UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

WASHINGTON D.C., 20460

OFFICE OF CHEMICAL SAFETY 

AND POLLUTION PREVENTION

Date: August 4, 2010 

Chemical: Imazosulfuron 

PC Code: 118602 

Barcode: DP 362652 and 366546

MEMORANDUM

SUBJECT: Transmittal Memo on “Ecological Risk Assessment for the First Food Use 

Registration of Imazosulfuron for Selective Sedge and Broadleaf Weed 

Control in Tomato, Pepper, and Rice and Revised Use Rates in Turfgrass” 

FROM: Sujatha Sankula, Ph.D. Lead Biologist 

Faruque Khan, Ph. D., Senior Scientist 

Brian Anderson, M.S., Acting Branch Chief 

Environmental Risk Branch I 

Environmental Fate and Effects Division (7507P) 

TO: Bethany Benbow, Risk Manager Reviewer 

 James Tompkins, Risk Manager 

Registration Division (7505P) 

Valent USA Corporation (Valent) submitted a petition to the Environmental Protection Agency 

(EPA) proposing the first food use registration of the herbicide imazosulfuron (both technical 

grade active ingredient (TGAI) and V-10142 Ag) as a selective herbicide for the control of 

sedges and broadleaf weeds in tomato, pepper (bell and non-bell), and rice. Valent also 

submitted mitigated labels for imazosulfuron (for the formulated product V-10142) in response 

to the risk assessment conducted for its registration as new chemical in turf, ornamentals, 

conifers, and bare ground non-crop areas (DP 348003). The revised labels for imazolsulfuron 

removed all other uses (ornamental plants, conifers, deciduous trees, non-bearing fruit and nut 

trees, and bare ground non-crop areas) except turfgrass from labels; reduced the maximum single 

application rate in turfgrass from 0.75 lb ai/A to 0.67 lb ai/A; removed aerial applications in 

turfgrass; strengthened drift management and sprayer clean-out sections; disallowed the use of 

flood nozzles; and added 10-foot vegetative buffer strip between treated areas and water bodies. 

Therefore, this memorandum summarizes the attached Environmental Fate and Effects Division 

(EFED)‘s ecological risk assessment for imazosulfuron in support of the proposed new uses in 

tomato, pepper, and rice and revised uses in turfgrass (residential and commercial). Furthermore, 

the attached risk assessment serves as EFED’s response to the registrant’s rebuttal (MRID 

477668-22) on the ecological risk analysis conducted by EFED on the new chemical registration 

of imazosulfuron in turfgrass, ornamentals, conifers, and bare ground non-crop areas 

(DP348003). 
2

The maximum single rate evaluated in this assessment is 0.3 lb ai/A for food uses and 0.67 lb 

ai/A for turfgrass. Maximum annual application rates permitted are 0.3 lb ai/A for food uses and 

1.34 lb ai/A for turfgrass. The label states a single application in tomato and pepper whereas two 

applications are allowed in rice and turfgrass with a 21-day interval between applications. 

Data Gaps 

The available environmental fate and transport data set for imazosulfuron is considered 

complete and no additional fate data is required at this time. 

Table A-2 identifies the status of ecological effects study requirements for imazosulfuron. 

The following are the studies being requested in view of the data gaps identified in this 

environmental risk assessment: 

• An aquatic vascular plant (Lemna gibba) study using the degradate IPSN demonstrated 

no toxicity to the plant. However, greater toxicity was noted to mammals due to exposure 

to IPSN. Therefore, there is uncertainty regarding acute toxicity to fish, aquatic 

invertebrates (water column-dwelling), and aquatic non-vascular plants exposed to the 

degradates. Studies (Guideline numbers: 850.1075 for fish, 850.1300 for invertebrates, 

and 850.5400 for non-vascular plants) are required to address this uncertainty. 

• The recently revised (October 2007) FIFRA data requirements (CFR 40 Part 158) require 

an avian acute oral toxicity study (850.2100) be conducted using a passerine species 

(Passeriformes). Valent submitted a request to waive the study requirement for acute oral 

toxicity of imazosulfuron to passerine birds because of the lack of a guideline study on 

passerines, unwillingness of research organizations to conduct the study using redwinged blackbirds (the preferred species), lack of availability of commercial source of 

red-winged blackbirds, and EPA’s non-approval of alternative passerine species (MRID 

47679113). However, the waiver was not granted as the revised Part 158 data 

requirements specify that acute avian oral toxicity data be submitted for either one 

waterfowl or one upland game species and one passerine species for pesticides with 

proposed terrestrial, aquatic, forestry, and residential outdoor uses. 

• Research (Fletcher et al., 1993, 1996; Bhatti et al., 1995) involving chlorsulfuron, the 

first SU registered in the US (1981) has indicated that chlorsulfuron may have effects on 

plant seed/fruit production at extremely low concentrations. Researchers have also 

reported reproductive effects in cherry, canola, soybean, sunflower and Polygonum spp. 

at application rates as low as 1000x below the label rate. Therefore, studies that document 

the reproduction effects on plants due to imazosulfuron applications are required. 
3

Labeling Recommendations 

According to the Label Review Manual, the following label statements are recommended for 

imazosulfuron: 

Environmental Hazards 

“Do not apply directly to water, or to areas where surface water is present or to intertidal 

areas below the mean high water mark. Do not contaminate water when disposing of 

equipment washwater or rinsate." 

Ground Water Advisory 

Imazosulfuron and its several degradates have properties and characteristics associated 

with chemicals detected in ground water. These chemicals may leach into ground water if 

used in areas where soils are permeable, particularly where the water table is shallow. 

Surface Water Label Advisories 

Imazosulfuron and its degradates may impact surface water quality through spray and 

runoff of rain water. This is especially true for poorly draining soils and soils with 

shallow ground water. Imazosulfuron and degradates are classified as having high 

potential for reaching surface water via runoff for several months or more after 

application. A level, well maintained vegetative buffer strip between areas to which this 

product is applied and surface water features such as ponds, streams, and springs will 

reduce the potential loading of imazosulfuron and degradates from runoff water and 

sediment. Runoff of this product will be reduced by avoiding applications when rainfall 

is forecasted to occur within 48 hours. 
4

Table A-1: Environmental Fate Data Requirements for Imazosulfuron 

Guideline # Data Requirement MRID #s Study Classification 

161-1 835.2120 Hydrolysis 473051-19 

47766821 

Acceptable 

Supplemental 

161-2 835.224 Photodegradation in Water 473051-20 Acceptable 

161-3 835.241 Photodegradation on Soil 473051-21 Supplemental 

161-4 835.237 Photodegradation in Air NA --- 

162-1 835.41 Aerobic Soil Metabolism 473051-22 

477668-01 

Supplemental 

Supplemental 

162-2 835.42 Anaerobic Soil Metabolism 477668-02 Supplemental 

162-3 835.44 Anaerobic Aquatic Metabolism 473051-23 Supplemental 

162-4 835.43 Aerobic Aquatic Metabolism 476397-02 

476791-05 

Supplemental 

Supplemental 

163-1 835.1240 

835.1230 Leaching-Adsorption/Desorption 473051-17 Supplemental 

163-1 835.1230 Adsorption/Desorption 473051-18 Supplemental 

163-2 835.141 Laboratory Volatility NA --- 

163-3 835.81 Field Volatility NA --- 

164-1 

835.61 Terrestrial Field Dissipation 

473051-26 

473051-27 

47679108 

47679109 

47679110 

Acceptable 

Acceptable 

Acceptable 

Acceptable 

Acceptable 

164-2 835.62 Aquatic Field Dissipation 476791-07 Supplemental 

165-4 850.173 Accumulation in Fish 473052-02 Waived 

201-1 840.1100 Spray droplet Size Spectrum 473051-28 Supplemental 

1 Not Available
5

Table A-2 : Available Ecological Effects Data for Imazosulfuron 

Guideline # Type of Study Formulation MRID Study Classification 

71-1 850.2100 Avian Oral LD50 Technical 

Technical 

IPSN 

473052-03 

473052-04 

477668-10 

Acceptable 

Acceptable 

Supplemental 

71-2 850.2200 Avian Dietary LC50 Technical 

Technical 

IPSN 

473052-05 

473052-06 

477668-11 

Acceptable 

Acceptable 

Acceptable 

71-4 850.2300 Avian Reproduction Technical 

Technical 

Technical 

473052-07 

473052-08 

476791-14 

Acceptable 

Supplemental 

Supplemental 

72-1 850.1075 Freshwater Fish LC50 Technical 

Technical 

Technical 

Technical 

473051-35 

473051-36 

473051-37 

476791-11 

Supplemental 

Acceptable 

Acceptable 

Acceptable 

72-2 850.1010 Freshwater Invertebrate LC50 Technical 

Technical 

473051-30 

473051-31 

Invalid 

Acceptable 

72-3(a) 850.1075 Estuarine/Marine Fish LC50 Technical 473051-34 Acceptable 

72-3(b) 850.1025 Estuarine/Marine Mollusk 

EC50

Technical 473051-32 Acceptable 

72-3(c) 850.1035 

850.1045 

Estuarine/Marine Shrimp LC50 Technical 473051-33 Acceptable 

72-4(a) 850.1400 Freshwater Fish Early Life 

Stage 

Technical 476791-14 Acceptable 

72-4(b) 850.1300 

850.1350 

850.1300 

Aquatic Invertebrate Lifecycle Technical 473052-01 Acceptable

 OECD 219 Benthic Organisms (long-term 

sediment toxicity) 

IPSN 477821-03 Supplemental 

72-5 850.1500 Freshwater Fish Life-Cycle Technical Not submitted 

123-1(a) 850.4225 Seed Germination/ 

Seedling Emergence 

Tier II 

V-10142 75WDG 473052-11 Acceptable 

123-1(a) 850.4225 Vegetative Vigor 

Tier II 

V-10142 75WDG 473052-12 Acceptable 

122-2 850.4400 Aquatic Plant (Non-Vascular) 

Tier 1&II 

Technical 

Technical 

Technical 

Technical 

470532-14 

470532-15 

470532-16 

470532-17 

Acceptable 

Acceptable 

Supplemental 

Acceptable 

122-2 850.4400 Aquatic Plant (Vascular) 

Tier 2 

Technical 

IPSN 

476397-01 

473052-13 

Supplemental 

Acceptable 

141-1 850.3020 Honey Bee Acute Oral and 

Contact LD50

Technical 

Technical 

473052-09 

473052-10 

Supplemental 

Supplemental 

 OECD 207 

OECD 207 

Acute Toxicity to Earthworms Technical 

IPSN 

477668-14 

477668-12 

Not available 

 ISO 11268-

2 

Chronic Toxicity to 

Earthworms 

IPSN 477668-13 Supplemental 

141-2 850.3030 Honey Bee Residue on 

Foliage 

NA NA Not available 

Non-guideline Acute Toxicity to Beetles IPSN 

IPSN 

477668-05 

477821-02 

Supplemental 

Supplemental 
6

Environmental Fate and Effects Divisions’ Response to the Registrant’s Rebuttal of Risk 

Assessment Pertaining to the New Chemical Registration Imazosulfuron (DP 348003) 

Valent submitted a response (MRID 477668-22; DP 366546) to the ecological risk assessment 

conducted for the proposed first uses of imazosulfuron (DP348003). To address the uncertainty 

regarding environmental persistence of imazosulfuron, uncertainty factors were applied by 

EFED to environmental parameters for modeling inputs including metabolites in degradation 

parameter estimates in the previous assessment. Valent submitted additional data to address this 

uncertainty, which were incorporated into the fate characterization and model inputs of this 

assessment. Model inputs from the required environmental degradation studies except anaerobic 

aquatic metabolism were chosen to represent the upper confidence bound of the mean, and are 

not expected to be exceeded in the environment 90% of the time. Since a single anaerobic 

aquatic metabolism half-life is available, input half-life was multiplied by 3 to represent upper 

bound value. 

The Environmental Fate and Effects Division disagrees with the registrant that the 

PRZM/EXAMS modeling should be based on the degradation rate of imazosulfuron alone. 

Imazosulfuron degradates (IPSN, UDPM and ADPM) are more acutely toxic to mammals than 

the parent. In addition, HMS retains both IM and PM ring structures and its toxicity is likely 

comparable to the parent. Deductive Estimation of Risk based on Existing Knowledge (DEREK) 

analysis of IPSN, ADPM, SDPM, and UDPM showed that all of these cleavage products 

retained at least one of the same structural alerts as the parent. Therefore, IPSN, ADPM, SDPM, 

and UDPM can not be excluded by hazard considerations and there is potential for exposure, 

these compounds cannot be excluded as residues of concern. There is no toxicity data related to 

aquatic species except Lemna (for both TGAI and IPSN) to exclude any of the degradates listed 

above. Therefore, a total toxic residue approach is expected to provide protective exposure 

estimation for aquatic organisms exposed to the major degradates of imazosulfuron. 

In its comments to EFED, Valent opposed the Recommended Ground Water Advisory Language 

for imazosulfuron. The recommended ground water advisory language was developed based on 

terrestrial field studies as well as various fate data and deemed appropriate for imazosulfuron and 

its degradates. The above recommendation is based on a terrestrial field dissipation study (MRID 

473051-27) in which imazosulfuron was detected in the 45-60 cm soil depth at a maximum of 

0.11 ppm at 14 days and in the 60-75 cm and 75-90 cm soil depths at a maximum of 0.03 ppm 

following the second application in New York. IPSN was also detected in the 30-45 cm, 45-60 

cm, and 75-90 cm soil depths at 0.02 ppm following the second application. 

In response to the uncertainty on the greater toxicity of the degradates, IPSN, UDPM and 

ADPM, which were found to be more acutely toxic to mammals than the parent, with IPSN, 

being the most toxic, the registrant submitted new studies using IPSN on midge (28-day chronic 

study), bobwhite quail (acute dose and dietary studies), insects (acute studies on ground beetle 

and rove beetle), and earthworms (acute studies). As midge data is not available for the TGAI, 

toxicity comparisons could not be made between the TGAI and IPSN. The bird studies suggested 

that IPSN is practically non-toxic to birds both on a single dose and dietary basis, similar to the 

parent imazosulfuron. However, the LOAEC values for IPSN were lower than the parent in both 

the dose and dietary-based studies suggesting that adverse effects could be noted at lower 
7

concentrations with IPSN compared to the parent. Regarding the non-target insects, although 

studies that evaluated the effects of IPSN were submitted on ground beetle and rove beetle, 

comparable studies were not available for TGAI. Therefore, the uncertainty related to the effects 

of TGAI versus IPSN could not be resolved for terrestrial insects. New studies submitted by the 

registrant suggest that the toxicity of imazosulfuron and IPSN is similar to earthworms. 

However, similar to that noted in bird studies, the NOAEC value for IPSN is lower compared to 

the TGAI, indicating effects due to IPSN at lower doses compared to the TGAI. Therefore, IPSN 

toxicity studies on fish (850.1075), aquatic invertebrates (850.1300), and aquatic non-vascular 

plants (850.5400) are needed to resolve the above uncertainty. Furthermore, a midge study using 

the parent imazosulfuron will be useful to understand the differential toxicity of TGAI and IPSN. 

The registrant submitted an early life stage toxicity study on fathead minnow, which fulfilled the 

data gap pointed out by EFED. Since the previously submitted acute toxicity studies were on 

rainbow trout, an additional acute exposure study was submitted on fathead minnow. 

The registrant submitted a new mallard duck study to document the chronic exposure effects of 

imazosulfuron as the previously-submitted study did not determine a NOAEC value for egg shell 

thickness. Endpoints generated from this new study were used in the risk estimation of the 

current assessment. The uncertainty regarding the toxicity of degradates to birds was resolved 

through the submission of two avian studies which showed no differences between the parent 

and IPSN toxicity to birds. 
8

Ecological Risk Assessment for the First Food Use 

Registration of Imazosulfuron for Selective Sedge and Broadleaf Weed 

Control in Tomato, Pepper, and Rice and Revised Use rates in Turfgrass 

Imazosulfuron 

CAS#: 122548-33-8 

USEPA PC Code: 118602 

Team Members

Sujatha Sankula, Ph.D. Lead Biologist 

Faruque Khan, Ph.D., Senior Scientist 

Peer Reviewers

James Lin, Ph.D. Environmental Engineer 

Brian Anderson, M.S., Acting Branch Chief 

Acting Branch Chief 

Brian Anderson, M.S. 

Date of Approval 

August 4, 2010 
9

TABLE OF CONTENTS 

1 Executive Summary.............................................................................................................. 12 

1.1 Nature of Chemical Stressor ......................................................................................... 12 

1.2 Potential Risks to Non-target Organisms...................................................................... 12 

1.3 Conclusions: Exposure Characterization ...................................................................... 15 

1.4 Conclusions: Effects Characterization.......................................................................... 16 

1.5 Uncertainties and Data Gaps......................................................................................... 17 

2 Problem Formulation ............................................................................................................ 18 

2.1 Nature of Regulatory Action......................................................................................... 18 

2.2 Stressor Source and Distribution .................................................................................. 19 

2.2.1 Nature of the Chemical Stressor ............................................................................... 19 

2.2.2 Mode of Action......................................................................................................... 20 

2.3 Overview of Pesticide Usage........................................................................................ 20 

2.4 Receptors....................................................................................................................... 21 

2.4.1 Aquatic and Terrestrial Effects ................................................................................. 21 

2.4.2 Ecosystems Potentially at Risk ................................................................................. 21 

2.4.3 Ecological Effects ..................................................................................................... 22 

2.5 Conceptual Model......................................................................................................... 23 

2.5.1 Risk Hypotheses........................................................................................................ 23 

2.5.2 Conceptual Diagram ................................................................................................. 23 

2.6 Analysis Plan ................................................................................................................ 25 

2.6.1 Measures of Effect and Exposure ............................................................................. 25 

2.6.2 Data Gaps.................................................................................................................. 27 

3 ANALYSIS........................................................................................................................... 28 

3.1 Use Characterization..................................................................................................... 28 

3.2 Exposure Assessment.................................................................................................... 29 

3.2.1 Environmental Fate and Transport Characterization ................................................ 29 

3.2.2 Aquatic Exposure Estimates for Imazosulfuron ....................................................... 41 

3.2.3 Terrestrial Wildlife Exposures.................................................................................. 46 

3.2.4 Terrestrial and Semi-Aquatic Plant Exposures......................................................... 48 

3.3 Ecological Effects Characterization.............................................................................. 48 

3.3.1 Aquatic Effects Characterization .............................................................................. 51 

3.3.2 Terrestrial Effects Characterization .......................................................................... 54 

3.3.3 Review of Incident Data ........................................................................................... 57 

3.3.4 Review of ECOTOX Data ........................................................................................ 57 
10

4 RISK CHARACTERIZATION............................................................................................ 58 

4.1 Risk Estimation: Integration of Exposure and Effects Data ......................................... 59 

4.1.1 Non-target Aquatic Fish, Invertebrates, and Plants.................................................. 59 

4.1.2 Non-target Terrestrial Animals and Plants ............................................................... 61 

4.1.3 Terrestrial and Semi-aquatic Plants Risk.................................................................. 63 

4.2 Risk Description............................................................................................................ 64 

4.2.1 Risks to Aquatic Organisms...................................................................................... 65 

4.2.2 Risks to Terrestrial Organisms.................................................................................. 65 

4.2.3 Endocrine Disruption Assessment ............................................................................ 67 

4.3 Threatened and Endangered Species Concern.............................................................. 68 

4.3.1 Action Area............................................................................................................... 68 

4.3.2 Taxonomic Groups Potentially at Risk: Direct Effects............................................. 69 

4.3.3 Use of Probit Slope Response Relationship to Provide Information on the 

Endangered Species Levels of Concern................................................................................ 70 

4.3.4 Indirect Effects Analysis........................................................................................... 70 

4.3.5 Critical Habitat for Listed Species............................................................................ 71 

5 Description of Assumptions, Uncertainties, Strengths, and Limitations.............................. 72 

5.1 Assumptions and Limitations Related to Exposure for all Taxa .............................. 72 

5.2 Assumptions and Limitations Related to Exposure for Aquatic Species ................. 72 

5.3 Assumptions and Limitations Related to Exposure for Terrestrial Species ............. 73 

5.4 Assumptions and Limitations Related to Effects Assessment.................................. 75 

6 LITERATURE CITED ......................................................................................................... 76 

APPENDIX A: Status of Fate and Ecological Effects Data Requirements.................................. 79 

APPENDIX B: Calculations of Half-life for Total Toxic Residues............................................. 81 

APPENDIX C: PRZM EXAMS Output Files .............................................................................. 89 

APPENDIX D: Rice Model........................................................................................................ 111 

APPENDIX E: ECOTOX Output............................................................................................... 112 

APPENDIX F: Example TERR-PLANT Output........................................................................ 116 

APPENDIX G: EXAMPLE TREX Output ................................................................................ 116 
11

LIST OF TABLES 

Table 1. Listed Species Risks Aassociated with Direct or Indirect Effects due to Applications of 

Imazosulfuron Parent..................................................................................................... 15 

Table 2. Nature and Product Chemistry of the Chemical Stressor - Imazosulfuron..................... 20 

Table 3. Measures of Environmental Exposure and Ecological Effects Used to Assess the 

Potential Risks of Imazosulfuron to Non-Target Organisms......................................... 26 

Table 4. Application Information from the Proposed Imazosulfuron Labels.............................. 29 

Table 5. Summary of Environmental Fate and Transport Properties of Imazosulfuron.............. 29

Table 6. Major and Minor Degradates of Imazosufuron .............................................................. 39 

Table 7. Summary of Metabolites and Degradates to be Included in the Surface Water Exposure 

Assessment..................................................................................................................... 42 

Table 8. PRZM/EXAMS Input Parameter Values for Total Residues of Imazosulfuron ............ 43 

Table 9. Rice Model Input Parameters for Imazosulfuron ........................................................... 45 

Table 10. Estimated Environmental Concentrations for Total Toxic Residues of Imazosulfuron in 

Surface Water................................................................................................................. 45 

Table 11. Estimated Environmental Concentrations for Imazosulfuron Parent on Avian and 

Mammalian Food Items (ppm) at Maximum Application Rates................................... 46 

Table 12. Avian EEC Equivalent Dose Adjusted for Body Weight for Imazosulfuron Application 

to Turfgrass. ................................................................................................................... 47 

Table 13. Mammalian EEC Equivalent Dose Adjusted for Body Weight for Imazosulfuron 

Application to Turfgrass. ............................................................................................... 47 

Table 14. Imazosulfuron Estimated Environmental Concentrations for Terrestrial and SemiAquatic Plants for Aerial and/or Ground Application to Turfgarss............................... 48 

Table 15. Imazosulfuron Toxicity Values for Aquatic Organisms.............................................. 49 

Table 16. Mammalian Acute Oral and Chronic Toxicity to Imazosulfuron................................. 50 

Table 17. Imazosulfuron Toxicity Reference Values (TRVs) for Terrestrial Organisms ........... 50 

Table 18. Differential Toxicity of Sulfonyl Urea Herbicides in Aquatic Plants ........................ 50

Table 19. Aquatic Vascular Plant RQs for Imazosulfuron ........................................................... 61 

Table 20. Chronic Avian RQs based on Upper Bound and Mean EECs for Imazosulfuron use on 

Turf grass....................................................................................................................... 61 

Table 21. Mammalian Acute Risk based on Exposure to Imosulfuron Degradates ..................... 63 

Table 22. Mammalian Chronic RQs Based on Upper Bound Residues for Imazosulfuron Use on 

Tomato, Pepper, and Rice.............................................................................................. 62 

Table 23. Mammalian Dose-Based Chronic RQs based on Upper Bound Residues for 

Imazosulfuron use on Turfgrass..................................................................................... 62 

Table 24. Risk quotient (RQ) values for Plants in Dry and Semi-aquatic Areas Exposed to 

Imazosulfuron Through Runoff and/or Spray drift........................................................ 64 

Table 25. Listed Species Risks Associated with Direct or Indirect Effects Due to Applications of

Imazosulfuron Parent..................................................................................................... 69 

LIST OF FIGURES 

Figure 1. Conceptual Model Depicting Ecological Risk Based on Proposed Imazosulfuron 

Applications ................................................................................................................... 24 

Figure 2. The Proposed Metabolic Pathways for the Degradation of Imazosufuron and the 

Formation of Major Degradates..................................................................................... 37 
12

1 Executive Summary 

1.1 Nature of Chemical Stressor 

Valent USA Corporation (Valent) is seeking registration for the first food uses of imazosulfuron 

in tomato, pepper, and rice. Additionally, Valent submitted mitigated labels for imazosulfuron in 

response to the risk assessment conducted for its registration as new chemical for use in turf, 

ornamentals, conifers, and bare ground non-crop areas (DP 348003). The revised labels for 

imazolsulfuron removed all uses except turfgrass from labels; reduced the maximum single 

application rate in turfgrass from 0.75 lb ai/A to 0.67 lb ai/A; removed aerial applications in 

turfgrass; strengthened drift management and sprayer clean-out sections; disallowed the use of 

flood nozzles; and added 10-foot vegetative buffer strip between treated areas and water bodies. 

Therefore, this ecological risk assessment for imazosulfuron is based on its new uses in tomato, 

pepper, rice and revised uses in turfgrass (residential and commercial). Furthermore, this risk 

assessment serves as EFED’s response to the registrant’s rebuttal (MRID 477668-22) on the 

ecological risk analysis conducted by EFED on the new chemical registration of imazosulfuron 

in turfgrass, ornamentals, conifers, and bare ground non-crop areas (DP348003). 

Imazosulfuron is a sulfonylurea (SU) herbicide that provides both pre- or post-emergence and 

selective control of sedges and broadleaf weeds. It is a systemic herbicide that is absorbed both 

by roots and foliage and is translocated in xylem and phloem. The proposed registration is for the 

formulated products (V-10142 Ag) of imazosulfuron for use in tomato, pepper, rice, and V10142 for established residential and commercial turfgrass. Both V-10142 and V-10142 Ag are 

formulated as water dispersible granules that contain 75% of the active ingredient. 

It is proposed that imazosulfuron will be applied in row middles, under plastic mulch, on bare 

soil, or as directed spray at 0.2 – 0.3 lb ai/A in pepper; as pre-transplant spray under plastic 

mulch, over the top (direct-seeded or post-transplant), or directed spray (direct-seeded or posttransplant) at 0.2 – 0.3 lb ai/A in tomato; and to moist soil until 2-inch internode stage of drillseeded, dry, or water-seeded rice. The maximum single application rate proposed for the food 

uses is 0.3 lb ai/A. A single application is permitted in tomato and pepper whereas two 

applications, 21 days apart, are allowed in rice. In view of crop injury, only ground applications 

are allowed in tomato and pepper. In addition to ground application, aerial application is 

permitted in rice only. 

For turfgrass, the revised labels suggest the use of 0.5 – 0.67 lb ai/A per application. Two postemergence applications are permitted with 21-day interval between applications for turfgrass. 

Applications in turfgrass should be made after nutsedge has reached the 3-leaf stage of growth. 

Similar to tomato and pepper, only ground applications of imazosulfuron are allowed in 

turfgrass. 

1.2 Potential Risks to Non-target Organisms 

A screening-level risk assessment, based on total toxic residue approach (parent + degradates of 

concern), suggests that imazosulfuron presents a high level of risk to both endangered and nonendangered species of aquatic vascular plants and terrestrial plants. There is also a potential for 

acute risk to aquatic non-vascular plants and chronic risk to birds and mammals. 
13

In response to the uncertainty pointed in the previous assessment (DP 348003) on the greater 

toxicity of the degradates, IPSN, UDPM and ADPM, which were found to be more acutely toxic 

to mammals than the parent, with IPSN, being the most toxic, the registrant submitted new 

studies using IPSN on midge (28-day chronic study), bobwhite quail (acute dose and dietary 

studies), insects (acute studies on ground beetle and rove beetle), and earthworms (acute studies). 

As midge data is not available for the TGAI, toxicity comparisons could not be made between 

the TGAI and IPSN. The bird studies suggested that IPSN is practically non-toxic to birds both 

on a single dose and dietary basis, similar to the parent imazosulfuron. However, the LOAEC 

values for IPSN were lower than the parent in both the dose and dietary-based studies suggesting 

that adverse effects could be noted at lower concentrations with IPSN compared to the parent. 

Regarding the non-target insects, although studies that evaluated the effects of IPSN were 

submitted on ground beetle and rove beetle, comparable studies were not available for TGAI. 

Therefore, the uncertainty related to the effects of TGAI versus IPSN could not be resolved for 

terrestrial insects. New studies submitted by the registrant suggest that the toxicity of 

imazosulfuron and IPSN is similar to earthworms. However, similar to that noted in bird studies, 

the NOAEC value for IPSN is lower compared to the TGAI, indicating effects due to IPSN at 

lower doses compared to the TGAI. 

Terrestrial Organisms 

Plants 

Imazosulfuron exposure results in significant reductions in growth and survival to non-target 

terrestrial plants with EC25 values as low as 0.034 lbs ai/A (corresponding NOAEC value of 0.025 

lbs ai/A). Many of the EC25 values for terrestrial plants are approximately an order of magnitude 

lower than the proposed single application rates [0.3 (tomato, pepper, and rice) – 0.67 (turfgrass) 

lb ai/A). Based on a single ground application on tomato, pepper, and rice at the maximum rate, 

the LOC was exceeded for listed and non-listed non-target terrestrial plants in semi-aquatic 

environments only. For a single aerial application on rice, the LOC was exceeded for listed and 

non-listed non-target terrestrial plants in semi-aquatic environments and listed plants in dry 

upland areas. For a single ground application to turfgrass, the LOC was exceeded for listed and 

non-listed non-target terrestrial plants in dry upland and semi-aquatic environments. 

Effects in the seedling emergence and vegetative vigor studies were observed for plants in a wide 

range of plant families. However, there were minimal effects observed in monocots compared to 

dicots because imazosulfuron is not a grass herbicide. In addition to the growth effects observed 

for several plant species, unusually high mortality was observed for some plants in the seedling 

emergence and vegetative vigor tests. There were significant reductions in survival at 21 days for 

soybean at 2 lb ai/A (32%), flax at 0.67 lb ai/A (37%), and radish at 0.67 lb ai/A (60%). 

Imazosulfuron exposure may result in non-target plant mortality. 

There is also concern for incidence to plants at the proposed application rates for imazosulfuron, 

given that major incidences have occurred as a result of application of other SU’s at much lower 

rates. The proposed maximum single application rates for imazosulfuron (0.3 – 0.67 lb ai/A) are 

much greater than other registered SU herbicides. For example, the following are the most 

common use rates based on the recent RED documents for some SU herbicides: 
14

• Chlorsulfuron (Glean): 0.0625 lb ai/A 

• Sulfometuron-methyl (Oust): 0.0231 - 0.375 lb ai/A 

• Nicosulfuron (Accent): 0.0625 lb ai/acre 

• Chlorimuron (Classic): 0.008 - 0.12 lb ai/A 

Research involving chlorsulfuron, the first SU registered in the US (1981) has indicated that 

chlorsulfuron may have effects on plant seed/fruit production at extremely low concentrations. 

Researchers (Fletcher et al., 1993, 1996; Bhatti et al., 1995), have reported reproductive effects 

in cherry, canola, soybean, sunflower and Polygonum spp. at application rates as much as 1000x 

below the label rate (0.0625 lb ai/A). Among the incidents recorded for chlorsulfuron, the 

highest profile incident is Horse Heaven Hills, where chlorsulfuron applied to nearby wheat 

fields was implicated in the reduced yields in cherry and peach trees over a number of years in 

the 1980s. At this time, it is not known whether reproductive effects are associated with SUs 

other than chlorsulfuron; however, effects to plants at very low exposures to the SU 

sulfometuron-methyl (the second SU registered) have been implicated in the loss of 100,000 

acres of sugar beets in Idaho in the year 2000. 

Birds and Mammals 

Chronic LOCs are exceeded for birds and mammals due to imazosulfuron use in turfgrass only. 

Chronic avian risk LOCS were not exceeded for any of the food (tomato, pepper, and rice) uses 

(RQ = 0.1 – 0.7). Chronic risk LOCS exceeded for birds consuming short grass, tall grass, and 

broadleaf plants and small insects for turfgrass use only (RQ = 0.2 – 2.7). 

Only dose-based chronic risk LOC exceeded for turfgrass use for all sized mammals. There are 

no LOC exceedances for chronic dose-based risk for any sized mammals based on imazosulfuron 

uses in tomato, pepper, and rice. Similarly, dietary-based chronic risk LOCS were not exceeded 

for mammals for any of the proposed food or non-food uses for imazosulfuron. 

There is no acute LOC exceedances for birds, mammals and terrestrial invertebrates from 

imazosulfuron TGAI for all of the proposed uses. However, the degradates, IPSN, UDPM and 

ADPM are more acutely toxic to mammals than the parent with IPSN, being the most toxic. 

Therefore, there is uncertainty regarding chronic risk to birds and mammals and risk to terrestrial 

plants from these degradates. 

Aquatic Organisms 

There is risk to non-listed aquatic vascular plants based on exposure to imazosulfuron from all 

the proposed new uses (RQs = 7 – 607, LOC = 1). LOCs for endangered aquatic vascular plants 

are also exceeded for all the proposed uses (RQs = 17 - 1468). Registrant-submitted studies are 

not available to demonstrate the effects of imazosulfuron on aquatic non-vascular plants. RQs 

calculated based on an open literature study (Mohammed et al., 2005) suggested that risk (RQ = 

1.4) exceeded levels of concern for imazosulfuron use in rice only. 

 
15

Imazosulfuron is not acutely toxic to freshwater or estuarine/marine fish and invertebrates. 

Calculated chronic risk quotients for freshwater fish ranged from 0.001 (tomato) – 0.09 (rice). 

Therefore, imazosulfuron is not expected to pose any risk to freshwater fish based on chronic 

exposure. 

An aquatic vascular plant (Lemna gibba) study using the degradate, IPSN, demonstrated no 

toxicity to the plant. A single study submitted on the degradate IPSN (no data is submitted on the 

parent) suggested that IPSN is practically non-toxic to the benthic invertebrate midge larvae (RQ 

= 0.0004). However, there is uncertainty regarding IPSN toxicity to fish, invertebrates, and 

aquatic non-vascular plants. 

Listed Species 

There is a potential concern for direct effects for listed aquatic vascular and non-vascular plants, 

terrestrial plants, birds and mammals from the proposed imazosulfuron uses in tomato, pepper, 

rice, and turfgrass (Table 1). There is potential for imazosulfuron to exert indirect effects upon 

the listed organisms by, for example, perturbing forage or prey availability, altering habitat, 

pollination and/or dispersal, etc. With additional refinement, such as exploring more detailed use 

patterns and species biology (e.g., geographic location, specific feeding habits, time of year the 

listed species are likely to utilize crop fields), it may be determined that some (or all) listed 

species may not be affected. 

Table 1. Listed Species Risks Associated with Direct or Indirect Effects Due to Applications of 

Imazosulfuron in Tomato, Pepper, Rice, and Turfgrass 

Listed Taxa Direct Effects Indirect Effects 

Terrestrial and semi-aquatic plants – monocots Yes Yes

Terrestrial and semi-aquatic plants – dicots Yes Yes 

Terrestrial invertebrates No Yes 

Birds (surrogate for terrestrial-phase amphibians and 

reptiles) 

Yes – chronic effects Yes 

Mammals Yes – chronic effects Yes 

Aquatic vascular plants Yes Yes 

Aquatic non-vascular plants Yes Yes 

Freshwater fish (surrogate for aquatic-phase 

amphibians) 

No Yes 

Freshwater Invertebrates No Yes 

Freshwater Benthic Invertebrates No Yes 

Estuarine/Marine Fish No Yes 

Estuarine/Marine Crustaceans No Yes 

Estuarine/Marine Mollusks No Yes 

1.3 Conclusions: Exposure Characterization 

Imazosulfuron is a systemic herbicide containing dimethoxypyrimidine and imidazopyridine 

rings. Major routes of imazosulfuron dissipation are aerobic and anaerobic biodegradation and 

aqueous photolysis. Degradation half-lives in soil and water range from few weeks to several 

months due to aerobic soil metabolism and anaerobic aquatic metabolism. There are several 

major degradates (HMS, IPSN, IOHA, ADPM, UPDM and SPDM) identified in the 

environmental fate studies. Photolytic half-life of 3.5 days is expected to hasten degradation of 
16

imazosulfuron in clear, shallow aqueous environments but not in soil (stable). Imazosulfuron is 

also stable to abiotic hydrolysis except at low pH. Because imazosulfuron is mobile to 

moderately mobile in soil, it is expected to move from the application site into groundwater and 

surface water. Additionally, off-site movement of imazosulfuron is expected through spray drift 

from aerial and ground spray. A total toxic residue (parent plus degradates of concern) approach 

is considered for the aquatic exposure assessment. 

1.4 Conclusions: Effects Characterization 

Imazosulfuron is practically non-toxic to freshwater and estuarine/marine fish, water flea, and 

mysid shrimp at concentrations of up to 100 mg ai/L nominal concentration. It is slightly toxic to 

estuarine/marine mollusks. In a life cycle toxicity test using Daphnia magna, parental mortality 

was observed in addition to a significant decrease in the mean number offspring per parent at 3.3 

mg ai/L. A freshwater fish early life-stage study suggested that hatching success was the most 

sensitive parameter affected by imazosulfuron. A 28-day study on the sediment-dwelling midge 

larvae suggested that IPSN did not affect emergence or larval mortality up to 25 mg ai/L. 

