UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON D.C., 20460

OFFICE OF CHEMICAL SAFETY AND 

POLLUTION PREVENTION

December 15, 2015

PC Code: 035505

DP Barcode: 423230

MEMORANDUM

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

Risk, Endangered Species, and Drinking Water Assessments

FROM: Freeborn Jewett, M.S., Biologist

Michael Lowit, Ph.D., Ecologist

Environmental Risk Branch I

Environmental Fate and Effects Division (7507P)

James Breithaupt, Agronomist (LP for JB) 

David Bays, Biologist

Siroos Mostaghimi, Senior Scientist

Risk Assessment and Science Support Branch

Antimicrobials Division (7510P)

THRU: Sujatha Sankula, Ph.D., Branch Chief

Environmental Risk Branch 1

Environmental Fate and Effects Division (7507P)

Laura Parsons, Associate Branch Chief

Risk Assessment and Science Support Branch

Antimicrobials Division (7510P)

TO: Katherine St. Clair, Chemical Review Manager

Tom Myers, Team Leader

Kevin Costello, Branch Chief

Risk Management and Implementation Branch 2

Pesticide Re-Evaluation Division (7508P)

SanYvette Williams, DVM, Chemical Review Manager

Rose Kyprianou, Team Leader

Lance Wormell, Branch Chief

Regulatory Management Branch 2

Antimicrobials Division (7510P)
2

TABLE OF CONTENTS 

1) Executive Summary..............................................................................................................................3

2) Introduction..........................................................................................................................................4

4) Conclusions from Previous Risk Assessments.....................................................................................5

5) Environmental Fate and Transport......................................................................................................6

6) Receptors............................................................................................................................................11

7) Exposure Pathways of Concern .........................................................................................................17

8) Analysis Plan.......................................................................................................................................17

9) Endangered Species Assessment.......................................................................................................19

10) Endocrine Disruptor Screening Program...........................................................................................20

11) Preliminary Identification of Data Gaps............................................................................................20

12) References..........................................................................................................................................26

Appendix 1: Maximum Application Rates of Diuron (Conventional Uses) ..............................................28

Appendix 2: Diuron Degradates Identified in Environmental Fate Studies.............................................31

Appendix: 3: Complete List of Toxicity Endpoints for Diuron...................................................................36

Appendix 4: Ecological Incidents Associated with Diuron (EIIS database)...............................................42

Appendix 5: SIP (v1.0) Input and Output Data..........................................................................................44

Appendix 6: STIR (v.1) Inputs and Outputs...............................................................................................45
3

1) Executive Summary

The Environmental Fate and Effects Division (EFED) and Antimicrobials Division (AD) have completed the 

problem formulation for the environmental fate, ecological risk, endangered species, and drinking water 

exposure assessments to be conducted as part of the registration review of the herbicide diuron (N’-

(3,4-dichlorophenyl)-N,N-dimethylurea), a systemic substituted phenylurea herbicide and an 

antimicrobial mildewcide and algaecide. Functioning as the first stage of the risk assessment process for 

registration review, this problem formulation provides an overview of what is currently known about 

the environmental fate and ecological effects associated with diuron and its degradates. It also describes 

the preliminary ecological risk hypothesis and analysis plan for evaluating and characterizing drinking 

water exposure and risk to non-target species and the environment in support of the registration review 

of diuron. This document also recommends studies that should be included in a data call-in (DCI) to 

address uncertainties surrounding the environmental fate and potential ecological effects of diuron for 

both conventional and antimicrobial uses.

The following studies are recommended to reduce uncertainty in the risk assessment for conventional 

uses only:

• 850.2100: Avian acute oral toxicity with a passerine species (diuron)

• 850.2300: Avian reproduction with an upland game species (diuron)

• 850.4100: Seedling emergence and seedling growth toxicity (TEP)1

• 850.4150: Vegetative vigor toxicity (TEP)2

• Non-Guideline (OECD 213): Tier I Honeybee acute adult oral toxicity (diuron)

• Non-Guideline: Tier I Honeybee adult chronic oral toxicity (diuron)

• Non-Guideline: Tier I Honeybee larval acute and chronic oral toxicity (diuron)

• Non-Guideline: Tier II Residue in pollen and nectar (based on risks identified in Tier I studies) (TEP)

• Non-Guideline: Tier II Semi-field testing for honeybees toxicity (based on risks identified in Tier I 

studies) (TEP)

• 850.3040: Tier III field testing for pollinator toxicity (based on risks identified in Tier II studies) (TEP)

• 850.6100: Independent laboratory validation (ILV) report for analytical method in soil (diuron and 

DCPMU)

• 850.6100: Environmental chemistry method (ECM) and independent laboratory validation (ILV) 

reports for analytical method in water (ECM and ILV for PDMU and mCPMU; ILV only for diuron, 

DCPMU, and mCPDMU

The following studies are recommended to reduce uncertainty in the risk assessment for conventional 

and antimicrobial uses: 

• 850.1400: Estuarine/marine fish early-life stage toxicity (diuron)

• 850.4500: Aquatic plant toxicity study with freshwater diatom, Navicula pelliculosa (diuron)

• 850.4500: Aquatic plant toxicity study with the marine diatom, Skeletonema costatum (diuron)

• 850.4550: Aquatic plant toxicity study with blue-green alga, Anabaena flos-aquae (diuron)

• 850.4500/850.4550: Algal/Cyanobacteria Toxicity (DCPMU)

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

corn and soybean. Study must include the correct number and type of test species as specified by guideline 850.4100. 2 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.
4

o Testing should be with the non-vascular plant species most sensitive to diuron.

• 850.4500: Algal/Cyanobacteria Toxicity (mCPDMU)

o Testing should be with the non-vascular plant species most sensitive to diuron.

The following studies are recommended to reduce uncertainty in the risk assessment for antimicrobial 

uses only: 

• Non-Guideline: Special leaching study for paint 

EFED recommends the following information to reduce uncertainty in the risk assessment:

EFED 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/season (if applicable) and per year (all uses), and minimum application intervals (all uses).

2) Introduction

The purpose of this problem formulation is to provide an understanding of what is known about the 

environmental fate and ecological effects of diuron considering its currently registered uses. This 

document provides a plan for analyzing data relevant to diuron and for conducting ecological risk, 

endangered species, and drinking water exposure assessments for its registered uses. This problem 

formulation is intended to identify data gaps, uncertainties, and potential assumptions used to address 

those uncertainties relative to characterizing the ecological risk associated with the registered uses of 

diuron.

Diuron is a pre- and post-emergence systemic herbicide belonging to the substituted urea class of 

herbicides used to control both grasses and broadleaf species. In the U.S., diuron is used on a variety of 

crops and non-agricultural uses such as recreational areas, impervious surfaces, and paved areas. It also 

may be used in irrigation and drainage systems when water is not present. As a conventional pesticide, 

diuron is applied alone or as part of formulated product using ground and aerial equipment. It is also 

registered to be used as an antimicrobial pesticide (material preservative) in paints, coatings, and 

adhesives that may be used on building exteriors.

EFED evaluated the most recent ecological risk assessments for diuron in association with the updated 

toxicity, exposure, and usage information to determine if sufficient data are available and if further 

updates are needed to support registration review. The most recent risk assessments for diuron include 

the Environmental Risk Assessment for the Reregistration of Diuron (USEPA, 2003a) and two 

endangered species assessments: Determination of Risks of Diuron Use to Federally Threatened 

California Red-legged Frog (USEPA, 2009) and the Endangered and Threatened Salmon and Steelhead 

Assessment (USEPA, 2003b). In addition, EFED considered the latest Agency science policies and risk 

assessment methodologies.

3) Use Characterization

a) Mode of Action

Diuron is systemic and easily taken up by plants and rapidly translocated. Diuron primarily functions by 

inhibiting the Hill reaction in photosynthesis, limiting the production of high-energy compounds such as 

adenosine triphosphate (ATP), which is used for various metabolic processes.
5

b) Overview of Pesticide Use and Usage

i) Uses – Conventional and Antimicrobial

Diuron was first registered in the U.S. as a pre- and post-emergence herbicide, algaecide, and 

mildewcide in 1967. In the U.S., diuron is registered for use on numerous crop species including alfalfa, 

apples, artichokes, asparagus, bananas, barley, caneberries, citrus, clover, corn, cotton, grapes, nut 

trees, mint, oats, papayas, pasture, peaches, pears, peas, pineapple, sorghum, sugarcane, ornamental 

plants, flowers and shrubs, and wheat (USEPA, 2014a). Non-agricultural uses include ornamental ponds, 

commercial fishery water systems, patios, rights-of-way (railroad), and industrial sites (outdoors). Enduse products are available as flowable concentrates, soluble concentrates, water dispersible granules 

(dry flowable), granules, and pellets/tablets for pre- and post-emergence control of weeds. Diuron 

products registered for conventional uses may be applied using ground and aerial equipment.

Diuron is used as an antimicrobial material preservative in outdoor building materials such as paints, 

stains, stucco, caulks, sealants, masonry coatings, plaster, joint sealants, and roof coatings. Diuron is 

added as the building material is being manufactured.

ii) Usage – Conventional

Estimates of the actual usage of diuron on agricultural crops between 2004 and 2012 were provided by

the Biological and Economic Analysis Division (BEAD) (Screening Level Usage Analysis (SLUA); USEPA, 

2014b). The greatest use of diuron in terms of pounds applied was for cotton and oranges (1.2-1.4 

million lb ai/A). Asparagus was the use with the highest percentage of treated crop (65%-75%). Diuron 

uses and application rates are summarized in Appendix 1. This information was obtained from the 

most recent Label Use Information System (LUIS) report provided by BEAD (USEPA, 2014c). The 

registration review risk assessment will be based on current label information at the time of assessment 

as provided by BEAD.

There are numerous instances where important information is missing from the labels including but not 

limited to the annual maximum application rate, maximum number of applications per crop/season 

and/or year, and minimum reapplication interval. EFED requests that the registrant update labels to 

include this information. The LUIS report (USEPA, 2014c) may be consulted for a list of missing 

information identified by the Agency. EFED will make conservative assumptions in the absence of label 

information on application rates.

iii) Usage – Antimicrobial

Current use information is not available at this time; however, it was reported that less than 1% of paint 

was treated with diuron at the time of the Registration Eligibility Decision (RED; USEPA, 2003c). 

