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Sodium Acifluorfen Proposed Interim Decision 

Table of Contents

Contents

I. INTRODUCTION....................................................................................3

II. USE AND USAGE....................................................................................5

III. SCIENTIFIC ASSESSMENTS.....................................................................5

A. Human Health.....................................................................................5

1. Risk Conclusions............................................................................6

2. Human Incidents.............................................................................6

3. Tolerances.....................................................................................6

B. Ecological Risk Assessment....................................................................7

1. Risk Conclusions............................................................................7

2. Ecological Incidents........................................................................10

3. Characterization of Ecological Risk......................................................10

C. Benefits Assessment............................................................................12

D. Endangered Species Assessment.............................................................12

E. Endocrine Disruptor Screening Program....................................................13

IV. PROPOSED INTERIM REGISTRATION REVIEW DECISION...........................14

V. NEXT STEPS AND TIMELINE..................................................................18

Appendix A: Summary of Actions Taken for Sodium acifluorfen.....................................19

Appendix B: Sodium acifluorfen Label Table............................................................19
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I. INTRODUCTION

This document is the Environmental Protection Agency’s (EPA or the Agency) Proposed Interim 

Registration Review Decision for sodium acifluorfen (case 2605, PC 114402) and is being issued 

pursuant to 40 CFR sections 155.56 and 155.58. A registration review decision is the Agency's 

determination whether a pesticide meets, or does not meet, the standard for registration in the 

Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA). The Agency may issue, when it 

determines it to be appropriate, an Interim Registration Review Decision before completing a 

registration review. Among other things, the Interim Registration Review Decision may: 1)

require new risk mitigation measures; 2) impose interim risk mitigation measures; 3) identify 

data or information required to complete the review; and 4) include schedules for submitting the 

required data, conducting the new risk assessment and completing the registration review. For 

further information on sodium acifluorfen, additional documents can be found in EPA’s public 

docket (EPA-HQ-OPP-2010-0135) at www.regulations.gov. 

FIFRA, as amended by the Food Quality Protection Act (FQPA) of 1996, mandated the 

continuous review of existing pesticides. All pesticides distributed or sold in the United States 

generally must be registered by the EPA based on scientific data showing that they will not cause

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

labeling. The registration review program is intended to make sure that, as the ability to assess 

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

meet the statutory standard of no unreasonable adverse effects. Changes in science, public 

policy, and pesticide use practices will occur over time. Through the registration review 

program, the Agency periodically re-evaluates pesticides to make sure that as these changes 

occur, products in the marketplace can continue to be used safely. Information on this program is 

provided as http://www.epa.gov/pesticide-reevaluation/registration-review-process. 

In 2006, the Agency implemented the registration review program pursuant to FIFRA section 

3(g) and will review each registered pesticide every 15 years to determine whether it continues to 

meet the FIFRA standard for registration.

EPA is issuing a proposed interim registration review decision for sodium acifluorfen so that it 

can (1) move forward with aspects of the registration review that are complete and (2) implement 

interim risk mitigation. The Agency is currently working with the U.S. Fish and Wildlife Service 

and the National Marine Fisheries Service to develop methodologies for conducting national 

endangered species assessments for pesticides. Therefore, although EPA has not yet fully 

evaluated risks to threatened and endangered species, the Agency will complete its endangered 

species assessment and any necessary consultation with the Services for sodium acifluorfen prior 

to completing the sodium acifluorfen registration review. Likewise, the Agency will complete 

endocrine screening for sodium acifluorfen, pursuant to the Federal Food, Drug, and Cosmetic 

Act (FFDCA) section 408(p), before completing this registration review. Last, EPA will 

determine whether additional pollinator exposure and effects data are necessary to make a final 

registration review decision for sodium acifluorfen and issue a data call-in (DCI) to obtain any 

such data prior to completing the sodium acifluorfen registration review.

Sodium acifluorfen is a selective, diphenyl ether herbicide and a light dependent peroxidizing 

herbicide (LDPH) registered for post-emergent weed control on soybeans, peanuts, rice, and 
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strawberries. There are currently 12 FIFRA Section 3 registrations. All sodium acifluorfen 

residential use products have either been cancelled or are undergoing cancellation. On February 

26, 2016, Bonide Products, Inc. requested the voluntary cancellation of the one remaining 

residential product (EPA Registration Number 4-433), which has been suspended for several 

years and not marketed. The Agency expects to announce shortly the notice of receipt of this 

request through the Federal Register and anticipates granting the voluntary cancellation request 

by the end of the year. Sodium acifluorfen was first registered in the United States in 1980, and a 

Reregistration Eligibility Decision (RED) was issued in September of 2003. Acifluorfen is a 

degradate of the herbicide lactofen and is a dissociated product of sodium acifluorfen. EPA 

assessed lactofen (case number 7210) separately in its own registration review case and issued an 

interim decision for that active ingredient in December 2014 (EPA-HQ-OPP-2005-0287).

Summary of Sodium Acifluorfen Registration Review

Pursuant to 40 CFR section 155.50, EPA formally initiated registration review for sodium 

acifluorfen (case 2605). The following summary highlights significant events that have occurred 

during the registration review of sodium acifluorfen. Documentation of these events can be 

found in EPA’s sodium acifluorfen public docket, EPA-HQ-OPP-2010-0135, accessed at 

www.regulations.gov:

 March 24, 2010 – Sodium acifluorfen Summary Document was issued for a 90-day public 

comment period. The Summary Document included the Preliminary Work Plan (PWP)

and was accompanied by the scoping document and problem formulation.

 September 3, 2010 - Final Work Plan (FWP) for sodium acifluorfen was issued. The 

Agency received one comment during the 90-day public comment period on the PWP.

This comment did not change the risk assessment, data needs, or time line identified in 

the PWP.

 October 19, 2011 – Generic Data Call-In (GDCI) for sodium acifluorfen was issued.

