UNITED STA TES ENVIRONMENT AL PROTECTION AGENCY 

WASHINGTON, D.C. 20460 

OFFICE OF 

CHEMICAL SAFETY AND 

POLLUTION PREVENTION 

MEMORANDUM 

Date: 15 September 2015 

SUBJECT: Tribenuron methyl. Draft Human Health Risk Assessment in Support of 

Registration Review. 

FROM: 

THROUGH: 

TO: 

PC Code: 128887 DP Barcode: 0421388 

Decision No.: 492900 Registration No.: NA 

Petition No.: NA Case No.: 7217 

Risk Assessment Type: Single Chemica l Aggregate Regulatory Action: Registration Review 

TXR No.: NA CAS No.: I 01200-48-0 

MRID No.: None 40 CFR: 180.451 

Michael A. Doherty, Ph.D., Senior Chemist ~~ d<v" 

Zaida Figueroa, Dr PH, Industrial Hygieni .). 

Karlyn Middleton, M.S., Toxicologist 

Risk Assessment Branch II 

Health Effects Division (7509P) 

Christina Swartz, Branch Chief oQ;_.~ Risk Assessment Branch II 

Health Effects Division (7509P) 

Brittany Pruitt, Chemical Review Manager 

Kelly Sherman, Branch Chief 

Risk Management and Implementation Branch 3 (RMIB 3) 

Pesticide Re-Evaluation Division (7508P) 

As part of registration review, HED has examined the toxicological and exposure databases for 

assessing human health risks associated with tribenuron methyl and conducted a new risk 

assessment following current practices and policies. Significant changes relative to the last risk 

assessment (D358876, B. Hanson. 28 September 2009) include: 

• Establishment of endpoints and points of departure for assessing acute dietary exposure 

for all populations as well as dermal and incidental oral exposure for children; 

• Assessment of acute dietary and spray drift risks. 

Page 1of36 
Page 2 of 36

Table of Contents

1.0 Executive Summary............................................................................................................. 3

2.0 HED Recommendations....................................................................................................... 4

2.1 Tolerance Considerations ................................................................................................ 4

2.2 Label Considerations ....................................................................................................... 5

3.0 Introduction.......................................................................................................................... 5

3.1 Chemical Identity and Physical/Chemical Characteristics............................................... 5

3.2 Pesticide Use Pattern and Anticipated Exposure Pathways............................................. 5

3.3 Consideration of Environmental Justice .......................................................................... 7

4.0 Hazard Identification/Toxicology........................................................................................ 8

4.1 Summary of Toxicological Effects....................................................................................... 8

4.2 Safety Factor for Infants and Children (FQPA Safety Factor)............................................. 9

4.3 Toxicity Endpoint and Point of Departure Selections.......................................................... 9

4.4 Endocrine Disruptor Screening Program ....................................................................... 11

5.0 Dietary Exposure and Risk Assessment ............................................................................ 12

5.1 Water Residue Profile .................................................................................................... 12

5.2 Food Residue Profile...................................................................................................... 13

5.3 Dietary Exposure and Risk Estimates............................................................................ 13

6.0 Residential (Non-Occupational) Exposure/Risk Characterization .................................... 13

6.1 Spray Drift...................................................................................................................... 13

6.1.1 Combined Risk Estimates from Lawn Deposition Adjacent to Applications.............. 14

6.2 Residential Bystander Post-Application Inhalation Exposure ....................................... 15

7.0 Aggregate Exposure/Risk Characterization....................................................................... 15

8.0 Cumulative Exposure/Risk Characterization..................................................................... 15

9.0 Occupational Exposure/Risk Characterization .................................................................. 15

9.1 Occupational Handler Exposure/Risk Estimates............................................................ 15

9.2 Occupational Post-application Exposure/Risk Estimates .............................................. 19

9.2.1 Occupational Post-application Inhalation Exposure/Risk Estimates........................... 19

9.2.2 Occupational Post-application Dermal Exposure/Risk Estimates............................... 19

10.0 Public Health and Pesticide Epidemiology Data ............................................................... 22

11.0 Literature References......................................................................................................... 23

12.0 References.......................................................................................................................... 23

Appendix A. Toxicology Data Requirements and Toxicology Profile..................................... 24

Appendix B. Review of Human Research................................................................................ 29

Appendix C. Occupational Algorithms .................................................................................... 30

Appendix D. Dietary Exposure/Risk Modeling Input and Output ........................................... 32

Appendix E. Nomenclature and Physical/Chemical Properties............................................... 34

Appendix F. Spray Drift Detailed Description......................................................................... 35
Page 3 of 36

1.0 Executive Summary

Tribenuron methyl, methyl-2-[[[[[4-methoxy-6-methyl-1,3,5-triazin-2-yl] methylamino] 

carbonyl] amino] sulfonyl], is a sulfonylurea herbicide that works via inhibition of acetolactate 

synthase (ALS). It is currently registered for use on cereal grains (barley, field corn, oats, rice, 

sorghum, and wheat), oilseed crops (canola, flax, and sunflower), soybeans, and cotton. There is 

also a tolerance with regional registration for grass forage, fodder, and hay (except Bermuda 

grass forage and hay). It is registered for use as pre-emergence, at-planting, and post-emergence 

burndown application(s) for the selective control of broadleaf weeds. It is applied using common 

agricultural equipment (i.e., aerial, groundboom, airblast). There are no registered residential 

uses for tribenuron methyl. 

A human health scoping document was conducted for tribenuron methyl in 2011 (D383555, D. 

Dotson); acute and subchronic neurotoxicity and immunotoxicity studies were identified as data 

gaps. These studies have since been submitted and reviewed, and the hazard assessment has been 

updated considering the new toxicology data. In addition, a subchronic inhalation toxicity and 

guideline dermal toxicity study are not available for tribenuron methyl, as required in the current 

Part 158 Guidelines (40 CFR Part 158). A non-guideline 28-day dermal toxicity study was 

conducted in rabbits; however, testing was done only at the limit dose. The Hazard and Science 

Policy Council (HASPOC) determined that the studies are not required at this time (TXR# 

0056650). The toxicology database for tribenuron methyl is considered complete and adequate 

for risk assessment. For this assessment, an acute dietary risk assessment has been conducted 

based on results observed in the new acute neurotoxicity study, and an incidental oral endpoint

has been selected for assessing spray drift. Also, the adult dermal and inhalation risk assessments 

have been revised based on results observed in the new subchronic neurotoxicity study. A 

separate children’s dermal risk assessment was conducted since a more appropriate endpoint for 

this population was identified in the reproduction study. The chronic dietary endpoint/point of 

departure (POD) selected for risk assessment remains the same as in previous assessments. The 

current draft risk assessment incorporates all newly received data and includes updates to hazard 

and exposure assessments, science policies, and procedures. 

For dietary exposure, HED has conducted screening-level acute and chronic dietary risk 

assessments for tribenuron methyl using tolerance-level residues in foods and a screening-level 

estimate of residues in drinking water. The acute dietary risk estimates are <1% of the acute 

population-adjusted dose (PAD), and the chronic dietary risk estimates range from 6 to 18% of

the chronic PAD; all dietary risk estimates are not of concern.

There are no registered residential uses or uses resulting in direct residential exposure associated 

with tribenuron methyl. Therefore, a quantitative residential exposure assessment was not 

performed. 

Tribenuron methyl can be applied via ground and aerial equipment for the registered agricultural 

uses, and there is the potential for indirect exposure to residues as a result of spray drift. 

Therefore, HED estimated risks associated with spray drift. The highest exposure resulted from 

drift following tribenuron methyl applications using aerial equipment for children 1 < 2 years old 

[Margins of Exposure (MOEs) ≥ 2,100 with a level of concern (LOC) =100]. There are no risks 
Page 4 of 36

of concern at the field’s edge (i.e., assuming a residential lawn is directly adjacent to a field 

where agricultural crops are grown and treated with agricultural equipment). 

Since there are no residential exposure pathways for tribenuron methyl, the aggregate exposure 

and risk estimates are equivalent to the dietary exposure and risk estimates and do not exceed 

HED’s level of concern.

No chemical-specific handler exposure data were submitted in support of this draft risk 

assessment; therefore, HED relied on the best available data to assess handler exposure. Default 

assumptions established by HED’s Science Advisory Council for Exposure (ExpoSAC) were 

used for parameters such as body weight and amount handled. All occupational handler scenarios 

for the registered uses resulted in MOEs greater than the LOC of 100 at baseline level of risk 

mitigation (i.e., baseline attire with no gloves or respirator) or engineering controls for aerial 

applicators (i.e., enclosed cockpits). The current label personal protective equipment (PPE)

requires baseline attire, gloves, and coveralls; therefore, the calculated risk estimates are not of 

concern, and no additional PPE is required. 

Based on the Agency's current practices, a quantitative non-cancer occupational post-application 

inhalation exposure assessment was not performed for tribenuron methyl. If new policies or 

procedures are put into place, the Agency may revisit the need for such an assessment. Postapplication dermal exposure and risk estimates for the registered agricultural uses resulted in 

MOEs that are not of concern on day 0 (i.e., 12 hours following application). The restricted entry 

interval (REI) of 12 hours specified on the registered labels is adequate to protect agricultural 

workers from post-application exposures.

HED has not identified any risk concerns associated with the registered uses of tribenuron

methyl. There are no data gaps that would require submission of additional toxicity, residue 

chemistry, or exposure data.

2.0 HED Recommendations

2.1 Tolerance Considerations

The residue definition for tolerance enforcement is tribenuron methyl only. The existing 

tolerances (40 CFR 180.451) are supported by the available residue chemistry data. At this time, 

there are Canadian Maximum Residue Levels (MRLs) for residues of tribenuron methyl in 

barley, oats, soybean seed, sunflower seed, and wheat at 0.05 ppm; and flaxseed and rapeseed at 

0.02 ppm. There are no Codex MRLs for tribenuron methyl at this time. The U.S. tolerances for 

residues of tribenuron methyl are harmonized with their counterpart Canadian MRLs. No 

revisions to the existing U.S. tolerances are needed during registration review. 

An analytical reference standard for tribenuron methyl is currently available in EPA’s National 

Pesticide Standards Repository (NPSR) and has an expiration date of 29 March 2019 (email 

communication between G. Verdin and J. Van Alstine, 5/11/2015). The registrant is required to

maintain reasonable amounts of the reference standards for tribenuron methyl in the NPSR as 

long as tolerances remain published in 40 CFR §180.451. When necessary, new reference 
Page 5 of 36

standards, or updated certificates of analysis (COAs), should be sent to the Analytical Chemistry 

Branch (ACB), which is located at Fort Meade, MD. It should be sent to the attention of either 

Theresa Cole or Thuy Nguyen at the address listed below, along with a letter of transmittal. 

Please note that the full 9-digit ZIP Code is required, or the mail will be returned to the 

registrant. 

 USEPA

 National Pesticide Standards Repository

 Analytical Chemistry Branch/BEAD/OPP

 701 Mapes Road

 Fort George G. Meade, MD 20755-5350

The letter of transmittal should include the assay of the standard, name of the analytical method 

used, a statement of principal impurities, purification procedures employed, storage 

requirements, and special precautions for safe handling. Replacement of standards, or updated 

COAs, may be required periodically if supplies are exhausted, if the standards expire, or if 

decomposition occurs during storage. Safety Data Sheets (SDSs) must accompany all analytical 

standards as specified by the Occupational Safety and Health Administration (OSHA) in 29CFR 

§1910.1200. 

2.2 Label Considerations

None.

