UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON, DC 20460

 OFFICE OF CHEMICAL SAFETY AND POLLUTION PREVENTION

PC Code: 128847

DP Barcode: 409484 and 409488

 Date: November 8, 2013

MEMORANDUM

Subject: Ecological Risk Assessment for the Proposed New Use of Difenoconazole on 

Canola and Oilseed Subgroup 20A

To: Rosemary Kearns, Risk Manager Reviewer

Tony Kish, Risk Manager

Registration Division (7505P)

From: Michael Lowit, Ph.D., Ecologist

Faruque Khan, Ph.D., Senior Fate Scientist

Sujatha Sankula, Ph.D., Branch Chief

Environmental Risk Branch I

Environmental Fate and Effects Division (7507P)

This memorandum summarizes the ecological risks associated with the proposed new use of 

the fungicide difenoconazole. The risk assessment considers use of the product Inspire ®on 

canola and oilseed subgroup 20A. 

Foliar applications (ground or aerial spray and chemigation) are proposed at 0.113 lb 

ai/A/crop. It is assumed that there is one crop/year and an annual limit of 0.113 lb ai/A for 

this use.

The single maximum application rate is similar to previously assessed uses and EECs are 

lower than those for many previously assessed uses. However, a risk assessment was 

conducted to incorporate additional toxicity data that has been reviewed since the last risk 

assessment (D402993, 8/29/2012). The recently reviewed difenoconazole studies addressed 

acute and chronic toxicity to freshwater fish (MRID 48453201 and 48453205), avian acute 

oral toxicity (MRID 48453202), and terrestrial plant toxicity (MRID 48453203 and 

48453204). The major degradate (1,2,4-triazole and triazole acetic acid) studies addressed 

acute toxicity to freshwater fish (MRID 48474301 and 48453209) and freshwater 

invertebrates (MRID 48453206 and 48453208).
2

As in recent risk assessments, total toxic residue (TTR) EECs were used to characterize risk 

when guideline data were not available for the major degradates (1,2,4-triazole and triazole 

acetic acid) and toxicity of the degradates was assumed equal to that of difenoconazole.

1. Executive Summary

The Environmental Fate and Effects Division (EFED) evaluated the proposed new use of the 

broad-spectrum fungicide difenoconazole (Inspire®) on canola and oilseed subgroup 20A. 

Difenoconazole is a fungicide in the conazole chemical class. Fungicidal activity of the conazole 

class is attributed to the inhibition of ergosterol biosynthesis. 

A number of risk assessments have been conducted on difenoconazole. Previous 

assessments identified risk concerns primarily for aquatic invertebrates, fish, birds, and 

mammals on a chronic basis (on an acute basis for estuarine/marine invertebrates for certain 

uses). In past assessments, a risk concern was not precluded for terrestrial plants due to lack 

of acceptable data. Taxonomic groups for which concern levels were exceeded for the 

proposed use (Table 1) are similar to those identified in previous assessments. 

Table 1. Potential Effects to Listed Species Associated with the Proposed New Use of 

Difenoconazole

Listed Taxa Direct Effects1Indirect Effects

Terrestrial and semi-aquatic plants – monocots 

and dicots Yes (listed dicots) Yes

Birds No – Acute 

Yes – Chronic Yes

Terrestrial-phase amphibians No – Acute 

Yes – Chronic Yes

Reptiles No – Acute 

Yes – Chronic Yes

Mammals No – Acute 

Yes – Chronic Yes

Aquatic plants No2 Yes

Freshwater fish No – Acute

Yes – Chronic Yes

Aquatic-phase amphibians No – Acute

Yes – Chronic Yes

Freshwater invertebrates No – Acute

No – Chronic Yes

Estuarine/marine fish No – Acute

Yes – Chronic Yes

Estuarine/marine invertebrates No – Acute

Yes – Chronic Yes

Terrestrial invertebrates No Yes3

1 RQs for aquatic plants and chronic risk to fish and aquatic invertebrates were based on total toxic residues (TTR) 

due to a lack of guideline toxicity data for 1,2,4-triazole and triazole acetic acid. Degradate toxicity was assumed 

equal to that of difenoconazole for those endpoints.
3

Listed Taxa Direct Effects1Indirect Effects

2 There is some uncertainty for non-vascular plants because an acceptable study with cyanobacteria is not available; 

however, there are not currently any listed non-vascular plant species.

3 Only for obligate relationships with listed terrestrial plant species (dicots).

2. Data Gaps

Several data gaps remain, as identified in past risk assessments (data unavailable or available 

data is insufficient). The impact of these data gaps on the risk conclusions varies with the use 

and application rate of difenoconazole.

 850.1350 (Estuarine-marine invertebrate life-cycle) – TGAI, difenoconazole

 850.2100 (Acute oral toxicity to birds) – CGA-71019 (1,2,4-triazole) and CGA-142856 

(triazole acetic acid)

 850.4550 (Cyanobacteria toxicity) – TGAI, difenoconazole

 850.4100 (Terrestrial plant toxicity, seedling emergence) – TEP

- Tier II testing is required or a Tier I test can be used if a NOAEC is established at the 

maximum labeled single application rate. See section 8.1.3 for additional issues with 

available study.

 850.4150 (Terrestrial plant toxicity, vegetative vigor) – TEP

- Tier II testing is required or a Tier I test can be used if a NOAEC is established at the 

maximum labeled single application rate.

 There is uncertainty associated with chronic risk to benthic invertebrates given that 

porewater EECs are similar to water column EECs and a lack of acceptable toxicity data

for benthic invertebrates. Although a sediment toxicity study (range finding) determining 

the effects of difenoconazole on benthic organisms has been submitted and reviewed, the 

numerous deviations in the study limit its use for quantitative purposes. Data is 

recommended given that the chronic LOC (1.0) is exceeded for aquatic invertebrates 

based on comparison of water column species toxicity data to porewater EECs.

In addition, a guideline chronic fish study (850.1400) with the major degradates (1,2,4-

triazole and triazole acetic acid) would be useful for reducing uncertainty in the risk 

conclusions. 

3. Uncertainties

 The assessment of chronic risk to benthic invertebrates was based on toxicity to water 

column species due to a lack of data suitable for quantitative risk assessment. Risk 
4

conclusions for the proposed use are the same for benthic invertebrates because the pore 

water EECs are similar to water column EECs; that is, there is a chronic risk concern for 

estuarine/marine invertebrates but not a risk concern for freshwater invertebrates. The risk 

concern triggered for water column estuarine/marine species is protective of estuarine/marine 

invertebrate species in general (i.e., there is a risk concern); however, the magnitude of the 

RQ associated with that concern is uncertain for both water column invertebrates (nondefinitive endpoint) and benthic invertebrates (lack of data). There is more uncertainty in the 

risk conclusions for freshwater invertebrates given that benthic species may be more 

sensitive than water column species.

 There is some uncertainty about risk to aquatic plants because an acceptable study with blue 

green algae is not available. There are not currently any listed non-vascular plants so the 

uncertainty is for non-listed species. Blue-green algae would need to be about 33x more 

sensitive than Navicula pelliculosa to exceed the LOC (non-listed species).

 There would not be a chronic risk concern for fish if the degradates are less toxic than 

difenoconazole (RQ = 0.89 based on a 60-day difenoconazole-only EEC = 0.77 μg/L); 

therefore, guideline chronic fish studies with the major degradates (1,2,4-triazole and 

triazole acetic acid) would be useful for refining the risk conclusions if they demonstrate less 

toxicity than difenoconazole.

 Before difenoconazole breaks down to 1,2,4-triazole, it forms CGA-205375, (1-[2-Chloro-4-

(4-chlorophenoxy)-phenyl]-2-[1,2,4]triazol-1-yl-ethanol). CGA-205375 has potential to be 

slightly more mobile in the soil than difenoconazole based on the registrant-submitted 

adsorption/desorption study. The potential adverse effect of this degradate on the ecological 

environment was not addressed in this risk assessment. If this degradate is shown to have 

potential ecological or human health concerns, additional fate and transport studies may be 

requested at a later time.

 Because it is persistent, difenoconazole and its degradates may accumulate in soil after 

repeated use. This repeated or continuous exposure may result in significant risks to nontarget organisms, especially birds and mammals. 

 This risk assessment only considered the most sensitive of the species evaluated in the 

registrant-submitted studies. The position of the tested species relative to the distribution of 

all species’ sensitivities to difenoconazole is unknown. Extrapolating the risk conclusions 

from the most sensitive tested species to non-tested species may either underestimate or 

overestimate the potential risks to those species. 