4) Conclusions from Previous Risk Assessments

a) Ecological Risk Assessment

The Agency has conducted multiple ecological risk assessments on diuron. The documents that serve as a 

basis for this problem formulation are the Environmental Risk Assessment for the Reregistration of Diuron

(USEPA, 2003a), the Endangered and Threatened Salmon and Steelhead Assessment (USEPA, 2003b), and 

the California Red-legged Frog Assessment (USEPA, 2009). The primary risk concerns identified in these 

documents are:

• Acute and chronic risk to birds (listed and non-listed)
6

• Acute dose based (listed) and chronic dose based (listed and non-listed) risk to mammals

• Terrestrial plants (monocots and dicots) (listed and non-listed)

• Acute and chronic risk to freshwater fish (listed and non-listed)

• Acute and chronic risk to terrestrial and aquatic-phase amphibians

• Acute risk to estuarine/marine fish (listed)

• Acute and chronic risk to freshwater invertebrates (listed and non-listed)

• Acute (listed) and chronic risk to estuarine/marine invertebrates

• Aquatic plants

b) Drinking Water Exposure Assessments

The most recent drinking water assessment (DWA) was conducted in 2001 (USEPA, 2001a) and

evaluated use on citrus. In 2003, monitoring data were evaluated and considered robust enough to use 

in place of chronic but not acute estimated drinking water concentrations (EDWC) (USEPA, 2003d). The 

monitoring data were collected in Florida, Georgia, and California by state and federal agencies. A new 

DWA will be conducted in registration review for all registered uses of diuron to reflect current models 

and methodology. 

c) Clean Water Programs

Diuron is identified as a cause of impairment for eight water bodies in California listed as impaired under 

section 303(d) of the Clean Water Act (as of 11/2014).3

 A Total Maximum Daily Load (TMDL) has not 

been developed.4 The Impaired Waters and TMDL website can be consulted for more information.5

 

Aquatic benchmarks have been established for diuron.6

5) Environmental Fate and Transport

Vapor pressure (9.19 x 10-6 Pa at 25°C) and Henry's Law Constant (7.39 x 10-5 Pa·m3 mol-1

) indicate a low 

possibility of volatilization of diuron from soil and water. Laboratory data indicate that diuron is 

persistent based on relatively slow degradation by hydrolysis, soil photolysis, soil metabolism (aerobic 

and anaerobic), and aerobic aquatic metabolism (depending on the system). However, diuron degraded 

more quickly in water by photolysis, anaerobic aquatic metabolism, and aerobic aquatic metabolism 

(depending on the system). The adsorption coefficient for diuron (mean Koc = 920) indicates moderate 

mobility and suggests that leaching could be a route of dissipation. The available terrestrial field 

dissipation studies showed diuron was typically detected at a depth range of 0-30 cm at all test sites. 

Consistent with laboratory data, the terrestrial field dissipation studies indicate that diuron is persistent 

(73-139 day half-lives) in terrestrial environments. The aquatic field dissipation studies, conducted in 

soils (berm and slope) of drainage channels, also showed persistence of diuron in soils (115-142 day 

half-lives) and that some of the dissipation was the result of transport into channel sediment and water.

The physical, chemical, and environmental fate properties of diuron and major degradates are 

summarized in Table 1 and Table 2, respectively. Appendix 2 summarizes the maximum formation of 

diuron degradation products. 

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

4 http://iaspub.epa.gov/tmdl_waters10/attains_nation.tmdl_pollutant_detail?p_pollutant_group_id=885&p_pollut

ant_group_name=PESTICIDES

5

http://www.epa.gov/tmdl/ 6

http://www2.epa.gov/pesticide-science-and-assessing-pesticide-risks/aquatic-life-benchmarks-pesticideregistration/
7

Table 1: Physical, Chemical, and Environmental Fate Properties of Diuron

Parameter Value Reference

(MRID unless 

specified)

Comments

Chemical Diuron None --

Chemical Name N`(3,4-dichlorophenyl)-N,Ndimethylurea42661901 --

Empirical Formula C9H10Cl2N2O --

CAS Number 330-54-1 EPI Suite v 4.11 --

Structure 42661901 --

SMILES O=C(N(C)C)Nc(ccc(c1Cl)Cl)c1 EPI Suite v 4.11 --

Selected Physical/Chemical Parameters

Molecular mass 233.1 41719303 --

Water Solubility 29 mg/L (20°C)

42 mg/L (25°C)

46879701

41719303

--

Log Pow (22.5°C) 2.88 46879701 --

Vapor pressure (25°C) 9.19 x10-6 Pa 46894801 --

Henry’s law constant 7.39 x10-5 Pa·m3/mol None Calculated assuming 

solubility at 20°C

Persistence2

Hydrolysis (pH 5, 7, and 9) >500 days3 41418804

Acceptable

4% decline at 30 days

Aqueous Photolysis (t 1⁄2 ) 43 days 41418805

Acceptable

--

Soil Photolysis (t 1⁄2 ) 173 days3 41719302

Acceptable

~14% decline at 30 

days

Aerobic Soil Metabolism (t 1⁄2 ) 372 days 41719303

Acceptable

--

Anaerobic Soil Metabolism (t 1⁄2 ) 1000 days3 41418806

Acceptable

Based on 60 days of 

anaerobic exposure 

Aerobic Aquatic Metabolism (t 1⁄2 ) 33, 48, and 231 days* 42260501

Acceptable

45703101

Supplemental

* t 1⁄2 = 231 days 

based on 24.7 % 

decline at study 

termination

Anaerobic Aquatic Metabolism 

(t 1⁄2 )

5 days 42661901

Acceptable

--

O

N

CH3

NH CH3

Cl

Cl
8

Parameter Value Reference

(MRID unless 

specified)

Comments

Mobility

Koc

Kads

468-1666 mL/g

7.9-28

44490501

(“Upgradeable”)

Supplemental

--

Field Dissipation

Aquatic Field Dissipation (t 1⁄2 ) 115-142 days 43978901

43762901

“Satisfied”

Classification 

TBD

t 1⁄2 based on 

combined data for 

slope and berm soils

Dissipation (t 1⁄2 ) 73-139 days 44654001

44865001

Acceptable

--

1 http Terrestrial Field://www2.epa.gov/tsca-screening-tools/epi-suitetm-estimation-program-interface 2 Half-lives may be recalculated at the time of risk assessment using the most up-to-date guidance. 3 Half-life was extrapolated well beyond the study duration.

a) Transformation Products

Several degradates of diuron were identified in the available laboratory and field studies: four major 

(mCPDMU (once-dechlorinated diuron), PDMU (twice-dechlorinated diuron), DCPMU (oncedemethylated diuron), and mCPMU (once-dechlorinated, once-demethylated diuron); >10% applied)

and three minor (3,4-DCA7

, DCPU (twice-demethylated diuron), and TCAB8; <10% applied)9. DCPMU is 

also a degradate of linuron and 3,4-DCA is also a degradate of linuron and propanil. Degradate 

characteristics are reported in Table 2.

Limited data are available for the four major degradates of diuron. Laboratory transformation data are 

only available for mCPDMU, which is stable to hydrolysis, aerobic soil metabolism, and aquatic 

metabolism (aerobic and anaerobic). The available terrestrial field dissipation study suggests that 

DCPMU is more persistent than diuron. The adsorption coefficients for mCPDMU (mean Koc = 245) and 

PDMU (mean Koc = 70) suggest that they are more mobile than diuron. Although laboratory mobility 

data are not available for DCPMU, the available terrestrial field dissipation study suggests that diuron 

and DCPMU have similar mobility characteristics because both were typically detected at the same 

depth range (0-30 cm). No data are available for mCPMU.

 7 3,4-dichloroaniline 8 Tetrachloroazobenzene (dimer of N-benzyl portion of diuron molecule) 9 Unidentified minor degradates were observed in several studies.
9

Table 2: Physical, Chemical, and Environmental Fate Properties of Major Degradates

Parameter Value Reference

(MRID unless 

specified)

Comments

Chemical mCPDMU Once-dechlorinated 

diuron

Chemical Name N’-(3-chlorophenyl)-N,Ndimethylurea42661901 --

Empirical Formula C9H11ClN2O --

CAS Number 587-34-8 EPI Suite v 4.11 --

Structure 42661901 --

SMILES CN(C)C(=O)Nc1cccc(Cl)c1 EPI Suite v 4.11 --

Selected Physical/Chemical Parameters

Molecular mass 198.65 47311702 --

Persistence2

Hydrolysis (pH 4, 7, and 9) Stable3 46996704

Supplemental

Study conducted at 

50-70°C. Estimated 

to be stable at 20°C

Aerobic Soil Metabolism (t 1⁄2 ) 204 and 5333 47311703

Supplemental

Based on 120 days 

study duration

Aerobic Aquatic Metabolism (t 1⁄2 ) Stable3 47311701

Supplemental

DT50 > 100 days for 

both test systems 

based on 20-38% 

decline at study 

termination. 

t 1⁄2 = 182 days for 

one test system and 

was not determined 

for the other

Anaerobic Aquatic Metabolism 

(t 1⁄2 )

Stable3 47311702

Supplemental

DT50 > 100 days

t 1⁄2 was not 

determined 

CH3

N

CH3

O

NH

Cl
10

Parameter Value Reference

(MRID unless 

specified)

Comments

Mobility

Koc

Kads

139-418 mL/g

2.3-8.0

44490501

(“Upgradeable”)

Supplemental

--

Chemical PDMU Fenuron (twicedechlorinated diuron)

Chemical Name 1,1-dimethyl-3-phenylurea 42661901 --

Empirical Formula C9H12N2O --

CAS Number 101-42-8 EPI Suite v 4.111 --

Structure 42661901 --

SMILES CN(C)C(=O)NC1=CC=CC=C1 EPI Suite v 4.111 --

Selected Physical/Chemical Parameters

Molecular mass 164.21 Calculated --

Mobility

Koc

Kads

38-132 mL/g

0.66-1.7

44490501

(“Upgradeable”)

Supplemental

--

Chemical DCPMU Once-demethylated 

diuron

Chemical Name N-(3,4-dichlorophenyl)-N`-

methylurea

42661901 --

Empirical Formula C8H8Cl2N2O --

Structure --

SMILES CNC(=O)NC1=CC(=C(C=C1)Cl)

Cl

EPI Suite v 4.111 --

Selected Physical/Chemical Parameters

Molecular mass 219.07 Calculated --

CH3

N

CH3

O

NH

 

CH3

NH

O

Cl NH

Cl

 
11

Parameter Value Reference

(MRID unless 

specified)

Comments

Persistence

Terrestrial Field Dissipation (t 1⁄2 ) 217-1733 days 44654001

44865001

Acceptable

--

Chemical mCPMU Once-demethylated, 

once-dechlorinated 

diuron

Chemical Name N`-(3-chlorophenyl)-N`-

methylurea

42661901 --

Empirical Formula C8H9ClN2O --

Structure --

SMILES CNC(=O)Nc1cccc(Cl)c1 EPI Suite v 4.111 --

Selected Physical/Chemical Parameters

Molecular mass 184.63 Calculated --

1 http://www2.epa.gov/tsca-screening-tools/epi-suitetm-estimation-program-interface 2 Half-lives may be recalculated at the time of risk assessment using the most up-to-date guidance. 3 Stable indicates half-life was extrapolated well beyond the study duration or was not determined due to insufficient

decline.

6) Receptors

Consistent with the process described in the Overview Document (USEPA, 2004), the risk assessment for 

diuron relies on a surrogate species approach. Toxicological data generated from surrogate test species, 

which are intended to be representative of broad taxonomic groups, will be used to extrapolate the 

potential effects on a variety of species (receptors) included under these taxonomic groupings. Table 3 

lists the most sensitive endpoints of registrant-submitted studies that are valid for risk assessment. 

