INTRODUCTION

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

the registration review of oxadiazon. This work plan addresses public comments received 

concerning the Preliminary Work Plan (PWP), which was posted in the oxadiazon registration 

review docket (EPA-HQ-OPP-2014-0782). Oxadiazon is a selective herbicide that is registered 

for use as pre- and early post-emergence treatments for the control of many annual broadleaf and 

grass weeds. It was first registered in the U.S. in 1978. Today, major use sites of oxadiazon are 

established or newly established bermudagrass, perennial ryegrass, fescue turf, and various 

ornamentals including landscape ornamental beds. There are no registered food or feed uses for 

oxadiazon. 

The Agency is implementing the registration review program pursuant to Section 3(g) of the 

Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA), and will review each registered 

pesticide every 15 years to determine whether it continues to meet the FIFRA standard for 

registration. Changes in science, public policy, and pesticide use practices 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 the statutory standard. 

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

Information on this program is provided on the Agency’s website.

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The FWP begins with any updates since the PWP was issued. Next is a summary of substantive

comments received during the public comment period for the PWP concerning anticipated data 

needs, expected risk assessments, or the estimated timeline identified in the PWP, and a 

summary of the Agency’s responses to those comments. This section is followed by registration 

review planned data needs, risk assessments expected to be conducted, and the projected

registration review timeline for oxadiazon. Lastly, there is a discussion of next steps.

UPDATES SINCE THE PWP WAS ISSUED

In the PWP, the Agency identified Guideline Number (GLN) 875.2100, which includes 

dislodgeable foliar residue (DFR) and turf transferable residue (TTR) studies, as an anticipated 

data requirement for the registration review of oxadiazon. Since the PWP, the Agency received 

comments from Bayer Environmental Sciences (Bayer) which provided information about 

existing TTR data for liquid formulations of oxadiazon as well as estimates of post application 

exposure for granular formulations using the default transfer coefficients specified in the 

Agency’s 2012 Residential SOP. As a result, the Agency has determined that a new TTR study is 

not needed. Therefore, in this FWP, the TTR portion of GLN 875.2100 is no longer listed as a 

data need. However, the DFR portion of GLN 875.2100 is still required.

The following two data requirements from GDCI-109001-24733 are no longer listed as

outstanding: seedling emergence (GLN 850.4100) and vegetative vigor (GLN 850.4150). EPA 

has received acceptable data to fulfill these data requirements.

1 http://www.epa.gov/oppsrrd1/registration_review/

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In addition, the Agency has added a honey bee toxicity of residues on foliage study (GLN 

850.3030) to the list of data needs for the registration review of oxadiazon, and has also revised 

the study timeframe for the full-field testing for pollinators (GLN 850.3040) from 36 months to 

24 months, based on the most up-to-date pollinator implementation guidance.

Finally, as noted in the PWP, the Agency has revisited the need for an aggregate risk assessment 

during the registration review of oxadiazon. The table of planned risk assessments in the FWP 

now indicates that EPA plans to conduct an aggregate assessment that will consider the 

combined exposure from drinking water and residential sources.

SUMMARY OF COMMENTS AND AGENCY RESPONSES

During the 60-day public comment period on the oxadiazon Preliminary Work Plan, which 

opened on December 19, 2014 and closed on February 17, 2015, the Agency received public 

comments from three stakeholders. Comments were submitted by the Center for Biological 

Diversity (CBD), FIFRA Endangered Species Task Force (FESTF), and Bayer Environmental 

Science (Bayer). The comments do not address the timeline described in the PWP, but they do 

address the planned human health risk assessments and ecological and human health data 

requirements. In the PWP, EPA also solicited comments on the specific topics of environmental 

justice, water quality concerns, and trade irritants, but no comments or information were received 

on those issues.

