1

OFFICE OF CHEMICAL SAFETY

AND POLLUTION PREVENTION

UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON, D.C. 20460

PC Code: 128847

Decision #: 447590

DP Barcode: 395784

Date: December 20, 2011

MEMORANDUM

SUBJECT: 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). 

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 recent 

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

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

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

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

CGA 205375) on the requested crops, 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).
2

Difenoconazole can be applied as a foliar spray through ground or aerial application on 

various crops according to the InspireTM (EPA Reg. No. 100-1262) label. Table 1 below provides 

information of previous actions related to drinking water assessments. Revised drinking water 

assessment was performed only for the scenarios with highest EDWCs for crops listed in Table 

1. Table 2 provides information related to modeled scenarios for this assessment. The modeling 

approach for surface water and ground water are consistent with the earlier approach except the 

half-life values for biotic degradation in the environment. The percent of CGA-205375 formation 

during biotic metabolism in soil and aquatic environments was included into half-life

calculations (Appendix A) and used in the revised modeling. Since abiotic (i.e. hydrolysis and 

aquatic photolysis) degradation of difenoconazole is stable, no further half-life estimation is 

required. The EDWCs are also based on the maximum proposed application rates ranging from 

0.33 to 0.5 lbs/A for aerial application specified in the product label. 

The EDWCs for the human health risk assessment are presented in Table 2. For surface 

water, the EDWCs for the crops modeled in this assessment did not exceed the EDWCs for grape 

reported in the previous drinking water assessment (U.S. EPA 2009a; D361398). The Estimated 

Drinking Water Concentrations (EDWCs) for grape scenario provided the highest exposure in 

surface water (U.S. EPA 2009; D361398). The reported values for acute, annual mean (chronic) 

concentration and the highest 30 year annual average concentrations were 15.8 μg/L, 10.4 μg/L, 

and 7.62 μg/L respectively. Therefore, the current EDWCs for surface water do not supersede 

the drinking water concentrations previously estimated for this chemical.

Estimated ground water concentration of 1.30x 10-2μg/L for citrus is higher than the 

previously recommended concentration of 1.28x 10-2μg/L for ornamentals (US EPA, 2007; 

D333319). Therefore, recommended EDWCs for ground water is 1.30x 10-2μg/L and this 

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

Table 1. List of previous actions for drinking water assessment

DP 

Barcodes

Date Title of Assessment

333319 

and

340041

June 19, 2007 Amended Difenoconazole (Parent Only) Drinking Water 

Assessment in Support of New Use Registration Action for Fruiting 

Vegetables1, Tuberous, Corn1, Vegetables Subgroup, Pome Fruit, 

Ornamentals, and Sugar beets.

361398 May 28, 2009 Difenoconazole (Parent Only) Drinking Water Assessment in

Support of New Use Registration Action for Bulb Vegetables,

Brassica (Cole) Leafy Vegetables, Cucurbit Vegetables, Citrus

Fruit1, Grapes, and Tree Nuts.

375778 

and 

380513

Dec 16, 2010 Drinking Water Exposure Assessment to Establish a Tolerance of

parent difenoconazole on carrot, chickpeas, soybean, stone fruits,

and strawberry1. 

1 Scenarios with higher EDWCs were modeled in this revised assessment
3

Table 2. Estimated Drinking Water Concentrations (EDWCs) in Surface Water and 

Ground Water Resulting from Applications of Difenoconazole

Drinking Water 

Source (model)

Use

Scenario

(modeled rate)

1-in-10 year acute

(μg/L)

1-in-10 year chronic

(μg/L)

30- year average 

(μg/L)

Surface Water1

(PRZM/EXAMS)

Fruiting Vegetables:

PA Tomato STD

FL Pepper STD

(0.46 lbs ai/acre)

10.31

8.36

6.02

2.85

4.52

2.19

Citrus:

FL Citrus STD

(0.5lbs ai/acre)

8.01 3.30 2.63

Low growing berry

FL Strawberry STD

(0.46 lbs ai/acre)

9.89 3.56 2.97

Pome Fruits:

PA Apple STD

(0.33 lbs ai/acre)

7.08 3.99 3.01

Tuberous and corm

vegetables

ME Potato STD

(0.46lbs ai/acre)

10.25 6.62 5.38

Groundwater 

(SCI-GROW)

For Citrus crops

(4 app. X 0.125 lbs ai/acre) 1.30 x 10-2

1.30 x 10-21.30x 10-2

Bold text denotes maximum estimated EDWC values for this assessment. All values were adjusted with PCA factor 

of 0.87.

