UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

Registration Review

Ecological Risk Assessment

Problem Formulation for: 

FOMESAFEN

Prepared By:

Paige Doelling Brown, Ph.D., Fisheries Biologist

James Hetrick, Ph.D., Senior Chemist

Environmental Risk Branch 1

Environmental Fate and Effects Division

Office of Pesticide Programs

Approved By:

Nancy Andrews, Ph.D., Branch Chief

Environmental Risk Branch 1

Environmental Fate and Effects Division

Office of Pesticide Programs



Stressor Source and Distribution

The source of the stressor considered in this document is sodium salt of
fomesafen.  

Fomesafen is an herbicide.  It is applied as a foliar spray (both
pre-emergent and post-emergent) for control of broad-leaved weeds,
grasses, and sedges. Fomesafen is a diphenylether.  It disrupts the cell
membrane of the plant (  HYPERLINK
"http://www.syngentacroprotection-us.com" 
www.syngentacroprotection-us.com ) by penetrating into the cytoplasm and
causing formation of peroxides and free electrons (  HYPERLINK
"http://www.abcbids.org"  www.abcbids.org ). The specific mode of action
is inhibition of protoporphyrinogen oxidase (  HYPERLINK
http://www.weeds.iastate.edu)  www.weeds.iastate.edu) .  Fomesafen
generally acts quickly, and does not translocate.  It has both foliar
and soil activity.  Other herbicides in this group include aciflourfen,
lactofen, and oxyfluorfen.  

Fomesafen is highly persistent in soil (63-527 days, dependent on soil
type) resulting in a potential for accumulation in terrestrial
environments.  The label suggests not planting sensitive crops in a
fomesafen-treated field for a 3-18 month period, due to the persistence
of fomesafen in the soil. Additionally, it is highly mobile, and is
expected to leach into groundwater and be transported from the site via
runoff into surface waters.  Based on physical properties,
bioaccumulation and long-range transport are not expected to be of
concern.  It is extremely toxic to terrestrial plants, especially
dicots, but of fairly low acute toxicity to fish and wildlife.  Some
chronic reproductive effects have been noted in mammals, and may also
occur in birds. No major degradates of toxicological concern have been
identified.

	

Integration of Available Information

The risk assessments available in the docket, and which serves as the
basis for this problem formulation, include the following:

Ecological Risk Assessment in Support of Docket Preparation for
Registration Review of Fomesafen (DP 306023), January 18, 2006

Ecological Effects

Available Toxicity Studies

Toxicity endpoints are established based on data generated from
guideline studies submitted by the registrant, and from open literature
studies that meet the criteria for inclusion into the ECOTOX database
maintained by EPA/ORD.  EFED policy is to use the most sensitive
endpoint for each taxa evaluated.  In aquatic systems, taxa evaluated
include aquatic plants, invertebrates, and fish.  Fish serve as a
surrogate for aquatic-phase amphibians.  Where data are available,
separate endpoints are used for freshwater and estuarine/marine
organisms.  In terrestrial systems, taxa evaluated include birds and
mammals.  Bird endpoints are generally derived from guideline studies on
bobwhite quail and/or mallard duck.  Bird data is used as a surrogate
for reptiles and terrestrial-phase amphibians.  Mammal data is derived
from guideline studies conducted on laboratory rats, mice, or rabbits.

	Aquatic Guideline Data

Fomesafen was originally registered for use in the 1980s.  Guideline
studies from that time were available for aquatic invertebrates and
fish, both freshwater and marine/estuarine.  Although some of the
studies were conducted on formulated product, and would not be
acceptable under current standards, they were classified as core or
supplemental under the guidelines at the time they were submitted.  When
necessary, endpoints were re-calculated and/or data were converted to
express toxicity on the basis of active ingredient.  Details of
conversion are included in Appendix E.  Aquatic plant data were
submitted by the registrant (upon request by EFED), during the
development of this risk assessment.  Although the Data Evaluation
Review (DER) process has not yet been completed for these studies, they
have been provisionally classifed as Supplemental, and the toxicity data
has been incorporated into the assessment.  Overall, fomesafen is
slightly toxic to practically nontoxic to invertebrates and practically
non-toxic to fish on an acute basis (Table 1).  Chronic data were also
available, and are presented in Table 2.

Table 1  Acute Aquatic Data from Registrant-submitted Studies

Species	LC50 (ppm)	95% C.I. (ppm)	NOAEC (ppm)	Classification

(MRID)

Freshwater Organisms

Green alga1 (Selenastrum capricornutum)	0.12

(biomass)	0.05-0.34	0.02	Supplemental

(46673804)

Technical

Water flea

(Daphnia magna)	376

(practically nontoxic)	323-437	117	Core2, 3

(163169)

Formulation

Rainbow Trout

(Onchorynchus mykiss)	126

(practically nontoxic)	117-135	80	Core2, 3

(103023)

Formulation

Estuarine/ Marine organisms

Marine diatom1 (Skeletonema costatum)	1.51

(biomass)	ND	0.94	Supplemental

(46673806)

Technical

Mysid shrimp

(Mysidopsis bahia)	25

(slightly toxic)	19-38	ND	Core2

(135647)

Technical

Sheepshead minnow

(Cyprinodon varigetus)	>163

(practically nontoxic)	ND	>163	Core2, 3 

(135651)

Formulation

1Provisional data and classification, pending final review.  2Data are
from studies originally reviewed and classified in 1984, some of which
used formulated product.  3For purposes of this risk assessment, test
concentrations were adjusted for percent a.i. if necessary, and
endpoints were re-calculated using TOXANAL software.  ND-not determined.

