2

Diuron Preliminary Work Plan – Table of Contents

OVERVIEW ................................................................................................................................... 4

ANTICIPATED DATA NEEDS .................................................................................................... 5

STATUTORY AND REGULATORY AUTHORITY................................................................... 9

CHEMICAL FACTS ...................................................................................................................... 9

USE AND USAGE INFORMATION.......................................................................................... 10

RECENT ACTIONS..................................................................................................................... 12

ANTICIPATED RISK ASSESSMENTS FOR REGISTRATION REVIEW.............................. 13

TIMELINE.................................................................................................................................... 17

NEXT STEPS ............................................................................................................................... 17

Appendix – Additional Areas Considered in the Diuron Registration Review........................ 18

References:

This Preliminary Work Plan summarizes the Environmental Protection Agency's current position 

based on the following documents:

1. Diuron: Registration Review Problem Formulation for the Environmental Fate, 

Ecological Risk, Endangered Species, and Drinking Water Assessments. Jewett, F.; Lowit, 

M.; Breithaupt, J.; Bays, D.; Mostaghimi, S. December 16, 2015.

2. Diuron. Human Health Assessment Scoping Document in Support of Registration Review. 

Middleton, K; Figueroa, Z; Drew, W; Dole, T. December 9, 2015.

3. Diuron: Tier 1 (Scoping) Review of Human Incidents/Epidemiology. Recore, S; Evans, E. 

August 6, 2015.

4. BEAD Chemical Profile (BCP) for Registration Review: Diuron (035505). Ratnayake, S; 

Haddad, S.; Smearman, S. November 6, 2014.

5. Diuron (035505) Screening Level Usage Analysis (SLUA). March 24, 2015.
3

6. Diuron (035505) EFED Table 1 Report. November 12, 2014.

7. Diuron (035505) HED Master Label Report. November 12, 2014.

8. Diuron (035505) AD Label Data Report. November 12, 2014.

These and other supporting documents for the diuron registration review case may be found in

the docket EPA-HQ-OPP-2015-0077 at http://www.regulations.gov.
4

OVERVIEW

The docket for diuron is now open, initiating the first public comment period for this registration 

review (docket number EPA-HQ-OPP-2015-0077). Diuron is registered for conventional 

pesticide uses as a pre- and post-emergent herbicide to control annual and perennial broadleaf 

and grassy weeds in a variety of agricultural crops, ornamental plants, and non-crop sites and for 

conventional uses as an algaecide in commercial fish production. It is also registered for 

antimicrobial uses as a mildewcide and as an algaecide in paints and stains. Registered 

residential uses include ponds, aquariums, and paints. This Preliminary Work Plan (PWP) 

document explains what EPA's Office of Pesticide Programs knows about diuron, highlighting 

anticipated data and assessment needs, identifying the types of information that would be 

especially useful to the Agency in conducting the review, and providing an anticipated timeline 

for completing the registration review for diuron.

The registration review process was designed to include a public participation component to 

solicit input from interested stakeholders. The Agency intends, by sharing this information in the 

docket, to inform the public of what it knows about diuron and what types of new data or other 

information would be helpful for the Agency to receive as it moves toward a decision on diuron.

The Agency encourages all interested stakeholders to review the PWP and Appendix and to 

provide comments and additional information that will help the Agency’s decision-making 

process for this chemical. In addition to general areas on which persons may wish to comment, 

there are some areas identified in the PWP and Appendix about which the Agency specifically 

seeks comments and information. Interested stakeholders could include: environmental nonprofit or interest groups; pesticide manufacturers; agricultural labor or commodity groups; 

commercial, institutional, residential, and other users of pesticides; or the public at large.

The PWP begins by listing the anticipated data needs for diuron. Next, it discusses the statutory 

and regulatory authority for Registration Review. Then the document provides chemical facts, 

use and usage information, recent actions, the anticipated risk assessments, and a projected 

registration review timeline for diuron. Finally, the Appendix to this document includes 

identification and discussion of some areas that are considered generally in Registration Review 

along with some additional chemical case-specific information.
5

ANTICIPATED DATA NEEDS

Table 1 below summarizes anticipated data needs for diuron. For additional discussion of the 

anticipated data needs, see the Diuron: Registration Review Problem Formulation for the 

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

Diuron. Human Health Assessment Scoping Document in Support of Registration Review.