 July 8, 2015 – The Agency published the Preliminary Environmental Fate and 

Ecological Risk Assessment Endangered Species Effects Determination for Acifluorfen

and the Sodium Acifluorfen. Draft Human Health Risk Assessment for Registration 

Review for a 60-day public comment period. No comments were received.

 March, 2016 - The Agency is now publishing the Sodium Acifluorfen Proposed Interim 

Registration Review Decision, in docket number EPA-HQ-OPP-2010-0135, for a 60-day 

public comment period. In addition to this document, the Agency is publishing the 

following supporting documents:

o Addendum to: Registration Review: Preliminary Environmental Fate and 

Ecological Risk Assessment Endangered Species Effects Determination for 

Acifluorfen, March 1, 2016.

o Sodium Acifluorfen Usage Information, March 17, 2016.
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II. USE AND USAGE

Sodium acifluorfen is a selective, post-emergent contact herbicide registered for use to control 

annual broadleaf weeds and some grasses in soybeans, rice, peanuts, and strawberries. Sodium 

acifluorfen is a member of the diphenyl ether group of herbicides and it belongs to a class of 

compounds, light dependent peroxidizing herbicides (LDPH), known to have a phototropic mode 

of action in plants. LDPHs act in plants through inhibition of the enzyme protoporphyrinogen 

oxidase, leading to cell membrane disruption through reactive oxygen species in the presence of 

light.

Sodium acifluorfen is applied to approximately one million acres of cropland annually in the 

United States. The crops that are most dependent on sodium acifluorfen in terms of average 

percent crop treated (PCT) include peanuts (17%) and rice (5%). For soybeans about 1% of the 

crop is treated on average which accounts for about 800,000 acres of cropland treated annually 

with sodium acifluorfen. Between 2004 and 2012, the average annual pounds (lbs) active 

ingredient (AI) used are as follows: peanuts (50,000 lbs AI/year), rice (20,000 lbs AI/year), 

soybeans (80,000 lbs AI/year), and strawberries (500 lbs AI/year). During the same time period, 

on average, one application of sodium acifluorfen was applied per year to these registered uses. 

More recently, between 2009 and 2013, 2.5% of treated peanuts, 4.6% of treated rice, and 10% 

of treated soybeans, received two applications.

While aerial application is permitted for all labeled crops, EPA market research data indicate that 

sodium acifluorfen is applied aerially to two crops only, rice and soybeans. Aerial application to 

rice and soybeans accounts for 10% of the total acres treated with sodium acifluorfen per year. 

Most of the aerial applications of sodium acifluorfen are made on rice with an average of up to 

83,000 acres treated annually. This accounts for approximately 70% of the acres treated aerially 

with sodium acifluorfen annually from 2010-2014. For soybeans, aerial applications are made 

on about 33,000 acres treated on average, which accounts for the remaining 30% of the acres 

treated aerially with sodium acifluorfen annually from 2010-2014 (Market Research Data, 2010-

2014). On average, 4% of the sodium acifluorfen applied to soybeans is made aerially, while 

approximately 66% of the sodium acifluorfen applications to rice are made aerially. Aerial 

applications are made to accommodate wet or overgrown fields that are unable to be entered by 

foot or ground machinery. For weed control in strawberries, sodium acifluorfen is typically 

applied using ground equipment as a band application during renovation (over the top of straw 

mulch) or after transplanting the plants (before laying plastic mulch).

See Sodium Acifluorfen Usage Information, dated March 17, 2016; for additional detail on 

sodium acifluorfen use and usage information.

III. SCIENTIFIC ASSESSMENTS

A. Human Health 

A summary of the Agency’s human health risk assessment is presented below. The Agency used 

the most recent Agency science policies and risk assessment methodologies to prepare a 

quantitative risk assessment in support of the registration review of sodium acifluorfen. For a 

detailed discussion of the human health assessment and anticipated tolerance modifications for
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sodium acifluorfen, see Sodium Acifluorfen. Draft Human Health Risk Assessment for 

Registration Review dated June 17, 2015. This document is available in the public docket EPAHQ-OPP-2010-0135, which can be accessed at http://www.regulations.gov/.

1. Risk Conclusions

EPA has no dietary risks of concern for sodium acifluorfen from exposure to residues in 

either food or drinking water. The Agency did not conduct a residential risk assessment 

because all residential products are either suspended or undergoing cancellation. In fact, 

there is only one residential product that is currently registered, EPA Reg. No. 4-433, but 

that product has been suspended and not marketed for several years. On February 26, 

2016, the registrant of the suspended product, Bonide Products, Inc., requested voluntary 

cancellation of that product. EPA expects to announce the notice of receipt of this 

voluntary cancellation request in the Federal Register shortly, and anticipates issuing a 

final cancellation order for that product by the end of the year. Therefore, the aggregate 

exposure assessment is equivalent to the dietary assessment and not of concern. As 

acifluorfen is formed from the use of two registered herbicides, sodium acifluorfen and 

lactofen, the aggregate assessment considered potential exposures to acifluorfen from 

both of these active ingredients. However, EPA has not made a common mechanism of 

toxicity finding for sodium acifluorfen and any other substance for this assessment. 

For pesticide handlers with occupational exposure to sodium acifluorfen, EPA has found 

no risks of concern. The Agency also evaluated exposure and risk to agricultural workers 

who enter areas treated with sodium acifluorfen after application. EPA determined that 

postapplication exposures and risks were not of concern. In addition, EPA evaluated off 

target exposure of adults and children to spray drift and no risk estimates of concern were 

identified.

2. Human Incidents

On March 26, 2015, the Agency completed a review of sodium acifluorfen incidents in 

the OPP Incident Data System (IDS) and the Centers for Disease Control and 

Prevention/National Institute for Occupational Safety and Health (CDC/NIOSH) Sentinel 

Event Notification System for Occupational Risk-Pesticides (SENSOR) databases. One

minor incident case was identified. Based on the low frequency and low severity of 

incident cases reported, there does not appear to be a concern at this time that would 

warrant further investigation. In addition, while sodium acifluorfen is included in the 

Agricultural Health Study, data are not yet available from this study. The Agency will 

continue to monitor the incident and epidemiology information and, if a concern is 

triggered, additional analysis will be conducted.

