1

OFFICE OF CHEMICAL SAFETY

AND POLLUTION PREVENTION

UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON, D.C. 20460

PC Code: 128847

DP Barcode: 398836

Date: February 23, 2012

MEMORANDUM

SUBJECT: Revised drinking water exposure assessment of parent difenoconazole and its 

major metabolite, CGA-205375 (M1) for grape. 

TO: Sidney Jackson, Risk Manager Reviewer

Barbara Madden, Risk Manager

Registration Division (7505P)

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

Environmental Risk Branch I

Environmental Fate and Effects Division (7507P)

APPROVED

BY: Nancy Andrews, Ph.D., Branch Chief, 

Sujatha Sankula, Ph.D. Lead Biologist

Environmental Risk Branch I

Environmental Fate and Effects Division (7507P)

This memorandum provides a revised drinking water assessment based on a recent 

recommendation from the Health Effects Division’s Residues of Concern Knowledgebase Subcommittee (ROCKS). The ROCKS recommended to include parent difenoconazole and its major 

metabolite, CGA-205375 (M1) for drinking water assessment to establish tolerances for 

difenoconazole in support of human health risk assessment (US EPA, 2011a, D391350). 

Previously recommended Estimated Drinking Water Concentrations (EDWCs) were based on 

aerial application of difenoconazole (parent only) for grape scenario (USEPA 2009, D361398). 

This drinking water assessment was performed using total residue method (i.e. parent plus CGA 

205375) for grape following the approach used in a recent drinking water assessment for various 

crops (US EPA 2011b, DP395784). The EDWCs values for acute (peak), annual mean (chronic) 

and the highest 30 year annual average (cancer chronic) concentrations were 17.4 μg/L, 11.8

μg/L, and 8.6 μg/L respectively. Since the revised EDWCs for surface water are higher than the 
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previously recommended EDWCs for this chemical, the current EDWCs for surface water 

supersede the EDWCs previously recommended for this chemical.

Estimated ground water concentration of 1.12x 10-2μg/L for grape is lower than the 

previously recommended concentration of 1.30x 10-2μg/L for citrus (US EPA, 2011b; 

D395784). Therefore, recommended EDWC for ground water is 1.30x 10-2μg/L and this 

concentration can be considered as both the acute and chronic values.

. Drinking Water Exposure Modeling

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

modification of input parameters for PRZM/EXAMS and SCIGROW models, detailed 

description of models and inputs parameters can be obtained from the previous assessment 

(USEPA, 2011b, D395784). However, inputs for PRZM/EXAMS in Table A-1 and for 

SCIGROW in Table A-2 as well as outputs of PRZM/EXAMS and SCIGROW models for grape 

scenario were provided in the Appendix A.

Standard percent cropped areas (PCA) were used for grape as estimates of the extent of 

watershed on which crops is grown (Effland et al., 1999). The default agricultural PCA of 0.87 

was used for the proposed uses because they are not confined to specific regions of the U.S
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References

Effland, W. R., N. C. Thurman, I. Kennedy. 1999. Proposed Methods for Determining 

Watershed-derived Percent Crop Areas and Considerations for Applying Crop Area Adjustments 

to Surface Water Screening Models. Presentation to the FIFRA Science Advisory Panel, May

27, 1999. Online at: http://www.epa.gov/scipoly/sap/1999/index.htm

US EPA, 2009a. Difenoconazole (Parent Only) 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. Water Models. U.S. Environmental Protection Agency, Pesticides: Science and 

Policy. Online at: http://www.epa.gov/oppefed1/models/water/

US EPA, 2011a. Difenoconazole: Report of the Residues of Concern Knowledgebase Subcommittee (ROCKS). DP Code: D391350. 

US EPA, 2011b. Revised drinking water exposure assessment to establish a tolerance of parent 

difenoconazole and its major CGA-205375 (M1) metabolite on fruiting vegetables group 8-10, 

low growing berry subgroup, 13-07G except cranberry, citrus fruit group 10-10, pome fruit 

group, (subgroup 11), and tuberous and corm vegetable (subgroup 1C). December 20, 2011. 

(D395784) 
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APPENDIX A

The input parameters used for PRZM/EXAMS modeling.