The modeling results of various scenarios for EDWCs are listed in Appendix B. Standard 

percent cropped areas (PCA) were used for all uses 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. Since there is no 

modification of input parameters for PRZM/EXAMS and SCI-GROW models except biotic 

degradation half-life parameters, detailed description of models can be obtained from the 

previous assessment for grapes (U.S.EPA, 2009a, D361398). Inputs for PRZM/EXAMS in 

Table B-1 and for SCIGROW in Table B-2 as well as examples output of PRZM/EXAMS and 

SCIGROW models were provided in the Appendix B. Tables B-3 provides pre-PCA and postPCA adjusted EDWCs for difenoconazole.

Monitoring Data

Difenconazole is not included as one of the analytes monitored in U.S. surface and 

groundwater under the USGS’s National Water Quality Assessment (NAWQA) program. 

Drinking Water Exposure Modeling

Estimated drinking water concentrations (EDWCs) were generated using EFED’s 

standard suite of models. The proposed uses from the provided label were assessed. 
4

Models

Pesticide Root Zone Model (PRZM v3.12.2, May 12, 2005) and Exposure Analysis

Modeling System (EXAMS v2.98.04.06, April 25, 2005) are simulation models coupled with the 

input PE5.pl shell (PE5, PE Version 5.0, November 15, 2006) to generate EDWCs of 

difenoconazole residues that may occur in surface water used as drinking water. The PRZM 

model simulates pesticide movement and transformation on and across the agricultural field 

resulting from crop applications. The EXAMS model simulates pesticide loading via runoff, 

erosion, and spray drift assuming a standard watershed of 172.8 ha that drains into an adjacent 

standard drinking water index reservoir of 5.26 ha, an average depth of 2.74 m. A more detailed 

description of the index reservoir watershed can be found in Jones et al., 1998. The coupled 

PRZM/EXAMS model and users manuals may be downloaded from the U.S. Environmental 

Protection Agency (EPA) Water Models web-page (U.S. EPA, 2010). Percent Crop Areas 

(PCA) that account for the maximum area within a watershed that may be planted with the 

modeled crop are applied to concentrations predicted by PRZM/EXAMS.

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

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

water used as 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. The RILP is a function of aerobic soil metabolism and 

the soil-water partition coefficient. The output of SCI-GROW represents the concentrations of

residues that might be expected in shallow unconfined aquifers under sandy soils, which is 

representative of the ground water most vulnerable to pesticide contamination and likely to serve 

as a drinking water source. The SCI-GROW user’s manual is currently under development; 

however, information concerning the model can be found on the EPA Water Models web-page 

(USEPA, 2010). 
5

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

Jones, R. D., S. Abel, W. R. Effland, R. Matzner, R. Parker. 1998. An Index Reservoir for Use 

in Assessing Drinking Water Exposure. Proposed Methods for Basin-scale Estimation of 

Pesticide Concentrations in Flowing Water and Reservoirs for Tolerance Reassessment. 

Presentation to FIFRA Science Advisory Panel, June 29-30, 1998. Online at: 

http://www.epa.gov/scipoly/sap/1998/index.htm

USEPA. 2007. Amended Difenoconazole (Parent Only) Drinking Water Assessment in Support 

of New Use Registration Action for Fruiting Vegetables, Tuberous, Corn, Vegetables Subgroup, 

Pome Fruit, Ornamentals, and Sugar beets. U.S. Environmental Protection Agency, Office of 

Pesticide Programs, Environmental Fate and Effects Division, DWA Memorandum, June 19, 

2007. (D333319 and D340041)

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, 2011. Difenoconazole: Report of the Residues of Concern Knowledgebase Subcommittee (ROCKS). DP Code: D391350. 
6

APPENDIX A

Total Residue Half-life Calculation

Aerobic Soil Metabolism

Chemical: Difenoconazole

MRID: 46950109

PC: 128847

Guideline: 162-1

Linear halflife (days): 126.0

Days 

posttreatme

nt

(% of

applied)

ln (% 

applied)

0 101.0 4.6151

0 100.4 4.6092

3 100.2 4.6072

7 98.6 4.5911

7 98.6 4.5911

14 95.8 4.5623

28 87.4 4.4705

28 90.8 4.5087

56 77.3 4.3477

56 75.9 4.3294

84 67.8 4.2166

84 70.2 4.2513

100 55.8 4.0218

120 51.7 3.9455

120 56.3 4.0307

190 40.5 3.7013

293 19.6 2.9755

293 19.8 2.9857

Data from Table 3, p. 42 of the study report.

