Page 1 of 71

UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON D.C., 20460

MEMORANDUM May 4, 2011

Subject: Registration Review – Preliminary Problem Formulation for Ecological 

Risk and Environmental Fate, Endangered Species, and Drinking Water 

Assessments for Fipronil (PC Code 129121; DP 387319)

To: Susan Bartow, Chemical Review Manager

Eric Olson, Team Leader

Risk Management and Implementation Branch IV

Pesticide Re-evaluation Division (PRD)

Office of Pesticide Programs

From: Edward Odenkirchen, Ph.D., Senior Biologist

Stephen Wente, Ph.D., Biologist

Environmental Risk Branch 1

Environmental Fate and Effects Division (EFED)

Office of Pesticide Programs

Through: Nancy Andrews, Ph.D., Chief

Sujatha Sankula, Ph.D., Risk Assessment Process Leader

Environmental Risk Branch 1

Environmental Fate and Effects Division (EFED)

Office of Pesticide Programs

The Environmental Fate and Effects Division (EFED) has completed the preliminary

problem formulation (attached) for the ecological risk, environmental fate, endangered 

species, and drinking water assessments to be conducted as part of the Registration 

Review of the insecticide, fipronil (PC 129121). The problem formulation draws on 

information from both open literature and studies submitted by the technical registrants in 

response to data requirements. This document is intended to provide an overview of 

what is currently known regarding the environmental fate and ecological effects 

associated with fipronil and all of its degradates and outlines uncertainties regarding 

attributes of the parent compound and its transformation products. It describes the 

preliminary ecological risk hypothesis and the processes that will be used during the 

completion of drinking water and ecological risk assessments in support of registration 

review. This document also recommends studies that should be included in a data call-in 

(DCI) to address uncertainties surrounding the environmental fate and potential 

ecological effects of fipronil.
Page 2 of 71

OFFICE OF CHEMICAL SAFETY

AND POLLUTION PREVENTION

Problem Formulation for the 

Environmental Fate and Ecological Risk, 

Endangered Species, 

and Drinking Water Assessments

in Support of the Registration Review of Fipronil

N

N

Cl

Cl

H2N

S

C

CF3

O

CF3

N

Fipronil (CAS # 120068-37-3)

Prepared by:

Edward Odenkirchen, Ph.D., Senior Biologist 

Stephen Wente, Ph.D., Biologist

U. S. Environmental Protection Agency

Office of Pesticide Programs

Environmental Fate and Effects Division

Environmental Risk Branch I

1200 Pennsylvania Ave., NW

Mail Code 7507P

Washington, DC 20460

Reviewed by:

Anita Ullagaddi, Biologist

Faruque Khan, Ph.D., Senior Scientist
Page 3 of 71

Table of Contents

I. Purpose ........................................................................................................................... 5

II. Problem Formulation..................................................................................................... 5

A. Nature of Regulatory Action..................................................................................... 5

B. Conclusions from Previous Risk Assessments.......................................................... 6

1. Fipronil Ecological Risk Assessments................................................................... 6

2. Drinking Water Exposure Assessments ................................................................. 7

III. Stressor Source and Distribution ................................................................................. 8

A. Mechanism of Action................................................................................................ 8

B. Overview of Pesticide Usage .................................................................................... 8

C. Environmental Fate and Transport.......................................................................... 12

IV. Receptors ................................................................................................................... 18

A. Effects to Aquatic Organisms................................................................................. 19

B. Effects to Terrestrial Organisms ............................................................................. 20

C. Degradate toxicity ................................................................................................... 21

D. Ecological Incidents................................................................................................ 21

D. Ecosystems Potentially at Risk ............................................................................... 22

V. Assessment Endpoints................................................................................................. 22

VI. Conceptual Model....................................................................................................... 22

A. Risk Hypothesis ...................................................................................................... 23

B. Conceptual Diagram................................................................................................ 23

VII. Analysis Plan............................................................................................................ 25

A. Stressors of Concern ............................................................................................... 26

B. Measures of Exposure ............................................................................................. 26

C. Measures of Effect .................................................................................................. 28

D. Integration of Exposure and Effects........................................................................ 29

1. Deterministic and Probabilistic Assessment Methods......................................... 30

E. Endangered Species Assessments ........................................................................... 30

F. Drinking Water Assessment .................................................................................... 31

G. Preliminary Identification of Data Gaps................................................................. 31

H. Preliminary Identification of Data Gaps................................................................. 32

1. Fate ...................................................................................................................... 32

2. Effects................................................................................................................... 35

VIII. References............................................................................................................... 40

Appendix 1. Currently Registered Uses of Fipronil. ....................................................... 43

Appendix 2. Chemical Names, Structures, Maximum Reported Amounts of Fipronil and 

its Degradates and Overview of Degradation Pathways................................................... 51

Appendix 3. Available Effects data from most recent ecological risk assessment in 2007

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

List of Tables

Table 1. History of U.S. Environmental Protection Agency ecological risk assessments 

for fipronil........................................................................................................................... 6

Table 2. General physico-chemical and environmental fate properties of fipronil and 
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degradates of concern. ...................................................................................................... 13

Table 3. Test Species Evaluated for Assessing Potential Ecological Effects of Fipronil 

and the Associated Acute Toxicity Classification. ........................................................... 19

Table 4. Available environmental fate data for fipronil and remaining data gaps. ......... 32

Table 5. Available environmental fate data for fipronil sulfide (MB 54950) and 

remaining data gaps. ......................................................................................................... 33

Table 6. Available environmental fate data for fipronil sulfone (MB 46136) and 

remaining data gaps. ......................................................................................................... 34

Table 7. Available environmental fate data for MB46513 and remaining data gaps. ..... 34

Table 8. Non-Target Organism Toxicity Data Gaps........................................................ 35

Table 9. Terrestrial Organism Toxicity Endpoints Used in Past Risk Assessment......... 38

Table 10. Aquatic Organism Toxicity Endpoints Used in Past Risk Assessment........... 38

List of Figures

Figure 1. Corn Production Areas in the United States..................................................... 10

Figure 2. General Fire Ant Quarantine Area in the United States (updated and more 

detailed 2009 map available at: 

http://www.aphis.usda.gov/plant_health/plant_pest_info/fireants/downloads/fireant.pdf).

........................................................................................................................................... 10

Figure 3. Sweet Potato Production Areas in the United States........................................ 11

Figure 4. Potato Production Areas in the United States................................................... 11

Figure 5. Conceptual model depicting stressors, exposure pathways, and potential effects 

to aquatic organisms from the use of fipronil. Dotted lines indicate exposure pathways 

that have a low likelihood of contributing to ecological risk............................................ 24

Figure 6. Conceptual model depicting stressors, generic exposure pathways, and 

potential effects to terrestrial organisms (terrestrial plants, terrestrial invertebrates, and 

dietary routes of exposure for terrestrial vertebrates) from the use of fipronil. Dotted lines 

indicate exposure pathways that have a low likelihood of contributing to ecological risk.

........................................................................................................................................... 25
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I. Purpose

The purpose of this problem formulation is to provide an understanding of the 

environmental fate and ecological effects of the registered uses of fipronil, also known as 

MB 46030. Fipronil is a non-systemic, chiral phenylpyrazole insecticide. The chiral 

center is associated with the sulfur in parent fipronil. The current registrations are only 

for the racemic mixture of stereoisomers (50% R: 50% S). It is formulated as a technical 

chemical, formulation intermediate, dust, granular, pelletted/tabletted, wettable powder, 

impregnated materials, emulsifiable concentrate, flowable concentrate, soluble 

concentrate, solution-ready to use, or pressurized liquid, depending on the use. Current

outdoor fipronil uses include broadcast treatment for control of fire ants, carpenter ants, 

and nuisance ants; in-furrow treatment for control of corn root worm on corn and wire 

worms on sweet potatoes/potatoes; seed treatments for corn; soil injection for control of 

termites; and bait treatments for fire ants, fruit flies, and Texas leaf-cutter ants. This 

document will provide a plan for analyzing data relevant to fipronil and for conducting 

environmental fate and ecological risk, endangered species and drinking water 

assessments for its registered uses. Additionally, this problem formulation is intended to 

identify data gaps, uncertainties, and potential assumptions used to address those 

uncertainties, relative to characterizing the ecological risk associated with the registered 

uses of fipronil.

II. Problem Formulation

A. Nature of Regulatory Action

The Food Quality Protection Act of 1996 mandated EPA to implement a new program for 

assessing the risks of pesticides, 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 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 ensure 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 fipronil continues to meet the 

FIFRA standard for registration. This problem formulation for the environmental fate 
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and ecological risk aTable 1Table 1essment chapter in support of the registration review 

is intended for the initial docket opening the public phase of the review process. 

B. Conclusions from Previous Risk Assessments

Fipronil was first registered in 1993. The Agency conducted multiple subsequent 

ecological risk and drinking water assessments on fipronil between 1993 and present.

1. Fipronil Ecological Risk Assessments

Because of the large number of fipronil ecological risk assessments and revisions to those 

assessments, the ecological risk assessments are very briefly summarized in Table 1. 

Fipronil was not subject to the reregistration process due to its recent initial registration

occurring after the November 1st, 1984 initial registration cut-off date for chemicals 

required to undergo reregistration. However, a comprehensive risk assessment was 

performed (dated April 26, 1996) that is similar to the science chapters produced by 

EFED in support of Reregistration Eligibility Decisions (RED).

Table 1. History of U.S. Environmental Protection Agency ecological risk assessments for fipronil.

Date Title Risk Concerns

1/16/96

Request for a Section 3 of FIFRA for use of Fipronil 

(GAUNTLET 0.1G) on golf and commercial turfgrass (not for 

use on domestic turf or sod farms) (D214746)

Risks to estuarine/marine

invertebrates

4/26/96 Fipronil: Environmental Assessment, Current for the Turf 

Registration (No DP Barcode)

Possible risks to 

estuarine/marine invertebrates

7/12/96 Request for a Section 3 of FIFRA for use of Fipronil (REGENT 

1.5G) on corn (D214762)

Risk to freshwater and 

estuarine invertebrate species

8/21/96

Request for Section 3 of FIFRA for use of Fipronil (Termidor 80 

WG) as a termiticide for preconstruction, post-construction,

hollow block foundations, soil excavation, and post poles and

wood landscape ornamentation. (D227607)

None

No date

EFED's Section 3 Registration Eligibility Decision Chapter' for 

Fipronil Use on Corn (D236430, D236432, D237516, D228555, 

D237727, D236394, D237516, D237517, D236956, D23971)

Risk for direct chronic effects 

to both fresh and salt water 

fish species

11/20/97 EFED's Section 3 Registration Eligibility Decision Chapter for 

Fipronil Use on Corn

Acute and chronic estuarine 

invertebrate risks

4/16/99

EFED's Section 3 Registra on Eligibility Decision Chapter for 

Fipronil Use Rice as a Pre-Plant Broadcast Treatment (No DP 

Barcode)

Risks for estuarine organisms

7/6/99

EFED's Section 3 Registration Review for Fipronil Use in 

Potting Soil for Fire Ant Control and Other Insect Pests 

(D254052)

None

7/19/99 Fipronil: Emergency Exemption Use on Rangeland in Wyoming: 

Environmental Risk Assessment Conclusions (D253226)

None

8/19/99

EFED's Section 3 Registration Eligibility Decision Chapter for 

Fipronil Use as Granular and Bait applications for control of Fire 

Ants and Other Turf pests (D253952, D254316, D254075, 

D253660)

Acute and chronic estuarine 

invertebrate and fish risks
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Date Title Risk Concerns

12/6/99

EFED's Section 3 Registration Eligibility Decision Chapter for 

Fipronil Use as Granular and Bait applications for control of Fire 

Ants and Other Turf pests (Revised) (D260843, D253952, 

D254316, D254075, D253660, D244061)

Risks to estuarine/marine

invertebrates

4/10/01

EFED's Section 3 Registration Eligibility Decision Chapter for 

Fipronil Use as Granular Applications for Control of Fire Ants 

and Other Turf Pests (Addendum) (D260607, D273236, 

D273241, D273375, D274014)

Acute and chronic risks to 

freshwater and 

estuarine/marine invertebrates

6/20/01 Section 3 Registration Eligibility Decision Chapter for Fipronil 

Use on Cotton (D236414)

Acute and chronic estuarine 

invertebrate and fish risks

11/15/01

Updated Environmental Risk Assessment for Fipronil. Corn: infurrow application and seed treatment (D277292, D277291, 

D277289, D278506, D269236)

Acute and chronic risks to 

freshwater and 

estuarine/marine invertebrates

12/5/01

Updated Environmental Risk Assessment for Fipronil. Corn: infurrow application and seed treatment (D277292, D277291, 

D277289, D278506, D269236)

Chronic freshwater aquatic 

invertebrate 

4/18/02

Section 3 Registration Request for Uses of Firponil in Maxforce 

Tick Management System Bait Station Treatment of Small 

Mammals (D281019)

None

1/26/05 Special Local Needs Registration [Section 24(c)] for Fipronil 

(Topchoice®) Use to Control Fire Ants in Arizona (D311943)

Acute endangered freshwater 

aquatic invertebrates

8/31/05 Section 18 Ecological Risk Assessment for Fipronil Use to 

Control Cabbage Maggot in Turnip and Rutabaga (D356402)

Acute lethal and reproduction 

risks to birds; reproductive

effects in insectivorous 

mammals; acute and chronic 

effects to freshwater 

invertebrates

2/6/07

Ecological Risk Assessment for Fipronil Uses (D331595,

331519, 331593, 329522, 314530, 332424, 325983, 326009,

326000, 325999, 325997, 325990, 326003, 331867, 314530,

322414, 314197, 331714, 331713, 313295, 331872, 335805)

Acute and chronic risks to 

freshwater and 

estuarine/marine invertebrates

3/30/07

Ecological Risk Assessment for Fipronil Uses (Addendum)

(D331595, 331519, 331593, 329522, 314530, 332424, 325983,

326009, 326000, 325999, 325997, 325990, 326003, 331867,

314530, 322414, 314197, 331714, 331713, 313295, 331872,

335805)

Acute and chronic terrestrial 

vertebrate risk based on revise 

assessment for onion-seed 

treatment

4/18/07

Updated Section 18 Ecological Risk Assessment for Fipronil 

Use to Control Cabbage Maggot in Turnip and Rutabaga

(D338854)

Acute and chronic effects to 

freshwater invertebrates

5/15/07

Section 18 Ecological Risk Assessment for Fipronil Use to 

Control Cabbage Maggot in Turnip and Rutabaga. Addendum 

regarding assessment of potential for effects to listed fishes

(D338854)

Indirect effects to endangered 

fish species due to acute and 

chronic risk to freshwater 

invertebrates

2. Drinking Water Exposure Assessments

A drinking water exposure assessment was conducted in 2006 in support of human health 

risk assessment (DP Barcode 322415), which was subsequently revised in 2007 (under 

the same DP Barcode 322415) for the parent fipronil and the individual degradation 

products, MB 46513, MB 46136 and MB45950. PRZM (3.12 beta) and EXAM (2.97.5) 

using PE4V0l.pl (August 13, 2003) were used to estimate fipronil residue concentrations 

in drinking water. From the registered and proposed uses for fipronil, the highest 
Page 8 of 71

concentrations of fipronil and its degradation products in surface source drinking water 

were expected to be from the proposed use on onion seeds. Fipronil concentrations in 

surface source water are not expected to exceed 2,654.1 ng/L for the 1 in 10 year peak 

concentration, 317.9 ng/L for 1 in 10 year annual average concentration, and 161.2 ng/L 

for the 30 year annual average concentration. However, the onion seed treatment was not 

approved. Therefore, the drinking water exposure may need to be re-assessed.

Ground water concentrations for fipronil and its degradation products were estimated 

using SC2.3 (July 29, 2003). The proposed use on in-furrow corn and rutabagas/turnip 

uses had the highest predicted concentration (21 ng/L) in ground water.

III. Stressor Source and Distribution

Fipronil is a broad-spectrum phenylpyrazole insecticide. The current and proposed new 

uses for fipronil are in-furrow treatments, broadcast treatments, seed treatments, and bait 

stations for control of insect pests. The use pattern includes residential uses for control of 

termites, fire ants, carpenter/nuisance ants, leaf cutter ants, and fruit flies on the following 

crops: corn, corn seed, sweet potato, potato, and pine seedlings. Fipronil use for control 

of fire ant is limited to the USDA 14 state plus Puerto Rico fire ant quarantine area. 

Distributions of the crops were determined based on 1997 AgCensus data and 70 Code of 

Federal Regulation, 1996. Maps showing these distributions are included in Section B 

(below). Because fipronil degradation products are persistent in soil (soil degradation t1/2

~ 700 day), they are expected to accumulate in soil from successive use of fipronil 

(MRID 46477001). The persistence of fipronil degradation products is expected to 

prolong ecological exposure.

A. Mechanism of Action

Fipronil affects the gamma-aminobutyric acid neurotransmission system by interfering 

with the passage of chloride. In addition, research data indicate that fipronil displays a 

higher potency in the insect GABA chloride channel than in the vertebrate GABA 

chloride channel, which may indicate selective toxicity (Hainzl and Casida, 1996). 

Additionally, there are open-literature data showing enantioselective biodegradation of 

fipronil in rainbow trout (Konwick et al, 2006).

B. Overview of Pesticide Usage

Current labels allow outdoor use of fipronil on forestry uses (forest tree 

management/forest pest management, forest trees (softwoods, conifers), and pine 

(forest/shelterbelt)); outdoor residential uses (household/domestic dwellings outdoor 

premises, refuse/solid waste containers (garbage cans), and residential lawns); terrestrial 

food + feed crop uses (orchards (unspecified), potato and white/Irish); terrestrial non-
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food + outdoor residential uses (fencerows/hedgerows, ornamental and/or shade trees, 

and paths/patios); and terrestrial non-food crop uses (Christmas tree plantations, 

commercial storages/warehouses premises, commercial/industrial lawns, 

commercial/institutional/industrial premises/equipment (outdoor), field corn, golf course 

turf, industrial / construction areas (outdoor), nonagricultural outdoor 

buildings/structures, nonagricultural uncultivated areas/soils, nursery stock, ornamental 

and/or shade trees, ornamental herbaceous plants, ornamental lawns and turf, ornamental 

non-flowering plants, ornamental sod farm (turf), ornamental woody shrubs and vines, 

paved areas (private roads/sidewalks), potting soil/topsoil, recreation area lawns, 

recreational areas, refuse/solid waste sites (outdoor), utility poles / right-of-way, wood 

protection treatment to buildings/products outdoor, and zoos. Indoor use of fipronil

include indoor food uses (dairy farm milk handling facilities/equipment, 

food/grocery/marketing/storage/distribution facility premise, and household/domestic 

dwellings indoor food handling areas); indoor medical uses (hospitals/medical 

institutions premises (human/veterinary)); indoor non-food uses (bathroom 

premises/hard surfaces, commercial storages/warehouses premises, commercial 

transportation facilities-nonfeed/nonfood, commercial/institutional/industrial 

premises/equip. (indoor), dairies/cheese processing plant premises (nonfood contact), 

eating establishments, eating establishments food handling areas (nonfood contact), 

eating establishments food serving areas (nonfood contact), eating establishments nonfood areas (nonfood contact), feed mills/feed processing plants, food processing plant 

non-food handling areas, food processing plant premises (nonfood contact), food 

stores/markets/supermarkets premises, meat processing plant premises (nonfood contact), 

refuse/solid waste sites (indoor), ships and boats, and zoos); and indoor residential uses

(cats (adults/kittens), dogs/canines (adults/puppies), household/domestic dwellings 

contents, household/domestic dwellings indoor premises, and refuse/solid waste 

containers (garbage cans). Currently registered uses of fipronil (with maximum 

application rates, maximum number of applications, and minimum re-treatment intervals) 

are listed in Appendix 1.

