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UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

WASHINGTON D.C., 20460 

OFFICE OF CHEMICAL SAFETY 

AND POLLUTION PREVENTION 

 PC Code: 128810 

 DP Barcodes: 389703, 394475 

MEMORANDUM November 28, 2011

SUBJECT: Drinking Water Exposure Assessment for New Uses of Azoxystrobin on 

Wasabi, Dragon-fruit and Sugarcane, and the Proposed Tolerances for 

Residues of Azoxystrobin for Use on Onion subgroups, Fruiting Vegetables 

Subgroups, Small Fruit & Berry Subgroups, Oilseed Subgroups; and the 

Proposed Increased Tolerance for Tuberous & Corm Vegetables Subgroup. 

 

TO: Meheret Negussie, Risk Assessor 

Kristin Rury, Risk Assessor 

Paula Deschamp, Branch Chief 

 Risk Assessment Branch 3 

 Health Effects Division (7509P) 

 AND 

 Barbara Madden, Risk Manager (RM05) 

 Registration Division (7505P) 

 AND 

 Shaja Joyner, Risk Manager (RM20) 

 Registration Division (7505P) 

FROM: Reuben Baris, Environmental Scientist 

 Mark Corbin, Chief 

Environmental Risk Branch 6 

 Environmental Fate and Effects Division (7507P) 

REVIEWED 

BY: Stephanie Syslo, RAPL 

Environmental Risk Branch 6 

 Environmental Fate and Effects Division (7507P) 

Syngenta Crop Protection has petitioned to include sugarcane as a new use for azoxystrobin 

(methyl (E)-2- {2-[6-(6-2-cyanophenoxy)pyrimidin-4-yloxy]pheny}-3-methoxyacrylate; PC 

code 128810; CAS No. ) on sugarcane for two technical (EPA Reg. No. 100-1120 and 100-1220) 

and two end use products (Abound®: ERA Reg. No. 100-1098; and Quilt Xcel®: EPA Reg. No. 

100-1324) (Tolerance Petition # 1F7891). Additionally, the IR-4 has petitioned for tolerances 
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for azoxystrobin for the following uses: tuberous and corm vegetables subgroup 1C; bulb onion 

subgroup 3-07A; green onion subgroup 3-07B; citrus group 10-10; caneberry subgroup 13-07A; 

bushberry subgroup 13-07B; small fruit vine climbing, except fuzzy kiwifruit subgroup 13-07F; 

low-growing berry subgroup 13-07G (except cranberry); low growing berry subgroup 13-07H 

(except strawberry); rapeseed subgroup 20A; sunflower subgroup 10B, cottonseed subgroup 

20C, dragon-fruit, and wasabi for one technical product (EPA Reg. No. 100-1120) and three enduse products (Abound® EPA Reg. No. 100-1098; Graduate A+® EPA Reg. No. 100-1308; 

Quadris Top® EPA Reg. No. 100-1313; Quilt Xcel® EPA Reg. No. 100-1324; Quilt® EPA Reg. 

No. 100-1178) (Tolerance Petition # 1E7851). Four end use products (Quilt, Quilt Xcel, Quadris 

Top, and Graduate A+) are formulated with at least one other active ingredient (difenconazole, 

fludioxonil, or propiconazole). This memorandum only addresses the contribution of 

azoxystrobin to estimated drinking water concentrations (EDWCs) resulting from applications in 

compliance with the proposed tolerance petitions and label ammendments. EDWCs for the other 

a.i.’s will be addressed in separate assessments. 

Azoxystrobin is a fungicide in the class of compounds called β-methoxyacrylates, which are 

derived from the naturally occurring strobilurins. The biochemical mode of action in this class of 

compounds is the inhibition of electron transport. The Health Effects Division (HED) has 

previously determined that the only residue of concern for dietary exposure is parent 

azoxystrobin. Thus, only the parent was considered in this drinking water assessment. 

