### Thidiazuron Human Health Risk Assessment DP No. 0424978

UNITED STATES ENV IRONMENTAL PROTECTION AGENCY

WASH I NGTON, O.C. 20460

M E MORAND U M

D ate : June 9

, 2015 OFFICE OF
CHEMICAL SAFETY AND
POLLUTION PREVENTION

SU BJE CT: Thidiazuron: Human Health Comb in ed Scoping Document and Draft Risk

Assessment for Registration Review. D424978.

P C Co de : 12030 I

Dec i s i o n No.: 498947

Petition No.: NA

Ri s k As sess ment T y p e : Sing l e Chemical
Aggregate

TX R No.: NA

MRI D No.: NA DP Barcode: 0424978

R eg i s trati o n No

. : NA

R eg ul a tory Act ion : Registratio n R eview

Case No .: 4092

CAS No. : 51707-55-2

40 CFR: § 180.412

FROM : Ronnie J. Bever Jr

., PhD, DABT ; Risk

# Asse~or/ j

# ·**~** 

# ;

. ld e liz Negr6n

- Encarnac i 6n, PhD

, Chemist**!() ~**  Alexandra Gavelek, Biologist .; 

## I**,,CJ~** L 

## 0_ Ct

Ri sk Assessment Branch es V and V II (RAB V N II )

Health Effects Div i s i on ( I IED; 7509 P )

THROU G H : Michael S. Metzge r
, Chief

, RAB VNII 

# r. 

# I ;J /} ). 

# /Id

HED (7509 P ) 

# f(**tlft-~** 

# '

T O: Khue Nguyen/Thomas Moriarty

, Ri sk Manager

Risk Management and Impl ementation Branch J

Pe stic ide Re-evaluation Division

Page l of SSThidiazuron Human Health Ri sk Assessment DP No. D424978

Tab l e of Co ntent s

1. 0 Execut i ve Sum1nary

.... ................. ... ..... .. ........... ... ..... ... .......... ..... ... . ..................................... 4

2.0 HED Recom1nendations

.............................. ... .................. ... ................................................. 6

2 .1 Data Deficiencies / Cond iti ons of R eg i stra tion and Re-Re g istration

................................. 6

2.2 Toleranc e Considerations

............... . ....... . ............ ... ..... ..................................................... 7

2.2.1 Enforcement Analyt i cal Method

............................................................................... 7

2.2.2 Recommended Tolerances

........................................................................................ 7

2.2.3 In terna ti onal Harmonization

..................................................................................... 9

2

. 3 Labe l R ecommendat ions

.................................................................................................. 9

2.3 .1 Recommendations from Residue Reviews

............................................................... 9

2.3.2 Recommendations from Occupational Assessment.

................. .... ............................ 9

3.0 Introduction

.......................................................................................................................... 9

3.1 C h en1ical Id entity

........ ...... .. .. ..... ... .. ...... .. ... ..... ... . ........... ..... . ............................................ 9

3

. 2 Phy s ical/ C hemic al Characteristics

................................................................................. I 0

3

. 3 P est i cide Use Pattern

...................................................................................................... 10

3.4 Anticipated Exposure Pathways

.............................................................................. .. .. ... l 0

3 .5 Considera tion of Environmental Ju st ice

........................................................................ 10

4.0 Ha zard C haract erizat ion and Dose-Response Assessment..

.............................................. 1 l

4 .1 Toxicology Studies Available for Analysis

................................................................... 11

4.2 Absorption

, Distribution

, Metabolism

, & Elimination (ADME)

................................... l l

4.2.1 D

. ennal Absorption

.... . ....... .. .. ..... ... .......................................................................... 12

4.3 Toxicological Effec t s

..................................................................................................... 12

4.4 Safety Factor for Infants and Childre n (FQPA Safety Factor)

................ ..... ........ ... ....... 1 3

4.4.1 Completeness of the Toxi co lo gy Database

............................................................. 13

4.4.2 Ev id e nce of Neurotoxicity

...................... .. ...... ..................... .. ..... .......................... .. 14

4.4.3 Ev id ence of Sensit ivit y / Susceptibility in th e D eveloping or Young Animal

......... 14

4.4.4 Residual Uncertainty in the Exposure Database

..................................................... 14

4.5 Toxicity Endpoint and Point of Departure Selections

............................................. .. ........ 14

4.5 .1 Dose-Response Assessment

.................................................................................... 14

4.5.2 R econ un enda tion for Co mbining Rout es of Exposures for Risk Assessment.

.. ..... l 6

4.5.3 Cancer Classification a nd Risk Assessment Recommendation

.. ...... ......... ............. 16

4.5.4 Summary of Points of Departure and Toxicity En dpoint s

...................................... 16

4

. 6 Endocrine Disruption

.............................................................................. .. ..................... 17

5.0 Dietary Exposure and Ri sk Assessment

............................................................................ 18

5.1 Residues of Co nc ern S ummar y and Rationale

................. ....................................... 18

5.2 food Residue Profile

.. ... ................. ................................................................................ 19

5.3 Water Residue Profile

.......................................... .. ...... ... ........................ .. ..... .. .............. 20

5.4 Dietary Risk Assessment

................................................................................................ 20

5.4. l Description o[ Residue Data Used in Dietary Assessment..

................................... 20

Pa ge 2of55Thidiazuron Human Health Risk Assessment DP No. D424978

Page 3 of 55 5.4.2 Percent Crop Treated Used in Dietary Assessment

................................ ................ 20

5.4.3 Acute Dietary Risk Assessment

................................ ................................ .............. 20

5.4.4 Chronic Dietary Risk Assessment

................................ ................................ .......... 20

5.4.5 Cancer Dietary Risk Assessment

................................ ................................ ............ 20

5.4.6 Summary Table

................................ ................................ ................................ ....... 20

6.0 Residential (Non

- Occupational) Exposure/Risk Characterization

................................ .... 21

6.1 Residential Bystander Post

- application Inhalation Exposure

................................ ........ 21

6.2 Spray Drift

................................ ................................ ................................ ...................... 21

7.0 Aggregate Exposure/Risk Characterization

................................ ................................ ....... 23

7.1 Acute Aggregate Risk

................................ ................................ ................................ .... 23

7.2 Short

- Term Aggregate Risk

................................ ................................ ........................... 24

7.3 Intermediate

- and Long

- Term Aggregate Risk

................................ .............................. 24

7.4 Long

- Term Aggregate Risk

................................ ................................ ........................... 24

7.5 Cancer Aggregate Risk

................................ ................................ ................................ ... 24

8. 0 Cumulative Exposure/Risk Characterization

................................ ................................ ..... 24 9.0 Occupational Exposure/Risk Characterization

................................ ................................ ....... 24

9.1 Short

- /Intermediate

- Term Handler Risk

................................ ................................ ............. 24

9.2 Short

- /Intermediate

- Term Post

- Application Risk

................................ .......................... 26

9.2.1 Dermal Post

- Application Risk

................................ ................................ ....................... 26

9.2.2 Inhalation Post

- Application Risk

................................ ................................ ................... 26

10.0 Incident Report

................................ ................................ ................................ ............... 27

11.0 R eferences

................................ ................................ ................................ .......................... 29 Appendix A. Toxicology Profile and Executive Summaries

................................ ....................... 31

A.1 Toxicology Data Requirements

................................ ................................ ...................... 31

A.2 Toxicity Profiles

................................ ................................ ................................ ............. 32

A.3 Ha zard Identification and Endpoint Selection

................................ ............................... 36

A.4 Executive Summaries

................................ ................................ ................................ ..... 38 Appendix B. International Residue Limits Table

................................ ................................ ........ 53 Appendix C. Metabolites

................................ ................................ ................................ ............. 54 Appe ndix D. Physical/Chemical Properties

................................ ................................ ................. 54 Appendix E. Review of Human Research

................................ ................................ ................... 55Thidiazuron Human Health Risk Assessment DP No. D424978

Page 4 of 55 1.0 Executive Summary

As part of Registration Review, the Pesticide Re

- evaluation Division (PRD) of the O ffice of

P esticide P rogram (OPP) has requested that the Health Effects Divis ion ( HED ) evaluate the hazard and exposure data base and conduct dietary, and occupational and residential exposure assessments, as needed, to estimate the risk to human health that will result from the currently registered uses of thidiazuron . This memora ndum serves both as HED’s Draft Registration

Review risk assessment of the current ly registered uses of thidiazuron and obviates the need for a

separate scoping document.

Thidiazuron (

N

- phenyl

- N′

- 1,2,3

- thiadiazol

- 5

- ylurea ) is a phenylurea herbicide used for the defoliation of cotton. In cotton, thidiazuron defoliates green leaves and immature fruiting

structures. Thidiazuron can be applied by ground or air to late season cotton. The registered formulations include wettable powders (WP) in water

- soluble bags (WSB), soluble concentrates (SC), emulsifiable concentrates (EC), and liquids.

The chronic toxicity studies in rats and mice show that thidiazuron caused decreased body weights, body weight gains, and/or food consu mption; adverse effects on the kidney and male reproductive system were also noted. Similar effects were also noted in the subchronic rat study.

In the subchronic mouse study , only marginal effects were noted at the mid

- dose, whereas a ll

mice died at the hi gh dose. Anemia and marked hemosiderosis in liver and spleen were apparent in the chronic dog study.

The data from the develop m ental toxicity studies in rat suggested a quantitative susceptibility to fetuses. The only finding was a similar decrease in b ody weight in both dams and fetuses; however, the marginal effect in the fetus is a concern. There was no increased quantitative or qualitative susceptibility observed for rabbit fetuses, and the point of departure in the rabbit developmental study is prot ective for all effects noted in the rat developmental and reproduction studies. In the rabbit developmental study, maternal effects included abortions and decreased food consumption and body weight gain. Similarly, body weights were decreased in

the fetus es; more runts and delayed skeletal ossification were observed, in addition to the

abortions. Reproductive toxicity was conservatively set based on a delay of 3 days in vaginal opening; no adverse effects were noted on parental or offspring toxicity.

Dermal toxicity was not observed at the limit dose in a 28

- day dermal study in rats. Dermal absorption is extremely limited to 1% or less

. No definitive evidence of neurotoxicity was reported in any of the submitted studies. Carcinogenicity studies in bot h rats and m ice produced

no treat m ent

- related increase in tu m or incidence. The standard battery of genotoxicity tests was negative. The available toxicity data indicate the acute oral, der m al, inhalation, and pri m ary eye and der m al irritation toxicity of thidiazuron to be in toxicity categories III and IV. Thidiazuron is

not a der m al sensitizer n or a skin irritant.

Based on the toxicity, duration of exposure, and uses of thidiazuron , the following toxicity endpoints were selected:Thidiazuron Human Health Risk Assessment DP No. D424978

Page 5 of 55 Acute dietary ( all population s ): Not required

. Chronic dietary (all populations) : c hronic PAD (cPAD) = 0. 0393 mg/kg/day derived

from a NOAEL of 3.93 mg/kg/day in a chronic dog toxicity study. LOAEL = 11.1 mg/kg/day based on increased incidence of anemia, changes in hemato logical parameters and marked hemosiderosis in liver and spleen

. I ncidental oral exposures (short

- and intermediate

- term): NOAEL = 25 mg/kg/day in a developmental study in rabbit . LOAEL = 125 mg/kg/day based on abortions

. Dermal ( short

- and intermediate

- t erm): No point of departure was determined

, as a hazard was not identified. Inhalation (short

- and intermediate

- term): NOAEL = 25 mg/kg/day in a developmental study in rabbit. LOAEL = 125 mg/kg/day based on abortions

.

For the occupational and residential risk assessments

, the level of concern (LOC) is for MOEs less than 100. The FQPA safety factor has been reduced to 1X since the database is complete, concern for quantitative susceptibility is low due to the marginal endpoints of fetal toxicity (7% decrease in fetal body weight; 6% in dams) and 3

- day delay in vaginal opening, points of departure are protective in the fetus and offspring

, and exposure estimates are not likely to

underestimate risk.

The residue chemistry database for thid iazuron is incomplete but adequate to support registration

review

. Tolerances are established in the 40 CFR 180.403 for residues of thidiazuron in/on cotton and livestock commodities. The tolerance expression needs to be modified according to
the residue of concern definition, and the interim guidance for writing tolerance expressions. Adequate enforcement methods for plant and livestock commodities are available; however,

radio

- validation data for the tolerance enforcement method in livestock commoditie s was not submitted and is still required. Based on the results of storage stability studies

, the residue data

for thidiazuron was reevaluated. A tolerance of 0.5 ppm is recommended for cotton un

- delinted

seed

, 1.5 ppm for cotton hulls , and 30 ppm for cot ton gin byproducts . A reevaluation of the secondary residues of thidiazuron on livestock commodities show that the current tolerance levels are adequate. There are no Canadian , Mexican or Codex maximum residue limits ( MRLs ) established or proposed for re sidues of thidiazuron. Therefore, there are no issues regarding

international harmonization with established U.S. tolerances.

A revised dietary assessment was conducted. An acute dietary assessment was not performed, because a toxicological endpoint was not identified. The c hronic dieta ry exposure and risk

assessment were highly conservative, using tolerance levels residues and 100% of crop treated assumptions. The c hronic dietary (food and water) estimated risks were all well below HED’s

level of concern ( < 100% of the cPAD) for the U.S. population and all population subgroups. The highest exposure and risk estimates were for children 1 to 2 years old which occupied 9.3%

of the cPAD for thidiazuron.

There are no residential uses of thidiazuron. A spray drift assessment was completed . The spray drift risk estimates are based on an estimated deposited residue concentration

, as a result of the screening level agric ultural application scenarios. Children’s (1 to < 2 year old) incidental oralThidiazuron Human Health Risk Assessment DP No. D424978

Page 6 of 5 5 risk estimates from indirect exposure to thidiazuron, related to spray drift, result in no buffers for any application scenario, including ground boom or aerial applications. Ris k estimates from ground boom and aerial applications are not of concern at the field edge for all situations

considered.

HED conducted occupational handler exposure and risk assessments for all registered uses.

Short

- and intermediate

- term MOEs for h andlers were not of concern to HED , because they exceeded the target MOE of 100. Inhalation MOEs for the occupational handler assessment range from 30,000 to 1,500,000. As quantitation of dermal risk assessment is not required ; a quantitative occupationa l post

- application risk assessment was not performed since only dermal exposures are expected, and no dermal hazard was identified for thidiazuron

.

This risk assessment relies in part on data from studies in which adult human subjects were intentionally exposed to a pesticide to determine their exposure. Appendix E provides additional information on the review of human research used to complete the risk assessment. There is no regulatory barrier to continued reliance on these studies, and all applicable requirements of EPA’s Rule for the Protection of Human Subjects of Research (40 CFR Part 26) have been

satisfied.

2.0 HED Recommendations

HED did not identify any risks of concern related to current uses of thidiazuron

.

The data needs are specified in section 2.1, and t olerance recommendations in section 2.2

. Phenylurea and 4

- hydroxy

- thidiazuron reference standards are not available at the EPA National

Pest icide Standards Repository. The s e standards need to be sent by the registrant. Please, refer

to section 5.1.4 for instructions.

2.1 Data Deficiencies/Conditions of Registration and Re

- Registration

The toxicity and ORE exposure data bases are considered complete. Although HED would typically require dislodgeable foliar residue (DFR) studies based on the existing use pattern, no studies are required , because no quantitation of dermal risk is required for thidiazuron.

The residue chemistry database for thidiazuron is incomplete but adequate to support registration

review. R adio

- validation data for the tolerance enforcement method ( TU

- 002

- A06

- 01 ) in livestock commodities was not submitted and is required. This data is necessary because the livestock metabolism study was performed following a different extraction procedure than that

used in the analytical method for livestock.Thidiazuron Human Health Risk Assessment DP No. D424978

Page 7 of 55 2.2 Tolerance Considerations

2.2.1 Enforcement Analytical Method

Plants: Analytical methods are available for enforcing tolerances in plant commodities. The Pesticide Analytical Manual, Volume II lists Methods I an d A. Method I is no longer recommended for enforcement on plant commodities. Method A is a reverse

- phase HPLC with

UV detection

, which determines parent thidiazuron

, and is recommended for tolerance enforcement. Additionally, a method that determines par ent thidiazuron in cotton un

- delinted seed and gin trash by HPLC with UV detection is available for enforcement (AW

- 94R

- 08).

Livestock: Method TU

- 002

- A06

- 01 is available for the determination of residues of thidiazuron,

4

- hydroxy

- thiadiazuron

, and pheny lurea in bovine kidney, muscle, liver, fat, and milk. Briefly,

thid iazuron, 4

- hydroxy

- thiadiazuron and phenylurea residues are extracted from bovine tissues

and milk with acetonitrile

, and from fat with a mixture of hexane and acetonitrile. After

extract ion, a mixture of isotopically labeled internal standards is added to the extract. The extracts are filtered, diluted or further separated, and concentrated. The samples are analyzed via liquid chromatography/mass spectroscopy/mass spectroscopy (LC

- MS/MS ) with electrospray ionization. Primary and confirmatory transition ions were monitored for each analyte. The validated limit of quantitation (LOQ) for each analyte is 0.05 ppm in bovine tissues and 0.01 ppm in bovine milk.

