United States Prevention, Pesticides EPA 738-R­


04-012 


Environmental Protection and Toxic Substances 


September 2005 


Agency (7508C) 


Reregistration 


Eligibility 


Decision for 


Thidiazuron


List D 

Case No. 4092 

Approved by: Date:______________ 

Debra Edwards, Ph. D. 

Director 

Special Review and Reregistration Division 
Table of Contents 

Executive Summary ................................................................................................................................... iv 

I. Introduction .........................................................................................................................................1 

II. Chemical Overview .............................................................................................................................2 

A. Regulatory History.....................................................................................................................2 

B. Chemical Identification..............................................................................................................2 

C. Use Profile ...................................................................................................................................3 

D. Estimated Usage of Pesticide.....................................................................................................4 

III. Summary of Thidiazuron Risk Assessment ......................................................................................4 

A. Human Health Risk Assessment ...............................................................................................5

1. Toxicity of Thidiazuron .......................................................................................................5 

a. Toxicity Profile .........................................................................................................5 

b. FQPA Safety Factor .................................................................................................6 

c. Endocrine Effects .....................................................................................................6 

d. Toxicological Endpoints for Risk Assessment ......................................................7 

e. Cancer Classification ...............................................................................................7 

2. Dietary Exposure and Risk from Food and Water ...........................................................8 

a. Exposure Assumptions and Data ............................................................................8 

b. Population Adjusted Dose (PAD)............................................................................9 

3. Residential and Other Non-Occupational Exposure.........................................................9 

4. Aggregate Risk......................................................................................................................9 

5. Occupational Risk ................................................................................................................9 

a. Occupational Toxicity............................................................................................10 

b. Occupational Handler Exposure...........................................................................10 

c. Occupational Handler Risk Summary .................................................................11 

d. Occupational Post-application Risk .....................................................................11 

6. Cumulative Assessment .....................................................................................................12 

7. Human Incident Data.........................................................................................................12 

B. Environmental Risk Assessment.............................................................................................13 

1. Environmental Exposure...................................................................................................13 

a. Environmental Fate and Transport......................................................................13 

b. Aquatic Organism Exposure .................................................................................13 

c. Terrestrial Organism Exposure............................................................................14 

(1) Birds.........................................................................................................................15 

(2) Mammals.................................................................................................................15 

d. Non-target Terrestrial Plant Exposure ................................................................15 

2. Environmental Effects (Toxicity)......................................................................................15 

a. Toxicity to Aquatic Organisms .............................................................................15 

(1) Freshwater and Estuarine/Marine Fish ...............................................................15 

(2) Freshwater and Estuarine Invertebrates .............................................................16 

b. Toxicity to Aquatic Plants .....................................................................................16 
c. Toxicity to Terrestrial Organisms ........................................................................17 

(1) Birds.........................................................................................................................17 

(2) Mammals.................................................................................................................17 

d. Toxicity to Non-target Insects ...............................................................................18 

e. Toxicity to Terrestrial Plants ................................................................................19 

3. Ecological Risk Estimation (RQs) ....................................................................................20 

a. Risk to Aquatic Organisms....................................................................................20 

(1) Fish and Aquatic Invertebrates ............................................................................20 

b. Risk to Aquatic Plants............................................................................................21 

c. Risk to Non-target Terrestrial Organisms...........................................................21 

(1) Birds.........................................................................................................................21 

(2) Mammals.................................................................................................................22 

d. Risk to Non-target Insects .....................................................................................23 

e. Risk to Non-target Terrestrial Plants...................................................................23 

4. Ecological Incidents............................................................................................................24 

5. Endangered Species Concerns ..........................................................................................24 

a. Risk to Endangered Species ..................................................................................24 

6. Risk Characterization ........................................................................................................25 

IV. Risk Management, Reregistration and Tolerance Reassessment Decision..................................26 

A. Determination of Reregistration Eligibility ...........................................................................26 

B. Public Comments and Responses............................................................................................26

C. Regulatory Position..................................................................................................................27 

1. Food Quality Protection Act Findings..............................................................................27 

a. ARisk Cup@ Determination.....................................................................................27 

b. Determination of Safety to the U.S. Population Including Infants 

and Children ...........................................................................................................27 

c. Endocrine Disruptor Effects .................................................................................28 

d. Cumulative Risks....................................................................................................28 

2. Tolerance Reassessment Summary...................................................................................29 

a. Tolerances Currently Listed Under 40 CFR '180.403.........................................29 

b. Codex Harmonization............................................................................................30 

D. Regulatory Rationale ...............................................................................................................30 

1. Labeling Requirements......................................................................................................30 

2. Other Labeling Requirements...........................................................................................31 

3. Endangered Species Considerations.................................................................................31 

4. Spray Drift Management...................................................................................................32 

V. What Registrants Need to Do ...........................................................................................................32 

A. Manufacturing Use Products ..................................................................................................32 

1. Additional Generic Data Requirements...........................................................................32 

2. Labeling for Manufacturing-Use Products......................................................................33 

B. End-Use Products.....................................................................................................................33 

1. Additional Product-Specific Data Requirements............................................................33 

2. Labeling for End-Use Products.........................................................................................33 

C. Labeling Changes Summary Table.........................................................................................33 

VI. Appendices .........................................................................................................................................39 
A. Use Patterns Subject to Reregistration for Thidiazuron (Case 4092) .....................................40 

B. Table of Generic Data Requirements and Studies Used to Make the Reregistration 

Decision..........................................................................................................................................41 

C. Technical Support Documents ....................................................................................................49 

D. Citations Considered to be Part of the Data Base Supporting the Reregistration 

 Eligibility Decision (Bibliography) for Thidiazuron .................................................................51 

E. Generic Data Call-In ....................................................................................................................62 

F. Product Specific Data Call-In......................................................................................................64 

G. Batching.........................................................................................................................................66 

H. List of Registrants Sent this Data Call-In ..................................................................................68 

I. List of Available Related Documents and Electronically Available Forms ............................70 
Thidiazuron Reregistration Eligibility Decision Team 

Office of Pesticide Programs: 

Biological and Economic Analysis Assessment 

Mojmir Mazur 

Sharlita Harris 

Nicole Zinn 

Environmental Fate and Effects Risk Assessment 

William Evans 

Alex Clem 

James Hetrick 

Edward Odenkirchen 

Health Effects Risk Assessment 

Paul Chin 

Jeff Dawson 

Toiya Goodlow 

Registration Support 

Joanne Miller 

Risk Management 

John W. Pates, Jr. 

Tom Brennan 

Barbara Briscoe 

i 
Glossary of Terms and Abbreviations 

AGDCI Agricultural Data Call-In 

ai Active Ingredient 

aPAD Acute Population Adjusted Dose 

AR Anticipated Residue 

BCF Bioconcentration Factor 

CARES -------

CCA Comparative Cholinesterase Assay 

CFR Code of Federal Regulations 

cPAD Chronic Population Adjusted Dose 

CSF Confidential Statement of Formula 

CSFII USDA Continuing Surveys for Food Intake by Individuals 

DCI Data Call-In 

DEEM Dietary Exposure Evaluation Model 

DFR Dislodgeable Foliar Residue 

DNT Developmental Neurotoxicity 

DWLOC Drinking Water Level of Comparison. 

EC Emulsifiable Concentrate Formulation 

EC Engineering Control 

EDWC Estimated Drinking Water Concentration 

EEC Estimated Environmental Concentration 

EPA Environmental Protection Agency 

EUP End-Use Product 

FATE5 -------

FDA Food and Drug Administration 

FIFRA Federal Insecticide, Fungicide, and Rodenticide Act 

FFDCA Federal Food, Drug, and Cosmetic Act 

FQPA Food Quality Protection Act 

FOB Functional Observation Battery 

G Granular Formulation 

GENEEC Tier I Surface Water Computer Model 

GLN Guideline Number 

HAFT Highest Average Field Trial 

IR Index Reservoir 

LC50 Median Lethal Concentration. A statistically derived concentration of a substance that can be expected to cause 

death in 50% of test animals. It is usually expressed as the weight of substance per weight or volume of water, air 

or feed, e.g., mg/l, mg/kg or ppm. 

LD50 Median Lethal Dose. A statistically derived single dose that can be expected to cause death in 50% of the test 

animals when administered by the route indicated (oral, dermal, inhalation). It is expressed as a weight of 

substance per unit weight of animal, e.g., mg/kg. 

Lifeline ------

LOC Level of Concern 

LOD Limit of Detection 

LOAEL Lowest Observed Adverse Effect Level 

MATC Maximum Acceptable Toxicant Concentration 

Fg/g Micrograms Per Gram 

Fg/L Micrograms Per Liter 

mg/kg/day Milligram Per Kilogram Per Day 

mg/L Milligrams Per Liter 

MOE Margin of Exposure 

MRID Master Record Identification (number). EPA's system of recording and tracking studies submitted. 

ii 
MUP Manufacturing-Use Product 

NA Not Applicable 

NAWQA USGS National Water Quality Assessment 

NPDES National Pollutant Discharge Elimination System 

NR Not Required 

NOAEL No Observed Adverse Effect Level 

OP Organophosphate 

OPP EPA Office of Pesticide Programs 

OPPTS EPA Office of Prevention, Pesticides and Toxic Substances 

PAD Population Adjusted Dose 

PCA Percent Crop Area 

PDP USDA Pesticide Data Program 

PHED Pesticide Handler's Exposure Data 

PHI Preharvest Interval 

ppb Parts Per Billion 

PPE Personal Protective Equipment 

ppm Parts Per Million 

PRZM/ Tier II Surface Water Computer Model 

EXAMS 

Q1* The Carcinogenic Potential of a Compound, Quantified by the EPA's Cancer Risk Model 

RAC Raw Agriculture Commodity 

RED Reregistration Eligibility Decision 

REI Restricted Entry Interval 

RfD Reference Dose 

RQ Risk Quotient 

SCI-GROW Tier I Ground Water Computer Model 

SAP Science Advisory Panel 

SF Safety Factor 

SLC Single Layer Clothing 

SLN Special Local Need (Registrations Under Section 248) of FIFRA) 

TCPSA 2,3,3-trichloroprop-2-ene sulfonic acid ([chemical name] Metabolite) 

TGAI Technical Grade Active Ingredient 

TRR Total Radioactive Residue 

USDA United States Department of Agriculture 

USGS United States Geological Survey 

UF Uncertainty Factor 

UFdb Database Uncertainty Factor 

UV Ultraviolet 

WPS Worker Protection Standard 

iii 
Executive Summary 

This document presents the Environmental Protection Agency’s (hereafter the Agency or 

EPA) decision regarding the reregistration eligibility of the registered uses of thidiazuron [1­

phenyl-3-(1,2,3-thidiazol-5-yl)urea]. The Agency made its reregistration eligibility 

determination based on its review of the required data and current guidelines for conducting 

acceptable studies to generate such data. The Agency has found that currently registered uses of 

thidiazuron are eligible for reregistration, provided that the changes specified in this document 

are made to the label. 

Thidiazuron is a member of the phenylurea class of herbicides and is used as a growth 

regulator only on cotton. The first registration was in 1982. Currently, there are 22 tolerances 

for thidiazuron. 

Dietary Risk from Food and Water 

An acute dietary assessment was not performed on thidiazuron because there were no 

effects observed in the available toxicology studies that could be attributable to a single exposure 

(dose). Chronic dietary risk estimates for food and water are below the Agency’s level of 

concern. The highest chronic exposure and risk estimates were for children 1 to 2 years old. 

The chronic dietary risks are less than 100% of the chronic Population Adjusted Dose (cPAD) 

for all population subgroups. Therefore, no mitigation is warranted at this time for dietary 

exposure to thidiazuron. 

Occupational Risk 

To address occupational exposure, short-term inhalation, and intermediate-term inhalation 

risks were assessed. MOEs were not calculated for dermal exposures, since no hazard concern 

was identified for exposures via the dermal route. For handlers, in all scenarios considered, risks 

were not of concern (MOEs ranged from 150 to 1,300,000 at baseline protection). Therefore, no 

mitigation is warranted at this time for occupational risk to thidiazuron. 

Residential Risk 

There are no residential uses of thidiazuron. Therefore, residential exposures are not 

expected and a residential exposure assessment was not conducted. 

Aggregate Risk 

An acute dietary assessment was not performed on thidiazuron because there were no 

effects observed in the available toxicology studies that could be attributable to a single exposure 

(dose). Therefore, no mitigation is warranted at this time for acute aggregate risk to thidiazuron. 

A chronic aggregate risk assessment was conducted for thidiazuron. The chronic aggregate risk 

looked at the combined risk from dietary exposure (food and drinking water pathways), since 

iv 
there are no residential uses. Chronic risks from food exposures were below the Agency's level 

of concern. Therefore, no mitigation is warranted at this time for aggregate risk to thidiazuron. 

Ecological Risk 

Non-target terrestrial and semi-aquatic plants are at potential direct risk from thidiazuron 

use. Dicots are sensitive to thidiazuron, but monocots do not appear to be affected at expected 

environmental concentrations. Aquatic plants do not appear to be at risk. However, if terrestrial 

non-target plants come in contact with thidiazuron, these plants may be killed or damaged 

enough to prevent the plant from reproducing or successfully competing with other plants for 

resources. For mammals, acute risks did not exceed levels of concern, but there is a potential 

for chronic risk when maximum (high-end) EECs are assumed. For birds, acute risk quotients 

did not exceed levels of concern. Chronic risks to birds cannot be estimated due to absence of 

data; however such data will be required as a follow-up to this RED. To help mitigate 

environmental risks, specific language clarifying allowable use rates and conditions shall be 

required. 

Endangered Species 

The Agency’s screening level risk assessment for listed species indicates that thidiazuron 

exceeds the endangered species levels of concern for endangered and threatened terrestrial and 

semi-aquatic dicots, and exceeds chronic levels of concern for certain mammals. 

Next Steps 

The Agency is issuing this RED document for thidiazuron as announced in a Notice of 

Availability published in the Federal Register. In the near future, EPA will issue a generic DCI 

for additional data necessary to confirm the conclusions of this RED for the active ingredient 

thidiazuron. EPA will also issue a product specific DCI for data necessary to complete product 

reregistration for products containing thidiazuron. 

v 
I. Introduction 

The Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) was amended in 1988 to 

accelerate the reregistration of products with active ingredients registered prior to November 1, 

1984. The amended Act calls for the development and submission of data to support the 

reregistration of an active ingredient, as well as a review of all submitted data by the U.S. 

Environmental Protection Agency (referred to as EPA or "the Agency"). Reregistration involves 

a thorough review of the scientific database underlying a pesticide's registration. The purpose of 

the Agency's review is to reassess the potential risks arising from the currently registered uses of 

the pesticide; to determine the need for additional data on health and environmental effects; and 

to determine whether or not the pesticide meets the "no unreasonable adverse effects" criteria of 

FIFRA. 

On August 3, 1996, the Food Quality Protection Act of 1996 (FQPA) was signed into law. 

This Act amends FIFRA and the Federal Food Drug and Cosmetic Act (FFDCA) to require 

reassessment of all existing tolerances for pesticides in food. FQPA also requires EPA to review 

all tolerances in effect on August 2, 1996, by August 3, 2006. In reassessing these tolerances, 

the Agency must consider, among other things, aggregate risks from non-occupational sources of 

pesticide exposure, whether there is increased susceptibility to infants and children, and the 

cumulative effects of pesticides with a common mechanism of toxicity. When a safety finding 

has been made that aggregate risks are not of concern and the Agency concludes that there is a 

reasonable certainty of no harm from aggregate exposure, the tolerances are considered 

reassessed. EPA decided that, for those chemicals that have tolerances and are undergoing 

reregistration, tolerance reassessment will be accomplished through the reregistration process. 

As mentioned above, FQPA requires EPA to consider "available information" concerning 

the cumulative effects of a particular pesticide's residues and "other substances that have a 

common mechanism of toxicity" when considering whether to establish, modify, or revoke a 

tolerance. Potential cumulative effects of chemicals with a common mechanism of toxicity are 

considered because low-level exposures to multiple chemicals causing a common toxic effect by 

a common mechanism could lead to the same adverse health effect as would a higher level of 

exposure to any one of these individual chemicals. 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 the 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://epa.gov/pesticides/cumulative/.] 

Unlike other pesticides for which EPA has considered cumulative risk based on a common 

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

thidiazuron. The Agency has found no information indicating thidiazuron shares a common 

mechanism of toxicity with other substances. Thidiazuron does not appear to produce a toxic 

metabolite produced by other substances. Therefore, for the purposes of tolerance reassessment 

and a decision on reregistration eligibility, EPA has assumed that thidiazuron does not share a 

1 
common mechanism of toxicity with other compounds. In the future, if additional information 

suggests thidiazuron shares a common mechanism of toxicity with other compounds, additional 

testing may be required and a cumulative assessment may be necessary. 

This document presents EPA=s revised human health and ecological risk assessments and 

the reregistration eligibility decision for thidiazuron. The document consists of six sections. 

Section I contains the regulatory framework for reregistration/tolerance reassessment. Section II 

provides a profile of the use and usage of the chemical. Section III gives an overview of the 

revised human health and environmental effects risk assessments based on data, public 

comments, and other information received in response to the preliminary risk assessments. 

Section IV presents the Agency=s reregistration eligibility and risk management decisions. 

Section V summarizes label changes necessary to implement the risk mitigation measures 

outlined in Section IV. Finally, the Appendices list related information and supporting 

documents. The preliminary and revised risk assessments for thidiazuron are available in the 

Public Docket, under docket number(s) OPP-2004-0382 and on the Agency=s web page, 

http://www.epa.gov/edockets. 

II. Chemical Overview 

A. Regulatory History 

Thidiazuron has been registered for use as a pre-harvest cotton defoliant or growth 

regulator. It removes green leaves and immature fruiting structures, which contribute to cotton 

staining. Currently, there are eighteen active products containing thidiazuron (one technical 

product) registered under Section 3 of the Federal Insecticide, Fungicide, and Rodenticide Act 

(FIFRA). 

B. Chemical Identification 

Technical Thidiazuron 

O S 

H H 

N C N N 

N 

Common Name: Thidiazuron 

Trade Name: Dropp7

Chemical Name: 1-phenyl-3-(1,2,3-thidiazol-5-yl)urea 

Chemical Family: Phenylurea herbicide 

2 
Case Number: 4092 

CAS Registry Number: 51707-55-2 

OPP Chemical Code: 120301 

Moleculer weight: 220.25 

Empirical Formula: C9H8N4OS 

Basic Manufacturers: Bayer CropScience LP 

C. Use Profile 

The following is information on the currently registered uses including an overview of 

use sites and application methods. A detailed table of the uses of thidiazuron eligible for 

reregistration is contained in Appendix A. 

Type of Pesticide: Herbicide 

Target organism(s): N/A 

Mode of action: Used as a defoliant or growth regulator by removing green leaves 

and immature fruiting structures, which contribute to cotton 

staining. 

Use Sites: Cotton (only) 

Food uses: Tolerances have been established for cottonseed, milk, eggs, meat 

and meat by-products of cattle, goat, hog, horse, and sheep because 

livestock and poultry feed on cottonseed and other by-products 

that may be treated with thidiazuron. 

Non-Food & 

Residential Uses: N/A 

Public Health Uses: N/A 

Use Classification: General Use 

Formulation Types: Thidiazuron registered formulations include wettable powders 

(WP) (50 percent active ingredient), soluble concentrates (SC) (12 

percent active ingredient), and emulsifiable concentrates (EC) 

(8.4-50 percent active ingredient). 

3 
Application Methods: Thidiazuron can be applied with aerial or ground equipment, such 

as groundboom sprayers. 

Application Rates: The maximum single application rate on labels when thidiazuron is 

the sole active ingredient is 0.2 lb. a.i. (active ingredient)/A on 

cotton. The maximum seasonal rate is 0.3 lb. a.i./A. (A maximum 

of two 0.1-0.2 lb. a.i./acre applications may be applied to mature 

cotton plants, not exceeding a total rate of 0.3 lb. a.i./A/season 

(0.337 kg a.i./ha/season)). 

Application Timing: Applications of thidiazuron to cotton are made prior to harvesting. 

The minimum pre-harvest interval (PHI) is 5 days and the Re-entry 

interval (REI) is 24 hours. 