3.0 Introduction

3.1 Chemical Identity and Physical/Chemical Characteristics

Tribenuron methyl {methyl-2-[[[[[4-methoxy-6-methyl-1,3,5-triazin-2-yl] methylamino] 

carbonyl] amino] sulfonyl]} is a sulfonylurea herbicide (Group 2). The chemical properties of 

tribenuron methyl do not suggest that there are any particular exposure issues that warrant 

special consideration. The technical-grade compound has a dissociation constant of 4.7 at 25°C, 

making its water solubility dependent on pH, with low solubility below pH 3. The potential for 

tribenuron methyl to partition into fatty matrices is also, by extension, pH dependent; however, 

based on the octanol/water partitioning coefficient of 0.3 at pH 7, such partitioning is unlikely to 

occur at physiological pH levels. Tribenuron methyl has a relatively low vapor pressure, 

indicating that inhalation of vapors is unlikely to be a significant source of exposure under 

ambient conditions. The nomenclature and physical/chemical properties of tribenuron methyl are 

provided in Appendix E.

3.2 Pesticide Use Pattern and Anticipated Exposure Pathways

Tribenuron methyl is registered for postemergence application to cereal grains, soybean, 

sunflower, and grasses grown for seed. It is also registered for use as a preemergence or postharvest burn-down broadcast application for numerous crops. In addition to these crop uses, it is 

also registered for use on agricultural fallow land. Tribenuron methyl is formulated as dry-
Page 6 of 36

flowable (DF), dry-granular (DG), and soluble-granular (SG) end-use products. There are 4 

actively registered technical products and 17 actively registered end-use products, and they are 

applied as broadcast applications using common agricultural ground, aerial, or chemigation

equipment.

The registered use patterns allows one or two application per season; therefore, the duration of 

exposure for occupational handlers is expected to be short-term (i.e., 1 to 30 days) and 

intermediate-term (i.e., 1 to 6 months); long-term exposures (greater than 6 months) are not 

anticipated. The PPE statements on registered labels require applicators, flaggers and other 

handlers to wear the following: coveralls, shoes plus socks, and chemical-resistant gloves. The 

restricted entry interval (REI) on all labels is 12 hours.

Table 3.2. Summary of Directions for Registered Uses of Tribenuron methyl.1

Applic. Timing, 

Type, and Equip.

Formulation and 

Products

[EPA Reg No.]

Applic. 

Rate

(lb ai/A)

Max. No. 

Applic. per 

Season

Max. Seasonal 

Applic. Rate 

(lb ai/A)

Use Directions and 

Limitations

Cereal Grains

Between 2-leaf and 

flag-leaf stage

Broadcast by ground 

boom, aerial, or 

chemigation

DF, DG, SG

[352-509, 352-538, 

352-610, 352-611, 

352-617, 352-632, 

352-641, 352-661, 

352-714, 352-715, 

352-751, 352-875, 

352-876, 352-899]

0.00234-

0.03125

2 0.03125 14-day retreatment interval

Do not harvest within 45 days 

of application.

Soybean

Do not apply later 

than flowering

Broadcast by ground 

boom, aerial, or 

chemigation

SG

[352-632]

0.0078-

0.03125

1 0.03125

Sunflower

After 2-leaf stage but 

before bud formation

Broadcast by ground 

boom, aerial, or 

chemigation

DF, SG

[352-509, 352-632]

0.0078-

0.0156

0.03125 14-day retreatment interval

Do not apply within 70 days 

of harvest

Grasses Grown for Seed

60 days preplant

Broadcast by ground 

boom, aerial, or 

chemigation

DF, SG

[352-509, 352-632]

0.0047-

0.0126

1 0.0156 For use only in ID, OR, UT, 

and WA

 1 The information in this table was supplied by the registrants via the Pesticide Re-Evaluation Division. It has not 

undergone review by the Biological and Economic Analysis Division for completeness or accuracy.
Page 7 of 36

Table 3.2. Summary of Directions for Registered Uses of Tribenuron methyl.1

Applic. Timing, 

Type, and Equip.

Formulation and 

Products

[EPA Reg No.]

Applic. 

Rate

(lb ai/A)

Max. No. 

Applic. per 

Season

Max. Seasonal 

Applic. Rate 

(lb ai/A)

Use Directions and 

Limitations

Preplant or Post-Harvest Burn-down

Fall-Spring

Broadcast by ground 

boom, aerial, or 

chemigation

DF, DG, SG

[352-509, 352-538, 

352-611, 352-617, 

352-632, 352-635, 

352-641, 352-661, 

352-714, 352-755

AR-080014, 352-

875, 352-889, 352-

899]

0.00375-

0.03125

2 0.03125 30-day retreatment interval

Preplant burn-down

After application, allow at 

least:

7 days before planting 

soybean

14 days before planting 

cotton

60 days before planting 

sugar beet and canola

45 days before planting 

other crops

Fallow

Spring-Fall

Broadcast by ground 

boom, aerial, or 

chemigation

DF, DG, SG

[352-538, 352-610, 

352-611, 352-617, 

352-641, 352-661, 

352-714, 352-715, 

352-751, 352-899]

0.0026-

0.0094

1 0.0156 Apply to fallow fields when 

the majority of weeds have 

emerged and are actively 

growing

After application, allow at 

least:

14 days before planting 

field corn, cotton, grain 

sorghum, rice, ory soybean

60 days before planting 

sugar beet and canola

45 days before planting

other crops

Exposure Pathways

Individuals may be exposed to tribenuron methyl via their diet (food and drinking water). There 

are no registered uses for tribenuron methyl that will result in direct non-dietary (i.e., residential) 

exposures. However, there is the potential for indirect exposure (incidental oral and dermal) to 

tribenuron methyl related to spray drift. Agricultural workers may be exposed to tribenuron

methyl during mixing, loading, and/or applying the herbicide (dermal and inhalation routes) as 

well as during post-application activities (dermal route).

3.3 Consideration of Environmental Justice

Potential areas of environmental justice concerns, to the extent possible, were considered in this 

human health risk assessment, in accordance with U.S. Executive Order 12898, "Federal Actions 

to Address Environmental Justice in Minority Populations and Low-Income Populations," 

(http://epa.gov/compliance/ej/resources/policy/exec_order_12898.pdf). As a part of every 

pesticide risk assessment, OPP considers a large variety of consumer subgroups according to 

well-established procedures. In line with OPP policy, HED estimates risks to population 

subgroups from pesticide exposures that are based on patterns of that subgroup’s food and water 

consumption, and activities in and around the home that involve pesticide use in a residential 
Page 8 of 36

setting. Extensive data on food consumption patterns are compiled by the USDA under the 

National Health and Nutrition Examination Surveys – What We Eat in America (NHANESWWEIA) and are used in pesticide risk assessments for all registered food uses of a pesticide. 

These data are analyzed and categorized by subgroups based on age, season of the year, ethnic 

group, and region of the country. Additionally, OPP is able to assess dietary exposure to smaller, 

specialized subgroups and exposure assessments are performed when conditions or 

circumstances warrant. Whenever appropriate, non-dietary exposures based on home use of 

pesticide products and associated risks for adult applicators and for toddlers, youths, and adults 

entering or playing on treated areas post-application are evaluated. Further considerations are 

currently in development as OPP has committed resources and expertise to the development of 

specialized software and models that consider exposure to bystanders and farm workers as well 

as lifestyle and traditional dietary patterns among specific subgroups.

4.0 Hazard Identification/Toxicology

The toxicology database for tribenuron methyl is adequate for risk assessment. A subchronic 

inhalation toxicity and guideline dermal toxicity study are not available for tribenuron methyl, as 

required in accordance with the current Part 158 Guidelines (40 CFR Part 158). A non-guideline 

28-day dermal toxicity study was conducted in rabbits; however, testing was done only at the 

limit dose. Based on the existing uses, the Hazard and Science Policy Council (HASPOC) 

determined that the studies are not required at this time based on a weight of evidence approach 

and considering all of the available tribenuron methyl hazard and exposure information (TXR# 

0056650). Since the last risk assessment (D358876, B. Hanson, 28 September 2009), new dermal 

penetration, acute and subchronic neurotoxicity, and immunotoxicity studies have been 

submitted for tribenuron methyl.

4.1 Summary of Toxicological Effects

Signs of general toxicity, such as body weight changes and reduced food consumption, were 

observed in the majority of studies conducted. No one particular organ appeared to be the target 

as effects on multiple organs were observed including the liver, heart, kidney, testes, and spleen. 

Subchronic oral exposure in rats resulted in decreases in body weight gain, food consumption, 

and food efficiency; decreases in multiple organ weights (heart, liver, kidney, testes, and spleen); 

and decreases in serum glucose, globulin, and cholesterol. Chronic exposure led to decreased 

absolute body weights, as well as polyarteritis in the pancreas, decreased secretion in seminal 

vesicles, lymphoid depletion in the spleen, and mineralization of the aorta and stomach 

(associated with glomerulonephropathy) in males. Dilation of the renal pelvis and uterine horns, 

and retinal degeneration were seen in females. There was also an increased incidence of 

mammary gland adenocarcinomas observed in females after chronic exposure. As a result, 

tribenuron is classified as a “possible human carcinogen.” In mice, subchronic oral studies are 

not available; however, chronic exposure resulted in bilateral seminiferous degeneration and 

oligospermia in males, while decreased body weight was noted in females. No treatment related 

tumors were observed in mice after chronic exposure. In dogs, no treatment-related effects were 

seen after subchronic oral exposure, and effects after chronic exposure were limited to decreased 

body weight gain and increased serum bilirubin and aspartate aminotransferase (AST) in both 

sexes. No corroborative findings were observed for the elevated enzymes.
Page 9 of 36

Dermal exposure resulted in treatment site lesions, hypokinesia, decreased body weights and 

food consumption, kidney pathology, and death at the limit dose. 

Clinical signs were observed in the acute neurotoxicity study only. Effects on motor activity and 

rearing were seen at the limit dose, along with body weight changes and decreases in food 

consumption. In the subchronic neurotoxicity study, decreased body weight/body weight gains, 

reduced food consumption, and food efficiency were observed. No immunotoxicity was 

observed in the immunotoxicity study at doses up to the highest dose tested.

 

No evidence of increased susceptibility of the young was seen in developmental or reproduction 

studies with tribenuron methyl. In the rat developmental study, decreased fetal weights were 

observed at the mid dose while increased resorptions, mortality, and incomplete ossification were 

seen at the high dose. In the rabbit developmental study, decreased fetal weights and abortions 

were observed. However, all developmental effects were observed in the presence of comparable 

maternal toxicity. In the rat reproduction study, offspring effects were limited to decreased body 

weight gain and spleen weights observed in the presence of comparable maternal toxicity. 

Tribenuron methyl has low to moderate acute toxicity via the oral (Toxicity Category IV), 

inhalation (Toxicity Category III), and dermal (Toxicity Category III) routes of exposure. It is 

not a dermal irritant, but was found to be mildly irritating to the eye, and it is a skin sensitizer.

Tribenuron is readily absorbed in rats. The excretion half-life for the low dose was 26 to 33 

hours; the excretion half-life for the high dose was 51 to 54 hours for males and 69 to 96 hours 

for females. After 168 hours, the major route of excretion was the urine (2-4x feces). Although 

tissue levels increased with dose, there was no accumulation in any particular tissue. Major 

metabolites in urine and feces included metsulfuron methyl, saccharin, and O-demethyl triazine 

amine. 

4.2 Safety Factor for Infants and Children (FQPA Safety Factor)

HED recommends that the FQPA Safety Factor be reduced to 1x for tribenuron methyl. The 

toxicology database is complete, and there are no concerns/residual uncertainties with regard to 

pre- and/or postnatal toxicity, and no concern for neurotoxicity. No increased 

quantitative/qualitative susceptibility was seen in the rat and rabbit developmental and rat 

reproduction studies, and fetal/offspring effects were observed in the presence of comparable 

maternal effects. Additionally, there are clear no-observed adverse-effect levels (NOAELs) for 

the effects seen in the studies. Furthermore, the endpoints and points of departure selected for 

risk assessment are protective of the effects observed in the studies. 

