3

TRIBENURON METHYL FINAL WORK PLAN

Introduction

This is the Environmental Protection Agency’s (EPA or the Agency) Final Work Plan (FWP)

for the registration review of tribenuron methyl. The FWP includes the expected registration

review timeline. The FWP also addresses public comments received concerning the 

Preliminary Work Plan (PWP) in the Summary Document, which was posted in the tribenuron 

methyl registration review docket (EPA-HQ-OPP-2010-0626), and any other comments 

concerning the initial docket postings. The Summary Document provided information on what

EPA knows about this pesticide and what additional risk analyses and data or information the

Agency believes are needed to make a registration review decision. 

The Agency’s implementation of the registration review program requires review of each

registered pesticide every 15 years to determine whether it continues to meet the Federal

Insecticide, Fungicide, and Rodenticide Act (FIFRA) standard for registration. Changes in

science, public policy, and pesticide use practices will occur over time. The registration review

program is intended to make sure that, as the ability to assess risk evolves and as policies and

practices change, all registered pesticides continue to meet that statutory standard. The public

phase of registration review begins when the initial docket is opened for each case. 

Information on this program is provided at http://www.epa.gov/oppsrrd1/registration_review/.

Tribenuron methyl is a sulfonylurea herbicide registered for use on cereal grains (barley, field 

corn, oats, rice, sorghum, and wheat), oilseed crops (canola, flax, and sunflower), soybeans, 

and cotton to control broadleaf weeds. There is also a tolerance with regional registrations for 

grass forage, fodder, and hay (except Bermuda grass forage and hay). There are no registered 

residential uses of tribenuron methyl. Tribenuron methyl was first registered in 1989; 

therefore, it was not subject to the reregistration requirements of FIFRA. In 2004, in 

conjunction with the establishment of new tribenuron methyl tolerances (69 FR 56711-56718), 

EPA reassessed the existing tribenuron methyl tolerances as required by the Food Quality 

Protection Act (FQPA).

Updates Since the Preliminary Work Plan was Issued

Two plant studies (GLNs 850.4150 and 850.5400) were erroneously listed as data requirements 

for the parent tribenuron methyl in the “Summary of Data Gaps – Tribenuron Methyl” table in 

the March 2011 Tribenuron Methyl PWP. While Guideline 850.4150 remains a data gap for 

the tribenuron methyl degradates triazine amine, sulfonamide, and saccharin, it is not required 

for the parent tribenuron methyl. The table listing the data gaps for tribenuron methyl has been 

corrected in the “Summary of Data Gaps – Tribenuron Methyl” section of the FWP.

To summarize, the following ecological data requirements are being removed from the table of

data requirements for tribenuron methyl:
4

• 850.4150 Vegetative Vigor, Tier II (parent tribenuron methyl only)

• 850.5400 Algal toxicity, Tier II

All other environmental fate and ecological effects data requirements remain as listed in the

tribenuron methyl PWP.

Comments Received on the Preliminary Work Plan

The tribenuron methyl registration review docket was open for a 60-day comment period 

beginning on March 30, 2011. During the public comment period, the Agency received 

comments from E.I. DuPont Nemours & Co., Inc. (DuPont) and the Federal Endangered 

Species Task Force (FESTF). The comments received did not change the planned risk 

assessment, data needs, or the timeline detailed in the tribenuron methyl PWP. EPA also 

solicited comments, through the PWP, on three specific topics: environmental justice, water 

body impairment, and trade irritants. No comments or information were received during the 

comment period on these topics. 

A general overview of the comments and the Agency’s responses to the comments are 

presented in the “Summary of Comments and Agency Responses” section of this document. 

The complete Agency responses can be found in EFED Response to Public Comments for

Tribenuron methyl Preliminary Work Plan (PWP) located in the tribenuron methyl registration 

review docket (EPA-HQ-OPP-2010-0626). 

Risk Assessment and Data Needs

The Agency will require data and will conduct a comprehensive ecological risk assessment, 

including an endangered species assessment, and will require data and conduct human exposure 

risk assessments for all uses of tribenuron methyl. Below is a summary of the issues relevant to 

the registration review of tribenuron methyl.

