: A95-4211: 790-FM. Unpublished study prepared by T. R. 

Wilbury Labs, Inc. 38 p. 

44165014 2014020 Ward, T.; Kowalski, P.; Boeri, R. (1995) Acute Toxicity of F8426-

Chloropropionic Acid to the Freshwater Alga, Selenastrum capricornutum: 

(Final Report): Lab Project Number: A95-4215: 783-FM. Unpublished study 

prepared by T. R. Wilbury Labs, Inc. 38 p. 

44176102 2013817 Cunningham, F. (1995) F8426-Cinnamic Acid: Toxicity to the Freshwater 

Green Alga, Selenastrum capricornutum, Under Static Test Conditions: Lab 

Project Number: A95-4219: J9506003C: FMC/E106.9. Unpublished study 

prepared by Toxikon Environmental Sciences. 52 p. 

44419005 2013837 Ward, T.; Kowalski, P.; Boeri, R. (1997) Growth and Reproduction Toxicity 

Test with F8426 Technical and the Freshwater Alga, Selenastrum 

capricornutum: Lab Project Number: A96-4496: 1069-FM. Unpublished study 

prepared by T.R. Wilbury Labs., Inc. 41 p. 

45626901 Hahne, R.; Koch, D.; Jackson-Gheissani, A. (2002) Toxicity of a Mixture of 

Parent (F8426 Technical) and Two Metabolites to Duckweed, Lemna gibba G3, 

Determined Under Static Test Conditions: Lab Project Number: 47254: A2002-

5498. Unpublished study prepared by ABC Laboratories, Inc. 59 p. 

141-1 Honey bee acute contact

MRID Citation Reference

44176108 2013827 Beech, P. (1995) Carfentrazone (F8426): A Determination of Topical and Oral 

LD50s for the Honey Bee, Apis mellifera: Lab Project Number: FMC-95-1: 

842AF95304. Unpublished study prepared by Agrochemical Evaluation Unit. 

21 p. 

44633502 2013843 Liu, H.; Kranzfelder, J. (1998) F8426: Honey Bee Acute Contact LD50: Lab 

Project Number: J9710009: A97-4748: F605. Unpublished study prepared by 

Toxikon Environmental Sciences. 30 p. 

Non Guideline Selections

44165002 Analytical 

Method 

Validation

Wenger, K. (1996) F8426 Technical: Analytical Method Validation in Filtered 

and Unfiltered Saltwater: Lab Project Number: V96-0046: J9602001D: 

FMC/SWMV/F8426. Unpublished study prepared by Toxikon Environmental 

Sciences. 32 p. 

44165008 2036868 Ward, T.; Magazu, J.; Boeri, R. (1995) Acute Toxicity of F8426-Benzoic Acid 

to the Earthworm, Eisenia foetida: (Final Report): Lab Project Number: A95-

4209: 784-FM. Unpublished study prepared by T. R. Wilbury Labs, Inc. 32 p. 

44165012 2036870 Ward, T.; Kowalski, P.; Boeri, R. (1995) Acute Toxicity of F8426-Propionic 

Acid to the Earthworm, Eisenia foetida: (Final Report): Lab Project Number: 

A95-4213: 787-FM. Unpublished study prepared by T. R. Wilbury Labs, Inc. 

31 p. 
53

44165017 2036871 Ward, T.; Kowalski, P.; Boeri, R. (1995) Acute Toxicity of F8426-

Chloropropionic Acid to the Earthworm, Eisenia foetida: (Final Report): Lab 

Project Number: A95-4218: 780-FM. Unpublished study prepared by T. R. 

Wilbury Labs, Inc. 31 p. 

44176101 2036867 Sword, M.; Bucksath, J.; Bussard, J. (1994) 14-Day Toxicity of F8426 

Technical to the Earthworm, Eisenia foetida: Final Report: Lab Project 

Number: 40963: A93-3802: 040963. Unpublished study prepared by ABC 

Labs., Inc. 236 p. 

44176104 2036869 Aufderheide, J.; Kranzfelder, J. (1995) F8426-Cinnamic Acid: Acute Toxicity 

to the Earthworm, Eisenia foetida (Soil Test): Lab Project Number: A95-4221: 

J9506003D: J9506003D/FMC A95-42. Unpublished study prepared by 

Toxikon Environmental Sciences. 37 p. 

44419007 Ward, T.; Magazu, J.; Boeri, R. (1997) Acute Toxicity of F8426--

Chloropropionic Acid to the Earthworm, Eisenia foetida: Report Addendum: 

Lab Project Number: A95-4218-01: 780-FM. Unpublished study prepared by 

T.R. Wilbury Labs., Inc. 15 p. 

44419008 Ward, T.; Magazu, J.; Boeri, R. (1997) Acute Toxicity of F8426--Propionic 

Acid to the Earthworm, Eisenia foetida: Report Addendum: Lab Project 

Number: A95-4213-01: 787-FM. Unpublished study prepared by T.R. Wilbury 

Labs., Inc. 15 p. 

44419009 Ward, T.; Magazu, J.; Boeri, R. (1997) Acute Toxicity of F8426--Benzoic Acid 

to the Earthworm, Eisenia foetida: Report Addendum: Lab Project Number: 

A95-4209-01: 784-FM. Unpublished study prepared by T.R. Wilbury Labs., 

Inc. 15 p. 

