1

OFFICE OF 

CHEMICAL SAFETY AND 

POLLUTION PREVENTION

 

Problem Formulation for the 

Ecological Risk and 

Drinking Water Exposure Assessments 

In Support of the Registration Review of 

Sodium Acifluorfen 

Sodium acifluorfen (CAS 62476-59-9) 

Sodium 5-(2-chloro-a,a,a-trifluoro-p-tolyloxy)-2-nitrobenzoate 

5-(2-chloro-4-(trifluoromethyl)phenoxy)-2-nitrobenzoic acid, sodium salt 

Prepared by:

Donna Judkins, Ph.D. Biologist 

Stephanie Syslo, Environmental Scientist 

Reviewed by:

Dana Spatz, Branch Chief 

Date

March 24, 2010 

U. S. Environmental Protection Agency 

Office of Pesticide Programs 

Environmental Fate and Effects Division

Environmental Risk Branch III

1200 Pennsylvania Ave., NW 

Mail Code 7507P

Washington, DC 20460
2

Table of Contents

I. Purpose............................................................................................................................................ 3 

II. Nature of Regulatory Action......................................................................................................... 3 

A. Conclusions from Previous Risk Assessments.......................................................................4 

III. Stressor Source and Distribution................................................................................................ 5 

A. Mechanism of Action ...............................................................................................................5 

B. Overview of Pesticide Usage....................................................................................................5 

C. Environmental Fate and Transport .......................................................................................9 

A. Physical and Chemical Properties..........................................................................................9 

B. Environmental Fate Summary ...............................................................................................9 

1. Environmental Fate ........................................................................................................ 9 

2. Transformation Products............................................................................................. 11 

3. Environmental Transport ............................................................................................ 11 

Monitoring Data......................................................................................................................... 12 

IV. Receptors.................................................................................................................................... 13 

A. Effects on Aquatic Organisms ..............................................................................................14 

B. Effects on Terrestrial Organisms..........................................................................................17 

D. Ecosystems at Risk.................................................................................................................18 

V. Assessment Endpoints................................................................................................................. 20 

VI. Conceptual Model....................................................................................................................... 20 

A. Risk Hypotheses .....................................................................................................................20 

B. Diagram...................................................................................................................................20 

Direct Terrestrial Uses ............................................................................................................. 20 

VII. Analysis Plan Options............................................................................................................... 21 

A. Ecological Risk Assessment...................................................................................................22 

C. Drinking Water Assessment..................................................................................................23 

D. Clean Water Act.....................................................................................................................23 

E. Endocrine Disruptor Screening Program............................................................................24 

F. Anticipated Data Needs .........................................................................................................24 
3

I. Purpose 

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

fate and ecological effects of the registered uses of sodium acifluorfen (sodium 5-(2-chloro-a,a,atrifluoro-p-tolyloxy)-2-nitrobenzoate). Sodium acifluorfen is a non-selective, postemergent contact 

herbicide used to control annual broadleaf weeds and some grasses in soybean, peanuts, rice and 

strawberries. This document will provide a plan for analyzing data relevant to sodium acifluorfen 

and for conducting updated ecological risk and drinking water exposure assessments for its 

registered uses. Additionally, this problem formulation is intended to identify remaining data gaps, 

uncertainties and potential assumptions used to address those uncertainties relative to characterizing

the ecological risk associated with the registered uses of sodium acifluorfen. 

The problem formulation is based on a bridging strategy linking the dissociation of sodium 

acifluorfen salt to the formation of acifluorfen and sodium ions. The active ingredient is acifluorfen 

acid and application rates will be referred to in this problem formulation in terms of acid equivalents 

(ae). Acifluorfen acid is also a break-down product of lactofen, a herbicide used on agricultural 

crops and in forestry. Because lactofen will degrade to acifluorfen in the environment, the EFED 

drinking water assessment for sodium acifluorfen will aggregate the potential exposure to acifluorfen 

from both pesticides. 

II. Nature of Regulatory Action 

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

assessing the risks of pesticides, i.e., registration review.1 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 sodium acifluorfen continues to meet the FIFRA standard for 

registration. This problem formulation for the ecological risk assessment chapter in support of the 

registration review is intended for the initial docket opening for the public phase of the review 

process. 

 

1

http://www.epa.gov/oppsrrd1/registration_review/
4

A. Conclusions from Previous Risk Assessments 

The Agency has conducted previous ecological risk assessments on sodium acifluorfen that serve as 

a basis for this problem formulation. Each of the previous risk assessments is briefly discussed 

below. 

Sodium acifluorfen was first registered in the United States in 1980 for post-emergent weed control 

on agricultural crops and was subsequently registered for residential spot treatment. Four data callins (DCIs) were issued in June 1991, March 1995, October 1995 and January, 2006. 

• Re-registration Eligibility Decision (RED) 

A RED for sodium acifluorfen was completed in 2003. EPA conducted an aggregate drinking water 

assessment for lactofen and sodium acifluorfen because they share an environmental degradate, 

acifluorfen. Because lactofen was first registered after 1984, it was not subject to reregistration under 

FIFRA; however, under The Federal Food, Drug and Cosmetic Act (FFDCA), as amended by the 

Food Quality Protection Act (FQPA), it was necessary to reassess the lactofen tolerances. 

The Agency conducted a screening level ecological risk assessment using modeling to determine the 

potential impact of sodium acifluorfen use on non-target terrestrial and aquatic organisms. The 

Agency had some concerns for chronic risk to birds that feed on short grasses. The Agency had no 

concerns for the impacts of sodium acifluorfen on mammalian species or aquatic organisms. 

The Agency determined that sodium acifluorfen will have “no effect” on threatened and endangered 

aquatic organisms, mammals, and birds. Although chronic RQs for birds that eat short grass 

exceeded the level of concern, the only listed endangered species that consumes short grass is the 

Hawaiian goose, which resides on golf courses in Hawaii. Because sodium acifluorfen was not used 

in or around this bird’s habitat, the Agency concluded that there was “no effect” to endangered birds.

Limited plant information was available about the toxicity of sodium acifluorfen, so the Agency was 

unable to conduct a risk assessment for non-target plants. Because sodium acifluorfen is an 

herbicide, there may be some risk to nontarget plants exposed via drift. The Agency was unable to 

conduct a risk assessment for insects due to a data gap for the honey bee acute contact study. 

As part of the RED, the Agency required several label amendments to limit the potential for drift. In 

addition, the Agency required confirmatory plant toxicity data (the vegetative vigor and seedling 

emergence studies), and the honey bee acute contact study. In addition, since sodium acifluorfen 

belongs to a class of compounds known to have a phototropic mode of action in plants and animals, 

and there is evidence that such chemicals have increased toxicity in the presence of light, a 

confirmatory phototoxicity study was required. In 2006, a DCI was issued for testing the lightdependent peroxidizing herbicide (LDPH) effects of sodium aciflourfen. See Section: Data required 

for existing DCIs, for more detailed information. 
5

III. Stressor Source and Distribution 

A. Mechanism of Action 

Sodium acifluorfen (CAS number 62476-59-9) [Sodium 5-(2-chloro-a,a,a-trifluoro-p-tolyloxy)-2-

nitrobenzoate] belongs to the nitrophenyl ether class of herbicides. Compounds in this group cause 

rapid disruption of cell membranes and very rapid kill. Acifluorfen penetrates into the cytoplasm, 

and causes the formation of peroxides and free electrons (light is required) that destroy the cell 

membranes almost immediately. Rapid destruction of cell membranes prevents translocation to other 

regions of the plant. Partial coverage of a plant with spray results in spotting and/or partial shoot

kill, and new growth on surviving plants will be normal in appearance. 

