1

 UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON, D.C. 20460

OFFICE OF

PREVENTION, PESTICIDES

AND TOXIC SUBSTANCES

Environmental Fate and Ecological Risk Assessment

for the Reregistration of Sulfometuron-methyl: Vegetative 

Management and Other Non-crop Uses

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

O

O

CH3

S

O

O

N

H

N

O

H

N

N

CH3

CH3

SULFOMETURON METHYL

PC Code: 122001; CAS Number: 74222-97-2

Note: Appendix A has been slightly revised from 

the 11/28/07 review (DP Barcode D346171) per 

registrant comment.

Prepared by:

M. Barrett, Chemist, 

Environmental Fate Reviewer, ERB V

K. Sappington, Biologist, 

Ecological Effects Reviewer, ERB V

Approved by:

Mah Shamim, PhD, Chief ERB V

February 14, 2008

DP Barcode D334277

United States Environmental Protection Agency

Office of Pesticide Programs

Environmental Fate and Effects Division

Environmental Risk Branch V

1200 Pennsylvania Ave.

Mail Code 7507P 

Washington, D.C. 20460
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TABLE OF CONTENTS

1. EXECUTIVE SUMMARY____________________________________________________ 8

1.1. Nature of Chemical Stressor __________________________________________________ 8

1.2. Conclusions- Exposure Characterization ________________________________________ 8

1.3. Conclusions- Effects Characterization __________________________________________ 9

1.4. Potential Risks to Non-target Animals and Plants________________________________ 10

1.5. Conclusions - Endangered Species ____________________________________________ 11

1.6. Identification of Uncertainties and Their Impact on the Risk Assessment ____________ 13

1.6.1. Environmental Fate and Exposure ____________________________________________________13

1.6.2. Ecological Effects_________________________________________________________________14

2. PROBLEM FORMULATION________________________________________________ 15

2.1. Nature of the Regulatory Action ______________________________________________ 15

2.2. Stressor Source and Distribution______________________________________________ 15

2.2.1. Nature of the Chemical Stressor______________________________________________________15

2.2.2. Overview of Pesticide Usage ________________________________________________________17

2.3. Receptors _________________________________________________________________ 17

2.3.1. Aquatic and Terrestrial Effects_______________________________________________________17

2.3.2. Ecosystems at Risk ________________________________________________________________19

2.4. Assessment Endpoints_______________________________________________________ 19

2.5. Conceptual Model __________________________________________________________ 20

2.5.1. Risk Hypotheses __________________________________________________________________20

2.5.2. Conceptual Diagram_______________________________________________________________20

2.6. Analysis Plan ______________________________________________________________ 24

2.6.1. Conclusions from Previous Risk Assessments ___________________________________________24

2.6.2. Preliminary Identification of Data Gaps and Analysis Plan _________________________________25

2.6.3. Measures of Effect and Exposure_____________________________________________________25

3. ANALYSIS_______________________________________________________________ 27

3.1. USE CHARACTERIZATION________________________________________________ 27

3.2. EXPOSURE CHARACTERIZATION_________________________________________ 33

3.2.1. Environmental Fate and Transport Characterization ______________________________________33

3.2.2. Measures of Aquatic Exposure_______________________________________________________44

3.2.2.1. Aquatic Exposure Monitoring and Field Data ______________________________________44

3.2.2.2. Aquatic Exposure Modeling ____________________________________________________44

3.2.3. Measures of Terrestrial Exposure ____________________________________________________53

3.2.3.1. Terrestrial Exposure Modeling __________________________________________________53

3.2.3.2. Residue Studies______________________________________________________________58

3.2.4. Uncertainties and Limitations for this Exposure Assessment________________________________58

3.2.4.1. Limitations In Knowledge Of Actual Use Patterns___________________________________58

3.2.4.2. Variability In Sulfometuron Environmental Persistence_______________________________59

3.2.4.3. Exposure To Sulfometuron Methyl Degradates _____________________________________59

3.3. ECOLOGICAL EFFECTS CHARACTERIZATION ____________________________ 59
3

3.3.1. Aquatic Effects Characterization _____________________________________________________61

3.3.1.1. Freshwater Fish, Acute ________________________________________________________61

3.3.1.2. Freshwater Invertebrates, Acute _________________________________________________62

3.3.1.3. Estuarine and marine Fish, Acute ________________________________________________62

3.3.1.4. Estuarine and marine Invertebrates, Acute _________________________________________63

3.3.1.5. Freshwater Fish, Chronic ______________________________________________________64

3.3.1.6. Freshwater Invertebrate, Chronic ________________________________________________64

3.3.1.7. Aquatic Animal Sublethal Effects: Formulated Product and Degradate Toxicity ___________65

3.3.1.8. Field Studies ________________________________________________________________66

3.3.1.9. Aquatic Plants _______________________________________________________________67

3.3.2. Terrestrial Effects Characterization ___________________________________________________68

3.3.2.1. Acute Effects on Birds ________________________________________________________68

3.3.2.2. Acute Effects on Mammals_____________________________________________________69

3.3.2.3. Acute Effects on Terrestrial-phase Amphibians, Reptiles and Beneficial Insects ___________70

3.3.2.4. Chronic Effects on Birds_______________________________________________________70

3.3.2.5. Mammals, Reproductive Effects ________________________________________________71

3.3.2.6. Terrestrial Animal Sublethal Effects, Formulated Product and Degradation Products________71

3.3.2.7. Field Studies ________________________________________________________________72

3.3.2.8. Terrestrial Plants _____________________________________________________________72

4. RISK CHARACTERIZATION________________________________________________ 75

4.1. Risk Estimation - Integration of Exposure and Effects Data _______________________ 75

4.1.1. Non-target Aquatic Animals and Plants ________________________________________________77

4.1.1.1. Fish and Aquatic Invertebrates __________________________________________________77

4.1.1.2. Aquatic Plants _______________________________________________________________78

4.1.2. Non-target Terrestrial Animals_______________________________________________________79

4.1.2.1. Birds, Acute Risks ___________________________________________________________79

4.1.2.2. Birds, Chronic Risks __________________________________________________________80

4.1.2.3. Mammals, Acute Risks ________________________________________________________80

4.1.2.4. Mammals, Chronic Risks ______________________________________________________81

4.1.2.5. Non-Target Terrestrial-phase Amphibians, Reptiles and Terrestrial Invertebrates___________82

4.1.3. Non-target Terrestrial Plants ________________________________________________________83

4.1.3.1. Non-Endangered and Endangered Plant Risks ______________________________________83

4.1.4. Use of Contaminated Irrigation Waters ________________________________________________84

4.2. RISK DESCRIPTION ______________________________________________________ 85

4.2.1. Risk to Aquatic Animals and Plants ___________________________________________________85

4.2.1.1. Fish and Aquatic Invertebrates __________________________________________________85

4.2.1.2. Non-target Aquatic-phase Amphibians____________________________________________87

4.2.1.3. Aquatic Plants _______________________________________________________________88

4.2.1.4. Aquatic Toxicity of Sulfometuron Methyl Degradates________________________________89

4.2.2. Risk to Terrestrial Animals__________________________________________________________92

4.2.2.1. Birds ______________________________________________________________________92

4.2.2.2. Mammals __________________________________________________________________94

4.2.2.3. Non-target Terrestrial-phase Amphibians, Reptiles, and Beneficial Insects________________94

4.2.3. Risk to Terrestrial Plants ___________________________________________________________94

4.2.3.1. Tier 1 Modeling of Runoff and Spray Drift ________________________________________94

4.2.3.2. Field and Greenhouse Studies___________________________________________________95

4.2.3.3. Contaminated Irrigation Water __________________________________________________96

4.2.4. Refined Spray Drift Analysis ________________________________________________________97

4.2.5. Review of Incident Data____________________________________________________________99

4.2.6. Overall Ecological Risk Conclusions _________________________________________________100

4.2.7. Endocrine Effects ________________________________________________________________101

4.2.8. Federally Threatened and Endangered (Listed) Species___________________________________101
4

4.2.8.1. Action Area________________________________________________________________101

4.2.8.2. Taxonomic Groups Potentially at Risk ___________________________________________102

4.3. Description of Assumptions, Limitations, Uncertainties, and Data Gaps ____________ 107

4.3.1. Assumptions and Limitations Related to Effects on all Species_____________________________107

4.3.2. Assumptions and Limitations Related to Effects on Aquatic Species ________________________109

4.3.3. Assumptions and Limitations Related to Effects on Terrestrial Species ______________________109

5. Literature Cited _________________________________________________________ 110

6. APPENDICES __________________________________________________________ 113

APPENDIX A: Structures and Chemical Names of Sulfometuron methyl Metabolites _______ 113

APPENDIX B: Environmental Fate Data Requirements______________________________ 115

APPENDIX C: Ecological Aquatic Exposure Modeling______________________________ 117

APPENDIX D: Terrplant Spreadsheet ___________________________________________ 125

APPENDIX E: Adverse Ecological Incidents Associated with Sulfometuron Methyl Use ____ 127

APPENDIX F: T-REX Output __________________________________________________ 129

APPENDIX G: Modeling of Terrestrial plant Exposure from Contaminated irrigation Water 131

APPENDIX H: Ecological Effects Data Summaries _________________________________ 133

APPENDIX I; Ecological Effects Data Requirements________________________________ 146

APPENDIX J: Ecological Effects Studies Rejected by OPP ___________________________ 148
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LIST OF TABLES

Table 1. Listed Taxonomic Groups Potentially at Risk from Direct or Indirect Effects of 

Sulfometuron Methyl Application for Vegetative Management Throughout the U.S................... 12

Table 2. Nature and product chemistry of the chemical stressor - Sulfometuron methyl.............. 15

Table 3. Taxonomic Groups, Test Species and Acute Toxicity Classification for Assessing 

Ecological Risks of Sulfometuron Methyl to Non-target Organisms. ........................................... 18

Table 4. Measures of Ecological Effects and Exposure for Sulfometuron Methyl....................... 26

Table 5. Permitted application methods for sulfometuron methyl, DuPont Products.................... 28

Table 6. Permitted application methods for sulfometuron methyl, Vegetation Management LLC 

Products.......................................................................................................................................... 28

Table 7. States with high sulfometuron usage (based upon DuPont sales data, 2001-2004)........ 28

Table 8. Annual usage of sulfometuron methyl in the US by use site. ......................................... 29

Table 9. Sulfometuron application rate ranges by product label and use site............................... 30

Table 10. Key results of sulfometuron methyl environmental fates studies. ................................. 35

Table 11. Models Used to Estimate Exposure Concentrations for Aquatic Ecosystem................ 45

Table 12. Aquatic exposure with PRZM – EXAMS: Modeling scenarios and representative usage 

pattern summary............................................................................................................................. 47

Table 13. PRZM/EXAMS input parameters for modeling (Aquatic ecological EECs). .............. 47

Table 14. Estimated environmental concentrations (μg/L) for aquatic exposure to parent 

sulfometuron methyl: scenario-specific results from PRZM-EXAMS modeling.......................... 50

Table 15. Sulfometuron methyl surface water EECs used in aquatic risk assessment. ................ 52

Table 16. Estimated concentrations of sulfometuron methyl in ground water (SCI-GROW inputs 

and results). .................................................................................................................................... 52

Table 17. Unadjusted Dietary Terrestrial EECs for Birds and Mammals Following Sulfometuron 

Methyl Spray Application For Non-Crop Vegetative Management. ............................................. 54

Table 18. EECs for Terrestrial Plants Located Adjacent to Sulfometuron Methyl (aerial and 

ground spray application) Treated Sites......................................................................................... 55

Table 19. Selected AgDRIFT inputs for high-end exposure from aerial applications of 

sulfometuron methyl using best management practices................................................................. 56

Table 20. Estimated percentage of sulfometuron methyl spray drift from ground or aerial 

applications at various distances from a treated field..................................................................... 57

Table 21. Estimated amount of sulfometuron methyl spray drift from ground or aerial 

applications at various distances from a field treated with the maximum labeled rate of 0.375 lb 

ai/A. ................................................................................................................................................ 58

Table 22. The Most Sensitive Endpoints Used In The Sulfometuron Methyl Screening-Level 

Risk Estimation. ............................................................................................................................. 61

Table 23. Freshwater Fish Acute Toxicity of Sulfometuron Methyl. ........................................... 62

Table 24. Freshwater Invertebrate Acute Toxicity of Sulfometuron Methyl................................ 62

Table 25. Estuarine/Marine Fish Acute Toxicity of Sulfometuron Methyl. ................................. 63

Table 26. Freshwater Invertebrate Acute Toxicity of Sulfometuron Methyl................................ 64

Table 27. Freshwater Aquatic Invertebrate Chronic Toxicity for Sulfometuron Methyl. ............ 65

Table 28. Non-target Aquatic Plant Toxicity for Sulfometuron Methyl....................................... 68

Table 29. Avian Acute Oral Toxicity for Sulfometuron Methyl................................................... 69

Table 30. Avian Subacute Dietary Studies for Sulfometuron Methyl. ......................................... 69
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Table 31. Mammalian Acute Toxicity for Sulfometuron Methyl. ................................................ 70

Table 32. Non-Target Insects - Acute Contact Toxicity for Sulfometuron Methyl. ..................... 70

Table 33. Mammalian Developmental Toxicity of Sulfometuron Methyl ................................... 71

Table 34. Mammalian Acute Toxicity to Sulfometuron Methyl in Formulated Product: DPXT5486-87 ........................................................................................................................................ 72

Table 35. Summary of Most Sensitive Tier II Terrestrial Non-target Plant Seedling Emergence 

and Vegetative Vigor Toxicity Data for Sulfometuron Methyl. .................................................... 74

Table 36. Risk Presumptions for Aquatic Animals....................................................................... 76

Table 37. Risk Presumptions for Terrestrial Animals................................................................... 76

Table 38. Risk Presumptions for Plants. ....................................................................................... 76

Table 39. Endpoints Used for Estimating Risks of Sulfometuron Methyl to Aquatic Animals and 

Plants. ............................................................................................................................................. 77

Table 40. Summary of Acute Aquatic Plant Risk Quotients for Rights of Way Uses.................. 78

Table 41. Endpoints Used for Estimating Risks of Sulfometuron Methyl to Terrestrial Animals.

........................................................................................................................................................ 79

Table 42. Upper Bound Kenaga, Acute Avian Dose-Based Risk Quotients (Bounding Analysis 

Only)............................................................................................................................................... 80

Table 43. Upper Bound Kenaga, Subacute Dietary-Based Risk Quotients (Bounding Analysis 

Only)............................................................................................................................................... 80

Table 44. Upper Bound Kenaga, Acute Mammalian Dose-Based Risk Quotients (Bounding 

Analysis Only)................................................................................................................................ 81

Table 45. Upper Bound Kenaga, Chronic Mammalian Dose-Based Risk Quotients.................... 81

Table 46. Upper Bound Kenaga, Chronic Mammalian Dietary-Based Risk Quotients................ 82

Table 47. Summary of Selected Endpoints from Terrestrial Plant Toxicity Studies of 

Sulfometuron Methyl ..................................................................................................................... 83

Table 48. RQ Values For Plants In Dry And Semi-Aquatic Areas Exposed To Sulfometuron 

Methyl Through Runoff And/Or Spray Drift................................................................................. 83

Table 49. Risk Quotients for Non-target and Endangered Plants, Resulting From Exposure to 

Sulfometuron Methyl in Irrigation Water ...................................................................................... 84

Table 50. Toxicity of sulfometuron methyl to the African clawed frog from a study by Fort et al. 

(1999). ............................................................................................................................................ 88

Table 51. ECOSAR-predicted toxicity values for major degradates of sulfometuron methyl...... 90

Table 52. Risks to Terrestrial Plants from Spray Drift According to Distance Downwind, 

Application Method, and Drift Exposure Conditions .................................................................... 97

Table 53. Listed Taxonomic Groups Potentially at Risk from Direct or Indirect Effects of 

Sulfometuron Methyl Application for Vegetative Management Throughout the U.S................. 106
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LIST OF FIGURES

Figure 1. Conceptual model for sulfometuron methyl fate and effects in aquatic ecosystems...... 22

Figure 2. Conceptual model for sulfometuron methyl fate and effects in terrestrial ecosystems. . 23

Figure 3. Chronic Toxicity of Sulfonylurea Herbicides to Freshwater Fish.................................. 86

Figure 4. Chronic Avian Toxicity of Sulfonylurea Herbicides...................................................... 93
8

1. EXECUTIVE SUMMARY

1.1. Nature of Chemical Stressor

Sulfometuron methyl, (2-[[[[(4,6-Dimethyl-2-pyrimidinyl) amino] carbonyl] amino] sulfonyl] 

benzoic acid, methyl ester), is a broad-spectrum pre- and post-emergence herbicide that is 

currently registered for weed control in forestry and non-food crop situations, including 

vegetative management in right of ways and railroads. It is used to control a variety of broad-leaf 

weeds and grasses. Similar to other sulfonylurea herbicides, the mode of action of sulfometuron 

methyl involves inhibiting the activity of the enzyme acetolactate synthase (ALS), which in turn 

inhibits the synthesis of selected amino acids that are required for cell proliferation in plants. 

Sulfometuron methyl is formulated as a water dispersible granule (WDG) and applied using a 

variety of methods including helicopter, fixed-wing aircraft, ground spray (boom and backpack) 

and spot treatment. It is generally applied once per year for non-crop areas in years that 

vegetation management is needed. In some instances (weed escapes) a second application may be 

made, but all products limit the total quantity of sulfometuron methyl that may be applied (from 

any source) to 6 ounces of active ingredient per acre per year (0.375 lb ai/A). Therefore, 

application rates in general forestry, and for site preparation and/or release in conifer, hardwood 

and Christmas tree plantations, will vary significantly depending upon the specific purpose of the 

application and the desirable tree species. In forestry, uses can be similar to plantation sites, but 

may also include the maintenance of access routes and fire breaks. It is further noted that use 

rates can also vary with climate and soil type. 

1.2. Conclusions- Exposure Characterization

1.2.1. Environmental Fate

a. Persistence

Sulfometuron methyl is expected to be relatively persistent in soil and water (half-life ranging 

from about 2 weeks to 6 months, depending on environmental conditions). The persistence of 

sulfometuron is likely to be lowest under low pH conditions in soil and water.

Abiotic and microbially-mediated hydrolysis / degradation are both major routes of 

transformation of sulfometuron methyl in water, soil, and water-sediment systems. The 

degradation in soil and water appears to be enhanced in the presence of an active microbial 

population (aerobic and anaerobic degradation both proceed more slowly under sterile 

conditions).
9

b. Transport and Bioaccumulation

Sulfometuron has a low potential to volatilize from soil or water or to bioaccumulate. Off-site 

transport of sulfometuron methyl occurs via spray drift, and the wind erosion of soil particulates 

containing sulfometuron methyl. 

Sulfometuron methyl does not sorb strongly to soils and has the potential to leach to ground water 

and/or reach surface water during runoff events. Sulfometuron methyl is a weak acid (pKa of 

5.2). The mobility of sulfometuron methyl is expected to increase with increasing pH based upon 

available data submitted to EPA for related sulfonylurea herbicides and published studies; 

however direct, definitive evidence of this for sulfometuron methyl has not been produced.

1.3. Conclusions- Effects Characterization 

Available acute toxicity data for freshwater fish and invertebrates indicate that sulfometuron 

methyl is practically non-toxic on an acute exposure basis. All EC50s/ LC50s are >100 mg/L. For 

marine and estuarine fish and invertebrates, available acute toxicity data indicate that 

sulfometuron methyl is at most slightly toxic on an acute exposure basis (EC50/ LC50s range from 

>38 to >45 mg ai/L).

No acceptable studies were available for evaluating the effects of chronic exposure to 

sulfometuron methyl on freshwater, estuarine or marine fish. Chronic NOAEC for freshwater fish 

was therefore estimated to be >21 mg ai/L using an acute-chronic ratio derived from 

flazasulfuron, another sulfonylurea herbicide with the same mode of action. The aquatic 

invertebrate NOAEC is 97 mg ai/L (highest concentration tested) at which survival and 

reproduction were not significantly different from controls. Estimated chronic effects for 

estuarine/marine fish and invertebrates are uncertain because no chronic data on saltwater species 

were submitted by the registrant. However, comparison of freshwater and saltwater species acute 

toxicity values does not suggest considerable differences in sensitivity between freshwater and 

saltwater species.

Aquatic vascular plants are more sensitive than any of the aquatic nonvascular plants tested. The 

14-day EC50 and NOAEC for the freshwater vascular plant (duckweed) for frond count (the most 

sensitive endpoint tested) was 0.48 and 0.21 μg/L, respectively. The green-algae was the most 

sensitive non-vascular plant tested with EC50 and NOAEC values of 4.6 and 0.63 μg/L, 

respectively, based on cell density. 

Sulfometuron methyl is practically non-toxic to birds (LD50 >4,650 mg/kg-bw; LC50 >4,600

mg/kg-diet), mammals (LD50 >5000 mg/kg-bw), and bees (LD50 >100 ug/bee) on an acute 

toxicity basis. No sublethal effects were observed from the acute toxicity studies of birds and 

mammals. Data on reproductive effects of sulfometuron methyl to birds were not available. 

Acceptable data on mammalian reproductive effects were also not available. Data on the effects 

of gestational exposure to sulfometuron methyl were available from a rabbit developmental 

toxicity study which resulted in a NOAEL of 300 mg ai/kg-bw/d (highest dose tested). 
10

Seedling emergence and vegetative vigor studies in terrestrial plants were submitted by the 

registrant. Based on the most sensitive species and endpoints reported, sulfometuron methyl is 

slightly more toxic to terrestrial plants in the vegetative vigor study compared to seedling 

emergence. The seedling emergence EC25 for the most sensitive dicot (sugar beet) and monocot 

(sorghum) are 3.2 x 10 -5 and 1.9 x 10 -4 lb ai/A, respectively. The vegetative vigor EC25 for the 

most sensitive dicot (soybean) and monocot (corn) are 1.8 x 10 -5 and 3.7 x 10 -5 lb ai/A, 

respectively. The guideline seedling emergence and vegetative vigor studies reported non-lethal 

effects of sulfometuron methyl exposure on plants such as chlorosis, growth retardation, necrosis, 

and unusual pigmentation. 

1.4. Potential Risks to Non- target Animals and Plants

Potential risks to aquatic and terrestrial plants are indicated by this risk assessment, as LOCs are 

widely exceeded for terrestrial and aquatic plants at the maximum application rate. For terrestrial 

plants, RQs calculated at the edge of a treated field resulting from spray drift alone were as high 

as 22,000 for non-endangered plants and 400,000 for endangered plants. Terrestrial plant RQs 

dropped substantially 50 ft from the edge of a treated field but still exceeded Agency LOCs at 900 

ft (700 to 12,000 for non-endangered and endangered plants, respectively. The impact of spray 

drift practices recommended by the label did not reduce RQ values below LOCs for terrestrial 

plants (RQs were reduced only by a factor of three compared to ‘high end’ exposure 

assumptions). Potential risks to terrestrial plants from irrigation with sulfometuron methyl 

contaminated surface water were also evident (RQ = 3.9 and 71 for non-endangered and 

endangered species, respectively). 

The RQ values for aquatic plants exceeded LOCs and ranged from 49 to 148 for endangered 

nonvascular and vascular plants, respectively and from 6.7 to 65 for non-endangered nonvascular 

and vascular plants, respectively. Based on comparisons of adverse effect levels with longer-term 

average EECs predicted from the PRZM/EXAMS model (e.g., 90-d EEC of 16 μg/L), the ability 

of duckweed and other vascular aquatic plants to recover from predicted long-term exposure 

concentrations of sulfometuron methyl in adjacent, static aquatic systems appears unlikely under 

the exposure conditions modeled. 

Although use of ‘typical’ application rates would result in RQs of up to one order of magnitude 

lower than the maximum application rate, RQs would still exceed Agency LOCs for terrestrial 

and aquatic plants. The conclusion of potential risks to aquatic and terrestrial plants from 

sulfometuron methyl application in non-crop uses is consistent with findings from other 

sulfonylurea herbicide risk assessments and ecological incident reports associated with 

sulfometuron methyl usage. Wind-driven erosion and drift of sulfometuron was implicated in one 

of the largest ecological incidents reported following its application (as Oust) to fire-damaged 

rangeland (crop damage estimated at $72 million). Although LOCs were not exceeded for 

terrestrial or aquatic animals, animals that depend on plants for survival or reproduction 

(presumably all taxa at the screening level) are also potentially at risk from indirect effects 

resulting from direct effects of sulfometuron to aquatic or terrestrial plants. 
11

An analysis of the of the effects of various spray drift management practices (using the AgDRIFT 

model; see http://www.agdrift.com/AgDRIFt2/DownloadAgDrift2_0.htm ) demonstrates that a 

substantial reduction in off-site exposure is possible with the implementation of application 

methods known to reduce drift. Droplet size is important in controlling spray drift. Using larger 

droplet sizes, such as coarse or extremely coarse spraying, reduces the downwind drift to adjacent 

areas compared to when medium or fine spraying is used. Thus, this assessment suggests that by 

placing drift management practices on labels such as specifying coarse or extremely coarse sprays 

(based on the ASAE standard), risks to non-target plants would not extend as far from the treated 

area. Reducing boom height during application and applying when wind speeds are between 3 and 

10 mph are other examples of practices that control drift. Many of these practices are 

recommended, but not required by the product labels (see Section 3.2.3.1 and 4.2.3.1 for more 

details).

In addition, in regions where sulfometuron methyl has been used regularly, sulfometuron methyl

concentrations in surface irrigation water may result in damage to agricultural crops that are 

sensitive to sulfometuron methyl. 

1.5. Conclusions - Endangered Species

Direct effects LOCs were exceeded for endangered aquatic and terrestrial plants. In addition, 

there is potential for indirect effects to all animal taxa that depend on plants for survival, growth, 

or reproduction, which are presumably all animal taxa at the screening level. Therefore, listed 

species from all taxonomic groups are potentially at risk from sulfometuron methyl uses.

The results of this screening risk assessment indicate that direct effects to plant species could 

present an indirect risk at the higher levels of organization (i.e. population, trophic level, 

community, and ecosystem). The distance from the treated area that risks could extend is greater 

than 900 ft, which is the maximum distance that EFED’s Tier 2 spray drift model (AgDRIFT; 

information on this model is available at http://www.agdrift.com/AgDRIFt2/DownloadAgDrift2_0.htm )

can estimate. Due to the wide geographic distribution of potential application areas for non-crop 

uses of sulfometuron methyl, an action area for endangered species cannot be defined at this time 

for this assessment. A model is available for extending predictions of deposition from spray drift 

beyond 1000 feet (AgDISP with Gaussian extension; see Teske and Thistle, 2004; and Thistle et 

al., 2005). However, the trends observed in modeling of drift out to 900 feet downwind from 

treated areas imply that potential risks to the most sensitive species (non-target terrestrial plants) 

are likely to extend well beyond 1000 feet given the currently available information for our Tier II 

assessment. Field studies are not available to quantify actual risk to plant and animal communities 

in forest/edge and wetland/riparian habitats. However, in terrestrial and shallow-water aquatic 

communities, plants are the primary producers upon which the succeeding trophic levels depend. 

If the available plant material is impacted due to the effects of sulfometuron methyl, this may 

have negative effects not only on the herbivores, but also throughout the food chain. Also, 

depending on the severity of impacts to the plant communities [i.e., forests, wetlands, ecotones 

(edge and riparian habitats)], community assemblages and ecosystem stability may be altered (i.e. 

reduced bird populations in edge habitats; reduced riparian vegetation resulting in increased light 
12

penetration and temperature in aquatic habitats, loss of cover and food for fish). In addition, 

riparian vegetation, which is a significant component of the food supply for aquatic herbivores 

and detritivores provides habitat (i.e. leaf packs, materials for case-building for invertebrates) may 

also be affected.

The following table provides listed taxonomic groups that may be at risk from direct or indirect 

effects due to applications of sulfometuron methyl for vegetative management uses nationwide. 

Table 1. Listed Taxonomic Groups Potentially at Risk from Direct or Indirect 

Effects of Sulfometuron Methyl Application for Vegetative Management 

Throughout the U.S.

Listed Taxon Direct 

Effects

Basis for Direct Effects Concern Indirect 

Effects

Basis for Indirect Effects Concern

Terrestrial and 

Semi-Aquatic 

Plants –

monocots and 

dicots

Yes

The endangered and non-endangered 

species LOCs are exceeded for 

terrestrial plants. 

Yes

Potential concerns from shifts in plant 

community structure and function due to 

from selective impacts on plant species. 

Terrestrial 

Invertebrates No

Sulfometuron methyl is practically 

nontoxic to honeybees, suggesting no 

direct effect concerns for terrestrial 

invertebrates.

Yes

Potential concerns for terrestrial invertebrates 

that use plants for habitat, feeding, or cover 

requirements.

Birds and 

Reptiles1 No The LOC is not exceeded Yes

Potential concerns for birds and reptiles that 

use plants for habitat, feeding, or cover 

requirements.

Terrestrial-phase 

Amphibians(1) No The LOC is not exceeded Yes

Potential concerns for terrestrial-phase 

amphibians that use plants for habitat, 

feeding, or cover requirements. 

Mammals No The LOC is not exceeded Yes

Potential concerns for mammals that use 

plants for habitat, feeding, or cover 

requirements. 

Aquatic Vascular 

Plants and 

Nonvascular 

Plants

Yes

The endangered and non-endangered 

species LOCs are exceeded for aquatic 

vascular and nonvascular plants. 

Yes

Potential concerns from shifts in plant 

community structure and function due to 

from selective impacts on plant species.

Freshwater and 

Marine/Estuarine 

fish and Aquaticphase 

Amphibians(2)

No The LOC is not exceeded Yes

Potential concerns for fish and aquatic-phase 

amphibians that use plants for habitat, 

feeding, or cover requirements. 

Freshwater and 

Marine/Estuarine 

Crustaceans

No The LOC is not exceeded Yes

Potential concerns for crustaceans that use 

plants for habitat, feeding, or cover 

requirements. 

Mollusks No The LOC is not exceeded Yes

Potential concerns for mollusks that use 

plants for habitat, feeding, or cover 

requirements. 

(1) Birds are used as surrogate species for terrestrial-phase amphibians and reptiles; therefore, potential direct and indirect effects to endangered avian, 

terrestrial-phase amphibians and reptilian species are considered equivalent.

(2) Fish are used as a surrogate for aquatic phase amphibians; therefore, potential direct and indirect effects to endangered fish and aquatic-phase 

amphibian species are considered equivalent.
13

1.6. Identification of Uncertainties and Their Impact on the 

Risk Assessment

1.6.1. Environmental Fate and Exposure

Limitations In Knowledge Of Actual Use Patterns

• Specific regions of use are not known. The use pattern of sulfometuron methyl does not 

lend itself to easy characterization geographically: There are a variety of vegetation 

management uses on sites that are less clearly defined than agricultural crops and have 

disjoint or unusual treatment area configurations (e.g., as with rights of way and railroad 

uses, or industrial site grounds)

• Practical limits on usage rates long-term at particular sites may different from legally 

allowable use levels (e.g., usage is highly unlikely to occur every year at a particular site 

even though this is allowable under the label language)

Variability In Sulfometuron Environmental Persistence

• Sulfometuron methyl 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 sulfometuron methyl 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 

Insufficient Data And Methods Are Currently Available For Predicting Exposure To 

Sulfometuron Methyl Degradates.

• The total residues of sulfometuron methyl including environmentally significant 

degradates were not modeled with PRZM-EXAMS because of data and model limitations.

• Limitations in environmental fate data for the degradates constrains the modeling. The 

data on individual degradates, environmental persistence and mobility is insufficient to 

model each compound separately. Furthermore, total residue modeling with the currently 

available receiving water body assumes residues concentrate in that body (pond) since:

o available data require assumptions of total stability of sulfometuron total residues 

(because insufficient decline data are available from the laboratory studies);

o The existing surface water exposure scenario assumes these stable residues do not 

migrate from the pond and simply concentrate in the pond as applications of 

sulfometuron methyl are applied to the watershed.

• Data on sulfometuron effects on plants implies that low levels of sulfometuron methyl in 

soil and water may adversely affect the growth of sensitive terrestrial or aquatic species. 

For some sulfonylurea herbicides concentrations below 1ug/L in water or 1ug/kg in soil 

have been shown to affect the growth of sensitive plant species.
14

1.6.2. Ecological Effects

• Indirect Effects to Animals. In this screening-level risk assessment, aquatic and 

terrestrial plants were found to be at potential risk from the modeled sulfometuron methyl 

uses. Therefore, the potential exists for indirect effects on aquatic and terrestrial animals 

that depend on plants adversely affected by exposure to sulfometuron methyl. These 

indirect effects on aquatic and terrestrial animals could be expressed at the organism, 

population, community or ecosystem level of organization. No acceptable field studies 

were available to quantify the indirect effects of sulfometuron methyl to aquatic or 

terrestrial animals. Because risks associated with indirect effects on aquatic and terrestrial 

animals could not be assessed, ecological risks to animals could be underestimated to the 

extent that such indirect effects occur. 

• Ecological Risk of Sulfometuron Methyl Degradation Products. In this screening level 

ecological risk assessment, ecological risks associated with the major degradates of 

sulfometuron methyl (e.g., pyrimidine amine, pyrimidine-ol, saccharin, sulfonamide) 

could not be reliably assessed. Reasons for this limitation are two-fold. First, the vastly 

different chemistries of the degradates (and likely correspondent differences in 

toxicological profiles) essentially precluded a meaningful application of the total residue 

approach in the exposure assessment. Second, acceptable ecotoxicity data were not 

available for the degradates. Because the chemical structure and environmental behavior 

of the major degradates differ substantially from the parent molecule (i.e., degradation 

involves cleavage of the sulfonylurea bridge, essentially splitting the molecule in half), it 

could not be assumed with reasonable confidence that the degradates are equivalent in 

toxicity to the parent compound. 

• Toxicity Data Quality and Data Gaps. Acceptable or supplemental toxicity data were 

not available for assessing the chronic toxicity of sulfometuron methyl to freshwater fish 

or the reproductive toxicity to birds and mammals. A bounding analysis suggests that the 

risk assessment results are not likely to be sensitive to the lack of chronic toxicity data for 

fish, given the large difference between EECs and extrapolated toxicity limits. For 

mammals, the NOAEL of 300 mg ai/kg-bw/d was used from a developmental toxicity 

study to rabbits. While providing some information on the effect of sulfometuron methyl 

on mammalian development during gestational exposure, results from this study do not 

capture the potential effects of sulfometuron methyl on reproductive endpoints including 

courtship, mating, sex ratios and offspring survival, growth and development. Diet and 

dose-based RQs based on this NOAEL were 0.01 or lower, thus indicating that 

reproductive toxicity would have to occur at exposures that are approximately two orders 

of magnitude lower than developmental effects.

• Vascular Plant Reproduction. Terrestrial and aquatic plants appear most sensitive to 

sulfometuron methyl exposure. While toxicity data were available for endpoints related to 

systemic growth, seedling emergence and visual injury, these guideline studies are not 

designed to capture reproductive endpoints. There is some evidence to suggest plant 

reproduction may be affected by sulfonylurea herbicides at levels below effects on 
15

vegetative growth or visual injury (Fletcher et al., 1993). Therefore, to the extent that 

terrestrial and aquatic plant reproduction are more sensitive to sulfometuron methyl than 

growth endpoints, risks to aquatic and terrestrial plants may be underestimated in this risk 

assessment. 

2. PROBLEM FORMULATION

The purpose of problem formulation is to provide the foundation for the ecological risk 

assessment being conducted for sulfometuron methyl. It sets the objectives for the risk 

assessment, evaluates the nature of the problem, and provides a plan for analyzing the data and 

characterizing the risk (US EPA, 1998). 

2.1. Nature of the Regulatory Action

Under section 4 of the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA), EPA is 

reevaluating existing pesticides to ensure that they meet current scientific and regulatory 

standards. With this document, EPA has completed its baseline environmental fate and ecological 

effects risk assessment to support a Reregistration Eligibility Decision (RED) for the 

herbicide, sulfometuron methyl. Sulfometuron methyl was first registered for use in 1982 by E.I. 

du Pont de Nemours and Company (DuPont); all registered uses then and now have been for 

vegetation control in non-agricultural areas. Currently, both DuPont and Vegetation 

Management, LLC have registered end-use products containing sulfometuron methyl.

2.2. Stressor Source and Distribution 

2.2.1. Nature of the Chemical Stressor 

Sulfometuron methyl, a broad-spectrum pre- and post-emergence herbicide, is currently registered 

for weed control in forestry and non-food crop situations, including vegetative management in 

rights-of-ways and railroads. It is used to control a variety of broad-leaf weeds and grasses. 

Similar to other sulfonylurea herbicides, the mode of action of sulfometuron methyl involves 

inhibiting the activity of the enzyme acetolactate synthase (ALS), which in turn inhibits the 

synthesis of selected amino acids that are required for cell proliferation in plants. A brief 

summary of the product chemistry data on sulfometuron methyl is provided in Table 2.

Table 2. Nature and product chemistry of the chemical stressor - Sulfometuron 

methyl.

Common name Sulfometuron methyl

IUPAC Chemical Name 2-(4,6-Dimethylpyrimidin-2-ylcarbamoylsulfamoyl) benzoic 

acid, methyl ester

OR

2-[3-(4,6-dimethylpyrimidin-2-yl)ureidosulfonyl] benzoic acid, 
16

methyl ester

CAS Chemical Name 2-[[[[(4,6-Dimethyl-2-pyrimidinyl) amino] carbonyl]

amino] sulfonyl] benzoic acid, methyl ester

Structure

O

O

CH3

S

O

O

N

H

N

O

H

N

N

CH3

CH3

Pesticide type Herbicide

Chemical class Sulfonylurea herbicide

CAS number 74222-97-2

Empirical formula C15H16N4SO5

Molecular Mass (g/mol) 364.38

Vapor pressure at 20o C 5.4 x10-16 Torr

Henry’s Law Constant at 

20o C

(atm m3/mol)

1.1 x 10-18, calculated

from vapor pressure

Solubility in water (mg/L)at 

200C

pH 5 buffer...... 6.42 ppm

pH 7 buffer ...... 244 ppm

pH 8.6 buffer.. 12,500 ppm

Log Kow pH 5 = 1.03

pH 7 = -0.46

pH 9 = -1.87

pKa at 25°C 5.2 

Sulfometuron methyl may be persistent and mobile and may have a significant impact on ground 

water and surface water resources. Degradation half-lives in soil and water range from about 2 

weeks to 6 months due to aerobic metabolism, anaerobic aquatic, aerobic aquatic, and hydrolysis 

(except in acidic solution the half-life is only about 1 week). Parent persistence is similar under 

anaerobic and aerobic conditions. Complete degradation / mineralization is more rapid under 

aerobic conditions and is generally enhanced substantially when microbes are present. The 

primary route of degradation is by the following pathway involving cleavage of the sulfonylurea 

bridge:

(1) Hydrolytic cleavage generating a sulfonamide plus the aminopyrimidine (resulting in 

elimination of a carbon dioxide molecule)

(2) The sulfonamide (produced by hydrolysis of the sulfonylurea) is further cyclized with the 

carbomethoxy group in the ortho position, yielding a saccharin.

Degradation by this same pathway occurs at a slower rate under sterile conditions.
17

Sulfometuron methyl is considered “mobile” according to the classification system of the Food 

and Agricultural Organization, Agriculture and Consumer Protection Department’s “Assessing 

Soil Contamination: A Reference Manual” (see: 

http://www.fao.org/DOCREP/003/X2570E/X2570E06.htm ). Sulfometuron methyl mobility is

“high” to “very high” based upon the classification system of McCall et al. (1981; see also 

http://www.epa.gov/oppefed1/ecorisk_ders/terrestrial_field_dissipation.htm for a description).

Soil persistence is sufficient such that vulnerable aquifers may be expected to be impacted. 

Sulfometuron methyl 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.

2.2.2. Overview of Pesticide Usage

Sulfometuron methyl is formulated as a water dispersible granule (WDG) and applied using a 

variety of methods including helicopter, fixed-wing aircraft, ground spray (boom and backpack) 

and spot treatment. Sulfometuron methyl is registered for non-crop agricultural and vegetative 

management uses throughout the United States. The most significant uses include forestry and 

tree nurseries (weed control to promote seedling growth), vegetative management in utility rightof-ways, roadsides and railroads, industrial sites (e.g., to maintain bare ground in utility 

substations), under asphalt and concrete prior to paving and for broadleaf weed control in 

unimproved turf and on non-crop restoration sites. The highest use areas are believed to be in 

Pacific Coast states and the southeastern United States.

The application rates and frequency varies widely depending on use and the specific pest 

situation, but all uses are restricted to an annual maximum application of 6 oz ai./acre.

2.3. Receptors

2.3.1. Aquatic and Terrestrial Effects

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

receptors potentially at risk include (but are not limited to): fish, amphibians, invertebrates (e.g., 

aquatic insects, mollusks, crustaceans, and worms), vascular plants and algae. Terrestrial 

receptors potentially at risk include (but are not limited to): birds, mammals, reptiles, amphibians, 

terrestrial invertebrates (e.g., insects, worms, arachnids), and plants.

Consistent with the process described in the Overview Document (US EPA, 2004), this risk 

assessment uses a surrogate species approach in its evaluation of sulfometuron methyl. 

Toxicological data generated from surrogate test species, that 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. 
18

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

available open literature are used to evaluate potential direct effects of sulfometuron methyl 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 sulfometuron methyl on biotic 

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

functional characteristics of the affected communities. 

Table 3 provides a summary of the taxonomic groups and the surrogate species tested to help 

understand potential acute ecological effects of pesticides to these non-target taxonomic groups. 

In addition, the table provides a preliminary overview of the potential acute toxicity of 

sulfometuron methyl by providing the acute toxicity classifications. Based on a preliminary 

review of the ecological effect data, sulfometuron methyl is, for the most part, practically nontoxic to freshwater fish, freshwater invertebrates, birds, mammals, and honeybees under acute 

exposure conditions. Acute toxicity to estuarine/marine fish and invertebrates was not observed 

at the highest concentrations tested, which fell into the slightly toxic category. Under chronic 

exposure conditions, the sulfometuron methyl inhibited reproduction of both fathead minnow 

(Pimephales promelas) and water fleas (Daphnia magna). Acceptable chronic reproductive 

toxicity data were not available for birds or mammals. As expected, aquatic and terrestrial plants 

show the greatest sensitivity to the parent compound.

Major environmental degradates of sulfometuron methyl most commonly include: the 

sulfometuron sulfonamide, the sulfometuron pyrimidine amine, and saccharin; other degradates 

occur less commonly (see Table 10 and APPENDIX A: Structures and Chemical Names of 

Sulfometuron methyl Metabolites). Other than deesterification from sulfometuron methyl to the 

free acid, the degradates are formed from cleavage of the sulfonyl urea bridge between the phenyl 

and pyrimidine ring structures. The latter compounds are not expected to be substantially 

phytotoxic, however, information is requested from the registrant to confirm this. 

Table 3. Taxonomic Groups, Test Species and Acute Toxicity Classification for 

Assessing Ecological Risks of Sulfometuron Methyl to Non-target Organisms.

Taxonomic Group Example(s) of Surrogate Species Acute Toxicity Classification

Birds1 Mallard duck (Anas platyrhynchos)

Bobwhite quail (Colinus virginianus) Practically non-toxic

Mammals Laboratory rat (Rattus norvegicus) Practically non-toxic

Insects Honey bee (Apis mellifera L.) Practically non-toxic

Freshwater fish2 Bluegill sunfish (Lepomis macrochirus)

Rainbow trout (Oncorhynchus mykiss)

Practically non-toxic

Practically non-toxic

Freshwater invertebrates Water flea (Daphnia magna) Practically non-toxic

Estuarine/marine fish Sheepshead minnow (Cyprinodon 

variegatus) > Slightly toxic4

Estuarine/marine 

invertebrates

Mysid shrimp (Mysidopsis bahia)

Eastern oyster (Crassostrea virginica)

> Slightly toxic4

> Slightly toxic4
19

Taxonomic Group Example(s) of Surrogate Species Acute Toxicity Classification

Terrestrial plants3 Monocots – corn (Zea mays)

Dicots – soybean (Glycine max) Not classified

Aquatic plants and algae

Duckweed (Lemna gibba) 

Green algae (Selenastrum capricornutum)

Bluegreen algae (Anabaena flos-aquae)

Diatom (Navicula pelliculosa)

Not classified

1 In absence of data, birds are used as surrogates for terrestrial-phase amphibians and reptiles. 2 In absence of data, freshwater fish may be surrogates for aquatic-phase amphibians. 3 Data required for 4 species of monocots from 2 families (must include corn) and 6 species of dicots from 4 families (must 

include soybean). 

4 Toxicity endpoint was greater than the highest concentration tested, which fell in the slightly toxic category.

2.3.2. Ecosystems at Risk

The ecosystems at potential risk from sulfometuron methyl are extensive in scope due to the wide 

geographic distribution of potential sulfometuron methyl application sites. As a result, it is not 

possible to identify specific ecosystems at risk during the development of this baseline risk 

assessment. However, in general terms, terrestrial ecosystems potentially at risk could include the 

treatment areas directly and adjacent areas that may receive herbicide drift or runoff. This could 

include the treatment area itself as well as other cultivated fields, fencerows and hedgerows, 

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

Within these ecosystems, available toxicity data indicate terrestrial plants are highly sensitive to 

sulfometuron methyl and thus, they could be directly affected. Organisms dependent on sensitive 

terrestrial plants could be affected indirectly, which could result in subsequent effects at the

community and ecosystem levels. Birds and mammals appear to be much less sensitive to the 

direct exposure of sulfometuron methyl compared to plants, although they could be affected 

indirectly to the extent they depend on affected plants for food and habitat.