45902901 Herrick, R. (2003) Efficacy of F-8426 Aquatic Herbicide for Aquatic Weed 

Control: Lab Project Number: PDM-037-03. Unpublished study prepared by 

FMC Corporation. 33 p. {OPPTS 810.1000} 

45902903 Jackson-Gheissari, A. (2003) Ecological Exposure and Risk Assessment for 

Aquatic Applications of Carfentrazone-Ethyl: Lab Project Number: A2003-

5602. Unpublished study prepared by FMC Corporation. 37 p. 

45902904 Keifer, D. (2003) Application of F8426 and F8426-Chloropropionic Acid to 

Plant Foliage in Irrigation Water: Lab Project Number: P-3594: G030.202. 

Unpublished study prepared by FMC Corporation

46305703 Nissin-Meyer, S.; McCoy, E.; Holihan, J.; et. al. (2003) Ecological Exposure 

and Risk Assessment for the Use of Carfentrazone-Ethyl (F8426) Herbicide for 

Site Preparation. Project Number: A2003/5667. Unpublished study prepared by 

FMC Corp. Agricultural Products Group. 30 p.

46305704 Nissen-Meyer, S. (2004) Ecological Exposure and Risk Assessment for NonTarget Terrestrial, Semi-Aquatic, and Aquatic Plants from the Use of 

Carfentrazone ROW Herbicide. Project Number: P/3713. Unpublished study 

prepared by FMC Corp. Agricultural Products Group. 30 p.
54

APPENDIX B: Environmental Degradates of Carfentrazone-ethyl.

TABLE B1. Carfentrazone-ethyl and Its Major Environmental Degradates.

Code Name/ 

Synonym

Chemical Name Chemical Structure Study Type Maximum 

%AR (day)

Final %AR 

(study length)

PARENT COMPOUND

Carfentrazoneethyl

F8426

FMC 116426

Ethyl α,2-dichloro-5-[4-

(difluoromethyl)-4,5-dihydro-3-

methyl-5-oxo-1H-1,2,4-triazol-1-

yl]-4-fluorobenzenepropanoate

CAS No.: 128639-02-1

Formula: C15H14Cl2F3N3O3

MW: 412.20 g/mol

Cl F

Cl

O

O

N

N

N

O

F

F

Aerobic soil MRID 44165034

Aqueous photolysis MRID 44934201

Hydrolysis MRID 43189231

Aerobic aquatic MRID 44419016

Field studies MRID 44165039

MRID 44419017

MRID 44419019

MRID 46253901

TRANSFORMATION PRODUCTS

Carfentrazone

F8426-chloropropionic acid

F8426-Cl-PAc

FMC 124161

α,2-dichloro-5-[4-

(difluoromethyl)-4,5-dihydro-3-

methyl-5-oxo-1H-1,2,4-triazol-1-

yl]-4-fluorobenzenepropanoic acid

CAS No.: 128621-72-7

Formula: C13H10Cl2F3N3O3

MW: 384.14 g/mol

Cl F

Cl

O

OH

N

N

N

O

F

F

Aerobic soil 90% (1.3 d) n.d. A(365 d)

Aqueous photolysis not identified

Hydrolysis–pH 5

 –pH 7

 –pH 9

9.5% (30 d)

90.0% (30 d)

99.7% (14 d)

9.5% (30 d)

90.0% (30 d)

97.5% (30 d)

Aerobic aquatic 80% (1 d, 7 d) 59% (30 d)

Field studies

 Water:

 Sediment:

 Water:

 Sediment:

49 μg/L (1 d) n.d. A(356 d)

33 μg/L (0 d) n.d. A(178 d)

81 μg/L (0 d)

34 μg/kg (0 d)

n.d. A(80 d)

1-5 μg/kg (365 d)

6.8 μg/L (1 d)

1.9 μg/kg (30 d)

n.d. A(30 d)

1.9 μg/kg (30 d)

F8426-cinnamic 

acid

F8426-CAc

FMC 125151

2-chloro-5-[4-(difluoromethyl)-

4,5-dihydro-3-methyl-5-oxo-1H1,2,4-triazol-1-yl]-4-

fluorobenzenepropenoic acid

Formula: C13H9ClF3N3O3

MW: 347.68 g/mol

Cl F

O

OH

N

N

N

O

F

F

Aerobic soil 51% (33 d) 31% (365 d)

Aqueous photolysis not identified

Hydrolysis not identified

Aerobic aquatic 11% (21 d) 8.8% (30 d)

Field studies

 Water:

 Sediment:

5.0 μg/L (7 d) n.d. A(356 d)

6.1 μg/L (14 d) n.d. A(652 d)

5 μg/L (21 d)

10 μg/kg (1 d)

n.d. A(80 d)

1-5 μg/kg (365 d)

not analyzed
55

Code Name/ 

Synonym

Chemical Name Chemical Structure Study Type Maximum 

%AR (day)

Final %AR 

(study length)

F8426-propionic 

acid

F8426-PAc

FMC 125165

2-chloro-5-[4-(difluoromethyl)-

4,5-dihydro-3-methyl-5-oxo-1H1,2,4-triazol-1-yl]-4-

fluorobenzenepropanoic acid

Formula: C13H11ClF3N3O3

MW: 349.70 g/mol

Cl F

O

OH

N

N

N

O

F

F

Aerobic soil 23% (270 d) 20% (365 d)

Aqueous photolysis not identified

Hydrolysis not identified

Aerobic aquatic 16% (30 d) 16% (30 d)

Field studies

 Water:

 Sediment:

6.2 μg/L (14 d) n.d. A(356 d)

3.7 μg/L (14 d) n.d. A(178 d)

9 μg/L (7 d)

11 μg/kg (7 d)

n.d. A(80 d)

1-5 μg/kg (365 d)

not analyzed

F8426-benzoic 

acid

F8426-BAc

FMC 97083

2-chloro-5-[4-(difluoromethyl)-

4,5-dihydro-3-methyl-5-oxo-1H1,2,4-triazol-1-yl]-4-fluorobenzoic 

acid

Formula: C11H7ClF3N3O3

MW: 321.64 g/mol

Cl F

N

N

N

O

F

O F

OH

Aerobic soil 22% (365 d) 22% (365 d)