2.2. 2 Recommended Tol erances

Tolerances are established in the 40 CFR 180.403 for residues of thidiazuron in/on cotton and

livestock commodities. Based on the evaluation of the residue data received the following changes to the tolerance levels are recommended:

Table 2.2.1 . Tolerance Summary for Thidiazuron

. Commodity Established Tolerance (ppm) HED

- Recommended

Tolerance (ppm) Comments

( correct commodity definition )
Cotton, undelinted seed 0.3 0.5
Cotton, hulls None 1.5 Cotton, gin byproducts 24.0 30 OECD rounding procedures

The tolerance expression needs to be modified according to the interim guidance for writing tolerance expressions, and the residues of concern need to be modified according to the

recommendations of the 2005 RED and the Metabolism Assessment Review Committee (MARC). The residues of concern to be included are parent thidiazuron for plants and parent thidiazuron, 4

- hydroxy thidiazuron, and phenylurea for livestock co mmodities. Consequently

, two sections are needed in the CFR, one for tolerances for cotton commodities and the other for

livestock commodities as described below.Thidiazuron Human Health Risk Assessment DP No. D424978

Page 8 of 55 (a) General. (1) Tolerances are established for residues of the defoliant thidiazuron , incl uding its metabolites and degradates, in or on the commodities in the table in this paragraph. Compliance with the tolerance levels specified in this paragraph is to be determined by measuring only thidiazuron, N

- phenyl

- N

- 1,2,3

- thiadiazol

- 5

- ylurea, in or o n the commodity.

Commodity Parts per million

Cotton, gin byproducts 30

Cotton, undelinted seed 0.5

Cotton, hulls 1.5

(a) General. (2) Tolerances are established for residues of the defoliant thidiazuron , including its metabolites and degradates, in or on the commodities in the table in this paragraph. Compliance with the tolerance levels specified in this paragraph is to be determined by measuring thidiazuron ( N

- phenyl

- N

- 1,2,3

- thiadiazol

- 5

- ylurea), 4

- hyd roxy thidiazuron ( N

- (4

- Hydroxyphenyl)

- N ’

- 1,2,3

- thiadiazol

- 5

- ylurea ), and phenylurea in or on the commodity.

Commodity Parts per million

Cattle, fat 0.4

Cattle, meat 0.4

Cattle, meat byproducts 0.4

Goat, fat 0.4

Goat, meat 0.4

Goat, meat byproducts 0.4

Hog, fat 0.4

Hog, meat 0.4

Hog, meat byproducts 0.4

Horse, fat 0.4

Horse, meat 0.4

Horse, meat byproducts 0.4

Milk 0.05

Sheep, fat 0.4

Sheep, meat 0.4

Sheep, meat byproducts 0.4Thidiazuron Human Health Risk Assessment DP No. D424978

Page 9 of 55 2.2. 3 International Harmonization

No Canadian , Mexican or Codex maximum residue limits (MRLs) are established or proposed for residues of thidiazuron. Therefore, there are no issues regarding international harmonization

with the established U.S. tolerances. The International Residue Limits (IRL) table is include d in Appendix B.

2.3 Label Recommendations

There are no label recommendations at this time.

2.3.1 Recommendations from Residue Reviews

None.

2.3.2 Recommendations from Occupational Assessment

No revisions to the labels are required.

3.0 In troduction

Thidiazuron is a phenylurea herbicide used for the defoliation of cotton. In cotton, thidiazuron defoliates green leaves and immature fruiting structures.

3 .1 Chemical Identity

The structure and chemical identi t y for thidiazuron are shown in Table 3.1. The structures for metabolites discussed in this risk assessment are shown in Appendix C

.

TABLE 3.1. Thidiazuron Nomenclature.
Compound Chemical Structure

Common Name Thidiazuron

Trade and other Names DROPP

, FreeFall, Ginstar

, Leafless

IUPAC Name 1

- phenyl

- 3

- (1,2,3

- thidiazol

- 5

- yl)urea

CAS Name N

- phenyl

- N 

- 1,2,3

- thidiazol

- 5

- ylurea CAS Registry Number 51707

- 55

- 2

End

- Use Product (EP) Not applicabl eThidiazuron Human Health Risk Assessment DP No. D424978

Page 10 of 55 3.2 Physical/Chemical Characteristics

Thidiazuron is readily soluble in water and is not volatile. It has a low octanol/water p artition

coefficient ; therefore, it is not likely to bioaccumulate

. The physical and chemical properties are detailed in Appendix D.

3.3 Pesticide Use Pattern

Thidiazuron can be applied by ground or air to late season cotton. The registered formulations include wettable powders (WP) in water

- soluble bags (WSB), soluble concentrates (SC), emulsifiable concentrates (EC), and liquids. The maximum single applicati on rate is 0.2 lb

ai/acre

, and the maximum seasonal application rate is 0.3 lb ai/A per year. Rotational crop

restrictions are included in the label. Plant back intervals (PBI) are similar or longer than those required based on rotational studies, i.e. 2 weeks for small grain crops and 1 month for root and leafy vegetable . There are no res idential uses of thidiazuron.

3.4 Anticipated Exposure Pathways

Thidiazuron is use d as a defoliant on cotton

. Exposure to thidiazuron may occur from ingestion

of residues on foods and in drinking water and via the dermal and inhalation routes for adults using thidiazuron products in occupational settings. In addition, both adults and children may be exposed orally and /or dermally due to spray drift . There is a potential for post

- application dermal exposure for workers re

- entering treated fields.

3.5 Consideration of Environmental Justice

Potential areas of environmental justice concerns, to the extent possible, were considered in t his human health risk assessment, in accordance with U.S. Executive Order 12898, "Federal Actions to Address Environmental Justice in Minority Populations and Low

- Income Populations," ( http://www.eh.doe.gov/oepa/guidance/justice/eo12898.pdf

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

, according to well

- established procedures. In line with OPP policy, HED estimates risks to populat ion subgroups from pesticide exposures that are based on patterns of that subgro up’s food and water consumption and activities in and around the home that involve pesticide use in a residential setting.

Extensive data on food co nsumption patterns are comp iled by the USDA under the Continuing Survey of Food Intake by Individuals (CSFII) and/or the CDC under the National Health and Nutrition Examination Survey/What W e Eat in America (NHANES/WWEIA) and are used in pesticide risk assessments for all registered food uses of a pesticide. These data are analyzed and categorized by subgroups based on age, season of the year, ethnic group, and region of the country. Additionally, OPP is able to assess dietary exposure to smaller, specialized subgroups

, and exposur e assessments are performed when conditions or circumstances warrant. Whenever appropriate, non

- dietary exposures are evaluated based on home use of pesticide products and associated risks for adult applicators and for toddlers, youths, and adults enterin g or playing on

treated areas post

- application . Further considerations are currently in development as OPP hasThidiazuron Human Health Risk Assessment DP No. D424978

Page 11 of 55 committed resources and expertise to the development of specialized software and models that consider exposure to bystanders and farm workers

, a s well as lifestyle and traditional dietary patterns among specific subgroups.

4.0 Hazard Characterization and Dose

- Response Assessment

4.1 Toxicology Studies Available for Analysis

The toxicology database for thidiazuron provides a robust characterization of the hazard potential of this pesticide. The toxicology studies for thidiazuron are summarized in Table A.1 in Appendix A.1. There are studies available for toxicity endpoint selection , which include:

S ubchronic ora l toxicity studies in rats and mice

C hronic oral toxicity studies in rats , mice, and dogs

C arcinogenicity studies in rats and mice

M utagenicity battery

D evelopmental studies in rats and rabbits

R eproduction stud y in rats Dermal toxicity study in rats Metabolism study in rats

Hazard and Science Policy Council (HASPOC) determined that immunotoxicity ( Habiba , 201 3

, TXR# 005 6795 ), 90

- day inhalation, acute neurotoxicity, and subchronic neurotoxicity studies ( Habiba, 2015, TXR# 0057116 ) were not needed for the risk assessment of thidiazuron

. The

studies available for consideration of thidiazuron toxicity provide a comprehensive database, with routes of administration that are consistent with potential exposure scenarios.

4.2 Absorption, Distribution, Metabolism, & Elimination (ADME)

In the metabolism study, thidiazuron was administered in dimethyl sulfoxide at a single oral gavage dose (10 or 1000 mg/kg)

. Additionally , thidiazuron was administered by gavage in daily

doses at 10 mg/kg for 14 days followed by a single oral dose of 14 C

- thidiazuron at 10 mg/kg

. Absorption (considered the sum of residues in the urine, cage wash, and carcass) occurred predominantly within 24 hours at 10 mg/kg (single or repeated dosing) and within 48 hours at 1000 mg/k g. Absorption was 61

- 68% of the administered dose (AD) after a single 10 mg/kg

dose , slightly higher after repeated 10 mg/kg doses ( 74

- 76% AD ), but only 41

- 48% AD after 1000 mg/kg. After a single 10 mg/kg dose, urinary excretion accounted for 59

- 74 % AD , a nd

fecal excretion accounted for 2 6

- 31% AD (single and repeated)

. Compared to the low dose, a fter a single 1000 mg/kg dose, uri nary excretion decreased to 40

- 47% AD , and fecal excretion

increased to 56

- 60% AD . Approximately 0.1% AD or less was found in t he expired air. At 120 hours post

- dose, <2% AD remained in the body, and the highest concentration was found in the thyroid. Concentrations were also sometimes higher than in whole blood in the female kidney

and in male and female ad renal glands. A negligi ble amount of the parent was isolated in theThidiazuron Human Health Risk Assessment DP No. D424978

Page 12 of 55 excreta. The primary metabolites were 4

- hydroxy thidiazuron and 3 different conjugates of

4

- hydroxy thidiazuron.

4.2.1 Dermal Absorption

A dermal absorption study is available for thidiazuron, which identified a dermal absorption
factor of ≤1%. Q uantification of dermal risk is not required, as discussed in Section 4.5.1 (Dose

Response Assessment).

4.3 Toxicological Effects

Th e mode of action for thidiazuron in animals is unknown

. Both subchronic and chronic toxicity

studies in rats show that thidiazuron causes decreased body weights, body weight gains, and /or

food consu m

ption ; adverse effects on the kidney and seminal vesicles are also noted

. Findings in the kidney included glo m erular m ineralization , bilateral hyperplasia of the pelvic epithelium,

m ineralized concretions of the renal pelvis, focal m ononuclear cell infla mm ation, renal collecting

duct hyperplasia, papillary m ineralization

, f ocal m ineralization of the inner m edulla,

suburothelial congestion

, bilateral pelvic dilatation

, chronic progressive nephropathy

, urothelial

m ineralization

, and increased relative weight

. Seminal vesicles are described as small or atrophied with decreased secretions. The prostate gland was also small in the subchronic rat study. In the mouse , only marginal effects were noted at the mid

- dose in the subchronic study, whereas all mice died at the high dose. In the chronic mouse study

, as with the rat, decreased body weights, body weight gains

, and food consu m ption were observed, in conjunction with nephrotoxicity. Additionally, epididymis toxicity was observed as indicated by dilated tubules, interstitial mononuclear cell infiltrate, unilateral and bilateral oligospermia, and spermatic granul oma . Anemia and marked hemosiderosis in liver and spleen was apparent in the chronic dog study.

The data from the develop m ental toxicity studies in rat suggested a quantitative susceptibility to

fetuses. The only finding was a similar decrease in body weight in both dams (↓6%) and fetuses (↓7%) ; however

, the marginal effect in fetuses is of concern . There was no increased quantitative or qualitative susceptibility observed for rabbit fetuses, and the poin t of departure in the rabbit developmental study is protective for all effects noted in the rat developmental and reproduction studies. In the rabbit developmental study, m aternal effects included abortions. Similarly, body weights were decreased in the f etuses ; more runts and delayed skeletal ossification were observed, in addition to the abortions. Reproductive toxicity was conservatively set based on a delay of 3 days in vaginal opening; no adverse effects were noted on parental or offspring toxicity. N o adverse effect was noted on parents or reproduction

parameters.

Dermal toxicity was not observed at the limit dose in a 2 8

- day dermal study in rats. Dermal absorption is extremely limited , as detailed above

. No definitive evidence of neurotoxicity was reported in any of the submitted studies. Acute and subchronic neurotoxicity studies , as well as an inhalation toxicity study, were not submitted

, but the requirement for these studies was waivedThidiazuron Human Health Risk Assessment DP No. D424978

Page 13 of 55 by HAPSOC ( Habiba, 2015, TXR# 0057116 )

. Carcinogenicity studies in both rats and m ice produced no treat m ent

- related increase in tu m or incidence. The standard battery of genotoxicity

tests was negative.

The available toxicity data indicate the acute oral, der m al, inhalation, and pri m ary eye and

der m al irritation toxicity of thidiazuron to be in toxicity categories III and IV. Thidiazuron is

not a der m al sensitizer n or a skin irritant.

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

HED recommends that the 10X FQPA Safety Factor (for the protection of infants and children) be reduced to 1X. An FQPA Safety Factor of 1X is appropriate for the following reasons:

 The toxicological database for thidiazuron is complete under the new 40 CFR Part 158 data requirements for conventional pest icides.

 There is evidence of increased susceptibil ity/sensitivity in rats to pre natal exposure to
thidiazuron . However, the concern is low based on clear no observed adverse effect (NOAEL) levels for the findings that are greater than the chosen points of departure.

 There was no conclusive evidence of neurotoxicity or neuropathology in the available

studies. The acute and subchronic neurotoxicity study requirements have been waived.

 The exposure assessment will not underestimate children’s exposure to thi diazuron

.

Further details may be found in the following sections.

4.4.1 Completeness o f the Toxicology Database

The database of toxicology studies for thidiazuron is complete and considered adequate for risk

assessment (see Appendix A.1) . D evelopmental toxicity studies in rats and rabbits and a reproductive toxicity stud y in rats are available. Waivers were granted by HED’s HASPOC for

the acute and subchronic neurotoxicity studies ( Habiba, 2015, TXR# 0057116 ) and immunotoxicity study ( Habib a , 2013, TXR# 0056795)

.

4.4.2 Evidence of N eurotoxicity

There is no conclusive evidence of neurotoxicity or neuropathology in the available studies. In a mouse carcinogenicity study (MRID 46346001), tremors were observed at 280/330 mg/kg/day (M/F) in 3/120 animals in the presence of numerous other indications of systemic toxicity. Additionally in the combined chronic toxicity and carcinogenicity study (MRID 46345201), decreased motor activity was observed as a clinical sign in the 76 mg/kg/day male rat s (22/59) compared to controls (6/59); however, only 13% of these animals survived 24 months. No other evidence of neurotoxicity was found in the database . T herefore, the tremors and motor activity findings were considered unlikely to be frank neurotoxic effects , but were more likely the resultThidiazuron Human Health Risk Assessment DP No. D424978

Page 14 of 55 of the general systemic toxicity of the pesticide . Without any evidence of neurotoxicity in the toxicity database, there is not a concern for developmental neurotoxicity

.

4.4.3 Evidence o f Sensitivity/Su sceptibilit y in the Developing o r Young Animal

There is evidence of increased susceptibility following in utero exposure to thidiazuron in the rabbit developmental toxicity study. However, there is low concern because clear NOAELs were defined for these effects, and the chosen points of departure for risk assessment for each exposure scenario are protective for these effects

.

4.4.4 Residual Uncertainty in the Exposure Datab ase

There are no residual uncertainties in th e exposure database. The dietary exposure estimates

were based on tolerance

- level residue s and 100% of crop treated assumption . U pper

- bound drinking water estimates based on modeling were used which are conservativ e assumptions ( see Section 5.4 ) . HED is confident that the dietary risk is not underestimated. Additionally, HED

does not believe that non

- occupational exposure and risk estimates are underestimated. The assumptions are detailed in Section 6.0.

4.5 Toxicity Endpoint and Point of D eparture Se lections

4.5.1 Dose

- Response Assessment

There have been no changes since the last risk assessment to the dose

- response assessment, endpoint selection

, or cancer classification, except for revisions to the executive summaries of

the rat developmental and reproduction studies. The studies selected for risk assessment for each exposure scenario represent the lowest point s of departure in the database and as such are protective for any other effects observed for the exposure scenario. T he detailed description of the toxicity studies used for selecting toxicity endpoints and points of departure for various exposure scenarios are presented in A ppendix A.4.

Acute Dietary Endpoint ( All Population s ) : A dose and endpoint were not selected fo r this population group, because there were no effects observed in the available toxicology studies that could be attributed to a single exposure (dose).

Chronic Dietary Endpoint (All Populations) : The chronic dietary endpoint was from a dog chronic toxicity study. The chronic PAD (c PAD ) of 0. 0393 mg/kg/day is based on a NOAEL of

3.93 mg/kg/day with a 100

- fold uncertainty factor (10X interspecies and 10X intraspecies) applied and an FQPA SF of 1 . At the study LOAEL of 11.1 mg/kg, increased incidence of anemia, changes in hematological parameters, and marked hemosiderosis in liver and spleen

were observed.