Ecological Risk:

• The most recent ecological risk assessment for tribenuron methyl was completed in 

August 2009 for the registration of tribenuron methyl-containing pesticides on 

herbicide-tolerant field corn and soybean.

• An ecological risk assessment of all registered uses of tribenuron methyl will be 

conducted during registration review. The new assessment will incorporate the most 

up-to-date modeling methodologies, updated toxicological endpoints, and data 

submitted under the registration review data call-in.

• The Agency has not conducted a risk assessment that supports a complete endangered 

species determination for tribenuron methyl. The ecological risk assessment planned 

during registration review will allow the Agency to determine whether tribenuron 
5

methyl’s use has “no effect” or “may affect” federally listed threatened or endangered 

species (listed species) or their designated critical habitats. When an assessment 

concludes that a pesticide’s use “may affect” a listed species or its designated critical 

habitat, the Agency will consult with the U.S. Fish and Wildlife Service and/or National 

Marine Fisheries Service (the Services), as appropriate.

• The Agency will require the following data for parent tribenuron methyl in order to 

conduct the planned ecological risk assessment, including an endangered species 

assessment:

• GDLN 835.6100 – Environmental Chemistry Analytical Methods and 

 Independent Laboratory Validation (ILV) for Soil 

• GDLN 835.6200 – Aquatic Field Dissipation (including Environmental 

 Chemistry Methods and ILV for Soil and Water)

• GDLN 850.1025 – Oyster Acute Toxicity Test (shell deposition)

• GDLN 850.1300 – Invertebrate Life-cycle Toxicity Test (freshwater)

• GDLN 850.1400 – Fish Early-Life Stage Toxicity (estuarine/marine)

• GDLN 850.2100 – Avian Acute Oral Toxicity Test (passerine)

• GDLN 850.4100 – Seedling Emergence (Tier II)

• GDLN 850.4400 – Aquatic Plant Toxicity Test using Lemna spp. (Tier II)

• NON-GDLN – Special Study for Non-Target Plant Reproductive Toxicity

• The Agency will require the following data for the major tribenuron methyl degradates: 

o-denethyl-triazine amine; triazine amine; sulfonamide; and saccharin, in order to 

conduct a complete ecological risk assessment, including an endangered species 

assessment:

• GDLN 850.1300 – Invertebrate Life-cycle Toxicity Test (freshwater; 

 excluding o-denethyl triazine amine)

• GDLN 850.4100 – Seedling Emergence (Tier II)

• GDLN 850.4150 – Vegetative Vigor (Tier II, excluding 

 o-denethyl triazine amine)

• GDLN 850.4400 – Aquatic Plant Toxicity Test using Lemna gibba (Tier II)

• Please refer to Registration Review– Preliminary Problem Formulation for the 

Environmental Fate, Ecological Risk, and Endangered Species and Drinking Water 

Assessments for Tribenuron methyl, dated March 15, 2011; and the EFED Response to 

Public Comments for Tribenuron methyl Preliminary Work Plan (PWP), dated July 29, 

2011, located in the docket (EPA-HQ-OPP-2010-0626), for a detailed discussion of the 

risk assessment and data needs.
6

Human Health Risk:

• The most recent human health risk assessment, including a drinking water assessment, 

for tribenuron methyl was completed in September 2009 for the registration of use on 

herbicide-tolerant field corn and soybean to control broadleaf weeds.

• The Agency will require the following data for tribenuron methyl in order to conduct a 

complete human health risk assessment:

o GDLN 870.3200 – Dermal Toxicity

o GDLN 870.3465 – 90-Day Inhalation Toxicity

o GDLN 870.6200 – Acute and Subchronic Neurotoxicity Battery 

o GDLN 870.7800 – Immunotoxicity

• After the required toxicology studies are submitted and reviewed, EPA will re-evaluate 

endpoints and safety/uncertainty factors for tribenuron methyl. 

• During registration review, the Agency will update the dietary risk assessment with 

revised estimated drinking water concentrations, changes in toxicological endpoints,

and incorporate any degradates that are determined to be of human toxicological 

concern.