Table 1: Anticipated Data Needs for the Diuron Registration Review

Guideline 

Number1 Study Title Test 

Material

Estimated 

Timeframe

(Months 

from 

receipt of 

DCI)

Study is 

needed to 

support the 

antimicrobial 

uses of diuron 

(Yes/No)

Study is 

needed to 

support the 

conventional 

uses of diuron 

(Yes/No)

Anticipated Data Needs for the Parent Diuron

850.6100

Independent laboratory 

validation (ILV) report 

for analytical method 

in soil (ECM not 

required)

TGAI 12 No Yes

850.6100

Independent laboratory 

validation (ILV) report 

for analytical method 

in water (ECM not 

required)

TGAI 12 No Yes

850.1400 Estuarine/marine fish 

early-life stage toxicity TGAI 12 Yes Yes

850.2100 Avian oral toxicity 

(passerine species) TGAI 12 No Yes

850.2300

Avian reproduction 

with an upland game 

species

TGAI 24 No Yes

850.4100

Terrestrial plant 

toxicity, seedling 

emergence2

TEP 12 No Yes

850.4150

Terrestrial plant 

toxicity, vegetative 

vigor3

TEP 12 No Yes

 1 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 2 Valid endpoints have been submitted for Oilseed Rape, Sugar Beet, Tomato, Onion, and Wheat. Study must 

include the correct number and type of test species as specified by guideline 850.4100. 3 Valid endpoints have been submitted for Pea, Oilseed Rape, Onion, Sorghum and Wheat. Study must include the 

correct number and type of test species as specified by guideline 850.4150.
6

Table 1: Anticipated Data Needs for the Diuron Registration Review

Guideline 

Number1 Study Title Test 

Material

Estimated 

Timeframe

(Months 

from 

receipt of 

DCI)

Study is 

needed to 

support the 

antimicrobial 

uses of diuron 

(Yes/No)

Study is 

needed to 

support the 

conventional 

uses of diuron 

(Yes/No)

850.4500

Aquatic plant toxicity 

study with freshwater 

diatom, Navicula 

pelliculosa

TGAI 12 Yes Yes

850.4500

Aquatic plant toxicity 

study with the marine 

diatom, Skeletonema 

costatum

TGAI 12 Yes Yes

850.4550

Aquatic plant toxicity 

study with blue-green 

alga, Anabaena flosaquae

TGAI 12 Yes Yes

870.6200

Acute oral 

neurotoxicity study 

(rat)

TGAI 12 Yes Yes

NonGDLN 

(OECD 

213)

Tier I honeybee adult 

acute oral toxicity TGAI 12 No Yes

NonGDLNTier I honeybee adult 

chronic oral toxicity TGAI 12 No Yes

NonGDLNTier I honeybee larval 

acute oral toxicity TGAI 12 No Yes

NonGDLNTier I honeybee larval 

chronic oral toxicity TGAI 12 No Yes

NonGDLNTier II residue in 

pollen and nectar4 TEP 24 No Yes

NonGDLN

Tier II semi-field 

testing for honeybee 

toxicity 

(tunnel/enclosure or 

colony feeding)4

TEP 24 No Yes

850.3040 Tier III field testing for 

pollinator toxicity4 TEP 24 No Yes

NonGDLNSpecial leaching study 

for paint TGAI 12 Yes No

 4 The need for these anticipated data requirements 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).
7

Table 1: Anticipated Data Needs for the Diuron Registration Review

Guideline 

Number1 Study Title Test 

Material

Estimated 

Timeframe

(Months 

from 

receipt of 

DCI)

Study is 

needed to 

support the 

antimicrobial 

uses of diuron 

(Yes/No)

Study is 

needed to 

support the 

conventional 

uses of diuron 

(Yes/No)

860.1340

Residue analytical 

method (ILV of the 

livestock enforcement 

method)