D. Estimated Usage of Pesticide 

The predominant usage is in the major cotton producing areas of the Mid-South, 

Southeast, and Western United States. Approximately 30% of the annual U.S. cotton crop is 

treated with thidiazuron. 

III. Summary of Thidiazuron Risk Assessment 

The following is a summary of EPA=s human health and ecological risk findings and 

conclusions for thidiazuron as presented fully in the documents “Thidiazuron: Revised HED 

Chapter of the Reregistration Eligibility Decision Document (RED)” written by T. Goodlow, B. 

Chin, and J. Dawson and “Environmental Fate and Effects Division Revised Risk Assessment 

for the Reregistration Eligibility Decision of Thidiazuron” written by W. Evans, A. Clem, J. 

Hetrick and E. Odenkirchen. 

The purpose of this section is to summarize the key features and findings of the risk 

assessment in order to help the reader better understand the risk management decisions reached 

by the Agency. While the risk assessments and related addenda are not included in the 

document, they are available in the public docket (docket number OPP-2004-0382) and may also 

be accessed on the Agency’s website at http://www.epa.gov/pesticides/reregistration/status.htm. 

4 
A. Human Health Risk Assessment 

EPA released its preliminary risk assessments for thidiazuron for public comment on 

May 11, 2005 (Phase 3 of the public participation process). In response to comments received, 

the risk assessments were updated and refined. 

1. Toxicity of Thidiazuron 

Further details on the toxicity of thidiazuron can be found in the revised human health 

risk assessment, dated August 31, 2005, as listed in the technical support documents cited in 

Appendix C. 

a. Toxicity Profile 

The available toxicity data indicate the acute oral, dermal, inhalation, and primary eye 

and dermal irritation toxicity of thidiazuron to be in toxicity categories III and IV. Thidiazuron 

is not a dermal sensitizer or a skin irritant. The acute toxicity of thidiazuron is listed in Table 1. 

Both subchronic and chronic toxicity studies in rats show that thidiazuron causes 

decreased body weight gains and food consumption. In addition, chronic toxicity studies 

showed bilateral vesicle atrophy in rats, and dilated tubules of epididymis in mice. In the 

subchronic toxicity study, small seminal vesicles and prostate were also reported. The data from 

the developmental toxicity studies in rats and rabbits and of the 2-generation reproduction study 

indicated no increase in susceptibility of fetuses and pups to the in utero and/or postnatal 

exposure to thidiazuron. 

No neurotoxicity was reported in any of the studies. Carcinogenicity studies in both rats 

and mice produced no treatment-related increase in tumor incidence. The standard battery of 

genotoxicity tests was negative. Therefore, thidiazuron has been classified as “not likely to be 

carcinogenic to humans.” 

5 
Table 1. Acute Toxicity Data for Thidiazuron 

Guideline No./ Study Type MRID 

Number 

Results Toxicity 

Category 

(870.1100) Acute Oral Toxicity- Rat 46121501 LD50 > 2 g/kg III 

(870.1200) Acute Dermal Toxicity- Rat 46121502 LD50 > 5 g/kg 2000mg/kg IV 

(870.1300) Acute Inhalation Toxicity- Rat 46121503 LC50 > 3.48 mg/L IV 

(870.2400) Acute Eye Irritation- Rabbit 42099601 Irritation clearing in 48 hours IV 

(870.2500) Acute Dermal Irritation- Rabbit 42099602 No dermal effects IV 

(870.2600) Skin Sensitization- Guinea Pig 46121504 Not a skin sensitizer N/A 

b. FQPA Safety Factor 

The Federal Food Drug and Cosmetic Act (FFDCA) as amended by the Food Quality 

Protection Act (FQPA) directs the Agency to use an additional tenfold (10X) safety factor to 

take into account potential pre- and post-natal toxicity and completeness of the data with respect 

to exposure and toxicity to infants and children. FFDCA authorizes the Agency to modify the 

tenfold safety factor only if reliable data demonstrate that the resulting level of exposure would 

be safe for infants and children. 

FQPA Special Safety Factor 

After evaluating hazard and exposure data for thidiazuron, EPA reduced the default 10X 

FQPA special safety factor to 1X. The toxicity database for thidiazuron includes acceptable 

developmental and reproductive toxicity studies, and there is no evidence in the developmental 

toxicity study of susceptibility following in utero exposure. Also, the Agency has a low level of 

concern and no residual uncertainties for the effects seen in the developmental toxicity studies 

after establishing toxicity endpoints and traditional uncertainty factors to be used in the risk 

assessment. Therefore, the 10X FQPA special safety factor was reduced to 1X. 

c. Endocrine Effects 

When the appropriate screening and/or testing protocols being considered under the 

Agency’s EDSP have been developed, thidiazuron may be subject to additional screening and/or 

testing to better characterize effects related to possible endocrine disruption. 

d. Toxicological Endpoints for Risk Assessment 

6 
The toxicological doses and endpoints used in the human health risk assessment for 

thidiazuron are summarized below in Table 2. 

Table 2. Toxicity Endpoints for Human Health Risk Assessment for Thidiazuron 

Exposure 

Scenario 

Dose used in 

Risk Assessment 

(mg/kg/day); 

Uncertainty 

Factors 

FQPA Safety Factor; 

Level of Concern for 

Risk Assessment 

Study and Toxicological Effects 

(MRID) 

Acute 

Dietary 

NOT APPLICABLE. A dose and endpoint were not identified for this population group 

because there were no effects observed in the available toxicology studies which could be 

attributable to a single exposure (dose). 

Chronic Dietary 

(All populations) 

NOAEL= 3.93 

mg/kg/day 

UF =100 

Chronic RfD = 

0.0393 

mg/kg/day 

FQPA SF = 1X 

cPAD = 

chronic RfD

 FQPA SF 

= 0.0393 mg/kg/day 

Dog chronic toxicity study 

LOAEL =11.1 mg/kg/day based on 

increased incidence of anemia, 

changes in hematological parameters 

and marked hemosiderosis in liver and 

spleen. 

(MRID No. 00159344) 

Dermal, Short, 

Intermediate 

and Long-Term 

Quantitation of dermal exposure to thidiazuron is not necessary because dermal absorption 

in rats was low (MRID 46261502) and no dermal or systemic toxicity is expected, based on 

studies with both rats and rabbits. 

Inhalation, 

Short-Terma 

(1-30 days) 

NOAEL= 25 

mg/kg/day 

UF: 100 

 0.25 mg/kg/day 

(target MOE of 100) 

 Developmental Toxicity - Rabbit 

LOAEL = 125 mg/kg/day based on 

decreased body weight gains 

(decreased. 70% during GD 6-29) and 

food consumption (decreased 19 

during GD 6-8; 44% during GD 14­

18). 

(MRID No. 46121507) 

Cancer Thidiazuron is classified as “not likely to be carcinogenic to humans". a Since an oral NOAEL was selected, an inhalation absorption factor of 100% (default value) was used in route-toroute extrapolation to correct for differences in exposure routes. 

e. Cancer Classification 

Based on the weight of evidence and lack of evidence of carcinogenicity in both rats and 

mice (no treatment-related increase in tumor incidences), thidiazuron is classified as “not likely to 

be carcinogenic to humans". 

7 
2. Dietary Exposure and Risk from Food and Water 

a. Exposure Assumptions and Data 

The tier 1 unrefined chronic dietary exposure assumptions and risk analysis for 

thidiazuron was conducted using the Dietary Exposure Evaluation Model (DEEM-FCIDJ, 

Version 2.02) and the Lifeline J Model Version 2.0, both of which use food consumption data 

from the United States Department of Agriculture=s (USDA=s) Continuing Surveys of Food 

Intakes by Individuals (CSFII) from 1994-1996 and 1998. The assumptions of these dietary 

exposure assessments were tolerance level residues and 100% crop treated, with the exception of 

meat, meat byproducts, and fat tolerances. Existing meat, meat byproduct, and fat tolerance 

levels for ruminant livestock were not used in the aggregate assessment because the magnitude 

of the residue study suggests higher residue values than the current tolerance level. Therefore, 

the Agency extrapolated from the existing magnitude of residue study to obtain reasonable high 

end estimates of total thidiazuron residues in livestock commodities. 

In order to account for possible degradates of concern for the drinking water pathway, the 

Agency modeled four different scenarios using FIRST, Version 1.0 (surface water) and SCIGROW (groundwater), Version 2.3. Estimated Environmental Concentrations (EECs) from 

modeling showed negligible differences regardless of application timing (all at once or split in 

two) based on lack of thidiazuron degradation in soil. The estimated annual average (chronic) 

surface water concentration for the parent and both photoproducts, photo-thidiazuron and 1­

cyano-3-phenylurea, was 1.0 ppb. 

Estimated ground water concentrations are based on the Screening Concentration in 

Ground Water (SCI-GROW) (Ver. 2.3; Nov. 4, 2003) model, which is a Tier 1 assessment that 

provides a high-end estimate. The SCI-GROW model generates a single EDWC value of 

pesticide concentration in ground water used for drinking water and provides a ground water 

screening concentration for use in determining potential risk to human health from drinking 

water contaminated with a pesticide. Further, this EDWC is used in assessments of both acute 

and chronic dietary risk. It is not unusual for the ground water EDWC to be significantly lower 

than that for the surface water. The value for the chronic groundwater concentration was 

estimated to be 0.066 ppb. The most conservative estimate was used to assess chronic risk and 

included thidiazuron and both photoproducts, photo-thidiazuron and 1-cyano-3-phenylurea. The 

water concentration estimate used was 1.0 ppb. 

The dietary exposure analyses in this assessment for thidiazuron result in dietary risk 

estimates for food and water that are below the Agency’s level of concern for chronic dietary 

exposure. For the chronic analyses, the highest exposure and risk estimates were for children 1 

to 2 years old. Using DEEM-FCIDTM, the chronic exposure for children 1 to 2 years old was 

0.002867 mg/kg/day, which utilizes 7.3% of the chronic Population-Adjusted Dose (cPAD) for 

thidiazuron. Using the Lifeline Model, the chronic exposure for children 1 to 2 years old was 

0.00254 mg/kg/day, which also utilizes 6.5% of the cPAD for thidiazuron. The results of the 

8 
chronic dietary analysis for food and water are below the Agency’s level of concern and are 

summarized below in Table 3. 

Table 3. Result of Chronic Dietary Exposure and Risk Estimates for Thidiazuron- Food and Water 

Population 

Subgroup 

PAD, 

mg/kg/day 

DEEM-FCID Lifeline Water 

Concentration 

Estimates 

(ppb) 

Exposure, 

mg/kg/day 

% PAD Exposure, 

mg/kg/day 

%PAD 

Chronic Dietary Estimates 

U.S. Population 0.0393 0.000899 2.3 0.000832 2.1 1.0 

Children 1-2 yrs 0.0393 0.002867 7.3 0.00254 6.5 1.0 

b. Population Adjusted Dose (PAD) 

A population adjusted dose, or PAD, is the reference dose (RfD) adjusted for the FQPA 

safety factor. A risk estimate that is less than 100% of the chronic PAD, the dose at which an 

individual could be exposed over the course of a lifetime and no adverse health effects would be 

expected, does not exceed EPA=s level of concern. 

3. Residential and Other Non-Occupational Exposure 

Thidiazuron is not registered for residential (home/garden) use, nor is it used in or around 

public buildings, schools or recreational areas where children might be exposed. Thus, there was 

no residential assessment developed for thidiazuron. 

4. Aggregate Risk 

Since there are no residential uses registered, the aggregate exposure assessment for 

thidiazuron considered exposures from food and drinking water only. A Tier 1 chronic dietary 

risk assessment was conducted, which resulted in risk estimates for food and water that are 

below the Agency’s level of concern for all population subgroups (<8% of the cPAD). 

5. Occupational Risk 

Workers can be exposed to a pesticide through mixing, loading, and/or applying a 

pesticide, or re-entering treated sites. Occupational risk is measured by a Margin of Exposure 

(MOE) which determines how close the occupational exposure comes to a No Observed Adverse 

Effect Level (NOAEL). In the case of thidiazuron, MOEs greater than 100 do not exceed the 

Agency=s level of concern. This MOE level of concern is derived from the standard safety 

factors of 10X for intraspecies variability and 10X for interspecies variability. 

Occupational risk is assessed for exposure at the time of application (termed Ahandler@

exposure) and for exposure following application, or post-application exposure. Application 

9 
parameters are generally defined by the physical nature of the formulation (e.g., formula and 

packaging), by the equipment required to deliver the chemical to the use site, and by the 

application rate required to achieve an efficacious dose. 

For more information on the assumptions and calculations of potential risk of thidiazuron 

to workers, see the Section 9.0 of, “Thidiazuron: Revised HED Chapter of the Reregistration 

Eligibility Decision Document (RED)” dated August 31, 2005. 

a. Occupational Toxicity 

The toxicity endpoint used in the occupational risk assessment for thidiazuron was from 

an oral developmental toxicity study in rabbits (MRID 46121507). The dose used in the risk 

assessment was a NOAEL of 25 mg/kg/day for maternal toxicity based on abortions and 

decreased body weight gain and food consumption at the LOAEL of 125 mg/kg/day. Inhalation 

absorption was assumed to be equivalent to oral absorption. 

b. Occupational Handler Exposure 

Occupational handler risks from inhalation were assessed for both short- and 

intermediate-term durations of exposure. Occupational handler risk from dermal exposure was 

not assessed because dermal absorption is low, and no dermal or systemic toxicity is expected 

from the dermal route. Chronic occupational risks were not assessed because exposure for more 

than 6 months is unlikely, since the cultivation and harvesting of cotton is a predominately 

mechanized process. The assessment of intermediate-term risks provides an upper-bound 

assessment of the potential risks. 

Occupational handler assessments are conducted using increasing levels of personal 

protective measures. The Agency typically evaluates all exposures with minimal protection and 

then considers additional protective measures using a tiered approach (going from minimal to 

maximum levels of protection) until risks fall below EPA’s level of concern. The lowest tier is 

represented by the baseline clothing scenario (i.e., single layer clothing, socks, shoes, and no 

respirator), followed by increasing levels of risk mitigation such as personal protective 

equipment (PPE) and engineering controls (EC) if the MOEs indicate a potential risk concern at 

the baseline scenario. In the case of thidiazuron, MOEs for every occupational exposure 

scenario are above 100 at baseline PPE (long-sleeved shirt, long pants, socks, shoes, and no 

respirator) and therefore do not exceed the Agency’s level of concern. The assessment for 

thidiazuron as an active ingredient does not indicate a need for additional PPE, but the need for 

end-use product PPE will be assessed on a product-by-product basis. 

c. Occupational Handler Risk Summary 

10 
Based on the use patterns, 5 major occupational handler exposure scenarios were 

identified as follows: 

Mixing/Loading: 

(1a) Liquids for Aerial; 

(1b) Liquids for Groundboom/Commercial Applications; 

(1c) Liquids for Groundboom/Grower Applications; 

(2a) Wettable Powders for Aerial; 

(2b) Wettable Powders for Groundboom/Commercial Applications; 

(2c) Wettable Powders for Groundboom/Grower Applications; 

Applicator: 

(3) Aerial/Liquid Application; 

(4a) Groundboom Application/Commercial; 

(4b) Groundboom Application/Grower; and 

Flaggers: 

(5) Flagging for Liquid Sprays. 

Summary of Risk Estimates for Handlers 

Short- and intermediate-term inhalation MOEs for occupational handler scenarios are 

greater than 100 at the baseline level of protection (i.e., long-sleeved shirt, long pants, shoes plus 

socks, and no respirator). MOEs range from 150 for mixer/loaders (aerial) to >1 million for 

applying with groundboom. Therefore, short- and intermediate-term occupational risk is below 

EPA’s level of concern. 

For more information, see the Occupational Exposure/Risk Pathway (Section 9.0) in the 

Thidiazuron: Revised HED Chapter of the Reregistration Eligibility Decision Document (RED) 

dated August 31, 2005. 

d. Occupational Post-application Risk 

EPA did not quantify occupational post-application risks to agricultural workers 

following application to cotton, because there were no dermal toxicological endpoints of concern 

identified, and because post-application inhalation exposure is expected to be negligible once 

sprays have dried. 

6. Cumulative Assessment 

Risks summarized in this document are those that result only from the use of thidiazuron. 

11 
The Food Quality Protection Act (FQPA) requires that the Agency consider available 

information concerning the cumulative effects of a particular pesticide’s residues and other 

substances that have a common mechanism of toxicity. The reason for consideration of other 

substances is due to the possibility that low-level exposures to multiple chemical substances that 

cause a common toxic effect by a common toxic mechanism could lead to the same adverse 

health effect as would a higher level of exposure to any of the substances individually. 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 for 

thidiazuron and any other substances. Therefore, for the purposes of this action, EPA has 

assumed that thidiazuron does not share a common mechanism of toxicity with other 

compounds. 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/. 

7. Human Incident Data 

In evaluating incidents to humans, the Agency reviewed reports from the National Poison 

Control Centers (PCC), the Agency=s Office of Pesticide Program=s Incident Data System (IDS), 

and the California Pesticide Illness Surveillance Program. The following databases have been 

consulted for the poisoning incident data on the active ingredient thidiazuron. 

Relatively few incidents of illness have been reported due to thidiazuron. Since 1992, 

OPP IDS has only reported 5 incidents as a result of thidiazuron exposure, which all show 

similar symptoms such as skin rash, nausea, and weakness. However, no medical treatment was 

required. 

The PCC database reported no incidents from 1993-1998; from 1999-2001, there was one 

report of a child exposed. However, there were no symptoms reported and the child was not 

seen at a health care facility. NIOSH SENSOR data from 1998-2002 reported a single 

thidiazuron exposure incident due to drift from an aerial application in 1998. There were no 

poisoning reports due to thidiazuron in California from 1982- 2002, according to the California 

Department of Pesticide Regulation (CDPR). Additionally, there were no incidents of poisoning 

or other human health effects related to thidiazuron found in scientific literature. Relatively few 

incidents of illness have been reported due to thidiazuron; as a result, no recommendations based 

on incident occurrence are warranted. 

12 
B. Environmental Risk Assessment 

A summary of the Agency=s environmental risk assessment for thidiazuron is presented 

below. Thidiazuron’s use as a cotton defoliant resulted in potential environmental risks to nontarget plants (both terrestrial and semi-aquatic dicots) and mammals (herbivores and 

insectivores) foraging on short grass and broadleaf forage, as well as foraging on small insects, 

when maximum (high-end) EECs are assumed. More detailed information associated with the 

environmental risk from the use of thidiazuron can be found in the Environmental Fate and 

Effects Division’s Revised Risk Assessment for the Reregistration Eligibility Decision of 

Thidiazuron for Use on Cotton, dated September 15, 2005. The complete environmental risk 

assessment is not included in this RED, but may be accessed in the OPP Public Docket (docket 

number OPP-2004-0382) and on the Agency’s website at 

http://www.epa.gov/pesticides/reregistration/status.htm. 

1. Environmental Exposure 

a. Environmental Fate and Transport 

The environmental fate database is sufficient to characterize the environmental exposure 

associated with thidiazuron use. However, EPA intends to issue a data call-in (DCI) following 

the issuance of this RED to require submission of additional data for the parent compound and 

potential degradates (photodegradates) as well as spray drift data to address areas of uncertainty. 

These data are expected to confirm the conclusions of this environmental risk assessment. 

In soil, thidiazuron is persistent, as evidenced by laboratory and field half-lives of 

approximately one year. It has intermediate soil adsorption coefficients. Such persistence and 

intermediate mobility would allow some year-to-year accumulation and the potential for runoff 

from application sites to occur. Based on its solubility, vapor pressure, and other laboratory 

evidence, thidiazuron is non-volatile. In addition, based on its relatively low octanol/water 

partitioning coefficient, thidiazuron is not expected to bioconcentrate. 

