Page 3 of 70

5.4.2 Chronic and Cancer Dietary Exposure and Risk ...................................................23

6.0 RESIDENTIAL EXPOSURE AND RISK........................................................................24

6.1 Residential Bystander Postapplication Inhalation Exposure .............................................24

6.2 Spray Drift .........................................................................................................................25

7.0 AGGREGATE EXPOSURE AND RISK ASSESSMENT...............................................25

7.1 Short-Term Aggregate Risk to Residential Applicators....................................................26

7.2 Short-Term Aggregate Risk for Residential Post-Application Exposure..........................26

8.0 CUMULATIVE RISK.......................................................................................................27

9.0 OCCUPATIONAL EXPOSURE AND RISK...................................................................28

9.1 Handler Exposure ..............................................................................................................28

9.1.1 Handler Exposure Scenarios..................................................................................28

9.1.2 Handler Exposure Data and Assumptions .............................................................29

9.1.3 Handler Exposure and Risk Estimates...................................................................29

9.2 Post Applicatoin Exposure ................................................................................................31

9.2.1 Post Application Exposure Scenarios....................................................................32

9.2.2 Post Application Exposure Data and Assumptions for Field Crops......................32

9.2.3 Post Application Exposure Data and Assumptions for Post Harvest Potato .........33

9.2.3 Post Application Exposure and Risk Estimates.....................................................33

10.0 REFERENCES ..................................................................................................................35

Appendix A. Toxicity Profile and Executive Summaries..............................................................36

A.1 Toxicity Data Requirements..................................................................................36

A.2 Toxicity Profiles.....................................................................................................37

A.3 Hazard Identification and Endpoint Selection .......................................................42

A.4 Executive Summaries.............................................................................................44

Appendix B. Metabolism ..............................................................................................................64

Appendix C. Physical/Chemical Properties...................................................................................70

Appendix D. Review of Human Research.....................................................................................70
Page 4 of 70

1.0 EXECUTIVE SUMMARY

This assessment provides information to support amended Section 3 registrations for the 

new postharvest use of difenoconazole on Tuberous and Corm Vegetables Subgroup 1C and the 

expansion of currently registered foliar uses for fruiting vegetables, citrus fruits, pome fruits, and 

strawberries to include the additional commodities specified under Fruiting Vegetables Group 8-

10, Citrus Fruits Group 10-10, Pome Fruits Group 11-10, and Low growing Berry Subgroup 13-

07G, Except Cranberry. This document assesses dietary and drinking water risks associated with 

exposures resulting from currently registered and proposed new uses of and tolerances for 

difenoconazole. It also assesses potential enhanced sensitivity of infants and children from 

dietary and/or residential exposure as required under the Food Quality Protection Act (FQPA) of 

1996.

Use Profile

Difenoconazole is a broad spectrum fungicide belonging to the triazole group of 

fungicides. It is currently registered in the U.S. for use as a seed treatment on barley, canola, 

cotton, sweet corn, wheat, and triticale and for foliar application to numerous food crops and 

ornamentals. Tolerances for difenoconazole, currently established under 40 CFR §180.475, 

range from 0.01-95 ppm. Difenoconazole acts by blocking demethylation during sterol 

biosysnthesis which, in turn, disrupts membrane synthesis. Difenoconazole is available as 

emulsifiable concentrate, soluble concentrate, emulsion [oil] in water, flowable suspension, and 

ready-to-use formulations. As a seed treatment, it is applied with commercial grade seed 

treatment equipment. As a foliar treatment, it is applied to field and vegetable crops, landscape 

ornamentals and golf course turf by commercial applicators using aerial and ground application 

methods and equipment. It is applied to ornamentals by residential applicators using hand held 

sprayers. 

Proposed New Uses

The Interregional Research Project No. 4 (IR-4) is requesting the following actions. 

1) Establishment of tolerances for residues of difenoconazole in/on Fruiting Vegetables 

Group 8-10, Citrus Fruits Group 10-10, Pome Fruits Group 11-10, and Low growing 

Berry Subgroup 13-07G, Except Cranberry. 

2) An increase in the existing tolerance in/on Vegetable, tuberous and corm, subgroup 1C 

from 0.01 ppm to 4.0 ppm;

3) Removal of existing tolerances in/on potato, processed waste, fruiting vegetable (group 

8), citrus (group 10), pome fruit(group 11), and strawberry; 

4) An amendment for the Section 3 registration for ThesisTM Fungicide (EPA Reg. No. 100-

1386) to add a postharvest use on Vegetables, tuberous and corm, subgroup 1C (1 

application at 0.0070 lb ai/ton tubers); and 

5) Amendments for the Section 3 registrations for InspireTM Fungicide (EPA Reg. No. 100-

1262), InspireTM XT Fungicide (EPA Reg. No. 100-1312), Quadris TopTM Fungicide

(EPA Reg. No. 100-1313) and Inspire Super TM Fungicide (EPA Reg. No. 100-1317) to 

expand currently registered foliar uses for fruiting vegetables, citrus fruits, pome fruits, 
Page 5 of 70

and strawberries to include the additional commodities specified under the following new 

crop groups/subgroup; Fruiting Vegetables Group 8-10, Citrus Fruits Group 10-10, Pome 

Fruits Group 11-10, and Low growing Berry Subgroup 13-07G, Except Cranberry. No 

substantive changes to the currently registered foliar use patterns on the subject crops 

have been proposed. 

Hazard Identification

Subchronic and chronic toxicity studies with difenoconazole in mice and rats showed 

decreased body weights, decreased body weight gains and effects on the liver. Acute and 

subchronic neurotoxicity studies showed evidence of neurotoxic effects. However, the observed 

effects were transient and the dose-response was well characterized with identified dose levels at 

which no observed adverse effects were seen. The available toxicity studies indicated no 

increased susceptibility of rats or rabbits from in utero or postnatal exposure to difenoconazole. 

There are no indications of immunotoxicity in the available studies. No evidence of 

carcinogenicity was seen in the chronic/cancer rat study. Evidence for carcinogenicity was seen 

in mice as induction of liver tumors at doses which were considered to be excessively high for 

carcinogenicity testing. Difenoconazole has been classified as “Suggestive Evidence of 

Carcinogenic Potential” with risk quantified using a non-linear (Margin of Exposure) approach. 

The cancer classification is based on excessive toxicity observed at the two highest doses, the 

absence of tumors at the lower doses and the absence of genotoxic effects. The FQPA Safety 

Factor is reduced to 1X. Difenoconazole exhibits low acute toxicity by the oral, dermal and 

inhalation routes of exposure. It is not an eye or skin irritant and is not a sensitizer.

The toxicological database for difenoconazole is sufficient to conduct this risk 

assessment. An immunotoxicity study, required under Part 158 Toxicology Data requirements, 

has been submitted and is under review. 

Dose Response Assessment

Toxicological points of departure (PODs) were selected for dietary and drinking water

exposures for the assessment of proposed new uses of difenoconazole. Acute and chronic PODs

were selected for assessment of food and water exposures. An acute POD for all populations 

was selected from an acute neurotoxicity study in rats based on reduced grip strength. A chronic 

POD was selected from a chronic/carcinogenicity study in rats based on body weight effects. 

Short and intermediate-term incidental oral, dermal and inhalation PODs were selected from an 

oral rat reproduction study based on decreased body weight effects in pups and parental animals. 

A dermal absorption factor is applied when dermal exposure endpoints are selected from oral 

toxicity studies. A dermal absorption factor of 6% was used for the dermal exposure assessment. 

Inhalation toxicity is assumed to be equivalent to oral toxicity. An uncertainty factor of 100X 

was applied endpoints selected for all exposures routes (10X for interspecies extrapolation, 10X 

for intraspecies variation). 
Page 6 of 70

Exposure/Risk Assessment and Risk Characterization

Risk assessments were conducted for dietary (food and water), occupational and 

aggregate exposure for the proposed new uses of difenoconazole. A new residential assessment 

is not required because the proposed new use does not include residential applications or 

exposures. Screening level acute and refined chronic dietary and drinking water risk assessments 

indicate that for all commodities, dietary and drinking water exposure estimates are below 

HED’s level of concern. Additionally, the requested uses of difenoconazole resulted in an 

increase in dietary exposure estimates for free triazole or conjugated triazoles. Therefore, dietary 

exposure analyses for the triazole metabolites needed to be updated (T. Morton, D397591, 

1/26/12).Risk estimates for worker handler and post-application exposure scenarios exposures 

are not of concern at maximum use rates for existing and proposed new uses. Aggregate risks 

are not of concern.

Aggregate Assessment of Free Triazole & its Conjugates

The addition of the new proposed uses increases the aggregate exposure to free triazoles and its 

conjugates. Therefore, the aggregate human health risk assessment was updated for free 

triazoles and its conjugates and the aggregate estimates remain below HED’s level of concern.

Use of Human Studies

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

were intentionally exposed to a pesticide or other chemical. These studies, listed in Appendix D

have been determined to require a review of their ethical conduct. Some of these studies are also 

subject to review by the Human Studies Review Board. All of the studies used have received the

appropriate review.

2.0 HED RECOMMENDATIONS

2.1 Data Deficiencies

Submission of a revised Section B and a revised Section F are required (see 

Section 2.2.3). An immunotoxicity study, required under Part 158 Toxicology Data 

requirements, has been submitted and is under review. The Hazard and Science Policy Council 

(HASPOC) concluded based on a weight of evidence (WOE) approach that a 28-day inhalation 

toxicity study is not required at this time. This approach considered all of the available hazard 

and exposure information for difenoconazole, including: (1) the use of an oral POD that results 

in MOEs greater than 1,300 (the lowest MOE) for risk via the inhalation route resulting from 

occupational and residential; (2) the physical/chemical properties and very low vapor pressure of 

difenoconazole; and (3) the toxicological profile of difenoconazole. 
Page 7 of 70

2.2 Tolerance Considerations

2.2.1 Enforcement Analytical Method

An adequate enforcement method, GC/NPD method AG-575B, is available for the 

determination of residues of difenoconazole per se in/on plant commodities. An adequate 

enforcement method, LC/MS/MS method REM 147.07b, is available for the determination of 

residues of difenoconazole and CGA-205375 in livestock commodities. Adequate confirmatory 

methods are also available. 

2.2.2 International Harmonization

Codex maximum residue levels (MRLs) for residues of difenoconazole per se have been 

established at 0.5 ppm for tomato; 0.5 ppm for pome fruits; and 0.02 ppm for potato. Based on 

the available magnitude of the residue data, harmonization with these established Codex MRLs 

is not possible because, due to differences in good agricultural practices (GAP) the Codex MRLs 

are too low to adequately cover residues resulting from the proposed use rates in the U.S. 

Mexican and Canadian MRLs have been established for difenoconazole; however, no Mexican 

MRLs have been established for the requested crops. Canadian MRLs for residues of 

difenoconazole per se have been established at 0.6 ppm for a number of fruiting vegetables and 

1.0 ppm for a number of pome fruit, and are in harmony with proposed U.S. tolerances. HED 

has been informed by RD that Canada has agreed to harmonize with the proposed U.S. tolerance 

for vegetable, tuberous and corm, subgroup 1C at 4.0 ppm. 

2.2.3 Recommended Tolerances

HED has examined the residue chemistry database for difenoconazole and pending 

submission of a revised Section F (see requirements under Revisions to Petitioned for

Tolerances), there are no residue chemistry issues that would preclude establishment of 

tolerances for residues of difenoconazole only in/on the commodities listed below:

Vegetable, fruiting, group 8-10 ................................................0.60 ppm

Fruit, citrus, group 10-10 ..........................................................0.60 ppm

Fruit, pome, group 11-10 ..........................................................1.0 ppm

Berry, low growing, subgroup 13-07G, except cranberry........2.5 ppm

Vegetable, tuberous and corm, subgroup 1C............................4.0 ppm

Potato, wet peel.........................................................................7.3 ppm

Currently established tolerances for residues of difenoconazole in/on Vegetable, fruiting, 

group 8 (0.60 ppm); Fruit, citrus, group 10 (0.60 ppm); Fruit, pome group 11 (1.0 ppm); and 

Strawberry (2.5 ppm) should be removed.
Page 8 of 70

Notes to PM:

1. A tolerance for Low growing berry subgroup 13-07G, except cranberry was specified in the 

Notice of Filing. Available data would support a tolerance in/on Berry, low growing, subgroup 

13-07G. The petition is unclear as to why the petitioner wants to restrict the use on cranberry.

 

2. As directed by RD, the proposed use on Grapes and other small fruit vine climbing subgroup 

(except fuzzy kiwifruit) was not considered because the Notice of Filing did not include a 

tolerance proposal for this subgroup. 

3. No data were submitted to address existing residue chemistry conditions of registration for the 

end-use products under consideration. Although not reiterated here, these data remain 

outstanding and are relevant to the current petition.

4. Use information was taken from Section B of the petition only. No additional draft labeling 

was provided for review. RD informed HED that the petitioner is requesting a postharvest use 

on all commodities listed under Vegetables, tuberous and corm, subgroup 1C and not just potato 

as specified in Section B of the petition. 

2.2.4 Revisions to Petitioned-For Tolerances

HED’s recommended revisions to the tolerances and/or commodity definitions submitted 

by IR-4 for this Section 3 petition are listed in Table 1. The proposed removal of the currently 

established tolerance for residues of difenoconazole on potato, processed waste is not 

appropriate; a tolerance is needed for residues of difenoconazole in potato, wet peel at 7.3 ppm. 

Table 1. Tolerance Summary for Difenoconazole.

Commodity Proposed 

Tolerance (ppm)

Recommended 

Tolerance (ppm)

Correct Commodity Definition;

Comments

Vegetable, fruiting, group 8-10 0.6 0.60

Fruit, citrus, group 10-10 0.6 0.60

Fruit, pome, group 11-10 1.0 1.0

Low growing berry subgroup 13-

07G, except cranberry

2.5 2.5 Berry, low growing, subgroup 13-

07G, except cranberry

Vegetable, tuberous and corm, 

subgroup 1C

4.0 4.0

Potatoes, processed waste remove 7.3 Potato, wet peel

Vegetable, fruiting, group 8 remove remove

Fruit, citrus, group 10 remove remove

Fruit, pome, group 11 remove remove

Strawberry remove remove
Page 9 of 70

2.2.5 Label Recommendations

- For InspireTM Fungicide, Section B of the petition must be amended to: remove the 

restriction for use on small tomatoes (page 25 of 68); and remove all use directions for 

grapes and other small fruit vine climbing except fuzzy kiwifruit (page 26 of 68).

- For InspireTM XT Fungicide, Section B of the petition must be amended to: remove all 

use directions for bulb vegetables (page 41 of 68). 

- For Quadris TopTM Fungicide, Section B of the petition must be amended to: remove the 

restriction for use on small tomatoes (page 39 of 68); and remove all use directions for 

grapes and other small fruit vine climbing except fuzzy kiwifruit (page 36 of 68).

- For Inspire SuperTM Fungicide, Section B of the petition must be amended to: remove 

the restriction for use on small tomatoes (page 30 of 68); and remove all use directions 

for grapes and other small fruit vine climbing except fuzzy kiwifruit (page 31 of 68).

- For ThesisTM Fungicide, Section B of the petition must be amended to: specify a 

maximum use rate of 0.0070 lb ai/ton of tubers (not just 0.3 fl. oz. product/ton of tubers); 

specify a delivery rate of 0.5 gal/ton of tubers; prohibit the use of adjuvants; and specify 

use on all tuberous and corm vegetables listed under subgroup 1C. . RD informed HED 

that the petitioner is requesting a postharvest use on all commodities listed under 

Vegetables, tuberous and corm, subgroup 1C and not just potato as specified in Section B 

of the petition.

- Concerning rotational crop restrictions and foliar uses under consideration: Although no 

information was provided on this topic in Section B of the petition, HED has determined 

that available data support a 30-day plantback interval (PBI) for cereal and root/tuber 

crops not already registered for foliar use with difenoconazole and a 60-day PBI for all 

other crops not already registered for foliar use with difenoconazole. 
Page 10 of 70

3.0 INGREDIENT PROFILE 

3.1 Chemical Identity

Table 2. Structures and Nomenclature. 

Chemical structure of 

difenoconazole

Common name Difenoconazole

Company experimental name CGA-169374

IUPAC name 1-({2-[2-chloro-4-(4-chlorophenoxy)phenyl]-4-methyl-1,3-dioxolan-2-

yl}methyl)-1H-1,2,4-triazole

CAS name 1-[[2-[2-chloro-4-(4-chlorophenoxy)phenyl]-4-methyl-1,3-dioxolan-2-yl]methyl]-

1H-1,2,4-triazole

CAS registry number 119446-68-3

End-use products (EP) InspireTM Fungicide (100-1262), InspireTM XT Fungicide (100-1312), Quadris 

TopTM Fungicide (100-1313), Inspire SuperTM Fungicide (100-1317), ThesisTM 

Fungicide (100-1386), 

3.2 Physical/Chemical Characteristics 

A detailed description of the physiochemical properties of difenoconazole is provided in 

Appendix C. Difenoconazole exhibits relatively low solubility in water and higher solubility in 

solvents. It has a very low vapor pressure. Based on the field and laboratory studies, 

difenoconazole is persistent in soil and slightly mobile. It has low potential to reach ground 

water, except in soils of high sand and low organic matter content. Difenoconazole does not 

present significant concerns for bioaccumulation based on the lipophilicity of the compound, as 

well as the mammalian metabolism studies. 

3.3 Pesticide Use Pattern

Difenoconazole is currently registered in the U.S. for use as a seed treatment on barley, 

wheat, and triticale, canola, sweet corn and cotton. It is also registered for foliar applications to 

numerous fruit and vegetable crops, ornamentals and golf course turf. Proposed new uses 

include a post-harvest use on potato. The use patterns for the amended use are provided in Table 

3.

O O

O

N N Cl

N

CH3

Cl
Page 11 of 70

Table 3. Summary of Proposed Amended Use for Difenoconazole.