Short

- and Intermediate

- Term Incidental Oral: T he dose and endpoint selected for short

- and

intermediate

- term incidental oral exposure was from a ra bbi t developmental study . The maternalThidiazuron Human Health Risk Assessment DP No. D424978

Page 15 of 55 NOAEL of 25 mg/kg/day and maternal LOAEL of 125 mg/kg/day were chosen based on based on 5 abortions occurring at GD 27

- 29

. This endpoint is the most sensitive effect identified for the short and intermediate term exposure and is protective for offspring effects seen in the reproduction study (NOAEL = 35.4 mg/kg/day). The standard 100X UF was applied to account for interspecies extrapolation and intraspecies variation. A margin of exposure (MOE) of 100 is considered adequate for incidental oral risk assessment level of concern.

Short

- and Intermediate

- Term Dermal Endpoints: In a 28

- day dermal toxicity study in rats, no

ad verse local or systemic effects were observed at the limit dose. Additionally, the dermal absorption factor is only 1%. Correcting the NOAELs from the developmental and reproduction studies for 1% dermal absorption results in PODs well above the limit do se. Therefore, no toxicity is expected to result from dermal exposure to thidiazuron, and a quantitative dermal risk assessment is not required.

Short

- and Intermediate

- Term Inhalation Endpoints: HASPOC waived the requirement for

s ubchronic inhalation study after a weight of evidence analysis considering the physical

chemical properties of the compound, use pattern and exposure scenarios, margins of exposure, and inhalation toxicity in structural analogs. The absorption through the inhalation route was

assumed to be similar to the oral route. The dose and endpoint selected for short

- and

intermediate

- term inhalation exposure was from a rabbit developmental study. The maternal NOAEL of 25 mg/kg/day and maternal LOAEL of 125 mg/kg/day were chosen based on based on 5 abortions occurring at GD 27

- 29

. The standard 100X UF was applied to account for interspecies extrapola tion and intraspecies variation. A margin of exposure (MOE) of 100 is considered adequate for the inhalation risk assessment level of concern.

Carcinogenicity: Both rat and mouse carcinogenicity studies did not show treatment related

increase in tumor in cidences, and assays from the muta genicity battery w ere negative

. Therefore, a quantitative cancer risk assessment is not required.

4.5.2 Recommendation for Combining Routes of Exposures for Risk Assessment

As indicated by 1996 FQPA, when there are po tential residential exposures to the pesticide, aggregate risk assessment must consider exposures from three major routes : oral, dermal, and

inhalation. There are no residential uses for thidiazuron ; therefore, combining routes of exposures for risk asses sment is unnecessary

.

4.5.3 Cancer Classification and Risk Assessment Recommendation

There is no evidence of carcinogenicity in acceptable rat and mouse carcinogenicity studies, and assays from the mutagenicity battery were negative.

4.5.4 Summary of Points of Departure and Toxicity EndpointsThidiazuron Human Health Risk Assessment DP No. D424978

Page 16 of 55 Table 4.5.4.1. Summary of Toxicological Doses and Endpoints for Thidiazuron for Use in H uman Health

Risk Assessments

Exposure/

Scenario Point of

Departure Uncertainty/

FQPA Safety

Factors RfD, PAD,

Level of

Concern for

Risk

Assessment Study and Toxicological Effects

Acut e Dietary (All Populations ) No toxic effects were identified likely to be a result of a single exposure.

Chronic Dietary (All Populations) NOAEL=

3.93 mg/kg/day UF A =10 x

UF H =10 x
FQPA SF= 1 x Chronic RfD

= cPAD =

0.0393 mg/kg/day 00159344, C hronic toxicity in dog

LOAEL = 11.1 mg/kg/day based on increased incidence of anemia, changes in hematological parameters and marked hemosiderosis in liver and spleen

Incidental

Oral Short

Term (1

- 30 days)

Incidental

Oral

Intermediate

Term (1

- 6 months) NOAEL=

25 mg/kg/day UF A =10 x

UF H =10 x
FQPA SF= 1 x Residential

LOC for

MOE = 100 46121507, Developmental toxicity in

rabbit

LOAEL = 125 mg/kg/day based on

abortions

Dermal Short

Term (1

- 30 days)

Dermal

Intermediate

Term (1

- 6 months) Not needed ; no dermal hazard identified . No dermal toxicity was observed at the limit dose in

the 28

- day dermal toxicity study . V ery low (< 1% ) dermal absorption results in calculated PoDs

above the limit dose

.

Inhalation

Short

- Term (1

- 30 days)

Inhalation

Intermediate

Term (1

- 6 months) NOAEL=

25 mg/kg/day UF A =10 x

UF H =10 x
FQPA SF= 1 x Occupational

LOC for

MOE = 100 46121507, Developmental toxicity in

rabbit

LOAEL = 125 mg/kg/day based on

abortions

Cancer (oral, dermal, inhalation) Classification: No increase in tumorigenesis or genotoxicity was observed.

Point of Departure (POD) = A data point or an estimated point that is derived from observed dose

- response data and used to mark the beginning of extrapolation to dete rmine risk associated with lower environmentally relevant human exposures. NOAEL = no observed adverse effect level. LOAEL = lowest observed adverse effect level. UF =Thidiazuron Human Health Risk Assessment DP No. D424978

Page 17 of 55 uncertainty factor. UF A = extrapolation from animal to human (interspecies). UF H = potential variation in sensitivity among members of the human population (intraspecies). UF L = use of a LOAEL to extrapolate a

NOAEL. UF S = use of a short

- term study for long

- term risk assessment. UF DB = to account for the absence of key data (i.e., lack of a critical study). FQPA SF = FQPA Safety Factor. PAD = population adjusted dose (a = acute, c = chronic). RfD = reference dose. MOE = margin of exposure. LOC = level of concern. N/A = not applicable.

4.6 Endocrine Disruption

As required by FIFRA and FFDCA, EPA reviews numerous studies to assess potential adverse outcomes from exposure to chemicals. Collectively, these studies include acute, subchronic and chronic toxicity, including assessments of carcinogenicity, neurotoxicity, developmenta l, reproductive, and general or systemic toxicity. These studies include endpoints which may be susceptible to endocrine influence, including effects on endocrine target organ histopathology, organ weights, estrus cyclicity, sexual maturation, fertility, p regnancy rates, reproductive loss, and sex ratios in offspring. For ecological hazard assessments, EPA evaluates acute tests and chronic studies that assess growth, developmental and reproductive effects in different taxonomic groups. As part of its prelim inary re

- registration decision for thidiazuron , EPA reviewed these data and selected the most sensitive endpoints for relevant risk assessment scenarios from the existing hazard database. However , as required by FFDCA section 408(p),

thidiazuron is subject to the endocrine screening part of the Endocrine Disruptor Screening Program (EDSP).

EPA has developed the EDSP to determine whether certain substances (including pesticide active and other ingredients) may have an effect in humans or wildlife similar to an effect produced by a “naturally occurring estrogen, or other such endocrine effects as the Administrator may designate.” The EDSP employs a two

- tiered approach to making the statutorily required determinations. Tier 1 consists of a battery of 11 scre ening assays to identify the potential of a chemical substance to interact with the estrogen, androgen, or thyroid (E, A, or T) hormonal systems. Chemicals that go through Tier 1 screening and are found to have the potential to interact with E, A, or T hor monal systems will proceed to the next stage of the EDSP where EPA will determine which, if any, of the Tier 2 tests are necessary based on the available data. Tier 2 testing is designed to identify any adverse endocrine

- related effects caused by the subst ance, and

establish a dose

- response relationship between the dose and the E, A, or T effect.

Under FFDCA section 408(p), the Agency must screen all pesticide chemicals. Between October 2009 and February 2010, EPA issued test orders/data call

- ins for the f irst group of 67 chemicals, which contains 58 pesticide active ingredients and 9 inert ingredients. A second list of chemicals identified for EDSP screening was published on June 14, 2013 1 and includes some pesticides scheduled for registration review and chemicals found in water

. Neither of these lists should be construed as a list of known or likely endocrine disruptors.

1 See http://www.regulations.gov/#!documentDetail;D=EPA

- HQ

- OPPT

- 2009

- 0477

- 0074 for the final second list of chemicals.Thidiazuron Human Health Risk Assessment DP No. D424978

Page 18 of 55 For further information on the status of the EDSP, the policies and procedures, the lists of chemicals, future lists, the test guideli nes and the Tier 1 screening battery, please visit our

website 2

.

5.0 Dietary Exposure and Risk Assessment

5.1 Residues of Concern Summary and Rationale
Residue Chemistry Memo, D425934, I. Negr ó n

- Encarnaci ó n, 05/07 /2015

The qualitative nature of the residue in cotton and livestock commodities is adequately understood. The parent compound thidiazuron is the residue of concern in cotton

. T hidiazuron,

and its metabolites

, 4

- hydroxythidiazuron and phenyl urea
, are the residues of concern for

livestock commodities. Estimated drinking water concentrations (EDWCs) that include thidiazuron, its two photodegradates (photo

- thidiazuron, 1

- cyano

- 3

- phenylurea), and thidiazolurea were provided by EFED. P hotothidiazuron, 1

- cyano

- 3

- phenylurea

, and thidiazolurea are not expected to be more toxic than parent thidiazuron (I. Negron

- Encarnacion, D425935, 05/ 13 /2015 )

.

Table 5.1 . Summary of Metabolites and Degradates to be included in the Risk Assessment and Tolerance Expressi on 1 ,2

Matrix Residues included in Risk

Assessment Residues included in Tolerance Expression

Plants Primary Crop Thidiazuron Thidiazuron

Rotational Crop

Livestock Ruminant Thidiazuron

, 4

- hydroxythidiazuron, Phenylurea Thidiazuron

, 4

- hydroxythidiazuron, Phenylurea Poultry

Drinking Water Thidiazuron, Photo

thidiazuron, 1

- cyano

- 3

- phenylurea, Thidiazolurea Not Applicable

1 2005 Registration Eligibility Decision. The residues of concern for plant and livestock commodities were determined by the HED Metabolism Committee (9/29/95, F. Fort).

2 Thidiazolurea was included as a residue of concern in the most recent drinking water assessment ( I. Maher

, D427241,

05/13/20 15 ). The risk assessment team has characterized the relative toxicity of the environmental degradates of thidiazuron with respect to parent thidiazuron.

.

2 http://www.epa.gov/endo/Thidiazuron Human Health Risk Assessment DP No. D424978

Page 19 of 55 5 .2 Food Residue Profile
Residue Chemistry Memo, D 425934

, I. Negrón

- Encarnación

, 05/07 /2015 Dietary Assessment Memo, D425935, I. Negrón

- Encarnación, 05/13 /2015

Crop field trial and processing studies are available to support the registration for the use of thidiazuron on cotton. The residue data were reevaluated to consider the results of storag e stability studies. Storage stability data indicates that residues of thidiazuron in/on cotton undelinted seed, meal and hulls should be adjusted for loss during storage. Tolerances for

thidiazuron in/on cotton undelinted seed and cotton hulls are recomm ended at 0.5 ppm and 1.5 ppm, respectively. The tolerance for cotton undelinted seed covers potential residues in cotton meal. Residues of thidiazuron in cotton gin byproducts are stable; therefore, the established tolerance (24.0 ppm) is adequate; howev er, a tolerance of 30 ppm is recommended following OECD rounding procedures. The field rotational crop study showed that residues of thidiazuron are not expected in rotated crops following the recommended PBI specified on the label. Storage stability data indicates that residues of 4

- hydroxy

- thidiazuron are not stable in muscle, kidney and fat but stable in milk, and residues of thidiazuron and phenyl urea in milk are stable in muscle, kidney, fat and milk. Tolerances are established in 40 CFR 180.403 for residues of thidiazuron in ruminant commodities: 0.4 ppm for meat, meat byproducts, fat, and 0.05 for milk. The dietary burden was reassessed to consider updated residue data and the current guidance.

Residues in livestock commodities were estimated usin g the results of the livestock metabolism study. HED concludes that the tolerances established for ruminant commodities are adequate.

5.3 Water Residue Profile

The drinking water residues used in the dietary risk assessment were provided by EFED in the following memorandum: “ Thidiazuron: Drinking Water Exposure Assessment Memorandum for Preliminary Risk Assessment in Support of Thidiazuron Registration Review

. ” ( I. Maher, D427241, 05/13/2015 ) and incorporated directly into this dietary assessment

. Potential drinking water concentrations for the chronic assessments were estimated using two EFED Tier 1 screening

- level models: SWCC, Version 1.106 and SCI

- GROW, Version 1. 07

. The highest water concentration value obtained, 0.0215 ppm for the FL citrus scenario modeled by PRZM

GW , was incorporated in the chronic dietary assessment.

Table 5.3 . Estimated Drinking Water Concentrations (EDWCs) for Thidiazuron, its Photodegradates (I and II) and Thidiazolurea Residues A

Drinkin g water source (model) Use

(modeled rate) 1

- in

- 10 year acute (μg/L) 1

- in

- 10 year

chronic (μg/L) 30

- year average (μg/L)

Surface water (SWCC) Cotton (MS) (0.31 lb ai/A) aerial 3.8 0.66 0.46

Ground water (PRZM

- GW) Cotton (as FL citrus) (0.31 lb ai/A) aerial Max. Daily

Conc (μg/L) Post

- breakthrough

mean (μg/L) Entire Simulation

Mean (μg/L)

21.7 21.5 10.6

A Based on the total annual rate of 0.31 lbs ai/A/yr (2 apps, 5

- d interval, 0. 21b a.i

. /A and 0.1 a.i/A, respectively).

Surface water corrected for national maximum cotton PCA of 0.21.Thidiazuron Human Health Risk Assessment DP No. D424978

Page 20 of 55 5.4 Dietary Risk Assessment
Dietary Assessment Memo, D425935, I. Negrón

- Encarnación, 05/13/2015

5. 4.1 Description of Residue Data Used in Dietary Assessment

The chro nic dietary exposure assessment for thidiazuron on food crops used tolerance level

residues and DEEM default processing factor s

.

5.4.2 Percent Crop Treated Used in Dietary Assessment

100% of the crop was assumed to be treated.

5.4.3 Acute Dietary Risk Assessment

N o acute endpoint was selected for thidiazuron; therefore, a quantitative acute dietary assessment

was not needed.

5.4.4 Chronic Dietary Risk Assessment

An unrefined dietary exposure assessment was performed for thidia zuron. The assumptions of

this dietary exposure assessment were tolerance level residues and 100% crop treated. The dietary exposure analysis in this assessment for thidiaz ur on result in dietary risk for food and water estimates that are below the Agency’s level of concern for chronic dietary exposure ( < 100 % of the cPAD) . The highest exposure and risk estimates were for children 1 to 2 years

old. T he chronic exposure for children 1 to 2 years old was 0.003647 mg/kg/day, which utilizes

9.3 % of the cPAD fo r thidiazuron ( see Table 5.4.6.).

5.4.5 Cancer Dietary Risk Assessment

Thidiazuron is not classified by CARC. However, n o increase in tumorigenes is or genotoxicity

was observed ; therefore, a dietary cancer exposure and risk analysis was not conducted.

5.4.6 Summary Table

Tab le 5.4.6. Summary of Dietary Exposure and Risk for Thidiazuron Food

and Drinking Water

Population Subgroup Chronic Dietary Dietary Exposure (mg/kg/day) % cPAD General U.S. Population 0.00124 8 3.2
All Infants (< 1 year old) 0.001967 5.0

Children 1

- 2 years old 0.003647 9.3

Children 3

- 5 years old 0.00262 8 6.7

Children 6

- 12 years old 0.0017 10 4. 4

Youth 13

- 19 years old 0.00106 9 2.7

Adults 20

- 49 years old 0.00106 4 2.7

Adults 50

- 99 years old 0.000970 2.5Thidiazuron Human Health Risk Assessment DP No. D424978

Page 21 of 55 Tab le 5.4.6. Summary of Dietary Exposure and Risk for Thidiazuron Food

and Drinking Water

Population Subgroup Chronic Dietary Dietary Exposure (mg/kg/day) % cPAD

Females 13

- 49 years old 0.00098 3 2.5

*The subpopulation(s) with the highest risk estimates

.

The chronic assessment is un refined, tolerance level residues and 100% of crop treated assumptions were incorporated in the dietary assessment. Therefore, this dietary assessment represents a high end est imate of potential dietary risks. HED is confident that the dietary risk is

not underestimated.

6.0 Residential (Non

- Occupational) Exposure/Risk Characterization

There are no registered residential (non

- occupational) uses of thidiazuron ; therefore

, a reside ntial exposure and risk assessment is not required.

6. 1 Residential Bystander Post

- A pplication Inhalation Exposure

Volatilization of pesticides may be a source of post

- application inhalation exposure to individuals nearby pesticide applications. The agency sought expert advice and input on issues related to volatilization of pesticides from its Federal Insecticide, Fungicide, and Rodenticide Act Scientific Advisory Panel (SAP) in December 2009, and received the SAP’s final report on March 2, 2010 ( htt p://www.epa.gov/scipoly/SAP/meetings/2009/120109meeting.html ). The agency has evaluated the SAP report and has developed a Volatilization Screening Tool and a subsequent Volatilization Screening Analysis ( http://www.regulations.gov/#!docketDetail;D=EPA

- HQ

- OPP

- 2014

- 0219 ). The Agency is currently not assessing volatility for non

- fumigants; however, the Agency will utilized this analysis in the future to determine if data (i .e., flux studies and route

- specific inhalation toxicological studies) or further analysis is required for thidiazuron

.