Table A-1. PRZM/EXAMS Chemical Specific Input Parameters for Difenoconazole

Parameter Input Value and Unit Source/Comments

Maximum application rate Grape: 0.46 lbs ai/A Product InspireTM

(EPA Reg. No.) 100-1262

Maximum number of applications 4 Product Label as above

Method of application (CAM = 2) Foliar spray -Aerial Product Label as above

Application date NY Gape: August 18 Application date was assumed 7-14 

days before harvest based on crop 

profile and label instructions: 

Minimum interval between 

applications 

10 days Product Label as above

Application efficiency 0.95 (aerial Application) EFED Model Input Guidance, 

Version 2.1 (2009b)

a

Spray drift 0.16 (Aerial Application) EFED Model Input Guidance, 

Version 2.1 (2009b)

Partition coefficient Koc

b

5381 mL/g MRIDs: 42245135 and 46950121

Henry’s Law constant 8.9 x 10-12 atm x m

3

/mol MRID 46515901

Hydrolysis Stable MRID 42245127

Aerobic soil metabolism(t1/2)

c

489.6 days MRIDs.: 46950109-12 and 

46950114

Aerobic aquatic metabolism (t1/2)

d

632.9 days MRIDs.: 46950116 & 46950117

Anaerobic aquatic metabolism (t1/2)

e

1485.3 days MRID 46950119

Aquatic photolysis t1/2 (days) Stable 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

Percent cropped area 0.87 U.S. EPA 2003

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

(Version 2.1; Oct. 22, 2009b)

b There was a positive correlation between the KF values vs. organic matter content; therefore, the average Koc was used as an

parameter. 

c The 90% of the upper confidence limit (UCL) of the mean metabolism half-life.

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

e At proposed application rate only one half-life was available, the half-life was multiplied by three (i.e., 3 x 495.1 days).
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An example (PA Tomato STD) input and output of PRZM/EXAMS modeling.

stored as NYgrapeA.out

Chemical: Difenconazole

PRZM environment: NYGrapesSTD.txt modified Tueday, 29 May 2007 at 12:59:44

EXAMS environment: ir298.exv modified Tueday, 26 August 2008 at 05:14:08

Metfile: w14860.dvf modified Tueday, 26 August 2008 at 05:15:12

Water segment concentrations (ppb)