Appl. 

Timing, 

Type, and 

Equip.

Formulation

[EPA Reg. 

No.]

Max. 

Appl. Rate 

(AR)

(lb ai/A)

Max. No. 

Appl. per 

Season

Max. 

Seasonal 

AR

(lb ai/A)

PHI

(days)

Use Directions and 

Limitations

Potato PostHarvest (PH)

In-line 

aqueous spray 

application 

using T-ject, 

CDA, or 

similar 

application 

system.

3.0 lb ai/gal 

FS

[100-1386]

0.3 fl. oz 

of 

product/ton 

of tubers

1 N/A N/A For treatment of certain 

postharvest rots caused by 

Silver scurf 

(Helminthosporium solani) and 

Fusium species. 

Ensure proper coverage of the 

tubers. Tubers should be 

tumbling as they are treated.

Mix the fungicide solution in 

an appropriate amount of water 

for the crop being treated. 

Must be used in tank mixture 

with fludioxonil and 

azoxystrobin.

Fruiting Vegetables

Foliar,

Broadcast, 

Ground, 

aerial, or 

chemigation

2.08 lb/gal 

EC

[100-1262]

0.114 Not 

Specified 

(NS)

0.46 0 A 7-day minimum RTI is 

specified. 

Do not use on varieties in 

which the mature tomatoes will 

be less than 2 inches (such as 

cherry tomatoes).

1.05 lb/gal 

MAI SC

[100-1313]

Peppers

0.115

Tomatoes

0.07

0.73 lb/gal 

MAI EW

[100-1317]

0.114

Citrus Fruits

Foliar,

Broadcast, 

Ground or 

aerial 

2.08 lb/gal 

EC

[100-1262]

0.125 NS 0.5 0 A 7-day minimum RTI is 

specified. 

1.05 lb/gal 

MAI SC

[100-1313]

0.126

Pome Fruits 

Foliar,

Broadcast, 

Ground or 

aerial

2.08 lb/gal 

EC

[100-1262]

0.07 NS 0.33 72

14

A 7-day minimum RTI is 

specified. 

0.73 lb/gal 

MAI EW

[100-1317]

0.07

Strawberries and other low growing berries (except cranberry)

Foliar,

Broadcast, 

Ground , 

aerial or 

chemigation

2.08 lb/gal 

EC

[100-1262]

0.114 NS 0.46 0 A 7-day minimum RTI is 

specified. 

2.08 lb/gal 

MAI EC

[100-1312]

0.114

1.05 lb/gal 

MAI SC

0.115
Page 12 of 70

Table 3. Summary of Proposed Amended Use for Difenoconazole.

Appl. 

Timing, 

Type, and 

Equip.

Formulation

[EPA Reg. 

No.]

Max. 

Appl. Rate 

(AR)

(lb ai/A)

Max. No. 

Appl. per 

Season

Max. 

Seasonal 

AR

(lb ai/A)

PHI

(days)

Use Directions and 

Limitations

[100-1313]

0.73 lb/gal 

MAI EW

[100-1317]

0.114

3.4 Anticipated Exposure Pathways

Dietary (food and water) and occupational exposures are expected based on existing and 

proposed new use difenoconazole as a post harvest use on potato. A new residential exposure 

assessment is not required because there are no residential uses or exposures associated with the 

proposed new use. The short-term aggregate exposure assessment, which takes into account 

residential exposure plus average exposure levels to food and water, has been updated to 

incorporate dietary exposure from the proposed new uses. 

3.5 Considerations of Environmental Justice

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

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

Actions to Address Environmental Justice in Minority Populations and Low-Income 

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

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

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

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

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

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

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

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

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

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

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

4.0 HAZARD CHARACTERIZATION/ASSESSMENT

4.1 Toxicology Studies Available for Analysis

The toxicology database for difenoconazole is adequate for evaluating and characterizing 

difenoconazole toxicity and selecting endpoints for purposes of this risk assessment. All toxicity 

studies required in accordance with new 40 CFR Part 158 the data requirements have been 

submitted. An immunotoxicity study has been submitted and is under review. 
Page 13 of 70

4.2 Absorption, Distribution, Metabolism and Excretion

The absorption, distribution, metabolism, and excretion of difenoconazole were studied 

in rats. In one study, the test compound was labeled with C14 at either the phenyl or triazole ring. 

Animals were administered a single oral gavage dose of 0.5 or 300 mg/kg of radiolabeled 

compound or 0.5 mg/kg unlabeled compound by gavage for 14 days followed by a single gavage 

dose of 0.5 mg/kg [14C]-difenoconazole on day 15. In a second follow-up study [

14C]-

difenoconazole (phenyl ring label) was administered as single oral gavage dose of 0.5 or 300 

mg/kg. The second study was conducted to address deficiencies in the initial study by providing 

biliary excretion and identification of metabolites.

Difenoconazole was rapidly absorbed and extensively distributed, metabolized, and 

excreted in rats for all dosing regimens. Distribution, metabolism and elimination of 

difenoconazole were not sex related in the first study. Recovery of administered dose was 96-

108%. Biliary excretion, examined in the second study, constituted the main route of elimination 

with some dose and sex dependency (75% at the low dose for both sexes; 56% for males and 

39% for females at the high dose). Urinary and fecal eliminations exhibited a dose-related 

pattern at 48 hours. In bile duct cannulated rats, 9-l4% of dose was eliminated in the urine at the 

low dose versus 1% in the high-dose rats. In bile duct cannulated rats, 2-4% was eliminated in 

the feces at the low dose versus 17-22% at the high dose. Half-lives of elimination are

approximately 20 hours for the low dose groups and 33-48 hours for the high dose group. 

Radioactivity in the blood peaked at 2 to 4 hours at the low and high dose respectively. 

Difenoconazole undergoes successive oxidation and conjugation reactions. Following 

administration of 300 mg/kg of (

14C-phenyl) difenoconazole, three major urinary metabolites 

were identified as CGA 205375 and HO-CGA 205375 (6% of dose), sulfate conjugates (and 

their isomers) of HO-205375 (3.9% of dose), and the hydroxyacetic metabolite of HO-CGA 

205375 (2.0% of dose). No single unknown urinary metabolite accounted for >1.1% of the dose. 

Free triazole metabolite was detected in the urine of the triazole-label groups and its byproduct 

was detected in the liver of phenyl labeled groups only.

The study results indicate that difenoconazole and/or its metabolites do not 

bioaccumulate appreciably following oral exposure since all tissues contained negligible levels 

(<1%) or radioactivity 7 days post exposure.

A dermal absorption factor of 6% was derived based on data from a triple pack of a 28 rat 

in vivo dermal absorption study and in vitro dermal absorption studies conducted with rat and 

human skin. Inhalation toxicity is assumed to be equivalent to oral toxicity.

4.3 Toxicological Effects

Subchronic and chronic studies with difenoconazole in mice and rats showed decreased 

body weights, decreased body weight gains and effects on the liver (e.g. hepatocellular 

hypertrophy, liver necrosis, fatty changes in the liver). In an acute neurotoxicity study in rats, 

reduced fore-limb grip strength was observed on day 1 in males and clinical signs of 

neurotoxicity were observed in females at the limit dose of 2000 mg/kg. In a subchronic 
Page 14 of 70

neurotoxicity study in rats, decreased hind limb strength was observed in males only at the midand high-doses. However, the effects observed in acute and subchronic neurotoxicity studies are 

transient, and the dose-response is well characterized with identified no observed adverse effect 

levels (NOAELs). No systemic toxicity was observed at the limit dose in the most recently 

submitted 28-day rat dermal toxicity study. 

The available toxicity studies indicated no increased susceptibility of rats or rabbits from

in utero or postnatal exposure to difenoconazole. In prenatal developmental toxicity studies in 

rats and rabbits and in the two-generation reproduction study in rats, fetal/offspring toxicity, 

when observed, occurred at equivalent or higher doses than in the maternal/parental animals. 

There are no indications in the available studies that organs associated with immune 

function, such as the thymus and spleen, are affected by difenoconazole. An immunotoxicity 

study, required under Part 158 Toxicology Data requirements, has been submitted and is under 

review. 

In accordance with HED’s current policy and EPA’s 2005 Cancer Guidelines, 

difenoconazole is classified as “Suggestive Evidence of Carcinogenic Potential” based on liver 

tumors observed in mice at 300 ppm and higher, the absence of tumors at two lower doses of 10 

and 30 ppm, excessive toxicity observed at the two highest doses of 2500 and 4500 ppm, the 

absence of genotoxic and no evidence of carcinogenicity in rats. HED’s Cancer Peer Review 

Committee recommended use of an MOE approach to risk assessment using the chronic point of 

departure (POD) based on effects observed in the chronic mouse study relevant to tumor 

development (i.e., hepatocellular hypertrophy, liver necrosis, fatty changes in the liver and bile 

stasis). The POD is considered protective of the cancer effects. 

Difenoconazole possesses low acute toxicity by the oral, dermal and inhalation routes of 

exposure. It is not an eye or skin irritant and is not a sensitizer. 

The toxicity profiles for difenoconazole are provided in Appendix A. 

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

The FQPA factor for increased susceptibility to infants and children is reduced to 1x 

based on the following considerations. Further discussion may be found in the following 

sections.

- The toxicology data base for difenoconazole is complete and adequate for assessing 

increased susceptibility under FQPA.

- There is no indication of increased susceptibility of rats or rabbit fetuses to in utero 

and/or postnatal exposure in the developmental and reproductive toxicity data.

- There are no residual uncertainties in the exposure database.

- The dietary risk assessment is conservative and will not underestimate dietary exposure 

to difenoconazole.
Page 15 of 70

4.4.1 Completeness of the Toxicology Database

The toxicity database is sufficient for a full hazard evaluation and is considered adequate 

to evaluate risks to infants and children. Acceptable acute and subchronic neurotoxicity studies 

are available. An immunotoxicity study required under new 40 CFR Part 158 data requirements 

for registration of a pesticide (food and non-food uses) has been submitted and is under review. 

The Hazard and Science Policy Council (HASPOC) concluded based on a weight of evidence 

(WOE) approach that a 28-day inhalation toxicity study is not required at this time. This 

approach considered all of the available hazard and exposure information for difenoconazole, 

including: (1) the use of an oral POD that results in MOEs greater than 1,300 (the lowest MOE) 

for risk via the inhalation route resulting from occupational and residential; (2) the 

physical/chemical properties and very low vapor pressure of difenoconazole; and (3) the 

toxicological profile of difenoconazole. 

4.4.2 Evidence of Neurotoxicity

In an acute neurotoxicity study in rats, reduced fore-limb grip strength was observed on 

day 1 in males. Clinical signs of neurotoxicity were observed in females at the limit dose of 

2000 mg/kg. The effect in males is considered transient since it was not observed at later 

observation points. Toxicity in females was observed only at the limit dose. In a subchronic 

neurotoxicity study in rats decreased hind limb strength was observed in males only. The effects 

observed in acute and subchronic neurotoxicity studies are transient, and the dose-response is 

well characterized with identified NOAELs. Based on the toxicity profile, and lack of concern 

for neurotoxicity, a developmental neurotoxicity study in rats is not required.

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

The available Agency Guideline studies indicated no increased susceptibility of rats or 

rabbits to in utero and/or postnatal exposure to difenoconazole. In the prenatal developmental 

toxicity studies in rats and rabbits and the two-generation reproduction study in rats, toxicity to 

the fetuses/offspring, when observed, occurred at equivalent or higher doses than in the 

maternal/parental animals. 

In a rat developmental toxicity study developmental effects were observed at doses 

higher than those which caused maternal toxicity. Developmental effects in the rat included 

increased incidence ossification of the thoracic vertebrae and hyoid, decreased number of sternal 

centers of ossification, increased number of ribs and thoracic vertebrae, and decreased number of 

lumbar vertebrae. In the rabbit study, developmental effects (increases in post-implantation loss 

and resorptions and decreases in fetal body weight) were also seen at maternally toxic doses. In 

the two-generation reproduction study in rats, toxicity to the fetuses/offspring, when observed, 

occurred at equivalent or higher doses than in the maternal/parental animals.
Page 16 of 70

4.4.4 Residual Uncertainty in the Exposure Database

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

is conservative and will not underestimate dietary exposure to difenoconazole.

4.5 Toxicity Endpoint and Point of Departure

4.5.1 Dose-Response Assessment

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

occupational, and residential exposure scenarios are summarized below. A detailed description 

of the studies used as a basis for the selected endpoints are presented in Appendix A. 

An acute POD of 25 mg/kg/day (NOAEL) was selected from an acute neurotoxicity 

study in rats based on reduced fore-limb grip strength in males on day 1 at the LOAEL of 200 

mg/kg/day. An uncertainty factor (UF) of 100x (10x to account for interspecies extrapolation 

and 10x for intraspecies variation) was applied to the NOAEL to obtain an acute reference dose 

(aRfD) of 1.0 mg/kg/day. Since the FQPA factor has been reduced to 1X, the acute population 

adjusted dose (aPAD) is equivalent to the aRfD. The selected endpoint is considered appropriate 

for acute dietary exposure because effects were seen after a single dose. The endpoint is 

protective of the general population and all subpopulations for effects seen in the acute 

neurotoxicity study in rats. It is also protective of developmental and maternal effects observed 

in the rabbit developmental toxicity study at the LOAEL of 75 mg/kg/day and NOAEL of 25 

mg/kg/day.

A chronic POD of 0.96 mg/kg/day (NOAEL) was selected from a chronic/oncogenicity

oral study in rats based on cumulative decreases in body weight gains in males observed at the 

LOAEL of 24 mg/kg/day. A UF of 100x (10x to account for interspecies extrapolation and 10x 

for intraspecies variation) was applied to the dose to obtain a chronic reference dose 

(cRfD/cPAD) of 0.01 mg/kg/day. 

Short-term incidental oral and short- and intermediate term dermal and inhalation PODs

of 1.25 mg/kg/day were selected from a two generation reproduction study in rats based on 

decreased pup weight in males at 12.5 mg/kg/day (LOAEL) on day 21, and reductions in body 

weight gain in F0 females. Although dermal toxicity studies are available, a POD from an oral 

study was selected because effects in young animals (decreased pup weight) the primary effect of 

concern for short, intermediate and long term exposure is not specifically evaluated in the 

available dermal toxicity studies that only assess adult animals. The selected endpoint is 

protective of offspring effects from dermal exposure. An MOE 100 is required for the shortand intermediate-term dermal and inhalation exposure scenarios based on the conventional 

uncertainty factor of 100 (10x for interspecies extrapolation and 10x for intraspecies variation). 

There are no residential uses for difenoconazole that would result in incidental oral exposure to 

children. 

A dermal absorption factor (DAF) is applied when dermal exposure endpoints are 

selected from oral toxicity studies. The dermal factor converts the oral dose to an equivalent 
Page 17 of 70

dermal dose for the risk assessment. A DAF of 6% was selected for use in risk assessment based 

on available in vivo dermal absorption studies in rat and in vitro dermal absorption studies 

conducted with rat and human skin. Further discussion of the dermal absorption may be found in 

Attachment A.3.

4.5.2 Recommendations for Combining Exposure Routes

When there are potential residential exposures to the pesticide, aggregate risk assessment 

must consider exposures from three major sources: oral, dermal and inhalation exposures. Oral, 

dermal and inhalation exposures to residents should be aggregated for difenoconazole because 

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

4.5.3 Classification of Carcinogenic Potential

Difenoconazole is not mutagenic, and no evidence of carcinogenicity was seen in rats. 

Evidence for carcinogenicity was seen in mice, where liver tumors were induced at doses which 

were considered to be excessively high for carcinogenicity testing. Liver tumors were observed 

in mice at 300 ppm and higher; however, based on excessive toxicity observed at the two highest 

doses of 2500 and 4500 ppm (females terminated after two weeks due to excessive toxicity 

resulting in moribundity and death), the absence of tumors at two lower doses of 10 and 30 ppm,

the absence of genotoxic effects, and no evidence of carcinogenicity in rats. In accordance with 

HED’s current policy and EPA’s 2005 Cancer Guidelines, difenoconazole is classified as 

“Suggestive Evidence of Carcinogenic Potential,” based on excessive toxicity observed at the 

two highest doses, the absence of tumors at the lower doses and the absence of genotoxic effects. 

Based on the CPRC recommendation, the risk assessment uses an (MOE) approach utilizing the 

no-observable-adverse-effects-level (NOAEL) of 30 ppm (4.7 and 5.6 mg/kg/day in males and 

females, respectively) and the lowest-observable-adverse-effects-level (LOAEL) of 300 ppm (46

and 58 mg/kg/day in males and females, respectively) from the mouse study using only those 

biological endpoints which were relevant to tumor development (i.e., hepatocellular hypertrophy, 

liver necrosis, fatty changes in the liver and bile stasis). The chronic POD of 0.96 mg/kg/day 

selected based on bodyweight effects is protective of the cancer effects. 

4.5.4 Summary of Points of Departure Used in Risk Assessment

Toxicological doses/endpoints selected for the difenoconazole risk assessment are 

provided in Tables 4 and 5.
Page 18 of 70

Table 4. Summary of Toxicological Doses and Endpoints for Difenoconazole for Use in Dietary and Non-Occupational 

Human Health Risk Assessments

Exposure 

Scenario

Point of 

Departure

Uncertainty/FQPA 

Safety Factors

RfD, PAD, LOC 

for Risk 

Assessment

Study and Relevant Toxicological 

Effects

Acute Dietary (All 

populations)

NOAEL = 25

mg/kg

UFA = 10X

UFH = 10X

UFFQPA = 1X

aRfD = aPAD = 

0.25 mg/kg/day

Acute Neurotoxicity Study in Rats

LOAEL= 200 mg/kg in males based 

on reduced fore-limb grip strength in 

males on day 1.