Aquatic ecosystems potentially at risk include water bodies adjacent to, or down stream from, the 

treatment area and might include impounded bodies such as ponds, lakes, reservoirs and wetland 

areas, or flowing waterways such as streams and rivers. For uses in coastal areas, aquatic habitat 

also includes marine ecosystems, including estuaries and salt marshes. Similar to the terrestrial 

ecosystems, available toxicity data indicate aquatic plants are highly sensitive to sulfometuron 

methyl exposure and thus could be directly affected. Other organisms dependent on aquatic 

plants could be affected indirectly. Aquatic animals appear to be much less sensitive to direct 

exposure to sulfometuron methyl compared to plants, although they could be affected indirectly to 

the extent they depend on affected plants for food and habitat.

2.4. Assessment Endpoints

Assessment endpoints represent the actual environmental value that is to be protected, defined by 

an ecological entity (species, community, or other entity) and its attribute or characteristics (US 

EPA, 1998). For sulfometuron methyl, the ecological entities may include the following: birds, 

mammals, freshwater fish and invertebrates, estuarine/marine fish and invertebrates, terrestrial 
20

plants, insects, and aquatic plants and algae. The attributes for each of these entities may include 

growth, reproduction, and survival and are discussed further in the Analysis Plan (Section 2.6). 

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 is used in this risk assessment to provide a written and visual description of 

the predicted relationships between sulfometuron methyl, 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 (US EPA, 1998).

2.5.1. Risk Hypotheses

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

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

models, or probability models (EPA 1998a). For sulfometuron methyl, the following ecological 

risk hypothesis is being employed for this baseline risk assessment:

Given persistence and mobility of sulfometuron methyl and some of its degradates, there is 

a likelihood that terrestrial and/or aquatic organisms will be exposed when sulfometuron 

methyl is used in accordance with the label. Consequently, considering the mode of 

action, direct toxicity and potential indirect effects, labeled uses of sulfometuron methyl 

have the potential to cause adverse effects upon the survival, growth, and reproduction of 

non-target terrestrial and aquatic plants and animals.

2.5.2. Conceptual Diagram

Based on the iterative process of examining the usage information, fate and effects data, the risk 

hypotheses described previously, conceptual diagrams are shown in Figure 1 and Figure 2 for 

aquatic and terrestrial ecosystems, respectively. These conceptual models illustrate: (1) the most 

likely stressors/exposure pathways, and (2) the organisms that are most relevant and applicable to 

this assessment. 

The dominant sources/transport pathways of sulfometuron methyl to aquatic ecosystems include 

spray drift, runoff and erosion from treated areas to surface waters and aquatic sediments. 

Sulfometuron methyl also has the potential to leach to groundwater which 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. Once in surface water and sediments, sulfometuron methyl 

may be directly toxic to aquatic vascular plants (rooted macrophytes) and nonvascular plants 

(algae) via uptake through the roots or cell membrane. Sulfometuron methyl exposure in surface 
21

water and sediments may also cause direct toxicity to aquatic animals, although the generally low 

toxicity to aquatic animals renders this pathway less of a concern compared to aquatic plants. 

Indirect effects on aquatic animals via impacts on aquatic plants is also a concern, but is not 

explicitly modeled in this risk assessment due to model and data limitations.

The dominant sources/transport pathways of sulfometuron methyl to terrestrial ecosystems

include direct spray on terrestrial food items, spray drift, runoff and erosion from herbicide 

treated areas, and leaching to groundwater. Wind-driven erosion of treated soils is also a potential 

source of concern, particularly to non-target plants but is not modeled in this risk assessment due 

to data and modeling limitations. Volatilization of sulfometuron methyl is also a potential source 

of exposure for terrestrial animals via inhalation, but is of less concern given its low volatility and 

low inhalation toxicity based on mammalian data (MRID 430892-03). Once sorbed onto food 

items, terrestrial animals (birds, mammals) may be exposed to sulfometuron methyl via diet and 

dermal absorption, although its low toxicity to birds and mammals suggest that effects from this 

exposure pathway are much less likely than effects on terrestrial plants. Adverse effects on nontarget terrestrial plants may occur through exposure to herbicide spray drift, contaminated runoff 

and groundwater, erosion of herbicide treated soil via direct contact and root uptake, and 

irrigation with contaminated ground water or surface water sources. Indirect impacts may occur 

on animals that depend on affected terrestrial plants for food or habitat.
22

Figure 1. Conceptual model for sulfometuron methyl fate and effects in aquatic 

ecosystems.

1 Bold lines and text boxes represent exposure pathways and effects that were assessed quantitatively in this risk 

assessment. Dashed lines indicate potential exposure pathways or effects that were not assessed quantitatively.

Stressor Sulfometuron Methyl Applied To Foliage Via Aerial And Ground Sprays

Source/ 

Transport

Pathways 

Receptor

Spray

Drift

Runoff/

Erosion

Leaching/ 

Infiltration

Source/ 

Exposure 

Media

Surface Water/ 

Sediment

Exposure 

Point

Aquatic 

Animals

Attribute 

Change

Individual Animals

Reduced survival, 

growth and/or 

reproduction

Vascular Aquatic 

Plants

Gill/Integument Uptake 

& Ingestion

Individual Plants

Reduced Survival 

and Growth

Groundwater

Indirect effects

Direct Contact & 

Root Uptake

Plant Population

Reduced 

Population Growth

Nonvascular 

Aquatic Plants
23

Figure 2. Conceptual model for sulfometuron methyl fate and effects in terrestrial 

ecosystems. 

1 Solid lines and text boxes represent exposure pathways and effects that were assessed quantitatively in this risk 

assessment. Dashed lines indicate potential exposure pathways or effects that were not assessed quantitatively.

Stressor Sulfometuron methyl applied to foliage via aerial and ground sprays

Source/ 

Transport

Pathways 

Receptor

Volatilization

/Wind 

Erosion

Direct 

Deposition

Spray

Drift

Runoff/

Erosion

Leaching/ 

Infiltration

Source/ 

Exposure 

Media

Terrestrial Food 

(foliage, fruits 

insects)

Air/ Soil 

Particles

Inhalation/ 

Dermal

Foliage/Soil

Exposure 

Point Ingestion

Terrestrial 

Animals

Attribute 

Change

Individual Animals

Reduced survival, 

growth and/or 

reproduction

Terrestrial 

Plants

Direct Contact/ 

Root Uptake

Individual Plants

Reduced Survival 

and Growth

Groundwater

Indirect effects
24

2.6. Analysis Plan 

This document characterizes the environmental fate and effects of sulfometuron methyl to assess 

whether existing label uses for reregistration of this compound result in potential risk to nontarget organisms above the Agency’s levels of concern (LOCs). Available environmental fate, 

ecotoxicity, and physicochemical property data were taken from studies submitted previously to 

EPA and where available, the open scientific literature. At or near the time of their submission to 

EPA, 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 re-reviewed to ensure that studies met current acceptability guidelines. 

For the environmental fate studies, new data or information or new studies were submitted in 

response to Agency reviews of earlier data submissions; most of these new study addendums or 

replacements for older studies were submitted in the early 1990s but were not previously subject 

to formal review by the Agency. Any literature studies used in this risk assessment were 

evaluated according to EPA/OPP/EFED review guidelines in place at the time of submission and 

accepted if deemed scientifically valid; however, test conditions deviate in some ways from the 

current OECD Guidelines (See 

http://www.epa.gov/oppefed1/ecorisk_ders/toera_analysis_exp.htm#WSAN2 and 

http://www.oecd.org/department/0,3355,en_2649_34377_1_1_1_1_1,00.html ).

2.6.1. Conclusions from Previous Risk Assessments

No previous environmental fate and ecological risk assessment was available for sulfometuron 

methyl that was comparable to current OPP practices. However, comprehensive ecological risk 

assessments were available from two other Federal sources: US Forest Service (USDA, 2004) and 

the Bureau of Land Management (BLM, 2005). In many cases, the overall methodology and data 

used in these assessments was similar to that used by OPP, although some differences in the 

models, interpretation of data, and associated assumptions were evident. 

Results from the US Forest Service Ecological Risk assessment (USDA, 2004) indicate that risk 

of direct toxicity to aquatic and terrestrial animals is unlikely, due to exposure via contaminated 

diet, dermal contact, and inhalation. Risks were evident to terrestrial and aquatic plants, with 

hazard quotients (equivalent to Agency RQ values) up to 4 for aquatic plants (peak 

concentrations) and up to 15,000 for terrestrial plants based on the NOAEC for vegetative vigor. 

The US Forest Service assessment considered only ground applications, which would likely result 

in lower RQs compared to aerial applications that are modeled in the OPP ecological risk 

assessment.

Results from the BLM ecological risk assessment (BLM, 2005) are similar to those of the US 

Forest Service. No risks from direct spray, drift, or surface runoff of sulfometuron methyl were 

identified for terrestrial animals, fish or aquatic invertebrates. Risks to terrestrial and aquatic 

plants from off site drift and surface runoff were evident, with RQs up to 2,500 associated with 

aerial application 100ft from the treated area and up to 40 for aquatic plants from surface runoff to 
25

a model pond. Results from modeling wind-driven erosion did not indicate risk to terrestrial 

plants, although results depended largely on the treatment area size and may underestimate risks 

from larger scale applications. 

2.6.2. Preliminary Identification of Data Gaps and Analysis Plan

Data from registrant-submitted studies and the open literature were used to assess the potential 

effects of sulfometuron methyl and its major metabolites on non-target organisms. For aquatic 

and terrestrial plants, a re-review of the toxicity data indicated that the ecological effect studies 

meet basic guideline requirements and no data gaps were identified for terrestrial and freshwater 

aquatic plants. For aquatic animals, a re-review of the toxicity data indicates that no acceptable 

data were available for chronic toxicity to fish (freshwater, or marine/estuarine). For birds, no 

data were available to assess effects on avian growth or reproduction. Similarly for mammals, no 

acceptable data were available on reproductive effects of sulfometuron methyl. Thus, for 

ecological effects, the following data gaps are identified along with associated uncertainties: 

• Avian Reproduction Study (71-4)

• Fish Early Life Stage Study for Freshwater or Estuarine/Marine Species (72-4)

• 2-generation reproduction study with rat (83-4)

There are no outstanding environmental fate data gaps.

In accordance with OPP practices for conducting baseline ecological risk assessments of 

pesticides (see the “Overview Document; US EPA, 2004), the primary method used to assess risk 

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

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

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

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

the RQ exceeds an LOC, then risks are identified.

2.6.3. Measures of Effect and Exposure

Considering the previous discussion of data gaps and risk assessment procedures, the following 

measures of effects and exposure presented in Table 4 are selected for this baseline risk 

assessment.
26

Table 4. Measures of Ecological Effects and Exposure for Sulfometuron Methyl

Assessment Endpoint Surrogate Species and Measures of 

Ecological Effect1 

Measures of Exposure

Birds2 Survival Bobwhite acute oral LD50

Bobwhite and mallard subacute 

dietary LC50

Maximum residues on food 

items (foliar)

Reproduction and growth Bobwhite and mallard chronic 

reproduction NOAEC and 

LOAEC

(no studies available)

Mammals Survival Laboratory rat acute oral LD50

Reproduction and growth

Laboratory rat oral reproduction 

chronic NOAEC and LOAEC 

(no acceptable studies available)

Freshwater fish3 Survival Rainbow trout and bluegill sunfish 

acute LC50

Peak EEC4

Reproduction and growth Fathead minnow

 chronic (early life-stage) 

NOAEC and LOAEC

(no acceptable studies available)

60-day average EEC4

Freshwater 

invertebrates

Survival Water flea acute EC50 Peak EEC4

Reproduction and growth Water flea chronic (life cycle) 

LOAEC

21-day average EEC4

Estuarine/marine 

fish

Survival Sheepshead minnow acute LC50 Peak EEC4

Reproduction and growth Sheepshead minnow chronic (early 

life-stage) NOAEC and LOAEC

(No studies available)

60-day average EEC4

Estuarine/marine 

invertebrates

Survival Eastern oyster acute EC50 and mysid 

acute LC50

Peak EEC4

Reproduction and growth Mysid chronic NOAEC and LOAEC

(no data available)

21-day average EEC4

Terrestrial plants5 Survival and growth Monocot and dicot seedling 

emergence and vegetative vigor 

EC25, EC05, and NOAEC values

Estimates of runoff and spray 

drift to non-target areas

Insects Survival (not 

quantitatively assessed)

Honeybee acute contact LD50 Maximum application rate

Aquatic plants and 

algae

Survival and growth Algal and vascular plant (i.e., 

duckweed) EC50 and NOAEC 

values for growth rate and 

biomass measurements

Peak EEC
27

1 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 may be used as surrogates for amphibians (terrestrial phase) and reptiles. 3 Freshwater fish may be used as surrogates for amphibians (aquatic phase). 4 One in 10-year return frequency. 5 Data required for 4 species of monocots from 2 families (must include corn) and 6 species of dicots from 4 families (must 

include soybean). 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.

3. ANALYSIS

3.1. USE CHARACTERIZATION

Information in this section is taken from the “Sulfometuron Methyl Use Closure Memo” from 

John Pates, Special Review and Reregistration Division (dated January 30, 2007). In addition, 

some data submitted to the Agency by DuPont Corp. is used by permission.

Sulfometuron methyl is a broad-spectrum sulfonylurea herbicide (numerous other herbicides in 

this class are also registered for various uses in the United States). There are no agricultural uses 

for sulfometuron methyl, but it is used on a wide variety of non-crop situations for vegetation 

management (railroad, highway, power line, and other rights-of-way; suppression of vegetation 

at utility substations, unimproved turf in industrial areas, in preparation of ground for asphalt or 

concrete paving, etc.) and in forestry plantings. It is applied either post-emergent or preemergent. It works by blocking the active growing regions of stem and root tips. Sulfometuron 

methyl is formulated as a water dispersible granule (WDG) and applied using a variety of 

methods including helicopter, fixed-wing aircraft, ground spray (boom and backpack) and spot 

treatment (Table 5 and Table 6). 

Sulfometuron methyl is generally applied once per year for non-crop areas. In some instances 

(weed escapes) a second application may be made, but all products limit the total quantity of 

sulfometuron methyl that may be applied (from any source) to 6 ounces1

Table 9

of active ingredient 

per year. Therefore, application rates in general forestry, and for site preparation and/or release 

in conifer, hardwood and Christmas tree plantations, will vary significantly depending upon the 

specific purpose of the application and the desirable tree species. In forestry, uses can be similar 

to plantation sites, but may also include the maintenance of access routes and fire breaks. It is 

further noted that use rates can also vary with climate and soil type. Ranges of application rates 

by use are summarized in .

Considering all types of uses, regions of the U.S. where sulfometuron methyl appears to have the 

greatest use include the southeast and west coast states. Data from DuPont (used by permission)

indicate that OR and TX are the highest use states overall (Table 7). However, Vegetation 

 1 That is, 0.375 pounds of active ingredient per acre per year.
28

Management LLC also markets sulfometuron methyl products and the geographical distribution 

of the use of its products could be somewhat different. The total amount used annually is 

estimated to be close to 250,000 pounds active ingredient Table 8.

Table 5. Permitted application methods for sulfometuron methyl, DuPont 

Products

Forestry/

Plantations

Aerial (fixed wing, helicopter), ground (closed cab), and backpack 

(spot spray).

Vegetative 

Management

Aerial (helicopter) and ground (closed and open cab).

Railroad Aerial (helicopter) and ground (closed and open cab).

Table 6. Permitted application methods for sulfometuron methyl, 

Vegetation Management LLC Products

SFM Ground (broadcast, directed), air (helicopter- only), backpack sprayers 

(forestry applications include banded or spot hand applications).

SFM Extra Ground (broadcast, directed), air (helicopter or fixed wing aircraft, 

backpack sprayers (forestry applications include banded or spot hand 

applications).

Table 7. States with high sulfometuron usage (based upon DuPont sales data, 

2001-2004).

Thousands of Pounds A.I. Applied Annually Statewide

Use Site 1 to 5 5 to 10 10 to 20 > 20

Forestry OR, TX, LA, 

GA, VA

AR, MS, AL --- ---

Vegetation 

Management

WA, OK, LA, 

MS, AL, GA, 

SC, VA, PA

CA, TX OR ---

Railroad WA, OR, CA, 

NM, ND, NE, 

KS, TX, IL, MS, 

OH, FL, MA

TN, WV --- ---

Total Uses 

(sales)

MT, CO, NM, 

ND, NE, KS, 

OK, MN, IL, 

OH, PA, VA, 

SC, FL, MA

OR, CA, AR, 

LA, TN, MS, 

AL, GA, WV

TX OR
29

Table 8. Annual usage of sulfometuron methyl in the US by use site.

Use Site

Low 

Estim.

High 

Estim.

Annual Usage,

Lbs ai

(Commercial Christmas Trees - Nurseries) 50 830

Forestry 89,000 100,000

Non-crop Vegetative Management (VM - includes 

Roadway, Utility & Pipeline) 80,000 100,000

Railroad (RR) 50,000 71,000

Total 230,000 261,000

Estimates reflect ranges from combined registrant and OPP-BEAD generated 

estimates. Registrant estimates are combined for DuPont and Vegetation 

Management for any and all years of reported data. BEAD estimates reflect multiple 

data sources from 1999 to 2003 period.
30

Table 9. Sulfometuron application rate ranges by product label and use site.

Product Name Type of 

Formulation

Additional 

Active 

Ingredient(s)

Use Site(s) Single App. Low 

Rate (pounds a.i.)

Single App. High 

Rate (pounds a.i.)

DuPontTM Oust® 

Herbicide

Or “Sulfometuron methyl 

75”

Dispersible

granules

None (may be tank 

mixed)

Forestry

Non-Crop

0.047

0.047

0.375

0.375

DuPontTM Oust® XP 

Herbicide

Dispersible

granules

None (may be tank 

mixed)

Forestry 

Non-Crop

0.023

0.047

0.375

0.375

DuPontTM 

Oust® Extra Herbicide

Dispersible

granules

Metsulfuron Methyl Conifer 

Plantations

Non-Crop

0.023

0.016

0.281

0.188

DuPontTM Oustar® 

Herbicide

Dispersible

granules

Hexazinone Forestry 0.075 0.175

DuPontTM Westar® 

Herbicide

Dispersible

granules

Hexazinone Christmas 

Trees

Forestry

Non-Crop

0.025

0.100

0.131

0.100

0.131

0.194

DuPontTM Landmark® 

MP Herbicide

Dispersible

granules

Chlorsulfuron Non-Crop 0.023 0.281

DuPontTM Landmark® II 

MP Herbicide

Dispersible

granules

Chlorsulfuron Non-Crop 0.035 0.350

DuPontTM Landmark® 

XP Herbicide

Dispersible

granules

Chlorsulfuron Non-Crop 0.023 0.281

DuPontTM Landmark® II 

XP Herbicide

Dispersible

granules

Chlorsulfuron Non-Crop 0.035 0.350

DuPontTM 

ThrottleTM MP Herbicide

Dispersible

granules

Sulfentrazone

Chlorsulfuron

Non-Crop ** 0.141 0.141

DuPontTM 

ThrottleTM XP

Herbicide

Dispersible

granules

Sulfentrazone

Chlorsulfuron

Non-Crop 0.141 0.141
31

Product Name Type of 

Formulation

Additional 

Active 

Ingredient(s)

Use Site(s) Single App. Low 

Rate (pounds a.i.)

Single App. High 

Rate (pounds a.i.)

SFM 75, SFM Extra Dispersible

granules

Only in tank mixes Conifer Site 

Preparation 

(pre-plant)

0.063 0.250

SFM 75, SFM Extra Dispersible

granules

Only in tank mixes Conifer 

Release 

(posttransplant)

0.125 0.188

SFM 75, SFM Extra Dispersible

granules

Only in tank mixes Conifer Site 

Preparation 

or Posttransplant 

for specific 

weeds (e.g., 

Kudzu)

0.281 0.375

SFM 75, SFM Extra Dispersible

granules

Only in tank mixes Hardwoods

(seedlings 

or 

transplants 

in 

dormancy)

0.023 0.234

SFM 75, SFM Extra Dispersible

granules

Only in tank mixes Non-Crop:

“NonAgricultural

”*

0.035 0.375
32

Product Name Type of 

Formulation

Additional 

Active 

Ingredient(s)

Use Site(s) Single App. Low 

Rate (pounds a.i.)

Single App. High 

Rate (pounds a.i.)

SFM 75, SFM Extra Dispersible

granules

Only in tank mixes Non-Crop: 

Under 

asphalt and 

concrete 

pavements

(before 

paving)

0.188 0.375

SFM 75, SFM Extra Dispersible

granules

Only in tank mixes Non-crop:

Turf 

(unimprove

d)

0.023 0.188

** Non-Crop lumps together uses such as rights-of-way, industrial site weed management, applications prior to 

concrete or asphalt paving, unimproved turf, etc.

* “Non-agricultural” is a term on Vegetation Management LLC labels that includes most of the non-crop uses not 

otherwise specifically listed.
33

3.2. EXPOSURE CHARACTERIZATION

3.2.1. Environmental Fate and Transport Characterization

The body of environmental fate data submitted demonstrates sulfometuron is mobile and 

persistent in the environment (Table 10). Sulfometuron methyl is more soluble in neutral and 

alkaline water than in acidic water. The major route of dissipation for sulfometuron methyl is 

believed to be aerobic and anaerobic degradation / metabolism in soil and water (pseudo firstorder degradation half-lives2 generally around 2 to 6 months), with hydrolysis potentially 

dominant under acidic conditions. First-order rate aerobic soil metabolism half lives range from 

52 to 58 days in two laboratory studies (technically both with the same soil type, but measured in 

two independent studies several years apart). In comparison, lump dissipation half-lives in the 

field ranged from 44 to 128 days at four sites (when considering only the residues remaining in 

the upper 15 cm of topsoil and calculating a lumped pseudo first-order rate including all residue 

data during the entire ca. 350 to 500 days of each study)

3

Sorption was not found to be strongly dependent on any of the major properties of the tested 

soils in the registrant-submitted studies. The pKa of sulfometuron methyl is 5.4, and 

theoretically, adsorption may increase in very acidic soils where the methyl ester form of 

. At all four field study sites, about 99 

% of the applied sulfometuron methyl had dissipated from the upper six inches of the soil profile 

within 3 to 6 months after application, but dissipation of the small amount of sulfometuron 

methyl remaining in the topsoil a few months after application was much slower. Sulfometuron 

methyl is subject to hydrolysis at environmental pHs; with significantly more rapid hydrolysis 

occurring under acidic conditions (e.g., a hydrolysis half-life of 9 days at pH 5 and 139 days at 

pH 7). None of the laboratory and field studies in soil or sediment / water environments, albeit 

all at measured pHs somewhat greater than 5, show as rapid degradation as measured in the pH 5

hydrolysis study.

. 

Metabolism in the aquatic environment is variable, ranging from half-life of 17 to 104 days in 

anaerobic conditions and 9 to 187 days for aerobic conditions (the more rapid degradation with a 

9-day total system half-life took place in a test system with sediment pH of 5.4 and water pH of 

7.6). Although sulfometuron methyl persistence is expected to generally increase with higher 

soil pH (rotational crop restrictions for many other sulfonylureas, which are all weak acids, 

reflect this), a consistent trend was not found in the available studies. 

Soil retention of sulfometuron methyl is low, with Freundlich adsorption KF values ranging between 

0.15 and 2.1 (mg/kg)/(mg/L)n in four test soils with soil organic carbon content ranging between 0.6 and 

2.6 percent.

 2

 All first-order rates / degradation half-lives discussed in this document, were, unless otherwised 

specified, calculated from linear regression of log-transformed decay data.

3

 In most cases simple first-order degradation rates and half-lives (calculated from linear regression of logtransformed data) are used (often along with DT50 and DT90 values) to represent sulfometuron methyl persistence 

in the environmental fate studies. However, particularly in the field dissipation studies, over time pseudo first-order 

kinetics often became less of an adequate descriptor for residue decline; in such cases the DT50 and DT90 values 

provide perspective on how much the decline patterns deviated from that predicted by a first-order model.
34

sulfometuron would predominate. However, the pH range of the four test soils in the batch 

equilibrium adsorption / desorption study was only 6.7 to 7.7 . The published literature do seem 

to show more of a relationship of sulfometuron methyl and other sulfonylureas to mobility in 

soil; Weber et al. (2004) have reviewed the literature and concluded that there is consistent 

relationship between pH and mobility of sulfonylureas (“NHSO2 acid herbicides” means 

sulfonylurea herbicides):

OM and pH were also the primary soil properties in best-fit Kd equations obtained for 

five of the six NHSO2 acid herbicides, with all three soil properties utilized in the Kd

equation for sulfometuron-methyl. Cl was also one component of the Kd equation for 

sulfometuron-methyl, but Cl and pH were also related soil properties. As was the case for 

the COOH acid herbicides, sorption increased as OM increased or as pH decreased.

Other abbreviations used in the above excerpt from the Weber et al. article:

OM = Soil organic mater content

Cl = Chloride ion concentration

COOH acid herbicides = Herbicides with a carboxy acid functional group such as 2,4-D and 

Imazethapyr

Weber et al. developed the following specific equation for predicting sulfometuron adsorption 

from soil properties:

Kd = 3.0 + 0.49(OM) – 0.03(Cl) – 0.47(pH) ± 2.3

In general, sulfonylureas were found to have the strongest correlation between soil pH and the 

measured pesticide Kd of any of ten families of pesticides tested; the correlation of soil percent 

OM and Kd was second to “OH acid” (uracil) herbicides such as bromacil. Similarly, soil pH and 

% OM together accounted for more of the variability in soil Kd for these two classes of 

herbicides (54% for sulfonylureas and 67% for uracils) than for any of the other pesticide 

families evaluated.

Based on the of McCall et al. (1981) mobility classification system sulfometuron methyl is 

mobile to highly mobile in each of the test soils.

In terrestrial field dissipation studies at four US sites, leaching of parent sulfometuron methyl 

occurred at measurable concentrations; (>10 ppb in depth increments from 15 to 90 cm) was 

noted at each test site. Consistent with the terrestrial field dissipation and the aged leaching 

results, minimal levels (but possibly still high enough to be phytotoxic) of sulfometuron methyl 

residues were estimated for ground water (0.33 ug/L for vulnerable aquifers) using the SCIGROW model. Leaching of the degradates was not evaluated in the field dissipation studies.

Sulfometuron persistence in water indicates that if, either via spray drift or any runoff event, 

sulfometuron methyl reaches surface water, it may persist for a few weeks to several months and 

present some concern to surface water resources. The fairly low use rate (maximum annual rate 

of 0.375 lb ai/A) and the apparent typical use pattern of applying in only one or two years out of 
35

a several year period should limit the actual exposure of sulfometuron methyl parent residues in 

surface water (however, note that sulfometuron methyl could negatively affect certain sensitive 

plants at very low exposure levels because it is such a potent herbicide with respect to many 

plant species). 

Aquatic modeling at the highest application rate applied every year results in a peak surface 

water estimated environmental concentration (EEC) of 31.5 μg/L; additional assumptions for this 

modeling are discussed in “Section 3.2.2.2, Aquatic Exposure Modeling”. Note that 

sulfometuron methyl was not predicted to accumulate in the receiving pond so the effect of 

sulfometuron methyl on EECs determined only was significant for the chronic (not acute) 

exposure estimates.

Volatility studies were not reported. However, based its chemical properties, volatilization is not 

expected to be a route of dissipation of sulfometuron methyl in water or soils. 

Sulfometuron methyl degrades to CO2 under aerobic, non-sterile conditions (relatively little 

mineralization occurs under sterile conditions), but with significant accumulation of intermediate 

degradates, including a sulfonamide and saccharin from the phenyl ring part of the parent 

molecule and a pyrimidine amine from the pyrimidine ring portion (see “APPENDIX A: 

Structures and Chemical Names of Sulfometuron methyl Metabolites”). For the phenyl ring 

labeled studies, CO2 was up to 28 to 44 % of applied at study termination whereas for the 

pyrimdine-ring labeled studies CO2 was up to 53% of applied at study termination (see Table 10, 

aerobic soil metabolism studies, for further information). Additional details on the accumulation 

of sulfometuron methyl degradates in the various studies will be provided in a Drinking Water 

Assessment for Sulfometuron Methyl.

The only submitted studies directly evaluating the fate of sulfometuron methyl degradates were 

adsorption / desorption studies on the pyrimidine amine and saccharin. The soil retention 

characteristics of two of the sulfometuron methyl degradates were studied in batch equilibrium 

adsorption / desorption studies: saccharin Kfs were 0.03 to 0.27 and the pyrimidine amine Kfs 

were 0.17 to 3.70 in the four test soils (Table 10). This means saccharin would be slightly more 

mobile and the pyrimidine amine slightly less mobile than parent (Kfs of 0.15 to 2.12 in the same 

four soils)

Table 10. Key results of sulfometuron methyl environmental fates studies.

Parameter

[Guideline #] Value1 MRID(s)

Hydrolysis

[161-1]

t1⁄2= 8.8 days @ 25 oC, pH 5;

t1⁄2=139 days @ 25 oC, pH 7;

t1⁄2= 224 days @ 25 o

C, pH 9.

Major degradates (from cleavage of the sulfonylurea bridge): 

Sulfonamide – only in acidic water

Saccharin – all pH levels

Pyrimidine amine – all pH levels

42715201
36

Table 10. Key results of sulfometuron methyl environmental fates studies.

Parameter

[Guideline #] Value1 MRID(s)

Direct 

photolysis in 

water

[161-2]

Combined labels results:

t1⁄2= 428 days @ 24 oC, pH 5;

t1⁄2= stable @ 24 o

C, pH 7;

t1⁄2= stable @ 24 o

C, pH 9.

(calculated by the difference in degradation rates between irradiated 

and dark controls and adjusting for typical light levels on sunny days)

Major degradates (irradiated water):

pH 5: sulfonamide, pyrimidine amine;

pH 7: none;

pH 9: none.

42182401

43174101

Photolysis on 

soil

[161-3]

t1⁄2= 72.1 days @ 25 oC, 

Study duration was 33 days, substantial degradation occurred in dark 

controls and the calculated photolysis half-life represents the 

difference in the dissipation rate in the irradiated and the dark control 

samples.

Major degradates (from cleavage of the sulfonylurea bridge):

Saccharin reached a maximum of 48.4% of the applied at 33 days 

(study termination.)

Pyrimidine amine reached a maximum of 53.1% at 33 days (study 

termination.)

There was no substantial difference in the degradation pathway of 

sulfometuron methyl between the irradiated- and the dark control soil.

No other degradate accounted for >4% of the applied radioactivity 

regardless of whether the phenyl ring or the pyrimidine ring was 14Clabeled.

41420601
37

Table 10. Key results of sulfometuron methyl environmental fates studies.

Parameter

[Guideline #] Value1 MRID(s)

Aerobic soil 

metabolism

[162-1]

Study with [pyrimidine-2-

14C] Sulfometuron Methyl

Soil: Keyport Silt loam (pH 6.3, 1.6% O.C.) from Delaware

First Order t1⁄2: 57.8 days (r2 = 0.9239).

Observed DT50: 23 days.

Observed DT90: 110 days.

Sterile soil First Order t1⁄2: 364 days

Major transformation products:

Pyrimidine amine (maximum 41.0% of the applied)

Pyrimidine-ol (maximum 10.5% of the applied).

CO2 (maximum 53.1% of applied).

Minor transformation products:

Free acid sulfometuron methyl.

Pyrimidine urea. 

42091401

Aerobic soil 

metabolism

[162-1]

Study with U- 14C-phenyl-label

43174102 

and 

245375

ed Sulfometuron Methyl

Soil: Keyport Silt loam (pH 6.4, 1.6 % O.C.) from Delaware (0.12 

mg a.i./kg).

First Order t1⁄2: 52.5 days (r2 = 0.9239).

Observed DT50: 29 days.

Observed DT90: 162 days.

Major transformation products:

Sulfonamide.

Saccharin.

Free acid sulfonamide plus urea (1.0 mg a.i./Kg only).

CO2.

Minor transformation products:

Free acid sulfonamide plus urea (0.12 mg a.i./Kg only)
38

Table 10. Key results of sulfometuron methyl environmental fates studies.

Parameter

[Guideline #] Value1 MRID(s)

Anaerobic 

aquatic 

metabolism

[162-3]

Study performed with [pyrimidine-2-

14C] Sulfometuron Methyl

Matrix: Bradenton Pond water-sand sediment.

First Order t1⁄2: 37.4 days (r2 = 0.6125).

Observed total system DT50: 22 to 61 days (inconsistent decline 

data).

Observed total system DT90: 102 days.

Matrix: Landenberg Pond water-sandy loam sediment.

First Order t1⁄2; total system: 17.1 days (r2 = 0. 0.6394).

Observed total system DT50: 6.1 days.

Observed total system DT90: 21.7 days.

Major transformation products (both systems):

free acid sulfometuron methyl.

pyrimidine amine.

Minor identified transformation products:

pyrimidine-ol.

CO2.

42091402 

and 

43188601
39

Table 10. Key results of sulfometuron methyl environmental fates studies.

Parameter

[Guideline #] Value1 MRID(s)

Anaerobic 

aquatic 

metabolism

[162-3]

Study with [phenyl-U14C] Sulfometuron Methyl

Matrix: Pond water-sandy loam sediment from Bradenton, 

Florida.

(water pH 5.5 . Sediment: pH 5.1; O.C. = 5.9 %).

First Order t1⁄2; total system: 104 days (r2 = 0.4883)*.

Observed DT50 in total system: ca. 21 days.

Sterile t1⁄2; total system: 44 days

* Based upon limited and inconsistent data.

Matrix: Pond water-silt loam sediment from Landenberg, 

Pennsylvania.

(water pH 5.8 . Sediment: pH 5.6; O.C. = 2.1 %).

First Order t1⁄2; total system: 87 days (r2 = 0.3577).

Observed DT50 in total system: ca. 28 days.

Sterile t1⁄2; total system: 175 days

Matrix: Pond water-loam sediment from Saskatoon, Canada. 

(water pH 8.3 . Sediment: pH 7.8; O.C. = 0.9 %).

First Order t1⁄2; total system: 77 days (r2 = 0.5853).

Observed DT50 in total system: ca. 70 days.

Sterile t1⁄2; total system: 399 days

Matrix: Pond water-silt loam sediment from Walnut Grove, 

Tennessee. (water pH 5.5 . Sediment: pH 5.1; O.C. = 0.5 %).

First Order t1⁄2; total system: 73 days (r2 = 0.5691).

Observed DT50 in total system: ca. 28 days.

Sterile t1⁄2; total system: 95 days

Major transformation products:

saccharin.

free acid sulfonamide.

Minor identified transformation products:

Methyl-2-aminocarbonyl(aminosulfonyl)benzoate.

4413010-

20 

(143540)
40

Table 10. Key results of sulfometuron methyl environmental fates studies.

Parameter

[Guideline #] Value1 MRID(s)

Aerobic aquatic 

metabolism

[162-4]

Study performed with [pyrimidine-2-

14C] Sulfometuron Methyl

Matrix used: Pond water-silt loam sediment (Landenberg, acidic 

system).

First Order t1⁄2; total system: 9.2 days (r2 = 0.94).

Observed DT50 in total system: 15 days.

Observed DT90 in total system: 31 days (extrapolated).

Major transformation products:

Pyrimidine amine (pyrimidine label).

Hydroxymethyl-pyrimidine sulfometuron methyl.

Free acid sulfonamide (phenyl label).

Sulfonamide (phenyl label).

Minor identified transformation products:

CO2.

Matrix used: Pond water-sand sediment (Bradenton, alkaline 

system).

First Order t1⁄2; total system: 187.3 days (r2 = 0.5713).

Observed DT50 in total system: >39 days.

Major transformation products:

Pyrimidine amine (pyrimidine label).

Free acid sulfonamide (phenyl label).

Minor identified transformation products:

Hydroxymethyl-pyrimidine sulfometuron methyl.

Sulfonamide (phenyl label).

CO2.

42091403 

and 

43174103
41

Table 10. Key results of sulfometuron methyl environmental fates studies.

Parameter

[Guideline #] Value1 MRID(s)

Adsorption/

Desorption 

(Kd and 

Koc in L Kg-1

)

Parent sulfometuron methyl:

Soil type: Chino Sandy loam; pH 7.1, organic carbon 1.0%.

Adsorption Kd: 0.35.

Adsorption Koc: 35.

Freundlich adsorption KF: 0.153.

Freundlich adsorption KFoc: 14.7.

1/N 0.504

Soil type: Fargo silt loam ; pH 7.7, organic carbon 2.6%.

Adsorption Kd: 2.07.

Adsorption Koc: 79.6.

Freundlich adsorption KF: 2.12.

Freundlich adsorption KFoc: 83.2.

1/N 1.23

Soil type: Miaka Sand ; pH 7.0, organic carbon 0.6%.

Adsorption Kd: Not applicable.

Adsorption Koc: Not applicable. 

Freundlich adsorption KF: 0.508.

Freundlich adsorption KFoc: 87.6.

1/N 1.61

Soil type: Tama Silt loam ; pH 6.7, organic carbon 1.5%.

Adsorption Kd: 0.79.

Adsorption Koc: 52.7.

Freundlich adsorption KF: 0.974.

Freundlich adsorption KFoc: 67.2.

1/N 0.851

42789301
42

Table 10. Key results of sulfometuron methyl environmental fates studies.

Parameter

[Guideline #] Value1 MRID(s)

Adsorption/

Desorption 

Of Degradates

Pyrimidine amine

Although the registrant conducted adsorption / desorption studies for 

the pyrimidine amine degradate, the results were insufficiently 

documented to verify their calculations of adsorption coefficients (and 

furthermore, they only reported Freundlich adsorption “KF” and 

“KFoc” values without 1/N values (or sufficient data for the reviewer to 

calculate them) and Kd values were also not reported.

For rimsulfuron, a structurally similar pyrimidine amine degradate 

(but with 4-, 6-dimethoxy rather than 4-, 6-dimethyl substitution of the 

pyrmidine amine) was reported to have Kd values of 0.23 to 1.52 and 

Koc values of 19 to 61 in four test soils. See DP Barcode D326660, 

EFED review of rimsulfuron methyl new uses dated 3/14/07 for more 

details.

Saccharin

Although the registrant conducted adsorption / desorption studies for 

saccharin, the results were insufficiently documented to verify their 

calculations of adsorption coefficients (and furthermore, they only 

reported Freundlich adsorption “KF” and “KFoc” values without 1/N 

values and Kd values were also not reported.

Saccharin has been reported elsewhere to be quite mobile, e.g.:

When tested as a degradate of metsulfuron methyl 

(http://ec.europa.eu/food/plant/protection/evaluation/existactive/list1-

13_en.pdf )

42789301
43

Table 10. Key results of sulfometuron methyl environmental fates studies.

Parameter

[Guideline #] Value1 MRID(s)

Terrestrial 

Field/Lysimeter

Dissipation 2

Greenville, MS silty clay loam soil: pH 6.7, 0.6% O.C.

Half-life: 49.2 days (based on 0- to 359-day data); 

12.2 days (based on 0- to 91-day data).

DT90: 32 days

Major transformation products detected (>0.01 ppm): 

Sulfometuron free acid (SFA)

Pyrimdine amine (PYA)

Sulfonamide IN-D5803 (SFN)

Saccharin IN-581 (SCC)

Rochelle, IL silty clay loam soil: pH 6.8, 1.0% O.C.

Half-life: 128 days (based on 0- to 723-day data, residues in 0-15 cm 

depth only); 

14.4 days (based on 0- to 90-day data).

DT90: 35 days

Major transformation products detected (>0.01 ppm): 

PYA, SFN, and SCC

Uvale, TX clay soil: pH 7.9, 1.3% O.C.

Half-life: 53.3 days (based on 0- to 447-day data); 

13.0 days (based on 0- to 90-day data).

DT90: 25 days

Major transformation products detected (>0.01 ppm): 

PYA, SFN, and SCC 

Maldera, CA sandy loam soil: pH 7.8, 0.7% O.C.

Half-life: 44.1 days (based on 0- to 420-day data); 

22.9 days (based on 0- to 180-day data).

DT90: 55 days

Major transformation products detected (>0.01 ppm):

PYA, SFN, and SCC

Numbers 

43212101 

and 

43637101

1 Unless otherwise specified, half-lives were derived with a “Log-linear” degradation rate calculation; a process 

of calculating degradation rates and half-lives from linear regression of log-transformed concentration 

measurements over time. This provides a first-order type of measurement of pesticide decline.

2 For these field dissipation studies, differences between half-lives measured over various time durations 

apparently reflect both slowing of degradation at lower temperatures and a large variability in measured 

concentrations; also, a 2-compartment degradation model for adsorbed and dissolved sulfometuron is quite 

possibility more appropriate (little dissipation of the remaining residues in the topsoil occurred during the second 

year of these studies, for example). A 2-compartment model was not used to represent dissipation rate here 

because the data are not sufficient robust (e.g., very high variability between replicate measurements), the effects 

of weather changes on degradation rate cannot easily be isolated, and the amount of residues lost through 

dissipation out of the topsoil also cannot be separated from the amount lost to degradation. At all four of these 

field study sites about 99% of the applied sulfometuron methyl dissipated from the topsoil within 3 to 6 months.
44

3.2.2. Measures of Aquatic Exposure

3.2.2.1. Aquatic Exposure Monitoring and Field Data

A few surface-water monitoring studies are available for sulfometuron methyl. In streams, most 

recently Michael (2003) found, after application of sulfometuron methyl at 0.42 kg/ha to 

watersheds of unspecified area (reflecting a forestry planting usage) that concentrations of 

sulfometuron methyl in runoff water collected at the edge of the field reached a maximum of 49 

ug/L (24-hour average). However, samples taken approximately 150 meters downstream never 

exceeded the minimum detection limit of 1 ug/L (a fairly high MDL given the potency of this 

herbicide) reported in this study (stream flow data were not supplied). 

In the most widespread monitoring survey available, sulfometuron methyl was detected only 

rarely (2 of 132 samples from 52 sites – mostly Midwestern US streams and rivers, but including 

some reservoirs as well); see Battaglin et al. (2000). The maximum concentration of 

sulfometuron methyl detected was 0.018 ug/L; but it is not known how much sulfometuron 

methyl usage was associated with the watersheds included in this monitoring survey. 

Blomquist et al. (2001) in a monitoring study of 12 reservoir systems across the United States 

found sulfometuron occurred above the minimum reporting limit of 0.05 ug/L in 12% of the 

samples collected with a maximum concentration of 0.16 ug/L and a 95th percentile 

concentration of 0.10 ug/L. This study focused on drinking water supplies and may not represent 

the most vulnerable water bodies for ecological exposure.

3.2.2.2. Aquatic Exposure Modeling

EFED’s PRZM (Pesticide Root Zone Model) and EXAMS (EXposure Analysis Modeling 

System) models (Table 11) were used in this assessment to estimate the exposure of 

sulfometuron methyl residues to the aquatic environment as a result of the proposed uses in 

forestry and various non-crop land vegetation control uses. PRZM simulates pesticide transport 

as a result of runoff and erosion from an 10-hectare agricultural field and EXAMS considers 

environmental fate and transport of pesticides in surface water and predicts EECs in a standard 

pond (10,000-m

2 pond, 2-m deep), with the assumption that the small field is cropped at 100%. 

Calculations are carried out with the linkage program shell – PE5.pl - which incorporates the 

standard scenarios developed by EFED. (For additional information see 

http://www.epa.gov/oppefed1/models/water/index.htm). Potential exposure from ground-water 

(for, example, via contaminated irrigation water) was also estimated using the SCI-GROW 

model.
45

Table 11. Models Used to Estimate Exposure Concentrations for Aquatic 

Ecosystem.

Exposure Estimate Type Models Used

Aquatic ecosystems

Surface water (Tier II)

PE v5.0, PRZM v3.12.2, EXAMS v2.98.04.06 

Details of executables:

PRZM 3.12.2, named przm3122.exe (dated May 12, 2005) 

EXAMS 2.98.04.06, executable file named EXAMS.EXE

(dated April 12, 2005)

PE v5.0, Executable file PE5.pl (dated July 24, 2006)

Ground water (Tier I) SCI-GROW v2.3

Executable file sg23.exe (dated May 16, 2006)

The estimated environmental concentrations (EECs) were predicted assuming 1 aerial or ground 

application at the maximum allowable single application rate of 0.375 lbs. a.i./A (which also 

represents the maximum annual application amount permitted on all labels). Applications were 

broadcast without incorporation, according the uses endorsed by the label. None of the available 

modeling scenarios as currently set up represents a clear match for the sulfometuron methyl use 

pattern as described in Section 3.1 . Nonetheless, a combination of scenarios which represent 

usage patterns and locations that can reasonably be expected to represent a range of conditions 

for the forestry planting and non-crop uses of sulfometuron methyl were able to be selected from 

the suite of available standard scenarios and, with slight adjustments, the available regional 

scenarios (see Table 12). The major adjustments to the standard scenario modeling were:

1. Specific regional scenario adjustments. The rights-of-way regional scenarios were selected 

for this national assessment because they are the only scenarios currently approved in EFED for 

specific modeling of this type of use. However, they were run with both their native 

meteorological files as the source of weather data and with alternate weather data files believed 

to represent more runoff-prone climates that may represent areas with significant use of 

sulfometuron methyl 

2. Modeling with multiple application dates. The multiple PRZM – EXAMS runs with 

multiple application dates were used for final development of EECs for the highest exposure 

scenarios because the product labels frequently refer to uses that are recommended for spring, 

summer, fall, and even winter application (although only spring, summer, and fall dates were 

tested with our modeling, as they were judged to be significantly more common than winter 

applications). 