4. Summary of Proposed Use

Foliar applications (ground or aerial spray and chemigation) are proposed at 0.113 lb 

ai/A/crop. EFED assumes that there is typically one crop of canola per year on a given field; 

thus, the annual limit for this use is assumed to be 0.113 lb ai/A.
5

5. Fate and Transport Summary

Difenoconazole is a fungicide in the conazole chemical class. Fungicidal activity of the conazole 

class of compounds is attributed to the inhibition of ergosterol biosynthesis 1. Ergosterol, which 

controls cell membrane permeability, is a critical component in fungal cell membranes2. The 

mechanism of controlling ergosterol biosynthesis is through the disruption of the fungal 

cytochrome P-450-mediated 14 α-lanosterol demethylation. Accumulation of 14 α-methyl 

sterols correlates with the subsequent loss of ergosterol in the fungal cell wall. 

Based on a low vapor pressure of 2.5 x 10-10 mm Hg and solubility in water of 15 mg/L, 

difenoconazole has a low propensity to volatilize and generate vapors after application. At test 

termination in laboratory studies, the residues detected in an organic volatiles trap totaled 0.7% 

or less; most instances were less than 0.1% of the applied difenoconazole. The concentrations of 

the applied difenoconazole lost through volatilization were not measured in the terrestrial field 

dissipation studies. Selected physical and chemical properties are presented in Table 2.

Table 2. Physical and Chemical Properties of Difenoconazole

Property Value Source

Common Name Difenoconazole MRID 469501-04

CAS Registry No. 119446-68-3

PC Code 128847

Structure MRID 469501-04

Chemical Name (CAS) 1-{2-[4-(chlorophenoxy)-2-

chlorophenyl-(4-methyl -1,3-

dioxolan-2-yl)-methyl]} -1H-1,2,4-

triazole

MRID 469501-04

SMILES notation O1CC(C)OC1(Cn2ncnc2)c3c(Cl)cc(O

c4ccc(Cl)cc4)cc3 

EPI Suite, v3.12 SMILES

Molecular Formula C19H17Cl2N3O3 MRID 469501-04

Molecular Weight 406.27 MRID 469501-04

Physical State Red Liquid

Vapor pressure 2.5 x 10-10 mm Hg (25 oC) MRID 465159-01

 

1 www.centerwatch.com/patient/drugs/dru784.html

2 www.hull.ac.uk/php/chsanb/fungweb/fungweb7.htm
6

Property Value Source

Henry’s Law constant 8.9 x 10-12 atm x m3/mol MRID 465159-01

Specific Gravity/ Density 1.14g/cm3 @ 25 oC MRID 469501-04

Solubility in water 15.0 mg/L @ 25 oC MRID 469501-04

log Kow 4.4 (25 oC) MRID 469501-05

In soil, difenoconazole is persistent and slightly mobile. Difenoconazole has low potential to 

reach groundwater, except in soils of high sand and low organic matter content. During a runoff 

event, difenoconazole will potentially enter adjacent bodies of surface water. In an aquatic 

environment, difenoconazole’s main route of dissipation is partitioning into the bottom sediment 

as shown in an aerobic aquatic metabolism study (MRID 42245134), in which the distribution 

ratio of sediment and water phases was 8:1 at 1 day post-treatment and 40:1 at 30 days posttreatment. Difenoconazole has the potential to undergo slow to relatively fast aqueous photolysis 

in clear water. Table 3 summarizes the environmental fate data of difenoconazole. Additional 

environmental fate data, including major degradates and maximum percent formation can be 

found in a previous assessment (DP377719, 7/20/2010). 

Table 3. Summary of the Environmental Fate Properties of Difenoconazole

Property Value Source

Name Difenoconazole

Henry’s Law constant 8.9 x 10-12 atm x m3/mol MRID 465159-01

Soil adsorption coefficient 

Koc (L/kg)

3867, 3518, 3471, and 7734

3870, 4587, 4799, and 11202

MRID 422451-35 A

MRID 469501-21

Hydrolysis half-life

pH = 5

pH = 7

pH = 9

Stable

Stable

Stable

MRID 422451-27

Photolysis half-life in water 6 days – ca. 1 ppm in sterile buffer solution 

(30-day study)

ca. 9.2 days – 1mg ai/L in natural water 

228 days – 1.52 ml ai/L in sterile buffer 

solution (15-day study)

MRID 422451-28

MRID 469501-04

MRID 469501-05B

Photolysis half-life in soil 349 - 823 days MRID 469501-06C
7

Property Value Source

Aerobic soil metabolism half-life 84.5 days – at 0.1 ppm concentration

1600 days – at 10 ppm in loam

1059 days – at 10 ppm in sandy loam

120 days – at 0.13 ppm; Swiss loam

104 days – at 0.13 ppm; Swiss loam

165 (158) days – at 0.23 ppm; Swiss sandy 

loam

204 (187) days – at 0.23 ppm; Swiss 

sandy loam/loamy sand 

204 (198) days – at 0.23 ppm; French silty 

clay loam

433 (408) days – at ca. 0.1 ppm in CA loamy 

sand at 25 oC

533 days – at ca. 0.1 ppm in CA loamy sand 

at 25 oC

MRID 422451-31

MRID 422451-32D

MRID 422451-33D

MRID 469501-09

MRID 469501-10

MRID 469501-11

MRID 469501-12

MRID 469501-14

Anaerobic soil metabolism halflife947 days – at 10 ppm in loam MRID 422451-32

Aerobic aquatic metabolism halflife860 days (10 mg ai/L)

315 (330) days (nominal 0.1 kg ai/ha =0.17 

mg ai/L); Swiss pond water-silty clay loam 

sediment)

335 (301) days (0.17 mg ai/L; Swiss river 

water-sandy loam sediment)

565 days (0.04 mg ai/L)

MRID 422451-34 E

MRID 469501-16

MRID 469501-17

Anaerobic aquatic metabolism 

half-life 

1245 days (10mg ai/L)

370 days (433) (0.04 mg ai/L)

MRID 422451-34 E

MRID 469501-19

Terrestrial field dissipation halflife252 days - determined in the 0- to 3-inch 

depth – CA bare loamy sand

231 days – GA bare loamy sand (four 

applications of 0.13 lb ai/A)

139 days – CA bare plot of loam soil (four 

applications of 0.13 lb ai/A)

462 days – ND bare sandy clay loam

MRID 422451-40

MRID 469501-26

MRID 469501-27

MRID 469501-29 

Laboratory accumulation in fish

bioaccumulation factor 

(Lepomis macrochirus)

a depuration half-life

170x in edible tissues

570x nonedible tissues

330x for whole body

1 day 

MRID 422451-42

A

There was another adsorption/desorption study (MRID 422451-36) reviewed in which the test soils were autoclaved prior to conducting the 

study which could distort the mobility characteristic of difenoconazole, thus, the study results were not used for calculation of modeling input 

parameters. 

B

For modeling purposes, the longest half-life was used as it represents the most conservative scenario. However, there is considerable 

uncertainty in the photolysis half-lives because the duration of the studies was considerably shorter than the extrapolated half-life (MRIDs 

469501-05 and 469501-06). 

C The soil photolysis half-life under xenon light condition was recalculated to represent the conditions under natural sunlight intensity during 

30-day periods between June and September (104.7-246.9 W∙min/cm2), as a result, a range of half-lives was obtained.

D In those aerobic soil metabolism studies (MRID 422451-32 and MRID 422451-33) the test application rate was significantly higher than 

expected under registrant-proposed use condition for difenoconazole.

E

In those aquatic metabolism studies, the test application rates were significantly higher than expected under registrant-proposed use condition 

for difenoconazole.
8

6. Exposure Summary

6.1 Terrestrial Exposure

EECs were calculated based on the maximum single application rate (0.113 lb ai/A). EECs were 

calculated in T-REX (v 1.5.2)

3

(Table 4) and TerrPlant (v 1.2.2)3(Appendix 1).