4.3 Toxicity Endpoint and Point of Departure Selections

The toxicological endpoints and PODs have been updated considering the new toxicology data. 

An acute dietary risk assessment has been conducted based on results observed in the new acute 

neurotoxicity (ACN) study, and an incidental oral endpoint has been chosen for assessing spray 

drift. Also, the adult dermal and inhalation risk assessments have been revised based on results 
Page 10 of 36

observed in the new subchronic neurotoxicity (SCN) study. A separate children’s dermal risk 

assessment was conducted since a more appropriate endpoint for this population was identified 

in the reproduction study. The chronic dietary endpoint/POD selected for risk assessment 

remains the same as in previous assessments. 

It should be noted that the endpoints and PODs presented in the toxicology profile table 

(Appendix A) have not been updated to comply with current policy regarding what constitutes an 

adverse effect. The NOAELs and LOAELS have not been changed. Therefore, the 

endpoints/PODs selected for risk assessment may be conservative. The PODs selected for risk 

assessment are protective of the effects observed in the tribenuron methyl database.

A summary of toxicological doses and endpoints used in the tribenuron methyl human health risk 

assessments is presented below:

Table 4.3a. Toxicological Doses and Endpoints for Tribenuron Methyl for Use in Dietary and Non-occupational 

Risk Assessments.

Exposure/

Scenario

Point of 

Departure

Uncertainty/

FQPA Safety 

Factors

RfD, PAD, Level 

of Concern for Risk 

Assessment

Study and Toxicological Effects

Acute Dietary 

(All populations)

NOAEL = 300 

mg/kg/day

UFA = 10X

UFH = 10X

FQPA SF = 1X

Acute RfD =3 

mg/kg/day

aPAD = 3 

mg/kg/day 

Acute Neurotoxicity-Rat.

LOAEL=1000 mg/kg/day, based on 

body weight changes (BW loss in 

males, decreased BWG in females), 

reduced food consumption, and/or 

food efficiency, and transient effects 

on motor activity and rearing.

Chronic Dietary 

(All Populations)

NOAEL = 0.8 

mg/kg/day

UFA = 10X

UFH = 10X

FQPA SF = 1X

Chronic RfD = 

0.008 mg/kg/day

cPAD = 0.008 

mg/kg/day

Chronic-Dog:

LOAEL = 8.16 [M] mg/kg/day based 

on decreased body weight gain 

(20%), elevated bilirubin, AST, and 

increased urinary volume.

Incidental oral 

(short-term)

NOAEL = 2.5 

mg/kg/day

UFA = 10X

UFH = 10X

FQPA SF = 1X

Residential LOC 

for MOE = 100

2-Generation Reproduction -Rat

Offspring LOAEL= 25 mg/kg/day 

based on decreased pup weight (F1b 

up to 8%; F2b up to 9%) and 

decreased absolute and relative 

spleen weights in pups.

Children

Dermal,

Short-term (1-30 

days) 

Intermediate-term

(1-6 months)

NOAEL = 2.5 

mg/kg/day

DAF=17.7%

UFA = 10X

UFH = 10X

FQPA SF = 1X

Residential LOC 

for MOE = 100

2-Generation Reproduction -Rat

Offspring LOAEL= 25 mg/kg/day 

based on decreased pup weight (F1b 

up to 8%; F2b up to 9%) and 

decreased absolute and relative 

spleen weights in pups. 

Adults Dermal,

Short-term (1-30 

days) 

Intermediate-term

(1-6 months)

NOAEL = 

11.3 

mg/kg/day

DAF=17.7%

UFA = 10X

UFH = 10X

Residential LOC 

for MOE = 100

Subchronic neurotoxicity

LOAEL=40.1 mg/kg/day, based on 

decreased body weight (up to 13% 

both sexes) and body weight gains, 

reduced food consumption, and food 

efficiency.

Cancer Classified as Group C (possible human carcinogen). Not mutagenic. The chronic RfD is 

considered to be protective of any potential cancer risk.

Point of Departure = A data point or an estimated point that is derived from observed dose-response data and used to mark the beginning of 

extrapolation to determine risk associated with lower environmentally relevant human exposures. NOAEL = no observed adverse effect level. 
Page 11 of 36

LOAEL = lowest observed adverse effect level. UF = uncertainty factor. UFA = extrapolation from animal to human (interspecies). UFH = 

potential variation in sensitivity among members of the human population (intraspecies). FQPA SF = FQPA Safety Factor. PAD = population 

adjusted dose (a = acute, c = chronic). RfD = reference dose. N/A = not applicable.

Table 4.3b. Toxicological Doses and Endpoints for Tribenuron Methyl for Use in Occupational Risk 

Assessments.

Exposure/

Scenario

Point of 

Departure

Uncertainty 

Factors

Level of 

Concern for 

Risk 

Assessment

Study and Toxicological Effects

Adults Dermal,

Short-term (1-30 

days) 

Intermediate-term

(1-6 months)

NOAEL = 

11.3 

mg/kg/day

DAF=17.7% 

UFA = 10X

UFH = 10X

Occupational 

LOC for MOE 

= 100

Subchronic neurotoxicity

LOAEL=40.1 mg/kg/day, based on 

decreased body weight (up to 13% 

both sexes) and body weight gains, 

reduced food consumption, and food 

efficiency.

Inhalation Shortterm

(1-30 days)

Intermediate-term

(1-6 months)

NOAEL = 

11.3 

mg/kg/day

UFA = 10X

UFH = 10X

Occupational 

LOC for MOE 

= 100

Subchronic neurotoxicity

LOAEL=40.1 mg/kg/day, based on 

decreased body weight (up to 13% 

both sexes) and body weight gains, 

reduced food consumption, and food 

efficiency.

Cancer (oral, 

dermal, inhalation)

Classified as Group C (possible human carcinogen). Not mutagenic. Quantitative 

estimation of cancer risk is not recommended.

Point of Departure (POD) = A data point or an estimated point that is derived from observed dose-response data and used to mark the beginning 

of extrapolation to determine risk associated with lower environmentally relevant human exposures. NOAEL = no observed adverse effect level. 

LOAEL = lowest observed adverse effect level. DAF= Dermal absorption factor. IAF=Inhalation absorption factor. UF = uncertainty factor. UFA

= extrapolation from animal to human (interspecies). UFH = potential variation in sensitivity among members of the human population 

(intraspecies). MOE = margin of exposure. LOC = level of concern. N/A = not applicable.

4.4 Endocrine Disruptor Screening Program

As required by FIFRA and FFDCA, EPA reviews numerous studies to assess potential adverse 

outcomes from exposure to chemicals. Collectively, these studies include acute, subchronic and 

chronic toxicity, including assessments of carcinogenicity, neurotoxicity, developmental, 

reproductive, and general or systemic toxicity. These studies include endpoints which may be 

susceptible to endocrine influence, including effects on endocrine target organ histopathology, 

organ weights, estrus cyclicity, sexual maturation, fertility, pregnancy rates, reproductive loss, 

and sex ratios in offspring. For ecological hazard assessments, EPA evaluates acute tests and 

chronic studies that assess growth, developmental and reproductive effects in different 

taxonomic groups. As part of its most recent registration decision for tribenuron methyl, EPA 

reviewed these data and selected the most sensitive endpoints for relevant risk assessment 

scenarios from the existing hazard database. However, as required by FFDCA section 408(p), 

tribenuron methyl is subject to the endocrine screening part of the Endocrine Disruptor 

Screening Program (EDSP). 

EPA has developed the EDSP to determine whether certain substances (including pesticide 

active and other ingredients) may have an effect in humans or wildlife similar to an effect 

produced by a “naturally occurring estrogen, or other such endocrine effects as the Administrator 

may designate.” The EDSP employs a two-tiered approach to making the statutorily required

determinations. Tier 1 consists of a battery of 11 screening assays to identify the potential of a 

chemical substance to interact with the estrogen, androgen, or thyroid (E, A, or T) hormonal 
Page 12 of 36

systems. chemicals that go through Tier 1 screening and are found to have the potential to 

interact with E, A, or T hormonal systems will proceed to the next stage of the EDSP where EPA 

will determine which, if any, of the Tier 2 tests are necessary based on the available data. Tier 2 

testing is designed to identify any adverse endocrine-related effects caused by the substance, and 

establish a dose-response relationship between the dose and the E, A, or T effect. 

Under FFDCA section 408(p), the Agency must screen all pesticide chemicals. Between October 

2009 and February 2010, EPA issued test orders/data call-ins for the first group of 67 chemicals, 

which contains 58 pesticide active ingredients and 9 inert ingredients. A second list of chemicals 

identified for EDSP screening was published on June 14, 20132 and includes some pesticides 

scheduled for Registration Review and chemicals found in water. For further information on the 

status of the EDSP, the policies and procedures, the lists of chemicals, future lists, the test 

guidelines and the Tier 1 screening battery, please visit our website.3

5.0 Dietary Exposure and Risk Assessment 

5.1 Water Residue Profile

Screening ground water-sourced drinking water exposure estimates were generated with the 

Pesticide Root Zone Model for GroundWater (PRZM-GW; v.1.07) for use in the sulfonylurea 

(SU) dietary risk assessments. EFED initially provided coarse-screen estimates that should 

exceed the upper-bound chemical-specific EDWCs for any SU; however, for several of the SUs, 

the coarse-screen EDWCs resulted in dietary risks of concern and EFED subsequently generated 

refined-screen EDWCs for these SUs. The application inputs for the refined-screen EDWCs 

represent the maximum application rate pattern for the chemical, considering the maximum 

single application rate first, then the maximum seasonal application rate, using usage data 

provided by BEAD if the labels do not provide a maximum seasonal rate. The modeled sorption 

coefficient is also chemical-specific. All other inputs, including the screening assumptions of 

stability to degradation and application every year, remained the same as for the coarse 

screen. The resulting refined-screen EDWCs from PRZM-GW can be used as a conservative 

estimate of exposure and are summarized in Table 5.1 (D427429 G. Orrick). 

The acute and chronic dietary assessments for tribenuron methyl used the maximum daily 

concentration of 35 μg/L (0.035 ppm) and the post-breakthrough mean value of 23 μg/L (0.023

ppm), respectively. 

Table 5.1. Results of PRZM-GW Modeling for Tribenuron Methyl Estimated Drinking Water 

Concentrations.

Sulfonylurea (Use) PRZM-GW 

Scenario Max. Daily Conc. (μg/L) Post-breakthrough Mean (μg/L)

Mean Breakthrough 

Time (yrs)

Tribenuron-methyl (corn) NC cotton 35 23 6.1

 2 See http://www.regulations.gov/#!documentDetail;D=EPA-HQ-OPPT-2009-0477-0074 for the final second list of 

chemicals.

3 http://www.epa.gov/endo/
Page 13 of 36

5.2 Food Residue Profile 

The residue of concern for dietary risk assessment of tribenuron methyl is the parent compound 

itself. In conducting this assessment, HED has assumed tolerance-level residues in the raw 

agricultural commodities and processed products of registered crops, and that 100 percent of 

those crops are treated with tribenuron methyl.

5.3 Dietary Exposure and Risk Estimates

Exposure and risk estimates were obtained from the Dietary Exposure Evaluation Model using 

the Food Commodity Intake Database (DEEM-FCID; version 3.18). The model uses food 

consumption data from the 2003-2008 NHANES/WWEIA database, coupled with recipe files 

and residues in foods, to derive estimates of dietary exposure and risk. Generally, HED is 

concerned when dietary exposure estimates exceed 100% of the population adjusted dose (PAD). 