TGAI 12 No Yes

860.1360

Multi-residue method 

(MRM testing for 

diuron in livestock 

commodities)

TGAI 12 No Yes

875.1400 Inhalation Indoor 

Exposure Study5 TEP 24 Yes No

875.2100

Dislodgeable Foliar 

Residue (DFR) 

Dissipation Study

TEP 12 No Yes

Anticipated Data Needs for the DCPMU Degradate

850.6100

Independent laboratory 

validation (ILV) report 

for analytical method 

in soil (ECM not 

required)

DCPMU 

Degradate 12 No Yes

850.6100

Independent laboratory 

validation (ILV) report 

for analytical method 

in water (ECM not 

required)

DCPMU 

Degradate 12 No Yes

850.4500/

850.4550

Algal/cyanobacteria 

toxicity testing with 

the non-vascular plant 

species most sensitive 

to diuron

DCPMU 

Degradate 12 Yes Yes

Anticipated Data Needs for the mCPDMU Degradate

850.6100

Independent laboratory 

validation (ILV) report 

for analytical method 

in water (ECM not 

required)

mCPDMU

Degradate 12 No Yes

 5 Data is anticipated to be required for the following scenarios for antimicrobial uses: (1) Mixing/loading liquids for 

material preservation and (2) Brush/roller and airless sprayer application of preserved paints.
8

Table 1: Anticipated Data Needs for the Diuron Registration Review

Guideline 

Number1 Study Title Test 

Material

Estimated 

Timeframe

(Months 

from 

receipt of 

DCI)

Study is 

needed to 

support the 

antimicrobial 

uses of diuron 

(Yes/No)

Study is 

needed to 

support the 

conventional 

uses of diuron 

(Yes/No)

850.4500/

850.4550

Algal/cyanobacteria 

toxicity testing with 

the non-vascular plant 

species most sensitive 

to diuron

mCPDMU 

Degradate 12 Yes Yes

Anticipated Data Needs for the PDMU Degradate

850.6100

Environmental 

chemistry method 

(ECM) and associated 

independent laboratory 

validation (ILV) 

reports for analytical 

method in water

PDMU 

Degradate 12 No Yes

Anticipated Data Needs for the mCPMU Degradate

850.6100

Environmental 

chemistry method 

(ECM) and associated 

independent laboratory 

validation (ILV) 

reports for analytical 

method in water

mCPMU 

Degradate 12 No Yes

TGAI = technical grade active ingredient; TEP = typical end-use product
9

STATUTORY AND REGULATORY AUTHORITY

The Food Quality Protection Act (FQPA) of 1996 mandated a registration review program. All 

pesticides distributed or sold in the United States (U.S.) generally must be registered by the 

Environmental Protection Agency (EPA or the Agency), based on scientific data showing that 

they will not cause unreasonable risks to human health or the environment when used as directed 

on product labeling. 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 of no unreasonable adverse effects to human health or the 

environment. Changes in science, public policy, and pesticide use practices will occur over time. 

Through the registration review program, the Agency periodically reevaluates pesticides to make 

sure that as change occurs, products in the marketplace can be used safely. Information on this 

program is provided on EPA’s website.

6

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. The regulations governing registration review begin at 40 CFR 155.40. The Agency 

will consider benefits information and data as required by FIFRA. The public phase of 

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

Agency’s opportunity to state what it knows about the pesticide and what additional risk analyses 

and data or information it believes are needed to make a registration review decision. After 

reviewing and responding to comments and data received in the docket during this initial 

comment period, the Agency will develop a Final Work Plan (FWP) and anticipated schedule for 

the registration review of diuron.

CHEMICAL FACTS

Table 2 provides a summary of the chemical facts for diuron.

Table 2: Chemical Facts for Diuron

PC code 035505

Case Number 0046

CAS Number 330-54-1

Year first registered 1967

Pesticide Type Herbicide and algaecide (conventional); algaecide and 

mildewcide (antimicrobial)

Chemical class Urea (Group 7)

Reregistration Eligibility 

Decision (RED)

2003

Tolerance Reassessment 

Eligibility Decision 

(TRED)

2002

 6 Available at: http://www2.epa.gov/pesticide-reevaluation
10

Table 2: Chemical Facts for Diuron

Cumulative group Not applicable. Diuron has not been identified as a member of a 

cumulative group that shares a common mechanism of toxicity.