Chronic Dietary 

(All populations)

NOAEL = 0.96

mg/kg/day

UFA = 10X

UFH = 10X

UFFQPA = 1X

cRfD = cPAD = 

0.01mg/kg/day

Combined chronic 

toxicity/carcinogenicity (rat; dietary) 

LOAEL = 24.1/32.8 mg/kg/day 

(M/F) based on cumulative decreases 

in body-weight gains.

Incidental Oral 

Short-Term (1-30 

days)

Oral NOAEL = 

1.25

mg/kg/day

UFA = 10X

UFH = 10X

UFFQPA = 1X

Residential LOC 

for MOE<100

Reproduction and fertility Study (rat; 

dietary) Parental/Offspring LOAEL 

= 12.5 mg/kg/day based on decreased 

pup weight in males on day 21 and 

reduction in body-weight gain of F0

females prior to mating, gestation 

and lactation.

Dermal

Short- and 

Intermediate- Term 

(1-30 days and 1-6 

months) 

DAF = 6%

Oral NOAEL = 

1.25

mg/kg/day

UFA = 10X

UFH = 10X

UFFQPA = 1X

Residential LOC 

for MOE<100

Reproduction and fertility Study (rat; 

dietary) Parental/Offspring LOAEL 

= 12.5 mg/kg/day based on decreased 

pup weight in males on day 21 and 

reduction in body-weight gain of F0

females prior to mating, gestation 

and lactation.

Inhalation

(Short- and 

Intermediate-term)

Inhalation and oral 

absorption assumed 

equivalent

Oral NOAEL = 

1.25

mg/kg/day

UFA = 10X

UFH = 10X

UFFQPA = 1X

Residential LOC 

for MOE<100

Reproduction and fertility Study (rat; 

dietary) Parental/Offspring LOAEL 

= 12.5 mg/kg/day based on decreased 

pup weight in males on day 21 and 

reduction in body-weight gain of F0

females prior to mating, gestation 

and lactation.

Cancer (oral, 

dermal, inhalation)

Difenoconazole is classified “Suggestive Evidence of Carcinogenic Potential” with a non-linear (MOE) 

approach for human risk characterization (CPRC Document, 7/27/94, Memo, P. V. Shah dated March 

3, 2007, HED Doc. No. 0054532).

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

mark the beginning of extrapolation to determine risk associated with lower environmentally relevant human exposures. NOAEL 

= no observed adverse effect level. LOAEL = lowest observed adverse effect level. UF = uncertainty factor. UFA = 

extrapolation from animal to human (interspecies). UFH = potential variation in sensitivity among members of the human 

population (intraspecies DAF = Dermal Absorption Factor
Page 19 of 70

Table 5. Summary of Toxicological Doses and Endpoints for Difenoconazole for Use Occupational Human Health Risk 

Assessments

Exposure 

Scenario

Point of 

Departure

Uncertainty/FQPA 

Safety Factors

RfD, PAD, Level of 

Concern for Risk 

Assessment

Study and Toxicological Effects

Dermal

Short- and 

Intermediate- Term 

(1-30 days and 1-6 

months)

DAF = 6%

Oral NOAEL 

= 1.25

mg/kg/day

UFA = 10X

UFH = 10X Occupational LOC for 

MOE<100

Reproduction and fertility Study (rat; 

dietary) Parental/Offspring LOAEL 

= 12.5 mg/kg/day based on decreased 

pup weight in males on day 21 and 

reduction in body-weight gain of F0

females prior to mating, gestation 

and lactation.

Inhalation

(Short- and 

Intermediate-term)

Inhalation and oral 

absorption assumed 

equivalent

Oral NOAEL 

= 1.25

mg/kg/day

UFA = 10X

UFH = 10X Occupational LOC for 

MOE<100

Reproduction and fertility Study (rat; 

dietary) Parental/Offspring LOAEL 

= 12.5 mg/kg/day based on decreased 

pup weight in males on day 21 and 

reduction in body-weight gain of F0

females prior to mating, gestation 

and lactation.

Cancer (oral, 

dermal, inhalation)

Difenoconazole is classified “Suggestive Evidence of Carcinogenic Potential” with a non-linear (MOE) 

approach for human risk characterization (CPRC Document, 7/27/94, Memo, P. V. Shah dated March 

3, 2007, HED Doc. No. 0054532).

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

mark the beginning of extrapolation to determine risk associated with lower environmentally relevant human exposures. NOAEL 

= no observed adverse effect level. LOAEL = lowest observed adverse effect level. UF = uncertainty factor. UFA = 

extrapolation from animal to human (interspecies). UFH = potential variation in sensitivity among members of the human 

population (intraspecies). 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.

5.0 DIETARY AND DRINKING WATER EXPOSURE AND RISK ASSESSMENT

5.1 Metabolite/Degradate Residue Profile

5.1.1 Summary of Plant and Animal Metabolism Studies

The nature of the residue in plants is understood based on acceptable plant metabolism 

studies reflecting foliar applications in canola, grape, potato, tomato, and wheat, and seed 

treatment in wheat. HED concludes that the residue of concern for both tolerance enforcement 

and risk assessment for crops included in this petition is difenoconazole per se. The nature of the 

residue in livestock is understood based on acceptable goat and hen metabolism studies. The 

residues of concern for both tolerance setting and risk assessment for livestock commodities are 

difenoconazole per se and its metabolite CGA-205375. In addition, metabolite OH-CGA169374, which comprised 15% of the TRR in goat milk from the phenyl-labeled study, should be 

considered as a residue of concern for the dietary risk assessment. 

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

of difenoconazole in rotational crops is similar to that of primary crops. The available 

difenoconazole confined and limited field rotational crop trials are deemed adequate to satisfy 

data requirements under Guidelines 860.1850 and 860.1900. Taken together, these data support 

a 30-day plantback interval (PBI) for cereal and root/tuber crops not already registered for foliar 

use with difenoconazole and a 60-day PBI for all other crops not already registered for foliar use 
Page 20 of 70

with difenoconazole. With these PBIs, tolerances for residues of difenoconazole are not needed 

for rotational crops. 

5.1.2 Comparison of Metabolic Pathways

Little information is available on the toxicity of the major difenoconazole metabolites. 

The CGA-205375 metabolite formed in livestock appears to be formed in the rat also and is, 

therefore, part of the total toxic exposure for these animals. 

5.1.3 Residues of Concern Summary and Rationale

Residues of concern were determined based on recommendations from the HED 

Residues of Concern Knowledgebase Sub-committee (ROCKS) (D391350, 9/19/11). The 

residue of concern for plant commodities for tolerance expression and risk assessment purposes 

is difenoconazole per se. The HED ROCKS has determined that the parent compound and the 

CGA-205375 metabolite are the residues of concern in livestock commodities for both the 

tolerance expression and the risk assessment. In addition, metabolite OH-CGA-169374, which 

comprised 15% of the TRR in goat milk from the phenyl-labeled study, should be considered as 

a residue of concern for the dietary risk assessment. Based on available goat metabolism data, 

total residues of concern in milk for dietary risk assessments (parent, CGA-205375, and OHCGA-169374), should be calculated by multiplying the tolerance in milk by a factor of 1.5x. 

Table 6 summarizes tolerance expression and the residues of concern in plant and livestock 

commodities. 

Table 6. Difenoconazole Residues of Concern in Plants and Ruminants.

Matrix

Residues of Concern

For Risk Assessment For Tolerance Expression

Plants Primary and Rotational crops Parent Only Parent Only

Livestock Ruminant and Poultry Parent and CGA 205375 Parent and CGA 205375

Milk Parent, CGA 205375 and 

OH-CGA-169374

Parent and CGA 205375

Drinking Water Parent and CGA 205375 NA

Note: The triazole-containing metabolites 1,2,4-T, TA, and TAA should be included in the residues of concern for risk 

assessment purposes only for plant and livestock commodities. Since these metabolites are common to the entire class of 

traizole-derivative fungicides and because of differential toxicity between metabolites and the various parent compounds, risks 

associated with exposure to 1,2,4-T and to TA/TAA are addressed separately.

5.2 Food Residue Profile

5.2.1 Residues in Crops

The submitted postharvest potato magnitude of the residue data, conducted with a 3.0

lb/gal flowable suspension (FS) formulation of difenoconazole adequately reflect the proposed 

use pattern for potato postharvest. Provided the use is expanded to all tuber and corm vegetables 

listed under subgroup 1C, for which potato is the representative commodity, these data will 

support a tolerance of 4.0 ppm in/on Vegetables, tuberous and corm, subgroup 1C. 
Page 21 of 70

Previously submitted field trial data are adequate to support the proposed amended uses. 

It is important to note that the proposed amendments to existing labels are limited to expansions 

to add the commodities specified under the new crop groups/subgroups and do not include 

substantive changes to currently registered use patterns (i.e., maximum use rates, retreatment 

intervals, preharvest intervals, use of adjuvants, etc.). The proposed tolerances in/on Fruiting 

Vegetables Group 8-10 (0.6 ppm); Citrus Fruits Group 10-10 (0.6 ppm), Pome Fruits Group 11-

10 (1.0 ppm), and Low growing Berry Subgroup 13-07G, Except Cranberry (2.5 ppm) are 

appropriate. 

5.2.2 Residue in Livestock and Poultry

There are no new livestock feedstuffs associated with the proposed uses since 

difenoconazole is already registered for foliar uses on potatoes, citrus fruits, and pome fruits. 

However, due to the proposed postharvest use on potatoes, difenoconazole residue estimates 

in/on potato culls and potato processing waste, which are beef and dairy feedstuffs, have 

increased substantially. Potato culls and potato processing waste are both carbohydrate 

concentrates which are sometimes used in cattle feeding and considered alternative feedstuffs. 

There are no poultry or swine feedstuffs associated with the proposed uses. Adequate cattle and 

poultry feeding studies are available for difenoconazole. 

The dietary burdens for beef and dairy cattle are recalculated for this Section 3 action. In 

accordance with ChemSAC recommendations concerning blended commodities (ChemSAC 

meeting minutes 12/21/11), the difenoconazole residue estimate in/on potato processing waste 

for livestock MRBD calculations (3.5 ppm) was based on the median residue value for potato 

reflecting the proposed post harvest use (1.13 ppm) and the average concentration factor for 

potato wet peel (3.1x). Potato processing waste replaces AGF and wet apple pomace as the 

major contributors to the MRBDs of cattle for difenoconazole. The MRBDs are recalculated to 

be: 7.4 ppm for beef cattle and 2.8 ppm for dairy cattle. Based on the recalculated dietary 

burdens and the feeding study data, HED concludes that the currently established tolerances for 

milk, meat, fat, meat byproducts (except liver) and liver are adequate to support the proposed 

uses.

5.2.3 Residues in Processed Commodities

Adequate processing data for potato were submitted with the petition. The potato 

processing data indicate that residues of difenoconazole do not concentrate in flakes and chips 

but do concentrate in wet peel. Based on the HAFT for residues in/on potatoes postharvest (2.34 

ppm) and the average processing factor for potato wet peel (3.1x), expected residues of 

difenoconazole from the proposed postharvest use on potato would be 7.3 ppm in potato, peel, 

wet. The proposed removal of the currently established tolerance for residues of difenoconazole 

on potato, processed waste is not appropriate; a tolerance is needed for residues of 

difenoconazole in potato, peel, wet at 7.3 ppm. Apple, tomato, and orange processing data were 

previously submitted and are adequate to support the proposed uses. No changes to the currently 

established tolerances in apple, wet pomace (4.5 ppm), citrus, dried pulp (2.0 ppm), and citrus oil 

(25 ppm) are needed. 
Page 22 of 70

5.3 Water Residue Profile

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

Environmental Fate and Effects Division. EFED conducted a Tier II drinking water assessment 

for surface water sources using the Pesticide Root Zone/Exposure Analysis Modeling System 

(PRZM/EXAMS) for the registered and proposed new uses. Among the registered and 

proposed new uses, the highest estimated drinking water concentrations (EDWCs) for surface 

water sources were derived for aerial applications of difenoconazole to New York grapes at the 

maximum annual application rate of 0.46 lb ai/acre The estimated drinking water residues for 1-

in-10 year annual peak, 1-in-10 year annual mean, and 36-year annual mean are 17.4, 11.8, and 

8.6 μg/L (ppb) respectively. The highest Screening Concentration In GROund Water (SCIGROW) estimated drinking water concentration of difenoconazole from shallow ground water 

sources is 1.28 x 10-2μg/L, obtained for the maximum application rate for ornamentals (0.52 lb 

ai/A). These concentrations can be considered as both the acute and chronic groundwater values. 

The EDWCs from ground water sources are expected to be the same for the proposed golf course 

turf uses as estimated for ornamentals. The 1-in-10 year annual peak EDWC of 17.4 μg/L (ppb) 

was used for the acute dietary (food plus water) exposure analysis and the 1-in-10 year annual 

mean EDWC of 11.8 μg/L (ppb) was used for the chronic dietary (food plus water) exposure 

analysis.

5.4 Dietary and Drinking Water Exposure and Risk

Screening level acute and refined chronic dietary and drinking water exposure and risk 

assessments were conducted using the Dietary Exposure Evaluation Model with the Food 

Commodity Intake Database (DEEM-FCIDTM). Dietary risk assessment incorporates both 

exposure and toxicity of a given pesticide. For acute and chronic dietary assessments, the risk is 

expressed as a percentage of a maximum acceptable dose (i.e., the dose which HED has 

concluded will result in no unreasonable adverse health effects). This dose is referred to as the 

population adjusted dose (PAD). The PAD is equivalent to the POD divided by the uncertainty 

factors. For acute and non-cancer chronic exposures, HED is concerned when estimated dietary 

risk exceeds 100% of the PAD. 

5.4.1 Acute Dietary Risk Assessment

The unrefined acute analysis for food and water assumed tolerance-level residues, 100% 

crop treated (CT), and the available empirical or DEEM (ver. 7.81) default processing factors. 

The resulting acute food plus water exposure estimates were less than HED’s level of concern (-

<100% of the acute population-adjusted dose (aPAD)) at the 95th percentile of the exposure 

distribution for the general U.S. population (12 % aPAD) and all population sub-groups; the 

most highly exposed population subgroup was children1-2 years old with 27 % aPAD. 
Page 23 of 70

Table 7. Summary of Acute Dietary Exposure (Food and Drinking Water) and Risk for Difenoconazole at 

the 95th Percentile.

Population Subgroup aPAD (mg/kg/day) Exposure (mg/kg/day) %aPAD

General U.S. Population

0.25

0.030385 12

All Infants (< 1 year old) 0.056767 23

Children 1-2 years old 0.066505 27

Children 3-5 years old 0.053081 21

Children 6-12 years old 0.034395 14

Youth 13-19 years old 0.023787 10

Adults 20-49 years old 0.022687 9

Adults 50+ years old 0.025302 10

Females 13-49 years old 0.022729 9

5.4.2 Chronic Dietary Risk Assessment

The somewhat refined chronic analysis for food and water assumed tolerance-level 

residues for some commodities, average field trial residues for the majority of commodities, the 

available empirical or DEEM (ver. 7.81) default processing factors, and 100 % CT. The 

resulting chronic food plus water exposure estimates were less than HED’s level of concern (-

<100% of the chronic population-adjusted dose (cPAD)) for the general U.S. population (30 % 

cPAD) and all population sub-groups; the most highly exposed population subgroup was 

children 1 - 2 years old with 75 % cPAD. 

Table 8. Summary of Chronic Dietary (Food and Drinking Water) Exposure and Risk for Difenoconazole.

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

General U.S. Population

0.01

0.002987 30

All Infants (< 1 year old) 0.004701 47

Children 1-2 years old 0.007460 75

Children 3-5 years old 0.006242 62

Children 6-12 years old 0.003903 39

Youth 13-19 years old 0.002574 26

Adults 20-49 years old 0.002382 24

Adults 50+ years old 0.002594 26

Females 13-49 years old 0.002304 23

Dietary Assessment of Free Triazole and its Conjugates

Reference: Common Triazole Metabolites: Updated Dietary (Food + Water) Exposure and Risk Assessment to 

Address The Amended Propiconazole Section 3 Registration to Add Uses on Snap beans, succulent shelled beans, 

dry beans, tomato (post-harvest, citrus (post-harvest), and stone fruit (post-harvest); The Amended Difenoconazole 

Section 3 Registration to Add Use on Root and Tuber group 1C; and the Amended Flutriafol Section 3 Registration 

to Add Use on Field Corn.T. Morton, DP397591.drs, 1/26/12.
Page 24 of 70

The proposed Section 3 uses of propiconazole results in an increase in dietary exposure estimates for 

free triazole or conjugated triazoles. Therefore, the last dietary exposure analyses for the triazole 

metabolites needed to be updated. The proposed Section 3 uses of difenoconazole results in dietary 

risk estimates below HED’s level of concern; see Table 9.

Table 9. Summary of Dietary (Food and Drinking Water) Exposure and Risk for the Common Triazole 

Metabolites Adding the new Section 3 Uses for Propiconazole, Flutriafol, and Difenoconazole.

Population Subgroup

Acute Dietary

(95th Percentile) Chronic Dietary Cancer

Dietary 

Exposure 

(mg/kg/day)

% aPAD*

Dietary 

Exposure

(mg/kg/day)

% cPAD*

Dietary 

Exposure

(mg/kg/day)

Risk

1,2,4-Triazole

General U.S. Population 0.008892 30 0.001409 28

Not 

Applicable

Not 

Applicable

All Infants (< 1 year old) 0.012475 42 0.001923 39

Children 1-2 years old 0.023049 77 0.003723 75

Children 3-5 years old 0.017674 59 0.002994 60

Children 6-12 years old 0.011632 39 0.001891 38

Youth 13-19 years old 0.008196 27 0.001266 25

Adults 20-49 years old 0.006959 23 0.001162 23

Adults 50+ years old 0.006050 20 0.001097 22

Females 13-49 years old 0.007007 23 0.001166 23

Triazolylalanine + Triazolylacetic Acid 

General U.S. Population

Not 

Applicable

Not 

Applicable

0.019824 22

Not 

Applicable

Not 

Applicable

All Infants (< 1 year old) 0.020308 23

Children 1-2 years old 0.056263 63

Children 3-5 years old 0.045007 50

Children 6-12 years old 0.028078 31

Youth 13-19 years old 0.018635 21

Adults 20-49 years old 0.015881 18

Adults 50+ years old 0.014719 16

Females 13-49 years old 0.086155 86 0.016036 18

* The values for the highest exposed population for each type of risk assessment are bolded.