In the case of tribenuron methyl, the dietary risk estimates (Table 5.3) are not of concern. The 

acute estimates are <1% of the aPAD for all population groups, and the chronic estimates range

from 6 to 18% of the cPAD across all representative population groups. Because of the very 

conservative assumptions used in the analysis (tolerance level residues, 100 % crop treated, 

upper-bound modeled drinking water estimates), actual exposure and risk are expected to be 

much lower than those shown in Table 5.3. The listings of inputs and outputs to the assessment 

are included in Appendix D. 

Table 5.3. Summary of dietary exposure and risk estimates for tribenuron methyl.

Acute Estimates (95th Percentile) Chronic Estimates

Population Group

Exposure, 

mg/kg bw Risk, % aPAD

Exposure, 

mg/kg bw/day Risk, % cPAD

Total US Population 0.0021 <1 0.00061 8

All Infants (< 1 year old) 0.0062 <1 0.0014 18

Children 1-2 years old 0.0033 <1 0.0010 12

Children 3-5 years old 0.0027 <1 0.00087 11

Children 6-12 years old 0.0021 <1 0.00063 8

Youth 13-19 years old 0.0017 <1 0.00048 6

Adults 20-49 years old 0.0020 <1 0.00059 7

Adults 50-99 years old 0.0018 <1 0.00056 7

Female 13-49 years old 0.0020 <1 0.00058 7

6.0 Residential (Non-Occupational) Exposure/Risk Characterization

There are no registered residential uses or occupational/commercial uses resulting in residential 

exposure associated with tribenuron-methyl. Therefore, a quantitative residential exposure 

assessment was not performed.

6.1 Spray Drift

A detailed description about HED’s spray drift policy and how to evaluate the drift potential and 

associated risks is available in Appendix F.
Page 14 of 36

6.1.1 Combined Risk Estimates from Lawn Deposition Adjacent to Applications

The spray drift risk estimates are based on an estimated deposited residue concentration as a 

result of the screening level agricultural application scenarios. The potential risk estimates from 

these residues can be calculated using drift modeling onto 50 feet wide lawns coupled with 

methods employed for residential risk assessments for turf products. 

Tribenuron methyl is registered for use on cereal grains (barley, field corn, oats, rice, sorghum, 

and wheat), oilseed crops (canola, flax, and sunflower), soybeans, cotton, and for grass forage, 

fodder, and hay (except Bermuda grass forage and hay). Corn and soybean are the predominant 

registered agricultural usage crops with the highest application rates, and therefore, are

considered protective/representative of the registered uses. The recommended drift scenario 

screening level options are listed below:

Groundboom applications are based on the AgDrift option for high boom height and using very 

fine to fine spray type using the 90th percentile results. 

Aerial applications are based on the use of AgDrift Tier 1 aerial option for a fine to medium 

spray type and a series of other parameters which will be described in more detail below (e.g., 

wind vector assumed to be 10 mph in a downwind direction for entire application/drift event). 

Airblast applications are based on the AgDrift option for Sparse (Young/Dormant) tree canopies.

The spray drift assessment is based on dermal and incidental oral exposures. The highest 

exposure resulted from drift following tribenuron applications using aerial equipment for 

children 1 to <2 years old (combined dermal + incidental oral MOEs ≥ 2,100, with a LOC =100). 

There are no risks of concern at the field’s edge (i.e., assuming a residential lawn is directly 

adjacent to a field where agricultural crops are grown and treated with aerial, groundboom or 

airblast equipment). See Tables 6.1.1 and 6.1.2 for detailed results.

1 HED’s default assumption that 10% of the application is available for transfer on day 0 following the application and the 

residues dissipate at a rate of 10% each following day.

1 HED’s default assumption that 10% of the application is available for transfer on day 0 following the application and the 

residues dissipate at a rate of 10% each following day.

Table 6.1.1. Adult Risk Estimates (MOEs) Related to Dermal Exposure to Spray Drift from Tribenuron Methyl.

Crop/Rate 

Group Spray Type/ Nozzle Configuration Appl. Rate (lb ai/A) TTR1 (ug/cm2) At Edge of the Field

Dermal

Aerial Fine to Medium

0.03125 0.00347

21,000

Groundboom High Boom Very fine to Fine 29,000

Airblast Sparse 38,000

Table 6.1.2. Children (1<2 years old) Risk Estimates (MOEs) Related to Dermal and Indirect Exposure to Spray Drift 

from Tribenuron Methyl.

Crop/Rate 

Group Spray Type/ Nozzle Configuration Appl. Rate (lb ai/A) TTR1 (ug/cm2) At Edge of the Field

Dermal & Incidental Oral (Combined)

Aerial Fine to Medium

0.03125 0.00347

2,100

Groundboom High Boom Very fine to Fine 2,900

Airblast Sparse 3,800
Page 15 of 36

6.2 Residential Bystander Post-Application Inhalation Exposure

Volatilization of pesticides may be a source of post-application inhalation exposure to 

individuals nearby pesticide applications. The agency sought expert advice and input on issues 

related to volatilization of pesticides from its Federal Insecticide, Fungicide, and Rodenticide Act 

Scientific Advisory Panel (SAP) in December 2009, and received the SAP’s final report4 on 

March 2, 2010. The agency has evaluated the SAP report and has developed a Volatilization 

Screening Tool and a subsequent Volatilization Screening Analysis5

. During Registration 

Review, the agency will use this analysis to determine if data (i.e., flux studies, route-specific 

inhalation toxicological studies) or further analysis is required for tribenuron methyl.

7.0 Aggregate Exposure/Risk Characterization

The Food Quality Protection Act of 1996 directs EPA to assess aggregate exposure to pesticide 

chemical residues, including all anticipated dietary exposures and all other exposures for which 

there is reliable information. In the case of tribenuron methyl, aggregate exposure and risk 

estimates are equivalent to the dietary exposure and risk estimates in Section 5, above, and are 

not of concern.

8.0 Cumulative Exposure/Risk Characterization

In 2015, EPA’s Office of Pesticide Programs released a guidance document entitled, Pesticide 

Cumulative Risk Assessment: Framework for Screening Analysis 

[http://www.epa.gov/oppfead1/cb/csb_page/updates/2015/framework-for-screeninganalysis.html]. This document provides guidance on how to screen groups of pesticides for 

cumulative evaluation using a two-step approach beginning with the evaluation of available 

toxicological information and if necessary, followed by a risk-based screening approach. This 

framework supplements the existing guidance documents for establishing common mechanism 

groups (CMGs)6 and conducting cumulative risk assessments (CRA)7

. The Agency has utilized 

this framework to evaluate the SUs of which orthosulfamuron is a member (J. D’Agostino; 

D428798; 9/9/15). Although the SUs share some chemical and toxicological characteristics, the 

toxicological database does not support a testable hypothesis for a common mechanism of action. 

No further mechanistic data are required and no further cumulative evaluation is necessary.

9.0 Occupational Exposure/Risk Characterization

9.1 Occupational Handler Exposure/Risk Estimates

Based on current labeling, types of equipment and techniques that can potentially be used, 

occupational handler exposure is expected from the registered uses. The quantitative 

 4 http://www.epa.gov/scipoly/SAP/meetings/2009/120109meeting.html

5 http://www.regulations.gov/#!docketDetail;D=EPA-HQ-OPP-2014-0219 6 Guidance For Identifying Pesticide Chemicals and Other Substances that have a Common Mechanism of Toxicity 

(USEPA, 1999)

7 Guidance on Cumulative Risk Assessment of Pesticide Chemicals That Have a Common Mechanism of Toxicity 

(USEPA, 2002)
Page 16 of 36

exposure/risk assessment developed for occupational handlers is based on the scenarios listed in 

Table 9.1. Based on the use pattern and agricultural practices, occupational exposure from the 

registered food uses is expected to be short-term (1-30 days) and intermediate-term (i.e., 1-6 

months) in duration. Since the same endpoint and POD were selected for short- and 

intermediate-term durations, short-term exposure and risk estimates are considered to be 

protective of intermediate-term exposure and risk. Long-term exposures (i.e., more than 6 

months) are not anticipated.

Occupational Handler Exposure Data and Assumptions

A series of assumptions and exposure factors served as the basis for completing the occupational 

handler risk assessments. Each assumption and factor is detailed below on an individual basis.

Application Rate: The maximum single application rates are listed in Table 3.2. Refer to section 

3.0 for a complete use pattern description.

Body Weight: The standard body weight for the general population (80 kg) was used for all 

dermal and inhalation exposure scenarios covered in this risk assessment because the endpoint 

selected was not developmental and/or based on fetal effects. 

Absorption Factor: Since no inhalation absorption data are available, toxicity by the inhalation 

route is considered to be equivalent to the estimated toxicity by the oral route of exposure. A 

dermal absorption factor of 17.7% was used for the exposure assessment and is based on results 

from a dermal penetration study in rats. 

Unit Exposures: It is the policy of HED to use the best available data to assess handler exposure. 

Sources of generic handler data, used as surrogate data in the absence of chemical-specific data, 

include PHED 1.1, and the AHETF database. Some of these data are proprietary (e.g., AHETF 

data), and subject to the data protection provisions of FIFRA. The standard values recommended 

for use in predicting handler exposure that are used in this assessment, known as “unit 

exposures”, are outlined in the “Occupational Pesticide Handler Unit Exposure Surrogate 

Reference Table8

.” HED policy on use of surrogate data, including descriptions of the various 

sources, can be found at the Agency website9

. 

Area Treated or Amount Handled: The inputs for area treated or amount handled were based on 

the Science Advisory Council for Exposure Policy 9.1: Standard Values for Daily Acres Treated 

in Agriculture (values are listed in Table 9.1). The acres treated for high acreage crops for aerial 

and groundboom applications, and orchard/vineyards for airblast applications were used as 

screening for the occupational assessment.

Risk Estimate Equations: The algorithms used to estimate non-cancer exposure and dose for 

occupational handlers can be found in Appendix C.

 8 Available: http://www.epa.gov/opp00001/science/handler-exposure-table.pdf 9 Available: http://www.epa.gov/pesticides/science/handler-exposure-data.html
Page 17 of 36

Combining Exposures/Risk Estimates: Dermal and inhalation risk estimates were combined in 

this assessment, since the toxicological effects for these exposure routes were similar. Dermal 

and inhalation risk estimates were combined using the following formula:

Total MOE = Point of Departure (mg/kg/day) ÷ Combined Dermal + Inhalation Dose 

(mg/kg/day)

Summary of Occupational Handler Non-Cancer Exposure and Risk Estimate

The exposure scenarios presented in Table 9.1 are considered protective of all existing uses. All 

occupational handler scenarios for the registered uses resulted in total MOEs (dermal+inhalation) 

greater than the LOC of 100 at baseline level of risk mitigation (i.e., baseline attire with no 

gloves or respirator), or engineering controls for aerial applicators (i.e., enclosed cockpits). The 

current label PPE requires baseline attire, gloves, and coveralls; therefore, the calculated risk 

estimates are not of concern, and no additional PPE is required. The lowest total MOE is 490 

associated with total exposure during mixing/loading activities for a dispersible granule 

formulation being applied aerially over up to 1,200 acres. All other MOEs were higher ranging 

from 2,300 to 130,000. 

The Agency matches quantitative occupational exposure assessment with appropriate 

characterization of exposure potential. While HED presents quantitative risk estimates for human 

flaggers where appropriate, agricultural aviation has changed dramatically over the past two 

decades. According the 2012 National Agricultural Aviation Association (NAAA) survey of 

their membership, the use of GPS for swath guidance in agricultural aviation has grown steadily 

from the mid 1990’s. Over the same time period, the use of human flaggers for aerial pesticide 

applications has decreased steadily from ~15% in the late 1990’s to only 1% in the most recent 

(2012) NAAA survey. The Agency will continue to monitor all available information sources to 

best assess and characterize the exposure potential for human flaggers in agricultural aerial 

applications.

