UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON, D.C. 20460

OFFICE OF

PREVENTION, PESTICIDES

AND TOXIC SUBSTANCES

Environmental Fate and Ecological Risk Assessment

For the Proposed New Use of Rimsulfuran on

OPTIMUM® GAT® Soybean and Amended 

Tolerance for OPTIMUM® GAT® Field Corn

For Use as Pre/Early post Emergence Herbicide for Selective Control of Certain Broadleaf Weeds & Grasses

RIMSULFURON

CAS Name: N-[[(4,6-dimethoxy-2-pyrimidinyl)amino]carbonyl]-3-(ethylsulfonyl)-2-

pyridinesulfonamide; PC Code: 129009; CAS Number: 122931-48-0

Prepared by:

José L. Meléndez, Chemist, 

Environmental Fate Reviewer, ERB V

Joseph DeCant, Ecologist, 

Ecological Effects Reviewer, ERB V

Approved by:

Mah Shamim, PhD, Chief ERB V

8/4/09

United States Environmental Protection Agency

Office of Pesticide Programs

Environmental Fate and Effects Division

Environmental Risk Branch V

1200 Pennsylvania Ave.

Mail Code 7507P 

Washington, D.C. 20460

N

N

O

O

H3C

H3C

N

H N

S O

O

CH2

H3C

N

H

S

O

O

O
2

TABLE OF CONTENTS

I. EXECUTIVE SUMMARY...................................................................................................... 3

A. NATURE OF CHEMICAL STRESSOR........................................................................................... 3

B. POTENTIAL RISK TO NON-TARGET ORGANISMS ...................................................................... 3

C. CONCLUSIONS: EXPOSURE CHARACTERIZATION ..................................................................... 3

D. CONCLUSIONS: EFFECTS CHARACTERIZATION ........................................................................ 4

E. DATA GAPS AND UNCERTAINTIES ........................................................................................... 5

II. PROBLEM FORMULATION ............................................................................................... 6

A. STRESSOR SOURCE AND DISTRIBUTION .................................................................................. 6

B. RECEPTORS.............................................................................................................................. 7

C. ASSESSMENT ENDPOINTS ........................................................................................................ 8

D. CONCEPTUAL MODEL.............................................................................................................. 9

E. ANALYSIS PLAN ...................................................................................................................... 9

III. ANALYSIS............................................................................................................................ 11

A. USE CHARACTERIZATION...................................................................................................... 11

B. EXPOSURE CHARACTERIZATION............................................................................................ 14

C. ECOLOGICAL EFFECTS CHARACTERIZATION ......................................................................... 25

IV. RISK CHARACTERIZATION .......................................................................................... 26

A. RISK ESTIMATION ................................................................................................................. 26

B. RISK DESCRIPTION ................................................................................................................ 27

C. ENDANGERED SPECIES ASSESSMENT..................................................................................... 28

REFERENCES............................................................................................................................ 37

APPENDIX I. ECOLOGICAL EFFECTS INFORMATION............................................... 39

APPENDIX II. TERRPLANT SPREADSHEET..................................................................... 42

APPENDIX III. ECOLOGICAL AQUATIC EXPOSURE MODELING ............................ 44

APPENDIX IV. LOCATES PRINTOUT.................ERROR! BOOKMARK NOT DEFINED.
3

I. EXECUTIVE SUMMARY

A. Nature of Chemical Stressor

Rimsulfuron is a pyrimidinyl sulfonylurea selective/systematic herbicide which belongs to the 

sulfonylurea family1 (HRAC Group B). The chemical is proposed for new uses on OPTIMUM® 

GAT® soybeans and an amended tolerance on OPTIMUM® GAT® field corn. The mode of 

action of rimsulfuron involves inhibition of acetolactate synthase, also known as 

acetohydroxyacid synthase AHAS2

B. Potential Risk to Non-target Organisms

, a key enzyme in the biosynthesis of certain amino acids in 

plants. Rimsulfuron selectively controls certain broadleaf weeds and grasses and is proposed to 

be applied as preemergence or postemergence. Resistance management may be required with 

repeated use. The chemical is formulated as a water soluble granule (25% a.i.) and proposed to

be applied by ground broadcast or aerial spray.

For the purpose of this risk assessment, exposure is calculated based on expected terrestrial and 

aquatic residues of parent rimsulfuron. If studies determine that transformation 

products/degradates pose a hazard to non-target plants, for example, then the period of risk to 

plants (already identified) would be extended.

Rinsulfuron poses a risk to non-target terrestrial endangered and non-endangered plants (RQs = 

6.25 – 264.42) and aquatic endangered plants (RQ = 5.10 – 15.3 across all crops, using 

PRZM/EXAMS). Because of potential direct effects to plants, indirect effects are also possible 

to all other endangered species taxonomic groups.

C. Conclusions: Exposure Characterization

Upon application of rimsulfuron to bare soils, the major quantities of the applied material is 

expected to be deposited on soil surfaces and be distributed within the surface layer of the soil 

depending on the amount of rainfall/irrigation for the required wetting-in. Other relatively 

smaller quantities of the parent are expected to reach nearby terrestrial/aquatic systems by drift. 

Later undegraded parent and aerobic soil transformation products/degradates are expected to 

reach surface waters by run-off/erosion. 

Rimsulfuron has a low vapor pressure (1.447 x10-11 atms. at 25 o

C) and is highly soluble in water 

(solubility 7.3 ppm at 20 oC3

 1 ULR: 

). Based on submitted environmental fate studies, the chemical is 

short lived in aqueous systems (mainly affected by hydrolysis with hydrolysis half-lives ranging 

http://www.alanwood.net/pesticides/

2 URL: http://www.plantprotection.org/hrac/Bindex.cfm?doc=moa2002.htm
4

from 5-7 days in acidic/neutral conditions and <day in alkaline conditions). Also the chemical is 

short-lived in aerobic/anaerobic soil systems (t1/2= 19-21 days determined for only one soil, 

shorter half-lives were determined under field conditions: t1/2= 5 to 18 days). Rimsulfuron 

appears not to be affected by aqueous or soil photolysis. In the natural environment, the major 

route of dissipation of rimsulfuron is expected to be hydrolysis followed by bio-transformation. 

Adsorption/desorption studies suggest that rimsulfuron may be highly mobile and vulnerable to 

run-off and leaching (Koc ranged from 19-74 L Kg-1

). Therefore, the chemical may enter aquatic 

systems via run-off and erosion.

Rimsulfuron is expected to transform/degrade into a number of transformation/degradation 

products under different environmental conditions. The three major degradates for rimsulfuron 

result from contraction or cleavage of the sulfonurea-bridge (IN-70941 and IN-70942 from 

contraction while IN-E9260 from cleavage). In contrast, the minor degradates are cleavage 

degradates (IN-J9260 in systems other than aerobic soil, IN-J290 and IN-T5831). Mobility of 

the transformation products/degradates were checked by TLC (thin layer chromatography) and 

results indicate high mobility to IN-E9260 and high to medium mobility for IN-70941, IN-70942 

and IN-J290. Solubility was reported for only IN-70941 and IN-70942 and was 0.7 ppm for the 

first and 0.2 ppm for the second. Considering quantities formed and relative persistent of 

transformation products/degradates, all are expected to reach aquatic systems in varied 

concentrations. In addition, most of the parent that reaches aquatic systems by drift is expected 

to transform by hydrolysis into transient IN-70941 then into the persistent IN-70942. The timeline for this event is expected to be as follows: IN-79041 at the short to medium-term (because it 

transforms into IN-70942), IN-70942/IN-E9290/In-J290 at the medium to long-term. Finally, IN70942 is expected to be the terminal and persistent degradate. 

The risk assessment for rimsulfuron is based on its EEC’s in important environmental 

compartments. These EEC’s were estimated using available physicochemical and fate properties. 

The EEC’s along with related ecological effects data (i.e., available aquatic and terrestrial 

toxicity data) were used to evaluate and characterize ecological risk of rimsulfuron application to 

the environment.

D. Conclusions: Effects Characterization

Rimsulfuron is considered practically non-toxic to most terrestrial animals. This includes birds 

(mallard LD50 > 2000 mg/kg; bobwhite quail LD50 > 2250 mg/kg; mallard and bobwhite quail 

LC50s > 5620 ppm) and mammals (rat LD50 > 5000 mg/kg).

Rimsulfuron is considered practically non-toxic to most aquatic animals. This includes 

freshwater fish (rainbow trout LC50 > 390 ppm; bluegill sunfish LC50 > 390 ppm), freshwater 

invertebrates (Daphnia magna LC50 > 360 ppm), and estuarine/marine organisms (sheepshead 

minnow LC50 > 110 ppm; mysid shrimp LC50 > 110 ppm; oyster shell deposition EC50 > 120 

ppm).

In contrast, vascular plants are extremely sensitive to rimsulfuron. For seedling emergence, plant 

height was the most sensitive parameter (EC25 = 0.0006 lb ai/A for the most sensitive monocot 

and 0.00013 for the most sensitive dicot). For vegetative vigor, root weight was the most 

sensitive parameter (EC25 = 0.00004 lb ai/A for the most sensitive monocot and 0.00003 lb ai/A 
5

for the most sensitive dicot). The most sensitive aquatic plant tested is duckweed (EC50 = 11.6 

ppb).

E. Data Gaps and Uncertainties 

The screening level assessment for rimsulfuron has been conducted despite unfulfilled guideline 

requirements and existing environmental fate and ecological data gaps. 

The evaluation of the environmental fate and transport data identified three important data gaps. 

An aerobic soil half-life was determined for only one soil (MRID 41356334, Acceptable), an 

aerobic aquatic metabolism study was conducted in the presence of light (MRID 43288502, 

supplemental), and no anaerobic aquatic metabolism study has been submitted. These data gaps

may result in non-representative estimated aquatic exposure concentrations (EECs). These data 

gaps also cause uncertainty in conclusions associated with the behavior of the chemical in these 

relevant systems. In order to address these data gaps, the following fate studies have been 

required:

• One aerobic soil metabolism study (§835.4100) (using two US soils from relevant use 

areas)

• One anaerobic aquatic metabolism study (§835.4400) (in a relevant natural water 

sediment system)

• One aerobic aquatic metabolism study (§835.4300) (in a relevant natural water sediment 

system)

Since the EFED LOC’s for plants are based on acute risk, the plant risk assessment is also based 

on acute risk (to parent rimsulfuron). While studies of the toxicity of the degradates IN-70941,

IN-70942, and IN-E9260 to both terrestrial and aquatic plants have been submitted, they have 

not yet been reviewied. However, if the degradates are similarly phytotoxic, the period of 

phytotoxicity in the field (in both terrestrial and aquatic environments) would be longer. 

The following studies on the transformation product/degradate IN-70942 have not been 

submitted but are needed for ecological risk assessment:

• Freshwater fish early life-stage (§850.1400)

• aquatic invertebrate life-cycle (§850.1300) 
6

II. PROBLEM FORMULATION

A. Stressor Source and Distribution 

1. Sources and Intensity 

The source of stressor is the proposed application of rimsulfuron as a water soluble granule (25% 

a.i.). This systematic herbicide is proposed to be applied by aerial spray or by ground broadcast 

application to OPTIMUM® GAT® soybeans and OPTIMUM® GAT® field corn. The proposed 

maximum rate of application to these crops is 0.0625 lb a.i./A/crop season.

Rimsulfuron and its major transformation/degradation products (IN-70941, IN-70942, and INE9260) are considered, at this problem formulation stage, to be the important stressors that 

would result from the proposed application. Application of the rimsulfuron formulation is the 

source of parent while parent transformation/degradation and transport are the source of 

transformation products/degradates. Processes dominant in various compartments of the natural 

environment are expected to control exposure timing/intensity of assigned stressors where the 

chemical is expected to reach.

2. Physicochemical, Fate, and Transport Properties

Rimsulfuron is characterized by relative high solubility (7300 ppm) and low vapor 

pressure/Henrys’ Law constant (1.45x10-11 atms. and 1.40x10-12 atms. m3 mole-1

, respectively). 

Therefore, rimsulfuron is not expected to partition into the air from water and/or dry/wet soil 

surfaces. Available data suggest that rimsulfuron is not expected to be bio-concentrated by 

aquatic organisms such as fish (Kow <1 at pH 7).

Rimsulfuron is expected to be of relative low persistence in important compartments of the 

environment. The chemical is highly vulnerable to hydrolysis as it hydrolyzes with half-lives in 

the range of 5-7 days at pHs 5 and 7. In alkaline conditions, the chemical hydrolyzes with halflives in hours (half-lives of 4-11 hours at pH 9). Relatively longer half-lives were observed in 

aerobic/anaerobic soil systems (18-21 days) and in the field (5-18 days). Data suggest that 

higher persistence is expected in colder climates and in dry soil systems. The same studies had 

also shown the chemical to transform into many transformation products/degradates including 

three major ones, namely: IN-70941, IN-70942, and IN-E9260. Combined data on rimsulfuron 

and its major transformation products/degradates indicate that short-term environmental 

exposure will involve the parent and its major transient transformation products IN-70941 

(transforms into IN-70942), IN-70942 and IN-E9260 at the medium-term and the terminal 

transformation product IN-70942 at the long-term. Parent rimsulfuron appears to be highly 

mobile in tested soils. In comparison, the two contraction transformation products (IN-70941

and IN-70942) and one of the cleavage degradates (IN-E9260) appear to be similar or slightly 

less mobile than their parent. In most natural environmental compartments, the transformation 

product IN-70942 is expected to persist with relatively high potential for mobility.
7

3. Pesticide Type, Class, and Mode of Action

Rimsulfuron is a selective/systemic pyrimidinyl sulfonylurea herbicide and a member of the 

sulfonylurea class of compounds4

. It has a mode of action that inhibits acetolactate synthase 

ALS (ALS is also known as acetohydroxyacid synthase AHAS) (HRAC Group B)5

4. Overview of Pesticide Usage 

Currently, this herbicide is registered as pre/post emergence weed control in field corn, potatoes, 

potatoes grown for seed, field grown tomatoes, grapes, stone fruit, tree nuts, pistachios, pome 

fruit, and citrus fruit (first registered in 1994). It is also registered for the control of grasses and 

broadleaf weeds in grassland restoration as well as roadside control. This assessment addresses 

the proposed new use on OPTIMUM® GAT® soybeans and the amended application rate to

OPTIMUM® GAT® field corn. The application methods associated with the new uses are as a 

water soluble granule applied through ground broadcast application or aerial spray. It is expected 

that rimsulfuron will be widely used in many areas of the United States. 

. ALS or 

AHAS is a key enzyme in the biosynthesis of certain amino acids in plants. The mode of action 

appears to require relatively low concentrations of the chemical. It is noted that repeated 

application might cause weeds to develop resistance to the sulfonurea family of herbicides that 

would require the application of an herbicide resistance program.

