Fenbuconazole Summary of Analytical Chemistry and Residue Data Barcode D403620

Page 3 of 25

5.3.3 Processed Food and Feed (860.1520)..................................................................... 18

5.3.4 Meat, Milk, Poultry and Eggs (860.1480) .............................................................. 19

5.3.5 Dietary Burden........................................................................................................ 19

5.3.6 Estimated Secondary Residues in Livestock .......................................................... 19

5.3.7 Food Handling (860.1460)...................................................................................... 19

5.3.8 Water, Fish, and Irrigated Crops (860.1400).......................................................... 19

5.4 Food Residue Profile...................................................................................................... 19

6.0 Tolerance Derivation ......................................................................................................... 19

Appendix A. International Residue Limits Table. ....................................................................... 21

Appendix B. OECD MRL Calculation Procedure Inputs/Outputs. ............................................. 22

Appendix C. Proposed Metabolic Pathway for Fenbuconazole in Crops.................................... 23

Appendix D. Fenbuconazole and Its Metabolites in Plants and Animals.................................... 24
Fenbuconazole Summary of Analytical Chemistry and Residue Data Barcode D403620

Page 4 of 25

1.0 Executive Summary

Fenbuconazole [α-[2-(4-chlorophenyl)ethyl]-α-phenyl-1H-1,2,4-triazole-1-propanenitrile] is a 

broad spectrum, triazole-type fungicide that acts by inhibiting sterol biosynthesis in fungi. It is 

currently registered for use on the following food/feed crops: almonds, apples, bananas, 

bushberries (subgroup 13-B), citrus fruits (group 10), cranberries, pecans, peanuts, peppers, 

stone fruits (group 12), sugar beets, and wheat. Permanent tolerances are established for the 

combined residues of fenbuconazole and its lactone metabolites, RH-9129 and RH-9130 [transor cis-5-(4-chlorophenyl)dihydro-3-phenyl-3-(1H-1,2,4-triazol-1-ylmethyl)-2(3H)-furanone], 

expressed as parent in/on plant commodities at levels ranging from 0.05 ppm in/on almonds and 

pecans to 40 ppm in citrus oil [40 CFR §180.553(a)]. Permanent tolerances have also been 

established at 0.05 ppm for the combined residues in meat byproducts of cattle, goats, horses, 

and sheep.

In this petition, a tolerance increase from 0.4 ppm to 1.0 ppm is being requested for the use of 

fenbuconazole on peppers. The tolerance was established initially based on field trial data 

submitted for the Indar Water Soluble Packets (WSP) formulation. The registrant then submitted 

a bridging study to translate residue data from Indar 75WSP to the proposed new product Enable 

2F, a suspension concentrate (SC) formulation of fenbuconazole. The bridging study was 

conducted using bell peppers and consisted of side-by-side trials in six different locations, in 

which both formulations were applied in accordance with the maximum labeled use rate. The 

bridging data indicated that residues values could be higher than the current 0.4 ppm tolerance, 

for both the existing WSP use and the proposed new SC formulation use on peppers. HED‘s 

previous review of the formulation bridging study indicated that a 1.0 ppm tolerance is 

appropriate (D390352, S. Oonnithan, 8 Sept 2011).

The 75% WP formulation of fenbuconazole (INDAR®75WSP; EPA Reg, No. 62719-421) is 

currently registered for use on peppers. The proposed use is for up to four broadcast foliar 

applications to peppers at up to 0.188 lb ai/A/application with a minimum retreatment interval 

(RTI) of 10 days, for a maximum seasonal use rate of 0.75 lb ai/A. Applications may be made 

using either ground or aerial equipment. The minimum preharvest interval (PHI) is 7 days for 

peppers. In conjunction with this use, Dow AgroSciences is proposing the following permanent 

tolerance for the combined residues of fenbuconazole and its lactone metabolites, RH-9129 and 

RH-9130, expressed as fenbuconazole:

Pepper ..................................................................................1.0 ppm

The qualitative nature of fenbuconazole residues in plants is adequately understood based upon 

adequate peanut, peach, sugar beet and wheat metabolism studies. The residues of concern in/on 

peppers are the parent fenbuconazole (RH-7592) and its lactone metabolites, RH-9129 and RH9130.

The qualitative nature of the residue in livestock is adequately understood. Based on adequate 

ruminant metabolism data, the residues of concern in animal matrices are fenbuconazole and its 

lactone metabolites, RH-9129 and RH-9130. Although the poultry metabolism studies were 

deemed inadequate, additional poultry metabolism data are not required for this petition as the 
Fenbuconazole Summary of Analytical Chemistry and Residue Data Barcode D403620

Page 5 of 25

expected dietary exposure of poultry is low (0.09 ppm) and the available metabolism data and 

poultry feeding study indicate that tolerances will not be required for poultry commodities.

An adequate Gas Chromatography – Nitrogen Phosphorous Detector (GC-NPD) Method (Report 

No. TR 34-99-41R) has been proposed for enforcing tolerances for residues of fenbuconazole 

and its lactone metabolites, RH-9129 and RH-9130, in peppers. The limits of quantitation 

(LOQ) and limit of detection (LOD) of the method for each of the analytes were set at 0.01 ppm 

and 0.003 ppm, respectively for each analyte. 

Adequate confined rotational crop studies are available and indicate that the metabolite profile in 

rotational crops is similar to the metabolite profile in primary crops. For rotational crops other 

than the primary crop, the submitted rotational crop study supports a 210-day plant-back interval 

(PBI) following fenbuconazole applications totaling 1.0 lb ai/A, and a 35-day PBI following 

applications totaling up to 0.188 lb ai/A. Limited field rotational crop trials and rotational crop 

tolerances are not required.

2.0 Regulatory Recommendations

HED has examined the residue chemistry database for fenbuconazole. There are no residue 

chemistry issues that would preclude increasing the tolerance for fenbuconazole on peppers. The 

recommended tolerance is listed in Table 2.2.2.

2.1 Data Deficiencies/Data Needs

NA

2.2 Tolerance Considerations

2.2.1 Enforcement Analytical Method

The available GC/NPD method, TR 34-90-47R, is adequate for enforcing tolerances and 

collecting data on fenbuconazole residues in/on peppers.

