1

OFFICE OF CHEMICAL SAFETY

AND POLLUTION PREVENTION

UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON, D.C. 20460

PC Code: 128847

DP Barcode: 421092

Date: November 13, 2014

MEMORANDUM

SUBJECT: Drinking Water Exposure Assessment in support of the new use registration 

of multiple difenoconazole formulated products on Artichoke, Berry

Bushberry Subgroup 13-07B, Ginseng, and Bean and Pea, Dried Shelled 

(except Soybean) Subgroup 6C as well as Conversion of Stone Fruit Crop 

Group 12-12 and Tree Nuts Crop Group 14-12. 

TO: Laura Nollen, Risk Manager Reviewer

Barbara Madden, Risk Manager

Marion Johnson, Branch Chief

Registration Division (7505P)

Thurston Morton, Chemist

Elissa Reaves, Branch Chief

Risk Assessment Branch IV

Health Effects Division (7509P)

FROM: Faruque Khan, Ph.D., Senior Fate Scientist

Environmental Risk Branch I

Environmental Fate and Effects Division (7507P)

APPROVED

BY: Sujatha Sankula, Ph.D., Branch Chief, 

Environmental Risk Branch I

Environmental Fate and Effects Division (7507P)

This assessment provides estimated drinking water concentrations (EDWCs) of 

difenoconazole and its major metabolite, CGA-205375 (M1) in surface water and groundwater in 

support of human health risk assessment on the Interregional Research Project Number 4 (IR4)

proposed new uses on ginseng, artichoke, and conversion on stone fruit group 12-12 and tree nut 

group 14-12. The Residues of Concern Knowledgebase Subcommittee (ROCKS) of the Health 
2

Effects Division (HED) recommended to include CGA-205375 as a residue of concern for 

drinking water (USEPA, 2011, DP 391350). Therefore, this drinking water assessment was 

performed using total toxic residue (TTR; i.e. parent plus CGA 205375) method in support of the 

proposed Section 3 new uses following the approach used in a previous drinking water 

assessment for canola (US EPA 2013a, DP412614). Foliar spray applications (both aerial and 

ground spray applications) and chemigation, are being proposed for these crops. The EDWCs of 

difenoconazole and its major metabolite, CGA-205375 (M1) were generated using application 

rates of 0.46 to 0.52 lbs a.i./A.with the Surface Water Concentration Calculator model for 

surface water as well as the maximum application rate of 0.52 lbs a.i./A with the PRZM-GW and 

SCI-GROW models for groundwater. 

The Interregional Research Project Number 4 (IR-4) also revised the existing crop 

groupings by converting stone fruit Group 12 to stone fruit Group 12-12 and nut tree Group 12 to 

nut tree Group 14-12. Since there are no changes in the application rates and methods for the 

revised crop groupings, previous drinking water assessments (stone fruit; USEPA, 2010; 

DP426124 and tree nut; USEPA 2009, DP340378) fulfill the requirement for refining EDWCs 

for these crops. EFED noticed that the application rate for cucurbit is higher in the submitted 

Inspire Super (EPA Reg. No. 100-1317) label as compared to previous label, which was stamped 

on August 03, 2012. Since the maximum applicant rate of 0.52 lbs a.i./A for cucurbit is higher 

than previously assessed application rate of 0.46 lbs a.i./A (USEPA 2009; DP361398 the 

EDWCs for the revised rate of cucurbit was reassessed. 

Surface water and groundwater modeling were conducted for the maximum annual 

application rate of 0.46 to 0.52 lbs a.i./A for aerial application only as aerial applications 

produce conservative estimates. Remaining model input parameters were chosen according to 

current guidance (USEPA, 2009 and USEPA, 2013b). For surface water, the EDWCs for new 

uses and the revised application rate for cucurbit did not exceed the recommended peak (acute) 

concentration of 20.0 μg/L, annual mean (non-cancer chronic) concentration of 13.6 μg/L and 

the 30 year annual average concentration (cancer chronic) of 9.9 μg/L reported in the previous 

drinking water assessment based on grape use (US EPA, 2013; DP 398836). Recently, PRGMGW scenarios were revised and consequently the estimated PZRM-GW groundwater 

concentrations were reduced to 1.77 μg/L from 2.24 μg/L and chronic concentration of 0.66 

μg/L from 0.78 μg/L for the maximum application rate for FL citrus scenario. Recommended 

surface water and groundwater EDWCs for human health are listed in Table 1.