B. Receptors

1. Ecological Effects

Ecological measures of effect for rimsulfuron are based on registrant-submitted toxicity studies. 

Acute and chronic endpoints are selected from available test data, as the data set allows. A 

discussion of available toxicity data is located in Section III. C. (Analysis/Ecological Effects 

Characterization). 

2. Ecosystems at Risk

Aquatic ecosystems potentially at risk include wetlands and water bodies that could be exposed 

via runoff. Such ecosystems could be coastal (saltwater) or inland (freshwater). Since plants are 

highly sensitive to rimsulfuron, they could be directly affected. Other organisms dependent on 

plants could then be indirectly affected. 

Terrestrial ecosystems potentially at risk include areas which might receive direct use, drift, and 

runoff or erosion. These areas might include other cultivated fields, fence rows and hedgerows, 

meadows, fallow fields or grasslands, woodlands, riparian habitats and other uncultivated areas 

that may be exposed. Since plants are highly sensitive to rimsulfuron, they could be directly 

affected. Other organisms dependent on plants could then be indirectly affected. 

 4 URL: http://www.alanwood.net/pesticides/

5 URL: http://www.plantprotection.org/hrac/Bindex.cfm?doc=moa2002.htm
8

C. Assessment Endpoints

Assessment endpoints are explicit expressions of the actual environmental value that is to be 

protected. Assessment endpoint selection is based on valued entities or ecological receptors, the 

ecosystems potentially at risk, pesticide migration pathways, and routes by which ecological 

receptors may be exposed to the stressor. A generic listing of potential assessment endpoints and 

measures of ecological effect (depending on data availability and other factors) that may be used 

to characterize potential ecological risks is shown in Table 1. 

Table 1. Potential Assessment Endpoints for Ecological Risk Assessment.

Taxonomic Group

Assessment 

Endpoint

Measures of Effect

(Toxicity Endpoints)

Measures of Exposure

(Exposure Endpoints)

Birds

Survival

Oral LD50 and dietary LC50 (most sensitive 

species), adjusted for size for 20 g bird

Maximum residue on food 

items (foliar) or LD50/ft2

Reproduction, 

Growth

NOAEC/LOAEC from avian chronic study 

(most sensitive species)

Maximum residue on food 

items (foliar) or LD50/ft2

Mammals

Survival

Acute oral LD50, dietary LC50 (most 

sensitive species)

Maximum concentration on 

food items (foliar) or LD50/ft2

Reproduction, 

Growth

NOAEC/LOAEC from chronic reproduction 

study (most sensitive species)

Maximum concentration on 

food items

Non-target Terrestrial 

Invertebrates Survival Honey-bee acute contact LD50 Maximum application rate

Terrestrial Plants 

Survival and 

Growth Tier I, Tier II plant toxicity data; EC25

Estimates of runoff to nontarget areas

Freshwater Fish

Survival 96-hr LC50 (most sensitive species) Peak EEC

Reproduction, 

Growth

Fish Early Life Stage NOAEC/LOAEC for 

Growth 60-day average EEC 

Freshwater 

Invertebrate

Survival 48-hr LC50 (most sensitive species) Peak EEC

Reproduction, 

Growth Invertebrate Life Cycle NOAEC 21-day average EEC

Marine/estuarine Fish

Survival 96-hr LC50 (most sensitive species) Peak EEC

Reproduction, 

Growth Estuarine/Marine Fish NOAEC for growth 60-day average EEC

Marine/estuarine 

Invertebrate

Survival 48-hr EC50 (most sensitive species) Peak EEC

Reproduction, 

Growth

NOAEC for reproduction for most sensitive 

species 21-day average EEC

Aquatic Plants Survival, Growth Tier I, Tier II plant toxicity estimates; EC25 1-in-10 year peak concentration
9

D. Conceptual Model 

1. 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 (EPA 1998a). For this assessment, the risk is stressor-initiated, 

where the stressor is the release of rimsulfuron into the environment. The following risk 

hypothesis is presumed for this screening-level assessment:

The proposed new use of rimsulfuron on OPTIMUM® GAT® soybeans and the amended 

application rate on OPTIMUM® GAT® field corn will likely involve situations where terrestrial 

and aquatic animals and plants will be exposed to the chemical and/or its 

transformation/degradation products. Based on information on environmental fate, mode of 

action, direct toxicity and potential indirect effects, EFED assumes that rimsulfuron may have 

the potential to cause reduced survival, growth, and reproduction to terrestrial and/or aquatic 

plants as a result of the proposed uses of the pesticide.

Various ecological receptors may potentially be exposed to rimsulfuron and its transformation 

products/degradates in the short, medium, and long term. The receptors are as follows: terrestrial 

and semi-aquatic wildlife (i.e., mammals, birds, amphibians, and reptiles), terrestrial and semiaquatic plants, and soil invertebrates. In addition, aquatic receptors (e.g., freshwater and 

estuarine/marine fish and invertebrates, amphibians, and aquatic plants) may also be exposed as 

a result of potential migration of rimsulfuron and its transformation products/degradates via 

spray drift and/or runoff/erosion.

2. Diagram

Based on the preliminary iterative process of examining fate and effects data, the conceptual 

model or the risk hypothesis model for spray application of rimsulfuron to OPTIMUM® GAT® 

soybeans and OPTIMUM® GAT® field corn has been established, refined and included in

Figure 1. In establishing the diagram for the conceptual model it was necessary to go through an 

iterative process to identify: (1) likely stressors/exposure pathways and (2) organisms that are 

most relevant and applicable to this assessment. 

E. Analysis Plan 

1. Methods for Conducting Ecological Risk Assessment and Identification of Data Gaps

This document characterizes the environmental fate and effects of rimsulfuron to assess whether 

proposed label new uses of this compound results in potential risk to non-target organisms at 

levels above the Agency’s level of concern (LOC). The primary method used to assess risk in 

this screening-level assessment is the risk quotient (RQ). The RQ is the result of comparing 

measures of exposure to measures of effect. A commonly used measure of exposure is the 

estimated exposure concentration (EEC), and commonly used measures of effect include toxicity 

values such as the LD50 or NOAEC. The resulting RQ is then compared to a specified LOC.

If the RQ exceeds an LOC, then risks are identified.
10

Figure 1. The conceptual model for rimsulfuron.

Rimsulfuron applied on corn and soybeans via ground broadcast and aerial spray Stressor 

Source and 

Transport

Pathways 

Water/

Sediment

Volatilization/

Wind Suspension

Direct 

Deposition

(Parent)

Spray

Drift

(Parent)

Runoff/

Erosion

(Parent + Deg1+2+3)

Source and 

Transport

Pathways

Terrestrial Food 

Residues (Foliage, 

fruits, insets)

Upland 

Foliage/Soil

Riparian/

Wetland 

Foliage/Soil

Groundwater

Terrestrial

Organisms:

Birds, Mammals, 

Reptiles & Insects

Terrestrial 

Upland 

Plants

Wetland/

Riparian 

Plants

Aquatic

Plants

Aquatic 

Invertebrates, 

Vertebrates & 

Amphibians

Exposure

Point

Individual Animals

Reduced survival, 

growth and/or 

reproduction

Individual Plants

Seedling 

emergence and 

/or Vegetative 

vigor

Plant Population

Reduced 

population 

growth

Individual Animals

Reduced survival, 

growth and/or 

reproduction

Leaching/Infiltration

/Percolation

(Parent+Deg1+2+3

Direct Contact & Root Uptake

Gill/Integument

Uptake & Ingestion

Receptors

Attribute

Change

Ingestion & Dermal

Deg1 = IN-70941; Deg2 = IN-70942; Deg3 = IN-E9260

Dotted lines represent unlikely routes of exposure while bold arrows/boxes represent important routes of 
11

Available environmental fate, ecotoxicity, and physicochemical property data were taken from 

previous assessments conducted by EFED. Previously submitted data were not re-evaluated for 

this assessment. Generation of robust RQs is dependent on the quality of data from both fate and 

toxicological studies. The adequacy of the submitted data was evaluated relative to Agency 

guidelines. 

2. Measures to Evaluate Risk Hypotheses and Conceptual Model

a. Measures of Exposure 

Exposure to aquatic plants is assumed to occur through direct contact with contaminated water. 

Aquatic exposures can be estimated from monitoring data or by simulation modeling. In this 

assessment, measures of exposure are made with simulation modeling. Generally, aquatic 

exposure estimates are generated from EFED models and incorporate maximum proposed use 

rates and empirically-derived fate properties. Rimsulfuron aquatic exposure concentrations were 

calculated to capture the proposed new use patterns using Tier II linked PRZM/EXAMS 

modeling. Further details of the exposure models are discussed on the web at:

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

Measures of exposure for terrestrial and semi-aquatic plants are incorporated as part of the model 

TerrPlant. This model uses application rate and a runoff value dependent on solubility. 

b. Measures of Effect

III. ANALYSIS

The measure of effect for aquatic plants is the EC50 for the most sensitive species available. The 

measures of effect for terrestrial and semi-aquatic plants are the seedling emergence EC25 and 

vegetative vigor EC25 for the most sensitive monocot and dicot plant species available. More 

details concerning measures of effects used in this assessment can be found in the Ecological 

Effects Characterization section of this document.

A. Use Characterization

1. Acreage

Currently, rimsulfuron is registered for use on field corn, potatoes, and tomatoes, grapes, citrus, 

tree nuts, and pome/stone fruits. According to the 2007 Census of Agriculture by the USDA, the 

total acreages harvested in 2007 for the various crops were nearly 1.6 million acres of potatoes 

and tomatoes together, 86 million acres of field corn, 1.1 million acres of grapes, 1 million acres 

of citrus, 1.8 million acres of tree nuts, and nearly 1 million acres of pome and stone fruits. 

These figures may underestimate the total application area due to the additional registered uses 

of roadsides and natural area restoration. The new use on OPTIMUM® GAT® soybeans could 

potentially apply rimsulfuron to an additional 64 million acres of cropland, which was harvested 

for soybeans in 2007. Figures 2 and 3 show the USA acreage for the proposed new uses 

(USDA, 
12

NASS../../../../../../../../../Users/Tom/AppData/Local/Temp/notesF17874/(http:/ca.water.usgs.gov/

pnsp/use92/metiram.html) Agriculture Census county-level crop data for 2007).
13

Figure 2. Area planted for all purposes of field corn in 2008 by county.

2. Label

The herbicide formulation (RESOLVETM SG) contains 25.0% of the active ingredient 

rimsulfuron and is proposed to be applied as a water soluble granule through ground broadcast or 

aerial spray. For ground application, the herbicide may be applied as a broadcast spray to 

OPTIMUM® GAT® corn and OPTIMUM® GAT® soybeans for weed control, and may be 

used in combination with other suitable registered pesticides. Applications of the formulation 

may be made pre-plant, pre-emergence, post-emergence, and/or post-harvest. Rainfall or 

irrigation is required to move the herbicide into the soil for root uptake. Residual weed control 

depends on rainfall or sprinkler irrigation for herbicide activation. One single application of 0.5 

to 4 ounces of product in 15 gallons of clean water/acre/year is recommended for treatments. 

Both uses on soybeans and field corn have a maximum use rate of 4 ounces active ingredient per

acre per crop season.
14

Figure 3. Area planted for all purposes of soybeans in 2008 by county.

B. Exposure Characterization 

1. Environmental Fate and Transport Characterization

The fate of rimsulfuron was evaluated by considering previously submitted data on its stability to 

both hydrolysis and direct photolysis and its degradation processes in aqueous phases as well as 

soil and field environments. Rimsulfuron is short-lived in systems examined as it appears to be 

highly affected by hydrolysis, direct photolysis followed by aerobic soil degradation. Table 2

contains a summary of important physiochemical properties of rimsulfuron. 

Table 2. Nomenclature and physicochemical properties of rimsulfuron.

Parameter Value Reference

Chemical Classification Pyrimidinyl Sulfonylurea

Registrant 

Data and 

the Web 1

Molecular Formula C14H17N5O7S2

PC Code 129009

Chemical Name (IUPAC)

1-(4,6-dimethoxypyrimidin-2-yl)-3-(3-ethylsulfonyl-2-

pyridylsulfonyl)urea

Chemical Name (CAS)

N-[[(4,6-dimethoxy-2-pyrimidinyl)amino]carbonyl]-3-

(ethylsulfonyl)-2-pyridine sulfonamide

CAS Number 122931-48-0
15

Parameter Value Reference

Pesticide Classification Herbicide

MRIDs

413563-01

Molecular Weight 431.44

Physical State Solid

pKa 4

Water 

Solubility 

(ppm)

Parent 7,300 @ pH 7/25 oC

IN-70941 0.7 @ pH 7/25 oC

IN-70942 0.2 @ pH 7/25 oC

Vapor pressure (25oC) 1.1x10-8 torr Equal to 1.447x10-11 atms.

Henry's Law Constant 1.40x10-12 atms. m 3 . mole -1 (Calculated)

Octanol/Water Partition, Kow 1 @ pH7 and 87 @ pH 5 (log KOW 0.034 @ pH7 &1.94 @ pH 5) 1 URL: http://www.scorecard.org/chemical-profiles/text-search.tcl?query_string=Rimsulfuron

Rimsulfuron is a soluble compound in water and its low vapor pressure/Henry’s Law constant 

suggests that partitioning into the air, from dry/wet soil may not be an important route of its 

dissipation in the environment. The pKa of rimsulfuron is 4.0 suggesting that it would be anionic 

in soil pHs over 4 and bind weakly to most soil particles (usually negatively charged). Finally, 

the chemical has a Kow <100 suggesting that it will not potentially be bio-concentrated by aquatic 

organisms such as fish.

Fate and transport properties, for rimsulfuron and its major degradates, are based entirely on 

previously submitted studies used in previous section 3 risk assessments. A summary of this 

data is included Table 3. 

Table 3. A summary of the environmental fate data for rimsulfuron.

Parameter Value MRID

Hydrolysis

t1⁄2= 4.5- 4.7days @ 25 oC, pH 5;

t1⁄2= 7.1- 7.3days @ 25 oC, pH 7;

t1⁄2= 4.2- 10.9Hours @ 25 o

C, pH 9.

Major degradates (from contraction of the sulfonurea bridge): IN-70941 

(degrading into IN-70942)

Minor degradates (from cleavage of the sulfonurea bridge): IN-E9260 and 

IN-J290 and IN-T5831 (only @ pH 5).

413563-33,

Acceptable
16

Parameter Value MRID

Direct 

photolysis in 

water

at pH 7

Half-lives in irradiated samples (11.0-12.4 days) were longer than the dark 

controls (6.4-6.5 days) indicating that Direct photolysis is NOT an 

important degradation pathway.