6. 2 Spray Drift

Off

- target movement of pesticides can occur via many types of pathways

, and it is governed by a variety of factors. Sprays that are released and do not deposit in the application area end up off

target and can lead to exposures to those it may directly contact. They can also deposit on

surfaces where contact with residues ca n eventually lead to indirect exposures ( e.g. , children playing on lawns where residues have deposited next to treated fields). The potential risk estimates from these residues can be calculated using drift modeling onto 50

- feet wide lawns coupled with met hods employed for residential risk assessments for turf products.

The approach to be used for quantitatively incorporating spray drift into risk assessment is based on a premise of compliant applications which, by definition, should not result in direct e xposures to individuals because of existing label language and other regulatory requirements intended toThidiazuron Human Health Risk Assessment DP No. D424978

Page 22 of 55 prevent them. 3 Direct exposures would include inhalation of the spray plume or being sprayed directly. Rather, the exposures addressed here are thoug ht to occur indirectly through contact with impacted areas, such as residential lawns, when compliant applications are conducted. Given this premise, exposures for children (1 to 2 years old) and adults who have contact with

turf where residues are assume d to have deposited via spray drift

, thus resulting in an indirect

exposure
, are the focus of this analysis analogous to how exposures to turf products are

considered in risk assessment.

In order to evaluate the drift potential and associated risks, an approach based on drift modeling coupled with techniques used to evaluate residential uses of pesticides was utilized. Essentially, a residential turf assessment based on exposure to deposit ed residues has been completed to address drift from the agricultural applications of thidiazuron

. In the spray drift scenario, the deposited residue value was determined based on the amount of spray drift that may occur at varying distances from the edge of the treated field using the AgDrift (v2.1.1) model and the Residential Exposure Assessment Standard Operating Procedures Addenda 1: Consideration of Spray Drift Policy . Once the deposited residue values were determined, the remainder of the spray drift assessment was based on the algorithms and input values specified in the recently revised (2012) Standard Operating Procedures For Residential Risk Assessment (SOPs)

.

A screening approach was developed based on the use of the AgDrift model in situations where specific label guidance that defines application parameters is not available. 4

, 5 AgDrift is appropriate for use only when applications are made by aircraft, airblast orchard sprayers, and groundboom sprayers. When AgDrift was developed, a series of screening values (i.e., the Tier 1 option) were incorporated into the model and represent each equipment type and use under varied conditions. The screening options specifically recommended in this methodology were selected because they are plausible and represent a reasonable upper bound level of drift for common application methods in agriculture. These screening options are consistent with how spray drift is considered in a number of ecological risk assessments and in the process used to develop drink ing water concentrations used for risk assessment. In all cases, each scenario is to

be evaluated

, unless it is not plausible based on the anticipated use pattern (e.g., herbicides are

not typically applied to tree canopies) or specific label prohibitions (e.g., aerial applications are not allowed). Section 6. 2 .1 provides the screening level drift

- related risk estimates.

3 This approach is consistent with the requirements of the EPA’s Worker Protection Standard.

4 http://www.agdrift.com/

5 Note that for many cases the scenarios outlined in the screening approach represent actual use practice so risk assessors sho uld

be aware and characteriz e these appropriately.Thidiazuron Human Health Risk Assessment DP No. D424978

Page 23 of 55 6

. 2 .1 Risk Estimates From Lawn Deposition Adjacent to Applications

The spray drift risk estimates are based on an estimated deposited residue concentration

, as a result of the screening level agricultural application scenarios. Thidiazuron is used on cotton and can be applied via groundboom and aerial equipment. The spray drift assessment was completed assuming the highest registered application rate of 0.2 lb ai/A. The recommended drift scenario screening level options are listed below:

 Groundboom applications are based on the AgDrift option for high boom height and using very fine to fine spray type using the 90 th percentile result s.

 Aerial applications are based on the use of AgDrift Tier 1 aerial option for a fine to medium spray type and a series of other parameters which will be described in more detail below (e.g., wind vector assumed to be 10 mph in a downwind direction for entire application/drift event). 6

Only incidental oral risk estimates are shown since quantitation of dermal risk to thidiazuron is not required . The applicable Level of Concern is 100

, so MOEs < 100 would be of concern. Exposures were considered for 50 feet wide lawns where th e nearest side of the property was directly adjoining the treated field (at field edge). Results are presented in Table 6.4.1; no risk estimates of concern were identified at field edge.

Table 6. 2 .1 Children (1<2 years old) Risk Estimates (MOEs) Related to Indirect Exposure to Spray Drift for Thidiazuron for the Oral Route of Exposure

Crop/Rate Group Spray Type/ Nozzle Configuration Appl. Rate (lb ai/A) TTR (μg/cm 2 ) At Edge

Cotton

Groundboom High Boom Very fine to Fine

0.2 0.022 44,000

Aerial Fine to Medium 32,000

7.0 Aggregate Exposure/Risk Characterization

In accordance with the FQPA, HED must consider and aggregate pesticide exposures and risks from three major sources: food, drinking water, and residential exposures. Since there are no residential uses, an aggregate exposure assessment for thidiazuron includes consideration of exposures from food and drinking water (see Section 5).

7.1 Acute Aggregate Risk

There are no acute aggregate risks for thidiazuron , as a hazard was not identi fied that could result from a single exposure

.

6 AgDrift allows for consideration of even finer spray patterns characterized as very fine to fine. However, this spray pattern was not selected as the common screening basis since it is used less commonly for most agriculture.Thidiazuron Human Health Risk Assessment DP No. D424978

Page 24 of 55 7.2 Short

- Term Aggregate Risk

There are no short

- term aggregate risks for thid i azuron, as there are no residential uses

.

7.3 Intermediate

- and Long

- Term Aggregate Risk

There are no intermediate

- or long

- term aggregate risks for thid i azuron , as there are no

residential uses.

7. 4 Chronic Aggregate Risk

Since there are no residential uses, the chronic aggregate risk is equal to the aggregate risk from dietary sources, food plus drinking water , summarized i n Section 5.4. There are no chronic aggregate risks of concern for thidiazuron.

7. 5 Cancer Aggregate Risk

Both rat and mouse carcinogenicity studies did not show treatment related increase in tumor incidences. Thus, a cancer dietary risk assessment wa s not performed.

8.0 Cumulative Exposure/Risk Characterization

Unlike other pesticides for which EPA has followed a cumulative risk approach based on a common mechanism of toxicity, EPA has not made a common mechanism of toxicity finding as

to thidiazuron and any other substances. 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/.

Both rat and mouse carcinogenicity studies did not show treatment related increase in tumor incidences. Thus, a cancer dietary exposure assessment was not performed.

9.0 Occupational Exposure/Risk Characterization

An occupational exposure and risk assessment was completed to include all registere d uses of

thidiazuron.

9.1 Short

- /Intermediate

- Term Handler Risk

HED uses the term “handlers” to describe those individuals who are involved in the pesticide application process. HED has determined that there are potential exposures to handlers duringThidiazuron Human Health Risk Assessment DP No. D424978

Page 25 of 55 a pplication of thidiazuron. Scenarios assessed include mixing/loading liquids and water soluble packets (WSPs) formulations for groundboom and aerial applications, applying sprays via groundboom and aerial equipment, and flagging.

It is the policy of HED to use the best available data to assess handler exposure. Sources of generic handler data, used as surrogate data in the absence of chemical

- specific data, include PHED 1.1, the AHETF database, the Outdoor Residential Exposure Task Force (ORETF)

databas e, or other registrant

- submitted occupational exposure studies

. Some of these data are proprietary (e.g., AHETF data), and subject to the data protection provisions of FIFRA. The standard values recommended for use in predicting handler exposure that are used in this assessment, known as “unit exposures”, are outlined in the “Occupational Pesticide Handler Unit Exposure Surrogate Reference Table 7 ”, which, along with additional information on HED policy on use of surrogate data, including descriptions of t he various sources, can be found at the Agency website 8

.

Respirators are not required on the labels. The occupational handler exposure and risk estimates

indicate that short

- and intermediate

- term MOEs are not of concern to HED (i.e., MOEs > 100).

Inha lation MOEs for the occupational handler assessment range from 30,000 to 1,500,000.

Table 9.1.1. Occupational Handler Short

- and Intermediate

- Term Non

- Cancer Exposure and Risk Estimates for Thidiazuron

.

Exposure Scenario Crop or Target Inhalation Unit

Exposure (μg/lb ai) 1 Maximum

Application

Rate 2 Area Treated or

Amount Handled Daily 3 Inhalation

Mitigation Level Dose (mg/kg/day) 4 MOE 5

Mixer/Loader

L/SC/EC

- Aerial applications

Cotton No Respirator: 0.219

0.2 1200 0.000762 33,000

L/SC/EC

- Groundboom applications 200 0.000127 200,000

WSP

– Aerial Application
Eng. Control: 0.24 1200 0.000835 30,000

WSP

– Groundboom applications 200 0.000139 180,000

Applicator

Spray

- Aerial applications

Cotton Eng. Control: 0.0049

0.2 1200 0.0000171 1,500,000

Spray

– Groundboom applications No Respirator: 0.34 200 0.000197 130.000

Flagger

Spray

- Flagger Cotton No Respirator: 0.35 0.2 350 0.000355 70,000

1 Based on the “Occupational Pesticide Handler Unit Exposure Surrogate Reference Table” (March 2014); Level of mitigation: Baseline, PPE, Eng. Controls.

2 Based on registered labels.

3 Exposure Science Advisory Council Policy #9.1.

4 Inhalation Dose = Inhalation Unit Exposure (μg/lb ai) × Conversion Factor (0.001 mg/μg) × Application Rate (lb ai/acre or gal) × Area Treated or Amount Handled (A or gal/day) ÷ BW (kg).

5 Inhalation MOE = Inhalation NOAEL ( 25 mg/kg/day) ÷ Inhalation Dose (mg/kg/day).

7 Av ailable: http://www.epa.gov/opp00001/science/handler

- exposure

- table.pdf

8 Available: http://www. epa.gov/pesticides/science/handler

- exposure

- data.htmlThidiazuron Human Health Risk Assessment DP No. D424978

Page 26 of 55 9.2 Short

- /Intermediate

- Term Post

- Application Risk

HED uses the term post

- application to describe exposures that occur when individuals are present in an environment that has been previously treated with a pesticide (also referred to as re

entry exposure). Such exposures may occur when workers enter previously treated areas to perform job fu nctions, including activities related to crop production, such as scouting for pests or harvesting. Post

- application exposure levels vary over time and depend on such things as the type of activity, the nature of the crop or target that was treated, the t ype of pesticide application, and the chemical’s degradation properties. In addition, the timing of pesticide applications, relative to harvest activities, can greatly reduce the potential for post

- application exposure.

9.2.1 Dermal Post

- Application Risk

HED uses the term post

- application to describe exposures that occur when individuals are present in an environment that has been previously treated with a pesticide (also referred to as re

entry exposure). HED has determined that there are potential exp osures to persons entering treated sites (e.g., harvesters) after application of thidiazuron is complete.

Since quantitation of dermal risk is not required for thidiazuron, a quantitative occupational dermal post

- application risk assessment is not requi red.

Restricted Entry Interval

The REI specified on the labels is based on the acute toxicity of thidiazuron. Thidiazuron is classified as Toxicity Category IV via the dermal route, Toxicity Category IV for skin irritation, and Toxicity Category IV for e ye irritation. It is not a skin sensitizer. Under 40 CFR 156.208 (c) (2) (iii), active ingredient’s classified as Acute III or IV for acute dermal, eye irritation and primary skin irritation are assigned a 12

- hour REI. Therefore, the [156 subpart K] Wor ker Protection Statement interim REI of 12 hours is adequate to protect agricultural workers from

post

- application exposures to thidiazuron.

9.2.2 Inhalation Post

- Application Risk

There are multiple potential sources of post

- application inhalation exposure to individuals performing post

- application activities in previously treated fields. These potential sources include volatilization of pesticides and resuspension of dusts and/or particulates that contain pesticides. The agency sought expert advic e and input on issues related to volatilization of pesticides from its Federal Insecticide, Fungicide, and Rodenticide Act Scientific Advisory Panel (SAP) in December 2009, and received the SAP’s final report on March 2, 2010 ( http://www.epa.gov/scipoly/SA P/meetings/2009/120109meeting.html ). The agency has evaluated the SAP report and has developed a Volatilization Screening Tool and a subsequent Volatilization Screening Analysis ( http://www.regulations.gov/#!docketDetail;D=EPA

- HQ

OPP

- 2014

- 0219 ).Thidiazuron Human Health Risk Assessment DP No. D424978

Page 27 of 55 In addition, the Agency is continuing to evaluate the available post

- application inhalation exposure data generated by the Agricultural Reentry Task Force. Given these two eff orts, the Agency will continue to identify the need for and, subsequently, the way to incorporate occupational post

- application inhalation exposure into the agency's risk assessments.

Although a quantitative occupational post

- application inhalation exposu re assessment was not performed, an inhalation exposure assessment was performed for occupational/commercial handlers. Handler exposure resulting from application of pesticides outdoors is likely to result in higher exposure than post

- application exposure . Therefore, it is expected that these handler inhalation exposure estimates would be protective of most occupational post

- application inhalation exposure scenarios. Handler inhalation risks are not of concern (see Section 9.1).

10 .0 Incident Report

One component of the Agency’s registration review program is consideration of human observational information including incident data, medical case reports, general medical information, and epidemiology studies. In conjunction with a human health risk assessment based on other data sources, such human incident and other human data can assist the Agency in better defining and characterizing the risk of pesticides/pesticide products.

Based on the low frequency and severity of incident cases reported fo r thidiazuron in both IDS

and CDC/ NIOSH SENSOR

- Pesticides, there does not appear to be a concern at this time with respect to incident cases that would warrant further investigation. The Agency will continue to

monitor the incident information and will re

- evaluate these conclusions as needed.

HED has prepared a thidiazuron incident report review ( Recore and Evans

, 2015 , D 425469 ). The review considers a variety of types and sources of human observational information including human incident data, medical data/case report information, and epidemiological information in

an effort to inform the re

- evaluation of thidiazuron in this phase of registration review. The

human incident databases that were reviewed are: t he OPP Incident Data System (IDS) and

CDC/ NIOSH’s Sentinel Event Notification System fo r Occupational Risks (SENSOR).

OPP’s IDS includes reports of alleged human health incidents from various sources, including mandatory Federal Insecticide, Fungicide and Rodenticide Act (FIFRA) Section 6(a)(2) reports from registrants, other federal and state health and environmental agencies, and individual

consumers. Overall, there are few incidents involving thidiazuron reported to IDS. Incidents in the IDS system include:

 For the Ma in IDS, from January 1, 20 10 to December 30 , 2014, there were no incidents reported involving thidiazuron

.

 In Aggregate IDS, from January 1, 20 10 to December 30 , 2014, 1 incident of minor severity was reported involving thidiazuron

.Thidiazuron Human Health Risk Assessment DP No. D424978

Page 28 of 55 The SENS OR

- Pesticides database covers 12 states from 1998

- 2011 , although reporting varies from state to state. Cases of pesticide

- related illnesses are ascertained from a variety of sources, including: reports from local Poison Control Centers, state Department of Labor workers’ compensation claims when reported by physicians, reports from State Departments of Agriculture, and physician reports to state Departments of Health. A query of SENSOR

Pesticides 1998

- 2010 identifies sixteen cases involving thidiazuron ( PC Code 120301 ), one of which involved a single active ingredient. This case occurred in Texas in 1998 and was low in severity. The case is described in SENSOR as follows, “ Complainant heard an aerial application

occu rring nearby. She went outside and saw an aerial applicator spraying a cotton field .”

In addition to the incident/poisoning data and medical case reports, epidemiological research can be an important source for human observational data and can potentially assist in identifying, characterizing, and (ideally) quantifying linkages between human exposures and resulting health

effects. For thidiazuron , epidemiological data is not available from the AHS.

In summary, based on the low frequency and severity of cases involving thidiazuron reported in

both IDS and SENSOR

- Pesticides, there does not appear to be a concern at this time that would warrant further investigation. The Agency will continue to monitor the incident information and if a concern is triggered, additional analysis will be included in the risk assessment.Thidiazuron Human Health Risk Assessment DP No. D424978

Page 29 of 55 1 1 .0 References

Assaad, A. and Bonner, M. 03/19/2003. TXR# 0051694

. THIDIAZURON

- Second Report of

the Hazard Identification Assessment Review Committee.

Cheng, L. 04/04/97. Thidiazuron . Case 2600. Phase V Review of Soybeans, Tomatoes, Goats, and Poultry Metabolism Studies. CBRS17851. DP Barcode: None.