6.0 RESIDENTIAL EXPOSURE AND RISK

A new residential exposure assessment is not required for the proposed amended/new

uses because there are no homeowner uses or application to residential areas associated with 

these uses. However, difenoconazole is registered on ornamentals and golf coarse turf which 

will result in residential exposure. Therefore, theses residential uses were aggregated with the 

recent dietary exposure.

6.1 Residential Bystander Post Application Inhalation Exposure

Based on the Agency's current practices, a quantitative residential bystander 

postapplication inhalation exposure assessment was not performed for difenoconazole at this 

time. However, volatilization of pesticides may be a potential source of postapplication 

inhalation exposure to individuals nearby to pesticide applications. The Agency sought expert 

advice and input on issues related to volatilization of pesticides from its Federal Insecticide, 
Page 25 of 70

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

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

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

process of evaluating the SAP report and may, as appropriate, develop policies and procedures, 

to identify the need for and, subsequently, the way to incorporate postapplication inhalation 

exposure into the Agency's risk assessments. If new policies or procedures are put into place, the 

Agency may revisit the need for a quantitative postapplication inhalation exposure assessment 

for difenoconazole.

6.2 Spray Drift

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

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

be a potential source of exposure from the ground application method employed for 

difenoconazole. The Agency has been working with the Spray Drift Task Force, EPA Regional 

Offices and State Lead Agencies for pesticide regulation and other parties to develop the best 

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

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

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

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

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

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

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

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

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

associated with drift.

7.0 AGGREGATE EXPOSURE AND RISK ASSESSMENT 

In accordance with the FQPA, when there are potential residential exposures to a 

pesticide, aggregate risk assessment must consider exposures from three major routes: oral, 

dermal, and inhalation. There are three sources for these types of exposures: food, drinking 

water, and residential uses. In an aggregate assessment, risks from relevant sources are added 

together and compared to a level of concern. Since a common effect has been identified for 

assessment of short-term oral, dermal, and inhalation exposures (changes in body weights and 

body-weight gains) for difenoconazole, the short-term aggregate risk assessment combines 

exposure from food, water, and residential sources. Only short-term residential exposures are 

expected based on current use patterns. The acute and chronic exposure estimates from the 

dietary exposure analyses represent aggregate risk for acute and chronic exposures. 

Difenoconazole is currently registered for the following uses that could result in residential 

exposures: Ornamentals. EPA assessed residential exposure using the 

following assumptions: Adults may be exposed to difenoconazole from its currently registered 

use on ornamentals. Residential pesticide handlers may be exposed to short-term duration (1 - 30 

days) only. The dermal and inhalation (short-term) residential exposure was assessed for 

"homeowners" mixer/loader/applicator wearing short pants and short-sleeved shirts as well as 
Page 26 of 70

shoes plus socks using garden hose-end sprayer, “pump-up” compressed air sprayer, and 

backpack sprayer. Residential post-application exposure may occur from use of difenoconozole 

on golf course turf. Short-term dermal exposure was assessed for post-application exposure to 

golf course turf. Further information regarding EPA standard assumptions and generic inputs for 

residential exposures may be found at http://www.epa.gov/pesticides/trac/science/trac6a05.pdf. 

7.1 Short-Term Aggregate Risk to Residential Applicators

Short term aggregate exposure takes into account residential exposure plus average 

exposure levels to food and water (considered to be a background exposure level). The short 

term aggregate risk for residential handlers is the estimated risk associated with combined risks 

from average food and drinking water exposures and dermal and inhalation exposures to adult 

applicators. Short term aggregate risk estimates for residential handlers are provided in Table 10

aggregates the short-term risk for adults from residential handler exposure and average food and 

water exposure (as a background). The lowest aggregate MOE is 200, which is greater than the 

target MOE of 100 and therefore not of concern.

Table 10: Estimated Difenoconazole Short-term Aggregate Risk to Adults from Residential Handler Activities

Exposure Scenario Target 

MOE1

Route of 

Exposure

Daily dose

mg/kg/day

NOAELs

mg/kg/day

MOE at Day 0 Combined MOE4

Average Food and Water 

(As background)

N/A Food and 

water

0.002958

1.25

420 2 NA

Hose End Sprayer -

Ornamentals

100 

Dermal and 

Inhalation

0.0022 575 3240

Handheld Pump Spray -

Ornamentals 0.0031 400 200

Hose End Sprayer – Flower 

Gardens 0.0019 660 260

Handheld Pump Spray –

Flower Gardens 0.0021 590 250

1 Target MOE= 100, Developmental rat- increased incidence of rudimentary risks. NOAEL = 0.96

2 MOE food and water = [(short-term oral NOAEL)/(chronic dietary exposure)] 

3 MOE dermal and inhalation = [(short -term NOAEL (1.25)/(high-end inhalation and dermal residential exposure)] 

4 Aggregate Combined MOE (food, water, and residential) = 1÷ [(1÷MOE food and water) + (1÷MOE handler inhalation and 

dermal)].

7.2 Short-Term Aggregate Risk for Residential Post-Application Exposure

Table 11 aggregates the short-term risk for adults from residential post application, and 

average food and water exposure. The highest post application exposure from residential use on 

turf was used in the short term aggregate. The aggregate MOE is 600, which is greater than the 

target MOE of 100. This aggregate exposure assessment is considered very conservative

because the assumptions used for each of the scenarios separately are already high end (i.e., time 

spent outdoors, dislodgeable residues). 
Page 27 of 70

Table 11: Estimated Difenoconazole Short-term Aggregate Risk from Residential Post-Application Activities

Exposure Scenario Target 

MOE1

Route of 

Exposure

Daily Dose

mg/kg/day NOAELs MOE at Day 

0

Combined 

MOE4

Average Food and Water 

Adult

N/A Food and 

water

0.002958

1.25

420 2 NA

Adult Golfer 100 Dermal 0.00024 5200 3390

1 Target MOE= 100, Developmental rat- increased incidence of rudimentary risks. NOAEL = 0.96

2 MOE food and water = [(short-term oral NOAEL)/(chronic dietary exposure)] 

3 MOE dermal = [(short -term dermal NOAEL)/(high-end dermal residential exposure)] 

4 Aggregate Combined MOE (food, water, and residential) = 1÷ [(1÷MOE food and water) + (1÷MOE post appl. dermal)].

Updated Aggregate Assessment of Free Triazole & its Conjugates

Reference: Common Triazole Metabolites: Updated Aggregate Human Health Risk Assessment to Address 

Tolerance Petitions for Propiconazole, Difenoconazole, and Flutriafol. DP397592, T. Morton, 1/26/12.

The addition of the new proposed uses increase the aggregate exposure to free triazoles and its 

conjugates. Therefore, the aggregate human health risk assessment for free triazoles and its 

conjugates was updated and the aggregate estimates are below HED’s level of concern

(DP397592, T. Morton, 1/26/12).

8.0 CUMULATIVE RISK

Difenoconazole is a member of the triazole-containing class of pesticides. Although conazoles 

act similarly in plants (fungi) by inhibiting ergosterol biosynthesis, there is not necessarily a 

relationship between their pesticidal activity and their mechanism of toxicity in mammals. 

Structural similarities do not constitute a common mechanism of toxicity. Evidence is needed to 

establish that the chemicals operate by the same, or essentially the same, sequence of major 

biochemical events (EPA, 2002). In conazoles, however, a variable pattern of toxicological 

responses is found; some are hepatotoxic and hepatocarcinogenic in mice. Some induce thyroid 

tumors in rats. Some induce developmental, reproductive, and neurological effects in rodents. 

Furthermore, the conazoles produce a diverse range of biochemical events including altered 

cholesterol levels, stress responses, and altered DNA methylation. It is not clearly understood 

whether these biochemical events are directly connected to their toxicological outcomes. Thus, 

there is currently no evidence to indicate that conazoles share common mechanisms of toxicity 

and EPA is not following a cumulative risk approach based on a common mechanism of toxicity 

for the conazoles. For information regarding EPA’s procedures for cumulating effects from 

substances found to have a common mechanism of toxicity, see EPA’s website at 

http://www.epa.gov/pesticides/cumulative.

Difenoconazole is a triazole-derived pesticide. This class of compounds can form the common 

metabolite 1,2,4-triazole and two triazole conjugates (triazolylalanine and triazolylacetic acid). 

To support existing tolerances and to establish new tolerances for triazole-derivative pesticides, 

including propiconazole, U.S. EPA conducted a human health risk assessment for exposure to 

1,2,4-triazole, triazolylalanine, and triazolylacetic acid resulting from the use of all current and 
Page 28 of 70

pending uses of any triazole-derived fungicide. The risk assessment is a highly conservative, 

screening-level evaluation in terms of hazards associated with common metabolites (e.g., use of 

a maximum combination of uncertainty factors) and potential dietary and non-dietary exposures 

(i.e., high end estimates of both dietary and non-dietary exposures). In addition, the Agency 

retained the additional 10X FQPA safety factor for the protection of infants and children. The 

assessment includes evaluations of risks for various subgroups, including those comprised of 

infants and children. The Agency’s complete risk assessment is found in the propiconazole 

reregistration docket at http://www.regulations.gov, Docket Identification (ID) Number EPAHQ-OPP-2005-0497.

9.0 OCCUPATIONAL EXPOSURE/RISK CHARACTERIZATION

Occupational handler and post-application exposure scenarios are assessed for the risk 

assessment of the uses. Based on the product labels and information provided by the registrant, 

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

activities. Chronic exposure is not expected for the proposed use patterns. Dermal and 

inhalation exposures to workers are aggregated for difenoconazole because the PODs for these 

routes are based on common toxicological effects. 

9.1 Handler Exposure 

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

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

activities through inhalation routes only. Difenoconazole products are applied to using aerial, 

groundboom, chemigation, and handheld sprayers. The proposed new post harvest use on 

potatoes is by automated spray application.

9.1.1 Handler Exposure Scenarios

The following handler exposure scenarios evaluated for this assessment are based on 

information provided in the proposed labels. 

9.2.1.1 Foliar Applications to Field Crops

• Open mixing/loading liquid formulation for groundboom, aerial, chemigation, and 

airblast application; 

• Applying with aerial, groundboom, and airblast sprayer equipment; and

• Flagging for aerial application. 

9.2.1.2 Post-Harvest Application to Potatoes

• Open mixing/loading liquid for automated spray application. 
Page 29 of 70

9.1.2 Handler Exposure Data and Assumptions

No chemical-specific handler exposure data were submitted in support of this 

registration. 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 the Pesticide Handlers Exposure Database Version 1.1 (PHED 1.1), the Agricultural 

Handler Exposure Task Force (AHETF) database, the Outdoor Residential Exposure Task Force 

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

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

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

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

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

including descriptions of the various sources, can be found at 

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

• Average body weight of an adult handler is 80 kg.

• Dermal absorption factor is 6%

• Exposure duration short-term (1- 30 days), intermediate-term (1-6 months)

• Maximum label application rates for aerial, groundboom and airblast to fruit, vegetable 

and berry crops:

- 0.07 – 0.13 lb ai/A

• Area treated for aerial, groundboom, airblast and chemigation application to field crops: 

- 350 acres per day for aerial application

- 80 acres per day for groundboom application 

- 40 acres per day for airblast application 

• Maximum label application rates post-harvest use on potatoes

- 0.00025 gal ai/lb potato

• Amount of potatoes treated/processed 

- 1,440,000 lbs per day (180,000 lbs per hour x 8 hrs per day)

9.1.3 Handler Exposure and Risk Estimates

All worker exposures are assessed as short- and intermediate-term based on label 

prescribed uses and expected exposure durations. Exposure and risk estimates indicate noncancer risks are not of concern for occupational handler activities for the proposed new uses 

(MOEs > 100). A summary of occupational handler exposure and risk calculations, assumptions,

and results are provided in Tables 12 and 13.
Page 30 of 70

Table 12. Occupational Handler Short-/Intermediate-Term Dermal and Inhalation Exposure Estimated Risk

Exposure 

Scenario Crop

Unit Exposure1

(ug/lb ai) App. 

Rate2

(lb ai/A)

Area 

Treated3

(A/Day)

ST & IT Dose

(mg/kg/day)

ST & IT MOEs

LOC = 100

Combined 

MOEs8

LOC=100

Dermal

Baseline

Inhal

BL

Dermal4

Baseline

Inhal.

5

Baseline

Dermal6

Baseline

Inhal.

7

Baseline

Inhal + 

Dermal

Mixing/Loading – Liquid

Groundboom

Citrus fruits

220 0.219

0.13

80 0.0017 0.000028 730 44,000 720

Airblast 40 0.00086 0.000014 1,500 88,000 1,400

Aerial & 

Chem. 350 0.0075 0.00012 170 10,000 160

Groundboom Fruiting 

Vegetables;

Strawberry/ 

low 

growing 

berry

0.11

80 0.0015 0.000024 860 52,000 850

Airblast 40 0.0007 0.000012 1,700 100,000 1,700

Aerial & 

Chem. 350 0.0064 0.00011 200 12,000 190

Groundboom

Pome 

Fruits 0.07

80 0.0009 0.000015 1,400 82,000 1,300

Airblast 40 0.0005 0.000008 2,700 160,000 2,700

Aerial & 

Chem. 350 0.0040 0.000067 310 19,000 300

Groundboom Strawberry/ 

low 

growing 

berry

0.11

80 0.0015 0.000024 860 52,000 850

Airblast 40 0.0007 0.000012 1,700 100,000 1,700

Aerial & 

Chem. 350 0.0064 0.00011 200 12,000 190

Applying Liquid

Groundboom

Citrus fruits

78.6 0.34

0.13

80 0.00061 0.000044 2,000 28,000 1,900

Airblast 1770 4.71 40 0.0069 0.00031 180 4,100 170

Aerial N/A 0.068 350 N/A 0.000039 N/A 32,000 N/A

Groundboom Fruiting 

Vegetables; 

Strawberry/ 

low 

growing 

berry

78.6 0.34

0.11

80 0.00052 0.000037 2,400 33,000 2,200

Airblast 1770 4.71 40 0.0058 0.00026 210 4,800 200

Aerial N/A 0.068 350 N/A 0.000033 N/A 38,000 N/A

Groundboom

Pome 

Fruits

78.6 0.34

0.07

80 0.00033 0.000024 3,800 53,000 3,500

Airblast 1770 4.71 40 0.0037 0.00016 340 7,600 320

Aerial N/A 0.068 350 N/A 0.000021 N/A 60,000 N/A

Groundboom Strawberry/ 

low 

growing 

berry

78.6 0.34

0.11

80 0.00052 0.000037 2,400 33,000 2,200

Airblast 1770 4.71 40 0.0058 0.00026 210 4,800 200

Aerial N/A 0.068 350 N/A 0.000033 N/A 38,000 N/A

Flagging

Aerial

Citrus fruits

11 0.35

0.13

350

0.0063 0.00020 200 6,300 190

Fruiting 

Vegetables; 

Strawberry/ 

low 

growing 

berry

0.11 0.0053 0.00017 240 7,400 230

Pome 

Fruits 0.07 0.0034 0.00011 370 12,000 360
Page 31 of 70

Table 12. Occupational Handler Short-/Intermediate-Term Dermal and Inhalation Exposure Estimated Risk

Exposure 

Scenario Crop

Unit Exposure1

(ug/lb ai) App. 

Rate2

(lb ai/A)

Area 

Treated3

(A/Day)

ST & IT Dose

(mg/kg/day)

ST & IT MOEs

LOC = 100

Combined 

MOEs8

LOC=100

Dermal

Baseline

Inhal

BL

Dermal4

Baseline

Inhal.

5

Baseline

Dermal6

Baseline

Inhal.

7

Baseline

Inhal + 

Dermal

Strawberry/ 

low 

growing 

berry

0.11 0.0053 0.00017 240 7,400 230

1 Based on “Occupational Pesticide Handler Unit Exposure Surrogate Reference Table” (September 26, 2011); includes data from

PHED/ORETF/AHETF .

2 Based on proposed label.

3 Exposure Science Advisory Council Policy #9.1.

4 Dermal Dose = Dermal Unit Exposure (mg/lb ai) x Application Rate (lb ai/acre) x Area Treated (Acres/day) x DAF (6%)/BW (80 kg).

5 Inhalation Dose = Inhalation Unit Exposure (mg/kg) x Application Rate (lb ai/acre) x Area Treated (Acres/day) x DAF (6%)/BW (80 kg).

6 Dermal MOE = Dermal NOAEL (1.25 mg/kg/day)/Dermal Dose (mg/kg/day). Level of concern = 100.

7 Inhalation MOE = Inhalation NOAEL (1.25 mg/kg/day)/ Inhalation Dose (mg/kg/day). Level of concern = 100.

8 Total MOE = NOAEL (mg/kg/day)/Dermal Dose + Inhalation Dose.

Table 13. Occupational Handler Short- and Intermediate-Term Dermal and Inhalation Exposure and Risk Estimates 

for Potato Post-Harvest Use

Exposure 

Scenario

Solution 

Conc.2

(lb ai/gal 

soln)

Amount 

Treated/

Day3

( gal/lb)

Amount 

Processed

4

(lbs/hr)

Dermal 

UE

(mg/lb ai)

Inhal. 

UE5

(mg/lb ai)

Daily Dose6 

(mg ai/kg/day)

MOEs

LOC=100

Dermal Inhal. Dermal Inhal.