Major and Minor degradates: Similar to hydrolysis although irradiation 

appeared to reduce conversion of the transformation product IN-70941 into IN70942 and/or enhance the degradation of IN-70942. Formation of IN-E9260, 

IN-J290, and the un-identified polar compounds appeared to be enhanced.

419316-08, 

Acceptable

Photolysis on 

soil

Half-lives in irradiated/dark control samples were in the range of 11-12 

days indicating that photolysis on soil is NOT an important degradation 

pathway.

Major and Minor degradates: Similar to hydrolysis although irradiation 

appeared to increase the formation of soluble un-identified polar compounds.

419316-09, 

Acceptable

Aerobic soil 

metabolism

t1⁄2 = 21.3 days for two labels (R2= 0.87-0.94) in Sassafras sandy loam soil from 

Penns Grove, NJ (Sand= 77%, Silt= 14%, Clay 9%, pH 6.7, Organic matter= 

1.1%, CEC= 3.2 meq/100 g).

Major degradates (from contraction of the sulfonurea bridge): IN-70941 

(degrading into IN-70942) plus IN-E9260 (from cleavage of the sulfonurea 

bridge)

Minor degradates (from cleavage of the sulfonurea bridge): IN-J290 and 

IN-T5831.

413563-34, 

Acceptable 

(Partial)

Anaerobic soil 

metabolism

t1⁄2 = 17.9-18.1 days for two labels (R2= 0.91-0.99) in Sassafras sandy loam soil 

from Penns Grove, NJ (same soil used in the aerobic soil study).

Major/Minor degradates: Same as the aerobic soil.

413563-35, 

Acceptable

Aerobic aquatic 

metabolism

t1⁄2 =0.5-2 Days at 25 oC in the water column;

t1⁄2 = 59-77 Days at 5 oC in the water column.

Important Note:

432885-02, 

Supplemental

Calculated half-lives may NOT represent an aerobic aquatic 

system because of exposure to light and the use of extremely diluted sediment. 

Major/Minor degradates: Similar to hydrolysis.

Adsorption/

Desorption 

(Kd and 

Koc in L Kg-1

) 413563-36, 

Acceptable

[Pyrimidine-2-

14C]:

Cecil sandy loam (NC): Kd = 0.23 and Koc= 19

Fargo clay loam (ND): Kd = 1.36 and Koc= 55

Sassafras sandy loam (NJ): Kd = 0.32 and Koc= 55

Flanagan silt loam (IL): Kd = 1.52 and Koc= 61

Terrestrial 

Field/Lysimeter

Dissipation 1

Greenville, MS: t1⁄2 = 09 Days (average in the top 0-3”)

Madera, CA: t1⁄2 = 08 Days (average in the top 0-3”)

Rochelle, IL: t1⁄2 = 18 Days (average in the top 0-3”)

Newark, DE: t1⁄2 = 05 Days (average in the top 0-3”)

Major degradates: IN-70941 (degrading into IN-70942)

Minor degradates: None identified as the bridge-cleavage degradates may 

have fallen below the LOD (LOD=<10% of the applied) 

419316-06,

419316-10, 

Acceptable

Accumulation in Fish: Waived following request (MRID 413563-39) due to low Kow=1 at pH7.

1 The terrestrial field dissipation study for a soil in Newark, Delaware submitted under MRID 419316-10 was 

originally classified as unacceptable study.
17

Based on data summarized in Table 4, the main process involved in rimsulfuron fate in aqueous 

systems is hydrolysis. Its fate in the soil system appears to be also controlled by hydrolysis 

followed by biotic degradation. The chemical has very low affinity to the solid phase in either 

soil or sediment. Therefore, rimsulfuron is expected to be highly mobile in the natural 

environment although its availability for leaching is expected to be limited by its vulnerability to 

degradation. However, leaching is expected to occur in certain environmental conditions such as 

low availability of moisture, cold climatic conditions, sandy soils, and shallow ground water.

1 K d calculated from a 4-hour/4 concentrations adsorption/desorption experiments; 2 K d calculated from R f values using Hamaker equation; 3 ND= No Data; 4 Mobility class as per: McCall, et al. 1980. Estimation of chemical mobility in soil from liquid chromatographic 

retention times. Bull. Environmtal Contamination. Toxicology. 24, 190-195.

appears to only form in acidic media. Therefore, the expected terminal transformation 

products/degradates are the major transformation product IN-70942 and the minor degradation 

product IN-J920. In neutral/acidic media the minor degradate IN-E9260 is expected to be present 

with the minor degradate IN-T5831 being present in only acidic media.

a. Abiotic Degradation

Rimsulfuran hydrolyzed in pH 5, 7, and 9 buffered solutions with half-lives ranging from hours 

(4-11 hours) to days (5-7 days) at 25 ± 1 oC. The rates in hours were observed in alkaline media 

(pH 9) while rates in days were observed in neutral>acidic media. Rates of degradation were 

similar for pyridine and pyrimidine14C labels. Results from both labels suggested that 

contraction of the sulfonurea bridge (transformation into IN-70941) is the major process of 

hydrolytic transformation. In contrast, cleavage of the sulfonurea bridge (degradation into INJ920, IN-E9260 and IN-T5831) appeared to be a minor process of hydrolytic transformation. 

The degradation profile suggests that the transformation product IN-70941 further transforms 

into IN-70942. Additionally, the degradate IN-J920 forms in minor amounts in all tested pHs 

while the degradate IN-E9260 forms in minor amounts at pH 7 and 5. The degradate IN-T5831

Table 4. Mobility of parent rimsulfuron and its transformation products/degradates (Koc values).

Aqueous direct photolysis appears to be an un-important mechanism of transformation of 

rimsulfuron (half-lives in irradiated samples at pH 7= 11.0-12.4 days) were longer than those for 

the dark controls (6.4-6.5 days). The degradation profile is similar to hydrolysis although 

irradiation appeared to reduce conversion of the transformation product IN-70941 into IN-70942 

and/or increase the degradation of IN-70942. Additionally, photolysis appears to enhance the 

formation of IN-E9260, IN-J290, and the un-identified polar compounds. Similarly, photolysis 

Ad/Des Method 1 TLC Method 2

Parent Parent IN-70941 IN-70942 IN-E9260 IN-J290

Cecil sandy loam 19 51 58 41 44 284

Fargo clay loam 55 63 357 317 6 ND 3

Sassafras sandy loam 55 41 79 207 110 ND

Flanagan silt loam 61 74 142 1,398* 6 834

Woodstown sandy loam ND ND ND ND ND 393

Keyport silt loam ND ND ND ND ND 362

Mobility Class 4 Very high-High High- Medium (except *=Low) Medium
18

on soil appeared to be un-important (half-lives in irradiated samples and dark control were 

practically the same) although radiation energy appears to increase the formation of many unidentified polar compounds. At termination of the 27-day experiment, the bound residue ranged 

from 6-7% in irradiated samples compared to 3-4% in dark control with a maximum evolved 

CO2 of nearly 1%. 

As stated above, hydrolysis appears to be the only important abiotic transformation/degradation 

process that is expected to affect rimsulfuron. This is also the case for its 

transformation/degradation products. Examination of hydrolysis at pH 7, reveals that the major 

degradate IN-70941 forms and reaches maximums (13-17%) early (3-7 days) and then declines 

as it transforms into the second major degradate IN-70942 which reaches maximums (81-84%) 

at 30-day (experiment termination) with no decline. The cleavage degradates form as minor 

degradates from which IN-290 reaches a maximum of 7% within the two weeks followed by a 

very slight decline to 6% while IN-E9260 reaches a maximum of 10% at 30-day (experiment 

termination) with no decline.

Soils

Only one study was submitted on aerobic soil metabolism of rimsulfuron covering only one soil 

using two rimsulfuron labels (pyridine and pyrimidine-2-

14C labels). Calculated half-lives for 

the two labels were the same (21.3 days) indicating relatively low persistence in the soil tested. 

The degradation profile for the two labels suggests that rimsulfuron transforms into the major 

transformation product IN-70941 by contraction of the Sulfonurea Bridge. IN-70941 appears to 

transform further into IN-70942. In contrast to hydrolysis, cleavage of the sulfonurea bridge 

appears to be more pronounced in aerobic soil conditions resulting in another major degradate;

IN-E9260. The minor aerobic soil degradates (IN-290 and IN-T5831) are the result of cleavage 

of the sulfonurea bridge. In this study the maximum amount of un-characterized bound residue 

reached 28-33% @ 9 months and declined slightly into 24-27% at the 1-year study termination. 

Evolved CO2 and SO2 reached maximums of 4-8% at study termination.

In the one year aerobic soil system, profiles for formation and decline of transformation 

products/degradates suggest slow decline of the major degradate IN-70941 (reached maximums 

of 41-55% @ 1⁄2-2 months and declined to 30-33% at study termination) and very slow decline of 

the degradates IN-E9260 (reached a maximum of 19% @ 6 months and declined to 16% at study 

termination), IN-290 (reached a maximum of 3% @ 1 month and declined to 1% at study 

termination) and IN-T5831 (reached a maximum of 1% @ 3-9 months and declined to 0.5% at 

study termination). In contrast, the major degradate IN-70942 shows no decline (reached 

maximums of 24-30% at the study termination) reflecting its persistence as it forms from the 

declining transformation product IN-70941.

b. Bio-degradation

Using the same soil, the experiment was repeated with a 10-day aerobic incubation followed by 

60 days of anaerobic incubation. Although anaerobic conditions were not confirmed 

(supplemental study), calculated half-lives were near 19 days, which is comparable to the aerobic 

soil half-life of 20 days. The degradation profiles under anaerobic conditions suggested that the 
19

degradate IN-70941 is less persistent under anaerobic condition than under aerobic condition, 

while IN-70942 and IN-E9260 are persistent and relatively persistent, respectively, in both 

media. In the anaerobic profiles, formation and decline of transformation products/degradates

suggest sharp decline of the major degradate IN-70941, in contrast to the aerobic study (reached 

maximums of 30-32% @ 5-10 days and declined to 6% at study termination), very slow decline 

of the degradates IN-290 (reached a maximum of 8% @ 28 days and declined to 6% at study 

termination), and no decline for the transformation product IN-70942 (same to the aerobic study) 

and the degradates IN-E9260 and IN-T5831 (Maximums of 47-56%, 23%, and 1%, respectively,

at termination). 

Sediment/Water Systems

The only submitted study was an aerobic aquatic study for pH 7.9 pond water/sediment system

(MRID 432885-02). The study was classified supplemental because of the use of small amount 

of the sediment relative to water and the repeated dark/light exposure (experiment should have 

been kept in the dark. The study was conducted under sterile/non-sterile conditions and 

incubation temperatures of 25/5 o

C. On the assumption of minimal effects of light energy 

(MRID 419316-08), the results indicated that abiotic hydrolysis is the important degradation 

pathway of parent rimsulfuron. Half-lives were calculated for the water column and were within 

a range of 0.5-2 days with shorter half-lives being associated with non-sterile conditions. 

Furthermore, low temperature conditions resulted in a significant decrease in the rate of 

degradation (half-lives in the range of 59-77 days at 5 oC). The degradation pattern in the 

aerobic aquatic system was similar to hydrolysis although biodegradation appeared to affect the 

terminal transformation product IN-70942 as it showed its relative susceptibility to 

biodegradation/photolysis (reached a maximum of 98% @ day 7 then declined to 65% @ 6-

month study termination coinciding with an increase in evolved CO2 from <<1% to 10%). The 

pattern of formation and decline for the transformation product IN-70941 suggested its early 

transformation into IN-70942 while degradates IN-E9260/IN-J290 formed at minor amounts

(Maximums of 8/9%) and showed very small/no decline within the 6-month period. This latter 

degradation profile was similar to that observed in hydrolysis/aerobic soil studies.

Adsorption/desorption characteristics for rimsulfuron were studied for four US soils and 

coefficients were calculated based on measurements of radioactivity (not parent) associated with 

solid/water phases (MRID 413563-36). Therefore, the study was considered supplemental as 

results represent adsorption/desorption of parent and any degradate that might have been formed 

within the 4+ hour’s period of incubation. Based on hydrolysis data and reported soil pH values 

(pHs 5.4-7.7), the only degradate that might be present within the 4+ hour’s period of incubation 

is IN-70941 at levels << 10%. Therefore, radioactivity data may be taken to largely represent 

that of parent along with calculated Koc’s. In a separate experiment, mobility of the parent and 

its transformation products/degradates were established using the TLC method (MRID 413563-

37). Although the TLC method is not recommended by the Agency, parent results appeared to 

be comparable to results obtained by the recommended method. Therefore, TLC data may be 

taken to at least indicate mobility of the transformation products/degradates relative to parent. 

All of the results are included in Table 4.

c. Mobility
20

Parent rimsulfuron appears to be highly mobile in tested soils with variable organic carbon (0.6-

2.5%) and clay contents (4-30%) (Koc 19-61 L Kg-1

). Examination of parent data also indicated 

that the adsorption affinity of parent rimsulfuron is directly correlated to organic matter content, 

not correlated with clay content, and that it is not affected by changes in concentration (1/n of the

Freundlich isotherms were not significantly different from 1 for four concentrations: 0.1, 0.5, 1, 

and 5 ppm). In comparison, the two contraction transformation products of rimsulfuron (IN70941/2) and one of the cleavage degradates (IN-E9260) appear to be similar or slightly less 

mobile than their parent (Koc 06- 357 L Kg-1, with the exception of one soil with a Koc value of 

1,398 L Kg-1 “low mobility”) while medium mobility can be assigned to the cleavage degradates 

IN-J290 (Koc 284- 362 L Kg-1). 

d. Field Dissipation

The registrant submitted two terrestrial field dissipation studies which were conducted in steel 

lysimeters (MRIDs 419316-06/10). In these studies, >80% of the applied radioactivity did not 

move below the 6” depth and movement to this depth was observed only after 2-4 months. The 

parent degraded with calculated first order half-lives ranging from 5 days in DE to 18 days in IL. 

Long half-life of parent in the top 0-3” of the soil in IL may have resulted from slower 

degradation attributed to cooler climates. In contrast to parent, the main two transformation 

products IN-J70941/2 were identified and their relative amounts appeared to be related to site 

characteristics. IN-J70941 predominated in the acidic soils of DE and cooler soils of IL 

(maximums of at days). Comparable amounts of both degradates were observed in the 

neutral/alkaline soils of MS and CA. Cleavage degradates were not identified, and as shown in 

aerobic soils, these bridge-cleavage degradates were usually <10% of the applied radioactivity.

f. Transformation Profiles

Available fate and transport data on rimsulfuron indicate that it transforms by sulfonurea bridgecontraction into the major/non-persistent transformation product IN-70941. IN-70941 appears to 

transform further into the major/persistent transformation product IN-70942. In addition, 

cleavage of the sulfonurea bridge produces three degradates: the minor (major in aerobic soil) 

degradate IN-E9260 and the minor degradates IN-J920 and IN-T5831. Registrant’s chemical 

codes and IUPAC names for rimsulfuron transformation products/degradates are included in 

Table 5.