HED has no data to assess exposures to pilots using open cockpits. The only data available 

reflects exposure to pilots in enclosed cockpits. Therefore, risks to pilots are assessed using the 

engineering control (i.e., enclosed cockpits) and baseline attire (i.e., long-sleeve shirt, long pants, 

shoes, and socks); per the Agency’s Worker Protection Standard stipulations for engineering 

controls, pilots are not required to wear protective gloves for the duration of the application. 

With this level of protection, there are no risk estimates of concern for applicators.

Table 9.1. Short-term Handler Exposure and Risk Estimates for Tribenuron methyl.

Exposure 

Scenario

Dermal Unit 

Exposure 

(ug/lb ai)

[Level of 

PPE]ab

Inhalation 

Unit 

Exposure

(ug/lb ai)

[Level of 

PPE]ab

Application 

Ratec

Area 

Treatedd

Dermal 

Dosee

Dermal 

MOEf

Inhalation 

Doseg

Inhalation 

MOEh

Total 

MOEi

Mixer/Loader

Dry Flowable 

(Dispersible 

Granule) for 

227

(Baseline)

8.96 

(Baseline)

0.03125 lb 

ai/A

1,200 A 0.01880 600 0.0042 2,700 490
Page 18 of 36

Table 9.1. Short-term Handler Exposure and Risk Estimates for Tribenuron methyl.

Exposure 

Scenario

Dermal Unit 

Exposure 

(ug/lb ai)

[Level of 

PPE]ab

Inhalation 

Unit 

Exposure

(ug/lb ai)

[Level of 

PPE]ab

Application 

Ratec

Area 

Treatedd

Dermal 

Dosee

Dermal 

MOEf

Inhalation 

Doseg

Inhalation 

MOEh

Total 

MOEi

Aerial 

Application

Dry Flowable 

(Dispersible 

Granule) for 

Groundboom 

Application

227 

(Baseline)

8.96 

(Baseline)

0.03125 lb 

ai/A

200 A 0.00140 3,600 0.0007 16,000 2,900

Dry Flowable 

(Dispersible 

Granule) for 

Airblast 

Application

227 

(Baseline)

8.96 

(Baseline)

0.03125 lb 

ai/A

40 A 0.000628 18,000 0.00014 81,000 15,000

Granular for 

Aerial 

Application

8.4 

(Baseline)

1.7 

(Baseline)

0.03125 lb 

ai/A

1200 A 0.000697 16,000 0.000798 14,000 7,500

Granular for 

Tractor-drawn 

Spreader

8.4 

(Baseline)

1.7 

(Baseline)

0.03125 lb 

ai/A

200 A 0.000116 97,000 0.000133 85,000 45,000

Applicator

Sprays for 

Aerial 

Application

2.08

(Engineering 

Controls –

Enclosed 

Cockpit)

0.0049

(Engineering 

Controls –

Enclosed 

Cockpit)

0.03125 lb 

ai/A

1,200 A 0.000173 65,000 0.0000023 4,900,000 64,000

Sprays for 

Groundboom 

Application

78.6 

(Baseline)

0.34 

(Baseline)

0.03125 lb 

ai/A

200 A 0.00109 10,000 0.0000266 420,000 9,800

Sprays for 

Airblast 

Application

1,770 

(Baseline)

4.71 

(Baseline)

0.03125 lb 

ai/A

40 A 0.00489 2,300 0.0000736 150,000 2,300

Granules for 

Aerial 

Application

1.7

(Engineering 

Controls –

Enclosed 

Cockpit)

1.3

(Engineering 

Controls –

Enclosed 

Cockpit)

0.03125 lb 

ai/A

1200 A 0.000141 80,000 0.00061 19,000 15,000

Granules for 

Tractor-drawn 

Spreader

9.9

(Baseline)

1.2 

(Baseline)

0.03125 lb 

ai/A

200 A 0.000137 82,000 0.0000938 120,000 49,000

Flagger

Sprays for 

Aerial 

Application

11 (Baseline) 0.35 

(Baseline)

0.03125 lb 

ai/A

350 A 0.000266 42,000 0.0000479 240,000 36,000

Granules for 

Aerial 

Application

2.75

(Baseline)

0.15

(Baseline)

0.03125 lb 

ai/A

350 A 0.000067 170,000 0.0000205 550,000 130,000

a. Level of PPE: level of PPE represented by the numerical unit exposure. “baseline” (i.e., single layer of clothing consisting of 

a long sleeved shirt, long pants, shoes plus socks, no gloves, and no respirator); “engineering controls” (i.e., enclosed cockpit for 

aerial applications). Current label required PPE = coveralls, shoes plus socks, and chemical-resistant gloves. 

b. Based on the “Occupational Pesticide Handler Unit Exposure Surrogate Reference Table” (February, 2015).

c. Based on the maximum single application rates listed on registered labels (Table 3.2).

d. Based on the Science Advisory Council for Exposure Policy 9.1: Standard Values for Daily Acres Treated in Agriculture.

e. Dermal Dose (mg/kg/day) = [Rate x UE x 0.0001 x Dermal Absorption (17.7%) x Area Treated]/BW (80 kg). 

f. Dermal MOE = Dermal NOAEL (11.3 mg/kg/day)/ Dermal Dose (mg/kg/day). LOC=100.

g. Inhalation Dose (mg/kg/day) = [Rate x UE x 0.0001 x Area Treated]/BW (80 kg).
Page 19 of 36

h. Inhalation MOE = Inhalation NOAEL (11.3 mg/kg/day)/ Inhalation Dose (mg/kg/day). LOC=100.

i. Total MOE = NOAEL (mg/kg/day)/ [Dermal + Inhalation Dose (mg/kg/day)]. LOC=100.

9.2 Occupational Post-application Exposure/Risk Estimates

HED uses the term post-application to describe exposures that occur when individuals are 

present in an environment that has been previously treated with a pesticide (also referred to as reentry exposure). Such exposures may occur when workers enter previously treated areas to 

perform job functions, including activities related to crop production, such as scouting for pests 

or harvesting. Post-application exposure levels vary over time and depend on such things as the 

type of activity, the nature of the crop or target that was treated, the type of pesticide application, 

and the chemical’s degradation properties. In addition, the timing of pesticide applications, 

relative to harvest activities, can greatly reduce the potential for post-application exposure.

9.2.1 Occupational Post-application Inhalation Exposure/Risk Estimates

There are multiple potential sources of post-application inhalation exposure to individuals 

performing post-application activities in previously treated fields. These potential sources 

include volatilization of pesticides and resuspension of dusts and/or particulates that contain 

pesticides. The agency sought expert advice and input on issues related to volatilization of 

pesticides from its Federal Insecticide, Fungicide, and Rodenticide Act Scientific Advisory Panel 

(SAP) in December 2009, and received the SAP’s final report on March 2, 2010 

(http://www.epa.gov/scipoly/SAP/meetings/2009/120109meeting.html). The agency has 

evaluated the SAP report and has developed a Volatilization Screening Tool and a subsequent 

Volatilization Screening Analysis (http://www.regulations.gov/#!docketDetail;D=EPA-HQOPP-2014-0219). During Registration Review, the agency will utilize this analysis to determine 

if data (i.e., flux studies, route-specific inhalation toxicological studies) or further analysis is 

required for tribenuron.

In addition, the Agency is continuing to evaluate the available post-application inhalation 

exposure data generated by the Agricultural Reentry Task Force. Given these two efforts, the 

Agency will continue to identify the need for and, subsequently, the way to incorporate 

occupational post-application inhalation exposure into the agency's risk assessments.

Although a quantitative occupational post-application inhalation exposure assessment was not 

performed, an inhalation exposure assessment was performed for occupational handlers. Handler 

exposure resulting from application of pesticides outdoors is likely to result in higher exposure 

than post-application exposure. Therefore, it is expected that these handler inhalation exposure 

estimates would be protective of most occupational post-application inhalation exposure 

scenarios.

9.2.2 Occupational Post-application Dermal Exposure/Risk Estimates

A series of assumptions and exposure factors served as the basis for completing the occupational 

post-application dermal risk assessment, including the following:
Page 20 of 36

Exposure Duration: Based on the use pattern and agricultural practices, occupational postapplication exposure from the registered food uses is expected to be short-term (1-30 days) and 

intermediate-term (i.e., 1-6 months) in duration. Since the same endpoint and POD were selected 

for short- and intermediate-term durations, short-term exposure and risk estimates are considered 

to be protective of intermediate-term exposure and risk. Long-term exposures (i.e., more than 6 

months) are not anticipated.

Transfer Coefficients: It is the policy of HED to use the best available data to assess postapplication exposure. Sources of generic post-application data, used as surrogate data in the 

absence of chemical-specific data, are derived from the Agricultural Reentry Task Force (ARTF)

exposure monitoring studies, and, as proprietary data, are subject to the data protection 

provisions of FIFRA. The standard values recommended for use in predicting post-application 

exposure that are used in this assessment, known as “transfer coefficients”, are presented in the 

ExpoSAC Policy 310” which, along with additional information about the ARTF data, can be 

found at the Agency website11. Table 9.2.2.1 provides a summary of the anticipated high-contact 

post-application activities and associated transfer coefficients for the proposed crops/use sites. 

These activities were selected as a worst-case assessment of potential post-application exposure, 

and are considered protective of all post-application activities associated with these crops.

Table 9.2.2.1. Anticipated High-contact Post-Application Activities and Dermal Transfer Coefficients.

Proposed Crops

Policy Crop 

Group 

Category

Crop 

Height

Foliage 

Density

Transfer 

Coefficients 

(cm2

/hr)

Activities

Corn, sweet, grain, 

processing Field, row, tall High Full 1,900 Irrigation (Hand set)

Corn, sweet, grain Field, row, tall High Full 8,800 Hand, Detasseling

Barley, Wheat, 

Soybean, Rice, Canola

Field, row, 

medium Low Full 1,100 Scouting

Forage, Hay Field, row, 

medium High Full 1,900 Irrigation (Hand set)

Sunflower Field, row, tall Low/High Full 90 Scouting, Bird Control

Sorghum Field, row, tall High Full 210 Scouting

Cotton Field, row, 

medium Low Full

900 Harvesting Mechanical 

(Module Builder)

2400 Harvesting Mechanical 

(Picker Operator; Raker)

5050 Harvesting Mechanical (Tramper)

Application Rate: The maximum single application rates are listed in Table 3.2. Refer to section 

3.0 for a complete use pattern description.

Exposure Time: The average occupational workday is assumed to be 8 hours. 

 10 Available: http://www.epa.gov/pesticides/science/exposac_policy3.pdf 11 Available: http://www.epa.gov/pesticides/science/post-app-exposure-data.html
Page 21 of 36

Dislodgeable Foliar Residues: Chemical-specific dislodgeable foliar residue data have not been 

submitted for tribenuron during registration review. This assessment uses HED’s default 

assumption that 25% of the application is available for transfer on day 0 following the 

application and the residues dissipate at a rate of 10% each following day.

Risk Estimate Equations: The algorithms used to estimate non-cancer exposure and dose for 

occupational post-application workers can be found in Appendix C.

Occupational Post-application Non-Cancer Dermal Risk Estimates

A summary of the post-application exposure and risk estimates for the registered uses is provided 

in Table 9.2.2.2. Only risk estimates for the highest contact activity for each crop and the highest 

application rates are shown below. Post-application dermal exposure and risk estimates for the 

scenarios shown below resulted in MOEs greater than 100 and are not of concern on day 0 (i.e., 

12 hours following application). All other scenarios involving lower contact activities would 

have higher MOEs and are also not of concern.