B. Overview of Pesticide Usage 

Sodium acifluorfen is labeled for use as a non-selective herbicide on the agricultural crops soybeans,

peanuts, rice, and strawberries, and as a spot treatment in residential areas. Based on usage data 

provided by the Biological and Economic Analysis Division (BEAD), on average, roughly 300,000 

pounds of sodium acifluorfen are applied annually to agricultural crops (Table 1). Sodium 

acifluorfen usage is highest on soybeans, with annual average applications of 200,000 lbs a.i. applied

(representing >50% of the total use on agricultural crops). The crop with the highest average percent

crop treated with sodium acifluorfen is peanuts (20%), followed by rice and soybeans (5% each). 

No data were provided for the strawberry use. 

Table 1. Screening Level Estimates of Agricultural Uses of Acifluorfen 

(Source: BEAD SLUA report dated June 5, 2009) 

Crop Lbs. A.I. Percent Crop Ttd. 

 Avg. Max. 

Fallow, Summer+ 1,000 <1 5 

Peanuts 50,000 10 20 

Peas, Green+ <500 <1 <2.5 

Rice 20,000 5 5 

Soybeans 200,000 <2.5 5 

All numbers rounded. 

<500 indicates less than 500 lbs. of active ingredient. 

<2.5 indicates less than 2.5 percent of crop is treated. 

<1 indicates less than 1 percent of crop is treate

+ These crops were not known to be listed on active end use product registrations when this report was run. 

SLUA data sources include: USDA-NASS (United States Department of Agriculture's National Agricultural Statistics 

Service; use years 2001-2007); Private Pesticide Market Research, 2001-2007; NPUD 2002 (National Pesticide Use 

Database) of the CropLife America Foundation; and California DPR data. These results reflect amalgamated data 

developed by the Agency and are releasable to the public. 

As shown in Figure 1, based on U.S. Geological Survey (USGS) National Water Quality 

Assessment Program (NAWQA) data from 2002, acifluorfen is used on agricultural crops only east 

of the Rocky Mountains, predominantly in the Mississippi Delta region, the Corn Belt, and 

Southeastern states from Maryland to Florida. In 2002, the use of acifluorfen on soybeans 

represented about 75% of the national use (out of roughly 400,000 pounds applied). 
6

Figure 1. Map of Estimated Annual Agricultural Use of Sodium acifluorfen in 2002 

(Source: http://water.usgs.gov/nawqa/pnsp/usage/maps/ ). 

NAWQA data for the years 1997 and 1992 (Figures 2 and 3, respectively) reported substantial use 

in Nebraska, South Dakota, North Dakota, Minnesota, and Michigan. Approximately 1.7 and 1.25 

million pounds active ingredient (a.i.) of sodium acifluorfen were used in those years, respectively, 

with approximately 90% used on soybeans. Apparently, use of sodium acifluorfen has been 

declining in recent years with the availability of Roundup Ready®soybeans. 

Formulations used in sodium acifluorfen products include liquid (20.1% single active ingredient; 

13.4% active ingredient, co-formulated with bentazon), liquid ready-to-use (0.12% active ingredient, 

co-formulated with glyphosate), and soluble concentrate (44% active ingredient, manufacturers use 

product). 
7

Figure 2. Map of Estimated Annual Agricultural Use of Sodium acifluorfen in 1997 

(Source: http://water.usgs.gov/nawqa/pnsp/usage/maps/ ). 
8

Figure 3. Map of Estimated Annual Agricultural Use of Sodium acifluorfen in 1992 

(Source: http://water.usgs.gov/nawqa/pnsp/usage/maps/ ). 

Sodium acifluorfen is applied by aircraft and by broadcast and band treatment using ground 

equipment for agricultural crops, and by trigger spray bottle for spot treatments. It can be applied to 

peanuts both pre- and post emergence and at cracking; for rice, from the tiller through boot stage; for 

soybeans both preplant and foliar; and for strawberries at dormant, pretransplant, and postharvest. 

Single application rates for agricultural crops range from 0.25 to 0.375 pounds active ingredient/acre

(lbs a.i./A) and seasonal application rates are up to 0.75 lbs a.i./A. Applications intended for spot

treatment are to be made until the foliage is wet, so in these cases the application rate is estimated. 

Sites that can be treated are: fencerows/hedgerows; mulch; ornamental and shade trees; ornamental 

lawns and turf; ornamental wood shrubs and vines; paths/patios; and paved areas (private 

roads/sidewalks). 
9

C. Environmental Fate and Transport 

 A. Physical and Chemical Properties 

Common name: Sodium acifluorfen 

CAS No.: 62476-59-9 

Chemical name: Sodium 5-(2-chloro-a,a,a-trifluoro-p-tolyloxy)-2-nitrobenzoate or 

5-(2-chloro-4-(trifluoromethyl)phenoxy)-2-nitrobenzoic acid, sodium salt 

Trade name(s): BlazerTM, StormTM, UltrablazerTM, Kleeraway Grass and Weed KillerTM

Table 2. Summary of Physical and Chemical Properties of Flurprimidol 

Parameter Value Reference/Comments 

Molecular formula C14H7ClF3NO5 RED* 

Molecular weight 361.66 g/mol RED 

Physical state Light yellow powder RED 

Melting point 274-279oC (with decomposition) RED 

Vapor pressure (25oC) <1.33 x 10-5 Pa RED 

Water Solubility (20°C) 62.07 g/ 100 mL RED 

Henry's Law Constant 7.65 x 10-10 atm m3/mol Reviewer-calculated 

Dissociation constant (pKa) 3.5 RED 

Octanol/Water Partition 

Coefficient (Kow; pH 7) 

1.55 RED 

* http://www.epa.gov/oppsrrd1/REDs/acifluorfen_red.pdf 

 B. Environmental Fate Summary 

 1. Environmental Fate 

The dominant dissipation mechanism for sodium acifluorfen in the environment is dissociation to the 

negatively charged acifluorfen anion. The acifluorfen anion is persistent in soil (aerobic soil 

metabolism half life 170 days) and in aerobic aquatic environments (estimated aerobic half-life 117 

days); it is less persistent in anaerobic conditions (aquatic half-life estimated to be 2.75 days). The 

acifluorfen ion is relatively mobile; Kds range from 0.148 to 3.10 g/mL. Adsorption and desorption 

were strongly correlated with soil clay content. Acifluorfen undergoes photolytic degradation in water 

with a half-lives ranging from 21.7 hours to 352 hours depending on the pH and buffer systems used. 

Thus acifluorfen may degrade rapidly in surface water bodies with clear and/or shallow water that is 

able to transmit adequate light. It is stable to hydrolysis, and photodegradation on soil is not a major 

degradation route in the environment. Volatilization does not appear to be a significant dissipation 

pathway for acifluorfen (vapor pressure is <1.33 x 10-5 Pa; Henry's Law constant is 7.65 x 10-10 atm 

m

3

/mol). Acifluorfen is not expected to bioaccumulate in aquatic organisms because of the low Kow. 

The environmental fate data shown in the following Tables are taken from required studies 

submitted in support of registration of sodium acifluorfen. 
10

Table 3. Environmental Fate Laboratory Data for Sodium acifluorfen

 

 

 

 

 

1

 Major degradates are defined as those which reach >10% of the applied. 2 OM = Organic matter content of soil

Study Value Major Degradates1

, 

Comments

MRID # 

Abiotic Hydrolysis Half-life Stable at pHs 3, 6, and 9 

(at up to 40°C for 28 days) 

Stable at pHs 4.5, 7.2, and 

9.7 (at 25°C) 

None 00071584, 

00122757 

00107479 

Direct Aqueous Photolysis 21.7 to 352 hours Numerous polar photoproducts; 

none >6.5% of total radioactive 

residues (TRR) 

41891208,

42793502,

44195001,

44195002 

Soil Photolysis Half-life > 15 days Degradation in dark control was 

comparable to that in irradiated 

samples 

44412901 

Aerobic Soil Metabolism 

Half-life 

170 days 6 month incubation period 

Degradates < 5% TRR each 

00143572 

Anaerobic Aquatic 

Metabolism 

Half-life

2.75 days 

(Water- clay soil system 

under N2 atmosphere) 

Degradation of parent determined 

during incubation of 10 days; 

incubation for formation and decline 

of degradates conducted for 375 

days. Amino acifluorfen persisted 

through the incubation period.