Difenoconazole and M1

y = -0.0055x + 4.6412

R2 = 0.9924

2.9

3.2

3.5

3.8

4.1

4.4

4.7

0 50 100 150 200 250 300

Ln (% applied)

Days Posttreatment

Dissipation of difenoconazole in 

aerobic loam soil

(0-293 days)

MRID: 46950110

PC: 128847

Guideline: 162-1

Linear half-life

(days): 113.6

Days 

posttreatment

(% of

applied)

ln (% 

applied)

0 95.0 4.5539

0 93.9 4.5422

3 97.5 4.5799

7 95.0 4.5539

7 90.6 4.5065

14 89.2 4.4909

28 85.3 4.4462

28 81.9 4.4055

56 67.9 4.2180

56 72.4 4.2822

84 63.3 4.1479

84 57.1 4.0448

100 52.6 3.9627

120 44.1 3.7865

120 48.6 3.8836

135 41.0 3.7136

190 32.6 3.4843

293 16.4 2.7973

293 16.0 2.7726

Data from Table 3, p. 42 of the study report. 

Difenoconazole and M1

y = -0.0061x + 4.5795

R2 = 0.9954

2.5

3.0

3.5

4.0

4.5

5.0

0 50 100 150 200 250 300

Ln (% applied)

Days Posttreatment

Dissipation of difenoconazole in aerobic 

loam soil

(0-293 days)
7

Chemical: Difenoconazole

MRID: 46950111

PC: 128847

Guideline: 162-1

Soil: Schanz sandy loam

Half-life: 

(days) 216.6

(% 

applied)

Ln (% 

applied)

0 98.9 4.594

0 99.7 4.602

14 94.2 4.545

14 91.8 4.520

28 91.8 4.520

56 78.5 4.363

84 72.9 4.289

120 66.1 4.191

120 66.1 4.191

175 55.3 4.013

228 47.7 3.865

Data obtained from Table 8, p. 40 of the study report.

Days 

Posttreat

ment

Difenoconazole and M1

y = -0.0032x + 4.5826

R2 = 0.9935

3.50

3.75

4.00

4.25

4.50

4.75

5.00

0 50 100 150 200 250

Ln (% of applied)

Days posttreatment

Dissipation of difenoconazole in 

aerobic sandy loam soil (days 0-228)

Chemical: Difenoconazole

MRID: 46950111

PC: 128847

Guideline: 162-1

Soil: Pappelacker sandy loam/loamy sand

Half-life (da247. ys)6

(% applied)Ln (% applied)

0 96.7 4.572

0 98.8 4.593

14 96.4 4.569

14 92.8 4.530

28 92.6 4.528

56 79.1 4.371

84 76.1 4.332

120 64.6 4.168

120 67.3 4.209

175 54.9 4.006

228 57.0 4.043

Data were obtained from Table 9, p. 41 of the study report.

Posttreat

ment

Difenoconazole

y = -0.0028x + 4.5694

R2 = 0.9424

3.50

3.75

4.00

4.25

4.50

4.75

5.00

0 50 100 150 200 250

Ln (% of applied)

Days posttreatment

Dissipation of difenoconazole in 

aerobic sandy loam/laomy sand soil 

(days 0-228)
8

Chemical: Difenoconazole

MRID: 46950111

PC: 128847

Guideline: 162-1

Soil: Senozan silty clay loam

Half-life 

(days) 223.6

(%

applied)

Ln (%

applied)

0 97.9 4.584

0 98.0 4.585

14 91.8 4.520

14 92.9 4.532

28 84.7 4.439

56 79.9 4.381

84 74.6 4.312

120 69.0 4.234

120 64.0 4.159

175 55.5 4.016

228 47.4 3.859

Data were obtained from Table 10, p. 42 of the study report.