When thidiazuron reaches surface water, photolysis is expected to be the major route of 

transformation; other degradative processes are essentially negligible by comparison. Aqueous 

photolysis rapidly yields two photoproducts. One of the photodegradates (photothidiazuron) is a 

structural isomer of the parent, while the other has a substantially altered chemical structure (1­

cyano-3-phenylurea). Only photothidiazuron was included in the risk assessment. Ground water 

is not impacted by these degradates because all field studies show that the parent is long-lived in 

soil (half-lives of the order of one year) with only minimal evidence of photolysis. 

b. Aquatic Organism Exposure 

For exposure to aquatic fish and invertebrates, EPA considers surface water only, since 

most aquatic organisms are not found in ground water. Surface water models are used to 

estimate exposure to freshwater aquatic animals. Available monitoring data are generally not 

13 
from studies targeted on small water bodies and primary streams, where many aquatic animals 

are found. The Agency used modeling to derive estimated environmental concentrations (EECs) 

for thidiazuron and its degradate, photothidiazuron. The modeling results used in risk 

calculations for thidiazuron are detailed in the EFED chapter.

 Unlike the drinking water assessment described in the human health risk assessment 

section of this document, the ecological water resource assessment does not include the Index 

Reservoir (IR) and Percent-Crop Area (PCA) factor refinements. The IR and PCA factors 

represent a drinking water reservoir, not the variety of aquatic habitats, such as ponds adjacent to 

treated fields, relevant to a risk assessment for aquatic animals. Therefore, the EEC values used 

to assess exposure to aquatic animals are not the same as the values used to assess human dietary 

exposure from drinking water sources. 

Thidiazuron is assumed to be introduced to surface waters via runoff and spray drift. 

The Estimated Environmental Concentrations (EECs) used to determine the risk quotients (RQs) 

were estimated by modeling for surface water in a farm pond scenario. Based on the 

intermediate range of its adsorption coefficients and the supplemental field evidence, leaching 

should not be a major route of dissipation. Resulting concentrations for the parent compound 

plus photothidiazuron are below in Table 4. 

Table 4. Estimated Environmental Concentrations (EECs) of Thidiazuron and 

Photothidiazuron in Surface Water (ppb) 

Peak 96-hour Average 21-day Average 60-day Average 90-Day Average 

11 11 9.7 8.6 8.2 

c. Terrestrial Organism Exposure 

The Agency assessed exposure to terrestrial organisms by first predicting the amount of 

thidiazuron residues found on animal food items and then determining the amount of pesticide 

consumed based on typical food consumption by various species of birds and mammals. The 

amount of residues on animal feed items is based on the Fletcher nomogram and the current 

maximum application rate for thidiazuron. Residues may be compared directly with dietary 

toxicity data or converted to an oral dose, as is the case for small mammals. Current labels allow 

a maximum single application of 0.2 lbs a.i./A (active ingredient/Acre) and up to 0.3 lbs a.i./A 

applications per season for a total seasonal maximum rate of 0.3 lbs a.i./A. Accordingly, all 

thidiazuron labels allow two applications. The sum of these is a maximum of 0.3 lbs a.i./A/yr 

(0.2 lb a.i./A for the first application and up to 0.1 lb a.i./A for the second application). 

14 
(1) Birds 

For birds, toxicant concentrations (EECs) on food items following multiple applications 

were predicted based on Agency models. 

(2) Mammals 

The exposure route emphasis for mammals is on uptake through the diet via food items. 

The residue estimates are based on a nomogram that relates food item residues to a pesticide’s 

application rate. Residues may be compared directly with dietary toxicity data or converted to 

an oral dose, as is the case for small mammals. For mammals, the residue concentration is 

converted to daily oral dose based on fractions of body weight consumed daily, as estimated 

through mammalian allometric relationships. 

d. Non-target Terrestrial Plant Exposure 

Terrestrial plants inhabiting dry and semi-aquatic areas may be exposed to pesticides from 

runoff, spray drift, or volatilization. Volatilization was not included in the assessment. Semiaquatic areas are those low-lying wet areas that may be dry at certain times of the year. The 

Agency’s runoff exposure estimate is characterized as "sheet runoff" (one treated acre to an 

adjacent acre) for dry areas, or as "channelized runoff". 

2. Environmental Effects (Toxicity) 

a. Toxicity to Aquatic Organisms 

(1) Freshwater and Estuarine/Marine Fish 

An acute freshwater fish toxicity classification for thidiazuron cannot be definitively 

established because no mortality or signs of intoxication were observed at the highest 

concentration tested 19 and 32 mg/L. Thidiazuron can be considered practically non-toxic for 

risk assessment purposes. 

A chronic toxicity study was submitted for freshwater fish early life-stage (fathead 

minnow) for parent thidiazuron. The NOAEC of the parent was 5,700 Fg/L based on 

hatchability, fry survival, and total survival (MRID 421320-02). A chronic full life cycle test 

was not submitted for freshwater fish or marine/estuarine fish. 

15 
(2) Freshwater and Estuarine/Marine Invertebrates 

Acute freshwater invertebrate data for the parent thidiazuron resulted in an LC50 of 5,700 

Fg/L and a NOAEC of 1200 ug/L. Therefore, this LC50 value classifies the parent compound as 

moderately toxic to freshwater invertebrates. Acute freshwater invertebrate studies on the major 

degradates were also submitted and showed LC50 > 12,000 ug/L. 

Acute marine invertebrate studies show that the mysid shrimp and the eastern oyster 

embryo/larvae LC50s are 3,240 and 5,384 Fg/L, and NOAECs are 1400 and 1.06 ug/L, 

respectively. This classifies thidiazuron as moderately toxic to marine acute invertebrates. No 

studies were submitted for any of the metabolites. In addition, no invertebrate full-life-cycle 

toxicity studies were submitted to the Agency. 

A chronic daphnid toxicity study showed a LOAEC of <100 Fg/L based on length. Even 

though a definitive NOAEC could not be obtained, the 21-day EC10 was found to be 720 Fg/L. 

No chronic data were submitted for marine invertebrates. 

b. Toxicity to Aquatic Plants 

Aquatic plant testing was conducted on the parent compound thidiazuron. The EC50 was 

determined to be >24,000 Fg/L for the vascular plant (Lemna gibba) based on frond count as the 

most sensitive parameter. The NOAEC and EC05 were determined to be 8,600 and 570 Fg/L, 

respectively. Non-vascular plant data were submitted for the green alga, blue-green algae, and 

the marine diatom. The most sensitive of these non-vascular plants was the marine diatom with 

an EC50 of 850 Fg/L, a NOAEC of 110 Fg/L, and EC05 of 56 Fg/L. No data are currently 

available for the freshwater diatom. 

Additional non-vascular plant data (green alga) was submitted for three degradates and 

metabolite. All these studies were considered as Tier 1 studies and classified as supplemental 

because they were conducted for 3 days instead of 5 days as required by the Agency. Acute 

toxicity values for aquatic plants are shown in Table 5. 

Table 5. Acute Toxicity of Thidiazuron to Aquatic Plants 

Species %a.i. EC50, 

(Fg/L) 

NOAEC/EC05 

(Fg/L) a.i. 

MRID, Author, Year 

Vascular Plant 

Duckweed 

(Lemna gibba) 99.5 >24,000 8600 / 570 46203506 Desjardins, D. et.al., 

2003. 

16 
Table 5. Acute Toxicity of Thidiazuron to Aquatic Plants (continued) 

Species %a.i. EC50, 

(Fg/L) 

NOAEC/EC05 

(Fg/L) a.i. 

MRID, Author, Year 

Nonvascular Plants 

Green algae 

(Selenastrum capricornutum) 99.3 >150 150 45638221, Jenkins, 1998.a 

Blue-green algae (Anabaena 

flos-aquae) 99.5 6000 2800 / 1800 46203504, Desjardins, D. et.al., 

2003.a 

Marine diatom (Skeletonema 

costatum) 99.5 860 110/56 46203505, Desjardins, D. et.al., 

2003. 

Thidiazuron Photometabolite (AE F132347) 

Nonvascular Plants 

Greeen Algae 

(Scenedesmus subspicatus) 97.4 980 220 / 310 46203510, Desjardins, D. et.al., 

2003.a 

Thidiazuron Urea Metabolite (AE F132345) 

Nonvascular Plants 

Greeen Algae 

(Scenedesmus subspicatus) 

91 w/w 

ai 3400 1300 / 1200 46203517, Desjardins, D. et.al., 

2003. a 

Thidiazuron Photodegradate (AE C421200) 

Nonvascular Plants 

Green Algae 

(Scenedesmus subspicatus) 98.4 70000 49,000 / 53,000 46203513, Desjardins, D. et.al., 

2003. a 

a

 Since the study duration was for 3 days instead of 5, the study can only be classified as a Tier 1 study. 

c. Toxicity to Terrestrial Organisms 

(1) Birds 

Thidiazuron is classified as practically non-toxic to birds and no sub-lethal effects or 

other treatment related effects were observed in any of the studies. No avian chronic testing data 

was submitted to the Agency for thidiazuron. 

(2) Mammals 

Thidiazuron is classified as a category III compound (moderately toxic) for mammals 

based on an acute oral LD50 value of 2000 mg/kg-body weight. However, minimal adverse 

effects (anemia, blood related effects and decreased body weight) were demonstrated in the 

17 
mammalian subchronic toxicity and pre-natal developmental toxcicity studies. See Table 6 for 

endpoints. 

Table 6. Summary of Subchronic and Chronic Toxicity Endpoints for Mammals 

Toxicity 

Study Test Species % a.i. NOAEL/LOAEL (mg/kg-bwt) MRID 

Subchronic 

52-week Oral 

Toxicity 

Dog 98.8 3.93/11.1 00159344 

Chronic (reproductive) 

Prenatal 

Developmental 

Toxicity 

Rat 99.4 100/300 00077127 

Prenatal 

Developmental 

Toxicity 

Rabbit 99.5 25/125 46121507 

2-generation 

Reproductive Rat 99.5 

Parental = 35.4/108.5 

Repro = 108.5/ND* 

Offspring = 35.4/108.5 

46209601 

*ND= Not Determined 

The results from a 2-generation rat study were used to assess chronic risks to mammals. 

The NOAEL for both parental and offspring toxicity in this study was 400 ppm diet and the 

LOAEL for these endpoints was 1200 ppm diet. Table 7 discusses the data that support the 

chronic toxicity data used in assessing the risks to mammals. 

Table 7: Mammalian Developmental and Chronic Toxicity to Thidiazuron 

Test Type % a.i. NOAEC 

(mg ai/kg-diet) 

LOAEC 

(mg ai/kg-diet) Effects MRID #, Author, Year 

EPA PC Code: 120301 - Thidiazuron Technical SN 49537 

2-generation 

reproductive 

(rat) 

400 ppm 

(35.4/39.8 mg/kg/day 

[M/F]) 

1200 ppm 

(108.5/121.1 

mg/kg/day [M/F]) 

Delayed sexual 

maturity, disrupted 

estrous cycling 

46209601 

3-generation 

reproductive 

(rats) 

100 

200 ppm 

(10 mg/kg bw/da) 

600 

(30 mg/kbw/da)a 

Decreased F3 litter 

size at 200 ppm. 

429589-01, Rees, S.J., 1992. 

(Core-Supplementary) 

a

 Based on decrease epidermal sperm counts. 

d. Toxicity to Non-Target Insects 

Acute contact toxicity studies to honeybees revealed contact LD50s of greater than 100 

Fg ai /bee for thidiazuron technical and greater than 98.1 Fg ai /bee for the SC42 water miscible 

suspension concentrate 500 g/L. In addition, a 72-hour acute oral toxicity test was conducted for 

the SC42 water miscible suspension concentrate 500 g/L in accordance with OECD guidelines. 

18 
This study resulted in an oral contact LD50 greater than 197.8 Fg ai/bee. These results classify 

thidiazuron as practically non-toxic to non-target insects. Based on thidiazuron’s use pattern, 

minimal risk is expected to non-target insects. 

e. Toxicity to Terrestrial Plants 

Since thidiazuron is used as a defoliant on cotton to inhibit regrowth and removal of both 

mature and juvenile leaves in cotton, non-target terrestrial plant data are required. Several nonguideline studies evaluating thidiazuron phytotoxicity were submitted and two are summarized 

below. 

Combined tier I and II testing for seedling emergence and vegetative vigor (MRID #s 

459085-01 and 459215-01) for the SC42 formulated product have been submitted. The seedling 

emergence tests indicated negative growth responses to plant emergence for onion and oat by 

more than 25% at the maximum single application label rate of 0.2 lb a.i./A. This would indicate 

that a need exists for tier II testing for these two monocot species. All other tested species 

showed an EC25 above the maximum single application rate which mean no further data are 

required for seedling emergence for those species. 

Similar results were shown in vegetative vigor tests. Negative growth responses below 

the EC25 level were indicated for all the monocots at the maximum single application rate. This 

indicates that tier II testing will need to be performed for these monocot species. All of the dicot 

plants were tested at the tier II level with the exception of turnip and cabbage and since these 

plants are not among the most sensitive dicots tested, further testing will not be required. The 

results from these tests are shown in Table 8. 

Table 8: Terrestrial Plant Toxicity Summary for Thidiazuron SC 42 

Study Type Most sensitive 

Crop 

EC25 / NOEC 

or EC05 

(lb ai/A) 

Least sensitive 

Crop / Active 

Ingredient 

EC25 / NOEC 

or EC05 

(lb ai/A) 

Seedling 

Emergence 

Monocot Onion & oat <0.1783 / 

<0.1783 

Corn & wheat >0.1783 / 0.1783 

Dicot Turnip 0.0152 / 0.0031 Tomato >0.1783 / 

>0.1783 

Vegetative Vigor Monocot Onion, corn, & 

oat 

>0.1783 / 

<0.1783 

Wheat > 0.1783 / 0.1783 

Dicot Lettuce 0.0011 / 0.00005 Turnip & 

cabbage 

>0.1783 / 

<0.1783 

19 
3. Ecological Risk Estimation (RQs) 

The Agency’s ecological risk assessment compares toxicity endpoints from ecological 

toxicity studies to EECs based on environmental fate characteristics and pesticide use data. To 

evaluate the potential risk to non-target organisms from the use of thidiazuron products, the 

Agency calculates an RQ, which is the ratio of the EEC to the most sensitive toxicity endpoint 

values, such as the median lethal dose (LD50) or the median lethal concentration (LC50). These 

RQ values are then compared to the Agency’s levels of concern (LOCs), given in Table 9 , 

which indicate whether a pesticide, when used as directed, may have the potential to cause 

adverse effects on non-target organisms. When the RQ exceeds the LOC for a particular 

category (e.g., endangered species), the Agency presumes a potential risk of concern to that 

category. These potential risks of concern may be addressed by further refinements of the risk 

assessment or mitigation. Use, toxicity, fate, and exposure are considered when characterizing 

the risk, as well as the levels of certainty and uncertainty in the assessment. EPA further 

characterizes ecological risk based on any reported incidents to non-target terrestrial or aquatic 

organisms in the field (e.g., fish or bird kills). 

Table 9. EPA’s Levels of Concern and Associated Risk Presumptions. 

Risk Presumption LOC 

Terrestrial 

Animals 

LOC 

Aquatic 

Animals 

LOC 

Plants 

Acute Risk - there is potential for acute risk; regulatory action 

may be warranted in addition to restricted use classification. 

0.5 0.5 1 

Acute Restricted Use - there is potential for acute risk, but may 

be mitigated through restricted use classification. 

0.2 0.1 N/A 

Acute Endangered Species - endangered species may be 

adversely affected; regulatory action may be warranted. 

0.1 0.05 1 

Chronic Risk - there is potential for chronic risk; regulatory 

action may be warranted. 

1 1 N/A 

For a more detailed explanation of the ecological risks posed by the use of thidiazuron, 

refer to the “Environmental Fate and Effects Division’s Revised Risk Assessment for the 

Reregistration Eligibility Decision of Thidiazuron for Use on Cotton”, dated September 15, 

2005. 

a. Risk to Aquatic Organisms 

(1) Fish and Aquatic Invertebrates 

Acute risks to all freshwater and marine fish and invertebrates are below all levels of 

concern established by the Agency’s screening level assessment for thidiazuron. The acute risk 

quotients ranged from <0.0003 (marine fish) to 0.002 (freshwater fish and estuarine 

20 
invertebrates). 

Chronic risks to all freshwater and marine fish and invertebrates are below all levels of 

concern established by the Agency’s screening level assessment for thidiazuron. Chronic risk 

quotients ranged from 0.002 (freshwater fish) to >0.1 (freshwater invertebrates). Although there 

may be some uncertainty with respect to chronic risk to freshwater and marine invertebrates 

because a definitive NOAEC value could not be obtained, it is possible to estimate chronic risk 

based on a 21-day EC10 value which was obtained in the chronic freshwater invertebrate study. 

The 21-day EC10 value was 720 Fg/L based on the length of the test organisms. Using this 

generated EC10 value, the definitive 21-day RQ value of 0.015 is well below the chronic level of 

concern. 

b. Risk to Aquatic Plants 

An aquatic plant risk assessment for acute risk to non-target plants (non-endangered and 

endangered) was conducted with endpoints from the most sensitive aquatic plant. The acute risk 

quotient for non-target plants was determined by dividing the peak concentration of thidiazuron 

in surface water by the EC50 value for the most sensitive aquatic plant species. The acute 

endangered species risk quotient was determined by dividing the peak concentration of 

thidiazuron in surface water by the NOAEC. As a result, the acute risk quotients for the nonendangered and endangered species were well below all established levels of concern for aquatic 

plants. 

Aquatic plants do not appear to be at risk; however, semi-aquatic dicots, not monocots, 

are at potential direct and indirect risk. The Agency does not conduct chronic risk assessments 

for plants. Preliminary data indicate that there may be potential aquatic plant risks from the 

photoproducts of thidiazuron. The Agency intends to call in additional data in order to assess the 

risk. 

c. Risk to Non-target Terrestrial Organisms 

(1) Birds 

There are no exceedences for any acute, acute restricted use, endangered species, or 

chronic LOCs for birds. Acute RQs from two applications of thidiazuron (for a seasonal 

maximum of 0.3 lb a.i./A) range from less than 0.013 to 0.001. Avian chronic risks cannot be 

quantitatively evaluated at this time because chronic data were not submitted. However, 

available data showing that chronic levels of concern for mammals are exceeded and that 

thidiazuron is persistent in the field suggest that there is also potential for chronic risk to birds 

should they be of equal or greater sensitivity than mammals. 

21 
(2) Mammals 

Acute RQs are calculated for three separate weight classes of mammals (15, 35, and 1000 g), 

each presumed to consume four different kinds of food (grass, forage, insects, and seeds). Chronic 

mammalian RQs are calculated using the most sensitive NOAEC from the 2-generation rat study and 

the residue concentration expected on food items from Hoerger and Kenaga (1972) as modified by 

Fletcher et al. (1994) listed in the ecological risk assessment. There are no exceedences of any acute 

LOCs for mammals as all RQs were <0.03. 

Chronic RQs for mammals did exceed LOCs, with RQs ranging from 1.8 (15-g mammal 

feeding on short grass) to 0.01 (1000-g mammal feeding on large insects). Potential effects at 

predicted maximum and mean residues for single applications were also evaluated. No RQ 

exceeds the chronic level of concern when considering mean predicted residues (See Table 10). 

Table 10. Mammalian Chronic Risk Quotient Calculations for Spray Applications 

(NOAEL = 35.4 mg/kg-bw/da) 

Animal 

Body 

Weight 

(g) 

% Body 

Weight 

Consumed 

Scenario Predicted Maximum 

Residue Levels 

Predicted Mean 

Residue Levels 

EEC 

(mg/kg-diet) 

Chronic RQ EEC 

(mg/kg-diet) 

Chronic RQ 

15 95 Short grass 67 1.8 * 23.73 0.64 

Broadleaf forage, small 

insects 

37 1.0 * 12.33 0.33 

Large insects 4.2 0.1 1.96 0.05 

35 66 Short grass 67 1.2 * 23.73 0.44 

Broadleaf forage, small 

insects 

37 0.7 12.33 0.23 

Large insects 4.2 0.08 1.96 0.04 

1000 15 Short grass 67 0.3 23.73 0.10 

Broadleaf forage, small 

insects 

37 0.2 12.33 0.05 

Large insects 4.2 0.02 1.96 0.01 

* indicates an exceedence of Chronic Level of Concern (LOC). 

