UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

WASHINGTON, D.C. 20460 

OFFICE OF CHEMICAL SAFETY AND POLLUTION PREVENTION 

MEMORANDUM 

December 12, 20 13 

SUBJECT: Diflubenzuron: Human Health Risk Assessment for an Amended Section 3 

Registration for the Expanded Citrus Crop Group 10-10. 

PC Code: 1 0820 1 DP Barcode: 403078, 403079, & 403080 

Decision No.: 465090, 465087, & 465092 Registration No.: 400-461 , 400-466, 400-

487 

Petition No.: 2F80 15 Regulatory Action: Section 3 

Risk Assessment Type: Human Health Risk Case No.: 0144 

Assessment 

TXRNo.: NA CAS No: 35367-38-5 

MRIDNo.: NA 40 CFR: 180.377 

-ziAL - . FROM . Thurston G. Morton, Chemtst ~ ;J 

Susan V. Hummel, Senior Scientist / -::;?~ /1/ ) I/ 

James S Miller, Environmental Scien{l t'st·- ,-yt-a_~ / /lf.L---( A 

Ayaad Assad, PhD., Toxicologist /1 , f\~ ;I .il L/ '--

Risk Assessment Branch 4 _. q f/c / A-{;1_ "1::> 

Health Effects Division (7509P) ~ 

THROUGH: Elissa Reaves, Ph.D., Branch Chief ~ ~ Risk Assessment Branch 4, HED (7509P) -~. 

TO: Rita Kumar/ John Hebert 

Insecticide/Rodenticide Branch/RD (7505P) 

This document provides the Health Effects Division's (HED's) risk assessment of the amended 

Section 3 use of diflubenzuron on the expanded citrus fruit crop group 10-10. 

Page 1 of66 
1.0 EXECUTIVE SUMMARY ................................................................................................ 5 

2.0 HED Recommendations ...................................................................................................•. 9 

2.1 Data Deficiencies/Conditions of Registration ................................................................ 9 

2.2 Tolerance Considerations ............................................................................................. 10 

2.2.1 Enforcement Analytical Method ........................................................................... 10 

2.2.2 International Harmonization ................................................................................. 10 

2.2.3 Recommended Tolerances ...................................................................................... 10 

2.2.4 Revisions to Petitioned-For Tolerances ................................................................ 12 

2.3 Label Recommendations ............................................................................................... 12 

3.0 Introduc·tion ...•........................................................................................•.......................... 12 

3.1 Chemical Identity .......................................................................................................... 12 

3.2 Physical/Chemical Characteristics ............................................................................... 13 

3.3 Pesticide Use Patter·n .......................................................................•............................. 14 

3.3.1 Registered Products ....................•........................................................................... 14 

3.3.2 Proposed New Uses ................................................................................................. 14 

3.4 Anticipated Exposure Pathways ........................................•.......................................... 15 

3.5 Considerations of Environmental Justice .................................................................... 15 

4.0 Hazard Characterization and Dose-Response Assessment ........................................... 15 

4.1 Toxicology Studies Available for Analysis ............................................•.•................... 15 

4.2 Absorption, Distribution, Metabolism and Excretion ................................................ 16 

4.2.1 Dermal Absorption ...............................................................•..................................... 16 

4.3 Toxicological Effects .........•..............•.•...................................................................•....... 16 

4.4 Safety Factor for Infants and Children (FQP A Safety Factor) ................................. 17 

4.4.1 Completeness of the Toxicology Database ............................................................ 17 

4.4.2 Evidence of Neurotoxicity ...................................................................................... 18 

4.4.3 Evidence of Sensitivity/Susceptibility in the Developing or Young Animal •..... 18 

4.4.4 Residual Uncertainty in the Exposure Database .................................................. 18 

4.5 Toxicity Endpoint and Point of Departure ...•..............................•............................... 18 

4.5.1 Dose-Response _ Assessment ......... ~ ................................................. .......................... 18 

4.5.2 Recommendations for Combining Exposure Routes ........................................... 19 

4.5.3 Classification of Carcinogenic Potential ............................................................... 19 

4.5.4 Summary of Points of Departure Used in Risk Assessment ............................... 20 

5.0 Dietary Exposure and Risk Assessment ...............................................•.......................... 23 

5.1 Metabolite/Degradate Residue Profile ..............................................•.......................... 23 

Page 2 of66 
Page 3 of 66

5.1.1 Summary of Plant and Animal Metabolism Studies............................................... 23

5.1.2 Summary of Environmental Degradation................................................................ 23

5.1.3 Comparison of Metabolic Pathways......................................................................... 23

5.1.4 Residues of Concern Summary and Rationale ........................................................ 24

5.2 Food Residue Profile ..................................................................................................... 24

5.3 Water Residue Profile ................................................................................................... 26

5.4 Dietary Risk Assessment............................................................................................... 27

5.4.1 Description of Residue Data Used in Dietary Assessment...................................... 27

5.4.2 Percent Crop Treated Used in Dietary Assessment................................................ 27

5.4.3 Acute Dietary Risk Assessment................................................................................. 27

5.4.4 Chronic Dietary Risk Assessment............................................................................. 27

5.4.5 Cancer Dietary Risk Assessment .............................................................................. 28

5.4.6 Summary Table .......................................................................................................... 28

6.0 Residential (Non-Occupational) Exposure/Risk Characterization .............................. 29

6.1 Residential Bystander Post-application Inhalation Exposure................................... 29

6.2 Spray Drift...................................................................................................................... 29

7.0 Aggregate Exposure/Risk Characterization................................................................... 30

7.1 Acute & Chronic Aggregate Risk................................................................................. 30

7.2 Short- and Intermediate-Term Aggregate Risk ......................................................... 30

8.0 Cumulative Exposure/Risk Characterization ................................................................ 30

9.0 Occupational Exposure/Risk Characterization ............................................................. 31

9.1 Exposure Scenarios....................................................................................................... 31

9.2 Handler Exposure.......................................................................................................... 31

9.2.1 Handler Exposure Scenarios.................................................................................. 31

9.2.2 Handler Exposure Data.......................................................................................... 32

9.2.3 Handler Exposure Assumptions............................................................................ 33

9.2.4 Handler Exposure and Risk Estimates................................................................. 35

9.3 Post Application Exposure............................................................................................ 38

9.3.1 Post Application Inhalation Exposure Scenarios................................................. 38

9.3.2 Post Application Dermal Exposure Assumptions................................................ 39

9.3.3 Post-Application Exposure and Risk Estimates................................................... 41

10. REFERENCES.................................................................................................................. 43

APPENDIX A TOXICOLOGY DATA SUMMARY........................................................... 44

A.1 Guideline Data Requirements................................................................................ 44
Page 4 of 66

A.2 Toxicity Profiles............................................................................................................. 45

A.3 Toxicological Endpoints................................................................................................ 45

A.4 Executive Summaries.................................................................................................... 53

APPENDIX B. Chemical Names And Structures Of Diflubenzuron and Metabolites ....... 65

APPENDIX C. Physical/Chemical Properties.......................................................................... 66

APPENDIX D. Studies Reviewed for Ethical Conduct.......................................................... 66
Page 5 of 66

1.0 EXECUTIVE SUMMARY

This document addresses the exposures and risks associated with exposures from currently 

registered uses and the proposed amended use of diflubenzuron. It also assesses potential 

enhanced sensitivity of infants and children from dietary and/or residential exposure as required 

under the Food Quality Protection Act (FQPA) of 1996.

Under PP#2F8015, Chemtura Corporation is proposing to expand the use of diflubenzuron to

include all members of the citrus crop group 10-10. Chemtura also requests a decrease in the 

retreatment interval from 90 to 30 days, and a decrease in the pre-harvest (PHI) interval from 21 

to 7 days. 

In addition to the petition, separate submissions were made for Diflubenzuron 90% Concentrate 

(EPA Reg No. 400-466) to allow formulation into products for use on citrus, including low 

volume application (D403089), and for Dimilin 2L (2 lb/gal Flowable; EPA Reg. No. 400-461; 

D403090) at the rate of 0.156 lb ai/A, not to exceed 0.47 lb ai/A/season. The same restrictions 

are on this label, as well as the recommendation to add a petroleum spray oil, except for the 

minimum aerial spray volume of 3 gal/A (10 gal/A in CA). A separate amendment request for 

Micromite 80 WGS (EPA Reg No 400-487), requests an aerial spray volume of 3 gal/A 

(D403088).

Use Profile

Diflubenzuron, (N-[((4-chlorophenyl) amino) carbonyl]-2, 6-difluorobenzimide), a member of 

the urea-derivative chemical family, is classified as an insect growth regulator and is used as 

both an acaricide and insecticide. It is currently registered in the U.S. for use as a chitin inhibitor, 

which promotes an inability of immature insects to synthesize chitin to form a hard exoskeleton 

prevents development from the immature to the juvenile and adult stages. The main agriculture 

pests targeted for control with diflubenzuron are the twig borer; stink bug; grasshopper; beet 

armyworm; soybean looper; rust mite; artichoke plume moth; citrus leafminer; citrus root weevil; 

asian citrus psyllid; katydids, and peanuts root know nematode. Tolerances for diflubenzuron, 

currently established under 40 CFR §180.377, range from 0.05-55 ppm. 

The chemical structure and nomenclature of diflubenzuron and its regulated metabolites are 

presented in Appendix B. The physicochemical properties of the technical grade of 

diflubenzuron are presented in Appendix C.

Occupational application methods include, aerial; groundboom; airblast; chemigation; and 

pressurized handguns used for low and high volume applications. (i.e., low-pressure handwand, 

handgun sprayer, backpack sprayer). Also, it is applied by hand (granular), through bait stations, 

and feed through systems. Diflubenzuron is applied to numerous crops across 16 EPA crop 

group categories, and to agricultural non-crop sites including livestock barns; agricultural 

structures and equipment. Residential applications are made with handheld equipment, however 

Chemtura Corp. has maintained that all residential uses are obsolete and to be removed from all 

labels. 
Page 6 of 66

Proposed New Uses

Chemtura Corporation has submitted an application for the registration of products containing 

diflubenzuron for an amended use on fruit citrus (crop group 10-10). The products are 

manufactured by Chemtura Agro-Solutions, Inc. under the trade name Micromite 80WG®

Insecticide (EPA Reg. No. 400-487), and Dimilin®2LInsecticide (EPA Reg. No. 400-461). 

Occupational application methods include; aerial; airblast and chemigation. Chemtura is 

amending the use by lowering the pre-harvest interval (PHI) from 90 to 7 days for fruit citrus, 

(crop group 10-09). REI is 12 hours. The amended use is not proposed for residential use and 

residential exposures are not expected based on the proposed uses.

The acute oral, dermal and inhalation toxicity of diflubenzuron is low. It is a mild eye irritant 

and not a skin irritant in laboratory animals. It is negative for sensitization in the guinea pig. In 

subchronic and chronic feeding studies, the primary endpoint of concern was 

methemoglobinemia and/or sulfhemoglobinemia. These effects were evident in both sexes of 

mice, rats, and dogs and were produced by more than one route of administration in rats [i.e., 

oral, dermal and inhalation]. The general consequence of methemoglobinemia and/or 

sulfhemoglobinemia is the impairment of the oxygen transportation capacity of the blood, which 

is generally known to be caused by aromatic amines in both humans and animals.

The overall toxicology database is sufficient for a determination of potential hazard to infants 

and children. The data provide no indication of an increased susceptibility to rats or to rabbits 

from in utero or post-natal exposure to diflubenzuron. Developmental and reproduction studies 

in rats and rabbits indicate a very low hazard potential for adverse effects. Developmental 

studies were tested at the limit dose of 1000 mg/kg/day without apparent effects in both dams 

and the fetuses. The reproduction study indicated that effects in offspring occurred at doses that 

were higher than the doses producing effects in parents. There was no indication of 

abnormalities in fetal development in the prenatal developmental toxicity studies in either rats or 

rabbits at the maternal limit doses of 1000 mg/kg/day. In addition, there was no evidence of 

sensitivity following pre- and/or post-natal exposure in a two-generation reproduction study in 

rats. The acute and subchronic neurotoxicity studies were recently waived by HASPOC (TXR 

0056309) based on a weight of evidence approach. The recently submitted immunotoxicity 

study has been reviewed and immunotoxicity was not observed above the limit dose. 

Dose Response Assessment

Toxicological endpoints were selected for dietary/drinking water, occupational and residential 

exposure scenarios. Acute and chronic points of departure (PODs) were selected for assessment 

of food and drinking water exposures. No appropriate acute endpoint was identified in the 

hazard database to quantitate the risk to the general population or to females 13-50 years old 

from single dose administration of diflubenzuron. Therefore, there is no acute reference dose 

(aRfD) or acute population-adjusted dose (aPAD). A chronic/cancer POD for the general 

population was selected from a chronic toxicity study in dog. Short and intermediate-term 

occupational exposures via the dermal and inhalation routes may occur based on the use pattern 

and label directions. Toxicological endpoint for the short-term dermal scenario was selected 

from a 21-day rat dermal study and intermediate-term dermal endpoint was selected from a 13-

week oral (capsule) study in the dog. The short- and intermediate-term inhalation endpoints 
Page 7 of 66

were selected from a 28-day rat inhalation toxicity study. An uncertainty factor of 100X was 

applied to endpoints selected for all exposure routes (10X for interspecies extrapolation, 10X for 

intraspecies variation). 

The HED RfD/Peer Review Committee classified diflubenzuron as “Group E,” evidence of noncarcinogenicity for humans, based on lack of evidence of carcinogenicity in rats and mice (April 

27, 1995). PCA, a metabolite of diflubenzuron, tested positive for splenic tumors in male rats 

and hepatocellular adenomas/carcinomas in male mice in a National Toxicology Program (NTP) 

study. Therefore, the RfD/Peer Review Committee classified PCA as a “Group B2" probable 

human carcinogen. However, recently submitted acceptable rat metabolism studies show that 

diflubenzuron was not metabolized to either PCA or CPU. On May 8, 2001 (D272976), the

MARC reviewed the recently submitted metabolism studies, accepted the study findings, and 

concluded that cancer risks for CPU and PCA should be assessed individually. However, the 

non-cancer toxicities of CPU and PCA are well understood. CPU is less toxic and does not 

cause methemoglobin formation while PCA is similar in potency as diflubenzuron. Therefore, 

including the metabolites in the assessment is health protective. Additional toxicity data on 

these metabolites are not required.

Exposure/Risk Assessment and Risk Characterization

The chronic assessment assumed that diflubenzuron residues are present in all commodities at 

established/recommended tolerance levels except for orange, grapefruit, and lemon where 

average field trial residues were used and that 100% of all crops are treated. For the chronic noncancer dietary exposure analysis, drinking water was incorporated directly into the dietary 

assessment using the estimated drinking water concentration (EDWC) for surface water of 12.8

ppb generated by the Pesticide Root Zone Model/Exposure Analysis Modeling System 

(PRZM/EXAMS) with index reservoir (IR) scenarios and percent crop area (PCA) adjustment 

factors. The highest annual mean EDWCs for diflubenzuron (0.26 μg /L ) and CPU (12.52 μg 

/L ) were combined (12.8 μg /L ) to assess chronic non-cancer dietary risk For the CPU cancer 

dietary exposure analysis an EDWC of 8.81 ppb was incorporated.

The resulting chronic dietary-exposure estimates for combined food and drinking water are 

below HED’s LOC (i.e., <100% of the cPAD of 0.02 mg/kg bw/day) for the overall U.S. 

population and all population subgroups. Using the Dietary Exposure Evaluation Model 

software with the Food Commodity Intake Database (DEEM-FCID ) software, dietary 

exposure is estimated to be ≤37% of the cPAD for the U.S. population and all population 

subgroups, including children 1 to 2 years old, the population subgroup with the highest 

estimated exposure.

The cancer assessment for PCA includes food only. For PCA, the cancer dietary exposure 

estimate for the U.S. population is 1 x 10-6. The cancer assessment for CPU includes milk and 

water only. The cancer chronic EDWC in surface water for CPU is 8.81 ppb. For CPU, the 

cancer dietary exposure estimate for the U.S. population is 3 x 10-6.

Although there are no registered homeowner uses, there are registered uses for professional 

applications to outdoor residential and recreational areas to control mosquitoes, moths, and other 
Page 8 of 66

insects. However, the potential for post-application residential exposure is expected to be 

limited. Due to the low intermediate-term dermal absorption rate (0.5%) of diflubenzuron, and 

since it is only applied to the tree canopy, minimal bystander contact is expected.

Based upon the proposed use patterns, short-term (1-30 days) dermal and inhalation exposures 

are typically expected for commercial and private (i.e., grower) pesticide mixers, loaders, and 

applicators. The toxicological endpoints for short-term dermal and short-term inhalation effects 

were derived from two different studies; however, both studies indicate similar toxicological 

effects (i.e., methemoglobinemia). Since the results of the two studies indicate similar 

toxicological effects, the MOEs are shown as combined MOEs. HED’s level of concern (LOC) 

is a margin of exposure (MOE) <100.

No chemical-specific data were available with which to assess potential exposure to pesticide 

handlers. Therefore, the exposure and risk estimates presented in this document are based upon 

surrogate data in the Pesticide Handlers Exposure Database (PHED) Ver. 1.1, Surrogate 

Exposure Guide (August 1998). Occupational exposures are assessed for pesticide handlers (i.e., 

mixers, loaders, applicators and flaggers) for agricultural workers. Intermediate-term MOEs 

range from 460 for mixer/loaders using protective gloves to 7,200 for airblast mixer and loaders

using protective gloves. For occupational exposures, the MOEs do not exceed HED’s LOC and 

therefore not of concern. 

A conservative, screening-level assessment of intermediate-term post-application exposure to 

agricultural workers yields MOEs of 350 on “Day after Treatment (DAT) 0” and 430 on “DAT 

1” for hand harvesting citrus fruit. However a PHI of 7 day is stipulated on labels (EPA Reg 

No.: 400-461, and 400-487). For the most conservative intermediate post-application exposure 

scenario, MOEs at DAT 7 = 10,000; do not exceed HED's LOC and therefore not of concern.

Aggregate exposure risk assessments were assessed by incorporating the drinking water directly 

into the dietary-exposure assessment for the following scenario: chronic aggregate exposure 

(food + drinking water). Short-, intermediate-, and long-term aggregate-risk assessments were 

not performed because there are no registered or proposed uses of diflubenzuron which result in 

residential exposures. Acute and cancer aggregate-risk assessments were not performed because 

no appropriate endpoint was available to determine the aRfD for the general population or any 

population subgroup and diflubenzuron is not carcinogenic. 

Use of Human Studies

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

intentionally exposed to a pesticide or other chemical. These studies were determined to require 

a review of their ethical conduct, have received that review and have been determined to be 

ethical.

Environmental Justice

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

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

to Address Environmental Justice in Minority Populations and Low-Income Populations," 
Page 9 of 66

http://www.eh.doe.gov/oepa/guidance/justice/eo12898.pdf).