A spatial analysis of the fipronil use areas in the United States suggests the predominant

fipronil use areas are the Midwestern and Southeastern United States (Figures 1 and 2). 

These use areas are associated with conditional registrations for in-furrow use of fipronil 

corn and broadcast/bait fipronil use for fire ant use in residential areas.
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Figure 1. Corn Production Areas in the United States

Figure 2. General Fire Ant Quarantine Area in the United States (updated and more detailed 2009 map 

available at: http://www.aphis.usda.gov/plant_health/plant_pest_info/fireants/downloads/fireant.pdf).

Proposed uses of fipronil on sweet potato are not expected to extend the use area beyond 

the fire ant quarantine use areas (Figure 3). However, the use of fipronil on potatoes is 

expected to extend the fipronil use area into the Northeastern United States (Maine). 
Page 11 of 71

Figure 3. Sweet Potato Production Areas in the United States

Figure 4. Potato Production Areas in the United States

The proposed pine seedling use for fipronil is expected to be in pine nursery areas for 

plantations associated with pulp and paper mill production (i.e., Southeastern United 

States). Although the AMULETTM C-L label for fruit fly bait does not restrict the 

geographical use, the use area is expected to be limited to Hawaii (Personal 

Communication from Jack Arthur, BASF, 10/5/06). The proposed perimeter house 

treatment use of fipronil (TERMIDOR® SC, EPA Reg. No. 7969-210) will be 

predominantly associated with urban and suburban areas. The geographic range of house 

perimeter use is expected to be correlated with geographic extent of termites.

The screening-level use assessment (SLUA) estimates of agricultural uses of fipronil 

indicate that use on: corn (~100,000 lbs. a.i./year on average) accounts for < 2.5% of the 

total pesticide use on corn on average (maximum of ~5 %); potatoes (~2,000 lbs. a.i./year 

on average) accounts for < 2.5% of the total use pesticide use on potatoes on average 

(maximum of < 2.5 %); sweet corn < 500 lbs. a.i./year on average) accounts for < 1% of 

the total use pesticide use on sweet corn on average (maximum of < 2.5 %) (USEPA 
Page 12 of 71

2010) (Values are calculated by merging pesticide usage data sources together; averaging 

across all observations, then rounding.)

C. Environmental Fate and Transport

Fipronil dissipation appears to be dependent on photodegradation in water, microbially

mediated degradation, and soil binding. Data indicate that fipronil is relatively persistent 

and immobile in terrestrial environments. In aquatic environments, a determination of the 

environmental behavior of fipronil is more tentative because soil and aquatic metabolism 

studies provide contradictory data on fipronil persistence to microbially-mediated 

degradation processes. Photolysis is expected to be a major factor in controlling fipronil 

dissipation in aquatic environments. Fipronil degrades to form persistent and immobile 

degradates (fipronil sulfide (MB 45950), fipronil sulfone (MB 46136), and MB 46513). 

These degradates are considered in the HED dietary tolerance expression for fipronil. 

Because fipronil and its degradates have a moderate to high sorption affinity to organic 

carbon, it is likely sorption on soil organic matter will limit fipronil residue movement 

into ground and surface waters. However, fipronil residue may have the potential to move 

in very vulnerable soils (e.g., coarse-textured soils with low organic matter content) and 

in erodable soils when bound to particles entrained in runoff. In-furrow fipronil 

applications are expected to limit runoff potential.

Registrant-submitted data defining the physical, chemical, fate and transport 

characteristics associated with fipronil and combined residues of concern are summarized 

in Table 2. (Structural representations of fipronil and degradates may be found in 

Appendix 2.)
Page 13 of 71

Table 2. General physico-chemical and environmental fate properties of fipronil and degradates of concern.

Fipronil Fipronil Sulfide (MB 45950)

Fipronil Sulfone (MB 

46136) MB 46513

Parameter Value(s)

Source 

(MRID) Value(s)

Source 

(MRID) Value(s)

Source 

(MRID) Value(s)

Source 

(MRID)

Physico-chemical Parameters

Molecular weight 437.14 g/mol 44262826 421.1 g/mol 44262826 453.15 g/mol 44262826 389.09 g/mol 44262826

Vapor pressure (at 25C) 7.5 × 10-8

torr 47723916 1.7 × 10-8torr 44262803 5.7 × 10-9torr 44262802 3.0 × 10-8torr 44262801

Water solubility (at 20C) 2.3 mg/L 47723915 No Data 0.16 mg/L 44350001 0.95 mg/L 44350002

Henry’s law constant (at 

25C) 5.2 × 10-13 atm-m

3

/mol (calculated) No Data 2.7 × 10-15

atmm

3

/mol (calculated) 9.6 × 10-14

atmm

3

/mol (calculated)

Octanol-air partition 

coefficient (KOA) (at 25C) 11.463 EpiSuite 

v4.00 Not Estimated Not Estimated Not Estimated

Octanol-to-water partition 

coefficient (log POW)

3.5 44350003 No Data 3.8 44350004 3.4 44350005

Persistence

Hydrolysis half-lives 

(20C)

Stable pH 5

Stable pH 7

28 d pH 9

42977905 No Data No Data No Data

Aqueous photolysis halflife 0.33 d 42918661 No Data No Data No Data

Soil photolysis half-life 34 d 42918662 No Data No Data No Data

Aerobic soil metabolism 

half-life

sandy loam 128 d

sand 308 d 42918663 No Data No Data loamy sand I 630 dloamy sand II 693 d 44262830

Aerobic aquatic 

metabolism half-life

sandy loam 14.5 d

Ongar 35.5 d

Manningtree 16.42 d

44261909

44661301

44661301

No Data No Data No Data

Anaerobic aquatic 

metabolism half-life 160 d (total system) 43291704 No Data No Data No Data
Page 14 of 71

Fipronil Fipronil Sulfide (MB 45950)

Fipronil Sulfone (MB 

46136) MB 46513

Parameter Value(s)

Source 

(MRID) Value(s)

Source 

(MRID) Value(s)

Source 

(MRID) Value(s)

Source 

(MRID)

Soil Mobility

Organic carbonnormalized adsorption 

coefficient (KOC)

1248 mL/g

800 mL/g

673 mL/g

427 mL/g

486 mL/g

44039003

5621 mL/g

3530 mL/g

4362 mL/g

4349 mL/g

1695 mL/g

44537902

5310 mL/g

4054 mL/g

6745 mL/g

1448 mL/g

3486 mL/g

44537901

1150 mL/g

1498 mL/g

1164 mL/g

1245 mL/g

1392 mL/g

44262831

Dissipation

Terrestrial field 

dissipation half-life

(soil texture or crop)

1.1 months (FL bare sand)

0.4 months (FL turfed sand)

1.5 months (NC bare loamy 

sand)

1.5 months (NC turfed sand)

3.4 months (loam soil)

3.0 months (clay loam)

3.8 months (sand)

7.3 months (loamy sand)

159 d (CA cotton)

30.2 d (TX cotton)

192 d (WA potato)

44078601

43401103

44262826

No Data No Data No Data

Aquatic field dissipation 

half-life

(soil texture or crop)

Seed Treatment:

14.6 d (MS loam)

12.6 d (TX sandy loam)

11.9 d (CA clay)

Soil Pre-plant Incorporated:

17.4 d (MS loam)

18.8 d (TX sandy loam)

119 d (CA clay)

44443402 No Data No Data No Data
Page 15 of 71

Fipronil Fipronil Sulfide (MB 45950)

Fipronil Sulfone (MB 

46136) MB 46513

Parameter Value(s)

Source 

(MRID) Value(s)

Source 

(MRID) Value(s)

Source 

(MRID) Value(s)

Source 

(MRID)

Fish bioconcentration 

factors (BCF)

164× (edible)

575× (non-edible)

380× (whole fish)

43291706 No Data No Data No Data
Page 16 of 71

Abiotic Degradation

The chemical degradation of fipronil appears to be dependent predominantly on 

photodegradation in water and, to a lesser extent, on alkaline-catalyzed hydrolysis. 

Fipronil is stable (t1/2 > 30 days) in pH 5 and pH 7 buffer solution and hydrolyzes slowly

(t1/2=28 days) in pH 9 buffer solution. The major hydrolysis degradate is RPA 200766 (5-

amino-3-carbamoyl-1-(2,6-dichloro-4-trifluoromethylphenyl)-4-trifluoro-methanesulfinyl 

pyrazole. Photodegradation of fipronil is a major route of degradation (photodegradation 

in water half-life=3.63 hours) in aquatic environment. In contrast, fipronil 

photodegradation on soil surfaces (dark control corrected half-life=149 days) does not 

appear to be a major degradation pathway. Major photolysis products of fipronil are MB 

46513 (5-amino-3-cyano-1-(2,6-dichloro-4-trifluoromethyl-phenyl)-4-trifluoromethylpyrazole 350, and RPA 104615 (5-amino-3-cyano-1-(2,6-dichloro-4-trifluoro 

methyl phenyl) pyrazole-4-sulfonic acid).

Biotic Degradation

Fipronil degradation in terrestrial and aquatic systems appears to be controlled by slow 

microbially-mediated processes. In aerobic mineral soil, fipronil is moderately persistent 

to persistent (t1/2= 128 to 300 days). Major aerobic soil degradates (>10% of applied of 

fipronil) are RPA 200766 and MB 46136 (5-amino-1-(2,6-dichloro-4-trifluoro 

methylphenyl)-3-cyano-4-trifluoromethyl-sulphonyl-pyrazole). Minor degradates (<10% 

of applied fipronil) are MB 45950(5-amino-1-(2,6-dichloro-4-trifluoromethylphenyl)-3-

cyano-4-trifluoro-methyl-thio-pyrazole) and MB46513. These degradation products are 

not unique soil metabolism degradation products. Fipronil degraded (t1/2=14.5 days to 35 

days) under stratified redox aquatic/sediment systems. Fipronil also is moderately 

persistent (anaerobic aquatic t1/2 = 116-130 days) in anoxic aquatic environments. Major 

anaerobic aquatic degradates are MB 45950 and RPA 200766. Supplemental aerobic 

aquatic metabolism data indicate that fipronil degradation (t1/2=14 days) is rapid in 

aquatic environments with stratified redox potentials. These data contradict the longer 

fipronil persistence reported in anaerobic aquatic and aerobic soil studies.

Mobility

Fipronil has a moderate sorption affinity (Kf=4.19 to 20.69 mL/g; 1/n= 0.938 to 0.969; 

Koc= 427 to 1248 mL/g) on five non-United States soils (FAO mobility class: slightly

mobile). Fipronil sorption appears to be lower (Kf< 5 mL/g) on coarse-textured soils with 

low organic matter contents. Desorption coefficients for fipronil ranged from 7.25 to 

21.51 mL/g. These data suggest that fipronil sorption on soil is not a completely

reversible process. Since the fipronil sorption affinity correlates with soil organic matter 

content, fipronil mobility may be adequately described using a Koc partitioning model. 

Soil column leaching studies confirm the immobility of fipronil.
Page 17 of 71

Terrestrial Field Dissipation

Terrestrial field studies confirm observations of the relative persistence and immobility of 

fipronil residues in laboratory studies. Fipronil, formulated as a 1% granular, had halflives of 1.1 to 1.5 months on bare ground in North Carolina (NC) and Florida (FL), 0.4 to 

0.5 months on turf in NC and FL, and 3.4 to 7.3 months for in-furrow applications on 

field corn in California (CA), Nebraska (NE), NC, and Washington (WA). Fipronil, 

formulated as 80WG and applied as afoliar spray at 0.3 lbs ai/A, had a field dissipation 

half-life of 159 days on a cotton site in California, 30.2 days on a cotton site in 

Washington, and 192 days on a potato site in Washington.

The fipronil degradates MB 46136, MB45950, and RPA 200766 were detected in the 

field studies for in-furrow and turf uses. The degradate MB46513 was detected during 

field trials with the foliar spray. Fipronil residues were predominantly detected in the 0 to 

15 cm soil depth at all test sites. However, there was detection of fipronil, MB 45950, 

MB 46136 and RPA 200766 at a depth of 15 to 45 cm for in-furrow treatments on coarse 

sandy loam soil in Ephrata, Washington. Although the field dissipation half-life of 

individual residues was not reported, the half-life of combined fipronil residues 

(including fipronil, MB 46136, MB 46513, MB 45950, and RPA 200766) ranged from 9 

to 16 months.

Long-term field dissipation studies in Nebraska, Illinois, Ohio, Mississippi, Texas, and 

Washington show fipronil, applied at 0.13 to 0.20 lbs ai/A as a broadcast application with 

soil incorporation or foliar spray, is moderately persistent (t1/2 = 5.1 to 144.4 days) in 

surface soils. There was no discernable year-to-year accumulation of MB46513. There 

was year-to-year soil accumulation of MB 45950 and MB 46136. There were no 

detectable patterns of movement of fipronil residues except for MB46136. MB46136 was 

detected below 0.15 meter soil layer at all test sites except IL. The major routes of 

fipronil dissipation were through microbial-mediated oxidation to form MB46136, 

microbial-mediated reduction to MB45950, and photodegradation to form MB 46513.

Aquatic Field Dissipation

Fipronil residues were detected in soil samples in the California, Mississippi, and Texas 

field studies. Fipronil had calculated half-lives of 14.6 days (r2=0.94) and 17.4 days 

(r2=0.92) for Mississippi dry seeding and pre-plant incorporated (PPI) treatments, 12.6 

days (r

2

=0.53) and 18.8 days (r2=0.85) for Texas dry seeding, and PPI treatments, and 

11.9 days (r2=0.94) and 119 days (extrapolated) for California wet seeding and PPI

treatment, respectively. The calculated half-lives for combined Fipronil residues (fipronil, 

MB 46513, MB 45950, MB 46136, and RPA 200766) are 35.0 days (r2=0.67) and 97.6 

days (r2=0.63) for Mississippi dry seeding and PPI treatments, 99.0 days (r2=0.19) and 

347 days (r2=0.28) for Texas dry seeding and PPI treatments, and 210 days (r2=0.20) and 

257 (r2=0.41) days for California wet seeding and PPI treatments. (MRID 44443402)

Bioconcentration in Fish
Page 18 of 71

The bioconcentration factor for radiolabeled fipronil was 380× in whole fish, 164× in 

edible tissues, and 575× in non-edible tissues. Accumulated fipronil residues were 

eliminated (>96%) after a 14-day depuration period. Because fipronil exhibited a high 

depuration rate, fipronil is not expected to accumulate under flowing water conditions.

Environmental Fate of Fipronil Degradates

Because discernable decline patterns for the fipronil degradates were not observed in 

laboratory metabolism studies, the degradates are believed to be persistent (t1/2700 days) 

to microbially mediated degradation in terrestrial and aquatic environments. However, 

the fipronil degradate, MB46136, rapidly photodegrades (t1/2=7 days) in water. 

Radiolabelled MB 46513, applied at 0.1 μg/g, had an extrapolated half-life of 630 or 693 

days in loamy sand soils when incubated aerobically in the dark at 25oC. The major 

metabolite of MB 46513 was RPA 105048(5-amino-3-carbamoyl-1-(2,6-dichloro-4-

trifluoromethylphenyl)-4-trifluoromethyl sulfonyl pyrazone).

Fipronil degradation products have a relatively low potential mobility because of a 

moderate to high sorption affinity to soil organic matter. Organic carbon partitioning 

coefficients for fipronil degradates can range from 1150 to 1498 ml/g for MB 46513, 

1619 to 3521 ml/g for MB 45950, and 1448 to 6745 ml/g for MB 46136. The high 

sorption affinity of fipronil degradation products is expected to limit movement into 

ground and surface water (FAO Classification of mobility is “hardly mobile” for parent 

and all degradates).

IV. Receptors

Consistent with the process described in the Overview Document (USEPA 2004), the risk 

assessment for fipronil will rely on a surrogate species approach. Toxicological data 

generated from surrogate test species, which 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. 

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 fipronil on aquatic and terrestrial receptors. This includes toxicity data on the 

technical grade active ingredient, degradates, and when available, formulated products 

(e.g., “Six-Pack” studies). The open literature studies are identified using EPA’s 

ECOTOX database (USEPA 2007), which employs a literature search engine for locating 

chemical toxicity data for aquatic life, terrestrial plants, and wildlife. The evaluation of 

both sources of data can also provide insight into the direct and indirect effects of fipronil 

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

changes in structure and functional characteristics of the affected communities. The 

ECOTOX database was searched in 2007 and data discovered during that search is 

summarized herein. The Agency intends to conduct an updated search of the database 

prior to initiation of the draft risk assessment.
Page 19 of 71

The effects section of this document summarizes the endpoints used in past fipronil risk 

assessments. Table 2 below describes the test species surrogate applications to various 

receptor taxonomic categories.

Table 3. Test Species Evaluated for Assessing Potential Ecological Effects of Fipronil and the 

Associated Acute Toxicity Classification.

Taxonomic Group Surrogate Species

Acute Toxicity

--

Chronic Toxicity

Birds1 Bobwhite quail

(Colinus virginianus)

1-day LD50

8-day LC50

--

Reproduction NOAEC

Mammals Laboratory rat (Rattus norvegicus)

96-hr LD50

--

Reproduction NOAEC/LOAEC

Insects Honey bee 

(Apis mellifera L.)

Extended contact 72 hr

Freshwater fish2

Bluegill sunfish

(Leponis macrochirus)

--

Rainbow trout (Oncorynchus mykis) 

ACR applied to bluegill

96-hr LC50

--

ACR-based NOAEC

Freshwater invertebrates

Blackfly

(Simulium vittatum)

--

Water flea (Daphnia magna) ACR 

applied to blackfly

48-hr EC50

--

ACR-based NOAEC/LOAEC

Estuarine/marine fish Sheepshead minnow

(Cyprinodont variegatus)

96-hr LC50

--

NOAEC/LOAEC

Estuarine/marine 

invertebrates

Mysid 

(Americamysis bahia)

Eastern oyster

(Crassostrea virginica)

96-hr LC50

--

NOAEC/LOAEC

Terrestrial plants3

Seedling Emergence

(no data)

Vegetative Vigor (no data)

EC25/NOAEC

Aquatic plants and algae

Diatom

(Navicula pelliculosa)

Duckweed

(Lemna gibba)

5-day EC50

NOAEC

--

14-day EC50

NOAEC

A. Effects to Aquatic Organisms

Fipronil parent has been tested for acute effects in three species of fish with acute lethal 

endpoints ranging from 83 to 560 μg/L. Acute affects testing for freshwater invertebrates 

is available on at least 25 species and acute lethal endpoints range from 0.22 μg/L to 

>2000 μg/L. Available acute fish toxicity data for the three degradates of concern fall 

within these ranges in toxicity, though the number of species tested is far less than for the 
Page 20 of 71

parent compound. There are limited species tested in estuarine /marine organisms, but 

the invertebrate and fish endpoints are close to the range established for freshwater 

organisms. Chronic effects thresholds for fish are generally a half to two orders of 

magnitude lower than acute effects depending on the within species comparison made. In 

invertebrates, chronic effects endpoints are approximately an order of magnitude lower 

than the acute effects endpoint.