22 
d. Risk to Non-Target Insects 

Available data from a honeybee acute contact toxicity study indicated that technical 

thidiazuron and formulated product are practically nontoxic to the honeybee. The two other nontarget insect OECD studies showed no significant effects at the highest maximum single rate (0.2 

lb ai/A); therefore there is little concern for non-target insects. Thidiazuron use on cotton is 

predicted to pose minimal risk to non-target insects. 

e. Risk to Non-target Terrestrial Plants 

Thidiazuron poses potential risks to terrestrial plants based on the results of a screeninglevel assessment. The risk quotients exceed the levels of concern for non-endangered and 

endangered plants adjacent to treated sites as well as plants inhabiting semi–aquatic sites. This 

is especially true for dicots for both single and multiple applications. The RQs resulting from 

single applications at the maximum label rates range from 0.39 to 9.09 for non-endangered 

plants (Table 11) and up to as high as 52.63 for endangered plants (See Table 12). 

Tier I testing data for vegetative vigor indicated negative growth response (<25%) in one 

of the four monocots (onion) and five of the six species of dicots that were tested. Accordingly, 

Tier II studies are required for all low dose herbicides with maximum use rates of 0.5 lbs ai/A or 

less and any pesticide showing a negative response equal to or greater than 25% in Tier I tests. 

Recently submitted data combined Tier I and II testing for seedling emergence and vegetative 

vigor (MRID #s 45908501 and 45921501) for the SC42 formulated product, which have 

indicated that a need exists for Tier II testing for both onion and oat. Currently, EPA does not 

perform chronic risk assessments for terrestrial and semi-aquatic plants. 

Adverse effects in terrestrial plants from thidiazuron applied at current labeled rates are 

expected, particularly in dicots (not monocots). As a result, if non-target plants come in contact 

with thidiazuron, they may be killed or damaged enough to prevent the plant from reproducing 

or successfully competing with other plants for resources. 

Table 11. Terrestrial Plant Risk Quotients for Single Applications 

Plant Group 

(nonEndangered / 

Endangered) 

Type of 

Plant Study 

Type of Plant 

(monocot / 

dicot) 

Most Sensitive EC25 

(Non-Endangered) 

or NOAEC / EC05 

(Endangered) 

Risk Quotient 

Range (Plants 

Adjacent to 

Treated Sites) 

Risk Quotient 

Range (Plants in 

Semi-Aquatic 

Areas) 

Non-endangered Seedling 

Emergence 

Monocot <0.1783 >0.03 - >0.07 >0.17 - > 0.22 

Dicot 0.0152 0.39 - 0.79 1.97 - 2.63* 

Vegetative 

Vigor 

Monocot >0.1783 <0.01 - <0.06 <0.01 - <0.06 

Dicot 0.0011 1.82 - 9.09* 1.82 - 9.09* 

* Exceeds terrestrial plant Levels of Concern (LOC) 

4. Ecological Incidents 

23 
There are no reports or incidents of wildlife poisonings associated with thidiazuron in the 

Ecological Incident Information System (EIIS) data base. 

5. Endangered Species Concerns 

The screening level ecological risk assessment results in a determination that use of 

thidiazuron will have no direct acute effects on fresh water or marine/estuarine fish and 

invertebrates, insects, aquatic plants, terrestrial and semi-aquatic monocots, avian species, and 

mammals. However, the Agency’s level of concern for direct effects to endangered and 

threatened terrestrial and semi-aquatic plants, and for direct chronic effects to mammals is 

exceeded for the use of thidiazuron on cotton. In addition, the Agency can not quantitatively 

predict potential chronic risks to birds; however, if avian species are as sensitive, or more 

sensitive than mammals, a potential effect could be of concern for avian species. Further, 

potential indirect effects to any species dependent upon a species that experiences effects from 

use of thidiazuron, can not be precluded based on the screening level ecological risk assessment. 

a. Risk to Endangered Species 

The screening level risk assessment for listed species indicates that thidiazuron exceeds 

the endangered species LOCs for the following combinations of analyzed uses and species: (1) 

use of thidiazuron on cotton indicates that the chronic LOC of 1.0 is exceeded for 15 g mammals 

foraging on short grass and broadleaf forage and small insects. Chronic mammalian RQs range 

up to 1.8; and (2) use of thidiazuron on cotton results in an exceedence of the LOC for terrestrial 

and semi-aquatic plants. 

County-level location data for listed species (terrestrial plants and mammals) were 

compared with county-level information on crop production to identify coarse overlaps of listed 

species with the proposed labeled use areas of thidaizuron. More information on the number of 

species at potential risk can be found in the Environmental Fate and Effects Division Revised 

Risk Assessment for the Reregistration Eligibility Decision of Thidiazuron for Use on Cotton, 

dated September 15, 2005. 

In addition to these potential direct effects, there may be potential for indirect effects to 

taxa of listed that are dependent upon a taxa that may experience effects from the use of this 

pesticide. Potential risks to endangered species identified in the Environmental Fate and 

Ecological Risk Assessment and reflected in this RED for thidiazuron are based solely on EPA's 

screening level ecological risk assessment and do not constitute "may effect" findings under the 

Endangered Species Act. 

Table 12: Acute Endangered Terrestrial Plant Risk Quotient Calculations For Single 

Spray Applications of thidiazuron 

24 
Scenario Toxicity Threshold, 

NOEC or EC05 

(lb ai/ac) 

Plants Adjacent to Treated Sites Plants in Semi-aquatic Areas 

Total Drift 

(lb ai/ac) 

Total Loading 

(Sheet runoff + 

Drift) 

(lb ai/ac) 

RQa Total 

Drift 

(lb ai/ac) 

Total Loading 

(Channel runoff 

+ Drift) 

(lb ai/ac) 

RQa 

Cotton - Ground Applications (0.2 lbs ai/ac/app) 

Seed 

Emergence 

Monocot 0.1783 N/A 0.006 0.03 N/A 0.04 0.22 

Dicot 0.0111 N/A 0.006 0.54 N/A 0.04 3.60* 

Vegetative 

Vigor 

Monocot 0.1783 0.002 N/A 0.01 0.002 N/A 0.01 

Dicot 0.00019 0.002 N/A 10.53* 0.002 N/A 10.53* 

Cotton - Aerial Applications (0.2 lbs ai/ac/app) 

Seed 

Emergence 

Monocot 0.1783 N/A 0.012 0.07 N/A 0.03 0.17 

Dicot 0.0111 N/A 0.012 1.08* N/A 0.03 2.70* 

Vegetative 

Vigor 

Monocot 0.1783 0.01 N/A 0.06 0.01 N/A 0.06 

Dicot 0.00019 0.01 N/A 52.63* 0.01 N/A 52.63* 

a Indicates acute risk to endangered plants. 

6. Risk Characterization 

Thidiazuron has a limited use pattern. It is used exclusively as a cotton defoliant to 

facilitate the uniform removal of both mature and juvenile leaves prior to machine harvesting. 

Thidiazuron is only applied during the cotton harvesting period, which is typically in late August 

and early September. All labels indicate that citrus trees are particularly sensitive to thidiazuron. 

Product labels indicate that the areas potentially at direct and/or indirect risk from the application 

of thidiazuron are the cotton agronomic environments. In the case of mixed products, the risk 

assessment was conducted to focus on the fraction of the application rate contributed by 

thidiazuron (only) instead of the sums of both active ingredients. 

The main ecological risk concerns, based on toxicity testing with typical end-use 

products containing thidiazuron as the only active ingredient and the small amount of data on 

three transformation products, are the following: (1) Non-target terrestrial and semi-aquatic 

dicots (not monocots) are at potential direct risks, whereas aquatic plants do not appear to be at 

risk. If non-target plants come into contact with thidiazuron, these plants may be killed or 

damaged enough to prevent the plant from reproducing or successfully competing with other 

plants for resources. (2) Mammals are at potential chronic risk, but not acute risk. (3) Potential 

acute risks to birds are below all levels of concern. However, potential chronic risk to birds 

cannot be determined, due to the absence of chronic data. 

25 
The risk assessment for terrestrial plants was based on RQs calculated from toxicity 

studies using a typically formulated end-use product (TEP) Thidiazuron SC42. However, it 

appears that no surfactants or other adjuvants were added to the product during the studies and 

all labels clearly state the addition of adjuvants has been shown to improve the performance. 

Therefore, the risk to terrestrial non-target plants may be greater than thidiazuron RQs indicate. 

Acute risk quotients for mammals did not exceed levels of concern (LOCs). However, 

chronic risk quotients for mammals did exceed LOCs for 15g mammals foraging in short grass, 

broadleaf forage, and on small and large insects when maximum (high-end) EECs are assumed. 

Potential effects at predicted maximum and mean residues for single applications were also 

evaluated. No RQ exceeds the chronic level of concern when considering mean predicted 

residues. 

IV. Risk Management, Reregistration, and Tolerance Reassessment Decision 

A. Determination of Reregistration Eligibility 

Section 4(g)(2)(A) of FIFRA calls for the Agency to determine, after submission of 

relevant data concerning an active ingredient, whether or not products containing the active 

ingredient are eligible for reregistration. The Agency has previously identified and required the 

submission of the generic (i.e., active ingredient-specific) data to support reregistration of 

products containing thidiazuron as an active ingredient. The Agency has completed its review of 

these generic data, and has determined that the data are sufficient to support reregistration of all 

uses of thidiazuron. 

The Agency has completed its assessment of the dietary, occupational, and ecological risk 

associated with the use of pesticide products containing the active ingredient thidiazuron. Based 

on a review of these data and on public comments on the Agency=s assessments for the active 

ingredient thidiazuron, the Agency has sufficient information on the human health and 

ecological effects of thidiazuron to make decisions as part of the tolerance reassessment process 

under FFDCA and reregistration process under FIFRA, as amended by FQPA. The Agency has 

determined that thidiazuron containing products are eligible for reregistration provided that: 

(i) the risk mitigation measures outlined in this document are adopted; and (ii) label amendments 

are made to reflect these measures. 

B. Public Comments and Responses 

Through the Agency=s public participation process, EPA worked extensively with 

stakeholders and the public to reach the regulatory decisions for thidiazuron. During the public 

comment period on the risk assessments, which closed on July 11, 2005, the Agency received 

comments from four commentors, Bayer CropScience, Siemer and Associates, and two private 

citizens. The comments pertained to the importance of particular uses and urged the Agency to 

consider how it regulated these commodities. These comments in their entirety are available in 

26 
the public docket (OPP-2004-0382) at http://www.epa.gov/edockets. An individual response to 

these comments is being prepared by EPA and will be made available in the public docket (OPP2004-0382). 

The RED and technical supporting documents for thidiazuron are available to the public 

through EPA=s electronic public docket and comment system, EPA Dockets, under docket 

identification (ID) number OPP-2004-0382. The public may access EPA Dockets at 

http://www.epa.gov/edockets. In addition, the thidiazuron RED may be downloaded or viewed 

through the Agency=s website at http://www.epa.gov/pesticides/reregistration/status.htm. 

C. Regulatory Position 

1. Food Quality Protection Act Findings 

a. ARisk Cup@ Determination 

As part of the FQPA tolerance reassessment process, EPA assessed the risks associated 

with this pesticide. EPA has determined that risk from dietary (food sources only) exposure to 

thidiazuron is within its own Arisk cup.@ An aggregate assessment was conducted for exposures 

through food and drinking water. The Agency has determined that the human health risks from 

these combined exposures are within acceptable levels. In other words, EPA has concluded that 

the tolerances for thidiazuron meet FQPA safety standards. 

b. Determination of Safety to the U.S. Population Including 

Infants and Children 

The Agency has determined that the established tolerances for thidiazuron, with 

amendments and changes as specified in this document, meet the safety standards under the 

FQPA amendments to section 408(b)(2)(D) of the FFDCA, and that there is a reasonable 

certainty no harm will result to the general population, infants and children or any subgroup from 

the use of thidiazuron. In reaching this conclusion, the Agency has considered all available 

information on the toxicity, use practices and exposure scenarios, and the environmental 

behavior of thidiazuron. As discussed in Chapter 3, the total acute dietary (food alone) risk was 

not assessed, since no appropriate acute endpoint was identified. Also, the chronic dietary risk 

estimates for food (only) as well as food and water are both below the Agency’s level of 

concern. 

In determining whether or not infants and children are particularly susceptible to toxic 

effects from exposure to residues of thidiazuron, the Agency considered the completeness of the 

hazard database for developmental and reproductive effects, the nature of the effects observed, 

and the possibility of increased dietary exposure due to the specific consumption patterns of 

infants and children. The FQPA Safety Factor has been reduced to 1X for thidiazuron because: 

(1) there are no concerns and no indication of quantitative or qualitative increased susceptibility 

27 
of rats or rabbits to in utero or postnatal exposure; and 2) the dietary (food and drinking water) 

exposure assessments will not underestimate the potential exposures to infants and children. 

c. Endocrine Disruptor Effects 

EPA is required under the FFDCA, as amended by FQPA, to develop a screening program 

to determine whether certain substances (including all pesticide active and other ingredients) 

Amay have an effect in humans that is similar to an effect produced by a naturally occurring 

estrogen, or other endocrine effects as the Administrator may designate.@ Following 

recommendations of its Endocrine Disruptor Screening and Testing Advisory Committee 

(EDSTAC), EPA determined that there was a scientific basis for including, as part of the 

program, the androgen and thyroid hormone systems, in addition to the estrogen hormone 

system. EPA also adopted EDSTAC=s recommendation that EPA include evaluations of 

potential effects in wildlife. For pesticides, EPA will use FIFRA and, to the extent that effects in 

wildlife may help determine whether a substance may have an effect in humans, FFDCA 

authority to require the wildlife evaluations. As the science develops and resources allow, 

screening of additional hormone systems may be added to the Endocrine Disruptor Screening 

Program (EDSP). The available data on thidiazuron indicated that there was no toxicologically 

significant evidence of endocrine disruption effects. 

d. Cumulative Risks 

Risks summarized in this document are those that result only from the use of thidiazuron. 

The Food Quality Protection Act (FQPA) requires that the Agency consider “available 

information” concerning the cumulative effects of a particular pesticide’s residues and “other 

substances that have a common mechanism of toxicity.” The reason for consideration of other 

substances is due to the possibility that low-level exposures to multiple chemical substances that 

cause a common toxic effect by a common toxic mechanism could lead to the same adverse 

health effect as would a higher level of exposure to any of the substances individually. Unlike 

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

mechanism of toxicity, EPA has not assumed that thidiazuron shares a common mechanism of 

toxicity with other compounds. 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 effects from substances found to have a common 

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

28 
2. Tolerance Reassessment Summary 

a. Tolerances Currently Listed Under 40 CFR '180.403 

The existing tolerances for residues of thidiazuron [1-phenyl-3-(1,2,3-thidiazol-5-yl)urea] 

are established under 40 CFR '180.403. Although additional data are required to confirm the 

existing tolerances in/on the following commodities, the Agency has no dietary or drinking water 

risk concerns associated with these tolerances and considers them reassessed (see Table 13). 

Table 13. Tolerance Reassessment Summary for Thidiazuron. 

Commodity Current 

Tolerance 

(ppm) 

Tolerance 

Reassessment 

(ppm) 

Comment 

Tolerances Listed Under 40 CFR '180.403(a) 

Cattle, fat 0.2 0.4 Proposed tolerances are considered reassessed 

and will be confirmed upon the submission of 

Cattle, meat 0.2 0.4 additional data (see Regulatory Rationale).

Cattle, meat 

byproducts 

0.2 0.4 

Cotton, undelinted 

seed 

0.4 0.3 Available residue data from crop field trials 

provide sufficient information to reduce the 

tolerance. 

Cotton, hulls 0.8 Revoke A processing study was performed for 

cottonseed meal, oil, and hulls. Cottonseed hull 

residues are not expected to exceed the current 

recommended RAC tolerance of 0.3 ppm for 

cottonseed. Therefore, it is recommended that 

the current 0.8 ppm tolerance for cottonseed 

hulls be revoked. 

Egg 0.1 Revoke Cottonseed meal is a common feeding source 

for poultry. Thidiazuron residues in a 

cottonseed meal processing study demonstrated 

that tolerances are no longer required on eggs as 

there is no reasonable expectation of finite 

residues. 

Goat, fat 0.2 0.4 Proposed tolerances are considered reassessed 

and will be confirmed upon the submission of 

additional data (see Regulatory Rationale).

Goat, meat 0.2 0.4 

Goat, meat 

byproducts 

0.2 0.4 

Hog, fat 0.2 0.4 

Hog, meat 0.2 0.4 

Hog, meat 

byproducts 

0.2 0.4 

Horse, fat 0.2 0.4 

Horse, meat 0.2 0.4 

29 
Commodity Current 

Tolerance 

(ppm) 

Tolerance 

Reassessment 

(ppm) 

Comment 

Horse, meat 

byproducts 

0.2 0.4 

Milk 0.05 0.05 

Poultry, fat 0.2 Revoke Cottonseed meal is a common feeding source 

for poultry. Thidiazuron residues in a 

cottonseed meal processing study demonstrated 

that tolerances are no longer required on poultry 

as there is no reasonable expectation of finite 

residues. 

Poultry, meat 0.2 Revoke 

Poultry, meat 

byproducts 

0.2 Revoke 

Sheep, fat 0.2 0.4 Proposed tolerances are considered reassessed 

and will be confirmed upon the submission of 

additional data (see Regulatory Rationale). Sheep, meat 0.2 0.4 

Sheep, meat 

byproducts 

0.2 0.4 

Tolerances To Be Proposed Under 40 CFR '180.403(a)(2) 

Cotton, gin 

byproduct 

Not established 24 Available residue data from crop field suggest 

that a tolerance of 24 ppm be established for 

cotton gin byproducts. 

b. Codex Harmonization 

No CODEX maximum residue levels (MRLs) have been established or proposed for 

thidiazuron. Therefore, issues of compatibility between CODEX MRLs and U.S. tolerances do 

not exist. 

D. Regulatory Rationale 

The Agency has determined that thidiazuron is eligible for reregistration, in compliance 

with FIFRA, provided that: the risk mitigation measures outlined in this document are adopted 

and label amendments are made to reflect these measures. Once an Endangered Species 

assessment is completed, further changes to these registrations may be necessary as explained in 

section 3 below. 

1. Labeling Requirements 

 The environmental risks for thidiazuron were based on a screening-level assessment for 

both terrestrial and aquatic environments. The assessment was performed for geographic areas 

where the highest use rates and expected exposures are likely to occur. Results show some 

concerns for acute risks to aquatic plants, terrestrial and wetland/riparian plants (which are not 

unexpected due to the herbicidal nature of the compound), as well as some chronic risks to 

mammals when maximum EECs are assumed. In order to address the risks identified in this 

screening-level assessment, registrants will be required to decrease the maximum labeled use 

30 
rate from 0.2 lbs ai/acre to 0.125 lbs ai/acre under normal conditions of use, with an annual 

maximum application of 0.3 lbs ai/acre. However, under certain circumstances such as during 

periods of rank growth/high fertilizer conditions, extreme weather conditions (such as extended 

periods of rain and/or low temperatures - 60o to 65o degree Fahrenheit), as well as on full-season 

cotton varieties, the higher rate (0.2 lbs ai/acre) may be used but total seasonal use may not 

exceed 0.3 lbs ai/acre. 

2. Other Labeling Requirements 

In order to be eligible for reregistration, various use and safety information will be 

included in the labeling of all end-use products containing thidiazuron. For the specific labeling 

statements and a list of outstanding data, refer to Section V of this RED document. 

3. Endangered Species Considerations 

The Agency has developed the Endangered Species Protection Program to identify 

pesticides whose use may cause adverse impacts on endangered and threatened species, and to 

implement mitigation measures that address these impacts. The Endangered Species Act 

requires federal agencies to ensure that their actions are not likely to jeopardize listed species or 

adversely modify designated critical habitat. To analyze the potential of registered pesticide 

uses that may affect any particular species, EPA uses basic toxicity and exposure data developed 

for the REDs and considers ecological parameters, pesticide use information, geographic 

relationship between specific pesticide uses and species locations, and biological requirements 

and behavioral aspects of the particular species. When conducted, this species-specific analysis 

will take into consideration any regulatory changes recommended in this RED that are being 

implemented at that time. 