2.2.2 Recommended Tolerances

The tolerance expression should be revised to read: “Tolerances are established for residues of 

the fungicide fenbuconazole, including its metabolites and degradates, in or on the commodities 

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

measuring only the sum of fenbuconazole, alpha–[2–(4–chlorophenyl)– ethyl]–alpha–phenyl–3–

(1H–1,2,4–triazole)– 1–propanenitrile, and its metabolites RH–9129, cis–5–(4–chlorophenyl)–

dihydro–3–phenyl–3–(1H–1,2,4– triazole–1–ylmethyl)–2–3 H–furanone, and RH–9130, trans–

5–(4– chlorophenyl)-dihydro–3–phenyl–3– (1H–1,2,4–triazole–1–ylmethyl)–2–3 H– furanone, 

calculated as the stoichiometric equivalent of fenbuconazole, in or on the following agricultural 

commodities.”
Fenbuconazole Summary of Analytical Chemistry and Residue Data Barcode D403620

Page 6 of 25

Table 2.2.2. Tolerance Summary for Fenbuconazole.

Commodity Established/Proposed 

Tolerance (ppm)

HED-Recommended 

Tolerance (ppm)

Comments 

(correct commodity definition)

Pepper 0.4 ppm 1.0 ppm Commodity definition: Pepper

2.2.3 Revisions to Petitioned-For Tolerances

None.

2.2.4 International Harmonization

As summarized in Appendix A, maximum residue limits (MRLs) for residues of fenbuconazole 

have been established by Codex, Canada, and Mexico. The residue definition for both Codex 

and Mexico is fenbuconazole, and the Canadian residue definition is the combined residues of 

fenbuconazole and its metabolites, RH-9129 and RH-9130, each expressed as parent (i.e., the 

same as the U.S. tolerance definition). The Codex MRL for pepper is 0.6 ppm and was most 

likely established before the Enable 2F formulation was proposed for use on peppers, and 

includes only residues of the parent compound. This new formulation has higher residues values 

ranging up to 0.7 ppm, and does include the two lactone metabolites. Harmonization with the 

0.6 ppm tolerance is not feasible given the proposed new use pattern. There is no extant 

Canadian or Mexican MRL, for fenbuconazole on peppers, and thus there are no harmonization 

issues in North America.

2.3 Label Recommendations

The following rotational crop restrictions should appear on the final label: the minimum plantback interval is 35 days when the last application of the product is <0.188 lb ai/A, and 210 days 

when the last application of the product is 0.188-1.0 lb ai/A.

3.0 Introduction

Fenbuconazole is a broad spectrum, triazole-type fungicide used to control various fungal 

diseases. It acts by inhibiting sterol biosynthesis in fungi (MOA Group 3). Fenbuconazole is 

formulated as a 2-lb ai/gal SC and a 75% WP; both currently registered to Dow AgroSciences, 

LLC, for use on almonds, apples, bananas, bush berries, citrus fruits, cranberries, pecans, 

peanuts, stone fruits, sugar beets, and wheat.
Fenbuconazole Summary of Analytical Chemistry and Residue Data Barcode D403620

Page 7 of 25

3.1 Chemical Identity

Table 3.1. Fenbuconazole Nomenclature.

Compound

Common name Fenbuconazole

Company experimental name RH-7592

IUPAC name (RS)-4-(4-chlorophenyl)-2-phenyl-2-(1H-1,2,4-triazol-1-ylmethyl)butyronitrile

CAS name α-[2-(4-chlorophenyl)ethyl]-α-phenyl-1H-1,2,4-triazole-1-propanenitrile

CAS # 114369-43-6

End-use product/EP 75% WP (Indar®75 WSP Fungicide, EPA Reg. No. 62719-421)

Metabolites

cis and trans isomers

Common name cis and trans lactone metabolites; Lactones A and B

Company experimental names RH-9129 and RH-9130

IUPAC names (3R,5R) or (3S,5R)-5-(4-chlorophenyl)-3-phenyl-3-(1H-1,2,4-triazol-1-

ylmethyl)dihydrofuran-2(3H)-one

CAS names trans- or cis-5-(4-chlorophenyl)dihydro-3-phenyl-3-(1H-1,2,4-triazol-1-ylmethyl)-2(3H)-

furanone

CAS # cis isomer, 146887-38-9; trans isomer, 146887-37-8

3.2 Physical/Chemical Characteristics

Table 3.2. Physicochemical Properties of the Technical Grade Fenbuconazole

Parameter Value Reference

Melting point 126.5–127.0°C DP# D310959, S. 

Oonnithan, 7/25/2006 pH not available

Bulk Density 0.50 g/mL

Water solubility at 22°C 3.8 mg/L

N

N

N

Cl

CN

O

N

N

N

O

Cl
Fenbuconazole Summary of Analytical Chemistry and Residue Data Barcode D403620

Page 8 of 25

Table 3.2. Physicochemical Properties of the Technical Grade Fenbuconazole

Parameter Value Reference

Solvent solubility (g/L) at 25°C Acetonitrile: 231

Cyclohexanone: 445

ethyl alcohol: 39

1-octanol: 13

aromatic 200: 77

ethyl acetate: 159

heptane: 1.0

Vapor pressure at 25°C (PAI) 3.7 ×10-8 mm Hg (4.9 × 10-6Pa)

Dissociation constant (pKa) (PAI) Not expected to dissociate in water

Octanol/water partition 

coefficient Log(KOW)

302 ± 0.08

UV/visible absorption spectrum λ max (nm) ε (L mol-1

cm-1)

 196 53,000 

 262 750

 268 740

 275 480

3.3 Pesticide Use Pattern/Directions for Use (860.1200)

Dow AgroSciences is proposing the first use of Enable 2FTM (2.0 lbs ai/gallon, EPA Reg. No.

62719-416) on peppers. The proposed use directions are summarized below in Table 3.3.

Table 3.3. Summary of Directions for Use of Fenbuconazole.

Applic. Timing, Type, and 

Equip. 1

Formulation

[EPA Reg. 

No.]

Applic. 

Rate 

(lb ai/A)

Max. No. 