3. Tolerances

The Agency will modify the tolerance expression so that it appropriately covers the 

metabolites and degradates of sodium acifluorfen and specifies the residues to be 

measured for each commodity. In addition, tolerances will be modified to include the 

recommended number of significant figures as indicated below. No Codex maximum 

residue limits have been established for sodium acifluorfen. The U.S. is unable to 
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harmonize its tolerance (0.1 ppm) for soybean seed with the Canadian maximum residue 

limit (0.02 ppm) for this commodity as the limit of quantitation of the analytical method

used to measure residues is 0.1 ppm. 

Table 1: Sodium Acifluorfen Tolerances (40 CFR 180.383)

Commodity Established Tolerance 

(ppm)

Recommended Tolerance 

(ppm)

Peanut 0.1 0.10

Rice, grain 0.1 0.10

Rice, straw 0.2 0.20

Soybean, seed 0.1 0.10

Strawberry 0.05 0.05

B. Ecological Risk Assessment

A summary of the Agency’s ecological risk assessment is presented below. The Agency used 

the most updated Agency science policies and risk assessment methodologies to prepare a 

quantitative risk assessment in support of the registration review of sodium acifluorfen. For a 

detailed discussion of the ecological assessment for sodium acifluorfen, see Preliminary 

Environmental Fate and Ecological Risk Assessment Endangered Species Effects Determination 

for Acifluorfen, dated June 11, 2015, and Addendum to: Registration Review: Preliminary 

Environmental Fate and Ecological Risk Assessment Endangered Species Effects Determination 

for Acifluorfen, March 1, 2016. These documents are available in the public docket EPA-HQOPP-2010-0135, which can be accessed at http://www.regulations.gov/.

EPA is currently working with its federal partners and other stakeholders to implement an 

interim approach for assessing potential risk to listed species and their designated critical 

habitats. Once the scientific methods necessary to complete risk assessments for listed species 

and their designated critical habitats are finalized, the Agency will complete its endangered

species assessment for sodium acifluorfen. As such, the risk conclusions described below 

pertain to non-listed species.

1. Risk Conclusions

Terrestrial Assessment

Mammals – In the preliminary risk assessment for sodium acifluorfen, the Agency 

identified chronic risks of concern for mammals, with the highest dose-based risk 

quotients (RQs) associated with the strawberry use (RQ up to 3.4). Using the dietarybased risk quotient method (i.e. not adjusted for body weight), there are no chronic risks 

of concern. In addition, no acute risks of concern were identified for any labeled use 

pattern.

Birds and Surrogates (Reptiles and Terrestrial Amphibians) – The acute dose-based RQ 

(0.76) exceeds the level of concern (LOC of 0.5) for small birds only (and surrogates) 

foraging on short grass for the strawberry use. However, there are no exceedances of the 
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LOC using the dietary-based RQ method for any size class/forage item combination.

There are chronic LOC exceedances for all use patterns for the short grass, tall grass, 

broadleaf plants and arthropod forage categories, with RQs up to 8 for the strawberry use 

pattern. There are no chronic LOC exceedances for the fruit/pods/seeds forage class for 

any use pattern.

Invertebrates – The only available data for this taxon is an acute contact to honey bees

study, which classifies sodium acifluorfen as practically non-toxic. Potential risk to 

nontarget terrestrial invertebrates will be evaluated upon receipt of additional data.

When initially scoping the registration review for sodium acifluorfen, EPA did not 

identify the need for any additional studies to evaluate potential effects on 

pollinators. However, since the issuance of the June 2014 Guidance for Assessing 

Pesticide Risks to Bees[1], EPA has begun to require these data where applicable. EPA is 

currently determining whether additional pollinator data are needed for active ingredients 

in registration review whose dockets opened prior to June 2014. For those active 

ingredients where EPA determines that additional pollinator exposure and effects data are 

necessary to help make a final registration review decision, EPA intends to issue a DCI to 

obtain these data. In the near future, EPA will provide further information and guidance 

on this effort. 

For sodium acifluorofen, the acute contact toxicity study with adult honey bees (guideline 

#850.3010) study has already been submitted. Additional pollinator studies that could be 

required in the future are listed in Table 2 below. The Agency will require data it believes 

are necessary to help inform the pollinator risk assessment.

Table 2. Potential Pollinator Data Requirements

Guideline # Study

850.3030* Honey bee toxicity of residues on foliage

850.3040** Field testing for pollinators

Non-Guideline* 

(OECD 213)

Honey bee adult acute oral toxicity

Non-Guideline* 

(OECD 237)

Honey bee larvae acute oral toxicity

Non-Guideline* Honey bee adult chronic oral toxicity

Non-Guideline* Honey bee larvae chronic oral toxicity

Non-Guideline** Residues in pollen and nectar/field residue analysis

Non-Guideline** 

(OECD 75) Semi-field testing for pollinators (tunnel or colony feeding studies)

*Tier 1 (Laboratory-based studies)

**Tier 2 and 3 (Semi-field and full field colony-level studies) The need for a higher tier test for pollinators will be determined 

based upon lower-tiered tests and/or other lines of data and the need for a refined pollinator risk assessment.

 

[1] http://www2.epa.gov/sites/production/files/2014-

06/documents/pollinator_risk_assessment_guidance_06_19_14.pdf
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Plants – As expected with an herbicide, effects on biomass and stand height were 

observed in terrestrial plant studies. The vegetative vigor exposure route (foliar spray) 

and life stage is generally more sensitive to sodium acifluorfen than the seedling 

emergence exposure route (soil exposure) and life stage, based on the available studies. 