A determination that there is a likelihood of potential impact to a listed species may result 

in limitations on use of the pesticide, other measures to mitigate any potential impact, or 

consultations with the Fish and Wildlife Service and/or the National Marine Fisheries Service as 

necessary. If the Agency determines use of thidiazuron “may affect” listed species or their 

designated critical habitat, EPA will employ the provisions in the Services regulations (50 CFR 

Part 402). Until that species specific analysis is completed, the risk mitigation measures being 

implemented through this RED will reduce the likelihood that endangered and threatened species 

may be exposed to thidiazuron at levels of concern. 

 EPA is not requiring specific label language at the present time relative to threatened and 

endangered species. If in the future specific measures are necessary for the protection of listed 

species, the Agency will implement them through the Endangered Species Protection Program. 

31 
4. Spray Drift Management 

The Agency has been working closely with stakeholders to develop improved approaches 

for mitigating risks to human health and the environment from pesticide spray and dust drift. As 

part of the reregistration process, we will continue to work with all interested parties on this 

important issue. 

From its assessment of thidiazuron as summarized in this document, the Agency 

concludes that no drift mitigation measures are needed for thidiazuron. In the future, thidiazuron 

product labels may need to be revised to include additional or different drift label statements. 

V. What Registrants Need to Do 

The Agency has determined that thidiazuron is eligible for reregistration provided that: 

(i) label changes outlined in this document are adopted as outlined in the Label Summary Table 

in Section C (Table 15) below. In the near future, the Agency intends to issue Data Call-In 

Notices (DCIs) requiring label amendments, product specific data and additional generic 

confirmatory (technical grade) data. Generally, registrants will have 90 days from receipt of a 

DCI to complete and submit response forms or request time extension and/or waiver requests 

with a full written justification. For product specific data, the registrant will have eight months 

to submit data and amended labels. For generic data, due dates can vary depending on the 

specific studies being required. Below are tables of additional generic data and label 

amendments that the Agency intends to require. 

A. Manufacturing Use Products 

1. Additional Generic Data Requirements 

The generic data base supporting the reregistration of thidiazuron for the above eligible 

uses has been reviewed and determined to be substantially complete. However, the data listed 

below (Table 14) are necessary to confirm the reregistration eligibility decision documented in 

this RED. 

Table 14. Data Requirements for the Reregistration Eligibility Decision on Thidiazuron 

Guideline Study Name 

New OPPTS 

Guideline 

No. 

Old 

Guideline 

No. 

Avian Chronic Tests on the Mallard Duck and Bobwhite Quail 850.2300 71-4A 

Tier 2 Terrestrial Plant Toxicity (seedling emergence) on Onion and Oat 850.4225 123-1A 

Residue Analytical Method – Livestock 860.1340 171-4D 

Storage Stability Data – Plant and Livestock 860.1380 171-4E 

32 
Guideline Study Name 

New OPPTS 

Guideline 

No. 

Old 

Guideline 

No. 

Meat, Milk, Poultry, and Eggs – (Additional data for the ruminant feeding 

study are required). 

860.1480 171-4J 

2. Labeling for Manufacturing-Use Products 

To ensure compliance with FIFRA and to be eligible for reregistration, manufacturing use 

product (MUP) labeling must be revised to comply with all current EPA regulations, PR Notices, 

and applicable policies. Currently, there are only a few label language statements needed for 

reregistration eligibility for thidiazuron. Therefore, the labeling must bear the following 

statements contained in Table 15. 

B. End-Use Products 

1. Additional Product-Specific Data Requirements 

Section 4(g)(2)(B) of FIFRA calls for the Agency to obtain any needed product-specific 

data regarding the pesticide after a determination of eligibility has been made. The Registrant 

must review previous data submissions to ensure that they meet current EPA acceptance criteria 

and if not, commit to conduct new studies. If a registrant believes that previously submitted data 

meet current testing standards, then the study MRID numbers should be cited according to the 

instructions in the Requirement Status and Registrants Response Form provided for each 

product. The Agency intends to issue a separate product-specific data call-in (PDCI), outlining 

specific data requirements. 

2. Labeling for End-Use Products 

In order to be eligible for reregistration, all thidiazuron product labels must be amended to 

incorporate the risk mitigation measures outlined in Section IV of this document. (See Table 15). 

C. Labeling Changes Summary Table 

In order to be eligible for reregistration, amend all product labels to incorporate the 

required language outlined in Section IV and V of this document. The following table (Table 

15) describes how language on the labels should be amended. 

33 
Table 15: Summary of Labeling Changes for Thidiazuron 

Description Amended Labeling Language 

Manufacturing Use Products 

For all Manufacturing Use Products 

“Only for formulation into an herbicide for the following uses(s) [fill blank only with those uses that are being supported by MP registrant.]” 

One of these statements may be added to a label to allow reformulation of the product for a specific use or all additional uses supported by a formulator or user group 

“This product may be used to formulate products for specific use(s) not listed on the MP label if the formulator, user group, or grower has complied with U.S. EPA submission requirements regarding support of suchuse(s).” “This product may be used to formulate products for any additional use(s) not listed on the MP label if the formulator, user group, or grower has complied with U.S. EPA submission requirements regarding support of such use.” 

Environmental Hazards Statements Required by the RED and Agency Label Policies 

"Do not discharge effluent containing this product into lakes, streams, ponds, estuaries, oceans, or other waters unless in accordance with the requirements of a National Pollution Discharge Elimination System (NPDES) permit and the permitting authority has been notified in writing prior to discharge. Do not discharge effluent containing this product to sewer systems without previously notifying the local sewage treatment plant authority. For guidance contact your State Water Board or Regional Office of the EPA." 

End Use Products Intended for Occupational Use 

PPE Requirements Established by the RED for all Formulations 

“Personal Protective Equipment (PPE) All mixers, loaders and applicators must wear: -Long sleeved shirt, -Long pants, and -Shoes and socks.” 

34 
Description Amended Labeling Language 

See Engineering Controls for Requirements.” 

Engineering Controls for Aerial Application 

Enclosed Cockpits “Engineering Controls: Pilots must use an enclosed cockpit that meets the requirements listed in the WPS for agricultural pesticides [40 CFR 170.240(d)(6)].” 

User Safety Requirements “Follow manufacturer’s instructions for cleaning/maintaining PPE. If no such instructions for 

washables exist, use detergent and hot water. Keep and wash PPE separately from other laundry.” 

User Safety Recommendations 

“USER SAFETY RECOMMENDATIONS” “Users should wash hands before eating, drinking, chewing gum, using tobacco, or using the toilet.” “Users should remove clothing/ PPE immediately if pesticide gets inside. Then wash thoroughly and put on clean clothing.” “Users should remove PPE immediately after handling this product. Wash the outside of gloves before removing. As soon as possible, wash thoroughly and change into clean clothing.” [Note: Glove statements can be removed if the acute toxicity testing of the end use product does not require gloves] 

35 
Description Amended Labeling Language 

Environmental Hazards “Do not apply directly to water, or to areas where surface water is present or to intertidal areas 

below the mean high water mark. Do not contaminate water when disposing of equipment washwater or rinsate.” “This product may contaminate water through drift of spray in wind. This product has a high potential for runoff for several months or more after application. Poorly draining soils and soils with shallow water tables are more prone to produce runoff that contains this product. A level, well-maintained vegetative buffer strip between areas to which this product is applied and surface water features such as ponds, streams, and springs will reduce the potential for contamination of water from runoff. Runoff of this product will be reduced by avoiding applications when rainfall is forecasted to occur within 48 hours. Sound erosion control practices will reduce this product’s contribution to surface water contamination.” “This chemical has properties and characteristics associated with chemicals detected in ground water. Use of this chemical in areas where soils are permeable, particularly where the water table is shallow, may result in groundwater contamination.” 

Restricted Entry Interval “Do not enter or allow worker entry into treated areas during the restricted entry interval of 24 

hours.” 

Early Reentry Personal Protective Equipment for Products subject to WPS as required by Supplement Three of PR Notice of 93-7 

“PPE required for early entry to treated areas that is permitted under the Worker Protection Standard and that involves contact with anything that has been treated, such as soil or water, is: For all end-use products: -coveralls, -chemical-resistant gloves made of any waterproof material, - shoes plus socks.” 

Application Restrictions The following label recommendations must be reflected in the directions for use: 

36 
General Use Rate Information (under normal conditions) for Cotton: 

0.125 lbs ai/A Maximum application rate of 0.3 lbs ai/A/year Maximum of 2 applications, but not to exceed 0.3 lbs ai/A/year. General Use Rate Information (under variable conditions) for Cotton:

(See section IV- A for more detailed information)

Maximum application rate of 0.2 lbs ai/A Maximum application rate of 0.3 lbs ai/A/year Maximum of 2 applications, but not to exceed 0.3 lbs ai/A/year. Additional language and application rates (in bold) to be added to existing end-use product labels 

containing only the active ingredient Thidiazuron: For cutout and mature cotton under normal weather patterns, use (insert product name) at 

0.05 to 0.10 lb. active ingredient per acre. The 0.05 lb. rate is most effective when used in a 

tank mix with other cotton defoliant products. Increased rates of (insert product name) above 0.10 lb. of active ingredient per acre may be needed to defoliate and control regrowth during periods of rank growth/high fertilizer conditions, extreme weather conditions, such as extended periods of rain and/or low 

temperatures (60°–65°F), and on full-season cotton varieties. 

37 
Additional language (in bold) to be added to existing products that contain a mixture of 

Thidiazuron and Diuron: TANK MIX OF (insert product name) plus other cotton defoliant products. 

The tank mix of (insert product name) plus other cotton defoliant products is recommended to improve overall defoliation, and as an aid in accelerating the opening of mature, unopened cotton bolls. Best activity will be obtained where the tank mix is applied to mature cotton plants. Do not apply tank mix before sufficient unopened bolls have matured to produce the desired cotton yield. For cotton produced in non-arid conditions, apply (insert product name) at a rate of 3.2 to 6.4 

fluid ounces per acre plus other cotton defoliant products at a rate of 21 to 42 fluid ounces per acre. For cotton produced in arid conditions, apply (insert product name) at a rate of 6.4 to 16 fluid ounces per acre plus other cotton defoliant products at a rate of 21 to 42 fluid ounces per acre. 

To Achieve an Application 

Rate of: 

Use This Amount of Product At the Indicated Rate, One 

Gallon of Product Will Treat: 

0.07 lbs. ai/Acre 2.3 fluid oz/A 56 Acres 0.17 lbs. ai/Acre 5.4 fluid oz/A 23.5 Acres 

Application Restrictions for Drift 

Thidiazuron products can not be applied by air within 1⁄2 mile of lettuce or 5 miles downwind of the point of application when citrus is in flush (burst of new growth, as in springtime) in the Rio Grande valley of Texas. Ground applications are restricted to 100 feet away from lettuce and 1⁄2 mile downwind from the point of application for citrus. (In general, a decrease in droplet size or increase in wind speed at the time of application will result in risk to non-target organisms. Alternatively, if droplet size is coarser or wind speeds are lower, exposures due to drift would be reduced). 

Instructions in the Labeling section appearing in quotations represent the exact language that should appear on the label. 

Instructions in the Labeling section not in quotes represents actions that the registrant should take to amend their labels or product regis

38 
VI. Appendices 

39 
Appendix A: Use Patterns Subject to Reregistration for Thidiazuron (Case 4092) 

Use Site Formulation Max. Single 

App. Rate 

Unit Max # App. 

Per Crop 

Cycle/Yr 

Max App. 

Rate Per 

Crop 

Cycle/Yr 

Min. 

Restriction 

Interval 

(Days) 

Reentry Interval 

(REI) 

Prehar

Inter

(PH

Cotton Wettable 

Powder (WP) [50% a.i.] Soluble Concentrate (SC) [12% a.i.] Emulsifiable Concentrate (EC) [8.4 - 50% a.i.] 

0.125 

*[for end-use products under normal conditions] 

0.2 

*[for end-use products under variable conditions] 

Lbs ai/acre 2 per season 0.3 lbs ai/acre N/A 24 hours Minimu

PHI= 5 

40 
Appendix B. Table of Generic Data Requirements and Studies Used to Make the 

Reregistration Decision 

GUIDE TO APPENDIX B 

Appendix B contains listing of data requirements which support the reregistration for 

active ingredients within the case 0153 covered by this IRED. It contains generic data 

requirements that apply to methyl parathion in all products, including data requirements for 

which a "typical formulation" is the test substance. 

The data table is organized in the following formats: 

1. Data Requirement (Column 1). The data requirements are listed in the order in 

which they appear in 40 CFR part 158. The reference numbers accompanying 

each test refer to the test protocols set in the Pesticide Assessment Guidance, 

which are available from the National technical Information Service, 5285 Port 

Royal Road, Springfield, VA 22161 (703) 487-4650. 

2. Use Pattern (Column 2). This column indicates the use patterns for which the 

data requirements apply. The following letter designations are used for the given 

use patterns. 

A. Terrestrial food 

B. Terrestrial feed 

C. Terrestrial non-food 

D. Aquatic food 

E. Aquatic non-food outdoor 

F. Aquatic non-food industrial 

G. Aquatic non-food residential 

H. Greenhouse food 

I. Greenhouse non-food 

J. Forestry 

K. Residential 

L. Indoor food 

M. Indoor non-food 

N. Indoor medical 

O. Indoor residential 

3. Bibliographic Citation (Column 3). If the Agency has acceptable data in its files, 

this column list the identify number of each study. This normally is the Master 

Record Identification (MIRD) number, but may be a "GS" number if no MRID 

number has been assigned. Refer to the Bibliography appendix for a complete 

citation of the study. 

41 
APPENDIX B

Data Supporting Guideline Requirements for the Reregistration of Thiabendazole 

REQUIREMENT USE 

PATTERN 

CITATION(S) 

PRODUCT CHEMISTRY 

New 

Guideline 

Number 

Old 

Guideline 

Number 

830.1550 61-1 Product Identity and Composition All 45915701 

830.1600 61-2A Start. Mat. & Mnfg. Process All 45915701 

830.1620 61-2B Description of Production Process All 45915701 

830.1670 61-2B Formation of Impurities All 45915701 

830.1700 62-1 Preliminary Analysis All 45915701 

830.1750 62-2 Certification of limits All 45915701 

830.1800 62-3 Enforcement Analytical Method All 45915701 

830.6302 63-2 Color All 45934001 

830.6303 63-3 Physical State All 45934001 

830.6304 63-4 Odor All 45934001 

830.6313 63-13 Stability to Normal and Elevated 

Temperatures, Metals and Metal Ions 

All 45934001 

830.6314 63-14 Oxidation/Reduction: Chemical 

Incompatibility 

All 45934001 

830.6315 63-15 Flammability All N/A 

830.6316 63-16 Explodability All 45934001 

830.6317 63-17 Storage Stability All 45934001; Study (1 year) in 

progress and must be 

submitted to the Agency 

upon completion. 

830.6319 63-19 Miscibility All N/A 

830.6320 63-20 Corrosion Characteristics All 45934001; Study (1 year) in 

progress and must be 

submitted to the Agency 

upon completion. 

830.7000 63-12 pH All 45934001 

42 
�����������������������������������

���� ���

�����������������������������������

������������������������������

�����������������������������������

���� ���

�����������������������������������

������������������������������

�����������������������������������

���� ���

�����������������������������������

������������������������������

���� ���

�����������������������������������

������������������������������

�����������������������������������

�����������������������������������

���� ���

�����������������������������������

������������������������������

�����������������������������������

Data Supporting Guideline Requirements for the Reregistration of Thiabendazole 

REQUIREMENT USE 

PATTERN 

CITATION(S) 

830.7050 None UV/Visable Absorption All 45934001 

830.7100 63-18 Viscosity All N/A 

830.7200 63-5 Melting Point All 45934001 

830.7220 63-6 Boiling Point All N/A 

830.7300 63-7 Relative Density All 45934001 

830.7370 63-10 Dissociation Constants in Water All 41364901 

830.7550 63-11 Octanol/Water Partition Coefficient All 41364906 

830.7840 63-8 Water solubility: column elution 

method; shake flask method 

All 41364906 and 41786202 

830.7950 63-9 Vapor Pressure All 94246001 

ECOLOGICAL EFFECTS 

850.2100 71-1 Avian Acute Oral Toxicity ����

����

���

���

������������������������������

������������������������������

 099189 

850.2200 71-2A Avian Dietary Toxicity - Quail ���� ���

�����������������������������������

������������������������������ 0081629, 46203502 

850.2200 71-2B Avian Dietary Toxicity - Duck ����������������������������������� 00066169 

850.2300 71-4 Avian Reproduction –Avian chronic 

tests on the Mallard Duck and 

Bobwhite Quail 

���� ���

�����������������������������������

�����������������������������������

�����������������������������������

������������������������������

������������������������������

Data Gap; Avian Chronic 

Tests (Mallard Duck and 

Bobwhite Quail) are 

required. 

850.1075 72-1A Fish Toxicity- Bluegill 

����

����

���

������������������������������ 42069201 ���

850.1075 72-1C Fish Toxicity- Rainbow Trout ���� ���

�����������������������������������

������������������������������ 42069202, 46203511, 

46203515 

850.1010 72-2A Invertebrate Toxicity ���� ��� �����������������������������������

�����������������������������������

������������������������������

������������������������������

 099189, 00066167, 

46203509, 46203503, 

46203516 

850.1075 72-3A Estuarine/Marine Toxicity - Fish 

����

����

���

������������������������������ 41846101 ���

850.1025 72-3B Estuarine/Marine Toxicity - Mollusk ����������������������������������� 42132001 

850.1035 

850.1045 

72-3C Estuarine/Marine Toxicity - Shrimp ���� ���

�����������������������������������

�����������������������������������

������������������������������ 41846101 

850.1300 72-4A Freshwater Fish- Early Life Stage ����������������������������������� 42270301 

43 
���� ���

�����������������������������������

������������������������������

�����������������������������������

���� ��� ����������������������������������� ������������������������������

���� ���

�����������������������������������

������������������������������

�����������������������������������

���� ���

�����������������������������������

������������������������������

�����������������������������������

�����������������������������������

�����������������������������������

�����������������������������������

�����������������������������������

�����������������������������������

�����������������������������������

�����������������������������������

�����������������������������������

�����������������������������������

�����������������������������������

����������������������������������� �����������������������������������

���� ���

�����������������������������������

������������������������������

�����������������������������������

���� ���

�����������������������������������

������������������������������

Data Supporting Guideline Requirements for the Reregistration of Thiabendazole 

REQUIREMENT USE 

PATTERN 

CITATION(S) 

850.1350 72-4B Estuarine/Marine Invertebrate Life 

Cycle 

���� ��� ����������������������������������� ������������������������������

������������������������������

42132002 

850.1500 72-5 Life Cycle Fish 

����

����

���

������������������������������ N/A��

850.4100 122-1A Terrestrial Toxicity; Seedling 

Emergence 

���� ���

�����������������������������������

������������������������������ 41821301 

850.4150 122-1B Terrestrial Plant Toxicity; Vegetative 

Vigor 

���� ���

�����������������������������������

������������������������������

������������������������������

41819101 

850.5400 122-2 Aquatic Plant Growth 

����

����

��� ������������������������������ N/A��

850.4225 123-1A Seed Germination and Seedling 

Emergence (Tier 2) 

���� ���

�����������������������������������

�����������������������������������

������������������������������ 45908501; Data Gap-

(onion and oat) 

850.4250 123-1B Vegetative Vigor (Tier 2) �����������������������������������

������������������������������

45921501 

850.4400 123-2 Aquatic Plant Growth (Tier2) 

����

����

���

������������������������������ 46203504 ���

850.3020 141-1 Honey Bee Acute Contact ����

����

���

���

������������������������������

������������������������������

 46203501, 46203518 

850.3030 141-2 Honey Bee Residue on Foliage ����������������������������������� N/A 

TOXICOLOGY 

81-1 Acute Oral Toxicity ����

����

���

���

������������������������������

������������������������������

 46121501 

870.1200 81-2 Acute Dermal Toxicity-Rat �����������������������������������

������������������������������

46121502 

870.1300 81-3 Acute Inhalation Toxicity-Rat 

����

����

���

������������������������������ 46121503 ���

870.2400 81-4 Primary Eye Irritation-Rabbit ����

����

���

���

������������������������������

������������������������������

 42099601 

870.2500 81-5 Primary Skin Irritation- Rabbit �����������������������������������

������������������������������

42099602 

870.2600 81-6 Dermal Sensitization- Guinea pig 

����

����

���

������������������������������ 46121504 ���

870.6100 81-7 Acute Delayed Neurotoxicity - Hen ����

����

���

���

������������������������������

������������������������������

 N/A 

870.6100 82-5A 90-Day Neurotoxicity- Hen �����������������������������������

������������������������������

N/A 

870.6200 81-8 Acute Neurotox. Screening Battery-Rat 

����

����

��� ������������������������������ N/A��

870.6200 82-7 90-Day Neurotox. Screening BatteryRat 

����

����

���

��� �����������������������������������

������������������������������

������������������������������

 N/A 

870.6300 83-6 Developmental Neurotoxicity Study �����������������������������������

������������������������������

N/A 

870.3100 82-1A 90-Day Feeding - Rodent 

����

����

���

���

�����������������������������������

������������������������������ 46121505, 46121506, 

46121509 

44 
���� ���

�����������������������������������

������������������������������

�����������������������������������

�����������������������������������

�����������������������������������

���� ���

�����������������������������������

������������������������������

�����������������������������������

�����������������������������������

���� ���

�����������������������������������

������������������������������

�����������������������������������

���� ���

�����������������������������������

������������������������������

�����������������������������������

�����������������������������������

���� ���

�����������������������������������

������������������������������

���� ���

�����������������������������������

������������������������������

�����������������������������������

����������������������������������� �����������������������������������

�����������������������������������

�����������������������������������

�����������������������������������

Data Supporting Guideline Requirements for the Reregistration of Thiabendazole 

REQUIREMENT USE 

PATTERN 

CITATION(S) 

870.3150 82-1B 90-Day Feeding - Non-rodent ���� ��� �����������������������������������

����������������������������������� �����������������������������������

����������������������������������� �����������������������������������

�����������������������������������

������������������������������

������������������������������

No subchronic oral study is 

required at this time, since 

the toxicological data 

requirements for 90-day 

feeding study in non-rodents 

are satisfied by the 1-yr. 

feeding study in dogs. 