The most important reason for modeling with multiple application dates is that there is 

significant variability in the results (calculated EECs) of the modeling that can arise strictly as a 

factor of the application date chosen. In fact, when, for example, the Texas Right-of-Way

scenario (using Port Arthur, Texas meteorological data) was rerun with 28 different application 

dates, the acute (peak daily value) EECs (a distribution of 1 in 10-year return frequency values) 
46

ranged from 8.5 to 49.5 ug/L and the 90-day EECs ranged from 5.5 to 27.2 ug/L4

The pesticide-specific input parameters for this modeling (summarized in 

. This is quite a 

significant difference when it is considered that this variability is solely for the 1 in 10 year 

return frequency exposure levels, not for all of the year-to-year differences in EECs from the 

modeling.

Sulfometuron methyl product labels allow for flexibility in when sulfometuron methyl is applied 

and there is not as much consistency in the optimal application season as there would be, for 

example, with most agricultural crops. In this case, the 90th percentile application date model 

results were chosen for risk calculations.

Both aerial and ground applications were simulated, but ground applications were only simulated

for a few scenarios since the ground application assumption yielded lower EEC estimates for 

sulfometuron methyl than aerial applications at the same site.

Table 13) were 

selected from the environmental fate studies submitted by the registrant, and in accordance with 

the US EPA-OPP EFED water model parameter selection guidelines, Guidance for Selecting 

Input Parameters in Modeling the Environmental Fate and Transport of Pesticides, Version II, 

February 28, 2002. 

We considered modeling total residues of sulfometuron methyl (including sulfometuron methyl, 

sulfometuron free acid, the sulfonamide, saccharin, and the pyrimidine amine) as well, since the 

Health Effects Division has made a preliminary call that they might contribute to toxicity in 

mammals (electronic mail message from Larry Chitlik, HED dated /7/2007). However, with the 

available data total residue model inputs would be different from assumptions for the parent 

compound (Table 13) in that stability to hydrolysis, aerobic aquatic metabolism, and anaerobic 

aquatic metabolism hand to be assumed (only aerobic soil metabolism had a measurable total 

residue half-life: 136 days). This would lead to an assumption of no degradation in the pond 

represented by EXAMS, which is set up for a pond with no turnover in ecological risk 

assessments (an additional conservative assumption). Further details on the limitations of the 

modeling and uncertainties regarding exposure to sulfometuron methyl degradates are provided 

in Section 3.2.4.3.

 4 A measure of how often (on average) an event will occur that is greater than some chosen value. In this 

case, the chosen frequency is 1 in 10 years; the chosen EEC is such that the sulfometuron methyl concentration 

would equal or exceed the EEC on average of one in ten years. The full distribution of the 1 in 10 year return 

frequency values is provided in APPENDIX C: Ecological Aquatic Exposure Modeling.
47

TABLE 12. AQUATIC EXPOSURE WITH PRZM – EXAMS: MODELING SCENARIOS 

AND REPRESENTATIVE USAGE PATTERN SUMMARY.

Scenario ID1 WBAN 

(met. 

file)2

appl. 

meth.

CAM3 applictn. 

dates 

(MM-DD)

Use(s) represented

PA Apples 

(std)

W14751 Aerial 2 03-15 Forestry, Conifer Plantations

FL Citrus (std) W12844 Ground 1 03-01 Forestry, Conifer Plantations

FL Citrus (std) W12844 Aerial 1 03-01 Forestry, Conifer Plantations

FL Turf (std) W12834 Ground 1 03-01 Non-crop (e.g., unimproved turf & rights of 

way)

FL Turf (std) W12834 Aerial 2 03-01 Unimproved turf, non-crop

PA Turf (std) W14751 Aerial 2 03-01 Unimproved turf, non-crop

OR Xmas 

Trees (std)

W24232 Ground 1 03-01 Christmas Trees, Forestry, Conifer 

Plantations

OR Xmas 

Trees (std)

W24232 Aerial 2 03-01 Christmas Trees, Forestry, Conifer 

Plantations

CA right of 

way (RLF)

W23234 Aerial 2 03-01 Non-Crop (rights of way, unimproved turf, 

railroads, etc.)

CA right of 

way (RLF)

W94224 Aerial 2 03-01 Non-Crop (rights of way, unimproved turf, 

railroads, etc.)

CA right of 

way (RLF)

W94224 Aerial 2 Feb to Oct4 Non-Crop (rights of way, unimproved turf, 

railroads, etc.)

TX right of 

way (BSS)

W13958 Aerial 2 03-01 Non-Crop (rights of way, unimproved turf, 

railroads, etc.)

TX right of 

way (BSS)

W12917 Aerial 2 03-01 Non-Crop (rights of way, unimproved turf, 

railroads, etc.)

TX right of 

way (BSS)

W12917 Aerial 2 Feb to Oct4 Non-Crop (rights of way, unimproved turf, 

railroads, etc.)

TX right of 

way (BSS)

W12917 Ground 2 Feb to Oct4 Non-Crop (rights of way, unimproved turf, 

railroads, etc.)

1 Native scenario designation state and use site. Native scenario target in parenthesis, where: std = std scenario used 

in nationwide assessments; RLF = scenario originally developed for regional assessments related to the California 

red-legged frog; and BSS = scenario originally developed for regional assessments related to the Barton Springs 

salamander.

2 The Weather Bureau Automated Network (WBAN) meteorological station used for weather inputs in the runoff 

modeling.

3 CAM = Chemical application method. CAM 1 is application direct to soil, although a 4 cm incorporation depth is

automatically assumed, to account for surface roughness. CAM 2 is linear foliar decay based on crop canopy, 

default soil incorporation depth for non-foliar intercepted chemical is 4 cm.

4 Only one application per year in each model run. PRZM-EXAMS was separately run for application dates 

between February 1 and October 29, increasing the application date by 10 Julian days with each successive model 

run (2/1, 2/11, 2/21, etc.).

Table 13. PRZM/EXAMS input parameters for modeling (Aquatic ecological EECs).

Input Parameter Value* Reference
48

Table 13. PRZM/EXAMS input parameters for modeling (Aquatic ecological EECs).

Input Parameter Value* Reference

Molecular Weight (gram mole -1) 364.38

Vapor Pressure (torr) 5.4x10 MRID: 416728-02 -16

Aerobic Soil Metabolism Half-life 

(days) 60.9

90% Upper Confidence Limit of the mean of measured 

values (MRIDs 42091401; 43174102 and 245375)

Water column Half-life (days)

(Aerobic Aquatic Metabolism 

half-life) 292

90% Upper Confidence Limit of the mean of measured 

values (MRIDs 42091403 and 43174103 )

Benthic sediment Half-life (days) 

(Anaerobic Aquatic Metabolism 

half-life) 76

90% Upper Confidence Limit of the mean of measured 

values (MRIDs 43174102, 245375, 42091402, and 

43188601)

Application Rate (Kg a.i./ha) 0.41 Efficiency= 0.99 for ground spray, 0.95 for aerial.

Application Number (Method of 

application) One Product Label; typical use.

Application method; Depth of 

Incorporation (cm)

Aerial or ground;

0 CAM=1 or CAM=2 depending on the use.

Spray Drift (fraction)

0.01 (GS), 0.05 

(aerial)

Default values per guidance document. (GS= ground 

spray)

Solubility (ppm) 244

Highest solubility was recorded for alkaline water 

(12,500 ppm at pH 8.6). However, experience from 

other studies indicates these experimental values are too 

high (Therefore, this value was not multiplied by 10 as 

normally recommended).

Koc (L Kg-1) 47.5

Average of four values (MRID 42789301). 

Koc model was determined to be appropriate.

Hydrolysis Half-life @ pH 7 

(days) 139 days MRID 42715201.

Direct Aqueous Photolysis Halflife(days) Stable

Maximum dark control corrected value (MRIDs 

42182401 and 43174101)

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

Transport of Pesticides; Version II February 28, 2002.

The highest exposures were determined to occur with aerial applications at rights of way sites; 

the southeast Texas (using Port Arthur, Texas weather) scenario and a scenario for Pacific 

Coastal areas utilizing Astoria, Oregon weather). The Florida citrus scenario also yielded 

relatively high EEC estimates, and it provides some representation of forestry planting and other 

uses in the southeastern US (Table 14). Chosen EEC values for the aquatic risk assessments are 

provided in Table 15. Note that whereas in the modeling sulfometuron methyl applications were 
49

simulated for every year of a 30-year simulation period for each scenario (standard EFED 

practices if the product labels do not expressly prohibit this), in most cases sulfometuron does 

not appear to be repeatedly used from year to year at a particular site. However, in this modeling, 

sulfometuron methyl was not predicted to accumulate in the receiving pond so the effect of 

sulfometuron methyl on EECs determined only was significant (e.g., if the 30 applications 

simulated were to be spread over 150 years, the acute EECs would remain about the same, but 

the chronic EECs estimated would be lower).
50

Table 14. Estimated environmental concentrations (μg/L) for aquatic exposure to parent sulfometuron 

methyl: scenario-specific results from PRZM-EXAMS modeling.

(all values are listed as ppb or ug/L)

Scenario Description Site1 Peak 96 hr

21 

Day

60 

Day

90 

Day Yearly Lifetime

Applictn. 

Date, 

mm-yy App-Type3

PA Apple Fr 2.28 2.23 2.05 1.61 1.39 0.45 0.31 3-15 aerial

FL Citrus Fr 9.39 9.09 7.97 6.03 4.93 1.48 0.72 3-01 aerial

FL Citrus Fr 7.32 7.08 6.19 4.71 3.81 1.14 0.43 3-01 ground

FL Turf NC 1.47 1.43 1.27 1.01 0.86 0.29 0.20 3-01 aerial

FL Turf NC 0.46 0.44 0.39 0.30 0.25 0.09 0.05 3-01 ground

PA Turf NC 1.22 1.20 1.12 0.96 0.84 0.29 0.26 3-01 aerial

OR Xmas Fr 1.57 1.53 1.42 1.21 1.06 0.40 0.29 3-01 aerial

OR(Astoria) Xmas Fr 2.87 2.82 2.61 2.18 1.91 0.73 0.42 3-01 aerial

OR(Astoria) Xmas Fr 1.78 1.74 1.58 1.29 1.13 0.43 0.35 9-01 aerial

CA RightsWay NC 8.33 8.15 7.47 6.17 5.35 2.00 0.84 3-01 aerial

CA(As-OR) 4 RightsWay NC 13.64 13.37 12.39 10.35 9.04 3.42 1.34 3-01 aerial

CA(As-OR) RightsWay 90th

date5 NC 11.01 10.83 10.10 8.46 6.73 2.73 1.44 various 6 aerial

TX RightsWay NC 6.96 6.74 5.99 4.72 3.94 1.22 0.64 3-01 aerial

TX(PtAr) 7 RightsWay NC 11.87 11.55 10.66 8.84 7.41 2.30 1.06 3-01 aerial

TX(PtAr) RightsWay 50th date NC 21.75 20.93 18.33 13.51 10.99 3.39 1.97 Various aerial

TX(PtAr) RightsWay 90th date NC 31.45 30.34 26.24 20.45 16.49 5.26 3.14 Various aerial

TX(PtAr) RightsWay 90th date NC 26.08 25.20 21.64 15.51 12.48 3.92 2.05 Various ground

1 Fr = forestry plantings uses. NC = Non-crop uses on rights of way, industrial land with unimproved turf, on ground prior to paving, railroads, etc. 2 CAF = crop area factor.

3 App-Type = application type.

4 As-OR = Astoria, Oregon meteorological weather substituted for the original San Francisco, CA weather data for this regional scenario.

5 90th Date or 50th Date = For the specified exposure distribution the 90th percentile of the 10th percentile exceedence probability (1 in 10 year return 
51

frequency) values were sorted for each model run with different Julian day application dates (single application per year). Then each of the 1 in 10 

year values were sorted and the concentration exceeded for 1 in 10 of the possible application dates was selected to be representative for the 

scenario.

6 Pt-Ar = Port Arthur, Texas meteorological weather substituted for the original Austin, TX weather data for this regional scenario. 7 Only one application per year in each model run. PRZM-EXAMS was separately run for application dates between February 1 and October 29, 

increasing the application date by 10 Julian days with each successive model run (2/1, 2/11, 2/21, etc.).
52

Table 15. Sulfometuron methyl surface water EECs used in aquatic risk 

assessment.

Surface Water EECs in ug/L1

Application 

method Peak 96-hr 21-day 60-day 90-day Annual Average

Yearly 

Average

Aerial 31.45 30.34 26.24 20.45 16.49 5.26 3.14

Ground 26.08 25.20 21.64 15.51 12.48 3.92 2.05 1 Results based on PRZM/EXAMS modeling described in Section 3.2.2.2 using the maximum annual application 

rate of 0.375 lb ai/A.

Since some exposure to sensitive terrestrial plants is possible from contaminated ground water as 

well as from ground-water entering surface waters during base flow periods, a Tier I estimate of 

ground-water exposure was conducted using SCI-GROW 2.3 (executable file dated 5/16/2006). 

The estimate of 0.33 ug/L concentrations in vulnerable ground water (defined as aquifers where 

the water table is about 10 to 30 feet in depth and the overlying soil layers are permeable) would 

indicate that contributions from ground water into surface waters would not reach levels 

estimated to enter surface waters from direct runoff and spray drift in the PRZM – EXAMS 

modeling . However, the levels of sulfometuron methyl in contaminated well water used for 

irrigation could be phytotoxicologically significant.

Table 16. Estimated concentrations of sulfometuron methyl in ground water (SCIGROW inputs and results).

Input Parameter Value* Reference

Aerobic Soil Metabolism Half-life 

(days) 55.2

Mean of measured values (MRIDs 42091401; 

43174102 and 245375)

Application Rate (Kg a.i./ha) 0.41 Maximum permitted single (and annual) rate.

Application Number (Method of 

application) One Typical use.

Koc (L Kg-1) 73.4

Median of four values (MRID 42789301). 

SCI-GROW Modeling Results

Acute Exposure EEC, ug/L 0.33

Chronic Exposure EEC, ug/L 0.33
53

3.2.3. Measures of Terrestrial Exposure

3.2.3.1. Terrestrial Exposure Modeling

Terrestrial Animals. Estimates of terrestrial wildlife exposure to pesticides are typically 

evaluated for the dietary pathway for birds and mammals (USEPA, 2004). Birds are used as 

surrogates for reptiles and terrestrial phase amphibians when specific data are unavailable for 

these taxonomic groups. Consistent with this practice and with the conceptual model for 

sulfometuron in Section 2.5, a screening-level risk assessment was conducted for spray 

applications of sulfometuron methyl for estimating wildlife exposure to sulfometuron methyl via 

dietary uptake. Specifically, pesticide residues on food items of wildlife (birds and mammals) 

were estimated based on the assumption that animals are exposed to a single pesticide residue 

(sulfometuron methyl) in a given exposure scenario. For this terrestrial exposure assessment, 

only spray application methods for sulfometuron methyl are considered, since labeling does not 

permit granular applications. 

Estimating sulfometuron methyl concentrations on wildlife food items focuses on quantifying 

possible dietary ingestion of residues on vegetative matter and insects. No field residue data or 

field study information is available for sulfometuron methyl except for lump dissipation rates 

from the application of sulfometuron methyl to two forest sites (MRIDs 42091404 and 

43174104), therefore, the residue estimates were based on a nomogram that relates food item 

residues to pesticide application rate. The residue EECs were generated from a spreadsheetbased model (T-REX Version 1.3.1) that calculates the decay of a chemical applied to foliar 

surfaces for single or multiple applications and is based on the methods of Hoerger and Kenaga 

(1972) as modified by Fletcher et al. (1994). Residue EECs were calculated for an application 

rate at 0.375 lbs a.i./A (i.e., the maximum annual application rate allowed according to the label) 

applied one time over a single year. As discussed in Section 3.1, the typical application 

frequency of sulfometuron methyl is not well documented and expected to be highly variable 

depending on site conditions and the type of vegetation to be controlled. However, because 

application of sulfometuron methyl is limited to an annual maximum rate of no more than 0.375 

lb a.i./A for its registered uses, a one-time application at the maximum rate was chosen to 

represent a conservative estimate of the EEC for wildlife dietary exposure. Residue data 

supporting a specific value for foliar dissipation half-life were not available for sulfometuron 

(e.g., total magnitude of residue [171-4], reduction of residue [171.5], and foliar dissipation 

[132-1]). Although the default foliar dissipation default half-life of 35 days (Willis and 

McDowell, 1987) would apply to sulfometuron methyl, a foliar dissipation half-life was not used 

since only one application event was modeled. 

The EECs on terrestrial food items may be compared directly with dietary toxicity data or 

converted to an oral dose and compared to dose-based toxicity data. This screening-level risk 

assessment for sulfometuron methyl uses estimated upper bound (i.e., 90th percentile) residues as 

the initial measure of exposure. For comparisons with avian and mammalian dietary-based 

toxicity data, the maximum predicted upper bound residues of sulfometuron methyl are used 

directly without adjustment (Table 17). For a single application season, these EECs are 

considered to represent an estimate of the upper bound exposure following sulfometuron methyl 
54

application at the maximum label rate. For comparisons with dose-based toxicity data, EECs are 

adjusted to an average daily dose (mg/kg-bw/d) using standard allometric relationships. 

Additional information on the modeling of sulfometuron methyl exposure to terrestrial animals is 

provided in APPENDIX F: T-REX Output

Table 17. Unadjusted Dietary Terrestrial EECs for Birds and Mammals 

Following Sulfometuron Methyl Spray Application For Non-Crop Vegetative 

Management.

Uses # of App. x App. Rate

(application method)

Food Items Upper Bound EECs

(ppm)

Non-Crop 

Vegetative 

Management 1

1 x 0.375 lb a.i./A 

(ground broadcast)

Short Grass

Tall Grass

Sm. Insects, Broadleaf Plants

Lg. Insects, Fruits, Pods

90.0

41.3

50.6

5.6

1 Includes uses on unimproved turf, forestry (Christmas trees & other conifer plantations), non-crop vegetative management 

including roadsides, railroads and industrial sites

Terrestrial Plants. For non-target plants, exposures to sulfometuron methyl are considered most 

likely to occur as a result of spray drift and/or runoff from aerial and ground applications. Spray 

drift and runoff are important factors in characterizing the risk of sulfometuron methyl to nontarget plants, which is assumed to reach off-site areas. Two different models were used to 

evaluate impacts on terrestrial plants:

1. TerrPlant, which focuses more on selection of the environmental setting for exposure and 

the combined contributions from runoff and spray drift; and

2. AgDRIFT, which focused on evaluation of the effects of different application procedures 

on spray drift; only environmental concentrations from spray drift are measured.

AgDRIFT is designed to provide quantification of spray drift amounts at distances of less 

than 1000 feet from the treatment area.

The TerrPlant model (Ver.1.2.2) predicts EECs for terrestrial plants located in dry and semiaquatic areas adjacent to the treated areas. The EECs are based on the application rate, solubility 

of the pesticide in water and drift characteristics, which depend on application method. Different 

loading ratios are used for runoff to dry and semi-aquatic areas. For dry areas, pesticide runoff 

exposure is estimated as sheet runoff. In the model, sheet runoff is defined as the amount of 

pesticide in water that runs off of the soil surface of a treated field which is equal in size to the 

non-target area (1:1 ratio of areas). For semi-aquatic areas, runoff exposure is estimated as 

channelized runoff. In the model, channelized runoff is the amount of pesticide that runs off of a 

treated field 10 times the size of the area adjacent to the treated field (10:1 ratio of areas).

According to the TerrPlant model, the amount of sulfometuron methyl that runs off is a 

proportion of the application rate and is assumed to be 5% based on a solubility of >100 mg/L

for sulfometuron methyl in water (pH 7 or above). Drift from aerial applications is assumed to 

be 5% of the application rate, whereas drift from ground spray applications is assumed to be 1%

(this differs from AgDRIFT, for which spray drift is not predefined). Predicted terrestrial plant 
55

EECs (expressed as a fraction of the application rate) following single, aerial and ground spray 

application at the maximum application rate of sulfometuron methyl are summarized in Table 18.

Details on inputs and outputs from the TerrPlant model are provided in “APPENDIX D: 

Terrplant Spreadsheet”.

Table 18. EECs for Terrestrial Plants Located Adjacent to Sulfometuron Methyl 

(aerial and ground spray application) Treated Sites.

Terrestrial Use

Application 

Method

(Non-granular)

EEC (lbs ai/A)

Total Loading to 

Dry Areas Adjacent 

to Treated Areas2

Total Loading to SemiAquatic Areas Adjacent 

to Treated Areas3

Drift to 

Adjacent Areas4

Vegetative 

management1

(1 x 0.375 lb ai/A)

Aerial 0.038 0.21 0.019

Ground 

(unincorporated) 0.023 0.19 0.0038

1 Includes uses on unimproved turf, forestry (Christmas trees & other conifer plantations), non-crop vegetative management 

including roadsides, railroads and industrial sites

2 EEC = Sheet Runoff + Drift (5% for aerial or 1% for ground) assuming 1:1 runoff loading ratio 3 EEC = Channelized Runoff + Drift (5% for aerial or 1% for ground) assuming 10:1 runoff loading ratio

4 EEC for aerial (appl. rate x 5% drift) or ground application (appl. rate x 1% drift)

Because sulfometuron methyl is an herbicide, a more in-depth spray drift exposure assessment 

utilizing Tier I and II5

TABLE 20

AgDRIFT® (version 2.01) modeling is also provided to better 

characterize potential exposure of terrestrial plants. AgDRIFT® utilizes empirical data to 

estimate off-site deposition of aerial and ground applied pesticides, and acts as a tool for 

evaluating the potential of buffer zones to protect sensitive habitats from undesired exposures. 

contains EECs at several distances from the edge of the field.

A total of four different application scenarios were modeled (Columns labeled [A] through [D]) 

to illustrate predicted spray deposition of sulfometuron at various distances from the edge of the 

field under:

1. what may be characterized as typical applications that mostly follow best management 

practices (that are recommended on the sulfometuron label) – columns A and C. 

2. Reasonable worst case assumptions following use scenarios that are not necessarily 

typical or recommended, but are plausible and permitted on the label. See columns B and 

D. 

For ground applications, there is only a “Tier 1” module in AgDRIFT, but there are some input 

options still available to vary. For this assessment, only the boom height was varied between the 

 5 Note that the AgDRIFT Tier I and II terminology should not be confused with the Tier 1 and 2 

used for most other EFED models. In AgDRIFT, Tier I refers to an operating mode with more limited 

options and Tier II refers to a mode where there is much more user access to selection of model inputs. 

Unlike with most EFED models, a Tier I AgDRIFT assessment should not be presumed to represent more 

conservative (higher exposure) scenarios than those represented in a Tier II AgDRIFT assessment.
56

ground spray scenario [A] (0.51 meter height) and the scenario [C] (1.27 m height). Other key 

assumptions in the ground application spray drift modeling include:

1. Drop Size Distribution: ASAE very fine to fine classification (ASAE is now ASABE: the 

American Society of Agricultural and Biological Engineers)

2. Number of swaths = 20

3. Swath Width = 45 feet 

4. Application Efficiency (20 rows): 97.96 %

5. Use of the 90 %ile upper bound numbers from the empirical data set which is the basis of 

AgDRIFT spray drift estimates.

Aerial applications were simulated with the AgDRIFT tier 2 module, which allowed 

incorporation of some the best management practices to minimize spray drift recommended (but 

not mandated) on product labels. The more high-end exposure use condition assumptions for 

aerial applications in scenario [B] are given in Table 19. Factors varied for the more typical-use 

scenario [D] with some best-management practices include:

1. Wind speed of 10 mph

2. ASAE droplet size of fine to medium

3. Temperature = 86 deg F

4. Relative Humidity = 75 percent

5. Boom Height = 10 feet

The model results demonstrate a several fold to 30-fold difference in the percentage and amount 

of sulfometuron deposited off-site (the percentage difference between estimates with each 

scenario increases with increasing distance from the targeted field); see TABLE 20 and TABLE 

21.

Table 19. Selected AgDRIFT inputs for high-end exposure from aerial 

applications of sulfometuron methyl using best management practices.

 

Input type Input value Justification

Aircraft Air Tractor AT-401 Commonly used aircraft. Typical size and weight. Aircraft type 

does not greatly affect drift.

Boom length 76.3% of wingspan Recommended to reduce drift and increase application efficiency. 

Greater boom lengths generate more drift. 3/4 wingspan should 

be specified on the label.

Release (boom) 

height 

15 ft. Estimated upper bound under normal conditions. Should be 

specified on labels with no-spray zones.

Flight lines 20 Approximate standard scenario field size.
57

Swath width 60 ft. Typical. Does not greatly affect drift.

Swath displacement 

fraction (as a 

fraction of the 

swath width)

fine: 0.6833 Swath offset is good application practice. The value used results 

in 50% deposition at the edge of the field. 

Drop size 

Distribution

Fine (ASAE 

definition)

Dependent upon product. 

Spray material 50% water

50% nonvolatile

Dependent on tank mix. Calculate nonvolatile rate based on the 

portion of the tank mix which is not easily evaporated (e.g. the 

fraction that is not water or high vapor pressure solvent). 

Wind speed

(at 2 meters above 

the surface.

15 mph

Typical wind speed varies greatly with geographic region and 

other factors. Ten mph is an adequate, high drift, input for many 

areas. Model runs for the plains states may require higher wind 

speeds. Wind speed limitations should be specified on the label.

Humidity 50% Conservative input adequate for much of the US. Extreme values 

may significantly affect drift levels under certain conditions. 

Temperature 86 degrees F Conservative input adequate for much of the US. Extreme values 

may significantly affect drift levels under certain conditions. 

TABLE 20. ESTIMATED PERCENTAGE OF SULFOMETURON METHYL 

SPRAY DRIFT FROM GROUND OR AERIAL APPLICATIONS AT VARIOUS 

DISTANCES FROM A TREATED FIELD.

DISTANCE 

DOWN 

WIND 

(FEET)

[A] GROUND 

APPLICATION 

(LOW BOOM)

[B] GROUND 

APPLICATION 

(HIGH BOOM)

[C] AERIAL 

(FOLLOWING MANY 

LABEL 

RECOMMENDATIONS)

[D] AERIAL 

(HIGH-END 

EXPOSURE 

SCENARIO)

Percent Percent Percent Percent

0 102.0 106.0 50.00 77.35

50 1.77 5.00 17.12 38.32

100 0.95 2.48 9.79 25.11

200 0.51 1.20 4.69 14.07

500 0.21 0.39 1.92 5.40

750 0.13 0.22 1.39 3.82

900 0.11 0.17 1.24 3.32
58

TABLE 21. ESTIMATED AMOUNT OF SULFOMETURON METHYL SPRAY DRIFT 

FROM GROUND OR AERIAL APPLICATIONS AT VARIOUS DISTANCES FROM A 

FIELD TREATED WITH THE MAXIMUM LABELED RATE OF 0.375 LB AI/A. 

 

DISTANCE 

DOWN 

WIND 

(FEET)

[A] GROUND 

APPLICATION 

(LOW BOOM)

[B] GROUND 

APPLICATION 

(HIGH BOOM)

[C] AERIAL (FOLLOWING 

MANY LABEL 

RECOMMENDATIONS)

[D] AERIAL 

(HIGH-END 

EXPOSURE 

SCENARIO)

Lbs ai/A Lbs ai/A Lbs ai/A Lbs ai/A

0 0.3822 0.3956 0.1874 0.2900

50 0.0066 0.0187 0.0642 0.1437

100 0.0036 0.0093 0.0367 0.0941

200 0.0019 0.0045 0.0176 0.0527

500 0.0008 0.0015 0.0072 0.0203

750 0.0005 0.0008 0.0052 0.0143

900 0.0004 0.0006 0.0046 0.0125

The AgDRIFT results illustrate the importance of droplet size in controlling spray drift. Using 

larger droplet sizes, such as coarse or extremely coarse spraying, reduces the downwind drift to 

adjacent areas compared to when medium or fine spraying is used. Reducing boom height during 

application and applying when wind speeds are between 3 and 10 mph are also important in 

controlling drift.

3.2.3.2. Residue Studies

Environmental residue studies can also provide useful information regarding the potential 

exposure of terrestrial wildlife receptors. This data can be used to corroborate modeling results 

or to provide additional insights into chemical fate with respect to exposure. For sulfometuron 

methyl, no studies are available; all estimates of exposure are based on modeling efforts

3.2.4. Uncertainties and Limitations for this Exposure 

Assessment

3.2.4.1. Limitations In Knowledge Of Actual Use Patterns

Knowledge on the specific regions of use of sulfometuron methyl is limited. The use pattern of 

sulfometuron methyl does not lend itself to easy characterization geographically: There are a 

variety of vegetation management uses on sites that are less clearly defined than agricultural 
59

crops and have disjoint or unusual treatment area configurations (e.g., as with rights of way and 

railroad uses, or industrial site grounds).

Practical limits on usage rates long-term at particular sites may different from legally allowable 

use levels (e.g., usage is highly unlikely to occur every year at a particular site even though this 

is allowable under the label language).

3.2.4.2. Variability In Sulfometuron Environmental Persistence

Sulfometuron methyl persistence is significantly affected by soil or water chemistry and may not 

always easy to predict from typically available soil / water property data alone. A clearer picture 

of the range of variability in sulfometuron methyl 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.

3.2.4.3. Exposure To Sulfometuron Methyl Degradates

Limitations in environmental fate data for the degradates made specific modeling for exposure to 

each of the degradates very problematic. The data on individual degradates, environmental 

persistence and mobility is insufficient to model each compound separately. This may not 

provide realistic estimates with the PRZM / EXAMS models which utilize a receiving pond with 

no turnover or outflow of residues. If any of the degradation products of sulfometuron methyl 

should be found to be of toxicological concern at potential environmental exposure levels, than 

additional data and exposure assessment specific to the degradates of concern would be needed.

3.3. ECOLOGICAL EFFECTS CHARACTERIZATION

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

the types of effects a pesticide can potentially produce in an animal or plant. The toxicity data 

used in the effects characterization for sulfometuron methyl are derived primarily from 

registrant-submitted toxicity studies that are conducted (and reviewed) according to OPP test 

guidelines. These “guideline” studies are also supplemented by data reported in the USEPA 

ECOTOX database that have met Agency criteria for acceptability. 

Toxicity testing reported in this section does not include all species potentially affected by 

sulfometuron methyl usage. Only a few surrogate species for fish, aquatic invertebrates and 

birds are used to represent all species in the United States. For mammals, effects are typically 

extrapolated from laboratory rat studies. Also, neither reptiles nor amphibians are tested, 

although data from reptiles and amphibians may be available from the literature as reported in 

ECOTOX. In absence of such data, the risk assessment assumes that avian and reptilian and 

terrestrial-phase amphibian sensitivities to the chemical are similar. A similar assumption is 

made for fish as surrogates for aquatic-phase amphibians. Terrestrial plant data are derived from 

the vegetative vigor and seedling emergence tests, typically conducted on 10 agricultural crop

species, and do not account for potential chronic or reproductive effects. Lack of plant 
60

reproduction data is particularly relevant to sulfometuron methyl because some data suggest 

plant reproduction may be more sensitive to sulfonylurea herbicide exposure compared to growth 

and endpoints measured in the seedling emergence and vegetative vigor tests (Fletcher et al, 

1993). For aquatic plants, five aquatic plant species (1 vascular, 4 nonvascular) are used to 

represent potential toxicity to all aquatic plant species.

Most of the studies with non-target organisms were conducted with sulfometuron methyl 

technical (i.e., > 90% purity). These studies provide the effects basis for risk estimation. 

Registrant-submitted studies of the acute, oral toxicity of end use product (Oust®) were available 

only for rats. Other toxicity studies of end- use product were obtained from ECOTOX for 

selected aquatic invertebrates and terrestrial plants. Details of each of the guideline and 

literature studies of sulfometuron methyl effects on non-target organisms are provided in 

“APPENDIX H: Ecological Effects Data Summaries.”

Toxicological information on the primary degradates of sulfometuron methyl (e.g., pyrimidine 

amine, pyrimidine-ol, saccharin, sulfonamide) appears very limited. Specifically, no guideline 

toxicity studies with ecologically relevant endpoints (e.g., growth, reproduction, development, 

survival) were identified for the primary degradates of sulfometuron methyl. Based on literature 

searches conducted with ECOTOX, toxicological studies were identified only for one major 

degradate (saccharin). Of the nine saccharin studies identified in ECOTOX, all were considered 

inapplicable to the ecological risk assessment because they lack evaluation of saccharin effects 

using ecologically relevant endpoints (e.g., survival, growth, reproduction, development). This 

finding is not surprising given the role of saccharin as a sugar substitute and the corresponding 

toxicological focus on measures of effect that pertain to human health (e.g., biochemical, organlevel, mutagenicity and carcinogenicity assays). A summary of the ecological toxicity studies 

involving the saccharin metabolite of sulfometuron methyl is provided in “APPENDIX H: 

Ecological Effects Data Summaries.” Appendix J contains the results of the ECOTOX literature 

search with respect to those studies found to be acceptable to ECOTOX but not OPP for the 

purposes of this risk assessment.

Table 22 contains a summary of the most sensitive ecological effects endpoints used in this risk 

assessment. As expected, the acute toxicity of sulfometuron methyl to animals is very low 

(slightly to practically non-toxic) while its toxicity to plants is very high. This finding is 

consistent with the mode of action of sulfometuron methyl (inhibition of ALS) and is similar to 

toxicity findings from other sulfonylurea herbicides. 
61

Table 22. The Most Sensitive Endpoints Used In The Sulfometuron Methyl 

Screening-Level Risk Estimation.

Environment Taxa Type of 

Risk

Type of 

Endpoint Endpoint Units MRID

Aquatic

Freshwater 

Fish Acute LC50 > 148 mg ai/L 435018-02

Chronic NOAEC Data gap (A)

Freshwater 

Invertebrates Acute EC50 > 150 mg ai/L 435018-03

Chronic NOAEC 97 mg ai/L 416728-06(A)

Saltwater Fish Acute LC50 > 45 mg ai/L 416728-03

Saltwater 

Invertebrates Acute EC50 > 38.2 mg ai/L 416728-04

Plants Non-Listed EC50 0.48 μg ai/L 435385-03

Listed NOAEC 0.21 μg ai/L 435385-03

Terrestrial Avian Acute LD50 > 4650 mg ai/kg-bw 245375

Acute LC50 > 4600 mg ai/kg-diet 00071414

Mammalian Acute LD50 > 5000 mg ai/kg-bw 430892-01

Chronic NOAEC > 300 mg ai/kg-bw/d 78798

Plants Non-Listed EC25 1.8 x 10-5 lb ai/A 435385-01(A)

Listed EC5

(B) 9.9 x 10-7 lb ai/A 435385-01(A)

(A)

Toxicity value was revised after a re-review and analysis of the study results in 2007.

(B) 

EC5 was used for estimating effects to listed (endangered) terrestrial plants because the NOAEC equaled or exceeded the EC25, as discussed 

in the terrestrial effect characterization section.

3.3.1. Aquatic Effects Characterization 

3.3.1.1. Freshwater Fish, Acute

Acute toxicity studies with the technical grade active ingredient (TGAI) were required for two 

freshwater fish species for sulfometuron methyl. Preferred test species are bluegill sunfish 

(warm water fish) and rainbow trout (cold water fish). Based on results from preliminary range 

finding tests, definitive toxicity tests were not required for bluegill or rainbow trout (i.e., LC50

>200 mg ai/L). Therefore, toxicity ‘limit’ tests were conducted at a single test concentration of 

150 mg ai/L (bluegill, MRID 435018-01; rainbow trout, 435018-02). 

Results from these studies are summarized in Table 23 and indicate that sulfometuron methyl is 

practically non-toxic to freshwater fish on an acute toxicity basis. No mortality was reported in 

the test concentration of 150 mg ai/L (nominal) and measured concentrations were within 80-

120% of nominal concentrations in both tests. To prevent formation of insoluble precipitate, the 

pH of test solutions were buffered w/ addition of sodium hydroxide, which resulted in pH values 

that exceeded guideline recommendations (up to pH 9.0). The authors report no formation of 

precipitate or solubility problems in test solutions and no mortality in pH buffered controls. The 
62

pH range deviation is therefore considered a necessary byproduct of increasing the solubility of 

the test chemical. All other test guideline deviations are considered minor. These studies are 

classified as acceptable and meet the guideline requirements for an acute toxicity study with 

warm water and cold water fish. 

Table 23. Freshwater Fish Acute Toxicity of Sulfometuron Methyl.

Guideline Species % ai

96-hour

LC50

(mg/L) 

Toxicity 

Category

MRID No.

Author/Year

Study 

Classification

72-1 Bluegill sunfish 

(Lepomis macrochirus) 99.6 > 150

Practically

non-toxic

435018-01

Brown (1994a) Acceptable

72-1 Rainbow trout

(Oncorhynchus mykiss) 99.6 > 148

Practically

non-toxic

435018-02

Brown (1994b) Acceptable

3.3.1.2. Freshwater Invertebrates, Acute

The toxicity of sulfometuron methyl to freshwater invertebrates is indicated by a 48-hr acute 

toxicity test with the water flea, Daphnia magna (MRID 435018-03; Table 24. As observed 

with freshwater fish, no mortality was observed in a range finding test up to 200 mg ai/L or the 

follow-up toxicity limit test at 150 mg ai/L. Buffering of test solutions was required to prevent 

formation of precipitates which resulted in a greater pH range (8.4-9.0) than recommended (7.2-

7.6). No mortality was observed in the 150 mg/L treatment or in the negative control. One 

daphnid died in the pH adjusted control (mortality 3%). The test concentration was measured 

and found to be 100% of nominal. The pH range deviation is therefore considered a necessary 

byproduct of increasing the solubility of the test chemical. This study was originally classified 

as ‘supplemental’ by EFED in 1995 because of concerns over chemical composition of the 

dilution water. A re-review of this study in conjunction with other data on the dilution water 

from a separate study with the same lab indicates that it is acceptable. A detailed study review 

and explanation of the study reclassification are provided in “APPENDIX H: Ecological Effects 

Data Summaries.”

Table 24. Freshwater Invertebrate Acute Toxicity of Sulfometuron Methyl.

Guideline Species % ai

48-hour

LC50

(mg/L) 

Toxicity 

Category

MRID No.

Author/Year

Study 

Classification

72-2 Water flea

(Daphnia magna) 99.6 > 150

Practically

Non-toxic

435018-03

Brown (1994c) Acceptable(1)

(1) reclassified as acceptable for this risk assessment, see APPENDIX H: Ecological Effects Data Summaries for details.

3.3.1.3. Estuarine and marine Fish, Acute

The toxicity of sulfometuron methyl to estuarine and marine fish is indicated by a 96-hr acute 

toxicity test with the sheepshead minnow, Cyprinodon variegatus conducted at nominal 
63

concentrations ranging from 15 to 100 mg ai/L (MRID 416728-03, Table 25. The LC50 based on 

measured concentrations from this study was found to be greater than 45 mg ai/L. No mortality 

or observable signs of sublethal effects occurred in the study except for one dead fish (5%) at 8.2 

mg/L (measured). 

This study was re-reviewed for this risk assessment and found to contain several significant 

deficiencies which render its classification as supplemental. Specifically, measured 

concentrations ranged widely from test initiation to termination (4 to 7 times), which is believed 

due to the formation of an observable precipitate in test solutions. This occurred despite 

buffering of the dilution water to an initial pH of 8.5 (pH ranged thereafter from 7.4 to 8.5). 

Although these deficiencies could render the study classification as “unacceptable,” it is 

considered to provide some useful information in this risk assessment (i.e., an indication of a 

lack of toxicity at or near solubility limits in test solutions). Furthermore, when viewed in the 

context of screening level EECs (i.e., a maximum peak concentration of 0.031 ppm in water, 

Table 15), the bioavailable (dissolved) portion sulfometuron methyl would have to be 

approximately 1500-fold lower than the highest measured test concentration (~45 ppm) in order 

for risks to be evident. Therefore, this study is classified as supplemental but is not 

recommended for repeat testing at this time because a repeat test would be highly unlikely to 

alter the risk assessment conclusions.

Table 25. Estuarine/Marine Fish Acute Toxicity of Sulfometuron Methyl.

Guideline Species % ai

96-hour

LC50

(mg/L) 

Toxicity 

Category

MRID No.

Author/Year

Study 

Classification

72-3 Sheepshead minnow

(Cyprinodon variegatus) 99.1 > 45

> Slightly

toxic

416728-03

Ward and Boeri (1990a) Supplemental(1)

(1) Reclassified as supplemental for the purposes of this risk assessment. See APPENDIX H: Ecological Effects Data 

Summaries for additional study details.

3.3.1.4. Estuarine and marine Invertebrates, Acute

The toxicity of sulfometuron methyl to estuarine and marine invertebrates is indicated by acute 

toxicity tests with mysid shrimp, Mysidopsis bahia, and embryo/larvae of the eastern oyster, 

Crassostrea virginica. For mysids, a 96-h assay was conducted at nominal concentrations 

ranging from 15 to 100 mg/L. The 96-h LC50 based on measured concentrations from this study 

was found to be greater than 44.8 mg ai/L. No mortality or observable signs of sublethal effects 

occurred in the study at any test concentration or the control. For oysters, a 48-h assay was 

conducted on embryos at the same nominal concentrations as used for mysids. The 48-h EC50

based on measured concentrations for this study was found to be greater than 38.2 mg ai/L. No 

mortality occurred and 99% of the surviving control oysters were normal. 

A re-review of both the mysid and oyster studies indicates they have several significant 

deficiencies which render their classification as supplemental. Specifically, measured 

concentrations of sulfometuron methyl ranged widely from test initiation to termination (3X to 

13X in the mysid tests; 3X in the oyster test) and were substantially below nominal 

concentrations. The low % nominal is believed due to the formation of an observable precipitate 
64

in test solutions. In the mysid test, low % nominal occurred despite buffering of the dilution 

water to an initial pH of 8.5 (pH ranged thereafter from 7.6 to 8.5). In the oyster test, pH ranged 

from 7.7 to 8.0. The pH range in both the mysid and oyster tests extended beyond the 

recommended range for test guidelines (7.7-8.0 for euryhaline shrimp; 8.0-8.3 for stenohaline 

oysters).

Although these deficiencies could render both study classifications as “unacceptable,” they are

considered to provide some useful information in this risk assessment (i.e., an indication of a 

lack of toxicity at or near solubility limits in test solutions). Furthermore, when viewed in the 

context of screening level EECs (i.e., a maximum peak concentration of 0.031 ppm in water, 

Table 15), the bioavailable (dissolved) portion sulfometuron methyl would have to be 

approximately 1300-fold lower than the highest measured test concentration (~ 40 ppm) in order 

for risks to be evident. Therefore, this study is classified as supplemental but is not 

recommended for repeat testing at this time because a repeated test would not likely affect the 

risk assessment conclusions.

Table 26. Freshwater Invertebrate Acute Toxicity of Sulfometuron Methyl.

Guideline Species % ai

96-hour

LC50 or 

48-h EC50

(mg/L) 

Toxicity 

Category

MRID No.

Author/Year

Study 

Classification

72-3 Mysid shrimp(1)

(Mysidopsis bahia) 99.1 > 44.8

> Slightly 

toxic

416728-04

Ward and Boeri (1990c) Supplemental (2)

72-3 Eastern oyster(1)

(Crassostrea virginica) 99.1 > 38.2

> Slightly 

toxic

416728-05

Ward and Boeri (1990b) Supplemental(2)

(1) 96-h LC50 applies to mysids; 48-h EC50 applies to oyster.

(2) Reclassified as supplemental for the purposes of this risk assessment. See APPENDIX H: Ecological Effects Data 

Summaries for additional study details.

3.3.1.5. Freshwater Fish, Chronic

No acceptable or supplemental data on the chronic toxicity of sulfometuron methyl to freshwater 

fish were available. A chronic, early life-stage toxicity test was conducted in 1982 to determine 

the effect of sulfometuron methyl on fathead minnow embryo hatching, larval survival, and 

growth (MRID 423857-04; Accession No. 249796), however upon further review, this study was 

classified as unacceptable. 

3.3.1.6. Freshwater Invertebrate, Chronic

The chronic toxicity of sulfometuron methyl to freshwater invertebrates is indicated by a 21-day 

life cycle test conducted on the water flea, Daphnia magna (MRID 416728-06; Table 27). 

Daphnids (<24-h old) were exposed to six concentrations of sulfometuron methyl ranging from 

0.1 to 100 mg/L (nominal) in a static-renewal system. In order to promote solubility of the test 

substance, the pH of the stock solutions of the 25 mg/L and 100 mg/L treatments were adjusted 

with NaOH to pH 8.5. Both a negative and pH-adjusted controls were included. Mean measured 
65

concentrations were close to nominal concentrations (i.e., within 20%), thus indicating that 

variability in test concentrations was well within the acceptable limits of 1.5X. Survival and 

growth (length) were not affected at any test concentration. Reproduction, as measured by the 

number of neonates produced/daphnid, was not significantly different from negative controls in 

any treatment (ANOVA, 0.05). Although the Dunnett’s multiple comparison test indicated a 

marginally significant difference in the 24 mg/L treatment (mean measured concentration), it is 

not considered statistically valid to apply means testing when ANOVA results indicate lack of 

significant differences among treatments. Furthermore, an inconsistent concentration-response 

relationship is indicated by the lack of a significant reduction in daphnid reproduction at 97 mg/L 

(the highest treatment tested). Therefore, the NOAEC for daphnid reproduction is re-interpreted 

as 97 mg/L (unbounded) and the LOAEC is > 97 mg/L. This study is classified as acceptable 

and meets the guideline requirements for a chronic study using a freshwater invertebrate. 