Rimsulfuron structure contains a pyridine ring linked with a substituted pyrimidine ring by a 

sulfonylurea bridge. The main degradation pathway of the chemical is through bridge contraction 

which involves elimination of the sulfonyl and urea groups followed by re-bridging. This 

process results in the formation of the rimsulfuron transformation product IN-70941, which 

further transforms into IN-70942. In addition, another minor degradation pathway is observed 

and it involves degradation of rimsulfuron through sulfonylurea bridge cleavage resulting in the 

formation of the degradate IN-E9260 from the pyridine ring and IN-J290 and IN-T5831 from the 

pyrimidine ring. These two transformation/degradation pathways are illustrated in Figure 4.
21

Table 5. Rimsulfuron transformation products/degradate code/chemical names.

Degradation data suggests that the parent will be relatively short lived in aquatic compartments 

of the environment as it hydrolyzes with a half-life of one week. However, the parent becomes 

relatively more persistent in aerobic/anaerobic soil systems (half-life of 3 weeks) possibly as a 

result of the relative deficiency in water for hydrolysis and the relative persistence to biodegradation. In terms of persistence, the transformation product IN-70941 appears to be unstable 

and transforms into the persistent transformation product IN-70942. From IN-70941, hydrolysis 

produces the highest stable maximum of the degradate IN-70942 (nearly 80%) while aerobic soil 

appears to slow the transformation resulting in a maximum of IN-70942 of nearly 30%. In all 

systems, the three cleavage degradates appear to form in minor amounts (except IN-E9260 in 

aerobic soil) and show no or very slow decline.

2. Measures of Aquatic Exposure for the Ecological Risk Assessment 

Tier II linked PRZM/EXAMS

Surface water EECs for rimsulfuron were obtained by modeling using tier I GENEEC2 and 

because of exceedances, Tier II linked PRZM/EXAMS was finally used. The proposed new use 

patterns include soybeans and the amended tolerance for field corn, therefore several scenarios 

were used to represents these use patterns. Table 6 summarizes the crop use patterns, and 

associated scenarios/parameters used for modeling. 

Applicant's Code IUPAC Chemical Name

(01) IN-70941 N-(4, 6-Dimethoxy-2-pyrimidinyl)-N-((3-ethylsulfonyl)-2-pyridinyl))Urea

(02) In-70942 N-((3-Ethylsulfonyl)-2-pyridinyl)-4, 6-dimethoxy-2-pyrimidineamine)

(03) IN-E9260 3-(Ethylsulfonyl)-2-pyridine sulfonamide

(04) IN-J290 2-Amino-4, 6-dimethoxy pyrimidine

(05) IN-T5831 N-(4, 6-Dimethoxy-2pyrimidinyl) Urea
22

N

S O

O

CH2

H3C

S

O

O

H2N

Figure 4: Transformation/degradation pathways for rimsulfuron in various environmentally 

relevant systems.

Parent Rimsulfuron 

N

S O

O

CH2

H3C

N

N

O

O

H3C

H3C

N

CO

NH2

IN-70941

N

S O

O

CH2

H3C

N

N

O

O

H3C

H3C

NH

N

N

O

O

H3C

H3C

NH2

IN-E9260: Pyridine Sulfonamide IN-J290: Pyrimidine Amine

N

N

O

O

H3C

H3C

NH

CO

NH2

Sulfonurea-Brigde Cleavage (MINOR 

in all systems, Except as indicated)

MAJOR in

Aerobic 

Soil Only

Sulfonurea-Brigde Contraction (MAJOR 

in all systems)

Sulfonylurea Bridge

Pyrimidine Ring Pyridine Ring

N

N

O

O

H3C

H3C

N

H N

S O

O

CH2

H3C

N

H

S

O

O

O
23

Table 6. PRZM/EXAMS modeled crop scenarios/parameters.

Table 6. PRZM/EXAMS modeled crop scenarios/ parameters.

Use Pattern Representative Scenario Application Date: dd/mm Number of Applications & Intervals

DUPONTTM 

OPTIMUM® 

GAT® Corn

IL corn 22-05

One application three weeks 

postemergence for all scenarios (from 

Metadata file)

MS corn 01-05

NC corn 05-05

OH corn 22-05

PA corn 07-05

DUPONTTM 

OPTIMUM® 

GAT® Soybean

MS soybean 07-05

Source: See Appendix

Other input values used in modeling based on the above mentioned assumptions/scenarios are 

included in Table 7.

Table 7. PRZM/EXAMS input parameters for modeling (Aquatic ECO EECs).

Table 7. PRZM/EXAMS input parameters for modeling.

Input Parameter Value* Reference

Chemical Name Rimsulfuron

Output file name RIMSULFU

Molecular Weight (g mole-1) 431.44

Vapor Pressure (torr, at 25°C) 1.1x10 MRIDs: 413563-01 and 419316-02 -8

Henry's Law Constant (Atm m-3 

mole-1) 8.56x10-13 Calculated

Aerobic Soil Metabolism Half-life 

(days) 64

One half-life x 3 (21.3x3; MRID 413563-

34)

Water column Half-life (days)

(Aerobic Aquatic Metabolism halflife) Stable

No aerobic aquatic metabolism data and 

there is significant hydrolysis.

Benthic sediment Half-life (days) 

(Anaerobic Aquatic Metabolism 

half-life) Stable

No anaerobic aquatic metabolism data and 

there is significant hydrolysis.

Application Rate (Kg a.i./ha) 0.0701 0.0626 lb a.i./A

Application Number (Method of 

application) One (aerial) Product Label

Depth of Incorporation (cm) 0 Product Label
24

Table 7. PRZM/EXAMS input parameters for modeling.

Input Parameter Value* Reference

CAM (chemical application 

method) 2 Linear foliar based on crop canopy

IPSCND (disposition of pesticide 

remaining on foliage after harvest) 1

Pesticide remaining on foliage is converted 

to surface application to the top soil layer

Application Efficiency 0.95

95% application efficiency for aerial 

applications

Spray Drift (fraction) 0.05 5% spray drift for aerial applications 

Solubility (ppm) 73,000

10X the value at pH 7 and 25°C of 7,300 

ppm. MRIDs: 41356301

KOC (L Kg-1) 47.5

Average of four values (MRID 413563-36). 

KOC model was determined to be 

appropriate.

Hydrolysis Half-life @ pH 7 (days) 7.2 Average value at pH 7 (MRID 413563-33) 

Direct Aqueous Photolysis Halflife(days) Stable

Maximum dark control corrected value 

(MRID 419316-08)

FEXTRC, Foliar extraction 0.5

EFED guidance on input parameters for 

PRZM/ EXAMS dated 2/28/02

PLDKRT, Decay rate on foliage 0

PLVKRT, Volatilization rate from 

foliage

0

UPTKF, Uptake factor 0

*Fate data values are as per Guidance for Selecting Input Parameters in Modeling the Environmental Fate and 

Transport of Pesticides; Version II, February 28, 2002.

Resultant modeling EEC’s that were used for the ecological risk assessment are summarized in 

Table 8. For reference, an example of a model run is included in Appendix III. 

Table 8. Modeled Ecological EECs (ppb) for Rimsulfuron

Crop Scenario Peak 21-day 60-day

IL corn 0.744 0.326 0.156

MS corn 1.380 0.705 0.291

NC corn 0.459 0.221 0.0930

OH corn 0.578 0.301 0.131

PA corn 0.477 0.238 0.103

MS soybean 1.096 0.513 0.211

The above stated values represent upper-bound estimates of the parent concentrations that might 

be found in aquatic systems due to the use of rimsulfuron on field corn and soybeans. Modeling 
25

is performed using the highest application rates/number and shortest application intervals. 

Therefore, these values represent the highest exposure scenario for the various proposed use 

patterns.

b. Ecological Aquatic Exposure from Monitoring Data

Although rimsulfuron was first registered in 1994, it appears that it was not included in the 

national monitoring program. No monitoring data were found in the NAWQA database at the 

following site.

http://infotrek.er.usgs.gov/traverse/f?p=NAWQA:HOME:2972429206327222289

Monitoring studies were submitted by the registrant on or around 1998, but it appears that the 

studies have not been reviewed.

3. Measure of Terrestrial Exposure

a.

Measures of exposure for terrestrial and semi-aquatic plants are incorporated as part of the model 

TerrPlant. This model uses application rate and a runoff value dependent on solubility. The 

model generates risk quotients for comparison to LOCs.

Terrestrial Exposure Modeling

C. Ecological Effects Characterization

In screening-level ecological risk assessments, effects characterization describes the types of 

effects a pesticide can produce in an aquatic or terrestrial organism. This characterization is 

based on registrant-submitted studies that describe acute and chronic effects toxicity information

for various aquatic and terrestrial animals and plants. Toxicity testing reported in this section 

does not represent all species of bird, mammal, or aquatic organism. Since not all wildlife 

species can ever be tested, representatives from large groups of species must be used. Generally, 

only two surrogate species for both freshwater fish and birds are used to represent all freshwater 

fish (2000+) and bird (680+) species in the United States. For mammals, acute studies are 

usually limited to the Norway rat or the house mouse. Estuarine/marine testing is usually limited 

to a crustacean, a mollusc, and a fish. Also, neither reptiles nor amphibians are tested. The 

assessment of risk or hazard makes the assumption that avian and reptilian toxicity are similar. 

The same assumption is used for fish and amphibians. Generally, the most toxic endpoints for 

the technical grade active ingredient (TGAI) are used in the assessment to represent each group 

of organism. 

Toxicity to Terrestrial Organisms

Rimsulfuron is considered practically non-toxic to most terrestrial animals. This includes birds 

(mallard LD50 > 2000 mg/kg; bobwhite quail LD50 > 2250 mg/kg; mallard and bobwhite quail 
26

LC50’s > 5620 ppm), mammals (rat LD50 > 5000 mg/kg), and bees (LD50 > 100 ug/bee). The 

NOAEC in an avian reproduction study with bobwhite quail is 1250 ppm. 

In contrast, plants are extremely sensitive to rimsulfuron. For seedling emergence, plant height 

was the most sensitive parameter (EC25 = 0.0006 lb ai/A for the most sensitive monocot and 

0.00013 for the most sensitive dicot). For vegetative vigor, root weight was the most sensitive 

parameter (EC25 = 0.00004 lb ai/A for the most sensitive monocot and 0.00003 lb ai/A for the 

most sensitive dicot). 

Toxicity to Aquatic Organisms

Rimsulfuron is considered practically non-toxic to most aquatic animals. This includes 

freshwater fish (rainbow trout LC50 > 390 ppm; bluegill sunfish LC50 > 390 ppm), freshwater 

invertebrates (Daphnia magna LC50 > 360 ppm), and estuarine/marine organisms (sheepshead 

minnow LC50 > 110 ppm; mysid shrimp LC50 > 110 ppm; oyster shell deposition EC50 > 120 

ppm). In contrast, vascular plants are extremely sensitive to rimsulfuron. The most sensitive 

aquatic plant tested is duckweed (EC50 = 11.6 ppb).

IV. RISK CHARACTERIZATION

A. Risk Estimation 

Since rimsulfuron is considered practically non-toxic to terrestrial and aquatic animals, the focus 

of this risk assessment is on terrestrial and aquatic plants which are highly sensitive. 

The model TerrPlant was run to develop risk quotients (RQs) for terrestrial plants. Emergence 

RQ’s for areas adjacent to treatment sites (EEC/seedling emergence EC25) range from 6.25 –

10.42 for monocots and 28.85 – 48.08 for dicots. Emergence RQs for semi-aquatic areas 

(EEC/seedling emergence EC25) range from 53.12 – 57.29 for monocots and 245.19 – 264.42 for 

dicots. Drift RQs (drift EEC/vegetative vigor EC25) range from 15.62 – 78.12 for monocots and 

20.83 – 104.17 for dicots. See the TerrPlant printout for further details (Appendix II).

The above RQs for terrestrial plants all far exceed the Acute Risk LOC of 1 for terrestrial and 

semi-aquatic non-endangered plants. Although NOAEC values are not available to develop 

specific RQ values for endangered species, they would be even further exceeded for endangered 

plants. This exceedance can be expected because NOAEC values would be lower than the EC25

values that are used for non-endangered plants. 

To develop risk quotients (RQs) for non-endangered aquatic plants, the highest peak aquatic 

EEC across all crops (1.38 ppb, MS corn scenario, PRZM/EXAMS) is compared to the lowest 

aquatic plant EC50 (11.6 ppb). This produces an RQ of 0.12. Thus, the LOC of 1 is not 

exceeded for non-endangered aquatic plants. For endangered aquatic plants, this EEC is 

compared to the NOAEC (0.09 ppb). Table 9 shows that this comparison results in an RQ of 
27

15.3, indicating that the endangered species LOC of 1 is exceeded. All six of the scenarios (see 

Exposure Characterization) result in exceedance of the aquatic plant endangered species LOC.

Table 9. Aquatic Plant Risk Quotients (Endangered Species). 

Crop Scenario Peak EEC (ppb) Risk Quotient

IL corn 0.744 8.27

MS corn 1.380 15.3

NC corn 0.459 5.10

OH corn 0.578 6.42

PA corn 0.477 5.30

MS soybean 1.096 12.2

B. Risk Description 

The risk hypothesis states that the use of rimsulfuron could expose sensitive terrestrial and 

aquatic plants, resulting in adverse effects. Based on available ecotoxicity data and predicted 

environmental exposures, this ecological risk assessment supports the presumption of risk to 

sensitive terrestrial and aquatic plants, including federally-listed species. 

As shown above under Risk Estimation, terrestrial plant risk quotients far exceed LOC’s for even 

non-endangered species. This is true for adjacent areas and semi-aquatic areas (calculation uses 

seedling emergence EC25), and areas affected by drift (calculation uses vegetative vigor EC25), 

and is true for both monocots and dicots. As indicated, endangered species LOCs are considered 

exceeded as well, since the threshold for them is lower. 

For aquatic plants, rimsulfuron EEC’s do not exceed the LOC for non-endangered plants. 

However, this information is derived from a study with uncertainty around the measured 

concentrations to which Lemna gibba was exposed, thereby introducing uncertainty into the RQ 

estimate (MRID 42471308). The RQ derived from this study may underestimate risk to aquatic 

vascular plants. In contrast to non-endangered plant species, the endangered species LOC is 

exceeded for all six of the scenarios used to evaluate the proposed new use in soybean and new 

tolerance limit in field corn.