As a part of every pesticide risk assessment, OPP considers a large variety of consumer 

subgroups according to well-established procedures. In line with OPP policy, HED estimates 

risks to population subgroups from pesticide exposures that are based on patterns of that 

subgroup’s food and water consumption, and activities in and around the home that involve 

pesticide use in a residential setting. Whenever appropriate, non-dietary exposures based on 

home use of pesticide products and associated risks for adult applicators and for toddlers, youths, 

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

considerations are currently in development, as OPP has committed resources and expertise to 

the development of specialized software and models that consider exposure to bystanders and 

farm workers as well as lifestyle and traditional dietary patterns among specific subgroups. 

Tolerance Recommendation

Pending submission of a revised Section F (see requirements under Proposed Tolerances), there 

are no residue chemistry issues that would preclude granting an amended Section 3 registration 

for the requested amended use of diflubenzuron on Crop Group 10-10, or establishment of the 

following tolerances for residues of diflubenzuron. 

Fruit, citrus, group 10-10 ..................................................... 3.0 ppm

Citrus, oil............................................................................... 32 ppm

The Codex Alimentarius has established maximum residue limits (MRL), expressed in terms of 

diflubenzuron per se, for many commodities including: citrus fruits (0.5 ppm). As the U.S. 

residue definition includes CPU and PCA, compatibility is not possible with the proposed 

tolerances. Numerical compatibility with CODEX is not possible as the Good Agricultural 

Practices (GAP) used for the CODEX MRL is different from the proposed use pattern in the US.

 

2.0 HED Recommendations

2.1 Data Deficiencies/Conditions of Registration 

HED can recommend for registration and permanent tolerances for the proposed amended uses 

of diflubenzuron. 

The amendments for Micromite 80 WGS (EPA Reg No 400-487) and Dimilin 2L Concentrate 

(EPA Reg No. 400-461) are acceptable. The amendment for Diflubenzuron 90% Concentrate 

(EPA Reg No. 400-466) to allow formulation into products for use on citrus, including low 

volume application is acceptable, providing that the formulations to be used are limited to WDG 

and FlC formulations, at the same rates proposed here for the respective formulations.

Deficiencies are stated below. The specific tolerance recommendations are discussed in Section 

2.2, and label modifications are discussed in Section 2.3.
Page 10 of 66

Note to PM:

Revised Section F required.

Analytical reference standard for diflubenzuron metabolite 13-C-PCA is expired (expired 

11/7/2004), and must be replaced.

2.2 Tolerance Considerations

2.2.1 Enforcement Analytical Method

Three enforcement methods for diflubenzuron are published in the Pesticide Analytical Manual 

(PAM, Vol. II) as Methods I, II, and III. Method I is a GC/ECD method that determines 

diflubenzuron in plants as derivatized PCA. Method II is a GC/ECD method that can separately 

determine residues of diflubenzuron, CPU and PCA in eggs, milk, and livestock tissues, each as 

derivatized PCA. Method III is a high-performance liquid chromatography/ultraviolet 

(HPLC/UV) method that determines diflubenzuron per se in eggs, milk, and livestock tissues. 

All three methods have undergone successful Agency validations. The Diflubenzuron RED 

stated that Methods I and II are the preferred enforcement methods because they are easier to 

perform, have less interference, and are more sensitive.

In conjunction with PP#8F4925 on rice, a new analytical methodology for plant commodities 

was successfully validated by an independent laboratory as well as by Agency chemists at 

ACB/BEAD, and was forwarded to FDA for publication in PAM Vol. II as Roman Numeral 

Methods. These methods can separately determine residues of diflubenzuron by GC/ECD, CPU 

by GC/ECD, and PCA by GC/MS using an isotopically labeled internal standard and by 

summing the response of the two ions. The reported LOQ for diflubenzuron in/on rice grain, 

straw, and bran is 0.01 ppm, and is 0.05 ppm in/on rice hull. In rice straw, the LOQ for CPU is 

0.01 ppm and 0.005 ppm for PCA.

2.2.2 International Harmonization

The Codex Alimentarius has established maximum residue limits (MRL), expressed in terms of 

diflubenzuron per se, for many commodities including: citrus fruits (0.5 ppm). As the U.S. 

residue definition includes CPU and PCA, compatibility is not possible with the proposed 

tolerances. Numerical compatibility with CODEX is not possible as the GAP used for the 

CODEX MRL is different from the proposed use pattern in the US.

2.2.3 Recommended Tolerances

The tolerance expression for 40 CFR 180.377 (a)(1) should read:

Tolerances are established for residues of diflubenzuron, including its metabolites and 

degradates, in or on the commodities in the table below. Compliance with the tolerance levels 

specified below is to be determined by measuring only diflubenzuron (N -[[(4-

chlorophenyl)amino]carbonyl]-2,6-difluorobenzamide).
Page 11 of 66

The tolerance expression for 40 CFR 180.377 (a)(2) should read:

Tolerances are established for residues of the insecticide diflubenzuron (N -[[(4-

chlorophenyl)amino]carbonyl]-2,6-difluorobenzamide), in or on the commodities in the table 

below. Compliance with the tolerance levels specified below is to be determined by measuring 

only the sum of diflubenzuron (N -[[(4-chlorophenyl)amino]carbonyl]-2,6-difluorobenzamide), 

4-chlorophenylyurea and 4-chloroaniline, calculated as the stoichiometric equivalent of 

diflubenzuron, in or on the commodity.

The tolerance expression for 40 CFR 180.377 (b) should read:

Time-limited tolerances are established for of the insecticide diflubenzuron, (N-[[(4-

chlorophenyl)amino]carbonyl]-2,6- difluorobenzamide and its metabolites, in connection with 

use of the pesticide under section 18 emergency exemptions granted by EPA. Compliance with 

the tolerance levels specified below is to be determined by measuring only the sum of 

diflubenzuron (N -[[(4-chlorophenyl)amino]carbonyl]-2,6-difluorobenzamide), 4-

chlorophenylyurea and 4-chloroaniline, calculated as the stoichiometric equivalent of 

diflubenzuron, in or on the commodity. The tolerances are specified in the following table, and 

will expire and are revoked on the dates specified. 

A revised Section F is needed to specify that the tolerances are to be set in 40 CFR 180.377 

(a)(2). The proposed commodities and tolerance levels need to be revised to 

Pending submission of revised Section F, there are no residue chemistry issues that would 

preclude granting registration for the requested amended use of diflubenzuron. Available data 

support the following tolerances under 40 CFR 180.470 for residues of diflubenzuron in/on the 

following raw agricultural commodities:

Fruit, citrus, group 10-10........................................................3.0 ppm

Citrus, oil...........................................................................32 ppm

Adequate crop field trial data reflecting the proposed use patterns were submitted for purposes of 

establishing tolerances on the requested amended use. The Organization for Economic 

Cooperation and Development tolerance calculation procedures were utilized in determining the 

appropriate tolerance level for the requested amended use. Changes in recommended tolerance 

are based on the use of these calculation procedures and are shown in Table 1.

The proposed and recommended tolerances for diflubenzuron as a result of the subject action are 

presented in the table below.
Page 12 of 66

Table 2.2.3. Tolerance Summary for Diflubenzuron.

Commodity

Proposed Tolerance 

(ppm)

Recommended 

Tolerance (ppm)

Comments;

[Correct Commodity Definition]

Tolerances Proposed in PP#2F8015

Citrus, Group 10-10 1.3 3.0 Fruit, citrus, group 10-10

Recommended tolerance from OECD 

calculator

Citrus Oil 39 32 Citrus, oil

HAFT of 0.54 ppm multiplied by 55x 

concentration factor.

2.2.4 Revisions to Petitioned-For Tolerances

Revised Section F, proposing the following tolerances

Fruit, citrus, group 10-10........................................................3.0 ppm

Citrus, oil...........................................................................32 ppm

2.3 Label Recommendations

A statement must be added to diflubenzuron labels stating “Not For Homeowner Use”. 

Flowable concentrates are considered comparable to a wettable granular formulation. 

Additionally, the proposed rate for the flowable formulation is lower than that for the WDG 

formulation. The petitioner/registrant should be reminded that each formulation to be used must 

be properly supported by residue data.

3.0 Introduction

3.1 Chemical Identity

Structure and nomenclature are reported in Table 3.1.
Page 13 of 66

TABLE 3.1. Diflubenzuron Nomenclature.

Compound

Common Name Diflubenzuron

Trade and other Names Dimilin, Vigilante, Micromite, Adept

IUPAC Name 1-(4-chlorophenyl)-3-(2,6-difluorobenzoyl)urea

CAS Name N-[[(4-chlorophenyl)amino]carbonyl]-2,6-difluorobenzamide

CAS Registry Number 35367-38-5

End-Use Products (EP) 2 lb/gal FlC formulation; DIMILIN®2L (EPA Reg. No. 400-461);

25% WP formulation; DIMILIN®25W (EPA Reg. No. 400-465);

80% G formulation; Micromite®80WGS (EPA Reg. No. 400-487);

Regulated Metabolite

Common name 4-chlorophenylurea (CPU)

Regulated Metabolite

Common Name 4-chloroaniline (PCA)

3.2 Physical/Chemical Characteristics 

The physicochemical properties of diflubenzuron are reported in Appendix C. 

TABLE 3.2 Physicochemical Properties of Diflubenzuron.

Parameter Value Reference

Melting range 230-232 °C http://www.arsusda.gov/acsl/

services/ppdb/textfiles/DIFL

UBENZURON

pH Not available

Density Not available

Water solubility (25 °C) 0.08 ppm

Solvent solubility (25 °C) (ppm) 6.5 x 103 Acetone 

2 x 103 Acetonitrile 

2.4 x 104 Dioxane 

1.04 x 105 Dimethylformamide 

1.2 x 105 Dimethylsulfoxide 

1 x 103 Methanol 

6 x 102 Dichloromethane 

Vapor pressure (25 °C) 1.2 x 10- 4 mPa

Dissociation constant, pKa Not available

Octanol/water partition coefficient, Log(KOW) 3.89

F

F O

N

H

O

N

H

Cl

O

N

H

Cl

H2N

Cl

H2N
Page 14 of 66

3.3 Pesticide Use Pattern

3.3.1 Registered Products

There are 78 active diflubenzuron registrations, 40 Section 3s, 5 Section 18s, 9 EUPs, and 24

SLNs (24(c)s).

3.3.2 Proposed New Uses 

A summary of the proposed end-use products and summary of proposed use patterns are listed 

below.

Table 3.3.2.1 Summary of Proposed End-Use Products.

Trade Name Reg. No.

% ai 

(formulation)

Formulation 

Type Target New 

Crops

Target Pests

Label 

Date

Micromite®

80WGS 400-487 80%

Waterdispersible 

granule Citrus Fruit 

group

(10-10)

Citrus rust mite, Lepidopterous 

miners, and citrus root weevil 

complex

Undated 

specimen 

label

Dimilin®2L 400-461 22% Flowable

Concentrate

Table 3.3.2.2. Summary of Proposed Directions for Use of Diflubenzuron.

Applic. Timing, Type, 

Equipment.

Formulation

[EPA Reg. No.]

Applic. Rate 

(lb ai/A)

Max. No. Applic. 

per Season

Max. Seasonal 

Applic. Rate

(lb ai/A)

PHI

(days)

Citrus

Foliar

Aerial (3-20 GPA)

Ground (50-1,000 GPA)

(Airblast, and 

Chemigation)

Use Directions and Limitations: Maintain a minimum of 30 days between applications, except 

where split applications are used. Do not harvest cover crops for livestock feed or graze 

livestock in treated groves. The addition of a petroleum spray oil is recommended. Reentry 

interval of 12 hours.

80% WGS

[400-487] 0.3125 3

0.9375

(max yearly rate) 7

2 lb/gal FlC 0.156 3 0.47 7

Although not included in the petition, separate submissions were made for Diflubenzuron 90% 

Concentrate (EPA Reg No. 400-466) to allow formulation into products for use on citrus, and for 

Dimilin 2L (2 lb/gal Flowable) at the rate of 0.156 lb ai/A, not to exceed 0.47 lb ai/A/season. 

The same restrictions are on this label, as well as the recommendation to add a petroleum spray 

oil, except for the minimum aerial spray volume of 3 gal/A (10 gal/A in CA). A separate 

amendment request for Micromite 80 WGS requests an aerial spray volume of 3 gal/A.

Conclusions. The submitted labels are adequate to allow evaluation of the residue data relative 

to the proposed uses. The additional amended uses will be acceptable once the tolerances are 

established. Flowable concentrates are considered comparable to a wettable granular 
Page 15 of 66

formulation. Additionally, the proposed rate for the flowable formulation is lower than that for 

the WDG formulation. The petitioner/registrant should be reminded that each formulation to be 

used must be properly supported by residue data.

3.4 Anticipated Exposure Pathways

The Registration Division has requested an assessment of human health risk to support the 

proposed amended use of diflubenzuron on the remaining commodities in the citrus fruit 

subgroup. For domestic uses, humans may be exposed to diflubenzuron in food and drinking 

water, since diflubenzuron may be applied directly to growing crops and application may result 

in diflubenzuron reaching surface and ground water sources of drinking water. There are no

residential uses of diflubenzuron. In an occupational setting, applicators may be exposed while 

handling the pesticide prior to application, as well as during application. There is a potential for 

post-application exposure for workers re-entering treated fields. 

Risk assessments have been previously prepared for the existing uses of diflubenzuron. This risk 

assessment considers all of the aforementioned exposure pathways based on the proposed new 

uses of diflubenzuron, but also considers the existing uses as well, particularly for the dietary 

exposure assessment.

3.5 Considerations of Environmental Justice

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

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

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

http://www.eh.doe.gov/oepa/guidance/justice/eo12898.pdf).

As a part of every pesticide risk assessment, OPP considers a large variety of consumer 

subgroups according to well-established procedures. In line with OPP policy, HED estimates 

risks to population subgroups from pesticide exposures that are based on patterns of that 

subgroup’s food and water consumption, and activities in and around the home that involve 

pesticide use in a residential setting. Whenever appropriate, non-dietary exposures based on 

home use of pesticide products and associated risks for adult applicators and for toddlers, youths, 

and adults entering or playing on treated areas postapplication are evaluated. Further 

considerations are currently in development, as OPP has committed resources and expertise to 

the development of specialized software and models that consider exposure to bystanders and 

farm workers as well as lifestyle and traditional dietary patterns among specific subgroups. 

4.0 Hazard Characterization and Dose-Response Assessment

4.1 Toxicology Studies Available for Analysis

The overall toxicology database is sufficient for a determination of potential hazard to infants 

and children. The data provide no indication of an increased susceptibility to rats or to rabbits 

from in utero or post-natal exposure to diflubenzuron. Developmental and reproduction studies 

in rats and rabbits indicate a very low hazard potential for adverse effects. Developmental 
Page 16 of 66

studies were tested at the limit dose of 1000 mg/kg/day without apparent effects in both dams 

and the fetuses. The reproduction study indicated that effects in offspring occurred at doses that 

were higher than the doses producing effects in parents. There was no indication of 

abnormalities in the developing fetus in the prenatal developmental toxicity studies in either rats 

or rabbits at maternal limit doses of 1000 mg/kg/day. In addition, there was no evidence of 

sensitivity following pre- and/or post-natal exposure in a two-generation reproduction rat study. 

The acute and subchronic neurotoxicity studies were recently waived by HASPOC (TXR 

0056309) based on a weight of evidence approach. The recently submitted immunotoxicity study 

has been reviewed and immunotoxicity was not observed above the limit dose. 

4.2 Absorption, Distribution, Metabolism and Excretion

Rat metabolism data (MRID#s 44875501 and 44875502) indicate that diflubenzuron does not 

metabolize to PCA or CPU nor is CPU converted to PCA. The HED MARC met several times 

(02/20/2001 and 05/8/2001), concurred with the study findings, and concluded that a 2% in vivo

conversion factor for diflubenzuron to PCA or CPU should be dropped (MARC memo, 

05/31/2001). Based on the toxicity observed only at higher doses in the NTP studies for both 

CPU and PCA, additional CPU and PCA toxicity data are not needed. The toxicity of CPA and 

PCA will be considered equal to diflubenzuron for the non-cancer risk assessment. The MARC 

recommended that non-carcinogenic risk assessment include parent, CPU and PCA.

4.2.1 Dermal Absorption

Sprague-Dawley rats were given 0.005 or 0.05 mg/cm.sq. of C-14 diflubenzuron technical in 

gum tragacanth [0.25%]. Systemic absorption was less than 0.5% at each time interval regardless 

of the dose. Approximately 4.7 - 6.2% diflubenzuron was bound to the skin at the application 

site. A Dermal Absorption Factor of 0.5 % was determined.

4.3 Toxicological Effects

For diflubenzuron, the hemopoietic system is the target site with effects including increased 

sulfhemoglobin and/or methemoglobin levels in rat and dog studies. The non-cancer endpoints 

from diflubenzuron are protective of the non-cancer toxicity of the metabolites, CPU and PCA. 

The toxicity of CPA is well understood (WHO 2003) with the primary effect methemoglobin 

formation. High doses in the NTP study with CPU did not show methemoglobin formation.

Therefore, additional studies with CPU and PCA are not required.

The acute oral, dermal and inhalation toxicity of diflubenzuron is low. It is a mild eye irritant 

and not a skin irritant in laboratory animals. It is negative for sensitization in the guinea pig. In 

subchronic and chronic feeding studies, the primary endpoint of concern was 

methemoglobinemia and/or sulfhemoglobinemia. These effects were evident in both sexes of 

mice, rats, and dogs and were produced by more than one route of administration in rats [i.e., 

oral, dermal and inhalation]. The general consequence of methemoglobinemia and/or 

sulfhemoglobinemia is the impairment of the oxygen transportation capacity of the blood, which 

is generally known to be caused by aromatic amines in both humans and animals.
Page 17 of 66

No appropriate acute endpoint was identified in the hazard database to quantitate the risk to the 

general population or to females 13-50 years old from single dose administration of 

diflubenzuron. Therefore, there is no aRfD or acute population-adjusted dose (aPAD). The 

short-term dermal endpoint was selected from a 21-day rat dermal study with a NOAEL of 500 

mg/kg/day based on a significant increase in methemoglobinemia observed at the lowestobserved-adverse-effect level (LOAEL) of 1000 mg/kg/day. The intermediate-term dermal 

endpoint was selected from a 13-week oral (capsule) study in the dog with a NOAEL of 2 

mg/kg/day based on increased methemoglobinemia observed at the LOAEL 6.24 mg/kg/day. 

The short-, and intermediate-term inhalation endpoints were selected from a 28-day rat 

inhalation toxicity study with a NOAEL of 0.109 mg/L (highest dose tested, HDT), based on a 

statistically significant increase in methemoglobin levels observed at 0.12 mg/L (LOAEL). The 

chronic dietary, long-term dermal and long-term inhalation endpoints were selected from a 

chronic dog study with a NOAEL of 2 mg/kg/day based on increased methemoglobin levels 

observed at 10 mg/kg/day (LOAEL). The cRfD is 0.02 mg/kg/day and the cPAD is 0.02 

mg/kg/day. 