Toxic effects were observed in an aquatic vascular plant study using duckweed (Lemna minor) 

exposed to imazosulfuron parent. The metabolite, IPSN, was not toxic to the duckweed (Lemna 

gibba) up to 100 mg ai/L. Imazosulfuron is not toxic to the marine diatom, Skeletonema 

costatum, freshwater diatom, Nitzschia palea, and the freshwater algae, Selenastrum 

capricornutum. The blue-green algae, Anabaena flos-aquae toxicity test resulted in a EC50 of 11 

mg ai/L. An ECOTOX study, Mohammad, M. et al., 2005 (ECOTOX # 104861) supported the 

results of the registrant studies. In the ECOTOX study, vascular plants were two orders of 

magnitude more sensitive than non-vascular plants for imazosulfuron. 

Imazosulfuron is practically non-toxic to birds, mammals, and terrestrial invertebrates on an 

acute-exposure basis. Additional studies indicated that toxicity of IPSN to birds (both on single 

dose and dietary basis) and earthworms is similar to imazosulfuron TGAI. Based on chronic 

avian studies, number of eggs laid was the most sensitive affected parameter, which occurred at 

202 mg ai/kg diet. 

The metabolites, IHOA and M-1 are also not acutely toxic to mammals. The metabolites, IPSN, 

UDPM and ADPM are more acutely toxic to mammals than the parent with IPSN, being the 

most toxic. A 2-generation laboratory rat reproduction study with technical imazosulfuron 

resulted in no reproductive effects. There were parental effects based on mortality, clinical signs 

of toxicity, and decreased body weight and food consumption. 

Significant reductions in growth and survival toxicity to terrestrial plants were observed in both 

the seedling emergence and vegetative vigor tests. In the seedling emergence test, the most 

sensitive monocot was onion, which resulted in the EC25, NOAEC and EC05 values of 0.034, 

0.025, and 0.0052 lb ai/A, respectively, based on dry weight. There was 80% reduction at highest 

test concentration of 0.67 lb ai/A, which is the maximum single application rate proposed on the 

revised turfgrass label. The most sensitive dicot was lettuce and resulted in the EC25, NOAEC 

and EC05 values of 0.041, 0.22, and 0.0028 lb ai/A, respectively, based on dry weight. There was 

32% reduction of lettuce dry weight at LOAEC (0.074 lb ai/A). There were also significant 

reductions in survival at 21 days for soybean at 2 lb ai/A (32%) and flax at 0.67 lb ai/A (37%). 
17

In the vegetative vigor test, the most sensitive monocot was onion and resulted in the EC25, 

NOAEC and EC05 values of 0.25, 0.025, and 0.02 lb ai/A based on dry weight. The most 

sensitive dicot was radish and resulted in the EC25, NOAEC and EC05 values of 0.08, 0.074, and 

0.0079 lb ai/A, respectively, based on percent survival. At the maximum dose tested for radish, 

0.67 lb ai/A (the proposed maximum single application rate for turfgrass), there was a 60% 

reduction in survival compared to the control. There were also significant effects on dry weight 

and plant height for radish. There were significant effects to ryegrass, buckwheat, tomato, 

soybean, lettuce and flax. 

The nontarget terrestrial plant toxicity studies, as specified by the Agency guidelines, are 

designed to evaluate sublethal effects to plant growth, which can then be extrapolated to 

community level effects. Mortality as an endpoint in these studies, as is the case with 

imazosulfuron, is atypical and of concern to Agency. 

1.5 Uncertainties and Data Gaps 

The following Environmental Fate uncertainties, limitations, and data gaps (Appendix A) were 

identified in this environmental risk assessment: 

• This assessment is based on limited biodegradation fate data. Imazosulfuron persistence 

is significantly affected by soil or water chemistry and may not always be easy to predict 

from typically available soil/water property data alone. A clearer picture of the range of 

variability in imazosulfuron persistence in the environment would require environmental 

fate studies on a greater variety of soils/waters/sediments with a greater range of pH 

levels and other soil properties. This is particularly true for the aerobic soil and anaerobic 

aquatic metabolism studies. 

• Even though imazosulfuron is soluble and moderately mobile to mobile based on the 

results of batch equilibrium studies, unextractable residues were identified at maximums 

of 87.7% of applied radioactivity in anaerobic aquatic metabolism and 35.7% of applied 

radioactivity in aerobic soil metabolism. The unextractable residues are uncharacterized 

and it is uncertain whether they consist of degradates of risk concern. Under sterile 

conditions these unextractable residues were not formed suggesting that the formation of 

them is microbially mediated. Metabolism half-lives were estimated based on total 

residue approach that includes parent and major degradates concentrations (excluding 

unextractable residues). To the extent that these unextractable residues are of risk 

concern, the estimated half-lives will be underestimated compared to a total toxic residue 

approach for estimating half-lives. However, given the persistence of total toxic residue 

of imazosulfuron, inclusion of unextractable residues in total toxic approach for 

calculating metabolism half-life would not impact PRZM/EXAMS modeled EECs 

appreciably. 

The following Environmental Effects uncertainties, limitations, and assumptions were identified 

in this environmental risk assessment: 

• An aquatic vascular plant (Lemna gibba) study using the degradate IPSN demonstrated 

no toxicity to the plant. However, greater toxicity was noted to mammals due to exposure 

to IPSN. Therefore, there is uncertainty regarding acute toxicity to fish, aquatic 
18

invertebrates (water column-dwelling), and aquatic non-vascular plants exposed to the 

degradates. Studies are required to address this uncertainty. 

• The recently revised (October 2007) FIFRA data requirements (CFR 40 Part 158) require 

an avian acute oral toxicity study (850.2100) be conducted using a passerine species 

(Passeriformes). Valent submitted a request to waive the study requirement for acute oral 

toxicity of imazosulfuron to passerine birds because of the lack of a guideline study on 

passerines, unwillingness of research organizations to conduct the study using redwinged blackbirds (the preferred species), lack of availability of commercial source of 

red-winged blackbirds, and EPA’s non-approval of alternative passerine species (MRID 

47679113). However, the waiver was not granted as the revised Part 158 data 

requirements specify that acute avian oral toxicity data be submitted for either one 

waterfowl or one upland game species and one passerine species for pesticides with 

proposed terrestrial, aquatic, forestry, and residential outdoor uses. 

• Research (Fletcher et al., 1993, 1996; Bhatti et al., 1995) involving chlorsulfuron, the 

first SU registered in the US (1981) has indicated that chlorsulfuron may have effects on 

plant seed/fruit production at extremely low concentrations. Researchers have also 

reported reproductive effects in cherry, canola, soybean, sunflower and Polygonum spp. 

at application rates as low as 1000x below the label rate. Therefore, studies that document 

the reproduction effects on plants due to imazosulfuron applications are required. 

2 Problem Formulation 

2.1 Nature of Regulatory Action 

The purpose of this assessment is to evaluate the environmental fate and ecological risks 

resulting from the new food use registration of imazosulfuron in pepper, tomato, and rice. 

Additionally, this assessment will focus on analyzing risk from the revised use rates of 

imazosulfuron in turfgrass. In response to the risk assessment conducted for its registration as 

new chemical for use in turf, ornamentals, conifers, and bare ground non-crop areas (DP 

348003), the registrant of imazosulfuron, Valent, submitted revised labels to the Agency. The 

label changes include removal of all uses except turfgrass; reduction of the maximum single 

application rate in turfgrass from 0.75 lb ai/A to 0.67 lb ai/A; removal of aerial applications in 

turfgrass; strengthening of drift management and sprayer clean-out sections; disallowing the use 

of flood nozzles; and addition of 10-foot vegetative buffer strip between treated areas and water 

bodies. Therefore, this ecological risk assessment for imazosulfuron is in support of the proposed 

new uses in tomato, pepper, rice and revised use rates in turfgrass (residential and commercial). 

Imazosulfuron is a pre/post-emergence herbicide to selectively control sedges and certain 

broadleaf weed. As the first food use being proposed for use in the United States, EPA is 

required under the Federal Insecticide Fungicide and Rodenticide Act (FIFRA) to ensure that 

imazosulfuron does not have the potential to cause unreasonable adverse effects to the 

environment. Potential effects to listed species (i.e., species on the Federal list of endangered 

and threatened wildlife and plants) are also considered under the Endangered Species Act in 

order to ensure that the registration of imazosulfuron is not likely to jeopardize the continued 

existence of such listed species or adversely modify their habitat. To these ends, this assessment 

follows EPA guidance on conducting ecological risk assessments (USEPA 1998) and the Office 
19

of Pesticide Program’s policies for assessing risk to non-target and listed organisms (USEPA 

2004). 

Among the end products of the EPA pesticide registration process is a determination of whether 

a product is eligible for registration and, if so, a description of how the product may be used. A 

label represents the legal document which stipulates how and where a given pesticide may be 

used. End-use labels describe the formulation type, acceptable methods of application, where the 

product may be applied, and any restrictions on how applications may be conducted. Thus, the 

use, or potential use, described by the pesticide’s labels is considered “the action” being 

assessed. This assessment is in support of the first food use and revised non-food use registration 

of imazosulfuron. 

2.2 Stressor Source and Distribution 

 2.2.1 Nature of the Chemical Stressor 

Imazosulfuron is a selective sulfonylurea herbicide containing dimethoxypyridine and 

imididazopyridine rings. The major routes of degradation are aerobic and anaerobic 

biodegradation and abiotic aqueous photolysis. Degradation half-lives in soil and water range 

from few days to several months due to aerobic soil metabolism, anaerobic aquatic metabolism 

and photolysis. There are several major degradates (HMS, IPSN, IOHA, ADPM, UPDM and 

SPDM) identified in the environmental fate studies. HMS, retains both imidazolyl (IM) and 

pyrimidinyl (PM) ring structures, its toxicity is likely comparable to the parent. Deductive 

Estimation of Risk based on Existing Knowledge (DEREK) analysis of IPSN, IHOA, ADPM, 

SDPM, and UDPM showed that all of these cleavage products except IHOA (a low molecular 

weight acid) retained at least one of the same structural alerts as the parent. Therefore aquatic 

exposure of total toxic residue (parent plus HMS, IPSN, ADPM, UPDM and SPDM) is 

considered in this assessment Imazosulfuron is mobile to moderately mobile (FAO 

classification) in the environment. Imazosulfuron is a non-volatile (<2.63 x 10-8 Torr at 20°C) 

compound. Imazosulfuron has two ionizable functional groups (pKa 0.30 and 3.54), therefore it 

water solubility limit varies with pH. Water solubility is 429 mg/L at pH 7 but less soluble 

(1mg/l at pH 4) in acidic environment. Based on the log Kow of -0.07 at pH 7, the potential for 

bioaccumulation in organisms is very low for imazosulfuron under neutral environment. A brief 

summary of the product chemistry data on imazosulfuron is provided in Table 2. 
20

2.2.2 Mode of Action 

Imazosulfuron is a systemic sulfonylurea herbicide that is absorbed both by roots and foliage of 

treated plants. The mode of action of imazosulfuron is through the inhibition of the enzyme 

acetolactate synthase (ALS) leading to the blocking of the synthesis of the branch-chain amino 

acids such as valine, leucine, and isoleucine that are essential in the formation of new cells. 

Injury symptoms, which may not be apparent until 1-2 weeks after treatment, include interveinal 

chlorosis, red venation, purpling, stunting, root pruning, and gradual death. 

2.3 Overview of Pesticide Usage 

Imazosulfuron, a systemic herbicide, is being proposed for the control of sedges and broadleaf 

weeds in tomato, pepper, rice, and turfgrass. The proposed first food uses are not limited to a 

geographical region in the United States. According to proposed labels, imazosulfuron can be 

applied in row middles, under plastic mulch, on bare soil, or as directed spray at 0.2 – 0.3 lb ai/A 

in pepper; as pre-transplant spray under plastic mulch, over the top (direct-seeded or posttransplant), or directed spray (direct-seeded or post-transplant) at 0.2 – 0.3 lb ai/A in tomato; and 

to moist soil until 2-inch internode stage of drill-seeded, dry, or water-seeded rice. The 

Table 2. Nature and Product Chemistry1 of the Stressor - Imazosulfuron 

Pesticide Class: Sulfonyl urea herbicide 

EPA PC Code: 118602 

IUPAC Name: 1-(2-chloroimidazo[1,2-a]pyridin-3-ylsulfonyl)-3-(4,6-dimethoxypyrimidin-2-yl)urea 

CAS Name: 2-chloro-N-[[(4,6-dimethoxy-2-pyrimidinyl)amino]carbonyl] imidazo[1,2-a]pyridine3-sulfonamide] 

CAS No: 122548-33-8 

Formula: C14H13ClN6O5S 

Structure: 

Molecular Mass (g/mol) 412.81 

Vapor pressure (torr) at 25o C < 2.63 x 10-8

Henry’s Law Constant at 25o C 

(atm m3/mol) < 3.33 x 10-11

Solubility in water (mg/L)at 200C 

1.00 at pH 4 

429 at pH 7 

3936 at pH 9 

Octanol- water Coefficient (Log Kow ) 

2.43 at pH 4 

- 0.07 at pH 7 

-1.56 at pH 9 

Dissociation Constant pKa at 20°C 3.94, 0.30 

1

MRID 473051-01 
21

maximum single application rate proposed for the food uses is 0.3 lb ai/A. A single application 

of imazosulfuron is proposed in tomato and pepper where as two applications are proposed in 

rice. A 21-day interval between applications is proposed for sequential application in rice. Aerial 

application is limited to rice only. For turfgrass, the revised labels suggest the use of 0.5 – 0.67 lb 

ai/A per application. Two post-emergence applications are permitted with 21-day interval 

between applications. Applications in turfgrass should be made after nutsedge has reached the 3-

leaf stage of growth. Similar to tomato and pepper, only ground applications are allowed in 

turfgrass. 

2.4 Receptors 

2.4.1 Aquatic and Terrestrial Effects 

The receptor is the biological entity that is exposed to the stressor (EPA, 1998). Consistent with 

the process described in the Overview Document (EPA, 2004), this risk assessment uses a 

surrogate species approach in its evaluation of imazosulfuron. Toxicological data generated 

from surrogate test species, which are intended to be representative of broad taxonomic groups, 

are used to extrapolate to potential effects on a variety of species (receptors) included under 

these taxonomic groupings. 

Acute and chronic toxicity data from studies submitted by pesticide registrants along with the 

available open literature are used to evaluate the potential direct effects of imazosulfuron to the 

aquatic and terrestrial receptors identified in this section. This includes toxicity data on the 

technical grade active ingredient, degradates, and when available, formulated products (e.g. “SixPack” studies). The open literature studies are identified through EPA’s ECOTOX database 

(http://cfpub.epa.gov/ecotox/), which employs a literature search engine for locating chemical 

toxicity data for aquatic life, terrestrial plants, and wildlife. The evaluation of both sources of 

data can also provide insight into the direct and indirect effects of imazosulfuron on biotic 

communities from loss of species that are sensitive to the chemical and from changes in structure 

and functional characteristics of the affected communities. 

2.4.2 Ecosystems Potentially at Risk 

An ecosystem may be defined as a functional unit made up of all living organisms (animals, 

plants, and microbes) in a designated area, and all the non-living physical and chemical factors 

of their environment, linked together through nutrient cycling and energy flow. Moreover, an 

ecosystem can be of any size, i.e., a log, pond, field, forest, or the earth's biosphere, but it always 

functions as a whole unit. Ecosystems are commonly described according to the major type of 

vegetation, for example, forest ecosystem, old-growth ecosystem, or range ecosystem. 

Ecosystems potentially at risk are expressed in terms of the selected assessment endpoints. The 

typical assessment endpoints for screening-level pesticide ecological risks are reduced survival, 

and reproductive and growth impairment for both aquatic and terrestrial animal species. Aquatic 

animal species of potential concern include freshwater fish and invertebrates, estuarine/marine 

fish and invertebrates, and amphibians. Terrestrial animal species of potential concern include 

birds, mammals, and beneficial insects. For both aquatic and terrestrial animal species, direct 
22

acute and direct chronic exposures are considered. In order to protect threatened and endangered 

species, all assessment endpoints are measured at the individual level. Although endpoints are 

measured at the individual level, they provide insight about risks at higher levels of biological 

organization (e.g., populations and communities). For example, pesticide effects on individual 

survivorship have important implications for both population rates of increase and habitat 

carrying capacity. 

For terrestrial and semi-aquatic plants, the screening assessment endpoint is the perpetuation of 

populations of non-target plant species (crops and non-crop species). Existing testing 

requirements have the capacity to evaluate emergence of seedlings and vegetative vigor. 

Although it is recognized that the endpoints of seedling emergence and vegetative vigor may not 

address all terrestrial and semi-aquatic plant life cycle components, it is assumed that impacts at 

emergence and in active growth have the potential to impact individual competitive ability and 

reproductive success. 

For aquatic plants, the assessment endpoint is the maintenance and growth of standing crop or 

biomass. Measurement endpoints for this assessment endpoint focus on vascular plant (i.e., 

duckweed) growth rates and biomass measurements. 

The ecological relevance of selecting the above-mentioned assessment endpoints is as follows: 1) 

the identification of exposure pathways for these receptors; 2) the receptors may be potentially 

sensitive to pesticides in affected media and in residues on plants, seeds, and insects; and 3) the 

receptors could potentially inhabit areas where pesticides are applied, or areas where runoff 

and/or spray drift may impact the sites because suitable habitat is available. 

Given the relative persistence of imazosulfuron and its degradates in soil and water environments 

and the widespread distribution of the plant species with proposed uses, ecosystems at risk can 

be generally defined as any adjoining field or water body where imazosulfuron is applied. 

2.4.3 Ecological Effects 

Each assessment endpoint requires one or more “measures of ecological effect,” which are 

defined as changes in the attributes of an assessment endpoint itself or changes in a surrogate 

entity or attribute in response to exposure to a pesticide. Ecological measurement endpoints for 

this risk assessment are based on toxicity information for imazosulfuron in the ECOTOX 

database and a suite of registrant-submitted toxicity studies performed on a limited number of 

organisms in the following broad groupings: 

1. Birds (mallard duck and bobwhite quail), also used as a surrogate for terrestrial-phase 

amphibians and reptiles, 

2. Mammals (laboratory rat and mouse), 

3. Freshwater fish (rainbow trout), also used as a surrogate for aquatic-phase amphibians, 

4. Freshwater invertebrates (daphnid), 

5. Estuarine/marine fish (sheepshead minnow), 

6. Estuarine/marine invertebrates (Eastern oyster), 

7. Terrestrial plants (monocots and dicots), 
23

8. Aquatic plants (vascular and non-vascular plants), and 

9. Terrestrial invertebrates (honeybee) 

Within each of these very broad taxonomic groups, an acute and chronic endpoint is selected 

from the available test data, as the data sets allow. Additional ecological effects data were 

available for other taxa and have been incorporated into the risk characterization as other lines of 

evidence, including acute contact and oral toxicity on honeybees. 

2.5 Conceptual Model 

For a pesticide to pose an ecological risk, it must reach ecological receptors in biologically 

significant concentrations. An exposure pathway is the means by which a pesticide moves in the 

environment from a source to an ecological receptor. For an ecological pathway to be complete, 

it must have a source, a release mechanism, an environmental transport medium, a point of 

exposure for ecological receptors, and a feasible route of exposure. 

A conceptual model provides a written description and visual representation of the predicted 

relationships between imazosulfuron, potential routes of exposure, and the predicted effects for 

the assessment endpoint. A conceptual model consists of two major components: risk hypotheses 

and a conceptual diagram (USEPA, 1998). 

2.5.1 Risk Hypotheses 

• Terrestrial and aquatic organisms are subject to adverse direct effects such as reduced 

survival, growth, and reproduction when exposed to imazosulfuron/degradate residues as a 

result of labeled use of the pesticide. 

• Non-target terrestrial, semi-aquatic, and aquatic plants are subject to adverse effects such as 

reductions in vegetative vigor and seedling emergence (terrestrial) or biomass and growth 

rate (aquatic) when exposed to imazosulfuron/degradate residues as a result of labeled use of 

the pesticide 

• Indirect effects, such as habitat, food web dynamics, perturbing forage or prey availability, 

and altering the extent and nature of nesting, will potentially occur if residue concentrations 

exceed levels of concern for acute or chronic exposure for terrestrial and/or aquatic species. 

• Listed species are subject to adverse effects if calculated risk quotients exceed acute Listed or 

chronic levels of concern 

2.5.2 Conceptual Diagram 

In order for a chemical to pose an ecological risk, it must reach ecological receptors in 

biologically significant concentrations. An exposure pathway is the means by which a 

contaminant moves in the environment from a source to an ecological receptor. For an ecological 

exposure pathway to be complete, it must have a source, a release mechanism, an environmental 

transport medium, a point of exposure for ecological receptors, and a feasible route of exposure. 

In addition, the potential mechanisms of transformation (i.e., which degradates may form in the 

environment, in which media, and how much) must be known, especially for a chemical whose 

metabolites/degradates are of greater toxicological concern. The assessment of ecological 
24

exposure pathways, therefore, includes an examination of the source and potential migration 

pathways for constituents, and the determination of potential exposure routes (e.g., ingestion, 

inhalation, and dermal absorption). 

Figure 1. Conceptual Model Depicting Ecological Risk Based on Proposed Imazosulfuron 

Applications* 

*The pathways include both the parent and the degradates; Dotted boxes indicate 

pathways not considered in the risk assessment 

Based on the labels submitted by the registrant, the source, and mechanisms of release for 

imazosulfuron are aerial (for uses in rice only) and/or ground (tomato, pepper, rice, and 

turfgrass) application in the form of water dispersible granular formulation. The conceptual 

model and subsequent analysis of exposure and effects are all based both on the parent and 

degradates of imazosulfuron. Potential emission of volatile compounds is not considered as a 

viable release mechanism for imazosulfuron, because vapor pressure information (less than 2.63 

x 10-8 torr at 20°C) suggests that volatilization is not expected to be a significant route of 

dissipation for this chemical (indicated by dashed lines in the diagram). Imazosulfuron 

concentrations in surface waters may be relatively high when significant runoff events occur 

after application and / or spray drift to water bodies in close proximity to the treatment area 

occurs. Imazosulfuron and its degradates also have the potential to leach to groundwater which 

Aquatic Invertebrates 

Aquatic Vertebrates 

Aquatic Plants 

Stressor 

Source/ 

Transport 

Pathway 

Source/ 

Exposure 

Media 

Exposure 

Method 

Receptors 

Direct 

Effects: 

NonEndangered 

Species 

Indirect 

Effects: 

Perturbing Forage or Prey 

Availability Habitat Alteration: impacting nesting 

ability, ability to seek cover, etc. 

Individual Terrestrial 

Animals

Reduced Survival 

Reduced Growth 

Reduced Reproduction 

Individual Terrestrial 

Plants

Seedling Emergence 

Vegetative Vigor 

Individual Aquatic 

Vertebrates and 

Invertebrates

Reduced Survival 

Reduced Growth 

Reduced Reproduction 

Bioaccumulation

Aquatic Plant 

Population

Reduced 

Growth Rates 

and Biomass 

Terrestrial Animals

Birds, Mammals, 

Reptiles, Terrestrialphase Amphibians, Bees 

Terrestrial 

Upland Plants 

Wetland/ 

Riparian 

Plants 

Imazosulfuron Applied as Aerial and Ground Spray

Volatilization/ 

Wind 

Suspension 

Ground 

Deposition 

Spray Drift Runoff/ 

Erosion

Leaching 

(Infiltration/ 

Percolation)

Terrestrial 

Food Residues 

(foliage, fruit, 

insects)/ Soil 

Upland 

Foliage/ 

Soil 

Riparian/ 

Wetland 

Foliage/Soil 

Surface 

Water, 

Sediment 

Dietary 

Uptake 

Direct Contact/ 

Root Uptake 

Gill/ Integument 

Uptake 

Direct Contact/ 

Root Uptake 

Ground 

water

Direct 

Ingestion
25

can serve as inputs to surface water, although this is not explicitly modeled for ecological effects 

in this risk assessment due to modeling and data limitations. Persistence of total toxic residue in 

soil is sufficient such that vulnerable aquifers may be expected to be impacted but the exposure 

will be minimal compared to surface water exposure. The conceptual model shown in Figure 1 

generically depicts the potential source of imazosulfuron, release mechanisms, abiotic receiving 

media, and biological receptor types. 

2.6 Analysis Plan 

This document characterizes the environmental fate and effects of imazosulfuron based on 

proposed uses in tomato, pepper, rice, and turfgrass. Available environmental fate, ecotoxicity, 

and physicochemical property data were taken from submitted studies to the Agency. The 

environmental fate and effect studies underwent formal data evaluation review (DER) to 

determine their acceptability relative to published EPA guidelines. For the ecotoxicity data, the 

studies and/or DERs were reviewed to ensure that studies met current acceptability guidelines. 

The maximum proposed label application rates for use of imazosulfuron on turf (0.67 lb ai/A) 

and tomato, pepper, and rice (0.3 lb ai/A) were selected for modeling environmental 

concentrations for this screening-level deterministic (risk-quotient based) assessment. The most 

sensitive toxicity endpoints from surrogate test species are used to estimate treatment-related 

effects on growth, and survival. Estimated environmental concentrations (EECs) used in 

terrestrial and aquatic ecological risk assessments are based on imazosulfuron parent compound 

and several major degradates of parent. 

The following sections characterize the use, environmental fate, and ecological effects of 

imazosulfuron and, the use of risk quotient (ratio of exposure concentration to effects 

concentration) approach to estimate the potential for adverse effects on non-target terrestrial and 

aquatic animals and plants. Although risk is often defined as the likelihood and magnitude of 

adverse ecological effects, the risk quotient-based approach does not provide a quantitative 

estimate of likelihood and/or magnitude of an adverse effect. Such estimates may be possible 

through a more refined, probabilistic assessment; however, they are beyond the scope of this 

base-level assessment. 

2.6.1 Measures of Effect and Exposure 

Table 3 lists the measures of environmental exposure and ecological effects used to assess the 

potential risks of imazosulfuron to non-target organisms (USEPA, 2004). 
26

Table 3. Measures of Environmental Exposure and Ecological Effects Used to Assess the Potential Risks of 

Imazosulfuron to Non-Target Organisms

Assessment Endpoint Measures of Effect Measures of Exposure 

1. Abundance (i.e., survival, reproduction, and 

growth) of individuals and populations of birds 

1a. Bobwhite quail/ mallard duck acute oral LD50 

1b. Bobwhite quail/ mallard duck sub-acute dietary LC50 

1c. Bobwhite quail/ mallard duck chronic reproduction 

NOAEC and LOAEC 

Abundance (i.e., survival, reproduction, and 

growth) of individuals and populations of 

mammals 

Laboratory rat acute oral LD50 

Laboratory rat 2-generation NOAEC and LOAEC 

Maximum residues on food 

items (foliar) 

Rainbow trout, carp, bluegill sunfish LC50 

Peak EEC4 Abundance (i.e., survival, reproduction, and 

growth) of individuals and communities of 

freshwater fish 

Fathead minnow NOAEC and LOAEC 

60-day average EEC4 

Daphnid EC50 Peak EEC Abundance (i.e., survival, reproduction, and 4

growth) of individuals and communities of 

freshwater invertebrates Daphnid life cycle NOAEC and LOAEC 

Midge NOAEC and LOAEC 21-day average EEC4 

Sheepshead minnow acute LC50 

Eastern oyster EC50 

Mysid shrimp LC50

Peak EEC4

Abundance (i.e., survival, reproduction, and 

growth) of individuals and communities of 

estuarine/marine fish and invertebrates 

Chronic marine invertebrate study not submitted 

21-day average EEC4 

Survival of beneficial organisms, insect 

populations and natural Lepidoptera predators 

Honeybee acute contact LD50 

Earthworm LC50 and NOAEC 

Single Maximum 

application rate 

Maintenance and growth of individuals and 

populations of terrestrial plants from standing crop 

or biomass 

Monocot EC25 and NOAEC values for seedling emergence 

and vegetative vigor (survival and growth rate) 

Dicot EC25 and NOAEC values for seedling emergence and 

vegetative vigor (survival and growth rate) 

Estimates of runoff and 

spray drift to non-target 

areas 

Maintenance and growth of individuals and 

populations of aquatic plants from standing crop 

or biomass 

Vascular plant (i.e., Lemna) EC50 and NOAEC values for 

growth rate and biomass measurements 

Non-vascular plant (i.e., green algae) EC50 and NOAEC 

values for growth rate and biomass measurements 

Peak EEC4

1 If species listed in this table represent most commonly encountered species from registrant-submitted studies, risk assessment guidance 

indicates most sensitive species tested within taxonomic group are to be used for baseline risk assessments. 

2 Birds represent surrogates for amphibians (terrestrial phase) and reptiles. 3 Freshwater fish may be surrogates for amphibians (aquatic phase). 4 One in 10-year return frequency. 

5 Four species of two families of monocots - one is corn, six species of at least four dicot families, of which one is soybeans. LD50 = Lethal 

dose to 50% of the test population; NOAEC = No observed adverse effect concentration; LOAEC = Lowest observed adverse effect 

concentration; LC50 = Lethal concentration to 50% of the test population; EC50/EC25 = Effect concentration to 50%/25% of the test population.
27

Data Gaps 

The following Environmental Fate uncertainties, limitations, and assumptions were identified in 

this environmental risk assessment: 

• This assessment is based on limited biodegradation fate data. Imazosulfuron persistence 

is significantly affected by soil or water chemistry and may not always be easy to predict 

from typically available soil / water property data alone. A clearer picture of the range of 

variability in imazosulfuron persistence in the environment would require environmental 

fate studies on a greater variety of soils / waters / sediments with a greater range of pH 

levels and other soil properties. This is particularly true for the aerobic soil and anaerobic 

aquatic metabolism studies. 

• Even though imazosulfuron is soluble and moderately mobile to mobile based on the 

results of batch equilibrium studies, unextractable residues were identified at maximums 

of 87.7% of applied radioactivity in anaerobic aquatic metabolism and 35.7% of applied 

radioactivity in aerobic soil metabolism. The unextractable residues are uncharacterized 

and it is uncertain whether they consist of degradates of risk concern. Under sterile 

conditions these unextractable residues were not formed suggesting that the formation of 

them is microbially mediated. Metabolism half-lives were estimated based on total 

residue approach that includes parent and major degradates concentrations (excluding 

unextractable residues). To the extent that these unextractable residues are of risk 

concern, the estimated half-lives will be underestimated compared to a total toxic residue 

approach for estimating half-lives. However, given the persistence of total toxic residue 

of imazosulfuron, inclusion of unextractable residues in total toxic approach for 

calculating metabolism half-life would not impact PRZM/EXAMS modeled EECs 

appreciably. 

The following Environmental Effects uncertainties, limitations, and assumptions were identified 

in this environmental risk assessment: 

• An aquatic vascular plant (Lemna gibba) study using the degradate IPSN demonstrated 

no toxicity to the plant. However, greater toxicity was noted to mammals due to exposure 

to IPSN. Therefore, there is uncertainty regarding acute toxicity to fish, aquatic 

invertebrates (water column-dwelling), and aquatic non-vascular plants exposed to the 

degradates. Studies are required to address this uncertainty. 

• The recently revised FIFRA data requirements (CFR 40 Part 158) require an avian acute 

oral toxicity study (850.2100) be conducted using a passerine species (Passeriformes) 

• Research (Fletcher et al., 1993, 1996; Bhatti et al., 1995) involving chlorsulfuron, the 

first SU registered in the US (1981) has indicated that chlorsulfuron may have effects on 

plant seed/fruit production at extremely low concentrations. Researchers have also 

reported reproductive effects in cherry, canola, soybean, sunflower and Polygonum spp. 

at application rates as low as 1000x below the label rate. Therefore, studies that document 

the reproduction effects on plants due to imazosulfuron applications are required. 
28

3 ANALYSIS 

3.1 Use Characterization 

Imazosulfuron is a new systemic herbicide that is undergoing registration (as the active 

ingredient with two end-use products) by the registrant Valent Corporation. The imazosulfuron 

end-use products being proposed for registration in the United States are V-10142 and V-10142 

Ag, both of which water dispersible granules with 75.0% ai. 

According to the proposed labels for the food uses of imazosulfuron, this product would be used 

to control of sedges and broadleaf weeds in tomato, pepper, and rice. It is proposed that 

imazosulfuron will be applied in row middles, under plastic mulch, on bare soil, or as directed 

spray at 0.2 – 0.3 lb ai/A in pepper; as pre-transplant spray under plastic mulch, over the top 

(direct-seeded or post-transplant), or directed spray (direct-seeded or post-transplant) at 0.2 – 0.3 

lb ai/A in tomato; and to moist soil until 2-inch internode stage of drill-seeded, dry, or waterseeded rice. The maximum single application rate proposed for the food uses is 0.3 lb ai/A. A 

single application is permitted in tomato and pepper whereas two applications, 21 days apart, are 

allowed in rice. In view of crop injury, only ground applications are allowed in tomato and 

pepper. In addition to ground application, aerial application is permitted in rice only. 

For turfgrass (residential and commercial), the revised label suggest the use of 0.5 – 0.67 lb ai/A 

per application. Two post-emergence applications are permitted with 21-day interval between 

applications. Applications in turfgrass should be made after nutsedge has reached the 3-leaf stage 

of growth. Similar to tomato and pepper, only ground applications of imazosulfuron are allowed 

in turfgrass (Table 4). 

The label for imazosulfuron specifies that a rainfall event or overhead irrigation supplying 0.5 to 

1 inch of water no sooner than 12 hours and not later than 5 days after application is necessary to 

move the herbicide to the root zone of the germinating weed seedlings. The label disallows` 

aerial applications in tomato, pepper, and turfgrass and applications to ratoon rice. Furthermore, 

the label instructs to apply imazosulfuron in field grown tomato and pepper only; in drill-seeded, 

dry, or water-seeded rice; and to well-established pepper that is at least 10 inches tall, tomato that 

is at least in 4 – 5 leaf stage of development, rice (drill-seeded) that is at least in 2-leaf stage, and 

in established turfgrass when nutsedge has reached 3-leaf stage of growth. 

The imazosulfuron label for tomato and pepper indicates that it controls wild buckwheat, burning 

nettle, hairy galinsoga, common lambsquarters, Mayweed, yellow nutsedge, pigweeds, common 

purslane, common ragweed, shepherd’s purse, sowthistle, Russian thistle, wild turnip, and 

morning glory and suppresses barnyardgrass, crabgrass, giant foxtail, black nightshade, purple 

nutsedge, and Pennsylvania smartweed. Imazosulfuron is labeled for the control of ducksalad, 

eclipta, flat sedge, hemp sesbania, yellow nutsedge, pigweed, Texasweed, dayflower, northern 

joint vetch, pitted morning glory, red stem, and ricefield bulrush in rice. The turfgrass label for 

imazosulfuron suggest that it selectively controls sedges (purple and yellow nutsedge and annual 

and cylindric sedge) and certain broadleaf weeds (California burclover, lawn burweed, 

chickweed, Carolina geranium, henbit, Piert parsley, and common purslane) in residential and 

commercial areas. 
29

3.2 Exposure Assessment 

3.2.1 Environmental Fate and Transport Characterization 

Imazosulfuron is a sulfonyl urea herbicide containing dimethoxypyrimidine and imidazopyridine 

rings. Environmental fate properties (Table 5) described below are based on the combined labels 

[imidazolyl (IM) and pyrimidinyl (PM)]. Major routes of imazosulfuron dissipation are aerobic 

and anaerobic biodegradation and aqueous photolysis. Imazosulfuron is expected to degrade with 

half-lives of several weeks in aerobic soil environment and anaerobic aquatic environment. 

Aquatic photolysis (half-life of 3.5 days) is expected to hasten degradation of imazosulfuron but 

not in soil (stable). Imazosulfuron is also stable to abiotic hydrolysis except at low pH. Because 

imazosulfuron is mobile to moderately mobile in soil, it is expected to move from the application 

site into groundwater and surface water. Additionally, off-site movement of imazosulfuron is 

expected through spray drift from aerial and ground spray. 

Table 5. Summary of Environmental Fate and Transport Properties of Imazosulfuron 

Parameter 

[Guideline #] Value MRID(s) 

Hydrolysis 

[161-1] 

Combined labels [imidazolyl (IM) and pyrimidinyl (PM)] results: 

t1⁄2= 7 days @ 25 o

C at pH 4; 

t1⁄2=stable @ 25 o

C at pH 7; 

t1⁄2= stable @ 25 o

C at pH 9. 

