MEMORANDUM 

Subject: 

TO: 

THROUGH: 

FROM: 

PEER REVIEW: 

UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

WASHINGTON D.C., 20460 

OFFICE OF 

CHEMICAL SAFETY AND 

POLLUTION PREVENTION 

PC Code: 108853 

DP Barcode: 423540 

Date: December 4, 2014 

Registration Review- Problem Formulation for the Ecological Risk and Drinking Water 

Exposure Assessments for Flufenpyr-ethyl 

Steven Snyderman, Chemical Review Manager 

Patricia Parrott, Chief 

Risk Management and Implementation Branch 3 

Pesticide Re-evaluation Division (7508P) 

Dana Spatz, Branch Chief 

Environmental Risk Branch 

Environmental Fate and Effects Division (7507P) 

Melissa Panger, Ph .D., Senior Biologist 

James Hetrick, Ph.D., Senior Advisor

Environmental Risk Branch 3 

Environmental Fate and Effects Division (7507P) 

The Environmental Fate and Effects Division (EFED) has completed the problem formulation for the 

ecological risk assessment to be conducted as part of the Registration Review of flufenpyr-ethyl (PC code: 

108853). 

The environmental fate and ecological effects data associated with flufenpyr-ethyl, as well as its use and 

usage, has remained mostly unchanged since its initial registration. In addition, the Office of Pesticide 

Programs could find no evidence of flufenpyr-ethyl use in the United States since its registration in 2003. 
2

Thus, this document provides a brief overview of the chemical, risk concerns previously identified in the

assessment done for the initial new chemical registration, and data needed to complete an update to the

ecological risk assessment in support of Registration Review.  

CHEMICAL OVERVIEW 

Flufenpyr‐ethyl is a contact herbicide currently registered for use to control post emergence broadleaf

weed species, and is a light‐dependent peroxidizing herbicide (LDPH).  This class of herbicide is known to

have a photo‐toxic mode of action in plants and possibly in animals.  LDPHs may be more toxic to plants

and aquatic animals when exposed to natural sunlight, such as exposure conditions in the field. 

Flufenpyr‐ethyl is formulated as a water dispersible granular. Application equipment and methods for

flufenpyr‐ethyl include ground application, soil band treatment, soil broadcast, direct spray, and aerial

application.

Currently, there is one end‐use product containing flufenpyr‐ethyl (EPA Reg. No. 59639‐110, S‐3153 WDG

Herbicide, 57.6% flufenpyr‐ethyl), which was registered for use on field corn, sugarcane, and soybeans in

2003. With the exception of broadcast application for soybean, the maximum single application rate for

all crops is 0.027 pound of active ingredient per acre (lb a.i./A). For control of velvetleaf (depending on its

height) in soybean, a single broadcast application can be made at a rate ranging from 0.027 – 0.054 lb

a.i./A. The total amount of flufenpyr‐ethyl cannot exceed 0.054 lb a.i./A per year for any crop. Refer to

Table 1 for uses and application rates for flufenpyr‐ethyl.

Table 1. Flufenpyr‐ethyl Uses and Application Rates 

Crop 

Single Maximum 

Application Rate 

(Lb a.i./A) 

Number of 

Applications 

Minimum 

Retreatment 

Interval 

(days) 

Maximum Annual 

Application Rate 

(lb a.i./A) 

Corn, field 0.027 2 14

Soybean 0.054

0.027 2 14

0.054 1 Not applicable

Sugarcane 0.027   2 14

OVERVIEW OF RISK ASSESSMENTS 

 

Drinking Water Exposure Assessments 

Drinking water exposure assessments were initially conducted as part of the new chemical registration

(USEPA 2003a, 2003b, 2003c1

).  In this upper bound tier I assessment, surface water (using FIRST)

resulted in the highest potential exposure to flufenpyr‐ethyl and its major degradates (S‐3153‐acid, S‐

3153‐1‐OH, and S‐3153‐1‐OCH3).  The peak concentration was 3.6 μg/L and the annual average was 1.5

μg/L.  