Table 4. Terrestrial Food-Item Residue Estimates for Mammals and Birds for Proposed 

Foliar Applications of Difenoconazole

Size 

Class

(grams)

Dietary and Dose-Based EECs1

Short Grass Tall Grass Broadleaf 

Plants

Fruits/Pods/

Seeds Arthropods

Mammals

Dose-Based EECs

15 25.86 11.85 14.54 1.62 10.13

35 17.87 8.19 10.05 1.12 6.99

1000 4.14 1.90 2.33 0.26 1.62

Dietary-Based EECs2

NA 27.12 12.43 15.26 1.7 10.62

Avian

Dose-Based EECs

20 30.89 14.16 17.37 1.93 12.10

100 17.61 8.07 9.91 1.10 6.90

1000 7.89 3.61 4.44 0.49 3.09

Dietary-Based EECs2

NA 27.12 12.43 15.26 1.7 10.62

1

0.113 lb ai/A

2

Size class not used for dietary EECs

6.2 Aquatic Exposure

The Tier II aquatic assessment was performed using PRZM (v3.12.2)/EXAMS (v. 2.98.04.06) 

modeling with the standard pond scenario. Detailed descriptions of these models can be found in 

a previous assessment (DP377719, 7/20/2010). Separate EECs were calculated for 

difenoconazole and its total toxic residues (TTR). Difenoconazole-only EECs were used to 

assess risk when data were available that indicated that the major degradates were less toxic than 

difenoconazole (acute risk to fish and invertebrates). This approach is different than that used in 

recent risk assessments (DP377719, 7/20/2010 and DP378927+, 2/22/2011) which calculated 

TTR EECs for characterization of acute risk to fish and invertebrates due to a lack of toxicity

data at that time. As in those previous assessments, TTR EECs were used to characterize risk 

when guideline data were not available for the major degradates (aquatic plants and chronic risk 

to fish and invertebrates).

6.2.1 Exposure Estimates for Difenoconazole

 

3 www.epa.gov/oppefed1/models/terrestrial/index.htm
9

The PRZM/EXAMS input parameters for difenoconazole are shown in Table 5. Inputs are 

equivalent to those used in previous assessments (e.g., DP377719, 7/20/2010). Results of the 

PRZM/EXAMS modeling are in Table 6. The PRZM/EXAMS outputs are included in 

Appendix 2. 

Table 5. PRZM/EXAMS Chemical Specific Input Parameters for Difenoconazole

Parameter Input Value and Unit Source/Comments

Scenario ND Canola STD Only ND Canola Scenario is 

available for this use

Maximum single application rate

Foliar Application 0.113 lbs ai/A (0.127 kg ai/ha)

Inspire Label

(EPA Reg. No. 100-1262), 

Method of application

CAM = 2 Foliar Spray 

Product Label as above

Maximum number of applications 1(Foliar) Product Label as above

Application efficiency 0.99 (Ground Spray)

0.95 (Aerial Spray)

No chemigation scenario was 

modeled but assumed similar to 

ground application.

EFED Model Input Guidance, 

Version 2.1 (2009b) a

Spray drift 0.01 (Ground Spray)

0.05 (Aerial Spray)

EFED Model Input Guidance, 

Version 2.1 (2009b)

Application date and minimum 

interval between applications (days)

July 18th---

Henry’s Law constant 8.9 x 10-12 atm x m3/mol MRID 46515901

Hydrolysis Stable MRID 42245127

Aerobic soil metabolism(t1/2)

b

313 days MRIDs: 42245131, 46950109-12, 

and 46950114

Aerobic aquatic metabolism (t1/2)

c

556 days MRIDs: 46950116 & 46950117

Anaerobic aquatic metabolism (t1/2)

d

1110 days MRID 46950119

Aquatic photolysis t1/2 (days) eStable MRID 46950105

Vapor pressure 2.5 x 10-10 mm Hg (25 oC) MRID 46515901

Solubility in water 15 mg/L (25 oC) MRID 46515901

Molecular Weight 406.27 MRID 46950104

Partition coefficient Koc 5381 mL/g MRIDs: 42245135 and 46950121

a Guidance for Selecting Input Parameters in Modeling the Environmental Fate and Transport of Pesticides

(Version 2.1; Oct. 22, 2009)

b The 90% of the UCL of the mean metabolism half-life.

c The 90% of the UCL of the mean metabolism half-life of all available half-lives but those obtained for high test rate.

d At proposed application rate only one half-life was available, the half-life was multiplied by three (i.e., 3 x 370 days).

e Estimated half-life is beyond the duration of study, thus considered stable.

Table 6. Estimated Environmental Concentrations (EECs) of Difenoconazole for Surface 

Water Based on Selected Crop Scenarios
10

Water Source 

(model)

Use

Scenario

(rate and interval)

Application 

Method

Peak EEC 

(μg/L)

21-Day

EEC (μg/L)

60-Day

EEC

(μg/L)

Concentrations (EECs) of Difenoconazole only

Surface Water 

(PRZM/EXAMS)

ND Canola STD

(1 application @ 0.113 lb 

ai/A)

Aerial 1.00 0.83 0.77

Ground 0.57 0.49 0.45

Concentrations (EECs) of Total Toxic Residues (Difenoconazole and Its Degradates)

Surface Water 

(GENEEC)

ND Canola STD

(1 application @ 0.113 lb 

ai/A)

Aerial 3.03 2.95 2.80

Ground 2.74 2.67 2.53

6.2.2 Exposure Estimates for the Total Toxic Residues of Difenoconazole 

Difenoconazole and its major degradates (1,2,4-triazole and its conjugates triazole alanine and 

triazole acetic acid), are assumed to be persistent in the environment with a low soil partition 

coefficient in all modeled media. In general, for persistent chemicals, yearly EECs of 

PRZM/EXAMS are not independent and are correlated to the previous year’s concentration in 

PRZM/EXAMS output. Therefore, the GENEEC model was used to estimate EECs for TTR 

(difenoconazole + 1,2,4-triazole + triazole acetic acid) to characterize potential effects on aquatic 

organisms. For the TTR GENEEC modeling, all input parameters were the same as listed in 

Table 5 with the exception of the photolysis half-life, the aerobic soil metabolism half-life, and 

the aerobic and anaerobic aquatic metabolism half-lives which were assumed to be zero (stable). 

A soil partition coefficient (Koc) of 1000 mg/L was also assumed for the total toxic residues. 

The TTR EECs for the proposed canola use are listed in Table 6. The GENEEC output file is

located in Appendix 2. 

6.2.3 Monitoring Data 

The U.S. Geological Survey’s National Water Quality Assessment program (NAWQA) has 

conducted some monitoring for difenoconazole.

4

Twelve surface water and sediment samples 

collected in California and Georgia were analyzed for difenoconazole. Difenoconazole was 

detected in only one of twelve surface water samples; the reported maximum concentration (18.2

ng/L) was detected in California. Difenoconazole was not detected in sediment samples (limit of 

quantitation (LOQ) was 0.6 μg/kg-sediment). NAQWA monitoring data were not targeted 

specifically to difenoconazole use areas or during times of known difenoconazole use; thus, the 

dataset may not reflect peak difenoconazole concentrations that may occur in surface waters

when runoff events occur shortly after difenoconazole is applied. 

Monitoring data for surface water, groundwater, and sediment from the California Department of 

Pesticide Regulation (CDPR) were searched on October 23, 20135. Difenoconazole monitoring 

data were not available.

 

4

http://water.usgs.gov/nawqa/pnsp/

5

http://www.cdpr.ca.gov/docs/emon/ehap.htm
11

7. Ecological Effects Summary

Toxicity data are summarized in Tables 7, 8, 9, and 10 (for details see D377719, 7/20/2010). 

Additional toxicity data has been reviewed since the last risk assessment (D402993, 8/29/2012),

is briefly summarized below, and is incorporated into the summary tables below as applicable.

The recently reviewed difenoconazole studies addressed acute and chronic toxicity to freshwater 

fish (MRID 48453201 and 48453205), avian acute oral toxicity (MRID 48453202), and 

terrestrial plant toxicity (MRID 48453203 and 48453204). The 1,2,4-triazole studies addressed

acute toxicity to freshwater fish (MRID 48474301) and freshwater invertebrates (MRID 

48453206). The triazole acetic acid studies addressed acute toxicity to freshwater fish (MRID 

48453209) and freshwater invertebrates (MRID 48453208). The available studies with 1,2,4-

triazole and triazole acetic acid indicate that they are less acutely toxic than difenoconazole to 

freshwater fish and invertebrates.

The acute oral toxicity of difenoconazole to canary study (MRID 48453202) was a limit test 

resulting in an LD50 > 2000 mg ai/kg bw. A single mortality was observed at the treatment rate; 

however, it was unclear if the death was treatment related or due solely to the observed abnormal 

heart function in that bird. No other effects were noted. The study is acceptable.