 

Major degradates: 

1. 2-chloroimidazo[1,2-α]pyridin-3-sulfonamide (IPSN)-

maximum 90.7% of the applied in IM label 

2. 2-amino-4,6-dimethoxypyrimidine (ADPM)- maximum 90.2% 

of the applied in PM label

IPSN: t1⁄2= Stable @ 25 o

C at pH 5; 

ADPM: t1⁄2= Stable @ 25 o

C at pH 5;

473051-19 

477668-21 

Table 4. Application Information from the Proposed/Revised Imazosulfuron Labels 

Product 

(% AI) Uses Application Methods 

Single application 

Rate (lb ai/A) 

Maximum # of 

Applications 

Maximum 

Application 

Rate/Year (lb 

ai/A) 

Tomato and Pepper Ground 0.2 – 0.3 1 0.3 

Rice Ground 

Aerial 

0.2 – 0.31 

0.15 – 0.22 

0.15 fb 0.153 

2 

21-day interval 

V-10142 0.3 

(75% ai) 

Turf Ground 0.5 - 0.67 2 

21-day interval 1.34 

1

Preemergence in drill-seeded rice; 2Postemergence in drill-seeded rice; 3Preemergence application followed by 

postemergence application 
30

Table 5. Summary of Environmental Fate and Transport Properties of Imazosulfuron 

Parameter 

[Guideline #] Value MRID(s) 

Direct photolysis in water 

[161-2] 

Combined labels (IM and PM) results: 

t1⁄2= 3.5 days @ 25 o

C at pH 7 

Major degradates (irradiated water): 

1. 2-(2-imino-1,2-dihydropyridin-1-yl)oxalic acid (IHOA)- 

maximum 20.4% of the applied in IM label 

2. ADPM – maximum 35.3% of the applied (PM ring) 

3. (4,6-dimethoxypyridine-2-yl) aminocarbonylsufamic acid 

(SDPM) – maximum 13.9% of the applied in PM label 

4. 4,6-dimethoxy-2-ureidopyrimidine (UDPM)- maximum 11.1% 

of the applied in PM label 

473051-20

Photolysis on soil 

[161-3] 

Combined labels (IM and PM) results: 

t1⁄2= Stable 

The estimated half-life is of uncertain value since it is extrapolated well 

beyond the duration of the study. Therefore, photolysis in soil is 

considered as stable. 

Major degradates: 

Maximum concentrations of the transformation products are not certain 

since only the 30-day samples were exhaustively extracted. All 

maximum concentrations were measured at 30 days posttreatment. 

473051-21

Aerobic soil metabolism 

[162-1] 

Combined labels (IM and PM) results: 

1. Loam soil ((pH 6.9, organic carbon content 1.2%) from New 

Jersey 

Linear half-life: 76.2 days (r2

 = 0.93). 

Non-linear half-life: 36.5 days (r2

 = 0.98). 

Observed DT50: ca. 27 days. 

Major transformation products: 

1. 1-(2-chloroimidazo [1,2a]pyridin-3-ylsulfonyl)-3-(4-hydroxy-6-

methoxypyrimidin-2-yl)urea (HMS) detected in both IM and IP 

labels 

-Maximum 11.9 % of the applied in IM label 

-Maximum 11.0 % of the applied in PM Label 

2. IPSN - maximum 14.2% of the applied in IM label. 

2. Loamy sand soil ((pH 6.1, organic carbon content 2.27%) from 

Germany 

Linear half-life: 58.2 days (r2

 = 0.88). 

Non-linear half-life: 42.3 days (r2

 = 0.90). 

Observed DT50: ca. 23 days. 

Major transformation products: 

 IPSN - maximum 26.0% of the applied in IM label at the time of 

study termination (120 days). 

473051-22 

477668-01 

Anaerobic soil metabolism Combined labels (IM and PM) results: 477668-02 
31

Table 5. Summary of Environmental Fate and Transport Properties of Imazosulfuron 

Parameter 

[Guideline #] Value MRID(s) 

[162-2] 1. Loam soil ((pH 6.7, organic carbon content 2.0%) from New 

Jersey 

Half–life/DT50 values reported as post-flood 

Linear half-life in water: 48.8 days (r2

 = 0.89). 

Linear half-life in soil: 72.2 days (r2

 = 0.87). 

Linear half-life in the total system: 73.7 days (r2

 = 0.88). 

Non-linear half-life in water: 61.9 days (r2

 = 0.91). 

Non-linear half-life in soil: 77.0days (r2

 = 0.83). 

Non-linear half-life in the total system: 90.0 days (r2

 = 0.90). 

Observed DT50 in water: ca. 77 days. 

Observed DT50 in soil: ca. 88 days. 

Observed DT50 in the total system: ca. 88 days. 

Major transformation products: 

1. 1-(2-chloroimidazo [1,2a]pyridin-3-ylsulfonyl)-3-(4-hydroxy-6-

methoxypyrimidin-2-yl)urea (HMS) detected in both IM and IP 

labels 

-Maximum 15.5 % of the applied in IM label 

-Maximum 17.4 % of the applied in PM Label 

2. IPSN - maximum 20.1% of the applied in IM label. 

3. ADPM - Maximum 12.7 % of the applied in PM Label 

Anaerobic aquatic metabolism 

[162-3] 

Combined labels (IM and PM) results: 

Matrix: Creek water-clay sediment (water pH 7.8; sediment pH 6.5, 

organic matter 3.6%) systems from Mississippi. 

Linear half-life in the total system: 47.2 days (r2

 = 0.78). 

Non-linear half-life in total system: 16.5 days (r2

 = 0.99) 

Observed DT50 in total system: ca. 21 days. 

Major transformation products in the total system: 

1. HMS 

 -Maximum 20.0 % of the applied in IM label 

 -Maximum 21.8 % of the applied in PM Label 

2. IPSN - maximum 19.8 % of the applied in IM label. 

473051-23 

Aerobic aquatic metabolism 

[162-4] 

Combined labels (IM and PM) results: 

Matrix: Millstream pond water-loam sediment (water pH 8.02; 

sediment pH 7.4-7.6, organic matter 7.0%) systems from U.K. 

Linear half-life in water: 20.6 days (r2

 = 0.93). 

Linear half-life in sediment: 31.9 days (r2

 = 0.87). 

Linear half-life in the total system: 22.1 days (r2

 = 0.89). 

Non-linear half-life in water: 17.6 days (r2

 = 0.97). 

Non-linear half-life in sediment: 43.3 days (r2

 = 0.70). 

Non-linear half-life in the total system: 27.9 days (r2

 = 0.97). 

476397-02 
32

Table 5. Summary of Environmental Fate and Transport Properties of Imazosulfuron 

Parameter 

[Guideline #] Value MRID(s) 

Observed DT50 in water: ca. 14 days. 

Observed DT50 in sediment: ca. 23 days. 

Observed DT50 in the total system: ca. 40 days.

Major transformation products in the total system: 

1. HMS 

 -Maximum 9.89 % of the applied in PM Label 

Matrix: Arkansas water-silt loam sediment (water pH 7.2; sediment 

pH 6.0, organic matter 1.3%) systems from U.K. 

Linear half-life in water: 24.2 days (r2

 = 0.60). 

Linear half-life in sediment: 117.5 days (r2

 = 0.46). 

Linear half-life in the total system: 52.5 days (r2

 = 0.71). 

Non-linear half-life in water: 10.7 days (r2

 = 0.75). 

Non-linear half-life in sediment: 111.8 days (r2

 = 0.49). 

Non-linear half-life in the total system: 44.1 days (r2

 = 0.76). 

Observed DT50 in water: ca. 0-6 days. 

Observed DT50 in sediment: > 36 days. 

Observed DT50 in the total system: ca. 42 days.

Major transformation products in the total system: 

2. HMS 

 -Maximum 17.5 % of the applied in IM Label 

 -Maximum 15.8 % of the applied in PM Label 

476791-05 

Adsorption/ 

Desorption 

(Kd and 

Koc in L Kg-1) 

[163-1] 

Parent: imazosulfuron: 

Soil type: Penn Loam. 

Adsorption Kd: 1.64. 

Adsorption Koc: 135. 

Freundlich adsorption Kf: 1.20. 

Freundlich adsorption Kfoc: 98. 

1/N: 0.84 

Desorption Kd: 3.10. 

Desorption Koc: 254. 

Freundlich desorption Kf: 1.14. 

Freundlich desorption Kfoc: 93. 

1/N: 0.87 

Soil type: Atwater Loamy sand. 

Adsorption Kd: 0.57. 

Adsorption Koc: 198. 

Freundlich adsorption Kf: 1.15. 

Freundlich adsorption Kfoc: 397 

1/N: 0.87 

473051-17
33

Table 5. Summary of Environmental Fate and Transport Properties of Imazosulfuron 

Parameter 

[Guideline #] Value MRID(s) 

Desorption Kd: 3.38. 

Desorption Koc: 1165. 

Freundlich desorption Kd: 1.01. 

Freundlich desorption Koc: 348. 

1/N: 1.00 

Soil type: Bosket Silt loam. 

Adsorption Kd: 0.60. 

Adsorption Koc: 208. 

Freundlich adsorption Kf: 1.13. 

Freundlich adsorption Kfoc: 390. 

1/N: 0.87 

Desorption Kd: 0.99. 

Desorption Koc: 341. 

Freundlich desorption Kf: 1.16. 

Freundlich desorption Kfoc: 400. 

1/N: 0.87 

Soil type: Rilla Silt loam. 

Adsorption Kd: 5.71. 

Adsorption Koc: 428. 

Freundlich adsorption Kf: 1.28. 

Freundlich adsorption Kfoc: 96. 

1/N: 0.78 

Desorption Kd: 7.06. 

Desorption Koc: 529. 

Freundlich desorption Kf: 1.22. 

Freundlich desorption Kfoc: 92. 

1/N: 0.82

Adsorption/ 

Desorption 

of Degradates 

The adsorption coefficients (Koc) of five transformation products of 

imazosulfuron were estimated using established HPLC estimation 

methods. This study was conducted in accordance with OECD Guideline 

for the Testing of Chemicals No. 121 and in compliance with USEPA 

GLP 40 CFR Part 160. Imazosulfuron is ionized at neutral pH and has a 

pKa of 3.94 at 20°C (pp. 15, 20). Based on the study results, the HPLCestimated Koc values for imazosulfuron changed greatly when the pH 

was reduced from pH 7 to pH 3. This was reportedly due to the 

transition below the pKa (to the non-ionized form). 

At pH 7, the calculated Koc values were <1 for imazosulfuron, HMS, 

SDPM, and IHOA, 33 for IPSN, and 38 for ADPM. At pH 3, the 

calculated Koc values were 2210 for imazosulfuron, <1 for HMS, SDPM, 

and IHOA, 36 for IPSN, and 69 for ADPM. 

At pH 3, the calculated Koc values were 2210 for imazosulfuron, <1 for 

HMS, SDPM, and IHOA, 36 for IPSN, and 69 for ADPM. 

473051-18 

Terrestrial Field 

Dissipation 

[164-1] 

Location/soil type: Near Athens, Georgia/Sandy clay (0-30 cm) over 

clay (30-90 cm). 

a) Soil

473051-26 
34

Table 5. Summary of Environmental Fate and Transport Properties of Imazosulfuron 

Parameter 

[Guideline #] Value MRID(s) 

Half-life: 6.2 days (r2 = 0.76) after first application; 15.2 days following 

the second application (r2

 = 0.41; based on residue data from 3 to 42 

days). 

Major transformation products detected: None greater than 10% of the 

total applied imazosulfuron. 

b) Turfgrass

Half-life: Half-life: 5.6 days (r2

 = 0.93) after first application and 25.2 

days following the second application (r2

 = 0.66); 4.3 days (r2 = 0.82) 

based on residue data from 0 to 10 days;). 

Major transformation products detected: Not analyzed for transformation 

products. 

Location/soil type: Near North Rose, New York/Loamy sand (0-60 

cm) over sand (60-90 cm). 

a) Soil

Half-life: 75.3 days following the second application (r2 = 0.71; based on 

residue data from 1 to 180 days;). 

Major transformation products detected: None greater than 10% of the 

total applied imazosulfuron. 

b) Turfgrass

Half-life: Half-life values of 6.4 days (r2

 = 0.72) and 30.4 days (r2 = 

0.64) following the first and second applications, respectively, calculated 

using linear regression. 

2.4 days following the second application (r2

 = 0.92; based on residue 

data from 0 to 10 days;). 

Major transformation products detected: Turfgrass was not analyzed for 

transformation products. 

473051-27 

Location/soil type: Madera, California/Loamy sand (0-60 cm) over 

sandy loam (60-90 cm). 

c) Soil (Bare Field)

Half-life: 18.0 days (r2

 = 0.81, linear, first-order). 

 4.9 days (r2

 = 0.89, nonlinear). 

DT50: Between 1 and 5 days (2.8 days). 

DT90: Between 14 and 28 days (25.1 days). 

Transformation products detected: ADPM, IPSN, and HMS 

476791-08 
35

Table 5. Summary of Environmental Fate and Transport Properties of Imazosulfuron 

Parameter 

[Guideline #] Value MRID(s) 

Location/soil type: Greenville, Mississippi/Silt loam (0-30 cm). 

a) Soil (Bare Field)

Half-life: 12.0 days (r2 = 0.8870, linear). 

 6.1 days (r2

 = 0.8561, nonlinear). 

DT50: Between 3 and 7 days (5.9 days). 

DT90: Between 14 and 28 days (26.9 days). 

Transformation products detected: ADPM, IPSN, and HMS. 

476791-09 

Location/soil type: Bumpass, Virginia/Sandy clay loam (0-30 cm) 

over clay/clay loam (30-90 cm).

a) Soil (Bare Field)

Application 1

Half-life: 8.4 days (r2

 = 0.9101, linear, first-order). 

 6.4 days (r2

 = 0.7943, nonlinear). 

DT50: Between 3 and 10 days (4.4 days). 

DT90: Not determined. 

Transformation products detected: IPSN. 

Application 2

Half-life: 9.0 days (r2

 = 0.8080, linear, first-order). 

 7.5 days (r2

 = 0.7425, nonlinear.. 

DT50: Between 5 and 10 days (7.0 days. 

DT90: Between 28 and 44 days (value could not be calculated). 

Transformation products detected: IPSN and ADPM. 

476791-10 

Aquatic Field 

Dissipation 

[164-2] 

Location/soil type: Yuba City, California/Clay loam (0-15 cm). 

(a) Water

Half-life: 5.3 days (r2

 = 0.84, linear). 

 5.8 days (r2

 = 0.93, nonlinear).. 

DT50: Between 5 and 7 days (6.6 days.). 

DT90: Between 14 and 28 days (21.5 days). 

Transformation products detected: UDPM, ADPM, and IPSN 

Dissipation routes: Transformation 

(b) Sediment 

Half-life: 83.5 days (r2

 = 0.36, linear, 5-120 day data). 

 65.4 days (r2

 = 0.89, nonlinear; reviewer-calculated, 5-120 

day data). 

DT50: Not determined. 

DT90: Not determined. 

Transformation products detected: IPSN, ADPM, and HMS 

Dissipation routes: Transformation 

476791-01 
36

Degradation 

The major route of dissipation for imazosulfuron is believed to be aerobic and anaerobic 

degradation/metabolism in soil and water (non-linear degradation half-lives generally around 

10.7 to 90 days) with a short half-life of 3.5 days for photolysis potentially dominant under 

aquatic conditions. The biodegradation of imazosulfuron was biphasic in aerobic and anaerobic 

systems with an initial rapid phase followed by much slower degradation rate for residual 

imazosulfuron. The biotransformation of imidazolyl and pyrimidinyl rings of imazosulfuron was 

studied in loam and loamy sand soils to evaluate aerobic soil metabolism. Based on non-linear 

regression analysis, imazosulfuron (combined labels) dissipated with half-lives of 36.5 and 42.3 

days and the observed DT50s were ca. 23 to 27 days. Two major transformation products 

(>10%), HMS and IPSN were detected in the aerobic soil metabolism study. 

In the anaerobic soil study, imazosulfuron (combined labels) dissipated from the total system 

with a nonlinear half-life of 90 days and a first order half-life of 74 days. In the soil, nonlinear 

and linear half lives were 77 and 72 days, respectively. The observed DT50 was ca. 88 days in 

the both the total system and soil. Three major transformation products (>10%), HMS, IPSN and 

ADPM were detected in the anaerobic soil metabolism study. 

The biotransformation of imidazolyl and pyrimidinyl rings of imazosulfuron was studied in two 

water-sediment system to evaluate aerobic aquatic metabolism. In the Millstream pond waterloam sediment system (combined labels), based on nonlinear regression analysis, imazosulfuron 

dissipated with a calculated the half-lives of 28 days in the total system, 25 days in the water, and 

43 days in the sediment. HMS was a major transformation product in the Millstream pond waterloam sediment systems (both labels). In a water-silt loam soil system from Arkansas, based on 

combined labels and nonlinear regression analysis, imazosulfuron dissipated with half-lives of 44 

days in the total system, 11 days in the water, and 112 days in the soil. Linear half-lives were 53 

days in the total system, 24 days in the water layer and 118 days in the soil. HMS was a major 

transformation product in both labels. 

In the anaerobic aquatic metabolism study, imazosulfuron (combined labels) decreased from an 

average of 90.0-93.7% of the applied at time 0 to 66.7-74.1% at 8 days posttreatment, 45.2-

54.0% at 17 days, 26.9-28.4% at 28 days and ≤2.0% at and after 112 days. Based on nonlinear 

regression analysis, imazosulfuron (combined labels) dissipated with calculated half-life of 16.5 

days and the observed DT50 was ca. 21 days in the total system. Two major transformation 

products (>10%), HMS and IPSN were also detected in the anaerobic aquatic metabolism study. 

In general, the pseudo first-order degradation half-lives are longer than the non-linear and DT50 

in the aerobic and anaerobic biodegradation studies. The biodegradation of imazosulfuron was 

biphasic with an initial rapid phase followed by much slower degradation rate for residual 

imazosulfuron in these studies. The biphasic degradation pattern in aerobic soil and anaerobic 

aquatic metabolism studies and the methods of calculating half-live have resulted discrepancies 

between calculated linear and non-linear half-lives as well as observed DT50. 

 

Considering abiotic degradation, imazosulfuron is photolyzed at pH 7 in water (half-life of 3.5 

days) but a longer half-life of 154 days in soil environments. Similar photolytic degradation half-
37

life of 3.5 days was also observed in synthetic humic water sample. The four major 

transformation products were IHOA, ADPM, SDPM, and UDMP in aquatic photolysis study. 

Imazosulfuron can be hydrolyzed under acidic environment (pH 4.0) but stable at neutral and 

alkaline conditions (pH 7-9). The proposed metabolic pathways for the degradation of 

imazosulfuron and the formation of major degradates are shown in Figure 2. 

Figure 2. The Proposed Metabolic Pathways for the Degradation of Imazosulfuron and the 

Formation of Major Degradates 
38

Field Studies 

The soil dissipation/accumulation of imazosulfuron under bare ground and cropped (turf) 

conditions was studied in Georgia, New York, California, Mississippi and Virginia in the United 

States (MRIDs 473051-26, 473051-27, 476791-08, 476791-09, and 476791-10. Under bare 

ground conditions, imazosulfuron dissipated from the entire soil profile with DT50s and DT90s 

ranging from 2.8 -5.9 days and 25.1 – 26.9 days, respectively. However, the observed DT90

value for sandy clay loam of Virginia could not be determined (beyond the range of the data). 

The soil dissipation/accumulation of imazosulfuron under cropped (turfgrass) conditions was 

studied in Georgia and New Jersey. Under field conditions in the soil, the calculated half-life 

values were 6.2 to 9.5 days following the first and 15.2 to 75.3 days following second 

applications, respectively, calculated using linear regression. Carryover of residues following the 

second application was 0% of the total applied imazosulfuron, based on two applications at the 

target application rates in Georgia and New York Sites. 

Under field conditions in the turfgrass, imazosulfuron had reviewer-calculated half-life values of 

5.6 to 6.4 days following the first and 25.9 to 30.4 days following second applications, 

respectively, calculated using linear regression. However, the dissipation patterns in both sites 

following the second application were bi-phasic and the observed DT50 values were 

approximately 0.75 to 5 days. Carryover of residues could not be determined because the 

calculation is based upon bulk density and corresponding soil layer. However, at the end of the 

study following the second application in Georgia and New York, imazosulfuron residues totaled 

0.08 0.15 ppm, at 120 days which is 4.5 to 7.1 % of the total residues originally recovered. 

In terrestrial field dissipation study (MRID 473051-27), imazosulfuron was detected in the 45-60 

cm soil depth at a maximum of 0.11 ppm at 14 days and in the 60-75 cm and 75-90 cm soil 

depths at a maximum of 0.03 ppm following the second application in New York. IPSN was also 

detected in the 30-45 cm, 45-60 cm, and 75-90 cm soil depths at 0.02 ppm following the second 

application. However, imazosulfuron and its degradates were not detected in soil below the 30-

45 cm depth in other terrestrial field dissipation studies. 

The aquatic field dissipation of imazosulfuron under U.S. field conditions was studied using a 

flooded plot of clay loam soil planted with rice at one site in California. Under aquatic field 

conditions, the calculated half-life value is 5.3 days in water for imazosulfuron. The calculated 

half-life value is 65.4 days based on nonlinear regression. The observed DT50 value could not be 

reliably determined due to data variability, and the observed DT90 value occurred beyond the 

range of the data set. The transformation products UDPM and IPSN were detected in the water at 

concentrations above the LOD. The transformation products ADPM, HMS, and IPSN were also 

detected in sediment at concentrations above the LOD. 

Degradates of Exposure Concern 

The environmental degradates of imazosulfuron that are of possible exposure concern for surface 

water include the parent compound’s major degradates, HMS, IPSN, IOHA, ADPM, UPDM and 

SPDM (Table 6). HMS is the only degradate that retains both imidazolyl (IM) and pyrimidinyl 
39

(PM) ring structures. HMS has been detected using both IM and PM radio-label rings in aquatic 

photolysis, aerobic soil metabolism and anaerobic aquatic metabolism studies. IPSN and ADPM 

are included for maximum formation at lower pH. IPSN (14.2%) and ADPM (35.3 %) in were 

also major degradates formed in aerobic soil metabolism and aquatic photolysis studies 

respectively. Carbon dioxide is a major degradate in the aerobic soil metabolism study of 

imazosulfuron, in which it was up to 53.3% of the applied. Major and minor degradates of 

imazosulfuron and their structures are listed in Table 6. 

Table 6. Major and Minor Degradates of Imazosulfuron 

Name of Degradate 

And 

Structure 

IUPAC Name Maximum 

Detected 

(%) 

Comments 

Major degradates 

HMS 

N

N

Cl

S

O

O

N

H

N

O

H N

N

O

O H

CH3

1-(2-chloroimidazo[1,2-α]pyridin-3-

ylsulfonyl)-3-(4-hydroxy-6-

methoxypyrimidin-2-yl)urea 

20.9 Detected under both imidazolyl 

(IM) and pyrimidinyl (PM) labels 

IPSN 

N

N

Cl

S

O

O

N

H

H

2-Chloroimidazo[1,2-a]pyridin-3-

sulfonamide. 

90.7 IM label at pH 4.0 

IOHA 

N

O NH

OH

O

2-(2-imino-1,2-dihydropyridin-1-yl)oxalic 

acid 

20.4 IM label 

ADPM 

H

N

N

N

O

O CH3

CH3

H

2-amino-4,6-dimethoxypyrimidine 91.2 PM label at pH 4.0 

UPDM 

N

H

N

O

H N

N

O

O CH3

CH3

H

4,6-dimethoxy-2-ureidopyrimidine 11.2 PM label 

SDPM 

S

O

O

N

H

N

O

H N

N

O

O CH3

CH3

OH

(4,6-dimethoxypyridine-2-

yl)aminocarbonylsufamic acid 

13.9 PM label 

CO2 

O C O

Carbon dioxide 53.3 PM label 

Minor degradates 

IP 2-Chloroimidazo[1,2-α]pyridine 3.2 IM label at pH 4.0 
40

Table 6. Major and Minor Degradates of Imazosulfuron 

Name of Degradate 

And 

Structure 

IUPAC Name Maximum 

Detected 

(%) 

Comments 

N

N

Cl

IPSA 

N

N

Cl

S

O

O

OH

2-chloroimidazo[1,2-α]pyridin-3-yl sulfonic 

acid 

5.8 IM label 

CDPM 

N

N

N

O

O CH3

CH3

H

N

2-cyano-4,6-dimethoxypyrimidine 5.3 PM label 

AHMP 

N

N

N

O

O H

CH3

H

H

2-Amino-4-hydroxy-6-methoxypyrimidine 4.7 PM label 

ACIS 

N

N

Cl

S

O

O

N

H

N

O

H NH2

NH

N-

({[Amino(imino)methyl]amino}carbonyl)-

2-chloroimidazo[1,2-a]pyridine-3-

sulfonamide 

9.4 IM Label 

Mobility 

Based on the batch equilibrium data, adsorption of imazosulfuron (Koc = 135 to 428 L/Kg) is 

characterized as being mobile to moderately mobile in the test soils. Desorption constants ranges 

from 254 to 1165 L/Kg for the same soil suggest that the compound desorbs at slower rates from 

soil metrics. In addition, a study was conducted to estimate the Koc of five transformation 

products (HMS, IPSN, IOHA, ADPM and SPDM of imazosulfuron using established HPLC 

estimation methods. The calculated Koc values were <1 L/Kg for HMS, SDPM, and IHOA, 33-

36 for IPSN, and 38-69 for ADPM. The HPLC estimated Koc values, SDPM, IHOA and HMS 

would be categorized as highly mobile in most soils. ADPM and IPSN would be categorized as 

mobile. The mobility classification of parent and degradates is based on mobility class of FAO 

(FAO 2000). However, for imazosulfuron, the calculated Koc values were <1 L/Kg at pH 7 and 

2210 L/Kg at pH 3, which are significantly different from the batch equilibrium values (Koc = 

135 to 428 L/Kg) suggest that the HPLC may not be a comparable method to characterize 

mobility class for this chemical. 
41

Imazosulfuron is a non-volatile (≤ 2.63 x 10-8 Torr at 20°C) compound and soluble (429 mg/L at 

20°C) in water. Therefore, dissipation of imazosulfuron in the environment is expected to occur 

predominantly via runoff and leaching. Imazosulfuron was detected in the 30- to 45-cm depth of 

soil at 14 days after second application, and was not detected at lower soil depths, which 

indicates that leaching of residues may occur under certain conditions. No major transformation 

products were detected in any soil depth at a concentration equivalent to >10% of the total 

applied imazosulfuron. Imazosulfuron in leachate is not expected to persist under an anaerobic 

soil conditions. 

Low vapor pressure and Henry’s Law Constant of imazosulfuron suggest that volatilization to 

atmosphere is an unlikely route of dissipation. Persistence of total toxic residue [imazosulfuron 

and degradates (HMS, IPSN, ADPM, IHOA and SPDM)] in soil is sufficient such that 

vulnerable aquifers may be expected to be impacted but exposure will be minimal compared to 

surface water concentrations. Imazosulfuron concentrations in surface waters may be relatively 

high when significant runoff events occur after application and / or spray drift to water bodies in 

close proximity to the treatment area occurs. 

3.2.2 Aquatic Exposure Estimates for Imazosulfuron 

A Tier II screening-level surface water exposure for aquatic risk assessment was conducted for 

the Section 3 proposed new use registration. Modeled application rates represent the maximum 

uses pattern of the proposed label for use on tomato, pepper, rice, and turfgrass. The aquatic 

exposure estimates presented in this assessment were based on the use of models as no surface 

and groundwater monitoring data is available for imazosulfuron within the continental U.S. To 

simulate surface water exposure for the ecological risk assessment, the Tier II PRZM/EXAMS 

model and Tier I Rice models were used. 

PRZM-EXAMS Model Inputs and Scenarios for Imazosulfuron 

The Pesticide Root Zone Model, (PRZM, Carsel et al., 1997) and the Exposure Analysis 

Modeling System (EXAMS, Burns, 1997) were used in tandem to generate aquatic estimated 

environmental concentrations (EECs). PRZM (3.12.2 dated May 12, 2005) simulates fate and 

transport on the agricultural field whereas EXAMS (2.98.04.06, dated April 25, 2005) simulates 

the fate and resulting daily concentrations in the water body. Simulations are carried out with 

the linkage program shell, PE5V01.pl (dated November 15, 2006), which incorporates the 

standard agricultural and non-agricultural scenarios developed by EFED. Simulations are run for 

multiple (usually 30) years, and the EECs represent peak values that are expected once every ten 

years based on the thirty years of daily values generated during the simulation. Additional 

information on these models can be found at: http://www.epa.gov/oppefed1/models/water 

/index.htm. 

The aquatic exposure is estimated for the maximum application pattern to a 10-ha field bordering 

a 1-ha pond, 2-m deep (20,000 m3

) with no outlet. Exposure estimates generated using this 

standard pond are intended to represent a wide variety of vulnerable water bodies that occur at 

the top of watersheds including prairie pot holes, playa lakes, wetlands, vernal pools, man-made 

and natural ponds, and intermittent and first-order streams. As a group, there are factors that 
42

make these water bodies more or less vulnerable than the standard surrogate pond. Static water 

bodies that have larger ratios of pesticide-treated drainage area to water body volume would be 

expected to have higher peak EECs than the standard pond. These water bodies will be either 

smaller in size or have large drainage areas. Smaller water bodies have limited storage capacity 

and thus may overflow and carry pesticide in the discharge, whereas the standard pond has no 

discharge. As watershed size increases beyond 10-ha, it becomes increasingly unlikely that the 

entire watershed is planted with a non-major single crop that is all treated simultaneously with 

the pesticide. Headwater streams can also have peak concentrations higher than the standard 

pond, but they likely persist for only short periods of time and are then carried and dissipated 

downstream. 

There are several major degradates identified in the environmental fate studies (DP 358472). The 

Residues of Concern Knowledgebase Subcommittee (ROCKS) of the Health Effects Division 

(HED) and EFED reviewed the structures of these degradates to determine residues of concern 

(DP Barcode: 359190). As the degradate HMS retains both imidazolyl (IM) and pyrimidinyl 

(PM) ring structures, its toxicity is likely comparable to the parent. Structure-activity relationship 

(SAR) analysis using the DEREK system (Deductive Estimate of Risk from Existing 

Knowledge) revealed the same structural alerts as the parent compound; therefore, HMS is 

considered a residue of concern. DEREK analysis of IPSN, IHOA, ADPM, SDPM, and UDPM 

showed that all of these cleavage products except IHOA (a low molecular weight acid) retained 

at least one of the same structural alerts as the parent. Therefore aquatic exposure of total toxic 

residue is considered in this assessment (parent plus five degradates listed in Table 7). 

Table 7. Metabolites and Degradates to be Included in the Surface Water Exposure Assessment 

Residues of concern- Imazosulfuron, HMS, IPSN, ADPM, UDPM, and SDPM 

CAS Name: 

Imazosulfuron = 2-chloro-N-[[(4,6-dimethoxy-2-pyrimidinyl)amino]carbonyl]imidazo[1,2-α]pyridine-3-

sulfonamide 

HMS = 2-chloro-N-[[(4-hydroxy-6-methoxy-2-pyrimidinyl)amino]carbonyl]imidazo[1,2-α]pyridine-3-sulfonamide 

IPSN = 2-chloroimidazo[1,2-alpha]pyridin-3-sulfonamide] 

ADPM = 2-amino-4,6-dimethoxypyrimidine 

UDPM = 4,6-dimethoxy-2-ureidopyrimidine 

SDPM = (4,6-dimethoxypyrimidine-2-yl)aminocarbonylsulfamic acid 

Table 8 summarizes the model input parameter values used in PRZM/EXAMS. These 

parameters were selected in accordance with EFED’s input parameter guidance (Environmental 

Fate and Effects Division, 2002). Aerobic soil metabolism half-life of 207.2 days, aerobic 

aquatic half-life of 207.2 and anaerobic aquatic metabolism half-life of 64.2 days for total toxic 

residue (imazosulfuron and listed degradates in Table 6) were used for surface water modeling 

with PRZM/EXAMS. Abiotic degradation half-life of 61.69 days for aquatic photolysis for total 

toxic residue was also used for surface water modeling. Since the experimental 

phototransformation half-lives of IM and PM labels are based on the continuous irradiation used 

in the laboratory study, estimated half-lives were adjusted by multiplying with 0.5 based on a 12-

hour light/12-hour dark cycle. Also, the intensity of the xenon lamp over the wavelengths 290-

800 nm was 558 W/m2

, compared to 380 W/m2 for natural sunlight over a 12-hour (solar) day at 

40°N latitude during June through August. Therefore, 1 hour of artificial light was equivalent to 
43

1.47 hours of natural sunlight. Calculation of first-order degradation rates for total toxic residue 

can be found in Appendix B. 

OPP standard PRZM crop scenarios, which consist of location-specific soils, weather, and 

cropping practices, were used in the simulations to represent proposed labeled uses of 

imazosulfuron. These scenarios were developed to represent high-end exposure sites in terms of 

vulnerability to runoff and erosion and subsequent off-site transport of pesticide. A 10-foot 

vegetative buffer strip between treated areas and water bodies was recommended in the 

submitted labels to reduce off-site movement of applied pesticide. However, current 

PRZM/EXAMS model does not have a specific routine to evaluate the effect of vegetative 

buffer. For the purposes of this assessment, it was assumed that applications were made week 

after the weed emergence (as specified in the standard scenarios). A summary of the input 

parameters and crop scenarios used to estimate imazosulfuron concentrations in the aquatic 

systems for ecological risk assessment are listed in Table 8. PRZM/EXAMS output files are 

provided in Appendix C of this document. 

Table 8. PRZM/EXAMS Input Parameter Values for Total Residuea of Imazosulfuron 

Parameter Value Source Comments

Maximum application 

Rate lb ai/A (kg ai/ha) 

Turfgrass: 0.67 (0.75) 

Food uses 0.30 (0.34) 

V-10142 Herbicide (75.0%) 

V-10142 Ag Herbicide 

(75.0%) 

FL and PA turf STD scenarios; 

FL and PA tomato STD scenarios 

FL Pepper STD scenario 

Number of Applications 2 (turfgrass) 

1 (food uses) 

V-10142 Herbicide (75.0%) -- 

Minimum Application 

Intervals (days) 21 

V-10142 Herbicide (75.0%) 

V-10142 Ag Herbicide 

(75.0%) 

For turf use only 

Application Date 

FL Turf February 8 

PA Turf April 8 

FL Tomato February 8 

PA Tomato April 23 

FL pepper September 8 

Based on PRZM/EXAMS 

Scenarios 

One week after crop emergence 

described in these scenarios 

Wetted in? No V-10142 Herbicide (75.0%) --- 

Depth of Incorporation 

(inches) 0 

V-10142 Herbicide (75.0%) 

V-10142 Ag Herbicide 

(75.0%) 

For foliar application according to Input 

parameter guidance (USEPA, 2009) 

Method of Application Ground spray 

V-10142 Herbicide (75.0%) 

V-10142 Ag Herbicide 

(75.0%) 

--- 

Application Efficiency 

Ground: 0.99 Input parameter guidance 

(USEPA, 2009) 

Default values for ground spray 
44

Table 8. PRZM/EXAMS Input Parameter Values for Total Residuea of Imazosulfuron 

Parameter Value Source Comments

Spray Drift Fraction Ground: 0.01 Input parameter guidance 

(USEPA, 2009) 

Default values for ground spray 

Default values for aerial spray 

Molecular Mass (g/mol) 412.81 MRID 473051-01 Product chemistry data 

Vapor Pressure (Torr) ≤ 2.63 x 10-8 MRID 473051-16 Product chemistry data 

Henry’s Law Constant 

(atm m3/mol) ≤ 3.33 x 10-11 Estimated Input parameter guidance (USEPA, 2009) 

Solubility in Water 

(mg/L) 429 MRID 473051-15 Input parameter guidance (USEPA, 2009) 

Hydrolysis t1/2 at pH 7.0 

(days) 

0 MRID 473051-19 Stable to hydrolysis @ pH 7.0 

Aquatic Photolysis t1/2

(d) 

61.7 MRID 473051-20 

90th percentile upper confidence bound 

on the mean of imidazolyl (IM) and 

pyrimidinyl (PM) rings of 

imazosulfuron 

Aerobic Soil 

Metabolism t1/2 (d) 207.2 

MRID 473051-17 

MRID 477668-01 

90th percentile upper confidence bound 

on the mean half-life of total toxic 

residue of imazosulfuron 

Aerobic Aquatic 

Metabolism t1/2 (d) 192.0 

MRID 476397-02 

MRID 476791-05 

90th percentile upper confidence bound 

on the mean half-life of total toxic 

residue of imazosulfuron 

Anaerobic Aquatic 

Metabolism t1/2 (d) 21.4 x 3 b MRID 473051-23 Input parameter guidance (USEPA, 

2009) 

Soil Partitioning 

Coefficient (Kfoc; 

ml/goc) 

154 MRID 473051-22 

Represent average Kfoc from 4 soils 

a

 = Residues of concern: total toxic residue (Parent plus degradates, i.e., HMS, IPSN, UDPM, ADPN and SDPM) 

b = Due to reported half-life for a single anaerobic aquatic metabolism study, input half-life was multiplied by 3 according to 

Guidance for selecting input parameters in modeling for environmental fate and transport of pesticides. Version 2.1 October 22,

2009. 

The EFED Rice Model (USEPA, 2007) was also used to estimate the concentration of 

imazosulfuron expected in surface water following application to rice. The model calculates 

exposure as a function of the amount of pesticide applied and the pesticide’s soil-to-water 

partition coefficient. Concentrations are assumed to immediately and evenly distribute 

throughout the rice paddy water. Dissipation processes, such as degradation, volatilization, and 

potential dilution with uncontaminated water outside the paddy are not accounted for by the 

model. The RICE model does not differentiate the concentrations of surface water and pore 

water. In addition, multiple application and application intervals as well as spray drift from aerial 

application were not considered in Tier I RICE model. 
45

Input parameters for the Rice Model are listed in Table 9 and Appendix D; data source and 

justification descriptors accompany values for each parameter. The mean Freundlich soil-towater partition coefficient (Kf) from four soils (1.19) was used to model partitioning to rice 

paddy sediment. The organic carbon partition coefficient (KOC) was not used, as it is a less 

precise descriptor of imazosulfuron’s mobility. The single exposure estimate produced with the 

Rice Model’s acute/chronic screening EECs represent high-end exposure in released flood water. 