Table 2 Chronic Aquatic Data from Registrant-submitted Studies

Species	NOAEC (ppm)	LOAEC

 (ppm)	Endpoints Affected	Classification1

(MRID)

Freshwater Organisms

Water flea

(Daphnia magna)	50	100	Reduced growth,

Total # of offspring	Core

(135642)

Formulation

Estuarine/ Marine organisms

Mysid shrimp

(Mysidopsis bahia)	0.7	1.7	Parental mortality	Core

(135648)

Formulation

Sheepshead minnow2

(Cyprinodon varigetus)	12.2	20.1	Reduced larval survival	Core

(135644)

Formulation

1Data are from studies originally reviewed and classified in 1984, some
of which used formulated product.  2For purposes of this risk
assessment, test concentrations were adjusted for percent a.i.  

	Aquatic Data from ECOTOX

The ECOTOX database was accessed, and no toxicity data for fomesafen
were located. 

	Terrestrial Plant Guideline Data

Terrestrial plant guideline studies were submitted during the
development of this risk assessment.  Data are shown below (Table 3),
but are considered provisional pending final data evaluation review. 
Fomesafen is effective, both pre- and post-emergent, against a variety
of plants, although dicots appear to be more sensitive than monocots for
both endpoints.  The product is marketed as a control for broad-leafed
weeds.  In some cases, calculated EC25s were below the concentrations
tested, so a NOAEC was not determined.  The most sensitive endpoint,
used in the risk assessment, is the vegetative vigor EC25 for radish
(0.0016 lb ai/A).

Table 3  Terrestrial Plant Guideline Data

Species	Common name	Class

	EC25 

(lb ai/A)	NOAEC 

(lb ai/A))	Classification1

(MRID)

Vegetative Vigor

Raphanus sativus	Radish	D	0.0016	0.00098	Supplementary

(46673802)

Echinochloa crus-galli	Barnyard grass	M	0.31	0.25

	Seedling emergence

Lycopersicon esculentum	Tomato	D	0.005	ND	Supplementary

(46673801)

Allium cepa	Onion	M	0.089	ND

	1 Provisional classification, pending final data evaluation review.

Efficacy data (MRID 135656) were part of the data package submitted. 
The efficacy data included pre-emergence and post-emergence treatment of
24 plant species, at two concentrations (0.25 and 1.0 kg ai/ha).  The
two concentrations bracket the currently proposed rates (0.42 and 0.54
kg ai/ha).  The plant species tested included both monocots (11 species)
and dicots (13 species).  Both crop (7 species) and non-crop (17
species) plants were evaluated.  With the exception of soybeans, all
plants tested experienced >20% “damage” when treated pre-emergence,
with a significant number (65%) experiencing >80% damage when treated
with the lower concentration (0.25 kg ai/ha).  Applied post-emergence,
fomesafen is slightly less effective, with “damage” typically in the
0-40% range for monocots and 40-80% range for dicots.  The report did
not specify how damage was quantified.

Avian and Small Mammal Guideline Data

Guideline studies were available for birds (both dose and dietary), and
small laboratory mammals (dose).  On the basis of both dose and dietary
values, fomesafen is practically non-toxic to birds and slightly toxic
to mammals (Table 4).  Endpoints for female guinea pigs and mallard
ducks were used to develop risk quotients.

Table 4  Avian and Small Mammal Guideline Data from Acute Studies

Species	LC50 (ppm)	95% C.I. (ppm)	NOAEC (ppm)	Classification1

(MRID)

Acute dose

Mallard duck	>5,000

(practically non-toxic)	ND	ND	Core

(163168)

Rat	F 1499

M 1858

(slightly toxic)	(1302-1749)

(1420-2546)	1219

975	Minimum

(164901)

Mouse	F  745

M  766

(slightly toxic)	(512-1286)

(525-1341)	487

312	Minimum

(164901)

Guinea Pig	F  607

(slightly toxic)	ND	244	Minimum

(164901)

Acute dietary

Bobwhite quail	>20,000

(practically non-toxic)	ND	13,333	Core

(103022)

Mallard duck	>20,000

(practically non-toxic)	ND	20,000	Core

(163384)

1Data are from studies originally reviewed and classified in 1984. 

ND-Not determined 

Chronic guideline studies (Table 5) were available for birds (mallard
duck and bobwhite quail) and small laboratory mammals (rat).  Bird
guideline studies did not establish a LOAEC, only determining that there
were no effects at the highest (mean-measured) concentration tested. 
This contributes significant uncertainty to the evaluation of chronic
risk to birds.  The mallard duck NOAEC (46 ppm) is used in the
determination of chronic risk to birds, but it may overestimate the risk
to birds.  In some cases, calculated exposure is near or above the
maximum tested concentration.

Table 5  Avian and Small Mammal Guideline Data from Chronic Studies

Species	NOAEC (ppm)	LOAEC

(ppm)	Endpoint Affected	Classification1

(MRID)

Bobwhite quail	51	ND	None	Core

(135640)

Mallard duck	46	ND	None	Core

(135639)

Rat	250	1000	Number of pups born live, number of pups surviving
Acceptable

(144862)

1Data are from studies originally reviewed and classified in 1984.