Aqueous photolysis not identified

Hydrolysis not identified

Aerobic aquatic 3.6% (30 d) 3.6% (30 d)

Field studies

 Water:

 Sediment:

14 μg/L (14 d) n.d. A(356 d)

5.4 μg/L (21 d) n.d. A(178 d)

n.d. A

1-5 μg/kg (0 d)

n.d. A(80 d)

n.d. A(365 d)

not analyzed

α,2,4-trihydroxyF8426

Ethyl α,2,4-trihydroxy-5-[4-

(difluoromethyl)-4,5-dihydro-3-

methyl-5-oxo-1H-1,2,4-triazol-1-

yl]-benzenepropanoate

Formula: C15H17F2N3O6

MW: 373.32 g/mol

HO OH

OH

O

O

N

N

N

O

F

F

Aerobic soil not identified

Aqueous photolysis 18% (15 d) 18% (15 d)

Hydrolysis not identified

Aerobic aquatic not identified

Field studies not analyzed

α-hydroxy-F8426 Ethyl α-hydroxy-2-dichloro-5-[4-

(difluoromethyl)-4,5-dihydro-3-

methyl-5-oxo-1H-1,2,4-triazol-1-

yl]-4-fluorobenzenepropanoate

Formula: C15H15ClF3N3O4

MW: 393.75 g/mol

Cl F

OH

O

O

N

N

N

O

F

F

Aerobic soil not identified

Aqueous photolysis 12% (8 d) 2.8% (15 d)

Hydrolysis not identified

Aerobic aquatic not identified

Field studies not analyzed
56

Code Name/ 

Synonym

Chemical Name Chemical Structure Study Type Maximum 

%AR (day)

Final %AR 

(study length)

α-hydroxymethyl2,4-dihydroxyF8426

Ethyl α-hydroxymethyl-2,4-

dihydroxy-5-[4-(difluoromethyl)-

4,5-dihydro-3-methyl-5-oxo-1H1,2,4-triazol-1-yl]-

benzeneethanoate

Formula: C15H17F2N3O6

MW: 373.32 g/mol

HO OH

O O

N

N

N

O

F

F HO

Aerobic soil not identified

Aqueous photolysis 15% (15 d) 15% (15 d)

Hydrolysis not identified

Aerobic aquatic not identified

Field studies not analyzed

3-hydroxymethylF8426-

chloropropionic 

acid

3-hydroxymethylcarfentrazone

α,2-dichloro-5-[4-

(difluoromethyl)-4,5-dihydro-3-

hydroxymethyl-5-oxo-1H-1,2,4-

triazol-1-yl]-4-

fluorobenzenepropanoic acid

Formula: C13H10Cl2F3N3O4

MW: 400.14 g/mol

Cl F

Cl

O

OH

N

N

N

O

F

F

HO

Aerobic soil 9.1% (100 d) 7.9% (365 d)

Aqueous photolysis not identified

Hydrolysis not identified

Aerobic aquatic not identified

Field studies not analyzed

3-hydroxymethylF8426-cinnamic 

acid

2-chloro-5-[4-(difluoromethyl)-

4,5-dihydro-3-hydroxymethyl-5-

oxo-1H-1,2,4-triazol-1-yl]-4-

fluorobenzenepropenoic acid

Formula: C13H9ClF3N3O4

MW: 363.68 g/mol

Cl F

O

OH

N

N

N

O

F

F

HO

Aerobic soil 5.9% (365 d) 5.9% (365 d)

Aqueous photolysis not identified

Hydrolysis not identified

Aerobic aquatic not identified

Field studies not analyzed

3-hydroxymethylF8426-benzoic 

acid

FMC 125171

2-chloro-5-[4-(difluoromethyl)-

4,5-dihydro-3-hydroxymethyl-5-

oxo-1H-1,2,4-triazol-1-yl]-4-

fluorobenzoic acid

Formula: C11H7ClF3N3O4

MW: 337.64 g/mol

Cl F

N

N

N

O

F

O F

OH

HO

Aerobic soil 24% (365 d) 24% (365 d)

Aqueous photolysis not identified

Hydrolysis not identified

Aerobic aquatic not identified

Field studies

 Water:

 Sediment:

not analyzed

1.6 μg/L (44 d) n.d. A(178 d)

1-5 μg/L (3 d)

1-5 μg/kg (14 d)

n.d. A(80 d)

n.d. A(365 d)

not analyzed

Unknown 7 (unknown)

(unknown) Aerobic soil 18% (365 d) 18% (365 d)
57

Code Name/ 

Synonym

Chemical Name Chemical Structure Study Type Maximum 

%AR (day)

Final %AR 

(study length)

Carbon dioxide Carbon dioxide

Formula: CO2

MW: 44.1 g/mol

O O

Aerobic soil not analyzed

Aqueous photolysis 4.6% (15 d) 4.6% (15 d)

Hydrolysis not analyzed

Aerobic aquatic not analyzed

Volatile 

compounds

(not applicable)

(not applicable)

Aerobic soil 2.5% (365 d) 2.5% (365 d)

Aqueous photolysis n.d. A(15 d) n.d. A(15 d)

Hydrolysis not analyzed

Aerobic aquatic 0.4% (30 d) 0.4% (30 d)

Unextracted 

residues

(not applicable)

(not applicable)

Aerobic soil 40.3% (365 d) 40.3% (365 d)

Aerobic aquatic 6.1% (21 d) 4.2% (30 d)

A

 “n.d.” means “not detected.”
APPENDIX C: Data Call-In Tables.