Table 1. Tier II Drinking Water Exposure Estimates for Total Toxic Residues of 

Difenoconazole Use on Canola/Oilseed Subgroup 20A.

Source Peak Exposure (μg/L) Annual Mean Exposure 

(μg/L)

30-year Average 

Exposure (μg/L)

Surface water120.0 13.6 9.9

Groundwater21.77 --- 0.66

1

EDWCs generated using PRZM/EXAMS model for aerial application of 0.46 lbs a.i./A for grape use 

(USEPA 2013)

2 Groundwater EDWCs are based on PRZM-GW 100 years simulation and the highest application rate for 

difenoconazole
3

Drinking Water Exposure Modeling

Models

The EDWCs were generated using EFED’s standard suite of models. Since there is no 

modification of input parameters for SWCC (same as PRZM/EXAMS, PRZM-GW and 

SCIGROW models, detailed description of models and inputs parameters can be obtained from 

the previous assessment (USEPA, 2013, D412416). However, inputs for SWCC in Table A-1,

for SCIGROW in Table A-2 , for PRZM-GW in Table A-3 as well as sample outputs of SWCC, 

PRZM-GW and SCIGROW models were provided in the Appendix A. Information concerning 

the model can be found on the EPA Water Models web-page1(USEPA, 2010b)

Surface Water

The Surface Water Concentration Calculator (SWCC v 1.106) model was used to 

generate EDWCs for the Tier II aquatic exposure assessment. The SWCC is a graphical user 

interface that runs the Pesticide Root Zone Model (PRZM, v 5, November 15, 2006) and the 

Variable Volume Water Body Model (VVWM, 3/6/2014) (USEPA, 2006b). Simulations are run 

for multiple (usually 30) years and the EDWCs represent peak values that are expected once 

every ten years based on the thirty years of daily values generated during the simulation. The 

default PCA of 1.0 was used for the proposed uses because difenoconazole can be used in both 

agricultural and non-agricultural settings (USEPA 2012). Estimated difenoconazole 

concentrations in surface water used for drinking water are summarized in Table 2. The EDWCs

for surface water for new uses and cucurbit did not supersede the previously recommended 

drinking water concentrations based on canola use (Table 1).

Table 2. EDWCs Based on Total Toxic Residues of Difenoconazole for Proposed New Uses 

Drinking Water 

Source Crop Crop Scenario

Peak (Acute) 

Exposure

Annual Mean 

(chronic)

Exposure 

30-year Mean 

(cancer 

chronic) 

Exposure

-----------------------(μg/L)-----------------------

Surface Water1 Artichoke CArowcropRLF 6.54 5.28 3.97

Ginseng MNsugarbeetST

D

7.48 5.50 4.19

Bushberry

NYgrapesSTD 15.0 10.4 7.52

ORberriesOP 7.58 5.61 4.54

Legumes

MIbeanSTD 8.89 5.38 3.96

WAbeanNMC 9.52 6.97 4.95

Cucurbit

FLcucumberSTD 8.81 3.66 2.74

CAmelonRLF 8.13 5.57 4.50

Ground water FL Citrus Scenario21.77 --- 0.66

Generic Scenario31.48E-02 --- 1.48E-02

1 EDWCs generated using SWCC model for aerial application

 

1

http://www.epa.gov/oppefed1/models/water /index.htm
4

Table 2. EDWCs Based on Total Toxic Residues of Difenoconazole for Proposed New Uses 

Drinking Water 

Source Crop Crop Scenario

Peak (Acute) 

Exposure

Annual Mean 

(chronic)