Appendix 3 provides a full listing of the aquatic animal and plant toxicity endpoints for diuron.

a) Effects to Aquatic Organisms

Diuron acute toxicity ranges from practically nontoxic to moderately toxic to freshwater fish; the most 

sensitive freshwater fish is the rainbow trout (Oncorhynchus mykiss) (TN1020). In addition to a reduction 

in survival following chronic exposure to fathead minnow (MRID 00141636), McCraren et al. (1969; 

MRID 05020229) observed gill damage and an initial lower growth rate in bluegill sunfish following 

chronic exposure to diuron. Diuron is slightly to moderately toxic to freshwater invertebrates on an 

acute basis. Chronic exposure to Daphnia magna resulted in significant reductions in adult length and 

dry weight. 

CH3

NH

O

NH

Cl

 
12

Diuron is moderately toxic to estuarine/marine fish on acute exposure basis (MRID 41418803). Chronic 

toxicity to this taxon is uncertain due to a non-definitive NOAEC (i.e., effects observed at the lowest test 

concentration). Diuron is moderately to highly toxic to estuarine/marine invertebrates. Chronic 

exposure to mysid shrimp affected growth and reproductive rates (MRID 42500601). 

An acceptable toxicity study with nonvascular aquatic plants with green algae (Pseudokirchneriella 

subcapitata) was submitted (MRID 42218401), but studies with the marine diatom, freshwater diatom 

and blue green algae are needed to quantitatively assess risk to nonvascular aquatic plants. As a result, 

toxicity to nonvascular aquatic plants remains uncertain until new studies with these species are 

submitted and found to be acceptable for quantitative use.

b) Effects to Terrestrial Organisms

Diuron is practically nontoxic to mammals (MRID 00146145) and birds (MRID 00115198) on an acute 

oral basis. When mallard ducks are exposed to diuron on a chronic basis, the reproductive endpoints 

affected are the proportion of eggs set to number eggs laid, number of eggs hatched and hatchling 

survivors at the highest exposure levels. Chronic exposure to laboratory rats results in a reduction in pup 

weight (MRID 41957301).

Based on the results of a single acute contact study on adult honeybees, diuron is practically non-toxic 

to terrestrial invertebrates. Stam et al. (1978; MRID 05016868) found that diuron is “practically nontoxic” to non-target insect species commonly found in cotton fields.

Acceptable endpoints for all ten recommended terrestrial plant species are not available. As a result, the 

full toxicological effects to plants are uncertain until these data are submitted. The 5 species where 

acceptable endpoints for effects on vegetative vigor were submitted were peas, oilseed rape, onion 

sorghum, and wheat. The 5 species where acceptable endpoints for effects on seedling emergence and 

germination were oilseed rape, sugarbeets, tomatoes, onion, and wheat. Based on effects on seedling 

emergence and growth, the onion is the most sensitive monocot and sugar beet is the most sensitive 

dicot (MRID 44113401). In terms of effects on vegetative vigor, the most sensitive monocot is wheat and 

the most sensitive dicot was pea (MRID 44113401). 

Table 3: Most Sensitive Aquatic and Terrestrial Toxicity Endpoints for Diuron 

Taxa Study Type % ai Species Toxicity Value 

& Category

MRID & Status Endpoints 

Affected

Freshwater 

Fish

Acute 

850.1075

95.0 Rainbow 

Trout

Oncorhynchus 

mykiss

96-hr LC50=

1.95 mg ai/L

Moderately 

Toxic

TN 1020

Acceptable

Survival 

Chronic 

850.1400

98.6 Fathead 

Minnow

Pimephales 

promelas

LOAEC= 

0.0618 mg 

ai/L 

NOAEC=

0.0264 mg 

ai/L 

00141636

SupplementalQuantitative

Survival 

Freshwater 

Invertebrates

Acute

850.1010

95.0 Water Flea 

Daphnia 

magna

48-hr EC50=

12 mg ai/L 

Slightly toxic 

42046003

Acceptable

Survival
13

Taxa Study Type % ai Species Toxicity Value 

& Category

MRID & Status Endpoints 

Affected

Chronic

850.1300

98.1 Water Flea

Daphnia 

magna

NOAEC= 0.057

mg ai/L 

LOAEC= 0.11

mg ai/L 

46996702

Acceptable

Length and dry 

weight

Estuarine/ 

Marine Fish

Acute 

850.1075

99.0 Sheepshead 

minnow

Cyprinodon 

variegatus

96-hr LC50=

6.7 mg ai/L 

NOAEL= 3.6 

mg ai/L

Moderately 

Toxic

41418803

Acceptable

Survival

Chronic

850.1400

96.8 Sheepshead 

minnow

Cyprinodon 

variegatus

LOAEC = 0.44 

mg ai/L 

NOAEC< 0.44 

mg ai/L

42312901

SupplementalQualitative

Weight and 

survival

Estuarine/ 

Marine 

Invertebrates

Acute

850.1035

99.0 Mysid shrimp 

Mysidopsis 

bahia

96-hr LC50=

0.16 mg ai/L

Highly Toxic

41418801

Acceptable 

Survival

Chronic

850.1350

96.8 Mysid Shrimp

Mysidopsis 

bahia

NOAEL= 0.96 

mg ai/L

LOAEL= 1.9 

mg ai/L

42500601

Acceptable

Length/ 

reproductive rate

Aquatic 

Plants

Vascular 

850.4400

99.1 Duckweed

Lemma gibba

EC50= 0.013

mg ai/L

NOAEC=

0.00249 mg 

ai/L 

LOAEC= Not 

Reported

46996701

Acceptable

EC50: Biomass

NOAEC: Frond 

number, 

biomass, growth 

rate

Non 

Vascular

850.4500

96.8 Green Algae

Pseudokirchne

riella

subcapitata

EC50= 0.00308 

mg ai/L

NOAEC=

0.00114 mg 

ai/L

LOAEC=

0.00225 mg 

ai/L

42218401

Acceptable

Biomass
14

Taxa Study Type % ai Species Toxicity Value 

& Category

MRID & Status Endpoints 

Affected

Mammals

Acute 98.6 Rat 

Rattus 

norvegicus

Male LD50= 

4721 mg 

ai/kg-bw

Female LD50

>10,000 mg 

ai/kg-bw

Practically 

nontoxic

00146145

Acceptable

Mortality

Chronic 97.1 Rat 

Rattus 

norvegicus

NOAEC= 250 

mg ai/kg-diet

LOAEC= 1750 

mg ai/kg-diet

41957301

Acceptable

Pup weight

Acute 

Inhalation

98.6 Rat 

Rattus 

norvegicus

LC50 >2.09 mg 

ai/L

45866203

Acceptable

Sublethal effects 

included ocular 

and nasal 

discharge, 

irregular 

respiration, 

hunched posture 

and/or 

hypoactivity.

Birds

Acute Oral

850.2100

95.0 Mallard Duck 

Anas 

platyrhynchos

LD50 >2000 

mg ai/kg-bw

Practically 

nontoxic

00115198

Acceptable

No sublethal 

effects. 

Acute 

Dietary

850.2200

95.0 Northern 

Bobwhite 

Quail

Colinus 

virginianus

5-Day LC50= 

1730 mg 

ai/kg-diet

Slightly Toxic

00022923

Acceptable

Mortality

Chronic

850.2300

98.4 Mallard Duck

Anas 

platyrhynchos

NOAEC= 9.80 

mg a.i./kgdiet

LOAEC= 33.3 

mg ai/kg-diet

47311704

Acceptable

Adult body 

weight (male and 

female), total egg 

production and 

fertility

Terrestrial 

Invertebrates

Adult acute 

contact

850.3020

80.0 Honeybee

Apis mellifera

LD50= 145.03

μg ai/bee

Practically 

Nontoxic

00036935 

Acceptable

Mortality

Terrestrial 

Plants

Seedling 

Emergence 

Monocot

850.4100

97.3 Onion Allium 

cepa

EC25= 0.099 lb

ai/A

NOAEL= 0.089 

lb ai/A

44113401 

SupplementalQuantitative

Shoot Dry Weight
15

Taxa Study Type % ai Species Toxicity Value 

& Category

MRID & Status Endpoints 

Affected

Terrestrial 

Plants

Seedling 

Emergence 

Dicot

850.4100

97.3 Sugar Beet 

Beta vulgaris

EC25= 0.092 lb 

ai/A

NOAEL= 0.047 

lb ai/A

44113401 

Supplemental -

Quantitative

Shoot Dry Weight

Vegetative 

Vigor 

Monocot

850.4150

97.3 Wheat

Triticum 

aestivum

EC25= 0.0294 

lb ai/A

NOAEL=

0.0117 lb ai/A

44113401 

SupplementalQuantitative

Shoot Dry Weight

Vegetative 

Vigor 

Dicot

850.4150

97.3 Pea Pisum 

sativum

EC25= 0.0124 

lb ai/A

NOAEL= 

0.0117 lb ai/A

44113401 

SupplementalQuantitative

Shoot Dry Weight

c) Degradate Toxicity 

ECOSAR was used to predict toxicity of the major degradates (>10% formation of applied) due to the

absence of toxicity data. ECOSAR uses quantitative structure activity relationships (QSAR) to predict

toxicity to aquatic organisms. Predicted and observed toxicity values for diuron and major degradates

are listed in Table 4. 

ECOSAR estimates provide no indication that any of the degradates are substantially more or less toxic 

to aquatic taxa than diuron, as all of the predicted toxicities of the degradates are within 1-2 orders of 

magnitude of the toxicity of diuron. Estimates suggest that PDMU may be the least toxic of the 

degradates. In most cases, ECOSAR provided reasonable predictions of diuron toxicity to aquatic 

organisms based on comparison of empirically-derived diuron toxicity endpoints to ECOSAR estimates.

However, there is less confidence in toxicity estimates for green algae and chronic exposure to 

estuarine/marine invertebrates because of the greater difference between the predicted and measured 

toxicity of diuron. Data are not available for any of the degradates to specifically judge confidence in 

ECOSAR estimates of the degradates.

Table 4: Acute and Chronic (mg ai/L) Toxicity Values Predicted through ECOSAR Modeling

Exposure 

(Acute/ 

Chronic) 

Taxa

Parent Degradate

Diuron 

(Lab 

Studies)

Diuron 

(Predicted)

DCPMU mCPDMU PDMU mCPMU

Acute Daphnia magna

LC50

12 5.71 8.59 20.48 71.25 30.48

Chronic Daphnia magna

NOAEC

0.06 0.55 0.75 1.45 3.72 1.95

Acute Freshwater fish 

LC50

1.4 18.21 25.56 52.82 148.64 73.34

Chronic Freshwater fish

NOAEC

0.06 0.43 0.58 1.10 2.72 1.46
16

Exposure 

(Acute/ 

Chronic) 

Taxa

Parent Degradate

Diuron 

(Lab 

Studies)

Diuron 

(Predicted)

DCPMU mCPDMU PDMU mCPMU

Acute Estuarine/ 

marine fish LC50

6.7 9.81 11.61 16.89 28.21 19.77

Chronic Estuarine/ 

marine fish 

NOAEC

-- 0.521 -- -- -- --

Acute Estuarine/marine 

invertebrates 

(Mysidopsis 

bahia)

LC50

0.16 2.91 4.12 8.67 25.07 19.77

Chronic Estuarine/marine 

invertebrates 

(Mysidopsis 

bahia)

NOEL

0.96 0.01 0.02 0.05 0.18 0.07

Acute Green algae

EC50

0.004 0.17 0.19 0.27 0.41 0.30

d) Ecological Incidents 

The Ecological Incident Information System (EIIS) maintained by the Environmental Fate and Effects 

Division, and the Avian Incident Monitoring System (AIMS) maintained by the American Bird 

Conservancy, were searched on November 3, 2015 to locate incidents resulting from the use of diuron. 