Sensitivity varies by species, with non-grasses generally more sensitive than grasses. All 

labeled uses of sodium acifluorfen pose potential risks of concern to non-target terrestrial 

plants when applied aerially. Non-target plants may also be at risk from runoff and 

drainage from fields. The Addendum to the preliminary ecological assessment corrects 

the rates used in the TerrPlant model and presents revised RQs that are roughly half of 

the original RQs (aerial drift RQ for non-grass species dropped from 9.9 to 4.9). LOCs 

are exceeded for three out of the ten plant species tested, which are intended to be 

representative of the non-target terrestrial plants species potentially exposed. When 

sodium acifluorfen is applied using ground equipment, spray drift RQs are below the 

LOC.

Aquatic Assessment

Several studies have documented enhanced toxicity of LDPHs to fish in the presence of 

ultra-violet (UV) light as compared to the toxicity observed under standard laboratory 

lighting. Given that aquatic organisms may be exposed simultaneously to LDPHs and 

UV light in natural settings, concerns have been raised that guideline chronic exposure 

laboratory tests may underestimate the toxicity of LDPHs in the field. The Agency is 

applying an interim adjustment factor of 29X to the no observed adverse effect 

concentration (NOAEC) values from standard chronic fish studies to account for the 

potential enhanced toxicity of LDPH chemicals under natural sunlight. This enhanced 

sensitivity to LDPHs is not necessarily limited to fish and could be observed in other taxa 

such as aquatic invertebrates, birds, and mammals. However, the Agency is only applying 

an adjustment factor to fish at this time. The Agency is currently working to finalize its 

approach based on special fish studies required by EPA and submitted by the LDPH Task 

Force.

As noted in the sodium acifluorfen preliminary ecological risk assessment, chronic 

exposure RQs for freshwater fish were calculated with both the endpoint derived from the 

guideline fish early life stage study (standard laboratory lighting) and with the 29X 

adjustment factor applied (enhanced UV lighting). RQs for fish that may not receive 

simultaneous exposure to sodium acifluorfen and enhanced UV light are below the

Agency’s LOC. RQs for fish with the LPDH adjustment factor applied exceed the LOC 

by up to 6-fold for the rice use only. The risk conclusions for freshwater fish also apply 

to amphibians in aquatic habitats. 

Potential chronic risk to estuarine/marine fish cannot be quantified because of lack of 

definitive data. Although a chronic toxicity study with the fathead minnow is available, it 

cannot be used to calculate an acute to chronic ratio (ACR), and thereby an estimation of 

risk, as there were no effects at the highest dose tested. However, given that the acute 

endpoint for sheepshead minnow is greater than that for the rainbow trout, chronic RQs 

for estuarine/marine fish would be expected to be lower than those for freshwater fish.
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Based on the available exposure data, acute risk to fish (freshwater and estuarine/marine), 

aquatic invertebrates, and aquatic plants is not expected. There are no chronic data 

available for freshwater invertebrates. However, chronic effects can be estimated using 

an acute to chronic ratio from the mysid endpoint (the estuarine/marine acute endpoint is 

two orders of magnitude lower than the acute daphnid endpoint). Based on the mysid 

endpoint, there are no exceedances for chronic exposure except for the rice use pattern, 

with the highest RQ = 1.3. The assessment of chronic risk for aquatic invertebrates is 

based on guideline data conducted with standard lighting. It is not clear whether 

invertebrates would experience similar enhanced toxicity from the simultaneous exposure 

to sodium acifluorfen and enhanced UV light, as chronic fish studies have demonstrated.

2. Ecological Incidents

In April 2015, the Agency reviewed the Ecological Incident Information System (EIIS) 

database for incidents involving sodium acifluorfen and the acifluorfen degradate and 

identified one fish incident report that was classified as unlikely. The Agency also reviewed 

the Avian Incident Monitoring System (AIMS) in April 2015, where no sodium acifluorfen 

incidents were identified. Pesticide registrants also report certain types of incidents to the 

Agency as aggregate counts of incidents per product per quarter. There were 43 aggregate 

plant incidents reported for acifluorfen between 1995 and 2003. For additional details on the

ecological incidents for sodium acifluorfen, see Preliminary Environmental Fate and 

Ecological Risk Assessment Endangered Species Effects Determination for Acifluorfen dated 

June 11, 2015.

3. Characterization of Ecological Risk

The preliminary risk assessment and risk assessment addendum for sodium acifluorfen

identified some risks that exceeded EPA’s LOC for non-listed species. The Agency uses the 

LOC as an indicator of potential adverse effects to non-target organisms. LOC exceedances 

are only one line of evidence used by EPA to describe the risks posed by a pesticide to nontarget organisms. This risk characterization section is an attempt to describe other lines of 

evidence for sodium acifluorfen, and put the LOC exceedances into a broader context. 

Mammals – While the LOC is exceeded for chronic risk to mammals, EPA does not 

expect risk to mammals based on the following lines of evidence. The greatest LOC 

exceedance (dose-based RQ of 3.4) is for small mammals feeding exclusively on short 

grass in treated strawberry fields receiving two applications at the maximum label rate of 

0.375 lbs AI per acre (A). Risks would be lower with one application, which appears to 

be more typical than two applications based on available usage data. Modeled estimates

assume that 100% of an exposed mammal’s diet is derived from treated food items and 

that the treated items contain maximum expected residues. In addition, there are no 

exceedances of the LOC when considering dietary-based RQs. Based on available usage 

data, less than 1% of strawberries are treated with sodium acifluorfen, thus any adverse 

impacts to mammals is expected to be limited in scale, and unlikely.