The 96-hr LC50 for fathead minnow was 1.8 mg ai/L (MRID 48453201). Sublethal effects 

(lethargy, loss of equilibrium, lying on the bottom, and floating at the surface) were observed at 

treatment concentrations 1.3 mg ai/L and higher. The observed NOAEC was 0.66 mg ai/L. The 

study is acceptable.

The freshwater fish (fathead minnow) life cycle study (MRID 48453205) resulted in a NOAEC = 

1.9 μg ai/L. The LOAEC was 3.7 μg ai/L based on reduced male length of the F0-generation 12 

weeks post-hatch. Additional endpoints were effected at higher test concentrations: F0 

generation length at 4 weeks, 8 weeks, and 12 weeks (female); F0 generation weight at 12 weeks 

(male and female); and F1 generation length at 8 weeks. This study is acceptable.

An acute-to-chronic ratio (ACR) of fathead minnow toxicity data (MRID 48453201 and 

48453205) was used to estimate chronic toxicity to rainbow trout because rainbow trout was the 

most sensitive species on an acute basis. Likewise, an ACR was used with fathead minnow data 

(acute and chronic) and sheepshead minnow data (acute) to estimate chronic toxicity to 

marine/estuarine fish. 

The recently submitted terrestrial plant studies (MRID 48453203 and 48453204) showed no 

statistically significant effects at the limit test concentration (0.111/0.112 lb ai/A for seedling 

emergence and 0.123 lb ai/A for vegetative vigor). However, in the seedling emergence study, 

the lack of statistical significance for three of the dicots (lettuce, soybean, and sugar beet) may

have been due to high experimental variability and the magnitude of some of the effects is 

considered potentially biologically significant. Lettuce showed reduced emergence (21%), 

survival (17%), shoot length (26%), and dry weight (24%). Soybean showed reduced shoot 

length (23%). Sugar beet showed reduced survival (18%). Additionally, there was poor 

emergence (63%) of the sugar beet control seeds; seedlings did not meet the minimum 

acceptable USDA control germination standard for this species (70%). These studies are 

supplemental because the limit test concentration is below the maximum labeled single rate 

(currently 0.26 lb ai/A, golf course turf). 
12

Table 7. Summary of Most Sensitive Aquatic Toxicity Endpoints for Difenoconazole

Type of Study Species Toxicity Value 

(μg ai/L) MRID

Acute – Freshwater 

Fish

Rainbow trout

(Oncorhynchus mykiss)

96-hr LC50 = 810 42245107

Chronic – Freshwater 

Fish

Fathead minnow

(Pimephales promelas)

NOAEC = 1.9

LOAEC = 3.7 based on reduced male 

length of F0-generation 12 weeks posthatch

48453205

Rainbow trout

(Oncorhynchus mykiss)

NOAEC = 0.86

Value used for risk assessment. Based on 

acute-to-chronic ratio of fathead minnow 

data to rainbow trout data (the most 

acutely sensitive species).1

-

Acute – Freshwater 

Invertebrate

Water flea 

(Daphnia magna)

48-hr EC50 = 770 42245110

Chronic – Freshwater 

Invertebrate

Water flea

(Daphnia magna)

NOAEC = 5.6

LOAEC = 13.0 based on reduced number 

of young/adult/reproductive day and adult 

length

42245114

Chronic – Freshwater 

Invertebrate 

(Sediment)

Midge

(Chironomus riparius)

EC50 >50 mg ai/kg-sediment (nominal)

NOAEC = 5 mg ai/kg-sediment (nominal) 

based on emergence rate & development 

rate

47648601

Acute –

Estuarine/Marine 

Fish

Sheepshead minnow

(Cyprinodon variegates)

96-hr LC50 = 819 42245112

Chronic –

Estuarine/Marine 

Fish

Sheepshead minnow

(Cyprinodon variegates)

NOAEC = 0.86

Based on acute-to-chronic ratio of fathead 

minnow data to sheepshead minnow data.1

-

Acute –

Estuarine/Marine 

Mollusk

Eastern oyster

(Crassostrea virginica)

96-hr EC50 = 424 42906701

Acute –

Estuarine/Marine 

Invertebrate

Mysid shrimp

(Americamysis bahia)

96-hr LC50 = 150 42245111

Chronic –

Estuarine/Marine 

Invertebrate

Mysid shrimp

(Americamysis bahia)

NOAEC < 0.115

LOAEC = 0.115 based on reduced number 

of young/adult/reproductive day

46950133

Vascular Plant –

Freshwater

Duckweed

(Lemna gibba)

EC50 = 1900

EC05 = 110

NOAEC < 110

LOAEC ≤ 100 based on reduced frond 

number

46920504

Non-vascular Plant –

Freshwater

Diatom

(Navicula pelliculosa)

EC50 = 98

NOAEC = 53

LOAEC = 150 based on reduced cell 

density

46920508

1 Acute toxicity to fathead minnow: LC50 = 1800 μg ai/L (MRID 48453201)

Table 8. Summary of Most Sensitive Terrestrial Toxicity Endpoints for Difenoconazole

Type of Study Species Toxicity Value MRID
13

Type of Study Species Toxicity Value MRID

Acute – Avian Oral 

Dose

Canary

(Serinus canaria)

LD50 > 2000 mg ai/kg-bw 48453202

Acute – Avian 

Dietary

Bobwhite quail

(Colinus virginianus)

LC50 = 4579 mg ai/kg-diet 42245103

Chronic – Avian 

Dietary

Bobwhite quail

(Colinus virginianus)

NOAEC = 21.9 mg ai/kg-diet

LOAEC = 108 mg ai/kg-diet based on 

reduction in hatchling body weight 

46950202

Acute – Mammalian 

Oral Dose

Laboratory rat

(Rattus norvegicus)

LD50 = 1453 mg ai/kg-bw 42090006

Two Generation 

Reproduction –

Mammalian

Laboratory rat

(Rattus norvegicus)

NOAEC = 25 mg ai/kg-diet

LOAEC = 250 mg ai/kg-diet 42090018

Acute – Contact Honey bee

(Apis mellifera)

LD50 >100 μg ai/bee 42245124

Acute – Contact Earthworm LC50 > 610 mg ai/kg-dw 42245125

Terrestrial Plants

Corn, Onion, Ryegrass, 

Wheat, Radish, Cabbage, 

Lettuce, Sugar beet, 

Soybean, and Tomato

Seedling Emergence

EC25 > 0.111/0.112 lb ai/A1

NOAEC ≥ 0.111/0.112 lb ai/A1,2

Vegetative Vigor

EC25 > 0.123 lb ai/A

NOAEC ≥ 0.123 lb ai/A

48453203

48453204

1

Some species were exposed to 0.111 lb ai/A and others were exposed to 0.112 lb ai/A.

2 Effects at 0.11 lb ai/A on lettuce, sugar beet, and soybean were considered biologically significant. Lettuce 

showed reduced emergence (21%), survival (17%), shoot length (26%), and dry weight (24%). Soybean showed 

reduced shoot length (23%). Sugar beet showed reduced survival (18%).

1,2,4-triazole

The recently reviewed studies with 1,2,4-triazole indicate that it is less acutely toxic than 

difenoconazole to freshwater fish and invertebrates. Both studies are acceptable. The 96-hr 

LC50 = 498 mg ai/L for rainbow trout (MRID 48474301). Sublethal effects (swimming 

behavior, loss of equilibrium, respiratory function, and pigmentation) were observed in treatment 

groups ≥ 132 mg ai/L. The 48-hr EC50 > 98.1 mg ai/L for daphnia (MRID 48453206); no 

mortality or sublethal effects were reported.

A supplemental study (MRID 45880405) evaluated the effects of 1,2,4-triazole on the growth of 

juvenile rainbow trout (Oncorhynchus mykiss). This 28-day study yielded an LC50 > 100 mg/L. 

Growth was not affected at concentrations up to 100 mg/L. However, significant sublethal 

effects were observed; from day 23 to day 28, three to five fish were observed to be inactive or 

have abnormally low activity, to have labored respiration, and to be lying inactive at the bottom 

of the aquarium in each of the 10, 32, and 100 mg/L test concentrations. The NOAEC for these 

sublethal effects was 3.2 mg/L. The data are not comparable to early life stage (ELS) studies 

submitted on difenoconazole. ELS studies are designed to examine effects such as hatching 

success and larval survival in addition to growth of early life stages. ELS studies may or may

not show greater toxicity than juvenile growth studies.