There were 42 incidents recorded in the EIIS database for diuron involving non-target species. Eight

incidents impacted aquatic taxa, 32 impacted terrestrial plants, and 2 impacted terrestrial/aquatic

animals. A summary list of all EIIS incidents is included in Appendix 4. 

The AIMS database recorded one incident in South Carolina where 70 birds were killed. In this case, 

diuron was applied as a mixture with isopropylamine salt of glyphosate and metsulfuron-methyl. No 

information was provided about the specific cause of the incident. 

In addition to the incidents recorded in EIIS and AIMS, additional incidents are reported to the Agency in 

aggregated form. Pesticide registrants report certain types of incidents to the Agency as aggregate 

counts of incidents occurring per product per quarter. Ecological incidents reported in aggregate 

reports include those categorized as ‘minor fish and wildlife’ (W-B), ‘minor plant’ (P-B), and ‘other nontarget’ (ONT) incidents. ‘Other non-target’ incidents include reports of adverse effects to insects and 

other terrestrial invertebrates. There are 44 reported incident summaries as of November 4, 2015. 

These summaries reported 18 minor fish and wildlife incidents and 33 minor plant incidents (several 

summaries reported more than one incident, and as a result some of the incident summaries include 

both terrestrial and plant incidents). These incident reports do not differentiate between conventional 

and antimicrobial uses. 
17

7) Exposure Pathways of Concern 

a) Conventional Uses

The Screening Imbibition Program (SIP v.1.0) and the Screening Tool for Inhalation Risk (STIR v.1.0) are

upper bound screening tools used during the problem formulation phase of registration review to assess 

the potential for exposure to birds and mammals through drinking water and inhalation, respectively.

These tools estimate risk to birds based on available mammalian and avian toxicity endpoints. The 

inputs and outputs for avian and mammalian risk are available for SIP in Appendix 5 and STIR in 

Appendix 6. 

SIP indicates that chronic exposure through drinking water alone may be a potential concern for birds; 

however, there is not an acute concern for birds nor and acute or chronic concern for mammals.

The STIR model indicates that avian exposure from the inhalation of droplets may be a potential 

exposure pathway of concern for birds. The non-definitive endpoints for avian acute oral exposure (LD50

>2000 mg ai/kg-bw) and acute mammalian inhalation exposure (LC50 >2.09 mg ai/L) indicate that there 

is uncertainty about the magnitude of the potential risk presented by this exposure pathway. The STIR 

model indicates that inhalation exposure through droplets remains a concern until either the inhalation 

LC50 approaches 7mg ai/L or the acute oral LD50 approaches 6900 mg ai/kg-bw. These hypothetical 

endpoints are 3.45x higher (indicating a 3.45x reduction in toxicity) than the highest concentrations 

tested in each study. As the available studies did not observe effects at the highest concentrations 

tested, it is possible that the actual LC50 and LD50 values are more than 3.45x less toxic. As a result, an

avian inhalation study is not requested at this time. 

b) Antimicrobial Uses

AD intends to conduct an aquatic ecological risk 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.

8) Analysis Plan

a) Stressors of Concern

i) Ecological Risk Assessment

For both the conventional and antimicrobial uses, the stressors of concern are diuron and major 

degradates mCPDMU and DCPMU (formed >10% of applied). Although PDMU and mCPMU are major 

degradates and could potentially be considered stressors of concern, they are expected to have only a 

minor impact on EECs, in part because the only evidence of their formation at >10% is by anaerobic 

aquatic metabolism. Nevertheless, they may be considered if it appears that risk conclusions may be 

impacted (past risk assessments suggest that risk conclusions would not be impacted). No toxicity 

studies have been submitted that evaluate the toxicity of any major or minor degradates to aquatic or 

terrestrial taxa.

10 Based on predictions from ECOSAR modeling, there is no evidence that major

degradates are more or less toxic than diuron to aquatic organisms. In the absence of toxicity data that 

indicates otherwise, the stressors of concern (mCPDMU and DCPMU; potentially PDMU and mCPMU) 

 10 DCPMU also forms from linuron, an herbicide like diuron. No DCPMU toxicity data have been submitted for the 

linuron registration. 
18

will be assumed to have similar toxicity to aquatic taxa as diuron. Furthermore, a TTR approach may be 

used to estimate aquatic exposure. DCPMU is the only stressor of concern for terrestrial environments 

because mCPDMU, PDMU, and mCPMU only form as major degradates in aquatic fate studies. In the 

absence of toxicity data, it will be assumed that diuron and DCPMU are similar in toxicity to terrestrial 

organisms. 

ii)Drinking Water Assessment

Conventional Uses

Diuron, mCPDMU, and DCPMU will be considered the stressors of concern in the diuron DWA, 

consistent with the conclusions of the Metabolism Assessment Review Committee (MARC) of the Health 

Effects Division (HED) (USEPA, 2001b). 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 DWA will be based on modeled estimates of exposure but will also include a summary of available 

surface and ground water monitoring data. The potential use of monitoring data in place of chronic DW 

EECs will be reevaluated based on the availability of data reflecting present use patterns.

Antimicrobial Uses

AD does not anticipate the need to conduct a DWA for antimicrobial uses because it is assumed that 

residues resulting from crop uses will be higher than those resulting from leaching from structural 

building elements. Therefore, it is anticipated that the drinking water residues incorporated into the 

human dietary assessment will be based on only conventional use scenarios. 

b) Measures of Exposure

The Agency will use standard available models to evaluate potential exposures to aquatic and terrestrial 

organisms.

11

i) Available Monitoring Data

EFED is aware of monitoring data collected by federal and state agencies. In 2003, monitoring data 

collected in Florida, Georgia, and California were evaluated and considered robust enough to use in 

place of chronic EDWCs (USEPA, 2003d). The risk assessment will incorporate available data on diuron 

and degradation products.

ii) Down-the-Drain (DtD) Exposure from Antimicrobial Uses

There are 17 products with antimicrobial uses of diuron for use in outdoor building materials. The 

diuron content (% w/w) varies among products, ranging from 0.12-0.61 % (paints, stains, and coatings), 

0.09-0.61% (stucco, caulks, sealants, masonry coatings, and plaster), 0.07-0.61 % (joint sealants), and 

0.25-0.61 % (roof coatings). According to the RED (USEPA, 2003c), about 1 % of paints contained diuron

at that time. AD does not expect any DtD exposure from diuron based on the registered antimicrobial 

 11 http://www2.epa.gov/pesticide-science-and-assessing-pesticide-risks/models-pesticide-risk-assessment
19

uses and the physical/chemical and environmental fate properties of diuron (Table 1) and its degradates 

(Table 2). While no wastewater treatment plant exposure is expected, there is limited potential for 

environmental exposure from diuron that may leach from paints and coatings used in structural building 

elements.

c) Measures of Effect

Toxicity data presented in Table 3 and Appendix 3 of this problem formulation will be used to calculate 

risk quotients. Any additional information submitted by the registrant or found in the open literature 

prior to conduct of the risk assessment will also be considered. The open literature studies are identified 

using EPA's ECOTOXicology database (ECOTOX), which employs a literature search engine for locating 

chemical toxicity data for aquatic life, terrestrial plants, and wildlife. The evaluation of both sources of 

data can also provide insight into the direct and indirect effects of pesticides on biotic communities from 

loss of species that are sensitive to the chemicals and from changes in structure and functional 

characteristics of the affected communities.

9) Endangered Species Assessment

Consistent with EPA’s responsibility under the Endangered Species Act (ESA), the Agency will evaluate 

risks to federally listed threatened and endangered (listed) species from registered uses of pesticides in 

accordance with the Joint Interim Approaches developed to implement the recommendations of the 

April 2013 National Academy of Sciences (NAS) report, Assessing Risks to Endangered and Threatened 

Species from Pesticides. The NAS report12 outlines recommendations on specific scientific and technical 

issues related to the development of pesticide risk assessments that EPA and the Services (U.S. Fish and 

Wildlife Service and National Marine Fisheries) must conduct in connection with their obligations under 

the ESA and FIFRA. EPA will address concerns specific to diuron in connection with the development of 

its final registration review decision for diuron. 

In November 2013, EPA, the Services, and USDA released a white paper containing a summary of their 

joint Interim Approaches for assessing risks to listed species from pesticides. These Interim Approaches 

were developed jointly by the agencies in response to the 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. Details of the joint Interim Approaches are contained in the 

November 1, 2013 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. 13

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, this ecological problem formulation supporting the Preliminary Work Plan for diuron does not 

describe the specific ESA analysis, including effects determinations for specific listed species or 

designated critical habitat, to be conducted during registration review. While the agencies continue to 

develop a common method for ESA analysis, the planned risk assessment for the registration review of 

diuron will describe the level of ESA analysis completed for this particular registration review case. This 

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. Once 

 12 http://www.nap.edu/catalog/18344/assessing-risks-to-endangered-and-threatened-species-from-pesticides 13http://www2.epa.gov/endangered-species/interim-approaches-pesticide-endangered-species-act-assessmentsbased-nas-report
20

the agencies have fully developed and implemented the scientific methods necessary to complete risk 

assessments for listed species and their designated critical habitats, these methods will be applied to 

subsequent analyses of diuron as part of completing this registration review.

Two endangered species assessments have been conducted for diuron: Determination of Risks of Diuron 

Use to Federally Threatened California Red-legged Frog (USEPA, 2009) and the Endangered and 

Threatened Salmon and Steelhead Assessment (USEPA, 2003b).

10) Endocrine Disruptor Screening Program 

Diuron was not included in the first group of chemicals issued an order to conduct Tier 1 endocrine 

disruption screening program (EDSP) testing.

14 Diuron was included in the second group of 109 

chemicals issued in order to conduct Tier I EDSP testing. 

11) Preliminary Identification of Data Gaps 

a) Environmental Fate

Table 5 lists the status of the fate and transport data requirements for diuron. Four degradates of 

diuron were identified as major (forming > 10% of applied).

15 A limited number of laboratory studies are 

available for mCPDMU (hydrolysis, aerobic soil metabolism, aerobic and anaerobic aquatic metabolism, 

adsorption/desorption) and PDMU (adsorption/desorption) whereas none are available for DCPMU and 

mCPMU. These degradates will be included in aquatic EECs for both ecological risk assessment 

(mCPDMU and DCPMU and potentially PDMU and mCPMU if risk conclusions will be impacted) and 

drinking water assessments (mCPDMU and DCPMU based on the most recent MARC memo (USEPA, 

2001b)). Conservative assumptions will be made about physical and chemical properties of degradates 

in the absence of data and sources such as EPI Suite16 may be used to estimate values. Study-sourced 

environmental fate and physiochemical properties of the major degradates may reduce uncertainty in

the aquatic exposure and drinking water assessments. 