Birds – While the LOC is exceeded for both acute and chronic risk to birds, EPA does not 

expect risk to birds based on the following lines of evidence. For acute risk, the LOC 
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(0.5) is only exceeded for small birds feeding on short grass in strawberry fields when 

using acute dose-based RQs (RQ of 0.76). There are no exceedances of the acute LOC 

when considering dietary-based RQs. For chronic risk, the greatest LOC exceedance 

(RQ of 7.8) is for small mammals feeding exclusively on short grass in treated strawberry 

fields receiving two applications at the maximum label rate of 0.375 lbs AI/A. Risks 

would be lower with one application, which appears to be typical based on available 

usage data. Modeled estimates assume that 100% of an exposed bird’s diet is derived 

from treated food items and that the treated items contain upper-bound expected residues, 

which may be conservative assumptions. In addition, based on available usage data, less 

than 1% of strawberries are treated with sodium acifluorfen, thus any adverse impact to 

birds is expected to be limited in scale.

Fish – Chronic RQs for fish that do not receive simultaneous exposure to sodium 

acifluorfen and enhanced ultraviolet (UV) light are below the Agency’s LOC. Chronic 

RQs for fish with the LPDH adjustment factor applied exceed the LOC by up to 6-fold 

for the rice use only. While the LOC is exceeded for chronic risk to fish for the rice use

under enhanced UV light, EPA does not expect widespread risk to fish based on the 

following lines of evidence. Not all fish would be expected to be exposed to both sodium 

acifluorfen and high UV light at the same time. It would seem reasonable to assume that 

fish inhabiting shallow, clear water bodies would be more susceptible to chronic effects 

than those in deeper, more turbid water bodies. Also, fish inhabiting water bodies at 

lower elevations or higher latitudes may also be less likely to exhibit chronic effects due 

to UV-enhanced toxicity. At higher latitudes, the sun is lower in the sky, so UV light 

must travel a greater distance through ozone-rich portions of the atmosphere, and 

therefore expose those latitudes to less UV radiation. Alternately, UV intensity decreases 

with lower elevation because there is more atmosphere to absorb UV rays. The Agency 

also realizes many other factors can impact the amount of UV light, such as time of day, 

time of year, stratospheric ozone and weather (cloud cover). Given the complexity of 

simultaneous exposure to sodium acifluorfen and enhanced UV light, the Agency has not 

yet determined the need to mitigate the potential risks of concern to fish and, if one were 

to mitigate, what measures might address the concern.

Terrestrial Plants - When using ground equipment, spray drift RQs do not exceed the 

LOC for non-target terrestrial plants. When aerial application is modeled, all labeled 

uses of sodium acifluorfen pose potential risks of concern to non-target terrestrial plants.

The Agency’s principal concern is off-target spray drift resulting from aerial applications.

The Addendum to the preliminary ecological assessment corrects the rates used in the 

TerrPlant model and presents revised RQs that are roughly half of the original number 

(revised aerial spray drift RQ for non-grass species is 4.9). In addition, the Addendum 

presents revised AgDRIFT modeling to reflect the current droplet size spectrum on labels 

(medium to coarse droplet size). Effects distances were significantly reduced using 

medium to coarse droplet size. However, to further address concern of spray drift impact 

to non-target plants, the sodium acifluorfen registrants have agreed to various label 

changes designed to reduce off-target spray drift. 

Listed Species - Although the Agency is not making a complete listed species finding at 

this time and the risk conclusions described in this document pertain to non-listed 
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species, the proposed label changes to address concern for and reduce spray drift impact 

to non-target (non-listed) terrestrial plants are also expected to reduce the extent of 

exposure and may reduce risk to the following listed taxa whose range and/or critical 

habitat co-occur with the use of sodium acifluorfen: terrestrial, semi-aquatic and aquatic 

plants; terrestrial invertebrates; birds; terrestrial and aquatic-phase amphibians; reptiles; 

mammals; freshwater and marine/estuarine fish and invertebrates.

EPA has not yet fully evaluated risks to listed species at this time. The Agency will 

complete its listed species assessment and any necessary consultation with the Services 

for sodium acifluorfen prior to completing the sodium acifluorfen registration review.

C. Benefits Assessment

Sodium acifluorfen is registered for use for selective control of broadleaf species and certain 

grass species in rice, soybeans, peanuts, and strawberries. In evaluating potential risk mitigation 

for sodium acifluorfen, EPA considered the risks, the benefits, and the use pattern of this 

compound. EPA believes that there may be potential risk to non-target plants from the use of 

sodium acifluorfen. However, these risks are outweighed by the benefits associated with use of 

this compound. About one million acres are treated annually with sodium acifluorfen. 

Approximately 17% of peanut acres and 5% of rice acres, on average, are treated with sodium 

acifluorfen, indicating that it is an important tool for controlling weeds in these crops. For 

soybeans about 1% of the crop is treated on average annually, which accounts for about 800,000 

acres of the one million acres treated annually with sodium acifluorfen. For strawberries, while 

overall usage is relatively low (<500 lbs AI used on average per year), sodium acifluorfen may 

be an important component of an herbicide program for some small-acreage producers who do 

not fumigate their strawberry beds. Minor strawberry producers who do not use fumigation may 

use herbicides such as sodium acifluorfen for weed control. EPA has limited data to confirm 

actual usage on strawberries. EPA market research data, however, do not show usage of sodium 

acifluorfen on strawberries in the major strawberry producing states of California and Florida.

Sodium acifluorfen is reported to be an important alternate mechanism of action (MOA) for 

crops with species of weeds resistant to other common herbicides such as glyphosate and ALSinhibitor herbicides1

.

For additional detail on the qualitative benefits of sodium acifluorfen, see Sodium Acifluorfen 

Usage Information, March 17, 2016.

D. Endangered Species Assessment

In November 2013, the EPA, along with the Services and the USDA, released a summary of 

their joint Interim Approaches for assessing risks to endangered and threatened (listed) species 

from pesticides. The Interim Approaches were developed jointly by the agencies in response to 

the National Academy of Sciences’ (NAS) recommendations and reflect a common approach to 

risk assessment shared by the agencies as a way of addressing scientific differences between the 

 

1 Available at http://www.gaweed.com/slides/PAC-08/PAC-08.pdf
13

EPA and the Services. The NAS report2outlines recommendations on specific scientific and 

technical issues related to the development of pesticide risk assessments that EPA and the 

Services must conduct in connection with their obligations under the ESA and FIFRA. 