The Environmental Fate and Effects Division (EFED) estimates drinking water concentrations of 

a chemical based on the highest rate of application of the chemical on all registered and proposed 

crops. In the case of azoxystrobin, turf, a previously registered crop, has the highest application 

rate (0.55 lb a.i./A, 9 applications per year with a 10-day interval between applications) 

(D278783, D279444, and D279561; memorandum from T. Nguyen to M. Rust, Feb. 4, 2002). 

Broccoli was also previously assessed at a maximum application rate of 0.25 lb a.i./A with a 

maximum of 6 applications per year at a 7-day interval between applications (D278783, 

D279444, and D279561; memorandum from T. Nguyen to M. Rust, Feb. 4, 2002). Both 

assessments were completed using the Tier I screening model FIRST. The proposed rates of 

application for wasabi and dragon-fruit are equal to broccoli or lower, therefore the EDWCs 

reported for broccoli and turf are representative of these current actions. EDWCs recommended 

for use in the human health risk assessment for wasabi and dragon-fruit are listed below in Table 

1. 

Sugarcane in the U.S. is grown in unique hydrologic environments, particularly in Florida where 

sugarcane crops are grown near the Florida Everglades where channelized flow, sheet flow, and 

groundwater/surface water interactions are common occurrences. Although the application rate 

for sugarcane is lower than what was previously assessed for cole crops, herbs, and other uses, 

the unique hydrologic environment may contribute to higher concentrations in drinking water. 

Sugarcane was modeled separately from the above uses using the Tier II linked PRZM and 

EXAMS models to estimate the azoxystrobin concentrations in surface water used for drinking 

water resulting from applications to sugarcane. The highest EDWCs in surface water drinking 

water from the use of azoxystrobin on sugarcane are 70.7, 12.1, and 7.3 μg/L, for the peak, 

annual mean and overall (30-year) mean concentrations, respectively (Table 1). The EDWCs for 
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sugarcane are lower than those estimated for applications to turf (173 μg/L), but higher than the 

EDWCs for other agricultural crops (e.g., broccoli). 

Table 1. Estimated Drinking Water Concentrations (EDWC) of azoxystrobin 

residues in surface water. Simulations used the highest rate proposed. 

Scenario 

Model 

(application rate lb 

a.i./A, frequency, 

interval) 

Surface Water 

 1-in-10 year Azoxystrobin 

Concentration (μg/L) 

Comments/Reference 

Peak Annual 

Mean 

30-Year 

Mean 

 Turf 

FIRST 

(0.55, 9x, 10-d) 

173 33 -- 

D278783, 

D279444, 

and D279561 

Broccoli 

FIRST 

(0.25, 6x, 7-d) 

54 10 -- 

D278783, 

D279444, 

and D279561 

Sugarcane 

PRZM/EXAMS 

(0.20, 4x, 14-d) 

71 12 7 

Tier II PRZM/EXAMS model 

runs. Model inputs, as well as 

output file are included in the 

attachment. 

Bolded values are recommended for use in the human health risk assessment. 

 
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Attachment 

PRZM inputs 

Table 2. Summary of environmental fate parameters for azoxystrobin and values used for modeling. 

Parameter Range Value Used in Model Source 

Solubility in water 6.7 mg/L 6.7 mg/L D218292 

Vapor Pressure 8.2 x 10-13 torr 8.2 x 10-13 torr D218292 

Hydrolysis t1⁄2 (at 25 C) stable at pHs 5, 7, 9 0 days MRID 43678172 

EFED. 2009 

Aquatic Photolysis t1⁄2 t1⁄2 = 11 and 17 days 

23.23 days (90th percent 

upper confidence bound 

on mean) 

MRID 43678173 

Soil Photolysis DT50 = 11 days 

t1⁄2 = 17.6 to 28.4 days. 