Open 

Mixing/Loading 

Liquids

0.014 0.00025 180,000 0.220 0.000219 0.00084 0.000014 1,500 90,000

1. Liquid Formulation – Thesis EPA Reg. No. 100-1386

2. Solution Concentration - fl oz product/gal water x lb ai/gal product x 1 gal/128 fl oz (e.g. 0.3 fl oz product/0.5 gal water x 3 lb 

ai/gal product x 1 gal/128 fl oz)

3. Amount Treated Per day - gallons/lb of tubers (e.g. 0.5 gal treats 2,000 lb tubers = 1 gal/4,000 lb tubers). Provided by the 

registrant, in an email correspondence.

4. Amount Processed - lbs boxes per hour. Assumed that a packing facility could potentially pack 2,000 boxes per hour, each 

weighing 90 lbs (2,000 boxes/hr x 90 lbs/box = 180,000 lbs/hr)

5. Unit Exposure Values - Baseline (e.g. no gloves or respirator)

6. Short- a nd Intermediate Term Inhalation Daily Dose - [Amount Processed (lb boxes/hr) x Amount Treated daily (gal/lb) x 

soln concentration (lb ai/gal soln) x Unit Exposure x 8 (hr/day) x absorption factor (0.06 dermal only ]/body weight

7. Short Term MOE - NOAEL (1.25 mg/kg/day)/Daily Dose (mg ai/kg/day)

8. Intermediate Term MOE - NOAEL (1.25 mg/kg/day)/Daily Dose (mg ai/kg/day)

9.2 Post-Application Exposure 

HED uses the term “post-application” to describe those individuals who can be exposed 

to pesticides after entering areas previously treated with pesticides and performing certain tasks 

or activities (also often referred to as reentry exposure). Post-application exposures are expected 

to occur primarily via the dermal route. Post-application exposures are expected to occur 

primarily via the dermal route. Based on the Agency's current practices, a quantitative post 

application inhalation exposure assessment was not performed for difenoconazole. However, 

volatilization of pesticides may be a potential source of post application inhalation exposure to 

individuals nearby to pesticide applications. The Agency sought expert advice and input on 

issues related to volatilization of pesticides from its Federal Insecticide, Fungicide, and 

Rodenticide Act Scientific Advisory Panel (SAP) in December 2009. The Agency received the 
Page 32 of 70

SAP’s final report on March 2, 2010 and is in the process of evaluating the SAP report. The 

Agency may, as appropriate, develop policies and procedures to identify the need for and, 

subsequently, the way to incorporate post application inhalation exposure into the Agency's risk 

assessments. If new policies or procedures are put into place, the Agency may revisit the need 

for a quantitative post application inhalation exposure assessment. 

9.2.1 Post-Application Exposure Scenarios

There are no compound specific data with which to estimate post-application exposures 

to agricultural workers. Estimates of post-application re-entry exposure to agricultural workers 

are based upon the EXPOSAC Standard Operating Procedures (SOPs) (3.1, Reference 4). This 

SOP lists a number of possible post-application agricultural activities for the proposed crop uses 

that might result in post-application.

The following post-application exposure scenarios were assessed for proposed postemergence uses of difenoconazole. 

 

- Citrus fruits, Crop group 10-10; hand harvesting, hand pruning, scouting, hand weeding, 

orchard maintenance

- Fruiting Vegetable Crop group 8-10; irrigation (hand set), hand harvesting, tying/training, 

transplanting, scouting, hand pruning; scouting; thinning, hand weeding

- Pome Fruit Crop group 11-10; hand harvesting, thinning, training, transplanting, hand 

weeding, propping, orchard maintenance. 

- Strawberry and other low growing berry (subgroup 13-07G, except cranberry); hand 

harvesting, leaf pulling, tying/training, irrigation (hand set), scouting, propagating, hand 

pruning, trellis repair; transplanting, hand pruning (shears); hand weeding, canopy 

management

- Post-harvest potato; sorting, packing and culling treated potatoes

In accordance with the Worker Protection Standard (WPS), a 12-hr restricted entry 

interval (REI) is required for chemicals classified under Toxicity Category III/IV. 

9.2.2 Post Application Exposure Data and Assumptions for Field Crops

• Average body weight of an adult handler is 70 kg.

• Dermal absorption factor is 6%

• Exposure duration is 8 hrs per day

• Maximum label application rates:

- 0.125 lb ai/A for citrus fruits

- 0.11 lb ai /A for fruiting vegetables

- 0.07 lb ai/A for pome fruit

- 0.114 lb ai/A for low growing berries

• Transfer Coefficients:

- 100 – 1400 cm2/hour for citrus fruit post-application activities

- 70 – 1900 cm2/hour for fruiting vegetable post-application activities

- 100 – 3600 cm2/hour for pome fruit post-application activities

- 70 – 5500 cm2/hour for low growing berry post-application activities

• Initial fraction of ai retained on foliage is 20% 

• Exposure is assumed to occur on the day of application (day 0)
Page 33 of 70

9.2.3 Post Application Exposure Assumptions for Post-Harvest Potato

The proposed occupational uses for difenoconazole addressed in this document involve 

post-harvest applications, resulting in the potential for exposure during sorting, packing and 

culling treated potatoes. Therefore a dermal risk assessment was performed. The estimates of 

exposure is derived from residue chemistry data, surface area calculations, a reentry study for 

citrus (used as surrogate) found in the scientific literature, and a study monitoring the amount of 

material transferred during contact with a treated surface (Refer to ExpoSAC draft policy by D. 

Jaquith, 11/2005). 

• A “standard” potato has a diameter of 2.25 to inches in diameter and weighs 213 grams;

• The residue level of pesticide for potatoes used in this assessment is 2.34 ppm (μg/g) 

obtained from chemical specific data (highest average field trial (HAFT) for this 

commodity.

• All of the pesticide residue is on the surface of the commodity. The chemical is not 

applied as a systemic product.

• Workers are assumed to perform the sorting/culling tasks for 8 hours per day.

• Dermal absorption is 6% for difenoconazole.

• The transfer efficiency of the chemical is less than 2 percent.

• The transfer coefficient for the palmar surface of the hands only is 408 cm2 per hour.

9.2.4 Post-Application Exposure and Risk Estimates

A target LOC or MOE of 100 is considered adequate for dermal exposure. Postapplication exposure and risk estimates are not of concern (MOEs > 100). A summary of postapplication exposure and risk calculations, assumptions, and results is provided in Tables 14 and 

15. 
Page 34 of 70

Table 14. Estimated Difenoconazole Exposure & MOEs for Occupational Post-Application Exposure 

Exposure 

Scenario

Post-application 

Activities

TC

(cm2/hr)

App 

Rate

(lb ai/A)

DFR

(mg/cm2)

Dermal 

Dose

(mg/kg/day)

MOE

LOC = 

100

Citrus fruits, Crop 

group 10-10

Harvesting, Hand 1400 0.125 0.00028 0.0024 530

Pruning, Hand; Scouting 580 0.125 0.00028 0.0010 1300

Transplanting 230 0.125 0.00028 0.0004 3200

Baiting/Trapping; 

Weeding, Hand; Orchard 

maintenance

100 0.125 0.00028 0.0002 7400

Fruiting 

Vegetable, Crop 

group 8-10

Irrigation (hand set) 1900 0.11 0.00025 0.00281 440

Harvesting, Hand; 

Tying/Training 1100 0.11 0.00025 0.00163 770

Harvesting, Hand; 

Tying/Training 550 0.11 0.00025 0.00081 1500

Transplanting 230 0.11 0.00025 0.00034 3700

Scouting 210 0.11 0.00025 0.00031 4000

Pruning, Hand; Scouting; 

Thinning Fruit; Weeding, 

Hand

90 0.11 0.00025 0.0001 9400

Weeding, Hand; Pruning, 

Hand 70 0.11 0.00025 0.0001 12000

Pome Fruit, Crop 

Group 11-10

Thinning Fruit 3600 0.07 0.00016 0.0034 370

Harvesting, Hand 1400 0.07 0.00016 0.0013 950

Scouting; Pruning, Hand; 

Training 580 0.07 0.00016 0.00055 2300

Transplanting 230 0.07 0.00016 0.00022 5800

Weeding, Hand; Propping; 

Orchard maintenance 100 0.07 0.00016 0.00009 13000

Strawberry and 

other low growing 

berry (subgroup 

13-07G, except 

cranberry)

Harvesting, Hand; Leaf 

Pulling; Tying/Training 5500 0.114 0.00026 0.0084 150

Irrigation (hand set) 1900 0.114 0.00026 0.0029 430

Harvesting, Hand; 

Tying/Training; 1400 0.114 0.00026 0.0021 580

Harvesting, Hand; 

Harvesting; Scouting; 1100 0.114 0.00026 0.0017 740

Propagating; Pruning, 

Hand; Scouting; Trellis 

Repair; Tying/Training; 

Weeding, Hand

640 0.114 0.00026 0.0010 1300

Transplanting 230 0.114 0.00026 0.00035 3500

Scouting 210 0.114 0.00026 0.00032 3900

Pruning, Hand (shears); 

Weeding, Hand; Canopy 

Management

70 0.114 0.00026 0.00011 12000

1. DFR = AR x F x (1-D)tx 4.54E8 μg/lb x 2.47E-8 acre/cm2

2. MOE = POD (NOAEL, 1.25 mg/kg/day) / Daily Dermal Dose. Daily Dermal Dose = [DFR (μg/cm2) x TC x 0.001 mg/μg x 8 hrs/day x 6% 

dermal absorption] body weight 80 kg adult). 
Page 35 of 70

Table 15. Summary of Estimated Post Harvest Post-application MOEs for Potatoes

Chemical in Specific Commodity1(Potato) Commodity 

Specific 

Surface area

(cm2)

Surface 

Residue

(μg/cm2)

Daily Dose2

(mg /kg 

/day)

Short & IntTerm MOE3

Chemical Residue LOC = 100

μg /g (PPM)

Commodity 

Avg. Weight (g)

Chemical 

Residue (μg)/ 

Commodity

2.34 213 498 214 2.3 0.000114 11,000

1Residue level calculations for potatoes based on highest average field trial

2Daily Dose = [(408 cm2/hr) x (2.3μg/cm2) x (8 hrs/day) x (6% of Dermal Absorption) x (2% Transfer Efficiency) x (0.001 

mg/μg)]/80 Kg

3 MOEmat = NOAEL / Daily Dose. (Short & Intermediate-Term NOAEL = 1.25 mg/kg/day)

10.0 REFERENCES

Difenoconazole. Petition for Postharvest (PH) Use on Potatoes and Expansions of Existing Crop 

Group/Representative Commodity Uses to Fruiting Vegetables Group 8-10, Citrus Fruits Group 

10-10, Pome Fruits Group 11-10, and Low growing Berry Subgroup 13-07G, Except Cranberry. 

Summary of Analytical Chemistry and Residue Data, B. Cropp-Kohlligian, D389912, 5/30/12

Difenoconazole. Acute and Chronic Aggregate Dietary Exposure and Risk Assessments for the 

Petition for Postharvest (PH) Use on Potatoes and Expansions of Existing Crop 

Group/Representative Commodity Uses to Fruiting Vegetables Group 8-10, Citrus Fruits Group 

10-10, Pome Fruits Group 11-10, and Low growing Berry Subgroup 13-07G, Except Cranberry.

T. Morton, D397664, 5/30/12

Difenoconazole. Occupational and Residential Exposure Assessment to Evaluate the Risk from 

Proposed Uses on Post-Harvest Potatoes, and the Expansion of Various Crop Groups Including: 

Citrus Fruit Group 10-10; Fruiting Vegetable Subgroups 8-10; Low Growing Berry Subgroup 

13-07G, except cranberry; Pome Fruit, Crop Group 11-10 and Fruiting Vegetable, Crop Group 8-

10), Ivan Nieves, D398608, 5/30/12

Difenoconazole (Parent Only) Drinking Water Assessment in Support of New Use Registration 

Action for Golf Course Turf. I. Maher, D371044, 6/1/10, Updated EFED; Memo, F. Khan, 23-

February-2012; D398836

Difenoconazole. Request for Restatement of 1994 EPA Cancer Classification and Risk 

Assessment Approach Using Current Terminology. P.V. Shah, D 318039, 3/1/07

Difenoconazole – with both available in vivo and in vitro dermal absorption studies, select an 

appropriate dermal absorption factor to be used for risk assessment, J. Chen, 12/18/08

Difenconazole: Summary of Hazard and Science Policy Council (HASPOC) Meeting of 

February 23, 2012: Recommendations on the need for a 28-day inhalation study, D. Smegal, 

TXR#0054074, 3/5/12. 
Page 36 of 70

APPENDICES

A. TOXICOLOGY DATA SUMMARY

A.1 Guideline Data Requirements

Guideline 

No. Study Type Technical MRID 

Required Submitted No.

870.3100

870.3150

870.3200

870.3250

870.3465

Subchronic (Oral) Toxicity - Rodent....................................................

Subchronic (Oral) Toxicity - Non-Rodent ...........................................

21/28-Day Dermal Toxicity .................................................................

90-Day Dermal Toxicity ......................................................................

90-Day Inhalation Toxicity .................................................................

Y

Y

N

N

N

Y

Y

Y

N

N

42090022

42090021

42090013

42090013

46950310

870.3700a

870.3700b

870.3800

Prenatal Developmental Toxicity - Rodent ..........................................

Prenatal Developmental Toxicity - Non-Rodent..................................

Reproduction and Fertility Effects.......................................................

Y

Y

Y

Y

Y

Y

42090016

42710008

42090017

42710008

42090018

870.4100a

870.4100b

870.4200a

870.4200b

870.4300

Chronic (Oral) Toxicity - Rodent.........................................................

Chronic (Oral) Toxicity - Non-Rodent (Dog) ......................................

Carcinogenicity - Rat......................................................................

Carcinogenicity - Mouse ......................................................................

Combined Chronic Toxicity /Carcinogenicity

Y

Y

Y

Y

Y

Y

Y

Y

Y

Y

42090015

42710006

42090012

42710005

42090019

42710010

42090015

42710006

42090015

42710006

870.6100a

870.6100b

870.6200a

870.6200b

870.6300

870.7800

Neurotoxicity - Acute Delayed Neurotox.- Hen...................................

Neurotoxicity - Subchronic - Hen .......................................................

Neurotoxicity - Acute - Rat..................................................................

Neurotoxicity -Subchronic - Rat ..........................................................

Developmental Neurotoxicity..................

Immunotoxicity............................. ..............................................

N

N

Y

Y

N

Y

N

N

Y

Y

N

Y

---

---

46950327

46950329

--

--
Page 37 of 70

A.2 Toxicity Profiles

Table A.1. Acute Toxicity Profile – Difenoconazole

Guideline No. Study Type MRID No. Results Toxicity Category

870.1100 Acute oral 42090006 LD50 = 1450 mg/kg III

870.1200 Acute dermal 42090007 LD50 > 2010 mg/kg III

870.1300 Acute inhalation 42090008 LC50 > 3.3 mg/L III

870.2400 Eye irritation 42090009 Mild irritation reversible in 7 days III

870.2500 Dermal irritation 40789807 Slight irritation IV

870.2600 Skin sensitization 42090011, 42710004 Negative N/A

Table A.2. Subchronic, Chronic and Other Toxicity Profile of Difenoconazole

Guideline 

No. 

Study Type MRID No. (year)/ 

Classification /Doses

Results

870.3100 90-Day oral 

toxicity (rat)

42090022 (1987)

Acceptable/guideline

0, 20, 200, 750, 1500 or 3000 

ppm

0, 1, 10, 37.5, 75 and 150 

mg/kg/d

NOAEL = 20 ppm (1 mg/kg/day)

LOAEL = 200 ppm (10 mg/kg/day) based on the 10% 

decrease in body weight in the 200 ppm females (as well 

as a negative trend in feed consumption) and Increases in 

absolute liver weights in both sexes

870.3100 90-Day oral 

toxicity (mouse)

42090021 (1987)

Minimum/guideline

0, 20, 200, 2500, 7500 or 

15,000 ppm 

M: 0, 2.9, 30.8, 383.6, 1125 and 

2250 mg/kg/d

F: 0, 4.1, 41.5, 558.9, 1125 and 

2250 mg/kg/d

NOAEL = 20 ppm (2.9 mg/kg/day)

LOAEL = 200 ppm (30.8 mg/kg/day) based on body 

weight changes & liver histopathology.

870.3150 26-Week oral 

toxicity

42090012 (1987)

Minimum/ guideline

0, 100, 1000, 3000 or 6000 ppm

M: 0, 3.6, 31.3, 96.6 and 157.8 

mg/kg/d

F: 0, 3.4, 34.8, 110.6 and 203.7 

mg/kg/d

NOAEL = 3000 ppm (31.3 mg/kg/day in males/34.8 

mg/kg/day in females)

LOAEL = 6000 ppm (96.6 mg/kg/day in males/110.6 

mg/kg/day in females), based primarily on microscopic 

examination of CGA 169374-related lenticular cataracts.

870.3200 21/28-Day dermal 

toxicity (rat)

42090013 (1987)

Minimum/ guideline

0, 10, 100 and 1000 mg/kg/d

NOAEL = 10 mg/kg/day

LOAEL = 100 mg/kg/day based on statistically 

significant decrements in body weight, body weight gain, 

and food consumption.

870.3200 21/28-Day dermal 

toxicity (rat)

46950310 (2000)

Acceptable/ guideline

0, 10, 100 and 1000 mg/kg/d

NOAEL (systemic) = 1000 mg/kg/day

LOAEL (systemic) was not determined.

NOAEL (dermal) = 100 mg/kg/day

LOAEL (dermal) = 1000 mg/kg/day based on 

hyperkeratosis at the skin application site.

870.3700a Prenatal 

developmental in 

(rat)

42090016, 42710007 (1987)

Minimum/ guideline

0, 2, 20, 100 or 200 mg/kg/d 

from GD 6-15 (nominal doses 

differed widely from 

theoretical, this required 

altering NOAEL/LOAEL 

values)

Maternal NOAEL = 16 mg/kg/day

LOAEL = 85 mg/kg/day based on decreased body weight 

gain and food consumption.