ND-Not determined  

	Terrestrial Insect Data

Guideline tests for honeybees were submitted (MRID 135651, Core), as was
a field chronic effects study on earthworms (MRID 135652).  The acute
oral LD50 for honeybees was >50 g ai/bee, and the acute contact LD50
was >100 g ai/bee.  The field test for earthworms included two
applications of fomesafen, applied at one-year intervals.  Fields were
treated with 0.5 kg ai/ha and 5.0 kg ai/ha.  No adverse effects on total
numbers, total weights, or numbers of individual species were noted at
the 0.5 kg ai/ha treatment level.  A significant change in numbers of
one species of earthworm (Allolobophura nocturna) was noted at the
higher treatment level, but authors attributed this to modifications in
grass cover caused by the herbicide treatment rather than direct toxic
effects.

Studies were also submitted  (MRID 135656) for eight species of
invertebrates, from the orders Acarina, Hemiptera, Diptera, Lepidoptera,
Coleoptera, and Nemotoda.  Fomsafen was applied to multiple life stages
at concentrations of 250 and 500 ppm.  The greatest level of mortality
in these tests was 9%.  Aphids (Aphis fabae) experienced mortality rates
of 9% at concentrations of 250 ppm and 500 ppm.

	Terrestrial Data from ECOTOX

The ECOTOX database was accessed, and no toxicity data for fomesafen
were located.

Incident Reports

EFED maintains EIIS, a database containing reported incidents of damage
to non-target species caused by pesticide use.  There are a total of 28
reported incidents for fomesafen, 27 of which are damage to agricultural
crops.  Incidents reported cover a range of 9 years (1994-2002), but
many of them (54%) were reported in 2002.  Corn was the crop most
frequently reported damaged, accounting for 21 out of the 24 cases for
which the specific crop was reported.  In some cases (5) the fomesafen
was applied directly to the damaged crop, and the legality was
classified as misuse or accidental misuse.  In other cases (17) the
damaged was caused by drift, legality of application unknown.  The
certainty that the incident was related to fomesafen use was generally
classified as probable.  Other crops damaged included green peas,
cotton, and soybeans under registered use conditions. 

 

There is one report of a fish kill.  In this incident, there was a
report of approximately 200 fish (channel catfish, crappie, largemouth
bass, and redear sunfish) dying following a legal application to a
soybean site.  The certainty of the kill being related to fomesafen
runoff is classified as possible.  Application was in accordance with
registered use. 

Exposure Characteristics

Major routes of fomesafen dissipation are leaching, runoff, and
microbial degradation.  Because fomesafen is persistent and mobile in
soil, it is expected to move from the application site into groundwater
and surface water.  Additionally, off-site movement of fomesafen is
expected through spray drift from aerial and ground spray.  The high
persistence of fomesafen is expected to contribute to year-to-year
accumulation in terrestrial and aquatic environments. 

Fomesafen is stable to abiotic hydrolysis.  It undergos slow
photodegradation in water

(t1/2= 49 to 289 days).  Fomesafen is persistent (t1/2=9 to 99 weeks) in
aerobic soil and aquatic environments.  However, it degrades rapidly
(t1/2< 20 days) in anaerobic environments.  The major degradation
product of fomesafen is
5-(2-chloro-(,(,(-trifluoro-p-tolyloxy)-N-methylsulphonyl-panthranilamid
e (fomesafen amine).  A minor degradation product is
5-(2-chloro-(,(,(-trifluoro-p-tolyloxy) anthranilic acid (fomesafen
amino acid).   Neither degradate has been identified as a toxicological
concern. 

Fomesafen is expected to be very mobile in soil.  Simple partitioning
coefficients range from 0.51 in loamy coarse sand to 2.45 in sandy clay
loam soil.  Regression analysis indicates fomesafen sorption is not
dependent on soil organic matter content.  Aged soil column leaching
studies indicate degradation products of fomesafen are not mobile in
soils; less than 0.06% of applied radioactivity was detected in the
leachate samples.

Field dissipation studies in NC, IL, MS, AR, AL, TX, LA, SD, MN, KY, IA
and MO indicate fomesafen is moderately persistent to persistent (t1/2=
50 to 150 days ) in surface soils under actual use conditions. 
Fomesafen was detected at depths up to 30 inches in the soil profile. 
Fomesafen amine was the only degradation product identified in field
dissipation studies.  Prospective ground water monitoring in NC
indicates fomesafen moved through the soil profile into medium and deep
ground water.  

Fomesafen has a low potential for bioaccumulation in fish tissues. 
Bioaccumulation factors for fosmesafen were 0.7 for whole fish, 0.2 for
edible tissues, and 5.2 for nonedible tissue.  Bioaccumulated residues
were depurated during a 14-day depuration period.  

	

Characteristics of Ecosystems Potentially at Risk

For typical crop applications, the ecosystem at risk is the field
itself, in terms of organisms that might be sprayed during application,
organisms affected by accumulation of fomesafen in the soil; and the
adjacent aquatic and terrestrial environments affected due to runoff,
spray drift, or groundwater contamination.  In water bodies receiving
runoff from agricultural fields, pelagic and benthic elements are
considered.  Terrestrial organisms assessed include non-target plants,
insects, amphibians, reptiles, birds, and mammals.  Because fomesafen is
an herbicide, potential affects on non-target plants have been addressed
at length.

Fomesafen is being proposed as a pre-plant, pre-emergence, and
post-emergence herbicide for use on broadleaf weeds, grasses, and
sedges, in snap beans, dry beans, and cotton.   Methods of application
are ground spray (0.5 lb ai/A, cotton) and aerial spray (0.375 lb ai/A,
dry beans, snap beans, and cotton).  Application is limited to once a
year, or in alternate years, depending on location.  Application rates
are regionally specific.  Maps 1, 2, and 3 show the locations of these
crops according to USDA crop data.