Exposure 

30-year Mean 

(cancer 

chronic) 

Exposure

-----------------------(μg/L)-----------------------

2 Highest EDWCs generated using PRZM-GW model based on 0.52 lbs a.i/A for cucurbit for the highest exposure 

observed in the previous drinking water assessment (USEPA, 2013)

3 EDWCs generated using SCIGROW model and assumed 5 equal application rate of 0.114 lbs a.i./A for cucurbit

Groundwater 

The Screening Concentration in Ground Water (SCI-GROW v2.3, Jul. 29, 2003) model1is a 

regression model used as a screening tool to estimate pesticide concentrations found in 

groundwater that is used for drinking water. SCI-GROW was developed by fitting a linear model 

to ground water concentrations with the Relative Index of Leaching Potential (RILP) as the 

independent variable. Ground water concentrations were taken from 90-day average high 

concentrations from Prospective Ground Water studies. PCAs are not applicable for the SCIGROW model.

In addition, Tier 1 groundwater EDWCs for difenoconazole, resulting from its use on 

cucurbit for its higher application rate of 0.52 lbs a.i./A was also estimated using the PRZM-GW 

model (USEPA, 2012c), with the GW-GUI (Graphical User Interface, version 1.0, August 31, 

2012). PRZM-GW is a one-dimensional, finite-difference model that estimates the 

concentrations of pesticides in groundwater. It accounts for pesticide fate in the crop root zone 

by simulating pesticide transport and degradation through the soil profile after a pesticide is 

applied to an agricultural field. PRZM-GW permits the assessment of multiple years of pesticide 

application (up to 100 years) on a single site. PRZM-GW output values represent pesticide 

concentrations in a vulnerable groundwater supply that is located directly beneath a rural 

agricultural field following many years of pesticide application.

Recently, PRGM-GW scenarios were revised and consequently the estimated PZRM-GW 

groundwater concentrations were reduced to 1.77 μg/L from 2.24 μg/L and chronic 

concentration of 0.66 μg/L from 0.78 μg/L for the maximum application rate for FL citrus 

scenario reported in previous drinking water assessment (USEPA, 2013, DP412416). The 

EDWCs for groundwater for new uses and cucurbit (Table 2) superseded the previously 

recommended drinking water concentrations (Table 1).

Monitoring Data

Monitoring data for difenoconazole were available from the United States Geological Survey

(USGS) National Water-Quality Assessment (NAWQA) Program Data Warehouse2, searched on 

November 06, 2014. Difenoconazole was detected in only one of seventy two surface water 

samples from multiple states (CA, GA, IA, IN, MO, NE and WI); the reported maximum 

 

2

(http://infotrek.er.usgs.gov/nawqa_queries/jsp/swmaster.jsp
5

concentration (18.2 ng/L) was detected in California. Difenoconazole was not detected at the 

limits of quantitation (LOQ) of 0.6 and 1.0 μg/kg-sediment in any of the 83 sediment samples 

collected from multiple states (GA, IA, IN, KS, KY, MO, NE, OH, SD and WI). However, the 

study design of NAWQA is not targeted to account for all difenoconazole use areas; timing of 

application and other factors which may more accurately represent spatially and temporally 

dependent variables influencing runoff vulnerability. No groundwater data are available at this 

time.

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

Pesticide Regulation (CDPR)3 were searched on November 06, 2014. No monitoring data were 

available for difenoconazole on CDPR’s website.

 

3

http://www.cdpr.ca.gov/docs/emon/ehap.htm
6

References

US EPA, 2009a. Difenoconazole Drinking Water Assessment in Support of New Use 

Registration Action for Bulb Vegetables, Brassica (Cole) Leafy Vegetables, Cucurbit 

Vegetables, Citrus Fruit, Grapes, and Tree Nuts. May 28, 2009. (D361398) 

USEPA. 2009b. Guidance for Selecting Input Parameters in Modeling the Environmental Fate 

and Transport of Pesticides, Version 2.1. U.S. Environmental Protection Agency, Office 

of Prevention, Pesticides and Toxic Substances, Office of Pesticide Programs, 

Environmental Fate and Effects Division, October 22, 2009. 