There are sediment toxicity data available for select midge species, but the effects in 

these species are quite similar to water only exposure-based effects endpoints in similar 

midge species.

Aquatic plant toxicity data are available to parent fipronil and with five species with no 

effects thresholds of 100 to 140 μg/L. Only the degradate MB46513 has been tested with 

aquatic plants and it is more potent than parent fipronil in the single species tested 

common to both chemicals. Owing to this potential difference and potential for 

degradates to be more potent than the parent, additional tier 1 aquatic plant testing 

(850.440 and 5400) is recommended.

B. Effects to Terrestrial Organisms

Fipronil has been tested in six species of birds for acute effects, including one 

passeriform species. The range in acute lethal endpoints is 11.3 to >2150 mg/kg-bw. 

The degradate MB46513 is the only degradate tested with birds, and within species 

comparisons suggest that the degradate is 2 to at least 5 times more acutely toxic than the 

parent. Sublethal dietary testing with the parent compound has been conducted in two 

species with the range in values of 48 to >5000 mg/kg-diet. Testing with all three 

degradates of concern with a species represented by the parent data set indicates the 

degradates are slightly less toxic than the parent via the dietary route. Chronic effects 

endpoints have only been empirically determined for the parent, but the relationship 

between acute and chronic endpoints for the parent has been routinely applied to the 

degradate acute data to derive chronic endpoints.

Acute and chronic mammalian data with the rat are the basis for mammalian wildlife risk 

assessment. Fipronil and MB45950 are relatively close in acute lethal potency with 

endpoints of 97 and 83 mg/kg-bw respectively. MB46136 is less toxic than the parent 

with an acute lethal endpoint of 218 mg/kg-bw and MB46513 is more toxic to rats than 

parent with an acute lethal endpoint of 16 mg/kg-bw. Only the parent has been tested for 

reproduction effects in mammals, but the relationship between acute and chronic 

endpoints for the parent has been routinely applied to the degradate acute data to derive 

chronic endpoints.

Terrestrial invertebrate testing is limited to a single honeybee extended foliar contact 

study showing an endpoint of 100 % mortality at a 25 g/a application rate. Acute contact 

and field studies are recommended for a more complete characterization of risks to insect 

pollinators.
Page 21 of 71

Tier 1 plant effects testing data are not available for fipronil products. Studies to provide 

suitable seedling emergence and vegetative vigor effects endpoints are recommended.

C. Degradate toxicity

Based on an analysis of available toxicity information and the prevalence of degradates in 

one or more environmental fate studies, the stressor of concern in the assessment include 

the parent (fipronil) and degradates: fipronil sulfide (MB 45950; CAS name: 5-amino-1-

(2,6-dichloro-4-(trifluoromethyl)phenyl)-4-trifluoromethylthio-1-pyrazole-3-

carbonitrile); fipronil sulfone (MB 46136; CAS name: 5-amino-1-(2,6-dichloro-a,a,atrifluoro-p-tolyl)-4-trifluoro-methylsulfonylpyrazole-3-carbonitrile); MB 46513 (CAS 

name: 5-amino-1-(2,6-dichloro-alpha,alpha,alpha-trifluoro-p-tolyl)-4-trifluoromethylpyrazole-3-carbonitrile).

D. Ecological Incidents

There are few incidents in the Agency database for effects on non-target organisms 

associated with the labeled use of fipronil. The degree to which the low number of years 

of outdoor use contributes to a lack of incidents is unknown.

Incident number I009142001 is a report of crayfish mortality following use of fipronil as 

a seed treatment on rice in Louisiana. The database classifies this incident as highly 

probable. In March of 1999 Louisiana Department of Agriculture and Safety issued a 

stop order to prevent the use of fipronil on rice seed in Allen, Calcasieu, Cameron, 

Lafayette, St. Martin, Iberia, St. Mary, St. Landry, Beauregard, Vermillion, Evangeline, 

Acadia, and Jefferson Davis Parishes. Fipronil was detected in 3 of 9 crawfish samples 

(mean detection 0.04 μg/kg). Fipronil was detected in water samples from 8 of 16 ponds 

(average 2.08 μg/L, high 6.09 μg/L), in all samples of the Mermentau River (average 

1.67 μg/L, high 3.16 μg/L), and 14 of 17 other water monitoring sites (average 0.84 μg/L, 

high 5.33 μg/L). the registrant (Rhone-Poulenc reported that 17 crawfish growers had 

reported to them observations of crawfish at the edges of ponds bordering rice fields 

planted with fipronil-treated rice. The LA department of Agriculture was investigating 

31 reported incidents of crawfish kills on rice. Among the department and registrant 

reports there were 45 total incidents. The Louisiana state university Agricultural center 

conducted a survey and several experiments which substantiated the link between 

fipronil-treated rice seed and reduced survival of crawfish under hot dry weather 

conditions. Fipronil is no longer registered for rice seed treatment.

There are two reports of corn crop damage (I011723098 300 acres in North Dakota, and 

I013103054300 550 acres in Idaho) following use of fipronil Regent SC. These incidents 

are classified in the database as possible (Idaho incident) and probable (North Dakota). In 

neither incident report are there any confirmatory residue analyses.
Page 22 of 71

Another probable incident, outside the United States, is also reported in the Agency

database. It involves locust control efforts on the island of Madagascar (I010380001). 

The incident was summarized in a BBC news article. The article refers to survey results 

citing declines in the Madagascar bee eater and a kestrel species. In addition, surveys of 

termite colonies showed a 90% elimination rate ten months after spraying. There are no 

confirmatory analytical data reported in the incident summary.

Finally, incident I010775001 reported that fipronil treated sunflower seeds were 

potentially responsible for observations of honeybee hive mortality in France. This 

incident is controversial as another, commonly accepted to be systemic pesticide, was 

also implicated. The incident report includes no third party confirmation or refutation of 

the fipronil alleged involvement in the incident.

D. Ecosystems Potentially at Risk

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.

Aquatic ecosystems potentially at risk 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.

V. Assessment Endpoints

Assessment endpoints represent the actual environmental value that is to be protected, as 

defined by an ecological entity (species, community, or other entity) and its attribute or 

characteristics (EPA 1998). For fipronil, the ecological entities include the following: 

birds, reptiles, terrestrial-phase amphibians, mammals, freshwater fish, freshwater 

aquatic-phase amphibians and invertebrates, estuarine/marine fish and invertebrates, 

terrestrial plants, insects, aquatic plants, and algae. The attributes for each of these 

entities include growth, reproduction, and survival.

VI. Conceptual Model

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

biologically significant concentrations. An exposure pathway is the means by which a 
Page 23 of 71

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

ecological 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.

The conceptual model for fipronil provides a written description and visual representation 

of the predicted relationships between fipronil, 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).

A. Risk Hypothesis

A risk hypothesis describes the predicted relationship among the stressor, exposure, and 

assessment endpoint response along with the rationale for their selection. For fipronil, 

the following ecological risk hypothesis is being employed for this national-level 

ecological risk assessment:

Fipronil, when used in accordance with current labels, can result in off-site 

movement of the compound via runoff, erosion of sediment-bound residues and 

spray drift leading to exposure of nontarget plants and animals. Applications to 

foliar surfaces may serve as a major source of fipronil exposure to wildlife. This 

potential exposure pathway may result in adverse effects upon the survival, 

growth, and reproduction of non-target terrestrial and aquatic organisms. These 

nontarget organisms include Federally-listed threatened and endangered species.

B. Conceptual Diagram

The environmental fate properties of fipronil indicate that runoff, erosion of sedimentbound residues, and spray drift represent potential transport mechanisms of fipronil to 

aquatic and terrestrial organisms. These transport mechanisms (e.g., sources) are 

depicted in the conceptual models below (Figures 5 and 6) and result in the movement of 

fipronil into aquatic (water and sediment) and terrestrial (soil and foliage) habitats. The 

movement away from the site of application in turn represents exposure pathways for a 

broad range of biological receptors of concern (nontarget animals) and the potential 

attribute changes, i.e., effects such as reduced survival, growth and reproduction, in the 

receptors due to fipronil exposure. 
Page 24 of 71

Figure 5. Conceptual model depicting stressors, exposure pathways, and potential effects to aquatic 

organisms from the use of fipronil. 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 

Stressor

Source

Receptors

Attribute

Change

Fipronil applied to use site

Spray drift

Aquatic animals

Invertebrates 

Vertebrates

**Piscivorous mammals 

 and birds 

Individual 

organisms

Reduced survival

Reduced growth

Reduced 

Food chain

Reduction in algae and 

 vascular plants

Reduction in prey

Modification of PCEs 

 related to prey availability

Habitat integrity

Reduction in primary 

 productivity

Reduced cover

Community change

Modification of PCEs related to 

 habitat

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
Page 25 of 71

Figure 6. Conceptual model depicting stressors, generic exposure pathways, and potential effects to 

terrestrial organisms (terrestrial plants, terrestrial invertebrates, and dietary routes of exposure for 

terrestrial vertebrates) from the use of fipronil. Dotted lines indicate exposure pathways that have a 

low likelihood of contributing to ecological risk.

VII. Analysis Plan 

In order to address the risk hypothesis, the potential for adverse effects on the 

environment is estimated. The use, environmental fate, and ecological effects of fipronil 

are characterized and integrated to assess the risks. This is accomplished using a risk 

quotient (ratio of exposure concentration to effects concentration) approach. Although 

risk is often defined as the likelihood and magnitude of adverse ecological effects, the 

risk quotient-based approach does not provide a quantitative estimate of likelihood and/or 

magnitude of an adverse effect. However, as outlined in the Overview Document 

(USEPA 2004), the likelihood of effects to individual organisms from particular uses of 

fipronil is estimated using the probit dose-response slope and either the level of concern 

(discussed below) or actual calculated risk quotient values.

Stressor

Source

Attribute

Change

Fipronil applied to use site

Direct

application Spray drift

Terrestrial 

vertebrates

Terrestrial 

inverts

Individual 

organisms

Reduced survival

Reduced growth

Reduced reproduction

Food chain

Reduction in prey and food

Modification of PCEs 

 related to prey availability

Habitat integrity

Reduction in primary productivity

Reduced cover

Community change

Modification of PCEs related

 to habitat

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
Page 26 of 71

This analysis plan will be revisited and may be revised depending upon the information 

submitted by the public in response to the opening of the Registration Review docket for 

fipronil.

A. Stressors of Concern

Based on an analysis of available toxicity information and the prevalence of degradates in 

one or more environmental fate studies the stressor of concern in the assessment include 

the parent (fipronil) plus the following degradates:

MB 45950 Fipronil Sulfide

CAS name: 5-amino-1-(2,6-dichloro-4-(trifluoromethyl)phenyl)-4-trifluoromethylthio-1-

pyrazole-3-carbonitrile

MB 46136 Fipronil Sulfone

CAS name: 5-amino-1-(2,6-dichloro-a,a,a-trifluoro-p-tolyl)-4-trifluoromethylsulfonylpyrazole-3-carbonitrile

MB 46513

CAS name: 5-amino-1-(2,6-dichloro-alpha,alpha,alpha-trifluoro-p-tolyl)-4-trifluoromethylpyrazole-3-carbonitrile

Evaluation of environmental pesticide mixtures is beyond the scope of this assessment 

because of the myriad factors that cannot be quantified based on the available data. 

Those factors include identification of other possible co-contaminants and their 

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

and the differential effects of other physical/chemical characteristics of the receiving 

waters (e.g., organic matter present in sediment and suspended water). Evaluation of 

factors that could influence additivity/synergism is beyond the scope of this assessment 

and the capabilities of the available data to allow for an evaluation. However, it is 

acknowledged that not considering mixtures could over- or under-estimate risks 

depending on the type of interaction and factors discussed above. The assessment will, 

however, analyze the toxicity of formulated products (including formulations involving 

more than one active ingredient) and will determine whether formulated products are 

more toxic than the technical grade active ingredient.

B. Measures of Exposure 

In order to estimate risks of fipronil exposures in aquatic and terrestrial environments, all 

exposure modeling and resulting risk conclusions will be based on maximum application 

rates and methods cited in Table 1 (of Appendix 1) and will be estimated for each use of 

fipronil. Measures of exposure are based on aquatic and terrestrial models that predict 

estimated environmental concentrations (EECs) of fipronil. The models used to predict 

aquatic EECs are the Pesticide Root Zone Model coupled with the Exposure Analysis 

Modeling System (PRZM/EXAMS). The model used to predict terrestrial EECs on food 
Page 27 of 71

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

plants is TerrPlant. These models are parameterized using relevant reviewed 

environmental fate data from registrant submissions and the literature; model input values

will be consistent with the most recent version of the input parameter guidance (Version 

2; EFED 2002).

PRZM and EXAMS are simulation models coupled with the linkage program shell, PE5, 

which incorporates the standard scenarios developed by EFED. The models generate 

daily exposures and calculated 1-in-10 year EECs of fipronil (and degradates of concern) 

that may occur in surface water bodies adjacent to application sites. PRZM simulates 

pesticide fate and transport as a result of leaching, direct spray drift, runoff and erosion 

from an agricultural field, and EXAMS estimates environmental fate and transport of 

pesticides in a surface water body for a 30-year period. The standard scenarios used for 

ecological pesticide assessments assume application to a 10-hectare agricultural field that 

drains into an adjacent 1-hectare water body that is 2 meters deep (20,000 m3volume) 

with no outlet. The combined models (i.e., PRZM/EXAMS) are designed to estimate 

pesticide concentrations found in the water body (standard pond) at the edge of the 

treated field. As such, they provide high-end values of the pesticide concentrations that 

might be found in ecologically sensitive environments following pesticide application. 

The location of the field is specific to the crop being simulated using site-specific 

information on the soils, weather, cropping, and management factors associated with the 

scenario. The crop/location scenario is intended to represent a high-end exposure site on

which the crop is normally grown. Based on historical rainfall patterns, the receiving 

water body receives multiple runoff events during the years simulated. Weather and 

agricultural practices are simulated for 30 years so that the 10-year exceedance 

probability at the site can be estimated. The simulation is generated using 30 years of 

meteorological data, typically, encompassing the years from 1961 to 1990. Additional 

information on these models can be found at: 

http://www.epa.gov/oppefed1/models/water/index.htm. 

To estimate exposure related to releases of fipronil and its degradates through domestic 

wastewater treatment plants, the Agency will rely on the Office of Pollution Prevention 

and Toxics (OPPT) model, Exposure and Fate Assessment Screening Tool (EFAST, 

version 2.0, or EFAST2, 2007). From this model, the Agency will use the “Down-theDrain” module, which is designed for releases to domestic wastewater treatment. It is 

suitable for all the sources of fipronil and its degradates that could potentially be exposed 

through a “down-the-drain” scenario. The model provides screening level estimate 

concentrations of chemicals in surface water that may result from household uses and the 

disposal of consumer products into wastewater using a few simple input parameters 

(production volume and fraction of the chemical removed during wastewater treatment).

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 chronic exposure to aquatic invertebrates.
Page 28 of 71

Exposure estimates for terrestrial animals assumed to be in the target area or in an area 

exposed to spray drift are derived using the T-REX model. This model incorporates the 

Kenega nomograph, as modified by Fletcher et al. (1994), which is based on a large set 

of field residue data. The upper limit values from the nomograph represent the 95th

percentile of residue values from actual field measurements (Hoerger and Kenega 1972). 

The Fletcher et al. (1994) modifications to the Kenega nomograph are based on measured 

field residues from 249 published research papers, including information on 118 species 

of plants, 121 pesticides, and 17 chemical classes. EECs for terrestrial plants inhabiting 

dry and wetland areas are derived using TerrPlant. 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.

Available monitoring data will be used to qualitatively characterize exposure and 

compare with modeling results. The Agency is aware of monitoring conducted by storm 

water management agencies and this route of exposure will be considered in the 

assessment to the extent that data on fipronil are available.

Two spray drift models, AGDISP and AgDRIFT will be used to assess exposures of 

terrestrial plants to fipronil deposited in terrestrial habitats by spray drift. AgDrift will be 

used to simulate ground applications.

C. Measures of Effect

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

receptors. Data were obtained from registrant-submitted studies or from literature studies 

identified by ECOTOX. The ECOTOXicology database (ECOTOX) was searched in 

order to provide more ecological effects data 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 

(USEPA 2007).

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

from the Ecological Incident Information System (EIIS; USEPA 2007c). 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.

Where available, sublethal effects observed in both registrant-submitted and open 

literature studies will be evaluated qualitatively. Such effects have included behavioral 

changes (e.g., lethargy, changes in coloration and effects olfaction). 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.
Page 29 of 71

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

that toxicity of fipronil to birds is similar to terrestrial-phase amphibians and reptiles. The 

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

The acute measures of effect used for animals in this screening-level assessment are the 

LD50, LC50 and EC50. 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/NOAEC and NOEC. NOAEL stands for “No 

Observed-Adverse-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-Observed-Adverse-Effect-Concentration”) is the highest test concentration at 

which none of the observed effects were statistically different from the control. The 

NOEC is the No-Observed-Effects-Concentration. 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.

In the absence of data for either acute or chronic effects for fipronil or degradates of 

concern, the risk assessment will make conservative assumptions based on extrapolations 

from the existing available data.

D. 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 fipronil on forestry uses (forest 

tree management/forest pest management, forest trees (softwoods, conifers), and pine 

(forest/shelterbelt)); outdoor residential uses (household/domestic dwellings outdoor 

premises, refuse/solid waste containers (garbage cans), and residential lawns); terrestrial 

food + feed crop uses (orchards (unspecified), potato and white/Irish); terrestrial nonfood + outdoor residential uses (fencerows/hedgerows, ornamental and/or shade trees, 

and paths/patios); and terrestrial non-food crop uses (Christmas tree plantations, 

commercial storages/warehouses premises, commercial/industrial lawns, 

commercial/institutional/industrial premises/equipment (outdoor), field corn, golf course 

turf, industrial / construction areas (outdoor), nonagricultural outdoor 

buildings/structures, nonagricultural uncultivated areas/soils, nursery stock, ornamental 

and/or shade trees, ornamental herbaceous plants, ornamental lawns and turf, ornamental 

non-flowering plants, ornamental sod farm (turf), ornamental woody shrubs and vines, 

paved areas (private roads/sidewalks), potting soil/topsoil, recreation area lawns, 

recreational areas, refuse/solid waste sites (outdoor), utility poles / right-of-way, wood 

protection treatment to buildings/products outdoor, and zoos 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 fipronil risks, the risk 
Page 30 of 71

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 are used to 

indicate when fipronil’s uses, as directed on the label, have the potential to cause adverse 

direct or indirect effects to non-target organisms. As noted previously, where data are 

lacking on the toxicity of fipronil, risk will be presumed.

1. Deterministic and Probabilistic Assessment Methods

The quantitative assessment of risk will primarily depend on the deterministic pointestimate based approach described in the risk assessment. An effort will be made to 

further qualitatively describe risk using probabilistic tools that the Agency has developed. 

These tools have been reviewed by FIFRA Scientific Advisory Panels and have been 

deemed as appropriate means of refining assessments where deterministic approaches 

have identified risks.

E. 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 fipronil. 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 registrations of fipronil 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 fipronil application occurs), plus all areas where offsite 

transport (i.e., spray drift, runoff, etc.) 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 sublethal 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 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.
Page 31 of 71

F. Drinking Water Assessment

A drinking water assessment will be conducted to support future human health dietary

risk assessments of fipronil. The drinking water assessment will incorporate model 

estimates of fipronil plus degradates of concern in surface water and ground water. 