Year Peak 96 hr 21 Day 60 Day 90 Day Yearly

1961 1.7 1.7 1.4 1.2 1.2 0.5

1962 9.8 9.1 7.3 5.7 5.4 2.7

1963 6.3 6.2 5.7 5.1 4.9 4.4

1964 10.3 9.8 8.9 7.5 7.0 5.5

1965 8.8 8.6 7.9 7.4 7.3 6.4

1966 11.7 11.2 10.1 8.8 8.4 7.3

1967 10.6 10.2 9.3 8.9 8.9 8.0

1968 9.2 9.0 8.7 8.4 8.2 7.8

1969 8.6 8.4 8.1 7.9 7.7 7.5

1970 13.5 13.0 12.2 10.7 10.2 8.1

1971 10.3 10.1 9.6 9.4 9.3 8.7

1972 10.0 9.9 9.4 9.1 9.0 8.6

1973 12.5 12.0 10.8 9.7 9.3 8.5

1974 13.0 12.5 11.1 10.0 9.6 8.6

1975 19.4 18.8 16.3 13.7 12.9 10.0

1976 11.9 11.6 11.3 11.0 10.9 10.5

1977 18.2 17.5 16.4 15.3 14.6 11.4

1978 16.4 16.0 14.9 14.2 13.9 12.4

1979 19.5 18.9 17.2 16.4 15.8 13.2

1980 20.6 20.0 18.3 17.0 16.5 14.3

1981 16.8 16.5 15.7 14.9 14.8 14.1

1982 15.7 15.4 14.7 14.2 14.0 13.3

1983 16.4 16.1 15.8 14.9 14.8 13.0

1984 18.9 18.2 16.4 14.7 14.2 12.9

1985 16.5 16.0 14.9 13.9 13.3 12.4

1986 20.0 19.2 17.5 15.3 14.6 12.6

1987 19.9 19.3 17.7 16.1 15.7 13.4

1988 17.0 16.6 15.7 14.9 14.8 13.6

1989 16.9 16.5 15.1 14.4 14.1 13.2

1990 21.3 20.5 18.9 16.7 16.1 13.4

Sorted results

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

0.0 21.3 20.5 18.9 17.0 16.5 14.3

0.1 20.6 20.0 18.3 16.7 16.1 14.1

0.1 20.0 19.3 17.7 16.4 15.8 13.6

0.1 19.9 19.2 17.5 16.1 15.7 13.4

0.2 19.5 18.9 17.2 15.3 14.8 13.4

0.2 19.4 18.8 16.4 15.3 14.8 13.3

0.2 18.9 18.2 16.4 14.9 14.8 13.2

0.3 18.2 17.5 16.3 14.9 14.6 13.2

0.3 17.0 16.6 15.8 14.9 14.6 13.0

0.3 16.9 16.5 15.7 14.7 14.2 12.9

0.4 16.8 16.5 15.7 14.4 14.1 12.6

0.4 16.5 16.1 15.1 14.2 14.0 12.4
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0.4 16.4 16.0 14.9 14.2 13.9 12.4

0.5 16.4 16.0 14.9 13.9 13.3 11.4

0.5 15.7 15.4 14.7 13.7 12.9 10.5

0.5 13.5 13.0 12.2 11.0 10.9 10.0

0.5 13.0 12.5 11.3 10.7 10.2 8.7

0.6 12.5 12.0 11.1 10.0 9.6 8.6

0.6 11.9 11.6 10.8 9.7 9.3 8.6

0.6 11.7 11.2 10.1 9.4 9.3 8.5

0.7 10.6 10.2 9.6 9.1 9.0 8.1

0.7 10.3 10.1 9.4 8.9 8.9 8.0

0.7 10.3 9.9 9.3 8.8 8.4 7.8

0.8 10.0 9.8 8.9 8.4 8.2 7.5

0.8 9.8 9.1 8.7 7.9 7.7 7.3

0.8 9.2 9.0 8.1 7.5 7.3 6.4

0.9 8.8 8.6 7.9 7.4 7.0 5.5

0.9 8.6 8.4 7.3 5.7 5.4 4.4

0.9 6.3 6.2 5.7 5.1 4.9 2.7

1.0 1.7 1.7 1.4 1.2 1.2 0.5

0.1 20.0 19.3 17.6 16.3 15.8 13.6

Average of yearly averages: 9.9

Inputs generated by pe5.pl - Novemeber 2006

Data used for this run:

Output File: NYgrapeA

Metfile: w14860.dvf

PRZM scenario: NYGrapesSTD.txt

EXAMS environment file: ir298.exv

Chemical Name: Difenconazole

Description Variable Name Value Units Comments

Molecular weightmwt 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

Photolysis half-life kdp 0 days Half-life

Aerobic Aquatic Metabolism kbacw 632.9 days Halfife

Anaerobic Aquatic Metabolism kbacs 1485.3 days Halfife

Aerobic Soil Metabolism asm 489.6 days Halfife

Hydrolysis: pH 7 0 days Half-life

Method: CAM 2 integer See PRZM manual

Incorporation Depth: DEPI cm

Application Rate:TAPP 0.128 kg/ha

Application Efficiency: APPEFF0.95 fraction

Spray Drift DRFT 0.16 fraction of application rate applied to pond

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

Interval 1 interval 10 days Set to 0 or delete line for single app.

app. rate 1 apprate kg/ha

Interval 2 interval 10 days Set to 0 or delete line for single app.

app. rate 2 apprate kg/ha

Interval 3 interval 10 days Set to 0 or delete line for single app.

app. rate 3 apprate kg/ha

Record 17: FILTRA

IPSCND1
7

UPTKF

Record 18: PLVKRT

PLDKRT

FEXTRC 0.5

Flag for Index Res. Run IR Reservoir

Flag for runoff calc. RUNOFF total none, monthly or total(average of entire run)

PCA Adjusted EDWCS

Peak 96 hr 21 Day 60 Day 90 Day Yearly

Average 

of 

yearly 

averages

20.0 19.3 17.6 16.3 15.8 13.6 9.9

PCA Adjusted 

(0.87) 17.4 16.8 15.4 14.2 13.7 11.8 8.6

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 0.114 lb. a.i./acre

Number of Applications 4

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.

Input and 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:Difenconazole

time is 9/20/2010 10:27:23

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

 Application Number of Total Use Koc Soil Aerobic

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

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

 0.114 4.0 0.456 3.47E+03 185.0

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

groundwater screening cond (ppb) = 1.12E-02 

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