The joint Interim Approaches were released prior to a stakeholder workshop held on November 

15, 2013. In addition, the EPA presented the joint Interim Approaches at the December 2013 

Pesticide Program Dialogue Committee (PPDC) and State-FIFRA Issues Research and 

Evaluation Group (SFIREG) meetings. The agencies also held stakeholder workshops —in April 

and October 2014, and in April 2015 — allowing additional opportunities for stakeholders to 

comment on the Interim Approaches. Additional workshops are planned to enhance stakeholder 

involvement. As part of a phased, iterative process for developing the Interim Approaches, the 

agencies will also consider public comments on the Interim Approaches in connection with the 

development of upcoming Registration Review decisions. The details of the joint Interim 

Approaches are contained in the white paper Interim Approaches for National-Level Pesticide 

Endangered Species Act (ESA) Assessments Based on the Recommendations of the National 

Academy of Sciences April 2013 Report3, dated November 1, 2013. 

Given that the agencies are continuing to develop and work toward implementation of the 

Interim Approaches to assess the potential risks of pesticides to listed species and their 

designated critical habitat, the ecological risk assessment supporting this Proposed Interim 

Decision for sodium acifluorfen does not contain a complete ESA analysis that includes effects 

determinations for specific listed species or designated critical habitat. Although EPA has not yet 

completed effects determinations for specific species or habitats, for this preliminary assessment 

EPA’s evaluation assumed, for all taxa of non-target wildlife and plants, that listed species and 

designated critical habitats may be present in the vicinity of the application of sodium 

acifluorfen. This assessment will allow EPA to focus its future evaluations on the types of 

species where the potential for effects exists once the scientific methods being developed by the 

agencies have been fully vetted. Once the agencies have fully developed and implemented the 

scientific methodology for evaluating risks for listed species and their designated critical 

habitats, these methods will be applied to subsequent analyses for sodium acifluorfen as part of 

completing this registration review. 

E. Endocrine Disruptor Screening Program

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

outcomes from exposure to chemicals. Collectively, these studies include acute, subchronic and 

chronic toxicity, including assessments of carcinogenicity, neurotoxicity, developmental, 

reproductive, and general or systemic toxicity. These studies include endpoints which may be 

susceptible to endocrine influence, including effects on endocrine target organ histopathology, 

organ weights, estrus cyclicity, sexual maturation, fertility, pregnancy rates, reproductive loss, 

and sex ratios in offspring. For ecological hazard assessments, EPA evaluates acute tests and 

chronic studies that assess growth, developmental and reproductive effects in different 

taxonomic groups. As part of its most recent registration decision for sodium acifluorfen, EPA 

 

2 Assessing Risks to Endangered and Threatened Species from Pesticides. Available at 

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

3 Available at http://www2.epa.gov/endangered-species/assessing-pesticides-under-endangered-species-act#report 
14

reviewed these data and selected the most sensitive endpoints for relevant risk assessment 

scenarios from the existing hazard database. However, as required by FFDCA section 408(p), 

sodium acifluorfen is subject to the endocrine screening part of the Endocrine Disruptor 

Screening Program (EDSP). 

EPA has developed the EDSP to determine whether certain substances (including pesticide 

active and other ingredients) may have an effect in humans or wildlife similar to an effect 

produced by a “naturally occurring estrogen, or other such endocrine effects as the Administrator 

may designate.” The EDSP employs a two-tiered approach to making the statutorily required 

determinations. Tier 1 consists of a battery of 11 screening assays to identify the potential of a 

chemical substance to interact with the estrogen, androgen, or thyroid (E, A, or T) hormonal 

systems. Chemicals that go through Tier 1 screening and are found to have the potential to 

interact with E, A, or T hormonal systems will proceed to the next stage of the EDSP where EPA 

will determine which, if any, of the Tier 2 tests are necessary based on the available data. Tier 2 

testing is designed to identify any adverse endocrine-related effects caused by the substance, and 

establish a dose-response relationship between the dose and the E, A, or T effect. 

Under FFDCA section 408(p), the Agency must screen all pesticide chemicals. Between 

October 2009 and February 2010, EPA issued test orders/data call-ins for the first group of 67 

chemicals, which contains 58 pesticide active ingredients and 9 inert ingredients. A second list of 

chemicals identified for EDSP screening was published on June 14, 20134and includes some 

pesticides scheduled for Registration Review and chemicals found in water. Neither of these 

lists should be construed as a list of known or likely endocrine disruptors. For further 

information on the status of the EDSP, the policies and procedures, the lists of chemicals, future 

lists, the test guidelines and the Tier 1 screening battery, please visit our website.5 

In this proposed interim decision, EPA is making no human health or environmental safety 

findings associated with the EDSP screening of sodium acifluorfen. Before completing this 

Registration Review, the Agency will make an EDSP FFDCA section 408(p) determination.

IV. PROPOSED INTERIM REGISTRATION REVIEW DECISION

A. Risk Mitigation and Regulatory Rationale

As discussed in the Ecological Risk Assessment Section of this document, sodium acifluorfen

may pose a potential risk concern for non-target terrestrial plants exposed to off-target spray drift 

from aerial applications. In evaluating potential risk mitigation for sodium acifluorfen, EPA 

considered the risks, the benefits, and the use pattern of this compound. EPA believes that there 

may be potential risk to non-target plants from the use of sodium acifluorfen. However, these 

risks are outweighed by the benefits associated with use of this compound. To address these 

potential risks to non-target plants, EPA is proposing risk mitigation measures.