Applic. per 

Season

Max. Seasonal 

Applic. Rate

(lb ai/A)

PHI

(days) Use Directions and Limitations 2

Peppers (Including but not limited to: bell, chili, cooking, non-bell, pimento and sweet)

Broadcast foliar 

applications to peppers 

when disease first appears

Ground or aerial 

equipment

75% WP

[62719-421] 0.188 3 NS 0.75 7

Apply in a minimum of 30 

gal/A, using ground equipment.

The minimum RTI is 10-14 

days. 

Broadcast foliar 

applications to peppers 

when disease first appears

Ground or aerial 

equipment

2.0 lbs 

ai/gal. SC

[62719-416]

0.188 3 NS 0.75 7

Apply in a minimum of 30 

gal/A, using ground equipment.

The minimum RTI is 10-14 

days. 

1 Do not apply through any type of irrigation system. Although application using aerial equipment is permitted, 

ground application is recommended.

2 Rotational crop restrictions: the minimum plant-back interval is 35 days when the last application of the product 

is <0.188 lb ai/A, and 210 days when the last application of the product is 0.188-1.0 lb ai/A.

3

The maximum use rate is based on the use of 4 oz product/acre/application.

NS = not specified.

Conclusions: The use directions are adequate to allow for evaluation of the residue data relative 

to the proposed use. The available field trial data and formulation bridging data on peppers are 

adequate and support the proposed use (4 oz product/A is equivalent to 0.188 lb ai/A). Although 

the single application rates used in the field trials were ~0.167 lb ai/A (0.9x rate), the residue 

data from these tests are adequate to support the 0.188 lb ai/A/application rate.
Fenbuconazole Summary of Analytical Chemistry and Residue Data Barcode D403620

Page 9 of 25

4.0 Metabolite/Degradate Residue Profile

4.1 Nature of the Residue

The qualitative nature of fenbuconazole residues in plants and livestock is adequately 

understood. Adequate studies are available depicting the metabolism of [14C]fenbuconazole in 

peaches, peanuts, sugar beets, and wheat. The residues of concern in/on peppers are 

fenbuconazole, its lactone metabolites, RH-9129 and RH-9130. In addition, the triazole 

metabolites 1,2,4-triazole, triazole alanine, and triazole acetic acid are residues of concern for 

risk assessment. These metabolites are common to the triazole-derivative class of fungicides and 

are addressed in a risk assessment separate from that for fenbuconazole.

There are no livestock feedstuffs associated with the use on peppers; therefore, data requirements 

for livestock metabolism are not relevant to this tolerance petition

4.1.1 Summary of Plant Metabolism (860.1300)

MARC Decision Memo (N. Dodd and W. Wassell, 3/9/94)

D200171, N. Dodd, 4/5/94

D241864, PP# 7F4887 - sugar beets

Adequate studies are available depicting the metabolism of fenbuconazole in peaches, peanuts, 

wheat, and sugar beets. Results from peach, wheat and peanut studies were previously 

summarized for review by the HED Metabolism Committee (Memo, N. Dodd and W. Wassell, 

12/10/93), and the sugar beet metabolism study is summarized under the petition for use on sugar 

beets (D241864, PP# 7F4887, 30 Mar 2006).

Based on the peach and wheat studies, the Metabolism Committee concluded that the residues of 

concern for uses on stone fruit, wheat, pecans, bananas, apples and almonds are fenbuconazole 

and its lactone metabolites, RH-9129 and RH-9130. This conclusion was contingent upon the 

petitioner providing data showing that RH-4911 is only a minor residue in these crops. The 

petitioner subsequently fulfilled this requirement by providing data from the wheat and peach 

metabolism studies showing that conjugates of RH-4911 accounted for <5% of the TRR in 

peaches and wheat straw (D200171, N. Dodd, 4/5/94). The Metabolism Committee also noted 

that the iminolactone metabolite (RH-6468) would be included de facto in the residues of 

concern as this compound is converted to the lactones by the analytical methodology. 

In the peanut metabolism study, vine and nutmeat samples were collected 28 days after the last 

of four foliar applications of either [phenyl14C] or [triazolyl14C] fenbuconazole (6.8% EC) at 

one-month intervals, at rates totaling ~2 lb ai/A. For both 14C-labels, the major residues in vines 

were parent (45-54% TRR), RH-9129 (4-5% TRR), RH-6467 (8-10% TRR), and the glucose 

conjugates of 4911 (18-19% TRR). Triazole alanine (7% TRR) was also identified in the 

[triazolyl14C]-labeled vines. The major residues in nutmeats were triazole alanine (88% TRR) 

from the [triazolyl14C]-label and the glucose conjugate of 4911 (29% TRR) from the [phenyl14C] label. In nutmeats, 29.4% total radioactive residue (TRR) was present as RH-7905 and in 

peanut vines, 24.5% of TRR was found as the glucosyl and glucosyl-malonyl conjugates of RH4911. Based on this data, for peanut commodities only, residues of RH-7905 (the glucosyl 

metabolite of RH-4911, determined as RH-4911) are also included in the risk assessment.
Fenbuconazole Summary of Analytical Chemistry and Residue Data Barcode D403620

Page 10 of 25

In addition to the above metabolism studies, an adequate sugar beet metabolism study was 

reviewed (D241864, 44343303.der) in conjunction with a petition for use on sugar beets. In this 

study, [phenyl14C] fenbuconazole was applied to sugar beets as three foliar applications at 39, 

103, and 183 days after planting, at rates totaling 3 lb ai/A, and samples of tops and roots were 

collected 7 days after the final application. The major residue identified in both tops and roots 

was parent (83-91% TRR), along with minor amounts of the lactone metabolites (<3% TRR). 

After reviewing the sugar beet data, HED has also determined that fenbuconazole and it lactone 

metabolites are the residues of concern for uses on sugar beets (D241864, PP# 7F4887, 30 Mar 

2006).

Conclusions: Adequate studies are available depicting the metabolism of [14C]fenbuconazole in 

peaches, peanuts, sugar beets, and wheat. The qualitative nature of fenbuconazole residues in 

plants is adequately understood. The residues of concern in/on peppers for tolerance setting are 

fenbuconazole and its lactone metabolites, RH-9129 and RH-9130. A separate risk assessment 

will be conducted for the triazole metabolites, 1,2,4-triazole, triazole alanine, and triazole acetic 

acid. All the metabolites are identified in Table 4.2.1, with the full details on their chemical 

structure summarized in Appendix D.