Not currently used in 

PRZM MRID 43678174 

Aerobic Soil Metabolism 

t1⁄2

72, 85, 164 days 

mean = 107 days 

std = 49.79 days 

median = 85 days 

(PRZM/EXAMS) 

90 percent upper bound 

on mean = 161.2 days 

MRID 43678175 

Aerobic Aquatic 

Metabolism t1⁄2

none available 

2 x aerobic soil 

metabolism 

2 x 161.2 = 322.2 days 

EFED. 2009

Anaerobic Aquatic 

Metabolism, t1⁄2

50 to 59 days 

(soil-water system) 

62.3 days 90 % upper 

bound 

 MRID 43678175 

 (Supplemental) 

Sorption Kf

1.5, 2.9, 4.0, 6.2, 9.5, 15, 

and 23 mL/g; mean – 8.87 

mL/g 

(PRZM-EXAMS) 

8.87 mL/g 

MRID 43678178 

MRID 43678181 

EFED. 2009 

Spray Drift PRZM variable 0.064 (DRFT) EFED. 2009 

Application Efficiency PRZM variable 0.99 (APPEFF) EFED. 2009 

Foliar Wash-Off PRZM variable 0.5 (FEXTRC) EFED. 2009 

Foliar Dissipation Not applicable 0 (PKDKRT) EFED. 2009 

CAM (chemical 

application method) 

 2 – interception on crop 

canopy (PRZM variable) Foliar spray Label 

DEPI (depth of soil 

incorporation) Default by model Default by model -- 

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

Transport of Pesticides. U.S. Environmental Protection Agency, Office of Prevention, Pesticides and Toxic 

Substances, Office of Pesticide Programs, Environmental Fate and Effects Division, Oct. 22, 2009. Online at: 

http://www.epa.gov/oppefed1/models/water/input_parameter_guidance.htm. 

SUGARCANE Output 

stored as sugarcane.out 

Chemical: azoxystrobin 

PRZM environment: FLsugarcaneSTD.txt modified Tueday, 29 May 2007 at 12:53:56 

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

Metfile: w12844.dvf modified Tueday, 26 August 2008 at 05:14:22 

Water segment concentrations (ppb) 

Year Peak 96 hr 21 Day 60 Day 90 Day Yearly 
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1961 17.25 16.43 14.75 11.83 9.227 2.278 