Concentrations of fipronil residues in surface waters will be estimated using 

PRZM/EXAMS (see description above).

An Estimated Drinking Water Concentration (EDWC) of fipronil residues in ground 

water will be estimated using EFED’s Tier I aquatic model SCI-GROW (Screening 

Concentration in Ground Water). SCI-GROW is a regression model used as a screening 

tool to estimate pesticide concentrations found in ground water used as drinking water. 

The output of SCI-GROW represents the concentrations that might be expected in 

shallow unconfined aquifers under sandy soils, which is representative of the ground 

water most vulnerable to pesticide contamination likely to serve as a drinking water 

source. The drinking water assessment will also include available surface and ground 

water monitoring data with consideration of changes in use patterns that may have 

occurred. States are encouraged to submit monitoring data for review.

G. Preliminary Identification of Data Gaps 

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, and 

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 postapplication agricultural scenarios. This list should not be construed as a list of known or 

likely endocrine disruptors.

Fipronil and its degradates of concern are not among the group of 58 pesticide active 

ingredients on the initial list to be screened under the EDSP. The Agency will review the 

EDSP Tier 1 data and any “other scientifically relevant information” submitted in 
Page 32 of 71

response to test orders. Based on this review the Agency will determine the need for 

additional testing. 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 refer to the following website: http://www.epa.gov/endo/ .

H. Preliminary Identification of Data Gaps 

1. Fate

The environmental fate data set is complete for the parent fipronil (Table 4). However, 

the fate data sets for the degradates of concern are incomplete. Fipronil sulfide (MB 

45950) is formed as a major degradate of fipronil (greater than 10% of parent applied) in 

both terrestrial and aquatic laboratory studies and aquatic field, terrestrial field, long-term 

soil dissapation studies. Therefore, both aquatic and terrestrial fate studies are needed for 

fipronil sulfide (Table 5). Fipronil sulfone (MB 46136) only occurs as a major degradate 

in terrestrial fate and field studies. Because of concerns with accumulation in the 

terrestrial environment and runoff from terrestrial environments, both aquatic and 

terrestrial fate studies are needed for fipronil sulfone (Table 6). MB 46513 only occurs as 

a major degradate in aquatic fate studies. Therefore, aquatic fate studies are needed for 

MB 46513 (Table 7). (See Appendix 1 Table B for maximum reported amounts of 

fipronil degradation products from each fate study.)

Table 4. Available environmental fate data for fipronil and remaining data gaps.

158

Guideline

(OPPTS)

Description Reference (MRID) Classification Data 

Gap? Comments

161-1

(835.2120)

Hydrolysis 42194701 Acceptable No

161-2

(835.2240)

Photodegradation 

in water

42918661 Acceptable No

161-3

(835.2410)

Photodegradation 

on soil

42918662 Acceptable No

162-1

(835.4100)

Aerobic soil 

metabolism

42918663

44262830

Acceptable

Acceptable

No

162-2

(835.4200)

Anaerobic soil 

metabolism

None Submitted Yes In absence of 

acceptable data, 2× 

the aerobic soil 

metabolism rate

will be used in 

exposure 

assessment.

162-3

(835.4400)

Anaerobic Aquatic 

Metabolism

43291704 Acceptable No

162-4

(835.4300)

Aerobic Aquatic 

Metabolism

44261909

44661301

Marginally acceptable No Conducted in 

stratified redox 

conditions.
Page 33 of 71

158

Guideline

(OPPTS)

Description Reference (MRID) Classification Data 

Gap? Comments

163-1

(835.1230)

(835.1240)

Leaching and 

adsorption/

desorption

42918664

43018801

44039003

44262831

44537901

44537902

44537903

Acceptable

Acceptable

Acceptable

Acceptable

Acceptable

Acceptable

Acceptable

No

164-1

(835.6100)

Terrestrial Field 

Dissipation

43291705

43401103

44262826

44262827

44298001

Acceptable

Acceptable

Acceptable

(supplemental material)

(supplemental material)

No

164-2 Aquatic field 

dissipation

44443402

45344701

46016801

Acceptable

Acceptable

Acceptable

No

164-5 Long term soil 

dissipation

44952701

45279901

46038001

46477001

Acceptable

Acceptable

Acceptable

Acceptable

No

165-4

(850.1730)

Bioaccumulation in 

Fish

43291706

43291707

44298002

Acceptable No

165-5 Bioaccumulation in 

aquatic non-target 

organisms

45183601 Acceptable No

Table 5. Available environmental fate data for fipronil sulfide (MB 54950) and remaining data gaps.

158

Guideline

(OPPTS)

Description Reference (MRID) Classification Data 

Gap? Comments

63-8

(830.7840)

Water Solubility None Yes

161-1

(835.2120)

Hydrolysis None Yes

161-2

(835.2240)

Photodegradation 

in water

None Yes

161-3

(835.2410)

Photodegradation 

on soil

None Yes

162-1

(835.4100)

Aerobic soil 

metabolism

None Yes

162-2

(835.4200)

Anaerobic soil 

metabolism

None Yes

162-3

(835.4400)

Anaerobic Aquatic 

Metabolism

None Yes

162-4

(835.4300)

Aerobic Aquatic 

Metabolism

None Yes
Page 34 of 71

158

Guideline

(OPPTS)

Description Reference (MRID) Classification Data 

Gap? Comments

163-1

(835.1230)

(835.1240)

Leaching and 

adsorption/

desorption

44537902 Acceptable No

164-1

(835.6100)

Terrestrial Field 

Dissipation

None Yes

165-4

(850.1730)

Bioaccumulation in 

Fish

None Yes

Table 6. Available environmental fate data for fipronil sulfone (MB 46136) and remaining data gaps.

158

Guideline

(OPPTS)

Description Reference (MRID) Classification Data 

Gap? Comments

161-1

(835.2120)

Hydrolysis None Yes

161-2

(835.2240)

Photodegradation 

in water

None Yes

161-3

(835.2410)

Photodegradation

on soil

None Yes

162-1

(835.4100)

Aerobic soil 

metabolism

None Yes

162-2

(835.4200)

Anaerobic soil 

metabolism

None Yes

162-3

(835.4400)

Anaerobic Aquatic 

Metabolism

None Yes

162-4

(835.4300)

Aerobic Aquatic 

Metabolism

None Yes

163-1

(835.1230)

(835.1240)

Leaching and 

adsorption/

desorption

44537901 Acceptable No

164-1

(835.6100)

Terrestrial Field 

Dissipation

None Yes

165-4

(850.1730)

Bioaccumulation in 

Fish

None Yes

Table 7. Available environmental fate data for MB46513 and remaining data gaps.

158

Guideline

(OPPTS)

Description Reference (MRID) Classification Data 

Gap? Comments

161-1

(835.2120)

Hydrolysis None Yes

161-2

(835.2240)

Photodegradation 

in water

None Yes
Page 35 of 71

158

Guideline

(OPPTS)

Description Reference (MRID) Classification Data 

Gap? Comments

161-3

(835.2410)

Photodegradation 

on soil

None No Occurs as a major 

degradate in 

aquatic fate studies 

only

162-1

(835.4100)

Aerobic soil 

metabolism

44262830 Acceptable No

162-2

(835.4200)

Anaerobic soil 

metabolism

None No Occurs as a major 

degradate in 

aquatic fate studies 

only

162-3

(835.4400)

Anaerobic Aquatic 

Metabolism

None Yes

162-4

(835.4300)

Aerobic Aquatic 

Metabolism

None Yes

163-1

(835.1230)

(835.1240)

Leaching and 

adsorption/

desorption

44262831 Acceptable No

164-1

(835.6100)

Terrestrial Field 

Dissipation

None No Occurs as a major 

degradate in 

aquatic fate studies 

only

165-4

(850.1730)

Bioaccumulation in 

Fish

None Yes

2. Effects

The following table presents the status of study submissions to comply with 40 CFR 

Section 148 data requirements applicable to fipronil and degradates of concern for the 

outdoor sues of the compound as formulated. Although many submissions have been 

made to provide data on the effects of fipronil and the three degradates of concern to 

aquatic and terrestrial organisms, gaps in experimental effects information still exist. 

With the exception of outstanding pollinator and plant testing there are no appreciable 

data gaps regarding laboratory testing for biological effects that have previously impacted 

the quantitative assessment of risks to the taxa that form the basis of risk assessment 

process described in the Overview of Ecological Risk Assessment process in the Office 

of Pesticide Programs (USEPA 2004).

Table 8. Non-Target Organism Toxicity Data Gaps

Test guideline 

Number Description Chemical Reference Classification

Data 

Gap? Comments

850.2100 Avian oral Fipronil 42918617

42918618

acceptable no 2

MB46136 -- -- yes 1

MB46513 43776601 acceptable yes 3

MB45950 -- -- yes 1

850.2200 Avian dietary Fipronil 42918620 acceptable no
Page 36 of 71

Test guideline 

Number Description Chemical Reference Classification

Data 

Gap? Comments

MB46136 44890301 acceptable no

MB46513 4529201 acceptable no

MB45950 44890302 acceptable no

850.2300 Avian 

reproduction

Fipronil 42918622/3 acceptable no

MB46136 -- -- yes 1

MB46513 -- -- yes 1

MB45950 -- -- yes 1

850.3020 Honey bee acute 

contact

Fipronil -- -- yes

MB46136 -- -- yes

MB46513 -- -- yes

MB45950 -- -- yes

850.3030 Honey bee foliage 

residue toxicity

Fipronil 44884101 supplemental yes

MB46136 -- -- yes

MB46513 -- -- yes

MB45950 -- -- yes

850.3040 Field testing for 

pollinators

Fipronil -- -- yes

MB46136 -- -- no 4

MB46513 -- -- no 4

MB45950 -- -- no 4

850.4100 Seedling 

emergence Tier 1

Fipronil -- -- yes

MB46136 -- -- no 4

MB46513 -- -- no 4

MB45950 -- -- no 4

850.4150 Vegetative vigor 

Tier 1

Fipronil -- -- yes

MB46136 -- -- no 4

MB46513 -- -- no 4

MB45950 -- -- no 4

850.1075 Freshwater fish 

acute toxicity

Fipronil 42977902

42918624

acceptable no

MB46136 429218673

42918674

acceptable no

MB46513 43279702

43291718

43279703

acceptable no

MB45950 -- -- yes 1

850.1010 Freshwater 

invertebrate acute 

toxicity

Fipronil 42918625 acceptable no 5

MB46136 42918671 acceptable no

MB46513 -- -- yes 5

MB45950 42918669 acceptable no

850.1300 Freshwater 

aquatic 

invertebrate life 

cycle

Fipronil 42918626 acceptable no

MB46136 -- -- yes 1

MB46513 43279704,

44812801

acceptable no

MB45950 -- -- yes 1

850.1400 Freshwater fish 

early life stage 

Fipronil 42918627 acceptable no

MB46136 -- -- yes 1

MB46513 -- -- yes 1

MB45950 -- -- yes 1

850.1025/1055 Oyster acute Fipronil 3291701 acceptable no
Page 37 of 71

Test guideline 

Number Description Chemical Reference Classification

Data 

Gap? Comments

toxicity/bivalve 

acute toxicity

MB46136 -- -- yes

MB46513 -- -- yes

MB45950 -- -- yes

850.1035/1045 Mysid acute 

toxicity/penaeid 

shrinp acute 

toxicity

Fipronil 43279701 acceptable no

MB46136 45156301 acceptable no

MB46513 45120001 acceptable no

MB45950 45156302 acceptable no

850.1075 Estuarine/marine 

fish

Fipronil 43291702 acceptable no

MB46136 -- -- yes 1

MB46513 -- -- yes 1

MB45950 -- -- yes 1

850.1350 Estuarine-marine 

invertebrate life 

cycle

Fipronil 43681201 supplemental yes 6

MB46136 45259203 acceptable no

MB46513 -- -- yes 1

MB45950 45259202 acceptable no

850.1400/1500 Estuarine-marine 

fish early life 

stage/full life 

cycle

Fipronil 44605502

45265101

acceptable no

MB46136 -- -- yes 1

MB46513 -- -- yes 1

MB45950 -- -- yes 1

850.4400/5400 Aquatic plant tier 

1

Fipronil 42918658

42918656

42918660

42918659

42918657

acceptable no

MB46136 -- -- yes 1

MB46513 43279705 acceptable yes 7

MB45950 -- -- yes 1

850.1735 Whole sediment 

acute freshwater 

invertebrate 

toxicity

Fipronil 45878001 acceptable yes 8

MB46136 45175901 acceptable yes 8

MB46513 45375901 acceptable yes 8

MB45950 45084801 acceptable yes 8

850.1740 Whole sediment 

acute estuarine 

marine 

invertebrate 

toxicity

Fipronil -- -- yes

MB46136 -- -- yes

MB46513 -- -- yes

MB45950 -- -- yes

850.1790 Chronic Sediment 

Toxicity

Fipronil -- -- yes

MB46136 -- -- yes

MB46513 -- -- yes

MB45950 -- -- yes

1- Estimated value used in previous risk assessments

2- Non-passerine and passerine requirements will be of lesser concern met

3-Non-passerine requirement met, passerine not met but available parent data suggest passerines

4- Testing with parent pesticide should suffice to represent contributions from degradates

5- Literature value used in place of guideline study in past risk assessments

6- Previously waived requirement of repeated study though no NOEC established

7- Single species tested, requirement outstanding for multiple unicellular and vascular aquatic plants

8- single species tested (Chironimus tentans), current requirements include two additional species (Hyalella 

azteca and Leptocheirus plumulosus)
Page 38 of 71

The following tables present the previous risk assessment approaches for establishing 

estimated effects endpoints for various taxonomic groups in the absence of empirical 

effects with the respective taxonomic group and chemical. In these tables, any

established effects threshold with an origin number of “1” is derived from direct testing. 

All other origin codes correspond to a situation here there are no available effects data 

suitable for risk assessment and where some estimation approach was used to continue 

with risk assessment. The Agency considers these estimation areas to be gaps in the 

available suite of empirical effects knowledge. The Agency proposes to reevaluate 

situations where estimation methods were used in past risk assessment, in light of new 

effects data searches, and determine if the same or similar estimation assumptions will 

continue for the Registration Review effort or if new data are available. The Agency

desires public comment in this regard.

Table 9. Terrestrial Organism Toxicity Endpoints Used in Past Risk Assessment

Chemical

Acute Toxicity 

Threshold

Chronic Toxicity 

Threshold

Acute 

Threshold 

Origin

Chronic 

Threshold 

Origin

Birds

Fipronil LD50 11.3 mg/kg-bw 

LC50 48 mg/kg-diet

NOEC 10 mg/kg-diet 1 1

MB46136 LD50 19.7 mg-bw

LC50 84mg/kg-diet

NOEC 10 mg/kg-diet 3

1

2

MB46513 LD50 5 mg/kg-bw

LC50 119.2 mg/kg-diet

NOEC 10 mg/kg-diet 1 2

MB45950 LD50 26.79 mg/kg-bw

LC50 114 mg/kg-bw

NOEC 10 mg/kg-diet 3

1

2

Mammals

Fipronil LD50 97 mg/kg-bw NOEC 30 mg/kg-diet 

NOEL 2.64 mg/kg-bw

1 1

MB46136 LD50 218 mg/kg-bw NOEC 30 mg/kg-diet 

NOEL 2.64 mg/kg-bw

1 2

MB46513 LD50 16 mg/kg-bw NOEC 30 mg/kg-diet 

NOEL 2.64 mg/kg-bw

1 2

MB45950 LD50 83 mg/kg-bw NOEC 30 mg/kg-diet 

NOEL 2.64 mg/kg-bw

1 2

Plants

Fipronil 0.025 lb/acre (NOEC) Not applicable 1 Not applicable

MB46136 0.025 lb/acre (NOEC) Not applicable 2 Not applicable

MB46513 0.025 lb/acre (NOEC) Not applicable 2 Not applicable

MB45950 0.025 lb/acre (NOEC) Not applicable 2 Not applicable

1 most sensitive species tested

2 assumed to be equivalent to parent fipronil

3 estimated by multiplying available LC50 by parent fipronil LD:LC50 ratio

Table 10. Aquatic Organism Toxicity Endpoints Used in Past Risk Assessment

Chemical

Acute Toxicity 

Threshold μg/L

Chronic Toxicity 

Threshold μg/L

Acute Threshold 

Origin

Chronic 

Threshold Origin

Freshwater Fish

Fipronil 83 6.6 1 1
Page 39 of 71

Chemical

Acute Toxicity 

Threshold μg/L

Chronic Toxicity 

Threshold μg/L

Acute Threshold 

Origin

Chronic 

Threshold Origin

MB46136 25 0.67 1 2

MB46513 20 0.59 1 2

MB45950 83 6.6 3 3

Estuarine/Marine Fish

Fipronil 130 0.24 1 1

MB46136 21 0.039 4 5

MB46513 31 0.057 4 5

MB45950 130 0.24 3 3

Freshwater Invertebrates

Fipronil 0.22 0.011 1 6

MB46136 0.72 0.037 1 6

MB46513 200 10.31 1 6

MB45950 2.13 0.11 1 6

Estuarine/Marine Invertebrates

Fipronil 0.14 <0.005 1 1

MB46136 0.56 <0.0026 1 1

MB46513 1.5 0.054 1 7

MB45950 0.077 0.0046 1 1

Freshwater Plants (endpoints non-listed/listed plants)

Fipronil Unicellular 

140/<140

Vascular 

>100/100

Not applicable 1 Not applicable

MB46136 Unicellular 

140/<140

Vascular 

>100/100

Not applicable 3 Not applicable

MB46513 Unicellular 

>76/7.5

Vascular 

>100/100

Not applicable 3 Not applicable

MB45950 Unicellular 

140/<140

Vascular 

>100/100

Not applicable 3 Not applicable

Estuarine/Marine Plants

Fipronil >140/140 Not applicable 1 Not applicable

MB46136 >140/140 Not applicable 3 Not applicable

MB46513 >76/7.5 Not applicable 1 Not applicable

MB45950 >140/140 Not applicable 3 Not applicable

1 most sensitive species tested

2 most sensitive species tested acute value divided by O. mykis acute:chronic ratio of parent fipronil

3 assumed to be equivalent to parent fipronil for vascular and most sensitive plant species for unicellular

4 estimated based on estuarine/marine value for parent fipronil divided by largest freshwater fish acute 

parent to degradate ratio 

5 estimated by dividing acute value by parent acute to chronic ratio for estuarine/marine fish

6 lowest acute value divided by parent fipronil acute:chronic ratio for D. magna

7 lowest acute value divided by parent fipronil acute:chronic ratio of A. bahia

A full accounting of data available at the time of the last ecological risk assessment 

performed in 2007 for fipronil are included in Appendix 3.
Page 40 of 71

VIII. References 

Ali, A., J.K. Nayar, and W. Gu. 1998. Toxicity of a phenyl pyrazole insecticide, 

fipronil, to mosquito and chironomid midge larvae in the laboratory. Journal of 

the American Mosquito Control Association 14:216-218.

Avery, M. L., T. M. Primus, E. M. Mihaich, D. G. Decker, and J. S. Humphrey. 1998. 

Consumption of fipronil-treated rice seed does not affect captive blackbirds. 

Pesticide Science 52:(91-96).

Biever, R.C., J.R. Hoberg, B. Jacobson, E. Dionne, M. Sulaaiman, and P McCahon. 

2003. Icon rice seed treatment toxicity to crayfish (Procambarus clarkii) in 

experimental rice paddies. Environmental Toxicology and Chemistry 22:167-

174.