• There are no residential uses of tribenuron methyl. However, residential bystander 

exposures might occur as a result of aerial application and off-site transport (e.g., spray 

drift or volatilization). The Agency will consider the need for a bystander inhalation 

risk assessment for tribenuron methyl during registration review.

• The Agency will revise the aggregate assessment to include changes in dietary exposure 

estimates and any residential bystander exposure estimates, if applicable.

• The Agency will conduct new occupational handler and post-application assessments as 

necessary, based on updated doses, endpoints, and procedures for both dermal and 

inhalation endpoints.

• The Agency will modify tolerances as needed, and work to harmonize tolerance/MRLs 

where possible in key export markets during registration review.

• For more information, please refer to Tribenuron methyl: Human Health Assessment 

Scoping Document in Support of Registration Review, March 2, 2011, located in the 

docket (EPA-HQ-OPP-2010-0626). 
7

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 tribenuron methyl registration decision, 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). 

Endocrine Disruptor Screening Program

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 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. Tribenuron 

methyl is not among the group of 58 pesticide active ingredients on the initial list to be 

screened under the EDSP. Accordingly, as part of registration review, EPA will issue future 

EDSP orders/data call-ins, requiring the submission of EDSP screening assays for tribenuron 

methyl. For further information on the status of the EDSP, the policies and procedures, the list 

of 67 chemicals, future lists, the test guidelines and the Tier 1 screening battery, please visit our 

website: http://www.epa.gov/endo/.
8

Timeline:

EPA has created the following estimated timeline for the completion of the tribenuron methyl

registration review.

Registration Review for Tribenuron methyl – Projected Registration Review Timeline

Activities Estimated Date

Opening the Docket

Open Docket and Public Comment Period 2011 – March

Close Public Comment 2011 – May

Case Development

Final Work Plan 2011 – August

Issue DCI 2012 – April – June

Data Submission 2014 – April – June

Open Public Comment Period for Draft Risk Assessments 2015 – Oct. – Dec.

Close Public Comment Period 2016 – Jan. – March

Registration Review Decision

Open Public Comment Period for Proposed Registration Review 

Decision 

2016 – April – June

Close Public Comment Period 2016 – July – Sept.

Registration Review Decision and Begin Post-Decision Follow-up 2017

Total (years) 6

Summary of Comments and Agency Responses

The tribenuron methyl registration review docket was open for a 60-day comment period 

beginning on March 30, 2011. During the comment period, comments were submitted by E.I. 

DuPont Nemours & Co., Inc. and the Federal Endangered Species Task Force. The comments 

received do not change the risk assessment, data needs, or the timeline detailed in the 

tribenuron methyl PWP. A general summary of these comments and the Agency’s response to 

comments is provided below. 

For a detailed description of the comments received and the Agency’s response to comments

please refer to EFED Response to Public Comments for Tribenuron methyl Preliminary Work 

Plan (PWP), dated July 29, 2011, which is located in the tribenuron methyl docket (EPA-HQOPP-2010-0626).

E.I. DuPont Nemours & Co., Inc. (DuPont)

Comment: DuPont questioned the need for a non-guideline terrestrial plant study for tribenuron 

methyl to evaluate the effects on seed production and viability at multiple stages of maturity. 

The registrant cited a review of existing data in the open literature and two studies not yet 

submitted to the Agency to support its view that the data currently provided by guideline 
9

terrestrial non-target plant studies evaluating effects on seedling plants is protective of potential 

reproductive effects. 

Agency Response: The Agency has concerns that sulfonylurea (SU) herbicides may affect plant 

reproduction at rates lower than those that cause phytotoxic effects to vegetative vigor. Due to 

these concerns, the Agency is requesting plant reproduction studies for all SUs during 

registration review. While DuPont contends that recently conducted greenhouse and field 

studies for chlorsulfuron demonstrate that guideline vegetative vigor studies (850.4150) are 

protective of reproduction endpoints, these studies have not been submitted for Agency review 

at this time. The Agency will evaluate these studies upon submission and determine the 

applicability of the data to other SU herbicides and test species. Until such time, the plant 

reproduction study for tribenuron methyl is still needed. 