The HED RfD/Peer Review Committee classified diflubenzuron as “Group E,” evidence of noncarcinogenicity for humans, based on lack of evidence of carcinogenicity in rats and mice 

(04/27/1995). PCA, a metabolite of diflubenzuron, tested positive for splenic tumors in male rats 

and hepatocellular adenomas/carcinomas in male mice in a National Toxicology Program (NTP) 

study. Therefore, the RfD/Peer Review Committee classified PCA as a “Group B2" probable 

human carcinogen. However, recently submitted acceptable rat metabolism studies show that 

diflubenzuron was not metabolized to either PCA or CPU. On May 8, 2001, the MARC 

reviewed the recently submitted metabolism studies, accepted the study findings, and concluded 

that cancer risks for CPU and PCA should be assessed individually. Based on 

methemoglobinemia observed only at higher doses in NTP studies for both monuron, similar to 

CPU and PCA (6 and 18 mg/kg/day, NTP Report No. 351, July 1989), additional CPU and PCA 

toxicity data are not needed. The toxicity of CPU and PCA will be considered equal to 

diflubenzuron for the non-cancer risk assessment. The non-carcinogenic risk assessment should 

include diflubenzuron, CPU and PCA.

The complete toxicity profile for diflubenzuron is provided in Appendix A. 

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

The FQPA may be reduced to 1x based on recently waived neurotoxicity studies and the lack of 

sensitivity in the database. 

4.4.1 Completeness of the Toxicology Database

The toxicological database for diflubenzuron is adequate for the purpose of this risk assessment. 

Adequate data are available for diflubenzuron as well as CPU and PCA. Specifically, the current 

diflubenzuron non-cancer endpoint for methemoglobinia is protective of the toxicity observed at 

higher doses in the NTP cancer studies conducted with either CPU or PCA. Based on a WOE 

approach considering all the available diflubenzuron hazard and exposure information, the 

HASPOC concluded that an acute and subchronic neurotoxicity study are not required at this 
Page 18 of 66

time (6/7/12, TXR #: 0056309). Furthermore, an acceptable immunotoxicity study has been 

submitted and reviewed by the Agency (TXR 0056396).

4.4.2 Evidence of Neurotoxicity

There are no clear signs of neurotoxicity following subchronic or chronic dosing in multiple 

species in the diflubenzuron database. The toxicity profile of diflubenzuron shows that the 

principal toxic effects are the formation of methemoglobinemia and/or sulfhemoglobinemia in 

the blood. Based on weight of evidence the acute and subchronic neurotoxicity studies are

waived (HASPOC, TXR 0056309).

4.4.3 Evidence of Sensitivity/Susceptibility in the Developing or Young Animal

The toxicology database for diflubenzuron is adequate for FQPA assessment. Based on the 

available developmental toxicity studies in rats and rabbits, there is no increased susceptibility to 

fetuses exposed in utero. The dietary food exposure assessment uses conservative assumptions 

which result in protective estimates of dietary exposure. The dietary drinking water assessment 

uses values generated by model and associated modeling parameters which are designed to 

provide protective, high-end estimates of water concentrations.

4.4.4 Residual Uncertainty in the Exposure Database 

There are no residual uncertainties in the exposure database. The dietary risk assessment is 

conservative and will not underestimate dietary and/or non-dietary residential exposure to 

diflubenzuron.

4.5 Toxicity Endpoint and Point of Departure

4.5.1 Dose-Response Assessment

Toxicity endpoints and points of departure (PODs) for dietary (food and water), and occupational 

exposure scenarios are summarized below. A detailed description of the studies used as a basis 

for the selected endpoints are presented in Appendix A. 

No appropriate toxicological endpoint attributable to a single exposure was identified in the 

hazard database, including oral developmental toxicity studies in rats and rabbits.

The chronic dog study was used to select the endpoint for establishing the cRfD of 0.02 

mg/kg/day. The standard 100x UF was applied to account for interspecies extrapolation and 

intraspecies variation. The NOAEL of 2.0 mg/kg/day was based on methemoglobinemia and 

sulfhemoglobinemia seen at 10 mg/kg/day (LOAEL). The FQPA safety factor of 1x is 

applicable for chronic dietary risk assessment. Thus, the cPAD is 0.02 mg/kg/day.

Incidental oral endpoints were not selected since there are no registered or proposed uses of 

diflubenzuron which result in residential exposure.
Page 19 of 66

A short-term dermal endpoint was selected from a 21-day rat dermal toxicity study. The 

NOAEL of 500 mg/kg/day was based on the significant increase in methemoglobinemia 

observed at 1000 mg/kg/day (limit dose). This study is route-specific, is of appropriate duration 

and measures the effects of concern; i.e., methemoglobin and/or sulfhemoglobin.

An intermediate-term dermal endpoint was selected from a subchronic oral toxicity dog study. 

The NOAEL of 2.0 mg/kg/day was based on increased methemoglobinemia at 6.24 mg/kg/day. 

This endpoint (methemoglobinemia/ sulfhemoglobinemia) was seen consistently in the 90-day 

dog study and chronic toxicity studies in rats, mice and dogs at similar dosages and it is 

appropriate for this exposure period of concern. Since an oral NOAEL was selected for a 

dermal-exposure scenario, a dermal-absorption factor of 0.5% should be used for this risk 

assessment when converting dermal exposure to oral equivalents.

A long-term dermal endpoint was selected from a chronic oral toxicity study in the dog ( see 

section 3.5.2, above). An oral study was selected since no appropriate long-term dermal study is 

available in the database. A 0.5% dermal-absorption factor should be used to convert to oral 

equivalents.

Inhalation endpoints were selected from a 28-day rat inhalation toxicity study. The NOAEL of 

0.109 mg/L (HDT) in the study was based on no effect at highest dose tested.

A long-term inhalation endpoint was selected from a chronic oral toxicity dog study, see section 

3.5.2, above. An oral study was selected since no appropriate long-term inhalation study is 

available in the database. A 100% inhalation-absorption factor should be used to convert to oral 

equivalents.

A MOE of 100 is adequate for occupational exposure.

4.5.2 Recommendations for Combining Exposure Routes

Aggregate exposure risk assessments were assessed by incorporating the drinking water directly 

into the dietary-exposure assessment for the following scenario: chronic aggregate exposure 

(food + drinking water). Short-, intermediate-, and long-term aggregate-risk assessments were 

not performed because there are no registered or proposed uses of diflubenzuron which result in 

residential exposures. Acute and cancer aggregate-risk assessments were not performed because 

no appropriate endpoint was available to determine the aRfD for the general population or any 

population subgroup and diflubenzuron is not carcinogenic. 

4.5.3 Classification of Carcinogenic Potential

Based on the available evidence, which included adequate carcinogenicity studies in rats and 

mice, and battery of negative mutagenicity studies, diflubenzuron was classified as “Group E,”

evidence of non-carcinogenicity for humans, by the RfD Peer Review Committee (04/27/1995). 

The following is excerpted from the HED Metabolism Committee Meeting Memorandum of 

5/31/01 (D272976).
Page 20 of 66

“CPU is the major degradate found in water and is a significant metabolite in milk. CPU is 

structurally related to monuron (N,N-dimethyl-CPU), a compound producing tumors of the 

kidney and liver in male rats. Given that there is no accepted mechanism of carcinogenicity for 

monuron and that CPU is major metabolite of monuron in rats, there is still concern for the 

toxicity of CPU. Thus, a literature search was conducted for any toxicity studies for CPU. As 

no pertinent information was found (Personal Communication, Alberto Protzel, 5/8/01), risk 

from CPU will be assessed as follows: 1) for carcinogenic effects, a Q1* will be calculated for 

monuron and applied to CPU;

EFED has determined that PCA is only a minor metabolite of DFB in the environment (K. 

Costello, Personal Communication, 2/28/01). Drinking water will thus not be considered in the 

risk assessment for PCA.

In summary, Cancer risks for CPU and PCA will be assessed individually. The tolerance 

expression should include parent, PCA and CPU. Although CPU is not of concern for the 

endpoints currently regulated for DFB, it is a major metabolite in milk and the major degradate 

found in water, with potential toxicity concerns.”

Therefore, a cancer assessment for CPU milk and water was conducted using a Q* of 1.52 x 10-2. 

In addition, a cancer assessment for PCA food only was conducted using a Q* of 1.12 x 10-1.

4.5.4 Summary of Points of Departure Used in Risk Assessment

Toxicological doses/endpoints selected for the diflubenzuron risk assessment are provided in 

Tables 4.5.4.1 and 4.5.4.2.
Page 21 of 66

Table 4.5.4.1. Summary of Toxicological Doses and Endpoints for Diflubenzuron for Use in Dietary Human Health Risk 

Assessments

Exposure/Scenario Point of 

Departure

Uncertainty/FQP

A Safety Factors

RfD, PAD, LOC for Risk 

Assessment

Study and Toxicological Effects

Acute Dietary 

all populations 

Not 

Applicable 

Not Applicable No appropriate endpoint attributable to single exposure was available.

Chronic Dietary 

all populations 

NOAEL= 2 

mg/kg/day 

UFA= 10X

UFH=10X

FQPA SF = 1x 

cPAD = 

chronic RfD 

FQPA SF 

= 0.02 mg/kg/day 

Chronic Dog Study 00146174

LOAEL = 10 mg/kg/day based on 

methemoglobinemia and 

sulfhemoglobinemia 

Cancer (all routes)

Diflubenzuron

Classification: “Group E” evidence of non- carcinogenicity for humans.

Cancer (oral, 

dermal, inhalation)

PCA “Group 

B2" 

probably 

human 

carcinogen

Q1

*

1.12 x 

10-1

(mg/kg/day)-

1

Not Applicable NTP Oral mouse study

Cancer (oral, 

dermal, inhalation)

CPU Q1

*

based on 

monuron a 

structural 

analog and 

the Q1

*

1.52 

x 10-2

Not Applicable NTP Oral rat study

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

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

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

potential variation in sensitivity among members of the human population (intraspecies). UFL = use of a LOAEL to extrapolate a NOAEL. UFS = 

use of a short-term study for long-term risk assessment. UFDB = to account for the absence of key date (i.e., lack of a critical study). FQPA SF = 

FQPA Safety Factor. PAD = population adjusted dose (a = acute, c = chronic). RfD = reference dose. MOE = margin of exposure. LOC = level 

of concern. N/A = not applicable
Page 22 of 66

Table 4.5.4.2. Summary of Toxicological Doses and Endpoints for Diflubenzuron for Use in Residential and Occupational 

Human Health Risk Assessments

Exposure/

Scenario

Point of 

Departure

Uncertainty 

Factors

Level of Concern 

for Risk 

Assessment

Study and Toxicological Effects

Short- and 

Intermediate-Term 

Incidental Oral 

(1 day - 6 months) 

(Residential) 

Not applicable Not applicable Not applicable These endpoints were not evaluated. There are no 

registered uses of diflubenzuron which result in 

significant residential exposure.

Short-Term Dermal 

(1 - 30 days) 

(Occupational) 

NOAEL = 500 

mg/kg/day 

UFA= 10X

UFH=10X

LOC for MOE = 

100

21-Day rat dermal 43954101

LOAEL = 1000 mg/kg/day based on 

methemoglobinemia

Dermal Intermediate 

Term (1-6 months)

NOAEL = 2 

mg/kg/day 

UFA= 10X

UFH=10X

Dermal 

Absorption: 

0.5%

LOC for MOE = 

100

13 - week oral dog 00038706

LOAEL = 6.4 mg/kg/day based on 

methemoglobinemia

Inhalation Short 

Term (1-30 days) 

NOAEL = 

0.109 mg/L

NOAEL = 

20.301

mg/kg/day 

UFA= 10X

UFH=10X

LOC for MOE = 

100 

28-day Inhalation rat Study, 44950601

No effect at HDT2, 0.109 mg/L

Inhalation 

Intermediate Term

(1-6 months) 

NOAEL = 

0.109 mg/L

NOAEL = 

20.301

mg/kg/day 

UFA= 10X

UFH=10X

LOC for MOE = 

100 

28-day Inhalation rat Study 44950601

No effect at HDT, 0.109 mg/L

Inhalation Long

Term

(1-6 months)

NOAEL = 2 

mg/kg/day 

UFA= 10X

UFH=10X

LOC for MOE = 

100

Chronic Dog Study -00146174

LOAEL = 10 mg/kg/day based on 

methemoglobinemia and sulfhemoglobinemia

Cancer (all routes) Classification: “Group E” evidence of non- carcinogenicity for humans.

1 Conversion from mg/L to oral dose (mg/kg/day) = mg/L x absorption (1.0) x [Respiratory Volume (Sprague-Dawley rats) for 6 

hours/day] x Duration of Exposure (5 days/week)/body weight x 7 days/week = 0.109 mg/L x 1.0 x [0.26(RV) x 6 hrs] x 5 d/wk 

÷ 0.236 kg x 7 d/wk = 20.3 mg/kg/day (TXR 0050503)

2 Highest Dose Tested

Based on the available toxicity database and the Agency's current practices, the short- and 

intermediate inhalation risk for diflubenzuron was assessed using a 28-day inhalation toxicity 

study. The long-term inhalation risk was assessed using a chronic toxicity study in dog. The 

Agency sought expert advice and input on issues related to this route to route extrapolation 

approach (i.e. the use of oral toxicity studies for inhalation risk assessment) from its Federal 

Insecticide, Fungicide, and Rodenticide Act Scientific Advisory Panel (SAP) in December 2009. 

The Agency received the SAP’s final report on March 2, 2010 

(http://www.epa.gov/scipoly/SAP/meetings/2009/120109meeting.html). The Agency is in the 

process of evaluating the SAP report and may, as appropriate, reexamine and develop new 

policies and procedures for conducting inhalation risk assessments, including route to route 

extrapolation of toxicity data. If any new policies or procedures are developed, the Agency may 

revisit the need for an inhalation toxicity study for diflubenzuron and/or a reexamination of the 

inhalation toxicity risk assessment.
Page 23 of 66

5.0 Dietary Exposure and Risk Assessment 

5.1 Metabolite/Degradate Residue Profile

5.1.1 Summary of Plant and Animal Metabolism Studies

The qualitative nature of the residue in plants and fungi is adequately understood based on data 

from citrus, mushroom, rice, and soybean metabolism studies. The metabolism of diflubenzuron

in crops tested is similar, and the radioactive components are also similar to those found in soil. 

The nature of the residue in rotational crops is adequately understood. The nature of the residue 

in livestock is also adequately understood based on acceptable poultry and ruminant metabolism 

studies reflecting oral dosing. The HED Metabolism Assessment Review Committee (MARC) 

has concluded that the residues of concern, for the purpose of tolerance expression, are 

diflubenzuron and its metabolites 4-chlorophenylurea (CPU) and 4-chloroaniline (PCA).

Structures and names of diflubenzuron metabolites are provided in Appendix B. 

5.1.2 Summary of Environmental Degradation

Under aerobic soil conditions, diflubenzuron appears to degrade to 4-chlorophenyl urea (CPU) 

which reached a maximum concentration of 37% of applied at 14 days post-treatment. The other 

major degradate, CO2, was reported to reach a maximum concentration of 26.3% of applied by 

21 days post-treatment. Three minor degradates, 2,6-difluorobenzoic acid, 2,6-

difluorobenzamide, and p-chloroaniline, each reaching a maximum concentration of <10% of 

applied, were identified in the aerobic soil metabolism study. These metabolites were detectable 

in an anaerobic soil metabolism study, as well. Due to the stability of diflubenzuron to abiotic 

processes, limited data are available on the persistence and mobility of diflubenzuron 

metabolites.

5.1.3 Comparison of Metabolic Pathways

Rat metabolism data (MRID#s 44875501 and 44875502) indicate that diflubenzuron does not 

metabolize to PCA or CPU nor is CPU converted to PCA. In mushroom metabolism studies, 

residues of parent, CPU, DFBA and PCA were detected. Extracts from treated soybean leaves 

collected the day of the first application, leaves and pods collected the day of the second 

application, and leaves collected at harvest contained unchanged parent as >90% of the TRR 

(ppm values were not provided). No DFBA, CPU, or PCA was detected. Radioactive residues 

in citrus fruit consisted almost entirely of unchanged diflubenzuron; no detectable levels (<1 

ppb) of PCA, CPU and DFBA were reported. Residues of diflubenzuron per se in apple fruit 

identified and residues of PCA, DFBA, and CPU were nondetectable (<1 ppb). Terminal 

residues identified in animal tissues, milk, and eggs include diflubenzuron, 2-

hydroxydiflubenzuron (2HDFB), 2,6-difluorobenzamide (DFBAM), DFBA, CPU, and PCA.
Page 24 of 66

5.1.4 Residues of Concern Summary and Rationale

The qualitative nature of the residue in plants and fungi is adequately understood based on data 

from citrus, mushroom, rice, and soybean metabolism studies. The metabolism of diflubenzuron 

in crops tested is similar, and the radioactive components are also similar to those found in soil. 

The nature of the residue in livestock is also adequately understood based on acceptable poultry 

and ruminant metabolism studies reflecting oral dosing. The HED Metabolism Assessment 

Review Committee (MARC) has concluded that the residues of concern, for the purpose of 

tolerance expression, are diflubenzuron and its metabolites 4-chlorophenylurea (CPU) and 4-

chloroaniline (PCA).

Table 5.1.4. Summary of Metabolites and Degradates to be included in the Risk Assessment and Tolerance 

Expression.

Matrix For Risk Assessment For Tolerance Expression

Plants diflubenzuron and its metabolites PCA and 

CPU

diflubenzuron and its metabolites PCA and 

CPU

Rotational crop diflubenzuron and its metabolites PCA and 

CPU

diflubenzuron and its metabolites PCA and 

CPU

Livestock: diflubenzuron and its metabolites PCA and 

CPU

diflubenzuron and its metabolites PCA and 

CPU

Water diflubenzuron and its metabolite CPU N/A

5.2 Food Residue Profile

Chemtura Corporation has submitted field trial data for diflubenzuron on grapefruit, lemon, and 

orange, the representative crops of the citrus crop group. A total of 20 citrus field trials were 

conducted in the United States during the 2008 and 2009 growing seasons. Nine orange trials 

were conducted encompassing North American Free Trade Agreement (NAFTA) Growing 

Zones 3 (FL; 5 trials), 6 (TX; 1 trial), and 10 (CA; 3 trials). Six grapefruit trials were conducted 

encompassing NAFTA Growing Zones 3 (FL; 3 trials), 6 (TX; 1 trial), and 10 (CA; 2 trials). 