 

1 USEPA. 2003c. Tier 1 Water Resources Assessment for Flufenpyr‐ethyl and its degradates (D268736, 08/08/03).
3

Since the new chemical assessment, EFED has updated modeling input guidance, and implemented

PRZM‐GW, an updated groundwater model2

, which considers 30 years of pesticide application. In an

updated groundwater exposure assessment (D423057; 09/30/14), the highest estimated peak was 11.8

μg/L, and the highest post‐breakthrough (chronic) average was 10.4 μg/L. These drinking water

concentrations supersede the original concentrations estimated for surface water in 2003 for use in the

human health risk assessment.

Previous Ecological Risk Assessments 

  

An ecological risk assessment for flufenpyr‐ethyl was conducted in support of the new chemical review

for the use of sugarcane, corn, and soybeans (USEPA, 2003a3

) and was followed by an addendum which

revised toxicity endpoints and risk quotients for these uses (USEPA, 2003b4

). Refer to these assessments

for additional details on the available fate and ecological effects data for flufenpyr‐ethyl, and previous risk

conclusions.  

Based on the previous assessments, there is a potential for risk to terrestrial (non‐listed RQs <15; listed

RQs of 7‐34) and aquatic vascular (listed RQs <5) from the use of flufenpyr‐ethyl. There is also the

potential for various indirect effects on non‐target animal species due to the effects on plants (for

example, depletion of food sources and habitat). Potential risk was identified from both aerial and ground

applications, and potentially through irrigation water that has received flufenpyr‐ethyl runoff or leached

to groundwater.   

Remaining Assessment Updates and Data Needs 

As noted earlier, the environmental fate and ecological effects data associated with flufenpyr‐ethyl, as

well as its use and usage, has remained mostly unchanged since its initial registration. EFED intends to

conduct updates to the risk assessment consistent with the most current policies and guidance. The

following sections describe what those updates will include, and the data needed to support the updated

ecological risk assessment. The risk concerns for flufenpyr‐ethyl are summarized in Table 2.

Birds and mammals. Since the initial chemical assessment for flufenpyr‐ethyl, EPA implemented the SIP

and STIR tools, to screen for potential drinking water and inhalation exposure routes, respectively, to

non‐target animals (birds and mammals). The results of running the SIP and STIR models are presented in

Appendix A and Appendix B. The analyses in SIP and STIR illustrate that the drinking water and inhalation

routes of exposure are not expected to be significant enough to cause concern for non‐target wildlife.

Therefore, the previous risk conclusions for birds and mammals remain the same.

Honey bee assessment. EPA has issued guidance for assessing the potential risks of pesticides to bees and

the data needed to support such assessments (USEPA et al., 2014). The guidance document indicates that

if exposure of bees to a pesticide is expected, a Tier I screening‐level risk assessment is conducted. The

Tier I assessment is intended to be sufficiently conservative that chemicals that pass the screen are

 

2 Detailed information concerning the current EFED models can be accessed from

http://www.epa.gov/pesticides/science/models_pg.htm#aquatic. 3 USEPA. 2003a. New Chemical Review for uses of flufenpyr‐ethyl on sugarcane and soybeans (D270231, D284046; 10/11/03). 4 USEPA. 2003b. Data review and addendum for flufenpyr (S‐3153 WDG Herbicide) terrestrial animals, aquatic organisms, and

plants. (11/04/03).
4

considered to represent a relatively low risk for potential adverse effects to bees. Tier I toxicity data that

are needed to complete screening‐level risk assessments include a suite of laboratory‐based studies of

individual bees and include the following tests: acute and chronic oral toxicity to adult honey bees, and

acute and chronic oral toxicity to honey bee larvae. If risk concerns are identified in the screening‐level

assessment, the assessment may be refined using data that further define exposure or through additional

toxicity data from Tier II semi‐field or Tier III full‐field studies conducted with whole colonies.