Donovan, W. H. 04/22/2005. Thidiazuron . HED Chemistry Chapter of the Reregistration Eligibility Decision (RED). Summary of Analytical Chemistry and Residue Data. Case No.

2600.

D rew , D. 3/ 30/05 . D3 12569

. Thidiazuron : H ED Chapter of the Reregistration Eligibility Decision (RED) Document.

Habiba, U. 09/25/13 . TXR# 005 6795. Forchlorfenuron and Phenyl Urea Herbicides: Summary

of Ha zard and Science Policy Council (HASPOC) Meeting of September 12

, 201 3 : Recommendations on the Data R equirement for an Immunotoxicity Study for Forchlorfenuron and for the Phenyl Urea Herbicides as a Class.

Habiba, U. 04/14/15 . TXR# 0057116

. Thidiazuron: Summary of Hazard and S cience Policy Council (HASPOC) M eeting of January 22, 2015 : Recommendations on the Need for a Subchronic Inhalation Toxicity Study and Neurotoxicity (Acute and Subchronic) Studies

King, K. 12/16/14. D422745. Thidiazuron . Acute and Chronic Aggregate Die tary (Food and Drinking Water) Exposure and Risk Assessments for the Proposed Uses on Highbush Blueberry and Fescue Grass as well as registration review for all registered crops and updating crop group

and sub

- groups for Thidiazuron

.

Knizner, S. 05/27/0 9. Interim Guidance on Tolerance Expressions.

Lin, J. 06/25/14. Thidiazuron : Drinking Water Exposure Assessment for IR

- 4 Petition on Fescue, Oilseeds, Fruits, and Vegetables

.

Loranger, R. 05/27/98. Thidiazuron . Conclusions of the 5/14/98 Meeting of the Metabloism

Assessment Review Committee.

Maher, I. 05/13/15. D427241

. Thidiazuron: Drinking Water Exposure Assessment Memorandum for Preliminary Risk Assessment in Support of Thidiazuron Registration Revie w

.

Recore, S. and Evans, E. 02/05 /15. D 425469 . Thidiazuron: Tier 1 Review of Human Incidents

Savoia, P. 12/ 18 /2014

. Thidiazuron . Section 3 Registration for Grass Grown for Seed; Request for an Amended Use on Blueberry; Crop Group Conversions; Group 3 to Group 3

- 07, Group 8 toThidiazuron Human Health Risk Assessment DP No. D424978

Page 30 of 55 Group 8

- 10, Group 10 to Group 10

- 10, Group 11 to Group 11

- 10; and Crop Subgroup Conversions: Caneberry to Subgroup 13

- 07A, Blueberry to Subgroup 13

- 07B, Grape to Subgroup 13

- 07F Except Fuzzy Kiwifruit, Strawberry to Subgroup 13

- 07G Except Cranberry, Cranberry to Subgroup 13

- 07H, Canola Seed to Subgroup 20A, Sunflower Seed to Subgroup 20B Except Safflower, and Cotton Undelinted Seed to Subgroup 20C. Summary of Analytical Chemistry and Residue Data.

Soderberg, D. 04/12/12. T hidiazuron : Submission of a Study of Residues on Safflower in Response to a RED Data Gap Requirement.

Tadayan , S. 10/30/14. Thidiazuron : Occupational and Residential Exposure and Risk Assessment for Registration Review and to Support the Registration o f Proposed Uses on High Bush Blueberry and Fine Fescue Grasses.Thidiazuron Human Health Risk Assessment DP No. D424978

Page 31 of 55 A ppendix A . Toxicology Profile and Executive Summaries

A.1 Toxicology Data Requirements
The requirements (40 CFR 158.500) for food

- use for thidiazuron are in Table 1. Use of the new guideline numbers does not imply that the new (1998) guideline protocols were used.

Study Technical

Required Satisfied

870.1100 Acute Oral Toxicity

................................ ....................... 870.1200 Acute Dermal Toxicity

................................ .................. 870.1300 Acute Inhalation Toxicity

................................ .............. 870.2400 Primary Eye Irritation

................................ .................... 870.2500 Primary Dermal Irritation

................................ .............. 870.2600 Dermal Sensitization

................................ ..................... yes

yes

yes

yes

yes

yes yes

yes

yes

yes

yes

yes

870.3100 Oral Subchronic (rodent)

................................ ............... 870.3150 Oral Subchronic (non

- rodent)

................................ ....... 870.3200 28

- Day Dermal

................................ .............................. 870.3250 90

- Day Dermal

................................ .............................. 870.3465 90

- Day Inhalation

................................ .......................... yes

yes

yes

no

yes yes

yes a

yes

- yes b

870.3700a Developmental Toxicity (rodent)

................................ .. 870.3700b Developmental Toxicity (non

- rodent)

........................... 870.3800 Reproduction

................................ ................................ . yes

yes

yes yes

yes

yes

870.4100a Chronic Toxicity (rodent)

................................ .............. 870.4100b Chronic Toxicity (non

- rodent)

................................ ...... 870.4200a Oncogenicity (rat)

................................ .......................... 870.4200b Oncogenicity (mouse)

................................ ................... yes

no

yes

yes yes

yes

yes

yes

870.5100 Mutagenicity

— Bacterial reverse mutation assay

.................... 870.5300 Mutagenicity

— In vitro mammalian cell gene mutation test

....... 870.5375 Mutagenicity

— In vitro mammalian chromosome aberration test 870.5385 Mutagenicity

— Mammalian bone marrow chromosomal aberration test 870.5395 Mutagenicity

— Mammalian erythrocyte micr onucleus test

........ yes

yes

yes

yes

yes yes

yes

yes

yes

yes c

870.6100a Acute Delayed Neurotoxicity (hen)

............................... 870.6100b 90

- Day Neurotoxicity (hen)

................................ .......... 870.6200a Acute Neurotoxicity Screening Battery (rat)

................. 870.6200b 90

- Day Neurotoxicity Screening Battery (rat)

.............. 870.6300 Developmental Neurotoxicity

................................ ....... no

no

yes

yes

no -

- yes b

yes b

-

870.7485 General Metabolism

................................ ...................... 870.7600 Dermal Penetration

................................ ........................ 870.7800 Immunotoxicity

................................ ............................. yes

yes

yes yes

yes

yes d

a Test was not submitted but is not required at this time because the toxicological data requirements for the 90

- day feeding study in non

- rodents are satisfied by the 1

- year feeding study in dogs.

b Requirement waived by HASPOC ( TXR # 0057116

, 2015 ).

c Alth ough not submitted, t here are mutagenicity studies that evaluate both somatic and germinal cells, and are considered sufficient to satisfy CFR requirements.

d Requirement waived by HASPOC (TXR # 0056795, 9/25/2013).Thidiazuron Human Health Risk Assessment DP No. D424978

Page 32 of 55 A.2 Toxicity Profiles

Table A.2.1 Acute Toxicity Profile

- Thidiazuron

Guideline No. Study Type MRID(s) Results Toxicity Category

870.1100 Acute oral

– Rat 46121501 LD 50 > 2 g/kg III

870.1200 Acute dermal

– Rat 46121502 LD 50 > 5 g/kg IV

870.1300 Acute inhalation

- Rat 46121503 LC 50 > 3.48 mg/L IV

870.2400 Acute eye irritation

- Rabbit 42099601 Irritation clearing

within 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 NA

Table A.2.2 Subchronic, Chronic and Other Toxicity Profile

- Thidiazuron

Guideline

No. Study Type MRID No. (year)/

Classification /Doses Results

870. 3 05 0 28

- Day oral

toxicity (rat) 46121509 (2001)

- see u nder 46121506

Acceptable, guideline ♂♀: 0, 900, 1800, 3600

ppm ♂♀: 0, 67, 135, 254
mg/kg/day NOAEL = 67 mg/kg/day

LOAEL = 135 mg/kg/day based on ↓ serum glucose and urinary pH, small seminal vesicles and prostate gland, prominent liver lobulation, and focal/multifocal basophilic tubules in the kidneys

870. 3100 90

- Day oral

toxicity (rat) 46121506 (2001)

Acceptable, guideline ♂♀: 0, 200, 600, 1800, 5400, 16,200 ppm ♂: 0, 11.2, 34.5, 102, 294, NC mg/kg/day ♀: 0, 14.0, 42.1, 123, 325, NC mg/kg/day
NC = highest dose not

calculated NOAEL = 34.5 mg/kg/day

LOAEL = 102 mg/kg/day based on ↓ body weights , body weight gains, and food consumption; ↓ epididymides and prostate gland weight; ↑ ALP; ↑ urea ; microscopic findings in : adrenal gland, kidney, liver, and spleen ( ♂♀ ) ; prostate gland, seminal vesicle,

mammar y gland, and thymus ( ♂ ); bone and marrow of the sternum and ovary ( ♀ ) ; small prostate and small seminal vesicles

At the high dose, a ll animals were either found dead or were sacrificed moribund by Day 10

.

870. 3100 90

- Day oral

toxicity (mouse) 46121505 (2001)

Acceptable, guideline ♂♀: 0, 500, 1000, 2000,

4000 ppm ♂: 0, 85.2, 170.9, 351.4 mg/kg/day ♀: 0, 99.8, 202.6, 383.9 mg/kg/day NOAEL = 85.2 mg/kg/day

LOAEL = 170.9 mg/kg/day based on ↓ cholesterol ( ♂ ) ; ↑ incidences of centrilobular hepatocellular hypertrophy ( ♂ ) and diffuse acinar hypertrophy in salivary glands ( ♀ )

At the high dose, a ll mice died or were sacrificed moribund on Days 6

- 9.Thidiazuron Human Health Risk Assessment DP No. D424978

Page 33 of 55 Table A.2.2 Subchronic, Chronic and Other Toxicity Profile

- Thidiazuron

Guideline

No. Study Type MRID No. (year)/

Classification /Doses Results

870. 3150 90

- Day oral

toxicity (dog) Not submitted Chronic dog study satisfies this data requirement

870. 3200 28

- Day dermal

toxicity (rat) 46261501 (2004)

Acceptable, guideline ♂♀: 0, 100, 300, 1000 mg/kg/day NOAEL = 1000 mg/kg/day

LOAEL was not determined

870. 3465 90

- Day inhalation

toxicity (species) Not submitted Study requirement w aived by HASPOC

870. 3700a Prenatal

developmental (rat) 00077127 (1981)

Acceptable, guideline
0, 25, 50, 100, 300 mg/kg/day Maternal NOAEL = 3 00 mg/kg/day

LOAEL was not observed Developmental NOAEL = 100 mg/kg/day

LOAEL = 3 00 mg/kg/day based on de creased fetal body weight

870. 3700b Prenatal

developmental (rabbit) 46121507 (2003)

Acceptable, guideline
0, 5, 25, 125 mg/kg/day

46252001

– historical

control data

46241001

– range

- finding developmental toxicity study Materna l NOAEL = 25 mg/kg/day

LOAEL = 125 mg/kg/day based on 5 abortions (GD 27

- 29) Developmenta l NOAEL = 25 mg/kg/day

LOAEL = 125 mg/kg/day based on 5 a bortions (GD 27

- 29), ↓ fetal body weights ( ↓ 12

- 13%) ; ↑ number of runts and delayed skeletal

ossification

870. 3800 Reproduction and

fertility effects (rat) 46209601 (2003)

Acceptable, guideline ♂♀: 0, 100, 400, 1200

ppm ♂: 0, 8.8, 35.4, 108.5
mg/kg/day ♀ : 0, 9.9, 39.8, 121.1 mg/kg/day Parental/Systemic NOAEL = 108.5 mg/kg/day

LOAEL was not observed Reproductive NOAEL = 108.5 mg/kg/day

LOAEL was not observed Offspring NOAEL = 35.4 mg/kg/day

LOAEL = 108.5 mg/kg/day based on delayed vaginal opening

870. 4100a Chronic toxicity

(rat) Not submitted. See

870.4300. -

870. 4100b Chronic toxicity

(dog) 00159344 (1985)

Acceptable, guideline ♂♀: 0, 100, 300, 1000

ppm ♂: 0, 3.93, 11.8, 38.3 mg/kg/day ♀ : 0, 4.01, 11.1, 36 mg/kg/day NOAEL = 3.93 mg/kg/day

LOAEL = 11.1 mg/kg/day based on increased incidence of anemia, changes in hematological

parameters

, and marked hemosiderosis in liver and spleen
Additionally at the high dose, findings such as increased spleen and lymph node weight,

localized infiltration of lymphocytes in the mucosa of the gallbladder

, early or progressive involution in the thymus, and interfoll ic ular cell increase in the thyroid were noted.Thidiazuron Human Health Risk Assessment DP No. D424978

Page 34 of 55 Table A.2.2 Subchronic, Chronic and Other Toxicity Profile

- Thidiazuron

Guideline

No. Study Type MRID No. (year)/

Classification /Doses Results

870. 4200 a Carcinogenicity

(rat) Not submitted. See

870.4300. -

870. 4200 b Carcinogenicity

(mouse) 46346001 (2004)

Acceptable, guideline ♂♀: 0, 200, 650, 2000

ppm ♂: 0, 26.5, 86.7, 279.9
mg/kg/day ♀ : 0, 33.4, 107.8, 329.7 mg/kg/day NOAEL = 86.7 mg/kg/day

LOAEL = 279.9 mg/kg/day based on : decreased body weight, body we ight gain, and food consumption, decrease in renal corticoepithelial vacuolation (♂) ; ↑ epididymis toxicity (indicated by ↑ interstit ial mononuclear cell infiltrate, unilat eral and bilateral oligospermia, spermatic granuloma (♂)); ↑ clinical signs of toxicity ( ♀ ) no evidence of carcinogenicity

870. 4 3 00 Combined

Chronic Toxicity/ Carcinogenicity (rat) 46345201 (2004)

Acceptable, guideline ♂♀: 0, 200, 900, 1800

ppm ♂: 0, 8.0, 36.4, 75.6
mg/kg/day ♀ : 0, 11.3, 51.4, 105 mg/kg/day NOAEL = 8 mg/kg/day

LOAEL = 36.4 mg/kg/day based on ↓ body weight and body w eigh t gain ( ♂ ), ↑ bilateral seminal vesicle atrophy and nephrotoxicity ( ♂♀ ) no evidence of carcinogenicity

870. 4 3 00 Combined

Chronic Toxicity/ Carcinogenicity (rat) 00159346 ( 1986 )

Acceptable, non

- guideline ♂♀: 0, 70, 200, 600 ppm ♂: 0, 3.7, 10.6, 31.7
mg/kg/day ♀ : 0, 4.6, 13, 40.1 mg/kg/day NOAEL = 31.7 mg/kg/day

LOAEL was not determined

no evidence of carcinogenicity

870.5100 Genotoxicity

Ames bacterial gene mutation

assay 46121508 (2001)

Acceptable, guideline ±S9, Trial 2: 0, 1.5, 5, 15, 50, 150, 500 , 1500 μg/plate No evidence of mutagenic activity was seen at any dose level tested in the presence or absence

of S

- 9 mix in either mutation test.

870.5300 Genotoxicity

In vitro

mammalian cell gene mutation in

the HGPRT locus

in Chinese

Hamster V79 cells 41761102 (1990)

Acceptable, guideline ±S9: 15, 30, 100, 250 μg/plate Not mutagenic. Test chemical did not cause

mutations at the HGPRT locus in V79 cells.

870.5375 Genotoxicity

In vitro

mammalian

chromosome aberration assay 46121510 (2001)

Acceptable, guideline

±S9: 0, 9.4, 18.75, 37.5, 75, 150, 200, 250 μg/mL No t mutagenic. There was no evidence of

chromosome aberration induction above background in the presence or absence of S9 at either time point.Thidiazuron Human Health Risk Assessment DP No. D424978

Page 35 of 55 Table A.2.2 Subchronic, Chronic and Other Toxicity Profile

- Thidiazuron

Guideline

No. Study Type MRID No. (year)/

Classification /Doses Results

870.5385 Genotoxicity

Mammalian bone

marrow chromosomal

aberration test 070129 (1981)

Acceptable, guideline
2.4, 24, 120 m g/mL No t mutagenic. No increase in micronucleated

cells was observed.

870.5395 Genotoxicity

In vivo

chromosome aberration (mouse micronucleus)

assay Not submitted

-

870.5550 Genotoxicity

Unscheduled DNA synthesis assay in primary

rat hepatocytes 41761103 (1990)

Acceptable, guideline
0.25, 0.75, 2.5, 7.5, 25 μg/mL Not mutagenic. There were no indications of UDS activity.

870.6200a Acute

neurotoxicity screening battery Not submitted Study requirement waived by HASPOC

870. 6200b Subchronic

neurotoxicity screening battery Not submitted Study requirement waived by HASPOCThidiazuron Human Health Risk Assessment DP No. D424978

Page 36 of 55 Table A.2.2 Subchronic, Chronic and Other Toxicity Profile

- Thidiazuron

Guideline

No. Study Type MRID No. (year)/

Classification /Doses Results

870.7485 Metabolism and

pharmacokinetics (rat) 42529001 (1992)

Acceptable, guideline (1) S ingle oral gavage dose (10 or 1000 mg/ k g) (2) 14

- day repeated oral

doses at 10 mg/ k g (not radiolabeled) followed by a 10 mg/kg radiolabeled

dose Absorption occurred predominantly within 24 hours at 10 mg/kg (single or repeated dosing) and within 48 hours at 1000 mg/kg. Absorption was 61

- 68% of the administered dose (AD) after a single 10 mg/kg dose, 74

- 76% AD after repeated 10 mg/kg doses, and

onl y 41

- 48% AD after 1000 mg/kg.