40 CFR Citation Tolerances for the conventional uses of diuron are established in

40CFR §180.106[a] and [c]. There are no tolerances or tolerance

exemptions for the antimicrobial uses of diuron.

Dual-use Diuron is registered for conventional pesticidal uses and 

antimicrobial uses.

Non-pesticidal uses There are no identified non-pesticidal uses of diuron.

Pesticide Re-evaluation 

Division, Chemical 

Review Manager

Katherine St. Clair, Stclair.Katherine@epa.gov, 703-347-8778

Antimicrobials Division, 

Chemical Review 

Manager

SanYvette Williams, Williams.Sanyvette@epa.gov, 703-305-

7702

Registration Division, 

Product Manager and 

Chemical Review 

Manager

Heather Garvie, Garvie.Heather@epa.gov, 703-308-0034

Banza Djapao, Djapao.Banza@epa.gov, 703-305-7269

USE AND USAGE INFORMATION

Table 3 summarizes the use and usage information for diuron. Please see the BEAD Chemical 

Profile (BCP) for Registration Review: Diuron (035505) in the registration review docket for 

more details.

Table 3: Diuron Use and Usage Information

Summary of Use Diuron is registered for conventional uses as a pre- and postemergent herbicide to control annual and perennial broadleaf and 

grassy weeds in a variety of agricultural crops, ornamental plants, 

and non-crop sites and is registered for conventional uses as an 

algaecide in commercial fish production. It is also registered for 

antimicrobial uses as a mildewcide and algaecide in paints and 

stains. Registered residential uses include ponds, aquariums, and 

paints.

Use Sites Agricultural Use Sites

Registered agricultural use sites include alfalfa, apples, 

artichokes, asparagus, bananas, barley, blueberries, cactus, 

caneberries, citrus, clover, corn, cotton, fish farm ponds, grapes, 

gooseberries, grass grown for seed, tree nuts, mint, oats, olives,

papayas, pasture, peaches, pears, peas, pineapples, plantains, 

prickly pear cactus pads, sorghum, sugarcane, trefoil, triticale, 

wheat, and ornamental trees, flowers, shrubs, and non-flowering 

plants.
11

Table 3: Diuron Use and Usage Information

Non-Agricultural Use Sites

Registered non-agricultural use sites include paints and coatings, 

adhesives, ornamental fish ponds, patios, paths, general outdoor 

areas, picnic areas, rights-of-way, general uncultivated areas, 

agricultural cultivated areas, irrigation and drainage ditches, and 

industrial sites. Registered residential use sites include ponds, 

aquariums, paints, patios, paths, and general outdoor areas.

Summary of Usage EPA has agricultural usage data for diuron, but the available nonagricultural usage data for diuron is limited.

Agricultural Usage

EPA obtained private market usage data from 1998-2012 on 

diuron agricultural usage. In the period from 1998-2012, usage 

averaged approximately 4.1 million pounds active ingredient (lbs. 

a.i.) applied annually on approximately 4.9 million acres treated.

However, the average annual agricultural usage of diuron in lbs. 

a.i. has decreased approximately 30 percent from the 1998-2003 

timeframe (4.7 million lbs. a.i. per year) to the 2007-2012 

timeframe (3.3 million lbs. a.i. per year). During both timeframes, 

the top two crops with the most lbs. a.i. applied were oranges and 

cotton, accounting for approximately 70 percent of total lbs. a.i. 

applied. 

Non-Agricultural Usage

EPA obtained limited information on diuron non-agricultural 

usage from two sources, 1) the USDA’s National Agricultural 

Statistics Service (NASS) 2006 and 2009 Nursery and 

Floriculture reports and 2) proprietary Kline & Company data. 

Data for more recent years (2012 to present) were not available. 