The following proposed Data Call-in tables include rationales for requiring the data requested in 

this problem formulation, explanations of the utility of the data, and explanations for how the 

data might impact risk assessment, following the format provided by the Pesticide Re-evaluation

Division.

Guideline Number: 835.2240

Study Title: Photodegradation in Water (Degradate)

Rationale for Requiring the Data

The Agency has a limited understanding of how carfentrazone acid (degradate of carfentrazone-ethyl)

behaves in the environment once the parent compound is applied. Depending on how quickly, to what 

extent, and to which transformation products the compound degrades, carfentrazone acid may or may 

not pose potential exposure concern in water bodies.

Submitted data regarding photodegradation of carfentrazone acid in water (MRID 44165032) are not 

acceptable for risk assessment. The sterility of the samples was not determined during the study and 

material balances were poor in some samples, showing a pattern of decline over time.

In order to better understand the photodegradation of carfentrazone acid residues in water, the Agency is 

requiring an aqueous photolysis study of carfentrazone (rather than carfentrazone-ethyl) that fulfills the 

data requirement.

Practical Utility of the Data

How will the data be used?

Submission of an acceptable aqueous photolysis study will facilitate a better understanding of 

carfentrazone under irradiated, aqueous conditions. If data indicate that photolysis of dissolved residues 

of concern is rapid, then the Agency could potentially determine that carfentrazone residues of concern 

do not persist in water bodies in which photolysis occurs (i.e., clear, shallow water bodies). If data 

indicate that photolysis of dissolved residues of concern is not appreciable in water, then the Agency 

would rely on hydrolysis and aqueous biometabolism data to determine whether carfentrazone residues 

persist in water.

How could the data change the Agency’s decision, or impact the Agency’s future decisionmaking? 

In the absence of adequate aqueous photolysis data, carfentrazone residues in water will be assumed 

stable to photodegradation. If the required data indicate that carfentrazone residues in water are readily 

photolyzed, then risk assessment conclusions and associated labeled use precautions and/or restrictions 

could change.

Guideline Number: 835.4400

Study Title: Anaerobic Aquatic Metabolism

Rationale for Requiring the Data

The Agency has a limited understanding of how carfentrazone-ethyl behaves in anaerobic aquatic 

environments once applied. Depending on how quickly, to what extent, and to which transformation 

products the compound degrades, carfentrazone-ethyl may or may not pose potential exposure concern 

in water. Because carfentrazone-ethyl degradation in anaerobic surface water systems is not well 

understood, the Agency is requiring data.
59

Practical Utility of the Data

How will the data be used?

Anaerobic aquatic metabolism data will facilitate a better understanding of the fate of carfentrazoneethyl residues in water. If data indicate that degradation in anaerobic conditions occurs rapidly in acidic, 

surficial aquatic systems and produces nontoxic transformation products, then the Agency could 

potentially determine that carfentrazone-ethyl residues of concern do not persist in these systems. If 

data indicate that degradation is not appreciable in acidic, surficial aquatic systems or that the 

transformation products are of similar or higher toxicity than the parent compound, then the Agency 

could conclude that carfentrazone-ethyl residues of concern persist in acidic, surficial aquatic systems 

under anaerobic conditions.

How could the data change the Agency’s decision or impact the Agency’s future decision-making? 

In the absence of the requested data, carfentrazone-ethyl will be assumed stable to biodegradation in 

anaerobic, surficial aquatic environments. If the required data indicate that carfentrazone-ethyl in 

anaerobic surficial aquatic environments is rapidly biodegraded to nontoxic degradation products, 

including in acidic conditions, then risk assessment conclusions and associated labeled use precautions 

and/or restrictions could be made less restrictive.

Guideline Number: 835.6100 (Independent Laboratory Validation Only)

Study Title: Independent Laboratory Validation of Analytical Method for Residues in Soil

Rationale for Requiring the Data

Independently validated analytical methods for residues in soil, water, sediment, and plant material 

(environmental chemistry methods) submitted by the registrant are used to evaluate analyses described 

in submitted environmental fate and ecological effects studies. Submitted analytical methods are also 

used by various Federal, State, Tribal, and local agencies to detect and monitor residues that are or are 

suspected to be in environmental compartments due to outdoor uses and accidental releases. 

Independent laboratory validations for submitted analytical methods are necessary to confirm that the 

methods are functional and to confirm the levels of detection and quantitation reported in registrantprepared validations.

An analytical method (a.k.a. environmental chemistry method) for carfentrazone-ethyl residues in soil 

(parent plus degradates carfentrazone, F8426-cinnamic acid, F8426-propionic acid, and F8426-benzoic 

acid), MRID 44161540, was submitted by the registrant in support of the terrestrial field dissipation 

study, MRID 44161539. However, an independent validation of this method was not submitted. 

Therefore, an independent laboratory validation of the submitted analytical method for carfentrazoneethyl residues in soil (MRID 44161540) is required in order to evaluate MRID 44161539. 

Practical Utility of the Data

How will the data be used?

In the absence of independent validation, the submitted environmental chemistry method MRID 

44161540 and the field study it supports, MRID 44161539, are not reviewable. An independently 

validated environmental chemistry method will be used to evaluate the submitted data and will be made 

available for enforcement and monitoring purposes at the federal, state, and local levels.

How could the data change the Agency’s decision, or impact the Agency’s future decisionmaking? 