Comment: DuPont also questioned the need for ecotoxicological studies on tribenuron methyl 

degradates, citing numerous studies which were conducted for its European Union (EU) 

registration. DuPont further stated that these studies indicate that the metabolites are at least 

2000 to 49000 times less toxic than the parent tribenuron methyl. 

Agency Response: The Agency will consider the aquatic toxicity data conducted for the EU that 

DuPont recently submitted to the Agency. If the submitted studies are found to be acceptable

and the metabolite data show a decrease in phytotoxicity to aquatic plants relative to the parent 

compound, then the toxicity data for terrestrial plants on those degradates would not be 

necessary. However, until the reviews are completed, the data gaps noted in the PWP remain.

Federal Endangered Species Task Force (FESTF)

Comment: In response to the PWP, specifically to the need for additional information to 

complete an assessment on federally-listed threatened and endangered species that may be 

exposed to tribenuron methyl, FESTF stated that its data on endangered species proximity 

contained in the FESTF Information Management System (FESTF IMS) submissions (2004,

05, 07) to the Agency “fulfill the data requirements... and provide the best available data 

necessary for the proximity analysis of tribenuron methyl use and listed species locations.” 

FESTF stated that the tribenuron methyl technical registrants DuPont, Cheminova A/S, Gowan 

Company, and Nufarm Limited are current members of FESTF and, as such, are entitled to the 

FESTF data on federally-listed threatened and endangered species. The technical registrants 

Arysta Lifescience North America and Rotam Limited are not currently eligible to rely on 

FESTF data. 

Agency Response: The Agency thanks FESTF for its comment and will consider this 

information at the time the risk assessments for tribenuron methyl are conducted.
10

Next Steps

The Agency will require several ecological effects and human health studies through a data

call-in, which is expected to be issued in mid-2012. This new information will be used to 

conduct risk assessments for tribenuron methyl uses. 
Summary of Data Gaps – Tribenuron methyl

The table below summarizes all data needs for tribenuron methyl in the Registration Review– Preliminary 

Problem Formulation for the Environmental Fate, Ecological Risk, and Endangered Species and 

Drinking Water Assessments for Tribenuron methyl, dated March 15, 2011, and the Tribenuron methyl: 

Human Health Assessment Scoping Document in Support of Registration Review, dated March 2, 2011.

Guideline 

Number Data Requirement Test Material Study Duration

835.6100 Environmental Chemistry Methods and ILV for Soil TEP 24

835.6200 Aquatic Field Dissipation (including Environmental 

Chemistry Methods and ILV for Soil and Water) TEP 24

850.1025 Oyster Acute Toxicity Test (shell deposition) TGAI 12

850.1300 Invertebrate Life-Cycle Toxicity Test (freshwater)

TGAI, 

(parent & 

degradates)1

12

850.1400 Fish Early-Life Stage Toxicity (saltwater) TGAI 12

850.2100 Avian Acute Oral Toxicity (passerine)2 TGAI 12

850.4100 Seedling Emergence, Tier II 

TEP, 

(parent & 

degradates)3

12

850.4150 Vegetative Vigor, Tier II TEP, 

(degradates)4 12

850.4400 Aquatic Plant Toxicity Test using Lemna spp. Tier II 

TEP, 

(parent & 

degradates)

12 3

870.3200 21/28-Day Dermal Toxicity TGAI 24

870.3465 90-Day Inhalation Toxicity5 TGAI 24

870.6200 Neurotoxicity Screening Battery (Acute and Subchronic) TGAI 24

870.7800 Immunotoxicity TGAI 12

NON-GDLN Special Study for Non-target Plant Reproductive Toxicity2 TEP 24

 1 The DCI will require this study for the parent tribenuron and the major degradates, triazine amine, saccharin, and sulfonamide. 2 The DCI will require that a protocol be submitted for review and approval by the Agency prior to initiation of this study. 3 The DCI will require this study for the parent tribenuron methyl and the major degradates, o-demethyl-triazine amine, triazine amine, 

saccharin, and sulfonamide.

4 The DCI will require this study for the major degradates, triazine amine, saccharin, and sulfonamide. 5 Based on expected duration of exposure, the DCI is expected to provide that registrants may conduct a 28-Day inhalation toxicity study in 

lieu of a 90-day study.