4.1.2 Summary of Livestock Metabolism (860.1300)

D182306, D182303, D181531, D181529, D181494, D195098, and D181498; W. Wassell; 1/11/94

D212471 and D212472, W. Wassell, 8/8/95

D223761 and D223758, W. Wassell, 4/23/96

There are no livestock feedstuffs associated with the established or proposed uses on peppers; 

therefore, data requirements for livestock metabolism are not relevant to this tolerance petition

The available goat and poultry metabolism data are adequate and HED concluded that, for 

ruminants, the residues of concern in animal matrices are fenbuconazole and its lactone 

metabolites, RH-9129 and RH-9130.

Although the poultry metabolism studies were deemed inadequate, a new poultry metabolism is 

not required at this time, as the available data are sufficient to conclude that tolerances will not 

be required for eggs and poultry tissues. Based on the current and proposed uses of 

fenbuconazole, the maximum dietary burden for poultry is expected to be low (0.063 ppm). The 

poultry metabolism studies were conducted at highly exaggerated rates (1,600x), and correcting 

residues levels in eggs and tissues from the metabolism studies to a 10x level indicates that 

individual residues in eggs and tissues will be <0.01 ppm. In addition, the results from the 

available poultry feeding study support this conclusion. If future uses of fenbuconazole result in 

a substantial increase in the dietary burden for poultry, then a new poultry metabolism study will 

be required.

Metabolism and distribution were investigated in lactating goats. In goats dosed at levels 

equivalent to 1, 10 and 100 ppm in the feed, less than 0.5% of the TRR remained in the milk and 

less than 1.6% in the tissues. Two major metabolites were identified in the milk as 1,2,4-triazole 

(0.24 mg/kg fenbuconazole equivalents at the highest dose) and triazolyl alanine (TA, 0.15 

mg/kg at the highest dose), with very low levels of the parent compound. At the highest dose, the 

levels of the TRR in the liver, kidney, muscle and fat were 12.4, 0.97, 0.22 and 0.11 mg/kg 
Fenbuconazole Summary of Analytical Chemistry and Residue Data Barcode D403620

Page 11 of 25

respectively. In the liver five major components were identified: the parent compound (0.95 

mg/kg), 4-(4-chlorophenyl)-2-hydroxymethyl-2-(phenyl)butanenitrile (RH-7968, 0.95 mg/kg), 

the glucuronide of the 4-hydroxy derivative (1.23 mg/kg), the triazole (1.79 mg/kg) and TA (4.95 

mg/kg). A further phenol metabolite was present in the kidney. 

Conclusions: The available goat and poultry metabolism data are adequate for purposes of this 

petition and HED concluded that, for ruminants, the residues of concern in animal matrices are 

fenbuconazole and its lactone metabolites, RH-9129 and RH-9130. The poultry metabolism 

studies were conducted at highly exaggerated rates (1,600x), and correcting residues levels in 

eggs and tissues from the metabolism studies to a 10x level indicates that individual residues in 

eggs and tissues will be <0.01 ppm. There are no livestock feedstuffs associated with the 

established or proposed uses on peppers; therefore, data requirements for livestock metabolism 

are not relevant to this tolerance petition

4.1.3 Summary of Confined Rotational Crops (860.l850)

D259204, S. Oonnithan, 7/25/06

An adequate confined rotational crop study is available indicating that the metabolite profile for 

fenbuconazole in rotational crops is similar to the metabolism in primary crops. Limited 

rotational crop field trials and rotational crop tolerances are not required provided that the labels 

specify a minimum PBI of 35 days following the last application to peppers of ≤0.188 lb ai/A,

and a minimum PBI of 210 days following a last application of 0.188 - 1.0 lb ai/A.

4.1.4 Summary of Rat Metabolism

In a rat general metabolism study (MRID 42900801), the absorption, distribution, metabolism 

and excretion of RH-7592 (fenbuconazole technical) were evaluated in Crl:CD BR rats 

(5/sex/group) dosed by a single gavage dose at 1 or 100 mg/kg in 5% aqueous methylcellulose 

vehicle (5 mL/kg). Figure 1 summarizes the proposed metabolic pathways of fenbuconazole in 

rats. 

Radiolabeled RH-7592 was rapidly absorbed, distributed and excreted following oral 

administration in rats. Total 3- or 4-day recoveries of the radioactivity were high for all groups 

(90.40-104.49% of the administered dose, or AD). Biliary excretion data indicated that systemic 

absorption of RH-7592 was high for all dosing groups. The feces were the major route of 

excretion (78.74-94.43% AD) after 4 days post dosing, while recovery in the urine was low 

(<1% AD). Tissue bioaccumulation of RH-7592 appeared to be minimal since <1% AD was 

recovered in tissues 4 days after oral administration for all dose groups. Except for the 

gastrointestinal tract, the highest levels were found in the liver (0.08 to 4.217 ppm). No sex- or 

dose-related differences in absorption, distribution or elimination were found. Metabolism of 

RH-7592 was extensive as shown by the numerous metabolites characterized and isolated in the 

feces, bile and urine. Metabolic pathways included glucuronide and sulfate conjugation, 

hydroxylation and oxidation. Furthermore, a dose-related difference in metabolism was evident. 

The higher amount of unmetabolized parent compound in the feces of the high dose group 

compared to the low- and repeated-dose groups suggest that saturation of the metabolic pathway 

may occur at the high dose.
Fenbuconazole Summary of Analytical Chemistry and Residue Data Barcode D403620

Page 12 of 25

4.1.5 Summary of Environmental Degradation

Fenbuconazole is considered to be moderately persistent to persistent in the environment and 

slightly mobile to mobile in soils. Because of its adsorption to soil, the potential for 

fenbuconazole to leach to ground water appears to be slight. However, the potential to 

contaminate groundwater may be greater at vulnerable sites, i.e., where soils have low organic 

matter and where groundwater is relatively close to the surface. The long half-lives of 

fenbuconazole in aerobic soil and terrestrial field dissipation studies indicate that when 

fenbuconazole is applied over multiple growing seasons, soil residue accumulation may result. 