Chandler, G.T., T.L. Cary, D.C. Volz, S.S. Walse, J.L. Ferry, and S.L. Klosterhaus. 

20034. Fipronil effects on estuarine copepod (Amphiascus tenuiremis) 

development, fertility, and reproduction: A rapid life-cycle assay in 96-well 

microplate format. Environmental Toxicology and Chemistry 23:117-124.

Chaton, P.F., P. Ravanel, M. Tissut, and J.C. Meyran. 2002. Toxicity and 

bioaccumulation of fipronil in the nontarget arthropodan fauna associated with 

subalpine mosquito breeding sites. Ecotoxicological and Environmental Safety 

52:8-12.

Key, P.B., K.W. Chung, A.D. Opatkiewicz, E.F. Wirth, and M.H. Fulton. 2003. 

Toxicity of the insecticides fipronil and endosulfan to selected life stages of the 

grass shrimp (Palaemonetes pugio). Bull. Environ. Contam. Toxicol 70:533-540.

Konwick, B.J., A.T. fisk, A.W. Garrison, J. K. Avantis, and M.C. Black. 2005. Acute 

enantioselective toxicity of fipronil and its desulfinyl photoproduct to 

Ceriodaphnia dubia. Environmental Toxicology and Chemistry 24: 2350-2355.

Maher, B. 2005a. The Case of the Anomalous Springs. Using all the clues to solve a 

karst mystery. USGS presentation to the ESI France-UT Karst Workshop; 

February 8, 2005

Mulder, P.G., Jr. 1997. Effects of insecticides on thrips populations peanut injury

growth and yield, 1995. in C.R. Saxena, Arthropod Management Tests, Volume 

22, Entomol. Soc. Of Am., Lanham, MD 22:284-285. 

Overmyer, J.P., B.N. Mason, K.L. Armbrust. 2005. Acute toxicity of imidacloprid and 

fipronil to a nontarget aquatic insect, Simulium vittatum Zetterstedt cytospecies 

IS-7. Bull. Environ. Toxicol. 74:872-879.
Page 41 of 71

Peveling, R., and S.A. Demba. 2003. Toxicity and pathogenicity of Metarhizium 

anisopliae var. acridum (Deuteromycotina, Hyphomycetes) and fipronil to the 

fringe-toed lizard Acanthodactylus dumerili (Squamata: Lacertidae). Environ 

Toxicol Chem.22: 1437-47.

Sandstrom, M.W. and J. E. Madison. 2003. Determination of Fipronil and Degradates in 

Environmental-Water Samples by Solid-Phase Extraction and Gas 

Chromatography/Mass Spectrometry (GC/MS). USGS, National Water Quality

Laboratory. SETAC Meeting Poster.

Schlenk, d., D.B. Huggett, J. Allgood, E. Bennett, J. Rimoldi, A.B. Beeler, D. Block, 

A.W. Holder, R. Hovinga, and P. Bedient. 2001. Toxicity of fipronil and its 

degradation products to Procambarus sp.; field and laboratory studies. Arch. 

Environ. Contam. Toxicol. 41: 325-332.

Shan, Z., L. Wang, D. cali, R. Gong, Z. Zhu, and F. Yu. 2003. Impact of fipronil on 

crustacean aquatic organisms in a paddy field-fishpond ecosystem. Bull. Environ. 

Contam. Toxicol. 70;746-752.

Stark, J.D., and R.I. Vargas. 2005. Toxicity and hazard assessment of firponil to 

Daphnia pulex. Ecotoxicology and Environmental Safety 62: 11-16.

Stevens, M.M., S. Helliwell, and G.N. Warren. 1998. Fipronil seed treatments for the 

control of chironomid larvae (diptera:Chironomidae) in aerially-sown rice crops. 

Field crops research 57:195-207.

Stevens, M.M., K.M. Fox , N.E. Coombes, and L.A. Lewin LA. 1999. Effect of fipronil 

seed treatments on the germination and early growth of rice, Pesticide Science 55: 

517-523.

United States Environmental protection Agency (YSEPA). 2004. Overview 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.

USEPA. (2010) Screening Level Estimates of Agricultural Uses on Fipronil. Biological 

and Economic Assessment Division, Office of Pesticide Programs. Dated August 

24, 2010.

United States Geological Survey (USGS). 2003. Fipronil and Degradation Products in 

the Rice-Producing Areas of the Mermentau River Basin, Louisiana, FebruarySeptember 2000. USGS Fact Sheet FS-010-03.

Volz , D.C., E.F. Wirth, M.H. Fulton, G.I. Scott, E. Strosier, D.S. block, J.L. ferry, S.S. 

Walse, and G.T. chandler. 2003. Effects of fipronil and chlorpyrifos on 

endocrine-related endpoints in female grass shrimp (Palaemonetes pugio). Bull. 
Page 42 of 71

Environ. Contam. Toxicol. 71:497-503.

Wirth, E.F., P.L. Pennington, J.C. Lawton, M.E. DeLorenzo, D. Bearden, B. Shaddrix, S. 

Siversten, and M.H.Fulton. 2004. The effect of contemporary-use insecticide 

(fipronil) in an estuarine mesocosm. Environmental Pollution 131:365-371.
Page 43 of 71

Appendix 1. Currently Registered Uses of Fipronil.

Table 1. Methods and rates of application of currently registered uses of fipronil.

Use Site

Max. Rate

per App

Max. Rate

Unit/Area

*UG Form

Max.#

Apps

cc & yr

Max. App

Rate/

cc & yr

Min. App

Interval

(days)

Application Equipment/Type

(Reg # Code)

Aquatic Non-Food Industrial

Drainage Systems

0.00245 lb/a B/S NS NS NS Bait application.

1713 lb/a EC NS NS NS Soil treatment (rodding and trenching).

0.0393 lb/drain EC NS NS NS Soil treatment (subslab injection).

1819 lb/a WP NS NS NS Soil treatment (rodding and trenching).

0.0418 lb/drain WP NS NS NS Soil treatment (subslab injection).

Sewage Systems

0.00245 lb/a B/S NS NS NS Bait application.

NDC B/S NS NS NS Bait application; Crack and crevice 

treatment; Spot treatment.

Forestry

Forest Tree 

Management/Forest Pest 

Management

NDC B/S NS NS 90 d Bait application.

Forest Trees (Softwoods, 

Conifers) 0.000556 lb/cu ft G NS NS NS Soil/media treatment.

Pine (Forest/Shelterbelt) 0.131 lb/a FlC 1 / yr .131 lb / a NS Soil injection treatment.

Indoor Food

Dairy Farm Milk Handling 

Facilities/Equipment NDC B/S NS NS NS Crack and crevice treatment.

Food/Grocery/Marketing/St

orage/Distribution Facility 

Premise

0.00000002 lb/spot B/S NS NS NS Crack and crevice treatment.

Household/Domestic 

Dwellings Indoor Food 

Handling Areas

0.00408 lb/a B/S NS NS NS Bait application.

Indoor Medical

Hospitals/Medical 

Institutions Premises 

(Human/Veterinary)

0.00408 lb/a B/S NS NS NS Bait application.

0.0000120 lb/placement B/L NS NS NS Bait application.

0.00000055 lb/placement B/S NS NS NS Bait application.

0.00000099 lb/room B/S NS NS NS Bait application.
Page 44 of 71

Use Site

Max. Rate

per App

Max. Rate

Unit/Area

*UG Form

Max.#

Apps

cc & yr

Max. App

Rate/

cc & yr

Min. App

Interval

(days)

Application Equipment/Type

(Reg # Code)

NDC B/S NS NS NS Crack and crevice treatment; Spot 

treatment.

Indoor Non-Food

Bathroom Premises/Hard 

Surfaces

0.00000055 lb/placement B/S NS NS NS Bait application.

NDC B/S NS NS NS Crack and crevice treatment; Spot 

treatment.

Commercial 

Storages/Warehouses 

Premises

0.00408 lb/a B/S NS NS NS Bait application.

0.0000120 lb/placement B/L NS NS NS Bait application.

0.00000055 lb/placement B/S NS NS NS Bait application.

0.00000099 lb/room B/S NS NS NS Bait application.

NDC B/S NS NS NS Crack and crevice treatment; Spot 

treatment.

Commercial Transportation 

FacilitiesNonfeed/Nonfood

0.00408 lb/a B/S NS NS NS Bait application.

0.0000120 lb/placement B/L NS NS NS Bait application.

0.00000055 lb/placement B/S NS NS NS Bait application.

0.00000099 lb/room B/S NS NS NS Bait application.

NDC B/S NS NS NS Crack and crevice treatment; Spot 

treatment.

Commercial/Institutional/In

dustrial Premises/Equip. 

(Indoor)

0.00408 lb/a B/S NS NS NS Bait application.

0.0000120 lb/placement B/L NS NS NS Bait application.

0.00000055 lb/placement B/S NS NS NS Bait application.

0.00000099 lb/room B/S NS NS NS Bait application.

0.00000002 lb/spot B/S NS NS NS Crack and crevice treatment.

NDC B/S NS NS NS Bait application; Crack and crevice 

treatment; Spot treatment.

Dairies/Cheese Processing 

Plant Premises (Nonfood 

Contact)

0.00000002 lb/spot B/S NS NS NS Crack and crevice treatment.

Eating Establishments 0.00000099 lb/room B/S NS NS NS Bait application.

NDC B/S NS NS NS Crack and crevice treatment.

Eating Establishments Food 

Handling Areas (Nonfood 

Contact)

0.00000002 lb/spot B/S NS NS NS Crack and crevice treatment.

NDC B/S NS NS NS Crack and crevice treatment.

Eating Establishments Food 

Serving Areas (Nonfood 

Contact)

0.00408319 lb/a B/S NS NS NS Bait application.

0.00001196 lb/placement B/L NS NS NS Bait application.

0.00000002 lb/spot B/S NS NS NS Crack and crevice treatment.
Page 45 of 71

Use Site

Max. Rate

per App

Max. Rate

Unit/Area

*UG Form

Max.#

Apps

cc & yr

Max. App

Rate/

cc & yr

Min. App

Interval

(days)

Application Equipment/Type

(Reg # Code)

Eating Establishments NonFood Areas (Nonfood 

Contact)

NDC B/S NS NS NS Crack and crevice treatment.

Feed Mills/Feed Processing 

Plants 0.00000002 lb/spot B/S NS NS NS Crack and crevice treatment.

Food Processing Plant 

Non-Food Handling Areas 0.00000099 lb/room B/S NS NS NS Bait application.

Food Processing Plant 

Premises (Nonfood 

Contact)

0.00408319 lb/a B/S NS NS NS Bait application.

0.00001196 lb/placement B/L NS NS NS Bait application.

NDC B/S NS NS NS Crack and crevice treatment.

Food 

Stores/Markets/Supermarke

ts Premises

NDC B/S NS NS NS Crack and crevice treatment.

Meat Processing Plant 

Premises (Nonfood 

Contact)

NDC B/S NS NS NS Crack and crevice treatment.

Refuse/Solid Waste Sites 

(Indoor)

0.00000055 lb/placement B/S NS NS NS Bait application.

NDC B/S NS NS NS Crack and crevice treatment; Spot 

treatment.

Ships And Boats

0.00408 lb/a B/S NS NS NS Bait application.

0.0000120 lb/placement B/L NS NS NS Bait application.

0.00000099 lb/room B/S NS NS NS Bait application.

Zoos

0.00408 lb/a B/S NS NS NS Bait application.

0.0000120 lb/placement B/L NS NS NS Bait application.

0.00000055 lb/placement B/S NS NS NS Bait application.

0.00000099 lb/room B/S NS NS NS Bait application.

NDC B/S NS NS NS Crack and crevice treatment; Spot 

treatment.

Indoor Residential

Cats (Adults/Kittens) NDC L NS / a 30 d Animal treatment (rub-on and spray).

Dogs/Canines 

(Adults/Puppies)

0.000904 lb/lb animal RTU NS NS 28 d Animal treatment (rub-on and spray).

NDC L NS / a 30 d Animal treatment (rub-on and spray).

Household/Domestic 

Dwellings Contents 0.00000099 lb/room B/S NS NS NS Bait application.

Household/Domestic 

Dwellings Indoor Premises

0.00408 lb/a B/S NS NS NS Bait application.

0.0000120 lb/placement B/L NS NS NS Bait application.
Page 46 of 71

Use Site

Max. Rate

per App

Max. Rate

Unit/Area

*UG Form

Max.#

Apps

cc & yr

Max. App

Rate/

cc & yr

Min. App

Interval

(days)

Application Equipment/Type

(Reg # Code)

0.00000055 lb/placement B/S NS NS NS Bait application.

0.00000099 lb/room B/S NS NS NS Bait application.

0.00000002 lb/spot B/S NS NS NS Crack and crevice treatment.

NDC B/S NS NS NS Bait application; Crack and crevice 

treatment; Spot treatment.

Refuse/Solid Waste 

Containers (Garbage Cans) NDC B/S NS NS NS Bait application.

Outdoor Residential

Household/Domestic 

Dwellings Outdoor 

Premises

0.005005 lb/1 gal EC 2 / yr NS NS Crack and crevice treatment; Outdoor 

general surface spray.

0.1305 lb/25 gal WP 2 / yr NS NS Crack and crevice treatment; Outdoor 

general surface spray.

0.00408319 lb/a B/S NS NS 75 d Bait application.

0.0000155 lb/linear ft EC 2 / yr NS NS Perimeter treatment.

0.00000259 lb/linear ft RTU 1 / yr NS NS Mound treatment; Perimeter treatment; 

Spot treatment; Spray.

0.0000163 lb/linear ft WP 2 / yr NS NS Perimeter treatment.

0.0000120 lb/placement B/L NS NS NS Bait application.

0.00000002 lb/spot B/S NS NS NS Crack and crevice treatment.

NDC B/S NS NS NS Bait application; Crack and crevice 

treatment; Spot treatment.

Refuse/Solid Waste 

Containers (Garbage Cans) NDC B/S NS NS NS Bait application.

Residential Lawns

0.0011271 lb/a B/S 4 / yr NS 21 d Bait application; Broadcast.

0.025 lb/a G 1 / yr .05 lb / a NS Broadcast; Subsurface/slit application 

treatment.

NDC B/S 4 / yr NS 21 d Mound treatment.

Terrestrial Food + Feed Crop

Orchards (Unspecified) NDC B/S NS NS 90 d Bait application.

Potato, White/Irish 0.0999775 lb/a FlC NS NS NS Soil in-furrow treatment.

Terrestrial Non-Food + Outdoor Residential

Fencerows/Hedgerows

0.0000120 lb/placement B/L NS NS NS Bait application.

0.00000002 lb/spot B/S NS NS NS Crack and crevice treatment.

NDC B/S NS NS NS Bait application.

Ornamental and/or Shade 

Trees NDC B/S NS NS NS Bait application.
Page 47 of 71

Use Site

Max. Rate

per App

Max. Rate

Unit/Area

*UG Form

Max.#

Apps

cc & yr

Max. App

Rate/

cc & yr

Min. App

Interval

(days)

Application Equipment/Type

(Reg # Code)

Paths/Patios 0.00244991 lb/a B/S NS NS NS Bait application.

Terrestrial Non-Food Crop

Christmas Tree Plantations 0.000556 lb/cu ft G NS NS NS Soil/media treatment.

Commercial 

Storages/Warehouses 

Premises

0.00408 lb/a B/S NS NS NS Bait application.

0.0000120 lb/placement B/L NS NS NS Bait application.

NDC B/S NS NS NS Bait application.

Commercial/Industrial 

Lawns

0.000025 lb/a B/S 4 / yr NS 21 d Broadcast.

0.025 lb/a G 1 / yr .05 lb / a NS Broadcast; Subsurface/slit application 

treatment.

NDC B/S 4 / yr NS 21 d Mound treatment.

Commercial/Institutional/In

dustrial 

Premises/Equipment 

(Outdoor)

0.00501 lb/1 gal EC 2 / yr NS NS Crack and crevice treatment; Outdoor 

general surface spray.

0.1305 lb/25 gal WP 2 / yr NS NS Crack and crevice treatment; Outdoor 

general surface spray.

0.00408 lb/a B/S NS NS NS Bait application.

0.025 lb/a G 1 / yr .05 lb / a NS Broadcast; Subsurface/slit application 

treatment.

0.0000155 lb/linear ft EC 2 / yr NS NS Perimeter treatment.

0.0000163 lb/linear ft WP 2 / yr NS NS Perimeter treatment.

0.0000120 lb/placement B/L NS NS NS Bait application.

0.00000002 lb/spot B/S NS NS NS Crack and crevice treatment.

NDC B/S NS NS NS Bait application; Crack and crevice 

treatment; Spot treatment.

Corn, Field 0.0976 lb/lb seed FlC NS NS NS Seed treatment.

Eating Establishments NDC B/S NS NS NS Bait application.

Golf Course Turf

0.000025 lb/a B/S 4 / yr NS 21 d Broadcast.

0.025 lb/a G 1 / yr .05 lb / a NS Broadcast; Subsurface/slit application 

treatment.

NDC B/S 4 / yr NS 21 d Mound treatment.

Industrial / Construction 

Areas (Outdoor)

1.044 lb/100 gal WP NS NS NS Soil treatment (subslab injection); Void 

treatment.

0.976 lb/98 gal EC NS NS NS Soil treatment (subslab injection); Void 

treatment.

64.3 lb/a EC NS NS NS Surface treatment.

68.2 lb/a WP NS NS NS Surface treatment.
Page 48 of 71

Use Site

Max. Rate

per App

Max. Rate

Unit/Area

*UG Form

Max.#

Apps

cc & yr

Max. App

Rate/

cc & yr

Min. App

Interval

(days)

Application Equipment/Type

(Reg # Code)

0.00393 lb/linear ft EC NS NS NS

Soil treatment (rodding and trenching); 

Soil treatment (subslab injection); Void 

treatment.

0.00418 lb/linear ft WP NS NS NS

Soil treatment (rodding and trenching); 

Soil treatment (subslab injection); Void 

treatment.

Nonagricultural Outdoor 

Buildings/Structures NDC B/S NS NS NS Bait application; Crack and crevice treatment; Spot treatment.

Nonagricultural 

Uncultivated Areas/Soils NDC B/S NS NS 90 d Bait application.

Nursery Stock 0.0250 lb/a G 1 / yr .025025 lb / a NS Broadcast.

Ornamental and/or Shade 

Trees

1.04 lb/100 gal WP NS NS NS Crack and crevice treatment; Foam 

application; Void treatment.

0.976 lb/98 gal EC NS NS NS Crack and crevice treatment; Foam 

application; Void treatment.

0.0250 lb/a G NS .025025 lb / a NS Broadcast.

0.000556 lb/cu ft G NS NS NS Soil/media treatment.

NDC B/S NS NS 90 d Bait application.

Ornamental Herbaceous 

Plants

0.0250 lb/a G NS .025025 lb / a NS Broadcast.

0.000556 lb/cu ft G NS NS NS Soil/media treatment.

Ornamental Lawns and 

Turf

0.000025 lb/a B/S 4 / yr NS 21 d Broadcast.

0.0250 lb/a G 1 / yr .05 lb / a NS Broadcast; Subsurface/slit application 

treatment.

NDC B/S 4 / yr NS 21 d Mound treatment.

Ornamental Nonflowering 

Plants

0.0250 lb/a G NS .025025 lb / a NS Broadcast.

0.000556 lb/cu ft G NS NS NS Soil/media treatment.

Ornamental Sod Farm 

(Turf)

0.000025 lb/a B/S 4 / yr NS 21 d Broadcast.