Table 27. Freshwater Aquatic Invertebrate Chronic Toxicity for Sulfometuron 

Methyl.

Species/

Static Renewal % ai

21-day NOAEC / 

LOAEC (mg/L)(1) Endpoints Affected MRID No.

Author (Year)

Study 

Classification

Water flea

(Daphnia magna) 99.1 97 / >97 Reproduction 416728-06Baer (1990) Acceptable

(1) NOAEC and LOAEC were re-analyzed as part of this risk assessment. See Appendix H for additional study details.

3.3.1.7. Aquatic Animal Sublethal Effects: Formulated Product 

and Degradate Toxicity 

No signs of toxicity or sublethal effects were observed in the acute or chronic toxicity tests of 

sulfometuron methyl that were described previously in this Exposure Characterization

(considering acceptable and supplemental studies). This is not surprising, given that 

sulfometuron methyl is practically nontoxic on an acute toxicity basis. 

Two studies of the toxicity of sulfometuron methyl in formulated product (e.g., Oust®) to aquatic 

animals were identified and discussed further below. The first study, Naqvi and Hawkins (1989) 

exposed four genera of field-collected microcrustaceans (Diaptomus sp. Eucyclops sp., Alonella 

sp., and Cypria sp.) to sulfometuron methyl from the Oust® formulated product at nominal 

concentrations of ranging from 100 to 2500 mg/L for 48-h. Consistent, monotonic exposureresponse relationships across the six treatments occurred for all four species and 48-h LC50s 

(probit analysis) were reported as follows: 

Species Test 

Chemical

48-h LC50 (mg/L) 

(95% confidence 

limits)

Classification Reference

Diaptomus sp.

Oust®

(~93% ai)

1315 (1207-1524) supplemental Naqvi and Hawkins 

(1989)

Eucyclops sp. 1320 (1154-1536)

Alonella sp. 802 (475-928)

Cypria sp 2241 (1744-4517)
66

This study is classified as supplemental primarily because test concentrations were not measured 

in the study and the field collected test organisms were provided a relatively short application 

period (96-h) vs. the 7-d minimum acclimation period recommend for freshwater invertebrate 

testing. Furthermore, organisms were not positively identified to the species level, thus 

indicating that more than one test species may have been tested in each study. Finally, the study 

authors do not indicate whether nominal concentrations were adjusted to reflect the percent 

active ingredient in the formulated product. Assessment of the relative acute toxicity of 

sulfometuron methyl as technical grade and in formulated to aquatic animals is somewhat 

uncertain because LC50 and EC50 values were not achieved for the technical grade herbicide 

(e.g., EC50 and LC50 varied from >38 to >150 mg ai/L). However, results from the Naqvi and 

Hawkins (1989) study indicate that sulfometuron methyl formulated in Oust® is practically 

nontoxic to aquatic microcrustaceans. Thus, the comparative toxicity of technical grade 

sulfometuron methyl and sulfometuron methyl formulated at least appear similar in terms of both 

ingredients being practically nontoxic to aquatic invertebrates. 

The second study was submitted by the registrant (DuPont) per FIFRA Section 6(a)2 

requirements on July 1, 1991. In this study, Romaire (1984) evaluated the acute toxicity of 

Oust® (% ai not reported) to juvenile red swamp crayfish, Procambarus clarkii. A static, acute 

toxicity study was conducted for 96 hours in 4 replicate aquaria (5 crayfish/aquarium) at 8 test 

concentrations ranging from 0 to 10,000 mg ai/L. Analytical measurements of sulfometuron 

methyl were not taken during the study. The authors report that the 96-h LC50 was > 5,000 mg 

ai/L for sulfometuron methyl and mortality did not exceed 50% in any test treatment. However, 

review of this study indicates that it is unacceptable because dissolved oxygen levels dropped 

precipitously throughout the study in test concentrations where mortality was observed, despite 

periodic aeration of test solutions. Dissolved oxygen levels repeatedly reached levels as low as 

2.1 mg/L or approximately 25% saturation, which is well below ASTM recommendations of 

60% saturation. Because the effect of dissolved oxygen on crayfish mortality could not be 

separated from the possible effects of sulfometuron methyl, this study is not considered 

scientifically sound for the purposes of describing the acute toxicity of sulfometuron methyl to 

juvenile crayfish. 

Regarding the aquatic toxicity of sulfometuron methyl degradates to aquatic animals, a literature 

search conducted in May, 2007 of EPA’s ECOTOX database revealed no acceptable or 

supplemental studies that described the toxicity of major sulfometuron metabolites: pyrimidine 

amine, pyrimidine-ol, saccharin, and sulfonamide. A list of studies considered acceptable to 

ECOTOX but not OPP is provided in “APPENDIX J: Ecological Effects Studies Rejected by 

OPP.”

3.3.1.8. Field Studies

No field studies (e.g., mesocosm and microcosm studies) were found concerning the aquatic 

toxicity of sulfometuron methyl, either based on OPP guidelines or from the aforementioned 

search of the ECOTOX database. 
67

3.3.1.9. Aquatic Plants

Aquatic plant toxicity studies using the TGAI are required to establish the toxicity of 

sulfometuron methyl to non-target aquatic plants (Table 28). Studies in five species are required 

for herbicides: freshwater green alga (Selenastrum capricornutum), blue-green algae (Anabaena 

flos-aquae), a freshwater diatom (Navicula pelliculosa), a marine diatom (Skeletonema 

costatum), and duckweed (Lemna gibba). Of the four non-vascular species tested, the green alga 

is the most sensitive non-vascular aquatic plant. This finding is consistent with the toxicity of 

flazasulfuron, another sulfonylurea herbicide with the same mode of action (DP Barcodes: 

D302482, D302484; EFED New Chemical review dated 4/11/2007).

The EC50 (reduction in cell density) for S. capricornutum is 4.6 μg ai/L and the NOAEC is 0.63 

ug ai/L. At the LOAEL of 1.3 μg/L, growth was reduced approximately 20%, while the cell 

growth at the NOAEC showed a slight increase relative to controls. These toxicity values are 

based on reported nominal concentrations. Although the study authors indicate that samples 

were taken for analytical measurement and would be analyzed “if deemed necessary,” results 

from chemical analysis were not provided in the study report. At these concentrations, solubility 

of the test compound is not expected to be problematic. 

Preliminary tests with the two diatom species indicated that Tier II tests would not be necessary. 

Based on results from Tier 1 tests, growth (cell density) of neither diatom was affected 

significantly relative to controls at measured concentrations of 370 μg/L and 410 μg/L (i.e., the 

maximum values calculated for sulfometuron methyl applied directly to a 6 inch deep pond. 

Measurements at test initiation and termination indicate stability of sulfometuron methyl in the 

test solutions.

A tier 2 test was conducted on the freshwater blue-green algae, Anabaena flos-aquae, at 

measured test concentrations ranging from 14 to180 μg/L. Measurements at test initiation and 

termination indicate stability of sulfometuron methyl in the test solutions. An EC50 of 41.6 μg/L 

(cell density) is calculated for Anabaena and a NOAEC of <14 μg/L (lowest test concentration). 

This NOAEC corresponds to a 20% reduction in cell growth relative to controls. This study is 

considered scientifically sound but classified as supplemental because a NOAEL was not 

determined.

The 14-day EC50 and NOAEC for the freshwater vascular plant (duckweed) for frond count (the 

most sensitive endpoint tested) are 0.48 and 0.21 μg/L, respectively, based on exposure to 

measured concentrations ranging from 0.13 to 1.05 μg/L. Frond counts were reduced 4% at the 

NOAEC and 20% at the LOAEC. Measurements at test initiation and termination indicate 

stability of sulfometuron methyl in the test solutions. 

Except for the test with blue-green algae, the toxicity studies of aquatic plants (Table 28) are 

classified as acceptable and meet the guideline requirements for toxicity tests with aquatic 

vascular and nonvascular plants. Toxicity values for the most sensitive species (green algae and 

duckweed) will be used to calculate risk quotients.
68

Table 28. Non-target Aquatic Plant Toxicity for Sulfometuron Methyl.

Species % ai EC50/ NOAEC

(μg/L)

Endpoints 

Affected

MRID No.

Author (Year)

Study 

Classification

Vascular Species: Duckweed

Duckweed

(Lemna gibba) 95.7 0.48 / 0.21 Frond Counti 435385-03

Kannuck (1995) Acceptable

Non-Vascular Species: Algae and Diatoms

Green Algae (1)

(Selenastrum capricornutum) 99.1 4.6 / 0.63 Cell Density

416801-02

Hobert (1990) Acceptable

Blue-green Algae(1)

(A. flos-aquae) 99.2 41.6 / <14 Cell Density

435385-02

Thompson (1994) Supplemental

Fresh Water Diatom (2)

(Navicula pelliculosa) 99.2 >370 Cell Density

435385-02

Thompson (1994) Acceptable

Salt Water Diatom(2)

(Skeletonema costatum) 99.2 >410 Cell Density

435385-02

Thompson (1994) Acceptable

(1) Tier II definitive test

(2) Tier I screening test

3.3.2. Terrestrial Effects Characterization

3.3.2.1. Acute Effects on Birds 

An acute oral toxicity study using the technical grade of the active ingredient is required to 

establish the acute toxicity of sulfometuron methyl to birds. The preferred guideline test species 

is either mallard duck (a waterfowl) or bobwhite quail (an upland gamebird). An acute oral 

toxicity study with the mallard indicates sulfometuron methyl is practically non-toxic on an acute 

basis, with a reported oral LD50 >4,650 mg ai/kg-bw (Table 29). No mortality occurred in any 

treatment and birds appeared normal throughout the 14-d test period. Food consumption varied 

widely across treatments, but did not exhibit a dose-dependent trend. Weight gain/loss also did 

not exhibit a dose-dependent trend within or across sexes. Weight gain in females may have 

been confounded by induction of the egg laying cycle by the photoperiod used. Lack of acute 

oral toxicity to birds is consistent with testing results from other sulfonylurea herbicides (e.g., 

flazasulfuron, rimsulfuron). The guideline requirement (71-1) is fulfilled for an acute oral 

toxicity study with birds for sulfometuron methyl and the study (Accession No. 245375) is 

classified as acceptable. 
69

Table 29. Avian Acute Oral Toxicity for Sulfometuron Methyl.

Species % ai LD50

(mg ai/kg-bw)

Toxicity 

Category

Accession No.

Author (Year)

Study

Classification

Mallard duck

(Anas platyrhynchos) >93 >4,650 Practicallynon-toxic

245375

Dudeck and Bristol (1981) Acceptable

Two dietary studies are required to establish the subacute dietary toxicity of sulfometuron methyl 

to birds. The preferred test species are mallard duck and bobwhite quail. The submitted data 

indicates that sulfometuron methyl is practically nontoxic to mallard and quail when 

administered via subacute, dietary exposure. The 8-day acute dietary LC50 values for bobwhite 

quail and mallard are > 5,620 mg ai/kg-diet and > 4,600 mg ai/kg-diet, respectively (Table 30. 

There was no mortality, signs of clinical toxicity, or abnormal behavior reported in the studies. 

The guideline (71-2) is fulfilled for a subacute dietary study with birds. The studies (Accession 

No. 246409 and MRID 71414) are classified as acceptable. 

Table 30. Avian Subacute Dietary Studies for Sulfometuron Methyl.

Species % ai 8-Day LC50

(mg ai/kg-diet)

Toxicity 

Category

MRID No.

Author (Year)

Study 

Classification

Northern bobwhite quail

(Colinus virginianus) 95.2 >5,620 Practicallynon-toxic

246409 (1)

Beavers and Fink (1981) Acceptable

Mallard duck

(Anas platyrhynchos) 92 >4,600 Practicallynon-toxic

71414

Hazelton Laboratories Inc 

(1980)

Acceptable

(1) Accession number.

3.3.2.2. Acute Effects on Mammals

Wild mammal testing is required by the Agency on a case-by-case basis, depending on the 

results of lower tier laboratory mammalian studies, intended use pattern and pertinent 

environmental fate characteristics. In most cases, rat or mouse toxicity values obtained from the 

Agency's Health Effects Division (HED) substitute for wild mammal testing. For sulfometuron 

methyl, the acute toxicity of sulfometuron methyl (technical grade active ingredient) is indicated 

by an acute, oral toxicity study with the rat (MRID 43089201; Table 31. In this study, 5 male 

and 5 female rats were administered a single oral dose of 5000 mg ai/kg-bw technical grade 

sulfometuron methyl (approx. 100% a.i.) in corn oil via gavage. Rats were observed for 

mortality, signs of ill health, pharmacologic and toxicological effects for 14 days after dosing. 

No mortality occurred at 5,000 mg ai/kg-bw and no clinical signs of toxicity were observed that 

were related to sulfometuron methyl exposure. Male and females continued to gain weight 

throughout the study. An acute, oral LD50 value of >5000 mg ai/kg-bw was determined from 

this study, indicating that sulfometuron methyl is categorized as practically non-toxic (toxicity 

category IV) to small mammals on an acute oral basis. This finding is consistent with lack of 

acute oral toxicity observed with other sulfonylurea herbicides to rats (e.g., flazasulfuron). This 

study is considered acceptable and satisfies the guideline requirement (81-1) for an acute toxicity 

study with mammals.
70

Table 31. Mammalian Acute Toxicity for Sulfometuron Methyl.

Species % ai Toxicity Affected Endpoints MRID No.

Author (Year)

Toxicity 

Category

Rat

(Sprague-Dawley) ~100 LD50 > 5,000 mg ai/kg bw (males/females)

Survival, weight gain, gross 

organ pathology

43089201

Dashiell and Sarver 

(1990)

IV

3.3.2.3. Acute Effects on Terrestrial-phase Amphibians, Reptiles 

and Beneficial Insects

A honeybee acute contact study is required for sulfometuron methyl because its post-emergence 

treatment use will likely result in honeybee exposure. The acute contact LD50, using the honey 

bee, Apis mellifera, is a single-dose laboratory study designed to estimate the quantity of toxicant 

required to cause 50% mortality in a test population of bees. For sulfometuron methyl, bees 

were exposed at 5 treatments ranging from 13 to 100 μg ai/bee and included a solvent and 

negative control (MRID 416728-10; Table 32). Results indicate that sulfometuron methyl is 

practically non-toxic to bees on an acute contact basis. The contact 48-h LD50 for sulfometuron 

methyl is >100 μg ai/bee. Cumulative mortality and immobility ranged from 4-8% in the 

controls to 0-2% in the treatments. No overt signs of toxicity were observed in the study. The 

guideline (141-1) is fulfilled (MRID 416728-10).

Table 32. Non-Target Insects - Acute Contact Toxicity for Sulfometuron Methyl.

Species % ai LD50

(μg ai/bee)

Toxicity 

Category

MRID No.

Author (Year)

Study 

Classification

Honey Bee

(Apis mellifera) ~100 >100 (contact) Practicallynon-toxic

416728-10

Hoxter and Smith (1990) Acceptable

No acceptable or supplemental terrestrial-phase amphibian or reptile toxicity studies were 

submitted or located in the open literature based on a search of the ECOTOX database.

3.3.2.4. Chronic Effects on Birds

Avian reproduction studies using the TGAI are required for pesticide registration if birds may be 

subject to repeated or continuous exposure to the pesticide, especially preceding or during the 

breeding season. The preferred test species are mallard duck and bobwhite quail. No data (71-4 

guideline or literature studies) were available on the reproductive toxicity of sulfometuron 

methyl to birds.
71

3.3.2.5. Mammals, Reproductive Effects

A combined 2-generation reproduction/oncogenicity study and 2-year chronic reproduction study 

with rats exposed to sulfometuron methyl was submitted to the agency (MRID 423857-05 and 

423857-06). However, study authors had to abandon the study on about day 200 due to disease 

of the test organisms that was not related to exposure and the study was classified as 

unacceptable by HED. The developmental toxicity study with rat (MRID 00078796) was also 

classified as unacceptable by HED. Since no acceptable mammalian reproduction or 

developmental toxicity study was available with the rat for sulfometuron methyl, the 

developmental toxicity study with the rabbit (Accession No. 78798) was used in this risk 

assessment (Table 33). 

In this study, rabbits were administered doses of 0, 30, 100, or 300 mg/kg/day from gestation 

days (GD) 6-18 and examined at GD 29. There were no mortalities and no treatment-related 

clinical signs or macroscopic findings. A slight decrease in maternal body weight occurred 

during the gestation period (GD 6-18) but this was judged biologically insignificant. There were 

no treatment related effects on fetal or maternal endpoints measured, including external, visceral 

or skeletal malformations, frequency of resorptions, live fetuses, or dead fetuses, or on the 

number of litters, sex ratio, or post-implantation loss. The developmental LOAEL was not 

observed. The developmental NOAEL is 300 mg/kg/day (highest dose tested). According to 

the data evaluation record provided by HED, this study is acceptable but does not fulfill the 

guideline requirement for a developmental toxicity study with rabbits because dose levels were 

not considered high enough to adequately assess developmental toxicity.

Table 33. Mammalian Developmental Toxicity of Sulfometuron Methyl .

Species % ai Test

Type Toxicity1 Affected Endpoints

Accession No.

Author (year) 

Rabbit

(New 

Zealand 

White)

100 Developmental NOAEL = 300 mg ai/kg/day (highest test dose)

LOAEL > 300 mg ai/kg/day None 78798

Serota (1981)

3.3.2.6. Terrestrial Animal Sublethal Effects, Formulated Product 

and Degradation Products 

No sublethal effects were reported in either the avian dose or dietary acute toxicity studies for 

birds. However, data on the chronic toxicity of sulfometuron methyl to birds (and therefore, data 

on other potential sublethal effects) were not available. For mammals, no clinical signs of 

toxicity or abnormal behavior were noted in the acute toxicity study (MRID 43089201). No 

acceptable data on the chronic toxicity of sulfometuron methyl to mammals were available. 

Therefore, other potential sublethal effects resulting from chronic exposure could not be 

evaluated. Based on the developmental toxicity study of sulfometuron methyl to rabbits, no 

signs of sublethal toxicity were evident (Accession No. 78798).
72

Formulated pesticide products may contain a number of other ‘inert’ ingredients that alter their

toxicity compared to the technical grade active ingredient (e.g., resulting in greater toxicity). For 

sulfometuron methyl, data on the oral toxicity of formulated products were available for one 

species of terrestrial animal (rat; Table 34). Results from this study indicate that the formulated 

product DPX-T5486-87 is practically nontoxic to laboratory rats, with a LD50 of >5,000 mg 

ai/kg-bw. No clinical signs of toxicity, weight loss or gross legions were observed in this study. 

This study satisfied guideline requirements for acute oral toxicity with rats and is considered 

acceptable.

Table 34. Mammalian Acute Toxicity to Sulfometuron Methyl in Formulated 

Product: DPX-T5486-87

Species % ai Toxicity Affected Endpoints MRID No. Toxicity 

Category

Rat

(Sprague-Dawley) 74% LD50 > 5,000 mg ai/kg bw (males/females)

Survival, weight gain, gross 

organ pathology 44874103 IV

Except for saccharin, no toxicity information was available on the other major degradation 

products of sulfometuron methyl (e.g., pyrimidine amine, pyrimidine-ol, sulfonamide). Data on 

the toxicity of saccharin that met ECOTOX and OPP screening criteria were available for nine

studies (Appendix J). However, further review of these data indicates they do not contain 

information on endpoints that are considered ecologically relevant (i.e., closely related to the 

assessment endpoints of survival, growth, reproduction and development). These studies mostly 

focused on saccharin as it relates to human health effects (e.g., carcinogenicity, mutagenicity, 

organ level endpoints, biochemical endpoints). The remaining ecologically-oriented saccharin 

studies evaluated the efficacy of saccharin as a deterrent to insect pest damage, fungal infection 

or its role as an attractant to aquatic life. A list of these studies with rationale for their rejection is 

provided at the end of “APPENDIX J: Ecological Effects Studies Rejected by OPP.”

3.3.2.7. Field Studies

Data from field studies of the effects of sulfometuron methyl on terrestrial animals were not 

available to evaluate effects at organism, population or community levels of biological 

organization (e.g., population size/growth rate, age-class structure, or species richness).

3.3.2.8. Terrestrial Plants

Terrestrial plant Tier 2 seedling emergence and vegetative vigor studies are required for all low 

dose pesticides (those with the maximum use rate of 0.5 lbs ai/acre or less) and for any pesticide 

showing a negative response equal to or greater than 25% in Tier 1 studies. Tier 2 terrestrial 

plant toxicity studies were conducted to establish the toxicity of sulfometuron methyl to nontarget terrestrial plants. The recommendations for seedling emergence and vegetative vigor 

studies are for testing of (1) six species of at least four dicotyledonous families, one species of 
73

which is soybean (Glycine max), and the second of which is a root crop, and (2) four species of 

at least two monocotyledonous families, one of which is corn (Zea mays). 

For sulfometuron methyl, six dicots (sugar beet, rape, tomato, pea, cucumber and soybean) and 

four monocots (onion, corn, wheat, sorghum) were tested using the Tier 2 protocols for effects 

on seedling emergence and vegetative vigor. Tier 1 tests were not conducted since preliminary 

testing indicated all plants would be promoted to Tier 2 testing. Test durations were 14 days and 

21 days for the seedling emergence and vegetative vigor studies, respectively. Depending on the 

species and test, seven to eleven treatments were used with application rates ranged from 

0.0000017 to 0.5625 lb ai/acre. For this risk assessment, a re-review and statistical analysis was 

conducted on the Tier 2 toxicity data from the more sensitive test species in both the seedling 

emergence and vegetative vigor tests. All statistical comparisons were made to negative controls 

(previous analyses in the DER made comparisons to solvent controls even though negative and 

solvent controls were not significantly different). For calculation of the EC25 and EC05, 

nonlinear regression was conducted using the methods of Bruce and Versteeg (1992). In 

situations where the NOAEC was found to be greater than or equal to the EC25, the EC05 was 

used for the comparison with threatened and endangered species. 

Results for the most sensitive endpoints and species with monocots and dicots indicate that 

seedling emergence and vegetative vigor are impacted at exposures well below the maximum 

application rate of 0.375 lb ai/acre for sulfometuron methyl (Table 35). For seedling emergence, 

the EC25 of 1.9 x 10 -4 lb ai/acre for the most sensitive monocot (sorghum) is about a factor of 5 

greater than the EC25 of 3.2 x 10 -5 lb ai/acre for the most sensitive dicot (sugar beet). The 

maximum application rate of 0.375 lb ai/acre exceeds these EC25 values for sorghum and sugar 

beet by approximately 2,000 and 10,000 times, respectively. For 9 of the 10 test species, a 

comparison of EC25 values indicates that species sensitivity is within a factor of 20 (based on 

summary data presented by McKelvey, 1995). This indicates that the most sensitive test species 

is not an outlier in terms of its relative sensitivity. The EC05 and NOAEC for the sorghum and 

sugar beet are 4.3 x 10-5 and 2.9 x 10-5

, respectively. A consistent, declining monotonic 

exposure-response curve was observed for sugar beet, while that for sorghum was monotonic 

following an increase in mean shoot height of 24% in the lowest test treatment and 2% in the 

next lowest treatment relative to the negative control. Because the statistical method of Bruce 

and Versteeg (1992) uses a pooled response from the non-monotonic portion of the doseresponse curve for calculating ECx values, the actual mean response associated with the EC05 for 

sorghum is slightly higher than the mean response observed for controls, rendering it a relatively 

conservative toxicological value. 

Results from the vegetative vigor study indicate the most sensitive monocot (corn) and dicot 

(soybean) are impacted at somewhat lower levels compared to the seedling emergence study. 

The EC25 values for corn and soybean (shoot dry weight) are 3.7 x 10-5 and 1.8 x 10-5, 

respectively. The maximum application rate for sulfometuron methyl is approximately 10,000 

and 20,000 times these EC25 values. Because the NOEC exceeded the EC25 values for both 

species, the EC05 is used for risk assessment with threatened and endangered species. The EC05

values for corn and soybean are 8.4 x 10-6 and 9.9 x 10-7, respectively. For all 10 test species, a 

comparison of EC25 values indicates that species sensitivity differences are within a factor of 20 

(based on summary data presented by McKelvey, 1995). This indicates that the most sensitive 
74

test species is not an outlier in terms of its relative sensitivity. A consistent, declining monotonic 

exposure-response curve was observed for corn and soybean in the vegetative vigor test. 

Table 35. Summary of Most Sensitive Tier II Terrestrial Non-target Plant

Seedling Emergence and Vegetative Vigor Toxicity Data for Sulfometuron 

Methyl.

Most 

Sensitive 

Species

EC25

(lb ai/A)

NOAEC/[EC05]*

(lb ai/A)

Endpoint

Affected

MRID No.

Author/year

Study 

Classification

Seedling Emergence

Monocots

Sorghum 1.9 x 10 -4 4.3 x 10 -5 (*) shoot height 435385-01

McKelvey 

(1995)

Acceptable

Dicots

sugar beet 3.2 x 10 -5 2.9 x 10 -5 shoot dry wt Acceptable

Vegetative Vigor

Monocots 435385-01

McKelvey 

(1995)

Corn 3.7 x 10 -5 9.9 x 10 -7 (*) shoot dry wt Acceptable

Dicots

Soybean 1.8 x 10 -5 8.4 x 10 -6 (*) shoot dry wt Acceptable

* The NOAEC value is above or equal to the EC25 or below the lowest concentration, therefore, an EC05 is used instead.
75

4. RISK CHARACTERIZATION

Risk characterization provides the final step in the risk assessment process. In this step, 

exposure and effects characterization are integrated to provide an estimate of risk relative to 

established levels of concern (LOCs). The results are then interpreted for the risk manager 

through a risk description and synthesized into an overall conclusion.

4.1. Risk Estimation - Integration of Exposure and Effects 

Data 

Risk characterization integrates EECs and toxicity estimates and evaluates the likelihood of 

adverse ecological effects to non-target species. For sulfometuron methyl, a deterministic 

approach is used to evaluate the likelihood of adverse ecological effects to non-target species. 

In this approach, risk quotients (RQs) are calculated by dividing estimated environmental 

exposures (EECs) by acute and chronic ecotoxicity values for non-target species. 

Risk Quotient (RQ) = Exposure Estimate/Toxicity Estimate

RQs are then compared to levels of concern (LOCs). These LOCs are criteria used to indicate 

potential risk to non-target organisms and the need to consider regulatory action. LOC 

exceedence is interpreted to mean that the labeled use (or proposed use) of the pesticide has the 

potential to cause adverse effects on non-target organisms. LOCs currently address the 

following risk presumption categories:

(1) acute - potential for acute risk to non-target organisms which may warrant regulatory 

action in addition to restricted use classification,

(2) acute restricted use – potential for acute risk to non-target organisms, but may be 

mitigated through restricted use classification,

(3) acute endangered species – endangered species may be potentially affected by use,

(4) chronic risk – potential for chronic risk may warrant regulatory action, endangered 

species may potentially be affected through chronic exposure,

(5) non-endangered plant risk - potential for effects in non-target (non-endangered) 

plants, and 

(6) endangered plant risk – potential for effects in endangered plants. 

Currently, EFED does not calculate formal risk quotients to assess chronic risk to plants or acute 

or chronic risks to non-target insects. However, these endpoints are evaluated on a case-by-case 

basis as data allow. 

Risk presumptions, along with the calculation of the corresponding RQs and LOCs, are tabulated 

below:
76

Table 36. Risk Presumptions for Aquatic Animals.

Risk Presumption RQ LOC

Acute Risk EEC(1)/LC50 or EC50 0.5

Acute Restricted Use EEC/LC50 or EC50 0.1

Acute Endangered Species EEC/LC50 or EC50 0.05

Chronic Risk EEC/NOAEC 1

(1)

 EEC units in (mg/L or μg/L) in water

Table 37. Risk Presumptions for Terrestrial Animals.

Risk Presumption RQ LOC

Acute Risk EEC(1)/LC50 or LD50/sqft(2) or LD50/day(3) 0.5

Acute Restricted Use EEC/LC50 or LD50/sqft or LD50/day

(or LD50 < 50 mg/kg) 0.2

Acute Endangered Species EEC/LC50 or LD50/sqft or LD50/day 0.1

Chronic Risk EEC/NOAEC 1

Acute Endangered Terrestrial Invertebrate EEC(4)

/LD50

(4) 0.05

(1) EEC units are in ppm diet

(2)

 mg/sqft 

LD50 * wt. of bird 

(3) mg of toxicant consumed/day

 LD50 * wt. of bird 

(4) EEC = ppm in small insects; LD50 = ug/g bw (ppm)

Table 38. Risk Presumptions for Plants.

Risk Presumption RQ LOC

Terrestrial Plants in Terrestrial and Semi-Aquatic Areas:

Non-Endangered Species EEC(1)/EC25 1

Endangered Species EEC/EC05 or NOAEC 1

Aquatic Plants:

Non-Endangered Species EEC(2)/EC50 1

Endangered Species EEC/EC05 or NOAEC 1

(1)

 EEC units in lbs ai/acre

(2)

 EEC units in μg/L or mg/L in water
77

4.1.1. Non- target Aquatic Animals and Plants 

A summary of the toxicity values used to derive risk quotients for aquatic animals and plants is 

provided in Table 39 below. 

Table 39. Endpoints Used for Estimating Risks of Sulfometuron Methyl to 

Aquatic Animals and Plants.

(1)

Organism Group Toxicity Units MRID #

Freshwater fish, LC50 > 148 mg ai/L 435018-02

Freshwater invertebrate EC50 > 150 mg ai/L 435018-03

Marine/estuarine fish LC50 > 45 mg ai/L 416728-03

Marine/estuarine invertebrate (mollusk - oyster) EC50 > 38 mg ai/L 416728-04

Chronic freshwater fish NOAEC Data gap

Chronic freshwater invertebrate NOAEC 97 mg ai/L 416728-06

Aquatic nonvascular plants EC50/NOAEC 4.6 / 0.63 μg ai/L 416801-02

Aquatic vascular plants EC50/NOAEC 0.48 / 0.21 μg ai/L 435385-03

(1) Details for each study are presented in earlier sections of this document and in APPENDIX H: Ecological Effects Data 

Summaries,

4.1.1.1. Fish and Aquatic Invertebrates

All available LC50 or EC50 values derived from acute toxicity tests on freshwater and 

marine/estuarine fish and invertebrates are greater than the highest test concentration measured 

in these studies (>38 to >150 mg ai/L; Table 39). Therefore, risks to these taxa are described 

qualitatively. Compared to these ‘indefinite’ toxicity values, the peak EEC derived from the 

PRZM/EXAMS scenario yielding the highest exposure (31 μg/L) is three orders of magnitude 

lower. For bounding purposes, if one assumes that these indefinite LC50 or EC50 values represent 

the lower bound of actual (definitive) LC50 or EC50 values from these tests, then the resulting 

acute RQs would be approximately three orders of magnitude lower than the LOCs for nonendangered aquatic animals. For endangered fish and aquatic invertebrates, the RQs would be 

approximately two orders of magnitude lower than the LOC of 0.05. Considering that no 

mortality was observed at the highest test concentrations from these acute toxicity tests, the 

actual RQ values clearly represent conservative estimates of acute risk to these species.

The lowest available chronic NOAEC in aquatic invertebrates is 97 mg/L (97,000 ug/L). 

Compared to the highest 21-d EEC of 26 μg/L derived from PRZM/EXAMS modeling, the 

chronic RQ for freshwater invertebrates would also be several orders of magnitude lower than 

the LOC of 1.0. 

For chronic toxicity to freshwater fish, no acceptable data were available. In the absence of 

chronic toxicity data, it is common to apply an extrapolation factor (e.g., acute-chronic ratio or 

ACR) to estimate chronic toxicity from acute toxicity test results. However, a valid ACR could 

not be determined from the sulfometuron methyl toxicity database because a definitive LC50 or 

EC50 was not established for any aquatic animals. Considering data for another sulfonylurea 
78

herbicide with a similar toxicity profile and the same mode of action (flazasulfuron, PC code: 

119011), an ACR of 7 can be calculated for rainbow trout: 

Rainbow trout LC50 = 115.2 mg ai/L (MRID 46220967; Sousa 2003)

Rainbow trout NOAEC = 17 mg ai/L (MRID 46220970; Sousa, 2004)

ACR = 115.2 / 17 = 7 (rounded)

Thus, applying an ACR of 7 to the LC50 of > 148 for freshwater fish yields an estimated NOAEC 

of >21 mg/L for sulfometuron methyl. Compared to the maximum 60-d average EEC of 20 ug/L 

derived from the PRZM/EXAMS modeling, the chronic RQ would be at least three orders of 

magnitude lower than the LOC of 1.0. 

Although chronic studies were not available for marine/estuarine fish and invertebrates, there is 

no evidence to indicate marine or estuarine animals are substantially more sensitive than 

freshwater animals such that the risk profile would differ markedly from freshwater animals. 

Furthermore, acute toxicity studies indicate that sulfometuron methyl is not acutely toxic at (or 

near) toxicity limits for both freshwater and saltwater fish and invertebrates. Considering that 

the freshwater chronic RQs for fish and invertebrates would be several orders of magnitude 

lower than the LOCs, it appears highly unlikely that marine and estuarine animals would be at 

risk from chronic exposures to sulfometuron methyl as determined by PRZM/EXAMS modeling.

Acute and chronic risk to aquatic animals is further discussed in the Risk Description (Section

4.2),

4.1.1.2. Aquatic Plants

Risk quotients were derived using the peak EEC of 31 ug/L (determined from the 

PRZM/EXAMS exposure scenario yielding the highest peak exposure concentrations) and EC50

and NOAEC values for vascular and non-vascular aquatic plants, respectively (Table 40). For 

sulfometuron methyl, RQs exceeded the endangered and non-endangered LOCs for both vascular 

and non-vascular aquatic plants receiving pesticide runoff/drift, indicating a potential risk to 

these species.

Table 40. Summary of Acute Aquatic Plant Risk Quotients for Rights of Way 

Uses.

Scenario Endangered Non-endangered

Vascular Non-vascular Vascular Non-vascular

TX Rights of Way (max rate of 0.375 

lbs ai/acre x 1 aerial application/ yr) (a,b) 148 (c) 49 (c) 65 (d) 6.7 (d)

(a) Based on a peak EEC of 31 ug/L derived from the TX rights of way exposure scenario which yielded the highest EECs. Details on scenarios 

and PRZM-EXAMS modeling are provided in Section 3.2.2.2 and APPENDIX C: Ecological Aquatic Exposure Modeling. (b) For sulfometuron methyl, endangered plants toxicity threshold (NOAEC) was 0.21μg ai/L for vascular and 0.63μg ai/L for non-vascular 

plants; acute toxicity thresholds (EC50) used for non-endangered plants were 0..48 and 4.6 μg ai/L for vascular and non-vascular plants, 

respectively.

(c) indicates an exceedence of Endangered Species Level of Concern (LOC); RQ > 1.0.
79

(d) indicates an exceedence of non-target (i.e., non-endangered) Species Level of Concern (LOC); RQ > 1.0.

4.1.2. Non- target Terrestrial Animals 

A summary of the toxicity values used to derive risk quotients for terrestrial animals is provided 

in Table 41 below. 

Table 41. Endpoints Used for Estimating Risks of Sulfometuron Methyl to 

Terrestrial Animals.

Organism Group (a) Toxicity MRID #

Bird LD50 (oral dose-based, mg ai/kg-bw) >4,650 245375

Bird LC50 (dietary-based, mg ai/kg-diet) >4,600 71414

Mammal LD50 (oral dose-based, mg ai/kg-bw) >5,000 430892-01

Honeybee LD50, μg ai/bee >100 416728-10

Mammal chronic NOAEL (dose-based, mg ai/kg-bw/day) 300(b) 78798 (c)

(a) Details for each study are presented in earlier sections of this document and in APPENDIX H: Ecological Effects Data 

Summaries. (c) Highest dose tested. (c) Accession number.

4.1.2.1. Birds, Acute Risks

The acute LC50/LD50s for birds are greater than the highest concentration/dose tested in each 

study. Therefore, while precise estimates of RQs are not possible with indefinite (i.e., “greater 

than”) LC50/LD50 values, a bounding analysis can be conducted to provide a conservative, upper 

bound estimate of the RQs (Table 42 and Table 43). 

In this bounding analysis, calculated EECs for various food items from the TREX terrestrial 

exposure model are compared to dose-base LD50 values (treated as definitive values) that have 

been adjusted for different avian size classes. The highest dose-based EEC (102 mg ai/kg-bw/d) 

is approximately 1/25th the lowest adjusted dose-based LD50 (> 2414 mg ai/kg-bw) thus yielding 

an upper bound RQ of < 0.04. This upper bound RQ is less than the LOCs for acute risk (0.5), 

acute restricted use (0.2) and acute endangered species (0.1) for terrestrial animals. 

Results from diet-based RQ calculations with birds are similar to those described above for dosebased RQs (Table 43). Specifically, the highest diet-based EEC (90 mg ai/kg-diet for short grass) 

is approximately 1/50th the avian subacute dietary LC50 of >4600 mg ai/kg-diet, thus yielding an 

upper bound RQ of <0.02. This upper bound RQ is less than the LOCs for acute risk (0.5), acute 

restricted use (0.2) and acute endangered species (0.1) for terrestrial animals. The potential for 

acute risk to birds is discussed further in the Risk Description (Section 4.2).
80

Table 42. Upper Bound Kenaga, Acute Avian Dose-Based Risk 

Quotients (Bounding Analysis Only).

Size Class

(grams)

Adjusted

LD50

(mg ai/kg-bw)

Short Grass(1)

EEC RQ(2)

20 > 2414 102.5 < 0.04

100 > 3074 58.5 < 0.02

1000 > 4342 26.2 < 0.01

(1) Calculations provided for short grass only because upper bound dose-based EECs were higher than any other food item 

modeled.

(2) RQs derived using unadjusted LD50 of >4650 mg ai/kg-bw for mallard and dose-based EECs (mg ai/kg-bw) calculated 

using TREX ver. 1.3.1 with a single application at the maximum allowable label rate (0.375 lb ai/acre/yr). See Section 3.2

and “APPENDIX H: Ecological Effects Data Summaries” for details on the model inputs, calculations and output.

Table 43. Upper Bound Kenaga, Subacute Dietary-Based Risk 

Quotients (Bounding Analysis Only).

Dietary-based LC50

(mg ai/kg-diet)

Short Grass(1)

EEC(2) RQ

> 4600 90.0 < 0.02

(1) Calculations provided for short grass only because upper bound residues were higher than any other food item modeled.

(2)

Diet-based EECs are expressed in units of mg ai/kg-diet and are calculated using TREX ver. 1.3.1 based on a single 

application at the maximum allowable label rate (0.375 lb ai/acre/yr). See Section 3.2 and “APPENDIX H: Ecological 

Effects Data Summaries” for details on the model inputs, calculations and output. Size class not used for dietary risk 

quotients.

4.1.2.2. Birds, Chronic Risks

As described in Section 3.3, no acceptable chronic toxicity data were available on the effects of 

sulfometuron methyl on birds. Therefore, chronic risks to avian fauna could not be 

characterized. Uncertainty associated with the lack of chronic toxicity data with avian fauna is 

further described in the Risk Description section.

4.1.2.3. Mammals, Acute Risks

The unadjusted, acute LD50 for mammals is greater than the highest dose tested in the study (> 

5000 mg ai/kg for rat; MRID 430892-01). Therefore, while a precise estimate of the mammalian 

acute RQ is not possible with an indefinite (i.e., “greater than”) LD50 value, a bounding analysis 

can be conducted to provide a conservative, upper bound estimate of the acute, mammalian RQ 

(Table 44). 

In this bounding analysis, calculated EECs for various food items from the TREX terrestrial 

exposure model are compared to dose-base LD50 values (treated as definitive values) that have 

been adjusted for different mammalian size classes. When the highest EECs (from the short 
81

grass food item) are compared to the size-class adjusted LD50 values, the largest upper bound RQ 

is < 0.02, which occurs for the 20g mammal size class. This upper bound RQ is less than the 

LOCs for acute risk (0.5), acute restricted use (0.2) and acute endangered species (0.1) for 

terrestrial animals. The RQ calculations are detailed in “APPENDIX F: T-REX Output” and 

acute mammalian risks are further described in the Risk Description (Section 4.2). “

Table 44. Upper Bound Kenaga, Acute Mammalian Dose-Based 

Risk Quotients (Bounding Analysis Only).

(1)

Size Class

(grams)

Adjusted

LD50

Short Grass(1)

EEC RQ(2)

15 > 10989 85.8 < 0.01

35 > 8891 59.3 < 0.01

1000 > 3846 13.8 < 0.01

(1) Calculations provided for short grass only because upper bound dose-based EECs were higher than any other

food item modeled.

(2)

RQs derived using unadjusted LD50 of >5000 mg ai/kg-bw and dose-based EECs (mg ai/kg-bw) calculated using 

TREX ver. 1.3.1 with a single application at the maximum allowable label rate (0.375 lb ai/acre/yr). See Section 

3.2 and “APPENDIX H: Ecological Effects Data Summaries” for details on the model inputs, calculations and 

output.

4.1.2.4. Mammals, Chronic Risks

To evaluate the chronic risk to mammals, dose-based and dietary-based RQs were calculated 

using the rabbit NOAEL of 300 mg ai/kg-bw/d from the developmental toxicity study 

(Accession No. 78798). The rabbit developmental toxicity study was selected for assessing 

chronic risks to mammals because an acceptable NOAEL was not available from the 2-

generation chronic rat reproduction study (that study is considered invalid by HED) or other 

small mammals (mouse). Because TREX assumes the test NOAEL corresponds to a 350g 

mammal (rat), calculation of size-class adjusted NOAELs for the rabbit (which averaged 3.9 kg 

in the study) first involved adjusting the rabbit NOAEL to a 350g mammal adjusted NOAEL 

using the same equation as TREX. This 350g, size-adjusted NOAEL (549 mg ai/kg-bw/d) was 

then input to TREX for the remainder of the chronic mammalian EEC and RQ.

Neither the chronic, dose-based risk quotients (Table 45) nor the dietary-based risk quotients 

(Table 46) exceed the chronic LOC for all weight classes (15 g, 35 g, and 1000g) of mammals 

consuming short grass, tall grass, broadleaf forage/small insects and seeds. Details of the RQ 

calculations are provided in (See APPENDIX F: T-REX Output).

Table 45. Upper Bound Kenaga, Chronic Mammalian Dose-Based Risk 

Quotients.

Size Class

(grams)

Adjusted 

NOAEL(1)

(mg ai/kg-bw/d)

EECs and RQs

Short 

Grass Tall Grass

Broadleaf 

Plants/

Small 

Insects

Fruits/Pods/

Seeds/

Large Insects

Granivore

EEC RQ EEC RQ EEC RQ EEC RQ EEC RQ
82

15 1206.6 85.8 0.07 39.3 0.03 48.3 0.04 5.36 <0.01 1.19 <0.01

35 976.3 59.3 0.06 27.2 0.03 33.4 0.03 3.71 <0.01 0.82 <0.01

1000 422.3 13.8 0.03 6.3 0.01 7.7 0.02 0.86 <0.01 0.19 <0.01

(1) RQs derived for different size classes using unadjusted NOAEL of >300 mg ai/kg-bw/d and dose-based EECs (mg ai/kg-bw/d) calculated 

using TREX ver. 1.3.1 with a single application at the maximum allowable label rate (0.375 lb ai/acre/yr). See Section 3.2 and “APPENDIX 

H: Ecological Effects Data Summaries” for details on the model inputs, calculations and output.

Table 46. Upper Bound Kenaga, Chronic Mammalian Dietary-Based Risk 

Quotients

NOAEC (ppm) EECs and RQs

Short Grass Tall Grass Broadleaf Plants/

Small Insects

Fruits/Pods/

Seeds/

Large Insects

EEC RQ EEC RQ EEC RQ EEC RQ

10980 90.00 0.01 41.25 <0.01 50.63 <0.01 5.63 <0.01

Dietary-based RQs derived by converting the rabbit NOAEL (>300 mg ai/kg-bw/d) to a diet-based NOAEC and comparing with diet-based EECs 

(mg ai/kg-diet) calculated using TREX ver. 1.3.1 at the single maximum allowable label rate (0.375 lb ai/acre/yr). See Section 3.2 and 

“APPENDIX H: Ecological Effects Data Summaries” for details on the model inputs, calculations and output. Size class not used for dietary risk 

quotients 

4.1.2.5. Non-Target Terrestrial-phase Amphibians, Reptiles and 

Terrestrial Invertebrates 

In absence of taxa-specific data, EFED currently uses birds as surrogates for terrestrial non-target 

terrestrial phase amphibians and reptiles and fish for aquatic phase amphibians. LOCs were not 

exceeded for any of the surrogate species; therefore, potential risks to reptiles and amphibians 

are also presumably lower than the Agency’s concern level. 

EFED does not currently estimate risk quotients for terrestrial non-target invertebrates. 