Five lemon trials were conducted encompassing NAFTA Growing Zones 3 (FL; 1 trial) and 10 

(CA; 4 trials). Although the petitioner reported that 23 trials were conducted on citrus fruits (12 

– orange, 6 – grapefruit, and 5 – lemon), HED has concluded that two of the orange trials 

conducted during 2008 constitute a single trial and three of orange trials conducted during 2009 

constitute another single trial because the trial conditions at the respective sites were very 

similar. For each year, the samples from these trial sites are considered replicate samples from a 

single trial for purposes of 860.1500 data requirements. The results from these studies are 

discussed in the appropriate data evaluation report (DER) and summarized in the following 

tables. 
Page 25 of 66

TABLE 5.2.1. Summary of Residue Data from Citrus Field Trials with Diflubenzuron.

Commodity Total Rate

lb a.i./A

[Spray Vol1]

PHI 

(days)

Analyte2 Residue Levels (ppm)3

n Sample 

Min.

Sample 

Max.

LAFT4 HAFT4 Median Mean Std. 

Dev.

Orange 0.9330-0.9588

[CONC+DIL]

7 DFB 9 0.096 0.730 0.104 0.565 0.256 0.332 0.163

CPU 9 <0.01 0.019 <0.01 <0.014 0.010 0.011 0.001

PCA 9 <0.005 <0.005 <0.005 <0.005 <0.005 <0.005 NA

CPU+PCA 9 <0.015 <0.024 <0.015 <0.019 0.015 0.016 0.001

Combined Residues 9 <0.111 <0.745 <0.123 <0.580 0.274 0.348 0.162

0.9443-1.0302

[ULV]

7 DFB 3 0.076 0.467 0.090 0.407 0.385 0.294 0.177

CPU 3 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 NA

PCA 3 <0.005 <0.005 <0.005 <0.005 <0.005 <0.005 NA

CPU+PCA 3 <0.015 <0.015 <0.015 <0.015 <0.015 <0.015 NA

Combined Residues 3 <0.091 <0.482 <0.105 <0.422 0.400 0.309 0.177

Grapefruit 0.9396-0.9609

[CONC+DIL]

7 DFB 6 0.073 0.571 0.105 0.476 0.170 0.233 0.152

CPU 6 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 NA

PCA 6 <0.005 <0.005 <0.005 <0.005 <0.005 <0.005 NA

CPU+PCA 6 <0.015 <0.015 <0.015 <0.015 <0.015 <0.015 NA

Combined Residues 6 <0.088 <0.586 <0.120 <0.491 <0.185 0.248 0.152

0.9510-0.9607

[ULV]

7 DFB 2 0.050 0.171 0.059 0.135 0.097 0.097 NA

CPU 2 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 NA

PCA 2 <0.005 <0.005 <0.005 <0.005 <0.005 <0.005 NA

CPU+PCA 2 <0.015 <0.015 <0.015 <0.015 <0.015 <0.015 NA

Combined Residues 2 <0.065 <0.186 <0.074 <0.150 0.112 0.112 NA

Lemon 0.9349-0.9469

[CONC+DIL]

7-8 DFB 5 0.186 1.242 0.227 1.068 0.593 0.636 0.385

CPU 5 <0.01 0.021 <0.01 <0.020 0.01 0.012 0.004

PCA 5 <0.005 <0.005 <0.005 <0.005 <0.005 <0.005 NA

CPU+PCA 5 <0.015 <0.026 <0.015 <0.025 0.015 0.017 0.004

Combined Residues 5 <0.201 <1.257 <0.242 <1.083 0.617 0.653 0.385

1 Application spray types: concentrate spray (CONC; 82-90 GPA); dilute spray (DIL; 158-170 GPA); ultra low volume spray 

(ULV; 3-4 GPA).

2 DFB = Diflubenzuron; CPU = 4-chlorophenylurea; PCA = 4-chloroaniline; Combined Residues = DFB + CPU + PCA.

3 Except for sample min/max, values reflect per trial averages; n = no. of field trials. For calculation of median, mean, and 

standard deviation, the LLMV (0.05 ppm for DFB, 0.01 ppm for CPU, and 0.005 ppm for PCA) was used for any results 

reported as <LLMV in Table C.3. NA = not applicable.

4

 LAFT = lowest average field trial; HAFT = highest average field trial.

Conclusions: The submitted residue data are scientifically adequate. Residue data for oranges 

are available from only 9 not the typically required 12 field trials. Although data from 12 orange 

field trials were included in the study, HED has concluded that two of the orange trials 

conducted during 2008 constitute a single field trial and three of the orange trials conducted 

during 2009 constitute another single trial. The petitioner should be reminded to adequately 

separate field trials. ULV aerial application did not result in higher residues than the ground 

applications; residues in ULV trials were significantly lower than residues in ground 

applications.

The residue decline studies demonstrate that residues of diflubenzuron per se in/on orange, 

grapefruit, and lemon either declined gradually or remained steady at post-treatment intervals out 
Page 26 of 66

to 21 days. With the exception of one orange sample with residues of CPU at 0.012 ppm (3 

DALA), residues of CPU and PCA were below the LLMV (0.01 and 0.005 ppm, respectively) 

in/on all samples from the decline studies.

An acceptable method was used for residue quantitation, and adequate storage stability data are 

available to support sample storage intervals and conditions for all analytes.

The submitted orange processing study is adequate. Combined residues of diflubenzuron, CPU, 

and PCA were <1.091 ppm in/on orange fruit harvested 7 days following three broadcast foliar 

applications of diflubenzuron (80% WG) totaling 3.71 lb a.i./A (4.16 kg a.i./ha; 4x rate). 

Combined residues were <0.073, <0.973, and 59.78 ppm in orange juice, dried pulp and citrus 

oil, respectively. These data indicate that the combined residues did not concentrate in orange 

juice (0.07x processing factor) or dried pulp (0.89x processing factor), but did concentrate in 

orange citrus oil (55x processing factor). 

5.3 Water Residue Profile

The drinking water residues used in the dietary risk assessment were provided by the 

Environmental Fate and Effects Division, summarized in the following memorandum: 

“Ecological Risk and Drinking Water Assessments for Proposed Label Amendments of 

Diflubenzuron.” (DP #: 400093, F. Khan and S. Wente, 11/20/2012) and incorporated directly 

into this dietary assessment. Water residues were incorporated in the DEEM-FCID into the food 

categories “water, direct, all sources” and “water, indirect, all sources.” 

The estimated drinking water concentrations (EDWCs) for diflubenzuron use on citrus are higher 

than the previously recommended annual mean (chronic/non cancer) and 30 year average 

(chronic/cancer) concentrations for surface water. Therefore, the currently calculated EDWCs 

(3.47μg /L for the peak (acute) concentration, 0.26 μg /L for the annual mean (chronic/non 

cancer) concentration, and 0.12 μg /L for the 30 year average concentration (chronic/cancer) are 

recommended for diflubenzuron. 

The current EDWCs of 4-chlorophenyl urea (CPU) for surface water do not supersede the 

drinking water concentrations previously estimated (US EPA, 2002: D279732) for drinking 

water. Therefore, the values (20.68 μg/L for the peak (acute) concentration, 12.52 μg /L for the 

annual mean (chronic/non-cancer) concentration, and 8. 81 μg /L for the 36 year average 

concentration (chronic/cancer) from the previous drinking water assessment are recommended.

Since requested label modifications have no implication in groundwater modeling, 

groundwater exposure for drinking water was not performed. The previous SCI-GROW model 

estimated the concentrations of parent diflubenzuron and the degradate CPU in drinking water 

from shallow ground water sources to be 0.006 μg /L and 0.201 μg /L, respectively (US EPA, 

2002). The above concentrations can be considered as both the acute and chronic value for the 

respective chemicals.
Page 27 of 66

Table 5.3. Summary of Estimated Surface Water and Groundwater Concentrations for Diflubenzuron.

Scenario Surface Water Conc., ppb

a Groundwater Conc., ppb b

Acute 24.2 0.207

Chronic (non-cancer) 12.8 (parent 12.52 ppb+ CPU 0.26 

ppb summed)

0.207

Chronic (cancer) 8.81 CPU

a

From the Tier II PRZM-EXAMS - Index Reservoir model. 

b

From the SCI-GROW model.

5.4 Dietary Risk Assessment

5.4.1 Description of Residue Data Used in Dietary Assessment

The chronic non-cancer dietary exposure analysis assumed diflubenzuron residues were present 

in all commodities at established/recommended tolerance levels for most commodities except 

orange (0.367 ppm), grapefruit (0.214 ppm) and lemon (0.653 ppm) which used average field 

trial residues. 

A residue value of 0.003 ppm was used for the PCA cancer assessment for all food commodities 

in DEEM. This represents 1⁄2 the LOQ. An average residue of 0.048 ppm was used for 

mushroom residue input value in the PCA cancer assessment. A residue value of 0.003 ppm was

used for the CPU cancer assessment for milk commodities.

5.4.2 Percent Crop Treated Used in Dietary Assessment

The chronic non-cancer dietary exposure analysis used 100% crop treated while the cancer 

dietary exposure analysis used the following average percent crop treated: soybeans (1%), 

peppers (1%), oranges (5%), tangerines (5%), grapefruit (15%), pear (5%), apricot (10%), peach 

(5%), almond, (10%), pecan (2.5%), rice (1%), wheat (1%), cotton (1%), artichoke (50%), and 

peanut (5%) .

5.4.3 Acute Dietary Risk Assessment

No toxic effects attributable to a single (i.e., acute) exposure to diflubenzuron have been 

identified; therefore, an acute reference dose (RfD) has not been established for diflubenzuron 

and an acute dietary exposure assessment has not been conducted. 

5.4.4 Chronic Dietary Risk Assessment

The slightly refined chronic dietary risk assessment for diflubenzuron shows that chronic dietary 

risk estimates do not exceed HED's level of concern (i.e. <100% chronic population adjusted 

doses (cPAD)). The highest chronic drinking water concentration of 12.8 ppb was used in this 

analysis. The results of the analysis indicate that chronic risk from the dietary (food + drinking 

water) exposure to diflubenzuron will not exceed HED’s level of concern for the general U.S. 

population, and all population subgroups. The chronic dietary risk estimate for the highest 

reported exposed population subgroup, children 1-2 years old, is 38% of the cPAD. The general 

US population utilizes 11% of the cPAD.
Page 28 of 66

5.4.5 Cancer Dietary Risk Assessment

Diflubenzuron is classified as “Group E,” evidence of non-carcinogenicity for humans, therefore, 

a dietary cancer assessment is not required. However, metabolites CPU and PCA are considered 

probable carcinogens and have Q*s assigned to them. Individual cancer dietary exposure 

analyses were conducted for each metabolite.

The cancer assessment for PCA includes food only. For PCA, the cancer dietary exposure 

estimate for the U.S. population is 1 x 10-6.The cancer assessment for CPU includes milk and 

water only. The cancer chronic EDWC in surface water for CPU is 8.81 ppb. For CPU, the 

cancer dietary exposure estimate for the U.S. population is 3 x 10-6.

5.4.6 Summary Table

Table 5.4.6. Summary of Dietary (Food and Drinking Water) Exposure and Risk for Diflubenzuron

Population Subgroup

Acute Dietary

(95 Percentile) Chronic Dietary Cancer

Dietary 

Exposure 

(mg/kg/day)

% aPAD*

Dietary 

Exposure

(mg/kg/day)

% cPAD*

Dietary 

Exposure

(mg/kg/day)

Risk

General U.S. Population

No toxic effects 

attributable to a single 

(i.e., acute) exposure to 

diflubenzuron have been 

identified; therefore, an 

acute reference dose 

(RfD) has not been 

established for 

diflubenzuron and an 

acute dietary exposure 

assessment has not been 

conducted.

0.002139 11

Diflubenzuron is 

classified as “Group E,” 

evidence of noncarcinogenicity for 

humans, therefore, a 

dietary cancer assessment 

is not required.

All Infants (< 1 year old) 0.002615 13

Children 1-2 years old 0.007606 38

Children 3-5 years old 0.005678 28

Children 6-12 years old 0.003006 15

Youth 13-19 years old 0.001800 9.0

Adults 20-49 years old 0.001634 8.2

Adults 50-99 years old 0.001667 8.3

Females 13-49 years old 0.001615 8.1

*The values for the highest exposed population for each type of risk assessment should be bolded
Page 29 of 66

Table 5.4.7. Summary of Dietary (Milk and Drinking Water) Exposure and Risk for Metabolite 

CPU

Population Subgroup

Acute Dietary

(95 Percentile) Chronic Dietary Cancer

Dietary 

Exposure 

(mg/kg/day)

% aPAD

Dietary 

Exposure

(mg/kg/day)

% cPAD

Dietary 

Exposure

(mg/kg/day)

Risk

General U.S. Population NA NA 0.000204 3 x 10-6

Table 5.4.8. Summary of Dietary (Food Only) Exposure and Risk for Metabolite PCA

Population Subgroup

Acute Dietary

(95 Percentile) Chronic Dietary Cancer

Dietary 

Exposure 

(mg/kg/day)

% aPAD

Dietary 

Exposure

(mg/kg/day)

% cPAD

Dietary 

Exposure

(mg/kg/day)

Risk

General U.S. Population NA NA 0.000010 1 x 10-6

6.0 Residential (Non-Occupational) Exposure/Risk Characterization

A residential assessment is not required because there are no diflubenzuron products registered 

for homeowner use and there are no products registered for application to residential areas. 

 

6.1 Residential Bystander Post-application Inhalation Exposure

Based on the Agency's current practices, a quantitative post-application inhalation exposure 

assessment was not performed for diflubenzuron at this time. However, volatilization of 

pesticides may be a potential source of post-application inhalation exposure to individuals nearby 

to pesticide applications. The Agency sought expert advice and input on issues related to 

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

Scientific Advisory Panel (SAP) in December 2009. The Agency received the SAP’s final report 

on March 2, 2010 (http://www.epa.gov/scipoly/SAP/meetings/2009/120109meeting.html) and is 

in the process of evaluating the SAP report. The Agency may, as appropriate, develop policies 

and procedures to identify the need for and, subsequently, the way to incorporate postapplication inhalation exposure into the Agency's risk assessments. If new policies or 

procedures are put into place, the Agency may revisit the need for a quantitative post-application 

inhalation exposure assessment for diflubenzuron.

6.2 Spray Drift

Spray drift is always a potential source of exposure to residents nearby to spraying operations. 

This is particularly the case with aerial application, but, to a lesser extent, could also be a 

potential source of exposure from the ground application method employed for diflubenzuron. 

The Agency has been working with the Spray Drift Task Force, EPA Regional Offices and State 
Page 30 of 66

Lead Agencies for pesticide regulation and other parties to develop the best spray drift 

management practices (see the Agency’s Spray Drift website for more information at 

(http://www.epa.gov/opp00001/factsheets/spraydrift.htm). On a chemical by chemical basis, the 

Agency is now requiring interim mitigation measures for aerial applications that must be placed 

on product labels/labeling. The Agency has completed its evaluation of the new database 

submitted by the Spray Drift Task Force, a membership of U.S. pesticide registrants, and is 

developing a policy on how to appropriately apply the data and the AgDRIFT computer model to 

its risk assessments for pesticides applied by air, orchard airblast and ground hydraulic methods. 

After the policy is in place, the Agency may impose further refinements in spray drift 

management practices to reduce off-target drift with specific products with significant risks 

associated with drift.

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

performed as a result of pesticide drift from neighboring treated agricultural fields, an inhalation 

exposure assessment was performed for flaggers. This exposure scenario is representative of a 

worse case inhalation (drift) exposure and may be considered protective of most outdoor 

agricultural and commercial post-application inhalation exposure scenarios. 

7.0 Aggregate Exposure/Risk Characterization

In accordance with the FQPA, HED must consider and aggregate (add) pesticide exposures and 

risks from three major sources: food, drinking water, and residential exposures (dermal and 

residential). In an aggregate assessment, exposures from relevant sources are added together and 

compared to quantitative estimates of hazard (e.g., a NOAEL or PAD), or the risks themselves 

can be aggregated. When aggregating exposures and risks from various sources, HED considers 

both the route and duration of exposure.

7.1 Acute & Chronic Aggregate Risk

Acute and chronic aggregate exposures include food plus drinking water exposures. As 

demonstrated under Section 5.4, acute and chronic aggregate risks are not of concern.

7.2 Short- and Intermediate-Term Aggregate Risk

A Short- and Intermediate- Term Aggregate Risk assessment is not required because there are no 

diflubenzuron products registered for homeowner use and there are no products registered for 

application to residential areas. 

8.0 Cumulative Exposure/Risk Characterization

Unlike other pesticides for which EPA has followed a cumulative risk approach based on a 

common mechanism of toxicity, EPA has not made a common mechanism of toxicity finding as 

to diflubenzuron and any other substances and diflubenzuron does not appear to produce a toxic 

metabolite produced by other substances. For the purposes of this tolerance action, therefore, 

EPA has not assumed that diflubenzuron has a common mechanism of toxicity with other 

substances.
Page 31 of 66

For information regarding EPA’s efforts to determine which chemicals have a common 

mechanism of toxicity and to evaluate the cumulative effects of such chemicals, see the policy 

statements released by EPA’s Office of Pesticide Programs concerning common mechanism 

determinations and procedures for cumulating effects from substances found to have a common 

mechanism on EPA’s website at http://www.epa.gov/pesticides/cumulative/.

9.0 Occupational Exposure/Risk Characterization

9.1 Exposure Scenarios

Occupational handler and post-application exposure scenarios were assessed for the proposed 

amended use on lemons. Based on the product labels and information provided by the registrant, 

short- and intermediate-term exposure is assessed for handlers and post-application activities. 

Dermal and inhalation exposures are combined for diflubenzuron because the toxicity endpoints 

for these exposure routes are based on common toxicological endpoints. Labels for the 

diflubenzuron proposed uses require that applicators and other handlers wear personal protective 

equipment (PPE) consisting of; long-sleeved shirt; long pants and shoes with socks plus 

chemical resistant gloves. Moreover, label (Dimilin® 2L) requires a respirator (MSHA/NIOSH 

approved TC-21C or any R, P, or HE filter) for mixing and loading for aerial fixed winged 

applications.

9.2 Handler Exposure 

The term “handler” applies to individuals who mix, load, and apply the pesticide product. 

There is a potential for exposure to diflubenzuron during mixing, loading, and application 

activities through the dermal and inhalation routes. For this registration action, diflubenzuron

products are applied using aerial, airblast, and chemigation equipment.

9.2.1 Handler Exposure Scenarios

Based on the anticipated use patterns and current labeling, types of equipment and techniques 

that can potentially be used, occupational handler exposure is expected from the proposed uses. 

The quantitative exposure/risk assessment developed for occupational handlers is based on the 

following scenarios: 

1. Mixer/loader using open-pour loading of a water dispersible granule for aerial, 

airblast, and chemigation applications.

2. Mixer/loader using open-pour loading of flowable concentrate for aerial, 

airblast, and chemigation applications.