0.025 lb/a G 2 / yr .05 lb / a NS Broadcast; Subsurface/slit application 

treatment.

NDC B/S 4 / yr NS 21 d Mound treatment.

Ornamental Woody Shrubs 

and Vines

0.0250 lb/a G NS .025025 lb / a NS Broadcast.

0.000556 lb/cu ft G NS NS NS Soil/media treatment.

NDC B/S NS NS 90 d Bait application.

Paved Areas (Private 

Roads/Sidewalks) NDC B/S NS NS NS Bait application.

Potting Soil/Topsoil 0.000556 lb/cu ft G NS NS NS Soil/media treatment.
Page 49 of 71

Use Site

Max. Rate

per App

Max. Rate

Unit/Area

*UG Form

Max.#

Apps

cc & yr

Max. App

Rate/

cc & yr

Min. App

Interval

(days)

Application Equipment/Type

(Reg # Code)

Recreation Area Lawns

0.000025 lb/a B/S 4 / yr NS 21 d Broadcast.

0.025 lb/a G 1 / yr .05 lb / a NS Broadcast; Subsurface/slit application 

treatment.

NDC B/S 4 / yr NS 21 d Mound treatment.

Recreational Areas 0.025 lb/a G 1 / yr .05 lb / a NS Broadcast; Subsurface/slit application 

treatment.

Refuse/Solid Waste Sites 

(Outdoor) NDC B/S NS NS NS Bait application; Crack and crevice treatment; Spot treatment.

Utility Poles / Right-OfWay

0.00393 lb/linear ft EC NS NS NS Soil treatment (subslab injection and 

trenching); Other soil treatment.

0.00418 lb/linear ft WP NS NS NS Soil treatment (subslab injection and 

trenching); Other soil treatment.

Wood Protection Treatment 

To Buildings/Products 

Outdoor

1.04 lb/100 gal WP NS NS NS Crack and crevice treatment; Foam 

application; Void treatment.

0.976 lb/98 gal EC NS NS NS Crack and crevice treatment; Foam 

application; Void treatment.

Zoos

0.00408 lb/a B/S NS NS NS Bait application.

0.0000120 lb/placement B/L NS NS NS Bait application.

NDC B/S NS NS NS Bait application.

LEGEND

HEADER ABBREVIATIONS

Use Site: The use site refers to the entity (crop, building, surface or article) where a pesticide is applied and/or which is being protected. 

Max.Rate per App: Maximum dose for a single application to a single site. System calculated. 

Max.Rate Unit/Area: Units and Area associated with the maximum dose. 

*UG: Use Group codes. 

Form: The physical form of the end use product found in the container. 

Max. # Apps cc & yr: The maximum number of applications. 

Max. App Rate/cc & yr: The maximum amount of pesticide product that can be applied to a site in one growing season (/cc) or during the span of one year (/yr). 

Min. App Interval (days): The minimum retreatment interval between applications in days (aggregated). 

Application Equipment: The equipment used to apply pesticide (aggregated). 

Application Type: The type of pesticide application (aggregated). 

ABBREVIATIONS

AN - As Needed. 

NA - Not Applicable. 

NS - Not Specified (on label). 
Page 50 of 71

(L) - The dosage information provided is from the label in terms of product (e.g., ounces, gallons, or pounds of the product) because there was insufficient 

information (e.g., missing density, area, or active ingredient percentages) to provide converted dosage information. 

~ - The tilde in "Max. Rate per App" indicates a dosage that includes information from a SLN label. 

UC - Unconverted due to lack of data (on label). 

APPLICATION RATE

W: PPM calculated by weight 

V: PPM calculated by volume 

U: Unknown whether PPM is given by weight or by volume 

cwt: Hundred Weight. 

nnE-xx: nn times (10 power -xx), for instance, "1.234E-4" is equivalent to ".0001234". 

--: No description available in LUIS unit conversion vocabulary. 

~: The dosage information includes a contribution from one or more (TQ, CL, BR, I) active ingredients. 

FORMULATION CODES

B/L – Bait Liquid

B/S – Bait Solid

EC – Emulsifiable Concentrate

FlC – Formulation Intermediate Concentrate

G – Granular

L – Liquid

RTU – Ready-to-use

WP – Wettable Powder
Page 51 of 71

Appendix 2. Chemical Names, Structures, Maximum 

Reported Amounts of Fipronil and its Degradates and

Overview of Degradation Pathways.

Table A. Chemical Names and Structures of Fipronil and its Degradates.

Chemical Name Structure

Fipronil (MB 46030)

IUPAC name: 5-amino-1-(2,6-

dichloro-α,α,α-trifluoro-p-tolyl)-4-

trifluoromethylsulfinylpyrazole-3-

carbonitrile

CAS name: 5-amino-1-[2,6-dichloro4-(trifluoromethyl)phenyl]-4-

[(trifluoromethyl)sulfinyl]-1Hpyrazole-3-carbonitrile

N

N

Cl

Cl

H2N

S

C

CF3

O

CF3

N

MB 45897

CAS name: 5-amino-1-(2,6-dichloroalpha,alpha,alpha-trifluoro-p-tolyl)-

1H-pyrazole-3-carbonitrile

N

N

Cl

Cl

H2N

C

CF3

N

Fipronil sulfide (MB 45950)

CAS name: 5-amino-1-(2,6-dichloro4-(trifluoromethyl)phenyl)-4-

trifluoromethylthio-1-pyrazole-3-

carbonitrile

N

N

Cl

Cl

H2N

S

C

CF3

CF3

N

Fipronil sulfone (MB 46136)

CAS name: 5-amino-1-(2,6-dichloroa,a,a-trifluoro-p-tolyl)-4-trifluoromethylsulfonylpyrazole-3-carbonitrile

N

N

Cl

Cl

H2N

S

C

CF3

O

CF3

N

O
Page 52 of 71

Chemical Name Structure

MB 46513

CAS name: 5-amino-1-(2,6-dichloroalpha,alpha,alpha-trifluoro-p-tolyl)-4-

trifluoro-methylpyrazole-3-carbonitrile

N

N

Cl

Cl

H2N

CF3

C

CF3

N

RPA 104615

CAS name: 5-amino-3-cyano-1-(2,6-

dichloro-4-trifluoromethylphenyl) 

pyrazole-4-sulfonic acid, potassium

N

N

Cl

Cl

H2N

S

C

CF3

O

OH

N

O

RPA 105048

CAS name: 1-(2,6-dichloro-4-

trifluoromethylphenyl)-3-amino-5-

amino-4-

trifluoromethylsulfonylpyrazole

N

N

Cl

Cl

H2N

CF3

C

CF3

O

H2N

Fipronil amide (RPA 200766)

CAS name: 5-amino-1-(2,6-dichloro4-(trifluoromethyl)phenyl)-4-

trifluoromethylsulfonyl-1H-pyrazole3-carboxamide

N

N

Cl

Cl

H2N

S

C

CF3

O

CF3

O

H2N

Table B. Maximum Reported Amounts of Fipronil Degradation Products.

Degradate

Maximum % of Applied (μg/L 

or μg/kg in Field Studies) Study Type MRID

MB 45897 Laboratory studies

0.76% (252 d)

1.0% (120 d)

Aerobic soil metabolism

Anaerobic aquatic metabolism

42918663

43291704

14.16% TRR (uptake edible)

22.92% TRR (uptake inedible) Bioaccumulation in Fish 43291707
Page 53 of 71

Degradate

Maximum % of Applied (μg/L 

or μg/kg in Field Studies) Study Type MRID

24.28% TRR (uptake whole fish)

31.97% TRR (depuration edible)

47.87% TRR (depuration inedible)

26.14% TRR (depuration whole)

Fipronil sulfide

(MB 45950)

Laboratory studies

12.7% (30 d, Control)

4.88% (336 d)

47.0% (365 d)

82.6% (365 d)

17% (35 d, 0-14 cm soil section)

Soil photolysis

Aerobic soil metabolism

Anaerobic aquatic metabolism

Aerobic aquatic metabolism

Aged column leaching

42918662

42918663

43291704

44261909

42918664

9.04% TRR (uptake edible)

9.03% TRR (uptake inedible)

8.55% TRR (uptake whole fish)

15.49% TRR (depuration edible)

16.33% TRR (depuration inedible)

11.21% TRR (depuration whole)

Bioaccumulation in Fish 43291707

Terrestrial field dissipation studies

66.6 μg/kg (12 m)

62.8 μg/kg (12 m)

49.9 μg/kg (8 m)

44.5 μg/kg (16 m)

18-m CA In furrow corn

18-m NE In furrow corn

18-m NC In furrow corn

18-m WA In furrow corn

43401103

8.3 μg/kg (after application 2)

11.5 μg/kg (183 d)

490 d CA foliar cotton

548 d WA foliar potato 44262826

Aquatic field dissipation studies

Water: 0.49 μg/L (3.9 d)

Sed./Soil: 7.3 μg/kg (drain ditch)

Water: 0.26 μg/L (-1 d)

Sed./Soil: 5.9 μg/kg (drain ditch)

Water: 0.15 μg/L (1 d)

Sed./Soil: 4.0 μg/kg (drain ditch)

Water: 0.33 μg/L (2.88 d)

Sed./Soil: <0.6 μg/kg

98 d LA rice trial 1

103 d LA rice trial 2

94 d LA rice trial 3

113 d LA rice trial 4

45344701

Water: <1 μg/L

Sed./Soil: 32 μg/kg (84 d)

Water: <1 μg/L

Sed./Soil: 7 μg/kg (55 d)

Water: <1 μg/L

Sed./Soil: 25 μg/kg (258 d)

Water: <1 μg/L

Sed./Soil: 15 μg/kg (258 d)

Water: <1 μg/L

Sed./Soil: 10 μg/kg (306 d)

Water: <1 μg/L

Sed./Soil: 13 μg/kg (127-252 d)

361 d MS rice seed Trt.

361 d MS rice soil Trt.

375 d TX rice seed Trt.

375 d TX rice soil Trt.

376 d CA rice seed Trt.

379 d CA rice soil Trt.

44443402

0.13 μg/L (3 d)

0.35 μg/L (1 d)

0.22 μg/L (23 d)

<0.083 μg/L

0.12 μg/L (3 d)

0.15 μg/L (1 d)

118 d LA drill-seeded rice, site 1

116 d LA dry-seeded rice, site 1

118 d LA pre-sprout rice, site 1

111 d LA drill-seeded rice, site 2

109 d LA dry-seeded rice, site 2

107 d LA pre-sprout rice, site 2

46016801

Long-term soil dissipation studies
Page 54 of 71

Degradate

Maximum % of Applied (μg/L 

or μg/kg in Field Studies) Study Type MRID

14 μg/kg (85 d, 3 y)

12 μg/kg (91 d, 3 y)

10 μg/kg (101 d, 3 y)

8 μg/kg (190 d, 3 y)

10 μg/kg (1 d, 4 y)

29 μg/kg (92 d, 2 y)

4 y NE Corn PPI

4 y IL Corn PPI

4 y OH Corn PPI

4 y MS Cotton foliar

4 y TX Cotton foliar

4 y WA Potato foliar

46477001

Fipronil sulfone

(MB 46136)

Laboratory studies

9.4% (30 d, Control)

24.4% (336 d)

0.6% (59 d)

19% (0 d, 0-13 cm soil section)

Soil photolysis

Aerobic soil metabolism

Anaerobic aquatic metabolism

Un-aged column leaching

42918662

42918663

43291704

42918664

54.9% TRR (uptake edible)

59.07% TRR (uptake inedible)

27.98% TRR (uptake whole fish)

47.96% TRR (depuration edible)

101.9% TRR (depuration inedible)

43.8% TRR (depuration whole)

Bioaccumulation in Fish 43291707

Terrestrial field dissipation studies

7.6 μg/kg (3 m)

8.9 μg/kg (2 m)

5.4 μg/kg (2 m)

6.2 μg/kg (4 m)

4-m FL Bare Soil

4-m FL Turfed Soil

4-m NC Bare Soil

4-m NC Turfed Soil

43291705

168.2 μg/kg (12 m)

168.6 μg/kg (12 m)

119.6 μg/kg (8 m)

182.5 μg/kg (16 m)

18-m CA In furrow corn

18-m NE In furrow corn

18-m NC In furrow corn

18-m WA In furrow corn

43401103

50.8 μg/kg (126 d)

36.1 μg/kg (7 d)

63.1 μg/kg (548 d)

490 d CA foliar cotton

553 d TX foliar cotton

548 d WA foliar potato

44262826

Aquatic field dissipation studies

Water: 0.81 μg/L (1 d)

Sed./Soil: <0.6 μg/kg

Water: 0.66 μg/L (1 d)

Sed./Soil: <0.6 μg/kg

Water: 0.86 μg/L (1 d)

Sed./Soil: <0.6 μg/kg

Water: 0.57 μg/L (0.5 d)

Sed./Soil: 4.3 μg/kg (drain ditch)

98 d LA rice trial 1

103 d LA rice trial 2

94 d LA rice trial 3

113 d LA rice trial 4

45344701

Water: <1 μg/L

Sed./Soil: 11 μg/kg (84 d)

Water: 1 μg/L (29 d)

Sed./Soil: 12 μg/kg (27 d)

Water: <1 μg/L

Sed./Soil: 14 μg/kg (39 d)

Water: <1 μg/L

Sed./Soil: 19 μg/kg (39 d)

Water: 1 μg/L (0 d)

Sed./Soil: <5 μg/kg

Water: <1 μg/L

Sed./Soil: 9 μg/kg (3 d)

361 d MS rice seed Trt.

361 d MS rice soil Trt.

375 d TX rice seed Trt.

375 d TX rice soil Trt.

376 d CA rice seed Trt.

379 d CA rice soil Trt.

44443402

0.41 μg/L (3 d)

2.14 μg/L (1 d)

118 d LA drill-seeded rice, site 1

116 d LA dry-seeded rice, site 1 46016801
Page 55 of 71

Degradate

Maximum % of Applied (μg/L 

or μg/kg in Field Studies) Study Type MRID

0.60 μg/L (0 d)

1.73 μg/L (66 d)

0.74 μg/L (3 d)

0.85 μg/L (2 d)

118 d LA pre-sprout rice, site 1

111 d LA drill-seeded rice, site 2

109 d LA dry-seeded rice, site 2

107 d LA pre-sprout rice, site 2

Long-term soil dissipation studies

68 μg/kg (85 d, 3 y)

72 μg/kg (91 d, 3 y)

48 μg/kg (101 d, 3 y)

108 μg/kg (351 d, 2 y)

68 μg/kg (3 d, 4 y)

138 μg/kg (92 d, 3 y)

4 y NE Corn PPI

4 y IL Corn PPI

4 y OH Corn PPI

4 y MS Cotton foliar

4 y TX Cotton foliar

4 y WA Potato foliar

46477001

MB 46513 Laboratory studies

44.4% (6 d)

6.9% (30 d)

0.9% (14 d)

1.0% (59 d)

1.6% (14 d)

Aqueous photolysis

Soil photolysis

Aerobic soil metabolism

Anaerobic aquatic metabolism

Aerobic aquatic metabolism

42918661

42918662

42918663

43291704

44261909

Terrestrial field dissipation studies

28.5 μg/kg (126 d)

12.9 μg/kg (3 d)

22.7 μg/kg (183 d)

490 d CA foliar cotton

553 d TX foliar cotton

548 d WA foliar potato

44262826

Aquatic field dissipation studies

Water: 1.9 μg/L (2 d)

Sed./Soil: <0.6 μg/kg

Water: 1.3 μg/L (1 d)

Sed./Soil: <0.6 μg/kg

Water: 12.3μg/L (1 d)

Sed./Soil: <0.6 μg/kg

Water: 0.39 μg/L (2 d)

Sed./Soil: <0.6 μg/kg

98 d LA rice trial 1

103 d LA rice trial 2

94 d LA rice trial 3

113 d LA rice trial 4

45344701

Water: <1 μg/L

Sed./Soil: <5 μg/kg

Water: <1 μg/L

Sed./Soil: <5 μg/kg

Water: <1 μg/L

Sed./Soil: <5 μg/kg

Water: <1 μg/L

Sed./Soil: <5 μg/kg

Water: 3 μg/L (3 d)

Sed./Soil: 11 μg/kg (376 d)

Water: 2 μg/L (1 d)

Sed./Soil: 10 μg/kg (3 d)

361 d MS rice seed Trt.

361 d MS rice soil Trt.

375 d TX rice seed Trt.

375 d TX rice soil Trt.

376 d CA rice seed Trt.

379 d CA rice soil Trt.

44443402

0.88 μg/L (2 d)

5.38 μg/L (1 d)

3.18 μg/L (2 d)

0.20 μg/L (9 d)

7.22 μg/L (1 d)

6.16 μg/L (1 d)

118 d LA drill-seeded rice, site 1

116 d LA dry-seeded rice, site 1

118 d LA pre-sprout rice, site 1

111 d LA drill-seeded rice, site 2

109 d LA dry-seeded rice, site 2

107 d LA pre-sprout rice, site 2

46016801

Long-term soil dissipation studies

3 μg/kg (3 d, 3 y)

<2 μg/kg

4 y NE Corn PPI

4 y IL Corn PPI 46477001
Page 56 of 71

Degradate

Maximum % of Applied (μg/L 

or μg/kg in Field Studies) Study Type MRID

3 μg/kg (1 d, 4 y)

22 μg/kg (3 d, 1 y)

14 μg/kg (1 d, 4 y)

11 μg/kg (3 d, 3 y)

4 y OH Corn PPI

4 y MS Cotton foliar

4 y TX Cotton foliar

4 y WA Potato foliar

RPA 104615 Laboratory studies

8.3% (6 d)

7.2% (30 d)

4% (35 d, 0-14 cm soil section)

Aqueous photolysis

Soil photolysis

Aged column leaching

42918661

42918662

42918664

RPA 105048 Laboratory studies

17.6% (368 d)

7.7% (365 d)

ASM of MB 46513

Aerobic aquatic metabolism

44262830

44261909

Fipronil amide

(RPA 200766)

Laboratory studies

54.2% (30 d, pH 9, HPLC)

8.6% (30 d)

38.3% (336 d)

18.7% (365 d)

11.1% (60 d)

26% (35 d, 0-14 cm soil section)

Hydrolysis

Soil photolysis

Aerobic soil metabolism

Anaerobic aquatic metabolism

Aerobic aquatic metabolism

Aged column leaching

42977905

42918662

42918663

43291704

44261909

42918664

Terrestrial field dissipation studies

3.7 μg/kg (3 m)

6.2 μg/kg (3 m)

4-m FL Bare Soil

4-m NC Bare Soil 43291705

90.1 μg/kg (4 m)

109.6 μg/kg (12 m)

40.5 μg/kg (4 m)

53.5 μg/kg (14 m)

18-m CA In furrow corn

18-m NE In furrow corn

18-m NC In furrow corn

18-m WA In furrow corn

43401103

14.9 μg/kg (126 d)

11 μg/kg (14 d)

490 d CA foliar cotton

548 d WA foliar potato 44262826

Aquatic field dissipation studies

Water: <1 μg/L

Sed./Soil: <5 μg/kg

Water: <1 μg/L

Sed./Soil: <5 μg/kg

Water: <1 μg/L

Sed./Soil: 8 μg/kg (47 d)

Water: <1 μg/L

Sed./Soil: 16 μg/kg (39 d)

Water: <1 μg/L

Sed./Soil: <5 μg/kg

Water: <1 μg/L

Sed./Soil: <5 μg/kg

361 d MS rice seed Trt.