This section does not capture every comment made about the PWP nor all of the Agency’s 

responses. Summarized below are public comments that resulted in changes to the anticipated

registration review data needs, risk assessments, or are of a broader regulatory nature. Public

comments in their entirety are located in the docket, EPA-HQ-OPP-2014-0782. Summarized 

public comments and Agency responses related to the anticipated ecological data needs are in the 

EFED memo titled EPA Response to Comments Related to the “Oxadiazon Preliminary Work 

Plan: Registration Review” while those relevant to the anticipated human health risk assessment 

and data needs are in the HED memo titled Oxadiazon. HED’s Response to Public Comments

Received on the Preliminary Work Plan for Registration Review. 

Comments submitted by CBD in EPA-HQ-OPP-2014-0782-0009.

1. Comment: The Center for Biological Diversity’s (CBD) comments focus on the EPA’s duty 

to consult with the U.S. Fish and Wildlife Service and the National Marine Fisheries Service 

(the Services) on the registration review of oxadiazon in accordance with the Endangered 

Species Act (ESA). The CBD comments mention various aspects of the risk assessment 

process, including use of the best available data to develop endangered species risk 

assessments, and evaluation of effects on endangered and threatened species and their 

designated critical habitat. CBD also expresses concern regarding the rigor of the Agency’s 

preliminary determinations regarding the effects of oxadiazon on endangered and threatened 

(listed) species and their designated critical habitat for the oxadiazon registration review. 

Response: EPA has reviewed the comments from CBD on the registration review docket 

opening for oxadiazon and plans to address many of the concerns raised by CBD as part of

the implementation plan for assessing the risks of pesticides to listed species based on the 

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recommendations of the April 2013 National Academy of Sciences (NAS) report. EPA will 

address concerns specific to oxadiazon in connection with the development of its final 

registration review decision for oxadiazon.

In November 2013, the EPA, along with the Services and the USDA, released a summary of 

their joint Interim Approaches for assessing risks to endangered and threatened (listed) 

species from pesticides. The Interim Approaches were developed jointly by the agencies in 

response to the National Academy of Sciences’ (NAS) recommendations and reflect a 

common approach to risk assessment shared by the agencies as a way of addressing scientific 

differences between the EPA and the Services. The NAS report outlines recommendations on 

specific scientific and technical issues related to the development of pesticide risk 

assessments that EPA and the Services must conduct in connection with their obligations 

under the ESA and FIFRA.

The joint Interim Approaches were released prior to a stakeholder workshop held on 

November 15, 2013. In addition, the EPA presented the joint Interim Approaches at the 

December 2013 Pesticide Program Dialogue Committee (PPDC) and State-FIFRA Issues 

Research and Evaluation Group (SFIREG) meetings. The agencies also held stakeholder 

workshops in April 2014 and October 2014, allowing additional opportunities for 

stakeholders to comment on the Interim Approaches. Additional workshops are planned to 

enhance stakeholder involvement. As part of a phased, iterative process for developing the 

Interim Approaches, the agencies will also consider public comments on the Interim 

Approaches in connection with the development of upcoming Registration Review 

decisions. The details of the joint Interim Approaches are contained in the white paper

“Interim Approaches for National-Level Pesticide Endangered Species Act Assessments 

Based on the Recommendations of the National Academy of Sciences April 2013 Report,” 

dated November 1, 2013.

Given that the agencies are continuing to develop and work toward implementation of the 

Interim Approaches to assess the potential risks of pesticides to listed species and their 

designated critical habitat, the ecological problem formulation supporting this Final Work 

Plan for oxadiazon does not describe the specific ESA analysis, including effects 

determinations for specific listed species or designated critical habitat, to be conducted 

during registration review. In the ecological problem formulation document for oxadiazon, 

EPA described the screening-level risk assessment to determine the potential effects of 

oxadiazon on all taxa of non-target wildlife and plants, which will assume that listed species 

and their designated critical habitats may be present in the vicinity of the application of 

oxadiazon. This screening-level assessment will allow EPA to focus its future evaluations on 

the types of species where the potential for effects exists once the scientific methods being 

developed by the agencies have been fully vetted. While the agencies continue to develop a 

common method for ESA analysis, the planned screening-level risk assessment for the 

registration review of oxadiazon will describe the level of ESA analysis completed for this 

particular registration review case. Once the agencies have fully developed and implemented 

the scientific methods necessary to complete risk assessments for endangered and threatened 

(listed) species and their designated critical habitats, these methods will be applied to 

subsequent analyses for oxadiazon as part of completing this registration review. 