A registrant submitted data summary (MRID 45342701) presented data from several submitted 

studies including data on birds (MRID 45284015), earthworms (MRID 45297201), daphnids 

(MRID 00133381), fish (MRID 45284017), and algae (MRID 00133382). The data suggest that 
14

1,2,4-triazole may be less toxic than difenoconazole to fish, daphnids, and aquatic plants, but 

more toxic to earthworms. However, these studies were typically non-GLP compliant studies or 

journal articles and are not considered to be reliable to make definitive conclusions regarding the 

toxicity of 1,2,4-triazole. In some cases, the available study reports are not legible or the study 

designs were markedly different than guideline protocols such that they provided little useful 

information. Therefore, these data are not used in the risk assessment.

Ecological Structure Activity Relationship (ECOSAR) methods6 were used to predict 1,2,4-

triazole toxicity to aquatic non-vascular plants and chronic toxicity to fish and invertebrates 

based on its structural similarity to chemicals for which aquatic toxicity data are known. A

comparison of 1,2,4-triazole ECOSAR estimates to experimentally derived difenoconazole 

toxicity endpoints suggests that 1,2,4-triazole is not more toxic than difenoconazole to aquatic 

non-vascular plants, fish (chronic basis), or aquatic freshwater invertebrates (chronic basis). 

There is a reasonable confidence in the ECOSAR estimates (at least for fish) given that the 

ECOSAR estimate of acute toxicity to fish is similar to toxicity observed in available studies.

Table 9. Summary of Most Sensitive Aquatic Toxicity Endpoints for 1,2,4-Triazole

Type of Study Species Toxicity Value 

(μg ai/L) MRID

Acute – Freshwater 

Fish

Rainbow trout

(Oncorhynchus mykiss)

96-hr LC50 = 498,000 48474301

Acute – Freshwater 

Invertebrate

Water flea 

(Daphnia magna)

48-hr EC50 > 98,100 48453206

Triazole Acetic Acid

The recently reviewed studies with triazole acetic acid indicate that it is less acutely toxic than 

difenoconazole to freshwater fish and invertebrates. Both studies are acceptable. The 96-hr 

LC50 > 101 mg ai/L for rainbow trout (MRID 48453209); no mortality or sublethal effects were 

reported. The 48-hr EC50 > 108 mg ai/L for daphnia (MRID 48453208); no mortality or 

sublethal effects were reported.

A comparison of triazole acetic acid ECOSAR estimates to experimentally derived 

difenoconazole toxicity endpoints suggests that triazole acetic acid is not more toxic than

difenoconazole to aquatic non-vascular plants, fish (chronic basis), or aquatic freshwater 

invertebrates (chronic basis). There is no basis for judging confidence in the ECOSAR estimates 

because the ECOSAR estimates for acute toxicity to fish and invertebrates are substantially

greater (less toxic) than the non-definitive endpoints observed in the available acute toxicity

studies.

Table 10. Summary of Most Sensitive Aquatic Toxicity Endpoints for Triazole Acetic Acid

Type of Study Species Toxicity Value 

(μg ai/L) MRID

Acute – Freshwater 

Fish

Rainbow trout

(Oncorhynchus mykiss)

96-hr LC50 > 101,000 48453209

Acute – Freshwater Water flea 48-hr EC50 > 108,000 48453208

 

6 ECOSAR predictive software is available publically though the Epi SuiteTM program. 

http://www.epa.gov/oppt/exposure/pubs/episuite.htm 
15

Type of Study Species Toxicity Value 

(μg ai/L) MRID

Invertebrate (Daphnia magna)

7.1 Incidents

Reviews were conducted of the Ecological Incident Information System (EIIS, version 2.1.1)7, 

the Agency’s Aggregated Incidents Reports database, and the Avian Incident Monitoring System 

(AIMS)8on October 28, 2013. No incidents were reported in EIIS or AIMS. Ten minor plant 

damage incidents were reported for one difenoconazole product (Revus Top) in the aggregated 

incident database. The Revus Top label indicates that it is a dual ai product containing 

mandipropamid as well as difenoconazole. No incidents were reported for the proposed product 

(Inspire®) which does not contain mandipropamid.

8. Ecological Risks Summary

8.1 Potential Risks of Difenoconazole Exposure to Terrestrial Organisms

The calculated EECs account for 1,2,4-triazole and triazole acetic acid because the proposed use 

is for a single application. If the degradates are substantially more toxic than difenoconazole 

then this risk assessment could underestimate potential risks. 

8.1.1 Birds

There is not an acute risk concern for birds from the proposed use. The acute listed LOC (0.1) 

was not exceeded on an acute dietary basis (RQs < 0.01). Acute dose-based RQs were not 

calculated because the available studies resulted in non-definitive endpoints. However, a 

conservative comparison can be made between the EEC and the highest concentration tested in 

the toxicity studies. EECs are less than 1/10th of the highest dose tested in these studies (i.e., 

size-class adjusted LD50); therefore acute dose-based risk is expected to be low from the 

proposed use. 

The chronic LOC (1.0) was exceeded for birds consuming short grass (RQ = 1.24) but not any

other food items (Table 11). The chronic risk concern assumes that birds consume 100% of 

their diet as short grass. There is a chronic risk concern for birds (listed and non-listed species) 

from the proposed use.

Table 11. Summary of Avian Acute and Chronic Risk Quotients for Proposed 

Difenoconazole Foliar Spray Applications

Feeding Category Acute Dietary-based RQs Chronic Dietary-based RQs

Short grass <0.01 1.24

Tall grass <0.01 0.57

Broadleaf plants/small insects <0.01 0.70

 

7

http://www.epa.gov/espp/consultation/ecorisk-overview.pdf

8

http://www.abcbirds.org/abcprograms/policy/toxins/aims/aims/index.cfm
16

Feeding Category Acute Dietary-based RQs Chronic Dietary-based RQs

Fruits/pods/seeds/large insects <0.01 0.08

Arthropods <0.01 0.49

BOLD exceeds chronic LOC (1.0).

8.1.2 Mammals

There is not an acute risk concern for mammals from the proposed use (RQs < 0.01). The 

chronic LOC (1.0) was exceeded for all mammal size-classes consuming short grass, tall grass, 

broadleaf plants/small insects, and arthropods (Table 12). Chronic dietary-based RQs exceed 

the LOC for mammals consuming short grass. There is a chronic risk concern for mammals 

(listed and non-listed species) from the proposed use.

Table 12. Summary of Mammalian Acute and Chronic Risk Quotients for Proposed 

Difenoconazole Foliar Spray Applications

Risk Quotients Based

on Kenaga

Upper Bound EEC

Dose-Based RQs Chronic 

DietaryBased RQs15 g 35 g 1000 g

Acute Chronic Acute Chronic Acute Chronic

Short grass <0.01 9.41 <0.01 8.04 <0.01 4.31 1.08

Tall grass <0.01 4.31 <0.01 3.68 <0.01 1.98 0.50

Broadleaf plants/small 

insects <0.01 5.29 <0.01 4.52 <0.01 2.42 0.61

Fruits/pods/seeds/lg 

insects <0.01 0.59 <0.01 0.50 <0.01 0.27 0.07

Arthropods <0.01 3.69 <0.01 3.15 <0.01 1.69 0.42

BOLD exceeds chronic LOC (1.0).

8.1.3 Terrestrial Plants

The LOC (1.0) was not exceeded for monocots (non-listed or listed species) located in dry or 

semi-aquatic locations (RQs < 0.1) or from spray drift (RQs = 0.25). There is uncertainty 

regarding the toxicity to dicots even though no statistical significance was detected in the 

seedling emergence study. The lack of statistical significance for three of the dicots (lettuce, 

soybean, and sugar beet) may have been due to the high experimental variability and the 

magnitude of some of the effects is considered potentially biologically significant. Lettuce 

showed reduced emergence (21%), survival (17%), shoot length (26%), and dry weight (24%). 