Days 

Posttreat

ment

Difenoconazole and M1

y = -0.0031x + 4.5675

R2 = 0.9907

3.50

3.75

4.00

4.25

4.50

4.75

5.00

0 50 100 150 200 250

Ln (% of applied)

Days posttreatment

Dissipation of difenoconazole in 

aerobic silty clay loam soil (days 0-228)

Chemical: Difenoconazole

MRID: 46950112 & 13

PC Code: 128847

Guideline: 162-1

Linear half-life (days): 693.1

Days

posttreat

ment % applied

Ln (%

applied)

0 96.8 4.5726

0 98.3 4.5880

3 73.6 4.2986

3 96.9 4.5737

7 93.4 4.5369

7 95.6 4.5602

15 96.0 4.5643

15 95.6 4.5602

30 98.5 4.5901

30 95.0 4.5539

58 90.4 4.5042

58 89.1 4.4898

99 86.0 4.4543

99 83.1 4.4200

120 83.7 4.4272

120 83.6 4.4260

150 82.9 4.4176

150 82.8 4.4164

181 79.9 4.3808

181 83.1 4.4200

269 74.8 4.3148

269 72.2 4.2794

360 66.8 4.2017

360 71.1 4.2641

Data obtained from Table 8, p. 43 of the study report.

Difenoconazole and M1

y = -0.001x + 4.5667

R2 = 0.9541

4.15

4.20

4.25

4.30

4.35

4.40

4.45

4.50

4.55

4.60

4.65

0 100 200 300 400

Ln (% of applied)

Days posttreatment

Dissipation of difenoconazole in

aerobic loamy sand soil
9

Table B-1. Estimated half-lives in aerobic soil

MRID # Half-life (days)

46950109 126.0

46950110 113.6

46950111 216.6

46950111 247.6

46950111 223.6

46950112-46950113 693.1

46950114-46950115 770.2

Half-life (90th Percentile): 489.6

Chemical: Difenoconazole

MRID: 46950114 & 15

PC Code: 128847

Guideline: 162-1

Linear half-life (days): 770.2

Days

posttreatment % appliedLn (% applied)

0 97.0 4.5747

0 97.7 4.5819

3 94.6 4.5497

3 95.1 4.5549

7 93.9 4.5422

7 92.8 4.5304

15 71.9 4.2753

15 92.8 4.5304

27 94.2 4.5454

27 91.9 4.5207

58 92.2 4.5240

58 92.7 4.5294

90 85.4 4.4473

90 86.1 4.4555

127 82.5 4.4128

127 82.2 4.4092

150 77.7 4.3529

150 77.8 4.3541

178 77.5 4.3503

178 81.7 4.4031

272 78.0 4.3567

272 74.8 4.3148

372 67.4 4.2106

372 68.9 4.2327

Data obtained from Table 8, p. 43 of the study report.

Difenoconazole and M1

y = -0.0009x + 4.5493

R2 = 0.9319

4.15

4.20

4.25

4.30

4.35

4.40

4.45

4.50

4.55

4.60

4.65

0 100 200 300 400

Ln (% of applied)

Days posttreatment

Dissipation of difenoconazole in aerobic loamy sand 

soil
10

Aerobic Aquatic Metabolism (Total System)

Chemical: Difenoconazole (CGA-169374)

PC: 128847

MRID: 46950116

Guideline: 162-4

Aerobic metabolism of [chlorophenyl-U-14C]difenoconazole in two Swiss water-sediment systems.

Half-life determination

River water-sandy loam sediment: total system.

Half-life (days) 495.1 (0- to 183-day data)

Days Posttreatment (% of Applied) Ln (% applied)

0 91.5 4.52

1 93.3 4.54

3 92.8 4.53

7 93.1 4.53

14 91.2 4.51

22 97.3 4.58

32 89.7 4.50

59 85.1 4.44

90 81.1 4.40

127 80.6 4.39

183 72.7 4.29

Results from Table 9, p. 38 of the study report.

Difenoconazole and M1

y = -0.0014x + 4.5411

R2 = 0.9129

4.0

4.1

4.2

4.3

4.4

4.5

4.6

4.7

4.8

4.9

5.0

0 25 50 75 100 125 150 175

Ln (% of applied)

Days posttreatment

Dissipation of difenoconazole (CGA169374) in

aerobic Swiss river water-sandy loam: total

system

Chemical: Difenoconazole (CGA-169374)

PC: 128847

MRID: 46950116

Guideline: 162-4

Aerobic metabolism of [chlorophenyl-U-14C]difenoconazole in two Swiss water-sediment systems.