 43155201 

Aerobic Aquatic Metabolism 

Half-life 

114 days (extrapolated; r2

0.728) (at 25°C for 35 days 

in well water - clay soil 

mixtures) 

Acifluorfen decreased to 81.8% of 

TRR by 35 days; sum of 10 minor 

components and CO2

 approximately 

5% each 

42330601 

Study Value MRID # 

Soil KF 1/n KFoc

sand 0.148 0.82 50 

sandy loam 0.346 0.89 74 

loam 1.51 0.85 57 

clay (1.6% 

OM2) 1.87 0.79 199 

Batch Equilibrium 

for parent acifluorfen 

 (mL/g) 

clay (3.2% OM) 3.10 0.75 165 

42793501 

Soil KF 1/n KFoc

loamy sand 47.01 0.94 7368 

loam 19.34 0.89 741 

clay 12.11 0.87 625 

Batch Equilibrium 

For amino acifluofen 

degradate 

(mL/g) 

sand 

1.25 0.80 431 

44412902 
11

Table 4. Environmental Fate Field Study Data for Sodium acifluorfen 

 2. Transformation Products 

The primary degradate of acifluorfen under anaerobic conditions was the corresponding amine from the 

reduction of the nitro group (amino acifluorfen (5-[2-chloro-4(trifluoromethyl) phenoxy]-2-

aminobenzoic) acid). When samples were incubated under anaerobic conditions for up to 375 days, 

the degradates amino acifluorfen, acifluorfen acetamide (5-[2-chloro-4-(trifluoromethyl) phenoxy]-

2-acetamidobenzoic acid), and desnitro acifluorfen (3-[2-chloro-4-(trifluoromethyl)phenoxy]-

benzoic acid) were identified in the soi1:water systems. Amino acifluorfen averaged 64 -71% of the 

radioactivity applied at 25 through 375 days; maximum concentrations of the other degradates were < 

5% throughout the study. These same three degradates were seen in the other metabolism studies; 

however, none were present at greater than 5% of the applied radioactivity. 

The amino acifluorfen degradate is less mobile than the parent; Kds range from 1.25 to 47 g/mL. 

Adsorption and desorption were strongly correlated between Kads and soil pH, with an increase in 

sorption with a decrease in pH. For sand, clay and loam a correlation existed between Kads and % 

organic matter; however, this relationship did not hold for loamy sand soil. The loamy sandy, 

however, had the highest level of sorption and the lowest pH value. This indicates that soil pH may 

have a stronger effect on sorption than organic matter. A correlation was not observed for % clay. 

3. Environmental Transport 

A small-scale prospective ground water monitoring study conducted on soybeans in the central sands 

of Wisconsin addressed both field dissipation and leaching potential for sodium acifluorfen. 

Although acifluorfen and two degradates were monitored, only the parent was detected. Residues 

Study Value MRID # 

Terrestrial Field 

Dissipation 

Half-life 

15 days 

59 days 

Estimated as part of limited 

prospective ground water study 

After 2 months, residue levels were 

near detection levels 

Mississippi silt loam; 

leaching below 3-in depth negligible 

during 179 days of study 

42152201 

00137756, 

00143573 

Aquatic Field 

Dissipation Half-life 

2.2-17.2 days In unvegetated rice fields in 

Mississippi and Loiusiana 

43270801 

Small scale 

prospective ground 

water study 

Acifuorfen residues detected in 

suction lysimeters and in ground 

water 

Soybeans in Wisconsin 

Detected in ground water at up to 46 

ppb 

41172801 

Small scale 

retrospective ground 

water study 

Residues leached through soil 

profile and under certain 

conditions were detected in 

ground water 

Five states: North Carolina, North 

Dakota, Indiana, Tennessee, and 

Virginia 

41160001,

41409501, 

41458901, 

41644901, 

41833202, 

42152201 
12

were detected in 56 out of 283 samples in soils to depths of 0.6 m and were detected in ground water 

at up to 46 ppb. Residues were also found in soil-water lysimeters. The ground water detects were 

uniformly distributed in the field and pesticide residues appear to have been transported down 

gradient. Residues were detected until 10 months after application. Results of the prospective 

monitoring study indicate that pesticide residues reached ground water by typical mechanisms, and 

not by preferential flow. 

In addition to the results of the small-scale prospective groundwater monitoring study 

conducted for sodium acifluorfen in a vulnerable area of Wisconsin discussed above, 

information on acifluorfen movement in soil is available from a small-scale prospective groundwater monitoring study for lactofen conducted in Michigan. Low level concentrations of acifluorfen 

(lactofen degradate) were detected during the lactofen PGW in soil-water at several depths (3- and 6-

feet) (acifluorfen LOD in soil water = 0.035 ppb), but there were no detections in the ground water 

(acifluorfen LOD in ground water = 0.035 ppb). The concentrations of acifluorfen observed in the 

lactofen PGW study were much lower than in the Wisconsin sodium acifluorfen PGW study; 

however, several factors contribute to this difference. The sodium acifluorfen rate applied (0.75 Ib 

a.i./ac) in the Wisconsin PGW study is almost twice the seasonal application rate for lactofen (0.4 Ib

a.i./ac per season); the sodium acifluorfen was applied in a single application, while the lactofen 

application was split into 2 applications at 0.2 Ib a.i./ac with a minimum 12 day interval; sodium 

acifluorfen dissociates to acifluorfen very rapidly (less than 1 day), but it takes longer for lactofen to 

transform to acifluorfen (half-life 3 to 7 days); and the maximum amount of acifluorfen that can be 

derived from lactofen is approximately 60 percent. 

When acifluorfen reaches ground water the compound will persist due to its stability to abiotic 

hydrolysis. Sodium acifluorfen may reach surface water from runoff events, or from discharge of 

acifluorfen-contaminated ground water into surface water. Acifluorfen reaching surface waters may 

persist for some time, unless there is some photodegradation. Sodium acifluorfen would not be 

expected to bioaccumulate in fish because of the low Kow value. Acifluorfen is not expected to be 

transported in the vapor phase, but it could be a threat to nontarget plants if it moves off-site via 

spray drift. 

 

Monitoring Data 

Acifluorfen (which can be formed from lactofen or sodium acifluorfen) has been detected in 

surface water and ground water. Degradates of acifluorfen (amino acifluorfen and 

desnitroacifluorfen) have generally not been included in monitoring studies. 

In Small Scale Retrospective Ground Water Monitoring studies conducted in five states (NC, ND, 

IN, TN, VA), acifluorfen was persistent and mobile in permeable soils (i.e., sands, loamy sands, 

sandy loams) low in clay content. However, survey monitoring studies (where existing water 

sources are sampled) are generally "non-targeted studies", so specific pesticide use is not known. 

Acifluorfen has been detected in both surface and ground water samples collected by the USGS 

in the National Water Quality Assessment (NAWQA) program. Results from 13,524 samples 
13

collected in the United States over the years 1993 -2007 showed quantifiable residues (estimated and 

measured) in 173 samples (1.28 %); 10 were from ground water (out of 6092 samples; 0.16%); 163 

were from surface water (out of 7432 samples; 2.19%). Maximum measured residues found in 

ground water were 0.33 μg/L (from agricultural land in North Carolina in April 2002); the maximum 

estimated residues in surface water were 2.2 μg/L (from agricultural land in Indiana in June 1994); 

maximum measured residues in surface water were 1.1 μg/L (from agricultural land in North 

Carolina in June 1993). 