Developmental NOAEL = 85 mg/kg/day

LOAEL = 171 mg/kg/day based on alterations in fetal 

ossification.
Page 38 of 70

Table A.2. Subchronic, Chronic and Other Toxicity Profile of Difenoconazole

Guideline 

No. 

Study Type MRID No. (year)/ 

Classification /Doses

Results

870.3700b Prenatal 

developmental in 

(rabbit)

42090017, 42710008 (1987)

Minimum/ guideline

0, 1, 25 or 75 mg/kg/d from GD 

7-19

Maternal NOAEL = 25 mg/kg/day

LOAEL = 75 mg/kg/day based on decreased body weight 

gain and food consumption. 

Developmental NOAEL = 25 mg/kg/day

LOAEL = 75 mg/kg/day based on nonsignificant 

increases in postimplantation loss and resorptions/doe and 

a significant decrease in fetal weight.

870.3800 Reproduction and 

fertility effects

(rat)

42090018 (1988)

Minimum/ guideline

0, 25, 250 or 2500 ppm

0, 1.25, 12.5 and 125 mg/kg/d

Parental/Systemic NOAEL = 25 ppm (1.25 mg/kg/day) 

LOAEL = 250 ppm (12.5 mg/kg/day) based on reductions 

(statistically nonsignificant) in body weight gain which 

appear to be part of a dose-related trend days 70-77 prior 

to mating, days 0-7 of gestation, and days 7-14 of 

lactation

Offspring NOAEL = 25 ppm (1.25 mg/kg/day)

LOAEL = 250 ppm (12.5 mg/kg/day) based on a 

significant reduction in the body weight of F1 male pups 

at day 21 in the 250 ppm group.

870.4100b Chronic toxicity

(dog)

42090012, 42710005 (1988)

Minimum/ guideline

0, 20, 100, 500 or 1500 ppm

M: 0, 0.71, 3.4, 16.4 and 51.2 

mg/kg/d

F: 0, 0.63, 3.7, 19.4 and 44.3 

mg/kg/d

NOAEL = 100 ppm (3.4 mg/kg/day in males/3.7 

mg/kg/day in females)

LOAEL = 500 ppm (16.4 mg/kg/day in males/19.4 

mg/kg/day in females), based on significant inhibition of 

body weight gain in females.

870.4200 Carcinogenicity

(rat)

42090019, 42710010 (1989)

Minimum/ guideline

0, 10, 20, 500 or 2500 ppm

M: o, 0.48, 0.96, 24.12 and 

123.7 mg/kg/d

F: 0, 0.64, 1.27, 32.79 and 

169.6 mg/kg/d

NOAEL = 20 ppm (0.96 mg/kg/day in males/1.27 

mg/kg/day in females)

LOAEL = 500 ppm (24.1 mg/kg/day in males/ 32.8 

mg/kg/day in females) based on reductions in cumulative 

body weight gains in the 500 and 2500 ppm groups.

No evidence of carcinogenicity

870.4300 Carcinogenicity

(mouse)

42090015, 42710006 (1989)

Minimum/ guideline

0, 10, 30, 300, 2500 or 3000 

ppm

M: 0, 1.51, 4.65, 46.29, 423.1 

and 818.9 mg/kg/d

F: 0, 1.9, 5.63, 57.79 and 512.6 

mg/kg/d

NOAEL = 30 ppm (4.7 mg/kg/day in males/5.6 

mg/kg/day in females)

LOAEL = 300 ppm (46.3 mg/kg/day in males/57.8 

mg/kg/day in females) based on reductions in the 

cumulative body weight gains and hepatocellular 

hypertrophy, liver necrosis, fatty changes in the liver and 

bile stasis in the 300, 2500 & 4500 ppm groups. 

Evidence of carcinogenicity (liver adenoma/carcinoma in 

both sexes)

870.5100 In vitro bacterial 

gene mutation

(Salmonella 

typhimurium/ E. 

coli)/ mammalian 

activation gene 

mutation assay

42090019, 42710010 (1989)

Minimum/ guideline

340 - 5447 μg/plate;

85 - 1362 μg/plate (repeat assay 

with TA1537 and TA98)

There were sufficient and valid data to conclude that 

CGA 169374 technical was negative in the microbial 

gene mutation assay.
Page 39 of 70

Table A.2. Subchronic, Chronic and Other Toxicity Profile of Difenoconazole

Guideline 

No. 

Study Type MRID No. (year)/ 

Classification /Doses

Results

870.5300 in vitro 

mammalian cell 

gene mutation 

assay in mouse 

lymphoma cells

42090024 (1986)

Unacceptable/ guideline

No conclusion can be reached from the three nonactivated 

and two S9 activated mouse lymphoma forward mutation 

assays conducted with difenoconazole technical. The 

study was seriously compromised.

870.5375 In vitro

Mammalian 

Cytogenetics

(chromosomal 

aberrations) assay

in Chinese 

hamster CHO 

cells

46950319 (2001)

Acceptable/ guideline

0, 21.99, 27.49, or 34.36 μg/mL 

(-S9)

0, 34.36, 53.69 or 67.11 μg/mL 

(+S9)

There was evidence of a weak induction of structural 

chromosomal aberrations over background in the 

presence of S9-mix.

870.5375 In vitro

Mammalian 

Cytogenetics

(chromosomal 

aberrations) assay

in Chinese 

hamster CHO 

cells

46950321 (2001)

Acceptable/ guideline

0, 26.3, 39.5 or 59.3 μg/mL (-

S9)

0, 11.7 or 17.6 μg/mL (+S9)

There was evidence of a weak induction of structural 

chromosomal aberrations over background.

870.5375 In vitro

Mammalian 

Cytogenetics

(chromosomal 

aberrations) assay

in human 

lymphocytes

46950323 (2001)

Acceptable/ guideline

0, 5, 30 or 75 μg/mL (-S9)

0, 5, 30 or 62 μg/mL (+S9)

There was no evidence of structural chromosomal 

aberrations induced over background.

870.5385 In vivo

mammalian 

chromosomal 

aberration test 

Assay in Mice

42090023 (1986)

Unacceptable/guideline

250, 500 or 1000 mg/kg

There was no evidence of a cytotoxic effect on the target 

organ or significant increase in the frequency of nuclear 

anomalies (micronuclei). However, the study was 

compromised.

870.5395 In vivo

mammalian 

cytogenetics -

erythrocyte 

micronucleus 

assay in mice

41710011 (1992)

Acceptable/guideline

Doses up to 1600 mg/kg

Mice bone marrow - No increase in micronucleated 

polychromatic erythrocytes occurred with CGA-1 69374 

(91.2% a.i).

870.5550 Unscheduled 

DNA Synthesis in 

Mammalian Cells 

in Culture

4210012 (1992)

Acceptable/ guideline

Doses up to 50 μg/mL

CGA-i69374 tech. (92.2% a.i.) was considered to be 

negative in the unscheduled DNA synthesis assay in rat 

primary hepatocytes as measured by an autoradiographic 

method at concentrations up to 50.0 μg/mL.

870.5550 Unscheduled 

DNA Synthesis in 

Mammalian Cells 

in Culture

42090027 (1985)

Unacceptable/ guideline

0.25-31.25 μg/mL

No conclusion can be reached from the unscheduled 

DNA synthesis (UDS) primary rat hepatocyte assay 

conducted with difenoconazole technical at 

concentrations ranging from 0.25 to 31.25 μg /mL. The 

sensitivity of the study was severely compromised.
Page 40 of 70

Table A.2. Subchronic, Chronic and Other Toxicity Profile of Difenoconazole

Guideline 

No. 

Study Type MRID No. (year)/ 

Classification /Doses

Results

870.5550 Unscheduled 

DNA Synthesis in 

Mammalian Cells 

in Culture

42090026 (1985)

Unacceptable/ guideline

0.08-10 μg/mL

No conclusion can be reached from the unscheduled 

DNA synthesis (UDS) human fibroblast assay conducted 

with difenoconazole tech. at conc. ranging from 0.08 to 

10 μg /mL. 

870.6200a Acute 

neurotoxicity 

screening battery

46950327 (2006)

Acceptable/ guideline

0, 25, 200 or 2000 mg/kg/d

NOAEL (M) = 25 mg/kg/day

LOAEL (M) = 200 mg/kg/day based on reduced forelimb grip strength in males on day 1 and increased motor 

activity on Day 1. 

NOAEL (F) = 200 mg/kg/day

LOAEL (F) = 2000 mg/kg/day based on decreased body 

weight, the following clinical signs: upward curvature of 

the spine, tip-toe gait, decreased activity, piloerection 

and sides pinched in and decreased motor activity.

870.6200b Subchronic 

neurotoxicity 

screening battery

46950329 (2006)

Acceptable/ guideline 

0, 40, 250, or 1500 ppm M; 0, 

2.8, 17.3 or 107.0 mg/kg/d 

F: 0, 3.2, 19.5, or 120.2 

mg/kg/d

NOAEL (M) = 40 ppm (2.8 mg/kg/day)

LOAEL (M) = 250 ppm (17.3 mg/kg/day) based on

decreased hind limb strength. 

NOAEL (F) = 250 ppm (19.5 mg/kg/day)

LOAEL (F) = 1500 (120.2 mg/kg/day) based on

decreased body weight, body weight gain and food 

efficiency. 

870.7485 Metabolism and 

pharmacokinetics

(rat)

42090028 (1990)

Acceptable/ guideline

14 daily doses of 0.5 or 300 

mg/kg

Male and female Sprague-Dawley rats. Animals were 

administered a single oral gavage dose of 0.5 or 300 

mg/kg [14C]CGA- 169374, or 0.5 mg/kg unlabeled GGA169374 by gavage for 14 days followed by a single 

gavage dose of 0.5 mg/kg [14C)CGA-169374 on day 15. 

The test compound was labeled with C14 at either the 

phenyl or triazole ring.

870.7485 Metabolism and 

pharmacokinetics

(rat)

42090028 (1990)

42090029 (1987)

42090030 (1987)

42090031 (1988)

Acceptable/ guideline

Single oral dose 0.5 or 300 

mg/kg

14 daily doses of 0.5 or 300 

mg/kg

Male and female Sprague-Dawley rats. Animals were 

administered a single oral gavage dose of 0.5 or 300 

mg/kg [14C]CGA- 169374, or 0.5 mg/kg unlabeled GGA169374 by gavage for 14 days followed by a single 

gavage dose of 0.5 mg/kg [14C)CGA-169374 on day 15. 

The test compound was labeled with C14 at either the 

phenyl or triazole ring.

[

14C] CCA 169374 was rapidly and extensively 

distributed, metabolized, and excreted in rats for all

dosing regimens. The metabolism of difenoconazole 

appears to be extensive because the metabolites 

accounted for most of the recovered radioactivity in the 

excrete. Three major metabolites were identified in the 

feces (i.e. metabolites A, B, and C). Two of the 

metabolites were separated into isomers (i.e., Al, A2, B1, 

and B2). Metabolite C was detected only in the highdose groups, indicating that metabolism of 

difenoconazole is dose-related and involves saturation of 

the metabolic pathway. Free triazole metabolite was 

detected in the urine of triazole-labeled groups and its 

byproduct was detected in the liver of phenyl labeled 

groups only. Other urinary metabolites were not 

characterized.
Page 41 of 70

Table A.2. Subchronic, Chronic and Other Toxicity Profile of Difenoconazole

Guideline 

No. 

Study Type MRID No. (year)/ 

Classification /Doses

Results

870.7485 Metabolism and 

pharmacokinetics

(rat)

42090028 (1990)

42090029 (1987)

42090030 (1987)

42090031 (1988)

Acceptable/ guideline in 

conjunction with MRIDs 

420710013, 42710014 listed 

below 

Single oral dose 0.5 or 300 

mg/kg

14 daily doses of 0.5 or 300 

mg/kg

The absorption, distribution, metabolism, and excretion 

of CGA 169374 were studied in groups of male and 

female Sprague-Dawley rats. Animals were administered 

a single oral gavage dose of 0.5 or 300 mg/kg [14C]CGA169374, or 0.5 mg/kg unlabeled GGA-169374 by gavage 

for 14 days followed by a single gavage dose of 0.5 

mg/kg [14C)CGA-169374 on day 15. The test compound 

was labeled with C14 at either the phenyl or triazole ring.

[

14C] CCA 169374 was rapidly and extensively 

distributed, metabolized, and excreted in rats for all

dosing regimens. the extent of absorption is undetermined 

pending determination of the extent of biliary excretion. 

The 4-day recoveries were 97.94-107.75% of the 

administered dose for all dosing groups. The elimination 

of radioactivity in the feces (78.06-94.61% of 

administered dose) and urine (8.48-21.86%) were almost 

comparable for all oral dose groups, with slightly higher 

radioactivity found in the feces of the high-dose group 

than the low-dose groups. This was probably due to 

biliary excretion, poor absorption or saturation of the 

metabolic pathway. The radioactivity in the blood peaked 

at about 24-48 hours for an dosing group. Half-lives of 

elimination appear to be approximately 20 hours for the 

low-dose groups and 33-48 hours for the high-dose 

group. The study results also indicate that difenoconazole 

and/or its metabolites do not bioaccumulate to an 

appreciable extent following oral exposure since all the 

tissues contained negligible levels (< 1%) of radioactivity 

7 days postexposure.

The metabolism of difenoconazole appears to be 

extensive because the metabolites accounted for most of 

the recovered radioactivity in the excrete. Three major 

metabolites were identified in the feces (i.e. metabolites 

A, B, and C). Two of the metabolites were separated into 

isomers (i.e., Al, A2, B1, and B2). Metabolite C was 

detected only in the high-dose groups, indicating that 

metabolism of difenoconazole is dose-related and 

involves saturation of the metabolic pathway. Free 

triazole metabolite was detected in the urine of triazolelabeled groups and its byproduct was detected in the liver 

of phenyl labeled groups only. Other urinary metabolites 

were not characterized.

These studies indicate that distribution, metabolism, and 

elimination of CGA-169374 were not sex related. There 

was a slight dose difference in the metabolism and 

elimination of CGA-169374. In phenyl and triazole 

labeling studies, fecal excretion of radioactivity was 

higher in the high dose animals compared to the low dose 

animals, and an additional metabolite was found in the 

feces of the high dose animals compared to the low dose 

animals. There was no major difference in the distribution 

and excretion of radioactivity with labeling at the phenyl 

and triazole ring positions, however, there were some 

different metabolites identified. The studies also showed 

that administration of 0.5 and 300 mg/kg CGA- 169314 

did not induce any treatment related clinical effects.
Page 42 of 70

APPENDIX A.3 HAZARD IDENTIFICATION AND ENDPOINT SELECTION 

A.3.1 Acute Population Adjusted Doses (aPAD) – All Populations

Selected Study: Acute Neurotoxicity Study in Rats 

MRID 46950327

Dose and Endpoint for Establishing an aPAD: NOAEL is 25 mg/kg/day. LOAEL is 200 

mg/kg/day based on reduced fore-limb grip strength in males on day 1. 

Uncertainty Factor (UF): 100 This includes 10x for interspecies extrapolation and 10x for 

intraspecies variation.

Comments about Study/Endpoint: The selected endpoint is considered appropriate for acute 

dietary exposure because effects were seen after a single dose. The endpoint is protective of the 

general population and all subpopulations for effects seen in the acute neurotoxicity study in rats. 

It is also protective of developmental and maternal effects observed in the rabbit developmental 

toxicity study at the LOAEL of 75 mg/kg/day and NOAEL of 25 mg/kg/day.

A.3.2 Chronic Population Adjusted Dose (cPAD) – All Populations

Selected Study: Chronic/Oncogenicity Study in Rats 

MRID 42090019/20

Dose and Endpoint for Establishing an cPAD: The NOAEL is 0.96 mg/kg/day. The LOAEL is 

24.12 mg/kg/day based on cumulative decreases in body weight gains at 24.12 mg/kg/day in 

males. 

Uncertainty Factor (UF): 100 This includes 10X for interspecies extrapolation and 10x for 

intraspecies variation.

A.3.3 Incidental Oral Exposure (Short-Term)

Selected Study: Two Generation Reproduction Study in Rats 

MRID 42090018

Dose and Endpoint for Establishing POD: The NOAEL is 1.25 mg/kg/day based on decreased 

pup weight in males at 12.5 mg/kg/day (LOAEL) on day 21, and reductions in body weight gain 

in F0 females.

Uncertainty Factor (UF): An MOE 100 is required for the short- and intermediate-term scenarios 

for dermal exposure is based on the conventional uncertainty factor of 100. This includes 10x 

for interspecies extrapolation and 10x for intraspecies variation.

Comments about Study/Endpoint: There are no residential uses for difenoconazole that would 

General Population aPAD = (NOAEL) 25 mg/kg = 0.25 mg/kg

 (UF) 100

General Population cPAD = (NOAEL) 0.96 mg/kg/day = 0.01 mg/kg/day

 (UF) 100
Page 43 of 70

result in incidental oral exposure to children. However, a short term oral exposure endpoint is 

required for aggregate risk assessment. 

A.3.4 Dermal Absorption

A dermal absorption factor (DAF) is applied when dermal exposure endpoints are 

selected from oral toxicity studies. The dermal factor converts the oral dose to an equivalent 

dermal dose for the risk assessment. A DAF of 6% was selected for use in risk assessment based 

on available in vivo dermal absorption studies in rat and in vitro dermal absorption studies 

conducted with rat and human skin. The DAF was selected by a special working group of the 

Antimicrobials Division Toxicity Endpoint Selection Committee (12/18/08 memorandum from J. 

Chen to M. Swindell – Attachment A.3).

A.3.5 Dermal Exposure (Short and Intermediate-Term)

Selected Study: Two Generation Reproduction Study in Rats (MRID 42090018)

See Section A.4.3

Dose and Endpoint for Establishing POD: The NOAEL is 1.25 mg/kg/day based on 

decreased pup weight in males at 12.5 mg/kg/day (LOAEL) on day 21 and reductions in body 

weight gain in F0 females.. Dermal absorption is 6%.