However, a label statement is required to protect foraging honeybees when the LD50 is <11 

μg/bee. Based on the acute contact toxicity study to honeybees, the LD50 for sulfometuron 

methyl is >100 μg/bee. This classifies sulfometuron methyl as practically non-toxic to 

honeybees on an acute contact exposure basis. For RQ derivation for endangered terrestrial 

invertebrates, the LD50 for honeybees (>100 ug a.i./bee) is converted to units of μg ai/g (of bee) 

by multiplying by 1 bee/0.128 g, thereby resulting in an LD50 of >780 μg ai/g. This LD50 value 

is then compared to the EEC of 50.6 ug/g for small insects/broadleaf plants (Table 17). The 

resulting RQ (EEC/LD50) is <0.06, which is at or below the LOC for endangered terrestrial 

invertebrates (0.05). Therefore, the risk of direct adverse effects to terrestrial invertebrates is 

considered low; however, due to the potential risk identified to plants, the potential for indirect 

effects to terrestrial invertebrates from sulfometuron methyl use cannot be discounted.

Additional discussion of potential risks to these taxa is qualitatively discussed in the Risk 

Description portion of this document (Section 4.2).
83

4.1.3. Non- target Terrestrial Plants 

A summary of the toxicity values used to derive risk quotients for terrestrial plants is provided in 

Table 47 below. 

Table 47. Summary of Selected Endpoints from Terrestrial Plant Toxicity Studies

of Sulfometuron Methyl

Organism Group Toxicity

(Lbs A.I./Acre)

MRID #

Terrestrial monocots emergence, EC25, lbs ai/acre

EC05 or NOAEC, lbs ai/acre

EC25 = 1.9 x 10-4

EC05 = 4.3 x 10-5 435385-01

Terrestrial dicots emergence, EC25, lbs ai/acre

EC05 or NOAEC, lbs ai/acre

EC25 = 3.2 x 10-5

NOAEC = 2.9 x 10-5 435385-01

Terrestrial monocots vegetative vigor, EC25, lbs ai/acre

EC05 or NOAEC, lbs ai/acre

EC25 = 3.7 x 10-5

EC05 = 8.4 x 10-6 435385-01

Terrestrial dicots vegetative vigor, EC25, lbs ai/acre

EC05 or NOAEC, lbs ai/acre

EC25 = 1.8 x 10-5

EC05 = 9.9 x 10-7 435385-01

a Details for each study are presented in earlier sections of this document and in “APPENDIX H: Ecological Effects Data Summaries”.

4.1.3.1. Non-Endangered and Endangered Plant Risks

Table 48 presents terrestrial plant RQs for sulfometuron methyl based on aerial and ground spray 

applications. These RQs were derived using TerrPlant (ver 1.2.2) using a single application rate 

at the annual maximum of 0.375 lb ai/A. TerrPlant is a Tier 1 model that estimates pesticide 

aerial drift and runoff to dry and semi-aquatic adjacent areas. Results indicate that the LOCs are

widely exceeded for non-endangered and endangered monocots and dicots located in adjacent 

dry areas and in semi-aquatic areas as the result of receiving a combination of runoff and spray 

drift from ground and aerial applications. In addition, the LOCs were exceeded for terrestrial 

plants receiving spray drift alone from ground and aerial application. These risks will be 

discussed in detail in the AgDrift spray drift analysis in the Risk Description (Section 4.2). 

However, TerrPlant modeling results are based on the assumption of a single application, risk 

quotients for non-target terrestrial plants may be underestimated. Bold indicates an LOC 

exceedence in Table 48.

Table 48. RQ Values For Plants In Dry And Semi-Aquatic Areas Exposed To 

Sulfometuron Methyl Through Runoff And/Or Spray Drift. 

Plant Type Application Method

Terrestrial 

Adjacent 

Areas

Semi-Aquatic Adjacent 

Areas Spray Drift

Non-endangered Plant RQs a,b,d

Monocot ground spray 118 1007 101

Dicot ground spray 703 5977 208

Monocot Aerial 197 1086 507

Dicot Aerial 1172 6445 1042

Endangered Plant RQs a,c,d
84

Monocot ground spray 523 4448 446

Dicot ground spray 776 6595 3788

Monocot Aerial 872 4797 2232

Dicot Aerial 1293 7112 18939 a

Detailed calculations for RQs and TerrPlant (ver 1.2.2) input and output are provided in “APPENDIX D: Terrplant Spreadsheet.” b Non-endangered toxicity thresholds (EC25) are 1.9 x 10-4 (seedling emergence, monocot), 3.2 x 10-5 (seedling emergence, dicot), 

3.7 x 10-5 (vegetative vigor, monocot), 1.8 x 10-5 (vegetative vigor, dicot) lb ai/A. c Endangered toxicity thresholds (NOAEC of EC05) are 4.3 x 10-5 (seedling emergence, monocot), 2.9 x 10-5 (seedling emergence, 

dicot), 8.4 x 10-6 (vegetative vigor, monocot), 9.9 x 10-7 (vegetative vigor, dicot) lb ai/A. d Bold RQ values exceed the Non-Endangered Species LOC and Endangered Species LOC (RQ >1.0).

4.1.4. Use of Contaminated Irrigation Waters

The potential risk to plants when exposed to irrigation water contaminated with sulfometuron 

methyl is presented in the form of RQs in Table 49. These RQs are derived using EECs of 0.33 

μg/L (ground water) and 31 μg/L (surface water). The EEC for ground water was calculated 

using the Tier 1 SCIGROW model (Table 16) while that for surface water was calculated using 

PRZM/EXAMS for the scenario yielding the highest EECs (Table 15). For semi-aquatic and 

terrestrial areas adjacent to irrigation fields, EECs in lb ai/acre were calculated assuming 1% of 

the irrigation water drifts into adjacent wetlands. It was further assumed that no runoff of 

irrigation water occurs. Toxicity endpoints were taken from the vegetative vigor study because it 

was assumed that non-target plants are exposed to sulfometuron methyl directly through spray 

drift from irrigation water. Details of the calculation of the irrigation EECs are provided in

APPENDIX G: Modeling of Terrestrial plant Exposure from Contaminated irrigation Water). 

Based on this screening analysis, results suggest that sulfometuron methyl levels in irrigation 

water from ground water sources would not exceed non-target or endangered species LOCs (i.e, 

RQs < 1.0). However, RQs based on sulfometuron methyl in irrigation water derived from 

surface water sources exceed the LOCs for both non-target and endangered species (3.9 and 71, 

respectively), thus indicating a potential risk to plants adjacent to areas irrigated with surface 

water sources. 

Table 49. Risk Quotients for Non-target and Endangered Plants, Resulting From 

Exposure to Sulfometuron Methyl in Irrigation Water

Location

Ground water and 

Surface Water EEC: 1, 2

(lbs ai/A)

Risk Quotients:

Ground water (GW) and Surface Water (SW) 

Irrigation

Non-target plants3

(EEC/EC25)

Endangered plants3

(EEC/NOAEC)

Semi-aquatic and terrestrial 

areas adjacent to irrigated 

fields

Ground water: 7.5 x 10-7

Surface water: 6.1 x 10-5

GW: 0.04

SW: 3.9

GW: 0.76

SW: 71

1 Estimated EEC assumes 1 inch of irrigation water is applied to the target field, 1% drift of irrigated water containing sulfometuron methyl, and 

no runoff of irrigated water. See Appendix G for details on irrigation exposure calculations. 2 EECs based on sulfometuron methyl concentrations of 0.33 ug/L in ground water and 31 ug/L in surface water 3 Based on non-target plant EC25 of 1.8 x 10-5 lb ai/A and endangered plant NOAEC of 9.9 x 10-7 (MRID 435385-01) for the most sensitive 

vegetative vigor endpoint. Bold RQ indicates exceedence of LOC of 1.0 (i.e., RQ > 1)
85

4.2. RISK DESCRIPTION

4.2.1. Risk to Aquatic Animals and Plants

In the conceptual model, spray drift and surface runoff/leaching to adjacent bodies of water were 

predicted as the most likely sources of exposure of sulfometuron methyl to non-target aquatic 

animals and plants. Risks to aquatic organisms (i.e. fish, invertebrates, and plants) were assessed 

based on modeled estimated environmental concentrations (EECs) and available toxicity data. 

Aquatic EECs for the ecological exposure to sulfometuron methyl were estimated using PRZMEXAMS employing the standard ecological water body (Section 3.2.2.2; Table 13).

The risk hypothesis stated that the use of sulfometuron methyl has the potential to cause adverse 

effects to aquatic animals and plants. This assessment confirms this hypothesis. Risks of direct 

effects to aquatic vascular and nonvascular plants are above the Agency’s LOCs. However, the 

assessment refutes the risk hypothesis regarding direct effects to aquatic animals, suggesting that 

direct effects to aquatic animals are unlikely. Although risk from direct toxicity to aquatic 

animals is not indicated in this screening level assessment, the dependence of aquatic animals on 

primary producers (plants) results in the potential for indirect effects to aquatic animals. 

4.2.1.1. Fish and Aquatic Invertebrates

The submitted acute toxicity data for aquatic species indicate that sulfometuron methyl is 

practically non-toxic to fish and invertebrates with LC50 and EC50 values >38 to >150 mg ai/L, 

respectively. A comparison of the PRZM/EXAMS peak EEC of sulfometuron methyl in surface 

water of 31 ug/L to toxicity values for fish and invertebrates indicates that these indefinite (i.e., 

‘greater than) acute toxicity values are three orders of magnitude above the highest peak EEC. A 

bounding analysis indicates that even if these indefinite LC50 and EC50 values are interpreted as 

the lower bounds for acute toxicity (a conservative assumption since no mortality occurred in 

these test concentrations), the resulting acute RQs would still be at least two orders of magnitude 

below the LOCs for non-endangered and endangered aquatic animals. This risk finding is 

consistent with those from other ecological risk assessments with sulfonylurea herbicides (e.g., 

florasulam, flazasulfuron). While it was noted in the Analysis Section (3.3) that uncertainty 

exists in the actual exposure concentration derived from the estuarine/marine acute toxicity tests, 

this uncertainty is not judged to be large enough to impact the risk conclusions, given the large 

difference between EECs and toxicity levels. 

Therefore, it is concluded that acute risk to aquatic animals from direct effects of sulfometuron 

methyl is expected to be minimal.

Similarly, chronic risk quotients are all less than the LOC of 1.0 for the modeled uses. For 

freshwater aquatic invertebrates and fish, the PRZM/EXAMS 21-day EEC (26 ug/L) and 60-d 

EEC (20 ug/L) are also three orders of magnitude below the chronic NOAEC of 97 mg/L and 

>21 mg/L, respectively. As noted in the Analysis Section (3.3), the chronic NOAEC for fish had 

to be estimated using an ACR of 7 derived from another chemical (flazasulfuron) with a similar

toxicity profile and mode of action. Clearly, there is uncertainty associated with extrapolation of 
86

an ACR across chemicals, as ACRs can vary by chemical, species, test designs, and other 

factors. In a recent analysis, Raimondo et al. (2007) evaluated the variability in ACRs derived 

from multiple sources, including EFED’s Pesticide Ecotoxicity database. Raimondo et al. (2007)

report a 90th percentile ACR of 80 across all chemicals, which if applied to the freshwater fish 

LC50 of > 148 mg/L, would yield an estimated NOAEC of > 2 mg/L. This value is still 100-fold 

higher than the chronic 60-d EEC of 20 ug/L. This 90th percentile ACR reflects pesticides with 

modes of action that differ from sulfometuron methyl and therefore may not reflect the 90th

percentile ACR within the sulfonylurea class of herbicides. However, for the purposes of 

evaluating uncertainty in acute-to-chronic toxicity extrapolations, it is considered a reasonable 

approximation of a “high end” ACR. 

The potential for chronic risks to fish was further evaluated by comparing the 60-d (chronic) 

EEC for freshwater fish with available chronic toxicity values (NOAECs) for other sulfonylurea 

herbicides (Figure 3). Results indicate that chronic toxicity of other sulfonylurea herbicides 

occurs at concentrations two to three orders of magnitude greater than the chronic EEC of 0.020 

mg/L. Therefore, based on the use of a conservative “high end” ACR and comparison with 

toxicity information for other sulfonylurea herbicides, the potential for chronic risk to aquatic 

animals from direct effects of sulfometuron methyl appears unlikely.

Figure 3. Chronic Toxicity of Sulfonylurea Herbicides to Freshwater Fish

0.01

0.1

1

10

100

1000

Foramsulfuron (FM)

Imazapyr (FM)

Bensulfuron Methyl (FM)

Prosulfuron (FM)

Sulfosulfuron (RT)

Chlorsulfuron (RT)

Halosulfuron methyl (RT)

Metsulfuron methyl (RT)

NOAEC (ppm)

60-d EEC = 0.020 ppm

Source: EPA/OPP Ecotoxicity Database, core studies only, Oct., 2007; FM = fathead minnow ; RT = rainbow 
87

Although no chronic studies in saltwater fish or invertebrates have been submitted to the 

Agency, the acute studies do not indicate that saltwater species are expected to be more sensitive 

than freshwater species. Given the low magnitude of the freshwater animal risk quotients, 

submission of chronic studies in saltwater species would not likely affect conclusions of this 

assessment. 

An ECOTOX literature search found no acceptable or supplemental studies on the acute toxicity 

of technical grade sulfometuron methyl to fish or invertebrates. Results from a supplemental 

study of microcrustaceans using the formulated product, Oust, indicates that sulfometuron 

methyl is practically nontoxic to these aquatic invertebrate crustaceans. Therefore, toxicity 

findings of the formulated product (Oust®) are consistent with those using the technical grade 

active ingredient with Daphnia magna (MRID 435018-03).

4.2.1.2. Non-target Aquatic-phase Amphibians

EFED currently uses surrogate data (fish) to estimate potential risks to non-target aquatic phase 

amphibians. Risks to fish species were discussed above and do not indicate significant risk to 

these organisms.

One study of the effect of sulfometuron methyl on an aquatic-phase amphibian was found was 

found that met OPP/ECOTOX screening criteria (Table 50). In this study, Fort et al. (1999)

conducted three separate tests of sulfometuron methyl exposure to the African clawed frog, 

Xenopus laevis: (1) a 4-day frog embryo teratogenesis assay (FETAX) to evaluate embryo 

mortality/ malformations; (2) a 14-d test to evaluate effects on tail resorption, and (3) a 30-d 

exposure to evaluate effects on limb development. Both analytically impure (85% ai) and 

purified (99.5% ai) sulfometuron methyl exposures were evaluated in the study, but due to the 

confounding influence of impurities on sulfometuron methyl toxicity, results from only the 

purified (99.5% ai) sulfometuron methyl are used here. 

In the FETAX assay, 2 replicates of 20 mid-blastula frog embryos (stage 8) were exposed to 11 

nominal test concentrations of sulfometuron methyl ranging from 0.001 to 24.9 mg ai/L for 96-h. 

Sulfometuron methyl stock solutions were prepared using a DMSO carrier and verified 

analytically (analytical results not reported). Both a negative and solvent control were included. 

Test procedures generally conformed to ASTM recommendations for the FETAX assay (ASTM, 

1996). Results indicate no statistically significant effect of sulfometuron methyl on embryo 

survival or percent malformations up to (and including) the highest test concentration (24.9 mg

ai/L). Solvent controls were not significantly different from negative controls.

Similar results were found in the 30-d study, whereby no statistically significant effect of 

sulfometuron methyl exposure was found on limb development (% malformations) up through 

24.9 mg ai/L. Results from the 14-d tail resorption study indicate a significant reduction in tail 

resorption at 9.95 and 24.9 mg ai/L beginning at development stage 64 through 66 (test 

termination). No significant reduction occurred at or below 1 mg ai/L.

This study is classified as supplemental primarily because exposure concentrations were not 

measured during the test. Although the authors report that sulfometuron methyl was ‘stable’ 
88

over the 24 to 96-h renewal cycles used in the studies, no analytical chemistry results were 

provided. Furthermore, randomization of study organisms and replicates was not indicated (an 

ASTM requirement). Collection and testing of embryos by separate clutches (an ASTM 

recommendation) was not apparent in the study. Finally, the final concentrations of carrier 

solvent in the various treatments was not reported (solvent concentrations were only reported for 

the stock solutions).

Table 50. Toxicity of sulfometuron methyl to the African clawed frog from a 

study by Fort et al. (1999).

Species Test 

Chemical

Exposure 

Duration

Endpoint (Effect) Effect 

Level 

(mg ai/L)

Study 

Classification

Ref.

Xenopus 

laevis

sulfometuron 

methyl 

(99.5% ai)

96-h LC50 (% mortality)

NOAEC (% malformations)

> 24.9

24.9 (a)

Supplemental Fort et al. 

(1999) 

14-d NOAEC (tail resorption)

LOAEC (tail resporption)

0.995

9.95

30-d NOAEC (limb deformation) 24.9(a)

(a) Highest tested dose, LOAEL not achieved in study.

Although results from the Fort et al (1999) study are not being used quantitatively in this risk 

assessment, they suggest that acute toxicity to Xenopus larvae occurs at levels > 1000 times the 

maximum EEC of 31 ug/L derived from the PRZM/EXAMS model. The lowest NOAEC from 

this study (1.0 mg/L) is approximately 45 times higher than the maximum 21-d EEC of 26 ug/L.

Therefore, based on conclusions for fish discussed previously and supplemental information 

from Fort et al (1999), risk to aquatic phase amphibians is also expected to be lower than the 

Agency’s concern level.

4.2.1.3. Aquatic Plants 

Toxicity studies indicate that sulfometuron methyl is classified as highly toxic to aquatic plants, 

and the RQ values (65-148 for vascular plants; 6.7-49 for nonvascular plants) indicates the 

potential risk to aquatic vascular and nonvascular plants is above the Agency’s concern level. 

The freshwater vascular plant (duckweed) is the most sensitive aquatic plant species (14-d EC50

and NOAEC are 0.48 and 0.21 μg/L, respectively) followed by the green algae (EC50 is 4.6 μg

ai/L and the NOAEC is 0.63 ug ai/L). Sulfometuron methyl was much less toxic to diatoms 

(>370 and >410 mg/L), and potential risks to this taxonomic group do not exceed the Agency’s 

concern level.

In the duckweed study described previously (MRID 435385-03), recovery from the 14-d 

sulfometuron methyl exposures was assessed at the end of the study by exposing organisms to 

untreated medium for an additional 14 days. Effects were expressed as percent inhibition of 

frond counts and biomass. The results are as follows: 
89

14-d Recovery 14-d Recovery:

14-d Exposure Conc. Frond Count Inhibition Biomass Inhibition

1.045 ppb 41.1% 38.3%

0.590 ppb 11.8% 10.8%

0.323 ppb 0.6% - 1.0%

Therefore, the study authors concluded that sulfometuron methyl was phytotoxic to duckweed at 

concentrations of > 0.590 ppb and phytostatic at 0.323 ppb. These data suggest that the effects 

of sulfometuron methyl to aquatic vascular plants may be reversible following 14-d exposures at 

selected concentrations (0.323 ppb and below). To evaluate the potential for duckweed (and by 

extension, other vascular plants) to recover from sulfometuron methyl exposures predicted using 

PRZM/EXAMS modeling, the predicted long-term exposures to sulfometuron methyl (e.g., 90-d 

average concentration) was compared to available toxicity information. Results indicate that the 

90-d average concentration (16 ug/L; Table 15) derived from the exposure scenario yielding the 

highest exposure concentrations still exceeds the 14-d EC50 (0.48 ug/L) by a factor of 33 and the 

14-d phytotoxic concentration (0.59 ppb) by a factor of 27. Therefore, the ability of duckweed 

and other vascular aquatic plants to recover from predicted long-term exposure concentrations of 

sulfometuron methyl in adjacent, static aquatic systems appears unlikely. The sensitivity of RQ 

estimates for aquatic vascular and nonvascular plants to different assumptions regarding 

application rates and timing of application is discussed later in Section 4.3. 

Byl et al. (1994) conducted a laboratory study on the effect of sulfometuron methyl on the 

aquatic vascular plant, Hydrilla verticillata. In this study, Byl et al. (1994) exposed plants to 

aqueous solutions ranging from 0.001 to 1.0 mg/L sulfometuron methyl (as Oust) in three 

replicate chambers per treatment for 5 days. The % ai was not reported nor is it clear whether 

nominal concentrations reflect adjustment for % ai. A significant decrease in combined shoot 

and root length was observed at or above 0.01 mg/L (approximating 30% of the controls). 

Although not conclusive, results from Byl et al. suggest that the combined root and shoot length 

response of Hydrilla is less sensitive to 5-d exposure to the formulated product (Oust) compared 

to the 14-d exposure to TGAI for duckweed (NOAEC = 0.21 ug ai/L), even if nominal 

concentrations are adjusted downward to reflect the typical 75% ai found in Oust. However, the 

relative toxicity of TGAI and formulated product can not be determined conclusively from 

comparison of these two studies because study protocols differed substantially (e.g., exposure 

duration, measurement endpoints). 

4.2.1.4. Aquatic Toxicity of Sulfometuron Methyl Degradates

As discussed earlier in Section 3.3.1.7, no acceptable or supplemental studies were available on 

the toxicity of the major sulfometuron methyl degradates to aquatic organisms. To characterize 

the potential toxicity of the major degradates of sulfometuron methyl, predicted toxicity values 

were determined from EPA’s ECOSAR model (v. 0.99h). Note that these QSAR results should 

not, by OPP policy, be used directly for risk management decisions. This model is based on 

quantitative structure activity relationships (QSAR) for chemical effects on fish, daphnids, and 

green algae. Table 51 displays the results of the ECOSAR model predictions for five major 

sulfometuron methyl degradates. 
90

Table 51. ECOSAR-predicted toxicity values for major degradates of 

sulfometuron methyl.

Degradate Name ECOSAR Class Organism Toxicity Endpoint Toxicity Value 

(mg/L)

2-Hydroxy, 4,6-dimethyl 

pyrimidine

Phenols Fish 96-h LC50

90-d Chronic Value

49

0.31

Daphnid 48-h LC50

21-d Chronic Value

13

5.3

Green Algae 96-h EC50 257

2-(Aminosulfonyl) benzoic acid Neutral organic 

acids

Fish 96-h LC50

30-d Chronic Value

137,000*

12,600

Daphnid 48-h LC50

16-d EC50

128,000*

2,620

Green Algae 96-h EC50 70,676

Saccharin Thiazolinone (iso-) Fish 96-h LC50

Chronic Value**

1.9

0.14

Daphnid 48-h LC50

Chronic Value**

1.6

0.057

Green Algae 96-h EC50 0.41

2-(Aminosulfonyl) benzoic acid, 

methyl ester

Esters Fish 96-h LC50

Chronic Value**

152

136

Daphnid 48-h LC50 2,350

Green Algae 96-h EC50

Chronic Value**

11.6

8.7

2-Pyrimidinamine, 4,6-dimethyl Aromatic amines Fish 96-h LC50

Chronic Value**

214

0.93

Daphnid 48-h LC50

Chronic Value**

1.6

0.042

Green Algae Chronic Value** 12.9

* predicted toxicity value may exceed compound’s aqueous solubility 

** duration associated with the reported chronic value was not reported by the ECOSAR program 

The peak, 21-d, and 90-d EECs predicted for the parent chemical, sulfometuron methyl are: 0.031, 0.026, and 0.016 mg/L, 

respectively (Table 15)

Toxicity predictions from the ECOSAR model ranged widely across the five degradates, likely 

due in part to the differences in chemical structure and ECOSAR class used for the predictions 

(e.g., phenols, neutral organic acids, thialozinone, esters and aromatic amines). 

Predicted toxicity and risk characterization for 2-(aminosulfonyl) benzoic acid 

Of the five degradates evaluated, 2-(aminosulfonyl) benzoic acid was predicted to be the least 

toxic, with toxicity predictions for all aquatic species tested ranging from 2,600 to 137,000 mg/L. 

Predicted EECs were not modeled for the any of the degradates due to lack of appropriate data 

on the environmental fate of these compounds. However, if one assumes the EECs for the 

degradates are similar that of the parent compound (sulfometuron methyl), then the toxicity value 

for 2-(aminosulfonyl) benzoic acid appears at least 5 orders of magnitude greater than the EEC 

for sulfometuron methyl. While this assumption may have uncertainty due to the potential 

differential environmental fate characteristics of sulfometuron methyl and 2-(aminosulfonyl) 

benzoic acid, it appears highly unlikely that such differences would span the 5 order of 
91

magnitude range between EECs and predicted toxicity values for 2-(aminosulfonyl) benzoic 

acid, thus suggesting that the potential ecological risk to fish, daphnids and green algae 

associated with 2-(aminosulfonyl) benzoic acid would be highly unlikely. 

Predicted toxicity and risk characterization for the other degradates

Effects on Fish. With the remaining four degradates (2-hydroxy, 4,6-dimethyl pyrimidine, 

saccharin, 2-(aminosulfonyl) benzoic acid, methyl ester, and 2-pyrimidinamine, 4,6-dimethyl), 

the predicted acute and chronic toxicity values for fish ranged from 1.9-214 mg/L and 0.14-136 

mg/L, respectively (Table 51). Except for saccharin, these predicted acute toxicity values for 

fish were comparable to those observed for sulfometuron methyl (>150 mg ai/L). The predicted 

acute toxicity of saccharin to fish was at least two orders of magnitude lower than that observed 

sulfometuron methyl. However, when compared to the peak predicted EEC for sulfometuron 

methyl (0.031 mg/L), the predicted acute toxicity of the degradates to fish is still at least two 

orders of magnitude greater (1.9-214 mg/L). The lowest predicted chronic toxicity value for fish

(0.14 mg/L for saccharin) was about an order of magnitude greater than the predicted 90-d EEC

for sulfometuron methyl (0.016 mg/L). Given the relatively long degradation half lives used to 

predict EECs for sulfometuron methyl (e.g., several months or longer, Table 13), it also appears 

unlikely that these degradates would reach concentrations that would exceed those of 

sulfometuron methyl by 1-2 orders of magnitude (although it is possible that exposure on a molar 

basis to the most persistent degradates could be somewhat higher than to parent).

Effects on daphnids. For daphnids, the acute and chronic toxicity values predicted from 

ECOSAR ranged from 1.6-2,350 mg/L and 0.042-5.3 mg/L, respectively, for the remaining four 

degradates: 2-hydroxy, 4,6-dimethyl pyrimidine, saccharin, 2-(aminosulfonyl) benzoic acid, 

methyl ester, and 2-pyrimidinamine, 4,6-dimethyl (Table 51). When compared to the peek EEC 

of 0.031 mg/L for sulfometuron methyl, the ECOSAR-predicted acute toxicity of the degradates 

was at least two orders of magnitude greater (1.6-2,350 mg/L). However, for two degradates 

(saccharin and 2-pyrimidinamine, 4,6-dimethyl), the ECOSAR-predicted chronic toxicity (0.052 

and 0.042 mg/L, respectively) are relatively close to the 21-d EEC of sulfometuron methyl 

(0.026 mg/L). Thus, if the EECs for these degradates are comparable to the parent compound 

(sulfometuron methyl) and the toxicity predictions from ECOSAR are accurate, chronic toxicity 

of these two degradates to daphnia would be just a factor of two greater than the degradate EECs.

Effects on green algae. For green algae, the ECOSAR-predicted acute and chronic toxicity 

values for the degradates (0.41 - 257 mg/L; (Table 51) are much greater than those of 

sulfometuron methyl (0.0046 and 0.00063 for acute and chronic toxicity, respectively. This 

finding is expected given the mode of action of the degradates likely differ from sulfometuron 

methyl, which is specific to ALS inhibition in plants. The most sensitive of these toxicity values 

(0.41 mg/L for saccharin) is about an order of magnitude greater than the peak EEC of 0.031 

mg/L for sulfometuron methyl. This implies the potential risks from sulfometuron methyl to 

aquatic plants (green algae) are much more of a concern compared to its degradates. However, 

the phytotoxicity of saccharin may not be discounted entirely, especially if there is an 

underestimation of saccharin toxicity by ECOSAR and/or a higher level of exposure to saccharin 

due to (possibly) greater environmental persistence.
92

Although the above comparisons are subject to considerable uncertainty in both the toxicity 

estimates (ECOSAR) and EECs (assumed to be similar to those for sulfometuron methyl), they 

do suggest that the toxicity of the degradates is likely not a dominant concern, with the possible 

exception of chronic toxicity to freshwater invertebrates (daphnia) and acute toxicity to algae.

4.2.2. Risk to Terrestrial Animals

In the conceptual model, direct deposition, spray drift, root uptake, sediment and water runoff 

water, wind erosion of soil particles, and volatilization/inhalation are identified as the most likely 

exposure routes for sulfometuron methyl exposure to non-target terrestrial organisms. Risks to

terrestrial animals and plants (i.e. birds, terrestrial-phase amphibians, reptiles, mammals, and 

plants) were assessed based on modeled EECs and available toxicity data. As part of this 

screening terrestrial risk assessment, exposure concentrations of sulfometuron methyl to nontarget terrestrial plants and animals were modeled according to maximum labeled application 

rates. For terrestrial birds, terrestrial-phase amphibians, reptiles and mammals, estimates of 

upper bound levels of sulfometuron methyl residues on various food items, which may be 

contacted or consumed by wildlife, were determined using the Fletcher nomogram followed by a 

first order decline model TREX 1.3.1. Likewise, the TerrPlant 1.2.2 model was used to estimate 

exposure to non-target plants and the AgDRIFT 2.0.1 model provided further refinement of 

spray drift dispersion and deposition to terrestrial plants located in proximity to treated fields.

Note that AgDRIFT offers the ability to examine the variation in the amount of spray drift with 

application practices and conditions whereas TerrPlant does not (fixed values are used). Since 

spray drift is a dominant contributor to off-site exposure to terrestrial animals, the AgDRIFT 

predicted exposures, depending on the input assumptions, may be higher than those estimated 

with TerrPlant.

The risk hypothesis stated that the use of sulfometuron methyl has the potential to cause adverse 

effects to terrestrial animals and plants. This risk hypothesis is confirmed for terrestrial plants, 

and also for adverse effects to non-target terrestrial animals via indirect effects resulting from 

potential effects to plants. However, the assessment refutes the risk hypothesis regarding direct 

effects to animals and suggests that direct effects to terrestrial animals are unlikely. 

4.2.2.1. Birds

Sulfometuron methyl is categorized as practically nontoxic to both waterfowl (mallard duck) on 

an acute oral basis (LD50 >4,650 mg/kg-bw) and practically nontoxic to both upland game birds 

and waterfowl by the subacute dietary route (LC50 >5,620 mg/kg-diet and > 4,600 mg/kg-diet, 

respectively). Since the LD50 and LC50 values are greater than the highest dose tested in the 

studies, with no effects occurring at any dose, a bounding analysis was conducted to evaluate 

potential effects associated with acute oral and subacute dietary exposure to sulfometuron methyl 

(Section 4.1; Table 42 and Table 43). This bounding analysis compared size class adjusted

‘indefinite’ LD50 values (i.e., ‘greater than’ values) based on a bird’s weight to predicted doses 

on food residues (EEC equivalent dose) following a single ground application of sulfometuron 

methyl at 0.375 lb ai/A. Based on this analysis, predicted RQs were all < 0.04 or lower, despite 
93

the conservative assumption that the ‘indefinite’ LC50 and LD50 values (at which no mortality 

was observed in the test) represent definitive LC50 and LD50 values (where 50% mortality 

occurred). Therefore, risk to birds from acute oral and subacute dietary exposure to 

sulfometuron methyl is judged to be highly unlikely.

No data were available on the effects of sulfometuron methyl to avian fauna from chronic 

exposures. Therefore, risks to birds from chronic exposure to sulfometuron methyl could not be 

directly quantified in this risk assessment. A qualitative assessment is conducted here based on 

chronic avian toxicity data obtained for 12 studies from 9 other sulfonylurea herbicides with the 

same mode of action (inhibition of acetolactate synthase; Figure 4). These data were obtained 

from EFED’s Ecotoxicity database using a cross reference with another EFED “Active 

Ingredient” database that links active ingredients with mode of action. Although these 12 

sulfonylurea herbicides likely do not represent the entire universe of sulfonylureas with chronic 

avian toxicity data, they are considered to provide a representative sample from which to 

qualitatively evaluate the uncertainty associated with lack of chronic avian toxicity data for 

sulfometuron methyl. 

Figure 4. Chronic Avian Toxicity of Sulfonylurea Herbicides

Results from Figure 4 indicate that out of the 12 chronic avian NOAECs examined for 

sulfonylurea herbicides, two occurred below the peek EEC of 90 mg ai/kg-diet calculated for 

short grass (Table 17). These two NOAECs were 30 mg ai/kg-diet for tribenuron methyl (MRID 

43594201) and 28 mg ai/kg-diet for prosulfuron (MRID 42949701). The LOAELs from these 

two studies (180 and 100 ppm, respectively) are above the 90 mg ai/kg-diet peek EEC. Thus, out 

of the 9 sulfonylureas evaluated, the peak EEC would exceed the LOC for 2 herbicides (or 12% 

of the chemicals). This finding is consistent with the generally low toxicity sulfonylurea 

herbicides terrestrial animals. Thus, while considerable uncertainty exists in extrapolating 

chronic NOAELs across chemicals even within the same mode of action, these results suggest 

that chronic toxicity to avian fauna is not likely to be a dominant concern in this risk assessment, 

1

10

100

1000

10000

Tribenuron methyl (BQ)

Chlorimuron Ethyl (BQ)

Triasulfuron (BQ)

Thifensulfuron-methyl (BQ)

Prosulfuron (MD)

Tribenuron methyl (MD)

Metsulfuron methyl (MD)

Sulfosulfuron (MD)

Primisulfuron-methyl (MD)

Chlorsulfuron (MD)

Triasulfuron (MD)

Soruce: OPP Ecotoxicity Database, core studies only (Oct, 2007); BQ = bobwhite quail, MD = Thifensulfuron-methyl (MD)

mallard duck

Peek EEC = 90 mg/kg-diet
94

although it cannot be discounted entirely since LOCs would be exceeded for 2 of the 9 herbicides 

evaluated. 

4.2.2.2. Mammals

As observed for avian fauna, sulfometuron methyl is classified as practically nontoxic on an 

acute basis to mammals. As described in Section 4.1, a bounding analysis compared predicted 

EECs to indefinite LD50 values (adjusted for different size classes) for the purposes of estimating 

the upper bound of acute toxicity risk. The highest EEC for mammals is 85.8 mg/kg-bw for 

short grass consumed by a 15 g mammal. The adjusted LD50 for 15 g mammals would be 10,989 

mg/kg bw. There is an approximately 120-fold difference between these two values. Since the 

acute RQs for all weight classes of mammals consuming all feed types are < 0.01 and less than 

the Agency LOCs (Table 44), acute risks from direct effects of sulfometuron methyl on 

mammals is not expected from the modeled uses. 

The chronic LOC for mammals was not exceeded for the modeled uses. Predicted residues of 

sulfometuron methyl on different food types was compared to size class adjusted NOAELs. The 

highest RQ (0.07) occurred for the 15g mammal (Table 45) which is below the Agency’s LOC of 

1.0 for chronic effects to terrestrial animals. Therefore, chronic risks from direct effects of 

sulfometuron methyl on mammals are not considered likely.

4.2.2.3. Non-target Terrestrial-phase Amphibians, Reptiles, and 

Beneficial Insects

EFED currently uses data on surrogate species (birds) to assess non-target terrestrial phase 

amphibians and reptiles and does not derive risk quotients for terrestrial non-target insects. Based 

on the evaluation of potential risks to birds as surrogates for reptiles, potential risks to reptiles 

and terrestrial phase amphibians is also considered lower than the Agency’s concern level. 

As previously discussed, EFED does not currently estimate risk quotients for terrestrial nontarget invertebrates. However, submitted terrestrial insect toxicity data, based on tests with 

honeybees, suggest that sulfometuron methyl is practically non-toxic to bees (LD50 of >100 

μg/bee). The mode of action of sulfometuron methyl suggests it is likely not to be highly toxic 

to terrestrial invertebrates. To the extent that honey bees are representative of the sensitivity of 

insects and other terrestrial invertebrates to sulfometuron methyl, potential risk to terrestrial 

insects and invertebrates in treatment area is expected to be minimal. 

4.2.3. Risk to Terrestrial Plants

4.2.3.1. Tier 1 Modeling of Runoff and Spray Drift

Results presented in Section 4.1 using the TerrPlant model indicate the modeled uses of 

sulfometuron methyl result in exposures to non-endangered and endangered plants adjacent to 

treated areas that exceed the Agency’s LOC of 1.0. Both monocots and dicots appear highly 
95

sensitive to sulfometuron methyl, with dicots appearing to be the more sensitive group of plants. 

At the maximum aerial application rate of 0.375 lb ai/A, the maximum predicted EEC resulting 

from combined drift and runoff to semi-aquatic areas (0.21 lb ai/A) exceeded terrestrial monocot 

and dicot EC25 values by approximately 1000 and 6500 times, respectively (Table 48). For 

endangered monocots and dicots where a more sensitive endpoint is used (NOAEC), the 

predicted EEC for combined drift and runoff were 4800 and 7100 for monocots and dicots, 

respectively. For the spray drift analysis, predicted EECs were compared to results from the 

vegetative vigor test, which resulted in RQs of 500 and 1000 for non-endangered monocots and 

dicots respectively (Table 48). RQ values for endangered monocots and dicots resulting from 

drift from aerial application were 2200 and 19000 for monocots and dicots, respectively. 

These high RQ values are generally consistent with results from other sulfonylurea herbicide risk 

assessments both internal and external to the Agency. Furthermore, it is worth noting that the 

most sensitive monocot and dicot from the seedling emergence and vegetative vigor test is used 

to calculate risks to terrestrial plants. However, examination of the sensitivity of the other 9 test 

species indicates they too would be at risk from adverse effects of sulfometuron methyl at the 

modeled application rate. Specifically, the range in EC25s between the least and most sensitive 

plant from the seedling emergence study was about a factor of 75, while that for the vegetative 

vigor study was a factor of 5 (MRID 435385-01). The RQ values for the most sensitive monocot 

and dicot species are well above this margin. This indicates the predicted exceedence of the 

Agency’s LOC would also occur for the 9 other terrestrial plants tested and are not simply a 

function of a single, highly sensitive species. 

Given these high RQ values for terrestrial plants, a more refined spray drift analysis for 

exposures to non-target terrestrial plants in dry and semi-aquatic areas is provided in Section 

4.2.4. The potential risk to endangered monocots and dicots will be discussed in greater detail

in Section 4.2.8.2.

4.2.3.2. Field and Greenhouse Studies 

Based on a search of EPA’s ECOTOX database, field and greenhouse studies on the effects of 

sulfometuron methyl or its degradates were reviewed. Most of the field studies that passed the 

ECOTOX and OPP screening criteria were concerned with the efficacy of sulfometuron methyl 

control of target plants (weeds) and therefore are not considered useful indicators of the effects 

of sulfometuron methyl on non-target plant species (See APPENDIX H: Ecological Effects Data 

Summaries). Those studies that contained relevant information on the effects of sulfometuron 

methyl or its degradates on non-target plants are summarized below.

In a greenhouse study, Busse et al. (2005) studied the effect of sulfometuron methyl (applied as 

the formulated product Oust) on ectomycorrhizal formation and seedling growth of three conifer 

species: ponderosa pine (Pinus ponderosa), Douglas fir (Pseudotsuga menziesii), and white fir 

(Abies concolor). Conifer seedlings (5 replicates) were grown in four different soil types and 

applied with sulfometuron methyl at 0, 1X and 2X its application rate of 0.14 kg ai/ha (0.125 

lb/A). Sulfometuron methyl was applied to soil at the onset of lateral root formation 

(approximately 45-55 d post planting) due to the high sensitivity of seedlings to sulfometuron 

methyl applied prior to this time period. Results indicate that ectomycorrhizal formation was not 
96

inhibited for any conifer regardless of soil type or application rate (1X or 2X). For ponderosa 

pine, seedling dry weight and root growth (number of root tips/plant) were significantly reduced 

relative to controls at 0.125 and 0.250 lb ai/A in two of the four soil types. For Douglas fir and 

white fir, no significant reduction in seedling dry weight occurred at any treatment level. 

However, root growth was reduced for Douglas fir at 0.125 lb ai/A for three of the four soil types 

and at 0.25 lb ai/A for the forth soil type. White fir appeared least sensitive to sulfometuron 

methyl, with significant reductions in root growth at 0.125 lb ai/A in one soil type and at 0.25 lb 

ai/A in a second soil type. The authors conclude that sulfometuron methyl does not inhibit 

mycorrhizal formation at the specified application rates but does inhibit plant growth of 

ponderosa pine and root growth of all three species, depending on soil type and application rate. 

The lowest NOAEC from this study is 1X the application rate or 0.125 lb ai/A, several orders of 

magnitude above NOECs observed in the seedling emergence and vegetative vigor guideline 

studies.

Boyle and Walters (2005) examined the effect of saccharin, a major degradation product of 

sulfometuron methyl, on resistance of broad bean (Vicia faba) to rust fungus. Although not 

conceived as a degradate study per se, these results nevertheless have some relevance to the 

ecotoxicology of one of the sulfometuron methyl degradation products. In this study, 200 ml of 

0.3 mM saccharin was applied either as a soil drench or to foliage of broad bean which were 

exposed to rust fungus four times over a 14-d period. Results indicate that saccharin did not 

induce resistance to rust fungus nor did it significantly affect shoot weight or leaf area. However 

the authors report the number of leaflets formed was significantly reduced relative to controls. 

Neary et al. (1984) evaluated the effects of sulfometuron methyl (as the formulated product 

Oust) on slash pine (Pinus elliottii) and loblolly pine (Pinus taeda) seedlings inhabiting coastal 

plain flatlands. In this study, 60 trees of each species were exposed to sulfometuron methyl via 

broadcast spray at 0.50 lb ai/A in a randomized factorial design involving different plot 

locations, irrigation and fertilization levels. Although this study was designed primarily to 

investigate the efficacy of different weed control methods, the authors reported three months 

after treatment, application of sulfometuron methyl did not reduce survival of slash or loblolly 

pine, suggesting an unbounded NOAEC of 0.50 lb ai/A (only dose tested).

4.2.3.3. Contaminated Irrigation Water

The potential risks to plants when exposed to irrigation water contaminated with sulfometuron 

methyl were estimated for both ground water and surface water irrigation sources (Section 4.1.4). 

The EEC for ground water (0.33 ug/L) was calculated using the Tier 1 SCIGROW model (Table 

16) while that for surface water (31 ug/L) was calculated using PRZM/EXAMS from the 

scenario yielding the highest EECs (Table 15). Comparisons were made to the most sensitive 

endpoint from vegetative vigor study assuming that runoff of irrigation water does not occur. 

Results suggest that sulfometuron methyl levels in irrigation water from ground water sources 

would not exceed non-endangered or endangered species LOCs (i.e, RQs < 1.0). However, RQs 

based on sulfometuron methyl in irrigation water derived from surface water sources exceed the 
97

LOCs for both non-endangered and endangered species (3.9 and 71, respectively), thus 

indicating a potential risk to plants adjacent to fields irrigated with surface water sources. 

4.2.4. Refined Spray Drift Analysis

As described in Section 3.2.3.1 (Terrestrial Exposure Modeling), a more in-depth spray drift 

exposure assessment utilizing Tier I and II AgDRIFT® (version 2.01) was conducted to better 

characterize potential exposure of terrestrial plants. AgDRIFT® is a useful too for evaluating the 

potential of buffer zones to protect sensitive habitats from undesired exposures. Four different 

application scenarios were modeled reflecting typical and reasonable worst case assumptions 

regarding potential exposure conditions (labeled A through D in TABLE 20 and TABLE 21).

TABLE 52. RISKS TO TERRESTRIAL PLANTS FROM SPRAY DRIFT 

ACCORDING TO DISTANCE DOWNWIND, APPLICATION METHOD, AND 

DRIFT EXPOSURE CONDITIONS 

DISTANCE 

DOWN WIND 

(FEET)

PERCENT OF 

APPLICATION 

RATE

EEC (1) NONENDANGERED 

PLANTS (2)

ENDANGERED 

PLANTS(3)

Percent lb ai/A RQ RQ

[A] Ground Application (Low Boom)

0 102.0 0.3822 21233 386061

50 1.77 0.0066 367 6667

100 0.95 0.0036 200 3636

200 0.51 0.0019 106 1919

500 0.21 0.0008 44 808

750 0.13 0.0005 28 505

900 0.11 0.0004 22 404

[B] Ground Application (High Boom)

0 106.0 0.3956 21978 399596

50 5.00 0.0187 1039 18889

100 2.48 0.0093 517 9394

200 1.20 0.0045 250 4545

500 0.39 0.0015 83 1515

750 0.22 0.0008 44 808

900 0.17 0.0006 33 606
98

[C] Aerial (Following Many Label Recommendations)

0 50.00 0.1874 10411 189293

50 17.12 0.0642 3567 64848

100 9.79 0.0367 2039 37071

200 4.69 0.0176 978 17778

500 1.92 0.0072 400 7273

750 1.39 0.0052 289 5253

900 1.24 0.0046 256 4646

[D] Aerial (High-End Exposure Scenario)

0 77.35 0.2900 16111 292929

50 38.32 0.1437 7983 145152

100 25.11 0.0941 5228 95051

200 14.07 0.0527 2928 53232

500 5.40 0.0203 1128 20505

750 3.82 0.0143 794 14444

900 3.32 0.0125 694 12626

(1) Details of the refined spray drift modeling are provided in Section 3.2.3.1. (2) Non-endangered plant RQs based on vegetative vigor EC25 for soybean of 1.8 x 10-5 lb ai/A (MRID 435385-01)

(3) Endangered plant RQs based on vegetative vigor EC05 for soybean of 9.9 x 10-7 lb ai/A (MRID 435385-01).