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Comments submitted by FESTF in EPA-HQ-OPP-2014-0782-0010.

2. Comment: “The technical registrants, as identified on the fact sheet included in the 

Registration Review work plan, are Bayer Environmental Science, which is a subsidiary of 

Bayer CropScience and Nufarm Limited, which is a subsidiary of Nufarm Americas, Inc., 

which are FESTF members and are entitled to rely on FESTF data.”

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

during registration review.

Comments submitted by Bayer in EPA-HQ-OPP-2014-0782-0011.

3. Comment: Bayer submitted comments regarding the anticipated HED data requirements for 

registration review and submitted information on the intended use patterns and application 

parameters of oxadiazon.

Response: For a detailed response to these comments, please refer to the HED memo titled 

Oxadiazon. HED’s Response to Public Comments Received on the Preliminary Work Plan 

for Registration Review. Note, as a result of Bayer’s comments, EPA has changed one of the 

anticipated HED data requirements. In the PWP, the Agency identified GLN 875.2100, 

which includes dislodgeable foliar residue (DFR) and turf transferable residue (TTR) studies, 

as an anticipated data requirement for the registration review of oxadiazon. As detailed in the 

section of this document “Updates Since the PWP was Issued,” the Agency received 

comments from Bayer which resulted in the Agency revisiting the need for new TTR data.

The Agency agrees with Bayer that the TTR portion of GLN 875.2100 is no longer needed; 

however, the DFR portion of GLN 875.2100 is still required.

4. Comment: Bayer submitted comments regarding the anticipated EFED data requirements 

for registration review as well as information regarding oxadiazon degradates, use patterns, 

and application parameters relevant to the planned ecological risk assessments.

Response: For a detailed response to these comments, please refer to the EFED memo titled 

EPA Response to Comments Related to the “Oxadiazon Preliminary Work Plan: Registration 

Review.” Note, in the FWP, the following two data requirements from GDCI-109001-24733 

are no longer listed as outstanding: seedling emergence (GLN 850.4100) and vegetative 

vigor (GLN 850.4150). Previously submitted data has been reviewed and found Acceptable 

by the EPA. 

PLANNED DATA NEEDS

Table 1 below summarizes the planned data needs for oxadiazon based on the EFED 

Registration Review Problem Formulation for Oxadiazon, the Oxadiazon. Human Health 

Scoping Document in Support of Registration Review, the EFED memo titled EPA Response to 

Comments Related to the “Oxadiazon Preliminary Work Plan: Registration Review” and the

HED memo titled Oxadiazon. HED’s Response to Public Comments Received on the 

Preliminary Work Plan for Registration Review. The table has been updated since the PWP to 

reflect public comments which resulted in changes to the data needs. 

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Table 1: Planned Data Needs for the Oxadiazon Registration Review

Guideline 

Number2 Study Title2

Test Material

Estimated 

Timeframe

(Months from 

receipt of DCI)