After a single 10 mg/kg dose, urinary excretion

accounted for 59

- 66% AD, and fecal excretion

accounted for 29

- 31% AD. After repeated 10 mg/kg dosing, urinary excretion accounted for

72

- 74% AD, and fecal excretion accounted f or 26

- 28% AD. After a single 1000 mg/kg dose, urinary excretion accounted for 40

- 47% AD,

and fecal excretion accounted for 56

- 60%. Approximately 0.1% AD or less was found in the expired air.

At 120 hours post

- dose, only <2% AD remained in the body, and the highest

concentration s was found in the thyroid, whole

blood , kidney, and adrenal glands.

Negligible amounts of the parent was isolated

in the excreta. The primary metabolites were

4

- hydroxy thidiazuron and 3 different conjugates of 4

- hydroxy thidiazu ron.

870. 7600 Dermal

penetration (rat) 46261502 ( 2004 )

Acceptable, guideline 0.004, 0.04, 5.0 mg/cm 2 Dermal absorption based on the amount in the systemic compartment (excreta & tissues) corresponding to the total amount of test chemical directly absorbed was similar after

24

- hour and 8

- hour exposures with termination at 120 hours post

- application (0.20% and 0.22% for high dose, 0.75% and 1.25% for middle dose, and 1.18% and 1.17 % for low dose).

870. 7800 Immunotoxicity

(rat) Not submitted Study requirement waived by HASPOC

A.3 Hazard Identification and Endpoint Selection

A.3.1 Acute Reference Dose (aRfD)

– All Populations

Study S elected : None. No endpoint could be considered due to a single exposure.Thidiazuron Human Health Risk Assessment DP No. D424978

Page 37 of 55 A.3.2 Chronic Reference Dose (cRfD)

Study S elected : C hronic toxicity study in dogs

MRID No. : 001 59344 Executive Summary : See Appendix A.4, Guideline OPPTS 870. 4200b Dose and Endpoint for Risk Assessment : NOAEL = 3.93 mg/kg/day; LOAEL = 11.1 mg/kg/day based on increased incidence of anemia, changes in hematological parameters and marked hemosiderosis in liver and spleen Comments about Study/Endpoint/Uncertainty Factors : The selected endpoints are the lowest

value s for this exposure scenario and are the most protective. A 100

- fold uncertainty factor (10X interspecies and 10X intraspecies) was applied. Thus, a cRfD of 0. 0393 mg/kg/day was calculated. The FQPA SF is 1X; therefore, the cPAD is also 0. 0393 mg/kg/day.

A.3.3 Incidental Oral Exposure ( Short

- and Intermediate

- Term)

St udy S elected : Prenatal developmental study in ra bbi ts
MRID No. : 46121507 Executive Summary : See Appendix A.4, Guideline OPPTS 870.3 7 00 b Dose and Endpoint for Risk Assessment : Maternal NOAEL = 25 mg/kg/day; LOAEL = 1 25 mg/kg/day based on abortions Comments about Study/Endpoint/Uncertainty Factors : The selected endpoints are the lowest values for this exposure scenario and are the most protective. A 100

- fold uncertainty facto r (10X interspecies and 10X intraspecies) was applied. The FQPA SF is 1X. The residential level of concern for MOE = 100; an occupational LOC is not appropriate for this exposure scenario.

A.3.4 Dermal Exposure (Short

- , Intermediate

- , and Long

- Term)

De rmal risk assessment was not required. No dermal or systemic toxicity was seen following repeated dermal applications at the limit dose (1000 mg/kg/day) in rats. D ermal absorption

factor was only 1%.

A.3.5 Inhalation Exposure (Short

- and Intermediate

- Term)

Study S elected : Prenatal developmental study in rabbits

MRID No. : 46121507 Executive Summary : See Appendix A.4, Guideline OPPTS 870.3 7 00 b Dose and Endpoint for Risk Assessment : Maternal NOAEL = 25 mg/kg/day; LOAEL = 1 25 mg/kg/day based on abortions Comments about Study/Endpoint/Uncertainty Factors : The selected endpoints are the lowest values for this exposure scenario and are the most protective. A 100

- fold uncertainty factor (10X interspecies and 10X intraspecies) was applied. The FQPA SF is 1X. The occupational level of concern for MOE = 100; a residential LOC is not appropriate for this exposure scenario (no residential uses, only considers spray drift)

.Thidiazuron Human Health Risk Assessment DP No. D424978

Page 38 of 55 A.4 Executive Summaries

A.4.1 Subchronic Toxicity

870.3100 90

- Day Oral Toxicity

- Rat

MRID 46121506 : In a subchronic oral toxicity study (MRID 46121506), thidiazuron (99.5% a.i., Batch # 107623

- 03) was ad m inistered to 10 W istar (RJ: W I[IOPS HAN]) rats/sex/dose in

the diet at dose levels of 0, 200, 600, 1800, 5400, or 16,200 ppm (equivalent to 0/0, 11.2/14.0, 34.5/42.1, 102/123, 294/325, and [highest dose not calculated] m g/kg/day) for 90 days.

No treat m ent

- related effects were observed at 20 0 o r 60 0 pp m
, or on ophthal m ology or he m atology at any dose.

At >=180 0 pp m in the m ales, decreased body weights, overall (Days 1

- 90) body weight gains,

and food consu mption were observed. Increased serum alkaline phosphatase was noted.

Decreases were noted in absolute epididy m ides weight and absolute and relative (to body)

prostate gland weight, and s m all prostate gland and s m all se m inal vesicles were observed. The following alterations in m icroscopic pathology were noted: (i) slight to m ild di m inished

secretion of the prostate gland; (ii) slight to m ild diffuse hypertrophy of the zona glo m erulosa

of the adrenal gland; (iii) slight to m ild vacuolation/ m ineralization glo m erulopathy of the kidney; (iv) slight to m ild bilateral hyperplasia of the pelvic epithelium of the kidney; (v) slight

to m ild m ineralized concretions of the renal pelvis; (vi) slight focal m ononuclear cell

infla mm ation of the kidney; (vii) slight to m ild centrilobular hepatocellular hypertrophy; (viii) slight to m ild hyperplasia of ger m inal centers in the spleen; (ix) slight to m arked di m inished

secretion of the se m inal vesicle; (x) sl i ght to m oderate diffuse atrophy of the m a mm ary gland;

and (xi) slight to m ild ger m inal centers in the m edulla of the thy m us.

At >=180 0 pp m in the fe m ales, the following alterations in m icroscopic pathology were noted: (i) slight to m ild diffuse hypertrophy of the zona glo m erulosa of the adrenal gland; (ii) slight to

m ild vacuolation/ m ineralization glo m erulopathy of the kidney; (iii) slight centrilobular hepatocellular hypertrophy; (iv) slight to m oderate adipose infiltr a tion of the bone and m arrow of the sternu m ; (v) slight to m ild hypertrophy of the interstitial gland of the ovary; and (vi) slight to m oderate hyperplasia of ger m inal centers in the spleen.

At >=180 0 pp m
, increased urea was observed in both sexes.

At 540 0 pp m in the m ales, the following increases in relative organ weights were observed: (i)

adrenal gland; (ii) kidney; (iii) liver; and (iv) spleen. R e lative testes weight was decreased. Additionally, the following alterations in m icroscopic pathology were observed: (i) slight focal

m ononuclear cell in f

la mm ation of the epididy m is; (ii) slight f ocal m ineralization of the inner

m edulla of the kidney; (iii) slight to m ild adipose infiltration of the bone and m arrow of the

sternu m ; (iv) slight focal foa m y alveolar m acrophages; (v) slight focal he m orrhage of the lung;Thidiazuron Human Health Risk Assessment DP No. D424978

Page 3 9 of 55 (vi) slight to m ild ger m inal centers of the m esenteric and inguinal ly m ph nodes; and (vii) slight

unilateral atrophy of the se m iniferous epithelium of the testes.
At 540 0 pp m in the fe m ales, decreased body weights, overall (Days 1

- 90) body weight gains,

and food consu m

ption were observed. Increased serum alkaline phosphatase and phosphorus

were noted. Decreases were noted in absolute and relative adrenal gland and uterus weights.

Increases in relative kidney and liver weights were observed, and decreased absolute

m esenteric ly mph node weight was noted. S m all uterus was observed. The following

alterations in m icroscopic pathology were observed: (i) slight to m ild atrophy of the zona reticularis of the adrenal gland; (ii) slight brown pig m ent in the zona reticularis of the adrenal gland; (iii) no cyclical activity of the uterus; (iv) slight to m arked diffuse atrophy of the

uterus; (v) slight to m arked diffuse atrophy of the vagina; (vi) reduced nu m bers of recent

corpora lutea in the ovary; (vii) slight to m ild diffuse atrophy of the m a mm ary gland; (viii) slight ger m inal centers of the m esenteric and inguinal ly mph nodes; and (ix) slight to m ild atrophy of the trabecular bone.

At 540 0 pp m in both sexes, rats exhibited piloerection, appeared thin, and excreted few feces.

Increased cholesterol and potassium were observed, and urine volu m e was increased.

At 16,20 0 pp m
, m ales were observed to have hunched posture, and all ani m als de m onstrated

deficits in righting, grasping, corneal, pupillary, head shaking, and auditory startle reflexes.

All ani m als in this dose group were either found dead or were sacrificed m oribund by Day 10.

The LOAEL is 1800 ppm (equivalent to 102/123 mg/kg/day [M/F]), based on decreased body w eights, overall (Days 1

- 90) body w eight gains, and food consumption, increased

serum alkaline phosphatase, decreased absolute epididymides and absolute and relative (to body) prostate gland w eight, small prostate and small seminal vesicles, and microscopic findings in the prostate gland, seminal vesicle, mammary gland, and thymus of the males, microscopic findings in the bone and marrow of the sternum and ovary of the females, and

increased urea and microscopic findings in the adrenal gland, kidney, liver, and spleen of

both sexes. The NOAEL is 600 ppm (equivalent to 34.5/42.1 mg/kg/day [M/F]).

This study is classified as acceptable/guideline and satisfies the guideline require m ents (OPPTS 870.3100a; OECD 408) for a subchronic oral toxicity study in the rat.

870.3100 90

- Day Oral Toxicity

- Mouse

MRID 46121505 : In a subchronic oral toxicity study (MRID 46121505), Thidiazuron (99.5% a.i., Batch/Lot #: 107623

- 03) was ad m inistered to 10 C57BL/6JICO m ice/sex/dose in the diet at
doses of 0, 500, 1000, 2000, or 4000 ppm (equivalent to 0/0, 85.2/99.8, 170.9/202.6, or 351.4/383.9 m g/kg/day [M/F]) for up to 90 days.

Urinalysis, he m atology, neurological evaluations, and ophthal m oscopic exa m inations were not perfor m ed. There were no treat m ent

- related m acroscopic findings.Thidiazuron Human Health Risk Assessment DP No. D424978

Page 40 of 55 All m ice in the 4000 ppm group died or were sacrificed m oribund on Days 6

- 9. In this group, ani m als exhibited the following clinical signs of toxicity p r ior to their death or sacrifice: (i)

reduced m otor activity, prostration, piloerection, dyspnea, cold to touch, thin appearance, and

hunched posture in both sexes; (ii) staggering step in m ales; and (iii) no feces in fe m ales. Body weights were decreased by 28

- 29% (p<=0.001) in the two m ales and three fe m ales still

alive on Day 8. Food consu m ption was decreased by 53

- 62% (p<=0.001) in both sexes for Days 1

- 8.

At 2000 pp m
, hunched posture was observed in two m ales and one fe m ale on Day 15, and

reduced m otor activity was noted in one fe m ale on Days 28

- 29. Body weights were decreased by 4

- 7% (p<=0.05) throughout treat m ent in the m ales, except Days 57 and 90, and throughout

treat m ent by 6

- 17% in the fe m ales. Overall (Days 1

- 90) body weight gains at this dose were decreased in the m ales (decr. 19%; not significant) and fe m ales (decr. 40%; p<=0.001).

W eekly food consu mption was decreased throughout treat m ent in the fe m ales (decr. 7

- 23%), resulting in decreased average food consu m ption for the overall (Days 1

- 90) study (decr. 12%; p<=0.01). Additionally in the 2000 ppm m ales, alkaline phosphatase was increased by 14% (p<=0.05), and albu m in was decreased by 9% (p<=0.05). At 2000 ppm in both sexes, ter m inal body weights were decreased by 5

- 9% (p<=0.05), and relative (to body) liver weights were increased by 10

- 16% (p<=0.01). Slight centrilobular hepatocellular hypertrophy was observed

in the 2000 ppm fe m ales (2/10 treated vs 0/10 controls).

At >=1000 ppm in the m ales, cholesterol was dose

- dependently decreased by 16

- 34% (p<=0.05) and absolute, relative (to body), and relative (to brain) kidney weights were decreased by 9

- 15% (p<=0.01). The organ weight changes in the kidney were consi d ered equivocal because there were no m acroscopic or m icroscopic findings in the kidney. Additionally, slight centrilobular hepatocellular hypertrophy was observed in the >=1000 ppm

m ales (1

- 9/10 treated vs 0/10 controls). Increased incidences of slight diffuse acinar hypertrophy were observed in the sub m axillary salivary glands of the >=1000 ppm fe m ales (4

- 8/10 treated vs 1/10 controls).

At 500 pp m
, no treat m ent

- related effects were found.

The LOAEL is 1000 ppm (equivalent to 170.9/202.6 mg/kg/day in M/F) based on decreased

cholesterol in the males and on increased incidences of centrilobular hepatocellular hypertrophy in the males and diffuse acinar hypertrophy in the salivary glands in the

females. The NOAEL is 500 ppm (equivalent to 85.2/99.8 mg/kg/day in M/F).

This study is classified acceptable/guideline and satisfies the guideline require m ent (OPPTS 870.3100; OECD 408) for a 90

- day oral toxicity study in the m ouse.Thidiazuron Human Health Risk Assessment DP No. D424978

Page 41 of 55 870.3150 90

- Day Oral Toxicity

– Dog ( no study submitted)

870.3200 21/28

- Day Dermal Toxicity

– Rat

MRID 46261501 : In a 28

- day der m al toxicity study (MRID 46261501), Thidiazuron (>99.9% a.i., Batch #: 107623

- 03) was m o istened with tap water and applied by se m i

- occlusive dressing

to the shaved intact skin of 10 HsdCpb: W U rats/sex/dose at dose levels of 0, 100, 300, or 1000

m g/kg bw/day (li m it dose), 6 hours/day for 5 days/week ( m ales and fe m ales received 20 and

21 applications, respectively) during a 29

- day period.

No co m pound

- related effects were observed in m ort a lity, clinical signs, der m al effects, body weight, body weight gain, food or water consu m ption, he m at o logy, clinical che m istry, ophthal m ology, absolute or relative organ weights, gross or histologic pathology.

The LOAEL w as not observed. The NOAEL w as 1000 mg/kg/day (HDT) (limit dose).

This study is classified as acceptable/guideline and satisfies the Guideline require m ent (OPPTS 870.3200; OECD 410) for a 28

- day der m al toxicity study in rats. A LOAEL was not observed; however, the co m pound was tested at the li m it dose.

870.3465 28

- Day Inhalation

– Rat (no study submitted)

A.4.2 Prenatal Developmental Toxicity

870.3700a Prenatal Developmental Toxicity Study

– Rat

MRID 00077127 : In a develop m ental toxicity study (MRID No. 00077127), 25 presu m ed

pregnant W istar Han 78 strain rats per group were ad m inistered thidiazuron (purity: 99.4%;

batch/lot No.: 271006B) by oral gavage in Myrj 53 solution at doses of 0, 25, 50, 100 or 300

m g/kg/day on gestation days (GD) 6

- 15, inclusive.

On GD 19, da m s were sacrificed and exa m ined grossly. The ovaries and uteri were excised and

the nu m ber of corpora lutea, live young, resorptions, fetal weights and the incidence of external

fetal abnor m alities were recorded. Approxi m ately 2/3 of the litters were exa m ined for skeletal

abnor m alities and the 1/3 were exa m ined for visceral abnor m alities. Uteri were exa m ined for

evidence of i mplantation. Da m s were observed daily and weighed on days 0, 6, 15 and 19 of

pregnancy.

No da m s died during the course of the study. No clinical observations of toxicity were noted. Although a slight decreased m ean body weight gain (87% of controls) was observed in the

fe m ales of the 300 m g/kg/day group; the absolute m aternal weight decrease was minor (6%;

Table 1).Thidiazuron Human Health Risk Assessment DP No. D424978

Page 42 of 55 The m aternal LOAEL was not observed. The m aternal NOAEL is 3 00 m g /kg/day.