Usage on most non-agricultural use sites (including aquatic areas, 

turf and ornamentals, and use by landscape/lawn care operators)

generally increased between the early-2000s to the mid-2000s, 

but nursery/greenhouse usage remained fairly steady.

Formulation Type(s) Diuron is formulated as a liquid, emulsifiable concentrate, dry 

flowable, flowable concentrate, granular, pellet/tablet, and readyto-use solution.

Application Method(s) Diuron products can be applied using ground, handheld, and 

aerial equipment. It can also be applied as an additive/industrial 

preservation treatment and as a water treatment.

Technical Registrant(s) Diuron technical registrants include E.I. DuPont De Nemours and 

Company, ADAMA AGAN Ltd., Drexel Chemical Company, 

Lanxess Corporation, Chemstarr LLC, Redeagle International 

LLC, Bayer Environmental Science, and Makhteshim Agan of 

North America, Inc.
12

Table 3: Diuron Use and Usage Information

No. of Registrations As of December 2015, there are 88 Section 3 registrations7 and 30 

Section 24c registrations.

Restricted Use Diuron is not classified as a restricted use pesticide.

Guidance for Commenters: Additional areas of use and usage related information

requested for this registration review, and of particular interest to EPA, are described below.

Conventional Uses

• Diuron labels are inconsistent with respect to the application parameters provided on the 

labels. The Agency requests that the registrant provide the following information for 

conventional uses: maximum annual application rates per acre (lb ai/A/year) for all uses, 

maximum number of applications per crop cycle or season (if applicable) and maximum 

number of applications per year (all uses), and minimum application intervals (all uses). 

When application rates or intervals are provided in terms or season or crop cycle, they 

should also be provided in terms of annual application rates or intervals. Without further 

information, EPA expects to use conservative assumptions to approximate these 

parameters in order to conduct a quantitative risk assessment. However, the Agency will 

work with registrants to clarify information on diuron product labels. 

• Confirmation of the following label information: sites of application; formulations;

application methods and equipment; maximum application rates (in terms of maximum 

amount of product applied per year and maximum amount of active ingredient applied 

per year); frequency of application, application intervals, and maximum number of 

applications per season; number of seasons in a year; and geographic limitations on use.

When application rates or intervals are provided in terms or season or crop cycle, they 

should also be provided in terms of annual application rates or intervals.

• Typical application timing (date of first application and application intervals) – national, 

state, and county.

• Usage information for non-agricultural uses.

• Typical application interval (days).

• Foreign technical registrants not listed above who supply technical diuron to the US 

market.

Antimicrobial Uses

• Confirmation of the use sites and application rates listed on the labels.

• Usage information for each of the antimicrobial uses, including use as an algaecide and

mildewcide in paints and coatings.

RECENT ACTIONS

Conventional Pesticidal Uses

 7 Section 3 product labels can be obtained from the Pesticide Product Label System (PPLS) website 

(http://oaspub.epa.gov/pestlabl/ppls.home).
13

The RED for diuron was signed in September 2003, and the product reregistration process has 

been completed.

As of December 2015, there are two pending registration actions for conventional diuron 

registrations (two applications for new technical registrations which would be “me-toos” of 

existing products).

Antimicrobial Uses

There is one pending registration action for an antimicrobial diuron registration.

ANTICIPATED RISK ASSESSMENTS FOR REGISTRATION REVIEW

The most recent comprehensive human health risk assessments for diuron were completed in

2003 in preparation for the Reregistration Eligibility Decision (RED) and in 2012 for a new use 

request. The most recent ecological and environmental fate risk assessments were completed in 

2003 for the RED and for the Endangered and Threatened Salmon and Steelhead Assessment, as 

well as in 2009 for the California Red-legged Frog Assessment. Findings and conclusions from 

these risk assessments are summarized in the document titled Diuron: Registration Review 

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

Drinking Water Assessments and the document titled Diuron. Human Health Assessment Scoping 

Document in Support of Registration Review.