Uncertainty Factor (UF): An MOE 100 is required for the short- and intermediate-term 

scenarios for dermal exposure is based on the conventional uncertainty factor of 100. This 

includes 10x for interspecies extrapolation and 10x for intraspecies variation.

Comments about Study/Endpoint: Although dermal toxicity studies are available, a POD 

from an oral study was selected because effects in young animals (decreased pup weight) the 

primary effect of concern for short, intermediate and long term exposure is not specifically 

evaluated in the available dermal toxicity studies that only assess adult animals. The selected 

endpoint is protective of offspring effects from dermal exposure. A DAF of 6% is applied to the 

POD for dermal exposure.

A.3.6 Inhalation Exposure (Short- and Intermediate-Term) 

Selected Study: Two Generation Reproduction Study in Rats (MRID 42090018)

See Section A.4.3
Page 44 of 70

A.4 EXECUTIVE SUMMARIES FOR SUPPORTING TOXICITY STUDIES

A.4.1 Subchronic Toxicity

870.3100 90-Day Oral Toxicity – Rat MRID 42090022

CGA-169374 Technical was administered orally in feed admixtures to six groups of rats of both 

sexes at 0 ppm, 20 ppm, 200 ppm, 750 ppm, 1500 ppm, and 3000 ppm for 13 weeks. The results 

of this dietary subchronic evaluation of the toxicity of the test article were generally 

unremarkable. There was a significant trend for decreased body weights in both sexes, and the 

200 ppm female rats showed an approximate 10% decrease in body weight relative to their 

controls concomitant with decreased food consumption. There was one dose—related effect of 

the chemical discovered during the histopathology examination, that identified modest diffuse 

hepatocellular enlargement, vis a vis. increased liver weights, in rats of both sexes at the two 

highest doses tested. Additionally, although not statistically significant, compared to the other 

groups there was an increase in the frequency and quantity of ketones in the urine of group 6 

males. The presence of elevated ketone levels may be due to gluconeogenesis driven by 

decreased protein intake from the diet as a result of decreased food intake. The somewhat 

compromised nutritional status of the rats could possibly and indirectly have promoted the 

hepatocellular enlargement as well.

It is possible to conclude from this study, that based on approximately 10% decrease in body 

weight in the 200 ppm females (concomitant with a negative trend for food consumption) and 

increases in absolute liver weights in both sexes appearing at 750 ppm, the LOAEL is 200 ppm. 

The NOAEL was 20 ppm.

Core Classification: Minimum

870.3100 90-Day Oral Toxicity – Mouse MRID 42090021

CGA 169374 was offered in feed admixtures to five groups of mice composed of 15 

animals/group/sex and 20 mice per sex for controls in dietary concentrations of 20 ppm, 200 

ppm, 2500 ppm, 7500 ppm, or 15000 ppm for 13 weeks. Most of the mice fed 7500 ppm or

15,000 ppm test article, groups 5 and 6 respectively, died during the first week on study. There 

were some CGA 169374-related effects. The statistical analysis of total food consumption and 

body weight changes over the course of the study showed significantly reduced body weight gain 

for paired group 4 (2500 ppm) females and a significant negative trend. Compound—related 

effects from histologic examination were confined to the liver. Hepatotoxicity in mice that DOS 

was evidenced by hepatocellular enlargement and necrosis of individual hepatocytes. Those mice 

that survived to the end of the study showed hepatotoxicity that included hepatocellular 

enlargement in group 4 animals and group 3 males and hepatocytic vacuolization in group 4 

animals. Furthermore, coagulative necrosis was observed in the livers of 4/9 group 4 females. 

This finding, however, was not considered treatment related, because the foci were frequently 

small and random. The animals in groups 5 and 6, which represent the unscheduled deaths, had a 

high incidence of changes consistent with stress. The changes included lymphoid depletion or 

necrosis of the spleen, lymph nodes, and thymus, hypocellularity of the femoral marrow, 

mucosal erosion/ulceration of the glandular stomach, and in the female mice necrosis of 

individual cells in the adrenal cortex, specifically in the zona reticularis. Hyperkeratosis of the 
Page 45 of 70

nonglandular stomach was observed in males especially from group 6. The study director 

suggests the “stress” effects may be related to inappetence and a failure to eat as opposed to a 

direct effect of the test article. On the strength of the available data as they relate to the dose 

levels tested and to the parameters observed, the body weight changes and the liver 

histopathology form the basis for setting the NOAEL at 20 ppm, and the LOAEL at 200 ppm. 

The mortality data indicate the MTD was exceeded and is likely S 7500 ppm.

870.3150 26 Week Oral Feeding study –dog OPPTS MRID 42090012

CGA 169374 was offered in feed admixtures to five groups of beagle dogs composed of three 

animals/group/sex in dietary concentrations of 0 ppm, 100 ppm, 1000 ppm, 3000 ppm, or 6000 

ppm for a minimum of 28 weeks. None of the dogs DOS. Compound— related effects, 

developed essentially at the 3000 ppm and 6000 ppm dose levels. The singularly most striking 

compound effect was bilateral lenticular cataracts ophthalmoscopically-observed in all dogs at 

6000 ppm and in one female beagle at 3000 ppm. Additionally, iridic changes (irregular 

pupillary margins, miosis), secondary to lens induced uveitis, were also present in the affected 

animals. There were also reductions in mean body weight in females and males at 6000 ppm test 

compound throughout the study; weight loss was observed during the first three weeks on study. 

Body weight loss was precipitated by moderate to severe reductions in mean food consumption 

in females and males at 6000 ppm during the study with slight reductions observed in males at 

3000 ppm and 1000 ppm and in one female at 3000 ppm. Furthermore, there were slight 

reductions in values for red blood cell count, hemoglobin, and hematocrit in females and males 

at 6000 ppm. There were also decrements in some serum clinical chemistry measurements 

including calcium and total protein in females at 6000 ppm and moderate increases in serum 

alkaline phosphatase in one or both sexes at 3000 ppm. There were modest alterations in several 

absolute and/or relative organ weight measurements to include the heart, prostate gland, salivary 

gland, uterus, kidney, liver, and brain at the highest dose tested (HOT). Nevertheless, liver 

weight measurements were also increased in Group 4 females. There were no other test article—

related changes in any other parameter examined. On the strength of the available data as they 

relate to the dose levels tested and the parameters observed, the LOAEL and the NOAEL for the 

test article in female and male beagle dogs were 3000 ppm and 1000 ppm, respectively, based 

primarily on microscopic examination of CGA 169374-related lenticular cataracts. Core 

Classification: Minimum

A.4.2 Prenatal Developmental Toxicity

870.3700a Prenatal Developmental Toxicity Study – Rat MRID 42090016

CGA 169347 technical was administered by gavage on days 6-15 of gestation to presumed 

pregnant rats at 0, 2, 20, 100, or 20a mg/kg. Significant decreases in maternal body weight gain 

and feed consumption were observed during the dosing period for the feed consumption were 

observed during the dosing period for the 100 and 200 mg/kg groups. These animals also 

exhibited a significant increase in the incidence of excess salivation. There was a non significant 

decrease in the mean number of fetuses per dam, and non significant increases in the mean 

number of resorptions per dam and % postimplantation loss in the 200 mg/kg group. There was a 

slight (non significant) decrease in mean fetal body weight at the 200 mg/kg group. The 
Page 46 of 70

following represents the significant alterations in the development of fetuses in the 200 mg/kg 

group. The incidence of bifid or unilateral ossification of the thoracic vertebrae was significantly 

increased on the fetal basis. There were also significant increases in the average number of 

ossified hyoid and decreases in the average number of sternal centers of ossification (per fetus 

per litter). The average number of ribs was significantly increased (with accompanying increases 

in the number of thoracic vertebrae), and decreases in the number of lumbar vertebrae in this 

group. These findings may be related to maternal toxicity. This study may be upgraded after 

satisfactory review of the response to the noted deficiencies.

core classification: supplementary. NOTE: Due to the relatively high percent deviation of the 

actual doses tested from the theoretical concentration the effect levels have been modified 

accordingly. This modification may be subject to change as the purity is currently unknown.

Maternal NOAEL = 16 mg/kg; Maternal LOEL = 85 mg/kg; Developmental Toxicity NOAEL = 

85 mg/kg; Developmental Toxicity LOAEL = 171 mg/kg

870.3700b Prenatal Developmental Toxicity Study – Rabbit MRID 42090017

CGA 169347 technical was administered by gavage on days 7—19 ofgestation to presumed

pregnant rabbits at 0, 1, 25, or 73 mg/kg. Maternal toxicity was observed in this study as the 

death of one doe and abortions observed in two other high dose does. In addition, significant 

reductions in body weight gain of high dose does, were present days 7-10, 10—14, 7-20, and 0—

29. These reductions correspond with reduced feed consumption during these intervals 

(significant reductions in feed consumption in the HDT were only observed during the treatment 

period, not after treatment). Slight nonsignificant increases in postimplantation loss and 

resorptions/doe were observed in the HDT. The significant decrease in fetal weight at the HDT 

may have been due to treatment. The significant differences in fetal weight observed at the low 

and mid dose were apparently not due to treatment.

Core Classification: supplementary

Maternal NOAEL = 25 mg/kg; Maternal LOEL = 75 mg/kg

Developmental Toxicity NOAEL 25 mg/kg; Developmental Toxicity LOEL = 75 mg/kg

A.4.3 Reproductive Toxicity

870.3800 Reproduction and Fertility Effects – Rat MRID 42090018

In a two generation reproduction study, difenoconazole was administered in the diet to male and 

female rats at 0, 25, 250, or 2500 ppm [0, 1.25, 12.5, or 125 mg/kg/day, respectively]. 

Statistically significant reductions in body weight gains of F0 and F1 males were observed at 

2500 ppm during Days 70-77 and during the course of the study [terminal body weight minus 

Day 0 body weight]. Significant reductions in body weight gains of F0 and F1 females were seen 

during the pre-mating, gestation, and lactation periods. A dose-related, but non-statistically 

significant decreases in body weight gain was seen in F0 females at 250 ppm during Days 70-77 

prior to mating, Days 0-7 of gestation, and Days 7-14 of lactation:

At 2500 ppm, significant reductions in pup body weight were detected on Days 0, 4 [pre- and 

post culling], 7, 14, and 21 for males and females of both generations. There was a significant 

reduction in the body weight of F1 male pups on Day 21 in the 250 ppm group. The percentage 

of male pups in the F1 generation surviving Days 0-4 was significantly reduced in the 2500 ppm 
Page 47 of 70

group: For parental toxicity, the LOAEL of 250 ppm [12.5 mg/kg/day is based on the decreased 

maternal body weight gain; the NOAEL is 25 ppm [1.25 mg/kg/day. For offspring toxicity, the 

LOAEL of 250 ppm [12.5 mg/kg/day] is based on decreased pup weights at Day 21; the NOAEL 

is 25 ppm [1.25 mg/kg/day].

A.4.4 Chronic Toxicity

870.4100a (870.4300) Combined Chronic Toxicity/Carcinogenicity – Rat MRIDs 

42090019/ -20

CGA 169374 was administered in the diet to male and female rats [80/sex/dose] for 104 weeks at 

0; 10; 20; 500; and 2500 ppm. There were reductions in cumulative body weight gains in the 500 

and the 2500 ppm groups. Mean liver weight was increased at week 53 and t termination in the 

2500 ppm group. Hepatocellular hypertrophy was observed in the 500 and the 2500 ppm animals 

at termination. Additional findings in the clinical chemistry data also indicated that liver was the 

primary target organ for toxicity. No treatment related increased incidences of neoplastic 

findings were observed in this study. The NOAEL for the study was 20 ppm which was equal to 

0.96 and 127 mg/kg/d for males and females respectively. The LOAEL was 500 ppm equal to 

24.12 and 32.79mg/kg/day for males and females respectively based on cumulative decreases in 

body weight gains. Discussion of Tumor Data No treatment related increased incidences of 

neoplastic findings were observed in this study. Adequacy of the Dose Levels Tested The dose 

levels tested were considered adequate by the Cancer Peer Review Committee. (memorandum of 

July 27,1994 from B. Rinde of the Health Effects Division)

870.4100b Chronic Toxicity - Dog MRID 42090012

CGA 169347 was administered in the diet to male and female dogs at 0, 20, 100, 500, or 1500 

ppm. The NOAEL was 100 ppm and the LOAEL was

500 ppm based on the following. Females receiving 1500 ppm in the diet had a significant 

reduction in body weight gain on day 7. Females in the 500 and 1500 ppm groups, although not 

statistically significant, had inhibited body weight gain throughout the study. These animals also 

had significant reductions in food consumption on days 7, 35, 70, and 357. The reduction in 

mean percent reticulocytes at the highest dose tested on day 359 may have been related to 

treatment, Significant increases (treatment related at day 85; dose—related at days 175 and 359) 

were observed in alkaline phosphatase in males receiving 1500 ppm. This study may be 

upgraded upon satisfactory review of the registrants response to the deficiencies (submission of 

the purity and raw daily observation data).

Classification: core—supplementary

A.4.5 Carcinogenicity

870.4200a Carcinogenicity/Chronic Study – Mice MRIDs 42090015 and 42710006

CD-I mice were fed diets containing difenoconazole at 0; 10; 30; 300; 2500or 4500 [males only] 

for 78 weeks. The NOAEL was 30 ppm equal to 4.65 mg/kg/d in males and 5.63mg/kg/d in 
Page 48 of 70

females respectively. The LOAEL was 300 ppm equal to 46.29 mg/kg/d in males and 

57.79mg/kg/d in females based on reductions in the cumulative body weight gains at the higher 

dose levels.

Discussion of Tumor Data: Difenoconazole was reviewed by the HED-CPRC on May 18,1994 

(memorandum of July 27, 1994 from E. Rinde of the NED CPRC to C. Giles-Parker of RD) and 

classified as a Category C carcinogen without a q-star. The margin-of-exposure (MOE) approach

was selected because there was only very weak (limited) evidence of carcinogenic potential at 

dose levels not considered to be excessive with significant changes observed only at excessive 

doses. There was no evidence for genotoxicity. There was a statistically significant increase in 

liver adenomas, carcinomas, and combined liver adenomas and carcinomas in both sexes at 

doses of 2500 and 4500 ppm. These doses were considered to be excessively high for cancer 

testing. Liver necrosis and liver adenomas were also noted in males at 300 ppm. There were no 

statistically significant increases in liver tumors at 10 or 30 ppm. Adequacy of the Dose Levels 

Tested: The Health Effects Division Cancer Peer Review Committee considered the doses 

adequate and the study acceptable.

870.4200b Carcinogenicity (feeding) – Rat MRIDs 42090019/ -20

CGA 169374 was administered in the diet to male and female rats [80/sex/dose] for 104 weeks at 

0; 10; 20; 500; and 2500 ppm. There were reductions in cumulative body weight gains in the 500 

and the 2500 ppm groups. Mean liver weight was increased at week 53 and t termination in the 

2500 ppm group . Hepatocellular hypertrophy was observed in the 500 and the 2500 ppm 

animals at termination. Additional findings in the clinical chemistry data also indicated that liver 

was the primary target organ for toxicity. No treatment related increased incidences of neoplastic 

findings were observed in this study. The NOAEL for the study was 20 ppm which was equal to 

0.96 and 127 mg/kg/d for males and females respectively. The LOAEL was 500 ppm equal to 

24.12 and 32.79 mg/kg/day for males and females respectively based on cumulative decreases in 

body weight gains. Discussion of Tumor Data No treatment related increased incidences of 

neoplastic findings were observed in this study. Adequacy of the Dose Levels Tested The dose 

levels tested were considered adequate by the Cancer Peer Review Committee. (memorandum of 

July 27,1994 from B. Rinde of the Health Effects Division)

A.4.6 Mutagenicity 

Gene Mutation

Guideline # 870.5100 Bacterial assay

42090019, 42710010 Minimum/ 

guideline

Guideline #870.5300, In vitro 

mammalian cell gene mutation test

MRID 42090024 

Unacceptable Guideline

Not mutagenic

No conclusion can be reached from the three nonactivated and two S9 

activated mouse lymphoma forward mutation assays conducted with 

difenoconazole technical. The study was seriously compromised.
Page 49 of 70

Cytogenetics

Guideline # 870.5375, 

Clastogenicity in mammalian cells

MRID 46950319, 46950321

Acceptable Guideline

MRID 46950323

Guideline #870.5395 

Micronucleus test in bone marrow

MRID 41710011 

Acceptable Guideline

Guideline #870.5550

Unscheduled DNA Synthesis in 

Mammalian Cells in Culture

4210012 (1992)

Acceptable/ guideline

There was evidence of a weak induction of structural chromosomal 

aberrations over background in the presence of S9-mix.

There was no evidence of structural chromosomal aberrations induced 

over background.Mice bone marrow - No increase in micronucleated 

polychromatic erythrocytes occurred with CGA-169374 (91.2% a.i).

CGA-169374 tech. (92.2% a.i.) was considered to be negative in the 

unscheduled DNA synthesis assay in rat primary hepatocytes as measured 

by an autoradiographic method at concentrations up to 50.0 μg/mL.

A.4.7 Neurotoxicity

870.6100 Delayed Neurotoxicity Study – Hen - NA

870.6200 Acute Neurotoxicity Screening Battery – Rat MRID 46950327

In an acute neurotoxicity study (MRID 46950327), groups of fasted Alpk:APfSD Wistar-derived 

rats (10/sex/dose), at least 42 days old, were given a single oral dose of difenoconazole technical 

(CGA169374) (94.3% w/w, batch/lot # WM806228) in 1% w/v aqueous carboxymethylcellulose 

(CMC) at doses of 0, 25, 200, or 2000 mg/kg bw and observed for 14 days. Dose levels selected 

for this study were based on the results of preliminary acute neurotoxicity study (MRID 

46950325). Neurobehavioral assessment (functional observational battery and motor activity 

testing) was performed on 10 animals/sex/group on days -7, 1, 8, and 15. Body weight and food 

consumption were measured weekly throughout the study. At study termination, 5 

animals/sex/group were euthanized and perfused in situ for neuropathological examination; brain 

weight was recorded from these animals. Of the perfused animals, 5 animals/sex from the control 

and high dose groups were subjected to histopathological evaluation of brain and peripheral 

nervous system tissues.