3. Applicator aerial (enclosed cockpit) of sprays.

4. Applicator using airblast equipment.

5. Flaggers supporting aerial application (spray) operations.

Note: Application for chemigation was not assessed, whereas this process is mechanically
Page 32 of 66

9.2.2 Handler Exposure Data

HED uses the term handlers to describe those individuals who are involved in the pesticide 

application process. HED believes that there are distinct job functions or tasks related to 

applications and exposures can vary depending on the specifics of each task. Job requirements 

(amount of chemical used in each application), the kinds of equipment used, the target being 

treated, and the level of protection used by a handler can cause exposure levels to differ in a 

manner specific to each application event. 

Application Rate: The maximum application rate for all exposure scenarios is 0.3125 lb ai/Acre

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

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

include PHED 1.1, the AHETF database, the Outdoor Residential Exposure Task Force 

(ORETF) database, or other registrant-submitted occupational exposure studies. Some of these 

data are proprietary (e.g., AHETF data), and subject to the data protection provisions of FIFRA. 

The standard values recommended for use in predicting handler exposure that are used in this 

assessment, known as “unit exposures”, are outlined in the “Occupational Pesticide Handler Unit 

Exposure Surrogate Reference Table” (http://www.epa.gov/opp00001/science/handler-exposuretable.pdf), which, along with additional information on HED policy on use of surrogate data, 

including descriptions of the various sources, can be found at 

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

Estimates of dermal and inhalation exposure were calculated for various levels of personal 

protective equipment (PPE). Results are presented for “baseline,” defined as a single layer of 

clothing consisting of a long sleeved shirt, long pants, shoes plus socks, no protective gloves, and 

no respirator, as well as baseline with various levels of PPE as necessary (e.g., gloves, respirator, 

etc). The Dimilin®2L label instructs applicators and other handlers to wear; long-sleeved shirt, 

long pants, chemical resistant gloves and shoes plus socks. Mixers and loaders supporting fixed 

wing aircraft must wear long-sleeved shirt, long pants, chemical resistant gloves, shoes plus 

socks and dust/mist filtering respirator with MSHA/NIOSH approval number prefix TC21C or a 

NIOSH approved respirator with R,P or HE filter.

HED’s HIARC met to discuss the adequacy of the toxicological database relative to 

diflubenzuron (Memo, G. Reddy, HED DOC. NO. 0050503, “DIFLUBENZURON – 3

rd Report 

of the Hazard Identification Assessment Review Committee, 03/06/2002). Diflubenzuron was 

classified in Acute Toxicity Category III for acute dermal toxicity and primary eye irritation. It 

was classified in Toxicity Category IV for acute inhalation and primary skin irritation and it is 

not a dermal sensitizer. Relative to this assessment of handler exposure and risk, the HIARC 

identified a short-term (1 – 30 days) dermal toxicological endpoint (methemoglobinemia) with a 

NOAEL of 500 mg/kg bw/day. The dermal endpoint was identified from a 21 day dermal study 

in the rat. The HIARC also identified a short-term inhalation endpoint (methemoglobinemia) 

with a NOAEL of 20.3 mg/kg bw/day. The endpoint was identified from a 28-day inhalation 

study in the rat. See Table 9.2.2 for a summary of exposure and risk to occupational pesticide 

handlers. The level of concern is for MOEs < 100. 
Page 33 of 66

9.2.3 Handler Exposure Assumptions

Based on HED ExpoSAC Policy No. 9.1, the area treated in a day was assumed to be:

350 acres for mixing/loading to support aerial applications,

350 acres for mixing /loading chemigation applications.

40 acres for mixing /loading airblast applications,

350 acres for applying with aerial equipment,

40 acres for applying with airblast equipment, and

350 acres for flagging to support aerial applications.

Body Weight

The standard body weight for the general population (80 kg) was used for all exposure scenarios 

covered in this risk assessment since the endpoints selected were not developmental and/or fetal 

effects.

Absorption Factors

The intermediate-term dermal absorption factor is 0.5%. No dermal absorption factor was needed 

for short-term exposure scenarios.

Exposure Duration: 

HED classifies exposures from 1 to 30 days as short-term and exposures 30 days to six months 

as intermediate-term. Exposure duration is determined by many things, including the exposed 

population, the use site, the pest pressure triggering the use of the pesticide, and the cultural 

practices surrounding that use site. For most agricultural uses, it is reasonable to believe that 

occupational handlers will not apply the same chemical every day for more than a one-month 

time frame; however, there may be a large agribusiness and/or commercial applicators who may 

apply a product over a period of weeks (e.g., completing multiple applications for multiple 

clients within a region). 

Personal Protective Equipment (PPE)

For pesticide handlers, this assessment presents “baseline” and “baseline with gloves PPE (i.e. 

workers wearing a single layer of work clothing consisting of a long sleeved shirt, long pants, 

shoes, plus socks and water resistant gloves) calculations. See table 9.2.2 for specifics.

Note: For aerial mixer and loading, label specific directions for Dimilin®2L instructs applicators 

and other handlers to wear; long-sleeved shirt, long pants, chemical resistant gloves and shoes 

plus socks. Mixers and loaders supporting fixed wing aircraft must wear long-sleeved shirt, long 

pants, chemical resistant gloves, shoes plus socks and dust/mist filtering respirator with 

MSHA/NIOSH approval number prefix TC21C or a NIOSH approved respirator with R,P or HE 

filter. Table 9.2.2 assesses baseline and label specific PPE. 

Occupational Non-Cancer Dermal Exposure and Risk Estimate Equations

Daily Dose:

Daily dose (dermal and inhalation) is calculated by normalizing the daily exposure (dermal or 

inhalation) value by body weight and accounting for absorption factors:
Page 34 of 66

Average Daily Dose (mg/kg/day) = Daily Exposure (mg ai/day) x {Absorption Factor }

 Body Weight (kg)

Where:

Average Daily Dose = Absorbed dose received from exposure to a pesticide in a given 

scenario (mg pesticide active ingredient/kg body weight/day),

Daily Exposure = Amount (mg ai/day) deposited on the surface of the skin that is 

available for dermal absorption or amount inhaled that is available 

for inhalation absorption,

Absorption Factor = A measure of the amount of chemical that crosses a biological 

boundary such as the skin or lungs, and

Body Weight = Body weight determined to represent the population of interest in a 

risk assessment.

Margin of Exposure (MOE):

Non-cancer risk estimates for each application handler scenario are calculated using a Margin of 

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

daily dermal and inhalation dose received by occupational handlers were compared to the 

appropriate POD (i.e. NOAEL) to assess the risk to occupational handlers for each exposure 

route. All MOE values were calculated using the following formula:

MOE = POD (typically a NOAEL in mg/kg/day) 

ADD (mg/kg/day)

where:

MOE = Margin of Exposure: value used by HED to represent risk or risk estimates 

(unitless),

POD = Point of Departure,

NOAEL = No Observed Adverse Effect Level (mg/kg/day): Dose level in a toxicity 

study, where no observed adverse effects occurred in the study, and

ADD = Average Daily Dose (mg/kg/day): the absorbed dose received from 

exposure to a pesticide in a given scenario.

Dermal and inhalation risk estimates were combined in this assessment, since the toxicological 

effects for these exposure routes were similar. Dermal and inhalation risk estimates were 

combined using the following formula:

Total MOE = 1/ (1/Dermal MOE) + (1/Inhalation MOE)

Note: The Agency has evaluated scenarios that may be limited in nature such as flagging during 

aerial applications because engineering controls (i.e., Global Positioning Satellite technology) 

are now predominantly used as indicated by the 1998 National Agricultural Aviation Association 

(NAAA) survey of their membership. It appears, however, flaggers are still used in 

approximately 10 to 15 percent of aerial application operations. In cases like these, the Agency 

strongly encourages the use of the engineering control system but will continue to evaluate risks 

for flaggers and any other population where a clear exposure pathway exists until the potential 

for exposure is eliminated. The Agency is aware that NAAA is conducting another survey on 
Page 35 of 66

exposure issues and will consider those results as are timely and appropriate.

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

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

engineering control (enclosed cockpits) and baseline attire (long-sleeve shirt, long pants, shoes, 

and socks); pilots are not required to wear protective gloves. With this level of protection, there 

are no risk estimates of concern for applicators.

9.2.4 Handler Exposure and Risk Estimates

Summaries of the combined, dermal plus inhalation short-, and intermediate-term risks for each 

exposure scenario are presented in Table 9.2.2. The combined dermal and inhalation exposure 

risks are not of concern (i.e., MOEs >100) at baseline PPE, however as directed on the label, 

chemical resistant gloves are to be worn during most mixing and loading activities, however a 

respirator is included while mixing and loading of a liquid for aerial applications.
Page 36 of 66

Table 9.2.2. Occupational Handler Non-Cancer Exposure and Risk Estimates for Diflubenzuron. 

Exposure 

Scenario

Crop or 

Target

Dermal Unit 

Exposure 

(μg/lb ai)1

Inhalation 

Unit 

Exposure

(μg/lb ai)1

Max App. 

Rate2

Area 

Treated 

or 

Amount 

Handled 

Daily3

Dermal

Intermediate-Term

Inhalation

Intermediate-Term

Total 

MOE8

Baseline

Baseline/ 

Gloves

Or

Eng. Ctrl.

Baseline lb ai/Acre Dose 

(mg/kg/day)4

MOE5

Baseline

or 

Eng. Ctrl.

Dose 

(mg/kg/day)6

MOE7

Baseline

ShortTerm Int.-Term 

BL BL

Label 

Specific 

PPE

or

Eng. Ctrl.

Mixer/Loader (WDG: water dispersible granular)

Aerial

Lemons

Group 10-

10

227 51.6 8.96 0.3125

350 0.0015 1,300 0.0123 1,700 1,500 740 1,300

Airblast 40 0.000178 11,000 0.0014 15,000 15,000 6,300 12,000

Chemigation 350 0.00155 1,300 0.0123 1,700 1,700 740 1,300

Mixer/Loader (FlC: flowable concentrate)

Aerial

Lemons

Group 10-

10

220 37.6 0.219 0.3125 350 0.0015 1,300 0.0003 68,000 56,000 1,300 7,600

Airblast

220 37.6 0.219 0.3125

40 0.00017 12,000 0.000034 590,000 490,000 12,000 61,000

Chemigation 350 0.0015 1,300 0.0003 68,000 56,000 1,300 7,000

Applicator (liquid)

Aerial Lemons

Group 

10-10

NA 5 0.068

0.3125

350 0.000034 58,000 0.000093 220,000 NA NA 46,0009

Airblast 1,770 1,590 4.71 40 0.00138 1,400 0.000736 28,000 26,000 1,300 1,500

Flagger

Aerial

Lemons

Group 10-

0

11 12 0.35 0.3125 350 0.000075 27,000 0.000479 42,000 42,000 16,000 15,000

1 Based on the “Occupational Pesticide Handler Unit Exposure Surrogate Reference Table” (03/2013); Level of mitigation: Baseline, PPE, Eng. Controls.

2 Based on registered or proposed labels (Reg. No. 400-487; 400-461).

3 Exposure Science Advisory Council Policy #9.1.

4 Dermal Dose = Dermal Unit Exposure (μg/lb ai) × Conversion Factor (0.001 mg/μg) × Application Rate (lb ai/acre or gal) × Area Treated or Amount Handled (A or gal/day) × DAF (%) ÷ BW (kg).

Intermediate-Term is protective of short-Term

5 Dermal MOE = Dermal NOAEL (mg/kg/day) ÷ Dermal Dose (mg/kg/day). Intermediate-Term is protective of short-Term
Page 37 of 66

6 Inhalation Dose = Inhalation Unit Exposure (μg/lb ai) × Conversion Factor (0.001 mg/μg) × Application Rate (lb ai/acre or gal) × Area Treated or Amount Handled (A or gal/day) ÷ BW ( kg).

Intermediate-Term is protective of short-Term

7 Inhalation MOE = Inhalation NOAEL (mg/kg/day) ÷ Inhalation Dose (mg/kg/day). Intermediate-Term is protective of short-Term

8 Total MOE = NOAEL (mg/kg/day) ÷ Dermal Dose + Inhalation Dose OR Total MOE = 1 ÷ (1/Dermal MOE + 1/Inhalation MOE).

9 Engineering Control.
Page 38 of 66

9.3 Post Application Exposure

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

present in an environment that has been previously treated with a pesticide (also referred to as a 

re-entry exposure). Such exposure may occur when workers enter previously treated areas to 

perform job functions, including activities related to crop production. In the case for 

diflubenzuron, post-application dermal exposure to field workers following aerial, airblast, and 

chemigation applications is probable.

9.3.1 Post Application Inhalation Exposure Scenarios

Based on the Agency's current practices, a quantitative post-application inhalation exposure 

assessment was not performed for diflubenzuron at this time primarily because of the low acute 

inhalation toxicity (Toxicity Category III and IV), low vapor pressure (insert VP), and the low 

proposed use rate (0.3125 lb ai/A). However, there are multiple potential sources of postapplication inhalation exposure to individuals performing post-application activities in 

previously treated fields. These potential sources include volatilization of pesticides and 

resuspension of dusts and/or particulates that contain pesticides. The Agency sought expert 

advice and input on issues related to volatilization of pesticides from its Federal Insecticide, 

Fungicide, and Rodenticide Act Scientific Advisory Panel (SAP) in December 2009, and 

received the SAP’s final report on March 2, 2010 

(http://www.epa.gov/scipoly/SAP/meetings/2009/120109meeting.html). The Agency is in the 

process of evaluating the SAP report as well as available post-application inhalation exposure 

data generated by the ARTF and may, as appropriate, develop policies and procedures, to 

identify the need for and, subsequently, the way to incorporate occupational post-application 

inhalation exposure into the Agency's risk assessments. If new policies or procedures are put 

into place, the Agency may revisit the need for a quantitative occupational post-application 

inhalation exposure assessment for diflubenzuron.

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

performed, an inhalation exposure assessment was performed for occupational/commercial 

handlers. Handler exposure resulting from application of pesticides outdoors is likely to result in 

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

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

inhalation exposure scenarios.
Page 39 of 66

9.3.2 Post Application Dermal Exposure Assumptions

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

post-application risk assessments. Each assumption and factor is detailed below on an individual 

basis. EPA has determined that there is an exposure potential for persons entering treated sites 

after application is complete. Representative post-application exposure scenarios are as follows:

1. Harvesting by hand.

2. Scouts and other crop advisors reentering treated orchards and fields

3. Pruning by hand.

4. Weeding by hand

5. Transplanting

6. Baiting and trapping

7. Transplanting

8. Orchard maintenance

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

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

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

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

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

“Science Advisory Council for Exposure (ExpoSAC) Policy 3” 

(http://www.epa.gov/pesticides/science/exposac_policy3.pdf), which, along with additional 

information about the ARTF data, can be found at http://www.epa.gov/pesticides/science/postapp-exposure-data.html. 

Body Weight

The standard body weight for the general population (80 kg) was used for all exposure scenarios 

covered in this risk assessment since the endpoints selected were not developmental and/or fetal 

effects 

Absorption Factors

The intermediate-term dermal absorption factor is 0.5%. No dermal absorption factor was needed 

for short-term exposure scenarios.

Chemical-specific dislodgeable foliar residue data have not been submitted for diflubenzuron. 

Therefore, this assessment uses HED’s default assumption that 25% of the application is 

available for transfer on day 0 following the application and the residues dissipate at a rate of 

10% each following day.

The highest (i.e., most conservative) TC relative to the subject crop (lemon) is for hand 

harvesting with a TC of 1,400 cm2/hr. For risk assessment purposes, a TC of 1,400 cm2/hr is 

used in conjunction with the maximum rate of application (0.3125 lb a.i./A). 
Page 40 of 66

Occupational Post-application Non-Cancer Dermal Exposure and Risk Estimate Equations

Average Daily Dose (ADD): Potential daily exposures for occupational post-application workers 

were calculated using the following formulas:

DFRt (μg/cm2) = AR (lb ai/A) * F * (1-D)t* 4.54E8 μg/lb * 2.47E-8 acre/cm2

where:

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

AR = Application Rate (lb ai/acre)

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

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

t = number of days after application day (days)

Daily Exposure (mg ai /day) = TC (cm2/hr) * CF1 * DFRt (μg/cm2) * ET (hrs /day) * 1E-3 

mg/μg

where:

Daily Exposure = Amount (mg ai/day) that is available for dermal absorption,

TC = Transfer coefficient (cm2/hr),

DFRt = Dislodgeable Foliar Residue on day “t” (μg/cm2), and

ET = Exposure Time (hours /day).

The daily doses were calculated using the following formula:

Average Daily Dose (mg ai/kg/day) = [Daily Exposure (mg ai/day) * Absorption (%)]

Body Weight (kg)

where:

Average Daily Dose = Absorbed dose received from exposure to a pesticide in a given 

scenario (mg pesticide active ingredient/kg body weight/day),

Daily Exposure = Amount (mg ai/day) that is available for dermal absorption,

Absorption Factor = A measure of the amount of chemical that crosses a biological 

boundary such as the skin (%), and

Body Weight = Body weight determined to represent the population of interest in a 

risk assessment (kg).

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

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

the daily dose of concern. The daily dermal dose received by occupational post-application

workers was compared to the appropriate POD (i.e. NOAEL) to assess the risk to occupational 

post-application workers. All MOE values were calculated using the following formula:

MOE = POD (typically a NOAEL in mg/kg/day) 

ADD (mg/kg/day)
Page 41 of 66

where:

MOE = Margin of Exposure: value used by HED to represent risk or risk estimates 

(unitless),

POD = Point of Departure,

NOAEL = No Observed Adverse Effect Level (mg/kg/day): Dose level in a toxicity 

study, where no observed adverse effects occurred in the study, and

ADD = Average Daily Dose (mg/kg/day): the absorbed dose received from 

exposure to a pesticide in a given scenario.

9.3.3 Post-Application Exposure and Risk Estimates

For all dermal post-application exposure scenarios, risk estimates do not exceed HED’s LOC 

(Dermal LOC = 100), therefore, are not of concern to HED. 

In accordance with the updated Part 158 data requirements (2007), one or more DFR studies are 

required when a pesticide has occupational uses that could result in post-application dermal 

exposure. HED analyzed a number of DFR studies and selected a new default value for the 

fraction of the application rate available to be dislodged after a foliar application (FAR). This 

default value is 25%. Of the analyzed DFR studies, the maximum FAR value seen was 89% or 

3.6 times higher than the default residue transfer value. Therefore, a calculated MOE of 

approximately 4 times higher than the LOC (i.e., an MOE > 400 if the LOC = 100) using the 

default dislodged residue value would provide an adequate margin of safety for any potentially 

higher residues seen in a chemical-specific DFR study. A conservative, screening-level 

assessment of intermediate-term post-application exposure to agricultural workers yields MOEs 

of 3,300 on “DAT 0”, which does not exceed HED's LOC and above the waiver criteria of 4x the 

LOC (400). Therefore, a DFR study is not required for diflubenzuron at this time. See table

9.3.3 for specifics.
Page 42 of 66

Table 9.3.3 Occupational Post-application Non-Cancer Exposure and Risk Estimates for Diflubenzuron.