Risk assessment conclusions could be altered if they are not supported by field study data or 

environmental monitoring detections that are based on independently validated environmental chemistry 

methods. 
60

Guideline Number: 835.6200 (Frozen Storage Stability Study Only)

Study Title: Storage Stability of Residues in Frozen Water and Sediment

Rationale for Requiring the Data

The Agency has a limited understanding of how carfentrazone-ethyl behaves when applied to rice 

paddies. Depending on how quickly and to what extent the compound and its main degradates dissipate 

from rice paddies, carfentrazone-ethyl residues may or may not pose potential exposure concern in and 

downstream from rice paddies. Because carfentrazone-ethyl dissipation in rice paddies is not well 

understood, the Agency required an aquatic field dissipation study of carfentrazone-ethyl applied to rice 

paddies in California and Louisiana. This study was submitted under MRID 44654701.

Storage stability data for carfentrazone-ethyl and analyzed degradates (carfentrazone, F8426-propionic 

acid, F8426-cinnamic acid, F8426-benzoic acid, and 3-hydroxymethyl-F8426-benzoic acid) in water and 

sediment samples in frozen storage were not submitted by the registrant in support of MRID 44654701. 

The field study data are not reviewable without storage stability data to indicate whether and how much 

residues degrade during handling, storage, and processing of samples. Therefore, these data are required 

in order to evaluate MRID 44654701.

Practical Utility of the Data

How will the data be used?

In the absence of frozen storage stability data, the submitted aquatic field dissipation study, MRID 

44654701, is not reviewable. Frozen storage stability data will be used to evaluate the submitted data, 

by indicating whether and how much residues degrade during handling, storage, and processing of 

samples.

How could the data change the Agency’s decision, or impact the Agency’s future decisionmaking? 

Risk assessment conclusions could be altered if they are not supported by field study data or if 

laboratory study data are not consistent with field study data that are supported with acceptable storage 

stability data.

Guideline Number: 850.1025

Study Title: Oyster Acute Toxicity Test (Shell Deposition) with carfentrazone acid

Rationale for Requiring the Data

Acute toxicity data are required per 40 CFR Part 158.630 for aquatic invertebrates for all terrestrial and 

aquatic uses. Since carfentrazone-ethyl converts rapidly, 2.3-2.7 h, into carfentrazone acid, which has 

an aerobic aquatic half-life of 39-72 d, the data are needed with carfentrazone acid.

Practical Utility of the Data

How will the data be used? 

Acute data on the acid degradate would allow the Agency to better assess and characterize toxicity; 

acute toxicity of carfentrazone-ethyl may be different from carfentrazone acid. The effects data would 

be used to determine the likelihood that the acute risks can potentially impact aquatic communities, 

either by direct effects on fish or by indirect effects by reducing their food sources. By refining the 

assessment, the Agency would be able to determine whether the mitigation imposed as part of the 

registration review process was appropriate due to toxicity concerns with carfentrazone-ethyl or its 

major degradate, carfentrazone acid. 

How could the data impact the Agency’s future decision-making?

If future endangered species risk assessments are performed without these data, the Agency would have 

to assume that carfentrazone-ethyl "may affect" endangered saltwater mollusks directly (and endangered 
61

species from other taxa indirectly), and use of carfentrazone-ethyl might need to be restricted in areas 

where endangered species could be exposed. The lack of these data will limit the flexibility the Agency 

and registrants have in coming into compliance with the Endangered Species Act and could result in use 

restrictions for carfentrazone-ethyl which are unnecessarily severe.

Guideline Number: 850.1075

Study Title: Fish Acute Toxicity Test (Saltwater) with carfentrazone acid

Rationale for Requiring the Data

Acute toxicity data are required per 40 CFR Part 158.630 for fish for all terrestrial and aquatic uses. 

Since carfentrazone-ethyl converts rapidly, 2.3-2.7 h, into carfentrazone acid, which has an aerobic 

aquatic half-life of 39-72 d, the data are needed with carfentrazone acid. The species used should be the 

same as the saltwater fish ELS test with the acid degradate.

Practical Utility of the Data

How will the data be used? 

Acute data on the acid degradate would allow the Agency to better assess and characterize toxicity; 

acute toxicity of carfentrazone-ethyl may be different from carfentrazone acid. The effects data would 

be used to determine the likelihood that the acute risks can potentially impact aquatic communities, 

either by direct effects on fish or by indirect effects by reducing their food sources. By refining the 

assessment, the Agency would be able to determine whether the mitigation imposed as part of the 

registration review process was appropriate due to toxicity concerns with carfentrazone-ethyl or its 

major degradate, carfentrazone acid. 

How could the data impact the Agency’s future decision-making?

If future endangered species risk assessments are performed without these data, the Agency would have 

to assume that carfentrazone-ethyl "may affect" endangered saltwater mollusks directly (and endangered 

species from other taxa indirectly), and use of carfentrazone-ethyl might need to be restricted in areas 

where endangered species could be exposed. The lack of these data will limit the flexibility the Agency 

and registrants have in coming into compliance with the Endangered Species Act and could result in use 

restrictions for carfentrazone-ethyl which are unnecessarily severe.

Guideline Number: 850.1400

Study Title: Fish Early Life-Stage Test (Saltwater) with carfentrazone acid

Rationale for Requiring the Data

Since carfentrazone-ethyl may be applied directly to water, this data is required per 40 CFR Part 

158.630. Since the aerobic aquatic half-life is 2.3-2.7 h for parent, but 39-72 d for carfentrazone acid, 

the data is being requested using carfentrazone acid, which is the dominant form expected in chronic 

aquatic exposure. The species used should be the same as the saltwater fish acute test with the acid 

degradate.

Practical Utility of the Data

How will the data be used? 