Half-life determination

Pond water-silty clay loam sediment: total system.

Half-life

(days) 407.7

Days Posttr(% eatofme Apntplied) Ln (% applied)

0 98.1 4.585987

1 96.7 4.571613

3 98.1 4.585987

7 98.7 4.592085

14 92.3 4.525044

22 100.0 4.60517

32 96.4 4.568506

59 87.5 4.471639

90 80.8 4.391977

127 71.0 4.26268

183 77.4 4.348987

Results from Table 7, p. 36 of the study report.

DifenoconazoleAnd M1

y = -0.0017x + 4.586

R2 = 0.8148

4.0

4.1

4.2

4.3

4.4

4.5

4.6

4.7

4.8

4.9

5.0

0 25 50 75 100 125 150 175

Ln (% of applied)

Days posttreatment

Dissipation of difenoconazole (CGA-169374) in

aerobic Swiss pond water-silty clay loam: total 

system
11

Table B-2. Estimated half-lives in aerobic aquatic system

MRID # Half-life (days)

46950116 495.1

46950116 407.7

46950117 and 46950118 630.1

Half-life (90th Percentile): 632.9

Chemical: Difenoconazole (CGA-169374)

PC: 128847

MRID: 46950117/46950118

Guideline: 162-4

Aerobic metabolism of [triazolyl-3,5-14C]difenoconazole in California river water-loamy sand sediment.

Half-life determination/water-sediment total system

Half-life (days) 630.1

Days Posttreatment (% of Applied)

Ln (%

applied)

0 85.05 4.44

0 86.08 4.46

2 94.27 4.55

5 88.77 4.49

7 90.35 4.50

14 88.49 4.48

28 94.78 4.55

47 85.86 4.45

70 82.58 4.41

84 79.91 4.38

98 78.99 4.37

112 81.53 4.40

Results imported from Parent worksheet.

Difenoconazole and M1

y = -0.0011x + 4.4996

R2 = 0.5807

4.35

4.40

4.45

4.50

4.55

4.60

0 20 40 60 80 100 120

LN (% of Applied)

Days (Post-treatment)
12

Anaerobic Aquatic Metabolism 

Chemical: Difenoconazole (CGA-169374)

PC: 128847

MRID: 46950119/46950120

Guideline: 162-3

Anaerobic metabolism of [triazolyl-3,5-14C]difenoconazole in California river water-sand sediment.

Half-life determination/total system

Half-life (days) 495.1 (0-hour to 350-day data)

Days Posttreatment (% of Applied) Ln (% applied)

0.00 96.50 4.569543008

0.00 86.02 4.454579827

0.04 88.42 4.482098188

0.04 90.42 4.504465482

7 96.35 4.567987395

7 93.31 4.535927283

15 96.34 4.567883601

15 100.66 4.611748501

22 96.93 4.573989069

22 98.03 4.585273554

29 98.19 4.586904377

29 97.10 4.575741375

57 95.96 4.563931438

57 86.87 4.464412748

85 90.00 4.49980967

85 96.20 4.566429358

119 92.72 4.529584199

119 97.11 4.575854654

147 100.10 4.606169686

147 87.26 4.468892168

175 86.80 4.463606622

175 101.75 4.622518824

245 70.07 4.249494742

245 69.70 4.244200318

302 64.70 4.169761202

302 71.63 4.271513981

350 50.77 3.927305629

350 47.50 3.860729711

Results imported from Profile worksheet.

Difenoconazole and M1

y = -0.0014x + 4.6124

R2 = 0.6915

3.0

3.3

3.5

3.8

4.0

4.3

4.5

4.8

5.0

0 25 50 75 100 125 150 175 200 225 250 275 300 325 350

Ln (% of applied)

Days posttreatment

Dissipation of [

14C]difenoconazole (CGA-169374) in 

anaerobic California river water-sand: total system
13

APPENDIX B

The input parameters used for PRZM/EXAMS modeling.