These residues may be available for rotational crop uptake or may be transported with sediments 
Fenbuconazole Summary of Analytical Chemistry and Residue Data Barcode D403620

Page 13 of 25

during runoff events. For purposes of human health risk assessment, the residue of concern in 

water is fenbuconazole.

4.1.6 Summary of Metabolites and Degradates

As summarized in Appendix C, the metabolic pathway in plants consists of three major routes. 

The first route is via oxidation of the carbon next to the chlorinated phenyl ring, forming the 

benzilic alcohol intermediate, which further reacts to form the lactone metabolites RH9129 and 

RH 9130 (which are diastereomers). Oxidation or nucleophilic substitution of the carbon 

adjacent to the triazole ring leads to the formation of the free triazole, which is transformed into 

triazole-alanine and the triazole acetic acid. Another route involves the hydrolation of 

fenbuconazole, which leads to the formation of various conjugates, including glucuronide and 

malonyl-glucoside conjugates.

Based on adequate ruminant metabolism data, the residues of concern in animal matrices are 

fenbuconazole and its lactone metabolites, RH-9129 and RH-9130. Residues of RH-7968 were a 

minor component of the total radioactive residues (≤7.2% TRR) in goat liver, muscle and fat in 

the supplemental goat metabolism study, this metabolite is not included in the tolerance 

expression for animal commodities. Although the poultry metabolism studies were deemed 

inadequate, additional poultry metabolism data are not required for this petition as the expected 

dietary exposure of poultry is low (0.09 ppm) and the available metabolism data and poultry 

feeding study indicate that tolerances will not be required for poultry commodities.

4.2 Comparison of Metabolic Pathways

Studies are available depicting the metabolism of [14C]fenbuconazole in rats, primary crops 

(peaches, peanuts, wheat, sugar beets), rotational crops (collards, turnips, wheat), and livestock 

(lactating goats, laying hens). Major residues consistently noted in these studies include parent 

fenbuconazole and the lactone metabolites RH-9129, RH-9130, and for peanuts only, the 

metabolite RH-6467. The common triazole metabolites 1,2,4-triazole, triazolylalanine, and 

triazolylacetic acid were observed in all of the metabolism studies, with the degree of metabolite 

formation highly dependent on the species being studied.

In rats, fenbuconazole is rapidly absorbed and excreted within 96 hours following a single low or 

high dose or following repeated low doses. Very low bioaccumulation of both the 

parent compound and metabolites was indicated by low levels in the tissues. Elimination 

occurred primarily by biliary excretion since the majority of the administered dose was 

recovered in the bile three days after exposure or in the feces four days after exposure. There 

were no sex- or dose-related differences in absorption, distribution, or elimination; these 

processes were also similar regardless of whether single or multiple exposure regimens were 

used. Extensive metabolism of fenbuconazole occurred, with sex- and dose-related differences. 

Very low (2-5%) parent compound was recovered in the feces following single or repeated low 

doses, but a higher percentage (21-37%) was found following a single high dose, indicating 

saturation of the metabolic pathway. More sulfate metabolites were found in female excreta 

compared to males, and more ketoacid metabolites were found in male urine compared to 

females.
Fenbuconazole Summary of Analytical Chemistry and Residue Data Barcode D403620

Page 14 of 25

Based on the peach and wheat studies, the Metabolism Committee (N. Dodd and W. Wassell, 

3/9/94) concluded that the residues of concern for uses on stone fruit, wheat, pecans, bananas, 

apples and almonds are fenbuconazole and its lactone metabolites, RH-9129 and RH-9130. This 

conclusion was contingent upon the petitioner providing data showing that RH-4911 is only a 

minor residue in these crops. The petitioner subsequently fulfilled this requirement by providing 

data from the wheat and peach metabolism studies showing that conjugates of RH-4911 

accounted for <5% of the TRR in peaches and wheat straw (D200171, N. Dodd, 4/5/94). The 

Metabolism Committee also noted that the iminolactone metabolite (RH-6468) would be 

included de facto in the residues of concern as this compound is converted to the lactones by the 

analytical methodology. After reviewing the sugar beet data, HED has also determined that 

fenbuconazole and it lactone metabolites are the residues of concern for uses on sugar beets 

(D241864, PP# 7F4887). Metabolite studies with peanuts show that RH-7905 and RH-4911 are 

significant residues of concern in this crop only (see Section 4.3).

4.3 Residues of Concern Summary and Rationale

MARC Decision Memo (N. Dodd/W. Wassell, 3/9/94)

D182303, W. Wassell, 1/11/94 

D200171, N. Dodd, 4/5/94

D212471, W. Wassell, 8/8/95

D223758, W. Wassell, 4/23/96

D403618, T. Morton, 8/1/2012.

HED has determined that the residues of concern for risk assessment are fenbuconazole and the 

following metabolites: RH-9129, RH-9130, RH-4911(peanut only), and RH-7905 (peanut only). 

RH-9129 and RH-9130 are cis/trans isomers of the lactone metabolite of fenbuconazole and may 

account for approximately one third of the total fenbuconazole residues. RH-9129 and RH-9130 

are residues of concern for both risk-assessment and tolerance-enforcement purposes. RH-7905 

is a minor metabolite except in peanut. In animals, the glucoside conjugate (RH-7905) will be 

cleaved to yield RH-4911. Although RH-4911, being a hydroxy-derivative of fenbuconazole, is 

likely to be less toxic than the parent, we have no specific toxicological information for this 

compound. Because it shares structural features with the parent, HED is assuming that it has the 

same toxicity as fenbuconazole. Therefore, RH-7905 and RH-4911 are being included as 

residues of concern for risk assessment (peanuts only). The current analytical enforcement 

method has been validated for the analysis of fenbuconazole as well as RH-9129 and RH-9130.

In addition, the Metabolism Committee noted that the iminolactone metabolite (RH-6468) would 

also be included de facto in the residues of concern, as the petitioner has indicated that this 

compound is converted to the lactones by the analytical method.