During registration review, the Agency anticipates the need to conduct a comprehensive

ecological risk assessment, including an endangered species assessment, for all conventional 

uses of diuron. The Agency also anticipates the need to conduct an aquatic assessment for the 

antimicrobial uses of diuron as it leaches from paints and coatings on structures and enters 

surface waters. For human health, EPA anticipates the need to conduct revised dietary, 

residential, occupational, and aggregate risk assessments for the conventional uses of diuron 

during registration review. Also, if formally requested by the registrant, the Agency will reevaluate the cancer classification for diuron. For the antimicrobial uses of diuron, the Agency 

anticipates the need to conduct revised occupational and residential risk assessments. If 

toxicological endpoints or points of departure are revised based on the data that are anticipated to 

be required for registration review, they will be considered in the new assessments, as will any 

changes to the standard operating procedures or default exposure assumptions.

Table 4 summarizes the anticipated registration review risk assessments based on the document 

titled Diuron: Registration Review Problem Formulation for the Environmental Fate, Ecological 

Risk, Endangered Species, and Drinking Water Assessments and the document titled Diuron. 

Human Health Assessment Scoping Document in Support of Registration Review.
14

Table 4: Anticipated Risk Assessments for the Diuron 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 EFED anticipates conducting an updated 

comprehensive ecological risk assessment during 

registration review for all conventional uses of diuron. 

The new assessment will incorporate the most up-todate modeling methodologies, updated toxicological 

endpoints, and data submitted under the anticipated 

registration review data call-in.

The stressors of concern (mCPDMU and DCPMU; 

potentially PDMU and mCPMU) will be assumed to 

have similar toxicity as diuron (in the absence of 

data). Furthermore, a TTR approach may be used to 

estimate aquatic exposure. 

 

AD anticipates conducting an aquatic assessment for 

the antimicrobial uses of diuron as it leaches from 

paints and coatings on structures and enters surface 

waters. This is likely to be a small contribution 

relative to the conventional uses, but is a potential 

exposure pathway.

Incidents Will check for 

updates

For a discussion of reported ecological incidents for 

diuron, see Section 6(d) and Appendix 4 of the

Problem Formulation.

Human Health

Dietary

Dietary Yes HED anticipates conducting revised dietary exposure 

analyses for the conventional uses of diuron to reflect 

updated dietary exposure models and updated 

drinking water assessments.

Food Yes
15

Table 4: Anticipated Risk Assessments for the Diuron Registration Review

Type of Risk Assessment Conduct? Notes

Drinking water Yes EFED anticipates conducting updated drinking water 

assessments for diuron during registration review to 

incorporate updated drinking water concentrations.

Diuron, mCPDMU, and DCPMU will be considered 

the stressors of concern in the diuron drinking water 

assessment. The residues of concern may be 

reevaluated pending reevaluation of existing data and 

receipt and review of additional data for diuron or its 

degradation products. 

The drinking water assessment will be based on 

modeled estimates of exposure but will also include a 

summary of available surface and ground water 

monitoring data. 

Occupational

Handlers (mixers, loaders, 

applicators)

Yes HED and AD anticipate conducting revised (noncancer and cancer) occupational exposure assessments 

to reflect the use of the most recent handler exposure 

data, the toxicity studies, and updated exposure 

inputs.

HED anticipates conducting updated (non-cancer and 

cancer) post-application exposure assessments for 

workers conducting post-application activities. 

Post-application Yes

Residential

Handlers Yes For the aquatic uses of diuron, HED anticipates

conducting revised (non-cancer and cancer) 

residential handler and residential post-application 

assessments that incorporate recently updated 

procedures found in the Health Effects Division’s 

2012 Standard Operating Procedures for Residential 

Pesticide Exposure Assessment.

For the use of diuron in paint, AD anticipates 

conducting revised residential handler application

exposure assessments (brush/roller and airless 

sprayer.

Post-application Yes

Other
16

Table 4: Anticipated Risk Assessments for the Diuron Registration Review

Type of Risk Assessment Conduct? Notes

Aggregate Yes Evaluates the combined risk from dietary and 

residential exposures.

HED anticipates conducting an updated aggregate 

assessment during registration review for all uses of 

diuron.

Cancer Yes A formal request for cancer reclassification should be 

submitted to the Agency if the registrant would like 

the Agency to consider a proposed mode of action for 

diuron.