Acifluorfen residues in ground water were reported in the Pesticides in Ground Water Data 

Base, PGWDB (USEPA, 1992), a summary of other groundwater monitoring studies. The 

PGWDB (USEPA, 1992) reports four of 1185 wells sampled with concentrations ranging from 

0.003 to 0.025 μg/L. Because the studies summarized in the PGWDB were conducted with 

many objectives and study designs, the results may reflect conditions where no lactofen or 

acifluorfen had been used or where there is a low susceptibility to ground water contamination. 

Therefore, EFED has low confidence that the monitoring reflects the potential contamination of 

ground water from acifluorfen. 

The highest measured levels of acifluorfen in ground water were from the small-scale 

prospective groundwater study in Wisconsin. This targeted study was conducted in a 

vulnerable area with maximum use rates. This study provided information with the highest 

degree of confidence, because the hydrology and acifluorfen use were known (e.g., the 

detection came from a known use). What is not as well known is how this site compares to 

other use sites in the US. Although the EPA is confident that the prospective study was 

conducted at a vulnerable site, the other monitoring studies were not specifically conducted for 

acifluorfen (excluding the retrospective study). Some sampling or study sites were probably in 

vulnerable areas, but the relationship between acifluorfen use and the monitoring sites, 

sampling dates, and so on are not well known (or not known). Use rates were not known. 

There is no Maximum Contaminant Level (MCL) established for acifluorfen; Health Advisories (for 

a 10-kg child) are 2 mg/L (1-day and 10-day), with a Reference Dose (RfD) of 0.01 mg/kg/day, and 

a Drinking Water Equivalent Level (DWEL) of 0.4 mg/L. The cancer descriptor for acifluorfen is 

L/N (Likely to be carcinogenic above a specified dose but not likely to be carcinogenic below that 

dose because a key event in tumor formation does not occur below that dose). 

IV. Receptors 

Consistent with the process described in the Overview Document (U.S. Environmental Protection 

Agency, 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. January 23, 2004), the risk assessment for sodium acifluorfen 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. 
14

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 sodium 

acifluorfen on aquatic and terrestrial receptors. Toxicity studies for the technical grade active 

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

assessment. Open literature studies are identified using EPA’s ECOTOX database2, which employs 

a literature search engine for locating chemical toxicity data for aquatic life, terrestrial plants, and 

wildlife. Research papers accepted into the ECOTOX database are screened using standard 

procedures to ensure consistent, high quality information; these studies will be considered during the

‘Analysis’ phase of risk assessment process. The Incident Data System (IDS), which tracks incident 

reports submitted to EPA, is used to identify supportive, line of evidence information on exposure of 

aquatic and terrestrial receptors. Data from all of these sources can also provide insight into the 

direct and indirect effects of sodium acifluorfen 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. 

A. Effects on Aquatic Organisms 

A fair amount of acute aquatic toxicity data is available for consideration in this ecological risk 

assessment for sodium acifluorfen, but not very much chronic data. Table 5 provides a summary of 

the taxonomic groups and the surrogate species tested to characterize the potential acute and chronic 

aquatic effects of sodium acifluorfen. Sodium acifluorfen is classified as slightly toxic, on an acute 

basis, to freshwater and saltwater fish and freshwater invertebrates, and moderately toxic to 

estuarine/marine invertebrates. 

The LC50 was 17 ppm a.i. for the rainbow trout using technical grade sodium acifluorfen (MRID 

000122752). For estuarine/marine fish, the Sheepshead minnow LC50 was 39 ppm a.i., also using 

technical grade (MRID 00122753). Two datasets were submitted of freshwater fish early life stage 

(ELS) tests using the Fathead minnow (Pimephales promelas). Reduced larval weight was reported 

at 1.5 ppm (the lowest level tested) in MRID 00124222. The study was supplemental since no 

NOEAC was found. There are no data from estuarine and marine fish early life-stage or life-cycle 

studies. No freshwater or saltwater fish ELS studies were required in the RED because 1) none of 

the criteria were exceeded except reproductive impairment in birds and 2) the 21-day 

PRZM/EXAMS value was less than 21 ppb a.i., which is below 1/100 of the lowest LC50 of 17 and 

39 ppm a.i., respectively.

The most sensitive acute endpoint for freshwater invertebrates was the Daphnia magna LC50 of 28.1 

ppm a.i. using technical grade sodium acifluorfen (MRID 071901). No freshwater invertebrate lifecycle study was required in the 2003 RED for sodium acifluorfen because 1) none of the criteria 

were exceeded except reproductive impairment in birds and 2) the 21-day PRZM/EXAMS value was 

less than 21 ppb a.i., which is below 1/100 of the lowest LC50 of (28 ppm a.i.). Sodium acifluorfen 

was categorized as moderately toxic to estuarine/marine invertebrates. The most sensitive endpoint 

was from a mysid shrimp study (MRID, 122755), with an LC50 of 3.8 mg/L. Sodium acifluorfen 

 

2

 http://www.epa.gov/ecotox 
15

was slightly toxic to practically nontoxic to estuarine mollusks on an acute basis. The Eastern oyster 

LC50 was 74 ppm ai for the technical grade (MRID 111964). 

Since the only aquatic sublethal endpoint found for sodium acifluorfen (MRID 00124222) did not 

produce an NOAEC, it is not possible to calculate an acute-to-chronic ratio (ACR) to estimate the 

chronic toxicity of sodium acifluorfen to aquatic organisms. However, using data from a closely 

related compound, lactofen3 (acifluorfen is a major degradate of lactofen and sodium acifluorfen 

readily dissociates into sodium and acifluorfen in water), when the ACR from lactofen fish data 

(349) is applied to the mysid acute sodium acifluorfen data, the resulting estimated mysid chronic 

endpoint is 12 ppb. When this estimated chronic endpoint is used to calculate a risk quotient (using 

the 60-day PRZM/EXAMS value), EPA’s level of concern is exceeded (RQ = 1.8). Therefore, EPA 

cannot preclude risk to aquatic invertebrates from chronic exposure to sodium acifluorfen. 

There are no toxicity data available to assess the potential risk of major degradates to fish or aquatic 

invertebrates; this is a major source of uncertainty in the ecological risk assessment. The breakdown 

products of sodium acifluorfen include: acifluorfen, amino acifluorfen acid, acifluorfen acetamide 

and desnitro acifluorfen. As mentioned in the Environmental Fate and Transport section, for this 

assessment, acifluorfen acid and sodium acifluorfen (also a breakdown product of lactofen) will be 

assumed to be equivalent and called sodium acifluorfen. 

 

3EFED Problem Formulation for Lactofen Registration Review, December 13,2006; DP 

Barcode: 323196. 
16

Table 5. Aquatic toxicity profile for sodium acifluorfen 

Taxon Exposure Duration Guideline Most Sensitive Species Tested Toxicity Value Acute Toxicity Category1 Classification 

Acute 850.1075 Rainbow trout, Oncorhynchus mykiss LC50= 17 mg a.i./L Slightly toxic Acceptable 

Freshwater Fish 

Chronic 850.1400 Fathead minnow, Pimephales promelas

NOAEC = <3.4 

mg a.i./L (<1.5 

mg/L Blazer at 

44.1% a.i.) 