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

Parameter Input Value and Unit Source/Comments

Maximum application rate Fruiting vegetable: 0.46 lbs ai/A 

Citurs: 0.5 lbs ai/A

Low growing berry: 0.46 lbs ai/A

Pome fruit: 0.33 ai/A

Tuberous & crom vegetable: 0.46 lbs 

Product InspireTM

(EPA Reg. No. 100-1262)

Maximum number of applications 4 (except Pome fruit)

5 pome fruit

Product Label as above

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

Minimum interval between 

applications 

7 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

Application date PA Tomato: June 30

FL Pepper: November 15

FL Strawberry: February 15

FL Citrus: June 08

PA Apple: June 30

ME Potato: June 20

Application dates were assumed 7-

14 days before harvest based on crop 

profile and label instructions: 

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) fStable 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 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).

f The maximum value available.
14

An example (PA Tomato STD) input and output of PRZM/EXAMS modeling.

stored as PATomato.out

Chemical: Difenoconazole

PRZM 

environm

ent: 

PAtomato

STD.txt

modified Tueday, 29 May 2007 at 13:01:58

EXAMS 

environm

ent: 

ir298.exv

modified Tueday, 26 August 2008 at 05:14:08

Metfile: 

w14751.d

vf

modified Tueday, 26 August 2008 at 05:15:00

Water segment concentrations (ppb)