A summary of the post-application dermal exposure and risk estimates from use of tribenuron on 

cotton during harvesting activities is provided in Table 9.2.2.3. Dislodgeable residue data for 

cotton bolls was not available for tribenuron; therefore, the dislodgeable residue value for cotton 

bolls was estimated from the field trial residues in/on cotton gin byproducts. The field trial 

residue is an upper-bound residue value collected at the pre-harvest interval which represents the 

amount of residue in and on the cotton boll; not just the amount of residue that could be 

dislodged. It is considered appropriate as an estimate of dislodgeable boll residue, and is used as 

a screening level approach to estimating exposure. Post-application dermal exposure and risk 

estimates resulted in MOEs greater than 100 and are not of concern. 

Table 9.2.2.2. Occupational Post-application Non-Cancer Exposure and Risk Estimates for Tribenuron

methyl.

Crop/Site Activities Transfer Coefficient 

(cm2/hr) DFR1 Dermal Dose (mg/kg/day)2 MOE3

Short- and Intermediate-term

Corn, sweet, grain, 

processing Irrigation (Hand set) 1,900 0.09 0.003 3,800

Corn, sweet, grain Hand, Detasseling 8,800 0.09 0.014 830

Barley, Wheat, 

Soybean, Rice, 

Canola

Scouting 1,100 0.09 0.002 6,600

Forage, Hay Irrigation (Hand set) 1,900 0.09 0.003 3,800

Sunflower Scouting, Bird Control 90 0.09 0.0001 81,000

Sorghum Scouting 210 0.09 0.0003 35,000

1. DFR = Application Rate (0.03125 lb ai/A) × F × (1-D)t × 4.54E8 μg/lb × 2.47E-8 acre/cm2; where F = 0.25 and D = 0.10 per day.

2. Daily Dermal Dose = [DFR (μg/cm2

) × Transfer Coefficient × 0.001 mg/μg × 8 hrs/day × Dermal Absorption (17.7%)] ÷ BW (80 kg).

3. MOE = Dermal NOAEL (11.3 mg/kg/day) / Dermal Dose (mg/kg/day); LOC=100. 
Page 22 of 36

Table 9.2.2.3. Post-Application Exposure and Risk Estimates for use of Tribenuron on Cotton during Harvesting 

Activities.

Crop

Maximum 

Application 

Rate

(lb ai/A)

Activity TC1

(g cotton/hr)

Days After 

Treatment

Residue from 

Cotton Field 

Trial 2

(mg ai/g 

cotton)

Daily Dose 

(mg/kg/d)3

Dermal 

MOE4

Short- and Intermediate-term

Cotton 0.009

Harvesting 

Mechanical 

(Module Builder)

900

133 0.00002

0.000319 35,000

Harvesting 

Mechanical 

(Picker Operator; 

Raker)

2,400 0.000869 13,000

Harvesting 

Mechanical 

(Tramper)

5,050 0.001788 6,200

1. Transfer Coefficients from HED Policy No. 3.0., Non-Foliar Transfer Coefficient Table, March 2012 (p 122). 

2. Residue Value from Cotton Field Trial adjusted to Max. Seasonal Application Rate (mg ai/g cotton) = (0.02 mg ai/kg cotton) (0.001 kg/g) 

((0.009 lb ai/A)/(0.009 lb ai/A)) = 0.00002 mg ai/g cotton.

3. Dermal Dose (mg/kg/day) = [Cotton Field Trial Residue Value adjusted (mg ai/g cotton) x TC (g cotton/hr) x 8 hrs/day x DAF (17.7%)]/ BW 

(80 kg).

4. Dermal MOE = NOAEL (11.3 mg/kg/day)/Dermal Dose (mg/kg/day); LOC = 100.

Restricted Entry Interval

The REI specified on the registered labels is 12 hours. Tribenuron is classified as Toxicity 

Category III via the dermal route and Toxicity Category IV for skin irritation potential. It is not a 

skin sensitizer. Short- and intermediate-term post-application risk estimates were not a concern 

on day 0 (i.e., 12 hours following application) for all post-application activities. Under 40 CFR 

156.208 (c) (2) (iii), active ingredients classified as Toxicity Category III or IV for acute dermal, 

eye irritation and primary skin irritation are assigned a 12-hour REI. Therefore, the [156 subpart 

K] Worker Protection Statement interim REI of 12 hours is adequate to protect agricultural 

workers from post-application exposures to tribenuron. The REI specified on the current labels is 

protective.

10.0 Public Health and Pesticide Epidemiology Data

D425816, S. Recore, 24 March 2015

Tribenuron methyl was previously reviewed in 2010 (S. Recore, 11/30/2010, D383633). At the 

time, there were no tribenuron methyl incidents found in Main IDS and eight incidents reported to 

Aggregate IDS from January 1, 2002 to May 27, 2010. Upon review of these incidents, it was 

concluded that “Based on the low frequency and severity of incident cases, there does not appear 

to be a concern at this time that would warrant further investigation.” 

The current IDS analysis from January 1, 2010 through March 10, 2015, shows no incidents 

reported involving tribenuron methyl in Main IDS and six incidents reported to Aggregate IDS. 

Further, a query of SENSOR-Pesticides 1998-2011 identifies eight cases involving multiple 

active ingredients, including tribenuron methyl. These incidents were classified as low severity.

Based on the low frequency and mostly low severity of incident cases reported for tribenuron 

methyl in both IDS and NIOSH SENSOR-Pesticides, there does not appear to be a concern at 
Page 23 of 36

this time that would warrant further investigation. The Agency will continue to monitor the 

incident information and if a concern is triggered, additional analysis will be conducted.

The Agricultural Health Study (AHS) is also a potential source of information associated with 

human health effects associated with certain pesticides. Tribenuron methyl is not included in the 

AHS, and therefore that study does not provide information for this assessment.

11.0 Literature References

A literature search was performed for tribenuron methyl. The search did not reveal information 

that would impact the current risk assessment. 

12.0 References

Author Barcode Date Title

Hanson, B. D358876 28 Sept. 2009 Tribenuron methyl. Human Health Risk 

Assessment for the Proposed Use of Tribenuron 

methyl on Corn and Soybean

Dotson, D. et al. D383555 2 March 2011 Tribenuron Methyl. Human Health Assessment 

Scoping Document in Support of Registration 

Review.

Van Alstine, J. TXR# 0056650 17 June 2013 Tribenuron methyl: Summary of Hazard and 

Science Policy Council (HASPOC) Meeting of 

April 25, 2013: Recommendations on the 

Requirements for Subchronic Inhalation and 

Subchronic Dermal Studies.

Recore, S. D425816 24 March 2015 Tribenuron-methyl: Tier 1 Update Review of 

Human Incidents/Epidemiology for Draft Risk 

Assessment

G. Orrick D427429 8/12/2015 Drinking Water Exposure Assessment for the 

Registration Review of 22 Sulfonylurea 

Herbicides 
Page 24 of 36

Appendix A. Toxicology Data Requirements and Toxicology Profile 

A.1. Toxicity Requirements

The toxicology requirements (40 CFR 158.340) for tribenuron methyl are presented below. 

Test Technical

Required Satisfied

870.1100 Acute Oral Toxicity

870.1200 Acute Dermal Toxicity

870.1300 Acute Inhalation Toxicity

870.2400 Primary Eye Irritation

870.2500 Primary Dermal Irritation

870.2600 Dermal Sensitization

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

870.3100 Oral Subchronic (rodent)

870.3150 Oral Subchronic (nonrodent)

870.3200 21-Day Dermal

870.3250 90-Day Dermal

870.3465 21/90-Day Inhalation

Yes

Yes

Yes

No

Yes

Yes

Yes

Not required*

No+

Not required*

870.3700a Developmental Toxicity (rodent)

870.3700b Developmental Toxicity (nonrodent)

870.3800 Reproduction

Yes

Yes

Yes

Yes

Yes

Yes

870.4100a Chronic Toxicity (rodent)

870.4100b Chronic Toxicity (nonrodent)

870.4200a Oncogenicity (rat)

870.4200b Oncogenicity (mouse)

870.4300 Chronic/Oncogenicity

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

870.5100 Mutagenicity—Gene Mutation - bacterial

870.5300 Mutagenicity—Gene Mutation - mammalian

870.5385 Mutagenicity—Mouse Micronucleus

870.5550 Mutagenicity—Unscheduled DNA Synthesis

Yes

Yes

Yes

No

Yes

Yes

Yes

---

870.6200a Acute Neurotoxicity Screening Battery (rat)

870.6200b 90-Day Neurotoxicity Screening Battery (rat)

870.6300 Developmental Neurotoxicity

Yes

Yes

No

Yes

Yes

No

870.7485 General Metabolism

870.7600 Dermal Penetration

870.7800 Immunotoxicity

Yes

No

Yes

Yes

Yes

* The Hazard and Science Policy Council (HASPOC) determined that subchronic inhalation and immunotoxicity studies are not 

required (TXR#s 0056650). + A non-guideline 28-day dermal toxicity study was conducted in rabbits; however, testing was done 

only at the limit dose. 
Page 25 of 36

A.2. Toxicity Profiles

TABLE A.2.1 Acute Toxicity Profile-Tribenuron Methyl (Technical Grade)

Test MRID Results Category

Oral LD50-rat 00149670 LD50>5000 mg/kg (limit test) IV

Dermal LD50-rabbit 00148632 LD50>2000 mg/kg (limit test) III

Inhalation LC50-rat 00148634 LC50>6.7 mg/L gravimetric concentration (4-

hour nose-only limit test); MMAD = 3.5 μm III

Eye Irritation-rabbit 40357401 Mild irritation in washed and unwashed eyes, 

redness with vessel injection at 1 and 4 hours. IV

Dermal irritation-rabbit 40357402 Non-irritating IV

Dermal sensitization-guinea 

pig

42364302 Sensitizer Not applicable

Table A.2.2. Subchronic, chronic, and Other Toxicology Profile for Tribenuron Methyl

Guide 

line

Study Title MRID Dose Levels Results

870.3100 90-Day oral toxicity, 

Rat

00148638 0, 100, 1750, 5000 ppm NOAEL=100 ppm (7/8 mg/kg/day, 

M/F, respectively)

LOAEL=1750 ppm (118/135 

mg/kg/day, M/F, respectively) for 

decreased body weight gain, food 

consumption and food

efficiency; decreased absolute heart, 

liver, and kidney weights; increase 

relative brain, heart, liver, kidney, 

testes, and spleen weights; decreased 

serum glucose and globulin; no 

histopathologic lesions; likely cachexia

870.3150 13-week subchronic 

oral toxicity, Dog

00148639 0, 50, 500, 2500 ppm NOAEL=2500 ppm (73.3/78.0 

mg/kg/day in M/F, respectively) HDT

870.3200 28-Day Dermal, Rabbit 42243101 Limit dose, 1000 

mg/kg/day (only dose 

tested),

1000 mg/kg/day (only dose tested), 

resulted in serious toxicity and death. 

Toxicity included treatment site 

lesions, hypokinesia, decreased body 

weights and food consumption, and 

kidney pathology, but the cause of 

death could not be determined. 

Although this study is classified as 

Core Supplementary, another study is 

not needed. Worker exposure is 

expected to be 4-5 orders of magnitude 

lower than the limit dose.

870.3700a Developmental 

Toxicity, Rat

00148640 0, 20, 125 or 500 

mg/kg/day

Maternal NOAEL=20 mg/kg/day

Maternal LOAEL=125 mg/kg/day 

(decreased maternal body weight gain 

and food consumption, increased liverto-body weight ratios (at the highest 

dose), and excess salivation)

Developmental NOAEL=20 

mg/kg/day
Page 26 of 36

Table A.2.2. Subchronic, chronic, and Other Toxicology Profile for Tribenuron Methyl

Guide 

line

Study Title MRID Dose Levels Results

Developmental LOAEL=125 

mg/kg/day, based on decreased body 

weight)

At 500 mg/kg/day (HDT) there were 

increased resorption, fetal deaths, and 

incomplete ossifications.