The fish full life-cycle study would allow the Agency to analyze chronic effects, including effects on 

reproductive success and growth, to fish and aquatic-phase amphibians. The effects data would be used 

to determine the likelihood that the chronic risks can potentially impact aquatic communities, either by 

direct effects on fish or by indirect effects by reducing their food sources. By refining the assessment, 

the Agency would be able to determine whether the mitigation imposed as part of the registration review 

process was appropriate due to toxicity concerns with carfentrazone-ethyl.

How could the data impact the Agency’s future decision-making?
62

If future endangered species risk assessments are performed without these data, the Agency would have 

to assume that carfentrazone-ethyl "may affect" endangered fish and aquatic-phase amphibians directly 

(and endangered species from other taxa indirectly), and use of carfentrazone-ethyl might need to be 

restricted in areas where endangered species could be exposed. The lack of these data will limit the 

flexibility the Agency and registrants have in coming into compliance with the Endangered Species Act 

and could result in use restrictions for carfentrazone-ethyl which are unnecessarily severe.

Guideline Number: 850.1500

Study Title: Fish Full Life-cycle Test (Freshwater) with carfentrazone acid

Rationale for Requiring the Data

Since carfentrazone-ethyl may be applied directly to water, and the expected EEC is > 0.1 of the early 

life stage NOAEC for rainbow trout (i.e., <16.4 μg a.i./L, based on LDPH toxicity, MRID 44963201), 

this study is required per 40 CFR Part 158.630. Available environmental fate data indicate that 

carfentrazone-ethyl is not persistent in aquatic environments (aerobic aquatic half-life is 2.3-2.7 h); 

however, chronic exposures are of potential concern for its major degradate, carfentrazone acid, which 

has aerobic aquatic half-lives ranging 39 to 72 d. At this time, chronic toxicity data are not available for 

fish exposed to carfentrazone acid. Therefore, the data is being requested using carfentrazone acid, 

which is the dominant form expected in chronic aquatic exposure. Rainbow trout should be used since 

acceptable acute toxicity data with the acid degradate are available for this species.

Practical Utility of the Data

How will the data be used? 

The fish full life-cycle study would allow the Agency to analyze chronic effects, including effects on 

reproductive success and growth, to fish and aquatic-phase amphibians. The effects data would be used 

to determine the likelihood that the chronic risks can potentially impact aquatic communities, either by 

direct effects on fish or by indirect effects by reducing their food sources. By refining the assessment, 

the Agency would be able to determine whether the mitigation imposed as part of the registration review 

process was appropriate due to toxicity concerns with carfentrazone-ethyl.

How could the data impact the Agency’s future decision-making?

If future endangered species risk assessments are performed without these data, the Agency would have 

to assume that carfentrazone-ethyl "may affect" endangered fish and aquatic-phase amphibians directly 

(and endangered species from other taxa indirectly), and use of carfentrazone-ethyl might need to be 

restricted in areas where endangered species could be exposed. The lack of these data will limit the 

flexibility the Agency and registrants have in coming into compliance with the Endangered Species Act 

and could result in use restrictions for carfentrazone-ethyl which are unnecessarily severe.

Guideline Number: 850.1300 

Study Title: Daphnid Chronic Toxicity Test with carfentrazone acid.

Rationale for Requiring the Data

Carfentrazone-ethyl is moderately toxic to aquatic invertebrates on an acute basis. It may be applied 

directly to water, and the persistence of carfentrazone-ethyl in water does not preclude the potential for 

chronic exposure to be sufficient to elicit toxic responses. This requirement is based on carfentrazoneethyl use in a variety of products applied directly to water and used in agriculture. Since carfentrazoneethyl may be applied directly to freshwater, a life-cycle study is required using a freshwater daphnid.

Since the aerobic aquatic half-life is 2.3-2.7 h for parent, but 39-72 d for carfentrazone acid, the data are

being requested on the acid form, which is the dominant form expected in chronic aquatic exposure. 

Daphnia magna should be used since acceptable acute toxicity data with the degradate are available.
63

Practical Utility of the Data

How will the data be used? The full life-cycle study would allow the Agency to further analyze 

potential chronic effects. The effects data would be used to determine the likelihood that the chronic 

risks can potentially impact aquatic communities, either by direct effects on aquatic invertebrates or by 

indirect effects by reducing their food sources. By refining the assessment, the Agency would be able to 

determine whether the mitigation imposed as part of the registration review process was appropriate due 

to toxicity concerns with carfentrazone-ethyl.

How could the data impact the Agency’s future decision-making? If future endangered species risk 

assessments are performed without these data, the Agency would have to assume that carfentrazoneethyl "may affect" endangered aquatic invertebrates directly (and endangered species from other taxa 

indirectly), and use of carfentrazone-ethyl might need to be restricted in areas where endangered species 

could be exposed. The lack of these data will limit the flexibility the Agency and registrants have in 

coming into compliance with the Endangered Species Act and could result in use restrictions for 

carfentrazone-ethyl which are unnecessarily severe.

Guideline Number: 850.1350 

Study Title: Mysid Chronic Toxicity Test with carfentrazone acid.

Rationale for Requiring the Data

Carfentrazone-ethyl is moderately toxic to aquatic invertebrates on an acute basis. It may be applied 

directly to water, and the persistence of carfentrazone-ethyl in water does not preclude the potential for 

chronic exposure to be sufficient to elicit toxic responses. This requirement is based on carfentrazoneethyl use in a variety of products applied directly to water and used in agriculture. Since carfentrazoneethyl may be applied directly to saltwater, a life-cycle study is required using a saltwater mysid. Since 

the aerobic aquatic half-life is 2.3-2.7 h for parent, but 39-72 d for carfentrazone acid, the data are being 

requested on the acid form, which is the dominant form expected in chronic aquatic exposure. 

Mysidopsis bahia should be used since acceptable acute data is available for this species with the acid 

degradate.