USEPA. 2010. Drinking Water Exposure Assessment to Establish a Tolerance of parent

difenoconazole on carrot, chickpeas, soybean, stone fruits, and strawberry. 

Environmental Fate and Effects Division, Office of Chemical Safety and Pollution 

Prevention. U. S. Environmental Protection Agency (D426124).

USEPA. 2011. Difenoconazole: Report of the Residues of Concern Knowledgebase Subcommittee (ROCKS). Health Effects Division, Office of Chemical Safety and Pollution 

Prevention. U. S. Environmental Protection Agency (D391350)

US EPA. 2012c. Memorandum: Approval of PRZM-GW for use of Drinking Water Exposure 

Assessment. Environmental Fate and Effects Division, Office of Chemical Safety and 

Pollution Prevention. U. S. Environmental Protection Agency.

USEPA 2013a. Drinking Water Exposure Assessment in support of the new use registration of 

difenoconazole formulated product Inspire on Canola/Oilseed Subgroup 20A.

Environmental Fate and Effects Division, Office of Chemical Safety and Pollution 

Prevention. U. S. Environmental Protection Agency (D 412614).

USEPA, 2013b. Guidance on modeling off-site deposition of pesticides via spray drift for 

ecological and drinking water assessments. Environmental Fate and Effects Division, 

Office of Chemical Safety and Pollution Prevention. U. S. Environmental Protection 

Agency
7

APPENDIX A

The input parameters used for SWCC modeling.

Table A-1. Chemical Specific SWCC Model Input Parameters for Difenoconazole

Parameter Input Value and Unit Source/Comments

Crops 

Artichoke

Ginseng

Bushberry

Legumes

Cucurbit

Scenario

CArowcrop RLF

MNsugarbeetSTD

ORberriesOP and NYgrapeSTD

MIbeanSTD and WAbeanNMC

FLcucumberSTD an CAMelonRLF

Surrogate scenario

Surrogate scenario

Surrogate scenarios

Standard and surrogate scenarios

Standard and surrogate scenarios

Maximum single application rate 

x Maximum # of application

Artichoke, ginseng, bushberry, and 

legumes

Cucurbit 

0.115 lbs a.i./A (0.129 kg a.i/HA) x 4

0.114 lbs a.i./A (0.128 kg a.i./HA) x 4 

and 0.064 lbs a.i./A (0.072 kg a.i./HA)

x 1

EPA Reg. No. 100-1262,

EPA Reg. No. 100-1312

EPA Reg. No. 100-1313

EPA Reg. No. 100-1317

EPA Reg. 100-1317

Method of application

CAM = 2 Foliar Spray Product Label as above

Application efficiency 0.95 (Aerial Spray) Generally aerial scenario generates 

higher exposure as compared to 

ground and chemigation scenarios 

EFED Model Input Guidance, 

Version 2.1 (2009b) a

Spray drift 0.135 (Aerial Spray) USEPA 2013. 

Crop

Scenario: Application date and

minimum interval between 

applications (days)

Artichoke

 CArowcrop: June 9 (14)

Assumed 21-days for application 

intervals between 2nd and 3rd

Ginseng

 MNsugarbeet: Sept 17 (7)

Assumed 14-days for application 

intervals between 2nd and 3rd

Busherry

 ORberries: June 19 (7)

 NYgrape: Sept 10 (7)

Assumed 14-days for application 

intervals between 2nd and 3rd

Legume

 MIbean:July 03

 WAbeanOP: July 01

Assumed 14-days for application 

intervals between 2nd and 3rd

Cucurbit

 FLcucumber: Oct 22 (7)

 CAmelon: June 14 (7)

Assumed 14-days for application 

intervals between 2nd and 3

rd and 

4

th and 5th

Hydrolysis Stable MRID 42245127
8

Parameter Input Value and Unit Source/Comments

Aerobic soil metabolism(t1/2)

b

489.6 days MRIDs: 42245131, 46950109-12, 

and 46950114

Aerobic aquatic metabolism (t1/2)

c

632.9 days MRIDs: 46950116 & 46950117

Anaerobic aquatic metabolism 

(t1/2)

d

1485.3 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 Half-life was multiplied by three (i.e., 3 x 495.1 days).