870.3700b Developmental 

Toxicity, Rabbit

40245514 0, 5, 20, or 80 

mg/kg/day

Maternal NOAEL=20 mg/kg/day

Maternal LOAEL=80 mg/kg/day, 

based on decreased food consumption, 

increased abortions (GD 19-29))

Developmental NOAEL=20 

mg/kg/day

Developmental LOAEL=80 mg/kg/day

(HDT-10% decrease in body weight 

compared to controls, not statistically 

significant) Abortions were increased 

at 80 mg/kg/day. Teratogenicity was 

not observed.

870.3800 2-Generation 

Reproduction, Rat

40245515 0, 25, 250, and 1000 

ppm 

M:F 1.9/2.2, 19/21, or 

75/88 mg/kg/day

Parental NOAEL=25 ppm (2

mg/kg/day)

Parental LOAEL=250 ppm (21

mg/kg/day) -decreased body weight 

gain in F1a adult females

Reproductive NOAEL=25 ppm (2.5 

mg/kg/day)

Reproductive LOAEL=250 ppm (25 

mg/kg/day) - decreased body weight 

gain during lactation for F1b and 

F2b pups

Offspring NOAEL= 25 ppm (2.5 

mg/kg/day)

Offspring LOAEL= 250 ppm (25 

mg/kg/day) - decreased absolute 

splenic weights.

870.4100b Chronic Feeding, Dog 40245512 0, 25, 250, and 1500 

ppm 

M:F: 0,0, 0.79/0.90, 

8.16/8.18, or 

51.46/52.02 mg/kg/day.

NOAEL (M) = 25 ppm (0.79 

mg/kg/day)

NOAEL (F) = 250 ppm (8.16 

mg/kg/day)

LOAEL (M) = 250 ppm (8.18 

mg/kg/day)- elevated serum bilirubin, 

AST, and urinary volume, 

reduced body weight gain (20%).

LOAEL (F) = 1500 ppm (52.02 

mg/kg/day)-increased serum 

creatinine, bilirubin, AST, and 

globulin, decreased body weight gain 

of 18.2%

870.4200b Carcinogenicity, 

Mouse

40245513 0, 20, 200, or 1500 ppm 

M:F: 0/0, 2.5/3.1, 25/31 

and 197/247 mg/kg/day.

NOAEL =20 ppm (3 mg/kg/day) M

LOAEL = 200 ppm (30 mg/kg/day) -

bilateral seminiferous degeneration

and oligospermia. Although frank 

toxicity was not observed in the 
Page 27 of 36

Table A.2.2. Subchronic, chronic, and Other Toxicology Profile for Tribenuron Methyl

Guide 

line

Study Title MRID Dose Levels Results

females, HED peer review judged the 

dose levels to be adequate. There was 

no evidence of carcinogenicity.

870.4300 Chronic 

Feeding/Carcinogenicit

y, Rat

40245511 0, 25, 250 or 1250 ppm 

0/0, 0.95/1.2, 10/13 and 

55/76 mg/kg/day. 

NOAEL=25 ppm(0.95/1.2 mg/kg/day, 

M/F)

LOAEL=250 ppm (10/13 mg/kg/day, 

M/F) -decreased body weight gain in 

both sexes.

Statistically significant increase in 

mammary gland adenocarcinomas in 

female rats at 1250 ppm (76 

mg/kg/day, HDT)

870.4300 Supplement-Estrogenic 

Activity in Rats

41181901 0 and 390 mg/kg/day 

for 90 days

Weak estrogenic activity was observed 

in female rats. The technical and 7 

metabolites may be agonists for the 

estrogen receptor.

870.5100 Gene Mutation 

Bacterial Reverse 

Mutation Assay

00148641 Up to 500 μg/plate

without metabolic 

activation

Up to 2000 μg/plate 

with metabolic 

activation

Negative.

870.5300 Gene Mutation in vitro

Mammalian Cell 

(Chinese Hamster 

Ovary)

00149671 0.5 to 5.0 mM 

with/without metabolic 

activation

Negative.

870.5395 Cytogenetics, Mouse 

Micronucleus Bone 

Marrow

00148644 5000 mg/kg/day Negative.

870.5395 Cytogenetics, Rat 

Micronucleus Bone 

Marrow

00148642 50, 500, 5000 

mg/kg/day

Negative.

870.5550 Other Effects –

Unscheduled DNA Rat 

Hepatocyte

00148643 0 to 2500μM Negative.

870.6200a Acute Oral 

Neurotoxicity Study -

Rats

48732501 0, 100, 300, and 1000

mg/kg/day

NOAEL=300 mg/kg/day

LOAEL = 1000 mg/kg/day, based on 

body weight changes (BW loss in 

males, decreased BWG in females), 

reduced food consumption, and/or 

food efficiency, and transient effects 

on motor activity and rearing. 

870.6200b Subchronic Oral 

Neurotoxicity Study -

Rats

48737601 0, 50, 200, or 700 ppm 

mg/kg/day M:F= 0/0, 

2.8/3.2, 11.3/12.8, and 

40.1/46.6.

NOAEL= 200 ppm (equivalent to 

11.3/12.8 mg/kg/day,).

LOAEL=700 ppm (equivalent to 

40.1/46.6 mg/kg/day) based on 

decreased body weight and body 

weight gains, reduced food 

consumption, and food efficiency. 
Page 28 of 36

Table A.2.2. Subchronic, chronic, and Other Toxicology Profile for Tribenuron Methyl

Guide 

line

Study Title MRID Dose Levels Results

870.7485 Metabolism Study -

Rat

40245516 Single: low-20 

mg/kg/day; high-1700 

to 2000 mg/kg/day

Repeated: 100 ppm for 

21 days followed by 20 

mg/kg/day single dose.

Single oral dose readily absorbed, low 

dose (20 mg/kg) single and repeated 

dose 26-33 hours (half-life); single 

high dose (1700-2000 mg/kg) 51-54 

hours in males and 69-96 hours in 

females. Major excretion via urine (2-

4 x feces). Tissue levels increased 

with dose. No accumulation in any 

particular tissue. 

870.7600 Dermal Penetration -

Rat

48625901 0.03, 0.3 and 3.0 mg/12 

cm2 (male) and 0.3 

mg/12 cm2

(female)

Based on the anticipated duration of 

human worker exposure (8-10 hours a 

day), the DAF of 17.7% from the 0.03 

mg/12 cm2 dose level group (10 hours 

of exposure) is considered the most 

appropriate for risk assessment. 

870.7800 28-Day 

Immunotoxicity study 

in Rats

48641101 50, 150, 300, or 600 

ppm (equivalent to 0, 

3.8, 11, 23, and 44 

mg/kg bw/day, 

respectively)

NOAEL=300 ppm (equivalent to 23 

mg/kg bw/day); 

LOAEL=600 ppm (equivalent to 44 

mg/kg bw/day) based on lower body 

weight, body weight gains, and food 

consumption when compared to the 

control.

Under conditions of this study, the 

immunotoxicity NOAEL is 600 ppm 

(equivalent to 44 mg/kg bw/day, the 

highest dose tested); the LOAEL was 

not determined.
Page 29 of 36

Appendix B. Review of Human Research

This risk assessment relies in part on data from studies in which adult human subjects were 

intentionally exposed to a pesticide or other chemical. These data are subject to ethics review 

pursuant to 40 CFR 26, have received that review, and are compliant with applicable ethics 

requirements. For certain studies that review may have included review by the Human Studies 

Review Board. Descriptions of data sources as well as guidance on their use can be found at:

http://www.epa.gov/pesticides/science/handler-exposure-data.html and 

http://www.epa.gov/pesticides/science/post-app-exposure-data.html.
Page 30 of 36

Appendix C. Occupational Algorithms

Occupational Non-cancer Handler Algorithms

Potential daily exposures for occupational handlers are calculated using the following formulas:

E=UE * AR * A * 0.001 mg/ug

where:

E = exposure (mg ai/day),

UE = unit exposure (μg ai/lb ai),

AR = maximum application rate according to registered labels (lb ai/A), and

A = area treated or amount handled (e.g., A/day or gal/day).

The daily doses are calculated using the following formula:

ADD= 

E * AF

BW

where:

ADD = average daily dose absorbed in a given scenario (mg ai/kg/day),

E = exposure (mg ai/day),

AF = absorption factor (dermal or inhalation), and

BW = body weight (kg).

Margin of Exposure: Non-cancer risk estimates for each application handler scenario are 

calculated using a Margin of Exposure (MOE), which is a ratio of the toxicological endpoint to 

the daily dose of concern. The daily dermal and/or inhalation doses received by occupational 

handlers are compared to the appropriate POD (i.e., NOAEL) to assess the risk to occupational 

handlers for each exposure route. All MOE values are calculated using the following formula:

MOE= 

POD

ADD

where:

MOE = margin of exposure: value used by HED to represent risk estimates (unitless),

POD = point of departure (mg/kg/day), and

ADD = average daily dose absorbed in a given scenario (mg ai/kg/day).

Occupational Non-cancer Post-application Algorithms

Potential daily exposures for occupational post-application workers are calculated using the 

following formulas:

DFRt=AR * F* (1-D)t

* �4.54E8 ug

lb� * �2.47E-8

A

cm2�
Page 31 of 36

where:

DFRt = dislodgeable foliage residue on day "t" (μg/cm2

),

AR = application rate (lb ai/acre),

F = fraction of ai retained on foliage or 25% (unitless),

D = fraction of residue that dissipates daily or 10% (unitless), and

t = number of days after application day (days).

E=TC * DFR t* ET * 0.001 mg

ug

where:

E = exposure (mg ai/day),

TC = transfer coefficient (cm2/hr),

DFRt = dislodgeable foliar residue on day “t” (μg/cm2

), and

ET = exposure time (hours/day).

The daily doses are calculated using the following formula:

ADD= 

E * AF

BW

where:

ADD = average daily dose absorbed in a given scenario (mg ai/kg/day),

E = exposure (mg ai/day),

AF = absorption factor (dermal), and

BW = body weight (kg).

Margin of Exposure: Non-cancer risk estimates for each scenario are calculated using a Margin 

of Exposure (MOE), which is a ratio of the toxicological endpoint to the daily dose of concern. 