Fish assessment. Based on the available information for several LDPH chemicals, fish exhibited increased

sensitivity in fish early life stage (ELS) tests conducted under lighting conditions intended to more closely

simulate natural sunlight, as compared to results from standard guideline ELS studies. The potential for

flufenpyr‐ethyl to be more toxic in the presence of natural sunlight may lead to the occurrence of

environmental effects at lower levels of exposure than are indicated by the current suite of guideline

toxicity tests conducted under normal laboratory lighting conditions (USEPA 20015

).   

In the absence of chemical‐specific data on LDPH toxicity under enhanced uV lighting and until the

analysis of the toxicity testing conducted by the LDPH task group is complete, an adjustment factor of 29X

will be applied to fish early life stage (ELS) and full life‐cycle (LC) toxicity endpoints for use in the risk

assessment. This factor will be applied to toxicity endpoints from freshwater and estuarine/marine fish

ELS and LC studies conducted under standard laboratory lighting.  The toxicity adjustment factor will be

used to adjust no observed adverse effect concentration (NOAEC) values to account for the potential

enhanced toxicity of LDPH chemicals under natural sunlight.  

Table 2. Summary of Risk Concerns Identified for Flufenpyr‐ethyl 

Birds  Mammals  Terrestrial 

Plants 

Terrestrial 

Inverts  Fish  Aquatic Inverts 

Aquatic 

Plants 

Groundwater 

Contamination  Persistence  Degradates of Concern 

‐  ‐  √  ? ? ?  √  ‐  ‐  √ 

In order to complete an updated risk assessment for registration review, the following data* are needed:

‐ Special Study; OECD TG 213; Honey bee adult acute oral toxicity

‐ Special Study; OECD TG 237; Honey bee larvae acute oral toxicity

‐ Special Study; Honey bee adult chronic oral toxicity

‐ Special Study; Honey bee larvae chronic oral toxicity

The following studies may be required based upon the results of the studies mentioned above:

‐ Special Study; OECD Guidance 75; Semi‐Field Testing for Pollinators

‐ Special Study; Field trial of residues in pollen and nectar

‐ Field testing for pollinators, Guideline 850.3040

*For further information on the background, and use of these studies please see: USEPA 2014. Guidance for

Assessing Pesticide Risk to Bees6

.

 

5 USEPA 2001. Memorandum: Request for Phototoxicity Study Protocol for Light‐Dependent Peroxidizing Herbicides.

Dated March 7, 2001. 6 USEPA, PMRA, and CDPR, 2014.  Guidance for Assessing Pesticide Risks to Bees. Office of Pesticide Programs,

USEPA, Washington D.C. Health Canada Pest Management Regulatory Agency, Ottawa, ON, Canada. California

Department of Pesticide Regulation, Sacramento, CA.  June 23, 2014.

http://www2.epa.gov/pollinator‐protection/pollinator‐risk‐assessment‐guidance
5

 

Ecological Incidents 

A search of the Ecological Incident Information System (EIIS), the Incident Data System (IDS) and the Avian

Incident Monitoring System (AIMS) databases did not result in reported incident data.  

 

Monitoring Programs  

There is no flufenpyr‐ethyl monitoring data currently available. An Aquatic Life Ambient Water Quality

Criteria document has not been published specifically for flufenpyr‐ethyl. Based on EPA’s WATERS Expert

Query Tool (http://iaspub.epa.gov/pls/waters/f?p=ASKWATERS:EXPERT:0), flufenpyr‐ethyl has not been

identified as a cause of impairment for any water bodies listed as impaired under section 303(d) of the

Clean Water Act. It does not appear as though any US states, territories, or tribes have developed Total

Maximum Daily Load (TMDL) criteria for flufenpyr‐ethyl.

ENDOCRINE DISRUPTOR SCREENING PROGRAM (EDSP) 

Flufenpyr‐ethyl was not included in the first group of 67 chemicals issued an order to conduct Tier 1 EDSP

testing, or the final second list of 109 chemicals identified for Tier 1 EDSP testing.  For additional

information on the EDSP program, visit http://www.epa.gov/endo/.

ENDANGERED SPECIES ASSESSMENT 

Consistent with the Agency’s responsibility under the Endangered Species Act (ESA), the Agency will

evaluate exposure and potential risks to federally listed, threatened and/or endangered (listed) species

from registered uses of pesticides in registration review.