361 d MS rice soil Trt.

375 d TX rice seed Trt.

375 d TX rice soil Trt.

376 d CA rice seed Trt.

379 d CA rice soil Trt.

44443402

d = days; m = months; Trt. = treatment; TRR = total radioactive residues; ASM = aerobic 

soil metabolism; PPI = pre-plant incorporated.
Page 57 of 71

Appendix 3. Available Effects data from most recent 

ecological risk assessment in 2007

a. Acute and Chronic Effects to Birds

The following tables summarize the submitted acute and chronic toxicity data for avian 

wildlife. It should be noted that all studies are registrant submissions and found to be 

either acceptable or supplemental and therefore suitable for use in the risk assessment. 

The Agency will be conducting an updated ECOTOX database search, not available at 

the time of this Problem Formulation document. The results of this updated database run 

will be used to more completely inform the available toxicity information for fipronil and 

degradates.

Comparison of parent fipronil and degradate single oral dose endpoints for the bobwhite 

quail suggests that the photodegradate MB46513 may be more toxic than the parent and 

that the other two major environmental degradates MB46136 and MB45950 are less toxic 

that parent fipronil. There is no evidence that formulated products are more toxic, on an 

active ingredient adjusted basis, than technical fipronil.

On first inspection the available acute oral dose data may suggest that fipronil is more 

toxic in gallinaceous birds (pheasants, quail grouse, etc.) than in other orders. However, 

the number of tested species within each order is very small (3 or less), precluding any 

definitive conclusion regarding any phylogenic relationship on sensitivity in birds. The 

Agency is interested in receiving public comment associated with any additional 

evidence that supports or refutes a hypothesis that galliformes are uniquely sensitive to 

fipronil in comparison to other birds.

Acute Oral Dose Toxicity Data for Birds

Species Chemical %A.I. LD50 mg/kg-bw MRID

Northern bobwhite fipronil 96 11.3 42918617

Mallard fipronil 96.8 >2150 42918616

Pigeon fipronil 97.7 >500 42918613

Red-legged partridge fipronil 95.4 34 42918614

Pheasant fipronil 95.4 31 42918615

House sparrow fipronil 96.7 1000 42918618

Northern bobwhite MB46513 99.7 5 43776601

Mallard duck MB46513 98.6 420 43776602

Northern bobwhite fipronil (1.6 WG) 1.6 1065 42918619
Page 58 of 71

Dietary Acute Toxicity Data for Birds

Species Chemical %A.I. LC50 mg/kg-diet MRID

Northern bobwhite fipronil 95 48 42918620

Mallard duck fipronil 95 >5000 42918621

Northern bobwhite MB46513 97.8 119.2 45259201

Northern bobwhite MB46513 97.8 <178 44920701

Northern bobwhite MB46136 99.7 84 44890301

Northern bobwhite MB45950 98.8 114 44890302

Reproduction Toxicity Data for Birds

Species Chemical %A.I.

LOEC 

mg/kg-diet

NOEC 

mg/kg-diet MRID

Northern bobwhite fipronil 96.7 >10 10 42918622

Mallard duck fipronil 96.7 >1000 1000 42918623

A search of the ECOTOX database identified additional data for fipronil administered via 

the diet to male red-winged blackbirds (Agelaius phoeniceus L) male and female brownheaded cowbirds (Molothrus ater Boddaert), and female boat-tailed grackles (Quiscalus 

major Viellot) (Avery et al. 1998). Fipronil was added to a rice seed medium at 0, 325, 

and 500 mg a.i./kg. Birds were allowed to feed at will from open cups of the treated diet. 

No adverse toxicological effects were noted and no reduction in food consumption 

(p>0.05) was noted for any species and any dose group.

Calculation of Acute LD50 or Acute LC50 Ratios and Other Extrapolation Factors for 

Terrestrial Organisms

From the data above it is evident that acute single oral dose studies are not available for 

MB45950 and MB46136. For the purposes of evaluating risks for these degradates, 

estimates for single oral dose LD50 values are necessary. EFED evaluated the 

relationship of the acute effects data (LD50:LC50) for bobwhite quail, the most sensitive 

species tested (LD50:LC50). The ratio of LD50 to LC50 from these data is 0.235 (11.3/48). 

This value will be used to estimate LD50 values for MB45950 and MB46136, using the 

following equation LC50*0.235=Estimated LD50.
Page 59 of 71

b. Acute and Chronic Effects to Mammals

The following table presents the available mammalian toxicity data for fipronil for acute 

oral dose and for reproduction endpoints. The Agency will be conducting an updated 

ECOTOX database search, not available at the time of this Problem Formulation 

document. The results of this updated database run will be used to more completely

inform the available toxicity information for fipronil and degradates

Toxicity Data for Mammals

Species % AI LD50 (mg/kg-bw) MRID 

Rat 93% LD50 (mg/kg-bw) 97

reproduction NOEC 30 mg/kg-diet effects: litter size 

and number of matings

reproduction NOEL 2.64 mg/kg-bw

42918628

42918647

Rat MB45950 LD50 (mg/kg-bw) 83 HED 

memo*

Rat MB46513 LD50 (mg/kg-bw) 16 43235402

Rat MB46136 (98%) LD50 (mg/kg-bw) 218 42918675

Rat 1.6(form.) 

EXP60655A

LD50 (mg/kg-bw)>5000 42918636

Rat 0.25(form.) 

RM1601c

LD50 (mg/kg-bw)>5000 43121104

*Fipronil - Review of toxicity studies (28-day studies with fipronil and metabolite RPA 200766, a 

developmental neurotoxicity study with fipronil and a paper on the toxicological significance of fipronil 

and its metabolites). From V.A. Dobozy (Registration Branch 1/HED) to M. Johnson (RD), 8/6/1997.

c. Other Terrestrial Vertebrate Effects

Fipronil was administered by gavage or by contaminated diet in a single exposure event at 

30 mg ai/kg body weight to fringe-toed lizards Acanthodactylus dumerili (Peveling and 

Demba 2003). By four weeks post treatment, 62.5% of the lizards feed treated diet and 

42% of gavaged lizards died. In both tests survivors showed reduced feeding activity, 

food consumption, body weight, and liver or fat to body weight ratios. It is notable that 

these values suggest an LD50 on the order of 30 mg/kg-bw which is bracketed by available 

LD50 values for birds.

d. Terrestrial Invertebrate Effects

The registrant submitted an extended laboratory contact toxicity test to evaluate the 

toxicity of fipronil residues on foliage to honeybees (MRID 44884101). Honeybees were 

exposed to bean cuttings treated with 25 g of fipronil 80wg for 72 hours. By 72 hours, 

mortality in treatments was 100% compared to 5 to 8.35 in controls. This study was found 

to be supplemental.

e. Terrestrial Plant Effects

Continuous seedling exposure to fipronil (up to 25 days) at 4000 mg/L did not affect rice 

(Oryza sativa) seedling growth, but that 4-day exposure to 200 mg/L did produce 
Page 60 of 71

reductions in seed germination (Stevens et al. 1999). Other data from the literature 

showed fipronil having no effect on biomass of peanuts (Arachis hypogaea) treated with 

fipronil at a rate of 0.025 lb/acre (Mulder 1997). This later study expresses effects 

information in units consisted with terrestrial plant exposure modeling and could as the 

basis for terrestrial plant risk assessment.

f. Acute and Chronic Aquatic Organism Effects 

The following section presents the following tables the available aquatic organism effects 

data for fipronil, formulated products and degradates for freshwater and estuarine/marine 

invertebrates and fish and well as aquatic plants. The data include studies originating as 

registrant submitted studies in compliance with 40 CFR Section 158 (identifiable as 

studies with MRID reference numbers). In addition effects data identified from the 

publicly available literature (ECOTOX database studies identifiable as studies with 

Author citations) are also included as captured in the 2007 ECOTOX database search. 

All MRID-based data have been described in previous risk assessments and those

appearing in the following tables meet either the Agency acceptable or supplemental 

criteria. Studies identified from the ECOTOX summary of available literature have been 

evaluated by the Office of Research and Development as suitable for ECOTOX inclusion 

and have undergone EFED evaluation for inclusion in the risk assessment for possible 

quantitative evaluation.

The following are short summaries of studies extracted from the ECOTOX search of 

available literature. The Agency will be conducting an updated ECOTOX database 

search, not available at the time of this Problem Formulation document. The results of 

this updated database run will be used to more completely inform the available toxicity

information for fipronil and degradates.

Analytical grade fipronil, (>98% purity) was tested for acute toxicity using 5th instar 

black fly larvae (Simulium vittatum), a native emergent aquatic insect species of the 

United States (Overmyer et al. 2005). Six concentrations of fipronil, a solvent control 

(equivalent to highest solvent in all fipronil treatments), and a test water control were 

included. Test concentrations of fipronil were measured at the start and termination of the 

48-hour exposure period. The study was conducted three times with one replicate at each 

control and test concentration. Medial lethal concentrations and corresponding probit 

slope estimates were reported: test 1 LC50 0.19 μg/L slope 2.25; test 2 LC50 0.19 μg/L 

slope 2.43; test 3 0.29 μg/L slope 1.21. The geometric mean of these values is LC50 0.22 

μg/L with a slope of 2.20.

Fipronil (99.9% purity) toxicity was tested in six aquatic invertebrate species (Chaton et 

al. 2002). Studies were preformed in triplicate with 20 individuals per replicate. 

Controls were performed in test water, which was de-chlorinated tap water. The 

following results were reported in nominal concentration units:
Page 61 of 71

Summary of Chaton et al. (2002) study.

Species 48-h LC50 μg/L Probit Slope

Cladocerans

Daphnia pulex >highest dose

Copepods

Acanthocyclops robustus 84.8 4.8

Diaptomus castor 3.4 4.7

Ostracods

Eucrypris virens >highest dose

Dipterans

Chaoborus crystallinus 646 1.5

Chironomus annularis 2.4 1.2

Fipronil (97.1% purity) was tested in 4th instar larvae of 6 species of mosquitoes and two 

species of field collected chironomid midges (Ali et al. 1998). The assays involved 20 

larvae in each of three replicates for six or seven test concentrations of fipronil. Tap 

water served as a diluent and control. The results in nominal units were reported as 

follows:

Summary of Ali et al. (1998) study.

Species 48-h LC50 μg/L Probit Slope

Mosquitoes

Aedes aegypti 1.54 4.28

Aedes albopictus 23 1.95

Aedes taeniorhynchus 0.43 4.19

Anopheles quadrimaculatus 0.43 2.51

Culex nigripalpus 0.87 3.16

Culex quinqefasciatus 7.3 5.46

Midges

Chironomus crassicaudatus 0.42 2

Glyptendipes paripes 0.42 2.18

Konwick et al. (2005) evaluated the acute enantioselective toxicity of fipronil and its 

desulfinyl photoproduct (MB46513) to the cladoceran Ceriodaphnia dubia. Neonates of 

less than 24 hours age were introduced by pipet to 30 mL polypropylene cups containing 

moderately hard water (control), a 0.1 % acetone solution in moderately hard water 

(vehicle control), or fipronil compound dissolved in acetone and diluted with moderately 

hard water. No feeding took place over the course of the study. Two series of tests were 

conducted for each fipronil enantiomer and for the racemic mixture. The first test series 

occurred under a normal photoperiod (16:8 light:dark fluorescent light source). The other 

test series was conducted dark conditions. For the desulfinyl product, only a 16:8 

photoperiod test was conducted. Three replicate tests were conducted for each compound 

under each photoperiod (except as noted for desulfinyl product). A total of 15 neonates 

(3 cups of 5) were exposed at all controls and test chemical exposure levels. Mortality

was assessed by response to a probe. At 48 hours test conditions (dissolved oxygen and 

pH) were measured with results ranging from 7.80-8.38 mg/L and 8.3-8.46, respectively. 

Control survival acceptability criteria was set and attained at >90%. All LC50 values are 

reported on the basis of measured water concentrations of test chemical (i.e., adjust of 

nominal by observed nominal-measured relationship for low and high doses). The 

following 48-h LC50 results were reported:
Page 62 of 71

Summary of Konwick et al. (2005) study.

Ceriodaphnia dubia Mean 48-h LC50 (μg/L)

Test compound Light Dark

fipronil (+) enantiomere 11.3 +2.0 9.4 +0.7

fipronil (-) enantiomere 35.4 +2.6 28.4 +2.4

fipronil racemic 17.9 +2.7 17.5 +1.3

desulfinyl product (MB46513) 355 +9.3

The toxicity of fipronil to three aquatic invertebrates (giant river prawn (Macrobrachium 

rosenbergii), oriental river shrimp (Macrobrachium nipponensis), and Chinese mitten 

crab (Eriocheir sinensis)) was determined under semi-static conditions (Shan et al. 2003). 

Test water consisted of aerated tap water (pH 7.1) and test temperature was 20 +1 C. 

Test chambers consisted of 25 l glass containers filled with 20 L of test solution. Fipronil 

material consisted of a 5% suspension provided by Aventis CropScience (no other 

information on the content of the suspension was provided). A total of 10 test organisms 

were added to each test container with average loading ranging from 0.5 to 1.15 g 

organism/L. Test solution was replaced every 24 hours. Mortality and any observations 

of abnormal behavior were recorded each 24 hours. All LC50s were reported as nominal 

concentrations:

Summary of the Shan et al. (2003) study.

Acute LC50 (μg/L)

Species 24 h 48h 72h 96h

Macrobrachium rosenbergii 6.41 2.24 1.63 0.98

Macrobrachium nipponense >25.7 11.61 7.02 4.32

Eriocheir sinensis 57.83 22.57 12.44 8.56

Stark and Vargas (2005) evaluated the acute toxicity of fipronil to Daphnia pulex. 

Regent 4Sc formulation of fipronil was serially diluted in reconstituted dilution water. 

Batches of 5 neonates (3rd filial generation <24 hours of age) were introduced to 30 mL

plastic cups containing 25 mL of each of five to eight logarithmically spaced fipronil 

concentrations and a water only control. Test conditions were static non renewal. 

Mortality of test subjects was evaluated based on movement under mechanical 

stimulation. The experiment was conducted three times with three different generations 

of test animals. The LC50 was expressed as nominal fipronil active ingredient and 

reported as 15.6 μg/L (95% CI 0.88- 83) with a slope of 0.93 (+ 0.26).

The toxicity of fipronil to the crayfish Procambarus clarkii was evaluated using static 

renewal (48 h interval) methods (Biever et al. 2003). Testing was conducted with the 

formulation ICON 6.2 FS diluted in well water (pH 6.9, hardness 38 mg/L as CaCO3). 

Test concentrations were performed in duplicate and each chamber consisted of 21 L 

aquaria filled with 15 L of test solution maintained at 22 +1 C. Crayfish were observed 

every 24 hours for mortality. The fipronil nominal 96-hr LC50 was reported as 180 μg/L.

Fipronil as Rhone-Poulenc “suspensible” concentrate EXP 60145A (200g ai/L) was 

tested for acute toxicity in the final larval instar of the midge Chironomus tepperi. Ten 

larvae were added to 25 ml glass specimen tubes containing 20 mL of fipronil solution or 
Page 63 of 71

untreated controls. Photoperiod was maintained at 15:9 (light:dark). The bioassays were 

run in triplicate and replicated 4 times with different larvae cultures all under static 

conditions. Mortality was assessed as response to manipulation by forceps. The mean 

24-hr LC50 was reported by the authors to be 0.43 μg/L (95% limits 0.39-0.47) with a 

mean slope of 3.29 + 0.44.

Field collected grass shrimp, Palaemonetes pugio, were evaluated for acute toxic 

response to fipronil (Stevens et al. 1998). One study involved the use of 10 adult shrimp 

housed in 4 L glass jars filled with 2 L of test media or control. There were two 

replicates per treatment. A second study involved the use of 10 larvae (one to two days 

old) per 600 ml beaker filled with 400 ml of media, three replicates per treatment. A 

third study involved the use of embryos in 24-well microtiter plates, one stage IV 

embryo/ 2 mL well. The control and each test concentration were allocated to a single 

plate for a total of 24 organisms per treatment. Pesticide grade acetone (0.1%) was used 

as a carrier solvent in all treatments and controls. The following 96-hr LC50 values were 

reported:

Summary of the Stevens et al. (1998) study.

Life Stage 96-hr LC50 (μg/l) Palaemonetes pugio

Adult 0.32

larvae 0.68

embryo >512

A 96-hr acute toxicity study with the adult copepod Amphiascus tenuiremis was 

conducted using 98% fipronil (Chandler 2004). Adult male and female organisms were 

exposed to four nominal concentrations of fipronil (4.3, 7.2, 12.0, and 20 μg/L) and an 

acetone control in artificial seawater. Four replicates per treatment level were employed 

and the test chambers consisted of 50 mL glass crystallizing dishes filled with 30 mL of 

test solution. Twenty organisms (evenly distributed between males and females) were 

introduced to each replicate, which were then incubated at 20 C for 96 hours in a 12:12 

light:dark photoperiod. The LC50 for combined sexes was 6.8 μg/L, with a male LC50 of 

3.5 μg/L and a female LC50 of 13.0 μg/L.

Chandler et al. (2004) conducted a life cycle study (21 days) with the estuarine copepod 

A. tenuiremis exposed to fipronil (98% technical) at measured concentrations of 0.16, 

0.22, and 0.42 μg/L in seawater. The study was conducted in 96-well microtiter plates. 

One hundred forty-four test microwells for each treatment and or control were distributed 

over three microplates per treatment or control. One animal per treatment well was 

introduced to a treatment or control solution volume of approximately 200 μL for 

portions of the experiment involving observed copepod rearing (endpoints specific to 

copepod survival and development). Alternating rows were evaluated for sexually

mature copepod pairing and mating and involved two animals (male and female) per cell. 

The animals were fed with 2 μL of mixed algal cell suspension. All plates were 

maintained covered at 25C with a photoperiod of 12:12 light:dark. Treatment or control 

solution was renewed every 3 days and food was introduced every 6 days. There were no 

adverse effects on copepod survival observed at either day 12 or day 21 of the study

(NOEC for survival 0.42 μg/L). Copepod development from stage 1 to adult was 
Page 64 of 71

significantly (p<0.01) delayed for treatment groups 0.22 and 0.42 μg/L (NOEC for 

delayed development 0.16 μg/L, LOEC 0.22 μg/L). Developmental delays were 

observed to range from 1.5 to 2.4 days at the LOEC of 0.22 μg/L. The number of mature 

adults at day 12 was also reduced at 0.22 μg/l , with controls averaging 97.8 adults and 

0.22 μg/l averaging 85.6 adults. Fipronil significantly reduced (p<0.010 the incidence of 

female egg production at the 0.22 and 0.42 μg/L by 71% and 94% , respectively (NOEC 

for incidence of female egg production 0.16 μg/L LOEC 0.22 μg/L). The most sensitive 

endpoint from this study was time from mating to female egg extrusion. Reproductively 

successful females took statistically longer than controls to extrude eggs at 0.16 and 0.22 

μg/L (p<00.05) than controls by average margins of 1.9 and 2.3 days, respectively

(NOEC for time to egg production <0.16 μg/L, LOEC o.16 μg/L).

Volz et al. (2003) examined the response of grass shrimp Palaemonetes pugio exposed to 

nominal concentrations of fipronil (technical 98%) at 0, 0.1 and 0.2 μg/L in seawater. 

Test chambers consisted of 70 L aquaria p[retreated for three weeks with test solutions. 