EFED assesses acute risk but not chronic or reproductive effects to terrestrial and aquatic plants. 

Rimsulfuron may therefore pose other risks that have not been assessed by EFED. Other 

sulfonyl urea herbicides have adversely affected plant reproduction such as seed formation and 

the production of viable seed (Chlorsulfuron Registration Eligibility Decision). Rimsulfuron is 

similar in structure and activity to other sulfonyl urea herbicides. Given this similarity, 

rimsulfuron may also inhibit various aspects of plant reproduction in both endangered and nonendangered plants at realistic environmental concentrations. 
28

EFED’s Ecological Incident Information System (EIIS) was checked for reported incidents of 

adverse affects. As of 4/14/09, there were 25 incidents shown where all incidents involved 

effects on plants. While many were claims of treated crop damage, there were seven listed as 

being due to drift or spray drift. Of these seven, three have been categorized as Possible and two 

as Probable. The AgDrift model, which EFED currently uses to assess risk from pesticide drift, 

confirms the risk posed by pesticide movement offsite to both terrestrial endangered and nonendangered terrestrial plants and endangered aquatic plants, Figure 5. The application 

parameters used in the model, e.g. boom height and spray type, are conservative but within the 

recommendations of the label. According to this screening model, risk to terrestrial nonendangered and endangered plants is above the level of concern (value of 1) beyond 900 ft from 

the edge of the field for both aerial and ground applications. However, risk to aquatic 

endangered plants is above the level of concern only up to 300 ft beyond the field edge for aerial 

applications and 100 ft for ground applications. While EFED’s risk assessment methods assume 

that pesticides can move off-site and potentially affect off-site non-target organisms (in addition 

to on-site affects), reported incidents (when available) can help confirm this risk. 

Endocrine Disruption

EPA is required under the FFDCA, as amended by FQPA, to develop a screening program to 

determine whether certain substances (including all pesticide active and other ingredients) “may 

have an effect in humans that is similar to an effect produced by a naturally occurring estrogen, 

or other such endocrine effects as the Administrator may designate.” Following the 

recommendations of its Endocrine Disruptor Screening and Testing Advisory Committee 

(EDSTAC), EPA determined that there were scientific bases for including, as part of the 

program, androgen and thyroid hormone systems, in addition to the estrogen hormone system. 

EPA also adopted EDSTAC’s recommendation that the Program include evaluations of potential 

effects in wildlife. When the appropriate screening and/or testing protocols being considered 

under the Agency’s Endocrine Disrupter Screening Program (EDSP) have been developed and 

vetted, Rimsulfuron may be subjected to additional screening and/or testing to better characterize 

any effects related to endocrine disruption.

C. Endangered Species Assessment

The following section discusses the screening-level assessment for federally-listed threatened 

and endangered species.

Listed Species

The Agency’s levels of concern for endangered and threatened species are exceeded for direct 

effects to federally-listed terrestrial and aquatic plants. The LOC is also exceeded for nonendangered terrestrial plants. As a result, there is also a concern for potential indirect effects to 

listed species that depend on terrestrial and/or aquatic plants.

a. Action Area

For listed species assessment purposes, the action area is considered to be the area affected 

directly or indirectly by the Federal action and not merely the immediate area involved in the 
29

action. At the initial screening-level, the risk assessment considers broadly described taxonomic 

groups and so conservatively assumes that listed species within those broad groups are 

collocated with the pesticide treatment area. This means that terrestrial plants and wildlife are

assumed to be located on or adjacent to the treated site and aquatic organisms are assumed to be 

located in a surface water body adjacent to the treated site. The assessment also assumes that the 

listed species are located within an assumed area which has the relatively highest potential 

exposure to the pesticide, and that exposures are likely to decrease with distance from the 

treatment area. Section II.A of this risk assessment presents the pesticide use sites that are 

employed to establish initial location of species with treatment areas.

b. Taxonomic Groups Potentially at Risk

If the assumptions associated with the screening-level action area result in RQs that are below 

the listed species LOCs, a "no effect" determination conclusion may be made with respect to 

listed species in that taxa (for direct effects), and no further refinement of the action area is 

necessary (assumptions include a complete data set for that taxa). Furthermore, RQs below the 

listed species LOCs for a given taxonomic group indicate no concern for indirect effects upon 

listed species that depend upon the taxonomic group covered by the RQ as a resource. However, 

in situations where the screening assumptions lead to RQs in excess of the listed species LOCs 

for a given taxonomic group, a potential for a "may affect" conclusion exists and may be 

associated with direct effects on listed species belonging to that taxonomic group or may extend 

to indirect effects upon listed species that depend upon that taxonomic group as a resource. In 

such cases, additional information on the biology of listed species, the locations of these species, 

and the locations of use sites could be considered along with available information on the fate 

and transport properties of the pesticide to determine the extent to which screening assumptions 

regarding an action area apply to a particular listed organism. These subsequent refinement steps 

could consider how this information would impact the action area for a particular listed organism 

and may potentially include areas of exposure that are downwind and downstream of the 

pesticide use site.

c. Indirect Effects Analysis

Pesticides have the potential to exert indirect effects upon the listed organisms by, for example, 

perturbing forage or prey availability, altering the extent of nesting habitat, and creating gaps in 

the food chain. In conducting a screen for indirect effects, direct effect LOCs for each 

taxonomic group are used to make inferences concerning the potential for indirect effects upon 

listed species that rely upon non-endangered organisms in these taxonomic groups as resources 

critical to their life cycle. These effects are summarized in Table 10. Species specific concerns 

for rimsulfuron indirect effects to listed organisms will require a determination of the 

coincidence of rimsulfuron use with locations of listed species and the biologically based 

resources upon which they depend.
30

0

5

10

15

20

25

Monocot

Dicot

0

20

40

60

80

100

Monocot

Dicot

0

0.5

1

1.5

2

2.5

3

0

1

2

3

4

5

0 200 400 600 800 1000

Terrestrial Scenario Aerial Application

Terrestrial Scenario Ground Application

Aquatic Scenario Aerial Application

Aquatic Scenario Ground Application

Distance from Edge of Field (ft)

Endangered Plant RQ Non-Endangered Plant RQ

0

5

10

15

20

25

Monocot

Dicot

0

20

40

60

80

100

Monocot

Dicot

0

0.5

1

1.5

2

2.5

3

0

1

2

3

4

5

0 200 400 600 800 1000

Terrestrial Scenario Aerial Application

Terrestrial Scenario Ground Application

Aquatic Scenario Aerial Application

Aquatic Scenario Ground Application

Distance from Edge of Field (ft)

Endangered Plant RQ Non-Endangered Plant RQ

Figure 5: Risk Quotient (EEC/EC25 for terrestrial scenario, EEC/NOAEC for aquatic scenario)

over distance from the edge of the field by exposure scenario. The exposure concentrations are 

based on the AgDrift screening tool with an application rate of 0.0625 lbs a.i./acre, boom height 

set to high and droplet size of very fine to fine for ground applications, and droplet size of fine to 

medium for aerial applications.
31

Based on the proposed usage of rinsulfuron, it appears at present that the principal risk of 

rimsulfuron is direct acute risk to plants and indirect risk to species that depend on plants. The 

screening level risk assessment also shows that there is a concern for indirect effects to listed 

species that may depend upon terrestrial and/or aquatic plants for their survival. As described 

above, acute RQs for terrestrial and aquatic plants exceed endangered species LOCs. Acute RQs 

for terrestrial plants also exceed the LOC for non-endangered species.

The Agency’s levels of concern for endangered and threatened species are exceeded for direct 

effects to federally-listed terrestrial and aquatic plants. The LOC is also exceeded for nonendangered terrestrial plants. As a result, there is also a concern for potential indirect effects to 

all species that depend on plants. The Program LOCATES was run to identify those species that 

are located in counties with potential rimsulfuron use, and that could be affected either directly 

or indirectly (summarized in Tables 11 – 14, listed in Appendix III). 

d. Data Related to Under-represented Taxa

No data are currently available in EFED that would indicate that taxa under-represented among 

those used for risk quotient calculations are more sensitive to rimsulfuron. 

Table 10. Potential Effects to Federally Listed Taxa Associated with Direct or Indirect Effects from the 

Proposed Application of Rimsulfuron on Soybeans and Field Corn.

Listed Taxon Direct 

Effects

Uses of Concern Indirect 

Effects

Uses of Concern

Terrestrial and semiaquatic plants -

monocots

Yes Soybeans and Field Corn No None

Terrestrial and semiaquatic plants - dicots Yes Soybeans and Field Corn No None

Terrestrial invertebrates No None Yes1 Soybeans and Field Corn

Birds No None Yes1 Soybeans and Field Corn

Terrestrial phase 

amphibians No None Yes1 Soybeans and Field Corn

Reptiles No None Yes1 Soybeans and Field Corn

Mammals No None Yes1 Soybeans and Field Corn

Aquatic vascular plants Yes Soybeans and Field Corn No None

Freshwater fish No None Yes1 Soybeans and Field Corn

Aquatic phase 

amphibians No None Yes1 Soybeans and Field Corn

Freshwater crustaceans No None Yes1 Soybeans and Field Corn

Mollusks No None Yes1 Soybeans and Field Corn

Marine/estuarine fish No None Yes1 Soybeans and Field Corn

Marine/estuarine 

invertebrates No None Yes1 Soybeans and Field Corn

Potential indirect effects on a taxon attributable to: 1 direct effects on terrestrial and aquatic plants
32

Table 11. Tabulation by State and Taxonomic Group of Listed Species that Occur in Rimsulfuron 

Use Areas for Corn for silage or greenchop.

No species exclusions corn for silage or greenchop

Minimum of 1 Acre All Medium Types Reported Amphibian Arachnid Bird Bivalve Conf/cycds Crustacean Dicot

FernsFishGastropodInsectLichenMammalMarine MonocotReptile

AL 2 0 3 26 0 1 10 3 14 10 0 0 4 0 3 5

AR 0 0 2 4 0 1 2 0 2 0 0 0 2 0 0 0

AZ 2 0 7 0 0 0 8 0 15 0 0 0 8 0 2 1

CA 5 0 14 0 0 9 118 0 25 0 13 0 19 1 12 7

CO 0 0 2 0 0 0 8 0 5 0 1 0 2 0 1 0

CT 0 0 2 1 0 0 1 0 1 0 1 0 1 0 1 1

DE 0 0 1 0 0 0 0 0 1 0 0 0 1 0 2 1

FL 1 0 8 7 1 1 38 0 3 0 1 1 8 1 2 9

GA 1 0 2 15 1 0 10 2 11 0 1 0 2 1 6 1

HI 0 0 12 0 0 0 87 7 0 38 0 0 1 1 7 2

IA 0 0 2 2 0 0 3 1 2 1 0 0 1 0 2 0

ID 0 0 1 0 0 0 1 0 7 6 0 0 3 0 0 0

IL 0 0 2 7 0 1 7 0 1 1 2 0 2 0 2 0

IN 0 0 2 11 0 0 4 0 0 0 2 0 2 0 1 1

KS 0 0 3 0 0 0 1 0 4 0 1 0 2 0 1 0

KY 0 0 6 22 0 1 9 0 5 0 1 0 3 0 0 0

LA 0 0 2 1 0 0 1 1 2 0 0 0 1 1 0 2

MA 0 0 3 0 0 0 1 0 1 0 3 0 1 0 2 2

MD 0 0 1 1 0 0 4 0 2 0 2 0 2 0 2 1

ME 0 0 2 0 0 0 1 0 2 0 0 0 1 0 2 0

MI 0 0 2 2 0 0 4 1 0 0 4 0 3 0 3 1

MN 0 0 1 2 0 0 2 0 1 0 1 0 2 0 2 0

MO 0 0 2 6 0 1 6 0 7 0 2 0 2 0 1 0

MS 0 0 3 9 0 0 2 1 3 0 0 0 2 0 0 7

MT 0 0 3 0 0 0 2 0 4 0 0 0 3 0 0 0

NC 0 1 1 7 0 0 18 0 4 1 1 1 4 1 4 2

ND 0 0 3 0 0 0 0 0 1 0 0 0 0 0 1 0

NE 0 0 3 0 0 0 2 0 2 0 1 0 1 0 1 0

NH 0 0 0 1 0 0 1 0 0 0 1 0 1 0 1 0

NJ 0 0 1 0 0 0 2 0 1 0 0 0 1 0 3 1

NM 1 0 6 0 0 2 10 0 13 5 0 0 5 0 0 1

NV 0 0 0 0 0 0 8 0 14 0 2 0 0 0 1 1

NY 0 0 2 1 0 0 4 1 1 1 1 0 1 0 1 1

OH 0 0 1 6 0 0 4 0 1 0 4 0 2 0 2 2

OK 0 0 5 2 0 0 0 0 4 0 1 0 3 0 1 0

OR 0 0 4 0 0 1 9 0 19 0 2 0 1 0 2 0

PA 0 0 1 2 0 0 0 0 0 0 0 0 2 0 2 1

RI 0 0 1 0 0 0 1 0 1 0 1 0 1 0 1 0

SC 1 0 4 1 0 0 11 1 1 0 0 0 1 3 3 5

SD 0 0 3 0 0 0 0 0 2 0 1 0 1 0 1 0

TN 0 1 2 36 0 1 16 1 16 3 0 1 3 0 1 0

TX 4 10 12 0 0 1 14 0 5 1 9 0 4 0 2 6

UT 0 0 2 0 0 0 19 0 8 0 0 0 2 0 2 1

VA 1 0 2 21 0 2 13 0 7 1 3 0 5 0 4 1

VT 0 0 0 1 0 0 1 0 0 0 0 0 1 0 1 0

WA 0 0 4 0 0 0 5 0 19 0 0 0 4 0 0 0

WI 0 0 3 2 0 0 4 0 0 0 2 0 2 0 2 0

WV 1 0 0 5 0 0 4 0 0 1 0 0 5 0 1 0

WY 0 0 0 0 0 0 2 0 0 0 0 0 4 0 0 0
33

Table 12. Tabulation by State and Taxonomic Group of Listed Species that Occur in Rimsulfuron 

Use Areas for Corn for Grain.