There were no differences between the control group and the all treated groups for nu m ber of

litter size, rate of i mplantation, and pre

- and post

- i m plantation losses. Mean fetal weights and

m ean litter body weights were significantly decreased in the 300 m g/kg/day group by 7% (Table 1). Although the magnitude of effect was similar in dams and fetuses, current ly EPA considers a 7% decrease in fetal body weights to be adverse, while a 6% decrease in maternal body weights

is not considered adverse. There were no treat m ent

- related external, visceral, or skeletal

m alfor m atio ns.

The develop m ental LOAEL was 300 m g/kg/day based on decreased fetal body weights. The develop m ental NOAEL was 100 m g/kg/day.

This study is classified acceptable, guideline ( O CSPP 870.3700a ) and satisfies the require m ents
for a develop m ental study in the rat.

COMMENTS : This is a revised Executive Summary only. The LOAEL statement for maternal toxicity was updated to reflect current EPA polices concerning body weight gain and body weight.

870.3700b Prenatal Developmental Toxicity Study

– Rabbit

MRID 46121507 : In a developmental toxicity study (MRID 46121507), Thidiazuron (99.5% a.i.; Lot/Batch # 107623

- 03) in 0.5% (w/v) aqueous methylcellulose was administered daily by oral gavage at a dose volume of 4 mL/kg body weight to 25 female New Zealand White [KBL (NZW) lOPS/SPF] rabbits/group at dose levels of 0, 5, 25, or 125 mg/kg on gestation days (GD)Thidiazuron Human Health Risk Assessment DP No. D424978

Page 43 of 55 6 through 28. All does were sacrificed on GD 29; their fetuses were removed by cesarean and

examined.

Maternal toxicity : At 125 mg/kg/day, five pregnant females aborted between GD 27 and 29. These abortions were considered to be due to the test substance. Red traces (8/25 treated vs 1/25 controls), pl acental tissue (4/25 treated vs 0/25 controls), and/or feto

- placental tissue (5/25 treated vs 0/25 controls) found on the cage trays corresponded to the abortions. Other clinical signs of toxicity at this dose included increased incidence of soft/mucoid fe ces (1

- 3/25 treated vs 0/25 controls), few feces (14/25 treated vs 3/25 controls), and localized soiled fur (4/25 treated vs 0/25 controls). Body weight gain (both correct and uncorrected for gravid uterine weight) was decreased, but no statistical effect was noted on body weight. Food consumption was decreased by 19

- 44% (p<=0.01) at this dose throughout treatment, except for during GD 26

- 29 which was decreased by 9% (not significant) compared to controls. As decreased food consumption did not adversely impact body weight, the effect was not considered adverse.

The only findings at 25 mg/kg/day were a single abortion thought to be due to maternal stress from gavage error (i.e., inflammation and red liquid in trachea) and clinical signs associated with

ab ortion (i.e, red traces and feto

- placental tissue on tray).

The maternal LOAEL is 125 mg/kg/day based on abortions. The maternal NOAEL is 25 mg/kg/day.

Developmental toxicity : No effects of treatment were noted on numbers of litters, fetuses (live or dead), resorptions (early, late, or complete litter), sex ratio, or post

- implantation loss.

At 125 mg/kg/day, fetal body weights were decreased (p<=0.01) by 12

- 13%, and the number of runts was increased compared to concurrent and historical controls. Fetal and/or litter incidences of the following variations, indicative of skeletal retardation, were increased at 125 mg/kg/day over concurrent and historical controls: (i) unilateral or bilateral holes in the frontal or parietal bones; (ii) unossification of the atlas centrum; (iii) unossification of the insertion point(s) on the pelvic girdle; and (iv) incomplete ossification or unossification of the pubis.

Aside from the above

- ment ioned skeletal retardations, there were no developmental variations that could definitely be attributed to treatment.

There were no treatment

- related external, visceral, or skeletal malformations.Thidiazuron Human Health Risk Assessment DP No. 424978

Page 44 of 55 The developmental LOAEL is 125 mg/kg/day bas ed on decreased fetal body weights, increased number of runts, and delayed skeletal ossification. The developmental NOAEL is 25 mg/kg/day.

This study is classified acceptable, guideline (OPPTS 870.3700b) and satisfies the requirements for a developmen tal study in the rabbit.

A.4.3 Reproductive Toxicity

870.3800 Reproduction and Fertility Effects

– Rat

MRID 46209601 : In a two

- generation reproduction toxicity study (MRID 46209601), Thidiazuron (99.5% a.i.; Batch 107623

- 03) was administered continuously in the diet to Han Wistar (HsdBrl Han:Wist) rats (28 animals/sex/dose) at dose levels of 0, 100, 400, or 1200 ppm (equi valent to 0/0, 8.8/9.9, 35.4/39.8, and 108.5/121.1 mg/kg/day [M/F]). The P and F1 parents were dosed for 10 weeks before they were mated to produce the F1 and F2 litters. The F1 pups were weaned on postnatal day (PND) 21, and 24 pups/sex/group (1 pup/sex/l itter as nearly as possible) were randomly selected as parents of the F2 generation.

In the parental animals, no treatment

- related effects were observed on survival, clinical signs, or food consumption or efficiency.

At 1200 ppm, body weight gains were decreased in the P males (statistics not performed) during

pre

- mating (Weeks 0

- 10) by 10%, and overall (Weeks 0

- 17) by 10% (p≤0.05). In the P females at this dose, body weight gains were decreased (p≤0.01) during pre

- mating by 16%. Body weight gains conti nued to be decreased (p≤0.05) by 10% throughout gestation (GD 0

- 20). Only minor

decreases of 5

- 7% (not statistically significant) in body weights were noted at Weeks 17 and 19 in the P and F1 generations, respectively.

In the F1 females at this dose, an i ncreased (p≤0.01) incidence of five day irregular estrous cycles or acyclicity was observed. However, since no effects were noted on fertility or reproductive performance, this finding was considered equivocal.

No treatment

- related findings were noted at 100 or 400 ppm.

The LOAEL for parental toxicity was not observed. The NOAEL is 1200 ppm (equivalent to 108.5/121.1 mg/kg/day [M/F]).

In the offspring, no treatment

- related effects were observed on post

- implantation survival, live birth, viability, or lac tation indices, on the sex ratio, clinical signs, organ weights, or gross pathology.

At 1200 ppm, body weight gains were decreased by 7

- 10% (p≤0.05) in the F1 pups during PND

1

- 21 and during PND 1

- 28, and in the F2 pups during PND 1

- 28 in the males, and d uring PND

1

- 21 and PND 1

- 28 in the females. No statistical differences were noted on body weights in either generation from Day 1 up to 28.Thidiazuron Human Health Risk Assessment DP No. 424978

Page 45 of 55 No effects of treatment were observed at 100 or 400 ppm.

The LOAEL for offspring toxicity was not observed . The NOAEL is 1200 ppm (equivalent to 108.5/121.1 mg/kg/day [M/F]).

In the parental animals, no treatment

- related effects were observed on sperm measures, ovarian follicles, corpora lutea, pre

- coital interval, duration of gestation, or on mating, fertili ty, gestation, or parturition indices.

At 1200 ppm, the day to vaginal opening was increased (p≤0.01) by 3 days (from 34.3 to 37.3 days). This effect was conservatively considered adverse.

The LOAEL for reproductive performance is 1200 ppm (equivalent to 108.5/121.1 mg/kg/day [M/F]) based on delay in vaginal opening. The NOAEL is 400 ppm (equivalent to 35.4/39.8 mg/kg/day [M/F]).

This study is classified as acceptable, guideline and satisfies the guideline requirements (OCSPP 870.3800; OECD 416) for a tw o

- generation reproduction study in the rat.

COMMENTS : This is a revised Executive Summary only. The LOAEL statement for maternal and offspring toxicity was updated to reflect current EPA polices concerning body weight gain and body weight. The effect on vaginal opening was added.

A.4.4 Chronic Toxicity/Carcinogenicity

870.4300a Chronic Toxicity/Carcinogenicity Study

– Rat

MRID 46345201 : In this combined chronic toxicity/carcinogenicity study (MRID 46345201), Thidiazuron (99.5% a.i.; Batch No.: 107623

- 03) was administered in the diet for 2 years to 70

WI

- IOPS AF Wistar rats/sex/dose at doses of 0, 200, 900, or 1800 ppm (equivalent to 0/0, 8.0/11.3, 36.4/51.4, and 75.6/105 mg/kg/day). After 12 months, 10 rats/sex/dose were sacrificed. Additionally , 15 rats/sex/dose were treated at 0 or 1800 ppm for 12 months, fed control diet for 3 months, and then sacrificed.

No treatment

- related effects were observed during the ophthalmoscopic examinations or hematology.

In the 200 ppm group, there were some mi nor changes seen after 24 months but these observations were equivocal and not considered adverse.

At >=900 ppm, the following findings were observed: (i) increased incidence of a wasted appearance in the males during the second year; (ii) decreased body weights in males, either sporadically (900 ppm) or generally throughout the study (1800 ppm); (iii) decreased overall (Days 1

- 708) body weight gains in males; (iii) decreased food consumption in females, frequently throughout the study; and (iv) increased serum urea in males at Months 6 and 12 (900Thidiazuron Human Health Risk Assessment DP No. 424978

Page 46 of 55 ppm) or throughout the study (1800 ppm). The following microscopic lesions were observed at 12 months: renal glomerular mineralization in both sexes; golden brown pigment in the tuboepithelial cells in the kidney in the males; and renal papillary mineralization in the females. The following lesions were observed at 24 months: (i) renal collecting duct hyperplasia in both sexes; (ii) suburothelial congestion in the females; (iii) glomerular mineralization in both s exes; (iv) bilateral pelvic dilatation in the males; (v) chronic progressive nephropathy in the females; (vi) urothelial mineralization in the females; and (vii) bilateral seminal vesicle atrophy.

At 1800 ppm, several additional findings were observed: (i ) reduced motor activity, general pallor, and soiling around the anogenital region in the males during the second year; (ii) increased mortality in the males; (iii) decreased body weights and overall (Days 1

- 708) body weight gain in males; (iv) decreased f ood consumption in males; (v) increased cholesterol, triglycerides, and phosphorus in the males; (vi) increased urea and cholesterol in the females; (vii) decreased albumin/globulin and glucose in males; and (viii) increased incidence of urinary protein concentration >=3 g/L in both sexes. Grossly, an increased incidence of irregular kidney surface was observed in males at 15 months (recovery). After 24 months, an increase of small seminal vesicles in males; and irregular kidney surface and pale kidney in both sexes were

observed. Increased relative

- to

- body kidney weights were observed after 24 months. Increased incidence of the following microscopic lesions were also observed: (i) chronic progressive nephropathy in both sexes at 12, 15, and 24 months; (ii ) bilateral renal pelvic dilatation in the females at 12 months; (iii) diffuse germinal cell atrophy in the testes, unilateral at 12 months and bilateral at 24 months; (iv) unilateral luminal dilation in the testes at 12 months; (v) oligospermia in the epi didymis, unilateral at 12 months and bilateral at 24 months; (vi) renal glomerular mineralization in both sexes at 15 months; (vii) golden brown pigment in the renal tuboepithelial cells in males at 15 and 24 months; and (viii) renal suburothelial congesti on in the females at 15 months. Additionally, increased incidence of the following microscopic lesions were observed in males at 24 months: (i) renal transitional cell hyperplasia; (ii) renal glomerular hyaline deposit, (iii) arteritis in kidneys, testes, and epididymis; (iv) epithelial degenerative changes in the epididymis; (v) mixed cell infiltrate in the seminal vesicles; (vi) diffuse parathyroid hyperplasia; (vii) focal/multifocal parathyroid hyperplasia; (viii) fibrous osteodystrophy in the sternum an d articular surface; and (ix) hyperosteoidosis in the articular surface.

Only 13% of the 1800 ppm males survived 24 months. The cause of death of 26/49 of these males was considered to be chronic progressive nephropathy, and at least 95% of the animals at this dose had chronic progressive nephropathy and renal glomerular mineralization. Therefore, findings in these animals may have been confounded by severe renal dysfunction. In particular, parathyroid hyperplasia, osteodystrophy, and hyperosteoidosis may have been related to renal dysfunction.

The LOAEL is 900 ppm (equivalent to 36.4/51.4 mg/kg/day in males/females), based on decreased body weight and body weight gain in the males, increased bilateral seminal vesicle atrophy, and nephrotoxicity in both se xes. The NOAEL is 200 ppm (equivalent to 8.0/11.3 mg/kg/day).

At the doses tested, there was not a treatment

- related increase in tumor incidence when compared to controls. Dosing was considered adequate based on decreased survival, bodyThidiazuron Human Health Risk Assessment DP No. 424978

Page 47 of 55 weights, body weig ht gains, and food consumption, increased clinical signs, differences in clinical chemistry parameters, nephrotoxicity, and male reproductive system toxicity.

This study is classified as acceptable, guideline and satisfies the guideline requirements (OPPT S 870.4300; OECD 453) for a combined chronic toxicity/carcinogenicity study in rats.

870.4 1 00b Chronic Toxicity Study

– Dog

MRID 00159344 : In a chronic toxicity study (MRID No. 00159344), thidiazuron (purity: 98.8% a.i.; Batch No: 7/9.82) was administered to 5 beagle dogs/sex/dose in the diet at levels of 0, 100, 300, or 1000 ppm for 1 year. Corresponding daily intakes of test material for the one

- year study were 0, 3.93, 11.8, or 38.3 mg/kg/day for males and 0, 4.01, 11.1, or 36 mg/kg/day for females.

No spontaneous deaths occurred during the study. One high

- dose male (No. 4744) and female (No. 4731) exhibited compound related signs of toxicity (apathy, high heart frequency, severe anemia, and inspiratory dyspnea). The male dog was sacrificed moribund in study week 7. The female dog was fed control diet for a reversibility study after week 38.

Thidiazuron caused no significant change in group mean body weights and food consumption except for the two high

- dose animals (Nos. 4744 and 4731) descr ibed above.

In the low

- dose group, no compound

- related clinical signs of toxicity were observed.

In the mid

- dose group, one male dog showed symptoms of anemia. Also, in two males (Nos. 4702 and 4728), decreased hematocrit (64

- 66% of controls at week 27), decreased hemoglobin (56% of controls at week 27), decreased red cell count (43

- 57% of controls at weeks 27 and 39), and increased reticulocyte count (280

- 1480% of controls at weeks 27 and 39) were observed.

Significant (p<0.05 or 0.01) compound

- related changes in clinical chemistry parameters (alkaline phosphatase and albumin/globulin ratio) were observed in the mid

- dose animals, however, the observed changes were not considered biologically significant because there were no clear dose

related trends.

The changes in organ weights were statistically insignificant because of t he small number of

animals used in the test. In mid

- dose males, increases in absolute and relative weights for liver (19% and 24% of controls, respectively), spleen (22% and 27% of c ontrols, respectively), and lymph nodes (48% and 49% of controls, respectively) were observed. In females, absolute and relative spleen weights (21% and 22% of control s, respectively) were increased . Histologically,

there was an increased incidence of mark ed hemosiderosis in Kupffer cells in liver (2/5) and spleen (1/5) and an incr ease in Kupffer cells in liver (3/5) of males.

In the high

- dose group, four animals (two of each sex) showed symptoms of anemia. Also, in the females, decreased hematocrit (at we eks 12 and 29), decreased hemoglobin (week 12) and increased reticulocyte count (week 12) were observed. Significant (p<0.05 or 0.01) compound

related changes in clinical chemistry parameters (alkaline phosphatase, total serum protein andThidiazuron Human Health Risk Assessment DP No. 424978

Page 48 of 55 albumin/globulin ratio) were observed in the high

- dose animals, however, the observed changes were not considered biologically significant because there were no clear dose

- related trends. The changes in organ weights were statistically insignificant because of the small nu mber of

animals used in the test. In high

- dose males, absolute and relative weights for liver (14 % and 19% of controls, respectively), spleen (123 and 107% of controls, respectively), and lymph nodes (116% and117% of controls, respectively) were increased . In females, absolute and relative weights for liver (29% and 12% of controls, respectively), spleen (167% and 132% of controls, respectively) and lymph node (54% and 31% of controls, respectively) were increased compared to controls.

Histologically, th ere was an increased incidence of pigment deposition in liver, kidney, and spleen and an increase in Kupffer cells in liver of high

- dose males and females. The two high

dose females with severe anemia had increased Kupffer cells, hemosiderin in the spleen, increased splenic hematopoiesis, and iron

- negative pigment in the tubular epithelium of the kidney. Localized infiltration of lymphocytes in the mucosa of the gallbladder was found in all high

- dose animals (2/5 control males; 1/5 control females). In addi tion, the following lesions were found in females: early or progressive involution in the thymus (high

- dose, 4/5; control, 1/5), interfollicular cell increase in the thyroid (high

- dose; 3/5; control, 0/5), and follicular hyperplasia in the lymph nodes (hig h

- dose, 2/5; control, 1/5).

The LOAEL is 300 ppm (11.1 mg/kg/day) based on increased incidence of anemia, changes in hematological parameters and marked hemosiderosis in liver and spleen. The NOAEL is 100 ppm (3.93 mg/kg/day).