Crop/Site Activities Transfer Coefficient 

(cm2/hr) DFR/TTR1 Dermal Dose(mg/kg/day)2 MOE3

Short-term

Orchard

Citrus: Crop Group

10-10

Hand Harvesting 1,400

0.876

0.000613 820,000

Scouting/Pruning 580 0.000254 20,000,00

Transplanting 230 0.000101 5,000,000

Baiting and Trapping

Hand Weeding

Orchard maintenance

100 0.0000438 11,000,000

Intermediate-term

Orchard

Citrus: Crop Group

10-10

Hand Harvesting 1,400

0.876

0.000613 3,300

Scouting/Pruning 580 0.000254 7,900

Transplanting 230 0.000101 20,000

Baiting and Trapping

Hand Weeding

Orchard maintenance

100 0.0000438 46,000

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

TTR = Application Rate × F × (1-D)t × 4.54E8 μg/lb × 2.47E-8 acre/cm2; where F = 0.1 and D = 0.10 per day OR 

cite chemical-specific study

2 Daily Dermal Dose = [DFR (μg/cm2) × Transfer Coefficient × 0.001 mg/μg × 8 hrs/day × dermal absorption (%)] BW (kg).

3 MOE = POD (mg/kg/day) / Daily Dermal Dose. Daily Dermal Dose = [DFR/TTR (μg/cm2) × TC × 0.001 mg/μg × 8 hrs/day × dermal 

absorption

Restricted Entry Interval (REI):

The REI for diflubenzuron is 12 hours based on the acute toxicity classification of III for acute 

dermal and eye irritation routes of exposure. It is classified in Toxicity Category IV for acute 

inhalation toxicity and primary skin irritation. It is not a dermal sensitizer. Therefore the interim 

worker protection standard REI of 12 hours is adequate to protect agricultural workers from postapplication exposures. 
Page 43 of 66

10. REFERENCES

Diflubenzuron on Citrus, Group 10-10. Summary of Analytical Chemistry and Residue Data., S. Hummel, 

D403082, 7/17/2013

Diflubenzuron Chronic Non-Cancer and Cancer Dietary and Drinking Water Exposure and Risk Assessments for 

the Amended Use on the Citrus Crop Group, T. Morton, D407784, 12/12/2013

Diflubenzuon: Occupational and Residential Assessment of Diflubenzuron Use in Citrus Crop Group 10-10. J.S. 

Miller, D403088 7/11/2013

IR-4/Section 3-Local and New Uses Registration for Diflubenzuron Use on Peanuts, Okra, Small grains (Winter, 

Spring, Durum, Barley, and Oats), Pummelo, Mustard Greens, Broccoli, Raab, Cabbafe (bok choy), Collards, Kale, 

Mizuna, Mustard spinach, Rape, Greens and Turnip greens. – A. Al-mudallal, D321156, 8/25/06

Diflubenzuron: Summary of Hazard and Science Policy Council (HASPOC) Meetings of April 26, 2012: 

Recommendations on the need for a neurotoxicity battery (acute and subchronic neurotoxicity studies), J. Van 

Alstine, TXR#0056309, 6/7/12. 

Health Effects Division (HED) Metabolism Assessment Review Committee (MARC) Meetings of 2/20/01 & 5/8/01. 

Diflubenzuron. Residues of Concern for Cancer Risk Assessment. Chemical 108201. Barcode D272976. Case 

239100. Submission S590172.
Page 44 of 66

APPENDICES

APPENDIX A TOXICOLOGY DATA SUMMARY

A.1 Guideline Data Requirements

Attachment 1. Diflubenzuron Toxicology Data Requirements

Test Technical

Required Satisfied

870.1100 Acute Oral Toxicity......................................................

870.1200 Acute Dermal Toxicity.................................................

870.1300 Acute Inhalation Toxicity.............................................

870.2400 Primary Eye Irritation...................................................

870.2500 Primary Dermal Irritation .............................................

870.2600 Dermal Sensitization ....................................................

yes

yes

yes

yes

yes

yes

yes

yes

yes

yes

yes

yes

870.3100 Oral Subchronic (rodent)..............................................

870.3150 Oral Subchronic (nonrodent)........................................

870.3200 21/28-Day Dermal........................................................

870.3250 90-Day Dermal.............................................................

870.3465 28-Day Inhalation.........................................................

yes

yes

yes

yes

yes

yes

yes

yes

yes

yes

870.3700 Developmental Toxicity (rodent) .................................

870.3700 Developmental Toxicity (nonrodent) ...........................

870.3800 Reproduction ................................................................

yes

yes

yes

yes

yes

yes

870.4100 Chronic Toxicity (rodent).............................................

870.4100 Chronic Toxicity (nonrodent).......................................

870.4200 Oncogenicity (rat).........................................................

870.4200 Oncogenicity (mouse) ..................................................

870.4300 Chronic/Oncogenicity (mouse) ....................................

870.4500 Chronic/Oncogenicity (rat)...........................................

yes

yes

yes

yes

yes

yes

yes

yes

yes

yes

yes

yes

870.5100 Mutagenicity—Gene Mutation - bacterial....................

870.5xxx Mutagenicity—other genotoxic effects ........................

870.5375 Mutagenicity—Structural Chromosomal Aberrations..

yes

yes

yes

yes

yes

yes

870.6100 Acute Delayed Neurotox. (hen)....................................

870.6100 90-Day Neurotoxicity (hen) .........................................

870.6200 Acute Neurotox. Screening Battery (rat)......................

870.6200 Chronic Neurotox. Screening Battery (rat)...................

870.6300 Develop. Neurotox .......................................................

no

no

yes*

yes*

no

......

......

......

......

......

870.7485 General Metabolism .....................................................

870.7600 Dermal Penetration.......................................................

870.7800 Immunotoxicity

yes

no

yes

Yes

---

yes

*HASPOC waived the acute and subchronic neurotoxicity studies.
Page 45 of 66

A.2 Toxicity Profiles

Table A.2: Diflubenzuron Acute Toxicity Profile

Guideline

No.

Study Type MRID # Results Toxicity Category

870.1100 Acute Oral Toxicity– rat

00157103 LD50 =>5,000 mg/kg IV

870.1200 Acute Dermal Toxicity-rabbit

00157104 LD50 =>2000 mg/kg III

870.1300 Acute Inhalation Toxicity– rat

00163311 LC50 =>2.49 mg/L IV

870.2400 Acute Eye Irritation

00157105 mild irritant III

870.2500 Acute Dermal Irritation

00157106 no irritation IV

870.2600 Skin Sensitization

42251101 negative

-

A.3 Toxicological Endpoints

Non-Guideline Short-Term Inhalation Exposure (1 - 30 Days)

Study Selected: Twenty-eight day rat inhalation 

MRID No.: 44950601

Executive Summary: In a subchronic inhalation toxicity study (MRID 44950601), dimilin 

technical (96.5% a.i., Batch FUX021000-FUN91A10A) was administered to groups of 10 male 

and 10 female Sprague-Dawley albino rats/concentration. Exposure was by nose-only inhalation 

at concentrations of 0, 12, 34, or 109 mg/m3(0. 0.012, 0.034, or 0.109 mg/L) for 6 hours/day, 5 

days/week, for approximately 4 weeks (22-23 consecutive exposures, excluding weekends, over 

a 30-31 day calendar period).

There was no test material-related effect on mortality, body weight or weight gain, food 

consumption, clinical signs, ophthalmoscopy, urinalysis, organ weights, and gross or 

microscopic pathology. Slight but statistically significant decreases were seen in erythrocyte 

counts, hemoglobin, and hematocrit in both sexes (93-95% of controls) and in serum bilirubin in 

males (increased from 0.1 to 0.2 mg/dL) administered 100 mg/m3. It is unclear whether these 

alterations were induced by treatment, however, they were too small to be biologically 

significant and lacked microscopic correlates, and were thus considered toxicologically 

unimportant. Under the conditions of this study, therefore, a LOAEL was not established and the 

NOAEL is the highest dose tested, i.e., 109 mg/m3(0.109 mg/L).

This subchronic inhalation toxicity study in the rat is Acceptable/Non-Guideline. The study 

satisfies the guideline requirement for a subchronic inhalation toxicity study in rats as requested 

by the HIARC. 
Page 46 of 66

Dose and Endpoint for Risk Assessment: NOAEL = 20.30 mg/kg/d1(0.109 mg/L; HDT).

Comments about Study/Endpoint: The study is of appropriate for route and duration of exposure. 

The concentration selected for risk assessment did not elicit any adverse effect following 28 days 

of inhalation exposure. The HIARC, however, selected this dose based on methemoglobinemia 

which was consistently observed across species and studies even though it was not seen in the 

critical study.

Non-Guideline Intermediate-Term Inhalation Exposure (1 - 6 months)

Study Selected: Twenty-eight day rat inhalation 

MRID No.: 44950601

Executive Summary: see Short-Term Inhalation

Dose and Endpoint for Risk Assessment: NOAEL = 20.30 mg/kg/d (0.109 mg/L; HDT).

Comments about Study/Endpoint: The study is of appropriate for route and duration of exposure. 

The concentration selected for risk assessment did not elicit any adverse effect following 28 days 

of inhalation exposure. The HIARC, however, selected this dose based on methemoglobinemia 

which was consistently observed across species and studies even though it was not seen in the 

critical study.

A.3.1 Acute Reference Dose (aRfD) -

No appropriate endpoints (effects) attributable to a single exposure (dose) were identified 

in any of the oral studies; therefore, an acute RfD is not established for diflubenzuron and 

acute dietary risk was not assessed. 

A.3.2 Chronic Reference Dose (cRfD) - All Populations

This endpoint was established in 1986. It was reassessed by this Committee pursuant to 

the FQPA and is discussed below.

Study Selected: Chronic Toxicity- Dog. §83-1a

MRID No.: 00146174

Executive Summary: In a 52-week chronic oral study, technical grade diflubenzuron was 

administered in gelatin capsules to beagle dogs once each day (7 days/week) at dose 

levels of 0 (control), 2, 10, 50 or 250 mg/kg/day. Groups of 6 male and 6 female dogs 

were used for each treated group and 12 male and 12 female dogs were used for the 

control group. Mortality, clinical signs, food consumption and water consumption were 

not affected by treatment with diflubenzuron. Except for a slight decrease in mean body 
Page 47 of 66

weight gain observed in female dogs at 250 mg/kg/day, body weights were also not 

affected. Ophthalmoscopic examinations, clinical chemistries and urinalyses were 

negative. Statistically significant increases in methemoglobin and sulfhemoglobin were 

observed in male and female dogs at dose levels of ≥10 mg/kg/day. Heinz bodies were 

also observed in the erythrocytes of male dogs at 250 mg/kg/day and in those of female 

dogs at ≥50 mg/kg/day. At dose levels of 50 mg/kg/day and higher, signs of hemolytic 

anemia, destruction of erythrocytes and of compensatory regeneration of erythrocytes 

were observed. Increased platelet counts were also noted in females at ≥50 mg/kg/day. 

Absolute spleen and liver weights, but not relative organ body weight ratios, were 

increased in male dogs at 50 and 250 mg/kg/day. Organ weights were not increased in 

female dogs. The NOAEL in this study is 2 mg/kg/day and the LOAEL is 10 mg/kg/day, 

based on methemoglobinemia and sulfhemoglobinemia. 

Dose and Endpoint for Establishing RFD: NOAEL = 2.0 mg/kg/d based on 

methemoglobinemia and sulfhemoglobinemia at 10 mg/kg/day (LOAEL).

Uncertainty Factor(s):

Chronic RfD = 2.0 mg/kg/day (NOAEL) = 0.02 mg/kg/day

100 (UF)

Comments about Study/Endpoint/Uncertainty Factor: The HIARC concurred with the 

dose, end point, and the uncertainty factor selected by the RFD Committee in 1986.

A.3.3 Dermal Absorption

Dermal Absorption Factor: 0.5 percent. 

Twenty four [24] male Sprague-Dawley rats were divided into two groups of twelve [12] 

males each and given either 0.005 or 0.05 mg/cm.sq. of C-14 diflubenzuron technical in 

gum tragacanth [0.25%]. Four [4] animals per dose group were sacrificed after either 1, 4, 

or 10 hours of exposure. The control group consisted of three [3] males with one [1] 

animal sacrificed at the end of 1,4, or 10 hours of exposure. Systemic absorption was less 

than 0.5% at each time interval regardless of the dose. Approximately 4.7 - 6.2% 

diflubenzuron was bound to the skin at the application site.
Page 48 of 66

A.3.4 Dermal Exposure (Short and Intermediate-Term)

Dermal Exposure (Short-Term)

Study Selected: 21-Day dermal toxicity study in rat. 

MRID No.: 43954101

Executive Summary: In a subchronic, 21-day dermal toxicity study (MRID 43954101), 

Dimilin (diflubenzuron tech. 96.7% a.i.) was administered to 10/sex/dose in 0.25% gum 

tragacanth in distilled, deionized water to the dorsal skin on the backs of the test animals 

at 0, 20, 500, or 1,000 mg/kg/day for 6 hour period each day.

Dermal treatment for 21 days did not affect mortality, clinical signs, body weight 

changes, food consumption and/or organ weight changes. At 1,000 mg/kg/day, slight 

dermal irritation and traces of acanthosis and hyperkeratosis were noted in males and 

females. Liver and kidney histopathology was remarkable. Males exhibited slight 

elevations in the white cell count in the mid and high dose groups. Males also had small 

reductions in hemoglobin and hematocrit at 1000 mg/kg dose group. In females at the 

top two dose there were statistically significant (P < 0.05) decreases in RBC count, 

hemoglobin levels and hematocrit values. Hematological changes in males and females 

were within in the historical ranges for this species and age of rat, and therefore, 

considered not biologically significant. Methemoglobin levels increased significantly (P 

< 0.05 & 0.01) in males and females at 1000 mg/kg dose. There was increased incidence 

of anisocytosis, hypochromasia and polychromasia in males and females at the top dose. 

On August 14, 2001, the HED HIARC re-evaluated the study and concluded that the 

increased methemoglobinemia in males and females at 1000 mg/kg should be considered 

as toxicity-induced change. Therefore, the NOAEL is 500 mg/kg and LOAEL is 1000 

mg/kg (Limit Dose), based on methemoglobinemia.

Dose and Endpoint for Risk Assessment: NOAEL = 500 mg/kg/day based on increased 

methemoglobinemia at 1000 mg/kg/day (Limit Dose). 

Comments about Study/Endpoint: This dermal toxicity study in rats is route- specific, is 

of appropriate duration and measures the effects of concern, i.e., methemoglobin and/or 

sulfhemoglobin. Previously, the end-points for short-term exposure was based on a 14-

day mouse feeding study. The HIARC re-evaluated the 21-day dermal study in rat and 

revised the NOAEL from 20 mg/kg/day to 500 mg/kg/day, since the methemoglobinemia 

seen at 500 mg/kg/day was within normal physiological parameters, but occurred at 

adverse levels at 1000 mg/kg/day (Limit Dose).
Page 49 of 66

Dermal Exposure (Intermediate-Term)

Study Selected: 13-week oral [subchronic] feeding study in dogs. §82-1b

MRID No.: 00038706

Executive Summary: In a subchronic feeding study, technical grade diflubenzuron 

(batch # P7227) was administered in the diet to beagle dogs at dose levels of 0 (control), 

10, 20, 40 and 160 ppm (equal to 0, 0.42, 0.84, 1.64 and 6.24 mg/kg/day). Groups of 3 

male and 3 female dogs were used for each treated and control group. Hematology and 

blood chemistries were performed at 2, 4, 6 and 12 weeks: methemoglobin, 

sulfhemoglobin and urinalyses were performed at 6 and 12 weeks. Ophthalmoscopic 

examinations were conducted at 6 and 12 weeks. Gross necropsies were performed on all 

dogs. Organ weights were determined and histopathological examinations were 

performed at the terminal sacrifice at 13 weeks. Mortality, clinical signs, body weights 

and food consumption were not affected by treatment with diflubenzuron. 

Ophthalmoscopic examinations were negative. Methemoglobinemia was observed in the 

dogs at 160 ppm (after 6 weeks). No gross necropsy, organ weight or histopathological 

changes were reported at any level that could be related to treatment with diflubenzuron. 

Endpoint and dose for use in risk assessment: NOAEL 2.0 mg/kg/day based on increased 

methemoglobinemia at 6.24 mg/kg/day. Corrected for 0.5% dermal absorption. See 

discussion below. 

Comments about studies and/or endpoint: In this 13-week feeding study in dogs, a steady 

state for methemoglobinemia was observed to occur after 6 weeks. In both the rat study 

and the mouse study, a NOAEL of about 2 mg/kg/day was calculated by regression 

analysis. Considering all the available data (including data from chronic feeding studies 

in rats, dogs and mice in which the NOAEL for methemoglobinemia/sulfhemoglobinemia 

to be used to calculate the RfD also was 2 mg/kg/day), it was concluded that the NOAEL 

for intermediate term risk assessments should be 2 mg/kg/day (rather than the slightly 

lower NOAEL of 1.64 mg/kg/day determined in the dog study above). However, since 

an oral NOAEL was selected for a dermal endpoint a dermal absorption factor of 0.5% 

should be used for this risk assessment when converting dermal exposure to oral 

equivalents Therefore, the dermal equivalent dose derived from a NOAEL by the oral 

route is 400.0 mg/kg/day [i.e., 2.0 mg/kg/day ÷ 0.005 = 400.0 mg/kg/day).

Dermal Exposure (Intermediate-Term)

Study Selected: Chronic Toxicity - Dog. §83-1a

MRID No.: 00146174

Executive Summary: In a 52-week chronic oral study, technical grade diflubenzuron was 

administered in gelatin capsules to beagle dogs once each day (7 days/week) at dose 
Page 50 of 66

levels of 0 (control), 2, 10, 50 or 250 mg/kg/day. Groups of 6 male and 6 female dogs 

were used for each treated group and 12 male and 12 female dogs were used for the 

control group. Mortality, clinical signs, food consumption and water consumption were 

not affected by treatment with diflubenzuron. Except for a slight decrease in mean body 

weight gain observed in female dogs at 250 mg/kg/day, body weights were also not 

affected. Ophthalmoscopic examinations, clinical chemistries and urinalyses were 

negative. Statistically significant increases in methemoglobin and sulfhemoglobin were 

observed in male and female dogs at dose levels of ≥10 mg/kg/day. Heinz bodies were 

also observed in the erythrocytes of male dogs at 250 mg/kg/day and in those of female 

dogs at ≥50 mg/kg/day. At dose levels of 50 mg/kg/day and higher, signs of hemolytic 

anemia, destruction of erythrocytes and of compensatory regeneration of erythrocytes 

were observed. Increased platelet counts were also noted in females at ≥50 mg/kg/day. 

Absolute spleen and liver weights, but not relative organ body weight ratios, were 

increased in male dogs at 50 and 250 mg/kg/day. Organ weights were not increased in 

female dogs.