No species exclusions Corn for grain

Minimum of 1 Acre All Medium Types Reported Amphibian Arachnid Bird Bivalve Conf/cycd Crustacean Dicot

FernsFishGastropodInsectLichenMammalMarineMonocotReptile

AL 2 0 3 30 0 1 10 3 15 10 0 0 4 0 3 5

AR 0 0 2 6 0 0 3 0 2 1 1 0 1 0 0 0

AZ 2 0 6 0 0 0 12 0 15 1 0 0 9 0 2 2

CA 6 0 12 0 1 8 102 0 24 1 12 0 16 2 12 7

CO 0 0 2 0 0 0 4 0 5 0 0 0 2 0 1 0

CT 0 0 2 1 0 0 1 0 1 0 0 0 1 0 1 1

DE 0 0 1 0 0 0 0 0 1 0 0 0 1 0 2 1

FL 1 0 8 7 1 1 40 0 4 0 1 1 7 1 2 9

GA 1 0 4 16 1 0 11 2 11 0 1 0 3 1 6 2

HI 0 1 26 0 0 1 200 11 0 39 1 0 1 1 19 2

IA 0 0 2 2 0 0 3 1 2 1 0 0 1 0 2 0

ID 0 0 0 0 0 0 1 0 8 6 0 0 3 0 0 0

IL 0 0 2 7 0 1 7 0 1 1 2 0 2 0 2 0

IN 0 0 2 11 0 0 4 0 0 0 2 0 2 0 1 1

KS 0 0 3 0 0 0 1 0 4 0 1 0 2 0 1 0

KY 0 0 6 22 0 1 10 0 5 0 1 0 3 0 0 0

LA 0 0 5 3 0 0 2 1 2 0 0 0 1 1 0 7

MA 0 0 3 0 0 0 0 0 1 0 1 0 1 0 2 2

MD 0 0 1 1 0 0 4 0 2 0 2 0 2 0 2 1

ME 0 0 2 0 0 0 1 0 2 0 0 0 1 0 2 0

MI 0 0 2 2 0 0 4 1 0 0 4 0 3 0 3 1

MN 0 0 1 2 0 0 2 0 1 0 1 0 2 0 2 0

MO 0 0 2 6 0 1 7 0 7 1 2 0 2 0 1 0

MS 1 0 5 9 0 0 2 1 3 0 0 0 3 0 0 7

MT 0 0 3 0 0 0 2 0 3 0 0 0 3 0 0 0

NC 0 1 4 8 0 0 21 0 4 1 1 1 4 1 5 5

ND 0 0 3 0 0 0 0 0 1 0 0 0 0 0 1 0

NE 0 0 3 0 0 0 2 0 2 0 1 0 1 0 1 0

NH 0 0 0 1 0 0 1 0 0 0 1 0 1 0 1 0

NJ 0 0 2 0 0 0 2 0 1 0 0 0 1 0 3 1

NM 1 0 6 0 0 1 7 0 7 2 0 0 5 0 0 1

NV 0 0 0 0 0 0 0 0 3 0 0 0 0 0 0 0

NY 0 0 2 1 0 0 4 1 1 1 1 0 1 0 1 1

OH 0 0 1 6 0 0 4 0 1 0 4 0 2 0 2 2

OK 0 0 6 2 0 0 0 0 4 0 1 0 3 0 2 0

OR 0 0 3 0 0 0 6 0 20 0 0 0 1 0 0 0

PA 0 0 1 2 0 0 0 0 0 0 0 0 2 0 2 1

RI 0 0 1 0 0 0 1 0 1 0 1 0 0 0 0 0

SC 1 0 4 1 0 0 12 1 1 0 0 1 1 3 6 5

SD 0 0 3 0 0 0 0 0 2 0 1 0 1 0 1 0

TN 0 1 3 38 0 1 16 1 16 3 0 1 3 0 2 0

TX 4 10 12 0 0 1 25 0 7 1 9 0 5 0 2 6

UT 0 0 1 0 0 0 15 0 6 0 0 0 2 0 2 1

VA 1 0 2 21 0 2 13 0 7 1 3 0 5 0 4 1

VT 0 0 0 1 0 0 1 0 0 0 0 0 1 0 1 0

WA 0 0 2 0 0 0 4 0 12 0 0 0 3 0 0 0

WI 0 0 3 2 0 0 4 0 0 0 2 0 2 0 2 0

WV 1 0 0 5 0 0 4 0 0 1 0 0 5 0 1 0

WY 0 0 0 0 0 0 2 0 0 0 0 0 4 0 0 0
34

Table 13. Tabulation by State and Taxonomic Group of Listed Species that Occur in Rimsulfuron Use Areas 

for Soybeans for Beans.

No species exclusions. Soybeans for bean

Minimum of 1 Acre All Medium Types Reported Amphibian Arachnid Bird Bivalve Conf/cycd Crustacean

DicotFernsFishGastropodInsectLichenMammalMarineMonocotReptile

AL 2 0 3 29 0 1 9 2 15 10 0 0 4 2 3 8

AR 0 0 2 5 0 1 3 0 3 1 1 0 1 0 0 0

CO 0 0 1 0 0 0 0 0 1 0 0 0 1 0 0 0

CT 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 6

DE 0 0 1 0 0 0 0 0 1 0 0 0 1 3 2 6

FL 1 0 7 7 1 0 23 0 2 0 0 1 4 5 1 8

GA 1 0 4 15 1 0 9 2 11 0 0 0 2 4 4 6

HI 0 1 13 0 0 1 72 2 0 1 0 0 1 2 11 4

IA 0 0 2 2 0 0 3 1 2 1 0 0 1 0 2 0

IL 0 0 2 7 0 1 7 0 1 1 2 0 2 0 2 0

IN 0 0 2 11 0 0 4 0 0 0 2 0 2 0 1 1

KS 0 0 3 0 0 0 1 0 4 0 1 0 2 0 1 0

KY 0 0 6 22 0 1 10 0 5 0 1 0 3 0 0 0

LA 0 0 5 3 0 0 2 0 2 0 0 0 1 3 0 6

MA 0 0 2 0 0 0 0 0 1 0 1 0 1 2 1 5

MD 0 0 1 1 0 0 4 0 2 0 2 0 2 3 2 5

ME 0 0 2 0 0 0 1 0 1 0 0 0 1 3 2 1

MI 0 0 2 2 0 0 3 0 0 0 4 0 3 0 3 1

MN 0 0 1 2 0 0 2 0 1 0 1 0 2 0 2 0

MO 0 0 2 6 0 1 7 0 7 1 2 0 2 0 1 0

MS 0 0 5 9 0 0 2 1 3 0 0 0 3 2 0 9

MT 0 0 3 0 0 0 0 0 1 0 0 0 3 0 0 0

NC 0 1 4 8 0 0 20 0 3 0 1 1 2 4 5 5

ND 0 0 3 0 0 0 0 0 1 0 0 0 0 0 1 0

NE 0 0 3 0 0 0 1 0 2 0 1 0 1 0 1 0

NH 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 1

NJ 0 0 2 0 0 0 2 0 1 0 0 0 1 3 3 5

NM 0 0 1 0 0 0 0 0 0 0 0 0 1 0 0 0

NY 0 0 2 1 0 0 4 1 1 1 1 0 1 3 1 6

OH 0 0 1 6 0 0 4 0 1 0 4 0 2 0 2 2

OK 0 0 6 2 0 0 0 0 4 0 1 0 3 0 2 0

PA 0 0 1 2 0 0 0 0 0 0 0 0 2 0 2 1

RI 0 0 1 0 0 0 1 0 1 0 1 0 0 3 0 4

SC 1 0 3 1 0 0 12 1 1 0 0 1 1 4 6 6

SD 0 0 3 0 0 0 0 0 2 0 1 0 1 0 1 0

TN 0 1 3 37 0 1 16 1 15 3 0 1 3 0 2 0

TX 3 7 12 0 0 1 14 0 3 0 6 0 4 2 2 6

VA 1 0 2 16 0 2 12 0 6 1 2 0 5 3 4 5

VT 0 0 0 1 0 0 1 0 0 0 0 0 1 0 0 0

WI 0 0 3 2 0 0 4 0 0 0 2 0 2 0 2 0

WV 1 0 0 1 0 0 3 0 0 1 0 0 4 0 1 0
35

e. Critical Habitat

In the evaluation of pesticide effects on designated critical habitat, consideration is given to the 

physical and biological features (constituent elements) of a critical habitat identified by the U.S 

Fish and Wildlife and National Marine Fisheries Services as essential to the conservation of a 

listed species and which may require special management considerations or protection. The 

evaluation of impacts for a screening level pesticide risk assessment focuses on the biological 

features that are constituent elements. It is accomplished using the screening-level taxonomic 

analysis (RQs) and listed species levels of concern that are used to evaluate direct and indirect 

effects to listed organisms.

The screening-level risk assessment has identified potential concerns for indirect effects on listed 

species for those organisms dependant upon terrestrial and/or aquatic plants. In light of the 

potential for indirect effects, the next step for EPA and the Service(s) is to identify which listed 

species and critical habitat are potentially implicated. Analytically, the identification of such 

species and critical habitat can occur in either of two ways. First, the agencies could determine 

whether the action area overlaps critical habitat or the occupied range of any listed species. If so, 

EPA would examine whether the pesticide's potential impacts on non-endangered species would 

affect the listed species indirectly or directly affect a constituent element of the critical habitat. 

Alternatively, the agencies could determine which listed species depend on biological resources, 

or have constituent elements that fall into, the taxa that may be directly or indirectly impacted by 

the pesticide. Then EPA would determine whether use of the pesticide overlaps the critical 

habitat or the occupied range of those listed species. 

At present, the information reviewed by EPA does not permit use of either analytical approach to 

make a definitive identification of species that are potentially impacted indirectly or critical 

habitats that is potentially impacted directly by the use of the pesticide. EPA and the Service(s) 

are working together to conduct the necessary analysis.

C. Uncertainties

In this ecological risk assessment, the uncertainties are listed as follows:

(1) Environmental Fate data availability

Table 14. Tabulation by State and Taxonomic Group of Listed Species 

that Occur in Rimsulfuron Use Areas for Soybeans for Beans.

No species exclusions corn (PR)

Minimum of 1 Acre All Medium Types Reported

Puerto Rico

Amphibian Bird Dicot Ferns Marine Monocot Reptile

PR 3 7 28 7 1 4 7
36

In a review dated March 14, 2007 (D326660), EFED requested the new studies indicated below. 

Based on the current status for rimsulfuron, data gaps exist, and the registrant is requested to 

satisfy them by conducting new studies as follows:

• One aerobic soil metabolism study, using two US soils from relevant use areas

(§835.4100)

• One anaerobic aquatic metabolism (relevant natural water sediment system) (§835.4400)

• One aerobic aquatic metabolism (relevant natural water sediment system) (§835.4300)

The above stated fate and transport studies are needed because it is necessary to represent soils 

from the wide use areas of the US. One aerobic soil metabolism is available (MRID 41356334, 

Acceptable), which was conducted in one soil. Since rimsulfuron use areas are extensive, studies 

conducted in two relevant US soils were requested. No anaerobic aquatic metabolism study has 

been submitted, and light exposure was used in a previously submitted aerobic aquatic 

metabolism study, which was deemed supplemental (MRID 43288502). A new study is 

required.

(2) Ecotoxicity data availability/quality

Data on the ecotoxicity of degradates is not available, including phytotoxicity. The following 

studies on the transformation product/degradate IN-70942 have not been submitted but are 

needed for ecological risk assessment:

• Freshwater fish early life-stage (§850.1400)

• aquatic invertebrate life-cycle (§850.1300) 

Since the EFED LOC’s for plants are based on acute risk, the plant risk assessment is also based 

on acute risk (to parent rimsulfuron). While studies of the toxicity of the degradates IN-70941, 

IN-70942, and IN-E9260 to both terrestrial and aquatic plants have been submitted, they have 

not yet been reviewied. However, if the degradates are similarly phytotoxic, the period of 

phytotoxicity in the field (in both terrestrial and aquatic environments) would be longer. 

(3) Lack of developed risk evaluation methods

The Agency currently does not perform assessments for chronic risk to plants. EFED uses 

adverse effect incident data in evaluating the chemical’s risk.
37

REFERENCES

Environmental Fate

DER (data evaluation report) for MRID: 41931602

Citation: Brennan, D. (1990) DPX-E9636: Physical and Chemical Characteristics : Room 

Temperature Storage Stability: Lab Project Number: AMR- 1816-90. Unpublished study 

prepared by E. I. du Pont de Nemours and Co. 16 p. 

DER for MRID: 41356301

Citation: Brennan, D. (1989) DPX-E9636: Product Identity and Composition, Analysis and 

Certification of Product Ingredients and Physical and Chemical Characteristics: Lab Project 

Number: E9636.A. Unpublished study prepared by E. I. du Pont de Nemours and Co., Inc. 193 p.

DER for MRID: 41356333

Citation: Horne, P.; Boucher, C. (1989) Hydrolysis of [Pyridine-2-Cardon 14] DPX-E9636 and 

[Pyrimidine-2-Carbon 14]DPX-E9636 in Buffer Solu- tions of 5, 7, and 9: Lab Project Number: 

AMR-1221-88. Unpub- lished study prepared by E. I. du Pont de Nemours & Co., Inc. 46 p. 

DER for MRID: 41931606

Citation: Naidu, M. (1991) Field Soil Dissipation Study of ?Pyridine-2-14C| DPX-E9636 and 

?Pyrimidine-2-14C|DPX-E9636: Lab Project Number: AMR-1451-89. Unpublished study 

prepared by E. I du Pont de Nem- ours and Co. 142 p. 

DER for MRID: 41931608

Citation: Horne, P.; Boucher, C. (1989) Photodegradation of ?Pyridine-2-14C| DPX-E9636 and 

?Pyrimidine-2-14C| in Water(Conducted in Sunlight) : Lab Project Number: AMR-1220-88. 

Unpublished study prepared by E. I. du Pont de Nemours and Co. 59 p. 

DER for MRID: 41931609

Citation: Brown, A.; Young, G. (1989) Photodegradation of ?Pyridine-2-14C|DPX -E9636 and 

?Pyrimidine-2-14C|DPX-E9636 on Soil: Lab Project Num- ber: AMR-1219-88. Unpublished 

study prepared by E. I du Pont de Nemours and Co. 54 p. 

DER for MRID: 41931610

Citation: Naidu, M. (1990) Field Soil Dissipation Study of ?Pyridine-2-14C| DPX-E9636 and 

?Pyrimidine-14C|DPX-E9636 at Newark, Delaware: Lab Project Number: AMR-1225-88. 

Unpublished study prepared by E. I du Pont de Nemours and Co. 51 p. 

DER for MRID: 41356334

Citation: Naidu, M. (1989) Aerobic Soil Metabolism of [Pyridine-2-carbon 14] DPX-E9636 and 

[Pyrimidine-2-carbon 14]DPX-E9636: Lab Project Number: AMR-1218-88. Unpublished study 

prepared by E. I. du Pont de Nemours and Co., Inc. 49 p. 
38

DER for MRID: 41356335

Citation: Naidu, M.; Fogiel, A. (1989) Anaerobic Soil Metabolism of [Pyri- dine-2-carbon 

14]DPX-E9636 and [Pyrimidine-2-carbon 14]DPX-E9636 Laboratory Project Number: AMR1217-88. Unpublished study pre- pared by E. I. du Pont de Nemours and Co., Inc. 53 p. 