Assessment Endpoints

Assessment endpoints are defined as “explicit expressions of the
actual environmental value that is to be protected.”  Defining an
assessment endpoint involves two steps: 1) identifying the valued
attributes of the environment that are considered to be at risk; and 2)
operationally defining the assessment endpoint in terms of an ecological
entity (i.e., a community of fish and aquatic invertebrates) and its
attributes (i.e., survival and reproduction).  Therefore, selection of
the assessment endpoints is based on valued entities (i.e., ecological
receptors), the ecosystems potentially at risk, the migration pathways
of pesticides, and the routes by which ecological receptors are exposed
to pesticide-related contamination.  The selection of clearly defined
assessment endpoints is important because they provide direction and
boundaries in the risk assessment for addressing risk management issues
of concern.  Changes to assessment endpoints are typically estimated
from the available toxicity studies, which are used as the measures of
effects to characterize potential ecological risks associated with
exposure to a pesticide, such as paclobutrazol.

To estimate exposure concentrations, the ecological risk assessment
considers a single application at the maximum application rate to fields
that have vulnerable soils.  The most sensitive toxicity endpoints are
used from surrogate test species to estimate treatment-related direct
effects on acute mortality and chronic reproductive, growth and survival
assessment endpoints.  Toxicity tests are intended to determine effects
of pesticide exposure on birds, mammals, fish, terrestrial and aquatic
invertebrates, and plants.  These tests include short-term acute,
sub-acute, and reproduction studies and are typically arranged in a
hierarchical or tiered system that progresses from basic laboratory
tests to applied field studies.  The toxicity studies are used to
evaluate the potential of a pesticide to cause adverse effects, to
determine whether further testing is required, and to determine the need
for precautionary label statements to minimize the potential adverse
effects to non-target animals and plants.

Evaluation of ecological effects focuses initially on direct effects to
the groups of organisms residing in the ecosystems at risk, based on
ratios of the estimated environmental concentration (EEC) to a
designated toxicity endpoint for a surrogate test organism.  If
pre-established levels of concern (LOCs) are exceeded for direct
effects, indirect effects to endangered species (e.g. food chain,
decrease in community diversity) are evaluated based on the group of
organisms exceeding the LOC.

Direct

Direct effects evaluated are the survival, growth, and reproduction of
various taxa of organisms potentially exposed to fomesafen.  Taxonomic
groups evaluated include aquatic plants (algae and vascular), aquatic
invertebrates, aquatic vertebrates, terrestrial plants, terrestrial
invertebrates, birds, and mammals.  Both acute and chronic effects are
considered.

Indirect

When herbicides are applied, indirect effects may include a decline in
primary productivity, or change in composition of plant communities
proximate to the treated area or systems (wetlands and water bodies)
receiving runoff from the site.  If LOCs are exceeded for any taxa,
potential indirect effects to endangered species are assessed.



Conceptual Model

In order for a chemical to pose an ecological risk, it must reach
ecological receptors in biologically significant concentrations.  An
exposure pathway is the means by which a pesticide moves in the
environment from a source to an ecological receptor.  For an ecological
exposure pathway to be complete, it must have a source, a release
mechanism, an environmental transport medium, a point of exposure for
ecological receptors, and a feasible route of exposure.  The conceptual
model (Figure 1) depicts the potential pathways for ecological risk
associated with fomesafen use.  The conceptual model provides an
overview of the expected exposure routes for organisms within the
fomesafen action area.  





 Risk Hypothesis

(	Fomesafen deposited on plant surfaces may affect growth, survival, or
fecundity of birds and/or small mammals ingesting the affected
vegetation.

(	Fomesafen accumulating in soil may be toxic to non-target plants.

(	Fomesafen in runoff from treated areas may kill aquatic plants,
aquatic invertebrates, or fish.

(	Fomesafen in runoff from treated areas may reduce populations of
aquatic plants, aquatic invertebrates, or fish, causing changes in the
community.

(	Fomesafen in runoff from treated areas may accumulate in sediments,
resulting in chronic impacts to the benthic community.

(	Fomesafen is expected to move from the application site by leaching
into groundwater and runoff into surface water.  Use of water resources
with fomesafen occurrence as an irrigation source water may adversely
impact non-target plants.

Analysis Plan Options

The registration review screening level risk assessment is based on an
overview document compliant risk assessment for fomesafen use on cotton,
dry beans, and snap beans (Ecological Risk Assessment in Support of
Docket Preparation for Registration Review of Fomesafen (DP 306023),
January 18, 2006.  .

Measures of Exposure

Aquatic Exposure

Tier II EFED aquatic exposure models use the linked Pesticide Root Zone
Model and Exposure Analysis Model System (PRZM-EXAMS).  PRZM uses the
chemical’s physical and environmental fate properties and the site
characteristics to predict the concentration of pesticide in runoff and
entrained sediment from the field.  EXAMS estimates the concentration of
pesticide in an edge-of-field small water-body receiving runoff from the
field.  The water-body has no outflow with a constant volume (20 million
liters), and is intended to represent an upper-end occurrence
concentration.

PRZM-EXAMS Modeling  for Surface Water

The aquatic exposure assessment for fomesafen was conducted to assess
use on soybeans and cotton.  Soybeans were used a surrogate for dry
beans and snap beans, as EFED currently has no standard scenarios for
these crops.  Standard scenarios were selected to assess runoff
potential from vulnerable use sites in MS (soybean and cotton), NC
(cotton), and TX (cotton).  Input parameters for fomesafen were selected
according to EFED Input Parameter Guidance for PRZM/EXAMS1.  Input
parameters are shown in Table 6.