Results from the refined spray drift modeling indicate that RQs exceed the Agency LOC of 1.0 

for endangered and non-endangered terrestrial plants based on all four exposure scenarios at the 

maximum distance modeled (the model limit of 900 ft downwind of the treated field; see 

TABLE 20). The highest initial RQ values occurred with ground applications (high and low 

boom), although RQs dropped substantially as the distance downwind increased. At a downwind 

distance of 900 ft, RQs dropped by approximately a factor of 1000 and 600 of the edge of field 

RQs (0 ft) for low boom and high boom ground applications, respectively. The 50 ft buffer 

resulted in the largest proportional decline in EECs relative to edge of field estimates, declining 

to 1.7% and 5.0 % of the initial EECs for low and high boom ground applications, respectively.

Compared to ground applications, aerial applications resulted in lower initial EECs at the edge of 

the field (downwind distance = 0), however, the attenuation of EECs with distance downwind 

was not as great as that observed with ground applications. The EECs (and RQs) declined to 
99

17% and 38% 50 ft from the edge of field for the typical and high end exposure scenarios, 

respectively. At 900 ft downwind, RQs for non-endangered plants are approximately 250 and 

700 for the typical and high end aerial application exposure scenarios, respectively. For 

endangered plants, RQs calculated at 900 ft downwind are approximately 4,600 and 12,600 for 

the typical and high end aerial application exposure scenarios, respectively. 

Pertinent to these modeling results are a number of recommendations (but not requirements) on 

the product labels for sulfometuron methyl. The labels suggest that “The most effective way to 

reduce drift potential is to apply large droplets (>I50 - 200 microns)”; but there is no specific 

mandate on the label. Other suggestions on the label include: that boom height less than 10 feet 

decreases the potential for spray drift from helicopter or aircraft applications, For ground 

applications; the applicator receives the following directions: “Setting the boom at the lowest 

height that provides uniform coverage and reduces the exposure of droplets to evaporation and 

wind.” The label notes that drift is minimized when the wind speed is between 3 and 10 mph.

4.2.5. Review of Incident Data

An analysis of the ecological incidents associated with a pesticide application (or misapplication) 

is an important part of EPA’s ecological risk assessment because such information can help 

establish additional lines of evidence to the risk assessment conclusions. A search of EPA’s 

Ecological Incident Information System (EIIS) was conducted in September, 2007 which 

revealed 35 incidents reports for sulfometuron methyl with varying degrees of confidence in the 

causal association. Of these 35 incidents, one was classified as highly probable, 20 were 

classified as probable and 14 were classified as possible (“APPENDIX E: Adverse Ecological 

Incidents Associated with Sulfometuron Methyl Use”). Only the incidents classified as either

highly probable or probable are discussed further here.

Highly Probable Incidents. The incident classified as highly probable is worthy of discussion 

here because it is one of the few incidents involving sulfonylurea herbicides where positive 

findings of pesticide residues were reported. In this case (Incident Report 1011666-001), Oust 

herbicide (containing sulfometuron methyl) was applied by the Bureau of Land Management 

(BLM) personnel to approximately 22,000 acres of Idaho forest and grassland in the autumn of 

2000 for weed control. These areas were severely damaged or burned by wildfires that occurred 

the previous year. Following the aerial application of Oust at a rate of 0.0625 lb ai/A, drought 

and windy conditions (up to 20-40 mph) caused pesticide drift, presumably via erosion of dry 

treated soils. Thousands of acres were alleged to have been affected, including sugar beets, 

small grains, garlic, potato, corn, and alfalfa. Soil residues of sulfometuron methyl measured on 

BLM land ranged from 0.079 to 0.82 ppb. Documentation by the State of Idaho Dept. of 

Agriculture showed that in one case, there was evidence to show that sulfometuron methyl was 

present 13 miles from the application site. Crop damage was estimated to be in excess of $72 

million.

Probable Incidents. Of the 20 probable incidents involving sulfometuron methyl, 5 involved 

accidental misuse and all but one of the remaining involved registered uses. Regarding the 

application method, the majority of probable incidents involved ground application, although 

about one third of the incident reports did not contain information on the application method. 
100

Relative to the type of application site, 7 involved railroad or road rights of way and 6 involved 

agriculture sites. In terms of route of exposure, pesticide drift (either alone or in combination 

with runoff) was reported for 11 probable incidents, while runoff (either alone or in combination 

with drift) was reported for 9 probable incidents. A total of 19 probable incidents reported for 

sulfometuron methyl involved damage to terrestrial plants and only one reported damages to 

aquatic plants and animals. 

Although these sulfometuron methyl ecological incident reports do not conclusively establish 

sulfometuron methyl as the cause of the reported damages, in the aggregate they suggest that 

non-target terrestrial plants in particular can be susceptible to both sulfometuron methyl drift and 

runoff, which was found to be the pathway and receptor of greatest concern in this risk 

assessment. The also are consistent with the risk assessment findings of no significant risk of 

direct toxicity to aquatic and terrestrial animals.

4.2.6. Overall Ecological Risk Conclusions

The results of this screening risk assessment indicate that potential risks from direct effects to 

aquatic and terrestrial animals from exposure to sulfometuron methyl modeled at the maximum 

annual application rate (0.375 lb ai/A) are below the Agency’s LOCs. Therefore, risk from 

direct effects to aquatic and terrestrial animals is considered unlikely. Given the mode of action 

of sulfometuron methyl (ALS inhibitor), the potential for direct effects to aquatic and terrestrial 

plants is indicated by this screening level risk assessment. Based on a refined analysis of 

sulfometuron methyl spray drift, RQs for terrestrial plants exceed the Agency’s LOC at 900 ft 

downwind from a treated field in all four application scenarios evaluated. While the potential for 

direct effects to aquatic and terrestrial animals is considered small, the potential exists for 

indirect effects on animals due to impairment of aquatic and terrestrial plants. Specifically, 

direct effects to plant species could present an indirect risk at the higher levels of organization 

(i.e. population, trophic level, community, and ecosystem). Field studies are not available to 

quantify actual risk to plant and animal communities in forest/edge and wetland/riparian habitats. 

However, in terrestrial and shallow-water aquatic communities, plants are the primary producers 

upon which the succeeding trophic levels depend. If the available plant material is impacted due 

to the effects of sulfometuron methyl, this may have negative effects not only on the herbivores, 

but throughout the food chain. Also, depending on the severity of impacts to the plant 

communities [i.e., forests, wetlands, ecotones (edge and riparian habitats)], community 

assemblages and ecosystem stability may be altered (i.e. reduced bird populations in edge 

habitats; reduced riparian vegetation resulting in increased light penetration and temperature in 

aquatic habitats, loss of cover and food for fish). In addition, riparian vegetation, which is a 

significant component of the food supply for aquatic herbivores and detritivores provides habitat 

(i.e. leaf packs, materials for case-building for invertebrates) may also be affected.
101

4.2.7. Endocrine Effects

EPA is required under the Federal Food, Drug, and Cosmetic Act (FFDCA), as amended by the 

Food Quality Protection Act (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 was a scientific basis for including, as part of the program, the 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 EDSP have 

been developed, sulfometuron methyl may be subjected to additional screening and/or testing to 

better characterize effects related to endocrine disruption.

4.2.8. Federally Threatened and Endangered (Listed) Species

Both acute endangered species and chronic risk LOCs are considered in this screening-level risk 

assessment of pesticide risks to listed species. Endangered species acute LOCs are a fraction of 

the non-endangered species LOCs or, in the case of endangered plants, RQs are derived using 

lower toxicity endpoints than non-endangered plants. Therefore, concerns regarding listed 

species within a taxonomic group are triggered in exposure situations where restricted use or 

acute risk LOCs are triggered for the same taxonomic group. The risk assessment also includes 

an evaluation of the potential probability of individual effects for exposures that may occur at the 

established endangered species LOC in both the risk characterization and the endangered species 

sections. This probability is calculated using the established dose/response relationship and 

assumes a probit (probability unit) dose/response relationship. This analysis is present below. 

4.2.8.1. Action Area

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

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 co-located 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 animals are assumed to be 

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

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

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

treatment area. 

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 
102

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 and could be considered along with available 

information on the fate and transport properties of the pesticide to determine the extent to which 

screening assumptions regarding an action area apply to a particular listed organism. These 

subsequent refinement steps could consider how this information would impact the action area 

for a particular listed organism and may potentially include areas of exposure that are downwind 

and downstream of the pesticide use site.

The results of this screening risk assessment indicate that direct effects to plant species could 

present an indirect risk at the higher levels of organization (i.e. population, trophic level, 

community, and ecosystem). The distance from the treated area that risks could extend is greater 

than 900 feet based on AgDRIFT spray drift modeling. Therefore, an action area for endangered 

species cannot be defined at this time for this assessment. We note that, while the AgDISP 

model with Gaussian extension model is available for extending predictions of deposition from 

spray drift beyond 1000 feet the exceedances of levels of concern for non-target plants are likely 

to extend well beyond 1000 feet given the trends observed with AgDRIFT up to 900 feet. This is 

evident from the risk quotient calculations for terrestrial plants exposed to spray drift in TABLE 

52 ( the RQ range at 900 feet ranged from 22 to 12626 using different ground and aerial 

application condition and equipment assumptions).

4.2.8.2. Taxonomic Groups Potentially at Risk

This screening level risk assessment for endangered species indicates that sulfometuron methyl

exceeds the Endangered Species LOCs for the specified use scenario for the following 

taxonomic groups:

- Terrestrial plants: monocots and dicots adjacent to treated areas, semiaquatic areas, and drift for turf use at a single application rate of 0.375

lbs ai/A via ground or aerial spray. 

- Freshwater, estuarine and marine aquatic vascular and nonvascular 

plants adjacent to treated areas receiving a combination of runoff and 

spray drift at a single application rate of 0.375 lbs ai/A.

No LOCs were exceeded for birds, mammals, reptiles, terrestrial-phase amphibians, fish, 

invertebrates, or aquatic-phase amphibians.

Discussion of Risk Quotients. For a screening level risk assessment, EFED determines what 

endangered species may be affected by performing a screening level assessment. If the RQs 

from this assessment do not exceed the listed species LOCs, endangered species may not be 
103

affected. However, the Agency’s LOC for endangered aquatic plants and terrestrial plants is 

exceeded for the uses of sulfometuron methyl as outlined in previous sections. Should estimated 

exposure levels occur in proximity to listed resources, the available screening level information 

suggests a potential concern for direct effects on listed terrestrial and aquatic vascular plants and 

species that rely on these taxa for survival, growth, or reproduction.

Probit Dose Response Relationship. A probit dose response analysis is usually performed for 

aquatic and terrestrial animal toxicity studies for which slopes with 95% confidence intervals are

available. The probit slope response relationship is evaluated to calculate the chance of an 

individual event corresponding to the listed species acute LOCs. It is important to note that the 

IEC model output can go as high as 1 x 1016 or as low as 1 x 10-16 in estimating the event 

probability. This cut-off is a limit in the Excel spreadsheet environment and is not to be 

interpreted as an agreed upon upper or lower bound threshold for concern for individual effects 

in any given listed species. To accomplish this interpretation, the Agency would use (1) the slope 

of the dose response relationship available from the toxicity study used to establish the acute 

toxicity measurement endpoints for each animal taxonomic group; (2) an assumption of a probit 

dose response relationship; (3) a mean estimate of slope consistent with current Agency 

statistical procedures; and (4) a lower limit to the estimate of individual effect chance based on 

what could be calculated by Excel spreadsheet "Normdist" function. . In cases where doseresponse curves are unavailable, event probabilities are calculated for the listed species LOC 

based on a default slope assumption of 4.5 as per original Agency assumptions of typical slope 

cited in Urban and Cook (1986).

For sulfometuron methyl, LC50 or EC50 values were not achieved in any of the aquatic or 

terrestrial animal acute toxicity studies. Therefore, it is not possible to estimate the slope and 

confidence limits directly from these studies. In lieu of such information, EFED default values 

are used for the slope (4.5) and confidence intervals (2 to 9) and applied to the LOC values. 

Probability of an individual effect from sulfometuron methyl was estimated at the acute 

endangered species LOC for aquatic and terrestrial animals. This analysis is presented in the 

following table.

For aquatic organisms, the LOC for endangered species is 0.05. The RQ is the ratio of exposure 

to toxicity, so at the point where that ratio equals 0.05, there is a 1 in 418 million chance of an 

individual being affected. The uncertainty in this number lies primarily in whether the actual 

exposure of sensitive species is likely to equal that modeled. For birds, terrestrial-phase 

Taxa Probit Slope Endangered 

Species 

LOC

Estimated Probability of an 

Individual Effect at the 

Endangered Species LOC

Comment

Fish 4.5 (2 – 9) 0.05 1 in 4 x 108

(1 in 2 x 102 to 1 in 2 x 1031)

Data insufficient to 

allow for probit 

slope derivation; 

therefore, the 

default slope of 4.5 

with lower and 

upper bounds of 2 

– 9 was used.

Aquatic 

Invertebrates

4.5 (2 – 9) 0.05 1 in 4 x 108

(1 in 2 x 102 to 1 in 2 x 1031)

Birds 4.5 (2 – 9) 0.1 1 in 2.9x 105 (1 in 44 to 

1 in 9 x 1018)

Mammals 4.5 (2 – 9) 0.1 1 in 2.9x 105 (1 in 44 to 

1 in 9 x 1018)
104

amphibians, reptiles and mammals, the endangered species LOC is 0.1. The chance of one 

individual being affected at an RQ equal to the LOC is 1 in 294,000

Because the screening level risk assessment indicates that sulfometuron methyl uses exceed the 

endangered species LOC for terrestrial and aquatic plants, a ‘may affect’ designation can not be 

precluded based on this assessment. Additionally, the acute level of concern for terrestrial and 

aquatic vascular plants is exceeded. The Agency considers this to be indicative of a potential for 

adverse effects to those listed species that rely either on a specific plant species (plant species 

obligate) or multiple plant species (plant dependant) for some important aspect of their life cycle. 

Further analysis regarding the overlap of individual species with each use site is required prior to 

determining the likelihood of potential impact to listed species. Such a refinement is outlined in 

the following sections.

Data Related to Under-represented Taxa. Data are not available to evaluate effects to underrepresented taxa.

Implications of Sublethal Effects. Sublethal effects were not observed in acute aquatic and 

terrestrial animal studies. Chronic studies were available for freshwater invertebrates, but not 

fish, birds or mammals. The chronic RQ for freshwater invertebrates did not exceed the chronic 

LOC. Similarly for fish, a chronic RQ, calculated from an NOAEC estimated using acutechronic ratio, did not exceed the chronic LOC. For birds, analysis of reproductive NOAECs 

from other sulfonylurea herbicides suggests that while potential chronic risks from sulfometuron 

methyl cannot be ruled out, they are considered unlikely. For mammals, results from a 

developmental toxicity test indicate the RQ does not exceed the chronic LOC, however, no data 

were available on the chronic, reproductive effects of sulfometuron methyl to mammals. 

Indirect Effects Analysis. The non-endangered and endangered species LOCs for non-target 

plants were exceeded for both terrestrial (monocots and dicots) and aquatic plants (vascular, 

nonvascular) located adjacent to treated areas, in semi-aquatic areas, and by spray drift for the 

scenarios analyzed. The guideline plant studies indicate direct adverse effects to seedling 

emergence, vegetative vigor, and aquatic vascular and non-vascular plants, as well as non-lethal 

effects such as chlorosis, growth retardation, necrosis, and unusual pigmentation. 

Damage to non-target plants may be sufficient to prevent the plant from competing successfully 

with other plants for resources and water. Sulfometuron methyl may increase a plant’s 

susceptibility to disease and can disrupt nutrient cycling in soil by inhibiting the ability of 

enzymes to break down cellulose and thereby, decompose plant material. Endangered species 

may be especially impacted by exposure to sulfometuron methyl because of the impact of the 

loss of a few individuals to the population. There is a potential concern for listed species with 

either broad or narrow dependencies on impacted plant species/populations/communities for 

habitat, feeding or cover requirements. In terrestrial and shallow-water aquatic communities, 

plants are the primary producers upon which the succeeding trophic levels depend. If the 

available plant material is impacted due to the effects of sulfometuron methyl, this may have 

negative effects not only on the herbivores, but also throughout the food chain. In addition, 

depending on the severity of impacts to the plant community [i.e., forest, wetlands, ecotones 
105

(edge and riparian habitats)], assemblages and ecosystem may be altered (i.e., reduced bird 

populations in edge habitats, reduced riparian vegetation resulting in increased light penetration 

and temperature in aquatic habitats, loss of cover and food for fish).

Critical Habitat. In the evaluation of pesticide effects on designated critical habitat, 

consideration is given to the physical and biological features (constituent elements) of a critical 

habitat identified by the U.S. Fish and Wildlife and National Marine Fisheries Services as 

essential to the conservation of a listed species and which may require special management 

considerations or protection. The evaluation of impacts for a screening level pesticide risk 

assessment focuses on the biological features that are constituent elements and is accomplished 

using the screening-level taxonomic analysis (risk quotients, RQs) and listed species levels of 

concern (LOCs) that are used to evaluate direct and indirect effects to listed animals.

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

species for those animals dependant upon aquatic plants, and terrestrial and semi-aquatic plants. 

In light of the potential for indirect effects, the next step for EPA and the Service(s) is to identify 

which listed species and critical habitat are potentially implicated. Analytically, the 

identification of such species and critical habitat can occur in either of two ways. First, the 

agencies could determine whether the action area overlaps critical habitat or the occupied range 

of any listed species. If so, EPA would examine whether the pesticide's potential impacts on

non-endangered species would affect the listed species indirectly or directly affect a constituent 

element of the critical habitat. Alternatively, the agencies could determine which listed species 

depend on biological resources, or have constituent elements that fall into, the taxa that may be 

directly or indirectly impacted by the pesticide. Then EPA would determine whether use of the 

pesticide overlaps the critical habitat or the occupied range of those listed species. At present, 

the information reviewed by EPA does not permit use of either analytical approach to make a 

definitive identification of species that are potentially impacted indirectly or critical habitats that 

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

together to conduct the necessary analysis.

This screening-level risk assessment for critical habitat provides a listing of potential biological 

features that, if they are 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 the following: aquatic plants, and terrestrial and semi-aquatic 

plants. 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.

Direct Effect Co-occurrence Analysis. Because the Endangered Species LOC for terrestrial 

and aquatic plants is exceeded for the proposed use of sulfometuron methyl, LOCATES would 

usually be run for all listed terrestrial and aquatic plants (monocots, dicots, ferns, lichen and 

conf/cycds) to determine the potential for co-occurrence of listed plant species location with 

areas of expected pesticide use. However, no preliminary analysis was performed for non-crop 

uses of sulfometuron methyl because the LOCATES tool does not include county-level location 

information for the proposed non-crop uses of sulfometuron methyl. Consequently, based on the 

information available at this step in the assessment process, it is presumed that all listed plant 

species are potentially directly affected from the broad range of sulfometuron methyl proposed 
106

uses which include vegetative management in railroad, utility, and roadside rights-of-ways, 

forestry, tree plantations, industrial sites, and road construction. These uses do not have a 

geographically distinct attribute which can be used to define the co-occurrence of listed species 

in the LOCATES database. Additional analysis of listed plant locations, refinement of the action 

area associated with sulfometuron methyl, and the biology of the potentially affected species 

would be needed before an effects determination can be made for any of the co-located species 

identified by this assessment. 

Indirect Effect Co-occurrence Analysis. The screening-level RQ for terrestrial monocots and 

dicots and aquatic nonvascular and vascular plants exceeds the LOC for endangered species. In 

accordance with established procedures such findings suggest a potential concern for indirect 

effects to listed animal species with both narrow (i.e., species that are obligates or have very 

specific habitat or feeding requirements) and general dependencies (i.e., cover type 

requirements) on plants as a resource or important habitat component. LOCATES would usually 

be used to preliminarily identify listed animal species that are located within the counties in USA 

where sulfometuron methyl could be used. This analysis would consider all animal taxonomic 

groups (i.e., birds, mammals, terrestrial and aquatic-phase amphibians, reptiles, insects, fish, 

bivalves, crustaceans, arachnids, and gastropods). However, no preliminary analysis was 

available for non-crop use of sulfometuron methyl because the LOCATES tool does not include 

county-level location information for the non-crop uses of sulfometuron methyl. Consequently, 

based on the information available at this step in the assessment process, it is presumed that all 

listed plant species are potentially directly affected from the broad range of sulfometuron methyl

proposed uses which include vegetative management in railroad, utility, and roadside rights of 

ways, forestry, tree plantations, industrial sites, and road construction. These uses do not have a 

geographically distinct attribute which can be used to define the co-occurrence of listed species 

in the LOCATES database. Additional analysis of listed plant locations, refinement of the action 

area associated with sulfometuron methyl, and the biology of the potentially affected species 

would be needed before an effects determination can be made for any of the co-located species 

identified by this assessment. 

The following table provides listed taxonomic groups that may be at risk from direct or indirect 

effects due to applications of sulfometuron methyl for vegetative management uses nationwide. 

Table 53. Listed Taxonomic Groups Potentially at Risk from Direct or Indirect Effects of 

Sulfometuron Methyl Application for Vegetative Management Throughout the U.S.

Listed Taxon Direct 

Effects

Basis for Direct Effects Concern Indirect 

Effects

Basis for Indirect Effects Concern

Terrestrial and 

Semi-Aquatic 

Plants –

monocots and 

dicots

Yes The endangered species LOC is 

exceeded for terrestrial plants. Yes

Potential concerns from shifts in plant 

community structure and function due to 

from selective impacts on plant species. 

Terrestrial 

Invertebrates No Sulfometuron methyl is practically 

nontoxic to honeybees, suggesting no

Yes Potential concerns for terrestrial invertebrates 

that use plants for habitat, feeding, or cover 
107

direct effect concerns for terrestrial 

invertebrates.

requirements.

Birds and 

Reptiles(1) No The LOC is not exceeded Yes

Potential concerns for birds and reptiles use 

plants for habitat, feeding, or cover 

requirements.

Terrestrial-phase 

Amphibians(1) No The LOC is not exceeded Yes

Potential concerns for terrestrial-phase 

amphibians that use plants for habitat, 

feeding, or cover requirements. 

Mammals No The LOC is not exceeded Yes

Potential concerns for mammals that use 

plants for habitat, feeding, or cover 

requirements. 

Aquatic Vascular 

Plants and 

Nonvascular 

Plants

Yes

The endangered species LOC is 

exceeded for aquatic vascular and 

nonvascular plants. 

No

Potential concerns from shifts in plant 

community structure and function due to 

from selective impacts on plant species.

Freshwater and 

Marine/Estuarine 

fish and Aquaticphase 

Amphibians(2)

No The LOC is not exceeded Yes

Potential concerns for fish and aquatic-phase 

amphibians that use plants for habitat, 

feeding, or cover requirements. 

Freshwater and 

Marine/Estuarine 

Crustaceans

No The LOC is not exceeded Yes

Potential concerns for crustaceans that use 

plants for habitat, feeding, or cover 

requirements. 

Mollusks No The LOC is not exceeded Yes

Potential concerns for mollusks that use 

plants for habitat, feeding, or cover 

requirements. 

(1) Birds are used as surrogate species for terrestrial-phase amphibians and reptiles; therefore, potential direct and indirect 

effects to endangered avian, terrestrial-phase amphibians and reptilian species are considered equivalent.

(2) Fish are used as a surrogate for aquatic phase amphibians; therefore, potential direct and indirect effects to endangered fish and aquatic-phase 

amphibian species are considered equivalent.

4.3. Description of Assumptions, Limitations, Uncertainties, 

and Data Gaps

4.3.1. Assumptions and Limitations Related to Effects on all 

Species

• Indirect Effects. Perhaps one of the largest uncertainties associated with the effects 

assessment for sulfometuron methyl is the inability to adequately quantify potential 

indirect effects resulting from adverse effects on aquatic and terrestrial plants. 

Specifically, direct effects to plant species could present an indirect risk at the higher 

levels of organization (i.e. population, trophic level, community, and ecosystem). Field 

studies are not available to quantify actual risk to plant and animal communities in 

forest/edge and wetland/riparian habitats. However, in terrestrial and shallow-water 

aquatic communities, plants are the primary producers upon which the succeeding trophic 

levels depend. If the available plant material is impacted due to the effects of 

sulfometuron methyl, this may have negative effects not only on the herbivores, but 

throughout the food chain. Also, depending on the severity of impacts to the plant 

communities [i.e., forests, wetlands, ecotones (edge and riparian habitats)], community 

assemblages and ecosystem stability may be altered (i.e. reduced bird populations in edge 
108

habitats; reduced riparian vegetation resulting in increased light penetration and 

temperature in aquatic habitats, loss of cover and food for fish). In addition, riparian 

vegetation, which is a significant component of the food supply for aquatic herbivores 

and detritivores provides habitat (i.e. leaf packs, materials for case-building for 

invertebrates) may also be affected.

• Toxicity of Degradation Products. In this screening level ecological risk assessment, 

the lack of data on major degradates is considered one of the primary limitations and 

uncertainty regarding the overall risk associated with one of the registered use of 

sulfometuron methyl. Since the chemical structure and environmental behavior of the 

major degradates differ substantially from the parent molecule (i.e., degradation involves 

cleavage of the sulfonylurea bridge, essentially splitting the molecule in half), it could not 

be assumed with reasonable confidence that the degradates were equivalent in toxicity to 

the parent compound. Limited toxicity data was available for one major degradation 

product: saccharin. However, this information was oriented towards human health 

concerns and lacked endpoints of ecological relevance that would be considered useful in 

this ecological risk assessment. This finding is somewhat expected since saccharin is 

used as a sugar substitute in the U.S. food supply.

• Variability in Species Sensitivity. 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 endpoints 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. For terrestrial and aquatic animals, uncertainty associated with the limited 

quantification of interspecies variability in sensitivity to sulfometuron methyl would 

probably not impact the risk assessment results substantially, given that sulfometuron 

methyl is practically nontoxic to animals. For aquatic and terrestrial plants, variability in 

sensitivity across species could substantially alter the risk assessment results (e.g., higher 

RQs if more sensitive species were tested). However, toxicity data were available for 5 

species of aquatic plants and 10 species of terrestrial plants distributed broadly across 

taxonomic groups, which suggests that at least a reasonable range of plant sensitivity to 

sulfometuron methyl was captured in this risk assessment.

• Effects of Pesticide Mixtures: This assessment considered only exposure to the active 

ingredient sulfometuron methyl. However, simultaneous exposures to multiple chemical 

and physical stressors are likely to occur in the environment. No acceptable data were 

located that evaluated potential additive, synergistic, or antagonistic interactions between 

sulfometuron methyl and other chemical stressors. If such interactions occur, then risks 

could be under or over-estimated. 
109

4.3.2. Assumptions and Limitations Related to Effects on

Aquatic Species

• Study Quality and Data Gaps. Several studies did not meet guideline requirements and 

therefore were classified as either supplemental or unacceptable. Specifically, all acute 

toxicity data for marine and estuarine organisms were classified as supplemental due to 

uncertainty associated with the bioavailability of sulfometuron methyl in these tests. 

However, conclusions of this risk assessment would not likely change with submission of 

additional acute toxicity data for marine and estuarine organisms because EECs were 

several orders of magnitude below reported toxicity limits. The freshwater chronic test 

with fathead minnow was found to be unacceptable, again because of uncertainty and 

variability associated with measurement of soluble (bioavailable) sulfometuron methyl. 

To address this data gap, acute-chronic ratios were applied to estimate chronic toxicity to 

freshwater fish. Results indicate that even with conservative assumptions regarding the 

selection of the ACR, risks from direct effects of chronic sulfometuron methyl exposure 

to freshwater fish are not likely.

4.3.3. Assumptions and Limitations Related to Effects on

Terrestrial Species

• Study Quality and Data Gaps. Lack of toxicity data was noted for the effect of 

sulfometuron methyl on avian and mammalian reproduction. For mammals, the NOAEL 

of 300 mg ai/kg-bw/d was used from a developmental toxicity study to rabbits. While 

providing some information on the effect of sulfometuron methyl on mammalian 

development during gestational exposure, results from this study do not capture the 

potential effects of sulfometuron methyl on reproductive endpoints including courtship, 

mating, sex ratios and offspring survival, growth and development. 

• Vascular Plant Reproduction. Terrestrial and aquatic plants appear most sensitive to 

sulfometuron methyl exposure. While toxicity data were available for endpoints related 

to systemic growth, seedling emergence and visual injury, these guideline studies are not 

designed to capture reproductive endpoints. Therefore, to the extent that plant 

reproduction is more sensitive to sulfometuron methyl exposure compared to growth or 

visual injury-related endpoints, risks to aquatic and terrestrial plants may be 

underestimated. 

• Use of Maximum Pesticide Application Rate. In this screening level analysis, risks of 

sulfometuron methyl to non-target plants and animals was evaluated using the maximum 

label application rate (0.375 lb ai/A). This was performed in concordance with the goals 

of a screening assessment: to rule out receptors and exposure pathways and identify those 

pathways where potential risks are evident. Other label application rates are available for 

sulfometuron methyl as identified in see Section 3.1 (Use Characterization). The lower 

range of application rates are mostly within a factor of 10 of the maximum application 

rates. Given that RQs for terrestrial and aquatic plants predicted using the maximum 

application rate are well above a factor of 10, use of the lower application rates would not 

likely change the risk assessment conclusions.
110

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McKelvey, RA. 1995. Influence of Sulfometuron Methyl (DPZ-T5648) on Seedling Emergence 

and Vegetative Vigor of Several Terrestrial Plants. Study No. AMR 2871-93. E.I. du Pont de 

Nemours and Co., Wilmington, DE 19880.

Naqvi, SM and Hawkins, RH 1989. Responses and LC50 Values for Selected Microcrustaceans 

Exposed to Spartan, Malathion, Sonar, Weedtrine-D, and Oust Pesticides. Bull. Environ. 

Contam. Toxicol. 43: 386-393.

Neary, DG, Conde, LF, and Smith, JE. 1984. Effects of Sulfometuron Methyl on Six Important 

Competing Species in Coastal Plain Flatwoods. Proc.South Weed Sci.Soc. 37: 193-199.

Raimondo, S, Montague, BJ, Barron, MG. (2007). Determinants of Variability in Acute-Chronic 

Ratios for Invertebrates and Fish. Environ. Tox. Chem. 26(9):

Romaire, RP. 1984. Acute Toxicity of Krenite and Oust to Juvenile Red Swamp Crawfish, 

Procambarus clarkia. (Decapoda, Cambaridae). Louisiana State University, Agricultural 

Experiment Station, Baton Rouge, LA. Prepared for C.Wood, E.I. DuPont Corporation, Haskell 

Laboratory, New Ark, Delaware. 19pp.

Teske, M.E and H.W. Thistle 2004. Aerial application model extension into the far field. 

Biosystems Engineering 89(1) 29-36.

Thistle, HW, ME Teske, JG Droppo, CJ Allwine, SL Bird, and RJ Londergan. 2005. 

AGDISP as a Source Term in Far Field Atmospheric Transport Modeling and Near Field 

Geometric Assumptions. Amer. Soc. Agric. and Biol. Engineers, St. Joseph, Michigan; 

www.asabe.org .

USDA. 2004. Sulfometuron Methyl- Human and Ecological Risk Assessment: Final Report. 

Prepared for: U.S. Dept. Agriculture, Forest Service. Contract No. GS-10F-0082F.

USEPA. 1998. Guidelines for Ecological Risk Assessment. U.S. Environmental Protection 

Agency, Risk Assessment Forum, Washington, DC, EPA/630/R095/002F

USEPA. 2004. Overview of the Ecological Risk Assessment Process in the Office of Pesticide 

Programs, U.S. Environmental Protection Agency. Endangered and Threatened Species Effects 

Determinations. Office of Prevention, Pesticides and Toxic Substances, Office of Pesticide 

Programs, Washington, D.C. January 23, 2004.

USEPA. 2007. Ecological Risk Assessment: Flazasulforon. Office of Pesticide Programs, 

Environmental Fate and Effects Division, Washington, DC.

Weber, J.B., G.G. Wilkersona and C.F. Reinhardt. 2004 Calculating pesticide sorption 

coefficients (Kd) using selected soil properties. Chemosphere 55:157–166

William A. Battaglin, Edward T. Furlong, Mark R. Burkhardt, C. John Peter. (2000).

Occurrence of Sulfonylurea, Sulfonamide, Imidazolinone, and other Herbicides in
112

Midwestern Rivers, Reservoirs, and Ground Water. The Science of the Total Environment 248: 

123-133

Willis, G. H. and L..L. McDowell, 1987. Pesticide Persistence on Foliage. in Reviews of 

Environmental Contamination and Toxicology. 100:23-73. 

Zhu QZ, Degelmann P, Niessner R, Knopp D. Selective trace analysis of sulfonylurea herbicides 

in water and soil samples based on solid-phase extraction using a molecularly imprinted 

polymer. Environ Sci Technol. 2002 Dec 15;36(24):5411-20
113

6. APPENDICES

APPENDIX A: STRUCTURES AND CHEMICAL NAMES OF 

SULFOMETURON METHYL METABOLITES

Chemical Structures

Trivial or common names

Company id or similar alternate names

Full chemical names

Sulfometuron methyl

DPX-T5648; DPX-5648; IN-T5648; IN 

T5648-18

Methyl 2-(4,6-dimethylpyrimidin-2-

ylcarbamoylsulfamoyl)benzoate

Saccharin

IN-581

1,2-Benzisothiazol-3(2H)-one, 1,1-dioxide

Sulfometuron pyrimidine amine

IN-X0993; IN-X993; PA

4,6-Dimethyl-2-pyrimidinamine

4,6-dimethyl-2-pyrimidinamine

Sulfometuron sulfonamide

IN-D5803; SA; methyl phenylsulfonamide

Methyl 2-(aminosulfonyl)benzoate.

2-(Aminosulfonyl)-benzoic acid, methyl ester
114

Pyrimidine-ol

IN-11859

4,6-Dimethyl-2-pyrimidinol

Sulfometuron free acid

FA-SM; IN-T6385

2-[[[[(4,6-Dimethyl-2-

pyrimidinyl)amino]carbonyl]amino]sulfonyl]-

benzoic acid

O

O

H

S

O

O

N

H

H

0Free acid Sulfonamide

FA-Sulfonamide; Free acid; IN-D5119

2-(Aminosulfonyl)benzoic acid
115

APPENDIX B: ENVIRONMENTAL FATE DATA 

REQUIREMENTS

Environmental Fate Data Requirements for Sulfometuron Methyl

Guideline Data 

Requirement Test Material MRID

Study 

Classification

Data 

Requirement 

Met? 

More 

Data 

Needed? 

[161-1] Hydrolysis sulfometuron 

methyl 42715201 Acceptable Yes No

[161-2]

Direct photolysis 

in water sulfometuron 

methyl

42182401

43174101

Acceptable Yes No

[161-3] Photolysis on soil sulfometuron 

methyl 41420601 Acceptable Yes No

[161-4] Photodegradation 

in Air NA NA not required NA NA

[162-1] Aerobic soil 

metabolism

sulfometuron 

methyl 42091401 Acceptable Yes No

[162-1] Aerobic soil 

metabolism

sulfometuron 

methyl

43174102

and 

245375

Acceptable Yes No

[162-2] Anaerobic Soil 

Metabolism NA NA ref 162-3 Yes No

[162-3]

Anaerobic aquatic 

metabolism

sulfometuron 

methyl

42091402

and 

43188601

Acceptable Yes No

[162-3]

Anaerobic aquatic 

metabolism

sulfometuron 

methyl

4413010-

20 

(143540)

Acceptable Yes No

[162-4]

Aerobic aquatic 

metabolism

sulfometuron 

methyl

42091403

and 

43174103

Acceptable Yes No

[163-1]

Adsorption/

Desorption

sulfometuron 

methyl 42789301 Acceptable Yes No

[163-1]

Adsorption/

Desorption

Pyrimidine 

amine 42789301 Acceptable Yes No

[163-1]

Adsorption/

Desorption saccharin 42789301 Acceptable Yes No

[163-2] Laboratory 

Volatility NA NA not required NA NA
116

Environmental Fate Data Requirements for Sulfometuron Methyl

Guideline Data 

Requirement Test Material MRID

Study 

Classification

Data 

Requirement 

Met? 

More 

Data 

Needed? 

[163-3] Field Volatility NA NA not required NA NA

[164-1] Terrestrial Field

Dissipation

Sulfometuron 

methyl

43212101

and 

43637101

Acceptable Yes No

[164-2] Aquatic Field 

Dissipation No study NA NA NA NA

[164-3] Forestry 

Dissipation

Sulfometuron 

methyl

42091404

and 

43174104 Acceptable Yes No

[165-4] Accumulation in 

Fish Waived NA NA NA NA

[165-5]

Accumulation in 

aquatic non-target 

organism 

(crayfish)

Waived NA NA NA NA

[166-1]

Ground Watersmall

scale prospective

No Study (not 

required) NA NA NA NA
117

APPENDIX C: ECOLOGICAL AQUATIC EXPOSURE 

MODELING

Multiple PRZM- EXAMS runs at single sites using 

different application date assumptions: Summary tables 

and sample input files

PRZM / EXAMS multiple application date assumption modeling: Sorted (by 21-day exposure 

estimates) List of 1 in 10 year return frequency for Various Exposure Durations - Aerial

application using the Texas / Barton Springs Salamander scenario and Port Arthur Texas 

meteorological data.

DATE Peak 96 hr 21 Day 60 Day 90 Day Yearly 30-Year

09-10 49.472 47.733 43.139 33.437 27.192 7.450 4.065

12-05 36.060 34.879 30.054 20.981 16.522 4.884 2.415

30-08 32.625 31.363 27.061 21.239 17.805 5.586 2.992

20-08 30.949 29.903 25.886 19.000 15.626 4.967 2.808

10-08 30.601 29.743 25.451 18.437 15.009 5.118 2.625

29-09 29.668 28.637 25.585 20.158 16.479 5.638 3.434

19-10 27.970 27.134 24.748 20.222 14.168 5.007 3.257

21-06 27.622 26.773 22.849 16.110 12.749 3.867 1.986

19-09 27.223 26.413 23.585 18.717 15.510 4.768 3.042

31-07 26.516 25.765 22.706 16.344 13.286 4.136 2.180

29-10 25.269 24.619 22.258 17.629 13.919 4.750 3.091

01-07 22.932 22.383 19.082 13.514 10.730 3.479 2.005

09-09 22.903 22.276 19.198 14.672 12.353 4.305 2.653

02-05 21.703 20.976 18.837 13.835 11.003 3.254 1.923

11-06 21.795 20.881 17.461 12.414 9.917 3.114 2.057

11-07 21.572 20.696 17.817 12.818 10.264 3.220 1.900

01-06 21.430 20.570 17.539 12.484 9.849 2.948 1.944

12-04 20.368 19.822 17.811 13.507 10.822 3.210 1.767

22-05 20.277 19.455 16.521 12.017 9.476 2.927 1.730

21-07 20.064 19.205 16.126 11.487 9.199 2.939 1.960

23-03 18.931 18.470 17.070 13.343 10.972 3.333 1.469

22-04 18.700 18.253 15.762 11.875 9.712 2.980 1.705

21-02 17.801 17.397 16.164 13.272 11.138 3.448 1.372

02-04 17.776 17.228 15.491 11.441 9.083 2.691 1.492

13-03 13.882 13.555 12.579 9.934 8.174 2.522 1.361

01-02 10.387 10.157 9.247 7.440 6.303 2.010 1.164

11-02 9.156 8.956 8.476 6.885 5.827 1.856 1.028

03-03 8.483 8.348 7.965 6.554 5.458 1.673 1.031

Sample input file, Texas Rights of Way Scenario, multi-run 
118

Output File: Sfmt_TXrway3_03-13_19-10

Metfile: w12917.dvf

PRZM scenario: RightOfWayBSS.txt

EXAMS environment file: pond298.exv

Chemical Name: Sulfometuron Methyl

Description

Variable 

Name Value Units Comments

Molecular weight mwt 364.38 g/mol

Henry's Law Const. henry atm-m^3/mol

Vapor Pressure vapr 5.40E-16 torr

Solubility sol 2.44E+02 mg/L

Kd Kd mg/L

Koc Koc 47.5 mg/L

Photolysis half-life kdp 0 days Half-life

Aerobic Aquatic 

Metabolism kbacw 292 days Half-life

Anaerobic Aquatic 

Metabolism kbacs 76 days Half-life

Aerobic Soil Metabolism asm 61 days Half-life

Hydrolysis: pH 5 8.8 days Half-life

Hydrolysis: pH 7 139 days Half-life

Hydrolysis: pH 9 224 days Half-life

Method: CAM 2 integer See PRZM manual

Incorporation Depth: DEPI 4 cm

Application Rate: TAPP 0.42 kg/ha

Application Efficiency: APPEFF 0.95 fraction

Spray Drift DRFT 0.05

fraction of application rate applied to 

pond

Application Date Date 19-10 dd/mm or dd/mmm or dd-mm or dd-mmm

Record 17: FILTRA

IPSCND 1

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

PRZM / EXAMS multiple application date assumption modeling: Sorted (by 21-day exposure 

estimates) List of 1 in 10 year return frequency for Various Exposure Durations - Ground

application using the Texas / Barton Springs Salamander scenario and Port Arthur Texas 

meteorological data.

DATE Peak 96 hr 21 Day 60 Day 90 Day Yearly 30-Year

09-10 39.996 38.810 34.507 27.791 21.603 6.172 2.769

30-08 27.463 26.544 22.992 16.878 13.881 3.981 1.858

10-08 26.457 25.737 21.998 15.903 12.933 4.017 1.582

20-08 25.924 24.975 21.491 15.348 12.142 3.568 1.734
119

12-05 24.414 23.588 20.408 14.954 12.292 3.887 1.786

29-09 22.197 21.464 18.230 12.916 10.207 3.063 1.297

21-02 19.582 19.078 17.362 14.267 9.967 3.834 2.171

19-09 20.200 19.568 17.226 13.829 11.935 3.896 2.025

23-03 18.665 18.003 16.757 12.319 9.776 2.873 1.427

21-06 19.217 18.836 16.746 13.167 9.414 3.404 2.094

29-10 19.558 18.836 16.599 12.734 10.828 3.451 1.788

12-04 20.279 19.472 16.553 11.997 9.737 2.922 1.350

02-05 18.100 17.658 16.324 12.773 10.517 3.192 1.213

31-07 17.670 17.268 16.064 13.203 11.090 3.430 1.271

19-10 17.914 17.355 15.893 12.284 9.832 2.912 1.344

09-09 18.029 17.253 14.468 10.227 8.170 2.563 1.316

11-07 17.639 16.926 14.442 10.422 8.227 2.487 1.340

11-06 17.352 16.770 14.329 10.381 8.286 2.588 1.210

21-07 16.643 16.227 14.228 10.881 9.213 2.866 1.560

22-04 15.884 15.392 13.645 9.657 7.589 2.260 1.105

13-03 16.502 15.962 13.631 9.510 7.553 2.318 1.371

22-05 14.795 14.375 13.013 9.882 7.969 2.400 1.258

01-07 15.183 14.562 12.420 9.190 7.325 2.219 1.299

01-06 12.986 12.623 12.026 9.563 7.867 2.421 1.183

02-04 13.375 12.975 11.704 8.802 7.076 2.106 1.148

01-02 9.992 9.763 8.891 7.158 6.070 1.927 1.043

11-02 8.705 8.496 8.064 6.565 5.558 1.766 0.907

03-03 8.054 7.928 7.533 6.214 5.176 1.580 0.902

PRZM / EXAMS multiple application date assumption modeling: Sorted (by 21-day exposure 

estimates) List of 1 in 10 year return frequency for Various Exposure Durations - Aerial

application using the California Red-Legged Frog scenario and Astoria, Oregon 

meteorological data.