870.3200 82-2 28-Day Dermal Toxicity- Rat 

����

����

���

������������������������������ 46261501 ���

870.3250 82-3 90-Day Dermal ����������������������������������� N/A 

870.3465 82-4 90-Day Inhalation-Rat �����������������������������������

������������������������������

N/A 

870.4100 83-1B Chronic Feeding Toxicity - NonRodent (Dog) 

����

����

���

���

�����������������������������������

������������������������������ 00159344 

870.4200 83-2B Oncogenicity - Mouse ����������������������������������� 46346001 

870.3700 83-3A Developmental Toxicity - Rat �����������������������������������

������������������������������

 00077126, 00077127 

870.3700 83-3B Developmental Toxicity - Rabbit 

����

����

���

���

�����������������������������������

������������������������������ 46121507, 46252001, 

46241001 

870.3800 83-4 2-Generation Reproduction - Rat ����

����

���

���

������������������������������

������������������������������

 46209601 

870.4300 83-5 2-year Combined 

Chronic/Oncogenicty- Rat 

���� ���

�����������������������������������

������������������������������

������������������������������

 00159346, 46345201 

870.5100 84-2 Mutagenicity-Gene Mutation- bacterial 

����

����

���

������������������������������ 46121508 ���

870.5265 None Reverse Gene Mutation Assay ����

����

���

���

������������������������������

������������������������������

 46121508 

870.5300 84-2 Mutagenicity-Gene Mutationmammalian 

���� ���

�����������������������������������

������������������������������

������������������������������

41761102 

870.5375 84-2B Mutagenicity- Structural Chromosomal 

Abberations 

����

����

���

���

�����������������������������������

������������������������������ 46121510 

870.5385 84-2 Micronuleus Assay ����

����

���

���

������������������������������

������������������������������

 070129 

870.5550 84-2 Unscheduled DNA Synthesis Assay �����������������������������������

������������������������������

41761103 

None 84-4 Other Genotoxic Effects 

����

����

���

������������������������������ N/A��

870.7485 85-1 General Metabolism- Rat ����

����

���

���

������������������������������

������������������������������

 42529001 

870.7600 85-2 Dermal Penetration ����������������������������������� 46261502 

OCCUPATIONAL/RESIDENTIAL EXPOSURE 

875.1500 235 Biological Monitoring ����

����

���

���

������������������������������

������������������������������ N/A; No residential uses 

45 
�����������������������������������

�����������������������������������

�����������������������������������

�����������������������������������

���� ���

�����������������������������������

������������������������������

���� ��� ����������������������������������� ������������������������������

�����������������������������������

�����������������������������������

���� ���

�����������������������������������

������������������������������

���� ���

�����������������������������������

������������������������������

�����������������������������������

�����������������������������������

�����������������������������������

�����������������������������������

�����������������������������������

�����������������������������������

�����������������������������������

����������������������������������� �����������������������������������

�����������������������������������

����������������������������������� �����������������������������������

�����������������������������������

���� ��� ����������������������������������� ������������������������������

Data Supporting Guideline Requirements for the Reregistration of Thiabendazole 

REQUIREMENT USE 

PATTERN 

CITATION(S) 

875.2100 132-1A Foliar Residue Dissipation ����������������������������������� ������������������������������

N/A; No residential uses 

875.2200 132-1B Soil Residue Dissipation 

����

����

���

��������������������������������

N/A; No residential uses 

875.2400 133-3 Dermal Passive Dosimetry Exposure ����������������������������������� N/A; No residential uses 

875.2500 133-4 Inhalation Passive Dosimetry Exposure ����������������������������������� ������������������������������

N/A; No residential uses 

None 231 Estimation of Dermal Exposure at 

Outdoor Sites 

����

����

���

���

����������������������������������� ������������������������������

N/A; No residential uses 

None 232 Estimation of Inhalation Exposure at 

Outdoor Sites 

���� ��� ����������������������������������� ������������������������������ N/A; No residential uses 

ENVIRONMENTAL FATE 

������������������������������

None 160-5 Chemical Identity 

����

����

���

������������������������������ N/A��

835.2120 161-1 Hydrolysis ����������������������������������� 42069203 

835.2240 161-2 Photodegradation - Water ���� ���

�����������������������������������

������������������������������

������������������������������

 41188201, 41364910, 

43075202, 44436901 

835.2410 161-3 Photodegradation - Soil 

����

����

���

���

�����������������������������������

������������������������������ 00156241, 41364902, 

44436901 

835.2370 161-4 Photodegradation - Air ����

����

���

���

������������������������������

������������������������������

 N/A 

835.4100 162-1 Aerobic Soil Metabolism �����������������������������������

������������������������������

 41950101, 46119601 

835.4200 162-2 Anaerobic Soil Metabolism 

����

����

���

������������������������������ 41945201 ���

835.4400 162-3 Anaerobic Aquatic Metabolism ����

����

���

���

������������������������������

������������������������������

 42666101 

835.4300 162-4 Aerobic Aquatic Metabolism �����������������������������������

������������������������������

N/A 

835.1240 163-1 Leaching/Adsorption/Desorption 

����

����

���

������������������������������ 41364909 ���

835.1410 163-2 Laboratory Volatilization ����

����

���

���

������������������������������

������������������������������

 N/A 

835.8100 163-3 Volatility- Field �����������������������������������

������������������������������

N/A 

835.6100 164-1 Terrestrial Field Dissipation 

����

����

��� �������������������������������� 41761105, 44454001 

835.6200 164-2 Aquatic Field Dissipation ����

����

���

���

������������������������������

������������������������������

 N/A 

835.6300 164-3 Forestry Dissipation �����������������������������������

������������������������������

N/A 

860.1950 165-4 Bioaccumulation in Fish 

����

����

���

������������������������������ N/A��

None 165-5 Bioaccumulation- Aquatic Nontarget ����

����

���

���

������������������������������

������������������������������

 N/A 

835-7100 166-1 Ground Water- Small Scale 

Prospective 

���� ���

�����������������������������������

������������������������������ N/A 

46 
�����������������������������������

���� ���

�����������������������������������

������������������������������

���� ��� ����������������������������������� ������������������������������

�����������������������������������

���� ���

�����������������������������������

������������������������������

���� ���

�����������������������������������

������������������������������

���� ���

�����������������������������������

� �����

���� ���

�����������������������������������

������������������������������

���� ���

�����������������������������������

������������������������������

Data Supporting Guideline Requirements for the Reregistration of Thiabendazole 

REQUIREMENT USE 

PATTERN 

CITATION(S) 

840.1100 201-1 Spray Droplet Size Spectrum ����������������������������������� ������������������������������ SDTF data 

840.1000 201-4 Background for Pesticide Aerial Drift 

(Evaluation) 

����

����

���

���

�����������������������������������

������������������������������ N/A 

840.1200 202-1 Spray Drift Field Deposition 

(Evaluation) 

���� ���

�����������������������������������

�����������������������������������

������������������������������ SDTF data 

RESIDUE CHEMISTRY 

������������������������������

860.1100 171-2 Chemical Identity 

����

����

���

�������������������������������� N/A 

860.1300 171-4A Nature of Residue - Plants ����

����

���

���

�����������������������������������

�����������������������������������

������������������������������

������������������������������ 94246026, 94246037, 

94246027, 94246038, 

94246028, 94246039 

860.1300 171-4B Nature of Residue - Livestock ���� ���

�����������������������������������

������������������������������

������������������������

 42529002, 42529003, 

42778001, 42778002 

860.1340 171-4C Residue Analytical Method - Plants ���� ���

�����������������������������������

�����������������������������������

�����������������������������������

�����������������������������������

������������������������������

������������������������������

 94246030, 94246029, 

94246040, 41950102 

[Pending methods for 

MRIDs 44558701 and 

44143601]. 

860.1340 171-4D Residue Analytical Method -

Livestock 

����

����

���

���

�����������������������������������

�����������������������������������

�����������������������������������

�����������������������������������

�����������������������������������

�����������������������������������

�����������������������������������

������������������������������ Data Gap; Animal 

analytical methods have 

been unsuccessful in 

simultaneously quantifying 

thidiazuron, 4-hydroxy 

thidiazuron, and phenylurea; 

unacceptable MRID 

43869001. 

860.1380 171-4E Storage Stability Data- Plant and 

Livestock 

���� ���

�����������������������������������

�����������������������������������

������������������������������ Data Gap; UnacceptableMRID 46298404 and 

42847601. 

47 
���� ���

�����������������������������������

������������������������������

���� ���

�����������������������������������

������������������������������

���� ���

�����������������������������������

������������������������������

���� ���

�����������������������������������

������������������������������

���� ���

�����������������������������������

������������������������������

Data Supporting Guideline Requirements for the Reregistration of Thiabendazole 

REQUIREMENT USE 

PATTERN 

CITATION(S) 

860.1480 171-4J Magnitude of Residues ­

Meat/Milk/Poultry /Egg 

���� ��� �����������������������������������

����������������������������������� �����������������������������������

����������������������������������� �����������������������������������

�����������������������������������

����������������������������������� �����������������������������������

�����������������������������������

�����������������������������������

�����������������������������������

�����������������������������������

�����������������������������������

�����������������������������������

�����������������������������������

������������������������������ Data Gap; 43781901 

(upgradable). Additional 

data for the ruminant 

feeding study are required: 

storage stability data, raw 

data to support findings in 

the study, and an analytical 

enforcement method that 

simultaneously quantifies 

residues of thidiazuron and 

its two livestock 

metabolites. 

Also, the poultry feeding 

study requirement has been 

waived; 43940701. 

860.1500 171-4K Crop Field Trials ���� ���

�����������������������������������

�����������������������������������

������������������������������ 94246031, 94246041, 

94246033, 94246042, 

46341001 

860.1520 171-4L Magnitude of Residue in Processed 

Food/Feed 

���� ���

�����������������������������������

������������������������������

������������������������������

 43940701, 44143601 

860.1850 165-1 Confined Accumulation in Rotational 

Crops Study 

����

����

���

���

�����������������������������������

������������������������������ 44415501 

860.1900 165-2 Field Accumulation in Rotational 

Crops Study 

���� ���

�����������������������������������

������������������������������ 46298401 

48 
Appendix C. Technical Support Documents 

Additional documentation in support of this RED is maintained in the OPP docket, 

located in Room 119, Crystal Mall #2, 1801 South Bell Street, Arlington, VA. It is open 

Monday through Friday, excluding Federal Holidays, from 8:30 am to 4 pm. 

The docket contains the risk assessments and related documents as of October 31, 2005. 

The availability announcement will be published in the Federal Register. All documents, in hard 

copy form, may be viewed in the OPP docket room or downloaded or viewed via the internet at 

the following site: www.epa.gov/pesticides/reregistration. The following list details all 

documents related to the Thidiazuron RED. 

Health Effects Documents: 

1. DP Barcode D244574. Alex Clem. September 24, 2004. Drinking Water 

Assessment. 

2. Felicia A. Fort. September 29, 1995. HED Metabolism Committee Decision 

following the 9/18/95 meeting. 

3. MRID 43781901. DP Barcode D220968. Stephen Funk. February 15, 1996. 

Thidiazuron: Response to the Phase 4 Review Magnitude of the Residue in 

Ruminants. 

4. DP Barcode D319302. Toiya Goodlow. August 31, 2005. Thidiazuron: Revised 

HED Chapter of the Reregistration Eligibility Decision Document (RED), Phase 3- 

Public Comments. 

5. Felecia A. Fort. September 29, 1995. HED Metabolism Committee Decision 

following the 9/18/95 meeting. 

6. DP Barcode D295368. Shyam B. Mathur. March 1, 2004. Product Chemistry 

Review of Thidiazuron Technical. 

7. Felecia A. Fort. September 8, 1995. Thidiazuron Metabolism. 

8. MRID No. 44415501. DP Barcode D241202. Toiya Jimerson. October 26, 2004. 

Thidiazuron: Registrant’s Response to Residue Chemistry Data Requirements. 

9. MRID No. 46298401. DP Barcode D294543. Toiya Jimerson. November 8, 2004. 

Magnitude of Residue in Rotational Crops Following Cotton Treated with 

DROPP® SC. 

10. MRID No. 42529001. DP Barcode D294560. Byong-Han Chin. Rat Metabolism. 

49 
11. MRID No. 44558701. DP Barcode D246804. Sherrie L. Mason. January 21, 1999. 

Independent Laboratory Validation of Analytical Method AW/02/96 for the 

Analysis of Thidiazuron and Photo-thidiazuron in/on Cottonseed Commodities. 

12. MRID 43781901. DP Barcode D220968. Stephen Funk. February 15, 1996. 

Thidiazuron: Response to the Phase 4 Review Magnitude of the Residue in 

Ruminants. 

13. DP Barcode D244574. Alex Clem. September 24, 2004. Drinking Water 

Assessment 

14. DP Barcode D316043. Toiya Jimerson. May 2, 2005. Thidiazuron: Chronic 

Dietary Exposure Assessment for the Reregistration Eligibility Decision- Revised. 

15. DP Barcode D311489. Jerry Blondell. December 21, 2004. Review of Thidiazuron 

Incident Reports. 

Ecological Fate and Effects Documents: 

1. DP Barcode D244574. Alex Clem. August 24, 2004. Thidiazuron (PC120301): 

Drinking Water Assessment 

50 
Appendix D. Citations Considered to be Part of the Data Base Supporting the 

Reregistration Eligibility Decision (Bibliography) for Thidiazuron 

Bibliography 

Citation Reference MRID 

66167 Vilkas, A.G.; Browne, A.M. (1979) The Acute Toxicity of Thidiazuron Technical to 

the Water Flea Daphnia magna: UCES Project No. 11506-74-04. (Unpublished study 

received Dec. 18, 1980 under 2139-EX-23; prepared by Union Carbide Corp., 

submitted by Nor-Am Agricultural Products, Inc., Naperville, Ill.; CDL:099819-C) 

66169 Fletcher, D.W. (1979) Report to..:8-day Dietary LC50 Study with Thidiazuron, 

Technical, in Mallard Ducklings:BLAL No. 79 DC 1. (Unpublished study received 

Dec 18, 1980 under 2139-EX-23; prepared by Bio-Life Associates, Ltd., submitted 

by Nor-Am Agricultural Products, Inc., Naperville, Ill.; CDL:099819-F) 

77126 Reprotox GmbH (1981) Thidiazuron (SN 49 537): Teratology Study in the Rat: 

Reprotox Order No. 413/A. Rev. final rept. (Unpub- lished study received May 29, 

1981 under 2139-122; submitted by Nor-Am Agricultural Products, Inc., Naperville, 

Ill.; CDL: 070129-B) 

77127 Reprotox GmbH (1981) Thidiazuron (SN 49 537): Teratology Study in the Rat: 

Reprotox Order No. 536/A. Rev. final rept. (Unpub- lished study received May 29, 

1981 under 2139-122; submitted by Nor-Am Agricultural Products, Inc., Naperville, 

Ill.; CDL: 070129-C) 

81629 Fletcher, D.W. (1981) Report to Nor-Am Agricultural Products, Inc.: 8-day Dietary 

LC50 Study with Thiazuron, Technical in Bob- white Quail: P.O. #R 818; BLAL No. 

81 QC 7. (Unpublished study received Sep 3, 1981 under 2939-122; prepared by BioLife Asso- ciates, Ltd., submitted by Farmer Seed & Nursery, Faribault, Minn.; 

CDL:245834-A) 

099189 Fletcher, Dale 1979. The Acute Oral Toxicity of Thiadiazuron Technical to the 

Bobwhite Quail. Received January 5, 1981. An unpublished report prepared by BioLife Associates, LTD for NOR-AM Agricultural Products, Inc. 

156241 Riemann, J. (1981) Photodegradation of Thidiazuron (SN 49537) on Soil Surfaces: 

Report No. APC 07/81. Unpublished study prepared by Schering AG. 37 p. 

159344 Khater, A. (1985) SN 49 537: Systemic Tolerance Study in Dogs following Daily 

Administration via the Feed over a Period of One Year: Report No. PF 55/84: Study 

No. TX 83.003. Unpublished study prepared by Schering AG and Tierarztlichen 

Hochschule Hannover. 463 p. 

51 
159346 Sachsse, K. (1986) 104-Week Chronic Toxicity and Oncogenicity Study with 

Thidiazuron Technical in the Rat: RCC Project No. 011924. Unpublished study 

prepared by Research & Consulting Co., AG and Experimental Pathology Consulting 

AG. 1498 p. 

41188201 Brehm, M. (1989) W63-Thidiazuron: The Photodegradation of Thidiazu- ron in 

Aqueous Solution: Project ID APC 34/09. Unpublished stu- dy prepared by Schering 

Ag. 101 p. 

41364901 Ottnad, M. (1976) C5-Thidiazuron: Determination of the Dissociation Constant of 

SN 49 537h: Lab Project Number: PA 49 537.11/5. Unpublished study prepared by 

Schering AG. 6 p. 

41364906 Brehm, M.; Miklautz, H. (1987) C40 Thidiazuron: Water Solubility and NOctanol/Water Partition Coefficient of Thidiazuron (Schering Code No. ZK 49 537): 

Lab Project No. APC 50/87; Study No. 87/169; 603.30. Unpublished study prepared 

by Schering AG. 27 p. 

41364909 Bruehl, R. (1988) W61 Thidiazuron: Absorption to and Desorption from Soil: Lab 

Project ID: UPSR 17/88 - PA 49537.7/6; PF-S 87 057; 05.14. Unpublished study 

prepared by Schering AG Pflanzen- schutz Umwelt, Produktsicherheit Registrierung. 

46 p. 

41364910 Brehm, M. (1989) W63 Supplement Thidiazuron: The Photodegradation of 

Thidiazuron in Aqueous Solution (Schering Code No. ZK 49537): Lab Project ID: 

APC 55/89; 87/217; 31.08. Unpublished study prepared by Schering AG. 25 p. 

41761102 Heidemann, A. (1990) T59 Thidiazuron: Gene Mutation Assay in Chinese Hamster 

V79 Cells in Vitro with Thidiazuron Technical (SN 49537): Lab Project Number: TB 

89 083. Unpublished study prepared by Cytotest Cell Research Gmbh & Co. KG. 30 

p. 