In addition, although the poultry metabolism studies were deemed inadequate, additional poultry 

metabolism data are not required for this petition as the expected dietary exposure of poultry is 

low (0.09 ppm) and the available metabolism data and poultry feeding study indicate that 

tolerances will not be required for poultry commodities.
Fenbuconazole Summary of Analytical Chemistry and Residue Data Barcode D403620

Page 15 of 25

Table 4.3. Summary of Metabolites and Degradates to be included in the Risk Assessment and Tolerance 

Expression*

Matrix Residues included in Risk 

Assessment

Residues included in Tolerance 

Expression

Plants Primary Crop Fenbuconazole + RH-9129 + RH9130 + RH-7905 (peanut only) + 

RH-4911 (peanut only)

Fenbuconazole + RH-9129 + RH-9130, 

expressed as fenbuconazole

Rotational Crop Not Applicable Not Applicable

Livestock Ruminant Fenbuconazole + RH-9129 + RH9130Fenbuconazole + RH-9129 + RH-9130, 

expressed as fenbuconazole

Poultry Not Applicable Not Applicable

Drinking Water Fenbuconazole Not Applicable

* The common triazole metabolites 1,2,4-triazole, triazolylalanine, and triazolylacetic acid have been identified as 

residues of concern for risk assessment. Separate assessments addressing these compounds have been conducted 

(see. T. Morton. D403618. 8/1/2012).

5.0 Residue Profile

5.1 Residue Analytical Methods (860.1340)

5.1.1 Data Collection Methods

See Tolerance Enforcement Method (Section 5.1.3)

5.1.2 Multi-Residue Methods (860.1360)

Data evaluating the recovery of fenbuconazole and the metabolites RH-9129 and RH-9130 

through FDA Multi residue Method Testing Protocols were submitted and forwarded to FDA for 

further review (Letter to L. Sawyer from N. Dodd, 1/27/93). The FDA PESTDATA database, 

dated 11/01 (PAM Vol. I, Appendix I), indicates that fenbuconazole is completely recovered 

using Multi residue Methods Section 302 (Protocol D), but is not recovered by Methods 303 and 

304 (Protocols E and F). The recovery of the lactone metabolites (RH-1929 and RH-9130) 

through Method 302 was variable or partial (50-80%). None of these metabolites were 

recovered through Methods 303 or 304.

5.1.3 Tolerance Enforcement Method

44869103.der

A GC/NPD tolerance enforcement method, 34-90-47R, is available for determining residues of 

fenbuconazole, RH-9129, and RH-9130 in/on stone fruits. For this method, residues are 

extracted with methanol, filtered through Celite, diluted with aqueous 9.1% NaCl, and 

partitioned into methylene chloride. Residues are then concentrated, redissolved in 

toluene:acetone (100:10, v:v), and cleaned up using a silica gel column eluted with 

toluene:acetone (100:30, v:v). Residues in the resulting eluate are concentrated to dryness, 

redissolved in toluene:acetone (100:5, v/v), and eluted through a Florisil column with 

toluene:acetone (100:30, v:v). Residues are again concentrated to dryness, redissolved in 
Fenbuconazole Summary of Analytical Chemistry and Residue Data Barcode D403620

Page 16 of 25

toluene:methanol (100:3, v:v), and analyzed by GC/NPD using external standards. The reported 

LOQ is 0.01 ppm each for fenbuconazole, RH-9129, and RH-9130.

Residues in/on peppers were determined using a slightly modified version of the above method. 

The modifications were made to improve the performance of the method. The GC/NPD method 

was adequately validated in conjunction with the analysis of field trial samples using control 

samples fortified with each analyte at 0.01-1.0 ppm. The validated LOQ for each analyte is 0.01 

ppm in/on peppers, for a combined LOQ of 0.03 ppm.

Conclusions: The available GC/NPD method, TR 34-90-47R, is adequate for enforcing 

tolerances and collecting data on fenbuconazole residues in/on peppers.

Note: The GC/NPD method (TR 34-94-142) is adequate for collecting data on residues of 

fenbuconazole, RH-9129 and RH-9130 in animal commodities.

5.2 Storage Stability (860.1380)

D249012, W. Wassell, 11/19/98

D223761, W. Wassell. 4/23/96

D239002, G. Otakie, 3/30/06

Adequate storage stability data are available indicating that fenbuconazole and its lactone 

metabolites (RH-9129 and RH-9130) are stable in frozen storage for up to 54 months in pecans 

and stone fruits, and 36 months in apples, wheat grain, and wheat straw.

In addition, a freezer storage stability study was conducted in conjunction with the pepper field 

trials. A separate control sample of homogenized peppers was fortified with fenbuconazole, RH9129, and RH-9130, each at 1.0 ppm, and stored under the same conditions (≤-10oC) as the field 

trial samples. No 0-day analysis was conducted prior to placing the samples in frozen storage;

therefore, the original fortification levels could not be verified. After 16.6 months of frozen 

storage, the stored samples were analyzed in triplicate along with a control sample and control 

samples freshly fortified with each analyte at 1.0 ppm. The average recovery (corrected for 

concurrent recovery) was 89% for fenbuconazole and RH-9130 and 91% for RH-9129. These 

data indicate that fenbuconazole, RH-9129, and RH-9130 are stable in frozen peppers for up to 

16.6 months. Samples from the pepper field trials were stored at <-10°C for up to 16.4 months 

prior to analysis.

Conclusions: In the pepper storage stability study, no 0-day analysis was conducted on the 

fortified samples prior to storage. However, for the purposes of this pepper tolerance petition, 

HED accepts the available data to support the pepper field trials.

5.3 Residue Data

5.3.1 Crop Field Trials (860.1500)

D390352, S. Oonnithan, 9/8/2011

Dow AgroSciences has submitted a bridging study on pepper to translate residues from Indar 

75WSP (EPA Reg. No. 62729-421) to Enable 2F (62719-416), thereby obviating the need for a 
Fenbuconazole Summary of Analytical Chemistry and Residue Data Barcode D403620

Page 17 of 25

full field trial data set for the Enable 2F formulation use on peppers. The original submission did 

not include a petition for a revised tolerance for fenbuconazole residues in pepper.