Dose and Endpoint for Risk Assessment: NOAEL = 2 mg/kg/day based on 

methemoglobinemia and sulfhemoglobinemia at 10.0 mg/kg/day (LOAEL). Corrected 

for 0.5% dermal absorption.

Comments about Study/Endpoint:. Long term dermal studies are not available for 

diflubenzuron therefore a chronic feeding study was chosen. However, since an oral 

NOAEL was selected for a dermal endpoint a dermal absorption factor of 0.5% should be 

used for this risk assessment when converting dermal exposure to oral equivalents. 

Therefore the dermal equivalent dose producing a NOAEL by the oral route is 400.0

mg/kg/d [i.e. 2.0 mg/kg/day ÷ 0.005 = 400.0 mg/kg/day.

This risk assessment is not required at this time since there does not appear to be 

any long term exposure scenarios associated with this use. However, if long term 

exposure is anticipated in the future based on the use pattern then this risk 

assessment will be required.

A.3.5 Inhalation Exposure (Short and Intermediate-Term)

Inhalation Exposure (Short-Term)

Study Selected: Twenty-eight day rat inhalation 

MRID No.: 44950601

Executive Summary: In a subchronic inhalation toxicity study (MRID 44950601), 

dimilin technical (96.5% a.i., Batch FUX021000-FUN91A10A) was administered to 

groups of 10 male and 10 female Sprague-Dawley albino rats/concentration. Exposure 

was by nose-only inhalation at concentrations of 0, 12, 34, or 109 mg/m3(0. 0.012, 0.034, 

or 0.109 mg/L) for 6 hours/day, 5 days/week, for approximately 4 weeks (22-23 
Page 51 of 66

consecutive exposures, excluding weekends, over a 30-31 day calendar period).

There was no test material-related effect on mortality, body weight or weight gain, food 

consumption, clinical signs, ophthalmoscopy, urinalysis, organ weights, and gross or 

microscopic pathology. Slight but statistically significant decreases were seen in 

erythrocyte counts, hemoglobin, and hematocrit in both sexes (93-95% of controls) and in 

serum bilirubin in males (increased from 0.1 to 0.2 mg/dL) administered 100 mg/m3. It is 

unclear whether these alterations were induced by treatment, however, they were too 

small to be biologically significant and lacked microscopic correlates, and were thus 

considered toxicologically unimportant. Under the conditions of this study, therefore, a 

LOAEL was not established and the NOAEL is the highest dose tested, i.e., 109 

mg/m3(0.109 mg/L).

This subchronic inhalation toxicity study in the rat is Acceptable/Non-Guideline. The 

study satisfies the guideline requirement for a subchronic inhalation toxicity study in rats 

as requested by the HIARC. 

Dose and Endpoint for Risk Assessment:: NOAEL = 20.30 mg/kg/d1(0.109 mg/L; 

HDT).

Comments about Study/Endpoint: The study is of appropriate for route and duration of 

exposure. The concentration selected for risk assessment did not elicit any adverse effect 

following 28 days of inhalation exposure. The HIARC, however, selected this dose 

based on methemoglobinemia which was consistently observed across species and studies 

even though it was not seen in the critical study. 

____________________________________

1

Conversion of mg/L to oral dose (mg/kg/day) = mg/L X absorption (1.0) X [Respiratory Volume (Sprague-Dawley 

rats) for 6 hours/day] X Duration of Exposure (5 days/wk)/ body weight X 7 days/week

= 0.109 mg/L X 1.0 X [10.26(RV) X 6 hrs] X 5d/wk ÷ 0.236 kg X 7d/wk

= 20.30 mg/kg/day

Inhalation Exposure (Intermediate-Term)

Study Selected: Twenty-eight day rat inhalation 

MRID No.: 44950601

Executive Summary: see Short-Term Inhalation

Dose and Endpoint for Risk Assessment:: NOAEL = 20.30 mg/kg/d (0.109 mg/L; HDT).

Comments about Study/Endpoint: The study is of appropriate for route and duration of 

exposure. The concentration selected for risk assessment did not elicit any adverse effect 

following 28 days of inhalation exposure. The HIARC, however, selected this dose 

based on methemoglobinemia which was consistently observed across species and studies 
Page 52 of 66

even though it was not seen in the critical study. 

Inhalation Exposure (Long-Term)

Study Selected: Chronic Toxicity - Dog 

MRID No.: 00146174

Executive Summary: see Chronic RfD

Dose and Endpoint for Risk Assessment: NOAEL = 2.0 mg/kg/d based on 

methemoglobinemia and sulfhemoglobinemia at 10 mg/kg/day (LOAEL).

Comments about Study/Endpoint/Uncertainty Factor: An oral study was selected since no 

appropriate inhalation study is available in the database. This study is of appropriate 

duration of exposure. Assume that inhalation absorption is equivalent to oral absorption.

Margin of Exposure

A margin of exposure of 100 is adequate for dermal and inhalation occupational 

exposure risk assessment. There are no residential uses at the present time
Page 53 of 66

A.4 Executive Summaries

870.3100 Oral Subchronic Toxicity - Rodent 

Study Selected: 14 day subchronic oral toxicity study in mice.

MRID No.: 00099713

Executive Summary: In a 14-day subchronic oral toxicity study, technical grade diflubenzuron 

was administered each day by gavage to 10 Swiss strain male mice at a dose level of 8, 40, 200, 

1000 or 5000 mg/kg/day. The mice were fasted for 16 hours prior to the first dose of test 

material. The test material was administered as a

suspension in 1% tragacanth. Twenty control animals were treated similarly with a blank 

suspension. Blood was drawn from all animals at 15 days after the first dose and analyzed for 

methemoglobin, sulfhemoglobin and Heinz bodies in the erythrocytes. At day 15, the animals 

were sacrificed and those of the control and highest dose groups were autopsied. Significantly 

increased (p < 0.05) levels of methemoglobin were

observed at 1000 and 5000 mg/kg/day. Significantly increased (p < 0.05) levels of 

sulfhemoglobinemia were observed at 200, 1000 and 5000 mg/kg/day. The

percentage of erythrocytes containing Heinz bodies was highly increased at 1000 and 5000 

mg/kg/day. No effect on body weights or on organs and tissues examined at

autopsy was observed.

Dose and Endpoint for Risk Assessment: NOEL = 40 mg/kg/day based on increased 

sulfhemoglobin at 200 mg/kg/day.

870.31050 Oral Subchronic Toxicity - Nonrodent 

Study Selected: 13 week oral [subchronic] feeding study in dogs. 

MRID No.: 00038706

Executive Summary: In a subchronic feeding study, technical grade diflubenzuron (batch # 

P7227) was administered in the diet to beagle dogs at dose levels of 0 (control), 10, 20, 40 and 

160 ppm (equal to 0, 0.42, 0.84, 1.64 and 6.24 mg/kg/day). Groups of 3 male and 3 female dogs 

were used for each treated and control group. Hematology and blood chemistries were performed 

at 2, 4, 6 and 12 weeks: methemoglobin, sulfhemoglobin and urinalyses were performed at 6 and 

12 weeks. Ophthalmoscopic examinations were conducted at 6 and 12 weeks. Gross necropsies 

were performed on all dogs. Organ weights were determined and histopathological examinations 

were performed at the terminal sacrifice at 13 weeks. Mortality, clinical

signs, body weights and food consumption were not affected by treatment with diflubenzuron. 

Ophthalmoscopic examinations were negative. Methemoglobinemia was observed in the dogs at 

160 ppm (after 6 weeks). No gross necropsy, organ weight or histopathological changes were 

reported at any level that could be related to treatment with diflubenzuron. 
Page 54 of 66

Endpoint and dose for use in risk assessment: Calculated NOEL 2.0 mg/kg/day based on 

increased methemoglobinemia at 6.24 mg/kg/day. 

Comments about studies and/or endpoint: In this 13-week feeding study in dogs, a steady state 

for methemoglobinemia was observed to occur after 6 weeks.

In both the rat study and the mouse study, a NOEL of about 2 mg/kg/day was calculated by 

regression analysis. Considering all the available data (including

data from chronic feeding studies in rats, dogs and mice in which the NOEL for 

methemoglobinemia/sulfhemoglobinemia to be used to calculate the RfD also

was 2 mg/kg/day), it was concluded that the NOEL for intermediate term risk assessments 

should be 2 mg/kg/day (rather than the slightly lower NOEL of 1.64

mg/kg/day determined in the dog study above). 

870.3200 21-Day Dermal Toxicity – Rat

Study Selected: 21-Day dermal toxicity study in rat

MRID No.: 43954101

Executive Summary: In a subchronic, 21-day dermal toxicity study, Dimilin (diflubenzuron tech. 

96.7% a.i.) was administered to 10/sex/dose in 0.25% gum tragacanth in distilled, deionized 

water to the dorsal skin on the backs of the test animals at 0, 20, 500, or 1,000 mg/kg/day for 6 

hour period each day.

Dermal treatment for 21 days did not affect mortality, clinical signs, body weight changes, food 

consumption and/or organ weight changes. At 1,000 mg/kg/day, slight dermal irritation and 

traces of acanthosis and hyperkeratosis were noted in males and females. Liver and kidney 

histopathology was remarkable. Males exhibited slight elevations in the white cell count in the 

mid and high dose groups. Males also had small reductions in hemoglobin and hematocrit at 

1000 mg/kg dose group. In females at the top two doses there were statistically significant (P < 

0.05) decreases in RBC count, hemoglobin levels and hematocrit values. Hematological changes 

in males and females were within in the historical ranges for this species and age of rat, and 

therefore, considered not biologically significant. Methemoglobin levels increased significantly 

(P < 0.05 & 0.01) in males and females at 1000 mg/kg dose. There was increased incidence of 

anisocytosis, hypochromasia and polychromasia in males and females at the top dose. On 

August 14, 2001, the HED HIARC re-evaluated the study and concluded that the increased 

methemoglobinemia in males and females at 1000 mg/kg should be considered as toxicityinduced change. Therefore, the NOAEL is 500 mg/kg and LOAEL is 1000 mg/kg based on 

methemoglobinemia.

Dose and Endpoint for Risk Assessment: NOAEL = 500 mg/kg/day based on increased 

methemoglobinemia at 1000 mg/kg/day. 
Page 55 of 66

Comments about Study/Endpoint: This dermal toxicity study in rats is route- specific, is of 

appropriate duration and measures the effects of concern, i.e., methemoglobin and/or 

sulfhemoglobin. Previously, the end-points for short-term exposure were based on a 14- day 

mouse feeding study. The HIARC re-evaluated the 21-day dermal study in rat and revised the 

NOAEL from 20 mg/kg/day to 500 mg/kg/day, since the methemoglobinemia seen at 500 

mg/kg/day was within normal physiological parameters, but occurred at adverse levels at 1000 

mg/kg/day.

870.3250 Intermediate-Term Dermal Toxicity – Dog

Study Selected: Chronic Toxicity - Dog.

MRID No.: 00146174

Executive Summary: See 870.4100b Chronic Toxicity – Nonrodent, below. 

Dose and Endpoint for Risk Assessment: NOAEL = 2 mg/kg/day based on methemoglobinemia 

and sulfhemoglobinemia at 10 mg/kg/day (LOAEL). Corrected for 0.5% dermal absorption.

Comments about Study/Endpoint: Long term dermal studies are not available for diflubenzuron 

therefore a chronic feeding study was chosen. However, since an oral NOAEL was selected for a 

dermal endpoint a dermal absorption factor of 0.5% should be used for this risk assessment when 

converting dermal exposure to oral equivalents. Therefore the dermal equivalent dose producing

a NOAEL by the oral route is 400.0 mg/kg/day [i.e. 2.0 mg/kg/day ÷ 0.005 = 400.0 mg/kg/day.]

870.3465 90-Day Inhalation – Rat

Study Selected: Chronic Toxicity - Dog 

MRID No.: 00146174

Executive Summary: See 870.4100b Chronic Toxicity – Nonrodent, below 

Dose and Endpoint for Risk Assessment: NOAEL = 2.0 mg/kg/d based on methemoglobinemia 

and sulfhemoglobinemia at 10 mg/kg/day (LOAEL).

Comments about Study/Endpoint/Uncertainty Factor: An oral study was selected since no 

appropriate inhalation study is available in the database. This study is of appropriate duration of 

exposure. Assume that inhalation absorption is equivalent to oral absorption.

870.3700 Developmental Toxicity

870.3700a Prenatal Developmental Toxicity Study – Rodent
Page 56 of 66

Study Selected: Developmental Toxicity – Rat

MRID No.: 41703504

Executive Summary: In a developmental toxicity in rats, Technical grade diflubenzuron [97.6% 

pure] was administered in 1.0% gum tragacanth solution by oral gavage to 2 groups of 24 

Sprague Dawley rats on days 6-15 of gestation at dose levels of either 0 or 1000 mg/kg/day [the 

limit dose]. No maternal or developmental toxicity was observed. For maternal and 

developmental toxicity, the NOAEL was 1000 mg/kg/day (Limit-Dose); a LOAEL was not 

achieved.

870.3700b Prenatal Developmental Toxicity Study – Nonrodent 

Study Selected: Developmental Toxicity – Rabbit

MRID No.: 41703505

Executive Summary: In a developmental toxicity study with rabbits, Technical grade 

diflubenzuron [97.6% pure] was administered in 1.0% gum tragacanth solution by oral gavage to 

2 groups of New Zealand White rabbits on days 7-19 of gestation at dose levels of either 0 or 

1000 mg/kg/day [the limit dose]. No maternal or developmental toxicity was observed. For 

maternal and developmental toxicity, the NOAEL was 1000 mg/kg/day (Limit-Dose); a LOAEL 

was not achieved.

870.3800 Reproduction and Fertility Effects – Rat

Study Selected: 2-Generation Reproduction Study - Rats

MRID No.: 42700002

Executive Summary: In a 2-generation reproduction study in rats (Sprague-Dawley) complete in 

1992, 30 rats/sex/dose received either 0, 10, 200, 2000, or 4000 ppm (0, 0.67, 13.3, 136, and 278 

mg/kg/day for P0 males and 0, 0.76, 15.3, 152, and 3l1 mg/kg/day for P0 females during the 

premating growth periods, respectively) of CGA-152005 (99.1% a.i.) mixed in the feed. Note 

that organ weights were not obtained in this study.

The study is classified as Core Minimum Data and satisfies the guideline

requirement for a reproduction study.

870.4100a

Study Selected: Carcinogenicity/Oncogenicity Study - Rat

MRID No. 00145467
Page 57 of 66

Executive Summary: See 870.4300 Carcinogenicity - Rat, below.

The combined chronic oral toxicity/oncogenicity study in the rat is classified 

Acceptable/guideline and satisfies the guideline requirements for a chronic toxicity and 

oncogenicity study in rats.

Adequacy of Dose Levels Tested: Dosing was considered adequate since the highest dose level 

tested, 500 mg/kg/day, approached the limit dose of 1000 mg/kg/day for cacinogenicity studies 

and significant toxicity (particulary methemoglobinemia, sulfhemoglobinemia, erythrocyte 

destruction, compensatory regeneration of erythrocytes and hemolytic anemia) was observed at 

this dose level.

870.4100b Chronic Toxicity – Nonrodent

Study Selected: Chronic Toxicity - Dog

MRID No.: 00146174

Executive Summary: In a 52-week chronic oral study, technical grade diflubenzuron was 

administered in gelatin capsules to beagle dogs once each day (7 days/week) at dose levels of 0 

(control), 2, 10, 50 or 250 mg/kg/day. Groups of 6 male and 6 female dogs were used for each 

treated group and 12 male and 12 female dogs were used for the control group. Mortality, 

clinical signs, food consumption and water consumption were not affected by treatment with 

diflubenzuron. Except for a slight decrease in mean body weight gain observed in female dogs 

at 250 mg/kg/day, body weights were also not affected. Ophthalmoscopic examinations, clinical 

chemistries and urinalyses were negative. Statistically significant increases in methemoglobin 

and sulfhemoglobin were observed in male and female dogs at dose levels of 310 mg/kg/day. 

Heinz bodies were also observed in the erythrocytes of male dogs at 250 mg/kg/day and in those 

of female dogs at 350 mg/kg/day. At dose levels of 50 mg/kg/day and higher, signs of hemolytic 

anemia, destruction of erythrocytes and of compensatory regeneration of erythrocytes were 

observed. Increased platelet counts were also noted in females at 350 mg/kg/day. Absolute 

spleen and liver weights, but not relative organ body weight ratios, were increased in male dogs 

at 50 and 250 mg/kg/day. Organ weights were not increased in female dogs. The NOAEL in 

this study is 2 mg/kg/day and the LOAEL is 10 mg/kg/day, based on methemoglobinemia and 

sulfhemoglobinemia.

Dose and Endpoint for Establishing RFD: NOAEL = 2.0 mg/kg/day based on 

methemoglobinemia and sulfhemoglobinemia at 10 mg/kg/day (LOAEL).

Uncertainty Factor(s):

Chronic RfD = 2.0 mg/kg/day (NOAEL) = 0.02 mg/kg/day

100 (UF)

Comments about Study/Endpoint/Uncertainty Factor: The HIARC concurred with the dose, end 
Page 58 of 66

point, and the uncertainty factor selected by the RFD Committee in 1986.

870.4200a Carcinogenicity – Rat

Study Selected: Oncogenicity Study - Rat

MRID No.: NTP Report No. 351, July 1989

Executive Summary: In a carcinogenicity study, p-choloroaniline (> 99% purity) was dissolved 

in equimolar equivalents of hydrochloric acid and administered by gavage (5 days/week) to 

F344/N rats at dose levels of 0, 2, 6, or 18 mg/kg/day for 24-months. Groups of 50 male and 50 

female rats were used for each treated groups and the control group. Hematology examinations 

and mehtemoglobin measurements were conducted on 15 rats/sex/group at 6, 12, 18, and 24 

months. Increased survival was observed in male rats at 2 and 6 mg/kg/day and in female rats at 

2, 6, and 18 mg/kg/day relative to control rats. The authors of the study attributed the increased 

survival in these treatment groups to a decreased incidence of mononuclear cell leukemia in the 

same groups. Mean body weights for treated male and female groups generally remained within 

5% of the control male and female weights throughout the study. Results of hematology 

examinations and methemoglobin measurements showed mild hemolytic anemia and doserelated increases in methemoglobin at dose levels of 6 and 18 mg/kg/day. Male rats at 6 and 18 

mg/kg/day and female rats at 18 mg/kg/day had blue extremities indicative of cyanosis. 