Practical Utility of the Data

How will the data be used? The full life-cycle study would allow the Agency to further analyze 

potential chronic effects. The effects data would be used to determine the likelihood that the chronic 

risks can potentially impact aquatic communities, either by direct effects on aquatic invertebrates or by 

indirect effects by reducing their food sources. By refining the assessment, the Agency would be able to 

determine whether the mitigation imposed as part of the registration review process was appropriate due 

to toxicity concerns with carfentrazone-ethyl.

How could the data impact the Agency’s future decision-making? If future endangered species risk 

assessments are performed without these data, the Agency would have to assume that carfentrazoneethyl "may affect" endangered aquatic invertebrates directly (and endangered species from other taxa 

indirectly), and use of carfentrazone-ethyl might need to be restricted in areas where endangered species 

could be exposed. The lack of these data will limit the flexibility the Agency and registrants have in 

coming into compliance with the Endangered Species Act and could result in use restrictions for 

carfentrazone-ethyl which are unnecessarily severe.
64

Guideline Numbers: 850.1735

Study Title: Whole sediment Acute Toxicity Invertebrates, Freshwater with TGAI using Hyalella

Rationale for Requiring the Data

Available information indicates that benthic organisms may be exposed via run-off or spray drift 

applications used in agricultural, forest, and residential settings, or by direct application to water. The 

Kow and dissipation half-lives meet the criteria for requiring an acute sediment organism toxicity study. 

Sediment toxicity tests are required to satisfy the Agency‟s updated data requirements for outdoor uses 

in 40 CFR Part 158 (October 26, 2007).

Acute tests using freshwater species, Hyalella azteca and Chironomus tentans, are requested. Although 

both Hyalella and Chironomus are freshwater species, they differ substantially in their ecological niche 

(i.e., epibenthic vs. infaunal), physiology, and potential sensitivities to pesticide exposure. 

Practical Utility of the Data

How will the data be used? 

Data from sediment toxicity studies will be used to estimate potential risks to benthic organisms 

associated with uses of carfentrazone-ethyl. The data will reduce uncertainties associated with the 

current risk assessment for benthic species and will improve our understanding of the potential effects of 

carfentrazone-ethyl.

How could the data impact the Agency’s future decision-making?

Acceptable data for benthic organisms will reduce the uncertainty from previous assessments. If the 

data indicate that registered carfentrazone-ethyl usage may pose a risk of adverse effects to non-target 

benthic organisms above the Agency Level of Concern, the Agency may explore decision options to 

mitigate this risk. The lack of these data will limit the flexibility the Agency and registrants have in 

coming into compliance with the Endangered Species Act, and could result in use restrictions for 

carfentrazone-ethyl which may otherwise be avoided, or which are unnecessarily severe.

Guideline Numbers: 850.1735

Study Title: Whole sediment Acute Toxicity Invertebrates, Freshwater with TGAI using 

Chironomus

Rationale for Requiring the Data

Available information indicates that benthic organisms may be exposed via run-off or spray drift 

applications used in agricultural, forest, and residential settings, or by direct application to water. The 

Kow and dissipation half-lives meet the criteria for requiring an acute sediment organism toxicity study. 

Sediment toxicity tests are required to satisfy the Agency‟s updated data requirements for outdoor uses 

in 40 CFR Part 158 (October 26, 2007).

Acute tests using freshwater species, Hyalella azteca and Chironomus tentans, are requested. Although 

both Hyalella and Chironomus are freshwater species, they differ substantially in their ecological niche 

(i.e., epibenthic vs. infaunal), physiology, and potential sensitivities to pesticide exposure. 

Practical Utility of the Data

How will the data be used? 

Data from sediment toxicity studies will be used to estimate potential risks to benthic organisms 

associated with uses of carfentrazone-ethyl. The data will reduce uncertainties associated with the 

current risk assessment for benthic species and will improve our understanding of the potential effects of 

carfentrazone-ethyl.

How could the data impact the Agency’s future decision-making?

Acceptable data for benthic organisms will reduce the uncertainty from previous assessments. If the 
65

data indicate that registered carfentrazone-ethyl usage may pose a risk of adverse effects to non-target 

benthic organisms above the Agency Level of Concern, the Agency may explore decision options to 

mitigate this risk. The lack of these data will limit the flexibility the Agency and registrants have in 

coming into compliance with the Endangered Species Act, and could result in use restrictions for 

carfentrazone-ethyl which may otherwise be avoided, or which are unnecessarily severe.

Guideline Numbers: 850.1740

Study Title: Whole sediment Acute Toxicity Invertebrates, Marine

Rationale for Requiring the Data

Available information indicates that benthic organisms may be exposed via run-off or spray drift 

applications used in agricultural, forest, and residential settings, or by direct application to water. The 

Kow and dissipation half-lives meets the criteria for requiring an acute sediment organism toxicity 

study. Sediment toxicity tests are required to satisfy the Agency‟s updated data requirements for 

outdoor uses in 40 CFR Part 158 (October 26, 2007).

Carfentrazone-ethyl has the potential to enter estuarine/marine water bodies based on current usuage 

patterns that include coastal areas. Therefore, testing is required for Leptocheirus plumulosus, an 

estuarine/marine sediment-dwelling invertebrate species.

Practical Utility of the Data

How will the data be used? 

Data from sediment toxicity studies will be used to estimate potential risks to benthic organisms 

associated with uses of carfentrazone-ethyl. The data will reduce uncertainties associated with the 

current risk assessment for benthic species and will improve our understanding of the potential effects of 

carfentrazone-ethyl.

How could the data impact the Agency’s future decision-making?