Table 5: Environmental Fate Data and Data Gaps for Diuron

Guideline Data 

Requirement MRID Classification Data Gap? Comments

835.2120 Hydrolysis 41418804 Acceptable No 1 Pending review

2 The available study tested one soil 

type; four are recommended. It is 

unlikely that additional data will 

demonstrate that diuron is not 

stable. Therefore, EFED does not 

recommend requesting additional 

data.

835.2240 Aqueous 

Photolysis 41418805 Acceptable No

835.2410 Soil Photolysis 41719302 Acceptable No

835.4100 Aerobic Soil 

Metabolism

41719303

44221001

Acceptable 

In Review Yes1

835.4200 Anaerobic Soil 

Metabolism 41418806 Acceptable Yes2

 14 http://www2.epa.gov/endocrine-disruption 15 Other major degradates could be identified in studies under review. 16 http://www2.epa.gov/tsca-screening-tools/epi-suitetm-estimation-program-interface
21

Guideline Data 

Requirement MRID Classification Data Gap? Comments

835.4300

Aerobic 

Aquatic 

Metabolism

42260501

45703101

Acceptable

Supplemental No 3 The available study tested one 

water-sediment system; two are 

recommended. Although the data 

requirement is not filled, additional 

data are not expected to 

substantially change exposure 

estimates. EFED does not 

recommend requesting additional 

data; however, conservative 

assumptions will be made following 

current EFED guidance. 

4 The available study tested three 

soil types; five are recommended 

including one with organic matter 

(OM) content ≤ 1%. Data on 

additional soils are not expected to 

differ substantially from the 

available data based on preliminary 

test results on two low OM content 

soils that was presented in the 

available study. EFED does not 

recommend requesting additional 

data.

5 Guideline satisfied; study 

classification to be determined 

(TBD).

6 ECM are available; however, ILV 

are required for diuron and 

DCPMU.

7 ECM are available for diuron, 

DCPMU, and mCPDMU; however, 

ILV are required for these 

compounds. ECM and ILV are 

required for PDMU and mCPMU.

835.4400

Anaerobic 

Aquatic 

Metabolism

42661901 Acceptable Yes3

835.1230

835.1240

Leaching

Adsorption/

Desorption

44490501 Supplemental Yes4

835.6100

Terrestrial 

Field 

Dissipation

44654001

44865001 Acceptable No

835.6200 Aquatic Field 

Dissipation

43762901

43978901 TBD5 No

850.6100

Analytical 

Method in Soil 41719305 Not applicable Yes6

Analytical 

Method in 

Water

47033303 Not 

applicable Yes7

850.1730 Accumulation 

in Fish 00025491 In Review Yes1

NonGuidelineSpecial 

Leaching 

Study - Paint

- - Yes

BOLD = Recommended Studies
22

b) Effects

Tables 6 and 7 identify ecological effect studies by MRID that offer data for each guideline requirement, 

as well as study classifications and whether or not further data are needed in order to conduct a risk 

assessment. Rationale for the additional data requested is present below the tables. 

EFED is recommending the submission of data to characterize the toxicity of major degradates mCPDMU 

and DCPMU to non-vascular aquatic plants for two reasons. First, ECOSAR estimates do not provide 

evidence that they are more or less toxic than diuron to aquatic plants; therefore, in the absence of data 

they will be assumed equal in toxicity to diuron. However, compared to other taxa there is less 

confidence in the presumption of equal toxicity of diuron and degradates to aquatic plants due to the 

greater difference between the predicted and measured toxicity of diuron. Second, previous 

assessments identified a risk concern for aquatic plants based on exposure to only diuron; thus, the risk 

conclusion (i.e., there is a risk concern) would not have changed if the degradates had been considered 

in the risk assessment. Nonetheless, assumptions made about degradate toxicity to aquatic nonvascular plants could have an impact on any future mitigation efforts. Data are recommended to 

confirm the assumption of equal toxicity of mCPDMU, DCPMU, and diuron given the greater uncertainty 

about this assumption for aquatic non-vascular plants than for other taxa.

At this point, study-sourced data on toxicity of mCPDMU and DCPMU to fish and invertebrate taxa are

not recommended because ECOSAR was able to provide reasonable toxicity estimates for degradates 

that suggested similar toxicity to diuron. In the absence of toxicity data, mCPDMU, DCPMU, and diuron 

will be assumed equally toxic to fish and aquatic invertebrates.

Table 6: Data Gap Table of Aquatic Effect Data for Diuron and Major Degradates

Guideline Data requirement MRID Classification Data 

Gap?

Comments

850.1010 Freshwater 

Invertebrate Acute 

Toxicity 

42046003 Acceptable No -

850.1025 Estuarine/Marine

Invertebrate Acute 

Toxicity 

41418801 Acceptable No -

850.1075 Freshwater Fish 

Acute Toxicity

TN 1020/ 

STODIU04

Acceptable No -

850.1075 Estuarine/Marine 

Fish Acute Toxicity

41418803 Acceptable No -

850.1300 Freshwater 

Invertebrate Life 

Cycle

46996702 Acceptable No -

850.1350 Estuarine/Marine

Invertebrate Life 

Cycle

42500601 Acceptable No -
23

Guideline Data requirement MRID Classification Data 

Gap?

Comments

850.1400 Freshwater Fish 

Early-Life Stage

00141636 Supplemental No Raw data are unavailable and 

test concentrations were not 

analytically confirmed 

throughout the study. Study 

may be used to fulfil guideline 

requirement for a Freshwater 

Fish Early-Life Stage test. 

850.1400 Estuarine/Marine

Fish Early-Life 

Stage

42312901 Supplemental Yes Study does not fulfill 

guideline requirements. 

Significant reductions in 

weight and/or survival at all 

concentrations meant that a

NOAEC value could not be 

established. In the absence of 

data, endpoints from linuron 

may be used in risk 

assessments. 

850.4400 Aquatic Vascular 

Plant Toxicity Test 

using Lemna spp. 

46996701 Acceptable No -

850.4500 Nonvascular 

Aquatic Plants: 

Algal Toxicity

Pseudokirchneriella 

subcapitata

42218401 Acceptable No -

850.4500 Nonvascular 

Aquatic Plants: 

Freshwater diatom

Navicula 

pelliculosa

47936502 Supplemental 

(qualitative)

Yes The shorter than 

recommended duration of the 

study means that this study 

may only be used

to assess risk qualitatively and 

does not satisfy guideline 

requirements.

850.4500 Nonvascular 

Aquatic Plants: 

Marine diatom

Skeletonema

costatum

- - Yes -

850.4550 Nonvascular 

Aquatic Plants: 

Blue Green Algae

Anabaena flosaquae

47936501 Supplemental 

(qualitative)

Yes The shorter than 

recommended duration of the 

study means that this study 

may only be used

to assess risk qualitatively and 

does not satisfy guideline 

requirements.
24

Guideline Data requirement MRID Classification Data 

Gap?

Comments

Degradate DCPMU There is uncertainty in the 

ECOSAR estimates, but 

ECOSAR suggests that 

degradates are potentially 

similar to diuron in toxicity. 

Recommending submission of 

algae data to refine risk 

conclusions given ECOSAR 

estimates and the mode of 

action as an herbicide.

Toxicity data are 

recommended only for the 

aquatic plant species most 

sensitive to diuron. The most 

sensitive aquatic plant species 

will be determined upon 

review of aquatic plant 

studies. 

850.4500/ 

850.4550

Algal/ 

Cyanobacteria

Toxicity

- - Yes

Degradate mCPDMU

850.4500/ 

850.4550

Algal/ 

Cyanobacteria

Toxicity

- - Yes

BOLD = Recommended Studies

Table 7: Data Gap Table of Terrestrial Effects Data for Diuron

Guideline Data 

requirement

Submitted 

Studies

(MRID)

Classification Data 

Gap?

Comments

850.2100 Avian Acute Oral 

Toxicity (Upland 

game or 

waterfowl 

species)

00115198 Acceptable No -

850.2100 Avian Acute Oral 

Toxicity 

(Passerine 

species)

- - Yes Measures of effect from a 

non-passerine species could 

potentially underestimate 

diuron toxicity to passerine 

species, consequently, 

additional information on 

diuron toxicity to a 

passerine species is needed 

to reduce the uncertainty. 

850.2200 Avian Dietary 

Toxicity

00022923 Acceptable No -
25

Guideline Data 

requirement

Submitted 

Studies

(MRID)

Classification Data 

Gap?

Comments

850.2300 Avian 

Reproduction

47311704 Acceptable Yes Data submitted are for 

mallard duck only; data are 

also required for an upland 

bird species.

850.3020 Tier I- Honeybee 

Acute Adult 

Contact Toxicity

00036935 Acceptable No -

NonGuideline

(OECD 213)

Tier I- Honeybee 

Acute Adult Oral 

Toxicity

- - Yes -

NonGuidelineTier I-Honeybee 

Adult Chronic 

Oral Exposure

- - Yes -

850.3030 Tier II-Honeybee 

Toxicity of 

Residues on 

Foliage

- - No The acute contact 48-hr 

LD50 was above 100 μg/bee. 

This study is triggered if 

contact toxicity is less than 

11 μg/bee.

NonGuidelineTier I- Honeybee 

Larval Acute and 

Chronic Oral 

Exposure 

- - Yes -

NonGuidelineTier II- Nectar 

and Pollen 

Residue Study 

for Insect 

Pollinators

- - Yes If risks are identified in the 

Tier I risk assessment then 

Tier II studies may be 

needed. Diuron is systemic 

and some registered uses 

are pollinator attractive 

crops17, so exposure 

through translocation to 

nectar and pollen could be a 

route of exposure to insect 

pollinators. In addition, 

incidental residues may 

occur on or near the 

treatment site. 

NonGuideline

(OECD 75)

Tier II- SemiField Testing for 

Honeybees

(tunnel and 

feeding studies)

- - Yes

850.3040 Tier III- Field 

Testing for 

Pollinators

- - Yes If risks are identified in the

Tier II risk assessment then 

Tier III field studies may be 

needed.

 17 USDA, 2014. Attractiveness of Agricultural Crops to Pollinating Bees for the Collection of Nectar and/or Pollen. 
26

Guideline Data 

requirement

Submitted 

Studies

(MRID)

Classification Data 

Gap?

Comments

850.4100 Seedling 

Emergence and 

Seedling Growth 

44113401 Supplemental Yes The seedling emergence and 

growth study (MRID 

44113401) submitted valid 

endpoints for the following 

species: 

• Oilseed Rape

• Sugar Beet

• Tomato

• Onion

• Wheat

The vegetative vigor study 

submitted valid endpoints 

for the following species: 

• Pea

• Oilseed Rape

• Onion

• Sorghum

• Wheat

To fulfil guideline 

requirements, valid 

endpoints must be 

submitted for the required 

number and type of species. 