N/A Supplemental2 O

Acute 850.1075 

Sheepshead minnow, 

Cyprinodon 

variegatus 

LC50= 39 mg 

a.i./L Estuarine/ Marine Slightly toxic Acceptable 

Fish 

Chronic 850.1400 No Data NA 

Acute 850.1010 Water Flea, Daphnia magna LC50= 28.1 mg Freshwater a.i./L Slightly toxic Acceptable 

Invertebrates 

Chronic 850.1300 No Data NA 

Acute Mysid shrimp, Americamysis bahia LC50 = 3.8 mg a.i./L Moderately toxic Estuarine/ Marine Acceptable 

Invertebrates Chronic 850.1350 No Data 

Tier I 850.5400 Anabaena flos-aquae EC50 = >355 ppm Practically nontoxic Acceptable 

Non-vascular plant Tier II 850.5400 Green algae, Selenastrum 

capricornutum 

NOAEC = 

>265 ppm NA Acceptable 

Tier I 850.4400 Duckweed, Lemna gibba EC50 = 378 ppm Practically nontoxic Acceptable 

Vascular plant 

Tier II 850.4400 L. gibba NOAEC = 180 ppm NA Acceptable 

1Categories of acute toxicity for aquatic organisms based on LC50 (mg/L): < 0.1 very highly toxic; 0.1-1 highly toxic; >1-10 moderately toxic; >10-100 slig

nontoxic. 

2LDPH (light-dependent peroxidizing herbicide) fish early life-stage testing has been requested; Data Call-in was issued for this chemical on January 25, 2003EPA’s level of concern is exceeded when an Acute:Chronic ratio (ACR) from lactofen fish data is applied to the mysid acute data and the resulting mysid ch

risk quotient. Therefore, EPA requests chronic saltwater invertebrate data. This data will, in turn, be used to calculate an invertebrate ACR for sodium aciflofreshwater invertebrate data to calculate a more refined chronic freshwater invertebrate toxicity endpoint.
17

Toxicity to Aquatic Plants 

Since the aquatic concentration that is equivalent to the maximum label rate (355 μg/L) caused 

no reduction in growth after 120 hours, sodium acifluorfen is considered to be practically 

nontoxic to algae at the Tier I level.

Aquatic Tier II studies are required for all low dose herbicides (those with the maximum use 

rate of 0.5 lbs a.i./A or less) (maximum currently-registered application rate for sodium 

acifluorfen is 0.375 lbs a.i./A) and any pesticide showing a negative response equal to or 

greater than 50% in Tier I studies. In the Tier II studies, Duckweed, with an EC50 of 378 ppb, 

was the most sensitive aquatic vascular plant. Nonvascular aquatic plants were not sensitive to 

sodium acifluorfen at maximum label rates. The Tier II results show that Selenastrum 

capricornutum is the most sensitive nonvascular aquatic plant. 

B. Effects on Terrestrial Organisms 

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

acifluorfen to birds (also surrogate for terrestrial-phase amphibians and reptiles), mammals, and 

terrestrial invertebrates. Table 6 provides a summary of the most sensitive species tested for each 

terrestrial taxonomic group. 

Sodium acifluorfen is categorized as moderately toxic to birds and slightly toxic to mammals, based 

on quail and rat acute oral tests (LD50 = 325 and 1540 mg/Kg, respectively; MRIDs 122747 and 

071887). Acceptable acute avian oral toxicity data were not submitted for a passerine species, which 

is now required under the 40 CFR Part 158 (CFR 40 2008) data requirements for conventional 

pesticides. 

Sub-acute and chronic studies, available for birds show sodium acifluorfen to be practically nontoxic 

via the dietary route (quail and mallard LC50 >10,000 ppm; MRID 083059 and 083060); however, 

sodium acifluorfen reduced the number of viable embryos (quail NOAEC = 20 ppm; MRID 107491) 

at 100 ppm. Studies done on laboratory rats were substituted for wild mammal testing in the last 

RED. In a rat developmental study (MRID 0122743) the NOAEC was 20 mg/kg/day (400 ppm) 

based on decreased fetal body weight. 

Terrestrial invertebrate toxicity data are required to quantitatively assess the potential impacts on this 

group of organisms. Data are especially needed from the honey bee acute contact study due to 

wide spread use and possible drift to off site vegetation in bloom. A honey bee acute contact 

study (GLN 850.3020; MRID 46650202) has been submitted and is currently under review. 

Phytotoxic effects (i.e., plant kills) have been demonstrated in the field (see Incidents section below)

and we anticipate that there may be a risk to offsite, nontarget plants, although the magnitude is 

uncertain. Previous data (MRID 41680701) for vegetative toxicity of sodium acifluorfen to 

nontarget terrestrial plants were not scientifically sound because the sodium acifluorfen 

solution applied to the experimental plants was too dilute and the water may have washed the 
18

chemical away from the plant. This caused uncertainty about the exposure. A new vegetative 

vigor study (GLN 123-2/850.4250; MRID 46431401) was submitted but was classified invalid 

because the EC25 for cucumber dry weight was less than the lowest treatment level. Since 

cucumber is likely the most sensitive plant tested, this data is needed to make an assessment of 

risk to sensitive plants. 

C. Adverse Ecological Incidents 

A preliminary review of the Ecological Incident Information System (EIIS)4

 maintained by the 

Agency’s Office of Pesticide Programs (OPP) produced only one incident (I003654-012), a fish kill 

(unknown number) in 1993 caused by runoff with sodium acifluorfen as the probable cause. A 

search of the American Bird Conservancy database on the same date revealed no incident data. 

Lactofen, of which sodium acifluorfen is the chief breakdown product, had four incidents occurring 

between 1995 and 1998 (3 plant, 1 fish; incidents I007776-006, I002969-061, I003062-004 and 

I002969-054, respectively). In 1995, an adjacent field sprayed with lactofen resulted in stunted 

snapbean growth in one incident and in stunted greenbean and snapbean growth in another. In 1998, 

soybeans were reportedly damaged by lactofen. The fish kill (unknown species and number) was 

possibly from over-spraying a product containing lactofen. Overall, the incident data that are 

available indicate that exposure pathways for sodium acifluorfen are complete and that exposure 

levels are sufficient to result in field-observable effects. 

D. Ecosystems at Risk 

Sodium acifluorfen may be applied as an aerial or ground spray herbicide to terrestrial habitats for 

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

Sodium acifluorfen has the potential to contaminate surface water at application from spray drift and 

runoff. In general terms, aquatic ecosystems potentially at risk include water bodies adjacent to, or

down stream 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. 

 

4 EIIS was accessed on October 29, 2009 
19

Table 6. Terrestrial toxicity profile for sodium acifluorfen 

Taxon Exposure Duration Most Sensitive Species Tested Guideline Toxicity Value Acute Toxicity Category Classification 

Acute Rat Rattus norvegicus 850.2400 LD50 = 1540 mg/kg bw Slightly toxic Acceptable 

Mammals 

Chronic Rat 

R. norvegicus

850.2400 

NOAEC = 400 ppm 

(20 mg/Kg/d) 

LOAEC = 1800 ppm 

(90 mg/Kg/d) 

N/A Acceptable 

Acute 

Oral 

Northern 

bobwhite quail 

Colinus 

virginianus

Mallard 

Anas 

platyrhynchos

Passerine 

850.2100 

LD50= 325 mg/Kg bw 

LD50= 4187 mg/Kg bw 

Data Gap 

Moderately toxic 

 Practically nontoxic 

-- 

Acceptable Acceptable 

-- 

Sub-acute 

Dietary 

Quail and mallard 

C. virginianu and

A. platyrhynchoss

850.2200 >10,000 ppm Practically nontoxic Acceptable 

Birds 

Chronic 

Reproduc

tion 

Quail 

C. virginianus 850.2300 NOAEC = 20 ppm LOAEC = 100 ppm N/A Acceptable 

Terrestrial 

Invertebrates Acute Honey Bee Apis mellifera 850.3020 -- -- In Review 

Tier I2 -- 850.4100 850.4150 -- -- -- 

Seedling 

Emergence 

Vegetative Vigor 

850.4100 850.4250 

Dicot EC25 = 0.021 lb 

a.i./A 

-- 

-- -- 

Seedling Emergence 

Acceptable 

Vegetative Vigor 

Unacceptable3

Terrestrial 

Plants 

Tier II 

Vegetative Vigor 850.4250 -- -- Vegetative Vigor 

Unacceptable3 

1All pesticides with exposure routes with consumption by passerine birds must be tested on a passerine species using guideline 

requirement.