Table 6  Input Parameters for PRZM-EXAMS Modeling of Fomesafen on Cotton
and Soybeans

Parameter	Value	Comments	Source

Application Rate (kg a.i./ha)- Cotton	0.42	Aerial Spray	Label1

Application Rate (kg a.i./ha)- Cotton	0.56	Ground Spray	Label1

Application Rate  (kg a.i/ha)- Soybean	0.42	Aerial Spray	Label1

Molecular Weight  (grams/mole)	420

EPA 2020220

Solubility (mg/L)	1200	@pH= 7; 200c	MRID 45048207

Vapor Pressure (torr)	<7.5x10-7	@ 50oC	HSDB

Henry’s Constant (atm m3/mol) 	7.5 x10-13	Estimated	HSDB

Kd  (L/kg)	0.68	Lowest non-sand Kd	Acc No. 259413

Aerobic Soil Metabolism Half-life (days)	428.8	Upper 90th percentile of
mean2	Acc No. 071059

Acc. No. 00135660

Aerobic Aquatic Metabolism Half-life (days)	115.7 	Upper 90th percentile
of mean3	Acc. No. 72158

Anaerobic Aquatic Metabolism Half-life  (days)	Stable	Conservative
Assumption 	No Data Available

Photodegradation in Water (days)	289	@pH=7	MRID 40451101

Hydrolysis Half-life (days)	Stable	@pH=7	Acc No. 071059

1-Reflect application rates on the REFLEX 2LC, REFLEX 2.5 and REFLEX
labels

2-Calculated from half-lives of 187.6, 630, 57, 693, 349.3, 527.1, 207
days using a mean of 387.84 days and standard deviation of 242.90 days. 

3- Calculated from half-lives of  139.9, 60.9, 92.4, and 115.5 days
using a mean of 102 days and standard deviation of 33.44 days.

For aerial applications (Table 7), peak 1 in 10 year estimated
environmental concentrations (EECs)  ranged from 7.5 ppb (soybeans, MS)
to 12.2 ppb (cotton, TX).   Chronic 1-in-10 year (21-day average and
60-day average) EECs ranged from 6.4 ppb (soybean, MS, 60-day average)
to 11.4 ppb (cotton, MS &TX, 21-day average).

Table 7  PRZM-EXAMS EECs for Fomesafen at 0.375 lb a.i/A1

Region	Crop	State	Peak	4 days	21 days	60 days



	(g/L (ppb)

1	Soybean	MS	7.462	7.382	7.133	6.443

1	Cotton	MS	12.102	11.964	11.411	10.115

1	Cotton	NC	9.856	9.728	9.201	8.067

1	Cotton	TX	12.201	12.045	11.437	9.973

1-Concentrations were derived for 0.375 lb ai/A using aerial
applications

Peak 1-in-10 year EECs for ground spray applications (Table 8) ranged
from 10.6 ppb (cotton, NC) to 15.1 ppb (cotton, MS).  Chronic 1 in 10
year (21-day average and 60-day average) concentrations ranged from 8.6
ppb (cotton, MS, 60-day average) to 14.2 ppb (cotton, MS, 21-day
average).

Table 8  PRZM-EXAMS EECs for Fomesafen at  0.50 lb ai/A

Region	Crop	State	Peak	4 days	21 days	60 days



	(g/L

1	Cotton	MS	15.106	14.939	14.249	12.621

1	Cotton	NC	10.609	10.471	9.905	8.680

1	Cotton	TX	14.63	14.445	13.713	11.954

1- Concentrations were derived for 0.50 lb ai/A using ground spray 

SCIGROW Modeling for Ground Water

Because fomesafen is mobile and persistent in soil, a screening level
groundwater assessment using SCIGROW (ver. 2.3) was conducted to
estimate the concentration of fomesafen in shallow groundwater, which
could potentially be used for crop irrigation.  Input parameters for
SCIGROW are listed in Table  9.  A groundwater monitoring study was
submitted (MRID 42247001), but the shallow groundwater wells were dry
during the study.  Fomesafen was detected in soil porewater at
concentrations of 1 g/L (at 4 months), up to 17g/L (at 1
month).  It was detected at a concentration of 1 g/L in the medium-
to deep-depth wells.

 

Table 9  Input Parameters for SCIGROW Modeling for Fomesafen 

Parameter	Value	Comments	Source

Application Rate (kg a.i./ha)- Cotton	0.56

Label1

Koc  (L/kg)	  68	Estimated2  	Acc No. 259413

Aerobic Soil Metabolism Half-life (days)	387.84	Mean3	Acc No. 071059

Acc. No. 00135660

1-Reflect maximum application rates on the REFLEX 2LC, REFLEX 2.5 and
REFLEX labels

2-Koc estimated using Kd/SOC=Koc; where Kd=0.68 and SOC=1% SOC
percentage

3-Calculated from half-lives of 187.6, 630, 57, 693, 349.3, 527.1, 207
days using a mean of 387.84 days and standard deviation of 242.90 days. 

g/L (at 4 months), up to 17g/L (at 1 month).  It was detected
at a concentration of 1 g/L in the medium- to deep-depth wells.

Because fomesafen is expected to leach to groundwater, EFED has
calculated the maximum application rate of fomesafen from two inches of
irrigation water, using the following equations. This calculation
assumes that two inches (0.167 ft) of irrigation water is required for
optimum plant growth.  The calculations are as follows:

g/L = fomesafen g/A

(fomesafen g/A)/ (106) = fomesafen grams/A*1lb/454 grams=fomesafen
lbs ai/A.