Soybean showed reduced shoot length (23%). Sugar beet showed reduced survival (18%). There 

is not a risk concern for non-listed dicots assuming that the EC25 = 0.111/0.112 lb ai/A (the test 

concentration9); this may be a reasonable assumption given that the maximum observed effect 

was 26%. Risk to listed dicot species cannot be precluded given the magnitude of the observed 

inhibition at 0.111 lb ai/A for lettuce, soybean, and sugar beet. The NOAEC would need to be 

about four times lower than 0.111 lb ai/A for a risk concern to semi-aquatic listed dicots. Tier II 

testing of lettuce, soybean, and sugar beet would reduce uncertainty for listed dicot species. At 

 

9

Some species were exposed to 0.111 lb ai/A and others were exposed to 0.112 lb ai/A.
17

this time, a risk concern cannot be precluded for listed dicots. There is not a risk concern for

monocots from the proposed use.

8.1.4 Terrestrial Invertebrates

There is not an acute contact risk concern for bees from the proposed use. The acute contactbased RQ was not calculated because the available study resulted in a non-definitive endpoint. 

However, a conservative comparison can be made between the EEC and the highest 

concentration tested in the toxicity study. The EEC (0.3051 μg ai/bee)10 is less than 1/2.511 of 

the non-definitive LD50 (>100 μg ai/bee).

Acute contact testing of difenoconazole on earthworms resulted in an LC50 greater than 610 mg 

ai/kg-dw of substrate, as survival was >95% in all treatment groups. No significant differences 

were detected in any treatment groups relative to the negative control for survival or weight 

change. The NOAEC and LOAEC were 610 and > 610 mg ai/kg-dw of substrate based on 

survival and weight change. A previous assessment presented an EEC in soil of 0.28 mg/kg-dry

soil for use on ornamentals (0.56 lb ai/A/season) which is over three orders of magnitude below 

the earthworm NOAEC; therefore, there was not a risk concern (see previous assessment for 

calculations; DP333319, 7/12/ 2007). There is no risk concern for earthworms from the 

proposed use given that the proposed application rate is lower than the seasonal application rate 

for ornamentals.

8.2 Potential Risks of Difenoconazole Exposure to Aquatic Organisms

Assessment of acute risk to fish and invertebrates was based on difenoconazole EECs because 

available data indicate that 1,2,4-triazole and triazole acetic acid are less acutely toxic than 

difenoconazole. 

TTR (difenoconazole + 1,2,4-triazole + triazole acetic acid) EECs were calculated for other 

endpoints due to a lack of guideline toxicity data. This risk assessment may over or 

underestimate potential risk given the lack of toxicity data. 1,2,4-triazole and triazole acetic acid 

are assumed equal in toxicity to difenoconazole in the absence of data. 

8.2.1 Fish

There is not an acute risk concern for fish from the proposed use. The acute listed-species LOC 

(0.05) was not exceeded for freshwater or estuarine/marine fish (RQs < 0.01). 

The chronic LOC (1.0) was exceeded for freshwater and estuarine/marine fish (RQ = 3.25). 

Given the lack of guideline toxicity data for the major degradates, a chronic risk concern for fish 

cannot be precluded for the proposed use.

ECOSAR estimates suggest that both degradates are not more toxic than difenoconazole and are 

potentially less toxic. There would not be a chronic risk concern for fish if the degradates are 

 

10

 The EEC = 0.113 lb ai/A * 2.7 μg ai/bee per lb ai/A = 0.3051 μg ai/bee

11 The LOC for bees is 0.4
18

less toxic than difenoconazole (RQ = 0.89 based on a 60-day difenoconazole-only EEC = 0.77 

μg/L); therefore, guideline chronic fish studies with the major degradates (1,2,4-triazole and 

triazole acetic acid) would be useful for refining the risk conclusions if they demonstrate less 

toxicity than difenoconazole. 

Table 13. Acute Risk Quotients for Freshwater and Estuarine/Marine Fish Exposed from 

the Proposed Difenoconazole Use (Difenoconazole EEC)

Peak 

EEC

(μg/L)

Freshwater

Acute RQ

(LC50 = 810 μg/L)

Estuarine/Marine 

Acute RQ 

(LC50 = 819 μg/L)

1 < 0.01 < 0.01

Table 14. Chronic Risk Quotients for Freshwater and Estuarine/Marine Fish Exposed from 

the Proposed Difenoconazole Use (TTR EEC)

60-day EEC

(μg/L)

Freshwater and Estuarine/Marine Chronic RQ

(NOAEC = 0.86 μg/L)

2.8 3.25

BOLD exceeds chronic LOC (1.0).

8.2.2 Aquatic Invertebrates

There is not an acute risk concern for aquatic invertebrates from the proposed use. The acute 

listed-species LOC (0.05) was not exceeded for freshwater or estuarine/marine aquatic 

invertebrates (RQs < 0.01).

The chronic LOC (1.0) was not exceeded for freshwater invertebrates (RQ = 0.52); however, the 

LOC was exceeded for estuarine/marine invertebrates (RQ > 25.6). There is a chronic risk 

concern for aquatic invertebrates (listed and non-listed estuarine/marine species) from the 

proposed use.

Risk to benthic invertebrates was considered given the fate properties of difenoconazole. Risk 

was not assessed using the submitted chronic toxicity range-finding study (MRID 47648601) due 

to problems with the study design. Instead, risk to benthic invertebrates was considered using 

water column invertebrate data (Daphnia and Americamysis) as surrogates. Pore water 

difenoconazole concentrations were determined using PRZM/EXAMS12 (see Appendix 2) and 

are similar to water column concentrations. Given the similar EECs, risk conclusions for benthic 

invertebrates are the same as those for water column invertebrates; that is, there is a risk concern 

for benthic estuarine/marine invertebrates but not a risk concern for benthic freshwater 

invertebrates. The risk concern triggered for water column estuarine/marine species (Table 16)

is protective of estuarine/marine invertebrate species in general (i.e., there is a risk concern); 

however, the magnitude of the RQ associated with that concern is uncertain for both water 

column invertebrates (non-definitive endpoint) and benthic invertebrates (lack of data). There is 

more uncertainty in the risk conclusions for freshwater invertebrates given that benthic species 

may be more sensitive than water column species.

 

12 GENNEC currently does not provide porewater concentrations; therefore, difenoconazole-only EECs were 

calculated instead of TTR EECs for considering risk to benthic invertebrates.
19

Table 15. Acute Risk Quotients for Freshwater and Estuarine/Marine Invertebrates 

Exposed from the Proposed Difenoconazole Use (Difenoconazole EEC)

Peak 

EEC

(μg/L)

Freshwater

Acute RQ

(LC50 = 770 μg/L)

Estuarine/

Marine Acute RQ

(LC50 = 150 μg/L)

1 < 0.01 < 0.01

Table 16. Chronic Risk Quotients for Freshwater and Estuarine/Marine Invertebrates 

Exposed from the Proposed Difenoconazole Use (TTR EEC)

21-day EEC

(μg/L)

Freshwater Chronic RQ

(NOAEC = 5.6 μg/L)

Estuarine/Marine Chronic RQ

(NOAEC <0.115 μg/L)

2.95 0.52 >25.6

BOLD exceeds chronic LOC (1.0).

8.2.3 Aquatic Plants

There is not a risk concern for aquatic plants from the proposed use based on available 

information. There were no LOC exceedances for listed or non-listed species (Table 17). There 

is some uncertainty about risk to non-vascular aquatic plants because an acceptable study with 

blue green algae is not available. There are not currently any listed non-vascular plants so the 

uncertainty is for non-listed species. Blue-green algae would need to be about 33x more 

sensitive than Navicula pelliculosa to exceed the LOC (non-listed species).

Table 17. Risk Quotients for Aquatic Plants Exposed to Difenoconazole from the Proposed 

Difenoconazole Use (TTR EEC) 

Peak EEC

(μg/L)

Vascular Plant 

Non-listed RQ

(EC50 = 1900 μg/L)

Vascular Plant

Listed RQ

(EC05 = 110 μg/L)

Non-vascular Plant

Non-listed RQ

(EC50 = 98 μg/L)

Non-vascular Plant

Listed RQ

(NOAEC = 53 μg/L)

3.03 0.0016 0.0275 0.0309 0.0572

8.3 Risk Summary

The primary risk concerns from the proposed use are for chronically exposed listed and nonlisted species of aquatic invertebrates (estuarine/marine), fish, birds, and mammals. In addition,

a risk concern cannot be precluded for terrestrial dicots (listed species) based on the available 

data.
20

Appendix 1: TerrPlant Output

Table 1. Chemical Identity.

Chemical Name Difenoconazole

PC code

Use Canola

Application Method Aerial

Application Form 

Solubility in Water 

(ppm) 15

Table 2. Input parameters used to derive EECs.