or Status

835.4100 Aerobic soil metabolism TGAI 24

850.2100 Avian oral toxicity (passerine species) TGAI 12

850.4550 Cyanobacteria toxicity TGAI 12

850.6100 Terrestrial field dissipation study (for turf) TEP 24

850.6100

Environmental chemistry methods and 

associated independent laboratory validations 

for the parent, oxadiazon, and three of its 

metabolites (methoxy, phenolic, and 

carboxylic) in soil/sediment and water

TGAI and three 

metabolites 12

Non-GDLN 

Special Study

Honey bee adult acute oral toxicity (OECD 

213) TGAI 12

Non-GDLN 

Special Study

Honey bee larvae acute oral toxicity (OECD 

237) TGAI 12

Non-GDLN 

Special Study Honey bee adult chronic oral toxicity TGAI 12

Non-GDLN 

Special Study Honey bee larvae chronic oral toxicity TGAI 12

Non-GDLN 

Special Study Field trial of residues in pollen and nectar3 TEP 24

Non-GDLN 

Special Study Semi-field testing for pollinators (OECD 75)3 TEP 24

850.3030 Honey bee toxicity of residues on foliage3 TEP 12

850.3040 Full-field testing for pollinators3 TEP 24

870.3465 28-day inhalation toxicity TGAI 12

875.2100 Dislodgeable foliar residue TGAI 12

Outstanding Data Requirements from GDCI-109001-247334

835.4300 Aerobic aquatic metabolism (address unidentified/un-extracted residue) TGAI

Supplemental 

(MRID 

46594701)

2 On June 27, 2012, EPA announced certain revisions in harmonized guideline series 850 – Ecological Effects Tests 

– including renumbering and other designations or changes for some guideline studies. See “Final Test 

Guidelines; OCSPP 850 Series; Notice of Availability” 77 FR 38282, June 27, 2012. 

http://www.regulations.gov/#!documentDetail;D=EPA-HQ-OPPT-2009-0154-0028 3 The need for this anticipated data requirement is contingent on results of the tier 1 bee studies (including acute oral 

toxicity to adult honey bees, acute oral toxicity to larval honey bees, chronic oral toxicity to adult honey bees, and 

chronic oral toxicity to larval honey bees). 4 The studies listed in this section were previously required through a generic data call-in issued in November 2004 

and are still outstanding, or in review. These studies will not be included in the anticipated Registration Review 

DCI because they are already required through the earlier DCI.

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Table 1: Planned Data Needs for the Oxadiazon Registration Review

Guideline 

Number2 Study Title2

Test Material

Estimated 

Timeframe

(Months from 

receipt of DCI)

or Status

850.1350

Mysid chronic toxicity test – life-cycle 

toxicity with Mysids (America mysis, 

formerly Mysidopsis bahia)

TGAI

In review 

(MRID 

46473304)

850.1400

Freshwater fish early-life stage (raw data for 

the previously submitted study with rainbow 

trout)

TGAI

In review 

(MRID 

41811601)

850.1735

Whole sediment acute toxicity freshwater 

invertebrates: toxicity to freshwater 

amphipods (Hyalella azteca) during a 10-day 

sediment exposure

TGAI

In review 

(MRID 

46473303)

850.1740

Whole sediment acute toxicity freshwater 

invertebrates: toxicity to midge (Chironomus 

riparius) during a 10-day sediment exposure

TGAI

In review 

(MRID 

46487301)

Non-GDLN 

Special Study

Freshwater fish early life-stage toxicity test 

with fathead minnow (Pimephales promelas) 

under high light conditions

TGAI

In review 

(MRID 

48759101)

TGAI = technical grade active ingredient; TEP = typical end-use product

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RISK ASSESSMENTS FOR REGISTRATION REVIEW

During registration review, the Agency will conduct a comprehensive ecological risk assessment, 

including an endangered species assessment, for all uses of oxadiazon. For human health, EPA 

will conduct revised dietary (drinking water only), residential, and occupational risk assessments 

during registration review; EPA also plans to conduct an aggregate (combined drinking water 

and residential) assessment based on currently available information and science/risk assessment 

policies. If toxicological endpoints or points of departure are revised based on the data that are 

required to be submitted for registration review, the revised endpoints or points of departure will 

be considered in the new assessments, as will any changes to the standard operating procedures 

or default exposure assumptions.

Table 2 below summarizes the planned registration review risk assessments based on the EFED 

Problem Formulation and HED Scoping Document. The table has been updated since the PWP 

to indicate that EPA plans to conduct an aggregate assessment. The other planned assessments 

have not changed from what was included in the PWP.

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Table 2: Planned Risk Assessments for the Oxadiazon Registration Review

Type of Risk Assessment Conduct? Notes

Ecological and Environmental Fate

Comprehensive ecological 

(species to be assessed 

include terrestrial and aquatic 

organisms), including 

endangered species 

Yes EPA anticipates conducting an updated 

comprehensive ecological risk assessment during 

registration review. The new assessment will 

incorporate the most up-to-date modeling 

methodologies, updated toxicological endpoints, and 

data submitted under the anticipated registration 

review data call-in. 