This chronic study in the dog is classified as acceptable, guideline and satisfies the guideline requirement for a chronic oral study in the dog [OPPTS 870.4100b].

A.4.5 Carcinogenicity

870.4300a Chronic Toxicity/Carcinogenicity Study

– Rat, MRID 46345201 (See Section A.4.4)

870.4200b Carcinogenicity Study

– Mouse

MRID 46346001: In a carcinogenicity study (MRID 46346001), Thidiazuron (99.5% a.i.; Batch

# 107623

- 03) was administered in the diet to C57BL/6 mice (60/sex/dose) at doses of 0, 200, 650, or 2000 ppm (0/0, 26.5/33.4 , 86.7/107.8, and 279.9/329.7 mg/kg/day in males/females) for up to 18 months. Ten mice/sex/dose were sacrificed at 52 weeks.

No treatment

- related effect was observed on mortality or hematology. At 2000 ppm, tremors were observed in both sexes. In the fem ales, increased incidences of wasted appearance, prolapsed rectum, and soiled anogenital region were observed. Body weights were decreased in both sexes throughout the study. Body weight gain was decreased at 2000 ppm in both sexes at Days 1

- 92, 92

- 540, an d 1

- 540. In both sexes, food consumption generally was decreased throughout treatment, and overall (Weeks 1

- 80) group mean food consumption was

also decreased.Thidiazuron Human Health Risk Assessment DP No. 424978

Page 49 of 55 At 2000 ppm at the interim sacrifice (n=10), increased incidence of slight renal cortical basophilic tubules was observed in the females.

At 2000 ppm at the terminal sacrifice, the epididymis and kidney were identified as target organs. The incidence of grossly enlarged epididymis was increased. The incidences of the following microscopic lesi ons in the epididymis were increased: (i) dilated tubules; (ii) interstitial mononuclear cell infiltrate; (iii) unilateral and bilateral oligospermia; and (iv) spermatic granuloma. Relative

- to

- body kidney weight was increased in the females, as was the

inc idence of gross renal pelvic dilatation. The incidences of the following microscopic renal lesions were increased: (i) cortical basophilic tubules in the females; (ii) proteinaceous casts in the males; (iii) interstitial mononuclear cell infiltrate in the males; and (iv) bilateral pelvic dilatation in the males and females. Additionally, there was a decrease in renal corticoepithelial

vacuolation in the males.

At 650 ppm, marginal effects were observed. At the terminal sacrifice, the incidences of the

foll owing lesions in the epididymis were slightly increased: (i) dilated tubules; (ii) interstitial mononuclear cell infiltrate; and (iii) bilateral oligospermia. Additionally, there was a decrease in renal corticoepithelial vacuolation in the males. In female s, minor decreases in body weight gain at Days 92

- 540 and at Days 1

- 540 and. overall group mean food consumption was observed. The incidence of renal cortical basophilic tubules was increased in the females. The above effects found in 650 ppm animals bec ame more severe and numerous at 2000 ppm indicating that the syndrome of toxicity may have begun at 650 ppm.

Hepatotoxicity was equivocally indicated as follows. At the interim sacrifice (n=10), slight to minimal centrilobular hypertrophy was observed in the 2000 ppm males. Relative

- to

- body liver weights were increased in the 2000 ppm males and the >=650 ppm females at the interim sacrifice. The incidences (and usually severity) of the following hepatic lesions were increased at

the terminal sacrifice: ova l cell proliferation in the >=650 ppm males and 2000 ppm females; centrilobular hepatocellular hypertrophy and focus(i) of altered hepatocytes (basophilic cells) in the 2000 ppm males. There was no indication that hepatic function was impaired nor that

car cinogenesis resulted from these observed effects.

The LOAEL is 650 ppm (equivalent to 86.7/107.8 mg/kg/day in males/females) based on decreased body weight gain, and food consumption; and increased nephrotoxicity in females; and increased epididymis toxic ity in males. The NOAEL is 200 ppm (equivalent to 26.5/33.4 mg/kg/day in males/females).

At the doses tested, there was not a treatment

- related increase in tumor incidence when compared to controls. Dosing was considered adequate based on systemic toxicit y and toxicity in the kidney and epididymis.

This st udy is classified as acceptable, guideline and satisfies the guideline requirements (OPPTS 870.4200b; OECD 451) for a carcinogenicity study in mice.Thidiazuron Human Health Risk Assessment DP No. 424978

Page 50 of 55 A.4.6 Mutagenicity

870.5100 Bacterial Reverse Gene Mutation Assay

MRID 46121508: In two independent reverse gene mutation assays in bacteria (MRID 46121508), Salmonella typhimurium strains TA98, TA100, TA1535, and TA1537 and Escherichia coli strain WP2 uvrA/pKM101 (CM891) were exposed to Thidiazuron (98.7 % purity, Batch/Lot #: CH 107623

- 02) in dimethylsulfoxide (DMSO) at concentrations of 0, 5, 15, 50, 150, 500, 1500, or 5000 μ g/plate (±S9, Trial 1), and 0, 1.5, 5, 15, 50, 150, 500, or 1500 :g/plate (±S9, Trial 2). The standard plate incorporation method was performed in Trial 1 and a

pre

- incubation step was added in Trial 2. Standard strain

- specific mutagens served as positive

controls.

Thidiazuron was tested at up to the limit dose (5000 μg/plate) in Trial 1, and up to cytotoxic concentrations (1500 μ g/plate) in Trial 2. Cytotoxicity (indicated by an incomplete background lawn) was obs erved in all strains at >=1500 μ g/plate in Trial 1 (plate incorporation test), and in

all strains at >=500 μ g/plate in Trial 2 (pre

- incubation test). No treatment

- related increases in the number of revertants/plate were observed in any bacterial strain at any dose level of Thidiazuron

in the presence or absence of S9

- activation, compared to solvent controls. The positive controls induced the appropriate responses. There wa s no evidence of induced mutant colonies over background under the conditions of these tests.

The st udy is classified as acceptable, guideline and satisfies the guideline requirement (OPPTS 870.5100; OECD 471) for in vitro mutagenicity (bacterial reverse gene mutation) data.

870.5375 In Vitro Chromosomal Aberration Assay in Human Peripheral Blood Lymphocytes

MRID 46121510: In independently performed mammalian cell cytogenetic (chromosome aberration) assays (MRID 46121510), lymphocyte cultures prepared from human peripheral

blood were exposed to Thidiazuron (98.7% a.i., Batch/Lot #: CH107623

- 02) in dimethyl sulfoxide for 4 hours at concentrations of 0, 9.4, 18. 75, 37.5, 75, 150, 200, or 250 μ g/mL both in the presence and absence of S9

- activation, and for 20 hours at concentrations of 0, 4.7, 9.4

, 18.75, 37.5, 75, 150, or 200 μ g/mL in the absence of S9

- activation. Cells were harvested at 20

hours after initiation of treatment.

Thidiazuron was tested up to cytotoxic concentrations (mito tic suppression; 53

- 60% at 150

μ g/mL [±S9] at 4 hou rs of exposure and 51% at 37.5 μ g/mL [

- S9] at 20 hours of exposure). No significant increases in aberration frequency were observed at up to 150 μ g/mL (±S9) after 4 hours of exposure or at up to 37.5 μ g/mL (

- S9) after 20 hours of exposure. The positive controls induced the appropriate response. There was no evidence of chromosome aberration induced over background in the presence or absence of S9

- activation at either time point.

This study is classified as acceptable, g uideline and satisfies the guideline requirement (OPPTS 870.5375, OECD 473) for in vitro cytogenetic mutagenicity (chromosome aberration) data.Thidiazuron Human Health Risk Assessment DP No. 424978

Page 51 of 55 A.4.7 Neurotoxicity (no study submitted)

A.4. 8 Metabolism

870.7485 Metabolism

– Rat

MRID 42529001 : In a metabolism study (MRID 42529001), groups of male and female Sprague

- Dawley CD rats were dosed with 14 C

- thidiazuron [( 14 C

- aniline) thidiazuron or ( 14 C

thiadizaole) thidiazuron (purity: >97% a.i.; batch No: 1695

- 3 and 1695

- 4)] at a single oral gavage do se (10 or 1000 mg/kg) or 14

- day repeated oral doses of thidiazuron at 10 mg/kg followed by a single oral dose of 14 C

- thidiazuron at 10 mg/kg. An intravenous dose group was not included in this study.

The results of the pilot study showed that less than 0. 2% of administered radioactivity was

eliminated as 14 CO 2 from administration of either ( 14 C

- aniline) thidiazuron or ( 14 C

- thiadizaole) thidiazuron. In addition, the study showed no significant differences in the percentages eliminated through urine or feces from administration of the two radiolabeled forms.

Absorption of thidiazuron was rapid but incomplete at both doses, and appeared decreased at the high dose relative to the low dose. Elimination of thidiazuron was relatively rapid at the single

low oral dose level. The major route of elimination was shown to be via urine. The single low, single high, and multiple low oral dose studies indicate that the total radioactivity recov ered within 5 days after dosing in the urine and feces were 91

- 104% of administ ered dose. At the low dose, the radioactivity recovered in the urine and feces was 60

- 66% and 29

- 31% of the dose over

a 5

- day period, respectively. At the repeated low oral dose, the radioactivity recovered in the

urine and feces was 73

- 75% and 26

- 28% of t he dose over a 5

- day period, respectively. At the high dose, the radioactivity recovered in the urine and feces was 41

- 47% and 56

- 60% of the dose

over a 5

- day period, respectively. Administration of a single high dose resulted in a decreased percentage of thidiazuron derived radioactivity eliminated in urine (approximately 20%), with concomitant rise in fecal elimination. This alteration is likely due to reduced absorption of test material at the high dose.

Terminal tissue distribution data showed that highest concentrations of thidiazuron derived radioactivity at sacrifice were found in the liver, kidneys, thyroid, whole blood and adrenals at both low and high doses. Repeated oral dosing did not significantly affect distribution of

thidiazuron derived r adioactivity.

Identification of urinary and fecal metabolites by TLC and HPLC indicated the presence of one oxidative metabolite in urine (4

- hydroxy thidiazuron, metabolite J) and the presence of sulfate and glucuronide conjugates of 4

- hydroxy thidiazuron (metabolites A/B, D, and F). However, insufficient evidence was presented to justify the presence of more than one sulfate and one glucuronide conjugate of 4

- hydroxy thidiazuron in urine. This deficiency does not render the study inadequate, as the other possible oxidative metabolite(s) as candidates for conjugation represent a minor percentage of metabolized thidiazuron.Thidiazuron Human Health Risk Assessment DP No. 424978

Page 52 of 55 In urine, the significant metabolites found at low dose were metabolite F (males, 36

- 38% of dose; females, 14

- 21%), metabolite J (males , 11%; females, 18

- 19%), metabolite A/B ( males, 4%; females, 3

- 6%), and metabolite D (males, 5

- 8%; females, 7

- 9%). Significant urinary metabolites in rats from the repeated low dose group were metabolites F (24

- 41%), metabolite J (12

- 25%), metabolite A/B (3

- 4%), and metabolite D (7

- 9%). Percentages of each of metabolites F and J rose slightly in both sexes of rats from repeated low dose administration, indicating a possible mild induction of metabolism. At high dose, the percentage of metabolite F in male s and females (2% of dose) was smaller than that of metabolite J (7

- 11%).

In feces, the major metabolites identified were 4

- hydroxy thidiazuron (14

- 16%) at the low and repeated low dose, and unmetabolized thidiazuron (37

- 44%) at the high dose.

This stud y is classified as acceptable, guideline and satisfie s the guideline data requirement for a metabolism study (85

- 1) in rats.

870.7600 Dermal Absorption

– Rat

MRID 46261502: In a der m al penetration study (MRID 46261502) Thidiazuron (99.9 %a.i.,

batch # OR 1844 (SEL/1098), [phenyl

- U

14 C]

- thidiazuron) was ad m inistered to 5 m ale Sprague Dawley CD rats/dose to a 12 c m 2 area of the back in a for m ulation and water dilution thereof at
dose levels of 5.0

, 0.0 4 an d 0.004 mg/cm 2 . Exposure durations and percent of dose absorbed are presented in the table below.

Dos e Level Mea n Percentag e o f Dos e Absorbed

1 hour 4 hours 8 hours 2 4 hours 2 4 hours* 7 2 hours* 12 0 hours*

5. 0 mg/cm 2 0.114 0.147 0.141 0.204 0.137 0.178 0.220
0.0 4 mg/cm 2 0.214 0.406 0.388 0.754 0.634 0.660 1.252

0.00 4 mg/cm 2 0.455 0.534 0.721 1.179 0.635 0.910 1.170

* washed at 8 hours

The m ean total recoveries were in the range 88% and 99.54% dose for all groups. The a m ount
in the stratum corneum was 0.73%, 10.68% and 8.14% at 24 hours for the high, m iddle and low

dose groups respectively after a 24

- hours exposure and 0.41%, 3.24% and 5.37% at 120 hours following 8

- hours exposure for the high, m iddle and low dose groups respectively. However,

the results showed that the m ajority of the radioactive m aterial in the stratum corneum was lost by desqua m ation and upward renewal of the stratum corneum with ti m e.

This study in the rat is acceptable, guideline and satisfies the guideline require m ent for a der m al penetration study (870.7600) in rats.

A.4.9 Immunotoxicity (n o study submitted)Thidiazuron Human Health Risk Assessment DP No. 424978

Page 53 of 55 Appendix B . International Residue Limits Table

Table B . Summary of US and International Tolerances and Maximum Residue Limits for Thidiazuron ( 120301 ) Residue Definition :
US Canada Mexico 2 Codex

40 CFR 180.403: thidiazuron (N

- phenyl

- N

- 1,2,3

- thiadiazol

- 5

- ylurea) and its aniline containing metabolites None None

Commodity 1 Tolerance (ppm) /Maximum Residue Limit (mg/kg)

US Canada Mexico 2 Codex
Cattle, fat 0.4

Cattle, meat 0.4

Cattle, meat byproducts 0.4
Cotton, gin byproducts 24.0

Cotton, undelinted seed 0.3

Goat, fat 0.4

Goat, meat 0.4
Goat, meat byproducts 0.4
Hog, fat 0.4
Hog, meat 0.4
Hog, meat byproducts 0.4

Horse, fat 0.4

Horse, meat 0.4
Horse, meat byproducts 0.4

Milk 0.05
Sheep, fat 0.4
Sheep, meat 0.4
Sheep, meat byproducts 0.4
Completed: M. Negussie; 12/31/2014

1 Includes only commodities of interest for this action. Tolerance values should be the HED recommendations and not those proposed by the applicant.

2 Mexico adopts US tolerances and/or Codex MRLs for its export purposes.Thidiazuron Human Health Risk Assessment DP No. 424978

Page 54 of 55 A ppendix C

. Metabolites

TABLE C

. Nomenclature for the Metabolites of Thidiazuron

. Compound Chemical Structure

Common Name 4

- Hydroxy Thidiazuron

IUPAC Name 1

- (4

- hydrophenyl)

- 3

- (1,2,3

- thidizol

- 5

- yl)urea

CAS Name N

- (4

- hydroxyphenyl

- N

- 1,2,3

- thidiazol

- 5

- yl)urea CAS Registry Number Not applicable Compound Chemical Structure

Common Name Phenylurea

IUPAC Name 1

- phenylurea

CAS Name N

- phenylurea CAS Registry Number 64

- 10

- 8

Appendix D . Physical/Chemical Properties

T able D

. Physicochemical Properties of the Technical Grade Compound (Thidiazuron)

. Parameter Value Reference
Melting point/range 217 °C D311632; T. Jimerson;

1/27/05 pH (20 °C) 5.21 Density (20 °C) 0.324 gm/cc Water solubility (2 5 °C , pH 7.0 ) 31.0 mg/L Solvent solubility ( temperature not specified ) Very soluble in dimethylsulfoxide, dimethylformanide, acetone, cyclohexanone, and isophrone. Slightly soluble in aliphatic and aromatic hydrocarbons and water
Vapour pressure (20 °C) 3.5 x 10

- 9 mPa

Dissociation constant

, pK
a (25 °C) 8.86 Octanol/water partition coefficient

, K O / W ( 2 5 °C , pH 7.3 ) 50.0

UV/visible absorption spectrum λ max = 238 nm; ε = 985M

- 1 cm - 1Thidiazuron Human Health Risk Assessment DP No. 424978

Page 55 of 55 Ap pendix E . Review of Human Research

This risk assessment relies in part on data from studies in which adult human subjects were intentionally exposed to a pesticide or other chemical. These data, which include studies from PHED 1.1; the AHETF database; and the Outdoor Residential Exposur e Task Force (ORETF)

database ; are (1) subject to ethics review pursuant to 40 CF R 26, (2) have received that review, and (3) are compliant with applicable ethics requirements. For certain studies, the ethics review may have included review by the Human Studies Review Board. Descriptions of data sources, as well as guidance on their use, can be found at http://www.epa.gov/pesticides/science/handler

exposure

- data.html and htt p://www.epa.gov/pesticides/science/post

- app

- exposure

- data.html

.