850.4100 Seedling 

Emergence and 

Seedling Growth 

42398501 Invalid

850.4150 Vegetative Vigor 44113401 Supplemental Yes

850.4150 Vegetative Vigor 42398501 Invalid Yes

BOLD = Recommended Studies

12) References

Johnson, W. and Finley, M., 1980. Handbook of acute toxicity of chemicals to fish and aquatic 

invertebrates. Resource Publication 137. U.S. Fish and Wildlife Service, Washington, D.C. 98p. 

McCraren, J.P., Cope, O.B., Eller, L., 1969. Some chronic effects of diuron on bluegills. Weed Science 

17(4): 497-504. MRID 05020229

Stam, P.A., D.F., Clower, J.B., Graves, and P.E., Schilling., 1978. Effects of certain herbicides on some 

insects and spiders found in Louisiana cotton fields. Journal of Economic Entomology. 71 

(3):477-480. MRID 05016868.

USEPA, 2001a. Drinking Water Assessment for Diuron and its Degradates. Environmental Fate and 

Effects Division, Office of Pesticide Programs, U.S. Environmental Protection Agency. D275046.

USEPA, 2001b. Diuron. Results of the Health Effects Division (HED) Metabolism Assessment Review 

Committee (MARC) Meeting Held on 03-July-2001. Health Effects Division, Office of Pesticide 

Programs, U.S. Environmental Protection Agency.
27

USEPA, 2003a. Environmental Risk Assessment for the Reregistration of Diuron. Environmental Fate and 

Effects Division, Office of Pesticide Programs, U.S. Environmental Protection Agency. D275045.

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

USEPA, 2003c. Registration Eligibility Decision (RED) for Diuron. Office of Pesticide Programs, U.S.

Environmental Protection Agency. 

http://archive.epa.gov/pesticides/reregistration/web/pdf/diuron_red-2.pdf

USEPA, 2003d. Surface Water Monitoring Data for Diuron. Environmental Fate and Effects Division, 

Office of Pesticide Programs, U.S. Environmental Protection Agency. D281404.

USEPA, 2004. Overview of the Ecological Risk Assessment Process in the Office of Pesticide Programs. 

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

Protection Agency. January 23, 2004.

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

USEPA, 2014a. BEAD Chemical Profile (BCP) for Registration Review: Diuron (035505). 

USEPA, 2014b. Diuron (035505) Screening Level Usage Analysis (SLUA).

USEPA, 2014c. Revised Diuron (035505) Label Use Report Package in Support of Registration Review. 

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

Protection Agency.
28

Appendix 1: Maximum Application Rates of Diuron (Conventional Uses)

The purpose of Table 1-1 is to summarize the maximum application rates reported in the most recent 

LUIS report (USEPA, 2014c). It does not include antimicrobial use rates which are based on applications 

to the paint or building material as they are being manufactured. The antimicrobial exposure 

assessment will be based on the amount leached from the materials and the amount of materials 

assumed to be used in the watershed and not based on the use rate. 

The table is not intended to capture all the nuance of the labeled rates; therefore, it should not be relied 

upon for risk assessment. For example, in some cases the highest maximum application rate may be 

applied to only a specific geographic area, using a specific application technique, under specific timing 

(e.g., relative to season or planting), etc. and a lower maximum application rate would apply under 

different restrictions. Furthermore, in some cases some labels may provide information such as the 

maximum number of applications per year and others do not. In these and similar cases either the lack 

of information or the most conservative value is reported below. For example, for a given 

use/application rate if the maximum number of applications is reported on one label and not another 

then NS (not stated) is reported below. Likewise, if an annual application limit is reported on one label 

and not another then NS is reported below. Along the same lines, if a use has a lower maximum single 

application rate without an associated annual limit then that rate is reported below in addition the 

highest maximum single application rate (e.g., see banana). The registration review risk assessment will 

be based on current label information at the time of assessment as provided by BEAD.

Table 1-1 A Summary of Maximum Application Rates of Diuron (Conventional Uses)

Use Max Single 

Application Rate 

(lb ai/A)

Max # 

Applications per 

Year/Crop Cycle

(lb ai/A)

Max 

Application 

Rate per Year/

Crop Cycle

(lb ai/A)

Minimum 

Retreatment 

Interval (days)

Airports/Landing Fields 121 NS 12 90

Alfalfa 2.4 1 2.4 NS

Apple 3.2 NS/NS 3.2/3.2 90

Artichoke 3.2 NS NS NS

Asparagus 2.4 2 NS NS

3.2 1 NA NA

Banana 4.8 NS 9.6215 42

2.4 NS NS NS

Barley 1.6 1/1 NS/NS NS

Blueberry 3.2 NS NS NS

Caneberries 1.6 2 NS NS

2.4 NS/1 NS/NS NS

Citrus 3.2 NS NS NS

6.4 NS 6.4 NS

Clover 1.6 1/1 NS/NS NS

Commercial Fishery Water Systems 3.22 9 NS 7

0.0253 9 NS 7

Corn, Field 1.1 NS NS NS
29

Use Max Single 

Application Rate 

(lb ai/A)

Max # 

Applications per 

Year/Crop Cycle

(lb ai/A)

Max 

Application 

Rate per Year/

Crop Cycle

(lb ai/A)

Minimum 

Retreatment 

Interval (days)

Cotton (Unspecified) 1.6 NS 2.2 21

2.2 NS 2.2 21

Drainage Systems 12 NS 12.0269 90

Filbert (Hazelnut) 2.2 NS/NS 3.2072/3.2072 150

Gooseberry 1.6 2/2 NS/NS NS

2.4 NS/1 NS/NS NS

Grapes 4 NS/NS 8.0179/8 90

Grasses Grown For Seed 2.4 1 2.4054 NS

Household/Domestic Dwellings Outdoor 

Premises 121 NS 12 90

Industrial / Construction Areas (Outdoor) 8 NS 12 90

121 NS 12 90

Irrigation Systems 12 NS 12.0269 90

Macadamia Nut (Bushnut) 4.8 NS 8.0179 NS

Nonagricultural Outdoor 

Buildings/Structures 121 NS 12 90

Nonagricultural Rights-OfWay/Fencerows/Hedgerows

8 NS 12 90

121 NS 12 90

Nonagricultural Uncultivated Areas/Soils 12 2 NS 90

Nonagricutural Uncultivated Soil 

Sterilization 121 NS 12 90

Oats 1.6 1 NS NS

Olive 1.6 2 NS NS

Ornamental and/or Shade Trees 4 NS NS NS

Ornamental Herbaceous Plants 4.4 NS/1 NS/4.3796 NS

4 NS 6.0134 NS

Ornamental Nonflowering Plants 3.2 NS/1 NS/NS NS

Ornamental Ponds/Aquaria 0.00014 NS NS NS

NDC NS NS 30

Papaya 4 NS NS NS

Pastures 2.4 NS NS NS

Paths/Patios 121 NS 12 90

Paved Areas (Private Roads & Sidewalks) 121 NS 12 90

Peach 3 NS NS NS

Pear 3.2 NS NS NS

Peas (Unspecified) 1.6 NS NS NS

Pecan 3.2 1 NS NS

Peppermint 2.4 NS NS NS

Pineapple 5 NS NS NS

6.4 NS/NS NS/12.8 NS

Plantain 4.8 NS 9.6215 42

2.4 NS NS 42

Pricklypear Cactus Pads 3.5 NS NS NS
30

Use Max Single 

Application Rate 

(lb ai/A)

Max # 

Applications per 

Year/Crop Cycle

(lb ai/A)

Max 

Application 

Rate per Year/

Crop Cycle

(lb ai/A)

Minimum 

Retreatment 

Interval (days)

Recreational Areas 121 NS 12 90

Rights-Of-Way (Railroad) 12 NS 12 90

Sorghum 0.4 NS NS NS

Spearmint 2.4 NS NS NS

Sugarcane 6.4 NS/NS NS/16 NS

5 NS 9.62 NS

4.8 NS NS NS

Trefoil 1.6 NS/1 NS/NS NS

Triticale 1.6 NS/1 NS/NS NS

Urban Areas 121 NS 12 90

Utility Poles / Rights-Of-Way 121 NS 12 90

Walnut (English/Black) 3 NS/NS 3.2/3.2072 150

Wheat 1.6 NS NS NS
31

Appendix 2: Diuron Degradates Identified in Environmental Fate Studies

Table 2-1. A Summary of Diuron Degradates Identified in Environmental Fate Studies

Degradate 

Name

Chemical Name Major Degradates 

(>10% formed)

Minor Degradates 

(<10% formed)

Maximum Percent Formed1

mCPDMU N’-(3-chlorophenyl)-

N,N-dimethylurea

Aerobic Aquatic Metabolism: 

25%, total system (study 

termination; increasing)

MRID 42260501

24.1%, total system (day 55; 

decreasing to study 

termination)

MRID 45703101

Anaerobic Aquatic Metabolism: 

76-83%, total system (day 7-98; 

decreasing to study 

termination)

MRID 42661901

--

PDMU

(fenuron)

1,1-dimethyl-3-

phenylurea

Anaerobic Aquatic Metabolism: 

13%, total system (day 288; 

decreasing to study 

termination)

MRID 42661901

--
32

Degradate 

Name

Chemical Name Major Degradates 

(>10% formed)

Minor Degradates 

(<10% formed)

Maximum Percent Formed1

DCPMU N-(3,4-

dichlorophenyl)-N’-

methylurea

Aerobic Soil Metabolism: 21.7% 

(study termination; increasing)

MRID 41719303

Anaerobic Soil Metabolism: 

10.3% (day 45 of anaerobic 

conditions; relatively constant 

through study termination)

MRID 41418806

Terrestrial Field Dissipation: 

13.7% of maximum diuron 

detection; 0-90 cm core (day 22 

FL site; decreasing to study 

termination)

MRID 44654001 & 44865001

Soil Photolysis: 3.6% (study 

termination)

MRID 41719302

Aerobic Aquatic Metabolism: 9.2%, 

total system (day 22; relatively 

constant through study 

termination)

MRID 42260501

4.4%, total system (day 91; 

constant to study termination)

MRID 45703101

4.1%, total system (study 

termination; increasing)

MRID 45703101

Terrestrial Field Dissipation: 6.9% of 

maximum diuron detection; 0-90 

cm core (day 29 MS site; decreasing 

to study termination)

MRID 44654001 & 44865001

9.9% of maximum diuron detection; 

0-90 cm core (day 120 CA site; 

decreasing to study termination)

MRID 44654001 & 44865001

Aquatic Field Dissipation: detected 

in berm soil, slope soil, and channel 

sediment (only silt loam application 

site); estimated < 10% of diuron 

detected immediately after 

application in berm and slope soil. 