Incidents Will check for 

updates

For a discussion of reported ecological incidents for 

oxadiazon, see page 14 of the Problem Formulation.

Human Health

Dietary

Food No There are no registered food uses for oxadiazon. EPA 

does not anticipate conducting an updated dietary 

assessment for registration review unless there are 

significant changes to the drinking water estimated 

concentrations or if there are significant changes to 

the points of departure, uncertainty factors, or safety 

factors.

Drinking water Yes EPA anticipates conducting an updated drinking 

water assessment during registration review to 

incorporate updated estimated drinking water 

concentrations.

Occupational

Handlers (mixers, loaders, 

applicators)

Yes The most recent occupational exposure assessment 

was conducted for the 2007 human health risk 

assessment. EPA anticipates conducting an updated 

occupational handler assessment during registration 

review.

Post-application Yes The most recent occupational exposure assessment 

was conducted for the 2007 human health risk 

assessment. EPA anticipates conducting an updated 

occupational post-application assessment during 

registration review.

Residential

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Handlers Yes A residential handler assessment has not been 

performed. Based on information submitted during 

the PWP comment period by Bayer confirming their 

intent to allow use of oxadiazon products on 

residential property, EPA plans to conduct a 

residential handler risk assessment for turn/lawn use 

of oxadiazon during registration review.

In the 2007 human health assessment for ornamentals 

and landscape use, it was assumed that there would be 

no residential handler exposure since the product 

could only be applied by professional landscape 

personnel (in accordance with the label). However, 

since the oxadiazon labels do not identify the end-use 

products as restricted use, a residential handler 

exposure assessment is now required to be protective 

of potential homeowners who apply oxadiazon to 

ornamentals. 

Post-application Yes The most recent residential post-application exposure 

assessment was conducted for the 2007 human health 

risk assessment. EPA anticipates conducting an 

updated residential post-application assessment 

during registration review.

Other

Aggregate Yes An aggregate assessment evaluates the combined risk

from dietary and residential exposures. The Agency

anticipates conducting an aggregate assessment that 

will consider the combined exposure from drinking 

water and residential sources.

Cumulative No Not applicable; oxadiazon has not been identified as a 

member of a cumulative group that shares a common 

mechanism of toxicity.

Tolerances No Not applicable; there are no established tolerances for 

oxadiazon.

Incidents Will check for 

updates

For a discussion of reported human incidents for 

oxadiazon, see page 15 of the Scoping Document and 

the Oxadiazon: Tier 1 Review of Human Incidents.

TIMELINE

EPA has created the following estimated timeline for the completion of the oxadiazon 

registration review in Table 3 below. The projected timeline has changed to reflect the revised 

study duration for the full-field testing for pollinators (GLN 850.3040).

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Table 3: Oxadiazon Projected Registration Review Timeline

Activity Estimated Date

Opening the Docket

Open Docket and 60-day Public Comment Period Dec. 2014 – Completed

Close Public Comment Period Feb. 2015 – Completed

Case Development

Issue Final Work Plan May 2015 – Completed

Issue DCI 2015 July – Sept.

Data Submission 2017 July – Sept.

60-day Public Comment Period for Draft Risk Assessments5 2019 Jan. - March

Registration Review Decision

60-day Public Comment Period for Proposed Registration Review 

Decision

2019 Oct. – Dec.

Issue Registration Review Decision and Begin Post-Decision Followup2020

Total (years) 6

NEXT STEPS

As noted previously, the Agency plans to require several environmental fate, ecological effects, 

and human health studies for oxadiazon through a Data Call-In Notice, expected to be issued in 

mid-to-late 2015. 

5 The regulations governing Registration Review generally require the Agency to provide a public comment period 

of at least 30 calendar days for draft risk assessments; see 40 CFR Part 155.53(c). For conventional pesticides, the 

Agency plans to provide a 60 calendar day public comment period generally for draft risk assessments.

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