Cumulative No Not applicable. Diuron has not been identified as a 

member of a cumulative group that shares a common 

mechanism of toxicity.

Tolerances Yes The tolerance expression for diuron (in 40CFR 

§180.106[a] and [c]) is not in accord with current 

guidance, as it does not contain the appropriate 

coverage and compliance statements. It should be 

revised during registration review to comply with the 

Agency’s guidance on tolerance expressions. 

There are no Codex MRLs established for diuron, so 

there are no harmonization issues with regard to 

Codex. US tolerances are generally not harmonized 

with Canadian MRLs, with the exception of asparagus 

at 7 ppm (mg/kg). Further harmonization with 

Canadian MRLs may be possible during registration 

review. 

Incidents Will check for 

updates

For a discussion of reported human incidents for 

diuron, see pages 19-20 of the Scoping Document and

see document titled Diuron: Tier 1 (Scoping) Review 

of Human Incidents/Epidemiology.

Guidance for Commenters: Additional ecological information requested for this 

registration review, and of particular interest to EPA, is described below.

• Maximum annual application rates per acre (maximum lb ai/A/year), maximum number 

of applications per season (if applicable) and/or year (if applicable), and minimum 

application intervals on all conventional uses on the labels.

• Ecological incidents (non-target plant damage and avian, fish, reptilian, amphibian and 

mammalian mortalities) not already reported to the Agency.

• Water quality monitoring data (see Appendix for further details).
17

TIMELINE

EPA has created the following estimated timeline for the completion of the diuron registration

review in Table 5.

Table 5: Projected Diuron Registration Review Timeline

Activity Estimated Date

Opening the Docket

Open Docket and 60-day Public Comment Period December 2015

Close Public Comment Period February 2016

Case Development

Issue Final Work Plan May 2016

Issue DCI July – Sept. 2016

Data Submission July – Sept. 2018

Open 60-day Public Comment Period for Draft Risk 

Assessments8

Jan. – March 2020

Registration Review Decision

Open 60-day Public Comment Period for Proposed 

Registration Review Decision

Oct. – Dec. 2020

Issue Registration Review Decision and Begin PostDecision Follow-up2021

Total (years) 6

NEXT STEPS

After the 60-day public comment period closes, the Agency will review and respond to any 

comments received in a timely manner and then issue a Final Work Plan for the registration 

review of diuron.

 8 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.
18

Appendix – Additional Areas Considered in the Diuron Registration Review

PUBLIC COMMENTS AND FEEDBACK:

Guidance for Commenters: The areas below highlight topics of special interest to the Agency 

where your comments, data submissions, or reference to sources of additional information could 

be of particular use.

Trade Irritants:

Through the registration review process, the Agency intends to solicit information on trade 

irritants and, to the extent feasible, take steps toward facilitating irritant resolution. The Agency 

will work to harmonize tolerances and international maximum residue limits (MRLs) and may 

modify tolerance levels to do so, when possible. Growers and other stakeholders are asked to 

comment on any trade irritant issues resulting from lack of MRLs or disparities between U.S. 

tolerances and MRLs in key export markets, providing as much specificity as possible regarding 

the nature of the concern.

Water Quality:

Diuron is identified as a cause of impairment, as defined under section 303(d) of the Clean Water 

Act, for eight water bodies in California, based on information provided at EPA’s website.9

However, no Total Maximum Daily Loads (TMDL) have been developed for diuron.

10 More 

information on impaired water bodies and TMDLs can be found at EPA’s website.

11 The 

Agency invites submission of water quality data for this pesticide. To the extent possible, 

data should conform to the quality standards in Appendix A of the OPP Standard Operating 

Procedure: Inclusion of Impaired Water Body and Other Water Quality Data in OPP’s 

Registration Review Risk Assessment and Management Process12 in order to ensure they can be 

used quantitatively or qualitatively in pesticide risk assessments.