DATE Peak 96 hr 21 Day 60 Day 90 Day Yearly 30-Year

13-03 11.346 11.125 10.256 8.581 7.493 2.779 1.194

29-10 11.134 10.934 10.233 8.604 6.248 2.715 1.610

19-10 11.046 10.854 10.202 8.547 6.635 2.788 1.629

11-02 10.995 10.813 10.059 8.418 7.375 2.811 1.648

01-02 10.284 10.105 9.405 7.891 6.932 2.696 1.317

23-03 9.964 9.816 9.119 7.570 6.591 2.455 1.145

21-02 9.996 9.786 9.049 7.574 6.639 2.528 1.351

22-04 9.587 9.432 8.660 7.130 6.146 2.227 0.826

03-03 8.919 8.739 8.146 6.838 5.990 2.250 1.360

12-04 8.775 8.674 8.055 6.686 5.789 2.111 0.859

09-10 8.495 8.366 7.783 6.526 5.464 1.963 1.081

19-09 8.390 8.237 7.550 6.240 5.484 1.987 0.998

12-05 7.639 7.473 6.855 5.553 4.763 1.709 0.563

09-09 7.313 7.145 6.531 5.356 4.704 1.549 0.913

02-04 6.253 6.167 5.795 4.808 4.167 1.544 0.867
120

02-05 6.182 6.045 5.514 4.535 3.905 1.417 0.765

01-06 5.513 5.389 5.037 4.131 3.543 1.272 0.749

29-09 5.466 5.382 4.939 4.118 3.627 1.094 0.754

20-08 5.518 5.387 4.841 3.886 3.353 1.394 0.683

30-08 4.742 4.628 4.216 3.437 2.999 1.026 0.695

22-05 4.562 4.466 4.086 3.335 2.859 1.049 0.509

21-06 4.304 4.211 3.833 3.084 2.643 0.980 0.554

01-07 3.938 3.853 3.516 2.863 2.437 0.866 0.466

10-08 3.738 3.644 3.277 2.627 2.265 0.911 0.542

21-07 3.677 3.584 3.273 2.643 2.281 0.855 0.490

11-07 3.705 3.607 3.250 2.577 2.200 0.802 0.505

11-06 3.351 3.273 2.999 2.427 2.072 0.750 0.461

31-07 3.347 3.266 2.936 2.353 2.028 0.856 0.538

Sample Input Files:

Output File: Sfmt_CArway4_02-

04

Metfile: w94224.dvf

PRZM scenario: CArightofwayRLF.txt

EXAMS environment file: pond298.exv

Chemical Name: Sulfometuron Methyl

Description Variable Name Value Units Comments

Molecular weight mwt 364.38 g/mol

Henry's Law Const. henry atm-m^3/mol

Vapor Pressure vapr 5.40E-16 torr

Solubility sol 2.44E+02 mg/L

Kd Kd mg/L

Koc Koc 47.5 mg/L

Photolysis half-life kdp 0 days Half-life

Aerobic Aquatic Metabolism kbacw 292 days Half-life

Anaerobic Aquatic Metabolism kbacs 76 days Half-life

Aerobic Soil Metabolism asm 61 days Half-life

Hydrolysis: pH 5 8.8 days Half-life

Hydrolysis: pH 7 139 days Half-life

Hydrolysis: pH 9 224 days Half-life

Method: CAM 2 integer See PRZM manual

Incorporation Depth: DEPI 4 cm

Application Rate: TAPP 0.42 kg/ha

Application Efficiency: APPEFF 0.95 fraction

Spray Drift DRFT 0.05 fraction of application rate applied to pond

Application Date Date April 2 dd/mm or dd/mmm or dd-mm or dd-mmm

Record 17: FILTRA

IPSCND 1

UPTKF

Record 18: PLVKRT

PLDKRT
121

FEXTRC 0.5

Flag for Index Res. Run IR EPA Pond

Flag for runoff calc. RUNOFF none none, monthly or total

Single PRZM- EXAMS runs for different sites: Sample EEC 

Summary tables and sample input files

Florida Citrus scenario

Sorted results

Prob. Peak 96 hr 21 Day 60 Day 90 Day Yearly

0.0323 1.642 1.592 1.403 1.072 1.000 0.340

0.0645 1.490 1.446 1.300 1.026 0.942 0.318

0.0968 1.487 1.446 1.279 1.020 0.864 0.292

0.1290 1.338 1.297 1.143 0.933 0.848 0.260

0.1613 1.199 1.172 1.056 0.918 0.782 0.248

0.1935 1.057 1.038 0.939 0.787 0.676 0.216

0.2258 1.057 1.028 0.928 0.767 0.666 0.210

0.2581 1.056 1.027 0.924 0.756 0.636 0.203

0.2903 1.056 1.026 0.921 0.731 0.606 0.198

0.3226 1.054 1.026 0.921 0.724 0.601 0.188

0.3548 1.053 1.025 0.921 0.721 0.600 0.187

0.3871 1.053 1.025 0.916 0.720 0.600 0.186

0.4194 1.053 1.025 0.915 0.720 0.595 0.185

0.4516 1.053 1.025 0.914 0.717 0.594 0.184

0.4839 1.053 1.024 0.914 0.714 0.593 0.184

0.5161 1.053 1.024 0.911 0.713 0.591 0.183

0.5484 1.053 1.024 0.910 0.709 0.587 0.182

0.5806 1.053 1.024 0.909 0.704 0.583 0.182

0.6129 1.053 1.024 0.908 0.703 0.579 0.181

0.6452 1.053 1.023 0.907 0.700 0.578 0.179

0.6774 1.053 1.023 0.907 0.700 0.578 0.177

0.7097 1.053 1.023 0.906 0.697 0.576 0.177

0.7419 1.052 1.023 0.905 0.695 0.573 0.177

0.7742 1.052 1.022 0.904 0.694 0.570 0.176

0.8065 1.052 1.022 0.904 0.694 0.570 0.175

0.8387 1.052 1.021 0.902 0.693 0.570 0.175

0.8710 1.052 1.021 0.902 0.691 0.570 0.174

0.9032 1.052 1.021 0.901 0.688 0.567 0.174

0.9355 1.052 1.020 0.900 0.688 0.566 0.173

0.9677 1.050 1.019 0.899 0.687 0.565 0.172

0.1000 1.472 1.431 1.265 1.011 0.863 0.28865

Average of 

yearly 

averages: 0.20175

Output File: Sfmt_FLcitrus1

Metfile: w12844.dvf

PRZM scenario: FLcitrusSTD.txt
122

EXAMS environment file: pond298.exv

Chemical Name: Sulfometuron Methyl

Description

Variable 

Name Value Units Comments

Molecular weight mwt 364.38 g/mol

Henry's Law Const. henry atm-m^3/mol

Vapor Pressure vapr

5.40E16 torr

Solubility sol 244 mg/L

Kd Kd mg/L

Koc Koc 47.5 mg/L

Photolysis half-life kdp 0 days Half-life

Aerobic Aquatic 

Metabolism kbacw 292 days Half-life

Anaerobic Aquatic 

Metabolism kbacs 76 days Half-life

Aerobic Soil Metabolism asm 61 days Half-life

Hydrolysis: pH 5 8.8 days Half-life

Hydrolysis: pH 7 139 days Half-life

Hydrolysis: pH 9 224 days Half-life

Method: CAM 2 integer See PRZM manual

Incorporation Depth: DEPI 4 cm

Application Rate: TAPP 0.42 kg/ha

Application Efficiency: APPEFF 0.95 fraction

Spray Drift DRFT 0.05

fraction of application rate applied to 

pond

Application Date Date 3-Jan dd/mm or dd/mmm or dd-mm or dd-mmm

Record 17: FILTRA

IPSCND 1

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

Florida Turf Scenario

Sorted results

Prob. Peak 96 hr 21 Day 60 Day 90 Day Yearly

0.032 0.707 0.686 0.604 0.457 0.372 0.128

0.065 0.639 0.622 0.558 0.429 0.354 0.109

0.097 0.464 0.451 0.398 0.303 0.259 0.090

0.129 0.379 0.367 0.323 0.255 0.221 0.076

0.161 0.360 0.353 0.318 0.244 0.218 0.071

0.194 0.226 0.220 0.200 0.168 0.150 0.048

0.226 0.213 0.207 0.186 0.162 0.141 0.045
123

0.258 0.212 0.206 0.185 0.153 0.130 0.042

0.290 0.212 0.206 0.184 0.147 0.125 0.041

0.323 0.212 0.206 0.184 0.146 0.121 0.039

0.355 0.211 0.206 0.184 0.145 0.120 0.037

0.387 0.211 0.206 0.184 0.144 0.120 0.037

0.419 0.211 0.205 0.183 0.144 0.119 0.037

0.452 0.211 0.205 0.183 0.144 0.119 0.037

0.484 0.211 0.205 0.183 0.143 0.119 0.037

0.516 0.211 0.205 0.183 0.143 0.119 0.037

0.548 0.211 0.205 0.182 0.142 0.117 0.037

0.581 0.211 0.205 0.182 0.141 0.117 0.036

0.613 0.211 0.205 0.182 0.141 0.117 0.036

0.645 0.211 0.205 0.182 0.141 0.116 0.036

0.677 0.211 0.205 0.182 0.141 0.116 0.036

0.710 0.211 0.205 0.181 0.140 0.115 0.036

0.742 0.211 0.205 0.181 0.139 0.115 0.035

0.774 0.211 0.204 0.181 0.139 0.114 0.035

0.806 0.211 0.204 0.181 0.139 0.114 0.035

0.839 0.211 0.204 0.181 0.139 0.114 0.035

0.871 0.210 0.204 0.180 0.138 0.114 0.035

0.903 0.210 0.204 0.180 0.138 0.113 0.035

0.935 0.210 0.204 0.180 0.138 0.113 0.035

0.968 0.210 0.204 0.180 0.138 0.113 0.034

0.100 0.456 0.442 0.391 0.298 0.255 0.089

Average of 

yearly 

averages: 0.046883

Inputs generated by pe5.pl - November 2006

Data used for this run:

Output File: Sfmt_FLturf2

Metfile: w12834.dvf

PRZM scenario: FLturfSTD.txt

EXAMS environment file: pond298.exv

Chemical Name: Sulfometuron Methyl

Description

Variable 

Name Value Units Comments

Molecular weight mwt 364.38 g/mol

Henry's Law Const. henry atm-m^3/mol

Vapor Pressure vapr

5.40E16 Torr

Solubility sol 244 mg/L

Kd Kd mg/L

Koc Koc 47.5 mg/L

Photolysis half-life kdp 0 Days Half-life

Aerobic Aquatic 

Metabolism kbacw 292 Days Half-life

Anaerobic Aquatic 

Metabolism kbacs 109 Days Half-life
124

Aerobic Soil Metabolism asm 61 Days Half-life

Hydrolysis: pH 5 8.8 Days Half-life

Hydrolysis: pH 7 139 Days Half-life

Hydrolysis: pH 9 224 Days Half-life

Method: CAM 1 integer See PRZM manual

Incorporation Depth: DEPI 0 Cm

Application Rate: TAPP 0.42 kg/ha

Application Efficiency: APPEFF 0.99 fraction

Spray Drift DRFT 0.01 fraction of application rate applied to pond

Application Date Date 3-Jan dd/mm or dd/mmm or dd-mm or dd-mmm

Record 17: FILTRA

IPSCND 1

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)

Inputs generated by pe5.pl - November 2006

Data used for this run:

Output File: Sfmt_FLturf1

Metfile: w12834.dvf

PRZM scenario: FLturfSTD.txt

EXAMS environment file: pond298.exv

Chemical Name: Sulfometuron Methyl

Description Variable Name Value Units Comments

Molecular weight mwt 364.38 g/mol

Henry's Law Const. henry atm-m^3/mol

Vapor Pressure vapr 5.40E-16 Torr

Solubility sol 2.44E+02 mg/L

Kd Kd mg/L

Koc Koc 47.5 mg/L

Photolysis half-life kdp 0 Days Half-life

Aerobic Aquatic 

Metabolism kbacw 292 Days Half-life

Anaerobic Aquatic 

Metabolism kbacs 76 Days Half-life

Aerobic Soil Metabolism asm 61 Days Half-life

Hydrolysis: pH 5 8.8 Days Half-life

Hydrolysis: pH 7 139 Days Half-life

Hydrolysis: pH 9 224 Days Half-life

Method: CAM 2 integer See PRZM manual

Incorporation Depth: DEPI 4 cm

Application Rate: TAPP 0.42 kg/ha

Application Efficiency: APPEFF 0.95 fraction
125

Spray Drift DRFT 0.05 fraction of application rate applied to pond

Application Date Date 3-Jan dd/mm or dd/mmm or dd-mm or dd-mmm

Record 17: FILTRA

IPSCND 1

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)

APPENDIX D: TERRPLANT SPREADSHEET

(TerrPlant Version 1.2.2)

Table D-1. Chemical Identity.

Chemical Name Sulfometuron 

Methyl

PC code 122001

Use non-crop vegetative management, forestry, rights of way

Application Method ground

Application Form water dispersible granule

Solubility in Water (ppm) 244 (pH 7)

Table D-2. Input parameters used to derive EECs.

Input Parameter Symbol Value Units

Application Rate A 0.375 lb a.i./A

Incorporation I 1 none

Runoff Fraction R 0.05 none

Drift Fraction D 0.01 none

Table D-3. EECs for Sulfometuron Methyl. Units in lb a.i./A.

Description Equation EEC

Runoff to dry areas (A/I)*R 0.01875

Runoff to semi-aquatic 

areas

(A/I)*R*10 0.1875

Spray drift A*D 0.00375

Total for dry areas ((A/I)*R)+(A*D) 0.0225

Total for semi-aquatic areas ((A/I)*R*10)+(A*D) 0.19125

Table D-4. Plant survival and growth data used for RQ derivation. Units are in lb a.i./A.

Seedling Emergence Vegetative Vigor

Plant type EC25 NOAEC EC25 NOAEC 
126

Monocot 1.90E-04 4.30E-05 3.70E-05 8.40E-06

Dicot 3.20E-05 2.90E-05 1.80E-05 9.90E-07

Table D-5. RQ values for plants in dry and semi-aquatic areas exposed to Sulfometuron Methyl 

through runoff and/or spray drift.*

Plant Type Listed Status Dry Semi-Aquatic Spray Drift

Monocot non-listed 118.42 1006.58 101.35

Monocot listed 523.26 4447.67 446.43

Dicot non-listed 703.13 5976.56 208.33

Dicot listed 775.86 6594.83 3787.88

*If RQ > 1.0, the LOC is exceeded, resulting in potential for risk to that plant group.
127

APPENDIX E: ADVERSE ECOLOGICAL INCIDENTS ASSOCIATED WITH 

SULFOMETURON METHYL USE

Incident ID Use Site Start 

Date

Legality Certainty State County Year Total 

Magnitud

e

Appl. Rate Appl. 

Method

Affected 

Species

Product

I011666-001 Municpal 

operation

01-Nov-00 Registered use Highly 

Probable

ID 2000 Thousand

s Of Acres

1 Oz/Acre Aerial 1 OUST

I013086-001 Right-ofway, rail15-Jun-02 Registered use Probable WA Kittitas 2002 Unknown 3 Oz Per 15 

Gallons

Spray 1 Oust

I009556-043 Agricultural 

area

15-May-92 Registered use Probable CO Costilla 1992 $4,400,00

0 

Damages

N/R Spray 1 OUST

I005972-001 PLANT 

SITE

01-Sep-97 Registered use Probable TX 1997 N/A N/R 1 OUST

I006010-003 Utility plant 19-Aug-97 Misuse 

(accidental)

Probable MS 1997 Unknown RUNOFF1

I000903-005 Forest 01-Sep-91 Misuse 

(accidental)

Probable TX Anderson 1991 N/R 500 Oz/

3000 Acres

Spray 1 OUST

I000903-002 Agricultural 

area

01-Jan-94 Registered use Probable TX Cherokee 1994 N/R N/R Spray 1 OUST

I006010-001 Right-ofway, road20-Aug-97 Misuse 

(accidental)

Probable LA 1997 Unknown N/R N/R 1

I000903-003 Agricultural 

Area

01-Jan-94 Registered use Probable TX 1994 N/R N/R Spray 2,3,4 OUST

I000903-001 Agricultural 

area

01-Sep-91 Registered use Probable TX Anderson 1991 N/R 2 Oz/25-30 

Gal Water

Spray 1 OUST

I006010-002 Agricultural 

area

20-Aug-97 Misuse 

(accidental)

Probable TX 1997 Unknown N/R N/R 1

I007269-001 Agricultural 

area

21-May-98 Registered use Probable CA Fresno 1998 All N/R N/R 1 OUST

I007269-002 YARD 29-May-98 Registered use Probable TN Davidson 1998 All N/R N/R 1 OUST

I015217-001 Forest 21-May-04 Registered use Probable OH Gallia 2004 8000 Sq 

Ft

3 Oz/Acre Spray 1 Oust 

herbicide

I015832-001 Right-ofway, road14-Dec-04 Registered use Probable LA Lafayette 2004 N/R Spray 1 Oust

I017481-001 Turf, 24-May-06 Undetermined Probable WI Waukesha 2006 Unknown Unknown N/R 1 DuPont 
128

Incident ID Use Site Start 

Date

Legality Certainty State County Year Total 

Magnitud

e

Appl. Rate Appl. 

Method

Affected 

Species

Product

residential Oust

I015576-001 Right-ofway, road01-Apr-04 Registered use Probable OR Multnomah 2004 $40,000 N/R N/R 1 Landmark 

MP

I016302-001 Right-ofway, road23-May-05 Registered use Probable WA Grant 2005 Less Than 

An Acre

N/R Spray 1 Oust

I016429-001 Industrial 

site

13-Jun-05 Registered use Probable WA Grant 2005 $90,000 

Damage

5 Oz/Acre Spray 1 Oust

I015440-001 Right-ofway, utility01-Jun-03 Misuse 

(accidental)

Probable MN Benton 2003 2 Acres 5 Oz/Acre Spray 1 Oust

I013194-001 Right-ofway, rail02-Jul-02 Registered use Probable ND Walsh 2002 10 Acres 3 Oz/15 

Gals Water

Spray 1 OUST

I014409-011 Right-ofway, road03-Jun-92 Registered use Possible WA Walla Walla 1992 Not Given 1

B000601-010 Right-ofway25-May-84 Registered use Possible CA Fresno 1984 N/R Spray 1 Oust

I015796-001 Right-ofway, utility08-Nov-04 Registered use Possible KY Jessamine 2004 1-4 Acres 3 Oz/Acre Nr 1 Oust XP 

Herbicide

B000601-011 N/R 16-May-88 Registered use Possible CA Kern 1988 N/R 1 Oust

I000071-001 Peach 01-Jan-92 Registered use Possible SC Saluda 1992 Numerous 

Trees

N/R N/R 1 OUST

B000601-009 N/R 23-May-85 Undetermined Possible LA Acadia 1985 Less Than 

50 Acres

Spray 1 Oust

I015265-001 Seedling 01-Mar-04 Registered use Possible TX Cass 2004 Unknown Unknown Unknow

n

1 Oustar

I016680-001 Right-ofway06-Apr-05 Undetermined Possible OR Douglas 2005 13 Acres Spray 1

I009556-005 Agricultural 

area

Misuse 

(accidental)

Possible NC 0 Unknown N/R N/R 1 OUST

B000601-001 N/R 04-May-88 Undetermined Possible CA Kern 1988 NR NR 1 Oust

I016312-001 Forest 01-Apr-05 Undetermined Possible OR Benton 2005 300 Acres 2 Lb/Acre Spray 1 Westar

B000601-008 Right-ofway, road23-May-85 Registered use Possible LA Acadia 1985 Nr Spray 1 Oust

B000601-007 Right-ofway, road23-May-85 Registered use Possible NE Scotts Bluff 1985 Nr 2 Oz/Acre 1 Oust

Source: USEPA, OPP Ecological Incident Information System, October, 2007.

Affected Species: 1 = terrestrial plants, 2 = aquatic plants, 3 = terrestrial animals, 4= aquatic animals
129

APPENDIX F: T- REX OUTPUT

Table F-1. T-REX Model Inputs Used for Sulfometuron Methyl

TREX MODEL INPUTS

Chemical Name: Sulfometuron methyl

 Use: non-crop; forest, rights-of-way

Product name and form: Oust (et al): water dispersible 

graunule

% A.I. (leading zero must be entered for formulations <1% 

a.i.):

100.00%

Application Rate (lbs/A): 0.375

Half-life (days): 35

Application Interval (days):

Number of Applications: 1

Note: Sources of wildlife diet are assumed to be available for 

less than one year for this model.

Endpoints

Avian Indicate test 

species below

LD50 (mg/kg-bw) 4650.00 2 (mallard)

LC50 (mg/kg-diet) 4600.00 2 (mallard)

NOAEL (mg/kg-bw) 2

NOAEC (mg/kgdiet)

1

Enter the Mineau et al. Scaling 

Factor

1.15

Mammals

LD50 (mg/kg-bw) 5000.00 Rat

LC50 (mg/kg-diet)

Reported Chronic Endpoint (mg/kg-bw/d)

549.00 Scaled to 350 g 

from Rabbit 

Developmental 

Tox Study

Is dietary concentration (mg/kg-diet) reported from the available chronic mammal 

study? (yes or no)

no

Enter dietary concentration (mg/kg-diet)

Estimated Chronic Diet Concentration Equivalent to Reported Chronic Daily Dose

10980 mg/kg-diet based 

on standard FDA 

lab rat conversion
130

Table F-5. T-REX Output: Upper Bound Kenaga, Chronic Mammalian Dietary 

Based Risk Quotients

NOAEC 

(ppm)

EECs and RQs

Short Grass Tall Grass Broadleaf 

Plants/

Small Insects

Fruits/Pods/

Seeds/

Large Insects

EEC RQ EEC RQ EEC RQ EEC RQ

10980 90.00 0.01 41.25 0.00 50.63 0.00 5.63 0.00

Size class not used for dietary risk quotients 

Table F-6: T-REX Output: Upper Bound Kenaga, Chronic Mammalian Dose-Based Risk Quotients

Size 

Class

(grams)

Adjusted 

NOAEL

EECs and RQs

Short Grass Tall Grass Broadleaf 

Plants/

Small Insects

Fruits/Pods/

Seeds/

Large Insects

Granivore

EEC RQ EEC RQ EEC RQ EEC RQ EEC RQ

15 1206.61 85.81 0.07 39.33 0.03 48.27 0.04 5.36 0.00 1.19 0.00

35 976.28 59.30 0.06 27.18 0.03 33.36 0.03 3.71 0.00 0.82 0.00

1000 422.27 13.75 0.03 6.30 0.01 7.73 0.02 0.86 0.00 0.19 0.00

Table F-2. T-REX Output: Upper Bound Kenaga, Acute Avian Dose-Based Risk Quotients

Size Class

(grams)

Adjusted

LD50

EECs and RQs

Short Grass Tall 

Grass

Broadleaf 

Plants/

Small Insects

Fruits/Pods/

Seeds/

Large Insects

EEC RQ EEC RQ EEC RQ EEC RQ

20 2414.40 102.50 0.04 46.98 0.02 57.66 0.02 6.41 0.00

100 3073.65 58.45 0.02 26.79 0.01 32.88 0.01 3.65 0.00

1000 4341.65 26.17 0.01 11.99 0.00 14.72 0.00 1.64 0.00

Table F-3. T-REX Output: Upper Bound Kenaga, Subacute Avian Dietary Based 

Risk Quotients

LC50

EECs and RQs

Short Grass Tall Grass Broadleaf 

Plants/

Small Insects

Fruits/Pods/

Seeds/

Large Insects

EEC RQ EEC RQ EEC RQ EEC RQ

4600 90.00 0.02 41.25 0.01 50.63 0.01 5.63 0.00

Size class not used for dietary risk quotients 

Table F-4. T-REX Output: Upper Bound Kenaga, Acute Mammalian Dose-Based Risk Quotients 

Size Class

(grams)

Adjusted

LD50

EECs and RQs

Short Grass Tall Grass Broadleaf Plants/

Small Insects

Fruits/Pods/

Seeds/

Large Insects

Granivore

EEC RQ EEC RQ EEC RQ EEC RQ EEC RQ

15 10989.15 85.81 0.01 39.33 0.00 48.27 0.00 5.36 0.00 1.19 0.00

35 8891.40 59.30 0.01 27.18 0.00 33.36 0.00 3.71 0.00 0.82 0.00

1000 3845.80 13.75 0.00 6.30 0.00 7.73 0.00 0.86 0.00 0.19 0.00
131

APPENDIX G: MODELING OF TERRESTRIAL PLANT 

EXPOSURE FROM CONTAMINATED IRRIGATION WATER

The following calculations were used for determining risk quotients for plants when groundwater 

or surface water contaminated by sulfometuron methyl is applied to areas as irrigation water and 

subsequently drift to adjacent areas.

SURFACE WATER IRRIGATION:

Assume a 1-acre field is irrigated with one inch of water containing 31 μg/L (or ppb) 

sulfometuron methyl (peak EEC for surface water, Table 15).

One acre has 6,272,640 square inches of surface area. A 1-acre field irrigated with 1 acre-inch of 

water (6,272,640 cubic inches of water) would have been treated with 3,630 cubic ft of water 

(6,272,640 cubic inches x 1 cubic ft/1728 cubic inches). Converting to gallons, the field has 

received 27,156 gallons of water (3,630 cubic ft x 7.481 gallons/cubic ft). On a pounds per acre 

basis, 1 inch of water applied to a 1-acre field weighs 226,625 lbs (27,156 gallons x 8.3453 

lbs/gallon of water).

So, if surface water containing 31 ppb sulfometuron methyl is used to provide of 1 acre-inch of 

irrigation water, sulfometuron methyl is applied at a rate of:

226,625 lb of water/A x 31 ppb (ai sulfometuron methyl) = 0.00703 lbs ai/A sulfometuron 

methyl 1,000,000,000

Therefore, the risk quotient for sensitive plants adjacent to a field that is irrigated with surface 

water containing 31 ppb (or μg/L) sulfometuron methyl is calculated as follows: 

EEC (spray drift) = application rate of contaminated irrigation water (0.00703 lb ai/A) * 1% drift 

= 7.03 x 10-5 lb ai/A.

Non-endangered Plant RQ:

From 1 acre-inch of surface water: EEC/EC25 for vegetative vigor = 7.03 x 10-5 lbs ai/A = 3.9

 1.8 x 10-5 lbs ai/A 

Endangered Plant RQ:

From 1 acre-inch of surface water: EEC/EC05 for vegetative vigor = 

7.03 x 10-5 lbs ai/A = 71

9.9 x 10-7 lbs ai/A 
132

GROUND WATER IRRIGATION

To calculate risk quotients for plants when ground water contaminated by sulfometuron methyl 

is applied as irrigation water and subsequently drifts to adjacent areas, the following method was 

used.

Assume a 1-acre field is irrigated with one inch of water containing 0.33 ppb (or μg/L) 

sulfometuron methyl (peak EEC for ground water, Table 15).

As calculated above, 1 acre-inch of irrigation water weighs 226,625 lbs. So, sulfometuron 

methyl is applied at a rate of:

226,625 lb of water/acre x 0.33 (ai sulfometuron methyl) = 7.48 x 10-5 lbs ai/A. 

1,000,000,000

Therefore, the risk quotient for sensitive plants adjacent to the irrigated area with ground 

water containing 0.33 ppb (or μg/L) sulfometuron methyl is calculated as follows: 

EEC (spray drift) = application rate of contaminated irrigation water (7.48 x 10-5 lb ai/A) * 1% 

drift = 7.03 x 10-7 lb ai/A.

Non-endangered Plant RQ:

From 1 acre-inch of ground water: EEC/EC25 for veg.vigor = 7.48 x 10-5 lb ai/A = 0.04

 1.8 x 10-5 lbs ai/A

Endangered Plant RQ:

From 1 acre-inch of ground water: EEC/EC25 for veg.vigor = 7.48 x 10-5 lb ai/A = 0.76

 9.9 x 10-7 lbs ai/A
133

APPENDIX H: ECOLOGICAL EFFECTS DATA SUMMARIES

I. OPP Guideline Toxicity Studies

Freshwater Fish, Acute

Bluegill Sunfish, (Lepomis macrochirus). For bluegill, results from the range finding test 

indicated no mortality when exposed to sulfometuron methyl up to 200 mg ai/L (i.e., LC50 >200 

mg/L). Accordingly, a definitive toxicity test was not required and a single treatment test was 

conducted at the toxicity limit of 150 mg ai/L using technical grade sulfometuron methyl (99.6% 

ai). Results from the limit test (MRID 435018-01) indicate no mortality to bluegill at an 

exposure concentration of 150 mg ai/L. To prevent the formation of chemical precipitate 

experienced during previous toxicity testing, test solutions were buffered with 5N sodium 

hydroxide. This resulted in a greater pH range (7.2 – 9.0) than recommended (7.2-7.6) in study 

guidelines. The study authors reported observing no precipitate or other signs of insolubility 

during the study. The test concentration were measured and found to be within 80% to 120% of 

nominal. The pH range deviation is therefore considered a necessary byproduct of increasing the 

solubility of the test chemical. No mortality was observed in the controls. All other test 

guideline deviations are considered minor. This study is classified as acceptable and meets the 

guideline requirements for acute toxicity to a fresh water fish. 

Rainbow Trout, (Oncorhynchus mykiss). Similarly for rainbow trout, no mortality was 

observed in a range finding test up to 200 mg ai/L or the follow-up toxicity limit test at 150 mg 

ai/L sulfometuron methyl (99.6% ai). Buffering of test solutions was required to prevent 

formation of precipitates which resulted in a greater pH range (7.9-8.7) than recommended (7.2-

7.6). The test concentration were measured and found to be within 80% to 120% of nominal. 

The pH range deviation is therefore considered a necessary byproduct of increasing the solubility 

of the test chemical. No mortality was observed at 148 mg ai/L (measured concentration) or in 

the controls. All other test guideline deviations are considered minor. This study is classified as 

acceptable and meets the guideline requirements for acute toxicity to a fresh water fish. 

Freshwater Invertebrates, Acute

Water flea (Daphnia magna). The toxicity of sulfometuron methyl to freshwater invertebrates 

is indicated by a 48-hr acute toxicity test with the water flea, Daphnia magna (MRID 435018-

03). As observed with freshwater fish, no mortality was observed in a range finding test up to 

200 mg ai/L or the follow-up toxicity limit test at 150 mg ai/L sulfometuron methyl (99.6% ai). 

Buffering of test solutions was required to prevent formation of precipitates which resulted in a 

greater pH range (8.4-9.0) than recommended (7.2-7.6). No mortality was observed in the 150 

mg/L treatment or in the negative control. One daphnid died in the pH adjusted control 

(mortality 3%). The test concentration was measured and found to be 100% of nominal. The pH 

range deviation is therefore considered a necessary byproduct of increasing the solubility of the 

test chemical. 
134

This test was originally classified as supplemental in 1995 by EFED because of concerns over 

chemical composition of the dilution water (filtered fish tank water housing fathead minnows) 

and the potential for microbial degradation. For the purposes of this risk assessment, this study 

was re-reviewed and upgraded to acceptable. According to the study authors, ammonia levels in 

the dilution water were not significantly raised and a summary of its chemical composition was 

provided in an earlier chronic life cycle test with the same organism (MRID 416728-06) and 

found to be acceptable. Furthermore, given the very low hydrophobicity of this chemical, 

alteration of its bioavailability due to sorption to organic carbon would not likely be significant, 

even if levels far exceeded those reported in the dilution water from the earlier daphnid study. 

Lastly, the chemical concentration was verified analytically which confirmed that significant 

chemical degradation was not occurring. This study is classified as acceptable and meets the 

guideline requirements for an acute toxicity study with a freshwater invertebrate. 

Estuarine and marine Fish, Acute

Sheepshead minnow (Cyprinodon variegatus). The toxicity of sulfometuron methyl to estuarine 

and marine fish is indicated by a 96-hr acute toxicity test with the sheepshead minnow, 

Cyprinodon variegatus conducted at nominal concentrations of sulfometuron methyl (99.1% ai) 

ranging from 15 to 100 mg ai/L (MRID 416728-03). The LC50 based on measured 

concentrations from this study was found to be greater than 45 mg ai/L. No mortality or 

observable signs of sublethal effects occurred in the study except for one dead fish (5%) at 8.2 

mg/L (measured). This study was re-reviewed for this risk assessment and found to contain 

several significant deficiencies which render its classification as supplemental. Specifically, 

measured concentrations ranged widely from test initiation to termination (4 to 7 times), which is 

believed due to the formation of an observable precipitate in test solutions. This occurred despite 

buffering of the dilution water to an initial pH of 8.5 (pH ranged thereafter from 7.4 to 8.5). 

Although originally classified as supplemental by EFED in 1993, the study was subsequently 

upgraded to core/acceptable by EFED in 1994 upon the registrant’s explanation that solubility 

limits in unbuffered water prevented adequate recovery of sulfometuron methyl from test 

solutions and that test concentrations were verified analytically. However, while this 

information may explain the low % of nominal concentrations observed in the study, there was 

high variability in measured test concentrations with treatments and substantial uncertainty in the 

actual exposure of organisms to dissolved sulfometuron methyl (no centrifugation of test samples 

prior to analysis). Although these deficiencies could render the study classification as 

“unacceptable,” it is considered to provide some useful information in this risk assessment (i.e., 

an indication of a lack of toxicity at or near solubility limits in test solutions). Furthermore, 

when viewed in the context of screening level EECs (i.e., a maximum peak concentration of 

0.031 ppm in water), the bioavailable (dissolved) portion sulfometuron methyl would have to be 

approximately 1500-fold lower than the highest measured test concentration (~45 ppm) in order 

for risks to be evident. Therefore, this study is classified as supplemental but is not 

recommended for repeat testing at this time because a repeat test would be highly unlikely to 

alter the risk assessment conclusions.

Estuarine and Marine Invertebrates, Acute
135

Mysid shrimp, Mysidopsis bahia. For mysids, a 96-h assay was conducted at nominal 

concentrations of sulfometuron methyl (99.1%) ranging from 15 to 100 mg ai/L (MRID 416728-

04). The 96-h LC50 based on measured concentrations from this study was found to be greater 

than 44.8 mg ai./L. No mortality or observable signs of sublethal effects occurred in the study at 

any test concentration or the control. A re-review of the mysid test indicates it has several 

significant deficiencies which render its classification as supplemental. Specifically, measured 

concentrations of sulfometuron methyl ranged widely from test initiation to termination (3X to 

13X in the mysid tests) and were substantially below nominal concentrations. The low % 

nominal is believed due to the formation of an observable precipitate in test solutions. The low 

% nominal occurred despite buffering of the dilution water to an initial pH of 8.5 (pH ranged 

thereafter from 7.6 to 8.5). The pH range in the mysid test extended beyond the recommended 

range in the test guidelines (7.7-8.0 for euryhaline shrimp).

Although the mysid study was originally classified as supplemental by EFED in 1993, the study 

was subsequently upgraded to core/acceptable in 1994 by EFED upon the registrant’s 

explanation that solubility limits in unbuffered water prevented adequate recovery of 

sulfometuron methyl from test solutions and that test concentrations were verified analytically. 

However, while this information may explain the low % of nominal concentrations observed in 

the study, there was high variability in measured test concentrations with treatments and 

substantial uncertainty in the actual exposure of organisms to dissolved sulfometuron methyl (no 

centrifugation of test samples prior to analysis per OPP test guidelines). Although these 

deficiencies could render the study classification as “unacceptable,” it is considered to provide 

some useful information in this risk assessment (i.e., an indication of a lack of toxicity at or near 

solubility limits in test solutions). Furthermore, when viewed in the context of screening level 

EECs (i.e., a maximum peak concentration of 0.031 ppm in water), the bioavailable (dissolved) 

portion sulfometuron methyl would have to be approximately 1300-fold lower than the highest 

measured test concentration (~ 45 ppm) in order for risks to be evident. Therefore, this study is 

classified as supplemental but is not recommended for repeat testing at this time because a 

repeated test would not likely affect the risk assessment conclusions.

Eastern oyster, Crassostrea virginica. For oysters, a 48-h assay was conducted on embryos at 

the same nominal concentrations as used for mysids (MRID 416728-05). The 48-h EC50 based 

on measured concentrations for this study was found to be greater than 38.2 mg ai/L. No 

mortality occurred and 99% of the surviving control oysters were normal. 

A re-review of the oyster study indicates it has several significant deficiencies which render its 

classification as supplemental. Specifically, measured concentrations of sulfometuron methyl 

ranged widely from test initiation to termination (up to 3X) and were substantially below 

nominal concentrations. The low % nominal is believed due to the formation of an observable 

precipitate in test solutions. In the oyster test, pH ranged from 7.7 to 8.0. The pH range in the 

oyster test extended beyond the recommended range in the test guidelines (8.0-8.3 for 

stenohaline oysters).

Although this study was originally classified as supplemental by EFED in 1993, it was 

subsequently upgraded to core/acceptable in 1994 by EFED upon the registrant’s explanation 
136

that solubility limits in unbuffered water prevented adequate recovery of sulfometuron methyl 

from test solutions and that test concentrations were verified analytically. However, while this 

information may explain the low % of nominal concentrations observed in the study, there was 

high variability in measured test concentrations with treatments and substantial uncertainty in the 

actual exposure of organisms to dissolved sulfometuron methyl (no centrifugation of test samples 

prior to analysis per OPP test guidelines). Although these deficiencies could render the study 

classifications as “unacceptable,” it is considered to provide some useful information in this risk 

assessment (i.e., an indication of a lack of toxicity at or near solubility limits in test solutions). 

Furthermore, when viewed in the context of screening level EECs (i.e., a maximum peak 

concentration of 0.031 ppm in water), the bioavailable (dissolved) portion sulfometuron methyl 

would have to be approximately 1000-fold lower than the highest measured test concentration (~ 

40 ppm) in order for risks to be evident. Therefore, this study is classified as supplemental but is 

not recommended for repeat testing at this time because a repeated test would not likely affect 

the risk assessment conclusions.

Freshwater Fish, Chronic

A chronic, early life-stage toxicity test was conducted in 1982 to determine the effect of 

sulfometuron methyl on fathead minnow embryo hatching, larval survival, and growth (MRID 

423857-04; Accession No. 249796). Fertilized embryos and hatched larvae were exposed to 5 

nominal concentrations ranging from 0.15 to 2.5 mg ai/L under flow-through conditions. 

Dimethylformamide (DMF) was used as a carrier (0.1 ml/L) and a solvent and negative control 

were used. Two replicates were used per test treatment, with each replicate containing 50 

embryos and subsequent to hatching, 20 larvae. A statistically-significant reduction in hatching 

was attributed to the highest test concentration (2.5 mg/L nominal, 1.16 mg/L measured) using 

chi-square analysis (but not significant using ANOVA). Mean percent hatch was 38% in the 

highest test concentration compared to 75% in the solvent and negative controls. Larval survival 

was not significantly affected in any test concentration (ranging from 85-100%) compared to 

92% in the negative control and 95% in the solvent control. Larval growth (length, weight) were 

also not significantly affected in any test concentration relative to either control. During the last 

week of the test, a diluter malfunction resulted in a precipitous drop in exposure concentrations 

in all treatments (at or below detection of 0.01 mg/L in several treatments). Thus, the NOAEC 

and LOAEC from this study (0.71 and 1.16 mg/L, respectively for % hatching) were determined 

by considering only the embryo exposure portion of the study prior up through hatching (i.e., 

prior to the diluter malfunction).

A re-review of this study conducted for this risk assessment the study is unacceptable primarily 

because of high uncertainty in quantifying exposure experienced by fathead minnows during the 

test. Specifically, temporal variability in test concentrations exceeded OPP test guidelines of < 

1.5X in all test concentrations. Even when measured concentrations from the last week are not 

considered, the ratio of the highest to the lowest test concentration ranged from 1.6 to 2.7. As 

reported in the study, the stability of the test substance in the DMF carrier is in question and is 

thought to be responsible for the low measured concentrations (48% of nominal on average). 

Follow-up testing indicated that at the pH of the study (7.2-7.5), the solubility of the 

sulfometuron methyl with the DMF carrier would be approximately 3 mg/L. At higher pH, the 
137

solubility of sulfometuron methyl increases substantially (>100 mg/L). At the time this study 

was conducted (1982), however, pH adjusted test solutions was not conducted reportedly due to 

lack of knowledge of the NaOH pH adjustment method. However, results from the Daphnia life 

cycle study discussed below indicate that with appropriate buffering, stable and consistent 

concentrations are achievable with sulfometuron methyl. Because the NOAEC for fathead 

minnow from this study (0.71 mg/L) is within an order of magnitude of EECs (0.031 mg/L), 

there is a reasonable probability that a valid NOAEC for chronic effects could fall in the range of 

the EECs. Finally, the precipitous drop in exposure concentrations brings into question the study 

findings of a lack of a significant affect on fathead minnow larval growth, since exposure was 

terminated up to a week prematurely. This study is considered unacceptable and does not fulfill 

the guideline requirements for chronic toxicity to freshwater fish.

Freshwater Invertebrate, Chronic

Chronic toxicity sulfometuron methyl to freshwater invertebrates is indicated by a 21-day life 

cycle test conducted on the water flea, Daphnia magna (MRID 416728-06). Daphnids (<24-h 

old) were exposed to six concentrations of sulfometuron methyl ranging from 0.1 to 100 mg/L 

(nominal) in a static-renewal system. Reproduction, growth and survival were measured in 7 

replicates per treatment (1 organism/rep.), while 3 additional replicates were designated solely 

for survival measurement (5 organisms/rep.). In order to promote solubility of the test substance, 

the pH of the stock solutions of the 25 mg/L and 100 mg/L treatments were adjusted with NaOH 

to pH 8.5. Both a negative and pH-adjusted controls were included.

Results indicate that mean measured concentrations were close to nominal concentrations (i.e., 

within 20% of the 0.1, 0.39, 1.6, 6.3, 25 and 100 mg/L nominal concentrations). Variability in 

test concentrations was well within the acceptable limits of 1.5X. Daphnid survival, growth and 

reproduction were not significantly different between negative and pH adjusted controls. 

Survival and growth (length) were not affected at any test concentration. Reproduction, as 

measured by the number of neonates produced/daphnid, was not significantly different from 

negative controls in any treatment (ANOVA, 0.05). Although the Dunnett’s multiple 

comparison test indicated a marginally significant difference in the 24 mg/L treatment (mean 

measured concentration), it is not considered statistically valid to apply means testing when 

ANOVA results indicate lack of significant differences among treatments. Furthermore, an 

inconsistent concentration-response relationship is indicated by the lack of a significant 

reduction in daphnid reproduction at 97 mg/L (the highest treatment tested). Therefore, the 

NOAEC for daphnid reproduction is re-interpreted as 97 mg/L (unbounded) and the LOAEC is > 

97 mg/L. This study is classified as acceptable and meets the guideline requirements for a 

chronic study using a freshwater invertebrate. 

Aquatic Plants

Green Algae, Selenastrum capricornutum. A tier 2 growth and reproduction study was 

conducted on the effects of sulfometuron methyl (99.1% ai) on the green algae, S. capricornutum

(MRID 416801-02). Six test concentrations were evaluated ranging from 0.63 to 20 ug ai/L 

(nominal). The 120 hr EC50 (reduction in cell density) for S. capricornutum was 4.6 μg ai/L and 

the NOAEC was 0.63 ug ai/L. At the LOAEC of 1.3 μg/L, growth was reduced approximately 
138

20%, while the cell growth at the NOAEC showed a slight increase relative to controls. A 

monotonic concentration-response relationship with cell density was observed. These toxicity 

values are based on reported nominal concentrations. Although the study authors indicate that 

samples were taken for analytical measurement and would be analyzed “if deemed necessary,” 

results from chemical analysis were not provided in the study report. At these concentrations, 

solubility of the test compound is not expected to be problematic. Therefore, this test is 

classified as acceptable and meets the guidelines requirement a test with a freshwater green algal 

species.

Freshwater and Marine Diatoms (Navicula pelliculosa and Skeletonema costatum).

Preliminary tests with the freshwater diatom (N. pelliculosa) and saltwater diatom (S. costatum) 

indicated a lack of toxicity such that Tier II tests were not necessary. Both species were exposed 

to a nominal ‘limit’ test concentration of 414 ug ai/L (99.2% ai) for 120 hours including negative 

controls (4 reps each). This ‘limit concentration’ corresponded to the maximum concentration 

calculated for sulfometuron methyl applied to a 6 in. deep, 1 acre pond. For N. pelliculosa, no 

significant reduction in cell density was observed following exposure to 370 ug ai/L (measured, 

MRID 435385-02). The pH ranged from 7.4 to 7.5. Similarly for S. costatum, no significant 

reduction in cell density was observed following exposure to 410 ug ai/L (measured, MRID 

435385-02). The test pH ranged from 7.9-8.7 at test termination. Measurements at test initiation 

and termination indicate stability of sulfometuron methyl in the test solutions. No significant 

guideline deviations were noted in these studies. These tests are considered acceptable and meet 

the guideline requirements for a freshwater and marine diatom.

Bluegreen Algae, Anabena flos-aquae. A tier 2 test was conducted on the freshwater blue-green 

algae, Anabaena flos-aquae, at 5 test concentrations of sulfometuron methyl (99.2% ai) ranging 

from 14 to180 μg/L (measured values, MRID 435385-02). Measurements at test initiation and 

termination indicate stability of sulfometuron methyl in the test solutions. The 120-hr EC50 (cell 

density) for Anabaena was calculated as 41.6 μg/L. A NOAEC for cell density was calculated as 

<14 μg/L (lowest concentration tested). This NOAEC corresponds to a 20% in cell growth 

relative to controls. This test is considered scientifically sound but is classified as supplemental 

because a NOAEC was not reached in the study. No other major guideline deviations were 

apparent in this test. 

Duckweed, Lemna gibba. The freshwater vascular plant (duckweed) was studied in a 14-day 

exposure to sulfometuron methyl (95.7% ai, MRID 435835-03) at 5 test doses ranging from 

0.13 to 1.045 ug ai/L plus a negative control. A total of 3-5 plants were tested per replicate with 

3-5 fronds per plant. The pH of test solutions ranged from 7.5 to 9.4 because test solutions were 

buffered to maintain adequate solubility. The 14-day exposure of EC50 and NOAEC for frond 

count (the most sensitive endpoint tested) were 0.48 and 0.21 μg/L, respectively. Frond counts 

were reduced 4% at the NOAEC and 20% at the LOAEC (0.32 ug/L). Measurements at test 

initiation and termination indicate stability of sulfometuron methyl in the test solutions. 

Following the 14-d exposure period, recovery of duckweed was assessed at the end of the study 

by exposing organisms to untreated medium for an additional 14 days. Effects were expressed as 

percent inhibition of frond counts and biomass. The results are as follows: 
139

14-d Recovery 14-d Recovery:

14-d Exposure Conc. Frond Count Inhibition Biomass Inhibition

1.045 ppb 41.1% 38.3%

0.590 ppb 11.8% 10.8%

0.323 ppb 0.6% - 1.0%

The study authors concluded that sulfometuron methyl was phytotoxic to duckweed at 

concentrations of > 0.590 ppb and phytostatic at 0.323 ppb. These data suggest that the effects 

of sulfometuron methyl to aquatic vascular plants may be reversible following 14-d exposures at 

selected concentrations (0.323 ppb and below) provided a sufficient recovery period is available. 