The bridging study conducted on bell pepper consisted of side-by-side trials in six locations, in 

which both formulations were applied to peppers. The submitted residue data (6 samples) for the 

WP and EC formulations were analyzed using the OECD MRL calculator for the purpose of 

comparing the data sets from the previously reviewed field trials used to establish the existing 

tolerance and the new bridging data. The results of the comparison are shown below:

Table 5.3.1. Fenbuconazole Total Residue1

Indar WSP

2008 Data

Indar WSP

Bridging Study

Enable 2F

Bridging Study

Current or recommended tolerance 0.40 0.70 1.0

Lowest residue 0.05 0.029 0.044

Highest residue 0.22 0.465 0.668

Mean residue 0.136 0.142 0.189

No. of samples (avg. of 2 replicates) 18 6 6

1 -- See D390352, S. Oonnithan, 8 Sept 2011.

Conclusions: Although the submitted bridging residue data on pepper using the WP (Indar) and 

SC (Enable 2F) formulations of fenbuconazole are limited, the results summarized above 

indicate the presence of significantly higher residues of fenbuconazole than found in the earlier 

field trials. Based on the submitted data, the current 0.40 ppm tolerance does not support the 

higher residues found on pepper with either the WP formulation or the SC formulation. 

Therefore, the existing tolerance should be increased to 1.0 ppm to support use of the SC 

formulation. HED notes that the residue values for bell and non-bell peppers in the original 

submission were very similar (MRID 47215801); therefore, we conclude that the use of only bell 

peppers in the bridging study is not an issue.

Triazole Metabolites

Residues of 1,2,4-triazole and triazole acetic acid were non-detectable (<0.003 ppm) in all 

treated pepper samples. Triazole alanine residue ranged from 0.0187 to 0.158 ppm in treated 

peppers. Untreated control pepper samples also had triazole alanine residues which ranged from 

0.0029 to 0.013 ppm. Table 5.3.2. lists the results from the triazole metabolite analyses and is 

taken directly for the study report. 
Fenbuconazole Summary of Analytical Chemistry and Residue Data Barcode D403620

Page 18 of 25

 Table 5.3.2. Bell Pepper Field Trial Data for Fenbuconazole (Triazole Metabolites).

Conclusions: There were no significant differences in triazole metabolite residue level resulting 

from treatment with either formulation. Residues of 1,2,4-triazole and triazole acetic acid were 

all non-detectable (<0.003 ppm). Residues of triazole alanine averaged 0.025 ppm, while the 

maximum observed residue for triazole alanine was 0.158 ppm. These triazole metabolites will 

be addressed in a separate forthcoming risk assessment. 

5.3.2 Field Rotational Crops (860.1900)

D259204, S. Oonnithan, 7/25/06

An adequate confined rotational crop study is available indicating that the metabolite profile for 

fenbuconazole in rotational crops is similar to the metabolism in primary crops. Limited 

rotational crop field trials and rotational crop tolerances are not required provided that the labels 

specify a minimum PBI of 35 days following the last application to peppers of ≤0.188 lb ai/A,

and a minimum PBI of 210 days following a last application of 0.188 - 1.0 lb ai/A. 

 

5.3.3 Processed Food and Feed (860.1520)

HED does not require residue data for any processed commodities associated with peppers. 

Therefore, data requirements for processed food and feed are not relevant to these tolerance 

petitions.
Fenbuconazole Summary of Analytical Chemistry and Residue Data Barcode D403620

Page 19 of 25

5.3.4 Meat, Milk, Poultry and Eggs (860.1480)

As there are no livestock feedstuffs associated with the proposed/established uses on peppers, 

data requirements pertaining to meat, milk, poultry, and eggs are not relevant to these tolerance 

petitions.

5.3.5 Dietary Burden

There are no animal feed commodities associated with use on peppers. Therefore, there is no 

change in the anticipated dietary burden for livestock commodities. 

Conclusions: There is no change in anticipated dietary burden and the current tolerances for 

livestock commodities are adequate.

5.3.6 Estimated Secondary Residues in Livestock 

There are no animal feed commodities associated with use on peppers.

Conclusions: The current tolerances for livestock commodities are adequate.

5.3.7. Food Handling (860.1460)

There are no proposed uses that are relevant to this guideline topic.

5.3.8 Water, Fish, and Irrigated Crops (860.1400)

There are no proposed uses that are relevant to this guideline topic.

5.4 Food Residue Profile

There are adequate data for risk assessment and tolerance assessment. There were finite residues 

of the parent compound in/on peppers in the bridging study, and there were very low levels or 

non-detectable levels of the metabolite RH-9129. Residue levels for the RH-9130 metabolite 

were all below the LOD. Residues of the parent compound tended to decline with increasing 

PHI with an estimated half-life of between 8 to 9 days.

6.0 Tolerance Derivation

The bridging study conducted using bell peppers consisted of side-by-side trials in six 

different locations, in which both formulations were applied in accordance with the 

registered application rate on peppers. The submitted residue data (6 samples/each an 

average of two duplicate samples) for the WP and EC formulations were analyzed using the 

OECD MRL calculator for the purpose of comparing the data sets from the field trials used 

to establish the tolerance and the new bridging data. The results of these tolerance 

calculations are summarized in Appendix B. 
Fenbuconazole Summary of Analytical Chemistry and Residue Data Barcode D403620

Page 20 of 25

Attachments:

Appendix A. International Residue Limits Table.

Appendix B. OECD MRL Calculation Procedure Inputs/Outputs.

Appendix C. Proposed Metabolic Pathway for Fenbuconazole in Crops.

Appendix D. Fenbuconazole and Its Metabolites in Plants and Animals.
Fenbuconazole Summary of Analytical Chemistry and Residue Data Barcode D403620

Page 21 of 25

Appendix A. International Residue Limits Table.