PRELIMINARY IDENTIFICATION OF DATA GAPS  

 

Environmental Fate 

 

There are no identified data gaps for the environmental fate evaluation.

Ecological Effects 

Table 3 identifies the ecological effects studies considered as data needs to support the updated risk

assessment for flufenpyr‐ethyl.  

   
6

Table 3. Ecological Effects Data Needs for Flufenpyr‐ethyl. 

OCSPP

Guideline Data Requirement Comments

850.3020 Honey bee adult

acute contact

toxicity

MRID 45119018, Study is Acceptable

850.3030 Honey bee toxicity

of residues on

foliage

Studies not required because the available acute contact toxicity LD50 is

greater than 11 micrograms per bee.

Special Study

OECD TG 213

Honey bee adult

acute oral toxicity

The acute oral toxicity study with young (newly emerged) adult bees

provides median lethal dose (LD50) value for honey bees (A. mellifera)

based on acute oral exposure following OECD test guideline 2137

.  These

data are used in conjunction with acute contact LD50 data obtained

through OCSPP 850.30208 to estimate the acute toxicity of technical grade

active ingredient (TGAI) to individual young adult honey bees.   

Special Study

OECD TG 237

Honey bee larvae

acute oral toxicity

The 7‐day single dose study with larval bees (newly hatched) provides

median lethal dose (LD50) value for honey bees (A. mellifera) based on

acute exposure following OECD test guideline 2379

.

Special Study Honey bee adult

chronic oral toxicity

The 10‐day toxicity study with young adult bees provides no‐observed

adverse effect level (NOAEL) and lowest‐observed adverse effect level

(LOAEL) for assessing chronic effects.  Although the study focuses primarily

on survival, growth (weight of bees) and sublethal effects on behavior and

food consumption can be obtained as well. Data obtained from this study

will be used in estimating chronic risk to individual adult bees.   

Special Study Honey bee larvae

chronic oral toxicity  

The 21‐day larval toxicity study under development by OECD provides

both acute and chronic toxicity data on developing bee brood and will

yield a median lethal dose (LD50) for assessing acute toxicity during the

early part of the study as well as a 21‐day no‐observed adverse effect level

(NOAEL) and lowest‐observed adverse effect level (LOAEL) for assessing

chronic effects.  Registrants are at liberty though to submit a separate

acute (single dose) larval toxicity study following OECD Guideline 23710 as

well as the 21‐day repeat dose chronic toxicity study.  Effects on survival

and development (adult bee emergence and body weight) from repeat

exposures to the active ingredient will be used in estimating chronic risk to

individual brood. In some cases, it may be possible to document food

consumption by larvae during the feeding component of the study.

Special Study

OECD Guidance

75

Semi‐Field Testing

for Pollinators

Dependent on results of the Tier I Honeybee toxicity tests and the

estimated exposures at the Tier I level.

Special Study Field trial of residues

in pollen and nectar

Dependent on result of the Tier I Honeybee toxicity tests and the

estimated exposures at the Tier I level.

850.3040 Field testing for

pollinators

Dependent on results of the Tier II Honeybee Colony toxicity tests.

 

7 Ibid OECD 1998a 8

Ibid USEPA 1996a. 9 Ibid OECD 1998a

10 Ibid OECD 2013. 
7

1 For further information on the background, and use of these studies please see: USEPA 2014. Guidance

for assessing pesticide risk to bees, available at http://www2.epa.gov/pollinator‐protection/pollinator‐

risk‐assessment‐guidance

   
8

APPENDIX A: RESULTS OF THE SIP MODEL 

Table 1. Inputs       

Parameter  Value    

Chemical name flufenpyr‐ethyl   

Solubility (in water at 25oC; mg/L) 4.1   

        

Mammalian LD50 (mg/kg‐bw) 5000   

Mammalian test species laboratory rat   

Body weight (g) of "other" mammalian

species      

        

Mammalian NOAEL (mg/kg‐bw) 1463   

Mammalian test species laboratory rat   

Body weight (g) of "other" mammalian

species      

        