Based on two inches of irrigation and the SCIGROW estimate, the
application rate of fomesafen is estimated at 0.003 lbs ai/A.  Using the
concentrations of 1 mg/L and 17mg/L (from the groundwater study) as
outer bounds, concentrations of fomesafen in irrigation water could
range from 0.0004-0.0077 lbs ai/A.

Soil Accumulation

Because of the persistence of fomesafen in soil, a screening level
assessment was conducted to quantify the accumulation of fomesafen
residues in soil.  A first-order decay model (A=Aoe-kt) was used to
estimate fomesafen soil concentrations. The time period in the model (t)
was set to 730 days to represent alternate years applications.  The
upper 90th percentile of the mean half-life (t1/2=428 days; k=0.00161950
days-1) was used to represent the microbial mediated decay rate of
fomesafen in soil.  The starting concentration (A0 ) was set at the
label recommended application rate of 0.375 lbs ai/A for aerial
applications and 0.5 lbs ai/A for ground applications.  The modeling
scenario assumes that 100% of fomesafen residue is applied to the soil
as recommended for a pre-emergent application.  The model scenario also
assumes that microbial degradation is the only route of dissipation from
the application site. These assumptions are expected to exaggerate
predicted formesafen soil concentrations.

Figure 2 illustrates the fomesafen concentrations in soil reach a
plateau after approximately 10 years regardless of the application rate.
 Application rates of 0.375 lbs/A can theoretically result in a maximum 
fomesafen concentration  of  0.14 mg/kg.  Higher application rates of
0.5 lbs ai/A can theoretically result in a maximum fomesafen
concentration of 0.19 mg/kg.

  

Figure 2 - Estimate of Fomesafen Loading in the Surface Soil (0-15 cm
depth) from alternate year applications of 0.375 lbs/A (solid line) and
0.5 lbs/A (dotted line)  



Terrestrial  Exposure

Avian 

For birds, dose estimates for the 0.2 lb ai/A application rate range
from 0.87 mg/kg bwt (1000g frugivores, granivores, and insectivores) to
54.7 mg/kg bwt (20 g herbivores) (Table 10). At the 0.37 lb ai/A
application rate, estimated doses range from 1.64 (1000g frugivores,
granivores, and insectivores) to 102 (1000g fruit and pods).  Dose
estimates for the 0.49 lb ai/A application rate range from 2.14 mg/kg
bwt (1000g frugivores, granivores, and insectivores) to 134 mg/kg bwt
(20 g herbivores).

Table 10  Bird Dose Estimates

Feeding Categories	Kenaga Upper Bound Dose (mg/kg bwt)

	Small

(20 g)	Medium 

(100 g)	Large

(1000 g)

0.2 lb ai/A Appllication Rate (Alternative)

Short grass	54.67	31.17	13.96

Tall grass	25.06	14.29	6.40

Broadleaf plants/small insects	30.75	17.54	7.85

Fruits/pods/seeds/large insects	3.42	1.95	0.87

0.375 lb ai/A Application Rate

Short grass	102.5	58.45	26.17

Tall grass	46.98	26.79	11.99

Broadleaf plants/small insects	57.66	32.88	14.72

Fruits/pods/seeds/large insects	6.41	3.65	1.64

0.50 lb ai/A Application Rate

Short grass	133.93	76.38	34.19

Tall grass	61.39	35.01	15.67

Broadleaf plants/small insects	75.34	42.96 	19.23

Fruits/pods/seeds/large insects	8.37	4.77	2.14



Small Mammals

For mammals dose estimates for the 0.2 lb ai/A application rate range
from 0.10 mg/kg bwt (1000g granivore) to 45.8 mg/kg bwt (20 g short
grass) (Table 11). At the 0.37 lb ai/A application rate, estimated doses
range from 0.19 (1000g granivore) to 85.8 (20 g short grass).  Dose
estimates for the 0.49 lb ai/A application rate range from 0.25 mg/kg
bwt (1000g granivore) to 112 mg/kg bwt (20 g short grass).

Table 11  Mammal Dose Estimates

Feeding Categories	Kenaga Upper Bound Dose (mg/kg bwt)

	Small

(15 g)	Medium 

(35 g)	Large

(1000 g)

0.2 lb ai/A Appllication Rate (Alternative)

Herbivores/Insectivores



	Short grass	45.76	31.63	7.33

Tall grass	20.98	14.50	3.36

Broadleaf plants/small insects	25.74	17.79	4.13

Fruits/pods/seeds/large insects	2.86	1.98	0.46

Granivores

Fruits/pods/seeds/large insects	0.64	0.44	0.10

0.375 lb ai/A Application Rate

Herbivores/Insectivores



	Short grass	85.81	59.30	13.75

Tall grass	39.33	27.18	6.30

Broadleaf plants/small insects	48.27	33.36	7.73

Fruits/pods/seeds/large insects	5.36	3.71	0.86

Granivores

Fruits/pods/seeds/large insects	1.19	0.82	0.19

0.50 lb ai/A Application Rate

Herbivores/Insectivores



	Short grass	112.12	77.49	17.97

Tall grass	51.39	35.52	8.23

Broadleaf plants/small insects	63.07	43.59	10.11

Fruits/pods/seeds/large insects	7.01	4.84	1.12

Granivores

Fruits/pods/seeds/large insects	1.56	1.08	0.25



Plants

TerrPlant has two basic exposure scenarios.  The first is an adjacent
upland area, which is exposed to the pesticide via drift and dissolved
concentrations in sheet runoff.  The second is an adjacent semi-aquatic
(wetland) area, which is exposed to the pesticide via drift and to
dissolved concentrations in channelized runoff.  Drift is calculated as
a percentage of the application rate (1% for ground, and 5% for aerial,
airblast, or spray chemigation) and is not adjusted for distance from
the application site.  The amount of dissolved pesticide in the runoff
component is estimated based on solubility of the active ingredient. 
TerrPlant estimates are shown in Table 12.