Spray Drift Reduction

As discussed in the ecological risk assessment section of this document, sodium acifluorfen

poses a potential risk concern for non-target terrestrial plants exposed to off-target spray drift 

 

4 See http://www.regulations.gov/#!documentDetail;D=EPA-HQ-OPPT-2009-0477-0074 for the final second list of chemicals.

5 http://www.epa.gov/endo/
15

from aerial applications. To address spray drift concerns, the sodium acifluorfen registrants have 

agreed to undertake label language amendments regarding spray drift parameters, including 

droplet size, uniform across all labels. 

These label amendments are expected to reduce the extent of environmental exposure and risk to 

non-target plants and animals. Although the Agency is not making a complete listed species 

safety finding at this time, these label amendments are expected to reduce the extent of exposure 

and may reduce risk to listed species whose range and/or critical habitat co-occur with the use of

sodium acifluorfen. For sodium acifluorfen, registrants have committed to amending labels 

where necessary to standardize the following parameters: 

 Select nozzles and pressure that deliver medium (VMD 226-325) or coarser spray 

droplets as indicated in nozzle manufacturer’s catalogs and in accordance with ASABE 

Standard S-572.

 Applicators may spray only when wind speed is between 3 and 10 mph. 

 For aerial applications, the release height must be no higher than 10 feet from the top of 

the crop canopy, unless a greater application height is required for pilot safety.

 For aerial applications, the distance of the outer most nozzles on the boom should not 

exceed three-fourths of the length of the wingspan or rotor diameter. To further reduce 

drift, use one-half of the length of the wingspan or rotor diameter at the edge of a field.

 Applicators may not spray during temperature inversions

 For ground applications, boom height must be no higher than 4 feet above the crop 

canopy.

The Agency is encouraging the development of pesticide drift reduction technologies (or DRTs; 

see http://www.epa.gov/reducing-pesticide-drift/about-drift-reduction-technology-program) that 

will help realize user, societal, and environmental benefits including:

 reducing the loss of pesticide from the application site,

 improving pest control,

 slowing the advancement of herbicide-resistant weed populations, 

 reducing pesticide exposures to people, wildlife, and the environment, and

 reducing risks of damage and liabilities from off-target deposition of drift.

Furthermore, EPA believes that the use of proven DRTs will provide users with a wider range of 

options for addressing drift concerns. Such DRTs could include specialized nozzles, spray 

shields, and drift-reducing adjuvant chemicals. The Agency encourages users and producers of 

sodium acifluorfen to consider, test, and use these types of innovations as part of the risk 

management plan for sodium acifluorfen. DRTs are expected to be useful in mitigating the risks 

drift poses to non-target species, and particularly in addressing risks to listed species.

Prohibiting Aerial Applications to Strawberries

Current sodium acifluorfen labels permit aerial applications to all registered use sites, including 

strawberries. Aerial applications provide the greatest potential for exposure to non-target plants 

and other taxa because of the increased potential for spray drift. To address spray drift concerns, 

sodium acifluorfen registrants have agreed to prohibit the aerial application method for

strawberries. Usage data available to EPA do not indicate that sodium acifluorfen is applied 
16

aerially to strawberries, and EPA believes that removal of this application method will not 

adversely affect growers. 

Herbicide-Resistance Management

The development and spread of herbicide resistant weeds in agriculture is a widespread problem 

that has the potential to fundamentally change production practices in US agriculture. While 

herbicide resistant weeds have been known since the 1950s, the number of species and their 

geographical extent, has been increasing rapidly. Currently there are 249 weed species 

worldwide with confirmed herbicide resistance, especially since the turn of the century. In the 

United States there are 155 weed species with confirmed resistance to one or more herbicides.

Management of herbicide resistant weeds, both in mitigating established herbicide resistant 

weeds and in slowing or preventing the development of new herbicide resistant weeds, is a 

complex problem without a simple solution. Coordinated efforts of growers, agricultural 

extension, academic researcher, scientific societies, pesticide registrants, and state and federal 

agencies are required to address this problem.

The EPA, Office of Pesticide Programs (OPP) is proposing measures for the pesticide registrants 

to provide growers and users with detailed information and recommendations to slow the 

development and spread of herbicide resistant weeds. This is part of a more holistic, proactive 

approach recommended by crop consultants, commodity organizations, professional/scientific 

societies, researchers, and the registrants themselves. OPP’s approach is measured, based on the 

inherent risk of weed resistance developing for a given herbicide, considering the target weeds 

and the agronomic practices of the registered crops. Situations with the least concern for the 

development of herbicide resistant weeds will have the fewest resistance management elements 

and the situations with the highest concern will have additional resistance management elements. 

Implementation Timeline and Opportunities for Public Comment on Herbicide Resistance 

Approach

OPP is proposing to implement herbicide resistance measures for existing chemicals during 

registration review, and to implement herbicide resistance measures for new chemicals and new 

uses at the time of registration. In registration review, proposed herbicide resistance elements 

will be included in every herbicide proposed interim decision. Comments on these chemical 

specific measures are welcomed. The Agency will also soon issue a Pesticide Registration Notice 

(PRN) that will provide additional guidance to registrants. All stakeholders are encouraged to 

comment. Public comments received on both the sodium acifluorfen PID and the PRN will be 

considered prior to the final decision on sodium acifluorfen.

Sodium acifluorfen acts to inhibit the protoporphyrinogen oxidase (PPO) enzyme, a key enzyme 

in the production of precursor molecules needed for the photosynthesis. PPO inhibitors also 

result in the formation of highly reactive molecules that attack and destroy lipids and protein 

membranes. This herbicide is classified by the Weed Science Society of America (WSSA) as 

belonging to mechanism of action (MOA) Group 14. This MOA has three confirmed herbicide 

resistant weeds. 
17

This MOA is of moderate concern for weed resistance development because of the existing cases 

of confirmed herbicide resistant weeds. Currently there are no herbicide resistant crops. 