2 Not required for herbicides; go directly to Tier II3Cucumber, most sensitive dicot, data unacceptable; study may be upgraded with acceptable cucumber rerun
20

V. Assessment Endpoints 

The most sensitive toxicity endpoints are used from surrogate test species to estimate treatmentrelated direct effects on acute mortality and chronic reproductive, growth, and survival assessment 

endpoints. Surrogate aquatic animals include freshwater and estuarine/marine fish and invertebrates, 

and surrogate terrestrial animals include birds and mammals. These tests include short-term acute, 

subacute, and reproduction studies and are typically arranged in a hierarchical or tiered system that 

progresses from basic laboratory tests to applied field studies. 

The most sensitive toxicity endpoints from surrogate species are also used for plants. Nonvascular 

(i.e., algae) and vascular (e.g., duckweed) plant mortality; growth and reproduction impairment 

endpoints are used. For plants in terrestrial and semi-aquatic environments, the screening 

assessment endpoint is the perpetuation of populations of non-target species (crops and non-crop 

plant species). When data are available, endpoints assessed include emergence of seedlings and 

vegetative vigor. 

VI. Conceptual Model 

A. Risk Hypotheses 

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

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

probability models. For this assessment, the risk is stressor-initiated, where the stressor is the release 

of sodium acifluorfen to the environment. The following risk hypothesis is presumed for this 

screening-level assessment: 

When used in accordance with current labels for terrestrial use patterns, acifluorfen can 

move off-site via runoff (in the dissolved phase) and spray-drift and expose non-target 

organisms. Application to foliar surfaces and soil may also result in exposure to non-target 

organisms. Monitoring data indicate detections of sodium acifluorfen in surface waters and 

near field sites from use areas presumably due to current uses. These potential exposure 

pathways may result in adverse effects on the survival, growth, and/or reproduction of nontarget terrestrial and aquatic organisms, including Federally-listed threatened and 

endangered species. 

B. Diagram 

Direct Terrestrial Uses 

The environmental fate properties of sodium acifluorfen along with monitoring data identifying its 

presence in surface waters indicate that runoff via dissolved phase and spray drift represent potential 

transport mechanisms of sodium acifluorfen to aquatic and terrestrial organisms. As depicted in 
21

Figure 4, these transport mechanisms (e.g., sources) for spray (ground, aerial) applications may 

result in the movement of sodium acifluorfen into aquatic (water) and terrestrial (soil and foliage) 

habitats. The movement away from the site of application represents exposure pathways for a broad 

range of biological receptors of concern (non-target animals) and the potential attribute changes, i.e., 

effects such as reduced survivals, growth, and reproduction in the receptors. 

Figure 4. Conceptual model for effects of sodium acifluorfen on non-target aquatic and 

terrestrial organisms 

VII. Analysis Plan Options

In Registration Review, pesticide ecological risk assessments will follow the Agency’s Guidelines 

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

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

Agency” (“Overview Document”) (USEPA, 2004), and will be done in accordance with Section 7 of 

the Endangered Species Act. 

Stressor 

Sodium acifluorfen applied as ground/aerial spray in agricultural and residential 

settings. 

Source/ 

Transport 

Pathways 

Volatilization/ 

Wind Suspension

Direct 

Deposition

Spray 

Drift 

Runoff Leaching 

(infiltration/ 

percolation) 

Source/ 

Exposure 

Media 

Terrestrial Food 

Residues (foliage, 

fruit, insects) 

Upland 

Foliage/Soil

Riparian/ 

Wetland 

Foliage/Soil

Water 

Column/ 

Sediment 

Groundwater 

Exposure 

Point 

Ingestion Direct contact Direct contact Gill/ 

 Integument Uptake 

Receptors

Attribute 

Changes 

Terrestrial Vertebrates

Birds, Small Mammals, 

Reptiles, Terrestrial 

Insects 

Terrestrial

Upland 

Plants 

Individual Animals

 Reduced survival 

 Reduced growth 

 Reduced reproduction 

Aquatic Invertebrates 

Aquatic Vertebrates 

Amphibians 

Aquatic Plants 

Wetland/ 

Riparian 

Plants 

Individual Plants

 Seedling emergence 

 Vegetative vigor 

Individual 

Vertebrates and 

Invertebrates

 Reduced 

 survival 

 Reduced 

 growth 

 Reduced 

 reproduction 

Food Web Exposure 

(bioconcentration) 

Piscivorous 

Vertebrates

Birds, 

Mammals 

Individual 

Animals

 Reduced 

 survival, 

 growth, and 

 reproduction 

Plant 

Population

 Reduced 

 population 

 growth 
22

 A. Ecological Risk Assessment 

Previously completed risk assessments and exceedances of Agency levels of concern indicate that 

acute effects are not expected for terrestrial animals, freshwater and estuarine animals, or aquatic 

plants. Chronic risk is anticipated for herbivorous and insectivorous birds but not for mammals. 

Insectivorous birds would be at chronic risk at maximum exposure levels. No data are available to 

assess the risk of sodium acifluorfen to the Passerine group of birds. 

Chronic risk is uncertain for freshwater and estuarine animals. Sodium acifluorfen is classified as a

light-dependent peroxidizing herbicide (LDPH). LDPHs may be more toxic to animals exposed to 

natural light than would be predicated from guideline toxicity data generated from standard EFED 

toxicity guideline studies (72 series), which are not conducted under lighting conditions with the 

same wavelength or intensity as sunlight. Evidence for this comes from a preliminary phototoxicity 

study with another LDPH (carfentrazone-ethyl) which showed a nearly 20-fold increase in toxicity 

when natural wavelength light was used. 

Terrestrial plant risk assessment could not be conducted due to lack of adequate data. Since sodium 

acifluorfen is an herbicide, an assumption has been made that risk exists to nontarget plants. The 

magnitude of this risk is unknown. 

The potential impact to water quality from the use of sodium acifluorfen and its degradates also 

considers the herbicide lactofen. Lactofen and sodium acifluorfen have many of the same 

degradates or break-down products including acifluorfen and amino acifluorfen. The likelihood of 

water contamination by acifluorfen from uses of sodium acifluorfen or lactofen is high due to the 

low sorption of acifluorfen and its long persistence under many conditions. The likelihood of water 

contamination from lactofen is low. Lactofen has a high binding potential. Thus, it will sorb to soil 

or sediment. Lactofen breaks down rapidly to form acifluorfen and other degradates. 

The potential for acifluorfen to contaminate water is confirmed by monitoring studies that found 

acifluorfen residues in ground water and surface water. Generally, there was inadequate usage 

information at the time of the 2003 RED to determine whether the detections resulted from the use 

of sodium acifluorfen or lactofen, so modeling was used (GENEECx, PRZM/EXAMS, and SCIGROW). The estimated concentrations correspond reasonably well with the maximum 

concentrations seen in NAWQA monitoring data. Fate data for lactofen show that it has a high 

binding potential and that it rapidly is transformed to acifluorfen. It is not clear whether bound 

lactofen can be degraded and released as acifluorfen. The ultimate fate of the acifluorfen 

degradation products in soil and water cannot be determined. Uncertainties remaining from 

previous assessments and potential paths forward are described below. 

B. Endangered Species 

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

evaluate risks to Federally-listed threatened and/or endangered (listed) species from registered uses 
23 

of sodium acifluorfen. This assessment will be conducted in accordance with the Overview 

Document, provisions of the ESA, and the Services’ Endangered Species Consultation Handbook

(U.S. Fish and Wildlife Service and National Marine Fisheries Service, 1998. Endangered Species 

Consultation Handbook: Procedures for Conducting Consultation and Conference Activities Under 

Section 7 of the Endangered Species Act. Final Draft. March 1998). 