Table 9. Rice Model Input Parameters for Imazosulfuron

Input Parameter Value Justification Source 

Application Rate 

(kg ai/ha) 

0.3 0.3 lb ai/A x 1.121 kg·A/ha·lb 

= 0.336 kg ai/ha 

Proposed label 

Soil-to-Water Partition 

Coefficient (Kf) (L/kg) 

1.19 Mean Kf is used when mean 

KOC use is not appropriate. 

MRID 46219074 

MRID 46578971 

The aquatic EECs for the various scenarios and application practices are listed in Table 10. 

EECs were highest for rice with peak and chronic values of 278 μg/L. The next highest peak 

exposure concentration is based on pepper with peak EEC of 12.21 μg/L, followed by turfgrass 

and tomato. Similar trend was also observed for the pore water concentrations. 

Table 10. Estimated Aquatic Concentrations for Imazosulfuron Total Toxic Residues 

Use/Application rate/ 

frequency 

Scenarios Peak EEC (μg ai/L) 21-day Average EEC 

(μg ai/L) 

60-day Average EEC (μg 

ai/L) 

Surface Water 

Turfgrass - FL Turf 4.67 4.49 4.28 

0.67 lb x 2 per season PA Turf 10.11 9.57 8.93 

Tomato FL Tomato 9.22 8.66 7.78 

0.3 lb x 1 per season 

PA Tomato 3.04 2.93 2.82 

Pepper 

0.3 lb x 1 per season 

FL Pepper 12.21 11.56 10.37 

Rice 

0.3 lb x 1 per season 

Tier I Rice 278.90 278.90 278.90 

Pore Water 

Turfgrass - FL Turf 4.80 4.76 4.71 

0.67 lb x 2 per season PA Turf 4.74 4.73 4.70 

Tomato FL Tomato 4.03 4.01 3.99 

0.3 lb x 1 per season 

PA Tomato 1.55 1.54 1.50 

Pepper 

0.3 lb x 1 per season 

FL Pepper 4.80 4.76 4.71 

Rice 

0.3 lb x 1 per season 

Tier I Rice 278.90 278.90 278.90 
46

Aquatic Exposure Monitoring and Field Data 

Since imazosulfuron is a new active ingredient, there were no national-scale monitoring data for 

this chemical available for this assessment. 

3.2.3 Terrestrial Wildlife Exposures 

Terrestrial wildlife exposure estimates are typically calculated for birds and mammals 

emphasizing a dietary exposure route for uptake of pesticide residues on vegetative matter and 

insects. These exposures are considered as surrogates for terrestrial-phase amphibians as well as 

reptiles. For exposure to terrestrial organisms, pesticide residues on food items are estimated 

based on the assumption that organisms are exposed to a single pesticide residue in a given 

exposure scenario. The residue estimates from spray applications are based on a nomogram by 

Hoerger and Kenaga (1972) as modified by Fletcher et al. (1994) that correlated residue levels, 

based on application rate, on various terrestrial items immediately following application in the 

field. The “maximum” residue concentration, an upper bound defined by Fletcher et al. (1994), 

for each food group was derived from literature and tolerance data. 

Determination of residue dissipation of the parent compound over time on food items following 

single and multiple applications are predicted using a first-order residue degradation half-life 

with EFED's “T-REX_V.1.3.1” model. The risk assessment uses a default foliar dissipation halflife estimate of 35 days. This half-life is used in lieu of representative foliar dissipation data for 

imazosulfuron parent, because no such data were provided to EFED. The predicted maximum 

residues on avian and mammalian food items based on applications to tomato, pepper, rice, and 

turfgrass as calculated by T-REX are provided in Table 11. 

Table 11. Estimated Environmental Concentrations for Imazosulfuron 

Parent on Avian and Mammalian Food Items at Maximum Application 

Rates Food Items 

Crop 

Broa

dl

e

af

/f

o

ra

g

e 

pl

a

nt

s 

a

n

d 

s

m

al

l 

in

s

e

ct

s

Fruits, 

pods

, 

seed

s, 

and 

larg

e 

inse

cts 

ppm 

Tom

at

o, 

pe

pp

er, 

an

d 

ric

e

1

 

(a 

si

ng

le 

ap

pl

ic

ati

on 

of 

0.

3 

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41 5 

Turf

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(0.67 

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150 17 

1

The sequential applications of imazosulfuron in rice at 0.15 lb ai/A each yielded lower EECs than a single application of 0.3 lb 

ai/A; therefore, EECs resulting from single application in rice were only presented in this assessment 

The residues or EECs on food items may be compared directly with sub-acute dietary toxicity 

data or converted to an ingested whole-body dose (single oral dose, as the later is the case for 

small mammals and birds. Single-oral dose estimates represent, for many pesticides, an exposure 

scenario where absorption of the pesticide is maximized over a single ingestion event. Sub-acute 

dietary estimates provide for possible effects of the dietary matrix and more extended time of gut 

exposure to pesticide absorption across the gut. However, dietary exposure endpoints are limited 

in their utility because the current food ingestion estimates are uncertain and may not be directly 
47

comparable from laboratory conditions to field conditions. The EEC is converted to an oral dose 

by multiplying the EEC by the percentage of body weight consumed as estimated through 

allometric relationships. These consumption-weighted EECs (i.e. EEC equivalent dose) are 

determined for each food source and body size for mammals (15, 35, and 1000 g) and birds (20, 

100, and 1000 g). The EEC equivalent doses for birds and mammals based on application to 

tomato, pepper, rice, and turfgrass are given in Tables 12 and 13, respectively. An example 

output from T-REX for turfgrass is included in Appendix G

Table 12. Avian EEC Equivalent Dose Adjusted for Body Weight for Imazosulfuron 

Application to Tomato, Pepper, Rice and Turfgrass

Avian Classes and Body Weights 

Small Mid Large EEC Equivalent Dose1 

(mg/kg-body weight) 20 g 100 g 1000 g 

Percent Body Weight Consumed 114% 65% 29% 

Tomato, Pepper and Rice (a single application of 0.3 lb ai/A)

Short Grass 82 47 21 

Tall Grass 38 21 10 

Broadleaf plants/small insects 46 26 12 

Fruits/pods/large insects 5 3 1 

Turf grass (0.67 lb ai/A/application, 2 applications, 21 day interval)

Short Grass 304 173 78 

Tall Grass 139 79 36 

Broadleaf plants/small insects 171 98 44 

Fruits/pods/large insects 19 11 5 1 EEC equivalent dose = EEC (from Table 10) * (percent body weight consumed/100) 

Table 13. Mammalian EEC Equivalent Dose Adjusted for Body Weight for Imazosulfuron 

Application to Tomato, Pepper, Rice and Turfgrass

Mammalian Classes and Body weight 

Herbivores/ Insectivores Granivores 

EEC Equivalent Dose1 

(mg/kg-body weight) 

15 g 35 g 1000 g 15 g 35 g 1000 g 

Percent Body Weight Consumed 95% 66% 15% 21% 15% 3% 

Tomato, Pepper and Rice (a single application of 0.3 lb ai/A)

Short Grass 69 47 11 

Tall Grass 31 22 5 

Broadleaf plants/sm Insects 39 27 6 

Fruits/pods/seeds/lg insects 4 3 1 1.0 0.7 0.2 

Turf grass (0.67 lb ai/A/application, 2 applications, 21 day interval)

Short Grass 254 176 41 

Tall Grass 117 81 19 

Broadleaf plants/small insects 143 99 23 

Fruits/pods/large insects 16 11 3 4 2 0.6 1

EEC equivalent dose = EEC (from Table 10) * (percent body weight consumed / 100) 
48

3.2.4 Terrestrial and Semi-Aquatic Plant Exposures 

Terrestrial and semi-aquatic plants may be exposed to pesticides from runoff, spray drift, or 

volatilization. Semi-aquatic plants are those that inhabit low-laying wet areas that may be dry at 

certain times of the year. The runoff scenario in TERRPLANT 1.2.2 is: (1) based on a pesticide's 

water solubility and the amount of pesticide present on the soil surface and its top one 

centimeter, (2) characterized as "sheet runoff" (one treated acre to an adjacent acre) for dry areas, 

(3) characterized as "channel runoff" (10 acres to a distant low-lying acre) for semi-aquatic or 

wetland areas, and (4) based on percent runoff values of 0.01, 0.02, and 0.05% for water 

solubility values of <10, 10-100, and >100 ppm, respectively. Spray drift is assumed as (1) 1% 

for ground application, (2) 5% for aerial, airblast, forced air, and spray chemigation applications, 

and (3) 0% for granular applications. Currently, EFED derives plant exposure concentrations 

from a single maximum application rate only. Exposure through volatilization is not accounted 

for in this screening-level assessment, and based on the low vapor pressure it is not expected to 

be a significant route of exposure. EECs for the proposed new uses are presented in Table 14. 

The TERRPLANT output for exposure due to use on turfgrass is provided in Appendix F 

Table 14. Estimated Environmental Concentrations of Imazosulfuron Parent for 

Terrestrial and Semi-Aquatic Plants 

Tomato, Pepper, and Rice 

(0.3 lb ai/A) 

Rice 

(0.3 lb ai/A) 

Turfgrass 

 (0.67 lb ai/A) 

Description Ground Aerial Ground 

EEC (lb ai/A)

Runoff to dry areas 0.015 0.015 0.033 

Runoff to semi-aquatic areas 0.15 0.15 0.335 

Spray drift 0.003 0.015 0.007 

Total for dry areas 0.018 0.03 0.04 

Total for semi-aquatic areas 0.153 0.165 0.342 

3.3 Ecological Effects Characterization 

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

effects a pesticide can produce in an animal or plant. This characterization is based on registrantsubmitted studies and the ECOTOX database that describe acute and chronic effects toxicity 

information for various aquatic and terrestrial animals and plants. 

Appendix E summarizes the results of all of the registrant-submitted toxicity studies for this risk 

assessment. Toxicity testing reported in this section does not represent all species of birds, 

mammals, or aquatic organisms. Only a few 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, toxicity studies are typically limited to the laboratory rat. Estuarine/marine testing is 

limited to a crustacean, a mollusk, and a fish. Also, neither reptiles nor amphibians are tested. 

The risk assessment assumes that avian and reptilian and terrestrial-phase amphibian toxicities 

are similar. The same assumption is used for fish and aquatic-phase amphibians. The most 

sensitive ecological toxicity endpoints for aquatic organisms, terrestrial organisms, and aquatic 

and terrestrial plants were used for risk characterization. 
49

The most sensitive ecological toxicity endpoints for aquatic organisms (Table 15), mammals 

(Table 16), birds, terrestrial invertebrates and plants (Table 17) which were used for risk 

characterization of imazosulfuron and the formulations are summarized below. Table 16 

summarizes the acute mammalian toxicity endpoints tested with the degradates of imazosulfuron. 

Discussions of the effects of imazosulfuron on aquatic and terrestrial taxonomic groups are also 

presented below. In addition, a review of the Ecological Incident Information System (EIIS) was 

conducted to further refine the characterization of potential ecological effects. 

In response to the data gaps identified in the previous risk assessment dated (DP 348003), Valent 

submitted 13 additional studies in support of the registration of imazosulfuron. Of these, 3 were 

classified as acceptable, 8 as supplemental, and 2 as invalid. Findings from both the acceptable 

and supplemental studies are incorporated into this assessment. 

Table 15. Imazosulfuron Toxicity Values for Aquatic Organisms 

Acute/ 

Chronic Species Exposure Duration Toxicity Value 

MRID 

(Classification) 

Freshwater Fish 

Acute Rainbow Trout 96 hours 96-Hour LC50 > 69 mg ai/L 

NOAEC = 69 mg/L 

MRID 47305137 

(Acceptable) 

Acute Fathead minnow 96 hours 96-Hour LC50 > 89 mg ai/L 

NOAEC = 89 mg/L 

MRID 47679111 

(Acceptable) 

Chronic* Fathead minnow 32 days NOAEC = 2.9 mg ai/L 

LOAEC = 8.8 mg ai/L 

(reduced hatching success) 

MRID 679112 

(Acceptable) 

Freshwater Invertebrates 

Acute Waterflea 48 hours 48-hour LC50 > 91 mg ai/L 

NOAEC = 12 mg ai/L 

MRID 47305131 

(Acceptable) 

Chronic Waterflea 21 days NOAEC = 0.84 mg ai/L 

LOAEC = 3.3 mg ai/L 

(parental mortality) 

MRID 47305137 

(Acceptable) 

Chronic* Degradate, IPSN 

Midge larvae 

28 days 28-Day EC50 = 45.7 mg ai/L 

NOAEC = 11mg/L (pore water) 

NOAEC = 50 mg/L 

MRID 47782103 

(Supplemental) 

Estuarine/Marine Fish 

Acute Sheepshead minnow 96 hours 96-Hour LC50 >94 mg ai/L 

NOAEC: 94 mg ai/L 

MRID 47305134 

(Acceptable) 

Chronic No data submitted 

Estuarine/Marine Invertebrates 

Acute Mysid shrimp 96 hours 96-Hour LC50 > 79 mg ai/L 

NOAEC: 79 mg ai/L 

MRID 47305133 

(Acceptable) 

Acute Eastern oyster 96 hours 96-hour EC50 = 63 mg ai/L 

NOAEC = 13 mg ai/L

MRID 473051-32 

(Acceptable) 

Chronic No data submitted 

Aquatic Plants 

Vascular Duckweed 7 days EC50 = 0.00146 mg ai/L ECOTOX 104861 

Vascular Degradate, IPSN 

Duckweed 

7 days EC50 > 113 mg ai/L 

NOAEC = 113 mg ai/L 

MRID 47035213 

(Acceptable) 

Non-Vascular Pseudokirchneriella 

subcapitata 

3 days EC50 = 0.206 mg ai/L ECOTOX 104861 

*New studies submitted by the registrant 
50

Table 17. Imazosulfuron Toxicity Reference Values (TRVs) for Terrestrial Organisms 

Exposure 

Scenario Species 

Exposure 

Duration Toxicity Reference Value 

Reference 

(Classification) 

Birds 

Acute 

(Dose-based) 

Mallard duck Single dose LD50 > 2250 mg ai/kg bw 

NOAEC = 1350 mg ai/kg bw 

MRID 473052-03 

(Acceptable) 

Acute* 

(Dose-based) 

Degradate, IPSN 

Bobwhite quail 

Single dose LD50 > 2000 mg ai/kg bw 

NOAEC = 100 mg ai/kg bw 

MRID 477668-10 

(Supplemental) 

Acute 

(Diet-based) 

Mallard duck; 

Bobwhite quail 

Acute dietary LC50 > 5042 mg ai/kg diet 

NOAEC = 5042 mg ai/kg diet 

MRID 473052-05 

MRID 473052-06 

(Acceptable) 

Acute* 

(Diet-based) 

Degradate, IPSN 

Bobwhite quail 

Acute dietary LC50 > 5720 mg ai/kg diet 

NOAEC = 1020 mg ai/kg diet 

MRID 477668-11 

(Acceptable) 

Chronic 

(Diet-based) 

Bobwhite quail 22 weeks LOAEC = 484 mg ai/kg diet 

NOAEC = 194 mg ai/kg diet 

Cracked eggs, number of hatchlings/eggs 

laid 

MRID 473052-07 

(Acceptable) 

Chronic 

(Diet-based) 

Mallard duck 22 weeks LOAEC = 242mg ai/kg diet 

NOAEC = <242 mg ai/kg diet 

Egg shell thickness and ratio of hatchling 

survivors to number hatched 

MRID 476791-14 

(Supplemental) 

Chronic* 

(Diet-based) 

Mallard duck 21 weeks LOAEC = 202 mg ai/kg diet 

NOAEC = 100 mg ai/kg diet 

Reduced number of eggs laid 

MRID 476791-14 

(Supplemental) 

Non-target Insects 

Oral Acute LD50 = 45.9 μg ai/bee 

Contact 

Acute 

Honey bee 96 hour

LD50 = 59.9 μg ai/bee 

MRID 473052-09 

(Acceptable) 

Acute* Degradate, IPSN 

Ground beetle 

14 days LD50 = >1000 mg ai/kg dw soil MRID 477668-05 

(Supplemental) 

Acute* Degradate, IPSN 

Rove beetle 

28 days LD50 = >1000 mg ai/kg dw soil MRID 477821-02 

(Supplemental) 

Table 16. Mammalian Acute Oral and Chronic Toxicity to Imazosulfuron 

Species Test Substance Toxicity Reference Value

MRID #, 

Author, Year Classification 

LD50 >5000 mg/kg (combined sexes) 473052-21 Laboratory rat 

(Rattus norvegicus)

Technical 

NOAEC = 1,000 mg/kg diet 473053-04 Acceptable 

Laboratory Mouse IHOA (Metabolite) LD50 >5212 mg/kg M; LD50 >5060 mg/kg (F) 473052-22 Acceptable 

Laboratory rat 

UDPM (Metabolite) LD50 = 677 mg/kg M; LD50 = 698 mg/kg (F) 473052-23 Acceptable 

Laboratory rat 

IPSN (Metabolite) LD50 = 513 mg/kg M; LD50 = 445 mg/kg (F) 473052-24 Acceptable 

Laboratory rat 

M-1 (Metabolite) LD50 >5000 (combined sexes) 473052-25 Acceptable 

Laboratory rat 

ADPM (Metabolite) LD50 = 879 mg/kg M; LD50 = 836 mg/kg (F) 473052-26 Acceptable 
51

Table 17. Imazosulfuron Toxicity Reference Values (TRVs) for Terrestrial Organisms 

Exposure 

Scenario Species 

Exposure 

Duration Toxicity Reference Value 

Reference 

(Classification) 

Other Non-target organisms 

Acute* Degradate, IPSN 

Earthworm 

14 days LC50 = >1000 mg ai/kg dw soil 

NOAEC = <100 mg ai/kg dw soil 

MRID 477668-12 

(Supplemental) 

Acute* Earthworm 14 days LC50 = >996 mg ai/kg dw soil 

NOAEC = 308 mg ai/kg dw soil 

MRID 477668-14 

(Supplemental) 

Chronic* Degradate, IPSN 

Earthworm 

56 days LC50 = >165 mg ai/kg dw soil 

NOAEC = 1.7 mg ai/kg dw soil 

MRID 477668-13 

(Supplemental) 

Plants – Seedling Emergence 

Monocot Onion Single 

application 

EC25 = 0.034 lbs ai/A 

NOAEC = 0.025 lbs ai/A 

Slope= 1.19 

Dry weight 

Dicot Lettuce Single 

application 

EC25 = 0.041 lbs ai/A 

NOAEC = 0.022 lbs ai/A 

Slope= 0.836 

Dry weight 

MRID 473052-11 

(Acceptable) 

Plants – Vegetative Vigor 

Monocot Onion Single 

application 

EC25 = 0.25 lbs ai/A 

NOAEC = 0.025 lbs ai/A 

Slope= 0.893 

Dry weight 

Dicot Radish Single 

application 

EC25 = 0.08 lbs ai/A 

NOAEC = 0.074 lbs ai/A 

Slope= 0.965 

Survival 

MRID 473052-11 

(Acceptable) 

*New studies submitted by the registrant 

3.3.1 Aquatic Effects Characterization 

Toxicity to Freshwater Fish 

Four acute toxicity fish studies indicate imazosulfuron was not toxic up to 100 mg ai/L nominal 

concentration. The LC50 values using mean measured concentrations ranged from >69 mg ai/L 

for the rainbow trout (MRID 473051-37), >112 mg ai/L for the carp (MRID 473051-35), >74 mg 

ai/L for the bluegill sunfish (MRID 473051-36), and >89 mg ai/L for the fathead minnow 

(MRID 476791-11). No sublethal effects were observed. Although the percent recovery of test 

material in the rainbow trout study (69%) is less than the established acceptable range in the 

guidelines (70- 120%) the measured concentration was stable over the course of the study (0-

hour to 96 hours). The rainbow trout, bluegill, and fathead minnow studies were classified as 

acceptable. However, the carp study was classified as supplemental because the sample size of 

seven fish per treatment (less than 1 gram of fish per liter) was smaller than recommended by 

guidelines. 

An early life-stage study was submitted on fathead minnow to document chronic exposure 

effects of imazosulfuron to freshwater fish (MRID 476791-12). Reported 32-day NOAEC and 

LOAEC values were 2.9 and 8.8 mg ai/L, respectively, based upon a treatment-related reduction 

in hatching success, the only endpoint affected in the study at the 8.8 mg ai/L level. 
52

 Toxicity to Freshwater Invertebrates 

Acute freshwater toxicity tests using Daphnia magna indicate that imazosulfuron is not toxic up 

to 100 mg ai/L nominal concentration, yielding an EC50 value of >91 mg ai/L based on mean 

measured concentration (MRID 473051-31). The NOAEC value is 12 mg ai/L based on 

immobilization (5%) and lethargy. A solvent was not used in this study. This study was 

classified as Acceptable. 

In the freshwater life cycle toxicity test using Daphnia magna (MRID 473052-01), the NOAEC 

and LOAEC are 0.84 and 3.3 mg ai/L, respectively, based on parental mortality using timeweighted averages of the measured test concentrations. There was 20% and 40% mortality in the 

3.3 and 8.9 mg ai/L treatment groups, respectively. The EC50 is > 8.9 mg ai/L, the highest test 

concentration. There was a significant decrease in the mean number offspring per parent (19%) 

in the 8.9 mg ai/L treatment group. The NOAEC and LOAEC are 3.3 and 8.9 mg ai/L, 

respectively, based on reduction in offspring per parent. This study was classified as Acceptable. 

Long-term effects of IPSN on the larvae of the midge, Chironomus riparius, was evaluated using 

the OECD Draft Guideline 219 (MRID 477851-03). The 28-day EC50 reported in this study was 

45.7 mg ai/L and NOAEC values were 18.3 (overlying water) and 11 (pore water) mg ai/L, 

based on mortality and decreased emergence rate. This study was classified as Supplemental as it 

did not fulfill any current U.S. EPA data requirement. 

Toxicity to Estuarine/Marine Fish 

An estuarine/marine fish acute toxicity test with sheepshead minnow (Cyprinodon variegates)

indicates that imazosulfuron was not toxic up to 100 mg ai/L nominal concentration (MRID 

473051-34). The LC50 is >94 mg ai/L using mean measured concentrations. No sublethal effects 

were observed. This study was classified as Acceptable. 

Toxicity to Estuarine/Marine Invertebrates 

Results from an acute toxicity study with mysid shrimp (Americamysis bahia) indicates that 

imazosulfuron was not toxic and was tested up to 100 mg ai/L nominal concentration (MRID 

473051-33). The LC50 is >79 mg ai/L using mean measured concentrations. This study was 

classified as Acceptable. 

Toxicity to Estuarine/Marine Mollusks 

The results from an estuarine/marine acute shell deposition toxicity test using the eastern oyster, 

Crassostrea virginica indicate that imazosulfuron is slightly toxic (EC50 = 63 mg ai/L, MRID 

473051-33). The NOAEC is 13 mg ai/L based on reduced shell deposition. This study was 

classified as Acceptable. 
53

Aquatic Plant Toxicity 

The results from the aquatic plant toxicity test using duckweed (Lemna minor) indicate that 

imazosulfuron technical is very highly toxic to aquatic vascular plants (MRID 476397-01). The 

measured concentrations were not reliable; therefore the results are based on nominal 

concentrations. The NOAEC and EC50 values, based on reduction in number of fronds at Day 14 

are 0.18 and 0.46 μg ai/L, respectively. Phytotoxic effects were reported. It was noted that 

fronds were smaller and roots were shorter than the control group in nominal test concentrations 

0.58 – 10 μg ai/A after both 7 and 14 days. In addition, roots were observed to be shorter after 7 

days in the 0.32 μg ai/A treatment group and in the 0.1 – 0.32 μg ai/A treatment groups after 14 

days. 

The results from the vascular aquatic plant toxicity test using duckweed (Lemna gibba) indicate 

that the imazosulfuron metabolite, IPSN, was not toxic and was tested up to 100 mg ai/L nominal 

concentration (MRID 473052-13). The EC50 is >113 mg ai/L using mean measured 

concentrations. This study was classified as Acceptable. 

Four non-vascular aquatic plant studies were submitted. Imazosulfuron is not toxic to the marine 

diatom, Skeletonema costatum and was tested up to 100 mg ai/L nominal concentration (MRID 

473052-14). The EC50 is >100 mg ai/L using mean measured concentrations. This study was 

classified as Acceptable. Imazosulfuron is also not toxic to the freshwater diatom, Nitzschia 

palea and was tested up to 100 mg ai/L nominal concentration (MRID 473052-16). The EC50 is 

>97 mg ai/L using mean measured concentrations. This toxicity study is classified as 

Supplemental based on guideline requirements for a tier II acute algal toxicity study. The 

recommended test species was not used and there is uncertainty regarding the sensitivity of the 

tested species. There were no effects observed and a positive control was not included. However, 

this study is upgradeable to Acceptable if the study author can demonstrate that the test species is 

as sensitive as the recommended test species. 

Imazosulfuron is not toxic to the freshwater algae, Selenastrum capricornutum. The NOAEC and 

EC50 values based on a lack of significant inhibitions in biomass, area under the growth curve 

and growth rate, were 5.10 and >5.10 mg ai/L, respectively, based on absorbance. The % growth 

inhibition in the treated algal culture as compared to the control was -3.8% for absorbance, -

0.50% for area under the growth curve and 3.5% for growth rate. The results are based on the 

absorbance values because initial and final cell density was not determined in the treatment 

group. Counts were performed only in the negative and solvent control cultures. There was no 

correlation given between absorbance and cell density. The study is classified as Acceptable. 

The green algae, Anabaena flos-aquae toxicity test resulted in a EC50 of 11 mg ai/L. The 

NOAEC and EC05 are 8.6 and 4.4 mg ai/L, respectively, based on cell density (MRID 470352-

15). This study is classified as Acceptable. 

An ECOTOX study, Mohammad, M. et al (2005, ECOTOX 104861) indicates vascular plants 

[Lemna gibba (EC50 = 1.46 μg ai/L)] are two orders of magnitude more sensitive than nonvascular plants Pseudokirchneriella subcapitata (EC50 = 206 μg ai/L) for imazosulfuron. The 

results for Lemna gibba is similar to the results found in the registrant study (Lemna minor (EC50
54

= 0.46 μg ai/L)) and the results for the Pseudokirchneriella subcapitata is more sensitive than the 

4 algae and diatom studies submitted by the registrant. The ECOTOX study results will be used 

quantitatively in this assessment. More information is provided in Section 3.3.4. 

3.3.2 Terrestrial Effects Characterization 

Acute (oral-gavage) Toxicity to Birds 

Acute avian oral-gavage studies were submitted for the northern bobwhite quail and the mallard 

duck using the technical grade active ingredient. The LD50 values (LD50>2250 mg ai/kg-body 

weight) for both studies show that imazosulfuron is practically non-toxic to avian receptors on an 

acute oral-gavage basis as no mortalities were reported in this study. In the quail study, no 

treatment-related effects were observed (NOAEC = 2250 mg ai/kg bw, MRID 473052-04). In the 

mallard study, there was a significant reduction in female body weight gain at highest treatment 

level (NOAEC = 1350 mg ai/kg bw, MRID 473052-03). These studies were classified as 

acceptable. 

An additional study was submitted to document the effects of the degradate IPSN on bobwhite 

quail (MRID 477668-10). Based on the 14-day LD50 value of >2000 mg ai/kg bw, IPSN is 

classified as practically non-toxic to birds. Reduction in body weight gain was the sublethal 

effect reported from this study, though it is uncertain whether the reduction in weight gain is due 

to treatment effect or food avoidance. This study was classified as Supplemental due to guideline 

deviations. 

Sub-acute (dietary) Toxicity to Birds 

Sub-acute avian dietary toxicity studies were submitted for the northern bobwhite quail (MRID 

473052-06) and the mallard duck (MRID 473052-05) using the TGAI. The LC50 values 

(LC50>5042 mg ai/kg-diet) for both studies show that imazosulfuron is practically non-toxic to 

avian receptors on an acute dietary basis as no mortalities were reported in this study. There were 

no treatment effects observed in both studies (NOAEC = 5042 mg ai/kg diet). These studies were 

classified as acceptable. 

A bobwhite quail study that tested the effects of the degradate IPSN demonstrated that IPSN is 

practically non-toxic based on dietary exposure (MRID 477668-11). Reported LC50 and NOAEC 

values were >5720 and 1020 mg ai/kg diet, respectively. This study was classified as Acceptable. 

Chronic Toxicity to Birds 

Three chronic toxicity studies were submitted to the Agency, 1 for northern bobwhite quail and 2 

for mallard duck using TGAI of imazosulfuron. In the first mallard duck study (MRID 473052-

08), there was a statistically significant reduction in eggshell thickness at all treatment levels, 

resulting in NOAEC and LOAEC values of <242 and 242 mg ai/kg diet. There was 5% reduction 

in the lowest treatment level. The ratio of hatchling survivors to number hatched was slightly 

adversely affected at the lowest (4.7%) and highest (2.9%) treatment levels. A definitive 

NOAEC could not be determined in this study, therefore this study is classified as Supplemental. 
55

The second mallard duck study (MRID 476791-14), however, reported definitive 

NOAEC/LOAEC values of 100/202 mg ai/kg diet based on reduced number of eggs laid. In view 

of guideline deviations such as the use of younger birds, smaller cages, and non-inclusion of 

male birds in the study, this study was classified as Supplemental. 

In the bobwhite quail study (MRID 473052-07), there was a statistically significant number of 

cracked eggs (5%) and a significant reduction in the number of hatchlings/eggs laid (14%) in the 

1230 mg ai/kg diet treatment group resulting in a NOAEC of 484 mg ai/kg diet. There was also a 

statistically significant reduction in female weight gain (28%) and reduction in shell thickness 

resulting in a NOAEC value of 194 mg ai/kg diet, however these effects were not doseresponsive and there is some uncertainty whether these effects were treatment related. This study 

is classified as Acceptable. 

Acute Oral Toxicity to Mammals 

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 

Registration Division (RD) and the Health Effects Division (HED) substitute for wild mammal 

testing. 

An acute oral mammalian (laboratory rat) study indicated technical imazosulfuron is not toxic 

(HED Toxicity Category IV) and resulted in the LD50 > 5000 mg ai/kg-bw (combined sexes, 

MRID 473052-21). This study is classified as Acceptable by HED. 

Five additional acute mammalian studies were submitted for the metabolites of imazosulfuron. 

Two of the metabolites, IHOA and M-1 are not toxic (no mortality was observed) and resulted in 

LD50 > 5060 mg ai/kg-bw (female, MRID 473052-22) and LD50 > 5000 mg ai/kg-bw (combined 

sexes, MRID 473052-25), respectively. Three metabolites, UDPM, ADPM and IPSN are more 

toxic than the parent. UDPM and ADPM resulted in LD50 = 677 mg ai/kg-bw (male, MRID 

473052-23) and LD50 = 836 mg ai/kg-bw (female, MRID 473052-26), respectively. The 

metabolite, UDPM, is the most toxic and resulted in LD50 = 445 mg ai/kg-bw (male, MRID 

473052-24). These studies are classified as Acceptable by HED. 

Chronic Toxicity to Mammals 

A 2-generation laboratory rat reproduction study (MRID 473053-04), with technical 

imazosulfuron resulted in no reproductive effects. The NOAEC and LOAEC for parental effects 

are 1,000 and 10,000 mg ai/kg diet, respectively, based on mortality, clinical signs of toxicity, 

and decreased body weight and food consumption. The NOAEC and LOAEC for offspring 

effects are also 1,000 and 10,000 mg ai/kg diet, respectively, based on decreased pup viability 

and body weights. This study is classified as Acceptable by HED. 

Acute Toxicity to Non-target Insects 

In a 48-hr acute contact and oral test, honey bees (Apis mellifera) were exposed to technicalgrade imazosulfuron at one test concentration 20 μg ai/bee. The resulting LD50 values for oral 
56

and contact endpoints were <20 μg ai/bee. Mortality was observed at the test concentration of 20 

μg ai/bee but the mortality was less than 50% (MRID 473052-10). In a subsequent 48-hr acute 

contact and oral test with honey bees, the resulting LD50 values for the oral and contact endpoints 

were 45.9 and 59.9 μg ai/bee, respectively, with a NOAEC of 35.2 μg ai/bee based on mortality 

for both tests. The slope was 5.3 the oral test and 4.3 for the contact test. Imazosulfuron is 

categorized as practically non-toxic to honey-bees. These studies are classified as acceptable. 

The effects of IPSN on non-target insects were documented through 2 non-guideline studies, 

using ground beetles (MRID 477668-05) and rove beetles (MRID 477821-02). Both the 14-day 

study on ground beetle and 28-day study on rove beetle reported LD50 values of >1000 mg ai/kg 

dw soil and no effects due to IPSN on the beetles. This study was classified as Supplemental as it 

is a non-guideline study. 

Toxicity to Earthworms 

Non-guideline studies were submitted to the Agency to demonstrate the acute (MRID 477668-12 

using IPSN and MRID 477668-14 using TGAI) and sub-chronic (MRID 477668-14 using IPSN) 

effects of imazosulfuron on earthworms. The 14-day acute exposure studies reported 

LC50/NOAEC values of >1000/<100 and >996/308 mg ai/kg dw soil for IPSN and TGAI, 

respectively. Reduced body weight was the reported endpoint in both studies. The sub-chronic 

reproduction study reported LC50/NOAEC values of 165/1.65 mg ai/kg dw soil, based on 

decreased juvenile production. All three studies were classified as Supplemental. 

Toxicity to Terrestrial Plants 

Four Tier II studies were submitted to assess the effects of the imazosulfuron formulation, V10142 75WDG, on the seedling emergence and vegetative vigor of monocot and dicot terrestrial 

plant species. In the seedling emergence test (MRID 473052-11), the maximum dose tested for 

following crops: onion, flax, and lettuce was 0.67 lb ai/A. The maximum dose tested for the 

remaining crops was 2.0 lb ai/A. The most sensitive monocot was onion and resulted in the EC25, 

NOAEC and EC05 values of 0.034, 0.025, and 0.0052 lb ai/A based on dry weight. There was 

44% reduction at the LOAEC (0.074 lb ai/A) and 80% at highest test concentration (0.67 lb 

ai/A). The growth inhibition at the proposed label maximum single application rate (1.0 lb ai/A) 

is unknown. The most sensitive dicot was lettuce and resulted in the EC25, NOAEC and EC05 

values of 0.041, 0.22, and 0.0028 lb ai/A based on dry weight. There was 32% reduction of 

lettuce dry weight at LOAEC (0.074 lb ai/A). There were also significant reductions in survival 

at 21 days for soybean at 2 lb ai/A (32%) and flax at 0.67 lb ai/A (37%). There were no adverse 

effects to wheat, corn, buckwheat and tomato. This study is classified as Acceptable. 

In the vegetative vigor test (MRID 473052-12), the maximum dose tested for all crops, except 

radish, was 2.0 lb ai/A. The most sensitive monocot was onion and resulted in the EC25, NOAEC 

and EC05 values of 0.25, 0.025, and 0.02 lb ai/A based on dry weight. The most dicot was radish 

and resulted in the EC25, NOAEC and EC05 values of 0.08, 0.074, and 0.0079 lb ai/A based on 

percent survival. At the maximum dose tested for radish, 0.67 lb ai/A there was a 60% reduction 

in survival compared to the control. The reduction in survival at the proposed label maximum 

single application rate (1.0 lb ai/A) is unknown. There were also significant effects on dry weight 
57

and plant height for radish. There were significant effects to ryegrass, buckwheat, tomato, 

soybean, lettuce and flax. There were no adverse effects to wheat and corn. This study is 

classified as Acceptable. 

3.3.3 Review of Incident Data 

Three databases, the Ecological Incident Information System or EIIS maintained by the 

Environmental Fate and Effects Division, the Aggregate Summary Module (ASM) of Office of 

Pesticide Program’s Incident database maintained by the Information Technology and Resource 

Management Division, and the Avian Incident Monitoring System (AIMS) maintained by the 

American Bird Conservancy, were searched on July 13, 2010 to locate incidents resulting from 

the use of imazosulfuron. There were no reported incidents in all three 3 databases. These results 

are expected with new pesticides because such chemicals have typically not been used widely in 

the environment. Although there were no reported incidences for this chemical, this does not rule 

out any existing risks that may potentially impact terrestrial and aquatic organisms. 