Input Parameter Symbol Value Units

Application Rate A 0.113

Incorporation I 1 none

Runoff Fraction R 0.02 none

Drift Fraction D 0.05 none

Table 3. EECs for Difenoconazole. Units in .

Description Equation EEC

Runoff to dry areas (A/I)*R 0.00226

Runoff to semi-aquatic areas (A/I)*R*10 0.0226

Spray drift A*D 0.00565

Total for dry areas ((A/I)*R)+(A*D) 0.00791

Total for semi-aquatic areas ((A/I)*R*10)+(A*D) 0.02825

Table 4. Plant survival and growth data used for RQ derivation. Units are in .

Seedling Emergence Vegetative Vigor

Plant type EC25 NOAEC EC25 NOAEC 

Monocot 0.111 0.111 0.123 0.123

Dicot 0.123 0.123

Table 5. RQ values for plants in dry and semi-aquatic areas exposed to Difenoconazole through 

runoff and/or spray drift.*

Plant Type Listed Status Dry Semi-Aquatic Spray Drift

Monocot non-listed <0.1 0.25 <0.1

Monocot listed <0.1 0.25 <0.1

Dicot non-listed #DIV/0! #DIV/0! <0.1

Dicot listed #DIV/0! #DIV/0! #DIV/0!

*If RQ > 1.0, the LOC is exceeded, resulting in potential for risk to that plant group.
21

Appendix 2: PRZM/EXAMS and GENEEC Outputs

Example Output of PRZM/EXAMS for Surface water (Aerial Application)

stored as NDConla_E_A.out

Chemical: Difenoconazole

PRZM environment: NDcanolaSTD.txt, modified Tueday, 29 May 2007 at 13:59:22

EXAMS environment: pond298.exv, modified Tueday, 26 August 2008 at 06:14:08

Metfile: w24013.dvf, modified Tueday, 26 August 2008 at 06:15:40

Water segment concentrations (ppb)

Year Peak 96 hr 21 Day 60 Day 90 Day Yearly

1961 0.31 0.26 0.15 0.08 0.07 0.02

1962 0.36 0.31 0.19 0.13 0.11 0.07

1963 0.42 0.36 0.28 0.21 0.19 0.13

1964 0.49 0.44 0.34 0.29 0.28 0.21

1965 0.56 0.51 0.41 0.34 0.32 0.28

1966 0.60 0.55 0.43 0.37 0.36 0.31

1967 0.64 0.59 0.47 0.40 0.39 0.35

1968 0.66 0.61 0.49 0.45 0.44 0.38

1969 0.70 0.65 0.53 0.46 0.44 0.41

1970 0.78 0.72 0.63 0.54 0.52 0.45

1971 0.93 0.86 0.71 0.63 0.61 0.52

1972 0.85 0.79 0.68 0.61 0.59 0.56

1973 0.84 0.79 0.68 0.62 0.61 0.56

1974 0.86 0.81 0.69 0.62 0.61 0.57

1975 0.88 0.83 0.72 0.65 0.65 0.60

1976 0.90 0.85 0.73 0.66 0.64 0.61

1977 0.91 0.85 0.74 0.67 0.66 0.62

1978 0.93 0.88 0.76 0.70 0.69 0.65

1979 0.97 0.91 0.79 0.72 0.70 0.67

1980 0.94 0.88 0.76 0.73 0.72 0.67

1981 0.96 0.92 0.81 0.73 0.71 0.68

1982 0.97 0.91 0.79 0.72 0.72 0.68

1983 0.97 0.92 0.80 0.73 0.73 0.70

1984 0.99 0.94 0.82 0.75 0.73 0.71

1985 0.99 0.93 0.82 0.77 0.75 0.71

1986 0.99 0.94 0.82 0.75 0.73 0.71

1987 1.27 1.17 0.97 0.88 0.85 0.74

1988 1.04 0.98 0.86 0.79 0.77 0.75

Sorted results

Prob. Peak 96 hr 21 Day 60 Day 90 Day Yearly
22

0.03 1.27 1.17 0.97 0.88 0.85 0.75

0.07 1.04 0.98 0.86 0.79 0.77 0.74

0.10 0.99 0.94 0.82 0.77 0.75 0.71

0.14 0.99 0.94 0.82 0.75 0.73 0.71

0.17 0.99 0.93 0.82 0.75 0.73 0.71

0.21 0.97 0.92 0.81 0.73 0.73 0.70

0.24 0.97 0.92 0.80 0.73 0.72 0.68

0.28 0.97 0.91 0.79 0.73 0.72 0.68

0.31 0.96 0.91 0.79 0.72 0.71 0.67

0.34 0.94 0.88 0.76 0.72 0.70 0.67

0.38 0.93 0.88 0.76 0.70 0.69 0.65

0.41 0.93 0.86 0.74 0.67 0.66 0.62

0.45 0.91 0.85 0.73 0.66 0.65 0.61

0.48 0.90 0.85 0.72 0.65 0.64 0.60

0.52 0.88 0.83 0.71 0.63 0.61 0.57

0.55 0.86 0.81 0.69 0.62 0.61 0.56

0.59 0.85 0.79 0.68 0.62 0.61 0.56

0.62 0.84 0.79 0.68 0.61 0.59 0.52

0.66 0.78 0.72 0.63 0.54 0.52 0.45

0.69 0.70 0.65 0.53 0.46 0.44 0.41

0.72 0.66 0.61 0.49 0.45 0.44 0.38

0.76 0.64 0.59 0.47 0.40 0.39 0.35

0.79 0.60 0.55 0.43 0.37 0.36 0.31

0.83 0.56 0.51 0.41 0.34 0.32 0.28

0.86 0.49 0.44 0.34 0.29 0.28 0.21

0.90 0.42 0.36 0.28 0.21 0.19 0.13

0.93 0.36 0.31 0.19 0.13 0.11 0.07

0.97 0.31 0.26 0.15 0.08 0.07 0.02

0.10 1.00 0.95 0.83 0.77 0.75 0.71

Average 

of yearly 

averages:

0.51

Inputs generated by pe5.pl - Novemeber 2006

Data used for this run:

Output File: NDConla_E_A

Metfile: w24013.dvf

PRZM 

scenario:

NDcanolaSTD.txt

EXAMS 

environm

ent file:

pond298.exv

Chemical 

Name:

Difenconazole

Descripti Variable Value Units Comments
23

on Name

Molecula

r weight

mwt 406.27 g/mol

Henry's 

Law 

Const.

henry 8.90E-12 atm-m^3/mol

Vapor 

Pressure

vapr 2.50E-10 torr

Solubility sol 15 mg/L

Kd Kd mg/L

Koc Koc 5381 mg/L

Photolysi

s half-life

kdp 0 days Half-life

Aerobic 

Aquatic 

Metabolis

m

kbacw 556 days Halfife

Anaerobi

c Aquatic 

Metabolis

m

kbacs 1110 days Halfife

Aerobic 

Soil 

Metabolis

m

asm 313 days Halfife

Hydrolysi

s:

pH 7 0 days Half-life

Method: CAM 2 integer See PRZM manual

Incorpora

tion 

Depth:

DEPI cm

Applicati

on Rate:

TAPP 0.127 kg/ha

Applicati

on 

Efficienc

y:

APPEFF 0.95 fraction

Spray 

Drift

DRFT 0.05 fraction of application rate applied to pond

Applicati

on Date

Date 18-07 dd/mm or dd/mmm or dd-mm or dd-mmm

Record 

17:

FILTRA

IPSCND 1

UPTKF

Record 

18:

PLVKRT

PLDKRT

FEXTRC 0.5

Flag for 

Index 

Res. Run

IR EPA 

Pond

Flag for 

runoff 

RUNOFF none none, monthly or total(average of entire run)
24

calc.