Table 12  Terrestrial Plant Exposure

Application Method	Total Loading (Runoff +Drift) (lb ai/A)	Drift EEC (lb
ai/A)

	Upland areas	Wetland areas	All areas

Use at 0.375 lb ai/A

Aerial	0.0263	0.0938	0.0188

Ground	0.0113	0.0788	0.0038

Use at 0.50 lb ai/A

Aerial	0.0343	0.1225	0.0245

Ground	0.0147	0.1029	0.0049



Summary of Risks

Aquatic Risks

Fomesafen appears to be of relatively low toxicity to aquatic organisms,
both animals and plants in freshwater and estuarine/marine systems
(Table 13). Both acute and chronic effects were considered.   Fomesafen
may indirectly affect aquatic systems by damaging plants in adjacent
wetland or riparian zones Modification of the vegetation in wetlands or
riparian zones could cause decreased allochthonous input, increased
sediment input, destabilization of the stream bank, or changes in the
structural components (plant).  Effects on waterbody-associated plant
communities can be minimized by ensuring an adequate offset distance is
maintained between the application site and the wetland or riparian
zone.  Appropriate distance is dependent on application rate,
application methods, and weather conditions.

Table 13 Summary of Aquatic RQs

Taxa	Acute RQ	Chronic RQ1	Endangered Species RQ2

Use on Beans at 0.375 lb a.i./A (MS scenario, aerial application)

FW Aquatic Plants	0.06	NA1	0.33 

FW Aquatic Invertebrates	<0.001	<0.001	<0.001

Fish	<0.001	NC	<0.001

SW Aquatic Plants	0.01	NA1	0.008 

SW Aquatic Invertebrates	<0.001	0.01	<0.001

SW Fish	<0.001	<0.001	<0.001

Use on Cotton at 0.375 lb a.i./A (MS scenario, aerial application)

FW Aquatic Plants	0.10	NA1	0.53

FW Aquatic Invertebrates	<0.001	<0.001	<0.001

FW Fish	<0.001	NC	<0.001

SW Aquatic Plants	0.01	NA1	0.013

SW Aquatic Invertebrates	<0.001	0.02	<0.001

SW Fish	<0.001	<0.001	<0.001

Use on Cotton at 0.5 lb a.i./A (MS scenario, ground application)

FW Aquatic Plants	0.13	NA1	0.66

FW Aquatic Invertebrates	<0.001	<0.001	<0.001

FW Fish	<0.001	NC	<0.001

SW Aquatic Plants	0.01	NA1	0.016

SW Aquatic Invertebrates	<0.001	0.02	<0.001

SW Fish	<0.001	0.001	<0.001

1 There are no chronic aquatic plants tests. 2  Endangered species RQ
for plants are calculated based on NOAEC.  Endangered species RQ for
animals are calculated in the same way as acute risk values, but
compared to a different LOC.    NA – not applicable, NC – Not
calculated, data not available.

Terrestrial Risks

Avian

At the proposed application rate of 0.5 lb ai/A, no acute dose- or
dietary-based LOCs are exceeded for birds (Table 14).  Chronic LOCs for
birds in three out of the four food categories (short grass, tall grass,
and broadleaf plants/small insects) are exceeded.

Table 14  Avian RQ Summary  0.5 lb ai/A

Risk quotients based on Kenaga upper bound EECs	Acute dose-based RQs
Acute dietary-based RQs	Chronic RQs

	20g	100g	1000g	All birds	All birds

Short grass	0.05	0.02	0.01	0.01	2.56 c

Tall grass	0.02	0.01	0.00	0.00	1.17 c

Broadleaf plants/small insects	0.03	0.01	0.00	0.00	1.44 c

Fruits/pods/seeds/lg insects	0.00	0.00	0.00	0.00	0.16 c

a exceeds acute risk LOC (0.5)

b exceeds endangered species acute risk LOC (0.1)

c exceeds chronic risk LOC (1.0)

At the proposed application rate of 0.375 lb ai/A, no acute dose- or
dietary-based RQs exceed any LOCs (Table 15).  The chronic LOC is
exceeded for birds consuming the food categories of short grass and
broadleaf plants/small insects.

Table 15  Avian RQ Summary: 0.375 lb ai/A 

Risk quotients based on Kenaga upper bound EECs	Acute dose-based RQs
Acute dietary-based RQs	Chronic RQs

	20g	100g	1000g	All birds	All birds

Short grass	0.04	0.02	0.01	0.00	1.96 c

Tall grass	0.02	0.01	0.00	0.00	0.90

Broadleaf plants/small insects	0.02	0.01	0.00	0.00	1.10 c

Fruits/pods/seeds/lg insects	0.00	0.00	0.00	0.00	0.12

a exceeds acute risk LOC (0.5)

b exceeds endangered species acute risk LOC (0.1)

c exceeds chronic risk LOC (1.0)

Small mammals

At the proposed application rate of 0.50 lb ai/A, dose-based RQs exceed
the endangered species LOC for two size classes of mammals (15g and 35
g) consuming short grass (Table 16).  Using the dose-based RQ, chronic
LOC is exceeded for mammals consuming the food categories of short grass
(all weights), tall grass (15g, 35g), and broadleaf plants/small insects
(15g, 35g).  No chronic dietary based-RQs exceed any LOCs.