Environmental Justice:

EPA seeks to achieve environmental justice, the fair treatment and meaningful involvement of all 

people, regardless of race, color, national origin, or income, in the development, implementation, 

and enforcement of environmental laws, regulations, and policies. To help address potential 

environmental justice issues, the Agency seeks information on any groups or segments of the 

population who, as a result of their location, cultural practices, or other factors, may have 

atypical, unusually high exposure to diuron compared to the general population. Please 

comment if you are aware of any sub-populations that may have atypical, unusually high 

exposure compared to the general population.

 9 http://iaspub.epa.gov/tmdl_waters10/attains_nation_cy.cause_detail_303d?p_cause_group_id=885

10http://iaspub.epa.gov/tmdl_waters10/attains_nation.tmdl_pollutant_detail?p_pollutant_group_id=885&p_pollutant

_group_name=PESTICIDES

11 www.epa.gov/tmdl 12 http://www2.epa.gov/pesticide-reevaluation/opp-guidance-submission-state-and-tribal-water-quality-monitoringdata
19

ENDANGERED SPECIES:

A risk assessment that supports a complete endangered species determination has not been 

conducted for diuron. The ecological risk assessment planned during registration review will 

allow the Agency to determine whether use of diuron 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.

On June 5, 2013, the Center for Biological Diversity and the Pesticide Action Network North 

America filed an amended complaint in its lawsuit in the United States District Court for the 

Northern District of California, against the EPA for allegedly failing to undergo consultation 

with the United States Fish and Wildlife Service and the National Marine Fisheries Service 

regarding the effects of over 50 pesticides, including diuron, on over 100 endangered and 

threatened species throughout the United States (Center for Biological Diversity, et al. v. EPA, et 

al., No. C 11-00293 (N.D.Cal.).

Previous endangered species assessments were conducted for Pacific Salmon and Steelhead in 

200313 and for the California Red-legged Frog in 200914. 

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 and reregistration decisions for diuron,

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), 

diuron 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 

 13 USEPA, 2003b. Diuron (035505): Analysis of Risks to Endangered and Threatened Salmon and Steelhead. 

Environmental Fate and Effects Division, Office of Pesticide Programs, U.S. Environmental Protection Agency. 

http://www.epa.gov/oppfead1/endanger/litstatus/effects/#diuron

14 USEPA, 2009. Diuron (035505): Risks of Diuron Use to Federally Threatened California Red-legged Frog (Rana 

aurora draytonii). Environmental Fate and Effects Division, Office of Pesticide Programs, U.S. Environmental 

Protection Agency. http://www.epa.gov/oppfead1/endanger/litstatus/effects/#diuron
20

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. A second list of 

chemicals identified for EDSP screening was published on June 14, 201315 and includes some 

pesticides scheduled for registration review and chemicals found in water. Neither of these lists 

should be construed as a list of known or likely endocrine disruptors. 

Diuron is on List 2. List 2 represents the next set of chemicals for which EPA intends to issue 

test orders/data call-ins in the near future. 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.16

HUMAN STUDIES:

Occupational and Residential

The previous diuron risk assessments relied in part on data from studies in which adult human 

subjects were intentionally exposed to a pesticide or other chemical. These data, which include 

studies from the Pesticide Handlers Exposure 1.1 (PHED) Database, Outdoor Residential 

Exposure Task Force (ORETF) database, Agricultural Handler Exposure Task Force (AHETF) 

database, are (1) subject to ethics review pursuant to 40 CFR 26, (2) have received that review, 

and (3) are compliant with applicable ethics requirements. For certain studies, the ethics 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 the Agency website17. In addition, the new studies 

that are being performed by the Antimicrobial Exposure Assessment Task Force (AEATF) are 

being reviewed by the Human Studies Review Board (HSRB) as they are designed and 

completed. The recommendations made by the HSRB are being implemented to ensure that 

AEATF study participants are fully informed and protected as required by the “Protection of 

Human Subjects” regulation.

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

chemicals. 16 http://www2.epa.gov/endocrine-disruption 17 Available at: http://www2.epa.gov/pesticide-science-and-assessing-pesticide-risks/occupational-pesticide-handlerexposure-data and http://www2.epa.gov/pesticide-science-and-assessing-pesticide-risks/occupational-pesticide-postapplication-exposure.