There is concern for incidence to plants to result at the proposed application rates for 

imazosulfuron, given that major incidences have occurred as a result of application of other SU’s 

at much lower rates (although comprehensive evaluation of toxicity/efficacy data was not 

performed). The proposed maximum single application rates for imazosulfuron (0.3 – 0.67 lb 

ai/A) are much greater than other registered SU herbicides. For example, the following are the 

most common use rates based on the recent RED documents some SU herbicides: 

• Chlorsulfuron (Glean): 0.0625 lb ai/A 

• Sulfometuron-methyl (Oust): 0.0231 - 0.375 lb ai/A 

• Nicosulfuron (Accent): 0.0625 lb ai/acre 

• Chlorimuron (Classic): 0.008 - 0.12 lb ai/A 

Research involving chlorsulfuron, the first SU registered in the US (1981) has indicated that 

chlorsulfuron may have effects on plant seed/fruit production at extremely low concentrations. 

Researchers (Fletcher et al., 1993, 1996; Bhatti et al., 1995), have reported reproductive effects 

in cherry, canola, soybean, sunflower and Polygonum spp. at application rates as much as 1000x 

below the label rate (0.0625 lb ai/A). Among the incidents recorded for chlorsulfuron, the 

highest profile incident is Horse Heaven Hills, where chlorsulfuron applied to nearby wheat 

fields was implicated in the reduced yields in cherry and peach trees over a number of years in 

the 1980s. At this time, it is not known whether reproductive effects are associated with SUs 

other than chlorsulfuron; however, effects to plants at very low exposures to the SU 

sulfometuron-methyl (the second SU registered) have been implicated in the loss of 100,000 

acres of sugar beets in Idaho in 2000. 

3.3.4 Review of ECOTOX Data 

A search of the ECOTOX database was completed on July 13, 2010 in which four papers were 

identified for aquatic organisms. These studies, classified as “Acceptable” for ECOTOX and 

OPP standards (Appendix E), evaluated the toxicity of imazosulfuron to aquatic plants. The 

papers: Kuk Y.I. et al (2002), Tanaka, Y. (2003), Wang G. X. et al (2000) will not be used in this 
58

risk assessment because they tested the resistance pattern of plant species to imazosulfuron and 

did not provide additional information about toxicity to non-target species. 

Mohammad, M et al (2005, ECOTOX 104861) investigated the relative sensitivity of the floating 

vascular plant, Lemna gibba and the unicellular algae, Pseudokirchneriella subcapitata to eight 

sulfonylurea (SU) herbicides in Japan to generalize previous work which showed that Lemna 

gibba had higher sensitivity (Fairchild et al. 1997). The results indicate that for five of the eight 

SU herbicides, Lemna gibba was more sensitive than Pseudokirchneriella subcapitata (Table 

18). For imazosulfuron, Lemna gibba (EC50 = 1.46 μg ai/L, 7-day study) was two orders of 

magnitude more sensitive than Pseudokirchneriella subcapitata (EC50 = 206 μg ai/L, 3-day 

study). The results for Lemna gibba is similar to the results found in the registrant study and the 

results for the Pseudokirchneriella subcapitata suggest that endpoints from open-literature study 

is more sensitive than the studies submitted by the registrant. The ECOTOX study results will be 

used quantitatively in this assessment. 

In this study, it was also noted that there was a highly significant correlation between Log Kow 

and toxicity to P. subcapitata (R2 = 0.987). Less water soluble SUs have greater toxicity (Table 

18). The same tendency was observed for Lemna species however the correlation is weaker (R2 

= 

0.630), in which pyrasulfuron-ethyl and imazosulfuron were somewhat outliers due to poor 

correlation of toxicity between the two species used in the study. In a previous study, the uptake 

of non-ionized chemicals by plant roots was reported to be greater when their lipophilicity 

increased within a Log Kow range from -0.57 – 4.6 (Briggs et al. 1982). This could be attributed 

to the lipophilic nature of the plasma membrane, with makes chemicals with low Kow easier to 

diffuse across the membrane into the cytoplasm. Stronger toxicity of SU with lower Kow may be 

explained by the hydrophobic property. Water solubility of SUs pesticides is pH dependent, in 

which they are less soluble in lower pH. Therefore, environmental acidity influences the toxicity 

of the SUs. Fahl et al (1995) reported that toxicity and bioconcentration of SUs were enhanced 

by lowering pH in the green algae, Chlorella fusca. 

* Tomlin (2000); ** Uesugi et al. (1997) Values are at pH 7; pH not stated for pyrazosulfuron-ethyl & flazasulfuron 

4 RISK CHARACTERIZATION 

Risk characterization is the integration of exposure and effects characterization to determine the 

ecological risk from the use of imazosulfuron and the likelihood of effects on aquatic life, 

wildlife, and plants based on different pesticide-use scenarios. The risk characterization provides 

an estimation and description of the risk; articulates risk assessment assumptions, limitations, 

Table 18. Differential Toxicity of Sulfonyl Urea Herbicides on Aquatic Plants 

Sulfonylurea herbicide Kow P. subcapitata [EC50 (μg ai/L)] Lemna species [EC50 (μg ai/L)] 

Bensulfuron-methyl 0.62* 11.8 2.23 

Pyrasulfuron-ethyl 1.3* 0.96 3.49 

Imazosulfuron 0.049* 206 1.46 

Cyclosulfamuron 1.41* 0.27 0.91 

Flazasulfuron 1.08** 1.29 1.66 

Ethoxysulfuron -1.01** 2.84 1.72 

Thifensulfuron-methyl 0.02* 359 7.16 

Nicosulfuron -1.8* >1000 14.5 
59

and uncertainties; synthesizes an overall conclusion; and provides the risk managers with 

information to make regulatory decisions. 

4.1 Risk Estimation: Integration of Exposure and Effects Data 

Results of the exposure and toxicity effects data are used to evaluate the likelihood of adverse 

ecological effects on non-target species. For the assessment of imazosulfuron risks, the risk 

quotient (RQ) method is used to compare exposure and measured toxicity values: 

RQ = EEC / (Acute or Chronic Toxicity Values) 

where: EEC is the estimated environmental concentration generated by the exposure scenarios. 

The RQs are compared to the Agency’s levels of concern (LOCs). These LOCs are the Agency’s 

interpretive policy and are used to analyze potential risk to non-target organisms and the need to 

consider regulatory action. These criteria are used to indicate when a pesticide’s use as directed 

on the label has the potential to cause adverse effects on non-target organisms. 

4.1.1 Non-target Aquatic Fish, Invertebrates, and Plants 

The highest surface water concentrations resulting from imazosulfuron application was predicted 

for rice (imazosulfuron total residues as peak EEC = 279 μg ai/L) followed by the Florida pepper 

scenario (imazosulfuron total residues as peak EEC = 12.2 μg ai/L). Application scenarios were 

selected to represent the entire range of soil and environmental conditions of the proposed 

actions. The estimated environmental concentrations are based on total residues; however the 

aquatic toxicity values are based on imazosulfuron parent or in some cases, specific degradates. 

This conservative approach will approximate maximum exposure. 

Peak EECs were compared to acute toxicity endpoints to derive acute risk quotients. The 21-day 

EECs were compared to chronic toxicity endpoints (NOAEC values) to derive chronic risk 

quotients for invertebrates. The 60-day EECs were compared to chronic toxicity endpoints 

(NOAEC values) to derive chronic risk quotients for fish. 

Fish (Freshwater and Estuarine/Marine) 

For acute risk to freshwater and marine fish, there was no toxicity observed at the highest 

concentration of the technical grade imazosulfuron tested, at 100 mg ai/L nominal concentration. 

Therefore, acute risk quotients were not calculated and there is not a potential acute risk to 

freshwater fish. 

Estimated chronic freshwater fish RQ, based on the highest EEC of 279 μg ai/L for rice and 

NOAEC value of 2900 μg ai/L, was 0.09. As the calculated RQ was less than the chronic risk 

LOC of 1.0 for all the proposed new uses including turfgrass, imazosulfuron is not expected to 

pose risk to freshwater fish at concern levels based on chronic exposure. Chronic toxicity data is 

not available for estuarine/marine fish. As the NOAEC value based on acute exposure studies on 

fathead minnow (for which chronic data is available) and sheepshead minnow were similar, it is 

reasonable to use the fathead minnow NOAEC value from chronic exposure study for 
60

sheepshead minnow. RQs calculated using the fathead minnow NOAEC value suggests that 

imazosulfuron may not pose risk to estuarine/marine fish. 

Freshwater Invertebrates 

For acute risk to freshwater invertebrates, there was no toxicity observed at the highest 

concentration of the technical grade imazosulfuron tested, at 100 mg ai/L nominal concentration. 

Therefore, acute risk quotients were not calculated and potential for acute risk does not exceed 

concern levels for freshwater invertebrates. 

In the freshwater life cycle toxicity test using Daphnia magna (MRID 473052-01), the NOAEC 

and LOAEC are 0.84 and 3.3 mg ai/L, respectively, based on parental mortality. There was 20% 

and 40% mortality in the 3.3 and 8.9 mg ai/L treatment groups, respectively. The EC50 is > 8.9 

mg ai/L, the highest test concentration. The RQ (0.093) was calculated using the highest EEC at 

21 days (279 μg ai/L for rice) and the NOAEC (0.84 mg ai/L). Chronic LOCs (1.0) are not 

exceeded for any of the proposed uses. 

Chronic RQs were also calculated for the sediment-dwelling midge larvae by comparing the 

highest pore water concentration of imazosulfuron that resulted from Rice scenario (279 μg /L) 

to the pore water-based NOAEC (11,000 μg ai/L ). The resulting RQ of 0.02 suggest that 

imazosulfuron is not expected to pose risk to freshwater benthic organisms at levels of concern 

due to chronic exposure. Comparison of EC50 value (45,7000 μg ai/L) generated from the above 

chronic study with peak EEC reported in rice (279 μg ai/L) also indicates that imazosulfuron 

does not pose risk to benthic invertebrates on acute exposure basis at concern levels. 

Estuarine/Marine Invertebrates 

For acute risk to marine crustaceans (mysid), there was no toxicity observed at the highest 

concentration of the technical grade imazosulfuron tested, at 100 mg ai/L nominal concentration. 

Therefore, acute risk quotients were not calculated and risk was presumably lower than concern 

levels for acute risk to estuarine/marine invertebrates. In the toxicity test for marine mollusks 

using the Eastern Oyster, the EC50 and NOAEC values were 63 and 13 mg ai/L, respectively, 

based on reduced shell deposition. The RQ (<0.01) was calculated using the highest peak EEC 

(279 μg ai/L for rice) and the EC50 (63,000 μg ai/L). There are no LOC exceedances for 

estuarine/marine mollusks. 

Aquatic Plants 

Based on a Lemna minor study (MRID 476397-01), the NOAEC and EC50 values, based on 

reduction in number of fronds at Day 14 are 0.18 and 0.46 μg ai/L, respectively. LOCs for nonlisted aquatic vascular plants are exceeded for all the proposed uses (RQs = 7 - 607, Table 19). 

LOCs for endangered aquatic vascular plants are exceeded for all the proposed uses (RQs = 17 - 

1468, Table 19). 

There was no toxicity observed at the highest concentration of the imazosulfuron degradate, 

IPSN, at 100 mg ai/L nominal concentration in the duckweed (Lemna gibba) aquatic plant test. 
61

Therefore, acute risk quotients were not calculated and there is no a potential acute risk to 

vascular aquatic plants based on exposure to IPSN. 

Table 19. Aquatic Vascular Plant RQs for Imazosulfuron 

Use Scenario Peak EEC (μg ai/L) Acute (non-listed) RQ * Acute (Listed) RQ 

* 

FL Tomato 

Ground 

Tomato 9.22 20* 51* 

PA Tomato Ground 3.04 7* 17* 

Pepper FL pepper 12.2 27* 68* 

Rice Rice – Tier 1 279 607* 1468* 

PA Turf 

Ground

Turf 10.1 22* 56* 

FL Turf 

Ground

4.7 10* 26* 

*LOC exceeded based on Lemna study (MRID 476397-01), EC50 = 0.46 μg ai/L and NOAEC = 0.18 μg ai/L 

Based on the study by Mohammad et al (2005) using Pseudokirchneriella subcapitata, the 

calculated RQ (1.4) exceeded risk LOC for rice only. No LOCs (1.0) exceeded for tomato, 

pepper, and turfgrass. 

4.1.2 Non-target Terrestrial Animals and Plants 

Avian Risk 

Since the LD50 and LC50 for birds (for TGAI) were both non-definitive values of >2250 mg/kg 

bw and >5042 mg/kg diet, respectively, and no treatment related mortality was observed, risk 

quotients were not calculated. Similar to TGAI, degradate IPSN LD50 for bobwhite quail was 

non-definitive (>2000 mg/kg bw) and no treatment-related mortality or effects were noted. 

Therefore, risk quotients were not calculated. Based on application rates and the results of the 

acute toxicity studies, acute risk concern levels would not be exceeded for birds. 

Based on the mallard duck NOAEC/LOAEC value of 100/202 mg ai/kg diet, chronic dose-based 

LOCs are exceeded for birds consuming shortgrass, tallgrass, and broadleaf plants/small insects 

for turfgrass use only (Table 20). Chronic dose-based LOCs were not exceeded for any of the 

food use. Chronic dietary-based RQs, on the other hand, were not exceeded for any of the 

proposed food or nonfood uses. 

Table 20. Dietary-Based Avian RQs Based on Imazosulfuron New Uses in Turfgrass 

Short Grass Tall Grass Broadleaf Plants and 

Small Insects 

Tomato, pepper, and rice 0.7 0.3 0.4 

Turfgrass 2.7* 1.2* 1.5* 

*Exceeds chronic avian LOC of 1.0
62

Mammalian Risk 

For imazosulfuron TGAI, the LD50 for mammals was a non-definitive value of >5000 mg/kg bw 

and no treatment related mortality was observed. Therefore, acute risk quotients were not 

calculated and there is not a potential acute risk to mammals. 

The dietary-based chronic risk quotients for mammals did not exceed concern levels for any of 

the proposed uses for imazosulfuron. Similarly, chronic dose-based risk LOCS were not 

exceeded for any sized mammals based on imazosulfuron uses in tomato, pepper, and rice. 

However, dose-based chronic risk LOC exceeded for turfgrass use for all sized mammals 

(Tables 21 and 22). Based on this, potential risk exists for mammals due to imazosulfuron uses 

in turfgrass only. 

There was increased acute sensitivity in mammals to the metabolites IPSN, ADPM and UDPM 

observed in the acute oral toxicity studies. In order to assess acute risk to mammals, the 

application rate for turfgrass (the highest proposed rate for imazosulfuron) was adjusted to the 

percent of the metabolite that may result from degradation processes on the leaf surface. The 

hydrolysis and aqueous photolysis study results were chosen for this reason. For all three 

metabolites, hydrolysis was stable at pH 7. Therefore, the results from the aqueous photolysis 

study (at pH 7) were used to adjust the application rate (Table 23). The percent detected for 

IPSN, ADPM and UPDM are 1.6, 35.3, and 11.2%, respectively. Based on the adjusted 

application rate, acute mammalian LOCs are not exceeded for these degradates. There is some 

uncertainty in this analysis as not all degradation processes in field may be incorporated. 

Table 21. Mammalian Dose-Based Chronic RQs Based on Upper Bound Residues for 

Imazosulfuron Use on Tomato, Pepper, and Rice 

15 g 35 g 1000 g 

Short Grass 0.6 0.5 0.3 

Tall Grass 0.3 0.2 0.1 

Broadleaf plants/sm insects 0.4 0.3 0.2 

Fruits/pods/lg insects 0.04 0.03 0.02 

Seeds (granivore) 0.01 0.01 <0.01 

Table 22. Mammalian Dose-based Chronic RQs for Imazosulfuron use on Turfgrass 

15 g 35 g 1000 g 

Short Grass 2.3* 2.0* 1.1* 

Tall Grass 1.1* 0.9 0.5 

Broadleaf plants/sm insects 1.3* 1.1* 0.6 

Fruits/pods/lg insects 0.1 0.1 0.07 

Seeds (granivore) 0.03 0.03 0.01 

*Exceeds chronic mammalian LOC of 1.0 
63

Table 23. Mammalian Acute Risk Based on Exposure to Imazosulfuron Degradates 

Degradate Maximum1 Percent Detected Adjusted Turf grass 

Application Rate 

Acute Oral 

LD50

LOC 

Exceedances 

IPSN 1.6% 

(aqueous photolysis at pH 7) 

0.67 * 1.6 % = 

0.01 lb ai/A, 

2 applications 

513 mg/kg M 

445 mg/kg F

No 

ADPM 35.3% 

(aqueous photolysis at pH 7) 

0.67 * 35.3 % = 

0.24 lb ai/A, 

2 applications 

879 mg/kg M 

836 mg/kg F

No 

UPDM 11.2% 

(aqueous photolysis at pH 7) 

0.67 * 11.2 % = 

0.08 lb ai/A, 

2 applications 

677 mg/kg M 

698 mg/kg F 

No 

1

Percent of degradates formed under natural environment are considered for the risk assessment 

Terrestrial Invertebrates 

EFED currently does not routinely quantify risks to terrestrial non-target insects. Risk quotients 

are therefore not calculated for these organisms. Imazosulfuron is classified as practically nontoxic based on the acute contact honey bee study (LD50 = 59.9 μg ai/bee); therefore, label 

statements are not warranted to protect pollinators. 

Earthworms 

The registrant submitted two 14-day acute earthworm toxicity studies that resulted in LC50

values of >1000 mg/kg-dw soil for imazosulfuron TGAI and >996 mg/kg dw soil for IPSN. Risk 

to earthworms was evaluated using the formula outlined below. 

RQ

application rate mg cm

soil incorporation depth cm bulk density kg cm

LC mg ai kg soil = ×

⎡

⎣

⎢

⎢

⎤

⎦

⎥

⎥

(/ )

() (/ )

(/ )

2

3

50

Soil bulk density of 1.3 g/cm3

 and incorporation depth of 3 cm (as imazosulfuron is most 

effective in the zone where germinations weed seedlings emerge from) were assumed for this 

analysis. Using the single maximum application rate of 0.67 lb ai/acre for turfgrass which 

resulted in imazosulfuron soil concentration of 1.9 mg/kg soil and a conservative LC50 of >966 

mg/kg soil, calculated RQ was <0.01. Based on this, minimal risk to earthworms is assumed 

from all the proposed new imazosulfuron uses. This screening assessment does not consider risks 

to earthworms from multiple applications of imazosulfuron in a single year or risks to 

earthworms if imazosulfuron accumulates in the soil over multiple years of applications. 

Accumulation of imazosulfuron in the soil is likely as this is a persistent chemical. 

4.1.3 Terrestrial and Semi-aquatic Plants Risk 

Terrestrial and semi-aquatic plants may be exposed to pesticides from runoff and spray drift. 

Semi-aquatic plants are those that inhabit low-lying wet areas that may be dry at certain times of 

the year. EECs for terrestrial and semi-aquatic plants are derived for areas adjacent to the 

treatment site. Acute RQs for terrestrial plants are derived by dividing the EEC by the EC25 from 
64

Tier II seedling emergence and vegetative vigor toxicity tests. Acute RQs for listed plant species 

are calculated by dividing the EEC by the NOAEC (if not available, an EC05 is used) value from 

Tier II toxicity tests. 

To calculate RQs, the results of the seedling emergence test (MRID 473052-11) were used. The 

most sensitive monocot was onion which resulted in the EC25 and NOAEC values of 0.034 and 

0.025 lb ai/A based on dry weight. The most sensitive dicot was lettuce which resulted in the 

EC25 and NOAEC values of 0.041 and 0.22 lb ai/A based on dry weight. 

In the vegetative vigor test (MRID 473052-12), the most sensitive monocot was onion and 

resulted in the EC25 and NOAECvalues of 0.25 and 0.025 lb ai/A based on dry weight. The most 

dicot was radish and resulted in the EC25 and NOAEC values of 0.08 and 0.074 lb ai/A based on 

percent survival. 

Terrestrial plant EECs and toxicity endpoints are provided in Table 13. EECs and RQs for turf 

are calculated using TERRPLANT 1.2.2 (Appendix F and summarized in Table 24. For a single 

ground application on tomato, pepper, and rice at the maximum rate, the LOC was exceeded for 

listed and non-listed non-target terrestrial plants in semi-aquatic environments only. For a single 

aerial application on rice, the LOC was exceeded for listed and non-listed non-target terrestrial 

plants in semi-aquatic environments and listed plants in dry upland areas. For a single ground 

application to turfgrass, the LOC was exceeded for listed and non-listed non-target terrestrial 

plants in dry upland and semi-aquatic environments. 

Table 24. Risk Quotients (RQ) for Plants in Dry and Semi-Aquatic Areas Exposed to 

Imazosulfuron Through Runoff and/or Spray Drift*

Listed Status Dry Semi-Aquatic Spray Drift 

Monocot non-listed 0.5 4.5* <0.1 

Monocot listed 0.7 6.1* 0.1 

Dicot non-listed 0.4 3.7* <0.1 

Tomato, pepper, and rice 

0.3 lb ai/A, 

Ground application Dicot listed 0.8 7.0* 0.1 

Monocot non-listed 0.9 4.9* 0.4 

Monocot listed 1.2* 6.6* 0.6 

Dicot non-listed 0.7 4.0* 0.4 

Rice 

0.3 lb ai/A 

Aerial application Dicot listed 1.4* 7.5* 0.7 

Monocot non-listed 1.2* 10.0* 0.2 

Monocot listed 1.6* 13.7* 0.3 

Dicot non-listed 1.0* 8.3* 0.2 

Turfgrass 

0.67 lb ai/A 

Ground application Dicot listed 1.8* 15.5* 0.3 

*If RQ > 1.0, the LOC is exceeded, resulting in potential for risk 

4.2 Risk Description 

A screening-level (Level I) risk assessment, based on the proposed uses of imazosulfuron on 

tomato, pepper, rice, and turfgrass, suggests that imazosulfuron exposure may result in direct 

chronic effects to birds and mammals and direct effects to aquatic vascular and terrestrial plants. 

These direct effects may also result in indirect risk to non-target species. Potential for risk does 

exist for neither fish, aquatic invertebrates and non-vascular plants nor birds, mammals, and 

terrestrial invertebrates based on acute exposure to imazosulfuron. 
65

4.2.1 Risks to Aquatic Organisms 

Potential for acute and chronic risk to freshwater and marine fish and aquatic invertebrates is 

lower than concern levels. However, there is a potential risk to vascular (all uses) and nonvascular (rice use only) aquatic plants. Imazosulfuron technical was very highly toxic to vascular 

plants (Lemna minor, MRID 476397-01). The NOAEC and EC50 values, based on reduction in 

number of fronds at Day 14 are 0.18 and 0.46 μg ai/L, respectively. LOCs for listed and nonlisted aquatic vascular plants are exceeded for all the proposed uses. Non-vascular plant RQs, on 

the other hand, exceeded concern levels for imazosulfuron use in rice only. This may have been 

due to the use of the RICE model which provided the most conservative EECs. 

An aquatic vascular plant (Lemna gibba) study using the degradate, IPSN demonstrated no 

toxicity to the plant. However, there is uncertainty regarding toxicity to fish, aquatic 

invertebrates, and aquatic non-vascular plants exposed to the degradates. 

4.2.2 Risks to Terrestrial Organisms 

Birds and Mammals 

The screening assessment for imazosulfuron suggests that potential acute risk to birds and 

mammals is lower than concern level for all proposed uses. Because the avian (oral and dietary) 

and mammalian (oral) acute studies did not establish definitive endpoints as no mortality was 

noted with the highest tested concentrations, standard RQ values for acute exposure were not 

calculated in the Risk Estimation section of this assessment. In order to gain a better 

understanding of how the EECs for the maximum proposed imazosulfuron application rate (for 

both food and non-food uses) relate to the toxicity data currently available for birds and 

mammals, TREX was used to calculate RQs using the conservative assumption that the highest 

concentration tested in the avian and mammalian studies represent endpoints (i.e., acute: LD50s = 

2250 mg/kg bw and 5042 mg/kg diet for birds; 5000 mg/kg bw for mammals). In this exercise all 

of the acute RQs calculated using upper bound Kenaga values were less than the listed species 

LOC of 0.1 for all size and dietary classes for both food and non-food uses. Therefore, direct risk 

to non-listed and listed birds and mammals from acute exposure to imazosulfuron is lower than 

concern levels. 

Reproductive effects were observed at similar concentrations in both the mallard duck (MRID 

47305-08) and bobwhite quail (MRID 47305-07) studies. In the bobwhite quail study, there was 

a statistically significant number of cracked eggs (5%) and a significant reduction in the number 

of hatchlings/eggs laid (14%) in the 1230 mg ai/kg diet treatment group resulting in a NOAEC of 

484 mg ai/kg diet. There was also a statistically significant reduction in female weight gain 

(28%) and reduction in shell thickness resulting in a NOAEC value of 194 mg ai/kg diet, 

however these effects were not dose-responsive and there is some uncertainty whether these 

effects were treatment related. However, similar results were reported in the mallard duck study, 

in which there was a statistically significant reduction in eggshell thickness (5%) at similar test 

concentration (242 mg ai/kg diet). The ratio of hatchling survivors to number hatched was 

slightly adversely affected at the lowest (4.7%) and highest (2.9%) treatment levels. A definitive 

NOAEC could not be determined in this study. To address the above uncertainty, the registrant 
66

submitted an additional study (MRID 476791-14) on mallard duck based on which a 

NOAEC/LOAEC value of 100/202 mg ai/kg diet was established. These endpoints were used in 

imazosulfuron effects determination to birds. Based on the mallard duck study NOAEC (100 mg 

ai/kg diet), chronic LOCs are exceeded based on upper bound residues for birds consuming 

shortgrass, tallgrass, and broadleaf plants/small insects for turfgrass use only. Chronic LOCs 

were not exceeded for any of the food uses. 

The potential for adverse effects to mammals appear to be likely based on chronic dose-based 

RQs. Chronic dose-based risk LOC exceeded for turfgrass use for all sized mammals. However, 

potential for dietary-based chronic risk for mammals was lower than concern levels for all the 

proposed food uses of imazosulfuron. 

Imazosulfuron degradates, IPSN, UDPM and ADPM are more acutely toxic to mammals than 

the parent with IPSN, being the most toxic. To address this uncertainty that was identified in the 

earlier assessment regarding the risk from degradates, the registrant submitted new acute 

exposure studies on birds and chronic exposure studies on terrestrial invertebrates. The bird 

studies suggested that the LOAEC values for IPSN were lower than the parent in both the dose 

and dietary-based studies and adverse effects were noted at lower concentrations with IPSN 

compared to the parent. Similar conclusions were also drawn based on earthworm toxicity data. 

Regarding the non-target insects, although studies that evaluated the effects of IPSN were 

submitted on ground beetle and rove beetle, comparable studies were not available for TGAI. 

Therefore, the uncertainty related to the effects of TGAI versus IPSN could not be resolved for 

terrestrial insects. 

Terrestrial plants 

Imazosulfuron exposure results in significant reductions in growth and survival of non-target 

terrestrial plants with EC25 values as low as 0.034 lbs ai/A (corresponding NOAEC value of 0.025 

lbs ai/A). Many of the EC25 values for terrestrial plants are approximately two orders of 

magnitude less than the proposed single application rates (0.3 – 0.67 lb ai/A). For a single 

ground application on tomato, pepper, and rice at the maximum rate, the LOC was exceeded for 

listed and non-listed non-target terrestrial plants in semi-aquatic environments only. For a single 

aerial application on rice, the LOC was exceeded for listed and non-listed non-target terrestrial 

plants in semi-aquatic environments and listed plants in dry upland areas. For a single ground 

application to turfgrass, the LOC was exceeded for listed and non-listed non-target terrestrial 

plants in dry upland and semi-aquatic environments. 

In addition to the growth effects observed for several plant species, unusually high mortality was 

observed for some plants in the seedling emergence and vegetative vigor tests. There were 

significant reductions in survival at 21 days for soybean at 2 lb ai/A (32%), flax at 0.67 lb ai/A 

(37%), and radish at 0.67 lb ai/A (60%). Imazosulfuron exposure may result in non-target plant 

mortality, especially for aerial applications. The nontarget terrestrial plant toxicity studies, as 

specified by the Agency guidelines, are designed to evaluate sublethal effects to plant growth, 

which can then be extrapolated to community level effects. Mortality as an endpoint in these 

studies, as is the case with imazosulfuron, is atypical and of concern to Agency. 
67

Effects in the seedling emergence and vegetative vigor studies were observed in a wide range of 

plants families, however, there were minimal effects observed in the Poaceae family (wheat, 

corn, and ryegrass). This is supported by the fact that imazosulfuron is not a grass herbicide. 

There is also concern for incidence to plants to result at the proposed application rates for 

imazosulfuron, given that major incidences have occurred as a result of application of other SU’s 

at much lower rates. The proposed maximum single application rates for imazosulfuron (0.3 – 

0.67 lb ai/A) are much greater than other registered SU herbicides. For example, the following 

are the most common use rates based on the recent RED documents some SU herbicides: 

• Chlorsulfuron (Glean): 0.0625 lb ai/A 

• Sulfometuron-methyl (Oust): 0.0231 - 0.375 lb ai/A 

• Nicosulfuron (Accent): 0.0625 lb ai/acre 

• Chlorimuron (Classic): 0.008 - 0.12 lb ai/A 

Research involving chlorsulfuron, the first SU registered in the US (1981) has indicated that 

chlorsulfuron may have effects on plant seed/fruit production at extremely low concentrations. 

Researchers (Fletcher et al., 1993, 1996; Bhatti et al., 1995), have reported reproductive effects 

in cherry, canola, soybean, sunflower and Polygonum spp. at application rates as much as 1000x 

below the label rate (0.0625 lb ai/A). Among the incidents recorded for chlorsulfuron, the 

highest profile incident is Horse Heaven Hills, where chlorsulfuron applied to nearby wheat 

fields was implicated in the reduced yields in cherry and peach trees over a number of years in 

the 1980s. At this time, it is not known whether reproductive effects are associated with SUs 

other than chlorsulfuron; however, effects to plants at very low exposures to the SU 

sulfometuron-methyl (the second SU registered) have been implicated in the loss of 100,000 

acres of sugar beets in Idaho in the year 2000. 

4.2.3 Endocrine Disruption Potential 

The potential for endocrine disruptor-related effects was observed in avian toxicity studies 

submitted to the Agency. Significant reproductive effects were observed in the bobwhite quail 

and mallard duck studies. In the bobwhite quail study, there was a statistically significant number 

of cracked eggs and a significant reduction in the number of hatchlings/eggs laid. There was also 

a statistically significant reduction in female weight gain and reduction in shell thickness, 

however these effects were not dose-responsive and there is some uncertainty whether these 

effects were treatment related. In mallard duck studies, there was a statistically significant 

reduction in number of eggs laid and eggshell thickness. The ratio of hatchling survivors to 

number hatched was slightly adversely affected. 

A two-generation laboratory rat reproduction study (MRID 473053-04), with imazosulfuron 

TGAI resulted in no reproductive effects. The NOAEC and LOAEC for parental effects are 

1,000 and 10,000, respectively, based on mortality, clinical signs of toxicity, and decreased body 

weight and food consumption. The NOAEC and LOAEC for offspring effects are also 1,000 and 

10,000, respectively, based on decreased pup viability and body weights. 
68

EPA is required under the Federal Food, Drug, and Cosmetic Act (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, imazosulfuron may be subjected to additional screening 

and/or testing to better characterize effects related to endocrine disruption. 

4.3 Threatened and Endangered Species Concern 

4.3.1 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 

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 colocated 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 

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. This risk assessment presents the use of imazosulfuron and establishes initial colocation of species with treatment areas. 

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 is made with respect to listed 

species in that taxa, and no further refinement of the action area is necessary. 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 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. 
69

4.3.2 Taxonomic Groups Potentially at Risk: Direct Effects 

Based on available screening level information, for the proposed uses of imazosulfuron, there is 

a potential for direct effects to listed birds, mammals, aquatic non-vascular plants, aquatic 

vascular plants, and terrestrial plants. Consequently, there is a potential concern for indirect 

effects upon the listed organisms by, for example, perturbing habitat, forage or prey availability. 

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. A 

summary of the risk conclusions and direct and indirect effects determinations is presented in 

Table 24. 

Table 25. Listed Species Risks Associated with Direct or Indirect Effects Due to Applications of 

Imazosulfuron Parent 

Listed Taxonomy Direct Effects Indirect Effects 

Terrestrial and semi-aquatic plants – monocots Yes Yes

Terrestrial and semi-aquatic plants – dicots Yes Yes 

Terrestrial invertebrates No Yes 

Birds (surrogate for terrestrial-phase amphibians and 

reptiles) 

Yes – chronic effects Yes 

Mammals Yes – chronic effects Yes 

Aquatic vascular plants Yes Yes 

Aquatic non-vascular plants Yes Yes 

Freshwater fish (surrogate for aquatic-phase 

amphibians) 

No Yes 

Freshwater Invertebrates No Yes 

Freshwater Benthic Invertebrates No Yes 

Estuarine/Marine Fish No Yes 

Estuarine/Marine Crustaceans No Yes 

Estuarine/Marine Mollusks No Yes 

The LOCATES database (version 2.9.7) identifies those U.S. counties that include tomato, 

pepper, rice, and turfgrass areas and that have federally-listed endangered or threatened species 

that may be directly or indirectly affected. The list of affected species derived from LOCATES 

was not included in this assessment because the uses cover most of the United States and the 

direct and indirect effects includes most species. With additional refinement by exploring more 

detailed use patterns and species biology (e.g., geographic location, specific feeding habits, time 

of year likely to utilize crop fields), some species listed may be determined to be not likely to be 

affected. 
70

4.3.3 Use of Probit Slope Dose-Response Relationship to Provide Information on the 

Endangered Species Levels of Concern 

The Agency uses the probit dose-response relationship as a tool for providing additional 

information on the listed animal species acute levels of concern. The acute listed species LOCs 

of 0.1 and 0.05 are used for terrestrial and aquatic animals, respectively. As part of the risk 

characterization, an interpretation of acute LOCs for listed species is discussed. This 

interpretation is presented in terms of the chance of an individual event (i.e., mortality or 

immobilization) should exposure at the estimated environmental concentration actually occur for 

a species with sensitivity to imazosulfuron on par with the acute toxicity endpoint selected for 

RQ calculation. To accomplish this interpretation, the Agency uses the slope of the dose 

response relationship available from the toxicity study used to establish the acute toxicity 

measurement endpoints for each taxonomic group. The individual effects probability associated 

with the LOCs is based on the mean estimate of the slope and an assumption of a probit dose 

response relationship. In addition to a single effects probability estimate based on the mean, 

upper and lower estimates of the effects probability are also provided to account for variance in 

the slope. The upper and lower bounds of the effects probability are based on available 

information on the 95% confidence interval of the slope. A statement regarding the confidence 

in the applicability of the assumed probit dose response relationship for predicting individual 

event probabilities is also included. Studies with good probit fit characteristics (i.e., statistically 

appropriate for the data set) are associated with a high degree of confidence. Conversely, a low 

degree of confidence is associated with data from studies that do not statistically support a probit 

dose response relationship. In addition, confidence in the data set may be reduced by high 

variance in the slope (i.e., large 95% confidence intervals), despite good probit fit characteristics. 

Individual effect probabilities are calculated based on an Excel spreadsheet tool IECV1.1 

(Individual Effect Chance Model Version 1.1) developed by Ed Odenkirchen of the U.S. EPA, 

OPP, Environmental Fate and Effects Division (June 22, 2004). The model allows for such 

calculations by entering the mean slope estimate (and the 95% confidence bounds of that 

estimate) as the slope parameter for the spreadsheet. In addition, the LOC (0.1 for terrestrial 

animals and 0.05 for aquatic animals) is entered as the desired threshold. 

Probit dose analysis was not completed for acute risk to aquatic and terrestrial fauna because no 

mortalities were observed in the toxicity testing. Probit dose analysis was not completed for risk 

to aquatic vascular plants, chronic risk to birds and mammals, nor terrestrial plants because it is 

not appropriate for these endpoints. 

4.3.4 Indirect Effects Analysis 

The Agency acknowledges that 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, etc. 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. 

 
71

Based on direct chronic risk to birds and mammals, there may be potential indirect effects to 

terrestrial species that depend on these organisms (including their surrogates) as a source of food 

or pollination. 

Vascular aquatic plants serve several important functions in aquatic ecosystems. They provide 

structure as attachment sites and refugia for many aquatic invertebrates, fish, and juvenile 

organisms, such as fish and frogs. In addition, vascular plants also provide primary productivity 

and oxygen to the aquatic ecosystem. Rooted plants help reduce sediment loading and provide 

stability to nearshore areas and lower streambanks. In addition, vascular aquatic plants are 

important as attachment sites for egg masses. 

Based on direct risk to terrestrial plants, there may be potential indirect effects to aquatic and 

terrestrial species that depend on these organisms (including their surrogates) as a source of food 

or habitat, including riparian habitats. Terrestrial plants serve several important habitat-related 

functions for listed species. In addition to providing habitat and cover for, terrestrial vegetation 

also provides shelter for and cover from predators while foraging. Terrestrial plants also provide 

energy to the terrestrial ecosystem through primary production. Upland vegetation including 

grassland and woodlands provides cover during dispersal. Riparian vegetation helps to maintain 

the integrity of aquatic systems by providing bank and thermal stability, serving as a buffer to 

filter out sediment, nutrients, and contaminants before they reach the watershed, and serving as 

an energy source. 

4.3.5 Critical Habitat for Listed Species 

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

physical and biological features (primary 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 primary constituent elements and is accomplished using the screening-level 

taxonomic analysis (RQs) and listed species’ levels of concern (LOCs) that are used to evaluate 

direct and indirect effects to listed organisms. 