Acceptable data for benthic organisms will reduce the uncertainty from previous assessments. If the 

data indicate that registered carfentrazone-ethyl usage may pose a risk of adverse effects to non-target 

benthic organisms above the Agency Level of Concern, the Agency may explore decision options to 

mitigate this risk. The lack of these data will limit the flexibility the Agency and registrants have in 

coming into compliance with the Endangered Species Act, and could result in use restrictions for 

carfentrazone-ethyl which may otherwise be avoided, or which are unnecessarily severe.

Guideline Number: 850.2100 

Study Title: Avian Acute Oral Toxicity Test

Rationale for Requiring the Data

Acceptable acute avian oral toxicity data were not submitted for a passerine species exposed to 

carfentrazone-ethyl, which is now required under the 40 CFR Part 158 (CFR 40 2008) data requirements 

for conventional pesticides. The revised Part 158 data requirements specify that acute avian oral toxicity 

data be submitted for either one waterfowl or one upland game species and one passerine species. Many 

passerine species utilizing forests, residential areas and surrounding areas, have the potential to be 

exposed to pesticides used in agricultural, forest, and residential settings. It is likely that, for most 

pesticide use patterns, passerines are more likely to be exposed to pesticides than upland game species 

and waterfowl. Because passerine species have higher metabolic rates due to their smaller sizes than 

either waterfowl or upland game bird species and because they may utilize different metabolic 

pathways, they may be more or less sensitive to carfentrazone-ethyl. In order to properly characterize 

risk to passerines, an avian oral toxicity test is required for passerine birds. A passerine study protocol 

must be submitted for review by the Agency prior to initiation of the study.
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Practical Utility of the Data

How will the data be used?

Acute avian oral toxicity data for passerine species will be used to refine the screening-level risk 

assessment by determining whether there are differences in avian species sensitivity to carfentrazoneethyl between currently tested passerine and upland game and/or waterfowl species that are beyond the 

simple allometric predictions currently employed in the absence of such passerine data. The current 

extrapolation method may be under- or over-estimating risks to passerines.

How could the data impact the Agency’s future decision-making?

If future risk assessments, including listed species assessments, are performed without these data, the 

Agency would have to assume that carfentrazone-ethyl “may affect” listed birds directly (and listed 

species from other taxa indirectly), and use of carfentrazone-ethyl and its formulated products may need 

to be restricted in areas where listed species could be exposed. The lack of these data will limit the 

flexibility the Agency and registrants have in complying with the Endangered Species Act and could 

result in restrictions for carfentrazone-ethyl use that might prove to be unnecessary given data to address 

this area of uncertainty.

Guideline Number: 850.4100 

Study Title: Tier 2 Seedling Emergence Test With TEP 

Rationale for Requiring the Data

Available terrestrial plant toxicity studies were submitted using technical product, rather than a typical 

endues product, TEP; guidelines require that plant testing be conducted using TEP. The proposed rule 

establishing use of the TEP for vegetative vigor and seedling emergence studies states, “The TEP that 

contains the highest percentage of active ingredient, and/or is the most commonly used, would be 

required.” (FR Vol. 70 No. 47; March 11, 2005; 12289). Tier II seedling emergence and vegetative 

vigor studies on monocot and dicot test species should be repeated using TEP. 

Practical Utility of the Data

How will the data be used? 

Toxicity data using TEP will be used to refine the screening-level risk assessment by estimating

potential risks to non-target terrestrial plants associated with uses of carfentrazone-ethyl. The data will 

reduce uncertainties associated with the current risk assessment for non-target plants and will improve 

our understanding of the potential effects of carfentrazone-ethyl.

How could the data impact the Agency’s future decision-making?

Acceptable data for terrestrial plants will reduce the uncertainty from previous assessments. If the data

indicate that registered carfentrazone-ethyl usage may pose a risk of adverse effects to non-target 

terrestrial plants above the Agency Level of Concern, the Agency may explore decision options to 

mitigate this risk. The lack of these data will limit the flexibility the Agency and registrants have in 

coming into compliance with the Endangered Species Act, and could result in use restrictions for 

carfentrazone-ethyl which may otherwise be avoided, or which are unnecessarily severe.
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Guideline Number: 850.4150

Study Title: Tier 2 Vegetative Vigor Test With TEP 

Rationale for Requiring the Data

Available terrestrial plant toxicity studies were submitted using technical product, rather than a typical 

endues product, TEP; guidelines require that plant testing be conducted using TEP. The proposed rule 

establishing use of the TEP for vegetative vigor and seedling emergence studies states, “The TEP that 

contains the highest percentage of active ingredient, and/or is the most commonly used, would be 

required.” (FR Vol. 70 No. 47; March 11, 2005; 12289). Tier II seedling emergence and vegetative 

vigor studies on monocot and dicot test species should be repeated using TEP. 

Practical Utility of the Data

How will the data be used? 

Toxicity data using TEP will be used to refine the screening-level risk assessment by estimating

potential risks to non-target terrestrial plants associated with uses of carfentrazone-ethyl. The data will 

reduce uncertainties associated with the current risk assessment for non-target plants and will improve 

our understanding of the potential effects of carfentrazone-ethyl.

How could the data impact the Agency’s future decision-making?

Acceptable data for terrestrial plants will reduce the uncertainty from previous assessments. If the data 

indicate that registered carfentrazone-ethyl usage may pose a risk of adverse effects to non-target 

terrestrial plants above the Agency Level of Concern, the Agency may explore decision options to 

mitigate this risk. The lack of these data will limit the flexibility the Agency and registrants have in 

coming into compliance with the Endangered Species Act, and could result in use restrictions for 

carfentrazone-ethyl which may otherwise be avoided, or which are unnecessarily severe.