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

Sample Output:

Summary of Water Modeling of Difenoconazole and the USEPA 

Standard Reservoir

Estimated Environmental Concentrations for Difenoconazole are presented in Table 1 for the USEPA 

standard reservoir with the NYGrapesSTD field scenario. A graphical presentation of the year-to-year 

peaks is presented in Figure 1. These values were generated with the Surface Water Concentration 

Calculator (SWCC Version 1.106). Critical input values for the model are summarized in Tables 2 and 3.

This model estimates that about 2.3% of Difenoconazole applied to the field eventually reaches the 

water body. The main mechanism of transport from the field to the water body is by erosion ( 68% of 

the total transport), followed by spray drift (17.6%) and runoff (14.5%).

In the water body, pesticide dissipates with an effective water column half-life of 199.7 days. (This value 

does not include dissipation by transport to the benthic region; it includes only processes that result in 

removal of pesticide from the complete system.) The main source of dissipation in the water column is 

washout (effective average half-life = 228.7 days) followed by metabolism (1579.9 days) and 

volatilization (3.965328E+07 days).

In the benthic region, pesticide dissipation is negligible (3702.7 days). The main source of dissipation in 

the benthic region is metabolism (effective average half-life = 3702.7 days). The vast majority of the 

pesticide in the benthic region (99.83%) is sorbed to sediment rather than in the pore water.

Table 1. Estimated Environmental Concentrations (ppb) for Difenoconazole.

Peak (1-in-10 yr) 15.0

4-day Avg (1-in-10 yr) 14.2

21-day Avg (1-in-10 yr) 12.6
9

60-day Avg (1-in-10 yr) 11.6

365-day Avg (1-in-10 yr) 10.4

Entire Simulation Mean 7.52

Table 2. Summary of Model Inputs for Difenoconazole.

Scenario NYGrapesSTD

Cropped Area Fraction 1.0

Koc (ml/g) 5381

Water Half-Life (days) @ 25 °C 632.9

Benthic Half-Life (days) @ 25 °C 1483.3

Photolysis Half-Life (days) @ 40 °Lat 0

Hydrolysis Half-Life (days) 0

Soil Half-Life (days) @ 25 °C 489.6

Foliar Half-Life (days)

Molecular Wt 406.27

Vapor Pressure (torr) 2.5E-10

Solubility (mg/l) 15

Table 3. Application Schedule for Difenoconazole.

Date (Mon/Day) Type Amount (kg/ha) Eff. Drift

09/10 Foliar 0.129 0.95 0.135

09/17 Foliar 0.129 0.95 0.135

10/01 Foliar 0.129 0.95 0.135

10/08 Foliar 0.129 0.95 0.135

Figure 1. Yearly Peak Concentrations
10
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Input and Output of SCI-GROW Model

The input parameters used for SCI-GROW modeling

Table A-2. SCI-GROW Input Parameters for Difenoconazole Applied on Multiple 

Crops at the Maximum Label Application Rate.

Model Input Variable Input Values

Koc (the lowest value of all available Kocs, MRIDs: 42245135 and 46950121)

1

3471 ml/g

Application Rate 0.114lb. a.i./acre

Number of Applications 5

Aerobic Soil Metabolism half-life2223.6 days

Hydrolysis Stable

1 The Koc shows greater than three-folds variation, thus, the lowest value was uses per guidance as of Oct. 22, 2009 (USEPA 2009b).