DER for MRID: 41356336

Citation: Naidu, M. (1989) Batch Equilibrium (Adsorption/Desorption) Studies of DPX-E9636: 

Lab Project Number: AMR-1204-88. Unpublished study prepared by E. I. du Pont de Nemours 

& Co., Inc. 38 p. 

DER for MRID: 41356337

Citation: Naidu, M.; Fogiel, A. (1989) Soil Mobility of DPX-E9636 and Its Soil Degradates by 

Soil TLC: Lab Project Number: AMR-1327-88. Unpublished study prepared by E. I. du Pont de 

Nemours & Co., Inc. 21 p. 

DER for MRID: 43288502

Citation: Naidu, M. (1991) Aerobic Aquatic Metabolism of (Pyridine-2-(carbon 14)) DPXE9636 and (Pyrimidin-2-(carbon 14)) DPX-E9636: Lab Project Number: AMR/1407/89. 

Unpublished study prepared by E.I. du Pont de Nemours and Co. 76 p. 

Ecological Effects

Chlorsulfuron Registration Eligibility Decision. 2004. Docket Title: Chlorsulfuron Risk 

Assessments and Preliminary Risk Reduction Options (Phase 3 of 4 Phase Process); Notice of 

Availability. ID: EPA-HQ-OPP-2004-0219-0008.

DER for MRID: 42471308

Citation: Hoberg, J. et al. (1992) Acute Toxicity of DPX-E9636 to Lemna gibba G3: Lab Project 

Number: 92-4-4236: 97.0991.6128.410. Unpublished study prepared by Springborn Laboratories 

Inc. 62 p.

Fletcher, J.S., J.E. Nellessen, and T.G. Pfleeger. 1994. Literature review and evaluation of the 

EPA food-chain (Kenaga) nomogram, an instrument for estimating pesticide residues on plants. 

Environ. Tox. Chem. 13:1383-1391.

Hoerger, F., and E.E. Kenaga. 1972. Pesticide residues on plants: Correlation of representative 

data as a basis for estimation of their magnitude in the environment. In F. Coulston and F. Korte, 

eds., Environmental Quality and Safety: Chemistry, Toxicology, and Technology, Georg Thieme 

Publ, Stuttgart, West Germany, pp. 9-28.

Kenega, E.E. 1977. In Pesticide Management and Insecticide Resistance, Academic Press, NY, 

pp. 51-94.
39

APPENDIX I. Ecological Effects Information

Summary:

This herbicide was practically non-toxic to both terrestrial avian species-(subacutely) and 

mammalian (acutely and chronically) species. Rimsulfuron is also practically non-toxic to both 

freshwater and saltwater animals on an acute basis. However, both aquatic and terrestrial 

vascular plants are highly susceptible to rimsulfuron. 

Toxicity to Terrestrial Animal

The results of acute/subacute toxicity testing indicate that rimsulfuron is practically nontoxic to 

avian species on both a subacute dietary basis and an acute oral basis. Results of avian toxicity 

testing with rimsulfuron are tabulated below.

Avian Acute/Subacute Toxicity

 

Species

 % 

ai

LC50 (ppm)/ 

LD50 (ppm)

 

Toxicity Category

MRID No.

Author/Year

 

Study Classification

Northern bobwhite quail 

(Colinus virginianus)

98.8 LD50 >2250 Practically non-toxic 41356304

J. Grimes 

and M. Jaber 

(1988)

Core

Northern bobwhite quail 

(Colinus virginianus)

98.8 LC50 >5620 Practically non-toxic 43414531

A.G. Murray 

(1992)

Core

Mallard duck

(Anas platyrhynchus)

98.8

Formulated 

Product

LD50 >2000 Practically non-toxic 41931630

J.S. Culotta 

et al (1993)

Core

Mallard duck

(Anas platyrhynchus)

98.8 LC50 >1378 Slightly toxic 41931633

J. Grimes 

and M. Jaber 

(1989)

Supplemental

Mallard duck

(Anas platyrhynchus)

98.8 LC50 >5620 practically non-toxic 41356306

J. Grimes 

and M. Jaber 

(1989)

Core

 

Avian Reproduction

Species % ai

NOAEC/LOAEC 

(ppm) Endpoints Affected

MRID No.

Author/Year

Study 

Classification

Northern bobwhite quail

(Colinus virginianus)

99 1250/>1250 N/A 43277201

J. B. Beavers et al

(1994) 

Core 

Mammals, Acute and Chronic

Wild mammal testing is required on a case-by-case basis, depending on the results of lower tier 

laboratory mammalian studies, intended use pattern, and pertinent environmental fate 

characteristics. In most cases, rat or mouse toxicity values obtained from the Agency's Health 

Effects Division (HED) substitute for wild mammal testing. Based on a laboratory rat LD50
40

value of >5000 mg/kg, rimsulfuron is practically nontoxic to small mammals on an acute oral 

basis. These toxicity values are reported below.

Mammalian acute toxicity

Species % ai Test Type 

Toxicity

Value

Affected

Endpoints MRID 

Rat

(Rattus norvegicus)

98.8 Oral LD50 >5000 mg/kg None 47091007

Rat

(Rattus norvegicus)

98.8 Acute Inhalation LC50 >5.0 mg/L None 41356314

Terrestrial Invertebrates

Insects

Based on a honey bee acute contact test, rimsulfuron is practically non-toxic to bees. The results 

of rimsulfuron testing using the honeybee are tabulated below:

Non-target insect toxicity

Species

% ai Results Toxicity Category/effects MRID

Study 

Classification

Honey bee

(Apis mellifera)

98.8% >100 μg a.i./bee Practically non-toxic 41356331

K. Hoxter and M. Jaber 

(1989)

Core

Toxicity to Aquatic Animals

The results of acute testing show that rimsulfuron is categorized as practically non-toxic to coldwater freshwater fish, freshwater invertebrates, and warm-water freshwater fish. Results of 

freshwater animal acute toxicity testing are tabulated below.

Freshwater Animal Acute Toxicity

Species % ai

EC50/

LC50 (ppm) Toxicity Category

MRID No.

Author/Year

Study 

Classification

Bluegill sunfish 

(Lepomis macrochirus)

98.8 EC50>390 practically non-toxic 41356308

D.G. Hutton (1989)

Core

Waterflea

(Daphnia magna)

98.8 EC50=1000 Practically non-toxic 41931621

K.N. Baer (1990)

Supplemental

Waterflea

(Daphnia magna)

98.8 EC50>360 Practically non-toxic 41356309 

D.G. Hutton (1989)

Core

Rainbow trout

(Oncorhynchus mykiss)

98.8 LC50>390 Practically non-toxic 41356307

D.G. Hutton (1989)

Core

Bluegill sunfish 

(Lepomis macrochirus)

98.8 LC50>390 Practically non-toxic 41931620

D.G. Hutton (1990)

Core
41

Rimsulfuron is also categorized as practically non-toxic to estuarine/marine fish and 

estuarine/marine invertebrates on an acute basis. The results of acute toxicity testing with 

estuarine/marine species are tabulated below.

Estuarine/Marine Acute Toxicity

Species % ai. LC50/EC50 (ppm) Toxicity Category

MRID No.

Author/Year

Study 

Classification

Sheepshead minnow

(Cypridon variegatus)

99 LC50 > 110 Practically non-toxic 42471303

W.C. Graves and J.P. 

Swigert

Core

Eastern oyster (shell 

deposition or embryo-larvae)

(Crassostrea virginica)

99 EC50 >120 Practically non-toxic 42471301

W.C. Graves and J.P. 

Swigert (1992)

Core

Mysid 

(Americamysis bahia)

99 LC50 >110 Practically non-toxic 42471302

W.C. Graves and J.P. 

Swigert (1992)

Core

 

The results indicate that rimsulfuron is highly toxic to both aquatic and terrestrial vascular plants. 

Aquatic and terrestrial plant testing results are tabulated below.

Nontarget Plant Toxicity 

Species %a.i. EC 25 NOAEC MRID No. 

Author/Year

Study 

Classification

Vascular Plants

6 Dicots/4 monocots 98.8 0.0006 lb a.i./A SE monocot 

0.00013 SE dicot 

0.00004 VV monocot 

0.00003 VV dicot

N/A 42471304 

R.A. McKelvey and 

H. Kuratle III (1992)

Supplemental

2 Dicots 98.1 0.025 oz a.i./A Slope=2.1 0.016 oz 

a.i./A

43539201 

R.A. McKelvey 

(1994)

Core

Duckweed 

Lemna gibba

98.57 EC50=11.6 ppb Slope=1.2 0.09 42471308 

J.R. Hoberg (1992)

Core

Nonvascular Plants

Green algae 

Selenastrum 

capricornutum

98.57 > 29 ppb 29 ppb 42471305 

J.S. Hughes (1992)

Core 

Marine diatom 

Skeletonema costatum

98.8 > 48 ppb 48 ppb 43043601 

S.G. Thompson 

(1993)

Core

Freshwater diatom 

Navicula pelliculosa 

98.57 N/A <30 ppb 42471307 

J.S. Hughes (1992)

Core

Blue-green algae 

Anabaena flos-aquae 

98.57 >35 ppb 35.9 ppb 42471306 

J.S. Hughes (1992)

Core

SE = Seedling Emergence, VV = Vegetative Vigor
42

Appendix II. TerrPlant Spreadsheet

TerrPlant output for ground applications.

Table 1. Chemical Identity.

Chemical Name Rimsulfuron

PC code 129009

Use Field Corn and Soybeans

Application Method Ground Broadcast

Application Form Spray 

Solubility in Water 

(ppm) 7300

Table 2. Input parameters used to derive EECs.

Input Parameter Symbol Value Units

Application Rate A 0.0625 lbs a.i./acre

Incorporation I 1 none

Runoff Fraction R 0.05 none

Drift Fraction D 0.01 none

Table 3. EECs for Rimsulfuron. Units in lbs a.i./acre.

Description Equation EEC

Runoff to dry areas (A/I)*R 0.003125

Runoff to semi-aquatic areas (A/I)*R*10 0.03125

Spray drift A*D 0.000625

Total for dry areas ((A/I)*R)+(A*D) 0.00375

Total for semi-aquatic areas ((A/I)*R*10)+(A*D) 0.031875

Table 4. Plant survival and growth data used for RQ derivation. Units are in lbs a.i./acre.

Seedling Emergence Vegetative Vigor

Plant type EC25 NOAEC EC25 NOAEC 

Monocot 0.0006 N/A 0.00004 N/A

Dicot 0.00013 N/A 0.00003 N/A

Table 5. RQ values for plants in dry and semi-aquatic areas exposed to Rimsulfuron through runoff 

and/or spray drift.*

Plant Type Listed Status Dry Semi-Aquatic Spray Drift

Monocot non-listed 6.25 53.13 15.63

Monocot listed -- -- --

Dicot non-listed 28.85 245.19 20.83

Dicot listed -- -- --

*If RQ > 1.0, the LOC is exceeded, resulting in potential for risk to that plant group.
43

TerrPlant output for aerial application.

Table 1. Chemical Identity.

Chemical Name Rimsulfuron

PC code 129009

Use Field Corn and Soybeans

Application Method Aerial 

Application Form Spray 

Solubility in Water 

(ppm) 7300

Table 2. Input parameters used to derive EECs.

Input Parameter Symbol Value Units

Application Rate A 0.0625 lbs a.i./acre

Incorporation I 1 none

Runoff Fraction R 0.05 none

Drift Fraction D 0.05 none

Table 3. EECs for Rimsulfuron. Units in lbs a.i./acre.

Description Equation EEC

Runoff to dry areas (A/I)*R 0.003125

Runoff to semi-aquatic areas (A/I)*R*10 0.03125

Spray drift A*D 0.003125

Total for dry areas ((A/I)*R)+(A*D) 0.00625

Total for semi-aquatic areas ((A/I)*R*10)+(A*D) 0.034375

Table 4. Plant survival and growth data used for RQ derivation. Units are in lbs a.i./acre.

Seedling Emergence Vegetative Vigor

Plant type EC25 NOAEC EC25 NOAEC 

Monocot 0.0006 N/A 0.00004 N/A

Dicot 0.00013 N/A 0.00003 N/A

Table 5. RQ values for plants in dry and semi-aquatic areas exposed to Rimsulfuron through runoff 

and/or spray drift.*

Plant Type Listed Status Dry Semi-Aquatic Spray Drift

Monocot non-listed 10.42 57.29 78.13

Monocot listed -- -- --

Dicot non-listed 48.08 264.42 104.17

Dicot listed -- -- --

*If RQ > 1.0, the LOC is exceeded, resulting in potential for risk to that plant group.
44

Appendix III. Ecological Aquatic Exposure Modeling

Sample of Model Output

IL Corn

stored as RIMSULFU.out

Chemical: Rimsulfuron

PRZM environment: ILCornSTD.txt modified Tueday, 29 May 2007 at 11:55:34

EXAMS environment: pond298.exv modified Thuday, 29 August 2002 at 15:33:30

Metfile: w14842.dvf modified Wedday, 3 July 2002 at 08:04:38

Water segment concentrations (ppb)