41761103 Fautz, R. (1990) T58 Thidiazuron: Unscheduled DNA Synthesis in Primary 

Hepatocytes of Male Rats in Vitro with Thidiazuron (SN 49537): Lab Project 

Number: TB 89 084. Unpublished study prepared by Cytotest Cell Research Gmbh & 

Co. KG. 36 p. 

41761104 Hughes, J.S. 1990. The Toxicity of Thiadiazuron Technical to Selenastrum 

capricornatum.Laboratory Project N. B643-01-3. Conducted by Malcom Pirnie, 

Inc., Pikeville, NC. 

41761105 Rucker, W. (1990) W67 Thidiazuron: Dissipation of Thidiazuron in Soil Following 

Application of Dropp 50WP to Bare Ground: Lab Project Number: 65/90. 

Unpublished study prepared by Schering AG. 76 p. 

41786202 Muller, T. (1991) Thidiazuron Product Chemistry/Solubility in Organic Solvents: 

Lab Project Number: C53, C54, C58. Unpublished prepared by Schering Ag. 70 p. 

41819101 Downey, S. (1990) Investigation into the Phytotoxic Effects of Thi- diazuron on 

52 
Vegetative Vigor (Tier 1): Lab Project Number: 502 AW. Unpublished study 

prepared by Nor-Am Chemical Co. 132 p. 

41821301 Downey, S. (1991) Investigation into the Phytotoxic Effects of Thi- diazuron on 

Seedling Emergence (Tier 1): Lab Project Number: 501 AW. Unpublished study 

prepared by Nor-Am Chemical Co. 63 p. 

41846101 Schupner, J.; Stachura, B. (1991) The Static Acute Toxicity of Thidiazuron to the 

Sheepshead minnow, Cyprinodon variegatus: Lab Project Number: 504AW. 

Unpublished study prepared by NOR-AM Chemical Co. 42 p. 

41945201 Feyerabend, M. (1991) W74 Thidiazuron: Anaerobic Degradation of ?UL-?carbon 

14||-Phenyl-Thidiazuron in a Sandy Loam Soil at 21 (degree) C: Lab Project Number: 

UPSR 20/91. Unpublished study prepared by Schering Ag. 47 p. 

41950101 Feyerabend, M. (1991) W75 Thidiazuron: Aerobic Degradation of ?UL- carbon 14| 

Phenyl-Thidiazuron in a Sandy Loam Soil at 21 C: Lab Project Number: UPSR 

21/91. Unpublished study prepared by Sche- ring AG. 49 p. 

41950102 Bowman, M. (1991) Testing of Thidiazuron through US FDA Multiresidue Methods: 

Lab Project Number: MCB-NOR-Am/MR-2. Unpublished study prepared by M.C. 

Bowman & Associates. 30 p. 

42069201 Schupner, J.; Stachura, B. (1991) The Acute Toxicity of Thidiazuron Technical to the 

Bluegill Sunfish, Lepomis macrochirus in a Static System: Lab Project Number: 

511AW. Unpublished study prepared by NOR-AM Chemical Co. 42 p. 

42069202 Schupner, J.; Stachura, B. (1991) The Acute Toxicity of Thidiazuron Technical to the 

Rainbow Trout, Oncorhynchus mykiss in a Static System: Lab Project Number: 

512AW. Unpublished study prepared by NOR-AM Chemical Co. 42 p. 

42069203 Tschampel, M. (1991) W78 Thidiazuron: The Determination of the Rate of 

Hydrolysis of Thidiazuron (Schering Code No. ZK 49537): Lab Project Number: 

APC/71/91. Unpublished study prepared by Schering Ag. 28 p. 

42099601 Liggett, M.; McRae, L. (1991) Thidiazuron (T-61): Rabbit Eye Irri- tancy Study: Lab 

Project Number: 91703D/SMS 340/SE: TOX 91116. Unpublished study prepared by 

Huntingdon Research Center, Ltd. 16 p. 

42099602 Liggett, M.; McRae, L. (1991) Thidiazuron (T-62): Rabbit Skin Irri- tancy Study: 

Lab Project Number: 91702D/SMS 339/SE: TOX 91115. Unpublished study 

prepared by Huntingdon Research Centre, Ltd. 15 p. 

42132001 Ward, S. (1991) Thidiazuron Technical: Acute Effect on New Shell Growth of, the 

Eastern Oyster, Crassostrea virginica: Lab Project Number: J9101006B. Unpublished 

study prepared by Toxi- kon Environmental Sciences. 54 p. 

42132002 Blakemore, G. (1991) Chronic Toxicity of Thidiazuron to Daphnia magna Under 

Flow-through Test Conditions: Final Report: Lab Pro- ject Number: 39114: 507-AW. 

53 
Unpublished study prepared by ABC Labs, Inc. 106 p. 

42270301 Cohle, P.; Muckerman, M. (1992) Early Life-Stage Toxicity of Thidiazuron to 

Fathead Minnows (Pimephales promelas) in a Flow-through System: Lab Project 

Number: 39113: 506/AW. Unpublished study prepared by ABC Laboratories, Inc. 86 

p. 

42529001 Hawkins, D.; Mayo, B.; McEwen, A.; et al. (1992) M13 Thidiazuron: The 

Metabolism of ?Carbon 14|-Thidiazuron in Rats: Lab Project Number: 

HRC/SMS/254/920450. Unpublished study prepared by Hundington Research Centre 

Ltd. 77 p. 

42529002 Hawkins, D.; Mayo, B.; Pollard, A.; et al. (1992) M13 Thidiazuron: The Metabolism 

of carbon 14- Thidiazuron in the Cow Part I: Lab Project Number: 

HRC/SMS/255/920556. Unpublished study prepared by Hundington Research Centre 

Ltd. 103 p. 

42529003 Hawkins, D.; Mayo, B.; Pollard, A.; et al. (1992) M13 Thidiazuron: The Metabolism 

of carbon 14- Thidiazuron in the Laying Hens Part I: Lab Project Number: 

HRC/SMS/253/921246. Unpublished study prepared by Hundington Research Centre 

Ltd. 89 p. 

42666101 Leake, C.; Allan, J. (1993) The Degradation of (carbon 14)-Thidiazuron under 

Laboratory Anaerobic Aquatic Conditions: Lab Project Number: 508AW. 

Unpublished study prepared by Nor-Am Chemical Co. 64 p. 

42778001 Hawkins, D.; Mayo, B.; Pollard, A.; et al. (1993) M-11 Thidiazuron: The Metabolism 

of (carbon 14)- Thidiazuron in the Laying Hens, Part II—Investigations into Tissue 

Metabolites: Addendum: Lab Project Number: HRC/SMS/253/921246: HRC/SMS 

253A/930518: TOX 90461. Unpublished study prepared by Huntingdon Research 

Centre Ltd. 28 p. 

42778002 Hawkins, D.; Mayo, B.; Pollard, A.; et al. (1993) M-12 Thidiazuron: The Metabolism 

of (carbon 14)- Thidiazuron in the Cow, Part II—Investigations into Tissue 

Metabolites: Addendum: Lab Project Number: HRC/SMS/255/920556: HRC/SMS 

255A/930527: TOX 90462. Unpublished study prepared by Huntingdon Research 

Centre Ltd. 36 p. 

42847601 Brady, S. (1993) Stability of Thidiazuron Residues in Cottonseed Analytical Samples 

Freezer-Stored for Four Years, USA, 1989: Lab Project Number: E332.02.89. 

Unpublished study prepared by Nor-Am Chemical Co. 38 p. 

43075202 Brehm, M. (1993) Thidiazuron: The Photodegredation of Thidiazuron in Aqueous 

Solution: W63, Addendum #1: Lab Project Number: APC 34/89. Unpublished study 

prepared by Schering AG. 19 p. 

43781901 Castro, L. (1995) Thidiazuron-Derived Residues in the Meat and Milk of Dairy Cows 

Resulting from Oral Ingestion of Thidiazuron (Second Edition): Lab Project Number: 

54 
AW-93R-01/02: 139-005-10. Unpublished study prepared by AgrEvo USA Co. 141 

p. 

43869001 Arguello, A. (1995) Independent Laboratory Validation of the Method of 

Determination of Thidiazuron and Its Metabolites, 4-Hydroxy Thidiazuron and 

Phenylurea, in Beef Tissues and Milk: Revised Report: Lab Project Number: 1435: 

1435-1. Unpublished study prepared by Analytical Development Corp. 140 p. 

43940701 Williams, L. (1996) At-Harvest Thidiazuron Residues In or On Processed 

Cottonseeds Following Two treatments with DROPP 50WP At Exaggerated Rates, 7 

Days PHI, USA, 1994: Lab Project Number: AW-94R-08: A55693. Unpublished 

study prepared by AgrEvo USA Co. 56 p. 

44143601 Williams, L. (1996) Supplement 1 to: At-Harvest Thidiazuron Derived Residues In 

or On Processed Cottonseeds Following Two treatments with DROPP 50WP At 

Exaggerated Rates, 7 Days PHI, USA, 1994: Lab Project Number: A61009: AW94R-08: A55693. Unpublished study prepared by AgrEvo USA Co. 59 p. 

44415501 Meyer, B.; Tull, P. (1997) Uptake of (5-(carbon 14)-Thiadazol)-Thidiazuron 

Residues in Soil by Rotational Crops under Confined Conditions: Lab Project 

Number: 524AW: A61011: THIDIAZURON/W89. Unpublished study prepared by 

AgrEvo USA Co. 115 p. 

44436901 Kelly, I. (1997) Thidiazuron Reregistration in the USA: Environmental Fate 

Overview, 1997: Lab Project Number: 526AW: AW97E526. Unpublished study 

prepared by AgrEvo USA Co. 34 p. 

44454001 Campbell, J.; Singer, S. (1997) Dissipation of Thidiazuron in Soil Following 

Application of Dropp 50 WP to Bare Soil USA, 1991 (Amended Report): Lab Project 

Number: AW-91R-03: A61018: THIDIAZURON/W88-AMEND. Unpublished study 

prepared by AgrEvo USA Co. 553 p. 

44558701 Koch, D.; Schrier, L. (1998) Independent Laboratory Confirmation of Determination 

of Thidiazuron and Photo-Thidiazuron in Cottonseed and Gin Trash by HPLC 

According to PR Notice 96-1 Guidelines: Lab Project Number: 43653: ACFS-43653: 

AW-96R-03. Unpublished study prepared by ABC Laboratories, Inc. 77 p. 

45915701 Smith, P. (2002) Analysis of Product Ingredients in Five Batches of Technical Grade 

Thidiazuron: Lab Project Number: 1136W. Unpublished study prepared by PTRL 

West, Inc. 87 p. {OPPTS 830.1550, 830.1600, 830.1620, 830.1670, 830.1700, 

830.1750, 830.1800, 830.1900} 

45921501 Teixeira, D. (2003) Thidiazuron SC42--Determination of Effects on Vegetative 

Vigor of Ten Plant Species: Lab Project Number: B004268: 13798.6114: 

02AW38345A. Unpublished study prepared by Springborn Smithers Laboratories. 

157 p. {OPPTS 850.4150 and 850.4250} 

45934001 Smith, P.; Cunningham, M. (2003) Physical/Chemical Characteristics of Thidiazuron 

55 
Tech: Lab Project Number: 1152W: KRR-071-02. Unpublished study prepared by 

PTRL West, Inc. and Kinetica, Inc. 55 p. {OPPTS 830.6302, 830.6303, 830.6304, 

830. 6313, 830.6314, 830.6316, 830.7000, 830.7050, 830.7200, 830.7300} 

46119601 Allan, J. (2003) The Kinetics of Degradation of ((Carbon 14)-Thiadiazol)-

Thidiazuron in Three Soils at 20 Degrees C Under Laboratory Aerobic Conditions. 

Project Number: B004299, 601AW, 601AW/F/218/221. Unpublished study prepared 

by Bayer CropScience LP. 78 p. 

46121501 Coleman, D. (2001) Rat Acute Oral Toxicity: Thidiazuron. Project Number: 

AES/026/004785/AC, TOX/201338. Unpublished study prepared by Huntingdon 

Life Sciences, Ltd. 22 p. 

46121502 Coleman, D. (2001) Rat Acute Dermal Toxicity: Thidiazuron. Project Number: 

AES/027/004628/AC, TOX/20139. Unpublished study prepared by Huntingdon Life 

Sciences, Ltd. 18 p. 

46121503 Wesson, C. (2001) Acute Inhalation Toxicity (Nose Only) Study in the Rat: 

Thidiazuron (AE B049537). Project Number: 374/096, TOX/20142. Unpublished 

study prepared by Safepharm Laboratories, Ltd. 46 p. 

46121504 Coleman, D. (2001) Guinea-Pig Skin Sensitization Study (Magnusson & Kligman 

Method): Thidiazuron. Project Number: AES/028/012112/SS, TOX/20140. 

Unpublished study prepared by Huntingdon Life Sciences, Ltd. 31 p. 

46121505 Foulon, O. (2001) Thidiazuron: 90-Day Toxicity Study in the Mouse by Dietary 

Adminstration: (Final Report). Project Number: SA/00593, K01/013, RTI/806/AN. 

Unpublished study prepared by Aventis Cropscience. 304 p. 

46121506 Foulon, O. (2001) Thidiazuron: 90-Day Toxicity Study in the Rat by Dietary 

Adminstration: (Final Report). Project Number: SA/00491, K01/003. Unpublished 

study prepared by Aventis Cropscience. 508 p. 

46121507 Wason, S. (2003) Thidiazuron: Developmental Toxicity Study in the Rabbit by 

Gavage. Project Number: SA/02046. Unpublished study prepared by Bayer 

Cropscience. 237 p. 

46121508 Kitching, J. (2001) Bacterial Mutation Assay: Thidiazuron. Project Number: 

AES/036, AES/036/004461, TOX/20144. Unpublished study prepared by 

Huntingdon Life Sciences, Ltd. 29 p. 

46121509 Steiblen, G. (2003) Thidiazuron: 28-Day Toxicity Study in the Rat by Dietary 

Adminstration (Investigation of Renal Function). Project Number: SA/01245. 

Unpublished study prepared by Bayer Cropscience. 179 p. 

46121510 Gudi, R.; Brown, C. (2001) In Vitro Mammalian Chromosome Aberration Test: Final 

Report. Project Number: AA39KC/341/BTL, SPGT341. Unpublished study prepared 

by Bioreliance. 37 p. 

56 
46203501 King, A. (2003) Assessment of Side Effects of AE B049537 00 1D99 0003 

(Thidiazuron, techn.) to the Honey Bee, Apis mellifera L. in the Laboratory: (Final 

Report). Project Number: 20021341/01/BLEU, C029693. Unpublished study 

prepared by GAB Biotechnologie Gmbh. 26 p. 

46203502 Bowers, L. (2003) Technical Thidiazuron: A Subacute Dietary LC50 with Northern 

Bobwhite. Project Number: TN721701, 200522, B004266. Unpublished study 

prepared by Bayer CropScience. 39 p. 

46203503 Blankinship, A.; Palmer, S.; Kendall, T.; et. al. (2003) Thidiazuron: A 48-Hour Static 

Acute Toxicity Test with the Cladoceran (Daphnia magna): Final Report. Project 

Number: 149A/151, C032042. Unpublished study prepared by Wildlife International, 

Ltd. 40 p. 

46203504 Desjardins, D., Kendall, T., and Krueger, H. 2003. Thidiazuron: A 72-Hour Toxicity 

Test with the Freshwater Alga (Anabaena flos-aquae). Unpublished study performed 

by Wildlife International, Ltd., Easton, Maryland. Laboratory Study No. 149A-152. 

Study sponsored by Bayer CropScience, Frankfurt am Main, Germany. Experimental 

start date April 7, 2003 and experimental termination date April 10, 2003. The final 

report issued April 25, 2003. 

46203505 Desjardins, D., Kendall, T., and Krueger, H. 2003. Thidiazuron: A 96-Hour Toxicity 

Test with the Marine Diatom (Skeletonema costatum). Unpublished study performed 

by Wildlife International, Ltd., Easton, Maryland. Laboratory Study No. 149A-153. 

Study sponsored by Bayer CropScience, Frankfurt am Main, Germany. Experimental 

start date April 21, 2003 and experimental termination date April 25, 2003. The final 

report issued June 5, 2003. 

46203506 Desjardins, D., Kendall, T., and Krueger, H. 2003. Thidiazuron: A 7-Day StaticRenewal Toxicity Test with Duckweed (Lemna gibba). Unpublished study 

performed by Wildlife International, Ltd., Easton, Maryland. Laboratory Study No. 

149A-154. Study sponsored by Bayer CropScience, Frankfurt am Main, Germany. 

Experimental start date April 1, 2003 and experimental termination date April 8, 

2003. The final report issued May 6, 2003. 

46203509 Blankinship, A.; Palmer, S.; Kendall, T.; et al. (2003) AE F132347: A 48-Hour Acute 

Toxicity Test with the Cladoceran (Daphnia magna): Final Report. Project Number: 

C032043, 149A/155. Unpublished study prepared by Wildlife International, Ltd. 41 

p. 

46203510 Desjardins, D., Kendall, T., and Krueger, H. 2003. AE F132347: A 72-Hour 

Toxicity Test with the Freshwater Alga (Scenedesmus subspicatus). Unpublished 

study performed by Wildlife International, Ltd., Easton, Maryland. Laboratory Study 

No. 149A-157. Study sponsored by Bayer CropScience, Frankfurt am Main, 

Germany. Experimental start date May 12, 2003 and experimental termination date 

May 15, 2003. The final report issued June 19, 2003. 

57 
46203511 Palmer, S.J., et al. 2003. AE C421200: A 96-Hour Static Acute Toxicity Test with 

the Rainbow Trout (Oncorhynchus mykiss). Unpublished study performed by 

Wildlife International, Ltd., Easton, MD. Laboratory Project No. 149A-159. Study 

sponsored by Bayer CropScience, Frankfurt am Main, Germany. Study initiated 

April 8, 2003 and completed June 30, 2003. 

46203513 Desjardins, D., Kendall, T., and Krueger, H. 2003. AE C421200: A 72-Hour 

Toxicity Test with the Freshwater Alga (Scenedesmus subspicatus). Unpublished 

study performed by Wildlife International, Ltd., Easton, Maryland. Laboratory Study 

No. 149A-160. Study sponsored by Bayer CropScience, Frankfurt am Main, 

Germany. Experimental start date May 9, 2003 and experimental termination date 

May 12, 2003. The final report issued June 5, 2003. 

46203515 Palmer, S.; Kendall, T.; Krueger, H. (2003) AE F132345: A 96-Hour Static Acute 

Toxicity Test with the Rainbow Trout (Oncorhynchus mykiss): Final Report. Project 

Number: C032041, 149A/161. Unpublished study prepared by Wildlife International, 

Ltd. 41 p. 

46203516 Palmer, S.; Kendall, T.; Krueger, H. (2003) AE F132345: A 48-Hour Static Acute 

Toxicity Test with the Cladoceran (Daphnia magna). Project Number: C032045, 

149A/149. Unpublished study prepared by Wildlife International, Ltd. 41 p. 

46203517 Desjardins, D., Kendall, T., and Krueger, H. 2003. AE F132345: A 72-Hour 

Toxicity Test with the Freshwater Alga (Scenedesmus subspicatus). Unpublished 

study performed by Wildlife International, Ltd., Easton, Maryland. Laboratory Study 

No. 149A-150. Study sponsored by Bayer CropScience, Frankfurt am Main, 

Germany. Experimental start date July 28, 2003 and experimental termination date 

July 31, 2003. The final report issued August 13, 2003. 

46203518 Waltersdorfer, A. (2002) Contact Toxicity (LD50) to Honey Bees (Apis mellifera L.) 

Thidiazuron Water Miscible Suspension Concentrate 500 g/l. Project Number: 

C027323, CW02/046. Unpublished study prepared by Bayer Cropscience Gmbh. 21 

p. 

46203522 Nienstedt, K. (2003) Thidiazuron, SC 500 G/L: A 14-Day Acute Toxicity Test with 

the Earthworm Eisenia Fetida. Project Number: C031948. Unpublished study 

prepared by Springborn Laboratories (Europe) Ag. 38 p. 