2 Median of seven values.

Output of SCIGROW modeling

SCIGROW

 VERSION 2.3

 ENVIRONMENTAL FATE AND EFFECTS DIVISION

 OFFICE OF PESTICIDE PROGRAMS

 U.S. ENVIRONMENTAL PROTECTION AGENCY

 SCREENING MODEL

 FOR AQUATIC PESTICIDE EXPOSURE

SciGrow version 2.3

chemical:Difenoconazole

time is 10/27/2014 16:32:17

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

 Application Number of Total Use Koc Soil Aerobic

 rate (lb/acre) applications (lb/acre/yr) (ml/g) metabolism (days)

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

 0.114 5.0 0.570 3.47E+03 223.6

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

groundwater screening cond (ppb) = 1.48E-02 

************************************************************************
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Input and Output of PRZM-GW modeling

Table A-3. PRZM-GWInput Parameters1for Difenoconazole Uses 

Variable Name Data Value

Data Source

MRID(s) Comment

Application Method Aerial (Cucurbit) Proposed labels EPA Reg# 100-1317

Maximum Single 

Application Rate X 

Maximum # of application

(lbs. a.i./acre) [kg/ha]

Cucurbit

0.114 [0.128] x 4 plus 

0.064 (0.072) x 1

Proposed labels EPA Reg# 100-1317

Application Interval (days) 7 Proposed labels EPA Reg# 100-1317

Hydrolysis, DT50 (Days) stable MRID 42245127 ---

Aerobic Soil Metabolism 

DT50 (Days) 489.6 days

MRIDs.: 

46950116 & 

46950117

The 90% of the upper 

confidence limit (UCL)

of the mean metabolism 

half-life.

Koc (mL/goc) 5381

MRIDs:

42245135 and 

46950121

Average Koc

1

EFED input parameter guidance: http://www.epa.gov/oppefed1/models/water/przm_gw/wqtt_przm_gw_input_guidance.htm

Groundwater Analysis for Difenoconazole and the Florida Citrus -

FL Central Ridge, Polk County - (Tampa) Met File (12842.Dvf) -

Astatula Sand, Hrgb A Scenario

Estimated groundwater concentrations and breakthrough times for Difenoconazole are presented 

in Table 1 for the Florida Citrus - FL Central Ridge, Polk County - (Tampa) Met File 

(12842.dvf) - Astatula sand, hrgb A groundwater scenario. A graphical presentation of the daily 

concentrations in the aquifer is presented in Figure 1. These values were generated with the 

PRZM-GW (Version 1.07). Critical input values for the model are summarized in Tables 2 and 

3.

Table 1. Groundwater Results for Difenoconazole and the Florida Citrus - FL Central Ridge, Polk County -

(Tampa) Met File (12842.dvf) - Astatula sand, hrgb A Scenario.

Peak Concentration (ppb) 1.78

Post-Breakthrough Mean 

Concentration (ppb)

Incomplete

Entire Simulation Mean 

Concentration (ppb)

 0.659
13

Average Breakthrough Time 

(days)

Incomplete

Throughputs 0.8163512

Table 2. Chemical Properties for Groundwater Modeling of Difenoconazole.

Koc (ml/g) 5381

Surface Soil Half Life (days) 490

Hydrolysis Half Life (days) 0

Diffusion Coefficint Air (cm2/day) 0

Henry's Constant 0.0

Enthalpy (kcal/mol) 0.0

Table 3. Pesticide application scheme used for Difenoconazole. This application scheme was applied every 

year of the simulation.

Application Date

(Month/Day)

Application Method Application Rate

(kg/ha)

10/22 Ground application with mass distribution 

increasing proportionally with depth to 4 

cm

0.128

10/29 Ground application with mass distribution 

increasing proportionally with depth to 4 

cm

0.128

11/12 Ground application with mass distribution

increasing proportionally with depth to 4 

cm

0.128

11/19 Ground application with mass distribution 

increasing proportionally with depth to 4 

cm

0.128

12/03 Ground application with mass distribution 

increasing proportionally with depth to 4 

cm

0.072

Figure 1. Aquifer Breakthrough Curve for Difenoconazole and the Florida Citrus - FL 

Central Ridge, Polk County - (Tampa) Met File (12842.Dvf) - Astatula Sand, Hrgb A 

Scenario
14