Histopathological examinations indicated nonneoplastic treatment-related effects in spleen, liver, 

bone marrow and adrenal gland. Treatment-related increased incidence of uncommon sarcomas 

of the spleen was observed in male rats in this study. These sarcomas included fibrosarcomas, 

hemangiosarcomas, and osteosarcomas, many of which metastasized to other sites. The 

combined incidence of these sarcomas in male rats was 0/49, 3/50, and 38/50 at dose levels of 0, 

2, 6 and 18 mg/kg/day, respectively. In addition, in female rats, 1 fibrosarcoma was observed at 

a 6 mg/kg/day and 1 osteosarcoma at 18 mg/kg/day. No additional uncommon sarcomas of the 

spleen were observed in female rats in this study. A marginally increased incidence of 

pheochromocytomas was also observed in the adrenal gland of male and female rats at 18 

mg/kg/day. For male rats, the incidence was 13/49, 14/48, 15/48 and 26/49 and for female rats

was 2/50, 3/50, 1/50, and 6/50 at dose levels of 0, 2, 6 and 18 mg/kg/day, respectively. 

Decreased incidences of mononuclear cell leukemias and of malignant lymphomas were also 

noted in the treated male and female rats in this study.

Systemic toxicity NOAEL was 2 mg/kg/day based on mild hemolytic anemia, dose- related 

increased in methemoglobin levels in males and females, cyanosis in females observed at 6 

mg/kg/day (LOAEL).

This oncogenicity study in the rat is classified Acceptable/non-guideline and does not satisfy the 

guideline requirements for a oncogenicity study in rats.

Discussion of Tumor Data: Treatment-related increased incidence of uncommon sarcomas of the 

spleen was observed in male rats in this study. These sarcomas included fibrosarcomas, 

hemangiosarcomas, and osteosarcomas, many of which metastasized to other sites. The 
Page 59 of 66

combined incidence of these sarcomas in male rats was 0/49, 3/50, and 38/50 at dose levels of 0, 

2, 6 and 18 mg/kg/day, respectively. In addition, in female rats, 1 fibrosarcoma was observed at 

a 6 mg/kg/day and 1 osteosarcoma at 18 mg/kg/day. No additional uncommon sarcomas of the 

spleen were observed in female rats in this study. A marginally increased incidence of 

pheochromocytomas was also observed in the adrenal gland of male and female rats at 18 

mg/kg/day. For male rats, the incidence was 13/49, 14/48, 15/48 and 26/49 and for female rats 

was 2/50, 3/50, 1/50, and 6/50 at dose levels of 0, 2, 6 and 18 mg/kg/day, respectively. 

Decreased incidences of mononuclear cell leukemias and of malignant lymphomas were also 

noted in the treated male and female rats in this study. There was no increased incidence 

neoplastic lesions in either male or female mice.

Adequacy of Dose Levels Tested: Dosing was considered adequate to test the carcinogenic 

potential of p-chloroaniline. Systemic toxicity (LOAEL) was observed in males and females at 6 

mg/kg/day as evidenced by mild hemolytic anemia, dose-related increased in methemoglobin 

levels, and cyanosis in females. The NOAEL was 2 mg/kg/day.

870.4200b Carcinogenicity – Mouse

1) Study Selected: Oncogenicity Study - Mouse

MRID No. 00142490

Executive Summary: In a 91-week carcinogenicity study, technical grade diflubenzuron was 

administered in the diet to HC/CFLP strain mice at dose levels of 0, 16, 80, 400, 2000, or 10000 

ppm (equivalent to 0, 2.4, 12, 60, 300, or 1500 mg/kg/day). Groups of 52 male and 52 female 

mice were used for each treated group and 104 male and 104 female mice were used for the 

control group. Mortality, body weights and food consumption were not affected by treatment 

with diflubenzuron. Increases in methemoglobin and sulfhemoglobin were consistently observed 

in male and female mice throughout the study at dose levels of 12 mg/kg/day and higher. A 

blue/gray discoloration of the skin and extremities and dark eyes accompanied the increased 

methemoglobin and sulfhemoglobin. At higher dose levels (particularly > 300 mg/kg/day), signs 

of hemolytic anemia, erythrocyte destruction and compensatory regeneration were observed as 

were histopathological effects in the liver. Treatment with diflubenzuron was not associated 

with an increased incidence of neoplastic lesions in either male or female mice. Dosing was 

considered adequate since the highest dose tested, 1500 mg/kg/day, exceeded the limit dose of 

1000 mg/kg/day for carcinogenicity studies.

The systemic toxicity NOAEL is determined to be 2.4 mg/kg/day. The systemic toxicity 

LOAEL is 12 mg/kg/day based on increased methemoglobin and sulfhemoglobin levels 

consistently observed in male and female mice throughout the study.

The study is classified Acceptable/guideline and it satisfies the guideline requirements for a 

carcinogenicity study in mice.

Discussion of Tumor Data: There was no increased incidence of neoplastic lesions in either 
Page 60 of 66

male or female mice.

Adequacy of Dose Levels Tested: Dosing was considered adequate since the highest dose level 

tested, 1500 mg/kg/day, exceeded the limit dose of 1000 mg/kg/day.

2) Study Selected: Oncogenicity Study - Mouse

MRID No.: NTP Study, Report No. 351, July 1989.

Executive Summary: In a carcinogenicity study, p-choloroaniline (> 99% purity) was dissolved 

in equimolar equivalents of hydrochloric acid and administered by gavage (5 days/week) to 

B6C3F1 mice at dose levels of 0, 3, 10, or 30 mg/kg/day for 24-months. Groups of 50 male and 

50 female mice were used for each treated group and the control group. Increased mortality was 

observed in male mice at 10 mg/kg/day after 99 weeks, but not at 30 mg/kg/day. Treatment did 

not affect mortality in female mice. Mean body weights for treated male and female groups were 

not affected by treatment with the test material. At 24 months, hemosiderin was observed in the 

kupffer cells of the livers of male and female mice and in the renal tubules of female mice at 30 

mg/kg/day. Proliferation of hematopoietic cells was noted in the livers of female mice at all 

treatment levels. Increased incidence of combined hepatocellular adenomas/carcinomas were 

observed in the male mice in this study. Incidences were 11/50, 21/49, 20/50 and 21/50 at dose 

levels of 0, 3, 10, and 30 mg/kg/day, respectively. The increase in combined tumors were 

primarily due to a dose-related increase in hepatocellular carcinomas as follows: 3/50, 7/49, 

11/50, and 17/50 at 0, 3, 10, and 30 mg/kg/day, respectively. Many of these carcinomas 

metastasized to the lungs (1/50, 1/49, 2/50, and 9/50 at 0, 3, 10, and 30 mg/kg/day, respectively). 

Increased incidence of hemangiosarcomas in the spleen and/or liver were also observed in the 

male mice in this study at 30 mg/kg/day. Incidences were 4/50, 4/49, 1/50, and 10/50 at dose 

levels of 0, 3, 10, and 30 mg/kg/day, respectively. Incidences of malignant lymphomas were 

decreased in the treated male and female mice. No evidence of carcinogenicity was observed in 

the female mice in this study.

Systemic toxicity NOAEL was 10 mg/kg/day based on hemosiderin accumulation in kupffer 

cells of the liver in male and female mice at 30 mg/kg/day (LOAEL).

This oncogenicity study in mice is classified Acceptable/non-guideline and does not satisfy the 

guideline requirements for a oncogenicity study in mice.

Discussion of Tumor Data: Increased incidence of combined hepatocellular 

adenomas/carcinomas were observed in the male mice in this study. Incidences were 11/50, 

21/49, 20/50 and 21/50 at dose levels of 0, 3, 10, and 30 mg/kg/day, respectively. The increase 

in combined tumors were primarily due to a dose-related increase in hepatocellular carcinomas 

as follows: 3/50, 7/49, 11/50, and 17/50 at 0, 3, 10, and 30 mg/kg/day, respectively. Many of 

these carcinomas metastasized to the lungs (1/50, 1/49, 2/50, and 9/50 at 0, 3, 10, and 30 

mg/kg/day, respectively). Increased incidence of hemangiosarcomas in the spleen and/or liver 

were also observed in the male mice in this study at 30 mg/kg/day. Incidences were 4/50, 4/49, 

1/50, and 10/50 at dose levels of 0, 3, 10, and 30 mg/kg/day, respectively.
Page 61 of 66

Adequacy of Dose Levels Tested: Dosing was considered adequate to test the carcinogenic 

potential of p-chloroaniline. Systemic toxicity (LOAEL) was observed in male and female mice 

at 30 mg/kg/day as evidenced by hemosiderin accumulation in kupffer cells of the liver. The 

NOAEL was 10 mg/kg/day.

870.4300 Chronic/Oncogenicity

Study Selected: Carcinogenicity Study - Rat

MRID No. 00145467

Executive Summary: In a 104-week carcinogenicity study, technical grade diflubenzuron was 

administered in the diet to Sprague-Dawley strain rats at dose levels of 0, 156, 625, 2500 or 

10,000 ppm (equivalent to 0, 7.8, 31, 125 or 500 mg/kg/day). Groups of 50 male and 50 female 

rats were used for each treated group and 100 male and 100 female rats were used for the control 

group. Mortality, clinical signs, body weights and food consumption were not affected by 

treatment with diflubenzuron. Increases in methemoglobin and sulfhemoglobin were observed at 

all treatment levels. Histopathological signs of erythrocyte destruction and compensatory 

regeneration were observed at levels of >7.8 mg/kg/day. Signs of hemolytic anemia, increased 

resticulocytes and increased spleen and liver weights were noted at >125 mg/kg/day. Treatment 

with diflubenzuron was not associated with increased incidence of neoplastic lesions in either 

males or females. Dosing was considered adequate since the highest dose level tested, 500 

mg/kg/day, approached the limit dose of 1000 mg/kg/day for cacinogenicity studies and 

significant toxicity (particulary methemoglobinemia, sulfhemoglobinemia, erythrocyte 

destruction, compensatory regeneration of erythrocytes and hemolytic anemia) was observed at 

this dose level. Systemic Toxicity NOAEL was not establised. The LOAEL is the lowest dose 

tested 7.8 mg/kg/day based on signs of erythrocyte destruction and compensatory regeneration. 

This combined chronic oral toxicity/oncogenicity study in the rat is classified 

Acceptable/guideline and satisfies the guideline requirements for a chronic toxicity and 

oncogenicity study in rats.

Discussion of Tumor Data: There was no increased incidence of neoplastic lesions in either male 

or female rats.

Adequacy of Dose Levels Tested: Dosing was considered adequate since the highest dose level 

tested, 500 mg/kg/day, approached the limit dose of 1000 mg/kg/day for cacinogenicity studies 

and significant toxicity (particulary methemoglobinemia, sulfhemoglobinemia, erythrocyte 

destruction, compensatory regeneration of erythrocytes and hemolytic anemia) was observed at 

this dose level.

870.7485 Metabolism – Rat

Study Selected: Metabolism Study - Rat
Page 62 of 66

MRID No.: 44875501, 44875502

Recently submitted rat metabolism data indicate that diflubenzuron does not metabolize to 

PCA or CPU nor is CPU converted to PCA. The HEDMARC met several times (2/20/01 and 

5/8/01), concurred with the findings and concluded that a 2% in vivo conversion factor for 

diflubenzuron to PCA or CPU should be dropped (MARC memo dated May 31, 2001). For 

risk assessment, the toxicity of the CPU and PCA will be considered equal to parent, 

diflubenzuron. In conclusion, the MARC recommended that non-carcinogenic risk 

assessment should include parent, CPU and PCA; and cancer risk for CPU and PCA should 

be assessed individually.

870.7600 Dermal Absorption – Rat

Dermal Absorption Factor: 0.5 percent.

Twenty four male Sprague-Dawley rats were divided into two groups of 12 males each and given 

0.005 or 0.05 mg/cm.sq. of C-14 diflubenzuron technical in gum tragacanth [0.25%]. Four 4 

animals per dose group were sacrificed after 1, 4, or 10 hours of exposure. The control group 

consisted of 3 males with 1 animal sacrificed at the end of 1, 4, or 10 hours of exposure. 

Systemic absorption was less than 0.5% at each time interval regardless of the dose. 

Approximately 4.7 - 6.2% diflubenzuron was bound to the skin at the application site.

870.6200b Subchronic Neurotoxicity

Waived by HASPOC TXR 0056309

870.5100, 870-5300 Mutagenicity

Mutagenicty – Bacterial

MRID No.: 41703503

Executive Summary: In a Salmonella/mammalian microsome plate incorporation assay, strains 

TA98, TA100, TA1535, TA1537 and TA1538 were exposed to technical grade diflubenzuron 

with and without S9 metabolic activation at concentrations of 0, 8, 40, 200, or 1000 ·g/plate. The

high dose was selected on the basis of slight compound precipitation at 1000 ·g/plaste. 

Preparations for metabolic S9 activation were made from Aroclor induced rat liver. The solvent 

used was DMSO. Diflubenzuron was not cytotoxic with or without S9 activation in any of the 

Salmonella strains in this assay. There was no evidence of induced mutant colonies over 

background levels at any of the evaluated concentrations.

Mutagenicty – Structural Chromosomal Aberrations
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MRID No.: 41703502

Executive Summary: In an in vitro chromosome damage assay, cultures of Chinese hamster 

ovary (CHO) cells were exposed to technical grade diflubenzuron with and without S9 metabolic 

activation. The test material was tested at concentrations up to cytotoxic/precipitating levels of 

200 - 250 ·g/ml. Preparations for S9 metabolic activation were made from Aroclor 1254 induced 

rat liver. The solvent used was DMSO. The test material did not induce an increase in structural 

chromosome aberrations over background levels at any of the evaluated concentrations.

Mutagenicty – Other

MRID No.: 41703501

Executive Summary: In an unscheduled DNA synthesis (UDS) assay, cultures of primary rat 

hepatocytes were exposed to technical grade diflubenzuron at concentrations ranging from 0.1 to 

333 ·g/ml. At the high dose of 333 ·g/ml, cytotoxicity was oserved (36% cell survival in an 

initial assay and 8% cell survival in a confirmatory assay). The solvent used was DMSO. 

Positive controls were adequate. The test material did not cause an appreciable increase in net 

nuclear grain counts compared to the solvent control at any of the evaluated concentrations. 

Diflubenzuron did not induce a gentoxic effect in this assay system.

870.7800 Immunotoxicity

28-Day (Dietary) Immunotoxicity Study – Mice

MRID No: 48760512, TXR 0056396

EXECUTIVE SUMMARY: In an immunotoxicity study (MRID48760512), Diflubenzuron

(99.2 % a.i., lot # AM8L17D481) was administered to female CD-1 mice (10/dose) at dose 

levels of 0 (vehicle control group), 80, 400, 2,000 or 10,000 ppm (equivalent to 0, 15, 77, 365 or 

1832 mg/kg/day, respectively) for 28 days. The positive control group consisting of 10 female 

mice was administered cyclophosphamide (25 mg/kg/day, dose volume 10 mL/kg) by 

intraperitoneal injection on Days 24-28. On Day 24, all animals in all groups received a single 

intravenous dose of sheep red blood cells (SRBC) 1 x108/mL (dose volume 0.2 mL/animal) into 

the tail vein. Parameters such as, clinical condition, body weight, food consumption, organ 

weights, and immunotoxicity related to the treatment were monitored. At necropsy on Day 29, 

the thymus, and spleen from animals were removed and weighed. The sheep red blood cell 

(SRBC) antibody response was measured with an enzyme-linked immunosorbent assay (ELISA). 

There were no premature dead and no treatment related clinical signs and symptoms observed. 

Increased mean food consumption for the 80, 400 and 2,000 ppm diflubenzuron groups were 

noted at Week 3, but it was a transient effect and there were no comparable changes in the 

10,000 ppm group. There were no treatment related effects on water consumption, weekly mean 

body weight and terminal mean body weight when compared to the vehicle control group. There 

were statistically significantly increase (p<0.05) of absolute and relative spleen weights at 2,000 

and 10,000 ppm, but no treatment related changes in thymus weights. Positive control group 
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(cyclophosphamide) had statistically significantly decrease (p<0.05) of absolute and relative 

spleen and thymus weights; but no cyclophosphamide-related effects on body weights. 

The systemic toxicity NOAEL is 400 ppm (equivalent to 77 mg/kg bw/day); the LOAEL is 

2000 ppm (equivalent to 365 mg/kg/day) based on increased spleen weight which was a 

consistent finding in previous toxicity studies. 

There were no statistically significant treatment-related effects on the specific anti-SRBC 

antibody response by ELISA test in all treated groups. A high inter-individual variability was 

noted in all the treatment groups as well as in the control group. Evaluation of individual animal 

data of this study did not show any trend or distribution that would demonstrate significant 

suppression of anti-SRBC IgM response. Animals in positive control group, showed a 

statistically significant (p<0.05) decrease of the anti-SRBC IgM response to a challenge with 

SRBCs. This confirmed the ability of the test system to detect immunosuppressive effects and 

confirmed the validity of the study design. 

The Natural Killer (NK) cells activity was not evaluated in this study. The toxicology database 

for Diflubenzuron does not reveal any evidence of treatment related effects on the immune 

system. The overall weight of evidence suggests that the chemical does not directly target the 

immune system. Under HED guidance a NK cell activity assay is not required at this time. 

The immunotoxicity NOAEL is 10,000 ppm (equivalent to 1832 mg/kg/day), tested above 

the limit dose. The immunotoxicity LOAEL is not established. 

This immunotoxicity study is classified acceptable/guideline; and satisfies the guideline 

requirement for an immunotoxicity study (OPPTS 870.7800) in mice. 
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APPENDIX B. Chemical Names And Structures Of Diflubenzuron and Metabolites

Diflubenzuron

F

F O

N

H

N

H

O

Cl

4-chlorophenylurea: CPU

Cl

N

H

H2N

O

4-chloroaniline: PCA

Cl

H2N
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APPENDIX C. Physical/Chemical Properties

APPENDIX D. Studies Reviewed for Ethical Conduct

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

exposed to a pesticide or other chemical. These studies were determined to require a review of their ethical 

conduct, have received that review and have been determined to be ethical.

The PHED Task Force, 1995. The Pesticide Handlers Exposure Database, Version 1.1. Task Force 

members Health Canada, U.S. Environmental Protection Agency, and the National Agricultural 

Chemicals Association, released February, 1995.

The Agricultural Handler Exposure Task Force (AHETF), 2011. The Occupational Handler Unit 

Exposure Surrogate Reference Table. U.S. Environmental Protection Agency. Released June 21, 2011.

Physicochemical Properties of Diflubenzuron.

Parameter Value Reference

Melting range 230-232 °C http://www.arsusda.gov/acsl/service

s/ppdb/textfiles/DIFLUBENZURO

N

pH Not available

Density Not available

Water solubility (25 °C) 0.08 ppm

Solvent solubility (25 °C) (ppm) 6.5 x 103 Acetone 

2 x 103 Acetonitrile 

2.4 x 104 Dioxane 

1.04 x 105 Dimethylformamide 

1.2 x 105 Dimethylsulfoxide 

1 x 103 Methanol 

6 x 102 Dichloromethane 

Vapor pressure (25 °C) 1.2 x 10- 4 mPa

Dissociation constant, pKa Not available

Octanol/water partition coefficient, 

Log(KOW)

3.89

UV/visible absorption spectrum Not available