Year Peak 96 hr 21 Day 60 Day 90 Day Yearly

1961 0.1752 0.1453 0.07489 0.05012 0.0361 0.008953

1962 0.7862 0.6645 0.3635 0.1579 0.106 0.02619

1963 0.3312 0.2747 0.144 0.08782 0.06432 0.01598

1964 0.3656 0.3082 0.1593 0.08977 0.06177 0.01527

1965 0.2353 0.2081 0.1255 0.05596 0.03804 0.009401

1966 0.6163 0.5113 0.2679 0.1151 0.07955 0.01973

1967 0.1923 0.1594 0.1249 0.07101 0.04882 0.01208

1968 0.3175 0.2633 0.1432 0.07446 0.05062 0.01248

1969 0.1752 0.1453 0.108 0.05564 0.0381 0.009419

1970 0.1842 0.1528 0.09906 0.06718 0.04557 0.01126

1971 0.3571 0.2961 0.1637 0.07518 0.05287 0.01309

1972 0.2085 0.1832 0.1222 0.07404 0.04999 0.01232

1973 0.2108 0.1748 0.1074 0.04523 0.03031 0.007483

1974 0.2478 0.2206 0.1566 0.07909 0.05316 0.01313

1975 0.4803 0.4021 0.2374 0.1007 0.06751 0.01667

1976 0.6953 0.5767 0.2974 0.1615 0.1111 0.02742

1977 0.1752 0.1453 0.0775 0.04234 0.03175 0.007905

1978 0.51 0.4229 0.23 0.1133 0.07644 0.01889

1979 0.1752 0.1453 0.07969 0.03636 0.0255 0.006316

1980 1.17 0.9704 0.5226 0.2301 0.1548 0.03811

1981 0.1752 0.1453 0.07475 0.04097 0.02764 0.006827

1982 0.3651 0.3027 0.1744 0.08079 0.05452 0.01347

1983 0.177 0.1468 0.08782 0.04193 0.02843 0.007025

1984 0.3538 0.2958 0.1912 0.08212 0.05507 0.01356

1985 0.2855 0.2381 0.1477 0.06434 0.04323 0.01068

1986 0.3486 0.2891 0.1736 0.09358 0.06311 0.01559

1987 0.516 0.4279 0.2203 0.1085 0.07327 0.01811

1988 0.2251 0.1867 0.097 0.03963 0.02653 0.006706

1989 0.1752 0.1498 0.08243 0.03376 0.02413 0.006

1990 0.7497 0.6217 0.3287 0.1411 0.09464 0.02337

Sorted results

Prob. Peak 96 hr 21 Day 60 Day 90 Day Yearly

0.032258064516129 1.17 0.9704 0.5226 0.2301 0.1548 0.03811

0.0645161290322581 0.7862 0.6645 0.3635 0.1615 0.1111 0.02742

0.0967741935483871 0.7497 0.6217 0.3287 0.1579 0.106 0.02619

0.129032258064516 0.6953 0.5767 0.2974 0.1411 0.09464 0.02337

0.161290322580645 0.6163 0.5113 0.2679 0.1151 0.07955 0.01973

0.193548387096774 0.516 0.4279 0.2374 0.1133 0.07644 0.01889

0.225806451612903 0.51 0.4229 0.23 0.1085 0.07327 0.01811

0.258064516129032 0.4803 0.4021 0.2203 0.1007 0.06751 0.01667

0.290322580645161 0.3656 0.3082 0.1912 0.09358 0.06432 0.01598

0.32258064516129 0.3651 0.3027 0.1744 0.08977 0.06311 0.01559

0.354838709677419 0.3571 0.2961 0.1736 0.08782 0.06177 0.01527
45

0.387096774193548 0.3538 0.2958 0.1637 0.08212 0.05507 0.01356

0.419354838709677 0.3486 0.2891 0.1593 0.08079 0.05452 0.01347

0.451612903225806 0.3312 0.2747 0.1566 0.07909 0.05316 0.01313

0.483870967741936 0.3175 0.2633 0.1477 0.07518 0.05287 0.01309

0.516129032258065 0.2855 0.2381 0.144 0.07446 0.05062 0.01248

0.548387096774194 0.2478 0.2206 0.1432 0.07404 0.04999 0.01232

0.580645161290323 0.2353 0.2081 0.1255 0.07101 0.04882 0.01208

0.612903225806452 0.2251 0.1867 0.1249 0.06718 0.04557 0.01126

0.645161290322581 0.2108 0.1832 0.1222 0.06434 0.04323 0.01068

0.67741935483871 0.2085 0.1748 0.108 0.05596 0.0381 0.009419

0.709677419354839 0.1923 0.1594 0.1074 0.05564 0.03804 0.009401

0.741935483870968 0.1842 0.1528 0.09906 0.05012 0.0361 0.008953

0.774193548387097 0.177 0.1498 0.097 0.04523 0.03175 0.007905

0.806451612903226 0.1752 0.1468 0.08782 0.04234 0.03031 0.007483

0.838709677419355 0.1752 0.1453 0.08243 0.04193 0.02843 0.007025

0.870967741935484 0.1752 0.1453 0.07969 0.04097 0.02764 0.006827

0.903225806451613 0.1752 0.1453 0.0775 0.03963 0.02653 0.006706

0.935483870967742 0.1752 0.1453 0.07489 0.03636 0.0255 0.006316

0.967741935483871 0.1752 0.1453 0.07475 0.03376 0.02413 0.006

0.1 0.74426 0.6172 0.32557 0.15622 0.104864 0.025908

Average of yearly averages: 0.0141145

Inputs generated by pe5.pl - Novemeber 2006

Data used for this run:

Output File: RIMSULFU

Metfile: w14842.dvf

PRZM scenario: ILCornSTD.txt

EXAMS environment file: pond298.exv

Chemical Name: Rimsulfuron

Description Variable Name Value Units Comments

Molecular weight mwt 431.44 g/mol

Henry's Law Const.henry 8.56e-13 atm-m^3/mol

Vapor Pressure vapr 1.1e-8 torr

Solubilitysol 73000 mg/L

Kd Kd mg/L

Koc Koc 47.5 mg/L

Photolysis half-life kdp 0 days Half-life

Aerobic Aquatic Metabolism kbacw 0 days Halfife

Anaerobic Aquatic Metabolism kbacs 0 days Halfife

Aerobic Soil Metabolism asm 64 days Halfife

Hydrolysis: pH 7 7.2 days Half-life

Method: CAM 2 integer See PRZM manual

Incorporation Depth: DEPI 0 cm

Application Rate: TAPP 0.0701 kg/ha

Application Efficiency: APPEFF 0.95 fraction

Spray Drift DRFT 0.05 fraction of application rate applied to pond

Application Date Date 22-05 dd/mm or dd/mmm or dd-mm or dd-mmm

Record 17: FILTRA

IPSCND 1

UPTKF 0

Record 18: PLVKRT0

PLDKRT0

FEXTRC0.5

Flag for Index Res. Run IR EPA Pond

Flag for runoff calc. RUNOFFnone none, monthly or total(average of entire run)
46

Selected Information from METADATA Files

ILLINOIS CORN 

The field used to represent corn production in Illinois is located in McLean County, 

although the crop is grown extensively throughout the state. According to the 1997 Census of 

Agriculture, Illinois is ranked 2nd among the major corn producing states in the U.S. The crop is 

generally planted the early Spring (April) in the south, early May in the north and harvested 

beginning in August. Continuous corn is practice is much of the region (approximately 30 

percent is continuous), however, rotation with other crops such as soybean, wheat, sorghum, and 

alfalfa is the dominant practice. Most of the corn is planted for feed grain, but may also be 

planted for oil, sweetener, and for export. Planting depth and row spacing (generally 30 inches) 

follows general practices for the U.S. Conservation tillage practices are regularly used for field 

corn with no-till practiced on about 20 percent of the corn acreage annually. About 50 percent of 

the acreage is cultivated with a row cultivator and an estimated 40 percent is rotary hoed 

annually. The crop is rarely grown under irrigation. The soil selected to simulate the field is an 

Adair clay loam. Adair clay loam is a fine, smectitic, mesic Aquertic Argiudolls. More than 50 

percent of the soil is used for the production of grains with the balance in meadow and pasture. 

Adair clay loam is a deep, somewhat poorly drained, medium to rapid runoff, slowly permeable 

soil formed on uplands in a thin mantle of loess or loess and pedisediments and a paleosol 

formed in glacial till. They are on convex summits of narrow interfluves and on convex side 

slopes at slightly lower elevations. Slopes are generally between 2 to 18 percent, but may range 

to 30 percent. The soils are extensive in MLRA 108 and found in many MLRA in the region. 

Adair clay loam is a Hydrologic Group C soil.

MISSISSIPPI CORN 

The field used to represent corn production in Mississippi is located in the Southern 

Mississippi Valley Uplands. According to the 1997 Census of Agriculture, Mississippi is not a 

major corn producing state in the U.S. (not among the top 20 states) with approximately 600,000 

acres in production. The crop is generally planted in the early Spring (April) and harvested 

beginning in August. Continuous corn is practiced in much of the region, however, rotation with 

other crops such as soybean is practiced as well. Most of the corn is planted for feed grain. 

Planting depth and row spacing (generally 30 inches) follows general practices for the U.S. 

Conventional tillage dominates with more than 50 percent of the practice, followed by 

conservation tillage, no-tillage, and ridge tillage. The crop is rarely grown under irrigation. The 

soil selected to simulate the field is a benchmark soil, Grenada silt loam. Grenada silt loam is a 

fine-silty, mixed, active, thermic Oxyaquic Fraglossudalfs. Most of the soil is used for the 

production of row crops such as corn, cotton, and soybeans, the principal crops. Grenada silt 

loam is a very deep, moderately well drained, medium to slow runoff, moderately permeable 

above a fragipan and slow in the fragipan soil. The fragipan is at a depth of about two feet. The 

soils formed in loess. They are located on uplands and stream terraces of low relief in the 

Southern Mississippi Valley Silty Uplands. Slopes are generally between 0 to 8 percent, but may 

range to 12 percent. The soils are extensive throughout the region. Grenada silt loam is a 

Hydrologic Group C soil.
47

NORTH CAROLINA CORN (Eastern)

The field used to represent corn production in Eastern North Carolina is located in Pitt 

County in the Piedmont. According to the 1997 Census of Agriculture, North Carolina is ranked 

9th among major corn producing states in the U.S. Corn is produced throughout the state with 

the largest production located in the coastal plain and tidewater regions. Sweet corn is produced 

mainly on the coastal plain (MLRA 153 A and B). The crop is generally planted in the early 

Spring (April) and harvested beginning in August. Continuous corn is practiced in much of the 

region, especially the Piedmont. However, rotation with other crops such as soybean is practiced 

on the coastal plain. Most of the corn is planted for feed grain. Planting depth and row spacing 

(generally 30 inches) follow general practices for the U.S. Conventional tillage dominates 

management practices, followed by no-tillage. However, conservation tillage is continuing to 

grow. The crop is rarely grown under irrigation, except for sweet corn. The soil selected to 

simulate the field is a Craven silt loam. Craven silt loam is a fine, mixed, subactive, thermic 

Aquic Hapludults. Approximately one-half of the series is used for the production of row crops 

such as corn, tobacco, cotton, small grain, peanuts and pasture. Craven silt loam is a deep, 

moderately well drained, medium to rapid runoff, slowly permeable soil formed in clayey 

Pleistocene sediments. They are located on nearly level to sloping Coastal Plain Uplands. 

Slopes are generally between 0 to 12 percent. The soils are extensive throughout the Coastal 

Plain region. Craven silt loam is a benchmark soil and a Hydrologic Group C soil.

OHIO CORN 

The field used to represent corn production in Ohio is located in Darke and/or Pickaway 

Counties, although the crop is grown extensively throughout the state. According to the 1997 

Census of Agriculture, Ohio is ranked 6th among the major corn producing states in the U.S. and 

Darke and Pickaway are ranked among the highest in Ohio. The crop is generally planted in 

early Spring (April 15 to May 10) in the north and from April 10 to May 10 in the south. Corn is 

harvested beginning in September depending on kernel moisture and may extend into late 

November. Continuous corn is practiced in the region (approximately 30 percent is continuous), 

however, rotation with mainly soybean is the most common. Rotation promotes weed control 

and has been shown to increase yields as much as 10 percent over continuous corn operations. 

Most of the corn is planted for feed grain, but may also be planted for oil, sweetener, and for 

export. Planting depth (1 - 1.5 inches) and row spacing (generally 30 inches, but may be as 

narrow as 15 to 22 inches) follows general practices for the U.S. Seeding rates in Ohio range 

from 20,000 to 30,000 plants/acre for corn grown for grain and 22,000 to 34,000 plants/acre for 

corn grown for silage. Conservation tillage practices are regularly used for field corn with no-till 

practiced on a small percentage of the corn acreage annually. Corn is generally cultivated with a 

row cultivator or rotary hoed. The crop is rarely grown under irrigation. The soil selected to 

simulate the field is a Cardington silt loam. Cardington silt loam is a fine, illitic, mesic Aquic 

Haplaudalfs. Most of the area is planted in row crops including production of grains with the 

balance in pasture and woodland. Cardington silt loam is a very deep, moderately well drained, 

negligible to very high runoff, slowly permeable soil with an intermittent perched water table at 

1-2 feet between November and April. These soils formed in loamy till of medium calcium 

carbonate content. These soils are on summits, shoulders, and backslopes on Wisconsin Age 

ground moraines and end moraines. Slopes are generally between 0 to 25 percent. The soils are 

extensive in MLRA 111 and 139. Cardington silt loam is a Hydrologic Group C soil.
48

PENNSYLVANIA CORN

The field used to represent corn production in Pennsylvania is located in Lancaster 

County in the south-east portion of the state. According to the 1997 Census of Agriculture, 

Pennsylvania is ranked 15th among major producers of corn in the U.S. The crop is generally 

planted in the Spring (April) and harvested beginning in September. Continuous corn is practiced 

in much of the region. However, rotation with other crops such as soybeans is also practiced. 

Most of the corn is planted for feed grain. Planting depth and row spacing (generally 30 inches) 

follows general practices for the U.S. Conventional tillage dominates management practices, 

followed by no-tillage. However, conservation tillage is continuing to grow. The soil selected to 

simulate the field is a benchmark soil, Hagerstown silt loam. Hagerstown silt loam is a fine, 

mixed, semiactive, mesic Typic Hapludalfs. These soils are used for general crops, pastures, 

orchards, and truck crops. Large portions are in non-farm uses. Hagerstown silt loam is a very 

deep, well drained, moderately permeable soil with moderate to rapid runoff. These soils formed 

in materials weathered from hard grey limestone of rather high purity. They are found on valley 

floors and the adjacent hills. In some areas rock outcrops are common surface features. Slopes 

are generally less than 15 percent, but may range up to 45 percent. Hagerstown silt loam is a 

Hydrologic Group C soil.

MISSISSIPPI SOYBEANS

The field used to represent soybean production in Mississippi is located in Yazoo County. 

According to the 1997 Census of Agriculture, Mississippi harvested more than 2 million acres of 

soybeans and ranks 12th in production in the U.S. The crop is generally planted in Spring (late 

April) and harvested beginning in September. Row spacing is generally 30 to 38-inches, but 

spacing could be a little as 7 inches. Field canopies tend to be very close to 100 percent early in 

the season and less as harvest nears. The crop may be grown under irrigation by furrow or canal 

systems. Most crops are planted by conventional tillage, but no-till or conservation methods are 

employed as well. The soil selected to simulate the field is a Loring silt loam. Loring silt loam is 

a fine-silty, mixed, active, thermic, Qxyaquic Fragiudalfs. Nearly all soils are cleared and used 

to grow cotton, small grains, soybeans, hay and pasture. Loring silt loam is a moderately well 

drained with a fragipan, medium to rapid runoff, moderate permeability above the fragipan and 

moderately slowly permeable in the fragipan soils formed in loess. They are located on level to 

strongly sloping uplands and stream terraces. Slopes are generally between 0 to 20 percent. The 

soils are extensive in the lower Mississippi drainage basin. Loring silt loam is a Hydrologic 

Group C soil.