1962 7.581 7.246 6.182 4.723 4.089 2.806 

1963 31.55 30.07 26.84 23.85 20.65 7.336 

1964 58.28 56.32 48.47 38.15 31.52 12.19 

1965 79.5 76.86 65.73 52.08 40.72 14.26 

1966 29.84 28.58 24.97 19.39 16.59 8.235 

1967 21.95 20.93 17.67 14.92 12.56 5.693 

1968 24.93 23.77 21.65 17.47 14.95 6.053 

1969 30.04 28.64 25.65 22.01 17.55 8.246 

1970 17.39 16.65 14.22 11.81 10.72 4.397 

1971 49.38 47.07 39.55 27.69 19.96 6.585 

1972 58.87 56.09 46.74 31.61 21.45 8.227 

1973 19.36 18.53 16.68 12.8 10.57 5.532 

1974 27.33 26.11 22.69 17.45 16.68 8.442 

1975 14.19 13.58 11.36 7.987 6.421 3.651 

1976 24.32 23.2 19.41 14.61 11.49 5.008 

1977 35.92 34.29 31.87 21.89 15.23 7.211 

1978 53.23 51.12 44.93 33.82 25.03 10.08 

1979 25 24.29 20.53 14.6 11.7 6.545 

1980 18.81 18.24 15.22 11.66 9.178 5.341 

1981 42.13 40.18 33.51 22.93 15.78 5.894 

1982 72.03 68.67 62.93 47.99 34.95 14.78 

1983 27.29 26.37 24.17 20.76 17.18 9.147 

1984 104 99.45 83.27 51.3 34.78 11.49 

1985 41.58 39.8 33.35 23.43 19.27 7.503 

1986 38 36.25 30.47 25.79 20.5 9.674 

1987 45.58 43.51 39.76 30.52 22.26 9.039 

1988 20.42 19.48 16.59 12 10.08 5.605 

1989 9.945 9.549 8.399 6.373 5.799 3.63 

1990 8.56 8.177 7.185 5.334 4.725 3.044 

Sorted results 

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

0.032258064516129 104 99.45 83.27 52.08 40.72 14.78 

0.0645161290322581 79.5 76.86 65.73 51.3 34.95 14.26 

0.0967741935483871 72.03 68.67 62.93 47.99 34.78 12.19 

0.129032258064516 58.87 56.32 48.47 38.15 31.52 11.49 

0.161290322580645 58.28 56.09 46.74 33.82 25.03 10.08 

0.193548387096774 53.23 51.12 44.93 31.61 22.26 9.674 

0.225806451612903 49.38 47.07 39.76 30.52 21.45 9.147 

0.258064516129032 45.58 43.51 39.55 27.69 20.65 9.039 

0.290322580645161 42.13 40.18 33.51 25.79 20.5 8.442 

0.32258064516129 41.58 39.8 33.35 23.85 19.96 8.246 

0.354838709677419 38 36.25 31.87 23.43 19.27 8.235 

0.387096774193548 35.92 34.29 30.47 22.93 17.55 8.227 

0.419354838709677 31.55 30.07 26.84 22.01 17.18 7.503 

0.451612903225806 30.04 28.64 25.65 21.89 16.68 7.336 

0.483870967741936 29.84 28.58 24.97 20.76 16.59 7.211 

0.516129032258065 27.33 26.37 24.17 19.39 15.78 6.585 

0.548387096774194 27.29 26.11 22.69 17.47 15.23 6.545 

0.580645161290323 25 24.29 21.65 17.45 14.95 6.053 

0.612903225806452 24.93 23.77 20.53 14.92 12.56 5.894 

0.645161290322581 24.32 23.2 19.41 14.61 11.7 5.693 

0.67741935483871 21.95 20.93 17.67 14.6 11.49 5.605 

0.709677419354839 20.42 19.48 16.68 12.8 10.72 5.532 

0.741935483870968 19.36 18.53 16.59 12 10.57 5.341 
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0.774193548387097 18.81 18.24 15.22 11.83 10.08 5.008 

0.806451612903226 17.39 16.65 14.75 11.81 9.227 4.397 

0.838709677419355 17.25 16.43 14.22 11.66 9.178 3.651 

0.870967741935484 14.19 13.58 11.36 7.987 6.421 3.63 

0.903225806451613 9.945 9.549 8.399 6.373 5.799 3.044 

0.935483870967742 8.56 8.177 7.185 5.334 4.725 2.806 

0.967741935483871 7.581 7.246 6.182 4.723 4.089 2.278 

0.1 70.714 67.435 61.484 47.006 34.454 12.12 

 Average of yearly averages: 7.26406666666667 

Inputs generated by pe5.pl - Novemeber 2006 

Data used for this run: 

Output File: sugarcane 

Metfile: w12844.dvf 

PRZM scenario: FLsugarcaneSTD.txt 

EXAMS environment file: ir298.exv 

Chemical Name: azoxystrobin 

Description Variable Name Value Units Comments 

Molecular weight mwt 403.3 g/mol 

Henry's Law Const. henry atm-m^3/mol 

Vapor Pressure vapr 8.0e-13 torr 

Solubility sol 6.7 mg/L 

Kd Kd 8.87 mg/L 

Koc Koc mg/L 

Photolysis half-life kdp 23.23 days Half-life 

Aerobic Aquatic Metabolism kbacw 322.2 days Halfife 

Anaerobic Aquatic Metabolism kbacs days Halfife 

Aerobic Soil Metabolism asm 161.2 days Halfife 

Hydrolysis: pH 7 0 days Half-life 

Method: CAM 2 integer See PRZM manual 

Incorporation Depth: DEPI cm 

Application Rate: TAPP 0.227 kg/ha 

Application Efficiency: APPEFF 0.99 fraction 

Spray Drift DRFT 0.064 fraction of application rate applied to pond 

Application Date Date 01-10 dd/mm or dd/mmm or dd-mm or dd-mmm 

Interval 1 interval 14 days Set to 0 or delete line for single app. 

app. rate 1 apprate 0.227 kg/ha 

Interval 2 interval 14 days Set to 0 or delete line for single app. 

app. rate 2 apprate 0.227 kg/ha 

Interval 3 interval 14 days Set to 0 or delete line for single app. 

app. rate 3 apprate 0.227 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)