Fenbuconazole (129011; 10/10/2012)

Summary of US and International Tolerances and Maximum Residue Limits 

Residue Definition:

US Canada Mexico2 Codex3

40 CFR § 180.480 

Plant/Livestock: combined residues of the 

fungicide fenbuconazole, alpha-[2-(4-

chlorophenyl)- ethyl]-alpha-phenyl-3-(1H1,2,4-triazole)- 1-propanenitrile, and its 

metabolites RH-9129, cis-5-(4-

chlorophenyl)- dihydro-3-phenyl-3-(1H1,2,4- triazole-1-ylmethyl)-2-3 H-furanone, 

and RH-9130, trans-5-(4-

chlorophenyl)dihydro-3-phenyl-3- (1H-1,2,4-

triazole-1-ylmethyl)-2-3 H- furanone, 

expressed as fenbuconazole 

α-[2-(4-chlorophenyl)ethyl]-αphenyl-1H-1,2,4-

triazole-1-propanenitrile, including 

the metabolites

cis-5-(4-chlorophenyl)-dihydro-3-

phenyl-3-(1H-1,2,4-

triazol-1-ylmethyl)-2-3H-furanone 

and trans-5-(4-

chlorophenyl)-dihydro-3-phenyl-3-

(1H-1,2,4-

triazol-1-ylmethyl)-2-3H-furanone

Fenbuconazole. The 

residue is fat-soluble.

Commodity1 Tolerance (ppm) /Maximum Residue Limit (mg/kg)

US Canada Mexico2 Codex3

Pepper 1.0

0.6 peppers 

2 peppers Chili, dried

(draft MRL awaiting 

ARfD evaluation)

Completed: M. Negussie; 10/12/2012

1

Includes only commodities of interest for this action. Tolerance values should be the HED recommendations and not those proposed by the 

applicant.2 Mexico adopts US tolerances and/or Codex MRLs for its export purposes. 

3 * = absent at the limit of quantitation; Po = postharvest 

treatment, such as treatment of stored grains. PoP = processed postharvest treated commodity, such as processing of treated stored wheat. (fat) = 

to be measured on the fat portion of the sample. MRLs indicated as proposed have not been finalized by the CCPR and the CAC.
Fenbuconazole Summary of Analytical Chemistry and Residue Data Barcode D403620

Page 22 of 25

Appendix B. OECD MRL Calculation Procedure Inputs/Outputs.

Peppers - Different Formulations

Crop Peppers – Enable formulation Peppers – Indar formulation

Region / Country USA USA

GAP 0.188 lbs ai/A/appln.

(0.75 lbs ai/A/season)

0.188 lbs ai/A/appln.

(0.75 lbs ai/A/season)

Total number of data (n) 6 6

Percentage of censored data 0% 0%

Number of non-censored data 6 6

Lowest residue 0.059 0.032

Highest residue 0.607 0.411

Median residue 0.124 0.100

Mean 0.189 0.142

Standard deviation (SD) 0.208 0.138

Correction factor for censoring 

(CF) 1.0 1.0

- Highest residue 0.607 0.411

- Mean + 4 SD 1.019 0.696

- CF x 3 Mean 0.567 0.427

Unrounded MRL 1.019 0.696

Rounded MRL 1 0.7

Residues (mg/kg)

0.607 0.411

0.077 0.062

0.059 0.032

0.141 0.124

0.107 0.075

0.143 0.150
Fenbuconazole Summary of Analytical Chemistry and Residue Data Barcode D403620

Page 23 of 25

Appendix C. Proposed Metabolic Pathway for Fenbuconazole in Crops.
Fenbuconazole Summary of Analytical Chemistry and Residue Data Barcode D403620

Page 24 of 25

Appendix D. Fenbuconazole and Its Metabolites in Plants and Animals.

Fenbuconazole and Its Metabolites in Plants and Animals.

Common name/code Chemical name Chemical structure

Fenbuconazole

RH-7592

α-[2-(4-chlorophenyl)ethyl]-α-phenyl1H-1,2,4-triazole-1-propanenitrile

Iminolactone 

Metabolite

RH-6468

5-(4-chlorophenyl)-3-phenyl-3-(1H1,2,4-triazol-1-ylmethyl)dihydrofuran2(3H)-imine

Lactone A and B 

Metabolites

RH-9129 and RH-9130

trans- or cis-5-(4-

chlorophenyl)dihydro-3-phenyl-3-(1H1,2,4-triazol-1-ylmethyl)-2(3H)-

furanone

Benzylic Alcohol 

Metabolite

RH-6648

4-(4-chlorophenyl)-4-hydroxy-2-

phenyl-2-(1H-1,2,4-triazol-1-ylmethyl) 

butanenitrile

Ketone Metabolite

RH-6467

4-(4-chlorophenyl)-4-oxo-2-phenyl-2-

(1H-1,2,4-triazol-1-

ylmethyl)butanenitrile

N

N

N

Cl

CN

O

N

N

N

HN

Cl

O

N

N

N

O

Cl

N

N

N

Cl

CN OH

N

N

N

Cl

CN O
Fenbuconazole Summary of Analytical Chemistry and Residue Data Barcode D403620

Page 25 of 25

Fenbuconazole and Its Metabolites in Plants and Animals.

Common name/code Chemical name Chemical structure

4-Phenol Metabolite

RH-1311

4-(4-chlorophenyl)-2-(4-

hydroxyphenyl)-2-(1H-1,2,4-triazol-1-

ylmethyl)butanenitrile

3-Hydroxy-4-

chlorophenyl 

Metabolite 

RH-4911

4-(4-chloro-3-hydroxyphenyl)-2-

phenyl-2-(1H-1,2,4-triazol-1-ylmethyl) 

butanenitrile

Glucosyl conjugate of 

RH-4911

RH-7905

α-[2-[4-chloro-3-(Dglucopyranosyloxy) phenyl]ethyl]-αphenyl-1H-1,2,4-triazole-1-

propanenitrile

Cleaved Alcohol 

Metabolite

RH-7968

4-(4-chlorophenyl)-2-(hydroxymethyl)-

2-phenylbutanenitrile

Triazole

RH-0118

1H-1,2,4-triazole

Triazolealanine 

TAA

RH-3968

2-amino-3-(1H-1,2,4-triazol-1-yl) 

propanoic acid

Triazoleacetic acid

TA

RH-3779

RH-4098

1H-1,2,4-triazol-1-yl acetic acid

N

N

N

Cl

CN

HO

N

N

N

Cl

CN

OH

N

N

N

O

Cl

CN

O

OH

HO HO

OH

Cl

CN

OH

NH

N

N

N

N

N NH2

HOOC

N

N

N COOH