MRID 43762901 & 43978901

mCPMU N’-(3-chlorophenyl)-

N’-methylurea

Anaerobic Aquatic Metabolism: 

21%, total system (study 

termination; increasing)

MRID 42661901

Aerobic Aquatic Metabolism: 1.1%, 

total system (study termination; 

increasing)

MRID 42260501

3,4-DCA 3,4-

dichlorobenzeneamine

-- Hydrolysis: 0.5% (study 

termination)

MRID 41418804

Soil Photolysis: 0.029% (day 14 

followed by decline to study 

termination)

MRID 41719302
33

Degradate 

Name

Chemical Name Major Degradates 

(>10% formed)

Minor Degradates 

(<10% formed)

Maximum Percent Formed1

DCPU 3,4-

dichlorophenylurea

-- Soil Photolysis: 0.6% (study 

termination)

MRID 41719302

Aerobic Soil Metabolism: 0.9% (day 

30; relatively constant through 

study termination)

MRID 41719303

TCAB 3,3’,4,4’-

tetrachloroazobenzene

-- Soil Photolysis: 0.038 ppm (day 14; 

stable to study termination)

MRID 41719302

-- 3-chloroaniline -- Hydrolysis (mCPDMU study): 

estimated < 10% (day 30 @ 20°C)

MRID 46996704
34

Degradate 

Name

Chemical Name Major Degradates 

(>10% formed)

Minor Degradates 

(<10% formed)

Maximum Percent Formed1

Unidentified -- Anaerobic Aquatic Metabolism 

(mCPDMU study): Mean total of 

unidentified peaks was 10.6% 

(total system at study 

termination); unidentified 

largest peak 12.7% (total 

system at study termination

MRID 47311702

Hydrolysis (mCPDMU study): one 

unknown estimated < 10% (day 30 

@ 20°C)

MRID 46996704

Aqueous Photolysis: < 9% (at least 

13 unknowns); the most substantial 

unknown formed 8.5% (day 51.4) 

then declined

MRID 41418805

Soil Photolysis: 3.2% (one unknown, 

study termination)

MRID 41719302

Aerobic Soil Metabolism: 3.3%, 

unknown B1 (day 30; relatively 

constant through study 

termination)

MRID 41719303

Aerobic Soil Metabolism: 

(mCPDMU study): largest unknown 

peaks; 1.8%, silty clay loam soil and 

4.1%, sandy loam soil (day 46 in 

both soils)

MRID 47311703

Aerobic Aquatic Metabolism: 1.1%, 

unknown A; total system (day 22; 

relatively constant through study

termination)

MRID 41719303
35

Degradate 

Name

Chemical Name Major Degradates 

(>10% formed)

Minor Degradates 

(<10% formed)

Maximum Percent Formed1

Unidentified -- 3.5%; sum of other unknowns each 

contributing < 0.6%; total system 

(study termination; increasing) 

MRID 41719303

0.6%; unclear if single unknown or 

sum of unknowns, total system 

(study termination, increasing)

MRID 45703101

3.2%; unclear if single unknown or 

sum of unknowns, total system 

(day 14; decreasing to study 

termination)

MRID 45703101

Aerobic Aquatic Metabolism 

(mCPDMU study): Unidentified 

peaks totaled 3.9%; total system of 

river water-loam sediment (study 

termination)

MRID 47311701

Unidentified peaks totaled 6.3%; 

total system of lake water-sandy 

loam sediment (day 76); decrease 

at day 100

MRID 47311701

Anaerobic Aquatic Metabolism: 

4.1%, sum of unknowns, total 

system (study termination; slightly 

increasing)

MRID 42661901

1 Fate studies for diuron unless indicated otherwise.
36

Appendix: 3: Complete List of Toxicity Endpoints for Diuron

Table 3-1: Summary of Toxicity Endpoints from Aquatic Toxicity Studies for Diuron 

Study Type Species % ai Toxicity Value & 

Category

MRID & Status

Freshwater fish 

Acute

Rainbow Trout

Oncorhynchus 

mykiss

80 96-hr LC50: 4.9 mg ai/L

Moderately toxic

400946021

Supplemental

Bluegill Sunfish

Lepomis 

macrochirus

95 96-hr LC50: 3.2 mg ai/L

Moderately Toxic

STODIV03

Acceptable

Rainbow Trout

Oncorhynchus 

mykiss

28 96-hr LC50: 23.8 mg 

ai/L

Slightly Toxic 

STODIV02

Acceptable

Bluegill Sunfish

Lepomis 

macrochirus

28 96-hr LC50: 84 mg ai/L

Slightly Toxic

STODIU04

Acceptable

Rainbow Trout

Oncorhynchus 

mykiss

95 96-hr LC50: 3.2 mg ai/L

Moderately Toxic

STODIU03

Acceptable

Rainbow Trout

Oncorhynchus 

mykiss

95 96-hr LC50: 1.95 mg 

ai/L

Moderately Toxic

TN 1020

Acceptable

Bluegill Sunfish

Lepomis 

macrochirus

80 96-hr LC50 >300 mg 

ai/L

Practically Nontoxic

42046001

Acceptable

Rainbow Trout 

Oncorhynchus 

mykiss

80 96-hr LC50: 190 mg ai/L

Practically Nontoxic 

42046002

Acceptable

Fathead Minnow

Pimephales 

promelas

98.6 96-hr LC50: 14.2 mg 

ai/L

Slightly Toxic

STODIU07

Acceptable

Cutthroat Trout

Oncorhynchus

clarki

95 96-hr LC50: 1.4 mg ai/L

Moderately Toxic

400946021

Supplemental

Lake Trout

Salvelinus 

namaycush 

95 96-hr LC50: 2.7 mg ai/L 

Moderately Toxic

400946021

Supplemental

Acute and 

Chronic (Early 

Life Stage)

Fathead minnow

Pimephales 

promelas

NS2 96-hr LC50: 14.2 mg 

ai/L

LOAEC: 0.0618 mg ai/L

NOAEC: 0.0264 mg 

ai/L

Sublethal Effects: 

lethargy 

Slightly Toxic 

00141636

Supplemental –

Qualitative 

Does not fulfill 

guideline- Raw data and 

percentage of active 

ingredient are not 

included
37

Study Type Species % ai Toxicity Value & 

Category

MRID & Status

Freshwater invertebrates

Acute

Water Flea

Daphnia pulex

95 48-hr EC50: 1.4 mg ai/L

Moderately Toxic

400946021 Supplemental

Zooplankton 

Simocephalus sp.

95 48-hr EC50: 2.0 mg ai/L

Moderately Toxic

400946021

Supplemental

Stone Fly

Pteronarcys sp.

95 96-hr LC50: 1.2 mg ai/L 

Moderately Toxic

400946021

Supplemental

Water Flea 

Daphnia magna

80 48-hr EC50: 12 mg ai/L 

Slightly toxic 

42046003

Acceptable 

Chronic

Water Flea

Daphnia magna

98.2 NOAEC: 0.2 mg ai/L

LOAEC > 0.2 mg ai/L

Endpoint: mortality

STODIV05

Acceptable

Water Flea

Daphnia magna

98.1 Length NOAEC: 0.057

mg ai/L

Length LOAEC: 0.11

mg ai/L

Endpoints affected: 

Adult Survival, Live 

Young Produced, 

Growth (Length and 

dry weight) 

46996702

Acceptable

Estuarine marine fish 

Acute

Sheepshead 

minnow

Cyprinodon 

variegatus

99 96-hr LC50: 6.7 mg ai/L

NOAEL: 3.6 mg ai/L

Moderately Toxic 

41418803

Acceptable

Chronic (Early 

Life Stage)

Sheepshead 

minnow

Cyprinodon 

variegatus

96.8 LOAEC: 0.44 mg ai/L

NOAEC: couldn’t be 

determined- Weight 

and survival 

significantly reduced 

at all tested 

concentrations

42312901

SupplementalQualitative

Does not fulfill 

guideline- could not 

establish a NOAEC

Estuarine Marine Invertebrates 

Acute

Mysid shrimp 

Mysidopsis bahia

99 48-hr LC50: 1.2 mg ai/L

NOAEL: 0.6 mg ai/L

Moderately Toxic

41418801

Acceptable 

Scud

Gammarus 

fasciatus

95 96-hr LC50: 0.16 mg 

ai/L

Highly Toxic

400946021

Supplemental

Eastern Oyster

Crassostrea 

virginica

96.8 48-hr EC50 = 4.8 mg 

ai/L

42217201

Acceptable 
38

Study Type Species % ai Toxicity Value & 

Category

MRID & Status

Reduction in shell 

thickness was 

observed at all test 

levels. 

Moderately Toxic

Chronic (Life 

Cycle Toxicity)

Mysid Shrimp

Mysidopsis bahia

96.8 NOAEL: 0.96 mg ai/L

LOAEL: 1.9 mg ai/L

Most sensitive 

parameter: Length/ 

reproductive rate

42500601

Acceptable 

Aquatic Plants

Vascular

Duckweed

Lemma gibba

99.1 EC50: 0.00019 mg ai/L

Biomass

NOAEC: 0.00249 mg 

ai/L

LOAEC: Not Reported

Most sensitive 

parameter:

Frond number, 

Biomass, Growth Rate

46996701

Acceptable

Non-Vascular

Green Algae

Pseudokirchneriella 

subcapitata

96.8 EC50: 0.00308 mg ai/L1

NOEC: 0.00114 mg 

ai/L

LOAEC: 0.00225 mg 

ai/L

biomass

42218401

Acceptable 

Blue-Green Alga

Synechococcus 

leopoliensis

96.8 EC50: 0.026 mg ai/L

Biomass

47936501

Supplementalqualitative

Freshwater 

Diatom Navicula 

pelliculosa

96.8 EC50: 0.022 mg ai/L

LOAEC: 0.033 mg ai/L

NOAEC: 0.011 mg ai/L

Biomass

47936502

Supplementalqualitative

Green Algae 

Scenedesmus 

subspicatus

96.7 EC50: 0.0079 mg ai/L

LOAEC: 0.0032 mg ai/L

NOAEC: 0.0056 mg 

ai/L

Biomass 

47946501

Supplementalqualitative

1 These endpoints (Johnson and Finley, 1980) were published as a collection of a produced by government 

laboratories. This collection is a useful resource for characterizing risk, but care should be taken as the 

data are not available for verification of accuracy of the analysis. As data are not reviewed, these 

endpoints are classified as supplemental and should only be used to characterize risk qualitatively. 

2

The %ai was not specified in this study

Table 3-2: Summary of Toxicity Endpoints from Terrestrial Toxicity Studies for Diuron 
39

Study Type Species %ai Toxicity Value & Category MRID & Status

Mammalian Toxicity

Acute (Oral)

Rat 

Rattus norvegicus

98.6 Male LD50 : 4721 mg/kg-bw

Female LD50 >10,000 mg/kgbw

Practically nontoxic

00146145

Acceptable

Chronic 

(2 generation)

Rat 

Rattus norvegicus

97.1 NOAEL/LOAEL: 250/1750 

mg/kg

Affected Endpoints: Pup 

weight

41957301

Acceptable

Acute 

(Inhalation)

Rat 

Rattus norvegicus

98.6 LC50 >2.09 mg ai/L

Sublethal effects: ventral 

staining, facial staining, 

reduced fecal volume, 

dyspnea. 