The screening-level risk assessment for imazosulfuron has identified potential concerns for direct 

effects on listed birds, mammals, aquatic non-vascular plants, aquatic vascular plants and 

terrestrial plants and indirect effect to those organisms dependant upon them for food and/or 

habitat. 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 

primary 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 a pesticide. Then EPA would determine 
72

whether or not use of the pesticide overlaps the critical habitat or the occupied range of those 

listed species. At present, the information reviewed by EPA is not sufficient to permit use of 

either analytical approach to make a definitive identification of species that are potentially 

impacted indirectly or critical habitats that are potentially impacted directly by the use of 

pesticides. EPA and the Service(s) are working together to conduct the necessary analysis. 

This screening-level risk assessment for critical habitat provides a listing of potential biological 

features that, if they are primary constituent elements of one or more critical habitats, would be 

of potential concern. These correspond to the taxa identified above as being of potential concern 

for indirect effects and include birds, reptiles, terrestrial phase amphibians, mammals, terrestrial 

plants and aquatic organisms. This list should serve as an initial step in problem formulation for 

further assessment of critical habitat impacts outlined above, should additional work be 

necessary. 

5 Description of Assumptions, Uncertainties, Strengths, and Limitations 

5.1 Assumptions and Limitations Related to Exposure for all Taxa 

There are a number of areas of uncertainty in the aquatic and terrestrial risk assessments. The 

toxicity assessment for terrestrial and aquatic animals is limited by the number of species tested 

in the available toxicity studies. Use of toxicity data on representative species does not provide 

information on the potential variability in susceptibility to acute and chronic exposures. 

This screening-level risk assessment relies on labeled statements of the maximum rate of 

imazosulfuron application, the maximum number of applications, and the shortest interval 

between applications. Together, these assumptions constitute a maximum use scenario. The 

frequency at which actual uses approach these maximums is dependant on resistance to the 

fungicide, timing of applications, and market forces. 

5.2 Assumptions and Limitations Related to Exposure for Aquatic Species

 

The fate and transport database for imazosulfuron was sufficient to conduct aquatic modeling for 

exposure assessment of aquatic species. However, this assessment is based on limited and 

supplemental biodegradation fate data. Imazosulfuron persistence is significantly affected by soil 

types or water chemistry and may not always be easy to predict from typically available 

soil/water property data alone. A clearer picture of the range of variability in imazosulfuron 

persistence in the environment would require environmental fate studies on a greater variety of 

soils/waters/ sediments with a greater range of pH levels and other soil properties. This is 

particularly true for the aerobic soil and anaerobic aquatic metabolism studies. 

Even though imazosulfuron is soluble and moderately mobile to mobile based on the results of 

batch equilibrium studies, unextractable residues were identified at maximums of 87.7 of applied 

radioactivity in anaerobic aquatic metabolism and 35.7% of applied radioactivity in aerobic soil 

metabolism. The unextractable residues are uncharacterized and it is uncertain whether they 

consist of degradates of risk concern. Under sterile conditions these unextractable residues were 

not formed suggesting that the formation of them is microbially mediated. Metabolism half-lives 
73

were estimated based on parent and major degradates concentrations (excluding unextractable 

residues). To the extent that these unextractable residues are of risk concern, the estimated halflives will be underestimated compared to a total toxic residue approach for estimating half-lives. 

However, given the persistence of total toxic residue of imazosulfuron, inclusion of 

unextractable residues in total toxic approach for calculating metabolism half-life would not 

impact PRZM/EXAMS modeled EECs appreciably. 

5.3 Assumptions and Limitations Related to Exposure for Terrestrial Species 

Variation in habitat and dietary requirements

For screening terrestrial risk assessments, a generic bird or mammal is assumed to occupy either 

the treated field or adjacent areas receiving pesticide at a rate commensurate with the treatment 

rate on the field. The habitat and feeding requirements of the modeled species and the wildlife 

species may be different. It is assumed that species occupy, exclusively and permanently, the 

treated area being modeled. This assumption leads to a maximum level of exposure in the risk 

assessment. 

The acute studies have a fixed exposure period, not allowing for the differences in response of 

individuals to different durations of exposure. Further, for the acute oral study, imazosulfuron is 

administered in a single dose which does not mimic wild birds' exposure through multiple 

feedings. Also, it does not account for the effect of different environmental matrices on the 

absorption rate of the chemical into the animal. Because exposure occurs over several days, both 

the accumulated dose and elimination of the chemical from the body for the duration of the 

exposure determine the exact exposure to wildlife, however they are not taken into account in the 

screening assessment. There was also no assumption of an effect of repeated doses that change 

the tolerance of an individual to successive doses. 

Variation in diet composition

The risk assessment and calculated RQs assume 100% of the diet is relegated to single food 

types foraged only from treated fields. The assumption of 100% diet from a single food type 

may be realistic for acute exposures, but diets are likely to be more variable over longer periods 

of time. This assumption is likely to be conservative and will tend to overestimate potential risks 

for chronic exposure, especially for larger organisms that have larger home ranges. These large 

animals (e.g., deer and geese) will tend to forage from a variety of areas and move on and off of 

treated fields. Small animals (e.g., mice, voles, and small birds) may have home ranges smaller 

than the size of a treated field and will have little or no opportunity to obtain foodstuffs that have 

not been treated with imazosulfuron. Even if their home range does cover area outside the treated 

field, imazosulfuron may have runoff to areas adjacent to the treated field. 

Exposure routes other than dietary

Only dietary and incidental ingestion of contaminated soils exposure is included in the exposure 

assessment. Other exposure routes are possible for animals in treated areas. These routes include 

ingestion of contaminated drinking water, dermal contact, inhalation, and preening. Because 
74

imazosulfuron does not volatilize appreciably (vapor pressure less than 2.63 x 10-8 torr), 

inhalation does not appear to be a significant contributor to the overall exposure. Given that 

imazosulfuron is soluble in water there exists the potential to dissolve in runoff and puddles on 

the treated field may contain the chemical. If toxicity is expected through any of these other 

routes of exposure, then the risks of a toxic response to imazosulfuron is underestimated in this 

risk assessment. 

Dietary Intake - The Differences Between Laboratory and Field Conditions 

There are several aspects of the dietary test that introduce uncertainty into calculation of the LC50

value (Mineau, et al., 1994; ECOFRAM, 1999). The endpoint of this test is reported as the 

concentration mixed with food that produces a response rather than as the dose ingested. 

Although food consumption sometimes allows for the estimate of a dose, calculations of the 

mg/kg/day are confounded by undocumented spillage of feed and how consumption is measured 

over the duration of the test. Usually, if measured at all, food consumption is estimated once at 

the end of the five-day exposure period. Further, group housing of birds undergoing testing only 

allows for a measure of the average consumption per day for a group; consumption estimates can 

be further confounded if birds die within a treatment group. The exponential growth of young 

birds also complicates the estimate of the dose; controls often nearly double in size over the 

duration of the test. Since weights are only taken at the initiation of the exposure period and at 

the end, the dose per body weight (mg/kg) is difficult to estimate with any precision. The 

interpretation of this test is also confounded because the response of birds is not only a function 

of the intrinsic toxicity of the pesticide, but also the willingness of the birds to consume treated 

food. 

Further, the acute and chronic characterization of risk rely on comparisons of wildlife dietary 

residues with LC50 or NOAEC values expressed in concentrations of pesticides in laboratory 

feed. These comparisons assume that ingestion of food items in the field occurs at rates 

commensurate with those in the laboratory. Although the screening assessment process adjusts 

dry-weight estimates of food intake to reflect the increased mass in fresh-weight wildlife food 

intake estimates, it does not allow for gross energy and assimilative efficiency differences 

between wildlife food items and laboratory feed. On gross energy content alone, direct 

comparison of a laboratory dietary concentration- based effects threshold to a fresh-weight 

pesticide residue estimate would result in an underestimation of field exposure by food 

consumption by a factor of 1.25 - 2.5 for most food items. Only for seeds would the direct 

comparison of dietary threshold to residue estimate lead to an overestimate of exposure. 

Differences in assimilative efficiency between laboratory and wild diets suggest that current 

screening assessment methods do not account for a potentially important aspect of food 

requirements. Depending upon species and dietary matrix, bird assimilation of wild diet energy 

ranges from 23 - 80%, and mammal's assimilation ranges from 41 - 85% (U.S. Environmental 

Protection Agency, 1993). If it is assumed that laboratory chow is formulated to maximize 

assimilative efficiency (e.g., a value of 85%), a potential for underestimation of exposure may 

exist by assuming that consumption of food in the wild is comparable with consumption during 

laboratory testing. In the screening process, exposure may be underestimated because metabolic 

rates are not related to food consumption. 
75

Finally, the screening procedure does not account for situations where the feeding rate may be 

above or below requirements to meet free living metabolic requirements. Gorging behavior is a 

possibility under some specific wildlife scenarios (e.g., bird migration) where the food intake 

rate may be greatly increased. Kirkwood (1983) has suggested that an upper-bound limit to this 

behavior might be the typical intake rate multiplied by a factor of 5. In contrast is the potential 

for avoidance, operationally defined as animals responding to the presence of noxious chemicals 

in their food by reducing consumption of treated dietary elements. This response is seen in 

nature where herbivores avoid plant secondary compounds. 

In the absence of additional information, the acute oral LD50 test provides the best estimate of 

acute effects for chemicals where exposure can be considered to occur over relatively short 

feeding periods, such as the diurnal feeding peaks common to avian species (ECOFRAM, 1999). 

Incidental Pesticide Releases Associated with Use

This risk assessment is based on the assumption that the entire treatment area is subject to 

imazosulfuron application at the rates specified on the label. In reality, there is the potential for 

uneven application of imazosulfuron through such plausible incidents as changes in calibration 

of application equipment, spillage, and localized releases at specific areas of the treated field that 

are associated with specifics of the type of application equipment used (e.g., increased 

application at turnabouts when using older application equipment). 

5.4 Assumptions and Limitations Related to Effects Assessment

There is uncertainty as to the significance of the reproductive endpoint used for assessment 

purposes with respect to wild mammal populations because frank developmental and 

reproductive effects were not observed in the study. Observed chronic effects in the twogeneration rat reproduction study (MRID 473053-04), with technical imazosulfuron resulted in 

no reproductive effects. The NOAEC and LOAEC for parental effects are 1,000 and 10,000, 

respectively, based on mortality, clinical signs of toxicity, and decreased body weight and food 

consumption. The NOAEC and LOAEC for offspring effects are also 1,000 and 10,000, 

respectively, based on decreased pup viability and body weights. The resulting NOAEC is 200 

mg/kg-diet. There were no reproductive effects or signs of reproductive impairment in males or 

females. This study is classified as Acceptable by HED. 

There is no potential acute oral risk to mammals exposed to imazosulfuron parent; however, 

there was increased acute sensitivity in mammals to the metabolites IPSN, ADPM and UDPM 

observed in the acute oral toxicity studies. Therefore, there is uncertainty regarding risk 

terrestrial plants exposed to these degradates. 

Age class and sensitivity of effects thresholds

It is generally recognized that test organism age may have a significant impact on the observed 

sensitivity to a toxicant. The screening risk assessment acute toxicity data for fish are collected 

on juvenile fish between 0.1 and 5 grams. Aquatic invertebrate acute testing is performed on 
76

recommended immature age classes (e.g., first instar for daphnids, second instar for amphipods, 

stoneflies and mayflies, and third instar for midges). Similarly, acute dietary testing with birds is 

also performed on juveniles, with mallard being 5-10 days old and quail 10-14 days old. 

Testing of juveniles may overestimate toxicity of older age classes for pesticidal active 

ingredients, such as imazosulfuron, that act directly (without metabolic transformation) because 

younger age classes may not have the enzymatic systems associated with detoxifying 

xenobiotics. The screening risk assessment has no current provisions for a generally applied 

method that accounts for this uncertainty. In so far as the available toxicity data may provide 

ranges of sensitivity information with respect to age class, the risk assessment uses the most 

sensitive life-stage information as the conservative screening endpoint. 

Use of the Most Sensitive Species Tested

Although the screening risk assessment relies on a selected toxicity endpoint from the most 

sensitive species tested, it does not necessarily mean that the selected toxicity endpoint reflect 

sensitivity of the most sensitive species existing in a given environment. The relative position of 

the most sensitive species tested in the distribution of all possible species is a function of the 

overall variability among species to a particular chemical. In the case of listed species, there is 

uncertainty regarding the relationship of the listed species' sensitivity and the most sensitive 

species tested. Furthermore, the Agency is not limited to a base set of surrogate toxicity 

information in establishing risk assessment conclusions. The Agency also considers toxicity data 

on non-standard test species when available. 

6 LITERATURE CITED 

Beyer, W. N., E. E. Connor and S. Gerould. 1994. Estimates of Soil Ingestion by Wildlife. 

Journal of Wildlife Management. 58(2):375-382. 

Bhatti, M.A., K. Al- Khatib, A.S. Felsot, R. Parker and S. Kadir. 1995. Effects of Simulated 

Chlorsulfuron Drift on Fruit Yield and Quality of Sweet Cherries (Prunus Avium L.). 

Environ. Tox. Chem. Vol 14 No. 3, pp. 537-544. 

Briggs GG, Bromilow RH, Evans AA (1982) Relationships between lipophilicity and root uptake 

and translocation of non-ionised chemicals by barley. Pestic Sci 13: 495-504. 

ECOFRAM. 1999. ECOFRAM Terrestrial Draft Report. Ecological Committee on FIFRA Risk 

Assessment Methods. USEPA, Washington D.C. 

Fahl GM, Kreft L, Altenburger R, Faust M, Boedeker W, Grimme LH (1995) pH-dependent 

sorption, bioconcentration and algal toxicity of sulfonurea herbicides. Aquat Toxicol 31: 

175-187. 
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Fletcher, J.S. 1991. Horse Heaven Hills/Badger Canyon, A case Study of Alleged Pesticide Drift 

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Columbia 91-150.7 

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EPA food-chain (Kenaga) nomogram, an instrument for estimating pesticide residues on 

plants. Environ Toxicol Chem 13(9):1383–1391. 

Fletcher J.S., T. G. Pfleeger and H.C. Ratsch 1995. Chlorsulfuron Influence on Garden Pea 

Reproduction. Physiologia Plantarum 94: pp 261-267. 

Fletcher J.S., T. G. Pfleeger, H.C. Ratsch and R. Hayes 1996. Potential Impacts of Low Levels 

of Chlorsulfuron and Other Herbicides on Growth and Yields of Non-target Plants. 

Environ, Tox. and Chem. Vol. 15, No. 7. pp 1189-1196. 

Food and Agriculture Organization of the United Nations. FAO PESTICIDE DISPOSAL 

SERIES 8. Assessing Soil Contamination: A Reference Manual. Appendix 2. 

Parameters of pesticides that influence processes in the soil. Editorial Group, FAO 

Information Division: Rome, 2000. 

http://www.fao.org/DOCREP/003/X2570E/X2570E00.htm

Gusey W.F., Z.D. Maturgo. 1973. Wildlife Utilization of Croplands. Environmental 

Conservation Department. Shell Oil Company, Houston, TX. 

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. 

HSDB, 2002 [Hazardous Substances Data Bank]. National Library of Medicine. Last update: 6-

8-2002. Access date: 6-5-2003. http://toxnet.nlm.nih.gov/cgibin/sis/htmlgen?HSDB. 

Kirkwood, J. 1983. A limit to metabolizable energy intake in mammals and birds. Comp. 

Biochem. Physiol. 75A:1-3. 

Martin, C. M., H. S. Zim & A. C. Nelson, 1951. American Wildlife and Plants - A Guide to 

Wildlife Food Habits, Dover Publ. Inc., New York. 

Merritt, R. W. and K. W. Cummins, eds. 1984. An Introduction to the Aquatic Insects of North 

America 2nd ed. Kendall/Hunt Publishing Company, Dubuque, Idaho. 722 pp. 

Mineau, P., B. Jobin and A. Baril. 1994. A critique of the avian 5-day dietary test (LC50) as the 
78

basis of avian risk assessment. Technical Report No. 215, Headquarters, Canadian 

Wildlife Service, Hull, Quebec. p. 23. 

NatureServe. 2005. NatureServe Explorer: An online encyclopedia of life [web application]. 

Version 4.5. NatureServe, Arlington, Virginia. Available 

http://www.natureserve.org/explorer. 

Syracuse Research Corporation. 2006. Surface Water Scenario Development for the Pesticide 

Root Zone Model (PRZM) for Modeling Pesticide Exposure in Outdoor Nurseries: 

Supplement to Metadata. GSA Contract No. GS-00F-0019L, Report No. SRC TR-06-

081, North Syracuse, NY. 

Tomlin CDS (ed) (2000) The Pesticide Manual, 12th Edition. British Crop Protection Council, 

UK. 

Uesugi Y, Ueji M, Koshioka M (ed) (1997) Pesticide Data Book, 3rd Edition. Soft Science 

Publications, Tokyo, Japan. 

Urban D.J. and N.J. Cook. 1986. Hazard Evaluation Division Standard Evaluation Procedure 

Ecological Risk Assessment. EPA 540/9-85-001. U.S. Environmental Protection 

Agency, Office of Pesticide Programs, Washington, DC. 

USDA Crop Profiles. http://www.ipmcenters.org/cropprofiles/CP_form.cfm 

USEPA 1993. Wildlife Exposure Factors Handbook. Volume I of II. EPA/600/R-93/187a. 

Office of Research and Development, Washington, D. C. 20460. EPA/600/R-93/187a. 

USEPA 1998. Guidance for Ecological Risk Assessment. Risk Assessment Forum. 

EPA/630/R-95/002F, April 1998. 

USEPA 2002. Guidance for Selecting Input Parameters in Modeling the Environmental Fate and 

Transport of Pesticides Input Parameter Guidance. Version II February 28, 2002. U.S. 

Environmental Protection Agency, Office of Pesticide Programs, Environmental Fate and 

Effects Division. 

USEPA 2004. Overview of the Ecological Risk Assessment Process in the Office of Pesticide 

Programs. Office of Prevention, Pesticides, and Toxic Substances. Office of Pesticide 

Programs. Washington, D.C. January 23, 2004. 
79

APPENDIX A: Status of Fate and Ecological Effects Data Requirements 

Table A-1: Environmental Fate Data Requirements for Imazosulfuron 

Guideline # Data Requirement MRID #s 

Study 

Classification 

161-1 835.212 Hydrolysis 473051-19 Acceptable 

161-2 835.224 Photodegradation in Water 473051-20 Acceptable 

161-3 835.241 Photodegradation on Soil 473051-21 Supplemental 

161-4 835.237 Photodegradation in Air NA --- 

162-1 835.41 Aerobic Soil Metabolism 473051-22 Supplemental 

162-2 835.42 Anaerobic Soil 

Metabolism NA --- 

162-3 835.44 Anaerobic Aquatic 

Metabolism 473051-23 Supplemental 

162-4 835.43 Aerobic Aquatic 

Metabolism 476397-02 In review 

163-1 835.1240 

835.1230 

LeachingAdsorption/Desorption 473051-17 Supplemental 

163-1 835.1230 Adsorption/Desorption 473051-18 Supplemental 

163-2 835.141 Laboratory Volatility NA --- 

163-3 835.81 Field Volatility NA --- 

164-1 

835.61 Terrestrial Field 

Dissipation 

473051-26 

473051-27 

Acceptable 

Acceptable 

165-4 850.173 Accumulation in Fish 473052-02 Request for 

waiver 

201-1 840.1100 Spray droplet Size 

Spectrum 473051-28 In review 

1 Not Available. 
80

Table A-2 : Available Ecological Effects Data for Imazosulfuron 

Guideline # Type of Study Formulation MRID Study Classification 

71-1 850.2100 Avian Oral LD50 Technical 

Technical 

IPSN 

473052-03 

473052-04 

477668-10 

Acceptable 

Acceptable 

Supplemental 

71-2 850.2200 Avian Dietary LC50 Technical 

Technical 

IPSN 

473052-05 

473052-06 

477668-11 

Acceptable 

Acceptable 

Acceptable 

71-4 850.2300 Avian Reproduction Technical 

Technical 

Technical 

473052-07 

473052-08 

476791-14 

Acceptable 

Supplemental 

Supplemental 

72-1 850.1075 Freshwater Fish LC50 Technical 

Technical 

Technical 

Technical 

473051-35 

473051-36 

473051-37 

476791-11 

Supplemental 

Acceptable 

Acceptable 

Acceptable 

72-2 850.1010 Freshwater Invertebrate 

LC50

Technical 

Technical 

473051-30 

473051-31 

Invalid 

Acceptable 

72-3(a) 850.1075 Estuarine/Marine Fish LC50 Technical 473051-34 Acceptable 

72-3(b) 850.1025 Estuarine/Marine Mollusk 

EC50

Technical 473051-32 Acceptable 

72-3(c) 850.1035 

850.1045 

Estuarine/Marine Shrimp 

LC50

Technical 473051-33 Acceptable 

72-4(a) 850.1400 Freshwater Fish Early Life 

Stage 

Technical 476791-14 Acceptable 

72-4(b) 850.1300 

850.1350 

850.1300 

Aquatic Invertebrate Lifecycle Technical 473052-01 Acceptable

 OECD 219 Benthic Organisms (longterm sediment toxicity) IPSN 477821-03 Supplemental 

72-5 850.1500 Freshwater Fish LifeCycle Technical Not submitted 

123-1(a) 850.4225 Seed Germination/ 

Seedling Emergence 

Tier II 

V-10142 75WDG 473052-11 Acceptable 

123-1(a) 850.4225 Vegetative Vigor 

Tier II 

V-10142 75WDG 473052-12 Acceptable 

122-2 850.4400 Aquatic Plant (NonVascular) 

Tier 1&II 

Technical 

Technical 

Technical 

Technical 

470532-14 

470532-15 

470532-16 

470532-17 

Acceptable 

Acceptable 

Supplemental 

Acceptable 

122-2 850.4400 Aquatic Plant (Vascular) 

Tier 2 

Technical 

IPSN 

476397-01 

473052-13 

Supplemental 

Acceptable 

141-1 850.3020 Honey Bee Acute Oral and 

Contact LD50

Technical 

Technical 

473052-09 

473052-10 

Supplemental 

Supplemental 

 OECD 207 

OECD 207 

Acute Toxicity to 

Earthworms 

TGAI 

IPSN 

477668-14 

477668-12 

Not available 

 ISO 11268-2 Chronic Toxicity to 

Earthworms 

IPSN 477668-13 Supplemental 

141-2 850.3030 Honey Bee Residue on 

Foliage 

NA NA Not available 

Non-guideline Acute Toxicity to Beetles IPSN 

IPSN 

477668-05 

477821-02 

Supplemental 

Supplemental 
81

APPENDIX B: Calculations of Half-life for total toxic residue 

Aerobic Soil Metabolism (MRID 473051-17 
82

Aerobic Soil Metabolism (MRID 477668-01 

- 
83

Aerobic Aquatic Metabolism (MRID 476397-02) 
84

Aerobic aquatic Metabolism (MRID 476791-05 
85

Anaerobic aquatic Metabolism (MRID 473051-23 
 86

Total Toxic Residue (Ananerobic Aquatic Metabolism) 

Days

0 100 200 300 400

Total Toxic Residue (%)

0

20

40

60

80

100

y= -0.0324X +93.35, r 2 = 0.95 

Calculated Half-life = 21.4 Days

Nonlinear Regression 

Data Source: Data 1 in Notebook1 

Equation: Exponential Decay, Single, 2 Parameter 

f = a*exp(-b*x) 

R Rsqr Adj Rsqr Standard Error of Estimate

0.9739 0.9485 0.9472 8.5793 

 Coefficient Std. Error t P VIF 

a 93.3543 2.3368 39.9501 <0.0001 1.4005 

b 0.0324 0.0028 11.7346 <0.0001 1.4005 

Analysis of Variance: 

Uncorrected for the mean of the observations: 

 DF SS MS 

Regression 2 164525.7142 82262.8571 

Residual 42 3091.3858 73.6044 

Total 44 167617.1000 3809.4795 

Corrected for the mean of the observations: 

 DF SS MS F P 

Regression 1 56892.8406 56892.8406 772.9541 <0.0001 

Residual 42 3091.3858 73.6044 

Total 43 59984.2264 1394.9820 
 87

Aquatic Photolysis (IM Ring) 
 88

Aquatic Photolysis (PM Ring) 

Half life calculation for total system: 

PM ring 32.66 Days 

IM Ring 4.72 Days 

90th %ile 61.69 Days 
 89

APPENDIX C: PRZM EXAMS Output Files 

 This appendix documents the output of water column and pore water from PRZM / 

EXAMS simulations for each of five location/crop scenarios: Florida/Turf, Tomato and Papper 

(ground application), Pennsylvania Turf and Tomato. The settings for each model run are 

presented first, followed by the raw data sorted by year and sorted in descending order by EEC. 

Values represent the estimated environmental concentrations (EECs) in units of micrograms per 

liter (μg/L) or parts per billion (ppb). The 1-in-10 year summary statistics for each run are 

presented at the very end of the sorted results in the row assigned a probability level of 0.10. 

Concentrations in Water Column

FL Turf (0.67 lbs a.i x 2 ground applications) 

stored as Turf_FL.out 

Chemical: Imazosulfuron 

PRZM environment: FLturfSTD.txt modified Tueday, 21 February 2006 at 15:38:26 

 

EXAMS environment: pond298.exv modified Tueday, 26 August 2008 at 06:14:08 

 

Metfile: w12834.dvf modified Tueday, 26 August 2008 at 06:14:18 

Water segment concentrations (ppb) 

 

Year Peak 96 hr 21 Day 60 Day 90 Day Yearly 

1961 3.45 3.40 3.22 2.90 2.72 0.91 

1962 2.03 2.01 1.93 1.83 1.76 1.49 

1963 1.40 1.39 1.33 1.22 1.19 1.02 

1964 4.68 4.64 4.43 4.08 3.88 1.84 

1965 2.94 2.93 2.87 2.73 2.63 1.91 

1966 2.80 2.76 2.62 2.37 2.22 1.36 

1967 3.04 3.01 2.87 2.62 2.47 1.55 

1968 3.47 3.42 3.26 2.95 2.76 1.84 

1969 7.47 7.37 6.98 6.56 6.20 3.06 

1970 4.61 4.58 4.50 4.30 4.15 2.80 

1971 1.78 1.76 1.68 1.53 1.45 1.20 

1972 7.10 7.00 6.63 5.95 5.55 2.32 

1973 4.00 3.98 3.89 3.71 3.57 2.59 

1974 3.07 3.04 2.90 2.68 2.58 1.64 

1975 3.37 3.33 3.18 2.88 2.71 1.82 

1976 3.14 3.11 2.96 2.70 2.56 1.83 

1977 3.51 3.47 3.30 3.09 2.97 2.03 

1978 2.17 2.15 2.11 2.02 1.96 1.67 

1979 2.69 2.66 2.53 2.29 2.15 1.40 

1980 1.64 1.62 1.59 1.52 1.46 1.21 

1981 3.39 3.35 3.27 3.02 2.83 1.40 

1982 2.12 2.11 2.06 1.97 1.89 1.42 

1983 3.17 3.13 2.98 2.70 2.54 1.36 

1984 1.93 1.92 1.89 1.81 1.74 1.44 

1985 1.94 1.91 1.84 1.70 1.59 1.09 

1986 1.22 1.20 1.16 1.13 1.10 0.94 

1987 1.06 1.04 0.99 0.90 0.84 0.69 

1988 1.07 1.06 1.02 0.94 0.88 0.60 
 90

1989 1.25 1.24 1.19 1.10 1.03 0.66 

1990 2.30 2.27 2.15 1.92 1.79 1.02 

 

Sorted results 

Prob. Peak 96 hr 21 Day 60 Day 90 Day Yearly 

0.03 7.47 7.37 6.98 6.56 6.20 3.06 

0.06 7.10 7.00 6.63 5.95 5.55 2.80 

0.10 4.68 4.64 4.50 4.30 4.15 2.59 

0.13 4.61 4.58 4.43 4.08 3.88 2.32 

0.16 4.00 3.98 3.89 3.71 3.57 2.03 

0.19 3.51 3.47 3.30 3.09 2.97 1.91 

0.23 3.47 3.42 3.27 3.02 2.83 1.84 

0.26 3.45 3.40 3.26 2.95 2.76 1.84 

0.29 3.39 3.35 3.22 2.90 2.72 1.83 

0.32 3.37 3.33 3.18 2.88 2.71 1.82 

0.35 3.17 3.13 2.98 2.73 2.63 1.67 

0.39 3.14 3.11 2.96 2.70 2.58 1.64 

0.42 3.07 3.04 2.90 2.70 2.56 1.55 

0.45 3.04 3.01 2.87 2.68 2.54 1.49 

0.48 2.94 2.93 2.87 2.62 2.47 1.44 

0.52 2.80 2.76 2.62 2.37 2.22 1.42 

0.55 2.69 2.66 2.53 2.29 2.15 1.40 

0.58 2.30 2.27 2.15 2.02 1.96 1.40 

0.61 2.17 2.15 2.11 1.97 1.89 1.36 

0.65 2.12 2.11 2.06 1.92 1.79 1.36 

0.68 2.03 2.01 1.93 1.83 1.76 1.21 

0.71 1.94 1.92 1.89 1.81 1.74 1.20 

0.74 1.93 1.91 1.84 1.70 1.59 1.09 

0.77 1.78 1.76 1.68 1.53 1.46 1.02 

0.81 1.64 1.62 1.59 1.52 1.45 1.02 

0.84 1.40 1.39 1.33 1.22 1.19 0.94 

0.87 1.25 1.24 1.19 1.13 1.10 0.91 

0.90 1.22 1.20 1.16 1.10 1.03 0.69 

0.94 1.07 1.06 1.02 0.94 0.88 0.66 

0.97 1.06 1.04 0.99 0.90 0.84 0.60 

 

0.10 4.67 4.64 4.49 4.28 4.12 2.56 

 Average of yearly averages: 1.54 

 

Inputs generated by pe5.pl - Novemeber 2006 

 

Data used for this run: 

Output File: Turf_FL 

Metfile: w12834.dvf 

PRZM scenario: FLturfSTD.txt 

EXAMS environment file: pond298.exv 

Chemical Name: Imazosulfuron 

Description Variable Name Value Units Comments 

Molecular weight mwt 412.81 g/mol 

Henry's Law Const. henry 3.33E-11 atm-m^3/mol 

Vapor Pressure vapr 2.63E-08 torr 

Solubility sol 429 mg/L 

Kd Kd mg/L 

Koc Koc 154 mg/L 

Photolysis half-life kdp 61.7 days Half-life 

Aerobic Aquatic Metabolism kbacw 192 days Halfife 
 91

Anaerobic Aquatic Metabolism kbacs 64.2 days Halfife 

Aerobic Soil Metabolism asm 207.2 days Halfife 

Hydrolysis: pH 7 0 days Half-life 

Method: CAM 2 integer See PRZM manual 

Incorporation Depth: DEPI cm 

Application Rate: TAPP 0.75 kg/ha 

Application Efficiency: APPEFF 0.99 fraction 

Spray Drift DRFT 0.01 fraction of application rate applied to pond 

Application Date Date 8-Feb dd/mm or dd/mmm or dd-mm or dd-mmm 

Interval 1 interval 21 days Set to 0 or delete line for single app. 

app. rate 1 apprate kg/ha 

Record 17: FILTRA 

 IPSCND 3 

 UPTKF 

Record 18: PLVKRT 

 PLDKRT 

 FEXTRC 0.5 

Flag for Index Res. Run IR EPA Pond 

Flag for runoff calc. RUNOFF none none, monthly or total(average of entire run) 

PA Turf (0.67 lbs a.i x 2 ground applications) 

stored as Turf_PA.out 

Chemical: Imazosulfuron 

PRZM environment: PAturfSTD.txt modified Thuday, 23 February 2006 at 18:55:08 

 

EXAMS environment: pond298.exv modified Tueday, 26 August 2008 at 06:14:08 

 

Metfile: w12834.dvf modified Tueday, 26 August 2008 at 06:14:18 

Water segment concentrations (ppb) 

Year Peak 96 hr 21 Day 60 Day 90 Day Yearly 

1961 8.29 8.18 7.74 6.96 6.52 2.16 

1962 5.21 5.15 4.91 4.75 4.52 3.71 

1963 4.21 4.15 3.97 3.64 3.46 2.72 

1964 10.26 10.17 9.7 9.06 8.6 4.37 

1965 6.46 6.43 6.29 6 5.77 4.05 

1966 2.48 2.47 2.42 2.31 2.22 1.83 

1967 4.38 4.33 4.12 3.75 3.54 1.8 

1968 6.9 6.83 6.5 5.87 5.5 3.12 

1969 8.07 7.97 7.65 6.96 6.57 4.04 

1970 5.39 5.36 5.26 5.03 4.85 3.25 

1971 3.97 3.92 3.72 3.38 3.18 1.86 

1972 19.27 19.02 18.01 16.15 15.09 6.02 

1973 10.9 10.84 10.6 10.1 9.71 6.85 

1974 8.21 8.11 7.76 7.29 6.98 4.34 

1975 6.58 6.5 6.19 5.64 5.31 4.2 

1976 6.64 6.56 6.24 5.69 5.39 3.64 

1977 6.5 6.42 6.09 5.54 5.24 3.78 

1978 5.12 5.06 4.94 4.68 4.6 3.47 

1979 6.57 6.48 6.24 5.68 5.34 3.36 

1980 4.05 4.03 3.95 3.77 3.63 2.77 

1981 8.81 8.7 8.38 7.79 7.32 3.33 

1982 5.49 5.46 5.35 5.09 4.88 3.5 

1983 7.18 7.1 6.79 6.21 5.85 3.16 
 92

1984 4.63 4.58 4.39 4.18 4.03 3.4 

1985 4.39 4.34 4.19 3.9 3.66 2.58 

1986 2.74 2.73 2.67 2.54 2.45 2.05 

1987 1.81 1.8 1.77 1.69 1.62 1.36 

1988 2.27 2.24 2.13 1.94 1.83 1.17 

1989 1.7 1.69 1.63 1.51 1.42 1.13 

1990 2.05 2.02 1.92 1.77 1.7 1.16 

Sorted results 

Prob. Peak 96 hr 21 Day 60 Day 90 Day Yearly 

0.03 19.27 19.02 18.01 16.15 15.09 6.85 

0.06 10.9 10.84 10.6 10.1 9.71 6.02 

0.1 10.26 10.17 9.7 9.06 8.6 4.37 

0.13 8.81 8.7 8.38 7.79 7.32 4.34 

0.16 8.29 8.18 7.76 7.29 6.98 4.2 

0.19 8.21 8.11 7.74 6.96 6.57 4.05 

0.23 8.07 7.97 7.65 6.96 6.52 4.04 

0.26 7.18 7.1 6.79 6.21 5.85 3.78 

0.29 6.9 6.83 6.5 6 5.77 3.71 

0.32 6.64 6.56 6.29 5.87 5.5 3.64 

0.35 6.58 6.5 6.24 5.69 5.39 3.5 

0.39 6.57 6.48 6.24 5.68 5.34 3.47 

0.42 6.5 6.43 6.19 5.64 5.31 3.4 

0.45 6.46 6.42 6.09 5.54 5.24 3.36 

0.48 5.49 5.46 5.35 5.09 4.88 3.33 

0.52 5.39 5.36 5.26 5.03 4.85 3.25 

0.55 5.21 5.15 4.94 4.75 4.6 3.16 

0.58 5.12 5.06 4.91 4.68 4.52 3.12 

0.61 4.63 4.58 4.39 4.18 4.03 2.77 

0.65 4.39 4.34 4.19 3.9 3.66 2.72 

0.68 4.38 4.33 4.12 3.77 3.63 2.58 

0.71 4.21 4.15 3.97 3.75 3.54 2.16 

0.74 4.05 4.03 3.95 3.64 3.46 2.05 

0.77 3.97 3.92 3.72 3.38 3.18 1.86 

0.81 2.74 2.73 2.67 2.54 2.45 1.83 

0.84 2.48 2.47 2.42 2.31 2.22 1.8 

0.87 2.27 2.24 2.13 1.94 1.83 1.36 

0.9 2.05 2.02 1.92 1.77 1.7 1.17 

0.94 1.81 1.8 1.77 1.69 1.62 1.16 

0.97 1.7 1.69 1.63 1.51 1.42 1.13 

 

0.1 10.11 10.02 9.57 8.93 8.48 4.37 

 Average of yearly averages: 3.14 

Inputs generated by pe5.pl - Novemeber 2006 

Data used for this run: 

Output File: Turf_PA 

Metfile: w12834.dvf 

PRZM scenario: PAturfSTD.txt 

EXAMS environment file: pond298.exv 

Chemical Name: Imazosulfuron 

Description Variable Name Value Units Comments 

Molecular weight mwt 412.81 g/mol 

Henry's Law Const. henry 3.33E-11 atm-m^3/mol 

Vapor Pressure vapr 2.63E-08 torr 
 93

Solubility sol 429 mg/L 

Kd Kd mg/L 

Koc Koc 154 mg/L 

Photolysis half-life kdp 61.7 days Half-life 

Aerobic Aquatic Metabolism kbacw 192 days Halfife 

Anaerobic Aquatic Metabolism kbacs 64.2 days Halfife 

Aerobic Soil Metabolism asm 207.2 days Halfife 

Hydrolysis: pH 7 0 days Half-life 

Method: CAM 2 integer See PRZM manual 

Incorporation Depth: DEPI cm 

Application Rate: TAPP 0.75 kg/ha 

Application Efficiency: APPEFF 0.99 fraction 

Spray Drift DRFT 0.01 fraction of application rate applied to pond 

Application Date Date 8-Apr dd/mm or dd/mmm or dd-mm or dd-mmm 

Interval 1 interval 21 days Set to 0 or delete line for single app. 