A total of 34 adult shrimp (17 male and 167 female) were assigned to each control and 

treatment chamber (three replicate chambers per treatment level). Measured 

concentrations of fipronil averaged 0.0979 μg/L (SD 0.02084) and 0.14298 μg/L (SD 

0.04052) for the 0.1 and 0.2 μg/L treatment groups. Fipronil significantly (p=0.01) 

reduced adult survival at 0.14298 μg/L, with an observed 19.6% decrease relative to 

controls (survival NOEC 0.0979 μg/l, LOEC 0.14298 μg/l). Among surviving shrimp, no 

significant (p 0.05) effects on the numbers of gravid females, female grass shrimp egg 

production, vitellogenin, cholesterol, and ecdysteroids were observed at any treatment 

level (NOEC 0.14298 μg/L).

Aquatic Animal Acute Toxicity data

Species Chemical %A.I.

LC50 or

EC50 μg/L MRID or Reference

Freshwater Acute Invertebrate Toxicity Data

Daphnia magna Fipronil 100 190 42918625

Ceriodaphnia dubia 98 (racemic) 17.9 (light 

condition)

17.5 (dark 

condition0

Konwick et al. 2005

Ceriodaphnia dubia 98.1 

(-) enantiomere

35.4 (light 

condition)

28.4 (dark 

condition)

Konwick et al. 2005

Ceriodaphnia dubia 97.3

(+) enantiomer

11.3 (light 

condition)

9.4 (dark condition)

Konwick et al. 2005

Corbicula fluminea 95 >2000 46329904

Lumbriculus 

variegatus

99.7 >1900 46329903

Simulium vittatum >98 0.22 Overmyer et al. 2005

Acanthocyclops 

robustus

99.9 84.8 Chaton et al. 2002

Diaptomus castor 99.9 3.4 Chaton et al. 2002

Chaoborus 

crystallinus

99.9 646 Chaton et al. 2002
Page 65 of 71

Species Chemical %A.I.

LC50 or

EC50 μg/L MRID or Reference

Giant river prawn

Macrobrachium 

rosenbergii

5 24h - 6.41

48h - 2.24

72h - 1.63

96h - 0.98

Shan et al. 2003

Oriental river shrimp 

Macrobrachium 

nipponense

5 24h - >25.70

48h - 11.61

72h - 7.02

96h - 4.32

Shan et al. 2003

Chinese mitten crab

Eriocheir sinensis

5 24h - >57.83

48h - 22.57

72h - 12.44

96h - 8.56

Shan et al. 2003

Procambarus clarkii -- 14.3 (96-h) Schlenk et al. 2001

Procambarus 

zonangulus

-- 19.5 (96-h) Schlenk et al. 2001

Chironomus 

annularis

99.9 2.4 Chaton et al. 2002

Chironomus 

crassicaudatus

97.1 0.42 Ali et al. 1998

Glyptendipes paripes 97.1 0.42 Ali et al. 1998

Chironomus tentans 98.3 0.41 45878001

(Water-based endpoint)

Hexagenia sp. 99.7 0.44 46329902

Aedes aegypti 97.1 1.54 Ali et al. 1998

Aedes albopictus 97.1 23 Ali et al. 1998

Aedes 

taeniorhynchus

97.1 0.43 Ali et al. 1998

Anopheles 

quadrimaculatus

97.1 0.43 Ali et al. 1998

Culex nigripalpus 97.1 0.87 Ali et al. 1998

Culex 

quinqefasciatus

97.1 7.3 Ali et al. 1998

Culex 

quinqefasciatus

-- 350 Ali et al. 1999

Daphnia magna RPA 10461 94.7 100,000 43291719

Chironomus riparius RPA 200766 99.8 430 46376701

Daphnia magna MB46136 100 29 42918671

Chironomus tentans 99.1 0.72 45175901 

(Water-based endpoint)

Daphnia magna MB45950 100 100 42918669

Chironomus tentans 99.5 2.13 45084801 

(Water-based endpoint)

Ceriodaphnia dubia MB46513 97.8 355 Konwick et al. 2005

Chironomus tentans 99.1 200 45375901 

(Water-based endpoint)

Procambarus clarkii ICON 6.2 FS 56.02 174 45029601

Procambarus clarkii ICON 6.2 FS -- 180 Biever et al. 2003

Daphnia pulex Regent 4SC -- 15.6 Stark and Vargas 

2005

Chironomus tepperi RP EXP 60145a 20% (adjusted) 0.43 (24 hr study) Stevens et al. 1998

Freshwater Acute Fish Toxicity Data

Onchorynchus mykis Fipronil 100 246 42977902

Lepomis 100 83 42918624
Page 66 of 71

Species Chemical %A.I.

LC50 or

EC50 μg/L MRID or Reference

macrochirus

Ictalurus punctatus 97 560 44299401

Onchorynchus mykis MB46136 99.2 39 42918673

Lepomis 

macrochirus

99.2 25 42918674

Lepomis 

macrochirus

MB46513 No data 20 43279702

Onchorynchus mykis 94.7 >100,000 43291718

Onchorynchus mykis 100 >100,000 43279703

Onchorynchus mykis RPA104615

94.7

94.7 >100,000 43291718

Estuarine/Marine Acute Invertebrate Toxicity Data

Amphiascus 

tenuiremis

Fipronil 98 (96 hr study)

6.8 combined 

3.5 male

13.0 female

Chandler et al. 2004

Palaemonetes pugio -- adult 0.32

larvae 0.68

embryo >512

Key et al. 2003

Crassostrea 

virginianus

96.1 770 43291701

Americamysis bahia 96.1 0.14 43279701

Americamysis bahia MB46513 97.8 1.5 45120001

Americamysis bahia MB46136 99.7 0.56 45156301

Americamysis bahia MB45950 99.7 0.077 45156302

Estuarine/Marine Acute Fish Toxicity Data

Cyprinodon 

variegatus

Fipronil 96.1 130 43291702

Aquatic Animal Chronic Toxicity data

Species Chemical %A.I.

LOEC/

NOEC μg/L MRID or Reference

Freshwater Invertebrate Chronic Toxicity Data

Daphnia magna Fipronil 100 20/9.8 42918626

Daphnia magna MB46513 -- 100/41 43279704, 44812801

Freshwater Fish Chronic Toxicity Data

Oncorynchus mykis Fipronil 96.7 15/6.6 42818627

Estuarine/Marine Invertebrate Chronic Toxicity Data

Americamysis bahia Fipronil 97.7 0.005/not 

determined

43681201

Palaemonetes pugio 98 adult survival

0.14298/0.0979

reproduction

>0.14298/0.14298

Volz et al. 2003

Amphiascus 

tenuiremis

98 Survival

0.22/0.16

Time to adult

0.22/0.16

Incident of female 

egg production

Chandler et al. 2004
Page 67 of 71

Species Chemical %A.I.

LOEC/

NOEC μg/L MRID or Reference

0.22/0.16

Time from mating to 

egg production

0.16/<0.16

Americamysis bahia MB45950 99.5 0.0087/0.0046 45259202

Americamysis bahia MB46136 99 0.0026 /< 0.0026 45259203

Estuarine/Marine Fish Chronic Toxicity Data

Cyprinodon 

variegatus

Fipronil 95

97

full life cycle

1.7/0.85

early life stage

0.41/0.24

45265101

44605502

Aquatic Plant Toxicity data

Species Tested Chemical % A.I.

5 Day

EC50 (μg/L)

NOEC 

(μg/L) MRID or Reference

Navicula pelliculosa

(FW diatom)

fipronil

96.1 >120 120 42918658 

Lemna gibba

(Duckweed) 96.1 >100 100 42918656 

Selenastrum capricornutum

(FW green alga) 96.1 140 <140 42918660 

Skeletonema costatum

(marine diatom) 96.1 >140 140 42918659 

Anabaena flos aquae

(FW Blue-green alga)

96.1 >170 140 42918657

Selenastrum capricornutum

(FW green alga)

MB46513 98.6 76 7.5 43279705

g. Effects on Infaunal Sediment organisms

The following table presents the results of sediment toxicity testing with fipronil and 

degradates.

Sediment Organism Toxicity Data

Species Tested Chemical % A.I.

10 Day

LC50/EC50

(NOEC)

μg/kg-sediment

10 Day

LC50/EC50

(NOEC) 

μg/l pore water MRID

Chironomus 

tentans

fipronil 98.3 mortality 30.7(16) mortality 0.41(0.24) 45878001

MB46513 97.8-99.6 mortality 1300(200)

growth 520(<200)

Not available

Not available 45375901

MB46136 99.01 mortality 44.8(14)

growth 34.8(9.1)

mortality 0.72(0.35)

growth 0.41(0.41) 45175901

MB45950 99.5 mortality 116.9(29) 

growth 50.9(54)

mortality 2.13(0.35)

growth 0.66 (0.94) 45084801
Page 68 of 71

h. Calculation of Acute to Chronic Ratios and Other Aquatic Organism 

Extrapolations

Chronic toxicity data are available for but a subset of the freshwater invertebrate species 

tested in acute toxicity studies. In order to capture the potential for interspecies 

differences in sensitivity observed in the acute studies, an assumption was made that such 

differences are conserved in chronic effects. The following acute:chronic ratios (ACRs) 

for fipronil are available from the data set: 

Acute:chronic ratios (ACRs) for fipronil.

Species

Invertebrate or 

Fish

Freshwater or 

Estuarine/marine Acute LC50 Chronic NOEC ACR

D. magna invertebrate freshwater 190 9.8 19.39

O. mykis fish freshwater 246 6.6 37.27

A. bahia invertebrate estuarine/marine 0.14 <0.005 >28.00

P. Pugio invertebrate estuarine/marine 0.32 0.0979 3.26

A. tenurans invertebrate estuarine/marine 6.8 <0.16 >42.50

C. variegates fish estuarine/marine 130 0.85

0.24

<152.9

<541.7

For the purposes of extrapolating acute freshwater invertebrate results to an estimated 

chronic effects NOEC when chronic data are unavailable, this risk assessment may use 

the single ACR for D. magna (19.39), where the resulting chronic NOEC estimate will be 

made using the calculation: LC50/ACR=NOECest. For estuarine/marine invertebrates, 

extrapolations of acute to chronic effects endpoints would employ the ACR for A. bahia,

where the resulting chronic NOEC estimate will be made using the calculation: 

LC50/ACR=NOECest. The selection of A. bahia is made because most acute testing 

available for degradates uses the same species and such extrapolations within the species 

have the least uncertainty.

There are data gaps for the degradates of concern for estuarine/marine fish. To address 

these gaps this risk assessment may assume the relationship between freshwater species 

sensitivities for parent fipronil and degradates are conserved. The following relationships 

can be calculated with available data

Relationship between freshwater species sensitivities for parent fipronil and degradates.

Species Fipronil LC50 Degradate LC50

Ratio Parent to 

Degradate

MB46136 

O. mykis 246 39 6.3

L. macrochirus 83 25 3.3

MB46513

O. mykis 246 >10,000 <.00246

L. macrochirus 83 20 4.15

i. Mesocosm, Microsom, and Field Studies

Wirth et al. (2004) evaluated the effects of fipronil (purity not stated) upon estuarine 

mesocosms. Each mesocosm chamber consisted of an aerated tank with a simulated 
Page 69 of 71

diurnal tidal volume 55l to 250 L. Each tank consisted of 2 plots of low marsh, 2 plots of 

mid marsh, and a simulated stream. Natural seawater and unspecified sediment were 

used. Three replicate mesocosm chambers were used for a control, and 0.150, 0.355, and 

5.00 μg/L nominal additions of fipronil. Dosing occurred in the seawater sump 

approximately one hour prior to flood tide, avoiding a plume event. Test organisms were 

acclimated in the mesocosms three days prior to dosing. The community consisted of 24 

6 month grass shrimp (P. pugio, 16 males 8 females), 30 oysters (C. virginica), 30 

juvenile clams (Mercenaria mercenaria), and 25 fish (C. variegatus). Exposure duration 

was for 28 days, evaporative loss in each chamber was offset through deionized water 

addition. Clams exhibited no adverse effects at all exposure levels. There were no 

significant (p=0.33) effects on oyster survival or oyster weight (p=0.38), but height of 

oysters was slightly reduced (p=0.01) at the highest dose tested. Grass shrimp exhibited

reduced survival (p<0.05) at the middle dose. Grass shrimp also exhibited a dose 

dependent reduction in number off oviparous females, though without statistical 

significance. Fish exhibited no significant effects on survival, length or weight. Because 

concentrations of fipronil in the water column decreased substantially over the course of 

the study the NOEC and LOEC for this study can be expressed both as nominal 

concentration (NOEC 0.150 μg/L, LOEC 0.355 μg/L) and as a 28-day average measured 

concentration (NOEC 0.076 μg/L, LOEC 0.148 μg/L). No monitoring of sediments nor 

for degradates was conducted in the study. Consequently the disappearance of fipronil 

parent from the water column cannot be reliably attributed to any particular fate or 

dissipation process. 

Shan et al. (2003) explored the potential effects of fipronil in rice paddy drainage water 

upon freshwater crustaceans. An experimental rice paddy was treated with fipronil (5% 

fipronil suspension) by spray application of 45 g ai./hectare. Water drawn from the 

experimental paddy was introduced to a fishpond (concrete lined with mud and planted 

with “water grass”) that contained 80 M. rosenbergii, 50 M. nipponensis, and 80 E. 

simensis. At 24 hours post fipronil application to the paddy draw water from the paddy 

was introduced to the pond in a 50% volumetric mixture with existing pond water. E. 

simensis, immediately after application of paddy water, showed signs of intoxication 

(convulsion and arched bodies). Within 10 days there was complete mortality of this 

species as compared to 50% mortality in an untreated control pond. The other test 

species also exhibited signs of agitation and complete mortality by 7 days (M. 

nipponensis) or 3 days (M. rosenbergii) compared to controls where mortality was 345 

and 13.85, respectively. Fipronil concentration in the fish ponds, upon application of 

treated paddy water was a measured 3.48 μg/L and declined to 2.6 μg/L 30 days later. 

Traces of MB046136 were detected, while the other two degradates were negligible. 

Bayer Crop Science submitted to the Agency an evaluation of fipronil effects on the 

fauna of outdoor simulated ponds (MRID46733901). Fipronil, as Chipco TopChoice, 

was used in the experiment. Eight outdoor ponds were used in the study (four replicates 

for treatment and control). Fipronil was introduced to pond surface water at a nominal 

initial concentration of 0.4 μg/L. The time-weighted average concentration of fipronil in 

treated mesocosms from initiation of biological exposure out to 84 days (holding nondetects at half detection limit) was 0.042 μg/L. Biological sampling commenced two 
Page 70 of 71

weeks prior to test substance treatment and continued for approximately 12 weeks after 

application. There were no statistically significant (P>0.05) differences in phytoplankton 

(determined by phaeophytin, chlorophyll, and total pigment analysis) between control 

and treatment. Mean arthropod abundance was lower in the treatment than control at day

7 (52% of control), and Day 14 (61% of control) This trend reversed for days 21, 28, 42, 

and 56, where treatments showed increases in abundance relative to controls ranging 

from 0.5% to 183 %. None of the overall arthropod effects, though marked were 

statistically significant (P>0.05). Within the arthropods, certain copepod species 

(Mesocyclops edax and Tropocyclops prasinus) showed statistically significant (p<0.05) 

reductions in abundance in treatment relative to control. Treatment abundances ranged 

from 65 to 365 of control values. By day 21 (the last day of analysis at species 

resolution) these reductions were not statistically significant, but were still markedly 

reduced 14% to 60% of controls. Hester-Dendy sampling results for clitellora (worms 

and leeches) showed statistically significant increase in treatments relative to control for 

sampling days 8, and 14, and 56 (increases greater than 200%). Gastropods (snails) 

showed similar increases in abundance, though not statistically significant, in treatments 

relative to control. Evaluation of total macroinvertebrate insect abundance showed mixed 

results as the study progressed. Reductions in total abundance were statistically

significant (P<0.5) for fipronil treatment at day 8, with reductions still evident at day 28 

and 56, though not statistically significant. Benthic sampling for mayfly juveniles 

showed significant reductions in the presence of fipronil (p<0.05) at days 8, 14, 28, and 

56 of the study. Juvenile chironomids were also reduced significantly (p<0.05) by 

fipronil at day 8, though these effects were largely reversed by day 56 of the study. 

Numbers of emergent insects were too small in the study to make definitive statistically

supported statements about individual taxonomic groups. However, total emergent 

insects were lower in the fipronil treatment than in control for all sampling days of the 

study. 

The registrant has submitted an interim report on the effects of in place sediment 

concentrations of fipronil on the re-colonization of natural streams (MRID 46936104). 

The objective of the study was to evaluate the long-term effects of fipronil on benthic 

macroinvertebrates in freshwater ecosystems. A total of eight separate surface water sites 

were considered in this evaluation. Surficial sediments were collected from each test site. 

These sediments were untreated (control), or treated with fipronil as a low dose 0.75 

μg/kg (wet) or high dose 1.5 μg/kg (wet) and replicates of control and fipronil doses (3 

each) were placed prepared using the aforementioned sediment placed into 700 ml trays. 

These trays were then reintroduced to the test sites. The study reports have not been 

completed at the time of the drafting of this risk assessment.

j. Incidents

There are few incidents in the Agency database for effects on non-target organisms 

associated with the labeled use of fipronil. The degree to which the low number of years 

of outdoor use contributes to a lack of incidents is unknown.

Incident number I009142001 is a report of crayfish mortality following use of fipronil as 
Page 71 of 71

a seed treatment on rice in Louisiana. The database classifies this incident as highly 

probable. In March of 1999 Louisiana Department of Agriculture and Safety issued a 

stop order to prevent the use of fipronil on rice seed in Allen, Calcasieu, Cameron, 

Lafayette, St. Martin, Iberia, St. Mary, St. Landry, Beauregard, Vermillion, Evangeline, 

Acadia, and Jefferson Davis Parishes. Fipronil was detected in 3 of 9 crawfish samples 

(mean detection 0.04 μg/kg). Fipronil was detected in water samples from 8 of 16 ponds 

(average 2,08 μg/L, high 6.09 μg/L), in all samples of the Mermentau River (average 1.67 

μg/L, high 3.16 μg/L), and 14 of 17 other water monitoring sites (average 0.84 μg/L, high 

5.33 μg/L). the registrant (Rhone-Poulenc reported that 17 crawfish growers had 

reported to them observations of crawfish at the edges of ponds bordering rice fields 

planted with fipronil-treated rice. The LA department of Agriculture was investigating 

31 reported incidents pf crawfish kills on rice. Among the department and registrant 

reports there were 45 total incidents. The Louisiana state university Agricultural center 

conducted a survey and several experiments which substantiated the link between 

fipronil-treated rice seed and reduced survival of crawfish under hot dry weather 

conditions. Fipronil is no longer registered for rice seed treatment.

There are two reports of corn crop damage (I011723098 300 acres in North Dakota, and 

I013103054300 550 acres in Idaho) following use of fipronil Regent SC. These incidents 

are classified in the database as possible (Idaho incident) and probable (North Dakota). In 

neither incident report are there any confirmatory residue analyses.

One other probable incident, outside the United States, is also reported in the Agency

database. It involves locust control efforts on the island of Madagascar (I010380001). 

The incident was summarized in a BBC news article. The article refers to survey results 

citing declines in the Madagascar bee eater and a kestrel species. In addition, surveys of 

termite colonies showed a 90% elimination rate ten months after spraying. There are no 

confirmatory analytical data reported in the incident summary.