Avian LD50 (mg/kg‐bw) 2250   

Avian test species mallard duck   

Body weight (g) of "other" avian species      

Mineau scaling factor 1.15   

        

Mallard NOAEC (mg/kg‐diet)      

Bobwhite quail NOAEC (mg/kg‐diet) 1040   

NOAEC (mg/kg‐diet) for other bird species      

Body weight (g) of other avian species      

NOAEC (mg/kg‐diet) for 2nd other bird

species      

Body weight (g) of 2nd other avian species      

        

Table 2. Mammalian Results       

Parameter  Acute  Chronic 

Upper bound exposure (mg/kg‐bw) 0.7052 0.7052

Adjusted toxicity value (mg/kg‐bw) 3845.8028 1125.2819

Ratio of exposure to toxicity 0.0002 0.0006

Conclusion*

Drinking water exposure 

alone is NOT a potential 

concern for mammals 

Drinking water exposure 

alone is NOT a potential 

concern for mammals 

        

Table 3. Avian Results       

Parameter  Acute  Chronic 

Upper bound exposure (mg/kg‐bw) 3.3210 3.3210

Adjusted toxicity value (mg/kg‐bw) 1168.2572 110.5503

Ratio of exposure to acute toxicity 0.0028 0.0300

Conclusion (this does not consider other

exposure routes, such as dermal or

dietary).

Drinking water exposure 

alone is NOT a potential 

concern for birds 

Drinking water exposure 

alone is NOT a potential 

concern for birds 
9

APPENDIX B: RESULTS OF THE STIR MODEL 

Input       

Application and Chemical Information       

Enter Chemical Name

flufenpyr‐

ethyl   

Enter Chemical Use Soybean   

Is the Application a Spray? (enter y or n) y   

If Spray What Type (enter ground or air) air   

Enter Chemical Molecular Weight (g/mole) 408.7   

Enter Chemical Vapor Pressure (mmHg) 3.80E‐07   

Enter Application Rate (lb a.i./acre) 5.4   

        

Toxicity Properties       

Bird       

Enter Lowest Bird Oral LD50 (mg/kg bw) 2250   

Enter Mineau Scaling Factor 1.15   

Enter Tested Bird Weight (kg) 0.178   

Mammal       

Enter Lowest Rat Oral LD50 (mg/kg bw) 5000   

Enter Lowest Rat Inhalation LC50 (mg/L) 1.39   

Duration of Rat Inhalation Study (hrs) 4   

Enter Rat Weight (kg) 0.35   

        

Output       

Results Avian (0.020 kg )       

Maximum Vapor Concentration in Air at Saturation (mg/m3) 8.36E‐03   

Maximum 1‐hour Vapor Inhalation Dose (mg/kg) 1.05E‐03   

Adjusted Inhalation  LD50   3.49E+00   

Ratio of Vapor Dose to Adjusted Inhalation LD50 3.01E‐04 Exposure not Likely Significant 

Maximum Post‐treatment Spray Inhalation Dose (mg/kg) 5.19E‐01   

Ratio of Droplet Inhalation Dose to Adjusted Inhalation LD50   1.49E‐01 Proceed to Refinements1 

    

Results Mammalian (0.015 kg )       

Maximum Vapor Concentration in Air at Saturation (mg/m3) 8.36E‐03   

Maximum 1‐hour Vapor Inhalation Dose (mg/kg) 1.32E‐03   

Adjusted Inhalation  LD50   8.28E+01   

Ratio of Vapor Dose to Adjusted Inhalation LD50 1.60E‐05 Exposure not Likely Significant 

Maximum Post‐treatment Spray Inhalation Dose (mg/kg) 6.52E‐01   

Ratio of Droplet Inhalation Dose to Adjusted Inhalation LD50   7.88E‐03 Exposure not Likely Significant  1

 The avian acute LD50 value was a non‐definitive value (>2250 mg/kg‐bw) and is not expected to be

representative of the actual LD50 value, thus the droplet inhalation dose is not expected to lead to an LOC

exceedance.