The assessment of effects associated with registrations of sodium acifluorfen 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 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 sodium acifluorfen application occurs), plus all areas where offsite 

transport (i.e., spray drift and runoff) 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. 

C. Drinking Water Assessment 

The drinking water assessment will be based on the PRZM-EXAMS model with the Index 

Reservoir and Crop Area Factors. In addition, an updated drinking water assessment will include 

any monitoring data that may be available. Both sodium acifluorfen and a related pesticide, 

lactofen, will degrade to the degradate acifluorfen in the environment. Therefore, EPA will conduct 

an aggregate drinking water assessment that will include the degradate acifluorfen from both 

lactofen and sodium acifluorfen sources. 

Ground water EDWCs for acifluorfen will be derived from a Tier I screening-level model 

(SCI-GROW), which estimates the maximum ground water concentrations from the application 

of a pesticide to crops. The ground water EEC for acifluorfen derived from lactofen will be derived 

from a prospective groundwater monitoring study for lactofen, which monitored for both 

compounds. 

D. Clean Water Act 

Sodium acifluorfen is not identified as a cause of impairment for any water bodies listed as 

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

http://iaspub.epa.gov/tmdl_waters10/attains_nation_cy.cause_detail_303d?p_cause_group_id=885. 

In addition, no Total Maximum Daily Loads (TMDL) have been developed for sodium acifluorfen, 

based on information provided at 

http://iaspub.epa.gov/tmdl_waters10/attains_nation.tmdl_pollutant_detail?p_pollutant_group_id=885&p_pol

lutant_group_name=PESTICIDES. More information on impaired water bodies and TMDLs can be 

found at http://www.epa.gov/owow/tmdl/.
24 

The Agency invites submission of water quality data for this pesticide. To the extent possible, data 

should conform to the quality standards in Appendix A of the OPP Standard Operating Procedure: 

Inclusion of Impaired Water Body and Other Water Quality Data in OPP’s Registration Review 

Risk Assessment and Management Process (see: 

http://www.epa.gov/oppfead1/cb/ppdc/2006/november06/session1-sop.pdf), in order to ensure they can be 

used quantitatively or qualitatively in pesticide risk assessments. 

 

E. Endocrine Disruptor Screening Program 

As required under FFDCA section 408(p), EPA has developed the Endocrine Disruptor Screening 

Program (EDSP) to determine whether certain substances (including pesticide active and other 

ingredients) may have an effect in humans or wildlife similar to an effect produced by a “naturally 

occurring estrogen, or other such endocrine effects as the Administrator may designate.” The EDSP 

employs a two-tiered approach to making the statutorily required determinations. Tier 1 consists of 

a battery of 11 screening assays to identify the potential of a chemical substance to interact with the 

estrogen, androgen, or thyroid (E, A, or T) hormonal systems. Chemicals that go through Tier 1 

screening and are found to have the potential to interact with E, A, or T hormonal systems will 

proceed to the next stage of the EDSP where EPA will determine which, if any, of the Tier 2 tests 

are necessary based on the available data. Tier 2 testing is designed to identify any adverse 

endocrine related effects caused by the substance, and establish a dose-response relationship 

between the dose and the E, A, or T effect. 

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

67 chemicals, which contains 58 pesticide active ingredients and 9 inert ingredients. This list of 

chemicals was selected based on the potential for human exposure through pathways such as food 

and water, residential activity, and certain post-application agricultural scenarios. This list should 

not be construed as a list of known or likely endocrine disruptors. 

Sodium acifluorfen is not among the group of 58 pesticide active ingredients on the initial list to be

screened under the EDSP. Under FFDCA sec. 408(p) the Agency must screen all pesticide 

chemicals. Accordingly, EPA anticipates issuing future EDSP test orders/data call-ins for all 

pesticide active ingredients. 

For further information on the status of the EDSP, the policies and procedures, the list of 67 

chemicals, the test guidelines and the Tier 1 screening battery, please visit our website: 

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

F. Anticipated Data Needs 

The following tables summarize the studies needed to reduce the amount of uncertainty in the 

ecological risk assessment. The passerine acute toxicity requirement is a recent decision within 

EPA that originated from a realization that passerine species may be more sensitive than bird 

species traditionally tested. EPA also requests chronic saltwater invertebrate toxicity data, which 

are provided by the saltwater aquatic invertebrate life cycle study. This data will, in turn, be used to 

calculate an invertebrate ACR for sodium acifluorfen, which will be applied to the freshwater 

invertebrate data to calculate a more refined chronic freshwater invertebrate toxicity endpoint. 
25 

Guideline Number: 850.2100 

Test Substance: Sodium acifluorfen 

Study Title: Avian Acute Oral Toxicity

Test Species: Passerine Species

Rationale for Requiring the Data 

Acute risk to passerines as a result of exposure to sodium acifluorfen has not been considered in previous 

assessments since there are no acute oral toxicity data available. Current Part 158 data requirements (CFR 

40 2007) specify that acute avian oral toxicity data be submitted for either mallard duck or bobwhite quail 

AND a passerine species. (A protocol for the acute oral toxicity test with a passerine species should be 

submitted to the Agency prior to test initiation.) Without this study, the Agency would have to presume risk 

to listed and non-listed passerines, but would not be able to quantify the risk. 

Practical Utility of the Data 

How will the data be used? 

Acute oral avian toxicity data will be used to quantitatively estimate the risk of sodium acifluorfen to birds 

(and terrestrial-phase amphibians and reptiles) and to define an action area for endangered species and 

explore risk mitigation strategies. These toxicity data will reduce uncertainties associated with the risk 

assessment for passerines. In the absence of data on sodium acifluorfen, quantitative risk estimation will 

not be possible. Therefore, determination of the distance from a treated field to which risk may extend and 

application rate reductions resulting in no LOC exceedances cannot be quantified without these data. 

How could the data change the Agency’s decision or impact the Agency’s future decision-making? 

The value of these acute oral toxicity studies would be in quantifying and potentially refining risks to 

passerine birds. Defining an action area for endangered species and exploring risk mitigation strategies 

cannot be evaluated without these data. If future endangered species risk assessments are performed 

without these data, the Agency will assume that sodium acifluorfen “may affect” passerines directly, and 

use of sodium acifluorfen may need to be restricted in areas where listed species could be exposed. The 

lack of these data will limit the flexibility the Agency and registrants have in coming into compliance with 

the Endangered Species Act and could result in use restrictions for sodium acifluorfen that are 

unnecessarily severe. 
26 

Guideline Number: 850.1350

Test Substance: Sodium acifluorfen 

Study Title: Aquatic Invertebrate Life-Cycle (saltwater)

Test Species: Mysid shrimp, Americamysis bahia

Rationale for Requiring the Data 

The acute toxicity of sodium acifluorfen to estuarine/marine invertebrates indicates the potential 

for chronic risk to this taxon. The chronic toxicity tests for both freshwater and estuarine/marine 

invertebrates were described as "conditionally required" in 40 CFR part 158 when the RED was 

signed, but sodium acifluorfen meets both the acute toxicity and exposure conditions for 

requirement of this study. 

Since the only aquatic sublethal endpoint found for sodium acifluorfen did not produce a noobserved effects concentration (Table 5), no sodium acifluorfen acute to chronic ratio (ACR) was 

available to estimate chronic toxicity to aquatic organisms. Using data from a closely related 

compound, lactofen5 (sodium acifluorfen is a major degradate of lactofen), EPA’s level of 

concern (LOC = 1 for chronic risk to aquatic animals) is exceeded when the ACR from lactofen 

fish data (349) is applied to the mysid acute sodium acifluorfen data and the resulting mysid 

chronic endpoint (12 ppb) is used to calculate a risk quotient (1.8). Therefore, EPA cannot 

preclude risk to aquatic invertebrates from chronic exposure. 