The daily dermal dose received by occupational post-application workers is compared to the 

appropriate POD (i.e., NOAEL) to assess the risk to occupational post-application workers. All 

MOE values are calculated using the following formula:

MOE= 

POD

ADD

where:

MOE = margin of exposure: value used by HED to represent risk estimates (unitless),

POD = point of departure (mg/kg/day), and

ADD = average daily dose absorbed in a given scenario (mg ai/kg/day).
Page 32 of 36

Appendix D. Dietary Exposure/Risk Modeling Input and Output

US EPA Ver. 3.16, 03-08-d

DEEM-FCID Chronic analysis for TRIBENURON METHYL

Residue file: Tribenuron methyl.R08

 Adjust. #2 NOT used

Analysis Date 07-30-2015 Residue file dated: 07-30-2015/10:22:46

Reference dose (RfD) = 0.008 mg/kg bw/day

----------------------------------------------------------------------------------

Food Crop Residue Adj.Factors

EPA Code Grp Food Name (ppm) #1 #2 

---------- ---- ------------------------------- ---------- ------ ------

1500025000 15 Barley, pearled barley 0.050000 1.000 1.000 

1500025001 15 Barley, pearled barley-babyfood 0.050000 1.000 1.000 

1500026000 15 Barley, flour 0.050000 1.000 1.000 

1500026001 15 Barley, flour-babyfood 0.050000 1.000 1.000 

1500027000 15 Barley, bran 0.050000 1.000 1.000 

1500120000 15 Corn, field, flour 0.010000 1.000 1.000 

1500120001 15 Corn, field, flour-babyfood 0.010000 1.000 1.000 

1500121000 15 Corn, field, meal 0.010000 1.000 1.000 

1500121001 15 Corn, field, meal-babyfood 0.010000 1.000 1.000 

1500122000 15 Corn, field, bran 0.010000 1.000 1.000 

1500123000 15 Corn, field, starch 0.010000 1.000 1.000 

1500123001 15 Corn, field, starch-babyfood 0.010000 1.000 1.000 

1500124000 15 Corn, field, syrup 0.010000 1.000 1.000 

1500124001 15 Corn, field, syrup-babyfood 0.010000 1.000 1.000 

1500125000 15 Corn, field, oil 0.010000 1.000 1.000 

1500125001 15 Corn, field, oil-babyfood 0.010000 1.000 1.000 

2003128000 20C Cottonseed, oil 0.020000 1.000 1.000 

2003128001 20C Cottonseed, oil-babyfood 0.020000 1.000 1.000 

2001163000 20A Flax seed, oil 0.020000 1.000 1.000 

1500231000 15 Oat, bran 0.050000 1.000 1.000 

1500232000 15 Oat, flour 0.050000 1.000 1.000 

1500232001 15 Oat, flour-babyfood 0.050000 1.000 1.000 

1500233000 15 Oat, groats/rolled oats 0.050000 1.000 1.000 

1500233001 15 Oat, groats/rolled oats-babyfood 0.050000 1.000 1.000 

2001319000 20A Rapeseed, oil 0.020000 1.000 1.000 

2001319001 20A Rapeseed, oil-babyfood 0.020000 1.000 1.000 

1500323000 15 Rice, white 0.050000 1.000 1.000 

1500323001 15 Rice, white-babyfood 0.050000 1.000 1.000 

1500324000 15 Rice, brown 0.050000 1.000 1.000 

1500324001 15 Rice, brown-babyfood 0.050000 1.000 1.000 

1500325000 15 Rice, flour 0.050000 1.000 1.000 

1500325001 15 Rice, flour-babyfood 0.050000 1.000 1.000 

1500326000 15 Rice, bran 0.050000 1.000 1.000 

1500326001 15 Rice, bran-babyfood 0.050000 1.000 1.000 

1500344000 15 Sorghum, grain 0.050000 1.000 1.000 

1500345000 15 Sorghum, syrup 0.050000 1.000 1.000 

0600347000 6 Soybean, seed 0.010000 1.000 1.000 

0603348000 6C Soybean, flour 0.010000 1.000 1.000 

0603348001 6C Soybean, flour-babyfood 0.010000 1.000 1.000 

0600349000 6 Soybean, soy milk 0.010000 1.000 1.000 

0600349001 6 Soybean, soy milk-babyfood or in 0.010000 1.000 1.000 

0600350000 6 Soybean, oil 0.010000 1.000 1.000 

0600350001 6 Soybean, oil-babyfood 0.010000 1.000 1.000 

1500381000 15 Triticale, flour 0.050000 1.000 1.000 

1500381001 15 Triticale, flour-babyfood 0.050000 1.000 1.000 

8601000000 86A Water, direct, all sources 0.035000 1.000 0.657 

8602000000 86B Water, indirect, all sources 0.035000 1.000 0.657 

1500401000 15 Wheat, grain 0.050000 1.000 1.000 

1500401001 15 Wheat, grain-babyfood 0.050000 1.000 1.000 

1500402000 15 Wheat, flour 0.050000 1.000 1.000 

1500402001 15 Wheat, flour-babyfood 0.050000 1.000 1.000 

1500403000 15 Wheat, germ 0.050000 1.000 1.000 

1500404000 15 Wheat, bran 0.050000 1.000 1.000 
Page 33 of 36

US EPA Ver. 3.18, 03-08-d

DEEM-FCID ACUTE Analysis for TRIBENURON METHYL NHANES 2003-2008 2-Day

Residue file: Tribenuron methyl.R08 Adjustment factor #2 NOT used.

Analysis Date: 07-30-2015/10:26:07 Residue file dated: 07-30-2015/10:22:46

RAC/FF intake summed over 24 hours

Run Comment: ""

===============================================================================

Summary calculations--per capita:

 95th Percentile 99th Percentile 99.9th Percentile

Exposure % aRfD Exposure % aRfD Exposure % aRfD 

 ---------- -------- ---------- -------- ---------- --------

Total US Population:

 0.002097 0.07 0.003365 0.11 0.006232 0.21 

All Infants:

 0.006201 0.21 0.008184 0.27 0.011901 0.40 

Children 1-2:

 0.003313 0.11 0.005022 0.17 0.011356 0.38 

Children 3-5:

 0.002719 0.09 0.003970 0.13 0.006338 0.21 

Children 6-12:

 0.002126 0.07 0.003248 0.11 0.004864 0.16 

Youth 13-19:

 0.001736 0.06 0.002771 0.09 0.004219 0.14 

Adults 20-49:

 0.001993 0.07 0.002879 0.10 0.004155 0.14 

Adults 50-99:

 0.001773 0.06 0.002696 0.09 0.004025 0.13 

Female 13-49:

 0.002033 0.07 0.002886 0.10 0.004016 0.13 

US EPA Ver. 3.16, 03-08-d

DEEM-FCID Chronic analysis for TRIBENURON METHYL NHANES 2003-2008 2-day

Residue file name: Tribenuron methyl.R08

 Adjustment factor #2 used.

Analysis Date 07-30-2015/10:23:43 Residue file dated: 07-30-2015/10:22:46

Reference dose (RfD, Chronic) = .008 mg/kg bw/day

===============================================================================

 Total exposure by population subgroup

-------------------------------------------------------------------------------

 Total Exposure

 -----------------------------------

 Population mg/kg Percent of 

 Subgroup body wt/day Rfd 

-------------------------------------- ------------- ----------------

Total US Population 0.000607 7.6%

Hispanic 0.000594 7.4%

Non-Hisp-White 0.000618 7.7%

Non-Hisp-Black 0.000515 6.4%

Non-Hisp-Other 0.000708 8.9%

Nursing Infants 0.000534 6.7%

Non-Nursing Infants 0.001797 22.5%

Female 13+ PREG 0.000556 7.0%

Children 1-6 0.000911 11.4%

Children 7-12 0.000594 7.4%

Male 13-19 0.000466 5.8%

Female 13-19/NP 0.000483 6.0%

Male 20+ 0.000560 7.0%

Female 20+/NP 0.000590 7.4%

Seniors 55+ 0.000544 6.8%

All Infants 0.001407 17.6%

Female 13-50 0.000575 7.2%

Children 1-2 0.001003 12.5%

Children 3-5 0.000874 10.9%

Children 6-12 0.000627 7.8%

Youth 13-19 0.000475 5.9%

Adults 20-49 0.000589 7.4%

Adults 50-99 0.000557 7.0%

Female 13-49 0.000575 7.2%

-------------------------------------------------------------------------------
Page 34 of 36

Appendix E. Nomenclature and Physical/Chemical Properties

TABLE E.1 Tribenuron methyl Nomenclature

Chemical structure

Common name Tribenuron methyl

Molecular formula C15H17N5O6S

Molecular weight 395.4

CAS name Methyl-2-[[[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)methylamino]

carbonyl]amino]sulfonyl]benzoate

IUPAC name Methyl-2-[4-methoxy-6-methyl-1,3,5-triazin-2-yl(methyl)carbamoylsulfamoyl]benzoate 

CAS registry number 101200-48-0

TABLE E.2 Physicochemical Properties of the Technical Grade Tribenuron Methyl 

Parameter Value Reference

Melting point/range (oC) 141 EPA Pesticide Fact Sheet 

Number 219: Tribenuron methyl

pH 4.27

Density (g/cm3) 1.54

Water solubility (g/L at 20oC) pH 5 0.049

pH 7 2.04

pH 9 18.3

Solvent solubility (g/L at 25oC) Acetone - 0.044

Acetonitrile - 0.054

Carbon tetrachloride - 0.003

Ethyl acetate - 0.0175

Hexane - <0.001 

Methanol - 0.0034

Vapor pressure (25oC) 5.3 x 10-8 Pa (4 x 10-10 mm Hg)

Dissociation constant (pKa) 4.7

Octanol/water partition coefficient

(Log [KOW])

pH 7 0.3
Page 35 of 36

Appendix F. Spray Drift Detailed Description

Off-target movement of pesticides can occur via many types of pathways and it is governed by a 

variety of factors. Sprays that are released and do not deposit in the application area end up offtarget and can lead to exposures to those the chemical may directly contact. Sprays can also 

deposit on surfaces where individuals come into contact with residues on these surfaces, leading

to indirect exposures (e.g., children playing on lawns where residues have deposited next to 

treated fields).

The approach to be used for quantitatively incorporating spray drift into risk assessment is based 

on a premise of compliant applications which, by definition, should not result in direct exposures 

to individuals because of existing label language and other regulatory requirements intended to 

prevent them12. [Direct exposures would include inhalation of the spray plume or being sprayed 

directly.] Rather, the exposures addressed here are thought to occur indirectly through contact 

with impacted areas, such as residential lawns, when compliant applications are conducted. 

Given this premise, exposures for children (1 to 2 years old) and adults who have contact with 

turf where residues are assumed to have deposited via spray drift thus resulting in an indirect 

exposure are the focus of this analysis analogous to how exposures to turf products are 

considered in risk assessment. 

In order to evaluate the drift potential and associated risks, an approach based on drift modeling 

coupled with techniques used to evaluate residential uses of pesticides was utilized. Essentially, a 

residential turf assessment based on exposure to deposited residues has been completed to 

address drift from the agricultural applications of tribenuron. In the spray drift scenario, the 

deposited residue value was determined based on the amount of spray drift that may occur at 

varying distances from the edge of the treated field using the AgDrift (v2.1.1) model and the 

Residential Exposure Assessment Standard Operating Procedures Addenda 1: Consideration of 

Spray Drift Policy. Once the deposited residue values were determined, the remainder of the

spray drift assessment was based on the algorithms and input values specified in the 2012 

Standard Operating Procedures for Residential Risk Assessment (SOPs). 

A screening approach was developed based on the use of the AgDrift model in situations where 

specific label guidance that defines application parameters is not available1314. AgDrift is 

appropriate for use only when applications are made by aircraft, airblast orchard sprayers, and 

groundboom sprayers. When AgDrift was developed, a series of screening values (i.e., the Tier 1 

option) were incorporated into the model and represent each equipment type and use under 

varied conditions. The screening options specifically recommended in this methodology were 

selected because they are plausible and represent a reasonable upper bound level of drift for 

common application methods in agriculture. These screening options are consistent with how 

spray drift is considered in a number of ecological risk assessments and in the process used to 

develop drinking water concentrations used for risk assessment. In all cases, each scenario is to 

be evaluated unless it is not plausible based on the anticipated use pattern (e.g., herbicides are 

 12 This approach is consistent with the requirements of the EPA’s Worker Protection Standard. 13 http://www.agdrift.com/ 14 Note that for many cases the scenarios outlined in the screening approach represent actual use practice so risk 

assessors should be aware and characterize these appropriately.
Page 36 of 36

not typically applied to tree canopies) or specific label prohibitions (e.g., aerial applications are 

not allowed). Section 6.1.1 provides the screening level drift related risk estimates. 

In many cases, risks are of concern when the screening level estimates for spray drift are used as 

the basis for the analysis. In order to account for this issue and to provide additional risk 

management options additional spray drift deposition fractions were also considered. These drift 

estimates represent plausible options for pesticide labels.