Example Output of PRZM/EXAMS for Porewater (Aerial Application)

stored as NDConla_E_Aben.out

Chemical: Difenconazole

PRZM environment: NDcanolaSTD.txt, modified Tueday, 29 May 2007 at 13:59:22

EXAMS environment: pond298.exv, modified Tueday, 26 August 2008 at 06:14:08

Metfile: w24013.dvf, modified Tueday, 26 August 2008 at 06:15:40

Benthic segment concentrations (ppb)

Year Peak 96 hr 21 Day 60 Day 90 Day Yearly

1961 0.04 0.04 0.04 0.04 0.04 0.02

1962 0.08 0.08 0.08 0.08 0.08 0.06

1963 0.15 0.15 0.15 0.15 0.15 0.11

1964 0.24 0.24 0.24 0.24 0.24 0.19

1965 0.28 0.28 0.28 0.28 0.28 0.25

1966 0.31 0.31 0.31 0.31 0.31 0.29

1967 0.34 0.34 0.34 0.34 0.34 0.32

1968 0.38 0.38 0.38 0.38 0.38 0.35

1969 0.40 0.40 0.40 0.40 0.40 0.38

1970 0.45 0.45 0.45 0.45 0.45 0.42

1971 0.54 0.54 0.54 0.54 0.54 0.47

1972 0.54 0.54 0.54 0.54 0.54 0.53

1973 0.55 0.55 0.55 0.55 0.54 0.53

1974 0.55 0.55 0.55 0.55 0.55 0.54

1975 0.59 0.59 0.59 0.59 0.58 0.56

1976 0.59 0.59 0.59 0.59 0.58 0.58

1977 0.60 0.60 0.60 0.60 0.60 0.58

1978 0.62 0.62 0.62 0.62 0.62 0.61

1979 0.64 0.64 0.64 0.64 0.64 0.62

1980 0.65 0.65 0.65 0.65 0.65 0.63

1981 0.65 0.65 0.65 0.65 0.65 0.64

1982 0.66 0.66 0.66 0.66 0.66 0.64

1983 0.67 0.67 0.67 0.67 0.67 0.65

1984 0.68 0.68 0.68 0.67 0.67 0.66

1985 0.68 0.68 0.68 0.68 0.68 0.66

1986 0.68 0.68 0.68 0.67 0.67 0.67

1987 0.75 0.75 0.75 0.74 0.74 0.68

1988 0.73 0.73 0.73 0.73 0.73 0.71

Sorted results

Prob. Peak 96 hr 21 Day 60 Day 90 Day Yearly

0.03 0.75 0.75 0.75 0.74 0.74 0.71

0.07 0.73 0.73 0.73 0.73 0.73 0.68
25

0.10 0.68 0.68 0.68 0.68 0.68 0.67

0.14 0.68 0.68 0.68 0.67 0.67 0.66

0.17 0.68 0.68 0.68 0.67 0.67 0.66

0.21 0.67 0.67 0.67 0.67 0.67 0.65

0.24 0.66 0.66 0.66 0.66 0.66 0.64

0.28 0.65 0.65 0.65 0.65 0.65 0.64

0.31 0.65 0.65 0.65 0.65 0.65 0.63

0.34 0.64 0.64 0.64 0.64 0.64 0.62

0.38 0.62 0.62 0.62 0.62 0.62 0.61

0.41 0.60 0.60 0.60 0.60 0.60 0.58

0.45 0.59 0.59 0.59 0.59 0.58 0.58

0.48 0.59 0.59 0.59 0.59 0.58 0.56

0.52 0.55 0.55 0.55 0.55 0.55 0.54

0.55 0.55 0.55 0.55 0.55 0.54 0.53

0.59 0.54 0.54 0.54 0.54 0.54 0.53

0.62 0.54 0.54 0.54 0.54 0.54 0.47

0.66 0.45 0.45 0.45 0.45 0.45 0.42

0.69 0.40 0.40 0.40 0.40 0.40 0.38

0.72 0.38 0.38 0.38 0.38 0.38 0.35

0.76 0.34 0.34 0.34 0.34 0.34 0.32

0.79 0.31 0.31 0.31 0.31 0.31 0.29

0.83 0.28 0.28 0.28 0.28 0.28 0.25

0.86 0.24 0.24 0.24 0.24 0.24 0.19

0.90 0.15 0.15 0.15 0.15 0.15 0.11

0.93 0.08 0.08 0.08 0.08 0.08 0.06

0.97 0.04 0.04 0.04 0.04 0.04 0.02

0.10 0.69 0.69 0.69 0.69 0.68 0.67

Average 

of yearly 

averages:

0.48

Inputs generated by pe5.pl - Novemeber 2006

Data used for this run:

Output File: NDConla_E_A

Metfile: w24013.dvf

PRZM 

scenario:

NDcanolaSTD.txt

EXAMS 

environm

ent file:

pond298.exv

Chemical 

Name:

Difenconazole

Descripti

on

Variable 

Name

Value Units Comments

Molecula mwt 406.27 g/mol
26

r weight

Henry's 

Law 

Const.

henry 8.90E-12 atm-m^3/mol

Vapor 

Pressure

vapr 2.50E-10 torr

Solubility sol 15 mg/L

Kd Kd mg/L

Koc Koc 5381 mg/L

Photolysi

s half-life

kdp 0 days Half-life

Aerobic 

Aquatic 

Metabolis

m

kbacw 556 days Halfife

Anaerobi

c Aquatic 

Metabolis

m

kbacs 1110 days Halfife

Aerobic 

Soil 

Metabolis

m

asm 313 days Halfife

Hydrolysi

s:

pH 7 0 days Half-life

Method: CAM 2 integer See PRZM manual

Incorpora

tion 

Depth:

DEPI cm

Applicati

on Rate:

TAPP 0.127 kg/ha

Applicati

on 

Efficienc

y:

APPEFF 0.95 fraction

Spray 

Drift

DRFT 0.05 fraction of application rate applied to pond

Applicati

on Date

Date 18-07 dd/mm or dd/mmm or dd-mm or dd-mmm

Record 

17:

FILTRA

IPSCND 1

UPTKF

Record 

18:

PLVKRT

PLDKRT

FEXTRC 0.5

Flag for 

Index 

Res. Run

IR EPA 

Pond

Flag for 

runoff 

calc.

RUNOFF none none, monthly or total(average of entire run)
27

Example Output of GENEEC

Aerial Application

RUN No. 1 FOR Difenoconazole ON Oilseed * INPUT VALUES * 

 --------------------------------------------------------------------

 RATE (#/AC) No.APPS & SOIL SOLUBIL APPL TYPE NO-SPRAY INCORP

 ONE(MULT) INTERVAL Koc (PPM ) (%DRIFT) (FT) (IN)

 --------------------------------------------------------------------

 .113( .113) 1 1 1000.0 15.0 AERL_B( 13.0) .0 .0

 FIELD AND STANDARD POND HALFLIFE VALUES (DAYS) 

 --------------------------------------------------------------------

 METABOLIC DAYS UNTIL HYDROLYSIS PHOTOLYSIS METABOLIC COMBINED

 (FIELD) RAIN/RUNOFF (POND) (POND-EFF) (POND) (POND) 

 --------------------------------------------------------------------

 .00 2 N/A .00- .00 .00 .00

 GENERIC EECs (IN MICROGRAMS/LITER (PPB)) Version 2.0 Aug 1, 2001

 --------------------------------------------------------------------

 PEAK MAX 4 DAY MAX 21 DAY MAX 60 DAY MAX 90 DAY

 GEEC AVG GEEC AVG GEEC AVG GEEC AVG GEEC

 --------------------------------------------------------------------

 3.03 3.01 2.95 2.80 2.70

Ground Application

RUN No. 2 FOR Difenconazole ON Canola * INPUT VALUES * 

 --------------------------------------------------------------------

 RATE (#/AC) No.APPS & SOIL SOLUBIL APPL TYPE NO-SPRAY INCORP

 ONE(MULT) INTERVAL Koc (PPM ) (%DRIFT) (FT) (IN)

 --------------------------------------------------------------------

 .113( .113) 1 1 1000.0 15.0 GRHIFI( 6.6) .0 .0

 FIELD AND STANDARD POND HALFLIFE VALUES (DAYS) 

 --------------------------------------------------------------------

 METABOLIC DAYS UNTIL HYDROLYSIS PHOTOLYSIS METABOLIC COMBINED

 (FIELD) RAIN/RUNOFF (POND) (POND-EFF) (POND) (POND) 

 --------------------------------------------------------------------

 .00 2 N/A .00- .00 .00 .00

 GENERIC EECs (IN MICROGRAMS/LITER (PPB)) Version 2.0 Aug 1, 2001

 --------------------------------------------------------------------

 PEAK MAX 4 DAY MAX 21 DAY MAX 60 DAY MAX 90 DAY

 GEEC AVG GEEC AVG GEEC AVG GEEC AVG GEEC

 --------------------------------------------------------------------

 2.74 2.73 2.67 2.53 2.44
28