This study is considered acceptable and satisfies the guideline requirement for a toxicity test 

using an aquatic vascular plant.

Avian, Oral Acute

Mallard duck, Anas platyrhynchos. An acute oral toxicity study with the mallard indicates 

sulfometuron methyl (> 93% ai) is practically non-toxic on an acute basis (MRID 245375). An 

oral LD50 of >4,650 mg ai/kg-bw was reported in this study (recalculated by reviewer for % ai). 

No mortality occurred in any treatment and birds appeared normal throughout the 14-d test 

period. Food consumption varied widely across treatments, but did not exhibit a dose-dependent 

trend. Weight gain/loss also did not exhibit a dose-dependent trend within or across sexes. 

Weight gain in females may have been confounded by induction of the egg laying cycle by the 

photoperiod used. The guideline requirement (71-1) is fulfilled for an acute oral toxicity study 

with birds for sulfometuron methyl and the study is classified as acceptable. 

Avian, Dietary Acute

Mallard duck, Anas platyrhynchos and bobwhite quail, Colinus virginianus. Two, 8-d dietary 

acute toxicity studies were submitted on the effects of sulfometuron methyl on bobwhite quail 

and mallard duck (Accession No. 246409 and MRID 71414, respectively). Both tests consisted 

of a 5-d exposure period followed by 3 days of observation. Mortality, food consumption and 

body weight were measured during the test. Mallards were 16 days old while quail were < 14 

days old at test initiation, with each test using 10 birds per treatment level. The submitted data 

indicates that sulfometuron methyl (92 to 95.2% ai) is practically nontoxic to mallard and quail 

when administered via subacute, dietary exposure. The 8-day acute dietary LC50 values for 

bobwhite quail and mallard are > 5,620 mg ai/kg-diet and > 4,600 mg ai/kg-diet, respectively 

(adjusted by reviewer for & ai). There were no signs of mortality, clinical toxicity, or abnormal 

behavior reported in the studies. The guideline (71-2) is fulfilled for a subacute dietary study 

with birds and these studies are classified as acceptable. 

Mammal, Acute

Rat, Sprague Dawley. The acute toxicity of sulfometuron methyl (technical grade active 

ingredient) is indicated by an acute, oral toxicity study with the rat (MRID 43089201). In this 

study, 5 male and 5 female rats were administered a single oral dose of 5000 mg ai/kg-bw 
140

technical grade sulfometuron methyl (approx. 100% a.i.) in corn oil via gavage. Rats were 

observed for mortality, signs of ill health, pharmacologic and toxicological effects for 14 days 

after dosing. No mortality occurred at 5,000 mg ai/kg-bw and no clinical signs of toxicity were 

observed that were related to sulfometuron methyl exposure. Male and females continued to gain 

weight throughout the study. An acute, oral LD50 value of >5000 mg ai/kg-bw was determined 

from this study, indicating that sulfometuron methyl is categorized as practically non-toxic 

(toxicity category IV) to small mammals on an acute oral basis. This study is considered 

acceptable and satisfies the guideline requirement (81-1) for an acute toxicity study with 

mammals.

Formulated Product, Rat (Sprague Dawley). Formulated pesticide products may contain a 

number of other ‘inert’ ingredients that alter their toxicity compared to the technical grade active 

ingredient (e.g., resulting in greater toxicity). For sulfometuron methyl, data on the oral toxicity 

of formulated products were available for one species of terrestrial animal (rat). Results from 

this study indicate that the formulated product DPX-T5486-87 (74% ai) is practically nontoxic to 

laboratory rats, with an LD50 of >5,000 mg ai/kg-bw. No clinical signs of toxicity, weight loss 

or gross legions were observed in this study. This study satisfied guideline requirements for 

acute oral toxicity with rats and is considered acceptable. 

Mammals, Chronic/Developmental

A combined 2-generation reproduction/oncogenicity study and 2-year chronic reproduction study 

with rats exposed to sulfometuron methyl was submitted to the agency (MRID 423857-05 and 

423857-06). However, study authors had to abandoned the study on about day 200 due to 

disease of the test organisms that was not related to exposure. Portions of this study were 

submitted to the Agency (e.g., 90-day and chronic reproduction) but were found unacceptable 

upon their review by HED. Similarly, a mammalian developmental toxicity study (MRID 

78796) with the rat was also found to be invalid by HED.

A developmental toxicity study with the rabbit (Accession No. 78798) was submitted to the 

Agency. In this study, rabbits were administered doses of 0, 30, 100, or 300 mg/kg/day from 

gestation days (GD) 6-18 and examined at GD 29. There were no mortalities and no treatmentrelated clinical signs or macroscopic findings. A slight decrease in maternal body weight 

occurred during the gestation period (GD 6-18) but this was judged biologically insignificant. 

There were no treatment related effects on fetal or maternal endpoints measured, including 

external, visceral or skeletal malformations, frequency of resorptions, live fetuses, or dead 

fetuses, or on the number of litters, sex ratio, or post-implantation loss. The developmental 

LOAEL was not observed. The developmental NOAEL is 300 mg/kg/day (highest dose tested). 

According to the data evaluation record provided by HED, this study is acceptable but does not 

fulfill the guideline requirement for a developmental toxicity study with rabbits because dose 

levels were not considered high enough to adequately assess developmental toxicity.

Terrestrial Invertebrate
141

Honeybee, Apis mellifera. A honeybee acute contact study is required for sulfometuron methyl

because its post-emergence treatment use will likely result in honeybee exposure. The acute 

contact LD50, using the honey bee is a single-dose laboratory study designed to estimate the 

quantity of toxicant required to cause 50% mortality in a test population of bees. For 

sulfometuron methyl, bees were exposed at 5 treatments ranging from 13 to 100 μg ai/bee and 

included a solvent and negative control (MRID 416728-10). Results indicate that sulfometuron 

methyl is practically non-toxic to bees on an acute contact basis. The contact 48-h LD50 for 

sulfometuron methyl is >100 μg ai/bee. Cumulative mortality and immobility ranged from 4-8% 

in the controls to 0-2% in the treatments. No overt signs of toxicity were observed in the study. 

The guideline (141-1) is fulfilled.

Terrestrial Plants

For sulfometuron methyl, six dicots (sugar beet, rape, tomato, pea, cucumber and soybean) and 

four monocots (onion, corn, wheat, sorghum) were tested using the Tier 2 protocols for effects 

on seedling emergence and vegetative vigor. Tier 1 tests were not conducted since preliminary 

testing indicated all plants would be promoted to Tier 2 testing. Test durations were 14 days and 

21 days for the seedling emergence and vegetative vigor studies, respectively. Depending on the 

species and test, seven to eleven treatments were used with application rates ranged from 

0.0000017 to 0.5625 lb ai/acre. For this risk assessment, a re-review and statistical analysis was 

conducted on the Tier 2 toxicity data from the more sensitive test species in both the seedling 

emergence and vegetative vigor tests. All statistical comparisons were made to negative controls 

(previous analyses in the DER made comparisons to solvent controls even though negative and 

solvent controls were not significantly different). For calculation of the EC25 and EC05, 

nonlinear regression was conducted using the methods of Bruce and Versteeg (1992). In 

situations where the NOAEC was found to be greater than or equal to the EC25, the EC05 was 

used for the comparison with threatened and endangered species. 

Results for the most sensitive endpoints and species with monocots and dicots indicate that 

seedling emergence and vegetative vigor are impacted at exposures well below the maximum 

application rate of 0.375 lb ai/acre for sulfometuron methyl. For seedling emergence, the EC25

of 1.9 x 10 -4 lb ai/acre for the most sensitive monocot (sorghum) is about a factor of 5 greater 

than the EC25 of 3.2 x 10 -5 lb ai/acre for the most sensitive dicot (sugar beet). For 9 of the 10 test 

species, a comparison of EC25 values indicates that interspecies sensitivity differences are within 

a factor of 20 (based on summary data presented by McKelvey, 1995). This indicates that the 

most sensitive test species are not ‘outliers’ in terms of their relative sensitivity. The EC05 and 

NOAEC for the sorghum and sugar beet are 4.3 x 10-5 and 2.9 x 10-5, respectively. A consistent, 

declining monotonic exposure-response curve was observed for sugar beet, while that for 

sorghum was monotonic following an increase in mean shoot height of 24% in the lowest test 

treatment and 2% in the next lowest treatment relative to the negative control. Because the 

statistical method of Bruce and Versteeg (1992) uses a pooled response from the non-monotonic 

portion of the dose-response curve for calculating ECx values, the actual mean response 

associated with the EC05 for sorghum is slightly higher than the mean response observed for 

controls, rendering it a relatively conservative toxicological value. 
142

Results from the vegetative vigor study indicate the most sensitive monocot (corn) and dicot 

(soybean) are impacted at somewhat lower levels compared to the seedling emergence study. 

The EC25 values for corn and soybean (shoot dry weight) are 3.7 x 10-5 and 1.8 x 10-5, 

respectively. Because the NOAEC exceeded the EC25 values for both species, the EC05 is used 

for risk assessment with threatened and endangered species. The EC05 values for corn and 

soybean are 8.4 x 10-6 and 9.9 x 10-7, respectively. For all 10 test species, a comparison of EC25

values indicates that interspecies sensitivity differences are within a factor of 20 (based on 

summary data presented by McKelvey, 1995). This indicates that the most sensitive test species 

are not ‘outliers’ in terms of their relative sensitivity. A consistent, declining monotonic 

exposure-response curve was observed for corn and soybean in the vegetative vigor test. 

II. Acceptable or Supplemental Studies from ECOTOX

Aquatic Organisms

Naqvi and Hawkins (1989). In this study, Naqvi and Hawkins (1989) exposed four genera of 

field-collected microcrustaceans (Diaptomus sp. Eucyclops sp., Alonella sp., and Cypria sp.) to 

sulfometuron methyl from the Oust® formulated product at nominal concentrations of ranging 

from 100 to 2500 mg/L for 48-h. Consistent, monotonic exposure-response relationships across 

the six treatments occurred for all four species and 48-h LC50s (probit analysis) were reported as 

follows: 

Species Test 

Chemical

48-h LC50 (mg/L) 

(95% confidence 

limits)

Classification Reference

Diaptomus sp.

Oust®

(~93% ai)

1315 (1207-1524) supplemental Naqvi and Hawkins 

(1989)

Eucyclops sp. 1320 (1154-1536)

Alonella sp. 802 (475-928)

Cypria sp 2241 (1744-4517)

This study is classified as supplemental primarily because test concentrations were not measured 

in the study and the field collected test organisms were provided a relatively short application 

period (96-h) vs. the 7-d minimum acclimation period recommend for freshwater invertebrate 

testing. Furthermore, organisms were not positively identified to the species level, thus 

indicating that more than one test species may have been tested in each study. Finally, the study 

authors do not indicate whether nominal concentrations were adjusted to reflect the percent 

active ingredient in the formulated product. 

Romaire (1984). A study was submitted by the registrant (DuPont) per FIFRA Section 6(a)2 

requirements on July 1, 1991. In this study, Romaire (1984) evaluated the acute toxicity of 

Oust® (% ai not reported) to juvenile red swamp crayfish, Procambarus clarkii. A static, acute 

toxicity study was conducted for 96 hours in 4 replicate aquaria (5 crayfish/aquarium) at 8 test 

concentrations ranging from 0 to 10,000 mg ai/L. Analytical measurements sulfometuron methyl 
143

were not taken during the study. The authors report that the 96-h LC50 was > 5,000 mg ai/L for 

sulfometuron methyl and mortality did not exceed 50% in any test treatment. However, review 

of this study indicates that it is unacceptable because dissolved oxygen levels dropped 

precipitously throughout the study in test concentrations where mortality was observed, despite 

periodic aeration of test solutions. Dissolved oxygen levels repeatedly reached levels as low as 

2.1 mg/L or approximately 25% saturation, which is well below ASTM recommendations of 

60% saturation. Because the effect of dissolved oxygen on crayfish mortality could not be 

separated from the possible effects of sulfometuron methyl, this study is not considered 

scientifically sound for the purposes of describing the acute toxicity of sulfometuron methyl to 

juvenile crayfish. 

Byl et al. (1994). The effects of sulfometuron methyl on the aquatic vascular plant, Hydrilla

verticillata, were evaluated in a laboratory study conducted by Byl et al (1994). In this study, 

Byl et al.) exposed plants to four aqueous solutions ranging from 0.001 to 1.0 mg/L sulfometuron 

methyl (as the formulated product, Oust®, % ai not reported) . Three replicates were used per 

treatment and exposures continued for 5 days. The number of plants tested per replicate was not 

reported. A significant decrease in shoot length was observed at or above 0.01 mg/L, with 

combined shoot and root length approximating 30% of the controls. Reduction in mean growth 

followed a concentration dependent monotonic relationship. A significant increase in peroxidase 

activity (a potential biochemical indicator of chemical exposure) was also measured at 0.01 mg/L 

relative to controls. This study is classified as supplemental because sulfometuron methyl was 

not measured in the study and it is unclear whether results reported reflect % ai or total 

formulated product.

Fort et al (1999). In this study, Fort et al. (1999) conducted three separate tests of sulfometuron 

methyl exposure to the African clawed frog, Xenopus laevis: (1) a 4-day frog embryo 

teratogenesis assay (FETAX) to evaluate embryo mortality/ malformations; (2) a 14-d test to 

evaluate effects on tail resporption, and (3) a 30-d exposure to evaluate effects on limb 

development. Both analytically impure (85% ai) and purified (99.5% ai) sulfometuron methyl 

exposures were evaluated in the study, but due to the confounding influence of impurities on 

sulfometuron methyl toxicity, results from only the purified (99.5% ai) sulfometuron methyl are 

used here. 

In the FETAX assay, 2 replicates of 20 mid-blastula frog embryos (stage 8) were exposed to 11 

nominal test concentrations of sulfometuron methyl ranging from 0.001 to 24.9 mg ai/L for 96-h. 

Sulfometuron methyl stock solutions were prepared using a DMSO carrier and verified 

analytically (analytical results not reported). Both a negative and solvent control were included. 

Test procedures generally conformed to ASTM recommendations for the FETAX assay (ASTM, 

1996). Results indicate no statistically significant effect of sulfometuron methyl on embryo 

survival or percent malformations up to (and including) the highest test concentration (24.9 

mg/L). Solvent controls were not significantly different from negative controls.

Similar results were found in the 30-d study, whereby no statistically significant effect of 

sulfometuron methyl exposure was found on limb development (% malformations) up through 

24.9 mg/L. Results from the 14-d tail resporption study indicate a significant reduction in tail 
144

resporption at 9.95 and 24.9 mg ai/L beginning at development stage 64 through 66 (test 

termination). No significant reduction occur at or below 1 mg ai/L.

This study is classified as supplemental primarily because exposure concentrations were not 

measured during the test. Although the authors report that sulfometuron methyl was ‘stable’ 

over the 24 to 96-h renewal cycles used in the studies, no analytical chemistry results were 

provided. Furthermore, randomization of study organisms and replicates was not indicated (an 

ASTM requirement). Collection and testing of embryos by separate clutches (an ASTM 

recommendation) was not apparent in the study. Finally, the final concentrations of carrier 

solvent in the various treatments was not reported (solvent concentrations were only reported for 

the stock solutions).

Toxicity of sulfometuron methyl to the African clawed frog from a study by 

Fort et al. (1999).

Species Test 

Chemical

Exposure 

Duration

Endpoint (Effect) Effect 

Level 

(mg ai/L)

Study 

Classification

Ref.

Xenopus 

laevis

sulfometuron 

methyl 

(99.5% ai)

96-h LC50 (% mortality)

NOAEC (% malformations)

> 24.9 

24.9 (a)

Supplemental Fort et al. 

(1999) 

14-d NOAEC (tail resorption)

LOAEC (tail resporption)

0.995

9.95

30-d NOAEC (limb deformation) 24.9(a)

(a) Highest tested dose, LOAEL not achieved in study.

Terrestrial Organisms

Busse et al. (2005). In a greenhouse study, Busse et al. (2005) studied the effect of sulfometuron 

methyl (applied as the formulated product Oust) on ectomycorrhizal formation and seedling 

growth of three conifer species: ponderosa pine (Pinus ponderosa), Douglas fir (Pseudosuga 

menziesii), and white fir (Abies concolor). Conifer seedlings (5 replicates) were grown in four 

different soil types and applied with sulfometuron methyl at 0, 1X and 2X its application rate of 

0.14 kg ai/ha (0.125 lb/A). Sulfometuron methyl was applied to soil at the onset of lateral root 

formation (approximately 45-55 d post planting) due to the high sensitivity of seedlings to 

sulfometuron methyl applied prior to this time period. Results indicate that ectomycorrhizal 

formation was not inhibited for any conifer regardless of soil type or application rate (1X or 2X). 

For ponderosa pine, seedling dry weight and root growth (number of root tips/plant) were 

significantly reduced relative to controls at 0.125 and 0.250 lb ai/A in two of the four soil types. 

For Douglas fir and white fir, no significant reduction in seedling dry weight occurred at any 

treatment level. However, root growth was reduced for Douglas fir at 0.125 lb ai/A for three of 

the four soil types and at 0.25 lb ai/A for the forth soil type. White fir appeared least sensitive to 

sulfometuron methyl, with significant reductions in root growth at 0.125 lb ai/A in one soil type 

and at 0.25 lb ai/A in a second soil type. The authors conclude that sulfometuron methyl does 

not inhibit mycorrhizal formation at the specified application rates but does inhibit plant growth 

of ponderosa pine and root growth of all three species, depending on soil type and application 
145

rate. The lowest NOAEC from this study is 1X the application rate or 0.125 lb ai/A, several 

orders of magnitude above NOECs observed in the seedling emergence and vegetative vigor 

guideline studies.

Boyle and Walters (2005) examined the effect of saccharin, a major degradation product of 

sulfometuron methyl, on resistance of broad bean (Vicia faba) to rust fungus. Although not 

conceived as a degradate study per se, these results nevertheless have some relevance to the 

ecotoxicology of one of the sulfometuron methyl degradation products. In this study, 200 ml of 

0.3 mM saccharin was applied either as a soil drench or to foliage of broad bean which were 

exposed to rust fungus four times over a 14-d period. Results indicate that saccharin did not 

induce resistance to rust fungus nor did it significantly affect shoot weight or leaf area. However 

the authors report the number of leaflets formed was significantly reduced relative to controls. 

Neary et al. (1984) evaluated the effects of sulfometuron methyl (as the formulated product 

Oust) on slash pine (Pinus elliottii) and loblolly pine (Pinus taeda) seedlings inhabiting coastal 

plain flatlands. In this study, 60 trees of each species were exposed to sulfometuron methyl via 

broadcast spray at 0.50 lb ai/A in a randomized factorial design involving different plot 

locations, irrigation and fertilization levels. Although this study was designed primarily to 

investigate the efficacy of different weed control methods, the authors did report that three 

months after treatment, application of sulfometuron methyl did not reduce survival of slash or 

loblolly pine, suggesting an unbounded NOAEC of 0.50 lb ai/A (only dose tested). 
146

APPENDIX I; ECOLOGICAL EFFECTS DATA 

REQUIREMENTS

Ecological Effects Data Requirements for Sulfometuron Methyl

Guideline Data Requirement Test Material MRID

Study 

Classification

Data 

Requirement 

Met? 

More 

Data 

Needed? 

71-1 Avian Oral LD50

sulfometuron 

methyl

245375 Acceptable Yes No

71-2 Avian Dietary LC50

sulfometuron 

methyl

71414

246409 (2)

Acceptable 

Acceptable Yes No

71-4 Avian Reproduction sulfometuron 

methyl

Data Gap No Reserved(3)

72-1

Freshwater Fish 

LC50

sulfometuron 

methyl

435018-01

435018-02

Acceptable Yes No

72-2

Freshwater 

Invertebrate Acute 

LC50

sulfometuron 

methyl 435018-03 Acceptable (1) Yes No

72-3(a) Estuarine/Marine 

Fish LC50

sulfometuron 

methyl 416728-03 Supplemental 

(1) No Reserved(3)

72-3(b) Estuarine/Marine 

Mollusk EC50

sulfometuron 

methyl 416728-05 Supplemental 

(1) No Reserved(3)

72-3(c) Estuarine/Marine 

Shrimp EC50

sulfometuron 

methyl 416728-04 Supplemental 

(1) No Reserved(3)

72-4(a) Freshwater Fish 

Early Life-Stage

sulfometuron 

methyl

423857-

04; 

249796 (2)

Invalid (1) No Reserved(3)

72-4(b)

Aquatic Invertebrate 

Life-Cycle 

(freshwater)

sulfometuron 

methyl 416728-06 Acceptable Yes No

123-1(a) Seedling Emergence

(Tier II)

sulfometuron 

methyl 435385-01 Acceptable Yes No

123-1(b) Vegetative Vigor 

(Tier II)

sulfometuron 

methyl 435385-01 Acceptable Yes No
147

Ecological Effects Data Requirements for Sulfometuron Methyl

Guideline Data Requirement Test Material MRID

Study 

Classification

Data 

Requirement 

Met? 

More 

Data 

Needed? 

123-2

Aquatic 

Plant 

Growth

Blue-green Algae

(Tier II)

sulfometuron 

methyl 435385-02 Acceptable Yes No

Duckweed, Lemna 

gibba

(Tier II)

sulfometuron 

methyl 435385-03 Acceptable Yes No

Freshwater Diatom, 

Navicula (Tier 1)

sulfometuron 

methyl 435385-02 Acceptable Yes No

Marine Diatom 

(Tier 1)

sulfometuron 

methyl 435385-02 Acceptable Yes No

Green algae (Tier II)

sulfometuron 

methyl 416801-02 Acceptable Yes No

141-1 Honey Bee Acute

Contact LD50

sulfometuron 

methyl 416728-10 Acceptable Yes No

(1) Study was re-classified as part of this risk assessment.

(2) Accession number.

(3) Data requirement not met for this guideline study. However, risk assessment results are not likely to change 

based on submission of new acceptable data. Therefore, the data requirement for this study is reserved but may be 

required in the future should additional information warrant additional testing. 
148

APPENDIX J: ECOLOGICAL EFFECTS STUDIES REJECTED 

BY OPP

SULFOMETURON METHYL + DEGRADATES

Papers that Were Accepted for ECOTOX But Ultimately Rejected By OPP (May 2007)

Initial Screen Acceptable for ECOTOX and OPP

Ahrens, J. F. (1985). Evaluation of Sulfometuron Methyl for Weed Control in Christmas Tree 

Plantings. Proc.Northeast.Weed Sci.Soc. 39: 249-253. (Rejection Rationale: 

Target/efficacy study, Mixtures; EcoReference No.: 31608)

Anderson, R. L., Lefever, F. R., and Maurer, J. K. (1988). The Effect of Various Saccharin 

Forms on Gastro-Intestinal Tract, Urine and Bladder of Male Rats. Food 

Chem.Toxicol. 26: 665-669. (Rejection Rationale: Endpoint Relevancy; 

EcoReference No.: 82947)

Byl, T. D. and Klaine, S. J. (1991). Peroxidase Activity as an Indicator of Sublethal Stress in the 

Aquatic Plant Hydrilla verticillata (Royle). In: J.W.Gorsuch, W.R.Lower, W.Wang, 

and M.A.Lewis (Eds.), Plants for Toxicity Assessment, 2nd Volume, ASTM STP 1115, 

Philadelphia, PA 101-106. (Rejection Rationale: Superceded by Byl et al, 1994; 

EcoReference No.: 17181)

Cumberland, P. F. T., Richold, M., Parsons, J. F., and Pratten, M. K. (1994). Further Evaluation 

of a Teratogenicity Screen Using an Intravitelline Injection Technique. Toxicol. In 

Vitro 8: 153-166. (Rejection Rationale: Endpoint Relevancy, Exposure Route; 

EcoReference No.: 91195)

Dodel, J. B., Everaere, L., Gauthier, B., and Issaly, G. (1983). Use of Dpx 5648 Or Methyl 2-

(((((4,6-Dimethyl-2-Pyrimidinyl)Amino)-Carbonyl)Amino)=Sulfonyl)Benzoate Or 

Dpx 5648, A New Herbicide for Weeding Uncultivated Plac. Columa 3: 257-265. 

(Rejection Rationale: Target/Efficacy study; EcoReference No.: 31204)

Epelbaum, S., Landstein, D., Arad, S., Barak, Z., Chipman, D. M., Larossa, R. A., and Vandyk, 

T. K. (1992). Is the Inhibitory Effect of the Herbicide Sulfometuron Methyl due to 2 

Ketobutyrate Accumulation? In: B.K.Singh, H.E.Flores, and J.C.Shannon (Eds.), 7th 

Annu. Penn. State Symp. in Plant Physiol., May 28-30, Univ.Park, PA, Am.Soc.of 

Plant Physiol., Rockville, MD 352-353. (Rejection Rationale: Target/Efficacy study, 

Toxicity mechanisms);

Fleischer, S. J., Gaylor, M. J., Dickens, R., and Turner, D. L. (1989). Roadside Management of 

Annual Fleabane (Erigeron annuus) and Wild Carrot (Daucus carota). Weed Technol.

3: 72-75. (Rejection Rationale: Target/Efficacy study; EcoReference No.: 90965) 

EcoReference No.: 49268)
149

Harada, K., Miyasaki, T., and Tamura, Y. (1994). Chemoattractant Effects of Sugars and Their 

Related Compounds on Black Abalone Haliotis discus. Comp.Biochem.Physiol.A

109: 111-115. (Rejection Rationale: Endpoint relevancy; EcoReference No.: 90554)

Hirose, M., Shirai, T., Tsuda, H., Fukushima, S., Ogiso, T., and Ito, N. (1981). Effect of 

Phenobarbital, Polychlorinated Biphenyl and Sodium Saccharin on Hepatic and Renal 

Carcinogenesis in Unilaterally Nephrectomized Rats Given N-Ethyl-NHydroxyethylnitrosasmine Orally. Carcinogenesis 2: 1299-1302. (Rejection 

Rationale: Endpoint relevancy; EcoReference No.: 82213)

Kim, H.-C., Cha, S.-W., Ha, C.-S., Roh, J.-K., Lee, Y.-S., Furukawa, F., Nishikawa, A., and 

Takahashi, M. (1996). Reappraisal of Eight Representative Carcinogenic and NonCarcinogenic Compounds in a New Medium-Term Rat Liver Bioassay Using. 

Cancer Lett. 104: 85-90. (Rejection Rationale: Endpoint relevancy; EcoReference 

No.: 90556)

King, J. W. and Rogers III, J. N. (1986). Bermudagrass Growth Suppression with Sulfometuron 

Methyl and Metsulfuron Methyl. Ark Farm Re 35(2): 1-4. (Rejection Rationale: 

Target/Efficacy study, Mixture; EcoReference No.: 31373)

Kitchin, K. T. and Ebron, M. T. (1983). Studies of Saccharin and Cyclohexylamine in a Coupled 

Microsomal activating/Embryo Culture System. Food Chem.Toxicol. 21: 537-541. 

(Rejection Rationale: Endpoint relevancy; EcoReference No.: 90513)

Kramers, P. G. N. (1977). Mutagenicity of Saccharin in Drosophila: The Possible Role of 

Contaminants. Mutat.Res. 56: 163-167. (Rejection Rationale: Endpoint relevancy; 

EcoReference No.: 90961)

Liscia, A., Masala, C., Crnjar, R., Sollai, G., and Solari, P. (2004). Saccharin Stimulates the 

"Deterrent" Cell in the Blowfly: Behavioral and Electrophysiological Evidence. 

Physiol.Behav. 80: 637-646. (Rejection Rationale: Endpoint relevancy; 

EcoReference No.: 90053)

Nascimento, M. G., De Oliveira, M. L. C. S., Lima, A. S., and De Camargo, J. L. V. (2006). 

Effects of Diuron [3-(3,4-Dichlorophenyl)-1,1-Dimethylurea] on the Urinary Bladder 

of Male Wistar Rats . Toxicology 224: 66-73. (Rejection Rationale: Endpoint 

relevancy; EcoReference No.: 90555)

Pszczolkowski, M. A. and Brown, J. J. (2003). Effect of Sugars and Non-Nutritive Sugar 

Substitutes on Consumption of Apple Leaves by Codling Moth Neonates. 

Phytoparasitica 31: 283-291. (Rejection Rationale: Target/Efficacy; EcoReference 

No.: 91055)

Sivan, A. and Arad, S. (1998). Intraspecific Transfer of Herbicide Resistance in the Red 

Microalga Porphyridium sp. (Rhodophyceae) via Protoplast Fusion. J.Phycol. 34: 

706-711. (Rejection Rationale: Target/Efficacy; EcoReference No.: 61449)
150

Initial Screen Acceptable for ECOTOX but not OPP

Amin, S., Moore, R. W., Peterson, R. E., and Schantz, S. L. (2000). Gestational and Lactational 

Exposure to TCDD or Coplanar PCBs Alters Adult Expression of Saccharin 

Preference Behavior in Female Rats. Neurotoxicol.Teratol. 22: 675-682.

EcoReference No.: 75076

Chemical of Concern: TCDD,PCB,SAC; Habitat: T; Effect Codes: 

REP,GRO,BEH; Rejection Code: NO ENDPOINT(SAC)//PCBRES 

CODED,RQA,DATA,ENTERED,DONE.

2. Asamoto, M., Mann, A. M., and Cohen, S. M. (1994). P53 Mutation is Infrequent and Might 

not give a Growth Advantage in Rat Bladder Carcinogenesis In Vivo. 

Carcinogenesis 15: 455-458.

EcoReference No.: 90517

Chemical of Concern: SAC; Habitat: T; Effect Codes: CEL; Rejection Code: NO 

MIXTURE(SAC),NO COC(SMM).

3. Bannasch, P., Griesemer, R. A., Anders, F., Becker, R., Cabral, J. R., Della Porta, G., Feron, 

V. J., Henschler, D., Ito, N., Kroes, R., Magee, P. N., McKnight, B., Montesano, R., 

Napalkov, N. P., Nesnow, S., Roberfroid, M., Slaga, T., Turusov, V. S., Wilbourn, J., 

and Williams, G. M. (1986). Assays for Initiating and Promoting Activities. In: 

R.Montesano, et al.(Eds.), IARC (Int.Agency for Res.on Cancer) Sci.Publ.No.83, 

Long-Term and Short-Term Assays for Carcinogens: A Critical Appraisal, Oxford 

Univ.Press, New York, NY 103-126.

EcoReference No.: 90967

Chemical of Concern: PbAC,EXQ,SAC,CTC; Habitat: T; Effect Codes: 

MOR,PHY; Rejection Code: NO CONTROL,ENDPOINT(SAC).

4. Bantle, J. A., Burton, D. T., Dawson, D. A., Dumont, J. N., Finch, R. A., Fort, D. J., Linder, 

G., and Rayburn, J. R. (1994). Fetax Interlaboratory Validation Study: Phase II 

Testing. Environ.Toxicol.Chem. 13: 1629-1637.

EcoReference No.: 13502

Chemical of Concern: SMM; Habitat: A; Rejection Code: NO CONTROL(SMM).

5. Boswell, K. J., Reid, M. L., Fitch, J. V., Bennett, S. M., Narciso, S. P., Hubbell, C. L., and 

Reid, L. D. (2005). Estradiol Valerate and Intake of Sweetened Water. 

Pharmacol.Biochem.Behav. 80: 1-7.

EcoReference No.: 90545

Chemical of Concern: SAC; Habitat: T; Effect Codes: GRO,BEH; Rejection Code: 
151

NO CONTROL,ENDPOINT(SAC).

6. Byl, T. D. and Klaine, S. J. (1991). Peroxidase Activity as an Indicator of Sublethal Stress in 

the Aquatic Plant Hydrilla verticillata (Royle). In: J.W.Gorsuch, W.R.Lower, 

W.Wang, and M.A.Lewis (Eds.), Plants for Toxicity Assessment, 2nd Volume, ASTM 

STP 1115, Philadelphia, PA 101-106.

EcoReference No.: 17181

Chemical of Concern: SMM,CuS; Habitat: A; Effect Codes: BCM,GRO; Rejection 

Code: LITE EVAL CODED(CuS),NO ENDPOINT(SMM).

7. Byl, T. D., Sutton, H. D., and Klaine, S. J. (1994). Evaluation of Peroxidase as a Biochemical 

Indicator of Toxic Chemical Exposure in the Aquatic Plant Hydrilla verticillata, 

Royle. Environ.Toxicol.Chem. 13: 509-515.

EcoReference No.: 4016

Chemical of Concern: SMM,CuS,Se,Cd; Habitat: A; Effect Codes: BCM,GRO; 

Rejection Code: LITE EVAL CODED(CuS),NO ENDPOINT(SMM).

8. Cumberland, P. F. T., Richold, M., Parsons, J., and Pratten, M. K. (1994). Intravitelline 

Injection of Rodent Conceptuses: An Improved In Vitro Developmental Toxicity

Screen. Toxicol.In Vitro 8: 731-733.

EcoReference No.: 91267

Chemical of Concern: ETU,SAC; Habitat: T; Effect Codes: GRO,BCM,CEL; 

Rejection Code: NO CONTROL,NO ENDPOINT(ETU,SAC).

9. Duan, J. J. and Prokopy, R. J. (1993). Toward Developing Pesticide-Treated Spheres for 

Controlling Apple Maggot Flies, Rhagoletis pomonella (Walsh) (Dipt., Tephritidae): 

I. Carbohydrates and Amino Acids as Feeding Stimulants. J.Appl.Entomol. 115: 176-

184.

EcoReference No.: 91063

Chemical of Concern: SAC; Habitat: T; Effect Codes: BEH; Rejection Code: NO 

CONTROL,ENDPOINT(SAC).

10. Fedtke, C., Schmalfuss, J., and Couderchet, M. (1999). Chloroacetanilides, 

Oxyacetamides, Tetrazolinones: Mode of Action. 1. Cross Resistance and Oleic 

Acid Incorporation in Algal Model Systems. Pestic.Sci. 55: 580-582 .

EcoReference No.: 90964

Chemical of Concern: SMM,PCP,PAQT,DU,ACR,BTC,ATZ,BSF,CPP,MBZ; 

Habitat: A; Effect Codes: POP; Rejection Code: NO 

CONTROL,ENDPOINT(SMM,PCP,ATZ).

11. Ferguson, S. A., Delclos, K. B., Newbold, R. R., and Flynn, K. M. (2003). Dietary 

Ethinyl Estradiol Exposure During Development Causes Increased Voluntary Sodium 
152

Intake and Mild Maternal and Offspring Toxicity in Rats. Neurotoxicol.Teratol. 25: 

491-501.

EcoReference No.: 90547

Chemical of Concern: EED,SAC; Habitat: T; Effect Codes: GRO,BEH; Rejection 

Code: NO ENDPOINT(SAC).

12. Ferguson, S. A., Flynn, K. M., Delclos, K. B., and Newbold, R. R. (2000). Maternal and 

Offspring Toxicity but few Sexually Dimorphic Behavioral Alterations Result from 

Nonylphenol Exposure. Neurotoxicol.Teratol. 22: 583-591.

EcoReference No.: 68835

Chemical of Concern: SAC,NYP; Habitat: T; Effect Codes: BEH,GRO,MOR,REP; 

Rejection Code: NO ENDPOINT(SAC).

13. Flynn, K. M., Ferguson, S. A., Delclos, K. B., and Newbold, R. R. (2000). Effects of 

Genistein Exposure on Sexually Dimorphic Behaviors in Rats. Toxicol.Sci. 55: 311-

319.

EcoReference No.: 90544

Chemical of Concern: SAC; Habitat: T; Effect Codes: GRO,BEH; Rejection Code: 

NO ENDPOINT(SAC).

14. Gonzalez, F. E., Atkins, R. L., and Brown, G. C. (1984). Sulfometuron Methyl, Rate and 

Timing Studies on Bermudagrass and Bahiagrass Roadside Turf. Proc.South Weed 

Sci.Soc. 37: 272-274.

EcoReference No.: 31768

Chemical of Concern: SMM; Habitat: T; Effect Codes: GRO; Rejection Code: NO 

ENDPOINT,NO CONTROL(TARGET-SMM).

15. Hannan, P. J. (1995). A Novel Detection Scheme for Herbicidal Residues. 

Environ.Toxicol.Chem. 14: 775-780.

EcoReference No.: 69628

Chemical of Concern: ATZ,PPZ,THF,CRME,TNM,AMTR,CZE,SMM; Habitat: 

AT; Effect Codes: PHY; Rejection Code: NO ENDPOINT(ALL CHEMS) .

16. Hartnett, M. E., Newcomb, J. R., and Hodson, R. C. (1987). Mutations in 

Chlamydomonas reinhardtii Conferring Resistance to the Herbicide Sulfometuron 

Methyl. Plant Physiol.(Bethesda) 85: 898-901.

EcoReference No.: 90536

Chemical of Concern: SMM; Habitat: A; Effect Codes: POP,PHY; Rejection Code: 

NO ENDPOINT(SMM).
153

17. Harvey, J. H. Jr., Dulka, J. J., and Anderson, J. J. (1985). Properties of Sulfometuron 

Methyl Affecting Its Environmental Fate: Aqueous Hydrolysis and Photolysis, 

Mobility and Adsorption on Soils, and Bioaccumulation Potential. J.Agric.Food 

Chem. 33: 590-596.

EcoReference No.: 90543

Chemical of Concern: SMM; Habitat: A; Effect Codes: ACC; Rejection Code: NO 

ENDPOINT(SMM).

18. Hicks, R. M., Wakefield, J. S. J., and Chowaniec, J. (1975). Evaluation of a New Model 

to Detect Bladder Carcinogens or Co-Carcinogens; Results Obtained with Saccharin, 

Cyclamate and Cyclophosphamide. Chem.-Biol.Interact. 11: 225-233.

EcoReference No.: 91040

Chemical of Concern: SAC; Habitat: T; Effect Codes: PHY; Rejection Code: NO 

ENDPOINT(SAC).

19. Ikeda, M., Mitsui, T., Setani, K., Tamura, M., Kakeyama, M., Sone, H., Tohyama, C., 

and Tomita, T. (2005). In Utero and Lactational Exposure to 2,3,7,8-

Tetrachlorodibenzo-p-Dioxin in Rats Disrupts Brain Sexual Differentiation. 

Toxicol.Appl.Pharmacol. 205: 98-105.

EcoReference No.: 80278

Chemical of Concern: TCDD,DXN,SAC; Habitat: T; Effect Codes: 

BEH,REP,GRO,BCM,PHY; Rejection Code: NO ENDPOINT(SAC)//PCBRES 

CODED,RQA,DATA ENTERED,DONE.

20. Ioannides, C., Lum, P. Y., and Parke, D. V. (1984). Cytochrome P-488 and the 

Activation of Toxic Chemicals and Carcinogens. Xenobiotica 14: 119-137 .

EcoReference No.: 90546

Chemical of Concern: ETHN,SAC,DDT,AND; Habitat: T; Effect Codes: 

CEL,BCM; Rejection Code: NO ENDPOINT(SAC).

21. Jaffe, R. L. (1995). Rapid Assay of Cytotoxicity Using Tetramitus flagellates. 

Toxicol.Ind.Health 11: 543-558.

EcoReference No.: 5895

Chemical of Concern: Cd,SMM; Habitat: A; Rejection Code: NO 

ENDPOINT(SMM).

22. Koeppe, M. K. and Mucha, C. F. (1991). Metabolism of Sulfometuron Methyl in 

Lactating Goats. J.Agric.Food Chem. 39: 2304-2309.

EcoReference No.: 90542

Chemical of Concern: SMM; Habitat: T; Effect Codes: ACC; Rejection Code: NO 

CONTROL,ENDPOINT(SMM).
154

23. Kovar, J. L., Zhang, J., Funke, R. P., and Weeks, D. P. (2002). Molecular Analysis of the 

Acetolactate Synthase Gene of Chlamydomonas reinhardtii and Development of a 

Genetically Engineered Gene as a Dominant Selectable Marker for Genetic 

Transformation. Plant J. 29: 109-117.

EcoReference No.: 90963

Chemical of Concern: SMM; Habitat: A; Effect Codes: CEL; Rejection Code: NO 

CONTROL(SMM).

24. Kuhns, L. J. and Kaps, M. A. (1986). Sulfometuron Methyl and Imazapyr Applied as a 

Directed Spray on White Pine. Proc.Northeast.Weed Sci.Soc. 40: 263-264 .

EcoReference No.: 31014

Chemical of Concern: IZP,SMM,SMU; Habitat: T; Effect Codes: POP,PHY; 

Rejection Code: NO ENDPOINT(ALL CHEMS,TARGET-IZP,SMM,SMU).

25. Landstein, D., Arad, S., Barak, Z., and Chipman, D. M. (1993). Relationships Among the 

Herbicide and Functional Sites of Acetohydroxy Acid Synthase from Chlorella 

emersonii. Planta 191: 1-6.

EcoReference No.: 91069

Chemical of Concern: SMM; Habitat: A; Effect Codes: BCM; Rejection Code: 

NO ENDPOINT(SMM).

26. Landstein, D., Epelbaum, S., Arad, S., Barak, Z., and Chipman, D. M. (1995). Metabolic 

Response of Chlorella emersonii to the Herbicide Sulfometuron Methyl. Planta 197: 

219-224.

EcoReference No.: 90966

Chemical of Concern: SMM; Habitat: A; Effect Codes: BCM,PHY; Rejection 

Code: NO ENDPOINT(TARGET-SMM).

27. Langeland, K. A. (1986). Management Program for Alligatorweed in North Carolina. 

Rep.No.224, Water Resour.Res.Inst.of the Univ.of N.Carolina 36 p.

EcoReference No.: 90590

Chemical of Concern: 

MTPN,SMM,TPR,HXZ,BMC,AMTL,DU,IZP,DMB,FDE,GYP,24DXY; Habitat: 

AT; Effect Codes: POP; Rejection Code: NO 

CONTROL(SMM,HXZ,IZP,GYP),NO ENDPOINT(SMM,HXZ,BMC).

28. Lapidot, M., Raveh, D., Sivan, A., Arad, S., and Shapira, M. (2002). Stable Chloroplast 

Transformation of the Unicellular Red Alga Porphyridium Species. Plant Physiol.

129: 7-12.
155

EcoReference No.: 90535

Chemical of Concern: SMM; Habitat: A; Effect Codes: POP,PHY; Rejection Code: 

NO ENDPOINT(SMM).

29. Naqvi, S. M., Hawkins, R., and Naqvi, N. H. (1987). Mortality Response and LC50 

Values for Juvenile and Adult Crayfish, Procambarus clarkii Exposed to Thiodan 

(Insecticide), Treflan, Msma, Oust. Environ.Pollut. 48: 275-283.

EcoReference No.: 12802

Chemical of Concern: SMM,TFN; Habitat: A; Effect Codes: MOR; Rejection 

Code: NO CONTROL(SMM).

30. Nishida, N., Farmer, J. D., Kodavanti, P. R. S., Tilson, H. A., and MacPhail, R. C. 

(1997). Effects of Acute and Repeated Exposures to Aroclor 1254 in Adult Rats: 

Motor Activity and Flavor Aversion Conditioning. Fundam.Appl.Toxicol. 40: 68-74.

EcoReference No.: 90537

Chemical of Concern: SAC,PCB; Habitat: T; Effect Codes: GRO,BEH; Rejection 

Code: NO CONTROL,ENDPOINT(SAC),OK(PCB).

31. Office of Pesticide Programs (2000). Pesticide Ecotoxicity Database (Formerly: 

Environmental Effects Database (EEDB)). Environmental Fate and Effects Division, 

U.S.EPA, Washington, D.C.

EcoReference No.: 344 Rejection Code: Secondary Duplicative Data

32. Peele, D. B., Farmer, J. D., and MacPhail, R. C. (1988). Behavioral Consequences of 

Chelator Administration in Acute Cadmium Toxicity. Fundam.Appl.Toxicol. 11: 

416-428.

EcoReference No.: 90538

Chemical of Concern: SAC,CdCl; Habitat: T; Effect Codes: GRO,BEH; Rejection 

Code: NO ENDPOINT(SAC).

33. Roshon, R. D., McCann, J. H., Thompson, D. G., and Stephenson, G. R. (1999). Effects 

of Seven Forestry Management Herbicides on Myriophyllum sibiricum, as Compared 

with Other Nontarget Aquatic Organisms. Can.J.For.Res. 29: 1158-1169.

EcoReference No.: 60978

Chemical of Concern: 24DXY,GYP,HXZ,IZP,MSFM,SMM,TPR; Habitat: A; 

Effect Codes: GRO,MOR; Rejection Code: NO CONTROL(ALL 

CHEMS),TARGET SMM.

34. Schiffman, S. S., Suggs, M. S., Donia, M. B. A., Erickson, R. P., and Nagle, H. T. (1995). 

Environmental Pollutants Alter Taste Responses in the Gerbil. 

Pharmacol.Biochem.Behav. 52: 189-194.
156

EcoReference No.: 74836

Chemical of Concern: 

CBF,PYT,MTM,ACP,CPY,DEM,MLN,CBL,FNV,PAQT,GYP,SMM ; Habitat: T; 

Effect Codes: PHY; Rejection Code: NO ENDPOINT(ALL CHEMS).

35. Van-Moppes, D., Barak, Z., Chipman, D. M., Gollop, N., and Arad, S. (1989). An 

Herbicide (Sulfometuron Methyl) Resistant Mutant in Porphyridium (Rhodophyta). 

J.Phycol. 25: 108-112.

EcoReference No.: 90533

Chemical of Concern: SMM; Habitat: A; Effect Codes: POP,PHY; Rejection Code: 

NO ENDPOINT(SMM)