Table 16  Small Mammal RQ Summary:  0.50 lb ai/A

Risk Quotients based 

on Kenaga 

upper bound EEC	Acute 

dose-based RQs	Chronic 

dose-based RQs	Chronic dietary-based RQs

	15 g	35 g	1000 g	15 g	35 g	1000 g 	All mammals

Short grass	0.13 b	0.11 b	0.06	4.08 c	3.49 c	1.87 c	0.47

Tall grass	0.06	0.05	0.03	1.87 c	1.60 c	0.86	0.22

Broadleaf plants/

small insects	0.07	0.06	0.03	2.30 c	1.96 c	1.05 c	0.26

Fruits/pods/seeds/

lg insects	0.01	0.01	0.00	0.26	0.22	0.12	0.03

Seeds (granivores)	0.00	0.00	0.00	0.06	0.05	0.03	NA

a exceeds acute risk LOC (0.5)

b exceeds endangered species acute risk LOC (0.1)

c exceeds chronic risk LOC (1.0)

At the proposed application rate of 0.375 lb ai/A, no acute dose-based
RQs for mammals exceed any LOCs, although the RQ for small (15g) mammals
consuming short grass equals the endangered species LOC (Table 17). 
Using the dose-based RQ, the chronic LOC is exceeded for mammals
consuming the food categories of short grass (all weights), tall grass
(15g, 35g), and broadleaf plants/small insects (15g, 35g).

Table 17  Small Mammal RQ Summary:  0.375lb ai/A

Risk Quotients based 

on Kenaga 

upper bound EEC	Acute 

dose-based RQs	Chronic 

dose-based RQs	Chronic dietary-based RQs

	15 g	35 g	1000 g	15 g	35 g	1000 g 	All mammals

Short grass	0.10b	0.08	0.05	3.12c	2.67 c	1.43 c	0.36

Tall grass	0.05 	0.04	0.02	1.43 c	1.22 c	0.66	0.17

Broadleaf plants/

small insects	0.06	0.05	0.03	1.76 c	1.50 c	0.80	0.20

Fruits/pods/seeds/

lg insects	0.01	0.01	0.00	0.20	0.17	0.09	0.20

Seeds (granivores)	0.00	0.00	0.00	0.04	0.04	0.02	NA

a exceeds acute risk LOC (0.5)

b exceeds endangered species acute risk LOC (0.1)

c exceeds chronic risk LOC (1.0)

Plants 

For both proposed uses of fomesafen, ground application at 0.5 lb ai/A
and aerial application at 0.375 lb ai/A, total loading RQs exceeded the
acute plant risk LOC (1) for both monocots and dicots in adjacent
wetland areas but not in upland areas (Table 18).  Drift-based RQs were
exceeded for dicots in all adjacent areas.  LOC exceedences for acute
risk to endangered plants followed the same pattern, but were of greater
magnitude.  RQs based on the two alternative ground application
scenarios (0.375 lb ai/A and 0.2 lb ai/A) were also generated.  At both
these rates, there were no exceedences for monocots.  RQs for both total
loading to wetland areas and drift only exceeded the acute risk and
endangered species acute risk LOCs for dicots.



Table 18  Terrestrial Plant Risk Quotients Based on TerrPlant 

Application Method	

Total Loading RQ (Seedling emergence)	Total Loading RQ (Seedling
Emergence) 	Drift RQ 

(Vegetative vigor)

	Upland areas	

Wetland areas	All areas

	Monocot	Dicot	Monocot	Dicot	Monocot	Dicot

Acute risk

Use at 0.2 lb ai/A (alternative)

Ground	0.07	0.08	0.47	0.53	0.01	2.04 a

Use at 0.375 lb ai/A

Aerial	0.29	0.33	1.05 a	1.19 a	0.06	11.72 a

Ground (alternative)	0.13	0.14	0.88	1.00 a	0.01	2.34 a

Use at 0.5 lb ai/A

Ground	0.17	0.19	1.16 a	1.30 a	0.02	3.06 a

Endangered species acute risk

Use at 0.2 lb ai/A (alternative)

Ground	0.07	0.08	0.47	0.53	0.01	1.25 a

Use at 0.375 lb ai/A

Aerial	0.29	0.33	1.05 a	1.19 a	0.08	19.13 a

Ground (alternative)	0.13	0.14	0.88	1.00 a	0.02	3.83 a

Use at 0.5 lb ai/A

Ground	0.17	0.19	1.16 a	1.30 a	0.02	5.00 a

a Exceeds or equals LOC of 1

Future Decisions

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1 Guidance for Selecting Input Parameters in Modeling the Environmental
Fate and Transport of Pesticides. Version II, 2/28/02.

 PAGE   1 

 PAGE   6 

 PAGE   - 16 - 

 PAGE   - 25 - 

	

Registration Review

Ecological Risk Assessment

Problem Formulation for thePlant Growth Rregulator Paclobutrazol		  DATE
\@ "M/d/yyyy"  3/7/2007 	

		

Figure 1 - Conceptual Model for Fomesafen

Fomesafen applied to crop

Stressor

Source

Runoff

Direct application

Spray drift

Receptors

Birds

Mammals

Terrestrial 

insects

Individual organisms

Reduced survival

Reduced growth

Reduced reproduction

Food chain

Reduction in primary productivity

Reduction in prey

Shift in community composition

Habitat integrity

Reduced cover

Community change

Attribute

Change

Aquatic 

plants

invertebrates

vertebrates

Terrestrial 

plants

Soil accumulation, leaching and runoff

Soil 

invertebrates