Without this study, the Agency would have to presume chronic risk to listed and non-listed 

estuarine/marine invertebrates, but would not be able to quantify the risk. 

Practical Utility of the Data 

How will the data be used? 

The aquatic invertebrate life-cycle toxicity study using a saltwater species would allow the 

Agency to refine the screening level risk assessment for Registration Review. The study would 

allow the Agency to analyze chronic effects, including effects on reproductive success and 

growth, to saltwater invertebrates. The effects data would be used to determine the likelihood 

that the chronic risks can potentially impact aquatic communities, either by direct effects on 

invertebrates or by indirect effects on fish and other organisms that feed on saltwater 

invertebrates. 

This data will, in turn, be used to calculate an invertebrate ACR for sodium acifluorfen, which 

will be applied to the freshwater invertebrate data to calculate a more refined chronic freshwater 

invertebrate toxicity endpoint. 

How could the data impact the Agency’s future decision-making? 

If future endangered species risk assessments are performed without these data, the Agency 

would have to assume that sodium acifluorfen "may affect" saltwater invertebrates directly and 

other taxa that feed on saltwater invertebrates, indirectly. The use of sodium acifluorfen might 

need to be restricted in areas where these species could be exposed. The lack of these data would 

limit the flexibility the Agency and registrants have and could result in unnecessarily severe use 

restrictions for sodium acifluorfen.

In addition, environmental chemistry methods and independent laboratory validation of those 

methods are required to support registration of products containing sodium aciflourfen. The 

following table summarizes the needed studies. 

 

5EFED Problem Formulation for Lactofen Registration Review, December 13,2006; DP 

Barcode: 323196. 
27 

Guideline Number: 835.6100 

Study Title: Environmental Chemistry Methods (ECM) and Independent Laboratory Validation 

(ILV) for Soil

Rationale for Requiring the Data 

According to the data requirements in 40 CFR Part 158, ECMs are currently required along with 

successful confirmatory method trials (validation) by an independent laboratory (i.e. ILVs). Acceptable 

ECMs for the residues of concern (parent and its transformation products) should have levels of 

quantitation that are adequate to address risk concerns or that are at levels below the toxicological 

endpoints for the relevant aquatic organisms. The ECMs should include parent and those residues found

in the laboratory studies that exceeded 10% of the applied. 

Practical Utility of the Data 

How will the data be used? 

The data will be used to verify the suitability of the methods. Subsequently the methods could be used 

by states or other enforcement agencies, departments or entities, to monitor concentrations of the 

residues of concern. Validated analytical methods in environmental media (a.k.a., ECMs) are useful for 

conducting and evaluating submitted environmental fate and toxicity field and monitoring studies and 

for addressing potential risks to the environment posed by the use and/or accidental release of pesticides. 

How could the data impact the Agency’s future decision-making? 

If monitoring of the chemical is required or performed, the Agency could be able to determine if the 

chemical is present in the environment at concentrations that are threatening to wildlife (or to humans, in 

the case of drinking waters), according to the levels of concern (LOCs). If that is the case, measures to 

prevent these concentrations to occur could be taken. The data could also be used by enforcement 

entities like the states or government agencies or departments. Without these data, the potential for the 

determination of residues of sodium acifluorfen in soil, water and sediment is restricted. 

Guideline Number: 835.6200 

Study Title: Environmental Chemistry Methods (ECM) and Independent Laboratory Validation 

(ILV) for Water and Sediment

Rationale for Requiring the Data 

According to the data requirements in 40 CFR Part 158, ECMs are currently required along with 

successful confirmatory method trials (validation) by an independent laboratory (i.e. ILVs). Acceptable 

ECMs for the residues of concern (parent and its transformation products) should have levels of 

quantitation that are adequate to address risk concerns or that are at levels below the toxicological 

endpoints for the relevant aquatic organisms. The ECMs should include parent and those residues found

in the laboratory studies that exceeded 10% of the applied. 

Practical Utility of the Data 

How will the data be used? 

The data will be used to verify the suitability of the methods. Subsequently the methods could be used 

by states or other enforcement agencies, departments or entities, to monitor concentrations of the 

residues of concern. Validated analytical methods in environmental media (a.k.a., ECMs) are useful for 

conducting and evaluating submitted environmental fate and toxicity field and monitoring studies and 

for addressing potential risks to the environment posed by the use and/or accidental release of pesticides. 

How could the data impact the Agency’s future decision-making? 

If monitoring of the chemical is required or performed, the Agency could be able to determine if the 

chemical is present in the environment at concentrations that are threatening to wildlife (or to humans, in 

the case of drinking waters), according to the levels of concern (LOCs). If that is the case, measures to 

prevent these concentrations to occur could be taken. The data could also be used by enforcement 

entities like the states or government agencies or departments. Without these data, the potential for the 

determination of residues of sodium acifluorfen in soil, water and sediment is restricted. 
28 

Data required for existing DCIs 

Non-target Area Phytotoxicity (Tier II) Seedling Emergence and Vegetative Vigor studies were 

submitted in 1990 (MRID 41680701). The study was reviewed and the seedling emergence portion 

of the study was acceptable. However, the vegetative vigor portion of the study was found to be 

unacceptable. A new Vegetative Vigor study (MRID 46431401) was submitted, and was found 

partially acceptable, but the data were unacceptable for the most sensitive dicot (cucumber, 

NOAEL not determined. Acceptable data establishing the NOAEL for cucumber are still 

required. 

In January 2006, a DCI was issued to a group of registrants who hold technical registrations for the 

LDPHs requiring submission of Guideline number 850.1400, fish early life-stage toxicity test, to 

measure how sunlight (particularly ultraviolet) affects the toxicity of the LDPHs on aquatic 

organisms. United Phosphorus, the technical registrant for sodium acifluorfen, has joined a work 

group which submitted a modified protocol for Guideline 850.1400, as required by EPA, to detect 

potential enhanced toxicity in fish in the presence of the LDPHs and ultraviolet lighting. The 

protocol has been reviewed by EPA, and the Agency has instructed the work group to proceed with 

pilot testing. An initial pilot test was initiated in November 2009, with an additional pilot study 

currently being conducted (March 2010) after modifications to the test design. Submission of the 

definitive toxicity data is expected in late 2010. 

Other Information Needs

There is specific information that will assist the Agency in refining the ecological risk assessment, 

including any species-specific effects determinations. The Agency is very much interested in 

obtaining the following information: 

1. confirmation on the following label information 

a. sites of application 

b. formulations 

c. application methods and equipment 

d. maximum application rates 

e. frequency of application, application intervals, and maximum number of applications 

per season 

f. geographic limitations on use 

2. use or potential use distribution (e.g., acreage and geographical distribution of relevant 

crops) 

3. use history 

4. median and 90th percentile reported use rates (lbs ai/acre) from usage data – national, state, 

and county 

5. application timing (date of first application and application intervals) by crop – national, 

state, and county 

6. sub-county crop location data 

7. usage/use information for non-agricultural uses (e.g., forestry, residential, rights-of-way) 

8. directly acquired county-level usage data (not derived from state level data) 

a. maximum reported use rate (lbs ai/acre) from usage data – county 

b. percent crop treated – county 

c. median and 90th percentile number of applications – county 
29 

d. total pounds per year – county 

e. the year the pesticide was last used in the county/sub-county area 

f. the years in which the pesticide was applied in the county/sub-county area 

9. typical interval (days) 

10. state or local use restrictions 

11. ecological incidents (non-target plant damage and avian, fish, reptilian, amphibian and 

mammalian mortalities) not already reported to the Agency 

12. monitoring data 

The analysis plan will be revisited and may be revised depending upon the data available in the 

open literature and the information submitted by the public in response to the opening of the 

Registration Review docket.