Year Peak 96 hr 21 Day 60 Day 90 Day Yearly

1961 4.28 3.90 3.16 2.66 2.37 0.98

1962 4.35 4.13 3.51 3.30 3.23 2.33

1963 5.04 4.81 4.28 3.99 3.64 3.03

1964 5.45 5.21 4.87 4.30 4.18 3.73

1965 5.24 5.06 4.75 4.56 4.37 3.93

1966 10.76 10.05 8.10 6.42 6.02 4.44

1967 8.90 8.54 7.57 6.57 6.21 5.30

1968 10.27 9.70 8.09 6.73 6.42 5.35

1969 16.70 15.53 13.14 9.85 8.89 6.31

1970 8.30 8.08 7.78 7.34 6.99 6.49

1971 11.91 11.24 9.44 8.18 7.62 6.40

1972 10.28 9.76 8.80 7.81 7.45 6.66

1973 11.34 10.77 9.19 7.88 7.50 6.67

1974 9.85 9.55 8.70 8.24 7.89 6.94

1975 16.48 15.38 12.43 9.83 9.04 7.05

1976 10.46 10.05 9.10 8.11 7.83 7.22

1977 7.58 7.39 7.08 6.86 6.81 6.43

1978 7.40 7.18 6.99 6.45 6.18 5.76

1979 7.57 7.32 6.83 6.38 6.11 5.69

1980 7.24 6.95 6.18 5.92 5.47 5.11

1981 7.57 7.25 6.77 6.07 5.77 5.25

1982 6.27 6.10 5.91 5.54 5.44 4.93

1983 7.18 6.90 6.21 5.49 5.22 4.77

1984 6.34 6.14 5.87 5.36 5.17 4.89

1985 6.16 5.93 5.30 4.90 4.88 4.53

1986 8.58 8.17 7.09 6.29 5.87 4.89

1987 8.12 7.78 7.01 6.14 6.00 5.10
15

1988 8.28 7.89 6.82 5.92 5.64 5.10

1989 7.56 7.27 6.78 6.29 6.04 5.24

1990 7.75 7.46 6.63 6.22 6.02 5.49

Sorted results

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

0.03 16.70 15.53 13.14 9.85 9.04 7.22

0.06 16.48 15.38 12.43 9.83 8.89 7.05

0.10 11.91 11.24 9.44 8.24 7.89 6.94

0.13 11.34 10.77 9.19 8.18 7.83 6.67

0.16 10.76 10.05 9.10 8.11 7.62 6.66

0.19 10.46 10.05 8.80 7.88 7.50 6.49

0.23 10.28 9.76 8.70 7.81 7.45 6.43

0.26 10.27 9.70 8.10 7.34 6.99 6.40

0.29 9.85 9.55 8.09 6.86 6.81 6.31

0.32 8.90 8.54 7.78 6.73 6.42 5.76

0.35 8.58 8.17 7.57 6.57 6.21 5.69

0.39 8.30 8.08 7.09 6.45 6.18 5.49

0.42 8.28 7.89 7.08 6.42 6.11 5.35

0.45 8.12 7.78 7.01 6.38 6.04 5.30

0.48 7.75 7.46 6.99 6.29 6.02 5.25

0.52 7.58 7.39 6.83 6.29 6.02 5.24

0.55 7.57 7.32 6.82 6.22 6.00 5.11

0.58 7.57 7.27 6.78 6.14 5.87 5.10

0.61 7.56 7.25 6.77 6.07 5.77 5.10

0.65 7.40 7.18 6.63 5.92 5.64 4.93

0.68 7.24 6.95 6.21 5.92 5.47 4.89

0.71 7.18 6.90 6.18 5.54 5.44 4.89

0.74 6.34 6.14 5.91 5.49 5.22 4.77

0.77 6.27 6.10 5.87 5.36 5.17 4.53

0.81 6.16 5.93 5.30 4.90 4.88 4.44

0.84 5.45 5.21 4.87 4.56 4.37 3.93

0.87 5.24 5.06 4.75 4.30 4.18 3.73

0.90 5.04 4.81 4.28 3.99 3.64 3.03

0.94 4.35 4.13 3.51 3.30 3.23 2.33

0.97 4.28 3.90 3.16 2.66 2.37 0.98

0.10 11.85 11.19 9.41 8.23 7.89 6.91

Average 

of yearly 

averages:

5.20

Inputs generated by pe5.pl - Novemeber 2006

Data used for this run:
16

Output File: PATomato

Metfile: w14751.dvf

PRZM 

scenario:

PAtomatoSTD.txt

EXAMS 

environm

ent file:

ir298.exv

Chemical 

Name:

Difenoconazole

Descriptio

n

Variable 

Name

Value Units Comment

s

Molecular 

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

Photolysis 

half-life

kdp 0 days Half-life

Aerobic 

Aquatic 

Metabolis

m

kbacw 632.9 days Halfife

Anaerobic

Aquatic 

Metabolis

m

kbacs 1485.3 days Halfife

Aerobic 

Soil 

Metabolis

m

asm 489.6 days Halfife

Hydrolysis

:

pH 7 0 days Half-life

Method: CAM 2 integer See PRZM manual

Incorporat

ion Depth:

DEPI cm

Applicatio

n Rate:

TAPP 0.128 kg/ha

Applicatio

n 

Efficiency:

APPEFF 0.95 fraction

Spray 

Drift

DRFT 0.16 fraction of application rate applied to pond

Applicatio

n Date

Date 30-06 dd/mm or dd/mmm or dd-mm or dd-mmm

Interval 1 interval 7 days Set to 0 or delete line for single app.

app. rate apprate kg/ha
17

1

Interval 2 interval 7 days Set to 0 or delete line for single app.

app. rate 

2

apprate kg/ha

Interval 3 interval 7 days Set to 0 or delete line for single app.

app. rate 

3

apprate kg/ha

Record 

17:

FILTRA

IPSCND 1

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)
18

The input parameters used for SCI-GROW modeling.

Table B-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 0.125 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:Difenoconazole

time is 12/19/2011 8:36:36

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

Application Number of Total Use Koc Soil Aerobic

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

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

0.125 4.0 0.500 3.47E+03 223.6

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

groundwater screening cond (ppb) = 1.30E-02

************************************************************************
19

Table B-3 Estimated drinking water concentrations before and after percent 

crop area (PCA) adjustment 

Non-Adjusted EDWCs

Scenarios Peak 96 hr 21 Day 60 Day 90 Day Yearly 

Average

Annual 

Average

PA Tomato 11.85 11.19 9.41 8.23 7.89 6.91 5.20

FL Pepper 9.61 8.62 6.22 4.74 4.32 3.28 2.51

FL Citrus 9.21 8.45 7.10 5.46 5.01 3.80 3.02

FL Strawberry 11.37 10.37 7.81 5.87 5.38 4.09 3.42

PA Apple 8.13 7.70 6.53 5.62 5.40 4.59 3.46

ME Potato 11.78 11.42 10.22 9.13 8.72 7.61 6.18

PCA Adjusted EDWCs

Scenarios Peak 96 hr 21 Day 60 Day 90 Day Yearly 

Average

Annual 

Average

PA Tomato 10.3119.74 8.19 7.16 6.86 6.02 4.52

FL Pepper 8.36 7.50 5.41 4.12 3.76 2.85 2.19

FL Citrus 8.01 7.35 6.18 4.75 4.36 3.30 2.63

FL Strawberry 9.89 9.02 6.80 5.11 4.68 3.56 2.97

PA Apple 7.08 6.70 5.69 4.89 4.70 3.99 3.01

ME Potato 10.25 9.93 8.89 7.95 7.59 6.62 5.38

1 Bolded values are the highest concentrations observed in modeled scenarios