app. rate 1 apprate kg/ha 

Record 17: FILTRA 

 IPSCND 3 

 UPTKF 

Record 18: PLVKRT 

 PLDKRT 

 FEXTRC 0.5 

Flag for Index Res. Run IR EPA Pond 

Flag for runoff calc. RUNOFF none none, monthly or total(average of entire run) 

FL Tomato (0.30 lbs a.i ground applications) 

stored as Tomato_FL.out 

Chemical: Imazosulfuron 

PRZM environment: FLtomatoSTD_V2.txt modified Tueday, 20 May 2008 at 12:00:14 

EXAMS environment: pond298.exv modified Tueday, 26 August 2008 at 06:14:08 

 

Metfile: w12844.dvf modified Tueday, 26 August 2008 at 06:14:22 

Water segment concentrations (ppb) 

Year Peak 96 hr 21 Day 60 Day 90 Day Yearly 

1961 2.90 2.86 2.73 2.43 2.25 0.78 

1962 4.33 4.27 4.15 3.76 3.49 1.85 

1963 2.39 2.36 2.27 2.12 1.99 1.65 

1964 2.57 2.53 2.42 2.18 2.03 1.27 

1965 1.40 1.39 1.36 1.27 1.21 0.97 

1966 9.29 9.16 8.72 7.82 7.24 2.97 

1967 8.18 8.07 7.65 6.88 6.40 4.21 

1968 13.61 13.42 12.72 11.53 10.73 5.65 

1969 8.57 8.48 8.11 7.40 6.92 5.49 

1970 4.47 4.45 4.34 4.12 3.95 3.11 

1971 2.23 2.21 2.16 2.03 1.94 1.45 

1972 0.96 0.95 0.92 0.86 0.81 0.65 

1973 2.60 2.56 2.46 2.23 2.08 0.96 

1974 3.50 3.45 3.33 3.02 2.81 1.54 

1975 1.80 1.78 1.72 1.60 1.52 1.14 

1976 7.37 7.27 6.90 6.23 5.87 2.45 

1977 4.06 4.01 3.88 3.63 3.47 2.86 

1978 2.33 2.30 2.19 2.00 1.92 1.57 
 94

1979 1.81 1.79 1.74 1.60 1.54 1.12 

1980 4.80 4.74 4.61 4.21 3.92 1.77 

1981 5.80 5.72 5.51 4.94 4.58 2.74 

1982 3.95 3.89 3.69 3.31 3.07 2.34 

1983 4.95 4.88 4.64 4.17 3.89 2.20 

1984 5.36 5.31 5.16 4.78 4.49 2.64 

1985 4.98 4.91 4.70 4.23 3.94 2.64 

1986 2.43 2.42 2.36 2.22 2.11 1.61 

1987 3.13 3.09 2.96 2.74 2.66 1.45 

1988 6.57 6.48 6.11 5.42 5.04 2.53 

1989 5.74 5.69 5.45 4.91 4.55 2.92 

1990 11.36 11.21 10.72 9.54 8.80 4.33 

Sorted results 

Prob. Peak 96 hr 21 Day 60 Day 90 Day Yearly 

0.03 13.61 13.42 12.72 11.53 10.73 5.65 

0.06 11.36 11.21 10.72 9.54 8.80 5.49 

0.10 9.29 9.16 8.72 7.82 7.24 4.33 

0.13 8.57 8.48 8.11 7.40 6.92 4.21 

0.16 8.18 8.07 7.65 6.88 6.40 3.11 

0.19 7.37 7.27 6.90 6.23 5.87 2.97 

0.23 6.57 6.48 6.11 5.42 5.04 2.92 

0.26 5.80 5.72 5.51 4.94 4.58 2.86 

0.29 5.74 5.69 5.45 4.91 4.55 2.74 

0.32 5.36 5.31 5.16 4.78 4.49 2.64 

0.35 4.98 4.91 4.70 4.23 3.95 2.64 

0.39 4.95 4.88 4.64 4.21 3.94 2.53 

0.42 4.80 4.74 4.61 4.17 3.92 2.45 

0.45 4.47 4.45 4.34 4.12 3.89 2.34 

0.48 4.33 4.27 4.15 3.76 3.49 2.20 

0.52 4.06 4.01 3.88 3.63 3.47 1.85 

0.55 3.95 3.89 3.69 3.31 3.07 1.77 

0.58 3.50 3.45 3.33 3.02 2.81 1.65 

0.61 3.13 3.09 2.96 2.74 2.66 1.61 

0.65 2.90 2.86 2.73 2.43 2.25 1.57 

0.68 2.60 2.56 2.46 2.23 2.11 1.54 

0.71 2.57 2.53 2.42 2.22 2.08 1.45 

0.74 2.43 2.42 2.36 2.18 2.03 1.45 

0.77 2.39 2.36 2.27 2.12 1.99 1.27 

0.81 2.33 2.30 2.19 2.03 1.94 1.14 

0.84 2.23 2.21 2.16 2.00 1.92 1.12 

0.87 1.81 1.79 1.74 1.60 1.54 0.97 

0.90 1.80 1.78 1.72 1.60 1.52 0.96 

0.94 1.40 1.39 1.36 1.27 1.21 0.78 

0.97 0.96 0.95 0.92 0.86 0.81 0.65 

0.10 9.22 9.10 8.66 7.78 7.21 4.32 

Average of yearly averages: 2.30 

Inputs generated by pe5.pl - Novemeber 2006 

Data used for this run: 

Output File: Tomato_FL 

Metfile: w12844.dvf 

PRZM scenario: FLtomatoSTD_V2.txt 

EXAMS environment file: pond298.exv 
 95

Chemical Name: Imazosulfuron 

Description Variable Name Value Units Comments 

Molecular weight mwt 412.81 g/mol 

Henry's Law Const. henry 3.33E-11 atm-m^3/mol 

Vapor Pressure vapr 2.63E-08 torr 

Solubility sol 429 mg/L 

Kd Kd mg/L 

Koc Koc 154 mg/L 

Photolysis half-life kdp 61.7 days Half-life 

Aerobic Aquatic Metabolism kbacw 192 days Halfife 

Anaerobic Aquatic Metabolism kbacs 64.2 days Halfife 

Aerobic Soil Metabolism asm 207.2 days Halfife 

Hydrolysis: pH 7 0 days Half-life 

Method: CAM 2 integer See PRZM manual 

Incorporation Depth: DEPI cm 

Application Rate: TAPP 0.34 kg/ha 

Application Efficiency: APPEFF 0.99 fraction 

Spray Drift DRFT 0.01 fraction of application rate applied to pond 

Application Date Date 8-Feb dd/mm or dd/mmm or dd-mm or dd-mmm 

Record 17: FILTRA 

 IPSCND 3 

 UPTKF 

Record 18: PLVKRT 

 PLDKRT 

 FEXTRC 0.5 

Flag for Index Res. Run IR EPA Pond 

Flag for runoff calc. RUNOFF none none, monthly or total(average of entire run) 

PA Tomato (0.30 lbs a.i ground applications) 

stored as Tomato_PA.out 

Chemical: Imazosulfuron 

PRZM environment: PAtomatoSTD.txt modified Tueday, 29 May 2007 at 14:01:58 

 

EXAMS environment: pond298.exv modified Tueday, 26 August 2008 at 06:14:08 

 

Metfile: w14751.dvf modified Tueday, 26 August 2008 at 06:15:00 

Water segment concentrations (ppb) 

Year Peak 96 hr 21 Day 60 Day 90 Day Yearly 

1961 0.24 0.24 0.23 0.21 0.20 0.12 

1962 0.50 0.50 0.48 0.47 0.46 0.30 

1963 0.42 0.41 0.41 0.40 0.39 0.30 

1964 1.12 1.11 1.07 0.98 0.97 0.61 

1965 0.82 0.82 0.79 0.78 0.75 0.59 

1966 1.02 1.01 0.98 0.91 0.86 0.61 

1967 1.12 1.11 1.08 1.01 0.96 0.68 

1968 2.22 2.21 2.13 2.05 1.99 1.23 

1969 1.23 1.22 1.19 1.15 1.10 0.97 

1970 0.90 0.89 0.87 0.84 0.81 0.65 

1971 0.94 0.93 0.90 0.84 0.80 0.56 

1972 1.22 1.21 1.17 1.11 1.05 0.70 

1973 1.40 1.39 1.36 1.31 1.25 0.84 

1974 2.00 1.98 1.94 1.81 1.71 1.09 

1975 2.67 2.64 2.57 2.42 2.30 1.51 
 96

1976 1.82 1.81 1.78 1.67 1.57 1.24 

1977 1.70 1.69 1.64 1.53 1.46 1.06 

1978 1.78 1.77 1.72 1.59 1.50 1.04 

1979 1.40 1.39 1.35 1.26 1.20 0.92 

1980 1.73 1.72 1.69 1.58 1.51 1.03 

1981 0.90 0.90 0.88 0.85 0.82 0.70 

1982 1.47 1.46 1.41 1.32 1.24 0.82 

1983 3.09 3.06 2.97 2.86 2.72 1.67 

1984 1.78 1.77 1.72 1.62 1.58 1.31 

1985 3.17 3.15 3.05 2.90 2.78 1.78 

1986 2.04 2.03 1.97 1.83 1.75 1.48 

1987 1.57 1.56 1.52 1.46 1.42 1.11 

1988 1.28 1.27 1.25 1.19 1.12 0.85 

1989 3.58 3.55 3.49 3.26 3.07 1.80 

1990 2.59 2.57 2.48 2.39 2.28 1.75 

Sorted results 

Prob. Peak 96 hr 21 Day 60 Day 90 Day Yearly 

0.03 3.58 3.55 3.49 3.26 3.07 1.80 

0.06 3.17 3.15 3.05 2.90 2.78 1.78 

0.10 3.09 3.06 2.97 2.86 2.72 1.75 

0.13 2.67 2.64 2.57 2.42 2.30 1.67 

0.16 2.59 2.57 2.48 2.39 2.28 1.51 

0.19 2.22 2.21 2.13 2.05 1.99 1.48 

0.23 2.04 2.03 1.97 1.83 1.75 1.31 

0.26 2.00 1.98 1.94 1.81 1.71 1.24 

0.29 1.82 1.81 1.78 1.67 1.58 1.23 

0.32 1.78 1.77 1.72 1.62 1.57 1.11 

0.35 1.78 1.77 1.72 1.59 1.51 1.09 

0.39 1.73 1.72 1.69 1.58 1.50 1.06 

0.42 1.70 1.69 1.64 1.53 1.46 1.04 

0.45 1.57 1.56 1.52 1.46 1.42 1.03 

0.48 1.47 1.46 1.41 1.32 1.25 0.97 

0.52 1.40 1.39 1.36 1.31 1.24 0.92 

0.55 1.40 1.39 1.35 1.26 1.20 0.85 

0.58 1.28 1.27 1.25 1.19 1.12 0.84 

0.61 1.23 1.22 1.19 1.15 1.10 0.82 

0.65 1.22 1.21 1.17 1.11 1.05 0.70 

0.68 1.12 1.11 1.08 1.01 0.97 0.70 

0.71 1.12 1.11 1.07 0.98 0.96 0.68 

0.74 1.02 1.01 0.98 0.91 0.86 0.65 

0.77 0.94 0.93 0.90 0.85 0.82 0.61 

0.81 0.90 0.90 0.88 0.84 0.81 0.61 

0.84 0.90 0.89 0.87 0.84 0.80 0.59 

0.87 0.82 0.82 0.79 0.78 0.75 0.56 

0.90 0.50 0.50 0.48 0.47 0.46 0.30 

0.94 0.42 0.41 0.41 0.40 0.39 0.30 

0.97 0.24 0.24 0.23 0.21 0.20 0.12 

0.10 3.04 3.02 2.93 2.82 2.68 1.74 

Average of yearly averages: 0.98 

Inputs generated by pe5.pl - Novemeber 2006 

Data used for this run: 

Output File: Tomato_PA 
 97

Metfile: w14751.dvf 

PRZM scenario: PAtomatoSTD.txt 

EXAMS environment file: pond298.exv 

Chemical Name: Imazosulfuron 

Description Variable Name Value Units Comments 

Molecular weight mwt 412.81 g/mol 

Henry's Law Const. henry 3.33E-11 atm-m^3/mol 

Vapor Pressure vapr 2.63E-08 torr 

Solubility sol 429 mg/L 

Kd Kd mg/L 

Koc Koc 154 mg/L 

Photolysis half-life kdp 61.7 days Half-life 

Aerobic Aquatic Metabolism kbacw 192 days Halfife 

Anaerobic Aquatic Metabolism kbacs 64.2 days Halfife 

Aerobic Soil Metabolism asm 207.2 days Halfife 

Hydrolysis: pH 7 0 days Half-life 

Method: CAM 2 integer See PRZM manual 

Incorporation Depth: DEPI cm 

Application Rate: TAPP 0.34 kg/ha 

Application Efficiency: APPEFF 0.99 fraction 

Spray Drift DRFT 0.01 fraction of application rate applied to pond 

Application Date Date 23-04 dd/mm or dd/mmm or dd-mm or dd-mmm 

Record 17: FILTRA 

 IPSCND 3 

 UPTKF 

Record 18: PLVKRT 

 PLDKRT 

 FEXTRC 0.5 

Flag for Index Res. Run IR EPA Pond 

Flag for runoff calc. RUNOFF none none, monthly or total(average of entire run) 

FL Pepper (0.30 lbs a.i ground applications) 

stored as Pepper_FL.out 

Chemical: Imazosulfuron 

PRZM environment: FLpeppersSTD.txt modified Thuday, 24 May 2007 at 10:44:22 

 

EXAMS environment: pond298.exv modified Tueday, 26 August 2008 at 06:14:08 

 

Metfile: w12844.dvf modified Tueday, 26 August 2008 at 06:14:22 

Water segment concentrations (ppb) 

Year Peak 96 hr 21 Day 60 Day 90 Day Yearly 

1961 4.23 4.17 3.98 3.55 3.29 1.13 

1962 3.95 3.90 3.75 3.49 3.25 2.04 

1963 2.22 2.20 2.14 2.02 1.93 1.53 

1964 5.40 5.32 5.08 4.57 4.25 1.90 

1965 2.92 2.90 2.82 2.65 2.52 1.83 

1966 2.14 2.11 2.05 1.86 1.74 1.11 

1967 9.45 9.32 8.81 7.88 7.31 3.05 

1968 18.63 18.37 17.46 16.05 14.96 7.31 

1969 12.32 12.17 11.77 10.65 9.89 7.70 

1970 6.55 6.51 6.36 6.04 5.78 4.52 

1971 3.27 3.25 3.17 2.98 2.85 2.05 
 98

1972 1.28 1.27 1.23 1.14 1.09 0.85 

1973 2.78 2.75 2.63 2.51 2.35 1.09 

1974 3.72 3.67 3.54 3.28 3.07 1.69 

1975 2.01 2.00 1.94 1.80 1.70 1.27 

1976 10.57 10.43 9.90 8.91 8.37 3.38 

1977 5.62 5.59 5.46 5.19 4.95 3.81 

1978 2.74 2.72 2.65 2.51 2.41 1.81 

1979 2.68 2.65 2.57 2.32 2.22 1.37 

1980 6.02 5.93 5.80 5.25 4.88 2.30 

1981 12.29 12.12 11.64 10.44 9.68 4.75 

1982 9.63 9.50 9.02 8.07 7.47 5.25 

1983 8.07 7.96 7.61 6.82 6.33 4.19 

1984 7.45 7.38 7.16 6.64 6.23 3.94 

1985 4.09 4.06 3.97 3.75 3.57 2.62 

1986 2.77 2.74 2.62 2.37 2.20 1.48 

1987 1.93 1.90 1.83 1.66 1.55 1.11 

1988 9.79 9.65 9.10 8.05 7.46 3.05 

1989 4.86 4.82 4.67 4.35 4.13 3.03 

1990 11.53 11.36 10.85 9.70 8.95 3.90 

Sorted results 

Prob. Peak 96 hr 21 Day 60 Day 90 Day Yearly 

0.03 18.63 18.37 17.46 16.05 14.96 7.70 

0.06 12.32 12.17 11.77 10.65 9.89 7.31 

0.10 12.29 12.12 11.64 10.44 9.68 5.25 

0.13 11.53 11.36 10.85 9.70 8.95 4.75 

0.16 10.57 10.43 9.90 8.91 8.37 4.52 

0.19 9.79 9.65 9.10 8.07 7.47 4.19 

0.23 9.63 9.50 9.02 8.05 7.46 3.94 

0.26 9.45 9.32 8.81 7.88 7.31 3.90 

0.29 8.07 7.96 7.61 6.82 6.33 3.81 

0.32 7.45 7.38 7.16 6.64 6.23 3.38 

0.35 6.55 6.51 6.36 6.04 5.78 3.05 

0.39 6.02 5.93 5.80 5.25 4.95 3.05 

0.42 5.62 5.59 5.46 5.19 4.88 3.03 

0.45 5.40 5.32 5.08 4.57 4.25 2.62 

0.48 4.86 4.82 4.67 4.35 4.13 2.30 

0.52 4.23 4.17 3.98 3.75 3.57 2.05 

0.55 4.09 4.06 3.97 3.55 3.29 2.04 

0.58 3.95 3.90 3.75 3.49 3.25 1.90 

0.61 3.72 3.67 3.54 3.28 3.07 1.83 

0.65 3.27 3.25 3.17 2.98 2.85 1.81 

0.68 2.92 2.90 2.82 2.65 2.52 1.69 

0.71 2.78 2.75 2.65 2.51 2.41 1.53 

0.74 2.77 2.74 2.63 2.51 2.35 1.48 

0.77 2.74 2.72 2.62 2.37 2.22 1.37 

0.81 2.68 2.65 2.57 2.32 2.20 1.27 

0.84 2.22 2.20 2.14 2.02 1.93 1.13 

0.87 2.14 2.11 2.05 1.86 1.74 1.11 

0.90 2.01 2.00 1.94 1.80 1.70 1.11 

0.94 1.93 1.90 1.83 1.66 1.55 1.09 

0.97 1.28 1.27 1.23 1.14 1.09 0.85 

0.10 12.21 12.04 11.56 10.37 9.61 5.20 

Average of yearly averages: 2.83 
 99

Inputs generated by pe5.pl - Novemeber 2006 

Data used for this run: 

Output File: Pepper_FL 

Metfile: w12844.dvf 

PRZM scenario: FLpeppersSTD.txt 

EXAMS environment file: pond298.exv 

Chemical Name: Imazosulfuron 

Description Variable Name Value Units Comments 

Molecular weight mwt 412.81 g/mol 

Henry's Law Const. henry 3.33E-11 atm-m^3/mol 

Vapor Pressure vapr 2.63E-08 torr 

Solubility sol 429 mg/L 

Kd Kd mg/L 

Koc Koc 154 mg/L 

Photolysis half-life kdp 61.7 days Half-life 

Aerobic Aquatic Metabolism kbacw 192 days Halfife 

Anaerobic Aquatic Metabolism kbacs 64.2 days Halfife 

Aerobic Soil Metabolism asm 207.2 days Halfife 

Hydrolysis: pH 7 0 days Half-life 

Method: CAM 2 integer See PRZM manual 

Incorporation Depth: DEPI cm 

Application Rate: TAPP 0.34 kg/ha 

Application Efficiency: APPEFF 0.99 fraction 

Spray Drift DRFT 0.01 fraction of application rate applied to pond 

Application Date Date 8-Sep dd/mm or dd/mmm or dd-mm or dd-mmm 

Record 17: FILTRA 

 IPSCND 3 

 UPTKF 

Record 18: PLVKRT 

 PLDKRT 

 FEXTRC 0.5 

Flag for Index Res. Run IR EPA Pond 

Flag for runoff calc. RUNOFF none none, monthly or total(average of entire run) 
 100

Concentrations in Pore Water

FL Turf (0.67 lbs a.i x 2 ground applications) 

stored as Turf_FLben.out 

Chemical: Imazosulfuron 

PRZM environment: FLturfSTD.txt modified Tueday, 21 February 2006 at 15:38:26 

 

EXAMS environment: pond298.exv modified Tueday, 26 August 2008 at 06:14:08 

 

Metfile: w12834.dvf modified Tueday, 26 August 2008 at 06:14:18 

Benthic segment concentrations (ppb) 

Year Peak 96 hr 21 Day 60 Day 90 Day Yearly 

1961 1.43 1.43 1.43 1.40 1.35 0.41 

1962 1.43 1.43 1.43 1.40 1.36 1.01 

1963 0.98 0.98 0.97 0.95 0.92 0.68 

1964 2.15 2.15 2.15 2.13 2.07 1.00 

1965 2.14 2.14 2.13 2.09 2.04 1.38 

1966 1.23 1.23 1.23 1.21 1.19 0.83 

1967 1.41 1.41 1.41 1.39 1.32 0.97 

1968 1.57 1.57 1.57 1.54 1.49 1.17 

1969 3.40 3.40 3.38 3.28 3.15 1.74 

1970 3.41 3.41 3.40 3.36 3.27 2.03 

1971 1.13 1.13 1.12 1.09 1.06 0.80 

1972 2.88 2.88 2.88 2.83 2.73 1.21 

1973 2.87 2.87 2.86 2.82 2.75 1.82 

1974 1.52 1.52 1.52 1.48 1.41 0.99 

1975 1.54 1.54 1.53 1.49 1.42 1.14 

1976 1.55 1.55 1.55 1.53 1.48 1.18 

1977 1.62 1.62 1.62 1.62 1.60 1.27 

1978 1.62 1.62 1.62 1.60 1.56 1.12 

1979 1.20 1.20 1.20 1.18 1.15 0.86 

1980 1.20 1.20 1.19 1.18 1.15 0.82 

1981 1.57 1.57 1.57 1.52 1.46 0.80 

1982 1.57 1.57 1.57 1.52 1.47 1.00 

1983 1.44 1.44 1.44 1.42 1.37 0.79 

1984 1.44 1.44 1.44 1.41 1.38 1.00 

1985 0.87 0.87 0.87 0.85 0.83 0.68 

1986 0.87 0.87 0.87 0.85 0.83 0.62 

1987 0.61 0.61 0.61 0.60 0.59 0.46 

1988 0.48 0.48 0.48 0.48 0.47 0.38 

1989 0.66 0.66 0.65 0.61 0.55 0.39 

1990 0.92 0.92 0.92 0.91 0.90 0.59 

Sorted results 

Prob. Peak 96 hr 21 Day 60 Day 90 Day Yearly 

0.03 3.41 3.41 3.40 3.36 3.27 2.03 

0.06 3.40 3.40 3.38 3.28 3.15 1.82 

0.10 2.88 2.88 2.88 2.83 2.75 1.74 

0.13 2.87 2.87 2.86 2.82 2.73 1.38 

0.16 2.15 2.15 2.15 2.13 2.07 1.27 

0.19 2.14 2.14 2.13 2.09 2.04 1.21 

0.23 1.62 1.62 1.62 1.62 1.60 1.18 

0.26 1.62 1.62 1.62 1.60 1.56 1.17 
 101

0.29 1.57 1.57 1.57 1.54 1.49 1.14 

0.32 1.57 1.57 1.57 1.53 1.48 1.12 

0.35 1.57 1.57 1.57 1.52 1.47 1.01 

0.39 1.55 1.55 1.55 1.52 1.46 1.00 

0.42 1.54 1.54 1.53 1.49 1.42 1.00 

0.45 1.52 1.52 1.52 1.48 1.41 1.00 

0.48 1.44 1.44 1.44 1.42 1.38 0.99 

0.52 1.44 1.44 1.44 1.41 1.37 0.97 

0.55 1.43 1.43 1.43 1.40 1.36 0.86 

0.58 1.43 1.43 1.43 1.40 1.35 0.83 

0.61 1.41 1.41 1.41 1.39 1.32 0.82 

0.65 1.23 1.23 1.23 1.21 1.19 0.80 

0.68 1.20 1.20 1.20 1.18 1.15 0.80 

0.71 1.20 1.20 1.19 1.18 1.15 0.79 

0.74 1.13 1.13 1.12 1.09 1.06 0.68 

0.77 0.98 0.98 0.97 0.95 0.92 0.68 

0.81 0.92 0.92 0.92 0.91 0.90 0.62 

0.84 0.87 0.87 0.87 0.85 0.83 0.59 

0.87 0.87 0.87 0.87 0.85 0.83 0.46 

0.90 0.66 0.66 0.65 0.61 0.59 0.41 

0.94 0.61 0.61 0.61 0.60 0.55 0.39 

0.97 0.48 0.48 0.48 0.48 0.47 0.38 

 

0.10 2.88 2.88 2.87 2.83 2.74 1.70 

 Average of yearly averages: 0.97 

Inputs generated by pe5.pl - Novemeber 2006 

Data used for this run: 

Output File: Turf_FL 

Metfile: w12834.dvf 

PRZM scenario: FLturfSTD.txt 

EXAMS environment file: pond298.exv 

Chemical Name: Imazosulfuron 

Description Variable Name Value Units Comments 

Molecular weight mwt 412.81 g/mol 

Henry's Law Const. henry 3.33E-11 atm-m^3/mol 

Vapor Pressure vapr 2.63E-08 torr 

Solubility sol 429 mg/L 

Kd Kd mg/L 

Koc Koc 154 mg/L 

Photolysis half-life kdp 61.7 days Half-life 

Aerobic Aquatic Metabolism kbacw 192 days Halfife 

Anaerobic Aquatic Metabolism kbacs 64.2 days Halfife 

Aerobic Soil Metabolism asm 207.2 days Halfife 

Hydrolysis: pH 7 0 days Half-life 

Method: CAM 2 integer See PRZM manual 

Incorporation Depth: DEPI cm 

Application Rate: TAPP 0.75 kg/ha 

Application Efficiency: APPEFF 0.99 fraction 

Spray Drift DRFT 0.01 fraction of application rate applied to pond 

Application Date Date 8-Feb dd/mm or dd/mmm or dd-mm or dd-mmm 

Interval 1 interval 21 days Set to 0 or delete line for single app. 

app. rate 1 apprate kg/ha 

Record 17: FILTRA 

 IPSCND 3 
 102

 UPTKF 

Record 18: PLVKRT 

 PLDKRT 

 FEXTRC 0.5 

Flag for Index Res. Run IR EPA Pond 

Flag for runoff calc. RUNOFF none none, monthly or total(average of entire run) 

PA Turf (0.67 lbs a.i x 2 ground applications)

stored as Turf_PAben.out 

Chemical: Imazosulfuron 

PRZM environment: PAturfSTD.txt modified Thuday, 23 February 2006 at 18:55:08 

 

EXAMS environment: pond298.exv modified Tueday, 26 August 2008 at 06:14:08 

 

Metfile: w12834.dvf modified Tueday, 26 August 2008 at 06:14:18 

Benthic segment concentrations (ppb) 

Year Peak 96 hr 21 Day 60 Day 90 Day Yearly 

1961 3.44 3.44 3.43 3.36 3.21 0.96 

1962 3.44 3.44 3.44 3.36 3.27 2.48 

1963 2.66 2.65 2.63 2.58 2.50 1.81 

1964 4.74 4.74 4.74 4.71 4.58 2.47 

1965 4.70 4.70 4.69 4.60 4.48 2.95 

1966 1.88 1.88 1.87 1.82 1.77 1.27 

1967 1.99 1.99 1.98 1.93 1.81 1.05 

1968 3.10 3.10 3.09 3.01 2.89 1.89 

1969 3.88 3.87 3.83 3.65 3.39 2.50 

1970 3.91 3.91 3.91 3.87 3.78 2.35 

1971 1.74 1.74 1.73 1.71 1.64 1.13 

1972 7.83 7.83 7.83 7.70 7.43 3.08 

1973 7.80 7.80 7.79 7.69 7.47 4.87 

1974 4.10 4.10 4.10 4.01 3.85 2.62 

1975 4.10 4.09 4.04 3.89 3.75 2.76 

1976 3.17 3.17 3.17 3.07 2.91 2.34 

1977 3.21 3.21 3.21 3.18 3.09 2.43 

1978 2.96 2.96 2.96 2.93 2.87 2.23 

1979 2.97 2.97 2.97 2.92 2.82 2.07 

1980 2.97 2.97 2.96 2.92 2.84 1.94 

1981 4.06 4.05 4.04 3.92 3.75 1.85 

1982 4.06 4.05 4.04 3.94 3.80 2.50 

1983 3.33 3.33 3.33 3.27 3.17 1.85 

1984 3.33 3.33 3.33 3.27 3.18 2.33 

1985 2.18 2.18 2.18 2.15 2.08 1.64 

1986 2.01 2.01 2.00 1.96 1.90 1.38 

1987 1.29 1.29 1.29 1.28 1.25 0.92 

1988 1.04 1.04 1.04 1.02 0.99 0.72 

1989 1.04 1.04 1.02 0.99 0.95 0.72 

1990 0.93 0.93 0.93 0.92 0.89 0.71 

Sorted results 

Prob. Peak 96 hr 21 Day 60 Day 90 Day Yearly 

0.03 7.83 7.83 7.83 7.70 7.47 4.87 

0.06 7.80 7.80 7.79 7.69 7.43 3.08 

0.10 4.74 4.74 4.74 4.71 4.58 2.95 
 103

0.13 4.70 4.70 4.69 4.60 4.48 2.76 

0.16 4.10 4.10 4.10 4.01 3.85 2.62 

0.19 4.10 4.09 4.04 3.94 3.80 2.50 

0.23 4.06 4.05 4.04 3.92 3.78 2.50 

0.26 4.06 4.05 4.04 3.89 3.75 2.48 

0.29 3.91 3.91 3.91 3.87 3.75 2.47 

0.32 3.88 3.87 3.83 3.65 3.39 2.43 

0.35 3.44 3.44 3.44 3.36 3.27 2.35 

0.39 3.44 3.44 3.43 3.36 3.21 2.34 

0.42 3.33 3.33 3.33 3.27 3.18 2.33 

0.45 3.33 3.33 3.33 3.27 3.17 2.23 

0.48 3.21 3.21 3.21 3.18 3.09 2.07 

0.52 3.17 3.17 3.17 3.07 2.91 1.94 

0.55 3.10 3.10 3.09 3.01 2.89 1.89 

0.58 2.97 2.97 2.97 2.93 2.87 1.85 

0.61 2.97 2.97 2.96 2.92 2.84 1.85 

0.65 2.96 2.96 2.96 2.92 2.82 1.81 

0.68 2.66 2.65 2.63 2.58 2.50 1.64 

0.71 2.18 2.18 2.18 2.15 2.08 1.38 

0.74 2.01 2.01 2.00 1.96 1.90 1.27 

0.77 1.99 1.99 1.98 1.93 1.81 1.13 

0.81 1.88 1.88 1.87 1.82 1.77 1.05 

0.84 1.74 1.74 1.73 1.71 1.64 0.96 

0.87 1.29 1.29 1.29 1.28 1.25 0.92 

0.90 1.04 1.04 1.04 1.02 0.99 0.72 

0.94 1.04 1.04 1.02 0.99 0.95 0.72 

0.97 0.93 0.93 0.93 0.92 0.89 0.71 

0.10 4.74 4.74 4.73 4.70 4.57 2.93 

Average of yearly averages: 1.99 

Inputs generated by pe5.pl - Novemeber 2006 

Data used for this run: 

Output File: Turf_PA 

Metfile: w12834.dvf 

PRZM scenario: PAturfSTD.txt 

EXAMS environment file: pond298.exv 

Chemical Name: Imazosulfuron 

Description Variable Name Value Units Comments 

Molecular weight mwt 412.81 g/mol 

Henry's Law Const. henry 3.33E-11 atm-m^3/mol 

Vapor Pressure vapr 2.63E-08 torr 

Solubility sol 429 mg/L 

Kd Kd mg/L 

Koc Koc 154 mg/L 

Photolysis half-life kdp 61.7 days Half-life 

Aerobic Aquatic Metabolism kbacw 192 days Halfife 

Anaerobic Aquatic Metabolism kbacs 64.2 days Halfife 

Aerobic Soil Metabolism asm 207.2 days Halfife 

Hydrolysis: pH 7 0 days Half-life 

Method: CAM 2 integer See PRZM manual 

Incorporation Depth: DEPI cm 

Application Rate: TAPP 0.75 kg/ha 

Application Efficiency: APPEFF 0.99 fraction 

Spray Drift DRFT 0.01 fraction of application rate applied to pond 
 104

Application Date Date 8-Apr dd/mm or dd/mmm or dd-mm or dd-mmm 

Interval 1 interval 21 days Set to 0 or delete line for single app. 

app. rate 1 apprate kg/ha 

Record 17: FILTRA 

 IPSCND 3 

 UPTKF 

Record 18: PLVKRT 

 PLDKRT 

 FEXTRC 0.5 

Flag for Index Res. Run IR EPA Pond 

Flag for runoff calc. RUNOFF none none, monthly or total(average of entire run) 

FL Tomato (0.30 lbs a.i ground applications) 

stored as Tomato_FLben.out 

Chemical: Imazosulfuron 

PRZM environment: FLtomatoSTD_V2.txt modified Tueday, 20 May 2008 at 12:00:14 

 

EXAMS environment: pond298.exv modified Tueday, 26 August 2008 at 06:14:08 

 

Metfile: w12844.dvf modified Tueday, 26 August 2008 at 06:14:22 

Benthic segment concentrations (ppb) 

Year Peak 96 hr 21 Day 60 Day 90 Day Yearly 

1961 1.05 1.05 1.05 1.04 1.03 0.34 

1962 1.66 1.66 1.66 1.66 1.65 1.03 

1963 1.65 1.64 1.61 1.55 1.48 1.07 

1964 1.03 1.03 1.03 1.02 1.01 0.76 

1965 0.97 0.97 0.96 0.93 0.89 0.63 

1966 3.43 3.43 3.42 3.40 3.39 1.45 

1967 3.34 3.33 3.26 3.18 3.15 2.55 

1968 5.31 5.31 5.31 5.28 5.24 3.19 

1969 5.19 5.17 5.09 4.90 4.75 3.55 

1970 3.30 3.29 3.26 3.16 3.04 2.07 

1971 1.61 1.61 1.59 1.52 1.46 0.98 

1972 0.66 0.66 0.64 0.61 0.59 0.41 

1973 0.98 0.98 0.98 0.97 0.96 0.49 

1974 1.34 1.34 1.34 1.33 1.32 0.86 

1975 1.28 1.27 1.24 1.16 1.10 0.75 

1976 2.89 2.89 2.88 2.86 2.83 1.22 

1977 2.81 2.81 2.80 2.74 2.63 1.86 

1978 1.57 1.57 1.55 1.51 1.46 1.02 

1979 0.92 0.92 0.91 0.89 0.86 0.69 

1980 1.92 1.92 1.92 1.91 1.87 0.93 

1981 2.28 2.28 2.28 2.27 2.24 1.61 

1982 2.24 2.23 2.19 2.08 1.97 1.46 

1983 1.88 1.88 1.88 1.87 1.85 1.26 

1984 2.21 2.21 2.21 2.20 2.17 1.54 

1985 2.06 2.06 2.05 2.00 1.92 1.59 

1986 1.73 1.73 1.71 1.64 1.57 1.06 

1987 1.37 1.37 1.37 1.36 1.34 0.78 

1988 2.39 2.39 2.38 2.36 2.34 1.37 

1989 2.28 2.27 2.22 2.14 2.13 1.73 

1990 4.09 4.09 4.08 4.05 4.01 2.27 
 105

Sorted results 

Prob. Peak 96 hr 21 Day 60 Day 90 Day Yearly 

0.03 5.31 5.31 5.31 5.28 5.24 3.55 

0.06 5.19 5.17 5.09 4.90 4.75 3.19 

0.10 4.09 4.09 4.08 4.05 4.01 2.55 

0.13 3.43 3.43 3.42 3.40 3.39 2.27 

0.16 3.34 3.33 3.26 3.18 3.15 2.07 

0.19 3.30 3.29 3.26 3.16 3.04 1.86 

0.23 2.89 2.89 2.88 2.86 2.83 1.73 

0.26 2.81 2.81 2.80 2.74 2.63 1.61 

0.29 2.39 2.39 2.38 2.36 2.34 1.59 

0.32 2.28 2.28 2.28 2.27 2.24 1.54 

0.35 2.28 2.27 2.22 2.20 2.17 1.46 

0.39 2.24 2.23 2.21 2.14 2.13 1.45 

0.42 2.21 2.21 2.19 2.08 1.97 1.37 

0.45 2.06 2.06 2.05 2.00 1.92 1.26 

0.48 1.92 1.92 1.92 1.91 1.87 1.22 

0.52 1.88 1.88 1.88 1.87 1.85 1.07 

0.55 1.73 1.73 1.71 1.66 1.65 1.06 

0.58 1.66 1.66 1.66 1.64 1.57 1.03 

0.61 1.65 1.64 1.61 1.55 1.48 1.02 

0.65 1.61 1.61 1.59 1.52 1.46 0.98 

0.68 1.57 1.57 1.55 1.51 1.46 0.93 

0.71 1.37 1.37 1.37 1.36 1.34 0.86 

0.74 1.34 1.34 1.34 1.33 1.32 0.78 

0.77 1.28 1.27 1.24 1.16 1.10 0.76 

0.81 1.05 1.05 1.05 1.04 1.03 0.75 

0.84 1.03 1.03 1.03 1.02 1.01 0.69 

0.87 0.98 0.98 0.98 0.97 0.96 0.63 

0.90 0.97 0.97 0.96 0.93 0.89 0.49 

0.94 0.92 0.92 0.91 0.89 0.86 0.41 

0.97 0.66 0.66 0.64 0.61 0.59 0.34 

0.10 4.03 4.02 4.01 3.99 3.95 2.52 

Average of yearly averages: 1.35 

Inputs generated by pe5.pl - Novemeber 2006 

Data used for this run: 