There were no unscheduled deaths at any dose level. Weight change on the day of dosing by the 

control, low-, mid-, and high-dose groups was -2.1, - 1.0, -7.8, and -18.3 g, respectively, for 

males and 0.0, 2.1, -3.8, and -13.0 g, respectively, for females. Body weight for females had 

recovered to control levels by day 8. Food consumption for males given 2000 mg/kg was 

approximately 20% less than control during week 1 only (p<0.01). Food consumption for these 

animals recovered to control levels during week 2. There were no differences from control for 

females at any dose level or for males at the lower dose levels. These effects on body weight and 

food consumption were not toxicologically significant.

At 2000 mg/kg, a number of adverse clinical signs were observed on day I (at the time of peak 

effect), including: upward curvature of the spine (8 males, 9 females); tip-toe gait (3, 8); 
Page 50 of 70

decreased activity (6, 7); piloerection (3, 5); sides pinched in (3, 7); and subdued (1, 0). Females 

were affected more than males. All treatment-related clinical signs observed on day 1 showed 

complete recovery by day 5 (males) or day 7 (females).

Significant decreases in fore-limb grip strength were seen in mid- (23%) and high-dose (26%) 

males on day 1. Females dosed with 2000 mg/kg had lower motor activities on day 1 (37%), at 

the time of peak effect, and on day 8 (31%). Males dosed with 200 or 2000 mg/kg had higher 

motor activities than the controls on day 1, 50% and 55%, respectively, at the time of peak 

effect. There were no effects on brain weight at any dose level. Neuropathological examination 

of the central and peripheral nervous system showed no effects of treatment at doses of 2000 

mg/kg in both sexes. The LOAEL for acute neurotoxicity of difenoconazole technical 

(CGA169374) in male rats is 200 mg/kg bw based on reduced fore-limb grip strength in males 

on day 1. The NOAEL is 25 mg/kg bw. The LOAEL for acute neurotoxicity of difenoconazole 

technical (CGA169374) in female rats is 2000 mg/kg. Based on decreased body weight, the 

following clinical signs: upward curvature of the spine, tip-toe gait, decreased activity, 

piloerection and sides pinched in, and decreased motor activity. The NOAEL is 200 mg/kg bw.

870.6200 Subchronic Neurotoxicity Screening Battery

In a subchronic neurotoxicity study (MRID 46950329) difenoconazole technical (94.5% w/w, 

batch no. WM806228) was administered to groups of 12 male and 12 female Alpk:APfSD 

(Wistar-derived) rats at concentrations of 0, 40, 250, or 1500 ppm in the diet for 90 days. 

Respective dose levels corresponded to 0, 2.8, 17.3 or 107.0 mg/kg bw/day for males and 0, 3.2, 

19.5, or 120.2 mg/kg bw/day for females. Neurobehavioral assessment (functional observational 

battery and motor activity testing) was performed in 12 animals/sex/group pretest and during 

weeks 2, 5, 9, and 14. Cholinesterase activity was not determined. At study termination, 5 

animals/sex/group were euthanized and perfused in situ for neuropathological examination. Of 

the perfused animals, 5/sex from the control group and 5/sex from the 1500 ppm group were 

subjected to histopathological evaluation of brain and peripheral nervous system tissues. 

Treatment with difenoconazole at concentrations up to 1500 ppm in the diet had no effect on 

mortality or clinical signs. Relative to respective control weight, final body weight of males and 

females in the 1500 ppm group was reduced by 9% and 7%. Body weight gain was reduced by 

22% in males and 23% in females. Food consumption was reduced in this group (statistically 

significant only in females [7%]), and food efficiency was significantly reduced in males by 21% 

(p≤0.05) and in females by 21% (ns). Lower dose groups were unaffected. Absolute liver 

weight in males and females in the 1500 ppm group was increased over respective control weight 

by 38% and 45%. Liver was not weighed in lower dose groups. The increase in liver weight 

was considered a normal response to chemical treatment.

During weeks 2, 9 and 14, hind-limb grip strength in males in the 1500 ppm group was reduced 

by 18 to 27% relative to the control values. At week 14, hind-limb grip strength in males in the 

250 ppm group was significantly (p≤0.05) reduced by 20% relative to the control values. FOB 

observations in females were unaffected by treatment. Motor activity was unaffected in both 

sexes at all observation times. Brain weight was unaffected by treatment and there were no 

treatment-related neuropathological lesions. 

The LOAEL in male rats is 250 ppm in the diet (17.3 mg/kg bw/day), based on decreased hind 
Page 51 of 70

limb strength. The NOAEL is 40 ppm (2.8 mg/kg bw/day). The LOAEL in female rats is 1500 

ppm in the diet (120.2 mg/kg bw/day), based on decreased body weight, body weight gain and 

food efficiency. The NOAEL is 250 ppm (19.5 mg/kg bw/day). The study is classified as 

Acceptable/Guideline

A.4.8 Metabolism

870.7485 Metabolism – Rat 

Study 1

The absorption, distribution, metabolism, and excretion of difenoconazole were studied in groups 

of male and, female Sprague-Dawley rats. Animals were administered a single oral gavage dose 

of 0.5 or 300 mg/kg [

14C] difenoconazole or 0.5 mg/kg unlabeled difenoconazole by gavage for 

14 days followed by a single gavage dose of 0.5 mg/kg [

14C] difenoconazole on day 15. The test 

compound was labeled with [

14C] at either the phenyl or triazole ring.

[

14C] CCA 169374 was rapidly and extensively distributed, metabolized, and excreted in rats for 

all dosing regimens. the extent of absorption is undetermined pending determination of the extent 

of biliary excretion. The 4-day recoveries were 97.94-107.75% of the administered dose for all 

dosing groups. The elimination of radioactivity in the feces (78.06-94.61% of administered dose) 

and urine (8.48-21.86%) were almost comparable for all oral dose groups, with slightly higher 

radioactivity found in the feces of the high-dose group than the low-dose groups. This was 

probably due to biliary excretion, poor absorption or saturation of the metabolic pathway. The 

radioactivity in the blood peaked at about 24-48 hours for an dosing group. Half-lives of 

elimination appear to be approximately 20 hours for the low-dose groups and 33-48 hours for the 

high-dose group. The study results also indicate that difenoconazole and/or its metabolites do not 

bioaccumulate to an appreciable extent following oral exposure since all the tissues contained 

negligible levels (< 1%) of radioactivity 7 days postexposure.

The metabolism of difenoconazole appears to be extensive because the metabolites accounted for 

most of the recovered radioactivity in the excrete. Three major metabolites were identified in the 

feces (i.e. metabolites A, B, and C). Two of the metabolites were separated into isomers (i.e., Al, 

A2, B1, and B2). Metabolite C was detected only in the high-dose groups, indicating that 

metabolism of difenoconazole is dose-related and involves saturation of the metabolic pathway. 

Free triazole metabolite was detected in the urine of triazole-labeled groups and its byproduct 

was detected in the liver of phenyl labeled groups only. Other urinary metabolites were not 

characterized.

These study results indicate that distribution, metabolism, and elimination of difenoconazole

were not sex related. There was a slight dose-related difference in the metabolism and 

elimination difenoconazole. In phenyl- and triazole-labeling studies, fecal excretion of 

radioactivity was higher in the high-dose animals compared to the low-dose animals, and an 

additional metabolite was found in the feces of the high-dose animals compared to the low-dose 

animals. There were no major differences in the distribution and excretion of radioactivity with 

labeling at the phenyl and triazole ring positions, however, there were some different metabolites 
Page 52 of 70

identified. The studies also showed that administration of 0.5 and 100 mg/kg difenoconazole did 

not induce any apparent treatment-related clinical effects.

The study is classified as acceptable guideline when considered together with data provided in 

additional rat metabolism studies (MRIDs 42710014, 42710013) submitted as supplemental to 

this study. This study may be upgraded if the following additional information is provided and is 

judged to be acceptable:

Study 2

These studies (MRIDs 42710014, 42710013) were submitted because EPA requested additional 

information not provided in the Sponsor’s previously submitted metabolism studies (MRID Nos. 

420900-28/29/30/31). The present studies describe the absorption, distribution, and excretion, as 

well as pharmacokinetics, of [

14C] difenoconazole after a single oral gavage dose of 0.5 or 300 

mg/kg in rats (Report 1) and isolated and identified urinary metabolites in three females after a 

single oral gavage dose of 300 mg/kg (Report 2).

Following oral administration of 0.5 or 300 mg/kg 14C-CCA 169374 in rats, the test compound 

was adequately absorbed and mainly eliminated via the bile; no evidence of bioaccumulation in 

any tissue was noted. After 48 hours, total recovery (independent of dose and sex) was ≈ 96% of 

the administered dose. Biliary excretion constituted the main route of elimination with some 

dose- and sex-dependency (≈ 75% at the low dose for both sexes; 56% for males and 39% for 

females at the high dose). Urinary and fecal eliminations exhibited a dose-related pattern at 48 

hours. In the urine, 9-l4% was eliminated at the low dose versus 1% in the high-dose rats. In the 

feces, 2-4% was eliminated at the low dose versus 17-22% at the high dose. In cannulated males 

after 48 hours, ≈ 80% was eliminated via the bile, while ≈ 4% and ≈ 14% were eliminated via 

urine and feces, respectively. Therefore, this study indicates that most of the dose following oral 

administration is absorbed as indicated by the biliary excretion data. The dose-related difference 

in elimination suggests that saturation is reached at the higher dose level resulting in an increase

of unabsorbed test material. 

Maximum concentration in blood was reached within 2 hours at the low dose and 4 hours at the 

high dose. By 24 hours, <0.05 ppm equivalent was detected in the blood. Total recovery ranged 

from 95% to 97% after 48 hours, irrespective of dose and sex. During the first 12 hours, slight 

differences were evident between males and females with regard to Tmax, Cmax, and rate of 

elimination. The concentration in females was approximately half of that in males and was 

eliminated faster than in males. Mean half-lives in males and females from Tmax to 12 hours, 

were 6.2 and 4.4 hours, respectively; from 24 to 168 hours, they were 2.8 and 3.7 days, 

respectively.

Following administration of 300 mg/kg of (

14C-phenyl) CGA 169374, 3 major urinary 

metabolites were identified: sulfate conjugates (and their isomers) of HO-CGA 205375, isomers 

of HO-CGA 205375, and the hydroxyacetic metabolite of H0-CGA 205373. The major urinary

metabolites of CGA 169374 have been identified and no single unknown metabolite accounted 

for >1.1% of the dose.

These studies alone do not meet the minimum requirements for Guidelines 85-1. However, these 
Page 53 of 70

studies combined with previously submitted studies (MRID Nos. 420900-28/29/30/31) are 

considered to be acceptable,

A.4.9 Immunotoxicity

870.7800 Immunotoxicity – Rat

A difenoconazole immunotoxicity has been submitted by the registrant and is under review.
Page 54 of 70

A.4.1 Dermal Toxicity
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B. METABOLISM

B.1 Chemical Names And Structures

Table B.1 Difenoconazole Nomenclature.

Chemical structure

Common name Difenoconazole

Company experimental name CGA-169374

IUPAC name 1-({2-[2-chloro-4-(4-chlorophenoxy)phenyl]-4-methyl-1,3-dioxolan-2-

yl}methyl)-1H-1,2,4-triazole

CAS name 1-[[2-[2-chloro-4-(4-chlorophenoxy)phenyl]-4-methyl-1,3-dioxolan-2-yl]methyl]-

1H-1,2,4-triazole

CAS registry number 119446-68-3

Chemical structure of 

CGA-205375 livestock 

metabolite

Chemical structure of 

1,2,4-Triazole (1,2,4-T)

Chemical structure of 

Triazolylalanine (TA)

Chemical structure of

Triazolylacetic acid (TAA)

O O

O

N N Cl

N

CH3

Cl

O

N N Cl

N

OH Cl

HN

N

N

N

N

N

HO

NH2

O

N

N

N

HO

O
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B.2 Metabolism Summary Table

Table B.2 Maximum Residues of CGA-205374, CGA-205375, and CGA-189138 in Metabolism Studies Reflecting Foliar Appls. 

Note: Excludes data reflecting 0-day PHIs (parent was >85% of TRR) and RACs having no detectable residues of the subject 

metabolites.

Crop

[MRID 

Citation]

RAC Radiolabel

Position

Number 

of 

Appls.

Times 

Rate

(lb ai/A)

PHI

(days)

Residues Expressed as ppm (% of TRR)

Difenoconazole CGA-205374 CGA-205375 CGA-189138

Wheat

[42090032]

Stalks 14C Phenyl 4 x 0.22 29 23 (50%) -- -- --

14C Triazole 27 (50%) -- 2.7 (5%) --

Canola

(Rape seed)

[44701701]

[44701702]

Stalks 14C Phenyl 2 x 0.11 53 0.745 (17.3%) -- 0.608 (14.1%)10.069 (1.6%)2

14C Triazole 0.828 (17.1%) 0.058 (1.2%)2

0.828 (17.1%)1--

Pods 14C Phenyl 0.570 (18.1%)10.009 (0.3%)20.340 (10.8%)10.054 (1.7%)2

14C Triazole 0.814 (17.3%)1

0.038 (0.8%)20.612 (13.0%)1--

Seed 14C Phenyl 0.022 (14.4%) -- 0.012 (7.9%) 0.0004 

(0.3%)

14C Triazole 0.093 (4.1%) -- 0.014 (0.6%) --

Potato3

[42090036]

Foliage 14C Phenyl 6 x 0.11 12 9.47 (76.4%) 0.14 (1.1%) 0.27 (2.2%) 0.07 (0.5%)

Tuber 14C Phenyl 0.001 (8.7%) 0.0004 (3.1%) 0.0004 (3.0%) --

Tomato

[42090035]

Foliage 14C Phenyl 3 x 0.22 40 1.1 (31%) 0.12 (3.4%) 0.18 (5.2%)

14C Triazole 2.1 (28%) 0.32 (4.3%) --

14C Phenyl 2 x 0.22 14 1.3 (59.1%) 0.08 (3.8%) 0.09 (4.3%)

14C Triazole 1.5 (52.1%) 0.10 (3.5%) --

Tomato

[42090038]

[42090039]

Foliage 14C Phenyl 6 x 0.11 35 5.36 (64.7%) 0.32 (3.9%) 0.20 (2.4%)40.08 (0.9%)

14C Triazole 5.25 (68.0%) 0.13 (1.63%) 0.76 (9.8%)5

--

Fruit 14C Phenyl 0.11 (66.3%) 0.002 (1.4%) 0.005 (2.6%)6--

14C Triazole 0.10 (50.9%) 0.001 (0.52%) 0.002 

(0.74%)

--

Grape

[43673201]

Fruit 14C Phenyl 3 x 0.22 20 0.065 (51.2%) 0.005 (4.1%) 0.008 (6.6%) 0.005 (4.0%)

14C Triazole 5 x 0.22 0.052 (45.1%) 0.002 (1.7%) 0.004 (3.5%) --

Leaves 14C Phenyl 3 x 0.22 4.260 (46.4%) 0.762 (8.3%) 0.395 (4.3%) 0.487 (5.3%)

14C Triazole 5 x 0.22 1.821 (31.5%) 0.173 (3.0%) 0.225 (3.9%) --
Page 66 of 70

B.3 Metabolic Pathways 

Plant

Goat Metabolism 
Page 67 of 70

Proposed metabolic pathway in the rat (urine)
Page 68 of 70

Proposed metabolic pathway in rat (feces). The ketone, CGA-205374, is presented as an intermediate from parent 

to CGA-205375.
Page 69 of 70

Proposed mechanism for formation of metabolites A & B by the NIH Shift
Page 70 of 70

C. PHYSICAL/CHEMICAL PROPERTIES

Table C.1 Physicochemical Properties of Difenoconazole.

Parameter Value Reference

Melting point 78.6 oC DP#s 172067 and 178394, 10/26/92, R. 

Lascola pH 6-8 at 20 oC (saturated solution)

Density 1.37 g/cm3at 20 oC

Water solubility 3.3 ppm at 20 oC

Solvent solubility g/100 mL at 25 oC:

n-hexane: 0.5

1-octanol: 35

toluene: 77

acetone: 88

ethanol: 89

Vapor pressure 2.5 x 10-10 mm Hg at 25 oC

Dissociation constant, pKa pure grade (99.3% ± 0.3%) 

difenoconazole in water (with 4% 

methanol) at 20oC is 1.1 

DP# 375159, 5/26/10, B. CroppKohlligian

Octanol/water partition 

coefficient, Log(KOW)

4.2 at 25 oC DP#s 172067 and 178394, 10/26/92, R. 

Lascola

UV/visible absorption spectrum max at about 200 and 238 nm 

(in methanol at 26 oC)

PMRA Proposed Regulatory Decision 

Document on Difenoconazole, 4/14/99 

(PRDD99-01)

D. REVIEW OF HUMAN RESEARCH

Klonne, D. (1999) Integrated Report for Evaluation of Potential Exposures to Homeowners and 

Professional Lawn Care Operators Mixing, Loading, and Applying Granular and Liquid 

Pesticides to Residential Lawns: Lab Project Number: OMA005: OMA001: OMA002. 

Unpublished study prepared by Riceerca, Inc., and Morse Laboratories. 2213 p. (MRID 

44972201).

The PHED Task Force, 1995. The Pesticide Handlers Exposure Database, Version 1.1. Task 

Force members Health Canada, U.S. Environmental Protection Agency, and the National 

Agricultural Chemicals Association, released February, 1995.