45866203

Acceptable

Avian Toxicity

Acute (Oral) Mallard Duck 

Anas platyrhynchos

95 LD50 >2000 mg/kg-bw

Practically nontoxic

00115198

Acceptable

Sub-Acute 

Dietary

Northern Bobwhite 

Quail

Colinus virginianus

95 5-Day LC50: 1730 mg ai/kg-bw 00022923

Acceptable

Japanese Quail 

Coturnix japonica

95 5-Day LC50 >5000 mg ai/kgbw00022923

Acceptable

Ring-Necked Pheasant 

Phasianus colchicus

95 5-Day LC50 >5000 mg ai/kgbw00022923

Acceptable

Mallard Duck 

Anas platyrhynchos

95 5-Day LC50: 5000 mg ai/kg-bw 00022923

Acceptable

Chronic 

(Reproductive)

Mallard Duck

Anas platyrhynchos

98.4 NOAEC: 9.80 mg ai/kg-diet

LOAEC: 33.3 mg ai/kg-diet

Endpoints affected: Adult 

body weight (male and 

female), total egg production 

and fertility 

47311704

Acceptable

Terrestrial Invertebrates

Adult-Acute 

(Contact)

Honeybee

Apis mellifera 

TEPnot 

speci

fied

LD50 >10μg ai/bee

Practically nontoxic 

00001999 

Acceptable

Adult-Acute 

(Contact)

Honeybee

Apis mellifera 

80 LD50: 2.77 μg ai/bee

Moderately toxic

00036935 

Acceptable

Terrestrial Plants (Seedling Emergence)

Monocot

species

Onion

Allium cepa

97.3 EC25: 0.099 lb ai/A

NOAEL: 0.089 lb ai/A

Shoot Dry Weight

44113401 

Supplemental1

Wheat

Triticum aestivum

97.3 EC25: 1.05 lb ai/A

NOAEL: 0.38 lb ai/A

Shoot Dry Weight

44113401 

Supplemental1
40

Study Type Species %ai Toxicity Value & Category MRID & Status

Dicot 

species

Rapeseed

Brassica napus

97.3 EC25: 0.094 lb ai/A

NOAEL: 0.047 lb ai/A

Shoot Dry Weight 

44113401 

Supplemental1

Sugar Beet

Beta vulgaris

97.3 EC25: 0.092 lb ai/A

NOAEL: 0.047 lb ai/A

Shoot Dry Weight 

44113401 

Supplemental1

Tomato

Lycopersicon 

esculentum

97.3 EC25: 1.05 lb ai/A

NOAEL: 0.38 lb ai/A

Shoot Dry Weight 

44113401 

Supplemental1

Terrestrial Plants (Vegetative Vigor)

Monocot 

species

Onion

Allium cepa

97.3 EC25: 0.187 lb ai/A

NOAEL: 0.375 lb ai/A

Shoot Dry Weight 

44113401 

Supplemental1

Sorghum

Sorghum bicolor

97.3 EC25: 0.0555 lb ai/A

NOAEL: 0.0117 lb ai/A

Shoot Dry Weight 

44113401 

Supplemental1

Wheat

Triticum aestivum

97.3 EC25: 0.0294 lb ai/A

NOAEL: 0.0117 lb ai/A

Shoot Dry Weight

44113401 

Supplemental1

Dicot

species

Pea

Pisum sativum

97.3 EC25: 0.0124 lb ai/A

NOAEL: 0.0117 lb ai/A

Shoot Dry Weight 

44113401 

Supplemental1

Rapeseed

Brassica napus

96.8 EC25: 0.0360 lb ai/A

NOAEL: 0.0469 lb ai/A 

Shoot Dry Weight 

44113401 

Supplemental1

1

The seedling emergence that provided valid endpoints for terrestrial plants (MRID 44113401) only tested 

onion, wheat, rapeseed, sugar beets, and tomatoes. The guideline requires that a minimum of 10 species 

need to be tested, 4 of which are monocot species, one of which must be corn, and 6 dicot species, one 

of which must be soybean. Until this guideline requirement is fulfilled, toxicity to terrestrial plants remains 

an uncertainty. 
41
42

Appendix 4: Ecological Incidents Associated with Diuron (EIIS database)

Table 4-1

Incident ID Type Total 

Magnitude

State Year Legality

B0000-300-

32 AQUATIC - SC 1982 Undetermined

B0000-300-

45 PLANTS - OK 1972 Undetermined

I000022-001 TERRESTRIAL/AQUATIC - SC 1992 Undetermined

I005925-001 AQUATIC - TX 1997 Undetermined

I005925-008 AQUATIC 3000 fish MD 1996 Undetermined

I005925-010 AQUATIC - OK 1996 Undetermined

I005925-014 AQUATIC - TX 1995 Undetermined

I005972-001 PLANTS - TX 1997 Registered Use

I007154-001 AQUATIC - MS 1998 Registered use

I007269-002 PLANTS - TN 1998 Registered use

I013194-001 PLANTS 10 acres ND 2002 Undetermined

I013281-008 AQUATIC - OK 2002 Undetermined

I013587-020 PLANTS - WA 1998 Registered use

I013850-001 PLANTS

1/3 of back 

yard MI 2002 Registered use

I013884-004 PLANTS - WA 1998 Registered use

I014177-001 PLANTS 30 acres CA 2002 Registered use

I014407-013 PLANTS - WA 1994 Undetermined

I014409-062 PLANTS - WA 1992 Undetermined

I0144700-

001 PLANTS - OK 2004 Registered use

I015278-001 PLANTS 67 acres OR 2003 Registered use

I015382-001 PLANTS - WY 2004 Undetermined

I015796-001 PLANTS 1-4 acres KY 2004 Registered use

I016036-024 PLANTS 53 acres CA 2004 Registered use

I016302-001 PLANTS

Less than an 

acre WA 2005 Undetermined

I016362-001 PLANTS - MI 2005 Undetermined

I016429-001 PLANTS

$90,000 

damage WA 2005 Registered use

I016569-001 PLANTS - NM 2005 Undetermined

I018428-010 PLANTS 4 acres CA 2006 Registered Use

I018527-001 PLANTS - WY 2007 Undetermined

I019519-045 PLANTS 7 acres CA 2008 Undetermined

I020180-033 PLANTS 9 acres CA 2008 Undetermined

I020274-001 AQUATIC 5,000 fish CA 2008 Undetermined

I020459-001 PLANTS - WA 2000 Undetermined

I020459-003 PLANTS - WA 2000 Undetermined

I020459-005 PLANTS - WA 1999 Undetermined
43

Incident ID Type Total 

Magnitude

State Year Legality

I020459-008 PLANTS - WA 1999 Undetermined

I020459-011 TERRESTRIAL - WA 2000 Undetermined

I020459-012 PLANTS - WA 2000 Undetermined

I021457-014 PLANTS $1,000.00 WA 2006 Undetermined

I021457-016 PLANTS 3 plant crops WA 2006 Undetermined

I021457-025 PLANTS - WA 2006 Undetermined

I022180-001 PLANTS

“A few”

trees NV 2010 Undetermined
44

Appendix 5: SIP (v1.0) Input and Output Data

Table 5-1: Inputs

Parameter Value

Chemical name Diuron

Solubility (in water at 25oC; mg/L) 42

Mammalian LD50 (mg/kg-bw) 5000

Mammalian test species laboratory rat

Body weight (g) of "other" mammalian species

Mammalian NOAEL (mg/kg-bw) 12.5

Mammalian test species laboratory rat

Body weight (g) of "other" mammalian species

Avian LD50 (mg/kg-bw) 2000

Avian test species mallard duck

Body weight (g) of "other" avian species

Mineau scaling factor 1.15

Mallard NOAEC (mg/kg-diet) 9.8

Bobwhite quail NOAEC (mg/kg-diet) 0

NOAEC (mg/kg-diet) for other bird species

Body weight (g) of other avian species

NOAEC (mg/kg-diet) for 2nd other bird species

Body weight (g) of 2nd other avian species

Table 5-2: Mammalian Results

Parameter Acute Chronic

Upper bound exposure (mg/kg-bw) 7.2240 7.2240

Adjusted toxicity value (mg/kg-bw) 3845.8028 9.6145

Ratio of exposure to toxicity 0.0019 0.7514

Conclusion*

Drinking water exposure 

alone is NOT a potential 

concern for mammals

Drinking water exposure 

alone is NOT a potential 

concern for mammals

Table 5-3: Avian Results

Parameter Acute Chronic

Upper bound exposure (mg/kg-bw) 34.0200 34.0200

Adjusted toxicity value (mg/kg-bw) 1038.4508 0.4862

Ratio of exposure to acute toxicity 0.0328 69.9708

Conclusion*

Drinking water exposure 

alone is NOT a potential 

concern for birds

Exposure through drinking 

water alone is a potential 

concern for birds

*Conclusion is for drinking water exposure alone. This does not combine all routes of exposure. Therefore, 

when aggregated with other routes (i.e., diet, inhalation, dermal), pesticide exposure through drinking water 

may contribute to a total exposure that has potential for effects to non-target animals.
45

Appendix 6: STIR (v.1) Inputs and Outputs

Input

Application and Chemical Information

Enter Chemical Name Diuron

Enter Chemical Use Herbicide

Is the Application a Spray? (enter y or n) y

If Spray What Type (enter ground or air) air

Enter Chemical Molecular Weight (g/mole) 233.1

Enter Chemical Vapor Pressure (mmHg) 6.90E-08

Enter Application Rate (lb ai/acre) 12

Toxicity Properties

Bird

Enter Lowest Bird Oral LD50 (mg/kg bw) 2000

Enter Mineau Scaling Factor 1.15

Enter Tested Bird Weight (kg) 1.58

Mammal

Enter Lowest Rat Oral LD50 (mg/kg bw) 5000

Enter Lowest Rat Inhalation LC50 (mg/L) 2.09

Duration of Rat Inhalation Study (hrs) 4

Enter Rat Weight (kg) 0.35

Output

Results Avian (0.020 kg )

Maximum Vapor Concentration in Air at Saturation 

(mg/m3) 8.66E-04

Maximum 1-hour Vapor Inhalation Dose (mg/kg) 1.09E-04

Adjusted Inhalation LD50 3.36E+00

Ratio of Vapor Dose to Adjusted Inhalation LD50 3.24E-05

Exposure not Likely 

Significant

Maximum Post-treatment Spray Inhalation Dose 

(mg/kg) 1.15E+00

Ratio of Droplet Inhalation Dose to Adjusted Inhalation 

LD50 3.43E-01 Proceed to Refinements

Results Mammalian (0.015 kg )

Maximum Vapor Concentration in Air at Saturation 

(mg/m3) 8.66E-04

Maximum 1-hour Vapor Inhalation Dose (mg/kg) 1.37E-04

Adjusted Inhalation LD50 1.24E+02

Ratio of Vapor Dose to Adjusted Inhalation LD50 1.10E-06

Exposure not Likely 

Significant

Maximum Post-treatment Spray Inhalation Dose 

(mg/kg) 1.45E+00

Ratio of Droplet Inhalation Dose to Adjusted Inhalation 

LD50 1.16E-02

Exposure not Likely 

Significant