Output File: Tomato_FL 

Metfile: w12844.dvf 

PRZM scenario: FLtomatoSTD_V2.txt 

EXAMS environment file: pond298.exv 

Chemical Name: Imazosulfuron 

Description Variable Name Value Units Comments 

Molecular weight mwt 412.81 g/mol 

Henry's Law Const. henry 3.33E-11 atm-m^3/mol 

Vapor Pressure vapr 2.63E-08 torr 

Solubility sol 429 mg/L 

Kd Kd mg/L 

Koc Koc 154 mg/L 

Photolysis half-life kdp 61.7 days Half-life 

Aerobic Aquatic Metabolism kbacw 192 days Halfife 

Anaerobic Aquatic Metabolism kbacs 64.2 days Halfife 

Aerobic Soil Metabolism asm 207.2 days Halfife 
 106

Hydrolysis: pH 7 0 days Half-life 

Method: CAM 2 integer See PRZM manual 

Incorporation Depth: DEPI cm 

Application Rate: TAPP 0.34 kg/ha 

Application Efficiency: APPEFF 0.99 fraction 

Spray Drift DRFT 0.01 fraction of application rate applied to pond 

Application Date Date 8-Feb dd/mm or dd/mmm or dd-mm or dd-mmm 

Record 17: FILTRA 

 IPSCND 3 

 UPTKF 

Record 18: PLVKRT 

 PLDKRT 

 FEXTRC 0.5 

Flag for Index Res. Run IR EPA Pond 

Flag for runoff calc. RUNOFF none none, monthly or total(average of entire run) 

PA Tomato (0.30 lbs a.i ground applications) 

stored as Tomato_PAben.out 

Chemical: Imazosulfuron 

PRZM environment: PAtomatoSTD.txt modified Tueday, 29 May 2007 at 14:01:58 

EXAMS environment: pond298.exv modified Tueday, 26 August 2008 at 06:14:08 

Metfile: w14751.dvf modified Tueday, 26 August 2008 at 06:15:00 

Benthic segment concentrations (ppb) 

Year Peak 96 hr 21 Day 60 Day 90 Day Yearly 

1961 0.12 0.12 0.12 0.12 0.12 0.07 

1962 0.26 0.26 0.26 0.25 0.25 0.20 

1963 0.25 0.25 0.25 0.24 0.24 0.22 

1964 0.53 0.53 0.53 0.53 0.52 0.39 

1965 0.51 0.51 0.51 0.50 0.50 0.45 

1966 0.51 0.51 0.51 0.50 0.48 0.42 

1967 0.60 0.60 0.59 0.58 0.57 0.50 

1968 1.13 1.13 1.12 1.09 1.07 0.80 

1969 0.94 0.94 0.94 0.93 0.92 0.76 

1970 0.62 0.62 0.62 0.61 0.61 0.50 

1971 0.48 0.48 0.48 0.47 0.46 0.40 

1972 0.63 0.63 0.62 0.61 0.59 0.48 

1973 0.74 0.74 0.74 0.73 0.71 0.58 

1974 0.95 0.95 0.95 0.92 0.90 0.74 

1975 1.34 1.34 1.34 1.31 1.28 1.04 

1976 1.07 1.06 1.06 1.05 1.04 0.94 

1977 0.93 0.93 0.93 0.91 0.89 0.78 

1978 0.88 0.88 0.88 0.87 0.85 0.74 

1979 0.76 0.76 0.75 0.74 0.73 0.68 

1980 0.91 0.91 0.90 0.88 0.85 0.71 

1981 0.73 0.73 0.73 0.72 0.71 0.56 

1982 0.71 0.71 0.71 0.70 0.69 0.56 

1983 1.55 1.55 1.54 1.51 1.47 1.11 

1984 1.28 1.28 1.27 1.26 1.25 1.03 

1985 1.64 1.64 1.64 1.61 1.58 1.22 

1986 1.41 1.41 1.41 1.39 1.38 1.15 

1987 0.96 0.96 0.95 0.94 0.93 0.83 

1988 0.74 0.74 0.74 0.72 0.71 0.64 

1989 1.66 1.66 1.65 1.63 1.60 1.16 

1990 1.49 1.49 1.48 1.46 1.44 1.32 

Sorted results 

Prob. Peak 96 hr 21 Day 60 Day 90 Day Yearly 

0.03 1.66 1.66 1.65 1.63 1.60 1.32 
 107

0.06 1.64 1.64 1.64 1.61 1.58 1.22 

0.10 1.55 1.55 1.54 1.51 1.47 1.16 

0.13 1.49 1.49 1.48 1.46 1.44 1.15 

0.16 1.41 1.41 1.41 1.39 1.38 1.11 

0.19 1.34 1.34 1.34 1.31 1.28 1.04 

0.23 1.28 1.28 1.27 1.26 1.25 1.03 

0.26 1.13 1.13 1.12 1.09 1.07 0.94 

0.29 1.07 1.06 1.06 1.05 1.04 0.83 

0.32 0.96 0.96 0.95 0.94 0.93 0.80 

0.35 0.95 0.95 0.95 0.93 0.92 0.78 

0.39 0.94 0.94 0.94 0.92 0.90 0.76 

0.42 0.93 0.93 0.93 0.91 0.89 0.74 

0.45 0.91 0.91 0.90 0.88 0.85 0.74 

0.48 0.88 0.88 0.88 0.87 0.85 0.71 

0.52 0.76 0.76 0.75 0.74 0.73 0.68 

0.55 0.74 0.74 0.74 0.73 0.71 0.64 

0.58 0.74 0.74 0.74 0.72 0.71 0.58 

0.61 0.73 0.73 0.73 0.72 0.71 0.56 

0.65 0.71 0.71 0.71 0.70 0.69 0.56 

0.68 0.63 0.63 0.62 0.61 0.61 0.50 

0.71 0.62 0.62 0.62 0.61 0.59 0.50 

0.74 0.60 0.60 0.59 0.58 0.57 0.48 

0.77 0.53 0.53 0.53 0.53 0.52 0.45 

0.81 0.51 0.51 0.51 0.50 0.50 0.42 

0.84 0.51 0.51 0.51 0.50 0.48 0.40 

0.87 0.48 0.48 0.48 0.47 0.46 0.39 

0.90 0.26 0.26 0.26 0.25 0.25 0.22 

0.94 0.25 0.25 0.25 0.24 0.24 0.20 

0.97 0.12 0.12 0.12 0.12 0.12 0.07 

0.10 1.55 1.54 1.54 1.50 1.47 1.15 

Average of yearly averages: 0.70 

Inputs generated by pe5.pl - Novemeber 2006 

Data used for this run: 

Output File: Tomato_PA 

Metfile: w14751.dvf 

PRZM scenario: PAtomatoSTD.txt 

EXAMS environment file: pond298.exv 

Chemical Name: Imazosulfuron 

Description Variable Name Value Units Comments 

Molecular weight mwt 412.81 g/mol 

Henry's Law Const. henry 3.33E-11 atm-m^3/mol 

Vapor Pressure vapr 2.63E-08 torr 

Solubility sol 429 mg/L 

Kd Kd mg/L 

Koc Koc 154 mg/L 

Photolysis half-life kdp 61.7 days Half-life 

Aerobic Aquatic Metabolism kbacw 192 days Halfife 

Anaerobic Aquatic Metabolism kbacs 64.2 days Halfife 

Aerobic Soil Metabolism asm 207.2 days Halfife 

Hydrolysis: pH 7 0 days Half-life 

Method: CAM 2 integer See PRZM manual 

Incorporation Depth: DEPI cm 

Application Rate: TAPP 0.34 kg/ha 

Application Efficiency: APPEFF 0.99 fraction 

Spray Drift DRFT 0.01 fraction of application rate applied to pond 

Application Date Date 23-04 dd/mm or dd/mmm or dd-mm or dd-mmm 

Record 17: FILTRA 

 IPSCND 3 

 UPTKF 
 108

Record 18: PLVKRT 

 PLDKRT 

 FEXTRC 0.5 

Flag for Index Res. Run IR EPA Pond 

Flag for runoff calc. RUNOFF none none, monthly or total(average of entire run) 

FL Pepper (0.30 lbs a.i ground applications) 

stored as Pepper_FLben.out 

Chemical: Imazosulfuron 

PRZM environment: FLpeppersSTD.txt modified Thuday, 24 May 2007 at 10:44:22 

 

EXAMS environment: pond298.exv modified Tueday, 26 August 2008 at 06:14:08 

 

Metfile: w12844.dvf modified Tueday, 26 August 2008 at 06:14:22 

Benthic segment concentrations (ppb) 

Year Peak 96 hr 21 Day 60 Day 90 Day Yearly 

1961 1.53 1.53 1.53 1.52 1.50 0.49 

1962 1.63 1.63 1.63 1.62 1.60 1.20 

1963 1.62 1.61 1.58 1.52 1.45 1.00 

1964 2.08 2.08 2.08 2.06 2.01 0.99 

1965 2.00 2.00 1.98 1.91 1.83 1.22 

1966 0.89 0.89 0.89 0.88 0.87 0.67 

1967 3.51 3.51 3.50 3.47 3.44 1.53 

1968 7.37 7.37 7.36 7.33 7.25 4.01 

1969 7.24 7.21 7.10 6.84 6.63 4.96 

1970 4.80 4.80 4.76 4.62 4.45 3.01 

1971 2.36 2.36 2.33 2.23 2.15 1.39 

1972 0.89 0.88 0.86 0.82 0.78 0.54 

1973 1.12 1.12 1.11 1.10 1.10 0.57 

1974 1.48 1.48 1.48 1.47 1.46 0.95 

1975 1.43 1.42 1.38 1.30 1.24 0.84 

1976 4.11 4.11 4.11 4.08 4.04 1.64 

1977 4.01 4.01 4.00 3.91 3.75 2.53 

1978 1.96 1.96 1.95 1.90 1.83 1.21 

1979 1.13 1.13 1.13 1.12 1.11 0.80 

1980 2.39 2.39 2.39 2.37 2.33 1.23 

1981 4.77 4.76 4.76 4.73 4.64 2.59 

1982 4.69 4.67 4.60 4.36 4.13 3.20 

1983 3.27 3.27 3.25 3.14 3.06 2.54 

1984 3.09 3.09 3.08 3.07 3.04 2.36 

1985 2.86 2.86 2.86 2.78 2.66 1.75 

1986 1.21 1.21 1.20 1.15 1.10 0.89 

1987 0.95 0.95 0.94 0.91 0.88 0.67 

1988 3.49 3.49 3.48 3.46 3.42 1.48 

1989 3.37 3.35 3.28 3.12 2.99 1.99 

1990 4.06 4.06 4.05 4.03 3.99 1.96 

Sorted results 

Prob. Peak 96 hr 21 Day 60 Day 90 Day Yearly 

0.03 7.37 7.37 7.36 7.33 7.25 4.96 

0.06 7.24 7.21 7.10 6.84 6.63 4.01 

0.10 4.80 4.80 4.76 4.73 4.64 3.20 

0.13 4.77 4.76 4.76 4.62 4.45 3.01 

0.16 4.69 4.67 4.60 4.36 4.13 2.59 
 109

0.19 4.11 4.11 4.11 4.08 4.04 2.54 

0.23 4.06 4.06 4.05 4.03 3.99 2.53 

0.26 4.01 4.01 4.00 3.91 3.75 2.36 

0.29 3.51 3.51 3.50 3.47 3.44 1.99 

0.32 3.49 3.49 3.48 3.46 3.42 1.96 

0.35 3.37 3.35 3.28 3.14 3.06 1.75 

0.39 3.27 3.27 3.25 3.12 3.04 1.64 

0.42 3.09 3.09 3.08 3.07 2.99 1.53 

0.45 2.86 2.86 2.86 2.78 2.66 1.48 

0.48 2.39 2.39 2.39 2.37 2.33 1.39 

0.52 2.36 2.36 2.33 2.23 2.15 1.23 

0.55 2.08 2.08 2.08 2.06 2.01 1.22 

0.58 2.00 2.00 1.98 1.91 1.83 1.21 

0.61 1.96 1.96 1.95 1.90 1.83 1.20 

0.65 1.63 1.63 1.63 1.62 1.60 1.00 

0.68 1.62 1.61 1.58 1.52 1.50 0.99 

0.71 1.53 1.53 1.53 1.52 1.46 0.95 

0.74 1.48 1.48 1.48 1.47 1.45 0.89 

0.77 1.43 1.42 1.38 1.30 1.24 0.84 

0.81 1.21 1.21 1.20 1.15 1.11 0.80 

0.84 1.13 1.13 1.13 1.12 1.10 0.67 

0.87 1.12 1.12 1.11 1.10 1.10 0.67 

0.90 0.95 0.95 0.94 0.91 0.88 0.57 

0.94 0.89 0.89 0.89 0.88 0.87 0.54 

0.97 0.89 0.88 0.86 0.82 0.78 0.49 

0.10 4.80 4.79 4.76 4.71 4.62 3.18 

Average of yearly averages: 1.67 

Inputs generated by pe5.pl - Novemeber 2006 

Data used for this run: 

Output File: Pepper_FL 

Metfile: w12844.dvf 

PRZM scenario: FLpeppersSTD.txt 

EXAMS environment file: pond298.exv 

Chemical Name: Imazosulfuron 

Description Variable Name Value Units Comments 

Molecular weight mwt 412.81 g/mol 

Henry's Law Const. henry 3.33E-11 atm-m^3/mol 

Vapor Pressure vapr 2.63E-08 torr 

Solubility sol 429 mg/L 

Kd Kd mg/L 

Koc Koc 154 mg/L 

Photolysis half-life kdp 61.7 days Half-life 

Aerobic Aquatic Metabolism kbacw 192 days Halfife 

Anaerobic Aquatic Metabolism kbacs 64.2 days Halfife 

Aerobic Soil Metabolism asm 207.2 days Halfife 

Hydrolysis: pH 7 0 days Half-life 

Method: CAM 2 integer See PRZM manual 

Incorporation Depth: DEPI cm 

Application Rate: TAPP 0.34 kg/ha 

Application Efficiency: APPEFF 0.99 fraction 

Spray Drift DRFT 0.01 fraction of application rate applied to pond 

Application Date Date 8-Sep dd/mm or dd/mmm or dd-mm or dd-mmm 

Record 17: FILTRA 
 110

 IPSCND 3 

 UPTKF 

Record 18: PLDKRT FEXTRC 0.5 

Flag for Index Res. Run IR EPA Pond 

Flag for runoff calc. RUNOFF none none, monthly or total(average of entire run) 
 111

APPENDIX D: RICE MODEL

Rice Model (USEPA, 2007). 

 The formula of the Tier I Rice Model v1.0 is as follows: 

d

ai

w K

m C

00013.0 00105.0

'

+ =

and, if appropriate: 

d = 01.0 KK oc

where: 

 Cw = water concentration [μg/L] 

mai' = mass applied per unit area [kg/ha] 

Kd = water-sediment partitioning coefficient [L/kg] 

Koc = organic carbon partitioning coefficient [L/kg] 

Example calculation: 

EEC = (0.336 kg a.i./ha) / [0.00105 + (0.00013 x 1.19 L/kg)] 

= 278.9 μg/L (ppb)
 112

APPENDIX E: ECOTOX OUTPUT 

IMAZOSULFURON 

Papers that Were Accepted for ECOTOX 

Kuk, Y. I., Kwon, O. D., Jung, H. I., Burgos, N. R., & Guh, J. O. Cross-Resistance Pattern and Alternative 

Herbicides for Rotala indica Resistant to Imazosulfuron in Korea. Pestic.Biochem.Physiol. 74[3], 129-138. 

2002. WATER,AQUA,MIXTURE. 

Notes: EcoReference No.: 71288 

Chemical of Concern: BSFM,IZP,IMQ,BTC,CFZ,TBC,MLT,MCPB,IMS 

Mohammad, M., Kishimoto, T., Itoh, K., Suyama, K., & Yamamoto, H. Comparative Sensitivity of 

Pseudokirchnetiella subcapitata vs.Lemna sp. to Eight Sulfonylurea Herbicides. 

Bull.Environ.Contam.Toxicol. 75[5], 866-872. 2005. WATER,AQUA. 

Notes: EcoReference No.: 104861 

Chemical of Concern: BSFM,IMS,FZS,NSF 

Tanaka, Y. Properties of Acetolactate Synthase from Sulfonylurea-Resistant Scirpus juncoides Roxb. var. ohwianus 

T. Koyama. Pestic.Biochem.Physiol. 77[3], 147-153. 2003. SOIL,WATER,ENV. 

Notes: EcoReference No.: 104887 

Chemical of Concern: IMS 

Wang, G. X., Watanabe, H., Uchino, A., & Itoh, K. Response of a Sulfonylurea (SU)-Resistant Biotype of 

Limnophila sessiliflora to Selected SU and Alternative Herbicides. Pestic.Biochem.Physiol. 68[2], 59-66. 

2000. ENV,MIXTURE. 

Notes: EcoReference No.: 75769 

Chemical of Concern: TBC,BSFM,MCPA,MCPB,IMS 

IMAZOSULFURON 

Bibliography of excluded ECOTOX Papers 

Akiyama, Y., Yoshioka, N., and Tsuji, M. Determination of Ten Sulfonyl Urea Herbicides in Unpolished Rice by 

Solid-Phase Extraction Cleanup and Lc-Diode Array Detection. Shokuhin eiseigaku zasshi. 2002, apr; 

43(2):99-103. [Shokuhin eiseigaku zasshi. Journal of the food hygienic society of japan]: Shokuhin Eiseigaku 

Zasshi. 

Ayano, Eri, Kanazawa, Hideko, Ando, Masanori, and Nishimura, Tetsuji (2004). Determination and quantitation of 

sulfonylurea and urea herbicides in water samples using liquid chromatography with electrospray ionization 

mass spectrometric detection. Anal. Chim. Acta 507:211-218. 

Ayano, Eri, Okada, Yuji, Sakamoto, Chikako, Kanazawa, Hideko, Okano, Teruo, Ando, Masanori, and Nishimura, 

Tetsuji (2005). Analysis of herbicides in water using temperature-responsive chromatography and an aqueous 

mobile phase. J. Chromatogr., A 1069:281-285. 

Brown, H. M. and Cotterman, J. C (1994). Recent advances in sulfonylurea herbicides. Chem. Plant Prot. 10:47-81. 

Degelmann, Petra, Egger, Sebastian, Juerling, Heinrich, Mueller, Josef, Niessner, Reinhard, and Knopp, Dietmar 

(2006). Determination of Sulfonylurea Herbicides in Water and Food Samples Using Sol-Gel Glass-Based 

Immunoaffinity Extraction and Liquid Chromatography-Ultraviolet/Diode Array Detection or Liquid 

Chromatography-Tandem Mass Spectrometry. J. Agric. Food Chem. 54:2003-2011. 

Degelmann, Petra, Wenger, Jean, Niessner, Reinhard, and Knopp, Dietmar (2004). Development of a class-specific 

ELISA for sulfonylurea herbicides (Sulfuron Screen). Environ. Sci. Technol. 38:6795-6802. 

Fidente, P., Manca, M. C., Morrica, P., and Seccia, S (2003). Imazosulfuron: preliminary test of photolysis.293-297. 
 113

Inui, H., Shiota, N., Ido, Y., Inoue, T., Hirose, S., Kawahigashi, H., Ohkawa, Y., and Ohkawa, H. (2001). Herbicide 

Metabolism and Tolerance in the Transgenic Rice Plants Expressing Human Cyp2c9 and Cyp2c19. Pesticide 

Biochemistry and Physiology [Pestic. Biochem. Physiol.]. Vol. 71, no. 3, pp. 156-169. Nov 2001. 

Inui, Hideyuki, Shiota, Noriaki, Motoi, Yukiko, Ido, Yoshiko, Inoue, Tomomi, Kodama, Takuya, Ohkawa, 

Yasunobu, and Ohkawa, Hideo (2001). Metabolism of herbicides and other chemicals in human cytochrome 

P450 species and in transgenic potato plants co-expressing human CYP1A1, CYP2B6 and CYP2C19.

Nippon Noyaku Gakkaishi 26:28-40. 

Ishida, Y., Yoshikawa, H., Ohta, K., and Kumazaki, Y. (1996). Development of a New Sulfonylurea Herbicide 

Imazosulfuron. Journal of pesticide science 21:247-258. 

Ishida, Yasuo, Yoshikawa, Harutoshi, Ohta, Kazunari, and Kumazaki, Yasunari (1996). Development of a new 

herbicide, imazosulfuron. Nippon Noyaku Gakkaishi 21:247-258. 

Kawai, Kiyoshi, Kaku, Koichiro, Izawa, Norihiko, Shimizu, Tsutomu, Fukuda, Atsunori, and Tanaka, Yoshiyuki 

(2007). A novel mutant acetolactate synthase gene from rice cells, which confers resistance to ALSinhibiting herbicides. J. Pestic. Sci. (Tokyo, Jpn.) 32:89-98. 

Lee, Jae Koo, Ahn, Ki Chang, Park, Oee Sook, Ko, Yong Kwan, and Kim, Dae-Whang (2002). Development of an 

immunoassay for the residues of the herbicide bensulfuron-methyl. J. Agric. Food Chem. 50:1791-1803. 

Mikata, K., SchnÖ, Der, F., Braunwarth, C., Ohta, K., and Tashiro, S. Mobility and Degradation of the 

Herbicide Imazosulfuron in Lysimeters Under Field Conditions. J agric food chem. 2003, jan 1; 51(1):177-

82. [Journal of agricultural and food chemistry]: J Agric Food Chem. 

Mikata, K., Yamamoto, A., and Tashiro, S. (1996). Degradation of Imazosulfuron in Flooded Soils. Journal of 

Pesticide Science, 21 (2) pp. 171-177, 1996. 

Mikata, Kazuki, Ohta, Kazunari, and Tashiro, Shigeki (2001). Degradation and leaching of herbicide imazosulfuron 

in upland soils. Nippon Noyaku Gakkaishi 26:376-382. 

Mikata, Kazuki, Ohta, Kazunari, and Tashiro, Shigeki (2000). Adsorption and desorption of herbicide imazosulfuron 

in soils. Nippon Noyaku Gakkaishi 25:212-216. 

Morrica, P., Barbato, F., Della Iacovo, R., Seccia, S., and Ungaro, F. Kinetics and Mechanism of Imazosulfuron 

Hydrolysis. J agric food chem. 2001, aug; 49(8):3816-20. [Journal of agricultural and food chemistry]: J 

Agric Food Chem. 

Morrica, P., Barbato, F., Giordano, A., Seccia, S., and Ungaro, F. Adsorption and Desorption of Imazosulfuron by 

Soil. J agric food chem. 2000, dec; 48(12):6132-7. [Journal of agricultural and food chemistry]: J Agric 

Food Chem. 

Morrica, P., Fidente, P., Seccia, S., and Ventriglia, M. Degradation of Imazosulfuron in Different Soils-Hplc 

Determination. Biomed chromatogr. 2002, dec; 16(8):489-94. [Biomedical chromatography : bmc]: Biomed 

Chromatogr. 

Morrica, P., Giordano, A., Seccia, S., Ungaro, F., and Ventriglia, M. Degradation of Imazosulfuron in Soil. Pest 

manag sci. 2001, apr; 57(4):360-5. [Pest management science]: Pest Manag Sci. 

Morrica, Patrizia, Fidente, Paola, and Seccia, Serenella (2004). Identification of photoproducts from imazosulfuron 

by HPLC. Biomed. Chromatogr. 18:450-456. 

Saari, L. L., Cotterman, J. C., and Thill, D. C. (1994). Resistance to Acetolactate Synthase Inhibiting Herbicides.

Powles, s. B. And j. A. M. Holtum (ed.). Herbicide resistance in plants: biology and biochemistry. Xi+353p. 
 114

Crc press, inc.: Boca raton, florida, usa London, england, uk. Isbn 0-87371-713-9.; 0:83-139. 

Schmuckler, Margaret E., Barefoot, Aldos C., Kleier, Daniel A., and Cobranchi, Daryl P (2000). Vapor pressures of 

sulfonylurea herbicides. Pest Manage. Sci. 56:521-532. 

Shim, Y. S., Gil, H. W., Yang, J. O., Lee, E. Y., Kim, S. H., and Hong, S. Y. A Case of Green Urine After Ingestion 

of Herbicides. Korean j intern med. 2008, mar; 23(1):42-4. [The korean journal of internal medicine]: 

Korean J Intern Med. 

Takatsuki, S., Nemoto, S., Matsuda, R., Sasaki, K., and Toyoda, M. (1999). Determination of 21 Pesticides in 

Agricultural Products by Hplc-Photodiode Array Detection. Shokuhin eiseigaku zasshi 40:314-319. 

Ventriglia, M., Restani, P., Morrica, P., David, P., De Angelis, L., and Galli, C. L. Liquid Chromatographic 

Determination of Imazosulfuron in Drinking Water and in Soil Using Ultraviolet Detection. J chromatogr a. 

1999, oct 1; 857(1-2):327-30. [Journal of chromatography. A]: J Chromatogr A. 

Vu, S. o. n. Hong, Ishihara Satoru, and Watanabe Hirozumi (2006). Exposure Risk Assessment and Evaluation of 

the Best Management Practice for Controlling Pesticide Runoff From Paddy Fields. Part 1: Paddy Watershed 

Monitoring. Pest Management Science [Pest Manage. Sci.]. Vol. 62, no. 12, pp. 1193-1206. Dec 2006. 

Yoshii, K., Tonogai, Y., Tsumura, Y., Nakamura, Y., and Shibata, T. (1998). Studies on Simultaneous 

Determination of 15 Pesticides in Cereals by Sf and Hplc. Journal of the food hygienic society of japan

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in vitro screening assay to discover novel inhibitors of 4-coumarate:CoA ligase. Pest Manage. Sci. 62:1065-

1071. 

Imazosulfuron 

Papers that Were Not Acceptable for ECOTOX 

Goto, T., Ukawa, S., & Miyauchi, H. Fentrazamide - A New Herbicide Effective on Grasses and Annual Sedges in 

Rice in Japan. Pflanzenschutz-Nachr.Bayer 54[1], 13-34. 2001. SOIL,WATER,ENV. 

Notes: EcoReference No.: 105849 

Chemical of Concern: IMS,BSFM 

Hirose, S., Kawahigashi, H., Inoue, T., Inui, H., Ohkawa, H., & Ohkawa, Y. Enhanced Expression of CYP2C9 and 

Tolerance to Sulfonylurea Herbicides in Transgenic Rice Plants. Plant Biotechnol. 22[2], 89-96. 2005. 

SOIL,WATER,ENV. 

Notes: EcoReference No.: 105846 

Chemical of Concern: IMS,CSF,TSF 

Ishida, Y., Ohta, K., Itoh, S., Nakahama, T., Miki, H., & Yoshikawa, H. Synthesis of Novel Herbicidal Sulfonylurea 

Compounds with Imidazo(1,2-a)Pyridine Moiety. J.Pestic.Sci. 18[2], 175-182. 1993. SOIL,ENV. 

Notes: EcoReference No.: 105002 

Chemical of Concern: IMS 

Kuk, Y. I., Jung, H. I., Kwon, O. D., Lee, D. J., Burgos, N. R., & Guh, J. O. Sulfonylurea Herbicide-Resistant 

Monochoria vaginalis in Korean Rice Culture. Pest Manag.Sci. 59[9], 949-961. 2003. 

SOIL,ENV,MIXTURE. 

Notes: EcoReference No.: 74168 

Chemical of Concern: MLT,IZP,IMQ,BSFM,BTC,DTP,TBC,24DXY,BT,IMS 

Sondhia, S. Determination of Imazosulfuron Persistence in Rice Crop and Soil. Environ.Monit.Assess. 137[1-3], 

205-211. 2008. SOIL,ENV. 
 115

Notes: EcoReference No.: 105008 

Chemical of Concern: IMS 

Imazosulfuron 

Target Papers 

Itoh, K., Wang, G. X., & Ohba, S. Sulfonylurea Resistance in Lindernia micrantha, an Annual Paddy Weed in Japan. 

Weed Res. 39[5], 413-423. 1999. G.X. Wang, Laboratory of Weed Science, Graduate School of 

Agriculture, Kyoto University, Kyoto 606-8502, Japan. Email: gxwang@kais.kyoto-u.ac.jp. 

Notes: EcoReference No.: 64651 

Chemical of Concern: MCPB,IMS 

Kuk, Y. I., Jung, H. I., Kwon, O. D., Lee, D. J., Burgos, N. R., & Guh, J. O. Rapid Diagnosis of Resistance to 

Sulfonylurea Herbicides in Monochoria (Monochoria vaginalis). Weed Sci. 51[3], 305-311. 2003. 

Notes: Chemical of Concern: IMS 
 116

APPENDIX F: Example TERR-PLANT Output – Turfgrass Scenario 

TerrPlant v. 1.2.2 

Green values signify user inputs (Tables 1, 2 and 4). 

Input and output guidance is in popups indicated by red arrows. 

 

Table 1. Chemical Identity. 

Chemical Name Imazosulfuron 

PC code 118602 

Use Turfgrass 

Application Method Ground 

Application Form Liquid 

Solubility in Water 

(ppm) 429 

 

Table 2. Input parameters used to derive EECs. 

Input Parameter Symbol Value Units 

Application Rate A 0.67 

Incorporation I 1 none 

Runoff Fraction R 0.05 none 

Drift Fraction D 0.01 none 

 

Table 3. EECs for Imazosulfuron . Units in . 

Description Equation EEC 

Runoff to dry areas (A/I)*R 0.0335 

Runoff to semi-aquatic areas (A/I)*R*10 0.335 

Spray drift A*D 0.0067 

Total for dry areas ((A/I)*R)+(A*D) 0.0402 

Total for semi-aquatic areas ((A/I)*R*10)+(A*D) 0.3417 

 

Table 4. Plant survival and growth data used for RQ derivation. Units are in . 

 Seedling Emergence Vegetative Vigor 

Plant type EC25 NOAEC EC25 NOAEC 

Monocot 0.034 0.025 0.25 0.025 

Dicot 0.041 0.022 0.08 0.074 

 

Table 5. RQ values for plants in dry and semi-aquatic areas exposed to Imazosulfuron through 

runoff and/or spray drift.* 

Plant Type Listed Status Dry Semi-Aquatic Spray Drift 

Monocot non-listed 1.18 10.05 0.20 

Monocot listed 1.61 13.67 0.27 

Dicot non-listed 0.98 8.33 0.16 

Dicot listed 1.83 15.53 0.30 

*If RQ > 1.0, the LOC is exceeded, resulting in potential for risk to that plant group. 
 117

APPENDIX G: EXAMPLE TREX OUTPUT –Turfgrass Scenario 

 Acute and Chronic RQs are based on the Upper Bound Upper Bound Kenaga Residues For RQ Calculation 

 Kenaga Residues. 

Chemical Name: 

Imazosulfuron The maximum single day residue estimation is used for 

 Use Turfgrass both the acute and reproduction RQs. 

 Formulation 0 

Application Rate 0.67 lbs a.i./acre RQs reported as "0.00" in the RQ tables below should be noted as 

Half-life 35 days <0.01 in your assessment. This is due to rounding and significant 

Application Interval 21 days figure issues in Excel. 

Maximum # Apps./Year 2 

Length of Simulation 1 year 

 

 

 Endpoints 

 

Bobwhite 

quail LD50 (mg/kg-bw) 2250.00 

Bobwhite 

quail LC50 (mg/kg-diet) 5042.00 

Mallard duck NOAEL(mg/kg-bw) 0.00 

Avian 

Bobwhite 

quail NOAEC (mg/kg-diet) 100.00 

 

LD50 (mg/kg-bw) 5000.00 

LC50 (mg/kg-diet) 0.00 

NOAEL (mg/kg-bw) 50.00 

Mammals 

NOAEC (mg/kg-diet) 1000.00 

 

Dietary-based Kenaga 

EECs (ppm) Values 

Short Grass 266.89 

Tall Grass 122.32 

Broadleaf 

plants/sm Insects 150.12 

Fruits/pods/seeds/lg 

insects 16.68 

Avian Results 

 

 Avian Body Ingestion (Fdry) Ingestion (Fwet) % body wgt FI 

 Class Weight (g) (g bw/day) (g/day) consumed (kg-diet/day)

 Small 20 5 23 114 2.28E-02 

 Mid 100 13 65 65 6.49E-02 

 Large 1000 58 291 29 2.91E-01 

 20 5 5 25 5.06E-03 
 118

 Granivores 100 13 14 14 1.44E-02 

 1000 58 65 6 6.46E-02 

 Avian Body Adjusted LD50 

 Weight (g) (mg/kg-bw) 

 20 1620.97 

 100 2063.57 

 1000 2914.87 

 

Avian Classes and Body Weights (grams) 

small mid large Granivores(grams) 

Dose-based EECs 

(mg/kg-bw) 

20 100 1000 20 100 1000 

Short Grass 303.96 173.33 77.60 

Tall Grass 139.31 79.44 35.57 

Broadleaf 

plants/sm Insects 170.98 97.50 43.65 

Fruits/pods/seeds/lg 

insects 19.00 10.83 4.85 4.22 2.41 1.08 

Avian Acute RQs 

Size Class (grams) 

 

Dose-based RQs 

(Dose-based 

EEC/adjusted 

LD50) 

20 100 

1000 

Short Grass 0.19 0.08 0.03 

Tall Grass 0.09 0.04 0.01 

Broadleaf 

plants/sm insects 0.11 0.05 0.01 

Fruits/pods/seeds/lg 

insects 0.01 0.01 0.00 

Seeds (granivore) 0.00 0.00 0.00 

 

 RQs 

 

Dietary-based RQs 

(Dietary-based 

EEC/LC50 or 

NOAEC) 

Acute Chronic 

Short Grass 0.05 2.67 

Tall Grass 0.02 1.22 

Broadleaf 

plants/sm Insects 0.03 1.50 

Fruits/pods/seeds/lg 

insects 0.00 0.17 

Imazosulfuron Turfgrass Upper bound Kenaga Residues 

Mammalian 

Results 

 

 Mammalian Body Ingestion (Fdry) Ingestion (Fwet) % body wgt FI 

 Class Weight (g bwt/day) (g/day) consumed (kg-diet/day) 

 15 3 14 95 1.43E-02 

 Herbivores/ 35 5 23 66 2.31E-02 

 insectivores 1000 31 153 15 1.53E-01 

 15 3 3 21 3.18E-03 

 Grainvores 35 5 5 15 5.13E-03 
 119

 1000 31 34 3 3.40E-02 

 

 Mammalian Body Adjusted Adjusted 

 Class Weight LD50 NOAEL 

 15 10989.15 109.89 

 Herbivores/ 35 8891.40 88.91 

 insectivores 1000 3845.80 38.46 

 15 10989.15 109.89 

 Grainvores 35 8891.40 88.91 

 1000 3845.80 38.46 

 

Mammalian Classes and Body weight 

Herbivores/ insectivores (grams) Granivores(grams) 

Dose-Based EECs 

(mg/kg-bw) 15 35 1000 15 35 1000 

Short Grass 254.46 175.86 40.77 

Tall Grass 116.63 80.60 18.69 

Broadleaf 

plants/sm Insects 143.13 98.92 22.94 

Fruits/pods/seeds/lg 

insects 15.90 10.99 2.55 3.53 2.44 0.57 

 

 

Small mammal Medium mammal Large mammal 

15 grams 35 grams 1000 grams 

Dose-based RQs 

(Dose-based 

EEC/LD50 or 

NOAEL) Acute Chronic Acute Chronic Acute Chronic 

Short Grass 0.02 2.32 0.02 1.98 0.01 1.06 

Tall Grass 0.01 1.06 0.01 0.91 0.00 0.49 

Broadleaf 

plants/sm insects 0.01 1.30 0.01 1.11 0.01 0.60 

Fruits/pods/lg 

insects 0.00 0.14 0.00 0.12 0.00 0.07 

Seeds (granivore) 0.00 0.03 0.00 0.03 0.00 0.01 

 

Mammal RQs 

 

Dietary-based RQs 

(Dietary-based 

EEC/LC50 or 

NOAEC) 

Acute Chronic 

Short Grass #DIV/0! 0.27 

Tall Grass #DIV/0! 0.12 

Broadleaf 

plants/sm insects #DIV/0! 0.15 

Fruits/pods/seeds/lg 

insects #DIV/0! 0.02