Proposed herbicide resistance management elements for sodium acifluorfen include:

On the label

1. List Mechanism of Action (MOA) WSSA Group 14.

2. List seasonal and annual maximum number of applications and rates for all crops.

3. List best management practices for Herbicide Resistance (as appropriate to crop).

4. State that user should scout before and after application.

5. List the definition of likely resistance on label.

6. State that user should report lack of performance to registrant or their representative. 

7. List confirmed resistant weeds in a separate table and list effective or recommended rates 

for these weeds with the table.

Reporting, Education, and Stewardship

8. Registrants should report new cases of likely and confirmed resistance to EPA and users 

yearly. This will be in addition to any adverse effects reporting.

 

B. Tolerance Amendments

The Agency will modify the tolerance expression so that it appropriately covers the metabolites 

and degradates of sodium acifluorfen and that it specifies the residues to be measured for each 

commodity. In addition, tolerances will be modified to include the recommended number of 

significant figures.

C. Proposed Interim Registration Review Decision

In accordance with 40 CFR Sections 155.56 and 155.58, the Agency is issuing this Proposed 

Interim Registration Review Decision. Except for the EDSP, ESA and pollinator components of 

this case, the Agency has made the following Proposed Interim Registration Review Decision: 

(1) no additional data are required at this time; and (2) changes to the affected registrations and 

their labeling are needed at this time.

In this proposed interim registration review decision, EPA is making no human health or 

environmental safety findings associated with the EDSP screening of sodium acifluorfen, nor is 

it making a complete endangered species finding or a complete assessment of effects to 

pollinators. Although the Agency is not making an Endangered Species safety finding at this 

time, the proposed mitigation described in this document is expected to reduce overall exposure 

and may reduce risk to listed species. The Agency’s final registration review decision for 

sodium acifluorfen will depend upon the results of an ESA Section 7 consultation with the 

Services, an EDSP FFDCA section 408(p) determination, and an assessment of the non-target 

exposure to bees.
18

V. NEXT STEPS AND TIMELINE

A. Interim Registration Review Decision

In accordance with 40 CFR Sections 155.56 and 155.58, the Agency is issuing this Proposed 

Interim Registration Review Decision, and placing it in the sodium acifluorfen registration 

review docket (EPA-HQ-OPP-2010-0135) for public comment for 60 days. A Federal Register 

Notice will announce the availability of this Proposed Interim Registration Review Decision for 

sodium acifluorfen and initiate a 60-day comment period. If there are no significant comments or 

additional information submitted to the docket during the comment period that leads the Agency 

to change its proposed decision, EPA will issue an Interim Registration Review Decision for 

sodium acifluorfen (case 2605). 

B. Implementation of Mitigation Measures

Once the Interim Registration Review Decision is issued in final form, registrants are to submit 

amended labels that include the label changes summarized in Appendix B to the Agency for 

approval within 60 days following issuance of the Interim Registration Review Decision in final 

form. A summary of the mitigation measures are described in Appendices A and B. 
19

Appendix B: Sodium Acifluorfen Label Table

Summary of Proposed Labeling Changes for Sodium Acifluorfen

Description Proposed Labeling Language for Sodium acifluorfen

Products

Placement on Label

SPRAY DRIFT

Spray Drift Language  Select nozzles and pressure that deliver medium

(VMD 226-325) or coarser spray droplets as 

indicated in nozzle manufacturer’s catalogs and in 

accordance with ASABE Standard S-572.

 Applicators may spray only when wind speed is 

between 3 and 10 mph.

 For aerial applications, the maximum release height 

must be no higher than 10 feet from the top of the 

crop canopy, unless a greater application height is 

required for pilot safety.

 For aerial applications, the distance of the outer most 

nozzles on the boom must not exceed three-fourths 

of the length of the wingspan or rotor diameter. To 

further reduce drift, use one-half of the length of the 

wingspan or rotor diameter at the edge of a field.

 Applicators may not spray during temperature 

inversions.

 For ground applications, boom height must be no 

higher than 4 feet above the crop canopy.

Directions for Use

HERBICIDE RESISTANCE MANAGEMENT- Products Labeled for Agricultural Use

Herbicide Mechanism 

of Action “Group 14 HERBICIDE”

Front Panel, upper right 

quadrant, surrounded by a 

black (or suitable color) 

rectangle

Weed Resistance 

Management

 Listing of herbicide mechanism of action (MOA), 

and/or WSSA herbicide group number, at the top of 

the first page of each product label; 

Directions for Use, prior to 

directions for specific crops 

under the heading “WEED 

Appendix A: Summary of Proposed Actions for Sodium Acifluorfen

Registration Review Case#: 2605

PC Code: 114402

Chemical Type: herbicide

Chemical Family: Diphenyl ether

Mechanism of Action: WSSA Group 14

Affected 

Population(s)

Source of 

Exposure

Route of 

Exposure

Duration of 

Exposure

Risk(s) of 

Concern

Proposed Action(s)

 Terrestrial 

Plants 

(dicots)

 Aerial 

Application

 Foliar 

absorption

 Acute  Acute 

toxicity

 Require spray drift reduction 

language

 Require herbicide resistance 

management language for 

moderate concern group

 Delete aerial application to 

strawberry
20

Summary of Proposed Labeling Changes for Sodium Acifluorfen

Description Proposed Labeling Language for Sodium acifluorfen

Products

Placement on Label

 List seasonal and annual maximum number of 

applications and pounds.

 Resistance Management language from PR Notice 

2001-5, and/or Best Management Practices 

(appropriate to crop) from Weed Science Society of 

America (WSSA) & Herbicide Resistance Action 

Committee (HRAC), and/or HRAC proposed 

guidelines for herbicide labels.

 User should scout before and after application. 

 Include the definition of likely resistance.

 User should report lack of performance to registrant 

or their representative.

 List confirmed resistant weeds in a separate table 

and list effective or recommended rates for these 

weeds with the table.

RESISTANCE 

MANAGEMENT”

DIRECTIONS FOR USE

Delete aerial 

application for 

strawberry

 For strawberry, aerial application is prohibited. Directions for Use for 

Strawberry