46209601 Myers, D. (2003) AE B049537 (Thidiazuron) Study of Reproductive Performance in 

Han Wistar Rats Treated Continuously Through Two Successive Generations by 

Dietary Administration. Project Number: AES/089, AES/089/024162. Unpublished 

study prepared by Huntingdon Life Sciences, Ltd. 930 p. 

46241001 Kennel, P. (2004) Range-Finding Study for Developmental Toxicity in the Rabbit by 

Gavage: (Thidiazuron). Project Number: SA/01070, C017597. Unpublished study 

prepared by Aventis CropScience. 114 p. 

46252001 Wason, S. (2004) Historical Control Data: Supplement to MRID 46121507: 

58 
Thidiazuron- Developmental Toxicity Study in the Rabbit by Gavage; Study No. SA 

02046. Project Number: DAL028/04, SA/02046, B004627. Unpublished study 

prepared by Bayer CropScience. 25 p. 

46261501 Krotlinger, F.; Rosenbruch, M. (2004) Thidiazuron: Subacute Dermal Toxicity Study 

in Rats (Four Week Dermal Administration). Project Number: AT01114, T8073134. 

Unpublished study prepared by Bayer Cropscience LP. 226 p. 

46261502 Artus-Jacenko, L. (2004) Thidiazuron: In Vivo Dermal Absorption Study in the Male 

Rat. Project Number: C040234, SA/02427. Unpublished study prepared by Bayer 

Cropscience. 156 p. 

46298401 Norris, F. (2002) Thidiazuron: Magnitude of Residues in Rotational Crops Following 

Cotton Treated with Dropp. Project Number: 00AW25819, B003793, 25819/02. 

Unpublished study prepared by Aventis CropScience and South Texas Ag. Research. 

248 p. 

46298404 Williams, L. (2002) Stability of Thidiazuron and its Metabolites 4-Hydroxy 

Thidiazuron and Phenyl Urea in Milk and Beef Tissues During Frozen Storage, USA, 

1995. Project Number: AW95R003, B03987, AW/95R/03. Unpublished study 

prepared by Bayer CropScience LP. 90 p. 

46341001 Mackie, S. (2001) DROPP SC: Magnitude of Residues in Cottonseed and Gin Trash 

Resulting from Foliar Applications of DROPP SC Under Maximum Proposed Label 

Specifications (2000): Final Study Report. Project Number: 00AW25588, B003303, 

AVENTIS/1373. Unpublished study prepared by Pyxant Labs Inc. and Mid South 

Agric. Research and Stoneville Associates. 336 p. 

46345201 Steiblen, G. (2004) Chronic Toxicity and Carcinogenicity Study of Thidiazuron in 

the Wistar Rat by Dietary Administration. Project Number: SA/01269. Unpublished 

study prepared by Bayer Cropscience. 2977 p. 

46346001 Wason, S. (2004) Carcinogenicity Study of Thidiazuron in the C57BL/6 Mouse by 

Dietary Administration. Project Number: SA/01333. Unpublished study prepared by 

Bayer Cropscience. 1687 p. 

94246001 Chow, N; Stevens, R. (1990) Nor-Am Chemical Company Phase 3 Summary of 

MRID 41364906 and Related MRIDs 00066172, 00066173, 41364901. Physical and 

Chemical Characteristics of Thidiazuron. 15 p. 

94246026 Guininvan, P.; Stevens, R. (1990) Nor-Am Chemical Company Phase 3 Summary of 

MRID 00039332. Determination of UL-[carbon 14]-phenyl-SN49537 Residues in 

Cotton Plants: Lab. ID NO. PA49537.61/2; M6/2. Prepared by Schering AG. 9 p. 

94246027 Guininvan, P.; Stevens, R. (1990) Nor-Am Chemical Company Phase 3 Summary of 

MRID 00064749. Residues of SN49537 in Cotton By-Products: Lab. ID No. 

PA49537.81/6; M8/2. Prepared by Schering AG. 9 p. 

94246028 Guininvan, P.; Stevens, R. (1990) Nor-Am Chemical Company Phase 3 Summary of 

59 
MRID 00064751. Metabolism of Thidiazuron in and on Cotton Plants: Lab. ID No. 

49537.81/6; M9/2. Prepared by Schering AG. 8 p. 

94246029 Guininvan, P.; Stevens, R. (1990) Nor-Am Chemical Company Phase 3 Summary of 

MRID 00039324. Residue Determination of SN 49537 in Cottonseed and Cotton 

Fiber (Prelim. Method) (49537/1): Lab. I.D. No. PA 49537.51/5. Prepared by 

Schering AG. 13 p. 

94246030 Chow, N.; Stevens, R. (1990) Nor-Am Chemical Company Phase 3 Summary of 

MRID 40178306. Analytical Method for the Determination of Residues of 

Thidiazuron and Diuron in Cottonseed by Gas Chromatography with Electron 

Capture Detection: Lab. I.D. No. 33001/A; R47. Prepared by NOR-AM Chemical 

Co. 20 p. 

94246031 Kelly, U.; Brown, R.; Stevens, R. (1990) Nor-Am Chemical Company Phase 3 

Summary of MRID 00136323 and Related MRIDs 00064747. Residues of Cotton 

Seed following the Application of DROPP; R23-R35. Prepared by Agricultural 

Products, Inc.12 p. 

94246033 Guininvan, P.; Stevens, R. (1990) Nor-Am Chemical Company Phase 3 Summary of 

MRID 00136323. Residues of Thidiazuron in Cotton By-products following the 

Application of DROPP: R24, R26-R30, R32, R33. Prepared by Nor-Am Agricultural 

Products. 34 p. 

94246037 Iwan, J. (1990) Nor-Am Chemical Company Phase 3 Reformat of MRID 00039332. 

M6/2 Thidiazuron: Determination of UL-[carbon 14]-phenyl-SN 49 537 Residues in 

Cotton Plants: Lab. Project ID: PA 49 537.61/2; M6/2. Prepared by Schering AG. 17 

p. 

94246038 Bruhl, R. (1990) Nor-Am Chemical Company Phase 3 Reformat of MRID 00064749. 

Thidiazuron: Residues of SN 49 537 in Cotton By-Products: Lab. Project ID: PA 49 

537.61/2; M8/2. Prepared by Schering AG. 20 p. 

94246039 Bruhl, R. (1990) Nor-Am Chemical Company Phase 3 Reformat of MRID 00064751. 

Thidiazuron: Metabolism of Thidiazuron in and on Cotton Plants: Lab Project ID: PA 

49 537.61/2; M9/2. Prepared by Schering AG. 17 p. 

94246040 Scheuermann, H. (1990) Nor-Am Chemical Company Phase 3 Reformat of MRID 

00039324. Residue Determination of SN 49 537 in Cotton Seed and Cotton Fiber 

(49537/1): Lab. Project ID: PA 49537.51/5; R1/2. Prepared by Schering AG. 19 p. 

94246041 Jenny, N. (1990) Nor-Am Chemical Company Phase 3 Reformat of MRID 00136323 

and Related MRIDs 00064747. Residues of Thidiazuron in Cotton Seed Following 

the Application of DROPP: R23-R35. Prepared by Nor-Am Agricultural Products, 

Inc. 113 p. 

94246042 Jenny, N. (1990) Nor-Am Chemical Company Phase 3 Reformat of MRID 00136323. 

Residues of Thidiazuron in Cotton By-Products Following the Application of 

60 
DROPP. Prepared by Nor-Am Agricultural Products, Inc. 111 p. 

61 
Appendix E. Generic Data Call-In 

62 
Appendix E. 

The generic data call-in will be posted at a later date. 

63 
Appendix F. Product Specific Data Call-In 

64 
Appendix F. 

The product specific data call-in will be posted at a later date. 

65 
Appendix G: Batching 

EPA'S BATCHING OF THIDIAZURON PRODUCTS FOR MEETING ACUTE TOXICITY 

DATA REQUIREMENTS FOR REREGISTRATION 

In an effort to reduce the time, resources and number of animals needed to fulfill the 

acute toxicity data requirements for reregistration of products containing Thidiazuron as the 

active ingredient, the Agency has batched products which can be considered similar for purposes 

of acute toxicity. Factors considered in the sorting process include each product's active and inert 

ingredients (identity, percent composition and biological activity), type of formulation (e.g., 

emulsifiable concentrate, aerosol, wettable powder, granular, etc.), and labeling (e.g., signal 

word, use classification, precautionary labeling, etc.). Note that the Agency is not describing 

batched products as "substantially similar" since some products within a batch may not be 

considered chemically similar or have identical use patterns. 

Using available information, batching has been accomplished by the process described in 

the preceding paragraph. Notwithstanding the batching process, the Agency reserves the right to 

require, at any time, acute toxicity data for an individual product should the need arise. 

Registrants of products within a batch may choose to cooperatively generate, submit or 

cite a single battery of six acute toxicological studies to represent all the products within that 

batch. It is the registrants' option to participate in the process with all other registrants, only 

some of the other registrants, or only their own products within a batch, or to generate all the 

required acute toxicological studies for each of their own products. If a registrant chooses to 

generate the data for a batch, he/she must use one of the products within the batch as the test 

material. If a registrant chooses to rely upon previously submitted acute toxicity data, he/she 

may do so provided that the data base is complete and valid by today's standards (see acceptance 

criteria attached), the formulation tested is considered by EPA to be similar for acute toxicity, 

and the formulation has not been significantly altered since submission and acceptance of the 

acute toxicity data. Regardless of whether new data is generated or existing data is referenced, 

registrants must clearly identify the test material by EPA Registration Number. If more than one 

confidential statement of formula (CSF) exists for a product, the registrant must indicate the 

formulation actually tested by identifying the corresponding CSF. 

In deciding how to meet the product specific data requirements, registrants must follow 

the directions given in the Data Call-In Notice and its attachments appended to the RED. The 

DCI Notice contains two response forms which are to be completed and submitted to the Agency 

within 90 days of receipt. The first form, "Data Call-In Response," asks whether the registrant 

will meet the data requirements for each product. The second form, "Requirements Status and 

Registrant's Response," lists the product specific data required for each product, including the 

standard six acute toxicity tests. A registrant who wishes to participate in a batch must decide 

whether he/she will provide the data or depend on someone else to do so. If a registrant supplies 

the data to support a batch of products, he/she must select one of the following options: 

Developing Data (Option 1), Submitting an Existing Study (Option 4), Upgrading an Existing 

66 
Study (Option 5) or Citing an Existing Study (Option 6). If a registrant depends on another's 

data, he/she must choose among: Cost Sharing (Option 2), Offers to Cost Share (Option 3) or 

Citing an Existing Study (Option 6). If a registrant does not want to participate in a batch, the 

choices are Options 1, 4, 5 or 6. However, a registrant should know that choosing not to 

participate in a batch does not preclude other registrants in the batch from citing his/her studies 

and offering to cost share (Option 3) those studies. 

Eighteen products were found which contain Thidiazuron as an active ingredient. These 

products have been placed into four batches and a no batch group in accordance with the active 

and inert ingredients and type of formulation. Furthermore, recent decisions by the OPP 

Registration Division were used to develop this batching approach. 

Batch # EPA Reg. No. Percent Active Ingredient 

1 51036-402 98.3 

72167-28 98.0 

73631-4 97.0 

2 264-622 50.0 

34704-859 50.0 

51036-401 50.0 

72167-30 50.0 

73631-3 50.0 

3 264-700 41.0 

34704-871 42.4 

51036-430 42.4 

4 264-634 12.0 

34704-872 12.0 

51036-429 12.0 

72167-47 12.0 

No Batch 400-505 8.4 

264-821 30.3 

264-661 50.0 

Appendix H. List of Registrants Sent This Data Call-In 

67 
United States Environmental Protection Agency 

Washington, D.C. 20460 

LIST OF ALL REGISTRANTS SENT THIS DATA CALL-IN NOTICE 

Case # and Name: 4092, Thidiazuron 

Co. 

Number 

Company Name Agent for Address City and State 

264 BAYER 

CROPSCIECNCE CROMPTON MANUFACTURING COMPANY, INC. LOVELAND PRODUCTS, INC. MICRO-FLO COMPANY LLC NATIONS AG II, LLC SRM CHEMICAL, LTD. CO. 

2 T.W. Alexander Drive 

74 Amity Road P.O. Box 1286 530 Oak Court Drive 4680 Monticello Avenue, 181-174 1436 Second Street, Suite 331 

Research Triangle Park Bethany Greeley Memphis Williamsburg NAPA 

400 34704 51036 72167 73631 

68 
Appendix I. List of Available Related Documents and Electronically Available Forms 

Pesticide Registration Forms are available at the following EPA internet site: 

 http://www.epa.gov/opprd001/forms/. 

Pesticide Registration Forms (These forms are in PDF format and require the Acrobat reader) 

Instructions 

1. Print out and complete the forms. (Note: Form numbers that are bolded can be 

filled out on your computer then printed.) 

2. The completed form(s) should be submitted in hardcopy in accord with the 

existing policy. 

3. Mail the forms, along with any additional documents necessary to comply with 

EPA regulations covering your request, to the address below for the Document 

Processing Desk. 

DO NOT fax or e-mail any form containing 'Confidential Business Information' or 'Sensitive 

Information.' 

If you have any problems accessing these forms, please contact Nicole Williams at (703) 308­

5551 or by e-mail at williams.nicole@epamail.epa.gov. 

The following Agency Pesticide Registration Forms are currently available via the internet: 

at the following locations: 

8570-1 Application for Pesticide 

Registration/Amendment 

http://www.epa.gov/opprd001/forms/8570-1.pdf. 

8570-4 Confidential Statement of Formula http://www.epa.gov/opprd001/forms/8570-4.pdf. 

8570-5 Notice of Supplemental Registration of 

Distribution of a Registered Pesticide 

Product 

http://www.epa.gov/opprd001/forms/8570-5.pdf. 

8570-17 Application for an Experimental Use Permit http://www.epa.gov/opprd001/forms/8570-17.pdf. 

8570-25 Application for/Notification of State 

Registration of a Pesticide To Meet a Special 

Local Need 

http://www.epa.gov/opprd001/forms/8570-25.pdf. 

8570-27 Formulator's Exemption Statement http://www.epa.gov/opprd001/forms/8570-27.pdf. 

8570-28 Certification of Compliance with Data Gap 

Procedures 

http://www.epa.gov/opprd001/forms/8570-28.pdf. 

8570-30 Pesticide Registration Maintenance Fee 

Filing 

http://www.epa.gov/opprd001/forms/8570-30.pdf. 

8570-32 Certification of Attempt to Enter into an 

Agreement with other Registrants for 

Development of Data 

http://www.epa.gov/opprd001/forms/8570-32.pdf. 

69 
8570-34 Certification with Respect to Citations of 

Data (in PR Notice 98-5) 

http://www.epa.gov/opppmsd1/PR_Notices/pr98-5.pdf. 

8570-35 Data Matrix (in PR Notice 98-5) http://www.epa.gov/opppmsd1/PR_Notices/pr98-5.pdf. 

8570-36 Summary of the Physical/Chemical 

Properties (in PR Notice 98-1) 

http://www.epa.gov/opppmsd1/PR_Notices/pr98-1.pdf. 

8570-37 Self-Certification Statement for the 

Physical/Chemical Properties (in PR Notice 

98-1) 

http://www.epa.gov/opppmsd1/PR_Notices/pr98-1.pdf. 

Pesticide Registration Kit www.epa.gov/pesticides/registrationkit/. 

Dear Registrant: 

For your convenience, we have assembled an online registration kit which contains the 

following pertinent forms and information needed to register a pesticide product with the U.S. 

Environmental Protection Agency's Office of Pesticide Programs (OPP): 

1. The Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) and the Federal 

Food, Drug and Cosmetic Act (FFDCA) as Amended by the Food Quality 

Protection Act (FQPA) of 1996. 

2. Pesticide Registration (PR) Notices 

a. 83-3 Label Improvement Program--Storage and Disposal Statements 

b. 84-1 Clarification of Label Improvement Program 

c. 86-5 Standard Format for Data Submitted under FIFRA 

d. 87-1 Label Improvement Program for Pesticides Applied through 

Irrigation Systems (Chemigation) 

e. 87-6 Inert Ingredients in Pesticide Products Policy Statement 

f. 90-1 Inert Ingredients in Pesticide Products; Revised Policy Statement 

g. 95-2 Notifications, Non-notifications, and Minor Formulation 

Amendments 

h. 98-1 Self Certification of Product Chemistry Data with Attachments (This

document is in PDF format and requires the Acrobat reader.) 

Other PR Notices can be found at http://www.epa.gov/opppmsd1/PR_Notices. 

3. Pesticide Product Registration Application Forms (These forms are in PDF format 

and will require the Acrobat reader.) 

a. EPA Form No. 8570-1, Application for Pesticide Registration/Amendment 

70 
b. EPA Form No. 8570-4, Confidential Statement of Formula 

c. EPA Form No. 8570-27, Formulator's Exemption Statement 

d. EPA Form No. 8570-34, Certification with Respect to Citations of Data 

e. EPA Form No. 8570-35, Data Matrix 

4. General Pesticide Information (Some of these forms are in PDF format and will 

require the Acrobat reader.) 

a. Registration Division Personnel Contact List 

I. b. Biopesticides and Pollution Prevention Division (BPPD) Contacts 

c. Antimicrobials Division Organizational Structure/Contact List 

d. 53 F.R. 15952, Pesticide Registration Procedures; Pesticide Data

Requirements (PDF format) 

e. 40 CFR Part 156, Labeling Requirements for Pesticides and Devices (PDF 

format) 

f.. 40 CFR Part 158, Data Requirements for Registration (PDF format) 

g.. 50 F.R. 48833, Disclosure of Reviews of Pesticide Data (November 27, 

1985) 

Before submitting your application for registration, you may wish to consult some 

additional sources of information. These include: 

1. The Office of Pesticide Programs' Web Site 

2. The booklet "General Information on Applying for Registration of Pesticides in 

the United States", PB92-221811, available through the National Technical 

Information Service (NTIS) at the following address: 

National Technical Information Service (NTIS) 

 5285 Port Royal Road 

 Springfield, VA 22161 

The telephone number for NTIS is (703) 605-6000. 

3. The National Pesticide Information Retrieval System (NPIRS) of Purdue 

University's Center for Environmental and Regulatory Information Systems. This 

service does charge a fee for subscriptions and custom searches. You can contact 

NPIRS by telephone at (765) 494-6614 or through their Web site. 

4. The National Pesticide Telecommunications Network (NPTN) can provide 

information on active ingredients, uses, toxicology, and chemistry of pesticides. 

71 
You can contact NPTN by telephone at (800) 858-7378 or through their Web site: 

ace.orst.edu/info/nptn. 

The Agency will return a notice of receipt of an application for registration or 

amended registration, experimental use permit, or amendment to a petition if the 

applicant or petitioner encloses with his submission a stamped, self-addressed 

postcard. The postcard must contain the following entries to be completed by 

OPP: 

• Date of receipt; 

• EPA identifying number; and 

• Product Manager assignment. 

Other identifying information may be included by the applicant to link the 

acknowledgment of receipt to the specific application submitted. EPA will stamp 

the date of receipt and provide the EPA identifying File Symbol or petition 

number for the new submission. The identifying number should be used whenever 

you contact the Agency concerning an application for registration, experimental 

use permit, or tolerance petition. 

To assist us in ensuring that all data you have submitted for the chemical are 

properly coded and assigned to your company, please include a list of all 

synonyms, common and trade names, company experimental codes, and other 

names which identify the chemical (including "blind" codes used when a sample 

was submitted for testing by commercial or academic facilities). Please provide a 

chemical abstract system (CAS) number if one has been assigned. 

Documents Associated with this RED 

The following documents are part of the Administrative Record for this RED document 

and may be included in the EPA's Office of Pesticide Programs Public Docket. Copies of these 

documents are not available electronically, but may be obtained by contacting the person listed 

on the respective Chemical Status Sheet. 

1. Health Effects Division and Environmental Fate and Effects Division Science 

Chapters, which include the complete risk assessments and supporting documents. 

2. Detailed Label Usage Information System (LUIS) Report. 

72